A

PROJECT REPORT

ON

SIGNALLING AND TELLECOMMUNICATION

SUBMITTED BY

ADRITA MAJUMDER

EMAIL ID- adritamajumdergmailcom

SUPERVISED BY MRATANU DEY

DEPARTMENT-ELECTRONICS AND COMMUNICATION

JUNE 2015

i | P a g e

CERTIFICATE

MRATANU DEY

DY CHIEF SIGNAL AND TELECOM ENGINEER

EASTERN RAILWAYS KOLKATA

This is to certify that project report of BTech held during the 6th

-7th

semester break entitled-SIGNALLING

AND TELECOMMUNICATION is a document of work done by Adrita Majumder of ACADEMY OF

TECHNOLOGY under my guidance and supervision during the period June 2015

MRATANU DEY

DY CHIEF SIGNAL AND TELECOM ENGINEER

EASTERN RAILWAYS KOLKATA

ii | P a g e

STATEMENT BY THE CANDIDATE

ADRITA MAJUMDER

BTech 7th

Semester

Department of ECE Roll Number 08

Academy Of Technology

I hereby state that the technical presentation entitled signaling and telecommunication has been prepared by

me to fulfill the requirement of the vocational training during the period JUNE 2015

ADRITA MAJUMDER

iii | P a g e

ACKNOWLEDGEMENT

I would really like to thank every person who has helped me to complete my report successfully All the

websites where I have taken help from and all my friends who have helped me to chose this topic and collect

every bit of information about the topic Special thanks to my project mentor MR ATANU DEY without

whom completion of this very report would have been just impossible He has given me his valuable time

and worthy opinion to create my project successfully Definitely my parents are worth mentioning who have

kept supporting me throughout and have kept faith that I could do it

iv | P a g e

ABSTRACT

In this report I have given an overview of the signal and telecommunication systems that have been used and

are presently being used in the Indian Railways as a part of the day-to-day signalling and communication

procedures

I have covered in this report the history and the latest developments in railway signal and communication as

well as related fields I have made an elaborate study on the various equipments that have been used and are

currently being used as part of communication in the railways

v | P a g e

TABLE OF CONTENTS

TITLE PAGE NUMBER

CERTIFICATE BY THE SUPERVISORS I

STATEMENT BY CANDIDATE II

ACKNOWLEDGEMENT III

ABSTRACT IV

SOLID STATE INTERLOCKING 1

INTEGRATED POWER SUPPLY 5

SINGLE SECTION DIGITAL AXLE COUNTER 9

DATA LOGGER 15

OPTIC FIBRE 22

SIGNALLING RELAYS 34

CONCLUSION 40

BIBLIOGRAPHY AND REFERENCES 41

1 | P a g e

SOLID STATE INTERLOCKING

INPUT CARDS All the field conditions (ie Field relay contacts) are connected to these input cards of EI system

The maximum inputs capacity of each RI card will depend on design of the RI cards by different

manufacturers The total number of inputs will depend on the yard layout

Total inputs means

Field inputs ECRs TPRs NWKR etc

Panel inputs GNs UNs NWNs RWNs etc

Read back inputs HR DR WNR WRR etc

Opto couplers are provided to isolate field optically from the system in Input cards These cards will read the

conditions of inputs and passes the information to EI system

PROCESSOR CARD This card is also called as central processing unit card of the System This is provided with microprocessor

RAM ROM EPROM EEPROM Memory ICrsquos These EEPROMS or EPROMrsquos (ROMrsquos) are programmed

with software required for executing the system commands

System software consists of the following

- Executive software programmed in system EPROMrsquos

- Application software programmed in DATA EPROMrsquos

-

EXECUTIVE SOFTWARE This software is common to all EIrsquos for the same company manufacturing

This is a factory installed software

Performs all operations

Cuts off vital supply voltage to output relays in case of unsafe failures

2 | P a g e

APPLICATION SOFTWARE This software is specific to each station and different for different stations

This is as per table of control of specific station

Can be installed at site by signal engineers

Logic installed through Boolean expressions or user-friendly equations

OUTPUT CARD (RELAY DRIVE CARD) This card receives the output of CPU card as input and picks up relevant output relay as per the panel

operatorsrsquo request The output of this card is terminated on phoenix terminals from there the output relays are

connected

The essential modules of an EI is as follows

Hardware module

Software module

HARDWARE MODULES USED IN THIS SYSTEM Equipment consists of

CARD FILE

Each card file is like a shelf having 20 Slots to accommodate various PCBs that are used in a system

Slot nos1 to 15 and 20 are used to accommodate Non-vital Input-output or Vital Input or Vital Output PCBs

Slot no16amp17 are used to accommodate Power supply PCB Slot no18amp19 are used to accommodate CPU

PCB In this cardfile a mother board is available in the rear side connecting all the 20 Slots This cardfile is

suitable to mount on a 19rdquo rack

Power

Supply

Card

CPU

Card

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19

20

CPU PCB Each card file to have one CPU PCB and always placed in slot no18amp19 In this card Micro

Controller used is Motorola 68332 and its speed is 21 MHz In this card 4 nos of flash EPROMs of 8 MB

are used to store executive and application software Two nos of fast Static RAM (each 64KB) are used to

process the vital data and Four nos of Static RAM (each 64KB) are used to store events and errors

The main functions of CPU is it monitors continuously status of Vital Boards It also monitors

system internal operation for faults and responds to detected faults It processes application logic based on

inputs

received and deliver outputs to drive external gears It records system faults and routine events in user-

accessible memory It monitors and controls the serial communication ports It controls power to vital outputs

through external VCOR relay

POWER SUPPLY PCB

3 | P a g e

Each card file to have one Power Supply PCB and always placed in slot no16amp17 Power supply

PCB is basically a DC-DC converter that converts 12V DC input supply is +12V -12V and +5V required for

various board functioning Based on diagnostic check by CPU Power Supply Card receives 250Hz signal

from CPU and extends supply to VCOR relay This card provides isolated supply to internal circuit

VITAL OUTPUT PCB Each Vital Output PCB has 16 Outputs It is available in 12V and 24V DC applications Each Vital

Output can drive an output device such as any Q-series relay This output relay in turn controls signals

points crank handle siding control level crossing etc Since Vital Output drives the relay which controls

important outdoor gears all the Vital Output boards are continuously diagnosed by a CPU Any abnormality

in any of the outputs will shut down the system to ensure safety

VITAL INPUT PCB Each Vital Input PCB has 16 Inputs It is available in 12V and 24V DC applications Each Vital Input

is assigned to read the status of outdoor gears such as Track circuits Point detectors Crank handles Siding

controls level crossing etc Since the Vital Inputs read the status of outdoor gears they are normally

configured with double cutting arrangement using relay contacts

NON-VITAL INPUTOUTPUT PCB Each Non-vital IO has 32 inputs and 32 outputs in one PCB It is available in 12V and 24V DC

applications Non-vital inputs are Panel push buttons and keys Non-vital outputs are Panel indication LEDs

counters and buzzers The status of Non-vital Inputoutput is known from LED indications available in front

of the card

VITAL CUT OFF RELAY- VCOR Each card file will have one VCOR to ensure the healthiness of the system VCOR has 6 FB

dependent contacts each rated for 3 Amps When system is healthy the coil receives voltage from Power

Supply PCB which in turn controlled by CPU Power to Vital output board is controlled by VCOR thus

ensuring safety

WIRING HARDWARE 48 Pin Address select PCB and Connector assembly is provided for Vital Input and Vital Output

cards 96 Pin Address select PCB and Connector assembly is provided for Non-Vital IO cards 48 Pin

Connector Assembly is provided for PS and CPU PCB EEPROM PCB which is provided on rear side of the

CPU connector to configure various serial communication ports Keying plugs are provided in the cardfile to

ensure coding to each type of cards

SOFTWARE MODULES USED IN THIS SYSTEM System software consists of the following

EXECUTIVE SOFTWARE This software is common to all EIrsquos for the same company manufacturing

This is a factory installed software

Performs all operations

Cuts off vital supply voltage to output relays in case of unsafe failures

APPLICATION SOFTWARE This software is specific to each station and different for different stations

This is as per table of control of specific station

Can be installed at site by signal engineers

Logic installed through Boolean expressions or user-friendly equations

4 | P a g e

A GEC-MANUFACTURED SSI INTERLOCKING CUBICLE

A PAIR OF DATA LINK MODULES

TRACKSIDE FUNCTIONAL MODULE

5 | P a g e

INTEGRATED POWER SUPPLY

INTRODUCTION A typical 4 line station requires power supplies of 24 V DC( 5 nos ) 12 VDC ( 5nos ) 6V (2 nos)

110 V DC and 110 V AC for signalling These require as many chargers and Secondary cells amp Invertors

requiring more maintenance amp spares Can they be Integrated in to one system

Thus the concept of Integrated Power Supply has been evolved by integrating concepts One Charger

One set of Battery Bank feeding Invertors and DC- DC converters for deriving various DC amp AC

voltages Integrated power supply system delivers both AC amp DC Power supplies as an output with the

output voltage tolerance of plusmn 2

ADVANTAGES Reduces maintenance on Batteries Battery charger amp overall maintenance

Its construction is in modules and hence occupies less space Reduced space requirement resulting in

saving of space for power supply rooms

Provides centralized power system for complete signaling installation with continuous display of

working status of system for easier monitoring

Defect in sub-units of system is shown both by visual amp audible indication Reflects the condition of

battery with warning

Replacement of defective modules is quick amp easy without disturbing the working of the system

It uses (n+1) modular technology hot standby arrangement and hence high reliability and more

availability of the system

The system provides uninterrupted supply to all signalling system even during the power failures

Thus No blank Signal for the approaching drivers

System can be easily configured to suit load requirement

The diesel generator set running (Non-RE area) is reduced almost to lsquoNILrsquo Hence low wear and tear

of DG set components amp reduced diesel oil consumption

COMPONENTS (a) Un-interrupted power supply (U P S)

(i) SMPS Battery chargers with Hot stand-by mode

(ii) Hot Standby PWM Inverters with auto changeover

(iii) CVT Regulator [FRVS]

(b) AC distribution board [ACDB]

(i) STEP DOWN TRANSFORMERS

(c) DC distribution board [DCDB]

(i) DC-DC converters

WORKING IPS works satisfactorily for AC input variation of 150V AC to 275V AC with single-phase power supply

and frequency variation from 48 Hz to 52 Hz The input is fed to SMPS charger which converts in to 110

VDC as output It is fed as input to three sub units

To battery bank charging the batteries

To ON line inverters that converts 110 VDC in to 230 VAC plusmn 2as output

6 | P a g e

As 110 VDC bus bar to DC Distribution Panel as an input to various DC-DC converters located in

it

A 110 V Battery Bank of VRLA cells are connected to SMPS Panel IPS Status Monitoring Panel is

located at ASM room or at SampT staff room if round the clock SampT staff is available at Station

CONSTRUCTION IPS mainly consists of

SMR (Switch Mode Rectifier) Panel SMPS based Float cum Boost Charger (FRBC) Panel

AC Distribution Panel

DC Distribution Panel

Battery Bank (110V DC)

Status Monitoring Panel

SMR (SWITCH MODE RECTIFIER) PANEL SMPS BASED FLOAT

CUM BOOST CHARGER (FRBC) PANEL It consists of SMR FRBC modules and Supervisory amp Control Unit SMPS based SMRs

(converters) SMPS based Float cum Boost Chargers (FRBC) modules are provided with (n+1) modular

technology hot standby arrangement with active load sharing basis and 1 additional module as a cold standby

(n+2) Supervisory amp Control Unit which controls and monitor the complete system It has various

indications on the panel reflecting the working of the panel

FRBCs are suitable for operating in parallel on active load sharing basis with one or more modules of similar

type make and rating

n = required no of modules to cater for actual current requirement

AC DISTRIBUTION PANEL It is made of ON-Line inverters with (1+1) modular technology hot standby arrangement amp CVT

(Constant Voltage Transformer) AVR (Automatic Voltage Regulator) and set of step down

transformersThe inverter is protected against overload and short circuit with auto reset facility Whenever

the failure occurs it trips and restart automatically after about 10 to 20 sec But if the problem persists the

protection is permanently gets latched and it will not be switched ON again unless the fault is cleared

followed by pressing of reset button The output of inverters is regulated to 230V AC plusmn 2 50Hz plusmn1Hz for

an input voltage variation of 90V DC to 140V DC Normally both the Inverters are powered ON and both are

delivering the Output voltage but only one (main) inverter is connected to the Load If main inverter is failed

then only the stand-by inverter will come on Load automatically with in 500msec At 70 Depth of

Discharge (DOD) of the battery bank 110VDC supply to the inverters will be cut-off So the Signals feed will

be cut-off The auto-change over arrangement is also provided for bringing the CVT in circuit with in

500msec when the both the inverters output is failed It has various indications on the panel reflecting the

working of the panel

DC DISTRIBUTION PANEL It takes care of DC Power supply requirements of our signalling It consists of sets of DC-DC

converters for individual DC power requirements with (n+1) modular technology hot standby arrangement

with active load sharing basis The DC-DC converters of Relay Internal are provided with (n+1) modular

technology hot standby arrangement with active load sharing basis and 1 additional module as a cold standby

(n+2) The DC-DC converter works satisfactorily with the input voltage variation of 98VDC to 138VDC At

90 Depth of Discharge (DOD) of the battery bank all the DC-DC converters 110VDC Input supply will be

cut-off except for Block Tele DC-DC converters The supply for Point operation is also catered through a

20A fuse by this unit It is also provided with various indications that reflect its working

7 | P a g e

STATUS MONITORING PANEL IPS status monitoring panel has been provided in the ASM room for giving the important alarms and

indications to ASM Status Panel tells present working status of IPS displaying battery voltage continuously

and five other indications which will light according to IPS status During normal working these indications

will not lit Whenever the battery has come on to the load and has discharged by 50 DOD (Depth of

Discharge) then first Red indication lit with description ldquoSTART GENERATORrdquo with audio Alarm ie DG

set is to be started and put on the load If DG set is not started with this warning then if battery gets further

discharged to 60 DOD and second Red indications appears with description ldquoEmergency Start generatorrdquo

with audio alarm even now if DG set is failed to be started the battery further gets discharged to 70

DOD and 3rd Red indications appear with description ldquo System shut downrdquo with audio alarm which will

continue till Generator is started resulting in AC output from IPS is automatically cut off results all the

signals will become blank

When there is any defect in any sub module of IPS even without affecting working of system the 4th

Red indication appears with description ldquoCall SampT Staffrdquo with audio alarm so the ASM advises SampT staff

accordingly Green LED 5th indication comes with the description ldquoStop Generatorrdquo with audio alarm when

the DG set is running and if the Battery bank is fully charged condition

EARTHING The IPS systems and its individual modules are having earth terminals and all these are properly

earthed with earth resistance of less than 1 ohm Earth provided shall preferably be maintenance free using

ground resistance improvement compound (The acceptable Earth Resistance at earth busbar shall not be

more than 1 ohm Code of practice for earthing and bonding system for signalling equipments)

LIGHTNING AND TRANSIENT PROTECTION IN IPS Manufacturer will provide Stage1 amp Stage 2 protection along with the IPS These are described

below

Stage 1 protection is of Class B type against Lightning Electro-Magnetic Impulse (LEMP) amp other

high surges provided at Power Distribution Panel It is provided with a 63 Amp fuse in phase line and is

connected between Line and the Neutral and also between the Neutral and Earth

Stage 2 protection (Power line protection at Equipment level) is of Class C type against low voltage

surges provided at the equipment input level This is thermal disconnecting type and equipped with

protection against SPD (surge protection device) failure due to open amp short circuit of SPDs and is connected

between the Line and the Neutral If supply data signalling lines (ACDC) are carried through overhead

wires or cables above ground to any nearby building or any location outside the equipment room additional

protection of Stage 2 type shall be provided at such locations Class B amp Class C arrestor is provided on a

separate wall mounting type enclosure in IPS room

Stage3 protection (Protection for signallingdata line) is of Class D type All external data signalling

lines (ACDC) shall be protected by using this Class D type device It consists of a combination of Varistors

and Gas Discharge Tube with voltage and current limiting facilities

FEATURES Chargers used in this system are of SMPS technology chargers with 90 efficiency These chargers

are supported with hot standby mode with (n+1) modular technology

Onetwo sets of Maintenance free Battery banks (110VDC) Normally one set (110VDC) of Battery

bank is used Conventional flooded type Lead Acid Batteries or Low Maintenance Lead Acid

batteries can also be used (SMRs settings are required to be adjusted depending on the type of

Batteries used) Various voltage levels of

8 | P a g e

battery banks are avoided Reduction in Battery maintenance amp less flour area required

DC-DC Converters working from 110V Central battery have been used for all dc supplies This has

improved overall efficiency of the system since number of conversion from AC to DC have been

reduced to 2 stage as compared to 3 stage conversion in case of transformer-rectifier system

DC-DC converters are available in modules Easy replacement of defective modules This ensures

less down time

DC-DC Converters are used in load sharing N+1 configuration (ie with hot standby with N+1

modular technology) to improve the reliability amp availability of the system

Capacity of inverter has been brought down to 15 KVA from 5 KVA and used for feeding only

Signals supply Hot standby inverter is provided with auto changeover facility This improves the

availability of the overall system

High efficiency inverter is used with PWM (Pulse Width Modulation) technology in place of Ferro-

resonant technology based inverter This improves the efficiency of the overall system

Continuous power to Signal Circuits even in absence of DG setLocal Power Supply

Generators need not be switched ON every time during train movement

Metal-to-metal relay installations and block working by axle counters have also been covered

Supply of spare modulesComponentsCells have been included as part of main supply

Provides highly regulated voltage to all signal relays amp lamps for better life

9 | P a g e

SINGLE SECTION DIGITAL AXLE COUNTER

INTRODUCTION- The axle counter equipment is working on high frequency and using amplitude modulation or phase

modulation for detection of presence of wheel The equipment described in this notes is Phase modulation type

for the detection of presence of wheel In the Phase modulation type track device the detection of presence of

wheel is with the phase reversal of 1800 out of phase which enables this system to be more healthy and safe

In Phase Reversal Modulation technique trolley suppression arrangements to prevent the counting of

wheels caused by push trolley passing over the track device are not required as the system will take care of

validation of generated pulses caused by passage of wheel over the track device depending up on the phase

shift of the pulse This phase shift of the pulse may be normally 160deg to 180deg for a train wheel and it may be

approximately 100deg to 120deg for a push trolley wheel

This is Digital Axle Counter equipment for single track sections containing 2 out of 2 micro-

controllers to count the axles establish the track occupancy of a track section and to provide this information

to the block or the interlocking equipment

In this system no separate evaluator is required and no analog data is being transmitted One set of

Axle counter equipment is provided at entry end and other set provided at exit end Both sets are being

connected through a twisted pair of telecom cable ie existing RE cable one PET quad is used for both UP

and DN Axle Counters Digital DATA is being transmitted between two ends of Axle counters (Outdoor

track side Detection points)This system is a fully duplex capable of operating according to CCITT V21 and

the Data will be transmitted at the rate of 300bitsec This data Transmitted ensure negligible interference of

the noise The system is highly reliable

FEATURES (a) The system consists of

(i) Single Section Digital Axle Counter (SSDAC) units

(ii) Tx Rx coils

(iii) Vital Relays

(b) TxRx coil axle detectors are mounted to the web of the rails The design of system consists of 21 KHz amp

23 KHz High frequency Phase Reversal type axle detectors

(c) Compatible with 90R 52Kg amp 60Kg rail profiles Easy to install commission amp maintain

(d) Track devices at both (entry amp exit) points of the section should be fixed on the same rail

(e) System is designed to detect the solid wheels with diameter gt 400mm with standard wheel flange

(f) The system works in pairs For monitoring single-track section one pair of SSDAC units are required and

to be installed near the trackside one at the beginning and another at the end of the track section ie

Trackside electronic counting equipment

(g) The basic design of the system is based on counting the number of axles passing at each detection point

These stored counts are transmitted to the second unit of the system and vice versa by means of modem

communication

(h) The communication consists of digital packets having details of Counts amp Health

10 | P a g e

(i) If counts registered at both detection points are equal the section is cleared otherwise the section is shown

as occupied The system ensures no error condition to arrive at the decision of clearance

(j) System is designed as per CENELEC SIL-4 (European standard) using micro controller along with other

electronic circuits and programmed using dedicated software When any of these circuits fail the system

goes to fail safe condition

(k) It is programmable for either Preparatory Reset or Conditional Hard Reset as per requirement

(l) Micro controller based design with 2 out of 2 decisions and counting through software

(m) V21 Modem communication (2-wire) on frac12 quad cables and also compatible to work on voice channel of

OFC amp Radio

(n) Opto isolated vital relay drive for Q-style 24V 1000 _ and Vital Relay output can be giving at both ends

of the system

APPLICATIONS The system can be widely used in Railways for Block Working (BPAC) Intermediate Block Signaling Auto

signalling and Track circuiting for i) Loop line ii) Main line iii) yard lines

SYSTEM DESCRIPTION

This system comprises of

Tx coils-2 nos

Rx coils-2 nos

Reset Box (RB 258A)

Card 1 Signal Conditioning Card ndash 1

Card 2 Signal Conditioning Card - 2

Card 3 Micro controller Logic Board ndash 1

Card 4 Micro controller Logic Board ndash 2

2 nos for independent resetting ndash when used in block sections

1 no for common resetting ndash when used for Track circuiting at stations

Card 5 Event Logger Card

Card 6 Modem Card

Card 7 Relay Driver Card

Card 8 DC-DC Converter Card

SSDAC (DACF 700AP) UNIT

(A) SIGNAL CONDITIONING CARD (CARD 1amp2) (SCC) -1 (SCC-1) generates 21 KHz carrier

signals

-2 (SCC-2) generates 23 KHz carrier signals which is transmitted to 2nd

set of Tx coils

s receive these signals

modulated

train pulses

11 | P a g e

(B) MICRO-CONTROLLER LOGIC BOARD CARD (CARD 3amp4) (MLB) The Micro-controller Logic Board (MLB) is the heart of the system

o 8051 Based Architecture

o 8 Bit Micro Controller

o ATMEL AT89S8252 Micro controller

o 2 out of 2 Decision

o Uses C subset language

- TOOLS

o KEIL μ Vision Development System

o Universal Programmer

o 2KB Program Memory

o 256 bytes RAM

o 8KB Flash memory

o 32 Programmable IO lines

o Wide Operating Voltage range of 4V-6V

o Full Duplex Serial Port

o Programmable Watch Dog Timer

o Fully Static operation up to 24MHz (Upgraded to 40MHz)

o Operating Temperature of ndash40degC - +85degC

o Use of State Machine for Axle Counting

o Use of ASCII MODBUS protocol

o Use of CRC16 technique for Error Checking during communication

o Wheel detection

o Train direction checking and

o Wheel counting functions

o It receives the remote wheel count and computes the status of the section for clear or occupied

o It also checks various supervisory signal levels like supervisory of TxRx coils presence of various

cards communication link failure etcThese cards communicate with each other for wheel count

At Entry-end if train enters into section (1st detection) the counts are incremented and when train

shunts back from the same detection ie if train exits from the section from the same detection the counts are

decremented At Exit-end if train enters into section (2nd detection) the counts are decremented and when

train shunts back from the same detection ie if train exits from the section from the same detection the

counts are incremented Both the track devices at Entry and Exit ends must be fixed on same side of the

track

This MLB card is having Extensive LED display

o A block of 8 LED indicators for count progress error display

o 2 independent LED indicators for section status

o The errors occurring in the system during the operation of the SSDAC are encoded and are indicated by

means of the 8-LED block present on the front panel of the MLB cards

(c) EVENT LOGGER CARD (CARD 5)

Event logger card is designed to capture and store important signals from the remote and local SSDAC units

The stored data can be downloaded from the event logger card for the purpose of analyzing the events

occurring during the operations of the SSDAC The data can be analyzed with the help of CEL data analyzer

software

12 | P a g e

The event logger card captures following signals

(i) Pulse signals

(ii) Supervisory signals

(iii) Card removal information

(iv) Serial packets from

Event Logger card has a Rabbit processor and 2 MB FLASH MEMORY to store packets The data is initially

stored in the buffer and subsequently transferred to FLASH memory every two minutes Normally 4096

pages of the data can be stored in flash memory on FIFO (first in first out) basis

Run This LED blinks continuously indicating the normal working of the event

Log This LED blinks whenever data is being logged into the flash memory (Approx after every 2 minutes)

Dnld This LED is ON when data is being downloaded from the flash memory of the card and becomes OFF

when download is complete

(D) MODEM CARD (CARD 6) (i) The modem card transmits and receives the digital packet information form one counting unit to the other

The packet will appear after every 18 sec and the packet carries the latest information such as

(ii) The modem card being used is V21 type (2-wire) in SSDAC

(iii) This card interfaces with serial RS232C port of both Micro-controller Logic Boards

(iv) It multiplexes the two RS232C inputs and selects one of the two channels and provides signal conversion

from digital to analog (FSK modulation) and vice-versa

(v) Data transmission rate is 300 bitssec

(vi) Automatic Gain Control circuit is incorporated hence no gain adjustments required

(vii) Mode selection on Modem card The modem has been set in lsquoORIGINATORrsquo mode for entry and in the

lsquoANSWERrsquo mode for exit in the factory

(viii) LED Indications provided on Modem card

-Transmitting the signal when LED is flashing

- Receiving the signal when LED is flashing

-Remains OFF in SSDAC

-Carrier is detected when LED is glowing

(E) RELAY DRIVER CARD (CARD 7) (i) The Relay Driver card (RD) provides the 24V DC output required for driving Vital Relay

(ii) One RD card is used in each SSDAC counting unit The RD card receives the command of clear and

clock signals from MLB1 amp MLB2 cards and drives the vital relay lsquoONrsquo when section is NOT OCCUPIED

through opto- isolator circuit

(iii) If a train occupies the section the vital relay is dropped The vital relay status is read back by the system

as per the driving output

(iv) It has

13 | P a g e

ndash LED flashes when the section is clear

ndash LED flashes when the section is clear

All the above LEDrsquos are lit for section clear condition

(F) DC-DC CONVERTER CARD (CARD 8)

INPUT VOLTAGE Nominal Voltage voltage 24V DC Maximum current drain= 12A

Required voltage 18V DC to 30V DC

Output voltage

Nominal Voltage +5 V DC 2 A Required voltage 4 7 5 t o 525V DC

Nominal Voltage +12V DC 200 mA Required voltage 1175 to 1225V DC

Nominal Voltage +24V DC 300 mA with common ground Required voltage 235 to 245V DC

Nominal Voltage +15V DC 100 mA with isolated ground Required voltage 145 to 155V DC

SURGE VOLTAGE AND LIGHTNING PROTECTION Transient surge voltages arise as a result of Lightning discharge switching operations in electrical

systems and electrostatic discharge These surge voltages often destroy the electronic equipment to a large

extent In order to prevent surge voltages from destroying the equipment all the input lines of SSDAC ie

Power Supply (24V) Reset (48V) amp Modem is to be routed through surge voltage protection devices for

effectively protecting the system These devices (3 numbers) are mounted in a box and supplied along with

the system One number of box is to be installed at each location and wired to the SSDAC

Each surge voltage protection device consists of two parts

(a) Base

(b) Plug Trab

The Base of the device is used for wiring the input and output signals The connection details from relay

room to the box and from box to SSDAC unit are provided on the box The Plug Trab consists of MOV and

GD Tube and diverts the excess energy during surge voltages or lightning into the ground connection The

operation of these devices relies on a high quality ground connection in order to safely shunt away the

unwanted energy The impedance of the ground connection is critical and it should be less than 2 Ohms

NOTE The 3 Plug Trab connections are not to be interchanged with one another The plug Trab is a

detachable device and can be replaced with SPARE unit in case of blown device which is indicated by

means of LED for 24 V

EFFECTIVENESS OF PLUG TRABS The effectiveness of plug Trab depends wholly on the Earth connection provided to the system The earth

provided to the system should be less than 1 ohms and connections should be firm and proper to the SSDAC

unit VR box etc

SURGE VOLTAGE AND PROTECTION DEVICE SV-120 The Surge Voltage protection device is to be installed at each location along with every SSDAC unit

14 | P a g e

EARTHING- The lead wires connecting the installation and the earth electrode shall ordinarily be of stranded

copper wire of 29 sq mm (19 strand wires of 14 mm diameter) Copper wire has been specified because GI

wires usually are having greater corrosion However in areas where copper wire may be frequently stolen

due to theft ACSR of size 64 sq mm (19 strands of 211 mm diameter) may be used

LIMITS OF EARTH RESISTANCE (a) Apparatus case connected to Earth (SSDAC and vital Relay Box is housed in Apparatus case and

Connected to earth at outdoor) shall be less than or equal to 1 ohm

(b) All cable connected to same earth shall be less than or equal to 1 ohm

(C) Reset box connected to earth near SM s Room shall be less than or equal to 1ohm

EQUIPMENT TO BE EARTHED A Common Earth should be provided for SSDAC for items 1(a) amp (b) of the above at the outdoor

(a) The Apparatus Case is to be connected to earth (the chassis of SSDAC amp Vital Relay Box should be

properly connected to apparatus case)

(b) Metallic sheath and armouring of all the underground main cables are to be earthed

(i) In RE area the metallic sheath and armouring of main telecom cables are earthed at both ends

(ii) In RE area the armouring of Jelly filled cable shall be earthed at both ends

(c) The Earthing shall be provided at every location box where cables are terminated

(d) Earth already available for other equipment may be used for earthing of Reset Box near SM s Room

Cabin etc

15 | P a g e

DATALOGGER

INTRODUCTION Datalogger is a Microprocessor based system which helps in analysing the failures of relay inter

locking system Electronic Interlocking system This is like a black box which stores all the information

regarding the changes take place in relays AC DC Voltages and DC currents along with date and time The

same information data can be transferred to the computer to analyse further ldquoon line ldquooff linerdquo analysis of

stored date A print out also can be obtained through a printer by connecting directly to the datalogger unit

The data belongs to Relay contacts is considered as digital inputs and the data belongs to voltage

levels currents is considered as Analog inputs Datalogger lsquos are mandatory for all new relay interlocking

(PIRRI) EI installations and it is also recommended to provide in all existing PIs RRIs To increase the

line capacity mechanical signalling equipments are upgraded to PI RRI or EI Due to complexity in the

circuits and wiring sometimes it is very difficult to rectify the failures So datalogger can monitor these

systems with real time clock Thus it can be named as black box of Samp T equipments and hence it is a vital

tool for accident investigation Datalogger is used at Stations yards Whereas in case of Auto Section amp IBH

Mini dataloggers called as Remote Terminal Unit (RTU) are used

ADVANTAGES OF DATALOGGERS (a) Dataloggers helps in monitoring the typical failures such as intermittent auto right failures

(b) It helps in analyzing the cause of the accidents

(c) It helps in detecting the human failures errors such as

(i) Drivers passing signal at Danger

(ii) Operational mistakes done by panel operators ASMrsquos of operating department

(iii) Signal and telecom engineering interferences in safety circuits

(iv) Engineering and electrical department interferences failures

(v) It helps as a ldquoTOOLrdquo in preventive maintenance of signaling gears

(d) Dataloggers can be connected in network Networked dataloggers helps to monitorthe PIRRIEI remotely

(e) Failure reports can be generated remotely with help of datalogger network

(f) On line and Off line track simulation is possible

(g) Speed of the train on point zones can be calculated

(h) Age of the equipment in terms of number of operations etc

COMMON EQUIPMENT FOR ALL DATALOGGERS ARE GIVEN

BELOW (a) CPU card

(b) Digital and Analog input cards

(c) Local terminal(PC)

(d) communication links

(e) Printer

All the dataloggers requires a potential free ( spare ) relay contact for monitoring digital inputs

through Digital input cards amp for monitoring Analog inputs such ACDC bus bar voltage levels through

Analog input cards Digital and Analog inputs are connected to the Processor card Processor card consists of

memory ICrsquos Memory ICrsquos are programmed as per requirement of the signal engineers

Provision of Dataloggers is mandatory with RRI systems and is optional for PI systems as per

amendment to the specification for Relay Interlocking systems ( IRSS-36 ) The data collected by the

datalogger can be used for failure analysis repetitive discrepancies and for accident investigations

16 | P a g e

Note

If the serial communications is more than 50m then line drivers shall be used up to 3 Kms

4wire leased line Modems shall be used if the serial communication is more than 3 Kms

STUDY OF EFFTRONICS DATALOGGER TECHNICAL DETAILS (a) 24V 12VDC Power Supply

(b) Total Storage Capacity of 10 Lakh events

(c) In-built Temperature sensors

(d) Internal Buzzer for alarming during failures

(e) Real Time clock with internal battery backup with data retention up to 10 years

(f) 512 LED matrix to indicate the status of 512 Digital inputs at a time page wise

(g) Seven segment LCD screen (2x24) to display the status of digitalanalog signalsTime Temperature etc

(h) Using the keyboard various functions can be viewed in the LCD panel

(i) Max Digital Inputs 4096

(j) Max Analog Inputs 96

(k) Digital Input Scanning Time 16 millisecond

(l) Analog Input Scanning Time is less than 1 Sec

HARDWARE (EQUIPMENT) Datalogger system consists of

(a) Datalogger (CPU - with Microprocessor 68000)

(b) Digital input cards

(c) Dual modem card

(d) Digital Scanner units (DSU)

(e) Analog Scanner units (ASU)

CPU CARD It is provided with Motorola microprocessor M 68000 It performs all the activities pertaining to the

datalogger It continuously scans (check) the Digital inputs(inbuilt) Digital Scanner Units and Analog

Scanner Units ie scanning of digital signals (Relay operations) for every 16-milli seconds and scanning of

analog signals (ie ACDC voltages amp DC currents) for less than 1 second

This card will support the IO interfaces of LCD (Liquid Crystal Display) - 2X24 alphanumeric Key

Board LED Matrix Display Real Time Clock LCD display and keyboard This will acts as man machine

interface between the datalogger and the signal engineer All the operations (Software) can be performed

using this LCD and keyboard

Real time display with 7 Segments This is built in real time clock within Datalogger and its current

time will be displayed on six 7-segment display provided (Real time clock depend upon DALLAS 1286

chip) This IC will come with internal battery backup hence there is no need to add external batteries

CPU card continuously scans (checks) the DSUs and ASUs Each input connected to digital scanner

units are optically isolated by Opto couplers When CPU card scans the digital inputs it compares with the

previous stored data and if there is any change from the previous status then only that data will be stored (the

status conditions of relay) with date and real time A total of minimum 10 Lac events can be stored in

memory on first in first out basis so that latest data is available in the system There is no loss of data from

datalogger memory in case of power supply failure of datalogger

DIGITAL INPUT CARDS (IN-BUILT) This system is having maximum 8nos of inbuilt Digital inputs cards Maximum 64nos of digital

inputs can be connected to each digital input card The potential free relay contact may be front or back

contact terminated at the Tag Block from the relay of signals tracks points Buttons etc and are

17 | P a g e

subsequently connected to Digital input cards through Flat Ribbon Cable (FRC) connectors These in-built

digital input cards can monitor a total 512 nos of relays status

DIGITAL SCANNER UNIT (DSU) Each DSU contains 8 nos of Digital Input cards Each input card can be connected with 64 inputs

Total input capacity of DSU unit is 512 inputs These scanner cards contain Optocouplers and Multiplexer

Inputs are connected to Stag card The stag card out put is connected to DSU through FRC connectors

Maximum 7 nos of DSUs can be connected to the system So Digital input capacity of the system is 4096

All these digital inputs are scanned at rate of 16 msec

ANALOG SCANNER UNIT (ASU) ASU contains maximum 3 nos of Analog input cards Each input card can be connected with 8nos of

Analog inputs Total input capacity of the ASU is 24 analog input channels Maximum 4nos of ASUs can be

connected to the system Analog input channel capacity of the system is 96 All these analog inputs are

scanned at a rate of less than 1 sec

PARALLEL PORT Parallel port is provided for connecting printer

RS-232 SERIAL PORTS At least 6 Serial communication ports are provided for communication with other dataloggers

Central Monitoring Unit Remote Terminal Unit Electronic Interlocking system Integrated Power Supply

system etc

EXTERNAL NON-VITAL RELAY CONTACTS These relays provided in the system where 16 number of the Relay contacts are provided on the rear

panel through Tele control port to extend alarms and to control the power equipment from remote or local

locations through computer in case of any occurrence of failures Each control can sink or source 100 m

amps of current

INTERNAL MODEM CARD DUAL MODEM CARD (IN-BUILT) It is fixed in datalogger Euro rack itself One card contains two modems The top modem is called

ANS (answer) modem and the bottom modem is called as ORG (originate) modem It is used in case of

networking of Dataloggers In network connect lsquoANSrsquo modem to the lsquoORGrsquo modem of one adjacent station

and connect lsquoORGrsquo modem to the lsquoANSrsquo modem of other adjacent station

POWER SUPPLY Normally 24V DC (12V DC is optional) supply with battery backup is required for the system

working

Input Voltage Range 18Vhellip32V DC (For 24V) 9Vhellip18V DC (For 12V)

INPUT REQUIREMENTS Relay inputs (digital inputs) and analog inputs (voltages currents etc) are required to be connected

to the system as per the requirements of RRI PI SSI as the case may be Some of the inputs to be

monitored is given below

(a) Digital inputs

(i) Field inputs All TPRs NWKRs RWKRs ECRs Crank Handle relays SidingSlot LC gate

control relays etc

(ii) Control Panel inputs All button Knob SMrsquos Key relays

18 | P a g e

(iii) Internal relays

British system All HR DR HHR WNR WRR ASR UCR RR LR UYRTLSR TRSR TSR

JSLR JR etc

SIEMENS system Z1UR Z1UR1 GZR ZDUCR ZU(R)R ZU(N)PRG(R)RG(N)R U(R)S

U(N)PS UDKR DUCR U(R)LR UYR1 UYR2 G(R)LRGR1GR2

GR3 GR4 OVZ2U(R)RW(RN)R (RN)WLR Z1NWR Z1RWRZ1WR1 WKR1 WKR2 WKR3 etc

(b) Analog channels

(i) 230 V AC (for power supplies in the power panel)

(ii) 110V AC (for Signal and Track transformers)

(iii) 110V DC (for Point operation)

(iv) 60V DC (Siemens relays)

(v) 24V DC (Q-series relays)

(vi) 24V DC (for Block Axle counters)

(vii) 12V DC (for indication)

(viii) 20A (for point operation current)

(ix) 10V AC 5KHz (for Axle counter channels) etc

SOFTWARE MODULES OF DATALOGGERS

(a) Network Management of Dataloggers (NMDL)

(b) Reports

(c) Fault Entry

(d) Track Offline Simulation

(e) Train Charting

NMDL SOFTWARE FEATURES (a) Online Relay Status

(b) Online Faults - To view information of various Online Faults as they occur in the stations where

the Dataloggers are connected

(c) Online Simulation - Graphical view of relay operations train movements etc

(d) Remote monitoring of stations with the help of NETWORKING

SOFTWARE OBJECTIVES (a) Predictive Maintenance

(b) Easy identification of failures

(c) Crew discipline

(d) Train charting

REMOTE MONITORING OF STATIONS WITH NETWORKING OF

DATALOGGERS The individual Dataloggers of various stations can be interconnected through networking technology

The data of Remote Panel stations can be viewed in a Computer at the Central Monitoring Station The data

of the network is collected by the FEP (Front End Processor) which in turn is transmitted to the computer

COMPONENTS OF NETWORK MANAGEMENT OF DATALOGGERS

(a) Datalogger at stations

(b) MODEM and Transmission medium

19 | P a g e

(c) Front End Processor (FEP)

(d) Central Monitoring Unit (CMU) Computer

FEP (FRONT END PROCESSOR)

FEP acts as a buffer between the Central Monitoring Unit (Computer) and the Network It is provided

at centralised place to retrieve data continuously from station dataloggers and store in memory and transfer to

computer on request It stores 10 Lac telegrams It works on 12V DC It draws 16A continuous current

when all the three modems are connected Normally it shows the number of packets pending to be sent to the

computer on its 7-segment LED display It is provided with MOTOROLA 68000 microprocessor It has 6-

nos of RS-232 communication ports such as COM1 COM2 COM3 COM4 COM5 and COM6 COM1 is

used for Fault Analysis System (FAS) ie Central Monitoring Unit (Computer) connection COM2 to COM6

are used for networking For Bi-directional 2- nos of ports and for Tri-directional (T-network) 3-nos of ports

are used

DATA TRANSMISSION Dataloggers can be networked in Uni-directional Mode or Bi-directional Mode or T ndash Network Mode

In case of loss of data retransmission of data takes place

(a) Uni-Directional Mode

Each Datalogger will send data in only one direction to the FEP Unidirectional mode network is not

preferred

(b) Bi-Directional Mode

Each end of Network is connected to FEP and each datalogger can now transmit data in both the directions

Bi-directional Mode is advantageous it enables the Data Transmission even in case of Network Failure

(c) T - Network Mode

If more no of stations are in network ie if the network is too lengthy then T- network mode is preferred

COMMUNICATION The communication protocol for transmitting data and command between datalogger and CMU is

standardized by the RDSO and is given in the Specifications of Dataloggers

(a) The type of communication used in the network is dependent on the distance between the dataloggers

(b) For shorter distances Opto Converter Box- Opto isolated current loop communication is used

(c) For longer distances Modem (Dial-up leased) Fiber Optic Satellite Microwave communication

MODEMS Modems are used for DATA transfer between Dataloggers and Front End ProcessorThese are

configured to RS 232 Serial Communication Network is connected with two types of 4-wire modems

(a) Internal modem card Dual Modem card (in-built)

It is fixed in datalogger Euro rack itself One card contains two modems The top modem is called

ANS (answer) modem and the bottom modem is called as ORG (originate) modem

Note In case of networking of Dataloggers connect lsquoANSrsquo modem to the lsquoORGrsquo modem of one adjacent

station and connect lsquoORGrsquo modem to the lsquoANSrsquo modem of other adjacent station

(b) External modems

20 | P a g e

These are generally used at FEP (Front End Processor) side to connect the Dataloggers

(i) To transfer Data from one datalogger to another datalogger FEP Baud rate is 9600bps

(ii) These modems are 4-wire line communication

(iii) To transfer the data from FEP to RMU (PC) the Baud rate is 57600 bps

There is no difference between these modems functionally

CENTRAL MONITORING UNIT (CMU) COMPUTER

Central monitoring unit (Fault Analysis Unit) is a Personal Computer and its minimum configuration

shall be specified by RDSO from time to time System Software Windows XPVista(OS) Norton Kaspersky

(Anti Virus) Interbase where Server is not available (DBMS) Oracle where Server is available (DBMS)

software are required to run Datalogger System It is provided with Graphical User interface (GUI) based

software and retrieve data from all Networked dataloggers (up to 32) at various stations It stores data in

standard data base files The CMU is capable of analyzing the data and generate reports audiovisual alarms

on defined conditions This data can be compressed to take backup In central monitoring unit Software used

for analysis of data prediction of faults etc is written in a structured format so that purchaser can

reconfigure it if required It displays the status of signaling gears at any selected time in graphic form for any

selected station yard It retrieves the stored data amp simulates train movement It sends commands to various

Dataloggers to activate audio visual alarm or operate and electromagnetic relay

CMU shares data available in it by other PCs through available local area network where this data can

be used for train charting passenger information purpose The system generates audiovisual alarm in

ASMrsquosSignal Maintainerrsquos room in the case of power supply failure (battery voltage low) or battery charger

defective with acknowledgement facility

(a) Each datalogger has its own identity code which will be transmitted along with data packet to central

monitoring unit

(b) Events recorded at each station are continuously transmitted to central monitoring unit Response time of

data transfer will not exceed 10 sec

21 | P a g e

22 | P a g e

OPTICAL FIBER CABLE

INTRODUCTION The demand for bandwidth on transmission networks is increasing rapidly because video and

graphical rich contents are exchanged through the corporate network or the Internet The Gigabit Ethernet

became ommonly used in the corporate network backbone and 10Gbit Ethernet will be adopted in the near

future Meanwhile in the home the demand for high-speed network becomes popular as the wide spread of

broadband access eg CATV xDSL and FTTH The transmission medium with capability to transmit high

bit rate signal is necessary to satisfy these requirements

The telecommunication transport technologies move from copper based networks to optical fiber

from timeslot based transport to wave length based transport from traditional circuit switching to terabit

router and all optical based networks entering into a new era of optical networking

BASIC PHYSICS OF OFC

OPTICAL FIBER CABLE OFC have Fibers which are long thin strands made with pure glass about the diameter of a human

hair OFC consists of Core Cladding Buffers and Jacket as shown in figure

MONOCHROMATIC LIGHT OR SINGLE COLOR LIGHT Light or visible light is electromagnetic radiation of a wavelength that is visible to the human eye (

about 400 ndash 700 nm) The word light is sometimes used to refer to the entire electromagnetic spectrum Light

is composed of elementary particles called photons Three primary properties of light are

Light can exhibit properties of both waves and particles This property is referred to as wave-particle

duality The study of light known as optics In free space light (of all wavelengths) travels in a straight path

at a constant maximum speed However the speed of light changes when it travels in a medium and this

change is not the same for all media or for all wavelengths By free space it is meant space that is free from

matter (vacuum) andor free from electromagnetic fields

Thus the speed of light in free space is defined by Einsteinrsquos equation E = mc2

Frequency ν speed of light in free space c and wavelength λ are interrelated by ν = cλ

From the energy relationships E = mc2 = hν and the last one an interesting relationship is obtained

the equivalent mass of a photon m = hνc2

When light is in the vicinity of a strong electromagnetic field it interacts with it From this interaction

and other influences its trajectory changes direction as shown in figure

23 | P a g e

INCIDENT RAY REFLECTED RAY AND REFRACTED RAY An incident ray is a ray of light that strikes a surface The angle between this ray and the

perpendicular or normal to the surface is the angle of incidence Reflection is the change in direction of a

wave front at an interface between two different media so that the wave front returns into the medium from

which it originated Common examples include the reflection of light sound and water waves

The reflected ray corresponding to a given incident ray is the ray that represents the light reflected by

the surface The angle between the surface normal and the reflected ray is known as the angle of reflection

The Law of Reflection says that for a specular (non-scattering) surface the angle of reflection always equals

the angle of incidence The refracted ray or transmitted ray corresponding to a given incident ray represents

the light that is transmitted through the surface The angle between this ray and the normal is known as the

angle of refraction and it is given by Snells Law

The figure shows Incident ray Reflected ray Refracted ray the angle of incidence and angle of refraction

REFRACTIVE INDEX - Refractive index is the speed of light in a vacuum ( c =299792458kmsecond) divided by the speed

of light in a material ( v ) Refractive index measures how much a material refracts light Refractive index of

a material abbreviated as lsquo n lsquo is defined as lsquo n=cv lsquo Light travels slower in physical media than it does

when transmitted through the air Refractive index (n) is a function of molecular structure of matter optical

frequency optical intensity determines optical propagation properties of each wavelength ( λ ) may not be

distributed equally in all directions is affected by external temperature pressure and fields

Refractive index of a medium is a measure for how much the speed of light is reduced inside the

medium For example typical glass has a refractive index of 15 which means that light travels at 1 15 =

067 times the speed in air or vacuum Two common properties of glass and other transparent materials are

directly related to their refractive index

First light rays change direction when they cross the interface from air to the material and effect that

is used in lenses and glasses

Second light reflects partially from surfaces that have a refractive index different from that of their

surroundings

SNELLrsquoS LAW-

24 | P a g e

When light passes from one transparent material to another it bends according to Snells law which

is defined as n1sin(θ1) = n2sin(θ2)

where n1 is the refractive index of the medium the light is leaving θ1 is the incident angle between the light

beam and the normal (normal is 90deg to the interface between two materials)

n2 is the refractive index of the material the light is entering

θ2 is the refractive angle between the light ray and the normal

Snellrsquos law gives the relationship between angle of incidence and angle of refraction

For the case of θ1 = 0deg (ie a ray perpendicular to the interface) the solution is θ2 = 0deg regardless of

the values of n1 and n2 That means a ray entering a medium perpendicular to the surface is never bent The

above is also valid for light going from a dense (higher n) to a less dense (lower n) material the symmetry of

Snells law shows that the same ray paths are applicable in opposite direction

TOTAL INTERNAL REFLECTION- When a light ray crosses an interface into a medium with a higher refractive index it bends towards

the normal Conversely light traveling cross an interface from a higher refractive index medium to a lower

refractive index medium will bend away from the normal

This has an interesting implication at some angle known as the critical angle θc light traveling from

a higher refractive index medium to a lower refractive index medium will be refracted at 90deg in other words

refracted alon g the interface If the light hits the interface at any angle larger than this critical angle it will

not pass through to the second medium at all Instead all of it will be reflected back into the first medium a

process known as total internal reflection

The critical angle can be calculated from Snells law putting in an angle of 90deg for the angle of the refracted

ray θ2 This gives θ1

Since θ2 = 90deg

So sin(θ2) = 1

25 | P a g e

Then θc = θ1 = arcsin(n2n1)

For example with light trying to emerge from glass with n1=15 into air (n2 =1) the ritical angle θc is

arcsin(115) or 418deg For any angle of incidence larger than the critical angle Snells law will not be able to

be solved for the angle of refraction because it will show that the refracted angle has a sine larger than 1

which is not possible In that case all the light is totally reflected off the interface obeying the law of

reflection

OPTICAL FIBER MODE An optical fiber guides light waves in distinct patterns called modes Mode describes the distribution

of light energy across the fiber The precise patterns depend on the wavelength of light transmitted and on the

variation in refractive index that shapes the core In essence the variations in refractive index create

boundary

conditions that shape how light waves travel through the fiber like the walls of a tunnel affect how sounds

echo inside

We can take a look at large-core step-index fibers Light rays enter the fiber at a range of angles and

rays at different angles can all stably travel down the length of the fiber as long as they hit the core-cladding

interface at an angle larger than critical angle These rays are different modes Fibers that carry more than

one mode at a specific light wavelength are called multimode fibers Some fibers have very small diameter

core that they can carry only one mode which travels as a straight line at the center of the core These fibers

are single mode fibers This is illustrated in the following picture

OPTICAL FIBER INDEX PROFILE Index profile is the refractive index distribution across the core and the cladding of a fiber Some

optical fiber has a step index profile in which the core has one uniformly distributed index and the cladding

has a lower uniformly distributed index Other optical fiber has a graded index profile in which refractive

index varies gradually as a function of radial distance from the fiber center Graded-index profiles include

power-law index profiles and parabolic index profiles The following figure shows some common types of

index profiles for single mode and multimode fiber

26 | P a g e

OPTICAL FIBERrsquoS NUMERICAL APERTURE ( NA )- Multimode optical fiber will only propagate light that enters the fiber within a certain cone known as

the acceptance cone of the fiber The half-angle of this cone is called the acceptance angle (see figure 18)

θmax For step-index multimode fiber the acceptance angle is determined only by the indices of refraction

Where

n is the refractive index of the medium light is traveling before entering the fiber

nf is the refractive index of the fiber core

nc is the refractive index of the cladding

NUMBER OF MODES IN A FIBER - Modes are sometimes characterized by numbers Single mode fibers carry only the lowest-order

mode assigned the number 0 Multimode fibers also carry higher-order modes The number of modes that

can propagate in a fiber depends on the fiberrsquos numerical aperture (or acceptance angle) as well as on its

core diameter and the wavelength of the light For a step-index multimode fiber the number of such modes

Nm

Where

D is the core diameter

λ is the operating wavelength

NA is the numerical aperture (or acceptance angle)

MODE FIELD DIAMETER - All light do not travels through the core of the fiber but is distributed through both the core and the

cladding The mode field is the distribution of light through the core and cladding of a particular fiber

Mode-Field Diameter (MFD) defines the size of the power distribution When coupling light into or out of a

fiber MFD is important in understanding light loss

27 | P a g e

ADVANTAGE OF OFC COMMUNICATION - bull More information carrying capacity Fibers can handle much higher data rates than copper More

information can be sent in a second

bull Free from Electromagnetic and Electrostatic interference Being insulator no electric current flows through

the fibre and due to this reason fibres neither radiate nor pick up electro - magnetic radiation So WPC

CLEARANCE is not required

bull Low attenuation 025 dbkm at 1550 nm Loss in twisted pair and coaxial cable increases with frequency

where as loss in the optical fibre cable remains flat over a wide range of frequencies

bull Use of WDM ndash Switching routing at Optical signal level

bull Self healing rings under NMS control

bull Small size makes fibre cable lighter in weight So easy to handleOptic fibre cable weight (approx)

500 kg km Copper cable weight (approx) 1000 kgkm

The reasons are photons of light in a fibre

do not affect each other as they have no electrical charge and they are not affected by stray photons outside

the fibre But in case of copper electrons move through the cable and these are affected by each other

Optical fibre does not carry any electricity even if the cable is damaged or short circuited it does

not cause any spark or fire hazard

As the fibre do not radiate energy it can not be detected by any nearby antenna or any

other detector The fibres are difficult to tap and therefore excellent for security

As the signal transmission is by digital modulation there is no chance of cross talk in

between channels

Only by adding a few additional terminal and repeater equipments the

capacity of the system can be increased at any time once the cable is laid

ical effects and temperature variations

LIMITATIONS OF OFC -

difficult

- utilised

APPLICATION IN SIGNAL AND TELECOMMUNICATIONS transmission circuits

-haul circuits for linking of telephone exchanges

28 | P a g e

PROPAGATION MODES CONCEPT -

MODE - Mode is an available distribution of electromagnetic field in a plane transverse to the direction of

light propagation Each mode is characterized by frequency polarization electric field strength and

magnetic field strength Available patterns are derived from Maxwellrsquos equations and boundary conditions

LINEARLY POLARIZED (LP) MODE A mode for which the field components in the direction of propagation are small compared to

components perpendicular to that direction An optical fibre supports only different field patterns called as

lsquoLinear Polarizedrsquo or lsquo LPrsquo modes The reasons are

requirements

de

the accrual of power carried by different modes

There are two basic types of fiber Multimode fiber and Single-mode fiber

Multimode fiber is best designed for short transmission distances This is suited for used in LAN systems and

video surveillance Single mode fibre is best designed for longer transmission distances This is suitable for

long distance telephony and multi channel television broadcast systems

29 | P a g e

MULTI MODE FIBER Multimode fiber the first to be manufactured and commercialized simply refers to the fact that

numerous modes or light rays are carried simultaneously through the waveguide Modes result from the fact

that light will only propagate in the fiber core at discrete angles within the cone of acceptance MM fiber type

has a much larger core diameter compared to single-mode fiber allowing for the larger number of modes

and

is easier to couple than single-mode optical fiber Multimode fiber further categorized as Multimode step-

index and Multimode graded index fiber

PROPAGATION THROUGH MMSI FIBER Figure shows the principle of total internal reflection applies to multimode step index fiber Because

the corersquos index of refraction is higher than the claddingrsquos index of refraction the light that enters at less than

the critical angle is guided along the fiber

Three different light waves travel down the fiber One mode travels straight down the center of the

core A second mode travels at a steep angle and bounces back and forth by total internal reflection The third

mode exceeds the critical angle and refracts into the cladding Naturally it can be seen that the second mode

travels a longer distance than the first mode causing the two modes to arrive at separate times

PROBLEMS WITH MMSI FIBER AND SOLUTION This disparity between arrival times of the different light rays is known as dispersion and the result is

a muddied signal at the receiving end It is important to note that high dispersion is an unavoidable

characteristic of multimode step-index fiber The solutions are either use Graded index fiber or Single mode

fiber

PROPAGATION THROUGH MMGI FIBER Multimode Graded-index refers to the fact that the refractive index of the core gradually decreases

farther from the center of the core The increased refraction in the center of the core slows the speed of some

light rays allowing all the light rays to reach the receiving end at approximately the same time reducing

dispersion Figure shows the Light propagation principle through multimode graded-index fiber The corersquos

central refractive index ( nA ) is greater than that of the outer corersquos refractive index ( nB )

It is very clear from the figure the light rays no longer follow straight lines they follow a serpentine path

being gradually bent back toward the center by the continuously declining refractive index This reduces the

arrival time disparity because all modes arrive at about the same time The modes traveling in a straight line

30 | P a g e

are in a higher refractive index so they travel slower than the serpentine modes These travel farther but

move faster in the lower refractive index of the outer core region

PROPAGATION THROUGH SMSI FIBER Single mode fiber has a much smaller core that allows only one mode of light at a time to propagate

through the core The figure shows the single mode fiber

Single-mode fiber exhibits no dispersion caused by multiple modes Single-mode fiber also offers lower fiber

attenuation than multimode fiber Thus more information can be transmitted per unit of time because it can

retain the fidelity of each light pulse over longer distances Like multimode fiber early single-mode fiber was

generally characterized as step-index fiber meaning the refractive index of the fiber core is a step above that

of the cladding rather than graduated as it is in graded-index fiber Modern single-mode fibers have evolved

into more complex designs such as matched clad depressed clad and other exotic structures

SINGLE-MODE FIBER DISADVANTAGES The smaller core diameter makes coupling light into the core more difficult The tolerances for single-

mode connectors and splices are also much more demanding

CUTOFF WAVE LENGTH - Cutoff wavelength is the wavelength above which a single-mode fiber supports and propagates only

one mode of light In other words an optical fiber that is single-mode at a particular wavelength may have

two or more modes at wavelengths lower than the cutoff wavelength The effective cutoff wavelength of a

fiber is dependent on the length of fiber and its deployment The longer the fiber the lower is the effective

cutoff

wavelength The smaller the bend radius of a loop of the fiber the lower is the effective cutoff wavelength If

a fiber is bent in a loop the effective cutoff wavelength is lowered

SIGNAL ATTENUATION IN FIBER - Optical fiber has a number of advantages over copper However it also suffers from degradation

problems which can not be ignored The first of these is loss or attenuation Attenuation is typically the result

of two sub properties They are scattering and absorption Both of which have cumulative effects The second

is

dispersion which is the spreading of the transmitted signal and is analogous to noise

SCATTERING Scattering occurs because of impurities or irregularities in the physical construction of the fiber The

well known form of scattering is Rayleigh Scattering It is caused by metal ions in the silica matrix and

results in light rays being scattered in various directions

31 | P a g e

Scattering limits the use of wavelengths below 800nm The short wavelengths are much affected than longer

wavelengths It is because of Rayleigh scattering that the sky appears to be blue ( shorter wave length ) The

shorter wavelengths ( blue ) of light are scattered more than the longer wavelengths of light

ABSORPTION Absorption results from three factors They are hydroxyl ions ( OH- water ) in the silica impurities

in the silica and incomplete residue from the manufacturing process These impurities tend to absorb the

energy of the transmitted signal and convert it to heat resulting in an overall weakening of the signal The

Hydroxyl absorption occurs at 125 and 139 micro The silica itself starts to absorb energy at 17 micro

because of the natural resonance of the silicon dioxide

MACRO BENDING LOSS Macro-bending loss is caused by bending of the entire fiber axis The bending radius shall not be

sharper than 30d where d is diameter of cable A single bend sharper than 30d can cause loss of 05dB

The fiber may break if bending is ever sharper

MICRO BENDING LOSS Micro-bending loss is caused by micro deformations of fiber axis which leads to failures in achieving

total internal reflection conditions Micro-bends are small scale perturbations along the fiber axis the

amplitude of which are on the order of microns These distortions can cause light to leak out of a fiber

Micro-bending may be induced at very cold temperatures because the glass has a different coefficient of

thermal expansion from the coating and cabling materials At low temperatures the coating and cable

become more rigid and may contract more than the glass Consequently enough load may be exerted on the

glass to cause micro bends

Coating material is selected by manufacturers to minimize loss due to micro-bending The linear thermal

expansion coefficient of coating material shall be compatible with that of fiber

32 | P a g e

DISPERSION Dispersion is the optical term for the spreading of the transmits in the fiber It is the bandwidth

limiting phenomenon and comes in two forms Multimode dispersion and chromatic dispersion Chromatic

dispersion is further subdivided into material dispersion and waveguide dispersion

DISPERSION PHENOMENON IN OPTICAL FIBER Dispersion is the time distortion of an optical signal that results from the differences of time of travel

for different components of that signal typically resulting in pulse broadening As the distance traveled by

the signal is more broadening of pulse is more In digital transmission dispersion limits on the maximum

data rate and the maximum distance ie the information-carrying capacity of a fiber link The interference

from broadened pulse in the next interval shall not lead to erroneous interpretation of received signal

OPTICAL DOMAIN Understanding where attenuation and dispersion problems occur helps optical design engineers

determine the better wavelengths at which information can be transmit taking into account distance type of

fiber and the other factors which can severely affect the integrity of the transmitted signal The graph shown

depicts the optical transmission domain as well as the areas where problems arise The wavelength (nm)

is shown on X-axis and attenuation ( dBkm) is shown on Y-axis

There are four transmission windows appear in the figure The first one is at around 850 nm the

second at 1310nm third at 1550 nm and fourth at 1625 nm The last two labeled as C and L band

respectively The 850 nm wavelength at which the original LED technology operated The second window at

1310 nm has low dispersion The 1550 nm called as C-band is ideal wavelength for long haul

communication systems The network engineers can avoid transmitting signal at 1000 nm where Rayleigh

scattering 1240 and 1390 nm where hydroxyl absorption by water occurs to avoid high degree of loss

Optical fibers also can be manufactured to have low dispersion wavelength in the 1550nm region

which is also the point where silica-based fibers have inherently minimal attenuation These fibers are

referred to as dispersion-shifted fibers and are used in long-distance applications with high bit rates For

33 | P a g e

applications utilizing multiple wavelengths it is undesirable to have the zero dispersion point within the

operating

wavelength range

34 | P a g e

SIGNALLING RELAYS

INTRODUCTION A relay is an electromagnetic device which is used to convey information from one circuit to another

circuit through a set of contact ie front or back contact Constructional and electrically relays may be

divided into DC and AC relays because the means by which the electrical energy in the coil is converted in

to mechanical Energy in order to move the contacts are fundamentally different In DC type the contacts are

carried on an armature forming part of a magnetic circuit in which a field is set up by the current flowing in

the coils In AC types the contacts are attached by a link mechanism to a metal sector disc or cylinder in

which currents are induced by the alternating magnetic field produced by the currents in the coils

Every endeavor has been made to explain the action of each type of relay in the simplest possible manner

Relays are sophisticated switch gears used for remote control and succession control of various

electrical equipment In present days they are widely used because they are capable of protecting the

controlled equipment from cross feeding and overloading even as they cater for speedy operations

Most of the relays in present day signaling are electromagnetic devices although some of the relays control

circuits through electronic components like diodetransistors Integrated Chips etc

Railway signaling relays are unique in that

(a) They operate on low voltage and current

(b) They are more articulate as according to their special features they can work under restrictive conditions

and in any specified manner Virtually they can cater for all situations while contributing to speed and

accuracy in operations

CLASSIFICATION OF SIGNALLING RELAYS (a) According to the method of their mounting or fixture they are classified as

(i) Shelf type Relays which are loosely kept on shelves

(ii) Plug in type Relays which are plugged into a pre- wired plug boards

(b) According to their connection and usage they are classified as

(i) Track relays Relay which is directly connected to the track to detect the presence of vehicle

(ii) Line Relays Other than track relay all are line relays Relays connected to the selection circuit

(c) According to their vitality or importance in ensuring train working safety they are classified as

(i) Vital Relays All relays used for traffic control such as signal point controls track detection etc

(ii) Non-vital Relays Relays which operate control aids and accessories like warnings buzzers

Indications etc

(d) According to their special provisions to ensure reliability of their contacts they are classified as

(i) Proved type are those whose normalization after each operation shall be proved in circuit

controlled by their contacts Contacts in which both the springs have metal surfaces on their tips They may

get fused due to high sparking current across them during operation These may prevent relay normalization

and causes unsafe condition in traffic control To avoid this proving of relay normalization after each

operation is necessary

(ii) Non - proved type Need not to be proved to have been normalized after each operation as their

contacts have at least one non-fusible contact (carbon contact)

(e) According to their feed source relays are broadly classified as

(i) DC relays The relay which requires DC power supply for its operations are called DC relays Among

the DC relays

o DC neutral relays This relay closes the same set of contacts on energization with Normal polarity

or Reverse polarity supply

o Polar Relays This relay closes different set of contacts when energized with Reverse polarity

supply They may or may not have contact to close when deenergized

35 | P a g e

(ii) AC Relay AC Induction motor track relays Time element relays flashing indication control etc

(iii) Electronic Relays DC relays with electronic components in them are called electronic relays

DC NEUTRAL RELAY Each Relay has usually one or two coils with a hollow center to accommodate a coreThe coils are

made up of a large numbers of turns of small gauge soft drawn copper wire The two coils can be connected

in series or parallel according to the requirement of relay resistance The ends of the coils are terminated on

binding post to which the control wires are connected Each coil is placed around a core of specially selected

Iron or steel having high permeability and low retentivity The core should be susceptible to magnetism and

at the same time should have little residual magnetism The cores are connected at the top by a yoke to

complete the magnetism coupling between two ends of coils The bottom of each core is equipped with a

large steel or Iron block known as pole piece or face

A flat piece of Iron or steel called armature is supported by brackets which are securely fastened to

the pole piece The armature yoke and the pole pieces are also made of specially selected iron or steel of the

same quality as the core The armature carries the metallic spring contacts which are insulated from it

The circuit through the coils of the relay is closed It sets up a magnetic flux through the core yoke and the

armature The flux passing between the armature and pole faces causes the armatures get attracted to the pole

faces and armature picks up and closes front contacts When the circuit is opened the magnetic flux collapses

and the armature drops away by gravity from the pole faces the front contacts break and back contacts close

The front and back contacts of the relay can be utilised to make or break other circuits Two stop pins of

nonmagnetic material are fixed either on the armature or pole faces so that the armature cannot

come in contact with the pole faces It is essential to maintain a small air-gap between the armature and pole

faces so that low value of residual magnetism may not retain the armature in picked up position and causes

the relay to fail to drop away with a break in its control circuit

GENERAL USAGE

DC Neutral line relays are most commonly used for Railway Signalling controls and detection

Among them plug-in type relays are preferred in larger installations for space considerations Shelf type

relays are also in use mostly in wayside stations

There are many DC Neutral line relays in use with special features such as

(i) Delayed operation

(ii) Biased DC control

(iii) DC control unaffected by AC interference currents

(iv) Getting latched in operated condition till further feeding and others

Usage of DC polar relays is mostly in conjunction with block instruments that control traffic between

stations AC line relays are almost extinct in installations of British Signalling practice They are however

used for time control operations flashing indication control and such other special purposes in installations

with Siemens signalling practice widely Track relays are used according to the type of track detection

circuits chosen for a given location and context While most of the track circuits are still of the DC working

type requiring DC neutral track relays with them the prospects of their being replaced with Electronic track

circuits directly feeding DC line relays in future are great AC Track Circuits are used in DC Traction area

as conventional DC Track Circuits are not suitable there AC Track relays are used with them almost all of

the induction motor type In the British practice of signalling which was first introduced on Indian Railways

non-proved type relays with carbon to metal switching contacts are generally used for vital controls

They facilitate simple circuit designs But with the advent of German Practice introduced by Ms

Siemens later proved type relays with all metal to metal contacts are widely accepted in spite of

complications in circuit design caused by them A recent introduction is that of the same type relays made by

Ms Integra control However for some time now the appreciable features of both the practices are getting

36 | P a g e

incorporated together in the indigenous designs of signalling by railwaymen With this the usage of all types

of relays anywhere can be found without straight jacketed segration of relay types

CHARACTERSTIC OF ELECTRO-MAGNETIC RELAY The following are the characteristic of electro-magnetic relays A brief study of them helps in

understanding the choice of their components and designs features

1) Force of attraction

2) Effect of air gap

3) Effect of Hysterisis

4) Transient condition

FORCE OF ATTRACTION In any electro-magnetic system the force of attraction is given by

Where B - is the flux density a - is the cross sectional area of the particular part of the magnetic

circuit

In the case of a DC neutral Relay B is proportional to the current that is flowing in the coil

surrounding the electro-magnet and thus the force of the attraction is directly proportional to the square of the

current This square relationship has its own advantage especially in the case of DC track relay in that a

small reduction in the current will have a great effect on the working of the relay Also for a given change of

current the make and the break will be quicker with lesser possibility of arcing

EFFECT OF AIR GAP

Curve lsquoArsquo is magnetisation curve for the iron and is all practical purpose a straight line up to the

saturation point Curve lsquoBrsquo is the magnetisation curve for the open-air gap which is a straight line through

out because per magnetisation curve of the whole

magnetic circuit of the relay and for a given force is the sum of the amp-turns for the iron part and the amp-

turns for the air gap

When the front contacts are open the force required to pick up the armature is shown on curve lsquoCrsquo to be F1

but after the armature has operated it will be separated from the core by stop pins In this position the amp-

turns required to maintain the armature is less as indicated by the dotted line from 1 on curve C to 2 on curve

37 | P a g e

F But actually the current in the coil is unaltered the force on the armature is greater than required as

indicated at 3 on curve F Part of this extra force is used to flex the front contacts sufficiently to give good

contact pressure when it is in energised position

The difference between the pick-up and the drop-away current should be as small as practicable in

track relay to ensure good shunting characteristics This is achieved firstly by the choice of good quality relay

iron and secondly by having a small air gap between armature and core If the air gap is not available then

the residual magnetism fluxes might cause the armature to be retained when the supply is disconnected For

this reason residual pins are provided to ensure a definite minimum air gap in the energised position

EFFECT OF HYSTERISIS

Hysterisis is the property by which the flux produced lags behind the current In the de-energized

condition there will be small residual flux in the core When the voltage is applied to the coils the current in

rising to its steady value first causes the flux to rise from 1 to 2 along the curve At this point the flux density

will be sufficient to attract the armature and reduce the air gap the flux then raise to 3 and continue to 4

which corresponds to the steady current in the coils When the voltage is disconnected the current in falling

caused the flux to fall from 4 to 5 along the curve At this point the flux density will fall below the value

required to maintain the armature which will release thus increasing the air gap and reducing the flux to 6

Finally the

flux will decrease from 6 to 1 where the current will again be zero

The relay core is made of material having high permeability and low retentivity As mentioned in

the IRS specification Electromagnet iron may be in the form of a

(a) Bar of silicon steel

(b) Best Yorkshire wrought iron

(c) Swedish charcoal iron

(d) Electrical steel sheets

` This reduces the difference between pick up value and Drop away value By selecting good quality

core material Percentage release and sensitivity of the relay will be improved

TRANSIENT CONDITION

38 | P a g e

When the voltage is applied or disconnected from the coils it takes some little time before the current

become steady These are known as transient conditionsrdquo and are important so far as track relays are

concerned When the voltage is first applied to the coils the magnetic flux in rising cuts the turns on the

coils and in so doing produces a back EMF that opposes the applied voltage and retards the growth of

current

The growth and decay of flux are decided by the relationship between the inductance and resistance

in the circuit is known as time constant It is not fixed quantity in the case of DC neutral relay This value of lsquo

Lrsquo is less when the relay is in de-energised condition (L1) than when the relay is in energised condition (L2)

The magnitude of flux that is established for a given change of current is different in two cases

When the current reaches the pick up value the armature closes and the inductance is increased to L2

due to reduced air gap the flux per amp is increased The increase in flux increased the back EMF during the

movement of the armature after which the current continuous to raise along a new curve corresponding to the

increased inductance until it reaches the final value (ER) This process is indicated above in fig24

When the supply is disconnected the current is obliviously reduced to zero immediately but the flux

decay comparatively slowly owing to the eddy currents produced in the core by the rapid flux change which

tend to maintain the flux The drop away time on a disconnection is however generally negligible See fig

below

If the relay releases due to the reduction in current from say I 2 to I 1 caused by the application of

shunt resistance (as in the case of track relay ) the time taken is much longer than the relay is simply

disconnected The rate of rise or fall of current during the transient conditions is also depends on exterior

circuit values because L and R apply to the whole circuit The production of eddy current in the core the flux

will decay at a slower rate than the current So that the actual release time will be a little longer than it takes

the current to fall to the release

L= Inductance

39 | P a g e

R= Resistance

It is now clear that to reduce releasing time to a minimum it is necessary that

- The relay iron should have low Hysterisis loss and low retentivity

- The degree of over energization of the relay should be restricted

- Connecting a suitable external resistance in series with the relay to keep LR ratio low

In non RE area for track circuit length less than 100M 9 ohm track relay only to be used Using relay

with minimum contacts as they require lesser current which keeps inductance value low

Train working safety is ensured only if the track relay of shortest length track circuit is released

before a light engine running at a highest permitted speed clears it Otherwise the track circuit occupation

may go undetected To avoid this a special provision has to be made in signal control circuits wherever

necessary

The following methods may be adopted for reducing the time lag of track relay

(a) Restrict the over energisation of relay since the release time depends on the initial working current

(b) Connecting a suitable external resistance in series with the relay to keep the LR ratio low

(c) Using relays with minimum contacts as they require lesser operating current keeping the inductance

value low

40 | P a g e

CONCLUSION

Modern signalling is vital for safe and punctual movements of trains In the Indian railways The Signalling

and Telecommunication Department is responsible for providing modern effective and relaible signalling

systems as well as telecommunication systems

The first mode of communication used in Indian Railways was the use of electric telegraph

with the help of Morose code Morose code is the method of providing text information as a series of on-off

tones and lights or clicks that can be directly understood by a skilled listener or observer without special

equipmentEach character (letter or numeral ) is represented by a unique sequence of dots and dashes Later

this system becomes obselete and beggan the era of wireless communication which operated at audio level

frequency range

In wireless communication the significant advances took place the transition to miniature

valves or filament tubesBut this was abandoned too because of excessive current consumption and over

heating of the filament tubes

Fibre-optic communication is a method of transmitting information from one place to another by

sending pulses of light through an optcial fibreThe light forms an electromagnetic carrier wave that is

modulated to carry information First developed in the 1970s fibre optic communication systems has

revolutionized the telecommunications industry and have palyed a major role in the advent of the information

age Because of its advantages over electrical transmissionsoptical fibres have largely replaced copper wire

communications in core networks in the developed world The Indian Railways too is undergoing a transition

from Microwave communication to fibre optic communications

41 | P a g e

BIBLIOGRAPHY AND REFERENCES

1 wwwwikipediacom

2 wwwbritaniccacom

3 wwwirfcacom

4 Motorola GP60 system manual

5 Harris FAS 7000 manual

6 TOSHIBA Manual

i | P a g e

CERTIFICATE

MRATANU DEY

DY CHIEF SIGNAL AND TELECOM ENGINEER

EASTERN RAILWAYS KOLKATA

This is to certify that project report of BTech held during the 6th

-7th

semester break entitled-SIGNALLING

AND TELECOMMUNICATION is a document of work done by Adrita Majumder of ACADEMY OF

TECHNOLOGY under my guidance and supervision during the period June 2015

MRATANU DEY

DY CHIEF SIGNAL AND TELECOM ENGINEER

EASTERN RAILWAYS KOLKATA

ii | P a g e

STATEMENT BY THE CANDIDATE

ADRITA MAJUMDER

BTech 7th

Semester

Department of ECE Roll Number 08

Academy Of Technology

I hereby state that the technical presentation entitled signaling and telecommunication has been prepared by

me to fulfill the requirement of the vocational training during the period JUNE 2015

ADRITA MAJUMDER

iii | P a g e

ACKNOWLEDGEMENT

I would really like to thank every person who has helped me to complete my report successfully All the

websites where I have taken help from and all my friends who have helped me to chose this topic and collect

every bit of information about the topic Special thanks to my project mentor MR ATANU DEY without

whom completion of this very report would have been just impossible He has given me his valuable time

and worthy opinion to create my project successfully Definitely my parents are worth mentioning who have

kept supporting me throughout and have kept faith that I could do it

iv | P a g e

ABSTRACT

In this report I have given an overview of the signal and telecommunication systems that have been used and

are presently being used in the Indian Railways as a part of the day-to-day signalling and communication

procedures

I have covered in this report the history and the latest developments in railway signal and communication as

well as related fields I have made an elaborate study on the various equipments that have been used and are

currently being used as part of communication in the railways

v | P a g e

TABLE OF CONTENTS

TITLE PAGE NUMBER

CERTIFICATE BY THE SUPERVISORS I

STATEMENT BY CANDIDATE II

ACKNOWLEDGEMENT III

ABSTRACT IV

SOLID STATE INTERLOCKING 1

INTEGRATED POWER SUPPLY 5

SINGLE SECTION DIGITAL AXLE COUNTER 9

DATA LOGGER 15

OPTIC FIBRE 22

SIGNALLING RELAYS 34

CONCLUSION 40

BIBLIOGRAPHY AND REFERENCES 41

1 | P a g e

SOLID STATE INTERLOCKING

INPUT CARDS All the field conditions (ie Field relay contacts) are connected to these input cards of EI system

The maximum inputs capacity of each RI card will depend on design of the RI cards by different

manufacturers The total number of inputs will depend on the yard layout

Total inputs means

Field inputs ECRs TPRs NWKR etc

Panel inputs GNs UNs NWNs RWNs etc

Read back inputs HR DR WNR WRR etc

Opto couplers are provided to isolate field optically from the system in Input cards These cards will read the

conditions of inputs and passes the information to EI system

PROCESSOR CARD This card is also called as central processing unit card of the System This is provided with microprocessor

RAM ROM EPROM EEPROM Memory ICrsquos These EEPROMS or EPROMrsquos (ROMrsquos) are programmed

with software required for executing the system commands

System software consists of the following

- Executive software programmed in system EPROMrsquos

- Application software programmed in DATA EPROMrsquos

-

EXECUTIVE SOFTWARE This software is common to all EIrsquos for the same company manufacturing

This is a factory installed software

Performs all operations

Cuts off vital supply voltage to output relays in case of unsafe failures

2 | P a g e

APPLICATION SOFTWARE This software is specific to each station and different for different stations

This is as per table of control of specific station

Can be installed at site by signal engineers

Logic installed through Boolean expressions or user-friendly equations

OUTPUT CARD (RELAY DRIVE CARD) This card receives the output of CPU card as input and picks up relevant output relay as per the panel

operatorsrsquo request The output of this card is terminated on phoenix terminals from there the output relays are

connected

The essential modules of an EI is as follows

Hardware module

Software module

HARDWARE MODULES USED IN THIS SYSTEM Equipment consists of

CARD FILE

Each card file is like a shelf having 20 Slots to accommodate various PCBs that are used in a system

Slot nos1 to 15 and 20 are used to accommodate Non-vital Input-output or Vital Input or Vital Output PCBs

Slot no16amp17 are used to accommodate Power supply PCB Slot no18amp19 are used to accommodate CPU

PCB In this cardfile a mother board is available in the rear side connecting all the 20 Slots This cardfile is

suitable to mount on a 19rdquo rack

Power

Supply

Card

CPU

Card

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19

20

CPU PCB Each card file to have one CPU PCB and always placed in slot no18amp19 In this card Micro

Controller used is Motorola 68332 and its speed is 21 MHz In this card 4 nos of flash EPROMs of 8 MB

are used to store executive and application software Two nos of fast Static RAM (each 64KB) are used to

process the vital data and Four nos of Static RAM (each 64KB) are used to store events and errors

The main functions of CPU is it monitors continuously status of Vital Boards It also monitors

system internal operation for faults and responds to detected faults It processes application logic based on

inputs

received and deliver outputs to drive external gears It records system faults and routine events in user-

accessible memory It monitors and controls the serial communication ports It controls power to vital outputs

through external VCOR relay

POWER SUPPLY PCB

3 | P a g e

Each card file to have one Power Supply PCB and always placed in slot no16amp17 Power supply

PCB is basically a DC-DC converter that converts 12V DC input supply is +12V -12V and +5V required for

various board functioning Based on diagnostic check by CPU Power Supply Card receives 250Hz signal

from CPU and extends supply to VCOR relay This card provides isolated supply to internal circuit

VITAL OUTPUT PCB Each Vital Output PCB has 16 Outputs It is available in 12V and 24V DC applications Each Vital

Output can drive an output device such as any Q-series relay This output relay in turn controls signals

points crank handle siding control level crossing etc Since Vital Output drives the relay which controls

important outdoor gears all the Vital Output boards are continuously diagnosed by a CPU Any abnormality

in any of the outputs will shut down the system to ensure safety

VITAL INPUT PCB Each Vital Input PCB has 16 Inputs It is available in 12V and 24V DC applications Each Vital Input

is assigned to read the status of outdoor gears such as Track circuits Point detectors Crank handles Siding

controls level crossing etc Since the Vital Inputs read the status of outdoor gears they are normally

configured with double cutting arrangement using relay contacts

NON-VITAL INPUTOUTPUT PCB Each Non-vital IO has 32 inputs and 32 outputs in one PCB It is available in 12V and 24V DC

applications Non-vital inputs are Panel push buttons and keys Non-vital outputs are Panel indication LEDs

counters and buzzers The status of Non-vital Inputoutput is known from LED indications available in front

of the card

VITAL CUT OFF RELAY- VCOR Each card file will have one VCOR to ensure the healthiness of the system VCOR has 6 FB

dependent contacts each rated for 3 Amps When system is healthy the coil receives voltage from Power

Supply PCB which in turn controlled by CPU Power to Vital output board is controlled by VCOR thus

ensuring safety

WIRING HARDWARE 48 Pin Address select PCB and Connector assembly is provided for Vital Input and Vital Output

cards 96 Pin Address select PCB and Connector assembly is provided for Non-Vital IO cards 48 Pin

Connector Assembly is provided for PS and CPU PCB EEPROM PCB which is provided on rear side of the

CPU connector to configure various serial communication ports Keying plugs are provided in the cardfile to

ensure coding to each type of cards

SOFTWARE MODULES USED IN THIS SYSTEM System software consists of the following

EXECUTIVE SOFTWARE This software is common to all EIrsquos for the same company manufacturing

This is a factory installed software

Performs all operations

Cuts off vital supply voltage to output relays in case of unsafe failures

APPLICATION SOFTWARE This software is specific to each station and different for different stations

This is as per table of control of specific station

Can be installed at site by signal engineers

Logic installed through Boolean expressions or user-friendly equations

4 | P a g e

A GEC-MANUFACTURED SSI INTERLOCKING CUBICLE

A PAIR OF DATA LINK MODULES

TRACKSIDE FUNCTIONAL MODULE

5 | P a g e

INTEGRATED POWER SUPPLY

INTRODUCTION A typical 4 line station requires power supplies of 24 V DC( 5 nos ) 12 VDC ( 5nos ) 6V (2 nos)

110 V DC and 110 V AC for signalling These require as many chargers and Secondary cells amp Invertors

requiring more maintenance amp spares Can they be Integrated in to one system

Thus the concept of Integrated Power Supply has been evolved by integrating concepts One Charger

One set of Battery Bank feeding Invertors and DC- DC converters for deriving various DC amp AC

voltages Integrated power supply system delivers both AC amp DC Power supplies as an output with the

output voltage tolerance of plusmn 2

ADVANTAGES Reduces maintenance on Batteries Battery charger amp overall maintenance

Its construction is in modules and hence occupies less space Reduced space requirement resulting in

saving of space for power supply rooms

Provides centralized power system for complete signaling installation with continuous display of

working status of system for easier monitoring

Defect in sub-units of system is shown both by visual amp audible indication Reflects the condition of

battery with warning

Replacement of defective modules is quick amp easy without disturbing the working of the system

It uses (n+1) modular technology hot standby arrangement and hence high reliability and more

availability of the system

The system provides uninterrupted supply to all signalling system even during the power failures

Thus No blank Signal for the approaching drivers

System can be easily configured to suit load requirement

The diesel generator set running (Non-RE area) is reduced almost to lsquoNILrsquo Hence low wear and tear

of DG set components amp reduced diesel oil consumption

COMPONENTS (a) Un-interrupted power supply (U P S)

(i) SMPS Battery chargers with Hot stand-by mode

(ii) Hot Standby PWM Inverters with auto changeover

(iii) CVT Regulator [FRVS]

(b) AC distribution board [ACDB]

(i) STEP DOWN TRANSFORMERS

(c) DC distribution board [DCDB]

(i) DC-DC converters

WORKING IPS works satisfactorily for AC input variation of 150V AC to 275V AC with single-phase power supply

and frequency variation from 48 Hz to 52 Hz The input is fed to SMPS charger which converts in to 110

VDC as output It is fed as input to three sub units

To battery bank charging the batteries

To ON line inverters that converts 110 VDC in to 230 VAC plusmn 2as output

6 | P a g e

As 110 VDC bus bar to DC Distribution Panel as an input to various DC-DC converters located in

it

A 110 V Battery Bank of VRLA cells are connected to SMPS Panel IPS Status Monitoring Panel is

located at ASM room or at SampT staff room if round the clock SampT staff is available at Station

CONSTRUCTION IPS mainly consists of

SMR (Switch Mode Rectifier) Panel SMPS based Float cum Boost Charger (FRBC) Panel

AC Distribution Panel

DC Distribution Panel

Battery Bank (110V DC)

Status Monitoring Panel

SMR (SWITCH MODE RECTIFIER) PANEL SMPS BASED FLOAT

CUM BOOST CHARGER (FRBC) PANEL It consists of SMR FRBC modules and Supervisory amp Control Unit SMPS based SMRs

(converters) SMPS based Float cum Boost Chargers (FRBC) modules are provided with (n+1) modular

technology hot standby arrangement with active load sharing basis and 1 additional module as a cold standby

(n+2) Supervisory amp Control Unit which controls and monitor the complete system It has various

indications on the panel reflecting the working of the panel

FRBCs are suitable for operating in parallel on active load sharing basis with one or more modules of similar

type make and rating

n = required no of modules to cater for actual current requirement

AC DISTRIBUTION PANEL It is made of ON-Line inverters with (1+1) modular technology hot standby arrangement amp CVT

(Constant Voltage Transformer) AVR (Automatic Voltage Regulator) and set of step down

transformersThe inverter is protected against overload and short circuit with auto reset facility Whenever

the failure occurs it trips and restart automatically after about 10 to 20 sec But if the problem persists the

protection is permanently gets latched and it will not be switched ON again unless the fault is cleared

followed by pressing of reset button The output of inverters is regulated to 230V AC plusmn 2 50Hz plusmn1Hz for

an input voltage variation of 90V DC to 140V DC Normally both the Inverters are powered ON and both are

delivering the Output voltage but only one (main) inverter is connected to the Load If main inverter is failed

then only the stand-by inverter will come on Load automatically with in 500msec At 70 Depth of

Discharge (DOD) of the battery bank 110VDC supply to the inverters will be cut-off So the Signals feed will

be cut-off The auto-change over arrangement is also provided for bringing the CVT in circuit with in

500msec when the both the inverters output is failed It has various indications on the panel reflecting the

working of the panel

DC DISTRIBUTION PANEL It takes care of DC Power supply requirements of our signalling It consists of sets of DC-DC

converters for individual DC power requirements with (n+1) modular technology hot standby arrangement

with active load sharing basis The DC-DC converters of Relay Internal are provided with (n+1) modular

technology hot standby arrangement with active load sharing basis and 1 additional module as a cold standby

(n+2) The DC-DC converter works satisfactorily with the input voltage variation of 98VDC to 138VDC At

90 Depth of Discharge (DOD) of the battery bank all the DC-DC converters 110VDC Input supply will be

cut-off except for Block Tele DC-DC converters The supply for Point operation is also catered through a

20A fuse by this unit It is also provided with various indications that reflect its working

7 | P a g e

STATUS MONITORING PANEL IPS status monitoring panel has been provided in the ASM room for giving the important alarms and

indications to ASM Status Panel tells present working status of IPS displaying battery voltage continuously

and five other indications which will light according to IPS status During normal working these indications

will not lit Whenever the battery has come on to the load and has discharged by 50 DOD (Depth of

Discharge) then first Red indication lit with description ldquoSTART GENERATORrdquo with audio Alarm ie DG

set is to be started and put on the load If DG set is not started with this warning then if battery gets further

discharged to 60 DOD and second Red indications appears with description ldquoEmergency Start generatorrdquo

with audio alarm even now if DG set is failed to be started the battery further gets discharged to 70

DOD and 3rd Red indications appear with description ldquo System shut downrdquo with audio alarm which will

continue till Generator is started resulting in AC output from IPS is automatically cut off results all the

signals will become blank

When there is any defect in any sub module of IPS even without affecting working of system the 4th

Red indication appears with description ldquoCall SampT Staffrdquo with audio alarm so the ASM advises SampT staff

accordingly Green LED 5th indication comes with the description ldquoStop Generatorrdquo with audio alarm when

the DG set is running and if the Battery bank is fully charged condition

EARTHING The IPS systems and its individual modules are having earth terminals and all these are properly

earthed with earth resistance of less than 1 ohm Earth provided shall preferably be maintenance free using

ground resistance improvement compound (The acceptable Earth Resistance at earth busbar shall not be

more than 1 ohm Code of practice for earthing and bonding system for signalling equipments)

LIGHTNING AND TRANSIENT PROTECTION IN IPS Manufacturer will provide Stage1 amp Stage 2 protection along with the IPS These are described

below

Stage 1 protection is of Class B type against Lightning Electro-Magnetic Impulse (LEMP) amp other

high surges provided at Power Distribution Panel It is provided with a 63 Amp fuse in phase line and is

connected between Line and the Neutral and also between the Neutral and Earth

Stage 2 protection (Power line protection at Equipment level) is of Class C type against low voltage

surges provided at the equipment input level This is thermal disconnecting type and equipped with

protection against SPD (surge protection device) failure due to open amp short circuit of SPDs and is connected

between the Line and the Neutral If supply data signalling lines (ACDC) are carried through overhead

wires or cables above ground to any nearby building or any location outside the equipment room additional

protection of Stage 2 type shall be provided at such locations Class B amp Class C arrestor is provided on a

separate wall mounting type enclosure in IPS room

Stage3 protection (Protection for signallingdata line) is of Class D type All external data signalling

lines (ACDC) shall be protected by using this Class D type device It consists of a combination of Varistors

and Gas Discharge Tube with voltage and current limiting facilities

FEATURES Chargers used in this system are of SMPS technology chargers with 90 efficiency These chargers

are supported with hot standby mode with (n+1) modular technology

Onetwo sets of Maintenance free Battery banks (110VDC) Normally one set (110VDC) of Battery

bank is used Conventional flooded type Lead Acid Batteries or Low Maintenance Lead Acid

batteries can also be used (SMRs settings are required to be adjusted depending on the type of

Batteries used) Various voltage levels of

8 | P a g e

battery banks are avoided Reduction in Battery maintenance amp less flour area required

DC-DC Converters working from 110V Central battery have been used for all dc supplies This has

improved overall efficiency of the system since number of conversion from AC to DC have been

reduced to 2 stage as compared to 3 stage conversion in case of transformer-rectifier system

DC-DC converters are available in modules Easy replacement of defective modules This ensures

less down time

DC-DC Converters are used in load sharing N+1 configuration (ie with hot standby with N+1

modular technology) to improve the reliability amp availability of the system

Capacity of inverter has been brought down to 15 KVA from 5 KVA and used for feeding only

Signals supply Hot standby inverter is provided with auto changeover facility This improves the

availability of the overall system

High efficiency inverter is used with PWM (Pulse Width Modulation) technology in place of Ferro-

resonant technology based inverter This improves the efficiency of the overall system

Continuous power to Signal Circuits even in absence of DG setLocal Power Supply

Generators need not be switched ON every time during train movement

Metal-to-metal relay installations and block working by axle counters have also been covered

Supply of spare modulesComponentsCells have been included as part of main supply

Provides highly regulated voltage to all signal relays amp lamps for better life

9 | P a g e

SINGLE SECTION DIGITAL AXLE COUNTER

INTRODUCTION- The axle counter equipment is working on high frequency and using amplitude modulation or phase

modulation for detection of presence of wheel The equipment described in this notes is Phase modulation type

for the detection of presence of wheel In the Phase modulation type track device the detection of presence of

wheel is with the phase reversal of 1800 out of phase which enables this system to be more healthy and safe

In Phase Reversal Modulation technique trolley suppression arrangements to prevent the counting of

wheels caused by push trolley passing over the track device are not required as the system will take care of

validation of generated pulses caused by passage of wheel over the track device depending up on the phase

shift of the pulse This phase shift of the pulse may be normally 160deg to 180deg for a train wheel and it may be

approximately 100deg to 120deg for a push trolley wheel

This is Digital Axle Counter equipment for single track sections containing 2 out of 2 micro-

controllers to count the axles establish the track occupancy of a track section and to provide this information

to the block or the interlocking equipment

In this system no separate evaluator is required and no analog data is being transmitted One set of

Axle counter equipment is provided at entry end and other set provided at exit end Both sets are being

connected through a twisted pair of telecom cable ie existing RE cable one PET quad is used for both UP

and DN Axle Counters Digital DATA is being transmitted between two ends of Axle counters (Outdoor

track side Detection points)This system is a fully duplex capable of operating according to CCITT V21 and

the Data will be transmitted at the rate of 300bitsec This data Transmitted ensure negligible interference of

the noise The system is highly reliable

FEATURES (a) The system consists of

(i) Single Section Digital Axle Counter (SSDAC) units

(ii) Tx Rx coils

(iii) Vital Relays

(b) TxRx coil axle detectors are mounted to the web of the rails The design of system consists of 21 KHz amp

23 KHz High frequency Phase Reversal type axle detectors

(c) Compatible with 90R 52Kg amp 60Kg rail profiles Easy to install commission amp maintain

(d) Track devices at both (entry amp exit) points of the section should be fixed on the same rail

(e) System is designed to detect the solid wheels with diameter gt 400mm with standard wheel flange

(f) The system works in pairs For monitoring single-track section one pair of SSDAC units are required and

to be installed near the trackside one at the beginning and another at the end of the track section ie

Trackside electronic counting equipment

(g) The basic design of the system is based on counting the number of axles passing at each detection point

These stored counts are transmitted to the second unit of the system and vice versa by means of modem

communication

(h) The communication consists of digital packets having details of Counts amp Health

10 | P a g e

(i) If counts registered at both detection points are equal the section is cleared otherwise the section is shown

as occupied The system ensures no error condition to arrive at the decision of clearance

(j) System is designed as per CENELEC SIL-4 (European standard) using micro controller along with other

electronic circuits and programmed using dedicated software When any of these circuits fail the system

goes to fail safe condition

(k) It is programmable for either Preparatory Reset or Conditional Hard Reset as per requirement

(l) Micro controller based design with 2 out of 2 decisions and counting through software

(m) V21 Modem communication (2-wire) on frac12 quad cables and also compatible to work on voice channel of

OFC amp Radio

(n) Opto isolated vital relay drive for Q-style 24V 1000 _ and Vital Relay output can be giving at both ends

of the system

APPLICATIONS The system can be widely used in Railways for Block Working (BPAC) Intermediate Block Signaling Auto

signalling and Track circuiting for i) Loop line ii) Main line iii) yard lines

SYSTEM DESCRIPTION

This system comprises of

Tx coils-2 nos

Rx coils-2 nos

Reset Box (RB 258A)

Card 1 Signal Conditioning Card ndash 1

Card 2 Signal Conditioning Card - 2

Card 3 Micro controller Logic Board ndash 1

Card 4 Micro controller Logic Board ndash 2

2 nos for independent resetting ndash when used in block sections

1 no for common resetting ndash when used for Track circuiting at stations

Card 5 Event Logger Card

Card 6 Modem Card

Card 7 Relay Driver Card

Card 8 DC-DC Converter Card

SSDAC (DACF 700AP) UNIT

(A) SIGNAL CONDITIONING CARD (CARD 1amp2) (SCC) -1 (SCC-1) generates 21 KHz carrier

signals

-2 (SCC-2) generates 23 KHz carrier signals which is transmitted to 2nd

set of Tx coils

s receive these signals

modulated

train pulses

11 | P a g e

(B) MICRO-CONTROLLER LOGIC BOARD CARD (CARD 3amp4) (MLB) The Micro-controller Logic Board (MLB) is the heart of the system

o 8051 Based Architecture

o 8 Bit Micro Controller

o ATMEL AT89S8252 Micro controller

o 2 out of 2 Decision

o Uses C subset language

- TOOLS

o KEIL μ Vision Development System

o Universal Programmer

o 2KB Program Memory

o 256 bytes RAM

o 8KB Flash memory

o 32 Programmable IO lines

o Wide Operating Voltage range of 4V-6V

o Full Duplex Serial Port

o Programmable Watch Dog Timer

o Fully Static operation up to 24MHz (Upgraded to 40MHz)

o Operating Temperature of ndash40degC - +85degC

o Use of State Machine for Axle Counting

o Use of ASCII MODBUS protocol

o Use of CRC16 technique for Error Checking during communication

o Wheel detection

o Train direction checking and

o Wheel counting functions

o It receives the remote wheel count and computes the status of the section for clear or occupied

o It also checks various supervisory signal levels like supervisory of TxRx coils presence of various

cards communication link failure etcThese cards communicate with each other for wheel count

At Entry-end if train enters into section (1st detection) the counts are incremented and when train

shunts back from the same detection ie if train exits from the section from the same detection the counts are

decremented At Exit-end if train enters into section (2nd detection) the counts are decremented and when

train shunts back from the same detection ie if train exits from the section from the same detection the

counts are incremented Both the track devices at Entry and Exit ends must be fixed on same side of the

track

This MLB card is having Extensive LED display

o A block of 8 LED indicators for count progress error display

o 2 independent LED indicators for section status

o The errors occurring in the system during the operation of the SSDAC are encoded and are indicated by

means of the 8-LED block present on the front panel of the MLB cards

(c) EVENT LOGGER CARD (CARD 5)

Event logger card is designed to capture and store important signals from the remote and local SSDAC units

The stored data can be downloaded from the event logger card for the purpose of analyzing the events

occurring during the operations of the SSDAC The data can be analyzed with the help of CEL data analyzer

software

12 | P a g e

The event logger card captures following signals

(i) Pulse signals

(ii) Supervisory signals

(iii) Card removal information

(iv) Serial packets from

Event Logger card has a Rabbit processor and 2 MB FLASH MEMORY to store packets The data is initially

stored in the buffer and subsequently transferred to FLASH memory every two minutes Normally 4096

pages of the data can be stored in flash memory on FIFO (first in first out) basis

Run This LED blinks continuously indicating the normal working of the event

Log This LED blinks whenever data is being logged into the flash memory (Approx after every 2 minutes)

Dnld This LED is ON when data is being downloaded from the flash memory of the card and becomes OFF

when download is complete

(D) MODEM CARD (CARD 6) (i) The modem card transmits and receives the digital packet information form one counting unit to the other

The packet will appear after every 18 sec and the packet carries the latest information such as

(ii) The modem card being used is V21 type (2-wire) in SSDAC

(iii) This card interfaces with serial RS232C port of both Micro-controller Logic Boards

(iv) It multiplexes the two RS232C inputs and selects one of the two channels and provides signal conversion

from digital to analog (FSK modulation) and vice-versa

(v) Data transmission rate is 300 bitssec

(vi) Automatic Gain Control circuit is incorporated hence no gain adjustments required

(vii) Mode selection on Modem card The modem has been set in lsquoORIGINATORrsquo mode for entry and in the

lsquoANSWERrsquo mode for exit in the factory

(viii) LED Indications provided on Modem card

-Transmitting the signal when LED is flashing

- Receiving the signal when LED is flashing

-Remains OFF in SSDAC

-Carrier is detected when LED is glowing

(E) RELAY DRIVER CARD (CARD 7) (i) The Relay Driver card (RD) provides the 24V DC output required for driving Vital Relay

(ii) One RD card is used in each SSDAC counting unit The RD card receives the command of clear and

clock signals from MLB1 amp MLB2 cards and drives the vital relay lsquoONrsquo when section is NOT OCCUPIED

through opto- isolator circuit

(iii) If a train occupies the section the vital relay is dropped The vital relay status is read back by the system

as per the driving output

(iv) It has

13 | P a g e

ndash LED flashes when the section is clear

ndash LED flashes when the section is clear

All the above LEDrsquos are lit for section clear condition

(F) DC-DC CONVERTER CARD (CARD 8)

INPUT VOLTAGE Nominal Voltage voltage 24V DC Maximum current drain= 12A

Required voltage 18V DC to 30V DC

Output voltage

Nominal Voltage +5 V DC 2 A Required voltage 4 7 5 t o 525V DC

Nominal Voltage +12V DC 200 mA Required voltage 1175 to 1225V DC

Nominal Voltage +24V DC 300 mA with common ground Required voltage 235 to 245V DC

Nominal Voltage +15V DC 100 mA with isolated ground Required voltage 145 to 155V DC

SURGE VOLTAGE AND LIGHTNING PROTECTION Transient surge voltages arise as a result of Lightning discharge switching operations in electrical

systems and electrostatic discharge These surge voltages often destroy the electronic equipment to a large

extent In order to prevent surge voltages from destroying the equipment all the input lines of SSDAC ie

Power Supply (24V) Reset (48V) amp Modem is to be routed through surge voltage protection devices for

effectively protecting the system These devices (3 numbers) are mounted in a box and supplied along with

the system One number of box is to be installed at each location and wired to the SSDAC

Each surge voltage protection device consists of two parts

(a) Base

(b) Plug Trab

The Base of the device is used for wiring the input and output signals The connection details from relay

room to the box and from box to SSDAC unit are provided on the box The Plug Trab consists of MOV and

GD Tube and diverts the excess energy during surge voltages or lightning into the ground connection The

operation of these devices relies on a high quality ground connection in order to safely shunt away the

unwanted energy The impedance of the ground connection is critical and it should be less than 2 Ohms

NOTE The 3 Plug Trab connections are not to be interchanged with one another The plug Trab is a

detachable device and can be replaced with SPARE unit in case of blown device which is indicated by

means of LED for 24 V

EFFECTIVENESS OF PLUG TRABS The effectiveness of plug Trab depends wholly on the Earth connection provided to the system The earth

provided to the system should be less than 1 ohms and connections should be firm and proper to the SSDAC

unit VR box etc

SURGE VOLTAGE AND PROTECTION DEVICE SV-120 The Surge Voltage protection device is to be installed at each location along with every SSDAC unit

14 | P a g e

EARTHING- The lead wires connecting the installation and the earth electrode shall ordinarily be of stranded

copper wire of 29 sq mm (19 strand wires of 14 mm diameter) Copper wire has been specified because GI

wires usually are having greater corrosion However in areas where copper wire may be frequently stolen

due to theft ACSR of size 64 sq mm (19 strands of 211 mm diameter) may be used

LIMITS OF EARTH RESISTANCE (a) Apparatus case connected to Earth (SSDAC and vital Relay Box is housed in Apparatus case and

Connected to earth at outdoor) shall be less than or equal to 1 ohm

(b) All cable connected to same earth shall be less than or equal to 1 ohm

(C) Reset box connected to earth near SM s Room shall be less than or equal to 1ohm

EQUIPMENT TO BE EARTHED A Common Earth should be provided for SSDAC for items 1(a) amp (b) of the above at the outdoor

(a) The Apparatus Case is to be connected to earth (the chassis of SSDAC amp Vital Relay Box should be

properly connected to apparatus case)

(b) Metallic sheath and armouring of all the underground main cables are to be earthed

(i) In RE area the metallic sheath and armouring of main telecom cables are earthed at both ends

(ii) In RE area the armouring of Jelly filled cable shall be earthed at both ends

(c) The Earthing shall be provided at every location box where cables are terminated

(d) Earth already available for other equipment may be used for earthing of Reset Box near SM s Room

Cabin etc

15 | P a g e

DATALOGGER

INTRODUCTION Datalogger is a Microprocessor based system which helps in analysing the failures of relay inter

locking system Electronic Interlocking system This is like a black box which stores all the information

regarding the changes take place in relays AC DC Voltages and DC currents along with date and time The

same information data can be transferred to the computer to analyse further ldquoon line ldquooff linerdquo analysis of

stored date A print out also can be obtained through a printer by connecting directly to the datalogger unit

The data belongs to Relay contacts is considered as digital inputs and the data belongs to voltage

levels currents is considered as Analog inputs Datalogger lsquos are mandatory for all new relay interlocking

(PIRRI) EI installations and it is also recommended to provide in all existing PIs RRIs To increase the

line capacity mechanical signalling equipments are upgraded to PI RRI or EI Due to complexity in the

circuits and wiring sometimes it is very difficult to rectify the failures So datalogger can monitor these

systems with real time clock Thus it can be named as black box of Samp T equipments and hence it is a vital

tool for accident investigation Datalogger is used at Stations yards Whereas in case of Auto Section amp IBH

Mini dataloggers called as Remote Terminal Unit (RTU) are used

ADVANTAGES OF DATALOGGERS (a) Dataloggers helps in monitoring the typical failures such as intermittent auto right failures

(b) It helps in analyzing the cause of the accidents

(c) It helps in detecting the human failures errors such as

(i) Drivers passing signal at Danger

(ii) Operational mistakes done by panel operators ASMrsquos of operating department

(iii) Signal and telecom engineering interferences in safety circuits

(iv) Engineering and electrical department interferences failures

(v) It helps as a ldquoTOOLrdquo in preventive maintenance of signaling gears

(d) Dataloggers can be connected in network Networked dataloggers helps to monitorthe PIRRIEI remotely

(e) Failure reports can be generated remotely with help of datalogger network

(f) On line and Off line track simulation is possible

(g) Speed of the train on point zones can be calculated

(h) Age of the equipment in terms of number of operations etc

COMMON EQUIPMENT FOR ALL DATALOGGERS ARE GIVEN

BELOW (a) CPU card

(b) Digital and Analog input cards

(c) Local terminal(PC)

(d) communication links

(e) Printer

All the dataloggers requires a potential free ( spare ) relay contact for monitoring digital inputs

through Digital input cards amp for monitoring Analog inputs such ACDC bus bar voltage levels through

Analog input cards Digital and Analog inputs are connected to the Processor card Processor card consists of

memory ICrsquos Memory ICrsquos are programmed as per requirement of the signal engineers

Provision of Dataloggers is mandatory with RRI systems and is optional for PI systems as per

amendment to the specification for Relay Interlocking systems ( IRSS-36 ) The data collected by the

datalogger can be used for failure analysis repetitive discrepancies and for accident investigations

16 | P a g e

Note

If the serial communications is more than 50m then line drivers shall be used up to 3 Kms

4wire leased line Modems shall be used if the serial communication is more than 3 Kms

STUDY OF EFFTRONICS DATALOGGER TECHNICAL DETAILS (a) 24V 12VDC Power Supply

(b) Total Storage Capacity of 10 Lakh events

(c) In-built Temperature sensors

(d) Internal Buzzer for alarming during failures

(e) Real Time clock with internal battery backup with data retention up to 10 years

(f) 512 LED matrix to indicate the status of 512 Digital inputs at a time page wise

(g) Seven segment LCD screen (2x24) to display the status of digitalanalog signalsTime Temperature etc

(h) Using the keyboard various functions can be viewed in the LCD panel

(i) Max Digital Inputs 4096

(j) Max Analog Inputs 96

(k) Digital Input Scanning Time 16 millisecond

(l) Analog Input Scanning Time is less than 1 Sec

HARDWARE (EQUIPMENT) Datalogger system consists of

(a) Datalogger (CPU - with Microprocessor 68000)

(b) Digital input cards

(c) Dual modem card

(d) Digital Scanner units (DSU)

(e) Analog Scanner units (ASU)

CPU CARD It is provided with Motorola microprocessor M 68000 It performs all the activities pertaining to the

datalogger It continuously scans (check) the Digital inputs(inbuilt) Digital Scanner Units and Analog

Scanner Units ie scanning of digital signals (Relay operations) for every 16-milli seconds and scanning of

analog signals (ie ACDC voltages amp DC currents) for less than 1 second

This card will support the IO interfaces of LCD (Liquid Crystal Display) - 2X24 alphanumeric Key

Board LED Matrix Display Real Time Clock LCD display and keyboard This will acts as man machine

interface between the datalogger and the signal engineer All the operations (Software) can be performed

using this LCD and keyboard

Real time display with 7 Segments This is built in real time clock within Datalogger and its current

time will be displayed on six 7-segment display provided (Real time clock depend upon DALLAS 1286

chip) This IC will come with internal battery backup hence there is no need to add external batteries

CPU card continuously scans (checks) the DSUs and ASUs Each input connected to digital scanner

units are optically isolated by Opto couplers When CPU card scans the digital inputs it compares with the

previous stored data and if there is any change from the previous status then only that data will be stored (the

status conditions of relay) with date and real time A total of minimum 10 Lac events can be stored in

memory on first in first out basis so that latest data is available in the system There is no loss of data from

datalogger memory in case of power supply failure of datalogger

DIGITAL INPUT CARDS (IN-BUILT) This system is having maximum 8nos of inbuilt Digital inputs cards Maximum 64nos of digital

inputs can be connected to each digital input card The potential free relay contact may be front or back

contact terminated at the Tag Block from the relay of signals tracks points Buttons etc and are

17 | P a g e

subsequently connected to Digital input cards through Flat Ribbon Cable (FRC) connectors These in-built

digital input cards can monitor a total 512 nos of relays status

DIGITAL SCANNER UNIT (DSU) Each DSU contains 8 nos of Digital Input cards Each input card can be connected with 64 inputs

Total input capacity of DSU unit is 512 inputs These scanner cards contain Optocouplers and Multiplexer

Inputs are connected to Stag card The stag card out put is connected to DSU through FRC connectors

Maximum 7 nos of DSUs can be connected to the system So Digital input capacity of the system is 4096

All these digital inputs are scanned at rate of 16 msec

ANALOG SCANNER UNIT (ASU) ASU contains maximum 3 nos of Analog input cards Each input card can be connected with 8nos of

Analog inputs Total input capacity of the ASU is 24 analog input channels Maximum 4nos of ASUs can be

connected to the system Analog input channel capacity of the system is 96 All these analog inputs are

scanned at a rate of less than 1 sec

PARALLEL PORT Parallel port is provided for connecting printer

RS-232 SERIAL PORTS At least 6 Serial communication ports are provided for communication with other dataloggers

Central Monitoring Unit Remote Terminal Unit Electronic Interlocking system Integrated Power Supply

system etc

EXTERNAL NON-VITAL RELAY CONTACTS These relays provided in the system where 16 number of the Relay contacts are provided on the rear

panel through Tele control port to extend alarms and to control the power equipment from remote or local

locations through computer in case of any occurrence of failures Each control can sink or source 100 m

amps of current

INTERNAL MODEM CARD DUAL MODEM CARD (IN-BUILT) It is fixed in datalogger Euro rack itself One card contains two modems The top modem is called

ANS (answer) modem and the bottom modem is called as ORG (originate) modem It is used in case of

networking of Dataloggers In network connect lsquoANSrsquo modem to the lsquoORGrsquo modem of one adjacent station

and connect lsquoORGrsquo modem to the lsquoANSrsquo modem of other adjacent station

POWER SUPPLY Normally 24V DC (12V DC is optional) supply with battery backup is required for the system

working

Input Voltage Range 18Vhellip32V DC (For 24V) 9Vhellip18V DC (For 12V)

INPUT REQUIREMENTS Relay inputs (digital inputs) and analog inputs (voltages currents etc) are required to be connected

to the system as per the requirements of RRI PI SSI as the case may be Some of the inputs to be

monitored is given below

(a) Digital inputs

(i) Field inputs All TPRs NWKRs RWKRs ECRs Crank Handle relays SidingSlot LC gate

control relays etc

(ii) Control Panel inputs All button Knob SMrsquos Key relays

18 | P a g e

(iii) Internal relays

British system All HR DR HHR WNR WRR ASR UCR RR LR UYRTLSR TRSR TSR

JSLR JR etc

SIEMENS system Z1UR Z1UR1 GZR ZDUCR ZU(R)R ZU(N)PRG(R)RG(N)R U(R)S

U(N)PS UDKR DUCR U(R)LR UYR1 UYR2 G(R)LRGR1GR2

GR3 GR4 OVZ2U(R)RW(RN)R (RN)WLR Z1NWR Z1RWRZ1WR1 WKR1 WKR2 WKR3 etc

(b) Analog channels

(i) 230 V AC (for power supplies in the power panel)

(ii) 110V AC (for Signal and Track transformers)

(iii) 110V DC (for Point operation)

(iv) 60V DC (Siemens relays)

(v) 24V DC (Q-series relays)

(vi) 24V DC (for Block Axle counters)

(vii) 12V DC (for indication)

(viii) 20A (for point operation current)

(ix) 10V AC 5KHz (for Axle counter channels) etc

SOFTWARE MODULES OF DATALOGGERS

(a) Network Management of Dataloggers (NMDL)

(b) Reports

(c) Fault Entry

(d) Track Offline Simulation

(e) Train Charting

NMDL SOFTWARE FEATURES (a) Online Relay Status

(b) Online Faults - To view information of various Online Faults as they occur in the stations where

the Dataloggers are connected

(c) Online Simulation - Graphical view of relay operations train movements etc

(d) Remote monitoring of stations with the help of NETWORKING

SOFTWARE OBJECTIVES (a) Predictive Maintenance

(b) Easy identification of failures

(c) Crew discipline

(d) Train charting

REMOTE MONITORING OF STATIONS WITH NETWORKING OF

DATALOGGERS The individual Dataloggers of various stations can be interconnected through networking technology

The data of Remote Panel stations can be viewed in a Computer at the Central Monitoring Station The data

of the network is collected by the FEP (Front End Processor) which in turn is transmitted to the computer

COMPONENTS OF NETWORK MANAGEMENT OF DATALOGGERS

(a) Datalogger at stations

(b) MODEM and Transmission medium

19 | P a g e

(c) Front End Processor (FEP)

(d) Central Monitoring Unit (CMU) Computer

FEP (FRONT END PROCESSOR)

FEP acts as a buffer between the Central Monitoring Unit (Computer) and the Network It is provided

at centralised place to retrieve data continuously from station dataloggers and store in memory and transfer to

computer on request It stores 10 Lac telegrams It works on 12V DC It draws 16A continuous current

when all the three modems are connected Normally it shows the number of packets pending to be sent to the

computer on its 7-segment LED display It is provided with MOTOROLA 68000 microprocessor It has 6-

nos of RS-232 communication ports such as COM1 COM2 COM3 COM4 COM5 and COM6 COM1 is

used for Fault Analysis System (FAS) ie Central Monitoring Unit (Computer) connection COM2 to COM6

are used for networking For Bi-directional 2- nos of ports and for Tri-directional (T-network) 3-nos of ports

are used

DATA TRANSMISSION Dataloggers can be networked in Uni-directional Mode or Bi-directional Mode or T ndash Network Mode

In case of loss of data retransmission of data takes place

(a) Uni-Directional Mode

Each Datalogger will send data in only one direction to the FEP Unidirectional mode network is not

preferred

(b) Bi-Directional Mode

Each end of Network is connected to FEP and each datalogger can now transmit data in both the directions

Bi-directional Mode is advantageous it enables the Data Transmission even in case of Network Failure

(c) T - Network Mode

If more no of stations are in network ie if the network is too lengthy then T- network mode is preferred

COMMUNICATION The communication protocol for transmitting data and command between datalogger and CMU is

standardized by the RDSO and is given in the Specifications of Dataloggers

(a) The type of communication used in the network is dependent on the distance between the dataloggers

(b) For shorter distances Opto Converter Box- Opto isolated current loop communication is used

(c) For longer distances Modem (Dial-up leased) Fiber Optic Satellite Microwave communication

MODEMS Modems are used for DATA transfer between Dataloggers and Front End ProcessorThese are

configured to RS 232 Serial Communication Network is connected with two types of 4-wire modems

(a) Internal modem card Dual Modem card (in-built)

It is fixed in datalogger Euro rack itself One card contains two modems The top modem is called

ANS (answer) modem and the bottom modem is called as ORG (originate) modem

Note In case of networking of Dataloggers connect lsquoANSrsquo modem to the lsquoORGrsquo modem of one adjacent

station and connect lsquoORGrsquo modem to the lsquoANSrsquo modem of other adjacent station

(b) External modems

20 | P a g e

These are generally used at FEP (Front End Processor) side to connect the Dataloggers

(i) To transfer Data from one datalogger to another datalogger FEP Baud rate is 9600bps

(ii) These modems are 4-wire line communication

(iii) To transfer the data from FEP to RMU (PC) the Baud rate is 57600 bps

There is no difference between these modems functionally

CENTRAL MONITORING UNIT (CMU) COMPUTER

Central monitoring unit (Fault Analysis Unit) is a Personal Computer and its minimum configuration

shall be specified by RDSO from time to time System Software Windows XPVista(OS) Norton Kaspersky

(Anti Virus) Interbase where Server is not available (DBMS) Oracle where Server is available (DBMS)

software are required to run Datalogger System It is provided with Graphical User interface (GUI) based

software and retrieve data from all Networked dataloggers (up to 32) at various stations It stores data in

standard data base files The CMU is capable of analyzing the data and generate reports audiovisual alarms

on defined conditions This data can be compressed to take backup In central monitoring unit Software used

for analysis of data prediction of faults etc is written in a structured format so that purchaser can

reconfigure it if required It displays the status of signaling gears at any selected time in graphic form for any

selected station yard It retrieves the stored data amp simulates train movement It sends commands to various

Dataloggers to activate audio visual alarm or operate and electromagnetic relay

CMU shares data available in it by other PCs through available local area network where this data can

be used for train charting passenger information purpose The system generates audiovisual alarm in

ASMrsquosSignal Maintainerrsquos room in the case of power supply failure (battery voltage low) or battery charger

defective with acknowledgement facility

(a) Each datalogger has its own identity code which will be transmitted along with data packet to central

monitoring unit

(b) Events recorded at each station are continuously transmitted to central monitoring unit Response time of

data transfer will not exceed 10 sec

21 | P a g e

22 | P a g e

OPTICAL FIBER CABLE

INTRODUCTION The demand for bandwidth on transmission networks is increasing rapidly because video and

graphical rich contents are exchanged through the corporate network or the Internet The Gigabit Ethernet

became ommonly used in the corporate network backbone and 10Gbit Ethernet will be adopted in the near

future Meanwhile in the home the demand for high-speed network becomes popular as the wide spread of

broadband access eg CATV xDSL and FTTH The transmission medium with capability to transmit high

bit rate signal is necessary to satisfy these requirements

The telecommunication transport technologies move from copper based networks to optical fiber

from timeslot based transport to wave length based transport from traditional circuit switching to terabit

router and all optical based networks entering into a new era of optical networking

BASIC PHYSICS OF OFC

OPTICAL FIBER CABLE OFC have Fibers which are long thin strands made with pure glass about the diameter of a human

hair OFC consists of Core Cladding Buffers and Jacket as shown in figure

MONOCHROMATIC LIGHT OR SINGLE COLOR LIGHT Light or visible light is electromagnetic radiation of a wavelength that is visible to the human eye (

about 400 ndash 700 nm) The word light is sometimes used to refer to the entire electromagnetic spectrum Light

is composed of elementary particles called photons Three primary properties of light are

Light can exhibit properties of both waves and particles This property is referred to as wave-particle

duality The study of light known as optics In free space light (of all wavelengths) travels in a straight path

at a constant maximum speed However the speed of light changes when it travels in a medium and this

change is not the same for all media or for all wavelengths By free space it is meant space that is free from

matter (vacuum) andor free from electromagnetic fields

Thus the speed of light in free space is defined by Einsteinrsquos equation E = mc2

Frequency ν speed of light in free space c and wavelength λ are interrelated by ν = cλ

From the energy relationships E = mc2 = hν and the last one an interesting relationship is obtained

the equivalent mass of a photon m = hνc2

When light is in the vicinity of a strong electromagnetic field it interacts with it From this interaction

and other influences its trajectory changes direction as shown in figure

23 | P a g e

INCIDENT RAY REFLECTED RAY AND REFRACTED RAY An incident ray is a ray of light that strikes a surface The angle between this ray and the

perpendicular or normal to the surface is the angle of incidence Reflection is the change in direction of a

wave front at an interface between two different media so that the wave front returns into the medium from

which it originated Common examples include the reflection of light sound and water waves

The reflected ray corresponding to a given incident ray is the ray that represents the light reflected by

the surface The angle between the surface normal and the reflected ray is known as the angle of reflection

The Law of Reflection says that for a specular (non-scattering) surface the angle of reflection always equals

the angle of incidence The refracted ray or transmitted ray corresponding to a given incident ray represents

the light that is transmitted through the surface The angle between this ray and the normal is known as the

angle of refraction and it is given by Snells Law

The figure shows Incident ray Reflected ray Refracted ray the angle of incidence and angle of refraction

REFRACTIVE INDEX - Refractive index is the speed of light in a vacuum ( c =299792458kmsecond) divided by the speed

of light in a material ( v ) Refractive index measures how much a material refracts light Refractive index of

a material abbreviated as lsquo n lsquo is defined as lsquo n=cv lsquo Light travels slower in physical media than it does

when transmitted through the air Refractive index (n) is a function of molecular structure of matter optical

frequency optical intensity determines optical propagation properties of each wavelength ( λ ) may not be

distributed equally in all directions is affected by external temperature pressure and fields

Refractive index of a medium is a measure for how much the speed of light is reduced inside the

medium For example typical glass has a refractive index of 15 which means that light travels at 1 15 =

067 times the speed in air or vacuum Two common properties of glass and other transparent materials are

directly related to their refractive index

First light rays change direction when they cross the interface from air to the material and effect that

is used in lenses and glasses

Second light reflects partially from surfaces that have a refractive index different from that of their

surroundings

SNELLrsquoS LAW-

24 | P a g e

When light passes from one transparent material to another it bends according to Snells law which

is defined as n1sin(θ1) = n2sin(θ2)

where n1 is the refractive index of the medium the light is leaving θ1 is the incident angle between the light

beam and the normal (normal is 90deg to the interface between two materials)

n2 is the refractive index of the material the light is entering

θ2 is the refractive angle between the light ray and the normal

Snellrsquos law gives the relationship between angle of incidence and angle of refraction

For the case of θ1 = 0deg (ie a ray perpendicular to the interface) the solution is θ2 = 0deg regardless of

the values of n1 and n2 That means a ray entering a medium perpendicular to the surface is never bent The

above is also valid for light going from a dense (higher n) to a less dense (lower n) material the symmetry of

Snells law shows that the same ray paths are applicable in opposite direction

TOTAL INTERNAL REFLECTION- When a light ray crosses an interface into a medium with a higher refractive index it bends towards

the normal Conversely light traveling cross an interface from a higher refractive index medium to a lower

refractive index medium will bend away from the normal

This has an interesting implication at some angle known as the critical angle θc light traveling from

a higher refractive index medium to a lower refractive index medium will be refracted at 90deg in other words

refracted alon g the interface If the light hits the interface at any angle larger than this critical angle it will

not pass through to the second medium at all Instead all of it will be reflected back into the first medium a

process known as total internal reflection

The critical angle can be calculated from Snells law putting in an angle of 90deg for the angle of the refracted

ray θ2 This gives θ1

Since θ2 = 90deg

So sin(θ2) = 1

25 | P a g e

Then θc = θ1 = arcsin(n2n1)

For example with light trying to emerge from glass with n1=15 into air (n2 =1) the ritical angle θc is

arcsin(115) or 418deg For any angle of incidence larger than the critical angle Snells law will not be able to

be solved for the angle of refraction because it will show that the refracted angle has a sine larger than 1

which is not possible In that case all the light is totally reflected off the interface obeying the law of

reflection

OPTICAL FIBER MODE An optical fiber guides light waves in distinct patterns called modes Mode describes the distribution

of light energy across the fiber The precise patterns depend on the wavelength of light transmitted and on the

variation in refractive index that shapes the core In essence the variations in refractive index create

boundary

conditions that shape how light waves travel through the fiber like the walls of a tunnel affect how sounds

echo inside

We can take a look at large-core step-index fibers Light rays enter the fiber at a range of angles and

rays at different angles can all stably travel down the length of the fiber as long as they hit the core-cladding

interface at an angle larger than critical angle These rays are different modes Fibers that carry more than

one mode at a specific light wavelength are called multimode fibers Some fibers have very small diameter

core that they can carry only one mode which travels as a straight line at the center of the core These fibers

are single mode fibers This is illustrated in the following picture

OPTICAL FIBER INDEX PROFILE Index profile is the refractive index distribution across the core and the cladding of a fiber Some

optical fiber has a step index profile in which the core has one uniformly distributed index and the cladding

has a lower uniformly distributed index Other optical fiber has a graded index profile in which refractive

index varies gradually as a function of radial distance from the fiber center Graded-index profiles include

power-law index profiles and parabolic index profiles The following figure shows some common types of

index profiles for single mode and multimode fiber

26 | P a g e

OPTICAL FIBERrsquoS NUMERICAL APERTURE ( NA )- Multimode optical fiber will only propagate light that enters the fiber within a certain cone known as

the acceptance cone of the fiber The half-angle of this cone is called the acceptance angle (see figure 18)

θmax For step-index multimode fiber the acceptance angle is determined only by the indices of refraction

Where

n is the refractive index of the medium light is traveling before entering the fiber

nf is the refractive index of the fiber core

nc is the refractive index of the cladding

NUMBER OF MODES IN A FIBER - Modes are sometimes characterized by numbers Single mode fibers carry only the lowest-order

mode assigned the number 0 Multimode fibers also carry higher-order modes The number of modes that

can propagate in a fiber depends on the fiberrsquos numerical aperture (or acceptance angle) as well as on its

core diameter and the wavelength of the light For a step-index multimode fiber the number of such modes

Nm

Where

D is the core diameter

λ is the operating wavelength

NA is the numerical aperture (or acceptance angle)

MODE FIELD DIAMETER - All light do not travels through the core of the fiber but is distributed through both the core and the

cladding The mode field is the distribution of light through the core and cladding of a particular fiber

Mode-Field Diameter (MFD) defines the size of the power distribution When coupling light into or out of a

fiber MFD is important in understanding light loss

27 | P a g e

ADVANTAGE OF OFC COMMUNICATION - bull More information carrying capacity Fibers can handle much higher data rates than copper More

information can be sent in a second

bull Free from Electromagnetic and Electrostatic interference Being insulator no electric current flows through

the fibre and due to this reason fibres neither radiate nor pick up electro - magnetic radiation So WPC

CLEARANCE is not required

bull Low attenuation 025 dbkm at 1550 nm Loss in twisted pair and coaxial cable increases with frequency

where as loss in the optical fibre cable remains flat over a wide range of frequencies

bull Use of WDM ndash Switching routing at Optical signal level

bull Self healing rings under NMS control

bull Small size makes fibre cable lighter in weight So easy to handleOptic fibre cable weight (approx)

500 kg km Copper cable weight (approx) 1000 kgkm

The reasons are photons of light in a fibre

do not affect each other as they have no electrical charge and they are not affected by stray photons outside

the fibre But in case of copper electrons move through the cable and these are affected by each other

Optical fibre does not carry any electricity even if the cable is damaged or short circuited it does

not cause any spark or fire hazard

As the fibre do not radiate energy it can not be detected by any nearby antenna or any

other detector The fibres are difficult to tap and therefore excellent for security

As the signal transmission is by digital modulation there is no chance of cross talk in

between channels

Only by adding a few additional terminal and repeater equipments the

capacity of the system can be increased at any time once the cable is laid

ical effects and temperature variations

LIMITATIONS OF OFC -

difficult

- utilised

APPLICATION IN SIGNAL AND TELECOMMUNICATIONS transmission circuits

-haul circuits for linking of telephone exchanges

28 | P a g e

PROPAGATION MODES CONCEPT -

MODE - Mode is an available distribution of electromagnetic field in a plane transverse to the direction of

light propagation Each mode is characterized by frequency polarization electric field strength and

magnetic field strength Available patterns are derived from Maxwellrsquos equations and boundary conditions

LINEARLY POLARIZED (LP) MODE A mode for which the field components in the direction of propagation are small compared to

components perpendicular to that direction An optical fibre supports only different field patterns called as

lsquoLinear Polarizedrsquo or lsquo LPrsquo modes The reasons are

requirements

de

the accrual of power carried by different modes

There are two basic types of fiber Multimode fiber and Single-mode fiber

Multimode fiber is best designed for short transmission distances This is suited for used in LAN systems and

video surveillance Single mode fibre is best designed for longer transmission distances This is suitable for

long distance telephony and multi channel television broadcast systems

29 | P a g e

MULTI MODE FIBER Multimode fiber the first to be manufactured and commercialized simply refers to the fact that

numerous modes or light rays are carried simultaneously through the waveguide Modes result from the fact

that light will only propagate in the fiber core at discrete angles within the cone of acceptance MM fiber type

has a much larger core diameter compared to single-mode fiber allowing for the larger number of modes

and

is easier to couple than single-mode optical fiber Multimode fiber further categorized as Multimode step-

index and Multimode graded index fiber

PROPAGATION THROUGH MMSI FIBER Figure shows the principle of total internal reflection applies to multimode step index fiber Because

the corersquos index of refraction is higher than the claddingrsquos index of refraction the light that enters at less than

the critical angle is guided along the fiber

Three different light waves travel down the fiber One mode travels straight down the center of the

core A second mode travels at a steep angle and bounces back and forth by total internal reflection The third

mode exceeds the critical angle and refracts into the cladding Naturally it can be seen that the second mode

travels a longer distance than the first mode causing the two modes to arrive at separate times

PROBLEMS WITH MMSI FIBER AND SOLUTION This disparity between arrival times of the different light rays is known as dispersion and the result is

a muddied signal at the receiving end It is important to note that high dispersion is an unavoidable

characteristic of multimode step-index fiber The solutions are either use Graded index fiber or Single mode

fiber

PROPAGATION THROUGH MMGI FIBER Multimode Graded-index refers to the fact that the refractive index of the core gradually decreases

farther from the center of the core The increased refraction in the center of the core slows the speed of some

light rays allowing all the light rays to reach the receiving end at approximately the same time reducing

dispersion Figure shows the Light propagation principle through multimode graded-index fiber The corersquos

central refractive index ( nA ) is greater than that of the outer corersquos refractive index ( nB )

It is very clear from the figure the light rays no longer follow straight lines they follow a serpentine path

being gradually bent back toward the center by the continuously declining refractive index This reduces the

arrival time disparity because all modes arrive at about the same time The modes traveling in a straight line

30 | P a g e

are in a higher refractive index so they travel slower than the serpentine modes These travel farther but

move faster in the lower refractive index of the outer core region

PROPAGATION THROUGH SMSI FIBER Single mode fiber has a much smaller core that allows only one mode of light at a time to propagate

through the core The figure shows the single mode fiber

Single-mode fiber exhibits no dispersion caused by multiple modes Single-mode fiber also offers lower fiber

attenuation than multimode fiber Thus more information can be transmitted per unit of time because it can

retain the fidelity of each light pulse over longer distances Like multimode fiber early single-mode fiber was

generally characterized as step-index fiber meaning the refractive index of the fiber core is a step above that

of the cladding rather than graduated as it is in graded-index fiber Modern single-mode fibers have evolved

into more complex designs such as matched clad depressed clad and other exotic structures

SINGLE-MODE FIBER DISADVANTAGES The smaller core diameter makes coupling light into the core more difficult The tolerances for single-

mode connectors and splices are also much more demanding

CUTOFF WAVE LENGTH - Cutoff wavelength is the wavelength above which a single-mode fiber supports and propagates only

one mode of light In other words an optical fiber that is single-mode at a particular wavelength may have

two or more modes at wavelengths lower than the cutoff wavelength The effective cutoff wavelength of a

fiber is dependent on the length of fiber and its deployment The longer the fiber the lower is the effective

cutoff

wavelength The smaller the bend radius of a loop of the fiber the lower is the effective cutoff wavelength If

a fiber is bent in a loop the effective cutoff wavelength is lowered

SIGNAL ATTENUATION IN FIBER - Optical fiber has a number of advantages over copper However it also suffers from degradation

problems which can not be ignored The first of these is loss or attenuation Attenuation is typically the result

of two sub properties They are scattering and absorption Both of which have cumulative effects The second

is

dispersion which is the spreading of the transmitted signal and is analogous to noise

SCATTERING Scattering occurs because of impurities or irregularities in the physical construction of the fiber The

well known form of scattering is Rayleigh Scattering It is caused by metal ions in the silica matrix and

results in light rays being scattered in various directions

31 | P a g e

Scattering limits the use of wavelengths below 800nm The short wavelengths are much affected than longer

wavelengths It is because of Rayleigh scattering that the sky appears to be blue ( shorter wave length ) The

shorter wavelengths ( blue ) of light are scattered more than the longer wavelengths of light

ABSORPTION Absorption results from three factors They are hydroxyl ions ( OH- water ) in the silica impurities

in the silica and incomplete residue from the manufacturing process These impurities tend to absorb the

energy of the transmitted signal and convert it to heat resulting in an overall weakening of the signal The

Hydroxyl absorption occurs at 125 and 139 micro The silica itself starts to absorb energy at 17 micro

because of the natural resonance of the silicon dioxide

MACRO BENDING LOSS Macro-bending loss is caused by bending of the entire fiber axis The bending radius shall not be

sharper than 30d where d is diameter of cable A single bend sharper than 30d can cause loss of 05dB

The fiber may break if bending is ever sharper

MICRO BENDING LOSS Micro-bending loss is caused by micro deformations of fiber axis which leads to failures in achieving

total internal reflection conditions Micro-bends are small scale perturbations along the fiber axis the

amplitude of which are on the order of microns These distortions can cause light to leak out of a fiber

Micro-bending may be induced at very cold temperatures because the glass has a different coefficient of

thermal expansion from the coating and cabling materials At low temperatures the coating and cable

become more rigid and may contract more than the glass Consequently enough load may be exerted on the

glass to cause micro bends

Coating material is selected by manufacturers to minimize loss due to micro-bending The linear thermal

expansion coefficient of coating material shall be compatible with that of fiber

32 | P a g e

DISPERSION Dispersion is the optical term for the spreading of the transmits in the fiber It is the bandwidth

limiting phenomenon and comes in two forms Multimode dispersion and chromatic dispersion Chromatic

dispersion is further subdivided into material dispersion and waveguide dispersion

DISPERSION PHENOMENON IN OPTICAL FIBER Dispersion is the time distortion of an optical signal that results from the differences of time of travel

for different components of that signal typically resulting in pulse broadening As the distance traveled by

the signal is more broadening of pulse is more In digital transmission dispersion limits on the maximum

data rate and the maximum distance ie the information-carrying capacity of a fiber link The interference

from broadened pulse in the next interval shall not lead to erroneous interpretation of received signal

OPTICAL DOMAIN Understanding where attenuation and dispersion problems occur helps optical design engineers

determine the better wavelengths at which information can be transmit taking into account distance type of

fiber and the other factors which can severely affect the integrity of the transmitted signal The graph shown

depicts the optical transmission domain as well as the areas where problems arise The wavelength (nm)

is shown on X-axis and attenuation ( dBkm) is shown on Y-axis

There are four transmission windows appear in the figure The first one is at around 850 nm the

second at 1310nm third at 1550 nm and fourth at 1625 nm The last two labeled as C and L band

respectively The 850 nm wavelength at which the original LED technology operated The second window at

1310 nm has low dispersion The 1550 nm called as C-band is ideal wavelength for long haul

communication systems The network engineers can avoid transmitting signal at 1000 nm where Rayleigh

scattering 1240 and 1390 nm where hydroxyl absorption by water occurs to avoid high degree of loss

Optical fibers also can be manufactured to have low dispersion wavelength in the 1550nm region

which is also the point where silica-based fibers have inherently minimal attenuation These fibers are

referred to as dispersion-shifted fibers and are used in long-distance applications with high bit rates For

33 | P a g e

applications utilizing multiple wavelengths it is undesirable to have the zero dispersion point within the

operating

wavelength range

34 | P a g e

SIGNALLING RELAYS

INTRODUCTION A relay is an electromagnetic device which is used to convey information from one circuit to another

circuit through a set of contact ie front or back contact Constructional and electrically relays may be

divided into DC and AC relays because the means by which the electrical energy in the coil is converted in

to mechanical Energy in order to move the contacts are fundamentally different In DC type the contacts are

carried on an armature forming part of a magnetic circuit in which a field is set up by the current flowing in

the coils In AC types the contacts are attached by a link mechanism to a metal sector disc or cylinder in

which currents are induced by the alternating magnetic field produced by the currents in the coils

Every endeavor has been made to explain the action of each type of relay in the simplest possible manner

Relays are sophisticated switch gears used for remote control and succession control of various

electrical equipment In present days they are widely used because they are capable of protecting the

controlled equipment from cross feeding and overloading even as they cater for speedy operations

Most of the relays in present day signaling are electromagnetic devices although some of the relays control

circuits through electronic components like diodetransistors Integrated Chips etc

Railway signaling relays are unique in that

(a) They operate on low voltage and current

(b) They are more articulate as according to their special features they can work under restrictive conditions

and in any specified manner Virtually they can cater for all situations while contributing to speed and

accuracy in operations

CLASSIFICATION OF SIGNALLING RELAYS (a) According to the method of their mounting or fixture they are classified as

(i) Shelf type Relays which are loosely kept on shelves

(ii) Plug in type Relays which are plugged into a pre- wired plug boards

(b) According to their connection and usage they are classified as

(i) Track relays Relay which is directly connected to the track to detect the presence of vehicle

(ii) Line Relays Other than track relay all are line relays Relays connected to the selection circuit

(c) According to their vitality or importance in ensuring train working safety they are classified as

(i) Vital Relays All relays used for traffic control such as signal point controls track detection etc

(ii) Non-vital Relays Relays which operate control aids and accessories like warnings buzzers

Indications etc

(d) According to their special provisions to ensure reliability of their contacts they are classified as

(i) Proved type are those whose normalization after each operation shall be proved in circuit

controlled by their contacts Contacts in which both the springs have metal surfaces on their tips They may

get fused due to high sparking current across them during operation These may prevent relay normalization

and causes unsafe condition in traffic control To avoid this proving of relay normalization after each

operation is necessary

(ii) Non - proved type Need not to be proved to have been normalized after each operation as their

contacts have at least one non-fusible contact (carbon contact)

(e) According to their feed source relays are broadly classified as

(i) DC relays The relay which requires DC power supply for its operations are called DC relays Among

the DC relays

o DC neutral relays This relay closes the same set of contacts on energization with Normal polarity

or Reverse polarity supply

o Polar Relays This relay closes different set of contacts when energized with Reverse polarity

supply They may or may not have contact to close when deenergized

35 | P a g e

(ii) AC Relay AC Induction motor track relays Time element relays flashing indication control etc

(iii) Electronic Relays DC relays with electronic components in them are called electronic relays

DC NEUTRAL RELAY Each Relay has usually one or two coils with a hollow center to accommodate a coreThe coils are

made up of a large numbers of turns of small gauge soft drawn copper wire The two coils can be connected

in series or parallel according to the requirement of relay resistance The ends of the coils are terminated on

binding post to which the control wires are connected Each coil is placed around a core of specially selected

Iron or steel having high permeability and low retentivity The core should be susceptible to magnetism and

at the same time should have little residual magnetism The cores are connected at the top by a yoke to

complete the magnetism coupling between two ends of coils The bottom of each core is equipped with a

large steel or Iron block known as pole piece or face

A flat piece of Iron or steel called armature is supported by brackets which are securely fastened to

the pole piece The armature yoke and the pole pieces are also made of specially selected iron or steel of the

same quality as the core The armature carries the metallic spring contacts which are insulated from it

The circuit through the coils of the relay is closed It sets up a magnetic flux through the core yoke and the

armature The flux passing between the armature and pole faces causes the armatures get attracted to the pole

faces and armature picks up and closes front contacts When the circuit is opened the magnetic flux collapses

and the armature drops away by gravity from the pole faces the front contacts break and back contacts close

The front and back contacts of the relay can be utilised to make or break other circuits Two stop pins of

nonmagnetic material are fixed either on the armature or pole faces so that the armature cannot

come in contact with the pole faces It is essential to maintain a small air-gap between the armature and pole

faces so that low value of residual magnetism may not retain the armature in picked up position and causes

the relay to fail to drop away with a break in its control circuit

GENERAL USAGE

DC Neutral line relays are most commonly used for Railway Signalling controls and detection

Among them plug-in type relays are preferred in larger installations for space considerations Shelf type

relays are also in use mostly in wayside stations

There are many DC Neutral line relays in use with special features such as

(i) Delayed operation

(ii) Biased DC control

(iii) DC control unaffected by AC interference currents

(iv) Getting latched in operated condition till further feeding and others

Usage of DC polar relays is mostly in conjunction with block instruments that control traffic between

stations AC line relays are almost extinct in installations of British Signalling practice They are however

used for time control operations flashing indication control and such other special purposes in installations

with Siemens signalling practice widely Track relays are used according to the type of track detection

circuits chosen for a given location and context While most of the track circuits are still of the DC working

type requiring DC neutral track relays with them the prospects of their being replaced with Electronic track

circuits directly feeding DC line relays in future are great AC Track Circuits are used in DC Traction area

as conventional DC Track Circuits are not suitable there AC Track relays are used with them almost all of

the induction motor type In the British practice of signalling which was first introduced on Indian Railways

non-proved type relays with carbon to metal switching contacts are generally used for vital controls

They facilitate simple circuit designs But with the advent of German Practice introduced by Ms

Siemens later proved type relays with all metal to metal contacts are widely accepted in spite of

complications in circuit design caused by them A recent introduction is that of the same type relays made by

Ms Integra control However for some time now the appreciable features of both the practices are getting

36 | P a g e

incorporated together in the indigenous designs of signalling by railwaymen With this the usage of all types

of relays anywhere can be found without straight jacketed segration of relay types

CHARACTERSTIC OF ELECTRO-MAGNETIC RELAY The following are the characteristic of electro-magnetic relays A brief study of them helps in

understanding the choice of their components and designs features

1) Force of attraction

2) Effect of air gap

3) Effect of Hysterisis

4) Transient condition

FORCE OF ATTRACTION In any electro-magnetic system the force of attraction is given by

Where B - is the flux density a - is the cross sectional area of the particular part of the magnetic

circuit

In the case of a DC neutral Relay B is proportional to the current that is flowing in the coil

surrounding the electro-magnet and thus the force of the attraction is directly proportional to the square of the

current This square relationship has its own advantage especially in the case of DC track relay in that a

small reduction in the current will have a great effect on the working of the relay Also for a given change of

current the make and the break will be quicker with lesser possibility of arcing

EFFECT OF AIR GAP

Curve lsquoArsquo is magnetisation curve for the iron and is all practical purpose a straight line up to the

saturation point Curve lsquoBrsquo is the magnetisation curve for the open-air gap which is a straight line through

out because per magnetisation curve of the whole

magnetic circuit of the relay and for a given force is the sum of the amp-turns for the iron part and the amp-

turns for the air gap

When the front contacts are open the force required to pick up the armature is shown on curve lsquoCrsquo to be F1

but after the armature has operated it will be separated from the core by stop pins In this position the amp-

turns required to maintain the armature is less as indicated by the dotted line from 1 on curve C to 2 on curve

37 | P a g e

F But actually the current in the coil is unaltered the force on the armature is greater than required as

indicated at 3 on curve F Part of this extra force is used to flex the front contacts sufficiently to give good

contact pressure when it is in energised position

The difference between the pick-up and the drop-away current should be as small as practicable in

track relay to ensure good shunting characteristics This is achieved firstly by the choice of good quality relay

iron and secondly by having a small air gap between armature and core If the air gap is not available then

the residual magnetism fluxes might cause the armature to be retained when the supply is disconnected For

this reason residual pins are provided to ensure a definite minimum air gap in the energised position

EFFECT OF HYSTERISIS

Hysterisis is the property by which the flux produced lags behind the current In the de-energized

condition there will be small residual flux in the core When the voltage is applied to the coils the current in

rising to its steady value first causes the flux to rise from 1 to 2 along the curve At this point the flux density

will be sufficient to attract the armature and reduce the air gap the flux then raise to 3 and continue to 4

which corresponds to the steady current in the coils When the voltage is disconnected the current in falling

caused the flux to fall from 4 to 5 along the curve At this point the flux density will fall below the value

required to maintain the armature which will release thus increasing the air gap and reducing the flux to 6

Finally the

flux will decrease from 6 to 1 where the current will again be zero

The relay core is made of material having high permeability and low retentivity As mentioned in

the IRS specification Electromagnet iron may be in the form of a

(a) Bar of silicon steel

(b) Best Yorkshire wrought iron

(c) Swedish charcoal iron

(d) Electrical steel sheets

` This reduces the difference between pick up value and Drop away value By selecting good quality

core material Percentage release and sensitivity of the relay will be improved

TRANSIENT CONDITION

38 | P a g e

When the voltage is applied or disconnected from the coils it takes some little time before the current

become steady These are known as transient conditionsrdquo and are important so far as track relays are

concerned When the voltage is first applied to the coils the magnetic flux in rising cuts the turns on the

coils and in so doing produces a back EMF that opposes the applied voltage and retards the growth of

current

The growth and decay of flux are decided by the relationship between the inductance and resistance

in the circuit is known as time constant It is not fixed quantity in the case of DC neutral relay This value of lsquo

Lrsquo is less when the relay is in de-energised condition (L1) than when the relay is in energised condition (L2)

The magnitude of flux that is established for a given change of current is different in two cases

When the current reaches the pick up value the armature closes and the inductance is increased to L2

due to reduced air gap the flux per amp is increased The increase in flux increased the back EMF during the

movement of the armature after which the current continuous to raise along a new curve corresponding to the

increased inductance until it reaches the final value (ER) This process is indicated above in fig24

When the supply is disconnected the current is obliviously reduced to zero immediately but the flux

decay comparatively slowly owing to the eddy currents produced in the core by the rapid flux change which

tend to maintain the flux The drop away time on a disconnection is however generally negligible See fig

below

If the relay releases due to the reduction in current from say I 2 to I 1 caused by the application of

shunt resistance (as in the case of track relay ) the time taken is much longer than the relay is simply

disconnected The rate of rise or fall of current during the transient conditions is also depends on exterior

circuit values because L and R apply to the whole circuit The production of eddy current in the core the flux

will decay at a slower rate than the current So that the actual release time will be a little longer than it takes

the current to fall to the release

L= Inductance

39 | P a g e

R= Resistance

It is now clear that to reduce releasing time to a minimum it is necessary that

- The relay iron should have low Hysterisis loss and low retentivity

- The degree of over energization of the relay should be restricted

- Connecting a suitable external resistance in series with the relay to keep LR ratio low

In non RE area for track circuit length less than 100M 9 ohm track relay only to be used Using relay

with minimum contacts as they require lesser current which keeps inductance value low

Train working safety is ensured only if the track relay of shortest length track circuit is released

before a light engine running at a highest permitted speed clears it Otherwise the track circuit occupation

may go undetected To avoid this a special provision has to be made in signal control circuits wherever

necessary

The following methods may be adopted for reducing the time lag of track relay

(a) Restrict the over energisation of relay since the release time depends on the initial working current

(b) Connecting a suitable external resistance in series with the relay to keep the LR ratio low

(c) Using relays with minimum contacts as they require lesser operating current keeping the inductance

value low

40 | P a g e

CONCLUSION

Modern signalling is vital for safe and punctual movements of trains In the Indian railways The Signalling

and Telecommunication Department is responsible for providing modern effective and relaible signalling

systems as well as telecommunication systems

The first mode of communication used in Indian Railways was the use of electric telegraph

with the help of Morose code Morose code is the method of providing text information as a series of on-off

tones and lights or clicks that can be directly understood by a skilled listener or observer without special

equipmentEach character (letter or numeral ) is represented by a unique sequence of dots and dashes Later

this system becomes obselete and beggan the era of wireless communication which operated at audio level

frequency range

In wireless communication the significant advances took place the transition to miniature

valves or filament tubesBut this was abandoned too because of excessive current consumption and over

heating of the filament tubes

Fibre-optic communication is a method of transmitting information from one place to another by

sending pulses of light through an optcial fibreThe light forms an electromagnetic carrier wave that is

modulated to carry information First developed in the 1970s fibre optic communication systems has

revolutionized the telecommunications industry and have palyed a major role in the advent of the information

age Because of its advantages over electrical transmissionsoptical fibres have largely replaced copper wire

communications in core networks in the developed world The Indian Railways too is undergoing a transition

from Microwave communication to fibre optic communications

41 | P a g e

BIBLIOGRAPHY AND REFERENCES

1 wwwwikipediacom

2 wwwbritaniccacom

3 wwwirfcacom

4 Motorola GP60 system manual

5 Harris FAS 7000 manual

6 TOSHIBA Manual

ii | P a g e

STATEMENT BY THE CANDIDATE

ADRITA MAJUMDER

BTech 7th

Semester

Department of ECE Roll Number 08

Academy Of Technology

I hereby state that the technical presentation entitled signaling and telecommunication has been prepared by

me to fulfill the requirement of the vocational training during the period JUNE 2015

ADRITA MAJUMDER

iii | P a g e

ACKNOWLEDGEMENT

I would really like to thank every person who has helped me to complete my report successfully All the

websites where I have taken help from and all my friends who have helped me to chose this topic and collect

every bit of information about the topic Special thanks to my project mentor MR ATANU DEY without

whom completion of this very report would have been just impossible He has given me his valuable time

and worthy opinion to create my project successfully Definitely my parents are worth mentioning who have

kept supporting me throughout and have kept faith that I could do it

iv | P a g e

ABSTRACT

In this report I have given an overview of the signal and telecommunication systems that have been used and

are presently being used in the Indian Railways as a part of the day-to-day signalling and communication

procedures

I have covered in this report the history and the latest developments in railway signal and communication as

well as related fields I have made an elaborate study on the various equipments that have been used and are

currently being used as part of communication in the railways

v | P a g e

TABLE OF CONTENTS

TITLE PAGE NUMBER

CERTIFICATE BY THE SUPERVISORS I

STATEMENT BY CANDIDATE II

ACKNOWLEDGEMENT III

ABSTRACT IV

SOLID STATE INTERLOCKING 1

INTEGRATED POWER SUPPLY 5

SINGLE SECTION DIGITAL AXLE COUNTER 9

DATA LOGGER 15

OPTIC FIBRE 22

SIGNALLING RELAYS 34

CONCLUSION 40

BIBLIOGRAPHY AND REFERENCES 41

1 | P a g e

SOLID STATE INTERLOCKING

INPUT CARDS All the field conditions (ie Field relay contacts) are connected to these input cards of EI system

The maximum inputs capacity of each RI card will depend on design of the RI cards by different

manufacturers The total number of inputs will depend on the yard layout

Total inputs means

Field inputs ECRs TPRs NWKR etc

Panel inputs GNs UNs NWNs RWNs etc

Read back inputs HR DR WNR WRR etc

Opto couplers are provided to isolate field optically from the system in Input cards These cards will read the

conditions of inputs and passes the information to EI system

PROCESSOR CARD This card is also called as central processing unit card of the System This is provided with microprocessor

RAM ROM EPROM EEPROM Memory ICrsquos These EEPROMS or EPROMrsquos (ROMrsquos) are programmed

with software required for executing the system commands

System software consists of the following

- Executive software programmed in system EPROMrsquos

- Application software programmed in DATA EPROMrsquos

-

EXECUTIVE SOFTWARE This software is common to all EIrsquos for the same company manufacturing

This is a factory installed software

Performs all operations

Cuts off vital supply voltage to output relays in case of unsafe failures

2 | P a g e

APPLICATION SOFTWARE This software is specific to each station and different for different stations

This is as per table of control of specific station

Can be installed at site by signal engineers

Logic installed through Boolean expressions or user-friendly equations

OUTPUT CARD (RELAY DRIVE CARD) This card receives the output of CPU card as input and picks up relevant output relay as per the panel

operatorsrsquo request The output of this card is terminated on phoenix terminals from there the output relays are

connected

The essential modules of an EI is as follows

Hardware module

Software module

HARDWARE MODULES USED IN THIS SYSTEM Equipment consists of

CARD FILE

Each card file is like a shelf having 20 Slots to accommodate various PCBs that are used in a system

Slot nos1 to 15 and 20 are used to accommodate Non-vital Input-output or Vital Input or Vital Output PCBs

Slot no16amp17 are used to accommodate Power supply PCB Slot no18amp19 are used to accommodate CPU

PCB In this cardfile a mother board is available in the rear side connecting all the 20 Slots This cardfile is

suitable to mount on a 19rdquo rack

Power

Supply

Card

CPU

Card

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19

20

CPU PCB Each card file to have one CPU PCB and always placed in slot no18amp19 In this card Micro

Controller used is Motorola 68332 and its speed is 21 MHz In this card 4 nos of flash EPROMs of 8 MB

are used to store executive and application software Two nos of fast Static RAM (each 64KB) are used to

process the vital data and Four nos of Static RAM (each 64KB) are used to store events and errors

The main functions of CPU is it monitors continuously status of Vital Boards It also monitors

system internal operation for faults and responds to detected faults It processes application logic based on

inputs

received and deliver outputs to drive external gears It records system faults and routine events in user-

accessible memory It monitors and controls the serial communication ports It controls power to vital outputs

through external VCOR relay

POWER SUPPLY PCB

3 | P a g e

Each card file to have one Power Supply PCB and always placed in slot no16amp17 Power supply

PCB is basically a DC-DC converter that converts 12V DC input supply is +12V -12V and +5V required for

various board functioning Based on diagnostic check by CPU Power Supply Card receives 250Hz signal

from CPU and extends supply to VCOR relay This card provides isolated supply to internal circuit

VITAL OUTPUT PCB Each Vital Output PCB has 16 Outputs It is available in 12V and 24V DC applications Each Vital

Output can drive an output device such as any Q-series relay This output relay in turn controls signals

points crank handle siding control level crossing etc Since Vital Output drives the relay which controls

important outdoor gears all the Vital Output boards are continuously diagnosed by a CPU Any abnormality

in any of the outputs will shut down the system to ensure safety

VITAL INPUT PCB Each Vital Input PCB has 16 Inputs It is available in 12V and 24V DC applications Each Vital Input

is assigned to read the status of outdoor gears such as Track circuits Point detectors Crank handles Siding

controls level crossing etc Since the Vital Inputs read the status of outdoor gears they are normally

configured with double cutting arrangement using relay contacts

NON-VITAL INPUTOUTPUT PCB Each Non-vital IO has 32 inputs and 32 outputs in one PCB It is available in 12V and 24V DC

applications Non-vital inputs are Panel push buttons and keys Non-vital outputs are Panel indication LEDs

counters and buzzers The status of Non-vital Inputoutput is known from LED indications available in front

of the card

VITAL CUT OFF RELAY- VCOR Each card file will have one VCOR to ensure the healthiness of the system VCOR has 6 FB

dependent contacts each rated for 3 Amps When system is healthy the coil receives voltage from Power

Supply PCB which in turn controlled by CPU Power to Vital output board is controlled by VCOR thus

ensuring safety

WIRING HARDWARE 48 Pin Address select PCB and Connector assembly is provided for Vital Input and Vital Output

cards 96 Pin Address select PCB and Connector assembly is provided for Non-Vital IO cards 48 Pin

Connector Assembly is provided for PS and CPU PCB EEPROM PCB which is provided on rear side of the

CPU connector to configure various serial communication ports Keying plugs are provided in the cardfile to

ensure coding to each type of cards

SOFTWARE MODULES USED IN THIS SYSTEM System software consists of the following

EXECUTIVE SOFTWARE This software is common to all EIrsquos for the same company manufacturing

This is a factory installed software

Performs all operations

Cuts off vital supply voltage to output relays in case of unsafe failures

APPLICATION SOFTWARE This software is specific to each station and different for different stations

This is as per table of control of specific station

Can be installed at site by signal engineers

Logic installed through Boolean expressions or user-friendly equations

4 | P a g e

A GEC-MANUFACTURED SSI INTERLOCKING CUBICLE

A PAIR OF DATA LINK MODULES

TRACKSIDE FUNCTIONAL MODULE

5 | P a g e

INTEGRATED POWER SUPPLY

INTRODUCTION A typical 4 line station requires power supplies of 24 V DC( 5 nos ) 12 VDC ( 5nos ) 6V (2 nos)

110 V DC and 110 V AC for signalling These require as many chargers and Secondary cells amp Invertors

requiring more maintenance amp spares Can they be Integrated in to one system

Thus the concept of Integrated Power Supply has been evolved by integrating concepts One Charger

One set of Battery Bank feeding Invertors and DC- DC converters for deriving various DC amp AC

voltages Integrated power supply system delivers both AC amp DC Power supplies as an output with the

output voltage tolerance of plusmn 2

ADVANTAGES Reduces maintenance on Batteries Battery charger amp overall maintenance

Its construction is in modules and hence occupies less space Reduced space requirement resulting in

saving of space for power supply rooms

Provides centralized power system for complete signaling installation with continuous display of

working status of system for easier monitoring

Defect in sub-units of system is shown both by visual amp audible indication Reflects the condition of

battery with warning

Replacement of defective modules is quick amp easy without disturbing the working of the system

It uses (n+1) modular technology hot standby arrangement and hence high reliability and more

availability of the system

The system provides uninterrupted supply to all signalling system even during the power failures

Thus No blank Signal for the approaching drivers

System can be easily configured to suit load requirement

The diesel generator set running (Non-RE area) is reduced almost to lsquoNILrsquo Hence low wear and tear

of DG set components amp reduced diesel oil consumption

COMPONENTS (a) Un-interrupted power supply (U P S)

(i) SMPS Battery chargers with Hot stand-by mode

(ii) Hot Standby PWM Inverters with auto changeover

(iii) CVT Regulator [FRVS]

(b) AC distribution board [ACDB]

(i) STEP DOWN TRANSFORMERS

(c) DC distribution board [DCDB]

(i) DC-DC converters

WORKING IPS works satisfactorily for AC input variation of 150V AC to 275V AC with single-phase power supply

and frequency variation from 48 Hz to 52 Hz The input is fed to SMPS charger which converts in to 110

VDC as output It is fed as input to three sub units

To battery bank charging the batteries

To ON line inverters that converts 110 VDC in to 230 VAC plusmn 2as output

6 | P a g e

As 110 VDC bus bar to DC Distribution Panel as an input to various DC-DC converters located in

it

A 110 V Battery Bank of VRLA cells are connected to SMPS Panel IPS Status Monitoring Panel is

located at ASM room or at SampT staff room if round the clock SampT staff is available at Station

CONSTRUCTION IPS mainly consists of

SMR (Switch Mode Rectifier) Panel SMPS based Float cum Boost Charger (FRBC) Panel

AC Distribution Panel

DC Distribution Panel

Battery Bank (110V DC)

Status Monitoring Panel

SMR (SWITCH MODE RECTIFIER) PANEL SMPS BASED FLOAT

CUM BOOST CHARGER (FRBC) PANEL It consists of SMR FRBC modules and Supervisory amp Control Unit SMPS based SMRs

(converters) SMPS based Float cum Boost Chargers (FRBC) modules are provided with (n+1) modular

technology hot standby arrangement with active load sharing basis and 1 additional module as a cold standby

(n+2) Supervisory amp Control Unit which controls and monitor the complete system It has various

indications on the panel reflecting the working of the panel

FRBCs are suitable for operating in parallel on active load sharing basis with one or more modules of similar

type make and rating

n = required no of modules to cater for actual current requirement

AC DISTRIBUTION PANEL It is made of ON-Line inverters with (1+1) modular technology hot standby arrangement amp CVT

(Constant Voltage Transformer) AVR (Automatic Voltage Regulator) and set of step down

transformersThe inverter is protected against overload and short circuit with auto reset facility Whenever

the failure occurs it trips and restart automatically after about 10 to 20 sec But if the problem persists the

protection is permanently gets latched and it will not be switched ON again unless the fault is cleared

followed by pressing of reset button The output of inverters is regulated to 230V AC plusmn 2 50Hz plusmn1Hz for

an input voltage variation of 90V DC to 140V DC Normally both the Inverters are powered ON and both are

delivering the Output voltage but only one (main) inverter is connected to the Load If main inverter is failed

then only the stand-by inverter will come on Load automatically with in 500msec At 70 Depth of

Discharge (DOD) of the battery bank 110VDC supply to the inverters will be cut-off So the Signals feed will

be cut-off The auto-change over arrangement is also provided for bringing the CVT in circuit with in

500msec when the both the inverters output is failed It has various indications on the panel reflecting the

working of the panel

DC DISTRIBUTION PANEL It takes care of DC Power supply requirements of our signalling It consists of sets of DC-DC

converters for individual DC power requirements with (n+1) modular technology hot standby arrangement

with active load sharing basis The DC-DC converters of Relay Internal are provided with (n+1) modular

technology hot standby arrangement with active load sharing basis and 1 additional module as a cold standby

(n+2) The DC-DC converter works satisfactorily with the input voltage variation of 98VDC to 138VDC At

90 Depth of Discharge (DOD) of the battery bank all the DC-DC converters 110VDC Input supply will be

cut-off except for Block Tele DC-DC converters The supply for Point operation is also catered through a

20A fuse by this unit It is also provided with various indications that reflect its working

7 | P a g e

STATUS MONITORING PANEL IPS status monitoring panel has been provided in the ASM room for giving the important alarms and

indications to ASM Status Panel tells present working status of IPS displaying battery voltage continuously

and five other indications which will light according to IPS status During normal working these indications

will not lit Whenever the battery has come on to the load and has discharged by 50 DOD (Depth of

Discharge) then first Red indication lit with description ldquoSTART GENERATORrdquo with audio Alarm ie DG

set is to be started and put on the load If DG set is not started with this warning then if battery gets further

discharged to 60 DOD and second Red indications appears with description ldquoEmergency Start generatorrdquo

with audio alarm even now if DG set is failed to be started the battery further gets discharged to 70

DOD and 3rd Red indications appear with description ldquo System shut downrdquo with audio alarm which will

continue till Generator is started resulting in AC output from IPS is automatically cut off results all the

signals will become blank

When there is any defect in any sub module of IPS even without affecting working of system the 4th

Red indication appears with description ldquoCall SampT Staffrdquo with audio alarm so the ASM advises SampT staff

accordingly Green LED 5th indication comes with the description ldquoStop Generatorrdquo with audio alarm when

the DG set is running and if the Battery bank is fully charged condition

EARTHING The IPS systems and its individual modules are having earth terminals and all these are properly

earthed with earth resistance of less than 1 ohm Earth provided shall preferably be maintenance free using

ground resistance improvement compound (The acceptable Earth Resistance at earth busbar shall not be

more than 1 ohm Code of practice for earthing and bonding system for signalling equipments)

LIGHTNING AND TRANSIENT PROTECTION IN IPS Manufacturer will provide Stage1 amp Stage 2 protection along with the IPS These are described

below

Stage 1 protection is of Class B type against Lightning Electro-Magnetic Impulse (LEMP) amp other

high surges provided at Power Distribution Panel It is provided with a 63 Amp fuse in phase line and is

connected between Line and the Neutral and also between the Neutral and Earth

Stage 2 protection (Power line protection at Equipment level) is of Class C type against low voltage

surges provided at the equipment input level This is thermal disconnecting type and equipped with

protection against SPD (surge protection device) failure due to open amp short circuit of SPDs and is connected

between the Line and the Neutral If supply data signalling lines (ACDC) are carried through overhead

wires or cables above ground to any nearby building or any location outside the equipment room additional

protection of Stage 2 type shall be provided at such locations Class B amp Class C arrestor is provided on a

separate wall mounting type enclosure in IPS room

Stage3 protection (Protection for signallingdata line) is of Class D type All external data signalling

lines (ACDC) shall be protected by using this Class D type device It consists of a combination of Varistors

and Gas Discharge Tube with voltage and current limiting facilities

FEATURES Chargers used in this system are of SMPS technology chargers with 90 efficiency These chargers

are supported with hot standby mode with (n+1) modular technology

Onetwo sets of Maintenance free Battery banks (110VDC) Normally one set (110VDC) of Battery

bank is used Conventional flooded type Lead Acid Batteries or Low Maintenance Lead Acid

batteries can also be used (SMRs settings are required to be adjusted depending on the type of

Batteries used) Various voltage levels of

8 | P a g e

battery banks are avoided Reduction in Battery maintenance amp less flour area required

DC-DC Converters working from 110V Central battery have been used for all dc supplies This has

improved overall efficiency of the system since number of conversion from AC to DC have been

reduced to 2 stage as compared to 3 stage conversion in case of transformer-rectifier system

DC-DC converters are available in modules Easy replacement of defective modules This ensures

less down time

DC-DC Converters are used in load sharing N+1 configuration (ie with hot standby with N+1

modular technology) to improve the reliability amp availability of the system

Capacity of inverter has been brought down to 15 KVA from 5 KVA and used for feeding only

Signals supply Hot standby inverter is provided with auto changeover facility This improves the

availability of the overall system

High efficiency inverter is used with PWM (Pulse Width Modulation) technology in place of Ferro-

resonant technology based inverter This improves the efficiency of the overall system

Continuous power to Signal Circuits even in absence of DG setLocal Power Supply

Generators need not be switched ON every time during train movement

Metal-to-metal relay installations and block working by axle counters have also been covered

Supply of spare modulesComponentsCells have been included as part of main supply

Provides highly regulated voltage to all signal relays amp lamps for better life

9 | P a g e

SINGLE SECTION DIGITAL AXLE COUNTER

INTRODUCTION- The axle counter equipment is working on high frequency and using amplitude modulation or phase

modulation for detection of presence of wheel The equipment described in this notes is Phase modulation type

for the detection of presence of wheel In the Phase modulation type track device the detection of presence of

wheel is with the phase reversal of 1800 out of phase which enables this system to be more healthy and safe

In Phase Reversal Modulation technique trolley suppression arrangements to prevent the counting of

wheels caused by push trolley passing over the track device are not required as the system will take care of

validation of generated pulses caused by passage of wheel over the track device depending up on the phase

shift of the pulse This phase shift of the pulse may be normally 160deg to 180deg for a train wheel and it may be

approximately 100deg to 120deg for a push trolley wheel

This is Digital Axle Counter equipment for single track sections containing 2 out of 2 micro-

controllers to count the axles establish the track occupancy of a track section and to provide this information

to the block or the interlocking equipment

In this system no separate evaluator is required and no analog data is being transmitted One set of

Axle counter equipment is provided at entry end and other set provided at exit end Both sets are being

connected through a twisted pair of telecom cable ie existing RE cable one PET quad is used for both UP

and DN Axle Counters Digital DATA is being transmitted between two ends of Axle counters (Outdoor

track side Detection points)This system is a fully duplex capable of operating according to CCITT V21 and

the Data will be transmitted at the rate of 300bitsec This data Transmitted ensure negligible interference of

the noise The system is highly reliable

FEATURES (a) The system consists of

(i) Single Section Digital Axle Counter (SSDAC) units

(ii) Tx Rx coils

(iii) Vital Relays

(b) TxRx coil axle detectors are mounted to the web of the rails The design of system consists of 21 KHz amp

23 KHz High frequency Phase Reversal type axle detectors

(c) Compatible with 90R 52Kg amp 60Kg rail profiles Easy to install commission amp maintain

(d) Track devices at both (entry amp exit) points of the section should be fixed on the same rail

(e) System is designed to detect the solid wheels with diameter gt 400mm with standard wheel flange

(f) The system works in pairs For monitoring single-track section one pair of SSDAC units are required and

to be installed near the trackside one at the beginning and another at the end of the track section ie

Trackside electronic counting equipment

(g) The basic design of the system is based on counting the number of axles passing at each detection point

These stored counts are transmitted to the second unit of the system and vice versa by means of modem

communication

(h) The communication consists of digital packets having details of Counts amp Health

10 | P a g e

(i) If counts registered at both detection points are equal the section is cleared otherwise the section is shown

as occupied The system ensures no error condition to arrive at the decision of clearance

(j) System is designed as per CENELEC SIL-4 (European standard) using micro controller along with other

electronic circuits and programmed using dedicated software When any of these circuits fail the system

goes to fail safe condition

(k) It is programmable for either Preparatory Reset or Conditional Hard Reset as per requirement

(l) Micro controller based design with 2 out of 2 decisions and counting through software

(m) V21 Modem communication (2-wire) on frac12 quad cables and also compatible to work on voice channel of

OFC amp Radio

(n) Opto isolated vital relay drive for Q-style 24V 1000 _ and Vital Relay output can be giving at both ends

of the system

APPLICATIONS The system can be widely used in Railways for Block Working (BPAC) Intermediate Block Signaling Auto

signalling and Track circuiting for i) Loop line ii) Main line iii) yard lines

SYSTEM DESCRIPTION

This system comprises of

Tx coils-2 nos

Rx coils-2 nos

Reset Box (RB 258A)

Card 1 Signal Conditioning Card ndash 1

Card 2 Signal Conditioning Card - 2

Card 3 Micro controller Logic Board ndash 1

Card 4 Micro controller Logic Board ndash 2

2 nos for independent resetting ndash when used in block sections

1 no for common resetting ndash when used for Track circuiting at stations

Card 5 Event Logger Card

Card 6 Modem Card

Card 7 Relay Driver Card

Card 8 DC-DC Converter Card

SSDAC (DACF 700AP) UNIT

(A) SIGNAL CONDITIONING CARD (CARD 1amp2) (SCC) -1 (SCC-1) generates 21 KHz carrier

signals

-2 (SCC-2) generates 23 KHz carrier signals which is transmitted to 2nd

set of Tx coils

s receive these signals

modulated

train pulses

11 | P a g e

(B) MICRO-CONTROLLER LOGIC BOARD CARD (CARD 3amp4) (MLB) The Micro-controller Logic Board (MLB) is the heart of the system

o 8051 Based Architecture

o 8 Bit Micro Controller

o ATMEL AT89S8252 Micro controller

o 2 out of 2 Decision

o Uses C subset language

- TOOLS

o KEIL μ Vision Development System

o Universal Programmer

o 2KB Program Memory

o 256 bytes RAM

o 8KB Flash memory

o 32 Programmable IO lines

o Wide Operating Voltage range of 4V-6V

o Full Duplex Serial Port

o Programmable Watch Dog Timer

o Fully Static operation up to 24MHz (Upgraded to 40MHz)

o Operating Temperature of ndash40degC - +85degC

o Use of State Machine for Axle Counting

o Use of ASCII MODBUS protocol

o Use of CRC16 technique for Error Checking during communication

o Wheel detection

o Train direction checking and

o Wheel counting functions

o It receives the remote wheel count and computes the status of the section for clear or occupied

o It also checks various supervisory signal levels like supervisory of TxRx coils presence of various

cards communication link failure etcThese cards communicate with each other for wheel count

At Entry-end if train enters into section (1st detection) the counts are incremented and when train

shunts back from the same detection ie if train exits from the section from the same detection the counts are

decremented At Exit-end if train enters into section (2nd detection) the counts are decremented and when

train shunts back from the same detection ie if train exits from the section from the same detection the

counts are incremented Both the track devices at Entry and Exit ends must be fixed on same side of the

track

This MLB card is having Extensive LED display

o A block of 8 LED indicators for count progress error display

o 2 independent LED indicators for section status

o The errors occurring in the system during the operation of the SSDAC are encoded and are indicated by

means of the 8-LED block present on the front panel of the MLB cards

(c) EVENT LOGGER CARD (CARD 5)

Event logger card is designed to capture and store important signals from the remote and local SSDAC units

The stored data can be downloaded from the event logger card for the purpose of analyzing the events

occurring during the operations of the SSDAC The data can be analyzed with the help of CEL data analyzer

software

12 | P a g e

The event logger card captures following signals

(i) Pulse signals

(ii) Supervisory signals

(iii) Card removal information

(iv) Serial packets from

Event Logger card has a Rabbit processor and 2 MB FLASH MEMORY to store packets The data is initially

stored in the buffer and subsequently transferred to FLASH memory every two minutes Normally 4096

pages of the data can be stored in flash memory on FIFO (first in first out) basis

Run This LED blinks continuously indicating the normal working of the event

Log This LED blinks whenever data is being logged into the flash memory (Approx after every 2 minutes)

Dnld This LED is ON when data is being downloaded from the flash memory of the card and becomes OFF

when download is complete

(D) MODEM CARD (CARD 6) (i) The modem card transmits and receives the digital packet information form one counting unit to the other

The packet will appear after every 18 sec and the packet carries the latest information such as

(ii) The modem card being used is V21 type (2-wire) in SSDAC

(iii) This card interfaces with serial RS232C port of both Micro-controller Logic Boards

(iv) It multiplexes the two RS232C inputs and selects one of the two channels and provides signal conversion

from digital to analog (FSK modulation) and vice-versa

(v) Data transmission rate is 300 bitssec

(vi) Automatic Gain Control circuit is incorporated hence no gain adjustments required

(vii) Mode selection on Modem card The modem has been set in lsquoORIGINATORrsquo mode for entry and in the

lsquoANSWERrsquo mode for exit in the factory

(viii) LED Indications provided on Modem card

-Transmitting the signal when LED is flashing

- Receiving the signal when LED is flashing

-Remains OFF in SSDAC

-Carrier is detected when LED is glowing

(E) RELAY DRIVER CARD (CARD 7) (i) The Relay Driver card (RD) provides the 24V DC output required for driving Vital Relay

(ii) One RD card is used in each SSDAC counting unit The RD card receives the command of clear and

clock signals from MLB1 amp MLB2 cards and drives the vital relay lsquoONrsquo when section is NOT OCCUPIED

through opto- isolator circuit

(iii) If a train occupies the section the vital relay is dropped The vital relay status is read back by the system

as per the driving output

(iv) It has

13 | P a g e

ndash LED flashes when the section is clear

ndash LED flashes when the section is clear

All the above LEDrsquos are lit for section clear condition

(F) DC-DC CONVERTER CARD (CARD 8)

INPUT VOLTAGE Nominal Voltage voltage 24V DC Maximum current drain= 12A

Required voltage 18V DC to 30V DC

Output voltage

Nominal Voltage +5 V DC 2 A Required voltage 4 7 5 t o 525V DC

Nominal Voltage +12V DC 200 mA Required voltage 1175 to 1225V DC

Nominal Voltage +24V DC 300 mA with common ground Required voltage 235 to 245V DC

Nominal Voltage +15V DC 100 mA with isolated ground Required voltage 145 to 155V DC

SURGE VOLTAGE AND LIGHTNING PROTECTION Transient surge voltages arise as a result of Lightning discharge switching operations in electrical

systems and electrostatic discharge These surge voltages often destroy the electronic equipment to a large

extent In order to prevent surge voltages from destroying the equipment all the input lines of SSDAC ie

Power Supply (24V) Reset (48V) amp Modem is to be routed through surge voltage protection devices for

effectively protecting the system These devices (3 numbers) are mounted in a box and supplied along with

the system One number of box is to be installed at each location and wired to the SSDAC

Each surge voltage protection device consists of two parts

(a) Base

(b) Plug Trab

The Base of the device is used for wiring the input and output signals The connection details from relay

room to the box and from box to SSDAC unit are provided on the box The Plug Trab consists of MOV and

GD Tube and diverts the excess energy during surge voltages or lightning into the ground connection The

operation of these devices relies on a high quality ground connection in order to safely shunt away the

unwanted energy The impedance of the ground connection is critical and it should be less than 2 Ohms

NOTE The 3 Plug Trab connections are not to be interchanged with one another The plug Trab is a

detachable device and can be replaced with SPARE unit in case of blown device which is indicated by

means of LED for 24 V

EFFECTIVENESS OF PLUG TRABS The effectiveness of plug Trab depends wholly on the Earth connection provided to the system The earth

provided to the system should be less than 1 ohms and connections should be firm and proper to the SSDAC

unit VR box etc

SURGE VOLTAGE AND PROTECTION DEVICE SV-120 The Surge Voltage protection device is to be installed at each location along with every SSDAC unit

14 | P a g e

EARTHING- The lead wires connecting the installation and the earth electrode shall ordinarily be of stranded

copper wire of 29 sq mm (19 strand wires of 14 mm diameter) Copper wire has been specified because GI

wires usually are having greater corrosion However in areas where copper wire may be frequently stolen

due to theft ACSR of size 64 sq mm (19 strands of 211 mm diameter) may be used

LIMITS OF EARTH RESISTANCE (a) Apparatus case connected to Earth (SSDAC and vital Relay Box is housed in Apparatus case and

Connected to earth at outdoor) shall be less than or equal to 1 ohm

(b) All cable connected to same earth shall be less than or equal to 1 ohm

(C) Reset box connected to earth near SM s Room shall be less than or equal to 1ohm

EQUIPMENT TO BE EARTHED A Common Earth should be provided for SSDAC for items 1(a) amp (b) of the above at the outdoor

(a) The Apparatus Case is to be connected to earth (the chassis of SSDAC amp Vital Relay Box should be

properly connected to apparatus case)

(b) Metallic sheath and armouring of all the underground main cables are to be earthed

(i) In RE area the metallic sheath and armouring of main telecom cables are earthed at both ends

(ii) In RE area the armouring of Jelly filled cable shall be earthed at both ends

(c) The Earthing shall be provided at every location box where cables are terminated

(d) Earth already available for other equipment may be used for earthing of Reset Box near SM s Room

Cabin etc

15 | P a g e

DATALOGGER

INTRODUCTION Datalogger is a Microprocessor based system which helps in analysing the failures of relay inter

locking system Electronic Interlocking system This is like a black box which stores all the information

regarding the changes take place in relays AC DC Voltages and DC currents along with date and time The

same information data can be transferred to the computer to analyse further ldquoon line ldquooff linerdquo analysis of

stored date A print out also can be obtained through a printer by connecting directly to the datalogger unit

The data belongs to Relay contacts is considered as digital inputs and the data belongs to voltage

levels currents is considered as Analog inputs Datalogger lsquos are mandatory for all new relay interlocking

(PIRRI) EI installations and it is also recommended to provide in all existing PIs RRIs To increase the

line capacity mechanical signalling equipments are upgraded to PI RRI or EI Due to complexity in the

circuits and wiring sometimes it is very difficult to rectify the failures So datalogger can monitor these

systems with real time clock Thus it can be named as black box of Samp T equipments and hence it is a vital

tool for accident investigation Datalogger is used at Stations yards Whereas in case of Auto Section amp IBH

Mini dataloggers called as Remote Terminal Unit (RTU) are used

ADVANTAGES OF DATALOGGERS (a) Dataloggers helps in monitoring the typical failures such as intermittent auto right failures

(b) It helps in analyzing the cause of the accidents

(c) It helps in detecting the human failures errors such as

(i) Drivers passing signal at Danger

(ii) Operational mistakes done by panel operators ASMrsquos of operating department

(iii) Signal and telecom engineering interferences in safety circuits

(iv) Engineering and electrical department interferences failures

(v) It helps as a ldquoTOOLrdquo in preventive maintenance of signaling gears

(d) Dataloggers can be connected in network Networked dataloggers helps to monitorthe PIRRIEI remotely

(e) Failure reports can be generated remotely with help of datalogger network

(f) On line and Off line track simulation is possible

(g) Speed of the train on point zones can be calculated

(h) Age of the equipment in terms of number of operations etc

COMMON EQUIPMENT FOR ALL DATALOGGERS ARE GIVEN

BELOW (a) CPU card

(b) Digital and Analog input cards

(c) Local terminal(PC)

(d) communication links

(e) Printer

All the dataloggers requires a potential free ( spare ) relay contact for monitoring digital inputs

through Digital input cards amp for monitoring Analog inputs such ACDC bus bar voltage levels through

Analog input cards Digital and Analog inputs are connected to the Processor card Processor card consists of

memory ICrsquos Memory ICrsquos are programmed as per requirement of the signal engineers

Provision of Dataloggers is mandatory with RRI systems and is optional for PI systems as per

amendment to the specification for Relay Interlocking systems ( IRSS-36 ) The data collected by the

datalogger can be used for failure analysis repetitive discrepancies and for accident investigations

16 | P a g e

Note

If the serial communications is more than 50m then line drivers shall be used up to 3 Kms

4wire leased line Modems shall be used if the serial communication is more than 3 Kms

STUDY OF EFFTRONICS DATALOGGER TECHNICAL DETAILS (a) 24V 12VDC Power Supply

(b) Total Storage Capacity of 10 Lakh events

(c) In-built Temperature sensors

(d) Internal Buzzer for alarming during failures

(e) Real Time clock with internal battery backup with data retention up to 10 years

(f) 512 LED matrix to indicate the status of 512 Digital inputs at a time page wise

(g) Seven segment LCD screen (2x24) to display the status of digitalanalog signalsTime Temperature etc

(h) Using the keyboard various functions can be viewed in the LCD panel

(i) Max Digital Inputs 4096

(j) Max Analog Inputs 96

(k) Digital Input Scanning Time 16 millisecond

(l) Analog Input Scanning Time is less than 1 Sec

HARDWARE (EQUIPMENT) Datalogger system consists of

(a) Datalogger (CPU - with Microprocessor 68000)

(b) Digital input cards

(c) Dual modem card

(d) Digital Scanner units (DSU)

(e) Analog Scanner units (ASU)

CPU CARD It is provided with Motorola microprocessor M 68000 It performs all the activities pertaining to the

datalogger It continuously scans (check) the Digital inputs(inbuilt) Digital Scanner Units and Analog

Scanner Units ie scanning of digital signals (Relay operations) for every 16-milli seconds and scanning of

analog signals (ie ACDC voltages amp DC currents) for less than 1 second

This card will support the IO interfaces of LCD (Liquid Crystal Display) - 2X24 alphanumeric Key

Board LED Matrix Display Real Time Clock LCD display and keyboard This will acts as man machine

interface between the datalogger and the signal engineer All the operations (Software) can be performed

using this LCD and keyboard

Real time display with 7 Segments This is built in real time clock within Datalogger and its current

time will be displayed on six 7-segment display provided (Real time clock depend upon DALLAS 1286

chip) This IC will come with internal battery backup hence there is no need to add external batteries

CPU card continuously scans (checks) the DSUs and ASUs Each input connected to digital scanner

units are optically isolated by Opto couplers When CPU card scans the digital inputs it compares with the

previous stored data and if there is any change from the previous status then only that data will be stored (the

status conditions of relay) with date and real time A total of minimum 10 Lac events can be stored in

memory on first in first out basis so that latest data is available in the system There is no loss of data from

datalogger memory in case of power supply failure of datalogger

DIGITAL INPUT CARDS (IN-BUILT) This system is having maximum 8nos of inbuilt Digital inputs cards Maximum 64nos of digital

inputs can be connected to each digital input card The potential free relay contact may be front or back

contact terminated at the Tag Block from the relay of signals tracks points Buttons etc and are

17 | P a g e

subsequently connected to Digital input cards through Flat Ribbon Cable (FRC) connectors These in-built

digital input cards can monitor a total 512 nos of relays status

DIGITAL SCANNER UNIT (DSU) Each DSU contains 8 nos of Digital Input cards Each input card can be connected with 64 inputs

Total input capacity of DSU unit is 512 inputs These scanner cards contain Optocouplers and Multiplexer

Inputs are connected to Stag card The stag card out put is connected to DSU through FRC connectors

Maximum 7 nos of DSUs can be connected to the system So Digital input capacity of the system is 4096

All these digital inputs are scanned at rate of 16 msec

ANALOG SCANNER UNIT (ASU) ASU contains maximum 3 nos of Analog input cards Each input card can be connected with 8nos of

Analog inputs Total input capacity of the ASU is 24 analog input channels Maximum 4nos of ASUs can be

connected to the system Analog input channel capacity of the system is 96 All these analog inputs are

scanned at a rate of less than 1 sec

PARALLEL PORT Parallel port is provided for connecting printer

RS-232 SERIAL PORTS At least 6 Serial communication ports are provided for communication with other dataloggers

Central Monitoring Unit Remote Terminal Unit Electronic Interlocking system Integrated Power Supply

system etc

EXTERNAL NON-VITAL RELAY CONTACTS These relays provided in the system where 16 number of the Relay contacts are provided on the rear

panel through Tele control port to extend alarms and to control the power equipment from remote or local

locations through computer in case of any occurrence of failures Each control can sink or source 100 m

amps of current

INTERNAL MODEM CARD DUAL MODEM CARD (IN-BUILT) It is fixed in datalogger Euro rack itself One card contains two modems The top modem is called

ANS (answer) modem and the bottom modem is called as ORG (originate) modem It is used in case of

networking of Dataloggers In network connect lsquoANSrsquo modem to the lsquoORGrsquo modem of one adjacent station

and connect lsquoORGrsquo modem to the lsquoANSrsquo modem of other adjacent station

POWER SUPPLY Normally 24V DC (12V DC is optional) supply with battery backup is required for the system

working

Input Voltage Range 18Vhellip32V DC (For 24V) 9Vhellip18V DC (For 12V)

INPUT REQUIREMENTS Relay inputs (digital inputs) and analog inputs (voltages currents etc) are required to be connected

to the system as per the requirements of RRI PI SSI as the case may be Some of the inputs to be

monitored is given below

(a) Digital inputs

(i) Field inputs All TPRs NWKRs RWKRs ECRs Crank Handle relays SidingSlot LC gate

control relays etc

(ii) Control Panel inputs All button Knob SMrsquos Key relays

18 | P a g e

(iii) Internal relays

British system All HR DR HHR WNR WRR ASR UCR RR LR UYRTLSR TRSR TSR

JSLR JR etc

SIEMENS system Z1UR Z1UR1 GZR ZDUCR ZU(R)R ZU(N)PRG(R)RG(N)R U(R)S

U(N)PS UDKR DUCR U(R)LR UYR1 UYR2 G(R)LRGR1GR2

GR3 GR4 OVZ2U(R)RW(RN)R (RN)WLR Z1NWR Z1RWRZ1WR1 WKR1 WKR2 WKR3 etc

(b) Analog channels

(i) 230 V AC (for power supplies in the power panel)

(ii) 110V AC (for Signal and Track transformers)

(iii) 110V DC (for Point operation)

(iv) 60V DC (Siemens relays)

(v) 24V DC (Q-series relays)

(vi) 24V DC (for Block Axle counters)

(vii) 12V DC (for indication)

(viii) 20A (for point operation current)

(ix) 10V AC 5KHz (for Axle counter channels) etc

SOFTWARE MODULES OF DATALOGGERS

(a) Network Management of Dataloggers (NMDL)

(b) Reports

(c) Fault Entry

(d) Track Offline Simulation

(e) Train Charting

NMDL SOFTWARE FEATURES (a) Online Relay Status

(b) Online Faults - To view information of various Online Faults as they occur in the stations where

the Dataloggers are connected

(c) Online Simulation - Graphical view of relay operations train movements etc

(d) Remote monitoring of stations with the help of NETWORKING

SOFTWARE OBJECTIVES (a) Predictive Maintenance

(b) Easy identification of failures

(c) Crew discipline

(d) Train charting

REMOTE MONITORING OF STATIONS WITH NETWORKING OF

DATALOGGERS The individual Dataloggers of various stations can be interconnected through networking technology

The data of Remote Panel stations can be viewed in a Computer at the Central Monitoring Station The data

of the network is collected by the FEP (Front End Processor) which in turn is transmitted to the computer

COMPONENTS OF NETWORK MANAGEMENT OF DATALOGGERS

(a) Datalogger at stations

(b) MODEM and Transmission medium

19 | P a g e

(c) Front End Processor (FEP)

(d) Central Monitoring Unit (CMU) Computer

FEP (FRONT END PROCESSOR)

FEP acts as a buffer between the Central Monitoring Unit (Computer) and the Network It is provided

at centralised place to retrieve data continuously from station dataloggers and store in memory and transfer to

computer on request It stores 10 Lac telegrams It works on 12V DC It draws 16A continuous current

when all the three modems are connected Normally it shows the number of packets pending to be sent to the

computer on its 7-segment LED display It is provided with MOTOROLA 68000 microprocessor It has 6-

nos of RS-232 communication ports such as COM1 COM2 COM3 COM4 COM5 and COM6 COM1 is

used for Fault Analysis System (FAS) ie Central Monitoring Unit (Computer) connection COM2 to COM6

are used for networking For Bi-directional 2- nos of ports and for Tri-directional (T-network) 3-nos of ports

are used

DATA TRANSMISSION Dataloggers can be networked in Uni-directional Mode or Bi-directional Mode or T ndash Network Mode

In case of loss of data retransmission of data takes place

(a) Uni-Directional Mode

Each Datalogger will send data in only one direction to the FEP Unidirectional mode network is not

preferred

(b) Bi-Directional Mode

Each end of Network is connected to FEP and each datalogger can now transmit data in both the directions

Bi-directional Mode is advantageous it enables the Data Transmission even in case of Network Failure

(c) T - Network Mode

If more no of stations are in network ie if the network is too lengthy then T- network mode is preferred

COMMUNICATION The communication protocol for transmitting data and command between datalogger and CMU is

standardized by the RDSO and is given in the Specifications of Dataloggers

(a) The type of communication used in the network is dependent on the distance between the dataloggers

(b) For shorter distances Opto Converter Box- Opto isolated current loop communication is used

(c) For longer distances Modem (Dial-up leased) Fiber Optic Satellite Microwave communication

MODEMS Modems are used for DATA transfer between Dataloggers and Front End ProcessorThese are

configured to RS 232 Serial Communication Network is connected with two types of 4-wire modems

(a) Internal modem card Dual Modem card (in-built)

It is fixed in datalogger Euro rack itself One card contains two modems The top modem is called

ANS (answer) modem and the bottom modem is called as ORG (originate) modem

Note In case of networking of Dataloggers connect lsquoANSrsquo modem to the lsquoORGrsquo modem of one adjacent

station and connect lsquoORGrsquo modem to the lsquoANSrsquo modem of other adjacent station

(b) External modems

20 | P a g e

These are generally used at FEP (Front End Processor) side to connect the Dataloggers

(i) To transfer Data from one datalogger to another datalogger FEP Baud rate is 9600bps

(ii) These modems are 4-wire line communication

(iii) To transfer the data from FEP to RMU (PC) the Baud rate is 57600 bps

There is no difference between these modems functionally

CENTRAL MONITORING UNIT (CMU) COMPUTER

Central monitoring unit (Fault Analysis Unit) is a Personal Computer and its minimum configuration

shall be specified by RDSO from time to time System Software Windows XPVista(OS) Norton Kaspersky

(Anti Virus) Interbase where Server is not available (DBMS) Oracle where Server is available (DBMS)

software are required to run Datalogger System It is provided with Graphical User interface (GUI) based

software and retrieve data from all Networked dataloggers (up to 32) at various stations It stores data in

standard data base files The CMU is capable of analyzing the data and generate reports audiovisual alarms

on defined conditions This data can be compressed to take backup In central monitoring unit Software used

for analysis of data prediction of faults etc is written in a structured format so that purchaser can

reconfigure it if required It displays the status of signaling gears at any selected time in graphic form for any

selected station yard It retrieves the stored data amp simulates train movement It sends commands to various

Dataloggers to activate audio visual alarm or operate and electromagnetic relay

CMU shares data available in it by other PCs through available local area network where this data can

be used for train charting passenger information purpose The system generates audiovisual alarm in

ASMrsquosSignal Maintainerrsquos room in the case of power supply failure (battery voltage low) or battery charger

defective with acknowledgement facility

(a) Each datalogger has its own identity code which will be transmitted along with data packet to central

monitoring unit

(b) Events recorded at each station are continuously transmitted to central monitoring unit Response time of

data transfer will not exceed 10 sec

21 | P a g e

22 | P a g e

OPTICAL FIBER CABLE

INTRODUCTION The demand for bandwidth on transmission networks is increasing rapidly because video and

graphical rich contents are exchanged through the corporate network or the Internet The Gigabit Ethernet

became ommonly used in the corporate network backbone and 10Gbit Ethernet will be adopted in the near

future Meanwhile in the home the demand for high-speed network becomes popular as the wide spread of

broadband access eg CATV xDSL and FTTH The transmission medium with capability to transmit high

bit rate signal is necessary to satisfy these requirements

The telecommunication transport technologies move from copper based networks to optical fiber

from timeslot based transport to wave length based transport from traditional circuit switching to terabit

router and all optical based networks entering into a new era of optical networking

BASIC PHYSICS OF OFC

OPTICAL FIBER CABLE OFC have Fibers which are long thin strands made with pure glass about the diameter of a human

hair OFC consists of Core Cladding Buffers and Jacket as shown in figure

MONOCHROMATIC LIGHT OR SINGLE COLOR LIGHT Light or visible light is electromagnetic radiation of a wavelength that is visible to the human eye (

about 400 ndash 700 nm) The word light is sometimes used to refer to the entire electromagnetic spectrum Light

is composed of elementary particles called photons Three primary properties of light are

Light can exhibit properties of both waves and particles This property is referred to as wave-particle

duality The study of light known as optics In free space light (of all wavelengths) travels in a straight path

at a constant maximum speed However the speed of light changes when it travels in a medium and this

change is not the same for all media or for all wavelengths By free space it is meant space that is free from

matter (vacuum) andor free from electromagnetic fields

Thus the speed of light in free space is defined by Einsteinrsquos equation E = mc2

Frequency ν speed of light in free space c and wavelength λ are interrelated by ν = cλ

From the energy relationships E = mc2 = hν and the last one an interesting relationship is obtained

the equivalent mass of a photon m = hνc2

When light is in the vicinity of a strong electromagnetic field it interacts with it From this interaction

and other influences its trajectory changes direction as shown in figure

23 | P a g e

INCIDENT RAY REFLECTED RAY AND REFRACTED RAY An incident ray is a ray of light that strikes a surface The angle between this ray and the

perpendicular or normal to the surface is the angle of incidence Reflection is the change in direction of a

wave front at an interface between two different media so that the wave front returns into the medium from

which it originated Common examples include the reflection of light sound and water waves

The reflected ray corresponding to a given incident ray is the ray that represents the light reflected by

the surface The angle between the surface normal and the reflected ray is known as the angle of reflection

The Law of Reflection says that for a specular (non-scattering) surface the angle of reflection always equals

the angle of incidence The refracted ray or transmitted ray corresponding to a given incident ray represents

the light that is transmitted through the surface The angle between this ray and the normal is known as the

angle of refraction and it is given by Snells Law

The figure shows Incident ray Reflected ray Refracted ray the angle of incidence and angle of refraction

REFRACTIVE INDEX - Refractive index is the speed of light in a vacuum ( c =299792458kmsecond) divided by the speed

of light in a material ( v ) Refractive index measures how much a material refracts light Refractive index of

a material abbreviated as lsquo n lsquo is defined as lsquo n=cv lsquo Light travels slower in physical media than it does

when transmitted through the air Refractive index (n) is a function of molecular structure of matter optical

frequency optical intensity determines optical propagation properties of each wavelength ( λ ) may not be

distributed equally in all directions is affected by external temperature pressure and fields

Refractive index of a medium is a measure for how much the speed of light is reduced inside the

medium For example typical glass has a refractive index of 15 which means that light travels at 1 15 =

067 times the speed in air or vacuum Two common properties of glass and other transparent materials are

directly related to their refractive index

First light rays change direction when they cross the interface from air to the material and effect that

is used in lenses and glasses

Second light reflects partially from surfaces that have a refractive index different from that of their

surroundings

SNELLrsquoS LAW-

24 | P a g e

When light passes from one transparent material to another it bends according to Snells law which

is defined as n1sin(θ1) = n2sin(θ2)

where n1 is the refractive index of the medium the light is leaving θ1 is the incident angle between the light

beam and the normal (normal is 90deg to the interface between two materials)

n2 is the refractive index of the material the light is entering

θ2 is the refractive angle between the light ray and the normal

Snellrsquos law gives the relationship between angle of incidence and angle of refraction

For the case of θ1 = 0deg (ie a ray perpendicular to the interface) the solution is θ2 = 0deg regardless of

the values of n1 and n2 That means a ray entering a medium perpendicular to the surface is never bent The

above is also valid for light going from a dense (higher n) to a less dense (lower n) material the symmetry of

Snells law shows that the same ray paths are applicable in opposite direction

TOTAL INTERNAL REFLECTION- When a light ray crosses an interface into a medium with a higher refractive index it bends towards

the normal Conversely light traveling cross an interface from a higher refractive index medium to a lower

refractive index medium will bend away from the normal

This has an interesting implication at some angle known as the critical angle θc light traveling from

a higher refractive index medium to a lower refractive index medium will be refracted at 90deg in other words

refracted alon g the interface If the light hits the interface at any angle larger than this critical angle it will

not pass through to the second medium at all Instead all of it will be reflected back into the first medium a

process known as total internal reflection

The critical angle can be calculated from Snells law putting in an angle of 90deg for the angle of the refracted

ray θ2 This gives θ1

Since θ2 = 90deg

So sin(θ2) = 1

25 | P a g e

Then θc = θ1 = arcsin(n2n1)

For example with light trying to emerge from glass with n1=15 into air (n2 =1) the ritical angle θc is

arcsin(115) or 418deg For any angle of incidence larger than the critical angle Snells law will not be able to

be solved for the angle of refraction because it will show that the refracted angle has a sine larger than 1

which is not possible In that case all the light is totally reflected off the interface obeying the law of

reflection

OPTICAL FIBER MODE An optical fiber guides light waves in distinct patterns called modes Mode describes the distribution

of light energy across the fiber The precise patterns depend on the wavelength of light transmitted and on the

variation in refractive index that shapes the core In essence the variations in refractive index create

boundary

conditions that shape how light waves travel through the fiber like the walls of a tunnel affect how sounds

echo inside

We can take a look at large-core step-index fibers Light rays enter the fiber at a range of angles and

rays at different angles can all stably travel down the length of the fiber as long as they hit the core-cladding

interface at an angle larger than critical angle These rays are different modes Fibers that carry more than

one mode at a specific light wavelength are called multimode fibers Some fibers have very small diameter

core that they can carry only one mode which travels as a straight line at the center of the core These fibers

are single mode fibers This is illustrated in the following picture

OPTICAL FIBER INDEX PROFILE Index profile is the refractive index distribution across the core and the cladding of a fiber Some

optical fiber has a step index profile in which the core has one uniformly distributed index and the cladding

has a lower uniformly distributed index Other optical fiber has a graded index profile in which refractive

index varies gradually as a function of radial distance from the fiber center Graded-index profiles include

power-law index profiles and parabolic index profiles The following figure shows some common types of

index profiles for single mode and multimode fiber

26 | P a g e

OPTICAL FIBERrsquoS NUMERICAL APERTURE ( NA )- Multimode optical fiber will only propagate light that enters the fiber within a certain cone known as

the acceptance cone of the fiber The half-angle of this cone is called the acceptance angle (see figure 18)

θmax For step-index multimode fiber the acceptance angle is determined only by the indices of refraction

Where

n is the refractive index of the medium light is traveling before entering the fiber

nf is the refractive index of the fiber core

nc is the refractive index of the cladding

NUMBER OF MODES IN A FIBER - Modes are sometimes characterized by numbers Single mode fibers carry only the lowest-order

mode assigned the number 0 Multimode fibers also carry higher-order modes The number of modes that

can propagate in a fiber depends on the fiberrsquos numerical aperture (or acceptance angle) as well as on its

core diameter and the wavelength of the light For a step-index multimode fiber the number of such modes

Nm

Where

D is the core diameter

λ is the operating wavelength

NA is the numerical aperture (or acceptance angle)

MODE FIELD DIAMETER - All light do not travels through the core of the fiber but is distributed through both the core and the

cladding The mode field is the distribution of light through the core and cladding of a particular fiber

Mode-Field Diameter (MFD) defines the size of the power distribution When coupling light into or out of a

fiber MFD is important in understanding light loss

27 | P a g e

ADVANTAGE OF OFC COMMUNICATION - bull More information carrying capacity Fibers can handle much higher data rates than copper More

information can be sent in a second

bull Free from Electromagnetic and Electrostatic interference Being insulator no electric current flows through

the fibre and due to this reason fibres neither radiate nor pick up electro - magnetic radiation So WPC

CLEARANCE is not required

bull Low attenuation 025 dbkm at 1550 nm Loss in twisted pair and coaxial cable increases with frequency

where as loss in the optical fibre cable remains flat over a wide range of frequencies

bull Use of WDM ndash Switching routing at Optical signal level

bull Self healing rings under NMS control

bull Small size makes fibre cable lighter in weight So easy to handleOptic fibre cable weight (approx)

500 kg km Copper cable weight (approx) 1000 kgkm

The reasons are photons of light in a fibre

do not affect each other as they have no electrical charge and they are not affected by stray photons outside

the fibre But in case of copper electrons move through the cable and these are affected by each other

Optical fibre does not carry any electricity even if the cable is damaged or short circuited it does

not cause any spark or fire hazard

As the fibre do not radiate energy it can not be detected by any nearby antenna or any

other detector The fibres are difficult to tap and therefore excellent for security

As the signal transmission is by digital modulation there is no chance of cross talk in

between channels

Only by adding a few additional terminal and repeater equipments the

capacity of the system can be increased at any time once the cable is laid

ical effects and temperature variations

LIMITATIONS OF OFC -

difficult

- utilised

APPLICATION IN SIGNAL AND TELECOMMUNICATIONS transmission circuits

-haul circuits for linking of telephone exchanges

28 | P a g e

PROPAGATION MODES CONCEPT -

MODE - Mode is an available distribution of electromagnetic field in a plane transverse to the direction of

light propagation Each mode is characterized by frequency polarization electric field strength and

magnetic field strength Available patterns are derived from Maxwellrsquos equations and boundary conditions

LINEARLY POLARIZED (LP) MODE A mode for which the field components in the direction of propagation are small compared to

components perpendicular to that direction An optical fibre supports only different field patterns called as

lsquoLinear Polarizedrsquo or lsquo LPrsquo modes The reasons are

requirements

de

the accrual of power carried by different modes

There are two basic types of fiber Multimode fiber and Single-mode fiber

Multimode fiber is best designed for short transmission distances This is suited for used in LAN systems and

video surveillance Single mode fibre is best designed for longer transmission distances This is suitable for

long distance telephony and multi channel television broadcast systems

29 | P a g e

MULTI MODE FIBER Multimode fiber the first to be manufactured and commercialized simply refers to the fact that

numerous modes or light rays are carried simultaneously through the waveguide Modes result from the fact

that light will only propagate in the fiber core at discrete angles within the cone of acceptance MM fiber type

has a much larger core diameter compared to single-mode fiber allowing for the larger number of modes

and

is easier to couple than single-mode optical fiber Multimode fiber further categorized as Multimode step-

index and Multimode graded index fiber

PROPAGATION THROUGH MMSI FIBER Figure shows the principle of total internal reflection applies to multimode step index fiber Because

the corersquos index of refraction is higher than the claddingrsquos index of refraction the light that enters at less than

the critical angle is guided along the fiber

Three different light waves travel down the fiber One mode travels straight down the center of the

core A second mode travels at a steep angle and bounces back and forth by total internal reflection The third

mode exceeds the critical angle and refracts into the cladding Naturally it can be seen that the second mode

travels a longer distance than the first mode causing the two modes to arrive at separate times

PROBLEMS WITH MMSI FIBER AND SOLUTION This disparity between arrival times of the different light rays is known as dispersion and the result is

a muddied signal at the receiving end It is important to note that high dispersion is an unavoidable

characteristic of multimode step-index fiber The solutions are either use Graded index fiber or Single mode

fiber

PROPAGATION THROUGH MMGI FIBER Multimode Graded-index refers to the fact that the refractive index of the core gradually decreases

farther from the center of the core The increased refraction in the center of the core slows the speed of some

light rays allowing all the light rays to reach the receiving end at approximately the same time reducing

dispersion Figure shows the Light propagation principle through multimode graded-index fiber The corersquos

central refractive index ( nA ) is greater than that of the outer corersquos refractive index ( nB )

It is very clear from the figure the light rays no longer follow straight lines they follow a serpentine path

being gradually bent back toward the center by the continuously declining refractive index This reduces the

arrival time disparity because all modes arrive at about the same time The modes traveling in a straight line

30 | P a g e

are in a higher refractive index so they travel slower than the serpentine modes These travel farther but

move faster in the lower refractive index of the outer core region

PROPAGATION THROUGH SMSI FIBER Single mode fiber has a much smaller core that allows only one mode of light at a time to propagate

through the core The figure shows the single mode fiber

Single-mode fiber exhibits no dispersion caused by multiple modes Single-mode fiber also offers lower fiber

attenuation than multimode fiber Thus more information can be transmitted per unit of time because it can

retain the fidelity of each light pulse over longer distances Like multimode fiber early single-mode fiber was

generally characterized as step-index fiber meaning the refractive index of the fiber core is a step above that

of the cladding rather than graduated as it is in graded-index fiber Modern single-mode fibers have evolved

into more complex designs such as matched clad depressed clad and other exotic structures

SINGLE-MODE FIBER DISADVANTAGES The smaller core diameter makes coupling light into the core more difficult The tolerances for single-

mode connectors and splices are also much more demanding

CUTOFF WAVE LENGTH - Cutoff wavelength is the wavelength above which a single-mode fiber supports and propagates only

one mode of light In other words an optical fiber that is single-mode at a particular wavelength may have

two or more modes at wavelengths lower than the cutoff wavelength The effective cutoff wavelength of a

fiber is dependent on the length of fiber and its deployment The longer the fiber the lower is the effective

cutoff

wavelength The smaller the bend radius of a loop of the fiber the lower is the effective cutoff wavelength If

a fiber is bent in a loop the effective cutoff wavelength is lowered

SIGNAL ATTENUATION IN FIBER - Optical fiber has a number of advantages over copper However it also suffers from degradation

problems which can not be ignored The first of these is loss or attenuation Attenuation is typically the result

of two sub properties They are scattering and absorption Both of which have cumulative effects The second

is

dispersion which is the spreading of the transmitted signal and is analogous to noise

SCATTERING Scattering occurs because of impurities or irregularities in the physical construction of the fiber The

well known form of scattering is Rayleigh Scattering It is caused by metal ions in the silica matrix and

results in light rays being scattered in various directions

31 | P a g e

Scattering limits the use of wavelengths below 800nm The short wavelengths are much affected than longer

wavelengths It is because of Rayleigh scattering that the sky appears to be blue ( shorter wave length ) The

shorter wavelengths ( blue ) of light are scattered more than the longer wavelengths of light

ABSORPTION Absorption results from three factors They are hydroxyl ions ( OH- water ) in the silica impurities

in the silica and incomplete residue from the manufacturing process These impurities tend to absorb the

energy of the transmitted signal and convert it to heat resulting in an overall weakening of the signal The

Hydroxyl absorption occurs at 125 and 139 micro The silica itself starts to absorb energy at 17 micro

because of the natural resonance of the silicon dioxide

MACRO BENDING LOSS Macro-bending loss is caused by bending of the entire fiber axis The bending radius shall not be

sharper than 30d where d is diameter of cable A single bend sharper than 30d can cause loss of 05dB

The fiber may break if bending is ever sharper

MICRO BENDING LOSS Micro-bending loss is caused by micro deformations of fiber axis which leads to failures in achieving

total internal reflection conditions Micro-bends are small scale perturbations along the fiber axis the

amplitude of which are on the order of microns These distortions can cause light to leak out of a fiber

Micro-bending may be induced at very cold temperatures because the glass has a different coefficient of

thermal expansion from the coating and cabling materials At low temperatures the coating and cable

become more rigid and may contract more than the glass Consequently enough load may be exerted on the

glass to cause micro bends

Coating material is selected by manufacturers to minimize loss due to micro-bending The linear thermal

expansion coefficient of coating material shall be compatible with that of fiber

32 | P a g e

DISPERSION Dispersion is the optical term for the spreading of the transmits in the fiber It is the bandwidth

limiting phenomenon and comes in two forms Multimode dispersion and chromatic dispersion Chromatic

dispersion is further subdivided into material dispersion and waveguide dispersion

DISPERSION PHENOMENON IN OPTICAL FIBER Dispersion is the time distortion of an optical signal that results from the differences of time of travel

for different components of that signal typically resulting in pulse broadening As the distance traveled by

the signal is more broadening of pulse is more In digital transmission dispersion limits on the maximum

data rate and the maximum distance ie the information-carrying capacity of a fiber link The interference

from broadened pulse in the next interval shall not lead to erroneous interpretation of received signal

OPTICAL DOMAIN Understanding where attenuation and dispersion problems occur helps optical design engineers

determine the better wavelengths at which information can be transmit taking into account distance type of

fiber and the other factors which can severely affect the integrity of the transmitted signal The graph shown

depicts the optical transmission domain as well as the areas where problems arise The wavelength (nm)

is shown on X-axis and attenuation ( dBkm) is shown on Y-axis

There are four transmission windows appear in the figure The first one is at around 850 nm the

second at 1310nm third at 1550 nm and fourth at 1625 nm The last two labeled as C and L band

respectively The 850 nm wavelength at which the original LED technology operated The second window at

1310 nm has low dispersion The 1550 nm called as C-band is ideal wavelength for long haul

communication systems The network engineers can avoid transmitting signal at 1000 nm where Rayleigh

scattering 1240 and 1390 nm where hydroxyl absorption by water occurs to avoid high degree of loss

Optical fibers also can be manufactured to have low dispersion wavelength in the 1550nm region

which is also the point where silica-based fibers have inherently minimal attenuation These fibers are

referred to as dispersion-shifted fibers and are used in long-distance applications with high bit rates For

33 | P a g e

applications utilizing multiple wavelengths it is undesirable to have the zero dispersion point within the

operating

wavelength range

34 | P a g e

SIGNALLING RELAYS

INTRODUCTION A relay is an electromagnetic device which is used to convey information from one circuit to another

circuit through a set of contact ie front or back contact Constructional and electrically relays may be

divided into DC and AC relays because the means by which the electrical energy in the coil is converted in

to mechanical Energy in order to move the contacts are fundamentally different In DC type the contacts are

carried on an armature forming part of a magnetic circuit in which a field is set up by the current flowing in

the coils In AC types the contacts are attached by a link mechanism to a metal sector disc or cylinder in

which currents are induced by the alternating magnetic field produced by the currents in the coils

Every endeavor has been made to explain the action of each type of relay in the simplest possible manner

Relays are sophisticated switch gears used for remote control and succession control of various

electrical equipment In present days they are widely used because they are capable of protecting the

controlled equipment from cross feeding and overloading even as they cater for speedy operations

Most of the relays in present day signaling are electromagnetic devices although some of the relays control

circuits through electronic components like diodetransistors Integrated Chips etc

Railway signaling relays are unique in that

(a) They operate on low voltage and current

(b) They are more articulate as according to their special features they can work under restrictive conditions

and in any specified manner Virtually they can cater for all situations while contributing to speed and

accuracy in operations

CLASSIFICATION OF SIGNALLING RELAYS (a) According to the method of their mounting or fixture they are classified as

(i) Shelf type Relays which are loosely kept on shelves

(ii) Plug in type Relays which are plugged into a pre- wired plug boards

(b) According to their connection and usage they are classified as

(i) Track relays Relay which is directly connected to the track to detect the presence of vehicle

(ii) Line Relays Other than track relay all are line relays Relays connected to the selection circuit

(c) According to their vitality or importance in ensuring train working safety they are classified as

(i) Vital Relays All relays used for traffic control such as signal point controls track detection etc

(ii) Non-vital Relays Relays which operate control aids and accessories like warnings buzzers

Indications etc

(d) According to their special provisions to ensure reliability of their contacts they are classified as

(i) Proved type are those whose normalization after each operation shall be proved in circuit

controlled by their contacts Contacts in which both the springs have metal surfaces on their tips They may

get fused due to high sparking current across them during operation These may prevent relay normalization

and causes unsafe condition in traffic control To avoid this proving of relay normalization after each

operation is necessary

(ii) Non - proved type Need not to be proved to have been normalized after each operation as their

contacts have at least one non-fusible contact (carbon contact)

(e) According to their feed source relays are broadly classified as

(i) DC relays The relay which requires DC power supply for its operations are called DC relays Among

the DC relays

o DC neutral relays This relay closes the same set of contacts on energization with Normal polarity

or Reverse polarity supply

o Polar Relays This relay closes different set of contacts when energized with Reverse polarity

supply They may or may not have contact to close when deenergized

35 | P a g e

(ii) AC Relay AC Induction motor track relays Time element relays flashing indication control etc

(iii) Electronic Relays DC relays with electronic components in them are called electronic relays

DC NEUTRAL RELAY Each Relay has usually one or two coils with a hollow center to accommodate a coreThe coils are

made up of a large numbers of turns of small gauge soft drawn copper wire The two coils can be connected

in series or parallel according to the requirement of relay resistance The ends of the coils are terminated on

binding post to which the control wires are connected Each coil is placed around a core of specially selected

Iron or steel having high permeability and low retentivity The core should be susceptible to magnetism and

at the same time should have little residual magnetism The cores are connected at the top by a yoke to

complete the magnetism coupling between two ends of coils The bottom of each core is equipped with a

large steel or Iron block known as pole piece or face

A flat piece of Iron or steel called armature is supported by brackets which are securely fastened to

the pole piece The armature yoke and the pole pieces are also made of specially selected iron or steel of the

same quality as the core The armature carries the metallic spring contacts which are insulated from it

The circuit through the coils of the relay is closed It sets up a magnetic flux through the core yoke and the

armature The flux passing between the armature and pole faces causes the armatures get attracted to the pole

faces and armature picks up and closes front contacts When the circuit is opened the magnetic flux collapses

and the armature drops away by gravity from the pole faces the front contacts break and back contacts close

The front and back contacts of the relay can be utilised to make or break other circuits Two stop pins of

nonmagnetic material are fixed either on the armature or pole faces so that the armature cannot

come in contact with the pole faces It is essential to maintain a small air-gap between the armature and pole

faces so that low value of residual magnetism may not retain the armature in picked up position and causes

the relay to fail to drop away with a break in its control circuit

GENERAL USAGE

DC Neutral line relays are most commonly used for Railway Signalling controls and detection

Among them plug-in type relays are preferred in larger installations for space considerations Shelf type

relays are also in use mostly in wayside stations

There are many DC Neutral line relays in use with special features such as

(i) Delayed operation

(ii) Biased DC control

(iii) DC control unaffected by AC interference currents

(iv) Getting latched in operated condition till further feeding and others

Usage of DC polar relays is mostly in conjunction with block instruments that control traffic between

stations AC line relays are almost extinct in installations of British Signalling practice They are however

used for time control operations flashing indication control and such other special purposes in installations

with Siemens signalling practice widely Track relays are used according to the type of track detection

circuits chosen for a given location and context While most of the track circuits are still of the DC working

type requiring DC neutral track relays with them the prospects of their being replaced with Electronic track

circuits directly feeding DC line relays in future are great AC Track Circuits are used in DC Traction area

as conventional DC Track Circuits are not suitable there AC Track relays are used with them almost all of

the induction motor type In the British practice of signalling which was first introduced on Indian Railways

non-proved type relays with carbon to metal switching contacts are generally used for vital controls

They facilitate simple circuit designs But with the advent of German Practice introduced by Ms

Siemens later proved type relays with all metal to metal contacts are widely accepted in spite of

complications in circuit design caused by them A recent introduction is that of the same type relays made by

Ms Integra control However for some time now the appreciable features of both the practices are getting

36 | P a g e

incorporated together in the indigenous designs of signalling by railwaymen With this the usage of all types

of relays anywhere can be found without straight jacketed segration of relay types

CHARACTERSTIC OF ELECTRO-MAGNETIC RELAY The following are the characteristic of electro-magnetic relays A brief study of them helps in

understanding the choice of their components and designs features

1) Force of attraction

2) Effect of air gap

3) Effect of Hysterisis

4) Transient condition

FORCE OF ATTRACTION In any electro-magnetic system the force of attraction is given by

Where B - is the flux density a - is the cross sectional area of the particular part of the magnetic

circuit

In the case of a DC neutral Relay B is proportional to the current that is flowing in the coil

surrounding the electro-magnet and thus the force of the attraction is directly proportional to the square of the

current This square relationship has its own advantage especially in the case of DC track relay in that a

small reduction in the current will have a great effect on the working of the relay Also for a given change of

current the make and the break will be quicker with lesser possibility of arcing

EFFECT OF AIR GAP

Curve lsquoArsquo is magnetisation curve for the iron and is all practical purpose a straight line up to the

saturation point Curve lsquoBrsquo is the magnetisation curve for the open-air gap which is a straight line through

out because per magnetisation curve of the whole

magnetic circuit of the relay and for a given force is the sum of the amp-turns for the iron part and the amp-

turns for the air gap

When the front contacts are open the force required to pick up the armature is shown on curve lsquoCrsquo to be F1

but after the armature has operated it will be separated from the core by stop pins In this position the amp-

turns required to maintain the armature is less as indicated by the dotted line from 1 on curve C to 2 on curve

37 | P a g e

F But actually the current in the coil is unaltered the force on the armature is greater than required as

indicated at 3 on curve F Part of this extra force is used to flex the front contacts sufficiently to give good

contact pressure when it is in energised position

The difference between the pick-up and the drop-away current should be as small as practicable in

track relay to ensure good shunting characteristics This is achieved firstly by the choice of good quality relay

iron and secondly by having a small air gap between armature and core If the air gap is not available then

the residual magnetism fluxes might cause the armature to be retained when the supply is disconnected For

this reason residual pins are provided to ensure a definite minimum air gap in the energised position

EFFECT OF HYSTERISIS

Hysterisis is the property by which the flux produced lags behind the current In the de-energized

condition there will be small residual flux in the core When the voltage is applied to the coils the current in

rising to its steady value first causes the flux to rise from 1 to 2 along the curve At this point the flux density

will be sufficient to attract the armature and reduce the air gap the flux then raise to 3 and continue to 4

which corresponds to the steady current in the coils When the voltage is disconnected the current in falling

caused the flux to fall from 4 to 5 along the curve At this point the flux density will fall below the value

required to maintain the armature which will release thus increasing the air gap and reducing the flux to 6

Finally the

flux will decrease from 6 to 1 where the current will again be zero

The relay core is made of material having high permeability and low retentivity As mentioned in

the IRS specification Electromagnet iron may be in the form of a

(a) Bar of silicon steel

(b) Best Yorkshire wrought iron

(c) Swedish charcoal iron

(d) Electrical steel sheets

` This reduces the difference between pick up value and Drop away value By selecting good quality

core material Percentage release and sensitivity of the relay will be improved

TRANSIENT CONDITION

38 | P a g e

When the voltage is applied or disconnected from the coils it takes some little time before the current

become steady These are known as transient conditionsrdquo and are important so far as track relays are

concerned When the voltage is first applied to the coils the magnetic flux in rising cuts the turns on the

coils and in so doing produces a back EMF that opposes the applied voltage and retards the growth of

current

The growth and decay of flux are decided by the relationship between the inductance and resistance

in the circuit is known as time constant It is not fixed quantity in the case of DC neutral relay This value of lsquo

Lrsquo is less when the relay is in de-energised condition (L1) than when the relay is in energised condition (L2)

The magnitude of flux that is established for a given change of current is different in two cases

When the current reaches the pick up value the armature closes and the inductance is increased to L2

due to reduced air gap the flux per amp is increased The increase in flux increased the back EMF during the

movement of the armature after which the current continuous to raise along a new curve corresponding to the

increased inductance until it reaches the final value (ER) This process is indicated above in fig24

When the supply is disconnected the current is obliviously reduced to zero immediately but the flux

decay comparatively slowly owing to the eddy currents produced in the core by the rapid flux change which

tend to maintain the flux The drop away time on a disconnection is however generally negligible See fig

below

If the relay releases due to the reduction in current from say I 2 to I 1 caused by the application of

shunt resistance (as in the case of track relay ) the time taken is much longer than the relay is simply

disconnected The rate of rise or fall of current during the transient conditions is also depends on exterior

circuit values because L and R apply to the whole circuit The production of eddy current in the core the flux

will decay at a slower rate than the current So that the actual release time will be a little longer than it takes

the current to fall to the release

L= Inductance

39 | P a g e

R= Resistance

It is now clear that to reduce releasing time to a minimum it is necessary that

- The relay iron should have low Hysterisis loss and low retentivity

- The degree of over energization of the relay should be restricted

- Connecting a suitable external resistance in series with the relay to keep LR ratio low

In non RE area for track circuit length less than 100M 9 ohm track relay only to be used Using relay

with minimum contacts as they require lesser current which keeps inductance value low

Train working safety is ensured only if the track relay of shortest length track circuit is released

before a light engine running at a highest permitted speed clears it Otherwise the track circuit occupation

may go undetected To avoid this a special provision has to be made in signal control circuits wherever

necessary

The following methods may be adopted for reducing the time lag of track relay

(a) Restrict the over energisation of relay since the release time depends on the initial working current

(b) Connecting a suitable external resistance in series with the relay to keep the LR ratio low

(c) Using relays with minimum contacts as they require lesser operating current keeping the inductance

value low

40 | P a g e

CONCLUSION

Modern signalling is vital for safe and punctual movements of trains In the Indian railways The Signalling

and Telecommunication Department is responsible for providing modern effective and relaible signalling

systems as well as telecommunication systems

The first mode of communication used in Indian Railways was the use of electric telegraph

with the help of Morose code Morose code is the method of providing text information as a series of on-off

tones and lights or clicks that can be directly understood by a skilled listener or observer without special

equipmentEach character (letter or numeral ) is represented by a unique sequence of dots and dashes Later

this system becomes obselete and beggan the era of wireless communication which operated at audio level

frequency range

In wireless communication the significant advances took place the transition to miniature

valves or filament tubesBut this was abandoned too because of excessive current consumption and over

heating of the filament tubes

Fibre-optic communication is a method of transmitting information from one place to another by

sending pulses of light through an optcial fibreThe light forms an electromagnetic carrier wave that is

modulated to carry information First developed in the 1970s fibre optic communication systems has

revolutionized the telecommunications industry and have palyed a major role in the advent of the information

age Because of its advantages over electrical transmissionsoptical fibres have largely replaced copper wire

communications in core networks in the developed world The Indian Railways too is undergoing a transition

from Microwave communication to fibre optic communications

41 | P a g e

BIBLIOGRAPHY AND REFERENCES

1 wwwwikipediacom

2 wwwbritaniccacom

3 wwwirfcacom

4 Motorola GP60 system manual

5 Harris FAS 7000 manual

6 TOSHIBA Manual

iii | P a g e

ACKNOWLEDGEMENT

I would really like to thank every person who has helped me to complete my report successfully All the

websites where I have taken help from and all my friends who have helped me to chose this topic and collect

every bit of information about the topic Special thanks to my project mentor MR ATANU DEY without

whom completion of this very report would have been just impossible He has given me his valuable time

and worthy opinion to create my project successfully Definitely my parents are worth mentioning who have

kept supporting me throughout and have kept faith that I could do it

iv | P a g e

ABSTRACT

In this report I have given an overview of the signal and telecommunication systems that have been used and

are presently being used in the Indian Railways as a part of the day-to-day signalling and communication

procedures

I have covered in this report the history and the latest developments in railway signal and communication as

well as related fields I have made an elaborate study on the various equipments that have been used and are

currently being used as part of communication in the railways

v | P a g e

TABLE OF CONTENTS

TITLE PAGE NUMBER

CERTIFICATE BY THE SUPERVISORS I

STATEMENT BY CANDIDATE II

ACKNOWLEDGEMENT III

ABSTRACT IV

SOLID STATE INTERLOCKING 1

INTEGRATED POWER SUPPLY 5

SINGLE SECTION DIGITAL AXLE COUNTER 9

DATA LOGGER 15

OPTIC FIBRE 22

SIGNALLING RELAYS 34

CONCLUSION 40

BIBLIOGRAPHY AND REFERENCES 41

1 | P a g e

SOLID STATE INTERLOCKING

INPUT CARDS All the field conditions (ie Field relay contacts) are connected to these input cards of EI system

The maximum inputs capacity of each RI card will depend on design of the RI cards by different

manufacturers The total number of inputs will depend on the yard layout

Total inputs means

Field inputs ECRs TPRs NWKR etc

Panel inputs GNs UNs NWNs RWNs etc

Read back inputs HR DR WNR WRR etc

Opto couplers are provided to isolate field optically from the system in Input cards These cards will read the

conditions of inputs and passes the information to EI system

PROCESSOR CARD This card is also called as central processing unit card of the System This is provided with microprocessor

RAM ROM EPROM EEPROM Memory ICrsquos These EEPROMS or EPROMrsquos (ROMrsquos) are programmed

with software required for executing the system commands

System software consists of the following

- Executive software programmed in system EPROMrsquos

- Application software programmed in DATA EPROMrsquos

-

EXECUTIVE SOFTWARE This software is common to all EIrsquos for the same company manufacturing

This is a factory installed software

Performs all operations

Cuts off vital supply voltage to output relays in case of unsafe failures

2 | P a g e

APPLICATION SOFTWARE This software is specific to each station and different for different stations

This is as per table of control of specific station

Can be installed at site by signal engineers

Logic installed through Boolean expressions or user-friendly equations

OUTPUT CARD (RELAY DRIVE CARD) This card receives the output of CPU card as input and picks up relevant output relay as per the panel

operatorsrsquo request The output of this card is terminated on phoenix terminals from there the output relays are

connected

The essential modules of an EI is as follows

Hardware module

Software module

HARDWARE MODULES USED IN THIS SYSTEM Equipment consists of

CARD FILE

Each card file is like a shelf having 20 Slots to accommodate various PCBs that are used in a system

Slot nos1 to 15 and 20 are used to accommodate Non-vital Input-output or Vital Input or Vital Output PCBs

Slot no16amp17 are used to accommodate Power supply PCB Slot no18amp19 are used to accommodate CPU

PCB In this cardfile a mother board is available in the rear side connecting all the 20 Slots This cardfile is

suitable to mount on a 19rdquo rack

Power

Supply

Card

CPU

Card

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19

20

CPU PCB Each card file to have one CPU PCB and always placed in slot no18amp19 In this card Micro

Controller used is Motorola 68332 and its speed is 21 MHz In this card 4 nos of flash EPROMs of 8 MB

are used to store executive and application software Two nos of fast Static RAM (each 64KB) are used to

process the vital data and Four nos of Static RAM (each 64KB) are used to store events and errors

The main functions of CPU is it monitors continuously status of Vital Boards It also monitors

system internal operation for faults and responds to detected faults It processes application logic based on

inputs

received and deliver outputs to drive external gears It records system faults and routine events in user-

accessible memory It monitors and controls the serial communication ports It controls power to vital outputs

through external VCOR relay

POWER SUPPLY PCB

3 | P a g e

Each card file to have one Power Supply PCB and always placed in slot no16amp17 Power supply

PCB is basically a DC-DC converter that converts 12V DC input supply is +12V -12V and +5V required for

various board functioning Based on diagnostic check by CPU Power Supply Card receives 250Hz signal

from CPU and extends supply to VCOR relay This card provides isolated supply to internal circuit

VITAL OUTPUT PCB Each Vital Output PCB has 16 Outputs It is available in 12V and 24V DC applications Each Vital

Output can drive an output device such as any Q-series relay This output relay in turn controls signals

points crank handle siding control level crossing etc Since Vital Output drives the relay which controls

important outdoor gears all the Vital Output boards are continuously diagnosed by a CPU Any abnormality

in any of the outputs will shut down the system to ensure safety

VITAL INPUT PCB Each Vital Input PCB has 16 Inputs It is available in 12V and 24V DC applications Each Vital Input

is assigned to read the status of outdoor gears such as Track circuits Point detectors Crank handles Siding

controls level crossing etc Since the Vital Inputs read the status of outdoor gears they are normally

configured with double cutting arrangement using relay contacts

NON-VITAL INPUTOUTPUT PCB Each Non-vital IO has 32 inputs and 32 outputs in one PCB It is available in 12V and 24V DC

applications Non-vital inputs are Panel push buttons and keys Non-vital outputs are Panel indication LEDs

counters and buzzers The status of Non-vital Inputoutput is known from LED indications available in front

of the card

VITAL CUT OFF RELAY- VCOR Each card file will have one VCOR to ensure the healthiness of the system VCOR has 6 FB

dependent contacts each rated for 3 Amps When system is healthy the coil receives voltage from Power

Supply PCB which in turn controlled by CPU Power to Vital output board is controlled by VCOR thus

ensuring safety

WIRING HARDWARE 48 Pin Address select PCB and Connector assembly is provided for Vital Input and Vital Output

cards 96 Pin Address select PCB and Connector assembly is provided for Non-Vital IO cards 48 Pin

Connector Assembly is provided for PS and CPU PCB EEPROM PCB which is provided on rear side of the

CPU connector to configure various serial communication ports Keying plugs are provided in the cardfile to

ensure coding to each type of cards

SOFTWARE MODULES USED IN THIS SYSTEM System software consists of the following

EXECUTIVE SOFTWARE This software is common to all EIrsquos for the same company manufacturing

This is a factory installed software

Performs all operations

Cuts off vital supply voltage to output relays in case of unsafe failures

APPLICATION SOFTWARE This software is specific to each station and different for different stations

This is as per table of control of specific station

Can be installed at site by signal engineers

Logic installed through Boolean expressions or user-friendly equations

4 | P a g e

A GEC-MANUFACTURED SSI INTERLOCKING CUBICLE

A PAIR OF DATA LINK MODULES

TRACKSIDE FUNCTIONAL MODULE

5 | P a g e

INTEGRATED POWER SUPPLY

INTRODUCTION A typical 4 line station requires power supplies of 24 V DC( 5 nos ) 12 VDC ( 5nos ) 6V (2 nos)

110 V DC and 110 V AC for signalling These require as many chargers and Secondary cells amp Invertors

requiring more maintenance amp spares Can they be Integrated in to one system

Thus the concept of Integrated Power Supply has been evolved by integrating concepts One Charger

One set of Battery Bank feeding Invertors and DC- DC converters for deriving various DC amp AC

voltages Integrated power supply system delivers both AC amp DC Power supplies as an output with the

output voltage tolerance of plusmn 2

ADVANTAGES Reduces maintenance on Batteries Battery charger amp overall maintenance

Its construction is in modules and hence occupies less space Reduced space requirement resulting in

saving of space for power supply rooms

Provides centralized power system for complete signaling installation with continuous display of

working status of system for easier monitoring

Defect in sub-units of system is shown both by visual amp audible indication Reflects the condition of

battery with warning

Replacement of defective modules is quick amp easy without disturbing the working of the system

It uses (n+1) modular technology hot standby arrangement and hence high reliability and more

availability of the system

The system provides uninterrupted supply to all signalling system even during the power failures

Thus No blank Signal for the approaching drivers

System can be easily configured to suit load requirement

The diesel generator set running (Non-RE area) is reduced almost to lsquoNILrsquo Hence low wear and tear

of DG set components amp reduced diesel oil consumption

COMPONENTS (a) Un-interrupted power supply (U P S)

(i) SMPS Battery chargers with Hot stand-by mode

(ii) Hot Standby PWM Inverters with auto changeover

(iii) CVT Regulator [FRVS]

(b) AC distribution board [ACDB]

(i) STEP DOWN TRANSFORMERS

(c) DC distribution board [DCDB]

(i) DC-DC converters

WORKING IPS works satisfactorily for AC input variation of 150V AC to 275V AC with single-phase power supply

and frequency variation from 48 Hz to 52 Hz The input is fed to SMPS charger which converts in to 110

VDC as output It is fed as input to three sub units

To battery bank charging the batteries

To ON line inverters that converts 110 VDC in to 230 VAC plusmn 2as output

6 | P a g e

As 110 VDC bus bar to DC Distribution Panel as an input to various DC-DC converters located in

it

A 110 V Battery Bank of VRLA cells are connected to SMPS Panel IPS Status Monitoring Panel is

located at ASM room or at SampT staff room if round the clock SampT staff is available at Station

CONSTRUCTION IPS mainly consists of

SMR (Switch Mode Rectifier) Panel SMPS based Float cum Boost Charger (FRBC) Panel

AC Distribution Panel

DC Distribution Panel

Battery Bank (110V DC)

Status Monitoring Panel

SMR (SWITCH MODE RECTIFIER) PANEL SMPS BASED FLOAT

CUM BOOST CHARGER (FRBC) PANEL It consists of SMR FRBC modules and Supervisory amp Control Unit SMPS based SMRs

(converters) SMPS based Float cum Boost Chargers (FRBC) modules are provided with (n+1) modular

technology hot standby arrangement with active load sharing basis and 1 additional module as a cold standby

(n+2) Supervisory amp Control Unit which controls and monitor the complete system It has various

indications on the panel reflecting the working of the panel

FRBCs are suitable for operating in parallel on active load sharing basis with one or more modules of similar

type make and rating

n = required no of modules to cater for actual current requirement

AC DISTRIBUTION PANEL It is made of ON-Line inverters with (1+1) modular technology hot standby arrangement amp CVT

(Constant Voltage Transformer) AVR (Automatic Voltage Regulator) and set of step down

transformersThe inverter is protected against overload and short circuit with auto reset facility Whenever

the failure occurs it trips and restart automatically after about 10 to 20 sec But if the problem persists the

protection is permanently gets latched and it will not be switched ON again unless the fault is cleared

followed by pressing of reset button The output of inverters is regulated to 230V AC plusmn 2 50Hz plusmn1Hz for

an input voltage variation of 90V DC to 140V DC Normally both the Inverters are powered ON and both are

delivering the Output voltage but only one (main) inverter is connected to the Load If main inverter is failed

then only the stand-by inverter will come on Load automatically with in 500msec At 70 Depth of

Discharge (DOD) of the battery bank 110VDC supply to the inverters will be cut-off So the Signals feed will

be cut-off The auto-change over arrangement is also provided for bringing the CVT in circuit with in

500msec when the both the inverters output is failed It has various indications on the panel reflecting the

working of the panel

DC DISTRIBUTION PANEL It takes care of DC Power supply requirements of our signalling It consists of sets of DC-DC

converters for individual DC power requirements with (n+1) modular technology hot standby arrangement

with active load sharing basis The DC-DC converters of Relay Internal are provided with (n+1) modular

technology hot standby arrangement with active load sharing basis and 1 additional module as a cold standby

(n+2) The DC-DC converter works satisfactorily with the input voltage variation of 98VDC to 138VDC At

90 Depth of Discharge (DOD) of the battery bank all the DC-DC converters 110VDC Input supply will be

cut-off except for Block Tele DC-DC converters The supply for Point operation is also catered through a

20A fuse by this unit It is also provided with various indications that reflect its working

7 | P a g e

STATUS MONITORING PANEL IPS status monitoring panel has been provided in the ASM room for giving the important alarms and

indications to ASM Status Panel tells present working status of IPS displaying battery voltage continuously

and five other indications which will light according to IPS status During normal working these indications

will not lit Whenever the battery has come on to the load and has discharged by 50 DOD (Depth of

Discharge) then first Red indication lit with description ldquoSTART GENERATORrdquo with audio Alarm ie DG

set is to be started and put on the load If DG set is not started with this warning then if battery gets further

discharged to 60 DOD and second Red indications appears with description ldquoEmergency Start generatorrdquo

with audio alarm even now if DG set is failed to be started the battery further gets discharged to 70

DOD and 3rd Red indications appear with description ldquo System shut downrdquo with audio alarm which will

continue till Generator is started resulting in AC output from IPS is automatically cut off results all the

signals will become blank

When there is any defect in any sub module of IPS even without affecting working of system the 4th

Red indication appears with description ldquoCall SampT Staffrdquo with audio alarm so the ASM advises SampT staff

accordingly Green LED 5th indication comes with the description ldquoStop Generatorrdquo with audio alarm when

the DG set is running and if the Battery bank is fully charged condition

EARTHING The IPS systems and its individual modules are having earth terminals and all these are properly

earthed with earth resistance of less than 1 ohm Earth provided shall preferably be maintenance free using

ground resistance improvement compound (The acceptable Earth Resistance at earth busbar shall not be

more than 1 ohm Code of practice for earthing and bonding system for signalling equipments)

LIGHTNING AND TRANSIENT PROTECTION IN IPS Manufacturer will provide Stage1 amp Stage 2 protection along with the IPS These are described

below

Stage 1 protection is of Class B type against Lightning Electro-Magnetic Impulse (LEMP) amp other

high surges provided at Power Distribution Panel It is provided with a 63 Amp fuse in phase line and is

connected between Line and the Neutral and also between the Neutral and Earth

Stage 2 protection (Power line protection at Equipment level) is of Class C type against low voltage

surges provided at the equipment input level This is thermal disconnecting type and equipped with

protection against SPD (surge protection device) failure due to open amp short circuit of SPDs and is connected

between the Line and the Neutral If supply data signalling lines (ACDC) are carried through overhead

wires or cables above ground to any nearby building or any location outside the equipment room additional

protection of Stage 2 type shall be provided at such locations Class B amp Class C arrestor is provided on a

separate wall mounting type enclosure in IPS room

Stage3 protection (Protection for signallingdata line) is of Class D type All external data signalling

lines (ACDC) shall be protected by using this Class D type device It consists of a combination of Varistors

and Gas Discharge Tube with voltage and current limiting facilities

FEATURES Chargers used in this system are of SMPS technology chargers with 90 efficiency These chargers

are supported with hot standby mode with (n+1) modular technology

Onetwo sets of Maintenance free Battery banks (110VDC) Normally one set (110VDC) of Battery

bank is used Conventional flooded type Lead Acid Batteries or Low Maintenance Lead Acid

batteries can also be used (SMRs settings are required to be adjusted depending on the type of

Batteries used) Various voltage levels of

8 | P a g e

battery banks are avoided Reduction in Battery maintenance amp less flour area required

DC-DC Converters working from 110V Central battery have been used for all dc supplies This has

improved overall efficiency of the system since number of conversion from AC to DC have been

reduced to 2 stage as compared to 3 stage conversion in case of transformer-rectifier system

DC-DC converters are available in modules Easy replacement of defective modules This ensures

less down time

DC-DC Converters are used in load sharing N+1 configuration (ie with hot standby with N+1

modular technology) to improve the reliability amp availability of the system

Capacity of inverter has been brought down to 15 KVA from 5 KVA and used for feeding only

Signals supply Hot standby inverter is provided with auto changeover facility This improves the

availability of the overall system

High efficiency inverter is used with PWM (Pulse Width Modulation) technology in place of Ferro-

resonant technology based inverter This improves the efficiency of the overall system

Continuous power to Signal Circuits even in absence of DG setLocal Power Supply

Generators need not be switched ON every time during train movement

Metal-to-metal relay installations and block working by axle counters have also been covered

Supply of spare modulesComponentsCells have been included as part of main supply

Provides highly regulated voltage to all signal relays amp lamps for better life

9 | P a g e

SINGLE SECTION DIGITAL AXLE COUNTER

INTRODUCTION- The axle counter equipment is working on high frequency and using amplitude modulation or phase

modulation for detection of presence of wheel The equipment described in this notes is Phase modulation type

for the detection of presence of wheel In the Phase modulation type track device the detection of presence of

wheel is with the phase reversal of 1800 out of phase which enables this system to be more healthy and safe

In Phase Reversal Modulation technique trolley suppression arrangements to prevent the counting of

wheels caused by push trolley passing over the track device are not required as the system will take care of

validation of generated pulses caused by passage of wheel over the track device depending up on the phase

shift of the pulse This phase shift of the pulse may be normally 160deg to 180deg for a train wheel and it may be

approximately 100deg to 120deg for a push trolley wheel

This is Digital Axle Counter equipment for single track sections containing 2 out of 2 micro-

controllers to count the axles establish the track occupancy of a track section and to provide this information

to the block or the interlocking equipment

In this system no separate evaluator is required and no analog data is being transmitted One set of

Axle counter equipment is provided at entry end and other set provided at exit end Both sets are being

connected through a twisted pair of telecom cable ie existing RE cable one PET quad is used for both UP

and DN Axle Counters Digital DATA is being transmitted between two ends of Axle counters (Outdoor

track side Detection points)This system is a fully duplex capable of operating according to CCITT V21 and

the Data will be transmitted at the rate of 300bitsec This data Transmitted ensure negligible interference of

the noise The system is highly reliable

FEATURES (a) The system consists of

(i) Single Section Digital Axle Counter (SSDAC) units

(ii) Tx Rx coils

(iii) Vital Relays

(b) TxRx coil axle detectors are mounted to the web of the rails The design of system consists of 21 KHz amp

23 KHz High frequency Phase Reversal type axle detectors

(c) Compatible with 90R 52Kg amp 60Kg rail profiles Easy to install commission amp maintain

(d) Track devices at both (entry amp exit) points of the section should be fixed on the same rail

(e) System is designed to detect the solid wheels with diameter gt 400mm with standard wheel flange

(f) The system works in pairs For monitoring single-track section one pair of SSDAC units are required and

to be installed near the trackside one at the beginning and another at the end of the track section ie

Trackside electronic counting equipment

(g) The basic design of the system is based on counting the number of axles passing at each detection point

These stored counts are transmitted to the second unit of the system and vice versa by means of modem

communication

(h) The communication consists of digital packets having details of Counts amp Health

10 | P a g e

(i) If counts registered at both detection points are equal the section is cleared otherwise the section is shown

as occupied The system ensures no error condition to arrive at the decision of clearance

(j) System is designed as per CENELEC SIL-4 (European standard) using micro controller along with other

electronic circuits and programmed using dedicated software When any of these circuits fail the system

goes to fail safe condition

(k) It is programmable for either Preparatory Reset or Conditional Hard Reset as per requirement

(l) Micro controller based design with 2 out of 2 decisions and counting through software

(m) V21 Modem communication (2-wire) on frac12 quad cables and also compatible to work on voice channel of

OFC amp Radio

(n) Opto isolated vital relay drive for Q-style 24V 1000 _ and Vital Relay output can be giving at both ends

of the system

APPLICATIONS The system can be widely used in Railways for Block Working (BPAC) Intermediate Block Signaling Auto

signalling and Track circuiting for i) Loop line ii) Main line iii) yard lines

SYSTEM DESCRIPTION

This system comprises of

Tx coils-2 nos

Rx coils-2 nos

Reset Box (RB 258A)

Card 1 Signal Conditioning Card ndash 1

Card 2 Signal Conditioning Card - 2

Card 3 Micro controller Logic Board ndash 1

Card 4 Micro controller Logic Board ndash 2

2 nos for independent resetting ndash when used in block sections

1 no for common resetting ndash when used for Track circuiting at stations

Card 5 Event Logger Card

Card 6 Modem Card

Card 7 Relay Driver Card

Card 8 DC-DC Converter Card

SSDAC (DACF 700AP) UNIT

(A) SIGNAL CONDITIONING CARD (CARD 1amp2) (SCC) -1 (SCC-1) generates 21 KHz carrier

signals

-2 (SCC-2) generates 23 KHz carrier signals which is transmitted to 2nd

set of Tx coils

s receive these signals

modulated

train pulses

11 | P a g e

(B) MICRO-CONTROLLER LOGIC BOARD CARD (CARD 3amp4) (MLB) The Micro-controller Logic Board (MLB) is the heart of the system

o 8051 Based Architecture

o 8 Bit Micro Controller

o ATMEL AT89S8252 Micro controller

o 2 out of 2 Decision

o Uses C subset language

- TOOLS

o KEIL μ Vision Development System

o Universal Programmer

o 2KB Program Memory

o 256 bytes RAM

o 8KB Flash memory

o 32 Programmable IO lines

o Wide Operating Voltage range of 4V-6V

o Full Duplex Serial Port

o Programmable Watch Dog Timer

o Fully Static operation up to 24MHz (Upgraded to 40MHz)

o Operating Temperature of ndash40degC - +85degC

o Use of State Machine for Axle Counting

o Use of ASCII MODBUS protocol

o Use of CRC16 technique for Error Checking during communication

o Wheel detection

o Train direction checking and

o Wheel counting functions

o It receives the remote wheel count and computes the status of the section for clear or occupied

o It also checks various supervisory signal levels like supervisory of TxRx coils presence of various

cards communication link failure etcThese cards communicate with each other for wheel count

At Entry-end if train enters into section (1st detection) the counts are incremented and when train

shunts back from the same detection ie if train exits from the section from the same detection the counts are

decremented At Exit-end if train enters into section (2nd detection) the counts are decremented and when

train shunts back from the same detection ie if train exits from the section from the same detection the

counts are incremented Both the track devices at Entry and Exit ends must be fixed on same side of the

track

This MLB card is having Extensive LED display

o A block of 8 LED indicators for count progress error display

o 2 independent LED indicators for section status

o The errors occurring in the system during the operation of the SSDAC are encoded and are indicated by

means of the 8-LED block present on the front panel of the MLB cards

(c) EVENT LOGGER CARD (CARD 5)

Event logger card is designed to capture and store important signals from the remote and local SSDAC units

The stored data can be downloaded from the event logger card for the purpose of analyzing the events

occurring during the operations of the SSDAC The data can be analyzed with the help of CEL data analyzer

software

12 | P a g e

The event logger card captures following signals

(i) Pulse signals

(ii) Supervisory signals

(iii) Card removal information

(iv) Serial packets from

Event Logger card has a Rabbit processor and 2 MB FLASH MEMORY to store packets The data is initially

stored in the buffer and subsequently transferred to FLASH memory every two minutes Normally 4096

pages of the data can be stored in flash memory on FIFO (first in first out) basis

Run This LED blinks continuously indicating the normal working of the event

Log This LED blinks whenever data is being logged into the flash memory (Approx after every 2 minutes)

Dnld This LED is ON when data is being downloaded from the flash memory of the card and becomes OFF

when download is complete

(D) MODEM CARD (CARD 6) (i) The modem card transmits and receives the digital packet information form one counting unit to the other

The packet will appear after every 18 sec and the packet carries the latest information such as

(ii) The modem card being used is V21 type (2-wire) in SSDAC

(iii) This card interfaces with serial RS232C port of both Micro-controller Logic Boards

(iv) It multiplexes the two RS232C inputs and selects one of the two channels and provides signal conversion

from digital to analog (FSK modulation) and vice-versa

(v) Data transmission rate is 300 bitssec

(vi) Automatic Gain Control circuit is incorporated hence no gain adjustments required

(vii) Mode selection on Modem card The modem has been set in lsquoORIGINATORrsquo mode for entry and in the

lsquoANSWERrsquo mode for exit in the factory

(viii) LED Indications provided on Modem card

-Transmitting the signal when LED is flashing

- Receiving the signal when LED is flashing

-Remains OFF in SSDAC

-Carrier is detected when LED is glowing

(E) RELAY DRIVER CARD (CARD 7) (i) The Relay Driver card (RD) provides the 24V DC output required for driving Vital Relay

(ii) One RD card is used in each SSDAC counting unit The RD card receives the command of clear and

clock signals from MLB1 amp MLB2 cards and drives the vital relay lsquoONrsquo when section is NOT OCCUPIED

through opto- isolator circuit

(iii) If a train occupies the section the vital relay is dropped The vital relay status is read back by the system

as per the driving output

(iv) It has

13 | P a g e

ndash LED flashes when the section is clear

ndash LED flashes when the section is clear

All the above LEDrsquos are lit for section clear condition

(F) DC-DC CONVERTER CARD (CARD 8)

INPUT VOLTAGE Nominal Voltage voltage 24V DC Maximum current drain= 12A

Required voltage 18V DC to 30V DC

Output voltage

Nominal Voltage +5 V DC 2 A Required voltage 4 7 5 t o 525V DC

Nominal Voltage +12V DC 200 mA Required voltage 1175 to 1225V DC

Nominal Voltage +24V DC 300 mA with common ground Required voltage 235 to 245V DC

Nominal Voltage +15V DC 100 mA with isolated ground Required voltage 145 to 155V DC

SURGE VOLTAGE AND LIGHTNING PROTECTION Transient surge voltages arise as a result of Lightning discharge switching operations in electrical

systems and electrostatic discharge These surge voltages often destroy the electronic equipment to a large

extent In order to prevent surge voltages from destroying the equipment all the input lines of SSDAC ie

Power Supply (24V) Reset (48V) amp Modem is to be routed through surge voltage protection devices for

effectively protecting the system These devices (3 numbers) are mounted in a box and supplied along with

the system One number of box is to be installed at each location and wired to the SSDAC

Each surge voltage protection device consists of two parts

(a) Base

(b) Plug Trab

The Base of the device is used for wiring the input and output signals The connection details from relay

room to the box and from box to SSDAC unit are provided on the box The Plug Trab consists of MOV and

GD Tube and diverts the excess energy during surge voltages or lightning into the ground connection The

operation of these devices relies on a high quality ground connection in order to safely shunt away the

unwanted energy The impedance of the ground connection is critical and it should be less than 2 Ohms

NOTE The 3 Plug Trab connections are not to be interchanged with one another The plug Trab is a

detachable device and can be replaced with SPARE unit in case of blown device which is indicated by

means of LED for 24 V

EFFECTIVENESS OF PLUG TRABS The effectiveness of plug Trab depends wholly on the Earth connection provided to the system The earth

provided to the system should be less than 1 ohms and connections should be firm and proper to the SSDAC

unit VR box etc

SURGE VOLTAGE AND PROTECTION DEVICE SV-120 The Surge Voltage protection device is to be installed at each location along with every SSDAC unit

14 | P a g e

EARTHING- The lead wires connecting the installation and the earth electrode shall ordinarily be of stranded

copper wire of 29 sq mm (19 strand wires of 14 mm diameter) Copper wire has been specified because GI

wires usually are having greater corrosion However in areas where copper wire may be frequently stolen

due to theft ACSR of size 64 sq mm (19 strands of 211 mm diameter) may be used

LIMITS OF EARTH RESISTANCE (a) Apparatus case connected to Earth (SSDAC and vital Relay Box is housed in Apparatus case and

Connected to earth at outdoor) shall be less than or equal to 1 ohm

(b) All cable connected to same earth shall be less than or equal to 1 ohm

(C) Reset box connected to earth near SM s Room shall be less than or equal to 1ohm

EQUIPMENT TO BE EARTHED A Common Earth should be provided for SSDAC for items 1(a) amp (b) of the above at the outdoor

(a) The Apparatus Case is to be connected to earth (the chassis of SSDAC amp Vital Relay Box should be

properly connected to apparatus case)

(b) Metallic sheath and armouring of all the underground main cables are to be earthed

(i) In RE area the metallic sheath and armouring of main telecom cables are earthed at both ends

(ii) In RE area the armouring of Jelly filled cable shall be earthed at both ends

(c) The Earthing shall be provided at every location box where cables are terminated

(d) Earth already available for other equipment may be used for earthing of Reset Box near SM s Room

Cabin etc

15 | P a g e

DATALOGGER

INTRODUCTION Datalogger is a Microprocessor based system which helps in analysing the failures of relay inter

locking system Electronic Interlocking system This is like a black box which stores all the information

regarding the changes take place in relays AC DC Voltages and DC currents along with date and time The

same information data can be transferred to the computer to analyse further ldquoon line ldquooff linerdquo analysis of

stored date A print out also can be obtained through a printer by connecting directly to the datalogger unit

The data belongs to Relay contacts is considered as digital inputs and the data belongs to voltage

levels currents is considered as Analog inputs Datalogger lsquos are mandatory for all new relay interlocking

(PIRRI) EI installations and it is also recommended to provide in all existing PIs RRIs To increase the

line capacity mechanical signalling equipments are upgraded to PI RRI or EI Due to complexity in the

circuits and wiring sometimes it is very difficult to rectify the failures So datalogger can monitor these

systems with real time clock Thus it can be named as black box of Samp T equipments and hence it is a vital

tool for accident investigation Datalogger is used at Stations yards Whereas in case of Auto Section amp IBH

Mini dataloggers called as Remote Terminal Unit (RTU) are used

ADVANTAGES OF DATALOGGERS (a) Dataloggers helps in monitoring the typical failures such as intermittent auto right failures

(b) It helps in analyzing the cause of the accidents

(c) It helps in detecting the human failures errors such as

(i) Drivers passing signal at Danger

(ii) Operational mistakes done by panel operators ASMrsquos of operating department

(iii) Signal and telecom engineering interferences in safety circuits

(iv) Engineering and electrical department interferences failures

(v) It helps as a ldquoTOOLrdquo in preventive maintenance of signaling gears

(d) Dataloggers can be connected in network Networked dataloggers helps to monitorthe PIRRIEI remotely

(e) Failure reports can be generated remotely with help of datalogger network

(f) On line and Off line track simulation is possible

(g) Speed of the train on point zones can be calculated

(h) Age of the equipment in terms of number of operations etc

COMMON EQUIPMENT FOR ALL DATALOGGERS ARE GIVEN

BELOW (a) CPU card

(b) Digital and Analog input cards

(c) Local terminal(PC)

(d) communication links

(e) Printer

All the dataloggers requires a potential free ( spare ) relay contact for monitoring digital inputs

through Digital input cards amp for monitoring Analog inputs such ACDC bus bar voltage levels through

Analog input cards Digital and Analog inputs are connected to the Processor card Processor card consists of

memory ICrsquos Memory ICrsquos are programmed as per requirement of the signal engineers

Provision of Dataloggers is mandatory with RRI systems and is optional for PI systems as per

amendment to the specification for Relay Interlocking systems ( IRSS-36 ) The data collected by the

datalogger can be used for failure analysis repetitive discrepancies and for accident investigations

16 | P a g e

Note

If the serial communications is more than 50m then line drivers shall be used up to 3 Kms

4wire leased line Modems shall be used if the serial communication is more than 3 Kms

STUDY OF EFFTRONICS DATALOGGER TECHNICAL DETAILS (a) 24V 12VDC Power Supply

(b) Total Storage Capacity of 10 Lakh events

(c) In-built Temperature sensors

(d) Internal Buzzer for alarming during failures

(e) Real Time clock with internal battery backup with data retention up to 10 years

(f) 512 LED matrix to indicate the status of 512 Digital inputs at a time page wise

(g) Seven segment LCD screen (2x24) to display the status of digitalanalog signalsTime Temperature etc

(h) Using the keyboard various functions can be viewed in the LCD panel

(i) Max Digital Inputs 4096

(j) Max Analog Inputs 96

(k) Digital Input Scanning Time 16 millisecond

(l) Analog Input Scanning Time is less than 1 Sec

HARDWARE (EQUIPMENT) Datalogger system consists of

(a) Datalogger (CPU - with Microprocessor 68000)

(b) Digital input cards

(c) Dual modem card

(d) Digital Scanner units (DSU)

(e) Analog Scanner units (ASU)

CPU CARD It is provided with Motorola microprocessor M 68000 It performs all the activities pertaining to the

datalogger It continuously scans (check) the Digital inputs(inbuilt) Digital Scanner Units and Analog

Scanner Units ie scanning of digital signals (Relay operations) for every 16-milli seconds and scanning of

analog signals (ie ACDC voltages amp DC currents) for less than 1 second

This card will support the IO interfaces of LCD (Liquid Crystal Display) - 2X24 alphanumeric Key

Board LED Matrix Display Real Time Clock LCD display and keyboard This will acts as man machine

interface between the datalogger and the signal engineer All the operations (Software) can be performed

using this LCD and keyboard

Real time display with 7 Segments This is built in real time clock within Datalogger and its current

time will be displayed on six 7-segment display provided (Real time clock depend upon DALLAS 1286

chip) This IC will come with internal battery backup hence there is no need to add external batteries

CPU card continuously scans (checks) the DSUs and ASUs Each input connected to digital scanner

units are optically isolated by Opto couplers When CPU card scans the digital inputs it compares with the

previous stored data and if there is any change from the previous status then only that data will be stored (the

status conditions of relay) with date and real time A total of minimum 10 Lac events can be stored in

memory on first in first out basis so that latest data is available in the system There is no loss of data from

datalogger memory in case of power supply failure of datalogger

DIGITAL INPUT CARDS (IN-BUILT) This system is having maximum 8nos of inbuilt Digital inputs cards Maximum 64nos of digital

inputs can be connected to each digital input card The potential free relay contact may be front or back

contact terminated at the Tag Block from the relay of signals tracks points Buttons etc and are

17 | P a g e

subsequently connected to Digital input cards through Flat Ribbon Cable (FRC) connectors These in-built

digital input cards can monitor a total 512 nos of relays status

DIGITAL SCANNER UNIT (DSU) Each DSU contains 8 nos of Digital Input cards Each input card can be connected with 64 inputs

Total input capacity of DSU unit is 512 inputs These scanner cards contain Optocouplers and Multiplexer

Inputs are connected to Stag card The stag card out put is connected to DSU through FRC connectors

Maximum 7 nos of DSUs can be connected to the system So Digital input capacity of the system is 4096

All these digital inputs are scanned at rate of 16 msec

ANALOG SCANNER UNIT (ASU) ASU contains maximum 3 nos of Analog input cards Each input card can be connected with 8nos of

Analog inputs Total input capacity of the ASU is 24 analog input channels Maximum 4nos of ASUs can be

connected to the system Analog input channel capacity of the system is 96 All these analog inputs are

scanned at a rate of less than 1 sec

PARALLEL PORT Parallel port is provided for connecting printer

RS-232 SERIAL PORTS At least 6 Serial communication ports are provided for communication with other dataloggers

Central Monitoring Unit Remote Terminal Unit Electronic Interlocking system Integrated Power Supply

system etc

EXTERNAL NON-VITAL RELAY CONTACTS These relays provided in the system where 16 number of the Relay contacts are provided on the rear

panel through Tele control port to extend alarms and to control the power equipment from remote or local

locations through computer in case of any occurrence of failures Each control can sink or source 100 m

amps of current

INTERNAL MODEM CARD DUAL MODEM CARD (IN-BUILT) It is fixed in datalogger Euro rack itself One card contains two modems The top modem is called

ANS (answer) modem and the bottom modem is called as ORG (originate) modem It is used in case of

networking of Dataloggers In network connect lsquoANSrsquo modem to the lsquoORGrsquo modem of one adjacent station

and connect lsquoORGrsquo modem to the lsquoANSrsquo modem of other adjacent station

POWER SUPPLY Normally 24V DC (12V DC is optional) supply with battery backup is required for the system

working

Input Voltage Range 18Vhellip32V DC (For 24V) 9Vhellip18V DC (For 12V)

INPUT REQUIREMENTS Relay inputs (digital inputs) and analog inputs (voltages currents etc) are required to be connected

to the system as per the requirements of RRI PI SSI as the case may be Some of the inputs to be

monitored is given below

(a) Digital inputs

(i) Field inputs All TPRs NWKRs RWKRs ECRs Crank Handle relays SidingSlot LC gate

control relays etc

(ii) Control Panel inputs All button Knob SMrsquos Key relays

18 | P a g e

(iii) Internal relays

British system All HR DR HHR WNR WRR ASR UCR RR LR UYRTLSR TRSR TSR

JSLR JR etc

SIEMENS system Z1UR Z1UR1 GZR ZDUCR ZU(R)R ZU(N)PRG(R)RG(N)R U(R)S

U(N)PS UDKR DUCR U(R)LR UYR1 UYR2 G(R)LRGR1GR2

GR3 GR4 OVZ2U(R)RW(RN)R (RN)WLR Z1NWR Z1RWRZ1WR1 WKR1 WKR2 WKR3 etc

(b) Analog channels

(i) 230 V AC (for power supplies in the power panel)

(ii) 110V AC (for Signal and Track transformers)

(iii) 110V DC (for Point operation)

(iv) 60V DC (Siemens relays)

(v) 24V DC (Q-series relays)

(vi) 24V DC (for Block Axle counters)

(vii) 12V DC (for indication)

(viii) 20A (for point operation current)

(ix) 10V AC 5KHz (for Axle counter channels) etc

SOFTWARE MODULES OF DATALOGGERS

(a) Network Management of Dataloggers (NMDL)

(b) Reports

(c) Fault Entry

(d) Track Offline Simulation

(e) Train Charting

NMDL SOFTWARE FEATURES (a) Online Relay Status

(b) Online Faults - To view information of various Online Faults as they occur in the stations where

the Dataloggers are connected

(c) Online Simulation - Graphical view of relay operations train movements etc

(d) Remote monitoring of stations with the help of NETWORKING

SOFTWARE OBJECTIVES (a) Predictive Maintenance

(b) Easy identification of failures

(c) Crew discipline

(d) Train charting

REMOTE MONITORING OF STATIONS WITH NETWORKING OF

DATALOGGERS The individual Dataloggers of various stations can be interconnected through networking technology

The data of Remote Panel stations can be viewed in a Computer at the Central Monitoring Station The data

of the network is collected by the FEP (Front End Processor) which in turn is transmitted to the computer

COMPONENTS OF NETWORK MANAGEMENT OF DATALOGGERS

(a) Datalogger at stations

(b) MODEM and Transmission medium

19 | P a g e

(c) Front End Processor (FEP)

(d) Central Monitoring Unit (CMU) Computer

FEP (FRONT END PROCESSOR)

FEP acts as a buffer between the Central Monitoring Unit (Computer) and the Network It is provided

at centralised place to retrieve data continuously from station dataloggers and store in memory and transfer to

computer on request It stores 10 Lac telegrams It works on 12V DC It draws 16A continuous current

when all the three modems are connected Normally it shows the number of packets pending to be sent to the

computer on its 7-segment LED display It is provided with MOTOROLA 68000 microprocessor It has 6-

nos of RS-232 communication ports such as COM1 COM2 COM3 COM4 COM5 and COM6 COM1 is

used for Fault Analysis System (FAS) ie Central Monitoring Unit (Computer) connection COM2 to COM6

are used for networking For Bi-directional 2- nos of ports and for Tri-directional (T-network) 3-nos of ports

are used

DATA TRANSMISSION Dataloggers can be networked in Uni-directional Mode or Bi-directional Mode or T ndash Network Mode

In case of loss of data retransmission of data takes place

(a) Uni-Directional Mode

Each Datalogger will send data in only one direction to the FEP Unidirectional mode network is not

preferred

(b) Bi-Directional Mode

Each end of Network is connected to FEP and each datalogger can now transmit data in both the directions

Bi-directional Mode is advantageous it enables the Data Transmission even in case of Network Failure

(c) T - Network Mode

If more no of stations are in network ie if the network is too lengthy then T- network mode is preferred

COMMUNICATION The communication protocol for transmitting data and command between datalogger and CMU is

standardized by the RDSO and is given in the Specifications of Dataloggers

(a) The type of communication used in the network is dependent on the distance between the dataloggers

(b) For shorter distances Opto Converter Box- Opto isolated current loop communication is used

(c) For longer distances Modem (Dial-up leased) Fiber Optic Satellite Microwave communication

MODEMS Modems are used for DATA transfer between Dataloggers and Front End ProcessorThese are

configured to RS 232 Serial Communication Network is connected with two types of 4-wire modems

(a) Internal modem card Dual Modem card (in-built)

It is fixed in datalogger Euro rack itself One card contains two modems The top modem is called

ANS (answer) modem and the bottom modem is called as ORG (originate) modem

Note In case of networking of Dataloggers connect lsquoANSrsquo modem to the lsquoORGrsquo modem of one adjacent

station and connect lsquoORGrsquo modem to the lsquoANSrsquo modem of other adjacent station

(b) External modems

20 | P a g e

These are generally used at FEP (Front End Processor) side to connect the Dataloggers

(i) To transfer Data from one datalogger to another datalogger FEP Baud rate is 9600bps

(ii) These modems are 4-wire line communication

(iii) To transfer the data from FEP to RMU (PC) the Baud rate is 57600 bps

There is no difference between these modems functionally

CENTRAL MONITORING UNIT (CMU) COMPUTER

Central monitoring unit (Fault Analysis Unit) is a Personal Computer and its minimum configuration

shall be specified by RDSO from time to time System Software Windows XPVista(OS) Norton Kaspersky

(Anti Virus) Interbase where Server is not available (DBMS) Oracle where Server is available (DBMS)

software are required to run Datalogger System It is provided with Graphical User interface (GUI) based

software and retrieve data from all Networked dataloggers (up to 32) at various stations It stores data in

standard data base files The CMU is capable of analyzing the data and generate reports audiovisual alarms

on defined conditions This data can be compressed to take backup In central monitoring unit Software used

for analysis of data prediction of faults etc is written in a structured format so that purchaser can

reconfigure it if required It displays the status of signaling gears at any selected time in graphic form for any

selected station yard It retrieves the stored data amp simulates train movement It sends commands to various

Dataloggers to activate audio visual alarm or operate and electromagnetic relay

CMU shares data available in it by other PCs through available local area network where this data can

be used for train charting passenger information purpose The system generates audiovisual alarm in

ASMrsquosSignal Maintainerrsquos room in the case of power supply failure (battery voltage low) or battery charger

defective with acknowledgement facility

(a) Each datalogger has its own identity code which will be transmitted along with data packet to central

monitoring unit

(b) Events recorded at each station are continuously transmitted to central monitoring unit Response time of

data transfer will not exceed 10 sec

21 | P a g e

22 | P a g e

OPTICAL FIBER CABLE

INTRODUCTION The demand for bandwidth on transmission networks is increasing rapidly because video and

graphical rich contents are exchanged through the corporate network or the Internet The Gigabit Ethernet

became ommonly used in the corporate network backbone and 10Gbit Ethernet will be adopted in the near

future Meanwhile in the home the demand for high-speed network becomes popular as the wide spread of

broadband access eg CATV xDSL and FTTH The transmission medium with capability to transmit high

bit rate signal is necessary to satisfy these requirements

The telecommunication transport technologies move from copper based networks to optical fiber

from timeslot based transport to wave length based transport from traditional circuit switching to terabit

router and all optical based networks entering into a new era of optical networking

BASIC PHYSICS OF OFC

OPTICAL FIBER CABLE OFC have Fibers which are long thin strands made with pure glass about the diameter of a human

hair OFC consists of Core Cladding Buffers and Jacket as shown in figure

MONOCHROMATIC LIGHT OR SINGLE COLOR LIGHT Light or visible light is electromagnetic radiation of a wavelength that is visible to the human eye (

about 400 ndash 700 nm) The word light is sometimes used to refer to the entire electromagnetic spectrum Light

is composed of elementary particles called photons Three primary properties of light are

Light can exhibit properties of both waves and particles This property is referred to as wave-particle

duality The study of light known as optics In free space light (of all wavelengths) travels in a straight path

at a constant maximum speed However the speed of light changes when it travels in a medium and this

change is not the same for all media or for all wavelengths By free space it is meant space that is free from

matter (vacuum) andor free from electromagnetic fields

Thus the speed of light in free space is defined by Einsteinrsquos equation E = mc2

Frequency ν speed of light in free space c and wavelength λ are interrelated by ν = cλ

From the energy relationships E = mc2 = hν and the last one an interesting relationship is obtained

the equivalent mass of a photon m = hνc2

When light is in the vicinity of a strong electromagnetic field it interacts with it From this interaction

and other influences its trajectory changes direction as shown in figure

23 | P a g e

INCIDENT RAY REFLECTED RAY AND REFRACTED RAY An incident ray is a ray of light that strikes a surface The angle between this ray and the

perpendicular or normal to the surface is the angle of incidence Reflection is the change in direction of a

wave front at an interface between two different media so that the wave front returns into the medium from

which it originated Common examples include the reflection of light sound and water waves

The reflected ray corresponding to a given incident ray is the ray that represents the light reflected by

the surface The angle between the surface normal and the reflected ray is known as the angle of reflection

The Law of Reflection says that for a specular (non-scattering) surface the angle of reflection always equals

the angle of incidence The refracted ray or transmitted ray corresponding to a given incident ray represents

the light that is transmitted through the surface The angle between this ray and the normal is known as the

angle of refraction and it is given by Snells Law

The figure shows Incident ray Reflected ray Refracted ray the angle of incidence and angle of refraction

REFRACTIVE INDEX - Refractive index is the speed of light in a vacuum ( c =299792458kmsecond) divided by the speed

of light in a material ( v ) Refractive index measures how much a material refracts light Refractive index of

a material abbreviated as lsquo n lsquo is defined as lsquo n=cv lsquo Light travels slower in physical media than it does

when transmitted through the air Refractive index (n) is a function of molecular structure of matter optical

frequency optical intensity determines optical propagation properties of each wavelength ( λ ) may not be

distributed equally in all directions is affected by external temperature pressure and fields

Refractive index of a medium is a measure for how much the speed of light is reduced inside the

medium For example typical glass has a refractive index of 15 which means that light travels at 1 15 =

067 times the speed in air or vacuum Two common properties of glass and other transparent materials are

directly related to their refractive index

First light rays change direction when they cross the interface from air to the material and effect that

is used in lenses and glasses

Second light reflects partially from surfaces that have a refractive index different from that of their

surroundings

SNELLrsquoS LAW-

24 | P a g e

When light passes from one transparent material to another it bends according to Snells law which

is defined as n1sin(θ1) = n2sin(θ2)

where n1 is the refractive index of the medium the light is leaving θ1 is the incident angle between the light

beam and the normal (normal is 90deg to the interface between two materials)

n2 is the refractive index of the material the light is entering

θ2 is the refractive angle between the light ray and the normal

Snellrsquos law gives the relationship between angle of incidence and angle of refraction

For the case of θ1 = 0deg (ie a ray perpendicular to the interface) the solution is θ2 = 0deg regardless of

the values of n1 and n2 That means a ray entering a medium perpendicular to the surface is never bent The

above is also valid for light going from a dense (higher n) to a less dense (lower n) material the symmetry of

Snells law shows that the same ray paths are applicable in opposite direction

TOTAL INTERNAL REFLECTION- When a light ray crosses an interface into a medium with a higher refractive index it bends towards

the normal Conversely light traveling cross an interface from a higher refractive index medium to a lower

refractive index medium will bend away from the normal

This has an interesting implication at some angle known as the critical angle θc light traveling from

a higher refractive index medium to a lower refractive index medium will be refracted at 90deg in other words

refracted alon g the interface If the light hits the interface at any angle larger than this critical angle it will

not pass through to the second medium at all Instead all of it will be reflected back into the first medium a

process known as total internal reflection

The critical angle can be calculated from Snells law putting in an angle of 90deg for the angle of the refracted

ray θ2 This gives θ1

Since θ2 = 90deg

So sin(θ2) = 1

25 | P a g e

Then θc = θ1 = arcsin(n2n1)

For example with light trying to emerge from glass with n1=15 into air (n2 =1) the ritical angle θc is

arcsin(115) or 418deg For any angle of incidence larger than the critical angle Snells law will not be able to

be solved for the angle of refraction because it will show that the refracted angle has a sine larger than 1

which is not possible In that case all the light is totally reflected off the interface obeying the law of

reflection

OPTICAL FIBER MODE An optical fiber guides light waves in distinct patterns called modes Mode describes the distribution

of light energy across the fiber The precise patterns depend on the wavelength of light transmitted and on the

variation in refractive index that shapes the core In essence the variations in refractive index create

boundary

conditions that shape how light waves travel through the fiber like the walls of a tunnel affect how sounds

echo inside

We can take a look at large-core step-index fibers Light rays enter the fiber at a range of angles and

rays at different angles can all stably travel down the length of the fiber as long as they hit the core-cladding

interface at an angle larger than critical angle These rays are different modes Fibers that carry more than

one mode at a specific light wavelength are called multimode fibers Some fibers have very small diameter

core that they can carry only one mode which travels as a straight line at the center of the core These fibers

are single mode fibers This is illustrated in the following picture

OPTICAL FIBER INDEX PROFILE Index profile is the refractive index distribution across the core and the cladding of a fiber Some

optical fiber has a step index profile in which the core has one uniformly distributed index and the cladding

has a lower uniformly distributed index Other optical fiber has a graded index profile in which refractive

index varies gradually as a function of radial distance from the fiber center Graded-index profiles include

power-law index profiles and parabolic index profiles The following figure shows some common types of

index profiles for single mode and multimode fiber

26 | P a g e

OPTICAL FIBERrsquoS NUMERICAL APERTURE ( NA )- Multimode optical fiber will only propagate light that enters the fiber within a certain cone known as

the acceptance cone of the fiber The half-angle of this cone is called the acceptance angle (see figure 18)

θmax For step-index multimode fiber the acceptance angle is determined only by the indices of refraction

Where

n is the refractive index of the medium light is traveling before entering the fiber

nf is the refractive index of the fiber core

nc is the refractive index of the cladding

NUMBER OF MODES IN A FIBER - Modes are sometimes characterized by numbers Single mode fibers carry only the lowest-order

mode assigned the number 0 Multimode fibers also carry higher-order modes The number of modes that

can propagate in a fiber depends on the fiberrsquos numerical aperture (or acceptance angle) as well as on its

core diameter and the wavelength of the light For a step-index multimode fiber the number of such modes

Nm

Where

D is the core diameter

λ is the operating wavelength

NA is the numerical aperture (or acceptance angle)

MODE FIELD DIAMETER - All light do not travels through the core of the fiber but is distributed through both the core and the

cladding The mode field is the distribution of light through the core and cladding of a particular fiber

Mode-Field Diameter (MFD) defines the size of the power distribution When coupling light into or out of a

fiber MFD is important in understanding light loss

27 | P a g e

ADVANTAGE OF OFC COMMUNICATION - bull More information carrying capacity Fibers can handle much higher data rates than copper More

information can be sent in a second

bull Free from Electromagnetic and Electrostatic interference Being insulator no electric current flows through

the fibre and due to this reason fibres neither radiate nor pick up electro - magnetic radiation So WPC

CLEARANCE is not required

bull Low attenuation 025 dbkm at 1550 nm Loss in twisted pair and coaxial cable increases with frequency

where as loss in the optical fibre cable remains flat over a wide range of frequencies

bull Use of WDM ndash Switching routing at Optical signal level

bull Self healing rings under NMS control

bull Small size makes fibre cable lighter in weight So easy to handleOptic fibre cable weight (approx)

500 kg km Copper cable weight (approx) 1000 kgkm

The reasons are photons of light in a fibre

do not affect each other as they have no electrical charge and they are not affected by stray photons outside

the fibre But in case of copper electrons move through the cable and these are affected by each other

Optical fibre does not carry any electricity even if the cable is damaged or short circuited it does

not cause any spark or fire hazard

As the fibre do not radiate energy it can not be detected by any nearby antenna or any

other detector The fibres are difficult to tap and therefore excellent for security

As the signal transmission is by digital modulation there is no chance of cross talk in

between channels

Only by adding a few additional terminal and repeater equipments the

capacity of the system can be increased at any time once the cable is laid

ical effects and temperature variations

LIMITATIONS OF OFC -

difficult

- utilised

APPLICATION IN SIGNAL AND TELECOMMUNICATIONS transmission circuits

-haul circuits for linking of telephone exchanges

28 | P a g e

PROPAGATION MODES CONCEPT -

MODE - Mode is an available distribution of electromagnetic field in a plane transverse to the direction of

light propagation Each mode is characterized by frequency polarization electric field strength and

magnetic field strength Available patterns are derived from Maxwellrsquos equations and boundary conditions

LINEARLY POLARIZED (LP) MODE A mode for which the field components in the direction of propagation are small compared to

components perpendicular to that direction An optical fibre supports only different field patterns called as

lsquoLinear Polarizedrsquo or lsquo LPrsquo modes The reasons are

requirements

de

the accrual of power carried by different modes

There are two basic types of fiber Multimode fiber and Single-mode fiber

Multimode fiber is best designed for short transmission distances This is suited for used in LAN systems and

video surveillance Single mode fibre is best designed for longer transmission distances This is suitable for

long distance telephony and multi channel television broadcast systems

29 | P a g e

MULTI MODE FIBER Multimode fiber the first to be manufactured and commercialized simply refers to the fact that

numerous modes or light rays are carried simultaneously through the waveguide Modes result from the fact

that light will only propagate in the fiber core at discrete angles within the cone of acceptance MM fiber type

has a much larger core diameter compared to single-mode fiber allowing for the larger number of modes

and

is easier to couple than single-mode optical fiber Multimode fiber further categorized as Multimode step-

index and Multimode graded index fiber

PROPAGATION THROUGH MMSI FIBER Figure shows the principle of total internal reflection applies to multimode step index fiber Because

the corersquos index of refraction is higher than the claddingrsquos index of refraction the light that enters at less than

the critical angle is guided along the fiber

Three different light waves travel down the fiber One mode travels straight down the center of the

core A second mode travels at a steep angle and bounces back and forth by total internal reflection The third

mode exceeds the critical angle and refracts into the cladding Naturally it can be seen that the second mode

travels a longer distance than the first mode causing the two modes to arrive at separate times

PROBLEMS WITH MMSI FIBER AND SOLUTION This disparity between arrival times of the different light rays is known as dispersion and the result is

a muddied signal at the receiving end It is important to note that high dispersion is an unavoidable

characteristic of multimode step-index fiber The solutions are either use Graded index fiber or Single mode

fiber

PROPAGATION THROUGH MMGI FIBER Multimode Graded-index refers to the fact that the refractive index of the core gradually decreases

farther from the center of the core The increased refraction in the center of the core slows the speed of some

light rays allowing all the light rays to reach the receiving end at approximately the same time reducing

dispersion Figure shows the Light propagation principle through multimode graded-index fiber The corersquos

central refractive index ( nA ) is greater than that of the outer corersquos refractive index ( nB )

It is very clear from the figure the light rays no longer follow straight lines they follow a serpentine path

being gradually bent back toward the center by the continuously declining refractive index This reduces the

arrival time disparity because all modes arrive at about the same time The modes traveling in a straight line

30 | P a g e

are in a higher refractive index so they travel slower than the serpentine modes These travel farther but

move faster in the lower refractive index of the outer core region

PROPAGATION THROUGH SMSI FIBER Single mode fiber has a much smaller core that allows only one mode of light at a time to propagate

through the core The figure shows the single mode fiber

Single-mode fiber exhibits no dispersion caused by multiple modes Single-mode fiber also offers lower fiber

attenuation than multimode fiber Thus more information can be transmitted per unit of time because it can

retain the fidelity of each light pulse over longer distances Like multimode fiber early single-mode fiber was

generally characterized as step-index fiber meaning the refractive index of the fiber core is a step above that

of the cladding rather than graduated as it is in graded-index fiber Modern single-mode fibers have evolved

into more complex designs such as matched clad depressed clad and other exotic structures

SINGLE-MODE FIBER DISADVANTAGES The smaller core diameter makes coupling light into the core more difficult The tolerances for single-

mode connectors and splices are also much more demanding

CUTOFF WAVE LENGTH - Cutoff wavelength is the wavelength above which a single-mode fiber supports and propagates only

one mode of light In other words an optical fiber that is single-mode at a particular wavelength may have

two or more modes at wavelengths lower than the cutoff wavelength The effective cutoff wavelength of a

fiber is dependent on the length of fiber and its deployment The longer the fiber the lower is the effective

cutoff

wavelength The smaller the bend radius of a loop of the fiber the lower is the effective cutoff wavelength If

a fiber is bent in a loop the effective cutoff wavelength is lowered

SIGNAL ATTENUATION IN FIBER - Optical fiber has a number of advantages over copper However it also suffers from degradation

problems which can not be ignored The first of these is loss or attenuation Attenuation is typically the result

of two sub properties They are scattering and absorption Both of which have cumulative effects The second

is

dispersion which is the spreading of the transmitted signal and is analogous to noise

SCATTERING Scattering occurs because of impurities or irregularities in the physical construction of the fiber The

well known form of scattering is Rayleigh Scattering It is caused by metal ions in the silica matrix and

results in light rays being scattered in various directions

31 | P a g e

Scattering limits the use of wavelengths below 800nm The short wavelengths are much affected than longer

wavelengths It is because of Rayleigh scattering that the sky appears to be blue ( shorter wave length ) The

shorter wavelengths ( blue ) of light are scattered more than the longer wavelengths of light

ABSORPTION Absorption results from three factors They are hydroxyl ions ( OH- water ) in the silica impurities

in the silica and incomplete residue from the manufacturing process These impurities tend to absorb the

energy of the transmitted signal and convert it to heat resulting in an overall weakening of the signal The

Hydroxyl absorption occurs at 125 and 139 micro The silica itself starts to absorb energy at 17 micro

because of the natural resonance of the silicon dioxide

MACRO BENDING LOSS Macro-bending loss is caused by bending of the entire fiber axis The bending radius shall not be

sharper than 30d where d is diameter of cable A single bend sharper than 30d can cause loss of 05dB

The fiber may break if bending is ever sharper

MICRO BENDING LOSS Micro-bending loss is caused by micro deformations of fiber axis which leads to failures in achieving

total internal reflection conditions Micro-bends are small scale perturbations along the fiber axis the

amplitude of which are on the order of microns These distortions can cause light to leak out of a fiber

Micro-bending may be induced at very cold temperatures because the glass has a different coefficient of

thermal expansion from the coating and cabling materials At low temperatures the coating and cable

become more rigid and may contract more than the glass Consequently enough load may be exerted on the

glass to cause micro bends

Coating material is selected by manufacturers to minimize loss due to micro-bending The linear thermal

expansion coefficient of coating material shall be compatible with that of fiber

32 | P a g e

DISPERSION Dispersion is the optical term for the spreading of the transmits in the fiber It is the bandwidth

limiting phenomenon and comes in two forms Multimode dispersion and chromatic dispersion Chromatic

dispersion is further subdivided into material dispersion and waveguide dispersion

DISPERSION PHENOMENON IN OPTICAL FIBER Dispersion is the time distortion of an optical signal that results from the differences of time of travel

for different components of that signal typically resulting in pulse broadening As the distance traveled by

the signal is more broadening of pulse is more In digital transmission dispersion limits on the maximum

data rate and the maximum distance ie the information-carrying capacity of a fiber link The interference

from broadened pulse in the next interval shall not lead to erroneous interpretation of received signal

OPTICAL DOMAIN Understanding where attenuation and dispersion problems occur helps optical design engineers

determine the better wavelengths at which information can be transmit taking into account distance type of

fiber and the other factors which can severely affect the integrity of the transmitted signal The graph shown

depicts the optical transmission domain as well as the areas where problems arise The wavelength (nm)

is shown on X-axis and attenuation ( dBkm) is shown on Y-axis

There are four transmission windows appear in the figure The first one is at around 850 nm the

second at 1310nm third at 1550 nm and fourth at 1625 nm The last two labeled as C and L band

respectively The 850 nm wavelength at which the original LED technology operated The second window at

1310 nm has low dispersion The 1550 nm called as C-band is ideal wavelength for long haul

communication systems The network engineers can avoid transmitting signal at 1000 nm where Rayleigh

scattering 1240 and 1390 nm where hydroxyl absorption by water occurs to avoid high degree of loss

Optical fibers also can be manufactured to have low dispersion wavelength in the 1550nm region

which is also the point where silica-based fibers have inherently minimal attenuation These fibers are

referred to as dispersion-shifted fibers and are used in long-distance applications with high bit rates For

33 | P a g e

applications utilizing multiple wavelengths it is undesirable to have the zero dispersion point within the

operating

wavelength range

34 | P a g e

SIGNALLING RELAYS

INTRODUCTION A relay is an electromagnetic device which is used to convey information from one circuit to another

circuit through a set of contact ie front or back contact Constructional and electrically relays may be

divided into DC and AC relays because the means by which the electrical energy in the coil is converted in

to mechanical Energy in order to move the contacts are fundamentally different In DC type the contacts are

carried on an armature forming part of a magnetic circuit in which a field is set up by the current flowing in

the coils In AC types the contacts are attached by a link mechanism to a metal sector disc or cylinder in

which currents are induced by the alternating magnetic field produced by the currents in the coils

Every endeavor has been made to explain the action of each type of relay in the simplest possible manner

Relays are sophisticated switch gears used for remote control and succession control of various

electrical equipment In present days they are widely used because they are capable of protecting the

controlled equipment from cross feeding and overloading even as they cater for speedy operations

Most of the relays in present day signaling are electromagnetic devices although some of the relays control

circuits through electronic components like diodetransistors Integrated Chips etc

Railway signaling relays are unique in that

(a) They operate on low voltage and current

(b) They are more articulate as according to their special features they can work under restrictive conditions

and in any specified manner Virtually they can cater for all situations while contributing to speed and

accuracy in operations

CLASSIFICATION OF SIGNALLING RELAYS (a) According to the method of their mounting or fixture they are classified as

(i) Shelf type Relays which are loosely kept on shelves

(ii) Plug in type Relays which are plugged into a pre- wired plug boards

(b) According to their connection and usage they are classified as

(i) Track relays Relay which is directly connected to the track to detect the presence of vehicle

(ii) Line Relays Other than track relay all are line relays Relays connected to the selection circuit

(c) According to their vitality or importance in ensuring train working safety they are classified as

(i) Vital Relays All relays used for traffic control such as signal point controls track detection etc

(ii) Non-vital Relays Relays which operate control aids and accessories like warnings buzzers

Indications etc

(d) According to their special provisions to ensure reliability of their contacts they are classified as

(i) Proved type are those whose normalization after each operation shall be proved in circuit

controlled by their contacts Contacts in which both the springs have metal surfaces on their tips They may

get fused due to high sparking current across them during operation These may prevent relay normalization

and causes unsafe condition in traffic control To avoid this proving of relay normalization after each

operation is necessary

(ii) Non - proved type Need not to be proved to have been normalized after each operation as their

contacts have at least one non-fusible contact (carbon contact)

(e) According to their feed source relays are broadly classified as

(i) DC relays The relay which requires DC power supply for its operations are called DC relays Among

the DC relays

o DC neutral relays This relay closes the same set of contacts on energization with Normal polarity

or Reverse polarity supply

o Polar Relays This relay closes different set of contacts when energized with Reverse polarity

supply They may or may not have contact to close when deenergized

35 | P a g e

(ii) AC Relay AC Induction motor track relays Time element relays flashing indication control etc

(iii) Electronic Relays DC relays with electronic components in them are called electronic relays

DC NEUTRAL RELAY Each Relay has usually one or two coils with a hollow center to accommodate a coreThe coils are

made up of a large numbers of turns of small gauge soft drawn copper wire The two coils can be connected

in series or parallel according to the requirement of relay resistance The ends of the coils are terminated on

binding post to which the control wires are connected Each coil is placed around a core of specially selected

Iron or steel having high permeability and low retentivity The core should be susceptible to magnetism and

at the same time should have little residual magnetism The cores are connected at the top by a yoke to

complete the magnetism coupling between two ends of coils The bottom of each core is equipped with a

large steel or Iron block known as pole piece or face

A flat piece of Iron or steel called armature is supported by brackets which are securely fastened to

the pole piece The armature yoke and the pole pieces are also made of specially selected iron or steel of the

same quality as the core The armature carries the metallic spring contacts which are insulated from it

The circuit through the coils of the relay is closed It sets up a magnetic flux through the core yoke and the

armature The flux passing between the armature and pole faces causes the armatures get attracted to the pole

faces and armature picks up and closes front contacts When the circuit is opened the magnetic flux collapses

and the armature drops away by gravity from the pole faces the front contacts break and back contacts close

The front and back contacts of the relay can be utilised to make or break other circuits Two stop pins of

nonmagnetic material are fixed either on the armature or pole faces so that the armature cannot

come in contact with the pole faces It is essential to maintain a small air-gap between the armature and pole

faces so that low value of residual magnetism may not retain the armature in picked up position and causes

the relay to fail to drop away with a break in its control circuit

GENERAL USAGE

DC Neutral line relays are most commonly used for Railway Signalling controls and detection

Among them plug-in type relays are preferred in larger installations for space considerations Shelf type

relays are also in use mostly in wayside stations

There are many DC Neutral line relays in use with special features such as

(i) Delayed operation

(ii) Biased DC control

(iii) DC control unaffected by AC interference currents

(iv) Getting latched in operated condition till further feeding and others

Usage of DC polar relays is mostly in conjunction with block instruments that control traffic between

stations AC line relays are almost extinct in installations of British Signalling practice They are however

used for time control operations flashing indication control and such other special purposes in installations

with Siemens signalling practice widely Track relays are used according to the type of track detection

circuits chosen for a given location and context While most of the track circuits are still of the DC working

type requiring DC neutral track relays with them the prospects of their being replaced with Electronic track

circuits directly feeding DC line relays in future are great AC Track Circuits are used in DC Traction area

as conventional DC Track Circuits are not suitable there AC Track relays are used with them almost all of

the induction motor type In the British practice of signalling which was first introduced on Indian Railways

non-proved type relays with carbon to metal switching contacts are generally used for vital controls

They facilitate simple circuit designs But with the advent of German Practice introduced by Ms

Siemens later proved type relays with all metal to metal contacts are widely accepted in spite of

complications in circuit design caused by them A recent introduction is that of the same type relays made by

Ms Integra control However for some time now the appreciable features of both the practices are getting

36 | P a g e

incorporated together in the indigenous designs of signalling by railwaymen With this the usage of all types

of relays anywhere can be found without straight jacketed segration of relay types

CHARACTERSTIC OF ELECTRO-MAGNETIC RELAY The following are the characteristic of electro-magnetic relays A brief study of them helps in

understanding the choice of their components and designs features

1) Force of attraction

2) Effect of air gap

3) Effect of Hysterisis

4) Transient condition

FORCE OF ATTRACTION In any electro-magnetic system the force of attraction is given by

Where B - is the flux density a - is the cross sectional area of the particular part of the magnetic

circuit

In the case of a DC neutral Relay B is proportional to the current that is flowing in the coil

surrounding the electro-magnet and thus the force of the attraction is directly proportional to the square of the

current This square relationship has its own advantage especially in the case of DC track relay in that a

small reduction in the current will have a great effect on the working of the relay Also for a given change of

current the make and the break will be quicker with lesser possibility of arcing

EFFECT OF AIR GAP

Curve lsquoArsquo is magnetisation curve for the iron and is all practical purpose a straight line up to the

saturation point Curve lsquoBrsquo is the magnetisation curve for the open-air gap which is a straight line through

out because per magnetisation curve of the whole

magnetic circuit of the relay and for a given force is the sum of the amp-turns for the iron part and the amp-

turns for the air gap

When the front contacts are open the force required to pick up the armature is shown on curve lsquoCrsquo to be F1

but after the armature has operated it will be separated from the core by stop pins In this position the amp-

turns required to maintain the armature is less as indicated by the dotted line from 1 on curve C to 2 on curve

37 | P a g e

F But actually the current in the coil is unaltered the force on the armature is greater than required as

indicated at 3 on curve F Part of this extra force is used to flex the front contacts sufficiently to give good

contact pressure when it is in energised position

The difference between the pick-up and the drop-away current should be as small as practicable in

track relay to ensure good shunting characteristics This is achieved firstly by the choice of good quality relay

iron and secondly by having a small air gap between armature and core If the air gap is not available then

the residual magnetism fluxes might cause the armature to be retained when the supply is disconnected For

this reason residual pins are provided to ensure a definite minimum air gap in the energised position

EFFECT OF HYSTERISIS

Hysterisis is the property by which the flux produced lags behind the current In the de-energized

condition there will be small residual flux in the core When the voltage is applied to the coils the current in

rising to its steady value first causes the flux to rise from 1 to 2 along the curve At this point the flux density

will be sufficient to attract the armature and reduce the air gap the flux then raise to 3 and continue to 4

which corresponds to the steady current in the coils When the voltage is disconnected the current in falling

caused the flux to fall from 4 to 5 along the curve At this point the flux density will fall below the value

required to maintain the armature which will release thus increasing the air gap and reducing the flux to 6

Finally the

flux will decrease from 6 to 1 where the current will again be zero

The relay core is made of material having high permeability and low retentivity As mentioned in

the IRS specification Electromagnet iron may be in the form of a

(a) Bar of silicon steel

(b) Best Yorkshire wrought iron

(c) Swedish charcoal iron

(d) Electrical steel sheets

` This reduces the difference between pick up value and Drop away value By selecting good quality

core material Percentage release and sensitivity of the relay will be improved

TRANSIENT CONDITION

38 | P a g e

When the voltage is applied or disconnected from the coils it takes some little time before the current

become steady These are known as transient conditionsrdquo and are important so far as track relays are

concerned When the voltage is first applied to the coils the magnetic flux in rising cuts the turns on the

coils and in so doing produces a back EMF that opposes the applied voltage and retards the growth of

current

The growth and decay of flux are decided by the relationship between the inductance and resistance

in the circuit is known as time constant It is not fixed quantity in the case of DC neutral relay This value of lsquo

Lrsquo is less when the relay is in de-energised condition (L1) than when the relay is in energised condition (L2)

The magnitude of flux that is established for a given change of current is different in two cases

When the current reaches the pick up value the armature closes and the inductance is increased to L2

due to reduced air gap the flux per amp is increased The increase in flux increased the back EMF during the

movement of the armature after which the current continuous to raise along a new curve corresponding to the

increased inductance until it reaches the final value (ER) This process is indicated above in fig24

When the supply is disconnected the current is obliviously reduced to zero immediately but the flux

decay comparatively slowly owing to the eddy currents produced in the core by the rapid flux change which

tend to maintain the flux The drop away time on a disconnection is however generally negligible See fig

below

If the relay releases due to the reduction in current from say I 2 to I 1 caused by the application of

shunt resistance (as in the case of track relay ) the time taken is much longer than the relay is simply

disconnected The rate of rise or fall of current during the transient conditions is also depends on exterior

circuit values because L and R apply to the whole circuit The production of eddy current in the core the flux

will decay at a slower rate than the current So that the actual release time will be a little longer than it takes

the current to fall to the release

L= Inductance

39 | P a g e

R= Resistance

It is now clear that to reduce releasing time to a minimum it is necessary that

- The relay iron should have low Hysterisis loss and low retentivity

- The degree of over energization of the relay should be restricted

- Connecting a suitable external resistance in series with the relay to keep LR ratio low

In non RE area for track circuit length less than 100M 9 ohm track relay only to be used Using relay

with minimum contacts as they require lesser current which keeps inductance value low

Train working safety is ensured only if the track relay of shortest length track circuit is released

before a light engine running at a highest permitted speed clears it Otherwise the track circuit occupation

may go undetected To avoid this a special provision has to be made in signal control circuits wherever

necessary

The following methods may be adopted for reducing the time lag of track relay

(a) Restrict the over energisation of relay since the release time depends on the initial working current

(b) Connecting a suitable external resistance in series with the relay to keep the LR ratio low

(c) Using relays with minimum contacts as they require lesser operating current keeping the inductance

value low

40 | P a g e

CONCLUSION

Modern signalling is vital for safe and punctual movements of trains In the Indian railways The Signalling

and Telecommunication Department is responsible for providing modern effective and relaible signalling

systems as well as telecommunication systems

The first mode of communication used in Indian Railways was the use of electric telegraph

with the help of Morose code Morose code is the method of providing text information as a series of on-off

tones and lights or clicks that can be directly understood by a skilled listener or observer without special

equipmentEach character (letter or numeral ) is represented by a unique sequence of dots and dashes Later

this system becomes obselete and beggan the era of wireless communication which operated at audio level

frequency range

In wireless communication the significant advances took place the transition to miniature

valves or filament tubesBut this was abandoned too because of excessive current consumption and over

heating of the filament tubes

Fibre-optic communication is a method of transmitting information from one place to another by

sending pulses of light through an optcial fibreThe light forms an electromagnetic carrier wave that is

modulated to carry information First developed in the 1970s fibre optic communication systems has

revolutionized the telecommunications industry and have palyed a major role in the advent of the information

age Because of its advantages over electrical transmissionsoptical fibres have largely replaced copper wire

communications in core networks in the developed world The Indian Railways too is undergoing a transition

from Microwave communication to fibre optic communications

41 | P a g e

BIBLIOGRAPHY AND REFERENCES

1 wwwwikipediacom

2 wwwbritaniccacom

3 wwwirfcacom

4 Motorola GP60 system manual

5 Harris FAS 7000 manual

6 TOSHIBA Manual

iv | P a g e

ABSTRACT

In this report I have given an overview of the signal and telecommunication systems that have been used and

are presently being used in the Indian Railways as a part of the day-to-day signalling and communication

procedures

I have covered in this report the history and the latest developments in railway signal and communication as

well as related fields I have made an elaborate study on the various equipments that have been used and are

currently being used as part of communication in the railways

v | P a g e

TABLE OF CONTENTS

TITLE PAGE NUMBER

CERTIFICATE BY THE SUPERVISORS I

STATEMENT BY CANDIDATE II

ACKNOWLEDGEMENT III

ABSTRACT IV

SOLID STATE INTERLOCKING 1

INTEGRATED POWER SUPPLY 5

SINGLE SECTION DIGITAL AXLE COUNTER 9

DATA LOGGER 15

OPTIC FIBRE 22

SIGNALLING RELAYS 34

CONCLUSION 40

BIBLIOGRAPHY AND REFERENCES 41

1 | P a g e

SOLID STATE INTERLOCKING

INPUT CARDS All the field conditions (ie Field relay contacts) are connected to these input cards of EI system

The maximum inputs capacity of each RI card will depend on design of the RI cards by different

manufacturers The total number of inputs will depend on the yard layout

Total inputs means

Field inputs ECRs TPRs NWKR etc

Panel inputs GNs UNs NWNs RWNs etc

Read back inputs HR DR WNR WRR etc

Opto couplers are provided to isolate field optically from the system in Input cards These cards will read the

conditions of inputs and passes the information to EI system

PROCESSOR CARD This card is also called as central processing unit card of the System This is provided with microprocessor

RAM ROM EPROM EEPROM Memory ICrsquos These EEPROMS or EPROMrsquos (ROMrsquos) are programmed

with software required for executing the system commands

System software consists of the following

- Executive software programmed in system EPROMrsquos

- Application software programmed in DATA EPROMrsquos

-

EXECUTIVE SOFTWARE This software is common to all EIrsquos for the same company manufacturing

This is a factory installed software

Performs all operations

Cuts off vital supply voltage to output relays in case of unsafe failures

2 | P a g e

APPLICATION SOFTWARE This software is specific to each station and different for different stations

This is as per table of control of specific station

Can be installed at site by signal engineers

Logic installed through Boolean expressions or user-friendly equations

OUTPUT CARD (RELAY DRIVE CARD) This card receives the output of CPU card as input and picks up relevant output relay as per the panel

operatorsrsquo request The output of this card is terminated on phoenix terminals from there the output relays are

connected

The essential modules of an EI is as follows

Hardware module

Software module

HARDWARE MODULES USED IN THIS SYSTEM Equipment consists of

CARD FILE

Each card file is like a shelf having 20 Slots to accommodate various PCBs that are used in a system

Slot nos1 to 15 and 20 are used to accommodate Non-vital Input-output or Vital Input or Vital Output PCBs

Slot no16amp17 are used to accommodate Power supply PCB Slot no18amp19 are used to accommodate CPU

PCB In this cardfile a mother board is available in the rear side connecting all the 20 Slots This cardfile is

suitable to mount on a 19rdquo rack

Power

Supply

Card

CPU

Card

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19

20

CPU PCB Each card file to have one CPU PCB and always placed in slot no18amp19 In this card Micro

Controller used is Motorola 68332 and its speed is 21 MHz In this card 4 nos of flash EPROMs of 8 MB

are used to store executive and application software Two nos of fast Static RAM (each 64KB) are used to

process the vital data and Four nos of Static RAM (each 64KB) are used to store events and errors

The main functions of CPU is it monitors continuously status of Vital Boards It also monitors

system internal operation for faults and responds to detected faults It processes application logic based on

inputs

received and deliver outputs to drive external gears It records system faults and routine events in user-

accessible memory It monitors and controls the serial communication ports It controls power to vital outputs

through external VCOR relay

POWER SUPPLY PCB

3 | P a g e

Each card file to have one Power Supply PCB and always placed in slot no16amp17 Power supply

PCB is basically a DC-DC converter that converts 12V DC input supply is +12V -12V and +5V required for

various board functioning Based on diagnostic check by CPU Power Supply Card receives 250Hz signal

from CPU and extends supply to VCOR relay This card provides isolated supply to internal circuit

VITAL OUTPUT PCB Each Vital Output PCB has 16 Outputs It is available in 12V and 24V DC applications Each Vital

Output can drive an output device such as any Q-series relay This output relay in turn controls signals

points crank handle siding control level crossing etc Since Vital Output drives the relay which controls

important outdoor gears all the Vital Output boards are continuously diagnosed by a CPU Any abnormality

in any of the outputs will shut down the system to ensure safety

VITAL INPUT PCB Each Vital Input PCB has 16 Inputs It is available in 12V and 24V DC applications Each Vital Input

is assigned to read the status of outdoor gears such as Track circuits Point detectors Crank handles Siding

controls level crossing etc Since the Vital Inputs read the status of outdoor gears they are normally

configured with double cutting arrangement using relay contacts

NON-VITAL INPUTOUTPUT PCB Each Non-vital IO has 32 inputs and 32 outputs in one PCB It is available in 12V and 24V DC

applications Non-vital inputs are Panel push buttons and keys Non-vital outputs are Panel indication LEDs

counters and buzzers The status of Non-vital Inputoutput is known from LED indications available in front

of the card

VITAL CUT OFF RELAY- VCOR Each card file will have one VCOR to ensure the healthiness of the system VCOR has 6 FB

dependent contacts each rated for 3 Amps When system is healthy the coil receives voltage from Power

Supply PCB which in turn controlled by CPU Power to Vital output board is controlled by VCOR thus

ensuring safety

WIRING HARDWARE 48 Pin Address select PCB and Connector assembly is provided for Vital Input and Vital Output

cards 96 Pin Address select PCB and Connector assembly is provided for Non-Vital IO cards 48 Pin

Connector Assembly is provided for PS and CPU PCB EEPROM PCB which is provided on rear side of the

CPU connector to configure various serial communication ports Keying plugs are provided in the cardfile to

ensure coding to each type of cards

SOFTWARE MODULES USED IN THIS SYSTEM System software consists of the following

EXECUTIVE SOFTWARE This software is common to all EIrsquos for the same company manufacturing

This is a factory installed software

Performs all operations

Cuts off vital supply voltage to output relays in case of unsafe failures

APPLICATION SOFTWARE This software is specific to each station and different for different stations

This is as per table of control of specific station

Can be installed at site by signal engineers

Logic installed through Boolean expressions or user-friendly equations

4 | P a g e

A GEC-MANUFACTURED SSI INTERLOCKING CUBICLE

A PAIR OF DATA LINK MODULES

TRACKSIDE FUNCTIONAL MODULE

5 | P a g e

INTEGRATED POWER SUPPLY

INTRODUCTION A typical 4 line station requires power supplies of 24 V DC( 5 nos ) 12 VDC ( 5nos ) 6V (2 nos)

110 V DC and 110 V AC for signalling These require as many chargers and Secondary cells amp Invertors

requiring more maintenance amp spares Can they be Integrated in to one system

Thus the concept of Integrated Power Supply has been evolved by integrating concepts One Charger

One set of Battery Bank feeding Invertors and DC- DC converters for deriving various DC amp AC

voltages Integrated power supply system delivers both AC amp DC Power supplies as an output with the

output voltage tolerance of plusmn 2

ADVANTAGES Reduces maintenance on Batteries Battery charger amp overall maintenance

Its construction is in modules and hence occupies less space Reduced space requirement resulting in

saving of space for power supply rooms

Provides centralized power system for complete signaling installation with continuous display of

working status of system for easier monitoring

Defect in sub-units of system is shown both by visual amp audible indication Reflects the condition of

battery with warning

Replacement of defective modules is quick amp easy without disturbing the working of the system

It uses (n+1) modular technology hot standby arrangement and hence high reliability and more

availability of the system

The system provides uninterrupted supply to all signalling system even during the power failures

Thus No blank Signal for the approaching drivers

System can be easily configured to suit load requirement

The diesel generator set running (Non-RE area) is reduced almost to lsquoNILrsquo Hence low wear and tear

of DG set components amp reduced diesel oil consumption

COMPONENTS (a) Un-interrupted power supply (U P S)

(i) SMPS Battery chargers with Hot stand-by mode

(ii) Hot Standby PWM Inverters with auto changeover

(iii) CVT Regulator [FRVS]

(b) AC distribution board [ACDB]

(i) STEP DOWN TRANSFORMERS

(c) DC distribution board [DCDB]

(i) DC-DC converters

WORKING IPS works satisfactorily for AC input variation of 150V AC to 275V AC with single-phase power supply

and frequency variation from 48 Hz to 52 Hz The input is fed to SMPS charger which converts in to 110

VDC as output It is fed as input to three sub units

To battery bank charging the batteries

To ON line inverters that converts 110 VDC in to 230 VAC plusmn 2as output

6 | P a g e

As 110 VDC bus bar to DC Distribution Panel as an input to various DC-DC converters located in

it

A 110 V Battery Bank of VRLA cells are connected to SMPS Panel IPS Status Monitoring Panel is

located at ASM room or at SampT staff room if round the clock SampT staff is available at Station

CONSTRUCTION IPS mainly consists of

SMR (Switch Mode Rectifier) Panel SMPS based Float cum Boost Charger (FRBC) Panel

AC Distribution Panel

DC Distribution Panel

Battery Bank (110V DC)

Status Monitoring Panel

SMR (SWITCH MODE RECTIFIER) PANEL SMPS BASED FLOAT

CUM BOOST CHARGER (FRBC) PANEL It consists of SMR FRBC modules and Supervisory amp Control Unit SMPS based SMRs

(converters) SMPS based Float cum Boost Chargers (FRBC) modules are provided with (n+1) modular

technology hot standby arrangement with active load sharing basis and 1 additional module as a cold standby

(n+2) Supervisory amp Control Unit which controls and monitor the complete system It has various

indications on the panel reflecting the working of the panel

FRBCs are suitable for operating in parallel on active load sharing basis with one or more modules of similar

type make and rating

n = required no of modules to cater for actual current requirement

AC DISTRIBUTION PANEL It is made of ON-Line inverters with (1+1) modular technology hot standby arrangement amp CVT

(Constant Voltage Transformer) AVR (Automatic Voltage Regulator) and set of step down

transformersThe inverter is protected against overload and short circuit with auto reset facility Whenever

the failure occurs it trips and restart automatically after about 10 to 20 sec But if the problem persists the

protection is permanently gets latched and it will not be switched ON again unless the fault is cleared

followed by pressing of reset button The output of inverters is regulated to 230V AC plusmn 2 50Hz plusmn1Hz for

an input voltage variation of 90V DC to 140V DC Normally both the Inverters are powered ON and both are

delivering the Output voltage but only one (main) inverter is connected to the Load If main inverter is failed

then only the stand-by inverter will come on Load automatically with in 500msec At 70 Depth of

Discharge (DOD) of the battery bank 110VDC supply to the inverters will be cut-off So the Signals feed will

be cut-off The auto-change over arrangement is also provided for bringing the CVT in circuit with in

500msec when the both the inverters output is failed It has various indications on the panel reflecting the

working of the panel

DC DISTRIBUTION PANEL It takes care of DC Power supply requirements of our signalling It consists of sets of DC-DC

converters for individual DC power requirements with (n+1) modular technology hot standby arrangement

with active load sharing basis The DC-DC converters of Relay Internal are provided with (n+1) modular

technology hot standby arrangement with active load sharing basis and 1 additional module as a cold standby

(n+2) The DC-DC converter works satisfactorily with the input voltage variation of 98VDC to 138VDC At

90 Depth of Discharge (DOD) of the battery bank all the DC-DC converters 110VDC Input supply will be

cut-off except for Block Tele DC-DC converters The supply for Point operation is also catered through a

20A fuse by this unit It is also provided with various indications that reflect its working

7 | P a g e

STATUS MONITORING PANEL IPS status monitoring panel has been provided in the ASM room for giving the important alarms and

indications to ASM Status Panel tells present working status of IPS displaying battery voltage continuously

and five other indications which will light according to IPS status During normal working these indications

will not lit Whenever the battery has come on to the load and has discharged by 50 DOD (Depth of

Discharge) then first Red indication lit with description ldquoSTART GENERATORrdquo with audio Alarm ie DG

set is to be started and put on the load If DG set is not started with this warning then if battery gets further

discharged to 60 DOD and second Red indications appears with description ldquoEmergency Start generatorrdquo

with audio alarm even now if DG set is failed to be started the battery further gets discharged to 70

DOD and 3rd Red indications appear with description ldquo System shut downrdquo with audio alarm which will

continue till Generator is started resulting in AC output from IPS is automatically cut off results all the

signals will become blank

When there is any defect in any sub module of IPS even without affecting working of system the 4th

Red indication appears with description ldquoCall SampT Staffrdquo with audio alarm so the ASM advises SampT staff

accordingly Green LED 5th indication comes with the description ldquoStop Generatorrdquo with audio alarm when

the DG set is running and if the Battery bank is fully charged condition

EARTHING The IPS systems and its individual modules are having earth terminals and all these are properly

earthed with earth resistance of less than 1 ohm Earth provided shall preferably be maintenance free using

ground resistance improvement compound (The acceptable Earth Resistance at earth busbar shall not be

more than 1 ohm Code of practice for earthing and bonding system for signalling equipments)

LIGHTNING AND TRANSIENT PROTECTION IN IPS Manufacturer will provide Stage1 amp Stage 2 protection along with the IPS These are described

below

Stage 1 protection is of Class B type against Lightning Electro-Magnetic Impulse (LEMP) amp other

high surges provided at Power Distribution Panel It is provided with a 63 Amp fuse in phase line and is

connected between Line and the Neutral and also between the Neutral and Earth

Stage 2 protection (Power line protection at Equipment level) is of Class C type against low voltage

surges provided at the equipment input level This is thermal disconnecting type and equipped with

protection against SPD (surge protection device) failure due to open amp short circuit of SPDs and is connected

between the Line and the Neutral If supply data signalling lines (ACDC) are carried through overhead

wires or cables above ground to any nearby building or any location outside the equipment room additional

protection of Stage 2 type shall be provided at such locations Class B amp Class C arrestor is provided on a

separate wall mounting type enclosure in IPS room

Stage3 protection (Protection for signallingdata line) is of Class D type All external data signalling

lines (ACDC) shall be protected by using this Class D type device It consists of a combination of Varistors

and Gas Discharge Tube with voltage and current limiting facilities

FEATURES Chargers used in this system are of SMPS technology chargers with 90 efficiency These chargers

are supported with hot standby mode with (n+1) modular technology

Onetwo sets of Maintenance free Battery banks (110VDC) Normally one set (110VDC) of Battery

bank is used Conventional flooded type Lead Acid Batteries or Low Maintenance Lead Acid

batteries can also be used (SMRs settings are required to be adjusted depending on the type of

Batteries used) Various voltage levels of

8 | P a g e

battery banks are avoided Reduction in Battery maintenance amp less flour area required

DC-DC Converters working from 110V Central battery have been used for all dc supplies This has

improved overall efficiency of the system since number of conversion from AC to DC have been

reduced to 2 stage as compared to 3 stage conversion in case of transformer-rectifier system

DC-DC converters are available in modules Easy replacement of defective modules This ensures

less down time

DC-DC Converters are used in load sharing N+1 configuration (ie with hot standby with N+1

modular technology) to improve the reliability amp availability of the system

Capacity of inverter has been brought down to 15 KVA from 5 KVA and used for feeding only

Signals supply Hot standby inverter is provided with auto changeover facility This improves the

availability of the overall system

High efficiency inverter is used with PWM (Pulse Width Modulation) technology in place of Ferro-

resonant technology based inverter This improves the efficiency of the overall system

Continuous power to Signal Circuits even in absence of DG setLocal Power Supply

Generators need not be switched ON every time during train movement

Metal-to-metal relay installations and block working by axle counters have also been covered

Supply of spare modulesComponentsCells have been included as part of main supply

Provides highly regulated voltage to all signal relays amp lamps for better life

9 | P a g e

SINGLE SECTION DIGITAL AXLE COUNTER

INTRODUCTION- The axle counter equipment is working on high frequency and using amplitude modulation or phase

modulation for detection of presence of wheel The equipment described in this notes is Phase modulation type

for the detection of presence of wheel In the Phase modulation type track device the detection of presence of

wheel is with the phase reversal of 1800 out of phase which enables this system to be more healthy and safe

In Phase Reversal Modulation technique trolley suppression arrangements to prevent the counting of

wheels caused by push trolley passing over the track device are not required as the system will take care of

validation of generated pulses caused by passage of wheel over the track device depending up on the phase

shift of the pulse This phase shift of the pulse may be normally 160deg to 180deg for a train wheel and it may be

approximately 100deg to 120deg for a push trolley wheel

This is Digital Axle Counter equipment for single track sections containing 2 out of 2 micro-

controllers to count the axles establish the track occupancy of a track section and to provide this information

to the block or the interlocking equipment

In this system no separate evaluator is required and no analog data is being transmitted One set of

Axle counter equipment is provided at entry end and other set provided at exit end Both sets are being

connected through a twisted pair of telecom cable ie existing RE cable one PET quad is used for both UP

and DN Axle Counters Digital DATA is being transmitted between two ends of Axle counters (Outdoor

track side Detection points)This system is a fully duplex capable of operating according to CCITT V21 and

the Data will be transmitted at the rate of 300bitsec This data Transmitted ensure negligible interference of

the noise The system is highly reliable

FEATURES (a) The system consists of

(i) Single Section Digital Axle Counter (SSDAC) units

(ii) Tx Rx coils

(iii) Vital Relays

(b) TxRx coil axle detectors are mounted to the web of the rails The design of system consists of 21 KHz amp

23 KHz High frequency Phase Reversal type axle detectors

(c) Compatible with 90R 52Kg amp 60Kg rail profiles Easy to install commission amp maintain

(d) Track devices at both (entry amp exit) points of the section should be fixed on the same rail

(e) System is designed to detect the solid wheels with diameter gt 400mm with standard wheel flange

(f) The system works in pairs For monitoring single-track section one pair of SSDAC units are required and

to be installed near the trackside one at the beginning and another at the end of the track section ie

Trackside electronic counting equipment

(g) The basic design of the system is based on counting the number of axles passing at each detection point

These stored counts are transmitted to the second unit of the system and vice versa by means of modem

communication

(h) The communication consists of digital packets having details of Counts amp Health

10 | P a g e

(i) If counts registered at both detection points are equal the section is cleared otherwise the section is shown

as occupied The system ensures no error condition to arrive at the decision of clearance

(j) System is designed as per CENELEC SIL-4 (European standard) using micro controller along with other

electronic circuits and programmed using dedicated software When any of these circuits fail the system

goes to fail safe condition

(k) It is programmable for either Preparatory Reset or Conditional Hard Reset as per requirement

(l) Micro controller based design with 2 out of 2 decisions and counting through software

(m) V21 Modem communication (2-wire) on frac12 quad cables and also compatible to work on voice channel of

OFC amp Radio

(n) Opto isolated vital relay drive for Q-style 24V 1000 _ and Vital Relay output can be giving at both ends

of the system

APPLICATIONS The system can be widely used in Railways for Block Working (BPAC) Intermediate Block Signaling Auto

signalling and Track circuiting for i) Loop line ii) Main line iii) yard lines

SYSTEM DESCRIPTION

This system comprises of

Tx coils-2 nos

Rx coils-2 nos

Reset Box (RB 258A)

Card 1 Signal Conditioning Card ndash 1

Card 2 Signal Conditioning Card - 2

Card 3 Micro controller Logic Board ndash 1

Card 4 Micro controller Logic Board ndash 2

2 nos for independent resetting ndash when used in block sections

1 no for common resetting ndash when used for Track circuiting at stations

Card 5 Event Logger Card

Card 6 Modem Card

Card 7 Relay Driver Card

Card 8 DC-DC Converter Card

SSDAC (DACF 700AP) UNIT

(A) SIGNAL CONDITIONING CARD (CARD 1amp2) (SCC) -1 (SCC-1) generates 21 KHz carrier

signals

-2 (SCC-2) generates 23 KHz carrier signals which is transmitted to 2nd

set of Tx coils

s receive these signals

modulated

train pulses

11 | P a g e

(B) MICRO-CONTROLLER LOGIC BOARD CARD (CARD 3amp4) (MLB) The Micro-controller Logic Board (MLB) is the heart of the system

o 8051 Based Architecture

o 8 Bit Micro Controller

o ATMEL AT89S8252 Micro controller

o 2 out of 2 Decision

o Uses C subset language

- TOOLS

o KEIL μ Vision Development System

o Universal Programmer

o 2KB Program Memory

o 256 bytes RAM

o 8KB Flash memory

o 32 Programmable IO lines

o Wide Operating Voltage range of 4V-6V

o Full Duplex Serial Port

o Programmable Watch Dog Timer

o Fully Static operation up to 24MHz (Upgraded to 40MHz)

o Operating Temperature of ndash40degC - +85degC

o Use of State Machine for Axle Counting

o Use of ASCII MODBUS protocol

o Use of CRC16 technique for Error Checking during communication

o Wheel detection

o Train direction checking and

o Wheel counting functions

o It receives the remote wheel count and computes the status of the section for clear or occupied

o It also checks various supervisory signal levels like supervisory of TxRx coils presence of various

cards communication link failure etcThese cards communicate with each other for wheel count

At Entry-end if train enters into section (1st detection) the counts are incremented and when train

shunts back from the same detection ie if train exits from the section from the same detection the counts are

decremented At Exit-end if train enters into section (2nd detection) the counts are decremented and when

train shunts back from the same detection ie if train exits from the section from the same detection the

counts are incremented Both the track devices at Entry and Exit ends must be fixed on same side of the

track

This MLB card is having Extensive LED display

o A block of 8 LED indicators for count progress error display

o 2 independent LED indicators for section status

o The errors occurring in the system during the operation of the SSDAC are encoded and are indicated by

means of the 8-LED block present on the front panel of the MLB cards

(c) EVENT LOGGER CARD (CARD 5)

Event logger card is designed to capture and store important signals from the remote and local SSDAC units

The stored data can be downloaded from the event logger card for the purpose of analyzing the events

occurring during the operations of the SSDAC The data can be analyzed with the help of CEL data analyzer

software

12 | P a g e

The event logger card captures following signals

(i) Pulse signals

(ii) Supervisory signals

(iii) Card removal information

(iv) Serial packets from

Event Logger card has a Rabbit processor and 2 MB FLASH MEMORY to store packets The data is initially

stored in the buffer and subsequently transferred to FLASH memory every two minutes Normally 4096

pages of the data can be stored in flash memory on FIFO (first in first out) basis

Run This LED blinks continuously indicating the normal working of the event

Log This LED blinks whenever data is being logged into the flash memory (Approx after every 2 minutes)

Dnld This LED is ON when data is being downloaded from the flash memory of the card and becomes OFF

when download is complete

(D) MODEM CARD (CARD 6) (i) The modem card transmits and receives the digital packet information form one counting unit to the other

The packet will appear after every 18 sec and the packet carries the latest information such as

(ii) The modem card being used is V21 type (2-wire) in SSDAC

(iii) This card interfaces with serial RS232C port of both Micro-controller Logic Boards

(iv) It multiplexes the two RS232C inputs and selects one of the two channels and provides signal conversion

from digital to analog (FSK modulation) and vice-versa

(v) Data transmission rate is 300 bitssec

(vi) Automatic Gain Control circuit is incorporated hence no gain adjustments required

(vii) Mode selection on Modem card The modem has been set in lsquoORIGINATORrsquo mode for entry and in the

lsquoANSWERrsquo mode for exit in the factory

(viii) LED Indications provided on Modem card

-Transmitting the signal when LED is flashing

- Receiving the signal when LED is flashing

-Remains OFF in SSDAC

-Carrier is detected when LED is glowing

(E) RELAY DRIVER CARD (CARD 7) (i) The Relay Driver card (RD) provides the 24V DC output required for driving Vital Relay

(ii) One RD card is used in each SSDAC counting unit The RD card receives the command of clear and

clock signals from MLB1 amp MLB2 cards and drives the vital relay lsquoONrsquo when section is NOT OCCUPIED

through opto- isolator circuit

(iii) If a train occupies the section the vital relay is dropped The vital relay status is read back by the system

as per the driving output

(iv) It has

13 | P a g e

ndash LED flashes when the section is clear

ndash LED flashes when the section is clear

All the above LEDrsquos are lit for section clear condition

(F) DC-DC CONVERTER CARD (CARD 8)

INPUT VOLTAGE Nominal Voltage voltage 24V DC Maximum current drain= 12A

Required voltage 18V DC to 30V DC

Output voltage

Nominal Voltage +5 V DC 2 A Required voltage 4 7 5 t o 525V DC

Nominal Voltage +12V DC 200 mA Required voltage 1175 to 1225V DC

Nominal Voltage +24V DC 300 mA with common ground Required voltage 235 to 245V DC

Nominal Voltage +15V DC 100 mA with isolated ground Required voltage 145 to 155V DC

SURGE VOLTAGE AND LIGHTNING PROTECTION Transient surge voltages arise as a result of Lightning discharge switching operations in electrical

systems and electrostatic discharge These surge voltages often destroy the electronic equipment to a large

extent In order to prevent surge voltages from destroying the equipment all the input lines of SSDAC ie

Power Supply (24V) Reset (48V) amp Modem is to be routed through surge voltage protection devices for

effectively protecting the system These devices (3 numbers) are mounted in a box and supplied along with

the system One number of box is to be installed at each location and wired to the SSDAC

Each surge voltage protection device consists of two parts

(a) Base

(b) Plug Trab

The Base of the device is used for wiring the input and output signals The connection details from relay

room to the box and from box to SSDAC unit are provided on the box The Plug Trab consists of MOV and

GD Tube and diverts the excess energy during surge voltages or lightning into the ground connection The

operation of these devices relies on a high quality ground connection in order to safely shunt away the

unwanted energy The impedance of the ground connection is critical and it should be less than 2 Ohms

NOTE The 3 Plug Trab connections are not to be interchanged with one another The plug Trab is a

detachable device and can be replaced with SPARE unit in case of blown device which is indicated by

means of LED for 24 V

EFFECTIVENESS OF PLUG TRABS The effectiveness of plug Trab depends wholly on the Earth connection provided to the system The earth

provided to the system should be less than 1 ohms and connections should be firm and proper to the SSDAC

unit VR box etc

SURGE VOLTAGE AND PROTECTION DEVICE SV-120 The Surge Voltage protection device is to be installed at each location along with every SSDAC unit

14 | P a g e

EARTHING- The lead wires connecting the installation and the earth electrode shall ordinarily be of stranded

copper wire of 29 sq mm (19 strand wires of 14 mm diameter) Copper wire has been specified because GI

wires usually are having greater corrosion However in areas where copper wire may be frequently stolen

due to theft ACSR of size 64 sq mm (19 strands of 211 mm diameter) may be used

LIMITS OF EARTH RESISTANCE (a) Apparatus case connected to Earth (SSDAC and vital Relay Box is housed in Apparatus case and

Connected to earth at outdoor) shall be less than or equal to 1 ohm

(b) All cable connected to same earth shall be less than or equal to 1 ohm

(C) Reset box connected to earth near SM s Room shall be less than or equal to 1ohm

EQUIPMENT TO BE EARTHED A Common Earth should be provided for SSDAC for items 1(a) amp (b) of the above at the outdoor

(a) The Apparatus Case is to be connected to earth (the chassis of SSDAC amp Vital Relay Box should be

properly connected to apparatus case)

(b) Metallic sheath and armouring of all the underground main cables are to be earthed

(i) In RE area the metallic sheath and armouring of main telecom cables are earthed at both ends

(ii) In RE area the armouring of Jelly filled cable shall be earthed at both ends

(c) The Earthing shall be provided at every location box where cables are terminated

(d) Earth already available for other equipment may be used for earthing of Reset Box near SM s Room

Cabin etc

15 | P a g e

DATALOGGER

INTRODUCTION Datalogger is a Microprocessor based system which helps in analysing the failures of relay inter

locking system Electronic Interlocking system This is like a black box which stores all the information

regarding the changes take place in relays AC DC Voltages and DC currents along with date and time The

same information data can be transferred to the computer to analyse further ldquoon line ldquooff linerdquo analysis of

stored date A print out also can be obtained through a printer by connecting directly to the datalogger unit

The data belongs to Relay contacts is considered as digital inputs and the data belongs to voltage

levels currents is considered as Analog inputs Datalogger lsquos are mandatory for all new relay interlocking

(PIRRI) EI installations and it is also recommended to provide in all existing PIs RRIs To increase the

line capacity mechanical signalling equipments are upgraded to PI RRI or EI Due to complexity in the

circuits and wiring sometimes it is very difficult to rectify the failures So datalogger can monitor these

systems with real time clock Thus it can be named as black box of Samp T equipments and hence it is a vital

tool for accident investigation Datalogger is used at Stations yards Whereas in case of Auto Section amp IBH

Mini dataloggers called as Remote Terminal Unit (RTU) are used

ADVANTAGES OF DATALOGGERS (a) Dataloggers helps in monitoring the typical failures such as intermittent auto right failures

(b) It helps in analyzing the cause of the accidents

(c) It helps in detecting the human failures errors such as

(i) Drivers passing signal at Danger

(ii) Operational mistakes done by panel operators ASMrsquos of operating department

(iii) Signal and telecom engineering interferences in safety circuits

(iv) Engineering and electrical department interferences failures

(v) It helps as a ldquoTOOLrdquo in preventive maintenance of signaling gears

(d) Dataloggers can be connected in network Networked dataloggers helps to monitorthe PIRRIEI remotely

(e) Failure reports can be generated remotely with help of datalogger network

(f) On line and Off line track simulation is possible

(g) Speed of the train on point zones can be calculated

(h) Age of the equipment in terms of number of operations etc

COMMON EQUIPMENT FOR ALL DATALOGGERS ARE GIVEN

BELOW (a) CPU card

(b) Digital and Analog input cards

(c) Local terminal(PC)

(d) communication links

(e) Printer

All the dataloggers requires a potential free ( spare ) relay contact for monitoring digital inputs

through Digital input cards amp for monitoring Analog inputs such ACDC bus bar voltage levels through

Analog input cards Digital and Analog inputs are connected to the Processor card Processor card consists of

memory ICrsquos Memory ICrsquos are programmed as per requirement of the signal engineers

Provision of Dataloggers is mandatory with RRI systems and is optional for PI systems as per

amendment to the specification for Relay Interlocking systems ( IRSS-36 ) The data collected by the

datalogger can be used for failure analysis repetitive discrepancies and for accident investigations

16 | P a g e

Note

If the serial communications is more than 50m then line drivers shall be used up to 3 Kms

4wire leased line Modems shall be used if the serial communication is more than 3 Kms

STUDY OF EFFTRONICS DATALOGGER TECHNICAL DETAILS (a) 24V 12VDC Power Supply

(b) Total Storage Capacity of 10 Lakh events

(c) In-built Temperature sensors

(d) Internal Buzzer for alarming during failures

(e) Real Time clock with internal battery backup with data retention up to 10 years

(f) 512 LED matrix to indicate the status of 512 Digital inputs at a time page wise

(g) Seven segment LCD screen (2x24) to display the status of digitalanalog signalsTime Temperature etc

(h) Using the keyboard various functions can be viewed in the LCD panel

(i) Max Digital Inputs 4096

(j) Max Analog Inputs 96

(k) Digital Input Scanning Time 16 millisecond

(l) Analog Input Scanning Time is less than 1 Sec

HARDWARE (EQUIPMENT) Datalogger system consists of

(a) Datalogger (CPU - with Microprocessor 68000)

(b) Digital input cards

(c) Dual modem card

(d) Digital Scanner units (DSU)

(e) Analog Scanner units (ASU)

CPU CARD It is provided with Motorola microprocessor M 68000 It performs all the activities pertaining to the

datalogger It continuously scans (check) the Digital inputs(inbuilt) Digital Scanner Units and Analog

Scanner Units ie scanning of digital signals (Relay operations) for every 16-milli seconds and scanning of

analog signals (ie ACDC voltages amp DC currents) for less than 1 second

This card will support the IO interfaces of LCD (Liquid Crystal Display) - 2X24 alphanumeric Key

Board LED Matrix Display Real Time Clock LCD display and keyboard This will acts as man machine

interface between the datalogger and the signal engineer All the operations (Software) can be performed

using this LCD and keyboard

Real time display with 7 Segments This is built in real time clock within Datalogger and its current

time will be displayed on six 7-segment display provided (Real time clock depend upon DALLAS 1286

chip) This IC will come with internal battery backup hence there is no need to add external batteries

CPU card continuously scans (checks) the DSUs and ASUs Each input connected to digital scanner

units are optically isolated by Opto couplers When CPU card scans the digital inputs it compares with the

previous stored data and if there is any change from the previous status then only that data will be stored (the

status conditions of relay) with date and real time A total of minimum 10 Lac events can be stored in

memory on first in first out basis so that latest data is available in the system There is no loss of data from

datalogger memory in case of power supply failure of datalogger

DIGITAL INPUT CARDS (IN-BUILT) This system is having maximum 8nos of inbuilt Digital inputs cards Maximum 64nos of digital

inputs can be connected to each digital input card The potential free relay contact may be front or back

contact terminated at the Tag Block from the relay of signals tracks points Buttons etc and are

17 | P a g e

subsequently connected to Digital input cards through Flat Ribbon Cable (FRC) connectors These in-built

digital input cards can monitor a total 512 nos of relays status

DIGITAL SCANNER UNIT (DSU) Each DSU contains 8 nos of Digital Input cards Each input card can be connected with 64 inputs

Total input capacity of DSU unit is 512 inputs These scanner cards contain Optocouplers and Multiplexer

Inputs are connected to Stag card The stag card out put is connected to DSU through FRC connectors

Maximum 7 nos of DSUs can be connected to the system So Digital input capacity of the system is 4096

All these digital inputs are scanned at rate of 16 msec

ANALOG SCANNER UNIT (ASU) ASU contains maximum 3 nos of Analog input cards Each input card can be connected with 8nos of

Analog inputs Total input capacity of the ASU is 24 analog input channels Maximum 4nos of ASUs can be

connected to the system Analog input channel capacity of the system is 96 All these analog inputs are

scanned at a rate of less than 1 sec

PARALLEL PORT Parallel port is provided for connecting printer

RS-232 SERIAL PORTS At least 6 Serial communication ports are provided for communication with other dataloggers

Central Monitoring Unit Remote Terminal Unit Electronic Interlocking system Integrated Power Supply

system etc

EXTERNAL NON-VITAL RELAY CONTACTS These relays provided in the system where 16 number of the Relay contacts are provided on the rear

panel through Tele control port to extend alarms and to control the power equipment from remote or local

locations through computer in case of any occurrence of failures Each control can sink or source 100 m

amps of current

INTERNAL MODEM CARD DUAL MODEM CARD (IN-BUILT) It is fixed in datalogger Euro rack itself One card contains two modems The top modem is called

ANS (answer) modem and the bottom modem is called as ORG (originate) modem It is used in case of

networking of Dataloggers In network connect lsquoANSrsquo modem to the lsquoORGrsquo modem of one adjacent station

and connect lsquoORGrsquo modem to the lsquoANSrsquo modem of other adjacent station

POWER SUPPLY Normally 24V DC (12V DC is optional) supply with battery backup is required for the system

working

Input Voltage Range 18Vhellip32V DC (For 24V) 9Vhellip18V DC (For 12V)

INPUT REQUIREMENTS Relay inputs (digital inputs) and analog inputs (voltages currents etc) are required to be connected

to the system as per the requirements of RRI PI SSI as the case may be Some of the inputs to be

monitored is given below

(a) Digital inputs

(i) Field inputs All TPRs NWKRs RWKRs ECRs Crank Handle relays SidingSlot LC gate

control relays etc

(ii) Control Panel inputs All button Knob SMrsquos Key relays

18 | P a g e

(iii) Internal relays

British system All HR DR HHR WNR WRR ASR UCR RR LR UYRTLSR TRSR TSR

JSLR JR etc

SIEMENS system Z1UR Z1UR1 GZR ZDUCR ZU(R)R ZU(N)PRG(R)RG(N)R U(R)S

U(N)PS UDKR DUCR U(R)LR UYR1 UYR2 G(R)LRGR1GR2

GR3 GR4 OVZ2U(R)RW(RN)R (RN)WLR Z1NWR Z1RWRZ1WR1 WKR1 WKR2 WKR3 etc

(b) Analog channels

(i) 230 V AC (for power supplies in the power panel)

(ii) 110V AC (for Signal and Track transformers)

(iii) 110V DC (for Point operation)

(iv) 60V DC (Siemens relays)

(v) 24V DC (Q-series relays)

(vi) 24V DC (for Block Axle counters)

(vii) 12V DC (for indication)

(viii) 20A (for point operation current)

(ix) 10V AC 5KHz (for Axle counter channels) etc

SOFTWARE MODULES OF DATALOGGERS

(a) Network Management of Dataloggers (NMDL)

(b) Reports

(c) Fault Entry

(d) Track Offline Simulation

(e) Train Charting

NMDL SOFTWARE FEATURES (a) Online Relay Status

(b) Online Faults - To view information of various Online Faults as they occur in the stations where

the Dataloggers are connected

(c) Online Simulation - Graphical view of relay operations train movements etc

(d) Remote monitoring of stations with the help of NETWORKING

SOFTWARE OBJECTIVES (a) Predictive Maintenance

(b) Easy identification of failures

(c) Crew discipline

(d) Train charting

REMOTE MONITORING OF STATIONS WITH NETWORKING OF

DATALOGGERS The individual Dataloggers of various stations can be interconnected through networking technology

The data of Remote Panel stations can be viewed in a Computer at the Central Monitoring Station The data

of the network is collected by the FEP (Front End Processor) which in turn is transmitted to the computer

COMPONENTS OF NETWORK MANAGEMENT OF DATALOGGERS

(a) Datalogger at stations

(b) MODEM and Transmission medium

19 | P a g e

(c) Front End Processor (FEP)

(d) Central Monitoring Unit (CMU) Computer

FEP (FRONT END PROCESSOR)

FEP acts as a buffer between the Central Monitoring Unit (Computer) and the Network It is provided

at centralised place to retrieve data continuously from station dataloggers and store in memory and transfer to

computer on request It stores 10 Lac telegrams It works on 12V DC It draws 16A continuous current

when all the three modems are connected Normally it shows the number of packets pending to be sent to the

computer on its 7-segment LED display It is provided with MOTOROLA 68000 microprocessor It has 6-

nos of RS-232 communication ports such as COM1 COM2 COM3 COM4 COM5 and COM6 COM1 is

used for Fault Analysis System (FAS) ie Central Monitoring Unit (Computer) connection COM2 to COM6

are used for networking For Bi-directional 2- nos of ports and for Tri-directional (T-network) 3-nos of ports

are used

DATA TRANSMISSION Dataloggers can be networked in Uni-directional Mode or Bi-directional Mode or T ndash Network Mode

In case of loss of data retransmission of data takes place

(a) Uni-Directional Mode

Each Datalogger will send data in only one direction to the FEP Unidirectional mode network is not

preferred

(b) Bi-Directional Mode

Each end of Network is connected to FEP and each datalogger can now transmit data in both the directions

Bi-directional Mode is advantageous it enables the Data Transmission even in case of Network Failure

(c) T - Network Mode

If more no of stations are in network ie if the network is too lengthy then T- network mode is preferred

COMMUNICATION The communication protocol for transmitting data and command between datalogger and CMU is

standardized by the RDSO and is given in the Specifications of Dataloggers

(a) The type of communication used in the network is dependent on the distance between the dataloggers

(b) For shorter distances Opto Converter Box- Opto isolated current loop communication is used

(c) For longer distances Modem (Dial-up leased) Fiber Optic Satellite Microwave communication

MODEMS Modems are used for DATA transfer between Dataloggers and Front End ProcessorThese are

configured to RS 232 Serial Communication Network is connected with two types of 4-wire modems

(a) Internal modem card Dual Modem card (in-built)

It is fixed in datalogger Euro rack itself One card contains two modems The top modem is called

ANS (answer) modem and the bottom modem is called as ORG (originate) modem

Note In case of networking of Dataloggers connect lsquoANSrsquo modem to the lsquoORGrsquo modem of one adjacent

station and connect lsquoORGrsquo modem to the lsquoANSrsquo modem of other adjacent station

(b) External modems

20 | P a g e

These are generally used at FEP (Front End Processor) side to connect the Dataloggers

(i) To transfer Data from one datalogger to another datalogger FEP Baud rate is 9600bps

(ii) These modems are 4-wire line communication

(iii) To transfer the data from FEP to RMU (PC) the Baud rate is 57600 bps

There is no difference between these modems functionally

CENTRAL MONITORING UNIT (CMU) COMPUTER

Central monitoring unit (Fault Analysis Unit) is a Personal Computer and its minimum configuration

shall be specified by RDSO from time to time System Software Windows XPVista(OS) Norton Kaspersky

(Anti Virus) Interbase where Server is not available (DBMS) Oracle where Server is available (DBMS)

software are required to run Datalogger System It is provided with Graphical User interface (GUI) based

software and retrieve data from all Networked dataloggers (up to 32) at various stations It stores data in

standard data base files The CMU is capable of analyzing the data and generate reports audiovisual alarms

on defined conditions This data can be compressed to take backup In central monitoring unit Software used

for analysis of data prediction of faults etc is written in a structured format so that purchaser can

reconfigure it if required It displays the status of signaling gears at any selected time in graphic form for any

selected station yard It retrieves the stored data amp simulates train movement It sends commands to various

Dataloggers to activate audio visual alarm or operate and electromagnetic relay

CMU shares data available in it by other PCs through available local area network where this data can

be used for train charting passenger information purpose The system generates audiovisual alarm in

ASMrsquosSignal Maintainerrsquos room in the case of power supply failure (battery voltage low) or battery charger

defective with acknowledgement facility

(a) Each datalogger has its own identity code which will be transmitted along with data packet to central

monitoring unit

(b) Events recorded at each station are continuously transmitted to central monitoring unit Response time of

data transfer will not exceed 10 sec

21 | P a g e

22 | P a g e

OPTICAL FIBER CABLE

INTRODUCTION The demand for bandwidth on transmission networks is increasing rapidly because video and

graphical rich contents are exchanged through the corporate network or the Internet The Gigabit Ethernet

became ommonly used in the corporate network backbone and 10Gbit Ethernet will be adopted in the near

future Meanwhile in the home the demand for high-speed network becomes popular as the wide spread of

broadband access eg CATV xDSL and FTTH The transmission medium with capability to transmit high

bit rate signal is necessary to satisfy these requirements

The telecommunication transport technologies move from copper based networks to optical fiber

from timeslot based transport to wave length based transport from traditional circuit switching to terabit

router and all optical based networks entering into a new era of optical networking

BASIC PHYSICS OF OFC

OPTICAL FIBER CABLE OFC have Fibers which are long thin strands made with pure glass about the diameter of a human

hair OFC consists of Core Cladding Buffers and Jacket as shown in figure

MONOCHROMATIC LIGHT OR SINGLE COLOR LIGHT Light or visible light is electromagnetic radiation of a wavelength that is visible to the human eye (

about 400 ndash 700 nm) The word light is sometimes used to refer to the entire electromagnetic spectrum Light

is composed of elementary particles called photons Three primary properties of light are

Light can exhibit properties of both waves and particles This property is referred to as wave-particle

duality The study of light known as optics In free space light (of all wavelengths) travels in a straight path

at a constant maximum speed However the speed of light changes when it travels in a medium and this

change is not the same for all media or for all wavelengths By free space it is meant space that is free from

matter (vacuum) andor free from electromagnetic fields

Thus the speed of light in free space is defined by Einsteinrsquos equation E = mc2

Frequency ν speed of light in free space c and wavelength λ are interrelated by ν = cλ

From the energy relationships E = mc2 = hν and the last one an interesting relationship is obtained

the equivalent mass of a photon m = hνc2

When light is in the vicinity of a strong electromagnetic field it interacts with it From this interaction

and other influences its trajectory changes direction as shown in figure

23 | P a g e

INCIDENT RAY REFLECTED RAY AND REFRACTED RAY An incident ray is a ray of light that strikes a surface The angle between this ray and the

perpendicular or normal to the surface is the angle of incidence Reflection is the change in direction of a

wave front at an interface between two different media so that the wave front returns into the medium from

which it originated Common examples include the reflection of light sound and water waves

The reflected ray corresponding to a given incident ray is the ray that represents the light reflected by

the surface The angle between the surface normal and the reflected ray is known as the angle of reflection

The Law of Reflection says that for a specular (non-scattering) surface the angle of reflection always equals

the angle of incidence The refracted ray or transmitted ray corresponding to a given incident ray represents

the light that is transmitted through the surface The angle between this ray and the normal is known as the

angle of refraction and it is given by Snells Law

The figure shows Incident ray Reflected ray Refracted ray the angle of incidence and angle of refraction

REFRACTIVE INDEX - Refractive index is the speed of light in a vacuum ( c =299792458kmsecond) divided by the speed

of light in a material ( v ) Refractive index measures how much a material refracts light Refractive index of

a material abbreviated as lsquo n lsquo is defined as lsquo n=cv lsquo Light travels slower in physical media than it does

when transmitted through the air Refractive index (n) is a function of molecular structure of matter optical

frequency optical intensity determines optical propagation properties of each wavelength ( λ ) may not be

distributed equally in all directions is affected by external temperature pressure and fields

Refractive index of a medium is a measure for how much the speed of light is reduced inside the

medium For example typical glass has a refractive index of 15 which means that light travels at 1 15 =

067 times the speed in air or vacuum Two common properties of glass and other transparent materials are

directly related to their refractive index

First light rays change direction when they cross the interface from air to the material and effect that

is used in lenses and glasses

Second light reflects partially from surfaces that have a refractive index different from that of their

surroundings

SNELLrsquoS LAW-

24 | P a g e

When light passes from one transparent material to another it bends according to Snells law which

is defined as n1sin(θ1) = n2sin(θ2)

where n1 is the refractive index of the medium the light is leaving θ1 is the incident angle between the light

beam and the normal (normal is 90deg to the interface between two materials)

n2 is the refractive index of the material the light is entering

θ2 is the refractive angle between the light ray and the normal

Snellrsquos law gives the relationship between angle of incidence and angle of refraction

For the case of θ1 = 0deg (ie a ray perpendicular to the interface) the solution is θ2 = 0deg regardless of

the values of n1 and n2 That means a ray entering a medium perpendicular to the surface is never bent The

above is also valid for light going from a dense (higher n) to a less dense (lower n) material the symmetry of

Snells law shows that the same ray paths are applicable in opposite direction

TOTAL INTERNAL REFLECTION- When a light ray crosses an interface into a medium with a higher refractive index it bends towards

the normal Conversely light traveling cross an interface from a higher refractive index medium to a lower

refractive index medium will bend away from the normal

This has an interesting implication at some angle known as the critical angle θc light traveling from

a higher refractive index medium to a lower refractive index medium will be refracted at 90deg in other words

refracted alon g the interface If the light hits the interface at any angle larger than this critical angle it will

not pass through to the second medium at all Instead all of it will be reflected back into the first medium a

process known as total internal reflection

The critical angle can be calculated from Snells law putting in an angle of 90deg for the angle of the refracted

ray θ2 This gives θ1

Since θ2 = 90deg

So sin(θ2) = 1

25 | P a g e

Then θc = θ1 = arcsin(n2n1)

For example with light trying to emerge from glass with n1=15 into air (n2 =1) the ritical angle θc is

arcsin(115) or 418deg For any angle of incidence larger than the critical angle Snells law will not be able to

be solved for the angle of refraction because it will show that the refracted angle has a sine larger than 1

which is not possible In that case all the light is totally reflected off the interface obeying the law of

reflection

OPTICAL FIBER MODE An optical fiber guides light waves in distinct patterns called modes Mode describes the distribution

of light energy across the fiber The precise patterns depend on the wavelength of light transmitted and on the

variation in refractive index that shapes the core In essence the variations in refractive index create

boundary

conditions that shape how light waves travel through the fiber like the walls of a tunnel affect how sounds

echo inside

We can take a look at large-core step-index fibers Light rays enter the fiber at a range of angles and

rays at different angles can all stably travel down the length of the fiber as long as they hit the core-cladding

interface at an angle larger than critical angle These rays are different modes Fibers that carry more than

one mode at a specific light wavelength are called multimode fibers Some fibers have very small diameter

core that they can carry only one mode which travels as a straight line at the center of the core These fibers

are single mode fibers This is illustrated in the following picture

OPTICAL FIBER INDEX PROFILE Index profile is the refractive index distribution across the core and the cladding of a fiber Some

optical fiber has a step index profile in which the core has one uniformly distributed index and the cladding

has a lower uniformly distributed index Other optical fiber has a graded index profile in which refractive

index varies gradually as a function of radial distance from the fiber center Graded-index profiles include

power-law index profiles and parabolic index profiles The following figure shows some common types of

index profiles for single mode and multimode fiber

26 | P a g e

OPTICAL FIBERrsquoS NUMERICAL APERTURE ( NA )- Multimode optical fiber will only propagate light that enters the fiber within a certain cone known as

the acceptance cone of the fiber The half-angle of this cone is called the acceptance angle (see figure 18)

θmax For step-index multimode fiber the acceptance angle is determined only by the indices of refraction

Where

n is the refractive index of the medium light is traveling before entering the fiber

nf is the refractive index of the fiber core

nc is the refractive index of the cladding

NUMBER OF MODES IN A FIBER - Modes are sometimes characterized by numbers Single mode fibers carry only the lowest-order

mode assigned the number 0 Multimode fibers also carry higher-order modes The number of modes that

can propagate in a fiber depends on the fiberrsquos numerical aperture (or acceptance angle) as well as on its

core diameter and the wavelength of the light For a step-index multimode fiber the number of such modes

Nm

Where

D is the core diameter

λ is the operating wavelength

NA is the numerical aperture (or acceptance angle)

MODE FIELD DIAMETER - All light do not travels through the core of the fiber but is distributed through both the core and the

cladding The mode field is the distribution of light through the core and cladding of a particular fiber

Mode-Field Diameter (MFD) defines the size of the power distribution When coupling light into or out of a

fiber MFD is important in understanding light loss

27 | P a g e

ADVANTAGE OF OFC COMMUNICATION - bull More information carrying capacity Fibers can handle much higher data rates than copper More

information can be sent in a second

bull Free from Electromagnetic and Electrostatic interference Being insulator no electric current flows through

the fibre and due to this reason fibres neither radiate nor pick up electro - magnetic radiation So WPC

CLEARANCE is not required

bull Low attenuation 025 dbkm at 1550 nm Loss in twisted pair and coaxial cable increases with frequency

where as loss in the optical fibre cable remains flat over a wide range of frequencies

bull Use of WDM ndash Switching routing at Optical signal level

bull Self healing rings under NMS control

bull Small size makes fibre cable lighter in weight So easy to handleOptic fibre cable weight (approx)

500 kg km Copper cable weight (approx) 1000 kgkm

The reasons are photons of light in a fibre

do not affect each other as they have no electrical charge and they are not affected by stray photons outside

the fibre But in case of copper electrons move through the cable and these are affected by each other

Optical fibre does not carry any electricity even if the cable is damaged or short circuited it does

not cause any spark or fire hazard

As the fibre do not radiate energy it can not be detected by any nearby antenna or any

other detector The fibres are difficult to tap and therefore excellent for security

As the signal transmission is by digital modulation there is no chance of cross talk in

between channels

Only by adding a few additional terminal and repeater equipments the

capacity of the system can be increased at any time once the cable is laid

ical effects and temperature variations

LIMITATIONS OF OFC -

difficult

- utilised

APPLICATION IN SIGNAL AND TELECOMMUNICATIONS transmission circuits

-haul circuits for linking of telephone exchanges

28 | P a g e

PROPAGATION MODES CONCEPT -

MODE - Mode is an available distribution of electromagnetic field in a plane transverse to the direction of

light propagation Each mode is characterized by frequency polarization electric field strength and

magnetic field strength Available patterns are derived from Maxwellrsquos equations and boundary conditions

LINEARLY POLARIZED (LP) MODE A mode for which the field components in the direction of propagation are small compared to

components perpendicular to that direction An optical fibre supports only different field patterns called as

lsquoLinear Polarizedrsquo or lsquo LPrsquo modes The reasons are

requirements

de

the accrual of power carried by different modes

There are two basic types of fiber Multimode fiber and Single-mode fiber

Multimode fiber is best designed for short transmission distances This is suited for used in LAN systems and

video surveillance Single mode fibre is best designed for longer transmission distances This is suitable for

long distance telephony and multi channel television broadcast systems

29 | P a g e

MULTI MODE FIBER Multimode fiber the first to be manufactured and commercialized simply refers to the fact that

numerous modes or light rays are carried simultaneously through the waveguide Modes result from the fact

that light will only propagate in the fiber core at discrete angles within the cone of acceptance MM fiber type

has a much larger core diameter compared to single-mode fiber allowing for the larger number of modes

and

is easier to couple than single-mode optical fiber Multimode fiber further categorized as Multimode step-

index and Multimode graded index fiber

PROPAGATION THROUGH MMSI FIBER Figure shows the principle of total internal reflection applies to multimode step index fiber Because

the corersquos index of refraction is higher than the claddingrsquos index of refraction the light that enters at less than

the critical angle is guided along the fiber

Three different light waves travel down the fiber One mode travels straight down the center of the

core A second mode travels at a steep angle and bounces back and forth by total internal reflection The third

mode exceeds the critical angle and refracts into the cladding Naturally it can be seen that the second mode

travels a longer distance than the first mode causing the two modes to arrive at separate times

PROBLEMS WITH MMSI FIBER AND SOLUTION This disparity between arrival times of the different light rays is known as dispersion and the result is

a muddied signal at the receiving end It is important to note that high dispersion is an unavoidable

characteristic of multimode step-index fiber The solutions are either use Graded index fiber or Single mode

fiber

PROPAGATION THROUGH MMGI FIBER Multimode Graded-index refers to the fact that the refractive index of the core gradually decreases

farther from the center of the core The increased refraction in the center of the core slows the speed of some

light rays allowing all the light rays to reach the receiving end at approximately the same time reducing

dispersion Figure shows the Light propagation principle through multimode graded-index fiber The corersquos

central refractive index ( nA ) is greater than that of the outer corersquos refractive index ( nB )

It is very clear from the figure the light rays no longer follow straight lines they follow a serpentine path

being gradually bent back toward the center by the continuously declining refractive index This reduces the

arrival time disparity because all modes arrive at about the same time The modes traveling in a straight line

30 | P a g e

are in a higher refractive index so they travel slower than the serpentine modes These travel farther but

move faster in the lower refractive index of the outer core region

PROPAGATION THROUGH SMSI FIBER Single mode fiber has a much smaller core that allows only one mode of light at a time to propagate

through the core The figure shows the single mode fiber

Single-mode fiber exhibits no dispersion caused by multiple modes Single-mode fiber also offers lower fiber

attenuation than multimode fiber Thus more information can be transmitted per unit of time because it can

retain the fidelity of each light pulse over longer distances Like multimode fiber early single-mode fiber was

generally characterized as step-index fiber meaning the refractive index of the fiber core is a step above that

of the cladding rather than graduated as it is in graded-index fiber Modern single-mode fibers have evolved

into more complex designs such as matched clad depressed clad and other exotic structures

SINGLE-MODE FIBER DISADVANTAGES The smaller core diameter makes coupling light into the core more difficult The tolerances for single-

mode connectors and splices are also much more demanding

CUTOFF WAVE LENGTH - Cutoff wavelength is the wavelength above which a single-mode fiber supports and propagates only

one mode of light In other words an optical fiber that is single-mode at a particular wavelength may have

two or more modes at wavelengths lower than the cutoff wavelength The effective cutoff wavelength of a

fiber is dependent on the length of fiber and its deployment The longer the fiber the lower is the effective

cutoff

wavelength The smaller the bend radius of a loop of the fiber the lower is the effective cutoff wavelength If

a fiber is bent in a loop the effective cutoff wavelength is lowered

SIGNAL ATTENUATION IN FIBER - Optical fiber has a number of advantages over copper However it also suffers from degradation

problems which can not be ignored The first of these is loss or attenuation Attenuation is typically the result

of two sub properties They are scattering and absorption Both of which have cumulative effects The second

is

dispersion which is the spreading of the transmitted signal and is analogous to noise

SCATTERING Scattering occurs because of impurities or irregularities in the physical construction of the fiber The

well known form of scattering is Rayleigh Scattering It is caused by metal ions in the silica matrix and

results in light rays being scattered in various directions

31 | P a g e

Scattering limits the use of wavelengths below 800nm The short wavelengths are much affected than longer

wavelengths It is because of Rayleigh scattering that the sky appears to be blue ( shorter wave length ) The

shorter wavelengths ( blue ) of light are scattered more than the longer wavelengths of light

ABSORPTION Absorption results from three factors They are hydroxyl ions ( OH- water ) in the silica impurities

in the silica and incomplete residue from the manufacturing process These impurities tend to absorb the

energy of the transmitted signal and convert it to heat resulting in an overall weakening of the signal The

Hydroxyl absorption occurs at 125 and 139 micro The silica itself starts to absorb energy at 17 micro

because of the natural resonance of the silicon dioxide

MACRO BENDING LOSS Macro-bending loss is caused by bending of the entire fiber axis The bending radius shall not be

sharper than 30d where d is diameter of cable A single bend sharper than 30d can cause loss of 05dB

The fiber may break if bending is ever sharper

MICRO BENDING LOSS Micro-bending loss is caused by micro deformations of fiber axis which leads to failures in achieving

total internal reflection conditions Micro-bends are small scale perturbations along the fiber axis the

amplitude of which are on the order of microns These distortions can cause light to leak out of a fiber

Micro-bending may be induced at very cold temperatures because the glass has a different coefficient of

thermal expansion from the coating and cabling materials At low temperatures the coating and cable

become more rigid and may contract more than the glass Consequently enough load may be exerted on the

glass to cause micro bends

Coating material is selected by manufacturers to minimize loss due to micro-bending The linear thermal

expansion coefficient of coating material shall be compatible with that of fiber

32 | P a g e

DISPERSION Dispersion is the optical term for the spreading of the transmits in the fiber It is the bandwidth

limiting phenomenon and comes in two forms Multimode dispersion and chromatic dispersion Chromatic

dispersion is further subdivided into material dispersion and waveguide dispersion

DISPERSION PHENOMENON IN OPTICAL FIBER Dispersion is the time distortion of an optical signal that results from the differences of time of travel

for different components of that signal typically resulting in pulse broadening As the distance traveled by

the signal is more broadening of pulse is more In digital transmission dispersion limits on the maximum

data rate and the maximum distance ie the information-carrying capacity of a fiber link The interference

from broadened pulse in the next interval shall not lead to erroneous interpretation of received signal

OPTICAL DOMAIN Understanding where attenuation and dispersion problems occur helps optical design engineers

determine the better wavelengths at which information can be transmit taking into account distance type of

fiber and the other factors which can severely affect the integrity of the transmitted signal The graph shown

depicts the optical transmission domain as well as the areas where problems arise The wavelength (nm)

is shown on X-axis and attenuation ( dBkm) is shown on Y-axis

There are four transmission windows appear in the figure The first one is at around 850 nm the

second at 1310nm third at 1550 nm and fourth at 1625 nm The last two labeled as C and L band

respectively The 850 nm wavelength at which the original LED technology operated The second window at

1310 nm has low dispersion The 1550 nm called as C-band is ideal wavelength for long haul

communication systems The network engineers can avoid transmitting signal at 1000 nm where Rayleigh

scattering 1240 and 1390 nm where hydroxyl absorption by water occurs to avoid high degree of loss

Optical fibers also can be manufactured to have low dispersion wavelength in the 1550nm region

which is also the point where silica-based fibers have inherently minimal attenuation These fibers are

referred to as dispersion-shifted fibers and are used in long-distance applications with high bit rates For

33 | P a g e

applications utilizing multiple wavelengths it is undesirable to have the zero dispersion point within the

operating

wavelength range

34 | P a g e

SIGNALLING RELAYS

INTRODUCTION A relay is an electromagnetic device which is used to convey information from one circuit to another

circuit through a set of contact ie front or back contact Constructional and electrically relays may be

divided into DC and AC relays because the means by which the electrical energy in the coil is converted in

to mechanical Energy in order to move the contacts are fundamentally different In DC type the contacts are

carried on an armature forming part of a magnetic circuit in which a field is set up by the current flowing in

the coils In AC types the contacts are attached by a link mechanism to a metal sector disc or cylinder in

which currents are induced by the alternating magnetic field produced by the currents in the coils

Every endeavor has been made to explain the action of each type of relay in the simplest possible manner

Relays are sophisticated switch gears used for remote control and succession control of various

electrical equipment In present days they are widely used because they are capable of protecting the

controlled equipment from cross feeding and overloading even as they cater for speedy operations

Most of the relays in present day signaling are electromagnetic devices although some of the relays control

circuits through electronic components like diodetransistors Integrated Chips etc

Railway signaling relays are unique in that

(a) They operate on low voltage and current

(b) They are more articulate as according to their special features they can work under restrictive conditions

and in any specified manner Virtually they can cater for all situations while contributing to speed and

accuracy in operations

CLASSIFICATION OF SIGNALLING RELAYS (a) According to the method of their mounting or fixture they are classified as

(i) Shelf type Relays which are loosely kept on shelves

(ii) Plug in type Relays which are plugged into a pre- wired plug boards

(b) According to their connection and usage they are classified as

(i) Track relays Relay which is directly connected to the track to detect the presence of vehicle

(ii) Line Relays Other than track relay all are line relays Relays connected to the selection circuit

(c) According to their vitality or importance in ensuring train working safety they are classified as

(i) Vital Relays All relays used for traffic control such as signal point controls track detection etc

(ii) Non-vital Relays Relays which operate control aids and accessories like warnings buzzers

Indications etc

(d) According to their special provisions to ensure reliability of their contacts they are classified as

(i) Proved type are those whose normalization after each operation shall be proved in circuit

controlled by their contacts Contacts in which both the springs have metal surfaces on their tips They may

get fused due to high sparking current across them during operation These may prevent relay normalization

and causes unsafe condition in traffic control To avoid this proving of relay normalization after each

operation is necessary

(ii) Non - proved type Need not to be proved to have been normalized after each operation as their

contacts have at least one non-fusible contact (carbon contact)

(e) According to their feed source relays are broadly classified as

(i) DC relays The relay which requires DC power supply for its operations are called DC relays Among

the DC relays

o DC neutral relays This relay closes the same set of contacts on energization with Normal polarity

or Reverse polarity supply

o Polar Relays This relay closes different set of contacts when energized with Reverse polarity

supply They may or may not have contact to close when deenergized

35 | P a g e

(ii) AC Relay AC Induction motor track relays Time element relays flashing indication control etc

(iii) Electronic Relays DC relays with electronic components in them are called electronic relays

DC NEUTRAL RELAY Each Relay has usually one or two coils with a hollow center to accommodate a coreThe coils are

made up of a large numbers of turns of small gauge soft drawn copper wire The two coils can be connected

in series or parallel according to the requirement of relay resistance The ends of the coils are terminated on

binding post to which the control wires are connected Each coil is placed around a core of specially selected

Iron or steel having high permeability and low retentivity The core should be susceptible to magnetism and

at the same time should have little residual magnetism The cores are connected at the top by a yoke to

complete the magnetism coupling between two ends of coils The bottom of each core is equipped with a

large steel or Iron block known as pole piece or face

A flat piece of Iron or steel called armature is supported by brackets which are securely fastened to

the pole piece The armature yoke and the pole pieces are also made of specially selected iron or steel of the

same quality as the core The armature carries the metallic spring contacts which are insulated from it

The circuit through the coils of the relay is closed It sets up a magnetic flux through the core yoke and the

armature The flux passing between the armature and pole faces causes the armatures get attracted to the pole

faces and armature picks up and closes front contacts When the circuit is opened the magnetic flux collapses

and the armature drops away by gravity from the pole faces the front contacts break and back contacts close

The front and back contacts of the relay can be utilised to make or break other circuits Two stop pins of

nonmagnetic material are fixed either on the armature or pole faces so that the armature cannot

come in contact with the pole faces It is essential to maintain a small air-gap between the armature and pole

faces so that low value of residual magnetism may not retain the armature in picked up position and causes

the relay to fail to drop away with a break in its control circuit

GENERAL USAGE

DC Neutral line relays are most commonly used for Railway Signalling controls and detection

Among them plug-in type relays are preferred in larger installations for space considerations Shelf type

relays are also in use mostly in wayside stations

There are many DC Neutral line relays in use with special features such as

(i) Delayed operation

(ii) Biased DC control

(iii) DC control unaffected by AC interference currents

(iv) Getting latched in operated condition till further feeding and others

Usage of DC polar relays is mostly in conjunction with block instruments that control traffic between

stations AC line relays are almost extinct in installations of British Signalling practice They are however

used for time control operations flashing indication control and such other special purposes in installations

with Siemens signalling practice widely Track relays are used according to the type of track detection

circuits chosen for a given location and context While most of the track circuits are still of the DC working

type requiring DC neutral track relays with them the prospects of their being replaced with Electronic track

circuits directly feeding DC line relays in future are great AC Track Circuits are used in DC Traction area

as conventional DC Track Circuits are not suitable there AC Track relays are used with them almost all of

the induction motor type In the British practice of signalling which was first introduced on Indian Railways

non-proved type relays with carbon to metal switching contacts are generally used for vital controls

They facilitate simple circuit designs But with the advent of German Practice introduced by Ms

Siemens later proved type relays with all metal to metal contacts are widely accepted in spite of

complications in circuit design caused by them A recent introduction is that of the same type relays made by

Ms Integra control However for some time now the appreciable features of both the practices are getting

36 | P a g e

incorporated together in the indigenous designs of signalling by railwaymen With this the usage of all types

of relays anywhere can be found without straight jacketed segration of relay types

CHARACTERSTIC OF ELECTRO-MAGNETIC RELAY The following are the characteristic of electro-magnetic relays A brief study of them helps in

understanding the choice of their components and designs features

1) Force of attraction

2) Effect of air gap

3) Effect of Hysterisis

4) Transient condition

FORCE OF ATTRACTION In any electro-magnetic system the force of attraction is given by

Where B - is the flux density a - is the cross sectional area of the particular part of the magnetic

circuit

In the case of a DC neutral Relay B is proportional to the current that is flowing in the coil

surrounding the electro-magnet and thus the force of the attraction is directly proportional to the square of the

current This square relationship has its own advantage especially in the case of DC track relay in that a

small reduction in the current will have a great effect on the working of the relay Also for a given change of

current the make and the break will be quicker with lesser possibility of arcing

EFFECT OF AIR GAP

Curve lsquoArsquo is magnetisation curve for the iron and is all practical purpose a straight line up to the

saturation point Curve lsquoBrsquo is the magnetisation curve for the open-air gap which is a straight line through

out because per magnetisation curve of the whole

magnetic circuit of the relay and for a given force is the sum of the amp-turns for the iron part and the amp-

turns for the air gap

When the front contacts are open the force required to pick up the armature is shown on curve lsquoCrsquo to be F1

but after the armature has operated it will be separated from the core by stop pins In this position the amp-

turns required to maintain the armature is less as indicated by the dotted line from 1 on curve C to 2 on curve

37 | P a g e

F But actually the current in the coil is unaltered the force on the armature is greater than required as

indicated at 3 on curve F Part of this extra force is used to flex the front contacts sufficiently to give good

contact pressure when it is in energised position

The difference between the pick-up and the drop-away current should be as small as practicable in

track relay to ensure good shunting characteristics This is achieved firstly by the choice of good quality relay

iron and secondly by having a small air gap between armature and core If the air gap is not available then

the residual magnetism fluxes might cause the armature to be retained when the supply is disconnected For

this reason residual pins are provided to ensure a definite minimum air gap in the energised position

EFFECT OF HYSTERISIS

Hysterisis is the property by which the flux produced lags behind the current In the de-energized

condition there will be small residual flux in the core When the voltage is applied to the coils the current in

rising to its steady value first causes the flux to rise from 1 to 2 along the curve At this point the flux density

will be sufficient to attract the armature and reduce the air gap the flux then raise to 3 and continue to 4

which corresponds to the steady current in the coils When the voltage is disconnected the current in falling

caused the flux to fall from 4 to 5 along the curve At this point the flux density will fall below the value

required to maintain the armature which will release thus increasing the air gap and reducing the flux to 6

Finally the

flux will decrease from 6 to 1 where the current will again be zero

The relay core is made of material having high permeability and low retentivity As mentioned in

the IRS specification Electromagnet iron may be in the form of a

(a) Bar of silicon steel

(b) Best Yorkshire wrought iron

(c) Swedish charcoal iron

(d) Electrical steel sheets

` This reduces the difference between pick up value and Drop away value By selecting good quality

core material Percentage release and sensitivity of the relay will be improved

TRANSIENT CONDITION

38 | P a g e

When the voltage is applied or disconnected from the coils it takes some little time before the current

become steady These are known as transient conditionsrdquo and are important so far as track relays are

concerned When the voltage is first applied to the coils the magnetic flux in rising cuts the turns on the

coils and in so doing produces a back EMF that opposes the applied voltage and retards the growth of

current

The growth and decay of flux are decided by the relationship between the inductance and resistance

in the circuit is known as time constant It is not fixed quantity in the case of DC neutral relay This value of lsquo

Lrsquo is less when the relay is in de-energised condition (L1) than when the relay is in energised condition (L2)

The magnitude of flux that is established for a given change of current is different in two cases

When the current reaches the pick up value the armature closes and the inductance is increased to L2

due to reduced air gap the flux per amp is increased The increase in flux increased the back EMF during the

movement of the armature after which the current continuous to raise along a new curve corresponding to the

increased inductance until it reaches the final value (ER) This process is indicated above in fig24

When the supply is disconnected the current is obliviously reduced to zero immediately but the flux

decay comparatively slowly owing to the eddy currents produced in the core by the rapid flux change which

tend to maintain the flux The drop away time on a disconnection is however generally negligible See fig

below

If the relay releases due to the reduction in current from say I 2 to I 1 caused by the application of

shunt resistance (as in the case of track relay ) the time taken is much longer than the relay is simply

disconnected The rate of rise or fall of current during the transient conditions is also depends on exterior

circuit values because L and R apply to the whole circuit The production of eddy current in the core the flux

will decay at a slower rate than the current So that the actual release time will be a little longer than it takes

the current to fall to the release

L= Inductance

39 | P a g e

R= Resistance

It is now clear that to reduce releasing time to a minimum it is necessary that

- The relay iron should have low Hysterisis loss and low retentivity

- The degree of over energization of the relay should be restricted

- Connecting a suitable external resistance in series with the relay to keep LR ratio low

In non RE area for track circuit length less than 100M 9 ohm track relay only to be used Using relay

with minimum contacts as they require lesser current which keeps inductance value low

Train working safety is ensured only if the track relay of shortest length track circuit is released

before a light engine running at a highest permitted speed clears it Otherwise the track circuit occupation

may go undetected To avoid this a special provision has to be made in signal control circuits wherever

necessary

The following methods may be adopted for reducing the time lag of track relay

(a) Restrict the over energisation of relay since the release time depends on the initial working current

(b) Connecting a suitable external resistance in series with the relay to keep the LR ratio low

(c) Using relays with minimum contacts as they require lesser operating current keeping the inductance

value low

40 | P a g e

CONCLUSION

Modern signalling is vital for safe and punctual movements of trains In the Indian railways The Signalling

and Telecommunication Department is responsible for providing modern effective and relaible signalling

systems as well as telecommunication systems

The first mode of communication used in Indian Railways was the use of electric telegraph

with the help of Morose code Morose code is the method of providing text information as a series of on-off

tones and lights or clicks that can be directly understood by a skilled listener or observer without special

equipmentEach character (letter or numeral ) is represented by a unique sequence of dots and dashes Later

this system becomes obselete and beggan the era of wireless communication which operated at audio level

frequency range

In wireless communication the significant advances took place the transition to miniature

valves or filament tubesBut this was abandoned too because of excessive current consumption and over

heating of the filament tubes

Fibre-optic communication is a method of transmitting information from one place to another by

sending pulses of light through an optcial fibreThe light forms an electromagnetic carrier wave that is

modulated to carry information First developed in the 1970s fibre optic communication systems has

revolutionized the telecommunications industry and have palyed a major role in the advent of the information

age Because of its advantages over electrical transmissionsoptical fibres have largely replaced copper wire

communications in core networks in the developed world The Indian Railways too is undergoing a transition

from Microwave communication to fibre optic communications

41 | P a g e

BIBLIOGRAPHY AND REFERENCES

1 wwwwikipediacom

2 wwwbritaniccacom

3 wwwirfcacom

4 Motorola GP60 system manual

5 Harris FAS 7000 manual

6 TOSHIBA Manual

v | P a g e

TABLE OF CONTENTS

TITLE PAGE NUMBER

CERTIFICATE BY THE SUPERVISORS I

STATEMENT BY CANDIDATE II

ACKNOWLEDGEMENT III

ABSTRACT IV

SOLID STATE INTERLOCKING 1

INTEGRATED POWER SUPPLY 5

SINGLE SECTION DIGITAL AXLE COUNTER 9

DATA LOGGER 15

OPTIC FIBRE 22

SIGNALLING RELAYS 34

CONCLUSION 40

BIBLIOGRAPHY AND REFERENCES 41

1 | P a g e

SOLID STATE INTERLOCKING

INPUT CARDS All the field conditions (ie Field relay contacts) are connected to these input cards of EI system

The maximum inputs capacity of each RI card will depend on design of the RI cards by different

manufacturers The total number of inputs will depend on the yard layout

Total inputs means

Field inputs ECRs TPRs NWKR etc

Panel inputs GNs UNs NWNs RWNs etc

Read back inputs HR DR WNR WRR etc

Opto couplers are provided to isolate field optically from the system in Input cards These cards will read the

conditions of inputs and passes the information to EI system

PROCESSOR CARD This card is also called as central processing unit card of the System This is provided with microprocessor

RAM ROM EPROM EEPROM Memory ICrsquos These EEPROMS or EPROMrsquos (ROMrsquos) are programmed

with software required for executing the system commands

System software consists of the following

- Executive software programmed in system EPROMrsquos

- Application software programmed in DATA EPROMrsquos

-

EXECUTIVE SOFTWARE This software is common to all EIrsquos for the same company manufacturing

This is a factory installed software

Performs all operations

Cuts off vital supply voltage to output relays in case of unsafe failures

2 | P a g e

APPLICATION SOFTWARE This software is specific to each station and different for different stations

This is as per table of control of specific station

Can be installed at site by signal engineers

Logic installed through Boolean expressions or user-friendly equations

OUTPUT CARD (RELAY DRIVE CARD) This card receives the output of CPU card as input and picks up relevant output relay as per the panel

operatorsrsquo request The output of this card is terminated on phoenix terminals from there the output relays are

connected

The essential modules of an EI is as follows

Hardware module

Software module

HARDWARE MODULES USED IN THIS SYSTEM Equipment consists of

CARD FILE

Each card file is like a shelf having 20 Slots to accommodate various PCBs that are used in a system

Slot nos1 to 15 and 20 are used to accommodate Non-vital Input-output or Vital Input or Vital Output PCBs

Slot no16amp17 are used to accommodate Power supply PCB Slot no18amp19 are used to accommodate CPU

PCB In this cardfile a mother board is available in the rear side connecting all the 20 Slots This cardfile is

suitable to mount on a 19rdquo rack

Power

Supply

Card

CPU

Card

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19

20

CPU PCB Each card file to have one CPU PCB and always placed in slot no18amp19 In this card Micro

Controller used is Motorola 68332 and its speed is 21 MHz In this card 4 nos of flash EPROMs of 8 MB

are used to store executive and application software Two nos of fast Static RAM (each 64KB) are used to

process the vital data and Four nos of Static RAM (each 64KB) are used to store events and errors

The main functions of CPU is it monitors continuously status of Vital Boards It also monitors

system internal operation for faults and responds to detected faults It processes application logic based on

inputs

received and deliver outputs to drive external gears It records system faults and routine events in user-

accessible memory It monitors and controls the serial communication ports It controls power to vital outputs

through external VCOR relay

POWER SUPPLY PCB

3 | P a g e

Each card file to have one Power Supply PCB and always placed in slot no16amp17 Power supply

PCB is basically a DC-DC converter that converts 12V DC input supply is +12V -12V and +5V required for

various board functioning Based on diagnostic check by CPU Power Supply Card receives 250Hz signal

from CPU and extends supply to VCOR relay This card provides isolated supply to internal circuit

VITAL OUTPUT PCB Each Vital Output PCB has 16 Outputs It is available in 12V and 24V DC applications Each Vital

Output can drive an output device such as any Q-series relay This output relay in turn controls signals

points crank handle siding control level crossing etc Since Vital Output drives the relay which controls

important outdoor gears all the Vital Output boards are continuously diagnosed by a CPU Any abnormality

in any of the outputs will shut down the system to ensure safety

VITAL INPUT PCB Each Vital Input PCB has 16 Inputs It is available in 12V and 24V DC applications Each Vital Input

is assigned to read the status of outdoor gears such as Track circuits Point detectors Crank handles Siding

controls level crossing etc Since the Vital Inputs read the status of outdoor gears they are normally

configured with double cutting arrangement using relay contacts

NON-VITAL INPUTOUTPUT PCB Each Non-vital IO has 32 inputs and 32 outputs in one PCB It is available in 12V and 24V DC

applications Non-vital inputs are Panel push buttons and keys Non-vital outputs are Panel indication LEDs

counters and buzzers The status of Non-vital Inputoutput is known from LED indications available in front

of the card

VITAL CUT OFF RELAY- VCOR Each card file will have one VCOR to ensure the healthiness of the system VCOR has 6 FB

dependent contacts each rated for 3 Amps When system is healthy the coil receives voltage from Power

Supply PCB which in turn controlled by CPU Power to Vital output board is controlled by VCOR thus

ensuring safety

WIRING HARDWARE 48 Pin Address select PCB and Connector assembly is provided for Vital Input and Vital Output

cards 96 Pin Address select PCB and Connector assembly is provided for Non-Vital IO cards 48 Pin

Connector Assembly is provided for PS and CPU PCB EEPROM PCB which is provided on rear side of the

CPU connector to configure various serial communication ports Keying plugs are provided in the cardfile to

ensure coding to each type of cards

SOFTWARE MODULES USED IN THIS SYSTEM System software consists of the following

EXECUTIVE SOFTWARE This software is common to all EIrsquos for the same company manufacturing

This is a factory installed software

Performs all operations

Cuts off vital supply voltage to output relays in case of unsafe failures

APPLICATION SOFTWARE This software is specific to each station and different for different stations

This is as per table of control of specific station

Can be installed at site by signal engineers

Logic installed through Boolean expressions or user-friendly equations

4 | P a g e

A GEC-MANUFACTURED SSI INTERLOCKING CUBICLE

A PAIR OF DATA LINK MODULES

TRACKSIDE FUNCTIONAL MODULE

5 | P a g e

INTEGRATED POWER SUPPLY

INTRODUCTION A typical 4 line station requires power supplies of 24 V DC( 5 nos ) 12 VDC ( 5nos ) 6V (2 nos)

110 V DC and 110 V AC for signalling These require as many chargers and Secondary cells amp Invertors

requiring more maintenance amp spares Can they be Integrated in to one system

Thus the concept of Integrated Power Supply has been evolved by integrating concepts One Charger

One set of Battery Bank feeding Invertors and DC- DC converters for deriving various DC amp AC

voltages Integrated power supply system delivers both AC amp DC Power supplies as an output with the

output voltage tolerance of plusmn 2

ADVANTAGES Reduces maintenance on Batteries Battery charger amp overall maintenance

Its construction is in modules and hence occupies less space Reduced space requirement resulting in

saving of space for power supply rooms

Provides centralized power system for complete signaling installation with continuous display of

working status of system for easier monitoring

Defect in sub-units of system is shown both by visual amp audible indication Reflects the condition of

battery with warning

Replacement of defective modules is quick amp easy without disturbing the working of the system

It uses (n+1) modular technology hot standby arrangement and hence high reliability and more

availability of the system

The system provides uninterrupted supply to all signalling system even during the power failures

Thus No blank Signal for the approaching drivers

System can be easily configured to suit load requirement

The diesel generator set running (Non-RE area) is reduced almost to lsquoNILrsquo Hence low wear and tear

of DG set components amp reduced diesel oil consumption

COMPONENTS (a) Un-interrupted power supply (U P S)

(i) SMPS Battery chargers with Hot stand-by mode

(ii) Hot Standby PWM Inverters with auto changeover

(iii) CVT Regulator [FRVS]

(b) AC distribution board [ACDB]

(i) STEP DOWN TRANSFORMERS

(c) DC distribution board [DCDB]

(i) DC-DC converters

WORKING IPS works satisfactorily for AC input variation of 150V AC to 275V AC with single-phase power supply

and frequency variation from 48 Hz to 52 Hz The input is fed to SMPS charger which converts in to 110

VDC as output It is fed as input to three sub units

To battery bank charging the batteries

To ON line inverters that converts 110 VDC in to 230 VAC plusmn 2as output

6 | P a g e

As 110 VDC bus bar to DC Distribution Panel as an input to various DC-DC converters located in

it

A 110 V Battery Bank of VRLA cells are connected to SMPS Panel IPS Status Monitoring Panel is

located at ASM room or at SampT staff room if round the clock SampT staff is available at Station

CONSTRUCTION IPS mainly consists of

SMR (Switch Mode Rectifier) Panel SMPS based Float cum Boost Charger (FRBC) Panel

AC Distribution Panel

DC Distribution Panel

Battery Bank (110V DC)

Status Monitoring Panel

SMR (SWITCH MODE RECTIFIER) PANEL SMPS BASED FLOAT

CUM BOOST CHARGER (FRBC) PANEL It consists of SMR FRBC modules and Supervisory amp Control Unit SMPS based SMRs

(converters) SMPS based Float cum Boost Chargers (FRBC) modules are provided with (n+1) modular

technology hot standby arrangement with active load sharing basis and 1 additional module as a cold standby

(n+2) Supervisory amp Control Unit which controls and monitor the complete system It has various

indications on the panel reflecting the working of the panel

FRBCs are suitable for operating in parallel on active load sharing basis with one or more modules of similar

type make and rating

n = required no of modules to cater for actual current requirement

AC DISTRIBUTION PANEL It is made of ON-Line inverters with (1+1) modular technology hot standby arrangement amp CVT

(Constant Voltage Transformer) AVR (Automatic Voltage Regulator) and set of step down

transformersThe inverter is protected against overload and short circuit with auto reset facility Whenever

the failure occurs it trips and restart automatically after about 10 to 20 sec But if the problem persists the

protection is permanently gets latched and it will not be switched ON again unless the fault is cleared

followed by pressing of reset button The output of inverters is regulated to 230V AC plusmn 2 50Hz plusmn1Hz for

an input voltage variation of 90V DC to 140V DC Normally both the Inverters are powered ON and both are

delivering the Output voltage but only one (main) inverter is connected to the Load If main inverter is failed

then only the stand-by inverter will come on Load automatically with in 500msec At 70 Depth of

Discharge (DOD) of the battery bank 110VDC supply to the inverters will be cut-off So the Signals feed will

be cut-off The auto-change over arrangement is also provided for bringing the CVT in circuit with in

500msec when the both the inverters output is failed It has various indications on the panel reflecting the

working of the panel

DC DISTRIBUTION PANEL It takes care of DC Power supply requirements of our signalling It consists of sets of DC-DC

converters for individual DC power requirements with (n+1) modular technology hot standby arrangement

with active load sharing basis The DC-DC converters of Relay Internal are provided with (n+1) modular

technology hot standby arrangement with active load sharing basis and 1 additional module as a cold standby

(n+2) The DC-DC converter works satisfactorily with the input voltage variation of 98VDC to 138VDC At

90 Depth of Discharge (DOD) of the battery bank all the DC-DC converters 110VDC Input supply will be

cut-off except for Block Tele DC-DC converters The supply for Point operation is also catered through a

20A fuse by this unit It is also provided with various indications that reflect its working

7 | P a g e

STATUS MONITORING PANEL IPS status monitoring panel has been provided in the ASM room for giving the important alarms and

indications to ASM Status Panel tells present working status of IPS displaying battery voltage continuously

and five other indications which will light according to IPS status During normal working these indications

will not lit Whenever the battery has come on to the load and has discharged by 50 DOD (Depth of

Discharge) then first Red indication lit with description ldquoSTART GENERATORrdquo with audio Alarm ie DG

set is to be started and put on the load If DG set is not started with this warning then if battery gets further

discharged to 60 DOD and second Red indications appears with description ldquoEmergency Start generatorrdquo

with audio alarm even now if DG set is failed to be started the battery further gets discharged to 70

DOD and 3rd Red indications appear with description ldquo System shut downrdquo with audio alarm which will

continue till Generator is started resulting in AC output from IPS is automatically cut off results all the

signals will become blank

When there is any defect in any sub module of IPS even without affecting working of system the 4th

Red indication appears with description ldquoCall SampT Staffrdquo with audio alarm so the ASM advises SampT staff

accordingly Green LED 5th indication comes with the description ldquoStop Generatorrdquo with audio alarm when

the DG set is running and if the Battery bank is fully charged condition

EARTHING The IPS systems and its individual modules are having earth terminals and all these are properly

earthed with earth resistance of less than 1 ohm Earth provided shall preferably be maintenance free using

ground resistance improvement compound (The acceptable Earth Resistance at earth busbar shall not be

more than 1 ohm Code of practice for earthing and bonding system for signalling equipments)

LIGHTNING AND TRANSIENT PROTECTION IN IPS Manufacturer will provide Stage1 amp Stage 2 protection along with the IPS These are described

below

Stage 1 protection is of Class B type against Lightning Electro-Magnetic Impulse (LEMP) amp other

high surges provided at Power Distribution Panel It is provided with a 63 Amp fuse in phase line and is

connected between Line and the Neutral and also between the Neutral and Earth

Stage 2 protection (Power line protection at Equipment level) is of Class C type against low voltage

surges provided at the equipment input level This is thermal disconnecting type and equipped with

protection against SPD (surge protection device) failure due to open amp short circuit of SPDs and is connected

between the Line and the Neutral If supply data signalling lines (ACDC) are carried through overhead

wires or cables above ground to any nearby building or any location outside the equipment room additional

protection of Stage 2 type shall be provided at such locations Class B amp Class C arrestor is provided on a

separate wall mounting type enclosure in IPS room

Stage3 protection (Protection for signallingdata line) is of Class D type All external data signalling

lines (ACDC) shall be protected by using this Class D type device It consists of a combination of Varistors

and Gas Discharge Tube with voltage and current limiting facilities

FEATURES Chargers used in this system are of SMPS technology chargers with 90 efficiency These chargers

are supported with hot standby mode with (n+1) modular technology

Onetwo sets of Maintenance free Battery banks (110VDC) Normally one set (110VDC) of Battery

bank is used Conventional flooded type Lead Acid Batteries or Low Maintenance Lead Acid

batteries can also be used (SMRs settings are required to be adjusted depending on the type of

Batteries used) Various voltage levels of

8 | P a g e

battery banks are avoided Reduction in Battery maintenance amp less flour area required

DC-DC Converters working from 110V Central battery have been used for all dc supplies This has

improved overall efficiency of the system since number of conversion from AC to DC have been

reduced to 2 stage as compared to 3 stage conversion in case of transformer-rectifier system

DC-DC converters are available in modules Easy replacement of defective modules This ensures

less down time

DC-DC Converters are used in load sharing N+1 configuration (ie with hot standby with N+1

modular technology) to improve the reliability amp availability of the system

Capacity of inverter has been brought down to 15 KVA from 5 KVA and used for feeding only

Signals supply Hot standby inverter is provided with auto changeover facility This improves the

availability of the overall system

High efficiency inverter is used with PWM (Pulse Width Modulation) technology in place of Ferro-

resonant technology based inverter This improves the efficiency of the overall system

Continuous power to Signal Circuits even in absence of DG setLocal Power Supply

Generators need not be switched ON every time during train movement

Metal-to-metal relay installations and block working by axle counters have also been covered

Supply of spare modulesComponentsCells have been included as part of main supply

Provides highly regulated voltage to all signal relays amp lamps for better life

9 | P a g e

SINGLE SECTION DIGITAL AXLE COUNTER

INTRODUCTION- The axle counter equipment is working on high frequency and using amplitude modulation or phase

modulation for detection of presence of wheel The equipment described in this notes is Phase modulation type

for the detection of presence of wheel In the Phase modulation type track device the detection of presence of

wheel is with the phase reversal of 1800 out of phase which enables this system to be more healthy and safe

In Phase Reversal Modulation technique trolley suppression arrangements to prevent the counting of

wheels caused by push trolley passing over the track device are not required as the system will take care of

validation of generated pulses caused by passage of wheel over the track device depending up on the phase

shift of the pulse This phase shift of the pulse may be normally 160deg to 180deg for a train wheel and it may be

approximately 100deg to 120deg for a push trolley wheel

This is Digital Axle Counter equipment for single track sections containing 2 out of 2 micro-

controllers to count the axles establish the track occupancy of a track section and to provide this information

to the block or the interlocking equipment

In this system no separate evaluator is required and no analog data is being transmitted One set of

Axle counter equipment is provided at entry end and other set provided at exit end Both sets are being

connected through a twisted pair of telecom cable ie existing RE cable one PET quad is used for both UP

and DN Axle Counters Digital DATA is being transmitted between two ends of Axle counters (Outdoor

track side Detection points)This system is a fully duplex capable of operating according to CCITT V21 and

the Data will be transmitted at the rate of 300bitsec This data Transmitted ensure negligible interference of

the noise The system is highly reliable

FEATURES (a) The system consists of

(i) Single Section Digital Axle Counter (SSDAC) units

(ii) Tx Rx coils

(iii) Vital Relays

(b) TxRx coil axle detectors are mounted to the web of the rails The design of system consists of 21 KHz amp

23 KHz High frequency Phase Reversal type axle detectors

(c) Compatible with 90R 52Kg amp 60Kg rail profiles Easy to install commission amp maintain

(d) Track devices at both (entry amp exit) points of the section should be fixed on the same rail

(e) System is designed to detect the solid wheels with diameter gt 400mm with standard wheel flange

(f) The system works in pairs For monitoring single-track section one pair of SSDAC units are required and

to be installed near the trackside one at the beginning and another at the end of the track section ie

Trackside electronic counting equipment

(g) The basic design of the system is based on counting the number of axles passing at each detection point

These stored counts are transmitted to the second unit of the system and vice versa by means of modem

communication

(h) The communication consists of digital packets having details of Counts amp Health

10 | P a g e

(i) If counts registered at both detection points are equal the section is cleared otherwise the section is shown

as occupied The system ensures no error condition to arrive at the decision of clearance

(j) System is designed as per CENELEC SIL-4 (European standard) using micro controller along with other

electronic circuits and programmed using dedicated software When any of these circuits fail the system

goes to fail safe condition

(k) It is programmable for either Preparatory Reset or Conditional Hard Reset as per requirement

(l) Micro controller based design with 2 out of 2 decisions and counting through software

(m) V21 Modem communication (2-wire) on frac12 quad cables and also compatible to work on voice channel of

OFC amp Radio

(n) Opto isolated vital relay drive for Q-style 24V 1000 _ and Vital Relay output can be giving at both ends

of the system

APPLICATIONS The system can be widely used in Railways for Block Working (BPAC) Intermediate Block Signaling Auto

signalling and Track circuiting for i) Loop line ii) Main line iii) yard lines

SYSTEM DESCRIPTION

This system comprises of

Tx coils-2 nos

Rx coils-2 nos

Reset Box (RB 258A)

Card 1 Signal Conditioning Card ndash 1

Card 2 Signal Conditioning Card - 2

Card 3 Micro controller Logic Board ndash 1

Card 4 Micro controller Logic Board ndash 2

2 nos for independent resetting ndash when used in block sections

1 no for common resetting ndash when used for Track circuiting at stations

Card 5 Event Logger Card

Card 6 Modem Card

Card 7 Relay Driver Card

Card 8 DC-DC Converter Card

SSDAC (DACF 700AP) UNIT

(A) SIGNAL CONDITIONING CARD (CARD 1amp2) (SCC) -1 (SCC-1) generates 21 KHz carrier

signals

-2 (SCC-2) generates 23 KHz carrier signals which is transmitted to 2nd

set of Tx coils

s receive these signals

modulated

train pulses

11 | P a g e

(B) MICRO-CONTROLLER LOGIC BOARD CARD (CARD 3amp4) (MLB) The Micro-controller Logic Board (MLB) is the heart of the system

o 8051 Based Architecture

o 8 Bit Micro Controller

o ATMEL AT89S8252 Micro controller

o 2 out of 2 Decision

o Uses C subset language

- TOOLS

o KEIL μ Vision Development System

o Universal Programmer

o 2KB Program Memory

o 256 bytes RAM

o 8KB Flash memory

o 32 Programmable IO lines

o Wide Operating Voltage range of 4V-6V

o Full Duplex Serial Port

o Programmable Watch Dog Timer

o Fully Static operation up to 24MHz (Upgraded to 40MHz)

o Operating Temperature of ndash40degC - +85degC

o Use of State Machine for Axle Counting

o Use of ASCII MODBUS protocol

o Use of CRC16 technique for Error Checking during communication

o Wheel detection

o Train direction checking and

o Wheel counting functions

o It receives the remote wheel count and computes the status of the section for clear or occupied

o It also checks various supervisory signal levels like supervisory of TxRx coils presence of various

cards communication link failure etcThese cards communicate with each other for wheel count

At Entry-end if train enters into section (1st detection) the counts are incremented and when train

shunts back from the same detection ie if train exits from the section from the same detection the counts are

decremented At Exit-end if train enters into section (2nd detection) the counts are decremented and when

train shunts back from the same detection ie if train exits from the section from the same detection the

counts are incremented Both the track devices at Entry and Exit ends must be fixed on same side of the

track

This MLB card is having Extensive LED display

o A block of 8 LED indicators for count progress error display

o 2 independent LED indicators for section status

o The errors occurring in the system during the operation of the SSDAC are encoded and are indicated by

means of the 8-LED block present on the front panel of the MLB cards

(c) EVENT LOGGER CARD (CARD 5)

Event logger card is designed to capture and store important signals from the remote and local SSDAC units

The stored data can be downloaded from the event logger card for the purpose of analyzing the events

occurring during the operations of the SSDAC The data can be analyzed with the help of CEL data analyzer

software

12 | P a g e

The event logger card captures following signals

(i) Pulse signals

(ii) Supervisory signals

(iii) Card removal information

(iv) Serial packets from

Event Logger card has a Rabbit processor and 2 MB FLASH MEMORY to store packets The data is initially

stored in the buffer and subsequently transferred to FLASH memory every two minutes Normally 4096

pages of the data can be stored in flash memory on FIFO (first in first out) basis

Run This LED blinks continuously indicating the normal working of the event

Log This LED blinks whenever data is being logged into the flash memory (Approx after every 2 minutes)

Dnld This LED is ON when data is being downloaded from the flash memory of the card and becomes OFF

when download is complete

(D) MODEM CARD (CARD 6) (i) The modem card transmits and receives the digital packet information form one counting unit to the other

The packet will appear after every 18 sec and the packet carries the latest information such as

(ii) The modem card being used is V21 type (2-wire) in SSDAC

(iii) This card interfaces with serial RS232C port of both Micro-controller Logic Boards

(iv) It multiplexes the two RS232C inputs and selects one of the two channels and provides signal conversion

from digital to analog (FSK modulation) and vice-versa

(v) Data transmission rate is 300 bitssec

(vi) Automatic Gain Control circuit is incorporated hence no gain adjustments required

(vii) Mode selection on Modem card The modem has been set in lsquoORIGINATORrsquo mode for entry and in the

lsquoANSWERrsquo mode for exit in the factory

(viii) LED Indications provided on Modem card

-Transmitting the signal when LED is flashing

- Receiving the signal when LED is flashing

-Remains OFF in SSDAC

-Carrier is detected when LED is glowing

(E) RELAY DRIVER CARD (CARD 7) (i) The Relay Driver card (RD) provides the 24V DC output required for driving Vital Relay

(ii) One RD card is used in each SSDAC counting unit The RD card receives the command of clear and

clock signals from MLB1 amp MLB2 cards and drives the vital relay lsquoONrsquo when section is NOT OCCUPIED

through opto- isolator circuit

(iii) If a train occupies the section the vital relay is dropped The vital relay status is read back by the system

as per the driving output

(iv) It has

13 | P a g e

ndash LED flashes when the section is clear

ndash LED flashes when the section is clear

All the above LEDrsquos are lit for section clear condition

(F) DC-DC CONVERTER CARD (CARD 8)

INPUT VOLTAGE Nominal Voltage voltage 24V DC Maximum current drain= 12A

Required voltage 18V DC to 30V DC

Output voltage

Nominal Voltage +5 V DC 2 A Required voltage 4 7 5 t o 525V DC

Nominal Voltage +12V DC 200 mA Required voltage 1175 to 1225V DC

Nominal Voltage +24V DC 300 mA with common ground Required voltage 235 to 245V DC

Nominal Voltage +15V DC 100 mA with isolated ground Required voltage 145 to 155V DC

SURGE VOLTAGE AND LIGHTNING PROTECTION Transient surge voltages arise as a result of Lightning discharge switching operations in electrical

systems and electrostatic discharge These surge voltages often destroy the electronic equipment to a large

extent In order to prevent surge voltages from destroying the equipment all the input lines of SSDAC ie

Power Supply (24V) Reset (48V) amp Modem is to be routed through surge voltage protection devices for

effectively protecting the system These devices (3 numbers) are mounted in a box and supplied along with

the system One number of box is to be installed at each location and wired to the SSDAC

Each surge voltage protection device consists of two parts

(a) Base

(b) Plug Trab

The Base of the device is used for wiring the input and output signals The connection details from relay

room to the box and from box to SSDAC unit are provided on the box The Plug Trab consists of MOV and

GD Tube and diverts the excess energy during surge voltages or lightning into the ground connection The

operation of these devices relies on a high quality ground connection in order to safely shunt away the

unwanted energy The impedance of the ground connection is critical and it should be less than 2 Ohms

NOTE The 3 Plug Trab connections are not to be interchanged with one another The plug Trab is a

detachable device and can be replaced with SPARE unit in case of blown device which is indicated by

means of LED for 24 V

EFFECTIVENESS OF PLUG TRABS The effectiveness of plug Trab depends wholly on the Earth connection provided to the system The earth

provided to the system should be less than 1 ohms and connections should be firm and proper to the SSDAC

unit VR box etc

SURGE VOLTAGE AND PROTECTION DEVICE SV-120 The Surge Voltage protection device is to be installed at each location along with every SSDAC unit

14 | P a g e

EARTHING- The lead wires connecting the installation and the earth electrode shall ordinarily be of stranded

copper wire of 29 sq mm (19 strand wires of 14 mm diameter) Copper wire has been specified because GI

wires usually are having greater corrosion However in areas where copper wire may be frequently stolen

due to theft ACSR of size 64 sq mm (19 strands of 211 mm diameter) may be used

LIMITS OF EARTH RESISTANCE (a) Apparatus case connected to Earth (SSDAC and vital Relay Box is housed in Apparatus case and

Connected to earth at outdoor) shall be less than or equal to 1 ohm

(b) All cable connected to same earth shall be less than or equal to 1 ohm

(C) Reset box connected to earth near SM s Room shall be less than or equal to 1ohm

EQUIPMENT TO BE EARTHED A Common Earth should be provided for SSDAC for items 1(a) amp (b) of the above at the outdoor

(a) The Apparatus Case is to be connected to earth (the chassis of SSDAC amp Vital Relay Box should be

properly connected to apparatus case)

(b) Metallic sheath and armouring of all the underground main cables are to be earthed

(i) In RE area the metallic sheath and armouring of main telecom cables are earthed at both ends

(ii) In RE area the armouring of Jelly filled cable shall be earthed at both ends

(c) The Earthing shall be provided at every location box where cables are terminated

(d) Earth already available for other equipment may be used for earthing of Reset Box near SM s Room

Cabin etc

15 | P a g e

DATALOGGER

INTRODUCTION Datalogger is a Microprocessor based system which helps in analysing the failures of relay inter

locking system Electronic Interlocking system This is like a black box which stores all the information

regarding the changes take place in relays AC DC Voltages and DC currents along with date and time The

same information data can be transferred to the computer to analyse further ldquoon line ldquooff linerdquo analysis of

stored date A print out also can be obtained through a printer by connecting directly to the datalogger unit

The data belongs to Relay contacts is considered as digital inputs and the data belongs to voltage

levels currents is considered as Analog inputs Datalogger lsquos are mandatory for all new relay interlocking

(PIRRI) EI installations and it is also recommended to provide in all existing PIs RRIs To increase the

line capacity mechanical signalling equipments are upgraded to PI RRI or EI Due to complexity in the

circuits and wiring sometimes it is very difficult to rectify the failures So datalogger can monitor these

systems with real time clock Thus it can be named as black box of Samp T equipments and hence it is a vital

tool for accident investigation Datalogger is used at Stations yards Whereas in case of Auto Section amp IBH

Mini dataloggers called as Remote Terminal Unit (RTU) are used

ADVANTAGES OF DATALOGGERS (a) Dataloggers helps in monitoring the typical failures such as intermittent auto right failures

(b) It helps in analyzing the cause of the accidents

(c) It helps in detecting the human failures errors such as

(i) Drivers passing signal at Danger

(ii) Operational mistakes done by panel operators ASMrsquos of operating department

(iii) Signal and telecom engineering interferences in safety circuits

(iv) Engineering and electrical department interferences failures

(v) It helps as a ldquoTOOLrdquo in preventive maintenance of signaling gears

(d) Dataloggers can be connected in network Networked dataloggers helps to monitorthe PIRRIEI remotely

(e) Failure reports can be generated remotely with help of datalogger network

(f) On line and Off line track simulation is possible

(g) Speed of the train on point zones can be calculated

(h) Age of the equipment in terms of number of operations etc

COMMON EQUIPMENT FOR ALL DATALOGGERS ARE GIVEN

BELOW (a) CPU card

(b) Digital and Analog input cards

(c) Local terminal(PC)

(d) communication links

(e) Printer

All the dataloggers requires a potential free ( spare ) relay contact for monitoring digital inputs

through Digital input cards amp for monitoring Analog inputs such ACDC bus bar voltage levels through

Analog input cards Digital and Analog inputs are connected to the Processor card Processor card consists of

memory ICrsquos Memory ICrsquos are programmed as per requirement of the signal engineers

Provision of Dataloggers is mandatory with RRI systems and is optional for PI systems as per

amendment to the specification for Relay Interlocking systems ( IRSS-36 ) The data collected by the

datalogger can be used for failure analysis repetitive discrepancies and for accident investigations

16 | P a g e

Note

If the serial communications is more than 50m then line drivers shall be used up to 3 Kms

4wire leased line Modems shall be used if the serial communication is more than 3 Kms

STUDY OF EFFTRONICS DATALOGGER TECHNICAL DETAILS (a) 24V 12VDC Power Supply

(b) Total Storage Capacity of 10 Lakh events

(c) In-built Temperature sensors

(d) Internal Buzzer for alarming during failures

(e) Real Time clock with internal battery backup with data retention up to 10 years

(f) 512 LED matrix to indicate the status of 512 Digital inputs at a time page wise

(g) Seven segment LCD screen (2x24) to display the status of digitalanalog signalsTime Temperature etc

(h) Using the keyboard various functions can be viewed in the LCD panel

(i) Max Digital Inputs 4096

(j) Max Analog Inputs 96

(k) Digital Input Scanning Time 16 millisecond

(l) Analog Input Scanning Time is less than 1 Sec

HARDWARE (EQUIPMENT) Datalogger system consists of

(a) Datalogger (CPU - with Microprocessor 68000)

(b) Digital input cards

(c) Dual modem card

(d) Digital Scanner units (DSU)

(e) Analog Scanner units (ASU)

CPU CARD It is provided with Motorola microprocessor M 68000 It performs all the activities pertaining to the

datalogger It continuously scans (check) the Digital inputs(inbuilt) Digital Scanner Units and Analog

Scanner Units ie scanning of digital signals (Relay operations) for every 16-milli seconds and scanning of

analog signals (ie ACDC voltages amp DC currents) for less than 1 second

This card will support the IO interfaces of LCD (Liquid Crystal Display) - 2X24 alphanumeric Key

Board LED Matrix Display Real Time Clock LCD display and keyboard This will acts as man machine

interface between the datalogger and the signal engineer All the operations (Software) can be performed

using this LCD and keyboard

Real time display with 7 Segments This is built in real time clock within Datalogger and its current

time will be displayed on six 7-segment display provided (Real time clock depend upon DALLAS 1286

chip) This IC will come with internal battery backup hence there is no need to add external batteries

CPU card continuously scans (checks) the DSUs and ASUs Each input connected to digital scanner

units are optically isolated by Opto couplers When CPU card scans the digital inputs it compares with the

previous stored data and if there is any change from the previous status then only that data will be stored (the

status conditions of relay) with date and real time A total of minimum 10 Lac events can be stored in

memory on first in first out basis so that latest data is available in the system There is no loss of data from

datalogger memory in case of power supply failure of datalogger

DIGITAL INPUT CARDS (IN-BUILT) This system is having maximum 8nos of inbuilt Digital inputs cards Maximum 64nos of digital

inputs can be connected to each digital input card The potential free relay contact may be front or back

contact terminated at the Tag Block from the relay of signals tracks points Buttons etc and are

17 | P a g e

subsequently connected to Digital input cards through Flat Ribbon Cable (FRC) connectors These in-built

digital input cards can monitor a total 512 nos of relays status

DIGITAL SCANNER UNIT (DSU) Each DSU contains 8 nos of Digital Input cards Each input card can be connected with 64 inputs

Total input capacity of DSU unit is 512 inputs These scanner cards contain Optocouplers and Multiplexer

Inputs are connected to Stag card The stag card out put is connected to DSU through FRC connectors

Maximum 7 nos of DSUs can be connected to the system So Digital input capacity of the system is 4096

All these digital inputs are scanned at rate of 16 msec

ANALOG SCANNER UNIT (ASU) ASU contains maximum 3 nos of Analog input cards Each input card can be connected with 8nos of

Analog inputs Total input capacity of the ASU is 24 analog input channels Maximum 4nos of ASUs can be

connected to the system Analog input channel capacity of the system is 96 All these analog inputs are

scanned at a rate of less than 1 sec

PARALLEL PORT Parallel port is provided for connecting printer

RS-232 SERIAL PORTS At least 6 Serial communication ports are provided for communication with other dataloggers

Central Monitoring Unit Remote Terminal Unit Electronic Interlocking system Integrated Power Supply

system etc

EXTERNAL NON-VITAL RELAY CONTACTS These relays provided in the system where 16 number of the Relay contacts are provided on the rear

panel through Tele control port to extend alarms and to control the power equipment from remote or local

locations through computer in case of any occurrence of failures Each control can sink or source 100 m

amps of current

INTERNAL MODEM CARD DUAL MODEM CARD (IN-BUILT) It is fixed in datalogger Euro rack itself One card contains two modems The top modem is called

ANS (answer) modem and the bottom modem is called as ORG (originate) modem It is used in case of

networking of Dataloggers In network connect lsquoANSrsquo modem to the lsquoORGrsquo modem of one adjacent station

and connect lsquoORGrsquo modem to the lsquoANSrsquo modem of other adjacent station

POWER SUPPLY Normally 24V DC (12V DC is optional) supply with battery backup is required for the system

working

Input Voltage Range 18Vhellip32V DC (For 24V) 9Vhellip18V DC (For 12V)

INPUT REQUIREMENTS Relay inputs (digital inputs) and analog inputs (voltages currents etc) are required to be connected

to the system as per the requirements of RRI PI SSI as the case may be Some of the inputs to be

monitored is given below

(a) Digital inputs

(i) Field inputs All TPRs NWKRs RWKRs ECRs Crank Handle relays SidingSlot LC gate

control relays etc

(ii) Control Panel inputs All button Knob SMrsquos Key relays

18 | P a g e

(iii) Internal relays

British system All HR DR HHR WNR WRR ASR UCR RR LR UYRTLSR TRSR TSR

JSLR JR etc

SIEMENS system Z1UR Z1UR1 GZR ZDUCR ZU(R)R ZU(N)PRG(R)RG(N)R U(R)S

U(N)PS UDKR DUCR U(R)LR UYR1 UYR2 G(R)LRGR1GR2

GR3 GR4 OVZ2U(R)RW(RN)R (RN)WLR Z1NWR Z1RWRZ1WR1 WKR1 WKR2 WKR3 etc

(b) Analog channels

(i) 230 V AC (for power supplies in the power panel)

(ii) 110V AC (for Signal and Track transformers)

(iii) 110V DC (for Point operation)

(iv) 60V DC (Siemens relays)

(v) 24V DC (Q-series relays)

(vi) 24V DC (for Block Axle counters)

(vii) 12V DC (for indication)

(viii) 20A (for point operation current)

(ix) 10V AC 5KHz (for Axle counter channels) etc

SOFTWARE MODULES OF DATALOGGERS

(a) Network Management of Dataloggers (NMDL)

(b) Reports

(c) Fault Entry

(d) Track Offline Simulation

(e) Train Charting

NMDL SOFTWARE FEATURES (a) Online Relay Status

(b) Online Faults - To view information of various Online Faults as they occur in the stations where

the Dataloggers are connected

(c) Online Simulation - Graphical view of relay operations train movements etc

(d) Remote monitoring of stations with the help of NETWORKING

SOFTWARE OBJECTIVES (a) Predictive Maintenance

(b) Easy identification of failures

(c) Crew discipline

(d) Train charting

REMOTE MONITORING OF STATIONS WITH NETWORKING OF

DATALOGGERS The individual Dataloggers of various stations can be interconnected through networking technology

The data of Remote Panel stations can be viewed in a Computer at the Central Monitoring Station The data

of the network is collected by the FEP (Front End Processor) which in turn is transmitted to the computer

COMPONENTS OF NETWORK MANAGEMENT OF DATALOGGERS

(a) Datalogger at stations

(b) MODEM and Transmission medium

19 | P a g e

(c) Front End Processor (FEP)

(d) Central Monitoring Unit (CMU) Computer

FEP (FRONT END PROCESSOR)

FEP acts as a buffer between the Central Monitoring Unit (Computer) and the Network It is provided

at centralised place to retrieve data continuously from station dataloggers and store in memory and transfer to

computer on request It stores 10 Lac telegrams It works on 12V DC It draws 16A continuous current

when all the three modems are connected Normally it shows the number of packets pending to be sent to the

computer on its 7-segment LED display It is provided with MOTOROLA 68000 microprocessor It has 6-

nos of RS-232 communication ports such as COM1 COM2 COM3 COM4 COM5 and COM6 COM1 is

used for Fault Analysis System (FAS) ie Central Monitoring Unit (Computer) connection COM2 to COM6

are used for networking For Bi-directional 2- nos of ports and for Tri-directional (T-network) 3-nos of ports

are used

DATA TRANSMISSION Dataloggers can be networked in Uni-directional Mode or Bi-directional Mode or T ndash Network Mode

In case of loss of data retransmission of data takes place

(a) Uni-Directional Mode

Each Datalogger will send data in only one direction to the FEP Unidirectional mode network is not

preferred

(b) Bi-Directional Mode

Each end of Network is connected to FEP and each datalogger can now transmit data in both the directions

Bi-directional Mode is advantageous it enables the Data Transmission even in case of Network Failure

(c) T - Network Mode

If more no of stations are in network ie if the network is too lengthy then T- network mode is preferred

COMMUNICATION The communication protocol for transmitting data and command between datalogger and CMU is

standardized by the RDSO and is given in the Specifications of Dataloggers

(a) The type of communication used in the network is dependent on the distance between the dataloggers

(b) For shorter distances Opto Converter Box- Opto isolated current loop communication is used

(c) For longer distances Modem (Dial-up leased) Fiber Optic Satellite Microwave communication

MODEMS Modems are used for DATA transfer between Dataloggers and Front End ProcessorThese are

configured to RS 232 Serial Communication Network is connected with two types of 4-wire modems

(a) Internal modem card Dual Modem card (in-built)

It is fixed in datalogger Euro rack itself One card contains two modems The top modem is called

ANS (answer) modem and the bottom modem is called as ORG (originate) modem

Note In case of networking of Dataloggers connect lsquoANSrsquo modem to the lsquoORGrsquo modem of one adjacent

station and connect lsquoORGrsquo modem to the lsquoANSrsquo modem of other adjacent station

(b) External modems

20 | P a g e

These are generally used at FEP (Front End Processor) side to connect the Dataloggers

(i) To transfer Data from one datalogger to another datalogger FEP Baud rate is 9600bps

(ii) These modems are 4-wire line communication

(iii) To transfer the data from FEP to RMU (PC) the Baud rate is 57600 bps

There is no difference between these modems functionally

CENTRAL MONITORING UNIT (CMU) COMPUTER

Central monitoring unit (Fault Analysis Unit) is a Personal Computer and its minimum configuration

shall be specified by RDSO from time to time System Software Windows XPVista(OS) Norton Kaspersky

(Anti Virus) Interbase where Server is not available (DBMS) Oracle where Server is available (DBMS)

software are required to run Datalogger System It is provided with Graphical User interface (GUI) based

software and retrieve data from all Networked dataloggers (up to 32) at various stations It stores data in

standard data base files The CMU is capable of analyzing the data and generate reports audiovisual alarms

on defined conditions This data can be compressed to take backup In central monitoring unit Software used

for analysis of data prediction of faults etc is written in a structured format so that purchaser can

reconfigure it if required It displays the status of signaling gears at any selected time in graphic form for any

selected station yard It retrieves the stored data amp simulates train movement It sends commands to various

Dataloggers to activate audio visual alarm or operate and electromagnetic relay

CMU shares data available in it by other PCs through available local area network where this data can

be used for train charting passenger information purpose The system generates audiovisual alarm in

ASMrsquosSignal Maintainerrsquos room in the case of power supply failure (battery voltage low) or battery charger

defective with acknowledgement facility

(a) Each datalogger has its own identity code which will be transmitted along with data packet to central

monitoring unit

(b) Events recorded at each station are continuously transmitted to central monitoring unit Response time of

data transfer will not exceed 10 sec

21 | P a g e

22 | P a g e

OPTICAL FIBER CABLE

INTRODUCTION The demand for bandwidth on transmission networks is increasing rapidly because video and

graphical rich contents are exchanged through the corporate network or the Internet The Gigabit Ethernet

became ommonly used in the corporate network backbone and 10Gbit Ethernet will be adopted in the near

future Meanwhile in the home the demand for high-speed network becomes popular as the wide spread of

broadband access eg CATV xDSL and FTTH The transmission medium with capability to transmit high

bit rate signal is necessary to satisfy these requirements

The telecommunication transport technologies move from copper based networks to optical fiber

from timeslot based transport to wave length based transport from traditional circuit switching to terabit

router and all optical based networks entering into a new era of optical networking

BASIC PHYSICS OF OFC

OPTICAL FIBER CABLE OFC have Fibers which are long thin strands made with pure glass about the diameter of a human

hair OFC consists of Core Cladding Buffers and Jacket as shown in figure

MONOCHROMATIC LIGHT OR SINGLE COLOR LIGHT Light or visible light is electromagnetic radiation of a wavelength that is visible to the human eye (

about 400 ndash 700 nm) The word light is sometimes used to refer to the entire electromagnetic spectrum Light

is composed of elementary particles called photons Three primary properties of light are

Light can exhibit properties of both waves and particles This property is referred to as wave-particle

duality The study of light known as optics In free space light (of all wavelengths) travels in a straight path

at a constant maximum speed However the speed of light changes when it travels in a medium and this

change is not the same for all media or for all wavelengths By free space it is meant space that is free from

matter (vacuum) andor free from electromagnetic fields

Thus the speed of light in free space is defined by Einsteinrsquos equation E = mc2

Frequency ν speed of light in free space c and wavelength λ are interrelated by ν = cλ

From the energy relationships E = mc2 = hν and the last one an interesting relationship is obtained

the equivalent mass of a photon m = hνc2

When light is in the vicinity of a strong electromagnetic field it interacts with it From this interaction

and other influences its trajectory changes direction as shown in figure

23 | P a g e

INCIDENT RAY REFLECTED RAY AND REFRACTED RAY An incident ray is a ray of light that strikes a surface The angle between this ray and the

perpendicular or normal to the surface is the angle of incidence Reflection is the change in direction of a

wave front at an interface between two different media so that the wave front returns into the medium from

which it originated Common examples include the reflection of light sound and water waves

The reflected ray corresponding to a given incident ray is the ray that represents the light reflected by

the surface The angle between the surface normal and the reflected ray is known as the angle of reflection

The Law of Reflection says that for a specular (non-scattering) surface the angle of reflection always equals

the angle of incidence The refracted ray or transmitted ray corresponding to a given incident ray represents

the light that is transmitted through the surface The angle between this ray and the normal is known as the

angle of refraction and it is given by Snells Law

The figure shows Incident ray Reflected ray Refracted ray the angle of incidence and angle of refraction

REFRACTIVE INDEX - Refractive index is the speed of light in a vacuum ( c =299792458kmsecond) divided by the speed

of light in a material ( v ) Refractive index measures how much a material refracts light Refractive index of

a material abbreviated as lsquo n lsquo is defined as lsquo n=cv lsquo Light travels slower in physical media than it does

when transmitted through the air Refractive index (n) is a function of molecular structure of matter optical

frequency optical intensity determines optical propagation properties of each wavelength ( λ ) may not be

distributed equally in all directions is affected by external temperature pressure and fields

Refractive index of a medium is a measure for how much the speed of light is reduced inside the

medium For example typical glass has a refractive index of 15 which means that light travels at 1 15 =

067 times the speed in air or vacuum Two common properties of glass and other transparent materials are

directly related to their refractive index

First light rays change direction when they cross the interface from air to the material and effect that

is used in lenses and glasses

Second light reflects partially from surfaces that have a refractive index different from that of their

surroundings

SNELLrsquoS LAW-

24 | P a g e

When light passes from one transparent material to another it bends according to Snells law which

is defined as n1sin(θ1) = n2sin(θ2)

where n1 is the refractive index of the medium the light is leaving θ1 is the incident angle between the light

beam and the normal (normal is 90deg to the interface between two materials)

n2 is the refractive index of the material the light is entering

θ2 is the refractive angle between the light ray and the normal

Snellrsquos law gives the relationship between angle of incidence and angle of refraction

For the case of θ1 = 0deg (ie a ray perpendicular to the interface) the solution is θ2 = 0deg regardless of

the values of n1 and n2 That means a ray entering a medium perpendicular to the surface is never bent The

above is also valid for light going from a dense (higher n) to a less dense (lower n) material the symmetry of

Snells law shows that the same ray paths are applicable in opposite direction

TOTAL INTERNAL REFLECTION- When a light ray crosses an interface into a medium with a higher refractive index it bends towards

the normal Conversely light traveling cross an interface from a higher refractive index medium to a lower

refractive index medium will bend away from the normal

This has an interesting implication at some angle known as the critical angle θc light traveling from

a higher refractive index medium to a lower refractive index medium will be refracted at 90deg in other words

refracted alon g the interface If the light hits the interface at any angle larger than this critical angle it will

not pass through to the second medium at all Instead all of it will be reflected back into the first medium a

process known as total internal reflection

The critical angle can be calculated from Snells law putting in an angle of 90deg for the angle of the refracted

ray θ2 This gives θ1

Since θ2 = 90deg

So sin(θ2) = 1

25 | P a g e

Then θc = θ1 = arcsin(n2n1)

For example with light trying to emerge from glass with n1=15 into air (n2 =1) the ritical angle θc is

arcsin(115) or 418deg For any angle of incidence larger than the critical angle Snells law will not be able to

be solved for the angle of refraction because it will show that the refracted angle has a sine larger than 1

which is not possible In that case all the light is totally reflected off the interface obeying the law of

reflection

OPTICAL FIBER MODE An optical fiber guides light waves in distinct patterns called modes Mode describes the distribution

of light energy across the fiber The precise patterns depend on the wavelength of light transmitted and on the

variation in refractive index that shapes the core In essence the variations in refractive index create

boundary

conditions that shape how light waves travel through the fiber like the walls of a tunnel affect how sounds

echo inside

We can take a look at large-core step-index fibers Light rays enter the fiber at a range of angles and

rays at different angles can all stably travel down the length of the fiber as long as they hit the core-cladding

interface at an angle larger than critical angle These rays are different modes Fibers that carry more than

one mode at a specific light wavelength are called multimode fibers Some fibers have very small diameter

core that they can carry only one mode which travels as a straight line at the center of the core These fibers

are single mode fibers This is illustrated in the following picture

OPTICAL FIBER INDEX PROFILE Index profile is the refractive index distribution across the core and the cladding of a fiber Some

optical fiber has a step index profile in which the core has one uniformly distributed index and the cladding

has a lower uniformly distributed index Other optical fiber has a graded index profile in which refractive

index varies gradually as a function of radial distance from the fiber center Graded-index profiles include

power-law index profiles and parabolic index profiles The following figure shows some common types of

index profiles for single mode and multimode fiber

26 | P a g e

OPTICAL FIBERrsquoS NUMERICAL APERTURE ( NA )- Multimode optical fiber will only propagate light that enters the fiber within a certain cone known as

the acceptance cone of the fiber The half-angle of this cone is called the acceptance angle (see figure 18)

θmax For step-index multimode fiber the acceptance angle is determined only by the indices of refraction

Where

n is the refractive index of the medium light is traveling before entering the fiber

nf is the refractive index of the fiber core

nc is the refractive index of the cladding

NUMBER OF MODES IN A FIBER - Modes are sometimes characterized by numbers Single mode fibers carry only the lowest-order

mode assigned the number 0 Multimode fibers also carry higher-order modes The number of modes that

can propagate in a fiber depends on the fiberrsquos numerical aperture (or acceptance angle) as well as on its

core diameter and the wavelength of the light For a step-index multimode fiber the number of such modes

Nm

Where

D is the core diameter

λ is the operating wavelength

NA is the numerical aperture (or acceptance angle)

MODE FIELD DIAMETER - All light do not travels through the core of the fiber but is distributed through both the core and the

cladding The mode field is the distribution of light through the core and cladding of a particular fiber

Mode-Field Diameter (MFD) defines the size of the power distribution When coupling light into or out of a

fiber MFD is important in understanding light loss

27 | P a g e

ADVANTAGE OF OFC COMMUNICATION - bull More information carrying capacity Fibers can handle much higher data rates than copper More

information can be sent in a second

bull Free from Electromagnetic and Electrostatic interference Being insulator no electric current flows through

the fibre and due to this reason fibres neither radiate nor pick up electro - magnetic radiation So WPC

CLEARANCE is not required

bull Low attenuation 025 dbkm at 1550 nm Loss in twisted pair and coaxial cable increases with frequency

where as loss in the optical fibre cable remains flat over a wide range of frequencies

bull Use of WDM ndash Switching routing at Optical signal level

bull Self healing rings under NMS control

bull Small size makes fibre cable lighter in weight So easy to handleOptic fibre cable weight (approx)

500 kg km Copper cable weight (approx) 1000 kgkm

The reasons are photons of light in a fibre

do not affect each other as they have no electrical charge and they are not affected by stray photons outside

the fibre But in case of copper electrons move through the cable and these are affected by each other

Optical fibre does not carry any electricity even if the cable is damaged or short circuited it does

not cause any spark or fire hazard

As the fibre do not radiate energy it can not be detected by any nearby antenna or any

other detector The fibres are difficult to tap and therefore excellent for security

As the signal transmission is by digital modulation there is no chance of cross talk in

between channels

Only by adding a few additional terminal and repeater equipments the

capacity of the system can be increased at any time once the cable is laid

ical effects and temperature variations

LIMITATIONS OF OFC -

difficult

- utilised

APPLICATION IN SIGNAL AND TELECOMMUNICATIONS transmission circuits

-haul circuits for linking of telephone exchanges

28 | P a g e

PROPAGATION MODES CONCEPT -

MODE - Mode is an available distribution of electromagnetic field in a plane transverse to the direction of

light propagation Each mode is characterized by frequency polarization electric field strength and

magnetic field strength Available patterns are derived from Maxwellrsquos equations and boundary conditions

LINEARLY POLARIZED (LP) MODE A mode for which the field components in the direction of propagation are small compared to

components perpendicular to that direction An optical fibre supports only different field patterns called as

lsquoLinear Polarizedrsquo or lsquo LPrsquo modes The reasons are

requirements

de

the accrual of power carried by different modes

There are two basic types of fiber Multimode fiber and Single-mode fiber

Multimode fiber is best designed for short transmission distances This is suited for used in LAN systems and

video surveillance Single mode fibre is best designed for longer transmission distances This is suitable for

long distance telephony and multi channel television broadcast systems

29 | P a g e

MULTI MODE FIBER Multimode fiber the first to be manufactured and commercialized simply refers to the fact that

numerous modes or light rays are carried simultaneously through the waveguide Modes result from the fact

that light will only propagate in the fiber core at discrete angles within the cone of acceptance MM fiber type

has a much larger core diameter compared to single-mode fiber allowing for the larger number of modes

and

is easier to couple than single-mode optical fiber Multimode fiber further categorized as Multimode step-

index and Multimode graded index fiber

PROPAGATION THROUGH MMSI FIBER Figure shows the principle of total internal reflection applies to multimode step index fiber Because

the corersquos index of refraction is higher than the claddingrsquos index of refraction the light that enters at less than

the critical angle is guided along the fiber

Three different light waves travel down the fiber One mode travels straight down the center of the

core A second mode travels at a steep angle and bounces back and forth by total internal reflection The third

mode exceeds the critical angle and refracts into the cladding Naturally it can be seen that the second mode

travels a longer distance than the first mode causing the two modes to arrive at separate times

PROBLEMS WITH MMSI FIBER AND SOLUTION This disparity between arrival times of the different light rays is known as dispersion and the result is

a muddied signal at the receiving end It is important to note that high dispersion is an unavoidable

characteristic of multimode step-index fiber The solutions are either use Graded index fiber or Single mode

fiber

PROPAGATION THROUGH MMGI FIBER Multimode Graded-index refers to the fact that the refractive index of the core gradually decreases

farther from the center of the core The increased refraction in the center of the core slows the speed of some

light rays allowing all the light rays to reach the receiving end at approximately the same time reducing

dispersion Figure shows the Light propagation principle through multimode graded-index fiber The corersquos

central refractive index ( nA ) is greater than that of the outer corersquos refractive index ( nB )

It is very clear from the figure the light rays no longer follow straight lines they follow a serpentine path

being gradually bent back toward the center by the continuously declining refractive index This reduces the

arrival time disparity because all modes arrive at about the same time The modes traveling in a straight line

30 | P a g e

are in a higher refractive index so they travel slower than the serpentine modes These travel farther but

move faster in the lower refractive index of the outer core region

PROPAGATION THROUGH SMSI FIBER Single mode fiber has a much smaller core that allows only one mode of light at a time to propagate

through the core The figure shows the single mode fiber

Single-mode fiber exhibits no dispersion caused by multiple modes Single-mode fiber also offers lower fiber

attenuation than multimode fiber Thus more information can be transmitted per unit of time because it can

retain the fidelity of each light pulse over longer distances Like multimode fiber early single-mode fiber was

generally characterized as step-index fiber meaning the refractive index of the fiber core is a step above that

of the cladding rather than graduated as it is in graded-index fiber Modern single-mode fibers have evolved

into more complex designs such as matched clad depressed clad and other exotic structures

SINGLE-MODE FIBER DISADVANTAGES The smaller core diameter makes coupling light into the core more difficult The tolerances for single-

mode connectors and splices are also much more demanding

CUTOFF WAVE LENGTH - Cutoff wavelength is the wavelength above which a single-mode fiber supports and propagates only

one mode of light In other words an optical fiber that is single-mode at a particular wavelength may have

two or more modes at wavelengths lower than the cutoff wavelength The effective cutoff wavelength of a

fiber is dependent on the length of fiber and its deployment The longer the fiber the lower is the effective

cutoff

wavelength The smaller the bend radius of a loop of the fiber the lower is the effective cutoff wavelength If

a fiber is bent in a loop the effective cutoff wavelength is lowered

SIGNAL ATTENUATION IN FIBER - Optical fiber has a number of advantages over copper However it also suffers from degradation

problems which can not be ignored The first of these is loss or attenuation Attenuation is typically the result

of two sub properties They are scattering and absorption Both of which have cumulative effects The second

is

dispersion which is the spreading of the transmitted signal and is analogous to noise

SCATTERING Scattering occurs because of impurities or irregularities in the physical construction of the fiber The

well known form of scattering is Rayleigh Scattering It is caused by metal ions in the silica matrix and

results in light rays being scattered in various directions

31 | P a g e

Scattering limits the use of wavelengths below 800nm The short wavelengths are much affected than longer

wavelengths It is because of Rayleigh scattering that the sky appears to be blue ( shorter wave length ) The

shorter wavelengths ( blue ) of light are scattered more than the longer wavelengths of light

ABSORPTION Absorption results from three factors They are hydroxyl ions ( OH- water ) in the silica impurities

in the silica and incomplete residue from the manufacturing process These impurities tend to absorb the

energy of the transmitted signal and convert it to heat resulting in an overall weakening of the signal The

Hydroxyl absorption occurs at 125 and 139 micro The silica itself starts to absorb energy at 17 micro

because of the natural resonance of the silicon dioxide

MACRO BENDING LOSS Macro-bending loss is caused by bending of the entire fiber axis The bending radius shall not be

sharper than 30d where d is diameter of cable A single bend sharper than 30d can cause loss of 05dB

The fiber may break if bending is ever sharper

MICRO BENDING LOSS Micro-bending loss is caused by micro deformations of fiber axis which leads to failures in achieving

total internal reflection conditions Micro-bends are small scale perturbations along the fiber axis the

amplitude of which are on the order of microns These distortions can cause light to leak out of a fiber

Micro-bending may be induced at very cold temperatures because the glass has a different coefficient of

thermal expansion from the coating and cabling materials At low temperatures the coating and cable

become more rigid and may contract more than the glass Consequently enough load may be exerted on the

glass to cause micro bends

Coating material is selected by manufacturers to minimize loss due to micro-bending The linear thermal

expansion coefficient of coating material shall be compatible with that of fiber

32 | P a g e

DISPERSION Dispersion is the optical term for the spreading of the transmits in the fiber It is the bandwidth

limiting phenomenon and comes in two forms Multimode dispersion and chromatic dispersion Chromatic

dispersion is further subdivided into material dispersion and waveguide dispersion

DISPERSION PHENOMENON IN OPTICAL FIBER Dispersion is the time distortion of an optical signal that results from the differences of time of travel

for different components of that signal typically resulting in pulse broadening As the distance traveled by

the signal is more broadening of pulse is more In digital transmission dispersion limits on the maximum

data rate and the maximum distance ie the information-carrying capacity of a fiber link The interference

from broadened pulse in the next interval shall not lead to erroneous interpretation of received signal

OPTICAL DOMAIN Understanding where attenuation and dispersion problems occur helps optical design engineers

determine the better wavelengths at which information can be transmit taking into account distance type of

fiber and the other factors which can severely affect the integrity of the transmitted signal The graph shown

depicts the optical transmission domain as well as the areas where problems arise The wavelength (nm)

is shown on X-axis and attenuation ( dBkm) is shown on Y-axis

There are four transmission windows appear in the figure The first one is at around 850 nm the

second at 1310nm third at 1550 nm and fourth at 1625 nm The last two labeled as C and L band

respectively The 850 nm wavelength at which the original LED technology operated The second window at

1310 nm has low dispersion The 1550 nm called as C-band is ideal wavelength for long haul

communication systems The network engineers can avoid transmitting signal at 1000 nm where Rayleigh

scattering 1240 and 1390 nm where hydroxyl absorption by water occurs to avoid high degree of loss

Optical fibers also can be manufactured to have low dispersion wavelength in the 1550nm region

which is also the point where silica-based fibers have inherently minimal attenuation These fibers are

referred to as dispersion-shifted fibers and are used in long-distance applications with high bit rates For

33 | P a g e

applications utilizing multiple wavelengths it is undesirable to have the zero dispersion point within the

operating

wavelength range

34 | P a g e

SIGNALLING RELAYS

INTRODUCTION A relay is an electromagnetic device which is used to convey information from one circuit to another

circuit through a set of contact ie front or back contact Constructional and electrically relays may be

divided into DC and AC relays because the means by which the electrical energy in the coil is converted in

to mechanical Energy in order to move the contacts are fundamentally different In DC type the contacts are

carried on an armature forming part of a magnetic circuit in which a field is set up by the current flowing in

the coils In AC types the contacts are attached by a link mechanism to a metal sector disc or cylinder in

which currents are induced by the alternating magnetic field produced by the currents in the coils

Every endeavor has been made to explain the action of each type of relay in the simplest possible manner

Relays are sophisticated switch gears used for remote control and succession control of various

electrical equipment In present days they are widely used because they are capable of protecting the

controlled equipment from cross feeding and overloading even as they cater for speedy operations

Most of the relays in present day signaling are electromagnetic devices although some of the relays control

circuits through electronic components like diodetransistors Integrated Chips etc

Railway signaling relays are unique in that

(a) They operate on low voltage and current

(b) They are more articulate as according to their special features they can work under restrictive conditions

and in any specified manner Virtually they can cater for all situations while contributing to speed and

accuracy in operations

CLASSIFICATION OF SIGNALLING RELAYS (a) According to the method of their mounting or fixture they are classified as

(i) Shelf type Relays which are loosely kept on shelves

(ii) Plug in type Relays which are plugged into a pre- wired plug boards

(b) According to their connection and usage they are classified as

(i) Track relays Relay which is directly connected to the track to detect the presence of vehicle

(ii) Line Relays Other than track relay all are line relays Relays connected to the selection circuit

(c) According to their vitality or importance in ensuring train working safety they are classified as

(i) Vital Relays All relays used for traffic control such as signal point controls track detection etc

(ii) Non-vital Relays Relays which operate control aids and accessories like warnings buzzers

Indications etc

(d) According to their special provisions to ensure reliability of their contacts they are classified as

(i) Proved type are those whose normalization after each operation shall be proved in circuit

controlled by their contacts Contacts in which both the springs have metal surfaces on their tips They may

get fused due to high sparking current across them during operation These may prevent relay normalization

and causes unsafe condition in traffic control To avoid this proving of relay normalization after each

operation is necessary

(ii) Non - proved type Need not to be proved to have been normalized after each operation as their

contacts have at least one non-fusible contact (carbon contact)

(e) According to their feed source relays are broadly classified as

(i) DC relays The relay which requires DC power supply for its operations are called DC relays Among

the DC relays

o DC neutral relays This relay closes the same set of contacts on energization with Normal polarity

or Reverse polarity supply

o Polar Relays This relay closes different set of contacts when energized with Reverse polarity

supply They may or may not have contact to close when deenergized

35 | P a g e

(ii) AC Relay AC Induction motor track relays Time element relays flashing indication control etc

(iii) Electronic Relays DC relays with electronic components in them are called electronic relays

DC NEUTRAL RELAY Each Relay has usually one or two coils with a hollow center to accommodate a coreThe coils are

made up of a large numbers of turns of small gauge soft drawn copper wire The two coils can be connected

in series or parallel according to the requirement of relay resistance The ends of the coils are terminated on

binding post to which the control wires are connected Each coil is placed around a core of specially selected

Iron or steel having high permeability and low retentivity The core should be susceptible to magnetism and

at the same time should have little residual magnetism The cores are connected at the top by a yoke to

complete the magnetism coupling between two ends of coils The bottom of each core is equipped with a

large steel or Iron block known as pole piece or face

A flat piece of Iron or steel called armature is supported by brackets which are securely fastened to

the pole piece The armature yoke and the pole pieces are also made of specially selected iron or steel of the

same quality as the core The armature carries the metallic spring contacts which are insulated from it

The circuit through the coils of the relay is closed It sets up a magnetic flux through the core yoke and the

armature The flux passing between the armature and pole faces causes the armatures get attracted to the pole

faces and armature picks up and closes front contacts When the circuit is opened the magnetic flux collapses

and the armature drops away by gravity from the pole faces the front contacts break and back contacts close

The front and back contacts of the relay can be utilised to make or break other circuits Two stop pins of

nonmagnetic material are fixed either on the armature or pole faces so that the armature cannot

come in contact with the pole faces It is essential to maintain a small air-gap between the armature and pole

faces so that low value of residual magnetism may not retain the armature in picked up position and causes

the relay to fail to drop away with a break in its control circuit

GENERAL USAGE

DC Neutral line relays are most commonly used for Railway Signalling controls and detection

Among them plug-in type relays are preferred in larger installations for space considerations Shelf type

relays are also in use mostly in wayside stations

There are many DC Neutral line relays in use with special features such as

(i) Delayed operation

(ii) Biased DC control

(iii) DC control unaffected by AC interference currents

(iv) Getting latched in operated condition till further feeding and others

Usage of DC polar relays is mostly in conjunction with block instruments that control traffic between

stations AC line relays are almost extinct in installations of British Signalling practice They are however

used for time control operations flashing indication control and such other special purposes in installations

with Siemens signalling practice widely Track relays are used according to the type of track detection

circuits chosen for a given location and context While most of the track circuits are still of the DC working

type requiring DC neutral track relays with them the prospects of their being replaced with Electronic track

circuits directly feeding DC line relays in future are great AC Track Circuits are used in DC Traction area

as conventional DC Track Circuits are not suitable there AC Track relays are used with them almost all of

the induction motor type In the British practice of signalling which was first introduced on Indian Railways

non-proved type relays with carbon to metal switching contacts are generally used for vital controls

They facilitate simple circuit designs But with the advent of German Practice introduced by Ms

Siemens later proved type relays with all metal to metal contacts are widely accepted in spite of

complications in circuit design caused by them A recent introduction is that of the same type relays made by

Ms Integra control However for some time now the appreciable features of both the practices are getting

36 | P a g e

incorporated together in the indigenous designs of signalling by railwaymen With this the usage of all types

of relays anywhere can be found without straight jacketed segration of relay types

CHARACTERSTIC OF ELECTRO-MAGNETIC RELAY The following are the characteristic of electro-magnetic relays A brief study of them helps in

understanding the choice of their components and designs features

1) Force of attraction

2) Effect of air gap

3) Effect of Hysterisis

4) Transient condition

FORCE OF ATTRACTION In any electro-magnetic system the force of attraction is given by

Where B - is the flux density a - is the cross sectional area of the particular part of the magnetic

circuit

In the case of a DC neutral Relay B is proportional to the current that is flowing in the coil

surrounding the electro-magnet and thus the force of the attraction is directly proportional to the square of the

current This square relationship has its own advantage especially in the case of DC track relay in that a

small reduction in the current will have a great effect on the working of the relay Also for a given change of

current the make and the break will be quicker with lesser possibility of arcing

EFFECT OF AIR GAP

Curve lsquoArsquo is magnetisation curve for the iron and is all practical purpose a straight line up to the

saturation point Curve lsquoBrsquo is the magnetisation curve for the open-air gap which is a straight line through

out because per magnetisation curve of the whole

magnetic circuit of the relay and for a given force is the sum of the amp-turns for the iron part and the amp-

turns for the air gap

When the front contacts are open the force required to pick up the armature is shown on curve lsquoCrsquo to be F1

but after the armature has operated it will be separated from the core by stop pins In this position the amp-

turns required to maintain the armature is less as indicated by the dotted line from 1 on curve C to 2 on curve

37 | P a g e

F But actually the current in the coil is unaltered the force on the armature is greater than required as

indicated at 3 on curve F Part of this extra force is used to flex the front contacts sufficiently to give good

contact pressure when it is in energised position

The difference between the pick-up and the drop-away current should be as small as practicable in

track relay to ensure good shunting characteristics This is achieved firstly by the choice of good quality relay

iron and secondly by having a small air gap between armature and core If the air gap is not available then

the residual magnetism fluxes might cause the armature to be retained when the supply is disconnected For

this reason residual pins are provided to ensure a definite minimum air gap in the energised position

EFFECT OF HYSTERISIS

Hysterisis is the property by which the flux produced lags behind the current In the de-energized

condition there will be small residual flux in the core When the voltage is applied to the coils the current in

rising to its steady value first causes the flux to rise from 1 to 2 along the curve At this point the flux density

will be sufficient to attract the armature and reduce the air gap the flux then raise to 3 and continue to 4

which corresponds to the steady current in the coils When the voltage is disconnected the current in falling

caused the flux to fall from 4 to 5 along the curve At this point the flux density will fall below the value

required to maintain the armature which will release thus increasing the air gap and reducing the flux to 6

Finally the

flux will decrease from 6 to 1 where the current will again be zero

The relay core is made of material having high permeability and low retentivity As mentioned in

the IRS specification Electromagnet iron may be in the form of a

(a) Bar of silicon steel

(b) Best Yorkshire wrought iron

(c) Swedish charcoal iron

(d) Electrical steel sheets

` This reduces the difference between pick up value and Drop away value By selecting good quality

core material Percentage release and sensitivity of the relay will be improved

TRANSIENT CONDITION

38 | P a g e

When the voltage is applied or disconnected from the coils it takes some little time before the current

become steady These are known as transient conditionsrdquo and are important so far as track relays are

concerned When the voltage is first applied to the coils the magnetic flux in rising cuts the turns on the

coils and in so doing produces a back EMF that opposes the applied voltage and retards the growth of

current

The growth and decay of flux are decided by the relationship between the inductance and resistance

in the circuit is known as time constant It is not fixed quantity in the case of DC neutral relay This value of lsquo

Lrsquo is less when the relay is in de-energised condition (L1) than when the relay is in energised condition (L2)

The magnitude of flux that is established for a given change of current is different in two cases

When the current reaches the pick up value the armature closes and the inductance is increased to L2

due to reduced air gap the flux per amp is increased The increase in flux increased the back EMF during the

movement of the armature after which the current continuous to raise along a new curve corresponding to the

increased inductance until it reaches the final value (ER) This process is indicated above in fig24

When the supply is disconnected the current is obliviously reduced to zero immediately but the flux

decay comparatively slowly owing to the eddy currents produced in the core by the rapid flux change which

tend to maintain the flux The drop away time on a disconnection is however generally negligible See fig

below

If the relay releases due to the reduction in current from say I 2 to I 1 caused by the application of

shunt resistance (as in the case of track relay ) the time taken is much longer than the relay is simply

disconnected The rate of rise or fall of current during the transient conditions is also depends on exterior

circuit values because L and R apply to the whole circuit The production of eddy current in the core the flux

will decay at a slower rate than the current So that the actual release time will be a little longer than it takes

the current to fall to the release

L= Inductance

39 | P a g e

R= Resistance

It is now clear that to reduce releasing time to a minimum it is necessary that

- The relay iron should have low Hysterisis loss and low retentivity

- The degree of over energization of the relay should be restricted

- Connecting a suitable external resistance in series with the relay to keep LR ratio low

In non RE area for track circuit length less than 100M 9 ohm track relay only to be used Using relay

with minimum contacts as they require lesser current which keeps inductance value low

Train working safety is ensured only if the track relay of shortest length track circuit is released

before a light engine running at a highest permitted speed clears it Otherwise the track circuit occupation

may go undetected To avoid this a special provision has to be made in signal control circuits wherever

necessary

The following methods may be adopted for reducing the time lag of track relay

(a) Restrict the over energisation of relay since the release time depends on the initial working current

(b) Connecting a suitable external resistance in series with the relay to keep the LR ratio low

(c) Using relays with minimum contacts as they require lesser operating current keeping the inductance

value low

40 | P a g e

CONCLUSION

Modern signalling is vital for safe and punctual movements of trains In the Indian railways The Signalling

and Telecommunication Department is responsible for providing modern effective and relaible signalling

systems as well as telecommunication systems

The first mode of communication used in Indian Railways was the use of electric telegraph

with the help of Morose code Morose code is the method of providing text information as a series of on-off

tones and lights or clicks that can be directly understood by a skilled listener or observer without special

equipmentEach character (letter or numeral ) is represented by a unique sequence of dots and dashes Later

this system becomes obselete and beggan the era of wireless communication which operated at audio level

frequency range

In wireless communication the significant advances took place the transition to miniature

valves or filament tubesBut this was abandoned too because of excessive current consumption and over

heating of the filament tubes

Fibre-optic communication is a method of transmitting information from one place to another by

sending pulses of light through an optcial fibreThe light forms an electromagnetic carrier wave that is

modulated to carry information First developed in the 1970s fibre optic communication systems has

revolutionized the telecommunications industry and have palyed a major role in the advent of the information

age Because of its advantages over electrical transmissionsoptical fibres have largely replaced copper wire

communications in core networks in the developed world The Indian Railways too is undergoing a transition

from Microwave communication to fibre optic communications

41 | P a g e

BIBLIOGRAPHY AND REFERENCES

1 wwwwikipediacom

2 wwwbritaniccacom

3 wwwirfcacom

4 Motorola GP60 system manual

5 Harris FAS 7000 manual

6 TOSHIBA Manual

1 | P a g e

SOLID STATE INTERLOCKING

INPUT CARDS All the field conditions (ie Field relay contacts) are connected to these input cards of EI system

The maximum inputs capacity of each RI card will depend on design of the RI cards by different

manufacturers The total number of inputs will depend on the yard layout

Total inputs means

Field inputs ECRs TPRs NWKR etc

Panel inputs GNs UNs NWNs RWNs etc

Read back inputs HR DR WNR WRR etc

Opto couplers are provided to isolate field optically from the system in Input cards These cards will read the

conditions of inputs and passes the information to EI system

PROCESSOR CARD This card is also called as central processing unit card of the System This is provided with microprocessor

RAM ROM EPROM EEPROM Memory ICrsquos These EEPROMS or EPROMrsquos (ROMrsquos) are programmed

with software required for executing the system commands

System software consists of the following

- Executive software programmed in system EPROMrsquos

- Application software programmed in DATA EPROMrsquos

-

EXECUTIVE SOFTWARE This software is common to all EIrsquos for the same company manufacturing

This is a factory installed software

Performs all operations

Cuts off vital supply voltage to output relays in case of unsafe failures

2 | P a g e

APPLICATION SOFTWARE This software is specific to each station and different for different stations

This is as per table of control of specific station

Can be installed at site by signal engineers

Logic installed through Boolean expressions or user-friendly equations

OUTPUT CARD (RELAY DRIVE CARD) This card receives the output of CPU card as input and picks up relevant output relay as per the panel

operatorsrsquo request The output of this card is terminated on phoenix terminals from there the output relays are

connected

The essential modules of an EI is as follows

Hardware module

Software module

HARDWARE MODULES USED IN THIS SYSTEM Equipment consists of

CARD FILE

Each card file is like a shelf having 20 Slots to accommodate various PCBs that are used in a system

Slot nos1 to 15 and 20 are used to accommodate Non-vital Input-output or Vital Input or Vital Output PCBs

Slot no16amp17 are used to accommodate Power supply PCB Slot no18amp19 are used to accommodate CPU

PCB In this cardfile a mother board is available in the rear side connecting all the 20 Slots This cardfile is

suitable to mount on a 19rdquo rack

Power

Supply

Card

CPU

Card

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19

20

CPU PCB Each card file to have one CPU PCB and always placed in slot no18amp19 In this card Micro

Controller used is Motorola 68332 and its speed is 21 MHz In this card 4 nos of flash EPROMs of 8 MB

are used to store executive and application software Two nos of fast Static RAM (each 64KB) are used to

process the vital data and Four nos of Static RAM (each 64KB) are used to store events and errors

The main functions of CPU is it monitors continuously status of Vital Boards It also monitors

system internal operation for faults and responds to detected faults It processes application logic based on

inputs

received and deliver outputs to drive external gears It records system faults and routine events in user-

accessible memory It monitors and controls the serial communication ports It controls power to vital outputs

through external VCOR relay

POWER SUPPLY PCB

3 | P a g e

Each card file to have one Power Supply PCB and always placed in slot no16amp17 Power supply

PCB is basically a DC-DC converter that converts 12V DC input supply is +12V -12V and +5V required for

various board functioning Based on diagnostic check by CPU Power Supply Card receives 250Hz signal

from CPU and extends supply to VCOR relay This card provides isolated supply to internal circuit

VITAL OUTPUT PCB Each Vital Output PCB has 16 Outputs It is available in 12V and 24V DC applications Each Vital

Output can drive an output device such as any Q-series relay This output relay in turn controls signals

points crank handle siding control level crossing etc Since Vital Output drives the relay which controls

important outdoor gears all the Vital Output boards are continuously diagnosed by a CPU Any abnormality

in any of the outputs will shut down the system to ensure safety

VITAL INPUT PCB Each Vital Input PCB has 16 Inputs It is available in 12V and 24V DC applications Each Vital Input

is assigned to read the status of outdoor gears such as Track circuits Point detectors Crank handles Siding

controls level crossing etc Since the Vital Inputs read the status of outdoor gears they are normally

configured with double cutting arrangement using relay contacts

NON-VITAL INPUTOUTPUT PCB Each Non-vital IO has 32 inputs and 32 outputs in one PCB It is available in 12V and 24V DC

applications Non-vital inputs are Panel push buttons and keys Non-vital outputs are Panel indication LEDs

counters and buzzers The status of Non-vital Inputoutput is known from LED indications available in front

of the card

VITAL CUT OFF RELAY- VCOR Each card file will have one VCOR to ensure the healthiness of the system VCOR has 6 FB

dependent contacts each rated for 3 Amps When system is healthy the coil receives voltage from Power

Supply PCB which in turn controlled by CPU Power to Vital output board is controlled by VCOR thus

ensuring safety

WIRING HARDWARE 48 Pin Address select PCB and Connector assembly is provided for Vital Input and Vital Output

cards 96 Pin Address select PCB and Connector assembly is provided for Non-Vital IO cards 48 Pin

Connector Assembly is provided for PS and CPU PCB EEPROM PCB which is provided on rear side of the

CPU connector to configure various serial communication ports Keying plugs are provided in the cardfile to

ensure coding to each type of cards

SOFTWARE MODULES USED IN THIS SYSTEM System software consists of the following

EXECUTIVE SOFTWARE This software is common to all EIrsquos for the same company manufacturing

This is a factory installed software

Performs all operations

Cuts off vital supply voltage to output relays in case of unsafe failures

APPLICATION SOFTWARE This software is specific to each station and different for different stations

This is as per table of control of specific station

Can be installed at site by signal engineers

Logic installed through Boolean expressions or user-friendly equations

4 | P a g e

A GEC-MANUFACTURED SSI INTERLOCKING CUBICLE

A PAIR OF DATA LINK MODULES

TRACKSIDE FUNCTIONAL MODULE

5 | P a g e

INTEGRATED POWER SUPPLY

INTRODUCTION A typical 4 line station requires power supplies of 24 V DC( 5 nos ) 12 VDC ( 5nos ) 6V (2 nos)

110 V DC and 110 V AC for signalling These require as many chargers and Secondary cells amp Invertors

requiring more maintenance amp spares Can they be Integrated in to one system

Thus the concept of Integrated Power Supply has been evolved by integrating concepts One Charger

One set of Battery Bank feeding Invertors and DC- DC converters for deriving various DC amp AC

voltages Integrated power supply system delivers both AC amp DC Power supplies as an output with the

output voltage tolerance of plusmn 2

ADVANTAGES Reduces maintenance on Batteries Battery charger amp overall maintenance

Its construction is in modules and hence occupies less space Reduced space requirement resulting in

saving of space for power supply rooms

Provides centralized power system for complete signaling installation with continuous display of

working status of system for easier monitoring

Defect in sub-units of system is shown both by visual amp audible indication Reflects the condition of

battery with warning

Replacement of defective modules is quick amp easy without disturbing the working of the system

It uses (n+1) modular technology hot standby arrangement and hence high reliability and more

availability of the system

The system provides uninterrupted supply to all signalling system even during the power failures

Thus No blank Signal for the approaching drivers

System can be easily configured to suit load requirement

The diesel generator set running (Non-RE area) is reduced almost to lsquoNILrsquo Hence low wear and tear

of DG set components amp reduced diesel oil consumption

COMPONENTS (a) Un-interrupted power supply (U P S)

(i) SMPS Battery chargers with Hot stand-by mode

(ii) Hot Standby PWM Inverters with auto changeover

(iii) CVT Regulator [FRVS]

(b) AC distribution board [ACDB]

(i) STEP DOWN TRANSFORMERS

(c) DC distribution board [DCDB]

(i) DC-DC converters

WORKING IPS works satisfactorily for AC input variation of 150V AC to 275V AC with single-phase power supply

and frequency variation from 48 Hz to 52 Hz The input is fed to SMPS charger which converts in to 110

VDC as output It is fed as input to three sub units

To battery bank charging the batteries

To ON line inverters that converts 110 VDC in to 230 VAC plusmn 2as output

6 | P a g e

As 110 VDC bus bar to DC Distribution Panel as an input to various DC-DC converters located in

it

A 110 V Battery Bank of VRLA cells are connected to SMPS Panel IPS Status Monitoring Panel is

located at ASM room or at SampT staff room if round the clock SampT staff is available at Station

CONSTRUCTION IPS mainly consists of

SMR (Switch Mode Rectifier) Panel SMPS based Float cum Boost Charger (FRBC) Panel

AC Distribution Panel

DC Distribution Panel

Battery Bank (110V DC)

Status Monitoring Panel

SMR (SWITCH MODE RECTIFIER) PANEL SMPS BASED FLOAT

CUM BOOST CHARGER (FRBC) PANEL It consists of SMR FRBC modules and Supervisory amp Control Unit SMPS based SMRs

(converters) SMPS based Float cum Boost Chargers (FRBC) modules are provided with (n+1) modular

technology hot standby arrangement with active load sharing basis and 1 additional module as a cold standby

(n+2) Supervisory amp Control Unit which controls and monitor the complete system It has various

indications on the panel reflecting the working of the panel

FRBCs are suitable for operating in parallel on active load sharing basis with one or more modules of similar

type make and rating

n = required no of modules to cater for actual current requirement

AC DISTRIBUTION PANEL It is made of ON-Line inverters with (1+1) modular technology hot standby arrangement amp CVT

(Constant Voltage Transformer) AVR (Automatic Voltage Regulator) and set of step down

transformersThe inverter is protected against overload and short circuit with auto reset facility Whenever

the failure occurs it trips and restart automatically after about 10 to 20 sec But if the problem persists the

protection is permanently gets latched and it will not be switched ON again unless the fault is cleared

followed by pressing of reset button The output of inverters is regulated to 230V AC plusmn 2 50Hz plusmn1Hz for

an input voltage variation of 90V DC to 140V DC Normally both the Inverters are powered ON and both are

delivering the Output voltage but only one (main) inverter is connected to the Load If main inverter is failed

then only the stand-by inverter will come on Load automatically with in 500msec At 70 Depth of

Discharge (DOD) of the battery bank 110VDC supply to the inverters will be cut-off So the Signals feed will

be cut-off The auto-change over arrangement is also provided for bringing the CVT in circuit with in

500msec when the both the inverters output is failed It has various indications on the panel reflecting the

working of the panel

DC DISTRIBUTION PANEL It takes care of DC Power supply requirements of our signalling It consists of sets of DC-DC

converters for individual DC power requirements with (n+1) modular technology hot standby arrangement

with active load sharing basis The DC-DC converters of Relay Internal are provided with (n+1) modular

technology hot standby arrangement with active load sharing basis and 1 additional module as a cold standby

(n+2) The DC-DC converter works satisfactorily with the input voltage variation of 98VDC to 138VDC At

90 Depth of Discharge (DOD) of the battery bank all the DC-DC converters 110VDC Input supply will be

cut-off except for Block Tele DC-DC converters The supply for Point operation is also catered through a

20A fuse by this unit It is also provided with various indications that reflect its working

7 | P a g e

STATUS MONITORING PANEL IPS status monitoring panel has been provided in the ASM room for giving the important alarms and

indications to ASM Status Panel tells present working status of IPS displaying battery voltage continuously

and five other indications which will light according to IPS status During normal working these indications

will not lit Whenever the battery has come on to the load and has discharged by 50 DOD (Depth of

Discharge) then first Red indication lit with description ldquoSTART GENERATORrdquo with audio Alarm ie DG

set is to be started and put on the load If DG set is not started with this warning then if battery gets further

discharged to 60 DOD and second Red indications appears with description ldquoEmergency Start generatorrdquo

with audio alarm even now if DG set is failed to be started the battery further gets discharged to 70

DOD and 3rd Red indications appear with description ldquo System shut downrdquo with audio alarm which will

continue till Generator is started resulting in AC output from IPS is automatically cut off results all the

signals will become blank

When there is any defect in any sub module of IPS even without affecting working of system the 4th

Red indication appears with description ldquoCall SampT Staffrdquo with audio alarm so the ASM advises SampT staff

accordingly Green LED 5th indication comes with the description ldquoStop Generatorrdquo with audio alarm when

the DG set is running and if the Battery bank is fully charged condition

EARTHING The IPS systems and its individual modules are having earth terminals and all these are properly

earthed with earth resistance of less than 1 ohm Earth provided shall preferably be maintenance free using

ground resistance improvement compound (The acceptable Earth Resistance at earth busbar shall not be

more than 1 ohm Code of practice for earthing and bonding system for signalling equipments)

LIGHTNING AND TRANSIENT PROTECTION IN IPS Manufacturer will provide Stage1 amp Stage 2 protection along with the IPS These are described

below

Stage 1 protection is of Class B type against Lightning Electro-Magnetic Impulse (LEMP) amp other

high surges provided at Power Distribution Panel It is provided with a 63 Amp fuse in phase line and is

connected between Line and the Neutral and also between the Neutral and Earth

Stage 2 protection (Power line protection at Equipment level) is of Class C type against low voltage

surges provided at the equipment input level This is thermal disconnecting type and equipped with

protection against SPD (surge protection device) failure due to open amp short circuit of SPDs and is connected

between the Line and the Neutral If supply data signalling lines (ACDC) are carried through overhead

wires or cables above ground to any nearby building or any location outside the equipment room additional

protection of Stage 2 type shall be provided at such locations Class B amp Class C arrestor is provided on a

separate wall mounting type enclosure in IPS room

Stage3 protection (Protection for signallingdata line) is of Class D type All external data signalling

lines (ACDC) shall be protected by using this Class D type device It consists of a combination of Varistors

and Gas Discharge Tube with voltage and current limiting facilities

FEATURES Chargers used in this system are of SMPS technology chargers with 90 efficiency These chargers

are supported with hot standby mode with (n+1) modular technology

Onetwo sets of Maintenance free Battery banks (110VDC) Normally one set (110VDC) of Battery

bank is used Conventional flooded type Lead Acid Batteries or Low Maintenance Lead Acid

batteries can also be used (SMRs settings are required to be adjusted depending on the type of

Batteries used) Various voltage levels of

8 | P a g e

battery banks are avoided Reduction in Battery maintenance amp less flour area required

DC-DC Converters working from 110V Central battery have been used for all dc supplies This has

improved overall efficiency of the system since number of conversion from AC to DC have been

reduced to 2 stage as compared to 3 stage conversion in case of transformer-rectifier system

DC-DC converters are available in modules Easy replacement of defective modules This ensures

less down time

DC-DC Converters are used in load sharing N+1 configuration (ie with hot standby with N+1

modular technology) to improve the reliability amp availability of the system

Capacity of inverter has been brought down to 15 KVA from 5 KVA and used for feeding only

Signals supply Hot standby inverter is provided with auto changeover facility This improves the

availability of the overall system

High efficiency inverter is used with PWM (Pulse Width Modulation) technology in place of Ferro-

resonant technology based inverter This improves the efficiency of the overall system

Continuous power to Signal Circuits even in absence of DG setLocal Power Supply

Generators need not be switched ON every time during train movement

Metal-to-metal relay installations and block working by axle counters have also been covered

Supply of spare modulesComponentsCells have been included as part of main supply

Provides highly regulated voltage to all signal relays amp lamps for better life

9 | P a g e

SINGLE SECTION DIGITAL AXLE COUNTER

INTRODUCTION- The axle counter equipment is working on high frequency and using amplitude modulation or phase

modulation for detection of presence of wheel The equipment described in this notes is Phase modulation type

for the detection of presence of wheel In the Phase modulation type track device the detection of presence of

wheel is with the phase reversal of 1800 out of phase which enables this system to be more healthy and safe

In Phase Reversal Modulation technique trolley suppression arrangements to prevent the counting of

wheels caused by push trolley passing over the track device are not required as the system will take care of

validation of generated pulses caused by passage of wheel over the track device depending up on the phase

shift of the pulse This phase shift of the pulse may be normally 160deg to 180deg for a train wheel and it may be

approximately 100deg to 120deg for a push trolley wheel

This is Digital Axle Counter equipment for single track sections containing 2 out of 2 micro-

controllers to count the axles establish the track occupancy of a track section and to provide this information

to the block or the interlocking equipment

In this system no separate evaluator is required and no analog data is being transmitted One set of

Axle counter equipment is provided at entry end and other set provided at exit end Both sets are being

connected through a twisted pair of telecom cable ie existing RE cable one PET quad is used for both UP

and DN Axle Counters Digital DATA is being transmitted between two ends of Axle counters (Outdoor

track side Detection points)This system is a fully duplex capable of operating according to CCITT V21 and

the Data will be transmitted at the rate of 300bitsec This data Transmitted ensure negligible interference of

the noise The system is highly reliable

FEATURES (a) The system consists of

(i) Single Section Digital Axle Counter (SSDAC) units

(ii) Tx Rx coils

(iii) Vital Relays

(b) TxRx coil axle detectors are mounted to the web of the rails The design of system consists of 21 KHz amp

23 KHz High frequency Phase Reversal type axle detectors

(c) Compatible with 90R 52Kg amp 60Kg rail profiles Easy to install commission amp maintain

(d) Track devices at both (entry amp exit) points of the section should be fixed on the same rail

(e) System is designed to detect the solid wheels with diameter gt 400mm with standard wheel flange

(f) The system works in pairs For monitoring single-track section one pair of SSDAC units are required and

to be installed near the trackside one at the beginning and another at the end of the track section ie

Trackside electronic counting equipment

(g) The basic design of the system is based on counting the number of axles passing at each detection point

These stored counts are transmitted to the second unit of the system and vice versa by means of modem

communication

(h) The communication consists of digital packets having details of Counts amp Health

10 | P a g e

(i) If counts registered at both detection points are equal the section is cleared otherwise the section is shown

as occupied The system ensures no error condition to arrive at the decision of clearance

(j) System is designed as per CENELEC SIL-4 (European standard) using micro controller along with other

electronic circuits and programmed using dedicated software When any of these circuits fail the system

goes to fail safe condition

(k) It is programmable for either Preparatory Reset or Conditional Hard Reset as per requirement

(l) Micro controller based design with 2 out of 2 decisions and counting through software

(m) V21 Modem communication (2-wire) on frac12 quad cables and also compatible to work on voice channel of

OFC amp Radio

(n) Opto isolated vital relay drive for Q-style 24V 1000 _ and Vital Relay output can be giving at both ends

of the system

APPLICATIONS The system can be widely used in Railways for Block Working (BPAC) Intermediate Block Signaling Auto

signalling and Track circuiting for i) Loop line ii) Main line iii) yard lines

SYSTEM DESCRIPTION

This system comprises of

Tx coils-2 nos

Rx coils-2 nos

Reset Box (RB 258A)

Card 1 Signal Conditioning Card ndash 1

Card 2 Signal Conditioning Card - 2

Card 3 Micro controller Logic Board ndash 1

Card 4 Micro controller Logic Board ndash 2

2 nos for independent resetting ndash when used in block sections

1 no for common resetting ndash when used for Track circuiting at stations

Card 5 Event Logger Card

Card 6 Modem Card

Card 7 Relay Driver Card

Card 8 DC-DC Converter Card

SSDAC (DACF 700AP) UNIT

(A) SIGNAL CONDITIONING CARD (CARD 1amp2) (SCC) -1 (SCC-1) generates 21 KHz carrier

signals

-2 (SCC-2) generates 23 KHz carrier signals which is transmitted to 2nd

set of Tx coils

s receive these signals

modulated

train pulses

11 | P a g e

(B) MICRO-CONTROLLER LOGIC BOARD CARD (CARD 3amp4) (MLB) The Micro-controller Logic Board (MLB) is the heart of the system

o 8051 Based Architecture

o 8 Bit Micro Controller

o ATMEL AT89S8252 Micro controller

o 2 out of 2 Decision

o Uses C subset language

- TOOLS

o KEIL μ Vision Development System

o Universal Programmer

o 2KB Program Memory

o 256 bytes RAM

o 8KB Flash memory

o 32 Programmable IO lines

o Wide Operating Voltage range of 4V-6V

o Full Duplex Serial Port

o Programmable Watch Dog Timer

o Fully Static operation up to 24MHz (Upgraded to 40MHz)

o Operating Temperature of ndash40degC - +85degC

o Use of State Machine for Axle Counting

o Use of ASCII MODBUS protocol

o Use of CRC16 technique for Error Checking during communication

o Wheel detection

o Train direction checking and

o Wheel counting functions

o It receives the remote wheel count and computes the status of the section for clear or occupied

o It also checks various supervisory signal levels like supervisory of TxRx coils presence of various

cards communication link failure etcThese cards communicate with each other for wheel count

At Entry-end if train enters into section (1st detection) the counts are incremented and when train

shunts back from the same detection ie if train exits from the section from the same detection the counts are

decremented At Exit-end if train enters into section (2nd detection) the counts are decremented and when

train shunts back from the same detection ie if train exits from the section from the same detection the

counts are incremented Both the track devices at Entry and Exit ends must be fixed on same side of the

track

This MLB card is having Extensive LED display

o A block of 8 LED indicators for count progress error display

o 2 independent LED indicators for section status

o The errors occurring in the system during the operation of the SSDAC are encoded and are indicated by

means of the 8-LED block present on the front panel of the MLB cards

(c) EVENT LOGGER CARD (CARD 5)

Event logger card is designed to capture and store important signals from the remote and local SSDAC units

The stored data can be downloaded from the event logger card for the purpose of analyzing the events

occurring during the operations of the SSDAC The data can be analyzed with the help of CEL data analyzer

software

12 | P a g e

The event logger card captures following signals

(i) Pulse signals

(ii) Supervisory signals

(iii) Card removal information

(iv) Serial packets from

Event Logger card has a Rabbit processor and 2 MB FLASH MEMORY to store packets The data is initially

stored in the buffer and subsequently transferred to FLASH memory every two minutes Normally 4096

pages of the data can be stored in flash memory on FIFO (first in first out) basis

Run This LED blinks continuously indicating the normal working of the event

Log This LED blinks whenever data is being logged into the flash memory (Approx after every 2 minutes)

Dnld This LED is ON when data is being downloaded from the flash memory of the card and becomes OFF

when download is complete

(D) MODEM CARD (CARD 6) (i) The modem card transmits and receives the digital packet information form one counting unit to the other

The packet will appear after every 18 sec and the packet carries the latest information such as

(ii) The modem card being used is V21 type (2-wire) in SSDAC

(iii) This card interfaces with serial RS232C port of both Micro-controller Logic Boards

(iv) It multiplexes the two RS232C inputs and selects one of the two channels and provides signal conversion

from digital to analog (FSK modulation) and vice-versa

(v) Data transmission rate is 300 bitssec

(vi) Automatic Gain Control circuit is incorporated hence no gain adjustments required

(vii) Mode selection on Modem card The modem has been set in lsquoORIGINATORrsquo mode for entry and in the

lsquoANSWERrsquo mode for exit in the factory

(viii) LED Indications provided on Modem card

-Transmitting the signal when LED is flashing

- Receiving the signal when LED is flashing

-Remains OFF in SSDAC

-Carrier is detected when LED is glowing

(E) RELAY DRIVER CARD (CARD 7) (i) The Relay Driver card (RD) provides the 24V DC output required for driving Vital Relay

(ii) One RD card is used in each SSDAC counting unit The RD card receives the command of clear and

clock signals from MLB1 amp MLB2 cards and drives the vital relay lsquoONrsquo when section is NOT OCCUPIED

through opto- isolator circuit

(iii) If a train occupies the section the vital relay is dropped The vital relay status is read back by the system

as per the driving output

(iv) It has

13 | P a g e

ndash LED flashes when the section is clear

ndash LED flashes when the section is clear

All the above LEDrsquos are lit for section clear condition

(F) DC-DC CONVERTER CARD (CARD 8)

INPUT VOLTAGE Nominal Voltage voltage 24V DC Maximum current drain= 12A

Required voltage 18V DC to 30V DC

Output voltage

Nominal Voltage +5 V DC 2 A Required voltage 4 7 5 t o 525V DC

Nominal Voltage +12V DC 200 mA Required voltage 1175 to 1225V DC

Nominal Voltage +24V DC 300 mA with common ground Required voltage 235 to 245V DC

Nominal Voltage +15V DC 100 mA with isolated ground Required voltage 145 to 155V DC

SURGE VOLTAGE AND LIGHTNING PROTECTION Transient surge voltages arise as a result of Lightning discharge switching operations in electrical

systems and electrostatic discharge These surge voltages often destroy the electronic equipment to a large

extent In order to prevent surge voltages from destroying the equipment all the input lines of SSDAC ie

Power Supply (24V) Reset (48V) amp Modem is to be routed through surge voltage protection devices for

effectively protecting the system These devices (3 numbers) are mounted in a box and supplied along with

the system One number of box is to be installed at each location and wired to the SSDAC

Each surge voltage protection device consists of two parts

(a) Base

(b) Plug Trab

The Base of the device is used for wiring the input and output signals The connection details from relay

room to the box and from box to SSDAC unit are provided on the box The Plug Trab consists of MOV and

GD Tube and diverts the excess energy during surge voltages or lightning into the ground connection The

operation of these devices relies on a high quality ground connection in order to safely shunt away the

unwanted energy The impedance of the ground connection is critical and it should be less than 2 Ohms

NOTE The 3 Plug Trab connections are not to be interchanged with one another The plug Trab is a

detachable device and can be replaced with SPARE unit in case of blown device which is indicated by

means of LED for 24 V

EFFECTIVENESS OF PLUG TRABS The effectiveness of plug Trab depends wholly on the Earth connection provided to the system The earth

provided to the system should be less than 1 ohms and connections should be firm and proper to the SSDAC

unit VR box etc

SURGE VOLTAGE AND PROTECTION DEVICE SV-120 The Surge Voltage protection device is to be installed at each location along with every SSDAC unit

14 | P a g e

EARTHING- The lead wires connecting the installation and the earth electrode shall ordinarily be of stranded

copper wire of 29 sq mm (19 strand wires of 14 mm diameter) Copper wire has been specified because GI

wires usually are having greater corrosion However in areas where copper wire may be frequently stolen

due to theft ACSR of size 64 sq mm (19 strands of 211 mm diameter) may be used

LIMITS OF EARTH RESISTANCE (a) Apparatus case connected to Earth (SSDAC and vital Relay Box is housed in Apparatus case and

Connected to earth at outdoor) shall be less than or equal to 1 ohm

(b) All cable connected to same earth shall be less than or equal to 1 ohm

(C) Reset box connected to earth near SM s Room shall be less than or equal to 1ohm

EQUIPMENT TO BE EARTHED A Common Earth should be provided for SSDAC for items 1(a) amp (b) of the above at the outdoor

(a) The Apparatus Case is to be connected to earth (the chassis of SSDAC amp Vital Relay Box should be

properly connected to apparatus case)

(b) Metallic sheath and armouring of all the underground main cables are to be earthed

(i) In RE area the metallic sheath and armouring of main telecom cables are earthed at both ends

(ii) In RE area the armouring of Jelly filled cable shall be earthed at both ends

(c) The Earthing shall be provided at every location box where cables are terminated

(d) Earth already available for other equipment may be used for earthing of Reset Box near SM s Room

Cabin etc

15 | P a g e

DATALOGGER

INTRODUCTION Datalogger is a Microprocessor based system which helps in analysing the failures of relay inter

locking system Electronic Interlocking system This is like a black box which stores all the information

regarding the changes take place in relays AC DC Voltages and DC currents along with date and time The

same information data can be transferred to the computer to analyse further ldquoon line ldquooff linerdquo analysis of

stored date A print out also can be obtained through a printer by connecting directly to the datalogger unit

The data belongs to Relay contacts is considered as digital inputs and the data belongs to voltage

levels currents is considered as Analog inputs Datalogger lsquos are mandatory for all new relay interlocking

(PIRRI) EI installations and it is also recommended to provide in all existing PIs RRIs To increase the

line capacity mechanical signalling equipments are upgraded to PI RRI or EI Due to complexity in the

circuits and wiring sometimes it is very difficult to rectify the failures So datalogger can monitor these

systems with real time clock Thus it can be named as black box of Samp T equipments and hence it is a vital

tool for accident investigation Datalogger is used at Stations yards Whereas in case of Auto Section amp IBH

Mini dataloggers called as Remote Terminal Unit (RTU) are used

ADVANTAGES OF DATALOGGERS (a) Dataloggers helps in monitoring the typical failures such as intermittent auto right failures

(b) It helps in analyzing the cause of the accidents

(c) It helps in detecting the human failures errors such as

(i) Drivers passing signal at Danger

(ii) Operational mistakes done by panel operators ASMrsquos of operating department

(iii) Signal and telecom engineering interferences in safety circuits

(iv) Engineering and electrical department interferences failures

(v) It helps as a ldquoTOOLrdquo in preventive maintenance of signaling gears

(d) Dataloggers can be connected in network Networked dataloggers helps to monitorthe PIRRIEI remotely

(e) Failure reports can be generated remotely with help of datalogger network

(f) On line and Off line track simulation is possible

(g) Speed of the train on point zones can be calculated

(h) Age of the equipment in terms of number of operations etc

COMMON EQUIPMENT FOR ALL DATALOGGERS ARE GIVEN

BELOW (a) CPU card

(b) Digital and Analog input cards

(c) Local terminal(PC)

(d) communication links

(e) Printer

All the dataloggers requires a potential free ( spare ) relay contact for monitoring digital inputs

through Digital input cards amp for monitoring Analog inputs such ACDC bus bar voltage levels through

Analog input cards Digital and Analog inputs are connected to the Processor card Processor card consists of

memory ICrsquos Memory ICrsquos are programmed as per requirement of the signal engineers

Provision of Dataloggers is mandatory with RRI systems and is optional for PI systems as per

amendment to the specification for Relay Interlocking systems ( IRSS-36 ) The data collected by the

datalogger can be used for failure analysis repetitive discrepancies and for accident investigations

16 | P a g e

Note

If the serial communications is more than 50m then line drivers shall be used up to 3 Kms

4wire leased line Modems shall be used if the serial communication is more than 3 Kms

STUDY OF EFFTRONICS DATALOGGER TECHNICAL DETAILS (a) 24V 12VDC Power Supply

(b) Total Storage Capacity of 10 Lakh events

(c) In-built Temperature sensors

(d) Internal Buzzer for alarming during failures

(e) Real Time clock with internal battery backup with data retention up to 10 years

(f) 512 LED matrix to indicate the status of 512 Digital inputs at a time page wise

(g) Seven segment LCD screen (2x24) to display the status of digitalanalog signalsTime Temperature etc

(h) Using the keyboard various functions can be viewed in the LCD panel

(i) Max Digital Inputs 4096

(j) Max Analog Inputs 96

(k) Digital Input Scanning Time 16 millisecond

(l) Analog Input Scanning Time is less than 1 Sec

HARDWARE (EQUIPMENT) Datalogger system consists of

(a) Datalogger (CPU - with Microprocessor 68000)

(b) Digital input cards

(c) Dual modem card

(d) Digital Scanner units (DSU)

(e) Analog Scanner units (ASU)

CPU CARD It is provided with Motorola microprocessor M 68000 It performs all the activities pertaining to the

datalogger It continuously scans (check) the Digital inputs(inbuilt) Digital Scanner Units and Analog

Scanner Units ie scanning of digital signals (Relay operations) for every 16-milli seconds and scanning of

analog signals (ie ACDC voltages amp DC currents) for less than 1 second

This card will support the IO interfaces of LCD (Liquid Crystal Display) - 2X24 alphanumeric Key

Board LED Matrix Display Real Time Clock LCD display and keyboard This will acts as man machine

interface between the datalogger and the signal engineer All the operations (Software) can be performed

using this LCD and keyboard

Real time display with 7 Segments This is built in real time clock within Datalogger and its current

time will be displayed on six 7-segment display provided (Real time clock depend upon DALLAS 1286

chip) This IC will come with internal battery backup hence there is no need to add external batteries

CPU card continuously scans (checks) the DSUs and ASUs Each input connected to digital scanner

units are optically isolated by Opto couplers When CPU card scans the digital inputs it compares with the

previous stored data and if there is any change from the previous status then only that data will be stored (the

status conditions of relay) with date and real time A total of minimum 10 Lac events can be stored in

memory on first in first out basis so that latest data is available in the system There is no loss of data from

datalogger memory in case of power supply failure of datalogger

DIGITAL INPUT CARDS (IN-BUILT) This system is having maximum 8nos of inbuilt Digital inputs cards Maximum 64nos of digital

inputs can be connected to each digital input card The potential free relay contact may be front or back

contact terminated at the Tag Block from the relay of signals tracks points Buttons etc and are

17 | P a g e

subsequently connected to Digital input cards through Flat Ribbon Cable (FRC) connectors These in-built

digital input cards can monitor a total 512 nos of relays status

DIGITAL SCANNER UNIT (DSU) Each DSU contains 8 nos of Digital Input cards Each input card can be connected with 64 inputs

Total input capacity of DSU unit is 512 inputs These scanner cards contain Optocouplers and Multiplexer

Inputs are connected to Stag card The stag card out put is connected to DSU through FRC connectors

Maximum 7 nos of DSUs can be connected to the system So Digital input capacity of the system is 4096

All these digital inputs are scanned at rate of 16 msec

ANALOG SCANNER UNIT (ASU) ASU contains maximum 3 nos of Analog input cards Each input card can be connected with 8nos of

Analog inputs Total input capacity of the ASU is 24 analog input channels Maximum 4nos of ASUs can be

connected to the system Analog input channel capacity of the system is 96 All these analog inputs are

scanned at a rate of less than 1 sec

PARALLEL PORT Parallel port is provided for connecting printer

RS-232 SERIAL PORTS At least 6 Serial communication ports are provided for communication with other dataloggers

Central Monitoring Unit Remote Terminal Unit Electronic Interlocking system Integrated Power Supply

system etc

EXTERNAL NON-VITAL RELAY CONTACTS These relays provided in the system where 16 number of the Relay contacts are provided on the rear

panel through Tele control port to extend alarms and to control the power equipment from remote or local

locations through computer in case of any occurrence of failures Each control can sink or source 100 m

amps of current

INTERNAL MODEM CARD DUAL MODEM CARD (IN-BUILT) It is fixed in datalogger Euro rack itself One card contains two modems The top modem is called

ANS (answer) modem and the bottom modem is called as ORG (originate) modem It is used in case of

networking of Dataloggers In network connect lsquoANSrsquo modem to the lsquoORGrsquo modem of one adjacent station

and connect lsquoORGrsquo modem to the lsquoANSrsquo modem of other adjacent station

POWER SUPPLY Normally 24V DC (12V DC is optional) supply with battery backup is required for the system

working

Input Voltage Range 18Vhellip32V DC (For 24V) 9Vhellip18V DC (For 12V)

INPUT REQUIREMENTS Relay inputs (digital inputs) and analog inputs (voltages currents etc) are required to be connected

to the system as per the requirements of RRI PI SSI as the case may be Some of the inputs to be

monitored is given below

(a) Digital inputs

(i) Field inputs All TPRs NWKRs RWKRs ECRs Crank Handle relays SidingSlot LC gate

control relays etc

(ii) Control Panel inputs All button Knob SMrsquos Key relays

18 | P a g e

(iii) Internal relays

British system All HR DR HHR WNR WRR ASR UCR RR LR UYRTLSR TRSR TSR

JSLR JR etc

SIEMENS system Z1UR Z1UR1 GZR ZDUCR ZU(R)R ZU(N)PRG(R)RG(N)R U(R)S

U(N)PS UDKR DUCR U(R)LR UYR1 UYR2 G(R)LRGR1GR2

GR3 GR4 OVZ2U(R)RW(RN)R (RN)WLR Z1NWR Z1RWRZ1WR1 WKR1 WKR2 WKR3 etc

(b) Analog channels

(i) 230 V AC (for power supplies in the power panel)

(ii) 110V AC (for Signal and Track transformers)

(iii) 110V DC (for Point operation)

(iv) 60V DC (Siemens relays)

(v) 24V DC (Q-series relays)

(vi) 24V DC (for Block Axle counters)

(vii) 12V DC (for indication)

(viii) 20A (for point operation current)

(ix) 10V AC 5KHz (for Axle counter channels) etc

SOFTWARE MODULES OF DATALOGGERS

(a) Network Management of Dataloggers (NMDL)

(b) Reports

(c) Fault Entry

(d) Track Offline Simulation

(e) Train Charting

NMDL SOFTWARE FEATURES (a) Online Relay Status

(b) Online Faults - To view information of various Online Faults as they occur in the stations where

the Dataloggers are connected

(c) Online Simulation - Graphical view of relay operations train movements etc

(d) Remote monitoring of stations with the help of NETWORKING

SOFTWARE OBJECTIVES (a) Predictive Maintenance

(b) Easy identification of failures

(c) Crew discipline

(d) Train charting

REMOTE MONITORING OF STATIONS WITH NETWORKING OF

DATALOGGERS The individual Dataloggers of various stations can be interconnected through networking technology

The data of Remote Panel stations can be viewed in a Computer at the Central Monitoring Station The data

of the network is collected by the FEP (Front End Processor) which in turn is transmitted to the computer

COMPONENTS OF NETWORK MANAGEMENT OF DATALOGGERS

(a) Datalogger at stations

(b) MODEM and Transmission medium

19 | P a g e

(c) Front End Processor (FEP)

(d) Central Monitoring Unit (CMU) Computer

FEP (FRONT END PROCESSOR)

FEP acts as a buffer between the Central Monitoring Unit (Computer) and the Network It is provided

at centralised place to retrieve data continuously from station dataloggers and store in memory and transfer to

computer on request It stores 10 Lac telegrams It works on 12V DC It draws 16A continuous current

when all the three modems are connected Normally it shows the number of packets pending to be sent to the

computer on its 7-segment LED display It is provided with MOTOROLA 68000 microprocessor It has 6-

nos of RS-232 communication ports such as COM1 COM2 COM3 COM4 COM5 and COM6 COM1 is

used for Fault Analysis System (FAS) ie Central Monitoring Unit (Computer) connection COM2 to COM6

are used for networking For Bi-directional 2- nos of ports and for Tri-directional (T-network) 3-nos of ports

are used

DATA TRANSMISSION Dataloggers can be networked in Uni-directional Mode or Bi-directional Mode or T ndash Network Mode

In case of loss of data retransmission of data takes place

(a) Uni-Directional Mode

Each Datalogger will send data in only one direction to the FEP Unidirectional mode network is not

preferred

(b) Bi-Directional Mode

Each end of Network is connected to FEP and each datalogger can now transmit data in both the directions

Bi-directional Mode is advantageous it enables the Data Transmission even in case of Network Failure

(c) T - Network Mode

If more no of stations are in network ie if the network is too lengthy then T- network mode is preferred

COMMUNICATION The communication protocol for transmitting data and command between datalogger and CMU is

standardized by the RDSO and is given in the Specifications of Dataloggers

(a) The type of communication used in the network is dependent on the distance between the dataloggers

(b) For shorter distances Opto Converter Box- Opto isolated current loop communication is used

(c) For longer distances Modem (Dial-up leased) Fiber Optic Satellite Microwave communication

MODEMS Modems are used for DATA transfer between Dataloggers and Front End ProcessorThese are

configured to RS 232 Serial Communication Network is connected with two types of 4-wire modems

(a) Internal modem card Dual Modem card (in-built)

It is fixed in datalogger Euro rack itself One card contains two modems The top modem is called

ANS (answer) modem and the bottom modem is called as ORG (originate) modem

Note In case of networking of Dataloggers connect lsquoANSrsquo modem to the lsquoORGrsquo modem of one adjacent

station and connect lsquoORGrsquo modem to the lsquoANSrsquo modem of other adjacent station

(b) External modems

20 | P a g e

These are generally used at FEP (Front End Processor) side to connect the Dataloggers

(i) To transfer Data from one datalogger to another datalogger FEP Baud rate is 9600bps

(ii) These modems are 4-wire line communication

(iii) To transfer the data from FEP to RMU (PC) the Baud rate is 57600 bps

There is no difference between these modems functionally

CENTRAL MONITORING UNIT (CMU) COMPUTER

Central monitoring unit (Fault Analysis Unit) is a Personal Computer and its minimum configuration

shall be specified by RDSO from time to time System Software Windows XPVista(OS) Norton Kaspersky

(Anti Virus) Interbase where Server is not available (DBMS) Oracle where Server is available (DBMS)

software are required to run Datalogger System It is provided with Graphical User interface (GUI) based

software and retrieve data from all Networked dataloggers (up to 32) at various stations It stores data in

standard data base files The CMU is capable of analyzing the data and generate reports audiovisual alarms

on defined conditions This data can be compressed to take backup In central monitoring unit Software used

for analysis of data prediction of faults etc is written in a structured format so that purchaser can

reconfigure it if required It displays the status of signaling gears at any selected time in graphic form for any

selected station yard It retrieves the stored data amp simulates train movement It sends commands to various

Dataloggers to activate audio visual alarm or operate and electromagnetic relay

CMU shares data available in it by other PCs through available local area network where this data can

be used for train charting passenger information purpose The system generates audiovisual alarm in

ASMrsquosSignal Maintainerrsquos room in the case of power supply failure (battery voltage low) or battery charger

defective with acknowledgement facility

(a) Each datalogger has its own identity code which will be transmitted along with data packet to central

monitoring unit

(b) Events recorded at each station are continuously transmitted to central monitoring unit Response time of

data transfer will not exceed 10 sec

21 | P a g e

22 | P a g e

OPTICAL FIBER CABLE

INTRODUCTION The demand for bandwidth on transmission networks is increasing rapidly because video and

graphical rich contents are exchanged through the corporate network or the Internet The Gigabit Ethernet

became ommonly used in the corporate network backbone and 10Gbit Ethernet will be adopted in the near

future Meanwhile in the home the demand for high-speed network becomes popular as the wide spread of

broadband access eg CATV xDSL and FTTH The transmission medium with capability to transmit high

bit rate signal is necessary to satisfy these requirements

The telecommunication transport technologies move from copper based networks to optical fiber

from timeslot based transport to wave length based transport from traditional circuit switching to terabit

router and all optical based networks entering into a new era of optical networking

BASIC PHYSICS OF OFC

OPTICAL FIBER CABLE OFC have Fibers which are long thin strands made with pure glass about the diameter of a human

hair OFC consists of Core Cladding Buffers and Jacket as shown in figure

MONOCHROMATIC LIGHT OR SINGLE COLOR LIGHT Light or visible light is electromagnetic radiation of a wavelength that is visible to the human eye (

about 400 ndash 700 nm) The word light is sometimes used to refer to the entire electromagnetic spectrum Light

is composed of elementary particles called photons Three primary properties of light are

Light can exhibit properties of both waves and particles This property is referred to as wave-particle

duality The study of light known as optics In free space light (of all wavelengths) travels in a straight path

at a constant maximum speed However the speed of light changes when it travels in a medium and this

change is not the same for all media or for all wavelengths By free space it is meant space that is free from

matter (vacuum) andor free from electromagnetic fields

Thus the speed of light in free space is defined by Einsteinrsquos equation E = mc2

Frequency ν speed of light in free space c and wavelength λ are interrelated by ν = cλ

From the energy relationships E = mc2 = hν and the last one an interesting relationship is obtained

the equivalent mass of a photon m = hνc2

When light is in the vicinity of a strong electromagnetic field it interacts with it From this interaction

and other influences its trajectory changes direction as shown in figure

23 | P a g e

INCIDENT RAY REFLECTED RAY AND REFRACTED RAY An incident ray is a ray of light that strikes a surface The angle between this ray and the

perpendicular or normal to the surface is the angle of incidence Reflection is the change in direction of a

wave front at an interface between two different media so that the wave front returns into the medium from

which it originated Common examples include the reflection of light sound and water waves

The reflected ray corresponding to a given incident ray is the ray that represents the light reflected by

the surface The angle between the surface normal and the reflected ray is known as the angle of reflection

The Law of Reflection says that for a specular (non-scattering) surface the angle of reflection always equals

the angle of incidence The refracted ray or transmitted ray corresponding to a given incident ray represents

the light that is transmitted through the surface The angle between this ray and the normal is known as the

angle of refraction and it is given by Snells Law

The figure shows Incident ray Reflected ray Refracted ray the angle of incidence and angle of refraction

REFRACTIVE INDEX - Refractive index is the speed of light in a vacuum ( c =299792458kmsecond) divided by the speed

of light in a material ( v ) Refractive index measures how much a material refracts light Refractive index of

a material abbreviated as lsquo n lsquo is defined as lsquo n=cv lsquo Light travels slower in physical media than it does

when transmitted through the air Refractive index (n) is a function of molecular structure of matter optical

frequency optical intensity determines optical propagation properties of each wavelength ( λ ) may not be

distributed equally in all directions is affected by external temperature pressure and fields

Refractive index of a medium is a measure for how much the speed of light is reduced inside the

medium For example typical glass has a refractive index of 15 which means that light travels at 1 15 =

067 times the speed in air or vacuum Two common properties of glass and other transparent materials are

directly related to their refractive index

First light rays change direction when they cross the interface from air to the material and effect that

is used in lenses and glasses

Second light reflects partially from surfaces that have a refractive index different from that of their

surroundings

SNELLrsquoS LAW-

24 | P a g e

When light passes from one transparent material to another it bends according to Snells law which

is defined as n1sin(θ1) = n2sin(θ2)

where n1 is the refractive index of the medium the light is leaving θ1 is the incident angle between the light

beam and the normal (normal is 90deg to the interface between two materials)

n2 is the refractive index of the material the light is entering

θ2 is the refractive angle between the light ray and the normal

Snellrsquos law gives the relationship between angle of incidence and angle of refraction

For the case of θ1 = 0deg (ie a ray perpendicular to the interface) the solution is θ2 = 0deg regardless of

the values of n1 and n2 That means a ray entering a medium perpendicular to the surface is never bent The

above is also valid for light going from a dense (higher n) to a less dense (lower n) material the symmetry of

Snells law shows that the same ray paths are applicable in opposite direction

TOTAL INTERNAL REFLECTION- When a light ray crosses an interface into a medium with a higher refractive index it bends towards

the normal Conversely light traveling cross an interface from a higher refractive index medium to a lower

refractive index medium will bend away from the normal

This has an interesting implication at some angle known as the critical angle θc light traveling from

a higher refractive index medium to a lower refractive index medium will be refracted at 90deg in other words

refracted alon g the interface If the light hits the interface at any angle larger than this critical angle it will

not pass through to the second medium at all Instead all of it will be reflected back into the first medium a

process known as total internal reflection

The critical angle can be calculated from Snells law putting in an angle of 90deg for the angle of the refracted

ray θ2 This gives θ1

Since θ2 = 90deg

So sin(θ2) = 1

25 | P a g e

Then θc = θ1 = arcsin(n2n1)

For example with light trying to emerge from glass with n1=15 into air (n2 =1) the ritical angle θc is

arcsin(115) or 418deg For any angle of incidence larger than the critical angle Snells law will not be able to

be solved for the angle of refraction because it will show that the refracted angle has a sine larger than 1

which is not possible In that case all the light is totally reflected off the interface obeying the law of

reflection

OPTICAL FIBER MODE An optical fiber guides light waves in distinct patterns called modes Mode describes the distribution

of light energy across the fiber The precise patterns depend on the wavelength of light transmitted and on the

variation in refractive index that shapes the core In essence the variations in refractive index create

boundary

conditions that shape how light waves travel through the fiber like the walls of a tunnel affect how sounds

echo inside

We can take a look at large-core step-index fibers Light rays enter the fiber at a range of angles and

rays at different angles can all stably travel down the length of the fiber as long as they hit the core-cladding

interface at an angle larger than critical angle These rays are different modes Fibers that carry more than

one mode at a specific light wavelength are called multimode fibers Some fibers have very small diameter

core that they can carry only one mode which travels as a straight line at the center of the core These fibers

are single mode fibers This is illustrated in the following picture

OPTICAL FIBER INDEX PROFILE Index profile is the refractive index distribution across the core and the cladding of a fiber Some

optical fiber has a step index profile in which the core has one uniformly distributed index and the cladding

has a lower uniformly distributed index Other optical fiber has a graded index profile in which refractive

index varies gradually as a function of radial distance from the fiber center Graded-index profiles include

power-law index profiles and parabolic index profiles The following figure shows some common types of

index profiles for single mode and multimode fiber

26 | P a g e

OPTICAL FIBERrsquoS NUMERICAL APERTURE ( NA )- Multimode optical fiber will only propagate light that enters the fiber within a certain cone known as

the acceptance cone of the fiber The half-angle of this cone is called the acceptance angle (see figure 18)

θmax For step-index multimode fiber the acceptance angle is determined only by the indices of refraction

Where

n is the refractive index of the medium light is traveling before entering the fiber

nf is the refractive index of the fiber core

nc is the refractive index of the cladding

NUMBER OF MODES IN A FIBER - Modes are sometimes characterized by numbers Single mode fibers carry only the lowest-order

mode assigned the number 0 Multimode fibers also carry higher-order modes The number of modes that

can propagate in a fiber depends on the fiberrsquos numerical aperture (or acceptance angle) as well as on its

core diameter and the wavelength of the light For a step-index multimode fiber the number of such modes

Nm

Where

D is the core diameter

λ is the operating wavelength

NA is the numerical aperture (or acceptance angle)

MODE FIELD DIAMETER - All light do not travels through the core of the fiber but is distributed through both the core and the

cladding The mode field is the distribution of light through the core and cladding of a particular fiber

Mode-Field Diameter (MFD) defines the size of the power distribution When coupling light into or out of a

fiber MFD is important in understanding light loss

27 | P a g e

ADVANTAGE OF OFC COMMUNICATION - bull More information carrying capacity Fibers can handle much higher data rates than copper More

information can be sent in a second

bull Free from Electromagnetic and Electrostatic interference Being insulator no electric current flows through

the fibre and due to this reason fibres neither radiate nor pick up electro - magnetic radiation So WPC

CLEARANCE is not required

bull Low attenuation 025 dbkm at 1550 nm Loss in twisted pair and coaxial cable increases with frequency

where as loss in the optical fibre cable remains flat over a wide range of frequencies

bull Use of WDM ndash Switching routing at Optical signal level

bull Self healing rings under NMS control

bull Small size makes fibre cable lighter in weight So easy to handleOptic fibre cable weight (approx)

500 kg km Copper cable weight (approx) 1000 kgkm

The reasons are photons of light in a fibre

do not affect each other as they have no electrical charge and they are not affected by stray photons outside

the fibre But in case of copper electrons move through the cable and these are affected by each other

Optical fibre does not carry any electricity even if the cable is damaged or short circuited it does

not cause any spark or fire hazard

As the fibre do not radiate energy it can not be detected by any nearby antenna or any

other detector The fibres are difficult to tap and therefore excellent for security

As the signal transmission is by digital modulation there is no chance of cross talk in

between channels

Only by adding a few additional terminal and repeater equipments the

capacity of the system can be increased at any time once the cable is laid

ical effects and temperature variations

LIMITATIONS OF OFC -

difficult

- utilised

APPLICATION IN SIGNAL AND TELECOMMUNICATIONS transmission circuits

-haul circuits for linking of telephone exchanges

28 | P a g e

PROPAGATION MODES CONCEPT -

MODE - Mode is an available distribution of electromagnetic field in a plane transverse to the direction of

light propagation Each mode is characterized by frequency polarization electric field strength and

magnetic field strength Available patterns are derived from Maxwellrsquos equations and boundary conditions

LINEARLY POLARIZED (LP) MODE A mode for which the field components in the direction of propagation are small compared to

components perpendicular to that direction An optical fibre supports only different field patterns called as

lsquoLinear Polarizedrsquo or lsquo LPrsquo modes The reasons are

requirements

de

the accrual of power carried by different modes

There are two basic types of fiber Multimode fiber and Single-mode fiber

Multimode fiber is best designed for short transmission distances This is suited for used in LAN systems and

video surveillance Single mode fibre is best designed for longer transmission distances This is suitable for

long distance telephony and multi channel television broadcast systems

29 | P a g e

MULTI MODE FIBER Multimode fiber the first to be manufactured and commercialized simply refers to the fact that

numerous modes or light rays are carried simultaneously through the waveguide Modes result from the fact

that light will only propagate in the fiber core at discrete angles within the cone of acceptance MM fiber type

has a much larger core diameter compared to single-mode fiber allowing for the larger number of modes

and

is easier to couple than single-mode optical fiber Multimode fiber further categorized as Multimode step-

index and Multimode graded index fiber

PROPAGATION THROUGH MMSI FIBER Figure shows the principle of total internal reflection applies to multimode step index fiber Because

the corersquos index of refraction is higher than the claddingrsquos index of refraction the light that enters at less than

the critical angle is guided along the fiber

Three different light waves travel down the fiber One mode travels straight down the center of the

core A second mode travels at a steep angle and bounces back and forth by total internal reflection The third

mode exceeds the critical angle and refracts into the cladding Naturally it can be seen that the second mode

travels a longer distance than the first mode causing the two modes to arrive at separate times

PROBLEMS WITH MMSI FIBER AND SOLUTION This disparity between arrival times of the different light rays is known as dispersion and the result is

a muddied signal at the receiving end It is important to note that high dispersion is an unavoidable

characteristic of multimode step-index fiber The solutions are either use Graded index fiber or Single mode

fiber

PROPAGATION THROUGH MMGI FIBER Multimode Graded-index refers to the fact that the refractive index of the core gradually decreases

farther from the center of the core The increased refraction in the center of the core slows the speed of some

light rays allowing all the light rays to reach the receiving end at approximately the same time reducing

dispersion Figure shows the Light propagation principle through multimode graded-index fiber The corersquos

central refractive index ( nA ) is greater than that of the outer corersquos refractive index ( nB )

It is very clear from the figure the light rays no longer follow straight lines they follow a serpentine path

being gradually bent back toward the center by the continuously declining refractive index This reduces the

arrival time disparity because all modes arrive at about the same time The modes traveling in a straight line

30 | P a g e

are in a higher refractive index so they travel slower than the serpentine modes These travel farther but

move faster in the lower refractive index of the outer core region

PROPAGATION THROUGH SMSI FIBER Single mode fiber has a much smaller core that allows only one mode of light at a time to propagate

through the core The figure shows the single mode fiber

Single-mode fiber exhibits no dispersion caused by multiple modes Single-mode fiber also offers lower fiber

attenuation than multimode fiber Thus more information can be transmitted per unit of time because it can

retain the fidelity of each light pulse over longer distances Like multimode fiber early single-mode fiber was

generally characterized as step-index fiber meaning the refractive index of the fiber core is a step above that

of the cladding rather than graduated as it is in graded-index fiber Modern single-mode fibers have evolved

into more complex designs such as matched clad depressed clad and other exotic structures

SINGLE-MODE FIBER DISADVANTAGES The smaller core diameter makes coupling light into the core more difficult The tolerances for single-

mode connectors and splices are also much more demanding

CUTOFF WAVE LENGTH - Cutoff wavelength is the wavelength above which a single-mode fiber supports and propagates only

one mode of light In other words an optical fiber that is single-mode at a particular wavelength may have

two or more modes at wavelengths lower than the cutoff wavelength The effective cutoff wavelength of a

fiber is dependent on the length of fiber and its deployment The longer the fiber the lower is the effective

cutoff

wavelength The smaller the bend radius of a loop of the fiber the lower is the effective cutoff wavelength If

a fiber is bent in a loop the effective cutoff wavelength is lowered

SIGNAL ATTENUATION IN FIBER - Optical fiber has a number of advantages over copper However it also suffers from degradation

problems which can not be ignored The first of these is loss or attenuation Attenuation is typically the result

of two sub properties They are scattering and absorption Both of which have cumulative effects The second

is

dispersion which is the spreading of the transmitted signal and is analogous to noise

SCATTERING Scattering occurs because of impurities or irregularities in the physical construction of the fiber The

well known form of scattering is Rayleigh Scattering It is caused by metal ions in the silica matrix and

results in light rays being scattered in various directions

31 | P a g e

Scattering limits the use of wavelengths below 800nm The short wavelengths are much affected than longer

wavelengths It is because of Rayleigh scattering that the sky appears to be blue ( shorter wave length ) The

shorter wavelengths ( blue ) of light are scattered more than the longer wavelengths of light

ABSORPTION Absorption results from three factors They are hydroxyl ions ( OH- water ) in the silica impurities

in the silica and incomplete residue from the manufacturing process These impurities tend to absorb the

energy of the transmitted signal and convert it to heat resulting in an overall weakening of the signal The

Hydroxyl absorption occurs at 125 and 139 micro The silica itself starts to absorb energy at 17 micro

because of the natural resonance of the silicon dioxide

MACRO BENDING LOSS Macro-bending loss is caused by bending of the entire fiber axis The bending radius shall not be

sharper than 30d where d is diameter of cable A single bend sharper than 30d can cause loss of 05dB

The fiber may break if bending is ever sharper

MICRO BENDING LOSS Micro-bending loss is caused by micro deformations of fiber axis which leads to failures in achieving

total internal reflection conditions Micro-bends are small scale perturbations along the fiber axis the

amplitude of which are on the order of microns These distortions can cause light to leak out of a fiber

Micro-bending may be induced at very cold temperatures because the glass has a different coefficient of

thermal expansion from the coating and cabling materials At low temperatures the coating and cable

become more rigid and may contract more than the glass Consequently enough load may be exerted on the

glass to cause micro bends

Coating material is selected by manufacturers to minimize loss due to micro-bending The linear thermal

expansion coefficient of coating material shall be compatible with that of fiber

32 | P a g e

DISPERSION Dispersion is the optical term for the spreading of the transmits in the fiber It is the bandwidth

limiting phenomenon and comes in two forms Multimode dispersion and chromatic dispersion Chromatic

dispersion is further subdivided into material dispersion and waveguide dispersion

DISPERSION PHENOMENON IN OPTICAL FIBER Dispersion is the time distortion of an optical signal that results from the differences of time of travel

for different components of that signal typically resulting in pulse broadening As the distance traveled by

the signal is more broadening of pulse is more In digital transmission dispersion limits on the maximum

data rate and the maximum distance ie the information-carrying capacity of a fiber link The interference

from broadened pulse in the next interval shall not lead to erroneous interpretation of received signal

OPTICAL DOMAIN Understanding where attenuation and dispersion problems occur helps optical design engineers

determine the better wavelengths at which information can be transmit taking into account distance type of

fiber and the other factors which can severely affect the integrity of the transmitted signal The graph shown

depicts the optical transmission domain as well as the areas where problems arise The wavelength (nm)

is shown on X-axis and attenuation ( dBkm) is shown on Y-axis

There are four transmission windows appear in the figure The first one is at around 850 nm the

second at 1310nm third at 1550 nm and fourth at 1625 nm The last two labeled as C and L band

respectively The 850 nm wavelength at which the original LED technology operated The second window at

1310 nm has low dispersion The 1550 nm called as C-band is ideal wavelength for long haul

communication systems The network engineers can avoid transmitting signal at 1000 nm where Rayleigh

scattering 1240 and 1390 nm where hydroxyl absorption by water occurs to avoid high degree of loss

Optical fibers also can be manufactured to have low dispersion wavelength in the 1550nm region

which is also the point where silica-based fibers have inherently minimal attenuation These fibers are

referred to as dispersion-shifted fibers and are used in long-distance applications with high bit rates For

33 | P a g e

applications utilizing multiple wavelengths it is undesirable to have the zero dispersion point within the

operating

wavelength range

34 | P a g e

SIGNALLING RELAYS

INTRODUCTION A relay is an electromagnetic device which is used to convey information from one circuit to another

circuit through a set of contact ie front or back contact Constructional and electrically relays may be

divided into DC and AC relays because the means by which the electrical energy in the coil is converted in

to mechanical Energy in order to move the contacts are fundamentally different In DC type the contacts are

carried on an armature forming part of a magnetic circuit in which a field is set up by the current flowing in

the coils In AC types the contacts are attached by a link mechanism to a metal sector disc or cylinder in

which currents are induced by the alternating magnetic field produced by the currents in the coils

Every endeavor has been made to explain the action of each type of relay in the simplest possible manner

Relays are sophisticated switch gears used for remote control and succession control of various

electrical equipment In present days they are widely used because they are capable of protecting the

controlled equipment from cross feeding and overloading even as they cater for speedy operations

Most of the relays in present day signaling are electromagnetic devices although some of the relays control

circuits through electronic components like diodetransistors Integrated Chips etc

Railway signaling relays are unique in that

(a) They operate on low voltage and current

(b) They are more articulate as according to their special features they can work under restrictive conditions

and in any specified manner Virtually they can cater for all situations while contributing to speed and

accuracy in operations

CLASSIFICATION OF SIGNALLING RELAYS (a) According to the method of their mounting or fixture they are classified as

(i) Shelf type Relays which are loosely kept on shelves

(ii) Plug in type Relays which are plugged into a pre- wired plug boards

(b) According to their connection and usage they are classified as

(i) Track relays Relay which is directly connected to the track to detect the presence of vehicle

(ii) Line Relays Other than track relay all are line relays Relays connected to the selection circuit

(c) According to their vitality or importance in ensuring train working safety they are classified as

(i) Vital Relays All relays used for traffic control such as signal point controls track detection etc

(ii) Non-vital Relays Relays which operate control aids and accessories like warnings buzzers

Indications etc

(d) According to their special provisions to ensure reliability of their contacts they are classified as

(i) Proved type are those whose normalization after each operation shall be proved in circuit

controlled by their contacts Contacts in which both the springs have metal surfaces on their tips They may

get fused due to high sparking current across them during operation These may prevent relay normalization

and causes unsafe condition in traffic control To avoid this proving of relay normalization after each

operation is necessary

(ii) Non - proved type Need not to be proved to have been normalized after each operation as their

contacts have at least one non-fusible contact (carbon contact)

(e) According to their feed source relays are broadly classified as

(i) DC relays The relay which requires DC power supply for its operations are called DC relays Among

the DC relays

o DC neutral relays This relay closes the same set of contacts on energization with Normal polarity

or Reverse polarity supply

o Polar Relays This relay closes different set of contacts when energized with Reverse polarity

supply They may or may not have contact to close when deenergized

35 | P a g e

(ii) AC Relay AC Induction motor track relays Time element relays flashing indication control etc

(iii) Electronic Relays DC relays with electronic components in them are called electronic relays

DC NEUTRAL RELAY Each Relay has usually one or two coils with a hollow center to accommodate a coreThe coils are

made up of a large numbers of turns of small gauge soft drawn copper wire The two coils can be connected

in series or parallel according to the requirement of relay resistance The ends of the coils are terminated on

binding post to which the control wires are connected Each coil is placed around a core of specially selected

Iron or steel having high permeability and low retentivity The core should be susceptible to magnetism and

at the same time should have little residual magnetism The cores are connected at the top by a yoke to

complete the magnetism coupling between two ends of coils The bottom of each core is equipped with a

large steel or Iron block known as pole piece or face

A flat piece of Iron or steel called armature is supported by brackets which are securely fastened to

the pole piece The armature yoke and the pole pieces are also made of specially selected iron or steel of the

same quality as the core The armature carries the metallic spring contacts which are insulated from it

The circuit through the coils of the relay is closed It sets up a magnetic flux through the core yoke and the

armature The flux passing between the armature and pole faces causes the armatures get attracted to the pole

faces and armature picks up and closes front contacts When the circuit is opened the magnetic flux collapses

and the armature drops away by gravity from the pole faces the front contacts break and back contacts close

The front and back contacts of the relay can be utilised to make or break other circuits Two stop pins of

nonmagnetic material are fixed either on the armature or pole faces so that the armature cannot

come in contact with the pole faces It is essential to maintain a small air-gap between the armature and pole

faces so that low value of residual magnetism may not retain the armature in picked up position and causes

the relay to fail to drop away with a break in its control circuit

GENERAL USAGE

DC Neutral line relays are most commonly used for Railway Signalling controls and detection

Among them plug-in type relays are preferred in larger installations for space considerations Shelf type

relays are also in use mostly in wayside stations

There are many DC Neutral line relays in use with special features such as

(i) Delayed operation

(ii) Biased DC control

(iii) DC control unaffected by AC interference currents

(iv) Getting latched in operated condition till further feeding and others

Usage of DC polar relays is mostly in conjunction with block instruments that control traffic between

stations AC line relays are almost extinct in installations of British Signalling practice They are however

used for time control operations flashing indication control and such other special purposes in installations

with Siemens signalling practice widely Track relays are used according to the type of track detection

circuits chosen for a given location and context While most of the track circuits are still of the DC working

type requiring DC neutral track relays with them the prospects of their being replaced with Electronic track

circuits directly feeding DC line relays in future are great AC Track Circuits are used in DC Traction area

as conventional DC Track Circuits are not suitable there AC Track relays are used with them almost all of

the induction motor type In the British practice of signalling which was first introduced on Indian Railways

non-proved type relays with carbon to metal switching contacts are generally used for vital controls

They facilitate simple circuit designs But with the advent of German Practice introduced by Ms

Siemens later proved type relays with all metal to metal contacts are widely accepted in spite of

complications in circuit design caused by them A recent introduction is that of the same type relays made by

Ms Integra control However for some time now the appreciable features of both the practices are getting

36 | P a g e

incorporated together in the indigenous designs of signalling by railwaymen With this the usage of all types

of relays anywhere can be found without straight jacketed segration of relay types

CHARACTERSTIC OF ELECTRO-MAGNETIC RELAY The following are the characteristic of electro-magnetic relays A brief study of them helps in

understanding the choice of their components and designs features

1) Force of attraction

2) Effect of air gap

3) Effect of Hysterisis

4) Transient condition

FORCE OF ATTRACTION In any electro-magnetic system the force of attraction is given by

Where B - is the flux density a - is the cross sectional area of the particular part of the magnetic

circuit

In the case of a DC neutral Relay B is proportional to the current that is flowing in the coil

surrounding the electro-magnet and thus the force of the attraction is directly proportional to the square of the

current This square relationship has its own advantage especially in the case of DC track relay in that a

small reduction in the current will have a great effect on the working of the relay Also for a given change of

current the make and the break will be quicker with lesser possibility of arcing

EFFECT OF AIR GAP

Curve lsquoArsquo is magnetisation curve for the iron and is all practical purpose a straight line up to the

saturation point Curve lsquoBrsquo is the magnetisation curve for the open-air gap which is a straight line through

out because per magnetisation curve of the whole

magnetic circuit of the relay and for a given force is the sum of the amp-turns for the iron part and the amp-

turns for the air gap

When the front contacts are open the force required to pick up the armature is shown on curve lsquoCrsquo to be F1

but after the armature has operated it will be separated from the core by stop pins In this position the amp-

turns required to maintain the armature is less as indicated by the dotted line from 1 on curve C to 2 on curve

37 | P a g e

F But actually the current in the coil is unaltered the force on the armature is greater than required as

indicated at 3 on curve F Part of this extra force is used to flex the front contacts sufficiently to give good

contact pressure when it is in energised position

The difference between the pick-up and the drop-away current should be as small as practicable in

track relay to ensure good shunting characteristics This is achieved firstly by the choice of good quality relay

iron and secondly by having a small air gap between armature and core If the air gap is not available then

the residual magnetism fluxes might cause the armature to be retained when the supply is disconnected For

this reason residual pins are provided to ensure a definite minimum air gap in the energised position

EFFECT OF HYSTERISIS

Hysterisis is the property by which the flux produced lags behind the current In the de-energized

condition there will be small residual flux in the core When the voltage is applied to the coils the current in

rising to its steady value first causes the flux to rise from 1 to 2 along the curve At this point the flux density

will be sufficient to attract the armature and reduce the air gap the flux then raise to 3 and continue to 4

which corresponds to the steady current in the coils When the voltage is disconnected the current in falling

caused the flux to fall from 4 to 5 along the curve At this point the flux density will fall below the value

required to maintain the armature which will release thus increasing the air gap and reducing the flux to 6

Finally the

flux will decrease from 6 to 1 where the current will again be zero

The relay core is made of material having high permeability and low retentivity As mentioned in

the IRS specification Electromagnet iron may be in the form of a

(a) Bar of silicon steel

(b) Best Yorkshire wrought iron

(c) Swedish charcoal iron

(d) Electrical steel sheets

` This reduces the difference between pick up value and Drop away value By selecting good quality

core material Percentage release and sensitivity of the relay will be improved

TRANSIENT CONDITION

38 | P a g e

When the voltage is applied or disconnected from the coils it takes some little time before the current

become steady These are known as transient conditionsrdquo and are important so far as track relays are

concerned When the voltage is first applied to the coils the magnetic flux in rising cuts the turns on the

coils and in so doing produces a back EMF that opposes the applied voltage and retards the growth of

current

The growth and decay of flux are decided by the relationship between the inductance and resistance

in the circuit is known as time constant It is not fixed quantity in the case of DC neutral relay This value of lsquo

Lrsquo is less when the relay is in de-energised condition (L1) than when the relay is in energised condition (L2)

The magnitude of flux that is established for a given change of current is different in two cases

When the current reaches the pick up value the armature closes and the inductance is increased to L2

due to reduced air gap the flux per amp is increased The increase in flux increased the back EMF during the

movement of the armature after which the current continuous to raise along a new curve corresponding to the

increased inductance until it reaches the final value (ER) This process is indicated above in fig24

When the supply is disconnected the current is obliviously reduced to zero immediately but the flux

decay comparatively slowly owing to the eddy currents produced in the core by the rapid flux change which

tend to maintain the flux The drop away time on a disconnection is however generally negligible See fig

below

If the relay releases due to the reduction in current from say I 2 to I 1 caused by the application of

shunt resistance (as in the case of track relay ) the time taken is much longer than the relay is simply

disconnected The rate of rise or fall of current during the transient conditions is also depends on exterior

circuit values because L and R apply to the whole circuit The production of eddy current in the core the flux

will decay at a slower rate than the current So that the actual release time will be a little longer than it takes

the current to fall to the release

L= Inductance

39 | P a g e

R= Resistance

It is now clear that to reduce releasing time to a minimum it is necessary that

- The relay iron should have low Hysterisis loss and low retentivity

- The degree of over energization of the relay should be restricted

- Connecting a suitable external resistance in series with the relay to keep LR ratio low

In non RE area for track circuit length less than 100M 9 ohm track relay only to be used Using relay

with minimum contacts as they require lesser current which keeps inductance value low

Train working safety is ensured only if the track relay of shortest length track circuit is released

before a light engine running at a highest permitted speed clears it Otherwise the track circuit occupation

may go undetected To avoid this a special provision has to be made in signal control circuits wherever

necessary

The following methods may be adopted for reducing the time lag of track relay

(a) Restrict the over energisation of relay since the release time depends on the initial working current

(b) Connecting a suitable external resistance in series with the relay to keep the LR ratio low

(c) Using relays with minimum contacts as they require lesser operating current keeping the inductance

value low

40 | P a g e

CONCLUSION

Modern signalling is vital for safe and punctual movements of trains In the Indian railways The Signalling

and Telecommunication Department is responsible for providing modern effective and relaible signalling

systems as well as telecommunication systems

The first mode of communication used in Indian Railways was the use of electric telegraph

with the help of Morose code Morose code is the method of providing text information as a series of on-off

tones and lights or clicks that can be directly understood by a skilled listener or observer without special

equipmentEach character (letter or numeral ) is represented by a unique sequence of dots and dashes Later

this system becomes obselete and beggan the era of wireless communication which operated at audio level

frequency range

In wireless communication the significant advances took place the transition to miniature

valves or filament tubesBut this was abandoned too because of excessive current consumption and over

heating of the filament tubes

Fibre-optic communication is a method of transmitting information from one place to another by

sending pulses of light through an optcial fibreThe light forms an electromagnetic carrier wave that is

modulated to carry information First developed in the 1970s fibre optic communication systems has

revolutionized the telecommunications industry and have palyed a major role in the advent of the information

age Because of its advantages over electrical transmissionsoptical fibres have largely replaced copper wire

communications in core networks in the developed world The Indian Railways too is undergoing a transition

from Microwave communication to fibre optic communications

41 | P a g e

BIBLIOGRAPHY AND REFERENCES

1 wwwwikipediacom

2 wwwbritaniccacom

3 wwwirfcacom

4 Motorola GP60 system manual

5 Harris FAS 7000 manual

6 TOSHIBA Manual

2 | P a g e

APPLICATION SOFTWARE This software is specific to each station and different for different stations

This is as per table of control of specific station

Can be installed at site by signal engineers

Logic installed through Boolean expressions or user-friendly equations

OUTPUT CARD (RELAY DRIVE CARD) This card receives the output of CPU card as input and picks up relevant output relay as per the panel

operatorsrsquo request The output of this card is terminated on phoenix terminals from there the output relays are

connected

The essential modules of an EI is as follows

Hardware module

Software module

HARDWARE MODULES USED IN THIS SYSTEM Equipment consists of

CARD FILE

Each card file is like a shelf having 20 Slots to accommodate various PCBs that are used in a system

Slot nos1 to 15 and 20 are used to accommodate Non-vital Input-output or Vital Input or Vital Output PCBs

Slot no16amp17 are used to accommodate Power supply PCB Slot no18amp19 are used to accommodate CPU

PCB In this cardfile a mother board is available in the rear side connecting all the 20 Slots This cardfile is

suitable to mount on a 19rdquo rack

Power

Supply

Card

CPU

Card

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19

20

CPU PCB Each card file to have one CPU PCB and always placed in slot no18amp19 In this card Micro

Controller used is Motorola 68332 and its speed is 21 MHz In this card 4 nos of flash EPROMs of 8 MB

are used to store executive and application software Two nos of fast Static RAM (each 64KB) are used to

process the vital data and Four nos of Static RAM (each 64KB) are used to store events and errors

The main functions of CPU is it monitors continuously status of Vital Boards It also monitors

system internal operation for faults and responds to detected faults It processes application logic based on

inputs

received and deliver outputs to drive external gears It records system faults and routine events in user-

accessible memory It monitors and controls the serial communication ports It controls power to vital outputs

through external VCOR relay

POWER SUPPLY PCB

3 | P a g e

Each card file to have one Power Supply PCB and always placed in slot no16amp17 Power supply

PCB is basically a DC-DC converter that converts 12V DC input supply is +12V -12V and +5V required for

various board functioning Based on diagnostic check by CPU Power Supply Card receives 250Hz signal

from CPU and extends supply to VCOR relay This card provides isolated supply to internal circuit

VITAL OUTPUT PCB Each Vital Output PCB has 16 Outputs It is available in 12V and 24V DC applications Each Vital

Output can drive an output device such as any Q-series relay This output relay in turn controls signals

points crank handle siding control level crossing etc Since Vital Output drives the relay which controls

important outdoor gears all the Vital Output boards are continuously diagnosed by a CPU Any abnormality

in any of the outputs will shut down the system to ensure safety

VITAL INPUT PCB Each Vital Input PCB has 16 Inputs It is available in 12V and 24V DC applications Each Vital Input

is assigned to read the status of outdoor gears such as Track circuits Point detectors Crank handles Siding

controls level crossing etc Since the Vital Inputs read the status of outdoor gears they are normally

configured with double cutting arrangement using relay contacts

NON-VITAL INPUTOUTPUT PCB Each Non-vital IO has 32 inputs and 32 outputs in one PCB It is available in 12V and 24V DC

applications Non-vital inputs are Panel push buttons and keys Non-vital outputs are Panel indication LEDs

counters and buzzers The status of Non-vital Inputoutput is known from LED indications available in front

of the card

VITAL CUT OFF RELAY- VCOR Each card file will have one VCOR to ensure the healthiness of the system VCOR has 6 FB

dependent contacts each rated for 3 Amps When system is healthy the coil receives voltage from Power

Supply PCB which in turn controlled by CPU Power to Vital output board is controlled by VCOR thus

ensuring safety

WIRING HARDWARE 48 Pin Address select PCB and Connector assembly is provided for Vital Input and Vital Output

cards 96 Pin Address select PCB and Connector assembly is provided for Non-Vital IO cards 48 Pin

Connector Assembly is provided for PS and CPU PCB EEPROM PCB which is provided on rear side of the

CPU connector to configure various serial communication ports Keying plugs are provided in the cardfile to

ensure coding to each type of cards

SOFTWARE MODULES USED IN THIS SYSTEM System software consists of the following

EXECUTIVE SOFTWARE This software is common to all EIrsquos for the same company manufacturing

This is a factory installed software

Performs all operations

Cuts off vital supply voltage to output relays in case of unsafe failures

APPLICATION SOFTWARE This software is specific to each station and different for different stations

This is as per table of control of specific station

Can be installed at site by signal engineers

Logic installed through Boolean expressions or user-friendly equations

4 | P a g e

A GEC-MANUFACTURED SSI INTERLOCKING CUBICLE

A PAIR OF DATA LINK MODULES

TRACKSIDE FUNCTIONAL MODULE

5 | P a g e

INTEGRATED POWER SUPPLY

INTRODUCTION A typical 4 line station requires power supplies of 24 V DC( 5 nos ) 12 VDC ( 5nos ) 6V (2 nos)

110 V DC and 110 V AC for signalling These require as many chargers and Secondary cells amp Invertors

requiring more maintenance amp spares Can they be Integrated in to one system

Thus the concept of Integrated Power Supply has been evolved by integrating concepts One Charger

One set of Battery Bank feeding Invertors and DC- DC converters for deriving various DC amp AC

voltages Integrated power supply system delivers both AC amp DC Power supplies as an output with the

output voltage tolerance of plusmn 2

ADVANTAGES Reduces maintenance on Batteries Battery charger amp overall maintenance

Its construction is in modules and hence occupies less space Reduced space requirement resulting in

saving of space for power supply rooms

Provides centralized power system for complete signaling installation with continuous display of

working status of system for easier monitoring

Defect in sub-units of system is shown both by visual amp audible indication Reflects the condition of

battery with warning

Replacement of defective modules is quick amp easy without disturbing the working of the system

It uses (n+1) modular technology hot standby arrangement and hence high reliability and more

availability of the system

The system provides uninterrupted supply to all signalling system even during the power failures

Thus No blank Signal for the approaching drivers

System can be easily configured to suit load requirement

The diesel generator set running (Non-RE area) is reduced almost to lsquoNILrsquo Hence low wear and tear

of DG set components amp reduced diesel oil consumption

COMPONENTS (a) Un-interrupted power supply (U P S)

(i) SMPS Battery chargers with Hot stand-by mode

(ii) Hot Standby PWM Inverters with auto changeover

(iii) CVT Regulator [FRVS]

(b) AC distribution board [ACDB]

(i) STEP DOWN TRANSFORMERS

(c) DC distribution board [DCDB]

(i) DC-DC converters

WORKING IPS works satisfactorily for AC input variation of 150V AC to 275V AC with single-phase power supply

and frequency variation from 48 Hz to 52 Hz The input is fed to SMPS charger which converts in to 110

VDC as output It is fed as input to three sub units

To battery bank charging the batteries

To ON line inverters that converts 110 VDC in to 230 VAC plusmn 2as output

6 | P a g e

As 110 VDC bus bar to DC Distribution Panel as an input to various DC-DC converters located in

it

A 110 V Battery Bank of VRLA cells are connected to SMPS Panel IPS Status Monitoring Panel is

located at ASM room or at SampT staff room if round the clock SampT staff is available at Station

CONSTRUCTION IPS mainly consists of

SMR (Switch Mode Rectifier) Panel SMPS based Float cum Boost Charger (FRBC) Panel

AC Distribution Panel

DC Distribution Panel

Battery Bank (110V DC)

Status Monitoring Panel

SMR (SWITCH MODE RECTIFIER) PANEL SMPS BASED FLOAT

CUM BOOST CHARGER (FRBC) PANEL It consists of SMR FRBC modules and Supervisory amp Control Unit SMPS based SMRs

(converters) SMPS based Float cum Boost Chargers (FRBC) modules are provided with (n+1) modular

technology hot standby arrangement with active load sharing basis and 1 additional module as a cold standby

(n+2) Supervisory amp Control Unit which controls and monitor the complete system It has various

indications on the panel reflecting the working of the panel

FRBCs are suitable for operating in parallel on active load sharing basis with one or more modules of similar

type make and rating

n = required no of modules to cater for actual current requirement

AC DISTRIBUTION PANEL It is made of ON-Line inverters with (1+1) modular technology hot standby arrangement amp CVT

(Constant Voltage Transformer) AVR (Automatic Voltage Regulator) and set of step down

transformersThe inverter is protected against overload and short circuit with auto reset facility Whenever

the failure occurs it trips and restart automatically after about 10 to 20 sec But if the problem persists the

protection is permanently gets latched and it will not be switched ON again unless the fault is cleared

followed by pressing of reset button The output of inverters is regulated to 230V AC plusmn 2 50Hz plusmn1Hz for

an input voltage variation of 90V DC to 140V DC Normally both the Inverters are powered ON and both are

delivering the Output voltage but only one (main) inverter is connected to the Load If main inverter is failed

then only the stand-by inverter will come on Load automatically with in 500msec At 70 Depth of

Discharge (DOD) of the battery bank 110VDC supply to the inverters will be cut-off So the Signals feed will

be cut-off The auto-change over arrangement is also provided for bringing the CVT in circuit with in

500msec when the both the inverters output is failed It has various indications on the panel reflecting the

working of the panel

DC DISTRIBUTION PANEL It takes care of DC Power supply requirements of our signalling It consists of sets of DC-DC

converters for individual DC power requirements with (n+1) modular technology hot standby arrangement

with active load sharing basis The DC-DC converters of Relay Internal are provided with (n+1) modular

technology hot standby arrangement with active load sharing basis and 1 additional module as a cold standby

(n+2) The DC-DC converter works satisfactorily with the input voltage variation of 98VDC to 138VDC At

90 Depth of Discharge (DOD) of the battery bank all the DC-DC converters 110VDC Input supply will be

cut-off except for Block Tele DC-DC converters The supply for Point operation is also catered through a

20A fuse by this unit It is also provided with various indications that reflect its working

7 | P a g e

STATUS MONITORING PANEL IPS status monitoring panel has been provided in the ASM room for giving the important alarms and

indications to ASM Status Panel tells present working status of IPS displaying battery voltage continuously

and five other indications which will light according to IPS status During normal working these indications

will not lit Whenever the battery has come on to the load and has discharged by 50 DOD (Depth of

Discharge) then first Red indication lit with description ldquoSTART GENERATORrdquo with audio Alarm ie DG

set is to be started and put on the load If DG set is not started with this warning then if battery gets further

discharged to 60 DOD and second Red indications appears with description ldquoEmergency Start generatorrdquo

with audio alarm even now if DG set is failed to be started the battery further gets discharged to 70

DOD and 3rd Red indications appear with description ldquo System shut downrdquo with audio alarm which will

continue till Generator is started resulting in AC output from IPS is automatically cut off results all the

signals will become blank

When there is any defect in any sub module of IPS even without affecting working of system the 4th

Red indication appears with description ldquoCall SampT Staffrdquo with audio alarm so the ASM advises SampT staff

accordingly Green LED 5th indication comes with the description ldquoStop Generatorrdquo with audio alarm when

the DG set is running and if the Battery bank is fully charged condition

EARTHING The IPS systems and its individual modules are having earth terminals and all these are properly

earthed with earth resistance of less than 1 ohm Earth provided shall preferably be maintenance free using

ground resistance improvement compound (The acceptable Earth Resistance at earth busbar shall not be

more than 1 ohm Code of practice for earthing and bonding system for signalling equipments)

LIGHTNING AND TRANSIENT PROTECTION IN IPS Manufacturer will provide Stage1 amp Stage 2 protection along with the IPS These are described

below

Stage 1 protection is of Class B type against Lightning Electro-Magnetic Impulse (LEMP) amp other

high surges provided at Power Distribution Panel It is provided with a 63 Amp fuse in phase line and is

connected between Line and the Neutral and also between the Neutral and Earth

Stage 2 protection (Power line protection at Equipment level) is of Class C type against low voltage

surges provided at the equipment input level This is thermal disconnecting type and equipped with

protection against SPD (surge protection device) failure due to open amp short circuit of SPDs and is connected

between the Line and the Neutral If supply data signalling lines (ACDC) are carried through overhead

wires or cables above ground to any nearby building or any location outside the equipment room additional

protection of Stage 2 type shall be provided at such locations Class B amp Class C arrestor is provided on a

separate wall mounting type enclosure in IPS room

Stage3 protection (Protection for signallingdata line) is of Class D type All external data signalling

lines (ACDC) shall be protected by using this Class D type device It consists of a combination of Varistors

and Gas Discharge Tube with voltage and current limiting facilities

FEATURES Chargers used in this system are of SMPS technology chargers with 90 efficiency These chargers

are supported with hot standby mode with (n+1) modular technology

Onetwo sets of Maintenance free Battery banks (110VDC) Normally one set (110VDC) of Battery

bank is used Conventional flooded type Lead Acid Batteries or Low Maintenance Lead Acid

batteries can also be used (SMRs settings are required to be adjusted depending on the type of

Batteries used) Various voltage levels of

8 | P a g e

battery banks are avoided Reduction in Battery maintenance amp less flour area required

DC-DC Converters working from 110V Central battery have been used for all dc supplies This has

improved overall efficiency of the system since number of conversion from AC to DC have been

reduced to 2 stage as compared to 3 stage conversion in case of transformer-rectifier system

DC-DC converters are available in modules Easy replacement of defective modules This ensures

less down time

DC-DC Converters are used in load sharing N+1 configuration (ie with hot standby with N+1

modular technology) to improve the reliability amp availability of the system

Capacity of inverter has been brought down to 15 KVA from 5 KVA and used for feeding only

Signals supply Hot standby inverter is provided with auto changeover facility This improves the

availability of the overall system

High efficiency inverter is used with PWM (Pulse Width Modulation) technology in place of Ferro-

resonant technology based inverter This improves the efficiency of the overall system

Continuous power to Signal Circuits even in absence of DG setLocal Power Supply

Generators need not be switched ON every time during train movement

Metal-to-metal relay installations and block working by axle counters have also been covered

Supply of spare modulesComponentsCells have been included as part of main supply

Provides highly regulated voltage to all signal relays amp lamps for better life

9 | P a g e

SINGLE SECTION DIGITAL AXLE COUNTER

INTRODUCTION- The axle counter equipment is working on high frequency and using amplitude modulation or phase

modulation for detection of presence of wheel The equipment described in this notes is Phase modulation type

for the detection of presence of wheel In the Phase modulation type track device the detection of presence of

wheel is with the phase reversal of 1800 out of phase which enables this system to be more healthy and safe

In Phase Reversal Modulation technique trolley suppression arrangements to prevent the counting of

wheels caused by push trolley passing over the track device are not required as the system will take care of

validation of generated pulses caused by passage of wheel over the track device depending up on the phase

shift of the pulse This phase shift of the pulse may be normally 160deg to 180deg for a train wheel and it may be

approximately 100deg to 120deg for a push trolley wheel

This is Digital Axle Counter equipment for single track sections containing 2 out of 2 micro-

controllers to count the axles establish the track occupancy of a track section and to provide this information

to the block or the interlocking equipment

In this system no separate evaluator is required and no analog data is being transmitted One set of

Axle counter equipment is provided at entry end and other set provided at exit end Both sets are being

connected through a twisted pair of telecom cable ie existing RE cable one PET quad is used for both UP

and DN Axle Counters Digital DATA is being transmitted between two ends of Axle counters (Outdoor

track side Detection points)This system is a fully duplex capable of operating according to CCITT V21 and

the Data will be transmitted at the rate of 300bitsec This data Transmitted ensure negligible interference of

the noise The system is highly reliable

FEATURES (a) The system consists of

(i) Single Section Digital Axle Counter (SSDAC) units

(ii) Tx Rx coils

(iii) Vital Relays

(b) TxRx coil axle detectors are mounted to the web of the rails The design of system consists of 21 KHz amp

23 KHz High frequency Phase Reversal type axle detectors

(c) Compatible with 90R 52Kg amp 60Kg rail profiles Easy to install commission amp maintain

(d) Track devices at both (entry amp exit) points of the section should be fixed on the same rail

(e) System is designed to detect the solid wheels with diameter gt 400mm with standard wheel flange

(f) The system works in pairs For monitoring single-track section one pair of SSDAC units are required and

to be installed near the trackside one at the beginning and another at the end of the track section ie

Trackside electronic counting equipment

(g) The basic design of the system is based on counting the number of axles passing at each detection point

These stored counts are transmitted to the second unit of the system and vice versa by means of modem

communication

(h) The communication consists of digital packets having details of Counts amp Health

10 | P a g e

(i) If counts registered at both detection points are equal the section is cleared otherwise the section is shown

as occupied The system ensures no error condition to arrive at the decision of clearance

(j) System is designed as per CENELEC SIL-4 (European standard) using micro controller along with other

electronic circuits and programmed using dedicated software When any of these circuits fail the system

goes to fail safe condition

(k) It is programmable for either Preparatory Reset or Conditional Hard Reset as per requirement

(l) Micro controller based design with 2 out of 2 decisions and counting through software

(m) V21 Modem communication (2-wire) on frac12 quad cables and also compatible to work on voice channel of

OFC amp Radio

(n) Opto isolated vital relay drive for Q-style 24V 1000 _ and Vital Relay output can be giving at both ends

of the system

APPLICATIONS The system can be widely used in Railways for Block Working (BPAC) Intermediate Block Signaling Auto

signalling and Track circuiting for i) Loop line ii) Main line iii) yard lines

SYSTEM DESCRIPTION

This system comprises of

Tx coils-2 nos

Rx coils-2 nos

Reset Box (RB 258A)

Card 1 Signal Conditioning Card ndash 1

Card 2 Signal Conditioning Card - 2

Card 3 Micro controller Logic Board ndash 1

Card 4 Micro controller Logic Board ndash 2

2 nos for independent resetting ndash when used in block sections

1 no for common resetting ndash when used for Track circuiting at stations

Card 5 Event Logger Card

Card 6 Modem Card

Card 7 Relay Driver Card

Card 8 DC-DC Converter Card

SSDAC (DACF 700AP) UNIT

(A) SIGNAL CONDITIONING CARD (CARD 1amp2) (SCC) -1 (SCC-1) generates 21 KHz carrier

signals

-2 (SCC-2) generates 23 KHz carrier signals which is transmitted to 2nd

set of Tx coils

s receive these signals

modulated

train pulses

11 | P a g e

(B) MICRO-CONTROLLER LOGIC BOARD CARD (CARD 3amp4) (MLB) The Micro-controller Logic Board (MLB) is the heart of the system

o 8051 Based Architecture

o 8 Bit Micro Controller

o ATMEL AT89S8252 Micro controller

o 2 out of 2 Decision

o Uses C subset language

- TOOLS

o KEIL μ Vision Development System

o Universal Programmer

o 2KB Program Memory

o 256 bytes RAM

o 8KB Flash memory

o 32 Programmable IO lines

o Wide Operating Voltage range of 4V-6V

o Full Duplex Serial Port

o Programmable Watch Dog Timer

o Fully Static operation up to 24MHz (Upgraded to 40MHz)

o Operating Temperature of ndash40degC - +85degC

o Use of State Machine for Axle Counting

o Use of ASCII MODBUS protocol

o Use of CRC16 technique for Error Checking during communication

o Wheel detection

o Train direction checking and

o Wheel counting functions

o It receives the remote wheel count and computes the status of the section for clear or occupied

o It also checks various supervisory signal levels like supervisory of TxRx coils presence of various

cards communication link failure etcThese cards communicate with each other for wheel count

At Entry-end if train enters into section (1st detection) the counts are incremented and when train

shunts back from the same detection ie if train exits from the section from the same detection the counts are

decremented At Exit-end if train enters into section (2nd detection) the counts are decremented and when

train shunts back from the same detection ie if train exits from the section from the same detection the

counts are incremented Both the track devices at Entry and Exit ends must be fixed on same side of the

track

This MLB card is having Extensive LED display

o A block of 8 LED indicators for count progress error display

o 2 independent LED indicators for section status

o The errors occurring in the system during the operation of the SSDAC are encoded and are indicated by

means of the 8-LED block present on the front panel of the MLB cards

(c) EVENT LOGGER CARD (CARD 5)

Event logger card is designed to capture and store important signals from the remote and local SSDAC units

The stored data can be downloaded from the event logger card for the purpose of analyzing the events

occurring during the operations of the SSDAC The data can be analyzed with the help of CEL data analyzer

software

12 | P a g e

The event logger card captures following signals

(i) Pulse signals

(ii) Supervisory signals

(iii) Card removal information

(iv) Serial packets from

Event Logger card has a Rabbit processor and 2 MB FLASH MEMORY to store packets The data is initially

stored in the buffer and subsequently transferred to FLASH memory every two minutes Normally 4096

pages of the data can be stored in flash memory on FIFO (first in first out) basis

Run This LED blinks continuously indicating the normal working of the event

Log This LED blinks whenever data is being logged into the flash memory (Approx after every 2 minutes)

Dnld This LED is ON when data is being downloaded from the flash memory of the card and becomes OFF

when download is complete

(D) MODEM CARD (CARD 6) (i) The modem card transmits and receives the digital packet information form one counting unit to the other

The packet will appear after every 18 sec and the packet carries the latest information such as

(ii) The modem card being used is V21 type (2-wire) in SSDAC

(iii) This card interfaces with serial RS232C port of both Micro-controller Logic Boards

(iv) It multiplexes the two RS232C inputs and selects one of the two channels and provides signal conversion

from digital to analog (FSK modulation) and vice-versa

(v) Data transmission rate is 300 bitssec

(vi) Automatic Gain Control circuit is incorporated hence no gain adjustments required

(vii) Mode selection on Modem card The modem has been set in lsquoORIGINATORrsquo mode for entry and in the

lsquoANSWERrsquo mode for exit in the factory

(viii) LED Indications provided on Modem card

-Transmitting the signal when LED is flashing

- Receiving the signal when LED is flashing

-Remains OFF in SSDAC

-Carrier is detected when LED is glowing

(E) RELAY DRIVER CARD (CARD 7) (i) The Relay Driver card (RD) provides the 24V DC output required for driving Vital Relay

(ii) One RD card is used in each SSDAC counting unit The RD card receives the command of clear and

clock signals from MLB1 amp MLB2 cards and drives the vital relay lsquoONrsquo when section is NOT OCCUPIED

through opto- isolator circuit

(iii) If a train occupies the section the vital relay is dropped The vital relay status is read back by the system

as per the driving output

(iv) It has

13 | P a g e

ndash LED flashes when the section is clear

ndash LED flashes when the section is clear

All the above LEDrsquos are lit for section clear condition

(F) DC-DC CONVERTER CARD (CARD 8)

INPUT VOLTAGE Nominal Voltage voltage 24V DC Maximum current drain= 12A

Required voltage 18V DC to 30V DC

Output voltage

Nominal Voltage +5 V DC 2 A Required voltage 4 7 5 t o 525V DC

Nominal Voltage +12V DC 200 mA Required voltage 1175 to 1225V DC

Nominal Voltage +24V DC 300 mA with common ground Required voltage 235 to 245V DC

Nominal Voltage +15V DC 100 mA with isolated ground Required voltage 145 to 155V DC

SURGE VOLTAGE AND LIGHTNING PROTECTION Transient surge voltages arise as a result of Lightning discharge switching operations in electrical

systems and electrostatic discharge These surge voltages often destroy the electronic equipment to a large

extent In order to prevent surge voltages from destroying the equipment all the input lines of SSDAC ie

Power Supply (24V) Reset (48V) amp Modem is to be routed through surge voltage protection devices for

effectively protecting the system These devices (3 numbers) are mounted in a box and supplied along with

the system One number of box is to be installed at each location and wired to the SSDAC

Each surge voltage protection device consists of two parts

(a) Base

(b) Plug Trab

The Base of the device is used for wiring the input and output signals The connection details from relay

room to the box and from box to SSDAC unit are provided on the box The Plug Trab consists of MOV and

GD Tube and diverts the excess energy during surge voltages or lightning into the ground connection The

operation of these devices relies on a high quality ground connection in order to safely shunt away the

unwanted energy The impedance of the ground connection is critical and it should be less than 2 Ohms

NOTE The 3 Plug Trab connections are not to be interchanged with one another The plug Trab is a

detachable device and can be replaced with SPARE unit in case of blown device which is indicated by

means of LED for 24 V

EFFECTIVENESS OF PLUG TRABS The effectiveness of plug Trab depends wholly on the Earth connection provided to the system The earth

provided to the system should be less than 1 ohms and connections should be firm and proper to the SSDAC

unit VR box etc

SURGE VOLTAGE AND PROTECTION DEVICE SV-120 The Surge Voltage protection device is to be installed at each location along with every SSDAC unit

14 | P a g e

EARTHING- The lead wires connecting the installation and the earth electrode shall ordinarily be of stranded

copper wire of 29 sq mm (19 strand wires of 14 mm diameter) Copper wire has been specified because GI

wires usually are having greater corrosion However in areas where copper wire may be frequently stolen

due to theft ACSR of size 64 sq mm (19 strands of 211 mm diameter) may be used

LIMITS OF EARTH RESISTANCE (a) Apparatus case connected to Earth (SSDAC and vital Relay Box is housed in Apparatus case and

Connected to earth at outdoor) shall be less than or equal to 1 ohm

(b) All cable connected to same earth shall be less than or equal to 1 ohm

(C) Reset box connected to earth near SM s Room shall be less than or equal to 1ohm

EQUIPMENT TO BE EARTHED A Common Earth should be provided for SSDAC for items 1(a) amp (b) of the above at the outdoor

(a) The Apparatus Case is to be connected to earth (the chassis of SSDAC amp Vital Relay Box should be

properly connected to apparatus case)

(b) Metallic sheath and armouring of all the underground main cables are to be earthed

(i) In RE area the metallic sheath and armouring of main telecom cables are earthed at both ends

(ii) In RE area the armouring of Jelly filled cable shall be earthed at both ends

(c) The Earthing shall be provided at every location box where cables are terminated

(d) Earth already available for other equipment may be used for earthing of Reset Box near SM s Room

Cabin etc

15 | P a g e

DATALOGGER

INTRODUCTION Datalogger is a Microprocessor based system which helps in analysing the failures of relay inter

locking system Electronic Interlocking system This is like a black box which stores all the information

regarding the changes take place in relays AC DC Voltages and DC currents along with date and time The

same information data can be transferred to the computer to analyse further ldquoon line ldquooff linerdquo analysis of

stored date A print out also can be obtained through a printer by connecting directly to the datalogger unit

The data belongs to Relay contacts is considered as digital inputs and the data belongs to voltage

levels currents is considered as Analog inputs Datalogger lsquos are mandatory for all new relay interlocking

(PIRRI) EI installations and it is also recommended to provide in all existing PIs RRIs To increase the

line capacity mechanical signalling equipments are upgraded to PI RRI or EI Due to complexity in the

circuits and wiring sometimes it is very difficult to rectify the failures So datalogger can monitor these

systems with real time clock Thus it can be named as black box of Samp T equipments and hence it is a vital

tool for accident investigation Datalogger is used at Stations yards Whereas in case of Auto Section amp IBH

Mini dataloggers called as Remote Terminal Unit (RTU) are used

ADVANTAGES OF DATALOGGERS (a) Dataloggers helps in monitoring the typical failures such as intermittent auto right failures

(b) It helps in analyzing the cause of the accidents

(c) It helps in detecting the human failures errors such as

(i) Drivers passing signal at Danger

(ii) Operational mistakes done by panel operators ASMrsquos of operating department

(iii) Signal and telecom engineering interferences in safety circuits

(iv) Engineering and electrical department interferences failures

(v) It helps as a ldquoTOOLrdquo in preventive maintenance of signaling gears

(d) Dataloggers can be connected in network Networked dataloggers helps to monitorthe PIRRIEI remotely

(e) Failure reports can be generated remotely with help of datalogger network

(f) On line and Off line track simulation is possible

(g) Speed of the train on point zones can be calculated

(h) Age of the equipment in terms of number of operations etc

COMMON EQUIPMENT FOR ALL DATALOGGERS ARE GIVEN

BELOW (a) CPU card

(b) Digital and Analog input cards

(c) Local terminal(PC)

(d) communication links

(e) Printer

All the dataloggers requires a potential free ( spare ) relay contact for monitoring digital inputs

through Digital input cards amp for monitoring Analog inputs such ACDC bus bar voltage levels through

Analog input cards Digital and Analog inputs are connected to the Processor card Processor card consists of

memory ICrsquos Memory ICrsquos are programmed as per requirement of the signal engineers

Provision of Dataloggers is mandatory with RRI systems and is optional for PI systems as per

amendment to the specification for Relay Interlocking systems ( IRSS-36 ) The data collected by the

datalogger can be used for failure analysis repetitive discrepancies and for accident investigations

16 | P a g e

Note

If the serial communications is more than 50m then line drivers shall be used up to 3 Kms

4wire leased line Modems shall be used if the serial communication is more than 3 Kms

STUDY OF EFFTRONICS DATALOGGER TECHNICAL DETAILS (a) 24V 12VDC Power Supply

(b) Total Storage Capacity of 10 Lakh events

(c) In-built Temperature sensors

(d) Internal Buzzer for alarming during failures

(e) Real Time clock with internal battery backup with data retention up to 10 years

(f) 512 LED matrix to indicate the status of 512 Digital inputs at a time page wise

(g) Seven segment LCD screen (2x24) to display the status of digitalanalog signalsTime Temperature etc

(h) Using the keyboard various functions can be viewed in the LCD panel

(i) Max Digital Inputs 4096

(j) Max Analog Inputs 96

(k) Digital Input Scanning Time 16 millisecond

(l) Analog Input Scanning Time is less than 1 Sec

HARDWARE (EQUIPMENT) Datalogger system consists of

(a) Datalogger (CPU - with Microprocessor 68000)

(b) Digital input cards

(c) Dual modem card

(d) Digital Scanner units (DSU)

(e) Analog Scanner units (ASU)

CPU CARD It is provided with Motorola microprocessor M 68000 It performs all the activities pertaining to the

datalogger It continuously scans (check) the Digital inputs(inbuilt) Digital Scanner Units and Analog

Scanner Units ie scanning of digital signals (Relay operations) for every 16-milli seconds and scanning of

analog signals (ie ACDC voltages amp DC currents) for less than 1 second

This card will support the IO interfaces of LCD (Liquid Crystal Display) - 2X24 alphanumeric Key

Board LED Matrix Display Real Time Clock LCD display and keyboard This will acts as man machine

interface between the datalogger and the signal engineer All the operations (Software) can be performed

using this LCD and keyboard

Real time display with 7 Segments This is built in real time clock within Datalogger and its current

time will be displayed on six 7-segment display provided (Real time clock depend upon DALLAS 1286

chip) This IC will come with internal battery backup hence there is no need to add external batteries

CPU card continuously scans (checks) the DSUs and ASUs Each input connected to digital scanner

units are optically isolated by Opto couplers When CPU card scans the digital inputs it compares with the

previous stored data and if there is any change from the previous status then only that data will be stored (the

status conditions of relay) with date and real time A total of minimum 10 Lac events can be stored in

memory on first in first out basis so that latest data is available in the system There is no loss of data from

datalogger memory in case of power supply failure of datalogger

DIGITAL INPUT CARDS (IN-BUILT) This system is having maximum 8nos of inbuilt Digital inputs cards Maximum 64nos of digital

inputs can be connected to each digital input card The potential free relay contact may be front or back

contact terminated at the Tag Block from the relay of signals tracks points Buttons etc and are

17 | P a g e

subsequently connected to Digital input cards through Flat Ribbon Cable (FRC) connectors These in-built

digital input cards can monitor a total 512 nos of relays status

DIGITAL SCANNER UNIT (DSU) Each DSU contains 8 nos of Digital Input cards Each input card can be connected with 64 inputs

Total input capacity of DSU unit is 512 inputs These scanner cards contain Optocouplers and Multiplexer

Inputs are connected to Stag card The stag card out put is connected to DSU through FRC connectors

Maximum 7 nos of DSUs can be connected to the system So Digital input capacity of the system is 4096

All these digital inputs are scanned at rate of 16 msec

ANALOG SCANNER UNIT (ASU) ASU contains maximum 3 nos of Analog input cards Each input card can be connected with 8nos of

Analog inputs Total input capacity of the ASU is 24 analog input channels Maximum 4nos of ASUs can be

connected to the system Analog input channel capacity of the system is 96 All these analog inputs are

scanned at a rate of less than 1 sec

PARALLEL PORT Parallel port is provided for connecting printer

RS-232 SERIAL PORTS At least 6 Serial communication ports are provided for communication with other dataloggers

Central Monitoring Unit Remote Terminal Unit Electronic Interlocking system Integrated Power Supply

system etc

EXTERNAL NON-VITAL RELAY CONTACTS These relays provided in the system where 16 number of the Relay contacts are provided on the rear

panel through Tele control port to extend alarms and to control the power equipment from remote or local

locations through computer in case of any occurrence of failures Each control can sink or source 100 m

amps of current

INTERNAL MODEM CARD DUAL MODEM CARD (IN-BUILT) It is fixed in datalogger Euro rack itself One card contains two modems The top modem is called

ANS (answer) modem and the bottom modem is called as ORG (originate) modem It is used in case of

networking of Dataloggers In network connect lsquoANSrsquo modem to the lsquoORGrsquo modem of one adjacent station

and connect lsquoORGrsquo modem to the lsquoANSrsquo modem of other adjacent station

POWER SUPPLY Normally 24V DC (12V DC is optional) supply with battery backup is required for the system

working

Input Voltage Range 18Vhellip32V DC (For 24V) 9Vhellip18V DC (For 12V)

INPUT REQUIREMENTS Relay inputs (digital inputs) and analog inputs (voltages currents etc) are required to be connected

to the system as per the requirements of RRI PI SSI as the case may be Some of the inputs to be

monitored is given below

(a) Digital inputs

(i) Field inputs All TPRs NWKRs RWKRs ECRs Crank Handle relays SidingSlot LC gate

control relays etc

(ii) Control Panel inputs All button Knob SMrsquos Key relays

18 | P a g e

(iii) Internal relays

British system All HR DR HHR WNR WRR ASR UCR RR LR UYRTLSR TRSR TSR

JSLR JR etc

SIEMENS system Z1UR Z1UR1 GZR ZDUCR ZU(R)R ZU(N)PRG(R)RG(N)R U(R)S

U(N)PS UDKR DUCR U(R)LR UYR1 UYR2 G(R)LRGR1GR2

GR3 GR4 OVZ2U(R)RW(RN)R (RN)WLR Z1NWR Z1RWRZ1WR1 WKR1 WKR2 WKR3 etc

(b) Analog channels

(i) 230 V AC (for power supplies in the power panel)

(ii) 110V AC (for Signal and Track transformers)

(iii) 110V DC (for Point operation)

(iv) 60V DC (Siemens relays)

(v) 24V DC (Q-series relays)

(vi) 24V DC (for Block Axle counters)

(vii) 12V DC (for indication)

(viii) 20A (for point operation current)

(ix) 10V AC 5KHz (for Axle counter channels) etc

SOFTWARE MODULES OF DATALOGGERS

(a) Network Management of Dataloggers (NMDL)

(b) Reports

(c) Fault Entry

(d) Track Offline Simulation

(e) Train Charting

NMDL SOFTWARE FEATURES (a) Online Relay Status

(b) Online Faults - To view information of various Online Faults as they occur in the stations where

the Dataloggers are connected

(c) Online Simulation - Graphical view of relay operations train movements etc

(d) Remote monitoring of stations with the help of NETWORKING

SOFTWARE OBJECTIVES (a) Predictive Maintenance

(b) Easy identification of failures

(c) Crew discipline

(d) Train charting

REMOTE MONITORING OF STATIONS WITH NETWORKING OF

DATALOGGERS The individual Dataloggers of various stations can be interconnected through networking technology

The data of Remote Panel stations can be viewed in a Computer at the Central Monitoring Station The data

of the network is collected by the FEP (Front End Processor) which in turn is transmitted to the computer

COMPONENTS OF NETWORK MANAGEMENT OF DATALOGGERS

(a) Datalogger at stations

(b) MODEM and Transmission medium

19 | P a g e

(c) Front End Processor (FEP)

(d) Central Monitoring Unit (CMU) Computer

FEP (FRONT END PROCESSOR)

FEP acts as a buffer between the Central Monitoring Unit (Computer) and the Network It is provided

at centralised place to retrieve data continuously from station dataloggers and store in memory and transfer to

computer on request It stores 10 Lac telegrams It works on 12V DC It draws 16A continuous current

when all the three modems are connected Normally it shows the number of packets pending to be sent to the

computer on its 7-segment LED display It is provided with MOTOROLA 68000 microprocessor It has 6-

nos of RS-232 communication ports such as COM1 COM2 COM3 COM4 COM5 and COM6 COM1 is

used for Fault Analysis System (FAS) ie Central Monitoring Unit (Computer) connection COM2 to COM6

are used for networking For Bi-directional 2- nos of ports and for Tri-directional (T-network) 3-nos of ports

are used

DATA TRANSMISSION Dataloggers can be networked in Uni-directional Mode or Bi-directional Mode or T ndash Network Mode

In case of loss of data retransmission of data takes place

(a) Uni-Directional Mode

Each Datalogger will send data in only one direction to the FEP Unidirectional mode network is not

preferred

(b) Bi-Directional Mode

Each end of Network is connected to FEP and each datalogger can now transmit data in both the directions

Bi-directional Mode is advantageous it enables the Data Transmission even in case of Network Failure

(c) T - Network Mode

If more no of stations are in network ie if the network is too lengthy then T- network mode is preferred

COMMUNICATION The communication protocol for transmitting data and command between datalogger and CMU is

standardized by the RDSO and is given in the Specifications of Dataloggers

(a) The type of communication used in the network is dependent on the distance between the dataloggers

(b) For shorter distances Opto Converter Box- Opto isolated current loop communication is used

(c) For longer distances Modem (Dial-up leased) Fiber Optic Satellite Microwave communication

MODEMS Modems are used for DATA transfer between Dataloggers and Front End ProcessorThese are

configured to RS 232 Serial Communication Network is connected with two types of 4-wire modems

(a) Internal modem card Dual Modem card (in-built)

It is fixed in datalogger Euro rack itself One card contains two modems The top modem is called

ANS (answer) modem and the bottom modem is called as ORG (originate) modem

Note In case of networking of Dataloggers connect lsquoANSrsquo modem to the lsquoORGrsquo modem of one adjacent

station and connect lsquoORGrsquo modem to the lsquoANSrsquo modem of other adjacent station

(b) External modems

20 | P a g e

These are generally used at FEP (Front End Processor) side to connect the Dataloggers

(i) To transfer Data from one datalogger to another datalogger FEP Baud rate is 9600bps

(ii) These modems are 4-wire line communication

(iii) To transfer the data from FEP to RMU (PC) the Baud rate is 57600 bps

There is no difference between these modems functionally

CENTRAL MONITORING UNIT (CMU) COMPUTER

Central monitoring unit (Fault Analysis Unit) is a Personal Computer and its minimum configuration

shall be specified by RDSO from time to time System Software Windows XPVista(OS) Norton Kaspersky

(Anti Virus) Interbase where Server is not available (DBMS) Oracle where Server is available (DBMS)

software are required to run Datalogger System It is provided with Graphical User interface (GUI) based

software and retrieve data from all Networked dataloggers (up to 32) at various stations It stores data in

standard data base files The CMU is capable of analyzing the data and generate reports audiovisual alarms

on defined conditions This data can be compressed to take backup In central monitoring unit Software used

for analysis of data prediction of faults etc is written in a structured format so that purchaser can

reconfigure it if required It displays the status of signaling gears at any selected time in graphic form for any

selected station yard It retrieves the stored data amp simulates train movement It sends commands to various

Dataloggers to activate audio visual alarm or operate and electromagnetic relay

CMU shares data available in it by other PCs through available local area network where this data can

be used for train charting passenger information purpose The system generates audiovisual alarm in

ASMrsquosSignal Maintainerrsquos room in the case of power supply failure (battery voltage low) or battery charger

defective with acknowledgement facility

(a) Each datalogger has its own identity code which will be transmitted along with data packet to central

monitoring unit

(b) Events recorded at each station are continuously transmitted to central monitoring unit Response time of

data transfer will not exceed 10 sec

21 | P a g e

22 | P a g e

OPTICAL FIBER CABLE

INTRODUCTION The demand for bandwidth on transmission networks is increasing rapidly because video and

graphical rich contents are exchanged through the corporate network or the Internet The Gigabit Ethernet

became ommonly used in the corporate network backbone and 10Gbit Ethernet will be adopted in the near

future Meanwhile in the home the demand for high-speed network becomes popular as the wide spread of

broadband access eg CATV xDSL and FTTH The transmission medium with capability to transmit high

bit rate signal is necessary to satisfy these requirements

The telecommunication transport technologies move from copper based networks to optical fiber

from timeslot based transport to wave length based transport from traditional circuit switching to terabit

router and all optical based networks entering into a new era of optical networking

BASIC PHYSICS OF OFC

OPTICAL FIBER CABLE OFC have Fibers which are long thin strands made with pure glass about the diameter of a human

hair OFC consists of Core Cladding Buffers and Jacket as shown in figure

MONOCHROMATIC LIGHT OR SINGLE COLOR LIGHT Light or visible light is electromagnetic radiation of a wavelength that is visible to the human eye (

about 400 ndash 700 nm) The word light is sometimes used to refer to the entire electromagnetic spectrum Light

is composed of elementary particles called photons Three primary properties of light are

Light can exhibit properties of both waves and particles This property is referred to as wave-particle

duality The study of light known as optics In free space light (of all wavelengths) travels in a straight path

at a constant maximum speed However the speed of light changes when it travels in a medium and this

change is not the same for all media or for all wavelengths By free space it is meant space that is free from

matter (vacuum) andor free from electromagnetic fields

Thus the speed of light in free space is defined by Einsteinrsquos equation E = mc2

Frequency ν speed of light in free space c and wavelength λ are interrelated by ν = cλ

From the energy relationships E = mc2 = hν and the last one an interesting relationship is obtained

the equivalent mass of a photon m = hνc2

When light is in the vicinity of a strong electromagnetic field it interacts with it From this interaction

and other influences its trajectory changes direction as shown in figure

23 | P a g e

INCIDENT RAY REFLECTED RAY AND REFRACTED RAY An incident ray is a ray of light that strikes a surface The angle between this ray and the

perpendicular or normal to the surface is the angle of incidence Reflection is the change in direction of a

wave front at an interface between two different media so that the wave front returns into the medium from

which it originated Common examples include the reflection of light sound and water waves

The reflected ray corresponding to a given incident ray is the ray that represents the light reflected by

the surface The angle between the surface normal and the reflected ray is known as the angle of reflection

The Law of Reflection says that for a specular (non-scattering) surface the angle of reflection always equals

the angle of incidence The refracted ray or transmitted ray corresponding to a given incident ray represents

the light that is transmitted through the surface The angle between this ray and the normal is known as the

angle of refraction and it is given by Snells Law

The figure shows Incident ray Reflected ray Refracted ray the angle of incidence and angle of refraction

REFRACTIVE INDEX - Refractive index is the speed of light in a vacuum ( c =299792458kmsecond) divided by the speed

of light in a material ( v ) Refractive index measures how much a material refracts light Refractive index of

a material abbreviated as lsquo n lsquo is defined as lsquo n=cv lsquo Light travels slower in physical media than it does

when transmitted through the air Refractive index (n) is a function of molecular structure of matter optical

frequency optical intensity determines optical propagation properties of each wavelength ( λ ) may not be

distributed equally in all directions is affected by external temperature pressure and fields

Refractive index of a medium is a measure for how much the speed of light is reduced inside the

medium For example typical glass has a refractive index of 15 which means that light travels at 1 15 =

067 times the speed in air or vacuum Two common properties of glass and other transparent materials are

directly related to their refractive index

First light rays change direction when they cross the interface from air to the material and effect that

is used in lenses and glasses

Second light reflects partially from surfaces that have a refractive index different from that of their

surroundings

SNELLrsquoS LAW-

24 | P a g e

When light passes from one transparent material to another it bends according to Snells law which

is defined as n1sin(θ1) = n2sin(θ2)

where n1 is the refractive index of the medium the light is leaving θ1 is the incident angle between the light

beam and the normal (normal is 90deg to the interface between two materials)

n2 is the refractive index of the material the light is entering

θ2 is the refractive angle between the light ray and the normal

Snellrsquos law gives the relationship between angle of incidence and angle of refraction

For the case of θ1 = 0deg (ie a ray perpendicular to the interface) the solution is θ2 = 0deg regardless of

the values of n1 and n2 That means a ray entering a medium perpendicular to the surface is never bent The

above is also valid for light going from a dense (higher n) to a less dense (lower n) material the symmetry of

Snells law shows that the same ray paths are applicable in opposite direction

TOTAL INTERNAL REFLECTION- When a light ray crosses an interface into a medium with a higher refractive index it bends towards

the normal Conversely light traveling cross an interface from a higher refractive index medium to a lower

refractive index medium will bend away from the normal

This has an interesting implication at some angle known as the critical angle θc light traveling from

a higher refractive index medium to a lower refractive index medium will be refracted at 90deg in other words

refracted alon g the interface If the light hits the interface at any angle larger than this critical angle it will

not pass through to the second medium at all Instead all of it will be reflected back into the first medium a

process known as total internal reflection

The critical angle can be calculated from Snells law putting in an angle of 90deg for the angle of the refracted

ray θ2 This gives θ1

Since θ2 = 90deg

So sin(θ2) = 1

25 | P a g e

Then θc = θ1 = arcsin(n2n1)

For example with light trying to emerge from glass with n1=15 into air (n2 =1) the ritical angle θc is

arcsin(115) or 418deg For any angle of incidence larger than the critical angle Snells law will not be able to

be solved for the angle of refraction because it will show that the refracted angle has a sine larger than 1

which is not possible In that case all the light is totally reflected off the interface obeying the law of

reflection

OPTICAL FIBER MODE An optical fiber guides light waves in distinct patterns called modes Mode describes the distribution

of light energy across the fiber The precise patterns depend on the wavelength of light transmitted and on the

variation in refractive index that shapes the core In essence the variations in refractive index create

boundary

conditions that shape how light waves travel through the fiber like the walls of a tunnel affect how sounds

echo inside

We can take a look at large-core step-index fibers Light rays enter the fiber at a range of angles and

rays at different angles can all stably travel down the length of the fiber as long as they hit the core-cladding

interface at an angle larger than critical angle These rays are different modes Fibers that carry more than

one mode at a specific light wavelength are called multimode fibers Some fibers have very small diameter

core that they can carry only one mode which travels as a straight line at the center of the core These fibers

are single mode fibers This is illustrated in the following picture

OPTICAL FIBER INDEX PROFILE Index profile is the refractive index distribution across the core and the cladding of a fiber Some

optical fiber has a step index profile in which the core has one uniformly distributed index and the cladding

has a lower uniformly distributed index Other optical fiber has a graded index profile in which refractive

index varies gradually as a function of radial distance from the fiber center Graded-index profiles include

power-law index profiles and parabolic index profiles The following figure shows some common types of

index profiles for single mode and multimode fiber

26 | P a g e

OPTICAL FIBERrsquoS NUMERICAL APERTURE ( NA )- Multimode optical fiber will only propagate light that enters the fiber within a certain cone known as

the acceptance cone of the fiber The half-angle of this cone is called the acceptance angle (see figure 18)

θmax For step-index multimode fiber the acceptance angle is determined only by the indices of refraction

Where

n is the refractive index of the medium light is traveling before entering the fiber

nf is the refractive index of the fiber core

nc is the refractive index of the cladding

NUMBER OF MODES IN A FIBER - Modes are sometimes characterized by numbers Single mode fibers carry only the lowest-order

mode assigned the number 0 Multimode fibers also carry higher-order modes The number of modes that

can propagate in a fiber depends on the fiberrsquos numerical aperture (or acceptance angle) as well as on its

core diameter and the wavelength of the light For a step-index multimode fiber the number of such modes

Nm

Where

D is the core diameter

λ is the operating wavelength

NA is the numerical aperture (or acceptance angle)

MODE FIELD DIAMETER - All light do not travels through the core of the fiber but is distributed through both the core and the

cladding The mode field is the distribution of light through the core and cladding of a particular fiber

Mode-Field Diameter (MFD) defines the size of the power distribution When coupling light into or out of a

fiber MFD is important in understanding light loss

27 | P a g e

ADVANTAGE OF OFC COMMUNICATION - bull More information carrying capacity Fibers can handle much higher data rates than copper More

information can be sent in a second

bull Free from Electromagnetic and Electrostatic interference Being insulator no electric current flows through

the fibre and due to this reason fibres neither radiate nor pick up electro - magnetic radiation So WPC

CLEARANCE is not required

bull Low attenuation 025 dbkm at 1550 nm Loss in twisted pair and coaxial cable increases with frequency

where as loss in the optical fibre cable remains flat over a wide range of frequencies

bull Use of WDM ndash Switching routing at Optical signal level

bull Self healing rings under NMS control

bull Small size makes fibre cable lighter in weight So easy to handleOptic fibre cable weight (approx)

500 kg km Copper cable weight (approx) 1000 kgkm

The reasons are photons of light in a fibre

do not affect each other as they have no electrical charge and they are not affected by stray photons outside

the fibre But in case of copper electrons move through the cable and these are affected by each other

Optical fibre does not carry any electricity even if the cable is damaged or short circuited it does

not cause any spark or fire hazard

As the fibre do not radiate energy it can not be detected by any nearby antenna or any

other detector The fibres are difficult to tap and therefore excellent for security

As the signal transmission is by digital modulation there is no chance of cross talk in

between channels

Only by adding a few additional terminal and repeater equipments the

capacity of the system can be increased at any time once the cable is laid

ical effects and temperature variations

LIMITATIONS OF OFC -

difficult

- utilised

APPLICATION IN SIGNAL AND TELECOMMUNICATIONS transmission circuits

-haul circuits for linking of telephone exchanges

28 | P a g e

PROPAGATION MODES CONCEPT -

MODE - Mode is an available distribution of electromagnetic field in a plane transverse to the direction of

light propagation Each mode is characterized by frequency polarization electric field strength and

magnetic field strength Available patterns are derived from Maxwellrsquos equations and boundary conditions

LINEARLY POLARIZED (LP) MODE A mode for which the field components in the direction of propagation are small compared to

components perpendicular to that direction An optical fibre supports only different field patterns called as

lsquoLinear Polarizedrsquo or lsquo LPrsquo modes The reasons are

requirements

de

the accrual of power carried by different modes

There are two basic types of fiber Multimode fiber and Single-mode fiber

Multimode fiber is best designed for short transmission distances This is suited for used in LAN systems and

video surveillance Single mode fibre is best designed for longer transmission distances This is suitable for

long distance telephony and multi channel television broadcast systems

29 | P a g e

MULTI MODE FIBER Multimode fiber the first to be manufactured and commercialized simply refers to the fact that

numerous modes or light rays are carried simultaneously through the waveguide Modes result from the fact

that light will only propagate in the fiber core at discrete angles within the cone of acceptance MM fiber type

has a much larger core diameter compared to single-mode fiber allowing for the larger number of modes

and

is easier to couple than single-mode optical fiber Multimode fiber further categorized as Multimode step-

index and Multimode graded index fiber

PROPAGATION THROUGH MMSI FIBER Figure shows the principle of total internal reflection applies to multimode step index fiber Because

the corersquos index of refraction is higher than the claddingrsquos index of refraction the light that enters at less than

the critical angle is guided along the fiber

Three different light waves travel down the fiber One mode travels straight down the center of the

core A second mode travels at a steep angle and bounces back and forth by total internal reflection The third

mode exceeds the critical angle and refracts into the cladding Naturally it can be seen that the second mode

travels a longer distance than the first mode causing the two modes to arrive at separate times

PROBLEMS WITH MMSI FIBER AND SOLUTION This disparity between arrival times of the different light rays is known as dispersion and the result is

a muddied signal at the receiving end It is important to note that high dispersion is an unavoidable

characteristic of multimode step-index fiber The solutions are either use Graded index fiber or Single mode

fiber

PROPAGATION THROUGH MMGI FIBER Multimode Graded-index refers to the fact that the refractive index of the core gradually decreases

farther from the center of the core The increased refraction in the center of the core slows the speed of some

light rays allowing all the light rays to reach the receiving end at approximately the same time reducing

dispersion Figure shows the Light propagation principle through multimode graded-index fiber The corersquos

central refractive index ( nA ) is greater than that of the outer corersquos refractive index ( nB )

It is very clear from the figure the light rays no longer follow straight lines they follow a serpentine path

being gradually bent back toward the center by the continuously declining refractive index This reduces the

arrival time disparity because all modes arrive at about the same time The modes traveling in a straight line

30 | P a g e

are in a higher refractive index so they travel slower than the serpentine modes These travel farther but

move faster in the lower refractive index of the outer core region

PROPAGATION THROUGH SMSI FIBER Single mode fiber has a much smaller core that allows only one mode of light at a time to propagate

through the core The figure shows the single mode fiber

Single-mode fiber exhibits no dispersion caused by multiple modes Single-mode fiber also offers lower fiber

attenuation than multimode fiber Thus more information can be transmitted per unit of time because it can

retain the fidelity of each light pulse over longer distances Like multimode fiber early single-mode fiber was

generally characterized as step-index fiber meaning the refractive index of the fiber core is a step above that

of the cladding rather than graduated as it is in graded-index fiber Modern single-mode fibers have evolved

into more complex designs such as matched clad depressed clad and other exotic structures

SINGLE-MODE FIBER DISADVANTAGES The smaller core diameter makes coupling light into the core more difficult The tolerances for single-

mode connectors and splices are also much more demanding

CUTOFF WAVE LENGTH - Cutoff wavelength is the wavelength above which a single-mode fiber supports and propagates only

one mode of light In other words an optical fiber that is single-mode at a particular wavelength may have

two or more modes at wavelengths lower than the cutoff wavelength The effective cutoff wavelength of a

fiber is dependent on the length of fiber and its deployment The longer the fiber the lower is the effective

cutoff

wavelength The smaller the bend radius of a loop of the fiber the lower is the effective cutoff wavelength If

a fiber is bent in a loop the effective cutoff wavelength is lowered

SIGNAL ATTENUATION IN FIBER - Optical fiber has a number of advantages over copper However it also suffers from degradation

problems which can not be ignored The first of these is loss or attenuation Attenuation is typically the result

of two sub properties They are scattering and absorption Both of which have cumulative effects The second

is

dispersion which is the spreading of the transmitted signal and is analogous to noise

SCATTERING Scattering occurs because of impurities or irregularities in the physical construction of the fiber The

well known form of scattering is Rayleigh Scattering It is caused by metal ions in the silica matrix and

results in light rays being scattered in various directions

31 | P a g e

Scattering limits the use of wavelengths below 800nm The short wavelengths are much affected than longer

wavelengths It is because of Rayleigh scattering that the sky appears to be blue ( shorter wave length ) The

shorter wavelengths ( blue ) of light are scattered more than the longer wavelengths of light

ABSORPTION Absorption results from three factors They are hydroxyl ions ( OH- water ) in the silica impurities

in the silica and incomplete residue from the manufacturing process These impurities tend to absorb the

energy of the transmitted signal and convert it to heat resulting in an overall weakening of the signal The

Hydroxyl absorption occurs at 125 and 139 micro The silica itself starts to absorb energy at 17 micro

because of the natural resonance of the silicon dioxide

MACRO BENDING LOSS Macro-bending loss is caused by bending of the entire fiber axis The bending radius shall not be

sharper than 30d where d is diameter of cable A single bend sharper than 30d can cause loss of 05dB

The fiber may break if bending is ever sharper

MICRO BENDING LOSS Micro-bending loss is caused by micro deformations of fiber axis which leads to failures in achieving

total internal reflection conditions Micro-bends are small scale perturbations along the fiber axis the

amplitude of which are on the order of microns These distortions can cause light to leak out of a fiber

Micro-bending may be induced at very cold temperatures because the glass has a different coefficient of

thermal expansion from the coating and cabling materials At low temperatures the coating and cable

become more rigid and may contract more than the glass Consequently enough load may be exerted on the

glass to cause micro bends

Coating material is selected by manufacturers to minimize loss due to micro-bending The linear thermal

expansion coefficient of coating material shall be compatible with that of fiber

32 | P a g e

DISPERSION Dispersion is the optical term for the spreading of the transmits in the fiber It is the bandwidth

limiting phenomenon and comes in two forms Multimode dispersion and chromatic dispersion Chromatic

dispersion is further subdivided into material dispersion and waveguide dispersion

DISPERSION PHENOMENON IN OPTICAL FIBER Dispersion is the time distortion of an optical signal that results from the differences of time of travel

for different components of that signal typically resulting in pulse broadening As the distance traveled by

the signal is more broadening of pulse is more In digital transmission dispersion limits on the maximum

data rate and the maximum distance ie the information-carrying capacity of a fiber link The interference

from broadened pulse in the next interval shall not lead to erroneous interpretation of received signal

OPTICAL DOMAIN Understanding where attenuation and dispersion problems occur helps optical design engineers

determine the better wavelengths at which information can be transmit taking into account distance type of

fiber and the other factors which can severely affect the integrity of the transmitted signal The graph shown

depicts the optical transmission domain as well as the areas where problems arise The wavelength (nm)

is shown on X-axis and attenuation ( dBkm) is shown on Y-axis

There are four transmission windows appear in the figure The first one is at around 850 nm the

second at 1310nm third at 1550 nm and fourth at 1625 nm The last two labeled as C and L band

respectively The 850 nm wavelength at which the original LED technology operated The second window at

1310 nm has low dispersion The 1550 nm called as C-band is ideal wavelength for long haul

communication systems The network engineers can avoid transmitting signal at 1000 nm where Rayleigh

scattering 1240 and 1390 nm where hydroxyl absorption by water occurs to avoid high degree of loss

Optical fibers also can be manufactured to have low dispersion wavelength in the 1550nm region

which is also the point where silica-based fibers have inherently minimal attenuation These fibers are

referred to as dispersion-shifted fibers and are used in long-distance applications with high bit rates For

33 | P a g e

applications utilizing multiple wavelengths it is undesirable to have the zero dispersion point within the

operating

wavelength range

34 | P a g e

SIGNALLING RELAYS

INTRODUCTION A relay is an electromagnetic device which is used to convey information from one circuit to another

circuit through a set of contact ie front or back contact Constructional and electrically relays may be

divided into DC and AC relays because the means by which the electrical energy in the coil is converted in

to mechanical Energy in order to move the contacts are fundamentally different In DC type the contacts are

carried on an armature forming part of a magnetic circuit in which a field is set up by the current flowing in

the coils In AC types the contacts are attached by a link mechanism to a metal sector disc or cylinder in

which currents are induced by the alternating magnetic field produced by the currents in the coils

Every endeavor has been made to explain the action of each type of relay in the simplest possible manner

Relays are sophisticated switch gears used for remote control and succession control of various

electrical equipment In present days they are widely used because they are capable of protecting the

controlled equipment from cross feeding and overloading even as they cater for speedy operations

Most of the relays in present day signaling are electromagnetic devices although some of the relays control

circuits through electronic components like diodetransistors Integrated Chips etc

Railway signaling relays are unique in that

(a) They operate on low voltage and current

(b) They are more articulate as according to their special features they can work under restrictive conditions

and in any specified manner Virtually they can cater for all situations while contributing to speed and

accuracy in operations

CLASSIFICATION OF SIGNALLING RELAYS (a) According to the method of their mounting or fixture they are classified as

(i) Shelf type Relays which are loosely kept on shelves

(ii) Plug in type Relays which are plugged into a pre- wired plug boards

(b) According to their connection and usage they are classified as

(i) Track relays Relay which is directly connected to the track to detect the presence of vehicle

(ii) Line Relays Other than track relay all are line relays Relays connected to the selection circuit

(c) According to their vitality or importance in ensuring train working safety they are classified as

(i) Vital Relays All relays used for traffic control such as signal point controls track detection etc

(ii) Non-vital Relays Relays which operate control aids and accessories like warnings buzzers

Indications etc

(d) According to their special provisions to ensure reliability of their contacts they are classified as

(i) Proved type are those whose normalization after each operation shall be proved in circuit

controlled by their contacts Contacts in which both the springs have metal surfaces on their tips They may

get fused due to high sparking current across them during operation These may prevent relay normalization

and causes unsafe condition in traffic control To avoid this proving of relay normalization after each

operation is necessary

(ii) Non - proved type Need not to be proved to have been normalized after each operation as their

contacts have at least one non-fusible contact (carbon contact)

(e) According to their feed source relays are broadly classified as

(i) DC relays The relay which requires DC power supply for its operations are called DC relays Among

the DC relays

o DC neutral relays This relay closes the same set of contacts on energization with Normal polarity

or Reverse polarity supply

o Polar Relays This relay closes different set of contacts when energized with Reverse polarity

supply They may or may not have contact to close when deenergized

35 | P a g e

(ii) AC Relay AC Induction motor track relays Time element relays flashing indication control etc

(iii) Electronic Relays DC relays with electronic components in them are called electronic relays

DC NEUTRAL RELAY Each Relay has usually one or two coils with a hollow center to accommodate a coreThe coils are

made up of a large numbers of turns of small gauge soft drawn copper wire The two coils can be connected

in series or parallel according to the requirement of relay resistance The ends of the coils are terminated on

binding post to which the control wires are connected Each coil is placed around a core of specially selected

Iron or steel having high permeability and low retentivity The core should be susceptible to magnetism and

at the same time should have little residual magnetism The cores are connected at the top by a yoke to

complete the magnetism coupling between two ends of coils The bottom of each core is equipped with a

large steel or Iron block known as pole piece or face

A flat piece of Iron or steel called armature is supported by brackets which are securely fastened to

the pole piece The armature yoke and the pole pieces are also made of specially selected iron or steel of the

same quality as the core The armature carries the metallic spring contacts which are insulated from it

The circuit through the coils of the relay is closed It sets up a magnetic flux through the core yoke and the

armature The flux passing between the armature and pole faces causes the armatures get attracted to the pole

faces and armature picks up and closes front contacts When the circuit is opened the magnetic flux collapses

and the armature drops away by gravity from the pole faces the front contacts break and back contacts close

The front and back contacts of the relay can be utilised to make or break other circuits Two stop pins of

nonmagnetic material are fixed either on the armature or pole faces so that the armature cannot

come in contact with the pole faces It is essential to maintain a small air-gap between the armature and pole

faces so that low value of residual magnetism may not retain the armature in picked up position and causes

the relay to fail to drop away with a break in its control circuit

GENERAL USAGE

DC Neutral line relays are most commonly used for Railway Signalling controls and detection

Among them plug-in type relays are preferred in larger installations for space considerations Shelf type

relays are also in use mostly in wayside stations

There are many DC Neutral line relays in use with special features such as

(i) Delayed operation

(ii) Biased DC control

(iii) DC control unaffected by AC interference currents

(iv) Getting latched in operated condition till further feeding and others

Usage of DC polar relays is mostly in conjunction with block instruments that control traffic between

stations AC line relays are almost extinct in installations of British Signalling practice They are however

used for time control operations flashing indication control and such other special purposes in installations

with Siemens signalling practice widely Track relays are used according to the type of track detection

circuits chosen for a given location and context While most of the track circuits are still of the DC working

type requiring DC neutral track relays with them the prospects of their being replaced with Electronic track

circuits directly feeding DC line relays in future are great AC Track Circuits are used in DC Traction area

as conventional DC Track Circuits are not suitable there AC Track relays are used with them almost all of

the induction motor type In the British practice of signalling which was first introduced on Indian Railways

non-proved type relays with carbon to metal switching contacts are generally used for vital controls

They facilitate simple circuit designs But with the advent of German Practice introduced by Ms

Siemens later proved type relays with all metal to metal contacts are widely accepted in spite of

complications in circuit design caused by them A recent introduction is that of the same type relays made by

Ms Integra control However for some time now the appreciable features of both the practices are getting

36 | P a g e

incorporated together in the indigenous designs of signalling by railwaymen With this the usage of all types

of relays anywhere can be found without straight jacketed segration of relay types

CHARACTERSTIC OF ELECTRO-MAGNETIC RELAY The following are the characteristic of electro-magnetic relays A brief study of them helps in

understanding the choice of their components and designs features

1) Force of attraction

2) Effect of air gap

3) Effect of Hysterisis

4) Transient condition

FORCE OF ATTRACTION In any electro-magnetic system the force of attraction is given by

Where B - is the flux density a - is the cross sectional area of the particular part of the magnetic

circuit

In the case of a DC neutral Relay B is proportional to the current that is flowing in the coil

surrounding the electro-magnet and thus the force of the attraction is directly proportional to the square of the

current This square relationship has its own advantage especially in the case of DC track relay in that a

small reduction in the current will have a great effect on the working of the relay Also for a given change of

current the make and the break will be quicker with lesser possibility of arcing

EFFECT OF AIR GAP

Curve lsquoArsquo is magnetisation curve for the iron and is all practical purpose a straight line up to the

saturation point Curve lsquoBrsquo is the magnetisation curve for the open-air gap which is a straight line through

out because per magnetisation curve of the whole

magnetic circuit of the relay and for a given force is the sum of the amp-turns for the iron part and the amp-

turns for the air gap

When the front contacts are open the force required to pick up the armature is shown on curve lsquoCrsquo to be F1

but after the armature has operated it will be separated from the core by stop pins In this position the amp-

turns required to maintain the armature is less as indicated by the dotted line from 1 on curve C to 2 on curve

37 | P a g e

F But actually the current in the coil is unaltered the force on the armature is greater than required as

indicated at 3 on curve F Part of this extra force is used to flex the front contacts sufficiently to give good

contact pressure when it is in energised position

The difference between the pick-up and the drop-away current should be as small as practicable in

track relay to ensure good shunting characteristics This is achieved firstly by the choice of good quality relay

iron and secondly by having a small air gap between armature and core If the air gap is not available then

the residual magnetism fluxes might cause the armature to be retained when the supply is disconnected For

this reason residual pins are provided to ensure a definite minimum air gap in the energised position

EFFECT OF HYSTERISIS

Hysterisis is the property by which the flux produced lags behind the current In the de-energized

condition there will be small residual flux in the core When the voltage is applied to the coils the current in

rising to its steady value first causes the flux to rise from 1 to 2 along the curve At this point the flux density

will be sufficient to attract the armature and reduce the air gap the flux then raise to 3 and continue to 4

which corresponds to the steady current in the coils When the voltage is disconnected the current in falling

caused the flux to fall from 4 to 5 along the curve At this point the flux density will fall below the value

required to maintain the armature which will release thus increasing the air gap and reducing the flux to 6

Finally the

flux will decrease from 6 to 1 where the current will again be zero

The relay core is made of material having high permeability and low retentivity As mentioned in

the IRS specification Electromagnet iron may be in the form of a

(a) Bar of silicon steel

(b) Best Yorkshire wrought iron

(c) Swedish charcoal iron

(d) Electrical steel sheets

` This reduces the difference between pick up value and Drop away value By selecting good quality

core material Percentage release and sensitivity of the relay will be improved

TRANSIENT CONDITION

38 | P a g e

When the voltage is applied or disconnected from the coils it takes some little time before the current

become steady These are known as transient conditionsrdquo and are important so far as track relays are

concerned When the voltage is first applied to the coils the magnetic flux in rising cuts the turns on the

coils and in so doing produces a back EMF that opposes the applied voltage and retards the growth of

current

The growth and decay of flux are decided by the relationship between the inductance and resistance

in the circuit is known as time constant It is not fixed quantity in the case of DC neutral relay This value of lsquo

Lrsquo is less when the relay is in de-energised condition (L1) than when the relay is in energised condition (L2)

The magnitude of flux that is established for a given change of current is different in two cases

When the current reaches the pick up value the armature closes and the inductance is increased to L2

due to reduced air gap the flux per amp is increased The increase in flux increased the back EMF during the

movement of the armature after which the current continuous to raise along a new curve corresponding to the

increased inductance until it reaches the final value (ER) This process is indicated above in fig24

When the supply is disconnected the current is obliviously reduced to zero immediately but the flux

decay comparatively slowly owing to the eddy currents produced in the core by the rapid flux change which

tend to maintain the flux The drop away time on a disconnection is however generally negligible See fig

below

If the relay releases due to the reduction in current from say I 2 to I 1 caused by the application of

shunt resistance (as in the case of track relay ) the time taken is much longer than the relay is simply

disconnected The rate of rise or fall of current during the transient conditions is also depends on exterior

circuit values because L and R apply to the whole circuit The production of eddy current in the core the flux

will decay at a slower rate than the current So that the actual release time will be a little longer than it takes

the current to fall to the release

L= Inductance

39 | P a g e

R= Resistance

It is now clear that to reduce releasing time to a minimum it is necessary that

- The relay iron should have low Hysterisis loss and low retentivity

- The degree of over energization of the relay should be restricted

- Connecting a suitable external resistance in series with the relay to keep LR ratio low

In non RE area for track circuit length less than 100M 9 ohm track relay only to be used Using relay

with minimum contacts as they require lesser current which keeps inductance value low

Train working safety is ensured only if the track relay of shortest length track circuit is released

before a light engine running at a highest permitted speed clears it Otherwise the track circuit occupation

may go undetected To avoid this a special provision has to be made in signal control circuits wherever

necessary

The following methods may be adopted for reducing the time lag of track relay

(a) Restrict the over energisation of relay since the release time depends on the initial working current

(b) Connecting a suitable external resistance in series with the relay to keep the LR ratio low

(c) Using relays with minimum contacts as they require lesser operating current keeping the inductance

value low

40 | P a g e

CONCLUSION

Modern signalling is vital for safe and punctual movements of trains In the Indian railways The Signalling

and Telecommunication Department is responsible for providing modern effective and relaible signalling

systems as well as telecommunication systems

The first mode of communication used in Indian Railways was the use of electric telegraph

with the help of Morose code Morose code is the method of providing text information as a series of on-off

tones and lights or clicks that can be directly understood by a skilled listener or observer without special

equipmentEach character (letter or numeral ) is represented by a unique sequence of dots and dashes Later

this system becomes obselete and beggan the era of wireless communication which operated at audio level

frequency range

In wireless communication the significant advances took place the transition to miniature

valves or filament tubesBut this was abandoned too because of excessive current consumption and over

heating of the filament tubes

Fibre-optic communication is a method of transmitting information from one place to another by

sending pulses of light through an optcial fibreThe light forms an electromagnetic carrier wave that is

modulated to carry information First developed in the 1970s fibre optic communication systems has

revolutionized the telecommunications industry and have palyed a major role in the advent of the information

age Because of its advantages over electrical transmissionsoptical fibres have largely replaced copper wire

communications in core networks in the developed world The Indian Railways too is undergoing a transition

from Microwave communication to fibre optic communications

41 | P a g e

BIBLIOGRAPHY AND REFERENCES

1 wwwwikipediacom

2 wwwbritaniccacom

3 wwwirfcacom

4 Motorola GP60 system manual

5 Harris FAS 7000 manual

6 TOSHIBA Manual

3 | P a g e

Each card file to have one Power Supply PCB and always placed in slot no16amp17 Power supply

PCB is basically a DC-DC converter that converts 12V DC input supply is +12V -12V and +5V required for

various board functioning Based on diagnostic check by CPU Power Supply Card receives 250Hz signal

from CPU and extends supply to VCOR relay This card provides isolated supply to internal circuit

VITAL OUTPUT PCB Each Vital Output PCB has 16 Outputs It is available in 12V and 24V DC applications Each Vital

Output can drive an output device such as any Q-series relay This output relay in turn controls signals

points crank handle siding control level crossing etc Since Vital Output drives the relay which controls

important outdoor gears all the Vital Output boards are continuously diagnosed by a CPU Any abnormality

in any of the outputs will shut down the system to ensure safety

VITAL INPUT PCB Each Vital Input PCB has 16 Inputs It is available in 12V and 24V DC applications Each Vital Input

is assigned to read the status of outdoor gears such as Track circuits Point detectors Crank handles Siding

controls level crossing etc Since the Vital Inputs read the status of outdoor gears they are normally

configured with double cutting arrangement using relay contacts

NON-VITAL INPUTOUTPUT PCB Each Non-vital IO has 32 inputs and 32 outputs in one PCB It is available in 12V and 24V DC

applications Non-vital inputs are Panel push buttons and keys Non-vital outputs are Panel indication LEDs

counters and buzzers The status of Non-vital Inputoutput is known from LED indications available in front

of the card

VITAL CUT OFF RELAY- VCOR Each card file will have one VCOR to ensure the healthiness of the system VCOR has 6 FB

dependent contacts each rated for 3 Amps When system is healthy the coil receives voltage from Power

Supply PCB which in turn controlled by CPU Power to Vital output board is controlled by VCOR thus

ensuring safety

WIRING HARDWARE 48 Pin Address select PCB and Connector assembly is provided for Vital Input and Vital Output

cards 96 Pin Address select PCB and Connector assembly is provided for Non-Vital IO cards 48 Pin

Connector Assembly is provided for PS and CPU PCB EEPROM PCB which is provided on rear side of the

CPU connector to configure various serial communication ports Keying plugs are provided in the cardfile to

ensure coding to each type of cards

SOFTWARE MODULES USED IN THIS SYSTEM System software consists of the following

EXECUTIVE SOFTWARE This software is common to all EIrsquos for the same company manufacturing

This is a factory installed software

Performs all operations

Cuts off vital supply voltage to output relays in case of unsafe failures

APPLICATION SOFTWARE This software is specific to each station and different for different stations

This is as per table of control of specific station

Can be installed at site by signal engineers

Logic installed through Boolean expressions or user-friendly equations

4 | P a g e

A GEC-MANUFACTURED SSI INTERLOCKING CUBICLE

A PAIR OF DATA LINK MODULES

TRACKSIDE FUNCTIONAL MODULE

5 | P a g e

INTEGRATED POWER SUPPLY

INTRODUCTION A typical 4 line station requires power supplies of 24 V DC( 5 nos ) 12 VDC ( 5nos ) 6V (2 nos)

110 V DC and 110 V AC for signalling These require as many chargers and Secondary cells amp Invertors

requiring more maintenance amp spares Can they be Integrated in to one system

Thus the concept of Integrated Power Supply has been evolved by integrating concepts One Charger

One set of Battery Bank feeding Invertors and DC- DC converters for deriving various DC amp AC

voltages Integrated power supply system delivers both AC amp DC Power supplies as an output with the

output voltage tolerance of plusmn 2

ADVANTAGES Reduces maintenance on Batteries Battery charger amp overall maintenance

Its construction is in modules and hence occupies less space Reduced space requirement resulting in

saving of space for power supply rooms

Provides centralized power system for complete signaling installation with continuous display of

working status of system for easier monitoring

Defect in sub-units of system is shown both by visual amp audible indication Reflects the condition of

battery with warning

Replacement of defective modules is quick amp easy without disturbing the working of the system

It uses (n+1) modular technology hot standby arrangement and hence high reliability and more

availability of the system

The system provides uninterrupted supply to all signalling system even during the power failures

Thus No blank Signal for the approaching drivers

System can be easily configured to suit load requirement

The diesel generator set running (Non-RE area) is reduced almost to lsquoNILrsquo Hence low wear and tear

of DG set components amp reduced diesel oil consumption

COMPONENTS (a) Un-interrupted power supply (U P S)

(i) SMPS Battery chargers with Hot stand-by mode

(ii) Hot Standby PWM Inverters with auto changeover

(iii) CVT Regulator [FRVS]

(b) AC distribution board [ACDB]

(i) STEP DOWN TRANSFORMERS

(c) DC distribution board [DCDB]

(i) DC-DC converters

WORKING IPS works satisfactorily for AC input variation of 150V AC to 275V AC with single-phase power supply

and frequency variation from 48 Hz to 52 Hz The input is fed to SMPS charger which converts in to 110

VDC as output It is fed as input to three sub units

To battery bank charging the batteries

To ON line inverters that converts 110 VDC in to 230 VAC plusmn 2as output

6 | P a g e

As 110 VDC bus bar to DC Distribution Panel as an input to various DC-DC converters located in

it

A 110 V Battery Bank of VRLA cells are connected to SMPS Panel IPS Status Monitoring Panel is

located at ASM room or at SampT staff room if round the clock SampT staff is available at Station

CONSTRUCTION IPS mainly consists of

SMR (Switch Mode Rectifier) Panel SMPS based Float cum Boost Charger (FRBC) Panel

AC Distribution Panel

DC Distribution Panel

Battery Bank (110V DC)

Status Monitoring Panel

SMR (SWITCH MODE RECTIFIER) PANEL SMPS BASED FLOAT

CUM BOOST CHARGER (FRBC) PANEL It consists of SMR FRBC modules and Supervisory amp Control Unit SMPS based SMRs

(converters) SMPS based Float cum Boost Chargers (FRBC) modules are provided with (n+1) modular

technology hot standby arrangement with active load sharing basis and 1 additional module as a cold standby

(n+2) Supervisory amp Control Unit which controls and monitor the complete system It has various

indications on the panel reflecting the working of the panel

FRBCs are suitable for operating in parallel on active load sharing basis with one or more modules of similar

type make and rating

n = required no of modules to cater for actual current requirement

AC DISTRIBUTION PANEL It is made of ON-Line inverters with (1+1) modular technology hot standby arrangement amp CVT

(Constant Voltage Transformer) AVR (Automatic Voltage Regulator) and set of step down

transformersThe inverter is protected against overload and short circuit with auto reset facility Whenever

the failure occurs it trips and restart automatically after about 10 to 20 sec But if the problem persists the

protection is permanently gets latched and it will not be switched ON again unless the fault is cleared

followed by pressing of reset button The output of inverters is regulated to 230V AC plusmn 2 50Hz plusmn1Hz for

an input voltage variation of 90V DC to 140V DC Normally both the Inverters are powered ON and both are

delivering the Output voltage but only one (main) inverter is connected to the Load If main inverter is failed

then only the stand-by inverter will come on Load automatically with in 500msec At 70 Depth of

Discharge (DOD) of the battery bank 110VDC supply to the inverters will be cut-off So the Signals feed will

be cut-off The auto-change over arrangement is also provided for bringing the CVT in circuit with in

500msec when the both the inverters output is failed It has various indications on the panel reflecting the

working of the panel

DC DISTRIBUTION PANEL It takes care of DC Power supply requirements of our signalling It consists of sets of DC-DC

converters for individual DC power requirements with (n+1) modular technology hot standby arrangement

with active load sharing basis The DC-DC converters of Relay Internal are provided with (n+1) modular

technology hot standby arrangement with active load sharing basis and 1 additional module as a cold standby

(n+2) The DC-DC converter works satisfactorily with the input voltage variation of 98VDC to 138VDC At

90 Depth of Discharge (DOD) of the battery bank all the DC-DC converters 110VDC Input supply will be

cut-off except for Block Tele DC-DC converters The supply for Point operation is also catered through a

20A fuse by this unit It is also provided with various indications that reflect its working

7 | P a g e

STATUS MONITORING PANEL IPS status monitoring panel has been provided in the ASM room for giving the important alarms and

indications to ASM Status Panel tells present working status of IPS displaying battery voltage continuously

and five other indications which will light according to IPS status During normal working these indications

will not lit Whenever the battery has come on to the load and has discharged by 50 DOD (Depth of

Discharge) then first Red indication lit with description ldquoSTART GENERATORrdquo with audio Alarm ie DG

set is to be started and put on the load If DG set is not started with this warning then if battery gets further

discharged to 60 DOD and second Red indications appears with description ldquoEmergency Start generatorrdquo

with audio alarm even now if DG set is failed to be started the battery further gets discharged to 70

DOD and 3rd Red indications appear with description ldquo System shut downrdquo with audio alarm which will

continue till Generator is started resulting in AC output from IPS is automatically cut off results all the

signals will become blank

When there is any defect in any sub module of IPS even without affecting working of system the 4th

Red indication appears with description ldquoCall SampT Staffrdquo with audio alarm so the ASM advises SampT staff

accordingly Green LED 5th indication comes with the description ldquoStop Generatorrdquo with audio alarm when

the DG set is running and if the Battery bank is fully charged condition

EARTHING The IPS systems and its individual modules are having earth terminals and all these are properly

earthed with earth resistance of less than 1 ohm Earth provided shall preferably be maintenance free using

ground resistance improvement compound (The acceptable Earth Resistance at earth busbar shall not be

more than 1 ohm Code of practice for earthing and bonding system for signalling equipments)

LIGHTNING AND TRANSIENT PROTECTION IN IPS Manufacturer will provide Stage1 amp Stage 2 protection along with the IPS These are described

below

Stage 1 protection is of Class B type against Lightning Electro-Magnetic Impulse (LEMP) amp other

high surges provided at Power Distribution Panel It is provided with a 63 Amp fuse in phase line and is

connected between Line and the Neutral and also between the Neutral and Earth

Stage 2 protection (Power line protection at Equipment level) is of Class C type against low voltage

surges provided at the equipment input level This is thermal disconnecting type and equipped with

protection against SPD (surge protection device) failure due to open amp short circuit of SPDs and is connected

between the Line and the Neutral If supply data signalling lines (ACDC) are carried through overhead

wires or cables above ground to any nearby building or any location outside the equipment room additional

protection of Stage 2 type shall be provided at such locations Class B amp Class C arrestor is provided on a

separate wall mounting type enclosure in IPS room

Stage3 protection (Protection for signallingdata line) is of Class D type All external data signalling

lines (ACDC) shall be protected by using this Class D type device It consists of a combination of Varistors

and Gas Discharge Tube with voltage and current limiting facilities

FEATURES Chargers used in this system are of SMPS technology chargers with 90 efficiency These chargers

are supported with hot standby mode with (n+1) modular technology

Onetwo sets of Maintenance free Battery banks (110VDC) Normally one set (110VDC) of Battery

bank is used Conventional flooded type Lead Acid Batteries or Low Maintenance Lead Acid

batteries can also be used (SMRs settings are required to be adjusted depending on the type of

Batteries used) Various voltage levels of

8 | P a g e

battery banks are avoided Reduction in Battery maintenance amp less flour area required

DC-DC Converters working from 110V Central battery have been used for all dc supplies This has

improved overall efficiency of the system since number of conversion from AC to DC have been

reduced to 2 stage as compared to 3 stage conversion in case of transformer-rectifier system

DC-DC converters are available in modules Easy replacement of defective modules This ensures

less down time

DC-DC Converters are used in load sharing N+1 configuration (ie with hot standby with N+1

modular technology) to improve the reliability amp availability of the system

Capacity of inverter has been brought down to 15 KVA from 5 KVA and used for feeding only

Signals supply Hot standby inverter is provided with auto changeover facility This improves the

availability of the overall system

High efficiency inverter is used with PWM (Pulse Width Modulation) technology in place of Ferro-

resonant technology based inverter This improves the efficiency of the overall system

Continuous power to Signal Circuits even in absence of DG setLocal Power Supply

Generators need not be switched ON every time during train movement

Metal-to-metal relay installations and block working by axle counters have also been covered

Supply of spare modulesComponentsCells have been included as part of main supply

Provides highly regulated voltage to all signal relays amp lamps for better life

9 | P a g e

SINGLE SECTION DIGITAL AXLE COUNTER

INTRODUCTION- The axle counter equipment is working on high frequency and using amplitude modulation or phase

modulation for detection of presence of wheel The equipment described in this notes is Phase modulation type

for the detection of presence of wheel In the Phase modulation type track device the detection of presence of

wheel is with the phase reversal of 1800 out of phase which enables this system to be more healthy and safe

In Phase Reversal Modulation technique trolley suppression arrangements to prevent the counting of

wheels caused by push trolley passing over the track device are not required as the system will take care of

validation of generated pulses caused by passage of wheel over the track device depending up on the phase

shift of the pulse This phase shift of the pulse may be normally 160deg to 180deg for a train wheel and it may be

approximately 100deg to 120deg for a push trolley wheel

This is Digital Axle Counter equipment for single track sections containing 2 out of 2 micro-

controllers to count the axles establish the track occupancy of a track section and to provide this information

to the block or the interlocking equipment

In this system no separate evaluator is required and no analog data is being transmitted One set of

Axle counter equipment is provided at entry end and other set provided at exit end Both sets are being

connected through a twisted pair of telecom cable ie existing RE cable one PET quad is used for both UP

and DN Axle Counters Digital DATA is being transmitted between two ends of Axle counters (Outdoor

track side Detection points)This system is a fully duplex capable of operating according to CCITT V21 and

the Data will be transmitted at the rate of 300bitsec This data Transmitted ensure negligible interference of

the noise The system is highly reliable

FEATURES (a) The system consists of

(i) Single Section Digital Axle Counter (SSDAC) units

(ii) Tx Rx coils

(iii) Vital Relays

(b) TxRx coil axle detectors are mounted to the web of the rails The design of system consists of 21 KHz amp

23 KHz High frequency Phase Reversal type axle detectors

(c) Compatible with 90R 52Kg amp 60Kg rail profiles Easy to install commission amp maintain

(d) Track devices at both (entry amp exit) points of the section should be fixed on the same rail

(e) System is designed to detect the solid wheels with diameter gt 400mm with standard wheel flange

(f) The system works in pairs For monitoring single-track section one pair of SSDAC units are required and

to be installed near the trackside one at the beginning and another at the end of the track section ie

Trackside electronic counting equipment

(g) The basic design of the system is based on counting the number of axles passing at each detection point

These stored counts are transmitted to the second unit of the system and vice versa by means of modem

communication

(h) The communication consists of digital packets having details of Counts amp Health

10 | P a g e

(i) If counts registered at both detection points are equal the section is cleared otherwise the section is shown

as occupied The system ensures no error condition to arrive at the decision of clearance

(j) System is designed as per CENELEC SIL-4 (European standard) using micro controller along with other

electronic circuits and programmed using dedicated software When any of these circuits fail the system

goes to fail safe condition

(k) It is programmable for either Preparatory Reset or Conditional Hard Reset as per requirement

(l) Micro controller based design with 2 out of 2 decisions and counting through software

(m) V21 Modem communication (2-wire) on frac12 quad cables and also compatible to work on voice channel of

OFC amp Radio

(n) Opto isolated vital relay drive for Q-style 24V 1000 _ and Vital Relay output can be giving at both ends

of the system

APPLICATIONS The system can be widely used in Railways for Block Working (BPAC) Intermediate Block Signaling Auto

signalling and Track circuiting for i) Loop line ii) Main line iii) yard lines

SYSTEM DESCRIPTION

This system comprises of

Tx coils-2 nos

Rx coils-2 nos

Reset Box (RB 258A)

Card 1 Signal Conditioning Card ndash 1

Card 2 Signal Conditioning Card - 2

Card 3 Micro controller Logic Board ndash 1

Card 4 Micro controller Logic Board ndash 2

2 nos for independent resetting ndash when used in block sections

1 no for common resetting ndash when used for Track circuiting at stations

Card 5 Event Logger Card

Card 6 Modem Card

Card 7 Relay Driver Card

Card 8 DC-DC Converter Card

SSDAC (DACF 700AP) UNIT

(A) SIGNAL CONDITIONING CARD (CARD 1amp2) (SCC) -1 (SCC-1) generates 21 KHz carrier

signals

-2 (SCC-2) generates 23 KHz carrier signals which is transmitted to 2nd

set of Tx coils

s receive these signals

modulated

train pulses

11 | P a g e

(B) MICRO-CONTROLLER LOGIC BOARD CARD (CARD 3amp4) (MLB) The Micro-controller Logic Board (MLB) is the heart of the system

o 8051 Based Architecture

o 8 Bit Micro Controller

o ATMEL AT89S8252 Micro controller

o 2 out of 2 Decision

o Uses C subset language

- TOOLS

o KEIL μ Vision Development System

o Universal Programmer

o 2KB Program Memory

o 256 bytes RAM

o 8KB Flash memory

o 32 Programmable IO lines

o Wide Operating Voltage range of 4V-6V

o Full Duplex Serial Port

o Programmable Watch Dog Timer

o Fully Static operation up to 24MHz (Upgraded to 40MHz)

o Operating Temperature of ndash40degC - +85degC

o Use of State Machine for Axle Counting

o Use of ASCII MODBUS protocol

o Use of CRC16 technique for Error Checking during communication

o Wheel detection

o Train direction checking and

o Wheel counting functions

o It receives the remote wheel count and computes the status of the section for clear or occupied

o It also checks various supervisory signal levels like supervisory of TxRx coils presence of various

cards communication link failure etcThese cards communicate with each other for wheel count

At Entry-end if train enters into section (1st detection) the counts are incremented and when train

shunts back from the same detection ie if train exits from the section from the same detection the counts are

decremented At Exit-end if train enters into section (2nd detection) the counts are decremented and when

train shunts back from the same detection ie if train exits from the section from the same detection the

counts are incremented Both the track devices at Entry and Exit ends must be fixed on same side of the

track

This MLB card is having Extensive LED display

o A block of 8 LED indicators for count progress error display

o 2 independent LED indicators for section status

o The errors occurring in the system during the operation of the SSDAC are encoded and are indicated by

means of the 8-LED block present on the front panel of the MLB cards

(c) EVENT LOGGER CARD (CARD 5)

Event logger card is designed to capture and store important signals from the remote and local SSDAC units

The stored data can be downloaded from the event logger card for the purpose of analyzing the events

occurring during the operations of the SSDAC The data can be analyzed with the help of CEL data analyzer

software

12 | P a g e

The event logger card captures following signals

(i) Pulse signals

(ii) Supervisory signals

(iii) Card removal information

(iv) Serial packets from

Event Logger card has a Rabbit processor and 2 MB FLASH MEMORY to store packets The data is initially

stored in the buffer and subsequently transferred to FLASH memory every two minutes Normally 4096

pages of the data can be stored in flash memory on FIFO (first in first out) basis

Run This LED blinks continuously indicating the normal working of the event

Log This LED blinks whenever data is being logged into the flash memory (Approx after every 2 minutes)

Dnld This LED is ON when data is being downloaded from the flash memory of the card and becomes OFF

when download is complete

(D) MODEM CARD (CARD 6) (i) The modem card transmits and receives the digital packet information form one counting unit to the other

The packet will appear after every 18 sec and the packet carries the latest information such as

(ii) The modem card being used is V21 type (2-wire) in SSDAC

(iii) This card interfaces with serial RS232C port of both Micro-controller Logic Boards

(iv) It multiplexes the two RS232C inputs and selects one of the two channels and provides signal conversion

from digital to analog (FSK modulation) and vice-versa

(v) Data transmission rate is 300 bitssec

(vi) Automatic Gain Control circuit is incorporated hence no gain adjustments required

(vii) Mode selection on Modem card The modem has been set in lsquoORIGINATORrsquo mode for entry and in the

lsquoANSWERrsquo mode for exit in the factory

(viii) LED Indications provided on Modem card

-Transmitting the signal when LED is flashing

- Receiving the signal when LED is flashing

-Remains OFF in SSDAC

-Carrier is detected when LED is glowing

(E) RELAY DRIVER CARD (CARD 7) (i) The Relay Driver card (RD) provides the 24V DC output required for driving Vital Relay

(ii) One RD card is used in each SSDAC counting unit The RD card receives the command of clear and

clock signals from MLB1 amp MLB2 cards and drives the vital relay lsquoONrsquo when section is NOT OCCUPIED

through opto- isolator circuit

(iii) If a train occupies the section the vital relay is dropped The vital relay status is read back by the system

as per the driving output

(iv) It has

13 | P a g e

ndash LED flashes when the section is clear

ndash LED flashes when the section is clear

All the above LEDrsquos are lit for section clear condition

(F) DC-DC CONVERTER CARD (CARD 8)

INPUT VOLTAGE Nominal Voltage voltage 24V DC Maximum current drain= 12A

Required voltage 18V DC to 30V DC

Output voltage

Nominal Voltage +5 V DC 2 A Required voltage 4 7 5 t o 525V DC

Nominal Voltage +12V DC 200 mA Required voltage 1175 to 1225V DC

Nominal Voltage +24V DC 300 mA with common ground Required voltage 235 to 245V DC

Nominal Voltage +15V DC 100 mA with isolated ground Required voltage 145 to 155V DC

SURGE VOLTAGE AND LIGHTNING PROTECTION Transient surge voltages arise as a result of Lightning discharge switching operations in electrical

systems and electrostatic discharge These surge voltages often destroy the electronic equipment to a large

extent In order to prevent surge voltages from destroying the equipment all the input lines of SSDAC ie

Power Supply (24V) Reset (48V) amp Modem is to be routed through surge voltage protection devices for

effectively protecting the system These devices (3 numbers) are mounted in a box and supplied along with

the system One number of box is to be installed at each location and wired to the SSDAC

Each surge voltage protection device consists of two parts

(a) Base

(b) Plug Trab

The Base of the device is used for wiring the input and output signals The connection details from relay

room to the box and from box to SSDAC unit are provided on the box The Plug Trab consists of MOV and

GD Tube and diverts the excess energy during surge voltages or lightning into the ground connection The

operation of these devices relies on a high quality ground connection in order to safely shunt away the

unwanted energy The impedance of the ground connection is critical and it should be less than 2 Ohms

NOTE The 3 Plug Trab connections are not to be interchanged with one another The plug Trab is a

detachable device and can be replaced with SPARE unit in case of blown device which is indicated by

means of LED for 24 V

EFFECTIVENESS OF PLUG TRABS The effectiveness of plug Trab depends wholly on the Earth connection provided to the system The earth

provided to the system should be less than 1 ohms and connections should be firm and proper to the SSDAC

unit VR box etc

SURGE VOLTAGE AND PROTECTION DEVICE SV-120 The Surge Voltage protection device is to be installed at each location along with every SSDAC unit

14 | P a g e

EARTHING- The lead wires connecting the installation and the earth electrode shall ordinarily be of stranded

copper wire of 29 sq mm (19 strand wires of 14 mm diameter) Copper wire has been specified because GI

wires usually are having greater corrosion However in areas where copper wire may be frequently stolen

due to theft ACSR of size 64 sq mm (19 strands of 211 mm diameter) may be used

LIMITS OF EARTH RESISTANCE (a) Apparatus case connected to Earth (SSDAC and vital Relay Box is housed in Apparatus case and

Connected to earth at outdoor) shall be less than or equal to 1 ohm

(b) All cable connected to same earth shall be less than or equal to 1 ohm

(C) Reset box connected to earth near SM s Room shall be less than or equal to 1ohm

EQUIPMENT TO BE EARTHED A Common Earth should be provided for SSDAC for items 1(a) amp (b) of the above at the outdoor

(a) The Apparatus Case is to be connected to earth (the chassis of SSDAC amp Vital Relay Box should be

properly connected to apparatus case)

(b) Metallic sheath and armouring of all the underground main cables are to be earthed

(i) In RE area the metallic sheath and armouring of main telecom cables are earthed at both ends

(ii) In RE area the armouring of Jelly filled cable shall be earthed at both ends

(c) The Earthing shall be provided at every location box where cables are terminated

(d) Earth already available for other equipment may be used for earthing of Reset Box near SM s Room

Cabin etc

15 | P a g e

DATALOGGER

INTRODUCTION Datalogger is a Microprocessor based system which helps in analysing the failures of relay inter

locking system Electronic Interlocking system This is like a black box which stores all the information

regarding the changes take place in relays AC DC Voltages and DC currents along with date and time The

same information data can be transferred to the computer to analyse further ldquoon line ldquooff linerdquo analysis of

stored date A print out also can be obtained through a printer by connecting directly to the datalogger unit

The data belongs to Relay contacts is considered as digital inputs and the data belongs to voltage

levels currents is considered as Analog inputs Datalogger lsquos are mandatory for all new relay interlocking

(PIRRI) EI installations and it is also recommended to provide in all existing PIs RRIs To increase the

line capacity mechanical signalling equipments are upgraded to PI RRI or EI Due to complexity in the

circuits and wiring sometimes it is very difficult to rectify the failures So datalogger can monitor these

systems with real time clock Thus it can be named as black box of Samp T equipments and hence it is a vital

tool for accident investigation Datalogger is used at Stations yards Whereas in case of Auto Section amp IBH

Mini dataloggers called as Remote Terminal Unit (RTU) are used

ADVANTAGES OF DATALOGGERS (a) Dataloggers helps in monitoring the typical failures such as intermittent auto right failures

(b) It helps in analyzing the cause of the accidents

(c) It helps in detecting the human failures errors such as

(i) Drivers passing signal at Danger

(ii) Operational mistakes done by panel operators ASMrsquos of operating department

(iii) Signal and telecom engineering interferences in safety circuits

(iv) Engineering and electrical department interferences failures

(v) It helps as a ldquoTOOLrdquo in preventive maintenance of signaling gears

(d) Dataloggers can be connected in network Networked dataloggers helps to monitorthe PIRRIEI remotely

(e) Failure reports can be generated remotely with help of datalogger network

(f) On line and Off line track simulation is possible

(g) Speed of the train on point zones can be calculated

(h) Age of the equipment in terms of number of operations etc

COMMON EQUIPMENT FOR ALL DATALOGGERS ARE GIVEN

BELOW (a) CPU card

(b) Digital and Analog input cards

(c) Local terminal(PC)

(d) communication links

(e) Printer

All the dataloggers requires a potential free ( spare ) relay contact for monitoring digital inputs

through Digital input cards amp for monitoring Analog inputs such ACDC bus bar voltage levels through

Analog input cards Digital and Analog inputs are connected to the Processor card Processor card consists of

memory ICrsquos Memory ICrsquos are programmed as per requirement of the signal engineers

Provision of Dataloggers is mandatory with RRI systems and is optional for PI systems as per

amendment to the specification for Relay Interlocking systems ( IRSS-36 ) The data collected by the

datalogger can be used for failure analysis repetitive discrepancies and for accident investigations

16 | P a g e

Note

If the serial communications is more than 50m then line drivers shall be used up to 3 Kms

4wire leased line Modems shall be used if the serial communication is more than 3 Kms

STUDY OF EFFTRONICS DATALOGGER TECHNICAL DETAILS (a) 24V 12VDC Power Supply

(b) Total Storage Capacity of 10 Lakh events

(c) In-built Temperature sensors

(d) Internal Buzzer for alarming during failures

(e) Real Time clock with internal battery backup with data retention up to 10 years

(f) 512 LED matrix to indicate the status of 512 Digital inputs at a time page wise

(g) Seven segment LCD screen (2x24) to display the status of digitalanalog signalsTime Temperature etc

(h) Using the keyboard various functions can be viewed in the LCD panel

(i) Max Digital Inputs 4096

(j) Max Analog Inputs 96

(k) Digital Input Scanning Time 16 millisecond

(l) Analog Input Scanning Time is less than 1 Sec

HARDWARE (EQUIPMENT) Datalogger system consists of

(a) Datalogger (CPU - with Microprocessor 68000)

(b) Digital input cards

(c) Dual modem card

(d) Digital Scanner units (DSU)

(e) Analog Scanner units (ASU)

CPU CARD It is provided with Motorola microprocessor M 68000 It performs all the activities pertaining to the

datalogger It continuously scans (check) the Digital inputs(inbuilt) Digital Scanner Units and Analog

Scanner Units ie scanning of digital signals (Relay operations) for every 16-milli seconds and scanning of

analog signals (ie ACDC voltages amp DC currents) for less than 1 second

This card will support the IO interfaces of LCD (Liquid Crystal Display) - 2X24 alphanumeric Key

Board LED Matrix Display Real Time Clock LCD display and keyboard This will acts as man machine

interface between the datalogger and the signal engineer All the operations (Software) can be performed

using this LCD and keyboard

Real time display with 7 Segments This is built in real time clock within Datalogger and its current

time will be displayed on six 7-segment display provided (Real time clock depend upon DALLAS 1286

chip) This IC will come with internal battery backup hence there is no need to add external batteries

CPU card continuously scans (checks) the DSUs and ASUs Each input connected to digital scanner

units are optically isolated by Opto couplers When CPU card scans the digital inputs it compares with the

previous stored data and if there is any change from the previous status then only that data will be stored (the

status conditions of relay) with date and real time A total of minimum 10 Lac events can be stored in

memory on first in first out basis so that latest data is available in the system There is no loss of data from

datalogger memory in case of power supply failure of datalogger

DIGITAL INPUT CARDS (IN-BUILT) This system is having maximum 8nos of inbuilt Digital inputs cards Maximum 64nos of digital

inputs can be connected to each digital input card The potential free relay contact may be front or back

contact terminated at the Tag Block from the relay of signals tracks points Buttons etc and are

17 | P a g e

subsequently connected to Digital input cards through Flat Ribbon Cable (FRC) connectors These in-built

digital input cards can monitor a total 512 nos of relays status

DIGITAL SCANNER UNIT (DSU) Each DSU contains 8 nos of Digital Input cards Each input card can be connected with 64 inputs

Total input capacity of DSU unit is 512 inputs These scanner cards contain Optocouplers and Multiplexer

Inputs are connected to Stag card The stag card out put is connected to DSU through FRC connectors

Maximum 7 nos of DSUs can be connected to the system So Digital input capacity of the system is 4096

All these digital inputs are scanned at rate of 16 msec

ANALOG SCANNER UNIT (ASU) ASU contains maximum 3 nos of Analog input cards Each input card can be connected with 8nos of

Analog inputs Total input capacity of the ASU is 24 analog input channels Maximum 4nos of ASUs can be

connected to the system Analog input channel capacity of the system is 96 All these analog inputs are

scanned at a rate of less than 1 sec

PARALLEL PORT Parallel port is provided for connecting printer

RS-232 SERIAL PORTS At least 6 Serial communication ports are provided for communication with other dataloggers

Central Monitoring Unit Remote Terminal Unit Electronic Interlocking system Integrated Power Supply

system etc

EXTERNAL NON-VITAL RELAY CONTACTS These relays provided in the system where 16 number of the Relay contacts are provided on the rear

panel through Tele control port to extend alarms and to control the power equipment from remote or local

locations through computer in case of any occurrence of failures Each control can sink or source 100 m

amps of current

INTERNAL MODEM CARD DUAL MODEM CARD (IN-BUILT) It is fixed in datalogger Euro rack itself One card contains two modems The top modem is called

ANS (answer) modem and the bottom modem is called as ORG (originate) modem It is used in case of

networking of Dataloggers In network connect lsquoANSrsquo modem to the lsquoORGrsquo modem of one adjacent station

and connect lsquoORGrsquo modem to the lsquoANSrsquo modem of other adjacent station

POWER SUPPLY Normally 24V DC (12V DC is optional) supply with battery backup is required for the system

working

Input Voltage Range 18Vhellip32V DC (For 24V) 9Vhellip18V DC (For 12V)

INPUT REQUIREMENTS Relay inputs (digital inputs) and analog inputs (voltages currents etc) are required to be connected

to the system as per the requirements of RRI PI SSI as the case may be Some of the inputs to be

monitored is given below

(a) Digital inputs

(i) Field inputs All TPRs NWKRs RWKRs ECRs Crank Handle relays SidingSlot LC gate

control relays etc

(ii) Control Panel inputs All button Knob SMrsquos Key relays

18 | P a g e

(iii) Internal relays

British system All HR DR HHR WNR WRR ASR UCR RR LR UYRTLSR TRSR TSR

JSLR JR etc

SIEMENS system Z1UR Z1UR1 GZR ZDUCR ZU(R)R ZU(N)PRG(R)RG(N)R U(R)S

U(N)PS UDKR DUCR U(R)LR UYR1 UYR2 G(R)LRGR1GR2

GR3 GR4 OVZ2U(R)RW(RN)R (RN)WLR Z1NWR Z1RWRZ1WR1 WKR1 WKR2 WKR3 etc

(b) Analog channels

(i) 230 V AC (for power supplies in the power panel)

(ii) 110V AC (for Signal and Track transformers)

(iii) 110V DC (for Point operation)

(iv) 60V DC (Siemens relays)

(v) 24V DC (Q-series relays)

(vi) 24V DC (for Block Axle counters)

(vii) 12V DC (for indication)

(viii) 20A (for point operation current)

(ix) 10V AC 5KHz (for Axle counter channels) etc

SOFTWARE MODULES OF DATALOGGERS

(a) Network Management of Dataloggers (NMDL)

(b) Reports

(c) Fault Entry

(d) Track Offline Simulation

(e) Train Charting

NMDL SOFTWARE FEATURES (a) Online Relay Status

(b) Online Faults - To view information of various Online Faults as they occur in the stations where

the Dataloggers are connected

(c) Online Simulation - Graphical view of relay operations train movements etc

(d) Remote monitoring of stations with the help of NETWORKING

SOFTWARE OBJECTIVES (a) Predictive Maintenance

(b) Easy identification of failures

(c) Crew discipline

(d) Train charting

REMOTE MONITORING OF STATIONS WITH NETWORKING OF

DATALOGGERS The individual Dataloggers of various stations can be interconnected through networking technology

The data of Remote Panel stations can be viewed in a Computer at the Central Monitoring Station The data

of the network is collected by the FEP (Front End Processor) which in turn is transmitted to the computer

COMPONENTS OF NETWORK MANAGEMENT OF DATALOGGERS

(a) Datalogger at stations

(b) MODEM and Transmission medium

19 | P a g e

(c) Front End Processor (FEP)

(d) Central Monitoring Unit (CMU) Computer

FEP (FRONT END PROCESSOR)

FEP acts as a buffer between the Central Monitoring Unit (Computer) and the Network It is provided

at centralised place to retrieve data continuously from station dataloggers and store in memory and transfer to

computer on request It stores 10 Lac telegrams It works on 12V DC It draws 16A continuous current

when all the three modems are connected Normally it shows the number of packets pending to be sent to the

computer on its 7-segment LED display It is provided with MOTOROLA 68000 microprocessor It has 6-

nos of RS-232 communication ports such as COM1 COM2 COM3 COM4 COM5 and COM6 COM1 is

used for Fault Analysis System (FAS) ie Central Monitoring Unit (Computer) connection COM2 to COM6

are used for networking For Bi-directional 2- nos of ports and for Tri-directional (T-network) 3-nos of ports

are used

DATA TRANSMISSION Dataloggers can be networked in Uni-directional Mode or Bi-directional Mode or T ndash Network Mode

In case of loss of data retransmission of data takes place

(a) Uni-Directional Mode

Each Datalogger will send data in only one direction to the FEP Unidirectional mode network is not

preferred

(b) Bi-Directional Mode

Each end of Network is connected to FEP and each datalogger can now transmit data in both the directions

Bi-directional Mode is advantageous it enables the Data Transmission even in case of Network Failure

(c) T - Network Mode

If more no of stations are in network ie if the network is too lengthy then T- network mode is preferred

COMMUNICATION The communication protocol for transmitting data and command between datalogger and CMU is

standardized by the RDSO and is given in the Specifications of Dataloggers

(a) The type of communication used in the network is dependent on the distance between the dataloggers

(b) For shorter distances Opto Converter Box- Opto isolated current loop communication is used

(c) For longer distances Modem (Dial-up leased) Fiber Optic Satellite Microwave communication

MODEMS Modems are used for DATA transfer between Dataloggers and Front End ProcessorThese are

configured to RS 232 Serial Communication Network is connected with two types of 4-wire modems

(a) Internal modem card Dual Modem card (in-built)

It is fixed in datalogger Euro rack itself One card contains two modems The top modem is called

ANS (answer) modem and the bottom modem is called as ORG (originate) modem

Note In case of networking of Dataloggers connect lsquoANSrsquo modem to the lsquoORGrsquo modem of one adjacent

station and connect lsquoORGrsquo modem to the lsquoANSrsquo modem of other adjacent station

(b) External modems

20 | P a g e

These are generally used at FEP (Front End Processor) side to connect the Dataloggers

(i) To transfer Data from one datalogger to another datalogger FEP Baud rate is 9600bps

(ii) These modems are 4-wire line communication

(iii) To transfer the data from FEP to RMU (PC) the Baud rate is 57600 bps

There is no difference between these modems functionally

CENTRAL MONITORING UNIT (CMU) COMPUTER

Central monitoring unit (Fault Analysis Unit) is a Personal Computer and its minimum configuration

shall be specified by RDSO from time to time System Software Windows XPVista(OS) Norton Kaspersky

(Anti Virus) Interbase where Server is not available (DBMS) Oracle where Server is available (DBMS)

software are required to run Datalogger System It is provided with Graphical User interface (GUI) based

software and retrieve data from all Networked dataloggers (up to 32) at various stations It stores data in

standard data base files The CMU is capable of analyzing the data and generate reports audiovisual alarms

on defined conditions This data can be compressed to take backup In central monitoring unit Software used

for analysis of data prediction of faults etc is written in a structured format so that purchaser can

reconfigure it if required It displays the status of signaling gears at any selected time in graphic form for any

selected station yard It retrieves the stored data amp simulates train movement It sends commands to various

Dataloggers to activate audio visual alarm or operate and electromagnetic relay

CMU shares data available in it by other PCs through available local area network where this data can

be used for train charting passenger information purpose The system generates audiovisual alarm in

ASMrsquosSignal Maintainerrsquos room in the case of power supply failure (battery voltage low) or battery charger

defective with acknowledgement facility

(a) Each datalogger has its own identity code which will be transmitted along with data packet to central

monitoring unit

(b) Events recorded at each station are continuously transmitted to central monitoring unit Response time of

data transfer will not exceed 10 sec

21 | P a g e

22 | P a g e

OPTICAL FIBER CABLE

INTRODUCTION The demand for bandwidth on transmission networks is increasing rapidly because video and

graphical rich contents are exchanged through the corporate network or the Internet The Gigabit Ethernet

became ommonly used in the corporate network backbone and 10Gbit Ethernet will be adopted in the near

future Meanwhile in the home the demand for high-speed network becomes popular as the wide spread of

broadband access eg CATV xDSL and FTTH The transmission medium with capability to transmit high

bit rate signal is necessary to satisfy these requirements

The telecommunication transport technologies move from copper based networks to optical fiber

from timeslot based transport to wave length based transport from traditional circuit switching to terabit

router and all optical based networks entering into a new era of optical networking

BASIC PHYSICS OF OFC

OPTICAL FIBER CABLE OFC have Fibers which are long thin strands made with pure glass about the diameter of a human

hair OFC consists of Core Cladding Buffers and Jacket as shown in figure

MONOCHROMATIC LIGHT OR SINGLE COLOR LIGHT Light or visible light is electromagnetic radiation of a wavelength that is visible to the human eye (

about 400 ndash 700 nm) The word light is sometimes used to refer to the entire electromagnetic spectrum Light

is composed of elementary particles called photons Three primary properties of light are

Light can exhibit properties of both waves and particles This property is referred to as wave-particle

duality The study of light known as optics In free space light (of all wavelengths) travels in a straight path

at a constant maximum speed However the speed of light changes when it travels in a medium and this

change is not the same for all media or for all wavelengths By free space it is meant space that is free from

matter (vacuum) andor free from electromagnetic fields

Thus the speed of light in free space is defined by Einsteinrsquos equation E = mc2

Frequency ν speed of light in free space c and wavelength λ are interrelated by ν = cλ

From the energy relationships E = mc2 = hν and the last one an interesting relationship is obtained

the equivalent mass of a photon m = hνc2

When light is in the vicinity of a strong electromagnetic field it interacts with it From this interaction

and other influences its trajectory changes direction as shown in figure

23 | P a g e

INCIDENT RAY REFLECTED RAY AND REFRACTED RAY An incident ray is a ray of light that strikes a surface The angle between this ray and the

perpendicular or normal to the surface is the angle of incidence Reflection is the change in direction of a

wave front at an interface between two different media so that the wave front returns into the medium from

which it originated Common examples include the reflection of light sound and water waves

The reflected ray corresponding to a given incident ray is the ray that represents the light reflected by

the surface The angle between the surface normal and the reflected ray is known as the angle of reflection

The Law of Reflection says that for a specular (non-scattering) surface the angle of reflection always equals

the angle of incidence The refracted ray or transmitted ray corresponding to a given incident ray represents

the light that is transmitted through the surface The angle between this ray and the normal is known as the

angle of refraction and it is given by Snells Law

The figure shows Incident ray Reflected ray Refracted ray the angle of incidence and angle of refraction

REFRACTIVE INDEX - Refractive index is the speed of light in a vacuum ( c =299792458kmsecond) divided by the speed

of light in a material ( v ) Refractive index measures how much a material refracts light Refractive index of

a material abbreviated as lsquo n lsquo is defined as lsquo n=cv lsquo Light travels slower in physical media than it does

when transmitted through the air Refractive index (n) is a function of molecular structure of matter optical

frequency optical intensity determines optical propagation properties of each wavelength ( λ ) may not be

distributed equally in all directions is affected by external temperature pressure and fields

Refractive index of a medium is a measure for how much the speed of light is reduced inside the

medium For example typical glass has a refractive index of 15 which means that light travels at 1 15 =

067 times the speed in air or vacuum Two common properties of glass and other transparent materials are

directly related to their refractive index

First light rays change direction when they cross the interface from air to the material and effect that

is used in lenses and glasses

Second light reflects partially from surfaces that have a refractive index different from that of their

surroundings

SNELLrsquoS LAW-

24 | P a g e

When light passes from one transparent material to another it bends according to Snells law which

is defined as n1sin(θ1) = n2sin(θ2)

where n1 is the refractive index of the medium the light is leaving θ1 is the incident angle between the light

beam and the normal (normal is 90deg to the interface between two materials)

n2 is the refractive index of the material the light is entering

θ2 is the refractive angle between the light ray and the normal

Snellrsquos law gives the relationship between angle of incidence and angle of refraction

For the case of θ1 = 0deg (ie a ray perpendicular to the interface) the solution is θ2 = 0deg regardless of

the values of n1 and n2 That means a ray entering a medium perpendicular to the surface is never bent The

above is also valid for light going from a dense (higher n) to a less dense (lower n) material the symmetry of

Snells law shows that the same ray paths are applicable in opposite direction

TOTAL INTERNAL REFLECTION- When a light ray crosses an interface into a medium with a higher refractive index it bends towards

the normal Conversely light traveling cross an interface from a higher refractive index medium to a lower

refractive index medium will bend away from the normal

This has an interesting implication at some angle known as the critical angle θc light traveling from

a higher refractive index medium to a lower refractive index medium will be refracted at 90deg in other words

refracted alon g the interface If the light hits the interface at any angle larger than this critical angle it will

not pass through to the second medium at all Instead all of it will be reflected back into the first medium a

process known as total internal reflection

The critical angle can be calculated from Snells law putting in an angle of 90deg for the angle of the refracted

ray θ2 This gives θ1

Since θ2 = 90deg

So sin(θ2) = 1

25 | P a g e

Then θc = θ1 = arcsin(n2n1)

For example with light trying to emerge from glass with n1=15 into air (n2 =1) the ritical angle θc is

arcsin(115) or 418deg For any angle of incidence larger than the critical angle Snells law will not be able to

be solved for the angle of refraction because it will show that the refracted angle has a sine larger than 1

which is not possible In that case all the light is totally reflected off the interface obeying the law of

reflection

OPTICAL FIBER MODE An optical fiber guides light waves in distinct patterns called modes Mode describes the distribution

of light energy across the fiber The precise patterns depend on the wavelength of light transmitted and on the

variation in refractive index that shapes the core In essence the variations in refractive index create

boundary

conditions that shape how light waves travel through the fiber like the walls of a tunnel affect how sounds

echo inside

We can take a look at large-core step-index fibers Light rays enter the fiber at a range of angles and

rays at different angles can all stably travel down the length of the fiber as long as they hit the core-cladding

interface at an angle larger than critical angle These rays are different modes Fibers that carry more than

one mode at a specific light wavelength are called multimode fibers Some fibers have very small diameter

core that they can carry only one mode which travels as a straight line at the center of the core These fibers

are single mode fibers This is illustrated in the following picture

OPTICAL FIBER INDEX PROFILE Index profile is the refractive index distribution across the core and the cladding of a fiber Some

optical fiber has a step index profile in which the core has one uniformly distributed index and the cladding

has a lower uniformly distributed index Other optical fiber has a graded index profile in which refractive

index varies gradually as a function of radial distance from the fiber center Graded-index profiles include

power-law index profiles and parabolic index profiles The following figure shows some common types of

index profiles for single mode and multimode fiber

26 | P a g e

OPTICAL FIBERrsquoS NUMERICAL APERTURE ( NA )- Multimode optical fiber will only propagate light that enters the fiber within a certain cone known as

the acceptance cone of the fiber The half-angle of this cone is called the acceptance angle (see figure 18)

θmax For step-index multimode fiber the acceptance angle is determined only by the indices of refraction

Where

n is the refractive index of the medium light is traveling before entering the fiber

nf is the refractive index of the fiber core

nc is the refractive index of the cladding

NUMBER OF MODES IN A FIBER - Modes are sometimes characterized by numbers Single mode fibers carry only the lowest-order

mode assigned the number 0 Multimode fibers also carry higher-order modes The number of modes that

can propagate in a fiber depends on the fiberrsquos numerical aperture (or acceptance angle) as well as on its

core diameter and the wavelength of the light For a step-index multimode fiber the number of such modes

Nm

Where

D is the core diameter

λ is the operating wavelength

NA is the numerical aperture (or acceptance angle)

MODE FIELD DIAMETER - All light do not travels through the core of the fiber but is distributed through both the core and the

cladding The mode field is the distribution of light through the core and cladding of a particular fiber

Mode-Field Diameter (MFD) defines the size of the power distribution When coupling light into or out of a

fiber MFD is important in understanding light loss

27 | P a g e

ADVANTAGE OF OFC COMMUNICATION - bull More information carrying capacity Fibers can handle much higher data rates than copper More

information can be sent in a second

bull Free from Electromagnetic and Electrostatic interference Being insulator no electric current flows through

the fibre and due to this reason fibres neither radiate nor pick up electro - magnetic radiation So WPC

CLEARANCE is not required

bull Low attenuation 025 dbkm at 1550 nm Loss in twisted pair and coaxial cable increases with frequency

where as loss in the optical fibre cable remains flat over a wide range of frequencies

bull Use of WDM ndash Switching routing at Optical signal level

bull Self healing rings under NMS control

bull Small size makes fibre cable lighter in weight So easy to handleOptic fibre cable weight (approx)

500 kg km Copper cable weight (approx) 1000 kgkm

The reasons are photons of light in a fibre

do not affect each other as they have no electrical charge and they are not affected by stray photons outside

the fibre But in case of copper electrons move through the cable and these are affected by each other

Optical fibre does not carry any electricity even if the cable is damaged or short circuited it does

not cause any spark or fire hazard

As the fibre do not radiate energy it can not be detected by any nearby antenna or any

other detector The fibres are difficult to tap and therefore excellent for security

As the signal transmission is by digital modulation there is no chance of cross talk in

between channels

Only by adding a few additional terminal and repeater equipments the

capacity of the system can be increased at any time once the cable is laid

ical effects and temperature variations

LIMITATIONS OF OFC -

difficult

- utilised

APPLICATION IN SIGNAL AND TELECOMMUNICATIONS transmission circuits

-haul circuits for linking of telephone exchanges

28 | P a g e

PROPAGATION MODES CONCEPT -

MODE - Mode is an available distribution of electromagnetic field in a plane transverse to the direction of

light propagation Each mode is characterized by frequency polarization electric field strength and

magnetic field strength Available patterns are derived from Maxwellrsquos equations and boundary conditions

LINEARLY POLARIZED (LP) MODE A mode for which the field components in the direction of propagation are small compared to

components perpendicular to that direction An optical fibre supports only different field patterns called as

lsquoLinear Polarizedrsquo or lsquo LPrsquo modes The reasons are

requirements

de

the accrual of power carried by different modes

There are two basic types of fiber Multimode fiber and Single-mode fiber

Multimode fiber is best designed for short transmission distances This is suited for used in LAN systems and

video surveillance Single mode fibre is best designed for longer transmission distances This is suitable for

long distance telephony and multi channel television broadcast systems

29 | P a g e

MULTI MODE FIBER Multimode fiber the first to be manufactured and commercialized simply refers to the fact that

numerous modes or light rays are carried simultaneously through the waveguide Modes result from the fact

that light will only propagate in the fiber core at discrete angles within the cone of acceptance MM fiber type

has a much larger core diameter compared to single-mode fiber allowing for the larger number of modes

and

is easier to couple than single-mode optical fiber Multimode fiber further categorized as Multimode step-

index and Multimode graded index fiber

PROPAGATION THROUGH MMSI FIBER Figure shows the principle of total internal reflection applies to multimode step index fiber Because

the corersquos index of refraction is higher than the claddingrsquos index of refraction the light that enters at less than

the critical angle is guided along the fiber

Three different light waves travel down the fiber One mode travels straight down the center of the

core A second mode travels at a steep angle and bounces back and forth by total internal reflection The third

mode exceeds the critical angle and refracts into the cladding Naturally it can be seen that the second mode

travels a longer distance than the first mode causing the two modes to arrive at separate times

PROBLEMS WITH MMSI FIBER AND SOLUTION This disparity between arrival times of the different light rays is known as dispersion and the result is

a muddied signal at the receiving end It is important to note that high dispersion is an unavoidable

characteristic of multimode step-index fiber The solutions are either use Graded index fiber or Single mode

fiber

PROPAGATION THROUGH MMGI FIBER Multimode Graded-index refers to the fact that the refractive index of the core gradually decreases

farther from the center of the core The increased refraction in the center of the core slows the speed of some

light rays allowing all the light rays to reach the receiving end at approximately the same time reducing

dispersion Figure shows the Light propagation principle through multimode graded-index fiber The corersquos

central refractive index ( nA ) is greater than that of the outer corersquos refractive index ( nB )

It is very clear from the figure the light rays no longer follow straight lines they follow a serpentine path

being gradually bent back toward the center by the continuously declining refractive index This reduces the

arrival time disparity because all modes arrive at about the same time The modes traveling in a straight line

30 | P a g e

are in a higher refractive index so they travel slower than the serpentine modes These travel farther but

move faster in the lower refractive index of the outer core region

PROPAGATION THROUGH SMSI FIBER Single mode fiber has a much smaller core that allows only one mode of light at a time to propagate

through the core The figure shows the single mode fiber

Single-mode fiber exhibits no dispersion caused by multiple modes Single-mode fiber also offers lower fiber

attenuation than multimode fiber Thus more information can be transmitted per unit of time because it can

retain the fidelity of each light pulse over longer distances Like multimode fiber early single-mode fiber was

generally characterized as step-index fiber meaning the refractive index of the fiber core is a step above that

of the cladding rather than graduated as it is in graded-index fiber Modern single-mode fibers have evolved

into more complex designs such as matched clad depressed clad and other exotic structures

SINGLE-MODE FIBER DISADVANTAGES The smaller core diameter makes coupling light into the core more difficult The tolerances for single-

mode connectors and splices are also much more demanding

CUTOFF WAVE LENGTH - Cutoff wavelength is the wavelength above which a single-mode fiber supports and propagates only

one mode of light In other words an optical fiber that is single-mode at a particular wavelength may have

two or more modes at wavelengths lower than the cutoff wavelength The effective cutoff wavelength of a

fiber is dependent on the length of fiber and its deployment The longer the fiber the lower is the effective

cutoff

wavelength The smaller the bend radius of a loop of the fiber the lower is the effective cutoff wavelength If

a fiber is bent in a loop the effective cutoff wavelength is lowered

SIGNAL ATTENUATION IN FIBER - Optical fiber has a number of advantages over copper However it also suffers from degradation

problems which can not be ignored The first of these is loss or attenuation Attenuation is typically the result

of two sub properties They are scattering and absorption Both of which have cumulative effects The second

is

dispersion which is the spreading of the transmitted signal and is analogous to noise

SCATTERING Scattering occurs because of impurities or irregularities in the physical construction of the fiber The

well known form of scattering is Rayleigh Scattering It is caused by metal ions in the silica matrix and

results in light rays being scattered in various directions

31 | P a g e

Scattering limits the use of wavelengths below 800nm The short wavelengths are much affected than longer

wavelengths It is because of Rayleigh scattering that the sky appears to be blue ( shorter wave length ) The

shorter wavelengths ( blue ) of light are scattered more than the longer wavelengths of light

ABSORPTION Absorption results from three factors They are hydroxyl ions ( OH- water ) in the silica impurities

in the silica and incomplete residue from the manufacturing process These impurities tend to absorb the

energy of the transmitted signal and convert it to heat resulting in an overall weakening of the signal The

Hydroxyl absorption occurs at 125 and 139 micro The silica itself starts to absorb energy at 17 micro

because of the natural resonance of the silicon dioxide

MACRO BENDING LOSS Macro-bending loss is caused by bending of the entire fiber axis The bending radius shall not be

sharper than 30d where d is diameter of cable A single bend sharper than 30d can cause loss of 05dB

The fiber may break if bending is ever sharper

MICRO BENDING LOSS Micro-bending loss is caused by micro deformations of fiber axis which leads to failures in achieving

total internal reflection conditions Micro-bends are small scale perturbations along the fiber axis the

amplitude of which are on the order of microns These distortions can cause light to leak out of a fiber

Micro-bending may be induced at very cold temperatures because the glass has a different coefficient of

thermal expansion from the coating and cabling materials At low temperatures the coating and cable

become more rigid and may contract more than the glass Consequently enough load may be exerted on the

glass to cause micro bends

Coating material is selected by manufacturers to minimize loss due to micro-bending The linear thermal

expansion coefficient of coating material shall be compatible with that of fiber

32 | P a g e

DISPERSION Dispersion is the optical term for the spreading of the transmits in the fiber It is the bandwidth

limiting phenomenon and comes in two forms Multimode dispersion and chromatic dispersion Chromatic

dispersion is further subdivided into material dispersion and waveguide dispersion

DISPERSION PHENOMENON IN OPTICAL FIBER Dispersion is the time distortion of an optical signal that results from the differences of time of travel

for different components of that signal typically resulting in pulse broadening As the distance traveled by

the signal is more broadening of pulse is more In digital transmission dispersion limits on the maximum

data rate and the maximum distance ie the information-carrying capacity of a fiber link The interference

from broadened pulse in the next interval shall not lead to erroneous interpretation of received signal

OPTICAL DOMAIN Understanding where attenuation and dispersion problems occur helps optical design engineers

determine the better wavelengths at which information can be transmit taking into account distance type of

fiber and the other factors which can severely affect the integrity of the transmitted signal The graph shown

depicts the optical transmission domain as well as the areas where problems arise The wavelength (nm)

is shown on X-axis and attenuation ( dBkm) is shown on Y-axis

There are four transmission windows appear in the figure The first one is at around 850 nm the

second at 1310nm third at 1550 nm and fourth at 1625 nm The last two labeled as C and L band

respectively The 850 nm wavelength at which the original LED technology operated The second window at

1310 nm has low dispersion The 1550 nm called as C-band is ideal wavelength for long haul

communication systems The network engineers can avoid transmitting signal at 1000 nm where Rayleigh

scattering 1240 and 1390 nm where hydroxyl absorption by water occurs to avoid high degree of loss

Optical fibers also can be manufactured to have low dispersion wavelength in the 1550nm region

which is also the point where silica-based fibers have inherently minimal attenuation These fibers are

referred to as dispersion-shifted fibers and are used in long-distance applications with high bit rates For

33 | P a g e

applications utilizing multiple wavelengths it is undesirable to have the zero dispersion point within the

operating

wavelength range

34 | P a g e

SIGNALLING RELAYS

INTRODUCTION A relay is an electromagnetic device which is used to convey information from one circuit to another

circuit through a set of contact ie front or back contact Constructional and electrically relays may be

divided into DC and AC relays because the means by which the electrical energy in the coil is converted in

to mechanical Energy in order to move the contacts are fundamentally different In DC type the contacts are

carried on an armature forming part of a magnetic circuit in which a field is set up by the current flowing in

the coils In AC types the contacts are attached by a link mechanism to a metal sector disc or cylinder in

which currents are induced by the alternating magnetic field produced by the currents in the coils

Every endeavor has been made to explain the action of each type of relay in the simplest possible manner

Relays are sophisticated switch gears used for remote control and succession control of various

electrical equipment In present days they are widely used because they are capable of protecting the

controlled equipment from cross feeding and overloading even as they cater for speedy operations

Most of the relays in present day signaling are electromagnetic devices although some of the relays control

circuits through electronic components like diodetransistors Integrated Chips etc

Railway signaling relays are unique in that

(a) They operate on low voltage and current

(b) They are more articulate as according to their special features they can work under restrictive conditions

and in any specified manner Virtually they can cater for all situations while contributing to speed and

accuracy in operations

CLASSIFICATION OF SIGNALLING RELAYS (a) According to the method of their mounting or fixture they are classified as

(i) Shelf type Relays which are loosely kept on shelves

(ii) Plug in type Relays which are plugged into a pre- wired plug boards

(b) According to their connection and usage they are classified as

(i) Track relays Relay which is directly connected to the track to detect the presence of vehicle

(ii) Line Relays Other than track relay all are line relays Relays connected to the selection circuit

(c) According to their vitality or importance in ensuring train working safety they are classified as

(i) Vital Relays All relays used for traffic control such as signal point controls track detection etc

(ii) Non-vital Relays Relays which operate control aids and accessories like warnings buzzers

Indications etc

(d) According to their special provisions to ensure reliability of their contacts they are classified as

(i) Proved type are those whose normalization after each operation shall be proved in circuit

controlled by their contacts Contacts in which both the springs have metal surfaces on their tips They may

get fused due to high sparking current across them during operation These may prevent relay normalization

and causes unsafe condition in traffic control To avoid this proving of relay normalization after each

operation is necessary

(ii) Non - proved type Need not to be proved to have been normalized after each operation as their

contacts have at least one non-fusible contact (carbon contact)

(e) According to their feed source relays are broadly classified as

(i) DC relays The relay which requires DC power supply for its operations are called DC relays Among

the DC relays

o DC neutral relays This relay closes the same set of contacts on energization with Normal polarity

or Reverse polarity supply

o Polar Relays This relay closes different set of contacts when energized with Reverse polarity

supply They may or may not have contact to close when deenergized

35 | P a g e

(ii) AC Relay AC Induction motor track relays Time element relays flashing indication control etc

(iii) Electronic Relays DC relays with electronic components in them are called electronic relays

DC NEUTRAL RELAY Each Relay has usually one or two coils with a hollow center to accommodate a coreThe coils are

made up of a large numbers of turns of small gauge soft drawn copper wire The two coils can be connected

in series or parallel according to the requirement of relay resistance The ends of the coils are terminated on

binding post to which the control wires are connected Each coil is placed around a core of specially selected

Iron or steel having high permeability and low retentivity The core should be susceptible to magnetism and

at the same time should have little residual magnetism The cores are connected at the top by a yoke to

complete the magnetism coupling between two ends of coils The bottom of each core is equipped with a

large steel or Iron block known as pole piece or face

A flat piece of Iron or steel called armature is supported by brackets which are securely fastened to

the pole piece The armature yoke and the pole pieces are also made of specially selected iron or steel of the

same quality as the core The armature carries the metallic spring contacts which are insulated from it

The circuit through the coils of the relay is closed It sets up a magnetic flux through the core yoke and the

armature The flux passing between the armature and pole faces causes the armatures get attracted to the pole

faces and armature picks up and closes front contacts When the circuit is opened the magnetic flux collapses

and the armature drops away by gravity from the pole faces the front contacts break and back contacts close

The front and back contacts of the relay can be utilised to make or break other circuits Two stop pins of

nonmagnetic material are fixed either on the armature or pole faces so that the armature cannot

come in contact with the pole faces It is essential to maintain a small air-gap between the armature and pole

faces so that low value of residual magnetism may not retain the armature in picked up position and causes

the relay to fail to drop away with a break in its control circuit

GENERAL USAGE

DC Neutral line relays are most commonly used for Railway Signalling controls and detection

Among them plug-in type relays are preferred in larger installations for space considerations Shelf type

relays are also in use mostly in wayside stations

There are many DC Neutral line relays in use with special features such as

(i) Delayed operation

(ii) Biased DC control

(iii) DC control unaffected by AC interference currents

(iv) Getting latched in operated condition till further feeding and others

Usage of DC polar relays is mostly in conjunction with block instruments that control traffic between

stations AC line relays are almost extinct in installations of British Signalling practice They are however

used for time control operations flashing indication control and such other special purposes in installations

with Siemens signalling practice widely Track relays are used according to the type of track detection

circuits chosen for a given location and context While most of the track circuits are still of the DC working

type requiring DC neutral track relays with them the prospects of their being replaced with Electronic track

circuits directly feeding DC line relays in future are great AC Track Circuits are used in DC Traction area

as conventional DC Track Circuits are not suitable there AC Track relays are used with them almost all of

the induction motor type In the British practice of signalling which was first introduced on Indian Railways

non-proved type relays with carbon to metal switching contacts are generally used for vital controls

They facilitate simple circuit designs But with the advent of German Practice introduced by Ms

Siemens later proved type relays with all metal to metal contacts are widely accepted in spite of

complications in circuit design caused by them A recent introduction is that of the same type relays made by

Ms Integra control However for some time now the appreciable features of both the practices are getting

36 | P a g e

incorporated together in the indigenous designs of signalling by railwaymen With this the usage of all types

of relays anywhere can be found without straight jacketed segration of relay types

CHARACTERSTIC OF ELECTRO-MAGNETIC RELAY The following are the characteristic of electro-magnetic relays A brief study of them helps in

understanding the choice of their components and designs features

1) Force of attraction

2) Effect of air gap

3) Effect of Hysterisis

4) Transient condition

FORCE OF ATTRACTION In any electro-magnetic system the force of attraction is given by

Where B - is the flux density a - is the cross sectional area of the particular part of the magnetic

circuit

In the case of a DC neutral Relay B is proportional to the current that is flowing in the coil

surrounding the electro-magnet and thus the force of the attraction is directly proportional to the square of the

current This square relationship has its own advantage especially in the case of DC track relay in that a

small reduction in the current will have a great effect on the working of the relay Also for a given change of

current the make and the break will be quicker with lesser possibility of arcing

EFFECT OF AIR GAP

Curve lsquoArsquo is magnetisation curve for the iron and is all practical purpose a straight line up to the

saturation point Curve lsquoBrsquo is the magnetisation curve for the open-air gap which is a straight line through

out because per magnetisation curve of the whole

magnetic circuit of the relay and for a given force is the sum of the amp-turns for the iron part and the amp-

turns for the air gap

When the front contacts are open the force required to pick up the armature is shown on curve lsquoCrsquo to be F1

but after the armature has operated it will be separated from the core by stop pins In this position the amp-

turns required to maintain the armature is less as indicated by the dotted line from 1 on curve C to 2 on curve

37 | P a g e

F But actually the current in the coil is unaltered the force on the armature is greater than required as

indicated at 3 on curve F Part of this extra force is used to flex the front contacts sufficiently to give good

contact pressure when it is in energised position

The difference between the pick-up and the drop-away current should be as small as practicable in

track relay to ensure good shunting characteristics This is achieved firstly by the choice of good quality relay

iron and secondly by having a small air gap between armature and core If the air gap is not available then

the residual magnetism fluxes might cause the armature to be retained when the supply is disconnected For

this reason residual pins are provided to ensure a definite minimum air gap in the energised position

EFFECT OF HYSTERISIS

Hysterisis is the property by which the flux produced lags behind the current In the de-energized

condition there will be small residual flux in the core When the voltage is applied to the coils the current in

rising to its steady value first causes the flux to rise from 1 to 2 along the curve At this point the flux density

will be sufficient to attract the armature and reduce the air gap the flux then raise to 3 and continue to 4

which corresponds to the steady current in the coils When the voltage is disconnected the current in falling

caused the flux to fall from 4 to 5 along the curve At this point the flux density will fall below the value

required to maintain the armature which will release thus increasing the air gap and reducing the flux to 6

Finally the

flux will decrease from 6 to 1 where the current will again be zero

The relay core is made of material having high permeability and low retentivity As mentioned in

the IRS specification Electromagnet iron may be in the form of a

(a) Bar of silicon steel

(b) Best Yorkshire wrought iron

(c) Swedish charcoal iron

(d) Electrical steel sheets

` This reduces the difference between pick up value and Drop away value By selecting good quality

core material Percentage release and sensitivity of the relay will be improved

TRANSIENT CONDITION

38 | P a g e

When the voltage is applied or disconnected from the coils it takes some little time before the current

become steady These are known as transient conditionsrdquo and are important so far as track relays are

concerned When the voltage is first applied to the coils the magnetic flux in rising cuts the turns on the

coils and in so doing produces a back EMF that opposes the applied voltage and retards the growth of

current

The growth and decay of flux are decided by the relationship between the inductance and resistance

in the circuit is known as time constant It is not fixed quantity in the case of DC neutral relay This value of lsquo

Lrsquo is less when the relay is in de-energised condition (L1) than when the relay is in energised condition (L2)

The magnitude of flux that is established for a given change of current is different in two cases

When the current reaches the pick up value the armature closes and the inductance is increased to L2

due to reduced air gap the flux per amp is increased The increase in flux increased the back EMF during the

movement of the armature after which the current continuous to raise along a new curve corresponding to the

increased inductance until it reaches the final value (ER) This process is indicated above in fig24

When the supply is disconnected the current is obliviously reduced to zero immediately but the flux

decay comparatively slowly owing to the eddy currents produced in the core by the rapid flux change which

tend to maintain the flux The drop away time on a disconnection is however generally negligible See fig

below

If the relay releases due to the reduction in current from say I 2 to I 1 caused by the application of

shunt resistance (as in the case of track relay ) the time taken is much longer than the relay is simply

disconnected The rate of rise or fall of current during the transient conditions is also depends on exterior

circuit values because L and R apply to the whole circuit The production of eddy current in the core the flux

will decay at a slower rate than the current So that the actual release time will be a little longer than it takes

the current to fall to the release

L= Inductance

39 | P a g e

R= Resistance

It is now clear that to reduce releasing time to a minimum it is necessary that

- The relay iron should have low Hysterisis loss and low retentivity

- The degree of over energization of the relay should be restricted

- Connecting a suitable external resistance in series with the relay to keep LR ratio low

In non RE area for track circuit length less than 100M 9 ohm track relay only to be used Using relay

with minimum contacts as they require lesser current which keeps inductance value low

Train working safety is ensured only if the track relay of shortest length track circuit is released

before a light engine running at a highest permitted speed clears it Otherwise the track circuit occupation

may go undetected To avoid this a special provision has to be made in signal control circuits wherever

necessary

The following methods may be adopted for reducing the time lag of track relay

(a) Restrict the over energisation of relay since the release time depends on the initial working current

(b) Connecting a suitable external resistance in series with the relay to keep the LR ratio low

(c) Using relays with minimum contacts as they require lesser operating current keeping the inductance

value low

40 | P a g e

CONCLUSION

Modern signalling is vital for safe and punctual movements of trains In the Indian railways The Signalling

and Telecommunication Department is responsible for providing modern effective and relaible signalling

systems as well as telecommunication systems

The first mode of communication used in Indian Railways was the use of electric telegraph

with the help of Morose code Morose code is the method of providing text information as a series of on-off

tones and lights or clicks that can be directly understood by a skilled listener or observer without special

equipmentEach character (letter or numeral ) is represented by a unique sequence of dots and dashes Later

this system becomes obselete and beggan the era of wireless communication which operated at audio level

frequency range

In wireless communication the significant advances took place the transition to miniature

valves or filament tubesBut this was abandoned too because of excessive current consumption and over

heating of the filament tubes

Fibre-optic communication is a method of transmitting information from one place to another by

sending pulses of light through an optcial fibreThe light forms an electromagnetic carrier wave that is

modulated to carry information First developed in the 1970s fibre optic communication systems has

revolutionized the telecommunications industry and have palyed a major role in the advent of the information

age Because of its advantages over electrical transmissionsoptical fibres have largely replaced copper wire

communications in core networks in the developed world The Indian Railways too is undergoing a transition

from Microwave communication to fibre optic communications

41 | P a g e

BIBLIOGRAPHY AND REFERENCES

1 wwwwikipediacom

2 wwwbritaniccacom

3 wwwirfcacom

4 Motorola GP60 system manual

5 Harris FAS 7000 manual

6 TOSHIBA Manual

4 | P a g e

A GEC-MANUFACTURED SSI INTERLOCKING CUBICLE

A PAIR OF DATA LINK MODULES

TRACKSIDE FUNCTIONAL MODULE

5 | P a g e

INTEGRATED POWER SUPPLY

INTRODUCTION A typical 4 line station requires power supplies of 24 V DC( 5 nos ) 12 VDC ( 5nos ) 6V (2 nos)

110 V DC and 110 V AC for signalling These require as many chargers and Secondary cells amp Invertors

requiring more maintenance amp spares Can they be Integrated in to one system

Thus the concept of Integrated Power Supply has been evolved by integrating concepts One Charger

One set of Battery Bank feeding Invertors and DC- DC converters for deriving various DC amp AC

voltages Integrated power supply system delivers both AC amp DC Power supplies as an output with the

output voltage tolerance of plusmn 2

ADVANTAGES Reduces maintenance on Batteries Battery charger amp overall maintenance

Its construction is in modules and hence occupies less space Reduced space requirement resulting in

saving of space for power supply rooms

Provides centralized power system for complete signaling installation with continuous display of

working status of system for easier monitoring

Defect in sub-units of system is shown both by visual amp audible indication Reflects the condition of

battery with warning

Replacement of defective modules is quick amp easy without disturbing the working of the system

It uses (n+1) modular technology hot standby arrangement and hence high reliability and more

availability of the system

The system provides uninterrupted supply to all signalling system even during the power failures

Thus No blank Signal for the approaching drivers

System can be easily configured to suit load requirement

The diesel generator set running (Non-RE area) is reduced almost to lsquoNILrsquo Hence low wear and tear

of DG set components amp reduced diesel oil consumption

COMPONENTS (a) Un-interrupted power supply (U P S)

(i) SMPS Battery chargers with Hot stand-by mode

(ii) Hot Standby PWM Inverters with auto changeover

(iii) CVT Regulator [FRVS]

(b) AC distribution board [ACDB]

(i) STEP DOWN TRANSFORMERS

(c) DC distribution board [DCDB]

(i) DC-DC converters

WORKING IPS works satisfactorily for AC input variation of 150V AC to 275V AC with single-phase power supply

and frequency variation from 48 Hz to 52 Hz The input is fed to SMPS charger which converts in to 110

VDC as output It is fed as input to three sub units

To battery bank charging the batteries

To ON line inverters that converts 110 VDC in to 230 VAC plusmn 2as output

6 | P a g e

As 110 VDC bus bar to DC Distribution Panel as an input to various DC-DC converters located in

it

A 110 V Battery Bank of VRLA cells are connected to SMPS Panel IPS Status Monitoring Panel is

located at ASM room or at SampT staff room if round the clock SampT staff is available at Station

CONSTRUCTION IPS mainly consists of

SMR (Switch Mode Rectifier) Panel SMPS based Float cum Boost Charger (FRBC) Panel

AC Distribution Panel

DC Distribution Panel

Battery Bank (110V DC)

Status Monitoring Panel

SMR (SWITCH MODE RECTIFIER) PANEL SMPS BASED FLOAT

CUM BOOST CHARGER (FRBC) PANEL It consists of SMR FRBC modules and Supervisory amp Control Unit SMPS based SMRs

(converters) SMPS based Float cum Boost Chargers (FRBC) modules are provided with (n+1) modular

technology hot standby arrangement with active load sharing basis and 1 additional module as a cold standby

(n+2) Supervisory amp Control Unit which controls and monitor the complete system It has various

indications on the panel reflecting the working of the panel

FRBCs are suitable for operating in parallel on active load sharing basis with one or more modules of similar

type make and rating

n = required no of modules to cater for actual current requirement

AC DISTRIBUTION PANEL It is made of ON-Line inverters with (1+1) modular technology hot standby arrangement amp CVT

(Constant Voltage Transformer) AVR (Automatic Voltage Regulator) and set of step down

transformersThe inverter is protected against overload and short circuit with auto reset facility Whenever

the failure occurs it trips and restart automatically after about 10 to 20 sec But if the problem persists the

protection is permanently gets latched and it will not be switched ON again unless the fault is cleared

followed by pressing of reset button The output of inverters is regulated to 230V AC plusmn 2 50Hz plusmn1Hz for

an input voltage variation of 90V DC to 140V DC Normally both the Inverters are powered ON and both are

delivering the Output voltage but only one (main) inverter is connected to the Load If main inverter is failed

then only the stand-by inverter will come on Load automatically with in 500msec At 70 Depth of

Discharge (DOD) of the battery bank 110VDC supply to the inverters will be cut-off So the Signals feed will

be cut-off The auto-change over arrangement is also provided for bringing the CVT in circuit with in

500msec when the both the inverters output is failed It has various indications on the panel reflecting the

working of the panel

DC DISTRIBUTION PANEL It takes care of DC Power supply requirements of our signalling It consists of sets of DC-DC

converters for individual DC power requirements with (n+1) modular technology hot standby arrangement

with active load sharing basis The DC-DC converters of Relay Internal are provided with (n+1) modular

technology hot standby arrangement with active load sharing basis and 1 additional module as a cold standby

(n+2) The DC-DC converter works satisfactorily with the input voltage variation of 98VDC to 138VDC At

90 Depth of Discharge (DOD) of the battery bank all the DC-DC converters 110VDC Input supply will be

cut-off except for Block Tele DC-DC converters The supply for Point operation is also catered through a

20A fuse by this unit It is also provided with various indications that reflect its working

7 | P a g e

STATUS MONITORING PANEL IPS status monitoring panel has been provided in the ASM room for giving the important alarms and

indications to ASM Status Panel tells present working status of IPS displaying battery voltage continuously

and five other indications which will light according to IPS status During normal working these indications

will not lit Whenever the battery has come on to the load and has discharged by 50 DOD (Depth of

Discharge) then first Red indication lit with description ldquoSTART GENERATORrdquo with audio Alarm ie DG

set is to be started and put on the load If DG set is not started with this warning then if battery gets further

discharged to 60 DOD and second Red indications appears with description ldquoEmergency Start generatorrdquo

with audio alarm even now if DG set is failed to be started the battery further gets discharged to 70

DOD and 3rd Red indications appear with description ldquo System shut downrdquo with audio alarm which will

continue till Generator is started resulting in AC output from IPS is automatically cut off results all the

signals will become blank

When there is any defect in any sub module of IPS even without affecting working of system the 4th

Red indication appears with description ldquoCall SampT Staffrdquo with audio alarm so the ASM advises SampT staff

accordingly Green LED 5th indication comes with the description ldquoStop Generatorrdquo with audio alarm when

the DG set is running and if the Battery bank is fully charged condition

EARTHING The IPS systems and its individual modules are having earth terminals and all these are properly

earthed with earth resistance of less than 1 ohm Earth provided shall preferably be maintenance free using

ground resistance improvement compound (The acceptable Earth Resistance at earth busbar shall not be

more than 1 ohm Code of practice for earthing and bonding system for signalling equipments)

LIGHTNING AND TRANSIENT PROTECTION IN IPS Manufacturer will provide Stage1 amp Stage 2 protection along with the IPS These are described

below

Stage 1 protection is of Class B type against Lightning Electro-Magnetic Impulse (LEMP) amp other

high surges provided at Power Distribution Panel It is provided with a 63 Amp fuse in phase line and is

connected between Line and the Neutral and also between the Neutral and Earth

Stage 2 protection (Power line protection at Equipment level) is of Class C type against low voltage

surges provided at the equipment input level This is thermal disconnecting type and equipped with

protection against SPD (surge protection device) failure due to open amp short circuit of SPDs and is connected

between the Line and the Neutral If supply data signalling lines (ACDC) are carried through overhead

wires or cables above ground to any nearby building or any location outside the equipment room additional

protection of Stage 2 type shall be provided at such locations Class B amp Class C arrestor is provided on a

separate wall mounting type enclosure in IPS room

Stage3 protection (Protection for signallingdata line) is of Class D type All external data signalling

lines (ACDC) shall be protected by using this Class D type device It consists of a combination of Varistors

and Gas Discharge Tube with voltage and current limiting facilities

FEATURES Chargers used in this system are of SMPS technology chargers with 90 efficiency These chargers

are supported with hot standby mode with (n+1) modular technology

Onetwo sets of Maintenance free Battery banks (110VDC) Normally one set (110VDC) of Battery

bank is used Conventional flooded type Lead Acid Batteries or Low Maintenance Lead Acid

batteries can also be used (SMRs settings are required to be adjusted depending on the type of

Batteries used) Various voltage levels of

8 | P a g e

battery banks are avoided Reduction in Battery maintenance amp less flour area required

DC-DC Converters working from 110V Central battery have been used for all dc supplies This has

improved overall efficiency of the system since number of conversion from AC to DC have been

reduced to 2 stage as compared to 3 stage conversion in case of transformer-rectifier system

DC-DC converters are available in modules Easy replacement of defective modules This ensures

less down time

DC-DC Converters are used in load sharing N+1 configuration (ie with hot standby with N+1

modular technology) to improve the reliability amp availability of the system

Capacity of inverter has been brought down to 15 KVA from 5 KVA and used for feeding only

Signals supply Hot standby inverter is provided with auto changeover facility This improves the

availability of the overall system

High efficiency inverter is used with PWM (Pulse Width Modulation) technology in place of Ferro-

resonant technology based inverter This improves the efficiency of the overall system

Continuous power to Signal Circuits even in absence of DG setLocal Power Supply

Generators need not be switched ON every time during train movement

Metal-to-metal relay installations and block working by axle counters have also been covered

Supply of spare modulesComponentsCells have been included as part of main supply

Provides highly regulated voltage to all signal relays amp lamps for better life

9 | P a g e

SINGLE SECTION DIGITAL AXLE COUNTER

INTRODUCTION- The axle counter equipment is working on high frequency and using amplitude modulation or phase

modulation for detection of presence of wheel The equipment described in this notes is Phase modulation type

for the detection of presence of wheel In the Phase modulation type track device the detection of presence of

wheel is with the phase reversal of 1800 out of phase which enables this system to be more healthy and safe

In Phase Reversal Modulation technique trolley suppression arrangements to prevent the counting of

wheels caused by push trolley passing over the track device are not required as the system will take care of

validation of generated pulses caused by passage of wheel over the track device depending up on the phase

shift of the pulse This phase shift of the pulse may be normally 160deg to 180deg for a train wheel and it may be

approximately 100deg to 120deg for a push trolley wheel

This is Digital Axle Counter equipment for single track sections containing 2 out of 2 micro-

controllers to count the axles establish the track occupancy of a track section and to provide this information

to the block or the interlocking equipment

In this system no separate evaluator is required and no analog data is being transmitted One set of

Axle counter equipment is provided at entry end and other set provided at exit end Both sets are being

connected through a twisted pair of telecom cable ie existing RE cable one PET quad is used for both UP

and DN Axle Counters Digital DATA is being transmitted between two ends of Axle counters (Outdoor

track side Detection points)This system is a fully duplex capable of operating according to CCITT V21 and

the Data will be transmitted at the rate of 300bitsec This data Transmitted ensure negligible interference of

the noise The system is highly reliable

FEATURES (a) The system consists of

(i) Single Section Digital Axle Counter (SSDAC) units

(ii) Tx Rx coils

(iii) Vital Relays

(b) TxRx coil axle detectors are mounted to the web of the rails The design of system consists of 21 KHz amp

23 KHz High frequency Phase Reversal type axle detectors

(c) Compatible with 90R 52Kg amp 60Kg rail profiles Easy to install commission amp maintain

(d) Track devices at both (entry amp exit) points of the section should be fixed on the same rail

(e) System is designed to detect the solid wheels with diameter gt 400mm with standard wheel flange

(f) The system works in pairs For monitoring single-track section one pair of SSDAC units are required and

to be installed near the trackside one at the beginning and another at the end of the track section ie

Trackside electronic counting equipment

(g) The basic design of the system is based on counting the number of axles passing at each detection point

These stored counts are transmitted to the second unit of the system and vice versa by means of modem

communication

(h) The communication consists of digital packets having details of Counts amp Health

10 | P a g e

(i) If counts registered at both detection points are equal the section is cleared otherwise the section is shown

as occupied The system ensures no error condition to arrive at the decision of clearance

(j) System is designed as per CENELEC SIL-4 (European standard) using micro controller along with other

electronic circuits and programmed using dedicated software When any of these circuits fail the system

goes to fail safe condition

(k) It is programmable for either Preparatory Reset or Conditional Hard Reset as per requirement

(l) Micro controller based design with 2 out of 2 decisions and counting through software

(m) V21 Modem communication (2-wire) on frac12 quad cables and also compatible to work on voice channel of

OFC amp Radio

(n) Opto isolated vital relay drive for Q-style 24V 1000 _ and Vital Relay output can be giving at both ends

of the system

APPLICATIONS The system can be widely used in Railways for Block Working (BPAC) Intermediate Block Signaling Auto

signalling and Track circuiting for i) Loop line ii) Main line iii) yard lines

SYSTEM DESCRIPTION

This system comprises of

Tx coils-2 nos

Rx coils-2 nos

Reset Box (RB 258A)

Card 1 Signal Conditioning Card ndash 1

Card 2 Signal Conditioning Card - 2

Card 3 Micro controller Logic Board ndash 1

Card 4 Micro controller Logic Board ndash 2

2 nos for independent resetting ndash when used in block sections

1 no for common resetting ndash when used for Track circuiting at stations

Card 5 Event Logger Card

Card 6 Modem Card

Card 7 Relay Driver Card

Card 8 DC-DC Converter Card

SSDAC (DACF 700AP) UNIT

(A) SIGNAL CONDITIONING CARD (CARD 1amp2) (SCC) -1 (SCC-1) generates 21 KHz carrier

signals

-2 (SCC-2) generates 23 KHz carrier signals which is transmitted to 2nd

set of Tx coils

s receive these signals

modulated

train pulses

11 | P a g e

(B) MICRO-CONTROLLER LOGIC BOARD CARD (CARD 3amp4) (MLB) The Micro-controller Logic Board (MLB) is the heart of the system

o 8051 Based Architecture

o 8 Bit Micro Controller

o ATMEL AT89S8252 Micro controller

o 2 out of 2 Decision

o Uses C subset language

- TOOLS

o KEIL μ Vision Development System

o Universal Programmer

o 2KB Program Memory

o 256 bytes RAM

o 8KB Flash memory

o 32 Programmable IO lines

o Wide Operating Voltage range of 4V-6V

o Full Duplex Serial Port

o Programmable Watch Dog Timer

o Fully Static operation up to 24MHz (Upgraded to 40MHz)

o Operating Temperature of ndash40degC - +85degC

o Use of State Machine for Axle Counting

o Use of ASCII MODBUS protocol

o Use of CRC16 technique for Error Checking during communication

o Wheel detection

o Train direction checking and

o Wheel counting functions

o It receives the remote wheel count and computes the status of the section for clear or occupied

o It also checks various supervisory signal levels like supervisory of TxRx coils presence of various

cards communication link failure etcThese cards communicate with each other for wheel count

At Entry-end if train enters into section (1st detection) the counts are incremented and when train

shunts back from the same detection ie if train exits from the section from the same detection the counts are

decremented At Exit-end if train enters into section (2nd detection) the counts are decremented and when

train shunts back from the same detection ie if train exits from the section from the same detection the

counts are incremented Both the track devices at Entry and Exit ends must be fixed on same side of the

track

This MLB card is having Extensive LED display

o A block of 8 LED indicators for count progress error display

o 2 independent LED indicators for section status

o The errors occurring in the system during the operation of the SSDAC are encoded and are indicated by

means of the 8-LED block present on the front panel of the MLB cards

(c) EVENT LOGGER CARD (CARD 5)

Event logger card is designed to capture and store important signals from the remote and local SSDAC units

The stored data can be downloaded from the event logger card for the purpose of analyzing the events

occurring during the operations of the SSDAC The data can be analyzed with the help of CEL data analyzer

software

12 | P a g e

The event logger card captures following signals

(i) Pulse signals

(ii) Supervisory signals

(iii) Card removal information

(iv) Serial packets from

Event Logger card has a Rabbit processor and 2 MB FLASH MEMORY to store packets The data is initially

stored in the buffer and subsequently transferred to FLASH memory every two minutes Normally 4096

pages of the data can be stored in flash memory on FIFO (first in first out) basis

Run This LED blinks continuously indicating the normal working of the event

Log This LED blinks whenever data is being logged into the flash memory (Approx after every 2 minutes)

Dnld This LED is ON when data is being downloaded from the flash memory of the card and becomes OFF

when download is complete

(D) MODEM CARD (CARD 6) (i) The modem card transmits and receives the digital packet information form one counting unit to the other

The packet will appear after every 18 sec and the packet carries the latest information such as

(ii) The modem card being used is V21 type (2-wire) in SSDAC

(iii) This card interfaces with serial RS232C port of both Micro-controller Logic Boards

(iv) It multiplexes the two RS232C inputs and selects one of the two channels and provides signal conversion

from digital to analog (FSK modulation) and vice-versa

(v) Data transmission rate is 300 bitssec

(vi) Automatic Gain Control circuit is incorporated hence no gain adjustments required

(vii) Mode selection on Modem card The modem has been set in lsquoORIGINATORrsquo mode for entry and in the

lsquoANSWERrsquo mode for exit in the factory

(viii) LED Indications provided on Modem card

-Transmitting the signal when LED is flashing

- Receiving the signal when LED is flashing

-Remains OFF in SSDAC

-Carrier is detected when LED is glowing

(E) RELAY DRIVER CARD (CARD 7) (i) The Relay Driver card (RD) provides the 24V DC output required for driving Vital Relay

(ii) One RD card is used in each SSDAC counting unit The RD card receives the command of clear and

clock signals from MLB1 amp MLB2 cards and drives the vital relay lsquoONrsquo when section is NOT OCCUPIED

through opto- isolator circuit

(iii) If a train occupies the section the vital relay is dropped The vital relay status is read back by the system

as per the driving output

(iv) It has

13 | P a g e

ndash LED flashes when the section is clear

ndash LED flashes when the section is clear

All the above LEDrsquos are lit for section clear condition

(F) DC-DC CONVERTER CARD (CARD 8)

INPUT VOLTAGE Nominal Voltage voltage 24V DC Maximum current drain= 12A

Required voltage 18V DC to 30V DC

Output voltage

Nominal Voltage +5 V DC 2 A Required voltage 4 7 5 t o 525V DC

Nominal Voltage +12V DC 200 mA Required voltage 1175 to 1225V DC

Nominal Voltage +24V DC 300 mA with common ground Required voltage 235 to 245V DC

Nominal Voltage +15V DC 100 mA with isolated ground Required voltage 145 to 155V DC

SURGE VOLTAGE AND LIGHTNING PROTECTION Transient surge voltages arise as a result of Lightning discharge switching operations in electrical

systems and electrostatic discharge These surge voltages often destroy the electronic equipment to a large

extent In order to prevent surge voltages from destroying the equipment all the input lines of SSDAC ie

Power Supply (24V) Reset (48V) amp Modem is to be routed through surge voltage protection devices for

effectively protecting the system These devices (3 numbers) are mounted in a box and supplied along with

the system One number of box is to be installed at each location and wired to the SSDAC

Each surge voltage protection device consists of two parts

(a) Base

(b) Plug Trab

The Base of the device is used for wiring the input and output signals The connection details from relay

room to the box and from box to SSDAC unit are provided on the box The Plug Trab consists of MOV and

GD Tube and diverts the excess energy during surge voltages or lightning into the ground connection The

operation of these devices relies on a high quality ground connection in order to safely shunt away the

unwanted energy The impedance of the ground connection is critical and it should be less than 2 Ohms

NOTE The 3 Plug Trab connections are not to be interchanged with one another The plug Trab is a

detachable device and can be replaced with SPARE unit in case of blown device which is indicated by

means of LED for 24 V

EFFECTIVENESS OF PLUG TRABS The effectiveness of plug Trab depends wholly on the Earth connection provided to the system The earth

provided to the system should be less than 1 ohms and connections should be firm and proper to the SSDAC

unit VR box etc

SURGE VOLTAGE AND PROTECTION DEVICE SV-120 The Surge Voltage protection device is to be installed at each location along with every SSDAC unit

14 | P a g e

EARTHING- The lead wires connecting the installation and the earth electrode shall ordinarily be of stranded

copper wire of 29 sq mm (19 strand wires of 14 mm diameter) Copper wire has been specified because GI

wires usually are having greater corrosion However in areas where copper wire may be frequently stolen

due to theft ACSR of size 64 sq mm (19 strands of 211 mm diameter) may be used

LIMITS OF EARTH RESISTANCE (a) Apparatus case connected to Earth (SSDAC and vital Relay Box is housed in Apparatus case and

Connected to earth at outdoor) shall be less than or equal to 1 ohm

(b) All cable connected to same earth shall be less than or equal to 1 ohm

(C) Reset box connected to earth near SM s Room shall be less than or equal to 1ohm

EQUIPMENT TO BE EARTHED A Common Earth should be provided for SSDAC for items 1(a) amp (b) of the above at the outdoor

(a) The Apparatus Case is to be connected to earth (the chassis of SSDAC amp Vital Relay Box should be

properly connected to apparatus case)

(b) Metallic sheath and armouring of all the underground main cables are to be earthed

(i) In RE area the metallic sheath and armouring of main telecom cables are earthed at both ends

(ii) In RE area the armouring of Jelly filled cable shall be earthed at both ends

(c) The Earthing shall be provided at every location box where cables are terminated

(d) Earth already available for other equipment may be used for earthing of Reset Box near SM s Room

Cabin etc

15 | P a g e

DATALOGGER

INTRODUCTION Datalogger is a Microprocessor based system which helps in analysing the failures of relay inter

locking system Electronic Interlocking system This is like a black box which stores all the information

regarding the changes take place in relays AC DC Voltages and DC currents along with date and time The

same information data can be transferred to the computer to analyse further ldquoon line ldquooff linerdquo analysis of

stored date A print out also can be obtained through a printer by connecting directly to the datalogger unit

The data belongs to Relay contacts is considered as digital inputs and the data belongs to voltage

levels currents is considered as Analog inputs Datalogger lsquos are mandatory for all new relay interlocking

(PIRRI) EI installations and it is also recommended to provide in all existing PIs RRIs To increase the

line capacity mechanical signalling equipments are upgraded to PI RRI or EI Due to complexity in the

circuits and wiring sometimes it is very difficult to rectify the failures So datalogger can monitor these

systems with real time clock Thus it can be named as black box of Samp T equipments and hence it is a vital

tool for accident investigation Datalogger is used at Stations yards Whereas in case of Auto Section amp IBH

Mini dataloggers called as Remote Terminal Unit (RTU) are used

ADVANTAGES OF DATALOGGERS (a) Dataloggers helps in monitoring the typical failures such as intermittent auto right failures

(b) It helps in analyzing the cause of the accidents

(c) It helps in detecting the human failures errors such as

(i) Drivers passing signal at Danger

(ii) Operational mistakes done by panel operators ASMrsquos of operating department

(iii) Signal and telecom engineering interferences in safety circuits

(iv) Engineering and electrical department interferences failures

(v) It helps as a ldquoTOOLrdquo in preventive maintenance of signaling gears

(d) Dataloggers can be connected in network Networked dataloggers helps to monitorthe PIRRIEI remotely

(e) Failure reports can be generated remotely with help of datalogger network

(f) On line and Off line track simulation is possible

(g) Speed of the train on point zones can be calculated

(h) Age of the equipment in terms of number of operations etc

COMMON EQUIPMENT FOR ALL DATALOGGERS ARE GIVEN

BELOW (a) CPU card

(b) Digital and Analog input cards

(c) Local terminal(PC)

(d) communication links

(e) Printer

All the dataloggers requires a potential free ( spare ) relay contact for monitoring digital inputs

through Digital input cards amp for monitoring Analog inputs such ACDC bus bar voltage levels through

Analog input cards Digital and Analog inputs are connected to the Processor card Processor card consists of

memory ICrsquos Memory ICrsquos are programmed as per requirement of the signal engineers

Provision of Dataloggers is mandatory with RRI systems and is optional for PI systems as per

amendment to the specification for Relay Interlocking systems ( IRSS-36 ) The data collected by the

datalogger can be used for failure analysis repetitive discrepancies and for accident investigations

16 | P a g e

Note

If the serial communications is more than 50m then line drivers shall be used up to 3 Kms

4wire leased line Modems shall be used if the serial communication is more than 3 Kms

STUDY OF EFFTRONICS DATALOGGER TECHNICAL DETAILS (a) 24V 12VDC Power Supply

(b) Total Storage Capacity of 10 Lakh events

(c) In-built Temperature sensors

(d) Internal Buzzer for alarming during failures

(e) Real Time clock with internal battery backup with data retention up to 10 years

(f) 512 LED matrix to indicate the status of 512 Digital inputs at a time page wise

(g) Seven segment LCD screen (2x24) to display the status of digitalanalog signalsTime Temperature etc

(h) Using the keyboard various functions can be viewed in the LCD panel

(i) Max Digital Inputs 4096

(j) Max Analog Inputs 96

(k) Digital Input Scanning Time 16 millisecond

(l) Analog Input Scanning Time is less than 1 Sec

HARDWARE (EQUIPMENT) Datalogger system consists of

(a) Datalogger (CPU - with Microprocessor 68000)

(b) Digital input cards

(c) Dual modem card

(d) Digital Scanner units (DSU)

(e) Analog Scanner units (ASU)

CPU CARD It is provided with Motorola microprocessor M 68000 It performs all the activities pertaining to the

datalogger It continuously scans (check) the Digital inputs(inbuilt) Digital Scanner Units and Analog

Scanner Units ie scanning of digital signals (Relay operations) for every 16-milli seconds and scanning of

analog signals (ie ACDC voltages amp DC currents) for less than 1 second

This card will support the IO interfaces of LCD (Liquid Crystal Display) - 2X24 alphanumeric Key

Board LED Matrix Display Real Time Clock LCD display and keyboard This will acts as man machine

interface between the datalogger and the signal engineer All the operations (Software) can be performed

using this LCD and keyboard

Real time display with 7 Segments This is built in real time clock within Datalogger and its current

time will be displayed on six 7-segment display provided (Real time clock depend upon DALLAS 1286

chip) This IC will come with internal battery backup hence there is no need to add external batteries

CPU card continuously scans (checks) the DSUs and ASUs Each input connected to digital scanner

units are optically isolated by Opto couplers When CPU card scans the digital inputs it compares with the

previous stored data and if there is any change from the previous status then only that data will be stored (the

status conditions of relay) with date and real time A total of minimum 10 Lac events can be stored in

memory on first in first out basis so that latest data is available in the system There is no loss of data from

datalogger memory in case of power supply failure of datalogger

DIGITAL INPUT CARDS (IN-BUILT) This system is having maximum 8nos of inbuilt Digital inputs cards Maximum 64nos of digital

inputs can be connected to each digital input card The potential free relay contact may be front or back

contact terminated at the Tag Block from the relay of signals tracks points Buttons etc and are

17 | P a g e

subsequently connected to Digital input cards through Flat Ribbon Cable (FRC) connectors These in-built

digital input cards can monitor a total 512 nos of relays status

DIGITAL SCANNER UNIT (DSU) Each DSU contains 8 nos of Digital Input cards Each input card can be connected with 64 inputs

Total input capacity of DSU unit is 512 inputs These scanner cards contain Optocouplers and Multiplexer

Inputs are connected to Stag card The stag card out put is connected to DSU through FRC connectors

Maximum 7 nos of DSUs can be connected to the system So Digital input capacity of the system is 4096

All these digital inputs are scanned at rate of 16 msec

ANALOG SCANNER UNIT (ASU) ASU contains maximum 3 nos of Analog input cards Each input card can be connected with 8nos of

Analog inputs Total input capacity of the ASU is 24 analog input channels Maximum 4nos of ASUs can be

connected to the system Analog input channel capacity of the system is 96 All these analog inputs are

scanned at a rate of less than 1 sec

PARALLEL PORT Parallel port is provided for connecting printer

RS-232 SERIAL PORTS At least 6 Serial communication ports are provided for communication with other dataloggers

Central Monitoring Unit Remote Terminal Unit Electronic Interlocking system Integrated Power Supply

system etc

EXTERNAL NON-VITAL RELAY CONTACTS These relays provided in the system where 16 number of the Relay contacts are provided on the rear

panel through Tele control port to extend alarms and to control the power equipment from remote or local

locations through computer in case of any occurrence of failures Each control can sink or source 100 m

amps of current

INTERNAL MODEM CARD DUAL MODEM CARD (IN-BUILT) It is fixed in datalogger Euro rack itself One card contains two modems The top modem is called

ANS (answer) modem and the bottom modem is called as ORG (originate) modem It is used in case of

networking of Dataloggers In network connect lsquoANSrsquo modem to the lsquoORGrsquo modem of one adjacent station

and connect lsquoORGrsquo modem to the lsquoANSrsquo modem of other adjacent station

POWER SUPPLY Normally 24V DC (12V DC is optional) supply with battery backup is required for the system

working

Input Voltage Range 18Vhellip32V DC (For 24V) 9Vhellip18V DC (For 12V)

INPUT REQUIREMENTS Relay inputs (digital inputs) and analog inputs (voltages currents etc) are required to be connected

to the system as per the requirements of RRI PI SSI as the case may be Some of the inputs to be

monitored is given below

(a) Digital inputs

(i) Field inputs All TPRs NWKRs RWKRs ECRs Crank Handle relays SidingSlot LC gate

control relays etc

(ii) Control Panel inputs All button Knob SMrsquos Key relays

18 | P a g e

(iii) Internal relays

British system All HR DR HHR WNR WRR ASR UCR RR LR UYRTLSR TRSR TSR

JSLR JR etc

SIEMENS system Z1UR Z1UR1 GZR ZDUCR ZU(R)R ZU(N)PRG(R)RG(N)R U(R)S

U(N)PS UDKR DUCR U(R)LR UYR1 UYR2 G(R)LRGR1GR2

GR3 GR4 OVZ2U(R)RW(RN)R (RN)WLR Z1NWR Z1RWRZ1WR1 WKR1 WKR2 WKR3 etc

(b) Analog channels

(i) 230 V AC (for power supplies in the power panel)

(ii) 110V AC (for Signal and Track transformers)

(iii) 110V DC (for Point operation)

(iv) 60V DC (Siemens relays)

(v) 24V DC (Q-series relays)

(vi) 24V DC (for Block Axle counters)

(vii) 12V DC (for indication)

(viii) 20A (for point operation current)

(ix) 10V AC 5KHz (for Axle counter channels) etc

SOFTWARE MODULES OF DATALOGGERS

(a) Network Management of Dataloggers (NMDL)

(b) Reports

(c) Fault Entry

(d) Track Offline Simulation

(e) Train Charting

NMDL SOFTWARE FEATURES (a) Online Relay Status

(b) Online Faults - To view information of various Online Faults as they occur in the stations where

the Dataloggers are connected

(c) Online Simulation - Graphical view of relay operations train movements etc

(d) Remote monitoring of stations with the help of NETWORKING

SOFTWARE OBJECTIVES (a) Predictive Maintenance

(b) Easy identification of failures

(c) Crew discipline

(d) Train charting

REMOTE MONITORING OF STATIONS WITH NETWORKING OF

DATALOGGERS The individual Dataloggers of various stations can be interconnected through networking technology

The data of Remote Panel stations can be viewed in a Computer at the Central Monitoring Station The data

of the network is collected by the FEP (Front End Processor) which in turn is transmitted to the computer

COMPONENTS OF NETWORK MANAGEMENT OF DATALOGGERS

(a) Datalogger at stations

(b) MODEM and Transmission medium

19 | P a g e

(c) Front End Processor (FEP)

(d) Central Monitoring Unit (CMU) Computer

FEP (FRONT END PROCESSOR)

FEP acts as a buffer between the Central Monitoring Unit (Computer) and the Network It is provided

at centralised place to retrieve data continuously from station dataloggers and store in memory and transfer to

computer on request It stores 10 Lac telegrams It works on 12V DC It draws 16A continuous current

when all the three modems are connected Normally it shows the number of packets pending to be sent to the

computer on its 7-segment LED display It is provided with MOTOROLA 68000 microprocessor It has 6-

nos of RS-232 communication ports such as COM1 COM2 COM3 COM4 COM5 and COM6 COM1 is

used for Fault Analysis System (FAS) ie Central Monitoring Unit (Computer) connection COM2 to COM6

are used for networking For Bi-directional 2- nos of ports and for Tri-directional (T-network) 3-nos of ports

are used

DATA TRANSMISSION Dataloggers can be networked in Uni-directional Mode or Bi-directional Mode or T ndash Network Mode

In case of loss of data retransmission of data takes place

(a) Uni-Directional Mode

Each Datalogger will send data in only one direction to the FEP Unidirectional mode network is not

preferred

(b) Bi-Directional Mode

Each end of Network is connected to FEP and each datalogger can now transmit data in both the directions

Bi-directional Mode is advantageous it enables the Data Transmission even in case of Network Failure

(c) T - Network Mode

If more no of stations are in network ie if the network is too lengthy then T- network mode is preferred

COMMUNICATION The communication protocol for transmitting data and command between datalogger and CMU is

standardized by the RDSO and is given in the Specifications of Dataloggers

(a) The type of communication used in the network is dependent on the distance between the dataloggers

(b) For shorter distances Opto Converter Box- Opto isolated current loop communication is used

(c) For longer distances Modem (Dial-up leased) Fiber Optic Satellite Microwave communication

MODEMS Modems are used for DATA transfer between Dataloggers and Front End ProcessorThese are

configured to RS 232 Serial Communication Network is connected with two types of 4-wire modems

(a) Internal modem card Dual Modem card (in-built)

It is fixed in datalogger Euro rack itself One card contains two modems The top modem is called

ANS (answer) modem and the bottom modem is called as ORG (originate) modem

Note In case of networking of Dataloggers connect lsquoANSrsquo modem to the lsquoORGrsquo modem of one adjacent

station and connect lsquoORGrsquo modem to the lsquoANSrsquo modem of other adjacent station

(b) External modems

20 | P a g e

These are generally used at FEP (Front End Processor) side to connect the Dataloggers

(i) To transfer Data from one datalogger to another datalogger FEP Baud rate is 9600bps

(ii) These modems are 4-wire line communication

(iii) To transfer the data from FEP to RMU (PC) the Baud rate is 57600 bps

There is no difference between these modems functionally

CENTRAL MONITORING UNIT (CMU) COMPUTER

Central monitoring unit (Fault Analysis Unit) is a Personal Computer and its minimum configuration

shall be specified by RDSO from time to time System Software Windows XPVista(OS) Norton Kaspersky

(Anti Virus) Interbase where Server is not available (DBMS) Oracle where Server is available (DBMS)

software are required to run Datalogger System It is provided with Graphical User interface (GUI) based

software and retrieve data from all Networked dataloggers (up to 32) at various stations It stores data in

standard data base files The CMU is capable of analyzing the data and generate reports audiovisual alarms

on defined conditions This data can be compressed to take backup In central monitoring unit Software used

for analysis of data prediction of faults etc is written in a structured format so that purchaser can

reconfigure it if required It displays the status of signaling gears at any selected time in graphic form for any

selected station yard It retrieves the stored data amp simulates train movement It sends commands to various

Dataloggers to activate audio visual alarm or operate and electromagnetic relay

CMU shares data available in it by other PCs through available local area network where this data can

be used for train charting passenger information purpose The system generates audiovisual alarm in

ASMrsquosSignal Maintainerrsquos room in the case of power supply failure (battery voltage low) or battery charger

defective with acknowledgement facility

(a) Each datalogger has its own identity code which will be transmitted along with data packet to central

monitoring unit

(b) Events recorded at each station are continuously transmitted to central monitoring unit Response time of

data transfer will not exceed 10 sec

21 | P a g e

22 | P a g e

OPTICAL FIBER CABLE

INTRODUCTION The demand for bandwidth on transmission networks is increasing rapidly because video and

graphical rich contents are exchanged through the corporate network or the Internet The Gigabit Ethernet

became ommonly used in the corporate network backbone and 10Gbit Ethernet will be adopted in the near

future Meanwhile in the home the demand for high-speed network becomes popular as the wide spread of

broadband access eg CATV xDSL and FTTH The transmission medium with capability to transmit high

bit rate signal is necessary to satisfy these requirements

The telecommunication transport technologies move from copper based networks to optical fiber

from timeslot based transport to wave length based transport from traditional circuit switching to terabit

router and all optical based networks entering into a new era of optical networking

BASIC PHYSICS OF OFC

OPTICAL FIBER CABLE OFC have Fibers which are long thin strands made with pure glass about the diameter of a human

hair OFC consists of Core Cladding Buffers and Jacket as shown in figure

MONOCHROMATIC LIGHT OR SINGLE COLOR LIGHT Light or visible light is electromagnetic radiation of a wavelength that is visible to the human eye (

about 400 ndash 700 nm) The word light is sometimes used to refer to the entire electromagnetic spectrum Light

is composed of elementary particles called photons Three primary properties of light are

Light can exhibit properties of both waves and particles This property is referred to as wave-particle

duality The study of light known as optics In free space light (of all wavelengths) travels in a straight path

at a constant maximum speed However the speed of light changes when it travels in a medium and this

change is not the same for all media or for all wavelengths By free space it is meant space that is free from

matter (vacuum) andor free from electromagnetic fields

Thus the speed of light in free space is defined by Einsteinrsquos equation E = mc2

Frequency ν speed of light in free space c and wavelength λ are interrelated by ν = cλ

From the energy relationships E = mc2 = hν and the last one an interesting relationship is obtained

the equivalent mass of a photon m = hνc2

When light is in the vicinity of a strong electromagnetic field it interacts with it From this interaction

and other influences its trajectory changes direction as shown in figure

23 | P a g e

INCIDENT RAY REFLECTED RAY AND REFRACTED RAY An incident ray is a ray of light that strikes a surface The angle between this ray and the

perpendicular or normal to the surface is the angle of incidence Reflection is the change in direction of a

wave front at an interface between two different media so that the wave front returns into the medium from

which it originated Common examples include the reflection of light sound and water waves

The reflected ray corresponding to a given incident ray is the ray that represents the light reflected by

the surface The angle between the surface normal and the reflected ray is known as the angle of reflection

The Law of Reflection says that for a specular (non-scattering) surface the angle of reflection always equals

the angle of incidence The refracted ray or transmitted ray corresponding to a given incident ray represents

the light that is transmitted through the surface The angle between this ray and the normal is known as the

angle of refraction and it is given by Snells Law

The figure shows Incident ray Reflected ray Refracted ray the angle of incidence and angle of refraction

REFRACTIVE INDEX - Refractive index is the speed of light in a vacuum ( c =299792458kmsecond) divided by the speed

of light in a material ( v ) Refractive index measures how much a material refracts light Refractive index of

a material abbreviated as lsquo n lsquo is defined as lsquo n=cv lsquo Light travels slower in physical media than it does

when transmitted through the air Refractive index (n) is a function of molecular structure of matter optical

frequency optical intensity determines optical propagation properties of each wavelength ( λ ) may not be

distributed equally in all directions is affected by external temperature pressure and fields

Refractive index of a medium is a measure for how much the speed of light is reduced inside the

medium For example typical glass has a refractive index of 15 which means that light travels at 1 15 =

067 times the speed in air or vacuum Two common properties of glass and other transparent materials are

directly related to their refractive index

First light rays change direction when they cross the interface from air to the material and effect that

is used in lenses and glasses

Second light reflects partially from surfaces that have a refractive index different from that of their

surroundings

SNELLrsquoS LAW-

24 | P a g e

When light passes from one transparent material to another it bends according to Snells law which

is defined as n1sin(θ1) = n2sin(θ2)

where n1 is the refractive index of the medium the light is leaving θ1 is the incident angle between the light

beam and the normal (normal is 90deg to the interface between two materials)

n2 is the refractive index of the material the light is entering

θ2 is the refractive angle between the light ray and the normal

Snellrsquos law gives the relationship between angle of incidence and angle of refraction

For the case of θ1 = 0deg (ie a ray perpendicular to the interface) the solution is θ2 = 0deg regardless of

the values of n1 and n2 That means a ray entering a medium perpendicular to the surface is never bent The

above is also valid for light going from a dense (higher n) to a less dense (lower n) material the symmetry of

Snells law shows that the same ray paths are applicable in opposite direction

TOTAL INTERNAL REFLECTION- When a light ray crosses an interface into a medium with a higher refractive index it bends towards

the normal Conversely light traveling cross an interface from a higher refractive index medium to a lower

refractive index medium will bend away from the normal

This has an interesting implication at some angle known as the critical angle θc light traveling from

a higher refractive index medium to a lower refractive index medium will be refracted at 90deg in other words

refracted alon g the interface If the light hits the interface at any angle larger than this critical angle it will

not pass through to the second medium at all Instead all of it will be reflected back into the first medium a

process known as total internal reflection

The critical angle can be calculated from Snells law putting in an angle of 90deg for the angle of the refracted

ray θ2 This gives θ1

Since θ2 = 90deg

So sin(θ2) = 1

25 | P a g e

Then θc = θ1 = arcsin(n2n1)

For example with light trying to emerge from glass with n1=15 into air (n2 =1) the ritical angle θc is

arcsin(115) or 418deg For any angle of incidence larger than the critical angle Snells law will not be able to

be solved for the angle of refraction because it will show that the refracted angle has a sine larger than 1

which is not possible In that case all the light is totally reflected off the interface obeying the law of

reflection

OPTICAL FIBER MODE An optical fiber guides light waves in distinct patterns called modes Mode describes the distribution

of light energy across the fiber The precise patterns depend on the wavelength of light transmitted and on the

variation in refractive index that shapes the core In essence the variations in refractive index create

boundary

conditions that shape how light waves travel through the fiber like the walls of a tunnel affect how sounds

echo inside

We can take a look at large-core step-index fibers Light rays enter the fiber at a range of angles and

rays at different angles can all stably travel down the length of the fiber as long as they hit the core-cladding

interface at an angle larger than critical angle These rays are different modes Fibers that carry more than

one mode at a specific light wavelength are called multimode fibers Some fibers have very small diameter

core that they can carry only one mode which travels as a straight line at the center of the core These fibers

are single mode fibers This is illustrated in the following picture

OPTICAL FIBER INDEX PROFILE Index profile is the refractive index distribution across the core and the cladding of a fiber Some

optical fiber has a step index profile in which the core has one uniformly distributed index and the cladding

has a lower uniformly distributed index Other optical fiber has a graded index profile in which refractive

index varies gradually as a function of radial distance from the fiber center Graded-index profiles include

power-law index profiles and parabolic index profiles The following figure shows some common types of

index profiles for single mode and multimode fiber

26 | P a g e

OPTICAL FIBERrsquoS NUMERICAL APERTURE ( NA )- Multimode optical fiber will only propagate light that enters the fiber within a certain cone known as

the acceptance cone of the fiber The half-angle of this cone is called the acceptance angle (see figure 18)

θmax For step-index multimode fiber the acceptance angle is determined only by the indices of refraction

Where

n is the refractive index of the medium light is traveling before entering the fiber

nf is the refractive index of the fiber core

nc is the refractive index of the cladding

NUMBER OF MODES IN A FIBER - Modes are sometimes characterized by numbers Single mode fibers carry only the lowest-order

mode assigned the number 0 Multimode fibers also carry higher-order modes The number of modes that

can propagate in a fiber depends on the fiberrsquos numerical aperture (or acceptance angle) as well as on its

core diameter and the wavelength of the light For a step-index multimode fiber the number of such modes

Nm

Where

D is the core diameter

λ is the operating wavelength

NA is the numerical aperture (or acceptance angle)

MODE FIELD DIAMETER - All light do not travels through the core of the fiber but is distributed through both the core and the

cladding The mode field is the distribution of light through the core and cladding of a particular fiber

Mode-Field Diameter (MFD) defines the size of the power distribution When coupling light into or out of a

fiber MFD is important in understanding light loss

27 | P a g e

ADVANTAGE OF OFC COMMUNICATION - bull More information carrying capacity Fibers can handle much higher data rates than copper More

information can be sent in a second

bull Free from Electromagnetic and Electrostatic interference Being insulator no electric current flows through

the fibre and due to this reason fibres neither radiate nor pick up electro - magnetic radiation So WPC

CLEARANCE is not required

bull Low attenuation 025 dbkm at 1550 nm Loss in twisted pair and coaxial cable increases with frequency

where as loss in the optical fibre cable remains flat over a wide range of frequencies

bull Use of WDM ndash Switching routing at Optical signal level

bull Self healing rings under NMS control

bull Small size makes fibre cable lighter in weight So easy to handleOptic fibre cable weight (approx)

500 kg km Copper cable weight (approx) 1000 kgkm

The reasons are photons of light in a fibre

do not affect each other as they have no electrical charge and they are not affected by stray photons outside

the fibre But in case of copper electrons move through the cable and these are affected by each other

Optical fibre does not carry any electricity even if the cable is damaged or short circuited it does

not cause any spark or fire hazard

As the fibre do not radiate energy it can not be detected by any nearby antenna or any

other detector The fibres are difficult to tap and therefore excellent for security

As the signal transmission is by digital modulation there is no chance of cross talk in

between channels

Only by adding a few additional terminal and repeater equipments the

capacity of the system can be increased at any time once the cable is laid

ical effects and temperature variations

LIMITATIONS OF OFC -

difficult

- utilised

APPLICATION IN SIGNAL AND TELECOMMUNICATIONS transmission circuits

-haul circuits for linking of telephone exchanges

28 | P a g e

PROPAGATION MODES CONCEPT -

MODE - Mode is an available distribution of electromagnetic field in a plane transverse to the direction of

light propagation Each mode is characterized by frequency polarization electric field strength and

magnetic field strength Available patterns are derived from Maxwellrsquos equations and boundary conditions

LINEARLY POLARIZED (LP) MODE A mode for which the field components in the direction of propagation are small compared to

components perpendicular to that direction An optical fibre supports only different field patterns called as

lsquoLinear Polarizedrsquo or lsquo LPrsquo modes The reasons are

requirements

de

the accrual of power carried by different modes

There are two basic types of fiber Multimode fiber and Single-mode fiber

Multimode fiber is best designed for short transmission distances This is suited for used in LAN systems and

video surveillance Single mode fibre is best designed for longer transmission distances This is suitable for

long distance telephony and multi channel television broadcast systems

29 | P a g e

MULTI MODE FIBER Multimode fiber the first to be manufactured and commercialized simply refers to the fact that

numerous modes or light rays are carried simultaneously through the waveguide Modes result from the fact

that light will only propagate in the fiber core at discrete angles within the cone of acceptance MM fiber type

has a much larger core diameter compared to single-mode fiber allowing for the larger number of modes

and

is easier to couple than single-mode optical fiber Multimode fiber further categorized as Multimode step-

index and Multimode graded index fiber

PROPAGATION THROUGH MMSI FIBER Figure shows the principle of total internal reflection applies to multimode step index fiber Because

the corersquos index of refraction is higher than the claddingrsquos index of refraction the light that enters at less than

the critical angle is guided along the fiber

Three different light waves travel down the fiber One mode travels straight down the center of the

core A second mode travels at a steep angle and bounces back and forth by total internal reflection The third

mode exceeds the critical angle and refracts into the cladding Naturally it can be seen that the second mode

travels a longer distance than the first mode causing the two modes to arrive at separate times

PROBLEMS WITH MMSI FIBER AND SOLUTION This disparity between arrival times of the different light rays is known as dispersion and the result is

a muddied signal at the receiving end It is important to note that high dispersion is an unavoidable

characteristic of multimode step-index fiber The solutions are either use Graded index fiber or Single mode

fiber

PROPAGATION THROUGH MMGI FIBER Multimode Graded-index refers to the fact that the refractive index of the core gradually decreases

farther from the center of the core The increased refraction in the center of the core slows the speed of some

light rays allowing all the light rays to reach the receiving end at approximately the same time reducing

dispersion Figure shows the Light propagation principle through multimode graded-index fiber The corersquos

central refractive index ( nA ) is greater than that of the outer corersquos refractive index ( nB )

It is very clear from the figure the light rays no longer follow straight lines they follow a serpentine path

being gradually bent back toward the center by the continuously declining refractive index This reduces the

arrival time disparity because all modes arrive at about the same time The modes traveling in a straight line

30 | P a g e

are in a higher refractive index so they travel slower than the serpentine modes These travel farther but

move faster in the lower refractive index of the outer core region

PROPAGATION THROUGH SMSI FIBER Single mode fiber has a much smaller core that allows only one mode of light at a time to propagate

through the core The figure shows the single mode fiber

Single-mode fiber exhibits no dispersion caused by multiple modes Single-mode fiber also offers lower fiber

attenuation than multimode fiber Thus more information can be transmitted per unit of time because it can

retain the fidelity of each light pulse over longer distances Like multimode fiber early single-mode fiber was

generally characterized as step-index fiber meaning the refractive index of the fiber core is a step above that

of the cladding rather than graduated as it is in graded-index fiber Modern single-mode fibers have evolved

into more complex designs such as matched clad depressed clad and other exotic structures

SINGLE-MODE FIBER DISADVANTAGES The smaller core diameter makes coupling light into the core more difficult The tolerances for single-

mode connectors and splices are also much more demanding

CUTOFF WAVE LENGTH - Cutoff wavelength is the wavelength above which a single-mode fiber supports and propagates only

one mode of light In other words an optical fiber that is single-mode at a particular wavelength may have

two or more modes at wavelengths lower than the cutoff wavelength The effective cutoff wavelength of a

fiber is dependent on the length of fiber and its deployment The longer the fiber the lower is the effective

cutoff

wavelength The smaller the bend radius of a loop of the fiber the lower is the effective cutoff wavelength If

a fiber is bent in a loop the effective cutoff wavelength is lowered

SIGNAL ATTENUATION IN FIBER - Optical fiber has a number of advantages over copper However it also suffers from degradation

problems which can not be ignored The first of these is loss or attenuation Attenuation is typically the result

of two sub properties They are scattering and absorption Both of which have cumulative effects The second

is

dispersion which is the spreading of the transmitted signal and is analogous to noise

SCATTERING Scattering occurs because of impurities or irregularities in the physical construction of the fiber The

well known form of scattering is Rayleigh Scattering It is caused by metal ions in the silica matrix and

results in light rays being scattered in various directions

31 | P a g e

Scattering limits the use of wavelengths below 800nm The short wavelengths are much affected than longer

wavelengths It is because of Rayleigh scattering that the sky appears to be blue ( shorter wave length ) The

shorter wavelengths ( blue ) of light are scattered more than the longer wavelengths of light

ABSORPTION Absorption results from three factors They are hydroxyl ions ( OH- water ) in the silica impurities

in the silica and incomplete residue from the manufacturing process These impurities tend to absorb the

energy of the transmitted signal and convert it to heat resulting in an overall weakening of the signal The

Hydroxyl absorption occurs at 125 and 139 micro The silica itself starts to absorb energy at 17 micro

because of the natural resonance of the silicon dioxide

MACRO BENDING LOSS Macro-bending loss is caused by bending of the entire fiber axis The bending radius shall not be

sharper than 30d where d is diameter of cable A single bend sharper than 30d can cause loss of 05dB

The fiber may break if bending is ever sharper

MICRO BENDING LOSS Micro-bending loss is caused by micro deformations of fiber axis which leads to failures in achieving

total internal reflection conditions Micro-bends are small scale perturbations along the fiber axis the

amplitude of which are on the order of microns These distortions can cause light to leak out of a fiber

Micro-bending may be induced at very cold temperatures because the glass has a different coefficient of

thermal expansion from the coating and cabling materials At low temperatures the coating and cable

become more rigid and may contract more than the glass Consequently enough load may be exerted on the

glass to cause micro bends

Coating material is selected by manufacturers to minimize loss due to micro-bending The linear thermal

expansion coefficient of coating material shall be compatible with that of fiber

32 | P a g e

DISPERSION Dispersion is the optical term for the spreading of the transmits in the fiber It is the bandwidth

limiting phenomenon and comes in two forms Multimode dispersion and chromatic dispersion Chromatic

dispersion is further subdivided into material dispersion and waveguide dispersion

DISPERSION PHENOMENON IN OPTICAL FIBER Dispersion is the time distortion of an optical signal that results from the differences of time of travel

for different components of that signal typically resulting in pulse broadening As the distance traveled by

the signal is more broadening of pulse is more In digital transmission dispersion limits on the maximum

data rate and the maximum distance ie the information-carrying capacity of a fiber link The interference

from broadened pulse in the next interval shall not lead to erroneous interpretation of received signal

OPTICAL DOMAIN Understanding where attenuation and dispersion problems occur helps optical design engineers

determine the better wavelengths at which information can be transmit taking into account distance type of

fiber and the other factors which can severely affect the integrity of the transmitted signal The graph shown

depicts the optical transmission domain as well as the areas where problems arise The wavelength (nm)

is shown on X-axis and attenuation ( dBkm) is shown on Y-axis

There are four transmission windows appear in the figure The first one is at around 850 nm the

second at 1310nm third at 1550 nm and fourth at 1625 nm The last two labeled as C and L band

respectively The 850 nm wavelength at which the original LED technology operated The second window at

1310 nm has low dispersion The 1550 nm called as C-band is ideal wavelength for long haul

communication systems The network engineers can avoid transmitting signal at 1000 nm where Rayleigh

scattering 1240 and 1390 nm where hydroxyl absorption by water occurs to avoid high degree of loss

Optical fibers also can be manufactured to have low dispersion wavelength in the 1550nm region

which is also the point where silica-based fibers have inherently minimal attenuation These fibers are

referred to as dispersion-shifted fibers and are used in long-distance applications with high bit rates For

33 | P a g e

applications utilizing multiple wavelengths it is undesirable to have the zero dispersion point within the

operating

wavelength range

34 | P a g e

SIGNALLING RELAYS

INTRODUCTION A relay is an electromagnetic device which is used to convey information from one circuit to another

circuit through a set of contact ie front or back contact Constructional and electrically relays may be

divided into DC and AC relays because the means by which the electrical energy in the coil is converted in

to mechanical Energy in order to move the contacts are fundamentally different In DC type the contacts are

carried on an armature forming part of a magnetic circuit in which a field is set up by the current flowing in

the coils In AC types the contacts are attached by a link mechanism to a metal sector disc or cylinder in

which currents are induced by the alternating magnetic field produced by the currents in the coils

Every endeavor has been made to explain the action of each type of relay in the simplest possible manner

Relays are sophisticated switch gears used for remote control and succession control of various

electrical equipment In present days they are widely used because they are capable of protecting the

controlled equipment from cross feeding and overloading even as they cater for speedy operations

Most of the relays in present day signaling are electromagnetic devices although some of the relays control

circuits through electronic components like diodetransistors Integrated Chips etc

Railway signaling relays are unique in that

(a) They operate on low voltage and current

(b) They are more articulate as according to their special features they can work under restrictive conditions

and in any specified manner Virtually they can cater for all situations while contributing to speed and

accuracy in operations

CLASSIFICATION OF SIGNALLING RELAYS (a) According to the method of their mounting or fixture they are classified as

(i) Shelf type Relays which are loosely kept on shelves

(ii) Plug in type Relays which are plugged into a pre- wired plug boards

(b) According to their connection and usage they are classified as

(i) Track relays Relay which is directly connected to the track to detect the presence of vehicle

(ii) Line Relays Other than track relay all are line relays Relays connected to the selection circuit

(c) According to their vitality or importance in ensuring train working safety they are classified as

(i) Vital Relays All relays used for traffic control such as signal point controls track detection etc

(ii) Non-vital Relays Relays which operate control aids and accessories like warnings buzzers

Indications etc

(d) According to their special provisions to ensure reliability of their contacts they are classified as

(i) Proved type are those whose normalization after each operation shall be proved in circuit

controlled by their contacts Contacts in which both the springs have metal surfaces on their tips They may

get fused due to high sparking current across them during operation These may prevent relay normalization

and causes unsafe condition in traffic control To avoid this proving of relay normalization after each

operation is necessary

(ii) Non - proved type Need not to be proved to have been normalized after each operation as their

contacts have at least one non-fusible contact (carbon contact)

(e) According to their feed source relays are broadly classified as

(i) DC relays The relay which requires DC power supply for its operations are called DC relays Among

the DC relays

o DC neutral relays This relay closes the same set of contacts on energization with Normal polarity

or Reverse polarity supply

o Polar Relays This relay closes different set of contacts when energized with Reverse polarity

supply They may or may not have contact to close when deenergized

35 | P a g e

(ii) AC Relay AC Induction motor track relays Time element relays flashing indication control etc

(iii) Electronic Relays DC relays with electronic components in them are called electronic relays

DC NEUTRAL RELAY Each Relay has usually one or two coils with a hollow center to accommodate a coreThe coils are

made up of a large numbers of turns of small gauge soft drawn copper wire The two coils can be connected

in series or parallel according to the requirement of relay resistance The ends of the coils are terminated on

binding post to which the control wires are connected Each coil is placed around a core of specially selected

Iron or steel having high permeability and low retentivity The core should be susceptible to magnetism and

at the same time should have little residual magnetism The cores are connected at the top by a yoke to

complete the magnetism coupling between two ends of coils The bottom of each core is equipped with a

large steel or Iron block known as pole piece or face

A flat piece of Iron or steel called armature is supported by brackets which are securely fastened to

the pole piece The armature yoke and the pole pieces are also made of specially selected iron or steel of the

same quality as the core The armature carries the metallic spring contacts which are insulated from it

The circuit through the coils of the relay is closed It sets up a magnetic flux through the core yoke and the

armature The flux passing between the armature and pole faces causes the armatures get attracted to the pole

faces and armature picks up and closes front contacts When the circuit is opened the magnetic flux collapses

and the armature drops away by gravity from the pole faces the front contacts break and back contacts close

The front and back contacts of the relay can be utilised to make or break other circuits Two stop pins of

nonmagnetic material are fixed either on the armature or pole faces so that the armature cannot

come in contact with the pole faces It is essential to maintain a small air-gap between the armature and pole

faces so that low value of residual magnetism may not retain the armature in picked up position and causes

the relay to fail to drop away with a break in its control circuit

GENERAL USAGE

DC Neutral line relays are most commonly used for Railway Signalling controls and detection

Among them plug-in type relays are preferred in larger installations for space considerations Shelf type

relays are also in use mostly in wayside stations

There are many DC Neutral line relays in use with special features such as

(i) Delayed operation

(ii) Biased DC control

(iii) DC control unaffected by AC interference currents

(iv) Getting latched in operated condition till further feeding and others

Usage of DC polar relays is mostly in conjunction with block instruments that control traffic between

stations AC line relays are almost extinct in installations of British Signalling practice They are however

used for time control operations flashing indication control and such other special purposes in installations

with Siemens signalling practice widely Track relays are used according to the type of track detection

circuits chosen for a given location and context While most of the track circuits are still of the DC working

type requiring DC neutral track relays with them the prospects of their being replaced with Electronic track

circuits directly feeding DC line relays in future are great AC Track Circuits are used in DC Traction area

as conventional DC Track Circuits are not suitable there AC Track relays are used with them almost all of

the induction motor type In the British practice of signalling which was first introduced on Indian Railways

non-proved type relays with carbon to metal switching contacts are generally used for vital controls

They facilitate simple circuit designs But with the advent of German Practice introduced by Ms

Siemens later proved type relays with all metal to metal contacts are widely accepted in spite of

complications in circuit design caused by them A recent introduction is that of the same type relays made by

Ms Integra control However for some time now the appreciable features of both the practices are getting

36 | P a g e

incorporated together in the indigenous designs of signalling by railwaymen With this the usage of all types

of relays anywhere can be found without straight jacketed segration of relay types

CHARACTERSTIC OF ELECTRO-MAGNETIC RELAY The following are the characteristic of electro-magnetic relays A brief study of them helps in

understanding the choice of their components and designs features

1) Force of attraction

2) Effect of air gap

3) Effect of Hysterisis

4) Transient condition

FORCE OF ATTRACTION In any electro-magnetic system the force of attraction is given by

Where B - is the flux density a - is the cross sectional area of the particular part of the magnetic

circuit

In the case of a DC neutral Relay B is proportional to the current that is flowing in the coil

surrounding the electro-magnet and thus the force of the attraction is directly proportional to the square of the

current This square relationship has its own advantage especially in the case of DC track relay in that a

small reduction in the current will have a great effect on the working of the relay Also for a given change of

current the make and the break will be quicker with lesser possibility of arcing

EFFECT OF AIR GAP

Curve lsquoArsquo is magnetisation curve for the iron and is all practical purpose a straight line up to the

saturation point Curve lsquoBrsquo is the magnetisation curve for the open-air gap which is a straight line through

out because per magnetisation curve of the whole

magnetic circuit of the relay and for a given force is the sum of the amp-turns for the iron part and the amp-

turns for the air gap

When the front contacts are open the force required to pick up the armature is shown on curve lsquoCrsquo to be F1

but after the armature has operated it will be separated from the core by stop pins In this position the amp-

turns required to maintain the armature is less as indicated by the dotted line from 1 on curve C to 2 on curve

37 | P a g e

F But actually the current in the coil is unaltered the force on the armature is greater than required as

indicated at 3 on curve F Part of this extra force is used to flex the front contacts sufficiently to give good

contact pressure when it is in energised position

The difference between the pick-up and the drop-away current should be as small as practicable in

track relay to ensure good shunting characteristics This is achieved firstly by the choice of good quality relay

iron and secondly by having a small air gap between armature and core If the air gap is not available then

the residual magnetism fluxes might cause the armature to be retained when the supply is disconnected For

this reason residual pins are provided to ensure a definite minimum air gap in the energised position

EFFECT OF HYSTERISIS

Hysterisis is the property by which the flux produced lags behind the current In the de-energized

condition there will be small residual flux in the core When the voltage is applied to the coils the current in

rising to its steady value first causes the flux to rise from 1 to 2 along the curve At this point the flux density

will be sufficient to attract the armature and reduce the air gap the flux then raise to 3 and continue to 4

which corresponds to the steady current in the coils When the voltage is disconnected the current in falling

caused the flux to fall from 4 to 5 along the curve At this point the flux density will fall below the value

required to maintain the armature which will release thus increasing the air gap and reducing the flux to 6

Finally the

flux will decrease from 6 to 1 where the current will again be zero

The relay core is made of material having high permeability and low retentivity As mentioned in

the IRS specification Electromagnet iron may be in the form of a

(a) Bar of silicon steel

(b) Best Yorkshire wrought iron

(c) Swedish charcoal iron

(d) Electrical steel sheets

` This reduces the difference between pick up value and Drop away value By selecting good quality

core material Percentage release and sensitivity of the relay will be improved

TRANSIENT CONDITION

38 | P a g e

When the voltage is applied or disconnected from the coils it takes some little time before the current

become steady These are known as transient conditionsrdquo and are important so far as track relays are

concerned When the voltage is first applied to the coils the magnetic flux in rising cuts the turns on the

coils and in so doing produces a back EMF that opposes the applied voltage and retards the growth of

current

The growth and decay of flux are decided by the relationship between the inductance and resistance

in the circuit is known as time constant It is not fixed quantity in the case of DC neutral relay This value of lsquo

Lrsquo is less when the relay is in de-energised condition (L1) than when the relay is in energised condition (L2)

The magnitude of flux that is established for a given change of current is different in two cases

When the current reaches the pick up value the armature closes and the inductance is increased to L2

due to reduced air gap the flux per amp is increased The increase in flux increased the back EMF during the

movement of the armature after which the current continuous to raise along a new curve corresponding to the

increased inductance until it reaches the final value (ER) This process is indicated above in fig24

When the supply is disconnected the current is obliviously reduced to zero immediately but the flux

decay comparatively slowly owing to the eddy currents produced in the core by the rapid flux change which

tend to maintain the flux The drop away time on a disconnection is however generally negligible See fig

below

If the relay releases due to the reduction in current from say I 2 to I 1 caused by the application of

shunt resistance (as in the case of track relay ) the time taken is much longer than the relay is simply

disconnected The rate of rise or fall of current during the transient conditions is also depends on exterior

circuit values because L and R apply to the whole circuit The production of eddy current in the core the flux

will decay at a slower rate than the current So that the actual release time will be a little longer than it takes

the current to fall to the release

L= Inductance

39 | P a g e

R= Resistance

It is now clear that to reduce releasing time to a minimum it is necessary that

- The relay iron should have low Hysterisis loss and low retentivity

- The degree of over energization of the relay should be restricted

- Connecting a suitable external resistance in series with the relay to keep LR ratio low

In non RE area for track circuit length less than 100M 9 ohm track relay only to be used Using relay

with minimum contacts as they require lesser current which keeps inductance value low

Train working safety is ensured only if the track relay of shortest length track circuit is released

before a light engine running at a highest permitted speed clears it Otherwise the track circuit occupation

may go undetected To avoid this a special provision has to be made in signal control circuits wherever

necessary

The following methods may be adopted for reducing the time lag of track relay

(a) Restrict the over energisation of relay since the release time depends on the initial working current

(b) Connecting a suitable external resistance in series with the relay to keep the LR ratio low

(c) Using relays with minimum contacts as they require lesser operating current keeping the inductance

value low

40 | P a g e

CONCLUSION

Modern signalling is vital for safe and punctual movements of trains In the Indian railways The Signalling

and Telecommunication Department is responsible for providing modern effective and relaible signalling

systems as well as telecommunication systems

The first mode of communication used in Indian Railways was the use of electric telegraph

with the help of Morose code Morose code is the method of providing text information as a series of on-off

tones and lights or clicks that can be directly understood by a skilled listener or observer without special

equipmentEach character (letter or numeral ) is represented by a unique sequence of dots and dashes Later

this system becomes obselete and beggan the era of wireless communication which operated at audio level

frequency range

In wireless communication the significant advances took place the transition to miniature

valves or filament tubesBut this was abandoned too because of excessive current consumption and over

heating of the filament tubes

Fibre-optic communication is a method of transmitting information from one place to another by

sending pulses of light through an optcial fibreThe light forms an electromagnetic carrier wave that is

modulated to carry information First developed in the 1970s fibre optic communication systems has

revolutionized the telecommunications industry and have palyed a major role in the advent of the information

age Because of its advantages over electrical transmissionsoptical fibres have largely replaced copper wire

communications in core networks in the developed world The Indian Railways too is undergoing a transition

from Microwave communication to fibre optic communications

41 | P a g e

BIBLIOGRAPHY AND REFERENCES

1 wwwwikipediacom

2 wwwbritaniccacom

3 wwwirfcacom

4 Motorola GP60 system manual

5 Harris FAS 7000 manual

6 TOSHIBA Manual

5 | P a g e

INTEGRATED POWER SUPPLY

INTRODUCTION A typical 4 line station requires power supplies of 24 V DC( 5 nos ) 12 VDC ( 5nos ) 6V (2 nos)

110 V DC and 110 V AC for signalling These require as many chargers and Secondary cells amp Invertors

requiring more maintenance amp spares Can they be Integrated in to one system

Thus the concept of Integrated Power Supply has been evolved by integrating concepts One Charger

One set of Battery Bank feeding Invertors and DC- DC converters for deriving various DC amp AC

voltages Integrated power supply system delivers both AC amp DC Power supplies as an output with the

output voltage tolerance of plusmn 2

ADVANTAGES Reduces maintenance on Batteries Battery charger amp overall maintenance

Its construction is in modules and hence occupies less space Reduced space requirement resulting in

saving of space for power supply rooms

Provides centralized power system for complete signaling installation with continuous display of

working status of system for easier monitoring

Defect in sub-units of system is shown both by visual amp audible indication Reflects the condition of

battery with warning

Replacement of defective modules is quick amp easy without disturbing the working of the system

It uses (n+1) modular technology hot standby arrangement and hence high reliability and more

availability of the system

The system provides uninterrupted supply to all signalling system even during the power failures

Thus No blank Signal for the approaching drivers

System can be easily configured to suit load requirement

The diesel generator set running (Non-RE area) is reduced almost to lsquoNILrsquo Hence low wear and tear

of DG set components amp reduced diesel oil consumption

COMPONENTS (a) Un-interrupted power supply (U P S)

(i) SMPS Battery chargers with Hot stand-by mode

(ii) Hot Standby PWM Inverters with auto changeover

(iii) CVT Regulator [FRVS]

(b) AC distribution board [ACDB]

(i) STEP DOWN TRANSFORMERS

(c) DC distribution board [DCDB]

(i) DC-DC converters

WORKING IPS works satisfactorily for AC input variation of 150V AC to 275V AC with single-phase power supply

and frequency variation from 48 Hz to 52 Hz The input is fed to SMPS charger which converts in to 110

VDC as output It is fed as input to three sub units

To battery bank charging the batteries

To ON line inverters that converts 110 VDC in to 230 VAC plusmn 2as output

6 | P a g e

As 110 VDC bus bar to DC Distribution Panel as an input to various DC-DC converters located in

it

A 110 V Battery Bank of VRLA cells are connected to SMPS Panel IPS Status Monitoring Panel is

located at ASM room or at SampT staff room if round the clock SampT staff is available at Station

CONSTRUCTION IPS mainly consists of

SMR (Switch Mode Rectifier) Panel SMPS based Float cum Boost Charger (FRBC) Panel

AC Distribution Panel

DC Distribution Panel

Battery Bank (110V DC)

Status Monitoring Panel

SMR (SWITCH MODE RECTIFIER) PANEL SMPS BASED FLOAT

CUM BOOST CHARGER (FRBC) PANEL It consists of SMR FRBC modules and Supervisory amp Control Unit SMPS based SMRs

(converters) SMPS based Float cum Boost Chargers (FRBC) modules are provided with (n+1) modular

technology hot standby arrangement with active load sharing basis and 1 additional module as a cold standby

(n+2) Supervisory amp Control Unit which controls and monitor the complete system It has various

indications on the panel reflecting the working of the panel

FRBCs are suitable for operating in parallel on active load sharing basis with one or more modules of similar

type make and rating

n = required no of modules to cater for actual current requirement

AC DISTRIBUTION PANEL It is made of ON-Line inverters with (1+1) modular technology hot standby arrangement amp CVT

(Constant Voltage Transformer) AVR (Automatic Voltage Regulator) and set of step down

transformersThe inverter is protected against overload and short circuit with auto reset facility Whenever

the failure occurs it trips and restart automatically after about 10 to 20 sec But if the problem persists the

protection is permanently gets latched and it will not be switched ON again unless the fault is cleared

followed by pressing of reset button The output of inverters is regulated to 230V AC plusmn 2 50Hz plusmn1Hz for

an input voltage variation of 90V DC to 140V DC Normally both the Inverters are powered ON and both are

delivering the Output voltage but only one (main) inverter is connected to the Load If main inverter is failed

then only the stand-by inverter will come on Load automatically with in 500msec At 70 Depth of

Discharge (DOD) of the battery bank 110VDC supply to the inverters will be cut-off So the Signals feed will

be cut-off The auto-change over arrangement is also provided for bringing the CVT in circuit with in

500msec when the both the inverters output is failed It has various indications on the panel reflecting the

working of the panel

DC DISTRIBUTION PANEL It takes care of DC Power supply requirements of our signalling It consists of sets of DC-DC

converters for individual DC power requirements with (n+1) modular technology hot standby arrangement

with active load sharing basis The DC-DC converters of Relay Internal are provided with (n+1) modular

technology hot standby arrangement with active load sharing basis and 1 additional module as a cold standby

(n+2) The DC-DC converter works satisfactorily with the input voltage variation of 98VDC to 138VDC At

90 Depth of Discharge (DOD) of the battery bank all the DC-DC converters 110VDC Input supply will be

cut-off except for Block Tele DC-DC converters The supply for Point operation is also catered through a

20A fuse by this unit It is also provided with various indications that reflect its working

7 | P a g e

STATUS MONITORING PANEL IPS status monitoring panel has been provided in the ASM room for giving the important alarms and

indications to ASM Status Panel tells present working status of IPS displaying battery voltage continuously

and five other indications which will light according to IPS status During normal working these indications

will not lit Whenever the battery has come on to the load and has discharged by 50 DOD (Depth of

Discharge) then first Red indication lit with description ldquoSTART GENERATORrdquo with audio Alarm ie DG

set is to be started and put on the load If DG set is not started with this warning then if battery gets further

discharged to 60 DOD and second Red indications appears with description ldquoEmergency Start generatorrdquo

with audio alarm even now if DG set is failed to be started the battery further gets discharged to 70

DOD and 3rd Red indications appear with description ldquo System shut downrdquo with audio alarm which will

continue till Generator is started resulting in AC output from IPS is automatically cut off results all the

signals will become blank

When there is any defect in any sub module of IPS even without affecting working of system the 4th

Red indication appears with description ldquoCall SampT Staffrdquo with audio alarm so the ASM advises SampT staff

accordingly Green LED 5th indication comes with the description ldquoStop Generatorrdquo with audio alarm when

the DG set is running and if the Battery bank is fully charged condition

EARTHING The IPS systems and its individual modules are having earth terminals and all these are properly

earthed with earth resistance of less than 1 ohm Earth provided shall preferably be maintenance free using

ground resistance improvement compound (The acceptable Earth Resistance at earth busbar shall not be

more than 1 ohm Code of practice for earthing and bonding system for signalling equipments)

LIGHTNING AND TRANSIENT PROTECTION IN IPS Manufacturer will provide Stage1 amp Stage 2 protection along with the IPS These are described

below

Stage 1 protection is of Class B type against Lightning Electro-Magnetic Impulse (LEMP) amp other

high surges provided at Power Distribution Panel It is provided with a 63 Amp fuse in phase line and is

connected between Line and the Neutral and also between the Neutral and Earth

Stage 2 protection (Power line protection at Equipment level) is of Class C type against low voltage

surges provided at the equipment input level This is thermal disconnecting type and equipped with

protection against SPD (surge protection device) failure due to open amp short circuit of SPDs and is connected

between the Line and the Neutral If supply data signalling lines (ACDC) are carried through overhead

wires or cables above ground to any nearby building or any location outside the equipment room additional

protection of Stage 2 type shall be provided at such locations Class B amp Class C arrestor is provided on a

separate wall mounting type enclosure in IPS room

Stage3 protection (Protection for signallingdata line) is of Class D type All external data signalling

lines (ACDC) shall be protected by using this Class D type device It consists of a combination of Varistors

and Gas Discharge Tube with voltage and current limiting facilities

FEATURES Chargers used in this system are of SMPS technology chargers with 90 efficiency These chargers

are supported with hot standby mode with (n+1) modular technology

Onetwo sets of Maintenance free Battery banks (110VDC) Normally one set (110VDC) of Battery

bank is used Conventional flooded type Lead Acid Batteries or Low Maintenance Lead Acid

batteries can also be used (SMRs settings are required to be adjusted depending on the type of

Batteries used) Various voltage levels of

8 | P a g e

battery banks are avoided Reduction in Battery maintenance amp less flour area required

DC-DC Converters working from 110V Central battery have been used for all dc supplies This has

improved overall efficiency of the system since number of conversion from AC to DC have been

reduced to 2 stage as compared to 3 stage conversion in case of transformer-rectifier system

DC-DC converters are available in modules Easy replacement of defective modules This ensures

less down time

DC-DC Converters are used in load sharing N+1 configuration (ie with hot standby with N+1

modular technology) to improve the reliability amp availability of the system

Capacity of inverter has been brought down to 15 KVA from 5 KVA and used for feeding only

Signals supply Hot standby inverter is provided with auto changeover facility This improves the

availability of the overall system

High efficiency inverter is used with PWM (Pulse Width Modulation) technology in place of Ferro-

resonant technology based inverter This improves the efficiency of the overall system

Continuous power to Signal Circuits even in absence of DG setLocal Power Supply

Generators need not be switched ON every time during train movement

Metal-to-metal relay installations and block working by axle counters have also been covered

Supply of spare modulesComponentsCells have been included as part of main supply

Provides highly regulated voltage to all signal relays amp lamps for better life

9 | P a g e

SINGLE SECTION DIGITAL AXLE COUNTER

INTRODUCTION- The axle counter equipment is working on high frequency and using amplitude modulation or phase

modulation for detection of presence of wheel The equipment described in this notes is Phase modulation type

for the detection of presence of wheel In the Phase modulation type track device the detection of presence of

wheel is with the phase reversal of 1800 out of phase which enables this system to be more healthy and safe

In Phase Reversal Modulation technique trolley suppression arrangements to prevent the counting of

wheels caused by push trolley passing over the track device are not required as the system will take care of

validation of generated pulses caused by passage of wheel over the track device depending up on the phase

shift of the pulse This phase shift of the pulse may be normally 160deg to 180deg for a train wheel and it may be

approximately 100deg to 120deg for a push trolley wheel

This is Digital Axle Counter equipment for single track sections containing 2 out of 2 micro-

controllers to count the axles establish the track occupancy of a track section and to provide this information

to the block or the interlocking equipment

In this system no separate evaluator is required and no analog data is being transmitted One set of

Axle counter equipment is provided at entry end and other set provided at exit end Both sets are being

connected through a twisted pair of telecom cable ie existing RE cable one PET quad is used for both UP

and DN Axle Counters Digital DATA is being transmitted between two ends of Axle counters (Outdoor

track side Detection points)This system is a fully duplex capable of operating according to CCITT V21 and

the Data will be transmitted at the rate of 300bitsec This data Transmitted ensure negligible interference of

the noise The system is highly reliable

FEATURES (a) The system consists of

(i) Single Section Digital Axle Counter (SSDAC) units

(ii) Tx Rx coils

(iii) Vital Relays

(b) TxRx coil axle detectors are mounted to the web of the rails The design of system consists of 21 KHz amp

23 KHz High frequency Phase Reversal type axle detectors

(c) Compatible with 90R 52Kg amp 60Kg rail profiles Easy to install commission amp maintain

(d) Track devices at both (entry amp exit) points of the section should be fixed on the same rail

(e) System is designed to detect the solid wheels with diameter gt 400mm with standard wheel flange

(f) The system works in pairs For monitoring single-track section one pair of SSDAC units are required and

to be installed near the trackside one at the beginning and another at the end of the track section ie

Trackside electronic counting equipment

(g) The basic design of the system is based on counting the number of axles passing at each detection point

These stored counts are transmitted to the second unit of the system and vice versa by means of modem

communication

(h) The communication consists of digital packets having details of Counts amp Health

10 | P a g e

(i) If counts registered at both detection points are equal the section is cleared otherwise the section is shown

as occupied The system ensures no error condition to arrive at the decision of clearance

(j) System is designed as per CENELEC SIL-4 (European standard) using micro controller along with other

electronic circuits and programmed using dedicated software When any of these circuits fail the system

goes to fail safe condition

(k) It is programmable for either Preparatory Reset or Conditional Hard Reset as per requirement

(l) Micro controller based design with 2 out of 2 decisions and counting through software

(m) V21 Modem communication (2-wire) on frac12 quad cables and also compatible to work on voice channel of

OFC amp Radio

(n) Opto isolated vital relay drive for Q-style 24V 1000 _ and Vital Relay output can be giving at both ends

of the system

APPLICATIONS The system can be widely used in Railways for Block Working (BPAC) Intermediate Block Signaling Auto

signalling and Track circuiting for i) Loop line ii) Main line iii) yard lines

SYSTEM DESCRIPTION

This system comprises of

Tx coils-2 nos

Rx coils-2 nos

Reset Box (RB 258A)

Card 1 Signal Conditioning Card ndash 1

Card 2 Signal Conditioning Card - 2

Card 3 Micro controller Logic Board ndash 1

Card 4 Micro controller Logic Board ndash 2

2 nos for independent resetting ndash when used in block sections

1 no for common resetting ndash when used for Track circuiting at stations

Card 5 Event Logger Card

Card 6 Modem Card

Card 7 Relay Driver Card

Card 8 DC-DC Converter Card

SSDAC (DACF 700AP) UNIT

(A) SIGNAL CONDITIONING CARD (CARD 1amp2) (SCC) -1 (SCC-1) generates 21 KHz carrier

signals

-2 (SCC-2) generates 23 KHz carrier signals which is transmitted to 2nd

set of Tx coils

s receive these signals

modulated

train pulses

11 | P a g e

(B) MICRO-CONTROLLER LOGIC BOARD CARD (CARD 3amp4) (MLB) The Micro-controller Logic Board (MLB) is the heart of the system

o 8051 Based Architecture

o 8 Bit Micro Controller

o ATMEL AT89S8252 Micro controller

o 2 out of 2 Decision

o Uses C subset language

- TOOLS

o KEIL μ Vision Development System

o Universal Programmer

o 2KB Program Memory

o 256 bytes RAM

o 8KB Flash memory

o 32 Programmable IO lines

o Wide Operating Voltage range of 4V-6V

o Full Duplex Serial Port

o Programmable Watch Dog Timer

o Fully Static operation up to 24MHz (Upgraded to 40MHz)

o Operating Temperature of ndash40degC - +85degC

o Use of State Machine for Axle Counting

o Use of ASCII MODBUS protocol

o Use of CRC16 technique for Error Checking during communication

o Wheel detection

o Train direction checking and

o Wheel counting functions

o It receives the remote wheel count and computes the status of the section for clear or occupied

o It also checks various supervisory signal levels like supervisory of TxRx coils presence of various

cards communication link failure etcThese cards communicate with each other for wheel count

At Entry-end if train enters into section (1st detection) the counts are incremented and when train

shunts back from the same detection ie if train exits from the section from the same detection the counts are

decremented At Exit-end if train enters into section (2nd detection) the counts are decremented and when

train shunts back from the same detection ie if train exits from the section from the same detection the

counts are incremented Both the track devices at Entry and Exit ends must be fixed on same side of the

track

This MLB card is having Extensive LED display

o A block of 8 LED indicators for count progress error display

o 2 independent LED indicators for section status

o The errors occurring in the system during the operation of the SSDAC are encoded and are indicated by

means of the 8-LED block present on the front panel of the MLB cards

(c) EVENT LOGGER CARD (CARD 5)

Event logger card is designed to capture and store important signals from the remote and local SSDAC units

The stored data can be downloaded from the event logger card for the purpose of analyzing the events

occurring during the operations of the SSDAC The data can be analyzed with the help of CEL data analyzer

software

12 | P a g e

The event logger card captures following signals

(i) Pulse signals

(ii) Supervisory signals

(iii) Card removal information

(iv) Serial packets from

Event Logger card has a Rabbit processor and 2 MB FLASH MEMORY to store packets The data is initially

stored in the buffer and subsequently transferred to FLASH memory every two minutes Normally 4096

pages of the data can be stored in flash memory on FIFO (first in first out) basis

Run This LED blinks continuously indicating the normal working of the event

Log This LED blinks whenever data is being logged into the flash memory (Approx after every 2 minutes)

Dnld This LED is ON when data is being downloaded from the flash memory of the card and becomes OFF

when download is complete

(D) MODEM CARD (CARD 6) (i) The modem card transmits and receives the digital packet information form one counting unit to the other

The packet will appear after every 18 sec and the packet carries the latest information such as

(ii) The modem card being used is V21 type (2-wire) in SSDAC

(iii) This card interfaces with serial RS232C port of both Micro-controller Logic Boards

(iv) It multiplexes the two RS232C inputs and selects one of the two channels and provides signal conversion

from digital to analog (FSK modulation) and vice-versa

(v) Data transmission rate is 300 bitssec

(vi) Automatic Gain Control circuit is incorporated hence no gain adjustments required

(vii) Mode selection on Modem card The modem has been set in lsquoORIGINATORrsquo mode for entry and in the

lsquoANSWERrsquo mode for exit in the factory

(viii) LED Indications provided on Modem card

-Transmitting the signal when LED is flashing

- Receiving the signal when LED is flashing

-Remains OFF in SSDAC

-Carrier is detected when LED is glowing

(E) RELAY DRIVER CARD (CARD 7) (i) The Relay Driver card (RD) provides the 24V DC output required for driving Vital Relay

(ii) One RD card is used in each SSDAC counting unit The RD card receives the command of clear and

clock signals from MLB1 amp MLB2 cards and drives the vital relay lsquoONrsquo when section is NOT OCCUPIED

through opto- isolator circuit

(iii) If a train occupies the section the vital relay is dropped The vital relay status is read back by the system

as per the driving output

(iv) It has

13 | P a g e

ndash LED flashes when the section is clear

ndash LED flashes when the section is clear

All the above LEDrsquos are lit for section clear condition

(F) DC-DC CONVERTER CARD (CARD 8)

INPUT VOLTAGE Nominal Voltage voltage 24V DC Maximum current drain= 12A

Required voltage 18V DC to 30V DC

Output voltage

Nominal Voltage +5 V DC 2 A Required voltage 4 7 5 t o 525V DC

Nominal Voltage +12V DC 200 mA Required voltage 1175 to 1225V DC

Nominal Voltage +24V DC 300 mA with common ground Required voltage 235 to 245V DC

Nominal Voltage +15V DC 100 mA with isolated ground Required voltage 145 to 155V DC

SURGE VOLTAGE AND LIGHTNING PROTECTION Transient surge voltages arise as a result of Lightning discharge switching operations in electrical

systems and electrostatic discharge These surge voltages often destroy the electronic equipment to a large

extent In order to prevent surge voltages from destroying the equipment all the input lines of SSDAC ie

Power Supply (24V) Reset (48V) amp Modem is to be routed through surge voltage protection devices for

effectively protecting the system These devices (3 numbers) are mounted in a box and supplied along with

the system One number of box is to be installed at each location and wired to the SSDAC

Each surge voltage protection device consists of two parts

(a) Base

(b) Plug Trab

The Base of the device is used for wiring the input and output signals The connection details from relay

room to the box and from box to SSDAC unit are provided on the box The Plug Trab consists of MOV and

GD Tube and diverts the excess energy during surge voltages or lightning into the ground connection The

operation of these devices relies on a high quality ground connection in order to safely shunt away the

unwanted energy The impedance of the ground connection is critical and it should be less than 2 Ohms

NOTE The 3 Plug Trab connections are not to be interchanged with one another The plug Trab is a

detachable device and can be replaced with SPARE unit in case of blown device which is indicated by

means of LED for 24 V

EFFECTIVENESS OF PLUG TRABS The effectiveness of plug Trab depends wholly on the Earth connection provided to the system The earth

provided to the system should be less than 1 ohms and connections should be firm and proper to the SSDAC

unit VR box etc

SURGE VOLTAGE AND PROTECTION DEVICE SV-120 The Surge Voltage protection device is to be installed at each location along with every SSDAC unit

14 | P a g e

EARTHING- The lead wires connecting the installation and the earth electrode shall ordinarily be of stranded

copper wire of 29 sq mm (19 strand wires of 14 mm diameter) Copper wire has been specified because GI

wires usually are having greater corrosion However in areas where copper wire may be frequently stolen

due to theft ACSR of size 64 sq mm (19 strands of 211 mm diameter) may be used

LIMITS OF EARTH RESISTANCE (a) Apparatus case connected to Earth (SSDAC and vital Relay Box is housed in Apparatus case and

Connected to earth at outdoor) shall be less than or equal to 1 ohm

(b) All cable connected to same earth shall be less than or equal to 1 ohm

(C) Reset box connected to earth near SM s Room shall be less than or equal to 1ohm

EQUIPMENT TO BE EARTHED A Common Earth should be provided for SSDAC for items 1(a) amp (b) of the above at the outdoor

(a) The Apparatus Case is to be connected to earth (the chassis of SSDAC amp Vital Relay Box should be

properly connected to apparatus case)

(b) Metallic sheath and armouring of all the underground main cables are to be earthed

(i) In RE area the metallic sheath and armouring of main telecom cables are earthed at both ends

(ii) In RE area the armouring of Jelly filled cable shall be earthed at both ends

(c) The Earthing shall be provided at every location box where cables are terminated

(d) Earth already available for other equipment may be used for earthing of Reset Box near SM s Room

Cabin etc

15 | P a g e

DATALOGGER

INTRODUCTION Datalogger is a Microprocessor based system which helps in analysing the failures of relay inter

locking system Electronic Interlocking system This is like a black box which stores all the information

regarding the changes take place in relays AC DC Voltages and DC currents along with date and time The

same information data can be transferred to the computer to analyse further ldquoon line ldquooff linerdquo analysis of

stored date A print out also can be obtained through a printer by connecting directly to the datalogger unit

The data belongs to Relay contacts is considered as digital inputs and the data belongs to voltage

levels currents is considered as Analog inputs Datalogger lsquos are mandatory for all new relay interlocking

(PIRRI) EI installations and it is also recommended to provide in all existing PIs RRIs To increase the

line capacity mechanical signalling equipments are upgraded to PI RRI or EI Due to complexity in the

circuits and wiring sometimes it is very difficult to rectify the failures So datalogger can monitor these

systems with real time clock Thus it can be named as black box of Samp T equipments and hence it is a vital

tool for accident investigation Datalogger is used at Stations yards Whereas in case of Auto Section amp IBH

Mini dataloggers called as Remote Terminal Unit (RTU) are used

ADVANTAGES OF DATALOGGERS (a) Dataloggers helps in monitoring the typical failures such as intermittent auto right failures

(b) It helps in analyzing the cause of the accidents

(c) It helps in detecting the human failures errors such as

(i) Drivers passing signal at Danger

(ii) Operational mistakes done by panel operators ASMrsquos of operating department

(iii) Signal and telecom engineering interferences in safety circuits

(iv) Engineering and electrical department interferences failures

(v) It helps as a ldquoTOOLrdquo in preventive maintenance of signaling gears

(d) Dataloggers can be connected in network Networked dataloggers helps to monitorthe PIRRIEI remotely

(e) Failure reports can be generated remotely with help of datalogger network

(f) On line and Off line track simulation is possible

(g) Speed of the train on point zones can be calculated

(h) Age of the equipment in terms of number of operations etc

COMMON EQUIPMENT FOR ALL DATALOGGERS ARE GIVEN

BELOW (a) CPU card

(b) Digital and Analog input cards

(c) Local terminal(PC)

(d) communication links

(e) Printer

All the dataloggers requires a potential free ( spare ) relay contact for monitoring digital inputs

through Digital input cards amp for monitoring Analog inputs such ACDC bus bar voltage levels through

Analog input cards Digital and Analog inputs are connected to the Processor card Processor card consists of

memory ICrsquos Memory ICrsquos are programmed as per requirement of the signal engineers

Provision of Dataloggers is mandatory with RRI systems and is optional for PI systems as per

amendment to the specification for Relay Interlocking systems ( IRSS-36 ) The data collected by the

datalogger can be used for failure analysis repetitive discrepancies and for accident investigations

16 | P a g e

Note

If the serial communications is more than 50m then line drivers shall be used up to 3 Kms

4wire leased line Modems shall be used if the serial communication is more than 3 Kms

STUDY OF EFFTRONICS DATALOGGER TECHNICAL DETAILS (a) 24V 12VDC Power Supply

(b) Total Storage Capacity of 10 Lakh events

(c) In-built Temperature sensors

(d) Internal Buzzer for alarming during failures

(e) Real Time clock with internal battery backup with data retention up to 10 years

(f) 512 LED matrix to indicate the status of 512 Digital inputs at a time page wise

(g) Seven segment LCD screen (2x24) to display the status of digitalanalog signalsTime Temperature etc

(h) Using the keyboard various functions can be viewed in the LCD panel

(i) Max Digital Inputs 4096

(j) Max Analog Inputs 96

(k) Digital Input Scanning Time 16 millisecond

(l) Analog Input Scanning Time is less than 1 Sec

HARDWARE (EQUIPMENT) Datalogger system consists of

(a) Datalogger (CPU - with Microprocessor 68000)

(b) Digital input cards

(c) Dual modem card

(d) Digital Scanner units (DSU)

(e) Analog Scanner units (ASU)

CPU CARD It is provided with Motorola microprocessor M 68000 It performs all the activities pertaining to the

datalogger It continuously scans (check) the Digital inputs(inbuilt) Digital Scanner Units and Analog

Scanner Units ie scanning of digital signals (Relay operations) for every 16-milli seconds and scanning of

analog signals (ie ACDC voltages amp DC currents) for less than 1 second

This card will support the IO interfaces of LCD (Liquid Crystal Display) - 2X24 alphanumeric Key

Board LED Matrix Display Real Time Clock LCD display and keyboard This will acts as man machine

interface between the datalogger and the signal engineer All the operations (Software) can be performed

using this LCD and keyboard

Real time display with 7 Segments This is built in real time clock within Datalogger and its current

time will be displayed on six 7-segment display provided (Real time clock depend upon DALLAS 1286

chip) This IC will come with internal battery backup hence there is no need to add external batteries

CPU card continuously scans (checks) the DSUs and ASUs Each input connected to digital scanner

units are optically isolated by Opto couplers When CPU card scans the digital inputs it compares with the

previous stored data and if there is any change from the previous status then only that data will be stored (the

status conditions of relay) with date and real time A total of minimum 10 Lac events can be stored in

memory on first in first out basis so that latest data is available in the system There is no loss of data from

datalogger memory in case of power supply failure of datalogger

DIGITAL INPUT CARDS (IN-BUILT) This system is having maximum 8nos of inbuilt Digital inputs cards Maximum 64nos of digital

inputs can be connected to each digital input card The potential free relay contact may be front or back

contact terminated at the Tag Block from the relay of signals tracks points Buttons etc and are

17 | P a g e

subsequently connected to Digital input cards through Flat Ribbon Cable (FRC) connectors These in-built

digital input cards can monitor a total 512 nos of relays status

DIGITAL SCANNER UNIT (DSU) Each DSU contains 8 nos of Digital Input cards Each input card can be connected with 64 inputs

Total input capacity of DSU unit is 512 inputs These scanner cards contain Optocouplers and Multiplexer

Inputs are connected to Stag card The stag card out put is connected to DSU through FRC connectors

Maximum 7 nos of DSUs can be connected to the system So Digital input capacity of the system is 4096

All these digital inputs are scanned at rate of 16 msec

ANALOG SCANNER UNIT (ASU) ASU contains maximum 3 nos of Analog input cards Each input card can be connected with 8nos of

Analog inputs Total input capacity of the ASU is 24 analog input channels Maximum 4nos of ASUs can be

connected to the system Analog input channel capacity of the system is 96 All these analog inputs are

scanned at a rate of less than 1 sec

PARALLEL PORT Parallel port is provided for connecting printer

RS-232 SERIAL PORTS At least 6 Serial communication ports are provided for communication with other dataloggers

Central Monitoring Unit Remote Terminal Unit Electronic Interlocking system Integrated Power Supply

system etc

EXTERNAL NON-VITAL RELAY CONTACTS These relays provided in the system where 16 number of the Relay contacts are provided on the rear

panel through Tele control port to extend alarms and to control the power equipment from remote or local

locations through computer in case of any occurrence of failures Each control can sink or source 100 m

amps of current

INTERNAL MODEM CARD DUAL MODEM CARD (IN-BUILT) It is fixed in datalogger Euro rack itself One card contains two modems The top modem is called

ANS (answer) modem and the bottom modem is called as ORG (originate) modem It is used in case of

networking of Dataloggers In network connect lsquoANSrsquo modem to the lsquoORGrsquo modem of one adjacent station

and connect lsquoORGrsquo modem to the lsquoANSrsquo modem of other adjacent station

POWER SUPPLY Normally 24V DC (12V DC is optional) supply with battery backup is required for the system

working

Input Voltage Range 18Vhellip32V DC (For 24V) 9Vhellip18V DC (For 12V)

INPUT REQUIREMENTS Relay inputs (digital inputs) and analog inputs (voltages currents etc) are required to be connected

to the system as per the requirements of RRI PI SSI as the case may be Some of the inputs to be

monitored is given below

(a) Digital inputs

(i) Field inputs All TPRs NWKRs RWKRs ECRs Crank Handle relays SidingSlot LC gate

control relays etc

(ii) Control Panel inputs All button Knob SMrsquos Key relays

18 | P a g e

(iii) Internal relays

British system All HR DR HHR WNR WRR ASR UCR RR LR UYRTLSR TRSR TSR

JSLR JR etc

SIEMENS system Z1UR Z1UR1 GZR ZDUCR ZU(R)R ZU(N)PRG(R)RG(N)R U(R)S

U(N)PS UDKR DUCR U(R)LR UYR1 UYR2 G(R)LRGR1GR2

GR3 GR4 OVZ2U(R)RW(RN)R (RN)WLR Z1NWR Z1RWRZ1WR1 WKR1 WKR2 WKR3 etc

(b) Analog channels

(i) 230 V AC (for power supplies in the power panel)

(ii) 110V AC (for Signal and Track transformers)

(iii) 110V DC (for Point operation)

(iv) 60V DC (Siemens relays)

(v) 24V DC (Q-series relays)

(vi) 24V DC (for Block Axle counters)

(vii) 12V DC (for indication)

(viii) 20A (for point operation current)

(ix) 10V AC 5KHz (for Axle counter channels) etc

SOFTWARE MODULES OF DATALOGGERS

(a) Network Management of Dataloggers (NMDL)

(b) Reports

(c) Fault Entry

(d) Track Offline Simulation

(e) Train Charting

NMDL SOFTWARE FEATURES (a) Online Relay Status

(b) Online Faults - To view information of various Online Faults as they occur in the stations where

the Dataloggers are connected

(c) Online Simulation - Graphical view of relay operations train movements etc

(d) Remote monitoring of stations with the help of NETWORKING

SOFTWARE OBJECTIVES (a) Predictive Maintenance

(b) Easy identification of failures

(c) Crew discipline

(d) Train charting

REMOTE MONITORING OF STATIONS WITH NETWORKING OF

DATALOGGERS The individual Dataloggers of various stations can be interconnected through networking technology

The data of Remote Panel stations can be viewed in a Computer at the Central Monitoring Station The data

of the network is collected by the FEP (Front End Processor) which in turn is transmitted to the computer

COMPONENTS OF NETWORK MANAGEMENT OF DATALOGGERS

(a) Datalogger at stations

(b) MODEM and Transmission medium

19 | P a g e

(c) Front End Processor (FEP)

(d) Central Monitoring Unit (CMU) Computer

FEP (FRONT END PROCESSOR)

FEP acts as a buffer between the Central Monitoring Unit (Computer) and the Network It is provided

at centralised place to retrieve data continuously from station dataloggers and store in memory and transfer to

computer on request It stores 10 Lac telegrams It works on 12V DC It draws 16A continuous current

when all the three modems are connected Normally it shows the number of packets pending to be sent to the

computer on its 7-segment LED display It is provided with MOTOROLA 68000 microprocessor It has 6-

nos of RS-232 communication ports such as COM1 COM2 COM3 COM4 COM5 and COM6 COM1 is

used for Fault Analysis System (FAS) ie Central Monitoring Unit (Computer) connection COM2 to COM6

are used for networking For Bi-directional 2- nos of ports and for Tri-directional (T-network) 3-nos of ports

are used

DATA TRANSMISSION Dataloggers can be networked in Uni-directional Mode or Bi-directional Mode or T ndash Network Mode

In case of loss of data retransmission of data takes place

(a) Uni-Directional Mode

Each Datalogger will send data in only one direction to the FEP Unidirectional mode network is not

preferred

(b) Bi-Directional Mode

Each end of Network is connected to FEP and each datalogger can now transmit data in both the directions

Bi-directional Mode is advantageous it enables the Data Transmission even in case of Network Failure

(c) T - Network Mode

If more no of stations are in network ie if the network is too lengthy then T- network mode is preferred

COMMUNICATION The communication protocol for transmitting data and command between datalogger and CMU is

standardized by the RDSO and is given in the Specifications of Dataloggers

(a) The type of communication used in the network is dependent on the distance between the dataloggers

(b) For shorter distances Opto Converter Box- Opto isolated current loop communication is used

(c) For longer distances Modem (Dial-up leased) Fiber Optic Satellite Microwave communication

MODEMS Modems are used for DATA transfer between Dataloggers and Front End ProcessorThese are

configured to RS 232 Serial Communication Network is connected with two types of 4-wire modems

(a) Internal modem card Dual Modem card (in-built)

It is fixed in datalogger Euro rack itself One card contains two modems The top modem is called

ANS (answer) modem and the bottom modem is called as ORG (originate) modem

Note In case of networking of Dataloggers connect lsquoANSrsquo modem to the lsquoORGrsquo modem of one adjacent

station and connect lsquoORGrsquo modem to the lsquoANSrsquo modem of other adjacent station

(b) External modems

20 | P a g e

These are generally used at FEP (Front End Processor) side to connect the Dataloggers

(i) To transfer Data from one datalogger to another datalogger FEP Baud rate is 9600bps

(ii) These modems are 4-wire line communication

(iii) To transfer the data from FEP to RMU (PC) the Baud rate is 57600 bps

There is no difference between these modems functionally

CENTRAL MONITORING UNIT (CMU) COMPUTER

Central monitoring unit (Fault Analysis Unit) is a Personal Computer and its minimum configuration

shall be specified by RDSO from time to time System Software Windows XPVista(OS) Norton Kaspersky

(Anti Virus) Interbase where Server is not available (DBMS) Oracle where Server is available (DBMS)

software are required to run Datalogger System It is provided with Graphical User interface (GUI) based

software and retrieve data from all Networked dataloggers (up to 32) at various stations It stores data in

standard data base files The CMU is capable of analyzing the data and generate reports audiovisual alarms

on defined conditions This data can be compressed to take backup In central monitoring unit Software used

for analysis of data prediction of faults etc is written in a structured format so that purchaser can

reconfigure it if required It displays the status of signaling gears at any selected time in graphic form for any

selected station yard It retrieves the stored data amp simulates train movement It sends commands to various

Dataloggers to activate audio visual alarm or operate and electromagnetic relay

CMU shares data available in it by other PCs through available local area network where this data can

be used for train charting passenger information purpose The system generates audiovisual alarm in

ASMrsquosSignal Maintainerrsquos room in the case of power supply failure (battery voltage low) or battery charger

defective with acknowledgement facility

(a) Each datalogger has its own identity code which will be transmitted along with data packet to central

monitoring unit

(b) Events recorded at each station are continuously transmitted to central monitoring unit Response time of

data transfer will not exceed 10 sec

21 | P a g e

22 | P a g e

OPTICAL FIBER CABLE

INTRODUCTION The demand for bandwidth on transmission networks is increasing rapidly because video and

graphical rich contents are exchanged through the corporate network or the Internet The Gigabit Ethernet

became ommonly used in the corporate network backbone and 10Gbit Ethernet will be adopted in the near

future Meanwhile in the home the demand for high-speed network becomes popular as the wide spread of

broadband access eg CATV xDSL and FTTH The transmission medium with capability to transmit high

bit rate signal is necessary to satisfy these requirements

The telecommunication transport technologies move from copper based networks to optical fiber

from timeslot based transport to wave length based transport from traditional circuit switching to terabit

router and all optical based networks entering into a new era of optical networking

BASIC PHYSICS OF OFC

OPTICAL FIBER CABLE OFC have Fibers which are long thin strands made with pure glass about the diameter of a human

hair OFC consists of Core Cladding Buffers and Jacket as shown in figure

MONOCHROMATIC LIGHT OR SINGLE COLOR LIGHT Light or visible light is electromagnetic radiation of a wavelength that is visible to the human eye (

about 400 ndash 700 nm) The word light is sometimes used to refer to the entire electromagnetic spectrum Light

is composed of elementary particles called photons Three primary properties of light are

Light can exhibit properties of both waves and particles This property is referred to as wave-particle

duality The study of light known as optics In free space light (of all wavelengths) travels in a straight path

at a constant maximum speed However the speed of light changes when it travels in a medium and this

change is not the same for all media or for all wavelengths By free space it is meant space that is free from

matter (vacuum) andor free from electromagnetic fields

Thus the speed of light in free space is defined by Einsteinrsquos equation E = mc2

Frequency ν speed of light in free space c and wavelength λ are interrelated by ν = cλ

From the energy relationships E = mc2 = hν and the last one an interesting relationship is obtained

the equivalent mass of a photon m = hνc2

When light is in the vicinity of a strong electromagnetic field it interacts with it From this interaction

and other influences its trajectory changes direction as shown in figure

23 | P a g e

INCIDENT RAY REFLECTED RAY AND REFRACTED RAY An incident ray is a ray of light that strikes a surface The angle between this ray and the

perpendicular or normal to the surface is the angle of incidence Reflection is the change in direction of a

wave front at an interface between two different media so that the wave front returns into the medium from

which it originated Common examples include the reflection of light sound and water waves

The reflected ray corresponding to a given incident ray is the ray that represents the light reflected by

the surface The angle between the surface normal and the reflected ray is known as the angle of reflection

The Law of Reflection says that for a specular (non-scattering) surface the angle of reflection always equals

the angle of incidence The refracted ray or transmitted ray corresponding to a given incident ray represents

the light that is transmitted through the surface The angle between this ray and the normal is known as the

angle of refraction and it is given by Snells Law

The figure shows Incident ray Reflected ray Refracted ray the angle of incidence and angle of refraction

REFRACTIVE INDEX - Refractive index is the speed of light in a vacuum ( c =299792458kmsecond) divided by the speed

of light in a material ( v ) Refractive index measures how much a material refracts light Refractive index of

a material abbreviated as lsquo n lsquo is defined as lsquo n=cv lsquo Light travels slower in physical media than it does

when transmitted through the air Refractive index (n) is a function of molecular structure of matter optical

frequency optical intensity determines optical propagation properties of each wavelength ( λ ) may not be

distributed equally in all directions is affected by external temperature pressure and fields

Refractive index of a medium is a measure for how much the speed of light is reduced inside the

medium For example typical glass has a refractive index of 15 which means that light travels at 1 15 =

067 times the speed in air or vacuum Two common properties of glass and other transparent materials are

directly related to their refractive index

First light rays change direction when they cross the interface from air to the material and effect that

is used in lenses and glasses

Second light reflects partially from surfaces that have a refractive index different from that of their

surroundings

SNELLrsquoS LAW-

24 | P a g e

When light passes from one transparent material to another it bends according to Snells law which

is defined as n1sin(θ1) = n2sin(θ2)

where n1 is the refractive index of the medium the light is leaving θ1 is the incident angle between the light

beam and the normal (normal is 90deg to the interface between two materials)

n2 is the refractive index of the material the light is entering

θ2 is the refractive angle between the light ray and the normal

Snellrsquos law gives the relationship between angle of incidence and angle of refraction

For the case of θ1 = 0deg (ie a ray perpendicular to the interface) the solution is θ2 = 0deg regardless of

the values of n1 and n2 That means a ray entering a medium perpendicular to the surface is never bent The

above is also valid for light going from a dense (higher n) to a less dense (lower n) material the symmetry of

Snells law shows that the same ray paths are applicable in opposite direction

TOTAL INTERNAL REFLECTION- When a light ray crosses an interface into a medium with a higher refractive index it bends towards

the normal Conversely light traveling cross an interface from a higher refractive index medium to a lower

refractive index medium will bend away from the normal

This has an interesting implication at some angle known as the critical angle θc light traveling from

a higher refractive index medium to a lower refractive index medium will be refracted at 90deg in other words

refracted alon g the interface If the light hits the interface at any angle larger than this critical angle it will

not pass through to the second medium at all Instead all of it will be reflected back into the first medium a

process known as total internal reflection

The critical angle can be calculated from Snells law putting in an angle of 90deg for the angle of the refracted

ray θ2 This gives θ1

Since θ2 = 90deg

So sin(θ2) = 1

25 | P a g e

Then θc = θ1 = arcsin(n2n1)

For example with light trying to emerge from glass with n1=15 into air (n2 =1) the ritical angle θc is

arcsin(115) or 418deg For any angle of incidence larger than the critical angle Snells law will not be able to

be solved for the angle of refraction because it will show that the refracted angle has a sine larger than 1

which is not possible In that case all the light is totally reflected off the interface obeying the law of

reflection

OPTICAL FIBER MODE An optical fiber guides light waves in distinct patterns called modes Mode describes the distribution

of light energy across the fiber The precise patterns depend on the wavelength of light transmitted and on the

variation in refractive index that shapes the core In essence the variations in refractive index create

boundary

conditions that shape how light waves travel through the fiber like the walls of a tunnel affect how sounds

echo inside

We can take a look at large-core step-index fibers Light rays enter the fiber at a range of angles and

rays at different angles can all stably travel down the length of the fiber as long as they hit the core-cladding

interface at an angle larger than critical angle These rays are different modes Fibers that carry more than

one mode at a specific light wavelength are called multimode fibers Some fibers have very small diameter

core that they can carry only one mode which travels as a straight line at the center of the core These fibers

are single mode fibers This is illustrated in the following picture

OPTICAL FIBER INDEX PROFILE Index profile is the refractive index distribution across the core and the cladding of a fiber Some

optical fiber has a step index profile in which the core has one uniformly distributed index and the cladding

has a lower uniformly distributed index Other optical fiber has a graded index profile in which refractive

index varies gradually as a function of radial distance from the fiber center Graded-index profiles include

power-law index profiles and parabolic index profiles The following figure shows some common types of

index profiles for single mode and multimode fiber

26 | P a g e

OPTICAL FIBERrsquoS NUMERICAL APERTURE ( NA )- Multimode optical fiber will only propagate light that enters the fiber within a certain cone known as

the acceptance cone of the fiber The half-angle of this cone is called the acceptance angle (see figure 18)

θmax For step-index multimode fiber the acceptance angle is determined only by the indices of refraction

Where

n is the refractive index of the medium light is traveling before entering the fiber

nf is the refractive index of the fiber core

nc is the refractive index of the cladding

NUMBER OF MODES IN A FIBER - Modes are sometimes characterized by numbers Single mode fibers carry only the lowest-order

mode assigned the number 0 Multimode fibers also carry higher-order modes The number of modes that

can propagate in a fiber depends on the fiberrsquos numerical aperture (or acceptance angle) as well as on its

core diameter and the wavelength of the light For a step-index multimode fiber the number of such modes

Nm

Where

D is the core diameter

λ is the operating wavelength

NA is the numerical aperture (or acceptance angle)

MODE FIELD DIAMETER - All light do not travels through the core of the fiber but is distributed through both the core and the

cladding The mode field is the distribution of light through the core and cladding of a particular fiber

Mode-Field Diameter (MFD) defines the size of the power distribution When coupling light into or out of a

fiber MFD is important in understanding light loss

27 | P a g e

ADVANTAGE OF OFC COMMUNICATION - bull More information carrying capacity Fibers can handle much higher data rates than copper More

information can be sent in a second

bull Free from Electromagnetic and Electrostatic interference Being insulator no electric current flows through

the fibre and due to this reason fibres neither radiate nor pick up electro - magnetic radiation So WPC

CLEARANCE is not required

bull Low attenuation 025 dbkm at 1550 nm Loss in twisted pair and coaxial cable increases with frequency

where as loss in the optical fibre cable remains flat over a wide range of frequencies

bull Use of WDM ndash Switching routing at Optical signal level

bull Self healing rings under NMS control

bull Small size makes fibre cable lighter in weight So easy to handleOptic fibre cable weight (approx)

500 kg km Copper cable weight (approx) 1000 kgkm

The reasons are photons of light in a fibre

do not affect each other as they have no electrical charge and they are not affected by stray photons outside

the fibre But in case of copper electrons move through the cable and these are affected by each other

Optical fibre does not carry any electricity even if the cable is damaged or short circuited it does

not cause any spark or fire hazard

As the fibre do not radiate energy it can not be detected by any nearby antenna or any

other detector The fibres are difficult to tap and therefore excellent for security

As the signal transmission is by digital modulation there is no chance of cross talk in

between channels

Only by adding a few additional terminal and repeater equipments the

capacity of the system can be increased at any time once the cable is laid

ical effects and temperature variations

LIMITATIONS OF OFC -

difficult

- utilised

APPLICATION IN SIGNAL AND TELECOMMUNICATIONS transmission circuits

-haul circuits for linking of telephone exchanges

28 | P a g e

PROPAGATION MODES CONCEPT -

MODE - Mode is an available distribution of electromagnetic field in a plane transverse to the direction of

light propagation Each mode is characterized by frequency polarization electric field strength and

magnetic field strength Available patterns are derived from Maxwellrsquos equations and boundary conditions

LINEARLY POLARIZED (LP) MODE A mode for which the field components in the direction of propagation are small compared to

components perpendicular to that direction An optical fibre supports only different field patterns called as

lsquoLinear Polarizedrsquo or lsquo LPrsquo modes The reasons are

requirements

de

the accrual of power carried by different modes

There are two basic types of fiber Multimode fiber and Single-mode fiber

Multimode fiber is best designed for short transmission distances This is suited for used in LAN systems and

video surveillance Single mode fibre is best designed for longer transmission distances This is suitable for

long distance telephony and multi channel television broadcast systems

29 | P a g e

MULTI MODE FIBER Multimode fiber the first to be manufactured and commercialized simply refers to the fact that

numerous modes or light rays are carried simultaneously through the waveguide Modes result from the fact

that light will only propagate in the fiber core at discrete angles within the cone of acceptance MM fiber type

has a much larger core diameter compared to single-mode fiber allowing for the larger number of modes

and

is easier to couple than single-mode optical fiber Multimode fiber further categorized as Multimode step-

index and Multimode graded index fiber

PROPAGATION THROUGH MMSI FIBER Figure shows the principle of total internal reflection applies to multimode step index fiber Because

the corersquos index of refraction is higher than the claddingrsquos index of refraction the light that enters at less than

the critical angle is guided along the fiber

Three different light waves travel down the fiber One mode travels straight down the center of the

core A second mode travels at a steep angle and bounces back and forth by total internal reflection The third

mode exceeds the critical angle and refracts into the cladding Naturally it can be seen that the second mode

travels a longer distance than the first mode causing the two modes to arrive at separate times

PROBLEMS WITH MMSI FIBER AND SOLUTION This disparity between arrival times of the different light rays is known as dispersion and the result is

a muddied signal at the receiving end It is important to note that high dispersion is an unavoidable

characteristic of multimode step-index fiber The solutions are either use Graded index fiber or Single mode

fiber

PROPAGATION THROUGH MMGI FIBER Multimode Graded-index refers to the fact that the refractive index of the core gradually decreases

farther from the center of the core The increased refraction in the center of the core slows the speed of some

light rays allowing all the light rays to reach the receiving end at approximately the same time reducing

dispersion Figure shows the Light propagation principle through multimode graded-index fiber The corersquos

central refractive index ( nA ) is greater than that of the outer corersquos refractive index ( nB )

It is very clear from the figure the light rays no longer follow straight lines they follow a serpentine path

being gradually bent back toward the center by the continuously declining refractive index This reduces the

arrival time disparity because all modes arrive at about the same time The modes traveling in a straight line

30 | P a g e

are in a higher refractive index so they travel slower than the serpentine modes These travel farther but

move faster in the lower refractive index of the outer core region

PROPAGATION THROUGH SMSI FIBER Single mode fiber has a much smaller core that allows only one mode of light at a time to propagate

through the core The figure shows the single mode fiber

Single-mode fiber exhibits no dispersion caused by multiple modes Single-mode fiber also offers lower fiber

attenuation than multimode fiber Thus more information can be transmitted per unit of time because it can

retain the fidelity of each light pulse over longer distances Like multimode fiber early single-mode fiber was

generally characterized as step-index fiber meaning the refractive index of the fiber core is a step above that

of the cladding rather than graduated as it is in graded-index fiber Modern single-mode fibers have evolved

into more complex designs such as matched clad depressed clad and other exotic structures

SINGLE-MODE FIBER DISADVANTAGES The smaller core diameter makes coupling light into the core more difficult The tolerances for single-

mode connectors and splices are also much more demanding

CUTOFF WAVE LENGTH - Cutoff wavelength is the wavelength above which a single-mode fiber supports and propagates only

one mode of light In other words an optical fiber that is single-mode at a particular wavelength may have

two or more modes at wavelengths lower than the cutoff wavelength The effective cutoff wavelength of a

fiber is dependent on the length of fiber and its deployment The longer the fiber the lower is the effective

cutoff

wavelength The smaller the bend radius of a loop of the fiber the lower is the effective cutoff wavelength If

a fiber is bent in a loop the effective cutoff wavelength is lowered

SIGNAL ATTENUATION IN FIBER - Optical fiber has a number of advantages over copper However it also suffers from degradation

problems which can not be ignored The first of these is loss or attenuation Attenuation is typically the result

of two sub properties They are scattering and absorption Both of which have cumulative effects The second

is

dispersion which is the spreading of the transmitted signal and is analogous to noise

SCATTERING Scattering occurs because of impurities or irregularities in the physical construction of the fiber The

well known form of scattering is Rayleigh Scattering It is caused by metal ions in the silica matrix and

results in light rays being scattered in various directions

31 | P a g e

Scattering limits the use of wavelengths below 800nm The short wavelengths are much affected than longer

wavelengths It is because of Rayleigh scattering that the sky appears to be blue ( shorter wave length ) The

shorter wavelengths ( blue ) of light are scattered more than the longer wavelengths of light

ABSORPTION Absorption results from three factors They are hydroxyl ions ( OH- water ) in the silica impurities

in the silica and incomplete residue from the manufacturing process These impurities tend to absorb the

energy of the transmitted signal and convert it to heat resulting in an overall weakening of the signal The

Hydroxyl absorption occurs at 125 and 139 micro The silica itself starts to absorb energy at 17 micro

because of the natural resonance of the silicon dioxide

MACRO BENDING LOSS Macro-bending loss is caused by bending of the entire fiber axis The bending radius shall not be

sharper than 30d where d is diameter of cable A single bend sharper than 30d can cause loss of 05dB

The fiber may break if bending is ever sharper

MICRO BENDING LOSS Micro-bending loss is caused by micro deformations of fiber axis which leads to failures in achieving

total internal reflection conditions Micro-bends are small scale perturbations along the fiber axis the

amplitude of which are on the order of microns These distortions can cause light to leak out of a fiber

Micro-bending may be induced at very cold temperatures because the glass has a different coefficient of

thermal expansion from the coating and cabling materials At low temperatures the coating and cable

become more rigid and may contract more than the glass Consequently enough load may be exerted on the

glass to cause micro bends

Coating material is selected by manufacturers to minimize loss due to micro-bending The linear thermal

expansion coefficient of coating material shall be compatible with that of fiber

32 | P a g e

DISPERSION Dispersion is the optical term for the spreading of the transmits in the fiber It is the bandwidth

limiting phenomenon and comes in two forms Multimode dispersion and chromatic dispersion Chromatic

dispersion is further subdivided into material dispersion and waveguide dispersion

DISPERSION PHENOMENON IN OPTICAL FIBER Dispersion is the time distortion of an optical signal that results from the differences of time of travel

for different components of that signal typically resulting in pulse broadening As the distance traveled by

the signal is more broadening of pulse is more In digital transmission dispersion limits on the maximum

data rate and the maximum distance ie the information-carrying capacity of a fiber link The interference

from broadened pulse in the next interval shall not lead to erroneous interpretation of received signal

OPTICAL DOMAIN Understanding where attenuation and dispersion problems occur helps optical design engineers

determine the better wavelengths at which information can be transmit taking into account distance type of

fiber and the other factors which can severely affect the integrity of the transmitted signal The graph shown

depicts the optical transmission domain as well as the areas where problems arise The wavelength (nm)

is shown on X-axis and attenuation ( dBkm) is shown on Y-axis

There are four transmission windows appear in the figure The first one is at around 850 nm the

second at 1310nm third at 1550 nm and fourth at 1625 nm The last two labeled as C and L band

respectively The 850 nm wavelength at which the original LED technology operated The second window at

1310 nm has low dispersion The 1550 nm called as C-band is ideal wavelength for long haul

communication systems The network engineers can avoid transmitting signal at 1000 nm where Rayleigh

scattering 1240 and 1390 nm where hydroxyl absorption by water occurs to avoid high degree of loss

Optical fibers also can be manufactured to have low dispersion wavelength in the 1550nm region

which is also the point where silica-based fibers have inherently minimal attenuation These fibers are

referred to as dispersion-shifted fibers and are used in long-distance applications with high bit rates For

33 | P a g e

applications utilizing multiple wavelengths it is undesirable to have the zero dispersion point within the

operating

wavelength range

34 | P a g e

SIGNALLING RELAYS

INTRODUCTION A relay is an electromagnetic device which is used to convey information from one circuit to another

circuit through a set of contact ie front or back contact Constructional and electrically relays may be

divided into DC and AC relays because the means by which the electrical energy in the coil is converted in

to mechanical Energy in order to move the contacts are fundamentally different In DC type the contacts are

carried on an armature forming part of a magnetic circuit in which a field is set up by the current flowing in

the coils In AC types the contacts are attached by a link mechanism to a metal sector disc or cylinder in

which currents are induced by the alternating magnetic field produced by the currents in the coils

Every endeavor has been made to explain the action of each type of relay in the simplest possible manner

Relays are sophisticated switch gears used for remote control and succession control of various

electrical equipment In present days they are widely used because they are capable of protecting the

controlled equipment from cross feeding and overloading even as they cater for speedy operations

Most of the relays in present day signaling are electromagnetic devices although some of the relays control

circuits through electronic components like diodetransistors Integrated Chips etc

Railway signaling relays are unique in that

(a) They operate on low voltage and current

(b) They are more articulate as according to their special features they can work under restrictive conditions

and in any specified manner Virtually they can cater for all situations while contributing to speed and

accuracy in operations

CLASSIFICATION OF SIGNALLING RELAYS (a) According to the method of their mounting or fixture they are classified as

(i) Shelf type Relays which are loosely kept on shelves

(ii) Plug in type Relays which are plugged into a pre- wired plug boards

(b) According to their connection and usage they are classified as

(i) Track relays Relay which is directly connected to the track to detect the presence of vehicle

(ii) Line Relays Other than track relay all are line relays Relays connected to the selection circuit

(c) According to their vitality or importance in ensuring train working safety they are classified as

(i) Vital Relays All relays used for traffic control such as signal point controls track detection etc

(ii) Non-vital Relays Relays which operate control aids and accessories like warnings buzzers

Indications etc

(d) According to their special provisions to ensure reliability of their contacts they are classified as

(i) Proved type are those whose normalization after each operation shall be proved in circuit

controlled by their contacts Contacts in which both the springs have metal surfaces on their tips They may

get fused due to high sparking current across them during operation These may prevent relay normalization

and causes unsafe condition in traffic control To avoid this proving of relay normalization after each

operation is necessary

(ii) Non - proved type Need not to be proved to have been normalized after each operation as their

contacts have at least one non-fusible contact (carbon contact)

(e) According to their feed source relays are broadly classified as

(i) DC relays The relay which requires DC power supply for its operations are called DC relays Among

the DC relays

o DC neutral relays This relay closes the same set of contacts on energization with Normal polarity

or Reverse polarity supply

o Polar Relays This relay closes different set of contacts when energized with Reverse polarity

supply They may or may not have contact to close when deenergized

35 | P a g e

(ii) AC Relay AC Induction motor track relays Time element relays flashing indication control etc

(iii) Electronic Relays DC relays with electronic components in them are called electronic relays

DC NEUTRAL RELAY Each Relay has usually one or two coils with a hollow center to accommodate a coreThe coils are

made up of a large numbers of turns of small gauge soft drawn copper wire The two coils can be connected

in series or parallel according to the requirement of relay resistance The ends of the coils are terminated on

binding post to which the control wires are connected Each coil is placed around a core of specially selected

Iron or steel having high permeability and low retentivity The core should be susceptible to magnetism and

at the same time should have little residual magnetism The cores are connected at the top by a yoke to

complete the magnetism coupling between two ends of coils The bottom of each core is equipped with a

large steel or Iron block known as pole piece or face

A flat piece of Iron or steel called armature is supported by brackets which are securely fastened to

the pole piece The armature yoke and the pole pieces are also made of specially selected iron or steel of the

same quality as the core The armature carries the metallic spring contacts which are insulated from it

The circuit through the coils of the relay is closed It sets up a magnetic flux through the core yoke and the

armature The flux passing between the armature and pole faces causes the armatures get attracted to the pole

faces and armature picks up and closes front contacts When the circuit is opened the magnetic flux collapses

and the armature drops away by gravity from the pole faces the front contacts break and back contacts close

The front and back contacts of the relay can be utilised to make or break other circuits Two stop pins of

nonmagnetic material are fixed either on the armature or pole faces so that the armature cannot

come in contact with the pole faces It is essential to maintain a small air-gap between the armature and pole

faces so that low value of residual magnetism may not retain the armature in picked up position and causes

the relay to fail to drop away with a break in its control circuit

GENERAL USAGE

DC Neutral line relays are most commonly used for Railway Signalling controls and detection

Among them plug-in type relays are preferred in larger installations for space considerations Shelf type

relays are also in use mostly in wayside stations

There are many DC Neutral line relays in use with special features such as

(i) Delayed operation

(ii) Biased DC control

(iii) DC control unaffected by AC interference currents

(iv) Getting latched in operated condition till further feeding and others

Usage of DC polar relays is mostly in conjunction with block instruments that control traffic between

stations AC line relays are almost extinct in installations of British Signalling practice They are however

used for time control operations flashing indication control and such other special purposes in installations

with Siemens signalling practice widely Track relays are used according to the type of track detection

circuits chosen for a given location and context While most of the track circuits are still of the DC working

type requiring DC neutral track relays with them the prospects of their being replaced with Electronic track

circuits directly feeding DC line relays in future are great AC Track Circuits are used in DC Traction area

as conventional DC Track Circuits are not suitable there AC Track relays are used with them almost all of

the induction motor type In the British practice of signalling which was first introduced on Indian Railways

non-proved type relays with carbon to metal switching contacts are generally used for vital controls

They facilitate simple circuit designs But with the advent of German Practice introduced by Ms

Siemens later proved type relays with all metal to metal contacts are widely accepted in spite of

complications in circuit design caused by them A recent introduction is that of the same type relays made by

Ms Integra control However for some time now the appreciable features of both the practices are getting

36 | P a g e

incorporated together in the indigenous designs of signalling by railwaymen With this the usage of all types

of relays anywhere can be found without straight jacketed segration of relay types

CHARACTERSTIC OF ELECTRO-MAGNETIC RELAY The following are the characteristic of electro-magnetic relays A brief study of them helps in

understanding the choice of their components and designs features

1) Force of attraction

2) Effect of air gap

3) Effect of Hysterisis

4) Transient condition

FORCE OF ATTRACTION In any electro-magnetic system the force of attraction is given by

Where B - is the flux density a - is the cross sectional area of the particular part of the magnetic

circuit

In the case of a DC neutral Relay B is proportional to the current that is flowing in the coil

surrounding the electro-magnet and thus the force of the attraction is directly proportional to the square of the

current This square relationship has its own advantage especially in the case of DC track relay in that a

small reduction in the current will have a great effect on the working of the relay Also for a given change of

current the make and the break will be quicker with lesser possibility of arcing

EFFECT OF AIR GAP

Curve lsquoArsquo is magnetisation curve for the iron and is all practical purpose a straight line up to the

saturation point Curve lsquoBrsquo is the magnetisation curve for the open-air gap which is a straight line through

out because per magnetisation curve of the whole

magnetic circuit of the relay and for a given force is the sum of the amp-turns for the iron part and the amp-

turns for the air gap

When the front contacts are open the force required to pick up the armature is shown on curve lsquoCrsquo to be F1

but after the armature has operated it will be separated from the core by stop pins In this position the amp-

turns required to maintain the armature is less as indicated by the dotted line from 1 on curve C to 2 on curve

37 | P a g e

F But actually the current in the coil is unaltered the force on the armature is greater than required as

indicated at 3 on curve F Part of this extra force is used to flex the front contacts sufficiently to give good

contact pressure when it is in energised position

The difference between the pick-up and the drop-away current should be as small as practicable in

track relay to ensure good shunting characteristics This is achieved firstly by the choice of good quality relay

iron and secondly by having a small air gap between armature and core If the air gap is not available then

the residual magnetism fluxes might cause the armature to be retained when the supply is disconnected For

this reason residual pins are provided to ensure a definite minimum air gap in the energised position

EFFECT OF HYSTERISIS

Hysterisis is the property by which the flux produced lags behind the current In the de-energized

condition there will be small residual flux in the core When the voltage is applied to the coils the current in

rising to its steady value first causes the flux to rise from 1 to 2 along the curve At this point the flux density

will be sufficient to attract the armature and reduce the air gap the flux then raise to 3 and continue to 4

which corresponds to the steady current in the coils When the voltage is disconnected the current in falling

caused the flux to fall from 4 to 5 along the curve At this point the flux density will fall below the value

required to maintain the armature which will release thus increasing the air gap and reducing the flux to 6

Finally the

flux will decrease from 6 to 1 where the current will again be zero

The relay core is made of material having high permeability and low retentivity As mentioned in

the IRS specification Electromagnet iron may be in the form of a

(a) Bar of silicon steel

(b) Best Yorkshire wrought iron

(c) Swedish charcoal iron

(d) Electrical steel sheets

` This reduces the difference between pick up value and Drop away value By selecting good quality

core material Percentage release and sensitivity of the relay will be improved

TRANSIENT CONDITION

38 | P a g e

When the voltage is applied or disconnected from the coils it takes some little time before the current

become steady These are known as transient conditionsrdquo and are important so far as track relays are

concerned When the voltage is first applied to the coils the magnetic flux in rising cuts the turns on the

coils and in so doing produces a back EMF that opposes the applied voltage and retards the growth of

current

The growth and decay of flux are decided by the relationship between the inductance and resistance

in the circuit is known as time constant It is not fixed quantity in the case of DC neutral relay This value of lsquo

Lrsquo is less when the relay is in de-energised condition (L1) than when the relay is in energised condition (L2)

The magnitude of flux that is established for a given change of current is different in two cases

When the current reaches the pick up value the armature closes and the inductance is increased to L2

due to reduced air gap the flux per amp is increased The increase in flux increased the back EMF during the

movement of the armature after which the current continuous to raise along a new curve corresponding to the

increased inductance until it reaches the final value (ER) This process is indicated above in fig24

When the supply is disconnected the current is obliviously reduced to zero immediately but the flux

decay comparatively slowly owing to the eddy currents produced in the core by the rapid flux change which

tend to maintain the flux The drop away time on a disconnection is however generally negligible See fig

below

If the relay releases due to the reduction in current from say I 2 to I 1 caused by the application of

shunt resistance (as in the case of track relay ) the time taken is much longer than the relay is simply

disconnected The rate of rise or fall of current during the transient conditions is also depends on exterior

circuit values because L and R apply to the whole circuit The production of eddy current in the core the flux

will decay at a slower rate than the current So that the actual release time will be a little longer than it takes

the current to fall to the release

L= Inductance

39 | P a g e

R= Resistance

It is now clear that to reduce releasing time to a minimum it is necessary that

- The relay iron should have low Hysterisis loss and low retentivity

- The degree of over energization of the relay should be restricted

- Connecting a suitable external resistance in series with the relay to keep LR ratio low

In non RE area for track circuit length less than 100M 9 ohm track relay only to be used Using relay

with minimum contacts as they require lesser current which keeps inductance value low

Train working safety is ensured only if the track relay of shortest length track circuit is released

before a light engine running at a highest permitted speed clears it Otherwise the track circuit occupation

may go undetected To avoid this a special provision has to be made in signal control circuits wherever

necessary

The following methods may be adopted for reducing the time lag of track relay

(a) Restrict the over energisation of relay since the release time depends on the initial working current

(b) Connecting a suitable external resistance in series with the relay to keep the LR ratio low

(c) Using relays with minimum contacts as they require lesser operating current keeping the inductance

value low

40 | P a g e

CONCLUSION

Modern signalling is vital for safe and punctual movements of trains In the Indian railways The Signalling

and Telecommunication Department is responsible for providing modern effective and relaible signalling

systems as well as telecommunication systems

The first mode of communication used in Indian Railways was the use of electric telegraph

with the help of Morose code Morose code is the method of providing text information as a series of on-off

tones and lights or clicks that can be directly understood by a skilled listener or observer without special

equipmentEach character (letter or numeral ) is represented by a unique sequence of dots and dashes Later

this system becomes obselete and beggan the era of wireless communication which operated at audio level

frequency range

In wireless communication the significant advances took place the transition to miniature

valves or filament tubesBut this was abandoned too because of excessive current consumption and over

heating of the filament tubes

Fibre-optic communication is a method of transmitting information from one place to another by

sending pulses of light through an optcial fibreThe light forms an electromagnetic carrier wave that is

modulated to carry information First developed in the 1970s fibre optic communication systems has

revolutionized the telecommunications industry and have palyed a major role in the advent of the information

age Because of its advantages over electrical transmissionsoptical fibres have largely replaced copper wire

communications in core networks in the developed world The Indian Railways too is undergoing a transition

from Microwave communication to fibre optic communications

41 | P a g e

BIBLIOGRAPHY AND REFERENCES

1 wwwwikipediacom

2 wwwbritaniccacom

3 wwwirfcacom

4 Motorola GP60 system manual

5 Harris FAS 7000 manual

6 TOSHIBA Manual

6 | P a g e

As 110 VDC bus bar to DC Distribution Panel as an input to various DC-DC converters located in

it

A 110 V Battery Bank of VRLA cells are connected to SMPS Panel IPS Status Monitoring Panel is

located at ASM room or at SampT staff room if round the clock SampT staff is available at Station

CONSTRUCTION IPS mainly consists of

SMR (Switch Mode Rectifier) Panel SMPS based Float cum Boost Charger (FRBC) Panel

AC Distribution Panel

DC Distribution Panel

Battery Bank (110V DC)

Status Monitoring Panel

SMR (SWITCH MODE RECTIFIER) PANEL SMPS BASED FLOAT

CUM BOOST CHARGER (FRBC) PANEL It consists of SMR FRBC modules and Supervisory amp Control Unit SMPS based SMRs

(converters) SMPS based Float cum Boost Chargers (FRBC) modules are provided with (n+1) modular

technology hot standby arrangement with active load sharing basis and 1 additional module as a cold standby

(n+2) Supervisory amp Control Unit which controls and monitor the complete system It has various

indications on the panel reflecting the working of the panel

FRBCs are suitable for operating in parallel on active load sharing basis with one or more modules of similar

type make and rating

n = required no of modules to cater for actual current requirement

AC DISTRIBUTION PANEL It is made of ON-Line inverters with (1+1) modular technology hot standby arrangement amp CVT

(Constant Voltage Transformer) AVR (Automatic Voltage Regulator) and set of step down

transformersThe inverter is protected against overload and short circuit with auto reset facility Whenever

the failure occurs it trips and restart automatically after about 10 to 20 sec But if the problem persists the

protection is permanently gets latched and it will not be switched ON again unless the fault is cleared

followed by pressing of reset button The output of inverters is regulated to 230V AC plusmn 2 50Hz plusmn1Hz for

an input voltage variation of 90V DC to 140V DC Normally both the Inverters are powered ON and both are

delivering the Output voltage but only one (main) inverter is connected to the Load If main inverter is failed

then only the stand-by inverter will come on Load automatically with in 500msec At 70 Depth of

Discharge (DOD) of the battery bank 110VDC supply to the inverters will be cut-off So the Signals feed will

be cut-off The auto-change over arrangement is also provided for bringing the CVT in circuit with in

500msec when the both the inverters output is failed It has various indications on the panel reflecting the

working of the panel

DC DISTRIBUTION PANEL It takes care of DC Power supply requirements of our signalling It consists of sets of DC-DC

converters for individual DC power requirements with (n+1) modular technology hot standby arrangement

with active load sharing basis The DC-DC converters of Relay Internal are provided with (n+1) modular

technology hot standby arrangement with active load sharing basis and 1 additional module as a cold standby

(n+2) The DC-DC converter works satisfactorily with the input voltage variation of 98VDC to 138VDC At

90 Depth of Discharge (DOD) of the battery bank all the DC-DC converters 110VDC Input supply will be

cut-off except for Block Tele DC-DC converters The supply for Point operation is also catered through a

20A fuse by this unit It is also provided with various indications that reflect its working

7 | P a g e

STATUS MONITORING PANEL IPS status monitoring panel has been provided in the ASM room for giving the important alarms and

indications to ASM Status Panel tells present working status of IPS displaying battery voltage continuously

and five other indications which will light according to IPS status During normal working these indications

will not lit Whenever the battery has come on to the load and has discharged by 50 DOD (Depth of

Discharge) then first Red indication lit with description ldquoSTART GENERATORrdquo with audio Alarm ie DG

set is to be started and put on the load If DG set is not started with this warning then if battery gets further

discharged to 60 DOD and second Red indications appears with description ldquoEmergency Start generatorrdquo

with audio alarm even now if DG set is failed to be started the battery further gets discharged to 70

DOD and 3rd Red indications appear with description ldquo System shut downrdquo with audio alarm which will

continue till Generator is started resulting in AC output from IPS is automatically cut off results all the

signals will become blank

When there is any defect in any sub module of IPS even without affecting working of system the 4th

Red indication appears with description ldquoCall SampT Staffrdquo with audio alarm so the ASM advises SampT staff

accordingly Green LED 5th indication comes with the description ldquoStop Generatorrdquo with audio alarm when

the DG set is running and if the Battery bank is fully charged condition

EARTHING The IPS systems and its individual modules are having earth terminals and all these are properly

earthed with earth resistance of less than 1 ohm Earth provided shall preferably be maintenance free using

ground resistance improvement compound (The acceptable Earth Resistance at earth busbar shall not be

more than 1 ohm Code of practice for earthing and bonding system for signalling equipments)

LIGHTNING AND TRANSIENT PROTECTION IN IPS Manufacturer will provide Stage1 amp Stage 2 protection along with the IPS These are described

below

Stage 1 protection is of Class B type against Lightning Electro-Magnetic Impulse (LEMP) amp other

high surges provided at Power Distribution Panel It is provided with a 63 Amp fuse in phase line and is

connected between Line and the Neutral and also between the Neutral and Earth

Stage 2 protection (Power line protection at Equipment level) is of Class C type against low voltage

surges provided at the equipment input level This is thermal disconnecting type and equipped with

protection against SPD (surge protection device) failure due to open amp short circuit of SPDs and is connected

between the Line and the Neutral If supply data signalling lines (ACDC) are carried through overhead

wires or cables above ground to any nearby building or any location outside the equipment room additional

protection of Stage 2 type shall be provided at such locations Class B amp Class C arrestor is provided on a

separate wall mounting type enclosure in IPS room

Stage3 protection (Protection for signallingdata line) is of Class D type All external data signalling

lines (ACDC) shall be protected by using this Class D type device It consists of a combination of Varistors

and Gas Discharge Tube with voltage and current limiting facilities

FEATURES Chargers used in this system are of SMPS technology chargers with 90 efficiency These chargers

are supported with hot standby mode with (n+1) modular technology

Onetwo sets of Maintenance free Battery banks (110VDC) Normally one set (110VDC) of Battery

bank is used Conventional flooded type Lead Acid Batteries or Low Maintenance Lead Acid

batteries can also be used (SMRs settings are required to be adjusted depending on the type of

Batteries used) Various voltage levels of

8 | P a g e

battery banks are avoided Reduction in Battery maintenance amp less flour area required

DC-DC Converters working from 110V Central battery have been used for all dc supplies This has

improved overall efficiency of the system since number of conversion from AC to DC have been

reduced to 2 stage as compared to 3 stage conversion in case of transformer-rectifier system

DC-DC converters are available in modules Easy replacement of defective modules This ensures

less down time

DC-DC Converters are used in load sharing N+1 configuration (ie with hot standby with N+1

modular technology) to improve the reliability amp availability of the system

Capacity of inverter has been brought down to 15 KVA from 5 KVA and used for feeding only

Signals supply Hot standby inverter is provided with auto changeover facility This improves the

availability of the overall system

High efficiency inverter is used with PWM (Pulse Width Modulation) technology in place of Ferro-

resonant technology based inverter This improves the efficiency of the overall system

Continuous power to Signal Circuits even in absence of DG setLocal Power Supply

Generators need not be switched ON every time during train movement

Metal-to-metal relay installations and block working by axle counters have also been covered

Supply of spare modulesComponentsCells have been included as part of main supply

Provides highly regulated voltage to all signal relays amp lamps for better life

9 | P a g e

SINGLE SECTION DIGITAL AXLE COUNTER

INTRODUCTION- The axle counter equipment is working on high frequency and using amplitude modulation or phase

modulation for detection of presence of wheel The equipment described in this notes is Phase modulation type

for the detection of presence of wheel In the Phase modulation type track device the detection of presence of

wheel is with the phase reversal of 1800 out of phase which enables this system to be more healthy and safe

In Phase Reversal Modulation technique trolley suppression arrangements to prevent the counting of

wheels caused by push trolley passing over the track device are not required as the system will take care of

validation of generated pulses caused by passage of wheel over the track device depending up on the phase

shift of the pulse This phase shift of the pulse may be normally 160deg to 180deg for a train wheel and it may be

approximately 100deg to 120deg for a push trolley wheel

This is Digital Axle Counter equipment for single track sections containing 2 out of 2 micro-

controllers to count the axles establish the track occupancy of a track section and to provide this information

to the block or the interlocking equipment

In this system no separate evaluator is required and no analog data is being transmitted One set of

Axle counter equipment is provided at entry end and other set provided at exit end Both sets are being

connected through a twisted pair of telecom cable ie existing RE cable one PET quad is used for both UP

and DN Axle Counters Digital DATA is being transmitted between two ends of Axle counters (Outdoor

track side Detection points)This system is a fully duplex capable of operating according to CCITT V21 and

the Data will be transmitted at the rate of 300bitsec This data Transmitted ensure negligible interference of

the noise The system is highly reliable

FEATURES (a) The system consists of

(i) Single Section Digital Axle Counter (SSDAC) units

(ii) Tx Rx coils

(iii) Vital Relays

(b) TxRx coil axle detectors are mounted to the web of the rails The design of system consists of 21 KHz amp

23 KHz High frequency Phase Reversal type axle detectors

(c) Compatible with 90R 52Kg amp 60Kg rail profiles Easy to install commission amp maintain

(d) Track devices at both (entry amp exit) points of the section should be fixed on the same rail

(e) System is designed to detect the solid wheels with diameter gt 400mm with standard wheel flange

(f) The system works in pairs For monitoring single-track section one pair of SSDAC units are required and

to be installed near the trackside one at the beginning and another at the end of the track section ie

Trackside electronic counting equipment

(g) The basic design of the system is based on counting the number of axles passing at each detection point

These stored counts are transmitted to the second unit of the system and vice versa by means of modem

communication

(h) The communication consists of digital packets having details of Counts amp Health

10 | P a g e

(i) If counts registered at both detection points are equal the section is cleared otherwise the section is shown

as occupied The system ensures no error condition to arrive at the decision of clearance

(j) System is designed as per CENELEC SIL-4 (European standard) using micro controller along with other

electronic circuits and programmed using dedicated software When any of these circuits fail the system

goes to fail safe condition

(k) It is programmable for either Preparatory Reset or Conditional Hard Reset as per requirement

(l) Micro controller based design with 2 out of 2 decisions and counting through software

(m) V21 Modem communication (2-wire) on frac12 quad cables and also compatible to work on voice channel of

OFC amp Radio

(n) Opto isolated vital relay drive for Q-style 24V 1000 _ and Vital Relay output can be giving at both ends

of the system

APPLICATIONS The system can be widely used in Railways for Block Working (BPAC) Intermediate Block Signaling Auto

signalling and Track circuiting for i) Loop line ii) Main line iii) yard lines

SYSTEM DESCRIPTION

This system comprises of

Tx coils-2 nos

Rx coils-2 nos

Reset Box (RB 258A)

Card 1 Signal Conditioning Card ndash 1

Card 2 Signal Conditioning Card - 2

Card 3 Micro controller Logic Board ndash 1

Card 4 Micro controller Logic Board ndash 2

2 nos for independent resetting ndash when used in block sections

1 no for common resetting ndash when used for Track circuiting at stations

Card 5 Event Logger Card

Card 6 Modem Card

Card 7 Relay Driver Card

Card 8 DC-DC Converter Card

SSDAC (DACF 700AP) UNIT

(A) SIGNAL CONDITIONING CARD (CARD 1amp2) (SCC) -1 (SCC-1) generates 21 KHz carrier

signals

-2 (SCC-2) generates 23 KHz carrier signals which is transmitted to 2nd

set of Tx coils

s receive these signals

modulated

train pulses

11 | P a g e

(B) MICRO-CONTROLLER LOGIC BOARD CARD (CARD 3amp4) (MLB) The Micro-controller Logic Board (MLB) is the heart of the system

o 8051 Based Architecture

o 8 Bit Micro Controller

o ATMEL AT89S8252 Micro controller

o 2 out of 2 Decision

o Uses C subset language

- TOOLS

o KEIL μ Vision Development System

o Universal Programmer

o 2KB Program Memory

o 256 bytes RAM

o 8KB Flash memory

o 32 Programmable IO lines

o Wide Operating Voltage range of 4V-6V

o Full Duplex Serial Port

o Programmable Watch Dog Timer

o Fully Static operation up to 24MHz (Upgraded to 40MHz)

o Operating Temperature of ndash40degC - +85degC

o Use of State Machine for Axle Counting

o Use of ASCII MODBUS protocol

o Use of CRC16 technique for Error Checking during communication

o Wheel detection

o Train direction checking and

o Wheel counting functions

o It receives the remote wheel count and computes the status of the section for clear or occupied

o It also checks various supervisory signal levels like supervisory of TxRx coils presence of various

cards communication link failure etcThese cards communicate with each other for wheel count

At Entry-end if train enters into section (1st detection) the counts are incremented and when train

shunts back from the same detection ie if train exits from the section from the same detection the counts are

decremented At Exit-end if train enters into section (2nd detection) the counts are decremented and when

train shunts back from the same detection ie if train exits from the section from the same detection the

counts are incremented Both the track devices at Entry and Exit ends must be fixed on same side of the

track

This MLB card is having Extensive LED display

o A block of 8 LED indicators for count progress error display

o 2 independent LED indicators for section status

o The errors occurring in the system during the operation of the SSDAC are encoded and are indicated by

means of the 8-LED block present on the front panel of the MLB cards

(c) EVENT LOGGER CARD (CARD 5)

Event logger card is designed to capture and store important signals from the remote and local SSDAC units

The stored data can be downloaded from the event logger card for the purpose of analyzing the events

occurring during the operations of the SSDAC The data can be analyzed with the help of CEL data analyzer

software

12 | P a g e

The event logger card captures following signals

(i) Pulse signals

(ii) Supervisory signals

(iii) Card removal information

(iv) Serial packets from

Event Logger card has a Rabbit processor and 2 MB FLASH MEMORY to store packets The data is initially

stored in the buffer and subsequently transferred to FLASH memory every two minutes Normally 4096

pages of the data can be stored in flash memory on FIFO (first in first out) basis

Run This LED blinks continuously indicating the normal working of the event

Log This LED blinks whenever data is being logged into the flash memory (Approx after every 2 minutes)

Dnld This LED is ON when data is being downloaded from the flash memory of the card and becomes OFF

when download is complete

(D) MODEM CARD (CARD 6) (i) The modem card transmits and receives the digital packet information form one counting unit to the other

The packet will appear after every 18 sec and the packet carries the latest information such as

(ii) The modem card being used is V21 type (2-wire) in SSDAC

(iii) This card interfaces with serial RS232C port of both Micro-controller Logic Boards

(iv) It multiplexes the two RS232C inputs and selects one of the two channels and provides signal conversion

from digital to analog (FSK modulation) and vice-versa

(v) Data transmission rate is 300 bitssec

(vi) Automatic Gain Control circuit is incorporated hence no gain adjustments required

(vii) Mode selection on Modem card The modem has been set in lsquoORIGINATORrsquo mode for entry and in the

lsquoANSWERrsquo mode for exit in the factory

(viii) LED Indications provided on Modem card

-Transmitting the signal when LED is flashing

- Receiving the signal when LED is flashing

-Remains OFF in SSDAC

-Carrier is detected when LED is glowing

(E) RELAY DRIVER CARD (CARD 7) (i) The Relay Driver card (RD) provides the 24V DC output required for driving Vital Relay

(ii) One RD card is used in each SSDAC counting unit The RD card receives the command of clear and

clock signals from MLB1 amp MLB2 cards and drives the vital relay lsquoONrsquo when section is NOT OCCUPIED

through opto- isolator circuit

(iii) If a train occupies the section the vital relay is dropped The vital relay status is read back by the system

as per the driving output

(iv) It has

13 | P a g e

ndash LED flashes when the section is clear

ndash LED flashes when the section is clear

All the above LEDrsquos are lit for section clear condition

(F) DC-DC CONVERTER CARD (CARD 8)

INPUT VOLTAGE Nominal Voltage voltage 24V DC Maximum current drain= 12A

Required voltage 18V DC to 30V DC

Output voltage

Nominal Voltage +5 V DC 2 A Required voltage 4 7 5 t o 525V DC

Nominal Voltage +12V DC 200 mA Required voltage 1175 to 1225V DC

Nominal Voltage +24V DC 300 mA with common ground Required voltage 235 to 245V DC

Nominal Voltage +15V DC 100 mA with isolated ground Required voltage 145 to 155V DC

SURGE VOLTAGE AND LIGHTNING PROTECTION Transient surge voltages arise as a result of Lightning discharge switching operations in electrical

systems and electrostatic discharge These surge voltages often destroy the electronic equipment to a large

extent In order to prevent surge voltages from destroying the equipment all the input lines of SSDAC ie

Power Supply (24V) Reset (48V) amp Modem is to be routed through surge voltage protection devices for

effectively protecting the system These devices (3 numbers) are mounted in a box and supplied along with

the system One number of box is to be installed at each location and wired to the SSDAC

Each surge voltage protection device consists of two parts

(a) Base

(b) Plug Trab

The Base of the device is used for wiring the input and output signals The connection details from relay

room to the box and from box to SSDAC unit are provided on the box The Plug Trab consists of MOV and

GD Tube and diverts the excess energy during surge voltages or lightning into the ground connection The

operation of these devices relies on a high quality ground connection in order to safely shunt away the

unwanted energy The impedance of the ground connection is critical and it should be less than 2 Ohms

NOTE The 3 Plug Trab connections are not to be interchanged with one another The plug Trab is a

detachable device and can be replaced with SPARE unit in case of blown device which is indicated by

means of LED for 24 V

EFFECTIVENESS OF PLUG TRABS The effectiveness of plug Trab depends wholly on the Earth connection provided to the system The earth

provided to the system should be less than 1 ohms and connections should be firm and proper to the SSDAC

unit VR box etc

SURGE VOLTAGE AND PROTECTION DEVICE SV-120 The Surge Voltage protection device is to be installed at each location along with every SSDAC unit

14 | P a g e

EARTHING- The lead wires connecting the installation and the earth electrode shall ordinarily be of stranded

copper wire of 29 sq mm (19 strand wires of 14 mm diameter) Copper wire has been specified because GI

wires usually are having greater corrosion However in areas where copper wire may be frequently stolen

due to theft ACSR of size 64 sq mm (19 strands of 211 mm diameter) may be used

LIMITS OF EARTH RESISTANCE (a) Apparatus case connected to Earth (SSDAC and vital Relay Box is housed in Apparatus case and

Connected to earth at outdoor) shall be less than or equal to 1 ohm

(b) All cable connected to same earth shall be less than or equal to 1 ohm

(C) Reset box connected to earth near SM s Room shall be less than or equal to 1ohm

EQUIPMENT TO BE EARTHED A Common Earth should be provided for SSDAC for items 1(a) amp (b) of the above at the outdoor

(a) The Apparatus Case is to be connected to earth (the chassis of SSDAC amp Vital Relay Box should be

properly connected to apparatus case)

(b) Metallic sheath and armouring of all the underground main cables are to be earthed

(i) In RE area the metallic sheath and armouring of main telecom cables are earthed at both ends

(ii) In RE area the armouring of Jelly filled cable shall be earthed at both ends

(c) The Earthing shall be provided at every location box where cables are terminated

(d) Earth already available for other equipment may be used for earthing of Reset Box near SM s Room

Cabin etc

15 | P a g e

DATALOGGER

INTRODUCTION Datalogger is a Microprocessor based system which helps in analysing the failures of relay inter

locking system Electronic Interlocking system This is like a black box which stores all the information

regarding the changes take place in relays AC DC Voltages and DC currents along with date and time The

same information data can be transferred to the computer to analyse further ldquoon line ldquooff linerdquo analysis of

stored date A print out also can be obtained through a printer by connecting directly to the datalogger unit

The data belongs to Relay contacts is considered as digital inputs and the data belongs to voltage

levels currents is considered as Analog inputs Datalogger lsquos are mandatory for all new relay interlocking

(PIRRI) EI installations and it is also recommended to provide in all existing PIs RRIs To increase the

line capacity mechanical signalling equipments are upgraded to PI RRI or EI Due to complexity in the

circuits and wiring sometimes it is very difficult to rectify the failures So datalogger can monitor these

systems with real time clock Thus it can be named as black box of Samp T equipments and hence it is a vital

tool for accident investigation Datalogger is used at Stations yards Whereas in case of Auto Section amp IBH

Mini dataloggers called as Remote Terminal Unit (RTU) are used

ADVANTAGES OF DATALOGGERS (a) Dataloggers helps in monitoring the typical failures such as intermittent auto right failures

(b) It helps in analyzing the cause of the accidents

(c) It helps in detecting the human failures errors such as

(i) Drivers passing signal at Danger

(ii) Operational mistakes done by panel operators ASMrsquos of operating department

(iii) Signal and telecom engineering interferences in safety circuits

(iv) Engineering and electrical department interferences failures

(v) It helps as a ldquoTOOLrdquo in preventive maintenance of signaling gears

(d) Dataloggers can be connected in network Networked dataloggers helps to monitorthe PIRRIEI remotely

(e) Failure reports can be generated remotely with help of datalogger network

(f) On line and Off line track simulation is possible

(g) Speed of the train on point zones can be calculated

(h) Age of the equipment in terms of number of operations etc

COMMON EQUIPMENT FOR ALL DATALOGGERS ARE GIVEN

BELOW (a) CPU card

(b) Digital and Analog input cards

(c) Local terminal(PC)

(d) communication links

(e) Printer

All the dataloggers requires a potential free ( spare ) relay contact for monitoring digital inputs

through Digital input cards amp for monitoring Analog inputs such ACDC bus bar voltage levels through

Analog input cards Digital and Analog inputs are connected to the Processor card Processor card consists of

memory ICrsquos Memory ICrsquos are programmed as per requirement of the signal engineers

Provision of Dataloggers is mandatory with RRI systems and is optional for PI systems as per

amendment to the specification for Relay Interlocking systems ( IRSS-36 ) The data collected by the

datalogger can be used for failure analysis repetitive discrepancies and for accident investigations

16 | P a g e

Note

If the serial communications is more than 50m then line drivers shall be used up to 3 Kms

4wire leased line Modems shall be used if the serial communication is more than 3 Kms

STUDY OF EFFTRONICS DATALOGGER TECHNICAL DETAILS (a) 24V 12VDC Power Supply

(b) Total Storage Capacity of 10 Lakh events

(c) In-built Temperature sensors

(d) Internal Buzzer for alarming during failures

(e) Real Time clock with internal battery backup with data retention up to 10 years

(f) 512 LED matrix to indicate the status of 512 Digital inputs at a time page wise

(g) Seven segment LCD screen (2x24) to display the status of digitalanalog signalsTime Temperature etc

(h) Using the keyboard various functions can be viewed in the LCD panel

(i) Max Digital Inputs 4096

(j) Max Analog Inputs 96

(k) Digital Input Scanning Time 16 millisecond

(l) Analog Input Scanning Time is less than 1 Sec

HARDWARE (EQUIPMENT) Datalogger system consists of

(a) Datalogger (CPU - with Microprocessor 68000)

(b) Digital input cards

(c) Dual modem card

(d) Digital Scanner units (DSU)

(e) Analog Scanner units (ASU)

CPU CARD It is provided with Motorola microprocessor M 68000 It performs all the activities pertaining to the

datalogger It continuously scans (check) the Digital inputs(inbuilt) Digital Scanner Units and Analog

Scanner Units ie scanning of digital signals (Relay operations) for every 16-milli seconds and scanning of

analog signals (ie ACDC voltages amp DC currents) for less than 1 second

This card will support the IO interfaces of LCD (Liquid Crystal Display) - 2X24 alphanumeric Key

Board LED Matrix Display Real Time Clock LCD display and keyboard This will acts as man machine

interface between the datalogger and the signal engineer All the operations (Software) can be performed

using this LCD and keyboard

Real time display with 7 Segments This is built in real time clock within Datalogger and its current

time will be displayed on six 7-segment display provided (Real time clock depend upon DALLAS 1286

chip) This IC will come with internal battery backup hence there is no need to add external batteries

CPU card continuously scans (checks) the DSUs and ASUs Each input connected to digital scanner

units are optically isolated by Opto couplers When CPU card scans the digital inputs it compares with the

previous stored data and if there is any change from the previous status then only that data will be stored (the

status conditions of relay) with date and real time A total of minimum 10 Lac events can be stored in

memory on first in first out basis so that latest data is available in the system There is no loss of data from

datalogger memory in case of power supply failure of datalogger

DIGITAL INPUT CARDS (IN-BUILT) This system is having maximum 8nos of inbuilt Digital inputs cards Maximum 64nos of digital

inputs can be connected to each digital input card The potential free relay contact may be front or back

contact terminated at the Tag Block from the relay of signals tracks points Buttons etc and are

17 | P a g e

subsequently connected to Digital input cards through Flat Ribbon Cable (FRC) connectors These in-built

digital input cards can monitor a total 512 nos of relays status

DIGITAL SCANNER UNIT (DSU) Each DSU contains 8 nos of Digital Input cards Each input card can be connected with 64 inputs

Total input capacity of DSU unit is 512 inputs These scanner cards contain Optocouplers and Multiplexer

Inputs are connected to Stag card The stag card out put is connected to DSU through FRC connectors

Maximum 7 nos of DSUs can be connected to the system So Digital input capacity of the system is 4096

All these digital inputs are scanned at rate of 16 msec

ANALOG SCANNER UNIT (ASU) ASU contains maximum 3 nos of Analog input cards Each input card can be connected with 8nos of

Analog inputs Total input capacity of the ASU is 24 analog input channels Maximum 4nos of ASUs can be

connected to the system Analog input channel capacity of the system is 96 All these analog inputs are

scanned at a rate of less than 1 sec

PARALLEL PORT Parallel port is provided for connecting printer

RS-232 SERIAL PORTS At least 6 Serial communication ports are provided for communication with other dataloggers

Central Monitoring Unit Remote Terminal Unit Electronic Interlocking system Integrated Power Supply

system etc

EXTERNAL NON-VITAL RELAY CONTACTS These relays provided in the system where 16 number of the Relay contacts are provided on the rear

panel through Tele control port to extend alarms and to control the power equipment from remote or local

locations through computer in case of any occurrence of failures Each control can sink or source 100 m

amps of current

INTERNAL MODEM CARD DUAL MODEM CARD (IN-BUILT) It is fixed in datalogger Euro rack itself One card contains two modems The top modem is called

ANS (answer) modem and the bottom modem is called as ORG (originate) modem It is used in case of

networking of Dataloggers In network connect lsquoANSrsquo modem to the lsquoORGrsquo modem of one adjacent station

and connect lsquoORGrsquo modem to the lsquoANSrsquo modem of other adjacent station

POWER SUPPLY Normally 24V DC (12V DC is optional) supply with battery backup is required for the system

working

Input Voltage Range 18Vhellip32V DC (For 24V) 9Vhellip18V DC (For 12V)

INPUT REQUIREMENTS Relay inputs (digital inputs) and analog inputs (voltages currents etc) are required to be connected

to the system as per the requirements of RRI PI SSI as the case may be Some of the inputs to be

monitored is given below

(a) Digital inputs

(i) Field inputs All TPRs NWKRs RWKRs ECRs Crank Handle relays SidingSlot LC gate

control relays etc

(ii) Control Panel inputs All button Knob SMrsquos Key relays

18 | P a g e

(iii) Internal relays

British system All HR DR HHR WNR WRR ASR UCR RR LR UYRTLSR TRSR TSR

JSLR JR etc

SIEMENS system Z1UR Z1UR1 GZR ZDUCR ZU(R)R ZU(N)PRG(R)RG(N)R U(R)S

U(N)PS UDKR DUCR U(R)LR UYR1 UYR2 G(R)LRGR1GR2

GR3 GR4 OVZ2U(R)RW(RN)R (RN)WLR Z1NWR Z1RWRZ1WR1 WKR1 WKR2 WKR3 etc

(b) Analog channels

(i) 230 V AC (for power supplies in the power panel)

(ii) 110V AC (for Signal and Track transformers)

(iii) 110V DC (for Point operation)

(iv) 60V DC (Siemens relays)

(v) 24V DC (Q-series relays)

(vi) 24V DC (for Block Axle counters)

(vii) 12V DC (for indication)

(viii) 20A (for point operation current)

(ix) 10V AC 5KHz (for Axle counter channels) etc

SOFTWARE MODULES OF DATALOGGERS

(a) Network Management of Dataloggers (NMDL)

(b) Reports

(c) Fault Entry

(d) Track Offline Simulation

(e) Train Charting

NMDL SOFTWARE FEATURES (a) Online Relay Status

(b) Online Faults - To view information of various Online Faults as they occur in the stations where

the Dataloggers are connected

(c) Online Simulation - Graphical view of relay operations train movements etc

(d) Remote monitoring of stations with the help of NETWORKING

SOFTWARE OBJECTIVES (a) Predictive Maintenance

(b) Easy identification of failures

(c) Crew discipline

(d) Train charting

REMOTE MONITORING OF STATIONS WITH NETWORKING OF

DATALOGGERS The individual Dataloggers of various stations can be interconnected through networking technology

The data of Remote Panel stations can be viewed in a Computer at the Central Monitoring Station The data

of the network is collected by the FEP (Front End Processor) which in turn is transmitted to the computer

COMPONENTS OF NETWORK MANAGEMENT OF DATALOGGERS

(a) Datalogger at stations

(b) MODEM and Transmission medium

19 | P a g e

(c) Front End Processor (FEP)

(d) Central Monitoring Unit (CMU) Computer

FEP (FRONT END PROCESSOR)

FEP acts as a buffer between the Central Monitoring Unit (Computer) and the Network It is provided

at centralised place to retrieve data continuously from station dataloggers and store in memory and transfer to

computer on request It stores 10 Lac telegrams It works on 12V DC It draws 16A continuous current

when all the three modems are connected Normally it shows the number of packets pending to be sent to the

computer on its 7-segment LED display It is provided with MOTOROLA 68000 microprocessor It has 6-

nos of RS-232 communication ports such as COM1 COM2 COM3 COM4 COM5 and COM6 COM1 is

used for Fault Analysis System (FAS) ie Central Monitoring Unit (Computer) connection COM2 to COM6

are used for networking For Bi-directional 2- nos of ports and for Tri-directional (T-network) 3-nos of ports

are used

DATA TRANSMISSION Dataloggers can be networked in Uni-directional Mode or Bi-directional Mode or T ndash Network Mode

In case of loss of data retransmission of data takes place

(a) Uni-Directional Mode

Each Datalogger will send data in only one direction to the FEP Unidirectional mode network is not

preferred

(b) Bi-Directional Mode

Each end of Network is connected to FEP and each datalogger can now transmit data in both the directions

Bi-directional Mode is advantageous it enables the Data Transmission even in case of Network Failure

(c) T - Network Mode

If more no of stations are in network ie if the network is too lengthy then T- network mode is preferred

COMMUNICATION The communication protocol for transmitting data and command between datalogger and CMU is

standardized by the RDSO and is given in the Specifications of Dataloggers

(a) The type of communication used in the network is dependent on the distance between the dataloggers

(b) For shorter distances Opto Converter Box- Opto isolated current loop communication is used

(c) For longer distances Modem (Dial-up leased) Fiber Optic Satellite Microwave communication

MODEMS Modems are used for DATA transfer between Dataloggers and Front End ProcessorThese are

configured to RS 232 Serial Communication Network is connected with two types of 4-wire modems

(a) Internal modem card Dual Modem card (in-built)

It is fixed in datalogger Euro rack itself One card contains two modems The top modem is called

ANS (answer) modem and the bottom modem is called as ORG (originate) modem

Note In case of networking of Dataloggers connect lsquoANSrsquo modem to the lsquoORGrsquo modem of one adjacent

station and connect lsquoORGrsquo modem to the lsquoANSrsquo modem of other adjacent station

(b) External modems

20 | P a g e

These are generally used at FEP (Front End Processor) side to connect the Dataloggers

(i) To transfer Data from one datalogger to another datalogger FEP Baud rate is 9600bps

(ii) These modems are 4-wire line communication

(iii) To transfer the data from FEP to RMU (PC) the Baud rate is 57600 bps

There is no difference between these modems functionally

CENTRAL MONITORING UNIT (CMU) COMPUTER

Central monitoring unit (Fault Analysis Unit) is a Personal Computer and its minimum configuration

shall be specified by RDSO from time to time System Software Windows XPVista(OS) Norton Kaspersky

(Anti Virus) Interbase where Server is not available (DBMS) Oracle where Server is available (DBMS)

software are required to run Datalogger System It is provided with Graphical User interface (GUI) based

software and retrieve data from all Networked dataloggers (up to 32) at various stations It stores data in

standard data base files The CMU is capable of analyzing the data and generate reports audiovisual alarms

on defined conditions This data can be compressed to take backup In central monitoring unit Software used

for analysis of data prediction of faults etc is written in a structured format so that purchaser can

reconfigure it if required It displays the status of signaling gears at any selected time in graphic form for any

selected station yard It retrieves the stored data amp simulates train movement It sends commands to various

Dataloggers to activate audio visual alarm or operate and electromagnetic relay

CMU shares data available in it by other PCs through available local area network where this data can

be used for train charting passenger information purpose The system generates audiovisual alarm in

ASMrsquosSignal Maintainerrsquos room in the case of power supply failure (battery voltage low) or battery charger

defective with acknowledgement facility

(a) Each datalogger has its own identity code which will be transmitted along with data packet to central

monitoring unit

(b) Events recorded at each station are continuously transmitted to central monitoring unit Response time of

data transfer will not exceed 10 sec

21 | P a g e

22 | P a g e

OPTICAL FIBER CABLE

INTRODUCTION The demand for bandwidth on transmission networks is increasing rapidly because video and

graphical rich contents are exchanged through the corporate network or the Internet The Gigabit Ethernet

became ommonly used in the corporate network backbone and 10Gbit Ethernet will be adopted in the near

future Meanwhile in the home the demand for high-speed network becomes popular as the wide spread of

broadband access eg CATV xDSL and FTTH The transmission medium with capability to transmit high

bit rate signal is necessary to satisfy these requirements

The telecommunication transport technologies move from copper based networks to optical fiber

from timeslot based transport to wave length based transport from traditional circuit switching to terabit

router and all optical based networks entering into a new era of optical networking

BASIC PHYSICS OF OFC

OPTICAL FIBER CABLE OFC have Fibers which are long thin strands made with pure glass about the diameter of a human

hair OFC consists of Core Cladding Buffers and Jacket as shown in figure

MONOCHROMATIC LIGHT OR SINGLE COLOR LIGHT Light or visible light is electromagnetic radiation of a wavelength that is visible to the human eye (

about 400 ndash 700 nm) The word light is sometimes used to refer to the entire electromagnetic spectrum Light

is composed of elementary particles called photons Three primary properties of light are

Light can exhibit properties of both waves and particles This property is referred to as wave-particle

duality The study of light known as optics In free space light (of all wavelengths) travels in a straight path

at a constant maximum speed However the speed of light changes when it travels in a medium and this

change is not the same for all media or for all wavelengths By free space it is meant space that is free from

matter (vacuum) andor free from electromagnetic fields

Thus the speed of light in free space is defined by Einsteinrsquos equation E = mc2

Frequency ν speed of light in free space c and wavelength λ are interrelated by ν = cλ

From the energy relationships E = mc2 = hν and the last one an interesting relationship is obtained

the equivalent mass of a photon m = hνc2

When light is in the vicinity of a strong electromagnetic field it interacts with it From this interaction

and other influences its trajectory changes direction as shown in figure

23 | P a g e

INCIDENT RAY REFLECTED RAY AND REFRACTED RAY An incident ray is a ray of light that strikes a surface The angle between this ray and the

perpendicular or normal to the surface is the angle of incidence Reflection is the change in direction of a

wave front at an interface between two different media so that the wave front returns into the medium from

which it originated Common examples include the reflection of light sound and water waves

The reflected ray corresponding to a given incident ray is the ray that represents the light reflected by

the surface The angle between the surface normal and the reflected ray is known as the angle of reflection

The Law of Reflection says that for a specular (non-scattering) surface the angle of reflection always equals

the angle of incidence The refracted ray or transmitted ray corresponding to a given incident ray represents

the light that is transmitted through the surface The angle between this ray and the normal is known as the

angle of refraction and it is given by Snells Law

The figure shows Incident ray Reflected ray Refracted ray the angle of incidence and angle of refraction

REFRACTIVE INDEX - Refractive index is the speed of light in a vacuum ( c =299792458kmsecond) divided by the speed

of light in a material ( v ) Refractive index measures how much a material refracts light Refractive index of

a material abbreviated as lsquo n lsquo is defined as lsquo n=cv lsquo Light travels slower in physical media than it does

when transmitted through the air Refractive index (n) is a function of molecular structure of matter optical

frequency optical intensity determines optical propagation properties of each wavelength ( λ ) may not be

distributed equally in all directions is affected by external temperature pressure and fields

Refractive index of a medium is a measure for how much the speed of light is reduced inside the

medium For example typical glass has a refractive index of 15 which means that light travels at 1 15 =

067 times the speed in air or vacuum Two common properties of glass and other transparent materials are

directly related to their refractive index

First light rays change direction when they cross the interface from air to the material and effect that

is used in lenses and glasses

Second light reflects partially from surfaces that have a refractive index different from that of their

surroundings

SNELLrsquoS LAW-

24 | P a g e

When light passes from one transparent material to another it bends according to Snells law which

is defined as n1sin(θ1) = n2sin(θ2)

where n1 is the refractive index of the medium the light is leaving θ1 is the incident angle between the light

beam and the normal (normal is 90deg to the interface between two materials)

n2 is the refractive index of the material the light is entering

θ2 is the refractive angle between the light ray and the normal

Snellrsquos law gives the relationship between angle of incidence and angle of refraction

For the case of θ1 = 0deg (ie a ray perpendicular to the interface) the solution is θ2 = 0deg regardless of

the values of n1 and n2 That means a ray entering a medium perpendicular to the surface is never bent The

above is also valid for light going from a dense (higher n) to a less dense (lower n) material the symmetry of

Snells law shows that the same ray paths are applicable in opposite direction

TOTAL INTERNAL REFLECTION- When a light ray crosses an interface into a medium with a higher refractive index it bends towards

the normal Conversely light traveling cross an interface from a higher refractive index medium to a lower

refractive index medium will bend away from the normal

This has an interesting implication at some angle known as the critical angle θc light traveling from

a higher refractive index medium to a lower refractive index medium will be refracted at 90deg in other words

refracted alon g the interface If the light hits the interface at any angle larger than this critical angle it will

not pass through to the second medium at all Instead all of it will be reflected back into the first medium a

process known as total internal reflection

The critical angle can be calculated from Snells law putting in an angle of 90deg for the angle of the refracted

ray θ2 This gives θ1

Since θ2 = 90deg

So sin(θ2) = 1

25 | P a g e

Then θc = θ1 = arcsin(n2n1)

For example with light trying to emerge from glass with n1=15 into air (n2 =1) the ritical angle θc is

arcsin(115) or 418deg For any angle of incidence larger than the critical angle Snells law will not be able to

be solved for the angle of refraction because it will show that the refracted angle has a sine larger than 1

which is not possible In that case all the light is totally reflected off the interface obeying the law of

reflection

OPTICAL FIBER MODE An optical fiber guides light waves in distinct patterns called modes Mode describes the distribution

of light energy across the fiber The precise patterns depend on the wavelength of light transmitted and on the

variation in refractive index that shapes the core In essence the variations in refractive index create

boundary

conditions that shape how light waves travel through the fiber like the walls of a tunnel affect how sounds

echo inside

We can take a look at large-core step-index fibers Light rays enter the fiber at a range of angles and

rays at different angles can all stably travel down the length of the fiber as long as they hit the core-cladding

interface at an angle larger than critical angle These rays are different modes Fibers that carry more than

one mode at a specific light wavelength are called multimode fibers Some fibers have very small diameter

core that they can carry only one mode which travels as a straight line at the center of the core These fibers

are single mode fibers This is illustrated in the following picture

OPTICAL FIBER INDEX PROFILE Index profile is the refractive index distribution across the core and the cladding of a fiber Some

optical fiber has a step index profile in which the core has one uniformly distributed index and the cladding

has a lower uniformly distributed index Other optical fiber has a graded index profile in which refractive

index varies gradually as a function of radial distance from the fiber center Graded-index profiles include

power-law index profiles and parabolic index profiles The following figure shows some common types of

index profiles for single mode and multimode fiber

26 | P a g e

OPTICAL FIBERrsquoS NUMERICAL APERTURE ( NA )- Multimode optical fiber will only propagate light that enters the fiber within a certain cone known as

the acceptance cone of the fiber The half-angle of this cone is called the acceptance angle (see figure 18)

θmax For step-index multimode fiber the acceptance angle is determined only by the indices of refraction

Where

n is the refractive index of the medium light is traveling before entering the fiber

nf is the refractive index of the fiber core

nc is the refractive index of the cladding

NUMBER OF MODES IN A FIBER - Modes are sometimes characterized by numbers Single mode fibers carry only the lowest-order

mode assigned the number 0 Multimode fibers also carry higher-order modes The number of modes that

can propagate in a fiber depends on the fiberrsquos numerical aperture (or acceptance angle) as well as on its

core diameter and the wavelength of the light For a step-index multimode fiber the number of such modes

Nm

Where

D is the core diameter

λ is the operating wavelength

NA is the numerical aperture (or acceptance angle)

MODE FIELD DIAMETER - All light do not travels through the core of the fiber but is distributed through both the core and the

cladding The mode field is the distribution of light through the core and cladding of a particular fiber

Mode-Field Diameter (MFD) defines the size of the power distribution When coupling light into or out of a

fiber MFD is important in understanding light loss

27 | P a g e

ADVANTAGE OF OFC COMMUNICATION - bull More information carrying capacity Fibers can handle much higher data rates than copper More

information can be sent in a second

bull Free from Electromagnetic and Electrostatic interference Being insulator no electric current flows through

the fibre and due to this reason fibres neither radiate nor pick up electro - magnetic radiation So WPC

CLEARANCE is not required

bull Low attenuation 025 dbkm at 1550 nm Loss in twisted pair and coaxial cable increases with frequency

where as loss in the optical fibre cable remains flat over a wide range of frequencies

bull Use of WDM ndash Switching routing at Optical signal level

bull Self healing rings under NMS control

bull Small size makes fibre cable lighter in weight So easy to handleOptic fibre cable weight (approx)

500 kg km Copper cable weight (approx) 1000 kgkm

The reasons are photons of light in a fibre

do not affect each other as they have no electrical charge and they are not affected by stray photons outside

the fibre But in case of copper electrons move through the cable and these are affected by each other

Optical fibre does not carry any electricity even if the cable is damaged or short circuited it does

not cause any spark or fire hazard

As the fibre do not radiate energy it can not be detected by any nearby antenna or any

other detector The fibres are difficult to tap and therefore excellent for security

As the signal transmission is by digital modulation there is no chance of cross talk in

between channels

Only by adding a few additional terminal and repeater equipments the

capacity of the system can be increased at any time once the cable is laid

ical effects and temperature variations

LIMITATIONS OF OFC -

difficult

- utilised

APPLICATION IN SIGNAL AND TELECOMMUNICATIONS transmission circuits

-haul circuits for linking of telephone exchanges

28 | P a g e

PROPAGATION MODES CONCEPT -

MODE - Mode is an available distribution of electromagnetic field in a plane transverse to the direction of

light propagation Each mode is characterized by frequency polarization electric field strength and

magnetic field strength Available patterns are derived from Maxwellrsquos equations and boundary conditions

LINEARLY POLARIZED (LP) MODE A mode for which the field components in the direction of propagation are small compared to

components perpendicular to that direction An optical fibre supports only different field patterns called as

lsquoLinear Polarizedrsquo or lsquo LPrsquo modes The reasons are

requirements

de

the accrual of power carried by different modes

There are two basic types of fiber Multimode fiber and Single-mode fiber

Multimode fiber is best designed for short transmission distances This is suited for used in LAN systems and

video surveillance Single mode fibre is best designed for longer transmission distances This is suitable for

long distance telephony and multi channel television broadcast systems

29 | P a g e

MULTI MODE FIBER Multimode fiber the first to be manufactured and commercialized simply refers to the fact that

numerous modes or light rays are carried simultaneously through the waveguide Modes result from the fact

that light will only propagate in the fiber core at discrete angles within the cone of acceptance MM fiber type

has a much larger core diameter compared to single-mode fiber allowing for the larger number of modes

and

is easier to couple than single-mode optical fiber Multimode fiber further categorized as Multimode step-

index and Multimode graded index fiber

PROPAGATION THROUGH MMSI FIBER Figure shows the principle of total internal reflection applies to multimode step index fiber Because

the corersquos index of refraction is higher than the claddingrsquos index of refraction the light that enters at less than

the critical angle is guided along the fiber

Three different light waves travel down the fiber One mode travels straight down the center of the

core A second mode travels at a steep angle and bounces back and forth by total internal reflection The third

mode exceeds the critical angle and refracts into the cladding Naturally it can be seen that the second mode

travels a longer distance than the first mode causing the two modes to arrive at separate times

PROBLEMS WITH MMSI FIBER AND SOLUTION This disparity between arrival times of the different light rays is known as dispersion and the result is

a muddied signal at the receiving end It is important to note that high dispersion is an unavoidable

characteristic of multimode step-index fiber The solutions are either use Graded index fiber or Single mode

fiber

PROPAGATION THROUGH MMGI FIBER Multimode Graded-index refers to the fact that the refractive index of the core gradually decreases

farther from the center of the core The increased refraction in the center of the core slows the speed of some

light rays allowing all the light rays to reach the receiving end at approximately the same time reducing

dispersion Figure shows the Light propagation principle through multimode graded-index fiber The corersquos

central refractive index ( nA ) is greater than that of the outer corersquos refractive index ( nB )

It is very clear from the figure the light rays no longer follow straight lines they follow a serpentine path

being gradually bent back toward the center by the continuously declining refractive index This reduces the

arrival time disparity because all modes arrive at about the same time The modes traveling in a straight line

30 | P a g e

are in a higher refractive index so they travel slower than the serpentine modes These travel farther but

move faster in the lower refractive index of the outer core region

PROPAGATION THROUGH SMSI FIBER Single mode fiber has a much smaller core that allows only one mode of light at a time to propagate

through the core The figure shows the single mode fiber

Single-mode fiber exhibits no dispersion caused by multiple modes Single-mode fiber also offers lower fiber

attenuation than multimode fiber Thus more information can be transmitted per unit of time because it can

retain the fidelity of each light pulse over longer distances Like multimode fiber early single-mode fiber was

generally characterized as step-index fiber meaning the refractive index of the fiber core is a step above that

of the cladding rather than graduated as it is in graded-index fiber Modern single-mode fibers have evolved

into more complex designs such as matched clad depressed clad and other exotic structures

SINGLE-MODE FIBER DISADVANTAGES The smaller core diameter makes coupling light into the core more difficult The tolerances for single-

mode connectors and splices are also much more demanding

CUTOFF WAVE LENGTH - Cutoff wavelength is the wavelength above which a single-mode fiber supports and propagates only

one mode of light In other words an optical fiber that is single-mode at a particular wavelength may have

two or more modes at wavelengths lower than the cutoff wavelength The effective cutoff wavelength of a

fiber is dependent on the length of fiber and its deployment The longer the fiber the lower is the effective

cutoff

wavelength The smaller the bend radius of a loop of the fiber the lower is the effective cutoff wavelength If

a fiber is bent in a loop the effective cutoff wavelength is lowered

SIGNAL ATTENUATION IN FIBER - Optical fiber has a number of advantages over copper However it also suffers from degradation

problems which can not be ignored The first of these is loss or attenuation Attenuation is typically the result

of two sub properties They are scattering and absorption Both of which have cumulative effects The second

is

dispersion which is the spreading of the transmitted signal and is analogous to noise

SCATTERING Scattering occurs because of impurities or irregularities in the physical construction of the fiber The

well known form of scattering is Rayleigh Scattering It is caused by metal ions in the silica matrix and

results in light rays being scattered in various directions

31 | P a g e

Scattering limits the use of wavelengths below 800nm The short wavelengths are much affected than longer

wavelengths It is because of Rayleigh scattering that the sky appears to be blue ( shorter wave length ) The

shorter wavelengths ( blue ) of light are scattered more than the longer wavelengths of light

ABSORPTION Absorption results from three factors They are hydroxyl ions ( OH- water ) in the silica impurities

in the silica and incomplete residue from the manufacturing process These impurities tend to absorb the

energy of the transmitted signal and convert it to heat resulting in an overall weakening of the signal The

Hydroxyl absorption occurs at 125 and 139 micro The silica itself starts to absorb energy at 17 micro

because of the natural resonance of the silicon dioxide

MACRO BENDING LOSS Macro-bending loss is caused by bending of the entire fiber axis The bending radius shall not be

sharper than 30d where d is diameter of cable A single bend sharper than 30d can cause loss of 05dB

The fiber may break if bending is ever sharper

MICRO BENDING LOSS Micro-bending loss is caused by micro deformations of fiber axis which leads to failures in achieving

total internal reflection conditions Micro-bends are small scale perturbations along the fiber axis the

amplitude of which are on the order of microns These distortions can cause light to leak out of a fiber

Micro-bending may be induced at very cold temperatures because the glass has a different coefficient of

thermal expansion from the coating and cabling materials At low temperatures the coating and cable

become more rigid and may contract more than the glass Consequently enough load may be exerted on the

glass to cause micro bends

Coating material is selected by manufacturers to minimize loss due to micro-bending The linear thermal

expansion coefficient of coating material shall be compatible with that of fiber

32 | P a g e

DISPERSION Dispersion is the optical term for the spreading of the transmits in the fiber It is the bandwidth

limiting phenomenon and comes in two forms Multimode dispersion and chromatic dispersion Chromatic

dispersion is further subdivided into material dispersion and waveguide dispersion

DISPERSION PHENOMENON IN OPTICAL FIBER Dispersion is the time distortion of an optical signal that results from the differences of time of travel

for different components of that signal typically resulting in pulse broadening As the distance traveled by

the signal is more broadening of pulse is more In digital transmission dispersion limits on the maximum

data rate and the maximum distance ie the information-carrying capacity of a fiber link The interference

from broadened pulse in the next interval shall not lead to erroneous interpretation of received signal

OPTICAL DOMAIN Understanding where attenuation and dispersion problems occur helps optical design engineers

determine the better wavelengths at which information can be transmit taking into account distance type of

fiber and the other factors which can severely affect the integrity of the transmitted signal The graph shown

depicts the optical transmission domain as well as the areas where problems arise The wavelength (nm)

is shown on X-axis and attenuation ( dBkm) is shown on Y-axis

There are four transmission windows appear in the figure The first one is at around 850 nm the

second at 1310nm third at 1550 nm and fourth at 1625 nm The last two labeled as C and L band

respectively The 850 nm wavelength at which the original LED technology operated The second window at

1310 nm has low dispersion The 1550 nm called as C-band is ideal wavelength for long haul

communication systems The network engineers can avoid transmitting signal at 1000 nm where Rayleigh

scattering 1240 and 1390 nm where hydroxyl absorption by water occurs to avoid high degree of loss

Optical fibers also can be manufactured to have low dispersion wavelength in the 1550nm region

which is also the point where silica-based fibers have inherently minimal attenuation These fibers are

referred to as dispersion-shifted fibers and are used in long-distance applications with high bit rates For

33 | P a g e

applications utilizing multiple wavelengths it is undesirable to have the zero dispersion point within the

operating

wavelength range

34 | P a g e

SIGNALLING RELAYS

INTRODUCTION A relay is an electromagnetic device which is used to convey information from one circuit to another

circuit through a set of contact ie front or back contact Constructional and electrically relays may be

divided into DC and AC relays because the means by which the electrical energy in the coil is converted in

to mechanical Energy in order to move the contacts are fundamentally different In DC type the contacts are

carried on an armature forming part of a magnetic circuit in which a field is set up by the current flowing in

the coils In AC types the contacts are attached by a link mechanism to a metal sector disc or cylinder in

which currents are induced by the alternating magnetic field produced by the currents in the coils

Every endeavor has been made to explain the action of each type of relay in the simplest possible manner

Relays are sophisticated switch gears used for remote control and succession control of various

electrical equipment In present days they are widely used because they are capable of protecting the

controlled equipment from cross feeding and overloading even as they cater for speedy operations

Most of the relays in present day signaling are electromagnetic devices although some of the relays control

circuits through electronic components like diodetransistors Integrated Chips etc

Railway signaling relays are unique in that

(a) They operate on low voltage and current

(b) They are more articulate as according to their special features they can work under restrictive conditions

and in any specified manner Virtually they can cater for all situations while contributing to speed and

accuracy in operations

CLASSIFICATION OF SIGNALLING RELAYS (a) According to the method of their mounting or fixture they are classified as

(i) Shelf type Relays which are loosely kept on shelves

(ii) Plug in type Relays which are plugged into a pre- wired plug boards

(b) According to their connection and usage they are classified as

(i) Track relays Relay which is directly connected to the track to detect the presence of vehicle

(ii) Line Relays Other than track relay all are line relays Relays connected to the selection circuit

(c) According to their vitality or importance in ensuring train working safety they are classified as

(i) Vital Relays All relays used for traffic control such as signal point controls track detection etc

(ii) Non-vital Relays Relays which operate control aids and accessories like warnings buzzers

Indications etc

(d) According to their special provisions to ensure reliability of their contacts they are classified as

(i) Proved type are those whose normalization after each operation shall be proved in circuit

controlled by their contacts Contacts in which both the springs have metal surfaces on their tips They may

get fused due to high sparking current across them during operation These may prevent relay normalization

and causes unsafe condition in traffic control To avoid this proving of relay normalization after each

operation is necessary

(ii) Non - proved type Need not to be proved to have been normalized after each operation as their

contacts have at least one non-fusible contact (carbon contact)

(e) According to their feed source relays are broadly classified as

(i) DC relays The relay which requires DC power supply for its operations are called DC relays Among

the DC relays

o DC neutral relays This relay closes the same set of contacts on energization with Normal polarity

or Reverse polarity supply

o Polar Relays This relay closes different set of contacts when energized with Reverse polarity

supply They may or may not have contact to close when deenergized

35 | P a g e

(ii) AC Relay AC Induction motor track relays Time element relays flashing indication control etc

(iii) Electronic Relays DC relays with electronic components in them are called electronic relays

DC NEUTRAL RELAY Each Relay has usually one or two coils with a hollow center to accommodate a coreThe coils are

made up of a large numbers of turns of small gauge soft drawn copper wire The two coils can be connected

in series or parallel according to the requirement of relay resistance The ends of the coils are terminated on

binding post to which the control wires are connected Each coil is placed around a core of specially selected

Iron or steel having high permeability and low retentivity The core should be susceptible to magnetism and

at the same time should have little residual magnetism The cores are connected at the top by a yoke to

complete the magnetism coupling between two ends of coils The bottom of each core is equipped with a

large steel or Iron block known as pole piece or face

A flat piece of Iron or steel called armature is supported by brackets which are securely fastened to

the pole piece The armature yoke and the pole pieces are also made of specially selected iron or steel of the

same quality as the core The armature carries the metallic spring contacts which are insulated from it

The circuit through the coils of the relay is closed It sets up a magnetic flux through the core yoke and the

armature The flux passing between the armature and pole faces causes the armatures get attracted to the pole

faces and armature picks up and closes front contacts When the circuit is opened the magnetic flux collapses

and the armature drops away by gravity from the pole faces the front contacts break and back contacts close

The front and back contacts of the relay can be utilised to make or break other circuits Two stop pins of

nonmagnetic material are fixed either on the armature or pole faces so that the armature cannot

come in contact with the pole faces It is essential to maintain a small air-gap between the armature and pole

faces so that low value of residual magnetism may not retain the armature in picked up position and causes

the relay to fail to drop away with a break in its control circuit

GENERAL USAGE

DC Neutral line relays are most commonly used for Railway Signalling controls and detection

Among them plug-in type relays are preferred in larger installations for space considerations Shelf type

relays are also in use mostly in wayside stations

There are many DC Neutral line relays in use with special features such as

(i) Delayed operation

(ii) Biased DC control

(iii) DC control unaffected by AC interference currents

(iv) Getting latched in operated condition till further feeding and others

Usage of DC polar relays is mostly in conjunction with block instruments that control traffic between

stations AC line relays are almost extinct in installations of British Signalling practice They are however

used for time control operations flashing indication control and such other special purposes in installations

with Siemens signalling practice widely Track relays are used according to the type of track detection

circuits chosen for a given location and context While most of the track circuits are still of the DC working

type requiring DC neutral track relays with them the prospects of their being replaced with Electronic track

circuits directly feeding DC line relays in future are great AC Track Circuits are used in DC Traction area

as conventional DC Track Circuits are not suitable there AC Track relays are used with them almost all of

the induction motor type In the British practice of signalling which was first introduced on Indian Railways

non-proved type relays with carbon to metal switching contacts are generally used for vital controls

They facilitate simple circuit designs But with the advent of German Practice introduced by Ms

Siemens later proved type relays with all metal to metal contacts are widely accepted in spite of

complications in circuit design caused by them A recent introduction is that of the same type relays made by

Ms Integra control However for some time now the appreciable features of both the practices are getting

36 | P a g e

incorporated together in the indigenous designs of signalling by railwaymen With this the usage of all types

of relays anywhere can be found without straight jacketed segration of relay types

CHARACTERSTIC OF ELECTRO-MAGNETIC RELAY The following are the characteristic of electro-magnetic relays A brief study of them helps in

understanding the choice of their components and designs features

1) Force of attraction

2) Effect of air gap

3) Effect of Hysterisis

4) Transient condition

FORCE OF ATTRACTION In any electro-magnetic system the force of attraction is given by

Where B - is the flux density a - is the cross sectional area of the particular part of the magnetic

circuit

In the case of a DC neutral Relay B is proportional to the current that is flowing in the coil

surrounding the electro-magnet and thus the force of the attraction is directly proportional to the square of the

current This square relationship has its own advantage especially in the case of DC track relay in that a

small reduction in the current will have a great effect on the working of the relay Also for a given change of

current the make and the break will be quicker with lesser possibility of arcing

EFFECT OF AIR GAP

Curve lsquoArsquo is magnetisation curve for the iron and is all practical purpose a straight line up to the

saturation point Curve lsquoBrsquo is the magnetisation curve for the open-air gap which is a straight line through

out because per magnetisation curve of the whole

magnetic circuit of the relay and for a given force is the sum of the amp-turns for the iron part and the amp-

turns for the air gap

When the front contacts are open the force required to pick up the armature is shown on curve lsquoCrsquo to be F1

but after the armature has operated it will be separated from the core by stop pins In this position the amp-

turns required to maintain the armature is less as indicated by the dotted line from 1 on curve C to 2 on curve

37 | P a g e

F But actually the current in the coil is unaltered the force on the armature is greater than required as

indicated at 3 on curve F Part of this extra force is used to flex the front contacts sufficiently to give good

contact pressure when it is in energised position

The difference between the pick-up and the drop-away current should be as small as practicable in

track relay to ensure good shunting characteristics This is achieved firstly by the choice of good quality relay

iron and secondly by having a small air gap between armature and core If the air gap is not available then

the residual magnetism fluxes might cause the armature to be retained when the supply is disconnected For

this reason residual pins are provided to ensure a definite minimum air gap in the energised position

EFFECT OF HYSTERISIS

Hysterisis is the property by which the flux produced lags behind the current In the de-energized

condition there will be small residual flux in the core When the voltage is applied to the coils the current in

rising to its steady value first causes the flux to rise from 1 to 2 along the curve At this point the flux density

will be sufficient to attract the armature and reduce the air gap the flux then raise to 3 and continue to 4

which corresponds to the steady current in the coils When the voltage is disconnected the current in falling

caused the flux to fall from 4 to 5 along the curve At this point the flux density will fall below the value

required to maintain the armature which will release thus increasing the air gap and reducing the flux to 6

Finally the

flux will decrease from 6 to 1 where the current will again be zero

The relay core is made of material having high permeability and low retentivity As mentioned in

the IRS specification Electromagnet iron may be in the form of a

(a) Bar of silicon steel

(b) Best Yorkshire wrought iron

(c) Swedish charcoal iron

(d) Electrical steel sheets

` This reduces the difference between pick up value and Drop away value By selecting good quality

core material Percentage release and sensitivity of the relay will be improved

TRANSIENT CONDITION

38 | P a g e

When the voltage is applied or disconnected from the coils it takes some little time before the current

become steady These are known as transient conditionsrdquo and are important so far as track relays are

concerned When the voltage is first applied to the coils the magnetic flux in rising cuts the turns on the

coils and in so doing produces a back EMF that opposes the applied voltage and retards the growth of

current

The growth and decay of flux are decided by the relationship between the inductance and resistance

in the circuit is known as time constant It is not fixed quantity in the case of DC neutral relay This value of lsquo

Lrsquo is less when the relay is in de-energised condition (L1) than when the relay is in energised condition (L2)

The magnitude of flux that is established for a given change of current is different in two cases

When the current reaches the pick up value the armature closes and the inductance is increased to L2

due to reduced air gap the flux per amp is increased The increase in flux increased the back EMF during the

movement of the armature after which the current continuous to raise along a new curve corresponding to the

increased inductance until it reaches the final value (ER) This process is indicated above in fig24

When the supply is disconnected the current is obliviously reduced to zero immediately but the flux

decay comparatively slowly owing to the eddy currents produced in the core by the rapid flux change which

tend to maintain the flux The drop away time on a disconnection is however generally negligible See fig

below

If the relay releases due to the reduction in current from say I 2 to I 1 caused by the application of

shunt resistance (as in the case of track relay ) the time taken is much longer than the relay is simply

disconnected The rate of rise or fall of current during the transient conditions is also depends on exterior

circuit values because L and R apply to the whole circuit The production of eddy current in the core the flux

will decay at a slower rate than the current So that the actual release time will be a little longer than it takes

the current to fall to the release

L= Inductance

39 | P a g e

R= Resistance

It is now clear that to reduce releasing time to a minimum it is necessary that

- The relay iron should have low Hysterisis loss and low retentivity

- The degree of over energization of the relay should be restricted

- Connecting a suitable external resistance in series with the relay to keep LR ratio low

In non RE area for track circuit length less than 100M 9 ohm track relay only to be used Using relay

with minimum contacts as they require lesser current which keeps inductance value low

Train working safety is ensured only if the track relay of shortest length track circuit is released

before a light engine running at a highest permitted speed clears it Otherwise the track circuit occupation

may go undetected To avoid this a special provision has to be made in signal control circuits wherever

necessary

The following methods may be adopted for reducing the time lag of track relay

(a) Restrict the over energisation of relay since the release time depends on the initial working current

(b) Connecting a suitable external resistance in series with the relay to keep the LR ratio low

(c) Using relays with minimum contacts as they require lesser operating current keeping the inductance

value low

40 | P a g e

CONCLUSION

Modern signalling is vital for safe and punctual movements of trains In the Indian railways The Signalling

and Telecommunication Department is responsible for providing modern effective and relaible signalling

systems as well as telecommunication systems

The first mode of communication used in Indian Railways was the use of electric telegraph

with the help of Morose code Morose code is the method of providing text information as a series of on-off

tones and lights or clicks that can be directly understood by a skilled listener or observer without special

equipmentEach character (letter or numeral ) is represented by a unique sequence of dots and dashes Later

this system becomes obselete and beggan the era of wireless communication which operated at audio level

frequency range

In wireless communication the significant advances took place the transition to miniature

valves or filament tubesBut this was abandoned too because of excessive current consumption and over

heating of the filament tubes

Fibre-optic communication is a method of transmitting information from one place to another by

sending pulses of light through an optcial fibreThe light forms an electromagnetic carrier wave that is

modulated to carry information First developed in the 1970s fibre optic communication systems has

revolutionized the telecommunications industry and have palyed a major role in the advent of the information

age Because of its advantages over electrical transmissionsoptical fibres have largely replaced copper wire

communications in core networks in the developed world The Indian Railways too is undergoing a transition

from Microwave communication to fibre optic communications

41 | P a g e

BIBLIOGRAPHY AND REFERENCES

1 wwwwikipediacom

2 wwwbritaniccacom

3 wwwirfcacom

4 Motorola GP60 system manual

5 Harris FAS 7000 manual

6 TOSHIBA Manual

7 | P a g e

STATUS MONITORING PANEL IPS status monitoring panel has been provided in the ASM room for giving the important alarms and

indications to ASM Status Panel tells present working status of IPS displaying battery voltage continuously

and five other indications which will light according to IPS status During normal working these indications

will not lit Whenever the battery has come on to the load and has discharged by 50 DOD (Depth of

Discharge) then first Red indication lit with description ldquoSTART GENERATORrdquo with audio Alarm ie DG

set is to be started and put on the load If DG set is not started with this warning then if battery gets further

discharged to 60 DOD and second Red indications appears with description ldquoEmergency Start generatorrdquo

with audio alarm even now if DG set is failed to be started the battery further gets discharged to 70

DOD and 3rd Red indications appear with description ldquo System shut downrdquo with audio alarm which will

continue till Generator is started resulting in AC output from IPS is automatically cut off results all the

signals will become blank

When there is any defect in any sub module of IPS even without affecting working of system the 4th

Red indication appears with description ldquoCall SampT Staffrdquo with audio alarm so the ASM advises SampT staff

accordingly Green LED 5th indication comes with the description ldquoStop Generatorrdquo with audio alarm when

the DG set is running and if the Battery bank is fully charged condition

EARTHING The IPS systems and its individual modules are having earth terminals and all these are properly

earthed with earth resistance of less than 1 ohm Earth provided shall preferably be maintenance free using

ground resistance improvement compound (The acceptable Earth Resistance at earth busbar shall not be

more than 1 ohm Code of practice for earthing and bonding system for signalling equipments)

LIGHTNING AND TRANSIENT PROTECTION IN IPS Manufacturer will provide Stage1 amp Stage 2 protection along with the IPS These are described

below

Stage 1 protection is of Class B type against Lightning Electro-Magnetic Impulse (LEMP) amp other

high surges provided at Power Distribution Panel It is provided with a 63 Amp fuse in phase line and is

connected between Line and the Neutral and also between the Neutral and Earth

Stage 2 protection (Power line protection at Equipment level) is of Class C type against low voltage

surges provided at the equipment input level This is thermal disconnecting type and equipped with

protection against SPD (surge protection device) failure due to open amp short circuit of SPDs and is connected

between the Line and the Neutral If supply data signalling lines (ACDC) are carried through overhead

wires or cables above ground to any nearby building or any location outside the equipment room additional

protection of Stage 2 type shall be provided at such locations Class B amp Class C arrestor is provided on a

separate wall mounting type enclosure in IPS room

Stage3 protection (Protection for signallingdata line) is of Class D type All external data signalling

lines (ACDC) shall be protected by using this Class D type device It consists of a combination of Varistors

and Gas Discharge Tube with voltage and current limiting facilities

FEATURES Chargers used in this system are of SMPS technology chargers with 90 efficiency These chargers

are supported with hot standby mode with (n+1) modular technology

Onetwo sets of Maintenance free Battery banks (110VDC) Normally one set (110VDC) of Battery

bank is used Conventional flooded type Lead Acid Batteries or Low Maintenance Lead Acid

batteries can also be used (SMRs settings are required to be adjusted depending on the type of

Batteries used) Various voltage levels of

8 | P a g e

battery banks are avoided Reduction in Battery maintenance amp less flour area required

DC-DC Converters working from 110V Central battery have been used for all dc supplies This has

improved overall efficiency of the system since number of conversion from AC to DC have been

reduced to 2 stage as compared to 3 stage conversion in case of transformer-rectifier system

DC-DC converters are available in modules Easy replacement of defective modules This ensures

less down time

DC-DC Converters are used in load sharing N+1 configuration (ie with hot standby with N+1

modular technology) to improve the reliability amp availability of the system

Capacity of inverter has been brought down to 15 KVA from 5 KVA and used for feeding only

Signals supply Hot standby inverter is provided with auto changeover facility This improves the

availability of the overall system

High efficiency inverter is used with PWM (Pulse Width Modulation) technology in place of Ferro-

resonant technology based inverter This improves the efficiency of the overall system

Continuous power to Signal Circuits even in absence of DG setLocal Power Supply

Generators need not be switched ON every time during train movement

Metal-to-metal relay installations and block working by axle counters have also been covered

Supply of spare modulesComponentsCells have been included as part of main supply

Provides highly regulated voltage to all signal relays amp lamps for better life

9 | P a g e

SINGLE SECTION DIGITAL AXLE COUNTER

INTRODUCTION- The axle counter equipment is working on high frequency and using amplitude modulation or phase

modulation for detection of presence of wheel The equipment described in this notes is Phase modulation type

for the detection of presence of wheel In the Phase modulation type track device the detection of presence of

wheel is with the phase reversal of 1800 out of phase which enables this system to be more healthy and safe

In Phase Reversal Modulation technique trolley suppression arrangements to prevent the counting of

wheels caused by push trolley passing over the track device are not required as the system will take care of

validation of generated pulses caused by passage of wheel over the track device depending up on the phase

shift of the pulse This phase shift of the pulse may be normally 160deg to 180deg for a train wheel and it may be

approximately 100deg to 120deg for a push trolley wheel

This is Digital Axle Counter equipment for single track sections containing 2 out of 2 micro-

controllers to count the axles establish the track occupancy of a track section and to provide this information

to the block or the interlocking equipment

In this system no separate evaluator is required and no analog data is being transmitted One set of

Axle counter equipment is provided at entry end and other set provided at exit end Both sets are being

connected through a twisted pair of telecom cable ie existing RE cable one PET quad is used for both UP

and DN Axle Counters Digital DATA is being transmitted between two ends of Axle counters (Outdoor

track side Detection points)This system is a fully duplex capable of operating according to CCITT V21 and

the Data will be transmitted at the rate of 300bitsec This data Transmitted ensure negligible interference of

the noise The system is highly reliable

FEATURES (a) The system consists of

(i) Single Section Digital Axle Counter (SSDAC) units

(ii) Tx Rx coils

(iii) Vital Relays

(b) TxRx coil axle detectors are mounted to the web of the rails The design of system consists of 21 KHz amp

23 KHz High frequency Phase Reversal type axle detectors

(c) Compatible with 90R 52Kg amp 60Kg rail profiles Easy to install commission amp maintain

(d) Track devices at both (entry amp exit) points of the section should be fixed on the same rail

(e) System is designed to detect the solid wheels with diameter gt 400mm with standard wheel flange

(f) The system works in pairs For monitoring single-track section one pair of SSDAC units are required and

to be installed near the trackside one at the beginning and another at the end of the track section ie

Trackside electronic counting equipment

(g) The basic design of the system is based on counting the number of axles passing at each detection point

These stored counts are transmitted to the second unit of the system and vice versa by means of modem

communication

(h) The communication consists of digital packets having details of Counts amp Health

10 | P a g e

(i) If counts registered at both detection points are equal the section is cleared otherwise the section is shown

as occupied The system ensures no error condition to arrive at the decision of clearance

(j) System is designed as per CENELEC SIL-4 (European standard) using micro controller along with other

electronic circuits and programmed using dedicated software When any of these circuits fail the system

goes to fail safe condition

(k) It is programmable for either Preparatory Reset or Conditional Hard Reset as per requirement

(l) Micro controller based design with 2 out of 2 decisions and counting through software

(m) V21 Modem communication (2-wire) on frac12 quad cables and also compatible to work on voice channel of

OFC amp Radio

(n) Opto isolated vital relay drive for Q-style 24V 1000 _ and Vital Relay output can be giving at both ends

of the system

APPLICATIONS The system can be widely used in Railways for Block Working (BPAC) Intermediate Block Signaling Auto

signalling and Track circuiting for i) Loop line ii) Main line iii) yard lines

SYSTEM DESCRIPTION

This system comprises of

Tx coils-2 nos

Rx coils-2 nos

Reset Box (RB 258A)

Card 1 Signal Conditioning Card ndash 1

Card 2 Signal Conditioning Card - 2

Card 3 Micro controller Logic Board ndash 1

Card 4 Micro controller Logic Board ndash 2

2 nos for independent resetting ndash when used in block sections

1 no for common resetting ndash when used for Track circuiting at stations

Card 5 Event Logger Card

Card 6 Modem Card

Card 7 Relay Driver Card

Card 8 DC-DC Converter Card

SSDAC (DACF 700AP) UNIT

(A) SIGNAL CONDITIONING CARD (CARD 1amp2) (SCC) -1 (SCC-1) generates 21 KHz carrier

signals

-2 (SCC-2) generates 23 KHz carrier signals which is transmitted to 2nd

set of Tx coils

s receive these signals

modulated

train pulses

11 | P a g e

(B) MICRO-CONTROLLER LOGIC BOARD CARD (CARD 3amp4) (MLB) The Micro-controller Logic Board (MLB) is the heart of the system

o 8051 Based Architecture

o 8 Bit Micro Controller

o ATMEL AT89S8252 Micro controller

o 2 out of 2 Decision

o Uses C subset language

- TOOLS

o KEIL μ Vision Development System

o Universal Programmer

o 2KB Program Memory

o 256 bytes RAM

o 8KB Flash memory

o 32 Programmable IO lines

o Wide Operating Voltage range of 4V-6V

o Full Duplex Serial Port

o Programmable Watch Dog Timer

o Fully Static operation up to 24MHz (Upgraded to 40MHz)

o Operating Temperature of ndash40degC - +85degC

o Use of State Machine for Axle Counting

o Use of ASCII MODBUS protocol

o Use of CRC16 technique for Error Checking during communication

o Wheel detection

o Train direction checking and

o Wheel counting functions

o It receives the remote wheel count and computes the status of the section for clear or occupied

o It also checks various supervisory signal levels like supervisory of TxRx coils presence of various

cards communication link failure etcThese cards communicate with each other for wheel count

At Entry-end if train enters into section (1st detection) the counts are incremented and when train

shunts back from the same detection ie if train exits from the section from the same detection the counts are

decremented At Exit-end if train enters into section (2nd detection) the counts are decremented and when

train shunts back from the same detection ie if train exits from the section from the same detection the

counts are incremented Both the track devices at Entry and Exit ends must be fixed on same side of the

track

This MLB card is having Extensive LED display

o A block of 8 LED indicators for count progress error display

o 2 independent LED indicators for section status

o The errors occurring in the system during the operation of the SSDAC are encoded and are indicated by

means of the 8-LED block present on the front panel of the MLB cards

(c) EVENT LOGGER CARD (CARD 5)

Event logger card is designed to capture and store important signals from the remote and local SSDAC units

The stored data can be downloaded from the event logger card for the purpose of analyzing the events

occurring during the operations of the SSDAC The data can be analyzed with the help of CEL data analyzer

software

12 | P a g e

The event logger card captures following signals

(i) Pulse signals

(ii) Supervisory signals

(iii) Card removal information

(iv) Serial packets from

Event Logger card has a Rabbit processor and 2 MB FLASH MEMORY to store packets The data is initially

stored in the buffer and subsequently transferred to FLASH memory every two minutes Normally 4096

pages of the data can be stored in flash memory on FIFO (first in first out) basis

Run This LED blinks continuously indicating the normal working of the event

Log This LED blinks whenever data is being logged into the flash memory (Approx after every 2 minutes)

Dnld This LED is ON when data is being downloaded from the flash memory of the card and becomes OFF

when download is complete

(D) MODEM CARD (CARD 6) (i) The modem card transmits and receives the digital packet information form one counting unit to the other

The packet will appear after every 18 sec and the packet carries the latest information such as

(ii) The modem card being used is V21 type (2-wire) in SSDAC

(iii) This card interfaces with serial RS232C port of both Micro-controller Logic Boards

(iv) It multiplexes the two RS232C inputs and selects one of the two channels and provides signal conversion

from digital to analog (FSK modulation) and vice-versa

(v) Data transmission rate is 300 bitssec

(vi) Automatic Gain Control circuit is incorporated hence no gain adjustments required

(vii) Mode selection on Modem card The modem has been set in lsquoORIGINATORrsquo mode for entry and in the

lsquoANSWERrsquo mode for exit in the factory

(viii) LED Indications provided on Modem card

-Transmitting the signal when LED is flashing

- Receiving the signal when LED is flashing

-Remains OFF in SSDAC

-Carrier is detected when LED is glowing

(E) RELAY DRIVER CARD (CARD 7) (i) The Relay Driver card (RD) provides the 24V DC output required for driving Vital Relay

(ii) One RD card is used in each SSDAC counting unit The RD card receives the command of clear and

clock signals from MLB1 amp MLB2 cards and drives the vital relay lsquoONrsquo when section is NOT OCCUPIED

through opto- isolator circuit

(iii) If a train occupies the section the vital relay is dropped The vital relay status is read back by the system

as per the driving output

(iv) It has

13 | P a g e

ndash LED flashes when the section is clear

ndash LED flashes when the section is clear

All the above LEDrsquos are lit for section clear condition

(F) DC-DC CONVERTER CARD (CARD 8)

INPUT VOLTAGE Nominal Voltage voltage 24V DC Maximum current drain= 12A

Required voltage 18V DC to 30V DC

Output voltage

Nominal Voltage +5 V DC 2 A Required voltage 4 7 5 t o 525V DC

Nominal Voltage +12V DC 200 mA Required voltage 1175 to 1225V DC

Nominal Voltage +24V DC 300 mA with common ground Required voltage 235 to 245V DC

Nominal Voltage +15V DC 100 mA with isolated ground Required voltage 145 to 155V DC

SURGE VOLTAGE AND LIGHTNING PROTECTION Transient surge voltages arise as a result of Lightning discharge switching operations in electrical

systems and electrostatic discharge These surge voltages often destroy the electronic equipment to a large

extent In order to prevent surge voltages from destroying the equipment all the input lines of SSDAC ie

Power Supply (24V) Reset (48V) amp Modem is to be routed through surge voltage protection devices for

effectively protecting the system These devices (3 numbers) are mounted in a box and supplied along with

the system One number of box is to be installed at each location and wired to the SSDAC

Each surge voltage protection device consists of two parts

(a) Base

(b) Plug Trab

The Base of the device is used for wiring the input and output signals The connection details from relay

room to the box and from box to SSDAC unit are provided on the box The Plug Trab consists of MOV and

GD Tube and diverts the excess energy during surge voltages or lightning into the ground connection The

operation of these devices relies on a high quality ground connection in order to safely shunt away the

unwanted energy The impedance of the ground connection is critical and it should be less than 2 Ohms

NOTE The 3 Plug Trab connections are not to be interchanged with one another The plug Trab is a

detachable device and can be replaced with SPARE unit in case of blown device which is indicated by

means of LED for 24 V

EFFECTIVENESS OF PLUG TRABS The effectiveness of plug Trab depends wholly on the Earth connection provided to the system The earth

provided to the system should be less than 1 ohms and connections should be firm and proper to the SSDAC

unit VR box etc

SURGE VOLTAGE AND PROTECTION DEVICE SV-120 The Surge Voltage protection device is to be installed at each location along with every SSDAC unit

14 | P a g e

EARTHING- The lead wires connecting the installation and the earth electrode shall ordinarily be of stranded

copper wire of 29 sq mm (19 strand wires of 14 mm diameter) Copper wire has been specified because GI

wires usually are having greater corrosion However in areas where copper wire may be frequently stolen

due to theft ACSR of size 64 sq mm (19 strands of 211 mm diameter) may be used

LIMITS OF EARTH RESISTANCE (a) Apparatus case connected to Earth (SSDAC and vital Relay Box is housed in Apparatus case and

Connected to earth at outdoor) shall be less than or equal to 1 ohm

(b) All cable connected to same earth shall be less than or equal to 1 ohm

(C) Reset box connected to earth near SM s Room shall be less than or equal to 1ohm

EQUIPMENT TO BE EARTHED A Common Earth should be provided for SSDAC for items 1(a) amp (b) of the above at the outdoor

(a) The Apparatus Case is to be connected to earth (the chassis of SSDAC amp Vital Relay Box should be

properly connected to apparatus case)

(b) Metallic sheath and armouring of all the underground main cables are to be earthed

(i) In RE area the metallic sheath and armouring of main telecom cables are earthed at both ends

(ii) In RE area the armouring of Jelly filled cable shall be earthed at both ends

(c) The Earthing shall be provided at every location box where cables are terminated

(d) Earth already available for other equipment may be used for earthing of Reset Box near SM s Room

Cabin etc

15 | P a g e

DATALOGGER

INTRODUCTION Datalogger is a Microprocessor based system which helps in analysing the failures of relay inter

locking system Electronic Interlocking system This is like a black box which stores all the information

regarding the changes take place in relays AC DC Voltages and DC currents along with date and time The

same information data can be transferred to the computer to analyse further ldquoon line ldquooff linerdquo analysis of

stored date A print out also can be obtained through a printer by connecting directly to the datalogger unit

The data belongs to Relay contacts is considered as digital inputs and the data belongs to voltage

levels currents is considered as Analog inputs Datalogger lsquos are mandatory for all new relay interlocking

(PIRRI) EI installations and it is also recommended to provide in all existing PIs RRIs To increase the

line capacity mechanical signalling equipments are upgraded to PI RRI or EI Due to complexity in the

circuits and wiring sometimes it is very difficult to rectify the failures So datalogger can monitor these

systems with real time clock Thus it can be named as black box of Samp T equipments and hence it is a vital

tool for accident investigation Datalogger is used at Stations yards Whereas in case of Auto Section amp IBH

Mini dataloggers called as Remote Terminal Unit (RTU) are used

ADVANTAGES OF DATALOGGERS (a) Dataloggers helps in monitoring the typical failures such as intermittent auto right failures

(b) It helps in analyzing the cause of the accidents

(c) It helps in detecting the human failures errors such as

(i) Drivers passing signal at Danger

(ii) Operational mistakes done by panel operators ASMrsquos of operating department

(iii) Signal and telecom engineering interferences in safety circuits

(iv) Engineering and electrical department interferences failures

(v) It helps as a ldquoTOOLrdquo in preventive maintenance of signaling gears

(d) Dataloggers can be connected in network Networked dataloggers helps to monitorthe PIRRIEI remotely

(e) Failure reports can be generated remotely with help of datalogger network

(f) On line and Off line track simulation is possible

(g) Speed of the train on point zones can be calculated

(h) Age of the equipment in terms of number of operations etc

COMMON EQUIPMENT FOR ALL DATALOGGERS ARE GIVEN

BELOW (a) CPU card

(b) Digital and Analog input cards

(c) Local terminal(PC)

(d) communication links

(e) Printer

All the dataloggers requires a potential free ( spare ) relay contact for monitoring digital inputs

through Digital input cards amp for monitoring Analog inputs such ACDC bus bar voltage levels through

Analog input cards Digital and Analog inputs are connected to the Processor card Processor card consists of

memory ICrsquos Memory ICrsquos are programmed as per requirement of the signal engineers

Provision of Dataloggers is mandatory with RRI systems and is optional for PI systems as per

amendment to the specification for Relay Interlocking systems ( IRSS-36 ) The data collected by the

datalogger can be used for failure analysis repetitive discrepancies and for accident investigations

16 | P a g e

Note

If the serial communications is more than 50m then line drivers shall be used up to 3 Kms

4wire leased line Modems shall be used if the serial communication is more than 3 Kms

STUDY OF EFFTRONICS DATALOGGER TECHNICAL DETAILS (a) 24V 12VDC Power Supply

(b) Total Storage Capacity of 10 Lakh events

(c) In-built Temperature sensors

(d) Internal Buzzer for alarming during failures

(e) Real Time clock with internal battery backup with data retention up to 10 years

(f) 512 LED matrix to indicate the status of 512 Digital inputs at a time page wise

(g) Seven segment LCD screen (2x24) to display the status of digitalanalog signalsTime Temperature etc

(h) Using the keyboard various functions can be viewed in the LCD panel

(i) Max Digital Inputs 4096

(j) Max Analog Inputs 96

(k) Digital Input Scanning Time 16 millisecond

(l) Analog Input Scanning Time is less than 1 Sec

HARDWARE (EQUIPMENT) Datalogger system consists of

(a) Datalogger (CPU - with Microprocessor 68000)

(b) Digital input cards

(c) Dual modem card

(d) Digital Scanner units (DSU)

(e) Analog Scanner units (ASU)

CPU CARD It is provided with Motorola microprocessor M 68000 It performs all the activities pertaining to the

datalogger It continuously scans (check) the Digital inputs(inbuilt) Digital Scanner Units and Analog

Scanner Units ie scanning of digital signals (Relay operations) for every 16-milli seconds and scanning of

analog signals (ie ACDC voltages amp DC currents) for less than 1 second

This card will support the IO interfaces of LCD (Liquid Crystal Display) - 2X24 alphanumeric Key

Board LED Matrix Display Real Time Clock LCD display and keyboard This will acts as man machine

interface between the datalogger and the signal engineer All the operations (Software) can be performed

using this LCD and keyboard

Real time display with 7 Segments This is built in real time clock within Datalogger and its current

time will be displayed on six 7-segment display provided (Real time clock depend upon DALLAS 1286

chip) This IC will come with internal battery backup hence there is no need to add external batteries

CPU card continuously scans (checks) the DSUs and ASUs Each input connected to digital scanner

units are optically isolated by Opto couplers When CPU card scans the digital inputs it compares with the

previous stored data and if there is any change from the previous status then only that data will be stored (the

status conditions of relay) with date and real time A total of minimum 10 Lac events can be stored in

memory on first in first out basis so that latest data is available in the system There is no loss of data from

datalogger memory in case of power supply failure of datalogger

DIGITAL INPUT CARDS (IN-BUILT) This system is having maximum 8nos of inbuilt Digital inputs cards Maximum 64nos of digital

inputs can be connected to each digital input card The potential free relay contact may be front or back

contact terminated at the Tag Block from the relay of signals tracks points Buttons etc and are

17 | P a g e

subsequently connected to Digital input cards through Flat Ribbon Cable (FRC) connectors These in-built

digital input cards can monitor a total 512 nos of relays status

DIGITAL SCANNER UNIT (DSU) Each DSU contains 8 nos of Digital Input cards Each input card can be connected with 64 inputs

Total input capacity of DSU unit is 512 inputs These scanner cards contain Optocouplers and Multiplexer

Inputs are connected to Stag card The stag card out put is connected to DSU through FRC connectors

Maximum 7 nos of DSUs can be connected to the system So Digital input capacity of the system is 4096

All these digital inputs are scanned at rate of 16 msec

ANALOG SCANNER UNIT (ASU) ASU contains maximum 3 nos of Analog input cards Each input card can be connected with 8nos of

Analog inputs Total input capacity of the ASU is 24 analog input channels Maximum 4nos of ASUs can be

connected to the system Analog input channel capacity of the system is 96 All these analog inputs are

scanned at a rate of less than 1 sec

PARALLEL PORT Parallel port is provided for connecting printer

RS-232 SERIAL PORTS At least 6 Serial communication ports are provided for communication with other dataloggers

Central Monitoring Unit Remote Terminal Unit Electronic Interlocking system Integrated Power Supply

system etc

EXTERNAL NON-VITAL RELAY CONTACTS These relays provided in the system where 16 number of the Relay contacts are provided on the rear

panel through Tele control port to extend alarms and to control the power equipment from remote or local

locations through computer in case of any occurrence of failures Each control can sink or source 100 m

amps of current

INTERNAL MODEM CARD DUAL MODEM CARD (IN-BUILT) It is fixed in datalogger Euro rack itself One card contains two modems The top modem is called

ANS (answer) modem and the bottom modem is called as ORG (originate) modem It is used in case of

networking of Dataloggers In network connect lsquoANSrsquo modem to the lsquoORGrsquo modem of one adjacent station

and connect lsquoORGrsquo modem to the lsquoANSrsquo modem of other adjacent station

POWER SUPPLY Normally 24V DC (12V DC is optional) supply with battery backup is required for the system

working

Input Voltage Range 18Vhellip32V DC (For 24V) 9Vhellip18V DC (For 12V)

INPUT REQUIREMENTS Relay inputs (digital inputs) and analog inputs (voltages currents etc) are required to be connected

to the system as per the requirements of RRI PI SSI as the case may be Some of the inputs to be

monitored is given below

(a) Digital inputs

(i) Field inputs All TPRs NWKRs RWKRs ECRs Crank Handle relays SidingSlot LC gate

control relays etc

(ii) Control Panel inputs All button Knob SMrsquos Key relays

18 | P a g e

(iii) Internal relays

British system All HR DR HHR WNR WRR ASR UCR RR LR UYRTLSR TRSR TSR

JSLR JR etc

SIEMENS system Z1UR Z1UR1 GZR ZDUCR ZU(R)R ZU(N)PRG(R)RG(N)R U(R)S

U(N)PS UDKR DUCR U(R)LR UYR1 UYR2 G(R)LRGR1GR2

GR3 GR4 OVZ2U(R)RW(RN)R (RN)WLR Z1NWR Z1RWRZ1WR1 WKR1 WKR2 WKR3 etc

(b) Analog channels

(i) 230 V AC (for power supplies in the power panel)

(ii) 110V AC (for Signal and Track transformers)

(iii) 110V DC (for Point operation)

(iv) 60V DC (Siemens relays)

(v) 24V DC (Q-series relays)

(vi) 24V DC (for Block Axle counters)

(vii) 12V DC (for indication)

(viii) 20A (for point operation current)

(ix) 10V AC 5KHz (for Axle counter channels) etc

SOFTWARE MODULES OF DATALOGGERS

(a) Network Management of Dataloggers (NMDL)

(b) Reports

(c) Fault Entry

(d) Track Offline Simulation

(e) Train Charting

NMDL SOFTWARE FEATURES (a) Online Relay Status

(b) Online Faults - To view information of various Online Faults as they occur in the stations where

the Dataloggers are connected

(c) Online Simulation - Graphical view of relay operations train movements etc

(d) Remote monitoring of stations with the help of NETWORKING

SOFTWARE OBJECTIVES (a) Predictive Maintenance

(b) Easy identification of failures

(c) Crew discipline

(d) Train charting

REMOTE MONITORING OF STATIONS WITH NETWORKING OF

DATALOGGERS The individual Dataloggers of various stations can be interconnected through networking technology

The data of Remote Panel stations can be viewed in a Computer at the Central Monitoring Station The data

of the network is collected by the FEP (Front End Processor) which in turn is transmitted to the computer

COMPONENTS OF NETWORK MANAGEMENT OF DATALOGGERS

(a) Datalogger at stations

(b) MODEM and Transmission medium

19 | P a g e

(c) Front End Processor (FEP)

(d) Central Monitoring Unit (CMU) Computer

FEP (FRONT END PROCESSOR)

FEP acts as a buffer between the Central Monitoring Unit (Computer) and the Network It is provided

at centralised place to retrieve data continuously from station dataloggers and store in memory and transfer to

computer on request It stores 10 Lac telegrams It works on 12V DC It draws 16A continuous current

when all the three modems are connected Normally it shows the number of packets pending to be sent to the

computer on its 7-segment LED display It is provided with MOTOROLA 68000 microprocessor It has 6-

nos of RS-232 communication ports such as COM1 COM2 COM3 COM4 COM5 and COM6 COM1 is

used for Fault Analysis System (FAS) ie Central Monitoring Unit (Computer) connection COM2 to COM6

are used for networking For Bi-directional 2- nos of ports and for Tri-directional (T-network) 3-nos of ports

are used

DATA TRANSMISSION Dataloggers can be networked in Uni-directional Mode or Bi-directional Mode or T ndash Network Mode

In case of loss of data retransmission of data takes place

(a) Uni-Directional Mode

Each Datalogger will send data in only one direction to the FEP Unidirectional mode network is not

preferred

(b) Bi-Directional Mode

Each end of Network is connected to FEP and each datalogger can now transmit data in both the directions

Bi-directional Mode is advantageous it enables the Data Transmission even in case of Network Failure

(c) T - Network Mode

If more no of stations are in network ie if the network is too lengthy then T- network mode is preferred

COMMUNICATION The communication protocol for transmitting data and command between datalogger and CMU is

standardized by the RDSO and is given in the Specifications of Dataloggers

(a) The type of communication used in the network is dependent on the distance between the dataloggers

(b) For shorter distances Opto Converter Box- Opto isolated current loop communication is used

(c) For longer distances Modem (Dial-up leased) Fiber Optic Satellite Microwave communication

MODEMS Modems are used for DATA transfer between Dataloggers and Front End ProcessorThese are

configured to RS 232 Serial Communication Network is connected with two types of 4-wire modems

(a) Internal modem card Dual Modem card (in-built)

It is fixed in datalogger Euro rack itself One card contains two modems The top modem is called

ANS (answer) modem and the bottom modem is called as ORG (originate) modem

Note In case of networking of Dataloggers connect lsquoANSrsquo modem to the lsquoORGrsquo modem of one adjacent

station and connect lsquoORGrsquo modem to the lsquoANSrsquo modem of other adjacent station

(b) External modems

20 | P a g e

These are generally used at FEP (Front End Processor) side to connect the Dataloggers

(i) To transfer Data from one datalogger to another datalogger FEP Baud rate is 9600bps

(ii) These modems are 4-wire line communication

(iii) To transfer the data from FEP to RMU (PC) the Baud rate is 57600 bps

There is no difference between these modems functionally

CENTRAL MONITORING UNIT (CMU) COMPUTER

Central monitoring unit (Fault Analysis Unit) is a Personal Computer and its minimum configuration

shall be specified by RDSO from time to time System Software Windows XPVista(OS) Norton Kaspersky

(Anti Virus) Interbase where Server is not available (DBMS) Oracle where Server is available (DBMS)

software are required to run Datalogger System It is provided with Graphical User interface (GUI) based

software and retrieve data from all Networked dataloggers (up to 32) at various stations It stores data in

standard data base files The CMU is capable of analyzing the data and generate reports audiovisual alarms

on defined conditions This data can be compressed to take backup In central monitoring unit Software used

for analysis of data prediction of faults etc is written in a structured format so that purchaser can

reconfigure it if required It displays the status of signaling gears at any selected time in graphic form for any

selected station yard It retrieves the stored data amp simulates train movement It sends commands to various

Dataloggers to activate audio visual alarm or operate and electromagnetic relay

CMU shares data available in it by other PCs through available local area network where this data can

be used for train charting passenger information purpose The system generates audiovisual alarm in

ASMrsquosSignal Maintainerrsquos room in the case of power supply failure (battery voltage low) or battery charger

defective with acknowledgement facility

(a) Each datalogger has its own identity code which will be transmitted along with data packet to central

monitoring unit

(b) Events recorded at each station are continuously transmitted to central monitoring unit Response time of

data transfer will not exceed 10 sec

21 | P a g e

22 | P a g e

OPTICAL FIBER CABLE

INTRODUCTION The demand for bandwidth on transmission networks is increasing rapidly because video and

graphical rich contents are exchanged through the corporate network or the Internet The Gigabit Ethernet

became ommonly used in the corporate network backbone and 10Gbit Ethernet will be adopted in the near

future Meanwhile in the home the demand for high-speed network becomes popular as the wide spread of

broadband access eg CATV xDSL and FTTH The transmission medium with capability to transmit high

bit rate signal is necessary to satisfy these requirements

The telecommunication transport technologies move from copper based networks to optical fiber

from timeslot based transport to wave length based transport from traditional circuit switching to terabit

router and all optical based networks entering into a new era of optical networking

BASIC PHYSICS OF OFC

OPTICAL FIBER CABLE OFC have Fibers which are long thin strands made with pure glass about the diameter of a human

hair OFC consists of Core Cladding Buffers and Jacket as shown in figure

MONOCHROMATIC LIGHT OR SINGLE COLOR LIGHT Light or visible light is electromagnetic radiation of a wavelength that is visible to the human eye (

about 400 ndash 700 nm) The word light is sometimes used to refer to the entire electromagnetic spectrum Light

is composed of elementary particles called photons Three primary properties of light are

Light can exhibit properties of both waves and particles This property is referred to as wave-particle

duality The study of light known as optics In free space light (of all wavelengths) travels in a straight path

at a constant maximum speed However the speed of light changes when it travels in a medium and this

change is not the same for all media or for all wavelengths By free space it is meant space that is free from

matter (vacuum) andor free from electromagnetic fields

Thus the speed of light in free space is defined by Einsteinrsquos equation E = mc2

Frequency ν speed of light in free space c and wavelength λ are interrelated by ν = cλ

From the energy relationships E = mc2 = hν and the last one an interesting relationship is obtained

the equivalent mass of a photon m = hνc2

When light is in the vicinity of a strong electromagnetic field it interacts with it From this interaction

and other influences its trajectory changes direction as shown in figure

23 | P a g e

INCIDENT RAY REFLECTED RAY AND REFRACTED RAY An incident ray is a ray of light that strikes a surface The angle between this ray and the

perpendicular or normal to the surface is the angle of incidence Reflection is the change in direction of a

wave front at an interface between two different media so that the wave front returns into the medium from

which it originated Common examples include the reflection of light sound and water waves

The reflected ray corresponding to a given incident ray is the ray that represents the light reflected by

the surface The angle between the surface normal and the reflected ray is known as the angle of reflection

The Law of Reflection says that for a specular (non-scattering) surface the angle of reflection always equals

the angle of incidence The refracted ray or transmitted ray corresponding to a given incident ray represents

the light that is transmitted through the surface The angle between this ray and the normal is known as the

angle of refraction and it is given by Snells Law

The figure shows Incident ray Reflected ray Refracted ray the angle of incidence and angle of refraction

REFRACTIVE INDEX - Refractive index is the speed of light in a vacuum ( c =299792458kmsecond) divided by the speed

of light in a material ( v ) Refractive index measures how much a material refracts light Refractive index of

a material abbreviated as lsquo n lsquo is defined as lsquo n=cv lsquo Light travels slower in physical media than it does

when transmitted through the air Refractive index (n) is a function of molecular structure of matter optical

frequency optical intensity determines optical propagation properties of each wavelength ( λ ) may not be

distributed equally in all directions is affected by external temperature pressure and fields

Refractive index of a medium is a measure for how much the speed of light is reduced inside the

medium For example typical glass has a refractive index of 15 which means that light travels at 1 15 =

067 times the speed in air or vacuum Two common properties of glass and other transparent materials are

directly related to their refractive index

First light rays change direction when they cross the interface from air to the material and effect that

is used in lenses and glasses

Second light reflects partially from surfaces that have a refractive index different from that of their

surroundings

SNELLrsquoS LAW-

24 | P a g e

When light passes from one transparent material to another it bends according to Snells law which

is defined as n1sin(θ1) = n2sin(θ2)

where n1 is the refractive index of the medium the light is leaving θ1 is the incident angle between the light

beam and the normal (normal is 90deg to the interface between two materials)

n2 is the refractive index of the material the light is entering

θ2 is the refractive angle between the light ray and the normal

Snellrsquos law gives the relationship between angle of incidence and angle of refraction

For the case of θ1 = 0deg (ie a ray perpendicular to the interface) the solution is θ2 = 0deg regardless of

the values of n1 and n2 That means a ray entering a medium perpendicular to the surface is never bent The

above is also valid for light going from a dense (higher n) to a less dense (lower n) material the symmetry of

Snells law shows that the same ray paths are applicable in opposite direction

TOTAL INTERNAL REFLECTION- When a light ray crosses an interface into a medium with a higher refractive index it bends towards

the normal Conversely light traveling cross an interface from a higher refractive index medium to a lower

refractive index medium will bend away from the normal

This has an interesting implication at some angle known as the critical angle θc light traveling from

a higher refractive index medium to a lower refractive index medium will be refracted at 90deg in other words

refracted alon g the interface If the light hits the interface at any angle larger than this critical angle it will

not pass through to the second medium at all Instead all of it will be reflected back into the first medium a

process known as total internal reflection

The critical angle can be calculated from Snells law putting in an angle of 90deg for the angle of the refracted

ray θ2 This gives θ1

Since θ2 = 90deg

So sin(θ2) = 1

25 | P a g e

Then θc = θ1 = arcsin(n2n1)

For example with light trying to emerge from glass with n1=15 into air (n2 =1) the ritical angle θc is

arcsin(115) or 418deg For any angle of incidence larger than the critical angle Snells law will not be able to

be solved for the angle of refraction because it will show that the refracted angle has a sine larger than 1

which is not possible In that case all the light is totally reflected off the interface obeying the law of

reflection

OPTICAL FIBER MODE An optical fiber guides light waves in distinct patterns called modes Mode describes the distribution

of light energy across the fiber The precise patterns depend on the wavelength of light transmitted and on the

variation in refractive index that shapes the core In essence the variations in refractive index create

boundary

conditions that shape how light waves travel through the fiber like the walls of a tunnel affect how sounds

echo inside

We can take a look at large-core step-index fibers Light rays enter the fiber at a range of angles and

rays at different angles can all stably travel down the length of the fiber as long as they hit the core-cladding

interface at an angle larger than critical angle These rays are different modes Fibers that carry more than

one mode at a specific light wavelength are called multimode fibers Some fibers have very small diameter

core that they can carry only one mode which travels as a straight line at the center of the core These fibers

are single mode fibers This is illustrated in the following picture

OPTICAL FIBER INDEX PROFILE Index profile is the refractive index distribution across the core and the cladding of a fiber Some

optical fiber has a step index profile in which the core has one uniformly distributed index and the cladding

has a lower uniformly distributed index Other optical fiber has a graded index profile in which refractive

index varies gradually as a function of radial distance from the fiber center Graded-index profiles include

power-law index profiles and parabolic index profiles The following figure shows some common types of

index profiles for single mode and multimode fiber

26 | P a g e

OPTICAL FIBERrsquoS NUMERICAL APERTURE ( NA )- Multimode optical fiber will only propagate light that enters the fiber within a certain cone known as

the acceptance cone of the fiber The half-angle of this cone is called the acceptance angle (see figure 18)

θmax For step-index multimode fiber the acceptance angle is determined only by the indices of refraction

Where

n is the refractive index of the medium light is traveling before entering the fiber

nf is the refractive index of the fiber core

nc is the refractive index of the cladding

NUMBER OF MODES IN A FIBER - Modes are sometimes characterized by numbers Single mode fibers carry only the lowest-order

mode assigned the number 0 Multimode fibers also carry higher-order modes The number of modes that

can propagate in a fiber depends on the fiberrsquos numerical aperture (or acceptance angle) as well as on its

core diameter and the wavelength of the light For a step-index multimode fiber the number of such modes

Nm

Where

D is the core diameter

λ is the operating wavelength

NA is the numerical aperture (or acceptance angle)

MODE FIELD DIAMETER - All light do not travels through the core of the fiber but is distributed through both the core and the

cladding The mode field is the distribution of light through the core and cladding of a particular fiber

Mode-Field Diameter (MFD) defines the size of the power distribution When coupling light into or out of a

fiber MFD is important in understanding light loss

27 | P a g e

ADVANTAGE OF OFC COMMUNICATION - bull More information carrying capacity Fibers can handle much higher data rates than copper More

information can be sent in a second

bull Free from Electromagnetic and Electrostatic interference Being insulator no electric current flows through

the fibre and due to this reason fibres neither radiate nor pick up electro - magnetic radiation So WPC

CLEARANCE is not required

bull Low attenuation 025 dbkm at 1550 nm Loss in twisted pair and coaxial cable increases with frequency

where as loss in the optical fibre cable remains flat over a wide range of frequencies

bull Use of WDM ndash Switching routing at Optical signal level

bull Self healing rings under NMS control

bull Small size makes fibre cable lighter in weight So easy to handleOptic fibre cable weight (approx)

500 kg km Copper cable weight (approx) 1000 kgkm

The reasons are photons of light in a fibre

do not affect each other as they have no electrical charge and they are not affected by stray photons outside

the fibre But in case of copper electrons move through the cable and these are affected by each other

Optical fibre does not carry any electricity even if the cable is damaged or short circuited it does

not cause any spark or fire hazard

As the fibre do not radiate energy it can not be detected by any nearby antenna or any

other detector The fibres are difficult to tap and therefore excellent for security

As the signal transmission is by digital modulation there is no chance of cross talk in

between channels

Only by adding a few additional terminal and repeater equipments the

capacity of the system can be increased at any time once the cable is laid

ical effects and temperature variations

LIMITATIONS OF OFC -

difficult

- utilised

APPLICATION IN SIGNAL AND TELECOMMUNICATIONS transmission circuits

-haul circuits for linking of telephone exchanges

28 | P a g e

PROPAGATION MODES CONCEPT -

MODE - Mode is an available distribution of electromagnetic field in a plane transverse to the direction of

light propagation Each mode is characterized by frequency polarization electric field strength and

magnetic field strength Available patterns are derived from Maxwellrsquos equations and boundary conditions

LINEARLY POLARIZED (LP) MODE A mode for which the field components in the direction of propagation are small compared to

components perpendicular to that direction An optical fibre supports only different field patterns called as

lsquoLinear Polarizedrsquo or lsquo LPrsquo modes The reasons are

requirements

de

the accrual of power carried by different modes

There are two basic types of fiber Multimode fiber and Single-mode fiber

Multimode fiber is best designed for short transmission distances This is suited for used in LAN systems and

video surveillance Single mode fibre is best designed for longer transmission distances This is suitable for

long distance telephony and multi channel television broadcast systems

29 | P a g e

MULTI MODE FIBER Multimode fiber the first to be manufactured and commercialized simply refers to the fact that

numerous modes or light rays are carried simultaneously through the waveguide Modes result from the fact

that light will only propagate in the fiber core at discrete angles within the cone of acceptance MM fiber type

has a much larger core diameter compared to single-mode fiber allowing for the larger number of modes

and

is easier to couple than single-mode optical fiber Multimode fiber further categorized as Multimode step-

index and Multimode graded index fiber

PROPAGATION THROUGH MMSI FIBER Figure shows the principle of total internal reflection applies to multimode step index fiber Because

the corersquos index of refraction is higher than the claddingrsquos index of refraction the light that enters at less than

the critical angle is guided along the fiber

Three different light waves travel down the fiber One mode travels straight down the center of the

core A second mode travels at a steep angle and bounces back and forth by total internal reflection The third

mode exceeds the critical angle and refracts into the cladding Naturally it can be seen that the second mode

travels a longer distance than the first mode causing the two modes to arrive at separate times

PROBLEMS WITH MMSI FIBER AND SOLUTION This disparity between arrival times of the different light rays is known as dispersion and the result is

a muddied signal at the receiving end It is important to note that high dispersion is an unavoidable

characteristic of multimode step-index fiber The solutions are either use Graded index fiber or Single mode

fiber

PROPAGATION THROUGH MMGI FIBER Multimode Graded-index refers to the fact that the refractive index of the core gradually decreases

farther from the center of the core The increased refraction in the center of the core slows the speed of some

light rays allowing all the light rays to reach the receiving end at approximately the same time reducing

dispersion Figure shows the Light propagation principle through multimode graded-index fiber The corersquos

central refractive index ( nA ) is greater than that of the outer corersquos refractive index ( nB )

It is very clear from the figure the light rays no longer follow straight lines they follow a serpentine path

being gradually bent back toward the center by the continuously declining refractive index This reduces the

arrival time disparity because all modes arrive at about the same time The modes traveling in a straight line

30 | P a g e

are in a higher refractive index so they travel slower than the serpentine modes These travel farther but

move faster in the lower refractive index of the outer core region

PROPAGATION THROUGH SMSI FIBER Single mode fiber has a much smaller core that allows only one mode of light at a time to propagate

through the core The figure shows the single mode fiber

Single-mode fiber exhibits no dispersion caused by multiple modes Single-mode fiber also offers lower fiber

attenuation than multimode fiber Thus more information can be transmitted per unit of time because it can

retain the fidelity of each light pulse over longer distances Like multimode fiber early single-mode fiber was

generally characterized as step-index fiber meaning the refractive index of the fiber core is a step above that

of the cladding rather than graduated as it is in graded-index fiber Modern single-mode fibers have evolved

into more complex designs such as matched clad depressed clad and other exotic structures

SINGLE-MODE FIBER DISADVANTAGES The smaller core diameter makes coupling light into the core more difficult The tolerances for single-

mode connectors and splices are also much more demanding

CUTOFF WAVE LENGTH - Cutoff wavelength is the wavelength above which a single-mode fiber supports and propagates only

one mode of light In other words an optical fiber that is single-mode at a particular wavelength may have

two or more modes at wavelengths lower than the cutoff wavelength The effective cutoff wavelength of a

fiber is dependent on the length of fiber and its deployment The longer the fiber the lower is the effective

cutoff

wavelength The smaller the bend radius of a loop of the fiber the lower is the effective cutoff wavelength If

a fiber is bent in a loop the effective cutoff wavelength is lowered

SIGNAL ATTENUATION IN FIBER - Optical fiber has a number of advantages over copper However it also suffers from degradation

problems which can not be ignored The first of these is loss or attenuation Attenuation is typically the result

of two sub properties They are scattering and absorption Both of which have cumulative effects The second

is

dispersion which is the spreading of the transmitted signal and is analogous to noise

SCATTERING Scattering occurs because of impurities or irregularities in the physical construction of the fiber The

well known form of scattering is Rayleigh Scattering It is caused by metal ions in the silica matrix and

results in light rays being scattered in various directions

31 | P a g e

Scattering limits the use of wavelengths below 800nm The short wavelengths are much affected than longer

wavelengths It is because of Rayleigh scattering that the sky appears to be blue ( shorter wave length ) The

shorter wavelengths ( blue ) of light are scattered more than the longer wavelengths of light

ABSORPTION Absorption results from three factors They are hydroxyl ions ( OH- water ) in the silica impurities

in the silica and incomplete residue from the manufacturing process These impurities tend to absorb the

energy of the transmitted signal and convert it to heat resulting in an overall weakening of the signal The

Hydroxyl absorption occurs at 125 and 139 micro The silica itself starts to absorb energy at 17 micro

because of the natural resonance of the silicon dioxide

MACRO BENDING LOSS Macro-bending loss is caused by bending of the entire fiber axis The bending radius shall not be

sharper than 30d where d is diameter of cable A single bend sharper than 30d can cause loss of 05dB

The fiber may break if bending is ever sharper

MICRO BENDING LOSS Micro-bending loss is caused by micro deformations of fiber axis which leads to failures in achieving

total internal reflection conditions Micro-bends are small scale perturbations along the fiber axis the

amplitude of which are on the order of microns These distortions can cause light to leak out of a fiber

Micro-bending may be induced at very cold temperatures because the glass has a different coefficient of

thermal expansion from the coating and cabling materials At low temperatures the coating and cable

become more rigid and may contract more than the glass Consequently enough load may be exerted on the

glass to cause micro bends

Coating material is selected by manufacturers to minimize loss due to micro-bending The linear thermal

expansion coefficient of coating material shall be compatible with that of fiber

32 | P a g e

DISPERSION Dispersion is the optical term for the spreading of the transmits in the fiber It is the bandwidth

limiting phenomenon and comes in two forms Multimode dispersion and chromatic dispersion Chromatic

dispersion is further subdivided into material dispersion and waveguide dispersion

DISPERSION PHENOMENON IN OPTICAL FIBER Dispersion is the time distortion of an optical signal that results from the differences of time of travel

for different components of that signal typically resulting in pulse broadening As the distance traveled by

the signal is more broadening of pulse is more In digital transmission dispersion limits on the maximum

data rate and the maximum distance ie the information-carrying capacity of a fiber link The interference

from broadened pulse in the next interval shall not lead to erroneous interpretation of received signal

OPTICAL DOMAIN Understanding where attenuation and dispersion problems occur helps optical design engineers

determine the better wavelengths at which information can be transmit taking into account distance type of

fiber and the other factors which can severely affect the integrity of the transmitted signal The graph shown

depicts the optical transmission domain as well as the areas where problems arise The wavelength (nm)

is shown on X-axis and attenuation ( dBkm) is shown on Y-axis

There are four transmission windows appear in the figure The first one is at around 850 nm the

second at 1310nm third at 1550 nm and fourth at 1625 nm The last two labeled as C and L band

respectively The 850 nm wavelength at which the original LED technology operated The second window at

1310 nm has low dispersion The 1550 nm called as C-band is ideal wavelength for long haul

communication systems The network engineers can avoid transmitting signal at 1000 nm where Rayleigh

scattering 1240 and 1390 nm where hydroxyl absorption by water occurs to avoid high degree of loss

Optical fibers also can be manufactured to have low dispersion wavelength in the 1550nm region

which is also the point where silica-based fibers have inherently minimal attenuation These fibers are

referred to as dispersion-shifted fibers and are used in long-distance applications with high bit rates For

33 | P a g e

applications utilizing multiple wavelengths it is undesirable to have the zero dispersion point within the

operating

wavelength range

34 | P a g e

SIGNALLING RELAYS

INTRODUCTION A relay is an electromagnetic device which is used to convey information from one circuit to another

circuit through a set of contact ie front or back contact Constructional and electrically relays may be

divided into DC and AC relays because the means by which the electrical energy in the coil is converted in

to mechanical Energy in order to move the contacts are fundamentally different In DC type the contacts are

carried on an armature forming part of a magnetic circuit in which a field is set up by the current flowing in

the coils In AC types the contacts are attached by a link mechanism to a metal sector disc or cylinder in

which currents are induced by the alternating magnetic field produced by the currents in the coils

Every endeavor has been made to explain the action of each type of relay in the simplest possible manner

Relays are sophisticated switch gears used for remote control and succession control of various

electrical equipment In present days they are widely used because they are capable of protecting the

controlled equipment from cross feeding and overloading even as they cater for speedy operations

Most of the relays in present day signaling are electromagnetic devices although some of the relays control

circuits through electronic components like diodetransistors Integrated Chips etc

Railway signaling relays are unique in that

(a) They operate on low voltage and current

(b) They are more articulate as according to their special features they can work under restrictive conditions

and in any specified manner Virtually they can cater for all situations while contributing to speed and

accuracy in operations

CLASSIFICATION OF SIGNALLING RELAYS (a) According to the method of their mounting or fixture they are classified as

(i) Shelf type Relays which are loosely kept on shelves

(ii) Plug in type Relays which are plugged into a pre- wired plug boards

(b) According to their connection and usage they are classified as

(i) Track relays Relay which is directly connected to the track to detect the presence of vehicle

(ii) Line Relays Other than track relay all are line relays Relays connected to the selection circuit

(c) According to their vitality or importance in ensuring train working safety they are classified as

(i) Vital Relays All relays used for traffic control such as signal point controls track detection etc

(ii) Non-vital Relays Relays which operate control aids and accessories like warnings buzzers

Indications etc

(d) According to their special provisions to ensure reliability of their contacts they are classified as

(i) Proved type are those whose normalization after each operation shall be proved in circuit

controlled by their contacts Contacts in which both the springs have metal surfaces on their tips They may

get fused due to high sparking current across them during operation These may prevent relay normalization

and causes unsafe condition in traffic control To avoid this proving of relay normalization after each

operation is necessary

(ii) Non - proved type Need not to be proved to have been normalized after each operation as their

contacts have at least one non-fusible contact (carbon contact)

(e) According to their feed source relays are broadly classified as

(i) DC relays The relay which requires DC power supply for its operations are called DC relays Among

the DC relays

o DC neutral relays This relay closes the same set of contacts on energization with Normal polarity

or Reverse polarity supply

o Polar Relays This relay closes different set of contacts when energized with Reverse polarity

supply They may or may not have contact to close when deenergized

35 | P a g e

(ii) AC Relay AC Induction motor track relays Time element relays flashing indication control etc

(iii) Electronic Relays DC relays with electronic components in them are called electronic relays

DC NEUTRAL RELAY Each Relay has usually one or two coils with a hollow center to accommodate a coreThe coils are

made up of a large numbers of turns of small gauge soft drawn copper wire The two coils can be connected

in series or parallel according to the requirement of relay resistance The ends of the coils are terminated on

binding post to which the control wires are connected Each coil is placed around a core of specially selected

Iron or steel having high permeability and low retentivity The core should be susceptible to magnetism and

at the same time should have little residual magnetism The cores are connected at the top by a yoke to

complete the magnetism coupling between two ends of coils The bottom of each core is equipped with a

large steel or Iron block known as pole piece or face

A flat piece of Iron or steel called armature is supported by brackets which are securely fastened to

the pole piece The armature yoke and the pole pieces are also made of specially selected iron or steel of the

same quality as the core The armature carries the metallic spring contacts which are insulated from it

The circuit through the coils of the relay is closed It sets up a magnetic flux through the core yoke and the

armature The flux passing between the armature and pole faces causes the armatures get attracted to the pole

faces and armature picks up and closes front contacts When the circuit is opened the magnetic flux collapses

and the armature drops away by gravity from the pole faces the front contacts break and back contacts close

The front and back contacts of the relay can be utilised to make or break other circuits Two stop pins of

nonmagnetic material are fixed either on the armature or pole faces so that the armature cannot

come in contact with the pole faces It is essential to maintain a small air-gap between the armature and pole

faces so that low value of residual magnetism may not retain the armature in picked up position and causes

the relay to fail to drop away with a break in its control circuit

GENERAL USAGE

DC Neutral line relays are most commonly used for Railway Signalling controls and detection

Among them plug-in type relays are preferred in larger installations for space considerations Shelf type

relays are also in use mostly in wayside stations

There are many DC Neutral line relays in use with special features such as

(i) Delayed operation

(ii) Biased DC control

(iii) DC control unaffected by AC interference currents

(iv) Getting latched in operated condition till further feeding and others

Usage of DC polar relays is mostly in conjunction with block instruments that control traffic between

stations AC line relays are almost extinct in installations of British Signalling practice They are however

used for time control operations flashing indication control and such other special purposes in installations

with Siemens signalling practice widely Track relays are used according to the type of track detection

circuits chosen for a given location and context While most of the track circuits are still of the DC working

type requiring DC neutral track relays with them the prospects of their being replaced with Electronic track

circuits directly feeding DC line relays in future are great AC Track Circuits are used in DC Traction area

as conventional DC Track Circuits are not suitable there AC Track relays are used with them almost all of

the induction motor type In the British practice of signalling which was first introduced on Indian Railways

non-proved type relays with carbon to metal switching contacts are generally used for vital controls

They facilitate simple circuit designs But with the advent of German Practice introduced by Ms

Siemens later proved type relays with all metal to metal contacts are widely accepted in spite of

complications in circuit design caused by them A recent introduction is that of the same type relays made by

Ms Integra control However for some time now the appreciable features of both the practices are getting

36 | P a g e

incorporated together in the indigenous designs of signalling by railwaymen With this the usage of all types

of relays anywhere can be found without straight jacketed segration of relay types

CHARACTERSTIC OF ELECTRO-MAGNETIC RELAY The following are the characteristic of electro-magnetic relays A brief study of them helps in

understanding the choice of their components and designs features

1) Force of attraction

2) Effect of air gap

3) Effect of Hysterisis

4) Transient condition

FORCE OF ATTRACTION In any electro-magnetic system the force of attraction is given by

Where B - is the flux density a - is the cross sectional area of the particular part of the magnetic

circuit

In the case of a DC neutral Relay B is proportional to the current that is flowing in the coil

surrounding the electro-magnet and thus the force of the attraction is directly proportional to the square of the

current This square relationship has its own advantage especially in the case of DC track relay in that a

small reduction in the current will have a great effect on the working of the relay Also for a given change of

current the make and the break will be quicker with lesser possibility of arcing

EFFECT OF AIR GAP

Curve lsquoArsquo is magnetisation curve for the iron and is all practical purpose a straight line up to the

saturation point Curve lsquoBrsquo is the magnetisation curve for the open-air gap which is a straight line through

out because per magnetisation curve of the whole

magnetic circuit of the relay and for a given force is the sum of the amp-turns for the iron part and the amp-

turns for the air gap

When the front contacts are open the force required to pick up the armature is shown on curve lsquoCrsquo to be F1

but after the armature has operated it will be separated from the core by stop pins In this position the amp-

turns required to maintain the armature is less as indicated by the dotted line from 1 on curve C to 2 on curve

37 | P a g e

F But actually the current in the coil is unaltered the force on the armature is greater than required as

indicated at 3 on curve F Part of this extra force is used to flex the front contacts sufficiently to give good

contact pressure when it is in energised position

The difference between the pick-up and the drop-away current should be as small as practicable in

track relay to ensure good shunting characteristics This is achieved firstly by the choice of good quality relay

iron and secondly by having a small air gap between armature and core If the air gap is not available then

the residual magnetism fluxes might cause the armature to be retained when the supply is disconnected For

this reason residual pins are provided to ensure a definite minimum air gap in the energised position

EFFECT OF HYSTERISIS

Hysterisis is the property by which the flux produced lags behind the current In the de-energized

condition there will be small residual flux in the core When the voltage is applied to the coils the current in

rising to its steady value first causes the flux to rise from 1 to 2 along the curve At this point the flux density

will be sufficient to attract the armature and reduce the air gap the flux then raise to 3 and continue to 4

which corresponds to the steady current in the coils When the voltage is disconnected the current in falling

caused the flux to fall from 4 to 5 along the curve At this point the flux density will fall below the value

required to maintain the armature which will release thus increasing the air gap and reducing the flux to 6

Finally the

flux will decrease from 6 to 1 where the current will again be zero

The relay core is made of material having high permeability and low retentivity As mentioned in

the IRS specification Electromagnet iron may be in the form of a

(a) Bar of silicon steel

(b) Best Yorkshire wrought iron

(c) Swedish charcoal iron

(d) Electrical steel sheets

` This reduces the difference between pick up value and Drop away value By selecting good quality

core material Percentage release and sensitivity of the relay will be improved

TRANSIENT CONDITION

38 | P a g e

When the voltage is applied or disconnected from the coils it takes some little time before the current

become steady These are known as transient conditionsrdquo and are important so far as track relays are

concerned When the voltage is first applied to the coils the magnetic flux in rising cuts the turns on the

coils and in so doing produces a back EMF that opposes the applied voltage and retards the growth of

current

The growth and decay of flux are decided by the relationship between the inductance and resistance

in the circuit is known as time constant It is not fixed quantity in the case of DC neutral relay This value of lsquo

Lrsquo is less when the relay is in de-energised condition (L1) than when the relay is in energised condition (L2)

The magnitude of flux that is established for a given change of current is different in two cases

When the current reaches the pick up value the armature closes and the inductance is increased to L2

due to reduced air gap the flux per amp is increased The increase in flux increased the back EMF during the

movement of the armature after which the current continuous to raise along a new curve corresponding to the

increased inductance until it reaches the final value (ER) This process is indicated above in fig24

When the supply is disconnected the current is obliviously reduced to zero immediately but the flux

decay comparatively slowly owing to the eddy currents produced in the core by the rapid flux change which

tend to maintain the flux The drop away time on a disconnection is however generally negligible See fig

below

If the relay releases due to the reduction in current from say I 2 to I 1 caused by the application of

shunt resistance (as in the case of track relay ) the time taken is much longer than the relay is simply

disconnected The rate of rise or fall of current during the transient conditions is also depends on exterior

circuit values because L and R apply to the whole circuit The production of eddy current in the core the flux

will decay at a slower rate than the current So that the actual release time will be a little longer than it takes

the current to fall to the release

L= Inductance

39 | P a g e

R= Resistance

It is now clear that to reduce releasing time to a minimum it is necessary that

- The relay iron should have low Hysterisis loss and low retentivity

- The degree of over energization of the relay should be restricted

- Connecting a suitable external resistance in series with the relay to keep LR ratio low

In non RE area for track circuit length less than 100M 9 ohm track relay only to be used Using relay

with minimum contacts as they require lesser current which keeps inductance value low

Train working safety is ensured only if the track relay of shortest length track circuit is released

before a light engine running at a highest permitted speed clears it Otherwise the track circuit occupation

may go undetected To avoid this a special provision has to be made in signal control circuits wherever

necessary

The following methods may be adopted for reducing the time lag of track relay

(a) Restrict the over energisation of relay since the release time depends on the initial working current

(b) Connecting a suitable external resistance in series with the relay to keep the LR ratio low

(c) Using relays with minimum contacts as they require lesser operating current keeping the inductance

value low

40 | P a g e

CONCLUSION

Modern signalling is vital for safe and punctual movements of trains In the Indian railways The Signalling

and Telecommunication Department is responsible for providing modern effective and relaible signalling

systems as well as telecommunication systems

The first mode of communication used in Indian Railways was the use of electric telegraph

with the help of Morose code Morose code is the method of providing text information as a series of on-off

tones and lights or clicks that can be directly understood by a skilled listener or observer without special

equipmentEach character (letter or numeral ) is represented by a unique sequence of dots and dashes Later

this system becomes obselete and beggan the era of wireless communication which operated at audio level

frequency range

In wireless communication the significant advances took place the transition to miniature

valves or filament tubesBut this was abandoned too because of excessive current consumption and over

heating of the filament tubes

Fibre-optic communication is a method of transmitting information from one place to another by

sending pulses of light through an optcial fibreThe light forms an electromagnetic carrier wave that is

modulated to carry information First developed in the 1970s fibre optic communication systems has

revolutionized the telecommunications industry and have palyed a major role in the advent of the information

age Because of its advantages over electrical transmissionsoptical fibres have largely replaced copper wire

communications in core networks in the developed world The Indian Railways too is undergoing a transition

from Microwave communication to fibre optic communications

41 | P a g e

BIBLIOGRAPHY AND REFERENCES

1 wwwwikipediacom

2 wwwbritaniccacom

3 wwwirfcacom

4 Motorola GP60 system manual

5 Harris FAS 7000 manual

6 TOSHIBA Manual

8 | P a g e

battery banks are avoided Reduction in Battery maintenance amp less flour area required

DC-DC Converters working from 110V Central battery have been used for all dc supplies This has

improved overall efficiency of the system since number of conversion from AC to DC have been

reduced to 2 stage as compared to 3 stage conversion in case of transformer-rectifier system

DC-DC converters are available in modules Easy replacement of defective modules This ensures

less down time

DC-DC Converters are used in load sharing N+1 configuration (ie with hot standby with N+1

modular technology) to improve the reliability amp availability of the system

Capacity of inverter has been brought down to 15 KVA from 5 KVA and used for feeding only

Signals supply Hot standby inverter is provided with auto changeover facility This improves the

availability of the overall system

High efficiency inverter is used with PWM (Pulse Width Modulation) technology in place of Ferro-

resonant technology based inverter This improves the efficiency of the overall system

Continuous power to Signal Circuits even in absence of DG setLocal Power Supply

Generators need not be switched ON every time during train movement

Metal-to-metal relay installations and block working by axle counters have also been covered

Supply of spare modulesComponentsCells have been included as part of main supply

Provides highly regulated voltage to all signal relays amp lamps for better life

9 | P a g e

SINGLE SECTION DIGITAL AXLE COUNTER

INTRODUCTION- The axle counter equipment is working on high frequency and using amplitude modulation or phase

modulation for detection of presence of wheel The equipment described in this notes is Phase modulation type

for the detection of presence of wheel In the Phase modulation type track device the detection of presence of

wheel is with the phase reversal of 1800 out of phase which enables this system to be more healthy and safe

In Phase Reversal Modulation technique trolley suppression arrangements to prevent the counting of

wheels caused by push trolley passing over the track device are not required as the system will take care of

validation of generated pulses caused by passage of wheel over the track device depending up on the phase

shift of the pulse This phase shift of the pulse may be normally 160deg to 180deg for a train wheel and it may be

approximately 100deg to 120deg for a push trolley wheel

This is Digital Axle Counter equipment for single track sections containing 2 out of 2 micro-

controllers to count the axles establish the track occupancy of a track section and to provide this information

to the block or the interlocking equipment

In this system no separate evaluator is required and no analog data is being transmitted One set of

Axle counter equipment is provided at entry end and other set provided at exit end Both sets are being

connected through a twisted pair of telecom cable ie existing RE cable one PET quad is used for both UP

and DN Axle Counters Digital DATA is being transmitted between two ends of Axle counters (Outdoor

track side Detection points)This system is a fully duplex capable of operating according to CCITT V21 and

the Data will be transmitted at the rate of 300bitsec This data Transmitted ensure negligible interference of

the noise The system is highly reliable

FEATURES (a) The system consists of

(i) Single Section Digital Axle Counter (SSDAC) units

(ii) Tx Rx coils

(iii) Vital Relays

(b) TxRx coil axle detectors are mounted to the web of the rails The design of system consists of 21 KHz amp

23 KHz High frequency Phase Reversal type axle detectors

(c) Compatible with 90R 52Kg amp 60Kg rail profiles Easy to install commission amp maintain

(d) Track devices at both (entry amp exit) points of the section should be fixed on the same rail

(e) System is designed to detect the solid wheels with diameter gt 400mm with standard wheel flange

(f) The system works in pairs For monitoring single-track section one pair of SSDAC units are required and

to be installed near the trackside one at the beginning and another at the end of the track section ie

Trackside electronic counting equipment

(g) The basic design of the system is based on counting the number of axles passing at each detection point

These stored counts are transmitted to the second unit of the system and vice versa by means of modem

communication

(h) The communication consists of digital packets having details of Counts amp Health

10 | P a g e

(i) If counts registered at both detection points are equal the section is cleared otherwise the section is shown

as occupied The system ensures no error condition to arrive at the decision of clearance

(j) System is designed as per CENELEC SIL-4 (European standard) using micro controller along with other

electronic circuits and programmed using dedicated software When any of these circuits fail the system

goes to fail safe condition

(k) It is programmable for either Preparatory Reset or Conditional Hard Reset as per requirement

(l) Micro controller based design with 2 out of 2 decisions and counting through software

(m) V21 Modem communication (2-wire) on frac12 quad cables and also compatible to work on voice channel of

OFC amp Radio

(n) Opto isolated vital relay drive for Q-style 24V 1000 _ and Vital Relay output can be giving at both ends

of the system

APPLICATIONS The system can be widely used in Railways for Block Working (BPAC) Intermediate Block Signaling Auto

signalling and Track circuiting for i) Loop line ii) Main line iii) yard lines

SYSTEM DESCRIPTION

This system comprises of

Tx coils-2 nos

Rx coils-2 nos

Reset Box (RB 258A)

Card 1 Signal Conditioning Card ndash 1

Card 2 Signal Conditioning Card - 2

Card 3 Micro controller Logic Board ndash 1

Card 4 Micro controller Logic Board ndash 2

2 nos for independent resetting ndash when used in block sections

1 no for common resetting ndash when used for Track circuiting at stations

Card 5 Event Logger Card

Card 6 Modem Card

Card 7 Relay Driver Card

Card 8 DC-DC Converter Card

SSDAC (DACF 700AP) UNIT

(A) SIGNAL CONDITIONING CARD (CARD 1amp2) (SCC) -1 (SCC-1) generates 21 KHz carrier

signals

-2 (SCC-2) generates 23 KHz carrier signals which is transmitted to 2nd

set of Tx coils

s receive these signals

modulated

train pulses

11 | P a g e

(B) MICRO-CONTROLLER LOGIC BOARD CARD (CARD 3amp4) (MLB) The Micro-controller Logic Board (MLB) is the heart of the system

o 8051 Based Architecture

o 8 Bit Micro Controller

o ATMEL AT89S8252 Micro controller

o 2 out of 2 Decision

o Uses C subset language

- TOOLS

o KEIL μ Vision Development System

o Universal Programmer

o 2KB Program Memory

o 256 bytes RAM

o 8KB Flash memory

o 32 Programmable IO lines

o Wide Operating Voltage range of 4V-6V

o Full Duplex Serial Port

o Programmable Watch Dog Timer

o Fully Static operation up to 24MHz (Upgraded to 40MHz)

o Operating Temperature of ndash40degC - +85degC

o Use of State Machine for Axle Counting

o Use of ASCII MODBUS protocol

o Use of CRC16 technique for Error Checking during communication

o Wheel detection

o Train direction checking and

o Wheel counting functions

o It receives the remote wheel count and computes the status of the section for clear or occupied

o It also checks various supervisory signal levels like supervisory of TxRx coils presence of various

cards communication link failure etcThese cards communicate with each other for wheel count

At Entry-end if train enters into section (1st detection) the counts are incremented and when train

shunts back from the same detection ie if train exits from the section from the same detection the counts are

decremented At Exit-end if train enters into section (2nd detection) the counts are decremented and when

train shunts back from the same detection ie if train exits from the section from the same detection the

counts are incremented Both the track devices at Entry and Exit ends must be fixed on same side of the

track

This MLB card is having Extensive LED display

o A block of 8 LED indicators for count progress error display

o 2 independent LED indicators for section status

o The errors occurring in the system during the operation of the SSDAC are encoded and are indicated by

means of the 8-LED block present on the front panel of the MLB cards

(c) EVENT LOGGER CARD (CARD 5)

Event logger card is designed to capture and store important signals from the remote and local SSDAC units

The stored data can be downloaded from the event logger card for the purpose of analyzing the events

occurring during the operations of the SSDAC The data can be analyzed with the help of CEL data analyzer

software

12 | P a g e

The event logger card captures following signals

(i) Pulse signals

(ii) Supervisory signals

(iii) Card removal information

(iv) Serial packets from

Event Logger card has a Rabbit processor and 2 MB FLASH MEMORY to store packets The data is initially

stored in the buffer and subsequently transferred to FLASH memory every two minutes Normally 4096

pages of the data can be stored in flash memory on FIFO (first in first out) basis

Run This LED blinks continuously indicating the normal working of the event

Log This LED blinks whenever data is being logged into the flash memory (Approx after every 2 minutes)

Dnld This LED is ON when data is being downloaded from the flash memory of the card and becomes OFF

when download is complete

(D) MODEM CARD (CARD 6) (i) The modem card transmits and receives the digital packet information form one counting unit to the other

The packet will appear after every 18 sec and the packet carries the latest information such as

(ii) The modem card being used is V21 type (2-wire) in SSDAC

(iii) This card interfaces with serial RS232C port of both Micro-controller Logic Boards

(iv) It multiplexes the two RS232C inputs and selects one of the two channels and provides signal conversion

from digital to analog (FSK modulation) and vice-versa

(v) Data transmission rate is 300 bitssec

(vi) Automatic Gain Control circuit is incorporated hence no gain adjustments required

(vii) Mode selection on Modem card The modem has been set in lsquoORIGINATORrsquo mode for entry and in the

lsquoANSWERrsquo mode for exit in the factory

(viii) LED Indications provided on Modem card

-Transmitting the signal when LED is flashing

- Receiving the signal when LED is flashing

-Remains OFF in SSDAC

-Carrier is detected when LED is glowing

(E) RELAY DRIVER CARD (CARD 7) (i) The Relay Driver card (RD) provides the 24V DC output required for driving Vital Relay

(ii) One RD card is used in each SSDAC counting unit The RD card receives the command of clear and

clock signals from MLB1 amp MLB2 cards and drives the vital relay lsquoONrsquo when section is NOT OCCUPIED

through opto- isolator circuit

(iii) If a train occupies the section the vital relay is dropped The vital relay status is read back by the system

as per the driving output

(iv) It has

13 | P a g e

ndash LED flashes when the section is clear

ndash LED flashes when the section is clear

All the above LEDrsquos are lit for section clear condition

(F) DC-DC CONVERTER CARD (CARD 8)

INPUT VOLTAGE Nominal Voltage voltage 24V DC Maximum current drain= 12A

Required voltage 18V DC to 30V DC

Output voltage

Nominal Voltage +5 V DC 2 A Required voltage 4 7 5 t o 525V DC

Nominal Voltage +12V DC 200 mA Required voltage 1175 to 1225V DC

Nominal Voltage +24V DC 300 mA with common ground Required voltage 235 to 245V DC

Nominal Voltage +15V DC 100 mA with isolated ground Required voltage 145 to 155V DC

SURGE VOLTAGE AND LIGHTNING PROTECTION Transient surge voltages arise as a result of Lightning discharge switching operations in electrical

systems and electrostatic discharge These surge voltages often destroy the electronic equipment to a large

extent In order to prevent surge voltages from destroying the equipment all the input lines of SSDAC ie

Power Supply (24V) Reset (48V) amp Modem is to be routed through surge voltage protection devices for

effectively protecting the system These devices (3 numbers) are mounted in a box and supplied along with

the system One number of box is to be installed at each location and wired to the SSDAC

Each surge voltage protection device consists of two parts

(a) Base

(b) Plug Trab

The Base of the device is used for wiring the input and output signals The connection details from relay

room to the box and from box to SSDAC unit are provided on the box The Plug Trab consists of MOV and

GD Tube and diverts the excess energy during surge voltages or lightning into the ground connection The

operation of these devices relies on a high quality ground connection in order to safely shunt away the

unwanted energy The impedance of the ground connection is critical and it should be less than 2 Ohms

NOTE The 3 Plug Trab connections are not to be interchanged with one another The plug Trab is a

detachable device and can be replaced with SPARE unit in case of blown device which is indicated by

means of LED for 24 V

EFFECTIVENESS OF PLUG TRABS The effectiveness of plug Trab depends wholly on the Earth connection provided to the system The earth

provided to the system should be less than 1 ohms and connections should be firm and proper to the SSDAC

unit VR box etc

SURGE VOLTAGE AND PROTECTION DEVICE SV-120 The Surge Voltage protection device is to be installed at each location along with every SSDAC unit

14 | P a g e

EARTHING- The lead wires connecting the installation and the earth electrode shall ordinarily be of stranded

copper wire of 29 sq mm (19 strand wires of 14 mm diameter) Copper wire has been specified because GI

wires usually are having greater corrosion However in areas where copper wire may be frequently stolen

due to theft ACSR of size 64 sq mm (19 strands of 211 mm diameter) may be used

LIMITS OF EARTH RESISTANCE (a) Apparatus case connected to Earth (SSDAC and vital Relay Box is housed in Apparatus case and

Connected to earth at outdoor) shall be less than or equal to 1 ohm

(b) All cable connected to same earth shall be less than or equal to 1 ohm

(C) Reset box connected to earth near SM s Room shall be less than or equal to 1ohm

EQUIPMENT TO BE EARTHED A Common Earth should be provided for SSDAC for items 1(a) amp (b) of the above at the outdoor

(a) The Apparatus Case is to be connected to earth (the chassis of SSDAC amp Vital Relay Box should be

properly connected to apparatus case)

(b) Metallic sheath and armouring of all the underground main cables are to be earthed

(i) In RE area the metallic sheath and armouring of main telecom cables are earthed at both ends

(ii) In RE area the armouring of Jelly filled cable shall be earthed at both ends

(c) The Earthing shall be provided at every location box where cables are terminated

(d) Earth already available for other equipment may be used for earthing of Reset Box near SM s Room

Cabin etc

15 | P a g e

DATALOGGER

INTRODUCTION Datalogger is a Microprocessor based system which helps in analysing the failures of relay inter

locking system Electronic Interlocking system This is like a black box which stores all the information

regarding the changes take place in relays AC DC Voltages and DC currents along with date and time The

same information data can be transferred to the computer to analyse further ldquoon line ldquooff linerdquo analysis of

stored date A print out also can be obtained through a printer by connecting directly to the datalogger unit

The data belongs to Relay contacts is considered as digital inputs and the data belongs to voltage

levels currents is considered as Analog inputs Datalogger lsquos are mandatory for all new relay interlocking

(PIRRI) EI installations and it is also recommended to provide in all existing PIs RRIs To increase the

line capacity mechanical signalling equipments are upgraded to PI RRI or EI Due to complexity in the

circuits and wiring sometimes it is very difficult to rectify the failures So datalogger can monitor these

systems with real time clock Thus it can be named as black box of Samp T equipments and hence it is a vital

tool for accident investigation Datalogger is used at Stations yards Whereas in case of Auto Section amp IBH

Mini dataloggers called as Remote Terminal Unit (RTU) are used

ADVANTAGES OF DATALOGGERS (a) Dataloggers helps in monitoring the typical failures such as intermittent auto right failures

(b) It helps in analyzing the cause of the accidents

(c) It helps in detecting the human failures errors such as

(i) Drivers passing signal at Danger

(ii) Operational mistakes done by panel operators ASMrsquos of operating department

(iii) Signal and telecom engineering interferences in safety circuits

(iv) Engineering and electrical department interferences failures

(v) It helps as a ldquoTOOLrdquo in preventive maintenance of signaling gears

(d) Dataloggers can be connected in network Networked dataloggers helps to monitorthe PIRRIEI remotely

(e) Failure reports can be generated remotely with help of datalogger network

(f) On line and Off line track simulation is possible

(g) Speed of the train on point zones can be calculated

(h) Age of the equipment in terms of number of operations etc

COMMON EQUIPMENT FOR ALL DATALOGGERS ARE GIVEN

BELOW (a) CPU card

(b) Digital and Analog input cards

(c) Local terminal(PC)

(d) communication links

(e) Printer

All the dataloggers requires a potential free ( spare ) relay contact for monitoring digital inputs

through Digital input cards amp for monitoring Analog inputs such ACDC bus bar voltage levels through

Analog input cards Digital and Analog inputs are connected to the Processor card Processor card consists of

memory ICrsquos Memory ICrsquos are programmed as per requirement of the signal engineers

Provision of Dataloggers is mandatory with RRI systems and is optional for PI systems as per

amendment to the specification for Relay Interlocking systems ( IRSS-36 ) The data collected by the

datalogger can be used for failure analysis repetitive discrepancies and for accident investigations

16 | P a g e

Note

If the serial communications is more than 50m then line drivers shall be used up to 3 Kms

4wire leased line Modems shall be used if the serial communication is more than 3 Kms

STUDY OF EFFTRONICS DATALOGGER TECHNICAL DETAILS (a) 24V 12VDC Power Supply

(b) Total Storage Capacity of 10 Lakh events

(c) In-built Temperature sensors

(d) Internal Buzzer for alarming during failures

(e) Real Time clock with internal battery backup with data retention up to 10 years

(f) 512 LED matrix to indicate the status of 512 Digital inputs at a time page wise

(g) Seven segment LCD screen (2x24) to display the status of digitalanalog signalsTime Temperature etc

(h) Using the keyboard various functions can be viewed in the LCD panel

(i) Max Digital Inputs 4096

(j) Max Analog Inputs 96

(k) Digital Input Scanning Time 16 millisecond

(l) Analog Input Scanning Time is less than 1 Sec

HARDWARE (EQUIPMENT) Datalogger system consists of

(a) Datalogger (CPU - with Microprocessor 68000)

(b) Digital input cards

(c) Dual modem card

(d) Digital Scanner units (DSU)

(e) Analog Scanner units (ASU)

CPU CARD It is provided with Motorola microprocessor M 68000 It performs all the activities pertaining to the

datalogger It continuously scans (check) the Digital inputs(inbuilt) Digital Scanner Units and Analog

Scanner Units ie scanning of digital signals (Relay operations) for every 16-milli seconds and scanning of

analog signals (ie ACDC voltages amp DC currents) for less than 1 second

This card will support the IO interfaces of LCD (Liquid Crystal Display) - 2X24 alphanumeric Key

Board LED Matrix Display Real Time Clock LCD display and keyboard This will acts as man machine

interface between the datalogger and the signal engineer All the operations (Software) can be performed

using this LCD and keyboard

Real time display with 7 Segments This is built in real time clock within Datalogger and its current

time will be displayed on six 7-segment display provided (Real time clock depend upon DALLAS 1286

chip) This IC will come with internal battery backup hence there is no need to add external batteries

CPU card continuously scans (checks) the DSUs and ASUs Each input connected to digital scanner

units are optically isolated by Opto couplers When CPU card scans the digital inputs it compares with the

previous stored data and if there is any change from the previous status then only that data will be stored (the

status conditions of relay) with date and real time A total of minimum 10 Lac events can be stored in

memory on first in first out basis so that latest data is available in the system There is no loss of data from

datalogger memory in case of power supply failure of datalogger

DIGITAL INPUT CARDS (IN-BUILT) This system is having maximum 8nos of inbuilt Digital inputs cards Maximum 64nos of digital

inputs can be connected to each digital input card The potential free relay contact may be front or back

contact terminated at the Tag Block from the relay of signals tracks points Buttons etc and are

17 | P a g e

subsequently connected to Digital input cards through Flat Ribbon Cable (FRC) connectors These in-built

digital input cards can monitor a total 512 nos of relays status

DIGITAL SCANNER UNIT (DSU) Each DSU contains 8 nos of Digital Input cards Each input card can be connected with 64 inputs

Total input capacity of DSU unit is 512 inputs These scanner cards contain Optocouplers and Multiplexer

Inputs are connected to Stag card The stag card out put is connected to DSU through FRC connectors

Maximum 7 nos of DSUs can be connected to the system So Digital input capacity of the system is 4096

All these digital inputs are scanned at rate of 16 msec

ANALOG SCANNER UNIT (ASU) ASU contains maximum 3 nos of Analog input cards Each input card can be connected with 8nos of

Analog inputs Total input capacity of the ASU is 24 analog input channels Maximum 4nos of ASUs can be

connected to the system Analog input channel capacity of the system is 96 All these analog inputs are

scanned at a rate of less than 1 sec

PARALLEL PORT Parallel port is provided for connecting printer

RS-232 SERIAL PORTS At least 6 Serial communication ports are provided for communication with other dataloggers

Central Monitoring Unit Remote Terminal Unit Electronic Interlocking system Integrated Power Supply

system etc

EXTERNAL NON-VITAL RELAY CONTACTS These relays provided in the system where 16 number of the Relay contacts are provided on the rear

panel through Tele control port to extend alarms and to control the power equipment from remote or local

locations through computer in case of any occurrence of failures Each control can sink or source 100 m

amps of current

INTERNAL MODEM CARD DUAL MODEM CARD (IN-BUILT) It is fixed in datalogger Euro rack itself One card contains two modems The top modem is called

ANS (answer) modem and the bottom modem is called as ORG (originate) modem It is used in case of

networking of Dataloggers In network connect lsquoANSrsquo modem to the lsquoORGrsquo modem of one adjacent station

and connect lsquoORGrsquo modem to the lsquoANSrsquo modem of other adjacent station

POWER SUPPLY Normally 24V DC (12V DC is optional) supply with battery backup is required for the system

working

Input Voltage Range 18Vhellip32V DC (For 24V) 9Vhellip18V DC (For 12V)

INPUT REQUIREMENTS Relay inputs (digital inputs) and analog inputs (voltages currents etc) are required to be connected

to the system as per the requirements of RRI PI SSI as the case may be Some of the inputs to be

monitored is given below

(a) Digital inputs

(i) Field inputs All TPRs NWKRs RWKRs ECRs Crank Handle relays SidingSlot LC gate

control relays etc

(ii) Control Panel inputs All button Knob SMrsquos Key relays

18 | P a g e

(iii) Internal relays

British system All HR DR HHR WNR WRR ASR UCR RR LR UYRTLSR TRSR TSR

JSLR JR etc

SIEMENS system Z1UR Z1UR1 GZR ZDUCR ZU(R)R ZU(N)PRG(R)RG(N)R U(R)S

U(N)PS UDKR DUCR U(R)LR UYR1 UYR2 G(R)LRGR1GR2

GR3 GR4 OVZ2U(R)RW(RN)R (RN)WLR Z1NWR Z1RWRZ1WR1 WKR1 WKR2 WKR3 etc

(b) Analog channels

(i) 230 V AC (for power supplies in the power panel)

(ii) 110V AC (for Signal and Track transformers)

(iii) 110V DC (for Point operation)

(iv) 60V DC (Siemens relays)

(v) 24V DC (Q-series relays)

(vi) 24V DC (for Block Axle counters)

(vii) 12V DC (for indication)

(viii) 20A (for point operation current)

(ix) 10V AC 5KHz (for Axle counter channels) etc

SOFTWARE MODULES OF DATALOGGERS

(a) Network Management of Dataloggers (NMDL)

(b) Reports

(c) Fault Entry

(d) Track Offline Simulation

(e) Train Charting

NMDL SOFTWARE FEATURES (a) Online Relay Status

(b) Online Faults - To view information of various Online Faults as they occur in the stations where

the Dataloggers are connected

(c) Online Simulation - Graphical view of relay operations train movements etc

(d) Remote monitoring of stations with the help of NETWORKING

SOFTWARE OBJECTIVES (a) Predictive Maintenance

(b) Easy identification of failures

(c) Crew discipline

(d) Train charting

REMOTE MONITORING OF STATIONS WITH NETWORKING OF

DATALOGGERS The individual Dataloggers of various stations can be interconnected through networking technology

The data of Remote Panel stations can be viewed in a Computer at the Central Monitoring Station The data

of the network is collected by the FEP (Front End Processor) which in turn is transmitted to the computer

COMPONENTS OF NETWORK MANAGEMENT OF DATALOGGERS

(a) Datalogger at stations

(b) MODEM and Transmission medium

19 | P a g e

(c) Front End Processor (FEP)

(d) Central Monitoring Unit (CMU) Computer

FEP (FRONT END PROCESSOR)

FEP acts as a buffer between the Central Monitoring Unit (Computer) and the Network It is provided

at centralised place to retrieve data continuously from station dataloggers and store in memory and transfer to

computer on request It stores 10 Lac telegrams It works on 12V DC It draws 16A continuous current

when all the three modems are connected Normally it shows the number of packets pending to be sent to the

computer on its 7-segment LED display It is provided with MOTOROLA 68000 microprocessor It has 6-

nos of RS-232 communication ports such as COM1 COM2 COM3 COM4 COM5 and COM6 COM1 is

used for Fault Analysis System (FAS) ie Central Monitoring Unit (Computer) connection COM2 to COM6

are used for networking For Bi-directional 2- nos of ports and for Tri-directional (T-network) 3-nos of ports

are used

DATA TRANSMISSION Dataloggers can be networked in Uni-directional Mode or Bi-directional Mode or T ndash Network Mode

In case of loss of data retransmission of data takes place

(a) Uni-Directional Mode

Each Datalogger will send data in only one direction to the FEP Unidirectional mode network is not

preferred

(b) Bi-Directional Mode

Each end of Network is connected to FEP and each datalogger can now transmit data in both the directions

Bi-directional Mode is advantageous it enables the Data Transmission even in case of Network Failure

(c) T - Network Mode

If more no of stations are in network ie if the network is too lengthy then T- network mode is preferred

COMMUNICATION The communication protocol for transmitting data and command between datalogger and CMU is

standardized by the RDSO and is given in the Specifications of Dataloggers

(a) The type of communication used in the network is dependent on the distance between the dataloggers

(b) For shorter distances Opto Converter Box- Opto isolated current loop communication is used

(c) For longer distances Modem (Dial-up leased) Fiber Optic Satellite Microwave communication

MODEMS Modems are used for DATA transfer between Dataloggers and Front End ProcessorThese are

configured to RS 232 Serial Communication Network is connected with two types of 4-wire modems

(a) Internal modem card Dual Modem card (in-built)

It is fixed in datalogger Euro rack itself One card contains two modems The top modem is called

ANS (answer) modem and the bottom modem is called as ORG (originate) modem

Note In case of networking of Dataloggers connect lsquoANSrsquo modem to the lsquoORGrsquo modem of one adjacent

station and connect lsquoORGrsquo modem to the lsquoANSrsquo modem of other adjacent station

(b) External modems

20 | P a g e

These are generally used at FEP (Front End Processor) side to connect the Dataloggers

(i) To transfer Data from one datalogger to another datalogger FEP Baud rate is 9600bps

(ii) These modems are 4-wire line communication

(iii) To transfer the data from FEP to RMU (PC) the Baud rate is 57600 bps

There is no difference between these modems functionally

CENTRAL MONITORING UNIT (CMU) COMPUTER

Central monitoring unit (Fault Analysis Unit) is a Personal Computer and its minimum configuration

shall be specified by RDSO from time to time System Software Windows XPVista(OS) Norton Kaspersky

(Anti Virus) Interbase where Server is not available (DBMS) Oracle where Server is available (DBMS)

software are required to run Datalogger System It is provided with Graphical User interface (GUI) based

software and retrieve data from all Networked dataloggers (up to 32) at various stations It stores data in

standard data base files The CMU is capable of analyzing the data and generate reports audiovisual alarms

on defined conditions This data can be compressed to take backup In central monitoring unit Software used

for analysis of data prediction of faults etc is written in a structured format so that purchaser can

reconfigure it if required It displays the status of signaling gears at any selected time in graphic form for any

selected station yard It retrieves the stored data amp simulates train movement It sends commands to various

Dataloggers to activate audio visual alarm or operate and electromagnetic relay

CMU shares data available in it by other PCs through available local area network where this data can

be used for train charting passenger information purpose The system generates audiovisual alarm in

ASMrsquosSignal Maintainerrsquos room in the case of power supply failure (battery voltage low) or battery charger

defective with acknowledgement facility

(a) Each datalogger has its own identity code which will be transmitted along with data packet to central

monitoring unit

(b) Events recorded at each station are continuously transmitted to central monitoring unit Response time of

data transfer will not exceed 10 sec

21 | P a g e

22 | P a g e

OPTICAL FIBER CABLE

INTRODUCTION The demand for bandwidth on transmission networks is increasing rapidly because video and

graphical rich contents are exchanged through the corporate network or the Internet The Gigabit Ethernet

became ommonly used in the corporate network backbone and 10Gbit Ethernet will be adopted in the near

future Meanwhile in the home the demand for high-speed network becomes popular as the wide spread of

broadband access eg CATV xDSL and FTTH The transmission medium with capability to transmit high

bit rate signal is necessary to satisfy these requirements

The telecommunication transport technologies move from copper based networks to optical fiber

from timeslot based transport to wave length based transport from traditional circuit switching to terabit

router and all optical based networks entering into a new era of optical networking

BASIC PHYSICS OF OFC

OPTICAL FIBER CABLE OFC have Fibers which are long thin strands made with pure glass about the diameter of a human

hair OFC consists of Core Cladding Buffers and Jacket as shown in figure

MONOCHROMATIC LIGHT OR SINGLE COLOR LIGHT Light or visible light is electromagnetic radiation of a wavelength that is visible to the human eye (

about 400 ndash 700 nm) The word light is sometimes used to refer to the entire electromagnetic spectrum Light

is composed of elementary particles called photons Three primary properties of light are

Light can exhibit properties of both waves and particles This property is referred to as wave-particle

duality The study of light known as optics In free space light (of all wavelengths) travels in a straight path

at a constant maximum speed However the speed of light changes when it travels in a medium and this

change is not the same for all media or for all wavelengths By free space it is meant space that is free from

matter (vacuum) andor free from electromagnetic fields

Thus the speed of light in free space is defined by Einsteinrsquos equation E = mc2

Frequency ν speed of light in free space c and wavelength λ are interrelated by ν = cλ

From the energy relationships E = mc2 = hν and the last one an interesting relationship is obtained

the equivalent mass of a photon m = hνc2

When light is in the vicinity of a strong electromagnetic field it interacts with it From this interaction

and other influences its trajectory changes direction as shown in figure

23 | P a g e

INCIDENT RAY REFLECTED RAY AND REFRACTED RAY An incident ray is a ray of light that strikes a surface The angle between this ray and the

perpendicular or normal to the surface is the angle of incidence Reflection is the change in direction of a

wave front at an interface between two different media so that the wave front returns into the medium from

which it originated Common examples include the reflection of light sound and water waves

The reflected ray corresponding to a given incident ray is the ray that represents the light reflected by

the surface The angle between the surface normal and the reflected ray is known as the angle of reflection

The Law of Reflection says that for a specular (non-scattering) surface the angle of reflection always equals

the angle of incidence The refracted ray or transmitted ray corresponding to a given incident ray represents

the light that is transmitted through the surface The angle between this ray and the normal is known as the

angle of refraction and it is given by Snells Law

The figure shows Incident ray Reflected ray Refracted ray the angle of incidence and angle of refraction

REFRACTIVE INDEX - Refractive index is the speed of light in a vacuum ( c =299792458kmsecond) divided by the speed

of light in a material ( v ) Refractive index measures how much a material refracts light Refractive index of

a material abbreviated as lsquo n lsquo is defined as lsquo n=cv lsquo Light travels slower in physical media than it does

when transmitted through the air Refractive index (n) is a function of molecular structure of matter optical

frequency optical intensity determines optical propagation properties of each wavelength ( λ ) may not be

distributed equally in all directions is affected by external temperature pressure and fields

Refractive index of a medium is a measure for how much the speed of light is reduced inside the

medium For example typical glass has a refractive index of 15 which means that light travels at 1 15 =

067 times the speed in air or vacuum Two common properties of glass and other transparent materials are

directly related to their refractive index

First light rays change direction when they cross the interface from air to the material and effect that

is used in lenses and glasses

Second light reflects partially from surfaces that have a refractive index different from that of their

surroundings

SNELLrsquoS LAW-

24 | P a g e

When light passes from one transparent material to another it bends according to Snells law which

is defined as n1sin(θ1) = n2sin(θ2)

where n1 is the refractive index of the medium the light is leaving θ1 is the incident angle between the light

beam and the normal (normal is 90deg to the interface between two materials)

n2 is the refractive index of the material the light is entering

θ2 is the refractive angle between the light ray and the normal

Snellrsquos law gives the relationship between angle of incidence and angle of refraction

For the case of θ1 = 0deg (ie a ray perpendicular to the interface) the solution is θ2 = 0deg regardless of

the values of n1 and n2 That means a ray entering a medium perpendicular to the surface is never bent The

above is also valid for light going from a dense (higher n) to a less dense (lower n) material the symmetry of

Snells law shows that the same ray paths are applicable in opposite direction

TOTAL INTERNAL REFLECTION- When a light ray crosses an interface into a medium with a higher refractive index it bends towards

the normal Conversely light traveling cross an interface from a higher refractive index medium to a lower

refractive index medium will bend away from the normal

This has an interesting implication at some angle known as the critical angle θc light traveling from

a higher refractive index medium to a lower refractive index medium will be refracted at 90deg in other words

refracted alon g the interface If the light hits the interface at any angle larger than this critical angle it will

not pass through to the second medium at all Instead all of it will be reflected back into the first medium a

process known as total internal reflection

The critical angle can be calculated from Snells law putting in an angle of 90deg for the angle of the refracted

ray θ2 This gives θ1

Since θ2 = 90deg

So sin(θ2) = 1

25 | P a g e

Then θc = θ1 = arcsin(n2n1)

For example with light trying to emerge from glass with n1=15 into air (n2 =1) the ritical angle θc is

arcsin(115) or 418deg For any angle of incidence larger than the critical angle Snells law will not be able to

be solved for the angle of refraction because it will show that the refracted angle has a sine larger than 1

which is not possible In that case all the light is totally reflected off the interface obeying the law of

reflection

OPTICAL FIBER MODE An optical fiber guides light waves in distinct patterns called modes Mode describes the distribution

of light energy across the fiber The precise patterns depend on the wavelength of light transmitted and on the

variation in refractive index that shapes the core In essence the variations in refractive index create

boundary

conditions that shape how light waves travel through the fiber like the walls of a tunnel affect how sounds

echo inside

We can take a look at large-core step-index fibers Light rays enter the fiber at a range of angles and

rays at different angles can all stably travel down the length of the fiber as long as they hit the core-cladding

interface at an angle larger than critical angle These rays are different modes Fibers that carry more than

one mode at a specific light wavelength are called multimode fibers Some fibers have very small diameter

core that they can carry only one mode which travels as a straight line at the center of the core These fibers

are single mode fibers This is illustrated in the following picture

OPTICAL FIBER INDEX PROFILE Index profile is the refractive index distribution across the core and the cladding of a fiber Some

optical fiber has a step index profile in which the core has one uniformly distributed index and the cladding

has a lower uniformly distributed index Other optical fiber has a graded index profile in which refractive

index varies gradually as a function of radial distance from the fiber center Graded-index profiles include

power-law index profiles and parabolic index profiles The following figure shows some common types of

index profiles for single mode and multimode fiber

26 | P a g e

OPTICAL FIBERrsquoS NUMERICAL APERTURE ( NA )- Multimode optical fiber will only propagate light that enters the fiber within a certain cone known as

the acceptance cone of the fiber The half-angle of this cone is called the acceptance angle (see figure 18)

θmax For step-index multimode fiber the acceptance angle is determined only by the indices of refraction

Where

n is the refractive index of the medium light is traveling before entering the fiber

nf is the refractive index of the fiber core

nc is the refractive index of the cladding

NUMBER OF MODES IN A FIBER - Modes are sometimes characterized by numbers Single mode fibers carry only the lowest-order

mode assigned the number 0 Multimode fibers also carry higher-order modes The number of modes that

can propagate in a fiber depends on the fiberrsquos numerical aperture (or acceptance angle) as well as on its

core diameter and the wavelength of the light For a step-index multimode fiber the number of such modes

Nm

Where

D is the core diameter

λ is the operating wavelength

NA is the numerical aperture (or acceptance angle)

MODE FIELD DIAMETER - All light do not travels through the core of the fiber but is distributed through both the core and the

cladding The mode field is the distribution of light through the core and cladding of a particular fiber

Mode-Field Diameter (MFD) defines the size of the power distribution When coupling light into or out of a

fiber MFD is important in understanding light loss

27 | P a g e

ADVANTAGE OF OFC COMMUNICATION - bull More information carrying capacity Fibers can handle much higher data rates than copper More

information can be sent in a second

bull Free from Electromagnetic and Electrostatic interference Being insulator no electric current flows through

the fibre and due to this reason fibres neither radiate nor pick up electro - magnetic radiation So WPC

CLEARANCE is not required

bull Low attenuation 025 dbkm at 1550 nm Loss in twisted pair and coaxial cable increases with frequency

where as loss in the optical fibre cable remains flat over a wide range of frequencies

bull Use of WDM ndash Switching routing at Optical signal level

bull Self healing rings under NMS control

bull Small size makes fibre cable lighter in weight So easy to handleOptic fibre cable weight (approx)

500 kg km Copper cable weight (approx) 1000 kgkm

The reasons are photons of light in a fibre

do not affect each other as they have no electrical charge and they are not affected by stray photons outside

the fibre But in case of copper electrons move through the cable and these are affected by each other

Optical fibre does not carry any electricity even if the cable is damaged or short circuited it does

not cause any spark or fire hazard

As the fibre do not radiate energy it can not be detected by any nearby antenna or any

other detector The fibres are difficult to tap and therefore excellent for security

As the signal transmission is by digital modulation there is no chance of cross talk in

between channels

Only by adding a few additional terminal and repeater equipments the

capacity of the system can be increased at any time once the cable is laid

ical effects and temperature variations

LIMITATIONS OF OFC -

difficult

- utilised

APPLICATION IN SIGNAL AND TELECOMMUNICATIONS transmission circuits

-haul circuits for linking of telephone exchanges

28 | P a g e

PROPAGATION MODES CONCEPT -

MODE - Mode is an available distribution of electromagnetic field in a plane transverse to the direction of

light propagation Each mode is characterized by frequency polarization electric field strength and

magnetic field strength Available patterns are derived from Maxwellrsquos equations and boundary conditions

LINEARLY POLARIZED (LP) MODE A mode for which the field components in the direction of propagation are small compared to

components perpendicular to that direction An optical fibre supports only different field patterns called as

lsquoLinear Polarizedrsquo or lsquo LPrsquo modes The reasons are

requirements

de

the accrual of power carried by different modes

There are two basic types of fiber Multimode fiber and Single-mode fiber

Multimode fiber is best designed for short transmission distances This is suited for used in LAN systems and

video surveillance Single mode fibre is best designed for longer transmission distances This is suitable for

long distance telephony and multi channel television broadcast systems

29 | P a g e

MULTI MODE FIBER Multimode fiber the first to be manufactured and commercialized simply refers to the fact that

numerous modes or light rays are carried simultaneously through the waveguide Modes result from the fact

that light will only propagate in the fiber core at discrete angles within the cone of acceptance MM fiber type

has a much larger core diameter compared to single-mode fiber allowing for the larger number of modes

and

is easier to couple than single-mode optical fiber Multimode fiber further categorized as Multimode step-

index and Multimode graded index fiber

PROPAGATION THROUGH MMSI FIBER Figure shows the principle of total internal reflection applies to multimode step index fiber Because

the corersquos index of refraction is higher than the claddingrsquos index of refraction the light that enters at less than

the critical angle is guided along the fiber

Three different light waves travel down the fiber One mode travels straight down the center of the

core A second mode travels at a steep angle and bounces back and forth by total internal reflection The third

mode exceeds the critical angle and refracts into the cladding Naturally it can be seen that the second mode

travels a longer distance than the first mode causing the two modes to arrive at separate times

PROBLEMS WITH MMSI FIBER AND SOLUTION This disparity between arrival times of the different light rays is known as dispersion and the result is

a muddied signal at the receiving end It is important to note that high dispersion is an unavoidable

characteristic of multimode step-index fiber The solutions are either use Graded index fiber or Single mode

fiber

PROPAGATION THROUGH MMGI FIBER Multimode Graded-index refers to the fact that the refractive index of the core gradually decreases

farther from the center of the core The increased refraction in the center of the core slows the speed of some

light rays allowing all the light rays to reach the receiving end at approximately the same time reducing

dispersion Figure shows the Light propagation principle through multimode graded-index fiber The corersquos

central refractive index ( nA ) is greater than that of the outer corersquos refractive index ( nB )

It is very clear from the figure the light rays no longer follow straight lines they follow a serpentine path

being gradually bent back toward the center by the continuously declining refractive index This reduces the

arrival time disparity because all modes arrive at about the same time The modes traveling in a straight line

30 | P a g e

are in a higher refractive index so they travel slower than the serpentine modes These travel farther but

move faster in the lower refractive index of the outer core region

PROPAGATION THROUGH SMSI FIBER Single mode fiber has a much smaller core that allows only one mode of light at a time to propagate

through the core The figure shows the single mode fiber

Single-mode fiber exhibits no dispersion caused by multiple modes Single-mode fiber also offers lower fiber

attenuation than multimode fiber Thus more information can be transmitted per unit of time because it can

retain the fidelity of each light pulse over longer distances Like multimode fiber early single-mode fiber was

generally characterized as step-index fiber meaning the refractive index of the fiber core is a step above that

of the cladding rather than graduated as it is in graded-index fiber Modern single-mode fibers have evolved

into more complex designs such as matched clad depressed clad and other exotic structures

SINGLE-MODE FIBER DISADVANTAGES The smaller core diameter makes coupling light into the core more difficult The tolerances for single-

mode connectors and splices are also much more demanding

CUTOFF WAVE LENGTH - Cutoff wavelength is the wavelength above which a single-mode fiber supports and propagates only

one mode of light In other words an optical fiber that is single-mode at a particular wavelength may have

two or more modes at wavelengths lower than the cutoff wavelength The effective cutoff wavelength of a

fiber is dependent on the length of fiber and its deployment The longer the fiber the lower is the effective

cutoff

wavelength The smaller the bend radius of a loop of the fiber the lower is the effective cutoff wavelength If

a fiber is bent in a loop the effective cutoff wavelength is lowered

SIGNAL ATTENUATION IN FIBER - Optical fiber has a number of advantages over copper However it also suffers from degradation

problems which can not be ignored The first of these is loss or attenuation Attenuation is typically the result

of two sub properties They are scattering and absorption Both of which have cumulative effects The second

is

dispersion which is the spreading of the transmitted signal and is analogous to noise

SCATTERING Scattering occurs because of impurities or irregularities in the physical construction of the fiber The

well known form of scattering is Rayleigh Scattering It is caused by metal ions in the silica matrix and

results in light rays being scattered in various directions

31 | P a g e

Scattering limits the use of wavelengths below 800nm The short wavelengths are much affected than longer

wavelengths It is because of Rayleigh scattering that the sky appears to be blue ( shorter wave length ) The

shorter wavelengths ( blue ) of light are scattered more than the longer wavelengths of light

ABSORPTION Absorption results from three factors They are hydroxyl ions ( OH- water ) in the silica impurities

in the silica and incomplete residue from the manufacturing process These impurities tend to absorb the

energy of the transmitted signal and convert it to heat resulting in an overall weakening of the signal The

Hydroxyl absorption occurs at 125 and 139 micro The silica itself starts to absorb energy at 17 micro

because of the natural resonance of the silicon dioxide

MACRO BENDING LOSS Macro-bending loss is caused by bending of the entire fiber axis The bending radius shall not be

sharper than 30d where d is diameter of cable A single bend sharper than 30d can cause loss of 05dB

The fiber may break if bending is ever sharper

MICRO BENDING LOSS Micro-bending loss is caused by micro deformations of fiber axis which leads to failures in achieving

total internal reflection conditions Micro-bends are small scale perturbations along the fiber axis the

amplitude of which are on the order of microns These distortions can cause light to leak out of a fiber

Micro-bending may be induced at very cold temperatures because the glass has a different coefficient of

thermal expansion from the coating and cabling materials At low temperatures the coating and cable

become more rigid and may contract more than the glass Consequently enough load may be exerted on the

glass to cause micro bends

Coating material is selected by manufacturers to minimize loss due to micro-bending The linear thermal

expansion coefficient of coating material shall be compatible with that of fiber

32 | P a g e

DISPERSION Dispersion is the optical term for the spreading of the transmits in the fiber It is the bandwidth

limiting phenomenon and comes in two forms Multimode dispersion and chromatic dispersion Chromatic

dispersion is further subdivided into material dispersion and waveguide dispersion

DISPERSION PHENOMENON IN OPTICAL FIBER Dispersion is the time distortion of an optical signal that results from the differences of time of travel

for different components of that signal typically resulting in pulse broadening As the distance traveled by

the signal is more broadening of pulse is more In digital transmission dispersion limits on the maximum

data rate and the maximum distance ie the information-carrying capacity of a fiber link The interference

from broadened pulse in the next interval shall not lead to erroneous interpretation of received signal

OPTICAL DOMAIN Understanding where attenuation and dispersion problems occur helps optical design engineers

determine the better wavelengths at which information can be transmit taking into account distance type of

fiber and the other factors which can severely affect the integrity of the transmitted signal The graph shown

depicts the optical transmission domain as well as the areas where problems arise The wavelength (nm)

is shown on X-axis and attenuation ( dBkm) is shown on Y-axis

There are four transmission windows appear in the figure The first one is at around 850 nm the

second at 1310nm third at 1550 nm and fourth at 1625 nm The last two labeled as C and L band

respectively The 850 nm wavelength at which the original LED technology operated The second window at

1310 nm has low dispersion The 1550 nm called as C-band is ideal wavelength for long haul

communication systems The network engineers can avoid transmitting signal at 1000 nm where Rayleigh

scattering 1240 and 1390 nm where hydroxyl absorption by water occurs to avoid high degree of loss

Optical fibers also can be manufactured to have low dispersion wavelength in the 1550nm region

which is also the point where silica-based fibers have inherently minimal attenuation These fibers are

referred to as dispersion-shifted fibers and are used in long-distance applications with high bit rates For

33 | P a g e

applications utilizing multiple wavelengths it is undesirable to have the zero dispersion point within the

operating

wavelength range

34 | P a g e

SIGNALLING RELAYS

INTRODUCTION A relay is an electromagnetic device which is used to convey information from one circuit to another

circuit through a set of contact ie front or back contact Constructional and electrically relays may be

divided into DC and AC relays because the means by which the electrical energy in the coil is converted in

to mechanical Energy in order to move the contacts are fundamentally different In DC type the contacts are

carried on an armature forming part of a magnetic circuit in which a field is set up by the current flowing in

the coils In AC types the contacts are attached by a link mechanism to a metal sector disc or cylinder in

which currents are induced by the alternating magnetic field produced by the currents in the coils

Every endeavor has been made to explain the action of each type of relay in the simplest possible manner

Relays are sophisticated switch gears used for remote control and succession control of various

electrical equipment In present days they are widely used because they are capable of protecting the

controlled equipment from cross feeding and overloading even as they cater for speedy operations

Most of the relays in present day signaling are electromagnetic devices although some of the relays control

circuits through electronic components like diodetransistors Integrated Chips etc

Railway signaling relays are unique in that

(a) They operate on low voltage and current

(b) They are more articulate as according to their special features they can work under restrictive conditions

and in any specified manner Virtually they can cater for all situations while contributing to speed and

accuracy in operations

CLASSIFICATION OF SIGNALLING RELAYS (a) According to the method of their mounting or fixture they are classified as

(i) Shelf type Relays which are loosely kept on shelves

(ii) Plug in type Relays which are plugged into a pre- wired plug boards

(b) According to their connection and usage they are classified as

(i) Track relays Relay which is directly connected to the track to detect the presence of vehicle

(ii) Line Relays Other than track relay all are line relays Relays connected to the selection circuit

(c) According to their vitality or importance in ensuring train working safety they are classified as

(i) Vital Relays All relays used for traffic control such as signal point controls track detection etc

(ii) Non-vital Relays Relays which operate control aids and accessories like warnings buzzers

Indications etc

(d) According to their special provisions to ensure reliability of their contacts they are classified as

(i) Proved type are those whose normalization after each operation shall be proved in circuit

controlled by their contacts Contacts in which both the springs have metal surfaces on their tips They may

get fused due to high sparking current across them during operation These may prevent relay normalization

and causes unsafe condition in traffic control To avoid this proving of relay normalization after each

operation is necessary

(ii) Non - proved type Need not to be proved to have been normalized after each operation as their

contacts have at least one non-fusible contact (carbon contact)

(e) According to their feed source relays are broadly classified as

(i) DC relays The relay which requires DC power supply for its operations are called DC relays Among

the DC relays

o DC neutral relays This relay closes the same set of contacts on energization with Normal polarity

or Reverse polarity supply

o Polar Relays This relay closes different set of contacts when energized with Reverse polarity

supply They may or may not have contact to close when deenergized

35 | P a g e

(ii) AC Relay AC Induction motor track relays Time element relays flashing indication control etc

(iii) Electronic Relays DC relays with electronic components in them are called electronic relays

DC NEUTRAL RELAY Each Relay has usually one or two coils with a hollow center to accommodate a coreThe coils are

made up of a large numbers of turns of small gauge soft drawn copper wire The two coils can be connected

in series or parallel according to the requirement of relay resistance The ends of the coils are terminated on

binding post to which the control wires are connected Each coil is placed around a core of specially selected

Iron or steel having high permeability and low retentivity The core should be susceptible to magnetism and

at the same time should have little residual magnetism The cores are connected at the top by a yoke to

complete the magnetism coupling between two ends of coils The bottom of each core is equipped with a

large steel or Iron block known as pole piece or face

A flat piece of Iron or steel called armature is supported by brackets which are securely fastened to

the pole piece The armature yoke and the pole pieces are also made of specially selected iron or steel of the

same quality as the core The armature carries the metallic spring contacts which are insulated from it

The circuit through the coils of the relay is closed It sets up a magnetic flux through the core yoke and the

armature The flux passing between the armature and pole faces causes the armatures get attracted to the pole

faces and armature picks up and closes front contacts When the circuit is opened the magnetic flux collapses

and the armature drops away by gravity from the pole faces the front contacts break and back contacts close

The front and back contacts of the relay can be utilised to make or break other circuits Two stop pins of

nonmagnetic material are fixed either on the armature or pole faces so that the armature cannot

come in contact with the pole faces It is essential to maintain a small air-gap between the armature and pole

faces so that low value of residual magnetism may not retain the armature in picked up position and causes

the relay to fail to drop away with a break in its control circuit

GENERAL USAGE

DC Neutral line relays are most commonly used for Railway Signalling controls and detection

Among them plug-in type relays are preferred in larger installations for space considerations Shelf type

relays are also in use mostly in wayside stations

There are many DC Neutral line relays in use with special features such as

(i) Delayed operation

(ii) Biased DC control

(iii) DC control unaffected by AC interference currents

(iv) Getting latched in operated condition till further feeding and others

Usage of DC polar relays is mostly in conjunction with block instruments that control traffic between

stations AC line relays are almost extinct in installations of British Signalling practice They are however

used for time control operations flashing indication control and such other special purposes in installations

with Siemens signalling practice widely Track relays are used according to the type of track detection

circuits chosen for a given location and context While most of the track circuits are still of the DC working

type requiring DC neutral track relays with them the prospects of their being replaced with Electronic track

circuits directly feeding DC line relays in future are great AC Track Circuits are used in DC Traction area

as conventional DC Track Circuits are not suitable there AC Track relays are used with them almost all of

the induction motor type In the British practice of signalling which was first introduced on Indian Railways

non-proved type relays with carbon to metal switching contacts are generally used for vital controls

They facilitate simple circuit designs But with the advent of German Practice introduced by Ms

Siemens later proved type relays with all metal to metal contacts are widely accepted in spite of

complications in circuit design caused by them A recent introduction is that of the same type relays made by

Ms Integra control However for some time now the appreciable features of both the practices are getting

36 | P a g e

incorporated together in the indigenous designs of signalling by railwaymen With this the usage of all types

of relays anywhere can be found without straight jacketed segration of relay types

CHARACTERSTIC OF ELECTRO-MAGNETIC RELAY The following are the characteristic of electro-magnetic relays A brief study of them helps in

understanding the choice of their components and designs features

1) Force of attraction

2) Effect of air gap

3) Effect of Hysterisis

4) Transient condition

FORCE OF ATTRACTION In any electro-magnetic system the force of attraction is given by

Where B - is the flux density a - is the cross sectional area of the particular part of the magnetic

circuit

In the case of a DC neutral Relay B is proportional to the current that is flowing in the coil

surrounding the electro-magnet and thus the force of the attraction is directly proportional to the square of the

current This square relationship has its own advantage especially in the case of DC track relay in that a

small reduction in the current will have a great effect on the working of the relay Also for a given change of

current the make and the break will be quicker with lesser possibility of arcing

EFFECT OF AIR GAP

Curve lsquoArsquo is magnetisation curve for the iron and is all practical purpose a straight line up to the

saturation point Curve lsquoBrsquo is the magnetisation curve for the open-air gap which is a straight line through

out because per magnetisation curve of the whole

magnetic circuit of the relay and for a given force is the sum of the amp-turns for the iron part and the amp-

turns for the air gap

When the front contacts are open the force required to pick up the armature is shown on curve lsquoCrsquo to be F1

but after the armature has operated it will be separated from the core by stop pins In this position the amp-

turns required to maintain the armature is less as indicated by the dotted line from 1 on curve C to 2 on curve

37 | P a g e

F But actually the current in the coil is unaltered the force on the armature is greater than required as

indicated at 3 on curve F Part of this extra force is used to flex the front contacts sufficiently to give good

contact pressure when it is in energised position

The difference between the pick-up and the drop-away current should be as small as practicable in

track relay to ensure good shunting characteristics This is achieved firstly by the choice of good quality relay

iron and secondly by having a small air gap between armature and core If the air gap is not available then

the residual magnetism fluxes might cause the armature to be retained when the supply is disconnected For

this reason residual pins are provided to ensure a definite minimum air gap in the energised position

EFFECT OF HYSTERISIS

Hysterisis is the property by which the flux produced lags behind the current In the de-energized

condition there will be small residual flux in the core When the voltage is applied to the coils the current in

rising to its steady value first causes the flux to rise from 1 to 2 along the curve At this point the flux density

will be sufficient to attract the armature and reduce the air gap the flux then raise to 3 and continue to 4

which corresponds to the steady current in the coils When the voltage is disconnected the current in falling

caused the flux to fall from 4 to 5 along the curve At this point the flux density will fall below the value

required to maintain the armature which will release thus increasing the air gap and reducing the flux to 6

Finally the

flux will decrease from 6 to 1 where the current will again be zero

The relay core is made of material having high permeability and low retentivity As mentioned in

the IRS specification Electromagnet iron may be in the form of a

(a) Bar of silicon steel

(b) Best Yorkshire wrought iron

(c) Swedish charcoal iron

(d) Electrical steel sheets

` This reduces the difference between pick up value and Drop away value By selecting good quality

core material Percentage release and sensitivity of the relay will be improved

TRANSIENT CONDITION

38 | P a g e

When the voltage is applied or disconnected from the coils it takes some little time before the current

become steady These are known as transient conditionsrdquo and are important so far as track relays are

concerned When the voltage is first applied to the coils the magnetic flux in rising cuts the turns on the

coils and in so doing produces a back EMF that opposes the applied voltage and retards the growth of

current

The growth and decay of flux are decided by the relationship between the inductance and resistance

in the circuit is known as time constant It is not fixed quantity in the case of DC neutral relay This value of lsquo

Lrsquo is less when the relay is in de-energised condition (L1) than when the relay is in energised condition (L2)

The magnitude of flux that is established for a given change of current is different in two cases

When the current reaches the pick up value the armature closes and the inductance is increased to L2

due to reduced air gap the flux per amp is increased The increase in flux increased the back EMF during the

movement of the armature after which the current continuous to raise along a new curve corresponding to the

increased inductance until it reaches the final value (ER) This process is indicated above in fig24

When the supply is disconnected the current is obliviously reduced to zero immediately but the flux

decay comparatively slowly owing to the eddy currents produced in the core by the rapid flux change which

tend to maintain the flux The drop away time on a disconnection is however generally negligible See fig

below

If the relay releases due to the reduction in current from say I 2 to I 1 caused by the application of

shunt resistance (as in the case of track relay ) the time taken is much longer than the relay is simply

disconnected The rate of rise or fall of current during the transient conditions is also depends on exterior

circuit values because L and R apply to the whole circuit The production of eddy current in the core the flux

will decay at a slower rate than the current So that the actual release time will be a little longer than it takes

the current to fall to the release

L= Inductance

39 | P a g e

R= Resistance

It is now clear that to reduce releasing time to a minimum it is necessary that

- The relay iron should have low Hysterisis loss and low retentivity

- The degree of over energization of the relay should be restricted

- Connecting a suitable external resistance in series with the relay to keep LR ratio low

In non RE area for track circuit length less than 100M 9 ohm track relay only to be used Using relay

with minimum contacts as they require lesser current which keeps inductance value low

Train working safety is ensured only if the track relay of shortest length track circuit is released

before a light engine running at a highest permitted speed clears it Otherwise the track circuit occupation

may go undetected To avoid this a special provision has to be made in signal control circuits wherever

necessary

The following methods may be adopted for reducing the time lag of track relay

(a) Restrict the over energisation of relay since the release time depends on the initial working current

(b) Connecting a suitable external resistance in series with the relay to keep the LR ratio low

(c) Using relays with minimum contacts as they require lesser operating current keeping the inductance

value low

40 | P a g e

CONCLUSION

Modern signalling is vital for safe and punctual movements of trains In the Indian railways The Signalling

and Telecommunication Department is responsible for providing modern effective and relaible signalling

systems as well as telecommunication systems

The first mode of communication used in Indian Railways was the use of electric telegraph

with the help of Morose code Morose code is the method of providing text information as a series of on-off

tones and lights or clicks that can be directly understood by a skilled listener or observer without special

equipmentEach character (letter or numeral ) is represented by a unique sequence of dots and dashes Later

this system becomes obselete and beggan the era of wireless communication which operated at audio level

frequency range

In wireless communication the significant advances took place the transition to miniature

valves or filament tubesBut this was abandoned too because of excessive current consumption and over

heating of the filament tubes

Fibre-optic communication is a method of transmitting information from one place to another by

sending pulses of light through an optcial fibreThe light forms an electromagnetic carrier wave that is

modulated to carry information First developed in the 1970s fibre optic communication systems has

revolutionized the telecommunications industry and have palyed a major role in the advent of the information

age Because of its advantages over electrical transmissionsoptical fibres have largely replaced copper wire

communications in core networks in the developed world The Indian Railways too is undergoing a transition

from Microwave communication to fibre optic communications

41 | P a g e

BIBLIOGRAPHY AND REFERENCES

1 wwwwikipediacom

2 wwwbritaniccacom

3 wwwirfcacom

4 Motorola GP60 system manual

5 Harris FAS 7000 manual

6 TOSHIBA Manual

9 | P a g e

SINGLE SECTION DIGITAL AXLE COUNTER

INTRODUCTION- The axle counter equipment is working on high frequency and using amplitude modulation or phase

modulation for detection of presence of wheel The equipment described in this notes is Phase modulation type

for the detection of presence of wheel In the Phase modulation type track device the detection of presence of

wheel is with the phase reversal of 1800 out of phase which enables this system to be more healthy and safe

In Phase Reversal Modulation technique trolley suppression arrangements to prevent the counting of

wheels caused by push trolley passing over the track device are not required as the system will take care of

validation of generated pulses caused by passage of wheel over the track device depending up on the phase

shift of the pulse This phase shift of the pulse may be normally 160deg to 180deg for a train wheel and it may be

approximately 100deg to 120deg for a push trolley wheel

This is Digital Axle Counter equipment for single track sections containing 2 out of 2 micro-

controllers to count the axles establish the track occupancy of a track section and to provide this information

to the block or the interlocking equipment

In this system no separate evaluator is required and no analog data is being transmitted One set of

Axle counter equipment is provided at entry end and other set provided at exit end Both sets are being

connected through a twisted pair of telecom cable ie existing RE cable one PET quad is used for both UP

and DN Axle Counters Digital DATA is being transmitted between two ends of Axle counters (Outdoor

track side Detection points)This system is a fully duplex capable of operating according to CCITT V21 and

the Data will be transmitted at the rate of 300bitsec This data Transmitted ensure negligible interference of

the noise The system is highly reliable

FEATURES (a) The system consists of

(i) Single Section Digital Axle Counter (SSDAC) units

(ii) Tx Rx coils

(iii) Vital Relays

(b) TxRx coil axle detectors are mounted to the web of the rails The design of system consists of 21 KHz amp

23 KHz High frequency Phase Reversal type axle detectors

(c) Compatible with 90R 52Kg amp 60Kg rail profiles Easy to install commission amp maintain

(d) Track devices at both (entry amp exit) points of the section should be fixed on the same rail

(e) System is designed to detect the solid wheels with diameter gt 400mm with standard wheel flange

(f) The system works in pairs For monitoring single-track section one pair of SSDAC units are required and

to be installed near the trackside one at the beginning and another at the end of the track section ie

Trackside electronic counting equipment

(g) The basic design of the system is based on counting the number of axles passing at each detection point

These stored counts are transmitted to the second unit of the system and vice versa by means of modem

communication

(h) The communication consists of digital packets having details of Counts amp Health

10 | P a g e

(i) If counts registered at both detection points are equal the section is cleared otherwise the section is shown

as occupied The system ensures no error condition to arrive at the decision of clearance

(j) System is designed as per CENELEC SIL-4 (European standard) using micro controller along with other

electronic circuits and programmed using dedicated software When any of these circuits fail the system

goes to fail safe condition

(k) It is programmable for either Preparatory Reset or Conditional Hard Reset as per requirement

(l) Micro controller based design with 2 out of 2 decisions and counting through software

(m) V21 Modem communication (2-wire) on frac12 quad cables and also compatible to work on voice channel of

OFC amp Radio

(n) Opto isolated vital relay drive for Q-style 24V 1000 _ and Vital Relay output can be giving at both ends

of the system

APPLICATIONS The system can be widely used in Railways for Block Working (BPAC) Intermediate Block Signaling Auto

signalling and Track circuiting for i) Loop line ii) Main line iii) yard lines

SYSTEM DESCRIPTION

This system comprises of

Tx coils-2 nos

Rx coils-2 nos

Reset Box (RB 258A)

Card 1 Signal Conditioning Card ndash 1

Card 2 Signal Conditioning Card - 2

Card 3 Micro controller Logic Board ndash 1

Card 4 Micro controller Logic Board ndash 2

2 nos for independent resetting ndash when used in block sections

1 no for common resetting ndash when used for Track circuiting at stations

Card 5 Event Logger Card

Card 6 Modem Card

Card 7 Relay Driver Card

Card 8 DC-DC Converter Card

SSDAC (DACF 700AP) UNIT

(A) SIGNAL CONDITIONING CARD (CARD 1amp2) (SCC) -1 (SCC-1) generates 21 KHz carrier

signals

-2 (SCC-2) generates 23 KHz carrier signals which is transmitted to 2nd

set of Tx coils

s receive these signals

modulated

train pulses

11 | P a g e

(B) MICRO-CONTROLLER LOGIC BOARD CARD (CARD 3amp4) (MLB) The Micro-controller Logic Board (MLB) is the heart of the system

o 8051 Based Architecture

o 8 Bit Micro Controller

o ATMEL AT89S8252 Micro controller

o 2 out of 2 Decision

o Uses C subset language

- TOOLS

o KEIL μ Vision Development System

o Universal Programmer

o 2KB Program Memory

o 256 bytes RAM

o 8KB Flash memory

o 32 Programmable IO lines

o Wide Operating Voltage range of 4V-6V

o Full Duplex Serial Port

o Programmable Watch Dog Timer

o Fully Static operation up to 24MHz (Upgraded to 40MHz)

o Operating Temperature of ndash40degC - +85degC

o Use of State Machine for Axle Counting

o Use of ASCII MODBUS protocol

o Use of CRC16 technique for Error Checking during communication

o Wheel detection

o Train direction checking and

o Wheel counting functions

o It receives the remote wheel count and computes the status of the section for clear or occupied

o It also checks various supervisory signal levels like supervisory of TxRx coils presence of various

cards communication link failure etcThese cards communicate with each other for wheel count

At Entry-end if train enters into section (1st detection) the counts are incremented and when train

shunts back from the same detection ie if train exits from the section from the same detection the counts are

decremented At Exit-end if train enters into section (2nd detection) the counts are decremented and when

train shunts back from the same detection ie if train exits from the section from the same detection the

counts are incremented Both the track devices at Entry and Exit ends must be fixed on same side of the

track

This MLB card is having Extensive LED display

o A block of 8 LED indicators for count progress error display

o 2 independent LED indicators for section status

o The errors occurring in the system during the operation of the SSDAC are encoded and are indicated by

means of the 8-LED block present on the front panel of the MLB cards

(c) EVENT LOGGER CARD (CARD 5)

Event logger card is designed to capture and store important signals from the remote and local SSDAC units

The stored data can be downloaded from the event logger card for the purpose of analyzing the events

occurring during the operations of the SSDAC The data can be analyzed with the help of CEL data analyzer

software

12 | P a g e

The event logger card captures following signals

(i) Pulse signals

(ii) Supervisory signals

(iii) Card removal information

(iv) Serial packets from

Event Logger card has a Rabbit processor and 2 MB FLASH MEMORY to store packets The data is initially

stored in the buffer and subsequently transferred to FLASH memory every two minutes Normally 4096

pages of the data can be stored in flash memory on FIFO (first in first out) basis

Run This LED blinks continuously indicating the normal working of the event

Log This LED blinks whenever data is being logged into the flash memory (Approx after every 2 minutes)

Dnld This LED is ON when data is being downloaded from the flash memory of the card and becomes OFF

when download is complete

(D) MODEM CARD (CARD 6) (i) The modem card transmits and receives the digital packet information form one counting unit to the other

The packet will appear after every 18 sec and the packet carries the latest information such as

(ii) The modem card being used is V21 type (2-wire) in SSDAC

(iii) This card interfaces with serial RS232C port of both Micro-controller Logic Boards

(iv) It multiplexes the two RS232C inputs and selects one of the two channels and provides signal conversion

from digital to analog (FSK modulation) and vice-versa

(v) Data transmission rate is 300 bitssec

(vi) Automatic Gain Control circuit is incorporated hence no gain adjustments required

(vii) Mode selection on Modem card The modem has been set in lsquoORIGINATORrsquo mode for entry and in the

lsquoANSWERrsquo mode for exit in the factory

(viii) LED Indications provided on Modem card

-Transmitting the signal when LED is flashing

- Receiving the signal when LED is flashing

-Remains OFF in SSDAC

-Carrier is detected when LED is glowing

(E) RELAY DRIVER CARD (CARD 7) (i) The Relay Driver card (RD) provides the 24V DC output required for driving Vital Relay

(ii) One RD card is used in each SSDAC counting unit The RD card receives the command of clear and

clock signals from MLB1 amp MLB2 cards and drives the vital relay lsquoONrsquo when section is NOT OCCUPIED

through opto- isolator circuit

(iii) If a train occupies the section the vital relay is dropped The vital relay status is read back by the system

as per the driving output

(iv) It has

13 | P a g e

ndash LED flashes when the section is clear

ndash LED flashes when the section is clear

All the above LEDrsquos are lit for section clear condition

(F) DC-DC CONVERTER CARD (CARD 8)

INPUT VOLTAGE Nominal Voltage voltage 24V DC Maximum current drain= 12A

Required voltage 18V DC to 30V DC

Output voltage

Nominal Voltage +5 V DC 2 A Required voltage 4 7 5 t o 525V DC

Nominal Voltage +12V DC 200 mA Required voltage 1175 to 1225V DC

Nominal Voltage +24V DC 300 mA with common ground Required voltage 235 to 245V DC

Nominal Voltage +15V DC 100 mA with isolated ground Required voltage 145 to 155V DC

SURGE VOLTAGE AND LIGHTNING PROTECTION Transient surge voltages arise as a result of Lightning discharge switching operations in electrical

systems and electrostatic discharge These surge voltages often destroy the electronic equipment to a large

extent In order to prevent surge voltages from destroying the equipment all the input lines of SSDAC ie

Power Supply (24V) Reset (48V) amp Modem is to be routed through surge voltage protection devices for

effectively protecting the system These devices (3 numbers) are mounted in a box and supplied along with

the system One number of box is to be installed at each location and wired to the SSDAC

Each surge voltage protection device consists of two parts

(a) Base

(b) Plug Trab

The Base of the device is used for wiring the input and output signals The connection details from relay

room to the box and from box to SSDAC unit are provided on the box The Plug Trab consists of MOV and

GD Tube and diverts the excess energy during surge voltages or lightning into the ground connection The

operation of these devices relies on a high quality ground connection in order to safely shunt away the

unwanted energy The impedance of the ground connection is critical and it should be less than 2 Ohms

NOTE The 3 Plug Trab connections are not to be interchanged with one another The plug Trab is a

detachable device and can be replaced with SPARE unit in case of blown device which is indicated by

means of LED for 24 V

EFFECTIVENESS OF PLUG TRABS The effectiveness of plug Trab depends wholly on the Earth connection provided to the system The earth

provided to the system should be less than 1 ohms and connections should be firm and proper to the SSDAC

unit VR box etc

SURGE VOLTAGE AND PROTECTION DEVICE SV-120 The Surge Voltage protection device is to be installed at each location along with every SSDAC unit

14 | P a g e

EARTHING- The lead wires connecting the installation and the earth electrode shall ordinarily be of stranded

copper wire of 29 sq mm (19 strand wires of 14 mm diameter) Copper wire has been specified because GI

wires usually are having greater corrosion However in areas where copper wire may be frequently stolen

due to theft ACSR of size 64 sq mm (19 strands of 211 mm diameter) may be used

LIMITS OF EARTH RESISTANCE (a) Apparatus case connected to Earth (SSDAC and vital Relay Box is housed in Apparatus case and

Connected to earth at outdoor) shall be less than or equal to 1 ohm

(b) All cable connected to same earth shall be less than or equal to 1 ohm

(C) Reset box connected to earth near SM s Room shall be less than or equal to 1ohm

EQUIPMENT TO BE EARTHED A Common Earth should be provided for SSDAC for items 1(a) amp (b) of the above at the outdoor

(a) The Apparatus Case is to be connected to earth (the chassis of SSDAC amp Vital Relay Box should be

properly connected to apparatus case)

(b) Metallic sheath and armouring of all the underground main cables are to be earthed

(i) In RE area the metallic sheath and armouring of main telecom cables are earthed at both ends

(ii) In RE area the armouring of Jelly filled cable shall be earthed at both ends

(c) The Earthing shall be provided at every location box where cables are terminated

(d) Earth already available for other equipment may be used for earthing of Reset Box near SM s Room

Cabin etc

15 | P a g e

DATALOGGER

INTRODUCTION Datalogger is a Microprocessor based system which helps in analysing the failures of relay inter

locking system Electronic Interlocking system This is like a black box which stores all the information

regarding the changes take place in relays AC DC Voltages and DC currents along with date and time The

same information data can be transferred to the computer to analyse further ldquoon line ldquooff linerdquo analysis of

stored date A print out also can be obtained through a printer by connecting directly to the datalogger unit

The data belongs to Relay contacts is considered as digital inputs and the data belongs to voltage

levels currents is considered as Analog inputs Datalogger lsquos are mandatory for all new relay interlocking

(PIRRI) EI installations and it is also recommended to provide in all existing PIs RRIs To increase the

line capacity mechanical signalling equipments are upgraded to PI RRI or EI Due to complexity in the

circuits and wiring sometimes it is very difficult to rectify the failures So datalogger can monitor these

systems with real time clock Thus it can be named as black box of Samp T equipments and hence it is a vital

tool for accident investigation Datalogger is used at Stations yards Whereas in case of Auto Section amp IBH

Mini dataloggers called as Remote Terminal Unit (RTU) are used

ADVANTAGES OF DATALOGGERS (a) Dataloggers helps in monitoring the typical failures such as intermittent auto right failures

(b) It helps in analyzing the cause of the accidents

(c) It helps in detecting the human failures errors such as

(i) Drivers passing signal at Danger

(ii) Operational mistakes done by panel operators ASMrsquos of operating department

(iii) Signal and telecom engineering interferences in safety circuits

(iv) Engineering and electrical department interferences failures

(v) It helps as a ldquoTOOLrdquo in preventive maintenance of signaling gears

(d) Dataloggers can be connected in network Networked dataloggers helps to monitorthe PIRRIEI remotely

(e) Failure reports can be generated remotely with help of datalogger network

(f) On line and Off line track simulation is possible

(g) Speed of the train on point zones can be calculated

(h) Age of the equipment in terms of number of operations etc

COMMON EQUIPMENT FOR ALL DATALOGGERS ARE GIVEN

BELOW (a) CPU card

(b) Digital and Analog input cards

(c) Local terminal(PC)

(d) communication links

(e) Printer

All the dataloggers requires a potential free ( spare ) relay contact for monitoring digital inputs

through Digital input cards amp for monitoring Analog inputs such ACDC bus bar voltage levels through

Analog input cards Digital and Analog inputs are connected to the Processor card Processor card consists of

memory ICrsquos Memory ICrsquos are programmed as per requirement of the signal engineers

Provision of Dataloggers is mandatory with RRI systems and is optional for PI systems as per

amendment to the specification for Relay Interlocking systems ( IRSS-36 ) The data collected by the

datalogger can be used for failure analysis repetitive discrepancies and for accident investigations

16 | P a g e

Note

If the serial communications is more than 50m then line drivers shall be used up to 3 Kms

4wire leased line Modems shall be used if the serial communication is more than 3 Kms

STUDY OF EFFTRONICS DATALOGGER TECHNICAL DETAILS (a) 24V 12VDC Power Supply

(b) Total Storage Capacity of 10 Lakh events

(c) In-built Temperature sensors

(d) Internal Buzzer for alarming during failures

(e) Real Time clock with internal battery backup with data retention up to 10 years

(f) 512 LED matrix to indicate the status of 512 Digital inputs at a time page wise

(g) Seven segment LCD screen (2x24) to display the status of digitalanalog signalsTime Temperature etc

(h) Using the keyboard various functions can be viewed in the LCD panel

(i) Max Digital Inputs 4096

(j) Max Analog Inputs 96

(k) Digital Input Scanning Time 16 millisecond

(l) Analog Input Scanning Time is less than 1 Sec

HARDWARE (EQUIPMENT) Datalogger system consists of

(a) Datalogger (CPU - with Microprocessor 68000)

(b) Digital input cards

(c) Dual modem card

(d) Digital Scanner units (DSU)

(e) Analog Scanner units (ASU)

CPU CARD It is provided with Motorola microprocessor M 68000 It performs all the activities pertaining to the

datalogger It continuously scans (check) the Digital inputs(inbuilt) Digital Scanner Units and Analog

Scanner Units ie scanning of digital signals (Relay operations) for every 16-milli seconds and scanning of

analog signals (ie ACDC voltages amp DC currents) for less than 1 second

This card will support the IO interfaces of LCD (Liquid Crystal Display) - 2X24 alphanumeric Key

Board LED Matrix Display Real Time Clock LCD display and keyboard This will acts as man machine

interface between the datalogger and the signal engineer All the operations (Software) can be performed

using this LCD and keyboard

Real time display with 7 Segments This is built in real time clock within Datalogger and its current

time will be displayed on six 7-segment display provided (Real time clock depend upon DALLAS 1286

chip) This IC will come with internal battery backup hence there is no need to add external batteries

CPU card continuously scans (checks) the DSUs and ASUs Each input connected to digital scanner

units are optically isolated by Opto couplers When CPU card scans the digital inputs it compares with the

previous stored data and if there is any change from the previous status then only that data will be stored (the

status conditions of relay) with date and real time A total of minimum 10 Lac events can be stored in

memory on first in first out basis so that latest data is available in the system There is no loss of data from

datalogger memory in case of power supply failure of datalogger

DIGITAL INPUT CARDS (IN-BUILT) This system is having maximum 8nos of inbuilt Digital inputs cards Maximum 64nos of digital

inputs can be connected to each digital input card The potential free relay contact may be front or back

contact terminated at the Tag Block from the relay of signals tracks points Buttons etc and are

17 | P a g e

subsequently connected to Digital input cards through Flat Ribbon Cable (FRC) connectors These in-built

digital input cards can monitor a total 512 nos of relays status

DIGITAL SCANNER UNIT (DSU) Each DSU contains 8 nos of Digital Input cards Each input card can be connected with 64 inputs

Total input capacity of DSU unit is 512 inputs These scanner cards contain Optocouplers and Multiplexer

Inputs are connected to Stag card The stag card out put is connected to DSU through FRC connectors

Maximum 7 nos of DSUs can be connected to the system So Digital input capacity of the system is 4096

All these digital inputs are scanned at rate of 16 msec

ANALOG SCANNER UNIT (ASU) ASU contains maximum 3 nos of Analog input cards Each input card can be connected with 8nos of

Analog inputs Total input capacity of the ASU is 24 analog input channels Maximum 4nos of ASUs can be

connected to the system Analog input channel capacity of the system is 96 All these analog inputs are

scanned at a rate of less than 1 sec

PARALLEL PORT Parallel port is provided for connecting printer

RS-232 SERIAL PORTS At least 6 Serial communication ports are provided for communication with other dataloggers

Central Monitoring Unit Remote Terminal Unit Electronic Interlocking system Integrated Power Supply

system etc

EXTERNAL NON-VITAL RELAY CONTACTS These relays provided in the system where 16 number of the Relay contacts are provided on the rear

panel through Tele control port to extend alarms and to control the power equipment from remote or local

locations through computer in case of any occurrence of failures Each control can sink or source 100 m

amps of current

INTERNAL MODEM CARD DUAL MODEM CARD (IN-BUILT) It is fixed in datalogger Euro rack itself One card contains two modems The top modem is called

ANS (answer) modem and the bottom modem is called as ORG (originate) modem It is used in case of

networking of Dataloggers In network connect lsquoANSrsquo modem to the lsquoORGrsquo modem of one adjacent station

and connect lsquoORGrsquo modem to the lsquoANSrsquo modem of other adjacent station

POWER SUPPLY Normally 24V DC (12V DC is optional) supply with battery backup is required for the system

working

Input Voltage Range 18Vhellip32V DC (For 24V) 9Vhellip18V DC (For 12V)

INPUT REQUIREMENTS Relay inputs (digital inputs) and analog inputs (voltages currents etc) are required to be connected

to the system as per the requirements of RRI PI SSI as the case may be Some of the inputs to be

monitored is given below

(a) Digital inputs

(i) Field inputs All TPRs NWKRs RWKRs ECRs Crank Handle relays SidingSlot LC gate

control relays etc

(ii) Control Panel inputs All button Knob SMrsquos Key relays

18 | P a g e

(iii) Internal relays

British system All HR DR HHR WNR WRR ASR UCR RR LR UYRTLSR TRSR TSR

JSLR JR etc

SIEMENS system Z1UR Z1UR1 GZR ZDUCR ZU(R)R ZU(N)PRG(R)RG(N)R U(R)S

U(N)PS UDKR DUCR U(R)LR UYR1 UYR2 G(R)LRGR1GR2

GR3 GR4 OVZ2U(R)RW(RN)R (RN)WLR Z1NWR Z1RWRZ1WR1 WKR1 WKR2 WKR3 etc

(b) Analog channels

(i) 230 V AC (for power supplies in the power panel)

(ii) 110V AC (for Signal and Track transformers)

(iii) 110V DC (for Point operation)

(iv) 60V DC (Siemens relays)

(v) 24V DC (Q-series relays)

(vi) 24V DC (for Block Axle counters)

(vii) 12V DC (for indication)

(viii) 20A (for point operation current)

(ix) 10V AC 5KHz (for Axle counter channels) etc

SOFTWARE MODULES OF DATALOGGERS

(a) Network Management of Dataloggers (NMDL)

(b) Reports

(c) Fault Entry

(d) Track Offline Simulation

(e) Train Charting

NMDL SOFTWARE FEATURES (a) Online Relay Status

(b) Online Faults - To view information of various Online Faults as they occur in the stations where

the Dataloggers are connected

(c) Online Simulation - Graphical view of relay operations train movements etc

(d) Remote monitoring of stations with the help of NETWORKING

SOFTWARE OBJECTIVES (a) Predictive Maintenance

(b) Easy identification of failures

(c) Crew discipline

(d) Train charting

REMOTE MONITORING OF STATIONS WITH NETWORKING OF

DATALOGGERS The individual Dataloggers of various stations can be interconnected through networking technology

The data of Remote Panel stations can be viewed in a Computer at the Central Monitoring Station The data

of the network is collected by the FEP (Front End Processor) which in turn is transmitted to the computer

COMPONENTS OF NETWORK MANAGEMENT OF DATALOGGERS

(a) Datalogger at stations

(b) MODEM and Transmission medium

19 | P a g e

(c) Front End Processor (FEP)

(d) Central Monitoring Unit (CMU) Computer

FEP (FRONT END PROCESSOR)

FEP acts as a buffer between the Central Monitoring Unit (Computer) and the Network It is provided

at centralised place to retrieve data continuously from station dataloggers and store in memory and transfer to

computer on request It stores 10 Lac telegrams It works on 12V DC It draws 16A continuous current

when all the three modems are connected Normally it shows the number of packets pending to be sent to the

computer on its 7-segment LED display It is provided with MOTOROLA 68000 microprocessor It has 6-

nos of RS-232 communication ports such as COM1 COM2 COM3 COM4 COM5 and COM6 COM1 is

used for Fault Analysis System (FAS) ie Central Monitoring Unit (Computer) connection COM2 to COM6

are used for networking For Bi-directional 2- nos of ports and for Tri-directional (T-network) 3-nos of ports

are used

DATA TRANSMISSION Dataloggers can be networked in Uni-directional Mode or Bi-directional Mode or T ndash Network Mode

In case of loss of data retransmission of data takes place

(a) Uni-Directional Mode

Each Datalogger will send data in only one direction to the FEP Unidirectional mode network is not

preferred

(b) Bi-Directional Mode

Each end of Network is connected to FEP and each datalogger can now transmit data in both the directions

Bi-directional Mode is advantageous it enables the Data Transmission even in case of Network Failure

(c) T - Network Mode

If more no of stations are in network ie if the network is too lengthy then T- network mode is preferred

COMMUNICATION The communication protocol for transmitting data and command between datalogger and CMU is

standardized by the RDSO and is given in the Specifications of Dataloggers

(a) The type of communication used in the network is dependent on the distance between the dataloggers

(b) For shorter distances Opto Converter Box- Opto isolated current loop communication is used

(c) For longer distances Modem (Dial-up leased) Fiber Optic Satellite Microwave communication

MODEMS Modems are used for DATA transfer between Dataloggers and Front End ProcessorThese are

configured to RS 232 Serial Communication Network is connected with two types of 4-wire modems

(a) Internal modem card Dual Modem card (in-built)

It is fixed in datalogger Euro rack itself One card contains two modems The top modem is called

ANS (answer) modem and the bottom modem is called as ORG (originate) modem

Note In case of networking of Dataloggers connect lsquoANSrsquo modem to the lsquoORGrsquo modem of one adjacent

station and connect lsquoORGrsquo modem to the lsquoANSrsquo modem of other adjacent station

(b) External modems

20 | P a g e

These are generally used at FEP (Front End Processor) side to connect the Dataloggers

(i) To transfer Data from one datalogger to another datalogger FEP Baud rate is 9600bps

(ii) These modems are 4-wire line communication

(iii) To transfer the data from FEP to RMU (PC) the Baud rate is 57600 bps

There is no difference between these modems functionally

CENTRAL MONITORING UNIT (CMU) COMPUTER

Central monitoring unit (Fault Analysis Unit) is a Personal Computer and its minimum configuration

shall be specified by RDSO from time to time System Software Windows XPVista(OS) Norton Kaspersky

(Anti Virus) Interbase where Server is not available (DBMS) Oracle where Server is available (DBMS)

software are required to run Datalogger System It is provided with Graphical User interface (GUI) based

software and retrieve data from all Networked dataloggers (up to 32) at various stations It stores data in

standard data base files The CMU is capable of analyzing the data and generate reports audiovisual alarms

on defined conditions This data can be compressed to take backup In central monitoring unit Software used

for analysis of data prediction of faults etc is written in a structured format so that purchaser can

reconfigure it if required It displays the status of signaling gears at any selected time in graphic form for any

selected station yard It retrieves the stored data amp simulates train movement It sends commands to various

Dataloggers to activate audio visual alarm or operate and electromagnetic relay

CMU shares data available in it by other PCs through available local area network where this data can

be used for train charting passenger information purpose The system generates audiovisual alarm in

ASMrsquosSignal Maintainerrsquos room in the case of power supply failure (battery voltage low) or battery charger

defective with acknowledgement facility

(a) Each datalogger has its own identity code which will be transmitted along with data packet to central

monitoring unit

(b) Events recorded at each station are continuously transmitted to central monitoring unit Response time of

data transfer will not exceed 10 sec

21 | P a g e

22 | P a g e

OPTICAL FIBER CABLE

INTRODUCTION The demand for bandwidth on transmission networks is increasing rapidly because video and

graphical rich contents are exchanged through the corporate network or the Internet The Gigabit Ethernet

became ommonly used in the corporate network backbone and 10Gbit Ethernet will be adopted in the near

future Meanwhile in the home the demand for high-speed network becomes popular as the wide spread of

broadband access eg CATV xDSL and FTTH The transmission medium with capability to transmit high

bit rate signal is necessary to satisfy these requirements

The telecommunication transport technologies move from copper based networks to optical fiber

from timeslot based transport to wave length based transport from traditional circuit switching to terabit

router and all optical based networks entering into a new era of optical networking

BASIC PHYSICS OF OFC

OPTICAL FIBER CABLE OFC have Fibers which are long thin strands made with pure glass about the diameter of a human

hair OFC consists of Core Cladding Buffers and Jacket as shown in figure

MONOCHROMATIC LIGHT OR SINGLE COLOR LIGHT Light or visible light is electromagnetic radiation of a wavelength that is visible to the human eye (

about 400 ndash 700 nm) The word light is sometimes used to refer to the entire electromagnetic spectrum Light

is composed of elementary particles called photons Three primary properties of light are

Light can exhibit properties of both waves and particles This property is referred to as wave-particle

duality The study of light known as optics In free space light (of all wavelengths) travels in a straight path

at a constant maximum speed However the speed of light changes when it travels in a medium and this

change is not the same for all media or for all wavelengths By free space it is meant space that is free from

matter (vacuum) andor free from electromagnetic fields

Thus the speed of light in free space is defined by Einsteinrsquos equation E = mc2

Frequency ν speed of light in free space c and wavelength λ are interrelated by ν = cλ

From the energy relationships E = mc2 = hν and the last one an interesting relationship is obtained

the equivalent mass of a photon m = hνc2

When light is in the vicinity of a strong electromagnetic field it interacts with it From this interaction

and other influences its trajectory changes direction as shown in figure

23 | P a g e

INCIDENT RAY REFLECTED RAY AND REFRACTED RAY An incident ray is a ray of light that strikes a surface The angle between this ray and the

perpendicular or normal to the surface is the angle of incidence Reflection is the change in direction of a

wave front at an interface between two different media so that the wave front returns into the medium from

which it originated Common examples include the reflection of light sound and water waves

The reflected ray corresponding to a given incident ray is the ray that represents the light reflected by

the surface The angle between the surface normal and the reflected ray is known as the angle of reflection

The Law of Reflection says that for a specular (non-scattering) surface the angle of reflection always equals

the angle of incidence The refracted ray or transmitted ray corresponding to a given incident ray represents

the light that is transmitted through the surface The angle between this ray and the normal is known as the

angle of refraction and it is given by Snells Law

The figure shows Incident ray Reflected ray Refracted ray the angle of incidence and angle of refraction

REFRACTIVE INDEX - Refractive index is the speed of light in a vacuum ( c =299792458kmsecond) divided by the speed

of light in a material ( v ) Refractive index measures how much a material refracts light Refractive index of

a material abbreviated as lsquo n lsquo is defined as lsquo n=cv lsquo Light travels slower in physical media than it does

when transmitted through the air Refractive index (n) is a function of molecular structure of matter optical

frequency optical intensity determines optical propagation properties of each wavelength ( λ ) may not be

distributed equally in all directions is affected by external temperature pressure and fields

Refractive index of a medium is a measure for how much the speed of light is reduced inside the

medium For example typical glass has a refractive index of 15 which means that light travels at 1 15 =

067 times the speed in air or vacuum Two common properties of glass and other transparent materials are

directly related to their refractive index

First light rays change direction when they cross the interface from air to the material and effect that

is used in lenses and glasses

Second light reflects partially from surfaces that have a refractive index different from that of their

surroundings

SNELLrsquoS LAW-

24 | P a g e

When light passes from one transparent material to another it bends according to Snells law which

is defined as n1sin(θ1) = n2sin(θ2)

where n1 is the refractive index of the medium the light is leaving θ1 is the incident angle between the light

beam and the normal (normal is 90deg to the interface between two materials)

n2 is the refractive index of the material the light is entering

θ2 is the refractive angle between the light ray and the normal

Snellrsquos law gives the relationship between angle of incidence and angle of refraction

For the case of θ1 = 0deg (ie a ray perpendicular to the interface) the solution is θ2 = 0deg regardless of

the values of n1 and n2 That means a ray entering a medium perpendicular to the surface is never bent The

above is also valid for light going from a dense (higher n) to a less dense (lower n) material the symmetry of

Snells law shows that the same ray paths are applicable in opposite direction

TOTAL INTERNAL REFLECTION- When a light ray crosses an interface into a medium with a higher refractive index it bends towards

the normal Conversely light traveling cross an interface from a higher refractive index medium to a lower

refractive index medium will bend away from the normal

This has an interesting implication at some angle known as the critical angle θc light traveling from

a higher refractive index medium to a lower refractive index medium will be refracted at 90deg in other words

refracted alon g the interface If the light hits the interface at any angle larger than this critical angle it will

not pass through to the second medium at all Instead all of it will be reflected back into the first medium a

process known as total internal reflection

The critical angle can be calculated from Snells law putting in an angle of 90deg for the angle of the refracted

ray θ2 This gives θ1

Since θ2 = 90deg

So sin(θ2) = 1

25 | P a g e

Then θc = θ1 = arcsin(n2n1)

For example with light trying to emerge from glass with n1=15 into air (n2 =1) the ritical angle θc is

arcsin(115) or 418deg For any angle of incidence larger than the critical angle Snells law will not be able to

be solved for the angle of refraction because it will show that the refracted angle has a sine larger than 1

which is not possible In that case all the light is totally reflected off the interface obeying the law of

reflection

OPTICAL FIBER MODE An optical fiber guides light waves in distinct patterns called modes Mode describes the distribution

of light energy across the fiber The precise patterns depend on the wavelength of light transmitted and on the

variation in refractive index that shapes the core In essence the variations in refractive index create

boundary

conditions that shape how light waves travel through the fiber like the walls of a tunnel affect how sounds

echo inside

We can take a look at large-core step-index fibers Light rays enter the fiber at a range of angles and

rays at different angles can all stably travel down the length of the fiber as long as they hit the core-cladding

interface at an angle larger than critical angle These rays are different modes Fibers that carry more than

one mode at a specific light wavelength are called multimode fibers Some fibers have very small diameter

core that they can carry only one mode which travels as a straight line at the center of the core These fibers

are single mode fibers This is illustrated in the following picture

OPTICAL FIBER INDEX PROFILE Index profile is the refractive index distribution across the core and the cladding of a fiber Some

optical fiber has a step index profile in which the core has one uniformly distributed index and the cladding

has a lower uniformly distributed index Other optical fiber has a graded index profile in which refractive

index varies gradually as a function of radial distance from the fiber center Graded-index profiles include

power-law index profiles and parabolic index profiles The following figure shows some common types of

index profiles for single mode and multimode fiber

26 | P a g e

OPTICAL FIBERrsquoS NUMERICAL APERTURE ( NA )- Multimode optical fiber will only propagate light that enters the fiber within a certain cone known as

the acceptance cone of the fiber The half-angle of this cone is called the acceptance angle (see figure 18)

θmax For step-index multimode fiber the acceptance angle is determined only by the indices of refraction

Where

n is the refractive index of the medium light is traveling before entering the fiber

nf is the refractive index of the fiber core

nc is the refractive index of the cladding

NUMBER OF MODES IN A FIBER - Modes are sometimes characterized by numbers Single mode fibers carry only the lowest-order

mode assigned the number 0 Multimode fibers also carry higher-order modes The number of modes that

can propagate in a fiber depends on the fiberrsquos numerical aperture (or acceptance angle) as well as on its

core diameter and the wavelength of the light For a step-index multimode fiber the number of such modes

Nm

Where

D is the core diameter

λ is the operating wavelength

NA is the numerical aperture (or acceptance angle)

MODE FIELD DIAMETER - All light do not travels through the core of the fiber but is distributed through both the core and the

cladding The mode field is the distribution of light through the core and cladding of a particular fiber

Mode-Field Diameter (MFD) defines the size of the power distribution When coupling light into or out of a

fiber MFD is important in understanding light loss

27 | P a g e

ADVANTAGE OF OFC COMMUNICATION - bull More information carrying capacity Fibers can handle much higher data rates than copper More

information can be sent in a second

bull Free from Electromagnetic and Electrostatic interference Being insulator no electric current flows through

the fibre and due to this reason fibres neither radiate nor pick up electro - magnetic radiation So WPC

CLEARANCE is not required

bull Low attenuation 025 dbkm at 1550 nm Loss in twisted pair and coaxial cable increases with frequency

where as loss in the optical fibre cable remains flat over a wide range of frequencies

bull Use of WDM ndash Switching routing at Optical signal level

bull Self healing rings under NMS control

bull Small size makes fibre cable lighter in weight So easy to handleOptic fibre cable weight (approx)

500 kg km Copper cable weight (approx) 1000 kgkm

The reasons are photons of light in a fibre

do not affect each other as they have no electrical charge and they are not affected by stray photons outside

the fibre But in case of copper electrons move through the cable and these are affected by each other

Optical fibre does not carry any electricity even if the cable is damaged or short circuited it does

not cause any spark or fire hazard

As the fibre do not radiate energy it can not be detected by any nearby antenna or any

other detector The fibres are difficult to tap and therefore excellent for security

As the signal transmission is by digital modulation there is no chance of cross talk in

between channels

Only by adding a few additional terminal and repeater equipments the

capacity of the system can be increased at any time once the cable is laid

ical effects and temperature variations

LIMITATIONS OF OFC -

difficult

- utilised

APPLICATION IN SIGNAL AND TELECOMMUNICATIONS transmission circuits

-haul circuits for linking of telephone exchanges

28 | P a g e

PROPAGATION MODES CONCEPT -

MODE - Mode is an available distribution of electromagnetic field in a plane transverse to the direction of

light propagation Each mode is characterized by frequency polarization electric field strength and

magnetic field strength Available patterns are derived from Maxwellrsquos equations and boundary conditions

LINEARLY POLARIZED (LP) MODE A mode for which the field components in the direction of propagation are small compared to

components perpendicular to that direction An optical fibre supports only different field patterns called as

lsquoLinear Polarizedrsquo or lsquo LPrsquo modes The reasons are

requirements

de

the accrual of power carried by different modes

There are two basic types of fiber Multimode fiber and Single-mode fiber

Multimode fiber is best designed for short transmission distances This is suited for used in LAN systems and

video surveillance Single mode fibre is best designed for longer transmission distances This is suitable for

long distance telephony and multi channel television broadcast systems

29 | P a g e

MULTI MODE FIBER Multimode fiber the first to be manufactured and commercialized simply refers to the fact that

numerous modes or light rays are carried simultaneously through the waveguide Modes result from the fact

that light will only propagate in the fiber core at discrete angles within the cone of acceptance MM fiber type

has a much larger core diameter compared to single-mode fiber allowing for the larger number of modes

and

is easier to couple than single-mode optical fiber Multimode fiber further categorized as Multimode step-

index and Multimode graded index fiber

PROPAGATION THROUGH MMSI FIBER Figure shows the principle of total internal reflection applies to multimode step index fiber Because

the corersquos index of refraction is higher than the claddingrsquos index of refraction the light that enters at less than

the critical angle is guided along the fiber

Three different light waves travel down the fiber One mode travels straight down the center of the

core A second mode travels at a steep angle and bounces back and forth by total internal reflection The third

mode exceeds the critical angle and refracts into the cladding Naturally it can be seen that the second mode

travels a longer distance than the first mode causing the two modes to arrive at separate times

PROBLEMS WITH MMSI FIBER AND SOLUTION This disparity between arrival times of the different light rays is known as dispersion and the result is

a muddied signal at the receiving end It is important to note that high dispersion is an unavoidable

characteristic of multimode step-index fiber The solutions are either use Graded index fiber or Single mode

fiber

PROPAGATION THROUGH MMGI FIBER Multimode Graded-index refers to the fact that the refractive index of the core gradually decreases

farther from the center of the core The increased refraction in the center of the core slows the speed of some

light rays allowing all the light rays to reach the receiving end at approximately the same time reducing

dispersion Figure shows the Light propagation principle through multimode graded-index fiber The corersquos

central refractive index ( nA ) is greater than that of the outer corersquos refractive index ( nB )

It is very clear from the figure the light rays no longer follow straight lines they follow a serpentine path

being gradually bent back toward the center by the continuously declining refractive index This reduces the

arrival time disparity because all modes arrive at about the same time The modes traveling in a straight line

30 | P a g e

are in a higher refractive index so they travel slower than the serpentine modes These travel farther but

move faster in the lower refractive index of the outer core region

PROPAGATION THROUGH SMSI FIBER Single mode fiber has a much smaller core that allows only one mode of light at a time to propagate

through the core The figure shows the single mode fiber

Single-mode fiber exhibits no dispersion caused by multiple modes Single-mode fiber also offers lower fiber

attenuation than multimode fiber Thus more information can be transmitted per unit of time because it can

retain the fidelity of each light pulse over longer distances Like multimode fiber early single-mode fiber was

generally characterized as step-index fiber meaning the refractive index of the fiber core is a step above that

of the cladding rather than graduated as it is in graded-index fiber Modern single-mode fibers have evolved

into more complex designs such as matched clad depressed clad and other exotic structures

SINGLE-MODE FIBER DISADVANTAGES The smaller core diameter makes coupling light into the core more difficult The tolerances for single-

mode connectors and splices are also much more demanding

CUTOFF WAVE LENGTH - Cutoff wavelength is the wavelength above which a single-mode fiber supports and propagates only

one mode of light In other words an optical fiber that is single-mode at a particular wavelength may have

two or more modes at wavelengths lower than the cutoff wavelength The effective cutoff wavelength of a

fiber is dependent on the length of fiber and its deployment The longer the fiber the lower is the effective

cutoff

wavelength The smaller the bend radius of a loop of the fiber the lower is the effective cutoff wavelength If

a fiber is bent in a loop the effective cutoff wavelength is lowered

SIGNAL ATTENUATION IN FIBER - Optical fiber has a number of advantages over copper However it also suffers from degradation

problems which can not be ignored The first of these is loss or attenuation Attenuation is typically the result

of two sub properties They are scattering and absorption Both of which have cumulative effects The second

is

dispersion which is the spreading of the transmitted signal and is analogous to noise

SCATTERING Scattering occurs because of impurities or irregularities in the physical construction of the fiber The

well known form of scattering is Rayleigh Scattering It is caused by metal ions in the silica matrix and

results in light rays being scattered in various directions

31 | P a g e

Scattering limits the use of wavelengths below 800nm The short wavelengths are much affected than longer

wavelengths It is because of Rayleigh scattering that the sky appears to be blue ( shorter wave length ) The

shorter wavelengths ( blue ) of light are scattered more than the longer wavelengths of light

ABSORPTION Absorption results from three factors They are hydroxyl ions ( OH- water ) in the silica impurities

in the silica and incomplete residue from the manufacturing process These impurities tend to absorb the

energy of the transmitted signal and convert it to heat resulting in an overall weakening of the signal The

Hydroxyl absorption occurs at 125 and 139 micro The silica itself starts to absorb energy at 17 micro

because of the natural resonance of the silicon dioxide

MACRO BENDING LOSS Macro-bending loss is caused by bending of the entire fiber axis The bending radius shall not be

sharper than 30d where d is diameter of cable A single bend sharper than 30d can cause loss of 05dB

The fiber may break if bending is ever sharper

MICRO BENDING LOSS Micro-bending loss is caused by micro deformations of fiber axis which leads to failures in achieving

total internal reflection conditions Micro-bends are small scale perturbations along the fiber axis the

amplitude of which are on the order of microns These distortions can cause light to leak out of a fiber

Micro-bending may be induced at very cold temperatures because the glass has a different coefficient of

thermal expansion from the coating and cabling materials At low temperatures the coating and cable

become more rigid and may contract more than the glass Consequently enough load may be exerted on the

glass to cause micro bends

Coating material is selected by manufacturers to minimize loss due to micro-bending The linear thermal

expansion coefficient of coating material shall be compatible with that of fiber

32 | P a g e

DISPERSION Dispersion is the optical term for the spreading of the transmits in the fiber It is the bandwidth

limiting phenomenon and comes in two forms Multimode dispersion and chromatic dispersion Chromatic

dispersion is further subdivided into material dispersion and waveguide dispersion

DISPERSION PHENOMENON IN OPTICAL FIBER Dispersion is the time distortion of an optical signal that results from the differences of time of travel

for different components of that signal typically resulting in pulse broadening As the distance traveled by

the signal is more broadening of pulse is more In digital transmission dispersion limits on the maximum

data rate and the maximum distance ie the information-carrying capacity of a fiber link The interference

from broadened pulse in the next interval shall not lead to erroneous interpretation of received signal

OPTICAL DOMAIN Understanding where attenuation and dispersion problems occur helps optical design engineers

determine the better wavelengths at which information can be transmit taking into account distance type of

fiber and the other factors which can severely affect the integrity of the transmitted signal The graph shown

depicts the optical transmission domain as well as the areas where problems arise The wavelength (nm)

is shown on X-axis and attenuation ( dBkm) is shown on Y-axis

There are four transmission windows appear in the figure The first one is at around 850 nm the

second at 1310nm third at 1550 nm and fourth at 1625 nm The last two labeled as C and L band

respectively The 850 nm wavelength at which the original LED technology operated The second window at

1310 nm has low dispersion The 1550 nm called as C-band is ideal wavelength for long haul

communication systems The network engineers can avoid transmitting signal at 1000 nm where Rayleigh

scattering 1240 and 1390 nm where hydroxyl absorption by water occurs to avoid high degree of loss

Optical fibers also can be manufactured to have low dispersion wavelength in the 1550nm region

which is also the point where silica-based fibers have inherently minimal attenuation These fibers are

referred to as dispersion-shifted fibers and are used in long-distance applications with high bit rates For

33 | P a g e

applications utilizing multiple wavelengths it is undesirable to have the zero dispersion point within the

operating

wavelength range

34 | P a g e

SIGNALLING RELAYS

INTRODUCTION A relay is an electromagnetic device which is used to convey information from one circuit to another

circuit through a set of contact ie front or back contact Constructional and electrically relays may be

divided into DC and AC relays because the means by which the electrical energy in the coil is converted in

to mechanical Energy in order to move the contacts are fundamentally different In DC type the contacts are

carried on an armature forming part of a magnetic circuit in which a field is set up by the current flowing in

the coils In AC types the contacts are attached by a link mechanism to a metal sector disc or cylinder in

which currents are induced by the alternating magnetic field produced by the currents in the coils

Every endeavor has been made to explain the action of each type of relay in the simplest possible manner

Relays are sophisticated switch gears used for remote control and succession control of various

electrical equipment In present days they are widely used because they are capable of protecting the

controlled equipment from cross feeding and overloading even as they cater for speedy operations

Most of the relays in present day signaling are electromagnetic devices although some of the relays control

circuits through electronic components like diodetransistors Integrated Chips etc

Railway signaling relays are unique in that

(a) They operate on low voltage and current

(b) They are more articulate as according to their special features they can work under restrictive conditions

and in any specified manner Virtually they can cater for all situations while contributing to speed and

accuracy in operations

CLASSIFICATION OF SIGNALLING RELAYS (a) According to the method of their mounting or fixture they are classified as

(i) Shelf type Relays which are loosely kept on shelves

(ii) Plug in type Relays which are plugged into a pre- wired plug boards

(b) According to their connection and usage they are classified as

(i) Track relays Relay which is directly connected to the track to detect the presence of vehicle

(ii) Line Relays Other than track relay all are line relays Relays connected to the selection circuit

(c) According to their vitality or importance in ensuring train working safety they are classified as

(i) Vital Relays All relays used for traffic control such as signal point controls track detection etc

(ii) Non-vital Relays Relays which operate control aids and accessories like warnings buzzers

Indications etc

(d) According to their special provisions to ensure reliability of their contacts they are classified as

(i) Proved type are those whose normalization after each operation shall be proved in circuit

controlled by their contacts Contacts in which both the springs have metal surfaces on their tips They may

get fused due to high sparking current across them during operation These may prevent relay normalization

and causes unsafe condition in traffic control To avoid this proving of relay normalization after each

operation is necessary

(ii) Non - proved type Need not to be proved to have been normalized after each operation as their

contacts have at least one non-fusible contact (carbon contact)

(e) According to their feed source relays are broadly classified as

(i) DC relays The relay which requires DC power supply for its operations are called DC relays Among

the DC relays

o DC neutral relays This relay closes the same set of contacts on energization with Normal polarity

or Reverse polarity supply

o Polar Relays This relay closes different set of contacts when energized with Reverse polarity

supply They may or may not have contact to close when deenergized

35 | P a g e

(ii) AC Relay AC Induction motor track relays Time element relays flashing indication control etc

(iii) Electronic Relays DC relays with electronic components in them are called electronic relays

DC NEUTRAL RELAY Each Relay has usually one or two coils with a hollow center to accommodate a coreThe coils are

made up of a large numbers of turns of small gauge soft drawn copper wire The two coils can be connected

in series or parallel according to the requirement of relay resistance The ends of the coils are terminated on

binding post to which the control wires are connected Each coil is placed around a core of specially selected

Iron or steel having high permeability and low retentivity The core should be susceptible to magnetism and

at the same time should have little residual magnetism The cores are connected at the top by a yoke to

complete the magnetism coupling between two ends of coils The bottom of each core is equipped with a

large steel or Iron block known as pole piece or face

A flat piece of Iron or steel called armature is supported by brackets which are securely fastened to

the pole piece The armature yoke and the pole pieces are also made of specially selected iron or steel of the

same quality as the core The armature carries the metallic spring contacts which are insulated from it

The circuit through the coils of the relay is closed It sets up a magnetic flux through the core yoke and the

armature The flux passing between the armature and pole faces causes the armatures get attracted to the pole

faces and armature picks up and closes front contacts When the circuit is opened the magnetic flux collapses

and the armature drops away by gravity from the pole faces the front contacts break and back contacts close

The front and back contacts of the relay can be utilised to make or break other circuits Two stop pins of

nonmagnetic material are fixed either on the armature or pole faces so that the armature cannot

come in contact with the pole faces It is essential to maintain a small air-gap between the armature and pole

faces so that low value of residual magnetism may not retain the armature in picked up position and causes

the relay to fail to drop away with a break in its control circuit

GENERAL USAGE

DC Neutral line relays are most commonly used for Railway Signalling controls and detection

Among them plug-in type relays are preferred in larger installations for space considerations Shelf type

relays are also in use mostly in wayside stations

There are many DC Neutral line relays in use with special features such as

(i) Delayed operation

(ii) Biased DC control

(iii) DC control unaffected by AC interference currents

(iv) Getting latched in operated condition till further feeding and others

Usage of DC polar relays is mostly in conjunction with block instruments that control traffic between

stations AC line relays are almost extinct in installations of British Signalling practice They are however

used for time control operations flashing indication control and such other special purposes in installations

with Siemens signalling practice widely Track relays are used according to the type of track detection

circuits chosen for a given location and context While most of the track circuits are still of the DC working

type requiring DC neutral track relays with them the prospects of their being replaced with Electronic track

circuits directly feeding DC line relays in future are great AC Track Circuits are used in DC Traction area

as conventional DC Track Circuits are not suitable there AC Track relays are used with them almost all of

the induction motor type In the British practice of signalling which was first introduced on Indian Railways

non-proved type relays with carbon to metal switching contacts are generally used for vital controls

They facilitate simple circuit designs But with the advent of German Practice introduced by Ms

Siemens later proved type relays with all metal to metal contacts are widely accepted in spite of

complications in circuit design caused by them A recent introduction is that of the same type relays made by

Ms Integra control However for some time now the appreciable features of both the practices are getting

36 | P a g e

incorporated together in the indigenous designs of signalling by railwaymen With this the usage of all types

of relays anywhere can be found without straight jacketed segration of relay types

CHARACTERSTIC OF ELECTRO-MAGNETIC RELAY The following are the characteristic of electro-magnetic relays A brief study of them helps in

understanding the choice of their components and designs features

1) Force of attraction

2) Effect of air gap

3) Effect of Hysterisis

4) Transient condition

FORCE OF ATTRACTION In any electro-magnetic system the force of attraction is given by

Where B - is the flux density a - is the cross sectional area of the particular part of the magnetic

circuit

In the case of a DC neutral Relay B is proportional to the current that is flowing in the coil

surrounding the electro-magnet and thus the force of the attraction is directly proportional to the square of the

current This square relationship has its own advantage especially in the case of DC track relay in that a

small reduction in the current will have a great effect on the working of the relay Also for a given change of

current the make and the break will be quicker with lesser possibility of arcing

EFFECT OF AIR GAP

Curve lsquoArsquo is magnetisation curve for the iron and is all practical purpose a straight line up to the

saturation point Curve lsquoBrsquo is the magnetisation curve for the open-air gap which is a straight line through

out because per magnetisation curve of the whole

magnetic circuit of the relay and for a given force is the sum of the amp-turns for the iron part and the amp-

turns for the air gap

When the front contacts are open the force required to pick up the armature is shown on curve lsquoCrsquo to be F1

but after the armature has operated it will be separated from the core by stop pins In this position the amp-

turns required to maintain the armature is less as indicated by the dotted line from 1 on curve C to 2 on curve

37 | P a g e

F But actually the current in the coil is unaltered the force on the armature is greater than required as

indicated at 3 on curve F Part of this extra force is used to flex the front contacts sufficiently to give good

contact pressure when it is in energised position

The difference between the pick-up and the drop-away current should be as small as practicable in

track relay to ensure good shunting characteristics This is achieved firstly by the choice of good quality relay

iron and secondly by having a small air gap between armature and core If the air gap is not available then

the residual magnetism fluxes might cause the armature to be retained when the supply is disconnected For

this reason residual pins are provided to ensure a definite minimum air gap in the energised position

EFFECT OF HYSTERISIS

Hysterisis is the property by which the flux produced lags behind the current In the de-energized

condition there will be small residual flux in the core When the voltage is applied to the coils the current in

rising to its steady value first causes the flux to rise from 1 to 2 along the curve At this point the flux density

will be sufficient to attract the armature and reduce the air gap the flux then raise to 3 and continue to 4

which corresponds to the steady current in the coils When the voltage is disconnected the current in falling

caused the flux to fall from 4 to 5 along the curve At this point the flux density will fall below the value

required to maintain the armature which will release thus increasing the air gap and reducing the flux to 6

Finally the

flux will decrease from 6 to 1 where the current will again be zero

The relay core is made of material having high permeability and low retentivity As mentioned in

the IRS specification Electromagnet iron may be in the form of a

(a) Bar of silicon steel

(b) Best Yorkshire wrought iron

(c) Swedish charcoal iron

(d) Electrical steel sheets

` This reduces the difference between pick up value and Drop away value By selecting good quality

core material Percentage release and sensitivity of the relay will be improved

TRANSIENT CONDITION

38 | P a g e

When the voltage is applied or disconnected from the coils it takes some little time before the current

become steady These are known as transient conditionsrdquo and are important so far as track relays are

concerned When the voltage is first applied to the coils the magnetic flux in rising cuts the turns on the

coils and in so doing produces a back EMF that opposes the applied voltage and retards the growth of

current

The growth and decay of flux are decided by the relationship between the inductance and resistance

in the circuit is known as time constant It is not fixed quantity in the case of DC neutral relay This value of lsquo

Lrsquo is less when the relay is in de-energised condition (L1) than when the relay is in energised condition (L2)

The magnitude of flux that is established for a given change of current is different in two cases

When the current reaches the pick up value the armature closes and the inductance is increased to L2

due to reduced air gap the flux per amp is increased The increase in flux increased the back EMF during the

movement of the armature after which the current continuous to raise along a new curve corresponding to the

increased inductance until it reaches the final value (ER) This process is indicated above in fig24

When the supply is disconnected the current is obliviously reduced to zero immediately but the flux

decay comparatively slowly owing to the eddy currents produced in the core by the rapid flux change which

tend to maintain the flux The drop away time on a disconnection is however generally negligible See fig

below

If the relay releases due to the reduction in current from say I 2 to I 1 caused by the application of

shunt resistance (as in the case of track relay ) the time taken is much longer than the relay is simply

disconnected The rate of rise or fall of current during the transient conditions is also depends on exterior

circuit values because L and R apply to the whole circuit The production of eddy current in the core the flux

will decay at a slower rate than the current So that the actual release time will be a little longer than it takes

the current to fall to the release

L= Inductance

39 | P a g e

R= Resistance

It is now clear that to reduce releasing time to a minimum it is necessary that

- The relay iron should have low Hysterisis loss and low retentivity

- The degree of over energization of the relay should be restricted

- Connecting a suitable external resistance in series with the relay to keep LR ratio low

In non RE area for track circuit length less than 100M 9 ohm track relay only to be used Using relay

with minimum contacts as they require lesser current which keeps inductance value low

Train working safety is ensured only if the track relay of shortest length track circuit is released

before a light engine running at a highest permitted speed clears it Otherwise the track circuit occupation

may go undetected To avoid this a special provision has to be made in signal control circuits wherever

necessary

The following methods may be adopted for reducing the time lag of track relay

(a) Restrict the over energisation of relay since the release time depends on the initial working current

(b) Connecting a suitable external resistance in series with the relay to keep the LR ratio low

(c) Using relays with minimum contacts as they require lesser operating current keeping the inductance

value low

40 | P a g e

CONCLUSION

Modern signalling is vital for safe and punctual movements of trains In the Indian railways The Signalling

and Telecommunication Department is responsible for providing modern effective and relaible signalling

systems as well as telecommunication systems

The first mode of communication used in Indian Railways was the use of electric telegraph

with the help of Morose code Morose code is the method of providing text information as a series of on-off

tones and lights or clicks that can be directly understood by a skilled listener or observer without special

equipmentEach character (letter or numeral ) is represented by a unique sequence of dots and dashes Later

this system becomes obselete and beggan the era of wireless communication which operated at audio level

frequency range

In wireless communication the significant advances took place the transition to miniature

valves or filament tubesBut this was abandoned too because of excessive current consumption and over

heating of the filament tubes

Fibre-optic communication is a method of transmitting information from one place to another by

sending pulses of light through an optcial fibreThe light forms an electromagnetic carrier wave that is

modulated to carry information First developed in the 1970s fibre optic communication systems has

revolutionized the telecommunications industry and have palyed a major role in the advent of the information

age Because of its advantages over electrical transmissionsoptical fibres have largely replaced copper wire

communications in core networks in the developed world The Indian Railways too is undergoing a transition

from Microwave communication to fibre optic communications

41 | P a g e

BIBLIOGRAPHY AND REFERENCES

1 wwwwikipediacom

2 wwwbritaniccacom

3 wwwirfcacom

4 Motorola GP60 system manual

5 Harris FAS 7000 manual

6 TOSHIBA Manual

10 | P a g e

(i) If counts registered at both detection points are equal the section is cleared otherwise the section is shown

as occupied The system ensures no error condition to arrive at the decision of clearance

(j) System is designed as per CENELEC SIL-4 (European standard) using micro controller along with other

electronic circuits and programmed using dedicated software When any of these circuits fail the system

goes to fail safe condition

(k) It is programmable for either Preparatory Reset or Conditional Hard Reset as per requirement

(l) Micro controller based design with 2 out of 2 decisions and counting through software

(m) V21 Modem communication (2-wire) on frac12 quad cables and also compatible to work on voice channel of

OFC amp Radio

(n) Opto isolated vital relay drive for Q-style 24V 1000 _ and Vital Relay output can be giving at both ends

of the system

APPLICATIONS The system can be widely used in Railways for Block Working (BPAC) Intermediate Block Signaling Auto

signalling and Track circuiting for i) Loop line ii) Main line iii) yard lines

SYSTEM DESCRIPTION

This system comprises of

Tx coils-2 nos

Rx coils-2 nos

Reset Box (RB 258A)

Card 1 Signal Conditioning Card ndash 1

Card 2 Signal Conditioning Card - 2

Card 3 Micro controller Logic Board ndash 1

Card 4 Micro controller Logic Board ndash 2

2 nos for independent resetting ndash when used in block sections

1 no for common resetting ndash when used for Track circuiting at stations

Card 5 Event Logger Card

Card 6 Modem Card

Card 7 Relay Driver Card

Card 8 DC-DC Converter Card

SSDAC (DACF 700AP) UNIT

(A) SIGNAL CONDITIONING CARD (CARD 1amp2) (SCC) -1 (SCC-1) generates 21 KHz carrier

signals

-2 (SCC-2) generates 23 KHz carrier signals which is transmitted to 2nd

set of Tx coils

s receive these signals

modulated

train pulses

11 | P a g e

(B) MICRO-CONTROLLER LOGIC BOARD CARD (CARD 3amp4) (MLB) The Micro-controller Logic Board (MLB) is the heart of the system

o 8051 Based Architecture

o 8 Bit Micro Controller

o ATMEL AT89S8252 Micro controller

o 2 out of 2 Decision

o Uses C subset language

- TOOLS

o KEIL μ Vision Development System

o Universal Programmer

o 2KB Program Memory

o 256 bytes RAM

o 8KB Flash memory

o 32 Programmable IO lines

o Wide Operating Voltage range of 4V-6V

o Full Duplex Serial Port

o Programmable Watch Dog Timer

o Fully Static operation up to 24MHz (Upgraded to 40MHz)

o Operating Temperature of ndash40degC - +85degC

o Use of State Machine for Axle Counting

o Use of ASCII MODBUS protocol

o Use of CRC16 technique for Error Checking during communication

o Wheel detection

o Train direction checking and

o Wheel counting functions

o It receives the remote wheel count and computes the status of the section for clear or occupied

o It also checks various supervisory signal levels like supervisory of TxRx coils presence of various

cards communication link failure etcThese cards communicate with each other for wheel count

At Entry-end if train enters into section (1st detection) the counts are incremented and when train

shunts back from the same detection ie if train exits from the section from the same detection the counts are

decremented At Exit-end if train enters into section (2nd detection) the counts are decremented and when

train shunts back from the same detection ie if train exits from the section from the same detection the

counts are incremented Both the track devices at Entry and Exit ends must be fixed on same side of the

track

This MLB card is having Extensive LED display

o A block of 8 LED indicators for count progress error display

o 2 independent LED indicators for section status

o The errors occurring in the system during the operation of the SSDAC are encoded and are indicated by

means of the 8-LED block present on the front panel of the MLB cards

(c) EVENT LOGGER CARD (CARD 5)

Event logger card is designed to capture and store important signals from the remote and local SSDAC units

The stored data can be downloaded from the event logger card for the purpose of analyzing the events

occurring during the operations of the SSDAC The data can be analyzed with the help of CEL data analyzer

software

12 | P a g e

The event logger card captures following signals

(i) Pulse signals

(ii) Supervisory signals

(iii) Card removal information

(iv) Serial packets from

Event Logger card has a Rabbit processor and 2 MB FLASH MEMORY to store packets The data is initially

stored in the buffer and subsequently transferred to FLASH memory every two minutes Normally 4096

pages of the data can be stored in flash memory on FIFO (first in first out) basis

Run This LED blinks continuously indicating the normal working of the event

Log This LED blinks whenever data is being logged into the flash memory (Approx after every 2 minutes)

Dnld This LED is ON when data is being downloaded from the flash memory of the card and becomes OFF

when download is complete

(D) MODEM CARD (CARD 6) (i) The modem card transmits and receives the digital packet information form one counting unit to the other

The packet will appear after every 18 sec and the packet carries the latest information such as

(ii) The modem card being used is V21 type (2-wire) in SSDAC

(iii) This card interfaces with serial RS232C port of both Micro-controller Logic Boards

(iv) It multiplexes the two RS232C inputs and selects one of the two channels and provides signal conversion

from digital to analog (FSK modulation) and vice-versa

(v) Data transmission rate is 300 bitssec

(vi) Automatic Gain Control circuit is incorporated hence no gain adjustments required

(vii) Mode selection on Modem card The modem has been set in lsquoORIGINATORrsquo mode for entry and in the

lsquoANSWERrsquo mode for exit in the factory

(viii) LED Indications provided on Modem card

-Transmitting the signal when LED is flashing

- Receiving the signal when LED is flashing

-Remains OFF in SSDAC

-Carrier is detected when LED is glowing

(E) RELAY DRIVER CARD (CARD 7) (i) The Relay Driver card (RD) provides the 24V DC output required for driving Vital Relay

(ii) One RD card is used in each SSDAC counting unit The RD card receives the command of clear and

clock signals from MLB1 amp MLB2 cards and drives the vital relay lsquoONrsquo when section is NOT OCCUPIED

through opto- isolator circuit

(iii) If a train occupies the section the vital relay is dropped The vital relay status is read back by the system

as per the driving output

(iv) It has

13 | P a g e

ndash LED flashes when the section is clear

ndash LED flashes when the section is clear

All the above LEDrsquos are lit for section clear condition

(F) DC-DC CONVERTER CARD (CARD 8)

INPUT VOLTAGE Nominal Voltage voltage 24V DC Maximum current drain= 12A

Required voltage 18V DC to 30V DC

Output voltage

Nominal Voltage +5 V DC 2 A Required voltage 4 7 5 t o 525V DC

Nominal Voltage +12V DC 200 mA Required voltage 1175 to 1225V DC

Nominal Voltage +24V DC 300 mA with common ground Required voltage 235 to 245V DC

Nominal Voltage +15V DC 100 mA with isolated ground Required voltage 145 to 155V DC

SURGE VOLTAGE AND LIGHTNING PROTECTION Transient surge voltages arise as a result of Lightning discharge switching operations in electrical

systems and electrostatic discharge These surge voltages often destroy the electronic equipment to a large

extent In order to prevent surge voltages from destroying the equipment all the input lines of SSDAC ie

Power Supply (24V) Reset (48V) amp Modem is to be routed through surge voltage protection devices for

effectively protecting the system These devices (3 numbers) are mounted in a box and supplied along with

the system One number of box is to be installed at each location and wired to the SSDAC

Each surge voltage protection device consists of two parts

(a) Base

(b) Plug Trab

The Base of the device is used for wiring the input and output signals The connection details from relay

room to the box and from box to SSDAC unit are provided on the box The Plug Trab consists of MOV and

GD Tube and diverts the excess energy during surge voltages or lightning into the ground connection The

operation of these devices relies on a high quality ground connection in order to safely shunt away the

unwanted energy The impedance of the ground connection is critical and it should be less than 2 Ohms

NOTE The 3 Plug Trab connections are not to be interchanged with one another The plug Trab is a

detachable device and can be replaced with SPARE unit in case of blown device which is indicated by

means of LED for 24 V

EFFECTIVENESS OF PLUG TRABS The effectiveness of plug Trab depends wholly on the Earth connection provided to the system The earth

provided to the system should be less than 1 ohms and connections should be firm and proper to the SSDAC

unit VR box etc

SURGE VOLTAGE AND PROTECTION DEVICE SV-120 The Surge Voltage protection device is to be installed at each location along with every SSDAC unit

14 | P a g e

EARTHING- The lead wires connecting the installation and the earth electrode shall ordinarily be of stranded

copper wire of 29 sq mm (19 strand wires of 14 mm diameter) Copper wire has been specified because GI

wires usually are having greater corrosion However in areas where copper wire may be frequently stolen

due to theft ACSR of size 64 sq mm (19 strands of 211 mm diameter) may be used

LIMITS OF EARTH RESISTANCE (a) Apparatus case connected to Earth (SSDAC and vital Relay Box is housed in Apparatus case and

Connected to earth at outdoor) shall be less than or equal to 1 ohm

(b) All cable connected to same earth shall be less than or equal to 1 ohm

(C) Reset box connected to earth near SM s Room shall be less than or equal to 1ohm

EQUIPMENT TO BE EARTHED A Common Earth should be provided for SSDAC for items 1(a) amp (b) of the above at the outdoor

(a) The Apparatus Case is to be connected to earth (the chassis of SSDAC amp Vital Relay Box should be

properly connected to apparatus case)

(b) Metallic sheath and armouring of all the underground main cables are to be earthed

(i) In RE area the metallic sheath and armouring of main telecom cables are earthed at both ends

(ii) In RE area the armouring of Jelly filled cable shall be earthed at both ends

(c) The Earthing shall be provided at every location box where cables are terminated

(d) Earth already available for other equipment may be used for earthing of Reset Box near SM s Room

Cabin etc

15 | P a g e

DATALOGGER

INTRODUCTION Datalogger is a Microprocessor based system which helps in analysing the failures of relay inter

locking system Electronic Interlocking system This is like a black box which stores all the information

regarding the changes take place in relays AC DC Voltages and DC currents along with date and time The

same information data can be transferred to the computer to analyse further ldquoon line ldquooff linerdquo analysis of

stored date A print out also can be obtained through a printer by connecting directly to the datalogger unit

The data belongs to Relay contacts is considered as digital inputs and the data belongs to voltage

levels currents is considered as Analog inputs Datalogger lsquos are mandatory for all new relay interlocking

(PIRRI) EI installations and it is also recommended to provide in all existing PIs RRIs To increase the

line capacity mechanical signalling equipments are upgraded to PI RRI or EI Due to complexity in the

circuits and wiring sometimes it is very difficult to rectify the failures So datalogger can monitor these

systems with real time clock Thus it can be named as black box of Samp T equipments and hence it is a vital

tool for accident investigation Datalogger is used at Stations yards Whereas in case of Auto Section amp IBH

Mini dataloggers called as Remote Terminal Unit (RTU) are used

ADVANTAGES OF DATALOGGERS (a) Dataloggers helps in monitoring the typical failures such as intermittent auto right failures

(b) It helps in analyzing the cause of the accidents

(c) It helps in detecting the human failures errors such as

(i) Drivers passing signal at Danger

(ii) Operational mistakes done by panel operators ASMrsquos of operating department

(iii) Signal and telecom engineering interferences in safety circuits

(iv) Engineering and electrical department interferences failures

(v) It helps as a ldquoTOOLrdquo in preventive maintenance of signaling gears

(d) Dataloggers can be connected in network Networked dataloggers helps to monitorthe PIRRIEI remotely

(e) Failure reports can be generated remotely with help of datalogger network

(f) On line and Off line track simulation is possible

(g) Speed of the train on point zones can be calculated

(h) Age of the equipment in terms of number of operations etc

COMMON EQUIPMENT FOR ALL DATALOGGERS ARE GIVEN

BELOW (a) CPU card

(b) Digital and Analog input cards

(c) Local terminal(PC)

(d) communication links

(e) Printer

All the dataloggers requires a potential free ( spare ) relay contact for monitoring digital inputs

through Digital input cards amp for monitoring Analog inputs such ACDC bus bar voltage levels through

Analog input cards Digital and Analog inputs are connected to the Processor card Processor card consists of

memory ICrsquos Memory ICrsquos are programmed as per requirement of the signal engineers

Provision of Dataloggers is mandatory with RRI systems and is optional for PI systems as per

amendment to the specification for Relay Interlocking systems ( IRSS-36 ) The data collected by the

datalogger can be used for failure analysis repetitive discrepancies and for accident investigations

16 | P a g e

Note

If the serial communications is more than 50m then line drivers shall be used up to 3 Kms

4wire leased line Modems shall be used if the serial communication is more than 3 Kms

STUDY OF EFFTRONICS DATALOGGER TECHNICAL DETAILS (a) 24V 12VDC Power Supply

(b) Total Storage Capacity of 10 Lakh events

(c) In-built Temperature sensors

(d) Internal Buzzer for alarming during failures

(e) Real Time clock with internal battery backup with data retention up to 10 years

(f) 512 LED matrix to indicate the status of 512 Digital inputs at a time page wise

(g) Seven segment LCD screen (2x24) to display the status of digitalanalog signalsTime Temperature etc

(h) Using the keyboard various functions can be viewed in the LCD panel

(i) Max Digital Inputs 4096

(j) Max Analog Inputs 96

(k) Digital Input Scanning Time 16 millisecond

(l) Analog Input Scanning Time is less than 1 Sec

HARDWARE (EQUIPMENT) Datalogger system consists of

(a) Datalogger (CPU - with Microprocessor 68000)

(b) Digital input cards

(c) Dual modem card

(d) Digital Scanner units (DSU)

(e) Analog Scanner units (ASU)

CPU CARD It is provided with Motorola microprocessor M 68000 It performs all the activities pertaining to the

datalogger It continuously scans (check) the Digital inputs(inbuilt) Digital Scanner Units and Analog

Scanner Units ie scanning of digital signals (Relay operations) for every 16-milli seconds and scanning of

analog signals (ie ACDC voltages amp DC currents) for less than 1 second

This card will support the IO interfaces of LCD (Liquid Crystal Display) - 2X24 alphanumeric Key

Board LED Matrix Display Real Time Clock LCD display and keyboard This will acts as man machine

interface between the datalogger and the signal engineer All the operations (Software) can be performed

using this LCD and keyboard

Real time display with 7 Segments This is built in real time clock within Datalogger and its current

time will be displayed on six 7-segment display provided (Real time clock depend upon DALLAS 1286

chip) This IC will come with internal battery backup hence there is no need to add external batteries

CPU card continuously scans (checks) the DSUs and ASUs Each input connected to digital scanner

units are optically isolated by Opto couplers When CPU card scans the digital inputs it compares with the

previous stored data and if there is any change from the previous status then only that data will be stored (the

status conditions of relay) with date and real time A total of minimum 10 Lac events can be stored in

memory on first in first out basis so that latest data is available in the system There is no loss of data from

datalogger memory in case of power supply failure of datalogger

DIGITAL INPUT CARDS (IN-BUILT) This system is having maximum 8nos of inbuilt Digital inputs cards Maximum 64nos of digital

inputs can be connected to each digital input card The potential free relay contact may be front or back

contact terminated at the Tag Block from the relay of signals tracks points Buttons etc and are

17 | P a g e

subsequently connected to Digital input cards through Flat Ribbon Cable (FRC) connectors These in-built

digital input cards can monitor a total 512 nos of relays status

DIGITAL SCANNER UNIT (DSU) Each DSU contains 8 nos of Digital Input cards Each input card can be connected with 64 inputs

Total input capacity of DSU unit is 512 inputs These scanner cards contain Optocouplers and Multiplexer

Inputs are connected to Stag card The stag card out put is connected to DSU through FRC connectors

Maximum 7 nos of DSUs can be connected to the system So Digital input capacity of the system is 4096

All these digital inputs are scanned at rate of 16 msec

ANALOG SCANNER UNIT (ASU) ASU contains maximum 3 nos of Analog input cards Each input card can be connected with 8nos of

Analog inputs Total input capacity of the ASU is 24 analog input channels Maximum 4nos of ASUs can be

connected to the system Analog input channel capacity of the system is 96 All these analog inputs are

scanned at a rate of less than 1 sec

PARALLEL PORT Parallel port is provided for connecting printer

RS-232 SERIAL PORTS At least 6 Serial communication ports are provided for communication with other dataloggers

Central Monitoring Unit Remote Terminal Unit Electronic Interlocking system Integrated Power Supply

system etc

EXTERNAL NON-VITAL RELAY CONTACTS These relays provided in the system where 16 number of the Relay contacts are provided on the rear

panel through Tele control port to extend alarms and to control the power equipment from remote or local

locations through computer in case of any occurrence of failures Each control can sink or source 100 m

amps of current

INTERNAL MODEM CARD DUAL MODEM CARD (IN-BUILT) It is fixed in datalogger Euro rack itself One card contains two modems The top modem is called

ANS (answer) modem and the bottom modem is called as ORG (originate) modem It is used in case of

networking of Dataloggers In network connect lsquoANSrsquo modem to the lsquoORGrsquo modem of one adjacent station

and connect lsquoORGrsquo modem to the lsquoANSrsquo modem of other adjacent station

POWER SUPPLY Normally 24V DC (12V DC is optional) supply with battery backup is required for the system

working

Input Voltage Range 18Vhellip32V DC (For 24V) 9Vhellip18V DC (For 12V)

INPUT REQUIREMENTS Relay inputs (digital inputs) and analog inputs (voltages currents etc) are required to be connected

to the system as per the requirements of RRI PI SSI as the case may be Some of the inputs to be

monitored is given below

(a) Digital inputs

(i) Field inputs All TPRs NWKRs RWKRs ECRs Crank Handle relays SidingSlot LC gate

control relays etc

(ii) Control Panel inputs All button Knob SMrsquos Key relays

18 | P a g e

(iii) Internal relays

British system All HR DR HHR WNR WRR ASR UCR RR LR UYRTLSR TRSR TSR

JSLR JR etc

SIEMENS system Z1UR Z1UR1 GZR ZDUCR ZU(R)R ZU(N)PRG(R)RG(N)R U(R)S

U(N)PS UDKR DUCR U(R)LR UYR1 UYR2 G(R)LRGR1GR2

GR3 GR4 OVZ2U(R)RW(RN)R (RN)WLR Z1NWR Z1RWRZ1WR1 WKR1 WKR2 WKR3 etc

(b) Analog channels

(i) 230 V AC (for power supplies in the power panel)

(ii) 110V AC (for Signal and Track transformers)

(iii) 110V DC (for Point operation)

(iv) 60V DC (Siemens relays)

(v) 24V DC (Q-series relays)

(vi) 24V DC (for Block Axle counters)

(vii) 12V DC (for indication)

(viii) 20A (for point operation current)

(ix) 10V AC 5KHz (for Axle counter channels) etc

SOFTWARE MODULES OF DATALOGGERS

(a) Network Management of Dataloggers (NMDL)

(b) Reports

(c) Fault Entry

(d) Track Offline Simulation

(e) Train Charting

NMDL SOFTWARE FEATURES (a) Online Relay Status

(b) Online Faults - To view information of various Online Faults as they occur in the stations where

the Dataloggers are connected

(c) Online Simulation - Graphical view of relay operations train movements etc

(d) Remote monitoring of stations with the help of NETWORKING

SOFTWARE OBJECTIVES (a) Predictive Maintenance

(b) Easy identification of failures

(c) Crew discipline

(d) Train charting

REMOTE MONITORING OF STATIONS WITH NETWORKING OF

DATALOGGERS The individual Dataloggers of various stations can be interconnected through networking technology

The data of Remote Panel stations can be viewed in a Computer at the Central Monitoring Station The data

of the network is collected by the FEP (Front End Processor) which in turn is transmitted to the computer

COMPONENTS OF NETWORK MANAGEMENT OF DATALOGGERS

(a) Datalogger at stations

(b) MODEM and Transmission medium

19 | P a g e

(c) Front End Processor (FEP)

(d) Central Monitoring Unit (CMU) Computer

FEP (FRONT END PROCESSOR)

FEP acts as a buffer between the Central Monitoring Unit (Computer) and the Network It is provided

at centralised place to retrieve data continuously from station dataloggers and store in memory and transfer to

computer on request It stores 10 Lac telegrams It works on 12V DC It draws 16A continuous current

when all the three modems are connected Normally it shows the number of packets pending to be sent to the

computer on its 7-segment LED display It is provided with MOTOROLA 68000 microprocessor It has 6-

nos of RS-232 communication ports such as COM1 COM2 COM3 COM4 COM5 and COM6 COM1 is

used for Fault Analysis System (FAS) ie Central Monitoring Unit (Computer) connection COM2 to COM6

are used for networking For Bi-directional 2- nos of ports and for Tri-directional (T-network) 3-nos of ports

are used

DATA TRANSMISSION Dataloggers can be networked in Uni-directional Mode or Bi-directional Mode or T ndash Network Mode

In case of loss of data retransmission of data takes place

(a) Uni-Directional Mode

Each Datalogger will send data in only one direction to the FEP Unidirectional mode network is not

preferred

(b) Bi-Directional Mode

Each end of Network is connected to FEP and each datalogger can now transmit data in both the directions

Bi-directional Mode is advantageous it enables the Data Transmission even in case of Network Failure

(c) T - Network Mode

If more no of stations are in network ie if the network is too lengthy then T- network mode is preferred

COMMUNICATION The communication protocol for transmitting data and command between datalogger and CMU is

standardized by the RDSO and is given in the Specifications of Dataloggers

(a) The type of communication used in the network is dependent on the distance between the dataloggers

(b) For shorter distances Opto Converter Box- Opto isolated current loop communication is used

(c) For longer distances Modem (Dial-up leased) Fiber Optic Satellite Microwave communication

MODEMS Modems are used for DATA transfer between Dataloggers and Front End ProcessorThese are

configured to RS 232 Serial Communication Network is connected with two types of 4-wire modems

(a) Internal modem card Dual Modem card (in-built)

It is fixed in datalogger Euro rack itself One card contains two modems The top modem is called

ANS (answer) modem and the bottom modem is called as ORG (originate) modem

Note In case of networking of Dataloggers connect lsquoANSrsquo modem to the lsquoORGrsquo modem of one adjacent

station and connect lsquoORGrsquo modem to the lsquoANSrsquo modem of other adjacent station

(b) External modems

20 | P a g e

These are generally used at FEP (Front End Processor) side to connect the Dataloggers

(i) To transfer Data from one datalogger to another datalogger FEP Baud rate is 9600bps

(ii) These modems are 4-wire line communication

(iii) To transfer the data from FEP to RMU (PC) the Baud rate is 57600 bps

There is no difference between these modems functionally

CENTRAL MONITORING UNIT (CMU) COMPUTER

Central monitoring unit (Fault Analysis Unit) is a Personal Computer and its minimum configuration

shall be specified by RDSO from time to time System Software Windows XPVista(OS) Norton Kaspersky

(Anti Virus) Interbase where Server is not available (DBMS) Oracle where Server is available (DBMS)

software are required to run Datalogger System It is provided with Graphical User interface (GUI) based

software and retrieve data from all Networked dataloggers (up to 32) at various stations It stores data in

standard data base files The CMU is capable of analyzing the data and generate reports audiovisual alarms

on defined conditions This data can be compressed to take backup In central monitoring unit Software used

for analysis of data prediction of faults etc is written in a structured format so that purchaser can

reconfigure it if required It displays the status of signaling gears at any selected time in graphic form for any

selected station yard It retrieves the stored data amp simulates train movement It sends commands to various

Dataloggers to activate audio visual alarm or operate and electromagnetic relay

CMU shares data available in it by other PCs through available local area network where this data can

be used for train charting passenger information purpose The system generates audiovisual alarm in

ASMrsquosSignal Maintainerrsquos room in the case of power supply failure (battery voltage low) or battery charger

defective with acknowledgement facility

(a) Each datalogger has its own identity code which will be transmitted along with data packet to central

monitoring unit

(b) Events recorded at each station are continuously transmitted to central monitoring unit Response time of

data transfer will not exceed 10 sec

21 | P a g e

22 | P a g e

OPTICAL FIBER CABLE

INTRODUCTION The demand for bandwidth on transmission networks is increasing rapidly because video and

graphical rich contents are exchanged through the corporate network or the Internet The Gigabit Ethernet

became ommonly used in the corporate network backbone and 10Gbit Ethernet will be adopted in the near

future Meanwhile in the home the demand for high-speed network becomes popular as the wide spread of

broadband access eg CATV xDSL and FTTH The transmission medium with capability to transmit high

bit rate signal is necessary to satisfy these requirements

The telecommunication transport technologies move from copper based networks to optical fiber

from timeslot based transport to wave length based transport from traditional circuit switching to terabit

router and all optical based networks entering into a new era of optical networking

BASIC PHYSICS OF OFC

OPTICAL FIBER CABLE OFC have Fibers which are long thin strands made with pure glass about the diameter of a human

hair OFC consists of Core Cladding Buffers and Jacket as shown in figure

MONOCHROMATIC LIGHT OR SINGLE COLOR LIGHT Light or visible light is electromagnetic radiation of a wavelength that is visible to the human eye (

about 400 ndash 700 nm) The word light is sometimes used to refer to the entire electromagnetic spectrum Light

is composed of elementary particles called photons Three primary properties of light are

Light can exhibit properties of both waves and particles This property is referred to as wave-particle

duality The study of light known as optics In free space light (of all wavelengths) travels in a straight path

at a constant maximum speed However the speed of light changes when it travels in a medium and this

change is not the same for all media or for all wavelengths By free space it is meant space that is free from

matter (vacuum) andor free from electromagnetic fields

Thus the speed of light in free space is defined by Einsteinrsquos equation E = mc2

Frequency ν speed of light in free space c and wavelength λ are interrelated by ν = cλ

From the energy relationships E = mc2 = hν and the last one an interesting relationship is obtained

the equivalent mass of a photon m = hνc2

When light is in the vicinity of a strong electromagnetic field it interacts with it From this interaction

and other influences its trajectory changes direction as shown in figure

23 | P a g e

INCIDENT RAY REFLECTED RAY AND REFRACTED RAY An incident ray is a ray of light that strikes a surface The angle between this ray and the

perpendicular or normal to the surface is the angle of incidence Reflection is the change in direction of a

wave front at an interface between two different media so that the wave front returns into the medium from

which it originated Common examples include the reflection of light sound and water waves

The reflected ray corresponding to a given incident ray is the ray that represents the light reflected by

the surface The angle between the surface normal and the reflected ray is known as the angle of reflection

The Law of Reflection says that for a specular (non-scattering) surface the angle of reflection always equals

the angle of incidence The refracted ray or transmitted ray corresponding to a given incident ray represents

the light that is transmitted through the surface The angle between this ray and the normal is known as the

angle of refraction and it is given by Snells Law

The figure shows Incident ray Reflected ray Refracted ray the angle of incidence and angle of refraction

REFRACTIVE INDEX - Refractive index is the speed of light in a vacuum ( c =299792458kmsecond) divided by the speed

of light in a material ( v ) Refractive index measures how much a material refracts light Refractive index of

a material abbreviated as lsquo n lsquo is defined as lsquo n=cv lsquo Light travels slower in physical media than it does

when transmitted through the air Refractive index (n) is a function of molecular structure of matter optical

frequency optical intensity determines optical propagation properties of each wavelength ( λ ) may not be

distributed equally in all directions is affected by external temperature pressure and fields

Refractive index of a medium is a measure for how much the speed of light is reduced inside the

medium For example typical glass has a refractive index of 15 which means that light travels at 1 15 =

067 times the speed in air or vacuum Two common properties of glass and other transparent materials are

directly related to their refractive index

First light rays change direction when they cross the interface from air to the material and effect that

is used in lenses and glasses

Second light reflects partially from surfaces that have a refractive index different from that of their

surroundings

SNELLrsquoS LAW-

24 | P a g e

When light passes from one transparent material to another it bends according to Snells law which

is defined as n1sin(θ1) = n2sin(θ2)

where n1 is the refractive index of the medium the light is leaving θ1 is the incident angle between the light

beam and the normal (normal is 90deg to the interface between two materials)

n2 is the refractive index of the material the light is entering

θ2 is the refractive angle between the light ray and the normal

Snellrsquos law gives the relationship between angle of incidence and angle of refraction

For the case of θ1 = 0deg (ie a ray perpendicular to the interface) the solution is θ2 = 0deg regardless of

the values of n1 and n2 That means a ray entering a medium perpendicular to the surface is never bent The

above is also valid for light going from a dense (higher n) to a less dense (lower n) material the symmetry of

Snells law shows that the same ray paths are applicable in opposite direction

TOTAL INTERNAL REFLECTION- When a light ray crosses an interface into a medium with a higher refractive index it bends towards

the normal Conversely light traveling cross an interface from a higher refractive index medium to a lower

refractive index medium will bend away from the normal

This has an interesting implication at some angle known as the critical angle θc light traveling from

a higher refractive index medium to a lower refractive index medium will be refracted at 90deg in other words

refracted alon g the interface If the light hits the interface at any angle larger than this critical angle it will

not pass through to the second medium at all Instead all of it will be reflected back into the first medium a

process known as total internal reflection

The critical angle can be calculated from Snells law putting in an angle of 90deg for the angle of the refracted

ray θ2 This gives θ1

Since θ2 = 90deg

So sin(θ2) = 1

25 | P a g e

Then θc = θ1 = arcsin(n2n1)

For example with light trying to emerge from glass with n1=15 into air (n2 =1) the ritical angle θc is

arcsin(115) or 418deg For any angle of incidence larger than the critical angle Snells law will not be able to

be solved for the angle of refraction because it will show that the refracted angle has a sine larger than 1

which is not possible In that case all the light is totally reflected off the interface obeying the law of

reflection

OPTICAL FIBER MODE An optical fiber guides light waves in distinct patterns called modes Mode describes the distribution

of light energy across the fiber The precise patterns depend on the wavelength of light transmitted and on the

variation in refractive index that shapes the core In essence the variations in refractive index create

boundary

conditions that shape how light waves travel through the fiber like the walls of a tunnel affect how sounds

echo inside

We can take a look at large-core step-index fibers Light rays enter the fiber at a range of angles and

rays at different angles can all stably travel down the length of the fiber as long as they hit the core-cladding

interface at an angle larger than critical angle These rays are different modes Fibers that carry more than

one mode at a specific light wavelength are called multimode fibers Some fibers have very small diameter

core that they can carry only one mode which travels as a straight line at the center of the core These fibers

are single mode fibers This is illustrated in the following picture

OPTICAL FIBER INDEX PROFILE Index profile is the refractive index distribution across the core and the cladding of a fiber Some

optical fiber has a step index profile in which the core has one uniformly distributed index and the cladding

has a lower uniformly distributed index Other optical fiber has a graded index profile in which refractive

index varies gradually as a function of radial distance from the fiber center Graded-index profiles include

power-law index profiles and parabolic index profiles The following figure shows some common types of

index profiles for single mode and multimode fiber

26 | P a g e

OPTICAL FIBERrsquoS NUMERICAL APERTURE ( NA )- Multimode optical fiber will only propagate light that enters the fiber within a certain cone known as

the acceptance cone of the fiber The half-angle of this cone is called the acceptance angle (see figure 18)

θmax For step-index multimode fiber the acceptance angle is determined only by the indices of refraction

Where

n is the refractive index of the medium light is traveling before entering the fiber

nf is the refractive index of the fiber core

nc is the refractive index of the cladding

NUMBER OF MODES IN A FIBER - Modes are sometimes characterized by numbers Single mode fibers carry only the lowest-order

mode assigned the number 0 Multimode fibers also carry higher-order modes The number of modes that

can propagate in a fiber depends on the fiberrsquos numerical aperture (or acceptance angle) as well as on its

core diameter and the wavelength of the light For a step-index multimode fiber the number of such modes

Nm

Where

D is the core diameter

λ is the operating wavelength

NA is the numerical aperture (or acceptance angle)

MODE FIELD DIAMETER - All light do not travels through the core of the fiber but is distributed through both the core and the

cladding The mode field is the distribution of light through the core and cladding of a particular fiber

Mode-Field Diameter (MFD) defines the size of the power distribution When coupling light into or out of a

fiber MFD is important in understanding light loss

27 | P a g e

ADVANTAGE OF OFC COMMUNICATION - bull More information carrying capacity Fibers can handle much higher data rates than copper More

information can be sent in a second

bull Free from Electromagnetic and Electrostatic interference Being insulator no electric current flows through

the fibre and due to this reason fibres neither radiate nor pick up electro - magnetic radiation So WPC

CLEARANCE is not required

bull Low attenuation 025 dbkm at 1550 nm Loss in twisted pair and coaxial cable increases with frequency

where as loss in the optical fibre cable remains flat over a wide range of frequencies

bull Use of WDM ndash Switching routing at Optical signal level

bull Self healing rings under NMS control

bull Small size makes fibre cable lighter in weight So easy to handleOptic fibre cable weight (approx)

500 kg km Copper cable weight (approx) 1000 kgkm

The reasons are photons of light in a fibre

do not affect each other as they have no electrical charge and they are not affected by stray photons outside

the fibre But in case of copper electrons move through the cable and these are affected by each other

Optical fibre does not carry any electricity even if the cable is damaged or short circuited it does

not cause any spark or fire hazard

As the fibre do not radiate energy it can not be detected by any nearby antenna or any

other detector The fibres are difficult to tap and therefore excellent for security

As the signal transmission is by digital modulation there is no chance of cross talk in

between channels

Only by adding a few additional terminal and repeater equipments the

capacity of the system can be increased at any time once the cable is laid

ical effects and temperature variations

LIMITATIONS OF OFC -

difficult

- utilised

APPLICATION IN SIGNAL AND TELECOMMUNICATIONS transmission circuits

-haul circuits for linking of telephone exchanges

28 | P a g e

PROPAGATION MODES CONCEPT -

MODE - Mode is an available distribution of electromagnetic field in a plane transverse to the direction of

light propagation Each mode is characterized by frequency polarization electric field strength and

magnetic field strength Available patterns are derived from Maxwellrsquos equations and boundary conditions

LINEARLY POLARIZED (LP) MODE A mode for which the field components in the direction of propagation are small compared to

components perpendicular to that direction An optical fibre supports only different field patterns called as

lsquoLinear Polarizedrsquo or lsquo LPrsquo modes The reasons are

requirements

de

the accrual of power carried by different modes

There are two basic types of fiber Multimode fiber and Single-mode fiber

Multimode fiber is best designed for short transmission distances This is suited for used in LAN systems and

video surveillance Single mode fibre is best designed for longer transmission distances This is suitable for

long distance telephony and multi channel television broadcast systems

29 | P a g e

MULTI MODE FIBER Multimode fiber the first to be manufactured and commercialized simply refers to the fact that

numerous modes or light rays are carried simultaneously through the waveguide Modes result from the fact

that light will only propagate in the fiber core at discrete angles within the cone of acceptance MM fiber type

has a much larger core diameter compared to single-mode fiber allowing for the larger number of modes

and

is easier to couple than single-mode optical fiber Multimode fiber further categorized as Multimode step-

index and Multimode graded index fiber

PROPAGATION THROUGH MMSI FIBER Figure shows the principle of total internal reflection applies to multimode step index fiber Because

the corersquos index of refraction is higher than the claddingrsquos index of refraction the light that enters at less than

the critical angle is guided along the fiber

Three different light waves travel down the fiber One mode travels straight down the center of the

core A second mode travels at a steep angle and bounces back and forth by total internal reflection The third

mode exceeds the critical angle and refracts into the cladding Naturally it can be seen that the second mode

travels a longer distance than the first mode causing the two modes to arrive at separate times

PROBLEMS WITH MMSI FIBER AND SOLUTION This disparity between arrival times of the different light rays is known as dispersion and the result is

a muddied signal at the receiving end It is important to note that high dispersion is an unavoidable

characteristic of multimode step-index fiber The solutions are either use Graded index fiber or Single mode

fiber

PROPAGATION THROUGH MMGI FIBER Multimode Graded-index refers to the fact that the refractive index of the core gradually decreases

farther from the center of the core The increased refraction in the center of the core slows the speed of some

light rays allowing all the light rays to reach the receiving end at approximately the same time reducing

dispersion Figure shows the Light propagation principle through multimode graded-index fiber The corersquos

central refractive index ( nA ) is greater than that of the outer corersquos refractive index ( nB )

It is very clear from the figure the light rays no longer follow straight lines they follow a serpentine path

being gradually bent back toward the center by the continuously declining refractive index This reduces the

arrival time disparity because all modes arrive at about the same time The modes traveling in a straight line

30 | P a g e

are in a higher refractive index so they travel slower than the serpentine modes These travel farther but

move faster in the lower refractive index of the outer core region

PROPAGATION THROUGH SMSI FIBER Single mode fiber has a much smaller core that allows only one mode of light at a time to propagate

through the core The figure shows the single mode fiber

Single-mode fiber exhibits no dispersion caused by multiple modes Single-mode fiber also offers lower fiber

attenuation than multimode fiber Thus more information can be transmitted per unit of time because it can

retain the fidelity of each light pulse over longer distances Like multimode fiber early single-mode fiber was

generally characterized as step-index fiber meaning the refractive index of the fiber core is a step above that

of the cladding rather than graduated as it is in graded-index fiber Modern single-mode fibers have evolved

into more complex designs such as matched clad depressed clad and other exotic structures

SINGLE-MODE FIBER DISADVANTAGES The smaller core diameter makes coupling light into the core more difficult The tolerances for single-

mode connectors and splices are also much more demanding

CUTOFF WAVE LENGTH - Cutoff wavelength is the wavelength above which a single-mode fiber supports and propagates only

one mode of light In other words an optical fiber that is single-mode at a particular wavelength may have

two or more modes at wavelengths lower than the cutoff wavelength The effective cutoff wavelength of a

fiber is dependent on the length of fiber and its deployment The longer the fiber the lower is the effective

cutoff

wavelength The smaller the bend radius of a loop of the fiber the lower is the effective cutoff wavelength If

a fiber is bent in a loop the effective cutoff wavelength is lowered

SIGNAL ATTENUATION IN FIBER - Optical fiber has a number of advantages over copper However it also suffers from degradation

problems which can not be ignored The first of these is loss or attenuation Attenuation is typically the result

of two sub properties They are scattering and absorption Both of which have cumulative effects The second

is

dispersion which is the spreading of the transmitted signal and is analogous to noise

SCATTERING Scattering occurs because of impurities or irregularities in the physical construction of the fiber The

well known form of scattering is Rayleigh Scattering It is caused by metal ions in the silica matrix and

results in light rays being scattered in various directions

31 | P a g e

Scattering limits the use of wavelengths below 800nm The short wavelengths are much affected than longer

wavelengths It is because of Rayleigh scattering that the sky appears to be blue ( shorter wave length ) The

shorter wavelengths ( blue ) of light are scattered more than the longer wavelengths of light

ABSORPTION Absorption results from three factors They are hydroxyl ions ( OH- water ) in the silica impurities

in the silica and incomplete residue from the manufacturing process These impurities tend to absorb the

energy of the transmitted signal and convert it to heat resulting in an overall weakening of the signal The

Hydroxyl absorption occurs at 125 and 139 micro The silica itself starts to absorb energy at 17 micro

because of the natural resonance of the silicon dioxide

MACRO BENDING LOSS Macro-bending loss is caused by bending of the entire fiber axis The bending radius shall not be

sharper than 30d where d is diameter of cable A single bend sharper than 30d can cause loss of 05dB

The fiber may break if bending is ever sharper

MICRO BENDING LOSS Micro-bending loss is caused by micro deformations of fiber axis which leads to failures in achieving

total internal reflection conditions Micro-bends are small scale perturbations along the fiber axis the

amplitude of which are on the order of microns These distortions can cause light to leak out of a fiber

Micro-bending may be induced at very cold temperatures because the glass has a different coefficient of

thermal expansion from the coating and cabling materials At low temperatures the coating and cable

become more rigid and may contract more than the glass Consequently enough load may be exerted on the

glass to cause micro bends

Coating material is selected by manufacturers to minimize loss due to micro-bending The linear thermal

expansion coefficient of coating material shall be compatible with that of fiber

32 | P a g e

DISPERSION Dispersion is the optical term for the spreading of the transmits in the fiber It is the bandwidth

limiting phenomenon and comes in two forms Multimode dispersion and chromatic dispersion Chromatic

dispersion is further subdivided into material dispersion and waveguide dispersion

DISPERSION PHENOMENON IN OPTICAL FIBER Dispersion is the time distortion of an optical signal that results from the differences of time of travel

for different components of that signal typically resulting in pulse broadening As the distance traveled by

the signal is more broadening of pulse is more In digital transmission dispersion limits on the maximum

data rate and the maximum distance ie the information-carrying capacity of a fiber link The interference

from broadened pulse in the next interval shall not lead to erroneous interpretation of received signal

OPTICAL DOMAIN Understanding where attenuation and dispersion problems occur helps optical design engineers

determine the better wavelengths at which information can be transmit taking into account distance type of

fiber and the other factors which can severely affect the integrity of the transmitted signal The graph shown

depicts the optical transmission domain as well as the areas where problems arise The wavelength (nm)

is shown on X-axis and attenuation ( dBkm) is shown on Y-axis

There are four transmission windows appear in the figure The first one is at around 850 nm the

second at 1310nm third at 1550 nm and fourth at 1625 nm The last two labeled as C and L band

respectively The 850 nm wavelength at which the original LED technology operated The second window at

1310 nm has low dispersion The 1550 nm called as C-band is ideal wavelength for long haul

communication systems The network engineers can avoid transmitting signal at 1000 nm where Rayleigh

scattering 1240 and 1390 nm where hydroxyl absorption by water occurs to avoid high degree of loss

Optical fibers also can be manufactured to have low dispersion wavelength in the 1550nm region

which is also the point where silica-based fibers have inherently minimal attenuation These fibers are

referred to as dispersion-shifted fibers and are used in long-distance applications with high bit rates For

33 | P a g e

applications utilizing multiple wavelengths it is undesirable to have the zero dispersion point within the

operating

wavelength range

34 | P a g e

SIGNALLING RELAYS

INTRODUCTION A relay is an electromagnetic device which is used to convey information from one circuit to another

circuit through a set of contact ie front or back contact Constructional and electrically relays may be

divided into DC and AC relays because the means by which the electrical energy in the coil is converted in

to mechanical Energy in order to move the contacts are fundamentally different In DC type the contacts are

carried on an armature forming part of a magnetic circuit in which a field is set up by the current flowing in

the coils In AC types the contacts are attached by a link mechanism to a metal sector disc or cylinder in

which currents are induced by the alternating magnetic field produced by the currents in the coils

Every endeavor has been made to explain the action of each type of relay in the simplest possible manner

Relays are sophisticated switch gears used for remote control and succession control of various

electrical equipment In present days they are widely used because they are capable of protecting the

controlled equipment from cross feeding and overloading even as they cater for speedy operations

Most of the relays in present day signaling are electromagnetic devices although some of the relays control

circuits through electronic components like diodetransistors Integrated Chips etc

Railway signaling relays are unique in that

(a) They operate on low voltage and current

(b) They are more articulate as according to their special features they can work under restrictive conditions

and in any specified manner Virtually they can cater for all situations while contributing to speed and

accuracy in operations

CLASSIFICATION OF SIGNALLING RELAYS (a) According to the method of their mounting or fixture they are classified as

(i) Shelf type Relays which are loosely kept on shelves

(ii) Plug in type Relays which are plugged into a pre- wired plug boards

(b) According to their connection and usage they are classified as

(i) Track relays Relay which is directly connected to the track to detect the presence of vehicle

(ii) Line Relays Other than track relay all are line relays Relays connected to the selection circuit

(c) According to their vitality or importance in ensuring train working safety they are classified as

(i) Vital Relays All relays used for traffic control such as signal point controls track detection etc

(ii) Non-vital Relays Relays which operate control aids and accessories like warnings buzzers

Indications etc

(d) According to their special provisions to ensure reliability of their contacts they are classified as

(i) Proved type are those whose normalization after each operation shall be proved in circuit

controlled by their contacts Contacts in which both the springs have metal surfaces on their tips They may

get fused due to high sparking current across them during operation These may prevent relay normalization

and causes unsafe condition in traffic control To avoid this proving of relay normalization after each

operation is necessary

(ii) Non - proved type Need not to be proved to have been normalized after each operation as their

contacts have at least one non-fusible contact (carbon contact)

(e) According to their feed source relays are broadly classified as

(i) DC relays The relay which requires DC power supply for its operations are called DC relays Among

the DC relays

o DC neutral relays This relay closes the same set of contacts on energization with Normal polarity

or Reverse polarity supply

o Polar Relays This relay closes different set of contacts when energized with Reverse polarity

supply They may or may not have contact to close when deenergized

35 | P a g e

(ii) AC Relay AC Induction motor track relays Time element relays flashing indication control etc

(iii) Electronic Relays DC relays with electronic components in them are called electronic relays

DC NEUTRAL RELAY Each Relay has usually one or two coils with a hollow center to accommodate a coreThe coils are

made up of a large numbers of turns of small gauge soft drawn copper wire The two coils can be connected

in series or parallel according to the requirement of relay resistance The ends of the coils are terminated on

binding post to which the control wires are connected Each coil is placed around a core of specially selected

Iron or steel having high permeability and low retentivity The core should be susceptible to magnetism and

at the same time should have little residual magnetism The cores are connected at the top by a yoke to

complete the magnetism coupling between two ends of coils The bottom of each core is equipped with a

large steel or Iron block known as pole piece or face

A flat piece of Iron or steel called armature is supported by brackets which are securely fastened to

the pole piece The armature yoke and the pole pieces are also made of specially selected iron or steel of the

same quality as the core The armature carries the metallic spring contacts which are insulated from it

The circuit through the coils of the relay is closed It sets up a magnetic flux through the core yoke and the

armature The flux passing between the armature and pole faces causes the armatures get attracted to the pole

faces and armature picks up and closes front contacts When the circuit is opened the magnetic flux collapses

and the armature drops away by gravity from the pole faces the front contacts break and back contacts close

The front and back contacts of the relay can be utilised to make or break other circuits Two stop pins of

nonmagnetic material are fixed either on the armature or pole faces so that the armature cannot

come in contact with the pole faces It is essential to maintain a small air-gap between the armature and pole

faces so that low value of residual magnetism may not retain the armature in picked up position and causes

the relay to fail to drop away with a break in its control circuit

GENERAL USAGE

DC Neutral line relays are most commonly used for Railway Signalling controls and detection

Among them plug-in type relays are preferred in larger installations for space considerations Shelf type

relays are also in use mostly in wayside stations

There are many DC Neutral line relays in use with special features such as

(i) Delayed operation

(ii) Biased DC control

(iii) DC control unaffected by AC interference currents

(iv) Getting latched in operated condition till further feeding and others

Usage of DC polar relays is mostly in conjunction with block instruments that control traffic between

stations AC line relays are almost extinct in installations of British Signalling practice They are however

used for time control operations flashing indication control and such other special purposes in installations

with Siemens signalling practice widely Track relays are used according to the type of track detection

circuits chosen for a given location and context While most of the track circuits are still of the DC working

type requiring DC neutral track relays with them the prospects of their being replaced with Electronic track

circuits directly feeding DC line relays in future are great AC Track Circuits are used in DC Traction area

as conventional DC Track Circuits are not suitable there AC Track relays are used with them almost all of

the induction motor type In the British practice of signalling which was first introduced on Indian Railways

non-proved type relays with carbon to metal switching contacts are generally used for vital controls

They facilitate simple circuit designs But with the advent of German Practice introduced by Ms

Siemens later proved type relays with all metal to metal contacts are widely accepted in spite of

complications in circuit design caused by them A recent introduction is that of the same type relays made by

Ms Integra control However for some time now the appreciable features of both the practices are getting

36 | P a g e

incorporated together in the indigenous designs of signalling by railwaymen With this the usage of all types

of relays anywhere can be found without straight jacketed segration of relay types

CHARACTERSTIC OF ELECTRO-MAGNETIC RELAY The following are the characteristic of electro-magnetic relays A brief study of them helps in

understanding the choice of their components and designs features

1) Force of attraction

2) Effect of air gap

3) Effect of Hysterisis

4) Transient condition

FORCE OF ATTRACTION In any electro-magnetic system the force of attraction is given by

Where B - is the flux density a - is the cross sectional area of the particular part of the magnetic

circuit

In the case of a DC neutral Relay B is proportional to the current that is flowing in the coil

surrounding the electro-magnet and thus the force of the attraction is directly proportional to the square of the

current This square relationship has its own advantage especially in the case of DC track relay in that a

small reduction in the current will have a great effect on the working of the relay Also for a given change of

current the make and the break will be quicker with lesser possibility of arcing

EFFECT OF AIR GAP

Curve lsquoArsquo is magnetisation curve for the iron and is all practical purpose a straight line up to the

saturation point Curve lsquoBrsquo is the magnetisation curve for the open-air gap which is a straight line through

out because per magnetisation curve of the whole

magnetic circuit of the relay and for a given force is the sum of the amp-turns for the iron part and the amp-

turns for the air gap

When the front contacts are open the force required to pick up the armature is shown on curve lsquoCrsquo to be F1

but after the armature has operated it will be separated from the core by stop pins In this position the amp-

turns required to maintain the armature is less as indicated by the dotted line from 1 on curve C to 2 on curve

37 | P a g e

F But actually the current in the coil is unaltered the force on the armature is greater than required as

indicated at 3 on curve F Part of this extra force is used to flex the front contacts sufficiently to give good

contact pressure when it is in energised position

The difference between the pick-up and the drop-away current should be as small as practicable in

track relay to ensure good shunting characteristics This is achieved firstly by the choice of good quality relay

iron and secondly by having a small air gap between armature and core If the air gap is not available then

the residual magnetism fluxes might cause the armature to be retained when the supply is disconnected For

this reason residual pins are provided to ensure a definite minimum air gap in the energised position

EFFECT OF HYSTERISIS

Hysterisis is the property by which the flux produced lags behind the current In the de-energized

condition there will be small residual flux in the core When the voltage is applied to the coils the current in

rising to its steady value first causes the flux to rise from 1 to 2 along the curve At this point the flux density

will be sufficient to attract the armature and reduce the air gap the flux then raise to 3 and continue to 4

which corresponds to the steady current in the coils When the voltage is disconnected the current in falling

caused the flux to fall from 4 to 5 along the curve At this point the flux density will fall below the value

required to maintain the armature which will release thus increasing the air gap and reducing the flux to 6

Finally the

flux will decrease from 6 to 1 where the current will again be zero

The relay core is made of material having high permeability and low retentivity As mentioned in

the IRS specification Electromagnet iron may be in the form of a

(a) Bar of silicon steel

(b) Best Yorkshire wrought iron

(c) Swedish charcoal iron

(d) Electrical steel sheets

` This reduces the difference between pick up value and Drop away value By selecting good quality

core material Percentage release and sensitivity of the relay will be improved

TRANSIENT CONDITION

38 | P a g e

When the voltage is applied or disconnected from the coils it takes some little time before the current

become steady These are known as transient conditionsrdquo and are important so far as track relays are

concerned When the voltage is first applied to the coils the magnetic flux in rising cuts the turns on the

coils and in so doing produces a back EMF that opposes the applied voltage and retards the growth of

current

The growth and decay of flux are decided by the relationship between the inductance and resistance

in the circuit is known as time constant It is not fixed quantity in the case of DC neutral relay This value of lsquo

Lrsquo is less when the relay is in de-energised condition (L1) than when the relay is in energised condition (L2)

The magnitude of flux that is established for a given change of current is different in two cases

When the current reaches the pick up value the armature closes and the inductance is increased to L2

due to reduced air gap the flux per amp is increased The increase in flux increased the back EMF during the

movement of the armature after which the current continuous to raise along a new curve corresponding to the

increased inductance until it reaches the final value (ER) This process is indicated above in fig24

When the supply is disconnected the current is obliviously reduced to zero immediately but the flux

decay comparatively slowly owing to the eddy currents produced in the core by the rapid flux change which

tend to maintain the flux The drop away time on a disconnection is however generally negligible See fig

below

If the relay releases due to the reduction in current from say I 2 to I 1 caused by the application of

shunt resistance (as in the case of track relay ) the time taken is much longer than the relay is simply

disconnected The rate of rise or fall of current during the transient conditions is also depends on exterior

circuit values because L and R apply to the whole circuit The production of eddy current in the core the flux

will decay at a slower rate than the current So that the actual release time will be a little longer than it takes

the current to fall to the release

L= Inductance

39 | P a g e

R= Resistance

It is now clear that to reduce releasing time to a minimum it is necessary that

- The relay iron should have low Hysterisis loss and low retentivity

- The degree of over energization of the relay should be restricted

- Connecting a suitable external resistance in series with the relay to keep LR ratio low

In non RE area for track circuit length less than 100M 9 ohm track relay only to be used Using relay

with minimum contacts as they require lesser current which keeps inductance value low

Train working safety is ensured only if the track relay of shortest length track circuit is released

before a light engine running at a highest permitted speed clears it Otherwise the track circuit occupation

may go undetected To avoid this a special provision has to be made in signal control circuits wherever

necessary

The following methods may be adopted for reducing the time lag of track relay

(a) Restrict the over energisation of relay since the release time depends on the initial working current

(b) Connecting a suitable external resistance in series with the relay to keep the LR ratio low

(c) Using relays with minimum contacts as they require lesser operating current keeping the inductance

value low

40 | P a g e

CONCLUSION

Modern signalling is vital for safe and punctual movements of trains In the Indian railways The Signalling

and Telecommunication Department is responsible for providing modern effective and relaible signalling

systems as well as telecommunication systems

The first mode of communication used in Indian Railways was the use of electric telegraph

with the help of Morose code Morose code is the method of providing text information as a series of on-off

tones and lights or clicks that can be directly understood by a skilled listener or observer without special

equipmentEach character (letter or numeral ) is represented by a unique sequence of dots and dashes Later

this system becomes obselete and beggan the era of wireless communication which operated at audio level

frequency range

In wireless communication the significant advances took place the transition to miniature

valves or filament tubesBut this was abandoned too because of excessive current consumption and over

heating of the filament tubes

Fibre-optic communication is a method of transmitting information from one place to another by

sending pulses of light through an optcial fibreThe light forms an electromagnetic carrier wave that is

modulated to carry information First developed in the 1970s fibre optic communication systems has

revolutionized the telecommunications industry and have palyed a major role in the advent of the information

age Because of its advantages over electrical transmissionsoptical fibres have largely replaced copper wire

communications in core networks in the developed world The Indian Railways too is undergoing a transition

from Microwave communication to fibre optic communications

41 | P a g e

BIBLIOGRAPHY AND REFERENCES

1 wwwwikipediacom

2 wwwbritaniccacom

3 wwwirfcacom

4 Motorola GP60 system manual

5 Harris FAS 7000 manual

6 TOSHIBA Manual

11 | P a g e

(B) MICRO-CONTROLLER LOGIC BOARD CARD (CARD 3amp4) (MLB) The Micro-controller Logic Board (MLB) is the heart of the system

o 8051 Based Architecture

o 8 Bit Micro Controller

o ATMEL AT89S8252 Micro controller

o 2 out of 2 Decision

o Uses C subset language

- TOOLS

o KEIL μ Vision Development System

o Universal Programmer

o 2KB Program Memory

o 256 bytes RAM

o 8KB Flash memory

o 32 Programmable IO lines

o Wide Operating Voltage range of 4V-6V

o Full Duplex Serial Port

o Programmable Watch Dog Timer

o Fully Static operation up to 24MHz (Upgraded to 40MHz)

o Operating Temperature of ndash40degC - +85degC

o Use of State Machine for Axle Counting

o Use of ASCII MODBUS protocol

o Use of CRC16 technique for Error Checking during communication

o Wheel detection

o Train direction checking and

o Wheel counting functions

o It receives the remote wheel count and computes the status of the section for clear or occupied

o It also checks various supervisory signal levels like supervisory of TxRx coils presence of various

cards communication link failure etcThese cards communicate with each other for wheel count

At Entry-end if train enters into section (1st detection) the counts are incremented and when train

shunts back from the same detection ie if train exits from the section from the same detection the counts are

decremented At Exit-end if train enters into section (2nd detection) the counts are decremented and when

train shunts back from the same detection ie if train exits from the section from the same detection the

counts are incremented Both the track devices at Entry and Exit ends must be fixed on same side of the

track

This MLB card is having Extensive LED display

o A block of 8 LED indicators for count progress error display

o 2 independent LED indicators for section status

o The errors occurring in the system during the operation of the SSDAC are encoded and are indicated by

means of the 8-LED block present on the front panel of the MLB cards

(c) EVENT LOGGER CARD (CARD 5)

Event logger card is designed to capture and store important signals from the remote and local SSDAC units

The stored data can be downloaded from the event logger card for the purpose of analyzing the events

occurring during the operations of the SSDAC The data can be analyzed with the help of CEL data analyzer

software

12 | P a g e

The event logger card captures following signals

(i) Pulse signals

(ii) Supervisory signals

(iii) Card removal information

(iv) Serial packets from

Event Logger card has a Rabbit processor and 2 MB FLASH MEMORY to store packets The data is initially

stored in the buffer and subsequently transferred to FLASH memory every two minutes Normally 4096

pages of the data can be stored in flash memory on FIFO (first in first out) basis

Run This LED blinks continuously indicating the normal working of the event

Log This LED blinks whenever data is being logged into the flash memory (Approx after every 2 minutes)

Dnld This LED is ON when data is being downloaded from the flash memory of the card and becomes OFF

when download is complete

(D) MODEM CARD (CARD 6) (i) The modem card transmits and receives the digital packet information form one counting unit to the other

The packet will appear after every 18 sec and the packet carries the latest information such as

(ii) The modem card being used is V21 type (2-wire) in SSDAC

(iii) This card interfaces with serial RS232C port of both Micro-controller Logic Boards

(iv) It multiplexes the two RS232C inputs and selects one of the two channels and provides signal conversion

from digital to analog (FSK modulation) and vice-versa

(v) Data transmission rate is 300 bitssec

(vi) Automatic Gain Control circuit is incorporated hence no gain adjustments required

(vii) Mode selection on Modem card The modem has been set in lsquoORIGINATORrsquo mode for entry and in the

lsquoANSWERrsquo mode for exit in the factory

(viii) LED Indications provided on Modem card

-Transmitting the signal when LED is flashing

- Receiving the signal when LED is flashing

-Remains OFF in SSDAC

-Carrier is detected when LED is glowing

(E) RELAY DRIVER CARD (CARD 7) (i) The Relay Driver card (RD) provides the 24V DC output required for driving Vital Relay

(ii) One RD card is used in each SSDAC counting unit The RD card receives the command of clear and

clock signals from MLB1 amp MLB2 cards and drives the vital relay lsquoONrsquo when section is NOT OCCUPIED

through opto- isolator circuit

(iii) If a train occupies the section the vital relay is dropped The vital relay status is read back by the system

as per the driving output

(iv) It has

13 | P a g e

ndash LED flashes when the section is clear

ndash LED flashes when the section is clear

All the above LEDrsquos are lit for section clear condition

(F) DC-DC CONVERTER CARD (CARD 8)

INPUT VOLTAGE Nominal Voltage voltage 24V DC Maximum current drain= 12A

Required voltage 18V DC to 30V DC

Output voltage

Nominal Voltage +5 V DC 2 A Required voltage 4 7 5 t o 525V DC

Nominal Voltage +12V DC 200 mA Required voltage 1175 to 1225V DC

Nominal Voltage +24V DC 300 mA with common ground Required voltage 235 to 245V DC

Nominal Voltage +15V DC 100 mA with isolated ground Required voltage 145 to 155V DC

SURGE VOLTAGE AND LIGHTNING PROTECTION Transient surge voltages arise as a result of Lightning discharge switching operations in electrical

systems and electrostatic discharge These surge voltages often destroy the electronic equipment to a large

extent In order to prevent surge voltages from destroying the equipment all the input lines of SSDAC ie

Power Supply (24V) Reset (48V) amp Modem is to be routed through surge voltage protection devices for

effectively protecting the system These devices (3 numbers) are mounted in a box and supplied along with

the system One number of box is to be installed at each location and wired to the SSDAC

Each surge voltage protection device consists of two parts

(a) Base

(b) Plug Trab

The Base of the device is used for wiring the input and output signals The connection details from relay

room to the box and from box to SSDAC unit are provided on the box The Plug Trab consists of MOV and

GD Tube and diverts the excess energy during surge voltages or lightning into the ground connection The

operation of these devices relies on a high quality ground connection in order to safely shunt away the

unwanted energy The impedance of the ground connection is critical and it should be less than 2 Ohms

NOTE The 3 Plug Trab connections are not to be interchanged with one another The plug Trab is a

detachable device and can be replaced with SPARE unit in case of blown device which is indicated by

means of LED for 24 V

EFFECTIVENESS OF PLUG TRABS The effectiveness of plug Trab depends wholly on the Earth connection provided to the system The earth

provided to the system should be less than 1 ohms and connections should be firm and proper to the SSDAC

unit VR box etc

SURGE VOLTAGE AND PROTECTION DEVICE SV-120 The Surge Voltage protection device is to be installed at each location along with every SSDAC unit

14 | P a g e

EARTHING- The lead wires connecting the installation and the earth electrode shall ordinarily be of stranded

copper wire of 29 sq mm (19 strand wires of 14 mm diameter) Copper wire has been specified because GI

wires usually are having greater corrosion However in areas where copper wire may be frequently stolen

due to theft ACSR of size 64 sq mm (19 strands of 211 mm diameter) may be used

LIMITS OF EARTH RESISTANCE (a) Apparatus case connected to Earth (SSDAC and vital Relay Box is housed in Apparatus case and

Connected to earth at outdoor) shall be less than or equal to 1 ohm

(b) All cable connected to same earth shall be less than or equal to 1 ohm

(C) Reset box connected to earth near SM s Room shall be less than or equal to 1ohm

EQUIPMENT TO BE EARTHED A Common Earth should be provided for SSDAC for items 1(a) amp (b) of the above at the outdoor

(a) The Apparatus Case is to be connected to earth (the chassis of SSDAC amp Vital Relay Box should be

properly connected to apparatus case)

(b) Metallic sheath and armouring of all the underground main cables are to be earthed

(i) In RE area the metallic sheath and armouring of main telecom cables are earthed at both ends

(ii) In RE area the armouring of Jelly filled cable shall be earthed at both ends

(c) The Earthing shall be provided at every location box where cables are terminated

(d) Earth already available for other equipment may be used for earthing of Reset Box near SM s Room

Cabin etc

15 | P a g e

DATALOGGER

INTRODUCTION Datalogger is a Microprocessor based system which helps in analysing the failures of relay inter

locking system Electronic Interlocking system This is like a black box which stores all the information

regarding the changes take place in relays AC DC Voltages and DC currents along with date and time The

same information data can be transferred to the computer to analyse further ldquoon line ldquooff linerdquo analysis of

stored date A print out also can be obtained through a printer by connecting directly to the datalogger unit

The data belongs to Relay contacts is considered as digital inputs and the data belongs to voltage

levels currents is considered as Analog inputs Datalogger lsquos are mandatory for all new relay interlocking

(PIRRI) EI installations and it is also recommended to provide in all existing PIs RRIs To increase the

line capacity mechanical signalling equipments are upgraded to PI RRI or EI Due to complexity in the

circuits and wiring sometimes it is very difficult to rectify the failures So datalogger can monitor these

systems with real time clock Thus it can be named as black box of Samp T equipments and hence it is a vital

tool for accident investigation Datalogger is used at Stations yards Whereas in case of Auto Section amp IBH

Mini dataloggers called as Remote Terminal Unit (RTU) are used

ADVANTAGES OF DATALOGGERS (a) Dataloggers helps in monitoring the typical failures such as intermittent auto right failures

(b) It helps in analyzing the cause of the accidents

(c) It helps in detecting the human failures errors such as

(i) Drivers passing signal at Danger

(ii) Operational mistakes done by panel operators ASMrsquos of operating department

(iii) Signal and telecom engineering interferences in safety circuits

(iv) Engineering and electrical department interferences failures

(v) It helps as a ldquoTOOLrdquo in preventive maintenance of signaling gears

(d) Dataloggers can be connected in network Networked dataloggers helps to monitorthe PIRRIEI remotely

(e) Failure reports can be generated remotely with help of datalogger network

(f) On line and Off line track simulation is possible

(g) Speed of the train on point zones can be calculated

(h) Age of the equipment in terms of number of operations etc

COMMON EQUIPMENT FOR ALL DATALOGGERS ARE GIVEN

BELOW (a) CPU card

(b) Digital and Analog input cards

(c) Local terminal(PC)

(d) communication links

(e) Printer

All the dataloggers requires a potential free ( spare ) relay contact for monitoring digital inputs

through Digital input cards amp for monitoring Analog inputs such ACDC bus bar voltage levels through

Analog input cards Digital and Analog inputs are connected to the Processor card Processor card consists of

memory ICrsquos Memory ICrsquos are programmed as per requirement of the signal engineers

Provision of Dataloggers is mandatory with RRI systems and is optional for PI systems as per

amendment to the specification for Relay Interlocking systems ( IRSS-36 ) The data collected by the

datalogger can be used for failure analysis repetitive discrepancies and for accident investigations

16 | P a g e

Note

If the serial communications is more than 50m then line drivers shall be used up to 3 Kms

4wire leased line Modems shall be used if the serial communication is more than 3 Kms

STUDY OF EFFTRONICS DATALOGGER TECHNICAL DETAILS (a) 24V 12VDC Power Supply

(b) Total Storage Capacity of 10 Lakh events

(c) In-built Temperature sensors

(d) Internal Buzzer for alarming during failures

(e) Real Time clock with internal battery backup with data retention up to 10 years

(f) 512 LED matrix to indicate the status of 512 Digital inputs at a time page wise

(g) Seven segment LCD screen (2x24) to display the status of digitalanalog signalsTime Temperature etc

(h) Using the keyboard various functions can be viewed in the LCD panel

(i) Max Digital Inputs 4096

(j) Max Analog Inputs 96

(k) Digital Input Scanning Time 16 millisecond

(l) Analog Input Scanning Time is less than 1 Sec

HARDWARE (EQUIPMENT) Datalogger system consists of

(a) Datalogger (CPU - with Microprocessor 68000)

(b) Digital input cards

(c) Dual modem card

(d) Digital Scanner units (DSU)

(e) Analog Scanner units (ASU)

CPU CARD It is provided with Motorola microprocessor M 68000 It performs all the activities pertaining to the

datalogger It continuously scans (check) the Digital inputs(inbuilt) Digital Scanner Units and Analog

Scanner Units ie scanning of digital signals (Relay operations) for every 16-milli seconds and scanning of

analog signals (ie ACDC voltages amp DC currents) for less than 1 second

This card will support the IO interfaces of LCD (Liquid Crystal Display) - 2X24 alphanumeric Key

Board LED Matrix Display Real Time Clock LCD display and keyboard This will acts as man machine

interface between the datalogger and the signal engineer All the operations (Software) can be performed

using this LCD and keyboard

Real time display with 7 Segments This is built in real time clock within Datalogger and its current

time will be displayed on six 7-segment display provided (Real time clock depend upon DALLAS 1286

chip) This IC will come with internal battery backup hence there is no need to add external batteries

CPU card continuously scans (checks) the DSUs and ASUs Each input connected to digital scanner

units are optically isolated by Opto couplers When CPU card scans the digital inputs it compares with the

previous stored data and if there is any change from the previous status then only that data will be stored (the

status conditions of relay) with date and real time A total of minimum 10 Lac events can be stored in

memory on first in first out basis so that latest data is available in the system There is no loss of data from

datalogger memory in case of power supply failure of datalogger

DIGITAL INPUT CARDS (IN-BUILT) This system is having maximum 8nos of inbuilt Digital inputs cards Maximum 64nos of digital

inputs can be connected to each digital input card The potential free relay contact may be front or back

contact terminated at the Tag Block from the relay of signals tracks points Buttons etc and are

17 | P a g e

subsequently connected to Digital input cards through Flat Ribbon Cable (FRC) connectors These in-built

digital input cards can monitor a total 512 nos of relays status

DIGITAL SCANNER UNIT (DSU) Each DSU contains 8 nos of Digital Input cards Each input card can be connected with 64 inputs

Total input capacity of DSU unit is 512 inputs These scanner cards contain Optocouplers and Multiplexer

Inputs are connected to Stag card The stag card out put is connected to DSU through FRC connectors

Maximum 7 nos of DSUs can be connected to the system So Digital input capacity of the system is 4096

All these digital inputs are scanned at rate of 16 msec

ANALOG SCANNER UNIT (ASU) ASU contains maximum 3 nos of Analog input cards Each input card can be connected with 8nos of

Analog inputs Total input capacity of the ASU is 24 analog input channels Maximum 4nos of ASUs can be

connected to the system Analog input channel capacity of the system is 96 All these analog inputs are

scanned at a rate of less than 1 sec

PARALLEL PORT Parallel port is provided for connecting printer

RS-232 SERIAL PORTS At least 6 Serial communication ports are provided for communication with other dataloggers

Central Monitoring Unit Remote Terminal Unit Electronic Interlocking system Integrated Power Supply

system etc

EXTERNAL NON-VITAL RELAY CONTACTS These relays provided in the system where 16 number of the Relay contacts are provided on the rear

panel through Tele control port to extend alarms and to control the power equipment from remote or local

locations through computer in case of any occurrence of failures Each control can sink or source 100 m

amps of current

INTERNAL MODEM CARD DUAL MODEM CARD (IN-BUILT) It is fixed in datalogger Euro rack itself One card contains two modems The top modem is called

ANS (answer) modem and the bottom modem is called as ORG (originate) modem It is used in case of

networking of Dataloggers In network connect lsquoANSrsquo modem to the lsquoORGrsquo modem of one adjacent station

and connect lsquoORGrsquo modem to the lsquoANSrsquo modem of other adjacent station

POWER SUPPLY Normally 24V DC (12V DC is optional) supply with battery backup is required for the system

working

Input Voltage Range 18Vhellip32V DC (For 24V) 9Vhellip18V DC (For 12V)

INPUT REQUIREMENTS Relay inputs (digital inputs) and analog inputs (voltages currents etc) are required to be connected

to the system as per the requirements of RRI PI SSI as the case may be Some of the inputs to be

monitored is given below

(a) Digital inputs

(i) Field inputs All TPRs NWKRs RWKRs ECRs Crank Handle relays SidingSlot LC gate

control relays etc

(ii) Control Panel inputs All button Knob SMrsquos Key relays

18 | P a g e

(iii) Internal relays

British system All HR DR HHR WNR WRR ASR UCR RR LR UYRTLSR TRSR TSR

JSLR JR etc

SIEMENS system Z1UR Z1UR1 GZR ZDUCR ZU(R)R ZU(N)PRG(R)RG(N)R U(R)S

U(N)PS UDKR DUCR U(R)LR UYR1 UYR2 G(R)LRGR1GR2

GR3 GR4 OVZ2U(R)RW(RN)R (RN)WLR Z1NWR Z1RWRZ1WR1 WKR1 WKR2 WKR3 etc

(b) Analog channels

(i) 230 V AC (for power supplies in the power panel)

(ii) 110V AC (for Signal and Track transformers)

(iii) 110V DC (for Point operation)

(iv) 60V DC (Siemens relays)

(v) 24V DC (Q-series relays)

(vi) 24V DC (for Block Axle counters)

(vii) 12V DC (for indication)

(viii) 20A (for point operation current)

(ix) 10V AC 5KHz (for Axle counter channels) etc

SOFTWARE MODULES OF DATALOGGERS

(a) Network Management of Dataloggers (NMDL)

(b) Reports

(c) Fault Entry

(d) Track Offline Simulation

(e) Train Charting

NMDL SOFTWARE FEATURES (a) Online Relay Status

(b) Online Faults - To view information of various Online Faults as they occur in the stations where

the Dataloggers are connected

(c) Online Simulation - Graphical view of relay operations train movements etc

(d) Remote monitoring of stations with the help of NETWORKING

SOFTWARE OBJECTIVES (a) Predictive Maintenance

(b) Easy identification of failures

(c) Crew discipline

(d) Train charting

REMOTE MONITORING OF STATIONS WITH NETWORKING OF

DATALOGGERS The individual Dataloggers of various stations can be interconnected through networking technology

The data of Remote Panel stations can be viewed in a Computer at the Central Monitoring Station The data

of the network is collected by the FEP (Front End Processor) which in turn is transmitted to the computer

COMPONENTS OF NETWORK MANAGEMENT OF DATALOGGERS

(a) Datalogger at stations

(b) MODEM and Transmission medium

19 | P a g e

(c) Front End Processor (FEP)

(d) Central Monitoring Unit (CMU) Computer

FEP (FRONT END PROCESSOR)

FEP acts as a buffer between the Central Monitoring Unit (Computer) and the Network It is provided

at centralised place to retrieve data continuously from station dataloggers and store in memory and transfer to

computer on request It stores 10 Lac telegrams It works on 12V DC It draws 16A continuous current

when all the three modems are connected Normally it shows the number of packets pending to be sent to the

computer on its 7-segment LED display It is provided with MOTOROLA 68000 microprocessor It has 6-

nos of RS-232 communication ports such as COM1 COM2 COM3 COM4 COM5 and COM6 COM1 is

used for Fault Analysis System (FAS) ie Central Monitoring Unit (Computer) connection COM2 to COM6

are used for networking For Bi-directional 2- nos of ports and for Tri-directional (T-network) 3-nos of ports

are used

DATA TRANSMISSION Dataloggers can be networked in Uni-directional Mode or Bi-directional Mode or T ndash Network Mode

In case of loss of data retransmission of data takes place

(a) Uni-Directional Mode

Each Datalogger will send data in only one direction to the FEP Unidirectional mode network is not

preferred

(b) Bi-Directional Mode

Each end of Network is connected to FEP and each datalogger can now transmit data in both the directions

Bi-directional Mode is advantageous it enables the Data Transmission even in case of Network Failure

(c) T - Network Mode

If more no of stations are in network ie if the network is too lengthy then T- network mode is preferred

COMMUNICATION The communication protocol for transmitting data and command between datalogger and CMU is

standardized by the RDSO and is given in the Specifications of Dataloggers

(a) The type of communication used in the network is dependent on the distance between the dataloggers

(b) For shorter distances Opto Converter Box- Opto isolated current loop communication is used

(c) For longer distances Modem (Dial-up leased) Fiber Optic Satellite Microwave communication

MODEMS Modems are used for DATA transfer between Dataloggers and Front End ProcessorThese are

configured to RS 232 Serial Communication Network is connected with two types of 4-wire modems

(a) Internal modem card Dual Modem card (in-built)

It is fixed in datalogger Euro rack itself One card contains two modems The top modem is called

ANS (answer) modem and the bottom modem is called as ORG (originate) modem

Note In case of networking of Dataloggers connect lsquoANSrsquo modem to the lsquoORGrsquo modem of one adjacent

station and connect lsquoORGrsquo modem to the lsquoANSrsquo modem of other adjacent station

(b) External modems

20 | P a g e

These are generally used at FEP (Front End Processor) side to connect the Dataloggers

(i) To transfer Data from one datalogger to another datalogger FEP Baud rate is 9600bps

(ii) These modems are 4-wire line communication

(iii) To transfer the data from FEP to RMU (PC) the Baud rate is 57600 bps

There is no difference between these modems functionally

CENTRAL MONITORING UNIT (CMU) COMPUTER

Central monitoring unit (Fault Analysis Unit) is a Personal Computer and its minimum configuration

shall be specified by RDSO from time to time System Software Windows XPVista(OS) Norton Kaspersky

(Anti Virus) Interbase where Server is not available (DBMS) Oracle where Server is available (DBMS)

software are required to run Datalogger System It is provided with Graphical User interface (GUI) based

software and retrieve data from all Networked dataloggers (up to 32) at various stations It stores data in

standard data base files The CMU is capable of analyzing the data and generate reports audiovisual alarms

on defined conditions This data can be compressed to take backup In central monitoring unit Software used

for analysis of data prediction of faults etc is written in a structured format so that purchaser can

reconfigure it if required It displays the status of signaling gears at any selected time in graphic form for any

selected station yard It retrieves the stored data amp simulates train movement It sends commands to various

Dataloggers to activate audio visual alarm or operate and electromagnetic relay

CMU shares data available in it by other PCs through available local area network where this data can

be used for train charting passenger information purpose The system generates audiovisual alarm in

ASMrsquosSignal Maintainerrsquos room in the case of power supply failure (battery voltage low) or battery charger

defective with acknowledgement facility

(a) Each datalogger has its own identity code which will be transmitted along with data packet to central

monitoring unit

(b) Events recorded at each station are continuously transmitted to central monitoring unit Response time of

data transfer will not exceed 10 sec

21 | P a g e

22 | P a g e

OPTICAL FIBER CABLE

INTRODUCTION The demand for bandwidth on transmission networks is increasing rapidly because video and

graphical rich contents are exchanged through the corporate network or the Internet The Gigabit Ethernet

became ommonly used in the corporate network backbone and 10Gbit Ethernet will be adopted in the near

future Meanwhile in the home the demand for high-speed network becomes popular as the wide spread of

broadband access eg CATV xDSL and FTTH The transmission medium with capability to transmit high

bit rate signal is necessary to satisfy these requirements

The telecommunication transport technologies move from copper based networks to optical fiber

from timeslot based transport to wave length based transport from traditional circuit switching to terabit

router and all optical based networks entering into a new era of optical networking

BASIC PHYSICS OF OFC

OPTICAL FIBER CABLE OFC have Fibers which are long thin strands made with pure glass about the diameter of a human

hair OFC consists of Core Cladding Buffers and Jacket as shown in figure

MONOCHROMATIC LIGHT OR SINGLE COLOR LIGHT Light or visible light is electromagnetic radiation of a wavelength that is visible to the human eye (

about 400 ndash 700 nm) The word light is sometimes used to refer to the entire electromagnetic spectrum Light

is composed of elementary particles called photons Three primary properties of light are

Light can exhibit properties of both waves and particles This property is referred to as wave-particle

duality The study of light known as optics In free space light (of all wavelengths) travels in a straight path

at a constant maximum speed However the speed of light changes when it travels in a medium and this

change is not the same for all media or for all wavelengths By free space it is meant space that is free from

matter (vacuum) andor free from electromagnetic fields

Thus the speed of light in free space is defined by Einsteinrsquos equation E = mc2

Frequency ν speed of light in free space c and wavelength λ are interrelated by ν = cλ

From the energy relationships E = mc2 = hν and the last one an interesting relationship is obtained

the equivalent mass of a photon m = hνc2

When light is in the vicinity of a strong electromagnetic field it interacts with it From this interaction

and other influences its trajectory changes direction as shown in figure

23 | P a g e

INCIDENT RAY REFLECTED RAY AND REFRACTED RAY An incident ray is a ray of light that strikes a surface The angle between this ray and the

perpendicular or normal to the surface is the angle of incidence Reflection is the change in direction of a

wave front at an interface between two different media so that the wave front returns into the medium from

which it originated Common examples include the reflection of light sound and water waves

The reflected ray corresponding to a given incident ray is the ray that represents the light reflected by

the surface The angle between the surface normal and the reflected ray is known as the angle of reflection

The Law of Reflection says that for a specular (non-scattering) surface the angle of reflection always equals

the angle of incidence The refracted ray or transmitted ray corresponding to a given incident ray represents

the light that is transmitted through the surface The angle between this ray and the normal is known as the

angle of refraction and it is given by Snells Law

The figure shows Incident ray Reflected ray Refracted ray the angle of incidence and angle of refraction

REFRACTIVE INDEX - Refractive index is the speed of light in a vacuum ( c =299792458kmsecond) divided by the speed

of light in a material ( v ) Refractive index measures how much a material refracts light Refractive index of

a material abbreviated as lsquo n lsquo is defined as lsquo n=cv lsquo Light travels slower in physical media than it does

when transmitted through the air Refractive index (n) is a function of molecular structure of matter optical

frequency optical intensity determines optical propagation properties of each wavelength ( λ ) may not be

distributed equally in all directions is affected by external temperature pressure and fields

Refractive index of a medium is a measure for how much the speed of light is reduced inside the

medium For example typical glass has a refractive index of 15 which means that light travels at 1 15 =

067 times the speed in air or vacuum Two common properties of glass and other transparent materials are

directly related to their refractive index

First light rays change direction when they cross the interface from air to the material and effect that

is used in lenses and glasses

Second light reflects partially from surfaces that have a refractive index different from that of their

surroundings

SNELLrsquoS LAW-

24 | P a g e

When light passes from one transparent material to another it bends according to Snells law which

is defined as n1sin(θ1) = n2sin(θ2)

where n1 is the refractive index of the medium the light is leaving θ1 is the incident angle between the light

beam and the normal (normal is 90deg to the interface between two materials)

n2 is the refractive index of the material the light is entering

θ2 is the refractive angle between the light ray and the normal

Snellrsquos law gives the relationship between angle of incidence and angle of refraction

For the case of θ1 = 0deg (ie a ray perpendicular to the interface) the solution is θ2 = 0deg regardless of

the values of n1 and n2 That means a ray entering a medium perpendicular to the surface is never bent The

above is also valid for light going from a dense (higher n) to a less dense (lower n) material the symmetry of

Snells law shows that the same ray paths are applicable in opposite direction

TOTAL INTERNAL REFLECTION- When a light ray crosses an interface into a medium with a higher refractive index it bends towards

the normal Conversely light traveling cross an interface from a higher refractive index medium to a lower

refractive index medium will bend away from the normal

This has an interesting implication at some angle known as the critical angle θc light traveling from

a higher refractive index medium to a lower refractive index medium will be refracted at 90deg in other words

refracted alon g the interface If the light hits the interface at any angle larger than this critical angle it will

not pass through to the second medium at all Instead all of it will be reflected back into the first medium a

process known as total internal reflection

The critical angle can be calculated from Snells law putting in an angle of 90deg for the angle of the refracted

ray θ2 This gives θ1

Since θ2 = 90deg

So sin(θ2) = 1

25 | P a g e

Then θc = θ1 = arcsin(n2n1)

For example with light trying to emerge from glass with n1=15 into air (n2 =1) the ritical angle θc is

arcsin(115) or 418deg For any angle of incidence larger than the critical angle Snells law will not be able to

be solved for the angle of refraction because it will show that the refracted angle has a sine larger than 1

which is not possible In that case all the light is totally reflected off the interface obeying the law of

reflection

OPTICAL FIBER MODE An optical fiber guides light waves in distinct patterns called modes Mode describes the distribution

of light energy across the fiber The precise patterns depend on the wavelength of light transmitted and on the

variation in refractive index that shapes the core In essence the variations in refractive index create

boundary

conditions that shape how light waves travel through the fiber like the walls of a tunnel affect how sounds

echo inside

We can take a look at large-core step-index fibers Light rays enter the fiber at a range of angles and

rays at different angles can all stably travel down the length of the fiber as long as they hit the core-cladding

interface at an angle larger than critical angle These rays are different modes Fibers that carry more than

one mode at a specific light wavelength are called multimode fibers Some fibers have very small diameter

core that they can carry only one mode which travels as a straight line at the center of the core These fibers

are single mode fibers This is illustrated in the following picture

OPTICAL FIBER INDEX PROFILE Index profile is the refractive index distribution across the core and the cladding of a fiber Some

optical fiber has a step index profile in which the core has one uniformly distributed index and the cladding

has a lower uniformly distributed index Other optical fiber has a graded index profile in which refractive

index varies gradually as a function of radial distance from the fiber center Graded-index profiles include

power-law index profiles and parabolic index profiles The following figure shows some common types of

index profiles for single mode and multimode fiber

26 | P a g e

OPTICAL FIBERrsquoS NUMERICAL APERTURE ( NA )- Multimode optical fiber will only propagate light that enters the fiber within a certain cone known as

the acceptance cone of the fiber The half-angle of this cone is called the acceptance angle (see figure 18)

θmax For step-index multimode fiber the acceptance angle is determined only by the indices of refraction

Where

n is the refractive index of the medium light is traveling before entering the fiber

nf is the refractive index of the fiber core

nc is the refractive index of the cladding

NUMBER OF MODES IN A FIBER - Modes are sometimes characterized by numbers Single mode fibers carry only the lowest-order

mode assigned the number 0 Multimode fibers also carry higher-order modes The number of modes that

can propagate in a fiber depends on the fiberrsquos numerical aperture (or acceptance angle) as well as on its

core diameter and the wavelength of the light For a step-index multimode fiber the number of such modes

Nm

Where

D is the core diameter

λ is the operating wavelength

NA is the numerical aperture (or acceptance angle)

MODE FIELD DIAMETER - All light do not travels through the core of the fiber but is distributed through both the core and the

cladding The mode field is the distribution of light through the core and cladding of a particular fiber

Mode-Field Diameter (MFD) defines the size of the power distribution When coupling light into or out of a

fiber MFD is important in understanding light loss

27 | P a g e

ADVANTAGE OF OFC COMMUNICATION - bull More information carrying capacity Fibers can handle much higher data rates than copper More

information can be sent in a second

bull Free from Electromagnetic and Electrostatic interference Being insulator no electric current flows through

the fibre and due to this reason fibres neither radiate nor pick up electro - magnetic radiation So WPC

CLEARANCE is not required

bull Low attenuation 025 dbkm at 1550 nm Loss in twisted pair and coaxial cable increases with frequency

where as loss in the optical fibre cable remains flat over a wide range of frequencies

bull Use of WDM ndash Switching routing at Optical signal level

bull Self healing rings under NMS control

bull Small size makes fibre cable lighter in weight So easy to handleOptic fibre cable weight (approx)

500 kg km Copper cable weight (approx) 1000 kgkm

The reasons are photons of light in a fibre

do not affect each other as they have no electrical charge and they are not affected by stray photons outside

the fibre But in case of copper electrons move through the cable and these are affected by each other

Optical fibre does not carry any electricity even if the cable is damaged or short circuited it does

not cause any spark or fire hazard

As the fibre do not radiate energy it can not be detected by any nearby antenna or any

other detector The fibres are difficult to tap and therefore excellent for security

As the signal transmission is by digital modulation there is no chance of cross talk in

between channels

Only by adding a few additional terminal and repeater equipments the

capacity of the system can be increased at any time once the cable is laid

ical effects and temperature variations

LIMITATIONS OF OFC -

difficult

- utilised

APPLICATION IN SIGNAL AND TELECOMMUNICATIONS transmission circuits

-haul circuits for linking of telephone exchanges

28 | P a g e

PROPAGATION MODES CONCEPT -

MODE - Mode is an available distribution of electromagnetic field in a plane transverse to the direction of

light propagation Each mode is characterized by frequency polarization electric field strength and

magnetic field strength Available patterns are derived from Maxwellrsquos equations and boundary conditions

LINEARLY POLARIZED (LP) MODE A mode for which the field components in the direction of propagation are small compared to

components perpendicular to that direction An optical fibre supports only different field patterns called as

lsquoLinear Polarizedrsquo or lsquo LPrsquo modes The reasons are

requirements

de

the accrual of power carried by different modes

There are two basic types of fiber Multimode fiber and Single-mode fiber

Multimode fiber is best designed for short transmission distances This is suited for used in LAN systems and

video surveillance Single mode fibre is best designed for longer transmission distances This is suitable for

long distance telephony and multi channel television broadcast systems

29 | P a g e

MULTI MODE FIBER Multimode fiber the first to be manufactured and commercialized simply refers to the fact that

numerous modes or light rays are carried simultaneously through the waveguide Modes result from the fact

that light will only propagate in the fiber core at discrete angles within the cone of acceptance MM fiber type

has a much larger core diameter compared to single-mode fiber allowing for the larger number of modes

and

is easier to couple than single-mode optical fiber Multimode fiber further categorized as Multimode step-

index and Multimode graded index fiber

PROPAGATION THROUGH MMSI FIBER Figure shows the principle of total internal reflection applies to multimode step index fiber Because

the corersquos index of refraction is higher than the claddingrsquos index of refraction the light that enters at less than

the critical angle is guided along the fiber

Three different light waves travel down the fiber One mode travels straight down the center of the

core A second mode travels at a steep angle and bounces back and forth by total internal reflection The third

mode exceeds the critical angle and refracts into the cladding Naturally it can be seen that the second mode

travels a longer distance than the first mode causing the two modes to arrive at separate times

PROBLEMS WITH MMSI FIBER AND SOLUTION This disparity between arrival times of the different light rays is known as dispersion and the result is

a muddied signal at the receiving end It is important to note that high dispersion is an unavoidable

characteristic of multimode step-index fiber The solutions are either use Graded index fiber or Single mode

fiber

PROPAGATION THROUGH MMGI FIBER Multimode Graded-index refers to the fact that the refractive index of the core gradually decreases

farther from the center of the core The increased refraction in the center of the core slows the speed of some

light rays allowing all the light rays to reach the receiving end at approximately the same time reducing

dispersion Figure shows the Light propagation principle through multimode graded-index fiber The corersquos

central refractive index ( nA ) is greater than that of the outer corersquos refractive index ( nB )

It is very clear from the figure the light rays no longer follow straight lines they follow a serpentine path

being gradually bent back toward the center by the continuously declining refractive index This reduces the

arrival time disparity because all modes arrive at about the same time The modes traveling in a straight line

30 | P a g e

are in a higher refractive index so they travel slower than the serpentine modes These travel farther but

move faster in the lower refractive index of the outer core region

PROPAGATION THROUGH SMSI FIBER Single mode fiber has a much smaller core that allows only one mode of light at a time to propagate

through the core The figure shows the single mode fiber

Single-mode fiber exhibits no dispersion caused by multiple modes Single-mode fiber also offers lower fiber

attenuation than multimode fiber Thus more information can be transmitted per unit of time because it can

retain the fidelity of each light pulse over longer distances Like multimode fiber early single-mode fiber was

generally characterized as step-index fiber meaning the refractive index of the fiber core is a step above that

of the cladding rather than graduated as it is in graded-index fiber Modern single-mode fibers have evolved

into more complex designs such as matched clad depressed clad and other exotic structures

SINGLE-MODE FIBER DISADVANTAGES The smaller core diameter makes coupling light into the core more difficult The tolerances for single-

mode connectors and splices are also much more demanding

CUTOFF WAVE LENGTH - Cutoff wavelength is the wavelength above which a single-mode fiber supports and propagates only

one mode of light In other words an optical fiber that is single-mode at a particular wavelength may have

two or more modes at wavelengths lower than the cutoff wavelength The effective cutoff wavelength of a

fiber is dependent on the length of fiber and its deployment The longer the fiber the lower is the effective

cutoff

wavelength The smaller the bend radius of a loop of the fiber the lower is the effective cutoff wavelength If

a fiber is bent in a loop the effective cutoff wavelength is lowered

SIGNAL ATTENUATION IN FIBER - Optical fiber has a number of advantages over copper However it also suffers from degradation

problems which can not be ignored The first of these is loss or attenuation Attenuation is typically the result

of two sub properties They are scattering and absorption Both of which have cumulative effects The second

is

dispersion which is the spreading of the transmitted signal and is analogous to noise

SCATTERING Scattering occurs because of impurities or irregularities in the physical construction of the fiber The

well known form of scattering is Rayleigh Scattering It is caused by metal ions in the silica matrix and

results in light rays being scattered in various directions

31 | P a g e

Scattering limits the use of wavelengths below 800nm The short wavelengths are much affected than longer

wavelengths It is because of Rayleigh scattering that the sky appears to be blue ( shorter wave length ) The

shorter wavelengths ( blue ) of light are scattered more than the longer wavelengths of light

ABSORPTION Absorption results from three factors They are hydroxyl ions ( OH- water ) in the silica impurities

in the silica and incomplete residue from the manufacturing process These impurities tend to absorb the

energy of the transmitted signal and convert it to heat resulting in an overall weakening of the signal The

Hydroxyl absorption occurs at 125 and 139 micro The silica itself starts to absorb energy at 17 micro

because of the natural resonance of the silicon dioxide

MACRO BENDING LOSS Macro-bending loss is caused by bending of the entire fiber axis The bending radius shall not be

sharper than 30d where d is diameter of cable A single bend sharper than 30d can cause loss of 05dB

The fiber may break if bending is ever sharper

MICRO BENDING LOSS Micro-bending loss is caused by micro deformations of fiber axis which leads to failures in achieving

total internal reflection conditions Micro-bends are small scale perturbations along the fiber axis the

amplitude of which are on the order of microns These distortions can cause light to leak out of a fiber

Micro-bending may be induced at very cold temperatures because the glass has a different coefficient of

thermal expansion from the coating and cabling materials At low temperatures the coating and cable

become more rigid and may contract more than the glass Consequently enough load may be exerted on the

glass to cause micro bends

Coating material is selected by manufacturers to minimize loss due to micro-bending The linear thermal

expansion coefficient of coating material shall be compatible with that of fiber

32 | P a g e

DISPERSION Dispersion is the optical term for the spreading of the transmits in the fiber It is the bandwidth

limiting phenomenon and comes in two forms Multimode dispersion and chromatic dispersion Chromatic

dispersion is further subdivided into material dispersion and waveguide dispersion

DISPERSION PHENOMENON IN OPTICAL FIBER Dispersion is the time distortion of an optical signal that results from the differences of time of travel

for different components of that signal typically resulting in pulse broadening As the distance traveled by

the signal is more broadening of pulse is more In digital transmission dispersion limits on the maximum

data rate and the maximum distance ie the information-carrying capacity of a fiber link The interference

from broadened pulse in the next interval shall not lead to erroneous interpretation of received signal

OPTICAL DOMAIN Understanding where attenuation and dispersion problems occur helps optical design engineers

determine the better wavelengths at which information can be transmit taking into account distance type of

fiber and the other factors which can severely affect the integrity of the transmitted signal The graph shown

depicts the optical transmission domain as well as the areas where problems arise The wavelength (nm)

is shown on X-axis and attenuation ( dBkm) is shown on Y-axis

There are four transmission windows appear in the figure The first one is at around 850 nm the

second at 1310nm third at 1550 nm and fourth at 1625 nm The last two labeled as C and L band

respectively The 850 nm wavelength at which the original LED technology operated The second window at

1310 nm has low dispersion The 1550 nm called as C-band is ideal wavelength for long haul

communication systems The network engineers can avoid transmitting signal at 1000 nm where Rayleigh

scattering 1240 and 1390 nm where hydroxyl absorption by water occurs to avoid high degree of loss

Optical fibers also can be manufactured to have low dispersion wavelength in the 1550nm region

which is also the point where silica-based fibers have inherently minimal attenuation These fibers are

referred to as dispersion-shifted fibers and are used in long-distance applications with high bit rates For

33 | P a g e

applications utilizing multiple wavelengths it is undesirable to have the zero dispersion point within the

operating

wavelength range

34 | P a g e

SIGNALLING RELAYS

INTRODUCTION A relay is an electromagnetic device which is used to convey information from one circuit to another

circuit through a set of contact ie front or back contact Constructional and electrically relays may be

divided into DC and AC relays because the means by which the electrical energy in the coil is converted in

to mechanical Energy in order to move the contacts are fundamentally different In DC type the contacts are

carried on an armature forming part of a magnetic circuit in which a field is set up by the current flowing in

the coils In AC types the contacts are attached by a link mechanism to a metal sector disc or cylinder in

which currents are induced by the alternating magnetic field produced by the currents in the coils

Every endeavor has been made to explain the action of each type of relay in the simplest possible manner

Relays are sophisticated switch gears used for remote control and succession control of various

electrical equipment In present days they are widely used because they are capable of protecting the

controlled equipment from cross feeding and overloading even as they cater for speedy operations

Most of the relays in present day signaling are electromagnetic devices although some of the relays control

circuits through electronic components like diodetransistors Integrated Chips etc

Railway signaling relays are unique in that

(a) They operate on low voltage and current

(b) They are more articulate as according to their special features they can work under restrictive conditions

and in any specified manner Virtually they can cater for all situations while contributing to speed and

accuracy in operations

CLASSIFICATION OF SIGNALLING RELAYS (a) According to the method of their mounting or fixture they are classified as

(i) Shelf type Relays which are loosely kept on shelves

(ii) Plug in type Relays which are plugged into a pre- wired plug boards

(b) According to their connection and usage they are classified as

(i) Track relays Relay which is directly connected to the track to detect the presence of vehicle

(ii) Line Relays Other than track relay all are line relays Relays connected to the selection circuit

(c) According to their vitality or importance in ensuring train working safety they are classified as

(i) Vital Relays All relays used for traffic control such as signal point controls track detection etc

(ii) Non-vital Relays Relays which operate control aids and accessories like warnings buzzers

Indications etc

(d) According to their special provisions to ensure reliability of their contacts they are classified as

(i) Proved type are those whose normalization after each operation shall be proved in circuit

controlled by their contacts Contacts in which both the springs have metal surfaces on their tips They may

get fused due to high sparking current across them during operation These may prevent relay normalization

and causes unsafe condition in traffic control To avoid this proving of relay normalization after each

operation is necessary

(ii) Non - proved type Need not to be proved to have been normalized after each operation as their

contacts have at least one non-fusible contact (carbon contact)

(e) According to their feed source relays are broadly classified as

(i) DC relays The relay which requires DC power supply for its operations are called DC relays Among

the DC relays

o DC neutral relays This relay closes the same set of contacts on energization with Normal polarity

or Reverse polarity supply

o Polar Relays This relay closes different set of contacts when energized with Reverse polarity

supply They may or may not have contact to close when deenergized

35 | P a g e

(ii) AC Relay AC Induction motor track relays Time element relays flashing indication control etc

(iii) Electronic Relays DC relays with electronic components in them are called electronic relays

DC NEUTRAL RELAY Each Relay has usually one or two coils with a hollow center to accommodate a coreThe coils are

made up of a large numbers of turns of small gauge soft drawn copper wire The two coils can be connected

in series or parallel according to the requirement of relay resistance The ends of the coils are terminated on

binding post to which the control wires are connected Each coil is placed around a core of specially selected

Iron or steel having high permeability and low retentivity The core should be susceptible to magnetism and

at the same time should have little residual magnetism The cores are connected at the top by a yoke to

complete the magnetism coupling between two ends of coils The bottom of each core is equipped with a

large steel or Iron block known as pole piece or face

A flat piece of Iron or steel called armature is supported by brackets which are securely fastened to

the pole piece The armature yoke and the pole pieces are also made of specially selected iron or steel of the

same quality as the core The armature carries the metallic spring contacts which are insulated from it

The circuit through the coils of the relay is closed It sets up a magnetic flux through the core yoke and the

armature The flux passing between the armature and pole faces causes the armatures get attracted to the pole

faces and armature picks up and closes front contacts When the circuit is opened the magnetic flux collapses

and the armature drops away by gravity from the pole faces the front contacts break and back contacts close

The front and back contacts of the relay can be utilised to make or break other circuits Two stop pins of

nonmagnetic material are fixed either on the armature or pole faces so that the armature cannot

come in contact with the pole faces It is essential to maintain a small air-gap between the armature and pole

faces so that low value of residual magnetism may not retain the armature in picked up position and causes

the relay to fail to drop away with a break in its control circuit

GENERAL USAGE

DC Neutral line relays are most commonly used for Railway Signalling controls and detection

Among them plug-in type relays are preferred in larger installations for space considerations Shelf type

relays are also in use mostly in wayside stations

There are many DC Neutral line relays in use with special features such as

(i) Delayed operation

(ii) Biased DC control

(iii) DC control unaffected by AC interference currents

(iv) Getting latched in operated condition till further feeding and others

Usage of DC polar relays is mostly in conjunction with block instruments that control traffic between

stations AC line relays are almost extinct in installations of British Signalling practice They are however

used for time control operations flashing indication control and such other special purposes in installations

with Siemens signalling practice widely Track relays are used according to the type of track detection

circuits chosen for a given location and context While most of the track circuits are still of the DC working

type requiring DC neutral track relays with them the prospects of their being replaced with Electronic track

circuits directly feeding DC line relays in future are great AC Track Circuits are used in DC Traction area

as conventional DC Track Circuits are not suitable there AC Track relays are used with them almost all of

the induction motor type In the British practice of signalling which was first introduced on Indian Railways

non-proved type relays with carbon to metal switching contacts are generally used for vital controls

They facilitate simple circuit designs But with the advent of German Practice introduced by Ms

Siemens later proved type relays with all metal to metal contacts are widely accepted in spite of

complications in circuit design caused by them A recent introduction is that of the same type relays made by

Ms Integra control However for some time now the appreciable features of both the practices are getting

36 | P a g e

incorporated together in the indigenous designs of signalling by railwaymen With this the usage of all types

of relays anywhere can be found without straight jacketed segration of relay types

CHARACTERSTIC OF ELECTRO-MAGNETIC RELAY The following are the characteristic of electro-magnetic relays A brief study of them helps in

understanding the choice of their components and designs features

1) Force of attraction

2) Effect of air gap

3) Effect of Hysterisis

4) Transient condition

FORCE OF ATTRACTION In any electro-magnetic system the force of attraction is given by

Where B - is the flux density a - is the cross sectional area of the particular part of the magnetic

circuit

In the case of a DC neutral Relay B is proportional to the current that is flowing in the coil

surrounding the electro-magnet and thus the force of the attraction is directly proportional to the square of the

current This square relationship has its own advantage especially in the case of DC track relay in that a

small reduction in the current will have a great effect on the working of the relay Also for a given change of

current the make and the break will be quicker with lesser possibility of arcing

EFFECT OF AIR GAP

Curve lsquoArsquo is magnetisation curve for the iron and is all practical purpose a straight line up to the

saturation point Curve lsquoBrsquo is the magnetisation curve for the open-air gap which is a straight line through

out because per magnetisation curve of the whole

magnetic circuit of the relay and for a given force is the sum of the amp-turns for the iron part and the amp-

turns for the air gap

When the front contacts are open the force required to pick up the armature is shown on curve lsquoCrsquo to be F1

but after the armature has operated it will be separated from the core by stop pins In this position the amp-

turns required to maintain the armature is less as indicated by the dotted line from 1 on curve C to 2 on curve

37 | P a g e

F But actually the current in the coil is unaltered the force on the armature is greater than required as

indicated at 3 on curve F Part of this extra force is used to flex the front contacts sufficiently to give good

contact pressure when it is in energised position

The difference between the pick-up and the drop-away current should be as small as practicable in

track relay to ensure good shunting characteristics This is achieved firstly by the choice of good quality relay

iron and secondly by having a small air gap between armature and core If the air gap is not available then

the residual magnetism fluxes might cause the armature to be retained when the supply is disconnected For

this reason residual pins are provided to ensure a definite minimum air gap in the energised position

EFFECT OF HYSTERISIS

Hysterisis is the property by which the flux produced lags behind the current In the de-energized

condition there will be small residual flux in the core When the voltage is applied to the coils the current in

rising to its steady value first causes the flux to rise from 1 to 2 along the curve At this point the flux density

will be sufficient to attract the armature and reduce the air gap the flux then raise to 3 and continue to 4

which corresponds to the steady current in the coils When the voltage is disconnected the current in falling

caused the flux to fall from 4 to 5 along the curve At this point the flux density will fall below the value

required to maintain the armature which will release thus increasing the air gap and reducing the flux to 6

Finally the

flux will decrease from 6 to 1 where the current will again be zero

The relay core is made of material having high permeability and low retentivity As mentioned in

the IRS specification Electromagnet iron may be in the form of a

(a) Bar of silicon steel

(b) Best Yorkshire wrought iron

(c) Swedish charcoal iron

(d) Electrical steel sheets

` This reduces the difference between pick up value and Drop away value By selecting good quality

core material Percentage release and sensitivity of the relay will be improved

TRANSIENT CONDITION

38 | P a g e

When the voltage is applied or disconnected from the coils it takes some little time before the current

become steady These are known as transient conditionsrdquo and are important so far as track relays are

concerned When the voltage is first applied to the coils the magnetic flux in rising cuts the turns on the

coils and in so doing produces a back EMF that opposes the applied voltage and retards the growth of

current

The growth and decay of flux are decided by the relationship between the inductance and resistance

in the circuit is known as time constant It is not fixed quantity in the case of DC neutral relay This value of lsquo

Lrsquo is less when the relay is in de-energised condition (L1) than when the relay is in energised condition (L2)

The magnitude of flux that is established for a given change of current is different in two cases

When the current reaches the pick up value the armature closes and the inductance is increased to L2

due to reduced air gap the flux per amp is increased The increase in flux increased the back EMF during the

movement of the armature after which the current continuous to raise along a new curve corresponding to the

increased inductance until it reaches the final value (ER) This process is indicated above in fig24

When the supply is disconnected the current is obliviously reduced to zero immediately but the flux

decay comparatively slowly owing to the eddy currents produced in the core by the rapid flux change which

tend to maintain the flux The drop away time on a disconnection is however generally negligible See fig

below

If the relay releases due to the reduction in current from say I 2 to I 1 caused by the application of

shunt resistance (as in the case of track relay ) the time taken is much longer than the relay is simply

disconnected The rate of rise or fall of current during the transient conditions is also depends on exterior

circuit values because L and R apply to the whole circuit The production of eddy current in the core the flux

will decay at a slower rate than the current So that the actual release time will be a little longer than it takes

the current to fall to the release

L= Inductance

39 | P a g e

R= Resistance

It is now clear that to reduce releasing time to a minimum it is necessary that

- The relay iron should have low Hysterisis loss and low retentivity

- The degree of over energization of the relay should be restricted

- Connecting a suitable external resistance in series with the relay to keep LR ratio low

In non RE area for track circuit length less than 100M 9 ohm track relay only to be used Using relay

with minimum contacts as they require lesser current which keeps inductance value low

Train working safety is ensured only if the track relay of shortest length track circuit is released

before a light engine running at a highest permitted speed clears it Otherwise the track circuit occupation

may go undetected To avoid this a special provision has to be made in signal control circuits wherever

necessary

The following methods may be adopted for reducing the time lag of track relay

(a) Restrict the over energisation of relay since the release time depends on the initial working current

(b) Connecting a suitable external resistance in series with the relay to keep the LR ratio low

(c) Using relays with minimum contacts as they require lesser operating current keeping the inductance

value low

40 | P a g e

CONCLUSION

Modern signalling is vital for safe and punctual movements of trains In the Indian railways The Signalling

and Telecommunication Department is responsible for providing modern effective and relaible signalling

systems as well as telecommunication systems

The first mode of communication used in Indian Railways was the use of electric telegraph

with the help of Morose code Morose code is the method of providing text information as a series of on-off

tones and lights or clicks that can be directly understood by a skilled listener or observer without special

equipmentEach character (letter or numeral ) is represented by a unique sequence of dots and dashes Later

this system becomes obselete and beggan the era of wireless communication which operated at audio level

frequency range

In wireless communication the significant advances took place the transition to miniature

valves or filament tubesBut this was abandoned too because of excessive current consumption and over

heating of the filament tubes

Fibre-optic communication is a method of transmitting information from one place to another by

sending pulses of light through an optcial fibreThe light forms an electromagnetic carrier wave that is

modulated to carry information First developed in the 1970s fibre optic communication systems has

revolutionized the telecommunications industry and have palyed a major role in the advent of the information

age Because of its advantages over electrical transmissionsoptical fibres have largely replaced copper wire

communications in core networks in the developed world The Indian Railways too is undergoing a transition

from Microwave communication to fibre optic communications

41 | P a g e

BIBLIOGRAPHY AND REFERENCES

1 wwwwikipediacom

2 wwwbritaniccacom

3 wwwirfcacom

4 Motorola GP60 system manual

5 Harris FAS 7000 manual

6 TOSHIBA Manual

12 | P a g e

The event logger card captures following signals

(i) Pulse signals

(ii) Supervisory signals

(iii) Card removal information

(iv) Serial packets from

Event Logger card has a Rabbit processor and 2 MB FLASH MEMORY to store packets The data is initially

stored in the buffer and subsequently transferred to FLASH memory every two minutes Normally 4096

pages of the data can be stored in flash memory on FIFO (first in first out) basis

Run This LED blinks continuously indicating the normal working of the event

Log This LED blinks whenever data is being logged into the flash memory (Approx after every 2 minutes)

Dnld This LED is ON when data is being downloaded from the flash memory of the card and becomes OFF

when download is complete

(D) MODEM CARD (CARD 6) (i) The modem card transmits and receives the digital packet information form one counting unit to the other

The packet will appear after every 18 sec and the packet carries the latest information such as

(ii) The modem card being used is V21 type (2-wire) in SSDAC

(iii) This card interfaces with serial RS232C port of both Micro-controller Logic Boards

(iv) It multiplexes the two RS232C inputs and selects one of the two channels and provides signal conversion

from digital to analog (FSK modulation) and vice-versa

(v) Data transmission rate is 300 bitssec

(vi) Automatic Gain Control circuit is incorporated hence no gain adjustments required

(vii) Mode selection on Modem card The modem has been set in lsquoORIGINATORrsquo mode for entry and in the

lsquoANSWERrsquo mode for exit in the factory

(viii) LED Indications provided on Modem card

-Transmitting the signal when LED is flashing

- Receiving the signal when LED is flashing

-Remains OFF in SSDAC

-Carrier is detected when LED is glowing

(E) RELAY DRIVER CARD (CARD 7) (i) The Relay Driver card (RD) provides the 24V DC output required for driving Vital Relay

(ii) One RD card is used in each SSDAC counting unit The RD card receives the command of clear and

clock signals from MLB1 amp MLB2 cards and drives the vital relay lsquoONrsquo when section is NOT OCCUPIED

through opto- isolator circuit

(iii) If a train occupies the section the vital relay is dropped The vital relay status is read back by the system

as per the driving output

(iv) It has

13 | P a g e

ndash LED flashes when the section is clear

ndash LED flashes when the section is clear

All the above LEDrsquos are lit for section clear condition

(F) DC-DC CONVERTER CARD (CARD 8)

INPUT VOLTAGE Nominal Voltage voltage 24V DC Maximum current drain= 12A

Required voltage 18V DC to 30V DC

Output voltage

Nominal Voltage +5 V DC 2 A Required voltage 4 7 5 t o 525V DC

Nominal Voltage +12V DC 200 mA Required voltage 1175 to 1225V DC

Nominal Voltage +24V DC 300 mA with common ground Required voltage 235 to 245V DC

Nominal Voltage +15V DC 100 mA with isolated ground Required voltage 145 to 155V DC

SURGE VOLTAGE AND LIGHTNING PROTECTION Transient surge voltages arise as a result of Lightning discharge switching operations in electrical

systems and electrostatic discharge These surge voltages often destroy the electronic equipment to a large

extent In order to prevent surge voltages from destroying the equipment all the input lines of SSDAC ie

Power Supply (24V) Reset (48V) amp Modem is to be routed through surge voltage protection devices for

effectively protecting the system These devices (3 numbers) are mounted in a box and supplied along with

the system One number of box is to be installed at each location and wired to the SSDAC

Each surge voltage protection device consists of two parts

(a) Base

(b) Plug Trab

The Base of the device is used for wiring the input and output signals The connection details from relay

room to the box and from box to SSDAC unit are provided on the box The Plug Trab consists of MOV and

GD Tube and diverts the excess energy during surge voltages or lightning into the ground connection The

operation of these devices relies on a high quality ground connection in order to safely shunt away the

unwanted energy The impedance of the ground connection is critical and it should be less than 2 Ohms

NOTE The 3 Plug Trab connections are not to be interchanged with one another The plug Trab is a

detachable device and can be replaced with SPARE unit in case of blown device which is indicated by

means of LED for 24 V

EFFECTIVENESS OF PLUG TRABS The effectiveness of plug Trab depends wholly on the Earth connection provided to the system The earth

provided to the system should be less than 1 ohms and connections should be firm and proper to the SSDAC

unit VR box etc

SURGE VOLTAGE AND PROTECTION DEVICE SV-120 The Surge Voltage protection device is to be installed at each location along with every SSDAC unit

14 | P a g e

EARTHING- The lead wires connecting the installation and the earth electrode shall ordinarily be of stranded

copper wire of 29 sq mm (19 strand wires of 14 mm diameter) Copper wire has been specified because GI

wires usually are having greater corrosion However in areas where copper wire may be frequently stolen

due to theft ACSR of size 64 sq mm (19 strands of 211 mm diameter) may be used

LIMITS OF EARTH RESISTANCE (a) Apparatus case connected to Earth (SSDAC and vital Relay Box is housed in Apparatus case and

Connected to earth at outdoor) shall be less than or equal to 1 ohm

(b) All cable connected to same earth shall be less than or equal to 1 ohm

(C) Reset box connected to earth near SM s Room shall be less than or equal to 1ohm

EQUIPMENT TO BE EARTHED A Common Earth should be provided for SSDAC for items 1(a) amp (b) of the above at the outdoor

(a) The Apparatus Case is to be connected to earth (the chassis of SSDAC amp Vital Relay Box should be

properly connected to apparatus case)

(b) Metallic sheath and armouring of all the underground main cables are to be earthed

(i) In RE area the metallic sheath and armouring of main telecom cables are earthed at both ends

(ii) In RE area the armouring of Jelly filled cable shall be earthed at both ends

(c) The Earthing shall be provided at every location box where cables are terminated

(d) Earth already available for other equipment may be used for earthing of Reset Box near SM s Room

Cabin etc

15 | P a g e

DATALOGGER

INTRODUCTION Datalogger is a Microprocessor based system which helps in analysing the failures of relay inter

locking system Electronic Interlocking system This is like a black box which stores all the information

regarding the changes take place in relays AC DC Voltages and DC currents along with date and time The

same information data can be transferred to the computer to analyse further ldquoon line ldquooff linerdquo analysis of

stored date A print out also can be obtained through a printer by connecting directly to the datalogger unit

The data belongs to Relay contacts is considered as digital inputs and the data belongs to voltage

levels currents is considered as Analog inputs Datalogger lsquos are mandatory for all new relay interlocking

(PIRRI) EI installations and it is also recommended to provide in all existing PIs RRIs To increase the

line capacity mechanical signalling equipments are upgraded to PI RRI or EI Due to complexity in the

circuits and wiring sometimes it is very difficult to rectify the failures So datalogger can monitor these

systems with real time clock Thus it can be named as black box of Samp T equipments and hence it is a vital

tool for accident investigation Datalogger is used at Stations yards Whereas in case of Auto Section amp IBH

Mini dataloggers called as Remote Terminal Unit (RTU) are used

ADVANTAGES OF DATALOGGERS (a) Dataloggers helps in monitoring the typical failures such as intermittent auto right failures

(b) It helps in analyzing the cause of the accidents

(c) It helps in detecting the human failures errors such as

(i) Drivers passing signal at Danger

(ii) Operational mistakes done by panel operators ASMrsquos of operating department

(iii) Signal and telecom engineering interferences in safety circuits

(iv) Engineering and electrical department interferences failures

(v) It helps as a ldquoTOOLrdquo in preventive maintenance of signaling gears

(d) Dataloggers can be connected in network Networked dataloggers helps to monitorthe PIRRIEI remotely

(e) Failure reports can be generated remotely with help of datalogger network

(f) On line and Off line track simulation is possible

(g) Speed of the train on point zones can be calculated

(h) Age of the equipment in terms of number of operations etc

COMMON EQUIPMENT FOR ALL DATALOGGERS ARE GIVEN

BELOW (a) CPU card

(b) Digital and Analog input cards

(c) Local terminal(PC)

(d) communication links

(e) Printer

All the dataloggers requires a potential free ( spare ) relay contact for monitoring digital inputs

through Digital input cards amp for monitoring Analog inputs such ACDC bus bar voltage levels through

Analog input cards Digital and Analog inputs are connected to the Processor card Processor card consists of

memory ICrsquos Memory ICrsquos are programmed as per requirement of the signal engineers

Provision of Dataloggers is mandatory with RRI systems and is optional for PI systems as per

amendment to the specification for Relay Interlocking systems ( IRSS-36 ) The data collected by the

datalogger can be used for failure analysis repetitive discrepancies and for accident investigations

16 | P a g e

Note

If the serial communications is more than 50m then line drivers shall be used up to 3 Kms

4wire leased line Modems shall be used if the serial communication is more than 3 Kms

STUDY OF EFFTRONICS DATALOGGER TECHNICAL DETAILS (a) 24V 12VDC Power Supply

(b) Total Storage Capacity of 10 Lakh events

(c) In-built Temperature sensors

(d) Internal Buzzer for alarming during failures

(e) Real Time clock with internal battery backup with data retention up to 10 years

(f) 512 LED matrix to indicate the status of 512 Digital inputs at a time page wise

(g) Seven segment LCD screen (2x24) to display the status of digitalanalog signalsTime Temperature etc

(h) Using the keyboard various functions can be viewed in the LCD panel

(i) Max Digital Inputs 4096

(j) Max Analog Inputs 96

(k) Digital Input Scanning Time 16 millisecond

(l) Analog Input Scanning Time is less than 1 Sec

HARDWARE (EQUIPMENT) Datalogger system consists of

(a) Datalogger (CPU - with Microprocessor 68000)

(b) Digital input cards

(c) Dual modem card

(d) Digital Scanner units (DSU)

(e) Analog Scanner units (ASU)

CPU CARD It is provided with Motorola microprocessor M 68000 It performs all the activities pertaining to the

datalogger It continuously scans (check) the Digital inputs(inbuilt) Digital Scanner Units and Analog

Scanner Units ie scanning of digital signals (Relay operations) for every 16-milli seconds and scanning of

analog signals (ie ACDC voltages amp DC currents) for less than 1 second

This card will support the IO interfaces of LCD (Liquid Crystal Display) - 2X24 alphanumeric Key

Board LED Matrix Display Real Time Clock LCD display and keyboard This will acts as man machine

interface between the datalogger and the signal engineer All the operations (Software) can be performed

using this LCD and keyboard

Real time display with 7 Segments This is built in real time clock within Datalogger and its current

time will be displayed on six 7-segment display provided (Real time clock depend upon DALLAS 1286

chip) This IC will come with internal battery backup hence there is no need to add external batteries

CPU card continuously scans (checks) the DSUs and ASUs Each input connected to digital scanner

units are optically isolated by Opto couplers When CPU card scans the digital inputs it compares with the

previous stored data and if there is any change from the previous status then only that data will be stored (the

status conditions of relay) with date and real time A total of minimum 10 Lac events can be stored in

memory on first in first out basis so that latest data is available in the system There is no loss of data from

datalogger memory in case of power supply failure of datalogger

DIGITAL INPUT CARDS (IN-BUILT) This system is having maximum 8nos of inbuilt Digital inputs cards Maximum 64nos of digital

inputs can be connected to each digital input card The potential free relay contact may be front or back

contact terminated at the Tag Block from the relay of signals tracks points Buttons etc and are

17 | P a g e

subsequently connected to Digital input cards through Flat Ribbon Cable (FRC) connectors These in-built

digital input cards can monitor a total 512 nos of relays status

DIGITAL SCANNER UNIT (DSU) Each DSU contains 8 nos of Digital Input cards Each input card can be connected with 64 inputs

Total input capacity of DSU unit is 512 inputs These scanner cards contain Optocouplers and Multiplexer

Inputs are connected to Stag card The stag card out put is connected to DSU through FRC connectors

Maximum 7 nos of DSUs can be connected to the system So Digital input capacity of the system is 4096

All these digital inputs are scanned at rate of 16 msec

ANALOG SCANNER UNIT (ASU) ASU contains maximum 3 nos of Analog input cards Each input card can be connected with 8nos of

Analog inputs Total input capacity of the ASU is 24 analog input channels Maximum 4nos of ASUs can be

connected to the system Analog input channel capacity of the system is 96 All these analog inputs are

scanned at a rate of less than 1 sec

PARALLEL PORT Parallel port is provided for connecting printer

RS-232 SERIAL PORTS At least 6 Serial communication ports are provided for communication with other dataloggers

Central Monitoring Unit Remote Terminal Unit Electronic Interlocking system Integrated Power Supply

system etc

EXTERNAL NON-VITAL RELAY CONTACTS These relays provided in the system where 16 number of the Relay contacts are provided on the rear

panel through Tele control port to extend alarms and to control the power equipment from remote or local

locations through computer in case of any occurrence of failures Each control can sink or source 100 m

amps of current

INTERNAL MODEM CARD DUAL MODEM CARD (IN-BUILT) It is fixed in datalogger Euro rack itself One card contains two modems The top modem is called

ANS (answer) modem and the bottom modem is called as ORG (originate) modem It is used in case of

networking of Dataloggers In network connect lsquoANSrsquo modem to the lsquoORGrsquo modem of one adjacent station

and connect lsquoORGrsquo modem to the lsquoANSrsquo modem of other adjacent station

POWER SUPPLY Normally 24V DC (12V DC is optional) supply with battery backup is required for the system

working

Input Voltage Range 18Vhellip32V DC (For 24V) 9Vhellip18V DC (For 12V)

INPUT REQUIREMENTS Relay inputs (digital inputs) and analog inputs (voltages currents etc) are required to be connected

to the system as per the requirements of RRI PI SSI as the case may be Some of the inputs to be

monitored is given below

(a) Digital inputs

(i) Field inputs All TPRs NWKRs RWKRs ECRs Crank Handle relays SidingSlot LC gate

control relays etc

(ii) Control Panel inputs All button Knob SMrsquos Key relays

18 | P a g e

(iii) Internal relays

British system All HR DR HHR WNR WRR ASR UCR RR LR UYRTLSR TRSR TSR

JSLR JR etc

SIEMENS system Z1UR Z1UR1 GZR ZDUCR ZU(R)R ZU(N)PRG(R)RG(N)R U(R)S

U(N)PS UDKR DUCR U(R)LR UYR1 UYR2 G(R)LRGR1GR2

GR3 GR4 OVZ2U(R)RW(RN)R (RN)WLR Z1NWR Z1RWRZ1WR1 WKR1 WKR2 WKR3 etc

(b) Analog channels

(i) 230 V AC (for power supplies in the power panel)

(ii) 110V AC (for Signal and Track transformers)

(iii) 110V DC (for Point operation)

(iv) 60V DC (Siemens relays)

(v) 24V DC (Q-series relays)

(vi) 24V DC (for Block Axle counters)

(vii) 12V DC (for indication)

(viii) 20A (for point operation current)

(ix) 10V AC 5KHz (for Axle counter channels) etc

SOFTWARE MODULES OF DATALOGGERS

(a) Network Management of Dataloggers (NMDL)

(b) Reports

(c) Fault Entry

(d) Track Offline Simulation

(e) Train Charting

NMDL SOFTWARE FEATURES (a) Online Relay Status

(b) Online Faults - To view information of various Online Faults as they occur in the stations where

the Dataloggers are connected

(c) Online Simulation - Graphical view of relay operations train movements etc

(d) Remote monitoring of stations with the help of NETWORKING

SOFTWARE OBJECTIVES (a) Predictive Maintenance

(b) Easy identification of failures

(c) Crew discipline

(d) Train charting

REMOTE MONITORING OF STATIONS WITH NETWORKING OF

DATALOGGERS The individual Dataloggers of various stations can be interconnected through networking technology

The data of Remote Panel stations can be viewed in a Computer at the Central Monitoring Station The data

of the network is collected by the FEP (Front End Processor) which in turn is transmitted to the computer

COMPONENTS OF NETWORK MANAGEMENT OF DATALOGGERS

(a) Datalogger at stations

(b) MODEM and Transmission medium

19 | P a g e

(c) Front End Processor (FEP)

(d) Central Monitoring Unit (CMU) Computer

FEP (FRONT END PROCESSOR)

FEP acts as a buffer between the Central Monitoring Unit (Computer) and the Network It is provided

at centralised place to retrieve data continuously from station dataloggers and store in memory and transfer to

computer on request It stores 10 Lac telegrams It works on 12V DC It draws 16A continuous current

when all the three modems are connected Normally it shows the number of packets pending to be sent to the

computer on its 7-segment LED display It is provided with MOTOROLA 68000 microprocessor It has 6-

nos of RS-232 communication ports such as COM1 COM2 COM3 COM4 COM5 and COM6 COM1 is

used for Fault Analysis System (FAS) ie Central Monitoring Unit (Computer) connection COM2 to COM6

are used for networking For Bi-directional 2- nos of ports and for Tri-directional (T-network) 3-nos of ports

are used

DATA TRANSMISSION Dataloggers can be networked in Uni-directional Mode or Bi-directional Mode or T ndash Network Mode

In case of loss of data retransmission of data takes place

(a) Uni-Directional Mode

Each Datalogger will send data in only one direction to the FEP Unidirectional mode network is not

preferred

(b) Bi-Directional Mode

Each end of Network is connected to FEP and each datalogger can now transmit data in both the directions

Bi-directional Mode is advantageous it enables the Data Transmission even in case of Network Failure

(c) T - Network Mode

If more no of stations are in network ie if the network is too lengthy then T- network mode is preferred

COMMUNICATION The communication protocol for transmitting data and command between datalogger and CMU is

standardized by the RDSO and is given in the Specifications of Dataloggers

(a) The type of communication used in the network is dependent on the distance between the dataloggers

(b) For shorter distances Opto Converter Box- Opto isolated current loop communication is used

(c) For longer distances Modem (Dial-up leased) Fiber Optic Satellite Microwave communication

MODEMS Modems are used for DATA transfer between Dataloggers and Front End ProcessorThese are

configured to RS 232 Serial Communication Network is connected with two types of 4-wire modems

(a) Internal modem card Dual Modem card (in-built)

It is fixed in datalogger Euro rack itself One card contains two modems The top modem is called

ANS (answer) modem and the bottom modem is called as ORG (originate) modem

Note In case of networking of Dataloggers connect lsquoANSrsquo modem to the lsquoORGrsquo modem of one adjacent

station and connect lsquoORGrsquo modem to the lsquoANSrsquo modem of other adjacent station

(b) External modems

20 | P a g e

These are generally used at FEP (Front End Processor) side to connect the Dataloggers

(i) To transfer Data from one datalogger to another datalogger FEP Baud rate is 9600bps

(ii) These modems are 4-wire line communication

(iii) To transfer the data from FEP to RMU (PC) the Baud rate is 57600 bps

There is no difference between these modems functionally

CENTRAL MONITORING UNIT (CMU) COMPUTER

Central monitoring unit (Fault Analysis Unit) is a Personal Computer and its minimum configuration

shall be specified by RDSO from time to time System Software Windows XPVista(OS) Norton Kaspersky

(Anti Virus) Interbase where Server is not available (DBMS) Oracle where Server is available (DBMS)

software are required to run Datalogger System It is provided with Graphical User interface (GUI) based

software and retrieve data from all Networked dataloggers (up to 32) at various stations It stores data in

standard data base files The CMU is capable of analyzing the data and generate reports audiovisual alarms

on defined conditions This data can be compressed to take backup In central monitoring unit Software used

for analysis of data prediction of faults etc is written in a structured format so that purchaser can

reconfigure it if required It displays the status of signaling gears at any selected time in graphic form for any

selected station yard It retrieves the stored data amp simulates train movement It sends commands to various

Dataloggers to activate audio visual alarm or operate and electromagnetic relay

CMU shares data available in it by other PCs through available local area network where this data can

be used for train charting passenger information purpose The system generates audiovisual alarm in

ASMrsquosSignal Maintainerrsquos room in the case of power supply failure (battery voltage low) or battery charger

defective with acknowledgement facility

(a) Each datalogger has its own identity code which will be transmitted along with data packet to central

monitoring unit

(b) Events recorded at each station are continuously transmitted to central monitoring unit Response time of

data transfer will not exceed 10 sec

21 | P a g e

22 | P a g e

OPTICAL FIBER CABLE

INTRODUCTION The demand for bandwidth on transmission networks is increasing rapidly because video and

graphical rich contents are exchanged through the corporate network or the Internet The Gigabit Ethernet

became ommonly used in the corporate network backbone and 10Gbit Ethernet will be adopted in the near

future Meanwhile in the home the demand for high-speed network becomes popular as the wide spread of

broadband access eg CATV xDSL and FTTH The transmission medium with capability to transmit high

bit rate signal is necessary to satisfy these requirements

The telecommunication transport technologies move from copper based networks to optical fiber

from timeslot based transport to wave length based transport from traditional circuit switching to terabit

router and all optical based networks entering into a new era of optical networking

BASIC PHYSICS OF OFC

OPTICAL FIBER CABLE OFC have Fibers which are long thin strands made with pure glass about the diameter of a human

hair OFC consists of Core Cladding Buffers and Jacket as shown in figure

MONOCHROMATIC LIGHT OR SINGLE COLOR LIGHT Light or visible light is electromagnetic radiation of a wavelength that is visible to the human eye (

about 400 ndash 700 nm) The word light is sometimes used to refer to the entire electromagnetic spectrum Light

is composed of elementary particles called photons Three primary properties of light are

Light can exhibit properties of both waves and particles This property is referred to as wave-particle

duality The study of light known as optics In free space light (of all wavelengths) travels in a straight path

at a constant maximum speed However the speed of light changes when it travels in a medium and this

change is not the same for all media or for all wavelengths By free space it is meant space that is free from

matter (vacuum) andor free from electromagnetic fields

Thus the speed of light in free space is defined by Einsteinrsquos equation E = mc2

Frequency ν speed of light in free space c and wavelength λ are interrelated by ν = cλ

From the energy relationships E = mc2 = hν and the last one an interesting relationship is obtained

the equivalent mass of a photon m = hνc2

When light is in the vicinity of a strong electromagnetic field it interacts with it From this interaction

and other influences its trajectory changes direction as shown in figure

23 | P a g e

INCIDENT RAY REFLECTED RAY AND REFRACTED RAY An incident ray is a ray of light that strikes a surface The angle between this ray and the

perpendicular or normal to the surface is the angle of incidence Reflection is the change in direction of a

wave front at an interface between two different media so that the wave front returns into the medium from

which it originated Common examples include the reflection of light sound and water waves

The reflected ray corresponding to a given incident ray is the ray that represents the light reflected by

the surface The angle between the surface normal and the reflected ray is known as the angle of reflection

The Law of Reflection says that for a specular (non-scattering) surface the angle of reflection always equals

the angle of incidence The refracted ray or transmitted ray corresponding to a given incident ray represents

the light that is transmitted through the surface The angle between this ray and the normal is known as the

angle of refraction and it is given by Snells Law

The figure shows Incident ray Reflected ray Refracted ray the angle of incidence and angle of refraction

REFRACTIVE INDEX - Refractive index is the speed of light in a vacuum ( c =299792458kmsecond) divided by the speed

of light in a material ( v ) Refractive index measures how much a material refracts light Refractive index of

a material abbreviated as lsquo n lsquo is defined as lsquo n=cv lsquo Light travels slower in physical media than it does

when transmitted through the air Refractive index (n) is a function of molecular structure of matter optical

frequency optical intensity determines optical propagation properties of each wavelength ( λ ) may not be

distributed equally in all directions is affected by external temperature pressure and fields

Refractive index of a medium is a measure for how much the speed of light is reduced inside the

medium For example typical glass has a refractive index of 15 which means that light travels at 1 15 =

067 times the speed in air or vacuum Two common properties of glass and other transparent materials are

directly related to their refractive index

First light rays change direction when they cross the interface from air to the material and effect that

is used in lenses and glasses

Second light reflects partially from surfaces that have a refractive index different from that of their

surroundings

SNELLrsquoS LAW-

24 | P a g e

When light passes from one transparent material to another it bends according to Snells law which

is defined as n1sin(θ1) = n2sin(θ2)

where n1 is the refractive index of the medium the light is leaving θ1 is the incident angle between the light

beam and the normal (normal is 90deg to the interface between two materials)

n2 is the refractive index of the material the light is entering

θ2 is the refractive angle between the light ray and the normal

Snellrsquos law gives the relationship between angle of incidence and angle of refraction

For the case of θ1 = 0deg (ie a ray perpendicular to the interface) the solution is θ2 = 0deg regardless of

the values of n1 and n2 That means a ray entering a medium perpendicular to the surface is never bent The

above is also valid for light going from a dense (higher n) to a less dense (lower n) material the symmetry of

Snells law shows that the same ray paths are applicable in opposite direction

TOTAL INTERNAL REFLECTION- When a light ray crosses an interface into a medium with a higher refractive index it bends towards

the normal Conversely light traveling cross an interface from a higher refractive index medium to a lower

refractive index medium will bend away from the normal

This has an interesting implication at some angle known as the critical angle θc light traveling from

a higher refractive index medium to a lower refractive index medium will be refracted at 90deg in other words

refracted alon g the interface If the light hits the interface at any angle larger than this critical angle it will

not pass through to the second medium at all Instead all of it will be reflected back into the first medium a

process known as total internal reflection

The critical angle can be calculated from Snells law putting in an angle of 90deg for the angle of the refracted

ray θ2 This gives θ1

Since θ2 = 90deg

So sin(θ2) = 1

25 | P a g e

Then θc = θ1 = arcsin(n2n1)

For example with light trying to emerge from glass with n1=15 into air (n2 =1) the ritical angle θc is

arcsin(115) or 418deg For any angle of incidence larger than the critical angle Snells law will not be able to

be solved for the angle of refraction because it will show that the refracted angle has a sine larger than 1

which is not possible In that case all the light is totally reflected off the interface obeying the law of

reflection

OPTICAL FIBER MODE An optical fiber guides light waves in distinct patterns called modes Mode describes the distribution

of light energy across the fiber The precise patterns depend on the wavelength of light transmitted and on the

variation in refractive index that shapes the core In essence the variations in refractive index create

boundary

conditions that shape how light waves travel through the fiber like the walls of a tunnel affect how sounds

echo inside

We can take a look at large-core step-index fibers Light rays enter the fiber at a range of angles and

rays at different angles can all stably travel down the length of the fiber as long as they hit the core-cladding

interface at an angle larger than critical angle These rays are different modes Fibers that carry more than

one mode at a specific light wavelength are called multimode fibers Some fibers have very small diameter

core that they can carry only one mode which travels as a straight line at the center of the core These fibers

are single mode fibers This is illustrated in the following picture

OPTICAL FIBER INDEX PROFILE Index profile is the refractive index distribution across the core and the cladding of a fiber Some

optical fiber has a step index profile in which the core has one uniformly distributed index and the cladding

has a lower uniformly distributed index Other optical fiber has a graded index profile in which refractive

index varies gradually as a function of radial distance from the fiber center Graded-index profiles include

power-law index profiles and parabolic index profiles The following figure shows some common types of

index profiles for single mode and multimode fiber

26 | P a g e

OPTICAL FIBERrsquoS NUMERICAL APERTURE ( NA )- Multimode optical fiber will only propagate light that enters the fiber within a certain cone known as

the acceptance cone of the fiber The half-angle of this cone is called the acceptance angle (see figure 18)

θmax For step-index multimode fiber the acceptance angle is determined only by the indices of refraction

Where

n is the refractive index of the medium light is traveling before entering the fiber

nf is the refractive index of the fiber core

nc is the refractive index of the cladding

NUMBER OF MODES IN A FIBER - Modes are sometimes characterized by numbers Single mode fibers carry only the lowest-order

mode assigned the number 0 Multimode fibers also carry higher-order modes The number of modes that

can propagate in a fiber depends on the fiberrsquos numerical aperture (or acceptance angle) as well as on its

core diameter and the wavelength of the light For a step-index multimode fiber the number of such modes

Nm

Where

D is the core diameter

λ is the operating wavelength

NA is the numerical aperture (or acceptance angle)

MODE FIELD DIAMETER - All light do not travels through the core of the fiber but is distributed through both the core and the

cladding The mode field is the distribution of light through the core and cladding of a particular fiber

Mode-Field Diameter (MFD) defines the size of the power distribution When coupling light into or out of a

fiber MFD is important in understanding light loss

27 | P a g e

ADVANTAGE OF OFC COMMUNICATION - bull More information carrying capacity Fibers can handle much higher data rates than copper More

information can be sent in a second

bull Free from Electromagnetic and Electrostatic interference Being insulator no electric current flows through

the fibre and due to this reason fibres neither radiate nor pick up electro - magnetic radiation So WPC

CLEARANCE is not required

bull Low attenuation 025 dbkm at 1550 nm Loss in twisted pair and coaxial cable increases with frequency

where as loss in the optical fibre cable remains flat over a wide range of frequencies

bull Use of WDM ndash Switching routing at Optical signal level

bull Self healing rings under NMS control

bull Small size makes fibre cable lighter in weight So easy to handleOptic fibre cable weight (approx)

500 kg km Copper cable weight (approx) 1000 kgkm

The reasons are photons of light in a fibre

do not affect each other as they have no electrical charge and they are not affected by stray photons outside

the fibre But in case of copper electrons move through the cable and these are affected by each other

Optical fibre does not carry any electricity even if the cable is damaged or short circuited it does

not cause any spark or fire hazard

As the fibre do not radiate energy it can not be detected by any nearby antenna or any

other detector The fibres are difficult to tap and therefore excellent for security

As the signal transmission is by digital modulation there is no chance of cross talk in

between channels

Only by adding a few additional terminal and repeater equipments the

capacity of the system can be increased at any time once the cable is laid

ical effects and temperature variations

LIMITATIONS OF OFC -

difficult

- utilised

APPLICATION IN SIGNAL AND TELECOMMUNICATIONS transmission circuits

-haul circuits for linking of telephone exchanges

28 | P a g e

PROPAGATION MODES CONCEPT -

MODE - Mode is an available distribution of electromagnetic field in a plane transverse to the direction of

light propagation Each mode is characterized by frequency polarization electric field strength and

magnetic field strength Available patterns are derived from Maxwellrsquos equations and boundary conditions

LINEARLY POLARIZED (LP) MODE A mode for which the field components in the direction of propagation are small compared to

components perpendicular to that direction An optical fibre supports only different field patterns called as

lsquoLinear Polarizedrsquo or lsquo LPrsquo modes The reasons are

requirements

de

the accrual of power carried by different modes

There are two basic types of fiber Multimode fiber and Single-mode fiber

Multimode fiber is best designed for short transmission distances This is suited for used in LAN systems and

video surveillance Single mode fibre is best designed for longer transmission distances This is suitable for

long distance telephony and multi channel television broadcast systems

29 | P a g e

MULTI MODE FIBER Multimode fiber the first to be manufactured and commercialized simply refers to the fact that

numerous modes or light rays are carried simultaneously through the waveguide Modes result from the fact

that light will only propagate in the fiber core at discrete angles within the cone of acceptance MM fiber type

has a much larger core diameter compared to single-mode fiber allowing for the larger number of modes

and

is easier to couple than single-mode optical fiber Multimode fiber further categorized as Multimode step-

index and Multimode graded index fiber

PROPAGATION THROUGH MMSI FIBER Figure shows the principle of total internal reflection applies to multimode step index fiber Because

the corersquos index of refraction is higher than the claddingrsquos index of refraction the light that enters at less than

the critical angle is guided along the fiber

Three different light waves travel down the fiber One mode travels straight down the center of the

core A second mode travels at a steep angle and bounces back and forth by total internal reflection The third

mode exceeds the critical angle and refracts into the cladding Naturally it can be seen that the second mode

travels a longer distance than the first mode causing the two modes to arrive at separate times

PROBLEMS WITH MMSI FIBER AND SOLUTION This disparity between arrival times of the different light rays is known as dispersion and the result is

a muddied signal at the receiving end It is important to note that high dispersion is an unavoidable

characteristic of multimode step-index fiber The solutions are either use Graded index fiber or Single mode

fiber

PROPAGATION THROUGH MMGI FIBER Multimode Graded-index refers to the fact that the refractive index of the core gradually decreases

farther from the center of the core The increased refraction in the center of the core slows the speed of some

light rays allowing all the light rays to reach the receiving end at approximately the same time reducing

dispersion Figure shows the Light propagation principle through multimode graded-index fiber The corersquos

central refractive index ( nA ) is greater than that of the outer corersquos refractive index ( nB )

It is very clear from the figure the light rays no longer follow straight lines they follow a serpentine path

being gradually bent back toward the center by the continuously declining refractive index This reduces the

arrival time disparity because all modes arrive at about the same time The modes traveling in a straight line

30 | P a g e

are in a higher refractive index so they travel slower than the serpentine modes These travel farther but

move faster in the lower refractive index of the outer core region

PROPAGATION THROUGH SMSI FIBER Single mode fiber has a much smaller core that allows only one mode of light at a time to propagate

through the core The figure shows the single mode fiber

Single-mode fiber exhibits no dispersion caused by multiple modes Single-mode fiber also offers lower fiber

attenuation than multimode fiber Thus more information can be transmitted per unit of time because it can

retain the fidelity of each light pulse over longer distances Like multimode fiber early single-mode fiber was

generally characterized as step-index fiber meaning the refractive index of the fiber core is a step above that

of the cladding rather than graduated as it is in graded-index fiber Modern single-mode fibers have evolved

into more complex designs such as matched clad depressed clad and other exotic structures

SINGLE-MODE FIBER DISADVANTAGES The smaller core diameter makes coupling light into the core more difficult The tolerances for single-

mode connectors and splices are also much more demanding

CUTOFF WAVE LENGTH - Cutoff wavelength is the wavelength above which a single-mode fiber supports and propagates only

one mode of light In other words an optical fiber that is single-mode at a particular wavelength may have

two or more modes at wavelengths lower than the cutoff wavelength The effective cutoff wavelength of a

fiber is dependent on the length of fiber and its deployment The longer the fiber the lower is the effective

cutoff

wavelength The smaller the bend radius of a loop of the fiber the lower is the effective cutoff wavelength If

a fiber is bent in a loop the effective cutoff wavelength is lowered

SIGNAL ATTENUATION IN FIBER - Optical fiber has a number of advantages over copper However it also suffers from degradation

problems which can not be ignored The first of these is loss or attenuation Attenuation is typically the result

of two sub properties They are scattering and absorption Both of which have cumulative effects The second

is

dispersion which is the spreading of the transmitted signal and is analogous to noise

SCATTERING Scattering occurs because of impurities or irregularities in the physical construction of the fiber The

well known form of scattering is Rayleigh Scattering It is caused by metal ions in the silica matrix and

results in light rays being scattered in various directions

31 | P a g e

Scattering limits the use of wavelengths below 800nm The short wavelengths are much affected than longer

wavelengths It is because of Rayleigh scattering that the sky appears to be blue ( shorter wave length ) The

shorter wavelengths ( blue ) of light are scattered more than the longer wavelengths of light

ABSORPTION Absorption results from three factors They are hydroxyl ions ( OH- water ) in the silica impurities

in the silica and incomplete residue from the manufacturing process These impurities tend to absorb the

energy of the transmitted signal and convert it to heat resulting in an overall weakening of the signal The

Hydroxyl absorption occurs at 125 and 139 micro The silica itself starts to absorb energy at 17 micro

because of the natural resonance of the silicon dioxide

MACRO BENDING LOSS Macro-bending loss is caused by bending of the entire fiber axis The bending radius shall not be

sharper than 30d where d is diameter of cable A single bend sharper than 30d can cause loss of 05dB

The fiber may break if bending is ever sharper

MICRO BENDING LOSS Micro-bending loss is caused by micro deformations of fiber axis which leads to failures in achieving

total internal reflection conditions Micro-bends are small scale perturbations along the fiber axis the

amplitude of which are on the order of microns These distortions can cause light to leak out of a fiber

Micro-bending may be induced at very cold temperatures because the glass has a different coefficient of

thermal expansion from the coating and cabling materials At low temperatures the coating and cable

become more rigid and may contract more than the glass Consequently enough load may be exerted on the

glass to cause micro bends

Coating material is selected by manufacturers to minimize loss due to micro-bending The linear thermal

expansion coefficient of coating material shall be compatible with that of fiber

32 | P a g e

DISPERSION Dispersion is the optical term for the spreading of the transmits in the fiber It is the bandwidth

limiting phenomenon and comes in two forms Multimode dispersion and chromatic dispersion Chromatic

dispersion is further subdivided into material dispersion and waveguide dispersion

DISPERSION PHENOMENON IN OPTICAL FIBER Dispersion is the time distortion of an optical signal that results from the differences of time of travel

for different components of that signal typically resulting in pulse broadening As the distance traveled by

the signal is more broadening of pulse is more In digital transmission dispersion limits on the maximum

data rate and the maximum distance ie the information-carrying capacity of a fiber link The interference

from broadened pulse in the next interval shall not lead to erroneous interpretation of received signal

OPTICAL DOMAIN Understanding where attenuation and dispersion problems occur helps optical design engineers

determine the better wavelengths at which information can be transmit taking into account distance type of

fiber and the other factors which can severely affect the integrity of the transmitted signal The graph shown

depicts the optical transmission domain as well as the areas where problems arise The wavelength (nm)

is shown on X-axis and attenuation ( dBkm) is shown on Y-axis

There are four transmission windows appear in the figure The first one is at around 850 nm the

second at 1310nm third at 1550 nm and fourth at 1625 nm The last two labeled as C and L band

respectively The 850 nm wavelength at which the original LED technology operated The second window at

1310 nm has low dispersion The 1550 nm called as C-band is ideal wavelength for long haul

communication systems The network engineers can avoid transmitting signal at 1000 nm where Rayleigh

scattering 1240 and 1390 nm where hydroxyl absorption by water occurs to avoid high degree of loss

Optical fibers also can be manufactured to have low dispersion wavelength in the 1550nm region

which is also the point where silica-based fibers have inherently minimal attenuation These fibers are

referred to as dispersion-shifted fibers and are used in long-distance applications with high bit rates For

33 | P a g e

applications utilizing multiple wavelengths it is undesirable to have the zero dispersion point within the

operating

wavelength range

34 | P a g e

SIGNALLING RELAYS

INTRODUCTION A relay is an electromagnetic device which is used to convey information from one circuit to another

circuit through a set of contact ie front or back contact Constructional and electrically relays may be

divided into DC and AC relays because the means by which the electrical energy in the coil is converted in

to mechanical Energy in order to move the contacts are fundamentally different In DC type the contacts are

carried on an armature forming part of a magnetic circuit in which a field is set up by the current flowing in

the coils In AC types the contacts are attached by a link mechanism to a metal sector disc or cylinder in

which currents are induced by the alternating magnetic field produced by the currents in the coils

Every endeavor has been made to explain the action of each type of relay in the simplest possible manner

Relays are sophisticated switch gears used for remote control and succession control of various

electrical equipment In present days they are widely used because they are capable of protecting the

controlled equipment from cross feeding and overloading even as they cater for speedy operations

Most of the relays in present day signaling are electromagnetic devices although some of the relays control

circuits through electronic components like diodetransistors Integrated Chips etc

Railway signaling relays are unique in that

(a) They operate on low voltage and current

(b) They are more articulate as according to their special features they can work under restrictive conditions

and in any specified manner Virtually they can cater for all situations while contributing to speed and

accuracy in operations

CLASSIFICATION OF SIGNALLING RELAYS (a) According to the method of their mounting or fixture they are classified as

(i) Shelf type Relays which are loosely kept on shelves

(ii) Plug in type Relays which are plugged into a pre- wired plug boards

(b) According to their connection and usage they are classified as

(i) Track relays Relay which is directly connected to the track to detect the presence of vehicle

(ii) Line Relays Other than track relay all are line relays Relays connected to the selection circuit

(c) According to their vitality or importance in ensuring train working safety they are classified as

(i) Vital Relays All relays used for traffic control such as signal point controls track detection etc

(ii) Non-vital Relays Relays which operate control aids and accessories like warnings buzzers

Indications etc

(d) According to their special provisions to ensure reliability of their contacts they are classified as

(i) Proved type are those whose normalization after each operation shall be proved in circuit

controlled by their contacts Contacts in which both the springs have metal surfaces on their tips They may

get fused due to high sparking current across them during operation These may prevent relay normalization

and causes unsafe condition in traffic control To avoid this proving of relay normalization after each

operation is necessary

(ii) Non - proved type Need not to be proved to have been normalized after each operation as their

contacts have at least one non-fusible contact (carbon contact)

(e) According to their feed source relays are broadly classified as

(i) DC relays The relay which requires DC power supply for its operations are called DC relays Among

the DC relays

o DC neutral relays This relay closes the same set of contacts on energization with Normal polarity

or Reverse polarity supply

o Polar Relays This relay closes different set of contacts when energized with Reverse polarity

supply They may or may not have contact to close when deenergized

35 | P a g e

(ii) AC Relay AC Induction motor track relays Time element relays flashing indication control etc

(iii) Electronic Relays DC relays with electronic components in them are called electronic relays

DC NEUTRAL RELAY Each Relay has usually one or two coils with a hollow center to accommodate a coreThe coils are

made up of a large numbers of turns of small gauge soft drawn copper wire The two coils can be connected

in series or parallel according to the requirement of relay resistance The ends of the coils are terminated on

binding post to which the control wires are connected Each coil is placed around a core of specially selected

Iron or steel having high permeability and low retentivity The core should be susceptible to magnetism and

at the same time should have little residual magnetism The cores are connected at the top by a yoke to

complete the magnetism coupling between two ends of coils The bottom of each core is equipped with a

large steel or Iron block known as pole piece or face

A flat piece of Iron or steel called armature is supported by brackets which are securely fastened to

the pole piece The armature yoke and the pole pieces are also made of specially selected iron or steel of the

same quality as the core The armature carries the metallic spring contacts which are insulated from it

The circuit through the coils of the relay is closed It sets up a magnetic flux through the core yoke and the

armature The flux passing between the armature and pole faces causes the armatures get attracted to the pole

faces and armature picks up and closes front contacts When the circuit is opened the magnetic flux collapses

and the armature drops away by gravity from the pole faces the front contacts break and back contacts close

The front and back contacts of the relay can be utilised to make or break other circuits Two stop pins of

nonmagnetic material are fixed either on the armature or pole faces so that the armature cannot

come in contact with the pole faces It is essential to maintain a small air-gap between the armature and pole

faces so that low value of residual magnetism may not retain the armature in picked up position and causes

the relay to fail to drop away with a break in its control circuit

GENERAL USAGE

DC Neutral line relays are most commonly used for Railway Signalling controls and detection

Among them plug-in type relays are preferred in larger installations for space considerations Shelf type

relays are also in use mostly in wayside stations

There are many DC Neutral line relays in use with special features such as

(i) Delayed operation

(ii) Biased DC control

(iii) DC control unaffected by AC interference currents

(iv) Getting latched in operated condition till further feeding and others

Usage of DC polar relays is mostly in conjunction with block instruments that control traffic between

stations AC line relays are almost extinct in installations of British Signalling practice They are however

used for time control operations flashing indication control and such other special purposes in installations

with Siemens signalling practice widely Track relays are used according to the type of track detection

circuits chosen for a given location and context While most of the track circuits are still of the DC working

type requiring DC neutral track relays with them the prospects of their being replaced with Electronic track

circuits directly feeding DC line relays in future are great AC Track Circuits are used in DC Traction area

as conventional DC Track Circuits are not suitable there AC Track relays are used with them almost all of

the induction motor type In the British practice of signalling which was first introduced on Indian Railways

non-proved type relays with carbon to metal switching contacts are generally used for vital controls

They facilitate simple circuit designs But with the advent of German Practice introduced by Ms

Siemens later proved type relays with all metal to metal contacts are widely accepted in spite of

complications in circuit design caused by them A recent introduction is that of the same type relays made by

Ms Integra control However for some time now the appreciable features of both the practices are getting

36 | P a g e

incorporated together in the indigenous designs of signalling by railwaymen With this the usage of all types

of relays anywhere can be found without straight jacketed segration of relay types

CHARACTERSTIC OF ELECTRO-MAGNETIC RELAY The following are the characteristic of electro-magnetic relays A brief study of them helps in

understanding the choice of their components and designs features

1) Force of attraction

2) Effect of air gap

3) Effect of Hysterisis

4) Transient condition

FORCE OF ATTRACTION In any electro-magnetic system the force of attraction is given by

Where B - is the flux density a - is the cross sectional area of the particular part of the magnetic

circuit

In the case of a DC neutral Relay B is proportional to the current that is flowing in the coil

surrounding the electro-magnet and thus the force of the attraction is directly proportional to the square of the

current This square relationship has its own advantage especially in the case of DC track relay in that a

small reduction in the current will have a great effect on the working of the relay Also for a given change of

current the make and the break will be quicker with lesser possibility of arcing

EFFECT OF AIR GAP

Curve lsquoArsquo is magnetisation curve for the iron and is all practical purpose a straight line up to the

saturation point Curve lsquoBrsquo is the magnetisation curve for the open-air gap which is a straight line through

out because per magnetisation curve of the whole

magnetic circuit of the relay and for a given force is the sum of the amp-turns for the iron part and the amp-

turns for the air gap

When the front contacts are open the force required to pick up the armature is shown on curve lsquoCrsquo to be F1

but after the armature has operated it will be separated from the core by stop pins In this position the amp-

turns required to maintain the armature is less as indicated by the dotted line from 1 on curve C to 2 on curve

37 | P a g e

F But actually the current in the coil is unaltered the force on the armature is greater than required as

indicated at 3 on curve F Part of this extra force is used to flex the front contacts sufficiently to give good

contact pressure when it is in energised position

The difference between the pick-up and the drop-away current should be as small as practicable in

track relay to ensure good shunting characteristics This is achieved firstly by the choice of good quality relay

iron and secondly by having a small air gap between armature and core If the air gap is not available then

the residual magnetism fluxes might cause the armature to be retained when the supply is disconnected For

this reason residual pins are provided to ensure a definite minimum air gap in the energised position

EFFECT OF HYSTERISIS

Hysterisis is the property by which the flux produced lags behind the current In the de-energized

condition there will be small residual flux in the core When the voltage is applied to the coils the current in

rising to its steady value first causes the flux to rise from 1 to 2 along the curve At this point the flux density

will be sufficient to attract the armature and reduce the air gap the flux then raise to 3 and continue to 4

which corresponds to the steady current in the coils When the voltage is disconnected the current in falling

caused the flux to fall from 4 to 5 along the curve At this point the flux density will fall below the value

required to maintain the armature which will release thus increasing the air gap and reducing the flux to 6

Finally the

flux will decrease from 6 to 1 where the current will again be zero

The relay core is made of material having high permeability and low retentivity As mentioned in

the IRS specification Electromagnet iron may be in the form of a

(a) Bar of silicon steel

(b) Best Yorkshire wrought iron

(c) Swedish charcoal iron

(d) Electrical steel sheets

` This reduces the difference between pick up value and Drop away value By selecting good quality

core material Percentage release and sensitivity of the relay will be improved

TRANSIENT CONDITION

38 | P a g e

When the voltage is applied or disconnected from the coils it takes some little time before the current

become steady These are known as transient conditionsrdquo and are important so far as track relays are

concerned When the voltage is first applied to the coils the magnetic flux in rising cuts the turns on the

coils and in so doing produces a back EMF that opposes the applied voltage and retards the growth of

current

The growth and decay of flux are decided by the relationship between the inductance and resistance

in the circuit is known as time constant It is not fixed quantity in the case of DC neutral relay This value of lsquo

Lrsquo is less when the relay is in de-energised condition (L1) than when the relay is in energised condition (L2)

The magnitude of flux that is established for a given change of current is different in two cases

When the current reaches the pick up value the armature closes and the inductance is increased to L2

due to reduced air gap the flux per amp is increased The increase in flux increased the back EMF during the

movement of the armature after which the current continuous to raise along a new curve corresponding to the

increased inductance until it reaches the final value (ER) This process is indicated above in fig24

When the supply is disconnected the current is obliviously reduced to zero immediately but the flux

decay comparatively slowly owing to the eddy currents produced in the core by the rapid flux change which

tend to maintain the flux The drop away time on a disconnection is however generally negligible See fig

below

If the relay releases due to the reduction in current from say I 2 to I 1 caused by the application of

shunt resistance (as in the case of track relay ) the time taken is much longer than the relay is simply

disconnected The rate of rise or fall of current during the transient conditions is also depends on exterior

circuit values because L and R apply to the whole circuit The production of eddy current in the core the flux

will decay at a slower rate than the current So that the actual release time will be a little longer than it takes

the current to fall to the release

L= Inductance

39 | P a g e

R= Resistance

It is now clear that to reduce releasing time to a minimum it is necessary that

- The relay iron should have low Hysterisis loss and low retentivity

- The degree of over energization of the relay should be restricted

- Connecting a suitable external resistance in series with the relay to keep LR ratio low

In non RE area for track circuit length less than 100M 9 ohm track relay only to be used Using relay

with minimum contacts as they require lesser current which keeps inductance value low

Train working safety is ensured only if the track relay of shortest length track circuit is released

before a light engine running at a highest permitted speed clears it Otherwise the track circuit occupation

may go undetected To avoid this a special provision has to be made in signal control circuits wherever

necessary

The following methods may be adopted for reducing the time lag of track relay

(a) Restrict the over energisation of relay since the release time depends on the initial working current

(b) Connecting a suitable external resistance in series with the relay to keep the LR ratio low

(c) Using relays with minimum contacts as they require lesser operating current keeping the inductance

value low

40 | P a g e

CONCLUSION

Modern signalling is vital for safe and punctual movements of trains In the Indian railways The Signalling

and Telecommunication Department is responsible for providing modern effective and relaible signalling

systems as well as telecommunication systems

The first mode of communication used in Indian Railways was the use of electric telegraph

with the help of Morose code Morose code is the method of providing text information as a series of on-off

tones and lights or clicks that can be directly understood by a skilled listener or observer without special

equipmentEach character (letter or numeral ) is represented by a unique sequence of dots and dashes Later

this system becomes obselete and beggan the era of wireless communication which operated at audio level

frequency range

In wireless communication the significant advances took place the transition to miniature

valves or filament tubesBut this was abandoned too because of excessive current consumption and over

heating of the filament tubes

Fibre-optic communication is a method of transmitting information from one place to another by

sending pulses of light through an optcial fibreThe light forms an electromagnetic carrier wave that is

modulated to carry information First developed in the 1970s fibre optic communication systems has

revolutionized the telecommunications industry and have palyed a major role in the advent of the information

age Because of its advantages over electrical transmissionsoptical fibres have largely replaced copper wire

communications in core networks in the developed world The Indian Railways too is undergoing a transition

from Microwave communication to fibre optic communications

41 | P a g e

BIBLIOGRAPHY AND REFERENCES

1 wwwwikipediacom

2 wwwbritaniccacom

3 wwwirfcacom

4 Motorola GP60 system manual

5 Harris FAS 7000 manual

6 TOSHIBA Manual

13 | P a g e

ndash LED flashes when the section is clear

ndash LED flashes when the section is clear

All the above LEDrsquos are lit for section clear condition

(F) DC-DC CONVERTER CARD (CARD 8)

INPUT VOLTAGE Nominal Voltage voltage 24V DC Maximum current drain= 12A

Required voltage 18V DC to 30V DC

Output voltage

Nominal Voltage +5 V DC 2 A Required voltage 4 7 5 t o 525V DC

Nominal Voltage +12V DC 200 mA Required voltage 1175 to 1225V DC

Nominal Voltage +24V DC 300 mA with common ground Required voltage 235 to 245V DC

Nominal Voltage +15V DC 100 mA with isolated ground Required voltage 145 to 155V DC

SURGE VOLTAGE AND LIGHTNING PROTECTION Transient surge voltages arise as a result of Lightning discharge switching operations in electrical

systems and electrostatic discharge These surge voltages often destroy the electronic equipment to a large

extent In order to prevent surge voltages from destroying the equipment all the input lines of SSDAC ie

Power Supply (24V) Reset (48V) amp Modem is to be routed through surge voltage protection devices for

effectively protecting the system These devices (3 numbers) are mounted in a box and supplied along with

the system One number of box is to be installed at each location and wired to the SSDAC

Each surge voltage protection device consists of two parts

(a) Base

(b) Plug Trab

The Base of the device is used for wiring the input and output signals The connection details from relay

room to the box and from box to SSDAC unit are provided on the box The Plug Trab consists of MOV and

GD Tube and diverts the excess energy during surge voltages or lightning into the ground connection The

operation of these devices relies on a high quality ground connection in order to safely shunt away the

unwanted energy The impedance of the ground connection is critical and it should be less than 2 Ohms

NOTE The 3 Plug Trab connections are not to be interchanged with one another The plug Trab is a

detachable device and can be replaced with SPARE unit in case of blown device which is indicated by

means of LED for 24 V

EFFECTIVENESS OF PLUG TRABS The effectiveness of plug Trab depends wholly on the Earth connection provided to the system The earth

provided to the system should be less than 1 ohms and connections should be firm and proper to the SSDAC

unit VR box etc

SURGE VOLTAGE AND PROTECTION DEVICE SV-120 The Surge Voltage protection device is to be installed at each location along with every SSDAC unit

14 | P a g e

EARTHING- The lead wires connecting the installation and the earth electrode shall ordinarily be of stranded

copper wire of 29 sq mm (19 strand wires of 14 mm diameter) Copper wire has been specified because GI

wires usually are having greater corrosion However in areas where copper wire may be frequently stolen

due to theft ACSR of size 64 sq mm (19 strands of 211 mm diameter) may be used

LIMITS OF EARTH RESISTANCE (a) Apparatus case connected to Earth (SSDAC and vital Relay Box is housed in Apparatus case and

Connected to earth at outdoor) shall be less than or equal to 1 ohm

(b) All cable connected to same earth shall be less than or equal to 1 ohm

(C) Reset box connected to earth near SM s Room shall be less than or equal to 1ohm

EQUIPMENT TO BE EARTHED A Common Earth should be provided for SSDAC for items 1(a) amp (b) of the above at the outdoor

(a) The Apparatus Case is to be connected to earth (the chassis of SSDAC amp Vital Relay Box should be

properly connected to apparatus case)

(b) Metallic sheath and armouring of all the underground main cables are to be earthed

(i) In RE area the metallic sheath and armouring of main telecom cables are earthed at both ends

(ii) In RE area the armouring of Jelly filled cable shall be earthed at both ends

(c) The Earthing shall be provided at every location box where cables are terminated

(d) Earth already available for other equipment may be used for earthing of Reset Box near SM s Room

Cabin etc

15 | P a g e

DATALOGGER

INTRODUCTION Datalogger is a Microprocessor based system which helps in analysing the failures of relay inter

locking system Electronic Interlocking system This is like a black box which stores all the information

regarding the changes take place in relays AC DC Voltages and DC currents along with date and time The

same information data can be transferred to the computer to analyse further ldquoon line ldquooff linerdquo analysis of

stored date A print out also can be obtained through a printer by connecting directly to the datalogger unit

The data belongs to Relay contacts is considered as digital inputs and the data belongs to voltage

levels currents is considered as Analog inputs Datalogger lsquos are mandatory for all new relay interlocking

(PIRRI) EI installations and it is also recommended to provide in all existing PIs RRIs To increase the

line capacity mechanical signalling equipments are upgraded to PI RRI or EI Due to complexity in the

circuits and wiring sometimes it is very difficult to rectify the failures So datalogger can monitor these

systems with real time clock Thus it can be named as black box of Samp T equipments and hence it is a vital

tool for accident investigation Datalogger is used at Stations yards Whereas in case of Auto Section amp IBH

Mini dataloggers called as Remote Terminal Unit (RTU) are used

ADVANTAGES OF DATALOGGERS (a) Dataloggers helps in monitoring the typical failures such as intermittent auto right failures

(b) It helps in analyzing the cause of the accidents

(c) It helps in detecting the human failures errors such as

(i) Drivers passing signal at Danger

(ii) Operational mistakes done by panel operators ASMrsquos of operating department

(iii) Signal and telecom engineering interferences in safety circuits

(iv) Engineering and electrical department interferences failures

(v) It helps as a ldquoTOOLrdquo in preventive maintenance of signaling gears

(d) Dataloggers can be connected in network Networked dataloggers helps to monitorthe PIRRIEI remotely

(e) Failure reports can be generated remotely with help of datalogger network

(f) On line and Off line track simulation is possible

(g) Speed of the train on point zones can be calculated

(h) Age of the equipment in terms of number of operations etc

COMMON EQUIPMENT FOR ALL DATALOGGERS ARE GIVEN

BELOW (a) CPU card

(b) Digital and Analog input cards

(c) Local terminal(PC)

(d) communication links

(e) Printer

All the dataloggers requires a potential free ( spare ) relay contact for monitoring digital inputs

through Digital input cards amp for monitoring Analog inputs such ACDC bus bar voltage levels through

Analog input cards Digital and Analog inputs are connected to the Processor card Processor card consists of

memory ICrsquos Memory ICrsquos are programmed as per requirement of the signal engineers

Provision of Dataloggers is mandatory with RRI systems and is optional for PI systems as per

amendment to the specification for Relay Interlocking systems ( IRSS-36 ) The data collected by the

datalogger can be used for failure analysis repetitive discrepancies and for accident investigations

16 | P a g e

Note

If the serial communications is more than 50m then line drivers shall be used up to 3 Kms

4wire leased line Modems shall be used if the serial communication is more than 3 Kms

STUDY OF EFFTRONICS DATALOGGER TECHNICAL DETAILS (a) 24V 12VDC Power Supply

(b) Total Storage Capacity of 10 Lakh events

(c) In-built Temperature sensors

(d) Internal Buzzer for alarming during failures

(e) Real Time clock with internal battery backup with data retention up to 10 years

(f) 512 LED matrix to indicate the status of 512 Digital inputs at a time page wise

(g) Seven segment LCD screen (2x24) to display the status of digitalanalog signalsTime Temperature etc

(h) Using the keyboard various functions can be viewed in the LCD panel

(i) Max Digital Inputs 4096

(j) Max Analog Inputs 96

(k) Digital Input Scanning Time 16 millisecond

(l) Analog Input Scanning Time is less than 1 Sec

HARDWARE (EQUIPMENT) Datalogger system consists of

(a) Datalogger (CPU - with Microprocessor 68000)

(b) Digital input cards

(c) Dual modem card

(d) Digital Scanner units (DSU)

(e) Analog Scanner units (ASU)

CPU CARD It is provided with Motorola microprocessor M 68000 It performs all the activities pertaining to the

datalogger It continuously scans (check) the Digital inputs(inbuilt) Digital Scanner Units and Analog

Scanner Units ie scanning of digital signals (Relay operations) for every 16-milli seconds and scanning of

analog signals (ie ACDC voltages amp DC currents) for less than 1 second

This card will support the IO interfaces of LCD (Liquid Crystal Display) - 2X24 alphanumeric Key

Board LED Matrix Display Real Time Clock LCD display and keyboard This will acts as man machine

interface between the datalogger and the signal engineer All the operations (Software) can be performed

using this LCD and keyboard

Real time display with 7 Segments This is built in real time clock within Datalogger and its current

time will be displayed on six 7-segment display provided (Real time clock depend upon DALLAS 1286

chip) This IC will come with internal battery backup hence there is no need to add external batteries

CPU card continuously scans (checks) the DSUs and ASUs Each input connected to digital scanner

units are optically isolated by Opto couplers When CPU card scans the digital inputs it compares with the

previous stored data and if there is any change from the previous status then only that data will be stored (the

status conditions of relay) with date and real time A total of minimum 10 Lac events can be stored in

memory on first in first out basis so that latest data is available in the system There is no loss of data from

datalogger memory in case of power supply failure of datalogger

DIGITAL INPUT CARDS (IN-BUILT) This system is having maximum 8nos of inbuilt Digital inputs cards Maximum 64nos of digital

inputs can be connected to each digital input card The potential free relay contact may be front or back

contact terminated at the Tag Block from the relay of signals tracks points Buttons etc and are

17 | P a g e

subsequently connected to Digital input cards through Flat Ribbon Cable (FRC) connectors These in-built

digital input cards can monitor a total 512 nos of relays status

DIGITAL SCANNER UNIT (DSU) Each DSU contains 8 nos of Digital Input cards Each input card can be connected with 64 inputs

Total input capacity of DSU unit is 512 inputs These scanner cards contain Optocouplers and Multiplexer

Inputs are connected to Stag card The stag card out put is connected to DSU through FRC connectors

Maximum 7 nos of DSUs can be connected to the system So Digital input capacity of the system is 4096

All these digital inputs are scanned at rate of 16 msec

ANALOG SCANNER UNIT (ASU) ASU contains maximum 3 nos of Analog input cards Each input card can be connected with 8nos of

Analog inputs Total input capacity of the ASU is 24 analog input channels Maximum 4nos of ASUs can be

connected to the system Analog input channel capacity of the system is 96 All these analog inputs are

scanned at a rate of less than 1 sec

PARALLEL PORT Parallel port is provided for connecting printer

RS-232 SERIAL PORTS At least 6 Serial communication ports are provided for communication with other dataloggers

Central Monitoring Unit Remote Terminal Unit Electronic Interlocking system Integrated Power Supply

system etc

EXTERNAL NON-VITAL RELAY CONTACTS These relays provided in the system where 16 number of the Relay contacts are provided on the rear

panel through Tele control port to extend alarms and to control the power equipment from remote or local

locations through computer in case of any occurrence of failures Each control can sink or source 100 m

amps of current

INTERNAL MODEM CARD DUAL MODEM CARD (IN-BUILT) It is fixed in datalogger Euro rack itself One card contains two modems The top modem is called

ANS (answer) modem and the bottom modem is called as ORG (originate) modem It is used in case of

networking of Dataloggers In network connect lsquoANSrsquo modem to the lsquoORGrsquo modem of one adjacent station

and connect lsquoORGrsquo modem to the lsquoANSrsquo modem of other adjacent station

POWER SUPPLY Normally 24V DC (12V DC is optional) supply with battery backup is required for the system

working

Input Voltage Range 18Vhellip32V DC (For 24V) 9Vhellip18V DC (For 12V)

INPUT REQUIREMENTS Relay inputs (digital inputs) and analog inputs (voltages currents etc) are required to be connected

to the system as per the requirements of RRI PI SSI as the case may be Some of the inputs to be

monitored is given below

(a) Digital inputs

(i) Field inputs All TPRs NWKRs RWKRs ECRs Crank Handle relays SidingSlot LC gate

control relays etc

(ii) Control Panel inputs All button Knob SMrsquos Key relays

18 | P a g e

(iii) Internal relays

British system All HR DR HHR WNR WRR ASR UCR RR LR UYRTLSR TRSR TSR

JSLR JR etc

SIEMENS system Z1UR Z1UR1 GZR ZDUCR ZU(R)R ZU(N)PRG(R)RG(N)R U(R)S

U(N)PS UDKR DUCR U(R)LR UYR1 UYR2 G(R)LRGR1GR2

GR3 GR4 OVZ2U(R)RW(RN)R (RN)WLR Z1NWR Z1RWRZ1WR1 WKR1 WKR2 WKR3 etc

(b) Analog channels

(i) 230 V AC (for power supplies in the power panel)

(ii) 110V AC (for Signal and Track transformers)

(iii) 110V DC (for Point operation)

(iv) 60V DC (Siemens relays)

(v) 24V DC (Q-series relays)

(vi) 24V DC (for Block Axle counters)

(vii) 12V DC (for indication)

(viii) 20A (for point operation current)

(ix) 10V AC 5KHz (for Axle counter channels) etc

SOFTWARE MODULES OF DATALOGGERS

(a) Network Management of Dataloggers (NMDL)

(b) Reports

(c) Fault Entry

(d) Track Offline Simulation

(e) Train Charting

NMDL SOFTWARE FEATURES (a) Online Relay Status

(b) Online Faults - To view information of various Online Faults as they occur in the stations where

the Dataloggers are connected

(c) Online Simulation - Graphical view of relay operations train movements etc

(d) Remote monitoring of stations with the help of NETWORKING

SOFTWARE OBJECTIVES (a) Predictive Maintenance

(b) Easy identification of failures

(c) Crew discipline

(d) Train charting

REMOTE MONITORING OF STATIONS WITH NETWORKING OF

DATALOGGERS The individual Dataloggers of various stations can be interconnected through networking technology

The data of Remote Panel stations can be viewed in a Computer at the Central Monitoring Station The data

of the network is collected by the FEP (Front End Processor) which in turn is transmitted to the computer

COMPONENTS OF NETWORK MANAGEMENT OF DATALOGGERS

(a) Datalogger at stations

(b) MODEM and Transmission medium

19 | P a g e

(c) Front End Processor (FEP)

(d) Central Monitoring Unit (CMU) Computer

FEP (FRONT END PROCESSOR)

FEP acts as a buffer between the Central Monitoring Unit (Computer) and the Network It is provided

at centralised place to retrieve data continuously from station dataloggers and store in memory and transfer to

computer on request It stores 10 Lac telegrams It works on 12V DC It draws 16A continuous current

when all the three modems are connected Normally it shows the number of packets pending to be sent to the

computer on its 7-segment LED display It is provided with MOTOROLA 68000 microprocessor It has 6-

nos of RS-232 communication ports such as COM1 COM2 COM3 COM4 COM5 and COM6 COM1 is

used for Fault Analysis System (FAS) ie Central Monitoring Unit (Computer) connection COM2 to COM6

are used for networking For Bi-directional 2- nos of ports and for Tri-directional (T-network) 3-nos of ports

are used

DATA TRANSMISSION Dataloggers can be networked in Uni-directional Mode or Bi-directional Mode or T ndash Network Mode

In case of loss of data retransmission of data takes place

(a) Uni-Directional Mode

Each Datalogger will send data in only one direction to the FEP Unidirectional mode network is not

preferred

(b) Bi-Directional Mode

Each end of Network is connected to FEP and each datalogger can now transmit data in both the directions

Bi-directional Mode is advantageous it enables the Data Transmission even in case of Network Failure

(c) T - Network Mode

If more no of stations are in network ie if the network is too lengthy then T- network mode is preferred

COMMUNICATION The communication protocol for transmitting data and command between datalogger and CMU is

standardized by the RDSO and is given in the Specifications of Dataloggers

(a) The type of communication used in the network is dependent on the distance between the dataloggers

(b) For shorter distances Opto Converter Box- Opto isolated current loop communication is used

(c) For longer distances Modem (Dial-up leased) Fiber Optic Satellite Microwave communication

MODEMS Modems are used for DATA transfer between Dataloggers and Front End ProcessorThese are

configured to RS 232 Serial Communication Network is connected with two types of 4-wire modems

(a) Internal modem card Dual Modem card (in-built)

It is fixed in datalogger Euro rack itself One card contains two modems The top modem is called

ANS (answer) modem and the bottom modem is called as ORG (originate) modem

Note In case of networking of Dataloggers connect lsquoANSrsquo modem to the lsquoORGrsquo modem of one adjacent

station and connect lsquoORGrsquo modem to the lsquoANSrsquo modem of other adjacent station

(b) External modems

20 | P a g e

These are generally used at FEP (Front End Processor) side to connect the Dataloggers

(i) To transfer Data from one datalogger to another datalogger FEP Baud rate is 9600bps

(ii) These modems are 4-wire line communication

(iii) To transfer the data from FEP to RMU (PC) the Baud rate is 57600 bps

There is no difference between these modems functionally

CENTRAL MONITORING UNIT (CMU) COMPUTER

Central monitoring unit (Fault Analysis Unit) is a Personal Computer and its minimum configuration

shall be specified by RDSO from time to time System Software Windows XPVista(OS) Norton Kaspersky

(Anti Virus) Interbase where Server is not available (DBMS) Oracle where Server is available (DBMS)

software are required to run Datalogger System It is provided with Graphical User interface (GUI) based

software and retrieve data from all Networked dataloggers (up to 32) at various stations It stores data in

standard data base files The CMU is capable of analyzing the data and generate reports audiovisual alarms

on defined conditions This data can be compressed to take backup In central monitoring unit Software used

for analysis of data prediction of faults etc is written in a structured format so that purchaser can

reconfigure it if required It displays the status of signaling gears at any selected time in graphic form for any

selected station yard It retrieves the stored data amp simulates train movement It sends commands to various

Dataloggers to activate audio visual alarm or operate and electromagnetic relay

CMU shares data available in it by other PCs through available local area network where this data can

be used for train charting passenger information purpose The system generates audiovisual alarm in

ASMrsquosSignal Maintainerrsquos room in the case of power supply failure (battery voltage low) or battery charger

defective with acknowledgement facility

(a) Each datalogger has its own identity code which will be transmitted along with data packet to central

monitoring unit

(b) Events recorded at each station are continuously transmitted to central monitoring unit Response time of

data transfer will not exceed 10 sec

21 | P a g e

22 | P a g e

OPTICAL FIBER CABLE

INTRODUCTION The demand for bandwidth on transmission networks is increasing rapidly because video and

graphical rich contents are exchanged through the corporate network or the Internet The Gigabit Ethernet

became ommonly used in the corporate network backbone and 10Gbit Ethernet will be adopted in the near

future Meanwhile in the home the demand for high-speed network becomes popular as the wide spread of

broadband access eg CATV xDSL and FTTH The transmission medium with capability to transmit high

bit rate signal is necessary to satisfy these requirements

The telecommunication transport technologies move from copper based networks to optical fiber

from timeslot based transport to wave length based transport from traditional circuit switching to terabit

router and all optical based networks entering into a new era of optical networking

BASIC PHYSICS OF OFC

OPTICAL FIBER CABLE OFC have Fibers which are long thin strands made with pure glass about the diameter of a human

hair OFC consists of Core Cladding Buffers and Jacket as shown in figure

MONOCHROMATIC LIGHT OR SINGLE COLOR LIGHT Light or visible light is electromagnetic radiation of a wavelength that is visible to the human eye (

about 400 ndash 700 nm) The word light is sometimes used to refer to the entire electromagnetic spectrum Light

is composed of elementary particles called photons Three primary properties of light are

Light can exhibit properties of both waves and particles This property is referred to as wave-particle

duality The study of light known as optics In free space light (of all wavelengths) travels in a straight path

at a constant maximum speed However the speed of light changes when it travels in a medium and this

change is not the same for all media or for all wavelengths By free space it is meant space that is free from

matter (vacuum) andor free from electromagnetic fields

Thus the speed of light in free space is defined by Einsteinrsquos equation E = mc2

Frequency ν speed of light in free space c and wavelength λ are interrelated by ν = cλ

From the energy relationships E = mc2 = hν and the last one an interesting relationship is obtained

the equivalent mass of a photon m = hνc2

When light is in the vicinity of a strong electromagnetic field it interacts with it From this interaction

and other influences its trajectory changes direction as shown in figure

23 | P a g e

INCIDENT RAY REFLECTED RAY AND REFRACTED RAY An incident ray is a ray of light that strikes a surface The angle between this ray and the

perpendicular or normal to the surface is the angle of incidence Reflection is the change in direction of a

wave front at an interface between two different media so that the wave front returns into the medium from

which it originated Common examples include the reflection of light sound and water waves

The reflected ray corresponding to a given incident ray is the ray that represents the light reflected by

the surface The angle between the surface normal and the reflected ray is known as the angle of reflection

The Law of Reflection says that for a specular (non-scattering) surface the angle of reflection always equals

the angle of incidence The refracted ray or transmitted ray corresponding to a given incident ray represents

the light that is transmitted through the surface The angle between this ray and the normal is known as the

angle of refraction and it is given by Snells Law

The figure shows Incident ray Reflected ray Refracted ray the angle of incidence and angle of refraction

REFRACTIVE INDEX - Refractive index is the speed of light in a vacuum ( c =299792458kmsecond) divided by the speed

of light in a material ( v ) Refractive index measures how much a material refracts light Refractive index of

a material abbreviated as lsquo n lsquo is defined as lsquo n=cv lsquo Light travels slower in physical media than it does

when transmitted through the air Refractive index (n) is a function of molecular structure of matter optical

frequency optical intensity determines optical propagation properties of each wavelength ( λ ) may not be

distributed equally in all directions is affected by external temperature pressure and fields

Refractive index of a medium is a measure for how much the speed of light is reduced inside the

medium For example typical glass has a refractive index of 15 which means that light travels at 1 15 =

067 times the speed in air or vacuum Two common properties of glass and other transparent materials are

directly related to their refractive index

First light rays change direction when they cross the interface from air to the material and effect that

is used in lenses and glasses

Second light reflects partially from surfaces that have a refractive index different from that of their

surroundings

SNELLrsquoS LAW-

24 | P a g e

When light passes from one transparent material to another it bends according to Snells law which

is defined as n1sin(θ1) = n2sin(θ2)

where n1 is the refractive index of the medium the light is leaving θ1 is the incident angle between the light

beam and the normal (normal is 90deg to the interface between two materials)

n2 is the refractive index of the material the light is entering

θ2 is the refractive angle between the light ray and the normal

Snellrsquos law gives the relationship between angle of incidence and angle of refraction

For the case of θ1 = 0deg (ie a ray perpendicular to the interface) the solution is θ2 = 0deg regardless of

the values of n1 and n2 That means a ray entering a medium perpendicular to the surface is never bent The

above is also valid for light going from a dense (higher n) to a less dense (lower n) material the symmetry of

Snells law shows that the same ray paths are applicable in opposite direction

TOTAL INTERNAL REFLECTION- When a light ray crosses an interface into a medium with a higher refractive index it bends towards

the normal Conversely light traveling cross an interface from a higher refractive index medium to a lower

refractive index medium will bend away from the normal

This has an interesting implication at some angle known as the critical angle θc light traveling from

a higher refractive index medium to a lower refractive index medium will be refracted at 90deg in other words

refracted alon g the interface If the light hits the interface at any angle larger than this critical angle it will

not pass through to the second medium at all Instead all of it will be reflected back into the first medium a

process known as total internal reflection

The critical angle can be calculated from Snells law putting in an angle of 90deg for the angle of the refracted

ray θ2 This gives θ1

Since θ2 = 90deg

So sin(θ2) = 1

25 | P a g e

Then θc = θ1 = arcsin(n2n1)

For example with light trying to emerge from glass with n1=15 into air (n2 =1) the ritical angle θc is

arcsin(115) or 418deg For any angle of incidence larger than the critical angle Snells law will not be able to

be solved for the angle of refraction because it will show that the refracted angle has a sine larger than 1

which is not possible In that case all the light is totally reflected off the interface obeying the law of

reflection

OPTICAL FIBER MODE An optical fiber guides light waves in distinct patterns called modes Mode describes the distribution

of light energy across the fiber The precise patterns depend on the wavelength of light transmitted and on the

variation in refractive index that shapes the core In essence the variations in refractive index create

boundary

conditions that shape how light waves travel through the fiber like the walls of a tunnel affect how sounds

echo inside

We can take a look at large-core step-index fibers Light rays enter the fiber at a range of angles and

rays at different angles can all stably travel down the length of the fiber as long as they hit the core-cladding

interface at an angle larger than critical angle These rays are different modes Fibers that carry more than

one mode at a specific light wavelength are called multimode fibers Some fibers have very small diameter

core that they can carry only one mode which travels as a straight line at the center of the core These fibers

are single mode fibers This is illustrated in the following picture

OPTICAL FIBER INDEX PROFILE Index profile is the refractive index distribution across the core and the cladding of a fiber Some

optical fiber has a step index profile in which the core has one uniformly distributed index and the cladding

has a lower uniformly distributed index Other optical fiber has a graded index profile in which refractive

index varies gradually as a function of radial distance from the fiber center Graded-index profiles include

power-law index profiles and parabolic index profiles The following figure shows some common types of

index profiles for single mode and multimode fiber

26 | P a g e

OPTICAL FIBERrsquoS NUMERICAL APERTURE ( NA )- Multimode optical fiber will only propagate light that enters the fiber within a certain cone known as

the acceptance cone of the fiber The half-angle of this cone is called the acceptance angle (see figure 18)

θmax For step-index multimode fiber the acceptance angle is determined only by the indices of refraction

Where

n is the refractive index of the medium light is traveling before entering the fiber

nf is the refractive index of the fiber core

nc is the refractive index of the cladding

NUMBER OF MODES IN A FIBER - Modes are sometimes characterized by numbers Single mode fibers carry only the lowest-order

mode assigned the number 0 Multimode fibers also carry higher-order modes The number of modes that

can propagate in a fiber depends on the fiberrsquos numerical aperture (or acceptance angle) as well as on its

core diameter and the wavelength of the light For a step-index multimode fiber the number of such modes

Nm

Where

D is the core diameter

λ is the operating wavelength

NA is the numerical aperture (or acceptance angle)

MODE FIELD DIAMETER - All light do not travels through the core of the fiber but is distributed through both the core and the

cladding The mode field is the distribution of light through the core and cladding of a particular fiber

Mode-Field Diameter (MFD) defines the size of the power distribution When coupling light into or out of a

fiber MFD is important in understanding light loss

27 | P a g e

ADVANTAGE OF OFC COMMUNICATION - bull More information carrying capacity Fibers can handle much higher data rates than copper More

information can be sent in a second

bull Free from Electromagnetic and Electrostatic interference Being insulator no electric current flows through

the fibre and due to this reason fibres neither radiate nor pick up electro - magnetic radiation So WPC

CLEARANCE is not required

bull Low attenuation 025 dbkm at 1550 nm Loss in twisted pair and coaxial cable increases with frequency

where as loss in the optical fibre cable remains flat over a wide range of frequencies

bull Use of WDM ndash Switching routing at Optical signal level

bull Self healing rings under NMS control

bull Small size makes fibre cable lighter in weight So easy to handleOptic fibre cable weight (approx)

500 kg km Copper cable weight (approx) 1000 kgkm

The reasons are photons of light in a fibre

do not affect each other as they have no electrical charge and they are not affected by stray photons outside

the fibre But in case of copper electrons move through the cable and these are affected by each other

Optical fibre does not carry any electricity even if the cable is damaged or short circuited it does

not cause any spark or fire hazard

As the fibre do not radiate energy it can not be detected by any nearby antenna or any

other detector The fibres are difficult to tap and therefore excellent for security

As the signal transmission is by digital modulation there is no chance of cross talk in

between channels

Only by adding a few additional terminal and repeater equipments the

capacity of the system can be increased at any time once the cable is laid

ical effects and temperature variations

LIMITATIONS OF OFC -

difficult

- utilised

APPLICATION IN SIGNAL AND TELECOMMUNICATIONS transmission circuits

-haul circuits for linking of telephone exchanges

28 | P a g e

PROPAGATION MODES CONCEPT -

MODE - Mode is an available distribution of electromagnetic field in a plane transverse to the direction of

light propagation Each mode is characterized by frequency polarization electric field strength and

magnetic field strength Available patterns are derived from Maxwellrsquos equations and boundary conditions

LINEARLY POLARIZED (LP) MODE A mode for which the field components in the direction of propagation are small compared to

components perpendicular to that direction An optical fibre supports only different field patterns called as

lsquoLinear Polarizedrsquo or lsquo LPrsquo modes The reasons are

requirements

de

the accrual of power carried by different modes

There are two basic types of fiber Multimode fiber and Single-mode fiber

Multimode fiber is best designed for short transmission distances This is suited for used in LAN systems and

video surveillance Single mode fibre is best designed for longer transmission distances This is suitable for

long distance telephony and multi channel television broadcast systems

29 | P a g e

MULTI MODE FIBER Multimode fiber the first to be manufactured and commercialized simply refers to the fact that

numerous modes or light rays are carried simultaneously through the waveguide Modes result from the fact

that light will only propagate in the fiber core at discrete angles within the cone of acceptance MM fiber type

has a much larger core diameter compared to single-mode fiber allowing for the larger number of modes

and

is easier to couple than single-mode optical fiber Multimode fiber further categorized as Multimode step-

index and Multimode graded index fiber

PROPAGATION THROUGH MMSI FIBER Figure shows the principle of total internal reflection applies to multimode step index fiber Because

the corersquos index of refraction is higher than the claddingrsquos index of refraction the light that enters at less than

the critical angle is guided along the fiber

Three different light waves travel down the fiber One mode travels straight down the center of the

core A second mode travels at a steep angle and bounces back and forth by total internal reflection The third

mode exceeds the critical angle and refracts into the cladding Naturally it can be seen that the second mode

travels a longer distance than the first mode causing the two modes to arrive at separate times

PROBLEMS WITH MMSI FIBER AND SOLUTION This disparity between arrival times of the different light rays is known as dispersion and the result is

a muddied signal at the receiving end It is important to note that high dispersion is an unavoidable

characteristic of multimode step-index fiber The solutions are either use Graded index fiber or Single mode

fiber

PROPAGATION THROUGH MMGI FIBER Multimode Graded-index refers to the fact that the refractive index of the core gradually decreases

farther from the center of the core The increased refraction in the center of the core slows the speed of some

light rays allowing all the light rays to reach the receiving end at approximately the same time reducing

dispersion Figure shows the Light propagation principle through multimode graded-index fiber The corersquos

central refractive index ( nA ) is greater than that of the outer corersquos refractive index ( nB )

It is very clear from the figure the light rays no longer follow straight lines they follow a serpentine path

being gradually bent back toward the center by the continuously declining refractive index This reduces the

arrival time disparity because all modes arrive at about the same time The modes traveling in a straight line

30 | P a g e

are in a higher refractive index so they travel slower than the serpentine modes These travel farther but

move faster in the lower refractive index of the outer core region

PROPAGATION THROUGH SMSI FIBER Single mode fiber has a much smaller core that allows only one mode of light at a time to propagate

through the core The figure shows the single mode fiber

Single-mode fiber exhibits no dispersion caused by multiple modes Single-mode fiber also offers lower fiber

attenuation than multimode fiber Thus more information can be transmitted per unit of time because it can

retain the fidelity of each light pulse over longer distances Like multimode fiber early single-mode fiber was

generally characterized as step-index fiber meaning the refractive index of the fiber core is a step above that

of the cladding rather than graduated as it is in graded-index fiber Modern single-mode fibers have evolved

into more complex designs such as matched clad depressed clad and other exotic structures

SINGLE-MODE FIBER DISADVANTAGES The smaller core diameter makes coupling light into the core more difficult The tolerances for single-

mode connectors and splices are also much more demanding

CUTOFF WAVE LENGTH - Cutoff wavelength is the wavelength above which a single-mode fiber supports and propagates only

one mode of light In other words an optical fiber that is single-mode at a particular wavelength may have

two or more modes at wavelengths lower than the cutoff wavelength The effective cutoff wavelength of a

fiber is dependent on the length of fiber and its deployment The longer the fiber the lower is the effective

cutoff

wavelength The smaller the bend radius of a loop of the fiber the lower is the effective cutoff wavelength If

a fiber is bent in a loop the effective cutoff wavelength is lowered

SIGNAL ATTENUATION IN FIBER - Optical fiber has a number of advantages over copper However it also suffers from degradation

problems which can not be ignored The first of these is loss or attenuation Attenuation is typically the result

of two sub properties They are scattering and absorption Both of which have cumulative effects The second

is

dispersion which is the spreading of the transmitted signal and is analogous to noise

SCATTERING Scattering occurs because of impurities or irregularities in the physical construction of the fiber The

well known form of scattering is Rayleigh Scattering It is caused by metal ions in the silica matrix and

results in light rays being scattered in various directions

31 | P a g e

Scattering limits the use of wavelengths below 800nm The short wavelengths are much affected than longer

wavelengths It is because of Rayleigh scattering that the sky appears to be blue ( shorter wave length ) The

shorter wavelengths ( blue ) of light are scattered more than the longer wavelengths of light

ABSORPTION Absorption results from three factors They are hydroxyl ions ( OH- water ) in the silica impurities

in the silica and incomplete residue from the manufacturing process These impurities tend to absorb the

energy of the transmitted signal and convert it to heat resulting in an overall weakening of the signal The

Hydroxyl absorption occurs at 125 and 139 micro The silica itself starts to absorb energy at 17 micro

because of the natural resonance of the silicon dioxide

MACRO BENDING LOSS Macro-bending loss is caused by bending of the entire fiber axis The bending radius shall not be

sharper than 30d where d is diameter of cable A single bend sharper than 30d can cause loss of 05dB

The fiber may break if bending is ever sharper

MICRO BENDING LOSS Micro-bending loss is caused by micro deformations of fiber axis which leads to failures in achieving

total internal reflection conditions Micro-bends are small scale perturbations along the fiber axis the

amplitude of which are on the order of microns These distortions can cause light to leak out of a fiber

Micro-bending may be induced at very cold temperatures because the glass has a different coefficient of

thermal expansion from the coating and cabling materials At low temperatures the coating and cable

become more rigid and may contract more than the glass Consequently enough load may be exerted on the

glass to cause micro bends

Coating material is selected by manufacturers to minimize loss due to micro-bending The linear thermal

expansion coefficient of coating material shall be compatible with that of fiber

32 | P a g e

DISPERSION Dispersion is the optical term for the spreading of the transmits in the fiber It is the bandwidth

limiting phenomenon and comes in two forms Multimode dispersion and chromatic dispersion Chromatic

dispersion is further subdivided into material dispersion and waveguide dispersion

DISPERSION PHENOMENON IN OPTICAL FIBER Dispersion is the time distortion of an optical signal that results from the differences of time of travel

for different components of that signal typically resulting in pulse broadening As the distance traveled by

the signal is more broadening of pulse is more In digital transmission dispersion limits on the maximum

data rate and the maximum distance ie the information-carrying capacity of a fiber link The interference

from broadened pulse in the next interval shall not lead to erroneous interpretation of received signal

OPTICAL DOMAIN Understanding where attenuation and dispersion problems occur helps optical design engineers

determine the better wavelengths at which information can be transmit taking into account distance type of

fiber and the other factors which can severely affect the integrity of the transmitted signal The graph shown

depicts the optical transmission domain as well as the areas where problems arise The wavelength (nm)

is shown on X-axis and attenuation ( dBkm) is shown on Y-axis

There are four transmission windows appear in the figure The first one is at around 850 nm the

second at 1310nm third at 1550 nm and fourth at 1625 nm The last two labeled as C and L band

respectively The 850 nm wavelength at which the original LED technology operated The second window at

1310 nm has low dispersion The 1550 nm called as C-band is ideal wavelength for long haul

communication systems The network engineers can avoid transmitting signal at 1000 nm where Rayleigh

scattering 1240 and 1390 nm where hydroxyl absorption by water occurs to avoid high degree of loss

Optical fibers also can be manufactured to have low dispersion wavelength in the 1550nm region

which is also the point where silica-based fibers have inherently minimal attenuation These fibers are

referred to as dispersion-shifted fibers and are used in long-distance applications with high bit rates For

33 | P a g e

applications utilizing multiple wavelengths it is undesirable to have the zero dispersion point within the

operating

wavelength range

34 | P a g e

SIGNALLING RELAYS

INTRODUCTION A relay is an electromagnetic device which is used to convey information from one circuit to another

circuit through a set of contact ie front or back contact Constructional and electrically relays may be

divided into DC and AC relays because the means by which the electrical energy in the coil is converted in

to mechanical Energy in order to move the contacts are fundamentally different In DC type the contacts are

carried on an armature forming part of a magnetic circuit in which a field is set up by the current flowing in

the coils In AC types the contacts are attached by a link mechanism to a metal sector disc or cylinder in

which currents are induced by the alternating magnetic field produced by the currents in the coils

Every endeavor has been made to explain the action of each type of relay in the simplest possible manner

Relays are sophisticated switch gears used for remote control and succession control of various

electrical equipment In present days they are widely used because they are capable of protecting the

controlled equipment from cross feeding and overloading even as they cater for speedy operations

Most of the relays in present day signaling are electromagnetic devices although some of the relays control

circuits through electronic components like diodetransistors Integrated Chips etc

Railway signaling relays are unique in that

(a) They operate on low voltage and current

(b) They are more articulate as according to their special features they can work under restrictive conditions

and in any specified manner Virtually they can cater for all situations while contributing to speed and

accuracy in operations

CLASSIFICATION OF SIGNALLING RELAYS (a) According to the method of their mounting or fixture they are classified as

(i) Shelf type Relays which are loosely kept on shelves

(ii) Plug in type Relays which are plugged into a pre- wired plug boards

(b) According to their connection and usage they are classified as

(i) Track relays Relay which is directly connected to the track to detect the presence of vehicle

(ii) Line Relays Other than track relay all are line relays Relays connected to the selection circuit

(c) According to their vitality or importance in ensuring train working safety they are classified as

(i) Vital Relays All relays used for traffic control such as signal point controls track detection etc

(ii) Non-vital Relays Relays which operate control aids and accessories like warnings buzzers

Indications etc

(d) According to their special provisions to ensure reliability of their contacts they are classified as

(i) Proved type are those whose normalization after each operation shall be proved in circuit

controlled by their contacts Contacts in which both the springs have metal surfaces on their tips They may

get fused due to high sparking current across them during operation These may prevent relay normalization

and causes unsafe condition in traffic control To avoid this proving of relay normalization after each

operation is necessary

(ii) Non - proved type Need not to be proved to have been normalized after each operation as their

contacts have at least one non-fusible contact (carbon contact)

(e) According to their feed source relays are broadly classified as

(i) DC relays The relay which requires DC power supply for its operations are called DC relays Among

the DC relays

o DC neutral relays This relay closes the same set of contacts on energization with Normal polarity

or Reverse polarity supply

o Polar Relays This relay closes different set of contacts when energized with Reverse polarity

supply They may or may not have contact to close when deenergized

35 | P a g e

(ii) AC Relay AC Induction motor track relays Time element relays flashing indication control etc

(iii) Electronic Relays DC relays with electronic components in them are called electronic relays

DC NEUTRAL RELAY Each Relay has usually one or two coils with a hollow center to accommodate a coreThe coils are

made up of a large numbers of turns of small gauge soft drawn copper wire The two coils can be connected

in series or parallel according to the requirement of relay resistance The ends of the coils are terminated on

binding post to which the control wires are connected Each coil is placed around a core of specially selected

Iron or steel having high permeability and low retentivity The core should be susceptible to magnetism and

at the same time should have little residual magnetism The cores are connected at the top by a yoke to

complete the magnetism coupling between two ends of coils The bottom of each core is equipped with a

large steel or Iron block known as pole piece or face

A flat piece of Iron or steel called armature is supported by brackets which are securely fastened to

the pole piece The armature yoke and the pole pieces are also made of specially selected iron or steel of the

same quality as the core The armature carries the metallic spring contacts which are insulated from it

The circuit through the coils of the relay is closed It sets up a magnetic flux through the core yoke and the

armature The flux passing between the armature and pole faces causes the armatures get attracted to the pole

faces and armature picks up and closes front contacts When the circuit is opened the magnetic flux collapses

and the armature drops away by gravity from the pole faces the front contacts break and back contacts close

The front and back contacts of the relay can be utilised to make or break other circuits Two stop pins of

nonmagnetic material are fixed either on the armature or pole faces so that the armature cannot

come in contact with the pole faces It is essential to maintain a small air-gap between the armature and pole

faces so that low value of residual magnetism may not retain the armature in picked up position and causes

the relay to fail to drop away with a break in its control circuit

GENERAL USAGE

DC Neutral line relays are most commonly used for Railway Signalling controls and detection

Among them plug-in type relays are preferred in larger installations for space considerations Shelf type

relays are also in use mostly in wayside stations

There are many DC Neutral line relays in use with special features such as

(i) Delayed operation

(ii) Biased DC control

(iii) DC control unaffected by AC interference currents

(iv) Getting latched in operated condition till further feeding and others

Usage of DC polar relays is mostly in conjunction with block instruments that control traffic between

stations AC line relays are almost extinct in installations of British Signalling practice They are however

used for time control operations flashing indication control and such other special purposes in installations

with Siemens signalling practice widely Track relays are used according to the type of track detection

circuits chosen for a given location and context While most of the track circuits are still of the DC working

type requiring DC neutral track relays with them the prospects of their being replaced with Electronic track

circuits directly feeding DC line relays in future are great AC Track Circuits are used in DC Traction area

as conventional DC Track Circuits are not suitable there AC Track relays are used with them almost all of

the induction motor type In the British practice of signalling which was first introduced on Indian Railways

non-proved type relays with carbon to metal switching contacts are generally used for vital controls

They facilitate simple circuit designs But with the advent of German Practice introduced by Ms

Siemens later proved type relays with all metal to metal contacts are widely accepted in spite of

complications in circuit design caused by them A recent introduction is that of the same type relays made by

Ms Integra control However for some time now the appreciable features of both the practices are getting

36 | P a g e

incorporated together in the indigenous designs of signalling by railwaymen With this the usage of all types

of relays anywhere can be found without straight jacketed segration of relay types

CHARACTERSTIC OF ELECTRO-MAGNETIC RELAY The following are the characteristic of electro-magnetic relays A brief study of them helps in

understanding the choice of their components and designs features

1) Force of attraction

2) Effect of air gap

3) Effect of Hysterisis

4) Transient condition

FORCE OF ATTRACTION In any electro-magnetic system the force of attraction is given by

Where B - is the flux density a - is the cross sectional area of the particular part of the magnetic

circuit

In the case of a DC neutral Relay B is proportional to the current that is flowing in the coil

surrounding the electro-magnet and thus the force of the attraction is directly proportional to the square of the

current This square relationship has its own advantage especially in the case of DC track relay in that a

small reduction in the current will have a great effect on the working of the relay Also for a given change of

current the make and the break will be quicker with lesser possibility of arcing

EFFECT OF AIR GAP

Curve lsquoArsquo is magnetisation curve for the iron and is all practical purpose a straight line up to the

saturation point Curve lsquoBrsquo is the magnetisation curve for the open-air gap which is a straight line through

out because per magnetisation curve of the whole

magnetic circuit of the relay and for a given force is the sum of the amp-turns for the iron part and the amp-

turns for the air gap

When the front contacts are open the force required to pick up the armature is shown on curve lsquoCrsquo to be F1

but after the armature has operated it will be separated from the core by stop pins In this position the amp-

turns required to maintain the armature is less as indicated by the dotted line from 1 on curve C to 2 on curve

37 | P a g e

F But actually the current in the coil is unaltered the force on the armature is greater than required as

indicated at 3 on curve F Part of this extra force is used to flex the front contacts sufficiently to give good

contact pressure when it is in energised position

The difference between the pick-up and the drop-away current should be as small as practicable in

track relay to ensure good shunting characteristics This is achieved firstly by the choice of good quality relay

iron and secondly by having a small air gap between armature and core If the air gap is not available then

the residual magnetism fluxes might cause the armature to be retained when the supply is disconnected For

this reason residual pins are provided to ensure a definite minimum air gap in the energised position

EFFECT OF HYSTERISIS

Hysterisis is the property by which the flux produced lags behind the current In the de-energized

condition there will be small residual flux in the core When the voltage is applied to the coils the current in

rising to its steady value first causes the flux to rise from 1 to 2 along the curve At this point the flux density

will be sufficient to attract the armature and reduce the air gap the flux then raise to 3 and continue to 4

which corresponds to the steady current in the coils When the voltage is disconnected the current in falling

caused the flux to fall from 4 to 5 along the curve At this point the flux density will fall below the value

required to maintain the armature which will release thus increasing the air gap and reducing the flux to 6

Finally the

flux will decrease from 6 to 1 where the current will again be zero

The relay core is made of material having high permeability and low retentivity As mentioned in

the IRS specification Electromagnet iron may be in the form of a

(a) Bar of silicon steel

(b) Best Yorkshire wrought iron

(c) Swedish charcoal iron

(d) Electrical steel sheets

` This reduces the difference between pick up value and Drop away value By selecting good quality

core material Percentage release and sensitivity of the relay will be improved

TRANSIENT CONDITION

38 | P a g e

When the voltage is applied or disconnected from the coils it takes some little time before the current

become steady These are known as transient conditionsrdquo and are important so far as track relays are

concerned When the voltage is first applied to the coils the magnetic flux in rising cuts the turns on the

coils and in so doing produces a back EMF that opposes the applied voltage and retards the growth of

current

The growth and decay of flux are decided by the relationship between the inductance and resistance

in the circuit is known as time constant It is not fixed quantity in the case of DC neutral relay This value of lsquo

Lrsquo is less when the relay is in de-energised condition (L1) than when the relay is in energised condition (L2)

The magnitude of flux that is established for a given change of current is different in two cases

When the current reaches the pick up value the armature closes and the inductance is increased to L2

due to reduced air gap the flux per amp is increased The increase in flux increased the back EMF during the

movement of the armature after which the current continuous to raise along a new curve corresponding to the

increased inductance until it reaches the final value (ER) This process is indicated above in fig24

When the supply is disconnected the current is obliviously reduced to zero immediately but the flux

decay comparatively slowly owing to the eddy currents produced in the core by the rapid flux change which

tend to maintain the flux The drop away time on a disconnection is however generally negligible See fig

below

If the relay releases due to the reduction in current from say I 2 to I 1 caused by the application of

shunt resistance (as in the case of track relay ) the time taken is much longer than the relay is simply

disconnected The rate of rise or fall of current during the transient conditions is also depends on exterior

circuit values because L and R apply to the whole circuit The production of eddy current in the core the flux

will decay at a slower rate than the current So that the actual release time will be a little longer than it takes

the current to fall to the release

L= Inductance

39 | P a g e

R= Resistance

It is now clear that to reduce releasing time to a minimum it is necessary that

- The relay iron should have low Hysterisis loss and low retentivity

- The degree of over energization of the relay should be restricted

- Connecting a suitable external resistance in series with the relay to keep LR ratio low

In non RE area for track circuit length less than 100M 9 ohm track relay only to be used Using relay

with minimum contacts as they require lesser current which keeps inductance value low

Train working safety is ensured only if the track relay of shortest length track circuit is released

before a light engine running at a highest permitted speed clears it Otherwise the track circuit occupation

may go undetected To avoid this a special provision has to be made in signal control circuits wherever

necessary

The following methods may be adopted for reducing the time lag of track relay

(a) Restrict the over energisation of relay since the release time depends on the initial working current

(b) Connecting a suitable external resistance in series with the relay to keep the LR ratio low

(c) Using relays with minimum contacts as they require lesser operating current keeping the inductance

value low

40 | P a g e

CONCLUSION

Modern signalling is vital for safe and punctual movements of trains In the Indian railways The Signalling

and Telecommunication Department is responsible for providing modern effective and relaible signalling

systems as well as telecommunication systems

The first mode of communication used in Indian Railways was the use of electric telegraph

with the help of Morose code Morose code is the method of providing text information as a series of on-off

tones and lights or clicks that can be directly understood by a skilled listener or observer without special

equipmentEach character (letter or numeral ) is represented by a unique sequence of dots and dashes Later

this system becomes obselete and beggan the era of wireless communication which operated at audio level

frequency range

In wireless communication the significant advances took place the transition to miniature

valves or filament tubesBut this was abandoned too because of excessive current consumption and over

heating of the filament tubes

Fibre-optic communication is a method of transmitting information from one place to another by

sending pulses of light through an optcial fibreThe light forms an electromagnetic carrier wave that is

modulated to carry information First developed in the 1970s fibre optic communication systems has

revolutionized the telecommunications industry and have palyed a major role in the advent of the information

age Because of its advantages over electrical transmissionsoptical fibres have largely replaced copper wire

communications in core networks in the developed world The Indian Railways too is undergoing a transition

from Microwave communication to fibre optic communications

41 | P a g e

BIBLIOGRAPHY AND REFERENCES

1 wwwwikipediacom

2 wwwbritaniccacom

3 wwwirfcacom

4 Motorola GP60 system manual

5 Harris FAS 7000 manual

6 TOSHIBA Manual

14 | P a g e

EARTHING- The lead wires connecting the installation and the earth electrode shall ordinarily be of stranded

copper wire of 29 sq mm (19 strand wires of 14 mm diameter) Copper wire has been specified because GI

wires usually are having greater corrosion However in areas where copper wire may be frequently stolen

due to theft ACSR of size 64 sq mm (19 strands of 211 mm diameter) may be used

LIMITS OF EARTH RESISTANCE (a) Apparatus case connected to Earth (SSDAC and vital Relay Box is housed in Apparatus case and

Connected to earth at outdoor) shall be less than or equal to 1 ohm

(b) All cable connected to same earth shall be less than or equal to 1 ohm

(C) Reset box connected to earth near SM s Room shall be less than or equal to 1ohm

EQUIPMENT TO BE EARTHED A Common Earth should be provided for SSDAC for items 1(a) amp (b) of the above at the outdoor

(a) The Apparatus Case is to be connected to earth (the chassis of SSDAC amp Vital Relay Box should be

properly connected to apparatus case)

(b) Metallic sheath and armouring of all the underground main cables are to be earthed

(i) In RE area the metallic sheath and armouring of main telecom cables are earthed at both ends

(ii) In RE area the armouring of Jelly filled cable shall be earthed at both ends

(c) The Earthing shall be provided at every location box where cables are terminated

(d) Earth already available for other equipment may be used for earthing of Reset Box near SM s Room

Cabin etc

15 | P a g e

DATALOGGER

INTRODUCTION Datalogger is a Microprocessor based system which helps in analysing the failures of relay inter

locking system Electronic Interlocking system This is like a black box which stores all the information

regarding the changes take place in relays AC DC Voltages and DC currents along with date and time The

same information data can be transferred to the computer to analyse further ldquoon line ldquooff linerdquo analysis of

stored date A print out also can be obtained through a printer by connecting directly to the datalogger unit

The data belongs to Relay contacts is considered as digital inputs and the data belongs to voltage

levels currents is considered as Analog inputs Datalogger lsquos are mandatory for all new relay interlocking

(PIRRI) EI installations and it is also recommended to provide in all existing PIs RRIs To increase the

line capacity mechanical signalling equipments are upgraded to PI RRI or EI Due to complexity in the

circuits and wiring sometimes it is very difficult to rectify the failures So datalogger can monitor these

systems with real time clock Thus it can be named as black box of Samp T equipments and hence it is a vital

tool for accident investigation Datalogger is used at Stations yards Whereas in case of Auto Section amp IBH

Mini dataloggers called as Remote Terminal Unit (RTU) are used

ADVANTAGES OF DATALOGGERS (a) Dataloggers helps in monitoring the typical failures such as intermittent auto right failures

(b) It helps in analyzing the cause of the accidents

(c) It helps in detecting the human failures errors such as

(i) Drivers passing signal at Danger

(ii) Operational mistakes done by panel operators ASMrsquos of operating department

(iii) Signal and telecom engineering interferences in safety circuits

(iv) Engineering and electrical department interferences failures

(v) It helps as a ldquoTOOLrdquo in preventive maintenance of signaling gears

(d) Dataloggers can be connected in network Networked dataloggers helps to monitorthe PIRRIEI remotely

(e) Failure reports can be generated remotely with help of datalogger network

(f) On line and Off line track simulation is possible

(g) Speed of the train on point zones can be calculated

(h) Age of the equipment in terms of number of operations etc

COMMON EQUIPMENT FOR ALL DATALOGGERS ARE GIVEN

BELOW (a) CPU card

(b) Digital and Analog input cards

(c) Local terminal(PC)

(d) communication links

(e) Printer

All the dataloggers requires a potential free ( spare ) relay contact for monitoring digital inputs

through Digital input cards amp for monitoring Analog inputs such ACDC bus bar voltage levels through

Analog input cards Digital and Analog inputs are connected to the Processor card Processor card consists of

memory ICrsquos Memory ICrsquos are programmed as per requirement of the signal engineers

Provision of Dataloggers is mandatory with RRI systems and is optional for PI systems as per

amendment to the specification for Relay Interlocking systems ( IRSS-36 ) The data collected by the

datalogger can be used for failure analysis repetitive discrepancies and for accident investigations

16 | P a g e

Note

If the serial communications is more than 50m then line drivers shall be used up to 3 Kms

4wire leased line Modems shall be used if the serial communication is more than 3 Kms

STUDY OF EFFTRONICS DATALOGGER TECHNICAL DETAILS (a) 24V 12VDC Power Supply

(b) Total Storage Capacity of 10 Lakh events

(c) In-built Temperature sensors

(d) Internal Buzzer for alarming during failures

(e) Real Time clock with internal battery backup with data retention up to 10 years

(f) 512 LED matrix to indicate the status of 512 Digital inputs at a time page wise

(g) Seven segment LCD screen (2x24) to display the status of digitalanalog signalsTime Temperature etc

(h) Using the keyboard various functions can be viewed in the LCD panel

(i) Max Digital Inputs 4096

(j) Max Analog Inputs 96

(k) Digital Input Scanning Time 16 millisecond

(l) Analog Input Scanning Time is less than 1 Sec

HARDWARE (EQUIPMENT) Datalogger system consists of

(a) Datalogger (CPU - with Microprocessor 68000)

(b) Digital input cards

(c) Dual modem card

(d) Digital Scanner units (DSU)

(e) Analog Scanner units (ASU)

CPU CARD It is provided with Motorola microprocessor M 68000 It performs all the activities pertaining to the

datalogger It continuously scans (check) the Digital inputs(inbuilt) Digital Scanner Units and Analog

Scanner Units ie scanning of digital signals (Relay operations) for every 16-milli seconds and scanning of

analog signals (ie ACDC voltages amp DC currents) for less than 1 second

This card will support the IO interfaces of LCD (Liquid Crystal Display) - 2X24 alphanumeric Key

Board LED Matrix Display Real Time Clock LCD display and keyboard This will acts as man machine

interface between the datalogger and the signal engineer All the operations (Software) can be performed

using this LCD and keyboard

Real time display with 7 Segments This is built in real time clock within Datalogger and its current

time will be displayed on six 7-segment display provided (Real time clock depend upon DALLAS 1286

chip) This IC will come with internal battery backup hence there is no need to add external batteries

CPU card continuously scans (checks) the DSUs and ASUs Each input connected to digital scanner

units are optically isolated by Opto couplers When CPU card scans the digital inputs it compares with the

previous stored data and if there is any change from the previous status then only that data will be stored (the

status conditions of relay) with date and real time A total of minimum 10 Lac events can be stored in

memory on first in first out basis so that latest data is available in the system There is no loss of data from

datalogger memory in case of power supply failure of datalogger

DIGITAL INPUT CARDS (IN-BUILT) This system is having maximum 8nos of inbuilt Digital inputs cards Maximum 64nos of digital

inputs can be connected to each digital input card The potential free relay contact may be front or back

contact terminated at the Tag Block from the relay of signals tracks points Buttons etc and are

17 | P a g e

subsequently connected to Digital input cards through Flat Ribbon Cable (FRC) connectors These in-built

digital input cards can monitor a total 512 nos of relays status

DIGITAL SCANNER UNIT (DSU) Each DSU contains 8 nos of Digital Input cards Each input card can be connected with 64 inputs

Total input capacity of DSU unit is 512 inputs These scanner cards contain Optocouplers and Multiplexer

Inputs are connected to Stag card The stag card out put is connected to DSU through FRC connectors

Maximum 7 nos of DSUs can be connected to the system So Digital input capacity of the system is 4096

All these digital inputs are scanned at rate of 16 msec

ANALOG SCANNER UNIT (ASU) ASU contains maximum 3 nos of Analog input cards Each input card can be connected with 8nos of

Analog inputs Total input capacity of the ASU is 24 analog input channels Maximum 4nos of ASUs can be

connected to the system Analog input channel capacity of the system is 96 All these analog inputs are

scanned at a rate of less than 1 sec

PARALLEL PORT Parallel port is provided for connecting printer

RS-232 SERIAL PORTS At least 6 Serial communication ports are provided for communication with other dataloggers

Central Monitoring Unit Remote Terminal Unit Electronic Interlocking system Integrated Power Supply

system etc

EXTERNAL NON-VITAL RELAY CONTACTS These relays provided in the system where 16 number of the Relay contacts are provided on the rear

panel through Tele control port to extend alarms and to control the power equipment from remote or local

locations through computer in case of any occurrence of failures Each control can sink or source 100 m

amps of current

INTERNAL MODEM CARD DUAL MODEM CARD (IN-BUILT) It is fixed in datalogger Euro rack itself One card contains two modems The top modem is called

ANS (answer) modem and the bottom modem is called as ORG (originate) modem It is used in case of

networking of Dataloggers In network connect lsquoANSrsquo modem to the lsquoORGrsquo modem of one adjacent station

and connect lsquoORGrsquo modem to the lsquoANSrsquo modem of other adjacent station

POWER SUPPLY Normally 24V DC (12V DC is optional) supply with battery backup is required for the system

working

Input Voltage Range 18Vhellip32V DC (For 24V) 9Vhellip18V DC (For 12V)

INPUT REQUIREMENTS Relay inputs (digital inputs) and analog inputs (voltages currents etc) are required to be connected

to the system as per the requirements of RRI PI SSI as the case may be Some of the inputs to be

monitored is given below

(a) Digital inputs

(i) Field inputs All TPRs NWKRs RWKRs ECRs Crank Handle relays SidingSlot LC gate

control relays etc

(ii) Control Panel inputs All button Knob SMrsquos Key relays

18 | P a g e

(iii) Internal relays

British system All HR DR HHR WNR WRR ASR UCR RR LR UYRTLSR TRSR TSR

JSLR JR etc

SIEMENS system Z1UR Z1UR1 GZR ZDUCR ZU(R)R ZU(N)PRG(R)RG(N)R U(R)S

U(N)PS UDKR DUCR U(R)LR UYR1 UYR2 G(R)LRGR1GR2

GR3 GR4 OVZ2U(R)RW(RN)R (RN)WLR Z1NWR Z1RWRZ1WR1 WKR1 WKR2 WKR3 etc

(b) Analog channels

(i) 230 V AC (for power supplies in the power panel)

(ii) 110V AC (for Signal and Track transformers)

(iii) 110V DC (for Point operation)

(iv) 60V DC (Siemens relays)

(v) 24V DC (Q-series relays)

(vi) 24V DC (for Block Axle counters)

(vii) 12V DC (for indication)

(viii) 20A (for point operation current)

(ix) 10V AC 5KHz (for Axle counter channels) etc

SOFTWARE MODULES OF DATALOGGERS

(a) Network Management of Dataloggers (NMDL)

(b) Reports

(c) Fault Entry

(d) Track Offline Simulation

(e) Train Charting

NMDL SOFTWARE FEATURES (a) Online Relay Status

(b) Online Faults - To view information of various Online Faults as they occur in the stations where

the Dataloggers are connected

(c) Online Simulation - Graphical view of relay operations train movements etc

(d) Remote monitoring of stations with the help of NETWORKING

SOFTWARE OBJECTIVES (a) Predictive Maintenance

(b) Easy identification of failures

(c) Crew discipline

(d) Train charting

REMOTE MONITORING OF STATIONS WITH NETWORKING OF

DATALOGGERS The individual Dataloggers of various stations can be interconnected through networking technology

The data of Remote Panel stations can be viewed in a Computer at the Central Monitoring Station The data

of the network is collected by the FEP (Front End Processor) which in turn is transmitted to the computer

COMPONENTS OF NETWORK MANAGEMENT OF DATALOGGERS

(a) Datalogger at stations

(b) MODEM and Transmission medium

19 | P a g e

(c) Front End Processor (FEP)

(d) Central Monitoring Unit (CMU) Computer

FEP (FRONT END PROCESSOR)

FEP acts as a buffer between the Central Monitoring Unit (Computer) and the Network It is provided

at centralised place to retrieve data continuously from station dataloggers and store in memory and transfer to

computer on request It stores 10 Lac telegrams It works on 12V DC It draws 16A continuous current

when all the three modems are connected Normally it shows the number of packets pending to be sent to the

computer on its 7-segment LED display It is provided with MOTOROLA 68000 microprocessor It has 6-

nos of RS-232 communication ports such as COM1 COM2 COM3 COM4 COM5 and COM6 COM1 is

used for Fault Analysis System (FAS) ie Central Monitoring Unit (Computer) connection COM2 to COM6

are used for networking For Bi-directional 2- nos of ports and for Tri-directional (T-network) 3-nos of ports

are used

DATA TRANSMISSION Dataloggers can be networked in Uni-directional Mode or Bi-directional Mode or T ndash Network Mode

In case of loss of data retransmission of data takes place

(a) Uni-Directional Mode

Each Datalogger will send data in only one direction to the FEP Unidirectional mode network is not

preferred

(b) Bi-Directional Mode

Each end of Network is connected to FEP and each datalogger can now transmit data in both the directions

Bi-directional Mode is advantageous it enables the Data Transmission even in case of Network Failure

(c) T - Network Mode

If more no of stations are in network ie if the network is too lengthy then T- network mode is preferred

COMMUNICATION The communication protocol for transmitting data and command between datalogger and CMU is

standardized by the RDSO and is given in the Specifications of Dataloggers

(a) The type of communication used in the network is dependent on the distance between the dataloggers

(b) For shorter distances Opto Converter Box- Opto isolated current loop communication is used

(c) For longer distances Modem (Dial-up leased) Fiber Optic Satellite Microwave communication

MODEMS Modems are used for DATA transfer between Dataloggers and Front End ProcessorThese are

configured to RS 232 Serial Communication Network is connected with two types of 4-wire modems

(a) Internal modem card Dual Modem card (in-built)

It is fixed in datalogger Euro rack itself One card contains two modems The top modem is called

ANS (answer) modem and the bottom modem is called as ORG (originate) modem

Note In case of networking of Dataloggers connect lsquoANSrsquo modem to the lsquoORGrsquo modem of one adjacent

station and connect lsquoORGrsquo modem to the lsquoANSrsquo modem of other adjacent station

(b) External modems

20 | P a g e

These are generally used at FEP (Front End Processor) side to connect the Dataloggers

(i) To transfer Data from one datalogger to another datalogger FEP Baud rate is 9600bps

(ii) These modems are 4-wire line communication

(iii) To transfer the data from FEP to RMU (PC) the Baud rate is 57600 bps

There is no difference between these modems functionally

CENTRAL MONITORING UNIT (CMU) COMPUTER

Central monitoring unit (Fault Analysis Unit) is a Personal Computer and its minimum configuration

shall be specified by RDSO from time to time System Software Windows XPVista(OS) Norton Kaspersky

(Anti Virus) Interbase where Server is not available (DBMS) Oracle where Server is available (DBMS)

software are required to run Datalogger System It is provided with Graphical User interface (GUI) based

software and retrieve data from all Networked dataloggers (up to 32) at various stations It stores data in

standard data base files The CMU is capable of analyzing the data and generate reports audiovisual alarms

on defined conditions This data can be compressed to take backup In central monitoring unit Software used

for analysis of data prediction of faults etc is written in a structured format so that purchaser can

reconfigure it if required It displays the status of signaling gears at any selected time in graphic form for any

selected station yard It retrieves the stored data amp simulates train movement It sends commands to various

Dataloggers to activate audio visual alarm or operate and electromagnetic relay

CMU shares data available in it by other PCs through available local area network where this data can

be used for train charting passenger information purpose The system generates audiovisual alarm in

ASMrsquosSignal Maintainerrsquos room in the case of power supply failure (battery voltage low) or battery charger

defective with acknowledgement facility

(a) Each datalogger has its own identity code which will be transmitted along with data packet to central

monitoring unit

(b) Events recorded at each station are continuously transmitted to central monitoring unit Response time of

data transfer will not exceed 10 sec

21 | P a g e

22 | P a g e

OPTICAL FIBER CABLE

INTRODUCTION The demand for bandwidth on transmission networks is increasing rapidly because video and

graphical rich contents are exchanged through the corporate network or the Internet The Gigabit Ethernet

became ommonly used in the corporate network backbone and 10Gbit Ethernet will be adopted in the near

future Meanwhile in the home the demand for high-speed network becomes popular as the wide spread of

broadband access eg CATV xDSL and FTTH The transmission medium with capability to transmit high

bit rate signal is necessary to satisfy these requirements

The telecommunication transport technologies move from copper based networks to optical fiber

from timeslot based transport to wave length based transport from traditional circuit switching to terabit

router and all optical based networks entering into a new era of optical networking

BASIC PHYSICS OF OFC

OPTICAL FIBER CABLE OFC have Fibers which are long thin strands made with pure glass about the diameter of a human

hair OFC consists of Core Cladding Buffers and Jacket as shown in figure

MONOCHROMATIC LIGHT OR SINGLE COLOR LIGHT Light or visible light is electromagnetic radiation of a wavelength that is visible to the human eye (

about 400 ndash 700 nm) The word light is sometimes used to refer to the entire electromagnetic spectrum Light

is composed of elementary particles called photons Three primary properties of light are

Light can exhibit properties of both waves and particles This property is referred to as wave-particle

duality The study of light known as optics In free space light (of all wavelengths) travels in a straight path

at a constant maximum speed However the speed of light changes when it travels in a medium and this

change is not the same for all media or for all wavelengths By free space it is meant space that is free from

matter (vacuum) andor free from electromagnetic fields

Thus the speed of light in free space is defined by Einsteinrsquos equation E = mc2

Frequency ν speed of light in free space c and wavelength λ are interrelated by ν = cλ

From the energy relationships E = mc2 = hν and the last one an interesting relationship is obtained

the equivalent mass of a photon m = hνc2

When light is in the vicinity of a strong electromagnetic field it interacts with it From this interaction

and other influences its trajectory changes direction as shown in figure

23 | P a g e

INCIDENT RAY REFLECTED RAY AND REFRACTED RAY An incident ray is a ray of light that strikes a surface The angle between this ray and the

perpendicular or normal to the surface is the angle of incidence Reflection is the change in direction of a

wave front at an interface between two different media so that the wave front returns into the medium from

which it originated Common examples include the reflection of light sound and water waves

The reflected ray corresponding to a given incident ray is the ray that represents the light reflected by

the surface The angle between the surface normal and the reflected ray is known as the angle of reflection

The Law of Reflection says that for a specular (non-scattering) surface the angle of reflection always equals

the angle of incidence The refracted ray or transmitted ray corresponding to a given incident ray represents

the light that is transmitted through the surface The angle between this ray and the normal is known as the

angle of refraction and it is given by Snells Law

The figure shows Incident ray Reflected ray Refracted ray the angle of incidence and angle of refraction

REFRACTIVE INDEX - Refractive index is the speed of light in a vacuum ( c =299792458kmsecond) divided by the speed

of light in a material ( v ) Refractive index measures how much a material refracts light Refractive index of

a material abbreviated as lsquo n lsquo is defined as lsquo n=cv lsquo Light travels slower in physical media than it does

when transmitted through the air Refractive index (n) is a function of molecular structure of matter optical

frequency optical intensity determines optical propagation properties of each wavelength ( λ ) may not be

distributed equally in all directions is affected by external temperature pressure and fields

Refractive index of a medium is a measure for how much the speed of light is reduced inside the

medium For example typical glass has a refractive index of 15 which means that light travels at 1 15 =

067 times the speed in air or vacuum Two common properties of glass and other transparent materials are

directly related to their refractive index

First light rays change direction when they cross the interface from air to the material and effect that

is used in lenses and glasses

Second light reflects partially from surfaces that have a refractive index different from that of their

surroundings

SNELLrsquoS LAW-

24 | P a g e

When light passes from one transparent material to another it bends according to Snells law which

is defined as n1sin(θ1) = n2sin(θ2)

where n1 is the refractive index of the medium the light is leaving θ1 is the incident angle between the light

beam and the normal (normal is 90deg to the interface between two materials)

n2 is the refractive index of the material the light is entering

θ2 is the refractive angle between the light ray and the normal

Snellrsquos law gives the relationship between angle of incidence and angle of refraction

For the case of θ1 = 0deg (ie a ray perpendicular to the interface) the solution is θ2 = 0deg regardless of

the values of n1 and n2 That means a ray entering a medium perpendicular to the surface is never bent The

above is also valid for light going from a dense (higher n) to a less dense (lower n) material the symmetry of

Snells law shows that the same ray paths are applicable in opposite direction

TOTAL INTERNAL REFLECTION- When a light ray crosses an interface into a medium with a higher refractive index it bends towards

the normal Conversely light traveling cross an interface from a higher refractive index medium to a lower

refractive index medium will bend away from the normal

This has an interesting implication at some angle known as the critical angle θc light traveling from

a higher refractive index medium to a lower refractive index medium will be refracted at 90deg in other words

refracted alon g the interface If the light hits the interface at any angle larger than this critical angle it will

not pass through to the second medium at all Instead all of it will be reflected back into the first medium a

process known as total internal reflection

The critical angle can be calculated from Snells law putting in an angle of 90deg for the angle of the refracted

ray θ2 This gives θ1

Since θ2 = 90deg

So sin(θ2) = 1

25 | P a g e

Then θc = θ1 = arcsin(n2n1)

For example with light trying to emerge from glass with n1=15 into air (n2 =1) the ritical angle θc is

arcsin(115) or 418deg For any angle of incidence larger than the critical angle Snells law will not be able to

be solved for the angle of refraction because it will show that the refracted angle has a sine larger than 1

which is not possible In that case all the light is totally reflected off the interface obeying the law of

reflection

OPTICAL FIBER MODE An optical fiber guides light waves in distinct patterns called modes Mode describes the distribution

of light energy across the fiber The precise patterns depend on the wavelength of light transmitted and on the

variation in refractive index that shapes the core In essence the variations in refractive index create

boundary

conditions that shape how light waves travel through the fiber like the walls of a tunnel affect how sounds

echo inside

We can take a look at large-core step-index fibers Light rays enter the fiber at a range of angles and

rays at different angles can all stably travel down the length of the fiber as long as they hit the core-cladding

interface at an angle larger than critical angle These rays are different modes Fibers that carry more than

one mode at a specific light wavelength are called multimode fibers Some fibers have very small diameter

core that they can carry only one mode which travels as a straight line at the center of the core These fibers

are single mode fibers This is illustrated in the following picture

OPTICAL FIBER INDEX PROFILE Index profile is the refractive index distribution across the core and the cladding of a fiber Some

optical fiber has a step index profile in which the core has one uniformly distributed index and the cladding

has a lower uniformly distributed index Other optical fiber has a graded index profile in which refractive

index varies gradually as a function of radial distance from the fiber center Graded-index profiles include

power-law index profiles and parabolic index profiles The following figure shows some common types of

index profiles for single mode and multimode fiber

26 | P a g e

OPTICAL FIBERrsquoS NUMERICAL APERTURE ( NA )- Multimode optical fiber will only propagate light that enters the fiber within a certain cone known as

the acceptance cone of the fiber The half-angle of this cone is called the acceptance angle (see figure 18)

θmax For step-index multimode fiber the acceptance angle is determined only by the indices of refraction

Where

n is the refractive index of the medium light is traveling before entering the fiber

nf is the refractive index of the fiber core

nc is the refractive index of the cladding

NUMBER OF MODES IN A FIBER - Modes are sometimes characterized by numbers Single mode fibers carry only the lowest-order

mode assigned the number 0 Multimode fibers also carry higher-order modes The number of modes that

can propagate in a fiber depends on the fiberrsquos numerical aperture (or acceptance angle) as well as on its

core diameter and the wavelength of the light For a step-index multimode fiber the number of such modes

Nm

Where

D is the core diameter

λ is the operating wavelength

NA is the numerical aperture (or acceptance angle)

MODE FIELD DIAMETER - All light do not travels through the core of the fiber but is distributed through both the core and the

cladding The mode field is the distribution of light through the core and cladding of a particular fiber

Mode-Field Diameter (MFD) defines the size of the power distribution When coupling light into or out of a

fiber MFD is important in understanding light loss

27 | P a g e

ADVANTAGE OF OFC COMMUNICATION - bull More information carrying capacity Fibers can handle much higher data rates than copper More

information can be sent in a second

bull Free from Electromagnetic and Electrostatic interference Being insulator no electric current flows through

the fibre and due to this reason fibres neither radiate nor pick up electro - magnetic radiation So WPC

CLEARANCE is not required

bull Low attenuation 025 dbkm at 1550 nm Loss in twisted pair and coaxial cable increases with frequency

where as loss in the optical fibre cable remains flat over a wide range of frequencies

bull Use of WDM ndash Switching routing at Optical signal level

bull Self healing rings under NMS control

bull Small size makes fibre cable lighter in weight So easy to handleOptic fibre cable weight (approx)

500 kg km Copper cable weight (approx) 1000 kgkm

The reasons are photons of light in a fibre

do not affect each other as they have no electrical charge and they are not affected by stray photons outside

the fibre But in case of copper electrons move through the cable and these are affected by each other

Optical fibre does not carry any electricity even if the cable is damaged or short circuited it does

not cause any spark or fire hazard

As the fibre do not radiate energy it can not be detected by any nearby antenna or any

other detector The fibres are difficult to tap and therefore excellent for security

As the signal transmission is by digital modulation there is no chance of cross talk in

between channels

Only by adding a few additional terminal and repeater equipments the

capacity of the system can be increased at any time once the cable is laid

ical effects and temperature variations

LIMITATIONS OF OFC -

difficult

- utilised

APPLICATION IN SIGNAL AND TELECOMMUNICATIONS transmission circuits

-haul circuits for linking of telephone exchanges

28 | P a g e

PROPAGATION MODES CONCEPT -

MODE - Mode is an available distribution of electromagnetic field in a plane transverse to the direction of

light propagation Each mode is characterized by frequency polarization electric field strength and

magnetic field strength Available patterns are derived from Maxwellrsquos equations and boundary conditions

LINEARLY POLARIZED (LP) MODE A mode for which the field components in the direction of propagation are small compared to

components perpendicular to that direction An optical fibre supports only different field patterns called as

lsquoLinear Polarizedrsquo or lsquo LPrsquo modes The reasons are

requirements

de

the accrual of power carried by different modes

There are two basic types of fiber Multimode fiber and Single-mode fiber

Multimode fiber is best designed for short transmission distances This is suited for used in LAN systems and

video surveillance Single mode fibre is best designed for longer transmission distances This is suitable for

long distance telephony and multi channel television broadcast systems

29 | P a g e

MULTI MODE FIBER Multimode fiber the first to be manufactured and commercialized simply refers to the fact that

numerous modes or light rays are carried simultaneously through the waveguide Modes result from the fact

that light will only propagate in the fiber core at discrete angles within the cone of acceptance MM fiber type

has a much larger core diameter compared to single-mode fiber allowing for the larger number of modes

and

is easier to couple than single-mode optical fiber Multimode fiber further categorized as Multimode step-

index and Multimode graded index fiber

PROPAGATION THROUGH MMSI FIBER Figure shows the principle of total internal reflection applies to multimode step index fiber Because

the corersquos index of refraction is higher than the claddingrsquos index of refraction the light that enters at less than

the critical angle is guided along the fiber

Three different light waves travel down the fiber One mode travels straight down the center of the

core A second mode travels at a steep angle and bounces back and forth by total internal reflection The third

mode exceeds the critical angle and refracts into the cladding Naturally it can be seen that the second mode

travels a longer distance than the first mode causing the two modes to arrive at separate times

PROBLEMS WITH MMSI FIBER AND SOLUTION This disparity between arrival times of the different light rays is known as dispersion and the result is

a muddied signal at the receiving end It is important to note that high dispersion is an unavoidable

characteristic of multimode step-index fiber The solutions are either use Graded index fiber or Single mode

fiber

PROPAGATION THROUGH MMGI FIBER Multimode Graded-index refers to the fact that the refractive index of the core gradually decreases

farther from the center of the core The increased refraction in the center of the core slows the speed of some

light rays allowing all the light rays to reach the receiving end at approximately the same time reducing

dispersion Figure shows the Light propagation principle through multimode graded-index fiber The corersquos

central refractive index ( nA ) is greater than that of the outer corersquos refractive index ( nB )

It is very clear from the figure the light rays no longer follow straight lines they follow a serpentine path

being gradually bent back toward the center by the continuously declining refractive index This reduces the

arrival time disparity because all modes arrive at about the same time The modes traveling in a straight line

30 | P a g e

are in a higher refractive index so they travel slower than the serpentine modes These travel farther but

move faster in the lower refractive index of the outer core region

PROPAGATION THROUGH SMSI FIBER Single mode fiber has a much smaller core that allows only one mode of light at a time to propagate

through the core The figure shows the single mode fiber

Single-mode fiber exhibits no dispersion caused by multiple modes Single-mode fiber also offers lower fiber

attenuation than multimode fiber Thus more information can be transmitted per unit of time because it can

retain the fidelity of each light pulse over longer distances Like multimode fiber early single-mode fiber was

generally characterized as step-index fiber meaning the refractive index of the fiber core is a step above that

of the cladding rather than graduated as it is in graded-index fiber Modern single-mode fibers have evolved

into more complex designs such as matched clad depressed clad and other exotic structures

SINGLE-MODE FIBER DISADVANTAGES The smaller core diameter makes coupling light into the core more difficult The tolerances for single-

mode connectors and splices are also much more demanding

CUTOFF WAVE LENGTH - Cutoff wavelength is the wavelength above which a single-mode fiber supports and propagates only

one mode of light In other words an optical fiber that is single-mode at a particular wavelength may have

two or more modes at wavelengths lower than the cutoff wavelength The effective cutoff wavelength of a

fiber is dependent on the length of fiber and its deployment The longer the fiber the lower is the effective

cutoff

wavelength The smaller the bend radius of a loop of the fiber the lower is the effective cutoff wavelength If

a fiber is bent in a loop the effective cutoff wavelength is lowered

SIGNAL ATTENUATION IN FIBER - Optical fiber has a number of advantages over copper However it also suffers from degradation

problems which can not be ignored The first of these is loss or attenuation Attenuation is typically the result

of two sub properties They are scattering and absorption Both of which have cumulative effects The second

is

dispersion which is the spreading of the transmitted signal and is analogous to noise

SCATTERING Scattering occurs because of impurities or irregularities in the physical construction of the fiber The

well known form of scattering is Rayleigh Scattering It is caused by metal ions in the silica matrix and

results in light rays being scattered in various directions

31 | P a g e

Scattering limits the use of wavelengths below 800nm The short wavelengths are much affected than longer

wavelengths It is because of Rayleigh scattering that the sky appears to be blue ( shorter wave length ) The

shorter wavelengths ( blue ) of light are scattered more than the longer wavelengths of light

ABSORPTION Absorption results from three factors They are hydroxyl ions ( OH- water ) in the silica impurities

in the silica and incomplete residue from the manufacturing process These impurities tend to absorb the

energy of the transmitted signal and convert it to heat resulting in an overall weakening of the signal The

Hydroxyl absorption occurs at 125 and 139 micro The silica itself starts to absorb energy at 17 micro

because of the natural resonance of the silicon dioxide

MACRO BENDING LOSS Macro-bending loss is caused by bending of the entire fiber axis The bending radius shall not be

sharper than 30d where d is diameter of cable A single bend sharper than 30d can cause loss of 05dB

The fiber may break if bending is ever sharper

MICRO BENDING LOSS Micro-bending loss is caused by micro deformations of fiber axis which leads to failures in achieving

total internal reflection conditions Micro-bends are small scale perturbations along the fiber axis the

amplitude of which are on the order of microns These distortions can cause light to leak out of a fiber

Micro-bending may be induced at very cold temperatures because the glass has a different coefficient of

thermal expansion from the coating and cabling materials At low temperatures the coating and cable

become more rigid and may contract more than the glass Consequently enough load may be exerted on the

glass to cause micro bends

Coating material is selected by manufacturers to minimize loss due to micro-bending The linear thermal

expansion coefficient of coating material shall be compatible with that of fiber

32 | P a g e

DISPERSION Dispersion is the optical term for the spreading of the transmits in the fiber It is the bandwidth

limiting phenomenon and comes in two forms Multimode dispersion and chromatic dispersion Chromatic

dispersion is further subdivided into material dispersion and waveguide dispersion

DISPERSION PHENOMENON IN OPTICAL FIBER Dispersion is the time distortion of an optical signal that results from the differences of time of travel

for different components of that signal typically resulting in pulse broadening As the distance traveled by

the signal is more broadening of pulse is more In digital transmission dispersion limits on the maximum

data rate and the maximum distance ie the information-carrying capacity of a fiber link The interference

from broadened pulse in the next interval shall not lead to erroneous interpretation of received signal

OPTICAL DOMAIN Understanding where attenuation and dispersion problems occur helps optical design engineers

determine the better wavelengths at which information can be transmit taking into account distance type of

fiber and the other factors which can severely affect the integrity of the transmitted signal The graph shown

depicts the optical transmission domain as well as the areas where problems arise The wavelength (nm)

is shown on X-axis and attenuation ( dBkm) is shown on Y-axis

There are four transmission windows appear in the figure The first one is at around 850 nm the

second at 1310nm third at 1550 nm and fourth at 1625 nm The last two labeled as C and L band

respectively The 850 nm wavelength at which the original LED technology operated The second window at

1310 nm has low dispersion The 1550 nm called as C-band is ideal wavelength for long haul

communication systems The network engineers can avoid transmitting signal at 1000 nm where Rayleigh

scattering 1240 and 1390 nm where hydroxyl absorption by water occurs to avoid high degree of loss

Optical fibers also can be manufactured to have low dispersion wavelength in the 1550nm region

which is also the point where silica-based fibers have inherently minimal attenuation These fibers are

referred to as dispersion-shifted fibers and are used in long-distance applications with high bit rates For

33 | P a g e

applications utilizing multiple wavelengths it is undesirable to have the zero dispersion point within the

operating

wavelength range

34 | P a g e

SIGNALLING RELAYS

INTRODUCTION A relay is an electromagnetic device which is used to convey information from one circuit to another

circuit through a set of contact ie front or back contact Constructional and electrically relays may be

divided into DC and AC relays because the means by which the electrical energy in the coil is converted in

to mechanical Energy in order to move the contacts are fundamentally different In DC type the contacts are

carried on an armature forming part of a magnetic circuit in which a field is set up by the current flowing in

the coils In AC types the contacts are attached by a link mechanism to a metal sector disc or cylinder in

which currents are induced by the alternating magnetic field produced by the currents in the coils

Every endeavor has been made to explain the action of each type of relay in the simplest possible manner

Relays are sophisticated switch gears used for remote control and succession control of various

electrical equipment In present days they are widely used because they are capable of protecting the

controlled equipment from cross feeding and overloading even as they cater for speedy operations

Most of the relays in present day signaling are electromagnetic devices although some of the relays control

circuits through electronic components like diodetransistors Integrated Chips etc

Railway signaling relays are unique in that

(a) They operate on low voltage and current

(b) They are more articulate as according to their special features they can work under restrictive conditions

and in any specified manner Virtually they can cater for all situations while contributing to speed and

accuracy in operations

CLASSIFICATION OF SIGNALLING RELAYS (a) According to the method of their mounting or fixture they are classified as

(i) Shelf type Relays which are loosely kept on shelves

(ii) Plug in type Relays which are plugged into a pre- wired plug boards

(b) According to their connection and usage they are classified as

(i) Track relays Relay which is directly connected to the track to detect the presence of vehicle

(ii) Line Relays Other than track relay all are line relays Relays connected to the selection circuit

(c) According to their vitality or importance in ensuring train working safety they are classified as

(i) Vital Relays All relays used for traffic control such as signal point controls track detection etc

(ii) Non-vital Relays Relays which operate control aids and accessories like warnings buzzers

Indications etc

(d) According to their special provisions to ensure reliability of their contacts they are classified as

(i) Proved type are those whose normalization after each operation shall be proved in circuit

controlled by their contacts Contacts in which both the springs have metal surfaces on their tips They may

get fused due to high sparking current across them during operation These may prevent relay normalization

and causes unsafe condition in traffic control To avoid this proving of relay normalization after each

operation is necessary

(ii) Non - proved type Need not to be proved to have been normalized after each operation as their

contacts have at least one non-fusible contact (carbon contact)

(e) According to their feed source relays are broadly classified as

(i) DC relays The relay which requires DC power supply for its operations are called DC relays Among

the DC relays

o DC neutral relays This relay closes the same set of contacts on energization with Normal polarity

or Reverse polarity supply

o Polar Relays This relay closes different set of contacts when energized with Reverse polarity

supply They may or may not have contact to close when deenergized

35 | P a g e

(ii) AC Relay AC Induction motor track relays Time element relays flashing indication control etc

(iii) Electronic Relays DC relays with electronic components in them are called electronic relays

DC NEUTRAL RELAY Each Relay has usually one or two coils with a hollow center to accommodate a coreThe coils are

made up of a large numbers of turns of small gauge soft drawn copper wire The two coils can be connected

in series or parallel according to the requirement of relay resistance The ends of the coils are terminated on

binding post to which the control wires are connected Each coil is placed around a core of specially selected

Iron or steel having high permeability and low retentivity The core should be susceptible to magnetism and

at the same time should have little residual magnetism The cores are connected at the top by a yoke to

complete the magnetism coupling between two ends of coils The bottom of each core is equipped with a

large steel or Iron block known as pole piece or face

A flat piece of Iron or steel called armature is supported by brackets which are securely fastened to

the pole piece The armature yoke and the pole pieces are also made of specially selected iron or steel of the

same quality as the core The armature carries the metallic spring contacts which are insulated from it

The circuit through the coils of the relay is closed It sets up a magnetic flux through the core yoke and the

armature The flux passing between the armature and pole faces causes the armatures get attracted to the pole

faces and armature picks up and closes front contacts When the circuit is opened the magnetic flux collapses

and the armature drops away by gravity from the pole faces the front contacts break and back contacts close

The front and back contacts of the relay can be utilised to make or break other circuits Two stop pins of

nonmagnetic material are fixed either on the armature or pole faces so that the armature cannot

come in contact with the pole faces It is essential to maintain a small air-gap between the armature and pole

faces so that low value of residual magnetism may not retain the armature in picked up position and causes

the relay to fail to drop away with a break in its control circuit

GENERAL USAGE

DC Neutral line relays are most commonly used for Railway Signalling controls and detection

Among them plug-in type relays are preferred in larger installations for space considerations Shelf type

relays are also in use mostly in wayside stations

There are many DC Neutral line relays in use with special features such as

(i) Delayed operation

(ii) Biased DC control

(iii) DC control unaffected by AC interference currents

(iv) Getting latched in operated condition till further feeding and others

Usage of DC polar relays is mostly in conjunction with block instruments that control traffic between

stations AC line relays are almost extinct in installations of British Signalling practice They are however

used for time control operations flashing indication control and such other special purposes in installations

with Siemens signalling practice widely Track relays are used according to the type of track detection

circuits chosen for a given location and context While most of the track circuits are still of the DC working

type requiring DC neutral track relays with them the prospects of their being replaced with Electronic track

circuits directly feeding DC line relays in future are great AC Track Circuits are used in DC Traction area

as conventional DC Track Circuits are not suitable there AC Track relays are used with them almost all of

the induction motor type In the British practice of signalling which was first introduced on Indian Railways

non-proved type relays with carbon to metal switching contacts are generally used for vital controls

They facilitate simple circuit designs But with the advent of German Practice introduced by Ms

Siemens later proved type relays with all metal to metal contacts are widely accepted in spite of

complications in circuit design caused by them A recent introduction is that of the same type relays made by

Ms Integra control However for some time now the appreciable features of both the practices are getting

36 | P a g e

incorporated together in the indigenous designs of signalling by railwaymen With this the usage of all types

of relays anywhere can be found without straight jacketed segration of relay types

CHARACTERSTIC OF ELECTRO-MAGNETIC RELAY The following are the characteristic of electro-magnetic relays A brief study of them helps in

understanding the choice of their components and designs features

1) Force of attraction

2) Effect of air gap

3) Effect of Hysterisis

4) Transient condition

FORCE OF ATTRACTION In any electro-magnetic system the force of attraction is given by

Where B - is the flux density a - is the cross sectional area of the particular part of the magnetic

circuit

In the case of a DC neutral Relay B is proportional to the current that is flowing in the coil

surrounding the electro-magnet and thus the force of the attraction is directly proportional to the square of the

current This square relationship has its own advantage especially in the case of DC track relay in that a

small reduction in the current will have a great effect on the working of the relay Also for a given change of

current the make and the break will be quicker with lesser possibility of arcing

EFFECT OF AIR GAP

Curve lsquoArsquo is magnetisation curve for the iron and is all practical purpose a straight line up to the

saturation point Curve lsquoBrsquo is the magnetisation curve for the open-air gap which is a straight line through

out because per magnetisation curve of the whole

magnetic circuit of the relay and for a given force is the sum of the amp-turns for the iron part and the amp-

turns for the air gap

When the front contacts are open the force required to pick up the armature is shown on curve lsquoCrsquo to be F1

but after the armature has operated it will be separated from the core by stop pins In this position the amp-

turns required to maintain the armature is less as indicated by the dotted line from 1 on curve C to 2 on curve

37 | P a g e

F But actually the current in the coil is unaltered the force on the armature is greater than required as

indicated at 3 on curve F Part of this extra force is used to flex the front contacts sufficiently to give good

contact pressure when it is in energised position

The difference between the pick-up and the drop-away current should be as small as practicable in

track relay to ensure good shunting characteristics This is achieved firstly by the choice of good quality relay

iron and secondly by having a small air gap between armature and core If the air gap is not available then

the residual magnetism fluxes might cause the armature to be retained when the supply is disconnected For

this reason residual pins are provided to ensure a definite minimum air gap in the energised position

EFFECT OF HYSTERISIS

Hysterisis is the property by which the flux produced lags behind the current In the de-energized

condition there will be small residual flux in the core When the voltage is applied to the coils the current in

rising to its steady value first causes the flux to rise from 1 to 2 along the curve At this point the flux density

will be sufficient to attract the armature and reduce the air gap the flux then raise to 3 and continue to 4

which corresponds to the steady current in the coils When the voltage is disconnected the current in falling

caused the flux to fall from 4 to 5 along the curve At this point the flux density will fall below the value

required to maintain the armature which will release thus increasing the air gap and reducing the flux to 6

Finally the

flux will decrease from 6 to 1 where the current will again be zero

The relay core is made of material having high permeability and low retentivity As mentioned in

the IRS specification Electromagnet iron may be in the form of a

(a) Bar of silicon steel

(b) Best Yorkshire wrought iron

(c) Swedish charcoal iron

(d) Electrical steel sheets

` This reduces the difference between pick up value and Drop away value By selecting good quality

core material Percentage release and sensitivity of the relay will be improved

TRANSIENT CONDITION

38 | P a g e

When the voltage is applied or disconnected from the coils it takes some little time before the current

become steady These are known as transient conditionsrdquo and are important so far as track relays are

concerned When the voltage is first applied to the coils the magnetic flux in rising cuts the turns on the

coils and in so doing produces a back EMF that opposes the applied voltage and retards the growth of

current

The growth and decay of flux are decided by the relationship between the inductance and resistance

in the circuit is known as time constant It is not fixed quantity in the case of DC neutral relay This value of lsquo

Lrsquo is less when the relay is in de-energised condition (L1) than when the relay is in energised condition (L2)

The magnitude of flux that is established for a given change of current is different in two cases

When the current reaches the pick up value the armature closes and the inductance is increased to L2

due to reduced air gap the flux per amp is increased The increase in flux increased the back EMF during the

movement of the armature after which the current continuous to raise along a new curve corresponding to the

increased inductance until it reaches the final value (ER) This process is indicated above in fig24

When the supply is disconnected the current is obliviously reduced to zero immediately but the flux

decay comparatively slowly owing to the eddy currents produced in the core by the rapid flux change which

tend to maintain the flux The drop away time on a disconnection is however generally negligible See fig

below

If the relay releases due to the reduction in current from say I 2 to I 1 caused by the application of

shunt resistance (as in the case of track relay ) the time taken is much longer than the relay is simply

disconnected The rate of rise or fall of current during the transient conditions is also depends on exterior

circuit values because L and R apply to the whole circuit The production of eddy current in the core the flux

will decay at a slower rate than the current So that the actual release time will be a little longer than it takes

the current to fall to the release

L= Inductance

39 | P a g e

R= Resistance

It is now clear that to reduce releasing time to a minimum it is necessary that

- The relay iron should have low Hysterisis loss and low retentivity

- The degree of over energization of the relay should be restricted

- Connecting a suitable external resistance in series with the relay to keep LR ratio low

In non RE area for track circuit length less than 100M 9 ohm track relay only to be used Using relay

with minimum contacts as they require lesser current which keeps inductance value low

Train working safety is ensured only if the track relay of shortest length track circuit is released

before a light engine running at a highest permitted speed clears it Otherwise the track circuit occupation

may go undetected To avoid this a special provision has to be made in signal control circuits wherever

necessary

The following methods may be adopted for reducing the time lag of track relay

(a) Restrict the over energisation of relay since the release time depends on the initial working current

(b) Connecting a suitable external resistance in series with the relay to keep the LR ratio low

(c) Using relays with minimum contacts as they require lesser operating current keeping the inductance

value low

40 | P a g e

CONCLUSION

Modern signalling is vital for safe and punctual movements of trains In the Indian railways The Signalling

and Telecommunication Department is responsible for providing modern effective and relaible signalling

systems as well as telecommunication systems

The first mode of communication used in Indian Railways was the use of electric telegraph

with the help of Morose code Morose code is the method of providing text information as a series of on-off

tones and lights or clicks that can be directly understood by a skilled listener or observer without special

equipmentEach character (letter or numeral ) is represented by a unique sequence of dots and dashes Later

this system becomes obselete and beggan the era of wireless communication which operated at audio level

frequency range

In wireless communication the significant advances took place the transition to miniature

valves or filament tubesBut this was abandoned too because of excessive current consumption and over

heating of the filament tubes

Fibre-optic communication is a method of transmitting information from one place to another by

sending pulses of light through an optcial fibreThe light forms an electromagnetic carrier wave that is

modulated to carry information First developed in the 1970s fibre optic communication systems has

revolutionized the telecommunications industry and have palyed a major role in the advent of the information

age Because of its advantages over electrical transmissionsoptical fibres have largely replaced copper wire

communications in core networks in the developed world The Indian Railways too is undergoing a transition

from Microwave communication to fibre optic communications

41 | P a g e

BIBLIOGRAPHY AND REFERENCES

1 wwwwikipediacom

2 wwwbritaniccacom

3 wwwirfcacom

4 Motorola GP60 system manual

5 Harris FAS 7000 manual

6 TOSHIBA Manual

15 | P a g e

DATALOGGER

INTRODUCTION Datalogger is a Microprocessor based system which helps in analysing the failures of relay inter

locking system Electronic Interlocking system This is like a black box which stores all the information

regarding the changes take place in relays AC DC Voltages and DC currents along with date and time The

same information data can be transferred to the computer to analyse further ldquoon line ldquooff linerdquo analysis of

stored date A print out also can be obtained through a printer by connecting directly to the datalogger unit

The data belongs to Relay contacts is considered as digital inputs and the data belongs to voltage

levels currents is considered as Analog inputs Datalogger lsquos are mandatory for all new relay interlocking

(PIRRI) EI installations and it is also recommended to provide in all existing PIs RRIs To increase the

line capacity mechanical signalling equipments are upgraded to PI RRI or EI Due to complexity in the

circuits and wiring sometimes it is very difficult to rectify the failures So datalogger can monitor these

systems with real time clock Thus it can be named as black box of Samp T equipments and hence it is a vital

tool for accident investigation Datalogger is used at Stations yards Whereas in case of Auto Section amp IBH

Mini dataloggers called as Remote Terminal Unit (RTU) are used

ADVANTAGES OF DATALOGGERS (a) Dataloggers helps in monitoring the typical failures such as intermittent auto right failures

(b) It helps in analyzing the cause of the accidents

(c) It helps in detecting the human failures errors such as

(i) Drivers passing signal at Danger

(ii) Operational mistakes done by panel operators ASMrsquos of operating department

(iii) Signal and telecom engineering interferences in safety circuits

(iv) Engineering and electrical department interferences failures

(v) It helps as a ldquoTOOLrdquo in preventive maintenance of signaling gears

(d) Dataloggers can be connected in network Networked dataloggers helps to monitorthe PIRRIEI remotely

(e) Failure reports can be generated remotely with help of datalogger network

(f) On line and Off line track simulation is possible

(g) Speed of the train on point zones can be calculated

(h) Age of the equipment in terms of number of operations etc

COMMON EQUIPMENT FOR ALL DATALOGGERS ARE GIVEN

BELOW (a) CPU card

(b) Digital and Analog input cards

(c) Local terminal(PC)

(d) communication links

(e) Printer

All the dataloggers requires a potential free ( spare ) relay contact for monitoring digital inputs

through Digital input cards amp for monitoring Analog inputs such ACDC bus bar voltage levels through

Analog input cards Digital and Analog inputs are connected to the Processor card Processor card consists of

memory ICrsquos Memory ICrsquos are programmed as per requirement of the signal engineers

Provision of Dataloggers is mandatory with RRI systems and is optional for PI systems as per

amendment to the specification for Relay Interlocking systems ( IRSS-36 ) The data collected by the

datalogger can be used for failure analysis repetitive discrepancies and for accident investigations

16 | P a g e

Note

If the serial communications is more than 50m then line drivers shall be used up to 3 Kms

4wire leased line Modems shall be used if the serial communication is more than 3 Kms

STUDY OF EFFTRONICS DATALOGGER TECHNICAL DETAILS (a) 24V 12VDC Power Supply

(b) Total Storage Capacity of 10 Lakh events

(c) In-built Temperature sensors

(d) Internal Buzzer for alarming during failures

(e) Real Time clock with internal battery backup with data retention up to 10 years

(f) 512 LED matrix to indicate the status of 512 Digital inputs at a time page wise

(g) Seven segment LCD screen (2x24) to display the status of digitalanalog signalsTime Temperature etc

(h) Using the keyboard various functions can be viewed in the LCD panel

(i) Max Digital Inputs 4096

(j) Max Analog Inputs 96

(k) Digital Input Scanning Time 16 millisecond

(l) Analog Input Scanning Time is less than 1 Sec

HARDWARE (EQUIPMENT) Datalogger system consists of

(a) Datalogger (CPU - with Microprocessor 68000)

(b) Digital input cards

(c) Dual modem card

(d) Digital Scanner units (DSU)

(e) Analog Scanner units (ASU)

CPU CARD It is provided with Motorola microprocessor M 68000 It performs all the activities pertaining to the

datalogger It continuously scans (check) the Digital inputs(inbuilt) Digital Scanner Units and Analog

Scanner Units ie scanning of digital signals (Relay operations) for every 16-milli seconds and scanning of

analog signals (ie ACDC voltages amp DC currents) for less than 1 second

This card will support the IO interfaces of LCD (Liquid Crystal Display) - 2X24 alphanumeric Key

Board LED Matrix Display Real Time Clock LCD display and keyboard This will acts as man machine

interface between the datalogger and the signal engineer All the operations (Software) can be performed

using this LCD and keyboard

Real time display with 7 Segments This is built in real time clock within Datalogger and its current

time will be displayed on six 7-segment display provided (Real time clock depend upon DALLAS 1286

chip) This IC will come with internal battery backup hence there is no need to add external batteries

CPU card continuously scans (checks) the DSUs and ASUs Each input connected to digital scanner

units are optically isolated by Opto couplers When CPU card scans the digital inputs it compares with the

previous stored data and if there is any change from the previous status then only that data will be stored (the

status conditions of relay) with date and real time A total of minimum 10 Lac events can be stored in

memory on first in first out basis so that latest data is available in the system There is no loss of data from

datalogger memory in case of power supply failure of datalogger

DIGITAL INPUT CARDS (IN-BUILT) This system is having maximum 8nos of inbuilt Digital inputs cards Maximum 64nos of digital

inputs can be connected to each digital input card The potential free relay contact may be front or back

contact terminated at the Tag Block from the relay of signals tracks points Buttons etc and are

17 | P a g e

subsequently connected to Digital input cards through Flat Ribbon Cable (FRC) connectors These in-built

digital input cards can monitor a total 512 nos of relays status

DIGITAL SCANNER UNIT (DSU) Each DSU contains 8 nos of Digital Input cards Each input card can be connected with 64 inputs

Total input capacity of DSU unit is 512 inputs These scanner cards contain Optocouplers and Multiplexer

Inputs are connected to Stag card The stag card out put is connected to DSU through FRC connectors

Maximum 7 nos of DSUs can be connected to the system So Digital input capacity of the system is 4096

All these digital inputs are scanned at rate of 16 msec

ANALOG SCANNER UNIT (ASU) ASU contains maximum 3 nos of Analog input cards Each input card can be connected with 8nos of

Analog inputs Total input capacity of the ASU is 24 analog input channels Maximum 4nos of ASUs can be

connected to the system Analog input channel capacity of the system is 96 All these analog inputs are

scanned at a rate of less than 1 sec

PARALLEL PORT Parallel port is provided for connecting printer

RS-232 SERIAL PORTS At least 6 Serial communication ports are provided for communication with other dataloggers

Central Monitoring Unit Remote Terminal Unit Electronic Interlocking system Integrated Power Supply

system etc

EXTERNAL NON-VITAL RELAY CONTACTS These relays provided in the system where 16 number of the Relay contacts are provided on the rear

panel through Tele control port to extend alarms and to control the power equipment from remote or local

locations through computer in case of any occurrence of failures Each control can sink or source 100 m

amps of current

INTERNAL MODEM CARD DUAL MODEM CARD (IN-BUILT) It is fixed in datalogger Euro rack itself One card contains two modems The top modem is called

ANS (answer) modem and the bottom modem is called as ORG (originate) modem It is used in case of

networking of Dataloggers In network connect lsquoANSrsquo modem to the lsquoORGrsquo modem of one adjacent station

and connect lsquoORGrsquo modem to the lsquoANSrsquo modem of other adjacent station

POWER SUPPLY Normally 24V DC (12V DC is optional) supply with battery backup is required for the system

working

Input Voltage Range 18Vhellip32V DC (For 24V) 9Vhellip18V DC (For 12V)

INPUT REQUIREMENTS Relay inputs (digital inputs) and analog inputs (voltages currents etc) are required to be connected

to the system as per the requirements of RRI PI SSI as the case may be Some of the inputs to be

monitored is given below

(a) Digital inputs

(i) Field inputs All TPRs NWKRs RWKRs ECRs Crank Handle relays SidingSlot LC gate

control relays etc

(ii) Control Panel inputs All button Knob SMrsquos Key relays

18 | P a g e

(iii) Internal relays

British system All HR DR HHR WNR WRR ASR UCR RR LR UYRTLSR TRSR TSR

JSLR JR etc

SIEMENS system Z1UR Z1UR1 GZR ZDUCR ZU(R)R ZU(N)PRG(R)RG(N)R U(R)S

U(N)PS UDKR DUCR U(R)LR UYR1 UYR2 G(R)LRGR1GR2

GR3 GR4 OVZ2U(R)RW(RN)R (RN)WLR Z1NWR Z1RWRZ1WR1 WKR1 WKR2 WKR3 etc

(b) Analog channels

(i) 230 V AC (for power supplies in the power panel)

(ii) 110V AC (for Signal and Track transformers)

(iii) 110V DC (for Point operation)

(iv) 60V DC (Siemens relays)

(v) 24V DC (Q-series relays)

(vi) 24V DC (for Block Axle counters)

(vii) 12V DC (for indication)

(viii) 20A (for point operation current)

(ix) 10V AC 5KHz (for Axle counter channels) etc

SOFTWARE MODULES OF DATALOGGERS

(a) Network Management of Dataloggers (NMDL)

(b) Reports

(c) Fault Entry

(d) Track Offline Simulation

(e) Train Charting

NMDL SOFTWARE FEATURES (a) Online Relay Status

(b) Online Faults - To view information of various Online Faults as they occur in the stations where

the Dataloggers are connected

(c) Online Simulation - Graphical view of relay operations train movements etc

(d) Remote monitoring of stations with the help of NETWORKING

SOFTWARE OBJECTIVES (a) Predictive Maintenance

(b) Easy identification of failures

(c) Crew discipline

(d) Train charting

REMOTE MONITORING OF STATIONS WITH NETWORKING OF

DATALOGGERS The individual Dataloggers of various stations can be interconnected through networking technology

The data of Remote Panel stations can be viewed in a Computer at the Central Monitoring Station The data

of the network is collected by the FEP (Front End Processor) which in turn is transmitted to the computer

COMPONENTS OF NETWORK MANAGEMENT OF DATALOGGERS

(a) Datalogger at stations

(b) MODEM and Transmission medium

19 | P a g e

(c) Front End Processor (FEP)

(d) Central Monitoring Unit (CMU) Computer

FEP (FRONT END PROCESSOR)

FEP acts as a buffer between the Central Monitoring Unit (Computer) and the Network It is provided

at centralised place to retrieve data continuously from station dataloggers and store in memory and transfer to

computer on request It stores 10 Lac telegrams It works on 12V DC It draws 16A continuous current

when all the three modems are connected Normally it shows the number of packets pending to be sent to the

computer on its 7-segment LED display It is provided with MOTOROLA 68000 microprocessor It has 6-

nos of RS-232 communication ports such as COM1 COM2 COM3 COM4 COM5 and COM6 COM1 is

used for Fault Analysis System (FAS) ie Central Monitoring Unit (Computer) connection COM2 to COM6

are used for networking For Bi-directional 2- nos of ports and for Tri-directional (T-network) 3-nos of ports

are used

DATA TRANSMISSION Dataloggers can be networked in Uni-directional Mode or Bi-directional Mode or T ndash Network Mode

In case of loss of data retransmission of data takes place

(a) Uni-Directional Mode

Each Datalogger will send data in only one direction to the FEP Unidirectional mode network is not

preferred

(b) Bi-Directional Mode

Each end of Network is connected to FEP and each datalogger can now transmit data in both the directions

Bi-directional Mode is advantageous it enables the Data Transmission even in case of Network Failure

(c) T - Network Mode

If more no of stations are in network ie if the network is too lengthy then T- network mode is preferred

COMMUNICATION The communication protocol for transmitting data and command between datalogger and CMU is

standardized by the RDSO and is given in the Specifications of Dataloggers

(a) The type of communication used in the network is dependent on the distance between the dataloggers

(b) For shorter distances Opto Converter Box- Opto isolated current loop communication is used

(c) For longer distances Modem (Dial-up leased) Fiber Optic Satellite Microwave communication

MODEMS Modems are used for DATA transfer between Dataloggers and Front End ProcessorThese are

configured to RS 232 Serial Communication Network is connected with two types of 4-wire modems

(a) Internal modem card Dual Modem card (in-built)

It is fixed in datalogger Euro rack itself One card contains two modems The top modem is called

ANS (answer) modem and the bottom modem is called as ORG (originate) modem

Note In case of networking of Dataloggers connect lsquoANSrsquo modem to the lsquoORGrsquo modem of one adjacent

station and connect lsquoORGrsquo modem to the lsquoANSrsquo modem of other adjacent station

(b) External modems

20 | P a g e

These are generally used at FEP (Front End Processor) side to connect the Dataloggers

(i) To transfer Data from one datalogger to another datalogger FEP Baud rate is 9600bps

(ii) These modems are 4-wire line communication

(iii) To transfer the data from FEP to RMU (PC) the Baud rate is 57600 bps

There is no difference between these modems functionally

CENTRAL MONITORING UNIT (CMU) COMPUTER

Central monitoring unit (Fault Analysis Unit) is a Personal Computer and its minimum configuration

shall be specified by RDSO from time to time System Software Windows XPVista(OS) Norton Kaspersky

(Anti Virus) Interbase where Server is not available (DBMS) Oracle where Server is available (DBMS)

software are required to run Datalogger System It is provided with Graphical User interface (GUI) based

software and retrieve data from all Networked dataloggers (up to 32) at various stations It stores data in

standard data base files The CMU is capable of analyzing the data and generate reports audiovisual alarms

on defined conditions This data can be compressed to take backup In central monitoring unit Software used

for analysis of data prediction of faults etc is written in a structured format so that purchaser can

reconfigure it if required It displays the status of signaling gears at any selected time in graphic form for any

selected station yard It retrieves the stored data amp simulates train movement It sends commands to various

Dataloggers to activate audio visual alarm or operate and electromagnetic relay

CMU shares data available in it by other PCs through available local area network where this data can

be used for train charting passenger information purpose The system generates audiovisual alarm in

ASMrsquosSignal Maintainerrsquos room in the case of power supply failure (battery voltage low) or battery charger

defective with acknowledgement facility

(a) Each datalogger has its own identity code which will be transmitted along with data packet to central

monitoring unit

(b) Events recorded at each station are continuously transmitted to central monitoring unit Response time of

data transfer will not exceed 10 sec

21 | P a g e

22 | P a g e

OPTICAL FIBER CABLE

INTRODUCTION The demand for bandwidth on transmission networks is increasing rapidly because video and

graphical rich contents are exchanged through the corporate network or the Internet The Gigabit Ethernet

became ommonly used in the corporate network backbone and 10Gbit Ethernet will be adopted in the near

future Meanwhile in the home the demand for high-speed network becomes popular as the wide spread of

broadband access eg CATV xDSL and FTTH The transmission medium with capability to transmit high

bit rate signal is necessary to satisfy these requirements

The telecommunication transport technologies move from copper based networks to optical fiber

from timeslot based transport to wave length based transport from traditional circuit switching to terabit

router and all optical based networks entering into a new era of optical networking

BASIC PHYSICS OF OFC

OPTICAL FIBER CABLE OFC have Fibers which are long thin strands made with pure glass about the diameter of a human

hair OFC consists of Core Cladding Buffers and Jacket as shown in figure

MONOCHROMATIC LIGHT OR SINGLE COLOR LIGHT Light or visible light is electromagnetic radiation of a wavelength that is visible to the human eye (

about 400 ndash 700 nm) The word light is sometimes used to refer to the entire electromagnetic spectrum Light

is composed of elementary particles called photons Three primary properties of light are

Light can exhibit properties of both waves and particles This property is referred to as wave-particle

duality The study of light known as optics In free space light (of all wavelengths) travels in a straight path

at a constant maximum speed However the speed of light changes when it travels in a medium and this

change is not the same for all media or for all wavelengths By free space it is meant space that is free from

matter (vacuum) andor free from electromagnetic fields

Thus the speed of light in free space is defined by Einsteinrsquos equation E = mc2

Frequency ν speed of light in free space c and wavelength λ are interrelated by ν = cλ

From the energy relationships E = mc2 = hν and the last one an interesting relationship is obtained

the equivalent mass of a photon m = hνc2

When light is in the vicinity of a strong electromagnetic field it interacts with it From this interaction

and other influences its trajectory changes direction as shown in figure

23 | P a g e

INCIDENT RAY REFLECTED RAY AND REFRACTED RAY An incident ray is a ray of light that strikes a surface The angle between this ray and the

perpendicular or normal to the surface is the angle of incidence Reflection is the change in direction of a

wave front at an interface between two different media so that the wave front returns into the medium from

which it originated Common examples include the reflection of light sound and water waves

The reflected ray corresponding to a given incident ray is the ray that represents the light reflected by

the surface The angle between the surface normal and the reflected ray is known as the angle of reflection

The Law of Reflection says that for a specular (non-scattering) surface the angle of reflection always equals

the angle of incidence The refracted ray or transmitted ray corresponding to a given incident ray represents

the light that is transmitted through the surface The angle between this ray and the normal is known as the

angle of refraction and it is given by Snells Law

The figure shows Incident ray Reflected ray Refracted ray the angle of incidence and angle of refraction

REFRACTIVE INDEX - Refractive index is the speed of light in a vacuum ( c =299792458kmsecond) divided by the speed

of light in a material ( v ) Refractive index measures how much a material refracts light Refractive index of

a material abbreviated as lsquo n lsquo is defined as lsquo n=cv lsquo Light travels slower in physical media than it does

when transmitted through the air Refractive index (n) is a function of molecular structure of matter optical

frequency optical intensity determines optical propagation properties of each wavelength ( λ ) may not be

distributed equally in all directions is affected by external temperature pressure and fields

Refractive index of a medium is a measure for how much the speed of light is reduced inside the

medium For example typical glass has a refractive index of 15 which means that light travels at 1 15 =

067 times the speed in air or vacuum Two common properties of glass and other transparent materials are

directly related to their refractive index

First light rays change direction when they cross the interface from air to the material and effect that

is used in lenses and glasses

Second light reflects partially from surfaces that have a refractive index different from that of their

surroundings

SNELLrsquoS LAW-

24 | P a g e

When light passes from one transparent material to another it bends according to Snells law which

is defined as n1sin(θ1) = n2sin(θ2)

where n1 is the refractive index of the medium the light is leaving θ1 is the incident angle between the light

beam and the normal (normal is 90deg to the interface between two materials)

n2 is the refractive index of the material the light is entering

θ2 is the refractive angle between the light ray and the normal

Snellrsquos law gives the relationship between angle of incidence and angle of refraction

For the case of θ1 = 0deg (ie a ray perpendicular to the interface) the solution is θ2 = 0deg regardless of

the values of n1 and n2 That means a ray entering a medium perpendicular to the surface is never bent The

above is also valid for light going from a dense (higher n) to a less dense (lower n) material the symmetry of

Snells law shows that the same ray paths are applicable in opposite direction

TOTAL INTERNAL REFLECTION- When a light ray crosses an interface into a medium with a higher refractive index it bends towards

the normal Conversely light traveling cross an interface from a higher refractive index medium to a lower

refractive index medium will bend away from the normal

This has an interesting implication at some angle known as the critical angle θc light traveling from

a higher refractive index medium to a lower refractive index medium will be refracted at 90deg in other words

refracted alon g the interface If the light hits the interface at any angle larger than this critical angle it will

not pass through to the second medium at all Instead all of it will be reflected back into the first medium a

process known as total internal reflection

The critical angle can be calculated from Snells law putting in an angle of 90deg for the angle of the refracted

ray θ2 This gives θ1

Since θ2 = 90deg

So sin(θ2) = 1

25 | P a g e

Then θc = θ1 = arcsin(n2n1)

For example with light trying to emerge from glass with n1=15 into air (n2 =1) the ritical angle θc is

arcsin(115) or 418deg For any angle of incidence larger than the critical angle Snells law will not be able to

be solved for the angle of refraction because it will show that the refracted angle has a sine larger than 1

which is not possible In that case all the light is totally reflected off the interface obeying the law of

reflection

OPTICAL FIBER MODE An optical fiber guides light waves in distinct patterns called modes Mode describes the distribution

of light energy across the fiber The precise patterns depend on the wavelength of light transmitted and on the

variation in refractive index that shapes the core In essence the variations in refractive index create

boundary

conditions that shape how light waves travel through the fiber like the walls of a tunnel affect how sounds

echo inside

We can take a look at large-core step-index fibers Light rays enter the fiber at a range of angles and

rays at different angles can all stably travel down the length of the fiber as long as they hit the core-cladding

interface at an angle larger than critical angle These rays are different modes Fibers that carry more than

one mode at a specific light wavelength are called multimode fibers Some fibers have very small diameter

core that they can carry only one mode which travels as a straight line at the center of the core These fibers

are single mode fibers This is illustrated in the following picture

OPTICAL FIBER INDEX PROFILE Index profile is the refractive index distribution across the core and the cladding of a fiber Some

optical fiber has a step index profile in which the core has one uniformly distributed index and the cladding

has a lower uniformly distributed index Other optical fiber has a graded index profile in which refractive

index varies gradually as a function of radial distance from the fiber center Graded-index profiles include

power-law index profiles and parabolic index profiles The following figure shows some common types of

index profiles for single mode and multimode fiber

26 | P a g e

OPTICAL FIBERrsquoS NUMERICAL APERTURE ( NA )- Multimode optical fiber will only propagate light that enters the fiber within a certain cone known as

the acceptance cone of the fiber The half-angle of this cone is called the acceptance angle (see figure 18)

θmax For step-index multimode fiber the acceptance angle is determined only by the indices of refraction

Where

n is the refractive index of the medium light is traveling before entering the fiber

nf is the refractive index of the fiber core

nc is the refractive index of the cladding

NUMBER OF MODES IN A FIBER - Modes are sometimes characterized by numbers Single mode fibers carry only the lowest-order

mode assigned the number 0 Multimode fibers also carry higher-order modes The number of modes that

can propagate in a fiber depends on the fiberrsquos numerical aperture (or acceptance angle) as well as on its

core diameter and the wavelength of the light For a step-index multimode fiber the number of such modes

Nm

Where

D is the core diameter

λ is the operating wavelength

NA is the numerical aperture (or acceptance angle)

MODE FIELD DIAMETER - All light do not travels through the core of the fiber but is distributed through both the core and the

cladding The mode field is the distribution of light through the core and cladding of a particular fiber

Mode-Field Diameter (MFD) defines the size of the power distribution When coupling light into or out of a

fiber MFD is important in understanding light loss

27 | P a g e

ADVANTAGE OF OFC COMMUNICATION - bull More information carrying capacity Fibers can handle much higher data rates than copper More

information can be sent in a second

bull Free from Electromagnetic and Electrostatic interference Being insulator no electric current flows through

the fibre and due to this reason fibres neither radiate nor pick up electro - magnetic radiation So WPC

CLEARANCE is not required

bull Low attenuation 025 dbkm at 1550 nm Loss in twisted pair and coaxial cable increases with frequency

where as loss in the optical fibre cable remains flat over a wide range of frequencies

bull Use of WDM ndash Switching routing at Optical signal level

bull Self healing rings under NMS control

bull Small size makes fibre cable lighter in weight So easy to handleOptic fibre cable weight (approx)

500 kg km Copper cable weight (approx) 1000 kgkm

The reasons are photons of light in a fibre

do not affect each other as they have no electrical charge and they are not affected by stray photons outside

the fibre But in case of copper electrons move through the cable and these are affected by each other

Optical fibre does not carry any electricity even if the cable is damaged or short circuited it does

not cause any spark or fire hazard

As the fibre do not radiate energy it can not be detected by any nearby antenna or any

other detector The fibres are difficult to tap and therefore excellent for security

As the signal transmission is by digital modulation there is no chance of cross talk in

between channels

Only by adding a few additional terminal and repeater equipments the

capacity of the system can be increased at any time once the cable is laid

ical effects and temperature variations

LIMITATIONS OF OFC -

difficult

- utilised

APPLICATION IN SIGNAL AND TELECOMMUNICATIONS transmission circuits

-haul circuits for linking of telephone exchanges

28 | P a g e

PROPAGATION MODES CONCEPT -

MODE - Mode is an available distribution of electromagnetic field in a plane transverse to the direction of

light propagation Each mode is characterized by frequency polarization electric field strength and

magnetic field strength Available patterns are derived from Maxwellrsquos equations and boundary conditions

LINEARLY POLARIZED (LP) MODE A mode for which the field components in the direction of propagation are small compared to

components perpendicular to that direction An optical fibre supports only different field patterns called as

lsquoLinear Polarizedrsquo or lsquo LPrsquo modes The reasons are

requirements

de

the accrual of power carried by different modes

There are two basic types of fiber Multimode fiber and Single-mode fiber

Multimode fiber is best designed for short transmission distances This is suited for used in LAN systems and

video surveillance Single mode fibre is best designed for longer transmission distances This is suitable for

long distance telephony and multi channel television broadcast systems

29 | P a g e

MULTI MODE FIBER Multimode fiber the first to be manufactured and commercialized simply refers to the fact that

numerous modes or light rays are carried simultaneously through the waveguide Modes result from the fact

that light will only propagate in the fiber core at discrete angles within the cone of acceptance MM fiber type

has a much larger core diameter compared to single-mode fiber allowing for the larger number of modes

and

is easier to couple than single-mode optical fiber Multimode fiber further categorized as Multimode step-

index and Multimode graded index fiber

PROPAGATION THROUGH MMSI FIBER Figure shows the principle of total internal reflection applies to multimode step index fiber Because

the corersquos index of refraction is higher than the claddingrsquos index of refraction the light that enters at less than

the critical angle is guided along the fiber

Three different light waves travel down the fiber One mode travels straight down the center of the

core A second mode travels at a steep angle and bounces back and forth by total internal reflection The third

mode exceeds the critical angle and refracts into the cladding Naturally it can be seen that the second mode

travels a longer distance than the first mode causing the two modes to arrive at separate times

PROBLEMS WITH MMSI FIBER AND SOLUTION This disparity between arrival times of the different light rays is known as dispersion and the result is

a muddied signal at the receiving end It is important to note that high dispersion is an unavoidable

characteristic of multimode step-index fiber The solutions are either use Graded index fiber or Single mode

fiber

PROPAGATION THROUGH MMGI FIBER Multimode Graded-index refers to the fact that the refractive index of the core gradually decreases

farther from the center of the core The increased refraction in the center of the core slows the speed of some

light rays allowing all the light rays to reach the receiving end at approximately the same time reducing

dispersion Figure shows the Light propagation principle through multimode graded-index fiber The corersquos

central refractive index ( nA ) is greater than that of the outer corersquos refractive index ( nB )

It is very clear from the figure the light rays no longer follow straight lines they follow a serpentine path

being gradually bent back toward the center by the continuously declining refractive index This reduces the

arrival time disparity because all modes arrive at about the same time The modes traveling in a straight line

30 | P a g e

are in a higher refractive index so they travel slower than the serpentine modes These travel farther but

move faster in the lower refractive index of the outer core region

PROPAGATION THROUGH SMSI FIBER Single mode fiber has a much smaller core that allows only one mode of light at a time to propagate

through the core The figure shows the single mode fiber

Single-mode fiber exhibits no dispersion caused by multiple modes Single-mode fiber also offers lower fiber

attenuation than multimode fiber Thus more information can be transmitted per unit of time because it can

retain the fidelity of each light pulse over longer distances Like multimode fiber early single-mode fiber was

generally characterized as step-index fiber meaning the refractive index of the fiber core is a step above that

of the cladding rather than graduated as it is in graded-index fiber Modern single-mode fibers have evolved

into more complex designs such as matched clad depressed clad and other exotic structures

SINGLE-MODE FIBER DISADVANTAGES The smaller core diameter makes coupling light into the core more difficult The tolerances for single-

mode connectors and splices are also much more demanding

CUTOFF WAVE LENGTH - Cutoff wavelength is the wavelength above which a single-mode fiber supports and propagates only

one mode of light In other words an optical fiber that is single-mode at a particular wavelength may have

two or more modes at wavelengths lower than the cutoff wavelength The effective cutoff wavelength of a

fiber is dependent on the length of fiber and its deployment The longer the fiber the lower is the effective

cutoff

wavelength The smaller the bend radius of a loop of the fiber the lower is the effective cutoff wavelength If

a fiber is bent in a loop the effective cutoff wavelength is lowered

SIGNAL ATTENUATION IN FIBER - Optical fiber has a number of advantages over copper However it also suffers from degradation

problems which can not be ignored The first of these is loss or attenuation Attenuation is typically the result

of two sub properties They are scattering and absorption Both of which have cumulative effects The second

is

dispersion which is the spreading of the transmitted signal and is analogous to noise

SCATTERING Scattering occurs because of impurities or irregularities in the physical construction of the fiber The

well known form of scattering is Rayleigh Scattering It is caused by metal ions in the silica matrix and

results in light rays being scattered in various directions

31 | P a g e

Scattering limits the use of wavelengths below 800nm The short wavelengths are much affected than longer

wavelengths It is because of Rayleigh scattering that the sky appears to be blue ( shorter wave length ) The

shorter wavelengths ( blue ) of light are scattered more than the longer wavelengths of light

ABSORPTION Absorption results from three factors They are hydroxyl ions ( OH- water ) in the silica impurities

in the silica and incomplete residue from the manufacturing process These impurities tend to absorb the

energy of the transmitted signal and convert it to heat resulting in an overall weakening of the signal The

Hydroxyl absorption occurs at 125 and 139 micro The silica itself starts to absorb energy at 17 micro

because of the natural resonance of the silicon dioxide

MACRO BENDING LOSS Macro-bending loss is caused by bending of the entire fiber axis The bending radius shall not be

sharper than 30d where d is diameter of cable A single bend sharper than 30d can cause loss of 05dB

The fiber may break if bending is ever sharper

MICRO BENDING LOSS Micro-bending loss is caused by micro deformations of fiber axis which leads to failures in achieving

total internal reflection conditions Micro-bends are small scale perturbations along the fiber axis the

amplitude of which are on the order of microns These distortions can cause light to leak out of a fiber

Micro-bending may be induced at very cold temperatures because the glass has a different coefficient of

thermal expansion from the coating and cabling materials At low temperatures the coating and cable

become more rigid and may contract more than the glass Consequently enough load may be exerted on the

glass to cause micro bends

Coating material is selected by manufacturers to minimize loss due to micro-bending The linear thermal

expansion coefficient of coating material shall be compatible with that of fiber

32 | P a g e

DISPERSION Dispersion is the optical term for the spreading of the transmits in the fiber It is the bandwidth

limiting phenomenon and comes in two forms Multimode dispersion and chromatic dispersion Chromatic

dispersion is further subdivided into material dispersion and waveguide dispersion

DISPERSION PHENOMENON IN OPTICAL FIBER Dispersion is the time distortion of an optical signal that results from the differences of time of travel

for different components of that signal typically resulting in pulse broadening As the distance traveled by

the signal is more broadening of pulse is more In digital transmission dispersion limits on the maximum

data rate and the maximum distance ie the information-carrying capacity of a fiber link The interference

from broadened pulse in the next interval shall not lead to erroneous interpretation of received signal

OPTICAL DOMAIN Understanding where attenuation and dispersion problems occur helps optical design engineers

determine the better wavelengths at which information can be transmit taking into account distance type of

fiber and the other factors which can severely affect the integrity of the transmitted signal The graph shown

depicts the optical transmission domain as well as the areas where problems arise The wavelength (nm)

is shown on X-axis and attenuation ( dBkm) is shown on Y-axis

There are four transmission windows appear in the figure The first one is at around 850 nm the

second at 1310nm third at 1550 nm and fourth at 1625 nm The last two labeled as C and L band

respectively The 850 nm wavelength at which the original LED technology operated The second window at

1310 nm has low dispersion The 1550 nm called as C-band is ideal wavelength for long haul

communication systems The network engineers can avoid transmitting signal at 1000 nm where Rayleigh

scattering 1240 and 1390 nm where hydroxyl absorption by water occurs to avoid high degree of loss

Optical fibers also can be manufactured to have low dispersion wavelength in the 1550nm region

which is also the point where silica-based fibers have inherently minimal attenuation These fibers are

referred to as dispersion-shifted fibers and are used in long-distance applications with high bit rates For

33 | P a g e

applications utilizing multiple wavelengths it is undesirable to have the zero dispersion point within the

operating

wavelength range

34 | P a g e

SIGNALLING RELAYS

INTRODUCTION A relay is an electromagnetic device which is used to convey information from one circuit to another

circuit through a set of contact ie front or back contact Constructional and electrically relays may be

divided into DC and AC relays because the means by which the electrical energy in the coil is converted in

to mechanical Energy in order to move the contacts are fundamentally different In DC type the contacts are

carried on an armature forming part of a magnetic circuit in which a field is set up by the current flowing in

the coils In AC types the contacts are attached by a link mechanism to a metal sector disc or cylinder in

which currents are induced by the alternating magnetic field produced by the currents in the coils

Every endeavor has been made to explain the action of each type of relay in the simplest possible manner

Relays are sophisticated switch gears used for remote control and succession control of various

electrical equipment In present days they are widely used because they are capable of protecting the

controlled equipment from cross feeding and overloading even as they cater for speedy operations

Most of the relays in present day signaling are electromagnetic devices although some of the relays control

circuits through electronic components like diodetransistors Integrated Chips etc

Railway signaling relays are unique in that

(a) They operate on low voltage and current

(b) They are more articulate as according to their special features they can work under restrictive conditions

and in any specified manner Virtually they can cater for all situations while contributing to speed and

accuracy in operations

CLASSIFICATION OF SIGNALLING RELAYS (a) According to the method of their mounting or fixture they are classified as

(i) Shelf type Relays which are loosely kept on shelves

(ii) Plug in type Relays which are plugged into a pre- wired plug boards

(b) According to their connection and usage they are classified as

(i) Track relays Relay which is directly connected to the track to detect the presence of vehicle

(ii) Line Relays Other than track relay all are line relays Relays connected to the selection circuit

(c) According to their vitality or importance in ensuring train working safety they are classified as

(i) Vital Relays All relays used for traffic control such as signal point controls track detection etc

(ii) Non-vital Relays Relays which operate control aids and accessories like warnings buzzers

Indications etc

(d) According to their special provisions to ensure reliability of their contacts they are classified as

(i) Proved type are those whose normalization after each operation shall be proved in circuit

controlled by their contacts Contacts in which both the springs have metal surfaces on their tips They may

get fused due to high sparking current across them during operation These may prevent relay normalization

and causes unsafe condition in traffic control To avoid this proving of relay normalization after each

operation is necessary

(ii) Non - proved type Need not to be proved to have been normalized after each operation as their

contacts have at least one non-fusible contact (carbon contact)

(e) According to their feed source relays are broadly classified as

(i) DC relays The relay which requires DC power supply for its operations are called DC relays Among

the DC relays

o DC neutral relays This relay closes the same set of contacts on energization with Normal polarity

or Reverse polarity supply

o Polar Relays This relay closes different set of contacts when energized with Reverse polarity

supply They may or may not have contact to close when deenergized

35 | P a g e

(ii) AC Relay AC Induction motor track relays Time element relays flashing indication control etc

(iii) Electronic Relays DC relays with electronic components in them are called electronic relays

DC NEUTRAL RELAY Each Relay has usually one or two coils with a hollow center to accommodate a coreThe coils are

made up of a large numbers of turns of small gauge soft drawn copper wire The two coils can be connected

in series or parallel according to the requirement of relay resistance The ends of the coils are terminated on

binding post to which the control wires are connected Each coil is placed around a core of specially selected

Iron or steel having high permeability and low retentivity The core should be susceptible to magnetism and

at the same time should have little residual magnetism The cores are connected at the top by a yoke to

complete the magnetism coupling between two ends of coils The bottom of each core is equipped with a

large steel or Iron block known as pole piece or face

A flat piece of Iron or steel called armature is supported by brackets which are securely fastened to

the pole piece The armature yoke and the pole pieces are also made of specially selected iron or steel of the

same quality as the core The armature carries the metallic spring contacts which are insulated from it

The circuit through the coils of the relay is closed It sets up a magnetic flux through the core yoke and the

armature The flux passing between the armature and pole faces causes the armatures get attracted to the pole

faces and armature picks up and closes front contacts When the circuit is opened the magnetic flux collapses

and the armature drops away by gravity from the pole faces the front contacts break and back contacts close

The front and back contacts of the relay can be utilised to make or break other circuits Two stop pins of

nonmagnetic material are fixed either on the armature or pole faces so that the armature cannot

come in contact with the pole faces It is essential to maintain a small air-gap between the armature and pole

faces so that low value of residual magnetism may not retain the armature in picked up position and causes

the relay to fail to drop away with a break in its control circuit

GENERAL USAGE

DC Neutral line relays are most commonly used for Railway Signalling controls and detection

Among them plug-in type relays are preferred in larger installations for space considerations Shelf type

relays are also in use mostly in wayside stations

There are many DC Neutral line relays in use with special features such as

(i) Delayed operation

(ii) Biased DC control

(iii) DC control unaffected by AC interference currents

(iv) Getting latched in operated condition till further feeding and others

Usage of DC polar relays is mostly in conjunction with block instruments that control traffic between

stations AC line relays are almost extinct in installations of British Signalling practice They are however

used for time control operations flashing indication control and such other special purposes in installations

with Siemens signalling practice widely Track relays are used according to the type of track detection

circuits chosen for a given location and context While most of the track circuits are still of the DC working

type requiring DC neutral track relays with them the prospects of their being replaced with Electronic track

circuits directly feeding DC line relays in future are great AC Track Circuits are used in DC Traction area

as conventional DC Track Circuits are not suitable there AC Track relays are used with them almost all of

the induction motor type In the British practice of signalling which was first introduced on Indian Railways

non-proved type relays with carbon to metal switching contacts are generally used for vital controls

They facilitate simple circuit designs But with the advent of German Practice introduced by Ms

Siemens later proved type relays with all metal to metal contacts are widely accepted in spite of

complications in circuit design caused by them A recent introduction is that of the same type relays made by

Ms Integra control However for some time now the appreciable features of both the practices are getting

36 | P a g e

incorporated together in the indigenous designs of signalling by railwaymen With this the usage of all types

of relays anywhere can be found without straight jacketed segration of relay types

CHARACTERSTIC OF ELECTRO-MAGNETIC RELAY The following are the characteristic of electro-magnetic relays A brief study of them helps in

understanding the choice of their components and designs features

1) Force of attraction

2) Effect of air gap

3) Effect of Hysterisis

4) Transient condition

FORCE OF ATTRACTION In any electro-magnetic system the force of attraction is given by

Where B - is the flux density a - is the cross sectional area of the particular part of the magnetic

circuit

In the case of a DC neutral Relay B is proportional to the current that is flowing in the coil

surrounding the electro-magnet and thus the force of the attraction is directly proportional to the square of the

current This square relationship has its own advantage especially in the case of DC track relay in that a

small reduction in the current will have a great effect on the working of the relay Also for a given change of

current the make and the break will be quicker with lesser possibility of arcing

EFFECT OF AIR GAP

Curve lsquoArsquo is magnetisation curve for the iron and is all practical purpose a straight line up to the

saturation point Curve lsquoBrsquo is the magnetisation curve for the open-air gap which is a straight line through

out because per magnetisation curve of the whole

magnetic circuit of the relay and for a given force is the sum of the amp-turns for the iron part and the amp-

turns for the air gap

When the front contacts are open the force required to pick up the armature is shown on curve lsquoCrsquo to be F1

but after the armature has operated it will be separated from the core by stop pins In this position the amp-

turns required to maintain the armature is less as indicated by the dotted line from 1 on curve C to 2 on curve

37 | P a g e

F But actually the current in the coil is unaltered the force on the armature is greater than required as

indicated at 3 on curve F Part of this extra force is used to flex the front contacts sufficiently to give good

contact pressure when it is in energised position

The difference between the pick-up and the drop-away current should be as small as practicable in

track relay to ensure good shunting characteristics This is achieved firstly by the choice of good quality relay

iron and secondly by having a small air gap between armature and core If the air gap is not available then

the residual magnetism fluxes might cause the armature to be retained when the supply is disconnected For

this reason residual pins are provided to ensure a definite minimum air gap in the energised position

EFFECT OF HYSTERISIS

Hysterisis is the property by which the flux produced lags behind the current In the de-energized

condition there will be small residual flux in the core When the voltage is applied to the coils the current in

rising to its steady value first causes the flux to rise from 1 to 2 along the curve At this point the flux density

will be sufficient to attract the armature and reduce the air gap the flux then raise to 3 and continue to 4

which corresponds to the steady current in the coils When the voltage is disconnected the current in falling

caused the flux to fall from 4 to 5 along the curve At this point the flux density will fall below the value

required to maintain the armature which will release thus increasing the air gap and reducing the flux to 6

Finally the

flux will decrease from 6 to 1 where the current will again be zero

The relay core is made of material having high permeability and low retentivity As mentioned in

the IRS specification Electromagnet iron may be in the form of a

(a) Bar of silicon steel

(b) Best Yorkshire wrought iron

(c) Swedish charcoal iron

(d) Electrical steel sheets

` This reduces the difference between pick up value and Drop away value By selecting good quality

core material Percentage release and sensitivity of the relay will be improved

TRANSIENT CONDITION

38 | P a g e

When the voltage is applied or disconnected from the coils it takes some little time before the current

become steady These are known as transient conditionsrdquo and are important so far as track relays are

concerned When the voltage is first applied to the coils the magnetic flux in rising cuts the turns on the

coils and in so doing produces a back EMF that opposes the applied voltage and retards the growth of

current

The growth and decay of flux are decided by the relationship between the inductance and resistance

in the circuit is known as time constant It is not fixed quantity in the case of DC neutral relay This value of lsquo

Lrsquo is less when the relay is in de-energised condition (L1) than when the relay is in energised condition (L2)

The magnitude of flux that is established for a given change of current is different in two cases

When the current reaches the pick up value the armature closes and the inductance is increased to L2

due to reduced air gap the flux per amp is increased The increase in flux increased the back EMF during the

movement of the armature after which the current continuous to raise along a new curve corresponding to the

increased inductance until it reaches the final value (ER) This process is indicated above in fig24

When the supply is disconnected the current is obliviously reduced to zero immediately but the flux

decay comparatively slowly owing to the eddy currents produced in the core by the rapid flux change which

tend to maintain the flux The drop away time on a disconnection is however generally negligible See fig

below

If the relay releases due to the reduction in current from say I 2 to I 1 caused by the application of

shunt resistance (as in the case of track relay ) the time taken is much longer than the relay is simply

disconnected The rate of rise or fall of current during the transient conditions is also depends on exterior

circuit values because L and R apply to the whole circuit The production of eddy current in the core the flux

will decay at a slower rate than the current So that the actual release time will be a little longer than it takes

the current to fall to the release

L= Inductance

39 | P a g e

R= Resistance

It is now clear that to reduce releasing time to a minimum it is necessary that

- The relay iron should have low Hysterisis loss and low retentivity

- The degree of over energization of the relay should be restricted

- Connecting a suitable external resistance in series with the relay to keep LR ratio low

In non RE area for track circuit length less than 100M 9 ohm track relay only to be used Using relay

with minimum contacts as they require lesser current which keeps inductance value low

Train working safety is ensured only if the track relay of shortest length track circuit is released

before a light engine running at a highest permitted speed clears it Otherwise the track circuit occupation

may go undetected To avoid this a special provision has to be made in signal control circuits wherever

necessary

The following methods may be adopted for reducing the time lag of track relay

(a) Restrict the over energisation of relay since the release time depends on the initial working current

(b) Connecting a suitable external resistance in series with the relay to keep the LR ratio low

(c) Using relays with minimum contacts as they require lesser operating current keeping the inductance

value low

40 | P a g e

CONCLUSION

Modern signalling is vital for safe and punctual movements of trains In the Indian railways The Signalling

and Telecommunication Department is responsible for providing modern effective and relaible signalling

systems as well as telecommunication systems

The first mode of communication used in Indian Railways was the use of electric telegraph

with the help of Morose code Morose code is the method of providing text information as a series of on-off

tones and lights or clicks that can be directly understood by a skilled listener or observer without special

equipmentEach character (letter or numeral ) is represented by a unique sequence of dots and dashes Later

this system becomes obselete and beggan the era of wireless communication which operated at audio level

frequency range

In wireless communication the significant advances took place the transition to miniature

valves or filament tubesBut this was abandoned too because of excessive current consumption and over

heating of the filament tubes

Fibre-optic communication is a method of transmitting information from one place to another by

sending pulses of light through an optcial fibreThe light forms an electromagnetic carrier wave that is

modulated to carry information First developed in the 1970s fibre optic communication systems has

revolutionized the telecommunications industry and have palyed a major role in the advent of the information

age Because of its advantages over electrical transmissionsoptical fibres have largely replaced copper wire

communications in core networks in the developed world The Indian Railways too is undergoing a transition

from Microwave communication to fibre optic communications

41 | P a g e

BIBLIOGRAPHY AND REFERENCES

1 wwwwikipediacom

2 wwwbritaniccacom

3 wwwirfcacom

4 Motorola GP60 system manual

5 Harris FAS 7000 manual

6 TOSHIBA Manual

16 | P a g e

Note

If the serial communications is more than 50m then line drivers shall be used up to 3 Kms

4wire leased line Modems shall be used if the serial communication is more than 3 Kms

STUDY OF EFFTRONICS DATALOGGER TECHNICAL DETAILS (a) 24V 12VDC Power Supply

(b) Total Storage Capacity of 10 Lakh events

(c) In-built Temperature sensors

(d) Internal Buzzer for alarming during failures

(e) Real Time clock with internal battery backup with data retention up to 10 years

(f) 512 LED matrix to indicate the status of 512 Digital inputs at a time page wise

(g) Seven segment LCD screen (2x24) to display the status of digitalanalog signalsTime Temperature etc

(h) Using the keyboard various functions can be viewed in the LCD panel

(i) Max Digital Inputs 4096

(j) Max Analog Inputs 96

(k) Digital Input Scanning Time 16 millisecond

(l) Analog Input Scanning Time is less than 1 Sec

HARDWARE (EQUIPMENT) Datalogger system consists of

(a) Datalogger (CPU - with Microprocessor 68000)

(b) Digital input cards

(c) Dual modem card

(d) Digital Scanner units (DSU)

(e) Analog Scanner units (ASU)

CPU CARD It is provided with Motorola microprocessor M 68000 It performs all the activities pertaining to the

datalogger It continuously scans (check) the Digital inputs(inbuilt) Digital Scanner Units and Analog

Scanner Units ie scanning of digital signals (Relay operations) for every 16-milli seconds and scanning of

analog signals (ie ACDC voltages amp DC currents) for less than 1 second

This card will support the IO interfaces of LCD (Liquid Crystal Display) - 2X24 alphanumeric Key

Board LED Matrix Display Real Time Clock LCD display and keyboard This will acts as man machine

interface between the datalogger and the signal engineer All the operations (Software) can be performed

using this LCD and keyboard

Real time display with 7 Segments This is built in real time clock within Datalogger and its current

time will be displayed on six 7-segment display provided (Real time clock depend upon DALLAS 1286

chip) This IC will come with internal battery backup hence there is no need to add external batteries

CPU card continuously scans (checks) the DSUs and ASUs Each input connected to digital scanner

units are optically isolated by Opto couplers When CPU card scans the digital inputs it compares with the

previous stored data and if there is any change from the previous status then only that data will be stored (the

status conditions of relay) with date and real time A total of minimum 10 Lac events can be stored in

memory on first in first out basis so that latest data is available in the system There is no loss of data from

datalogger memory in case of power supply failure of datalogger

DIGITAL INPUT CARDS (IN-BUILT) This system is having maximum 8nos of inbuilt Digital inputs cards Maximum 64nos of digital

inputs can be connected to each digital input card The potential free relay contact may be front or back

contact terminated at the Tag Block from the relay of signals tracks points Buttons etc and are

17 | P a g e

subsequently connected to Digital input cards through Flat Ribbon Cable (FRC) connectors These in-built

digital input cards can monitor a total 512 nos of relays status

DIGITAL SCANNER UNIT (DSU) Each DSU contains 8 nos of Digital Input cards Each input card can be connected with 64 inputs

Total input capacity of DSU unit is 512 inputs These scanner cards contain Optocouplers and Multiplexer

Inputs are connected to Stag card The stag card out put is connected to DSU through FRC connectors

Maximum 7 nos of DSUs can be connected to the system So Digital input capacity of the system is 4096

All these digital inputs are scanned at rate of 16 msec

ANALOG SCANNER UNIT (ASU) ASU contains maximum 3 nos of Analog input cards Each input card can be connected with 8nos of

Analog inputs Total input capacity of the ASU is 24 analog input channels Maximum 4nos of ASUs can be

connected to the system Analog input channel capacity of the system is 96 All these analog inputs are

scanned at a rate of less than 1 sec

PARALLEL PORT Parallel port is provided for connecting printer

RS-232 SERIAL PORTS At least 6 Serial communication ports are provided for communication with other dataloggers

Central Monitoring Unit Remote Terminal Unit Electronic Interlocking system Integrated Power Supply

system etc

EXTERNAL NON-VITAL RELAY CONTACTS These relays provided in the system where 16 number of the Relay contacts are provided on the rear

panel through Tele control port to extend alarms and to control the power equipment from remote or local

locations through computer in case of any occurrence of failures Each control can sink or source 100 m

amps of current

INTERNAL MODEM CARD DUAL MODEM CARD (IN-BUILT) It is fixed in datalogger Euro rack itself One card contains two modems The top modem is called

ANS (answer) modem and the bottom modem is called as ORG (originate) modem It is used in case of

networking of Dataloggers In network connect lsquoANSrsquo modem to the lsquoORGrsquo modem of one adjacent station

and connect lsquoORGrsquo modem to the lsquoANSrsquo modem of other adjacent station

POWER SUPPLY Normally 24V DC (12V DC is optional) supply with battery backup is required for the system

working

Input Voltage Range 18Vhellip32V DC (For 24V) 9Vhellip18V DC (For 12V)

INPUT REQUIREMENTS Relay inputs (digital inputs) and analog inputs (voltages currents etc) are required to be connected

to the system as per the requirements of RRI PI SSI as the case may be Some of the inputs to be

monitored is given below

(a) Digital inputs

(i) Field inputs All TPRs NWKRs RWKRs ECRs Crank Handle relays SidingSlot LC gate

control relays etc

(ii) Control Panel inputs All button Knob SMrsquos Key relays

18 | P a g e

(iii) Internal relays

British system All HR DR HHR WNR WRR ASR UCR RR LR UYRTLSR TRSR TSR

JSLR JR etc

SIEMENS system Z1UR Z1UR1 GZR ZDUCR ZU(R)R ZU(N)PRG(R)RG(N)R U(R)S

U(N)PS UDKR DUCR U(R)LR UYR1 UYR2 G(R)LRGR1GR2

GR3 GR4 OVZ2U(R)RW(RN)R (RN)WLR Z1NWR Z1RWRZ1WR1 WKR1 WKR2 WKR3 etc

(b) Analog channels

(i) 230 V AC (for power supplies in the power panel)

(ii) 110V AC (for Signal and Track transformers)

(iii) 110V DC (for Point operation)

(iv) 60V DC (Siemens relays)

(v) 24V DC (Q-series relays)

(vi) 24V DC (for Block Axle counters)

(vii) 12V DC (for indication)

(viii) 20A (for point operation current)

(ix) 10V AC 5KHz (for Axle counter channels) etc

SOFTWARE MODULES OF DATALOGGERS

(a) Network Management of Dataloggers (NMDL)

(b) Reports

(c) Fault Entry

(d) Track Offline Simulation

(e) Train Charting

NMDL SOFTWARE FEATURES (a) Online Relay Status

(b) Online Faults - To view information of various Online Faults as they occur in the stations where

the Dataloggers are connected

(c) Online Simulation - Graphical view of relay operations train movements etc

(d) Remote monitoring of stations with the help of NETWORKING

SOFTWARE OBJECTIVES (a) Predictive Maintenance

(b) Easy identification of failures

(c) Crew discipline

(d) Train charting

REMOTE MONITORING OF STATIONS WITH NETWORKING OF

DATALOGGERS The individual Dataloggers of various stations can be interconnected through networking technology

The data of Remote Panel stations can be viewed in a Computer at the Central Monitoring Station The data

of the network is collected by the FEP (Front End Processor) which in turn is transmitted to the computer

COMPONENTS OF NETWORK MANAGEMENT OF DATALOGGERS

(a) Datalogger at stations

(b) MODEM and Transmission medium

19 | P a g e

(c) Front End Processor (FEP)

(d) Central Monitoring Unit (CMU) Computer

FEP (FRONT END PROCESSOR)

FEP acts as a buffer between the Central Monitoring Unit (Computer) and the Network It is provided

at centralised place to retrieve data continuously from station dataloggers and store in memory and transfer to

computer on request It stores 10 Lac telegrams It works on 12V DC It draws 16A continuous current

when all the three modems are connected Normally it shows the number of packets pending to be sent to the

computer on its 7-segment LED display It is provided with MOTOROLA 68000 microprocessor It has 6-

nos of RS-232 communication ports such as COM1 COM2 COM3 COM4 COM5 and COM6 COM1 is

used for Fault Analysis System (FAS) ie Central Monitoring Unit (Computer) connection COM2 to COM6

are used for networking For Bi-directional 2- nos of ports and for Tri-directional (T-network) 3-nos of ports

are used

DATA TRANSMISSION Dataloggers can be networked in Uni-directional Mode or Bi-directional Mode or T ndash Network Mode

In case of loss of data retransmission of data takes place

(a) Uni-Directional Mode

Each Datalogger will send data in only one direction to the FEP Unidirectional mode network is not

preferred

(b) Bi-Directional Mode

Each end of Network is connected to FEP and each datalogger can now transmit data in both the directions

Bi-directional Mode is advantageous it enables the Data Transmission even in case of Network Failure

(c) T - Network Mode

If more no of stations are in network ie if the network is too lengthy then T- network mode is preferred

COMMUNICATION The communication protocol for transmitting data and command between datalogger and CMU is

standardized by the RDSO and is given in the Specifications of Dataloggers

(a) The type of communication used in the network is dependent on the distance between the dataloggers

(b) For shorter distances Opto Converter Box- Opto isolated current loop communication is used

(c) For longer distances Modem (Dial-up leased) Fiber Optic Satellite Microwave communication

MODEMS Modems are used for DATA transfer between Dataloggers and Front End ProcessorThese are

configured to RS 232 Serial Communication Network is connected with two types of 4-wire modems

(a) Internal modem card Dual Modem card (in-built)

It is fixed in datalogger Euro rack itself One card contains two modems The top modem is called

ANS (answer) modem and the bottom modem is called as ORG (originate) modem

Note In case of networking of Dataloggers connect lsquoANSrsquo modem to the lsquoORGrsquo modem of one adjacent

station and connect lsquoORGrsquo modem to the lsquoANSrsquo modem of other adjacent station

(b) External modems

20 | P a g e

These are generally used at FEP (Front End Processor) side to connect the Dataloggers

(i) To transfer Data from one datalogger to another datalogger FEP Baud rate is 9600bps

(ii) These modems are 4-wire line communication

(iii) To transfer the data from FEP to RMU (PC) the Baud rate is 57600 bps

There is no difference between these modems functionally

CENTRAL MONITORING UNIT (CMU) COMPUTER

Central monitoring unit (Fault Analysis Unit) is a Personal Computer and its minimum configuration

shall be specified by RDSO from time to time System Software Windows XPVista(OS) Norton Kaspersky

(Anti Virus) Interbase where Server is not available (DBMS) Oracle where Server is available (DBMS)

software are required to run Datalogger System It is provided with Graphical User interface (GUI) based

software and retrieve data from all Networked dataloggers (up to 32) at various stations It stores data in

standard data base files The CMU is capable of analyzing the data and generate reports audiovisual alarms

on defined conditions This data can be compressed to take backup In central monitoring unit Software used

for analysis of data prediction of faults etc is written in a structured format so that purchaser can

reconfigure it if required It displays the status of signaling gears at any selected time in graphic form for any

selected station yard It retrieves the stored data amp simulates train movement It sends commands to various

Dataloggers to activate audio visual alarm or operate and electromagnetic relay

CMU shares data available in it by other PCs through available local area network where this data can

be used for train charting passenger information purpose The system generates audiovisual alarm in

ASMrsquosSignal Maintainerrsquos room in the case of power supply failure (battery voltage low) or battery charger

defective with acknowledgement facility

(a) Each datalogger has its own identity code which will be transmitted along with data packet to central

monitoring unit

(b) Events recorded at each station are continuously transmitted to central monitoring unit Response time of

data transfer will not exceed 10 sec

21 | P a g e

22 | P a g e

OPTICAL FIBER CABLE

INTRODUCTION The demand for bandwidth on transmission networks is increasing rapidly because video and

graphical rich contents are exchanged through the corporate network or the Internet The Gigabit Ethernet

became ommonly used in the corporate network backbone and 10Gbit Ethernet will be adopted in the near

future Meanwhile in the home the demand for high-speed network becomes popular as the wide spread of

broadband access eg CATV xDSL and FTTH The transmission medium with capability to transmit high

bit rate signal is necessary to satisfy these requirements

The telecommunication transport technologies move from copper based networks to optical fiber

from timeslot based transport to wave length based transport from traditional circuit switching to terabit

router and all optical based networks entering into a new era of optical networking

BASIC PHYSICS OF OFC

OPTICAL FIBER CABLE OFC have Fibers which are long thin strands made with pure glass about the diameter of a human

hair OFC consists of Core Cladding Buffers and Jacket as shown in figure

MONOCHROMATIC LIGHT OR SINGLE COLOR LIGHT Light or visible light is electromagnetic radiation of a wavelength that is visible to the human eye (

about 400 ndash 700 nm) The word light is sometimes used to refer to the entire electromagnetic spectrum Light

is composed of elementary particles called photons Three primary properties of light are

Light can exhibit properties of both waves and particles This property is referred to as wave-particle

duality The study of light known as optics In free space light (of all wavelengths) travels in a straight path

at a constant maximum speed However the speed of light changes when it travels in a medium and this

change is not the same for all media or for all wavelengths By free space it is meant space that is free from

matter (vacuum) andor free from electromagnetic fields

Thus the speed of light in free space is defined by Einsteinrsquos equation E = mc2

Frequency ν speed of light in free space c and wavelength λ are interrelated by ν = cλ

From the energy relationships E = mc2 = hν and the last one an interesting relationship is obtained

the equivalent mass of a photon m = hνc2

When light is in the vicinity of a strong electromagnetic field it interacts with it From this interaction

and other influences its trajectory changes direction as shown in figure

23 | P a g e

INCIDENT RAY REFLECTED RAY AND REFRACTED RAY An incident ray is a ray of light that strikes a surface The angle between this ray and the

perpendicular or normal to the surface is the angle of incidence Reflection is the change in direction of a

wave front at an interface between two different media so that the wave front returns into the medium from

which it originated Common examples include the reflection of light sound and water waves

The reflected ray corresponding to a given incident ray is the ray that represents the light reflected by

the surface The angle between the surface normal and the reflected ray is known as the angle of reflection

The Law of Reflection says that for a specular (non-scattering) surface the angle of reflection always equals

the angle of incidence The refracted ray or transmitted ray corresponding to a given incident ray represents

the light that is transmitted through the surface The angle between this ray and the normal is known as the

angle of refraction and it is given by Snells Law

The figure shows Incident ray Reflected ray Refracted ray the angle of incidence and angle of refraction

REFRACTIVE INDEX - Refractive index is the speed of light in a vacuum ( c =299792458kmsecond) divided by the speed

of light in a material ( v ) Refractive index measures how much a material refracts light Refractive index of

a material abbreviated as lsquo n lsquo is defined as lsquo n=cv lsquo Light travels slower in physical media than it does

when transmitted through the air Refractive index (n) is a function of molecular structure of matter optical

frequency optical intensity determines optical propagation properties of each wavelength ( λ ) may not be

distributed equally in all directions is affected by external temperature pressure and fields

Refractive index of a medium is a measure for how much the speed of light is reduced inside the

medium For example typical glass has a refractive index of 15 which means that light travels at 1 15 =

067 times the speed in air or vacuum Two common properties of glass and other transparent materials are

directly related to their refractive index

First light rays change direction when they cross the interface from air to the material and effect that

is used in lenses and glasses

Second light reflects partially from surfaces that have a refractive index different from that of their

surroundings

SNELLrsquoS LAW-

24 | P a g e

When light passes from one transparent material to another it bends according to Snells law which

is defined as n1sin(θ1) = n2sin(θ2)

where n1 is the refractive index of the medium the light is leaving θ1 is the incident angle between the light

beam and the normal (normal is 90deg to the interface between two materials)

n2 is the refractive index of the material the light is entering

θ2 is the refractive angle between the light ray and the normal

Snellrsquos law gives the relationship between angle of incidence and angle of refraction

For the case of θ1 = 0deg (ie a ray perpendicular to the interface) the solution is θ2 = 0deg regardless of

the values of n1 and n2 That means a ray entering a medium perpendicular to the surface is never bent The

above is also valid for light going from a dense (higher n) to a less dense (lower n) material the symmetry of

Snells law shows that the same ray paths are applicable in opposite direction

TOTAL INTERNAL REFLECTION- When a light ray crosses an interface into a medium with a higher refractive index it bends towards

the normal Conversely light traveling cross an interface from a higher refractive index medium to a lower

refractive index medium will bend away from the normal

This has an interesting implication at some angle known as the critical angle θc light traveling from

a higher refractive index medium to a lower refractive index medium will be refracted at 90deg in other words

refracted alon g the interface If the light hits the interface at any angle larger than this critical angle it will

not pass through to the second medium at all Instead all of it will be reflected back into the first medium a

process known as total internal reflection

The critical angle can be calculated from Snells law putting in an angle of 90deg for the angle of the refracted

ray θ2 This gives θ1

Since θ2 = 90deg

So sin(θ2) = 1

25 | P a g e

Then θc = θ1 = arcsin(n2n1)

For example with light trying to emerge from glass with n1=15 into air (n2 =1) the ritical angle θc is

arcsin(115) or 418deg For any angle of incidence larger than the critical angle Snells law will not be able to

be solved for the angle of refraction because it will show that the refracted angle has a sine larger than 1

which is not possible In that case all the light is totally reflected off the interface obeying the law of

reflection

OPTICAL FIBER MODE An optical fiber guides light waves in distinct patterns called modes Mode describes the distribution

of light energy across the fiber The precise patterns depend on the wavelength of light transmitted and on the

variation in refractive index that shapes the core In essence the variations in refractive index create

boundary

conditions that shape how light waves travel through the fiber like the walls of a tunnel affect how sounds

echo inside

We can take a look at large-core step-index fibers Light rays enter the fiber at a range of angles and

rays at different angles can all stably travel down the length of the fiber as long as they hit the core-cladding

interface at an angle larger than critical angle These rays are different modes Fibers that carry more than

one mode at a specific light wavelength are called multimode fibers Some fibers have very small diameter

core that they can carry only one mode which travels as a straight line at the center of the core These fibers

are single mode fibers This is illustrated in the following picture

OPTICAL FIBER INDEX PROFILE Index profile is the refractive index distribution across the core and the cladding of a fiber Some

optical fiber has a step index profile in which the core has one uniformly distributed index and the cladding

has a lower uniformly distributed index Other optical fiber has a graded index profile in which refractive

index varies gradually as a function of radial distance from the fiber center Graded-index profiles include

power-law index profiles and parabolic index profiles The following figure shows some common types of

index profiles for single mode and multimode fiber

26 | P a g e

OPTICAL FIBERrsquoS NUMERICAL APERTURE ( NA )- Multimode optical fiber will only propagate light that enters the fiber within a certain cone known as

the acceptance cone of the fiber The half-angle of this cone is called the acceptance angle (see figure 18)

θmax For step-index multimode fiber the acceptance angle is determined only by the indices of refraction

Where

n is the refractive index of the medium light is traveling before entering the fiber

nf is the refractive index of the fiber core

nc is the refractive index of the cladding

NUMBER OF MODES IN A FIBER - Modes are sometimes characterized by numbers Single mode fibers carry only the lowest-order

mode assigned the number 0 Multimode fibers also carry higher-order modes The number of modes that

can propagate in a fiber depends on the fiberrsquos numerical aperture (or acceptance angle) as well as on its

core diameter and the wavelength of the light For a step-index multimode fiber the number of such modes

Nm

Where

D is the core diameter

λ is the operating wavelength

NA is the numerical aperture (or acceptance angle)

MODE FIELD DIAMETER - All light do not travels through the core of the fiber but is distributed through both the core and the

cladding The mode field is the distribution of light through the core and cladding of a particular fiber

Mode-Field Diameter (MFD) defines the size of the power distribution When coupling light into or out of a

fiber MFD is important in understanding light loss

27 | P a g e

ADVANTAGE OF OFC COMMUNICATION - bull More information carrying capacity Fibers can handle much higher data rates than copper More

information can be sent in a second

bull Free from Electromagnetic and Electrostatic interference Being insulator no electric current flows through

the fibre and due to this reason fibres neither radiate nor pick up electro - magnetic radiation So WPC

CLEARANCE is not required

bull Low attenuation 025 dbkm at 1550 nm Loss in twisted pair and coaxial cable increases with frequency

where as loss in the optical fibre cable remains flat over a wide range of frequencies

bull Use of WDM ndash Switching routing at Optical signal level

bull Self healing rings under NMS control

bull Small size makes fibre cable lighter in weight So easy to handleOptic fibre cable weight (approx)

500 kg km Copper cable weight (approx) 1000 kgkm

The reasons are photons of light in a fibre

do not affect each other as they have no electrical charge and they are not affected by stray photons outside

the fibre But in case of copper electrons move through the cable and these are affected by each other

Optical fibre does not carry any electricity even if the cable is damaged or short circuited it does

not cause any spark or fire hazard

As the fibre do not radiate energy it can not be detected by any nearby antenna or any

other detector The fibres are difficult to tap and therefore excellent for security

As the signal transmission is by digital modulation there is no chance of cross talk in

between channels

Only by adding a few additional terminal and repeater equipments the

capacity of the system can be increased at any time once the cable is laid

ical effects and temperature variations

LIMITATIONS OF OFC -

difficult

- utilised

APPLICATION IN SIGNAL AND TELECOMMUNICATIONS transmission circuits

-haul circuits for linking of telephone exchanges

28 | P a g e

PROPAGATION MODES CONCEPT -

MODE - Mode is an available distribution of electromagnetic field in a plane transverse to the direction of

light propagation Each mode is characterized by frequency polarization electric field strength and

magnetic field strength Available patterns are derived from Maxwellrsquos equations and boundary conditions

LINEARLY POLARIZED (LP) MODE A mode for which the field components in the direction of propagation are small compared to

components perpendicular to that direction An optical fibre supports only different field patterns called as

lsquoLinear Polarizedrsquo or lsquo LPrsquo modes The reasons are

requirements

de

the accrual of power carried by different modes

There are two basic types of fiber Multimode fiber and Single-mode fiber

Multimode fiber is best designed for short transmission distances This is suited for used in LAN systems and

video surveillance Single mode fibre is best designed for longer transmission distances This is suitable for

long distance telephony and multi channel television broadcast systems

29 | P a g e

MULTI MODE FIBER Multimode fiber the first to be manufactured and commercialized simply refers to the fact that

numerous modes or light rays are carried simultaneously through the waveguide Modes result from the fact

that light will only propagate in the fiber core at discrete angles within the cone of acceptance MM fiber type

has a much larger core diameter compared to single-mode fiber allowing for the larger number of modes

and

is easier to couple than single-mode optical fiber Multimode fiber further categorized as Multimode step-

index and Multimode graded index fiber

PROPAGATION THROUGH MMSI FIBER Figure shows the principle of total internal reflection applies to multimode step index fiber Because

the corersquos index of refraction is higher than the claddingrsquos index of refraction the light that enters at less than

the critical angle is guided along the fiber

Three different light waves travel down the fiber One mode travels straight down the center of the

core A second mode travels at a steep angle and bounces back and forth by total internal reflection The third

mode exceeds the critical angle and refracts into the cladding Naturally it can be seen that the second mode

travels a longer distance than the first mode causing the two modes to arrive at separate times

PROBLEMS WITH MMSI FIBER AND SOLUTION This disparity between arrival times of the different light rays is known as dispersion and the result is

a muddied signal at the receiving end It is important to note that high dispersion is an unavoidable

characteristic of multimode step-index fiber The solutions are either use Graded index fiber or Single mode

fiber

PROPAGATION THROUGH MMGI FIBER Multimode Graded-index refers to the fact that the refractive index of the core gradually decreases

farther from the center of the core The increased refraction in the center of the core slows the speed of some

light rays allowing all the light rays to reach the receiving end at approximately the same time reducing

dispersion Figure shows the Light propagation principle through multimode graded-index fiber The corersquos

central refractive index ( nA ) is greater than that of the outer corersquos refractive index ( nB )

It is very clear from the figure the light rays no longer follow straight lines they follow a serpentine path

being gradually bent back toward the center by the continuously declining refractive index This reduces the

arrival time disparity because all modes arrive at about the same time The modes traveling in a straight line

30 | P a g e

are in a higher refractive index so they travel slower than the serpentine modes These travel farther but

move faster in the lower refractive index of the outer core region

PROPAGATION THROUGH SMSI FIBER Single mode fiber has a much smaller core that allows only one mode of light at a time to propagate

through the core The figure shows the single mode fiber

Single-mode fiber exhibits no dispersion caused by multiple modes Single-mode fiber also offers lower fiber

attenuation than multimode fiber Thus more information can be transmitted per unit of time because it can

retain the fidelity of each light pulse over longer distances Like multimode fiber early single-mode fiber was

generally characterized as step-index fiber meaning the refractive index of the fiber core is a step above that

of the cladding rather than graduated as it is in graded-index fiber Modern single-mode fibers have evolved

into more complex designs such as matched clad depressed clad and other exotic structures

SINGLE-MODE FIBER DISADVANTAGES The smaller core diameter makes coupling light into the core more difficult The tolerances for single-

mode connectors and splices are also much more demanding

CUTOFF WAVE LENGTH - Cutoff wavelength is the wavelength above which a single-mode fiber supports and propagates only

one mode of light In other words an optical fiber that is single-mode at a particular wavelength may have

two or more modes at wavelengths lower than the cutoff wavelength The effective cutoff wavelength of a

fiber is dependent on the length of fiber and its deployment The longer the fiber the lower is the effective

cutoff

wavelength The smaller the bend radius of a loop of the fiber the lower is the effective cutoff wavelength If

a fiber is bent in a loop the effective cutoff wavelength is lowered

SIGNAL ATTENUATION IN FIBER - Optical fiber has a number of advantages over copper However it also suffers from degradation

problems which can not be ignored The first of these is loss or attenuation Attenuation is typically the result

of two sub properties They are scattering and absorption Both of which have cumulative effects The second

is

dispersion which is the spreading of the transmitted signal and is analogous to noise

SCATTERING Scattering occurs because of impurities or irregularities in the physical construction of the fiber The

well known form of scattering is Rayleigh Scattering It is caused by metal ions in the silica matrix and

results in light rays being scattered in various directions

31 | P a g e

Scattering limits the use of wavelengths below 800nm The short wavelengths are much affected than longer

wavelengths It is because of Rayleigh scattering that the sky appears to be blue ( shorter wave length ) The

shorter wavelengths ( blue ) of light are scattered more than the longer wavelengths of light

ABSORPTION Absorption results from three factors They are hydroxyl ions ( OH- water ) in the silica impurities

in the silica and incomplete residue from the manufacturing process These impurities tend to absorb the

energy of the transmitted signal and convert it to heat resulting in an overall weakening of the signal The

Hydroxyl absorption occurs at 125 and 139 micro The silica itself starts to absorb energy at 17 micro

because of the natural resonance of the silicon dioxide

MACRO BENDING LOSS Macro-bending loss is caused by bending of the entire fiber axis The bending radius shall not be

sharper than 30d where d is diameter of cable A single bend sharper than 30d can cause loss of 05dB

The fiber may break if bending is ever sharper

MICRO BENDING LOSS Micro-bending loss is caused by micro deformations of fiber axis which leads to failures in achieving

total internal reflection conditions Micro-bends are small scale perturbations along the fiber axis the

amplitude of which are on the order of microns These distortions can cause light to leak out of a fiber

Micro-bending may be induced at very cold temperatures because the glass has a different coefficient of

thermal expansion from the coating and cabling materials At low temperatures the coating and cable

become more rigid and may contract more than the glass Consequently enough load may be exerted on the

glass to cause micro bends

Coating material is selected by manufacturers to minimize loss due to micro-bending The linear thermal

expansion coefficient of coating material shall be compatible with that of fiber

32 | P a g e

DISPERSION Dispersion is the optical term for the spreading of the transmits in the fiber It is the bandwidth

limiting phenomenon and comes in two forms Multimode dispersion and chromatic dispersion Chromatic

dispersion is further subdivided into material dispersion and waveguide dispersion

DISPERSION PHENOMENON IN OPTICAL FIBER Dispersion is the time distortion of an optical signal that results from the differences of time of travel

for different components of that signal typically resulting in pulse broadening As the distance traveled by

the signal is more broadening of pulse is more In digital transmission dispersion limits on the maximum

data rate and the maximum distance ie the information-carrying capacity of a fiber link The interference

from broadened pulse in the next interval shall not lead to erroneous interpretation of received signal

OPTICAL DOMAIN Understanding where attenuation and dispersion problems occur helps optical design engineers

determine the better wavelengths at which information can be transmit taking into account distance type of

fiber and the other factors which can severely affect the integrity of the transmitted signal The graph shown

depicts the optical transmission domain as well as the areas where problems arise The wavelength (nm)

is shown on X-axis and attenuation ( dBkm) is shown on Y-axis

There are four transmission windows appear in the figure The first one is at around 850 nm the

second at 1310nm third at 1550 nm and fourth at 1625 nm The last two labeled as C and L band

respectively The 850 nm wavelength at which the original LED technology operated The second window at

1310 nm has low dispersion The 1550 nm called as C-band is ideal wavelength for long haul

communication systems The network engineers can avoid transmitting signal at 1000 nm where Rayleigh

scattering 1240 and 1390 nm where hydroxyl absorption by water occurs to avoid high degree of loss

Optical fibers also can be manufactured to have low dispersion wavelength in the 1550nm region

which is also the point where silica-based fibers have inherently minimal attenuation These fibers are

referred to as dispersion-shifted fibers and are used in long-distance applications with high bit rates For

33 | P a g e

applications utilizing multiple wavelengths it is undesirable to have the zero dispersion point within the

operating

wavelength range

34 | P a g e

SIGNALLING RELAYS

INTRODUCTION A relay is an electromagnetic device which is used to convey information from one circuit to another

circuit through a set of contact ie front or back contact Constructional and electrically relays may be

divided into DC and AC relays because the means by which the electrical energy in the coil is converted in

to mechanical Energy in order to move the contacts are fundamentally different In DC type the contacts are

carried on an armature forming part of a magnetic circuit in which a field is set up by the current flowing in

the coils In AC types the contacts are attached by a link mechanism to a metal sector disc or cylinder in

which currents are induced by the alternating magnetic field produced by the currents in the coils

Every endeavor has been made to explain the action of each type of relay in the simplest possible manner

Relays are sophisticated switch gears used for remote control and succession control of various

electrical equipment In present days they are widely used because they are capable of protecting the

controlled equipment from cross feeding and overloading even as they cater for speedy operations

Most of the relays in present day signaling are electromagnetic devices although some of the relays control

circuits through electronic components like diodetransistors Integrated Chips etc

Railway signaling relays are unique in that

(a) They operate on low voltage and current

(b) They are more articulate as according to their special features they can work under restrictive conditions

and in any specified manner Virtually they can cater for all situations while contributing to speed and

accuracy in operations

CLASSIFICATION OF SIGNALLING RELAYS (a) According to the method of their mounting or fixture they are classified as

(i) Shelf type Relays which are loosely kept on shelves

(ii) Plug in type Relays which are plugged into a pre- wired plug boards

(b) According to their connection and usage they are classified as

(i) Track relays Relay which is directly connected to the track to detect the presence of vehicle

(ii) Line Relays Other than track relay all are line relays Relays connected to the selection circuit

(c) According to their vitality or importance in ensuring train working safety they are classified as

(i) Vital Relays All relays used for traffic control such as signal point controls track detection etc

(ii) Non-vital Relays Relays which operate control aids and accessories like warnings buzzers

Indications etc

(d) According to their special provisions to ensure reliability of their contacts they are classified as

(i) Proved type are those whose normalization after each operation shall be proved in circuit

controlled by their contacts Contacts in which both the springs have metal surfaces on their tips They may

get fused due to high sparking current across them during operation These may prevent relay normalization

and causes unsafe condition in traffic control To avoid this proving of relay normalization after each

operation is necessary

(ii) Non - proved type Need not to be proved to have been normalized after each operation as their

contacts have at least one non-fusible contact (carbon contact)

(e) According to their feed source relays are broadly classified as

(i) DC relays The relay which requires DC power supply for its operations are called DC relays Among

the DC relays

o DC neutral relays This relay closes the same set of contacts on energization with Normal polarity

or Reverse polarity supply

o Polar Relays This relay closes different set of contacts when energized with Reverse polarity

supply They may or may not have contact to close when deenergized

35 | P a g e

(ii) AC Relay AC Induction motor track relays Time element relays flashing indication control etc

(iii) Electronic Relays DC relays with electronic components in them are called electronic relays

DC NEUTRAL RELAY Each Relay has usually one or two coils with a hollow center to accommodate a coreThe coils are

made up of a large numbers of turns of small gauge soft drawn copper wire The two coils can be connected

in series or parallel according to the requirement of relay resistance The ends of the coils are terminated on

binding post to which the control wires are connected Each coil is placed around a core of specially selected

Iron or steel having high permeability and low retentivity The core should be susceptible to magnetism and

at the same time should have little residual magnetism The cores are connected at the top by a yoke to

complete the magnetism coupling between two ends of coils The bottom of each core is equipped with a

large steel or Iron block known as pole piece or face

A flat piece of Iron or steel called armature is supported by brackets which are securely fastened to

the pole piece The armature yoke and the pole pieces are also made of specially selected iron or steel of the

same quality as the core The armature carries the metallic spring contacts which are insulated from it

The circuit through the coils of the relay is closed It sets up a magnetic flux through the core yoke and the

armature The flux passing between the armature and pole faces causes the armatures get attracted to the pole

faces and armature picks up and closes front contacts When the circuit is opened the magnetic flux collapses

and the armature drops away by gravity from the pole faces the front contacts break and back contacts close

The front and back contacts of the relay can be utilised to make or break other circuits Two stop pins of

nonmagnetic material are fixed either on the armature or pole faces so that the armature cannot

come in contact with the pole faces It is essential to maintain a small air-gap between the armature and pole

faces so that low value of residual magnetism may not retain the armature in picked up position and causes

the relay to fail to drop away with a break in its control circuit

GENERAL USAGE

DC Neutral line relays are most commonly used for Railway Signalling controls and detection

Among them plug-in type relays are preferred in larger installations for space considerations Shelf type

relays are also in use mostly in wayside stations

There are many DC Neutral line relays in use with special features such as

(i) Delayed operation

(ii) Biased DC control

(iii) DC control unaffected by AC interference currents

(iv) Getting latched in operated condition till further feeding and others

Usage of DC polar relays is mostly in conjunction with block instruments that control traffic between

stations AC line relays are almost extinct in installations of British Signalling practice They are however

used for time control operations flashing indication control and such other special purposes in installations

with Siemens signalling practice widely Track relays are used according to the type of track detection

circuits chosen for a given location and context While most of the track circuits are still of the DC working

type requiring DC neutral track relays with them the prospects of their being replaced with Electronic track

circuits directly feeding DC line relays in future are great AC Track Circuits are used in DC Traction area

as conventional DC Track Circuits are not suitable there AC Track relays are used with them almost all of

the induction motor type In the British practice of signalling which was first introduced on Indian Railways

non-proved type relays with carbon to metal switching contacts are generally used for vital controls

They facilitate simple circuit designs But with the advent of German Practice introduced by Ms

Siemens later proved type relays with all metal to metal contacts are widely accepted in spite of

complications in circuit design caused by them A recent introduction is that of the same type relays made by

Ms Integra control However for some time now the appreciable features of both the practices are getting

36 | P a g e

incorporated together in the indigenous designs of signalling by railwaymen With this the usage of all types

of relays anywhere can be found without straight jacketed segration of relay types

CHARACTERSTIC OF ELECTRO-MAGNETIC RELAY The following are the characteristic of electro-magnetic relays A brief study of them helps in

understanding the choice of their components and designs features

1) Force of attraction

2) Effect of air gap

3) Effect of Hysterisis

4) Transient condition

FORCE OF ATTRACTION In any electro-magnetic system the force of attraction is given by

Where B - is the flux density a - is the cross sectional area of the particular part of the magnetic

circuit

In the case of a DC neutral Relay B is proportional to the current that is flowing in the coil

surrounding the electro-magnet and thus the force of the attraction is directly proportional to the square of the

current This square relationship has its own advantage especially in the case of DC track relay in that a

small reduction in the current will have a great effect on the working of the relay Also for a given change of

current the make and the break will be quicker with lesser possibility of arcing

EFFECT OF AIR GAP

Curve lsquoArsquo is magnetisation curve for the iron and is all practical purpose a straight line up to the

saturation point Curve lsquoBrsquo is the magnetisation curve for the open-air gap which is a straight line through

out because per magnetisation curve of the whole

magnetic circuit of the relay and for a given force is the sum of the amp-turns for the iron part and the amp-

turns for the air gap

When the front contacts are open the force required to pick up the armature is shown on curve lsquoCrsquo to be F1

but after the armature has operated it will be separated from the core by stop pins In this position the amp-

turns required to maintain the armature is less as indicated by the dotted line from 1 on curve C to 2 on curve

37 | P a g e

F But actually the current in the coil is unaltered the force on the armature is greater than required as

indicated at 3 on curve F Part of this extra force is used to flex the front contacts sufficiently to give good

contact pressure when it is in energised position

The difference between the pick-up and the drop-away current should be as small as practicable in

track relay to ensure good shunting characteristics This is achieved firstly by the choice of good quality relay

iron and secondly by having a small air gap between armature and core If the air gap is not available then

the residual magnetism fluxes might cause the armature to be retained when the supply is disconnected For

this reason residual pins are provided to ensure a definite minimum air gap in the energised position

EFFECT OF HYSTERISIS

Hysterisis is the property by which the flux produced lags behind the current In the de-energized

condition there will be small residual flux in the core When the voltage is applied to the coils the current in

rising to its steady value first causes the flux to rise from 1 to 2 along the curve At this point the flux density

will be sufficient to attract the armature and reduce the air gap the flux then raise to 3 and continue to 4

which corresponds to the steady current in the coils When the voltage is disconnected the current in falling

caused the flux to fall from 4 to 5 along the curve At this point the flux density will fall below the value

required to maintain the armature which will release thus increasing the air gap and reducing the flux to 6

Finally the

flux will decrease from 6 to 1 where the current will again be zero

The relay core is made of material having high permeability and low retentivity As mentioned in

the IRS specification Electromagnet iron may be in the form of a

(a) Bar of silicon steel

(b) Best Yorkshire wrought iron

(c) Swedish charcoal iron

(d) Electrical steel sheets

` This reduces the difference between pick up value and Drop away value By selecting good quality

core material Percentage release and sensitivity of the relay will be improved

TRANSIENT CONDITION

38 | P a g e

When the voltage is applied or disconnected from the coils it takes some little time before the current

become steady These are known as transient conditionsrdquo and are important so far as track relays are

concerned When the voltage is first applied to the coils the magnetic flux in rising cuts the turns on the

coils and in so doing produces a back EMF that opposes the applied voltage and retards the growth of

current

The growth and decay of flux are decided by the relationship between the inductance and resistance

in the circuit is known as time constant It is not fixed quantity in the case of DC neutral relay This value of lsquo

Lrsquo is less when the relay is in de-energised condition (L1) than when the relay is in energised condition (L2)

The magnitude of flux that is established for a given change of current is different in two cases

When the current reaches the pick up value the armature closes and the inductance is increased to L2

due to reduced air gap the flux per amp is increased The increase in flux increased the back EMF during the

movement of the armature after which the current continuous to raise along a new curve corresponding to the

increased inductance until it reaches the final value (ER) This process is indicated above in fig24

When the supply is disconnected the current is obliviously reduced to zero immediately but the flux

decay comparatively slowly owing to the eddy currents produced in the core by the rapid flux change which

tend to maintain the flux The drop away time on a disconnection is however generally negligible See fig

below

If the relay releases due to the reduction in current from say I 2 to I 1 caused by the application of

shunt resistance (as in the case of track relay ) the time taken is much longer than the relay is simply

disconnected The rate of rise or fall of current during the transient conditions is also depends on exterior

circuit values because L and R apply to the whole circuit The production of eddy current in the core the flux

will decay at a slower rate than the current So that the actual release time will be a little longer than it takes

the current to fall to the release

L= Inductance

39 | P a g e

R= Resistance

It is now clear that to reduce releasing time to a minimum it is necessary that

- The relay iron should have low Hysterisis loss and low retentivity

- The degree of over energization of the relay should be restricted

- Connecting a suitable external resistance in series with the relay to keep LR ratio low

In non RE area for track circuit length less than 100M 9 ohm track relay only to be used Using relay

with minimum contacts as they require lesser current which keeps inductance value low

Train working safety is ensured only if the track relay of shortest length track circuit is released

before a light engine running at a highest permitted speed clears it Otherwise the track circuit occupation

may go undetected To avoid this a special provision has to be made in signal control circuits wherever

necessary

The following methods may be adopted for reducing the time lag of track relay

(a) Restrict the over energisation of relay since the release time depends on the initial working current

(b) Connecting a suitable external resistance in series with the relay to keep the LR ratio low

(c) Using relays with minimum contacts as they require lesser operating current keeping the inductance

value low

40 | P a g e

CONCLUSION

Modern signalling is vital for safe and punctual movements of trains In the Indian railways The Signalling

and Telecommunication Department is responsible for providing modern effective and relaible signalling

systems as well as telecommunication systems

The first mode of communication used in Indian Railways was the use of electric telegraph

with the help of Morose code Morose code is the method of providing text information as a series of on-off

tones and lights or clicks that can be directly understood by a skilled listener or observer without special

equipmentEach character (letter or numeral ) is represented by a unique sequence of dots and dashes Later

this system becomes obselete and beggan the era of wireless communication which operated at audio level

frequency range

In wireless communication the significant advances took place the transition to miniature

valves or filament tubesBut this was abandoned too because of excessive current consumption and over

heating of the filament tubes

Fibre-optic communication is a method of transmitting information from one place to another by

sending pulses of light through an optcial fibreThe light forms an electromagnetic carrier wave that is

modulated to carry information First developed in the 1970s fibre optic communication systems has

revolutionized the telecommunications industry and have palyed a major role in the advent of the information

age Because of its advantages over electrical transmissionsoptical fibres have largely replaced copper wire

communications in core networks in the developed world The Indian Railways too is undergoing a transition

from Microwave communication to fibre optic communications

41 | P a g e

BIBLIOGRAPHY AND REFERENCES

1 wwwwikipediacom

2 wwwbritaniccacom

3 wwwirfcacom

4 Motorola GP60 system manual

5 Harris FAS 7000 manual

6 TOSHIBA Manual

17 | P a g e

subsequently connected to Digital input cards through Flat Ribbon Cable (FRC) connectors These in-built

digital input cards can monitor a total 512 nos of relays status

DIGITAL SCANNER UNIT (DSU) Each DSU contains 8 nos of Digital Input cards Each input card can be connected with 64 inputs

Total input capacity of DSU unit is 512 inputs These scanner cards contain Optocouplers and Multiplexer

Inputs are connected to Stag card The stag card out put is connected to DSU through FRC connectors

Maximum 7 nos of DSUs can be connected to the system So Digital input capacity of the system is 4096

All these digital inputs are scanned at rate of 16 msec

ANALOG SCANNER UNIT (ASU) ASU contains maximum 3 nos of Analog input cards Each input card can be connected with 8nos of

Analog inputs Total input capacity of the ASU is 24 analog input channels Maximum 4nos of ASUs can be

connected to the system Analog input channel capacity of the system is 96 All these analog inputs are

scanned at a rate of less than 1 sec

PARALLEL PORT Parallel port is provided for connecting printer

RS-232 SERIAL PORTS At least 6 Serial communication ports are provided for communication with other dataloggers

Central Monitoring Unit Remote Terminal Unit Electronic Interlocking system Integrated Power Supply

system etc

EXTERNAL NON-VITAL RELAY CONTACTS These relays provided in the system where 16 number of the Relay contacts are provided on the rear

panel through Tele control port to extend alarms and to control the power equipment from remote or local

locations through computer in case of any occurrence of failures Each control can sink or source 100 m

amps of current

INTERNAL MODEM CARD DUAL MODEM CARD (IN-BUILT) It is fixed in datalogger Euro rack itself One card contains two modems The top modem is called

ANS (answer) modem and the bottom modem is called as ORG (originate) modem It is used in case of

networking of Dataloggers In network connect lsquoANSrsquo modem to the lsquoORGrsquo modem of one adjacent station

and connect lsquoORGrsquo modem to the lsquoANSrsquo modem of other adjacent station

POWER SUPPLY Normally 24V DC (12V DC is optional) supply with battery backup is required for the system

working

Input Voltage Range 18Vhellip32V DC (For 24V) 9Vhellip18V DC (For 12V)

INPUT REQUIREMENTS Relay inputs (digital inputs) and analog inputs (voltages currents etc) are required to be connected

to the system as per the requirements of RRI PI SSI as the case may be Some of the inputs to be

monitored is given below

(a) Digital inputs

(i) Field inputs All TPRs NWKRs RWKRs ECRs Crank Handle relays SidingSlot LC gate

control relays etc

(ii) Control Panel inputs All button Knob SMrsquos Key relays

18 | P a g e

(iii) Internal relays

British system All HR DR HHR WNR WRR ASR UCR RR LR UYRTLSR TRSR TSR

JSLR JR etc

SIEMENS system Z1UR Z1UR1 GZR ZDUCR ZU(R)R ZU(N)PRG(R)RG(N)R U(R)S

U(N)PS UDKR DUCR U(R)LR UYR1 UYR2 G(R)LRGR1GR2

GR3 GR4 OVZ2U(R)RW(RN)R (RN)WLR Z1NWR Z1RWRZ1WR1 WKR1 WKR2 WKR3 etc

(b) Analog channels

(i) 230 V AC (for power supplies in the power panel)

(ii) 110V AC (for Signal and Track transformers)

(iii) 110V DC (for Point operation)

(iv) 60V DC (Siemens relays)

(v) 24V DC (Q-series relays)

(vi) 24V DC (for Block Axle counters)

(vii) 12V DC (for indication)

(viii) 20A (for point operation current)

(ix) 10V AC 5KHz (for Axle counter channels) etc

SOFTWARE MODULES OF DATALOGGERS

(a) Network Management of Dataloggers (NMDL)

(b) Reports

(c) Fault Entry

(d) Track Offline Simulation

(e) Train Charting

NMDL SOFTWARE FEATURES (a) Online Relay Status

(b) Online Faults - To view information of various Online Faults as they occur in the stations where

the Dataloggers are connected

(c) Online Simulation - Graphical view of relay operations train movements etc

(d) Remote monitoring of stations with the help of NETWORKING

SOFTWARE OBJECTIVES (a) Predictive Maintenance

(b) Easy identification of failures

(c) Crew discipline

(d) Train charting

REMOTE MONITORING OF STATIONS WITH NETWORKING OF

DATALOGGERS The individual Dataloggers of various stations can be interconnected through networking technology

The data of Remote Panel stations can be viewed in a Computer at the Central Monitoring Station The data

of the network is collected by the FEP (Front End Processor) which in turn is transmitted to the computer

COMPONENTS OF NETWORK MANAGEMENT OF DATALOGGERS

(a) Datalogger at stations

(b) MODEM and Transmission medium

19 | P a g e

(c) Front End Processor (FEP)

(d) Central Monitoring Unit (CMU) Computer

FEP (FRONT END PROCESSOR)

FEP acts as a buffer between the Central Monitoring Unit (Computer) and the Network It is provided

at centralised place to retrieve data continuously from station dataloggers and store in memory and transfer to

computer on request It stores 10 Lac telegrams It works on 12V DC It draws 16A continuous current

when all the three modems are connected Normally it shows the number of packets pending to be sent to the

computer on its 7-segment LED display It is provided with MOTOROLA 68000 microprocessor It has 6-

nos of RS-232 communication ports such as COM1 COM2 COM3 COM4 COM5 and COM6 COM1 is

used for Fault Analysis System (FAS) ie Central Monitoring Unit (Computer) connection COM2 to COM6

are used for networking For Bi-directional 2- nos of ports and for Tri-directional (T-network) 3-nos of ports

are used

DATA TRANSMISSION Dataloggers can be networked in Uni-directional Mode or Bi-directional Mode or T ndash Network Mode

In case of loss of data retransmission of data takes place

(a) Uni-Directional Mode

Each Datalogger will send data in only one direction to the FEP Unidirectional mode network is not

preferred

(b) Bi-Directional Mode

Each end of Network is connected to FEP and each datalogger can now transmit data in both the directions

Bi-directional Mode is advantageous it enables the Data Transmission even in case of Network Failure

(c) T - Network Mode

If more no of stations are in network ie if the network is too lengthy then T- network mode is preferred

COMMUNICATION The communication protocol for transmitting data and command between datalogger and CMU is

standardized by the RDSO and is given in the Specifications of Dataloggers

(a) The type of communication used in the network is dependent on the distance between the dataloggers

(b) For shorter distances Opto Converter Box- Opto isolated current loop communication is used

(c) For longer distances Modem (Dial-up leased) Fiber Optic Satellite Microwave communication

MODEMS Modems are used for DATA transfer between Dataloggers and Front End ProcessorThese are

configured to RS 232 Serial Communication Network is connected with two types of 4-wire modems

(a) Internal modem card Dual Modem card (in-built)

It is fixed in datalogger Euro rack itself One card contains two modems The top modem is called

ANS (answer) modem and the bottom modem is called as ORG (originate) modem

Note In case of networking of Dataloggers connect lsquoANSrsquo modem to the lsquoORGrsquo modem of one adjacent

station and connect lsquoORGrsquo modem to the lsquoANSrsquo modem of other adjacent station

(b) External modems

20 | P a g e

These are generally used at FEP (Front End Processor) side to connect the Dataloggers

(i) To transfer Data from one datalogger to another datalogger FEP Baud rate is 9600bps

(ii) These modems are 4-wire line communication

(iii) To transfer the data from FEP to RMU (PC) the Baud rate is 57600 bps

There is no difference between these modems functionally

CENTRAL MONITORING UNIT (CMU) COMPUTER

Central monitoring unit (Fault Analysis Unit) is a Personal Computer and its minimum configuration

shall be specified by RDSO from time to time System Software Windows XPVista(OS) Norton Kaspersky

(Anti Virus) Interbase where Server is not available (DBMS) Oracle where Server is available (DBMS)

software are required to run Datalogger System It is provided with Graphical User interface (GUI) based

software and retrieve data from all Networked dataloggers (up to 32) at various stations It stores data in

standard data base files The CMU is capable of analyzing the data and generate reports audiovisual alarms

on defined conditions This data can be compressed to take backup In central monitoring unit Software used

for analysis of data prediction of faults etc is written in a structured format so that purchaser can

reconfigure it if required It displays the status of signaling gears at any selected time in graphic form for any

selected station yard It retrieves the stored data amp simulates train movement It sends commands to various

Dataloggers to activate audio visual alarm or operate and electromagnetic relay

CMU shares data available in it by other PCs through available local area network where this data can

be used for train charting passenger information purpose The system generates audiovisual alarm in

ASMrsquosSignal Maintainerrsquos room in the case of power supply failure (battery voltage low) or battery charger

defective with acknowledgement facility

(a) Each datalogger has its own identity code which will be transmitted along with data packet to central

monitoring unit

(b) Events recorded at each station are continuously transmitted to central monitoring unit Response time of

data transfer will not exceed 10 sec

21 | P a g e

22 | P a g e

OPTICAL FIBER CABLE

INTRODUCTION The demand for bandwidth on transmission networks is increasing rapidly because video and

graphical rich contents are exchanged through the corporate network or the Internet The Gigabit Ethernet

became ommonly used in the corporate network backbone and 10Gbit Ethernet will be adopted in the near

future Meanwhile in the home the demand for high-speed network becomes popular as the wide spread of

broadband access eg CATV xDSL and FTTH The transmission medium with capability to transmit high

bit rate signal is necessary to satisfy these requirements

The telecommunication transport technologies move from copper based networks to optical fiber

from timeslot based transport to wave length based transport from traditional circuit switching to terabit

router and all optical based networks entering into a new era of optical networking

BASIC PHYSICS OF OFC

OPTICAL FIBER CABLE OFC have Fibers which are long thin strands made with pure glass about the diameter of a human

hair OFC consists of Core Cladding Buffers and Jacket as shown in figure

MONOCHROMATIC LIGHT OR SINGLE COLOR LIGHT Light or visible light is electromagnetic radiation of a wavelength that is visible to the human eye (

about 400 ndash 700 nm) The word light is sometimes used to refer to the entire electromagnetic spectrum Light

is composed of elementary particles called photons Three primary properties of light are

Light can exhibit properties of both waves and particles This property is referred to as wave-particle

duality The study of light known as optics In free space light (of all wavelengths) travels in a straight path

at a constant maximum speed However the speed of light changes when it travels in a medium and this

change is not the same for all media or for all wavelengths By free space it is meant space that is free from

matter (vacuum) andor free from electromagnetic fields

Thus the speed of light in free space is defined by Einsteinrsquos equation E = mc2

Frequency ν speed of light in free space c and wavelength λ are interrelated by ν = cλ

From the energy relationships E = mc2 = hν and the last one an interesting relationship is obtained

the equivalent mass of a photon m = hνc2

When light is in the vicinity of a strong electromagnetic field it interacts with it From this interaction

and other influences its trajectory changes direction as shown in figure

23 | P a g e

INCIDENT RAY REFLECTED RAY AND REFRACTED RAY An incident ray is a ray of light that strikes a surface The angle between this ray and the

perpendicular or normal to the surface is the angle of incidence Reflection is the change in direction of a

wave front at an interface between two different media so that the wave front returns into the medium from

which it originated Common examples include the reflection of light sound and water waves

The reflected ray corresponding to a given incident ray is the ray that represents the light reflected by

the surface The angle between the surface normal and the reflected ray is known as the angle of reflection

The Law of Reflection says that for a specular (non-scattering) surface the angle of reflection always equals

the angle of incidence The refracted ray or transmitted ray corresponding to a given incident ray represents

the light that is transmitted through the surface The angle between this ray and the normal is known as the

angle of refraction and it is given by Snells Law

The figure shows Incident ray Reflected ray Refracted ray the angle of incidence and angle of refraction

REFRACTIVE INDEX - Refractive index is the speed of light in a vacuum ( c =299792458kmsecond) divided by the speed

of light in a material ( v ) Refractive index measures how much a material refracts light Refractive index of

a material abbreviated as lsquo n lsquo is defined as lsquo n=cv lsquo Light travels slower in physical media than it does

when transmitted through the air Refractive index (n) is a function of molecular structure of matter optical

frequency optical intensity determines optical propagation properties of each wavelength ( λ ) may not be

distributed equally in all directions is affected by external temperature pressure and fields

Refractive index of a medium is a measure for how much the speed of light is reduced inside the

medium For example typical glass has a refractive index of 15 which means that light travels at 1 15 =

067 times the speed in air or vacuum Two common properties of glass and other transparent materials are

directly related to their refractive index

First light rays change direction when they cross the interface from air to the material and effect that

is used in lenses and glasses

Second light reflects partially from surfaces that have a refractive index different from that of their

surroundings

SNELLrsquoS LAW-

24 | P a g e

When light passes from one transparent material to another it bends according to Snells law which

is defined as n1sin(θ1) = n2sin(θ2)

where n1 is the refractive index of the medium the light is leaving θ1 is the incident angle between the light

beam and the normal (normal is 90deg to the interface between two materials)

n2 is the refractive index of the material the light is entering

θ2 is the refractive angle between the light ray and the normal

Snellrsquos law gives the relationship between angle of incidence and angle of refraction

For the case of θ1 = 0deg (ie a ray perpendicular to the interface) the solution is θ2 = 0deg regardless of

the values of n1 and n2 That means a ray entering a medium perpendicular to the surface is never bent The

above is also valid for light going from a dense (higher n) to a less dense (lower n) material the symmetry of

Snells law shows that the same ray paths are applicable in opposite direction

TOTAL INTERNAL REFLECTION- When a light ray crosses an interface into a medium with a higher refractive index it bends towards

the normal Conversely light traveling cross an interface from a higher refractive index medium to a lower

refractive index medium will bend away from the normal

This has an interesting implication at some angle known as the critical angle θc light traveling from

a higher refractive index medium to a lower refractive index medium will be refracted at 90deg in other words

refracted alon g the interface If the light hits the interface at any angle larger than this critical angle it will

not pass through to the second medium at all Instead all of it will be reflected back into the first medium a

process known as total internal reflection

The critical angle can be calculated from Snells law putting in an angle of 90deg for the angle of the refracted

ray θ2 This gives θ1

Since θ2 = 90deg

So sin(θ2) = 1

25 | P a g e

Then θc = θ1 = arcsin(n2n1)

For example with light trying to emerge from glass with n1=15 into air (n2 =1) the ritical angle θc is

arcsin(115) or 418deg For any angle of incidence larger than the critical angle Snells law will not be able to

be solved for the angle of refraction because it will show that the refracted angle has a sine larger than 1

which is not possible In that case all the light is totally reflected off the interface obeying the law of

reflection

OPTICAL FIBER MODE An optical fiber guides light waves in distinct patterns called modes Mode describes the distribution

of light energy across the fiber The precise patterns depend on the wavelength of light transmitted and on the

variation in refractive index that shapes the core In essence the variations in refractive index create

boundary

conditions that shape how light waves travel through the fiber like the walls of a tunnel affect how sounds

echo inside

We can take a look at large-core step-index fibers Light rays enter the fiber at a range of angles and

rays at different angles can all stably travel down the length of the fiber as long as they hit the core-cladding

interface at an angle larger than critical angle These rays are different modes Fibers that carry more than

one mode at a specific light wavelength are called multimode fibers Some fibers have very small diameter

core that they can carry only one mode which travels as a straight line at the center of the core These fibers

are single mode fibers This is illustrated in the following picture

OPTICAL FIBER INDEX PROFILE Index profile is the refractive index distribution across the core and the cladding of a fiber Some

optical fiber has a step index profile in which the core has one uniformly distributed index and the cladding

has a lower uniformly distributed index Other optical fiber has a graded index profile in which refractive

index varies gradually as a function of radial distance from the fiber center Graded-index profiles include

power-law index profiles and parabolic index profiles The following figure shows some common types of

index profiles for single mode and multimode fiber

26 | P a g e

OPTICAL FIBERrsquoS NUMERICAL APERTURE ( NA )- Multimode optical fiber will only propagate light that enters the fiber within a certain cone known as

the acceptance cone of the fiber The half-angle of this cone is called the acceptance angle (see figure 18)

θmax For step-index multimode fiber the acceptance angle is determined only by the indices of refraction

Where

n is the refractive index of the medium light is traveling before entering the fiber

nf is the refractive index of the fiber core

nc is the refractive index of the cladding

NUMBER OF MODES IN A FIBER - Modes are sometimes characterized by numbers Single mode fibers carry only the lowest-order

mode assigned the number 0 Multimode fibers also carry higher-order modes The number of modes that

can propagate in a fiber depends on the fiberrsquos numerical aperture (or acceptance angle) as well as on its

core diameter and the wavelength of the light For a step-index multimode fiber the number of such modes

Nm

Where

D is the core diameter

λ is the operating wavelength

NA is the numerical aperture (or acceptance angle)

MODE FIELD DIAMETER - All light do not travels through the core of the fiber but is distributed through both the core and the

cladding The mode field is the distribution of light through the core and cladding of a particular fiber

Mode-Field Diameter (MFD) defines the size of the power distribution When coupling light into or out of a

fiber MFD is important in understanding light loss

27 | P a g e

ADVANTAGE OF OFC COMMUNICATION - bull More information carrying capacity Fibers can handle much higher data rates than copper More

information can be sent in a second

bull Free from Electromagnetic and Electrostatic interference Being insulator no electric current flows through

the fibre and due to this reason fibres neither radiate nor pick up electro - magnetic radiation So WPC

CLEARANCE is not required

bull Low attenuation 025 dbkm at 1550 nm Loss in twisted pair and coaxial cable increases with frequency

where as loss in the optical fibre cable remains flat over a wide range of frequencies

bull Use of WDM ndash Switching routing at Optical signal level

bull Self healing rings under NMS control

bull Small size makes fibre cable lighter in weight So easy to handleOptic fibre cable weight (approx)

500 kg km Copper cable weight (approx) 1000 kgkm

The reasons are photons of light in a fibre

do not affect each other as they have no electrical charge and they are not affected by stray photons outside

the fibre But in case of copper electrons move through the cable and these are affected by each other

Optical fibre does not carry any electricity even if the cable is damaged or short circuited it does

not cause any spark or fire hazard

As the fibre do not radiate energy it can not be detected by any nearby antenna or any

other detector The fibres are difficult to tap and therefore excellent for security

As the signal transmission is by digital modulation there is no chance of cross talk in

between channels

Only by adding a few additional terminal and repeater equipments the

capacity of the system can be increased at any time once the cable is laid

ical effects and temperature variations

LIMITATIONS OF OFC -

difficult

- utilised

APPLICATION IN SIGNAL AND TELECOMMUNICATIONS transmission circuits

-haul circuits for linking of telephone exchanges

28 | P a g e

PROPAGATION MODES CONCEPT -

MODE - Mode is an available distribution of electromagnetic field in a plane transverse to the direction of

light propagation Each mode is characterized by frequency polarization electric field strength and

magnetic field strength Available patterns are derived from Maxwellrsquos equations and boundary conditions

LINEARLY POLARIZED (LP) MODE A mode for which the field components in the direction of propagation are small compared to

components perpendicular to that direction An optical fibre supports only different field patterns called as

lsquoLinear Polarizedrsquo or lsquo LPrsquo modes The reasons are

requirements

de

the accrual of power carried by different modes

There are two basic types of fiber Multimode fiber and Single-mode fiber

Multimode fiber is best designed for short transmission distances This is suited for used in LAN systems and

video surveillance Single mode fibre is best designed for longer transmission distances This is suitable for

long distance telephony and multi channel television broadcast systems

29 | P a g e

MULTI MODE FIBER Multimode fiber the first to be manufactured and commercialized simply refers to the fact that

numerous modes or light rays are carried simultaneously through the waveguide Modes result from the fact

that light will only propagate in the fiber core at discrete angles within the cone of acceptance MM fiber type

has a much larger core diameter compared to single-mode fiber allowing for the larger number of modes

and

is easier to couple than single-mode optical fiber Multimode fiber further categorized as Multimode step-

index and Multimode graded index fiber

PROPAGATION THROUGH MMSI FIBER Figure shows the principle of total internal reflection applies to multimode step index fiber Because

the corersquos index of refraction is higher than the claddingrsquos index of refraction the light that enters at less than

the critical angle is guided along the fiber

Three different light waves travel down the fiber One mode travels straight down the center of the

core A second mode travels at a steep angle and bounces back and forth by total internal reflection The third

mode exceeds the critical angle and refracts into the cladding Naturally it can be seen that the second mode

travels a longer distance than the first mode causing the two modes to arrive at separate times

PROBLEMS WITH MMSI FIBER AND SOLUTION This disparity between arrival times of the different light rays is known as dispersion and the result is

a muddied signal at the receiving end It is important to note that high dispersion is an unavoidable

characteristic of multimode step-index fiber The solutions are either use Graded index fiber or Single mode

fiber

PROPAGATION THROUGH MMGI FIBER Multimode Graded-index refers to the fact that the refractive index of the core gradually decreases

farther from the center of the core The increased refraction in the center of the core slows the speed of some

light rays allowing all the light rays to reach the receiving end at approximately the same time reducing

dispersion Figure shows the Light propagation principle through multimode graded-index fiber The corersquos

central refractive index ( nA ) is greater than that of the outer corersquos refractive index ( nB )

It is very clear from the figure the light rays no longer follow straight lines they follow a serpentine path

being gradually bent back toward the center by the continuously declining refractive index This reduces the

arrival time disparity because all modes arrive at about the same time The modes traveling in a straight line

30 | P a g e

are in a higher refractive index so they travel slower than the serpentine modes These travel farther but

move faster in the lower refractive index of the outer core region

PROPAGATION THROUGH SMSI FIBER Single mode fiber has a much smaller core that allows only one mode of light at a time to propagate

through the core The figure shows the single mode fiber

Single-mode fiber exhibits no dispersion caused by multiple modes Single-mode fiber also offers lower fiber

attenuation than multimode fiber Thus more information can be transmitted per unit of time because it can

retain the fidelity of each light pulse over longer distances Like multimode fiber early single-mode fiber was

generally characterized as step-index fiber meaning the refractive index of the fiber core is a step above that

of the cladding rather than graduated as it is in graded-index fiber Modern single-mode fibers have evolved

into more complex designs such as matched clad depressed clad and other exotic structures

SINGLE-MODE FIBER DISADVANTAGES The smaller core diameter makes coupling light into the core more difficult The tolerances for single-

mode connectors and splices are also much more demanding

CUTOFF WAVE LENGTH - Cutoff wavelength is the wavelength above which a single-mode fiber supports and propagates only

one mode of light In other words an optical fiber that is single-mode at a particular wavelength may have

two or more modes at wavelengths lower than the cutoff wavelength The effective cutoff wavelength of a

fiber is dependent on the length of fiber and its deployment The longer the fiber the lower is the effective

cutoff

wavelength The smaller the bend radius of a loop of the fiber the lower is the effective cutoff wavelength If

a fiber is bent in a loop the effective cutoff wavelength is lowered

SIGNAL ATTENUATION IN FIBER - Optical fiber has a number of advantages over copper However it also suffers from degradation

problems which can not be ignored The first of these is loss or attenuation Attenuation is typically the result

of two sub properties They are scattering and absorption Both of which have cumulative effects The second

is

dispersion which is the spreading of the transmitted signal and is analogous to noise

SCATTERING Scattering occurs because of impurities or irregularities in the physical construction of the fiber The

well known form of scattering is Rayleigh Scattering It is caused by metal ions in the silica matrix and

results in light rays being scattered in various directions

31 | P a g e

Scattering limits the use of wavelengths below 800nm The short wavelengths are much affected than longer

wavelengths It is because of Rayleigh scattering that the sky appears to be blue ( shorter wave length ) The

shorter wavelengths ( blue ) of light are scattered more than the longer wavelengths of light

ABSORPTION Absorption results from three factors They are hydroxyl ions ( OH- water ) in the silica impurities

in the silica and incomplete residue from the manufacturing process These impurities tend to absorb the

energy of the transmitted signal and convert it to heat resulting in an overall weakening of the signal The

Hydroxyl absorption occurs at 125 and 139 micro The silica itself starts to absorb energy at 17 micro

because of the natural resonance of the silicon dioxide

MACRO BENDING LOSS Macro-bending loss is caused by bending of the entire fiber axis The bending radius shall not be

sharper than 30d where d is diameter of cable A single bend sharper than 30d can cause loss of 05dB

The fiber may break if bending is ever sharper

MICRO BENDING LOSS Micro-bending loss is caused by micro deformations of fiber axis which leads to failures in achieving

total internal reflection conditions Micro-bends are small scale perturbations along the fiber axis the

amplitude of which are on the order of microns These distortions can cause light to leak out of a fiber

Micro-bending may be induced at very cold temperatures because the glass has a different coefficient of

thermal expansion from the coating and cabling materials At low temperatures the coating and cable

become more rigid and may contract more than the glass Consequently enough load may be exerted on the

glass to cause micro bends

Coating material is selected by manufacturers to minimize loss due to micro-bending The linear thermal

expansion coefficient of coating material shall be compatible with that of fiber

32 | P a g e

DISPERSION Dispersion is the optical term for the spreading of the transmits in the fiber It is the bandwidth

limiting phenomenon and comes in two forms Multimode dispersion and chromatic dispersion Chromatic

dispersion is further subdivided into material dispersion and waveguide dispersion

DISPERSION PHENOMENON IN OPTICAL FIBER Dispersion is the time distortion of an optical signal that results from the differences of time of travel

for different components of that signal typically resulting in pulse broadening As the distance traveled by

the signal is more broadening of pulse is more In digital transmission dispersion limits on the maximum

data rate and the maximum distance ie the information-carrying capacity of a fiber link The interference

from broadened pulse in the next interval shall not lead to erroneous interpretation of received signal

OPTICAL DOMAIN Understanding where attenuation and dispersion problems occur helps optical design engineers

determine the better wavelengths at which information can be transmit taking into account distance type of

fiber and the other factors which can severely affect the integrity of the transmitted signal The graph shown

depicts the optical transmission domain as well as the areas where problems arise The wavelength (nm)

is shown on X-axis and attenuation ( dBkm) is shown on Y-axis

There are four transmission windows appear in the figure The first one is at around 850 nm the

second at 1310nm third at 1550 nm and fourth at 1625 nm The last two labeled as C and L band

respectively The 850 nm wavelength at which the original LED technology operated The second window at

1310 nm has low dispersion The 1550 nm called as C-band is ideal wavelength for long haul

communication systems The network engineers can avoid transmitting signal at 1000 nm where Rayleigh

scattering 1240 and 1390 nm where hydroxyl absorption by water occurs to avoid high degree of loss

Optical fibers also can be manufactured to have low dispersion wavelength in the 1550nm region

which is also the point where silica-based fibers have inherently minimal attenuation These fibers are

referred to as dispersion-shifted fibers and are used in long-distance applications with high bit rates For

33 | P a g e

applications utilizing multiple wavelengths it is undesirable to have the zero dispersion point within the

operating

wavelength range

34 | P a g e

SIGNALLING RELAYS

INTRODUCTION A relay is an electromagnetic device which is used to convey information from one circuit to another

circuit through a set of contact ie front or back contact Constructional and electrically relays may be

divided into DC and AC relays because the means by which the electrical energy in the coil is converted in

to mechanical Energy in order to move the contacts are fundamentally different In DC type the contacts are

carried on an armature forming part of a magnetic circuit in which a field is set up by the current flowing in

the coils In AC types the contacts are attached by a link mechanism to a metal sector disc or cylinder in

which currents are induced by the alternating magnetic field produced by the currents in the coils

Every endeavor has been made to explain the action of each type of relay in the simplest possible manner

Relays are sophisticated switch gears used for remote control and succession control of various

electrical equipment In present days they are widely used because they are capable of protecting the

controlled equipment from cross feeding and overloading even as they cater for speedy operations

Most of the relays in present day signaling are electromagnetic devices although some of the relays control

circuits through electronic components like diodetransistors Integrated Chips etc

Railway signaling relays are unique in that

(a) They operate on low voltage and current

(b) They are more articulate as according to their special features they can work under restrictive conditions

and in any specified manner Virtually they can cater for all situations while contributing to speed and

accuracy in operations

CLASSIFICATION OF SIGNALLING RELAYS (a) According to the method of their mounting or fixture they are classified as

(i) Shelf type Relays which are loosely kept on shelves

(ii) Plug in type Relays which are plugged into a pre- wired plug boards

(b) According to their connection and usage they are classified as

(i) Track relays Relay which is directly connected to the track to detect the presence of vehicle

(ii) Line Relays Other than track relay all are line relays Relays connected to the selection circuit

(c) According to their vitality or importance in ensuring train working safety they are classified as

(i) Vital Relays All relays used for traffic control such as signal point controls track detection etc

(ii) Non-vital Relays Relays which operate control aids and accessories like warnings buzzers

Indications etc

(d) According to their special provisions to ensure reliability of their contacts they are classified as

(i) Proved type are those whose normalization after each operation shall be proved in circuit

controlled by their contacts Contacts in which both the springs have metal surfaces on their tips They may

get fused due to high sparking current across them during operation These may prevent relay normalization

and causes unsafe condition in traffic control To avoid this proving of relay normalization after each

operation is necessary

(ii) Non - proved type Need not to be proved to have been normalized after each operation as their

contacts have at least one non-fusible contact (carbon contact)

(e) According to their feed source relays are broadly classified as

(i) DC relays The relay which requires DC power supply for its operations are called DC relays Among

the DC relays

o DC neutral relays This relay closes the same set of contacts on energization with Normal polarity

or Reverse polarity supply

o Polar Relays This relay closes different set of contacts when energized with Reverse polarity

supply They may or may not have contact to close when deenergized

35 | P a g e

(ii) AC Relay AC Induction motor track relays Time element relays flashing indication control etc

(iii) Electronic Relays DC relays with electronic components in them are called electronic relays

DC NEUTRAL RELAY Each Relay has usually one or two coils with a hollow center to accommodate a coreThe coils are

made up of a large numbers of turns of small gauge soft drawn copper wire The two coils can be connected

in series or parallel according to the requirement of relay resistance The ends of the coils are terminated on

binding post to which the control wires are connected Each coil is placed around a core of specially selected

Iron or steel having high permeability and low retentivity The core should be susceptible to magnetism and

at the same time should have little residual magnetism The cores are connected at the top by a yoke to

complete the magnetism coupling between two ends of coils The bottom of each core is equipped with a

large steel or Iron block known as pole piece or face

A flat piece of Iron or steel called armature is supported by brackets which are securely fastened to

the pole piece The armature yoke and the pole pieces are also made of specially selected iron or steel of the

same quality as the core The armature carries the metallic spring contacts which are insulated from it

The circuit through the coils of the relay is closed It sets up a magnetic flux through the core yoke and the

armature The flux passing between the armature and pole faces causes the armatures get attracted to the pole

faces and armature picks up and closes front contacts When the circuit is opened the magnetic flux collapses

and the armature drops away by gravity from the pole faces the front contacts break and back contacts close

The front and back contacts of the relay can be utilised to make or break other circuits Two stop pins of

nonmagnetic material are fixed either on the armature or pole faces so that the armature cannot

come in contact with the pole faces It is essential to maintain a small air-gap between the armature and pole

faces so that low value of residual magnetism may not retain the armature in picked up position and causes

the relay to fail to drop away with a break in its control circuit

GENERAL USAGE

DC Neutral line relays are most commonly used for Railway Signalling controls and detection

Among them plug-in type relays are preferred in larger installations for space considerations Shelf type

relays are also in use mostly in wayside stations

There are many DC Neutral line relays in use with special features such as

(i) Delayed operation

(ii) Biased DC control

(iii) DC control unaffected by AC interference currents

(iv) Getting latched in operated condition till further feeding and others

Usage of DC polar relays is mostly in conjunction with block instruments that control traffic between

stations AC line relays are almost extinct in installations of British Signalling practice They are however

used for time control operations flashing indication control and such other special purposes in installations

with Siemens signalling practice widely Track relays are used according to the type of track detection

circuits chosen for a given location and context While most of the track circuits are still of the DC working

type requiring DC neutral track relays with them the prospects of their being replaced with Electronic track

circuits directly feeding DC line relays in future are great AC Track Circuits are used in DC Traction area

as conventional DC Track Circuits are not suitable there AC Track relays are used with them almost all of

the induction motor type In the British practice of signalling which was first introduced on Indian Railways

non-proved type relays with carbon to metal switching contacts are generally used for vital controls

They facilitate simple circuit designs But with the advent of German Practice introduced by Ms

Siemens later proved type relays with all metal to metal contacts are widely accepted in spite of

complications in circuit design caused by them A recent introduction is that of the same type relays made by

Ms Integra control However for some time now the appreciable features of both the practices are getting

36 | P a g e

incorporated together in the indigenous designs of signalling by railwaymen With this the usage of all types

of relays anywhere can be found without straight jacketed segration of relay types

CHARACTERSTIC OF ELECTRO-MAGNETIC RELAY The following are the characteristic of electro-magnetic relays A brief study of them helps in

understanding the choice of their components and designs features

1) Force of attraction

2) Effect of air gap

3) Effect of Hysterisis

4) Transient condition

FORCE OF ATTRACTION In any electro-magnetic system the force of attraction is given by

Where B - is the flux density a - is the cross sectional area of the particular part of the magnetic

circuit

In the case of a DC neutral Relay B is proportional to the current that is flowing in the coil

surrounding the electro-magnet and thus the force of the attraction is directly proportional to the square of the

current This square relationship has its own advantage especially in the case of DC track relay in that a

small reduction in the current will have a great effect on the working of the relay Also for a given change of

current the make and the break will be quicker with lesser possibility of arcing

EFFECT OF AIR GAP

Curve lsquoArsquo is magnetisation curve for the iron and is all practical purpose a straight line up to the

saturation point Curve lsquoBrsquo is the magnetisation curve for the open-air gap which is a straight line through

out because per magnetisation curve of the whole

magnetic circuit of the relay and for a given force is the sum of the amp-turns for the iron part and the amp-

turns for the air gap

When the front contacts are open the force required to pick up the armature is shown on curve lsquoCrsquo to be F1

but after the armature has operated it will be separated from the core by stop pins In this position the amp-

turns required to maintain the armature is less as indicated by the dotted line from 1 on curve C to 2 on curve

37 | P a g e

F But actually the current in the coil is unaltered the force on the armature is greater than required as

indicated at 3 on curve F Part of this extra force is used to flex the front contacts sufficiently to give good

contact pressure when it is in energised position

The difference between the pick-up and the drop-away current should be as small as practicable in

track relay to ensure good shunting characteristics This is achieved firstly by the choice of good quality relay

iron and secondly by having a small air gap between armature and core If the air gap is not available then

the residual magnetism fluxes might cause the armature to be retained when the supply is disconnected For

this reason residual pins are provided to ensure a definite minimum air gap in the energised position

EFFECT OF HYSTERISIS

Hysterisis is the property by which the flux produced lags behind the current In the de-energized

condition there will be small residual flux in the core When the voltage is applied to the coils the current in

rising to its steady value first causes the flux to rise from 1 to 2 along the curve At this point the flux density

will be sufficient to attract the armature and reduce the air gap the flux then raise to 3 and continue to 4

which corresponds to the steady current in the coils When the voltage is disconnected the current in falling

caused the flux to fall from 4 to 5 along the curve At this point the flux density will fall below the value

required to maintain the armature which will release thus increasing the air gap and reducing the flux to 6

Finally the

flux will decrease from 6 to 1 where the current will again be zero

The relay core is made of material having high permeability and low retentivity As mentioned in

the IRS specification Electromagnet iron may be in the form of a

(a) Bar of silicon steel

(b) Best Yorkshire wrought iron

(c) Swedish charcoal iron

(d) Electrical steel sheets

` This reduces the difference between pick up value and Drop away value By selecting good quality

core material Percentage release and sensitivity of the relay will be improved

TRANSIENT CONDITION

38 | P a g e

When the voltage is applied or disconnected from the coils it takes some little time before the current

become steady These are known as transient conditionsrdquo and are important so far as track relays are

concerned When the voltage is first applied to the coils the magnetic flux in rising cuts the turns on the

coils and in so doing produces a back EMF that opposes the applied voltage and retards the growth of

current

The growth and decay of flux are decided by the relationship between the inductance and resistance

in the circuit is known as time constant It is not fixed quantity in the case of DC neutral relay This value of lsquo

Lrsquo is less when the relay is in de-energised condition (L1) than when the relay is in energised condition (L2)

The magnitude of flux that is established for a given change of current is different in two cases

When the current reaches the pick up value the armature closes and the inductance is increased to L2

due to reduced air gap the flux per amp is increased The increase in flux increased the back EMF during the

movement of the armature after which the current continuous to raise along a new curve corresponding to the

increased inductance until it reaches the final value (ER) This process is indicated above in fig24

When the supply is disconnected the current is obliviously reduced to zero immediately but the flux

decay comparatively slowly owing to the eddy currents produced in the core by the rapid flux change which

tend to maintain the flux The drop away time on a disconnection is however generally negligible See fig

below

If the relay releases due to the reduction in current from say I 2 to I 1 caused by the application of

shunt resistance (as in the case of track relay ) the time taken is much longer than the relay is simply

disconnected The rate of rise or fall of current during the transient conditions is also depends on exterior

circuit values because L and R apply to the whole circuit The production of eddy current in the core the flux

will decay at a slower rate than the current So that the actual release time will be a little longer than it takes

the current to fall to the release

L= Inductance

39 | P a g e

R= Resistance

It is now clear that to reduce releasing time to a minimum it is necessary that

- The relay iron should have low Hysterisis loss and low retentivity

- The degree of over energization of the relay should be restricted

- Connecting a suitable external resistance in series with the relay to keep LR ratio low

In non RE area for track circuit length less than 100M 9 ohm track relay only to be used Using relay

with minimum contacts as they require lesser current which keeps inductance value low

Train working safety is ensured only if the track relay of shortest length track circuit is released

before a light engine running at a highest permitted speed clears it Otherwise the track circuit occupation

may go undetected To avoid this a special provision has to be made in signal control circuits wherever

necessary

The following methods may be adopted for reducing the time lag of track relay

(a) Restrict the over energisation of relay since the release time depends on the initial working current

(b) Connecting a suitable external resistance in series with the relay to keep the LR ratio low

(c) Using relays with minimum contacts as they require lesser operating current keeping the inductance

value low

40 | P a g e

CONCLUSION

Modern signalling is vital for safe and punctual movements of trains In the Indian railways The Signalling

and Telecommunication Department is responsible for providing modern effective and relaible signalling

systems as well as telecommunication systems

The first mode of communication used in Indian Railways was the use of electric telegraph

with the help of Morose code Morose code is the method of providing text information as a series of on-off

tones and lights or clicks that can be directly understood by a skilled listener or observer without special

equipmentEach character (letter or numeral ) is represented by a unique sequence of dots and dashes Later

this system becomes obselete and beggan the era of wireless communication which operated at audio level

frequency range

In wireless communication the significant advances took place the transition to miniature

valves or filament tubesBut this was abandoned too because of excessive current consumption and over

heating of the filament tubes

Fibre-optic communication is a method of transmitting information from one place to another by

sending pulses of light through an optcial fibreThe light forms an electromagnetic carrier wave that is

modulated to carry information First developed in the 1970s fibre optic communication systems has

revolutionized the telecommunications industry and have palyed a major role in the advent of the information

age Because of its advantages over electrical transmissionsoptical fibres have largely replaced copper wire

communications in core networks in the developed world The Indian Railways too is undergoing a transition

from Microwave communication to fibre optic communications

41 | P a g e

BIBLIOGRAPHY AND REFERENCES

1 wwwwikipediacom

2 wwwbritaniccacom

3 wwwirfcacom

4 Motorola GP60 system manual

5 Harris FAS 7000 manual

6 TOSHIBA Manual

18 | P a g e

(iii) Internal relays

British system All HR DR HHR WNR WRR ASR UCR RR LR UYRTLSR TRSR TSR

JSLR JR etc

SIEMENS system Z1UR Z1UR1 GZR ZDUCR ZU(R)R ZU(N)PRG(R)RG(N)R U(R)S

U(N)PS UDKR DUCR U(R)LR UYR1 UYR2 G(R)LRGR1GR2

GR3 GR4 OVZ2U(R)RW(RN)R (RN)WLR Z1NWR Z1RWRZ1WR1 WKR1 WKR2 WKR3 etc

(b) Analog channels

(i) 230 V AC (for power supplies in the power panel)

(ii) 110V AC (for Signal and Track transformers)

(iii) 110V DC (for Point operation)

(iv) 60V DC (Siemens relays)

(v) 24V DC (Q-series relays)

(vi) 24V DC (for Block Axle counters)

(vii) 12V DC (for indication)

(viii) 20A (for point operation current)

(ix) 10V AC 5KHz (for Axle counter channels) etc

SOFTWARE MODULES OF DATALOGGERS

(a) Network Management of Dataloggers (NMDL)

(b) Reports

(c) Fault Entry

(d) Track Offline Simulation

(e) Train Charting

NMDL SOFTWARE FEATURES (a) Online Relay Status

(b) Online Faults - To view information of various Online Faults as they occur in the stations where

the Dataloggers are connected

(c) Online Simulation - Graphical view of relay operations train movements etc

(d) Remote monitoring of stations with the help of NETWORKING

SOFTWARE OBJECTIVES (a) Predictive Maintenance

(b) Easy identification of failures

(c) Crew discipline

(d) Train charting

REMOTE MONITORING OF STATIONS WITH NETWORKING OF

DATALOGGERS The individual Dataloggers of various stations can be interconnected through networking technology

The data of Remote Panel stations can be viewed in a Computer at the Central Monitoring Station The data

of the network is collected by the FEP (Front End Processor) which in turn is transmitted to the computer

COMPONENTS OF NETWORK MANAGEMENT OF DATALOGGERS

(a) Datalogger at stations

(b) MODEM and Transmission medium

19 | P a g e

(c) Front End Processor (FEP)

(d) Central Monitoring Unit (CMU) Computer

FEP (FRONT END PROCESSOR)

FEP acts as a buffer between the Central Monitoring Unit (Computer) and the Network It is provided

at centralised place to retrieve data continuously from station dataloggers and store in memory and transfer to

computer on request It stores 10 Lac telegrams It works on 12V DC It draws 16A continuous current

when all the three modems are connected Normally it shows the number of packets pending to be sent to the

computer on its 7-segment LED display It is provided with MOTOROLA 68000 microprocessor It has 6-

nos of RS-232 communication ports such as COM1 COM2 COM3 COM4 COM5 and COM6 COM1 is

used for Fault Analysis System (FAS) ie Central Monitoring Unit (Computer) connection COM2 to COM6

are used for networking For Bi-directional 2- nos of ports and for Tri-directional (T-network) 3-nos of ports

are used

DATA TRANSMISSION Dataloggers can be networked in Uni-directional Mode or Bi-directional Mode or T ndash Network Mode

In case of loss of data retransmission of data takes place

(a) Uni-Directional Mode

Each Datalogger will send data in only one direction to the FEP Unidirectional mode network is not

preferred

(b) Bi-Directional Mode

Each end of Network is connected to FEP and each datalogger can now transmit data in both the directions

Bi-directional Mode is advantageous it enables the Data Transmission even in case of Network Failure

(c) T - Network Mode

If more no of stations are in network ie if the network is too lengthy then T- network mode is preferred

COMMUNICATION The communication protocol for transmitting data and command between datalogger and CMU is

standardized by the RDSO and is given in the Specifications of Dataloggers

(a) The type of communication used in the network is dependent on the distance between the dataloggers

(b) For shorter distances Opto Converter Box- Opto isolated current loop communication is used

(c) For longer distances Modem (Dial-up leased) Fiber Optic Satellite Microwave communication

MODEMS Modems are used for DATA transfer between Dataloggers and Front End ProcessorThese are

configured to RS 232 Serial Communication Network is connected with two types of 4-wire modems

(a) Internal modem card Dual Modem card (in-built)

It is fixed in datalogger Euro rack itself One card contains two modems The top modem is called

ANS (answer) modem and the bottom modem is called as ORG (originate) modem

Note In case of networking of Dataloggers connect lsquoANSrsquo modem to the lsquoORGrsquo modem of one adjacent

station and connect lsquoORGrsquo modem to the lsquoANSrsquo modem of other adjacent station

(b) External modems

20 | P a g e

These are generally used at FEP (Front End Processor) side to connect the Dataloggers

(i) To transfer Data from one datalogger to another datalogger FEP Baud rate is 9600bps

(ii) These modems are 4-wire line communication

(iii) To transfer the data from FEP to RMU (PC) the Baud rate is 57600 bps

There is no difference between these modems functionally

CENTRAL MONITORING UNIT (CMU) COMPUTER

Central monitoring unit (Fault Analysis Unit) is a Personal Computer and its minimum configuration

shall be specified by RDSO from time to time System Software Windows XPVista(OS) Norton Kaspersky

(Anti Virus) Interbase where Server is not available (DBMS) Oracle where Server is available (DBMS)

software are required to run Datalogger System It is provided with Graphical User interface (GUI) based

software and retrieve data from all Networked dataloggers (up to 32) at various stations It stores data in

standard data base files The CMU is capable of analyzing the data and generate reports audiovisual alarms

on defined conditions This data can be compressed to take backup In central monitoring unit Software used

for analysis of data prediction of faults etc is written in a structured format so that purchaser can

reconfigure it if required It displays the status of signaling gears at any selected time in graphic form for any

selected station yard It retrieves the stored data amp simulates train movement It sends commands to various

Dataloggers to activate audio visual alarm or operate and electromagnetic relay

CMU shares data available in it by other PCs through available local area network where this data can

be used for train charting passenger information purpose The system generates audiovisual alarm in

ASMrsquosSignal Maintainerrsquos room in the case of power supply failure (battery voltage low) or battery charger

defective with acknowledgement facility

(a) Each datalogger has its own identity code which will be transmitted along with data packet to central

monitoring unit

(b) Events recorded at each station are continuously transmitted to central monitoring unit Response time of

data transfer will not exceed 10 sec

21 | P a g e

22 | P a g e

OPTICAL FIBER CABLE

INTRODUCTION The demand for bandwidth on transmission networks is increasing rapidly because video and

graphical rich contents are exchanged through the corporate network or the Internet The Gigabit Ethernet

became ommonly used in the corporate network backbone and 10Gbit Ethernet will be adopted in the near

future Meanwhile in the home the demand for high-speed network becomes popular as the wide spread of

broadband access eg CATV xDSL and FTTH The transmission medium with capability to transmit high

bit rate signal is necessary to satisfy these requirements

The telecommunication transport technologies move from copper based networks to optical fiber

from timeslot based transport to wave length based transport from traditional circuit switching to terabit

router and all optical based networks entering into a new era of optical networking

BASIC PHYSICS OF OFC

OPTICAL FIBER CABLE OFC have Fibers which are long thin strands made with pure glass about the diameter of a human

hair OFC consists of Core Cladding Buffers and Jacket as shown in figure

MONOCHROMATIC LIGHT OR SINGLE COLOR LIGHT Light or visible light is electromagnetic radiation of a wavelength that is visible to the human eye (

about 400 ndash 700 nm) The word light is sometimes used to refer to the entire electromagnetic spectrum Light

is composed of elementary particles called photons Three primary properties of light are

Light can exhibit properties of both waves and particles This property is referred to as wave-particle

duality The study of light known as optics In free space light (of all wavelengths) travels in a straight path

at a constant maximum speed However the speed of light changes when it travels in a medium and this

change is not the same for all media or for all wavelengths By free space it is meant space that is free from

matter (vacuum) andor free from electromagnetic fields

Thus the speed of light in free space is defined by Einsteinrsquos equation E = mc2

Frequency ν speed of light in free space c and wavelength λ are interrelated by ν = cλ

From the energy relationships E = mc2 = hν and the last one an interesting relationship is obtained

the equivalent mass of a photon m = hνc2

When light is in the vicinity of a strong electromagnetic field it interacts with it From this interaction

and other influences its trajectory changes direction as shown in figure

23 | P a g e

INCIDENT RAY REFLECTED RAY AND REFRACTED RAY An incident ray is a ray of light that strikes a surface The angle between this ray and the

perpendicular or normal to the surface is the angle of incidence Reflection is the change in direction of a

wave front at an interface between two different media so that the wave front returns into the medium from

which it originated Common examples include the reflection of light sound and water waves

The reflected ray corresponding to a given incident ray is the ray that represents the light reflected by

the surface The angle between the surface normal and the reflected ray is known as the angle of reflection

The Law of Reflection says that for a specular (non-scattering) surface the angle of reflection always equals

the angle of incidence The refracted ray or transmitted ray corresponding to a given incident ray represents

the light that is transmitted through the surface The angle between this ray and the normal is known as the

angle of refraction and it is given by Snells Law

The figure shows Incident ray Reflected ray Refracted ray the angle of incidence and angle of refraction

REFRACTIVE INDEX - Refractive index is the speed of light in a vacuum ( c =299792458kmsecond) divided by the speed

of light in a material ( v ) Refractive index measures how much a material refracts light Refractive index of

a material abbreviated as lsquo n lsquo is defined as lsquo n=cv lsquo Light travels slower in physical media than it does

when transmitted through the air Refractive index (n) is a function of molecular structure of matter optical

frequency optical intensity determines optical propagation properties of each wavelength ( λ ) may not be

distributed equally in all directions is affected by external temperature pressure and fields

Refractive index of a medium is a measure for how much the speed of light is reduced inside the

medium For example typical glass has a refractive index of 15 which means that light travels at 1 15 =

067 times the speed in air or vacuum Two common properties of glass and other transparent materials are

directly related to their refractive index

First light rays change direction when they cross the interface from air to the material and effect that

is used in lenses and glasses

Second light reflects partially from surfaces that have a refractive index different from that of their

surroundings

SNELLrsquoS LAW-

24 | P a g e

When light passes from one transparent material to another it bends according to Snells law which

is defined as n1sin(θ1) = n2sin(θ2)

where n1 is the refractive index of the medium the light is leaving θ1 is the incident angle between the light

beam and the normal (normal is 90deg to the interface between two materials)

n2 is the refractive index of the material the light is entering

θ2 is the refractive angle between the light ray and the normal

Snellrsquos law gives the relationship between angle of incidence and angle of refraction

For the case of θ1 = 0deg (ie a ray perpendicular to the interface) the solution is θ2 = 0deg regardless of

the values of n1 and n2 That means a ray entering a medium perpendicular to the surface is never bent The

above is also valid for light going from a dense (higher n) to a less dense (lower n) material the symmetry of

Snells law shows that the same ray paths are applicable in opposite direction

TOTAL INTERNAL REFLECTION- When a light ray crosses an interface into a medium with a higher refractive index it bends towards

the normal Conversely light traveling cross an interface from a higher refractive index medium to a lower

refractive index medium will bend away from the normal

This has an interesting implication at some angle known as the critical angle θc light traveling from

a higher refractive index medium to a lower refractive index medium will be refracted at 90deg in other words

refracted alon g the interface If the light hits the interface at any angle larger than this critical angle it will

not pass through to the second medium at all Instead all of it will be reflected back into the first medium a

process known as total internal reflection

The critical angle can be calculated from Snells law putting in an angle of 90deg for the angle of the refracted

ray θ2 This gives θ1

Since θ2 = 90deg

So sin(θ2) = 1

25 | P a g e

Then θc = θ1 = arcsin(n2n1)

For example with light trying to emerge from glass with n1=15 into air (n2 =1) the ritical angle θc is

arcsin(115) or 418deg For any angle of incidence larger than the critical angle Snells law will not be able to

be solved for the angle of refraction because it will show that the refracted angle has a sine larger than 1

which is not possible In that case all the light is totally reflected off the interface obeying the law of

reflection

OPTICAL FIBER MODE An optical fiber guides light waves in distinct patterns called modes Mode describes the distribution

of light energy across the fiber The precise patterns depend on the wavelength of light transmitted and on the

variation in refractive index that shapes the core In essence the variations in refractive index create

boundary

conditions that shape how light waves travel through the fiber like the walls of a tunnel affect how sounds

echo inside

We can take a look at large-core step-index fibers Light rays enter the fiber at a range of angles and

rays at different angles can all stably travel down the length of the fiber as long as they hit the core-cladding

interface at an angle larger than critical angle These rays are different modes Fibers that carry more than

one mode at a specific light wavelength are called multimode fibers Some fibers have very small diameter

core that they can carry only one mode which travels as a straight line at the center of the core These fibers

are single mode fibers This is illustrated in the following picture

OPTICAL FIBER INDEX PROFILE Index profile is the refractive index distribution across the core and the cladding of a fiber Some

optical fiber has a step index profile in which the core has one uniformly distributed index and the cladding

has a lower uniformly distributed index Other optical fiber has a graded index profile in which refractive

index varies gradually as a function of radial distance from the fiber center Graded-index profiles include

power-law index profiles and parabolic index profiles The following figure shows some common types of

index profiles for single mode and multimode fiber

26 | P a g e

OPTICAL FIBERrsquoS NUMERICAL APERTURE ( NA )- Multimode optical fiber will only propagate light that enters the fiber within a certain cone known as

the acceptance cone of the fiber The half-angle of this cone is called the acceptance angle (see figure 18)

θmax For step-index multimode fiber the acceptance angle is determined only by the indices of refraction

Where

n is the refractive index of the medium light is traveling before entering the fiber

nf is the refractive index of the fiber core

nc is the refractive index of the cladding

NUMBER OF MODES IN A FIBER - Modes are sometimes characterized by numbers Single mode fibers carry only the lowest-order

mode assigned the number 0 Multimode fibers also carry higher-order modes The number of modes that

can propagate in a fiber depends on the fiberrsquos numerical aperture (or acceptance angle) as well as on its

core diameter and the wavelength of the light For a step-index multimode fiber the number of such modes

Nm

Where

D is the core diameter

λ is the operating wavelength

NA is the numerical aperture (or acceptance angle)

MODE FIELD DIAMETER - All light do not travels through the core of the fiber but is distributed through both the core and the

cladding The mode field is the distribution of light through the core and cladding of a particular fiber

Mode-Field Diameter (MFD) defines the size of the power distribution When coupling light into or out of a

fiber MFD is important in understanding light loss

27 | P a g e

ADVANTAGE OF OFC COMMUNICATION - bull More information carrying capacity Fibers can handle much higher data rates than copper More

information can be sent in a second

bull Free from Electromagnetic and Electrostatic interference Being insulator no electric current flows through

the fibre and due to this reason fibres neither radiate nor pick up electro - magnetic radiation So WPC

CLEARANCE is not required

bull Low attenuation 025 dbkm at 1550 nm Loss in twisted pair and coaxial cable increases with frequency

where as loss in the optical fibre cable remains flat over a wide range of frequencies

bull Use of WDM ndash Switching routing at Optical signal level

bull Self healing rings under NMS control

bull Small size makes fibre cable lighter in weight So easy to handleOptic fibre cable weight (approx)

500 kg km Copper cable weight (approx) 1000 kgkm

The reasons are photons of light in a fibre

do not affect each other as they have no electrical charge and they are not affected by stray photons outside

the fibre But in case of copper electrons move through the cable and these are affected by each other

Optical fibre does not carry any electricity even if the cable is damaged or short circuited it does

not cause any spark or fire hazard

As the fibre do not radiate energy it can not be detected by any nearby antenna or any

other detector The fibres are difficult to tap and therefore excellent for security

As the signal transmission is by digital modulation there is no chance of cross talk in

between channels

Only by adding a few additional terminal and repeater equipments the

capacity of the system can be increased at any time once the cable is laid

ical effects and temperature variations

LIMITATIONS OF OFC -

difficult

- utilised

APPLICATION IN SIGNAL AND TELECOMMUNICATIONS transmission circuits

-haul circuits for linking of telephone exchanges

28 | P a g e

PROPAGATION MODES CONCEPT -

MODE - Mode is an available distribution of electromagnetic field in a plane transverse to the direction of

light propagation Each mode is characterized by frequency polarization electric field strength and

magnetic field strength Available patterns are derived from Maxwellrsquos equations and boundary conditions

LINEARLY POLARIZED (LP) MODE A mode for which the field components in the direction of propagation are small compared to

components perpendicular to that direction An optical fibre supports only different field patterns called as

lsquoLinear Polarizedrsquo or lsquo LPrsquo modes The reasons are

requirements

de

the accrual of power carried by different modes

There are two basic types of fiber Multimode fiber and Single-mode fiber

Multimode fiber is best designed for short transmission distances This is suited for used in LAN systems and

video surveillance Single mode fibre is best designed for longer transmission distances This is suitable for

long distance telephony and multi channel television broadcast systems

29 | P a g e

MULTI MODE FIBER Multimode fiber the first to be manufactured and commercialized simply refers to the fact that

numerous modes or light rays are carried simultaneously through the waveguide Modes result from the fact

that light will only propagate in the fiber core at discrete angles within the cone of acceptance MM fiber type

has a much larger core diameter compared to single-mode fiber allowing for the larger number of modes

and

is easier to couple than single-mode optical fiber Multimode fiber further categorized as Multimode step-

index and Multimode graded index fiber

PROPAGATION THROUGH MMSI FIBER Figure shows the principle of total internal reflection applies to multimode step index fiber Because

the corersquos index of refraction is higher than the claddingrsquos index of refraction the light that enters at less than

the critical angle is guided along the fiber

Three different light waves travel down the fiber One mode travels straight down the center of the

core A second mode travels at a steep angle and bounces back and forth by total internal reflection The third

mode exceeds the critical angle and refracts into the cladding Naturally it can be seen that the second mode

travels a longer distance than the first mode causing the two modes to arrive at separate times

PROBLEMS WITH MMSI FIBER AND SOLUTION This disparity between arrival times of the different light rays is known as dispersion and the result is

a muddied signal at the receiving end It is important to note that high dispersion is an unavoidable

characteristic of multimode step-index fiber The solutions are either use Graded index fiber or Single mode

fiber

PROPAGATION THROUGH MMGI FIBER Multimode Graded-index refers to the fact that the refractive index of the core gradually decreases

farther from the center of the core The increased refraction in the center of the core slows the speed of some

light rays allowing all the light rays to reach the receiving end at approximately the same time reducing

dispersion Figure shows the Light propagation principle through multimode graded-index fiber The corersquos

central refractive index ( nA ) is greater than that of the outer corersquos refractive index ( nB )

It is very clear from the figure the light rays no longer follow straight lines they follow a serpentine path

being gradually bent back toward the center by the continuously declining refractive index This reduces the

arrival time disparity because all modes arrive at about the same time The modes traveling in a straight line

30 | P a g e

are in a higher refractive index so they travel slower than the serpentine modes These travel farther but

move faster in the lower refractive index of the outer core region

PROPAGATION THROUGH SMSI FIBER Single mode fiber has a much smaller core that allows only one mode of light at a time to propagate

through the core The figure shows the single mode fiber

Single-mode fiber exhibits no dispersion caused by multiple modes Single-mode fiber also offers lower fiber

attenuation than multimode fiber Thus more information can be transmitted per unit of time because it can

retain the fidelity of each light pulse over longer distances Like multimode fiber early single-mode fiber was

generally characterized as step-index fiber meaning the refractive index of the fiber core is a step above that

of the cladding rather than graduated as it is in graded-index fiber Modern single-mode fibers have evolved

into more complex designs such as matched clad depressed clad and other exotic structures

SINGLE-MODE FIBER DISADVANTAGES The smaller core diameter makes coupling light into the core more difficult The tolerances for single-

mode connectors and splices are also much more demanding

CUTOFF WAVE LENGTH - Cutoff wavelength is the wavelength above which a single-mode fiber supports and propagates only

one mode of light In other words an optical fiber that is single-mode at a particular wavelength may have

two or more modes at wavelengths lower than the cutoff wavelength The effective cutoff wavelength of a

fiber is dependent on the length of fiber and its deployment The longer the fiber the lower is the effective

cutoff

wavelength The smaller the bend radius of a loop of the fiber the lower is the effective cutoff wavelength If

a fiber is bent in a loop the effective cutoff wavelength is lowered

SIGNAL ATTENUATION IN FIBER - Optical fiber has a number of advantages over copper However it also suffers from degradation

problems which can not be ignored The first of these is loss or attenuation Attenuation is typically the result

of two sub properties They are scattering and absorption Both of which have cumulative effects The second

is

dispersion which is the spreading of the transmitted signal and is analogous to noise

SCATTERING Scattering occurs because of impurities or irregularities in the physical construction of the fiber The

well known form of scattering is Rayleigh Scattering It is caused by metal ions in the silica matrix and

results in light rays being scattered in various directions

31 | P a g e

Scattering limits the use of wavelengths below 800nm The short wavelengths are much affected than longer

wavelengths It is because of Rayleigh scattering that the sky appears to be blue ( shorter wave length ) The

shorter wavelengths ( blue ) of light are scattered more than the longer wavelengths of light

ABSORPTION Absorption results from three factors They are hydroxyl ions ( OH- water ) in the silica impurities

in the silica and incomplete residue from the manufacturing process These impurities tend to absorb the

energy of the transmitted signal and convert it to heat resulting in an overall weakening of the signal The

Hydroxyl absorption occurs at 125 and 139 micro The silica itself starts to absorb energy at 17 micro

because of the natural resonance of the silicon dioxide

MACRO BENDING LOSS Macro-bending loss is caused by bending of the entire fiber axis The bending radius shall not be

sharper than 30d where d is diameter of cable A single bend sharper than 30d can cause loss of 05dB

The fiber may break if bending is ever sharper

MICRO BENDING LOSS Micro-bending loss is caused by micro deformations of fiber axis which leads to failures in achieving

total internal reflection conditions Micro-bends are small scale perturbations along the fiber axis the

amplitude of which are on the order of microns These distortions can cause light to leak out of a fiber

Micro-bending may be induced at very cold temperatures because the glass has a different coefficient of

thermal expansion from the coating and cabling materials At low temperatures the coating and cable

become more rigid and may contract more than the glass Consequently enough load may be exerted on the

glass to cause micro bends

Coating material is selected by manufacturers to minimize loss due to micro-bending The linear thermal

expansion coefficient of coating material shall be compatible with that of fiber

32 | P a g e

DISPERSION Dispersion is the optical term for the spreading of the transmits in the fiber It is the bandwidth

limiting phenomenon and comes in two forms Multimode dispersion and chromatic dispersion Chromatic

dispersion is further subdivided into material dispersion and waveguide dispersion

DISPERSION PHENOMENON IN OPTICAL FIBER Dispersion is the time distortion of an optical signal that results from the differences of time of travel

for different components of that signal typically resulting in pulse broadening As the distance traveled by

the signal is more broadening of pulse is more In digital transmission dispersion limits on the maximum

data rate and the maximum distance ie the information-carrying capacity of a fiber link The interference

from broadened pulse in the next interval shall not lead to erroneous interpretation of received signal

OPTICAL DOMAIN Understanding where attenuation and dispersion problems occur helps optical design engineers

determine the better wavelengths at which information can be transmit taking into account distance type of

fiber and the other factors which can severely affect the integrity of the transmitted signal The graph shown

depicts the optical transmission domain as well as the areas where problems arise The wavelength (nm)

is shown on X-axis and attenuation ( dBkm) is shown on Y-axis

There are four transmission windows appear in the figure The first one is at around 850 nm the

second at 1310nm third at 1550 nm and fourth at 1625 nm The last two labeled as C and L band

respectively The 850 nm wavelength at which the original LED technology operated The second window at

1310 nm has low dispersion The 1550 nm called as C-band is ideal wavelength for long haul

communication systems The network engineers can avoid transmitting signal at 1000 nm where Rayleigh

scattering 1240 and 1390 nm where hydroxyl absorption by water occurs to avoid high degree of loss

Optical fibers also can be manufactured to have low dispersion wavelength in the 1550nm region

which is also the point where silica-based fibers have inherently minimal attenuation These fibers are

referred to as dispersion-shifted fibers and are used in long-distance applications with high bit rates For

33 | P a g e

applications utilizing multiple wavelengths it is undesirable to have the zero dispersion point within the

operating

wavelength range

34 | P a g e

SIGNALLING RELAYS

INTRODUCTION A relay is an electromagnetic device which is used to convey information from one circuit to another

circuit through a set of contact ie front or back contact Constructional and electrically relays may be

divided into DC and AC relays because the means by which the electrical energy in the coil is converted in

to mechanical Energy in order to move the contacts are fundamentally different In DC type the contacts are

carried on an armature forming part of a magnetic circuit in which a field is set up by the current flowing in

the coils In AC types the contacts are attached by a link mechanism to a metal sector disc or cylinder in

which currents are induced by the alternating magnetic field produced by the currents in the coils

Every endeavor has been made to explain the action of each type of relay in the simplest possible manner

Relays are sophisticated switch gears used for remote control and succession control of various

electrical equipment In present days they are widely used because they are capable of protecting the

controlled equipment from cross feeding and overloading even as they cater for speedy operations

Most of the relays in present day signaling are electromagnetic devices although some of the relays control

circuits through electronic components like diodetransistors Integrated Chips etc

Railway signaling relays are unique in that

(a) They operate on low voltage and current

(b) They are more articulate as according to their special features they can work under restrictive conditions

and in any specified manner Virtually they can cater for all situations while contributing to speed and

accuracy in operations

CLASSIFICATION OF SIGNALLING RELAYS (a) According to the method of their mounting or fixture they are classified as

(i) Shelf type Relays which are loosely kept on shelves

(ii) Plug in type Relays which are plugged into a pre- wired plug boards

(b) According to their connection and usage they are classified as

(i) Track relays Relay which is directly connected to the track to detect the presence of vehicle

(ii) Line Relays Other than track relay all are line relays Relays connected to the selection circuit

(c) According to their vitality or importance in ensuring train working safety they are classified as

(i) Vital Relays All relays used for traffic control such as signal point controls track detection etc

(ii) Non-vital Relays Relays which operate control aids and accessories like warnings buzzers

Indications etc

(d) According to their special provisions to ensure reliability of their contacts they are classified as

(i) Proved type are those whose normalization after each operation shall be proved in circuit

controlled by their contacts Contacts in which both the springs have metal surfaces on their tips They may

get fused due to high sparking current across them during operation These may prevent relay normalization

and causes unsafe condition in traffic control To avoid this proving of relay normalization after each

operation is necessary

(ii) Non - proved type Need not to be proved to have been normalized after each operation as their

contacts have at least one non-fusible contact (carbon contact)

(e) According to their feed source relays are broadly classified as

(i) DC relays The relay which requires DC power supply for its operations are called DC relays Among

the DC relays

o DC neutral relays This relay closes the same set of contacts on energization with Normal polarity

or Reverse polarity supply

o Polar Relays This relay closes different set of contacts when energized with Reverse polarity

supply They may or may not have contact to close when deenergized

35 | P a g e

(ii) AC Relay AC Induction motor track relays Time element relays flashing indication control etc

(iii) Electronic Relays DC relays with electronic components in them are called electronic relays

DC NEUTRAL RELAY Each Relay has usually one or two coils with a hollow center to accommodate a coreThe coils are

made up of a large numbers of turns of small gauge soft drawn copper wire The two coils can be connected

in series or parallel according to the requirement of relay resistance The ends of the coils are terminated on

binding post to which the control wires are connected Each coil is placed around a core of specially selected

Iron or steel having high permeability and low retentivity The core should be susceptible to magnetism and

at the same time should have little residual magnetism The cores are connected at the top by a yoke to

complete the magnetism coupling between two ends of coils The bottom of each core is equipped with a

large steel or Iron block known as pole piece or face

A flat piece of Iron or steel called armature is supported by brackets which are securely fastened to

the pole piece The armature yoke and the pole pieces are also made of specially selected iron or steel of the

same quality as the core The armature carries the metallic spring contacts which are insulated from it

The circuit through the coils of the relay is closed It sets up a magnetic flux through the core yoke and the

armature The flux passing between the armature and pole faces causes the armatures get attracted to the pole

faces and armature picks up and closes front contacts When the circuit is opened the magnetic flux collapses

and the armature drops away by gravity from the pole faces the front contacts break and back contacts close

The front and back contacts of the relay can be utilised to make or break other circuits Two stop pins of

nonmagnetic material are fixed either on the armature or pole faces so that the armature cannot

come in contact with the pole faces It is essential to maintain a small air-gap between the armature and pole

faces so that low value of residual magnetism may not retain the armature in picked up position and causes

the relay to fail to drop away with a break in its control circuit

GENERAL USAGE

DC Neutral line relays are most commonly used for Railway Signalling controls and detection

Among them plug-in type relays are preferred in larger installations for space considerations Shelf type

relays are also in use mostly in wayside stations

There are many DC Neutral line relays in use with special features such as

(i) Delayed operation

(ii) Biased DC control

(iii) DC control unaffected by AC interference currents

(iv) Getting latched in operated condition till further feeding and others

Usage of DC polar relays is mostly in conjunction with block instruments that control traffic between

stations AC line relays are almost extinct in installations of British Signalling practice They are however

used for time control operations flashing indication control and such other special purposes in installations

with Siemens signalling practice widely Track relays are used according to the type of track detection

circuits chosen for a given location and context While most of the track circuits are still of the DC working

type requiring DC neutral track relays with them the prospects of their being replaced with Electronic track

circuits directly feeding DC line relays in future are great AC Track Circuits are used in DC Traction area

as conventional DC Track Circuits are not suitable there AC Track relays are used with them almost all of

the induction motor type In the British practice of signalling which was first introduced on Indian Railways

non-proved type relays with carbon to metal switching contacts are generally used for vital controls

They facilitate simple circuit designs But with the advent of German Practice introduced by Ms

Siemens later proved type relays with all metal to metal contacts are widely accepted in spite of

complications in circuit design caused by them A recent introduction is that of the same type relays made by

Ms Integra control However for some time now the appreciable features of both the practices are getting

36 | P a g e

incorporated together in the indigenous designs of signalling by railwaymen With this the usage of all types

of relays anywhere can be found without straight jacketed segration of relay types

CHARACTERSTIC OF ELECTRO-MAGNETIC RELAY The following are the characteristic of electro-magnetic relays A brief study of them helps in

understanding the choice of their components and designs features

1) Force of attraction

2) Effect of air gap

3) Effect of Hysterisis

4) Transient condition

FORCE OF ATTRACTION In any electro-magnetic system the force of attraction is given by

Where B - is the flux density a - is the cross sectional area of the particular part of the magnetic

circuit

In the case of a DC neutral Relay B is proportional to the current that is flowing in the coil

surrounding the electro-magnet and thus the force of the attraction is directly proportional to the square of the

current This square relationship has its own advantage especially in the case of DC track relay in that a

small reduction in the current will have a great effect on the working of the relay Also for a given change of

current the make and the break will be quicker with lesser possibility of arcing

EFFECT OF AIR GAP

Curve lsquoArsquo is magnetisation curve for the iron and is all practical purpose a straight line up to the

saturation point Curve lsquoBrsquo is the magnetisation curve for the open-air gap which is a straight line through

out because per magnetisation curve of the whole

magnetic circuit of the relay and for a given force is the sum of the amp-turns for the iron part and the amp-

turns for the air gap

When the front contacts are open the force required to pick up the armature is shown on curve lsquoCrsquo to be F1

but after the armature has operated it will be separated from the core by stop pins In this position the amp-

turns required to maintain the armature is less as indicated by the dotted line from 1 on curve C to 2 on curve

37 | P a g e

F But actually the current in the coil is unaltered the force on the armature is greater than required as

indicated at 3 on curve F Part of this extra force is used to flex the front contacts sufficiently to give good

contact pressure when it is in energised position

The difference between the pick-up and the drop-away current should be as small as practicable in

track relay to ensure good shunting characteristics This is achieved firstly by the choice of good quality relay

iron and secondly by having a small air gap between armature and core If the air gap is not available then

the residual magnetism fluxes might cause the armature to be retained when the supply is disconnected For

this reason residual pins are provided to ensure a definite minimum air gap in the energised position

EFFECT OF HYSTERISIS

Hysterisis is the property by which the flux produced lags behind the current In the de-energized

condition there will be small residual flux in the core When the voltage is applied to the coils the current in

rising to its steady value first causes the flux to rise from 1 to 2 along the curve At this point the flux density

will be sufficient to attract the armature and reduce the air gap the flux then raise to 3 and continue to 4

which corresponds to the steady current in the coils When the voltage is disconnected the current in falling

caused the flux to fall from 4 to 5 along the curve At this point the flux density will fall below the value

required to maintain the armature which will release thus increasing the air gap and reducing the flux to 6

Finally the

flux will decrease from 6 to 1 where the current will again be zero

The relay core is made of material having high permeability and low retentivity As mentioned in

the IRS specification Electromagnet iron may be in the form of a

(a) Bar of silicon steel

(b) Best Yorkshire wrought iron

(c) Swedish charcoal iron

(d) Electrical steel sheets

` This reduces the difference between pick up value and Drop away value By selecting good quality

core material Percentage release and sensitivity of the relay will be improved

TRANSIENT CONDITION

38 | P a g e

When the voltage is applied or disconnected from the coils it takes some little time before the current

become steady These are known as transient conditionsrdquo and are important so far as track relays are

concerned When the voltage is first applied to the coils the magnetic flux in rising cuts the turns on the

coils and in so doing produces a back EMF that opposes the applied voltage and retards the growth of

current

The growth and decay of flux are decided by the relationship between the inductance and resistance

in the circuit is known as time constant It is not fixed quantity in the case of DC neutral relay This value of lsquo

Lrsquo is less when the relay is in de-energised condition (L1) than when the relay is in energised condition (L2)

The magnitude of flux that is established for a given change of current is different in two cases

When the current reaches the pick up value the armature closes and the inductance is increased to L2

due to reduced air gap the flux per amp is increased The increase in flux increased the back EMF during the

movement of the armature after which the current continuous to raise along a new curve corresponding to the

increased inductance until it reaches the final value (ER) This process is indicated above in fig24

When the supply is disconnected the current is obliviously reduced to zero immediately but the flux

decay comparatively slowly owing to the eddy currents produced in the core by the rapid flux change which

tend to maintain the flux The drop away time on a disconnection is however generally negligible See fig

below

If the relay releases due to the reduction in current from say I 2 to I 1 caused by the application of

shunt resistance (as in the case of track relay ) the time taken is much longer than the relay is simply

disconnected The rate of rise or fall of current during the transient conditions is also depends on exterior

circuit values because L and R apply to the whole circuit The production of eddy current in the core the flux

will decay at a slower rate than the current So that the actual release time will be a little longer than it takes

the current to fall to the release

L= Inductance

39 | P a g e

R= Resistance

It is now clear that to reduce releasing time to a minimum it is necessary that

- The relay iron should have low Hysterisis loss and low retentivity

- The degree of over energization of the relay should be restricted

- Connecting a suitable external resistance in series with the relay to keep LR ratio low

In non RE area for track circuit length less than 100M 9 ohm track relay only to be used Using relay

with minimum contacts as they require lesser current which keeps inductance value low

Train working safety is ensured only if the track relay of shortest length track circuit is released

before a light engine running at a highest permitted speed clears it Otherwise the track circuit occupation

may go undetected To avoid this a special provision has to be made in signal control circuits wherever

necessary

The following methods may be adopted for reducing the time lag of track relay

(a) Restrict the over energisation of relay since the release time depends on the initial working current

(b) Connecting a suitable external resistance in series with the relay to keep the LR ratio low

(c) Using relays with minimum contacts as they require lesser operating current keeping the inductance

value low

40 | P a g e

CONCLUSION

Modern signalling is vital for safe and punctual movements of trains In the Indian railways The Signalling

and Telecommunication Department is responsible for providing modern effective and relaible signalling

systems as well as telecommunication systems

The first mode of communication used in Indian Railways was the use of electric telegraph

with the help of Morose code Morose code is the method of providing text information as a series of on-off

tones and lights or clicks that can be directly understood by a skilled listener or observer without special

equipmentEach character (letter or numeral ) is represented by a unique sequence of dots and dashes Later

this system becomes obselete and beggan the era of wireless communication which operated at audio level

frequency range

In wireless communication the significant advances took place the transition to miniature

valves or filament tubesBut this was abandoned too because of excessive current consumption and over

heating of the filament tubes

Fibre-optic communication is a method of transmitting information from one place to another by

sending pulses of light through an optcial fibreThe light forms an electromagnetic carrier wave that is

modulated to carry information First developed in the 1970s fibre optic communication systems has

revolutionized the telecommunications industry and have palyed a major role in the advent of the information

age Because of its advantages over electrical transmissionsoptical fibres have largely replaced copper wire

communications in core networks in the developed world The Indian Railways too is undergoing a transition

from Microwave communication to fibre optic communications

41 | P a g e

BIBLIOGRAPHY AND REFERENCES

1 wwwwikipediacom

2 wwwbritaniccacom

3 wwwirfcacom

4 Motorola GP60 system manual

5 Harris FAS 7000 manual

6 TOSHIBA Manual

19 | P a g e

(c) Front End Processor (FEP)

(d) Central Monitoring Unit (CMU) Computer

FEP (FRONT END PROCESSOR)

FEP acts as a buffer between the Central Monitoring Unit (Computer) and the Network It is provided

at centralised place to retrieve data continuously from station dataloggers and store in memory and transfer to

computer on request It stores 10 Lac telegrams It works on 12V DC It draws 16A continuous current

when all the three modems are connected Normally it shows the number of packets pending to be sent to the

computer on its 7-segment LED display It is provided with MOTOROLA 68000 microprocessor It has 6-

nos of RS-232 communication ports such as COM1 COM2 COM3 COM4 COM5 and COM6 COM1 is

used for Fault Analysis System (FAS) ie Central Monitoring Unit (Computer) connection COM2 to COM6

are used for networking For Bi-directional 2- nos of ports and for Tri-directional (T-network) 3-nos of ports

are used

DATA TRANSMISSION Dataloggers can be networked in Uni-directional Mode or Bi-directional Mode or T ndash Network Mode

In case of loss of data retransmission of data takes place

(a) Uni-Directional Mode

Each Datalogger will send data in only one direction to the FEP Unidirectional mode network is not

preferred

(b) Bi-Directional Mode

Each end of Network is connected to FEP and each datalogger can now transmit data in both the directions

Bi-directional Mode is advantageous it enables the Data Transmission even in case of Network Failure

(c) T - Network Mode

If more no of stations are in network ie if the network is too lengthy then T- network mode is preferred

COMMUNICATION The communication protocol for transmitting data and command between datalogger and CMU is

standardized by the RDSO and is given in the Specifications of Dataloggers

(a) The type of communication used in the network is dependent on the distance between the dataloggers

(b) For shorter distances Opto Converter Box- Opto isolated current loop communication is used

(c) For longer distances Modem (Dial-up leased) Fiber Optic Satellite Microwave communication

MODEMS Modems are used for DATA transfer between Dataloggers and Front End ProcessorThese are

configured to RS 232 Serial Communication Network is connected with two types of 4-wire modems

(a) Internal modem card Dual Modem card (in-built)

It is fixed in datalogger Euro rack itself One card contains two modems The top modem is called

ANS (answer) modem and the bottom modem is called as ORG (originate) modem

Note In case of networking of Dataloggers connect lsquoANSrsquo modem to the lsquoORGrsquo modem of one adjacent

station and connect lsquoORGrsquo modem to the lsquoANSrsquo modem of other adjacent station

(b) External modems

20 | P a g e

These are generally used at FEP (Front End Processor) side to connect the Dataloggers

(i) To transfer Data from one datalogger to another datalogger FEP Baud rate is 9600bps

(ii) These modems are 4-wire line communication

(iii) To transfer the data from FEP to RMU (PC) the Baud rate is 57600 bps

There is no difference between these modems functionally

CENTRAL MONITORING UNIT (CMU) COMPUTER

Central monitoring unit (Fault Analysis Unit) is a Personal Computer and its minimum configuration

shall be specified by RDSO from time to time System Software Windows XPVista(OS) Norton Kaspersky

(Anti Virus) Interbase where Server is not available (DBMS) Oracle where Server is available (DBMS)

software are required to run Datalogger System It is provided with Graphical User interface (GUI) based

software and retrieve data from all Networked dataloggers (up to 32) at various stations It stores data in

standard data base files The CMU is capable of analyzing the data and generate reports audiovisual alarms

on defined conditions This data can be compressed to take backup In central monitoring unit Software used

for analysis of data prediction of faults etc is written in a structured format so that purchaser can

reconfigure it if required It displays the status of signaling gears at any selected time in graphic form for any

selected station yard It retrieves the stored data amp simulates train movement It sends commands to various

Dataloggers to activate audio visual alarm or operate and electromagnetic relay

CMU shares data available in it by other PCs through available local area network where this data can

be used for train charting passenger information purpose The system generates audiovisual alarm in

ASMrsquosSignal Maintainerrsquos room in the case of power supply failure (battery voltage low) or battery charger

defective with acknowledgement facility

(a) Each datalogger has its own identity code which will be transmitted along with data packet to central

monitoring unit

(b) Events recorded at each station are continuously transmitted to central monitoring unit Response time of

data transfer will not exceed 10 sec

21 | P a g e

22 | P a g e

OPTICAL FIBER CABLE

INTRODUCTION The demand for bandwidth on transmission networks is increasing rapidly because video and

graphical rich contents are exchanged through the corporate network or the Internet The Gigabit Ethernet

became ommonly used in the corporate network backbone and 10Gbit Ethernet will be adopted in the near

future Meanwhile in the home the demand for high-speed network becomes popular as the wide spread of

broadband access eg CATV xDSL and FTTH The transmission medium with capability to transmit high

bit rate signal is necessary to satisfy these requirements

The telecommunication transport technologies move from copper based networks to optical fiber

from timeslot based transport to wave length based transport from traditional circuit switching to terabit

router and all optical based networks entering into a new era of optical networking

BASIC PHYSICS OF OFC

OPTICAL FIBER CABLE OFC have Fibers which are long thin strands made with pure glass about the diameter of a human

hair OFC consists of Core Cladding Buffers and Jacket as shown in figure

MONOCHROMATIC LIGHT OR SINGLE COLOR LIGHT Light or visible light is electromagnetic radiation of a wavelength that is visible to the human eye (

about 400 ndash 700 nm) The word light is sometimes used to refer to the entire electromagnetic spectrum Light

is composed of elementary particles called photons Three primary properties of light are

Light can exhibit properties of both waves and particles This property is referred to as wave-particle

duality The study of light known as optics In free space light (of all wavelengths) travels in a straight path

at a constant maximum speed However the speed of light changes when it travels in a medium and this

change is not the same for all media or for all wavelengths By free space it is meant space that is free from

matter (vacuum) andor free from electromagnetic fields

Thus the speed of light in free space is defined by Einsteinrsquos equation E = mc2

Frequency ν speed of light in free space c and wavelength λ are interrelated by ν = cλ

From the energy relationships E = mc2 = hν and the last one an interesting relationship is obtained

the equivalent mass of a photon m = hνc2

When light is in the vicinity of a strong electromagnetic field it interacts with it From this interaction

and other influences its trajectory changes direction as shown in figure

23 | P a g e

INCIDENT RAY REFLECTED RAY AND REFRACTED RAY An incident ray is a ray of light that strikes a surface The angle between this ray and the

perpendicular or normal to the surface is the angle of incidence Reflection is the change in direction of a

wave front at an interface between two different media so that the wave front returns into the medium from

which it originated Common examples include the reflection of light sound and water waves

The reflected ray corresponding to a given incident ray is the ray that represents the light reflected by

the surface The angle between the surface normal and the reflected ray is known as the angle of reflection

The Law of Reflection says that for a specular (non-scattering) surface the angle of reflection always equals

the angle of incidence The refracted ray or transmitted ray corresponding to a given incident ray represents

the light that is transmitted through the surface The angle between this ray and the normal is known as the

angle of refraction and it is given by Snells Law

The figure shows Incident ray Reflected ray Refracted ray the angle of incidence and angle of refraction

REFRACTIVE INDEX - Refractive index is the speed of light in a vacuum ( c =299792458kmsecond) divided by the speed

of light in a material ( v ) Refractive index measures how much a material refracts light Refractive index of

a material abbreviated as lsquo n lsquo is defined as lsquo n=cv lsquo Light travels slower in physical media than it does

when transmitted through the air Refractive index (n) is a function of molecular structure of matter optical

frequency optical intensity determines optical propagation properties of each wavelength ( λ ) may not be

distributed equally in all directions is affected by external temperature pressure and fields

Refractive index of a medium is a measure for how much the speed of light is reduced inside the

medium For example typical glass has a refractive index of 15 which means that light travels at 1 15 =

067 times the speed in air or vacuum Two common properties of glass and other transparent materials are

directly related to their refractive index

First light rays change direction when they cross the interface from air to the material and effect that

is used in lenses and glasses

Second light reflects partially from surfaces that have a refractive index different from that of their

surroundings

SNELLrsquoS LAW-

24 | P a g e

When light passes from one transparent material to another it bends according to Snells law which

is defined as n1sin(θ1) = n2sin(θ2)

where n1 is the refractive index of the medium the light is leaving θ1 is the incident angle between the light

beam and the normal (normal is 90deg to the interface between two materials)

n2 is the refractive index of the material the light is entering

θ2 is the refractive angle between the light ray and the normal

Snellrsquos law gives the relationship between angle of incidence and angle of refraction

For the case of θ1 = 0deg (ie a ray perpendicular to the interface) the solution is θ2 = 0deg regardless of

the values of n1 and n2 That means a ray entering a medium perpendicular to the surface is never bent The

above is also valid for light going from a dense (higher n) to a less dense (lower n) material the symmetry of

Snells law shows that the same ray paths are applicable in opposite direction

TOTAL INTERNAL REFLECTION- When a light ray crosses an interface into a medium with a higher refractive index it bends towards

the normal Conversely light traveling cross an interface from a higher refractive index medium to a lower

refractive index medium will bend away from the normal

This has an interesting implication at some angle known as the critical angle θc light traveling from

a higher refractive index medium to a lower refractive index medium will be refracted at 90deg in other words

refracted alon g the interface If the light hits the interface at any angle larger than this critical angle it will

not pass through to the second medium at all Instead all of it will be reflected back into the first medium a

process known as total internal reflection

The critical angle can be calculated from Snells law putting in an angle of 90deg for the angle of the refracted

ray θ2 This gives θ1

Since θ2 = 90deg

So sin(θ2) = 1

25 | P a g e

Then θc = θ1 = arcsin(n2n1)

For example with light trying to emerge from glass with n1=15 into air (n2 =1) the ritical angle θc is

arcsin(115) or 418deg For any angle of incidence larger than the critical angle Snells law will not be able to

be solved for the angle of refraction because it will show that the refracted angle has a sine larger than 1

which is not possible In that case all the light is totally reflected off the interface obeying the law of

reflection

OPTICAL FIBER MODE An optical fiber guides light waves in distinct patterns called modes Mode describes the distribution

of light energy across the fiber The precise patterns depend on the wavelength of light transmitted and on the

variation in refractive index that shapes the core In essence the variations in refractive index create

boundary

conditions that shape how light waves travel through the fiber like the walls of a tunnel affect how sounds

echo inside

We can take a look at large-core step-index fibers Light rays enter the fiber at a range of angles and

rays at different angles can all stably travel down the length of the fiber as long as they hit the core-cladding

interface at an angle larger than critical angle These rays are different modes Fibers that carry more than

one mode at a specific light wavelength are called multimode fibers Some fibers have very small diameter

core that they can carry only one mode which travels as a straight line at the center of the core These fibers

are single mode fibers This is illustrated in the following picture

OPTICAL FIBER INDEX PROFILE Index profile is the refractive index distribution across the core and the cladding of a fiber Some

optical fiber has a step index profile in which the core has one uniformly distributed index and the cladding

has a lower uniformly distributed index Other optical fiber has a graded index profile in which refractive

index varies gradually as a function of radial distance from the fiber center Graded-index profiles include

power-law index profiles and parabolic index profiles The following figure shows some common types of

index profiles for single mode and multimode fiber

26 | P a g e

OPTICAL FIBERrsquoS NUMERICAL APERTURE ( NA )- Multimode optical fiber will only propagate light that enters the fiber within a certain cone known as

the acceptance cone of the fiber The half-angle of this cone is called the acceptance angle (see figure 18)

θmax For step-index multimode fiber the acceptance angle is determined only by the indices of refraction

Where

n is the refractive index of the medium light is traveling before entering the fiber

nf is the refractive index of the fiber core

nc is the refractive index of the cladding

NUMBER OF MODES IN A FIBER - Modes are sometimes characterized by numbers Single mode fibers carry only the lowest-order

mode assigned the number 0 Multimode fibers also carry higher-order modes The number of modes that

can propagate in a fiber depends on the fiberrsquos numerical aperture (or acceptance angle) as well as on its

core diameter and the wavelength of the light For a step-index multimode fiber the number of such modes

Nm

Where

D is the core diameter

λ is the operating wavelength

NA is the numerical aperture (or acceptance angle)

MODE FIELD DIAMETER - All light do not travels through the core of the fiber but is distributed through both the core and the

cladding The mode field is the distribution of light through the core and cladding of a particular fiber

Mode-Field Diameter (MFD) defines the size of the power distribution When coupling light into or out of a

fiber MFD is important in understanding light loss

27 | P a g e

ADVANTAGE OF OFC COMMUNICATION - bull More information carrying capacity Fibers can handle much higher data rates than copper More

information can be sent in a second

bull Free from Electromagnetic and Electrostatic interference Being insulator no electric current flows through

the fibre and due to this reason fibres neither radiate nor pick up electro - magnetic radiation So WPC

CLEARANCE is not required

bull Low attenuation 025 dbkm at 1550 nm Loss in twisted pair and coaxial cable increases with frequency

where as loss in the optical fibre cable remains flat over a wide range of frequencies

bull Use of WDM ndash Switching routing at Optical signal level

bull Self healing rings under NMS control

bull Small size makes fibre cable lighter in weight So easy to handleOptic fibre cable weight (approx)

500 kg km Copper cable weight (approx) 1000 kgkm

The reasons are photons of light in a fibre

do not affect each other as they have no electrical charge and they are not affected by stray photons outside

the fibre But in case of copper electrons move through the cable and these are affected by each other

Optical fibre does not carry any electricity even if the cable is damaged or short circuited it does

not cause any spark or fire hazard

As the fibre do not radiate energy it can not be detected by any nearby antenna or any

other detector The fibres are difficult to tap and therefore excellent for security

As the signal transmission is by digital modulation there is no chance of cross talk in

between channels

Only by adding a few additional terminal and repeater equipments the

capacity of the system can be increased at any time once the cable is laid

ical effects and temperature variations

LIMITATIONS OF OFC -

difficult

- utilised

APPLICATION IN SIGNAL AND TELECOMMUNICATIONS transmission circuits

-haul circuits for linking of telephone exchanges

28 | P a g e

PROPAGATION MODES CONCEPT -

MODE - Mode is an available distribution of electromagnetic field in a plane transverse to the direction of

light propagation Each mode is characterized by frequency polarization electric field strength and

magnetic field strength Available patterns are derived from Maxwellrsquos equations and boundary conditions

LINEARLY POLARIZED (LP) MODE A mode for which the field components in the direction of propagation are small compared to

components perpendicular to that direction An optical fibre supports only different field patterns called as

lsquoLinear Polarizedrsquo or lsquo LPrsquo modes The reasons are

requirements

de

the accrual of power carried by different modes

There are two basic types of fiber Multimode fiber and Single-mode fiber

Multimode fiber is best designed for short transmission distances This is suited for used in LAN systems and

video surveillance Single mode fibre is best designed for longer transmission distances This is suitable for

long distance telephony and multi channel television broadcast systems

29 | P a g e

MULTI MODE FIBER Multimode fiber the first to be manufactured and commercialized simply refers to the fact that

numerous modes or light rays are carried simultaneously through the waveguide Modes result from the fact

that light will only propagate in the fiber core at discrete angles within the cone of acceptance MM fiber type

has a much larger core diameter compared to single-mode fiber allowing for the larger number of modes

and

is easier to couple than single-mode optical fiber Multimode fiber further categorized as Multimode step-

index and Multimode graded index fiber

PROPAGATION THROUGH MMSI FIBER Figure shows the principle of total internal reflection applies to multimode step index fiber Because

the corersquos index of refraction is higher than the claddingrsquos index of refraction the light that enters at less than

the critical angle is guided along the fiber

Three different light waves travel down the fiber One mode travels straight down the center of the

core A second mode travels at a steep angle and bounces back and forth by total internal reflection The third

mode exceeds the critical angle and refracts into the cladding Naturally it can be seen that the second mode

travels a longer distance than the first mode causing the two modes to arrive at separate times

PROBLEMS WITH MMSI FIBER AND SOLUTION This disparity between arrival times of the different light rays is known as dispersion and the result is

a muddied signal at the receiving end It is important to note that high dispersion is an unavoidable

characteristic of multimode step-index fiber The solutions are either use Graded index fiber or Single mode

fiber

PROPAGATION THROUGH MMGI FIBER Multimode Graded-index refers to the fact that the refractive index of the core gradually decreases

farther from the center of the core The increased refraction in the center of the core slows the speed of some

light rays allowing all the light rays to reach the receiving end at approximately the same time reducing

dispersion Figure shows the Light propagation principle through multimode graded-index fiber The corersquos

central refractive index ( nA ) is greater than that of the outer corersquos refractive index ( nB )

It is very clear from the figure the light rays no longer follow straight lines they follow a serpentine path

being gradually bent back toward the center by the continuously declining refractive index This reduces the

arrival time disparity because all modes arrive at about the same time The modes traveling in a straight line

30 | P a g e

are in a higher refractive index so they travel slower than the serpentine modes These travel farther but

move faster in the lower refractive index of the outer core region

PROPAGATION THROUGH SMSI FIBER Single mode fiber has a much smaller core that allows only one mode of light at a time to propagate

through the core The figure shows the single mode fiber

Single-mode fiber exhibits no dispersion caused by multiple modes Single-mode fiber also offers lower fiber

attenuation than multimode fiber Thus more information can be transmitted per unit of time because it can

retain the fidelity of each light pulse over longer distances Like multimode fiber early single-mode fiber was

generally characterized as step-index fiber meaning the refractive index of the fiber core is a step above that

of the cladding rather than graduated as it is in graded-index fiber Modern single-mode fibers have evolved

into more complex designs such as matched clad depressed clad and other exotic structures

SINGLE-MODE FIBER DISADVANTAGES The smaller core diameter makes coupling light into the core more difficult The tolerances for single-

mode connectors and splices are also much more demanding

CUTOFF WAVE LENGTH - Cutoff wavelength is the wavelength above which a single-mode fiber supports and propagates only

one mode of light In other words an optical fiber that is single-mode at a particular wavelength may have

two or more modes at wavelengths lower than the cutoff wavelength The effective cutoff wavelength of a

fiber is dependent on the length of fiber and its deployment The longer the fiber the lower is the effective

cutoff

wavelength The smaller the bend radius of a loop of the fiber the lower is the effective cutoff wavelength If

a fiber is bent in a loop the effective cutoff wavelength is lowered

SIGNAL ATTENUATION IN FIBER - Optical fiber has a number of advantages over copper However it also suffers from degradation

problems which can not be ignored The first of these is loss or attenuation Attenuation is typically the result

of two sub properties They are scattering and absorption Both of which have cumulative effects The second

is

dispersion which is the spreading of the transmitted signal and is analogous to noise

SCATTERING Scattering occurs because of impurities or irregularities in the physical construction of the fiber The

well known form of scattering is Rayleigh Scattering It is caused by metal ions in the silica matrix and

results in light rays being scattered in various directions

31 | P a g e

Scattering limits the use of wavelengths below 800nm The short wavelengths are much affected than longer

wavelengths It is because of Rayleigh scattering that the sky appears to be blue ( shorter wave length ) The

shorter wavelengths ( blue ) of light are scattered more than the longer wavelengths of light

ABSORPTION Absorption results from three factors They are hydroxyl ions ( OH- water ) in the silica impurities

in the silica and incomplete residue from the manufacturing process These impurities tend to absorb the

energy of the transmitted signal and convert it to heat resulting in an overall weakening of the signal The

Hydroxyl absorption occurs at 125 and 139 micro The silica itself starts to absorb energy at 17 micro

because of the natural resonance of the silicon dioxide

MACRO BENDING LOSS Macro-bending loss is caused by bending of the entire fiber axis The bending radius shall not be

sharper than 30d where d is diameter of cable A single bend sharper than 30d can cause loss of 05dB

The fiber may break if bending is ever sharper

MICRO BENDING LOSS Micro-bending loss is caused by micro deformations of fiber axis which leads to failures in achieving

total internal reflection conditions Micro-bends are small scale perturbations along the fiber axis the

amplitude of which are on the order of microns These distortions can cause light to leak out of a fiber

Micro-bending may be induced at very cold temperatures because the glass has a different coefficient of

thermal expansion from the coating and cabling materials At low temperatures the coating and cable

become more rigid and may contract more than the glass Consequently enough load may be exerted on the

glass to cause micro bends

Coating material is selected by manufacturers to minimize loss due to micro-bending The linear thermal

expansion coefficient of coating material shall be compatible with that of fiber

32 | P a g e

DISPERSION Dispersion is the optical term for the spreading of the transmits in the fiber It is the bandwidth

limiting phenomenon and comes in two forms Multimode dispersion and chromatic dispersion Chromatic

dispersion is further subdivided into material dispersion and waveguide dispersion

DISPERSION PHENOMENON IN OPTICAL FIBER Dispersion is the time distortion of an optical signal that results from the differences of time of travel

for different components of that signal typically resulting in pulse broadening As the distance traveled by

the signal is more broadening of pulse is more In digital transmission dispersion limits on the maximum

data rate and the maximum distance ie the information-carrying capacity of a fiber link The interference

from broadened pulse in the next interval shall not lead to erroneous interpretation of received signal

OPTICAL DOMAIN Understanding where attenuation and dispersion problems occur helps optical design engineers

determine the better wavelengths at which information can be transmit taking into account distance type of

fiber and the other factors which can severely affect the integrity of the transmitted signal The graph shown

depicts the optical transmission domain as well as the areas where problems arise The wavelength (nm)

is shown on X-axis and attenuation ( dBkm) is shown on Y-axis

There are four transmission windows appear in the figure The first one is at around 850 nm the

second at 1310nm third at 1550 nm and fourth at 1625 nm The last two labeled as C and L band

respectively The 850 nm wavelength at which the original LED technology operated The second window at

1310 nm has low dispersion The 1550 nm called as C-band is ideal wavelength for long haul

communication systems The network engineers can avoid transmitting signal at 1000 nm where Rayleigh

scattering 1240 and 1390 nm where hydroxyl absorption by water occurs to avoid high degree of loss

Optical fibers also can be manufactured to have low dispersion wavelength in the 1550nm region

which is also the point where silica-based fibers have inherently minimal attenuation These fibers are

referred to as dispersion-shifted fibers and are used in long-distance applications with high bit rates For

33 | P a g e

applications utilizing multiple wavelengths it is undesirable to have the zero dispersion point within the

operating

wavelength range

34 | P a g e

SIGNALLING RELAYS

INTRODUCTION A relay is an electromagnetic device which is used to convey information from one circuit to another

circuit through a set of contact ie front or back contact Constructional and electrically relays may be

divided into DC and AC relays because the means by which the electrical energy in the coil is converted in

to mechanical Energy in order to move the contacts are fundamentally different In DC type the contacts are

carried on an armature forming part of a magnetic circuit in which a field is set up by the current flowing in

the coils In AC types the contacts are attached by a link mechanism to a metal sector disc or cylinder in

which currents are induced by the alternating magnetic field produced by the currents in the coils

Every endeavor has been made to explain the action of each type of relay in the simplest possible manner

Relays are sophisticated switch gears used for remote control and succession control of various

electrical equipment In present days they are widely used because they are capable of protecting the

controlled equipment from cross feeding and overloading even as they cater for speedy operations

Most of the relays in present day signaling are electromagnetic devices although some of the relays control

circuits through electronic components like diodetransistors Integrated Chips etc

Railway signaling relays are unique in that

(a) They operate on low voltage and current

(b) They are more articulate as according to their special features they can work under restrictive conditions

and in any specified manner Virtually they can cater for all situations while contributing to speed and

accuracy in operations

CLASSIFICATION OF SIGNALLING RELAYS (a) According to the method of their mounting or fixture they are classified as

(i) Shelf type Relays which are loosely kept on shelves

(ii) Plug in type Relays which are plugged into a pre- wired plug boards

(b) According to their connection and usage they are classified as

(i) Track relays Relay which is directly connected to the track to detect the presence of vehicle

(ii) Line Relays Other than track relay all are line relays Relays connected to the selection circuit

(c) According to their vitality or importance in ensuring train working safety they are classified as

(i) Vital Relays All relays used for traffic control such as signal point controls track detection etc

(ii) Non-vital Relays Relays which operate control aids and accessories like warnings buzzers

Indications etc

(d) According to their special provisions to ensure reliability of their contacts they are classified as

(i) Proved type are those whose normalization after each operation shall be proved in circuit

controlled by their contacts Contacts in which both the springs have metal surfaces on their tips They may

get fused due to high sparking current across them during operation These may prevent relay normalization

and causes unsafe condition in traffic control To avoid this proving of relay normalization after each

operation is necessary

(ii) Non - proved type Need not to be proved to have been normalized after each operation as their

contacts have at least one non-fusible contact (carbon contact)

(e) According to their feed source relays are broadly classified as

(i) DC relays The relay which requires DC power supply for its operations are called DC relays Among

the DC relays

o DC neutral relays This relay closes the same set of contacts on energization with Normal polarity

or Reverse polarity supply

o Polar Relays This relay closes different set of contacts when energized with Reverse polarity

supply They may or may not have contact to close when deenergized

35 | P a g e

(ii) AC Relay AC Induction motor track relays Time element relays flashing indication control etc

(iii) Electronic Relays DC relays with electronic components in them are called electronic relays

DC NEUTRAL RELAY Each Relay has usually one or two coils with a hollow center to accommodate a coreThe coils are

made up of a large numbers of turns of small gauge soft drawn copper wire The two coils can be connected

in series or parallel according to the requirement of relay resistance The ends of the coils are terminated on

binding post to which the control wires are connected Each coil is placed around a core of specially selected

Iron or steel having high permeability and low retentivity The core should be susceptible to magnetism and

at the same time should have little residual magnetism The cores are connected at the top by a yoke to

complete the magnetism coupling between two ends of coils The bottom of each core is equipped with a

large steel or Iron block known as pole piece or face

A flat piece of Iron or steel called armature is supported by brackets which are securely fastened to

the pole piece The armature yoke and the pole pieces are also made of specially selected iron or steel of the

same quality as the core The armature carries the metallic spring contacts which are insulated from it

The circuit through the coils of the relay is closed It sets up a magnetic flux through the core yoke and the

armature The flux passing between the armature and pole faces causes the armatures get attracted to the pole

faces and armature picks up and closes front contacts When the circuit is opened the magnetic flux collapses

and the armature drops away by gravity from the pole faces the front contacts break and back contacts close

The front and back contacts of the relay can be utilised to make or break other circuits Two stop pins of

nonmagnetic material are fixed either on the armature or pole faces so that the armature cannot

come in contact with the pole faces It is essential to maintain a small air-gap between the armature and pole

faces so that low value of residual magnetism may not retain the armature in picked up position and causes

the relay to fail to drop away with a break in its control circuit

GENERAL USAGE

DC Neutral line relays are most commonly used for Railway Signalling controls and detection

Among them plug-in type relays are preferred in larger installations for space considerations Shelf type

relays are also in use mostly in wayside stations

There are many DC Neutral line relays in use with special features such as

(i) Delayed operation

(ii) Biased DC control

(iii) DC control unaffected by AC interference currents

(iv) Getting latched in operated condition till further feeding and others

Usage of DC polar relays is mostly in conjunction with block instruments that control traffic between

stations AC line relays are almost extinct in installations of British Signalling practice They are however

used for time control operations flashing indication control and such other special purposes in installations

with Siemens signalling practice widely Track relays are used according to the type of track detection

circuits chosen for a given location and context While most of the track circuits are still of the DC working

type requiring DC neutral track relays with them the prospects of their being replaced with Electronic track

circuits directly feeding DC line relays in future are great AC Track Circuits are used in DC Traction area

as conventional DC Track Circuits are not suitable there AC Track relays are used with them almost all of

the induction motor type In the British practice of signalling which was first introduced on Indian Railways

non-proved type relays with carbon to metal switching contacts are generally used for vital controls

They facilitate simple circuit designs But with the advent of German Practice introduced by Ms

Siemens later proved type relays with all metal to metal contacts are widely accepted in spite of

complications in circuit design caused by them A recent introduction is that of the same type relays made by

Ms Integra control However for some time now the appreciable features of both the practices are getting

36 | P a g e

incorporated together in the indigenous designs of signalling by railwaymen With this the usage of all types

of relays anywhere can be found without straight jacketed segration of relay types

CHARACTERSTIC OF ELECTRO-MAGNETIC RELAY The following are the characteristic of electro-magnetic relays A brief study of them helps in

understanding the choice of their components and designs features

1) Force of attraction

2) Effect of air gap

3) Effect of Hysterisis

4) Transient condition

FORCE OF ATTRACTION In any electro-magnetic system the force of attraction is given by

Where B - is the flux density a - is the cross sectional area of the particular part of the magnetic

circuit

In the case of a DC neutral Relay B is proportional to the current that is flowing in the coil

surrounding the electro-magnet and thus the force of the attraction is directly proportional to the square of the

current This square relationship has its own advantage especially in the case of DC track relay in that a

small reduction in the current will have a great effect on the working of the relay Also for a given change of

current the make and the break will be quicker with lesser possibility of arcing

EFFECT OF AIR GAP

Curve lsquoArsquo is magnetisation curve for the iron and is all practical purpose a straight line up to the

saturation point Curve lsquoBrsquo is the magnetisation curve for the open-air gap which is a straight line through

out because per magnetisation curve of the whole

magnetic circuit of the relay and for a given force is the sum of the amp-turns for the iron part and the amp-

turns for the air gap

When the front contacts are open the force required to pick up the armature is shown on curve lsquoCrsquo to be F1

but after the armature has operated it will be separated from the core by stop pins In this position the amp-

turns required to maintain the armature is less as indicated by the dotted line from 1 on curve C to 2 on curve

37 | P a g e

F But actually the current in the coil is unaltered the force on the armature is greater than required as

indicated at 3 on curve F Part of this extra force is used to flex the front contacts sufficiently to give good

contact pressure when it is in energised position

The difference between the pick-up and the drop-away current should be as small as practicable in

track relay to ensure good shunting characteristics This is achieved firstly by the choice of good quality relay

iron and secondly by having a small air gap between armature and core If the air gap is not available then

the residual magnetism fluxes might cause the armature to be retained when the supply is disconnected For

this reason residual pins are provided to ensure a definite minimum air gap in the energised position

EFFECT OF HYSTERISIS

Hysterisis is the property by which the flux produced lags behind the current In the de-energized

condition there will be small residual flux in the core When the voltage is applied to the coils the current in

rising to its steady value first causes the flux to rise from 1 to 2 along the curve At this point the flux density

will be sufficient to attract the armature and reduce the air gap the flux then raise to 3 and continue to 4

which corresponds to the steady current in the coils When the voltage is disconnected the current in falling

caused the flux to fall from 4 to 5 along the curve At this point the flux density will fall below the value

required to maintain the armature which will release thus increasing the air gap and reducing the flux to 6

Finally the

flux will decrease from 6 to 1 where the current will again be zero

The relay core is made of material having high permeability and low retentivity As mentioned in

the IRS specification Electromagnet iron may be in the form of a

(a) Bar of silicon steel

(b) Best Yorkshire wrought iron

(c) Swedish charcoal iron

(d) Electrical steel sheets

` This reduces the difference between pick up value and Drop away value By selecting good quality

core material Percentage release and sensitivity of the relay will be improved

TRANSIENT CONDITION

38 | P a g e

When the voltage is applied or disconnected from the coils it takes some little time before the current

become steady These are known as transient conditionsrdquo and are important so far as track relays are

concerned When the voltage is first applied to the coils the magnetic flux in rising cuts the turns on the

coils and in so doing produces a back EMF that opposes the applied voltage and retards the growth of

current

The growth and decay of flux are decided by the relationship between the inductance and resistance

in the circuit is known as time constant It is not fixed quantity in the case of DC neutral relay This value of lsquo

Lrsquo is less when the relay is in de-energised condition (L1) than when the relay is in energised condition (L2)

The magnitude of flux that is established for a given change of current is different in two cases

When the current reaches the pick up value the armature closes and the inductance is increased to L2

due to reduced air gap the flux per amp is increased The increase in flux increased the back EMF during the

movement of the armature after which the current continuous to raise along a new curve corresponding to the

increased inductance until it reaches the final value (ER) This process is indicated above in fig24

When the supply is disconnected the current is obliviously reduced to zero immediately but the flux

decay comparatively slowly owing to the eddy currents produced in the core by the rapid flux change which

tend to maintain the flux The drop away time on a disconnection is however generally negligible See fig

below

If the relay releases due to the reduction in current from say I 2 to I 1 caused by the application of

shunt resistance (as in the case of track relay ) the time taken is much longer than the relay is simply

disconnected The rate of rise or fall of current during the transient conditions is also depends on exterior

circuit values because L and R apply to the whole circuit The production of eddy current in the core the flux

will decay at a slower rate than the current So that the actual release time will be a little longer than it takes

the current to fall to the release

L= Inductance

39 | P a g e

R= Resistance

It is now clear that to reduce releasing time to a minimum it is necessary that

- The relay iron should have low Hysterisis loss and low retentivity

- The degree of over energization of the relay should be restricted

- Connecting a suitable external resistance in series with the relay to keep LR ratio low

In non RE area for track circuit length less than 100M 9 ohm track relay only to be used Using relay

with minimum contacts as they require lesser current which keeps inductance value low

Train working safety is ensured only if the track relay of shortest length track circuit is released

before a light engine running at a highest permitted speed clears it Otherwise the track circuit occupation

may go undetected To avoid this a special provision has to be made in signal control circuits wherever

necessary

The following methods may be adopted for reducing the time lag of track relay

(a) Restrict the over energisation of relay since the release time depends on the initial working current

(b) Connecting a suitable external resistance in series with the relay to keep the LR ratio low

(c) Using relays with minimum contacts as they require lesser operating current keeping the inductance

value low

40 | P a g e

CONCLUSION

Modern signalling is vital for safe and punctual movements of trains In the Indian railways The Signalling

and Telecommunication Department is responsible for providing modern effective and relaible signalling

systems as well as telecommunication systems

The first mode of communication used in Indian Railways was the use of electric telegraph

with the help of Morose code Morose code is the method of providing text information as a series of on-off

tones and lights or clicks that can be directly understood by a skilled listener or observer without special

equipmentEach character (letter or numeral ) is represented by a unique sequence of dots and dashes Later

this system becomes obselete and beggan the era of wireless communication which operated at audio level

frequency range

In wireless communication the significant advances took place the transition to miniature

valves or filament tubesBut this was abandoned too because of excessive current consumption and over

heating of the filament tubes

Fibre-optic communication is a method of transmitting information from one place to another by

sending pulses of light through an optcial fibreThe light forms an electromagnetic carrier wave that is

modulated to carry information First developed in the 1970s fibre optic communication systems has

revolutionized the telecommunications industry and have palyed a major role in the advent of the information

age Because of its advantages over electrical transmissionsoptical fibres have largely replaced copper wire

communications in core networks in the developed world The Indian Railways too is undergoing a transition

from Microwave communication to fibre optic communications

41 | P a g e

BIBLIOGRAPHY AND REFERENCES

1 wwwwikipediacom

2 wwwbritaniccacom

3 wwwirfcacom

4 Motorola GP60 system manual

5 Harris FAS 7000 manual

6 TOSHIBA Manual

20 | P a g e

These are generally used at FEP (Front End Processor) side to connect the Dataloggers

(i) To transfer Data from one datalogger to another datalogger FEP Baud rate is 9600bps

(ii) These modems are 4-wire line communication

(iii) To transfer the data from FEP to RMU (PC) the Baud rate is 57600 bps

There is no difference between these modems functionally

CENTRAL MONITORING UNIT (CMU) COMPUTER

Central monitoring unit (Fault Analysis Unit) is a Personal Computer and its minimum configuration

shall be specified by RDSO from time to time System Software Windows XPVista(OS) Norton Kaspersky

(Anti Virus) Interbase where Server is not available (DBMS) Oracle where Server is available (DBMS)

software are required to run Datalogger System It is provided with Graphical User interface (GUI) based

software and retrieve data from all Networked dataloggers (up to 32) at various stations It stores data in

standard data base files The CMU is capable of analyzing the data and generate reports audiovisual alarms

on defined conditions This data can be compressed to take backup In central monitoring unit Software used

for analysis of data prediction of faults etc is written in a structured format so that purchaser can

reconfigure it if required It displays the status of signaling gears at any selected time in graphic form for any

selected station yard It retrieves the stored data amp simulates train movement It sends commands to various

Dataloggers to activate audio visual alarm or operate and electromagnetic relay

CMU shares data available in it by other PCs through available local area network where this data can

be used for train charting passenger information purpose The system generates audiovisual alarm in

ASMrsquosSignal Maintainerrsquos room in the case of power supply failure (battery voltage low) or battery charger

defective with acknowledgement facility

(a) Each datalogger has its own identity code which will be transmitted along with data packet to central

monitoring unit

(b) Events recorded at each station are continuously transmitted to central monitoring unit Response time of

data transfer will not exceed 10 sec

21 | P a g e

22 | P a g e

OPTICAL FIBER CABLE

INTRODUCTION The demand for bandwidth on transmission networks is increasing rapidly because video and

graphical rich contents are exchanged through the corporate network or the Internet The Gigabit Ethernet

became ommonly used in the corporate network backbone and 10Gbit Ethernet will be adopted in the near

future Meanwhile in the home the demand for high-speed network becomes popular as the wide spread of

broadband access eg CATV xDSL and FTTH The transmission medium with capability to transmit high

bit rate signal is necessary to satisfy these requirements

The telecommunication transport technologies move from copper based networks to optical fiber

from timeslot based transport to wave length based transport from traditional circuit switching to terabit

router and all optical based networks entering into a new era of optical networking

BASIC PHYSICS OF OFC

OPTICAL FIBER CABLE OFC have Fibers which are long thin strands made with pure glass about the diameter of a human

hair OFC consists of Core Cladding Buffers and Jacket as shown in figure

MONOCHROMATIC LIGHT OR SINGLE COLOR LIGHT Light or visible light is electromagnetic radiation of a wavelength that is visible to the human eye (

about 400 ndash 700 nm) The word light is sometimes used to refer to the entire electromagnetic spectrum Light

is composed of elementary particles called photons Three primary properties of light are

Light can exhibit properties of both waves and particles This property is referred to as wave-particle

duality The study of light known as optics In free space light (of all wavelengths) travels in a straight path

at a constant maximum speed However the speed of light changes when it travels in a medium and this

change is not the same for all media or for all wavelengths By free space it is meant space that is free from

matter (vacuum) andor free from electromagnetic fields

Thus the speed of light in free space is defined by Einsteinrsquos equation E = mc2

Frequency ν speed of light in free space c and wavelength λ are interrelated by ν = cλ

From the energy relationships E = mc2 = hν and the last one an interesting relationship is obtained

the equivalent mass of a photon m = hνc2

When light is in the vicinity of a strong electromagnetic field it interacts with it From this interaction

and other influences its trajectory changes direction as shown in figure

23 | P a g e

INCIDENT RAY REFLECTED RAY AND REFRACTED RAY An incident ray is a ray of light that strikes a surface The angle between this ray and the

perpendicular or normal to the surface is the angle of incidence Reflection is the change in direction of a

wave front at an interface between two different media so that the wave front returns into the medium from

which it originated Common examples include the reflection of light sound and water waves

The reflected ray corresponding to a given incident ray is the ray that represents the light reflected by

the surface The angle between the surface normal and the reflected ray is known as the angle of reflection

The Law of Reflection says that for a specular (non-scattering) surface the angle of reflection always equals

the angle of incidence The refracted ray or transmitted ray corresponding to a given incident ray represents

the light that is transmitted through the surface The angle between this ray and the normal is known as the

angle of refraction and it is given by Snells Law

The figure shows Incident ray Reflected ray Refracted ray the angle of incidence and angle of refraction

REFRACTIVE INDEX - Refractive index is the speed of light in a vacuum ( c =299792458kmsecond) divided by the speed

of light in a material ( v ) Refractive index measures how much a material refracts light Refractive index of

a material abbreviated as lsquo n lsquo is defined as lsquo n=cv lsquo Light travels slower in physical media than it does

when transmitted through the air Refractive index (n) is a function of molecular structure of matter optical

frequency optical intensity determines optical propagation properties of each wavelength ( λ ) may not be

distributed equally in all directions is affected by external temperature pressure and fields

Refractive index of a medium is a measure for how much the speed of light is reduced inside the

medium For example typical glass has a refractive index of 15 which means that light travels at 1 15 =

067 times the speed in air or vacuum Two common properties of glass and other transparent materials are

directly related to their refractive index

First light rays change direction when they cross the interface from air to the material and effect that

is used in lenses and glasses

Second light reflects partially from surfaces that have a refractive index different from that of their

surroundings

SNELLrsquoS LAW-

24 | P a g e

When light passes from one transparent material to another it bends according to Snells law which

is defined as n1sin(θ1) = n2sin(θ2)

where n1 is the refractive index of the medium the light is leaving θ1 is the incident angle between the light

beam and the normal (normal is 90deg to the interface between two materials)

n2 is the refractive index of the material the light is entering

θ2 is the refractive angle between the light ray and the normal

Snellrsquos law gives the relationship between angle of incidence and angle of refraction

For the case of θ1 = 0deg (ie a ray perpendicular to the interface) the solution is θ2 = 0deg regardless of

the values of n1 and n2 That means a ray entering a medium perpendicular to the surface is never bent The

above is also valid for light going from a dense (higher n) to a less dense (lower n) material the symmetry of

Snells law shows that the same ray paths are applicable in opposite direction

TOTAL INTERNAL REFLECTION- When a light ray crosses an interface into a medium with a higher refractive index it bends towards

the normal Conversely light traveling cross an interface from a higher refractive index medium to a lower

refractive index medium will bend away from the normal

This has an interesting implication at some angle known as the critical angle θc light traveling from

a higher refractive index medium to a lower refractive index medium will be refracted at 90deg in other words

refracted alon g the interface If the light hits the interface at any angle larger than this critical angle it will

not pass through to the second medium at all Instead all of it will be reflected back into the first medium a

process known as total internal reflection

The critical angle can be calculated from Snells law putting in an angle of 90deg for the angle of the refracted

ray θ2 This gives θ1

Since θ2 = 90deg

So sin(θ2) = 1

25 | P a g e

Then θc = θ1 = arcsin(n2n1)

For example with light trying to emerge from glass with n1=15 into air (n2 =1) the ritical angle θc is

arcsin(115) or 418deg For any angle of incidence larger than the critical angle Snells law will not be able to

be solved for the angle of refraction because it will show that the refracted angle has a sine larger than 1

which is not possible In that case all the light is totally reflected off the interface obeying the law of

reflection

OPTICAL FIBER MODE An optical fiber guides light waves in distinct patterns called modes Mode describes the distribution

of light energy across the fiber The precise patterns depend on the wavelength of light transmitted and on the

variation in refractive index that shapes the core In essence the variations in refractive index create

boundary

conditions that shape how light waves travel through the fiber like the walls of a tunnel affect how sounds

echo inside

We can take a look at large-core step-index fibers Light rays enter the fiber at a range of angles and

rays at different angles can all stably travel down the length of the fiber as long as they hit the core-cladding

interface at an angle larger than critical angle These rays are different modes Fibers that carry more than

one mode at a specific light wavelength are called multimode fibers Some fibers have very small diameter

core that they can carry only one mode which travels as a straight line at the center of the core These fibers

are single mode fibers This is illustrated in the following picture

OPTICAL FIBER INDEX PROFILE Index profile is the refractive index distribution across the core and the cladding of a fiber Some

optical fiber has a step index profile in which the core has one uniformly distributed index and the cladding

has a lower uniformly distributed index Other optical fiber has a graded index profile in which refractive

index varies gradually as a function of radial distance from the fiber center Graded-index profiles include

power-law index profiles and parabolic index profiles The following figure shows some common types of

index profiles for single mode and multimode fiber

26 | P a g e

OPTICAL FIBERrsquoS NUMERICAL APERTURE ( NA )- Multimode optical fiber will only propagate light that enters the fiber within a certain cone known as

the acceptance cone of the fiber The half-angle of this cone is called the acceptance angle (see figure 18)

θmax For step-index multimode fiber the acceptance angle is determined only by the indices of refraction

Where

n is the refractive index of the medium light is traveling before entering the fiber

nf is the refractive index of the fiber core

nc is the refractive index of the cladding

NUMBER OF MODES IN A FIBER - Modes are sometimes characterized by numbers Single mode fibers carry only the lowest-order

mode assigned the number 0 Multimode fibers also carry higher-order modes The number of modes that

can propagate in a fiber depends on the fiberrsquos numerical aperture (or acceptance angle) as well as on its

core diameter and the wavelength of the light For a step-index multimode fiber the number of such modes

Nm

Where

D is the core diameter

λ is the operating wavelength

NA is the numerical aperture (or acceptance angle)

MODE FIELD DIAMETER - All light do not travels through the core of the fiber but is distributed through both the core and the

cladding The mode field is the distribution of light through the core and cladding of a particular fiber

Mode-Field Diameter (MFD) defines the size of the power distribution When coupling light into or out of a

fiber MFD is important in understanding light loss

27 | P a g e

ADVANTAGE OF OFC COMMUNICATION - bull More information carrying capacity Fibers can handle much higher data rates than copper More

information can be sent in a second

bull Free from Electromagnetic and Electrostatic interference Being insulator no electric current flows through

the fibre and due to this reason fibres neither radiate nor pick up electro - magnetic radiation So WPC

CLEARANCE is not required

bull Low attenuation 025 dbkm at 1550 nm Loss in twisted pair and coaxial cable increases with frequency

where as loss in the optical fibre cable remains flat over a wide range of frequencies

bull Use of WDM ndash Switching routing at Optical signal level

bull Self healing rings under NMS control

bull Small size makes fibre cable lighter in weight So easy to handleOptic fibre cable weight (approx)

500 kg km Copper cable weight (approx) 1000 kgkm

The reasons are photons of light in a fibre

do not affect each other as they have no electrical charge and they are not affected by stray photons outside

the fibre But in case of copper electrons move through the cable and these are affected by each other

Optical fibre does not carry any electricity even if the cable is damaged or short circuited it does

not cause any spark or fire hazard

As the fibre do not radiate energy it can not be detected by any nearby antenna or any

other detector The fibres are difficult to tap and therefore excellent for security

As the signal transmission is by digital modulation there is no chance of cross talk in

between channels

Only by adding a few additional terminal and repeater equipments the

capacity of the system can be increased at any time once the cable is laid

ical effects and temperature variations

LIMITATIONS OF OFC -

difficult

- utilised

APPLICATION IN SIGNAL AND TELECOMMUNICATIONS transmission circuits

-haul circuits for linking of telephone exchanges

28 | P a g e

PROPAGATION MODES CONCEPT -

MODE - Mode is an available distribution of electromagnetic field in a plane transverse to the direction of

light propagation Each mode is characterized by frequency polarization electric field strength and

magnetic field strength Available patterns are derived from Maxwellrsquos equations and boundary conditions

LINEARLY POLARIZED (LP) MODE A mode for which the field components in the direction of propagation are small compared to

components perpendicular to that direction An optical fibre supports only different field patterns called as

lsquoLinear Polarizedrsquo or lsquo LPrsquo modes The reasons are

requirements

de

the accrual of power carried by different modes

There are two basic types of fiber Multimode fiber and Single-mode fiber

Multimode fiber is best designed for short transmission distances This is suited for used in LAN systems and

video surveillance Single mode fibre is best designed for longer transmission distances This is suitable for

long distance telephony and multi channel television broadcast systems

29 | P a g e

MULTI MODE FIBER Multimode fiber the first to be manufactured and commercialized simply refers to the fact that

numerous modes or light rays are carried simultaneously through the waveguide Modes result from the fact

that light will only propagate in the fiber core at discrete angles within the cone of acceptance MM fiber type

has a much larger core diameter compared to single-mode fiber allowing for the larger number of modes

and

is easier to couple than single-mode optical fiber Multimode fiber further categorized as Multimode step-

index and Multimode graded index fiber

PROPAGATION THROUGH MMSI FIBER Figure shows the principle of total internal reflection applies to multimode step index fiber Because

the corersquos index of refraction is higher than the claddingrsquos index of refraction the light that enters at less than

the critical angle is guided along the fiber

Three different light waves travel down the fiber One mode travels straight down the center of the

core A second mode travels at a steep angle and bounces back and forth by total internal reflection The third

mode exceeds the critical angle and refracts into the cladding Naturally it can be seen that the second mode

travels a longer distance than the first mode causing the two modes to arrive at separate times

PROBLEMS WITH MMSI FIBER AND SOLUTION This disparity between arrival times of the different light rays is known as dispersion and the result is

a muddied signal at the receiving end It is important to note that high dispersion is an unavoidable

characteristic of multimode step-index fiber The solutions are either use Graded index fiber or Single mode

fiber

PROPAGATION THROUGH MMGI FIBER Multimode Graded-index refers to the fact that the refractive index of the core gradually decreases

farther from the center of the core The increased refraction in the center of the core slows the speed of some

light rays allowing all the light rays to reach the receiving end at approximately the same time reducing

dispersion Figure shows the Light propagation principle through multimode graded-index fiber The corersquos

central refractive index ( nA ) is greater than that of the outer corersquos refractive index ( nB )

It is very clear from the figure the light rays no longer follow straight lines they follow a serpentine path

being gradually bent back toward the center by the continuously declining refractive index This reduces the

arrival time disparity because all modes arrive at about the same time The modes traveling in a straight line

30 | P a g e

are in a higher refractive index so they travel slower than the serpentine modes These travel farther but

move faster in the lower refractive index of the outer core region

PROPAGATION THROUGH SMSI FIBER Single mode fiber has a much smaller core that allows only one mode of light at a time to propagate

through the core The figure shows the single mode fiber

Single-mode fiber exhibits no dispersion caused by multiple modes Single-mode fiber also offers lower fiber

attenuation than multimode fiber Thus more information can be transmitted per unit of time because it can

retain the fidelity of each light pulse over longer distances Like multimode fiber early single-mode fiber was

generally characterized as step-index fiber meaning the refractive index of the fiber core is a step above that

of the cladding rather than graduated as it is in graded-index fiber Modern single-mode fibers have evolved

into more complex designs such as matched clad depressed clad and other exotic structures

SINGLE-MODE FIBER DISADVANTAGES The smaller core diameter makes coupling light into the core more difficult The tolerances for single-

mode connectors and splices are also much more demanding

CUTOFF WAVE LENGTH - Cutoff wavelength is the wavelength above which a single-mode fiber supports and propagates only

one mode of light In other words an optical fiber that is single-mode at a particular wavelength may have

two or more modes at wavelengths lower than the cutoff wavelength The effective cutoff wavelength of a

fiber is dependent on the length of fiber and its deployment The longer the fiber the lower is the effective

cutoff

wavelength The smaller the bend radius of a loop of the fiber the lower is the effective cutoff wavelength If

a fiber is bent in a loop the effective cutoff wavelength is lowered

SIGNAL ATTENUATION IN FIBER - Optical fiber has a number of advantages over copper However it also suffers from degradation

problems which can not be ignored The first of these is loss or attenuation Attenuation is typically the result

of two sub properties They are scattering and absorption Both of which have cumulative effects The second

is

dispersion which is the spreading of the transmitted signal and is analogous to noise

SCATTERING Scattering occurs because of impurities or irregularities in the physical construction of the fiber The

well known form of scattering is Rayleigh Scattering It is caused by metal ions in the silica matrix and

results in light rays being scattered in various directions

31 | P a g e

Scattering limits the use of wavelengths below 800nm The short wavelengths are much affected than longer

wavelengths It is because of Rayleigh scattering that the sky appears to be blue ( shorter wave length ) The

shorter wavelengths ( blue ) of light are scattered more than the longer wavelengths of light

ABSORPTION Absorption results from three factors They are hydroxyl ions ( OH- water ) in the silica impurities

in the silica and incomplete residue from the manufacturing process These impurities tend to absorb the

energy of the transmitted signal and convert it to heat resulting in an overall weakening of the signal The

Hydroxyl absorption occurs at 125 and 139 micro The silica itself starts to absorb energy at 17 micro

because of the natural resonance of the silicon dioxide

MACRO BENDING LOSS Macro-bending loss is caused by bending of the entire fiber axis The bending radius shall not be

sharper than 30d where d is diameter of cable A single bend sharper than 30d can cause loss of 05dB

The fiber may break if bending is ever sharper

MICRO BENDING LOSS Micro-bending loss is caused by micro deformations of fiber axis which leads to failures in achieving

total internal reflection conditions Micro-bends are small scale perturbations along the fiber axis the

amplitude of which are on the order of microns These distortions can cause light to leak out of a fiber

Micro-bending may be induced at very cold temperatures because the glass has a different coefficient of

thermal expansion from the coating and cabling materials At low temperatures the coating and cable

become more rigid and may contract more than the glass Consequently enough load may be exerted on the

glass to cause micro bends

Coating material is selected by manufacturers to minimize loss due to micro-bending The linear thermal

expansion coefficient of coating material shall be compatible with that of fiber

32 | P a g e

DISPERSION Dispersion is the optical term for the spreading of the transmits in the fiber It is the bandwidth

limiting phenomenon and comes in two forms Multimode dispersion and chromatic dispersion Chromatic

dispersion is further subdivided into material dispersion and waveguide dispersion

DISPERSION PHENOMENON IN OPTICAL FIBER Dispersion is the time distortion of an optical signal that results from the differences of time of travel

for different components of that signal typically resulting in pulse broadening As the distance traveled by

the signal is more broadening of pulse is more In digital transmission dispersion limits on the maximum

data rate and the maximum distance ie the information-carrying capacity of a fiber link The interference

from broadened pulse in the next interval shall not lead to erroneous interpretation of received signal

OPTICAL DOMAIN Understanding where attenuation and dispersion problems occur helps optical design engineers

determine the better wavelengths at which information can be transmit taking into account distance type of

fiber and the other factors which can severely affect the integrity of the transmitted signal The graph shown

depicts the optical transmission domain as well as the areas where problems arise The wavelength (nm)

is shown on X-axis and attenuation ( dBkm) is shown on Y-axis

There are four transmission windows appear in the figure The first one is at around 850 nm the

second at 1310nm third at 1550 nm and fourth at 1625 nm The last two labeled as C and L band

respectively The 850 nm wavelength at which the original LED technology operated The second window at

1310 nm has low dispersion The 1550 nm called as C-band is ideal wavelength for long haul

communication systems The network engineers can avoid transmitting signal at 1000 nm where Rayleigh

scattering 1240 and 1390 nm where hydroxyl absorption by water occurs to avoid high degree of loss

Optical fibers also can be manufactured to have low dispersion wavelength in the 1550nm region

which is also the point where silica-based fibers have inherently minimal attenuation These fibers are

referred to as dispersion-shifted fibers and are used in long-distance applications with high bit rates For

33 | P a g e

applications utilizing multiple wavelengths it is undesirable to have the zero dispersion point within the

operating

wavelength range

34 | P a g e

SIGNALLING RELAYS

INTRODUCTION A relay is an electromagnetic device which is used to convey information from one circuit to another

circuit through a set of contact ie front or back contact Constructional and electrically relays may be

divided into DC and AC relays because the means by which the electrical energy in the coil is converted in

to mechanical Energy in order to move the contacts are fundamentally different In DC type the contacts are

carried on an armature forming part of a magnetic circuit in which a field is set up by the current flowing in

the coils In AC types the contacts are attached by a link mechanism to a metal sector disc or cylinder in

which currents are induced by the alternating magnetic field produced by the currents in the coils

Every endeavor has been made to explain the action of each type of relay in the simplest possible manner

Relays are sophisticated switch gears used for remote control and succession control of various

electrical equipment In present days they are widely used because they are capable of protecting the

controlled equipment from cross feeding and overloading even as they cater for speedy operations

Most of the relays in present day signaling are electromagnetic devices although some of the relays control

circuits through electronic components like diodetransistors Integrated Chips etc

Railway signaling relays are unique in that

(a) They operate on low voltage and current

(b) They are more articulate as according to their special features they can work under restrictive conditions

and in any specified manner Virtually they can cater for all situations while contributing to speed and

accuracy in operations

CLASSIFICATION OF SIGNALLING RELAYS (a) According to the method of their mounting or fixture they are classified as

(i) Shelf type Relays which are loosely kept on shelves

(ii) Plug in type Relays which are plugged into a pre- wired plug boards

(b) According to their connection and usage they are classified as

(i) Track relays Relay which is directly connected to the track to detect the presence of vehicle

(ii) Line Relays Other than track relay all are line relays Relays connected to the selection circuit

(c) According to their vitality or importance in ensuring train working safety they are classified as

(i) Vital Relays All relays used for traffic control such as signal point controls track detection etc

(ii) Non-vital Relays Relays which operate control aids and accessories like warnings buzzers

Indications etc

(d) According to their special provisions to ensure reliability of their contacts they are classified as

(i) Proved type are those whose normalization after each operation shall be proved in circuit

controlled by their contacts Contacts in which both the springs have metal surfaces on their tips They may

get fused due to high sparking current across them during operation These may prevent relay normalization

and causes unsafe condition in traffic control To avoid this proving of relay normalization after each

operation is necessary

(ii) Non - proved type Need not to be proved to have been normalized after each operation as their

contacts have at least one non-fusible contact (carbon contact)

(e) According to their feed source relays are broadly classified as

(i) DC relays The relay which requires DC power supply for its operations are called DC relays Among

the DC relays

o DC neutral relays This relay closes the same set of contacts on energization with Normal polarity

or Reverse polarity supply

o Polar Relays This relay closes different set of contacts when energized with Reverse polarity

supply They may or may not have contact to close when deenergized

35 | P a g e

(ii) AC Relay AC Induction motor track relays Time element relays flashing indication control etc

(iii) Electronic Relays DC relays with electronic components in them are called electronic relays

DC NEUTRAL RELAY Each Relay has usually one or two coils with a hollow center to accommodate a coreThe coils are

made up of a large numbers of turns of small gauge soft drawn copper wire The two coils can be connected

in series or parallel according to the requirement of relay resistance The ends of the coils are terminated on

binding post to which the control wires are connected Each coil is placed around a core of specially selected

Iron or steel having high permeability and low retentivity The core should be susceptible to magnetism and

at the same time should have little residual magnetism The cores are connected at the top by a yoke to

complete the magnetism coupling between two ends of coils The bottom of each core is equipped with a

large steel or Iron block known as pole piece or face

A flat piece of Iron or steel called armature is supported by brackets which are securely fastened to

the pole piece The armature yoke and the pole pieces are also made of specially selected iron or steel of the

same quality as the core The armature carries the metallic spring contacts which are insulated from it

The circuit through the coils of the relay is closed It sets up a magnetic flux through the core yoke and the

armature The flux passing between the armature and pole faces causes the armatures get attracted to the pole

faces and armature picks up and closes front contacts When the circuit is opened the magnetic flux collapses

and the armature drops away by gravity from the pole faces the front contacts break and back contacts close

The front and back contacts of the relay can be utilised to make or break other circuits Two stop pins of

nonmagnetic material are fixed either on the armature or pole faces so that the armature cannot

come in contact with the pole faces It is essential to maintain a small air-gap between the armature and pole

faces so that low value of residual magnetism may not retain the armature in picked up position and causes

the relay to fail to drop away with a break in its control circuit

GENERAL USAGE

DC Neutral line relays are most commonly used for Railway Signalling controls and detection

Among them plug-in type relays are preferred in larger installations for space considerations Shelf type

relays are also in use mostly in wayside stations

There are many DC Neutral line relays in use with special features such as

(i) Delayed operation

(ii) Biased DC control

(iii) DC control unaffected by AC interference currents

(iv) Getting latched in operated condition till further feeding and others

Usage of DC polar relays is mostly in conjunction with block instruments that control traffic between

stations AC line relays are almost extinct in installations of British Signalling practice They are however

used for time control operations flashing indication control and such other special purposes in installations

with Siemens signalling practice widely Track relays are used according to the type of track detection

circuits chosen for a given location and context While most of the track circuits are still of the DC working

type requiring DC neutral track relays with them the prospects of their being replaced with Electronic track

circuits directly feeding DC line relays in future are great AC Track Circuits are used in DC Traction area

as conventional DC Track Circuits are not suitable there AC Track relays are used with them almost all of

the induction motor type In the British practice of signalling which was first introduced on Indian Railways

non-proved type relays with carbon to metal switching contacts are generally used for vital controls

They facilitate simple circuit designs But with the advent of German Practice introduced by Ms

Siemens later proved type relays with all metal to metal contacts are widely accepted in spite of

complications in circuit design caused by them A recent introduction is that of the same type relays made by

Ms Integra control However for some time now the appreciable features of both the practices are getting

36 | P a g e

incorporated together in the indigenous designs of signalling by railwaymen With this the usage of all types

of relays anywhere can be found without straight jacketed segration of relay types

CHARACTERSTIC OF ELECTRO-MAGNETIC RELAY The following are the characteristic of electro-magnetic relays A brief study of them helps in

understanding the choice of their components and designs features

1) Force of attraction

2) Effect of air gap

3) Effect of Hysterisis

4) Transient condition

FORCE OF ATTRACTION In any electro-magnetic system the force of attraction is given by

Where B - is the flux density a - is the cross sectional area of the particular part of the magnetic

circuit

In the case of a DC neutral Relay B is proportional to the current that is flowing in the coil

surrounding the electro-magnet and thus the force of the attraction is directly proportional to the square of the

current This square relationship has its own advantage especially in the case of DC track relay in that a

small reduction in the current will have a great effect on the working of the relay Also for a given change of

current the make and the break will be quicker with lesser possibility of arcing

EFFECT OF AIR GAP

Curve lsquoArsquo is magnetisation curve for the iron and is all practical purpose a straight line up to the

saturation point Curve lsquoBrsquo is the magnetisation curve for the open-air gap which is a straight line through

out because per magnetisation curve of the whole

magnetic circuit of the relay and for a given force is the sum of the amp-turns for the iron part and the amp-

turns for the air gap

When the front contacts are open the force required to pick up the armature is shown on curve lsquoCrsquo to be F1

but after the armature has operated it will be separated from the core by stop pins In this position the amp-

turns required to maintain the armature is less as indicated by the dotted line from 1 on curve C to 2 on curve

37 | P a g e

F But actually the current in the coil is unaltered the force on the armature is greater than required as

indicated at 3 on curve F Part of this extra force is used to flex the front contacts sufficiently to give good

contact pressure when it is in energised position

The difference between the pick-up and the drop-away current should be as small as practicable in

track relay to ensure good shunting characteristics This is achieved firstly by the choice of good quality relay

iron and secondly by having a small air gap between armature and core If the air gap is not available then

the residual magnetism fluxes might cause the armature to be retained when the supply is disconnected For

this reason residual pins are provided to ensure a definite minimum air gap in the energised position

EFFECT OF HYSTERISIS

Hysterisis is the property by which the flux produced lags behind the current In the de-energized

condition there will be small residual flux in the core When the voltage is applied to the coils the current in

rising to its steady value first causes the flux to rise from 1 to 2 along the curve At this point the flux density

will be sufficient to attract the armature and reduce the air gap the flux then raise to 3 and continue to 4

which corresponds to the steady current in the coils When the voltage is disconnected the current in falling

caused the flux to fall from 4 to 5 along the curve At this point the flux density will fall below the value

required to maintain the armature which will release thus increasing the air gap and reducing the flux to 6

Finally the

flux will decrease from 6 to 1 where the current will again be zero

The relay core is made of material having high permeability and low retentivity As mentioned in

the IRS specification Electromagnet iron may be in the form of a

(a) Bar of silicon steel

(b) Best Yorkshire wrought iron

(c) Swedish charcoal iron

(d) Electrical steel sheets

` This reduces the difference between pick up value and Drop away value By selecting good quality

core material Percentage release and sensitivity of the relay will be improved

TRANSIENT CONDITION

38 | P a g e

When the voltage is applied or disconnected from the coils it takes some little time before the current

become steady These are known as transient conditionsrdquo and are important so far as track relays are

concerned When the voltage is first applied to the coils the magnetic flux in rising cuts the turns on the

coils and in so doing produces a back EMF that opposes the applied voltage and retards the growth of

current

The growth and decay of flux are decided by the relationship between the inductance and resistance

in the circuit is known as time constant It is not fixed quantity in the case of DC neutral relay This value of lsquo

Lrsquo is less when the relay is in de-energised condition (L1) than when the relay is in energised condition (L2)

The magnitude of flux that is established for a given change of current is different in two cases

When the current reaches the pick up value the armature closes and the inductance is increased to L2

due to reduced air gap the flux per amp is increased The increase in flux increased the back EMF during the

movement of the armature after which the current continuous to raise along a new curve corresponding to the

increased inductance until it reaches the final value (ER) This process is indicated above in fig24

When the supply is disconnected the current is obliviously reduced to zero immediately but the flux

decay comparatively slowly owing to the eddy currents produced in the core by the rapid flux change which

tend to maintain the flux The drop away time on a disconnection is however generally negligible See fig

below

If the relay releases due to the reduction in current from say I 2 to I 1 caused by the application of

shunt resistance (as in the case of track relay ) the time taken is much longer than the relay is simply

disconnected The rate of rise or fall of current during the transient conditions is also depends on exterior

circuit values because L and R apply to the whole circuit The production of eddy current in the core the flux

will decay at a slower rate than the current So that the actual release time will be a little longer than it takes

the current to fall to the release

L= Inductance

39 | P a g e

R= Resistance

It is now clear that to reduce releasing time to a minimum it is necessary that

- The relay iron should have low Hysterisis loss and low retentivity

- The degree of over energization of the relay should be restricted

- Connecting a suitable external resistance in series with the relay to keep LR ratio low

In non RE area for track circuit length less than 100M 9 ohm track relay only to be used Using relay

with minimum contacts as they require lesser current which keeps inductance value low

Train working safety is ensured only if the track relay of shortest length track circuit is released

before a light engine running at a highest permitted speed clears it Otherwise the track circuit occupation

may go undetected To avoid this a special provision has to be made in signal control circuits wherever

necessary

The following methods may be adopted for reducing the time lag of track relay

(a) Restrict the over energisation of relay since the release time depends on the initial working current

(b) Connecting a suitable external resistance in series with the relay to keep the LR ratio low

(c) Using relays with minimum contacts as they require lesser operating current keeping the inductance

value low

40 | P a g e

CONCLUSION

Modern signalling is vital for safe and punctual movements of trains In the Indian railways The Signalling

and Telecommunication Department is responsible for providing modern effective and relaible signalling

systems as well as telecommunication systems

The first mode of communication used in Indian Railways was the use of electric telegraph

with the help of Morose code Morose code is the method of providing text information as a series of on-off

tones and lights or clicks that can be directly understood by a skilled listener or observer without special

equipmentEach character (letter or numeral ) is represented by a unique sequence of dots and dashes Later

this system becomes obselete and beggan the era of wireless communication which operated at audio level

frequency range

In wireless communication the significant advances took place the transition to miniature

valves or filament tubesBut this was abandoned too because of excessive current consumption and over

heating of the filament tubes

Fibre-optic communication is a method of transmitting information from one place to another by

sending pulses of light through an optcial fibreThe light forms an electromagnetic carrier wave that is

modulated to carry information First developed in the 1970s fibre optic communication systems has

revolutionized the telecommunications industry and have palyed a major role in the advent of the information

age Because of its advantages over electrical transmissionsoptical fibres have largely replaced copper wire

communications in core networks in the developed world The Indian Railways too is undergoing a transition

from Microwave communication to fibre optic communications

41 | P a g e

BIBLIOGRAPHY AND REFERENCES

1 wwwwikipediacom

2 wwwbritaniccacom

3 wwwirfcacom

4 Motorola GP60 system manual

5 Harris FAS 7000 manual

6 TOSHIBA Manual

21 | P a g e

22 | P a g e

OPTICAL FIBER CABLE

INTRODUCTION The demand for bandwidth on transmission networks is increasing rapidly because video and

graphical rich contents are exchanged through the corporate network or the Internet The Gigabit Ethernet

became ommonly used in the corporate network backbone and 10Gbit Ethernet will be adopted in the near

future Meanwhile in the home the demand for high-speed network becomes popular as the wide spread of

broadband access eg CATV xDSL and FTTH The transmission medium with capability to transmit high

bit rate signal is necessary to satisfy these requirements

The telecommunication transport technologies move from copper based networks to optical fiber

from timeslot based transport to wave length based transport from traditional circuit switching to terabit

router and all optical based networks entering into a new era of optical networking

BASIC PHYSICS OF OFC

OPTICAL FIBER CABLE OFC have Fibers which are long thin strands made with pure glass about the diameter of a human

hair OFC consists of Core Cladding Buffers and Jacket as shown in figure

MONOCHROMATIC LIGHT OR SINGLE COLOR LIGHT Light or visible light is electromagnetic radiation of a wavelength that is visible to the human eye (

about 400 ndash 700 nm) The word light is sometimes used to refer to the entire electromagnetic spectrum Light

is composed of elementary particles called photons Three primary properties of light are

Light can exhibit properties of both waves and particles This property is referred to as wave-particle

duality The study of light known as optics In free space light (of all wavelengths) travels in a straight path

at a constant maximum speed However the speed of light changes when it travels in a medium and this

change is not the same for all media or for all wavelengths By free space it is meant space that is free from

matter (vacuum) andor free from electromagnetic fields

Thus the speed of light in free space is defined by Einsteinrsquos equation E = mc2

Frequency ν speed of light in free space c and wavelength λ are interrelated by ν = cλ

From the energy relationships E = mc2 = hν and the last one an interesting relationship is obtained

the equivalent mass of a photon m = hνc2

When light is in the vicinity of a strong electromagnetic field it interacts with it From this interaction

and other influences its trajectory changes direction as shown in figure

23 | P a g e

INCIDENT RAY REFLECTED RAY AND REFRACTED RAY An incident ray is a ray of light that strikes a surface The angle between this ray and the

perpendicular or normal to the surface is the angle of incidence Reflection is the change in direction of a

wave front at an interface between two different media so that the wave front returns into the medium from

which it originated Common examples include the reflection of light sound and water waves

The reflected ray corresponding to a given incident ray is the ray that represents the light reflected by

the surface The angle between the surface normal and the reflected ray is known as the angle of reflection

The Law of Reflection says that for a specular (non-scattering) surface the angle of reflection always equals

the angle of incidence The refracted ray or transmitted ray corresponding to a given incident ray represents

the light that is transmitted through the surface The angle between this ray and the normal is known as the

angle of refraction and it is given by Snells Law

The figure shows Incident ray Reflected ray Refracted ray the angle of incidence and angle of refraction

REFRACTIVE INDEX - Refractive index is the speed of light in a vacuum ( c =299792458kmsecond) divided by the speed

of light in a material ( v ) Refractive index measures how much a material refracts light Refractive index of

a material abbreviated as lsquo n lsquo is defined as lsquo n=cv lsquo Light travels slower in physical media than it does

when transmitted through the air Refractive index (n) is a function of molecular structure of matter optical

frequency optical intensity determines optical propagation properties of each wavelength ( λ ) may not be

distributed equally in all directions is affected by external temperature pressure and fields

Refractive index of a medium is a measure for how much the speed of light is reduced inside the

medium For example typical glass has a refractive index of 15 which means that light travels at 1 15 =

067 times the speed in air or vacuum Two common properties of glass and other transparent materials are

directly related to their refractive index

First light rays change direction when they cross the interface from air to the material and effect that

is used in lenses and glasses

Second light reflects partially from surfaces that have a refractive index different from that of their

surroundings

SNELLrsquoS LAW-

24 | P a g e

When light passes from one transparent material to another it bends according to Snells law which

is defined as n1sin(θ1) = n2sin(θ2)

where n1 is the refractive index of the medium the light is leaving θ1 is the incident angle between the light

beam and the normal (normal is 90deg to the interface between two materials)

n2 is the refractive index of the material the light is entering

θ2 is the refractive angle between the light ray and the normal

Snellrsquos law gives the relationship between angle of incidence and angle of refraction

For the case of θ1 = 0deg (ie a ray perpendicular to the interface) the solution is θ2 = 0deg regardless of

the values of n1 and n2 That means a ray entering a medium perpendicular to the surface is never bent The

above is also valid for light going from a dense (higher n) to a less dense (lower n) material the symmetry of

Snells law shows that the same ray paths are applicable in opposite direction

TOTAL INTERNAL REFLECTION- When a light ray crosses an interface into a medium with a higher refractive index it bends towards

the normal Conversely light traveling cross an interface from a higher refractive index medium to a lower

refractive index medium will bend away from the normal

This has an interesting implication at some angle known as the critical angle θc light traveling from

a higher refractive index medium to a lower refractive index medium will be refracted at 90deg in other words

refracted alon g the interface If the light hits the interface at any angle larger than this critical angle it will

not pass through to the second medium at all Instead all of it will be reflected back into the first medium a

process known as total internal reflection

The critical angle can be calculated from Snells law putting in an angle of 90deg for the angle of the refracted

ray θ2 This gives θ1

Since θ2 = 90deg

So sin(θ2) = 1

25 | P a g e

Then θc = θ1 = arcsin(n2n1)

For example with light trying to emerge from glass with n1=15 into air (n2 =1) the ritical angle θc is

arcsin(115) or 418deg For any angle of incidence larger than the critical angle Snells law will not be able to

be solved for the angle of refraction because it will show that the refracted angle has a sine larger than 1

which is not possible In that case all the light is totally reflected off the interface obeying the law of

reflection

OPTICAL FIBER MODE An optical fiber guides light waves in distinct patterns called modes Mode describes the distribution

of light energy across the fiber The precise patterns depend on the wavelength of light transmitted and on the

variation in refractive index that shapes the core In essence the variations in refractive index create

boundary

conditions that shape how light waves travel through the fiber like the walls of a tunnel affect how sounds

echo inside

We can take a look at large-core step-index fibers Light rays enter the fiber at a range of angles and

rays at different angles can all stably travel down the length of the fiber as long as they hit the core-cladding

interface at an angle larger than critical angle These rays are different modes Fibers that carry more than

one mode at a specific light wavelength are called multimode fibers Some fibers have very small diameter

core that they can carry only one mode which travels as a straight line at the center of the core These fibers

are single mode fibers This is illustrated in the following picture

OPTICAL FIBER INDEX PROFILE Index profile is the refractive index distribution across the core and the cladding of a fiber Some

optical fiber has a step index profile in which the core has one uniformly distributed index and the cladding

has a lower uniformly distributed index Other optical fiber has a graded index profile in which refractive

index varies gradually as a function of radial distance from the fiber center Graded-index profiles include

power-law index profiles and parabolic index profiles The following figure shows some common types of

index profiles for single mode and multimode fiber

26 | P a g e

OPTICAL FIBERrsquoS NUMERICAL APERTURE ( NA )- Multimode optical fiber will only propagate light that enters the fiber within a certain cone known as

the acceptance cone of the fiber The half-angle of this cone is called the acceptance angle (see figure 18)

θmax For step-index multimode fiber the acceptance angle is determined only by the indices of refraction

Where

n is the refractive index of the medium light is traveling before entering the fiber

nf is the refractive index of the fiber core

nc is the refractive index of the cladding

NUMBER OF MODES IN A FIBER - Modes are sometimes characterized by numbers Single mode fibers carry only the lowest-order

mode assigned the number 0 Multimode fibers also carry higher-order modes The number of modes that

can propagate in a fiber depends on the fiberrsquos numerical aperture (or acceptance angle) as well as on its

core diameter and the wavelength of the light For a step-index multimode fiber the number of such modes

Nm

Where

D is the core diameter

λ is the operating wavelength

NA is the numerical aperture (or acceptance angle)

MODE FIELD DIAMETER - All light do not travels through the core of the fiber but is distributed through both the core and the

cladding The mode field is the distribution of light through the core and cladding of a particular fiber

Mode-Field Diameter (MFD) defines the size of the power distribution When coupling light into or out of a

fiber MFD is important in understanding light loss

27 | P a g e

ADVANTAGE OF OFC COMMUNICATION - bull More information carrying capacity Fibers can handle much higher data rates than copper More

information can be sent in a second

bull Free from Electromagnetic and Electrostatic interference Being insulator no electric current flows through

the fibre and due to this reason fibres neither radiate nor pick up electro - magnetic radiation So WPC

CLEARANCE is not required

bull Low attenuation 025 dbkm at 1550 nm Loss in twisted pair and coaxial cable increases with frequency

where as loss in the optical fibre cable remains flat over a wide range of frequencies

bull Use of WDM ndash Switching routing at Optical signal level

bull Self healing rings under NMS control

bull Small size makes fibre cable lighter in weight So easy to handleOptic fibre cable weight (approx)

500 kg km Copper cable weight (approx) 1000 kgkm

The reasons are photons of light in a fibre

do not affect each other as they have no electrical charge and they are not affected by stray photons outside

the fibre But in case of copper electrons move through the cable and these are affected by each other

Optical fibre does not carry any electricity even if the cable is damaged or short circuited it does

not cause any spark or fire hazard

As the fibre do not radiate energy it can not be detected by any nearby antenna or any

other detector The fibres are difficult to tap and therefore excellent for security

As the signal transmission is by digital modulation there is no chance of cross talk in

between channels

Only by adding a few additional terminal and repeater equipments the

capacity of the system can be increased at any time once the cable is laid

ical effects and temperature variations

LIMITATIONS OF OFC -

difficult

- utilised

APPLICATION IN SIGNAL AND TELECOMMUNICATIONS transmission circuits

-haul circuits for linking of telephone exchanges

28 | P a g e

PROPAGATION MODES CONCEPT -

MODE - Mode is an available distribution of electromagnetic field in a plane transverse to the direction of

light propagation Each mode is characterized by frequency polarization electric field strength and

magnetic field strength Available patterns are derived from Maxwellrsquos equations and boundary conditions

LINEARLY POLARIZED (LP) MODE A mode for which the field components in the direction of propagation are small compared to

components perpendicular to that direction An optical fibre supports only different field patterns called as

lsquoLinear Polarizedrsquo or lsquo LPrsquo modes The reasons are

requirements

de

the accrual of power carried by different modes

There are two basic types of fiber Multimode fiber and Single-mode fiber

Multimode fiber is best designed for short transmission distances This is suited for used in LAN systems and

video surveillance Single mode fibre is best designed for longer transmission distances This is suitable for

long distance telephony and multi channel television broadcast systems

29 | P a g e

MULTI MODE FIBER Multimode fiber the first to be manufactured and commercialized simply refers to the fact that

numerous modes or light rays are carried simultaneously through the waveguide Modes result from the fact

that light will only propagate in the fiber core at discrete angles within the cone of acceptance MM fiber type

has a much larger core diameter compared to single-mode fiber allowing for the larger number of modes

and

is easier to couple than single-mode optical fiber Multimode fiber further categorized as Multimode step-

index and Multimode graded index fiber

PROPAGATION THROUGH MMSI FIBER Figure shows the principle of total internal reflection applies to multimode step index fiber Because

the corersquos index of refraction is higher than the claddingrsquos index of refraction the light that enters at less than

the critical angle is guided along the fiber

Three different light waves travel down the fiber One mode travels straight down the center of the

core A second mode travels at a steep angle and bounces back and forth by total internal reflection The third

mode exceeds the critical angle and refracts into the cladding Naturally it can be seen that the second mode

travels a longer distance than the first mode causing the two modes to arrive at separate times

PROBLEMS WITH MMSI FIBER AND SOLUTION This disparity between arrival times of the different light rays is known as dispersion and the result is

a muddied signal at the receiving end It is important to note that high dispersion is an unavoidable

characteristic of multimode step-index fiber The solutions are either use Graded index fiber or Single mode

fiber

PROPAGATION THROUGH MMGI FIBER Multimode Graded-index refers to the fact that the refractive index of the core gradually decreases

farther from the center of the core The increased refraction in the center of the core slows the speed of some

light rays allowing all the light rays to reach the receiving end at approximately the same time reducing

dispersion Figure shows the Light propagation principle through multimode graded-index fiber The corersquos

central refractive index ( nA ) is greater than that of the outer corersquos refractive index ( nB )

It is very clear from the figure the light rays no longer follow straight lines they follow a serpentine path

being gradually bent back toward the center by the continuously declining refractive index This reduces the

arrival time disparity because all modes arrive at about the same time The modes traveling in a straight line

30 | P a g e

are in a higher refractive index so they travel slower than the serpentine modes These travel farther but

move faster in the lower refractive index of the outer core region

PROPAGATION THROUGH SMSI FIBER Single mode fiber has a much smaller core that allows only one mode of light at a time to propagate

through the core The figure shows the single mode fiber

Single-mode fiber exhibits no dispersion caused by multiple modes Single-mode fiber also offers lower fiber

attenuation than multimode fiber Thus more information can be transmitted per unit of time because it can

retain the fidelity of each light pulse over longer distances Like multimode fiber early single-mode fiber was

generally characterized as step-index fiber meaning the refractive index of the fiber core is a step above that

of the cladding rather than graduated as it is in graded-index fiber Modern single-mode fibers have evolved

into more complex designs such as matched clad depressed clad and other exotic structures

SINGLE-MODE FIBER DISADVANTAGES The smaller core diameter makes coupling light into the core more difficult The tolerances for single-

mode connectors and splices are also much more demanding

CUTOFF WAVE LENGTH - Cutoff wavelength is the wavelength above which a single-mode fiber supports and propagates only

one mode of light In other words an optical fiber that is single-mode at a particular wavelength may have

two or more modes at wavelengths lower than the cutoff wavelength The effective cutoff wavelength of a

fiber is dependent on the length of fiber and its deployment The longer the fiber the lower is the effective

cutoff

wavelength The smaller the bend radius of a loop of the fiber the lower is the effective cutoff wavelength If

a fiber is bent in a loop the effective cutoff wavelength is lowered

SIGNAL ATTENUATION IN FIBER - Optical fiber has a number of advantages over copper However it also suffers from degradation

problems which can not be ignored The first of these is loss or attenuation Attenuation is typically the result

of two sub properties They are scattering and absorption Both of which have cumulative effects The second

is

dispersion which is the spreading of the transmitted signal and is analogous to noise

SCATTERING Scattering occurs because of impurities or irregularities in the physical construction of the fiber The

well known form of scattering is Rayleigh Scattering It is caused by metal ions in the silica matrix and

results in light rays being scattered in various directions

31 | P a g e

Scattering limits the use of wavelengths below 800nm The short wavelengths are much affected than longer

wavelengths It is because of Rayleigh scattering that the sky appears to be blue ( shorter wave length ) The

shorter wavelengths ( blue ) of light are scattered more than the longer wavelengths of light

ABSORPTION Absorption results from three factors They are hydroxyl ions ( OH- water ) in the silica impurities

in the silica and incomplete residue from the manufacturing process These impurities tend to absorb the

energy of the transmitted signal and convert it to heat resulting in an overall weakening of the signal The

Hydroxyl absorption occurs at 125 and 139 micro The silica itself starts to absorb energy at 17 micro

because of the natural resonance of the silicon dioxide

MACRO BENDING LOSS Macro-bending loss is caused by bending of the entire fiber axis The bending radius shall not be

sharper than 30d where d is diameter of cable A single bend sharper than 30d can cause loss of 05dB

The fiber may break if bending is ever sharper

MICRO BENDING LOSS Micro-bending loss is caused by micro deformations of fiber axis which leads to failures in achieving

total internal reflection conditions Micro-bends are small scale perturbations along the fiber axis the

amplitude of which are on the order of microns These distortions can cause light to leak out of a fiber

Micro-bending may be induced at very cold temperatures because the glass has a different coefficient of

thermal expansion from the coating and cabling materials At low temperatures the coating and cable

become more rigid and may contract more than the glass Consequently enough load may be exerted on the

glass to cause micro bends

Coating material is selected by manufacturers to minimize loss due to micro-bending The linear thermal

expansion coefficient of coating material shall be compatible with that of fiber

32 | P a g e

DISPERSION Dispersion is the optical term for the spreading of the transmits in the fiber It is the bandwidth

limiting phenomenon and comes in two forms Multimode dispersion and chromatic dispersion Chromatic

dispersion is further subdivided into material dispersion and waveguide dispersion

DISPERSION PHENOMENON IN OPTICAL FIBER Dispersion is the time distortion of an optical signal that results from the differences of time of travel

for different components of that signal typically resulting in pulse broadening As the distance traveled by

the signal is more broadening of pulse is more In digital transmission dispersion limits on the maximum

data rate and the maximum distance ie the information-carrying capacity of a fiber link The interference

from broadened pulse in the next interval shall not lead to erroneous interpretation of received signal

OPTICAL DOMAIN Understanding where attenuation and dispersion problems occur helps optical design engineers

determine the better wavelengths at which information can be transmit taking into account distance type of

fiber and the other factors which can severely affect the integrity of the transmitted signal The graph shown

depicts the optical transmission domain as well as the areas where problems arise The wavelength (nm)

is shown on X-axis and attenuation ( dBkm) is shown on Y-axis

There are four transmission windows appear in the figure The first one is at around 850 nm the

second at 1310nm third at 1550 nm and fourth at 1625 nm The last two labeled as C and L band

respectively The 850 nm wavelength at which the original LED technology operated The second window at

1310 nm has low dispersion The 1550 nm called as C-band is ideal wavelength for long haul

communication systems The network engineers can avoid transmitting signal at 1000 nm where Rayleigh

scattering 1240 and 1390 nm where hydroxyl absorption by water occurs to avoid high degree of loss

Optical fibers also can be manufactured to have low dispersion wavelength in the 1550nm region

which is also the point where silica-based fibers have inherently minimal attenuation These fibers are

referred to as dispersion-shifted fibers and are used in long-distance applications with high bit rates For

33 | P a g e

applications utilizing multiple wavelengths it is undesirable to have the zero dispersion point within the

operating

wavelength range

34 | P a g e

SIGNALLING RELAYS

INTRODUCTION A relay is an electromagnetic device which is used to convey information from one circuit to another

circuit through a set of contact ie front or back contact Constructional and electrically relays may be

divided into DC and AC relays because the means by which the electrical energy in the coil is converted in

to mechanical Energy in order to move the contacts are fundamentally different In DC type the contacts are

carried on an armature forming part of a magnetic circuit in which a field is set up by the current flowing in

the coils In AC types the contacts are attached by a link mechanism to a metal sector disc or cylinder in

which currents are induced by the alternating magnetic field produced by the currents in the coils

Every endeavor has been made to explain the action of each type of relay in the simplest possible manner

Relays are sophisticated switch gears used for remote control and succession control of various

electrical equipment In present days they are widely used because they are capable of protecting the

controlled equipment from cross feeding and overloading even as they cater for speedy operations

Most of the relays in present day signaling are electromagnetic devices although some of the relays control

circuits through electronic components like diodetransistors Integrated Chips etc

Railway signaling relays are unique in that

(a) They operate on low voltage and current

(b) They are more articulate as according to their special features they can work under restrictive conditions

and in any specified manner Virtually they can cater for all situations while contributing to speed and

accuracy in operations

CLASSIFICATION OF SIGNALLING RELAYS (a) According to the method of their mounting or fixture they are classified as

(i) Shelf type Relays which are loosely kept on shelves

(ii) Plug in type Relays which are plugged into a pre- wired plug boards

(b) According to their connection and usage they are classified as

(i) Track relays Relay which is directly connected to the track to detect the presence of vehicle

(ii) Line Relays Other than track relay all are line relays Relays connected to the selection circuit

(c) According to their vitality or importance in ensuring train working safety they are classified as

(i) Vital Relays All relays used for traffic control such as signal point controls track detection etc

(ii) Non-vital Relays Relays which operate control aids and accessories like warnings buzzers

Indications etc

(d) According to their special provisions to ensure reliability of their contacts they are classified as

(i) Proved type are those whose normalization after each operation shall be proved in circuit

controlled by their contacts Contacts in which both the springs have metal surfaces on their tips They may

get fused due to high sparking current across them during operation These may prevent relay normalization

and causes unsafe condition in traffic control To avoid this proving of relay normalization after each

operation is necessary

(ii) Non - proved type Need not to be proved to have been normalized after each operation as their

contacts have at least one non-fusible contact (carbon contact)

(e) According to their feed source relays are broadly classified as

(i) DC relays The relay which requires DC power supply for its operations are called DC relays Among

the DC relays

o DC neutral relays This relay closes the same set of contacts on energization with Normal polarity

or Reverse polarity supply

o Polar Relays This relay closes different set of contacts when energized with Reverse polarity

supply They may or may not have contact to close when deenergized

35 | P a g e

(ii) AC Relay AC Induction motor track relays Time element relays flashing indication control etc

(iii) Electronic Relays DC relays with electronic components in them are called electronic relays

DC NEUTRAL RELAY Each Relay has usually one or two coils with a hollow center to accommodate a coreThe coils are

made up of a large numbers of turns of small gauge soft drawn copper wire The two coils can be connected

in series or parallel according to the requirement of relay resistance The ends of the coils are terminated on

binding post to which the control wires are connected Each coil is placed around a core of specially selected

Iron or steel having high permeability and low retentivity The core should be susceptible to magnetism and

at the same time should have little residual magnetism The cores are connected at the top by a yoke to

complete the magnetism coupling between two ends of coils The bottom of each core is equipped with a

large steel or Iron block known as pole piece or face

A flat piece of Iron or steel called armature is supported by brackets which are securely fastened to

the pole piece The armature yoke and the pole pieces are also made of specially selected iron or steel of the

same quality as the core The armature carries the metallic spring contacts which are insulated from it

The circuit through the coils of the relay is closed It sets up a magnetic flux through the core yoke and the

armature The flux passing between the armature and pole faces causes the armatures get attracted to the pole

faces and armature picks up and closes front contacts When the circuit is opened the magnetic flux collapses

and the armature drops away by gravity from the pole faces the front contacts break and back contacts close

The front and back contacts of the relay can be utilised to make or break other circuits Two stop pins of

nonmagnetic material are fixed either on the armature or pole faces so that the armature cannot

come in contact with the pole faces It is essential to maintain a small air-gap between the armature and pole

faces so that low value of residual magnetism may not retain the armature in picked up position and causes

the relay to fail to drop away with a break in its control circuit

GENERAL USAGE

DC Neutral line relays are most commonly used for Railway Signalling controls and detection

Among them plug-in type relays are preferred in larger installations for space considerations Shelf type

relays are also in use mostly in wayside stations

There are many DC Neutral line relays in use with special features such as

(i) Delayed operation

(ii) Biased DC control

(iii) DC control unaffected by AC interference currents

(iv) Getting latched in operated condition till further feeding and others

Usage of DC polar relays is mostly in conjunction with block instruments that control traffic between

stations AC line relays are almost extinct in installations of British Signalling practice They are however

used for time control operations flashing indication control and such other special purposes in installations

with Siemens signalling practice widely Track relays are used according to the type of track detection

circuits chosen for a given location and context While most of the track circuits are still of the DC working

type requiring DC neutral track relays with them the prospects of their being replaced with Electronic track

circuits directly feeding DC line relays in future are great AC Track Circuits are used in DC Traction area

as conventional DC Track Circuits are not suitable there AC Track relays are used with them almost all of

the induction motor type In the British practice of signalling which was first introduced on Indian Railways

non-proved type relays with carbon to metal switching contacts are generally used for vital controls

They facilitate simple circuit designs But with the advent of German Practice introduced by Ms

Siemens later proved type relays with all metal to metal contacts are widely accepted in spite of

complications in circuit design caused by them A recent introduction is that of the same type relays made by

Ms Integra control However for some time now the appreciable features of both the practices are getting

36 | P a g e

incorporated together in the indigenous designs of signalling by railwaymen With this the usage of all types

of relays anywhere can be found without straight jacketed segration of relay types

CHARACTERSTIC OF ELECTRO-MAGNETIC RELAY The following are the characteristic of electro-magnetic relays A brief study of them helps in

understanding the choice of their components and designs features

1) Force of attraction

2) Effect of air gap

3) Effect of Hysterisis

4) Transient condition

FORCE OF ATTRACTION In any electro-magnetic system the force of attraction is given by

Where B - is the flux density a - is the cross sectional area of the particular part of the magnetic

circuit

In the case of a DC neutral Relay B is proportional to the current that is flowing in the coil

surrounding the electro-magnet and thus the force of the attraction is directly proportional to the square of the

current This square relationship has its own advantage especially in the case of DC track relay in that a

small reduction in the current will have a great effect on the working of the relay Also for a given change of

current the make and the break will be quicker with lesser possibility of arcing

EFFECT OF AIR GAP

Curve lsquoArsquo is magnetisation curve for the iron and is all practical purpose a straight line up to the

saturation point Curve lsquoBrsquo is the magnetisation curve for the open-air gap which is a straight line through

out because per magnetisation curve of the whole

magnetic circuit of the relay and for a given force is the sum of the amp-turns for the iron part and the amp-

turns for the air gap

When the front contacts are open the force required to pick up the armature is shown on curve lsquoCrsquo to be F1

but after the armature has operated it will be separated from the core by stop pins In this position the amp-

turns required to maintain the armature is less as indicated by the dotted line from 1 on curve C to 2 on curve

37 | P a g e

F But actually the current in the coil is unaltered the force on the armature is greater than required as

indicated at 3 on curve F Part of this extra force is used to flex the front contacts sufficiently to give good

contact pressure when it is in energised position

The difference between the pick-up and the drop-away current should be as small as practicable in

track relay to ensure good shunting characteristics This is achieved firstly by the choice of good quality relay

iron and secondly by having a small air gap between armature and core If the air gap is not available then

the residual magnetism fluxes might cause the armature to be retained when the supply is disconnected For

this reason residual pins are provided to ensure a definite minimum air gap in the energised position

EFFECT OF HYSTERISIS

Hysterisis is the property by which the flux produced lags behind the current In the de-energized

condition there will be small residual flux in the core When the voltage is applied to the coils the current in

rising to its steady value first causes the flux to rise from 1 to 2 along the curve At this point the flux density

will be sufficient to attract the armature and reduce the air gap the flux then raise to 3 and continue to 4

which corresponds to the steady current in the coils When the voltage is disconnected the current in falling

caused the flux to fall from 4 to 5 along the curve At this point the flux density will fall below the value

required to maintain the armature which will release thus increasing the air gap and reducing the flux to 6

Finally the

flux will decrease from 6 to 1 where the current will again be zero

The relay core is made of material having high permeability and low retentivity As mentioned in

the IRS specification Electromagnet iron may be in the form of a

(a) Bar of silicon steel

(b) Best Yorkshire wrought iron

(c) Swedish charcoal iron

(d) Electrical steel sheets

` This reduces the difference between pick up value and Drop away value By selecting good quality

core material Percentage release and sensitivity of the relay will be improved

TRANSIENT CONDITION

38 | P a g e

When the voltage is applied or disconnected from the coils it takes some little time before the current

become steady These are known as transient conditionsrdquo and are important so far as track relays are

concerned When the voltage is first applied to the coils the magnetic flux in rising cuts the turns on the

coils and in so doing produces a back EMF that opposes the applied voltage and retards the growth of

current

The growth and decay of flux are decided by the relationship between the inductance and resistance

in the circuit is known as time constant It is not fixed quantity in the case of DC neutral relay This value of lsquo

Lrsquo is less when the relay is in de-energised condition (L1) than when the relay is in energised condition (L2)

The magnitude of flux that is established for a given change of current is different in two cases

When the current reaches the pick up value the armature closes and the inductance is increased to L2

due to reduced air gap the flux per amp is increased The increase in flux increased the back EMF during the

movement of the armature after which the current continuous to raise along a new curve corresponding to the

increased inductance until it reaches the final value (ER) This process is indicated above in fig24

When the supply is disconnected the current is obliviously reduced to zero immediately but the flux

decay comparatively slowly owing to the eddy currents produced in the core by the rapid flux change which

tend to maintain the flux The drop away time on a disconnection is however generally negligible See fig

below

If the relay releases due to the reduction in current from say I 2 to I 1 caused by the application of

shunt resistance (as in the case of track relay ) the time taken is much longer than the relay is simply

disconnected The rate of rise or fall of current during the transient conditions is also depends on exterior

circuit values because L and R apply to the whole circuit The production of eddy current in the core the flux

will decay at a slower rate than the current So that the actual release time will be a little longer than it takes

the current to fall to the release

L= Inductance

39 | P a g e

R= Resistance

It is now clear that to reduce releasing time to a minimum it is necessary that

- The relay iron should have low Hysterisis loss and low retentivity

- The degree of over energization of the relay should be restricted

- Connecting a suitable external resistance in series with the relay to keep LR ratio low

In non RE area for track circuit length less than 100M 9 ohm track relay only to be used Using relay

with minimum contacts as they require lesser current which keeps inductance value low

Train working safety is ensured only if the track relay of shortest length track circuit is released

before a light engine running at a highest permitted speed clears it Otherwise the track circuit occupation

may go undetected To avoid this a special provision has to be made in signal control circuits wherever

necessary

The following methods may be adopted for reducing the time lag of track relay

(a) Restrict the over energisation of relay since the release time depends on the initial working current

(b) Connecting a suitable external resistance in series with the relay to keep the LR ratio low

(c) Using relays with minimum contacts as they require lesser operating current keeping the inductance

value low

40 | P a g e

CONCLUSION

Modern signalling is vital for safe and punctual movements of trains In the Indian railways The Signalling

and Telecommunication Department is responsible for providing modern effective and relaible signalling

systems as well as telecommunication systems

The first mode of communication used in Indian Railways was the use of electric telegraph

with the help of Morose code Morose code is the method of providing text information as a series of on-off

tones and lights or clicks that can be directly understood by a skilled listener or observer without special

equipmentEach character (letter or numeral ) is represented by a unique sequence of dots and dashes Later

this system becomes obselete and beggan the era of wireless communication which operated at audio level

frequency range

In wireless communication the significant advances took place the transition to miniature

valves or filament tubesBut this was abandoned too because of excessive current consumption and over

heating of the filament tubes

Fibre-optic communication is a method of transmitting information from one place to another by

sending pulses of light through an optcial fibreThe light forms an electromagnetic carrier wave that is

modulated to carry information First developed in the 1970s fibre optic communication systems has

revolutionized the telecommunications industry and have palyed a major role in the advent of the information

age Because of its advantages over electrical transmissionsoptical fibres have largely replaced copper wire

communications in core networks in the developed world The Indian Railways too is undergoing a transition

from Microwave communication to fibre optic communications

41 | P a g e

BIBLIOGRAPHY AND REFERENCES

1 wwwwikipediacom

2 wwwbritaniccacom

3 wwwirfcacom

4 Motorola GP60 system manual

5 Harris FAS 7000 manual

6 TOSHIBA Manual

22 | P a g e

OPTICAL FIBER CABLE

INTRODUCTION The demand for bandwidth on transmission networks is increasing rapidly because video and

graphical rich contents are exchanged through the corporate network or the Internet The Gigabit Ethernet

became ommonly used in the corporate network backbone and 10Gbit Ethernet will be adopted in the near

future Meanwhile in the home the demand for high-speed network becomes popular as the wide spread of

broadband access eg CATV xDSL and FTTH The transmission medium with capability to transmit high

bit rate signal is necessary to satisfy these requirements

The telecommunication transport technologies move from copper based networks to optical fiber

from timeslot based transport to wave length based transport from traditional circuit switching to terabit

router and all optical based networks entering into a new era of optical networking

BASIC PHYSICS OF OFC

OPTICAL FIBER CABLE OFC have Fibers which are long thin strands made with pure glass about the diameter of a human

hair OFC consists of Core Cladding Buffers and Jacket as shown in figure

MONOCHROMATIC LIGHT OR SINGLE COLOR LIGHT Light or visible light is electromagnetic radiation of a wavelength that is visible to the human eye (

about 400 ndash 700 nm) The word light is sometimes used to refer to the entire electromagnetic spectrum Light

is composed of elementary particles called photons Three primary properties of light are

Light can exhibit properties of both waves and particles This property is referred to as wave-particle

duality The study of light known as optics In free space light (of all wavelengths) travels in a straight path

at a constant maximum speed However the speed of light changes when it travels in a medium and this

change is not the same for all media or for all wavelengths By free space it is meant space that is free from

matter (vacuum) andor free from electromagnetic fields

Thus the speed of light in free space is defined by Einsteinrsquos equation E = mc2

Frequency ν speed of light in free space c and wavelength λ are interrelated by ν = cλ

From the energy relationships E = mc2 = hν and the last one an interesting relationship is obtained

the equivalent mass of a photon m = hνc2

When light is in the vicinity of a strong electromagnetic field it interacts with it From this interaction

and other influences its trajectory changes direction as shown in figure

23 | P a g e

INCIDENT RAY REFLECTED RAY AND REFRACTED RAY An incident ray is a ray of light that strikes a surface The angle between this ray and the

perpendicular or normal to the surface is the angle of incidence Reflection is the change in direction of a

wave front at an interface between two different media so that the wave front returns into the medium from

which it originated Common examples include the reflection of light sound and water waves

The reflected ray corresponding to a given incident ray is the ray that represents the light reflected by

the surface The angle between the surface normal and the reflected ray is known as the angle of reflection

The Law of Reflection says that for a specular (non-scattering) surface the angle of reflection always equals

the angle of incidence The refracted ray or transmitted ray corresponding to a given incident ray represents

the light that is transmitted through the surface The angle between this ray and the normal is known as the

angle of refraction and it is given by Snells Law

The figure shows Incident ray Reflected ray Refracted ray the angle of incidence and angle of refraction

REFRACTIVE INDEX - Refractive index is the speed of light in a vacuum ( c =299792458kmsecond) divided by the speed

of light in a material ( v ) Refractive index measures how much a material refracts light Refractive index of

a material abbreviated as lsquo n lsquo is defined as lsquo n=cv lsquo Light travels slower in physical media than it does

when transmitted through the air Refractive index (n) is a function of molecular structure of matter optical

frequency optical intensity determines optical propagation properties of each wavelength ( λ ) may not be

distributed equally in all directions is affected by external temperature pressure and fields

Refractive index of a medium is a measure for how much the speed of light is reduced inside the

medium For example typical glass has a refractive index of 15 which means that light travels at 1 15 =

067 times the speed in air or vacuum Two common properties of glass and other transparent materials are

directly related to their refractive index

First light rays change direction when they cross the interface from air to the material and effect that

is used in lenses and glasses

Second light reflects partially from surfaces that have a refractive index different from that of their

surroundings

SNELLrsquoS LAW-

24 | P a g e

When light passes from one transparent material to another it bends according to Snells law which

is defined as n1sin(θ1) = n2sin(θ2)

where n1 is the refractive index of the medium the light is leaving θ1 is the incident angle between the light

beam and the normal (normal is 90deg to the interface between two materials)

n2 is the refractive index of the material the light is entering

θ2 is the refractive angle between the light ray and the normal

Snellrsquos law gives the relationship between angle of incidence and angle of refraction

For the case of θ1 = 0deg (ie a ray perpendicular to the interface) the solution is θ2 = 0deg regardless of

the values of n1 and n2 That means a ray entering a medium perpendicular to the surface is never bent The

above is also valid for light going from a dense (higher n) to a less dense (lower n) material the symmetry of

Snells law shows that the same ray paths are applicable in opposite direction

TOTAL INTERNAL REFLECTION- When a light ray crosses an interface into a medium with a higher refractive index it bends towards

the normal Conversely light traveling cross an interface from a higher refractive index medium to a lower

refractive index medium will bend away from the normal

This has an interesting implication at some angle known as the critical angle θc light traveling from

a higher refractive index medium to a lower refractive index medium will be refracted at 90deg in other words

refracted alon g the interface If the light hits the interface at any angle larger than this critical angle it will

not pass through to the second medium at all Instead all of it will be reflected back into the first medium a

process known as total internal reflection

The critical angle can be calculated from Snells law putting in an angle of 90deg for the angle of the refracted

ray θ2 This gives θ1

Since θ2 = 90deg

So sin(θ2) = 1

25 | P a g e

Then θc = θ1 = arcsin(n2n1)

For example with light trying to emerge from glass with n1=15 into air (n2 =1) the ritical angle θc is

arcsin(115) or 418deg For any angle of incidence larger than the critical angle Snells law will not be able to

be solved for the angle of refraction because it will show that the refracted angle has a sine larger than 1

which is not possible In that case all the light is totally reflected off the interface obeying the law of

reflection

OPTICAL FIBER MODE An optical fiber guides light waves in distinct patterns called modes Mode describes the distribution

of light energy across the fiber The precise patterns depend on the wavelength of light transmitted and on the

variation in refractive index that shapes the core In essence the variations in refractive index create

boundary

conditions that shape how light waves travel through the fiber like the walls of a tunnel affect how sounds

echo inside

We can take a look at large-core step-index fibers Light rays enter the fiber at a range of angles and

rays at different angles can all stably travel down the length of the fiber as long as they hit the core-cladding

interface at an angle larger than critical angle These rays are different modes Fibers that carry more than

one mode at a specific light wavelength are called multimode fibers Some fibers have very small diameter

core that they can carry only one mode which travels as a straight line at the center of the core These fibers

are single mode fibers This is illustrated in the following picture

OPTICAL FIBER INDEX PROFILE Index profile is the refractive index distribution across the core and the cladding of a fiber Some

optical fiber has a step index profile in which the core has one uniformly distributed index and the cladding

has a lower uniformly distributed index Other optical fiber has a graded index profile in which refractive

index varies gradually as a function of radial distance from the fiber center Graded-index profiles include

power-law index profiles and parabolic index profiles The following figure shows some common types of

index profiles for single mode and multimode fiber

26 | P a g e

OPTICAL FIBERrsquoS NUMERICAL APERTURE ( NA )- Multimode optical fiber will only propagate light that enters the fiber within a certain cone known as

the acceptance cone of the fiber The half-angle of this cone is called the acceptance angle (see figure 18)

θmax For step-index multimode fiber the acceptance angle is determined only by the indices of refraction

Where

n is the refractive index of the medium light is traveling before entering the fiber

nf is the refractive index of the fiber core

nc is the refractive index of the cladding

NUMBER OF MODES IN A FIBER - Modes are sometimes characterized by numbers Single mode fibers carry only the lowest-order

mode assigned the number 0 Multimode fibers also carry higher-order modes The number of modes that

can propagate in a fiber depends on the fiberrsquos numerical aperture (or acceptance angle) as well as on its

core diameter and the wavelength of the light For a step-index multimode fiber the number of such modes

Nm

Where

D is the core diameter

λ is the operating wavelength

NA is the numerical aperture (or acceptance angle)

MODE FIELD DIAMETER - All light do not travels through the core of the fiber but is distributed through both the core and the

cladding The mode field is the distribution of light through the core and cladding of a particular fiber

Mode-Field Diameter (MFD) defines the size of the power distribution When coupling light into or out of a

fiber MFD is important in understanding light loss

27 | P a g e

ADVANTAGE OF OFC COMMUNICATION - bull More information carrying capacity Fibers can handle much higher data rates than copper More

information can be sent in a second

bull Free from Electromagnetic and Electrostatic interference Being insulator no electric current flows through

the fibre and due to this reason fibres neither radiate nor pick up electro - magnetic radiation So WPC

CLEARANCE is not required

bull Low attenuation 025 dbkm at 1550 nm Loss in twisted pair and coaxial cable increases with frequency

where as loss in the optical fibre cable remains flat over a wide range of frequencies

bull Use of WDM ndash Switching routing at Optical signal level

bull Self healing rings under NMS control

bull Small size makes fibre cable lighter in weight So easy to handleOptic fibre cable weight (approx)

500 kg km Copper cable weight (approx) 1000 kgkm

The reasons are photons of light in a fibre

do not affect each other as they have no electrical charge and they are not affected by stray photons outside

the fibre But in case of copper electrons move through the cable and these are affected by each other

Optical fibre does not carry any electricity even if the cable is damaged or short circuited it does

not cause any spark or fire hazard

As the fibre do not radiate energy it can not be detected by any nearby antenna or any

other detector The fibres are difficult to tap and therefore excellent for security

As the signal transmission is by digital modulation there is no chance of cross talk in

between channels

Only by adding a few additional terminal and repeater equipments the

capacity of the system can be increased at any time once the cable is laid

ical effects and temperature variations

LIMITATIONS OF OFC -

difficult

- utilised

APPLICATION IN SIGNAL AND TELECOMMUNICATIONS transmission circuits

-haul circuits for linking of telephone exchanges

28 | P a g e

PROPAGATION MODES CONCEPT -

MODE - Mode is an available distribution of electromagnetic field in a plane transverse to the direction of

light propagation Each mode is characterized by frequency polarization electric field strength and

magnetic field strength Available patterns are derived from Maxwellrsquos equations and boundary conditions

LINEARLY POLARIZED (LP) MODE A mode for which the field components in the direction of propagation are small compared to

components perpendicular to that direction An optical fibre supports only different field patterns called as

lsquoLinear Polarizedrsquo or lsquo LPrsquo modes The reasons are

requirements

de

the accrual of power carried by different modes

There are two basic types of fiber Multimode fiber and Single-mode fiber

Multimode fiber is best designed for short transmission distances This is suited for used in LAN systems and

video surveillance Single mode fibre is best designed for longer transmission distances This is suitable for

long distance telephony and multi channel television broadcast systems

29 | P a g e

MULTI MODE FIBER Multimode fiber the first to be manufactured and commercialized simply refers to the fact that

numerous modes or light rays are carried simultaneously through the waveguide Modes result from the fact

that light will only propagate in the fiber core at discrete angles within the cone of acceptance MM fiber type

has a much larger core diameter compared to single-mode fiber allowing for the larger number of modes

and

is easier to couple than single-mode optical fiber Multimode fiber further categorized as Multimode step-

index and Multimode graded index fiber

PROPAGATION THROUGH MMSI FIBER Figure shows the principle of total internal reflection applies to multimode step index fiber Because

the corersquos index of refraction is higher than the claddingrsquos index of refraction the light that enters at less than

the critical angle is guided along the fiber

Three different light waves travel down the fiber One mode travels straight down the center of the

core A second mode travels at a steep angle and bounces back and forth by total internal reflection The third

mode exceeds the critical angle and refracts into the cladding Naturally it can be seen that the second mode

travels a longer distance than the first mode causing the two modes to arrive at separate times

PROBLEMS WITH MMSI FIBER AND SOLUTION This disparity between arrival times of the different light rays is known as dispersion and the result is

a muddied signal at the receiving end It is important to note that high dispersion is an unavoidable

characteristic of multimode step-index fiber The solutions are either use Graded index fiber or Single mode

fiber

PROPAGATION THROUGH MMGI FIBER Multimode Graded-index refers to the fact that the refractive index of the core gradually decreases

farther from the center of the core The increased refraction in the center of the core slows the speed of some

light rays allowing all the light rays to reach the receiving end at approximately the same time reducing

dispersion Figure shows the Light propagation principle through multimode graded-index fiber The corersquos

central refractive index ( nA ) is greater than that of the outer corersquos refractive index ( nB )

It is very clear from the figure the light rays no longer follow straight lines they follow a serpentine path

being gradually bent back toward the center by the continuously declining refractive index This reduces the

arrival time disparity because all modes arrive at about the same time The modes traveling in a straight line

30 | P a g e

are in a higher refractive index so they travel slower than the serpentine modes These travel farther but

move faster in the lower refractive index of the outer core region

PROPAGATION THROUGH SMSI FIBER Single mode fiber has a much smaller core that allows only one mode of light at a time to propagate

through the core The figure shows the single mode fiber

Single-mode fiber exhibits no dispersion caused by multiple modes Single-mode fiber also offers lower fiber

attenuation than multimode fiber Thus more information can be transmitted per unit of time because it can

retain the fidelity of each light pulse over longer distances Like multimode fiber early single-mode fiber was

generally characterized as step-index fiber meaning the refractive index of the fiber core is a step above that

of the cladding rather than graduated as it is in graded-index fiber Modern single-mode fibers have evolved

into more complex designs such as matched clad depressed clad and other exotic structures

SINGLE-MODE FIBER DISADVANTAGES The smaller core diameter makes coupling light into the core more difficult The tolerances for single-

mode connectors and splices are also much more demanding

CUTOFF WAVE LENGTH - Cutoff wavelength is the wavelength above which a single-mode fiber supports and propagates only

one mode of light In other words an optical fiber that is single-mode at a particular wavelength may have

two or more modes at wavelengths lower than the cutoff wavelength The effective cutoff wavelength of a

fiber is dependent on the length of fiber and its deployment The longer the fiber the lower is the effective

cutoff

wavelength The smaller the bend radius of a loop of the fiber the lower is the effective cutoff wavelength If

a fiber is bent in a loop the effective cutoff wavelength is lowered

SIGNAL ATTENUATION IN FIBER - Optical fiber has a number of advantages over copper However it also suffers from degradation

problems which can not be ignored The first of these is loss or attenuation Attenuation is typically the result

of two sub properties They are scattering and absorption Both of which have cumulative effects The second

is

dispersion which is the spreading of the transmitted signal and is analogous to noise

SCATTERING Scattering occurs because of impurities or irregularities in the physical construction of the fiber The

well known form of scattering is Rayleigh Scattering It is caused by metal ions in the silica matrix and

results in light rays being scattered in various directions

31 | P a g e

Scattering limits the use of wavelengths below 800nm The short wavelengths are much affected than longer

wavelengths It is because of Rayleigh scattering that the sky appears to be blue ( shorter wave length ) The

shorter wavelengths ( blue ) of light are scattered more than the longer wavelengths of light

ABSORPTION Absorption results from three factors They are hydroxyl ions ( OH- water ) in the silica impurities

in the silica and incomplete residue from the manufacturing process These impurities tend to absorb the

energy of the transmitted signal and convert it to heat resulting in an overall weakening of the signal The

Hydroxyl absorption occurs at 125 and 139 micro The silica itself starts to absorb energy at 17 micro

because of the natural resonance of the silicon dioxide

MACRO BENDING LOSS Macro-bending loss is caused by bending of the entire fiber axis The bending radius shall not be

sharper than 30d where d is diameter of cable A single bend sharper than 30d can cause loss of 05dB

The fiber may break if bending is ever sharper

MICRO BENDING LOSS Micro-bending loss is caused by micro deformations of fiber axis which leads to failures in achieving

total internal reflection conditions Micro-bends are small scale perturbations along the fiber axis the

amplitude of which are on the order of microns These distortions can cause light to leak out of a fiber

Micro-bending may be induced at very cold temperatures because the glass has a different coefficient of

thermal expansion from the coating and cabling materials At low temperatures the coating and cable

become more rigid and may contract more than the glass Consequently enough load may be exerted on the

glass to cause micro bends

Coating material is selected by manufacturers to minimize loss due to micro-bending The linear thermal

expansion coefficient of coating material shall be compatible with that of fiber

32 | P a g e

DISPERSION Dispersion is the optical term for the spreading of the transmits in the fiber It is the bandwidth

limiting phenomenon and comes in two forms Multimode dispersion and chromatic dispersion Chromatic

dispersion is further subdivided into material dispersion and waveguide dispersion

DISPERSION PHENOMENON IN OPTICAL FIBER Dispersion is the time distortion of an optical signal that results from the differences of time of travel

for different components of that signal typically resulting in pulse broadening As the distance traveled by

the signal is more broadening of pulse is more In digital transmission dispersion limits on the maximum

data rate and the maximum distance ie the information-carrying capacity of a fiber link The interference

from broadened pulse in the next interval shall not lead to erroneous interpretation of received signal

OPTICAL DOMAIN Understanding where attenuation and dispersion problems occur helps optical design engineers

determine the better wavelengths at which information can be transmit taking into account distance type of

fiber and the other factors which can severely affect the integrity of the transmitted signal The graph shown

depicts the optical transmission domain as well as the areas where problems arise The wavelength (nm)

is shown on X-axis and attenuation ( dBkm) is shown on Y-axis

There are four transmission windows appear in the figure The first one is at around 850 nm the

second at 1310nm third at 1550 nm and fourth at 1625 nm The last two labeled as C and L band

respectively The 850 nm wavelength at which the original LED technology operated The second window at

1310 nm has low dispersion The 1550 nm called as C-band is ideal wavelength for long haul

communication systems The network engineers can avoid transmitting signal at 1000 nm where Rayleigh

scattering 1240 and 1390 nm where hydroxyl absorption by water occurs to avoid high degree of loss

Optical fibers also can be manufactured to have low dispersion wavelength in the 1550nm region

which is also the point where silica-based fibers have inherently minimal attenuation These fibers are

referred to as dispersion-shifted fibers and are used in long-distance applications with high bit rates For

33 | P a g e

applications utilizing multiple wavelengths it is undesirable to have the zero dispersion point within the

operating

wavelength range

34 | P a g e

SIGNALLING RELAYS

INTRODUCTION A relay is an electromagnetic device which is used to convey information from one circuit to another

circuit through a set of contact ie front or back contact Constructional and electrically relays may be

divided into DC and AC relays because the means by which the electrical energy in the coil is converted in

to mechanical Energy in order to move the contacts are fundamentally different In DC type the contacts are

carried on an armature forming part of a magnetic circuit in which a field is set up by the current flowing in

the coils In AC types the contacts are attached by a link mechanism to a metal sector disc or cylinder in

which currents are induced by the alternating magnetic field produced by the currents in the coils

Every endeavor has been made to explain the action of each type of relay in the simplest possible manner

Relays are sophisticated switch gears used for remote control and succession control of various

electrical equipment In present days they are widely used because they are capable of protecting the

controlled equipment from cross feeding and overloading even as they cater for speedy operations

Most of the relays in present day signaling are electromagnetic devices although some of the relays control

circuits through electronic components like diodetransistors Integrated Chips etc

Railway signaling relays are unique in that

(a) They operate on low voltage and current

(b) They are more articulate as according to their special features they can work under restrictive conditions

and in any specified manner Virtually they can cater for all situations while contributing to speed and

accuracy in operations

CLASSIFICATION OF SIGNALLING RELAYS (a) According to the method of their mounting or fixture they are classified as

(i) Shelf type Relays which are loosely kept on shelves

(ii) Plug in type Relays which are plugged into a pre- wired plug boards

(b) According to their connection and usage they are classified as

(i) Track relays Relay which is directly connected to the track to detect the presence of vehicle

(ii) Line Relays Other than track relay all are line relays Relays connected to the selection circuit

(c) According to their vitality or importance in ensuring train working safety they are classified as

(i) Vital Relays All relays used for traffic control such as signal point controls track detection etc

(ii) Non-vital Relays Relays which operate control aids and accessories like warnings buzzers

Indications etc

(d) According to their special provisions to ensure reliability of their contacts they are classified as

(i) Proved type are those whose normalization after each operation shall be proved in circuit

controlled by their contacts Contacts in which both the springs have metal surfaces on their tips They may

get fused due to high sparking current across them during operation These may prevent relay normalization

and causes unsafe condition in traffic control To avoid this proving of relay normalization after each

operation is necessary

(ii) Non - proved type Need not to be proved to have been normalized after each operation as their

contacts have at least one non-fusible contact (carbon contact)

(e) According to their feed source relays are broadly classified as

(i) DC relays The relay which requires DC power supply for its operations are called DC relays Among

the DC relays

o DC neutral relays This relay closes the same set of contacts on energization with Normal polarity

or Reverse polarity supply

o Polar Relays This relay closes different set of contacts when energized with Reverse polarity

supply They may or may not have contact to close when deenergized

35 | P a g e

(ii) AC Relay AC Induction motor track relays Time element relays flashing indication control etc

(iii) Electronic Relays DC relays with electronic components in them are called electronic relays

DC NEUTRAL RELAY Each Relay has usually one or two coils with a hollow center to accommodate a coreThe coils are

made up of a large numbers of turns of small gauge soft drawn copper wire The two coils can be connected

in series or parallel according to the requirement of relay resistance The ends of the coils are terminated on

binding post to which the control wires are connected Each coil is placed around a core of specially selected

Iron or steel having high permeability and low retentivity The core should be susceptible to magnetism and

at the same time should have little residual magnetism The cores are connected at the top by a yoke to

complete the magnetism coupling between two ends of coils The bottom of each core is equipped with a

large steel or Iron block known as pole piece or face

A flat piece of Iron or steel called armature is supported by brackets which are securely fastened to

the pole piece The armature yoke and the pole pieces are also made of specially selected iron or steel of the

same quality as the core The armature carries the metallic spring contacts which are insulated from it

The circuit through the coils of the relay is closed It sets up a magnetic flux through the core yoke and the

armature The flux passing between the armature and pole faces causes the armatures get attracted to the pole

faces and armature picks up and closes front contacts When the circuit is opened the magnetic flux collapses

and the armature drops away by gravity from the pole faces the front contacts break and back contacts close

The front and back contacts of the relay can be utilised to make or break other circuits Two stop pins of

nonmagnetic material are fixed either on the armature or pole faces so that the armature cannot

come in contact with the pole faces It is essential to maintain a small air-gap between the armature and pole

faces so that low value of residual magnetism may not retain the armature in picked up position and causes

the relay to fail to drop away with a break in its control circuit

GENERAL USAGE

DC Neutral line relays are most commonly used for Railway Signalling controls and detection

Among them plug-in type relays are preferred in larger installations for space considerations Shelf type

relays are also in use mostly in wayside stations

There are many DC Neutral line relays in use with special features such as

(i) Delayed operation

(ii) Biased DC control

(iii) DC control unaffected by AC interference currents

(iv) Getting latched in operated condition till further feeding and others

Usage of DC polar relays is mostly in conjunction with block instruments that control traffic between

stations AC line relays are almost extinct in installations of British Signalling practice They are however

used for time control operations flashing indication control and such other special purposes in installations

with Siemens signalling practice widely Track relays are used according to the type of track detection

circuits chosen for a given location and context While most of the track circuits are still of the DC working

type requiring DC neutral track relays with them the prospects of their being replaced with Electronic track

circuits directly feeding DC line relays in future are great AC Track Circuits are used in DC Traction area

as conventional DC Track Circuits are not suitable there AC Track relays are used with them almost all of

the induction motor type In the British practice of signalling which was first introduced on Indian Railways

non-proved type relays with carbon to metal switching contacts are generally used for vital controls

They facilitate simple circuit designs But with the advent of German Practice introduced by Ms

Siemens later proved type relays with all metal to metal contacts are widely accepted in spite of

complications in circuit design caused by them A recent introduction is that of the same type relays made by

Ms Integra control However for some time now the appreciable features of both the practices are getting

36 | P a g e

incorporated together in the indigenous designs of signalling by railwaymen With this the usage of all types

of relays anywhere can be found without straight jacketed segration of relay types

CHARACTERSTIC OF ELECTRO-MAGNETIC RELAY The following are the characteristic of electro-magnetic relays A brief study of them helps in

understanding the choice of their components and designs features

1) Force of attraction

2) Effect of air gap

3) Effect of Hysterisis

4) Transient condition

FORCE OF ATTRACTION In any electro-magnetic system the force of attraction is given by

Where B - is the flux density a - is the cross sectional area of the particular part of the magnetic

circuit

In the case of a DC neutral Relay B is proportional to the current that is flowing in the coil

surrounding the electro-magnet and thus the force of the attraction is directly proportional to the square of the

current This square relationship has its own advantage especially in the case of DC track relay in that a

small reduction in the current will have a great effect on the working of the relay Also for a given change of

current the make and the break will be quicker with lesser possibility of arcing

EFFECT OF AIR GAP

Curve lsquoArsquo is magnetisation curve for the iron and is all practical purpose a straight line up to the

saturation point Curve lsquoBrsquo is the magnetisation curve for the open-air gap which is a straight line through

out because per magnetisation curve of the whole

magnetic circuit of the relay and for a given force is the sum of the amp-turns for the iron part and the amp-

turns for the air gap

When the front contacts are open the force required to pick up the armature is shown on curve lsquoCrsquo to be F1

but after the armature has operated it will be separated from the core by stop pins In this position the amp-

turns required to maintain the armature is less as indicated by the dotted line from 1 on curve C to 2 on curve

37 | P a g e

F But actually the current in the coil is unaltered the force on the armature is greater than required as

indicated at 3 on curve F Part of this extra force is used to flex the front contacts sufficiently to give good

contact pressure when it is in energised position

The difference between the pick-up and the drop-away current should be as small as practicable in

track relay to ensure good shunting characteristics This is achieved firstly by the choice of good quality relay

iron and secondly by having a small air gap between armature and core If the air gap is not available then

the residual magnetism fluxes might cause the armature to be retained when the supply is disconnected For

this reason residual pins are provided to ensure a definite minimum air gap in the energised position

EFFECT OF HYSTERISIS

Hysterisis is the property by which the flux produced lags behind the current In the de-energized

condition there will be small residual flux in the core When the voltage is applied to the coils the current in

rising to its steady value first causes the flux to rise from 1 to 2 along the curve At this point the flux density

will be sufficient to attract the armature and reduce the air gap the flux then raise to 3 and continue to 4

which corresponds to the steady current in the coils When the voltage is disconnected the current in falling

caused the flux to fall from 4 to 5 along the curve At this point the flux density will fall below the value

required to maintain the armature which will release thus increasing the air gap and reducing the flux to 6

Finally the

flux will decrease from 6 to 1 where the current will again be zero

The relay core is made of material having high permeability and low retentivity As mentioned in

the IRS specification Electromagnet iron may be in the form of a

(a) Bar of silicon steel

(b) Best Yorkshire wrought iron

(c) Swedish charcoal iron

(d) Electrical steel sheets

` This reduces the difference between pick up value and Drop away value By selecting good quality

core material Percentage release and sensitivity of the relay will be improved

TRANSIENT CONDITION

38 | P a g e

When the voltage is applied or disconnected from the coils it takes some little time before the current

become steady These are known as transient conditionsrdquo and are important so far as track relays are

concerned When the voltage is first applied to the coils the magnetic flux in rising cuts the turns on the

coils and in so doing produces a back EMF that opposes the applied voltage and retards the growth of

current

The growth and decay of flux are decided by the relationship between the inductance and resistance

in the circuit is known as time constant It is not fixed quantity in the case of DC neutral relay This value of lsquo

Lrsquo is less when the relay is in de-energised condition (L1) than when the relay is in energised condition (L2)

The magnitude of flux that is established for a given change of current is different in two cases

When the current reaches the pick up value the armature closes and the inductance is increased to L2

due to reduced air gap the flux per amp is increased The increase in flux increased the back EMF during the

movement of the armature after which the current continuous to raise along a new curve corresponding to the

increased inductance until it reaches the final value (ER) This process is indicated above in fig24

When the supply is disconnected the current is obliviously reduced to zero immediately but the flux

decay comparatively slowly owing to the eddy currents produced in the core by the rapid flux change which

tend to maintain the flux The drop away time on a disconnection is however generally negligible See fig

below

If the relay releases due to the reduction in current from say I 2 to I 1 caused by the application of

shunt resistance (as in the case of track relay ) the time taken is much longer than the relay is simply

disconnected The rate of rise or fall of current during the transient conditions is also depends on exterior

circuit values because L and R apply to the whole circuit The production of eddy current in the core the flux

will decay at a slower rate than the current So that the actual release time will be a little longer than it takes

the current to fall to the release

L= Inductance

39 | P a g e

R= Resistance

It is now clear that to reduce releasing time to a minimum it is necessary that

- The relay iron should have low Hysterisis loss and low retentivity

- The degree of over energization of the relay should be restricted

- Connecting a suitable external resistance in series with the relay to keep LR ratio low

In non RE area for track circuit length less than 100M 9 ohm track relay only to be used Using relay

with minimum contacts as they require lesser current which keeps inductance value low

Train working safety is ensured only if the track relay of shortest length track circuit is released

before a light engine running at a highest permitted speed clears it Otherwise the track circuit occupation

may go undetected To avoid this a special provision has to be made in signal control circuits wherever

necessary

The following methods may be adopted for reducing the time lag of track relay

(a) Restrict the over energisation of relay since the release time depends on the initial working current

(b) Connecting a suitable external resistance in series with the relay to keep the LR ratio low

(c) Using relays with minimum contacts as they require lesser operating current keeping the inductance

value low

40 | P a g e

CONCLUSION

Modern signalling is vital for safe and punctual movements of trains In the Indian railways The Signalling

and Telecommunication Department is responsible for providing modern effective and relaible signalling

systems as well as telecommunication systems

The first mode of communication used in Indian Railways was the use of electric telegraph

with the help of Morose code Morose code is the method of providing text information as a series of on-off

tones and lights or clicks that can be directly understood by a skilled listener or observer without special

equipmentEach character (letter or numeral ) is represented by a unique sequence of dots and dashes Later

this system becomes obselete and beggan the era of wireless communication which operated at audio level

frequency range

In wireless communication the significant advances took place the transition to miniature

valves or filament tubesBut this was abandoned too because of excessive current consumption and over

heating of the filament tubes

Fibre-optic communication is a method of transmitting information from one place to another by

sending pulses of light through an optcial fibreThe light forms an electromagnetic carrier wave that is

modulated to carry information First developed in the 1970s fibre optic communication systems has

revolutionized the telecommunications industry and have palyed a major role in the advent of the information

age Because of its advantages over electrical transmissionsoptical fibres have largely replaced copper wire

communications in core networks in the developed world The Indian Railways too is undergoing a transition

from Microwave communication to fibre optic communications

41 | P a g e

BIBLIOGRAPHY AND REFERENCES

1 wwwwikipediacom

2 wwwbritaniccacom

3 wwwirfcacom

4 Motorola GP60 system manual

5 Harris FAS 7000 manual

6 TOSHIBA Manual

23 | P a g e

INCIDENT RAY REFLECTED RAY AND REFRACTED RAY An incident ray is a ray of light that strikes a surface The angle between this ray and the

perpendicular or normal to the surface is the angle of incidence Reflection is the change in direction of a

wave front at an interface between two different media so that the wave front returns into the medium from

which it originated Common examples include the reflection of light sound and water waves

The reflected ray corresponding to a given incident ray is the ray that represents the light reflected by

the surface The angle between the surface normal and the reflected ray is known as the angle of reflection

The Law of Reflection says that for a specular (non-scattering) surface the angle of reflection always equals

the angle of incidence The refracted ray or transmitted ray corresponding to a given incident ray represents

the light that is transmitted through the surface The angle between this ray and the normal is known as the

angle of refraction and it is given by Snells Law

The figure shows Incident ray Reflected ray Refracted ray the angle of incidence and angle of refraction

REFRACTIVE INDEX - Refractive index is the speed of light in a vacuum ( c =299792458kmsecond) divided by the speed

of light in a material ( v ) Refractive index measures how much a material refracts light Refractive index of

a material abbreviated as lsquo n lsquo is defined as lsquo n=cv lsquo Light travels slower in physical media than it does

when transmitted through the air Refractive index (n) is a function of molecular structure of matter optical

frequency optical intensity determines optical propagation properties of each wavelength ( λ ) may not be

distributed equally in all directions is affected by external temperature pressure and fields

Refractive index of a medium is a measure for how much the speed of light is reduced inside the

medium For example typical glass has a refractive index of 15 which means that light travels at 1 15 =

067 times the speed in air or vacuum Two common properties of glass and other transparent materials are

directly related to their refractive index

First light rays change direction when they cross the interface from air to the material and effect that

is used in lenses and glasses

Second light reflects partially from surfaces that have a refractive index different from that of their

surroundings

SNELLrsquoS LAW-

24 | P a g e

When light passes from one transparent material to another it bends according to Snells law which

is defined as n1sin(θ1) = n2sin(θ2)

where n1 is the refractive index of the medium the light is leaving θ1 is the incident angle between the light

beam and the normal (normal is 90deg to the interface between two materials)

n2 is the refractive index of the material the light is entering

θ2 is the refractive angle between the light ray and the normal

Snellrsquos law gives the relationship between angle of incidence and angle of refraction

For the case of θ1 = 0deg (ie a ray perpendicular to the interface) the solution is θ2 = 0deg regardless of

the values of n1 and n2 That means a ray entering a medium perpendicular to the surface is never bent The

above is also valid for light going from a dense (higher n) to a less dense (lower n) material the symmetry of

Snells law shows that the same ray paths are applicable in opposite direction

TOTAL INTERNAL REFLECTION- When a light ray crosses an interface into a medium with a higher refractive index it bends towards

the normal Conversely light traveling cross an interface from a higher refractive index medium to a lower

refractive index medium will bend away from the normal

This has an interesting implication at some angle known as the critical angle θc light traveling from

a higher refractive index medium to a lower refractive index medium will be refracted at 90deg in other words

refracted alon g the interface If the light hits the interface at any angle larger than this critical angle it will

not pass through to the second medium at all Instead all of it will be reflected back into the first medium a

process known as total internal reflection

The critical angle can be calculated from Snells law putting in an angle of 90deg for the angle of the refracted

ray θ2 This gives θ1

Since θ2 = 90deg

So sin(θ2) = 1

25 | P a g e

Then θc = θ1 = arcsin(n2n1)

For example with light trying to emerge from glass with n1=15 into air (n2 =1) the ritical angle θc is

arcsin(115) or 418deg For any angle of incidence larger than the critical angle Snells law will not be able to

be solved for the angle of refraction because it will show that the refracted angle has a sine larger than 1

which is not possible In that case all the light is totally reflected off the interface obeying the law of

reflection

OPTICAL FIBER MODE An optical fiber guides light waves in distinct patterns called modes Mode describes the distribution

of light energy across the fiber The precise patterns depend on the wavelength of light transmitted and on the

variation in refractive index that shapes the core In essence the variations in refractive index create

boundary

conditions that shape how light waves travel through the fiber like the walls of a tunnel affect how sounds

echo inside

We can take a look at large-core step-index fibers Light rays enter the fiber at a range of angles and

rays at different angles can all stably travel down the length of the fiber as long as they hit the core-cladding

interface at an angle larger than critical angle These rays are different modes Fibers that carry more than

one mode at a specific light wavelength are called multimode fibers Some fibers have very small diameter

core that they can carry only one mode which travels as a straight line at the center of the core These fibers

are single mode fibers This is illustrated in the following picture

OPTICAL FIBER INDEX PROFILE Index profile is the refractive index distribution across the core and the cladding of a fiber Some

optical fiber has a step index profile in which the core has one uniformly distributed index and the cladding

has a lower uniformly distributed index Other optical fiber has a graded index profile in which refractive

index varies gradually as a function of radial distance from the fiber center Graded-index profiles include

power-law index profiles and parabolic index profiles The following figure shows some common types of

index profiles for single mode and multimode fiber

26 | P a g e

OPTICAL FIBERrsquoS NUMERICAL APERTURE ( NA )- Multimode optical fiber will only propagate light that enters the fiber within a certain cone known as

the acceptance cone of the fiber The half-angle of this cone is called the acceptance angle (see figure 18)

θmax For step-index multimode fiber the acceptance angle is determined only by the indices of refraction

Where

n is the refractive index of the medium light is traveling before entering the fiber

nf is the refractive index of the fiber core

nc is the refractive index of the cladding

NUMBER OF MODES IN A FIBER - Modes are sometimes characterized by numbers Single mode fibers carry only the lowest-order

mode assigned the number 0 Multimode fibers also carry higher-order modes The number of modes that

can propagate in a fiber depends on the fiberrsquos numerical aperture (or acceptance angle) as well as on its

core diameter and the wavelength of the light For a step-index multimode fiber the number of such modes

Nm

Where

D is the core diameter

λ is the operating wavelength

NA is the numerical aperture (or acceptance angle)

MODE FIELD DIAMETER - All light do not travels through the core of the fiber but is distributed through both the core and the

cladding The mode field is the distribution of light through the core and cladding of a particular fiber

Mode-Field Diameter (MFD) defines the size of the power distribution When coupling light into or out of a

fiber MFD is important in understanding light loss

27 | P a g e

ADVANTAGE OF OFC COMMUNICATION - bull More information carrying capacity Fibers can handle much higher data rates than copper More

information can be sent in a second

bull Free from Electromagnetic and Electrostatic interference Being insulator no electric current flows through

the fibre and due to this reason fibres neither radiate nor pick up electro - magnetic radiation So WPC

CLEARANCE is not required

bull Low attenuation 025 dbkm at 1550 nm Loss in twisted pair and coaxial cable increases with frequency

where as loss in the optical fibre cable remains flat over a wide range of frequencies

bull Use of WDM ndash Switching routing at Optical signal level

bull Self healing rings under NMS control

bull Small size makes fibre cable lighter in weight So easy to handleOptic fibre cable weight (approx)

500 kg km Copper cable weight (approx) 1000 kgkm

The reasons are photons of light in a fibre

do not affect each other as they have no electrical charge and they are not affected by stray photons outside

the fibre But in case of copper electrons move through the cable and these are affected by each other

Optical fibre does not carry any electricity even if the cable is damaged or short circuited it does

not cause any spark or fire hazard

As the fibre do not radiate energy it can not be detected by any nearby antenna or any

other detector The fibres are difficult to tap and therefore excellent for security

As the signal transmission is by digital modulation there is no chance of cross talk in

between channels

Only by adding a few additional terminal and repeater equipments the

capacity of the system can be increased at any time once the cable is laid

ical effects and temperature variations

LIMITATIONS OF OFC -

difficult

- utilised

APPLICATION IN SIGNAL AND TELECOMMUNICATIONS transmission circuits

-haul circuits for linking of telephone exchanges

28 | P a g e

PROPAGATION MODES CONCEPT -

MODE - Mode is an available distribution of electromagnetic field in a plane transverse to the direction of

light propagation Each mode is characterized by frequency polarization electric field strength and

magnetic field strength Available patterns are derived from Maxwellrsquos equations and boundary conditions

LINEARLY POLARIZED (LP) MODE A mode for which the field components in the direction of propagation are small compared to

components perpendicular to that direction An optical fibre supports only different field patterns called as

lsquoLinear Polarizedrsquo or lsquo LPrsquo modes The reasons are

requirements

de

the accrual of power carried by different modes

There are two basic types of fiber Multimode fiber and Single-mode fiber

Multimode fiber is best designed for short transmission distances This is suited for used in LAN systems and

video surveillance Single mode fibre is best designed for longer transmission distances This is suitable for

long distance telephony and multi channel television broadcast systems

29 | P a g e

MULTI MODE FIBER Multimode fiber the first to be manufactured and commercialized simply refers to the fact that

numerous modes or light rays are carried simultaneously through the waveguide Modes result from the fact

that light will only propagate in the fiber core at discrete angles within the cone of acceptance MM fiber type

has a much larger core diameter compared to single-mode fiber allowing for the larger number of modes

and

is easier to couple than single-mode optical fiber Multimode fiber further categorized as Multimode step-

index and Multimode graded index fiber

PROPAGATION THROUGH MMSI FIBER Figure shows the principle of total internal reflection applies to multimode step index fiber Because

the corersquos index of refraction is higher than the claddingrsquos index of refraction the light that enters at less than

the critical angle is guided along the fiber

Three different light waves travel down the fiber One mode travels straight down the center of the

core A second mode travels at a steep angle and bounces back and forth by total internal reflection The third

mode exceeds the critical angle and refracts into the cladding Naturally it can be seen that the second mode

travels a longer distance than the first mode causing the two modes to arrive at separate times

PROBLEMS WITH MMSI FIBER AND SOLUTION This disparity between arrival times of the different light rays is known as dispersion and the result is

a muddied signal at the receiving end It is important to note that high dispersion is an unavoidable

characteristic of multimode step-index fiber The solutions are either use Graded index fiber or Single mode

fiber

PROPAGATION THROUGH MMGI FIBER Multimode Graded-index refers to the fact that the refractive index of the core gradually decreases

farther from the center of the core The increased refraction in the center of the core slows the speed of some

light rays allowing all the light rays to reach the receiving end at approximately the same time reducing

dispersion Figure shows the Light propagation principle through multimode graded-index fiber The corersquos

central refractive index ( nA ) is greater than that of the outer corersquos refractive index ( nB )

It is very clear from the figure the light rays no longer follow straight lines they follow a serpentine path

being gradually bent back toward the center by the continuously declining refractive index This reduces the

arrival time disparity because all modes arrive at about the same time The modes traveling in a straight line

30 | P a g e

are in a higher refractive index so they travel slower than the serpentine modes These travel farther but

move faster in the lower refractive index of the outer core region

PROPAGATION THROUGH SMSI FIBER Single mode fiber has a much smaller core that allows only one mode of light at a time to propagate

through the core The figure shows the single mode fiber

Single-mode fiber exhibits no dispersion caused by multiple modes Single-mode fiber also offers lower fiber

attenuation than multimode fiber Thus more information can be transmitted per unit of time because it can

retain the fidelity of each light pulse over longer distances Like multimode fiber early single-mode fiber was

generally characterized as step-index fiber meaning the refractive index of the fiber core is a step above that

of the cladding rather than graduated as it is in graded-index fiber Modern single-mode fibers have evolved

into more complex designs such as matched clad depressed clad and other exotic structures

SINGLE-MODE FIBER DISADVANTAGES The smaller core diameter makes coupling light into the core more difficult The tolerances for single-

mode connectors and splices are also much more demanding

CUTOFF WAVE LENGTH - Cutoff wavelength is the wavelength above which a single-mode fiber supports and propagates only

one mode of light In other words an optical fiber that is single-mode at a particular wavelength may have

two or more modes at wavelengths lower than the cutoff wavelength The effective cutoff wavelength of a

fiber is dependent on the length of fiber and its deployment The longer the fiber the lower is the effective

cutoff

wavelength The smaller the bend radius of a loop of the fiber the lower is the effective cutoff wavelength If

a fiber is bent in a loop the effective cutoff wavelength is lowered

SIGNAL ATTENUATION IN FIBER - Optical fiber has a number of advantages over copper However it also suffers from degradation

problems which can not be ignored The first of these is loss or attenuation Attenuation is typically the result

of two sub properties They are scattering and absorption Both of which have cumulative effects The second

is

dispersion which is the spreading of the transmitted signal and is analogous to noise

SCATTERING Scattering occurs because of impurities or irregularities in the physical construction of the fiber The

well known form of scattering is Rayleigh Scattering It is caused by metal ions in the silica matrix and

results in light rays being scattered in various directions

31 | P a g e

Scattering limits the use of wavelengths below 800nm The short wavelengths are much affected than longer

wavelengths It is because of Rayleigh scattering that the sky appears to be blue ( shorter wave length ) The

shorter wavelengths ( blue ) of light are scattered more than the longer wavelengths of light

ABSORPTION Absorption results from three factors They are hydroxyl ions ( OH- water ) in the silica impurities

in the silica and incomplete residue from the manufacturing process These impurities tend to absorb the

energy of the transmitted signal and convert it to heat resulting in an overall weakening of the signal The

Hydroxyl absorption occurs at 125 and 139 micro The silica itself starts to absorb energy at 17 micro

because of the natural resonance of the silicon dioxide

MACRO BENDING LOSS Macro-bending loss is caused by bending of the entire fiber axis The bending radius shall not be

sharper than 30d where d is diameter of cable A single bend sharper than 30d can cause loss of 05dB

The fiber may break if bending is ever sharper

MICRO BENDING LOSS Micro-bending loss is caused by micro deformations of fiber axis which leads to failures in achieving

total internal reflection conditions Micro-bends are small scale perturbations along the fiber axis the

amplitude of which are on the order of microns These distortions can cause light to leak out of a fiber

Micro-bending may be induced at very cold temperatures because the glass has a different coefficient of

thermal expansion from the coating and cabling materials At low temperatures the coating and cable

become more rigid and may contract more than the glass Consequently enough load may be exerted on the

glass to cause micro bends

Coating material is selected by manufacturers to minimize loss due to micro-bending The linear thermal

expansion coefficient of coating material shall be compatible with that of fiber

32 | P a g e

DISPERSION Dispersion is the optical term for the spreading of the transmits in the fiber It is the bandwidth

limiting phenomenon and comes in two forms Multimode dispersion and chromatic dispersion Chromatic

dispersion is further subdivided into material dispersion and waveguide dispersion

DISPERSION PHENOMENON IN OPTICAL FIBER Dispersion is the time distortion of an optical signal that results from the differences of time of travel

for different components of that signal typically resulting in pulse broadening As the distance traveled by

the signal is more broadening of pulse is more In digital transmission dispersion limits on the maximum

data rate and the maximum distance ie the information-carrying capacity of a fiber link The interference

from broadened pulse in the next interval shall not lead to erroneous interpretation of received signal

OPTICAL DOMAIN Understanding where attenuation and dispersion problems occur helps optical design engineers

determine the better wavelengths at which information can be transmit taking into account distance type of

fiber and the other factors which can severely affect the integrity of the transmitted signal The graph shown

depicts the optical transmission domain as well as the areas where problems arise The wavelength (nm)

is shown on X-axis and attenuation ( dBkm) is shown on Y-axis

There are four transmission windows appear in the figure The first one is at around 850 nm the

second at 1310nm third at 1550 nm and fourth at 1625 nm The last two labeled as C and L band

respectively The 850 nm wavelength at which the original LED technology operated The second window at

1310 nm has low dispersion The 1550 nm called as C-band is ideal wavelength for long haul

communication systems The network engineers can avoid transmitting signal at 1000 nm where Rayleigh

scattering 1240 and 1390 nm where hydroxyl absorption by water occurs to avoid high degree of loss

Optical fibers also can be manufactured to have low dispersion wavelength in the 1550nm region

which is also the point where silica-based fibers have inherently minimal attenuation These fibers are

referred to as dispersion-shifted fibers and are used in long-distance applications with high bit rates For

33 | P a g e

applications utilizing multiple wavelengths it is undesirable to have the zero dispersion point within the

operating

wavelength range

34 | P a g e

SIGNALLING RELAYS

INTRODUCTION A relay is an electromagnetic device which is used to convey information from one circuit to another

circuit through a set of contact ie front or back contact Constructional and electrically relays may be

divided into DC and AC relays because the means by which the electrical energy in the coil is converted in

to mechanical Energy in order to move the contacts are fundamentally different In DC type the contacts are

carried on an armature forming part of a magnetic circuit in which a field is set up by the current flowing in

the coils In AC types the contacts are attached by a link mechanism to a metal sector disc or cylinder in

which currents are induced by the alternating magnetic field produced by the currents in the coils

Every endeavor has been made to explain the action of each type of relay in the simplest possible manner

Relays are sophisticated switch gears used for remote control and succession control of various

electrical equipment In present days they are widely used because they are capable of protecting the

controlled equipment from cross feeding and overloading even as they cater for speedy operations

Most of the relays in present day signaling are electromagnetic devices although some of the relays control

circuits through electronic components like diodetransistors Integrated Chips etc

Railway signaling relays are unique in that

(a) They operate on low voltage and current

(b) They are more articulate as according to their special features they can work under restrictive conditions

and in any specified manner Virtually they can cater for all situations while contributing to speed and

accuracy in operations

CLASSIFICATION OF SIGNALLING RELAYS (a) According to the method of their mounting or fixture they are classified as

(i) Shelf type Relays which are loosely kept on shelves

(ii) Plug in type Relays which are plugged into a pre- wired plug boards

(b) According to their connection and usage they are classified as

(i) Track relays Relay which is directly connected to the track to detect the presence of vehicle

(ii) Line Relays Other than track relay all are line relays Relays connected to the selection circuit

(c) According to their vitality or importance in ensuring train working safety they are classified as

(i) Vital Relays All relays used for traffic control such as signal point controls track detection etc

(ii) Non-vital Relays Relays which operate control aids and accessories like warnings buzzers

Indications etc

(d) According to their special provisions to ensure reliability of their contacts they are classified as

(i) Proved type are those whose normalization after each operation shall be proved in circuit

controlled by their contacts Contacts in which both the springs have metal surfaces on their tips They may

get fused due to high sparking current across them during operation These may prevent relay normalization

and causes unsafe condition in traffic control To avoid this proving of relay normalization after each

operation is necessary

(ii) Non - proved type Need not to be proved to have been normalized after each operation as their

contacts have at least one non-fusible contact (carbon contact)

(e) According to their feed source relays are broadly classified as

(i) DC relays The relay which requires DC power supply for its operations are called DC relays Among

the DC relays

o DC neutral relays This relay closes the same set of contacts on energization with Normal polarity

or Reverse polarity supply

o Polar Relays This relay closes different set of contacts when energized with Reverse polarity

supply They may or may not have contact to close when deenergized

35 | P a g e

(ii) AC Relay AC Induction motor track relays Time element relays flashing indication control etc

(iii) Electronic Relays DC relays with electronic components in them are called electronic relays

DC NEUTRAL RELAY Each Relay has usually one or two coils with a hollow center to accommodate a coreThe coils are

made up of a large numbers of turns of small gauge soft drawn copper wire The two coils can be connected

in series or parallel according to the requirement of relay resistance The ends of the coils are terminated on

binding post to which the control wires are connected Each coil is placed around a core of specially selected

Iron or steel having high permeability and low retentivity The core should be susceptible to magnetism and

at the same time should have little residual magnetism The cores are connected at the top by a yoke to

complete the magnetism coupling between two ends of coils The bottom of each core is equipped with a

large steel or Iron block known as pole piece or face

A flat piece of Iron or steel called armature is supported by brackets which are securely fastened to

the pole piece The armature yoke and the pole pieces are also made of specially selected iron or steel of the

same quality as the core The armature carries the metallic spring contacts which are insulated from it

The circuit through the coils of the relay is closed It sets up a magnetic flux through the core yoke and the

armature The flux passing between the armature and pole faces causes the armatures get attracted to the pole

faces and armature picks up and closes front contacts When the circuit is opened the magnetic flux collapses

and the armature drops away by gravity from the pole faces the front contacts break and back contacts close

The front and back contacts of the relay can be utilised to make or break other circuits Two stop pins of

nonmagnetic material are fixed either on the armature or pole faces so that the armature cannot

come in contact with the pole faces It is essential to maintain a small air-gap between the armature and pole

faces so that low value of residual magnetism may not retain the armature in picked up position and causes

the relay to fail to drop away with a break in its control circuit

GENERAL USAGE

DC Neutral line relays are most commonly used for Railway Signalling controls and detection

Among them plug-in type relays are preferred in larger installations for space considerations Shelf type

relays are also in use mostly in wayside stations

There are many DC Neutral line relays in use with special features such as

(i) Delayed operation

(ii) Biased DC control

(iii) DC control unaffected by AC interference currents

(iv) Getting latched in operated condition till further feeding and others

Usage of DC polar relays is mostly in conjunction with block instruments that control traffic between

stations AC line relays are almost extinct in installations of British Signalling practice They are however

used for time control operations flashing indication control and such other special purposes in installations

with Siemens signalling practice widely Track relays are used according to the type of track detection

circuits chosen for a given location and context While most of the track circuits are still of the DC working

type requiring DC neutral track relays with them the prospects of their being replaced with Electronic track

circuits directly feeding DC line relays in future are great AC Track Circuits are used in DC Traction area

as conventional DC Track Circuits are not suitable there AC Track relays are used with them almost all of

the induction motor type In the British practice of signalling which was first introduced on Indian Railways

non-proved type relays with carbon to metal switching contacts are generally used for vital controls

They facilitate simple circuit designs But with the advent of German Practice introduced by Ms

Siemens later proved type relays with all metal to metal contacts are widely accepted in spite of

complications in circuit design caused by them A recent introduction is that of the same type relays made by

Ms Integra control However for some time now the appreciable features of both the practices are getting

36 | P a g e

incorporated together in the indigenous designs of signalling by railwaymen With this the usage of all types

of relays anywhere can be found without straight jacketed segration of relay types

CHARACTERSTIC OF ELECTRO-MAGNETIC RELAY The following are the characteristic of electro-magnetic relays A brief study of them helps in

understanding the choice of their components and designs features

1) Force of attraction

2) Effect of air gap

3) Effect of Hysterisis

4) Transient condition

FORCE OF ATTRACTION In any electro-magnetic system the force of attraction is given by

Where B - is the flux density a - is the cross sectional area of the particular part of the magnetic

circuit

In the case of a DC neutral Relay B is proportional to the current that is flowing in the coil

surrounding the electro-magnet and thus the force of the attraction is directly proportional to the square of the

current This square relationship has its own advantage especially in the case of DC track relay in that a

small reduction in the current will have a great effect on the working of the relay Also for a given change of

current the make and the break will be quicker with lesser possibility of arcing

EFFECT OF AIR GAP

Curve lsquoArsquo is magnetisation curve for the iron and is all practical purpose a straight line up to the

saturation point Curve lsquoBrsquo is the magnetisation curve for the open-air gap which is a straight line through

out because per magnetisation curve of the whole

magnetic circuit of the relay and for a given force is the sum of the amp-turns for the iron part and the amp-

turns for the air gap

When the front contacts are open the force required to pick up the armature is shown on curve lsquoCrsquo to be F1

but after the armature has operated it will be separated from the core by stop pins In this position the amp-

turns required to maintain the armature is less as indicated by the dotted line from 1 on curve C to 2 on curve

37 | P a g e

F But actually the current in the coil is unaltered the force on the armature is greater than required as

indicated at 3 on curve F Part of this extra force is used to flex the front contacts sufficiently to give good

contact pressure when it is in energised position

The difference between the pick-up and the drop-away current should be as small as practicable in

track relay to ensure good shunting characteristics This is achieved firstly by the choice of good quality relay

iron and secondly by having a small air gap between armature and core If the air gap is not available then

the residual magnetism fluxes might cause the armature to be retained when the supply is disconnected For

this reason residual pins are provided to ensure a definite minimum air gap in the energised position

EFFECT OF HYSTERISIS

Hysterisis is the property by which the flux produced lags behind the current In the de-energized

condition there will be small residual flux in the core When the voltage is applied to the coils the current in

rising to its steady value first causes the flux to rise from 1 to 2 along the curve At this point the flux density

will be sufficient to attract the armature and reduce the air gap the flux then raise to 3 and continue to 4

which corresponds to the steady current in the coils When the voltage is disconnected the current in falling

caused the flux to fall from 4 to 5 along the curve At this point the flux density will fall below the value

required to maintain the armature which will release thus increasing the air gap and reducing the flux to 6

Finally the

flux will decrease from 6 to 1 where the current will again be zero

The relay core is made of material having high permeability and low retentivity As mentioned in

the IRS specification Electromagnet iron may be in the form of a

(a) Bar of silicon steel

(b) Best Yorkshire wrought iron

(c) Swedish charcoal iron

(d) Electrical steel sheets

` This reduces the difference between pick up value and Drop away value By selecting good quality

core material Percentage release and sensitivity of the relay will be improved

TRANSIENT CONDITION

38 | P a g e

When the voltage is applied or disconnected from the coils it takes some little time before the current

become steady These are known as transient conditionsrdquo and are important so far as track relays are

concerned When the voltage is first applied to the coils the magnetic flux in rising cuts the turns on the

coils and in so doing produces a back EMF that opposes the applied voltage and retards the growth of

current

The growth and decay of flux are decided by the relationship between the inductance and resistance

in the circuit is known as time constant It is not fixed quantity in the case of DC neutral relay This value of lsquo

Lrsquo is less when the relay is in de-energised condition (L1) than when the relay is in energised condition (L2)

The magnitude of flux that is established for a given change of current is different in two cases

When the current reaches the pick up value the armature closes and the inductance is increased to L2

due to reduced air gap the flux per amp is increased The increase in flux increased the back EMF during the

movement of the armature after which the current continuous to raise along a new curve corresponding to the

increased inductance until it reaches the final value (ER) This process is indicated above in fig24

When the supply is disconnected the current is obliviously reduced to zero immediately but the flux

decay comparatively slowly owing to the eddy currents produced in the core by the rapid flux change which

tend to maintain the flux The drop away time on a disconnection is however generally negligible See fig

below

If the relay releases due to the reduction in current from say I 2 to I 1 caused by the application of

shunt resistance (as in the case of track relay ) the time taken is much longer than the relay is simply

disconnected The rate of rise or fall of current during the transient conditions is also depends on exterior

circuit values because L and R apply to the whole circuit The production of eddy current in the core the flux

will decay at a slower rate than the current So that the actual release time will be a little longer than it takes

the current to fall to the release

L= Inductance

39 | P a g e

R= Resistance

It is now clear that to reduce releasing time to a minimum it is necessary that

- The relay iron should have low Hysterisis loss and low retentivity

- The degree of over energization of the relay should be restricted

- Connecting a suitable external resistance in series with the relay to keep LR ratio low

In non RE area for track circuit length less than 100M 9 ohm track relay only to be used Using relay

with minimum contacts as they require lesser current which keeps inductance value low

Train working safety is ensured only if the track relay of shortest length track circuit is released

before a light engine running at a highest permitted speed clears it Otherwise the track circuit occupation

may go undetected To avoid this a special provision has to be made in signal control circuits wherever

necessary

The following methods may be adopted for reducing the time lag of track relay

(a) Restrict the over energisation of relay since the release time depends on the initial working current

(b) Connecting a suitable external resistance in series with the relay to keep the LR ratio low

(c) Using relays with minimum contacts as they require lesser operating current keeping the inductance

value low

40 | P a g e

CONCLUSION

Modern signalling is vital for safe and punctual movements of trains In the Indian railways The Signalling

and Telecommunication Department is responsible for providing modern effective and relaible signalling

systems as well as telecommunication systems

The first mode of communication used in Indian Railways was the use of electric telegraph

with the help of Morose code Morose code is the method of providing text information as a series of on-off

tones and lights or clicks that can be directly understood by a skilled listener or observer without special

equipmentEach character (letter or numeral ) is represented by a unique sequence of dots and dashes Later

this system becomes obselete and beggan the era of wireless communication which operated at audio level

frequency range

In wireless communication the significant advances took place the transition to miniature

valves or filament tubesBut this was abandoned too because of excessive current consumption and over

heating of the filament tubes

Fibre-optic communication is a method of transmitting information from one place to another by

sending pulses of light through an optcial fibreThe light forms an electromagnetic carrier wave that is

modulated to carry information First developed in the 1970s fibre optic communication systems has

revolutionized the telecommunications industry and have palyed a major role in the advent of the information

age Because of its advantages over electrical transmissionsoptical fibres have largely replaced copper wire

communications in core networks in the developed world The Indian Railways too is undergoing a transition

from Microwave communication to fibre optic communications

41 | P a g e

BIBLIOGRAPHY AND REFERENCES

1 wwwwikipediacom

2 wwwbritaniccacom

3 wwwirfcacom

4 Motorola GP60 system manual

5 Harris FAS 7000 manual

6 TOSHIBA Manual

24 | P a g e

When light passes from one transparent material to another it bends according to Snells law which

is defined as n1sin(θ1) = n2sin(θ2)

where n1 is the refractive index of the medium the light is leaving θ1 is the incident angle between the light

beam and the normal (normal is 90deg to the interface between two materials)

n2 is the refractive index of the material the light is entering

θ2 is the refractive angle between the light ray and the normal

Snellrsquos law gives the relationship between angle of incidence and angle of refraction

For the case of θ1 = 0deg (ie a ray perpendicular to the interface) the solution is θ2 = 0deg regardless of

the values of n1 and n2 That means a ray entering a medium perpendicular to the surface is never bent The

above is also valid for light going from a dense (higher n) to a less dense (lower n) material the symmetry of

Snells law shows that the same ray paths are applicable in opposite direction

TOTAL INTERNAL REFLECTION- When a light ray crosses an interface into a medium with a higher refractive index it bends towards

the normal Conversely light traveling cross an interface from a higher refractive index medium to a lower

refractive index medium will bend away from the normal

This has an interesting implication at some angle known as the critical angle θc light traveling from

a higher refractive index medium to a lower refractive index medium will be refracted at 90deg in other words

refracted alon g the interface If the light hits the interface at any angle larger than this critical angle it will

not pass through to the second medium at all Instead all of it will be reflected back into the first medium a

process known as total internal reflection

The critical angle can be calculated from Snells law putting in an angle of 90deg for the angle of the refracted

ray θ2 This gives θ1

Since θ2 = 90deg

So sin(θ2) = 1

25 | P a g e

Then θc = θ1 = arcsin(n2n1)

For example with light trying to emerge from glass with n1=15 into air (n2 =1) the ritical angle θc is

arcsin(115) or 418deg For any angle of incidence larger than the critical angle Snells law will not be able to

be solved for the angle of refraction because it will show that the refracted angle has a sine larger than 1

which is not possible In that case all the light is totally reflected off the interface obeying the law of

reflection

OPTICAL FIBER MODE An optical fiber guides light waves in distinct patterns called modes Mode describes the distribution

of light energy across the fiber The precise patterns depend on the wavelength of light transmitted and on the

variation in refractive index that shapes the core In essence the variations in refractive index create

boundary

conditions that shape how light waves travel through the fiber like the walls of a tunnel affect how sounds

echo inside

We can take a look at large-core step-index fibers Light rays enter the fiber at a range of angles and

rays at different angles can all stably travel down the length of the fiber as long as they hit the core-cladding

interface at an angle larger than critical angle These rays are different modes Fibers that carry more than

one mode at a specific light wavelength are called multimode fibers Some fibers have very small diameter

core that they can carry only one mode which travels as a straight line at the center of the core These fibers

are single mode fibers This is illustrated in the following picture

OPTICAL FIBER INDEX PROFILE Index profile is the refractive index distribution across the core and the cladding of a fiber Some

optical fiber has a step index profile in which the core has one uniformly distributed index and the cladding

has a lower uniformly distributed index Other optical fiber has a graded index profile in which refractive

index varies gradually as a function of radial distance from the fiber center Graded-index profiles include

power-law index profiles and parabolic index profiles The following figure shows some common types of

index profiles for single mode and multimode fiber

26 | P a g e

OPTICAL FIBERrsquoS NUMERICAL APERTURE ( NA )- Multimode optical fiber will only propagate light that enters the fiber within a certain cone known as

the acceptance cone of the fiber The half-angle of this cone is called the acceptance angle (see figure 18)

θmax For step-index multimode fiber the acceptance angle is determined only by the indices of refraction

Where

n is the refractive index of the medium light is traveling before entering the fiber

nf is the refractive index of the fiber core

nc is the refractive index of the cladding

NUMBER OF MODES IN A FIBER - Modes are sometimes characterized by numbers Single mode fibers carry only the lowest-order

mode assigned the number 0 Multimode fibers also carry higher-order modes The number of modes that

can propagate in a fiber depends on the fiberrsquos numerical aperture (or acceptance angle) as well as on its

core diameter and the wavelength of the light For a step-index multimode fiber the number of such modes

Nm

Where

D is the core diameter

λ is the operating wavelength

NA is the numerical aperture (or acceptance angle)

MODE FIELD DIAMETER - All light do not travels through the core of the fiber but is distributed through both the core and the

cladding The mode field is the distribution of light through the core and cladding of a particular fiber

Mode-Field Diameter (MFD) defines the size of the power distribution When coupling light into or out of a

fiber MFD is important in understanding light loss

27 | P a g e

ADVANTAGE OF OFC COMMUNICATION - bull More information carrying capacity Fibers can handle much higher data rates than copper More

information can be sent in a second

bull Free from Electromagnetic and Electrostatic interference Being insulator no electric current flows through

the fibre and due to this reason fibres neither radiate nor pick up electro - magnetic radiation So WPC

CLEARANCE is not required

bull Low attenuation 025 dbkm at 1550 nm Loss in twisted pair and coaxial cable increases with frequency

where as loss in the optical fibre cable remains flat over a wide range of frequencies

bull Use of WDM ndash Switching routing at Optical signal level

bull Self healing rings under NMS control

bull Small size makes fibre cable lighter in weight So easy to handleOptic fibre cable weight (approx)

500 kg km Copper cable weight (approx) 1000 kgkm

The reasons are photons of light in a fibre

do not affect each other as they have no electrical charge and they are not affected by stray photons outside

the fibre But in case of copper electrons move through the cable and these are affected by each other

Optical fibre does not carry any electricity even if the cable is damaged or short circuited it does

not cause any spark or fire hazard

As the fibre do not radiate energy it can not be detected by any nearby antenna or any

other detector The fibres are difficult to tap and therefore excellent for security

As the signal transmission is by digital modulation there is no chance of cross talk in

between channels

Only by adding a few additional terminal and repeater equipments the

capacity of the system can be increased at any time once the cable is laid

ical effects and temperature variations

LIMITATIONS OF OFC -

difficult

- utilised

APPLICATION IN SIGNAL AND TELECOMMUNICATIONS transmission circuits

-haul circuits for linking of telephone exchanges

28 | P a g e

PROPAGATION MODES CONCEPT -

MODE - Mode is an available distribution of electromagnetic field in a plane transverse to the direction of

light propagation Each mode is characterized by frequency polarization electric field strength and

magnetic field strength Available patterns are derived from Maxwellrsquos equations and boundary conditions

LINEARLY POLARIZED (LP) MODE A mode for which the field components in the direction of propagation are small compared to

components perpendicular to that direction An optical fibre supports only different field patterns called as

lsquoLinear Polarizedrsquo or lsquo LPrsquo modes The reasons are

requirements

de

the accrual of power carried by different modes

There are two basic types of fiber Multimode fiber and Single-mode fiber

Multimode fiber is best designed for short transmission distances This is suited for used in LAN systems and

video surveillance Single mode fibre is best designed for longer transmission distances This is suitable for

long distance telephony and multi channel television broadcast systems

29 | P a g e

MULTI MODE FIBER Multimode fiber the first to be manufactured and commercialized simply refers to the fact that

numerous modes or light rays are carried simultaneously through the waveguide Modes result from the fact

that light will only propagate in the fiber core at discrete angles within the cone of acceptance MM fiber type

has a much larger core diameter compared to single-mode fiber allowing for the larger number of modes

and

is easier to couple than single-mode optical fiber Multimode fiber further categorized as Multimode step-

index and Multimode graded index fiber

PROPAGATION THROUGH MMSI FIBER Figure shows the principle of total internal reflection applies to multimode step index fiber Because

the corersquos index of refraction is higher than the claddingrsquos index of refraction the light that enters at less than

the critical angle is guided along the fiber

Three different light waves travel down the fiber One mode travels straight down the center of the

core A second mode travels at a steep angle and bounces back and forth by total internal reflection The third

mode exceeds the critical angle and refracts into the cladding Naturally it can be seen that the second mode

travels a longer distance than the first mode causing the two modes to arrive at separate times

PROBLEMS WITH MMSI FIBER AND SOLUTION This disparity between arrival times of the different light rays is known as dispersion and the result is

a muddied signal at the receiving end It is important to note that high dispersion is an unavoidable

characteristic of multimode step-index fiber The solutions are either use Graded index fiber or Single mode

fiber

PROPAGATION THROUGH MMGI FIBER Multimode Graded-index refers to the fact that the refractive index of the core gradually decreases

farther from the center of the core The increased refraction in the center of the core slows the speed of some

light rays allowing all the light rays to reach the receiving end at approximately the same time reducing

dispersion Figure shows the Light propagation principle through multimode graded-index fiber The corersquos

central refractive index ( nA ) is greater than that of the outer corersquos refractive index ( nB )

It is very clear from the figure the light rays no longer follow straight lines they follow a serpentine path

being gradually bent back toward the center by the continuously declining refractive index This reduces the

arrival time disparity because all modes arrive at about the same time The modes traveling in a straight line

30 | P a g e

are in a higher refractive index so they travel slower than the serpentine modes These travel farther but

move faster in the lower refractive index of the outer core region

PROPAGATION THROUGH SMSI FIBER Single mode fiber has a much smaller core that allows only one mode of light at a time to propagate

through the core The figure shows the single mode fiber

Single-mode fiber exhibits no dispersion caused by multiple modes Single-mode fiber also offers lower fiber

attenuation than multimode fiber Thus more information can be transmitted per unit of time because it can

retain the fidelity of each light pulse over longer distances Like multimode fiber early single-mode fiber was

generally characterized as step-index fiber meaning the refractive index of the fiber core is a step above that

of the cladding rather than graduated as it is in graded-index fiber Modern single-mode fibers have evolved

into more complex designs such as matched clad depressed clad and other exotic structures

SINGLE-MODE FIBER DISADVANTAGES The smaller core diameter makes coupling light into the core more difficult The tolerances for single-

mode connectors and splices are also much more demanding

CUTOFF WAVE LENGTH - Cutoff wavelength is the wavelength above which a single-mode fiber supports and propagates only

one mode of light In other words an optical fiber that is single-mode at a particular wavelength may have

two or more modes at wavelengths lower than the cutoff wavelength The effective cutoff wavelength of a

fiber is dependent on the length of fiber and its deployment The longer the fiber the lower is the effective

cutoff

wavelength The smaller the bend radius of a loop of the fiber the lower is the effective cutoff wavelength If

a fiber is bent in a loop the effective cutoff wavelength is lowered

SIGNAL ATTENUATION IN FIBER - Optical fiber has a number of advantages over copper However it also suffers from degradation

problems which can not be ignored The first of these is loss or attenuation Attenuation is typically the result

of two sub properties They are scattering and absorption Both of which have cumulative effects The second

is

dispersion which is the spreading of the transmitted signal and is analogous to noise

SCATTERING Scattering occurs because of impurities or irregularities in the physical construction of the fiber The

well known form of scattering is Rayleigh Scattering It is caused by metal ions in the silica matrix and

results in light rays being scattered in various directions

31 | P a g e

Scattering limits the use of wavelengths below 800nm The short wavelengths are much affected than longer

wavelengths It is because of Rayleigh scattering that the sky appears to be blue ( shorter wave length ) The

shorter wavelengths ( blue ) of light are scattered more than the longer wavelengths of light

ABSORPTION Absorption results from three factors They are hydroxyl ions ( OH- water ) in the silica impurities

in the silica and incomplete residue from the manufacturing process These impurities tend to absorb the

energy of the transmitted signal and convert it to heat resulting in an overall weakening of the signal The

Hydroxyl absorption occurs at 125 and 139 micro The silica itself starts to absorb energy at 17 micro

because of the natural resonance of the silicon dioxide

MACRO BENDING LOSS Macro-bending loss is caused by bending of the entire fiber axis The bending radius shall not be

sharper than 30d where d is diameter of cable A single bend sharper than 30d can cause loss of 05dB

The fiber may break if bending is ever sharper

MICRO BENDING LOSS Micro-bending loss is caused by micro deformations of fiber axis which leads to failures in achieving

total internal reflection conditions Micro-bends are small scale perturbations along the fiber axis the

amplitude of which are on the order of microns These distortions can cause light to leak out of a fiber

Micro-bending may be induced at very cold temperatures because the glass has a different coefficient of

thermal expansion from the coating and cabling materials At low temperatures the coating and cable

become more rigid and may contract more than the glass Consequently enough load may be exerted on the

glass to cause micro bends

Coating material is selected by manufacturers to minimize loss due to micro-bending The linear thermal

expansion coefficient of coating material shall be compatible with that of fiber

32 | P a g e

DISPERSION Dispersion is the optical term for the spreading of the transmits in the fiber It is the bandwidth

limiting phenomenon and comes in two forms Multimode dispersion and chromatic dispersion Chromatic

dispersion is further subdivided into material dispersion and waveguide dispersion

DISPERSION PHENOMENON IN OPTICAL FIBER Dispersion is the time distortion of an optical signal that results from the differences of time of travel

for different components of that signal typically resulting in pulse broadening As the distance traveled by

the signal is more broadening of pulse is more In digital transmission dispersion limits on the maximum

data rate and the maximum distance ie the information-carrying capacity of a fiber link The interference

from broadened pulse in the next interval shall not lead to erroneous interpretation of received signal

OPTICAL DOMAIN Understanding where attenuation and dispersion problems occur helps optical design engineers

determine the better wavelengths at which information can be transmit taking into account distance type of

fiber and the other factors which can severely affect the integrity of the transmitted signal The graph shown

depicts the optical transmission domain as well as the areas where problems arise The wavelength (nm)

is shown on X-axis and attenuation ( dBkm) is shown on Y-axis

There are four transmission windows appear in the figure The first one is at around 850 nm the

second at 1310nm third at 1550 nm and fourth at 1625 nm The last two labeled as C and L band

respectively The 850 nm wavelength at which the original LED technology operated The second window at

1310 nm has low dispersion The 1550 nm called as C-band is ideal wavelength for long haul

communication systems The network engineers can avoid transmitting signal at 1000 nm where Rayleigh

scattering 1240 and 1390 nm where hydroxyl absorption by water occurs to avoid high degree of loss

Optical fibers also can be manufactured to have low dispersion wavelength in the 1550nm region

which is also the point where silica-based fibers have inherently minimal attenuation These fibers are

referred to as dispersion-shifted fibers and are used in long-distance applications with high bit rates For

33 | P a g e

applications utilizing multiple wavelengths it is undesirable to have the zero dispersion point within the

operating

wavelength range

34 | P a g e

SIGNALLING RELAYS

INTRODUCTION A relay is an electromagnetic device which is used to convey information from one circuit to another

circuit through a set of contact ie front or back contact Constructional and electrically relays may be

divided into DC and AC relays because the means by which the electrical energy in the coil is converted in

to mechanical Energy in order to move the contacts are fundamentally different In DC type the contacts are

carried on an armature forming part of a magnetic circuit in which a field is set up by the current flowing in

the coils In AC types the contacts are attached by a link mechanism to a metal sector disc or cylinder in

which currents are induced by the alternating magnetic field produced by the currents in the coils

Every endeavor has been made to explain the action of each type of relay in the simplest possible manner

Relays are sophisticated switch gears used for remote control and succession control of various

electrical equipment In present days they are widely used because they are capable of protecting the

controlled equipment from cross feeding and overloading even as they cater for speedy operations

Most of the relays in present day signaling are electromagnetic devices although some of the relays control

circuits through electronic components like diodetransistors Integrated Chips etc

Railway signaling relays are unique in that

(a) They operate on low voltage and current

(b) They are more articulate as according to their special features they can work under restrictive conditions

and in any specified manner Virtually they can cater for all situations while contributing to speed and

accuracy in operations

CLASSIFICATION OF SIGNALLING RELAYS (a) According to the method of their mounting or fixture they are classified as

(i) Shelf type Relays which are loosely kept on shelves

(ii) Plug in type Relays which are plugged into a pre- wired plug boards

(b) According to their connection and usage they are classified as

(i) Track relays Relay which is directly connected to the track to detect the presence of vehicle

(ii) Line Relays Other than track relay all are line relays Relays connected to the selection circuit

(c) According to their vitality or importance in ensuring train working safety they are classified as

(i) Vital Relays All relays used for traffic control such as signal point controls track detection etc

(ii) Non-vital Relays Relays which operate control aids and accessories like warnings buzzers

Indications etc

(d) According to their special provisions to ensure reliability of their contacts they are classified as

(i) Proved type are those whose normalization after each operation shall be proved in circuit

controlled by their contacts Contacts in which both the springs have metal surfaces on their tips They may

get fused due to high sparking current across them during operation These may prevent relay normalization

and causes unsafe condition in traffic control To avoid this proving of relay normalization after each

operation is necessary

(ii) Non - proved type Need not to be proved to have been normalized after each operation as their

contacts have at least one non-fusible contact (carbon contact)

(e) According to their feed source relays are broadly classified as

(i) DC relays The relay which requires DC power supply for its operations are called DC relays Among

the DC relays

o DC neutral relays This relay closes the same set of contacts on energization with Normal polarity

or Reverse polarity supply

o Polar Relays This relay closes different set of contacts when energized with Reverse polarity

supply They may or may not have contact to close when deenergized

35 | P a g e

(ii) AC Relay AC Induction motor track relays Time element relays flashing indication control etc

(iii) Electronic Relays DC relays with electronic components in them are called electronic relays

DC NEUTRAL RELAY Each Relay has usually one or two coils with a hollow center to accommodate a coreThe coils are

made up of a large numbers of turns of small gauge soft drawn copper wire The two coils can be connected

in series or parallel according to the requirement of relay resistance The ends of the coils are terminated on

binding post to which the control wires are connected Each coil is placed around a core of specially selected

Iron or steel having high permeability and low retentivity The core should be susceptible to magnetism and

at the same time should have little residual magnetism The cores are connected at the top by a yoke to

complete the magnetism coupling between two ends of coils The bottom of each core is equipped with a

large steel or Iron block known as pole piece or face

A flat piece of Iron or steel called armature is supported by brackets which are securely fastened to

the pole piece The armature yoke and the pole pieces are also made of specially selected iron or steel of the

same quality as the core The armature carries the metallic spring contacts which are insulated from it

The circuit through the coils of the relay is closed It sets up a magnetic flux through the core yoke and the

armature The flux passing between the armature and pole faces causes the armatures get attracted to the pole

faces and armature picks up and closes front contacts When the circuit is opened the magnetic flux collapses

and the armature drops away by gravity from the pole faces the front contacts break and back contacts close

The front and back contacts of the relay can be utilised to make or break other circuits Two stop pins of

nonmagnetic material are fixed either on the armature or pole faces so that the armature cannot

come in contact with the pole faces It is essential to maintain a small air-gap between the armature and pole

faces so that low value of residual magnetism may not retain the armature in picked up position and causes

the relay to fail to drop away with a break in its control circuit

GENERAL USAGE

DC Neutral line relays are most commonly used for Railway Signalling controls and detection

Among them plug-in type relays are preferred in larger installations for space considerations Shelf type

relays are also in use mostly in wayside stations

There are many DC Neutral line relays in use with special features such as

(i) Delayed operation

(ii) Biased DC control

(iii) DC control unaffected by AC interference currents

(iv) Getting latched in operated condition till further feeding and others

Usage of DC polar relays is mostly in conjunction with block instruments that control traffic between

stations AC line relays are almost extinct in installations of British Signalling practice They are however

used for time control operations flashing indication control and such other special purposes in installations

with Siemens signalling practice widely Track relays are used according to the type of track detection

circuits chosen for a given location and context While most of the track circuits are still of the DC working

type requiring DC neutral track relays with them the prospects of their being replaced with Electronic track

circuits directly feeding DC line relays in future are great AC Track Circuits are used in DC Traction area

as conventional DC Track Circuits are not suitable there AC Track relays are used with them almost all of

the induction motor type In the British practice of signalling which was first introduced on Indian Railways

non-proved type relays with carbon to metal switching contacts are generally used for vital controls

They facilitate simple circuit designs But with the advent of German Practice introduced by Ms

Siemens later proved type relays with all metal to metal contacts are widely accepted in spite of

complications in circuit design caused by them A recent introduction is that of the same type relays made by

Ms Integra control However for some time now the appreciable features of both the practices are getting

36 | P a g e

incorporated together in the indigenous designs of signalling by railwaymen With this the usage of all types

of relays anywhere can be found without straight jacketed segration of relay types

CHARACTERSTIC OF ELECTRO-MAGNETIC RELAY The following are the characteristic of electro-magnetic relays A brief study of them helps in

understanding the choice of their components and designs features

1) Force of attraction

2) Effect of air gap

3) Effect of Hysterisis

4) Transient condition

FORCE OF ATTRACTION In any electro-magnetic system the force of attraction is given by

Where B - is the flux density a - is the cross sectional area of the particular part of the magnetic

circuit

In the case of a DC neutral Relay B is proportional to the current that is flowing in the coil

surrounding the electro-magnet and thus the force of the attraction is directly proportional to the square of the

current This square relationship has its own advantage especially in the case of DC track relay in that a

small reduction in the current will have a great effect on the working of the relay Also for a given change of

current the make and the break will be quicker with lesser possibility of arcing

EFFECT OF AIR GAP

Curve lsquoArsquo is magnetisation curve for the iron and is all practical purpose a straight line up to the

saturation point Curve lsquoBrsquo is the magnetisation curve for the open-air gap which is a straight line through

out because per magnetisation curve of the whole

magnetic circuit of the relay and for a given force is the sum of the amp-turns for the iron part and the amp-

turns for the air gap

When the front contacts are open the force required to pick up the armature is shown on curve lsquoCrsquo to be F1

but after the armature has operated it will be separated from the core by stop pins In this position the amp-

turns required to maintain the armature is less as indicated by the dotted line from 1 on curve C to 2 on curve

37 | P a g e

F But actually the current in the coil is unaltered the force on the armature is greater than required as

indicated at 3 on curve F Part of this extra force is used to flex the front contacts sufficiently to give good

contact pressure when it is in energised position

The difference between the pick-up and the drop-away current should be as small as practicable in

track relay to ensure good shunting characteristics This is achieved firstly by the choice of good quality relay

iron and secondly by having a small air gap between armature and core If the air gap is not available then

the residual magnetism fluxes might cause the armature to be retained when the supply is disconnected For

this reason residual pins are provided to ensure a definite minimum air gap in the energised position

EFFECT OF HYSTERISIS

Hysterisis is the property by which the flux produced lags behind the current In the de-energized

condition there will be small residual flux in the core When the voltage is applied to the coils the current in

rising to its steady value first causes the flux to rise from 1 to 2 along the curve At this point the flux density

will be sufficient to attract the armature and reduce the air gap the flux then raise to 3 and continue to 4

which corresponds to the steady current in the coils When the voltage is disconnected the current in falling

caused the flux to fall from 4 to 5 along the curve At this point the flux density will fall below the value

required to maintain the armature which will release thus increasing the air gap and reducing the flux to 6

Finally the

flux will decrease from 6 to 1 where the current will again be zero

The relay core is made of material having high permeability and low retentivity As mentioned in

the IRS specification Electromagnet iron may be in the form of a

(a) Bar of silicon steel

(b) Best Yorkshire wrought iron

(c) Swedish charcoal iron

(d) Electrical steel sheets

` This reduces the difference between pick up value and Drop away value By selecting good quality

core material Percentage release and sensitivity of the relay will be improved

TRANSIENT CONDITION

38 | P a g e

When the voltage is applied or disconnected from the coils it takes some little time before the current

become steady These are known as transient conditionsrdquo and are important so far as track relays are

concerned When the voltage is first applied to the coils the magnetic flux in rising cuts the turns on the

coils and in so doing produces a back EMF that opposes the applied voltage and retards the growth of

current

The growth and decay of flux are decided by the relationship between the inductance and resistance

in the circuit is known as time constant It is not fixed quantity in the case of DC neutral relay This value of lsquo

Lrsquo is less when the relay is in de-energised condition (L1) than when the relay is in energised condition (L2)

The magnitude of flux that is established for a given change of current is different in two cases

When the current reaches the pick up value the armature closes and the inductance is increased to L2

due to reduced air gap the flux per amp is increased The increase in flux increased the back EMF during the

movement of the armature after which the current continuous to raise along a new curve corresponding to the

increased inductance until it reaches the final value (ER) This process is indicated above in fig24

When the supply is disconnected the current is obliviously reduced to zero immediately but the flux

decay comparatively slowly owing to the eddy currents produced in the core by the rapid flux change which

tend to maintain the flux The drop away time on a disconnection is however generally negligible See fig

below

If the relay releases due to the reduction in current from say I 2 to I 1 caused by the application of

shunt resistance (as in the case of track relay ) the time taken is much longer than the relay is simply

disconnected The rate of rise or fall of current during the transient conditions is also depends on exterior

circuit values because L and R apply to the whole circuit The production of eddy current in the core the flux

will decay at a slower rate than the current So that the actual release time will be a little longer than it takes

the current to fall to the release

L= Inductance

39 | P a g e

R= Resistance

It is now clear that to reduce releasing time to a minimum it is necessary that

- The relay iron should have low Hysterisis loss and low retentivity

- The degree of over energization of the relay should be restricted

- Connecting a suitable external resistance in series with the relay to keep LR ratio low

In non RE area for track circuit length less than 100M 9 ohm track relay only to be used Using relay

with minimum contacts as they require lesser current which keeps inductance value low

Train working safety is ensured only if the track relay of shortest length track circuit is released

before a light engine running at a highest permitted speed clears it Otherwise the track circuit occupation

may go undetected To avoid this a special provision has to be made in signal control circuits wherever

necessary

The following methods may be adopted for reducing the time lag of track relay

(a) Restrict the over energisation of relay since the release time depends on the initial working current

(b) Connecting a suitable external resistance in series with the relay to keep the LR ratio low

(c) Using relays with minimum contacts as they require lesser operating current keeping the inductance

value low

40 | P a g e

CONCLUSION

Modern signalling is vital for safe and punctual movements of trains In the Indian railways The Signalling

and Telecommunication Department is responsible for providing modern effective and relaible signalling

systems as well as telecommunication systems

The first mode of communication used in Indian Railways was the use of electric telegraph

with the help of Morose code Morose code is the method of providing text information as a series of on-off

tones and lights or clicks that can be directly understood by a skilled listener or observer without special

equipmentEach character (letter or numeral ) is represented by a unique sequence of dots and dashes Later

this system becomes obselete and beggan the era of wireless communication which operated at audio level

frequency range

In wireless communication the significant advances took place the transition to miniature

valves or filament tubesBut this was abandoned too because of excessive current consumption and over

heating of the filament tubes

Fibre-optic communication is a method of transmitting information from one place to another by

sending pulses of light through an optcial fibreThe light forms an electromagnetic carrier wave that is

modulated to carry information First developed in the 1970s fibre optic communication systems has

revolutionized the telecommunications industry and have palyed a major role in the advent of the information

age Because of its advantages over electrical transmissionsoptical fibres have largely replaced copper wire

communications in core networks in the developed world The Indian Railways too is undergoing a transition

from Microwave communication to fibre optic communications

41 | P a g e

BIBLIOGRAPHY AND REFERENCES

1 wwwwikipediacom

2 wwwbritaniccacom

3 wwwirfcacom

4 Motorola GP60 system manual

5 Harris FAS 7000 manual

6 TOSHIBA Manual

25 | P a g e

Then θc = θ1 = arcsin(n2n1)

For example with light trying to emerge from glass with n1=15 into air (n2 =1) the ritical angle θc is

arcsin(115) or 418deg For any angle of incidence larger than the critical angle Snells law will not be able to

be solved for the angle of refraction because it will show that the refracted angle has a sine larger than 1

which is not possible In that case all the light is totally reflected off the interface obeying the law of

reflection

OPTICAL FIBER MODE An optical fiber guides light waves in distinct patterns called modes Mode describes the distribution

of light energy across the fiber The precise patterns depend on the wavelength of light transmitted and on the

variation in refractive index that shapes the core In essence the variations in refractive index create

boundary

conditions that shape how light waves travel through the fiber like the walls of a tunnel affect how sounds

echo inside

We can take a look at large-core step-index fibers Light rays enter the fiber at a range of angles and

rays at different angles can all stably travel down the length of the fiber as long as they hit the core-cladding

interface at an angle larger than critical angle These rays are different modes Fibers that carry more than

one mode at a specific light wavelength are called multimode fibers Some fibers have very small diameter

core that they can carry only one mode which travels as a straight line at the center of the core These fibers

are single mode fibers This is illustrated in the following picture

OPTICAL FIBER INDEX PROFILE Index profile is the refractive index distribution across the core and the cladding of a fiber Some

optical fiber has a step index profile in which the core has one uniformly distributed index and the cladding

has a lower uniformly distributed index Other optical fiber has a graded index profile in which refractive

index varies gradually as a function of radial distance from the fiber center Graded-index profiles include

power-law index profiles and parabolic index profiles The following figure shows some common types of

index profiles for single mode and multimode fiber

26 | P a g e

OPTICAL FIBERrsquoS NUMERICAL APERTURE ( NA )- Multimode optical fiber will only propagate light that enters the fiber within a certain cone known as

the acceptance cone of the fiber The half-angle of this cone is called the acceptance angle (see figure 18)

θmax For step-index multimode fiber the acceptance angle is determined only by the indices of refraction

Where

n is the refractive index of the medium light is traveling before entering the fiber

nf is the refractive index of the fiber core

nc is the refractive index of the cladding

NUMBER OF MODES IN A FIBER - Modes are sometimes characterized by numbers Single mode fibers carry only the lowest-order

mode assigned the number 0 Multimode fibers also carry higher-order modes The number of modes that

can propagate in a fiber depends on the fiberrsquos numerical aperture (or acceptance angle) as well as on its

core diameter and the wavelength of the light For a step-index multimode fiber the number of such modes

Nm

Where

D is the core diameter

λ is the operating wavelength

NA is the numerical aperture (or acceptance angle)

MODE FIELD DIAMETER - All light do not travels through the core of the fiber but is distributed through both the core and the

cladding The mode field is the distribution of light through the core and cladding of a particular fiber

Mode-Field Diameter (MFD) defines the size of the power distribution When coupling light into or out of a

fiber MFD is important in understanding light loss

27 | P a g e

ADVANTAGE OF OFC COMMUNICATION - bull More information carrying capacity Fibers can handle much higher data rates than copper More

information can be sent in a second

bull Free from Electromagnetic and Electrostatic interference Being insulator no electric current flows through

the fibre and due to this reason fibres neither radiate nor pick up electro - magnetic radiation So WPC

CLEARANCE is not required

bull Low attenuation 025 dbkm at 1550 nm Loss in twisted pair and coaxial cable increases with frequency

where as loss in the optical fibre cable remains flat over a wide range of frequencies

bull Use of WDM ndash Switching routing at Optical signal level

bull Self healing rings under NMS control

bull Small size makes fibre cable lighter in weight So easy to handleOptic fibre cable weight (approx)

500 kg km Copper cable weight (approx) 1000 kgkm

The reasons are photons of light in a fibre

do not affect each other as they have no electrical charge and they are not affected by stray photons outside

the fibre But in case of copper electrons move through the cable and these are affected by each other

Optical fibre does not carry any electricity even if the cable is damaged or short circuited it does

not cause any spark or fire hazard

As the fibre do not radiate energy it can not be detected by any nearby antenna or any

other detector The fibres are difficult to tap and therefore excellent for security

As the signal transmission is by digital modulation there is no chance of cross talk in

between channels

Only by adding a few additional terminal and repeater equipments the

capacity of the system can be increased at any time once the cable is laid

ical effects and temperature variations

LIMITATIONS OF OFC -

difficult

- utilised

APPLICATION IN SIGNAL AND TELECOMMUNICATIONS transmission circuits

-haul circuits for linking of telephone exchanges

28 | P a g e

PROPAGATION MODES CONCEPT -

MODE - Mode is an available distribution of electromagnetic field in a plane transverse to the direction of

light propagation Each mode is characterized by frequency polarization electric field strength and

magnetic field strength Available patterns are derived from Maxwellrsquos equations and boundary conditions

LINEARLY POLARIZED (LP) MODE A mode for which the field components in the direction of propagation are small compared to

components perpendicular to that direction An optical fibre supports only different field patterns called as

lsquoLinear Polarizedrsquo or lsquo LPrsquo modes The reasons are

requirements

de

the accrual of power carried by different modes

There are two basic types of fiber Multimode fiber and Single-mode fiber

Multimode fiber is best designed for short transmission distances This is suited for used in LAN systems and

video surveillance Single mode fibre is best designed for longer transmission distances This is suitable for

long distance telephony and multi channel television broadcast systems

29 | P a g e

MULTI MODE FIBER Multimode fiber the first to be manufactured and commercialized simply refers to the fact that

numerous modes or light rays are carried simultaneously through the waveguide Modes result from the fact

that light will only propagate in the fiber core at discrete angles within the cone of acceptance MM fiber type

has a much larger core diameter compared to single-mode fiber allowing for the larger number of modes

and

is easier to couple than single-mode optical fiber Multimode fiber further categorized as Multimode step-

index and Multimode graded index fiber

PROPAGATION THROUGH MMSI FIBER Figure shows the principle of total internal reflection applies to multimode step index fiber Because

the corersquos index of refraction is higher than the claddingrsquos index of refraction the light that enters at less than

the critical angle is guided along the fiber

Three different light waves travel down the fiber One mode travels straight down the center of the

core A second mode travels at a steep angle and bounces back and forth by total internal reflection The third

mode exceeds the critical angle and refracts into the cladding Naturally it can be seen that the second mode

travels a longer distance than the first mode causing the two modes to arrive at separate times

PROBLEMS WITH MMSI FIBER AND SOLUTION This disparity between arrival times of the different light rays is known as dispersion and the result is

a muddied signal at the receiving end It is important to note that high dispersion is an unavoidable

characteristic of multimode step-index fiber The solutions are either use Graded index fiber or Single mode

fiber

PROPAGATION THROUGH MMGI FIBER Multimode Graded-index refers to the fact that the refractive index of the core gradually decreases

farther from the center of the core The increased refraction in the center of the core slows the speed of some

light rays allowing all the light rays to reach the receiving end at approximately the same time reducing

dispersion Figure shows the Light propagation principle through multimode graded-index fiber The corersquos

central refractive index ( nA ) is greater than that of the outer corersquos refractive index ( nB )

It is very clear from the figure the light rays no longer follow straight lines they follow a serpentine path

being gradually bent back toward the center by the continuously declining refractive index This reduces the

arrival time disparity because all modes arrive at about the same time The modes traveling in a straight line

30 | P a g e

are in a higher refractive index so they travel slower than the serpentine modes These travel farther but

move faster in the lower refractive index of the outer core region

PROPAGATION THROUGH SMSI FIBER Single mode fiber has a much smaller core that allows only one mode of light at a time to propagate

through the core The figure shows the single mode fiber

Single-mode fiber exhibits no dispersion caused by multiple modes Single-mode fiber also offers lower fiber

attenuation than multimode fiber Thus more information can be transmitted per unit of time because it can

retain the fidelity of each light pulse over longer distances Like multimode fiber early single-mode fiber was

generally characterized as step-index fiber meaning the refractive index of the fiber core is a step above that

of the cladding rather than graduated as it is in graded-index fiber Modern single-mode fibers have evolved

into more complex designs such as matched clad depressed clad and other exotic structures

SINGLE-MODE FIBER DISADVANTAGES The smaller core diameter makes coupling light into the core more difficult The tolerances for single-

mode connectors and splices are also much more demanding

CUTOFF WAVE LENGTH - Cutoff wavelength is the wavelength above which a single-mode fiber supports and propagates only

one mode of light In other words an optical fiber that is single-mode at a particular wavelength may have

two or more modes at wavelengths lower than the cutoff wavelength The effective cutoff wavelength of a

fiber is dependent on the length of fiber and its deployment The longer the fiber the lower is the effective

cutoff

wavelength The smaller the bend radius of a loop of the fiber the lower is the effective cutoff wavelength If

a fiber is bent in a loop the effective cutoff wavelength is lowered

SIGNAL ATTENUATION IN FIBER - Optical fiber has a number of advantages over copper However it also suffers from degradation

problems which can not be ignored The first of these is loss or attenuation Attenuation is typically the result

of two sub properties They are scattering and absorption Both of which have cumulative effects The second

is

dispersion which is the spreading of the transmitted signal and is analogous to noise

SCATTERING Scattering occurs because of impurities or irregularities in the physical construction of the fiber The

well known form of scattering is Rayleigh Scattering It is caused by metal ions in the silica matrix and

results in light rays being scattered in various directions

31 | P a g e

Scattering limits the use of wavelengths below 800nm The short wavelengths are much affected than longer

wavelengths It is because of Rayleigh scattering that the sky appears to be blue ( shorter wave length ) The

shorter wavelengths ( blue ) of light are scattered more than the longer wavelengths of light

ABSORPTION Absorption results from three factors They are hydroxyl ions ( OH- water ) in the silica impurities

in the silica and incomplete residue from the manufacturing process These impurities tend to absorb the

energy of the transmitted signal and convert it to heat resulting in an overall weakening of the signal The

Hydroxyl absorption occurs at 125 and 139 micro The silica itself starts to absorb energy at 17 micro

because of the natural resonance of the silicon dioxide

MACRO BENDING LOSS Macro-bending loss is caused by bending of the entire fiber axis The bending radius shall not be

sharper than 30d where d is diameter of cable A single bend sharper than 30d can cause loss of 05dB

The fiber may break if bending is ever sharper

MICRO BENDING LOSS Micro-bending loss is caused by micro deformations of fiber axis which leads to failures in achieving

total internal reflection conditions Micro-bends are small scale perturbations along the fiber axis the

amplitude of which are on the order of microns These distortions can cause light to leak out of a fiber

Micro-bending may be induced at very cold temperatures because the glass has a different coefficient of

thermal expansion from the coating and cabling materials At low temperatures the coating and cable

become more rigid and may contract more than the glass Consequently enough load may be exerted on the

glass to cause micro bends

Coating material is selected by manufacturers to minimize loss due to micro-bending The linear thermal

expansion coefficient of coating material shall be compatible with that of fiber

32 | P a g e

DISPERSION Dispersion is the optical term for the spreading of the transmits in the fiber It is the bandwidth

limiting phenomenon and comes in two forms Multimode dispersion and chromatic dispersion Chromatic

dispersion is further subdivided into material dispersion and waveguide dispersion

DISPERSION PHENOMENON IN OPTICAL FIBER Dispersion is the time distortion of an optical signal that results from the differences of time of travel

for different components of that signal typically resulting in pulse broadening As the distance traveled by

the signal is more broadening of pulse is more In digital transmission dispersion limits on the maximum

data rate and the maximum distance ie the information-carrying capacity of a fiber link The interference

from broadened pulse in the next interval shall not lead to erroneous interpretation of received signal

OPTICAL DOMAIN Understanding where attenuation and dispersion problems occur helps optical design engineers

determine the better wavelengths at which information can be transmit taking into account distance type of

fiber and the other factors which can severely affect the integrity of the transmitted signal The graph shown

depicts the optical transmission domain as well as the areas where problems arise The wavelength (nm)

is shown on X-axis and attenuation ( dBkm) is shown on Y-axis

There are four transmission windows appear in the figure The first one is at around 850 nm the

second at 1310nm third at 1550 nm and fourth at 1625 nm The last two labeled as C and L band

respectively The 850 nm wavelength at which the original LED technology operated The second window at

1310 nm has low dispersion The 1550 nm called as C-band is ideal wavelength for long haul

communication systems The network engineers can avoid transmitting signal at 1000 nm where Rayleigh

scattering 1240 and 1390 nm where hydroxyl absorption by water occurs to avoid high degree of loss

Optical fibers also can be manufactured to have low dispersion wavelength in the 1550nm region

which is also the point where silica-based fibers have inherently minimal attenuation These fibers are

referred to as dispersion-shifted fibers and are used in long-distance applications with high bit rates For

33 | P a g e

applications utilizing multiple wavelengths it is undesirable to have the zero dispersion point within the

operating

wavelength range

34 | P a g e

SIGNALLING RELAYS

INTRODUCTION A relay is an electromagnetic device which is used to convey information from one circuit to another

circuit through a set of contact ie front or back contact Constructional and electrically relays may be

divided into DC and AC relays because the means by which the electrical energy in the coil is converted in

to mechanical Energy in order to move the contacts are fundamentally different In DC type the contacts are

carried on an armature forming part of a magnetic circuit in which a field is set up by the current flowing in

the coils In AC types the contacts are attached by a link mechanism to a metal sector disc or cylinder in

which currents are induced by the alternating magnetic field produced by the currents in the coils

Every endeavor has been made to explain the action of each type of relay in the simplest possible manner

Relays are sophisticated switch gears used for remote control and succession control of various

electrical equipment In present days they are widely used because they are capable of protecting the

controlled equipment from cross feeding and overloading even as they cater for speedy operations

Most of the relays in present day signaling are electromagnetic devices although some of the relays control

circuits through electronic components like diodetransistors Integrated Chips etc

Railway signaling relays are unique in that

(a) They operate on low voltage and current

(b) They are more articulate as according to their special features they can work under restrictive conditions

and in any specified manner Virtually they can cater for all situations while contributing to speed and

accuracy in operations

CLASSIFICATION OF SIGNALLING RELAYS (a) According to the method of their mounting or fixture they are classified as

(i) Shelf type Relays which are loosely kept on shelves

(ii) Plug in type Relays which are plugged into a pre- wired plug boards

(b) According to their connection and usage they are classified as

(i) Track relays Relay which is directly connected to the track to detect the presence of vehicle

(ii) Line Relays Other than track relay all are line relays Relays connected to the selection circuit

(c) According to their vitality or importance in ensuring train working safety they are classified as

(i) Vital Relays All relays used for traffic control such as signal point controls track detection etc

(ii) Non-vital Relays Relays which operate control aids and accessories like warnings buzzers

Indications etc

(d) According to their special provisions to ensure reliability of their contacts they are classified as

(i) Proved type are those whose normalization after each operation shall be proved in circuit

controlled by their contacts Contacts in which both the springs have metal surfaces on their tips They may

get fused due to high sparking current across them during operation These may prevent relay normalization

and causes unsafe condition in traffic control To avoid this proving of relay normalization after each

operation is necessary

(ii) Non - proved type Need not to be proved to have been normalized after each operation as their

contacts have at least one non-fusible contact (carbon contact)

(e) According to their feed source relays are broadly classified as

(i) DC relays The relay which requires DC power supply for its operations are called DC relays Among

the DC relays

o DC neutral relays This relay closes the same set of contacts on energization with Normal polarity

or Reverse polarity supply

o Polar Relays This relay closes different set of contacts when energized with Reverse polarity

supply They may or may not have contact to close when deenergized

35 | P a g e

(ii) AC Relay AC Induction motor track relays Time element relays flashing indication control etc

(iii) Electronic Relays DC relays with electronic components in them are called electronic relays

DC NEUTRAL RELAY Each Relay has usually one or two coils with a hollow center to accommodate a coreThe coils are

made up of a large numbers of turns of small gauge soft drawn copper wire The two coils can be connected

in series or parallel according to the requirement of relay resistance The ends of the coils are terminated on

binding post to which the control wires are connected Each coil is placed around a core of specially selected

Iron or steel having high permeability and low retentivity The core should be susceptible to magnetism and

at the same time should have little residual magnetism The cores are connected at the top by a yoke to

complete the magnetism coupling between two ends of coils The bottom of each core is equipped with a

large steel or Iron block known as pole piece or face

A flat piece of Iron or steel called armature is supported by brackets which are securely fastened to

the pole piece The armature yoke and the pole pieces are also made of specially selected iron or steel of the

same quality as the core The armature carries the metallic spring contacts which are insulated from it

The circuit through the coils of the relay is closed It sets up a magnetic flux through the core yoke and the

armature The flux passing between the armature and pole faces causes the armatures get attracted to the pole

faces and armature picks up and closes front contacts When the circuit is opened the magnetic flux collapses

and the armature drops away by gravity from the pole faces the front contacts break and back contacts close

The front and back contacts of the relay can be utilised to make or break other circuits Two stop pins of

nonmagnetic material are fixed either on the armature or pole faces so that the armature cannot

come in contact with the pole faces It is essential to maintain a small air-gap between the armature and pole

faces so that low value of residual magnetism may not retain the armature in picked up position and causes

the relay to fail to drop away with a break in its control circuit

GENERAL USAGE

DC Neutral line relays are most commonly used for Railway Signalling controls and detection

Among them plug-in type relays are preferred in larger installations for space considerations Shelf type

relays are also in use mostly in wayside stations

There are many DC Neutral line relays in use with special features such as

(i) Delayed operation

(ii) Biased DC control

(iii) DC control unaffected by AC interference currents

(iv) Getting latched in operated condition till further feeding and others

Usage of DC polar relays is mostly in conjunction with block instruments that control traffic between

stations AC line relays are almost extinct in installations of British Signalling practice They are however

used for time control operations flashing indication control and such other special purposes in installations

with Siemens signalling practice widely Track relays are used according to the type of track detection

circuits chosen for a given location and context While most of the track circuits are still of the DC working

type requiring DC neutral track relays with them the prospects of their being replaced with Electronic track

circuits directly feeding DC line relays in future are great AC Track Circuits are used in DC Traction area

as conventional DC Track Circuits are not suitable there AC Track relays are used with them almost all of

the induction motor type In the British practice of signalling which was first introduced on Indian Railways

non-proved type relays with carbon to metal switching contacts are generally used for vital controls

They facilitate simple circuit designs But with the advent of German Practice introduced by Ms

Siemens later proved type relays with all metal to metal contacts are widely accepted in spite of

complications in circuit design caused by them A recent introduction is that of the same type relays made by

Ms Integra control However for some time now the appreciable features of both the practices are getting

36 | P a g e

incorporated together in the indigenous designs of signalling by railwaymen With this the usage of all types

of relays anywhere can be found without straight jacketed segration of relay types

CHARACTERSTIC OF ELECTRO-MAGNETIC RELAY The following are the characteristic of electro-magnetic relays A brief study of them helps in

understanding the choice of their components and designs features

1) Force of attraction

2) Effect of air gap

3) Effect of Hysterisis

4) Transient condition

FORCE OF ATTRACTION In any electro-magnetic system the force of attraction is given by

Where B - is the flux density a - is the cross sectional area of the particular part of the magnetic

circuit

In the case of a DC neutral Relay B is proportional to the current that is flowing in the coil

surrounding the electro-magnet and thus the force of the attraction is directly proportional to the square of the

current This square relationship has its own advantage especially in the case of DC track relay in that a

small reduction in the current will have a great effect on the working of the relay Also for a given change of

current the make and the break will be quicker with lesser possibility of arcing

EFFECT OF AIR GAP

Curve lsquoArsquo is magnetisation curve for the iron and is all practical purpose a straight line up to the

saturation point Curve lsquoBrsquo is the magnetisation curve for the open-air gap which is a straight line through

out because per magnetisation curve of the whole

magnetic circuit of the relay and for a given force is the sum of the amp-turns for the iron part and the amp-

turns for the air gap

When the front contacts are open the force required to pick up the armature is shown on curve lsquoCrsquo to be F1

but after the armature has operated it will be separated from the core by stop pins In this position the amp-

turns required to maintain the armature is less as indicated by the dotted line from 1 on curve C to 2 on curve

37 | P a g e

F But actually the current in the coil is unaltered the force on the armature is greater than required as

indicated at 3 on curve F Part of this extra force is used to flex the front contacts sufficiently to give good

contact pressure when it is in energised position

The difference between the pick-up and the drop-away current should be as small as practicable in

track relay to ensure good shunting characteristics This is achieved firstly by the choice of good quality relay

iron and secondly by having a small air gap between armature and core If the air gap is not available then

the residual magnetism fluxes might cause the armature to be retained when the supply is disconnected For

this reason residual pins are provided to ensure a definite minimum air gap in the energised position

EFFECT OF HYSTERISIS

Hysterisis is the property by which the flux produced lags behind the current In the de-energized

condition there will be small residual flux in the core When the voltage is applied to the coils the current in

rising to its steady value first causes the flux to rise from 1 to 2 along the curve At this point the flux density

will be sufficient to attract the armature and reduce the air gap the flux then raise to 3 and continue to 4

which corresponds to the steady current in the coils When the voltage is disconnected the current in falling

caused the flux to fall from 4 to 5 along the curve At this point the flux density will fall below the value

required to maintain the armature which will release thus increasing the air gap and reducing the flux to 6

Finally the

flux will decrease from 6 to 1 where the current will again be zero

The relay core is made of material having high permeability and low retentivity As mentioned in

the IRS specification Electromagnet iron may be in the form of a

(a) Bar of silicon steel

(b) Best Yorkshire wrought iron

(c) Swedish charcoal iron

(d) Electrical steel sheets

` This reduces the difference between pick up value and Drop away value By selecting good quality

core material Percentage release and sensitivity of the relay will be improved

TRANSIENT CONDITION

38 | P a g e

When the voltage is applied or disconnected from the coils it takes some little time before the current

become steady These are known as transient conditionsrdquo and are important so far as track relays are

concerned When the voltage is first applied to the coils the magnetic flux in rising cuts the turns on the

coils and in so doing produces a back EMF that opposes the applied voltage and retards the growth of

current

The growth and decay of flux are decided by the relationship between the inductance and resistance

in the circuit is known as time constant It is not fixed quantity in the case of DC neutral relay This value of lsquo

Lrsquo is less when the relay is in de-energised condition (L1) than when the relay is in energised condition (L2)

The magnitude of flux that is established for a given change of current is different in two cases

When the current reaches the pick up value the armature closes and the inductance is increased to L2

due to reduced air gap the flux per amp is increased The increase in flux increased the back EMF during the

movement of the armature after which the current continuous to raise along a new curve corresponding to the

increased inductance until it reaches the final value (ER) This process is indicated above in fig24

When the supply is disconnected the current is obliviously reduced to zero immediately but the flux

decay comparatively slowly owing to the eddy currents produced in the core by the rapid flux change which

tend to maintain the flux The drop away time on a disconnection is however generally negligible See fig

below

If the relay releases due to the reduction in current from say I 2 to I 1 caused by the application of

shunt resistance (as in the case of track relay ) the time taken is much longer than the relay is simply

disconnected The rate of rise or fall of current during the transient conditions is also depends on exterior

circuit values because L and R apply to the whole circuit The production of eddy current in the core the flux

will decay at a slower rate than the current So that the actual release time will be a little longer than it takes

the current to fall to the release

L= Inductance

39 | P a g e

R= Resistance

It is now clear that to reduce releasing time to a minimum it is necessary that

- The relay iron should have low Hysterisis loss and low retentivity

- The degree of over energization of the relay should be restricted

- Connecting a suitable external resistance in series with the relay to keep LR ratio low

In non RE area for track circuit length less than 100M 9 ohm track relay only to be used Using relay

with minimum contacts as they require lesser current which keeps inductance value low

Train working safety is ensured only if the track relay of shortest length track circuit is released

before a light engine running at a highest permitted speed clears it Otherwise the track circuit occupation

may go undetected To avoid this a special provision has to be made in signal control circuits wherever

necessary

The following methods may be adopted for reducing the time lag of track relay

(a) Restrict the over energisation of relay since the release time depends on the initial working current

(b) Connecting a suitable external resistance in series with the relay to keep the LR ratio low

(c) Using relays with minimum contacts as they require lesser operating current keeping the inductance

value low

40 | P a g e

CONCLUSION

Modern signalling is vital for safe and punctual movements of trains In the Indian railways The Signalling

and Telecommunication Department is responsible for providing modern effective and relaible signalling

systems as well as telecommunication systems

The first mode of communication used in Indian Railways was the use of electric telegraph

with the help of Morose code Morose code is the method of providing text information as a series of on-off

tones and lights or clicks that can be directly understood by a skilled listener or observer without special

equipmentEach character (letter or numeral ) is represented by a unique sequence of dots and dashes Later

this system becomes obselete and beggan the era of wireless communication which operated at audio level

frequency range

In wireless communication the significant advances took place the transition to miniature

valves or filament tubesBut this was abandoned too because of excessive current consumption and over

heating of the filament tubes

Fibre-optic communication is a method of transmitting information from one place to another by

sending pulses of light through an optcial fibreThe light forms an electromagnetic carrier wave that is

modulated to carry information First developed in the 1970s fibre optic communication systems has

revolutionized the telecommunications industry and have palyed a major role in the advent of the information

age Because of its advantages over electrical transmissionsoptical fibres have largely replaced copper wire

communications in core networks in the developed world The Indian Railways too is undergoing a transition

from Microwave communication to fibre optic communications

41 | P a g e

BIBLIOGRAPHY AND REFERENCES

1 wwwwikipediacom

2 wwwbritaniccacom

3 wwwirfcacom

4 Motorola GP60 system manual

5 Harris FAS 7000 manual

6 TOSHIBA Manual

26 | P a g e

OPTICAL FIBERrsquoS NUMERICAL APERTURE ( NA )- Multimode optical fiber will only propagate light that enters the fiber within a certain cone known as

the acceptance cone of the fiber The half-angle of this cone is called the acceptance angle (see figure 18)

θmax For step-index multimode fiber the acceptance angle is determined only by the indices of refraction

Where

n is the refractive index of the medium light is traveling before entering the fiber

nf is the refractive index of the fiber core

nc is the refractive index of the cladding

NUMBER OF MODES IN A FIBER - Modes are sometimes characterized by numbers Single mode fibers carry only the lowest-order

mode assigned the number 0 Multimode fibers also carry higher-order modes The number of modes that

can propagate in a fiber depends on the fiberrsquos numerical aperture (or acceptance angle) as well as on its

core diameter and the wavelength of the light For a step-index multimode fiber the number of such modes

Nm

Where

D is the core diameter

λ is the operating wavelength

NA is the numerical aperture (or acceptance angle)

MODE FIELD DIAMETER - All light do not travels through the core of the fiber but is distributed through both the core and the

cladding The mode field is the distribution of light through the core and cladding of a particular fiber

Mode-Field Diameter (MFD) defines the size of the power distribution When coupling light into or out of a

fiber MFD is important in understanding light loss

27 | P a g e

ADVANTAGE OF OFC COMMUNICATION - bull More information carrying capacity Fibers can handle much higher data rates than copper More

information can be sent in a second

bull Free from Electromagnetic and Electrostatic interference Being insulator no electric current flows through

the fibre and due to this reason fibres neither radiate nor pick up electro - magnetic radiation So WPC

CLEARANCE is not required

bull Low attenuation 025 dbkm at 1550 nm Loss in twisted pair and coaxial cable increases with frequency

where as loss in the optical fibre cable remains flat over a wide range of frequencies

bull Use of WDM ndash Switching routing at Optical signal level

bull Self healing rings under NMS control

bull Small size makes fibre cable lighter in weight So easy to handleOptic fibre cable weight (approx)

500 kg km Copper cable weight (approx) 1000 kgkm

The reasons are photons of light in a fibre

do not affect each other as they have no electrical charge and they are not affected by stray photons outside

the fibre But in case of copper electrons move through the cable and these are affected by each other

Optical fibre does not carry any electricity even if the cable is damaged or short circuited it does

not cause any spark or fire hazard

As the fibre do not radiate energy it can not be detected by any nearby antenna or any

other detector The fibres are difficult to tap and therefore excellent for security

As the signal transmission is by digital modulation there is no chance of cross talk in

between channels

Only by adding a few additional terminal and repeater equipments the

capacity of the system can be increased at any time once the cable is laid

ical effects and temperature variations

LIMITATIONS OF OFC -

difficult

- utilised

APPLICATION IN SIGNAL AND TELECOMMUNICATIONS transmission circuits

-haul circuits for linking of telephone exchanges

28 | P a g e

PROPAGATION MODES CONCEPT -

MODE - Mode is an available distribution of electromagnetic field in a plane transverse to the direction of

light propagation Each mode is characterized by frequency polarization electric field strength and

magnetic field strength Available patterns are derived from Maxwellrsquos equations and boundary conditions

LINEARLY POLARIZED (LP) MODE A mode for which the field components in the direction of propagation are small compared to

components perpendicular to that direction An optical fibre supports only different field patterns called as

lsquoLinear Polarizedrsquo or lsquo LPrsquo modes The reasons are

requirements

de

the accrual of power carried by different modes

There are two basic types of fiber Multimode fiber and Single-mode fiber

Multimode fiber is best designed for short transmission distances This is suited for used in LAN systems and

video surveillance Single mode fibre is best designed for longer transmission distances This is suitable for

long distance telephony and multi channel television broadcast systems

29 | P a g e

MULTI MODE FIBER Multimode fiber the first to be manufactured and commercialized simply refers to the fact that

numerous modes or light rays are carried simultaneously through the waveguide Modes result from the fact

that light will only propagate in the fiber core at discrete angles within the cone of acceptance MM fiber type

has a much larger core diameter compared to single-mode fiber allowing for the larger number of modes

and

is easier to couple than single-mode optical fiber Multimode fiber further categorized as Multimode step-

index and Multimode graded index fiber

PROPAGATION THROUGH MMSI FIBER Figure shows the principle of total internal reflection applies to multimode step index fiber Because

the corersquos index of refraction is higher than the claddingrsquos index of refraction the light that enters at less than

the critical angle is guided along the fiber

Three different light waves travel down the fiber One mode travels straight down the center of the

core A second mode travels at a steep angle and bounces back and forth by total internal reflection The third

mode exceeds the critical angle and refracts into the cladding Naturally it can be seen that the second mode

travels a longer distance than the first mode causing the two modes to arrive at separate times

PROBLEMS WITH MMSI FIBER AND SOLUTION This disparity between arrival times of the different light rays is known as dispersion and the result is

a muddied signal at the receiving end It is important to note that high dispersion is an unavoidable

characteristic of multimode step-index fiber The solutions are either use Graded index fiber or Single mode

fiber

PROPAGATION THROUGH MMGI FIBER Multimode Graded-index refers to the fact that the refractive index of the core gradually decreases

farther from the center of the core The increased refraction in the center of the core slows the speed of some

light rays allowing all the light rays to reach the receiving end at approximately the same time reducing

dispersion Figure shows the Light propagation principle through multimode graded-index fiber The corersquos

central refractive index ( nA ) is greater than that of the outer corersquos refractive index ( nB )

It is very clear from the figure the light rays no longer follow straight lines they follow a serpentine path

being gradually bent back toward the center by the continuously declining refractive index This reduces the

arrival time disparity because all modes arrive at about the same time The modes traveling in a straight line

30 | P a g e

are in a higher refractive index so they travel slower than the serpentine modes These travel farther but

move faster in the lower refractive index of the outer core region

PROPAGATION THROUGH SMSI FIBER Single mode fiber has a much smaller core that allows only one mode of light at a time to propagate

through the core The figure shows the single mode fiber

Single-mode fiber exhibits no dispersion caused by multiple modes Single-mode fiber also offers lower fiber

attenuation than multimode fiber Thus more information can be transmitted per unit of time because it can

retain the fidelity of each light pulse over longer distances Like multimode fiber early single-mode fiber was

generally characterized as step-index fiber meaning the refractive index of the fiber core is a step above that

of the cladding rather than graduated as it is in graded-index fiber Modern single-mode fibers have evolved

into more complex designs such as matched clad depressed clad and other exotic structures

SINGLE-MODE FIBER DISADVANTAGES The smaller core diameter makes coupling light into the core more difficult The tolerances for single-

mode connectors and splices are also much more demanding

CUTOFF WAVE LENGTH - Cutoff wavelength is the wavelength above which a single-mode fiber supports and propagates only

one mode of light In other words an optical fiber that is single-mode at a particular wavelength may have

two or more modes at wavelengths lower than the cutoff wavelength The effective cutoff wavelength of a

fiber is dependent on the length of fiber and its deployment The longer the fiber the lower is the effective

cutoff

wavelength The smaller the bend radius of a loop of the fiber the lower is the effective cutoff wavelength If

a fiber is bent in a loop the effective cutoff wavelength is lowered

SIGNAL ATTENUATION IN FIBER - Optical fiber has a number of advantages over copper However it also suffers from degradation

problems which can not be ignored The first of these is loss or attenuation Attenuation is typically the result

of two sub properties They are scattering and absorption Both of which have cumulative effects The second

is

dispersion which is the spreading of the transmitted signal and is analogous to noise

SCATTERING Scattering occurs because of impurities or irregularities in the physical construction of the fiber The

well known form of scattering is Rayleigh Scattering It is caused by metal ions in the silica matrix and

results in light rays being scattered in various directions

31 | P a g e

Scattering limits the use of wavelengths below 800nm The short wavelengths are much affected than longer

wavelengths It is because of Rayleigh scattering that the sky appears to be blue ( shorter wave length ) The

shorter wavelengths ( blue ) of light are scattered more than the longer wavelengths of light

ABSORPTION Absorption results from three factors They are hydroxyl ions ( OH- water ) in the silica impurities

in the silica and incomplete residue from the manufacturing process These impurities tend to absorb the

energy of the transmitted signal and convert it to heat resulting in an overall weakening of the signal The

Hydroxyl absorption occurs at 125 and 139 micro The silica itself starts to absorb energy at 17 micro

because of the natural resonance of the silicon dioxide

MACRO BENDING LOSS Macro-bending loss is caused by bending of the entire fiber axis The bending radius shall not be

sharper than 30d where d is diameter of cable A single bend sharper than 30d can cause loss of 05dB

The fiber may break if bending is ever sharper

MICRO BENDING LOSS Micro-bending loss is caused by micro deformations of fiber axis which leads to failures in achieving

total internal reflection conditions Micro-bends are small scale perturbations along the fiber axis the

amplitude of which are on the order of microns These distortions can cause light to leak out of a fiber

Micro-bending may be induced at very cold temperatures because the glass has a different coefficient of

thermal expansion from the coating and cabling materials At low temperatures the coating and cable

become more rigid and may contract more than the glass Consequently enough load may be exerted on the

glass to cause micro bends

Coating material is selected by manufacturers to minimize loss due to micro-bending The linear thermal

expansion coefficient of coating material shall be compatible with that of fiber

32 | P a g e

DISPERSION Dispersion is the optical term for the spreading of the transmits in the fiber It is the bandwidth

limiting phenomenon and comes in two forms Multimode dispersion and chromatic dispersion Chromatic

dispersion is further subdivided into material dispersion and waveguide dispersion

DISPERSION PHENOMENON IN OPTICAL FIBER Dispersion is the time distortion of an optical signal that results from the differences of time of travel

for different components of that signal typically resulting in pulse broadening As the distance traveled by

the signal is more broadening of pulse is more In digital transmission dispersion limits on the maximum

data rate and the maximum distance ie the information-carrying capacity of a fiber link The interference

from broadened pulse in the next interval shall not lead to erroneous interpretation of received signal

OPTICAL DOMAIN Understanding where attenuation and dispersion problems occur helps optical design engineers

determine the better wavelengths at which information can be transmit taking into account distance type of

fiber and the other factors which can severely affect the integrity of the transmitted signal The graph shown

depicts the optical transmission domain as well as the areas where problems arise The wavelength (nm)

is shown on X-axis and attenuation ( dBkm) is shown on Y-axis

There are four transmission windows appear in the figure The first one is at around 850 nm the

second at 1310nm third at 1550 nm and fourth at 1625 nm The last two labeled as C and L band

respectively The 850 nm wavelength at which the original LED technology operated The second window at

1310 nm has low dispersion The 1550 nm called as C-band is ideal wavelength for long haul

communication systems The network engineers can avoid transmitting signal at 1000 nm where Rayleigh

scattering 1240 and 1390 nm where hydroxyl absorption by water occurs to avoid high degree of loss

Optical fibers also can be manufactured to have low dispersion wavelength in the 1550nm region

which is also the point where silica-based fibers have inherently minimal attenuation These fibers are

referred to as dispersion-shifted fibers and are used in long-distance applications with high bit rates For

33 | P a g e

applications utilizing multiple wavelengths it is undesirable to have the zero dispersion point within the

operating

wavelength range

34 | P a g e

SIGNALLING RELAYS

INTRODUCTION A relay is an electromagnetic device which is used to convey information from one circuit to another

circuit through a set of contact ie front or back contact Constructional and electrically relays may be

divided into DC and AC relays because the means by which the electrical energy in the coil is converted in

to mechanical Energy in order to move the contacts are fundamentally different In DC type the contacts are

carried on an armature forming part of a magnetic circuit in which a field is set up by the current flowing in

the coils In AC types the contacts are attached by a link mechanism to a metal sector disc or cylinder in

which currents are induced by the alternating magnetic field produced by the currents in the coils

Every endeavor has been made to explain the action of each type of relay in the simplest possible manner

Relays are sophisticated switch gears used for remote control and succession control of various

electrical equipment In present days they are widely used because they are capable of protecting the

controlled equipment from cross feeding and overloading even as they cater for speedy operations

Most of the relays in present day signaling are electromagnetic devices although some of the relays control

circuits through electronic components like diodetransistors Integrated Chips etc

Railway signaling relays are unique in that

(a) They operate on low voltage and current

(b) They are more articulate as according to their special features they can work under restrictive conditions

and in any specified manner Virtually they can cater for all situations while contributing to speed and

accuracy in operations

CLASSIFICATION OF SIGNALLING RELAYS (a) According to the method of their mounting or fixture they are classified as

(i) Shelf type Relays which are loosely kept on shelves

(ii) Plug in type Relays which are plugged into a pre- wired plug boards

(b) According to their connection and usage they are classified as

(i) Track relays Relay which is directly connected to the track to detect the presence of vehicle

(ii) Line Relays Other than track relay all are line relays Relays connected to the selection circuit

(c) According to their vitality or importance in ensuring train working safety they are classified as

(i) Vital Relays All relays used for traffic control such as signal point controls track detection etc

(ii) Non-vital Relays Relays which operate control aids and accessories like warnings buzzers

Indications etc

(d) According to their special provisions to ensure reliability of their contacts they are classified as

(i) Proved type are those whose normalization after each operation shall be proved in circuit

controlled by their contacts Contacts in which both the springs have metal surfaces on their tips They may

get fused due to high sparking current across them during operation These may prevent relay normalization

and causes unsafe condition in traffic control To avoid this proving of relay normalization after each

operation is necessary

(ii) Non - proved type Need not to be proved to have been normalized after each operation as their

contacts have at least one non-fusible contact (carbon contact)

(e) According to their feed source relays are broadly classified as

(i) DC relays The relay which requires DC power supply for its operations are called DC relays Among

the DC relays

o DC neutral relays This relay closes the same set of contacts on energization with Normal polarity

or Reverse polarity supply

o Polar Relays This relay closes different set of contacts when energized with Reverse polarity

supply They may or may not have contact to close when deenergized

35 | P a g e

(ii) AC Relay AC Induction motor track relays Time element relays flashing indication control etc

(iii) Electronic Relays DC relays with electronic components in them are called electronic relays

DC NEUTRAL RELAY Each Relay has usually one or two coils with a hollow center to accommodate a coreThe coils are

made up of a large numbers of turns of small gauge soft drawn copper wire The two coils can be connected

in series or parallel according to the requirement of relay resistance The ends of the coils are terminated on

binding post to which the control wires are connected Each coil is placed around a core of specially selected

Iron or steel having high permeability and low retentivity The core should be susceptible to magnetism and

at the same time should have little residual magnetism The cores are connected at the top by a yoke to

complete the magnetism coupling between two ends of coils The bottom of each core is equipped with a

large steel or Iron block known as pole piece or face

A flat piece of Iron or steel called armature is supported by brackets which are securely fastened to

the pole piece The armature yoke and the pole pieces are also made of specially selected iron or steel of the

same quality as the core The armature carries the metallic spring contacts which are insulated from it

The circuit through the coils of the relay is closed It sets up a magnetic flux through the core yoke and the

armature The flux passing between the armature and pole faces causes the armatures get attracted to the pole

faces and armature picks up and closes front contacts When the circuit is opened the magnetic flux collapses

and the armature drops away by gravity from the pole faces the front contacts break and back contacts close

The front and back contacts of the relay can be utilised to make or break other circuits Two stop pins of

nonmagnetic material are fixed either on the armature or pole faces so that the armature cannot

come in contact with the pole faces It is essential to maintain a small air-gap between the armature and pole

faces so that low value of residual magnetism may not retain the armature in picked up position and causes

the relay to fail to drop away with a break in its control circuit

GENERAL USAGE

DC Neutral line relays are most commonly used for Railway Signalling controls and detection

Among them plug-in type relays are preferred in larger installations for space considerations Shelf type

relays are also in use mostly in wayside stations

There are many DC Neutral line relays in use with special features such as

(i) Delayed operation

(ii) Biased DC control

(iii) DC control unaffected by AC interference currents

(iv) Getting latched in operated condition till further feeding and others

Usage of DC polar relays is mostly in conjunction with block instruments that control traffic between

stations AC line relays are almost extinct in installations of British Signalling practice They are however

used for time control operations flashing indication control and such other special purposes in installations

with Siemens signalling practice widely Track relays are used according to the type of track detection

circuits chosen for a given location and context While most of the track circuits are still of the DC working

type requiring DC neutral track relays with them the prospects of their being replaced with Electronic track

circuits directly feeding DC line relays in future are great AC Track Circuits are used in DC Traction area

as conventional DC Track Circuits are not suitable there AC Track relays are used with them almost all of

the induction motor type In the British practice of signalling which was first introduced on Indian Railways

non-proved type relays with carbon to metal switching contacts are generally used for vital controls

They facilitate simple circuit designs But with the advent of German Practice introduced by Ms

Siemens later proved type relays with all metal to metal contacts are widely accepted in spite of

complications in circuit design caused by them A recent introduction is that of the same type relays made by

Ms Integra control However for some time now the appreciable features of both the practices are getting

36 | P a g e

incorporated together in the indigenous designs of signalling by railwaymen With this the usage of all types

of relays anywhere can be found without straight jacketed segration of relay types

CHARACTERSTIC OF ELECTRO-MAGNETIC RELAY The following are the characteristic of electro-magnetic relays A brief study of them helps in

understanding the choice of their components and designs features

1) Force of attraction

2) Effect of air gap

3) Effect of Hysterisis

4) Transient condition

FORCE OF ATTRACTION In any electro-magnetic system the force of attraction is given by

Where B - is the flux density a - is the cross sectional area of the particular part of the magnetic

circuit

In the case of a DC neutral Relay B is proportional to the current that is flowing in the coil

surrounding the electro-magnet and thus the force of the attraction is directly proportional to the square of the

current This square relationship has its own advantage especially in the case of DC track relay in that a

small reduction in the current will have a great effect on the working of the relay Also for a given change of

current the make and the break will be quicker with lesser possibility of arcing

EFFECT OF AIR GAP

Curve lsquoArsquo is magnetisation curve for the iron and is all practical purpose a straight line up to the

saturation point Curve lsquoBrsquo is the magnetisation curve for the open-air gap which is a straight line through

out because per magnetisation curve of the whole

magnetic circuit of the relay and for a given force is the sum of the amp-turns for the iron part and the amp-

turns for the air gap

When the front contacts are open the force required to pick up the armature is shown on curve lsquoCrsquo to be F1

but after the armature has operated it will be separated from the core by stop pins In this position the amp-

turns required to maintain the armature is less as indicated by the dotted line from 1 on curve C to 2 on curve

37 | P a g e

F But actually the current in the coil is unaltered the force on the armature is greater than required as

indicated at 3 on curve F Part of this extra force is used to flex the front contacts sufficiently to give good

contact pressure when it is in energised position

The difference between the pick-up and the drop-away current should be as small as practicable in

track relay to ensure good shunting characteristics This is achieved firstly by the choice of good quality relay

iron and secondly by having a small air gap between armature and core If the air gap is not available then

the residual magnetism fluxes might cause the armature to be retained when the supply is disconnected For

this reason residual pins are provided to ensure a definite minimum air gap in the energised position

EFFECT OF HYSTERISIS

Hysterisis is the property by which the flux produced lags behind the current In the de-energized

condition there will be small residual flux in the core When the voltage is applied to the coils the current in

rising to its steady value first causes the flux to rise from 1 to 2 along the curve At this point the flux density

will be sufficient to attract the armature and reduce the air gap the flux then raise to 3 and continue to 4

which corresponds to the steady current in the coils When the voltage is disconnected the current in falling

caused the flux to fall from 4 to 5 along the curve At this point the flux density will fall below the value

required to maintain the armature which will release thus increasing the air gap and reducing the flux to 6

Finally the

flux will decrease from 6 to 1 where the current will again be zero

The relay core is made of material having high permeability and low retentivity As mentioned in

the IRS specification Electromagnet iron may be in the form of a

(a) Bar of silicon steel

(b) Best Yorkshire wrought iron

(c) Swedish charcoal iron

(d) Electrical steel sheets

` This reduces the difference between pick up value and Drop away value By selecting good quality

core material Percentage release and sensitivity of the relay will be improved

TRANSIENT CONDITION

38 | P a g e

When the voltage is applied or disconnected from the coils it takes some little time before the current

become steady These are known as transient conditionsrdquo and are important so far as track relays are

concerned When the voltage is first applied to the coils the magnetic flux in rising cuts the turns on the

coils and in so doing produces a back EMF that opposes the applied voltage and retards the growth of

current

The growth and decay of flux are decided by the relationship between the inductance and resistance

in the circuit is known as time constant It is not fixed quantity in the case of DC neutral relay This value of lsquo

Lrsquo is less when the relay is in de-energised condition (L1) than when the relay is in energised condition (L2)

The magnitude of flux that is established for a given change of current is different in two cases

When the current reaches the pick up value the armature closes and the inductance is increased to L2

due to reduced air gap the flux per amp is increased The increase in flux increased the back EMF during the

movement of the armature after which the current continuous to raise along a new curve corresponding to the

increased inductance until it reaches the final value (ER) This process is indicated above in fig24

When the supply is disconnected the current is obliviously reduced to zero immediately but the flux

decay comparatively slowly owing to the eddy currents produced in the core by the rapid flux change which

tend to maintain the flux The drop away time on a disconnection is however generally negligible See fig

below

If the relay releases due to the reduction in current from say I 2 to I 1 caused by the application of

shunt resistance (as in the case of track relay ) the time taken is much longer than the relay is simply

disconnected The rate of rise or fall of current during the transient conditions is also depends on exterior

circuit values because L and R apply to the whole circuit The production of eddy current in the core the flux

will decay at a slower rate than the current So that the actual release time will be a little longer than it takes

the current to fall to the release

L= Inductance

39 | P a g e

R= Resistance

It is now clear that to reduce releasing time to a minimum it is necessary that

- The relay iron should have low Hysterisis loss and low retentivity

- The degree of over energization of the relay should be restricted

- Connecting a suitable external resistance in series with the relay to keep LR ratio low

In non RE area for track circuit length less than 100M 9 ohm track relay only to be used Using relay

with minimum contacts as they require lesser current which keeps inductance value low

Train working safety is ensured only if the track relay of shortest length track circuit is released

before a light engine running at a highest permitted speed clears it Otherwise the track circuit occupation

may go undetected To avoid this a special provision has to be made in signal control circuits wherever

necessary

The following methods may be adopted for reducing the time lag of track relay

(a) Restrict the over energisation of relay since the release time depends on the initial working current

(b) Connecting a suitable external resistance in series with the relay to keep the LR ratio low

(c) Using relays with minimum contacts as they require lesser operating current keeping the inductance

value low

40 | P a g e

CONCLUSION

Modern signalling is vital for safe and punctual movements of trains In the Indian railways The Signalling

and Telecommunication Department is responsible for providing modern effective and relaible signalling

systems as well as telecommunication systems

The first mode of communication used in Indian Railways was the use of electric telegraph

with the help of Morose code Morose code is the method of providing text information as a series of on-off

tones and lights or clicks that can be directly understood by a skilled listener or observer without special

equipmentEach character (letter or numeral ) is represented by a unique sequence of dots and dashes Later

this system becomes obselete and beggan the era of wireless communication which operated at audio level

frequency range

In wireless communication the significant advances took place the transition to miniature

valves or filament tubesBut this was abandoned too because of excessive current consumption and over

heating of the filament tubes

Fibre-optic communication is a method of transmitting information from one place to another by

sending pulses of light through an optcial fibreThe light forms an electromagnetic carrier wave that is

modulated to carry information First developed in the 1970s fibre optic communication systems has

revolutionized the telecommunications industry and have palyed a major role in the advent of the information

age Because of its advantages over electrical transmissionsoptical fibres have largely replaced copper wire

communications in core networks in the developed world The Indian Railways too is undergoing a transition

from Microwave communication to fibre optic communications

41 | P a g e

BIBLIOGRAPHY AND REFERENCES

1 wwwwikipediacom

2 wwwbritaniccacom

3 wwwirfcacom

4 Motorola GP60 system manual

5 Harris FAS 7000 manual

6 TOSHIBA Manual

27 | P a g e

ADVANTAGE OF OFC COMMUNICATION - bull More information carrying capacity Fibers can handle much higher data rates than copper More

information can be sent in a second

bull Free from Electromagnetic and Electrostatic interference Being insulator no electric current flows through

the fibre and due to this reason fibres neither radiate nor pick up electro - magnetic radiation So WPC

CLEARANCE is not required

bull Low attenuation 025 dbkm at 1550 nm Loss in twisted pair and coaxial cable increases with frequency

where as loss in the optical fibre cable remains flat over a wide range of frequencies

bull Use of WDM ndash Switching routing at Optical signal level

bull Self healing rings under NMS control

bull Small size makes fibre cable lighter in weight So easy to handleOptic fibre cable weight (approx)

500 kg km Copper cable weight (approx) 1000 kgkm

The reasons are photons of light in a fibre

do not affect each other as they have no electrical charge and they are not affected by stray photons outside

the fibre But in case of copper electrons move through the cable and these are affected by each other

Optical fibre does not carry any electricity even if the cable is damaged or short circuited it does

not cause any spark or fire hazard

As the fibre do not radiate energy it can not be detected by any nearby antenna or any

other detector The fibres are difficult to tap and therefore excellent for security

As the signal transmission is by digital modulation there is no chance of cross talk in

between channels

Only by adding a few additional terminal and repeater equipments the

capacity of the system can be increased at any time once the cable is laid

ical effects and temperature variations

LIMITATIONS OF OFC -

difficult

- utilised

APPLICATION IN SIGNAL AND TELECOMMUNICATIONS transmission circuits

-haul circuits for linking of telephone exchanges

28 | P a g e

PROPAGATION MODES CONCEPT -

MODE - Mode is an available distribution of electromagnetic field in a plane transverse to the direction of

light propagation Each mode is characterized by frequency polarization electric field strength and

magnetic field strength Available patterns are derived from Maxwellrsquos equations and boundary conditions

LINEARLY POLARIZED (LP) MODE A mode for which the field components in the direction of propagation are small compared to

components perpendicular to that direction An optical fibre supports only different field patterns called as

lsquoLinear Polarizedrsquo or lsquo LPrsquo modes The reasons are

requirements

de

the accrual of power carried by different modes

There are two basic types of fiber Multimode fiber and Single-mode fiber

Multimode fiber is best designed for short transmission distances This is suited for used in LAN systems and

video surveillance Single mode fibre is best designed for longer transmission distances This is suitable for

long distance telephony and multi channel television broadcast systems

29 | P a g e

MULTI MODE FIBER Multimode fiber the first to be manufactured and commercialized simply refers to the fact that

numerous modes or light rays are carried simultaneously through the waveguide Modes result from the fact

that light will only propagate in the fiber core at discrete angles within the cone of acceptance MM fiber type

has a much larger core diameter compared to single-mode fiber allowing for the larger number of modes

and

is easier to couple than single-mode optical fiber Multimode fiber further categorized as Multimode step-

index and Multimode graded index fiber

PROPAGATION THROUGH MMSI FIBER Figure shows the principle of total internal reflection applies to multimode step index fiber Because

the corersquos index of refraction is higher than the claddingrsquos index of refraction the light that enters at less than

the critical angle is guided along the fiber

Three different light waves travel down the fiber One mode travels straight down the center of the

core A second mode travels at a steep angle and bounces back and forth by total internal reflection The third

mode exceeds the critical angle and refracts into the cladding Naturally it can be seen that the second mode

travels a longer distance than the first mode causing the two modes to arrive at separate times

PROBLEMS WITH MMSI FIBER AND SOLUTION This disparity between arrival times of the different light rays is known as dispersion and the result is

a muddied signal at the receiving end It is important to note that high dispersion is an unavoidable

characteristic of multimode step-index fiber The solutions are either use Graded index fiber or Single mode

fiber

PROPAGATION THROUGH MMGI FIBER Multimode Graded-index refers to the fact that the refractive index of the core gradually decreases

farther from the center of the core The increased refraction in the center of the core slows the speed of some

light rays allowing all the light rays to reach the receiving end at approximately the same time reducing

dispersion Figure shows the Light propagation principle through multimode graded-index fiber The corersquos

central refractive index ( nA ) is greater than that of the outer corersquos refractive index ( nB )

It is very clear from the figure the light rays no longer follow straight lines they follow a serpentine path

being gradually bent back toward the center by the continuously declining refractive index This reduces the

arrival time disparity because all modes arrive at about the same time The modes traveling in a straight line

30 | P a g e

are in a higher refractive index so they travel slower than the serpentine modes These travel farther but

move faster in the lower refractive index of the outer core region

PROPAGATION THROUGH SMSI FIBER Single mode fiber has a much smaller core that allows only one mode of light at a time to propagate

through the core The figure shows the single mode fiber

Single-mode fiber exhibits no dispersion caused by multiple modes Single-mode fiber also offers lower fiber

attenuation than multimode fiber Thus more information can be transmitted per unit of time because it can

retain the fidelity of each light pulse over longer distances Like multimode fiber early single-mode fiber was

generally characterized as step-index fiber meaning the refractive index of the fiber core is a step above that

of the cladding rather than graduated as it is in graded-index fiber Modern single-mode fibers have evolved

into more complex designs such as matched clad depressed clad and other exotic structures

SINGLE-MODE FIBER DISADVANTAGES The smaller core diameter makes coupling light into the core more difficult The tolerances for single-

mode connectors and splices are also much more demanding

CUTOFF WAVE LENGTH - Cutoff wavelength is the wavelength above which a single-mode fiber supports and propagates only

one mode of light In other words an optical fiber that is single-mode at a particular wavelength may have

two or more modes at wavelengths lower than the cutoff wavelength The effective cutoff wavelength of a

fiber is dependent on the length of fiber and its deployment The longer the fiber the lower is the effective

cutoff

wavelength The smaller the bend radius of a loop of the fiber the lower is the effective cutoff wavelength If

a fiber is bent in a loop the effective cutoff wavelength is lowered

SIGNAL ATTENUATION IN FIBER - Optical fiber has a number of advantages over copper However it also suffers from degradation

problems which can not be ignored The first of these is loss or attenuation Attenuation is typically the result

of two sub properties They are scattering and absorption Both of which have cumulative effects The second

is

dispersion which is the spreading of the transmitted signal and is analogous to noise

SCATTERING Scattering occurs because of impurities or irregularities in the physical construction of the fiber The

well known form of scattering is Rayleigh Scattering It is caused by metal ions in the silica matrix and

results in light rays being scattered in various directions

31 | P a g e

Scattering limits the use of wavelengths below 800nm The short wavelengths are much affected than longer

wavelengths It is because of Rayleigh scattering that the sky appears to be blue ( shorter wave length ) The

shorter wavelengths ( blue ) of light are scattered more than the longer wavelengths of light

ABSORPTION Absorption results from three factors They are hydroxyl ions ( OH- water ) in the silica impurities

in the silica and incomplete residue from the manufacturing process These impurities tend to absorb the

energy of the transmitted signal and convert it to heat resulting in an overall weakening of the signal The

Hydroxyl absorption occurs at 125 and 139 micro The silica itself starts to absorb energy at 17 micro

because of the natural resonance of the silicon dioxide

MACRO BENDING LOSS Macro-bending loss is caused by bending of the entire fiber axis The bending radius shall not be

sharper than 30d where d is diameter of cable A single bend sharper than 30d can cause loss of 05dB

The fiber may break if bending is ever sharper

MICRO BENDING LOSS Micro-bending loss is caused by micro deformations of fiber axis which leads to failures in achieving

total internal reflection conditions Micro-bends are small scale perturbations along the fiber axis the

amplitude of which are on the order of microns These distortions can cause light to leak out of a fiber

Micro-bending may be induced at very cold temperatures because the glass has a different coefficient of

thermal expansion from the coating and cabling materials At low temperatures the coating and cable

become more rigid and may contract more than the glass Consequently enough load may be exerted on the

glass to cause micro bends

Coating material is selected by manufacturers to minimize loss due to micro-bending The linear thermal

expansion coefficient of coating material shall be compatible with that of fiber

32 | P a g e

DISPERSION Dispersion is the optical term for the spreading of the transmits in the fiber It is the bandwidth

limiting phenomenon and comes in two forms Multimode dispersion and chromatic dispersion Chromatic

dispersion is further subdivided into material dispersion and waveguide dispersion

DISPERSION PHENOMENON IN OPTICAL FIBER Dispersion is the time distortion of an optical signal that results from the differences of time of travel

for different components of that signal typically resulting in pulse broadening As the distance traveled by

the signal is more broadening of pulse is more In digital transmission dispersion limits on the maximum

data rate and the maximum distance ie the information-carrying capacity of a fiber link The interference

from broadened pulse in the next interval shall not lead to erroneous interpretation of received signal

OPTICAL DOMAIN Understanding where attenuation and dispersion problems occur helps optical design engineers

determine the better wavelengths at which information can be transmit taking into account distance type of

fiber and the other factors which can severely affect the integrity of the transmitted signal The graph shown

depicts the optical transmission domain as well as the areas where problems arise The wavelength (nm)

is shown on X-axis and attenuation ( dBkm) is shown on Y-axis

There are four transmission windows appear in the figure The first one is at around 850 nm the

second at 1310nm third at 1550 nm and fourth at 1625 nm The last two labeled as C and L band

respectively The 850 nm wavelength at which the original LED technology operated The second window at

1310 nm has low dispersion The 1550 nm called as C-band is ideal wavelength for long haul

communication systems The network engineers can avoid transmitting signal at 1000 nm where Rayleigh

scattering 1240 and 1390 nm where hydroxyl absorption by water occurs to avoid high degree of loss

Optical fibers also can be manufactured to have low dispersion wavelength in the 1550nm region

which is also the point where silica-based fibers have inherently minimal attenuation These fibers are

referred to as dispersion-shifted fibers and are used in long-distance applications with high bit rates For

33 | P a g e

applications utilizing multiple wavelengths it is undesirable to have the zero dispersion point within the

operating

wavelength range

34 | P a g e

SIGNALLING RELAYS

INTRODUCTION A relay is an electromagnetic device which is used to convey information from one circuit to another

circuit through a set of contact ie front or back contact Constructional and electrically relays may be

divided into DC and AC relays because the means by which the electrical energy in the coil is converted in

to mechanical Energy in order to move the contacts are fundamentally different In DC type the contacts are

carried on an armature forming part of a magnetic circuit in which a field is set up by the current flowing in

the coils In AC types the contacts are attached by a link mechanism to a metal sector disc or cylinder in

which currents are induced by the alternating magnetic field produced by the currents in the coils

Every endeavor has been made to explain the action of each type of relay in the simplest possible manner

Relays are sophisticated switch gears used for remote control and succession control of various

electrical equipment In present days they are widely used because they are capable of protecting the

controlled equipment from cross feeding and overloading even as they cater for speedy operations

Most of the relays in present day signaling are electromagnetic devices although some of the relays control

circuits through electronic components like diodetransistors Integrated Chips etc

Railway signaling relays are unique in that

(a) They operate on low voltage and current

(b) They are more articulate as according to their special features they can work under restrictive conditions

and in any specified manner Virtually they can cater for all situations while contributing to speed and

accuracy in operations

CLASSIFICATION OF SIGNALLING RELAYS (a) According to the method of their mounting or fixture they are classified as

(i) Shelf type Relays which are loosely kept on shelves

(ii) Plug in type Relays which are plugged into a pre- wired plug boards

(b) According to their connection and usage they are classified as

(i) Track relays Relay which is directly connected to the track to detect the presence of vehicle

(ii) Line Relays Other than track relay all are line relays Relays connected to the selection circuit

(c) According to their vitality or importance in ensuring train working safety they are classified as

(i) Vital Relays All relays used for traffic control such as signal point controls track detection etc

(ii) Non-vital Relays Relays which operate control aids and accessories like warnings buzzers

Indications etc

(d) According to their special provisions to ensure reliability of their contacts they are classified as

(i) Proved type are those whose normalization after each operation shall be proved in circuit

controlled by their contacts Contacts in which both the springs have metal surfaces on their tips They may

get fused due to high sparking current across them during operation These may prevent relay normalization

and causes unsafe condition in traffic control To avoid this proving of relay normalization after each

operation is necessary

(ii) Non - proved type Need not to be proved to have been normalized after each operation as their

contacts have at least one non-fusible contact (carbon contact)

(e) According to their feed source relays are broadly classified as

(i) DC relays The relay which requires DC power supply for its operations are called DC relays Among

the DC relays

o DC neutral relays This relay closes the same set of contacts on energization with Normal polarity

or Reverse polarity supply

o Polar Relays This relay closes different set of contacts when energized with Reverse polarity

supply They may or may not have contact to close when deenergized

35 | P a g e

(ii) AC Relay AC Induction motor track relays Time element relays flashing indication control etc

(iii) Electronic Relays DC relays with electronic components in them are called electronic relays

DC NEUTRAL RELAY Each Relay has usually one or two coils with a hollow center to accommodate a coreThe coils are

made up of a large numbers of turns of small gauge soft drawn copper wire The two coils can be connected

in series or parallel according to the requirement of relay resistance The ends of the coils are terminated on

binding post to which the control wires are connected Each coil is placed around a core of specially selected

Iron or steel having high permeability and low retentivity The core should be susceptible to magnetism and

at the same time should have little residual magnetism The cores are connected at the top by a yoke to

complete the magnetism coupling between two ends of coils The bottom of each core is equipped with a

large steel or Iron block known as pole piece or face

A flat piece of Iron or steel called armature is supported by brackets which are securely fastened to

the pole piece The armature yoke and the pole pieces are also made of specially selected iron or steel of the

same quality as the core The armature carries the metallic spring contacts which are insulated from it

The circuit through the coils of the relay is closed It sets up a magnetic flux through the core yoke and the

armature The flux passing between the armature and pole faces causes the armatures get attracted to the pole

faces and armature picks up and closes front contacts When the circuit is opened the magnetic flux collapses

and the armature drops away by gravity from the pole faces the front contacts break and back contacts close

The front and back contacts of the relay can be utilised to make or break other circuits Two stop pins of

nonmagnetic material are fixed either on the armature or pole faces so that the armature cannot

come in contact with the pole faces It is essential to maintain a small air-gap between the armature and pole

faces so that low value of residual magnetism may not retain the armature in picked up position and causes

the relay to fail to drop away with a break in its control circuit

GENERAL USAGE

DC Neutral line relays are most commonly used for Railway Signalling controls and detection

Among them plug-in type relays are preferred in larger installations for space considerations Shelf type

relays are also in use mostly in wayside stations

There are many DC Neutral line relays in use with special features such as

(i) Delayed operation

(ii) Biased DC control

(iii) DC control unaffected by AC interference currents

(iv) Getting latched in operated condition till further feeding and others

Usage of DC polar relays is mostly in conjunction with block instruments that control traffic between

stations AC line relays are almost extinct in installations of British Signalling practice They are however

used for time control operations flashing indication control and such other special purposes in installations

with Siemens signalling practice widely Track relays are used according to the type of track detection

circuits chosen for a given location and context While most of the track circuits are still of the DC working

type requiring DC neutral track relays with them the prospects of their being replaced with Electronic track

circuits directly feeding DC line relays in future are great AC Track Circuits are used in DC Traction area

as conventional DC Track Circuits are not suitable there AC Track relays are used with them almost all of

the induction motor type In the British practice of signalling which was first introduced on Indian Railways

non-proved type relays with carbon to metal switching contacts are generally used for vital controls

They facilitate simple circuit designs But with the advent of German Practice introduced by Ms

Siemens later proved type relays with all metal to metal contacts are widely accepted in spite of

complications in circuit design caused by them A recent introduction is that of the same type relays made by

Ms Integra control However for some time now the appreciable features of both the practices are getting

36 | P a g e

incorporated together in the indigenous designs of signalling by railwaymen With this the usage of all types

of relays anywhere can be found without straight jacketed segration of relay types

CHARACTERSTIC OF ELECTRO-MAGNETIC RELAY The following are the characteristic of electro-magnetic relays A brief study of them helps in

understanding the choice of their components and designs features

1) Force of attraction

2) Effect of air gap

3) Effect of Hysterisis

4) Transient condition

FORCE OF ATTRACTION In any electro-magnetic system the force of attraction is given by

Where B - is the flux density a - is the cross sectional area of the particular part of the magnetic

circuit

In the case of a DC neutral Relay B is proportional to the current that is flowing in the coil

surrounding the electro-magnet and thus the force of the attraction is directly proportional to the square of the

current This square relationship has its own advantage especially in the case of DC track relay in that a

small reduction in the current will have a great effect on the working of the relay Also for a given change of

current the make and the break will be quicker with lesser possibility of arcing

EFFECT OF AIR GAP

Curve lsquoArsquo is magnetisation curve for the iron and is all practical purpose a straight line up to the

saturation point Curve lsquoBrsquo is the magnetisation curve for the open-air gap which is a straight line through

out because per magnetisation curve of the whole

magnetic circuit of the relay and for a given force is the sum of the amp-turns for the iron part and the amp-

turns for the air gap

When the front contacts are open the force required to pick up the armature is shown on curve lsquoCrsquo to be F1

but after the armature has operated it will be separated from the core by stop pins In this position the amp-

turns required to maintain the armature is less as indicated by the dotted line from 1 on curve C to 2 on curve

37 | P a g e

F But actually the current in the coil is unaltered the force on the armature is greater than required as

indicated at 3 on curve F Part of this extra force is used to flex the front contacts sufficiently to give good

contact pressure when it is in energised position

The difference between the pick-up and the drop-away current should be as small as practicable in

track relay to ensure good shunting characteristics This is achieved firstly by the choice of good quality relay

iron and secondly by having a small air gap between armature and core If the air gap is not available then

the residual magnetism fluxes might cause the armature to be retained when the supply is disconnected For

this reason residual pins are provided to ensure a definite minimum air gap in the energised position

EFFECT OF HYSTERISIS

Hysterisis is the property by which the flux produced lags behind the current In the de-energized

condition there will be small residual flux in the core When the voltage is applied to the coils the current in

rising to its steady value first causes the flux to rise from 1 to 2 along the curve At this point the flux density

will be sufficient to attract the armature and reduce the air gap the flux then raise to 3 and continue to 4

which corresponds to the steady current in the coils When the voltage is disconnected the current in falling

caused the flux to fall from 4 to 5 along the curve At this point the flux density will fall below the value

required to maintain the armature which will release thus increasing the air gap and reducing the flux to 6

Finally the

flux will decrease from 6 to 1 where the current will again be zero

The relay core is made of material having high permeability and low retentivity As mentioned in

the IRS specification Electromagnet iron may be in the form of a

(a) Bar of silicon steel

(b) Best Yorkshire wrought iron

(c) Swedish charcoal iron

(d) Electrical steel sheets

` This reduces the difference between pick up value and Drop away value By selecting good quality

core material Percentage release and sensitivity of the relay will be improved

TRANSIENT CONDITION

38 | P a g e

When the voltage is applied or disconnected from the coils it takes some little time before the current

become steady These are known as transient conditionsrdquo and are important so far as track relays are

concerned When the voltage is first applied to the coils the magnetic flux in rising cuts the turns on the

coils and in so doing produces a back EMF that opposes the applied voltage and retards the growth of

current

The growth and decay of flux are decided by the relationship between the inductance and resistance

in the circuit is known as time constant It is not fixed quantity in the case of DC neutral relay This value of lsquo

Lrsquo is less when the relay is in de-energised condition (L1) than when the relay is in energised condition (L2)

The magnitude of flux that is established for a given change of current is different in two cases

When the current reaches the pick up value the armature closes and the inductance is increased to L2

due to reduced air gap the flux per amp is increased The increase in flux increased the back EMF during the

movement of the armature after which the current continuous to raise along a new curve corresponding to the

increased inductance until it reaches the final value (ER) This process is indicated above in fig24

When the supply is disconnected the current is obliviously reduced to zero immediately but the flux

decay comparatively slowly owing to the eddy currents produced in the core by the rapid flux change which

tend to maintain the flux The drop away time on a disconnection is however generally negligible See fig

below

If the relay releases due to the reduction in current from say I 2 to I 1 caused by the application of

shunt resistance (as in the case of track relay ) the time taken is much longer than the relay is simply

disconnected The rate of rise or fall of current during the transient conditions is also depends on exterior

circuit values because L and R apply to the whole circuit The production of eddy current in the core the flux

will decay at a slower rate than the current So that the actual release time will be a little longer than it takes

the current to fall to the release

L= Inductance

39 | P a g e

R= Resistance

It is now clear that to reduce releasing time to a minimum it is necessary that

- The relay iron should have low Hysterisis loss and low retentivity

- The degree of over energization of the relay should be restricted

- Connecting a suitable external resistance in series with the relay to keep LR ratio low

In non RE area for track circuit length less than 100M 9 ohm track relay only to be used Using relay

with minimum contacts as they require lesser current which keeps inductance value low

Train working safety is ensured only if the track relay of shortest length track circuit is released

before a light engine running at a highest permitted speed clears it Otherwise the track circuit occupation

may go undetected To avoid this a special provision has to be made in signal control circuits wherever

necessary

The following methods may be adopted for reducing the time lag of track relay

(a) Restrict the over energisation of relay since the release time depends on the initial working current

(b) Connecting a suitable external resistance in series with the relay to keep the LR ratio low

(c) Using relays with minimum contacts as they require lesser operating current keeping the inductance

value low

40 | P a g e

CONCLUSION

Modern signalling is vital for safe and punctual movements of trains In the Indian railways The Signalling

and Telecommunication Department is responsible for providing modern effective and relaible signalling

systems as well as telecommunication systems

The first mode of communication used in Indian Railways was the use of electric telegraph

with the help of Morose code Morose code is the method of providing text information as a series of on-off

tones and lights or clicks that can be directly understood by a skilled listener or observer without special

equipmentEach character (letter or numeral ) is represented by a unique sequence of dots and dashes Later

this system becomes obselete and beggan the era of wireless communication which operated at audio level

frequency range

In wireless communication the significant advances took place the transition to miniature

valves or filament tubesBut this was abandoned too because of excessive current consumption and over

heating of the filament tubes

Fibre-optic communication is a method of transmitting information from one place to another by

sending pulses of light through an optcial fibreThe light forms an electromagnetic carrier wave that is

modulated to carry information First developed in the 1970s fibre optic communication systems has

revolutionized the telecommunications industry and have palyed a major role in the advent of the information

age Because of its advantages over electrical transmissionsoptical fibres have largely replaced copper wire

communications in core networks in the developed world The Indian Railways too is undergoing a transition

from Microwave communication to fibre optic communications

41 | P a g e

BIBLIOGRAPHY AND REFERENCES

1 wwwwikipediacom

2 wwwbritaniccacom

3 wwwirfcacom

4 Motorola GP60 system manual

5 Harris FAS 7000 manual

6 TOSHIBA Manual

28 | P a g e

PROPAGATION MODES CONCEPT -

MODE - Mode is an available distribution of electromagnetic field in a plane transverse to the direction of

light propagation Each mode is characterized by frequency polarization electric field strength and

magnetic field strength Available patterns are derived from Maxwellrsquos equations and boundary conditions

LINEARLY POLARIZED (LP) MODE A mode for which the field components in the direction of propagation are small compared to

components perpendicular to that direction An optical fibre supports only different field patterns called as

lsquoLinear Polarizedrsquo or lsquo LPrsquo modes The reasons are

requirements

de

the accrual of power carried by different modes

There are two basic types of fiber Multimode fiber and Single-mode fiber

Multimode fiber is best designed for short transmission distances This is suited for used in LAN systems and

video surveillance Single mode fibre is best designed for longer transmission distances This is suitable for

long distance telephony and multi channel television broadcast systems

29 | P a g e

MULTI MODE FIBER Multimode fiber the first to be manufactured and commercialized simply refers to the fact that

numerous modes or light rays are carried simultaneously through the waveguide Modes result from the fact

that light will only propagate in the fiber core at discrete angles within the cone of acceptance MM fiber type

has a much larger core diameter compared to single-mode fiber allowing for the larger number of modes

and

is easier to couple than single-mode optical fiber Multimode fiber further categorized as Multimode step-

index and Multimode graded index fiber

PROPAGATION THROUGH MMSI FIBER Figure shows the principle of total internal reflection applies to multimode step index fiber Because

the corersquos index of refraction is higher than the claddingrsquos index of refraction the light that enters at less than

the critical angle is guided along the fiber

Three different light waves travel down the fiber One mode travels straight down the center of the

core A second mode travels at a steep angle and bounces back and forth by total internal reflection The third

mode exceeds the critical angle and refracts into the cladding Naturally it can be seen that the second mode

travels a longer distance than the first mode causing the two modes to arrive at separate times

PROBLEMS WITH MMSI FIBER AND SOLUTION This disparity between arrival times of the different light rays is known as dispersion and the result is

a muddied signal at the receiving end It is important to note that high dispersion is an unavoidable

characteristic of multimode step-index fiber The solutions are either use Graded index fiber or Single mode

fiber

PROPAGATION THROUGH MMGI FIBER Multimode Graded-index refers to the fact that the refractive index of the core gradually decreases

farther from the center of the core The increased refraction in the center of the core slows the speed of some

light rays allowing all the light rays to reach the receiving end at approximately the same time reducing

dispersion Figure shows the Light propagation principle through multimode graded-index fiber The corersquos

central refractive index ( nA ) is greater than that of the outer corersquos refractive index ( nB )

It is very clear from the figure the light rays no longer follow straight lines they follow a serpentine path

being gradually bent back toward the center by the continuously declining refractive index This reduces the

arrival time disparity because all modes arrive at about the same time The modes traveling in a straight line

30 | P a g e

are in a higher refractive index so they travel slower than the serpentine modes These travel farther but

move faster in the lower refractive index of the outer core region

PROPAGATION THROUGH SMSI FIBER Single mode fiber has a much smaller core that allows only one mode of light at a time to propagate

through the core The figure shows the single mode fiber

Single-mode fiber exhibits no dispersion caused by multiple modes Single-mode fiber also offers lower fiber

attenuation than multimode fiber Thus more information can be transmitted per unit of time because it can

retain the fidelity of each light pulse over longer distances Like multimode fiber early single-mode fiber was

generally characterized as step-index fiber meaning the refractive index of the fiber core is a step above that

of the cladding rather than graduated as it is in graded-index fiber Modern single-mode fibers have evolved

into more complex designs such as matched clad depressed clad and other exotic structures

SINGLE-MODE FIBER DISADVANTAGES The smaller core diameter makes coupling light into the core more difficult The tolerances for single-

mode connectors and splices are also much more demanding

CUTOFF WAVE LENGTH - Cutoff wavelength is the wavelength above which a single-mode fiber supports and propagates only

one mode of light In other words an optical fiber that is single-mode at a particular wavelength may have

two or more modes at wavelengths lower than the cutoff wavelength The effective cutoff wavelength of a

fiber is dependent on the length of fiber and its deployment The longer the fiber the lower is the effective

cutoff

wavelength The smaller the bend radius of a loop of the fiber the lower is the effective cutoff wavelength If

a fiber is bent in a loop the effective cutoff wavelength is lowered

SIGNAL ATTENUATION IN FIBER - Optical fiber has a number of advantages over copper However it also suffers from degradation

problems which can not be ignored The first of these is loss or attenuation Attenuation is typically the result

of two sub properties They are scattering and absorption Both of which have cumulative effects The second

is

dispersion which is the spreading of the transmitted signal and is analogous to noise

SCATTERING Scattering occurs because of impurities or irregularities in the physical construction of the fiber The

well known form of scattering is Rayleigh Scattering It is caused by metal ions in the silica matrix and

results in light rays being scattered in various directions

31 | P a g e

Scattering limits the use of wavelengths below 800nm The short wavelengths are much affected than longer

wavelengths It is because of Rayleigh scattering that the sky appears to be blue ( shorter wave length ) The

shorter wavelengths ( blue ) of light are scattered more than the longer wavelengths of light

ABSORPTION Absorption results from three factors They are hydroxyl ions ( OH- water ) in the silica impurities

in the silica and incomplete residue from the manufacturing process These impurities tend to absorb the

energy of the transmitted signal and convert it to heat resulting in an overall weakening of the signal The

Hydroxyl absorption occurs at 125 and 139 micro The silica itself starts to absorb energy at 17 micro

because of the natural resonance of the silicon dioxide

MACRO BENDING LOSS Macro-bending loss is caused by bending of the entire fiber axis The bending radius shall not be

sharper than 30d where d is diameter of cable A single bend sharper than 30d can cause loss of 05dB

The fiber may break if bending is ever sharper

MICRO BENDING LOSS Micro-bending loss is caused by micro deformations of fiber axis which leads to failures in achieving

total internal reflection conditions Micro-bends are small scale perturbations along the fiber axis the

amplitude of which are on the order of microns These distortions can cause light to leak out of a fiber

Micro-bending may be induced at very cold temperatures because the glass has a different coefficient of

thermal expansion from the coating and cabling materials At low temperatures the coating and cable

become more rigid and may contract more than the glass Consequently enough load may be exerted on the

glass to cause micro bends

Coating material is selected by manufacturers to minimize loss due to micro-bending The linear thermal

expansion coefficient of coating material shall be compatible with that of fiber

32 | P a g e

DISPERSION Dispersion is the optical term for the spreading of the transmits in the fiber It is the bandwidth

limiting phenomenon and comes in two forms Multimode dispersion and chromatic dispersion Chromatic

dispersion is further subdivided into material dispersion and waveguide dispersion

DISPERSION PHENOMENON IN OPTICAL FIBER Dispersion is the time distortion of an optical signal that results from the differences of time of travel

for different components of that signal typically resulting in pulse broadening As the distance traveled by

the signal is more broadening of pulse is more In digital transmission dispersion limits on the maximum

data rate and the maximum distance ie the information-carrying capacity of a fiber link The interference

from broadened pulse in the next interval shall not lead to erroneous interpretation of received signal

OPTICAL DOMAIN Understanding where attenuation and dispersion problems occur helps optical design engineers

determine the better wavelengths at which information can be transmit taking into account distance type of

fiber and the other factors which can severely affect the integrity of the transmitted signal The graph shown

depicts the optical transmission domain as well as the areas where problems arise The wavelength (nm)

is shown on X-axis and attenuation ( dBkm) is shown on Y-axis

There are four transmission windows appear in the figure The first one is at around 850 nm the

second at 1310nm third at 1550 nm and fourth at 1625 nm The last two labeled as C and L band

respectively The 850 nm wavelength at which the original LED technology operated The second window at

1310 nm has low dispersion The 1550 nm called as C-band is ideal wavelength for long haul

communication systems The network engineers can avoid transmitting signal at 1000 nm where Rayleigh

scattering 1240 and 1390 nm where hydroxyl absorption by water occurs to avoid high degree of loss

Optical fibers also can be manufactured to have low dispersion wavelength in the 1550nm region

which is also the point where silica-based fibers have inherently minimal attenuation These fibers are

referred to as dispersion-shifted fibers and are used in long-distance applications with high bit rates For

33 | P a g e

applications utilizing multiple wavelengths it is undesirable to have the zero dispersion point within the

operating

wavelength range

34 | P a g e

SIGNALLING RELAYS

INTRODUCTION A relay is an electromagnetic device which is used to convey information from one circuit to another

circuit through a set of contact ie front or back contact Constructional and electrically relays may be

divided into DC and AC relays because the means by which the electrical energy in the coil is converted in

to mechanical Energy in order to move the contacts are fundamentally different In DC type the contacts are

carried on an armature forming part of a magnetic circuit in which a field is set up by the current flowing in

the coils In AC types the contacts are attached by a link mechanism to a metal sector disc or cylinder in

which currents are induced by the alternating magnetic field produced by the currents in the coils

Every endeavor has been made to explain the action of each type of relay in the simplest possible manner

Relays are sophisticated switch gears used for remote control and succession control of various

electrical equipment In present days they are widely used because they are capable of protecting the

controlled equipment from cross feeding and overloading even as they cater for speedy operations

Most of the relays in present day signaling are electromagnetic devices although some of the relays control

circuits through electronic components like diodetransistors Integrated Chips etc

Railway signaling relays are unique in that

(a) They operate on low voltage and current

(b) They are more articulate as according to their special features they can work under restrictive conditions

and in any specified manner Virtually they can cater for all situations while contributing to speed and

accuracy in operations

CLASSIFICATION OF SIGNALLING RELAYS (a) According to the method of their mounting or fixture they are classified as

(i) Shelf type Relays which are loosely kept on shelves

(ii) Plug in type Relays which are plugged into a pre- wired plug boards

(b) According to their connection and usage they are classified as

(i) Track relays Relay which is directly connected to the track to detect the presence of vehicle

(ii) Line Relays Other than track relay all are line relays Relays connected to the selection circuit

(c) According to their vitality or importance in ensuring train working safety they are classified as

(i) Vital Relays All relays used for traffic control such as signal point controls track detection etc

(ii) Non-vital Relays Relays which operate control aids and accessories like warnings buzzers

Indications etc

(d) According to their special provisions to ensure reliability of their contacts they are classified as

(i) Proved type are those whose normalization after each operation shall be proved in circuit

controlled by their contacts Contacts in which both the springs have metal surfaces on their tips They may

get fused due to high sparking current across them during operation These may prevent relay normalization

and causes unsafe condition in traffic control To avoid this proving of relay normalization after each

operation is necessary

(ii) Non - proved type Need not to be proved to have been normalized after each operation as their

contacts have at least one non-fusible contact (carbon contact)

(e) According to their feed source relays are broadly classified as

(i) DC relays The relay which requires DC power supply for its operations are called DC relays Among

the DC relays

o DC neutral relays This relay closes the same set of contacts on energization with Normal polarity

or Reverse polarity supply

o Polar Relays This relay closes different set of contacts when energized with Reverse polarity

supply They may or may not have contact to close when deenergized

35 | P a g e

(ii) AC Relay AC Induction motor track relays Time element relays flashing indication control etc

(iii) Electronic Relays DC relays with electronic components in them are called electronic relays

DC NEUTRAL RELAY Each Relay has usually one or two coils with a hollow center to accommodate a coreThe coils are

made up of a large numbers of turns of small gauge soft drawn copper wire The two coils can be connected

in series or parallel according to the requirement of relay resistance The ends of the coils are terminated on

binding post to which the control wires are connected Each coil is placed around a core of specially selected

Iron or steel having high permeability and low retentivity The core should be susceptible to magnetism and

at the same time should have little residual magnetism The cores are connected at the top by a yoke to

complete the magnetism coupling between two ends of coils The bottom of each core is equipped with a

large steel or Iron block known as pole piece or face

A flat piece of Iron or steel called armature is supported by brackets which are securely fastened to

the pole piece The armature yoke and the pole pieces are also made of specially selected iron or steel of the

same quality as the core The armature carries the metallic spring contacts which are insulated from it

The circuit through the coils of the relay is closed It sets up a magnetic flux through the core yoke and the

armature The flux passing between the armature and pole faces causes the armatures get attracted to the pole

faces and armature picks up and closes front contacts When the circuit is opened the magnetic flux collapses

and the armature drops away by gravity from the pole faces the front contacts break and back contacts close

The front and back contacts of the relay can be utilised to make or break other circuits Two stop pins of

nonmagnetic material are fixed either on the armature or pole faces so that the armature cannot

come in contact with the pole faces It is essential to maintain a small air-gap between the armature and pole

faces so that low value of residual magnetism may not retain the armature in picked up position and causes

the relay to fail to drop away with a break in its control circuit

GENERAL USAGE

DC Neutral line relays are most commonly used for Railway Signalling controls and detection

Among them plug-in type relays are preferred in larger installations for space considerations Shelf type

relays are also in use mostly in wayside stations

There are many DC Neutral line relays in use with special features such as

(i) Delayed operation

(ii) Biased DC control

(iii) DC control unaffected by AC interference currents

(iv) Getting latched in operated condition till further feeding and others

Usage of DC polar relays is mostly in conjunction with block instruments that control traffic between

stations AC line relays are almost extinct in installations of British Signalling practice They are however

used for time control operations flashing indication control and such other special purposes in installations

with Siemens signalling practice widely Track relays are used according to the type of track detection

circuits chosen for a given location and context While most of the track circuits are still of the DC working

type requiring DC neutral track relays with them the prospects of their being replaced with Electronic track

circuits directly feeding DC line relays in future are great AC Track Circuits are used in DC Traction area

as conventional DC Track Circuits are not suitable there AC Track relays are used with them almost all of

the induction motor type In the British practice of signalling which was first introduced on Indian Railways

non-proved type relays with carbon to metal switching contacts are generally used for vital controls

They facilitate simple circuit designs But with the advent of German Practice introduced by Ms

Siemens later proved type relays with all metal to metal contacts are widely accepted in spite of

complications in circuit design caused by them A recent introduction is that of the same type relays made by

Ms Integra control However for some time now the appreciable features of both the practices are getting

36 | P a g e

incorporated together in the indigenous designs of signalling by railwaymen With this the usage of all types

of relays anywhere can be found without straight jacketed segration of relay types

CHARACTERSTIC OF ELECTRO-MAGNETIC RELAY The following are the characteristic of electro-magnetic relays A brief study of them helps in

understanding the choice of their components and designs features

1) Force of attraction

2) Effect of air gap

3) Effect of Hysterisis

4) Transient condition

FORCE OF ATTRACTION In any electro-magnetic system the force of attraction is given by

Where B - is the flux density a - is the cross sectional area of the particular part of the magnetic

circuit

In the case of a DC neutral Relay B is proportional to the current that is flowing in the coil

surrounding the electro-magnet and thus the force of the attraction is directly proportional to the square of the

current This square relationship has its own advantage especially in the case of DC track relay in that a

small reduction in the current will have a great effect on the working of the relay Also for a given change of

current the make and the break will be quicker with lesser possibility of arcing

EFFECT OF AIR GAP

Curve lsquoArsquo is magnetisation curve for the iron and is all practical purpose a straight line up to the

saturation point Curve lsquoBrsquo is the magnetisation curve for the open-air gap which is a straight line through

out because per magnetisation curve of the whole

magnetic circuit of the relay and for a given force is the sum of the amp-turns for the iron part and the amp-

turns for the air gap

When the front contacts are open the force required to pick up the armature is shown on curve lsquoCrsquo to be F1

but after the armature has operated it will be separated from the core by stop pins In this position the amp-

turns required to maintain the armature is less as indicated by the dotted line from 1 on curve C to 2 on curve

37 | P a g e

F But actually the current in the coil is unaltered the force on the armature is greater than required as

indicated at 3 on curve F Part of this extra force is used to flex the front contacts sufficiently to give good

contact pressure when it is in energised position

The difference between the pick-up and the drop-away current should be as small as practicable in

track relay to ensure good shunting characteristics This is achieved firstly by the choice of good quality relay

iron and secondly by having a small air gap between armature and core If the air gap is not available then

the residual magnetism fluxes might cause the armature to be retained when the supply is disconnected For

this reason residual pins are provided to ensure a definite minimum air gap in the energised position

EFFECT OF HYSTERISIS

Hysterisis is the property by which the flux produced lags behind the current In the de-energized

condition there will be small residual flux in the core When the voltage is applied to the coils the current in

rising to its steady value first causes the flux to rise from 1 to 2 along the curve At this point the flux density

will be sufficient to attract the armature and reduce the air gap the flux then raise to 3 and continue to 4

which corresponds to the steady current in the coils When the voltage is disconnected the current in falling

caused the flux to fall from 4 to 5 along the curve At this point the flux density will fall below the value

required to maintain the armature which will release thus increasing the air gap and reducing the flux to 6

Finally the

flux will decrease from 6 to 1 where the current will again be zero

The relay core is made of material having high permeability and low retentivity As mentioned in

the IRS specification Electromagnet iron may be in the form of a

(a) Bar of silicon steel

(b) Best Yorkshire wrought iron

(c) Swedish charcoal iron

(d) Electrical steel sheets

` This reduces the difference between pick up value and Drop away value By selecting good quality

core material Percentage release and sensitivity of the relay will be improved

TRANSIENT CONDITION

38 | P a g e

When the voltage is applied or disconnected from the coils it takes some little time before the current

become steady These are known as transient conditionsrdquo and are important so far as track relays are

concerned When the voltage is first applied to the coils the magnetic flux in rising cuts the turns on the

coils and in so doing produces a back EMF that opposes the applied voltage and retards the growth of

current

The growth and decay of flux are decided by the relationship between the inductance and resistance

in the circuit is known as time constant It is not fixed quantity in the case of DC neutral relay This value of lsquo

Lrsquo is less when the relay is in de-energised condition (L1) than when the relay is in energised condition (L2)

The magnitude of flux that is established for a given change of current is different in two cases

When the current reaches the pick up value the armature closes and the inductance is increased to L2

due to reduced air gap the flux per amp is increased The increase in flux increased the back EMF during the

movement of the armature after which the current continuous to raise along a new curve corresponding to the

increased inductance until it reaches the final value (ER) This process is indicated above in fig24

When the supply is disconnected the current is obliviously reduced to zero immediately but the flux

decay comparatively slowly owing to the eddy currents produced in the core by the rapid flux change which

tend to maintain the flux The drop away time on a disconnection is however generally negligible See fig

below

If the relay releases due to the reduction in current from say I 2 to I 1 caused by the application of

shunt resistance (as in the case of track relay ) the time taken is much longer than the relay is simply

disconnected The rate of rise or fall of current during the transient conditions is also depends on exterior

circuit values because L and R apply to the whole circuit The production of eddy current in the core the flux

will decay at a slower rate than the current So that the actual release time will be a little longer than it takes

the current to fall to the release

L= Inductance

39 | P a g e

R= Resistance

It is now clear that to reduce releasing time to a minimum it is necessary that

- The relay iron should have low Hysterisis loss and low retentivity

- The degree of over energization of the relay should be restricted

- Connecting a suitable external resistance in series with the relay to keep LR ratio low

In non RE area for track circuit length less than 100M 9 ohm track relay only to be used Using relay

with minimum contacts as they require lesser current which keeps inductance value low

Train working safety is ensured only if the track relay of shortest length track circuit is released

before a light engine running at a highest permitted speed clears it Otherwise the track circuit occupation

may go undetected To avoid this a special provision has to be made in signal control circuits wherever

necessary

The following methods may be adopted for reducing the time lag of track relay

(a) Restrict the over energisation of relay since the release time depends on the initial working current

(b) Connecting a suitable external resistance in series with the relay to keep the LR ratio low

(c) Using relays with minimum contacts as they require lesser operating current keeping the inductance

value low

40 | P a g e

CONCLUSION

Modern signalling is vital for safe and punctual movements of trains In the Indian railways The Signalling

and Telecommunication Department is responsible for providing modern effective and relaible signalling

systems as well as telecommunication systems

The first mode of communication used in Indian Railways was the use of electric telegraph

with the help of Morose code Morose code is the method of providing text information as a series of on-off

tones and lights or clicks that can be directly understood by a skilled listener or observer without special

equipmentEach character (letter or numeral ) is represented by a unique sequence of dots and dashes Later

this system becomes obselete and beggan the era of wireless communication which operated at audio level

frequency range

In wireless communication the significant advances took place the transition to miniature

valves or filament tubesBut this was abandoned too because of excessive current consumption and over

heating of the filament tubes

Fibre-optic communication is a method of transmitting information from one place to another by

sending pulses of light through an optcial fibreThe light forms an electromagnetic carrier wave that is

modulated to carry information First developed in the 1970s fibre optic communication systems has

revolutionized the telecommunications industry and have palyed a major role in the advent of the information

age Because of its advantages over electrical transmissionsoptical fibres have largely replaced copper wire

communications in core networks in the developed world The Indian Railways too is undergoing a transition

from Microwave communication to fibre optic communications

41 | P a g e

BIBLIOGRAPHY AND REFERENCES

1 wwwwikipediacom

2 wwwbritaniccacom

3 wwwirfcacom

4 Motorola GP60 system manual

5 Harris FAS 7000 manual

6 TOSHIBA Manual

29 | P a g e

MULTI MODE FIBER Multimode fiber the first to be manufactured and commercialized simply refers to the fact that

numerous modes or light rays are carried simultaneously through the waveguide Modes result from the fact

that light will only propagate in the fiber core at discrete angles within the cone of acceptance MM fiber type

has a much larger core diameter compared to single-mode fiber allowing for the larger number of modes

and

is easier to couple than single-mode optical fiber Multimode fiber further categorized as Multimode step-

index and Multimode graded index fiber

PROPAGATION THROUGH MMSI FIBER Figure shows the principle of total internal reflection applies to multimode step index fiber Because

the corersquos index of refraction is higher than the claddingrsquos index of refraction the light that enters at less than

the critical angle is guided along the fiber

Three different light waves travel down the fiber One mode travels straight down the center of the

core A second mode travels at a steep angle and bounces back and forth by total internal reflection The third

mode exceeds the critical angle and refracts into the cladding Naturally it can be seen that the second mode

travels a longer distance than the first mode causing the two modes to arrive at separate times

PROBLEMS WITH MMSI FIBER AND SOLUTION This disparity between arrival times of the different light rays is known as dispersion and the result is

a muddied signal at the receiving end It is important to note that high dispersion is an unavoidable

characteristic of multimode step-index fiber The solutions are either use Graded index fiber or Single mode

fiber

PROPAGATION THROUGH MMGI FIBER Multimode Graded-index refers to the fact that the refractive index of the core gradually decreases

farther from the center of the core The increased refraction in the center of the core slows the speed of some

light rays allowing all the light rays to reach the receiving end at approximately the same time reducing

dispersion Figure shows the Light propagation principle through multimode graded-index fiber The corersquos

central refractive index ( nA ) is greater than that of the outer corersquos refractive index ( nB )

It is very clear from the figure the light rays no longer follow straight lines they follow a serpentine path

being gradually bent back toward the center by the continuously declining refractive index This reduces the

arrival time disparity because all modes arrive at about the same time The modes traveling in a straight line

30 | P a g e

are in a higher refractive index so they travel slower than the serpentine modes These travel farther but

move faster in the lower refractive index of the outer core region

PROPAGATION THROUGH SMSI FIBER Single mode fiber has a much smaller core that allows only one mode of light at a time to propagate

through the core The figure shows the single mode fiber

Single-mode fiber exhibits no dispersion caused by multiple modes Single-mode fiber also offers lower fiber

attenuation than multimode fiber Thus more information can be transmitted per unit of time because it can

retain the fidelity of each light pulse over longer distances Like multimode fiber early single-mode fiber was

generally characterized as step-index fiber meaning the refractive index of the fiber core is a step above that

of the cladding rather than graduated as it is in graded-index fiber Modern single-mode fibers have evolved

into more complex designs such as matched clad depressed clad and other exotic structures

SINGLE-MODE FIBER DISADVANTAGES The smaller core diameter makes coupling light into the core more difficult The tolerances for single-

mode connectors and splices are also much more demanding

CUTOFF WAVE LENGTH - Cutoff wavelength is the wavelength above which a single-mode fiber supports and propagates only

one mode of light In other words an optical fiber that is single-mode at a particular wavelength may have

two or more modes at wavelengths lower than the cutoff wavelength The effective cutoff wavelength of a

fiber is dependent on the length of fiber and its deployment The longer the fiber the lower is the effective

cutoff

wavelength The smaller the bend radius of a loop of the fiber the lower is the effective cutoff wavelength If

a fiber is bent in a loop the effective cutoff wavelength is lowered

SIGNAL ATTENUATION IN FIBER - Optical fiber has a number of advantages over copper However it also suffers from degradation

problems which can not be ignored The first of these is loss or attenuation Attenuation is typically the result

of two sub properties They are scattering and absorption Both of which have cumulative effects The second

is

dispersion which is the spreading of the transmitted signal and is analogous to noise

SCATTERING Scattering occurs because of impurities or irregularities in the physical construction of the fiber The

well known form of scattering is Rayleigh Scattering It is caused by metal ions in the silica matrix and

results in light rays being scattered in various directions

31 | P a g e

Scattering limits the use of wavelengths below 800nm The short wavelengths are much affected than longer

wavelengths It is because of Rayleigh scattering that the sky appears to be blue ( shorter wave length ) The

shorter wavelengths ( blue ) of light are scattered more than the longer wavelengths of light

ABSORPTION Absorption results from three factors They are hydroxyl ions ( OH- water ) in the silica impurities

in the silica and incomplete residue from the manufacturing process These impurities tend to absorb the

energy of the transmitted signal and convert it to heat resulting in an overall weakening of the signal The

Hydroxyl absorption occurs at 125 and 139 micro The silica itself starts to absorb energy at 17 micro

because of the natural resonance of the silicon dioxide

MACRO BENDING LOSS Macro-bending loss is caused by bending of the entire fiber axis The bending radius shall not be

sharper than 30d where d is diameter of cable A single bend sharper than 30d can cause loss of 05dB

The fiber may break if bending is ever sharper

MICRO BENDING LOSS Micro-bending loss is caused by micro deformations of fiber axis which leads to failures in achieving

total internal reflection conditions Micro-bends are small scale perturbations along the fiber axis the

amplitude of which are on the order of microns These distortions can cause light to leak out of a fiber

Micro-bending may be induced at very cold temperatures because the glass has a different coefficient of

thermal expansion from the coating and cabling materials At low temperatures the coating and cable

become more rigid and may contract more than the glass Consequently enough load may be exerted on the

glass to cause micro bends

Coating material is selected by manufacturers to minimize loss due to micro-bending The linear thermal

expansion coefficient of coating material shall be compatible with that of fiber

32 | P a g e

DISPERSION Dispersion is the optical term for the spreading of the transmits in the fiber It is the bandwidth

limiting phenomenon and comes in two forms Multimode dispersion and chromatic dispersion Chromatic

dispersion is further subdivided into material dispersion and waveguide dispersion

DISPERSION PHENOMENON IN OPTICAL FIBER Dispersion is the time distortion of an optical signal that results from the differences of time of travel

for different components of that signal typically resulting in pulse broadening As the distance traveled by

the signal is more broadening of pulse is more In digital transmission dispersion limits on the maximum

data rate and the maximum distance ie the information-carrying capacity of a fiber link The interference

from broadened pulse in the next interval shall not lead to erroneous interpretation of received signal

OPTICAL DOMAIN Understanding where attenuation and dispersion problems occur helps optical design engineers

determine the better wavelengths at which information can be transmit taking into account distance type of

fiber and the other factors which can severely affect the integrity of the transmitted signal The graph shown

depicts the optical transmission domain as well as the areas where problems arise The wavelength (nm)

is shown on X-axis and attenuation ( dBkm) is shown on Y-axis

There are four transmission windows appear in the figure The first one is at around 850 nm the

second at 1310nm third at 1550 nm and fourth at 1625 nm The last two labeled as C and L band

respectively The 850 nm wavelength at which the original LED technology operated The second window at

1310 nm has low dispersion The 1550 nm called as C-band is ideal wavelength for long haul

communication systems The network engineers can avoid transmitting signal at 1000 nm where Rayleigh

scattering 1240 and 1390 nm where hydroxyl absorption by water occurs to avoid high degree of loss

Optical fibers also can be manufactured to have low dispersion wavelength in the 1550nm region

which is also the point where silica-based fibers have inherently minimal attenuation These fibers are

referred to as dispersion-shifted fibers and are used in long-distance applications with high bit rates For

33 | P a g e

applications utilizing multiple wavelengths it is undesirable to have the zero dispersion point within the

operating

wavelength range

34 | P a g e

SIGNALLING RELAYS

INTRODUCTION A relay is an electromagnetic device which is used to convey information from one circuit to another

circuit through a set of contact ie front or back contact Constructional and electrically relays may be

divided into DC and AC relays because the means by which the electrical energy in the coil is converted in

to mechanical Energy in order to move the contacts are fundamentally different In DC type the contacts are

carried on an armature forming part of a magnetic circuit in which a field is set up by the current flowing in

the coils In AC types the contacts are attached by a link mechanism to a metal sector disc or cylinder in

which currents are induced by the alternating magnetic field produced by the currents in the coils

Every endeavor has been made to explain the action of each type of relay in the simplest possible manner

Relays are sophisticated switch gears used for remote control and succession control of various

electrical equipment In present days they are widely used because they are capable of protecting the

controlled equipment from cross feeding and overloading even as they cater for speedy operations

Most of the relays in present day signaling are electromagnetic devices although some of the relays control

circuits through electronic components like diodetransistors Integrated Chips etc

Railway signaling relays are unique in that

(a) They operate on low voltage and current

(b) They are more articulate as according to their special features they can work under restrictive conditions

and in any specified manner Virtually they can cater for all situations while contributing to speed and

accuracy in operations

CLASSIFICATION OF SIGNALLING RELAYS (a) According to the method of their mounting or fixture they are classified as

(i) Shelf type Relays which are loosely kept on shelves

(ii) Plug in type Relays which are plugged into a pre- wired plug boards

(b) According to their connection and usage they are classified as

(i) Track relays Relay which is directly connected to the track to detect the presence of vehicle

(ii) Line Relays Other than track relay all are line relays Relays connected to the selection circuit

(c) According to their vitality or importance in ensuring train working safety they are classified as

(i) Vital Relays All relays used for traffic control such as signal point controls track detection etc

(ii) Non-vital Relays Relays which operate control aids and accessories like warnings buzzers

Indications etc

(d) According to their special provisions to ensure reliability of their contacts they are classified as

(i) Proved type are those whose normalization after each operation shall be proved in circuit

controlled by their contacts Contacts in which both the springs have metal surfaces on their tips They may

get fused due to high sparking current across them during operation These may prevent relay normalization

and causes unsafe condition in traffic control To avoid this proving of relay normalization after each

operation is necessary

(ii) Non - proved type Need not to be proved to have been normalized after each operation as their

contacts have at least one non-fusible contact (carbon contact)

(e) According to their feed source relays are broadly classified as

(i) DC relays The relay which requires DC power supply for its operations are called DC relays Among

the DC relays

o DC neutral relays This relay closes the same set of contacts on energization with Normal polarity

or Reverse polarity supply

o Polar Relays This relay closes different set of contacts when energized with Reverse polarity

supply They may or may not have contact to close when deenergized

35 | P a g e

(ii) AC Relay AC Induction motor track relays Time element relays flashing indication control etc

(iii) Electronic Relays DC relays with electronic components in them are called electronic relays

DC NEUTRAL RELAY Each Relay has usually one or two coils with a hollow center to accommodate a coreThe coils are

made up of a large numbers of turns of small gauge soft drawn copper wire The two coils can be connected

in series or parallel according to the requirement of relay resistance The ends of the coils are terminated on

binding post to which the control wires are connected Each coil is placed around a core of specially selected

Iron or steel having high permeability and low retentivity The core should be susceptible to magnetism and

at the same time should have little residual magnetism The cores are connected at the top by a yoke to

complete the magnetism coupling between two ends of coils The bottom of each core is equipped with a

large steel or Iron block known as pole piece or face

A flat piece of Iron or steel called armature is supported by brackets which are securely fastened to

the pole piece The armature yoke and the pole pieces are also made of specially selected iron or steel of the

same quality as the core The armature carries the metallic spring contacts which are insulated from it

The circuit through the coils of the relay is closed It sets up a magnetic flux through the core yoke and the

armature The flux passing between the armature and pole faces causes the armatures get attracted to the pole

faces and armature picks up and closes front contacts When the circuit is opened the magnetic flux collapses

and the armature drops away by gravity from the pole faces the front contacts break and back contacts close

The front and back contacts of the relay can be utilised to make or break other circuits Two stop pins of

nonmagnetic material are fixed either on the armature or pole faces so that the armature cannot

come in contact with the pole faces It is essential to maintain a small air-gap between the armature and pole

faces so that low value of residual magnetism may not retain the armature in picked up position and causes

the relay to fail to drop away with a break in its control circuit

GENERAL USAGE

DC Neutral line relays are most commonly used for Railway Signalling controls and detection

Among them plug-in type relays are preferred in larger installations for space considerations Shelf type

relays are also in use mostly in wayside stations

There are many DC Neutral line relays in use with special features such as

(i) Delayed operation

(ii) Biased DC control

(iii) DC control unaffected by AC interference currents

(iv) Getting latched in operated condition till further feeding and others

Usage of DC polar relays is mostly in conjunction with block instruments that control traffic between

stations AC line relays are almost extinct in installations of British Signalling practice They are however

used for time control operations flashing indication control and such other special purposes in installations

with Siemens signalling practice widely Track relays are used according to the type of track detection

circuits chosen for a given location and context While most of the track circuits are still of the DC working

type requiring DC neutral track relays with them the prospects of their being replaced with Electronic track

circuits directly feeding DC line relays in future are great AC Track Circuits are used in DC Traction area

as conventional DC Track Circuits are not suitable there AC Track relays are used with them almost all of

the induction motor type In the British practice of signalling which was first introduced on Indian Railways

non-proved type relays with carbon to metal switching contacts are generally used for vital controls

They facilitate simple circuit designs But with the advent of German Practice introduced by Ms

Siemens later proved type relays with all metal to metal contacts are widely accepted in spite of

complications in circuit design caused by them A recent introduction is that of the same type relays made by

Ms Integra control However for some time now the appreciable features of both the practices are getting

36 | P a g e

incorporated together in the indigenous designs of signalling by railwaymen With this the usage of all types

of relays anywhere can be found without straight jacketed segration of relay types

CHARACTERSTIC OF ELECTRO-MAGNETIC RELAY The following are the characteristic of electro-magnetic relays A brief study of them helps in

understanding the choice of their components and designs features

1) Force of attraction

2) Effect of air gap

3) Effect of Hysterisis

4) Transient condition

FORCE OF ATTRACTION In any electro-magnetic system the force of attraction is given by

Where B - is the flux density a - is the cross sectional area of the particular part of the magnetic

circuit

In the case of a DC neutral Relay B is proportional to the current that is flowing in the coil

surrounding the electro-magnet and thus the force of the attraction is directly proportional to the square of the

current This square relationship has its own advantage especially in the case of DC track relay in that a

small reduction in the current will have a great effect on the working of the relay Also for a given change of

current the make and the break will be quicker with lesser possibility of arcing

EFFECT OF AIR GAP

Curve lsquoArsquo is magnetisation curve for the iron and is all practical purpose a straight line up to the

saturation point Curve lsquoBrsquo is the magnetisation curve for the open-air gap which is a straight line through

out because per magnetisation curve of the whole

magnetic circuit of the relay and for a given force is the sum of the amp-turns for the iron part and the amp-

turns for the air gap

When the front contacts are open the force required to pick up the armature is shown on curve lsquoCrsquo to be F1

but after the armature has operated it will be separated from the core by stop pins In this position the amp-

turns required to maintain the armature is less as indicated by the dotted line from 1 on curve C to 2 on curve

37 | P a g e

F But actually the current in the coil is unaltered the force on the armature is greater than required as

indicated at 3 on curve F Part of this extra force is used to flex the front contacts sufficiently to give good

contact pressure when it is in energised position

The difference between the pick-up and the drop-away current should be as small as practicable in

track relay to ensure good shunting characteristics This is achieved firstly by the choice of good quality relay

iron and secondly by having a small air gap between armature and core If the air gap is not available then

the residual magnetism fluxes might cause the armature to be retained when the supply is disconnected For

this reason residual pins are provided to ensure a definite minimum air gap in the energised position

EFFECT OF HYSTERISIS

Hysterisis is the property by which the flux produced lags behind the current In the de-energized

condition there will be small residual flux in the core When the voltage is applied to the coils the current in

rising to its steady value first causes the flux to rise from 1 to 2 along the curve At this point the flux density

will be sufficient to attract the armature and reduce the air gap the flux then raise to 3 and continue to 4

which corresponds to the steady current in the coils When the voltage is disconnected the current in falling

caused the flux to fall from 4 to 5 along the curve At this point the flux density will fall below the value

required to maintain the armature which will release thus increasing the air gap and reducing the flux to 6

Finally the

flux will decrease from 6 to 1 where the current will again be zero

The relay core is made of material having high permeability and low retentivity As mentioned in

the IRS specification Electromagnet iron may be in the form of a

(a) Bar of silicon steel

(b) Best Yorkshire wrought iron

(c) Swedish charcoal iron

(d) Electrical steel sheets

` This reduces the difference between pick up value and Drop away value By selecting good quality

core material Percentage release and sensitivity of the relay will be improved

TRANSIENT CONDITION

38 | P a g e

When the voltage is applied or disconnected from the coils it takes some little time before the current

become steady These are known as transient conditionsrdquo and are important so far as track relays are

concerned When the voltage is first applied to the coils the magnetic flux in rising cuts the turns on the

coils and in so doing produces a back EMF that opposes the applied voltage and retards the growth of

current

The growth and decay of flux are decided by the relationship between the inductance and resistance

in the circuit is known as time constant It is not fixed quantity in the case of DC neutral relay This value of lsquo

Lrsquo is less when the relay is in de-energised condition (L1) than when the relay is in energised condition (L2)

The magnitude of flux that is established for a given change of current is different in two cases

When the current reaches the pick up value the armature closes and the inductance is increased to L2

due to reduced air gap the flux per amp is increased The increase in flux increased the back EMF during the

movement of the armature after which the current continuous to raise along a new curve corresponding to the

increased inductance until it reaches the final value (ER) This process is indicated above in fig24

When the supply is disconnected the current is obliviously reduced to zero immediately but the flux

decay comparatively slowly owing to the eddy currents produced in the core by the rapid flux change which

tend to maintain the flux The drop away time on a disconnection is however generally negligible See fig

below

If the relay releases due to the reduction in current from say I 2 to I 1 caused by the application of

shunt resistance (as in the case of track relay ) the time taken is much longer than the relay is simply

disconnected The rate of rise or fall of current during the transient conditions is also depends on exterior

circuit values because L and R apply to the whole circuit The production of eddy current in the core the flux

will decay at a slower rate than the current So that the actual release time will be a little longer than it takes

the current to fall to the release

L= Inductance

39 | P a g e

R= Resistance

It is now clear that to reduce releasing time to a minimum it is necessary that

- The relay iron should have low Hysterisis loss and low retentivity

- The degree of over energization of the relay should be restricted

- Connecting a suitable external resistance in series with the relay to keep LR ratio low

In non RE area for track circuit length less than 100M 9 ohm track relay only to be used Using relay

with minimum contacts as they require lesser current which keeps inductance value low

Train working safety is ensured only if the track relay of shortest length track circuit is released

before a light engine running at a highest permitted speed clears it Otherwise the track circuit occupation

may go undetected To avoid this a special provision has to be made in signal control circuits wherever

necessary

The following methods may be adopted for reducing the time lag of track relay

(a) Restrict the over energisation of relay since the release time depends on the initial working current

(b) Connecting a suitable external resistance in series with the relay to keep the LR ratio low

(c) Using relays with minimum contacts as they require lesser operating current keeping the inductance

value low

40 | P a g e

CONCLUSION

Modern signalling is vital for safe and punctual movements of trains In the Indian railways The Signalling

and Telecommunication Department is responsible for providing modern effective and relaible signalling

systems as well as telecommunication systems

The first mode of communication used in Indian Railways was the use of electric telegraph

with the help of Morose code Morose code is the method of providing text information as a series of on-off

tones and lights or clicks that can be directly understood by a skilled listener or observer without special

equipmentEach character (letter or numeral ) is represented by a unique sequence of dots and dashes Later

this system becomes obselete and beggan the era of wireless communication which operated at audio level

frequency range

In wireless communication the significant advances took place the transition to miniature

valves or filament tubesBut this was abandoned too because of excessive current consumption and over

heating of the filament tubes

Fibre-optic communication is a method of transmitting information from one place to another by

sending pulses of light through an optcial fibreThe light forms an electromagnetic carrier wave that is

modulated to carry information First developed in the 1970s fibre optic communication systems has

revolutionized the telecommunications industry and have palyed a major role in the advent of the information

age Because of its advantages over electrical transmissionsoptical fibres have largely replaced copper wire

communications in core networks in the developed world The Indian Railways too is undergoing a transition

from Microwave communication to fibre optic communications

41 | P a g e

BIBLIOGRAPHY AND REFERENCES

1 wwwwikipediacom

2 wwwbritaniccacom

3 wwwirfcacom

4 Motorola GP60 system manual

5 Harris FAS 7000 manual

6 TOSHIBA Manual

30 | P a g e

are in a higher refractive index so they travel slower than the serpentine modes These travel farther but

move faster in the lower refractive index of the outer core region

PROPAGATION THROUGH SMSI FIBER Single mode fiber has a much smaller core that allows only one mode of light at a time to propagate

through the core The figure shows the single mode fiber

Single-mode fiber exhibits no dispersion caused by multiple modes Single-mode fiber also offers lower fiber

attenuation than multimode fiber Thus more information can be transmitted per unit of time because it can

retain the fidelity of each light pulse over longer distances Like multimode fiber early single-mode fiber was

generally characterized as step-index fiber meaning the refractive index of the fiber core is a step above that

of the cladding rather than graduated as it is in graded-index fiber Modern single-mode fibers have evolved

into more complex designs such as matched clad depressed clad and other exotic structures

SINGLE-MODE FIBER DISADVANTAGES The smaller core diameter makes coupling light into the core more difficult The tolerances for single-

mode connectors and splices are also much more demanding

CUTOFF WAVE LENGTH - Cutoff wavelength is the wavelength above which a single-mode fiber supports and propagates only

one mode of light In other words an optical fiber that is single-mode at a particular wavelength may have

two or more modes at wavelengths lower than the cutoff wavelength The effective cutoff wavelength of a

fiber is dependent on the length of fiber and its deployment The longer the fiber the lower is the effective

cutoff

wavelength The smaller the bend radius of a loop of the fiber the lower is the effective cutoff wavelength If

a fiber is bent in a loop the effective cutoff wavelength is lowered

SIGNAL ATTENUATION IN FIBER - Optical fiber has a number of advantages over copper However it also suffers from degradation

problems which can not be ignored The first of these is loss or attenuation Attenuation is typically the result

of two sub properties They are scattering and absorption Both of which have cumulative effects The second

is

dispersion which is the spreading of the transmitted signal and is analogous to noise

SCATTERING Scattering occurs because of impurities or irregularities in the physical construction of the fiber The

well known form of scattering is Rayleigh Scattering It is caused by metal ions in the silica matrix and

results in light rays being scattered in various directions

31 | P a g e

Scattering limits the use of wavelengths below 800nm The short wavelengths are much affected than longer

wavelengths It is because of Rayleigh scattering that the sky appears to be blue ( shorter wave length ) The

shorter wavelengths ( blue ) of light are scattered more than the longer wavelengths of light

ABSORPTION Absorption results from three factors They are hydroxyl ions ( OH- water ) in the silica impurities

in the silica and incomplete residue from the manufacturing process These impurities tend to absorb the

energy of the transmitted signal and convert it to heat resulting in an overall weakening of the signal The

Hydroxyl absorption occurs at 125 and 139 micro The silica itself starts to absorb energy at 17 micro

because of the natural resonance of the silicon dioxide

MACRO BENDING LOSS Macro-bending loss is caused by bending of the entire fiber axis The bending radius shall not be

sharper than 30d where d is diameter of cable A single bend sharper than 30d can cause loss of 05dB

The fiber may break if bending is ever sharper

MICRO BENDING LOSS Micro-bending loss is caused by micro deformations of fiber axis which leads to failures in achieving

total internal reflection conditions Micro-bends are small scale perturbations along the fiber axis the

amplitude of which are on the order of microns These distortions can cause light to leak out of a fiber

Micro-bending may be induced at very cold temperatures because the glass has a different coefficient of

thermal expansion from the coating and cabling materials At low temperatures the coating and cable

become more rigid and may contract more than the glass Consequently enough load may be exerted on the

glass to cause micro bends

Coating material is selected by manufacturers to minimize loss due to micro-bending The linear thermal

expansion coefficient of coating material shall be compatible with that of fiber

32 | P a g e

DISPERSION Dispersion is the optical term for the spreading of the transmits in the fiber It is the bandwidth

limiting phenomenon and comes in two forms Multimode dispersion and chromatic dispersion Chromatic

dispersion is further subdivided into material dispersion and waveguide dispersion

DISPERSION PHENOMENON IN OPTICAL FIBER Dispersion is the time distortion of an optical signal that results from the differences of time of travel

for different components of that signal typically resulting in pulse broadening As the distance traveled by

the signal is more broadening of pulse is more In digital transmission dispersion limits on the maximum

data rate and the maximum distance ie the information-carrying capacity of a fiber link The interference

from broadened pulse in the next interval shall not lead to erroneous interpretation of received signal

OPTICAL DOMAIN Understanding where attenuation and dispersion problems occur helps optical design engineers

determine the better wavelengths at which information can be transmit taking into account distance type of

fiber and the other factors which can severely affect the integrity of the transmitted signal The graph shown

depicts the optical transmission domain as well as the areas where problems arise The wavelength (nm)

is shown on X-axis and attenuation ( dBkm) is shown on Y-axis

There are four transmission windows appear in the figure The first one is at around 850 nm the

second at 1310nm third at 1550 nm and fourth at 1625 nm The last two labeled as C and L band

respectively The 850 nm wavelength at which the original LED technology operated The second window at

1310 nm has low dispersion The 1550 nm called as C-band is ideal wavelength for long haul

communication systems The network engineers can avoid transmitting signal at 1000 nm where Rayleigh

scattering 1240 and 1390 nm where hydroxyl absorption by water occurs to avoid high degree of loss

Optical fibers also can be manufactured to have low dispersion wavelength in the 1550nm region

which is also the point where silica-based fibers have inherently minimal attenuation These fibers are

referred to as dispersion-shifted fibers and are used in long-distance applications with high bit rates For

33 | P a g e

applications utilizing multiple wavelengths it is undesirable to have the zero dispersion point within the

operating

wavelength range

34 | P a g e

SIGNALLING RELAYS

INTRODUCTION A relay is an electromagnetic device which is used to convey information from one circuit to another

circuit through a set of contact ie front or back contact Constructional and electrically relays may be

divided into DC and AC relays because the means by which the electrical energy in the coil is converted in

to mechanical Energy in order to move the contacts are fundamentally different In DC type the contacts are

carried on an armature forming part of a magnetic circuit in which a field is set up by the current flowing in

the coils In AC types the contacts are attached by a link mechanism to a metal sector disc or cylinder in

which currents are induced by the alternating magnetic field produced by the currents in the coils

Every endeavor has been made to explain the action of each type of relay in the simplest possible manner

Relays are sophisticated switch gears used for remote control and succession control of various

electrical equipment In present days they are widely used because they are capable of protecting the

controlled equipment from cross feeding and overloading even as they cater for speedy operations

Most of the relays in present day signaling are electromagnetic devices although some of the relays control

circuits through electronic components like diodetransistors Integrated Chips etc

Railway signaling relays are unique in that

(a) They operate on low voltage and current

(b) They are more articulate as according to their special features they can work under restrictive conditions

and in any specified manner Virtually they can cater for all situations while contributing to speed and

accuracy in operations

CLASSIFICATION OF SIGNALLING RELAYS (a) According to the method of their mounting or fixture they are classified as

(i) Shelf type Relays which are loosely kept on shelves

(ii) Plug in type Relays which are plugged into a pre- wired plug boards

(b) According to their connection and usage they are classified as

(i) Track relays Relay which is directly connected to the track to detect the presence of vehicle

(ii) Line Relays Other than track relay all are line relays Relays connected to the selection circuit

(c) According to their vitality or importance in ensuring train working safety they are classified as

(i) Vital Relays All relays used for traffic control such as signal point controls track detection etc

(ii) Non-vital Relays Relays which operate control aids and accessories like warnings buzzers

Indications etc

(d) According to their special provisions to ensure reliability of their contacts they are classified as

(i) Proved type are those whose normalization after each operation shall be proved in circuit

controlled by their contacts Contacts in which both the springs have metal surfaces on their tips They may

get fused due to high sparking current across them during operation These may prevent relay normalization

and causes unsafe condition in traffic control To avoid this proving of relay normalization after each

operation is necessary

(ii) Non - proved type Need not to be proved to have been normalized after each operation as their

contacts have at least one non-fusible contact (carbon contact)

(e) According to their feed source relays are broadly classified as

(i) DC relays The relay which requires DC power supply for its operations are called DC relays Among

the DC relays

o DC neutral relays This relay closes the same set of contacts on energization with Normal polarity

or Reverse polarity supply

o Polar Relays This relay closes different set of contacts when energized with Reverse polarity

supply They may or may not have contact to close when deenergized

35 | P a g e

(ii) AC Relay AC Induction motor track relays Time element relays flashing indication control etc

(iii) Electronic Relays DC relays with electronic components in them are called electronic relays

DC NEUTRAL RELAY Each Relay has usually one or two coils with a hollow center to accommodate a coreThe coils are

made up of a large numbers of turns of small gauge soft drawn copper wire The two coils can be connected

in series or parallel according to the requirement of relay resistance The ends of the coils are terminated on

binding post to which the control wires are connected Each coil is placed around a core of specially selected

Iron or steel having high permeability and low retentivity The core should be susceptible to magnetism and

at the same time should have little residual magnetism The cores are connected at the top by a yoke to

complete the magnetism coupling between two ends of coils The bottom of each core is equipped with a

large steel or Iron block known as pole piece or face

A flat piece of Iron or steel called armature is supported by brackets which are securely fastened to

the pole piece The armature yoke and the pole pieces are also made of specially selected iron or steel of the

same quality as the core The armature carries the metallic spring contacts which are insulated from it

The circuit through the coils of the relay is closed It sets up a magnetic flux through the core yoke and the

armature The flux passing between the armature and pole faces causes the armatures get attracted to the pole

faces and armature picks up and closes front contacts When the circuit is opened the magnetic flux collapses

and the armature drops away by gravity from the pole faces the front contacts break and back contacts close

The front and back contacts of the relay can be utilised to make or break other circuits Two stop pins of

nonmagnetic material are fixed either on the armature or pole faces so that the armature cannot

come in contact with the pole faces It is essential to maintain a small air-gap between the armature and pole

faces so that low value of residual magnetism may not retain the armature in picked up position and causes

the relay to fail to drop away with a break in its control circuit

GENERAL USAGE

DC Neutral line relays are most commonly used for Railway Signalling controls and detection

Among them plug-in type relays are preferred in larger installations for space considerations Shelf type

relays are also in use mostly in wayside stations

There are many DC Neutral line relays in use with special features such as

(i) Delayed operation

(ii) Biased DC control

(iii) DC control unaffected by AC interference currents

(iv) Getting latched in operated condition till further feeding and others

Usage of DC polar relays is mostly in conjunction with block instruments that control traffic between

stations AC line relays are almost extinct in installations of British Signalling practice They are however

used for time control operations flashing indication control and such other special purposes in installations

with Siemens signalling practice widely Track relays are used according to the type of track detection

circuits chosen for a given location and context While most of the track circuits are still of the DC working

type requiring DC neutral track relays with them the prospects of their being replaced with Electronic track

circuits directly feeding DC line relays in future are great AC Track Circuits are used in DC Traction area

as conventional DC Track Circuits are not suitable there AC Track relays are used with them almost all of

the induction motor type In the British practice of signalling which was first introduced on Indian Railways

non-proved type relays with carbon to metal switching contacts are generally used for vital controls

They facilitate simple circuit designs But with the advent of German Practice introduced by Ms

Siemens later proved type relays with all metal to metal contacts are widely accepted in spite of

complications in circuit design caused by them A recent introduction is that of the same type relays made by

Ms Integra control However for some time now the appreciable features of both the practices are getting

36 | P a g e

incorporated together in the indigenous designs of signalling by railwaymen With this the usage of all types

of relays anywhere can be found without straight jacketed segration of relay types

CHARACTERSTIC OF ELECTRO-MAGNETIC RELAY The following are the characteristic of electro-magnetic relays A brief study of them helps in

understanding the choice of their components and designs features

1) Force of attraction

2) Effect of air gap

3) Effect of Hysterisis

4) Transient condition

FORCE OF ATTRACTION In any electro-magnetic system the force of attraction is given by

Where B - is the flux density a - is the cross sectional area of the particular part of the magnetic

circuit

In the case of a DC neutral Relay B is proportional to the current that is flowing in the coil

surrounding the electro-magnet and thus the force of the attraction is directly proportional to the square of the

current This square relationship has its own advantage especially in the case of DC track relay in that a

small reduction in the current will have a great effect on the working of the relay Also for a given change of

current the make and the break will be quicker with lesser possibility of arcing

EFFECT OF AIR GAP

Curve lsquoArsquo is magnetisation curve for the iron and is all practical purpose a straight line up to the

saturation point Curve lsquoBrsquo is the magnetisation curve for the open-air gap which is a straight line through

out because per magnetisation curve of the whole

magnetic circuit of the relay and for a given force is the sum of the amp-turns for the iron part and the amp-

turns for the air gap

When the front contacts are open the force required to pick up the armature is shown on curve lsquoCrsquo to be F1

but after the armature has operated it will be separated from the core by stop pins In this position the amp-

turns required to maintain the armature is less as indicated by the dotted line from 1 on curve C to 2 on curve

37 | P a g e

F But actually the current in the coil is unaltered the force on the armature is greater than required as

indicated at 3 on curve F Part of this extra force is used to flex the front contacts sufficiently to give good

contact pressure when it is in energised position

The difference between the pick-up and the drop-away current should be as small as practicable in

track relay to ensure good shunting characteristics This is achieved firstly by the choice of good quality relay

iron and secondly by having a small air gap between armature and core If the air gap is not available then

the residual magnetism fluxes might cause the armature to be retained when the supply is disconnected For

this reason residual pins are provided to ensure a definite minimum air gap in the energised position

EFFECT OF HYSTERISIS

Hysterisis is the property by which the flux produced lags behind the current In the de-energized

condition there will be small residual flux in the core When the voltage is applied to the coils the current in

rising to its steady value first causes the flux to rise from 1 to 2 along the curve At this point the flux density

will be sufficient to attract the armature and reduce the air gap the flux then raise to 3 and continue to 4

which corresponds to the steady current in the coils When the voltage is disconnected the current in falling

caused the flux to fall from 4 to 5 along the curve At this point the flux density will fall below the value

required to maintain the armature which will release thus increasing the air gap and reducing the flux to 6

Finally the

flux will decrease from 6 to 1 where the current will again be zero

The relay core is made of material having high permeability and low retentivity As mentioned in

the IRS specification Electromagnet iron may be in the form of a

(a) Bar of silicon steel

(b) Best Yorkshire wrought iron

(c) Swedish charcoal iron

(d) Electrical steel sheets

` This reduces the difference between pick up value and Drop away value By selecting good quality

core material Percentage release and sensitivity of the relay will be improved

TRANSIENT CONDITION

38 | P a g e

When the voltage is applied or disconnected from the coils it takes some little time before the current

become steady These are known as transient conditionsrdquo and are important so far as track relays are

concerned When the voltage is first applied to the coils the magnetic flux in rising cuts the turns on the

coils and in so doing produces a back EMF that opposes the applied voltage and retards the growth of

current

The growth and decay of flux are decided by the relationship between the inductance and resistance

in the circuit is known as time constant It is not fixed quantity in the case of DC neutral relay This value of lsquo

Lrsquo is less when the relay is in de-energised condition (L1) than when the relay is in energised condition (L2)

The magnitude of flux that is established for a given change of current is different in two cases

When the current reaches the pick up value the armature closes and the inductance is increased to L2

due to reduced air gap the flux per amp is increased The increase in flux increased the back EMF during the

movement of the armature after which the current continuous to raise along a new curve corresponding to the

increased inductance until it reaches the final value (ER) This process is indicated above in fig24

When the supply is disconnected the current is obliviously reduced to zero immediately but the flux

decay comparatively slowly owing to the eddy currents produced in the core by the rapid flux change which

tend to maintain the flux The drop away time on a disconnection is however generally negligible See fig

below

If the relay releases due to the reduction in current from say I 2 to I 1 caused by the application of

shunt resistance (as in the case of track relay ) the time taken is much longer than the relay is simply

disconnected The rate of rise or fall of current during the transient conditions is also depends on exterior

circuit values because L and R apply to the whole circuit The production of eddy current in the core the flux

will decay at a slower rate than the current So that the actual release time will be a little longer than it takes

the current to fall to the release

L= Inductance

39 | P a g e

R= Resistance

It is now clear that to reduce releasing time to a minimum it is necessary that

- The relay iron should have low Hysterisis loss and low retentivity

- The degree of over energization of the relay should be restricted

- Connecting a suitable external resistance in series with the relay to keep LR ratio low

In non RE area for track circuit length less than 100M 9 ohm track relay only to be used Using relay

with minimum contacts as they require lesser current which keeps inductance value low

Train working safety is ensured only if the track relay of shortest length track circuit is released

before a light engine running at a highest permitted speed clears it Otherwise the track circuit occupation

may go undetected To avoid this a special provision has to be made in signal control circuits wherever

necessary

The following methods may be adopted for reducing the time lag of track relay

(a) Restrict the over energisation of relay since the release time depends on the initial working current

(b) Connecting a suitable external resistance in series with the relay to keep the LR ratio low

(c) Using relays with minimum contacts as they require lesser operating current keeping the inductance

value low

40 | P a g e

CONCLUSION

Modern signalling is vital for safe and punctual movements of trains In the Indian railways The Signalling

and Telecommunication Department is responsible for providing modern effective and relaible signalling

systems as well as telecommunication systems

The first mode of communication used in Indian Railways was the use of electric telegraph

with the help of Morose code Morose code is the method of providing text information as a series of on-off

tones and lights or clicks that can be directly understood by a skilled listener or observer without special

equipmentEach character (letter or numeral ) is represented by a unique sequence of dots and dashes Later

this system becomes obselete and beggan the era of wireless communication which operated at audio level

frequency range

In wireless communication the significant advances took place the transition to miniature

valves or filament tubesBut this was abandoned too because of excessive current consumption and over

heating of the filament tubes

Fibre-optic communication is a method of transmitting information from one place to another by

sending pulses of light through an optcial fibreThe light forms an electromagnetic carrier wave that is

modulated to carry information First developed in the 1970s fibre optic communication systems has

revolutionized the telecommunications industry and have palyed a major role in the advent of the information

age Because of its advantages over electrical transmissionsoptical fibres have largely replaced copper wire

communications in core networks in the developed world The Indian Railways too is undergoing a transition

from Microwave communication to fibre optic communications

41 | P a g e

BIBLIOGRAPHY AND REFERENCES

1 wwwwikipediacom

2 wwwbritaniccacom

3 wwwirfcacom

4 Motorola GP60 system manual

5 Harris FAS 7000 manual

6 TOSHIBA Manual

31 | P a g e

Scattering limits the use of wavelengths below 800nm The short wavelengths are much affected than longer

wavelengths It is because of Rayleigh scattering that the sky appears to be blue ( shorter wave length ) The

shorter wavelengths ( blue ) of light are scattered more than the longer wavelengths of light

ABSORPTION Absorption results from three factors They are hydroxyl ions ( OH- water ) in the silica impurities

in the silica and incomplete residue from the manufacturing process These impurities tend to absorb the

energy of the transmitted signal and convert it to heat resulting in an overall weakening of the signal The

Hydroxyl absorption occurs at 125 and 139 micro The silica itself starts to absorb energy at 17 micro

because of the natural resonance of the silicon dioxide

MACRO BENDING LOSS Macro-bending loss is caused by bending of the entire fiber axis The bending radius shall not be

sharper than 30d where d is diameter of cable A single bend sharper than 30d can cause loss of 05dB

The fiber may break if bending is ever sharper

MICRO BENDING LOSS Micro-bending loss is caused by micro deformations of fiber axis which leads to failures in achieving

total internal reflection conditions Micro-bends are small scale perturbations along the fiber axis the

amplitude of which are on the order of microns These distortions can cause light to leak out of a fiber

Micro-bending may be induced at very cold temperatures because the glass has a different coefficient of

thermal expansion from the coating and cabling materials At low temperatures the coating and cable

become more rigid and may contract more than the glass Consequently enough load may be exerted on the

glass to cause micro bends

Coating material is selected by manufacturers to minimize loss due to micro-bending The linear thermal

expansion coefficient of coating material shall be compatible with that of fiber

32 | P a g e

DISPERSION Dispersion is the optical term for the spreading of the transmits in the fiber It is the bandwidth

limiting phenomenon and comes in two forms Multimode dispersion and chromatic dispersion Chromatic

dispersion is further subdivided into material dispersion and waveguide dispersion

DISPERSION PHENOMENON IN OPTICAL FIBER Dispersion is the time distortion of an optical signal that results from the differences of time of travel

for different components of that signal typically resulting in pulse broadening As the distance traveled by

the signal is more broadening of pulse is more In digital transmission dispersion limits on the maximum

data rate and the maximum distance ie the information-carrying capacity of a fiber link The interference

from broadened pulse in the next interval shall not lead to erroneous interpretation of received signal

OPTICAL DOMAIN Understanding where attenuation and dispersion problems occur helps optical design engineers

determine the better wavelengths at which information can be transmit taking into account distance type of

fiber and the other factors which can severely affect the integrity of the transmitted signal The graph shown

depicts the optical transmission domain as well as the areas where problems arise The wavelength (nm)

is shown on X-axis and attenuation ( dBkm) is shown on Y-axis

There are four transmission windows appear in the figure The first one is at around 850 nm the

second at 1310nm third at 1550 nm and fourth at 1625 nm The last two labeled as C and L band

respectively The 850 nm wavelength at which the original LED technology operated The second window at

1310 nm has low dispersion The 1550 nm called as C-band is ideal wavelength for long haul

communication systems The network engineers can avoid transmitting signal at 1000 nm where Rayleigh

scattering 1240 and 1390 nm where hydroxyl absorption by water occurs to avoid high degree of loss

Optical fibers also can be manufactured to have low dispersion wavelength in the 1550nm region

which is also the point where silica-based fibers have inherently minimal attenuation These fibers are

referred to as dispersion-shifted fibers and are used in long-distance applications with high bit rates For

33 | P a g e

applications utilizing multiple wavelengths it is undesirable to have the zero dispersion point within the

operating

wavelength range

34 | P a g e

SIGNALLING RELAYS

INTRODUCTION A relay is an electromagnetic device which is used to convey information from one circuit to another

circuit through a set of contact ie front or back contact Constructional and electrically relays may be

divided into DC and AC relays because the means by which the electrical energy in the coil is converted in

to mechanical Energy in order to move the contacts are fundamentally different In DC type the contacts are

carried on an armature forming part of a magnetic circuit in which a field is set up by the current flowing in

the coils In AC types the contacts are attached by a link mechanism to a metal sector disc or cylinder in

which currents are induced by the alternating magnetic field produced by the currents in the coils

Every endeavor has been made to explain the action of each type of relay in the simplest possible manner

Relays are sophisticated switch gears used for remote control and succession control of various

electrical equipment In present days they are widely used because they are capable of protecting the

controlled equipment from cross feeding and overloading even as they cater for speedy operations

Most of the relays in present day signaling are electromagnetic devices although some of the relays control

circuits through electronic components like diodetransistors Integrated Chips etc

Railway signaling relays are unique in that

(a) They operate on low voltage and current

(b) They are more articulate as according to their special features they can work under restrictive conditions

and in any specified manner Virtually they can cater for all situations while contributing to speed and

accuracy in operations

CLASSIFICATION OF SIGNALLING RELAYS (a) According to the method of their mounting or fixture they are classified as

(i) Shelf type Relays which are loosely kept on shelves

(ii) Plug in type Relays which are plugged into a pre- wired plug boards

(b) According to their connection and usage they are classified as

(i) Track relays Relay which is directly connected to the track to detect the presence of vehicle

(ii) Line Relays Other than track relay all are line relays Relays connected to the selection circuit

(c) According to their vitality or importance in ensuring train working safety they are classified as

(i) Vital Relays All relays used for traffic control such as signal point controls track detection etc

(ii) Non-vital Relays Relays which operate control aids and accessories like warnings buzzers

Indications etc

(d) According to their special provisions to ensure reliability of their contacts they are classified as

(i) Proved type are those whose normalization after each operation shall be proved in circuit

controlled by their contacts Contacts in which both the springs have metal surfaces on their tips They may

get fused due to high sparking current across them during operation These may prevent relay normalization

and causes unsafe condition in traffic control To avoid this proving of relay normalization after each

operation is necessary

(ii) Non - proved type Need not to be proved to have been normalized after each operation as their

contacts have at least one non-fusible contact (carbon contact)

(e) According to their feed source relays are broadly classified as

(i) DC relays The relay which requires DC power supply for its operations are called DC relays Among

the DC relays

o DC neutral relays This relay closes the same set of contacts on energization with Normal polarity

or Reverse polarity supply

o Polar Relays This relay closes different set of contacts when energized with Reverse polarity

supply They may or may not have contact to close when deenergized

35 | P a g e

(ii) AC Relay AC Induction motor track relays Time element relays flashing indication control etc

(iii) Electronic Relays DC relays with electronic components in them are called electronic relays

DC NEUTRAL RELAY Each Relay has usually one or two coils with a hollow center to accommodate a coreThe coils are

made up of a large numbers of turns of small gauge soft drawn copper wire The two coils can be connected

in series or parallel according to the requirement of relay resistance The ends of the coils are terminated on

binding post to which the control wires are connected Each coil is placed around a core of specially selected

Iron or steel having high permeability and low retentivity The core should be susceptible to magnetism and

at the same time should have little residual magnetism The cores are connected at the top by a yoke to

complete the magnetism coupling between two ends of coils The bottom of each core is equipped with a

large steel or Iron block known as pole piece or face

A flat piece of Iron or steel called armature is supported by brackets which are securely fastened to

the pole piece The armature yoke and the pole pieces are also made of specially selected iron or steel of the

same quality as the core The armature carries the metallic spring contacts which are insulated from it

The circuit through the coils of the relay is closed It sets up a magnetic flux through the core yoke and the

armature The flux passing between the armature and pole faces causes the armatures get attracted to the pole

faces and armature picks up and closes front contacts When the circuit is opened the magnetic flux collapses

and the armature drops away by gravity from the pole faces the front contacts break and back contacts close

The front and back contacts of the relay can be utilised to make or break other circuits Two stop pins of

nonmagnetic material are fixed either on the armature or pole faces so that the armature cannot

come in contact with the pole faces It is essential to maintain a small air-gap between the armature and pole

faces so that low value of residual magnetism may not retain the armature in picked up position and causes

the relay to fail to drop away with a break in its control circuit

GENERAL USAGE

DC Neutral line relays are most commonly used for Railway Signalling controls and detection

Among them plug-in type relays are preferred in larger installations for space considerations Shelf type

relays are also in use mostly in wayside stations

There are many DC Neutral line relays in use with special features such as

(i) Delayed operation

(ii) Biased DC control

(iii) DC control unaffected by AC interference currents

(iv) Getting latched in operated condition till further feeding and others

Usage of DC polar relays is mostly in conjunction with block instruments that control traffic between

stations AC line relays are almost extinct in installations of British Signalling practice They are however

used for time control operations flashing indication control and such other special purposes in installations

with Siemens signalling practice widely Track relays are used according to the type of track detection

circuits chosen for a given location and context While most of the track circuits are still of the DC working

type requiring DC neutral track relays with them the prospects of their being replaced with Electronic track

circuits directly feeding DC line relays in future are great AC Track Circuits are used in DC Traction area

as conventional DC Track Circuits are not suitable there AC Track relays are used with them almost all of

the induction motor type In the British practice of signalling which was first introduced on Indian Railways

non-proved type relays with carbon to metal switching contacts are generally used for vital controls

They facilitate simple circuit designs But with the advent of German Practice introduced by Ms

Siemens later proved type relays with all metal to metal contacts are widely accepted in spite of

complications in circuit design caused by them A recent introduction is that of the same type relays made by

Ms Integra control However for some time now the appreciable features of both the practices are getting

36 | P a g e

incorporated together in the indigenous designs of signalling by railwaymen With this the usage of all types

of relays anywhere can be found without straight jacketed segration of relay types

CHARACTERSTIC OF ELECTRO-MAGNETIC RELAY The following are the characteristic of electro-magnetic relays A brief study of them helps in

understanding the choice of their components and designs features

1) Force of attraction

2) Effect of air gap

3) Effect of Hysterisis

4) Transient condition

FORCE OF ATTRACTION In any electro-magnetic system the force of attraction is given by

Where B - is the flux density a - is the cross sectional area of the particular part of the magnetic

circuit

In the case of a DC neutral Relay B is proportional to the current that is flowing in the coil

surrounding the electro-magnet and thus the force of the attraction is directly proportional to the square of the

current This square relationship has its own advantage especially in the case of DC track relay in that a

small reduction in the current will have a great effect on the working of the relay Also for a given change of

current the make and the break will be quicker with lesser possibility of arcing

EFFECT OF AIR GAP

Curve lsquoArsquo is magnetisation curve for the iron and is all practical purpose a straight line up to the

saturation point Curve lsquoBrsquo is the magnetisation curve for the open-air gap which is a straight line through

out because per magnetisation curve of the whole

magnetic circuit of the relay and for a given force is the sum of the amp-turns for the iron part and the amp-

turns for the air gap

When the front contacts are open the force required to pick up the armature is shown on curve lsquoCrsquo to be F1

but after the armature has operated it will be separated from the core by stop pins In this position the amp-

turns required to maintain the armature is less as indicated by the dotted line from 1 on curve C to 2 on curve

37 | P a g e

F But actually the current in the coil is unaltered the force on the armature is greater than required as

indicated at 3 on curve F Part of this extra force is used to flex the front contacts sufficiently to give good

contact pressure when it is in energised position

The difference between the pick-up and the drop-away current should be as small as practicable in

track relay to ensure good shunting characteristics This is achieved firstly by the choice of good quality relay

iron and secondly by having a small air gap between armature and core If the air gap is not available then

the residual magnetism fluxes might cause the armature to be retained when the supply is disconnected For

this reason residual pins are provided to ensure a definite minimum air gap in the energised position

EFFECT OF HYSTERISIS

Hysterisis is the property by which the flux produced lags behind the current In the de-energized

condition there will be small residual flux in the core When the voltage is applied to the coils the current in

rising to its steady value first causes the flux to rise from 1 to 2 along the curve At this point the flux density

will be sufficient to attract the armature and reduce the air gap the flux then raise to 3 and continue to 4

which corresponds to the steady current in the coils When the voltage is disconnected the current in falling

caused the flux to fall from 4 to 5 along the curve At this point the flux density will fall below the value

required to maintain the armature which will release thus increasing the air gap and reducing the flux to 6

Finally the

flux will decrease from 6 to 1 where the current will again be zero

The relay core is made of material having high permeability and low retentivity As mentioned in

the IRS specification Electromagnet iron may be in the form of a

(a) Bar of silicon steel

(b) Best Yorkshire wrought iron

(c) Swedish charcoal iron

(d) Electrical steel sheets

` This reduces the difference between pick up value and Drop away value By selecting good quality

core material Percentage release and sensitivity of the relay will be improved

TRANSIENT CONDITION

38 | P a g e

When the voltage is applied or disconnected from the coils it takes some little time before the current

become steady These are known as transient conditionsrdquo and are important so far as track relays are

concerned When the voltage is first applied to the coils the magnetic flux in rising cuts the turns on the

coils and in so doing produces a back EMF that opposes the applied voltage and retards the growth of

current

The growth and decay of flux are decided by the relationship between the inductance and resistance

in the circuit is known as time constant It is not fixed quantity in the case of DC neutral relay This value of lsquo

Lrsquo is less when the relay is in de-energised condition (L1) than when the relay is in energised condition (L2)

The magnitude of flux that is established for a given change of current is different in two cases

When the current reaches the pick up value the armature closes and the inductance is increased to L2

due to reduced air gap the flux per amp is increased The increase in flux increased the back EMF during the

movement of the armature after which the current continuous to raise along a new curve corresponding to the

increased inductance until it reaches the final value (ER) This process is indicated above in fig24

When the supply is disconnected the current is obliviously reduced to zero immediately but the flux

decay comparatively slowly owing to the eddy currents produced in the core by the rapid flux change which

tend to maintain the flux The drop away time on a disconnection is however generally negligible See fig

below

If the relay releases due to the reduction in current from say I 2 to I 1 caused by the application of

shunt resistance (as in the case of track relay ) the time taken is much longer than the relay is simply

disconnected The rate of rise or fall of current during the transient conditions is also depends on exterior

circuit values because L and R apply to the whole circuit The production of eddy current in the core the flux

will decay at a slower rate than the current So that the actual release time will be a little longer than it takes

the current to fall to the release

L= Inductance

39 | P a g e

R= Resistance

It is now clear that to reduce releasing time to a minimum it is necessary that

- The relay iron should have low Hysterisis loss and low retentivity

- The degree of over energization of the relay should be restricted

- Connecting a suitable external resistance in series with the relay to keep LR ratio low

In non RE area for track circuit length less than 100M 9 ohm track relay only to be used Using relay

with minimum contacts as they require lesser current which keeps inductance value low

Train working safety is ensured only if the track relay of shortest length track circuit is released

before a light engine running at a highest permitted speed clears it Otherwise the track circuit occupation

may go undetected To avoid this a special provision has to be made in signal control circuits wherever

necessary

The following methods may be adopted for reducing the time lag of track relay

(a) Restrict the over energisation of relay since the release time depends on the initial working current

(b) Connecting a suitable external resistance in series with the relay to keep the LR ratio low

(c) Using relays with minimum contacts as they require lesser operating current keeping the inductance

value low

40 | P a g e

CONCLUSION

Modern signalling is vital for safe and punctual movements of trains In the Indian railways The Signalling

and Telecommunication Department is responsible for providing modern effective and relaible signalling

systems as well as telecommunication systems

The first mode of communication used in Indian Railways was the use of electric telegraph

with the help of Morose code Morose code is the method of providing text information as a series of on-off

tones and lights or clicks that can be directly understood by a skilled listener or observer without special

equipmentEach character (letter or numeral ) is represented by a unique sequence of dots and dashes Later

this system becomes obselete and beggan the era of wireless communication which operated at audio level

frequency range

In wireless communication the significant advances took place the transition to miniature

valves or filament tubesBut this was abandoned too because of excessive current consumption and over

heating of the filament tubes

Fibre-optic communication is a method of transmitting information from one place to another by

sending pulses of light through an optcial fibreThe light forms an electromagnetic carrier wave that is

modulated to carry information First developed in the 1970s fibre optic communication systems has

revolutionized the telecommunications industry and have palyed a major role in the advent of the information

age Because of its advantages over electrical transmissionsoptical fibres have largely replaced copper wire

communications in core networks in the developed world The Indian Railways too is undergoing a transition

from Microwave communication to fibre optic communications

41 | P a g e

BIBLIOGRAPHY AND REFERENCES

1 wwwwikipediacom

2 wwwbritaniccacom

3 wwwirfcacom

4 Motorola GP60 system manual

5 Harris FAS 7000 manual

6 TOSHIBA Manual

32 | P a g e

DISPERSION Dispersion is the optical term for the spreading of the transmits in the fiber It is the bandwidth

limiting phenomenon and comes in two forms Multimode dispersion and chromatic dispersion Chromatic

dispersion is further subdivided into material dispersion and waveguide dispersion

DISPERSION PHENOMENON IN OPTICAL FIBER Dispersion is the time distortion of an optical signal that results from the differences of time of travel

for different components of that signal typically resulting in pulse broadening As the distance traveled by

the signal is more broadening of pulse is more In digital transmission dispersion limits on the maximum

data rate and the maximum distance ie the information-carrying capacity of a fiber link The interference

from broadened pulse in the next interval shall not lead to erroneous interpretation of received signal

OPTICAL DOMAIN Understanding where attenuation and dispersion problems occur helps optical design engineers

determine the better wavelengths at which information can be transmit taking into account distance type of

fiber and the other factors which can severely affect the integrity of the transmitted signal The graph shown

depicts the optical transmission domain as well as the areas where problems arise The wavelength (nm)

is shown on X-axis and attenuation ( dBkm) is shown on Y-axis

There are four transmission windows appear in the figure The first one is at around 850 nm the

second at 1310nm third at 1550 nm and fourth at 1625 nm The last two labeled as C and L band

respectively The 850 nm wavelength at which the original LED technology operated The second window at

1310 nm has low dispersion The 1550 nm called as C-band is ideal wavelength for long haul

communication systems The network engineers can avoid transmitting signal at 1000 nm where Rayleigh

scattering 1240 and 1390 nm where hydroxyl absorption by water occurs to avoid high degree of loss

Optical fibers also can be manufactured to have low dispersion wavelength in the 1550nm region

which is also the point where silica-based fibers have inherently minimal attenuation These fibers are

referred to as dispersion-shifted fibers and are used in long-distance applications with high bit rates For

33 | P a g e

applications utilizing multiple wavelengths it is undesirable to have the zero dispersion point within the

operating

wavelength range

34 | P a g e

SIGNALLING RELAYS

INTRODUCTION A relay is an electromagnetic device which is used to convey information from one circuit to another

circuit through a set of contact ie front or back contact Constructional and electrically relays may be

divided into DC and AC relays because the means by which the electrical energy in the coil is converted in

to mechanical Energy in order to move the contacts are fundamentally different In DC type the contacts are

carried on an armature forming part of a magnetic circuit in which a field is set up by the current flowing in

the coils In AC types the contacts are attached by a link mechanism to a metal sector disc or cylinder in

which currents are induced by the alternating magnetic field produced by the currents in the coils

Every endeavor has been made to explain the action of each type of relay in the simplest possible manner

Relays are sophisticated switch gears used for remote control and succession control of various

electrical equipment In present days they are widely used because they are capable of protecting the

controlled equipment from cross feeding and overloading even as they cater for speedy operations

Most of the relays in present day signaling are electromagnetic devices although some of the relays control

circuits through electronic components like diodetransistors Integrated Chips etc

Railway signaling relays are unique in that

(a) They operate on low voltage and current

(b) They are more articulate as according to their special features they can work under restrictive conditions

and in any specified manner Virtually they can cater for all situations while contributing to speed and

accuracy in operations

CLASSIFICATION OF SIGNALLING RELAYS (a) According to the method of their mounting or fixture they are classified as

(i) Shelf type Relays which are loosely kept on shelves

(ii) Plug in type Relays which are plugged into a pre- wired plug boards

(b) According to their connection and usage they are classified as

(i) Track relays Relay which is directly connected to the track to detect the presence of vehicle

(ii) Line Relays Other than track relay all are line relays Relays connected to the selection circuit

(c) According to their vitality or importance in ensuring train working safety they are classified as

(i) Vital Relays All relays used for traffic control such as signal point controls track detection etc

(ii) Non-vital Relays Relays which operate control aids and accessories like warnings buzzers

Indications etc

(d) According to their special provisions to ensure reliability of their contacts they are classified as

(i) Proved type are those whose normalization after each operation shall be proved in circuit

controlled by their contacts Contacts in which both the springs have metal surfaces on their tips They may

get fused due to high sparking current across them during operation These may prevent relay normalization

and causes unsafe condition in traffic control To avoid this proving of relay normalization after each

operation is necessary

(ii) Non - proved type Need not to be proved to have been normalized after each operation as their

contacts have at least one non-fusible contact (carbon contact)

(e) According to their feed source relays are broadly classified as

(i) DC relays The relay which requires DC power supply for its operations are called DC relays Among

the DC relays

o DC neutral relays This relay closes the same set of contacts on energization with Normal polarity

or Reverse polarity supply

o Polar Relays This relay closes different set of contacts when energized with Reverse polarity

supply They may or may not have contact to close when deenergized

35 | P a g e

(ii) AC Relay AC Induction motor track relays Time element relays flashing indication control etc

(iii) Electronic Relays DC relays with electronic components in them are called electronic relays

DC NEUTRAL RELAY Each Relay has usually one or two coils with a hollow center to accommodate a coreThe coils are

made up of a large numbers of turns of small gauge soft drawn copper wire The two coils can be connected

in series or parallel according to the requirement of relay resistance The ends of the coils are terminated on

binding post to which the control wires are connected Each coil is placed around a core of specially selected

Iron or steel having high permeability and low retentivity The core should be susceptible to magnetism and

at the same time should have little residual magnetism The cores are connected at the top by a yoke to

complete the magnetism coupling between two ends of coils The bottom of each core is equipped with a

large steel or Iron block known as pole piece or face

A flat piece of Iron or steel called armature is supported by brackets which are securely fastened to

the pole piece The armature yoke and the pole pieces are also made of specially selected iron or steel of the

same quality as the core The armature carries the metallic spring contacts which are insulated from it

The circuit through the coils of the relay is closed It sets up a magnetic flux through the core yoke and the

armature The flux passing between the armature and pole faces causes the armatures get attracted to the pole

faces and armature picks up and closes front contacts When the circuit is opened the magnetic flux collapses

and the armature drops away by gravity from the pole faces the front contacts break and back contacts close

The front and back contacts of the relay can be utilised to make or break other circuits Two stop pins of

nonmagnetic material are fixed either on the armature or pole faces so that the armature cannot

come in contact with the pole faces It is essential to maintain a small air-gap between the armature and pole

faces so that low value of residual magnetism may not retain the armature in picked up position and causes

the relay to fail to drop away with a break in its control circuit

GENERAL USAGE

DC Neutral line relays are most commonly used for Railway Signalling controls and detection

Among them plug-in type relays are preferred in larger installations for space considerations Shelf type

relays are also in use mostly in wayside stations

There are many DC Neutral line relays in use with special features such as

(i) Delayed operation

(ii) Biased DC control

(iii) DC control unaffected by AC interference currents

(iv) Getting latched in operated condition till further feeding and others

Usage of DC polar relays is mostly in conjunction with block instruments that control traffic between

stations AC line relays are almost extinct in installations of British Signalling practice They are however

used for time control operations flashing indication control and such other special purposes in installations

with Siemens signalling practice widely Track relays are used according to the type of track detection

circuits chosen for a given location and context While most of the track circuits are still of the DC working

type requiring DC neutral track relays with them the prospects of their being replaced with Electronic track

circuits directly feeding DC line relays in future are great AC Track Circuits are used in DC Traction area

as conventional DC Track Circuits are not suitable there AC Track relays are used with them almost all of

the induction motor type In the British practice of signalling which was first introduced on Indian Railways

non-proved type relays with carbon to metal switching contacts are generally used for vital controls

They facilitate simple circuit designs But with the advent of German Practice introduced by Ms

Siemens later proved type relays with all metal to metal contacts are widely accepted in spite of

complications in circuit design caused by them A recent introduction is that of the same type relays made by

Ms Integra control However for some time now the appreciable features of both the practices are getting

36 | P a g e

incorporated together in the indigenous designs of signalling by railwaymen With this the usage of all types

of relays anywhere can be found without straight jacketed segration of relay types

CHARACTERSTIC OF ELECTRO-MAGNETIC RELAY The following are the characteristic of electro-magnetic relays A brief study of them helps in

understanding the choice of their components and designs features

1) Force of attraction

2) Effect of air gap

3) Effect of Hysterisis

4) Transient condition

FORCE OF ATTRACTION In any electro-magnetic system the force of attraction is given by

Where B - is the flux density a - is the cross sectional area of the particular part of the magnetic

circuit

In the case of a DC neutral Relay B is proportional to the current that is flowing in the coil

surrounding the electro-magnet and thus the force of the attraction is directly proportional to the square of the

current This square relationship has its own advantage especially in the case of DC track relay in that a

small reduction in the current will have a great effect on the working of the relay Also for a given change of

current the make and the break will be quicker with lesser possibility of arcing

EFFECT OF AIR GAP

Curve lsquoArsquo is magnetisation curve for the iron and is all practical purpose a straight line up to the

saturation point Curve lsquoBrsquo is the magnetisation curve for the open-air gap which is a straight line through

out because per magnetisation curve of the whole

magnetic circuit of the relay and for a given force is the sum of the amp-turns for the iron part and the amp-

turns for the air gap

When the front contacts are open the force required to pick up the armature is shown on curve lsquoCrsquo to be F1

but after the armature has operated it will be separated from the core by stop pins In this position the amp-

turns required to maintain the armature is less as indicated by the dotted line from 1 on curve C to 2 on curve

37 | P a g e

F But actually the current in the coil is unaltered the force on the armature is greater than required as

indicated at 3 on curve F Part of this extra force is used to flex the front contacts sufficiently to give good

contact pressure when it is in energised position

The difference between the pick-up and the drop-away current should be as small as practicable in

track relay to ensure good shunting characteristics This is achieved firstly by the choice of good quality relay

iron and secondly by having a small air gap between armature and core If the air gap is not available then

the residual magnetism fluxes might cause the armature to be retained when the supply is disconnected For

this reason residual pins are provided to ensure a definite minimum air gap in the energised position

EFFECT OF HYSTERISIS

Hysterisis is the property by which the flux produced lags behind the current In the de-energized

condition there will be small residual flux in the core When the voltage is applied to the coils the current in

rising to its steady value first causes the flux to rise from 1 to 2 along the curve At this point the flux density

will be sufficient to attract the armature and reduce the air gap the flux then raise to 3 and continue to 4

which corresponds to the steady current in the coils When the voltage is disconnected the current in falling

caused the flux to fall from 4 to 5 along the curve At this point the flux density will fall below the value

required to maintain the armature which will release thus increasing the air gap and reducing the flux to 6

Finally the

flux will decrease from 6 to 1 where the current will again be zero

The relay core is made of material having high permeability and low retentivity As mentioned in

the IRS specification Electromagnet iron may be in the form of a

(a) Bar of silicon steel

(b) Best Yorkshire wrought iron

(c) Swedish charcoal iron

(d) Electrical steel sheets

` This reduces the difference between pick up value and Drop away value By selecting good quality

core material Percentage release and sensitivity of the relay will be improved

TRANSIENT CONDITION

38 | P a g e

When the voltage is applied or disconnected from the coils it takes some little time before the current

become steady These are known as transient conditionsrdquo and are important so far as track relays are

concerned When the voltage is first applied to the coils the magnetic flux in rising cuts the turns on the

coils and in so doing produces a back EMF that opposes the applied voltage and retards the growth of

current

The growth and decay of flux are decided by the relationship between the inductance and resistance

in the circuit is known as time constant It is not fixed quantity in the case of DC neutral relay This value of lsquo

Lrsquo is less when the relay is in de-energised condition (L1) than when the relay is in energised condition (L2)

The magnitude of flux that is established for a given change of current is different in two cases

When the current reaches the pick up value the armature closes and the inductance is increased to L2

due to reduced air gap the flux per amp is increased The increase in flux increased the back EMF during the

movement of the armature after which the current continuous to raise along a new curve corresponding to the

increased inductance until it reaches the final value (ER) This process is indicated above in fig24

When the supply is disconnected the current is obliviously reduced to zero immediately but the flux

decay comparatively slowly owing to the eddy currents produced in the core by the rapid flux change which

tend to maintain the flux The drop away time on a disconnection is however generally negligible See fig

below

If the relay releases due to the reduction in current from say I 2 to I 1 caused by the application of

shunt resistance (as in the case of track relay ) the time taken is much longer than the relay is simply

disconnected The rate of rise or fall of current during the transient conditions is also depends on exterior

circuit values because L and R apply to the whole circuit The production of eddy current in the core the flux

will decay at a slower rate than the current So that the actual release time will be a little longer than it takes

the current to fall to the release

L= Inductance

39 | P a g e

R= Resistance

It is now clear that to reduce releasing time to a minimum it is necessary that

- The relay iron should have low Hysterisis loss and low retentivity

- The degree of over energization of the relay should be restricted

- Connecting a suitable external resistance in series with the relay to keep LR ratio low

In non RE area for track circuit length less than 100M 9 ohm track relay only to be used Using relay

with minimum contacts as they require lesser current which keeps inductance value low

Train working safety is ensured only if the track relay of shortest length track circuit is released

before a light engine running at a highest permitted speed clears it Otherwise the track circuit occupation

may go undetected To avoid this a special provision has to be made in signal control circuits wherever

necessary

The following methods may be adopted for reducing the time lag of track relay

(a) Restrict the over energisation of relay since the release time depends on the initial working current

(b) Connecting a suitable external resistance in series with the relay to keep the LR ratio low

(c) Using relays with minimum contacts as they require lesser operating current keeping the inductance

value low

40 | P a g e

CONCLUSION

Modern signalling is vital for safe and punctual movements of trains In the Indian railways The Signalling

and Telecommunication Department is responsible for providing modern effective and relaible signalling

systems as well as telecommunication systems

The first mode of communication used in Indian Railways was the use of electric telegraph

with the help of Morose code Morose code is the method of providing text information as a series of on-off

tones and lights or clicks that can be directly understood by a skilled listener or observer without special

equipmentEach character (letter or numeral ) is represented by a unique sequence of dots and dashes Later

this system becomes obselete and beggan the era of wireless communication which operated at audio level

frequency range

In wireless communication the significant advances took place the transition to miniature

valves or filament tubesBut this was abandoned too because of excessive current consumption and over

heating of the filament tubes

Fibre-optic communication is a method of transmitting information from one place to another by

sending pulses of light through an optcial fibreThe light forms an electromagnetic carrier wave that is

modulated to carry information First developed in the 1970s fibre optic communication systems has

revolutionized the telecommunications industry and have palyed a major role in the advent of the information

age Because of its advantages over electrical transmissionsoptical fibres have largely replaced copper wire

communications in core networks in the developed world The Indian Railways too is undergoing a transition

from Microwave communication to fibre optic communications

41 | P a g e

BIBLIOGRAPHY AND REFERENCES

1 wwwwikipediacom

2 wwwbritaniccacom

3 wwwirfcacom

4 Motorola GP60 system manual

5 Harris FAS 7000 manual

6 TOSHIBA Manual

33 | P a g e

applications utilizing multiple wavelengths it is undesirable to have the zero dispersion point within the

operating

wavelength range

34 | P a g e

SIGNALLING RELAYS

INTRODUCTION A relay is an electromagnetic device which is used to convey information from one circuit to another

circuit through a set of contact ie front or back contact Constructional and electrically relays may be

divided into DC and AC relays because the means by which the electrical energy in the coil is converted in

to mechanical Energy in order to move the contacts are fundamentally different In DC type the contacts are

carried on an armature forming part of a magnetic circuit in which a field is set up by the current flowing in

the coils In AC types the contacts are attached by a link mechanism to a metal sector disc or cylinder in

which currents are induced by the alternating magnetic field produced by the currents in the coils

Every endeavor has been made to explain the action of each type of relay in the simplest possible manner

Relays are sophisticated switch gears used for remote control and succession control of various

electrical equipment In present days they are widely used because they are capable of protecting the

controlled equipment from cross feeding and overloading even as they cater for speedy operations

Most of the relays in present day signaling are electromagnetic devices although some of the relays control

circuits through electronic components like diodetransistors Integrated Chips etc

Railway signaling relays are unique in that

(a) They operate on low voltage and current

(b) They are more articulate as according to their special features they can work under restrictive conditions

and in any specified manner Virtually they can cater for all situations while contributing to speed and

accuracy in operations

CLASSIFICATION OF SIGNALLING RELAYS (a) According to the method of their mounting or fixture they are classified as

(i) Shelf type Relays which are loosely kept on shelves

(ii) Plug in type Relays which are plugged into a pre- wired plug boards

(b) According to their connection and usage they are classified as

(i) Track relays Relay which is directly connected to the track to detect the presence of vehicle

(ii) Line Relays Other than track relay all are line relays Relays connected to the selection circuit

(c) According to their vitality or importance in ensuring train working safety they are classified as

(i) Vital Relays All relays used for traffic control such as signal point controls track detection etc

(ii) Non-vital Relays Relays which operate control aids and accessories like warnings buzzers

Indications etc

(d) According to their special provisions to ensure reliability of their contacts they are classified as

(i) Proved type are those whose normalization after each operation shall be proved in circuit

controlled by their contacts Contacts in which both the springs have metal surfaces on their tips They may

get fused due to high sparking current across them during operation These may prevent relay normalization

and causes unsafe condition in traffic control To avoid this proving of relay normalization after each

operation is necessary

(ii) Non - proved type Need not to be proved to have been normalized after each operation as their

contacts have at least one non-fusible contact (carbon contact)

(e) According to their feed source relays are broadly classified as

(i) DC relays The relay which requires DC power supply for its operations are called DC relays Among

the DC relays

o DC neutral relays This relay closes the same set of contacts on energization with Normal polarity

or Reverse polarity supply

o Polar Relays This relay closes different set of contacts when energized with Reverse polarity

supply They may or may not have contact to close when deenergized

35 | P a g e

(ii) AC Relay AC Induction motor track relays Time element relays flashing indication control etc

(iii) Electronic Relays DC relays with electronic components in them are called electronic relays

DC NEUTRAL RELAY Each Relay has usually one or two coils with a hollow center to accommodate a coreThe coils are

made up of a large numbers of turns of small gauge soft drawn copper wire The two coils can be connected

in series or parallel according to the requirement of relay resistance The ends of the coils are terminated on

binding post to which the control wires are connected Each coil is placed around a core of specially selected

Iron or steel having high permeability and low retentivity The core should be susceptible to magnetism and

at the same time should have little residual magnetism The cores are connected at the top by a yoke to

complete the magnetism coupling between two ends of coils The bottom of each core is equipped with a

large steel or Iron block known as pole piece or face

A flat piece of Iron or steel called armature is supported by brackets which are securely fastened to

the pole piece The armature yoke and the pole pieces are also made of specially selected iron or steel of the

same quality as the core The armature carries the metallic spring contacts which are insulated from it

The circuit through the coils of the relay is closed It sets up a magnetic flux through the core yoke and the

armature The flux passing between the armature and pole faces causes the armatures get attracted to the pole

faces and armature picks up and closes front contacts When the circuit is opened the magnetic flux collapses

and the armature drops away by gravity from the pole faces the front contacts break and back contacts close

The front and back contacts of the relay can be utilised to make or break other circuits Two stop pins of

nonmagnetic material are fixed either on the armature or pole faces so that the armature cannot

come in contact with the pole faces It is essential to maintain a small air-gap between the armature and pole

faces so that low value of residual magnetism may not retain the armature in picked up position and causes

the relay to fail to drop away with a break in its control circuit

GENERAL USAGE

DC Neutral line relays are most commonly used for Railway Signalling controls and detection

Among them plug-in type relays are preferred in larger installations for space considerations Shelf type

relays are also in use mostly in wayside stations

There are many DC Neutral line relays in use with special features such as

(i) Delayed operation

(ii) Biased DC control

(iii) DC control unaffected by AC interference currents

(iv) Getting latched in operated condition till further feeding and others

Usage of DC polar relays is mostly in conjunction with block instruments that control traffic between

stations AC line relays are almost extinct in installations of British Signalling practice They are however

used for time control operations flashing indication control and such other special purposes in installations

with Siemens signalling practice widely Track relays are used according to the type of track detection

circuits chosen for a given location and context While most of the track circuits are still of the DC working

type requiring DC neutral track relays with them the prospects of their being replaced with Electronic track

circuits directly feeding DC line relays in future are great AC Track Circuits are used in DC Traction area

as conventional DC Track Circuits are not suitable there AC Track relays are used with them almost all of

the induction motor type In the British practice of signalling which was first introduced on Indian Railways

non-proved type relays with carbon to metal switching contacts are generally used for vital controls

They facilitate simple circuit designs But with the advent of German Practice introduced by Ms

Siemens later proved type relays with all metal to metal contacts are widely accepted in spite of

complications in circuit design caused by them A recent introduction is that of the same type relays made by

Ms Integra control However for some time now the appreciable features of both the practices are getting

36 | P a g e

incorporated together in the indigenous designs of signalling by railwaymen With this the usage of all types

of relays anywhere can be found without straight jacketed segration of relay types

CHARACTERSTIC OF ELECTRO-MAGNETIC RELAY The following are the characteristic of electro-magnetic relays A brief study of them helps in

understanding the choice of their components and designs features

1) Force of attraction

2) Effect of air gap

3) Effect of Hysterisis

4) Transient condition

FORCE OF ATTRACTION In any electro-magnetic system the force of attraction is given by

Where B - is the flux density a - is the cross sectional area of the particular part of the magnetic

circuit

In the case of a DC neutral Relay B is proportional to the current that is flowing in the coil

surrounding the electro-magnet and thus the force of the attraction is directly proportional to the square of the

current This square relationship has its own advantage especially in the case of DC track relay in that a

small reduction in the current will have a great effect on the working of the relay Also for a given change of

current the make and the break will be quicker with lesser possibility of arcing

EFFECT OF AIR GAP

Curve lsquoArsquo is magnetisation curve for the iron and is all practical purpose a straight line up to the

saturation point Curve lsquoBrsquo is the magnetisation curve for the open-air gap which is a straight line through

out because per magnetisation curve of the whole

magnetic circuit of the relay and for a given force is the sum of the amp-turns for the iron part and the amp-

turns for the air gap

When the front contacts are open the force required to pick up the armature is shown on curve lsquoCrsquo to be F1

but after the armature has operated it will be separated from the core by stop pins In this position the amp-

turns required to maintain the armature is less as indicated by the dotted line from 1 on curve C to 2 on curve

37 | P a g e

F But actually the current in the coil is unaltered the force on the armature is greater than required as

indicated at 3 on curve F Part of this extra force is used to flex the front contacts sufficiently to give good

contact pressure when it is in energised position

The difference between the pick-up and the drop-away current should be as small as practicable in

track relay to ensure good shunting characteristics This is achieved firstly by the choice of good quality relay

iron and secondly by having a small air gap between armature and core If the air gap is not available then

the residual magnetism fluxes might cause the armature to be retained when the supply is disconnected For

this reason residual pins are provided to ensure a definite minimum air gap in the energised position

EFFECT OF HYSTERISIS

Hysterisis is the property by which the flux produced lags behind the current In the de-energized

condition there will be small residual flux in the core When the voltage is applied to the coils the current in

rising to its steady value first causes the flux to rise from 1 to 2 along the curve At this point the flux density

will be sufficient to attract the armature and reduce the air gap the flux then raise to 3 and continue to 4

which corresponds to the steady current in the coils When the voltage is disconnected the current in falling

caused the flux to fall from 4 to 5 along the curve At this point the flux density will fall below the value

required to maintain the armature which will release thus increasing the air gap and reducing the flux to 6

Finally the

flux will decrease from 6 to 1 where the current will again be zero

The relay core is made of material having high permeability and low retentivity As mentioned in

the IRS specification Electromagnet iron may be in the form of a

(a) Bar of silicon steel

(b) Best Yorkshire wrought iron

(c) Swedish charcoal iron

(d) Electrical steel sheets

` This reduces the difference between pick up value and Drop away value By selecting good quality

core material Percentage release and sensitivity of the relay will be improved

TRANSIENT CONDITION

38 | P a g e

When the voltage is applied or disconnected from the coils it takes some little time before the current

become steady These are known as transient conditionsrdquo and are important so far as track relays are

concerned When the voltage is first applied to the coils the magnetic flux in rising cuts the turns on the

coils and in so doing produces a back EMF that opposes the applied voltage and retards the growth of

current

The growth and decay of flux are decided by the relationship between the inductance and resistance

in the circuit is known as time constant It is not fixed quantity in the case of DC neutral relay This value of lsquo

Lrsquo is less when the relay is in de-energised condition (L1) than when the relay is in energised condition (L2)

The magnitude of flux that is established for a given change of current is different in two cases

When the current reaches the pick up value the armature closes and the inductance is increased to L2

due to reduced air gap the flux per amp is increased The increase in flux increased the back EMF during the

movement of the armature after which the current continuous to raise along a new curve corresponding to the

increased inductance until it reaches the final value (ER) This process is indicated above in fig24

When the supply is disconnected the current is obliviously reduced to zero immediately but the flux

decay comparatively slowly owing to the eddy currents produced in the core by the rapid flux change which

tend to maintain the flux The drop away time on a disconnection is however generally negligible See fig

below

If the relay releases due to the reduction in current from say I 2 to I 1 caused by the application of

shunt resistance (as in the case of track relay ) the time taken is much longer than the relay is simply

disconnected The rate of rise or fall of current during the transient conditions is also depends on exterior

circuit values because L and R apply to the whole circuit The production of eddy current in the core the flux

will decay at a slower rate than the current So that the actual release time will be a little longer than it takes

the current to fall to the release

L= Inductance

39 | P a g e

R= Resistance

It is now clear that to reduce releasing time to a minimum it is necessary that

- The relay iron should have low Hysterisis loss and low retentivity

- The degree of over energization of the relay should be restricted

- Connecting a suitable external resistance in series with the relay to keep LR ratio low

In non RE area for track circuit length less than 100M 9 ohm track relay only to be used Using relay

with minimum contacts as they require lesser current which keeps inductance value low

Train working safety is ensured only if the track relay of shortest length track circuit is released

before a light engine running at a highest permitted speed clears it Otherwise the track circuit occupation

may go undetected To avoid this a special provision has to be made in signal control circuits wherever

necessary

The following methods may be adopted for reducing the time lag of track relay

(a) Restrict the over energisation of relay since the release time depends on the initial working current

(b) Connecting a suitable external resistance in series with the relay to keep the LR ratio low

(c) Using relays with minimum contacts as they require lesser operating current keeping the inductance

value low

40 | P a g e

CONCLUSION

Modern signalling is vital for safe and punctual movements of trains In the Indian railways The Signalling

and Telecommunication Department is responsible for providing modern effective and relaible signalling

systems as well as telecommunication systems

The first mode of communication used in Indian Railways was the use of electric telegraph

with the help of Morose code Morose code is the method of providing text information as a series of on-off

tones and lights or clicks that can be directly understood by a skilled listener or observer without special

equipmentEach character (letter or numeral ) is represented by a unique sequence of dots and dashes Later

this system becomes obselete and beggan the era of wireless communication which operated at audio level

frequency range

In wireless communication the significant advances took place the transition to miniature

valves or filament tubesBut this was abandoned too because of excessive current consumption and over

heating of the filament tubes

Fibre-optic communication is a method of transmitting information from one place to another by

sending pulses of light through an optcial fibreThe light forms an electromagnetic carrier wave that is

modulated to carry information First developed in the 1970s fibre optic communication systems has

revolutionized the telecommunications industry and have palyed a major role in the advent of the information

age Because of its advantages over electrical transmissionsoptical fibres have largely replaced copper wire

communications in core networks in the developed world The Indian Railways too is undergoing a transition

from Microwave communication to fibre optic communications

41 | P a g e

BIBLIOGRAPHY AND REFERENCES

1 wwwwikipediacom

2 wwwbritaniccacom

3 wwwirfcacom

4 Motorola GP60 system manual

5 Harris FAS 7000 manual

6 TOSHIBA Manual

34 | P a g e

SIGNALLING RELAYS

INTRODUCTION A relay is an electromagnetic device which is used to convey information from one circuit to another

circuit through a set of contact ie front or back contact Constructional and electrically relays may be

divided into DC and AC relays because the means by which the electrical energy in the coil is converted in

to mechanical Energy in order to move the contacts are fundamentally different In DC type the contacts are

carried on an armature forming part of a magnetic circuit in which a field is set up by the current flowing in

the coils In AC types the contacts are attached by a link mechanism to a metal sector disc or cylinder in

which currents are induced by the alternating magnetic field produced by the currents in the coils

Every endeavor has been made to explain the action of each type of relay in the simplest possible manner

Relays are sophisticated switch gears used for remote control and succession control of various

electrical equipment In present days they are widely used because they are capable of protecting the

controlled equipment from cross feeding and overloading even as they cater for speedy operations

Most of the relays in present day signaling are electromagnetic devices although some of the relays control

circuits through electronic components like diodetransistors Integrated Chips etc

Railway signaling relays are unique in that

(a) They operate on low voltage and current

(b) They are more articulate as according to their special features they can work under restrictive conditions

and in any specified manner Virtually they can cater for all situations while contributing to speed and

accuracy in operations

CLASSIFICATION OF SIGNALLING RELAYS (a) According to the method of their mounting or fixture they are classified as

(i) Shelf type Relays which are loosely kept on shelves

(ii) Plug in type Relays which are plugged into a pre- wired plug boards

(b) According to their connection and usage they are classified as

(i) Track relays Relay which is directly connected to the track to detect the presence of vehicle

(ii) Line Relays Other than track relay all are line relays Relays connected to the selection circuit

(c) According to their vitality or importance in ensuring train working safety they are classified as

(i) Vital Relays All relays used for traffic control such as signal point controls track detection etc

(ii) Non-vital Relays Relays which operate control aids and accessories like warnings buzzers

Indications etc

(d) According to their special provisions to ensure reliability of their contacts they are classified as

(i) Proved type are those whose normalization after each operation shall be proved in circuit

controlled by their contacts Contacts in which both the springs have metal surfaces on their tips They may

get fused due to high sparking current across them during operation These may prevent relay normalization

and causes unsafe condition in traffic control To avoid this proving of relay normalization after each

operation is necessary

(ii) Non - proved type Need not to be proved to have been normalized after each operation as their

contacts have at least one non-fusible contact (carbon contact)

(e) According to their feed source relays are broadly classified as

(i) DC relays The relay which requires DC power supply for its operations are called DC relays Among

the DC relays

o DC neutral relays This relay closes the same set of contacts on energization with Normal polarity

or Reverse polarity supply

o Polar Relays This relay closes different set of contacts when energized with Reverse polarity

supply They may or may not have contact to close when deenergized

35 | P a g e

(ii) AC Relay AC Induction motor track relays Time element relays flashing indication control etc

(iii) Electronic Relays DC relays with electronic components in them are called electronic relays

DC NEUTRAL RELAY Each Relay has usually one or two coils with a hollow center to accommodate a coreThe coils are

made up of a large numbers of turns of small gauge soft drawn copper wire The two coils can be connected

in series or parallel according to the requirement of relay resistance The ends of the coils are terminated on

binding post to which the control wires are connected Each coil is placed around a core of specially selected

Iron or steel having high permeability and low retentivity The core should be susceptible to magnetism and

at the same time should have little residual magnetism The cores are connected at the top by a yoke to

complete the magnetism coupling between two ends of coils The bottom of each core is equipped with a

large steel or Iron block known as pole piece or face

A flat piece of Iron or steel called armature is supported by brackets which are securely fastened to

the pole piece The armature yoke and the pole pieces are also made of specially selected iron or steel of the

same quality as the core The armature carries the metallic spring contacts which are insulated from it

The circuit through the coils of the relay is closed It sets up a magnetic flux through the core yoke and the

armature The flux passing between the armature and pole faces causes the armatures get attracted to the pole

faces and armature picks up and closes front contacts When the circuit is opened the magnetic flux collapses

and the armature drops away by gravity from the pole faces the front contacts break and back contacts close

The front and back contacts of the relay can be utilised to make or break other circuits Two stop pins of

nonmagnetic material are fixed either on the armature or pole faces so that the armature cannot

come in contact with the pole faces It is essential to maintain a small air-gap between the armature and pole

faces so that low value of residual magnetism may not retain the armature in picked up position and causes

the relay to fail to drop away with a break in its control circuit

GENERAL USAGE

DC Neutral line relays are most commonly used for Railway Signalling controls and detection

Among them plug-in type relays are preferred in larger installations for space considerations Shelf type

relays are also in use mostly in wayside stations

There are many DC Neutral line relays in use with special features such as

(i) Delayed operation

(ii) Biased DC control

(iii) DC control unaffected by AC interference currents

(iv) Getting latched in operated condition till further feeding and others

Usage of DC polar relays is mostly in conjunction with block instruments that control traffic between

stations AC line relays are almost extinct in installations of British Signalling practice They are however

used for time control operations flashing indication control and such other special purposes in installations

with Siemens signalling practice widely Track relays are used according to the type of track detection

circuits chosen for a given location and context While most of the track circuits are still of the DC working

type requiring DC neutral track relays with them the prospects of their being replaced with Electronic track

circuits directly feeding DC line relays in future are great AC Track Circuits are used in DC Traction area

as conventional DC Track Circuits are not suitable there AC Track relays are used with them almost all of

the induction motor type In the British practice of signalling which was first introduced on Indian Railways

non-proved type relays with carbon to metal switching contacts are generally used for vital controls

They facilitate simple circuit designs But with the advent of German Practice introduced by Ms

Siemens later proved type relays with all metal to metal contacts are widely accepted in spite of

complications in circuit design caused by them A recent introduction is that of the same type relays made by

Ms Integra control However for some time now the appreciable features of both the practices are getting

36 | P a g e

incorporated together in the indigenous designs of signalling by railwaymen With this the usage of all types

of relays anywhere can be found without straight jacketed segration of relay types

CHARACTERSTIC OF ELECTRO-MAGNETIC RELAY The following are the characteristic of electro-magnetic relays A brief study of them helps in

understanding the choice of their components and designs features

1) Force of attraction

2) Effect of air gap

3) Effect of Hysterisis

4) Transient condition

FORCE OF ATTRACTION In any electro-magnetic system the force of attraction is given by

Where B - is the flux density a - is the cross sectional area of the particular part of the magnetic

circuit

In the case of a DC neutral Relay B is proportional to the current that is flowing in the coil

surrounding the electro-magnet and thus the force of the attraction is directly proportional to the square of the

current This square relationship has its own advantage especially in the case of DC track relay in that a

small reduction in the current will have a great effect on the working of the relay Also for a given change of

current the make and the break will be quicker with lesser possibility of arcing

EFFECT OF AIR GAP

Curve lsquoArsquo is magnetisation curve for the iron and is all practical purpose a straight line up to the

saturation point Curve lsquoBrsquo is the magnetisation curve for the open-air gap which is a straight line through

out because per magnetisation curve of the whole

magnetic circuit of the relay and for a given force is the sum of the amp-turns for the iron part and the amp-

turns for the air gap

When the front contacts are open the force required to pick up the armature is shown on curve lsquoCrsquo to be F1

but after the armature has operated it will be separated from the core by stop pins In this position the amp-

turns required to maintain the armature is less as indicated by the dotted line from 1 on curve C to 2 on curve

37 | P a g e

F But actually the current in the coil is unaltered the force on the armature is greater than required as

indicated at 3 on curve F Part of this extra force is used to flex the front contacts sufficiently to give good

contact pressure when it is in energised position

The difference between the pick-up and the drop-away current should be as small as practicable in

track relay to ensure good shunting characteristics This is achieved firstly by the choice of good quality relay

iron and secondly by having a small air gap between armature and core If the air gap is not available then

the residual magnetism fluxes might cause the armature to be retained when the supply is disconnected For

this reason residual pins are provided to ensure a definite minimum air gap in the energised position

EFFECT OF HYSTERISIS

Hysterisis is the property by which the flux produced lags behind the current In the de-energized

condition there will be small residual flux in the core When the voltage is applied to the coils the current in

rising to its steady value first causes the flux to rise from 1 to 2 along the curve At this point the flux density

will be sufficient to attract the armature and reduce the air gap the flux then raise to 3 and continue to 4

which corresponds to the steady current in the coils When the voltage is disconnected the current in falling

caused the flux to fall from 4 to 5 along the curve At this point the flux density will fall below the value

required to maintain the armature which will release thus increasing the air gap and reducing the flux to 6

Finally the

flux will decrease from 6 to 1 where the current will again be zero

The relay core is made of material having high permeability and low retentivity As mentioned in

the IRS specification Electromagnet iron may be in the form of a

(a) Bar of silicon steel

(b) Best Yorkshire wrought iron

(c) Swedish charcoal iron

(d) Electrical steel sheets

` This reduces the difference between pick up value and Drop away value By selecting good quality

core material Percentage release and sensitivity of the relay will be improved

TRANSIENT CONDITION

38 | P a g e

When the voltage is applied or disconnected from the coils it takes some little time before the current

become steady These are known as transient conditionsrdquo and are important so far as track relays are

concerned When the voltage is first applied to the coils the magnetic flux in rising cuts the turns on the

coils and in so doing produces a back EMF that opposes the applied voltage and retards the growth of

current

The growth and decay of flux are decided by the relationship between the inductance and resistance

in the circuit is known as time constant It is not fixed quantity in the case of DC neutral relay This value of lsquo

Lrsquo is less when the relay is in de-energised condition (L1) than when the relay is in energised condition (L2)

The magnitude of flux that is established for a given change of current is different in two cases

When the current reaches the pick up value the armature closes and the inductance is increased to L2

due to reduced air gap the flux per amp is increased The increase in flux increased the back EMF during the

movement of the armature after which the current continuous to raise along a new curve corresponding to the

increased inductance until it reaches the final value (ER) This process is indicated above in fig24

When the supply is disconnected the current is obliviously reduced to zero immediately but the flux

decay comparatively slowly owing to the eddy currents produced in the core by the rapid flux change which

tend to maintain the flux The drop away time on a disconnection is however generally negligible See fig

below

If the relay releases due to the reduction in current from say I 2 to I 1 caused by the application of

shunt resistance (as in the case of track relay ) the time taken is much longer than the relay is simply

disconnected The rate of rise or fall of current during the transient conditions is also depends on exterior

circuit values because L and R apply to the whole circuit The production of eddy current in the core the flux

will decay at a slower rate than the current So that the actual release time will be a little longer than it takes

the current to fall to the release

L= Inductance

39 | P a g e

R= Resistance

It is now clear that to reduce releasing time to a minimum it is necessary that

- The relay iron should have low Hysterisis loss and low retentivity

- The degree of over energization of the relay should be restricted

- Connecting a suitable external resistance in series with the relay to keep LR ratio low

In non RE area for track circuit length less than 100M 9 ohm track relay only to be used Using relay

with minimum contacts as they require lesser current which keeps inductance value low

Train working safety is ensured only if the track relay of shortest length track circuit is released

before a light engine running at a highest permitted speed clears it Otherwise the track circuit occupation

may go undetected To avoid this a special provision has to be made in signal control circuits wherever

necessary

The following methods may be adopted for reducing the time lag of track relay

(a) Restrict the over energisation of relay since the release time depends on the initial working current

(b) Connecting a suitable external resistance in series with the relay to keep the LR ratio low

(c) Using relays with minimum contacts as they require lesser operating current keeping the inductance

value low

40 | P a g e

CONCLUSION

Modern signalling is vital for safe and punctual movements of trains In the Indian railways The Signalling

and Telecommunication Department is responsible for providing modern effective and relaible signalling

systems as well as telecommunication systems

The first mode of communication used in Indian Railways was the use of electric telegraph

with the help of Morose code Morose code is the method of providing text information as a series of on-off

tones and lights or clicks that can be directly understood by a skilled listener or observer without special

equipmentEach character (letter or numeral ) is represented by a unique sequence of dots and dashes Later

this system becomes obselete and beggan the era of wireless communication which operated at audio level

frequency range

In wireless communication the significant advances took place the transition to miniature

valves or filament tubesBut this was abandoned too because of excessive current consumption and over

heating of the filament tubes

Fibre-optic communication is a method of transmitting information from one place to another by

sending pulses of light through an optcial fibreThe light forms an electromagnetic carrier wave that is

modulated to carry information First developed in the 1970s fibre optic communication systems has

revolutionized the telecommunications industry and have palyed a major role in the advent of the information

age Because of its advantages over electrical transmissionsoptical fibres have largely replaced copper wire

communications in core networks in the developed world The Indian Railways too is undergoing a transition

from Microwave communication to fibre optic communications

41 | P a g e

BIBLIOGRAPHY AND REFERENCES

1 wwwwikipediacom

2 wwwbritaniccacom

3 wwwirfcacom

4 Motorola GP60 system manual

5 Harris FAS 7000 manual

6 TOSHIBA Manual

35 | P a g e

(ii) AC Relay AC Induction motor track relays Time element relays flashing indication control etc

(iii) Electronic Relays DC relays with electronic components in them are called electronic relays

DC NEUTRAL RELAY Each Relay has usually one or two coils with a hollow center to accommodate a coreThe coils are

made up of a large numbers of turns of small gauge soft drawn copper wire The two coils can be connected

in series or parallel according to the requirement of relay resistance The ends of the coils are terminated on

binding post to which the control wires are connected Each coil is placed around a core of specially selected

Iron or steel having high permeability and low retentivity The core should be susceptible to magnetism and

at the same time should have little residual magnetism The cores are connected at the top by a yoke to

complete the magnetism coupling between two ends of coils The bottom of each core is equipped with a

large steel or Iron block known as pole piece or face

A flat piece of Iron or steel called armature is supported by brackets which are securely fastened to

the pole piece The armature yoke and the pole pieces are also made of specially selected iron or steel of the

same quality as the core The armature carries the metallic spring contacts which are insulated from it

The circuit through the coils of the relay is closed It sets up a magnetic flux through the core yoke and the

armature The flux passing between the armature and pole faces causes the armatures get attracted to the pole

faces and armature picks up and closes front contacts When the circuit is opened the magnetic flux collapses

and the armature drops away by gravity from the pole faces the front contacts break and back contacts close

The front and back contacts of the relay can be utilised to make or break other circuits Two stop pins of

nonmagnetic material are fixed either on the armature or pole faces so that the armature cannot

come in contact with the pole faces It is essential to maintain a small air-gap between the armature and pole

faces so that low value of residual magnetism may not retain the armature in picked up position and causes

the relay to fail to drop away with a break in its control circuit

GENERAL USAGE

DC Neutral line relays are most commonly used for Railway Signalling controls and detection

Among them plug-in type relays are preferred in larger installations for space considerations Shelf type

relays are also in use mostly in wayside stations

There are many DC Neutral line relays in use with special features such as

(i) Delayed operation

(ii) Biased DC control

(iii) DC control unaffected by AC interference currents

(iv) Getting latched in operated condition till further feeding and others

Usage of DC polar relays is mostly in conjunction with block instruments that control traffic between

stations AC line relays are almost extinct in installations of British Signalling practice They are however

used for time control operations flashing indication control and such other special purposes in installations

with Siemens signalling practice widely Track relays are used according to the type of track detection

circuits chosen for a given location and context While most of the track circuits are still of the DC working

type requiring DC neutral track relays with them the prospects of their being replaced with Electronic track

circuits directly feeding DC line relays in future are great AC Track Circuits are used in DC Traction area

as conventional DC Track Circuits are not suitable there AC Track relays are used with them almost all of

the induction motor type In the British practice of signalling which was first introduced on Indian Railways

non-proved type relays with carbon to metal switching contacts are generally used for vital controls

They facilitate simple circuit designs But with the advent of German Practice introduced by Ms

Siemens later proved type relays with all metal to metal contacts are widely accepted in spite of

complications in circuit design caused by them A recent introduction is that of the same type relays made by

Ms Integra control However for some time now the appreciable features of both the practices are getting

36 | P a g e

incorporated together in the indigenous designs of signalling by railwaymen With this the usage of all types

of relays anywhere can be found without straight jacketed segration of relay types

CHARACTERSTIC OF ELECTRO-MAGNETIC RELAY The following are the characteristic of electro-magnetic relays A brief study of them helps in

understanding the choice of their components and designs features

1) Force of attraction

2) Effect of air gap

3) Effect of Hysterisis

4) Transient condition

FORCE OF ATTRACTION In any electro-magnetic system the force of attraction is given by

Where B - is the flux density a - is the cross sectional area of the particular part of the magnetic

circuit

In the case of a DC neutral Relay B is proportional to the current that is flowing in the coil

surrounding the electro-magnet and thus the force of the attraction is directly proportional to the square of the

current This square relationship has its own advantage especially in the case of DC track relay in that a

small reduction in the current will have a great effect on the working of the relay Also for a given change of

current the make and the break will be quicker with lesser possibility of arcing

EFFECT OF AIR GAP

Curve lsquoArsquo is magnetisation curve for the iron and is all practical purpose a straight line up to the

saturation point Curve lsquoBrsquo is the magnetisation curve for the open-air gap which is a straight line through

out because per magnetisation curve of the whole

magnetic circuit of the relay and for a given force is the sum of the amp-turns for the iron part and the amp-

turns for the air gap

When the front contacts are open the force required to pick up the armature is shown on curve lsquoCrsquo to be F1

but after the armature has operated it will be separated from the core by stop pins In this position the amp-

turns required to maintain the armature is less as indicated by the dotted line from 1 on curve C to 2 on curve

37 | P a g e

F But actually the current in the coil is unaltered the force on the armature is greater than required as

indicated at 3 on curve F Part of this extra force is used to flex the front contacts sufficiently to give good

contact pressure when it is in energised position

The difference between the pick-up and the drop-away current should be as small as practicable in

track relay to ensure good shunting characteristics This is achieved firstly by the choice of good quality relay

iron and secondly by having a small air gap between armature and core If the air gap is not available then

the residual magnetism fluxes might cause the armature to be retained when the supply is disconnected For

this reason residual pins are provided to ensure a definite minimum air gap in the energised position

EFFECT OF HYSTERISIS

Hysterisis is the property by which the flux produced lags behind the current In the de-energized

condition there will be small residual flux in the core When the voltage is applied to the coils the current in

rising to its steady value first causes the flux to rise from 1 to 2 along the curve At this point the flux density

will be sufficient to attract the armature and reduce the air gap the flux then raise to 3 and continue to 4

which corresponds to the steady current in the coils When the voltage is disconnected the current in falling

caused the flux to fall from 4 to 5 along the curve At this point the flux density will fall below the value

required to maintain the armature which will release thus increasing the air gap and reducing the flux to 6

Finally the

flux will decrease from 6 to 1 where the current will again be zero

The relay core is made of material having high permeability and low retentivity As mentioned in

the IRS specification Electromagnet iron may be in the form of a

(a) Bar of silicon steel

(b) Best Yorkshire wrought iron

(c) Swedish charcoal iron

(d) Electrical steel sheets

` This reduces the difference between pick up value and Drop away value By selecting good quality

core material Percentage release and sensitivity of the relay will be improved

TRANSIENT CONDITION

38 | P a g e

When the voltage is applied or disconnected from the coils it takes some little time before the current

become steady These are known as transient conditionsrdquo and are important so far as track relays are

concerned When the voltage is first applied to the coils the magnetic flux in rising cuts the turns on the

coils and in so doing produces a back EMF that opposes the applied voltage and retards the growth of

current

The growth and decay of flux are decided by the relationship between the inductance and resistance

in the circuit is known as time constant It is not fixed quantity in the case of DC neutral relay This value of lsquo

Lrsquo is less when the relay is in de-energised condition (L1) than when the relay is in energised condition (L2)

The magnitude of flux that is established for a given change of current is different in two cases

When the current reaches the pick up value the armature closes and the inductance is increased to L2

due to reduced air gap the flux per amp is increased The increase in flux increased the back EMF during the

movement of the armature after which the current continuous to raise along a new curve corresponding to the

increased inductance until it reaches the final value (ER) This process is indicated above in fig24

When the supply is disconnected the current is obliviously reduced to zero immediately but the flux

decay comparatively slowly owing to the eddy currents produced in the core by the rapid flux change which

tend to maintain the flux The drop away time on a disconnection is however generally negligible See fig

below

If the relay releases due to the reduction in current from say I 2 to I 1 caused by the application of

shunt resistance (as in the case of track relay ) the time taken is much longer than the relay is simply

disconnected The rate of rise or fall of current during the transient conditions is also depends on exterior

circuit values because L and R apply to the whole circuit The production of eddy current in the core the flux

will decay at a slower rate than the current So that the actual release time will be a little longer than it takes

the current to fall to the release

L= Inductance

39 | P a g e

R= Resistance

It is now clear that to reduce releasing time to a minimum it is necessary that

- The relay iron should have low Hysterisis loss and low retentivity

- The degree of over energization of the relay should be restricted

- Connecting a suitable external resistance in series with the relay to keep LR ratio low

In non RE area for track circuit length less than 100M 9 ohm track relay only to be used Using relay

with minimum contacts as they require lesser current which keeps inductance value low

Train working safety is ensured only if the track relay of shortest length track circuit is released

before a light engine running at a highest permitted speed clears it Otherwise the track circuit occupation

may go undetected To avoid this a special provision has to be made in signal control circuits wherever

necessary

The following methods may be adopted for reducing the time lag of track relay

(a) Restrict the over energisation of relay since the release time depends on the initial working current

(b) Connecting a suitable external resistance in series with the relay to keep the LR ratio low

(c) Using relays with minimum contacts as they require lesser operating current keeping the inductance

value low

40 | P a g e

CONCLUSION

Modern signalling is vital for safe and punctual movements of trains In the Indian railways The Signalling

and Telecommunication Department is responsible for providing modern effective and relaible signalling

systems as well as telecommunication systems

The first mode of communication used in Indian Railways was the use of electric telegraph

with the help of Morose code Morose code is the method of providing text information as a series of on-off

tones and lights or clicks that can be directly understood by a skilled listener or observer without special

equipmentEach character (letter or numeral ) is represented by a unique sequence of dots and dashes Later

this system becomes obselete and beggan the era of wireless communication which operated at audio level

frequency range

In wireless communication the significant advances took place the transition to miniature

valves or filament tubesBut this was abandoned too because of excessive current consumption and over

heating of the filament tubes

Fibre-optic communication is a method of transmitting information from one place to another by

sending pulses of light through an optcial fibreThe light forms an electromagnetic carrier wave that is

modulated to carry information First developed in the 1970s fibre optic communication systems has

revolutionized the telecommunications industry and have palyed a major role in the advent of the information

age Because of its advantages over electrical transmissionsoptical fibres have largely replaced copper wire

communications in core networks in the developed world The Indian Railways too is undergoing a transition

from Microwave communication to fibre optic communications

41 | P a g e

BIBLIOGRAPHY AND REFERENCES

1 wwwwikipediacom

2 wwwbritaniccacom

3 wwwirfcacom

4 Motorola GP60 system manual

5 Harris FAS 7000 manual

6 TOSHIBA Manual

36 | P a g e

incorporated together in the indigenous designs of signalling by railwaymen With this the usage of all types

of relays anywhere can be found without straight jacketed segration of relay types

CHARACTERSTIC OF ELECTRO-MAGNETIC RELAY The following are the characteristic of electro-magnetic relays A brief study of them helps in

understanding the choice of their components and designs features

1) Force of attraction

2) Effect of air gap

3) Effect of Hysterisis

4) Transient condition

FORCE OF ATTRACTION In any electro-magnetic system the force of attraction is given by

Where B - is the flux density a - is the cross sectional area of the particular part of the magnetic

circuit

In the case of a DC neutral Relay B is proportional to the current that is flowing in the coil

surrounding the electro-magnet and thus the force of the attraction is directly proportional to the square of the

current This square relationship has its own advantage especially in the case of DC track relay in that a

small reduction in the current will have a great effect on the working of the relay Also for a given change of

current the make and the break will be quicker with lesser possibility of arcing

EFFECT OF AIR GAP

Curve lsquoArsquo is magnetisation curve for the iron and is all practical purpose a straight line up to the

saturation point Curve lsquoBrsquo is the magnetisation curve for the open-air gap which is a straight line through

out because per magnetisation curve of the whole

magnetic circuit of the relay and for a given force is the sum of the amp-turns for the iron part and the amp-

turns for the air gap

When the front contacts are open the force required to pick up the armature is shown on curve lsquoCrsquo to be F1

but after the armature has operated it will be separated from the core by stop pins In this position the amp-

turns required to maintain the armature is less as indicated by the dotted line from 1 on curve C to 2 on curve

37 | P a g e

F But actually the current in the coil is unaltered the force on the armature is greater than required as

indicated at 3 on curve F Part of this extra force is used to flex the front contacts sufficiently to give good

contact pressure when it is in energised position

The difference between the pick-up and the drop-away current should be as small as practicable in

track relay to ensure good shunting characteristics This is achieved firstly by the choice of good quality relay

iron and secondly by having a small air gap between armature and core If the air gap is not available then

the residual magnetism fluxes might cause the armature to be retained when the supply is disconnected For

this reason residual pins are provided to ensure a definite minimum air gap in the energised position

EFFECT OF HYSTERISIS

Hysterisis is the property by which the flux produced lags behind the current In the de-energized

condition there will be small residual flux in the core When the voltage is applied to the coils the current in

rising to its steady value first causes the flux to rise from 1 to 2 along the curve At this point the flux density

will be sufficient to attract the armature and reduce the air gap the flux then raise to 3 and continue to 4

which corresponds to the steady current in the coils When the voltage is disconnected the current in falling

caused the flux to fall from 4 to 5 along the curve At this point the flux density will fall below the value

required to maintain the armature which will release thus increasing the air gap and reducing the flux to 6

Finally the

flux will decrease from 6 to 1 where the current will again be zero

The relay core is made of material having high permeability and low retentivity As mentioned in

the IRS specification Electromagnet iron may be in the form of a

(a) Bar of silicon steel

(b) Best Yorkshire wrought iron

(c) Swedish charcoal iron

(d) Electrical steel sheets

` This reduces the difference between pick up value and Drop away value By selecting good quality

core material Percentage release and sensitivity of the relay will be improved

TRANSIENT CONDITION

38 | P a g e

When the voltage is applied or disconnected from the coils it takes some little time before the current

become steady These are known as transient conditionsrdquo and are important so far as track relays are

concerned When the voltage is first applied to the coils the magnetic flux in rising cuts the turns on the

coils and in so doing produces a back EMF that opposes the applied voltage and retards the growth of

current

The growth and decay of flux are decided by the relationship between the inductance and resistance

in the circuit is known as time constant It is not fixed quantity in the case of DC neutral relay This value of lsquo

Lrsquo is less when the relay is in de-energised condition (L1) than when the relay is in energised condition (L2)

The magnitude of flux that is established for a given change of current is different in two cases

When the current reaches the pick up value the armature closes and the inductance is increased to L2

due to reduced air gap the flux per amp is increased The increase in flux increased the back EMF during the

movement of the armature after which the current continuous to raise along a new curve corresponding to the

increased inductance until it reaches the final value (ER) This process is indicated above in fig24

When the supply is disconnected the current is obliviously reduced to zero immediately but the flux

decay comparatively slowly owing to the eddy currents produced in the core by the rapid flux change which

tend to maintain the flux The drop away time on a disconnection is however generally negligible See fig

below

If the relay releases due to the reduction in current from say I 2 to I 1 caused by the application of

shunt resistance (as in the case of track relay ) the time taken is much longer than the relay is simply

disconnected The rate of rise or fall of current during the transient conditions is also depends on exterior

circuit values because L and R apply to the whole circuit The production of eddy current in the core the flux

will decay at a slower rate than the current So that the actual release time will be a little longer than it takes

the current to fall to the release

L= Inductance

39 | P a g e

R= Resistance

It is now clear that to reduce releasing time to a minimum it is necessary that

- The relay iron should have low Hysterisis loss and low retentivity

- The degree of over energization of the relay should be restricted

- Connecting a suitable external resistance in series with the relay to keep LR ratio low

In non RE area for track circuit length less than 100M 9 ohm track relay only to be used Using relay

with minimum contacts as they require lesser current which keeps inductance value low

Train working safety is ensured only if the track relay of shortest length track circuit is released

before a light engine running at a highest permitted speed clears it Otherwise the track circuit occupation

may go undetected To avoid this a special provision has to be made in signal control circuits wherever

necessary

The following methods may be adopted for reducing the time lag of track relay

(a) Restrict the over energisation of relay since the release time depends on the initial working current

(b) Connecting a suitable external resistance in series with the relay to keep the LR ratio low

(c) Using relays with minimum contacts as they require lesser operating current keeping the inductance

value low

40 | P a g e

CONCLUSION

Modern signalling is vital for safe and punctual movements of trains In the Indian railways The Signalling

and Telecommunication Department is responsible for providing modern effective and relaible signalling

systems as well as telecommunication systems

The first mode of communication used in Indian Railways was the use of electric telegraph

with the help of Morose code Morose code is the method of providing text information as a series of on-off

tones and lights or clicks that can be directly understood by a skilled listener or observer without special

equipmentEach character (letter or numeral ) is represented by a unique sequence of dots and dashes Later

this system becomes obselete and beggan the era of wireless communication which operated at audio level

frequency range

In wireless communication the significant advances took place the transition to miniature

valves or filament tubesBut this was abandoned too because of excessive current consumption and over

heating of the filament tubes

Fibre-optic communication is a method of transmitting information from one place to another by

sending pulses of light through an optcial fibreThe light forms an electromagnetic carrier wave that is

modulated to carry information First developed in the 1970s fibre optic communication systems has

revolutionized the telecommunications industry and have palyed a major role in the advent of the information

age Because of its advantages over electrical transmissionsoptical fibres have largely replaced copper wire

communications in core networks in the developed world The Indian Railways too is undergoing a transition

from Microwave communication to fibre optic communications

41 | P a g e

BIBLIOGRAPHY AND REFERENCES

1 wwwwikipediacom

2 wwwbritaniccacom

3 wwwirfcacom

4 Motorola GP60 system manual

5 Harris FAS 7000 manual

6 TOSHIBA Manual

37 | P a g e

F But actually the current in the coil is unaltered the force on the armature is greater than required as

indicated at 3 on curve F Part of this extra force is used to flex the front contacts sufficiently to give good

contact pressure when it is in energised position

The difference between the pick-up and the drop-away current should be as small as practicable in

track relay to ensure good shunting characteristics This is achieved firstly by the choice of good quality relay

iron and secondly by having a small air gap between armature and core If the air gap is not available then

the residual magnetism fluxes might cause the armature to be retained when the supply is disconnected For

this reason residual pins are provided to ensure a definite minimum air gap in the energised position

EFFECT OF HYSTERISIS

Hysterisis is the property by which the flux produced lags behind the current In the de-energized

condition there will be small residual flux in the core When the voltage is applied to the coils the current in

rising to its steady value first causes the flux to rise from 1 to 2 along the curve At this point the flux density

will be sufficient to attract the armature and reduce the air gap the flux then raise to 3 and continue to 4

which corresponds to the steady current in the coils When the voltage is disconnected the current in falling

caused the flux to fall from 4 to 5 along the curve At this point the flux density will fall below the value

required to maintain the armature which will release thus increasing the air gap and reducing the flux to 6

Finally the

flux will decrease from 6 to 1 where the current will again be zero

The relay core is made of material having high permeability and low retentivity As mentioned in

the IRS specification Electromagnet iron may be in the form of a

(a) Bar of silicon steel

(b) Best Yorkshire wrought iron

(c) Swedish charcoal iron

(d) Electrical steel sheets

` This reduces the difference between pick up value and Drop away value By selecting good quality

core material Percentage release and sensitivity of the relay will be improved

TRANSIENT CONDITION

38 | P a g e

When the voltage is applied or disconnected from the coils it takes some little time before the current

become steady These are known as transient conditionsrdquo and are important so far as track relays are

concerned When the voltage is first applied to the coils the magnetic flux in rising cuts the turns on the

coils and in so doing produces a back EMF that opposes the applied voltage and retards the growth of

current

The growth and decay of flux are decided by the relationship between the inductance and resistance

in the circuit is known as time constant It is not fixed quantity in the case of DC neutral relay This value of lsquo

Lrsquo is less when the relay is in de-energised condition (L1) than when the relay is in energised condition (L2)

The magnitude of flux that is established for a given change of current is different in two cases

When the current reaches the pick up value the armature closes and the inductance is increased to L2

due to reduced air gap the flux per amp is increased The increase in flux increased the back EMF during the

movement of the armature after which the current continuous to raise along a new curve corresponding to the

increased inductance until it reaches the final value (ER) This process is indicated above in fig24

When the supply is disconnected the current is obliviously reduced to zero immediately but the flux

decay comparatively slowly owing to the eddy currents produced in the core by the rapid flux change which

tend to maintain the flux The drop away time on a disconnection is however generally negligible See fig

below

If the relay releases due to the reduction in current from say I 2 to I 1 caused by the application of

shunt resistance (as in the case of track relay ) the time taken is much longer than the relay is simply

disconnected The rate of rise or fall of current during the transient conditions is also depends on exterior

circuit values because L and R apply to the whole circuit The production of eddy current in the core the flux

will decay at a slower rate than the current So that the actual release time will be a little longer than it takes

the current to fall to the release

L= Inductance

39 | P a g e

R= Resistance

It is now clear that to reduce releasing time to a minimum it is necessary that

- The relay iron should have low Hysterisis loss and low retentivity

- The degree of over energization of the relay should be restricted

- Connecting a suitable external resistance in series with the relay to keep LR ratio low

In non RE area for track circuit length less than 100M 9 ohm track relay only to be used Using relay

with minimum contacts as they require lesser current which keeps inductance value low

Train working safety is ensured only if the track relay of shortest length track circuit is released

before a light engine running at a highest permitted speed clears it Otherwise the track circuit occupation

may go undetected To avoid this a special provision has to be made in signal control circuits wherever

necessary

The following methods may be adopted for reducing the time lag of track relay

(a) Restrict the over energisation of relay since the release time depends on the initial working current

(b) Connecting a suitable external resistance in series with the relay to keep the LR ratio low

(c) Using relays with minimum contacts as they require lesser operating current keeping the inductance

value low

40 | P a g e

CONCLUSION

Modern signalling is vital for safe and punctual movements of trains In the Indian railways The Signalling

and Telecommunication Department is responsible for providing modern effective and relaible signalling

systems as well as telecommunication systems

The first mode of communication used in Indian Railways was the use of electric telegraph

with the help of Morose code Morose code is the method of providing text information as a series of on-off

tones and lights or clicks that can be directly understood by a skilled listener or observer without special

equipmentEach character (letter or numeral ) is represented by a unique sequence of dots and dashes Later

this system becomes obselete and beggan the era of wireless communication which operated at audio level

frequency range

In wireless communication the significant advances took place the transition to miniature

valves or filament tubesBut this was abandoned too because of excessive current consumption and over

heating of the filament tubes

Fibre-optic communication is a method of transmitting information from one place to another by

sending pulses of light through an optcial fibreThe light forms an electromagnetic carrier wave that is

modulated to carry information First developed in the 1970s fibre optic communication systems has

revolutionized the telecommunications industry and have palyed a major role in the advent of the information

age Because of its advantages over electrical transmissionsoptical fibres have largely replaced copper wire

communications in core networks in the developed world The Indian Railways too is undergoing a transition

from Microwave communication to fibre optic communications

41 | P a g e

BIBLIOGRAPHY AND REFERENCES

1 wwwwikipediacom

2 wwwbritaniccacom

3 wwwirfcacom

4 Motorola GP60 system manual

5 Harris FAS 7000 manual

6 TOSHIBA Manual

38 | P a g e

When the voltage is applied or disconnected from the coils it takes some little time before the current

become steady These are known as transient conditionsrdquo and are important so far as track relays are

concerned When the voltage is first applied to the coils the magnetic flux in rising cuts the turns on the

coils and in so doing produces a back EMF that opposes the applied voltage and retards the growth of

current

The growth and decay of flux are decided by the relationship between the inductance and resistance

in the circuit is known as time constant It is not fixed quantity in the case of DC neutral relay This value of lsquo

Lrsquo is less when the relay is in de-energised condition (L1) than when the relay is in energised condition (L2)

The magnitude of flux that is established for a given change of current is different in two cases

When the current reaches the pick up value the armature closes and the inductance is increased to L2

due to reduced air gap the flux per amp is increased The increase in flux increased the back EMF during the

movement of the armature after which the current continuous to raise along a new curve corresponding to the

increased inductance until it reaches the final value (ER) This process is indicated above in fig24

When the supply is disconnected the current is obliviously reduced to zero immediately but the flux

decay comparatively slowly owing to the eddy currents produced in the core by the rapid flux change which

tend to maintain the flux The drop away time on a disconnection is however generally negligible See fig

below

If the relay releases due to the reduction in current from say I 2 to I 1 caused by the application of

shunt resistance (as in the case of track relay ) the time taken is much longer than the relay is simply

disconnected The rate of rise or fall of current during the transient conditions is also depends on exterior

circuit values because L and R apply to the whole circuit The production of eddy current in the core the flux

will decay at a slower rate than the current So that the actual release time will be a little longer than it takes

the current to fall to the release

L= Inductance

39 | P a g e

R= Resistance

It is now clear that to reduce releasing time to a minimum it is necessary that

- The relay iron should have low Hysterisis loss and low retentivity

- The degree of over energization of the relay should be restricted

- Connecting a suitable external resistance in series with the relay to keep LR ratio low

In non RE area for track circuit length less than 100M 9 ohm track relay only to be used Using relay

with minimum contacts as they require lesser current which keeps inductance value low

Train working safety is ensured only if the track relay of shortest length track circuit is released

before a light engine running at a highest permitted speed clears it Otherwise the track circuit occupation

may go undetected To avoid this a special provision has to be made in signal control circuits wherever

necessary

The following methods may be adopted for reducing the time lag of track relay

(a) Restrict the over energisation of relay since the release time depends on the initial working current

(b) Connecting a suitable external resistance in series with the relay to keep the LR ratio low

(c) Using relays with minimum contacts as they require lesser operating current keeping the inductance

value low

40 | P a g e

CONCLUSION

Modern signalling is vital for safe and punctual movements of trains In the Indian railways The Signalling

and Telecommunication Department is responsible for providing modern effective and relaible signalling

systems as well as telecommunication systems

The first mode of communication used in Indian Railways was the use of electric telegraph

with the help of Morose code Morose code is the method of providing text information as a series of on-off

tones and lights or clicks that can be directly understood by a skilled listener or observer without special

equipmentEach character (letter or numeral ) is represented by a unique sequence of dots and dashes Later

this system becomes obselete and beggan the era of wireless communication which operated at audio level

frequency range

In wireless communication the significant advances took place the transition to miniature

valves or filament tubesBut this was abandoned too because of excessive current consumption and over

heating of the filament tubes

Fibre-optic communication is a method of transmitting information from one place to another by

sending pulses of light through an optcial fibreThe light forms an electromagnetic carrier wave that is

modulated to carry information First developed in the 1970s fibre optic communication systems has

revolutionized the telecommunications industry and have palyed a major role in the advent of the information

age Because of its advantages over electrical transmissionsoptical fibres have largely replaced copper wire

communications in core networks in the developed world The Indian Railways too is undergoing a transition

from Microwave communication to fibre optic communications

41 | P a g e

BIBLIOGRAPHY AND REFERENCES

1 wwwwikipediacom

2 wwwbritaniccacom

3 wwwirfcacom

4 Motorola GP60 system manual

5 Harris FAS 7000 manual

6 TOSHIBA Manual

39 | P a g e

R= Resistance

It is now clear that to reduce releasing time to a minimum it is necessary that

- The relay iron should have low Hysterisis loss and low retentivity

- The degree of over energization of the relay should be restricted

- Connecting a suitable external resistance in series with the relay to keep LR ratio low

In non RE area for track circuit length less than 100M 9 ohm track relay only to be used Using relay

with minimum contacts as they require lesser current which keeps inductance value low

Train working safety is ensured only if the track relay of shortest length track circuit is released

before a light engine running at a highest permitted speed clears it Otherwise the track circuit occupation

may go undetected To avoid this a special provision has to be made in signal control circuits wherever

necessary

The following methods may be adopted for reducing the time lag of track relay

(a) Restrict the over energisation of relay since the release time depends on the initial working current

(b) Connecting a suitable external resistance in series with the relay to keep the LR ratio low

(c) Using relays with minimum contacts as they require lesser operating current keeping the inductance

value low

40 | P a g e

CONCLUSION

Modern signalling is vital for safe and punctual movements of trains In the Indian railways The Signalling

and Telecommunication Department is responsible for providing modern effective and relaible signalling

systems as well as telecommunication systems

The first mode of communication used in Indian Railways was the use of electric telegraph

with the help of Morose code Morose code is the method of providing text information as a series of on-off

tones and lights or clicks that can be directly understood by a skilled listener or observer without special

equipmentEach character (letter or numeral ) is represented by a unique sequence of dots and dashes Later

this system becomes obselete and beggan the era of wireless communication which operated at audio level

frequency range

In wireless communication the significant advances took place the transition to miniature

valves or filament tubesBut this was abandoned too because of excessive current consumption and over

heating of the filament tubes

Fibre-optic communication is a method of transmitting information from one place to another by

sending pulses of light through an optcial fibreThe light forms an electromagnetic carrier wave that is

modulated to carry information First developed in the 1970s fibre optic communication systems has

revolutionized the telecommunications industry and have palyed a major role in the advent of the information

age Because of its advantages over electrical transmissionsoptical fibres have largely replaced copper wire

communications in core networks in the developed world The Indian Railways too is undergoing a transition

from Microwave communication to fibre optic communications

41 | P a g e

BIBLIOGRAPHY AND REFERENCES

1 wwwwikipediacom

2 wwwbritaniccacom

3 wwwirfcacom

4 Motorola GP60 system manual

5 Harris FAS 7000 manual

6 TOSHIBA Manual

40 | P a g e

CONCLUSION

Modern signalling is vital for safe and punctual movements of trains In the Indian railways The Signalling

and Telecommunication Department is responsible for providing modern effective and relaible signalling

systems as well as telecommunication systems

The first mode of communication used in Indian Railways was the use of electric telegraph

with the help of Morose code Morose code is the method of providing text information as a series of on-off

tones and lights or clicks that can be directly understood by a skilled listener or observer without special

equipmentEach character (letter or numeral ) is represented by a unique sequence of dots and dashes Later

this system becomes obselete and beggan the era of wireless communication which operated at audio level

frequency range

In wireless communication the significant advances took place the transition to miniature

valves or filament tubesBut this was abandoned too because of excessive current consumption and over

heating of the filament tubes

Fibre-optic communication is a method of transmitting information from one place to another by

sending pulses of light through an optcial fibreThe light forms an electromagnetic carrier wave that is

modulated to carry information First developed in the 1970s fibre optic communication systems has

revolutionized the telecommunications industry and have palyed a major role in the advent of the information

age Because of its advantages over electrical transmissionsoptical fibres have largely replaced copper wire

communications in core networks in the developed world The Indian Railways too is undergoing a transition

from Microwave communication to fibre optic communications

41 | P a g e

BIBLIOGRAPHY AND REFERENCES

1 wwwwikipediacom

2 wwwbritaniccacom

3 wwwirfcacom

4 Motorola GP60 system manual

5 Harris FAS 7000 manual

6 TOSHIBA Manual

41 | P a g e

BIBLIOGRAPHY AND REFERENCES

1 wwwwikipediacom

2 wwwbritaniccacom

3 wwwirfcacom

4 Motorola GP60 system manual

5 Harris FAS 7000 manual

6 TOSHIBA Manual