final industrial training (2).docx

7/30/2019 final industrial training (2).docx

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ABSTRACT

This report includes a brief company profile of SAIL . It also includes the understanding

Automation and its levels of Automation, understanding the basics of PLC (Programmable

Logic Controller) and its programming. This report gives a brief introduction to ladder logic,

functional block, structural text, and sequential functional chart. The working procedure as to

how a PLC program in connected to the HMI (Human Machine Interface) is also discussed.


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Chapter-1

INTRODUCTION

1.1Instrumentation and Automation

Automation is a delegation of human control to a technical equipment to increase

productivity, quality and safe working conditions and to decrease cost and errors. Automation

requires field instruments, control devices and control software. In the scope of

industrialization, automation is a step beyond mechanization. Automation greatly decreases

the need for human sensory and mental requirements as well. Automation plays an

increasingly important role in the world economy and in daily experience.

Automation of any system is divided into many levels which vary from domain to domain.

Following are the basic levels:

Level-0: Instrumentation- It contains the basic instruments which perform mechanical

operations as instructed by the user from the level 2 machine through the PLC of level 1. For

examples- Motor valves, desks, meters.

Level-1: Programmable Logic Controller- It contains the PLC whose main function is to

communicate with the level 1 device. It takes in commands from the user at the level 2

machine and instructs the movement of the level 0 device accordingly. Level I systems

should be rugged enough to be placed close to field devices without normally requiring

environmental enclosures, and should contain I/O suitable for industrial application

Level-2: Mathematical models of the Process, Production schedule-It contains the PC

which provides a GUI for input of commands from the user. It processes the input,

encapsulates it in a telegram and transmits the telegram to the PLC.

Level-3: Business Management (ERP) - It contains a process manager which maintains

several simultaneous processes such as ERP (Enterprise Resource Planning).


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For automation following are used:-

1. control hardwareplc, pid

2. control softwareSCADA (supervisory control and data acquisition)So the role of automation engineering is to design program of plc and design of SCADA.


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Chapter-2

PROGRAMMABLE LOGIC CONTROLLERS

2.1 Programmable Logic Controllers :

Programmable Logic Controllers (PLCs) are also referred to as programmable controllers.

They are used in industrial applications. A PLC monitors inputs, makes decisions based on its

program, and controls outputs to automate a process or machine. It is a device which can

perform discrete and sequential logic for industrial environment. It is an interface between

field input and field output.

Advantages

Cost effective for controlling complex systems.

Flexible and can be reapplied to control other systems quickly and easily.

Computational abilities allow more sophisticated control.

Trouble shooting aids make programming easier and reduce downtime.

Reliable components make these likely to operate for years before failure.


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Block diagram:

The PLC mainly consists of a CPU, memory areas, and appropriate circuits to receive

input/output data.

Input Relays(contacts)-These are connected to the outside world. They physically exist and

receive signals from switches, sensors, etc. Typically they are not relays but rather they are

transistors.

Internal Utility Relays(contacts)- These do not receive signals from the outside world nor do

they physically exist. They are simulated relays and are what enables a PLC to eliminate

external relays. There are also some special relays that are dedicated to performing only one

task. Some are always on while some are always off. Some are on only once during power-on

and are typically used for initializing data that was stored.


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Counters-These again do not physically exist. They are simulated counters and they can be

programmed to count pulses. Typically these counters can count up, down or both up and

down. Since they are simulated they are limited in their counting speed. Some manufacturers

also include high-speed counters that are hardware based. We can think of these as physically

existing. Most times these counters can count up, down or up and down.

Timers-These also do not physically exist. They come in many varieties and increments. The

most common type is an on-delay type. Others include off-delay and both retentive and non-

retentive types. Increments vary from 1ms through 1s.

Output Relays(coils)-These are connected to the outside world. They physically exist and

send on/off signals to solenoids, lights, etc. They can be transistors, relays, or triacs depending

upon the model chosen.

Data Storage-Typically there are registers assigned to simply store data. They are usually used

as temporary storage for math or data manipulation. They can also typically be used to store

data when power is removed from the PLC. Upon power-up they will still have the same

contents as before power was removed.


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Types of PLC:

Different PLCs in market has been listed below:-

1. Allen Bradley

SCADA-RS View 32

1. Micrologix 1000,1200,1500

2. Pic Logix

3. SLC (Sequential Logic Controller) 5/01,5/02,5/03,5/04,5/05

Driver softwareRS Linx Gateway

Programming software-RS Logix 500

4. Compact Logix

5. Control Logix

Programming software-RS Logix 5000

2. Siemens

SCADA- winncc-window control center

1. S7 200,S7 300,S7 400(step 7-siemens technical educational program

Programming software- microwin, simatic manager

3. GE Fanuc 90-30

SCADA- Cimplicity

Driver softwareVersamax

Programming software- Versa Pro


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2.2 Different modules of PLC

Backplane / Rack

Backplane is the base for PLC where different cards of different modules are connected. Itconveys signals from the processor to other module and from the module to the CPU. The rack

is the component that holds everything together. Depending on the needs of the control system

it can be ordered in different sizes to hold more modules. Like a human spine the rack has a

backplane at the rear which allows the cards to communicate with the CPU.

Power Supply

First Slot in PLC has Power supply which provides power to each module connected to

backplane. Power required for power supply is 24DC for digital input, 4-20mA 0-10 V for

Analog input, 115Vac and 230VAC. Interrogative Power Supply (24 DC) are used with input

module.

Input Module

Inputs to PLC are both analog and digital. Input Module has ADC. In smaller PLCs the inputs

are normally built in and are specified when purchasing the PLC. These are called as local

IOs. For larger PLCs the inputs are purchased as modules or cards, with 8 or 16 inputs of the

same type on each card. These are connected to PLC via Control net/bridge card. Thus the IOs

are called remote IOs. The list below shows typical ranges for input voltages, and is roughly

in order of popularity.

12-24 Vdc,100-120 Vac,10-60 Vdc,12-24 V ac/dc,5 V dc (TTL),200-240 Vac,48 Vdc,24 V ac.

PLC input cards rarely supply power, this means that an external power supply is needed to

supply power for the inputs and sensors. It has high impedance so they draw very less current.


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The example in Figure shows how to connect an AC input card.

As an example let us consider two

inputs, one is a normally open push

button, and the other is a

temperature switch or thermal relay.

Both of the switches are powered by

the positive/ hot output of the 24Vacpower supply - this is like the

positive terminal on a DC supply.

Power is supplied to the left side o

both of the switches. When the

switches are open there is no voltage

passed to the input card. If either o

the switches is closed power will be

supplied to the input card. In this case inputs 1 and 3 are used - notice that the inputs start at 0.

The input card compares these voltages to the common. If the input voltage is within a given

tolerance range the inputs will switch on.


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Output Module

PLC gives both analog and digital outputs. They are potential free, i.e. any potential can be

attached to the outputs. Output module can also be local or remote. It rarely supplies any

power, but instead acts as switches. External power supplies are connected to the output cardand the card will switch the power on or off for each output. Typical output voltages are listed

below, and roughly ordered by popularity.120 V ac, 24 Vdc,12-48 Vac,12-48 Vdc,5Vdc

(TTL),230 V ac. These cards typically have 8 to 16 outputs of the same type and can be

purchased with different current ratings. A common choice when purchasing output cards is

relays , transistors or triacs. Relays are the most flexible output devices. They are capable of

switching both AC and DC outputs. But, they are slower (about 10ms switching is typical),

bulkier, costlier and they will wear out after millions of cycles. Relay outputs are often called

dry contacts. Response times are often greater than 10ms. This method is the least sensitive to

voltage variations and spikes. Transistors are limited to DC outputs, and Triacs are limited to

AC outputs. Transistor and triac outputs are called switched outputs. Triacs are well suited to

AC devices requiring less than 1A. Transistor outputs use NPN or PNP transistors up to 1A

typically. Their response time is well under 1ms.

In this example the outputs are

connected to a low current light bulb(lamp) and a relay coil. Consider the

circuit through the lamp, starting at the

24Vdc supply. When the output 07 is

on, current can flow in 07 to the COM,

thus completing the circuit, and

allowing the light to turn on. If the

output is off the current cannot flow,and the light will not turn on. The output 03 for the relay is connected in a similar way. When

the output 03 is on, current will flow through the relay coil to close the contacts and supply

120Vac to the motor. Ladder logic for the outputs is shown in the bottom right of the figure.


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2.3 PLC Languages

The basic programmable controller languages consist of a set of instructions that will perform

the most common type of control functions like relay replacement, timing, counting,

sequencing, and logic. It may be extended or enhanced to perform other basic operations.

Ladder logic, statement list (stl), sequential function chart (sfc), functional block diagram,

structured text (st) are the most common types of languages encountered in programmable

controller system design. Ladder diagrams form the basic PC languages, while function blocks

and the sequential function charting are categorized as high-level languages.

The high-level languages have been brought about by a need to execute more powerful

instructions that go beyond the simple timing, counting and ON/OFF control. High-level

languages are used for analog control, data manipulation and other functions that are not

possible with the basic instruction sets.

The language used in a PC dictates the range of applications in which the controller can be

applied. Depending on the size and capabilities of the controller, one or more languages may

be used. Here are some typical combinations of the languages:

1. Ladder diagrams only.

2. Ladder diagrams and function blocks.

3. Ladder and sequential function chart.

4. Ladder, function blocks, sequential function chart.

Ladder Logic

Ladder logic is the main programming method used for

PLCs. As mentioned before, ladder logic has been

developed to mimic relay logic. The decision to use the

relay logic diagrams was a strategic one. By selecting

ladder logic as the main programming method, the

amount of retraining needed for engineers and trades

people was greatly reduced.


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The left vertical line of a ladder logic diagram represents the power or energized conductor.

The output element or instruction represents the neutral or return path of the circuit. The right

vertical line, which represents the return path on a hard-wired control line diagram, is

omitted. Ladder logic diagrams are read from left-to-right, top-to-bottom. Rungs are

sometimes referred to as networks. A network may have several control elements, but only

one output coil.

Statement list

A statement list (STL) provides another view of a set of

instructions. The operation, what is to be done, is shown

on the left. The operand, the item to be operated on by

the operation, is shown on the right. A comparison

between the statement list shown below, and the ladder

logic shown on the previous page, reveals a similar

structure. The set of instructions in this statement list perform the same task as the ladder

diagram.

Sequential Function Charts (SFCs)

Sequential Function Charts (SFCs) have been developed

to accommodate the programming of more advanced

systems. These are similar to flowcharts, but much more

powerful. The example seen in Figure is doing two

different things. To read the chart, start at the top where

is says start. Below this there is the double horizontal

line that says follow both paths. As a result the PLC will

start to follow the branch on the left and right hand sides

separately and simultaneously. On the left there are two

functions the first one is the power up function. This function will run until it decides it is

done, and the power down function will come after. On the right hand side is the flash

function; this will run until it is done. These functions look unexplained, but each function,


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such aspower up will be a small ladder logic program. This method is much different from

flowcharts because it does not have to follow a single path through the flowchart.

Structured Text

Structured Text programming has been developed as a more

modern programming language. It is quite similar to languages such

as BASIC. A simple example is:


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Chapter-3

RS-232 COMMUNICATION

RS-232 communications is the most popular method of plc to external device

communications. RS-232 is an asynchronous (a marching band must be "in sync" with

each other so that when one steps they all step. They are asynchronous in that they

follow the band leader to keep their timing) communications method. We use a binary

system (1's and 0's) to transmit our data in the ASCII format. (American Standard Code

for Information Interchange- pronounced ASS-KEY) This code translates human

readable code (letters/numbers) into "computer readable" code (1's and 0's). Our plcs

serial port is used for transmission/reception of the data. It works by sending/receiving a

voltage. A positive voltage is called a MARK and a negative voltage is called a

SPACE. Typically, the plc works with +/- 15volts. The voltage between +/- 3 volts is

generally not used and is considered noise.

There are 2 types of RS-232 devices. The first is called a DTE device. This means Data

Terminal Equipment and a common example is a computer. The other type is called a

DCE device. DCE means Data Communications Equipment and a common example is a

modem.

The plc serial port works by turning some pins on while turning other off. These pins

each are dedicated to a specific purpose. The serial port are of 2 types-- a 25-pin type

and a 9-pin type. The pins and their purposes are shown below. (This chart assumes your

plc is a DTE device)


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9-PIN 25-PIN Purpose

1 1 frame ground

2 3 receive data (RD)

3 2 transmit data (TD)

4 20 data terminal ready (DTR)

5 7 signal ground

6 6 data set ready (DSR)

7 4 request to send (RTS)

8 5 clear to send (CTS)

9 22 ring indicator (RI) *only for modems*

Each pins purpose in detail:

Frame ground- This pin should be internally connected to the chassis of the device.

Receive data- This pin is where the data from the external device enters the plc serial

port.

Transmit data- This pin is where the data from the plc serial port leaves the plc enroute

to the external device.

Data terminal ready- This pin is a master control for the external device. When this pinis 1 the external device will not transmit or receive data.

Signal ground- Since data is sent as + or - voltage, this pin is the ground that is

referenced.


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Rata set ready- Usually external devices have this pin as a permanent 0 and the plc

basically uses it to determine that the external device is powered up and ready.

Request to send- This is part of hardware handshaking. When the plc wants to send datato the external device it sets this pin to a 0. In other words, it sets the pin to a 0 and

basically says "I want to send you data. Is it ok?" The external device says it's OK to

send data by setting its clear to send pin to 0. The plc then sends the data.

Clear to send- This is the other half of hardware handshaking. As noted above, the

external device sets this pin to 0 when it is ready to receive data from the plc.

Ring indicator- only used when the plc is connected to a modem.

The external device turns on DSR which tells the plc that's it's powered up and "there".

The PLC turns on RTS which is like asking the external device "are you ready to receive

some data?" The external device responds by turning on it's CTS which says it's ok to for

the plc to send data. The plc sends the data on its TD terminal and the external device

receives it on its RD terminal. Some data is sent and received. After a while, the external

device can't process the data quick enough. So, it turns off its CTS terminal and the plc

pauses sending data. The external device catches up and then turns its CTS terminal back

on. The plc again starts sending data on its TD terminal and the external device receives

it on its RD terminal. The plc runs out of data to send and turns off its RTS terminal. The

external device sits and waits for more data.

Start bit- In RS-232 the first thing we send is called a start bit. This start bit ("invented"

during WW1 by Kleinschmidt) is a synchronizing bit added just before each character

we are sending. This is considered a SPACE or negative voltage or a 0.

Stop bit- The last thing we send is called a stop bit. This stop bit tells us that the last

character was just sent. Think of it as an end-of -character bit. This is considered a

MARK or positive voltage or a 1. The start and stop bits are commonly called framing

bits because they surround the character we are sending.


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Parity bit- Since most PLCs/external equipment are byte-oriented (8 bits=1byte) it

seems natural to handle data as a byte. Although ASCII is a 7-bit code it is rarely

transmitted that way. Typically, the 8th bit is used as a parity bit for error checking. This

method of error checking gets its name from the math idea of parity. (remember in

simple terms, parity means that all characters will either have an odd number of 1's or an

even number of 1's.

Common forms of parity are None, Even, and Odd.

In parity of None, the parity bit is always 0 so we send 10001010.

In parityof Even we must have an Even number of 1's in our total character so the

original character currently has 3 1's (1000101) therefore our parity bit we will add must

be a 1. (10001011) Now we have an even number of 1's.

In Odd parity we need an odd number of 1's. Since our original character already has an

odd number of 1's our parity bit will be a 0. (10001010)

During transmission, the sender calculates the parity bit and sends it. The receiver

calculates parity for the 7-bit character and compares the result to the parity bit received.

If the calculated and real parity bits don't match, an error occurred an we act

appropriately.

IBaud rate- Baud rate refers to the number of bits per second that are being transmitted.

So 1200 means 1200 bits per second are being sent and 9600 means 9600 bits are being

transmitted every second. Common values (speeds) are 1200, 2400, 4800, 9600, 19200,

and 38400.

RS232 data format- (baud rate-data,bits-parity-stop bits) This is the way the data

format is typically specified. For example, 9600-8-N-1 means a baud rate of 9600, 8 data

bits, parity of None, and 1 stop bit.

The picture below shows how data leaves the serial port for the character "E" (45h 100

0101b) and Even parity.


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Another important thing that is sometimes used is called software handshaking (flow

control). Software handshaking is used to make sure both devices are ready to

send/receive data. The most popular "character flow control" is called XON/XOFF. It's

very simple to understand. Simply put, the receiver sends the XOFF character when it

wants the transmitter to pause sending data. When it's ready to receive data again, it

sends the transmitter the XON character. XOFF is sometimes referred to as the hold off

character and XON as the release character.

Sometimes an STX and ETX pair is used for transmission/reception. STX is "start of

text" and ETX is "end of text". The STX is sent before the data and tells the external

device that data is coming. After all the data has been sent, an ETX character is sent.

We might also come across an ACK/NAK pair. This is rarely used but it should be

noted as well. Essentially, the transmitter sends its data. If the receiver gets it without

error, it sends back an ACK character. If there was an error, the receiver sends back aNAK character and the transmitter resends the data.


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Chapter-4

HUMAN MACHINE INTERFACES (HMI)

4.1 HUMAN MACHINE INTERFACES (HMI)

HMI or SCADA(supervisory control and data acquisition) is used to monitor the process

and controlling the field o/ps not fields i/ps. HMI acts as an interface between the

operator and the machine (or the process). This provides a complete visualization of the

entire operations to be performed in the plant. The HMI system is installed on a PC is

connected to the PLC.

These allow control systems to be much more interactive than before.

The basic purpose of an HMI is to allow easy graphical interface with a process.

These devices have been known by a number of names,

- touch screens

- displays

- Man Machine Interface (MMI)

- Human Machine Interface (HMI)

These allow an operator to use simple displays to determine real time values and

conditions of machine and make simple settings.

The most common uses are,

- display machine faults

- display machine status

- allow the operator to start and stop cycles


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- monitor part counts

These devices allow certain advantages such as,

- Color coding allows for easy identification (e.g. red for trouble)

- Pictures/icons allow fast recognition

- Use of pictures eases problems of illiteracy

- Screen can be changed to allow different levels of information and access

The general implementation steps are,

1. Layout screens on PC based software.

2. Download the screens to the HMI unit.

3. Connect the unit to a PLC.

4. Read and write to the HMI using PLC memory locations to get input and

update Screens

To control the HMI from a PLC the user inputs set bits in the PLC memory, and otherbits in the PLC memory can be set to turn on/off items on the HMI screen.

HMI DESIGN

The common trend is to adopt a user interface which often has,

- Icons

- A pointer device (such as a mouse)

- Full color

- Support for multiple windows, which run programs simultaneously

- Popup menus

- Windows can be moved, scaled, moved forward/back, etc.


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The current demands on user interfaces are,

- On-line help

- Adaptive dialog/response

- Feedback to the user

- Ability to interrupt processes

- Consistent modules

- A logical display layout

- Deal with many processes simultaneously

To design an HMI interface, the first step is to identify

1. Who needs what information?

2. How do they expect to see it presented?

3. When does information need to be presented?

4. Do the operators have any special needs?

5. Is sound important?

6. What choices should the operator have?


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4.2Creating a complete program and its HMI

1. Logix Software Programming software for the controller. It support three major

types of programming Viz. Ladder, Functional Block Diagram, Sequence Function

Charts, and Enhanced Basic. It also supports for communication on various protocolslike ModBus and ProFibus. Program is downloaded in PLC.

2. Linx Software This is the basic Communication software acting as a bridge

between the PLC and HMI. Ethernet industrial protocol is use for communication

between PLC and pc having HMI.

3. Factory Talk With ServerThis provides access to the Client software to fetch and

graphically display data on user forms in the client machine. This acts as a HumanMachine Interface (HMI).

4. The automation configuration includes client stations, redundant server, redundant

controllers and intelligent switches.

Factory Talk View

Studio (HMI)

LOGIX

PLC

Program is downloaded in PLC via

serial cable

LINX(ETHERNET/

INDUSTRIAL

PROTOCOL)

RIOs

Control/net

Bridge

AIP,DIP

,AOP


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5. Remote input output racks (RIOs) is remote rack having local input and output card

both analog and digital. It is connected to control/net bridge at plc backplane via

communication cable.


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Chapter-5

EXAMPLE

This example shows how to control lubricating oil being dispensed from a tank. This is

possible by using two sensors. One is placed near the bottom and one near the top, as

shown in the picture below.

We want the motor to pump lubricating oil into the tank until the high level sensor turns

on. At that point we want to turn off the motor until the level falls below the low level

sensor. Then we should turn on the fill motor and repeat the process.

Here we need 3 I/O (i.e. Inputs/Outputs). 2 are inputs (the sensors) and 1 is an output

(the fill motor). Both our inputs are NC (normally closed) fiber-optic level

sensors. When they are NOT immersed in liquid they will be ON. When they are

immersed in liquid they will be OFF.

We will give each input and output device an address. This lets the plc know where they

are physically connected. The addresses are shown in the following tables:


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Inputs Address Output Address Internal Utility Relay

Low 0000 Motor 0500 1000

High 0001

Below is what the ladder diagram will actually look like.

Below is what happens in this program scan by scan.

Initially the tank is empty. Therefore, input 0000 is TRUE and input 0001 is also TRUE.


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Scan 1 Scan 2-100

Gradually the tank fills because 500(fill motor) is on.

After 100 scans the oil level rises above the low level sensor and it becomes open. (i.e.

FALSE)

Scan 101-1000

Notice that even when the low level sensor is false there is still a path of true logic from

left to right. This is why we used an internal relay. Relay 1000 is latching the output

(500) on. It will stay this way until there is no true logic path from left to right.(i.e. when

0001 becomes false)

After 1000 scans the oil level rises above the high level sensor at it also becomes open

(i.e. false)


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Scan 1001 Scan 1002

Since there is no more true logic path, output 500 is no longer energized (true) and

therefore the motor turns off.

After 1050 scans the oil level falls below the high level sensor and it will become true

again.

Scan 1050

Even though the high level sensor became true there still is NO continuous true logic

path and therefore coil 1000 remains false.

After 2000 scans the oil level falls below the low level sensor and it will also become

true again. At this point the logic will appear the same as SCAN 1 above and the logic

will repeat as illustrated above.


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Chapter-6

CONCLUSION AND APPLICATION

5.1 Conclusion

PLCs are omnipresent in industries replacing the existing relay logics. Thus it has

application in every sector of industries and power plant. With the growth of automation

technology PLC plays a very important role and contribute to the growth and

development of the industry. With the use of PLCs production rate increased, tasks

carried out have become easier than before and quality of final product is improved .

5.2Major applications of PLCs

Automated Highway Systems:

The goal of this program is to have the first fully automated highway roadway or an

automated test track this system shall accommodate installation of equipment in new and

existing motor vehicles. Full automation commonly defined as requiring no control or

very limited control by the driver; such automation would be accomplished through a

combination of sensor, computer, and communications systems in vehicles and along the

roadway.

Automated manufacturing of steel and other alloys:

Automated manufacturing refers to the application of automation to produce things in

the factory way. Most of the advantages of the automation technology have its influence

in the manufacture processes.

Production machining:

This industry needs continuous monitoring of automotive production machine. So PLC is use for

monitoring total parts, rejected parts, machine cycle time and machine efficiency. PLC controls

and monitors automatic production machine at high efficiency rates. It also monitors piece count

production and machine status. Corrective action can be taken immediately if plc detects a

failure.


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Material handling and conveyors industries like steel making, load and unload of alloys in

metal industries are the other examples. Power plant systems, pulp and paper industries,

chemical matching and oil free industries.

Steel Production: PLCs are used in steel plants for procedures like controlling

temperature and pressure in boilers, lifting electrodes and feeding oxygen lance,

movement of raw materials using conveyer system, material handling etc.

The main advantage of the automated manufacturing are: higher consistency and quality,

reduce the lead times, simplification of production, reduce handling, improve work flow

and increase the morale of workers when a good implementation of the automation is

made.

Chemical and petrochemical industries:

Ammonia and ethylene processing: PLC is use to monitor and control large

compressors used during NH4 and ethylene manufacturing. The PLC monitors

temperature, operation of clearance pockets, compressor speed, power consumption,

vibration, and discharge temperature and section flow.

Dyes: PLC monitors and controls the dye processing used in the textile industry. They

match and blend colors to predetermined values.

Induced Draft or booster Fan control: PLC controls fans based on level of toxic gases

in a chemical production environment. This system effectively removes gases when a

preset level of contamination is reached.plc controls fans start and stop, cycle and speed.
http://en.wikipedia.org/wiki/Manufacturinghttp://en.wikipedia.org/wiki/Manufacturing


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REFERENCES

1. Studymaterials on PLC from Bokaro Steel Plant,SAIL.

2. www.plcmanual.com

3. www.plcs.net

4. Automating Manufacturing Systems with PLCs-Hugh Jack
http://www.plcmanual.com/http://www.plcmanual.com/http://www.plcs.net/http://www.plcs.net/http://www.plcs.net/http://www.plcmanual.com/

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