final_nidhi.doc
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TBRL REPORTTRANSCRIPT
SIX MONTHS PROJECT SEMESTER REPORT ON
DESIGN & DEVELOPMENT OF
SHOCK VELOCITY RECORDER
Submitted to:Electronics and Communication Department,
Thapar Institute Of Engg. & Technology, Patiala
For the partial fulfillment of degree ofBachelor of Engineering
inElectronics & Communication
Harbans Lal(Project Incharge)Deputy DirectorZone 3, TBRLChandigarh
Nidhi Jain1000636
Thapar Institute ofEngg. & Technology
Patiala
TERMINAL BALLISTICS RESEARCH LABORATORYDEFENCE R&D ORGANIZATION
MINISTRY OF DEFENCE, GOVT. OF INDIA
SECTOR-30, CHANDIGARH, INDIA-160020FAX: 91-172-657506
0172-651824,651825,651826
CERTIFICATE
This is to certify that Nidhi Jain, Roll No. 1000636, of Thapar Institute of Engg. and
Technology, Patiala has undergone six months project semester industrial training from
Jan 1, 2003 to June30, 2003 at Terminal Ballistics Research Lab (TBRL), Chandigarh.
She was assigned the project titled “Design and development of shock velocity
recorder”.
The work reported meets the standards necessary for partial fulfillment of requirement of
degree of B.E. Electronics & Communication awarded by Thapar Institute of Engg. and
Technology, Patiala.
Place: Chandigarh
Date:
Harbans Lal
Deputy Director,Zone-III
TERMINAL BALLISTICS RESEARCH LABORATORYDEFENCE R&D ORGANIZATION
MINISTRY OF DEFENCE, GOVT. OF INDIA
SECTOR-30, CHANDIGARH, INDIA-160020FAX: 91-172-657506
0172-651824,651825,651826
DECLARATION
This is to certify that the project report titled ‘Design and development of PC based
firing control unit’ submitted by Rajwinder Singh, Roll No.9902758, student of B.E
Electronics & Instrumentation , IITT College of Engineering, Pojewal is a record of the
student’s own work. The work presented has been done by him under my supervision and
guidance.
The reported work is of desired standards and has not been submitted in any other
university or institution for the award of any other degree or credentials.
Harbans Lal
Project Incharge
Acknowledgement
I would like to express my sincerest thanks to the director of TBRL, Padam Shri
Sh.V.S.Sethi, for permitting me to undergo 6-months industrial training in this institute.
It is with deep affection and appreciation that I acknowledge my indebtedness to
Mr. Harbans Lal, Deputy Director (Zone 3), not only for his enlightening guidance and
enthusiastic interest but also for his ever available help, cooperation and confidence at I
gained under him.
I sincerely thank Mrs. Rajesh Kumari, Mr. I.P.Singh, Mr. Pankaj Sajan, Mr.
Jatinder Pal, Mrs. Shalini Mahajan, Mr Dhanparkash , Mr Vijay Kumar and all the others
in the lab for their timely help and cooperation.
In the end I would like to thank my family who provided me help backstage and
whose blessings I always treasure.
Nidhi Jain
TABLE OF CONTENTS
1. About the Organization Terminal Ballistic Research Laboratory.
1.1 Aim of the Laboratory
1.2 Historical Background
1.3 Specialized Facilities
1.4 Areas of Work
1.5 Achievements
2. About the Blast and Damage Studies Zone.
2.1 Free Air Explosion
2.1.1 Blast Wave
2.2 Underwater Shock Study
2.3 Underground Shock Study
3. Project
3.1 Study of Instrumentation
3.1.1 Sensors
3.1.2 Signal Conditioners
3.1.3 Gauge Calibration
3.1.3.1 Static Calibration
3.1.3.2 Dynamic Calibration
3.1.4 Sensors used in Underground Trials
3.1.4.1 Geophone
3.1.4.2 Accelerometer
3.1.4.3 Blast Mate
3.1.4.4 Etna Accelerograph
3.1.5 Cables used for Data Transmission
3.1.6 Other Instruments used in Blast and Damage Study
3.1.6.1 LCR Meter
3.1.6.2 Strain Meter
3.1.7 Data Recording Instruments
3.1.7.1 Digital Storage Oscilloscope
3.1.7.2 Digital Phosphor Oscilloscope
3.1.7.3 Magnetic Recorder
3.1.7.4 Graphical Multimeter
3.1.8 Interfacing the Hardware
3.1.8.1 Parallel Port
3.1.8.2 Serial Port
3.2 Multi Channel Shock Velocity Recorder
3.2.1 Introduction
3.2.2 Aim of Project
3.2.3 Components Used
3.2.3.1 Comparator LM 339
3.2.3.2 Multivibrator 74121
3.2.3.3 J-K Flip Flop 7473
3.2.3.4 NAND Gate 7400
3.2.4 Circuit Diagram
3.2.5 Working of the System
3.3 Study of Analog to Digital Converter
4. Trials in the zone
1. ABOUT THE ORGANIZATIONABOUT THE ORGANIZATION
TERMINAL BALLISTICS RESEARCH LABORATORYTERMINAL BALLISTICS RESEARCH LABORATORY
1.1 AIM OF THE LABORATORY :
To conduct basic and applied research work in detonics, energetic materials, blast
& damage, defeat of armour, immunity, lethality; design, development and performance
evaluation of new armament stores.
1.2 HISTORICAL BACKGROUND:
Terminal Ballistics Research Laboratory (TBRL) was envisaged in 1961 as one of
the modern armament research laboratories under the Department of Defence Research &
Development. The laboratory became fully operational in 1967 and was formally
inaugurated in January 1968 by the then Defence Minister. While the main laboratory is
situated in Chandigarh, the firing range, spread over an area of 5000 acres, is located at
Ramgarh, 22 km away in Haryana. Over the past three decades, the Laboratory has
grown into an institution of excellence and has become one of the major technical bases
in the field of armament studies in DRDO.
The Laboratory facilitates basic and applied research in the fields of high
explosives, detonics and shock waves, evolving data and design parameters for new
armament stores and assess terminal effects of ammunition under indigenous
development or of foreign origin.
The Terminal Ballistics Research Laboratory, Chandigarh has been equipped with
a set of sophisticated instruments/techniques to obtain accurate and reliable data on
terminal ballistics. By well thought of design of experiments, the laboratory is capable of
getting a complete picture of the complex phenomena of weapon-target interaction. The
data obtained has immensely helped the armament designer and has also provided very
useful information to the engineers in designing protective structures immune against
weapon attacks.
The range is divided into eight specialized technical zones, which have been so
designed to conduct trials independent of each other. The instrumentation techniques
installed in this lab can be broadly categorized into three groups namely oscillographic,
radiographic and photographic.
1.3 SPECIALIZED FACILITIES:
High speed and ultra high speed framing and streak cameras.
High velocity pin oscillographic techniques.
Flash radiography.
Blast instrumentation.
Multi channel spark photography technique.
Electron microscope and allied instruments for metallographic studies.
Fragment launching gas gun for hyper velocity impact phenomena studies.
High speed data acquisition systems.
Precision casting and machining of explosives.
Warm isostatic press for plastic bonded explosives.
Pilot plants for HMX and PBX.
Rail Track Rocket Sled – a national test facility.
Shadowgraphy.
1.4 AREAS OF WORK: Performance of armour defeating projectiles and immunity profiles.
Studies of ground shock, blast damage, fragmentation and lethality.
Preparation of safety templates for various weapons.
Studies of underwater detonics and pressure wave propagation.
Explosive forming, cladding and welding.
Detonics of high explosives.
1.5 ACHIEVEMENTS:
1.5.1 High Explosives
Development of new HE compositions and filling techniques.
Establishment of wounding criteria of incapacitation and evaluation of body
armour.
Generation of immunity data for various types of tank armour.
Preparation of safety data around guns and safety templates for various
armaments.
Evaluation of lethality of ammunition in terms of Mean Area of Effect.
Generation of basic lethality design data for warheads/ammunition.
Development of techniques like explosive forming, cladding and welding.
Development of shaped charge warheads for different targets and tactical roles.
1.5.2 Instrumentation
Digital Blast Data Recorder.
Impulse Noise Generator for evaluation of earplugs.
Evaluation of wooden missiles for mob disposal for Bureau of Police Research &
Development (BPR&D).
Equipment for ground shock studies.
1.5.3 Ballistic Studies and Performance Evaluation Trials
A number of projects relating to performance and basic input data evaluation have
been completed successfully. Some of the recent important studies relate to:
Performance evaluation trials of Prithvi, Trishul & Akash warheads.
Assessment of lethality of 155 mm HE shell and mortar HE 51 mm MK-I and II.
Assessment of fragmentation pattern and blast parameters of 1000 lb MC MK-9
bomb, HD/LD 450 kg MC/HE bomb and mortar HE 51 mm MK-I and II.
Determination of safety distances for 122 mm D-30 a gun, 155 mm HE M107, HE
77B and HEER shells, mortar HE 51 mm Mk-I and II and ricochet trace for 122
mm D-30 A gun.
Safety in peace for firing of 160 mm Tempella mortar.
Generation of immunity data of armour for Main Battle Tank against attack of KE
Projectiles and small arms fire.
Assessment of fragmentation pattern and blast parameters of HS/LD 450 kg
MC/HE bomb under development at ARDE.
Determination of safe angle of inclination of armour plates under the attack of
improved T-72 FSAPDS ammunition.
Computation of safety distance in respect of infantry weapons for battle
inoculation training.
1.5.4 Zeroing of T-72 Tanks at 1600 m Range
Safety template with the danger zone depth of 35 km permitted conduct of field
trials/exercises, including zeroing of T-72 tanks with 125 mm FSAPDS
ammunition.
Acceptance of introduction of Reduced Safety Template leading to opening up of
ranges at Babina, Naraingarh and Ahmednagar for zeroing trials of T-72 tank
guns by the Armoured Regiments.
1.5.5 Baffle Range for Small Arms
The TBRL design for the baffle range has been accepted by the Army and the first
baffle range has come up at Infantry School, Mhow within an area of 2 hectares,
without compromising on safety.
1.5.6 Indigenous Plastic Bonded Explosives
Developed Plastic Bonded Explosives (PBX), the latest class of HE compositions
with high VOD and higher detonation pressures.
1.5.7 Indigenous Digital Blast Data Recorder
Developed based on a new design technique, for direct measurement of important
blast wave parameters.
1.5.8 Indigenous Transducer for Blast-Measurement
Developed a free air blast pressure transducer for measuring pressures up to 14
kgm cm2. It has a sensitivity of 1400 pc/kgm cm2 with a natural frequency of 200
KHz. These transducers are in regular production and use in the Laboratory.
1.5.9 Impulse Generator
Developed for the simulation of impulse noise (=190 dB) and testing of artificial
earplugs developed by Armed Forces Medical Services.
1.5.10 Bund Blasting Device (BBD)
Designed and developed Bund Blasting Device as per GSQR-573 for breaching
operation; it has been accepted for introduction in service. The device is man-
portable with a total weight of 24.5 kg.
1.5.11 General Purpose Anti-personnel Grenade (GSQR-459)
Designed and developed ‘Multi-mode’ grenade system replacing the existing 36-
M grenade for use as an offensive, defensive or rifle grenade.
2.2. ABOUT THE BLAST AND DAMAGE STUDIES ZONEABOUT THE BLAST AND DAMAGE STUDIES ZONE
During my training, I was associated with “Blast and Damage Studies” zone,
which is engaged in instrumentation studies carried out for assessment of response and
damage pattern of variety of structures. These structures may be above ground,
underground or underwater and hence are subjected to air blast, ground shock and
underwater shock. Various types of instrumentation techniques are employed to record
the terminal effects of explosives. Blast and damage study is related to effects and kill
mechanisms of blasts. It takes into consideration the various parameters related to blast
like peak over pressure, duration, impulse and shock. Damage due to blast is defined as
kill mechanism of the blast.
Various kill mechanisms of air blasts are:
Primary blast effect.
Tertiary blast effect.
Blast generating fragments.
Similarly are the kill mechanisms of underground blast:
Minor or major cracks.
Broken windows.
Fallen of buildings.
For the underwater blasts the important effects are:
Shattering effect.
Heaving effect.
The zone also deals with various sensors, signal conditioners and computer-based
data acquiring systems for measurement and analysis of intense shock and structure
response. I was associated with both lab and field activities for studying the effects of
free air explosions.
The detonation of explosive convert the original material into gases products at a
very high temperature (3000oC) and pressure (150Kbar) .The conversion takes place at
very high speed releasing a large amount of energy into the atmosphere in very short
duration. The measurement of these events requires very accurate and sophisticated
instruments, having time resolution of the order of microseconds. I was involved in use of
various types of equipments and sensors to record the transient events occurring at the
time of explosion. During the training period I was associated both lab as well as field
activities for studying the effects of
Free air explosion.
Under water explosion.
Under ground explosion.
2.1 FREE AIR EXPLOSION:
Blast damage and evaluation studies are essential activities for assessment of
terminal effects of high explosive bombs /warheads. These studies also play a major role
in design and construction of blast resistant structures using innovate concept of shock
observing techniques and construction materials.
When there is an explosion in atmosphere a system of shock waves called blast waves
are generated. In explosion blast wave is formed due to release of high pressure gases
into atmosphere at a supersonic speed, surrounding atmosphere gets compressed due to
this and results in formation of blast wave. To study the blast profile at a particular
distance the following instruments are involved.
Blast gauge (Transducer).
Charge to voltage converter.
Charge to voltage amplifier.
Filter stage.
Analog interfacing.
Analog to digital converter.
Charge simulator.
The measurement of blast events requires very accurate and sophisticated
instruments, having time resolution of few microseconds. In all the instrumentation
techniques, the basic system consists of a suitable transducer such as pressure sensor,
strain gauges, PZT gauge; a signal conditioner such as charge amplifier, strain meter etc.
and recording equipment such as an oscilloscope, or a magnetic tape recorder.
2.1.1 BLAST WAVE
One of the most significant measurements in experimental study of an explosive
is the blast wave, generated in surrounding medium when charge is detonated. Blast wave
originates at the charge and is propagated outwards and away from the charge at a
velocity which depends on nature of the charge i.e. geometry, size, type of explosive.
Initially, the pressure rises abruptly at the leading edge of the wave (shock front),
and then decreases continuously. This decrease may reduce the pressure to below the
ambient pressure; phases of continuous increase may also be observed .The primary
shock moves with a velocity greater than the velocity of sound in the medium ahead of it.
Eventually the pressure at any point must revert to the measurement, dependent on
pressure being recorded.
Involving above mentioned instrumentation systems we have evaluated following
blast parameters.
PEAK OVER PRESSURE
This is the pressure jump of blast wave phase measured by excess pressure above the
atmospheric pressure. It is also defined as the maximum pressure above the atmospheric
pressure level of the positive phase of the blast wave.
DURATION
It is a measure of time period elapsed between the arrivals of shock wave at the point up
till the peak over pressure becomes zero i.e. equal to atmospheric pressure.
IMPULSE
This is the important parameter to determine extend of damage. In pressure time curve, it
may be defined as area under the curve i.e. specific impulse (impulse/unit area). It
depends on peak over pressure, duration and decay constant. The blast parameters
calculated from blast profile contribute to define the damage on different targets.
Blast wave showing various parameters
If the response time of the structure is high compared to blast duration then,
impulse is taken as damage criteria. If the response time is small compared to duration of
load then peak over pressure is the criterion for the damage. In case both are compared
the peak over pressure and impulse are considered for accessing the damage in structures.
Some typical damage effect of blast, based on pressure criteria is obtained by using above
set of instrumentation: -
Pressure Damage
14 Kg/cm2 Severe internal injury to human beings.
2.5 Kg/cm2 Lungs injury.
1.6 Kg/cm2 Damage to brick structure.
1 Kg/cm2 Eardrum burst.
0.02 Kg/cm2 Damage to windowpanes.
2.2 UNDERWATER SHOCK STUDY:
When an explosive is detonated inside the water, the blast wave takes place in an
uncompressible medium. So unlike air blasts, there are two distinct phenomena:
Shock Wave.
Bubble Wave.
Peak-over Pressure
Impulse
Duration
Negative impulse
The two different phenomena produce two different effects on the target. While
the shock wave is responsible for producing a shattering effect, the bubble phenomenon
produces a heaving effect. The damage is caused by the cumulative effect of these two
phenomena.
Under water techniques are used for studying the following phenomenon.
Comparison of explosive performance used in different types of naval warhead.
Heat of detonation /energy of unknown explosives can be determined.
Shock energy in primary & secondary shocks is estimated, for the performance
evaluation of explosive related with its shattering and heaving power.
Under water explosion facility in T.B.R.L consists of tank fabricated from 20 mm thick
mild steel plate. Tank is 6 m diameter & 6m in depth. 1/3 of tank is embedded in ground,
to make it able to with stand high pressure. Small spherical charge up to the weight of
100g of explosive can be carried out in the tank. Pressure transducers are required to
position at required depth and at predetermined distance from point of explosion to
record the blast profile.
Water tank used in under water trials
The figure above shows the water tank of TBRL in which underwater trials are
conducted.
2.3 UNDERGROUND SHOCK STUDY:
Underground shock studies are conducted for the following objectives:
The assessment of damage due to creating & ground shock effects to structures by
under ground explosive and optimization of depth of burst for maximum damage.
Used to calculate the safety distance for the structures
To define different damage on structures subjected to ground shocks.
In underground explosions most of the energy is released is irreversible, transferred to
the immediate neighborhood of explosion. In the near region it results in formation of a
crater depending on depth of burst. At far of region stress level falls off below the elastic
limit and it degenerates into seismic waves. These waves carry small amount of energy,
about 2-3%.
Depending on the proximity of the target from the point of explosion the ground motion
results in the damage of buildings and other structures. In evaluating the structure-ground
motion interaction, the work is divided under as
Measurement and prediction of ground motion.
Measurement and prediction of damaged structures as a result of ground shocks.
In close vicinity of underground explosion the particle acceleration is of the order of 10 4
g to 105 g. As this shock travels in the surrounding soil it decays very fast into ground
motion. The dominant frequency in ground motion lies between 1-30Hz.
The instrumentation system used for capturing ground motion in this region is as
under.
Geophone
Accelerometer
Blast mate
Etna accelerograph
3.3. PROJECTPROJECT
My Project at BDS zone, TBRL has been divided into two parts:
The Study of Instrumentation in the zone.
Design and Development of Shock Velocity Recorder.
Study of Analog to Digital Converter.
3.1 STUDY OF INSTRUMENTATION:
3.1.1 SENSORS
BLAST GAUGE:
The fact that some materials produce an electrical charge on their faces when
subjected to a mechanical strain along certain axis and thereby exhibiting the phenomena
known as piezoelectricity has for a long time been used in the construction of pressure
transducers. The choice of this type of transducer for air blast gauges is fairly obvious as
it is probably the most robust, reproducible and linear. These advantages have to be paid
for in terms of low signal output and need to pay considerable attention to electrical
insulation but this is considered worthwhile in order to make accurate measurements of
air blast parameters.
The choice of piezoelectricity type of transducer for free air blast gauges is fairly
obvious as it is
Mechanically robust.
Offer the highest frequency response.
Non - pyroelectric.
Chemically stable.
Insensitive to humidity.
No hysterisis effects.
Reproducible.
Linear response.
Pyroelectric effects (the appearance of the charge on the faces of crystal due to a
change in temp of crystal) are observed with materials such as Barium Titanate and
Tourmaline. Other materials such as lithium Sulphate, Rochelle salt, are very brittle and
sensitive to humidity conditions.
Advantages in selecting the quartz crystal as sensing element:
Chemically stable.
Free from hysterisis.
Mechanically stable.
Available as a high quality material.
Non-pyroelectric.
Disadvantages of quartz crystal:
Low piezoelectric constant.
It is not sensitive to hydrostatic pressure.
These disadvantages can be obviated by using multiple crystal piles and by ensuring that
pressure is applied only to certain faces of crystal.
A quartz crystal is oriented with respect to three orthogonal axes designated X, Y
& Z. Z-axis is one of the optical symmetry. Light passed through crystal along this axis
suffers no change in polarization. X and Y-axes are polar axis, mutually perpendicular to
each other and perpendicular to Z- axis. When the crystal is strained in the direction of a
polar axis only, charge separation occurs. Equal and opposite charges are induced in the
conductors placed on surfaces cut perpendicular to a polar axis and the charge is the
linear function of the strain.
Components required for the construction of a pile are
12 X-cut quartz crystals
13 Copper foil electrodes
2 Dural pistons
Locking rings and neoprene pads
Prior to assembly the quartz crystals are checked for polarity and faces are
marked accordingly. Essentially this involves placing the crystal on a grounded plate and
applying the pressure on a metal electrode placed on the other surface. The polarity of
charge collected by the electrode is determined by connecting the crystal to DSO and
observing the deflection.
The blast gauge consists of pile of 12- octagonal x-cut quartz crystal of
approximate 0.01-inch thickness, 1.0-inch diameter. The crystal faces are of evaporated
aluminum or gold. The pile is formed to increase the gauge sensitivity. All 12 crystals are
assembled with proper polarity axis marker with copper foil electrodes. Both sides of
copper foil are coated with a solution of pure bitumen dissolved in benzene and allowed
to dry. This assembly is kept in a temperature-controlled oven at 140oC for two hours.
The pile is cooled in vacuum for 24 hours after which it is cleaned with benzene to get
extra bitumen out.
The following figure shows a gauge pile assembly.
Crystal and electrodes used in gauge.
Copper foil tabs, which form the alternate electrode, are grouped and soldered. The
insulation resistance measured from insulation tester is more than 50000 - 60000 M ohm.
Gauge pile construction
Electrode
+
+
-
-
+
Crystal
Secondary Explosive
A test pressure of 1kg/cm2 is applied at each side of the pile to confirm the proper
adhesion to crystal electrode .The complete pile is assembled in a brass body, having an
aerodynamic shape. The gage has sensitivity of 100pC/psi, and natural frequency of 200
kHz. It can be used for pressure measurement in the range of 1-200psi.
Blast gauge for measuring blast pressure
The figure above shows a typical blast gauge used for measuring the pressure produced
during blast.
Various gauges used for measuring blast parameters
Various other gauges used are Lollipop gauge, under water gauge and PZT gauge
normally called as shock arrival gauge. Figure above shows the four gauges generally
used in blast and damage studies.
3.1.2 SIGNAL CONDITIONERS
3.1.2.1 Charge amplifier:
The charge amplifier, which is the heart of blast instrumentation, converts charge into
voltage and is useful for carrying out field blast measurements. It can be used for
measurement of both free air as well as under water explosive pressures. Charge
amplifier consists of following stages:
Block diagram of Charge amplifier
3.1.2.2 Charge to voltage converter stage uses an Operational-amplifier as input stage.
The configuration of the Operational-amplifier with the capacitor of different values in
the ratio of 1:10:100 in the feedback loop operates as an integrator and integrates the
current at the input. This input current is the result of charge developed across the high
impedance piezoelectric elements inside the gauge. The amplifier works to nullify this
current and thus produces output voltage proportional to the charge. The low frequency
cut off limit of 1Hz is determined by feedback resistance placed parallel to the feedback
capacitors. These resistances are in the ratio of 100:10:1 with references to the capacitors.
Charge to Voltage
Converter
Transducer
Out
Charge
simulator
SensitivityControl
Amplifierand gain control
Low PassFilter
14KHz
Low passFilter
150 KHz
O/P
3.1.2.3 Transducer Sensitivity Control: It is a voltage amplifier stage. The sensitivity
control varies the gain of this stage inversely with the transducer sensitivity, which
establishes a direct relationship between the applied pressure and the amplifier output
making it independent of the transducer sensitivity. The transducer sensitivity can be set
accurately up to three decimal places over a range of 1pc/psi to 110pc/psi (14.22 pC per
Kg/cm2 to 1564.20 pC per Kg/cm2)
The sensitivity of charge amplifier is not affected by the change in capacitance caused by
changing cable length. When very long cables are used, the high frequency response is
slightly attenuated.
3.1.2.4 Amplification and Gain Control: The output of the second stage is further
amplified nearly ten fold so that it can be measured easily and accurately. The output is
normalized at 1 volt for minimum range settings. It can deliver the output voltage ten
times of the normalized value. Thus it allows the measurement of pressure over a wide
range extending from 1psi to 10000 psi (0.703 Kg/cm2 to 703 Kg/cm2).
3.1.2.5 Filter stage consists of two low pass filters having –3db cut off frequency at
14KHz and 150KHz. With the introduction of these circuits, the charge amplifier is made
capable of measuring free air as well as under water explosive pressures. The low
frequency response of a charge amplifier is determined by the time constant set by the
feedback circuit along the operational-amplifier and is unaffected by change in the input
load condition. Varying the feedback resistance changes the lower limiting frequency.
3.1.2.6 Charge simulator: The feedback capacitors put in the input stage must be
accurately set in the ratio of 1:10:100 in the three ranges. Practically there is slight
variation in this ratio due to tolerance limitation of capacitors. Therefore to maintain the
accuracy of the system, it must be calibrated for the particular range in use. For this
purpose calibration facility has been created with in the instrument itself. A charge
simulator has been in corrupted, which provides calibration signal in five steps from
10pC to 10000pC at frequency of 1 KHz. The calibration signal can be fed internally to
each channel one by one through a channel select control. The output of charge simulator
system is also available externally in voltage form.
3.1.3 GAUGE CALIBRATION
3.1.3.1 STATIC CALIBRATION:
It is necessary to determine the gauge sensitivity before the gauge is used in the
field. There are two types of calibration processes: static and dynamic. Static calibration
is done in the laboratory using a static calibration setup as shown.
Quasi-static calibration of blast gauges
Manometer
Compressor
Blast Gauge
SolenoidCharge Amplifier
Cellofin Sheet
Release valve
+
_
DSO
The gauge is fitted inside a small chamber, which is mounted on a bigger chamber. The
two chambers are separated by a cellophane diaphragm, which is pre-heated in an oven to
avoid sagging when pierced. The big chamber is filled with air to a pressure of 10 psi.
The diaphragm is punctured by a solenoid with a pointed pin. The gauge senses the
sudden release of air pressure. The signal from the gauge is fed to a charge amplifier, the
output of which is fed to an oscilloscope.
The sensitivity of the gauge is calibrated from the relation:
G= (total charge in pc x gauge deflection)/ (Cal. Deflection x chamber pressure)
The deflection due to gauge and calibration signal is measured from the records. The
chamber pressure is taken from a mercury manometer, just prior to puncturing the
diaphragm. Total charge in Pico-coulomb is obtained from the chart prepared from
measurements of the components of the preamplifier and calibration voltage.
3.1.3.2 DYNAMIC CALIBRATION:
The blast gauges are subjected to dynamic calibration trials to determine errors in
measurements and spurious response of the gauges due to defective assembly. Standard
spherical explosive charge are utilized with blast gauges symmetrically positioned as
shown in figure below:
Field set up of free air blast.
Distance of gauges from the charge:
G1: One Meter G3: Three Meters
G2: Two Meters G4: Four Meters
In practice a minimum of four gauges are mounted around the explosive charge
either at the same distance or at different distances in a line, all depending upon the
experimental requirements.
3.1.4 SENSORS USED IN UNDERGROUND TRIALS:
3.1.4.1 GEOPHONE:
The geophone is velocity transducer consists of a permanent bar magnet, which
moves up, & down within a long coil of two windings. When frequency of vibration is
higher than natural frequency of suspended system, the seismic mass remains in fixed
position and the case with the coil vibrate about it. The sensitivity is constant above the
resonance frequency.
The typical transducers used for measurement of ground particle velocity are triaxial
geophone of sensitivity 29V/m/s are:
Vertical uniaxial geophone of sensitivity 20V/m/s and natural frequency of 10Hz.
Uniaxial horizontal geophone of sensitivity of 19V/m/s, with a natural frequency
of 10Hz
ChargeG1
G2
G3
G4
A transducer used is a geo phone, which measures ground particle vibrations. Geo-
phones can be categorized as uniaxial transducers and triaxial transducers. Uniaxial
transducers measure particle velocity in one direction. Triaxial transducers measure
particle velocity in three directions i.e. x ,y ,z .
GEO-PHONE OPERATION:
Functionally a geo-phone sensor is a coil of wire suspended around a magnet. The
magnet is free to move in a field of magnetic flux lines. By Lenz’s law induced voltage is
proportional to the speed at which flux lines are traversed. Induced coil voltage is
therefore proportional to the relative velocity of the coil to the magnet. In practice, it does
not matter whether the coil or the magnet moves only the motion and speed relative to
each other are important.
Geo-phone sensor specifications give a number known as the ‘‘Intrinsic voltage
sensitivity”. It is the coil voltage induced for a given coil versus magnet speed with units
of V/in/sec. In seismic applications, the magnet is moved by the blast energy because it is
INDUCED VOLTAGE
COIL
Direction of motion of magnet
Relative to coil
Magnet
coupled to the particles of the surrounding terrain. The coil, because of its inertia, doesn’t
move and the resulting magnet versus coil motion induces a voltage, which is
proportional to particle velocity.
3.1.4.2 ACCELOROMETER:
Accelerometer is an instrument used to measure shock and vibration. It can be
initialized by mass element connected to the case by spring and a damping medium. The
transducing elements produces an electrical output proportional to the displacement of
the mass element relative to the case and also proportional to the acceleration applied to
the case.
Accelerometer uses a sensing method in which acceleration acts on a seismic
mass (proof mass) that is restrained by and whose motion is usually damped in a spring
mass system.
When acceleration is applied to accelerometer case the mass moves relative to the
case. When acceleration stops, the spring returns the mass to its original position. If
acceleration is applied in opposite direction to the transducer case, the spring would be
compressed rather than extended.
Under steady state conditions displacement of seismic mass is given by equation
We have F= k X Where , K =spring constant
X = displacement of seismic mass
3.1.4.3 BLASTMATE:
MassSpring
Damper
Simplified model of accelerometer
Blast Mate is used to record full field analysis of an event i.e., peak particle
velocity, peak acceleration, peak displacement, peak vector sum, zero crossing frequency
and peak air (sound) pressure.
Using the Blast Mate we can do event monitoring. Event monitoring measures
both ground vibrations and air pressure. Blast mate measures transverse, vertical and
longitudinal ground vibrations. Transverse ground vibrations agitate particles in a side to
side to motion. Vertical ground vibrations agitate particles in an up and down motion.
Longitudinal ground vibrations agitate particles in a forward and backward motion
progression outward from the event site. Events also affect air pressure by creating what
is commonly referred to as ‘‘air blast”. By measuring air pressures, we can determine the
effect of air blast energy on structures measured on the linear “L” scale or as perceived
by the human ear, measured on the “A” weight scale.
MICROPHONE:
The microphone measures air pressure. There are two types of microphones, linear ‘‘L”
(standard) and ‘‘A” weight (optional).
MEASUREMENT SCALES:
The Blast Mate supports two sound pressure measurement scale: linear ‘‘L” and ‘‘A”
weight:
LINEAR ‘‘L”:
Linear measurement is generally used to measure the effect of low frequency air pressure
on buildings. The linear scale records sound pressure without modification in the 2 to 300
Hz range. Measurement units may be in absolute, Pascal or relative dB scales.
‘‘A” WEIGHT:
‘‘A” weight measures noise levels people may consider an annoyance. The signal is then
converted to root mean square (RMS).
Units are measured using the decibel scale dB (A).
SOUND PRESSURE:
The Blast Mate III calculates two sound pressure parameters i.e., peak sound pressure and
zero crossing frequency, recorded by the microphone.
Peak sound pressure (psp):
The Blast Mater III checks the entire event waveform and displays the largest
sound pressure called the peak sound pressure, also referred to as the peak air
over-pressure.
Zero crossing frequency (zc freq):
The zero crossing frequency calculates the event waveform’s frequency at the
largest peak for sound pressure.
FEATURES:
Full waveform event analysis.
Multiple record modes---single shot, continuous, auto record.
300 full waveform event capacity.
Full PC compatibility.
Variable sample rates.
On-line Help.
Upgradeable.
Rugged design.
3.1.4.4 ETNA ACCELEROGRAPH:
Etna is used for the measurement of the ground particle acceleration at the time of under
ground explosion. The block diagram of the Etna is as shown.
Oscillator Capacitive
Transducer
DemodulatorAmplifier
CalibrationCoil Functional
Test PulseAnalogOutput
CalibrationControl
Block Diagram Of Etna
WORKING PRINCIPLE:
The oscillator applies an AC signal of opposite polarity to the two moving capacitor
plates. When the accelerometer is ”zeroed” and when no acceleration is applied, these
plates are symmetrical to the fixed central plate and no voltage is generated.
Acceleration causes the coil and Capacitive sensor plates, (which are a single assembly
mounted on mechanical flextures), to move with respect to the fixed central plate of the
capacitive transducer.
This displacement results in a signal on the center plate of the capacitor, which become
unbalanced, resulting in an AC signal of the same frequency as the oscillator being
passed to the amplifier. The amplifier amplifies this AC signal. This error signal is then
passed to the demodulator where it is synchronously demodulated and filtered, creating a
DC signal in feed back amplifier. The feed back loop compensates for this error signal by
passing current through coil to create a magnetic restoring force to balance the capacitor
plates back to their original null position.
The current traveling through the coil is thus directly proportional to the applied
acceleration. By passing this current through a complex impedance consisting of a
resistor and capacitor, it can be converted to voltage output proportional to acceleration
with a bandwidth of approximately 200 Hz. Selecting a particular resistor values are
determined by a high accuracy network, so the range can be set at 0.25g, 0.5g, 1g, 2g and
4g without re-calibrating the sensor span. The capacitor and overall loop is selected along
with resistor to ensure an identical transfer function on each range. The voltage output of
the resistor capacitor network is set at 2.5volts for the acceleration value corresponding to
the particular range. This voltage is then applied to the amplifier. The low power
amplifier amplifies this signal by either 1 or 4 to give a single ended output of either 2.5
or 10volts. A second amplifier is also present which inverts the signal form the first and
can be connected to the negative output lead. The system is used to study the ground
acceleration; it has built in triaxial forced balanced accelerometer, which has a range of
4g, with a nature of frequency of 100 Hz. The system has built ion 2Mb flash memory
with an addition of PCMCIA memory card to extend its memory capacity up to 8Mb. The
system has internal battery of 12V and 6.5 Ampere-hour and the sample rate of the
system is 100-250 cycles per second with 18- bit resolution. The system has three
channel frequency response is DC-80Hz Features:
(1) Each coil is equipped with a calibration coil. Applying a current to this simulates the
effect of acceleration applied to the sensor.
(2) The calibration coils are open circuit in normal, to prevent cross talk and noise pick
up. To utilize this, the enable signal must be activated by a DC voltage 5 volts to 12
volts with respect to ground.
SPECIFICATIONS:
Full scale range: + 4g
Frequency response: DC to 80 Hz @sps
Resolution: 18-bit resolution @sps
Sampling rate: 100, 200, 250 sps
Input range: + 2.5volts
3.1.5 CABLES USED FOR DATA TRANSMISSION:
The signal from the blast gauge is brought into the control room using special
coaxial cables. The cable used in blast and damage study is “anti micro phonic low noise
cable”. It has special graphite coating above the inner signal carrying wire to ground any
noise signal if present.
The important specifications of the cable used are:
Characteristic impedance: 75 ohm at 1MHz frequency in unbalanced condition
Frequency rate of operation: 1 MHz at 3dB gain
Breakdown voltage: 2.7KV
Nominal capacitance: 69pF/m
Nominal attenuation: 0.46 dB/100ft for 1MHz
Inner diameter: 0.193mm, 14 strands
Plain annealed copper polythene insulation: 5.08mm
Graphite conducting layer: 5.59mm
Outer conductor plain annealed copper: 6.48mm
Overall diameter with outer PVC sheath: 8.0mm
3.1.6 OTHER INSTRUMENTS USED IN BLAST AND DAMAGE
STUDY:
3.1.6.1 LCR METER:
The LCR meter bridge is an instrument used to measure the inductance, capacitance,
resistance and Q-factor of any component. In blast and damage study, this meter is used
to calculate the parameters of anti-micro phonic cables
There is a special input probe connected to the crocodile clips that hold the component.
The digital display on the meter directly gives us the value of the selected parameter. We
can select whether we want absolute values or relative values (with specified reference)
as percentages.
There are three modes in the instrument
AUTO MODE : This means that the instrument will itself select whether the
device is an inductor, capacitor or resistor. The value is displayed in Henry, Farad
or ohm.
LC MODE : In this mode only the inductance or capacitance of the component
will be reported and not its resistance, even if it is predominant.
R MODE : This mode displays the resistance of the component, be it a capacitor
or inductor.
Other selections that are available are:
Series.
Parallel.
This LCR meter is actually an AC bridge with the component under test forming one of
the arms. As each component has its own resistance, capacitance and inductance it can be
denoted and tested as any of the following two ways.
INDUCTOR C R
Series
INDUCTOR
C
R
Parallel
The low value components are measured in series combination and the higher valued
components in parallel.
Frequency selection: There are four frequencies to choose from as the bridge source.
1. 100Hz
2. 1KHz
3. 10KHz
4. 100KHz
There are certain optimum recommended values by the manufacturers for the various
combinations. Polarizing voltage can also be given to electrolytic capacitors for providing
a bias.
3.1.6.2 STRAIN METER:
If a metal conductor is stretched or compressed, its resistance changes on
account of the fact that both length and diameter of conductor changes. Also there is a
change in the value of resistivity of the conductor when it is strained and this property
is called piezoresistive effect. The strain gauges are used for measurement of strain
and associated stress. The gauge factor of strain gauge is given by the following
formula.
Gauge Factor, K= R/R/L/L
Where, R = change in resistance
R = Initial Resistance
L = change in length
L = Initial length of element.
Strain meter is used to show corresponding voltage or current for the strain
produced. Method of measuring strain uses a bridge composed of one strain gauge and
other resistances of same resistance value i.e. 120. This has an advantage of higher
output so it is widely applied to strain gauge based system.
In the quarter bridge with two wires, the affection to the lead wires due to change in
ambient temperature is roughly estimated as a strain of 5210-6/oC, when 10m long 2
parallel cables are used with 120 strain gage. This can be avoided by connecting bridge
as a quarter bridge in 3-wire system using three parallel cables. The third line is used for
connection to dummy arm of the bridge formed in bridge box to compensate the affection
of ambient temperature to lead wires.
STRAIN GAGE
A B
CD
Output
Voltage
Input
Voltage
R
R
R
Quarter 3-wire bridge connections.
Other connections in which gages can be connected are Full bridge, Half bridge etc.
FEATURES:
High frequency response ranging from DC to 200KHz.
Built in low pass and high pass filter.
Output can be obtained as voltage or current.
Digital sensitivity setting method: First select rated output of instrument from the
range of 1 to 10V. Secondly set the strain value corresponding to the output with
digital switch provided.
SOUND LEVEL MEASUREMENT:
Pressure can also be measured by measuring the sound pressure level. The
transducer used in this technique is a microphone, which converts sound pressure into
electrical signals.
The basic principle of a microphone is that when pressure is incident on it, its
membrane starts vibrating. This vibration is picked up and is transduced into an
electrical signal. Pressure level is calculated in decibels where the threshold level of
sound intensity, 2x10-10 bar is taken as the reference level of 0 dB. The formula used
for conversion of dB level to actual level is
dB = 20 log10(P/P0)
Where P = pressure in bars
P0 = 2*10-10 bar
The sound level meters used in the lab measure the dB level of blast. Using above
formula the actual pressure level obtained from the blast can be found.
The important considerations in using the sound level meters are:
Choosing the correct microphone: A choice has to be made between free-field
and diffused-field microphones. The usage depends on where the microphone
is to be used and what their application is. Other options include pre-polarized
and non-polarized microphones. A good knowledge of these is necessary
before one can get a good result in actual conditions.
Frequency weighting : Depending on the expected frequency response of the
explosive, the correct frequency weighting on the SLM has to be used. This is
essential to make sure that the required response signals are not attenuated.
Octave filters: Accessories such as octave filters are also required if a detailed
analysis of the response is to be made.
The SLM used in the lab is Bruel and Kjaer make. It is a portable device and can be
operated on a 6V battery for 8 hours. The important specifications of the unit are:
Maximum peak level: 153 dB
Frequency weighing: A, C, linear, all pass
Resolution: 0.1dB
Polarizing voltage: 0V, 28V, 200V
Storage rate: 1 value/sec
8KB ROM and 64KB RAM, total 99 memories
The microphone used is ½” free field prepolarized condenser microphone. It has a linear
frequency response till 10 KHz and has a sensitivity of 50mV/Pa.
The unit gives a direct display of the dB level of the ambient pressure. Additional values
reported include maximum pressure level, over range and under range.
3.1.7 DATA RECORDING INSTRUMENTS:
The information about the quantity under measurement has to be conveyed to the
personnel handling the instrument or the system for monitoring, control, or analysis
purposes. This function is done by data presentation element called recorders. In blast
instrumentation this job is assigned to high-speed oscilloscopes as below: -
Digital Storage Oscilloscopes (D.S.O.).
Dual Phosphorus Oscilloscopes (D.P.O.).
Magnetic Recorders.
Graphical Multimeters.
3.1.7.1 DIGITAL STORAGE OSCILLOSCOPES:
Digital storage oscilloscope is a tool for acquiring, displaying, and measuring
waveform signals. The DSO provides simultaneous multi-channel operation, as well as
measurement automation and waveform storage. Digital storage oscilloscope is available
in processing and non-processing type. Processing type include built in computing power,
which take advantage of the fact that all the data is ready in digital form. The inclusion of
interfacing and a microprocessor provides a complete system for information acquisition,
analysis and output. Processing capability ranges from simple functions (such as average,
area, rms, etc.) to complete Fast Fourier Transform (FFT) spectrum analysis capability.
DSO contains a hard copy plotter, which serve as digital scope high-speed recorders.
Non- processing digital scopes are designed as replacements for analog instruments or
both storage and non storage types. Their many features seen set to replace analog scope
entirely (within the bandwidth range where digitization is feasible).
A unique facility provided by the DSO is waveform math for inverting, adding,
subtracting and multiplying of waveforms. The TDS oscilloscope provides a means to
mathematically manipulate the waveforms. For example, if we have a waveform, which
is clouded by background noise, we can obtain a clear waveform by subtracting the
background noise from original waveform.
The scope operating controls are designed such that all confusing details are
placed on the backside and one appears to be using a conventional scope. Some digital
scope provides the facility of switching selectable to analog operation as one of the
operating modes.
The basic advantage of digital operation is storage capability, the stored
waveform can be repetitively read out, thus making transient appear repetitively and
allowing their convenient display on the scope screen.
The voltage and time scales of display are easily changed after the waveform has
been recorded, which allows expansion (typically to 64 times) of selectable portions, to
observe greater details.
A cross hair cursor can be positioned at any desired point on the waveform and
the voltage/time values displayed digitally on the screen.
Pre-triggering capability is also a significant advantage of DSO. Pre-triggering
recording allows the input signal preceding the trigger points to be recorded An
adjustable trigger delay allows operator control of the stop point, so that the trigger may
occur near the beginning, middle or end of the stored information.
Digital Oscilloscopes look at an input signal at discrete ‘sampling’ instants, rather
than continuously like an analog real time oscilloscope. They are therefore only aware of
the state of the signal at these instants and are completely ignorant of what happens in
between the samples.
The Digital Oscilloscopes offer unheard of bandwidth when compared to analog
oscilloscopes. The bandwidth limiting factors are Input Attenuator, Y-Amplifier, Y-
Deflection Plate and of course the CRT itself. The Digital Oscilloscopes avoid all these
limitations at one fell swoop by simply not attempting to deal with the whole signal in
real time. Instead it takes samples of the instantaneous voltage of the input signal on
successive cycles and assembles these samples to form a picture of the complete
waveform.
Thus the main requirement for a sampling oscilloscope is a circuit capable of
accurately sampling the input waveform at regular intervals.
Block Diagram of Digital Storage Oscilloscope
The first input stage of DSO is a Vertical Amplifier. Vertical Attenuation controls
allows to adjust the amplitude range of this stage. Next the Analog to Digital
Converter (ADC) in the acquisition system samples the signal at discrete points in
time and converts the signal’s voltage at these points to digital values called Sample
Points. The Horizontal System’s sample clock determines how often the ADC takes a
sample. The rate at which the clock “ticks” is called the Sample Rate and is expressed
in samples per second.
The sample points from the ADC are stored in memory as waveform
points. More than one sample point may make up one waveform point. Together the
waveform points make up one waveform record. The no of waveform points used to
make up a waveform record is called the Record Length. The trigger system
A/D DEMUXACQUISITION
MEMORY
P DISPLAY MEMORY
DISPLAY
AMP
determines the start and stop points of the record. The display receives these record
points after being stored in memory.
The DSO’s signal path includes a Microprocessor. The measured signal
passes through this device on its way to display. In addition to processing the signal ,
the microprocessor co-ordinates display activities , manages the front panel controls
and more. This is known as”Serial Processing” architecture.
GENERAL FEATURES:
Bandwidth: 100MHz
Memory: 1K/channel
Sampling rate: 400MS/s
High resolution, high contrast LCD displays with temperature compensation and
replaceable backlight.
Setup and waveform storage is possible in non-volatile memory.
Auto set for quick setup.
Waveform averaging and peak detection.
RS 232 communication port available for printing.
IEEE-488 interface available.
APPLICATIONS:
1. FAST FOURIER TRANSFORMS: The FFT computes and displays the
frequency contents of a waveform, which is acquired on a math waveform. FFT is used in
the following applications:
Testing impulse response of filters and systems.
Measuring harmonic content and distortion in systems.
Identifying noise sources in digital logic circuits.
2. WAVEFORM DIFFERENTIATION: This capability allows us to display a
derivative math waveform that indicates the instantaneous rate of change of the
waveform acquired. The derivative waveform is used in the measurement of slew rate of
amplifier and in analytical applications.
3. WAVEFORM INTEGRATION: This capability allows display of integral math
waveform as an integrated version of acquired waveform.
Integral waveforms find use in the following applications:
Measurement of power and energy, such as in power supplies.
Characterizing the mechanical transducers, as in integration of output of
accelerometer to obtain velocity.
3.1.7.2 DIGITAL PHOSPHOR OSCILLOSCOPE
Digital Phosphorous Oscilloscope is used for high-speed acquisition. The DPO
acquisition is made to produce a display that provides intensity information. DPO
acquisition mode reduces the dead time between waveform acquisition that normally
occurs when digitizing storage oscilloscope (DSO) acquires waveforms. The dead time
reduction enables DPO mode to capture and display transient deviations, such as glitches
or pulses often missed during longer dead times that accompany normal DSO operations
DPO acquisition mode differs from the normal acquisition mode used by digital storage
oscilloscope. A normal DSO mode follows a “capture waveform-digitize waveform –
update waveform memory – display waveform” cycles. Normal modes misses short-term
deviations occurring during the long dead times. Typical waveform capture rates are 50
waveforms per second. DPO mode increases the waveform capture rate to 200,000
waveforms per second, updating the waveform array many times between displays. This
very fast capture rate greatly increases the probability that runts, glitches and other in
frequent events will accumulate in waveform memory.
Digital Phosphorous Oscilloscope.
The digital phosphor oscilloscopes offer a new approach to oscilloscope
architecture. Like the analog oscilloscope, its first stage is vertical amplifier; like the
DSO, its second stage is an ADC. But after the analog to digital conversion, the DPO
looks quite different from the DSO. It has special features designed to recreate the
intensity grading of an analog CRT.
The DPO combines the best of the analog and digital worlds while going beyond
both technologies. With one instrument, it’s now possible to capture all of salient
information about a waveform in three dimensions: amplitude, time and the intensity axis
that reveals amplitude distribution over time. It offers all the traditional benefits of the
DSO, from data storage to sophisticated triggering. It answers, as, well the need for
analog-like-characteristics, such as intensity-graded display and real-time behaviour, by
digitally emulating the chemical phosphorescence process that creates the intensity
grading in an analog oscilloscope’s CRT.
The DPO is able to continuously acquire and display three-dimensions of
information because of its parallel processing architecture that integrates the display and
acquisition systems. The microprocessor is devoted to measurement automation and
analysis. This is very different from the typically DSO in which every bit of data going to
the display must pass through the processor, which is also carrying out computations,
managing the oscilloscope’s user interface, etc. This parallel processing enables the DPO
to support an exceptional waveform capture rate that provides a real-time display of
signal activity. Conventional DSO’s acquire signals only a small fraction of the time –
less than 1 percent. The rest of the time is spent processing the acquired waveform data
and creating the display, and, incidentally, ignoring all the signal activity occurring while
that is being done. In contrast, the DPO creates the waveform image directly in the
acquisition system as fast as the signal can be triggered. As a result, the image responds
to waveform activity in real time, and an abundance of data accurately represents the
waveform.
Rather than relying on a chemical phosphor as an analog scope does, the DPO has
purely electronic Digital Phosphor that’s actually a continuously updated database. This
database has a separate “cell” of information for every single pixel in the scopes display.
Each time a waveform is captured it is mapped into the Digital Phosphor database’s cells.
Each cell representing a screen location that is touched by the waveform gets reinforced
with intensity information. When the digital phosphor database is fed to the
oscilloscope’s display, the display reveals intensified waveform areas, in proportion to
the signal’s frequency of occurrence at each point-much like the intensity grading
characteristics of an analog oscilloscope (unlike an analog scope, though, the DPO allows
the varying levels to be expressed in contrasting colors if you wish). With a DPO, it’s
easy to see the difference between a waveform that occurs on almost every trigger and
one that occurs, say, every hundredth trigger.
Importantly the DPO uses a parallel processing architecture to achieve all this
manipulation without slowing down the whole acquisition process. Like the DSO, the
DPO uses a microprocessor for display management, measurement automation, and
analysis. But the DPO’s microprocessor is outside the acquisition/display signal path,
where it doesn’t affect the acquisition speed.
The digital phosphor oscilloscope surpasses the strengths of analog and digital
oscilloscopes. Its integrated acquisition and display architecture gives the DPO the real-
time intensity-graded, alias-free display expected from an analog oscilloscope, plus the
storage and analysis capabilities of a DSO. The resulting measurement tool is greater than
the sum of its parts, providing never-before-seen insights into signal behaviour.
GENERAL FEATURES:
Bandwidth: 500MHz
Memory: 50K/channel
Maximum sampling rate: 1GS/s
Computer compatible: waveform storage in floppy
Other display features also available
3.1.7.3 MAGNETIC RECORDER:
In recent years, need for recording and analyzing ultra wide-band measurements
such as acoustic data higher than the audible frequency are increasing rapidly in various
fields. Data recorders with ultra wide band frequency characteristics, portability,
compatibility etc are available. These have 4 channel * 160 KHz * 16 bit ultra-wide band
high-speed data recording capability. They apply new AIT technology, which enables
them to record 4 channel * 160 KHz measured data on the one cartridge in digital format
for 2 hours continuously.
AIT (Advanced intelligent tape) is new standard for high speed, large capacity
streamers (computer data backup). Today high-density magnetic recording technology
has achieved 25GB of storage capacity and 24 Mbps data transfer rate. The newly
developed AME (Advanced metal evaporated) tape assures remarkable output with
reliability and durability. The table of contents (TOC) information and file position
information is written into the in built memory.
The difference in the operation of magnetic recorders and digital storage
oscilloscopes is that a DSO is a trigger-based device. It would not store the signal if it is
not triggered. But the magnetic recorder is always ready and stores all the signals that are
input without any need for triggering.
MAJOR FEATURES:
Multichannel with analog wide band.
LSB digital channels with some sub channels.
Large capacity of AIT cartridge.
Error free recording.
Compatible i.e. data can be read out directly using computer.
Easy operation.
High quality recording and playback with low power consumption i.e.
1.6A at AC 100V and 7A at DC 12V.
3.1.7.4 GRAPHICAL MULTIMETER:
The most widely used device in an instrumentation lab is a multimeter. The Fluke
863 GMM used in our lab has a wealth of new features that makes taking measurements
easier.
It has different displaying modes such as Combo mode, View mode, Meter mode
etc.
It also provides Auto Diode Test Mode.
It has one important key namely "Save and Print". GMM can use an optical serial
interface cable to communicate with a PC or printer.
Frequency display can be obtained in many ways such as Hz, duty cycle, pulse
width or period.
It provides a component test mode: It is used to measure the characteristics of
passive components in or out of circuit with no power applied. On connection
with the component it results in a pattern, which provides information about that
component.
The Fluke graphical multimeter.
The specifications of GMM are listed below:
Input Impedance: 10Mohm
Accuracy: 0.05% of reading + 2 digits
Battery operating time: 6hrs
Battery recharge time: 16 hours minimum from full discharge
Measurement range: 3V – 1000V
3.1.8 INTERFACING THE HARDWARE
All IBM PC and compatible computers are typically equipped with two serial
ports and one parallel port. Although these two types of ports are used for communicating
with external devices, they work in different ways.
PARALLEL PORT : A parallel port sends and receives 'n' data bits at a same time
over (n+1) lines along with common ground line. This allows data to be
transferred very quickly; however the cable required is more bulky. Parallel ports
are generally used to connect PC to printer and are rarely used elsewhere.
SERIAL PORT: A serial port sends and receives data one bit at a time over one
wire. While it takes eight times as long to transfer each byte of data this way, only
few wires are required. In fact, two-way (full duplex) communications is possible
with only three separate wires - one to send, one to receive, and a common signal
ground wire.
3.1.8.1 PC PARALLEL PORT
The original IBM-PC's Parallel Printer Port had a total of 12 digital outputs and 5 digital inputs accessed via 3 consecutive 8-bit ports in the processor's I/O space.
8 output pins accessed via the DATA PORT.
5 input pins (one inverted) accessed via the STATUS PORT.
4 output pins (three inverted) accessed via the CONTROL PORT.
The remaining 8 pins are grounded
25-way Female D-Type Connector
The PC parallel port adapter is specifically designed to attach printers with a
parallel port interface, but it can be used as a general input/output port for any device or
application that matches its input/output capabilities. It has 12 TTL-buffer output points,
which are latched and can be written and read under program control using the processor
In or Out instruction. The adapter also has five steady state input points that may be read
using the processors instruction.
Parallel Port Connector.
This port allows the input of up to 9 bits or the output of 12 bits at any one given
time, thus requiring minimal external circuitry to implement many simpler tasks. The port
is composed of 4 control lines, 5 status lines and 8 data lines. It's found commonly on the
back of your PC as a D-Type 25 Pin female connector. There may also be a D-Type 25
pin male connector. This will be a serial RS-232 port and thus, is a totally incompatible
port.
IBM-PC PARALLEL PRINTER PORT
IBM originally supplied three adapters that included a parallel printer port for its
PC/XT/AT range of microcomputers. Depending on which were installed, each available
parallel port's base address in the processor's I/O space would be one of 278, 378 and
3BC (all Hex).
Most contemporary PCs, shipped with a single parallel printer port, seem to have the base
address at 378 Hex.
The PC parallel port adapter is specifically designed to attach printers with a parallel port
interface, but it can be used as a general input/output port for any device or application
that matches its input/output capabilities. It has 12 TTL-buffer output points, which are
latched and can be written and read under program control using the processor In or Out
instruction. The adapter also has five steady-state input points that may be read using the
processors in instruction.
In addition, one input can also be used to create a processor interrupt. This interrupt can
be enabled and disabled under program control. Reset from the power-on circuit is also
ORed with a program output point, allowing a device to receive a power-on reset when
the processor in reset.
The input/output signals are made available at the back of the adapter through a right-
angled, PCB-mounted, 25-pin, D-type female connector. This connector protrudes
through the rear panel of the system, where a cable may be attached.
When this adapter is used to attach a printer, data or printer commands are loaded into an
8-bit, latched, output port, and the strobe line is activated, writing data to the printer. The
program then may read the input ports for printer status indicating when the next
character can be written, or it may use the interrupt line to indicate "not busy" to the
software.
The output ports may also be read at the card's interface for diagnostic loop functions.
This allows faults to be isolated between the adapter and the attached device.
PROGRAMMING CONSIDERATIONS :
The printer adapter responds to five I/O instructions: two outputs and three inputs. The
output instructions transfer data into two latches whose outputs are presented on the pins
of a 25-pin D-type female connector.
Two of the three input instructions allow the processor to read back the contents of the
two latches. The third allows the processor to read the real time status of a group of pins
on the connector.
A description of each instruction follows
OUTPUT TO ADDRESS 278/378/3BC HEX:
Bit 7 6 5 4 3 2 1 0
Pin 9 8 7 6 5 4 3 2
The instruction captures data from the data bus and is present on the respective pins.
These pins are each capable of sourcing 2.6 am and sinking 24 am. It is essential that the
external device not try to pull these lines to ground.
OUTPUT TO ADDRESS 27A/37A/3BE HEX:
Bit 7 6 5 4 3 2 1 0
Pin - - - - 17 16 14 1
This instruction causes the latch to capture the least significant bits of the data bus. The
four least significant bits present their outputs, or inverted versions of their outputs, to the
respective pins shown above. If bit 4 is written as 1, the card will interrupt the processor
on the condition that pin 10 transitions high to low.
Open collector drivers pulled to +5 Vcc through 4.7 k resistors drive these pins. They
can each sink approximately 7 Amp and maintain 0.8 volts down level.
INPUT FROM ADDRESS 278/378/3BC HEX:
This command presents the processor with data present on the pins associated with the
corresponding output address. This should normally reflect the exact value that was last
written. If an external device should be driving data on these pins (in violation of usage
ground rules) at the time of an input, this data will be ORed with the latch contents.
INPUT FROM ADDRESS 279/379/3BD HEX:
This command presents real-time status to the processor from the pins as follows.
Bit 7 6 5 4 3 2 1 0
Pin 11 10 12 13 15 - - -
INPUT FROM ADDRESS 27A/37A/3BE HEX:
This instruction causes the data present on pins 1, 14, 16, 17 and the IRQ bit to be read by
the processor. In the absence of external drive applied to these pins, data read by the
processor will exactly match data last written to the corresponding output address in the
same bit positions. Note that data bits 0-2 are not included. If external drivers are dotted
to these pins, that data will be ORed with data applied to the pins by the output latch.
Bit 7 6 5 4 3 2 1 0
Pin - - - - 17 16 14 1
IBM-PC PARALLEL PRINTER PORTREGISTERS & PINOTS
REGISTER DB-25 I/OSignal Name Bit Pin Direction
Strobe C0 1 Output
+Data Bit 0 D0 2 Output +Data Bit 1 D1 3 Output +Data Bit 2 D2 4 Output +Data Bit 3 D3 5 Output +Data Bit 4 D4 6 Output +Data Bit 5 D5 7 Output +Data Bit 6 D6 8 Output +Data Bit 7 D7 9 Output -Acknowledge S6 10 Input +Busy S7 11 Input +Paper End S5 12 Input +Select In S4 13 Input -Auto Feed C1 14 Output -Error S3 15 Input -Initialize C2 16 Output -Select C3 17 Output
Ground 18-25 - (Note again that the S7, C0, C1 & C3 signals are inverted)
IBM-PC Parallel Printer Port Female DB-25 Socket external Pin layout
So it's also the Pin layout on the solder side of the Male DB-25 Cable Connector that plugs into it
13 12 11 10 9 8 7 6 5 4 3 2 1 25 24 23 22 21 20 19 18 17 16 15 14
Hardware inverted means that line is active low or in other words the signal is inverted by
the parallel card's hardware. The above table uses "n" in front of the signal name to
denote that the signal is active low e.g. error. If the printer has encountered an error then
this line is low. This line normally is high, should the printer be functioning correctly.
The "Hardware Inverted" means the signal is inverted by the Parallel card's hardware.
Such an example is the Busy line. If +5v (Logic 1) was applied to this pin and the status
register read, it would return back a 0 in Bit 7 of the Status Register.
The output of the Parallel Port is normally TTL logic levels. The voltage levels are the
easy part. The current you can sink and source varies from port to port. Most Parallel
Ports can sink and source around 12mA. However these are just some of the figures taken
from Data sheets, Sink/Source 6mA, Source 12mA/Sink 20mA, Sink 16mA/Source 4mA,
and Sink/Source 12mA. The best bet is to use a buffer, so the least current is drawn from
the Parallel Port.
PORT ADDRESSES:
The Parallel Port has three commonly used base addresses. These are listed in
table 2, below. The 3BCh base address was originally introduced used for Parallel Ports
on early Video Cards. This address then disappeared for a while, when Parallel Ports
were later removed from Video Cards. They has now reappeared as an option for Parallel
Ports integrated onto motherboards, upon which there configuration can be changed using
BIOS.
When the computer is first turned on, BIOS (Basic Input/Output System) will determine
the number of ports the computer has and assigns device labels LPT1, LPT2 & LPT3 to
them. The BIOS first looks at address 3BCh. If a Parallel Port is found here, it is assigned
as LPT1, and then it searches at location 378h. If a Parallel card is found there, it is
assigned the next free device label. This would be LPT1 if a card wasn't found at 3BCh
or LPT2 if a card was found at 3BCh. The last port of call is 278h and follows the same
procedure than the other two ports. Therefore it is possible to have a LPT2, which is at
378h and not at the expected address 278h.
In the MS-DOS operative system three parallel ports, called LPT1, LPT2 and LPT3, are
supported. So we can find three addresses dedicated to these ports in the memory map of
the PC.
ADDRESS NOTES
3BCh-3BFh Used for parallel ports, which were incorporated into video
cards and now commonly used for ports controlled by BIOS.
378h-37Fh Usual address for LPT1 (Line Printer)
278h-27Fh Usual address for LPT2
RELAY CONTROL USING PARALLEL PORT:
The first circuit I made to use the parallel port is shown on next page.
This port operates the LED’s when the computer gives the command. The LED’s are
connected to the data pins and grounded with the port. TTL levels of the port generate
enough current for the LED to glow brightly. The corresponding software is written
below.
3 3 0
3 3 0
3 3 0
3 3 0
3 3 0
3 3 0
3 3 0
3 3 0
P 1
C O N N E C TO R D B 2 5
1 32 51 22 41 12 31 02 292 182 071 961 851 741 631 521 41
Simple circuit to operate parallel port.
File LED_GLOW.CPP
** Illustrates simple use of printer port for LED glow in binary.
** Nidhi Jain
#include<iostream.h>
#include<dos.h>
void main()
{
for( int i=0; i<128; i++)
{
outport(0x378, i);
delay(1000);
}
}
My objective was to control switching of the relays using the parallel port and also
ascertain the dynamic parameters of the hardware like voltage levels at certain points.
This required both data input and output from the computer.
To understand data input and output from port, I used the following circuit. The
controlling software was written in C/C++.
Practical application of parallel port.
This typical application shows a normally open push button switch being read on the
BUSY input (Status Port, Bit 7) and an LED, which is controlled by Bit 0 on the Data
Port. A C language program causes the LED to flash at the rate of 5 times per second
when the push-button is depressed. The following code is used with the above circuit.
File LED_FLSH.CPP
** Illustrates simple use of printer port. When switch is
** Depressed LED flashes. When switch is not depressed,
** LED is turned off.
** Nidhi Jain
#include <iostream.h>
#include <dos.h> /* required for delay function */
#define DATA 0x03bc
#define STATUS DATA+1
#define CONTROL DATA+2
void main()
{
int in;
while(1) /* condition is always TRUE */
{
in = inportb(STATUS);
if (((in^0x80)&0x80)==0)
/* if BUSY bit is at 0 (switch is closed) */
{
outportb(DATA,0x00); /* turn LED on */
delay(100);
outportb(DATA, 0x01); /* turn it off */
delay(100);
}
else
{
outportb(DATA,0x01);
/* if PB not depressed, turn LED off */
}
}
}
This program helped me understand how to output data and use the hardware inverted
bits.
3.1.8.2 SERIAL PORT:
The serial port is harder to interface than the parallel port. In most cases, any
device you connect to the serial port will need the serial transmission converted back to
parallel so that can be used. Still there are many advantages of the serial port. They are:
Serial cables can be longer than Parallel cables. The serial port transmits a ‘1’
as ‘-3’ to ‘-25’ volts and a ‘0’ as ‘+3’ to ‘+25’ volts where as a parallel port
transmits a ‘0’ as 0 volts and a ‘1’ as 5 volts. Therefore the serial port can
have a maximum swing of 50 volts compared to the parallel port, which has a
maximum swing of 5 volts. Therefore cable losses are much less in serial
cables.
Lesser number of wires are needed for the serial communication as compared
to parallel communication.
Microcontroller’s have in built Serial Communications Interfaces (SCI),
which can be used to talk to the outside world. Serial communication reduces
the pin count of these MPU’s.
Devices, which use serial cables for their communications, are split into two
categories. These are DCE (Data Communication Equipment) and DTE (Data Terminal
Equipment). Data Communications Equipment are devices such as modem, adapter,
plotter, etc while Data Terminal Equipment is the computer or terminal.
The electrical specifications of the serial port is contained in the EIA (Electronics
Industry Association) RS232 Standard. It states:
A “Space” is logic0 and will be between +3 and +25 volts.
A “Mark” is logic 1 and will be between –3 and –25 volts.
The region between +3 and –3 volts is undefined.
A short circuit current should never exceed 500 mA.
DTE to DCE is the speed between your modem and computer, sometimes referred
to As your terminal sppeed. This should run at faster speeds than the DCE to DTE speed.
DCE to DCE is the link between modems, sometimes called the line speed.
Serial port is preferred where the requirement is of very fast data acquisition rate.
RS-232 C: RS-232 stands for Recommended Standard number 232 and C is the latest
version of the standard. The full RS-232C standard specifies a 25-pin D connectorof
which 22 pins are used. The RS-232 standard states that DTE devices use a 25-pin male
connector and DCE devices use a 25-pin female connector. The user can therefore
connect a DTE device to a DCE using a straight pin-for-pin connection.
25 Pin Connector on a DTE device:
PIN NUMBERS:
1. Protective Gound
2. Transmitted Data(TD) Outgoing Data (from a DTE to a DCE)
3. Received Data(RD) Incoming Data (from a DTE to a DCE)
4. Request To Send (RTS) Outgoing flow control signal controlled by DTE
5. Clear To Send(CTS) Incoming flow control signal controlled by DCE
6. Data Set Ready(DSR) Incoming handshaking signal controlled by DCE
7. Signal Ground Common reference voltage
8. Carrier Detect (CD) Incoming Siganl from a Modem
20. Data Terminal Ready (DTR) Outgoing handshaking siganl controlled by DTE
22. Ring Indicator (RI) Incoming signal from a modem
In a perfecet world, all serial ports on every computer would be DTE devices with 25-
pin male ‘D’ connectors. All other devices to would be DCE devices with 25-pi female
connectors. This would allow you to use a cable in which each pin on one end of the
cable is connected to the same pin on the other end.
The TD (transmit data) wire is the one through which data from a DTE device is
transmitted to a DCE device. This name can be deceiving , because a DCE device to
receive irs data uses this wire. The TD line is kept in a mrk condition by the DTE device
when it is idle. The RD(receive data) wire is the one on which data is received by a DTE
device and the DCE device keeps this line in a mark condition when idle.
RTS and CTS lines are used when hardware flow control is enabled in both the DTE and
DCE devices. The DTE device puts RTS line in a mark condition to tell the remote
device that it is ready and able to receive data. If the DTE device is not able to receive
data(because eit is full), it will put thisline in the space condition as a signal to the DCE
to stop sending the data
CTS is complement of RTS wire. The DCE device puts this line in amrk condition to tell
the DTE device that it is ready to receive the data.
DTR(Data Terminal Ready) and DSR(Data Set Ready) are used by some serial devices to
simply confirm that a device is connected and is turned on.
CD(Carrier Detect) is used by a modem to signal that it has made a connection with
another modem.
3.23.2 MULTI-CHANNEL SHOCK VELOCITY RECORDERMULTI-CHANNEL SHOCK VELOCITY RECORDER
3.2.1 INTRODUCTION
When an explosive charge is detonated in air, the gaseous products expand
rapidly and compress the surrounding air so that it moves outward with a high velocity,
thus initiating a shock wave. This layer of compressed air is bounded by an extremely
sharp front called shock front in which pressure rises abruptly. The shock front moves
outward with an initial velocity much greater than that of sound but after a short distance,
velocity decreases rapidly. The gaseous products of detonation move as a strong wind
behind shock front and are prevented by their own inertia from decreasing as rapidly as
pressure at point of detonation. As a result, there is produced a rarefaction effect and a
point of reduced pressure, which condition trails the shock front. When pressure becomes
less than the atmospheric pressure, the wind reverses in direction and blows back toward
point of detonation. The shock front, high-pressure area behind it and trailing rarefaction
condition form a complete wave, which is called blast or shock wave.
Mach wave is formed by combining of reflected wave with the incident wave and
the point where the three waves meet is called the triple point. At this point, peak
pressure and impulse are maximum.
A SHOCK WAVE is a violent disturbance moving with a loud bang along a
medium (such as air, water or earth) at a speed greater than that of sound (supersonic
speed).
A shock wave is an integral part of a detonation wave, which is a combination of a
shock wave and a chemical reaction. Shock waves formed by supersonic motion of
projectiles are usually weaker than those generated by powerful explosives and latter are
sometimes called blast waves.
The initial shock wave in air from a detonation has apparently only a very short
life, being superseded or swallowed up by another more energetic waves after
propagation of only a few diameters from charge. The wave that finally emerges from
expanding gas cloud comprising products of detonation is moreover, quite different than
initial shock; while it has a much lower peak pressure, it is much broader and much more
energetic.
3.2.2 AIM OF THE PROJECT
Pin Oscillographic Technique has been extensively used for determination of
velocity of detonation in high explosives, velocity of strong shock waves in solids, shapes
inclination of strong shock and detonation waves and rates of deformation under
explosive loading. These studies are important in the understanding of detonation
phenomena and the dynamic properties of materials under intense transient stresses.
This technique consists in recording the arrival of a fast coming event at
predetermined positions defined by locations of short contact probes. In general the
probes act as normally open switches whose contacts are shorted by the arrival of the
event at the respective probe locations. The shorting contact then discharges a condenser,
which produces an electrical impulse, which is subsequently recorded on oscilloscope
after passing through a system of cables.
POT is very much prone to noise in the field set-ups. Therefore a project
was undertaken to design a system with which detonation phenomena and dynamic
properties of materials under intense transient stresses can be studied with better accuracy
and reliability. Latest ultra fast IC-devices have been used in designing the systems. Thus
came into being the idea of SHOCK VELOCITY RECORDER.
This system can read time intervals directly in digital form. It is a six-
channel equipment with which velocity can be measured at six different pre-determined
locations by directly measuring the time intervals. Time intervals can be measured with
an accuracy of 100 nsec, with this equipment. Each channel’s data is stored in its
semiconductor memory, which can be displayed on a single common display. This
equipment has also been provided with Test facility. With which operation of all the
channels can be tested before firing. Each channel of the equipment also has an overflow
indication to show the instant the channel’s data exceed the maximum limit the
equipment can record.
The equipment has got six independent inputs. Arrival of shock/detonation wave
at a specified location is sensed by a sensor probe and after passing through cables, it
produces a transition at the corresponding output. Therefore, corresponding to six
different inputs, six output transitions are generated and these are recorded on a DSO.
Each channel of this equipment consists of a monostable circuit, which produces a fixed
duration pulse corresponding to an event sensed at its input terminal. This pulse in turn
triggers a JK flip flop through a NAND gate, during a selected fixed time interval only
and thus places the channel in the INHIBIT mode and also puts the glowing LED in the
OFF state thereby indicating that the event has been sensed and properly recorded. The
output of the JK flip-flop is fed to an output terminal for further recording on the transient
recorder.
A single channel consists of the following IC’s:
LM339 (Comparator)
74121(Multivibrator)
7473(JK flip flop)
7400(NAND gate)
INPUT OUTPUT
BLOCK DIAGRAM OF SHOCK VELOCITY RECORDER
3.2.3 COMPONENTS USED:
3.2.3.1 COMPARATOR LM339 :
The LM339 consists of four independent precision voltage comparators with an
offset voltage specification as low as 2 mV max for all four comparators. These were
designed specifically to operate from a single power supply over a wide range of
COMPAR ATOR
INHIBITCIRCUITRY
MULTI-VIBRATOR
FLIP- FLOP
voltages. Operation from split power supplies is also possible and the low power supply
current drain is independent of the magnitude of the power supply voltage. The LM139
series was designed to directly interface with TTL and CMOS.
FEATURES:
Wide supply voltage range
Very low supply current drain (0.8 mA) — independent of supply voltage
Low input biasing current: 25 nA, Low input offset current: ±5 nA
Offset voltage: ±3 mV
Differential input voltage range equal to the power supply voltage
Low output saturation voltage: 250 mV at 4 mA
Output voltage compatible with TTL, DTL, ECL, MOS and CMOS logic
systems
ADVANTAGES:
High precision comparators
Eliminates need for dual supplies
Allows sensing near GND
Compatible with all forms of logic
Power drain suitable for battery operation
The LM339 series are high gain, bandwidth devices that, like most comparators, can
easily oscillate if the output lead is inadvertently allowed to capacitively couple to the
inputs via stray capacitance. This shows up only during the output voltage transition
intervals as the comparator changes states. All pins of any unused comparators should be
grounded.
The output of the LM 339 series is the uncommitted collector of a grounded-emitter
NPN output transistor. Many collectors can be tied together to provide an output OR’ing
function. An output pull-up resistor can be connected to any available power supply
voltage with the permitted supply voltage range and there is no restriction on this
voltage due to the magnitude of the voltage which is applied to the V+ terminal of the
LM 339 package.
One of the Comparators of LM 339 is used to sense the input coming from a field
event. The comparator compares the input signal with the reference input voltage, which
is set to some value determined by the requirement, field setup, charge, and level of noise
in the field. The reference voltage can be set accordingly with the help of necessary
resistor combination.
The comparator then decides whether to give a high or a low at the output depending
upon the condition that input signal is greater or smaller in magnitude than the reference
input. If the input signal is more than the reference signal then the output will be a high.
If the input signal is less than the reference signal then the output will be low.
3.2.3.2 MUTIVIBRATOR 74121
The multivibrators feature dual negative-transition-triggered inputs and a single
positive-transition-triggered input which can be used as an inhibit input. Complementary
output pulses are provided.
Pulse triggering occurs at a particular voltage level and is not directly related to
the transition time of the input pulse. Schmitt-trigger input circuitry for the B input
allows jitter free triggering from inputs with transition rates as slow as 1 volt/second,
providing the circuit with an excellent noise immunity of typically 1.2 volts. A high
immunity to Vcc noise of typically 1.5 volts is also provided by internal latching
circuitry.
Once fires, the outputs are independent of further transitions of the inputs and are
a function only of the timing components. Input pulses may be of any duration relative to
the output pulse. Output pulse length may be varied from 40 nanoseconds to 28 seconds
by choosing appropriate timing components. With no external timing components (i.e.
Rint connected to Vcc, Cext and Rext/Cext open), an output pulse of typically 30 or 35
nanoseconds is achieved which may be used as a dc-triggered reset signal. Output rise
and fall times are TTL compatible and independent of pulse length.
Pulse width stability is achieved through internal compensation and is virtually
independent of Vcc and temperature. In most applications, pulse stability will only be
limited by the accuracy of external timing components.
TRUTH TABLE OF MULTIVIBRATOR
INPUTS OUTPUTS
A1 A2 B Q Q(BAR)
L X H L H
X L H L H
X X L L H
H H X L H
H H
H H
H
L X
X L
Jitter-free operation is maintained over the full temperature and Vcc ranges for
more than six decades of timing capacitance (10 pF to 10 F) and more than one decade
timing resistance (2k to 40k for the SN74121). Throughout these ranges, pulse width
is defined by the relationship t=Cext.Rt (ln2)=0.7Cext.Rt. In circuits where pulse cut-off
is not critical, timing capacitance upto 1000F and timing resistance as low as 1.4 K
maybe used. Also, the range of jitter-free output pulse widths is extended if Vcc is held to
5V and free air temperature is 25 deg Celsius. Duty cycles as high as 90% are achieved
when using maximum recommended Rt. High duty cycles are available if a certain
amount of pulse width jitter is allowed.
SPECIFICATIONS:
Supply Voltage: 7V
Input Voltage: 5.5V
Input pulse width: 50ns
External timing Resistance: 40k(maximum)
tPLH : 45ns
tPHL : 50ns
Operating Free air Temperature: 0oC to 70oC
Storage Temperature Range: -65oC to 150oC
External Timing Capacitance: 1000F
3.2.3.3 J-K FLIP FLOP 7473:
Any device or circuit that has two stable states is said to be bi-stable. For instance,
a toggle switch has two stable states. It is either open or closed. The switch is said to have
memory since it will at set until someone changes the position of the handle. A flip-flop
is a bi-stable electronic circuit that has two stable states- i.e., it’s output is either 0 or +5V
dc. The flip-flop also has memory since it’s output will remain as set until something is
done to change it.
In a J-K Flip Flop the variables J and K are called the control inputs because they
determine what the Flip Flop does when a clock edge arrives.
11 22
1 3
364
5
1
23
4
56
J
K
CLK
OUTP UT
OUTP UT(BA R)
J-K FLIP-FLOP
TRUTH TABLE OF J-K FLIP FLOPCLK J K Qn+1
X 0 0 Qn
0 1 0
1 0 1
1 1 Toggle
The 7473 contain two independent J-K Flip Flop with individual J-K, clock, and
direct clear inputs. The 7473 are negative edge triggered flip-flop. The J and K inputs
must be stable one set up time (Set up time is the minimum amount of time that the data
bit must be present before the clock edge hits) prior to the high to low transition for
predictable operation. When the clear is low, it overrides the clock and data inputs
forcing the Q output low. Also, there should be some minimum amount of time for which
the data bit must be present after the clock edge arrives, called the hold time for
predictable operation.
SPECIFICATIONS:
Supply Voltage: 5volts
Input set up time before CLK rises: 20ns
Input hold time data after CLK falls: 0ns
Operating free air temperature: 0oC to 70oC
Maximum clock frequency: 20 MHz
Storage Temperature Range: -65oC to 150oC
tPLH : 15ns
tPHL: 15ns
3.2.3.4 NAND GATE 7400:
7400 contain 4 independent 2 input NAND gates. They are characterized for
operation over the temperature range of 0oC to 70oC.
Function TableINPUT(A) INPUT(B) OUTPUT(Y)
H H L
L X H
X L H
Operating Conditions:
Supply voltage: 5 volts
Operating free air temperature: 0oC to 70oC
tPLH: 11ns
tPHL: 7ns
3.2.4 CIRCUIT DIAGRAM FOR SHOCK VELOCITY
RECORDER
3.2.5 WORKING OF THE SYSTEM:
The comparator gets the input at pin number 7 through a resistor of value 1k.
The input value is compared with the reference value, which has been set to 2.5 volts by
using the voltage divider network of resistors. Two resistors of values 1k divide the
voltage supply of 5 V in the ratio of 1:1 i.e. 2.5 volts is input as reference voltage. The
input value is compared with this reference value. If it is a noise signal then it will give a
low at output signal at pin number 1(because noise signals have a low magnitude). When
the blast pressure input comes at pin 7 it gives a high at pin 1(because blast pressure input
have magnitude of nearly 5 volts. The other used pins of the comparator are pin number
3, which has been given a supply of 5 volts, and the other pin used is ground at pin
number 12.
The output from the comparator is fed as input to the multivibrator. The
multivibrator has three inputs out of which one is given by the comparator, one is made
permanently high and the last one gets its input from the flip-flop. The purpose of the
multivibrator is to produce a pulse as soon as it encounters a high to low pulse at its
input. The multivibrator I have used is a monostable one which means that it has only one
stable state; here it is the low state. As soon as it goes high, it is tempted to go back to its
stable state i.e. low. So the output of the multivibrator is a pulse that goes from low to
high and then high to low. The pulse width is determined by resistances and capacitances
connected to the IC. The pulse width is given by t=0.7*R*C where R, C are the external
resistances and the capacitances. Pin number 7 is grounded and the 14 to the supply
voltage. The output at pin number 6 goes from high to low but we want that once our
circuit is triggered it should not be triggered again. But in this condition it will be
triggered again and again.
To stop this re-triggering we use the inhibit circuit consisting of J-K flip-flop and a
NAND gate. They also work for the resetting of the system. It works as follows: As our
J-K flip-flop is negative edge triggered, we use the output bar (Q bar) As an input to
clock pulse of the J-K flip-flop. The J input is kept at permanent high and the K input at
permanent low. So whenever a pulse is given to the J-K flip flop the output comes out to
be high at the falling edge of the pulse. So the input signal at the comparator gives a low
to high transition at the flip-flop. To stop the re-triggering the output of the system is
connected as an input to the multivibrator (a low to high edge). Hence no condition is
satisfied from the truth table of the multivibrator to give a pulse again at the output of
multivibrator. Hence no re-triggering occurs.
The system is reset by the clear signal from the NAND gate. The inverse output
(Q bar) of the J-K flip flop is sent as an input to the NAND gate whose output gives input
to the clear of the J-K flip flop. A low signal makes the clear signal active (because it is
active low). A de-bouncing circuit is made out of NAND gate and a SPDT mechanical
switch. When the switch is pushed there is a low signal at the clear input, which makes
the J-K flip flop inactive.
The coming of the signal on the system is notified by the switching off of the LED which
otherwise remains glowing. The low to high pulse is recorded on the Oscilloscope in
single sequence mode. As the system is multi channel the six records are taken on a logic
analyzer (32-channel). For the different channels there is some delay between
occurrences of events at recorder. This difference is due to the placement of the various
gauges in the field. As pressure arrives at the gauges at a time delay, so the records of the
various channels varies in time interval of microseconds. We know the distance between
the various gauges and also the time interval between the arrivals of events at these
gauges. So using the basic formula of speed=distance/time, we can calculate the velocity.
1st Gauge
T1
T2
T3
So Velocity is the respective distance divided by the respective time, e.g. distance
between the first and second gauges is to be divided by T1, distance between the second
and the third gauges is to be divide by T2, and so on. Then the mean of these different
velocities is calculated to get the average figure.
ALTERNATIVE TO THE ABOVE MENTIONED SYSTEM:
Another system can be also designed which can be used for the same purpose of
recording shock velocity after explosion. The alternative is to use a bistable multivibrator
which gives a high from a low as soon as it is triggered but remains in this state unless
2nd Gauge
3rd Gauge
4th Gauge
again triggered; if triggered again it goes to low. But the problem is with the resetting of
the system, which can be done by using a J-K flip flop and NAND gate only.
3.3 ANALOG TO DIGITAL CONVERTER ADC 0809:
Analog-to-Digital conversion is a very important aspect of digital data processing.
The process of changing an analog signal to an equivalent digital signal is accomplished
by the use of an A/D converter. For example, an A/D converter is used to change the
analog output signals from transducers (measuring temperature, pressure, vibration, etc.)
into equivalent digital signals. These signals would then be in a suitable form for entry
into a digital system. An A/D converter is often referred to as an encoding device since it
is used to encode signals for entry into a digital system.
A number of different methods have been developed for this conversion process.
Following are some of the most commonly used:
Simultaneous Conversion
Counter Method
Continuous Conversion
Single Slope Conversion
Dual Slope Conversion
Here I have studied IC having successive approximation method of
conversion. So we will discuss this method in detail.
If multiplexing is required, when successive approximation convertor is most
useful. The convertor operates while successively dividing the voltage ranges in half. The
counter is first reset to all zeroes and the MSB is then set. The MSB is then left in or
taken out, depending on the output of the comparator. Then the second MSB is set in and
a comparison is made to determine whether to reset the MSB flip flop. The process id
repeated down to the LSB, and at this time the desired in the counter. Since the
conversion involves operating on one flip flop at a time beginning with the MSB , ring
counter maybe used for flip flop selection.
The successive approximation method, thus is the process of
approximating the analog voltage, by trying one bit at a time beginning with the MSB.
Each conversion takes the same time and requires one conversion cycle for each bit.
Thus, the total conversion time is equal to the number of bits, n, times the time required
for one conversion cycle. One conversion cycle normally requires one cycle of the clock.
As an example, a 10 bit convertor operating with one megahertz clock has a conversion
time of 10X10-6 =10-5=10s.
When dealing with conversion times this shot, it is usually necessary to
take into account the other delays in the system (for example, switching time of the
multiplexer, settling time of the ladder network, comparator delay and settling time).
Another method for reducing the total conversion time of a simple counter
convertor is to divide the counter in the sections. Such a configuration is called a Section
Counter. To determine how the total conversion might be reduced by this method,
assume that we have a standard 8-bit counter. If this counter is divided into two equal
counters, of four bits each, we have a section convertor. The convertor operates by setting
the section conaining the four LSB’s to all ones and then advancing the other sections
until the ladder voltage exceeds the input voltage. At this point all the four LSB’s are
reset, and this section of the counter is then advance until the ladder voltage equals the
input voltage.
A maximum of 24=16 is required for each section to count full scale. Thus
this method requires only 32 counts to reach full scale. This is a considerable reduction
over the 256 counts required for the straight 8-bit counter. There is, of-course, some extra
time required to set the counters initially and to switch from counter to counter during the
conversion. This logical operation time is very small, however, compared with the total
time saved by this method, this type of convertor is often used digital voltmeters. Since it
is very convenient to divide the counters, by counts of 10. Each counter is then used to
represent one of the digits of the decimal number appearing at the output of the voltmeter.
AD0809: The ADC data acquisition component is a monolithic CMOS device
with an 8-bit analog-to-digital converter, 8-channel multiplexer and microprocessor
compatible control logic. The 8-bit A/D converter uses successive approximation As the
conversion technique. The converter features a high impedance chopper stabilized
comparator, a 256R voltage divider with analog switch free and a successive
approximation register. The 8-channel multiplexer can directly access any of 8-single-
ended analog signals.
Easy interfacing to microprocessors is provided by the latched and decoded
multiplexer address inputs. The ADC offers high speed, high accuracy, minimal
temperature dependence, excellent long-term accuracy and repeatability and consumes
minimal power. These features make this device ideally suited to applications from
process and machine control to consumer and automative applications.
FEATURES:
Easy interface to all microprocessors
Operates with 5 V dc
No zero or full scale adjust required
8-channel multiplexer with address logic
0 to 5 V input range with single 5 V power supply
Outputs meet TTL voltage specifications
Standard 28-pinpackage
SPECIFICATIONS:
Resolution: 8bits
Total unadjusted error: ½ LSB and 1 LSB
Single supply: 5Vdc
Low power: 15mW
Conversion Time: 100s
The device contains an 8-channel single-ended analog signal multiplexer. A particular
input channel is selected by using the address decoder. The address is latched into the
decoder on the low-to-high transition of the address latch enable signal.
The heart of this single chip data acquisition system is its 8-bit analog-to-digital
converter. The converter is designed to give fast, accurate and repeatable conversion over
wide range of temperatures. The converter is partitioned in to 3 major sections: the 256
ladder network, the successive approximation register and the comparator. The
converter’s digital outputs are positive true.
The 256R ladder network approach guarantees no missing digital codes.
Additionally, the 256R network does not cause load variations on the reference voltage.
The successive approximation register (SAR) performs iterations to approximate the
input voltage. For any SAR type converter, n-iterations are required for an n-bit
converter.
The A/D converter’s successive approximation register is reset on the positive
edge of the start conversion pulse. The conversion is begun on the falling edge of the start
conversion pulse. A conversion in process will be interrupted by receipt of a new start
conversion pulse. Continuous conversion may be accomplished by tying the end-of-
conversion output to the start conversion input. End-of-conversion will go low between 0
and 8 clock pulses after the rising edge of start conversion.
4. FIELD TRIALS:
During the training period I was also involved in the fieldwork. Some trials in which I
was engaged are:
Anti- Mine Boot Trials.
Anti-Mine Vehicle Trials.
4.1 ANTI-MINE BOOT TRIAL:
The aim of trial was to evaluate the performance of shoe if worn while walking on
mines. The shoes were to be tested against pressure released during explosion. The
boots are designed in such a way that wearer should feel comfortable while walking
on plains, deserts/ semi-deserts. The body of the shoe is made of very hard leather
with a complete inner lining of a poly-matting cloth. The sole is thick and made of
hard ballistic material wedge with vulcanized rubber covering. The sole material is
designed to absorb the blast. The shoe flexibility is minimal due to thickness and
rigidity of material and hampers the normal walking.
The trial was carried out in the field by arranging the set up as shown in the
figure. Pressure gage used is Kistler type 6215, whose sensitivity is 1.479 Pc/bar and
range is up to Kbar. The recording instrumentation used inside the lab includes Digital
Storage Oscilloscope, Digital Phosphorous Oscilloscope, Magnetic Recorder, and TTL
device called pulse generator.
The charge was placed under the muddy surface. Four blocks of 18 Kg each were
placed above the gauge holder of 3 Kg. This means that the total weight on shoe was 75
Kg. Sensor was placed inside the pipe filled with sand and was hold by the gauge holder.
Gauge holder was fitted into the shoe. The shoe was placed above the mine and below the
mine detonator along with TTL probe was placed. TTL probe is an aluminium foil, which
is pasted upon two wires. Normally connection is open but on arrival of detonating pulse
it gets shorted, indicating a high pulse. This helps in calculating the delay between the
supplying of high voltage from firing unit and energizing of detonator.
Setup of Boot Anti-mine trial.
Field set-up for Anti-Mine Boot Vehicle
4.2 BLAST EVALUATION TRIAL OF ANTIMINE VEHICLE:
An Anti-Mine Vehicle designed and developed by Ordnance Factory, Medak was
brought to the BDS zone of TBRL for blast evaluation and testing it’s strength. The
vehicle can house 12 occupants including driver and is designed to withstand the blast
effect from a land mine with an explosive content of 10 kg TNT. A prototype of this
vehicle was tested on 27/03/2003 at TBRL Range , Ramgarh to assess it’s effectiveness
and damage performance against design blast load.
A TNT cast cylindrical charge of weight 10.4 kg was placed in a small cavity made in the
ground underneath the vehicle at a distance of 1.75m from the rear end of the vehicle. It
was detonated by using the electrical detonator. The front wheels of the AMV were
provided protection by stacks of sandbags. Sandbags were also placed inside the vehicle
on the seats to simulate the weight of the personnel and ammunition. A live pig of about
60kg was tied inside the vehicle to test effect of blast on a living being.
Following sensors and recording instruments were used.
Gauge housing
Pressure sensor
Electric detonatorAPNM-14 mine/ CE Pallet
TTLProbe
Rigidly fixed fixture
Soil
MS Block 18 Kg each
Blast Gauges placed around the vehicle at various distances to record the incident
pressure on the vehicle as a result of explosion.
Sound Level Meter placed inside the vehicle to monitor the sound pressure level.
Thermocouple placed inside the vehicle to record the temperature rise at the time
of explosion.
Accelerometers mounted inside the vehicle to record acceleration observed by
the vehicle at the time of explosion.
Cameras were placed at distance of 80m to measure the vertical uplift of the
vehicle.
OBSERVATIONS:
It was observed, that the rear door of the vehicle remained closed during the trial.
Also, there was no damage observed on the rear tyres. The blast proof window panes
were intact after the blast. But the side rear view mirrors of the vehicle got damaged. The
rear portion of the vehicle was vertically lifted upward by about 40cm during the trial and
the vehicle remained engulfed in the fire zone for about a second. A crater was formed
under the belly of the vehicle. The pig survived the Blast loading and had no visible mark
of injury and it behaved normally after the trial. The vehicle was made road worthy
within a few hours by the skilled personnel from the Ordnance Factory , Medak.
GLOSSARY
Acquisition: Process of sampling signals from input channel, digitizing samples into data
points and assembling data points into a waveform record.
Attenuation: A decrease in signal voltage during its transmission from one point to
another.
Bandwidth: The highest frequency signal the oscilloscope can acquire with no more than
3 dB attenuation of the original signal.
Blast: Blast is the principle mode of transferring explosive energy to the target,
producing damage by giving a crusting blow, displacing and tumbling the target.
Detonation: The explosion is initiated through the process of detonation. A reaction can
be initiated if sufficient energy is provided at one point in the explosive. This is done by
means of a heated wire, which acts directly upon a small amount of especially sensitive
material thus generating a small low energy impulse (shock).
Digitizing: The process of converting a continuous analog signal such as a waveform to a
set of discrete numbers representing the amplitude of signal at specific points in time.
Equivalent time sampling: A sampling mode in which the oscilloscope constructs a
picture of a repetitive signal by capturing a little bit of information from each repetition
Explosive: An explosive is a substance or a mixture of substances which undergoes
rapid oxidative decomposition, producing a large volume of gases, accompanied by the
liberation of substantial thermal energy, in a very short span of time, when suitably
initiated. This process is known as explosion. Equivalently an explosion maybe defined
as chemical reaction wherein the original substance is converted into a gas at a very high
temperature and pressure within a very short interval of time with the evolution of
substantial quantity of heat..
Graticule: The grid lines on a screen for measuring oscilloscope traces.
Interpolation: A “connect-the-dots” processing technique to estimate what a fast
waveform looks like based on only a few sampled points.
Lethality: Lethality is the antipersonnel efficiency of a high explosive, that is, the ability
of an explosive to cause damage to others. It is measured in terms of MAE, that is, mean
area effect. In this the area of damage is calculated and the number of targets is known,
by which lethality is calculated.
Qauntizing: The process of converting analog input that has been sampled to a digital
value.
Real time Sampling: A sampling mode in which the oscilloscope collects as many
samples as it can as the signal occurs.
Record Length: The number of waveform points used to create a record of the signal.
Rise Time: The time taken for the leading edge of a pulse to rise from its minimum to its
maximum values (typically measured from 10% to 90% of these values).
Sample Interval: The time interval between the successive samples in a time base. It is
the reciprocal of sample rate.
Sample point: The raw data from an ADC used to calculate waveform points.
Sampling: The process of capturing an analog input at a discrete point in time and
holding it constant so that it can be quantized.
Single Shot: A signal measured by an oscilloscope that occurs only once (also called a
transient event).
Terminal Ballistics: Terminal Ballistics is defined as study of effect of blast or
explosion on a particular target.