6 MONTHS PROJECT SEMESTER REPORT ON

6 MONTHS PROJECT SEMESTER REPORT ON

DESIGN AND DEVELOPMENT OF PC BASED FIRING CONTROL UNITSubmitted byNavdeep Ojha

225/99

ELECTRONICS (INSTRUMENTATION AND CONTROL)

JULY 2002

DESIGN AND DEVELOPMENT OF PC BASED FIRING CONTROL UNIT6 MONTHS PROJECT SEMESTER REPORT

Submitted to

ELECTRONICS & INSTRUMENTATION DEPTT

For the partial fulfillment of degree of

Bachelor of engineering

in

Electronics & Instrumentation Engg.

Harbans Lal

(Project Incharge)

Joint Director,

Zone III, TBRL,

Chandigarh. Anu Sachdeva

BE 11706431

E.I.E

I.E.T. BHADDAL

ROPAR

TERMINAL BALLISTICS RESEARCH LABORATORY

DEFENCE R&D ORGANIZATION

MINISTRY OF DEFENCE, GOVT. OF INDIA

SECTOR-30, CHANDIGARH, INDIA-160020

FAX: 91-172-657506

0172-651824,651825,651826

CERTIFICATEtc "Certificate"This is to certify that Navdeep Ojha, Roll No. BE 225/99, of Thapar Institute of Engineering and Technology (TIET), Patiala has undergone six months project semester industrial training from Jan 9, 2002 to July 9, 2002 at Terminal Ballistics Research Lab (TBRL), Chandigarh. He was assigned the project titled Design and development of PC based firing control unit.

The work reported meets the standards necessary for partial fulfillment of requirement of degree of B.E. Electronics (Instrumentation and Control) awarded by Thapar Institute of Engineering and Technology (deemed university).

Place: Chandigarh

Date:( Harbans Lal )

Deputy Director,

Zone-III

TERMINAL BALLISTICS RESEARCH LABORATORY

DEFENCE R&D ORGANIZATION

MINISTRY OF DEFENCE, GOVT. OF INDIA

SECTOR-30, CHANDIGARH, INDIA-160020

FAX: 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 Navdeep Ojha, Roll No. BE 225/99, student of B.E Electronics (Instrumentation and Control), Thapar Institute of Engineering and Technology, Patiala (deemed university) is a record of the students 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 InchargeAcknowledgement

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 Joint Director (Zone 3), not only for his enlightening guidance and enthusiastic interest but also for his ever available help & cooperation.

I also express my gratitude to Ms. Rajesh Kumari (Scientist D) for her constructive discussions, healthy criticism and persistent encouragement that has brought this project to its present stage.

I sincerely thank Mr.Dhan Prakash, Pankaj Sajan, Jatinder Pal, Ms. Shalini 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.

HITESH PURI

About the organization

1.1 Terminal Ballistics Research Lab

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.

The Terminal Ballistics Research Laboratory, Chandigarh came into being in 1961 and 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. Following are some of the specialized facilities available at TBRL:

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

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, and

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.

1.2 Study of blast phenomenon:

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

1. Free air explosion

2. Under water explosion.

3. Under ground explosion.

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.

1. Blast gauge (Transducer)

2. Charge to voltage converter

3. Charge to voltage amplifier

4. Filter stage

5. Analog interfacing

6. Analog to digital converter

7. 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.

1.2.1 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

1. Mechanically robust

2. Offer the highest frequency response

3. Non - pyroelectric

4. Chemically stable

5. Insensitive to humidity

6. No hysterisis effects

7. Reproducible

8. 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:

1. Chemically stable.

2. Free from hysterisis.

3. Mechanically stable.

4. Available as a high quality material.

5. Non-pyroelectric.

Disadvantages of quartz crystal:

1. Low piezoelectric constant.

2. 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 padsPrior 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 0.001-inch thickness, 1.0-inch diameter. The crystal faces are of evaporated aluminium 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.

Fig 1.1: 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.

Fig 1.2: Gauge pile construction.

A test pressure of 1kg/cm2 is applied at each side of the pile to confirm the proper addition 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.

Fig 1.3: Blast gauge for measuring blast pressure.The figure above shows a typical blast gauge used for measuring the pressure produced during blast.

Fig 1.4 various gages used for measuring blast parameters.

Various other gages used are Lollipop gage, under water gage and PZT gage normally called as shock arrival gage. Figure above shows the four gages generally used in blast and damage studies.

1.2.2 Signal conditioners

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:

Fig 1.5: Block diagram of Charge amplifier.

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.

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 upto 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.

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).

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.

Charge simulator: The feedback capacitors are 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.

Gauge 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.

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.

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:

Fig 1.7 Field set up of free air blast.

Distance of gauges from the charge:

G1

One Meters

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.

1.3 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. Figure below shows one of the blast results:

Fig 1.8: Blast wave showing various parameters. PEAK OVER PRESSUREThis 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.

DURATIONIt 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.

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: -

1. 14 Kg/cm2

Severe internal injury to human beings.

2. 2.5 Kg/cm2

Lungs injury.

3. 1.6 Kg/cm2

Damage to brick structure.

4. 1 Kg/cm2

Eardrum burst.

5. 0.02 Kg/cm2

Damage to windowpanes.

1.4 Underwater shock study Under water techniques are used for studying the following phenomenon.

1. Comparison of explosive performance used in different types of naval warhead.

2. Heat of detonation /energy of unknown explosives can be determined.

3. 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.

Fig 1.9: Water tank used in under water trials.The figure above shows the water tank of TBRL in which underwater trials are conducted.

1.5 Underground shock study:

Underground shock studies are conducted for the following objectives:

1. 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.

2. Used to calculate the safety distance for the structures

3. 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

1. Measurement and prediction of ground motion.

2. 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.

1. Geophone

2. Accelerometer

3. Blast mate

4. Etna accelerograph

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

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 use 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. BLASTMATE:

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.

Theory of operation:

TRANSDUCER:

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 Lenzs 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.

GEOPHONE SENSOR OPERATION

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 coupled to the particles of the surrounding terrain. The coil, because of its inertia, doesnt move and the resulting magnet versus coil motion induces a voltage, which is proportional to particle velocity.

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 waveforms frequency at the largest peak for sound pressure.

FEATURES:

1) Full waveform event analysis

2) Multiple record modes---single shot, continuous, auto record

3) 300 full wave form event capacity

4) Full PC compatibility

5) Variable sample rates

6) On-line Help

7) Upgradeable

8) Rugged design

SPECIFICATIONS:

Seismic: Range 254 mm/s

Resolution 0.127mm/s to 0.0159mm/s

Trigger levels 0.127mm/s to 254mm/s in steps of 0.01mm/s

Air linear: Range 2 Pa to 500 Pa

Resolution 0.1 dB above 120 dB

Trigger levels 100 148 dB in 1 dB steps

Accuracy 0.2 dB at 30 Hz and 127 dB

A Weight (optional) Range 50 to 110 dB in steps of 0.1 dB

(Impulse response = 35 ms)

Sampling rate standard 1024 samples per second per

Channel to 16384 (8192 for 8 channel)

Event storage Full wave 300 standard, 900 and 1500 optional

Form events at standard sample rates of 1024.

Frequency response 2 to 300 Hz Ground and air

Independent of record time

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.

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 @spssampling rate : 100, 200, 250 sps.

Input range : + 2.5volts.

The tables below show the damage pattern by ground acceleration and particle velocity.

Table 1: Damage pattern by ground acceleration

No damage:

1g

Table 2: Damage pattern and ground particle velocity

No damage:

2.8 inch/sec

Fine cracking of plaster:4.3 inch/sec

Cracking:

6.3 inch/sec

Serious cracking:

9.1 inch/sec

Table 3: Human Threshold for ground vibration

Just perception:

0.01- 0.03 inch/sec

Clearly perceptible:

0.03- 0.1 inch/sec

Annoying:

>= 0.1 inch/sec

1.6 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 microphonic 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:

1. Characteristic impedance:75 ohm at 1MHz frequency in unbalanced condition

2. Frequency rate of operation:

1 MHz at 3dB gain

3. Breakdown voltage:

2.7KV

4. Nominal capacitance:

69pF/m

5. Nominal attenuation:

0.46 dB/100ft for 1MHz

6. Inner diameter:

0.193mm, 14 strands

7. Plain annealed copper polythene insulation:5.08mm

8. Graphite conducting layer:

5.59mm

9. Outer conductor plain annealed copper:6.48mm

10. Overall diameter with outer PVC sheath:8.0mm

1.7 Other instruments used in blast and damage study:

1.7.1 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-microphonic 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

1. Auto: 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.

2. LC: In this mode only the inductance or capacitance of the component will be reported and not its resistance, even if it is predominant.

3. R: This mode displays the resistance of the component, be it a capacitor or inductor.

Other selections that are available are:

1. Series; and

2. 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.

series 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.

1.7.2 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 52(10-6/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.

Fig 1.10 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.

1.7.3 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:

1. 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.

2. 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.

3. 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

8KB ROM and 64KB RAM, total 99 memories

Resolution:

0.1dB

Polarising voltage:0V, 28V, 200V

Storage rate:

1 value/sec

The microphone used is 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, overrange and underrange.

1.8 Data recording elementsThe 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.

1.8.1 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 basic principle of a digital scope is given in the figure. Considering a single channel of figure. The analog voltage input signal is digitized in a 10 bit A/D converter with a resolution of 25 KHz. The total digital memory storage capacity is 4096 for a single channel, 2048 for two channels each and 1024for four channel each.

DIGITAL STORAGE OSCILLOSCOPE

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.

GENERAL FEATURES:

100MHz bandwidth

Memory:

1K/channel

Sampling rate:400MS/s

High resolution, high contrast LCD display 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

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:

1. Measurement of power and energy, such as in power supplies.

2. Characterizing the mechanical transducers, as in integration of output of accelerometer to obtain velocity.

1.8.2 Digital Phosphorous 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) acquire 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.

Fig 1.11 Digital Phosphorous Oscilloscope.

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 rate 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.

The only disadvantage that DPO mode provides is that storage and later display of waveforms is not possible.

General features:

Bandwidth:500MHz

Memory:50K/channel

Maximum sampling rate:1GS/s

Computer compatible: waveform storage in floppy

Other display features also available

1.8.3 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.1.8.4 GMM 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.

1. It has different displaying modes such as Combo mode, View mode, Meter mode etc.

2. It also provides Auto Diode Test Mode.

3. It has one important key namely "Save and Print". GMM can use an optical serial interface cable to communicate with a PC or printer.

4. Frequency display can be obtained in many ways such as Hz, duty cycle, pulse width or period.

5. 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.

Fig 1.12 The Fluke graphical multimeter.

The specifications of GMM are listed below:

Input Impedance:

10Mohm

Accuracy:

(0.05% of reading + 2 digits

Amplitude resolution: 8 bits

Battery operating time: 6hrs

Battery recharge time: 16 hours minimum from full discharge

Measurement range:

3V 1000V

PC-based firing control unit

2.1 Introduction

2.1.1 Explosive:

A firing unit is a system used to detonate an explosive. An explosive consists of a primary explosive and a secondary explosive. The primary explosive is a highly sensitive substance that requires very little energy to explode and release shock which is used to detonate secondary explosive. The secondary explosive is the one which actually releases energy to be delivered to the surroundings for damage.

Fig 2.1: Explosive train showing detonator wire and explosive.

2.1.2 Firing control unit:

A firing control unit is a system that fires a detonator. It provides requisite energy (20 mJ) to the detonator for its explosion. This is a very controlled process and requires stringent safety measures. The firing is done when a safe signal is given by the trial officer of the trial signifying that the area has been cleared.

The present firing control unit is a mechanically controlled device and has a lock and key arrangement. After checking the detonator wire and the unit for any malfunction, the trial officer locks the firing unit and gives the key to the safety officer. When the area is cleared the safety officer passes back the key to the trial officer and the trial can then be conducted.

The design and development of a computer controlled firing control unit to obviate such a primitive-looking system is my assignment.

During my project semester I have been working on

1. Design, development and testing of prototype of PC controlled firing control unit.

2. Software development to make system computer controlled.

2.2 Block diagram and general working:

The general block diagram of the firing unit is shown below.

The circuit is compact and is operated by a 9 V DC power supply. The voltage that charges the capacitor is generated by a 12V-300V DC-DC converter. The 300V DC is used to charge a capacitor which holds the charge till the firing command is to be given. A discharging circuit is also incorporated if firing is to be aborted.

The continuity check circuit allows us to check any discontinuity in the detonating circuit before firing pulse is given. This is done to avoid any misfire. The last part is the firing circuit which gives the trigger to the detonator and the full voltage across the capacitor is made available to the detonator.

The most important aspect of the firing unit is safety. As the detonator is a highly sensitive device which can be triggered even by static charge, the current to be passed through the detonator must be very low during continuity check routine. Before the firing pulse is given one should ensure that there should not be any leakage in the circuit consisting of firing lead and detonator.

2.3 Features of the firing unit:

1. Computer controlled:

The unit is interfaced to the computer with the parallel port. The application executes the tasks asked for by the user and no other manual switching by the user is required.

2. No unauthorized access:

The unit is controlled by a computer and to enter the firing unit application a password is required. This removes any glitches of the lock and key arrangement. The unit hardware has no controls on the outside and is thus immune from tampering.

3. User-friendly:

The computer application is menu-based and can be easily operated by anyone and on any computer. The present firing unit has been simulated on the computer with a nice look and feel.

4. Safety:

The firing unit has been designed for utmost safety. The system comprises of many safety features starting from the password-enabled access. Then the software initiates a hardware check where the computer port, cables and the components are checked for any malfunction. When the system is running, the software checks the hardware before and after any action is taken. If the firing is aborted, the system itself goes into safe mode and then aborts.

System requirements:

1. 12V-300V, 30 mA max. output DC-DC converter: It is used for charging the capacitor. The output voltage must be spike free and output current should not be more than 50 mA. The converter is operated from a 12V, 4A battery.

2. Capacitor 10 microF, 350V: It stores the charge for firing the detonator. The capacitor should be able to store charge for some time (10 min) after switching off its supply and not leak through the air.

3. Solenoid relay 6V, 100 ohm: These are the heart of the firing unit. Each firing routine is managed by control of the relays that are being used. I am using SPDT solenoid relays which switch at 6V. An SPDT relay (single pole double throw) has one pole and two connections NO (normally open) and NC (normally closed). When no input is given to a relay it is connected to NC and when it is energized the connection shifts to NO. Thus a switching action can be performed with the control of a relay.

The computer operates the in a specific sequence and the firing procedure can be completed successfully.

Six relays have been used in my circuit for the following applications:

Charging of capacitor

Discharging of capacitor

Checking continuity of detonating circuit

Firing pulse

5.Solid state relay: These are also incorporated in the hardware in modules where fool-proof operation is required. These relays have lower ranges but higher accuracy.

4.Optoisolator: It is a device used for isolation of the computer port from the external power supplies. It has been explained later in detail.

5.BJT: These have been used in the circuit for current amplification. A series of transistors are used for higher beta amplification.

6.Comparator: It is used in various modules for checking signal levels and errors in the hardware.

A prototype of the circuit was first designed and tested. The relays were controlled using separate power supplies.

Considerations while selecting a relay:

The relays used in the circuit are solenoid relays which are also known as non-polarized DC relays. Their working principle is to open and close a series of contacts attached to a movable magnetic core in an electrical coil by exciting/de-exciting the coil.

The essential characteristics of these relays are

Safety ensured by the electrical isolation between contacts of relay and driving circuit.

Stability of the relay when subjected to impulse interference and other variations in the supply voltage.

These relays are generally used in rugged environments and have poor accuracy in terms of switching voltages and switching frequency. The important points to check out while using a relay are

1. Control voltage (generally 6V-24V)

2. Power consumed by coil (this value is necessary to calculate the circuitry which will control the relay).

3. Maximum current which can pass through the power contacts of the relay.

4. Maximum voltage that can be switched by the power contacts.

5. Switching capacity of power contacts (in AC or DC).

6. Switching time of relay.

2.4Working of the system:

The system operates in a set procedure although there is room for flexibility. The user can select what action he wants to perform from the software menu. The interaction with the hardware is done through the bidirectional parallel port. The following diagram helps to understand the system better.

Fig 2.4: Simplified circuit diagram of the system.

After the user has entered the correct password, he can move about in the software and perform the following procedure to conduct a trial.

1. Charging of capacitor to requisite voltage level:

The minimum energy required to explode a detonator is about 20 mJ.

The capacitor being used is 10,000 nF, 350 V which gives an energy of about 4 J. The capacitor should be able to hold charge for a long time, about 10 min. Also, the charging resistance should be adjusted so that charging time is low, preferably less than 10s.

2. Discharging of capacitor:

An arrangement for discharging of the capacitor to the ground has also been made. This is required in times of emergency when the firing is to be aborted.

3. Checking continuity of detonator:

This routine is followed to check the continuity of the detonator. A very small current (less than 10 microampere) is passed through the det. An open circuit means that the det wire is open somewhere or the det itself has a snag. A closed circuit shows the loop resistance. 4.Firing of detonator:

When this command is given the whole energy stored in the capacitor is made available across the det in a very small time.

2.5 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.2.5.1 PC parallel port:

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.

Fig 2.5 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.

Newer Parallel Ports are standardized under the IEEE 1284 standard first released in 1994. This standard specifies five modes of operation, each mode providing data transfer in either the forward direction (computer to peripheral), backward direction (peripheral to computer), or bi-directional (one direction at a time).

Compatibility mode is the original Centronics parallel interface and intended for use with dot matrix printers and older laser printers. The compatibility mode can be combined with the nibble mode for bi-directional data transfer.

Nibble mode allows data transfer back to the computer. The nibble mode uses the status lines to send 2 nibble (4-bit units) of data to the computer in two data transfer cycles. This mode is best used with printers.

Byte mode uses software drivers to disable the drivers that control the data lines in order for data to be sent from the printer to the computer. The data is sent at the same speed as when data is sent from the computer to the printer. One byte of data is transferred instead of the two data cycles required by the nibble mode.

ECP mode (Enhanced Capability Port mode) is an advanced bi-directional mode for use with printers and scanners. It allows data compression for images, FIFO (first in, first out) for items in a queue, and high-speed, bi-directional communication. Data transfer occurs at two to four megabytes per second. An advanced feature is channel addressing. This is used for multifunction devices such as printer/fax/modem devices. For example, if a printer/fax/modem device needs to print and send data over the modem at the same time, the channel address software driver of the ECP mode assigns a new channel to the modem so that both devices can work simultaneously.

EPP mode (Enhanced Parallel Port mode) was designed by Intel, Xircom, and Zenith Data Systems to provide a high-performance parallel interface that could also be used with the standard interface. EPP mode was adopted as part of the IEEE 1284 standard. The EPP mode uses data cycles that transfer data between the computer and the peripheral and address cycles that assign address, channel, or command information. This allows data transfer speeds of 500 kilobytes to 2 megabytes per second, depending on the speed of the slowest interface. The EPP mode is bi-directional. It is suited for network adapters, data acquisition, portable hard drives, and other devices that need speed.

2.5.2 Hardware Properties:

Below is a table of the "Pin Outs" of the D-Type 25 Pin connector and the Centronics 34 Pin connector. The D-Type 25 pin connector is the most common connector found on the Parallel Port of the computer, while the Centronics Connector is commonly found on printers. The IEEE 1284 standard however specifies 3 different connectors for use with the Parallel Port. The first one, 1284 Type A is the D-Type 25 connector found on the back of most computers. The 2nd is the 1284 Type B which is the 36 pin Centronics Connector found on most printers.

Figure 2.6: 25-way Female D-Type Connector

IEEE 1284 Type C however, is a 36 conductor connector like the Centronics, but smaller. This connector is claimed to have a better clip latch, better electrical properties and is easier to assemble. It also contains two more pins for signals which can be used to see whether the other device connected, has power. 1284 Type C connectors are recommended for new designs.

Pin No (D-Type 25)Pin No (Centronics)SPP SignalDirection In/outRegisterHardware Inverted

11nStrobeIn/OutControlYes

22Data 0OutData

33Data 1OutData

44Data 2OutData

55Data 3OutData

66Data 4OutData

77Data 5OutData

88Data 6OutData

99Data 7OutData

1010nAckInStatus

1111BusyInStatusYes

1212Paper-Out / Paper-EndInStatus

1313SelectInStatus

1414nAuto-LinefeedIn/OutControlYes

1532nError / nFaultInStatus

1631nInitializeIn/OutControl

1736nSelect-Printer / nSelect-InIn/OutControlYes

18 - 2519-30GroundGnd

Table 2.1: Pin Assignments of the D-Type 25 pin Parallel Port Connector.

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. nError. 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, Sink/Source 12mA. The best bet is to use a buffer, so the least current is drawn from the Parallel Port.

2.5.3 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 their 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-3BFhUsed for parallel ports which were incorporated into video cards and now commonly used for ports controlled by BIOS.

378h-37FhUsual address for LPT1 (Line PrinTer)

278h-27FhUsual address for LPT2

Table 2.2: Parallel port addresses.

Each parallel port uses three addresses of the I/O map. For LPT1 these addresses are 378H, 379H and 37AH.

2.5.4 Software Registers - Standard Parallel Port (SPP):

I have used the parallel port in this mode (SPP) for controlling the hardware of the firing unit. The port has been configured to work with all computers, even where bidirectional data transfer is not possible in SPP mode.

The base address, usually called the Data Port or Data Register is simply used for outputting data on the Parallel Port's data lines (Pins 2-9).

OffsetNameRead/WriteBit No.Properties

Base + 0Data PortWrite (Note-1)Bit 7Data 7

Bit 6Data 6

Bit 5Data 5

Bit 4Data 4

Bit 3Data 3

Bit 2Data 2

Bit 1Data 1

Bit 0Data 0

Table 2.3: Data Port

Note: If the Port is Bi-Directional then Read and Write Operations can be performed on the Data Register.

This register is normally a write only port. If you read from the port, you should get the last byte sent. However if your port is bi-directional, you can receive data on this address.

OffsetNameRead/WriteBit No.Properties

Base + 1Status PortRead OnlyBit 7Busy

Bit 6Ack

Bit 5Paper Out

Bit 4Select In

Bit 3Error

Bit 2IRQ (Not)

Bit 1Reserved

Bit 0Reserved

Table 2.4: Status Port

The Status Port (base address + 1) is a read only port. Any data written to this port will be ignored. The Status Port is made up of 5 input lines (Pins 10,11,12,13 & 15), an IRQ status register and two reserved bits. Bit 7 (Busy) is an active low input. E.g. If bit 7 happens to show a logic 0, this means that there is +5v at pin 11. Similarly if Bit 2 (nIRQ) shows a '1' then an interrupt has not occurred.

2.5.5 Relay control using parallel port:

The first circuit I made to use the parallel port is shown below.

Fig 2.7: Simple circuit to operate parallel port.

This port operates the LEDs when the command is given by the computer. The LEDs 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.

/* File LED_GLOW.CPP

**

** Illustrates simple use of printer port for LED glow in binary.

** Navdeep Ojha

*/

#include

#include

void main()

{

for( int i=0; i