Practical Training Report 1

8/3/2019 Practical Training Report 1

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PRACTICAL TRAINING REPORT

SUBMITTED IN PARTIAL FULFILLMENT FOR THE AWARD OF

BACHELORS DEGREE

IN

ELECTRONICS AND COMMUNICATION ENGINEERING

OF

RAJASTHAN TECHNICAL UNIVERSITY

SUBMITTED BY

NIKHIL VADERA(VII SEMESTER)

(2011-12)

Training at

DEFENCELABORATORY, JODHPUR (RAJ.)

DEPARTMENT OF ELECTRONICS AND COMMUNICATION ENGINEERING

JODHPUR INSTITUTE OF ENGINEERING AND TECHNOLOGYNH 65, MOGRA, JODHPUR 342 002.


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Acknowledgement

It is my pleasure to be indebted to various people who directly or indirectly

contributed in the development of this work and who influenced my

thinking, behavior and acts during the course of study.

I express my sincere gratitude to The Director, Defence Lab, Jodhpur for

providing me an opportunity to undergo summer training at Defence Lab.

I am thankful to Sh. J.P.Meena, Scientist D for his support, cooperation

and motivation provided to me during my training for constant inspiration,

presence and blessings.I also extend my sincere appreciation to Sh. Arivand Parihar, Scientist C

who provided his valuable suggestions and precious time in accomplishing

my project work.

Lastly, I would like to thank the almighty and my parents for their moral

support and my friends with whom I share my day-to-day experience and

received lots of suggestions that improve my quality of work.

NIKHIL VADERA


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Abstract

The report gives a brief description of nuclear radiation and its types.

Radiation threats are unique in that you can't see, smell, taste, hear or feel

them, until it's already done its damage and we suffer the effects. The report

also gives information about different radiation detectors and their basic

principles. Nuclear radiation detectors serve to determine the composition

and measure the intensity of radiation, to measure the energy spectra of

particles, to study the processes of interaction between fast particles andatomic nuclei, and to study the decay processes of unstable particles. The

operation of all nuclear radiation detectors is based on the ionization or

excitation by the radiation of the atoms of the substance that fills the

effective volume of the detector. Further, it describes in detail about the

radiation detection system. A nuclear radiation detection system consists of

a radiation detector and suitable electronics for the counting of radiation

events and their further analysis. Finally, the report describes the circuit

Acoustic Signal Detection and Processing Unit for the detection of an

acoustic signal from the Superheated Liquid Neutron Sensor (SLNS)

developed at DRDO, Defence Laboratory, Jodhpur and its further signal

processing to obtain output in the form of a pulse.


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Index

Page No.

Acknowledgement

AbstractCertificate from the Organization 1

1. Introduction 3

1.1 Types of Ionizing Radiation 4

1.2 Technical Uses of Ionizing Radiation and

Radiation Detection

6

2. General Principles of Radiation Detection 7

2.1 Nuclear Radiation detector 82.2 Need of Nuclear detector 12

3. Nuclear Radiation Detection Systems 13

3.1 Radiation Detector 13

3.2 Preamplifier 13

3.3 Amplifier 14

3.4 Comparator 14

3.5 Pulse Height Analyzers 15

4. Project: Acoustic Signal Detection & Processing Unit 18

Aim of the project

4.1 Operational Amplifier 18

4.2 Comparator 33

4.3 Monostable Multivibrator 36

4.4 Decade Counter 374.5 Design Of Power Supply 39

4.6 Design of Signal Processing Unit 46

Conclusion 49

Appendix 50


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Bibliography 61


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1. Introduction

Radiation is energy that comes from a source and travels through space and may be able

to penetrate various materials. Light, radio, and microwaves are types of radiation that are

called non-ionizing. The kind of radiation discussed in this document is called ionizing

radiation (10 eV -10 MeV) because it can produce charged particles (ions) in matter.

Ionizing radiation is produced by unstable atoms. Unstable atoms differ from stable

atoms because unstable atoms have an excess of energy or mass or both. Radiation can

also be produced by high-voltage devices (e.g., x-ray machines).

The kinds of radiation are electromagnetic (like light) and particulate (i.e., mass given off

with the energy of motion). Gamma radiation and x rays are examples of electromagnetic

radiation. Gamma radiation originates in the nucleus while x rays come from the

electronic part of the atom. Beta and alpha radiation are examples of particulate radiation.

These particles when interact with matter through different processes depending on the

type of radiation and their energy as shown in Fig.1.

Figure1. Interaction of Ionizing Radiation with Matter


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Unlike the visible and thermal radiations, the exposure to nuclear radiations is harmful to

human beings and therefore sensors for these radiations are essentially required for the

monitoring of areas such as nuclear reactors and other places where radioisotopes are

used for industrial and other applications. Amongst different types of nuclear radiations,

detection of neutrons is the most challenging task since these particles are neutral and do

not interact with the electrons of the atoms and molecules rather they cause nuclear

reaction with the nuclei of certain specific elements leading to generation of radio-

isotopes. This process is called nuclear activation. Moreover, the reaction cross sections

of neutrons with different nuclei also depend on their energy. Various types of sensors

have been reported for the detection of neutrons which include semiconductors, polymers

and super heated liquids. The report deals with the development of electronic circuit for

the detection of acoustic signals arising due to formation of bubbles in superheated

liquids on their exposure to neutrons.

The report begins with brief introduction to different kinds of nuclear radiations, their

characteristics and different methods for their detection including the basic principle of

detection of neutrons by super heated liquid sensor is also discussed. Further, the basic

module and its circuit components used for the detection of acoustic signals caused due to

the formation of bubbles in the SLNS sensor are discussed in detail in the present report.


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2. Organization Overview

The Defence Research and Development Organization (DRDO) is an agencyof theRepublic of India, responsible for the development oftechnologyfor use by the military,

headquartered inNew Delhi, India. It was formed in 1958 by the merger of Technical

Development Establishment and the Directorate of Technical Development and

Production (DTDP) with the Defence Science Organization (DSO).

DRDO has a network of 52 laboratories which are deeply engaged in developing defence

technologies covering various fields, like aeronautics, armaments, electronic and

computer sciences, human resource development, life sciences, materials, missiles,

combat vehicles development and naval research and development. The organization

includes more than 5,000 scientists and about 25,000 other scientific, technical and

supporting personnel.

DRDO is headed by Scientific Advisor to Raksha Mantri (Defence Minister), SA to RM,

who is also the secretary, Deptt of Defence R&D and Director General, R&D. The SA to

RM is assisted by a number of Chief Controllers. Prof. D.S. Kothari was the first SA to

RM in DRDO. The organization has a two tier system, viz., the Technical and Corporate

Directorates at DRDO Bhawan, New Delhi; and laboratories/establishments located atdifferent stations all over the country.

The responsibilities of DRDO can be consolidated under the following categories:-

Design, development & lead to produce state-of-art Sensors, Weapons Systems,

Platforms and allied equipment (Strategic systems, Tactical systems, Dual Use

technologies)

Research in Life Sciences, to optimize combat effectiveness and promote well-

being of service personnel in harsh environment

Develop infrastructure and highly trained Manpower for strong Defence

technology base.
http://en.wikipedia.org/wiki/Government_agencyhttp://en.wikipedia.org/wiki/Technologyhttp://en.wikipedia.org/wiki/Military_of_Indiahttp://en.wikipedia.org/wiki/New_Delhihttp://en.wikipedia.org/wiki/Government_agencyhttp://en.wikipedia.org/wiki/Technologyhttp://en.wikipedia.org/wiki/Military_of_Indiahttp://en.wikipedia.org/wiki/New_Delhi


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Some of the major Contributions of DRDO have been the following:-

S.No. Systems System Development/Accepted/Introduced

1Missile

SystemAgni, Prithvi, Brahmos, Dhanush, Trishul, Akash & Nag

2Naval

Systems

HUMSA, USHUS, TAL, Torpedoes-fire control system and Advanced

Experimental.

3Electronic

Systems

SARARI, ACCCS, Surveillance Radar, SUMUKTA, SANGRAHA, WLR,

SV-2000, CIDSS, CNR and Indra

4

Combat

Vehicle and

Engg.

MBT, Arjun, Armored, Engg recce Vehicle(AERV) Bridge Layer Tank,

Armoured Amphibious Dozer, SARVATRA, Trackway Expedient Mat

Ground Surfacing, Armoured Ambulance BMP-II, Career Mortar Trackedon BMP-II & Operation Theatre Complex on Wheels

5Aero

Systems

LCA, Lakshya Pilotless Aircraft, Nishant UAV "Tempest" EW Suite,

Tranquil Reader Warning Receiver (RWR), Tarang RWR Project Vetrivale,

High Accuracy Direction Finding (HADF) RWR, Jagur Mission Compter &

Bheema 1000 Aircraft Weapon Loading Trolley

6Armament

Systems

5.56mm INSAS (Amn. LMG & Rifle), Pinaka-Multibarrel Rocket Launcher

System, FSAPDS Mk-I/II Ammunition, Influence Mines Mk-I, Multimode

Grenade etc.

7 Materials

AB Class Steel for Naval Applicaton, Titanium Sponge, NBC Protective,

Clothing/Permeable Suites, Extreme cold weather Clothing systems, Blast

Protection Suits, Synthetic Life Jacket, Anti Riot Polycarbonate Shield, Anti

Riot Helmet, Brake pads for Aircrafts, Heavy alloy Armour Penetrator Rods,

Jackal Armour, Kanchan Armour, Spade M1.

8

Life

Sciences

Systems

Life Support Systems for Army, Navy and Airforce Personnel, NBC

Canister, Water Prison Detection Kit, Portable, Decontamination Apparatus,

NBC Filters/ventilation systems, First Aid Kit, CW Type A/B,Decontamination kit/solution.

Defence Laboratory (DL) is a laboratory of the Defence Research and Development

Organisation(DRDO). Located in Ratanada Palace, Jodhpur, it has three thrust areas for

R&D viz. (i) Camouflage and Low Observable Technologies; (ii) Nuclear Radiation
http://en.wikipedia.org/wiki/Defence_Research_and_Development_Organisationhttp://en.wikipedia.org/wiki/Defence_Research_and_Development_Organisationhttp://en.wikipedia.org/wiki/Defence_Research_and_Development_Organisationhttp://en.wikipedia.org/wiki/Defence_Research_and_Development_Organisation


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Management and Applications; and (iii) Desert Environmental Science and Technology.

The laboratory has developed a number of products and technologies in these areas. It is

providing support to the Indian Armed forces in a number of strategically important

areas.

Prestigious DRDO Titanium trophy for the year 2010 for the Best Science

Laboratory of the Defence Research Organization (DRDO) has been awarded to

Defence Laboratory, Jodhpur in recognition of its contribution in the area of

camouflage and low observable technologies for the Armed Forces and development

of critical Defence equipment.


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3. Technical Details of Project/Study

Fundamental study of nuclear radiation & detectors/Sensors

Study of Operational amplifiers

Design of power supply using 78XX and 79XX voltage regulator ICs

Design of signal processing circuit for radiation sensor using LM741

IC and LM393 IC

3.1 Nuclear Radiations

The nuclear radiations can be classified into the following two different classes (i)

Uncharged nuclear radiations, viz. -rays and neutrons; and (ii) Charged nuclear

radiations viz. alpha and beta. Due to difference in their mass and charged states these

radiations interact differently with matter. The characteristics of these radiations are

described briefly in the following sub-sections.

3.1.1 Types of Nuclear Radiation

Uncharged radiation

Electromagnetic radiation ( rays)

Neutrons (slow/fast, (ultra-)cold/hot)

Charged particulate radiation

Fast electrons and positrons ( particles),

Heavy charged particles ( particles)


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Gamma-Gamma rays are very high energy electromagnetic radiation with energy values

of the order of keV to MeV as shown in Fig. 2. Gamma rays are the most hazardous type

of external radiation as they can travel up to a mile in open air and penetrate all types ofmaterials (Fig.3). Since gamma rays penetrate more deeply through the body than alpha

or beta particles, all tissues and organs can be damaged by sources from outside of the

body. Only sufficiently dense shielding and/or distance from gamma ray emitting

radioactive material can provide protection.

Figure 2. The Electromagnetic spectrum

Alpha: An alpha particle is the same as a helium-4 nucleus, and both mass number and

atomic number are the same. These are actual particles that are electrically charged and

are commonly referred to asalpha particles.Alpha particles are the least penetrating

radiation, as they cannot travel more than four to seven inches in air and a single sheet of

paper (Fig.3) or the outermost layer of dead skin that covers the body will stop them.

However, if alpha particle emitting radioactive material is inhaled or ingested, they can

be a very damaging source of radiation with their short range being concentrated

internally in a very localized area.

Beta-minus () radiation consists of an energetic electron. It is more ionizing than alpha

radiation, but less than gamma. Beta particles travel faster and penetrate further than


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alpha particles. They can travel from a few millimeters up to about ten yards in open air

depending on the particular isotope and they can penetrate several millimeters through

tissue (Fig.3). Beta particle radiation is generally a slight external exposure hazard,

although prolonged exposure to large amounts can cause skin burns and it is also a major

hazard when interacting with the lens of the eye. However, like alpha particles, the

greatest threat is if beta particle emitting radioactive material is inhaled or ingested as it

can also do grave internal damage.

Neutron-Neutron radiation is sometimes called "indirectly ionizing radiation" since so

many of its interactions with matter eventually result in ionization. Neutron radiation

consists of free neutrons. These neutrons may be emitted during either spontaneous orinduced nuclear fission, nuclear fusion processes, or from any other nuclear reactions. It

does not ionize atoms in the same way that charged particles such as protons and

electrons do (exciting an electron), because neutrons have no charge. However, both

slow and fast neutrons react with the atomic nuclei of many elements upon collision with

nuclei, creating unstable isotopes and therefore inducing radioactivity in a previously

non-radioactive material. This process is known as neutron activation. High-energy

neutron impact on at atomic nucleus is also enough to impart enough energy for it to

break the atom's chemical bonds, again resulting in ionization of the molecule. Fast

neutrons can directly damage DNA in this fashion.

Figure3. Radiation hardness and penetrability
http://en.wikipedia.org/wiki/Neutron_activationhttp://en.wikipedia.org/wiki/Fast_neutronhttp://en.wikipedia.org/wiki/Fast_neutronhttp://en.wikipedia.org/wiki/Neutron_activationhttp://en.wikipedia.org/wiki/Fast_neutronhttp://en.wikipedia.org/wiki/Fast_neutron


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3.1.2 Technical uses of Ionizing Radiation and Radiation Detection

Radiography/ tomography by means of gamma or X rays (attenuation/

absorption)

Smoke detectors Radioactive labels and tracers (biology and chemistry)

Material Analysis

Archeology

Mining (petroleum exploration)

Nuclear non-proliferation and homeland security

Medicine (gamma ray emission tomography)- Drug development

- Nuclear medicine (cancer diagnosis and treatment)

3.2 General Principles of Radiation Detection

Interaction of radiation with matter produces ionization and electronic excitation or heat

that can be measured:

Either primary charges are collected:

Gas detectors Ionization chamber

Proportional counter

Geiger-Muller counter

The schematic diagram of a gas filled detector and mechanism of interaction of radiation

with the ionizing gas is shown in the schematic diagram given in Fig. 4 below.


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Figure 4. Schematic diagram of gas filled detector

Solid state detectors Si, Ge, CdZnTe, HgI2

Or photons resulting from de-excitation of molecules of the detector are converted to

secondary charges which are collected:

Scintillators Inorganic NaI (Tl), CsI (Tl), LaBr, BGO

Organic anthracence, stilbene, plastic

Superheated Emulsion Detector

3.2.1 Nuclear Radiation Detector

Nuclear radiation detectors serve to determine the composition and measure the intensity

of radiation, to measure the energy spectra of particles, to study the processes of

interaction between fast particles and atomic nuclei, and to study the decay processes of

unstable particles. The operation of all nuclear radiation detectors is based on the

ionization or excitation by charged particles of the atoms of the substance that fills the

effective volume of the detector. In the case ofy-quanta and neutrons, ionization and

excitation are accomplished by secondary charged particles that arise as a result of the

interaction between gamma quanta or neutrons and the working medium of the detector.

Thus, the passage of all nuclear particles through the medium is accompanied by the

formation of free electrons and ions, the appearance of flashes of light (scintillations),

and chemical and thermal effects. As a result, radiation can be registered by the

appearance of electrical signals (current or potential pulses) at the output of the detector,

by the darkening of a photo emulsion, or by other means. The electrical signals are

usually small and require amplification. The current intensity at the output, the average

pulse recurrence frequency, and the degree of darkening of the photo emulsion are

measures of the flux intensity of the nuclear radiation. There are several types of sensors

suitable for detecting and measuring nuclear (ionizing) radiation:


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i) Ionization Chambers

An ionization chamber typically is a metal cylinder, with an internal electrode running

down the axis. A high voltage usually several hundred or thousand volts, is applied

between the two. The chamber is filled with a gas, which could be as simple as dry air, orcould be an exotic gas like krypton or xenon, depending on the application. The

schematic diagram is shown in Fig.5. When radiation enters the chamber, it ionizes the

gas (frees electrons from atoms), allowing electrical current to flow. This current is

proportional to the radiation dose rate; hence it gives a good measurement of the radiation

level. The main advantage of the ionization chamber as a nuclear radiation sensor is that

it is simple and inexpensive to build. The disadvantages include the fact that the electrical

current produced is extremely weak, and must be amplified with sophisticated electronic

circuitry. Also, the output current tends to drift with time, and the system must be

frequently re-zeroed.

Figure5. Schematic Diagram of Ionization Chamber

Application:

Nuclear industryIonization chambers are widely used in the nuclear industry as they provide an output that

is proportional to radiation dose and have a greater operating lifetime than standard Geiger

tubes; in Geiger-Muller tubes the gas eventually breaks down due to incident radiation.

Smoke detectors

The ionization chamber has found wide and beneficial use in smoke detectors. In a

smoke, the gap between the plates is exposed to the open air. The chamber

contains a small amount of americium-241, which is an emitter of alpha particles. These

alpha particles carry a substantial amount of energy, and when they collide with gas


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in the ionization chamber (mostly nitrogen and oxygen) the momentum transferred

ionizes the gas moleculesthat is, the uncharged gas molecules will lose one or

more electrons and become charged ions.

Since the plates are at different voltages (in a typical smoke detector, the voltage

difference is a few volts) the ions and electrons will be attracted to the plates. This small

flow of ions between the plates represents a measurable electric current. If smoke enters

the detector, it disrupts this current because ions strike smoke particles and is

neutralized. This drop in current triggers the alarm.

ii) Proportional Counter

A proportional counter is very similar to an ionization chamber. The major difference is

that the applied voltage is higher. As a result, whenever a radiation particle enters the

counter and ionizes a gas molecule, the higher voltage accelerates the freed electron(s),

which cause them to ionize additional molecules. This causes a higher current to be

produced. The current is roughly proportional to the energy of the radiation, hence the

name of the detector. The output current is in the form of a single pulse. If this pulse is

measured, the energy of the incident radiation can be determined. As with ionization

chambers, sophisticated electronic circuitry is required to amplify and measure the output

pulses.

iii) Geiger Counter

A Geiger counter is virtually the same as a proportional counter, except that the voltage is

higher still. As a result, the current pulses all have roughly the same level. While

radiation energy information is lost, the output pulses are so large that they can be easily

counted, without the need for expensive amplifiers.

Figure 6. Schematic Diagram of Geiger Counter


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iv) Scintillation Detectors

A scintillation detector uses a special crystal, often sodium iodide (NaI) which converts

the radiation energy into light. This light is detected using a photo multiplier tube (PMT)

which converts it to electrical current and amplifies it. The result is very similar to a

proportional counter. The advantage is that the crystals often have a very high efficiency,

especially for higher energy gamma rays, so scintillation detectors are extremely

sensitive. The disadvantage is primarily cost - the crystals and PMTs are all very

expensive items.

Figure7. Schematic Diagram of Photomultiplier Tube

APPLICATIONS:

Scintillation counters can be used to measure radiation in a variety of applications.

Medical imaging

National and homeland security

Border security

Nuclear plant safety


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Several products have been introduced in the market utilizing scintillation counters

for detection of potentially dangerous gamma-emitting materials during transport.

These include scintillation counters designed for freight terminals, border security,

ports, weigh bridge applications, scrap metal yards and contamination monitoring of

nuclear waste. There are variants of scintillation counters mounted on pick-up trucks

and helicopters for rapid response in case of a security situation due to dirty bombs or

radioactive waste. Hand- held units are also commonly used.

v) Solid State Nuclear Radiation Sensors

There are a variety of solid state detectors available today. These are semiconductors,

which directly convert the incident radiation into electrical current, much as a

proportional counter tube does, except that rather than gas, a material such as silicon is

used. Other common materials are germanium, cadmium zinc telluride, etc. A major

advantage of such sensors is their extremely high energy resolution. That is, they are very

good at determining exactly what the energy of the incident radiation is. A disadvantage

is cost; the detectors themselves are quite expensive, as are the associated electronics

required.

vi) Superheated Emulsion Detector

Superheated emulsion based nuclear radiation detectors for detection of neutron and

gamma has emerged as a latest technology. A bubble detector, also called a superheated

droplet detector, consists of a suspension of superheated droplets in a polymer matrix.

Neutron interaction inside the bubble detector can deposit sufficient energy to overcome

the surface tension forces that prevent vaporization of individual droplets. Since the

length scale of nucleation is about 100 nm, gamma-ray interactions are unable to provide

a sufficiently localized energy deposition. Therefore, this type of detector is virtually

insensitive to gamma-rays. Neutron response is typically provided by nuclear recoil or

through the reaction 35Cl(n, p)35S. Particularly interesting for dosimetry is the ability of


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bubble detectors to discriminate among neutrons of various energies. Detectors that are

either insensitive or sensitive to thermalized neutrons can be now constructed.

Superheated emulsion detectors contains the superheated droplets of low boiling point

liquid suspended in polymer matrix, when exposed to neutrons these droplets get

converted into visible bubbles in proportion to radiation dose. The superheated emulsion

neutron sensor contains superheated drops of low boiling point refrigerants sensitive to

fission neutrons. The detector is gamma insensitive and energy independent. The SLNS

consists of is 4cm long polycarbonate tube filled with transparent elastic polymer

medium suspended with liquid drops of refrigerant.

When the pressure on the detector matrix is released by unscrewing the top of the detector,

the liquid droplets become superheated. The energy is supplied by incoming neutrons

which interact with the detector material. This interaction results in the production of

charged particles, which recoil and transfer their energy to superheated droplets at

the nucleation sites. This results in the formation of bubbles. The bubbles are fixed in

elastic medium and can be subsequently counted visually or with the help of macro lens.

The numbers of bubbles are proportional to effective neutron and gamma dose. Re-

compressing the cap detector material transforms the bubble back in to droplet and

detector can be reused. Instead of counting manually, these bubbles can also be detected

automatically through the acoustic signal sensing circuit and depending on the number of

counts dose values can be calculated.

The above detectors are useful in pure neutron radiation field as well as mixed field

(neutron & gamma) associated with wide range neutron and gamma energy spectrum.

The detectors of different sensitivity can be obtained by changing amount of superheated

liquid. It enables to measure neutron or gamma radiation in radiological event or nuclear

emergency.


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Superheated liquid neutron sensor

3.2.2. Need of Nuclear Detectors

Radiation threats are unique in that you can't see, smell, taste, hear or feel them, until it's

already done its damage and you are suffering the effects. Without a radiation detector

you would have to depend solely on the limited resources of the authorities to monitor

your location, then determine your risk level, decide the best protective action and

then to 'get the word out'.

Exclusively depending on others to monitor, evaluate, warn and advise you, in a rapidly

developing nuclear emergency crisis, would surely not be anywhere near as quick or

accurate in revealing your current risk as when you are capable of taking your own

independent radiation readings. Also, where authorities are warning of radiation fallout

not yet arrived, but anticipated to be heading your way, with a radiation meter you'll be

able to confirm that the suggested protective action is in fact reducing your exposure and

not inadvertently increasing it.

3.3. Nuclear Radiation Detection Systems

A nuclear radiation detection system consists of a radiation detector and suitable

electronics for the counting of radiation events and their further analysis. The schematic

diagram of a general nuclear radiation detection system is given in Fig.8.

Figure 8 Schematic Representation of the Nuclear Radiation Detection

System


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3.3.1Radiation Detector

The radiation detector interaction with nuclear radiation and generates an electrical signal

of an intensity. The height of the signal will depend on the energy of the radiation and its

intensity will depend on the intensity of the nuclear radiation. Different types of radiation

detectors are used for the sensing of different nuclear radiations.

3.3.2 Preamplifier

To amplify the relatively small signal from the detectors

To match the impedance levels between the detector and subsequent components

To shape the signal pulse for optimal subsequent processing

Preamplifier is located as close as possible to the detector to maximise the signal to

noise ratio (often in single unit).

The amplification for scintillation detectors is small (5-20) because the signals from

the detectors have already been amplified by photo-multiply tubes (105-1010).

Higher amplification is required for semiconductor detectors (103-104) due to small

detector signals.

3.3.3 Amplifier

To amplify the still small signals from the preamplifier (1-1000).

To reshape the slow decaying pulse from preamplifier into a narrow one (for high

count rate and increasing the S/N rate etc,).

Requirements for shaping: preserve the input signal information such as pulse

height and rise time.


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Figure 9 Output waveform of preamplifier and amplifier

3.3.4 ComparatorA comparator is the simplest circuit that moves signals between the analog and digital

worlds.

Simply put, a comparator compares two analog signals and produces a one bit digital

signal. The symbol for a comparator is shown below.

Comparator output satisfies the following rules:

o When V+ is larger than V- the output bit is 1.

o When V+ is smaller than V- the output bit is 0.

3.3.5 Pulse-Height Analysers

Basic Functions

Single Channel Analysers

Time Methods

Multi-channel Analysers


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Basic Function

The amplitude of output signal is proportional to the energy of the radiation event

detected.

Selective counting of those pulses within certain amplitude resulted in counting of

selective energy range.

A certain energy range or interval is called energy channel.

Single Channel Analysers

Counting only those within a single energy range.

Composed of three parts: Lower Level Discriminator (LLD), Upper Level

Discriminator (ULD) and Anticoincidence.

Percentage window: a certain percentage of the windows central voltage.

A single channel analyser without ULD is a circuit called discriminator.

Figure10.Principles of a single-channel pulse height analyser.


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Timing Method

Determine the timing of radiation event is important in Nuclear Medicine

applications

There are a number of timing methods available but two of those are often used in

nuclear medicine: leading-edge and zero-crossing.

Leading-edge uses the rising portion of the input pulse to trigger the lower level

discriminator which depends on the pulse amplitude (suffer certain amount of

inaccuracy--5 to 50 nsec for NaI (Tl)).

Zero-crossing requires bipolar pulses and is more accurate (4 nsec for NaI (Tl)).

Multichannel Analysers

Simultaneous recording of multiple energy radiations.

The principle of the popular Multichannel Analyser (MCA) is different from the

single channel analyser.

The centre of the Multichannel analyser is the analog-to-digital converter (ADC)

A memory is required for the sorting of energy channels (energy ranges, energy

spectrum).

Figure11. Principles of a multichannel analyzer (MCA). (A) Basic components.(B)

Example of pulse sorting according to amplitude for radiation events detected from an

object containing 990Tc.


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3.4 Project: Acoustic Signal Detection and Processing Unit

Aim: To design and develop a signal processing unit to amplify and reduce the noise in

the acoustic signal.

3.4.1 Operational Amplifier

Operational amplifiers are widely used in signal processing circuits, control circuits, and

instrumentation. Of all analog integrated circuits, the operational amplifier is the analog

integrated circuit which has the most sales and is the most widely used in the widest

variety of electronic circuits. The operational amplifier is a versatile component that can

do many things in measurement, signal processing and control. It can be used to amplify

dc as well as ac input signals. That versatility is the largest reason that you find so many

operational amplifiers being used! With the addition of suitable external feedbackcomponents, the op-amp can be used for a variety of application, active filters,

oscillators, comparators, regulators.

The 741 - A Typical Operational Amplifier

An operational amplifier is a direct-coupled high gain, differential, voltage amplifier.

It is a voltage amplifier. The input is a voltage and the output is a voltage.

The gain is high. Typically, the gain is over 100,000.

It is a differential amplifier. It actually amplifies the difference between two

voltages.

It's often referred to as an operational amplifier. It's important to notice that there is a

notch (sometimes a circular depression) on one end (the "top" of the chip in the picture)

of the operational amplifier. The pin shown in figure 12, the notch is pin 1, and the one

above is pin 8. They're numbered counter clockwise around the chip.


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Examine the pinout for the chip. Normally, the chip will either be inserted in a circuit

board, or wired into a printed circuit board. In either case, to power the chip you need to

make two connections:

The positive voltage from the supply to pin 7 on the chip.

The negative voltage from the supply to pin 4 on the chip.

Other connections to the chip:

Inverting input to pin 2 on the chip

Non-inverting input to pin 3 on the chip.

Output from pin 6 on the chip.

Figure12.Pin Diagram of op-amp uA741


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Figure 13 Typical 8-pin mini-Dip linear IC op-amp power supply

connections

Characteristics and Parameters of Operational Amplifiers

The characteristics of an ideal operational amplifier are described first, and the

characteristics and performance limitations of a practical operational amplifier are

described next.

IDEAL OPERATIONAL AMPLIFIER

The characteristics or the properties of an ideal operational amplifier are:

i. Infinite Open Loop Gain,

ii. Infinite Input Impedance& Zero Output Impedance,

iii. Infinite Bandwidth

iv., Zero Output Offset, and

v. Zero Noise Contribution.

The opamp, an abbreviation for the operational amplifier, is the most important linear IC.

The circuit symbol of an opamp shown in Fig. 14. The three terminals are: the non-

inverting input terminal, the inverting input terminal and the output terminal. The details

of power supply are not shown in a circuit symbol.

Out ut Inverting

Input

Noninverting

Input

+V

-V


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Figure14. Circuit Symbol of an opamp

i. Infinite Open Loop Gain

From Fig.14, it is found that vo = - Ao vi, where `Ao' is known as the open-loop gain of

the opamp. Let vo be -10 Volts and Ao be 105. Then vi is 100 uV. Here the input voltage

is very small compared to the output voltage. If Ao is very large, v i is negligibly small for

a finite vo. For the ideal opamp, Ao is taken to be infinite in value. That means, for an

ideal opamp vi = 0 for a finite vo. Typical values of Ao range from 20,000 in low-grade

consumer audio-range opamps to more than 2,000,000 in premium grade opamps

( typically 200,000 to 300,000).

The first property of an ideal opamp: Open Loop Gain Ao = infinity.

ii. Infinite Input Impedance and Zero Output Impedance

An ideal opamp has infinite input impedance and zero output impedance. The sketch in

Fig. 15 is used to illustrate these properties. From Fig. 15, it can be seen that I in is zero if

Rin is equal to infinity.

The second property of an ideal opamp: Rin= infinity or Iin=0.

Figure15. Model of opamp


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From Fig.15, we get that

If the output resistance Ro is very small, there is no drop in output voltage due to the

output resistance of an opamp.

The third property of an ideal opamp: Ro = 0.

iii. Infinite Bandwidth

An ideal opamp has an infinite bandwidth. A practical opamp has a limited bandwidth,

which falls far short of the ideal value. The variation of gain with frequency has been

shown in Fig. 16, which is obtained by modeling the opamp with a single dominant pole,

whereas the practical opamp may have more than a single pole. The asymptotic log-

magnitude plot in Fig. 16 can be expressed by a first-order equation shown below.

It is seen that two frequencies, wH and wT, have been marked in the frequency response

plot in Fig. 16.. Here wT is the frequency at which the gain A(jw) is equal to unity. If

A(jwT) is to be equal to unity,

Since Ao is very large, it means that wT = Ao * wH .


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Figure16. Change in gain of opamp with frequency

iv. Zero Noise Contribution and Zero Output Offset

A practical opamp generates noise signals, like any other device, whereas an ideal opamp

produces no noise. Premium opamps are available which contribute very low noise to the

rest of circuits. These devices are usually called as premium low noise types. The output

offset voltage of any amplifier is the output voltage that exists when it should be zero. In

an ideal opamp, this offset voltage is zero.

PRACTICAL OPERATIONAL AMPLIFIERS

This section describes the properties of practical opamps and relates these characteristics

to design of analog electronic circuits. A practical operational amplifier has limitations to

its performance. It is necessary to understand these limitations in order to select the

correct opamp for an application and design the circuit properly.

Like any other semiconductor device, a practical opamp also has a code number.

For example, let us take the code LM 741CP. The first two letters, LM here, denote the

manufacturer. The next three digits, 741 here, is the type number. 741 is a general-purpose opamp. The letter following the type number, C here, indicates the temperature

range. The temperature range codes are: (i) C commercial 0 o C to 70o C; (ii) I industrial

-25 o C to 85o C; and (iii) M military -55 o C to 125 o C.


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The last letter indicates the package. Package codes are: (i) D Plastic dual-in-line for

surface mounting on a pc board; (ii) J Ceramic dual-in-line; and (iii) N, P Plastic dual-in-

line for insertion into sockets.

Standard Operational Amplifier Parameters

Understanding operational amplifier circuits requires knowledge of the parameters given

in specification sheets. The list below represents the most commonly needed parameters.

Open-Loop Voltage Gain. Voltage gain is defined as the ratio of output voltage to an

input signal voltage, as shown in Fig. 14. The voltage gain is a dimensionless quantity.

Large Signal Voltage Gain. This is the ratio of the maximum allowable output voltage

swing (usually one to several volts less than V- and V++) to the input signal required to

produce a swing of 10 volts (or some other standard).

Slew rate. The slew rate is the maximum rate at which the output voltage of an opamp

can change and is measured in terms of voltage change per unit of time. It varies from 0.5

V/us to 35 V/us. Slew rate is usually measured in the unity gain noninverting amplifier

configuration.

Common Mode Rejection Ratio. A common mode voltage is one that is presented

simultaneously to both inverting and noninverting inputs. In an ideal opamp, the output

signal due to the common mode input voltage is zero, but it is nonzero in a practicaldevice. The common mode rejection ratio (CMRR) is the measure of the device's ability

to reject common mode signals, and is expressed as the ratio of the differential gain to the

common mode gain. The CMRR is usually expressed in decibels, with common devices

having ratings between 60 dB to 120 dB. The higher the CMRR is, the better the device

is deemed to be.

Input Offset Voltage. The dc voltage that must be applied at the input terminal to force

the quiescent dc output voltage to zero or other level, if specified, given that the input

signal voltage is zero. The output of an ideal opamp is zero when there is no input signal

applied to it.


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Power-supply rejection ratio. The power-supply rejection ratio PSRR is the ratio of the

change in input offset voltage to the corresponding change in one power-supply, with all

remaining power voltages held constant. The PSRR is also called "power supply

insensitivity". Typical values are in uV / V or mV/V.

Input Bias Current. The average of the currents into the two input terminals with the

output at zero volts.

Input Offset Current. The difference between the currents into the two input terminals

with the output held at zero.

Differential Input Impedance. The resistance between the inverting and the

noninverting inputs. This value is typically very high: 1 MS in low-cost bipolar opamps

and over 1012 Ohms in premium BiMOS devices.

Common-mode Input Impedance

The impedance between the ground and the input terminals, with the input terminals tied

together. This is a large value, of the order of several tens of MS or more.

Output Impedance. The output resistance is typically less than 100 Ohms.

Average Temperature Coefficient of Input Offset Current. The ratio of the change in

input offset current to the change in free-air or ambient temperature. This is an average

value for the specified range.

Average Temperature Coefficient of Input Offset Voltage. The ratio of the change in

input offset voltage to the change in free-air or ambient temperature. This is an average

value for the specified range.

Output offset voltage. The output offset voltage is the voltage at the output terminal

with respect to ground when both the input terminals are grounded.

Output Short-Circuit Current. The current that flows in the output terminal when the

output load resistance external to the amplifier is zero ohms (a short to the common

terminal).


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Channel Separation. This parameter is used on multiple opamp ICs (device in which

two or more opamps sharing the same package with common supply terminals). The

separation specification describes part of the isolation between the opamps inside the

same package. It is measured in decibels. The 747 dual opamp, for example, offers 120

dB of channel separation. From this specification, we may state that a 1 uV change will

occur in the output of one of the amplifiers, when the other amplifier output changes by 1

volt.

Minimum and Maximum Parameter Ratings

Operational amplifiers, like all electronic components, are subject to maximum ratings. If

these ratings are exceeded, the device failure is the normal consequent result. The ratings

described below are commonly used.

Maximum Supply Voltage. This is the maximum voltage that can be applied to the

opamp without damaging it. The opamp uses a positive and a negative DC power supply,

which are typically 18 V.

Maximum Differential Supply Voltage. This is the maximum difference signal that can

be applied safely to the opamp power supply terminals. Often this is not the same as the

sum of the maximum supply voltage ratings. For example, 741 has 18 V as the

maximum power supply voltage, whereas the maximum differential supply voltage is

only 30 V. It means that if the positive supply is 18 V, the negative supply can be only

-12 V.

Power dissipation, Pd. This rating is the maximum power dissipation of the opamp in

the normal ambient temperature range. A typical rating is 500 mW.

Maximum Power Consumption. The maximum power dissipation, usually under output

short circuit conditions, that the device can survive. This rating includes both internal

power dissipation as well as device output power requirements.

Maximum Input Voltage. This is the maximum voltage that can be applied

simultaneously to both inputs. Thus, it is also the maximum common-mode voltage. Inmost bipolar opamps, the maximum input voltage is nearly equal to the power supply

voltage. There is also a maximum input voltage that can be applied to either input when

the other input is grounded.


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Differential Input Voltage. This is the maximum differential-mode voltage that can be

applied across the inverting and noninverting inputs.

Maximum Operating Temperature. The maximum temperature is the highest ambient

temperature at which the device will operate according to specifications with a specified

level of reliability.

Minimum Operating Temperature. The lowest temperature at which the device

operates within specification.

Output Short-Circuit Duration. This is the length of time the opamp will safely sustain

a short circuit of the output terminal. Many modern opamps can carry short circuit

current indefinitely.

Maximum Output Voltage. The maximum output potential of the opamp is related to

the DC power supply voltages. Typical for a bipolar opamp with 15V power supply,

the maximum output voltage is typically about 13 V and the minimum - 13 V.

Maximum Output Voltage Swing. This is the maximum output swing that can be

obtained without significant distortion (at a given load resistance).

Full-power bandwidth. This is the maximum frequency at which a sinusoid whose size

is the output voltage range is obtained.


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Comparisons and Typical Values

Table presents a summary of features of an ideal and a typical practical opamp.

Comparison of an ideal and a typical practical op amp

Basic Opamp Applications

Noninverting Amplifier

The basic noninverting amplifier can be represented as shown in Fig. 17. Note that a

circuit diagram normally does not show the power supply connections explicitly.


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Figure17.Non-Inverting Amplifier

Analysis for an Ideal Opamp

An ideal opamp has infinite gain. This means that

1

Thus,

2

An ideal opamp has infinite input resistance. That is,

3

4

We obtain the output voltage as:

5

The gain of the noninverting amplifier is then:

6


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Analysis for an Opamp with a finite gain, Ao

Let the opamp have a finite gain. Then the noninverting amplifier can be represented by

the equivalent circuit in Fig.18.

Figure18. Equivalent Circuit

On re-arranging,

7

We can represent the circuit in Fig.18 by a block diagram that represents the feedback

that is present in the circuit. From Fig.18, we can state that,

The above equation can be represented by a block diagram as shown in Fig.19

From the block diagram, we get the same expression for the gain of the circuit. It can be

seen that if the open loop gain Ao tends to infinity, equation (7) reduces to equation (6).


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Figure19. Block diagram of Non-Inverting Amplifier

Figure20. An Inverting amplifier

Inverting Amplifeir

The inverting amplifier is analyzed below using both network theory and feedback theory

approach.

Analysis Based On Circuit Theory

Analysis is as follows. Apply KCL (Kirchoff's Current Law) at node `a' in Fig.

20, Then

For an ideal opamp, ii = 0. Hence is + i2 = 0. Thus the KCL at node 'a' is:


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For an ideal opamp, its output resistance is zero. Hence - Aovi = vo.

When the gain is infinity, vi is also zero. Therefore,

In other words,

When an opamp is considered to be ideal, vi and ii have zero value. If the NI input

(noninverting input) is grounded, the inverting input is at zero potential. We can find is &

i2 by treating the potential at inverting input terminal to be zero volts.

In this condition, the inverting input terminal behaves as if it is grounded and is called as

`virtual ground'. When the NI input is not grounded, the inverting input is not at ground

potential, it does not behave as if it is grounded and it is no longer called the virtual

ground. All that happens is that its potential is the same as that at the NI input.

Analysis Based on Negative Feedback

Now the circuit in Fig. 2.4 is to be represented as a system with feedback. From

Fig. 2.4, we get that

We can arrive at the result shown above by the use of either superposition theorem or by

adding the drop across R1 to Vs. From Fig.20, we get that

where Ao is the gain of the opamp. Here it is appropriate to call it as the opamp's open

loop gain. The above two equations can be represented by a block diagram as shown in

Fig.21


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Figure21. An operation Circuit connected as a System with negative feedback

For the block diagram in Fig.21, we get the ratio Vo/Vs as

Since the open loop gain tends to be infinite, we get the same ratio for Vo/Vs as obtained

earlier. In this case, the feedback that is present in the circuit is negative because the

opamp has a negative gain. An opamp has a negative gain when v i is measured as shown

in Fig.20.

3.4.2 Comparator

In electronics, a comparator is a device that compares two voltages orcurrents and

switches its output to indicate which is larger. They are commonly used in devices such

as Analog-to-digital converters (ADCs).

The LM193 series consists of two independent precision voltage comparators with an

offset voltage specification as low as 2.0 mV max for two comparators which were

designed specifically to operate from a single power supply over a wide range of

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. Thesecomparators also have a unique characteristic in that the input common-mode voltage

range includes ground, even though operated from a single power supply voltage.
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Application areas include limit comparators, simple analog to digital converters; pulse,

square wave and time delay generators; wide range VCO; MOS clock timers;

multivibrators and high voltage digital logic gates. The LM193 series was designed to

directly interface with TTL and CMOS. When operated from both plus and minus power

supplies, the LM193 series will directly interface with MOS logic where their low power

drain is a distinct advantage over standard comparators.

Figure22. Internal Block Diagram of LM393

Applications

High precision comparators

Reduced VOS drift over temperature

Eliminates need for dual supplies

Allows sensing near ground

Compatible with all forms of logic

Power drain suitable for battery operation


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Output Circuitry

The comparators are all open collector outputs. A diagram of the output circuitry showing

how the comparator is connected to the output transistor, and how the collector of the

transistor is connected to the output terminal on the chip.In this situation, the transistoracts like a switch.

When the output of the comparator is a 1, current flows from the comparator

through the base of the transistor, out the emitter to ground, as shown.

When that current flows, the transistor acts like a switch that permits current to

flow from the collect to the emitter to ground.

The way we connect the comparator is to put our load between five volts and the

collector connection on the chip - like this.


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3.4.3 Monostable Multivibrators

Multivibrators are Sequential regenerative circuits either synchronous or asynchronous

that are used extensively in timing applications. Multivibrators produce an output wave

shape of a symmetrical or asymmetrical square wave and are the most commonly used of

all the square wave generators. Multivibrators belong to a family of oscillators commonly

called "Relaxation Oscillators".

Monostable Multivibrators have only ONE stable state (hence their name: "Mono"),

and produce a single output pulse when it is triggered externally. Monostable

multivibrators only return back to their first original and stable state after a period of time

determined by the time constant of the RC coupled circuit. Monostable multivibrators or

"One-Shot Multivibrators" as they are also called, are used to generate a single output

pulse of a specified width, either "HIGH" or "LOW" when a suitable external trigger

signal or pulse T is applied. This trigger signal initiates a timing cycle which causes the

output of the monostable to change its state at the start of the timing cycle and will

remain in this second state, which is determined by the time constant of the timing

capacitor, CT and the resistor, RT until it resets or returns itself back to its original (stable)

state as shown in fig.23. It will then remain in this original stable state indefinitely until

another input pulse or trigger signal is received.
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Figure23. Monostable multivibrator waveform

74121 Monostable multivibrator

0.0.1 This monostable pulse generator IC can be configured to produce an output pulse

on either a rising-edge trigger pulse or a falling-edge trigger pulse. The 74121 can

produce pulse widths from about 10ns to about 10ms width a maximum timing resistor of

40k and a maximum timing capacitor of 1000uF.

3.4.4 Decade Counter

In digital logic and computing, a counter is a device which stores (and sometimes

displays) the number of times a particularevent or process has occurred, often in

relationship to a clock signal.A decade counter is one that counts in decimal digits, rather

than binary. A decade counter may have each digit binary encoded (that is, it may count

in binary-coded decimal, as the 7490 integrated circuit did) or other binary encodings

(such as thebi-quinary encoding of the 7490 integrated circuit). Alternatively, it may

have a "fully decoded" orone-hot output code in which each output goes high in turn

(the 4017 is such a circuit). The latter type of circuit finds applications

in multiplexers and demultiplexers, or wherever a scanning type of behavior is useful.

Similar counters with different numbers of outputs are also common. The decade counter

is also known as a mod-counter when it counts to ten (0, 1, 2, 3, 4, 5, 6, 7, 8, 9). A Mod

Counter that counts to 64 stops at 63 because 0 counts as a valid digit.
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7490 Decade Counter

The 7490 IC can be configured into different modes depending on the applications

required. In its most common mode, the 7490 is used as a general purpose decade

counter, where only one of its 10 lines is active at any given time. Sending in clock pulses into its CLK input pin causes the currently active line to shut off and

consequentially enables the next line in the sequence. After ten occurrences of this

pattern, the device resets and line 0 starts the sequence over. By running one of the output

lines into the reset pin, count sequences can be controlled to any length from one to ten.

3.4.5 Design of Power Supply

Purpose for making power supply circuit

A power supply is a vital part of all electronic systems. To design any electronic circuit

we must require regulated power supply because most digital ICs, including

microprocessors and memory ICs, operate on a +5v supply, while almost all linear ICs

(op-amps and special-purpose ICs) require +12V and -12 V supplies.

Description

A powersupply is a device that supplies electricalenergy to one or more electric loads.

The term is most commonly applied to devices that convert one form of electrical energy

to another, though it may also refer to devices that convert another form of energy (e.g.,

mechanical, chemical, solar) to electrical energy. A regulated power supply is one that

controls the output voltage or current to a specific value; the controlled value is held

nearly constant despite variations in either load current or the voltage supplied by the

power supply's energy source.

Figure24. Block Diagram of a typical Power Supply.

Transformer

Rectifier

Filter

Regulator

~230 V50 Hz

+

-

RegulatedOutput
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Fig.24. shows the block diagram of a typical power supply. The schematic diagram of the

power supply that provides output voltages of +12V and -12V and +5V is shown in

Fig.25. The supply voltages are obtained from 26.8-V centre-tapped (CT) transformer.

The output of these secondaries is then applied to the bridge rectifiers, which convert the

sinusoidal inputs into full-wave rectified outputs. The filter capacitors at the output of the

bridge rectifiers are charged to the peak value of the rectified output voltage whenever

the diodes are forward biased. Since the diodes are not forward biased during the entire

positive and negative half-cycle of the input waveform, the voltage across the filter

capacitors is a pulsating dc that is a combination of dc and a ripple voltage. From the

pulsating dc voltage, a regulated dc voltage is extracted by a regulator IC.

The +12V and -12V supply voltages are obtained in the circuit using 7812 and 7912 IC

regulators and both can deliver output current in excess of 1.0 A. They perform

satisfactorily in the circuit by providing +12V and -12V at 0.500A.However, since the

drop-out voltage (Vin-Vout) is 2v, the input voltage for the 7812 must be atleast +14v

and that for the 7912 must be atleast -14V, which in turn implies that the secondary

voltage must be larger than 28V peak or 20Vrms. The voltage across the centre-tapped

secondary is 26.8vrms, thus satisfying the minimum voltage requirement of 20Vrms.

Also, the peak voltage between either of the secondary terminals and the centre-tap

(ground terminal) is 18.95V peak, which is less than the maximum peak voltages of

+28V and -28V for the 7812 and 7912, respectively. The voltages across the two halves

of the centre-tapped secondary are equal in magnitude but opposite in phase. During the

positive half-cycle of the input voltage, diode D1 conducts and capacitor C1 charges

toward a positive peak value (18.95V). At the same time, diode D3 is also conducting;

hence capacitor C3 charges towards a negative peak value (-18.95V). This means that the

voltage across non-conducting diodes D2 and D4 is 37.90V peak, which implies that the

peak reverse voltage (PRV) rating of the bridge rectifier must be larger than 37.90V peak.

Finally, the size of the filter capacitor (C1 and C3) depends on the secondary current

rating of the transformer. Capacitors C2 and C4 at the output of ICs regulators are used to

help in improving the transient response.


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Figure25. Schematic Diagram of the Power Supply

Transformer only

Transformers convert AC electricity from one voltage to another with little loss of power.

Transformers work only with AC and this is one of the reasons why mains electricity is

AC. Step-up transformers increase voltage, step-down transformers reduce voltage. Most

power supplies use a step-down transformer to reduce the dangerously high mains

voltage (230V) to a safer low voltage.

The input coil is called the primary and the output coil is called the secondary. There is

no electrical connection between the two coils; instead they are linked by an alternating


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magnetic field created in the soft-iron core of the transformer. The two lines in the middle

of the circuit symbol represent the core. Transformers waste very little power so the

power out is (almost) equal to the power in. Note that as voltage is stepped down current

is stepped up. The ratio of the number of turns on each coil, called the turns ratio,

determines the ratio of the voltages. A step-down transformer has a large number of turns

on its primary (input) coil which is connected to the high voltage mains supply, and a

small number of turns on its secondary (output) coil to give a low output voltage.

Transformer + Rectifier

Thevarying DCoutput is suitable for lamps, heaters and standard motors. It

isnotsuitable for electronic circuits unless they include a smoothing capacitor. A bridge

rectifier can be made using four individual diodes, but it is also available in special

packages containing the four diodes required. It is called a full-wave rectifier because it

uses the entire AC wave (both positive and negative sections). 1.4V is used up in the

bridge rectifier because each diode uses 0.7V when conducting and there are always two

diodes conducting, as shown in the diagram below. Bridge rectifiers are rated by the

maximum current they can pass and the maximum reverse voltage they can withstand

(this must be at least three times the supply RMS voltage so the rectifier can withstand

the peak voltages).
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Transformer + Rectifier + Smoothing

Thesmooth DCoutput has a small ripple. It is suitable for most electronic circuits.

Smoothing is performed by a large value electrolytic capacitorconnected across the DCsupply to act as a reservoir, supplying current to the output when the varying DC voltage

from the rectifier is falling. The diagram shows the unsmoothed varying DC (dotted line)

and the smoothed DC (solid line). The capacitor charges quickly near the peak of the

varying DC, and then discharges as it supplies current to the output.

Note that smoothing significantly increases the average DC voltage to almost the peak

value (1.4 RMS value). For example 6V RMS AC is rectified to full wave DC of about

4.6V RMS (1.4V is lost in the bridge rectifier), with smoothing this increases to almost

the peak value giving 1.4 4.6 = 6.4V smooth DC.
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Smoothing is not perfect due to the capacitor voltage falling a little as it discharges,giving a small ripple voltage. For many circuits a ripple which is 10% of the supply

voltage is satisfactory. A larger capacitor will give less ripple.

Transformer + Rectifier + Smoothing + Regulator

The regulated DC output is very smooth with no ripple. It is suitable for all electronic

circuits. Voltage regulator ICs are available with fixed (typically 5, 12 and 15V) or

variable output voltages. They are also rated by the maximum current they can pass.

Negative voltage regulators are available, mainly for use in dual supplies. Most regulators

include some automatic protection from excessive current ('overload protection') and

overheating ('thermal protection').

The 78xx Series of Regulators

TypeNumber

Regulation

Voltage

MaximumCurrent

Minimum Input

Voltage

7805 +5V 1A +7V

7806 +6V 1A +8V7808 +8V 1A +10.5V

7812 +12V 1A +14.5V

7815 +15V 1A +17.5V

7824 +24V 1A +26V


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The 78xx regulators all have the pin-out shown in the left of figure.26

and are normally supplied in a case style known as TO-220.


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The 79xx Series of Regulators

TypeNumber

Regulation

Voltage

MaximumCurrent

Minimum Input

Voltage

7905 -5V -1A -7V

7906 -6V -1A -8V

7908 -8V -1A -0.5V

7912 -12V -1A -14.5V

7915 -15V -1A -17.5V

7924 -24V -1A -26V

The 79xx regulators all have the pin-out shown in the right of

figure.26 and are normally supplied in a case style known as TO-220.

Figure26. Pin-out diagram of ICs 78XX and 79XX

Components used

Transformer Primary: 230V, 50Hz

Secondary: 26.8V CT, 1.0A

Diodes 1N4007 (4): PRV =1000V

Iomax = 1.0A

IFSM = 30A

Electrolytic Capacitors 100uF (3).47uF (3)

Regulators +12V: MC7812

-12V: MC7912

+ 5V: MC7805


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3.4.6Design of Signal Detection and Processing Unit

The circuit shown in fig.27 is designed to sense the acoustic signal and count the number

of pulses. The acoustic signal is sensed by a piezoelectric transducer. The transducer

made of barium titanate material (BaTiO3) is used to sense the signal, which converts theacoustic signal into electrical signal. The output signal of transducer is relatively small

signal and contaminated with noise signal. This signal needs to be amplified in order to

increase its strength and reduce the contaminated noise. The operational amplifiers are

used to amplify the signal. The two op-amp IC 741 in a closed-loop configuration as

inverting amplifier are connected in cascade to form an amplifying stage. The amplified

signal is then passed through a comparator (IC 393) to eliminate noise by adjusting the

voltage range and obtain a TTL pulse. The TTL pulse is applied as a trigger input to a

monostable multivibrator IC 74121. The Monostable Multivibrator circuit has

only ONE stable state making it a "one-shot" pulse generator, once triggered by a short

external trigger pulse either positive or negative, the monostable changes state and

remains in this second state for an amount of time determined by the preset time period of

the RC feedback timing components used. Once this time period has passed the

monostable automatically returns itself back to its original low state awaiting a second

trigger pulse.This monostable pulse generator IC can be configured to produce an output

pulse on either a rising-edge trigger pulse or a falling-edge trigger pulse. The 74121 can

produce pulse widths from about 10ns to about 10ms width a maximum timing resistor of

40k and a maximum timing capacitor of 1000uF. The output of the monostable

multivibrator can be given to a decade counter and a seven segment display to count and

display the number of pulses.


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Figure27. Schematic Diagram of Acoustic Signal Detection and processing Unit

Description of counter circuit

The circuit shown (Fig.28) is of a simple 0 to 9 display that can be employed in a lot of

applications. The circuit is based on asynchronous decade counter 7490(IC2), a 7

segment display (D1), and a seven segment decoder/driver IC 7446 (IC1). The seven

segment display consists of 7 LEDs labelled a through g. By forward biasing different

LEDs, we can display the digits 0 through 9. Seven segment displays are of two types,

common cathode and common anode. In common anode type anodes of all the seven

LEDs are tied together, while in common cathode type all cathodes are tied together. The

seven segment display used here is a common anode type .Resistor R1 to R7 are current

limiting resistors. IC 7446 is a decoder/driver IC used to drive the seven segment display.

Working of this circuit is very simple. For every clock pulse the BCD output of the IC2

(7490) will advance by one bit. The IC1 (7446) will decode this BCD output to

corresponding the seven segment form and will drive the display to indicate the

corresponding digit.

U 9

S N 7 4 9 0

1 4

1

1 2

9

8

1 12

3

6

7

C L K A

C L K B

Q A

Q B

Q C

Q DR 0 1R 0 2

R 9 1

R 9 2

1 0 K

D r i v e r I C

A m p l i f i e r S t a g e

U 6

7 4 4 6

7

1

2

6

4

5

3

1 3

1 2

1 1

1 0

9

1 5

1 4

D 0

D 1

D 2

D 3

B I / R B O

R B I

L T

A

B

C

DE

F

G

-

+

U 2

L M 7 4 1

3

2

6

7 1

4 5

+ 5 V- 1 2 V

+ 1 2 V

A c o u s t i cS i g n a l

1 0 K

+ 5 V

R 5

-

+

U 3 A

L M 3 9 33

2

1

8

4 C 1

+ 5 V

J 1

1 2

1 K

1 K

- 1 2 V

-

+

U 2

L M 7 4 1

3

2

6

7 1

4 5

1 K

+ 1 2 V 1 0 K

U 1 0

7 4 L 1 2 1

9

3

4

5

6

1

1 0

1 1

R I N T

A 1

A 2

B

Q

Q

C E X T

R E X T / C E X T

P i e z o e l e c t r i cT r a n s d u c e r

D e c a d e C o u n t e r

1 K

1 K

+ 5 V

M o n o s t a b l e MC o m p a r a t o r


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Figure28. Schematic of the circuit diagram of decade counter and seven segment

display

Components used

Piezoelectric transducer made up of BaTiO3 material

Op-amp IC 741(2)

Comparator IC 393Monostable Multivibrator IC 74121

Decade Counter IC 7490

Driver IC7446

Capacitor 100uF

Resistors 220ohm (10)

1kohm (5)

2kohm

10kohm (3)

Trim port 10kohm

Seven segment display


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1.

4. Applications

The Acoustic Signal Detection & Processing Circuit is highly an important circuit with

many applications. Some of the important applications of this circuit include:

(i) To measure the levels of vibrations. The device can be used to detect and monitor

vibrational noise.

(ii) In combination with microcontroller and source of ultrasonic radiation, this circuit

can also be used as a component of proximity switch. Such devices find applications in

the automatic sector on cars and other vehicles.

(iii) Along with bubble detectors it is used to determine the radiation levels. Hence may

find applications in radiation dosimetry.


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5. Conclusion

The report describes the circuit Acoustic Signal Detection and Processing Unit for the

detection of an acoustic signal from the Superheated Liquid Neutron Sensor (SLNS)

developed at DRDO, Defence Laboratory, Jodhpur and its further signal processing to

obtain output in the form of a pulse. In beginning of the report a brief introduction about

different types of nuclear radiations together with their characteristics and applications is

given. Further, mechanism of interaction of radiation with matter has been described

which forms the basis for their detection. Barium titanate has been used as the

piezoelectric sensor for the detection of acoustic signals coming from SLNS. Various

circuit elements viz. amplifier based on OP AMP 741, comparator based on LM 393,

multi-vibrator based on IC 74121 and counter based on IC 7490 were fabricated for the

processing of the signal obtained from the acoustic sensor. The functioning of all

individual circuit elements was verified with help of CRO. A circuit for the power supply

with outputs of +12V, -12V and +5V was also fabricated for providing power to the

above referred circuit elements. All the circuit elements were integrated with the detector

to develop the Acoustic Signal Detection and Processing Unit.


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Appendix

DATA SHEETS

I. 1N4001 -1N4007

General Purpose Rectifiers (Glass Passivated)

1.1 Features:

Low forward voltage drop.

High surge current capability

1.2 Absolute Maximum Ratings* TA = 25C unless otherwise noted:

These ratings are limiting values above which the serviceability of any semiconductor device may be impaired


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1.3 Thermal Characteristics:

1.4 Electrical Characteristics TA = 25C unless otherwise noted

II. MC78XX/LM78XX/MC78XXA

3-Terminal 1A Positive Voltage Regulator

2.1 Absolute Maximum Ratings:


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2.2 Electrical Characteristics (MC7805/LM7805):

Refer to test circuit, 0C < TJ < 125C, IO = 500mA VI = 10V, CI= 0.33 F,

CO= 0.1F, unless otherwise specified

Note:

1. Load and line regulation are specified at constant junction temperature. Changes in Vo due to heating effects

must be taken into account separately. Pulse testing with low duty is used


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2.3 Electrical Characteristics (MC7812):

Refer to test circuit, 0C < TJ < 125C, IO = 500mA VI =19V, CI= 0.33F,

CO=0.1F, unless otherwise specified

Note:

1. Load and line regulation are specified at constant junction temperature. Changes in Vo due to heating effects



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III. LM79XX Series

3-Terminal Negative Regulators

3.1 Features:

Thermal, short circuit and safe area protection High ripple rejection

1.5A output current

4% tolerance on preset output voltage

3.2 ABSOLUTE MAXIMUM RATINGS (TA=+25C, unless otherwise

specified):


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3.3 LM7905

ELECTRICAL CHARACTERISTICS:

V1= 10V, Io =500mA, 0C=T=1250C C1=2.2F, Co=1F, unless

otherwise specified.

* Load and line regulation are specified at constant junction temperature. Changes in VO due to heating effects



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3.4 LM7912

ELECTRICAL CHARACTERISTICS:

V1= 18V, Io =500mA, 0C=T=125C C1=2.2F, Co=1F, unless otherwise

specified.

* Load and line regulation are specified at constant junction temperature. Changes in VO due to heating effects



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IV. LM741

Operational Amplifier

4.1 General Description:

The LM741 series are general purpose operational amplifiers which feature

improved performance over industry standards like the LM709. They are direct, plug-inreplacements for the 709C, LM201, MC1439 and 748 in most applications. The

amplifiers offer many features which make their application nearly foolproof:

overload protection on the input and output, no latch-up when the common mode

range is exceeded, as well as freedom from oscillations. The LM741C/LM741E areidentical to the LM741/LM741A except that the LM741C/LM741E have their

performance guaranteed over a 00C to 700C temperature range, instead of -550C to

+1250C

4.2 Absolute Maximum Ratings:


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4.3 Electrical Characteristics:


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4.4 Connection Diagrams:


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V LM193/ LM293/ LM393

LOW POWER DUAL VOLTAGE COMPARATORS

ELECTRICAL CHARACTERISTICS:Vcc+= +5V, Vcc-= 0V, Tamb= +25C (unless otherwise specified)

VI SN54121, SN74121

Monostable Multivibrators with Schmitt-Trigger Inputs


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VII DM7490A

Decade and Binary Counters


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7. References

The supporting Apparatus used were:

CATHODE RAY OSCILLOSCOPE

FUNCTION GENERATORELECTRONIC WORK BENCH

SOLDERING AND DESOLDERING STATION

Following books and websites proved to be a helping hand:

Op-Amps and Linear Integrated Circuits

By Ramakant A.GayakwadDIGITAL CIRCUITS AND DESIGNS

By S. Salivahnan and S. Arivazhaganwww.datasheetcatalog.com

en.wikipedia.org

For designing the circuits and layouts following softwares were

used:

ORCAD 9.2 LITE EDITION

PCB Express

Multisim
http://www.datasheetcatalog.com/http://www.datasheetcatalog.com/

Practical Training Report 1

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