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