Basics of Electrical,
Electronics and
Communication Engineering
K. A. NAVAS
Asst.Professor in ECE
Govt. Engineering College
Thrissur-9
kanavas@rediffmail.com
T. A. Suhail
Lecturer in ECE
Al-Ameen Engineering College
Shoranur-2
suhailta@gmail.com
Rajath Publishers
28/450-A, Club Road, Girinagar South, Kadavanthra, Kochi-682020
Basics of Electrical, Electronics and Communication Engineering
First edition
c
Copyright 2010
Rajath publishers and the authors jointly
This book is sold subjected to the condition that it shall not, by way of trade
or otherwise, be lent, resold, hired out, or otherwise circulated without publisher’s prior written consent in any form of binding or cover other than that
in which it is published and without a similar condition including this condition being imposed on the subsequent purchaser and without limiting the
rights under copyright reserved above, no part of this publication may be reproduced, stored in or introduced into a retrieval system, or transmitted in
any form or by any means (electronic, mechanical, photocopying, recording
or otherwise), without prior permission of the copyright owner.
Published by
Rajath Publishers
28/450-A, Club Road, Girinagar South
Kadavanthra, Kochi-682020
Phone:0484-2313911
e-mail:rajathpbs@yahoo.com
Price: Rs. 150.00
Type set in LATEX
Printed at Pioneer offset, Ravipuram, Kochi-15
Preface
This is an introductory level text book in electrical, electronics and
communication Engineering. It is prepared as per the syllabus for first
year B Tech in Calicut University. The resources used were many internationally reputed text books, suggestions from experienced faculty
members and students from electrical science branches of engineering
in various engineering institutions. This book intended also for the
students in non-electrical science branches.
We seek for suggestions from the readers for improving the book
in future editions.
Acknowledgements
With the deepest sense of gratitude we realize the invaluable helps and
encouragements rendered by many individuals during the preparation
of this book. It is unable to mention names of all of them due to the
limitation of available space.
We would like to express our indebtitude to Prof. P.A. Mercy, Prof.
Jose Jacob, Dr. M. Nandakumar, Smt. V. Beena, Sri. M.V Jayan, Sri.
T. G. Sanishkumar, Sri. Suresh K Damodaran and Smt. M. S. Sunila
of EEE Dept., Dr. Indiradevi, Sri. B. Premanand and Smt. T. Latha of
ECE Dept. of of Govt. Engineering College, Thrissur (GCET), Prof.
K. P Ahmed Koya, Sri. V. P Basheer, Smt. Sushma M, Smt. Thazni
K. H., Smt. Bindu. P, Smt. Laina A, Sri. Anoop V, Sri. Ashok K,
Sri. Mohammed Bin Shanavaz of ECE Dept., Sri. Harikrishnan B.S.,
Sri. Abdul Nazir E. K. and Sri. Faisal P of EEE Dept. of Al-Ameen
Engineering College, Shoranur, Sri. Riyas K. S, Rajiv Gandhi Institute
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of Technology, Kottayam, Prof. N. Ahmed kutty, IES College of Engineering, Thrissur for their invaluable suggestions, encouragement and
helps.
We would like to thank Dr. K Vijayakumar, Principal, GECT,
Dr. K. V Narayanan, Former Principal, Al-Ameen Engineering College, all the teaching and non-teaching faculty members of Electronics
& Communication Engineering and Electrical & Electronics Departments of GCET, Govt. Engineering College, Sreekrishnapuram and
Al-Ameen Engineering College for their support.
We place it on record our sincere thanks to the students of ECE
Dept of GECT for their strenuous efforts on proof reading.
We appreciate the support given by our family members during this
work.
Authors
iv
Contents
1
2
3
Basic Concepts in Electrical Engineering
1.1 Introductory concepts and basic elements . .
1.2 Resistances in series . . . . . . . . . . . . .
1.3 Resistances in parallel . . . . . . . . . . . . .
1.4 Effect of temperature on resistance . . . . . .
1.5 Ideal and non-ideal dc voltage sources . . . .
1.6 Ideal and non-ideal dc current sources . . . .
1.7 Open circuit voltage and short circuit current
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Kirchoff’s laws
2.1 Kirchoff’s Laws . . . . . . . . . . . . . . . . .
2.1.1 Kirchoff’s Current Law (KCL) . . . . .
2.1.2 Kirchoff’s Voltage Law (KVL) . . . . .
2.1.3 Steps to solve circuits by Kirchoff’s law
2.2 Voltage divider circuit . . . . . . . . . . . . . .
2.3 Current divider circuit . . . . . . . . . . . . . .
2.4 Source transformation . . . . . . . . . . . . . .
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Magnetic circuits
3.1 Introduction . . . . . . . . . . . . . . . . . . . . .
3.2 Magnetic field around a bar magnet . . . . . . . .
3.3 Magnetic field around a current carrying conductor
3.4 Magnetic flux . . . . . . . . . . . . . . . . . . . .
3.5 Magnetic flux density . . . . . . . . . . . . . . . .
3.6 Magneto motive force . . . . . . . . . . . . . . . .
3.7 Magnetic field intensity . . . . . . . . . . . . . . .
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xii
CONTENTS
3.8
3.9
3.10
3.11
3.12
3.13
4
Permeability . . . . . . . . . . . . . . . . . . . . .
Relative permeability . . . . . . . . . . . . . . . .
Reluctance . . . . . . . . . . . . . . . . . . . . . .
Permeance . . . . . . . . . . . . . . . . . . . . . .
Leakage flux in magnetic circuit . . . . . . . . . .
Electromagnetic induction . . . . . . . . . . . . .
3.13.1 Faraday’s laws of electromagnetic induction
3.13.2 Lenz’s law . . . . . . . . . . . . . . . . .
3.13.3 Electromagnetically Induced emf . . . . .
3.13.4 Dynamically Induced emf . . . . . . . . .
3.13.5 Fleming’s right hand rule (Generator rule) .
3.13.6 Fleming’s left hand rule (Motor rule) . . .
3.13.7 Statically induced emf . . . . . . . . . . .
3.13.8 Self induced emf . . . . . . . . . . . . . .
3.13.9 Self inductance . . . . . . . . . . . . . . .
3.13.10 Mutually induced emf . . . . . . . . . . .
3.13.11 Mutual inductance . . . . . . . . . . . . .
3.13.12 Coefficient of coupling . . . . . . . . . . .
Single Phase AC Circuits
4.1 AC Fundamentals . . . . . . . . . . . . . . . . .
4.2 Generation of sinusoidal emf . . . . . . . . . . .
4.3 Definitions . . . . . . . . . . . . . . . . . . . . .
4.4 Phasor representation of alternating quantities . .
4.5 Forms of phasor representation . . . . . . . . . .
4.6 Addition and subtraction of two phasors . . . . .
4.7 Multiplication and division of two phasors . . . .
4.8 AC through a purely resistive circuit . . . . . . .
4.9 AC through a purely inductive circuit . . . . . . .
4.10 AC through a purely capacitive circuit . . . . . .
4.11 AC through series R-L circuit . . . . . . . . . . .
4.12 AC through series R-C circuit . . . . . . . . . .
4.13 AC through series R-L-C circuit . . . . . . . . .
4.14 Active power, reactive power and apparent power
4.14.1 Active power (P) . . . . . . . . . . . . .
4.14.2 Reactive power (Q) . . . . . . . . . . . .
4.14.3 Apparent power (S) . . . . . . . . . . . .
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CONTENTS
4.14.4 Power factor . . . . . . . . . . . . . . . .
Impedance in polar and rectangular forms . . . . .
Admittance . . . . . . . . . . . . . . . . . . . . .
Resonance in series RLC circuit . . . . . . . . . .
Resonance in parallel RLC circuit . . . . . . . . .
Comparison of series and parallel resonant circuits
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Three Phase Circuits
5.1 Introduction . . . . . . . . . . . . . . . . . . . . .
5.2 Advantages of three-phase system . . . . . . . . .
5.3 Generation of 3-phase ac voltage . . . . . . . . . .
5.4 Phase sequence . . . . . . . . . . . . . . . . . . .
5.5 Three phase connections . . . . . . . . . . . . . .
5.6 Star or Wye (Y) connection . . . . . . . . . . . . .
5.6.1 Voltage and current in a Y connected circuit
5.6.2 Power in star connected system . . . . . .
5.6.3 Neutral current in Y connected system . . .
5.7 Delta or mesh connection . . . . . . . . . . . . . .
5.7.1 Power in delta connected system . . . . . .
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Transformers
6.1 Principle of operation . . . . . . . . . . . . .
6.2 Concept of an ideal transformer . . . . . . .
6.3 EMF equation . . . . . . . . . . . . . . . . .
6.4 Voltage transformation ratio and current ratio
6.5 Construction of transformer . . . . . . . . . .
6.5.1 Core type transformer . . . . . . . .
6.5.2 Shell type transformer . . . . . . . .
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4.15
4.16
4.17
4.18
4.19
5
6
7
xiii
DC machines
7.1 Introduction . . . . . . . . . . . . .
7.2 Principle of dc Generator . . . . . .
7.3 Simple loop generator . . . . . . . .
7.4 Constructional details of dc Machine
7.5 EMF equation of a dc generator . .
7.6 Types of dc generators . . . . . . .
7.7 Separately excited dc generator . . .
xiii
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xiv
CONTENTS
7.8
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Three phase induction motor
8.1 Introduction . . . . . . . . . . . . . . . . . . . . . . .
8.2 Construction . . . . . . . . . . . . . . . . . . . . . . .
8.2.1 Stator . . . . . . . . . . . . . . . . . . . . . .
8.2.2 Rotor . . . . . . . . . . . . . . . . . . . . . .
8.3 Concept of rotating magnetic field . . . . . . . . . . .
8.3.1 Principle of operation of induction motors . . .
8.3.2 Slip of an Induction motor . . . . . . . . . . .
8.3.3 Applications of three phase induction motors .
8.3.4 Comparison of squirrel cage induction motor
and slip ring induction motor . . . . . . . . . .
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Synchronous generators
9.1 Introduction . . . . . .
9.1.1 Construction .
9.2 Principle of operation .
9.2.1 EMF equation
7.9
8
9
Self excited dc generators . . . . . . . .
7.8.1 Shunt wound dc generator . . .
7.8.2 Series wound dc generator . . .
7.8.3 Compound wound dc generator
DC Motors . . . . . . . . . . . . . . .
7.9.1 Different types of dc motors . .
7.9.2 Applications of dc motors . . .
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10 Power system
10.1 Introduction . . . . . . . . . . . . . . . . .
10.2 Generation of electric power . . . . . . . .
10.3 Basic structure of AC power system . . . .
10.3.1 Typical power transmission scheme
10.4 Substations . . . . . . . . . . . . . . . . .
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11 Electrical estimation
185
11.1 Electrical installations-estimating and costing of material185
11.1.1 Steps for estimation . . . . . . . . . . . . . . 185
11.1.2 Example of wiring installation in a room . . . 186
xiv
CONTENTS
xv
12 Amplifiers and Oscillators
12.1 Principle of electronic amplifiers . . . . . . . . . . . .
12.2 Characteristics of an amplifier . . . . . . . . . . . . .
12.2.1 Gain . . . . . . . . . . . . . . . . . . . . . . .
12.2.2 Input resistance . . . . . . . . . . . . . . . . .
12.2.3 Output resistance . . . . . . . . . . . . . . . .
12.2.4 Equivalent circuit of an amplifier . . . . . . . .
12.3 Classification of amplifiers . . . . . . . . . . . . . . .
12.4 Frequency response of amplifier . . . . . . . . . . . .
12.5 Noise . . . . . . . . . . . . . . . . . . . . . . . . . .
12.5.1 Signal-to-noise ratio . . . . . . . . . . . . . .
12.6 Cascaded amplifiers . . . . . . . . . . . . . . . . . . .
12.7 Differential amplifiers . . . . . . . . . . . . . . . . . .
12.8 Concept of open loop and closed loop . . . . . . . . .
12.9 The operational amplifier . . . . . . . . . . . . . . . .
12.9.1 The ideal op-amp . . . . . . . . . . . . . . . .
12.9.2 Equivalent circuit of op-amp . . . . . . . . . .
12.9.3 Parameters of op-amp . . . . . . . . . . . . .
12.10Basic op-amp circuits . . . . . . . . . . . . . . . . . .
12.10.1 Non-inverting amplifier . . . . . . . . . . . . .
12.11Feedback systems . . . . . . . . . . . . . . . . . . . .
12.12Feedback in amplifiers . . . . . . . . . . . . . . . . .
12.12.1 The effects of negative feedback . . . . . . . .
12.12.2 Stabilization of gain with negative feedback . .
12.12.3 Frequency response and bandwidth . . . . . .
12.12.4 Effects of negative feedback on impedance . .
12.12.5 Reduction in distortion with negative feedback
12.12.6 Noise . . . . . . . . . . . . . . . . . . . . . .
12.12.7 Decrease in gain . . . . . . . . . . . . . . . .
12.13Oscillators . . . . . . . . . . . . . . . . . . . . . . . .
12.14Principle of oscillators . . . . . . . . . . . . . . . . .
12.15RC oscillators . . . . . . . . . . . . . . . . . . . . . .
12.15.1 Phase shift oscillator . . . . . . . . . . . . . .
12.15.2 Wien bridge oscillator . . . . . . . . . . . . .
12.16LC oscillators . . . . . . . . . . . . . . . . . . . . . .
12.16.1 Hartely oscillator . . . . . . . . . . . . . . . .
12.16.2 Colpitts oscillator . . . . . . . . . . . . . . . .
xv
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xvi
CONTENTS
12.16.3 Crystal oscillators
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13 Digital Systems
13.1 Digital systems . . . . . . . . . . . . . . . . . . . . .
13.1.1 Digital logic states . . . . . . . . . . . . . . .
13.1.2 Logic gates . . . . . . . . . . . . . . . . . . .
13.1.3 Compound gates . . . . . . . . . . . . . . . .
13.1.4 Universal gates . . . . . . . . . . . . . . . . .
13.1.5 Boolean algebra . . . . . . . . . . . . . . . .
13.2 De Morgan’s theorem . . . . . . . . . . . . . . . . . .
13.3 Forms of Boolean expressions . . . . . . . . . . . . .
13.3.1 Sum of Products (SOP) . . . . . . . . . . . . .
13.3.2 Product of Sums (POS) . . . . . . . . . . . . .
13.4 Simplification of Boolean expressions . . . . . . . . .
13.5 Generating Boolean expression from truth table . . . .
13.6 Implementing circuits from Boolean expressions . . .
13.7 Generating Boolean expression from logic circuit . . .
13.8 Implementation of logic circuits using universal gates .
13.8.1 Implementation using NAND gates only . . . .
13.8.2 Implementation using NOR gates only . . . . .
13.9 IC logic families . . . . . . . . . . . . . . . . . . . .
13.9.1 TTL logic family . . . . . . . . . . . . . . . .
13.9.2 CMOS logic family . . . . . . . . . . . . . . .
13.9.3 Comparison of TTL and CMOS logic families
13.10Programmable logic device . . . . . . . . . . . . . . .
13.11Advantages of PLDs . . . . . . . . . . . . . . . . . .
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14 Measurements and data acquisition systems
14.1 Electronic measurements . . . . . . . . .
14.2 Cathode ray oscilloscope . . . . . . . . .
14.2.1 Cathode ray tube . . . . . . . . .
14.2.2 Waveform display on a CRO . . .
14.3 Sensors and actuators . . . . . . . . . . .
14.3.1 Sensors . . . . . . . . . . . . . .
14.3.1.1 Temperature sensors . .
14.3.1.2 Light sensors . . . . . .
14.3.1.3 Force sensors . . . . .
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CONTENTS
14.4
14.5
14.6
14.7
14.8
xvii
14.3.1.4 Displacement sensors . . . . . . . .
14.3.1.5 Speed sensors . . . . . . . . . . . .
14.3.1.6 Sound sensors . . . . . . . . . . . .
14.3.2 Actuators . . . . . . . . . . . . . . . . . . . .
14.3.2.1 Light actuators . . . . . . . . . . . .
14.3.2.2 Force, displacement and motion actuators . . . . . . . . . . . . . . . .
14.3.2.3 Sound actuators . . . . . . . . . . .
14.3.2.4 Heat actuators . . . . . . . . . . . .
Digital voltmeter . . . . . . . . . . . . . . . . . . . .
Data acquisition systems . . . . . . . . . . . . . . . .
14.5.1 Sampling . . . . . . . . . . . . . . . . . . . .
14.5.2 Sample and hold circuits . . . . . . . . . . . .
Analog to digital converter . . . . . . . . . . . . . . .
Digital to analog converter . . . . . . . . . . . . . . .
Multiplexing . . . . . . . . . . . . . . . . . . . . . .
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15 Radio communication
15.1 Introduction . . . . . . . . . . . . . . . .
15.2 Modulation . . . . . . . . . . . . . . . .
15.3 Amplitude modulation . . . . . . . . . .
15.4 Frequency modulation . . . . . . . . . .
15.4.1 Comparison between AM and FM
15.5 Radio transmitters . . . . . . . . . . . . .
15.5.1 AM transmitter . . . . . . . . . .
15.5.2 FM transmitter . . . . . . . . . .
15.5.3 Radio receivers . . . . . . . . . .
15.5.4 AM super heterodyne receiver . .
15.5.5 FM radio receiver . . . . . . . . .
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295
295
297
298
301
302
303
304
304
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305
306
16 Radar and Navigation
16.1 Introduction . . . . . . . . . . .
16.2 Radar equation . . . . . . . . .
16.3 Radar classification . . . . . . .
16.3.1 Pulse Radar . . . . . . .
16.3.2 Continuous Wave Radar
16.4 Applications of radar . . . . . .
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309
310
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314
xvii
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xviii
CONTENTS
16.5 Navigational aids and systems . . . . . . . . . . . . . 315
17 Advanced communication Systems
17.1 Introduction . . . . . . . . . . . . . . . . . . . . .
17.2 Microwave communication . . . . . . . . . . . . .
17.2.1 Microwave frequency bands . . . . . . . .
17.2.2 Microwave communication system . . . . .
17.2.3 Advantages of microwave communication .
17.3 Satellite communication . . . . . . . . . . . . . .
17.4 Optical communication . . . . . . . . . . . . . . .
17.4.1 Fiber-optic technology . . . . . . . . . . .
17.4.2 Total internal reflection . . . . . . . . . . .
17.4.3 Snell’s law . . . . . . . . . . . . . . . . .
17.4.4 Light transmission through an optical fiber
17.4.5 Numerical aperture . . . . . . . . . . . . .
17.4.6 Optical fiber communication system . . . .
17.5 Cellular communications . . . . . . . . . . . . . .
17.5.1 Principles of cellular networks . . . . . . .
17.5.2 Frequency reuse . . . . . . . . . . . . . .
17.5.3 Operation of cellular system . . . . . . . .
17.5.4 Hand off . . . . . . . . . . . . . . . . . .
17.5.5 Roaming . . . . . . . . . . . . . . . . . .
17.5.6 Improving capacity in cellular system . . .
17.6 Global system for mobile communications . . . . .
17.6.1 GSM services . . . . . . . . . . . . . . . .
17.6.2 Architecture of the GSM network . . . . .
17.6.3 Code Division Multiple Access (CDMA) .
17.6.4 Comparison of GSM and CDMA . . . . .
17.7 General packet Radio Service (GPRS) . . . . . . .
17.7.1 Features of GPRS . . . . . . . . . . . . . .
17.7.2 GPRS services . . . . . . . . . . . . . . .
17.7.3 GPRS applications . . . . . . . . . . . . .
xviii
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317
317
318
318
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321
323
324
324
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327
327
328
329
330
331
333
335
336
337
337
338
338
341
342
343
343
343
344
Chapter 1
Basic Concepts in Electrical
Engineering
Basic concepts of electrical engineering are discussed in this chapter.
1.1
Introductory concepts and basic elements
Electric current
Electric current is the rate of flow of electric charges. Electrons are
negatively charged particles and their flow in conductors results in
electric current.
By definition, current i,
dq
(1.1)
dt
If Q is the amount of charge flowing through a conductor in T
seconds, then, current I is given by the expression,
i=
I=
Q
T
(1.2)
The unit of charge is Coulomb. 1 Coulomb = 6.24 ×1018 electrons.
The unit of current is Ampere, A. 1 Ampere = 1 Coulomb/sec.
1
2
Chapter 1. Basic Concepts in Electrical Engineering
Electromotive force
Energy is required for the movement of charge from one point to another. In order to move electrons along a conductor, some amount of
work is required. The work required must be supplied by an electromotive force (emf) provided by a battery or a similar device.
Potential difference
Potential difference is the difference between the voltages at two ends
of a conductor.
A current carrying element is shown in figure 1.1. The voltage
across the element vab is given by
Vab =
W
Q
(1.3)
where work done (W ) is measured in Joules and the charge (Q) in
Coulombs.
+
a
_
Element
b
Vab
Figure 1.1: Potential drop across a current carrying element
The positive (+) and negative (-) signs shown on figure 1.1 define
the polarity of the voltage Vab . With this definition, Vab represents the
voltage at point a relative to point b. Equivalently we may also say that
the voltage at point a is Vab volts higher than the voltage at point b.
Electric circuit
An electric circuit is a closed connection formed by various electric
elements (Resistor, inductor, capacitor, voltage source, current source
etc.). The fundamental circuit model is shown in figure 1.2. The circuit
is made up of a source VS which provides a voltage across its terminals
and a resistor RL as load.
2
1.7. Open circuit voltage and short circuit current
IS
RS
11
RL
Figure 1.9: Real current source
1.7
Open circuit voltage and short circuit current
Consider any circuit with two output terminals A and B (Figure 1.10(a)).
The open-circuit voltage Voc across terminals A and B is the voltage
which appears with nothing connected between them. i.e., RAB = ∞
A
A
Circuit
Circuit
VOC
B
ISC
B
(a) Open circuit
(b) Short circuit
Figure 1.10: Open circuit and short circuit
In the circuit shown in Figure 1.10(b) terminals A and B are connected together with a piece of wire i.e., zero resistance, then the shortcircuit current is the current that flows through the wire. Short circuit
current ISC is that current which flows between two terminals when
they are shorted. i.e., RAB = 0.
Example 1
A resistor of 5 Ω is connected in series with a parallel combination of
6 Ω and 3 Ω. Find the supply current taken from a 35 V dc source.
Solution
Let RP be the equivalent resistance of the parallel combination
of 3 Ω and 6 Ω.
11
12
Chapter 1. Basic Concepts in Electrical Engineering
3Ω
5Ω
6Ω
35 V
Then
1
1 1
3
= + =
RP
3 6
6
Therefore, RP = 2 Ω
Total resistance in the circuit, R = RP + 5 = 2 + 5 = 7 Ω
Supply current, I =
V
35
=
=5A
R
7
Example 2
Find the total resistance of the circuit across the terminals X and Y.
Also find the power consumed by the circuit if a 12 V battery is connected across XY.
4Ω
4Ω
4Ω
2Ω
X
2Ω
4Ω
Z
4Ω
4Ω
12 V
Solution
2×2
RXZ =
=1Ω
2+2
1
1 1 1 1
4
= + + + = = 1Ω
RZY
4 4 4 4
4
12
Y
18
Chapter 2. Kirchoff’s laws
which starting and end points for tracing the path are, in effect,
the same node and touches no other node more than once.
Mesh A mesh is a special case of loop that does not have any other
loops within it or in its interior. All meshes are loops but all
loops are not meshes.
2.1.1
Kirchoff’s Current Law (KCL)
KCL states that at any instant of time, the algebraic sum of currents at
a node is zero.
Mathematically,
N
X
in = 0
n=1
where N is the number of branches that are connected to the node.
The term ’algebraic sum’ indicates that we have to take account of
the current direction, as well as magnitude, when applying Kirchoff’s
Current Law. Consider the node shown in figure 2.1. By adopting the
sign convention that current flowing into a node is taken as positive
(+) while current flowing out of the node is negative (-), application of
KCL gives
i2
i1
i3
i4
Figure 2.1: KCL
+i1 + i2 − i3 − i4 = 0
18
2.1. Kirchoff’s Laws
19
i.e.,
i1 + i2 = i3 + i4
or sum of incoming currents = sum of outgoing currents.
Thus, Kirchoff’s Current Law (KCL) can be stated in other words:
At any instant of time, the sum of all currents flowing into a node is
equal to the sum of all currents leaving the same node.
2.1.2
Kirchoff’s Voltage Law (KVL)
KVL states that the algebraic sum of voltages around a closed path at
any instant of time is zero.
Mathematically,
N
X
Vn = 0
n=1
where N is the number of voltages in the loop. Voltages include
emf and voltage drop across resistors.
X
IR +
X
E.M.F = 0 in a closed circuit
When applying Kirchoff’s law attention should be made to the algebraic signs of voltage drops and emfs. The following sign convention may be followed.
Sign convention
While applying Kirchoff’s laws, attention should be paid while assigning the signs of emfs and voltage drops.
Sign of battery emf
A rise in voltage should be given a positive sign and a fall in voltage
should be given as negative sign. As we go from negative terminal of a
battery to its positive terminal, as shown in figure 2.2(a), there is a rise
in potential, hence the voltage should be given positive sign. If we go
from positive terminal to negative terminal as shown in figure 2.2(b),
then there is a fall in potential, hence this voltage is given negative
sign.
19
20
Chapter 2. Kirchoff’s laws
Ε
Β Α
+
Ι
Ι
(a) Rise in voltage +E
+
Ε
−
Β
−
Α
(b) Fall in voltage -E
Figure 2.2: Sign of battery emf
Sign of IR drops
If we go through a resistor in the same direction of the current, as
shown in figure 2.3(a), there is a fall in potential because current flows
from higher potential to lower potential. Therefore this voltage drop
is assigned negative sign. If we go in the direction opposite to that of
current, as shown in figure 2.3(b), then there is a rise in voltage. Hence
this voltage is given positive sign.
Α
V
+
Β Α
−
−
I
V
+
Β
I
(a) Fall in voltage -V
(b) Rise in voltage +V
Figure 2.3: Sign of battery emf
R2
R1
+ V1
E1
+ V2 _
_
_
+
_
+
E2
Figure 2.4: KVL
Illustration of KVL
Consider the figure 2.4 which shows a single loop circuit in which KVL
20
30
Chapter 2. Kirchoff’s laws
Example 5
Find the loop currents in the electric circuit shown in Figure 2.13.
2Ω
5Ω
I2
5V
+
−
1
2
1Ω
I1
2Ω
10 V
+
−
3
3Ω
I3
Figure 2.13:
Solution
From the loop 1 : 5I1 + (I1 − I2 ) = 5
5I1 + (I1 − I2 ) = 5
(2.8)
From loop 2 : 2I2 + (I2 − I1 ) + 2(I2 − I3 ) = 0
5I2 − I1 − 2I3 ) = 0
(2.9)
From loop 3: (I3 − I2 )2 + 3I3 = 10
5I3 − 2I2 = 10
Solving 2.8, 2.9 and 2.10, we get,
I1 = 1.03 A
I2 = 1.198 A
I3 = 2.48 A
30
(2.10)
2.4. Source transformation
31
Example 6
Find V3 and its polarity if the current I in the circuit shown in figure
2.14 is 0.4 A.
V2
5Ω
+ −
10 V
V1
+
− 50 V
20 Ω
I
a
b
V3
Figure 2.14:
Solution
Assume V3 has the polarity with terminal ’a’ is positive
Applying KVL and starting from left corner of the circuit,
V1 − 5I − V2 − 20I + V3 = 0
50 − 2 − 10 − 8 + V3 = 0
V3 = −30V
Negative value of V3 implies that the terminal ’b’ is positive with
respect to terminal ’a’ (opposite to the assumed polarity).
Example 7
Two coils connected in series have a total resistance of 9 Ω and when
connected in parallel have a resistance of 2 Ω. Find the resistance of
each coil.
Solution
Let the resistance of two coils be R1 and R2 .
31
36
Chapter 3. Magnetic circuits
3.6
Magneto motive force
Magneto motive force (mmf) is the force which establishes the magnetic flux in a magnetic circuit. When a current is passed through a
coil, a magnetic flux is set up around it. The product of current (I) and
number of turns (N ) of the coil gives MMF.
MMF F is given by the expression,
F = NI
Its unit is Ampere-turns (AT).
3.7
Magnetic field intensity
Magnetic field intensity is the magnetic motive force per unit length of
the magnetic circuit. It is denoted by H and its unit is Ampere-turns/
meter. Magnetic field intensity is also called magnetic field strength or
magnetizing force.
mmf
F
=
l
l
NI
H=
l
H=
Or
F = N I = Hl
3.8
(3.1)
Permeability
The ability of a material to conduct magnetic flux through it is called
permeability of that material. It is represented by the letter µ and the
unit Henry/meter. The flux and hence the flux density B are directly
proportional to the magnetizing force H.
i.e.,
B∝H
36
54
Chapter 3. Magnetic circuits
Thus coefficient of coupling may be defined as the ratio of actual
mutual inductance present between the two coils to the maximum possible value of mutual inductance.
Example 1
Find the induced emf in a conductor when rotated in a uniform field of
magnetic flux 2 mWb in 0.02 s. Given number of turns of the conductor
is 100.
Solution
Given N = 100 turns
dΦ
dt
2 × 10−3
= −100 ×
0.02
0.002
= −100 ×
= −10 V
0.02
Induced emf, e = −N
Example 2
A current of 5 A when flowing through a coil of 1000 turns, produces
a flux of 0.3 mWb. Determine the inductance of the coil.
Solution
Given,
I =5A
N = 1000 turns
Φ = 0.3 mWb = 0.3 × 10−3 Wb
We have, inductance of the coil, L =
=
NΦ
I
1000 × 0.3 × 10−3
= 0.06 H
5
Example 3
A coil consists of 750 turns and a current of 10 A in coil produces a
magnetic flux of 1.2 mWb. Calculate the inductance of the coil. If the
54
Chapter 4
Single Phase AC Circuits
4.1
AC Fundamentals
An alternating voltage is any voltage that varies both in magnitude
and polarity with respect to time. Similarly an alternating current is
any current that varies both in magnitude and direction with respect to
time. An ac circuit is a circuit in which alternating current flows that
reverses its direction at regular intervals of time. Alternating current
systems have many advantages compared to direct current systems.
Alternating currents can be easily generated, transmitted and utilized
as compared to direct current systems.
4.2
Generation of sinusoidal emf
A sinusoidal voltage can be generated either by rotating a coil in a
stationary magnetic field or by rotating a magnetic field within a stationary coil.
Consider a rectangular single turn coil rotating in a uniform magnetic field with a constant angular velocity ω rad/sec in the anticlockwise direction as shown in Figure 4.1.
59
60
Chapter 4. Single Phase AC Circuits
Φ
S
N
R
Slip rings
Figure 4.1: Generation of sinusoidal emf
N
S
(a) Maximum flux linkage (Φm ) when
θ = 0◦
N
S
φm cosθ
θ
(b) Flux linkage = Φm cos θ
N
S
(c) Minimum flux linkage (zero) when
θ = 90◦
Figure 4.2: Flux linkage when coil rotates in a magnetic field
60
62
Chapter 4. Single Phase AC Circuits
where Em and Im are peak values of induced emf and current respectively and ω is the angular velocity of the coil given by
ω = 2πf
where f is the frequency in Hz.
From the expressions of emf and current, it is clear that instantaneous values of emf and current vary as the sine functions of angle θ.
So they are known as sinusoidal voltage and current. When the emf or
current is plotted against time, a sine wave as shown in Figure 4.3 is
obtained.
v
Vm
t
2π radians
Figure 4.3: Sine wave
ο
θ = 90
θ = 60
N
N
ο
S
S
ο
θ=0
N
ο
θ = 360
ο
θ = 180
S
N
N
S
ο
θ = 270
N
S
Figure 4.4: Position of coil and induced emf
62
S
84
Chapter 4. Single Phase AC Circuits
where V and I are rms values of voltage and current.
The term cos φ is called power factor of the circuit and cos φ =
R
Z
(From impedance triangle shown in Figure 4.20(b))
4.12
AC through series R-C circuit
Consider an ac circuit in which a resistor of R ohms and a capacitor of
capacitance C Farads are connected in series as shown in figure 4.22.
Let V = rms value of applied voltage
I = rms value of resultant current
VR = IR = voltage drop across R (in phase with I)
VC = IXC = Voltage drop across capacitor C (lagging I by 90◦
)
where XC =
1
, reactance offered by capacitor
ωC
XL
R
VC
VR
VR
I
φ
V
VC
Vm sin ωt
Figure 4.22: Series RC circuit and phasor diagram
From the phasor diagram shown in Figure 4.22, the applied voltage
V is the vector sum of VR and VC and current I is leading the voltage
V by an angle φ.
84
4.12. AC through series R-C circuit
85
q
p
VR2 + VC2 = (IR)2 + (IXC )2 = I × R2 + XC2
V
V
Hence, I = q
=
Z
R2 + XC2
q
The term R2 + XC2 is called the impedance Z of the RC circuit.
i.e., V =
q
φ
R
Z
VR= IR
φ
VC = IXC
XC
V = IZ
(a) Impedance triangle
(b) Voltage triangle
Figure 4.23: Impedance triangle and voltage triangle for an RC circuit.
From the impedance triangle,
XC
tanφ =
R
XC
φ = tan−1
R
Hence the instantaneous value of applied voltage is given by
v = Vm sin ωt
and instantaneous value of current i = Im sin(ωt + φ)
where Im =
Vm
Vm
=q
Z
R2 + XC2
Voltage, current and power waveforms for R-C circuit are shown
in Figure 4.24.
Power in series R-C circuit
In a series R-C circuit, power consumed by capacitor is zero. Power is
consumed by resistance only. It is interesting to note that in the circuits
85
86
Chapter 4. Single Phase AC Circuits
discussed the sections 4.8 through 4.12, frequency of power waveform
is double of that of voltage and current waveforms.
v
p
i
t
φ
Figure 4.24: Voltage, current and power waveforms in RC circuit
i.e., Average power, P = VR I where VR = V cosφ from voltage
triangle shown in 4.23(b).
Therefore, P = V cos φ × I = V Icos φ
where V and I are rms values of voltage and current.
The term cos φ is called power factor of the circuit and cos φ =
R
Z
(From impedance triangle shown in Figure 4.20(b))
4.13
AC through series R-L-C circuit
Consider an ac circuit in which a resistor of resistance R Ω, an inductor of inductance L Henry and a capacitor of capacitance C Farads
connected in series across an ac supply of V volts as shown in Figure
4.25.
Let V = rms value of applied voltage
I = rms value of resultant current
86
Chapter 7
DC machines
7.1
Introduction
Direct current (dc) machines were the first electrical machines that
came to industrial use. The use of dc machines is now very much limited since the power supply is usually available in AC only. However,
they are still used in certain applications like traction, cranes etc.
There are two types of dc machines, the dc generator and the dc
motor. The dc machine which converts mechanical energy into electrical energy is called a dc generator. The dc machine which converts
electrical energy into mechanical energy is called a dc motor.
Mechanical energy
Generator
Electrical energy
(a) Generator
Electric energy
Motor
Mechanical energy
(b) Motor
Figure 7.1: Schematic representation of generator and motor
135
136
7.2
Chapter 7. DC machines
Principle of dc Generator
A dc generator is a rotating machine which converts mechanical energy
into electrical energy. DC generators work on the principle of electromagnetic induction. According to Faraday’s law of electromagnetic
induction, whenever a conductor cuts magnetic lines of flux a dynamic
emf is induced in the conductor. This emf causes a current flow if the
circuit is closed. The essential requirements of a dc generator are
1. A magnetic field
2. Conductors or coils
3. Relative motion between the magnetic field and the conductors
7.3
Simple loop generator
Shaft
A
D
B
C
G
M
Galvanometer
L
Figure 7.2: A simple loop generator
136
7.3. Simple loop generator
137
A
D D
A
B
C C
B
a b
M
L
b
a
M
L
(a)
emf
0
90
180
270
360
θ
(b)
Figure 7.3: emf generated by loop generator
Figure 7.2 shows the arrangement of a single turn coil ABCD rotating at a constant speed in a uniform magnetic field produced by two
poles. The two ends of the coil are connected to a split ring1 . An emf
is induced in the coil which is proportional to the rate of flux linkage.
Figure 7.3(a) shows the schematic diagram of coil connections with
split ring. The direction of induced current in the coil is from A to B
and from C to D during the first half revolution. Therefore the current
1
A slip ring splitted into two
137
138
Chapter 7. DC machines
will flow through the load resistor from M to L. In the next half revolution, the direction of induced current will be from D to C and from
B to A as shown in the figure. The current will again flow from M to
L through the load resistor.
In a dc generator the emf induced in the coil is alternating. In order
to get a unidirectional current an arrangement known as commutator is
used. The function of commutator in a dc generator is to convert the
alternating current produced in the armature (coil) into direct current in
the external circuit. In the figure the ends of the armature are connected
to a split ring which acts as commutator.
7.4
Constructional details of dc Machine
A direct current machine can be used as a generator or as a motor.
When the dc machine is driven by a prime mover, it converts mechanical energy into electrical energy and so it acts as a generator. If electrical energy is supplied to the machine, it works as a motor and it
converts electrical energy into mechanical energy.
Field winding
Pole shoe
Yoke or frame
Commutator
Shaft
Armature
conductors
Commutator
segments
Interpole
Figure 7.4: Construction of a dc generator
The constructional features of a dc machine are given below.
138
144
Chapter 7. DC machines
7.6
Types of dc generators
DC generators are classified according to the method of excitation of
their field windings. The production of the magnetic flux in the generator by circulating current in the field winding is called excitation. DC
generators are classified as given in the chart 7.8.
DC generators
Separately excited
DC generator
Series
generator
Self excited
DC generator
Shunt
generator
Compound
generator
Long shunt
compound
DC generator
short shunt
compound
DC generator
Figure 7.8: Different types of dc generators
7.7
Separately excited dc generator
In this type of machine, the field winding is excited by a separate dc
source. The schematic diagram of separately excited dc machines is
shown in figure 7.9.
Let Ia = Armature current
Ra = Armature resistance
E = Generated emf
IL = Current through the load
144
Chapter 8
Three phase induction motor
8.1
Introduction
Three phase induction motor is extensively used for various kinds of
industrial drives. The three phase induction motor has a three phase
wound stator to which the three phase supply is connected. The power
transfer to the rotor is by ’induction’ and that is why these motors are
called induction motors. Three phase induction motors possess many
advantages such as simple design, low cost, rugged construction and
reliable operation. They have good speed regulation and high starting
torque.
8.2
Construction
The main parts of a three phase induction motor are (i) Stator and (ii)
Rotor. The stator is the stationary part and the rotor is the rotating
part. The rotor is separated from the stator by a small air gap whose
thickness(length) depends on the power rating of the motor. There are
two types of three phase induction motors based on the construction of
rotor
1. Squirrel cage induction motor
2. Slip ring induction motor
159
8.3. Concept of rotating magnetic field
167
Therefore, rotor current frequency,
fr = sf
(8.6)
where f is the supply frequency in Hertz and s is the slip
Rotor current frequency = Slip × Supply frequency to stator
8.3.3
Applications of three phase induction motors
Squirrel cage induction motors are used in centrifugal pumps, fans,
conveyors, compressors, reciprocating pumps, line shafting, lathe works,
line shafting, etc.
Slip ring induction motors are used in lifts, hoists, cranes, conveyors,
pumps, flour mills, etc.
Advantages of induction motors
1. Simple design.
2. Low cost compared to other motors of the same capacity.
3. High overload capacity.
4. Very rugged construction.
5. Requires little maintenance.
6. Have reasonable good efficiency and provides reliable operation.
7. Has good speed regulation and high starting torque.
8. Uses readily available power supply (three phase AC).
Disadvantages of induction motors
1. Wide variation in speed is not possible.
2. Its speed decreases with increase in load.
167
182
Chapter 10. Power system
Generating station
11 kV
11/110 kV
Transformer
Primary transmission
110 kV substation
110/66 kV
Transformer
Secondary transmission
66 kV substation
66/11 kV
Transformer
Primary distribution
11 kV/415 V
Transformer
Secondary distribution
Consumers
Figure 10.1: Typical power transmission system
Secondary distribution system
The three phase four wire network, that supply power to low tension
consumer points from secondary distribution network. The specified
182
Chapter 11
Electrical estimation
Electrical estimation for a small residential building is discussed in this
section.
11.1
Electrical installations-estimating and costing of material
Electrical installation means electric wiring and fittings installed in a
particular place. i.e., a residential building, a factory, a commercial
complex etc. All installations should be in accordance with Indian
Electricity Rules 1956.
11.1.1
Steps for estimation
• Installation plan
Drawing installation plan on suitable scale and mark locations
of electrical points. Switch boards, main switch, energy meter
etc. are marked using specified symbols in discussion with the
client and architect.
• Load calculation and selection of switch gears
Calculation of total connected load. Choosing proper rating of
energy meter, main switch and fuse/MCB (Main circuit Breaker).
185
Basics of Electronics
and
Communication Engineering
Chapter 12
Amplifiers and Oscillators
12.1
Principle of electronic amplifiers
Amplification means making things bigger. In the context of electronics, it is the process of increasing the amplitude of signals. The functional block that accomplishes the task of signal amplification is called
amplifier. Here, the term amplifier usually describes an electronic amplifier, in which the input signal is usually a voltage or a current.
There are both passive and active amplifiers. Example for passive
amplifier is a step-up transformer. If an alternating voltage signal is
applied at the input, a larger voltage signal will be available at the
output. The power delivered to a load will be always less than the
power absorbed at the input. Thus a transformer may provide voltage
amplification but it cannot provide power amplification. Even though
several passive amplifiers exist there, the most important and useful
electronic amplifiers are active amplifiers.
A widely used symbol for an amplifier is shown in figure 12.1.
Here Vi is the input voltage, Vo is the output voltage and Av represents
voltage gain which is the ratio of the output voltage to input voltage.
The active amplifiers take power from an external energy source
and use it to boost the input signal. Thus it delivers an output signal
whose waveform corresponds to the input signal but its power level is
higher.
193
194
Chapter 12. Amplifiers and Oscillators
Av
Vi
Vo
Figure 12.1: Symbol of amplifier
The additional power content in the output signal is supplied by
the DC (Direct Current) power source used to bias the active device. A
block schematic for an active amplifier is given in figure 12.2.
DC
Power source
Signal input
Amplifier
Signal output
Figure 12.2: A schematic of active amplifier.
The output waveform of an amplifier must be an exact replica of
the input waveform. It preserves the details of the signal waveform
and any deviation of the output waveform from the shape of the input
waveform is considered as distortion.
12.2
Characteristics of an amplifier
Following are the important desirable characteristics of an amplifier.
1. Gain A =
V◦
should be large.
Vi
2. Input resistance Ri should be large.
3. Output resistance R◦ should be small.
194
12.11. Feedback systems
12.11
217
Feedback systems
A feedback system is one in which a part or fraction of the output is
combined with the input. Feedback systems use the output information
to modify the input signal to achieve the desired result.
Feedback systems are of two types (a). Negative feedback systems
(b). Positive feedback systems.
In the negative feedback systems, feedback tends to reduce the input. This kind of feedback is called degenerative feedback. Negative
feedback reduces the amplifier gain but it has many advantages such as
gain stability, reduction in distortion and noise, increase in bandwidth,
increase in input impedance and decrease in output impedance etc.
In the positive feedback systems, the feedback tends to increase the
input. This form of feedback is called regenerative feedback. Since
positive feedback causes excessive distortion and instability, it is seldom used in amplifiers. However, it increases the strength of the original signal and hence it is employed in oscillator circuits.
A feedback amplifier essentially consists of two parts, an amplifier
and a feedback network as shown in Figure 12.21. The function of
feedback network is to return a fraction of the output energy (voltage
or current) to the input of the amplifier.
12.12
Feedback in amplifiers
For an amplifier without feedback, the gain equals the ratio of output
to input of the amplifier. i.e., Gain A = Vo /Vi
A is called the open-loop gain. i.e., the gain of the amplifier without feedback.
A block diagram illustrating the principle of feedback in an amplifier is shown in Figure 12.21. Here xs represents the signal which may
be voltage or current applied to the whole system. The output of the
amplifier x◦ is applied to a feedback network which has a gain β. Thus
the feedback network produces a signal xf = βx◦ which is subtracted
from the input source signal, xs . The resulting signal, xi , also called
the error signal, is the input to the amplifier which in turn produces the
output signal V◦ = A × xi .
217
218
Chapter 12. Amplifiers and Oscillators
xs + xi =xs-xf
xf =βxo _
Amplifier
A
xo =Axi
Feedback
circuit
β
Figure 12.21: Block diagram illustrating the principle of feedback
Thus the actual input to the amplifier becomes
xi = xs − xf = xs − βx◦ in case of negative feedback and
xi = xs + xf = xs + βx◦ in case of positive feedback.
Consider a negative feedback case. The actual input to the amplifier,
xi = xs − βx◦
(12.12)
We have amplifier gain,
A=
x◦
xi
Axi = xo
(12.13)
(12.14)
Substituting equation 12.12 in equation 12.14, we get,
A(xs − βxo ) = xo
(12.15)
(1 + Aβ)xo = Axs
(12.16)
A
x◦
=
xs
1 + Aβ
(12.17)
Rearranging,
Or
x◦ /xs is the gain of the amplifier with feedback which is usually
given the symbol G. Therefore the gain with negative feedback is expressed as,
218
224
Chapter 12. Amplifiers and Oscillators
12.13
Oscillators
An oscillator can be described as a source of alternating voltage. An
amplifier delivers an amplified version of input signal while oscillator
generates an output waveform without an input signal. The additional
power content in the output signal is supplied by an external DC power
source.
The oscillator requires no external signal to initiate or maintain the
energy conversion process. Instead, an output signal is produced as
long as a DC power source is connected. Figure 12.23, depicts the
comparison between amplifier and oscillator.
DC source
Amplifier
Signal input
Signal output
(a)
DC source
Oscillator
Signal output
(b)
Figure 12.23: Comparison between amplifier and oscillator
12.14
Principle of oscillators
Oscillators are amplifiers with positive feedback. Consider a feedback
amplifier with an input signal Vin and output V◦ as shown in Figure
12.24.
A is the open loop gain of the amplifier. Without feedback, output
voltage of amplifier is V◦ = A × Vin . Since positive feedback is used,
feedback voltage Vf is added with input signal Vin . Thus the input to
the amplifier Ve = Vin + Vf .
224
244
Chapter 13. Digital Systems
Inputs
A B
0 0
0 1
1 0
1 1
Output
Q = A⊕ B
1
0
0
1
Table 13.9: Truth table for EX-NOR gate
13.1.4
Universal gates
It is possible to implement any Boolean expression using only NAND
gates. In a similar manner, it can be shown that NOR gates alone can
be used to implement any Boolean operation. Therefore NAND and
NOR gates are called universal gates.
Figure 13.12 illustrates that NOT, AND and OR gates can be implemented using NAND gates.
Figure 13.12 illustrates that NOT, OR and AND gates can also be
implemented using NOR gates.
A
A
A.A = A
A
B
A.B = AB
A
B
A
A.B
A
A.B =A+B
A
B
B
Figure 13.12: NAND as universal gate
244
A+B
13.7. Generating Boolean expression from logic circuit
13.7
257
Generating Boolean expression from logic
circuit
If a logic circuit is given, we can generate Boolean expression directly
from it. Consider the Figure 13.18. The Boolean expression for the
logic circuit is
Q = AB + (A + B)
A
Q
B
Figure 13.18:
A
AB
Q = AB + (A + B)
B
A+B
Figure 13.19: Obtaining Boolean expression
Example
Write the Boolean expression for the logic diagram given in Figure
13.20 and simplify it and draw the logic diagram to implement the
simplified expression.
257
258
Chapter 13. Digital Systems
A
A
B
Y
B
B
C
Figure 13.20:
Solution
A
A
A + (A + B)
A
B
B
A+B
Y = (A + (A + B)) (B + (B + C))
B
B + (B + C)
B
C
B+C
Figure 13.21:
From the circuit shown in Figure 13.21 we get the output expression
Y = (A + A + B)(B + B + C)
Using De Morgan’s law,
= (A + A + B) + (B + B + C)
= (A).(A + B) + (B).(B + C)
= A.(A + B) + B.(B + C)
= A.A + A. B + B.B + B.C
258
13.8. Implementation of logic circuits using universal gates
259
= A + AB + B + BC
= A(1 + B) + B(1 + C )
=A+B
The logic diagram to implement the simplified expression is shown
in Figure 13.22.
A
Y =A +B
B
Figure 13.22: Simplified logic diagram for (A + A + B)(B + B + C)
Exercise
Write the Boolean expression for the logic diagram given in Figure
13.23 and simplify it and draw the logic diagram to implement the
simplified expression.
A
B
C
Q
Figure 13.23: Circuit for exercise
13.8
Implementation of logic circuits using universal gates
As discussed in section 13.1.4 in page 244 NAND and NOR gates are
called universal gates, because any logic circuits can be fabricated us-
259
276
Chapter 14. Measurements and data acquisition systems
3. The horizontal deflection system, including the time-base generator and synchronization circuitry.
4. Power supplies.
Signal to be
displayed
Vertical
amplifier (Volts/Div)
Vertical deflection
plates
Electron
Gun
Trigger
circuit
Horizontal deflection
plates
Electron beam Screen
Time-base
generator
Horizontal
amplifier (Time/Div)
Figure 14.1: Block diagram for a CRO
The waveform to be displayed is fed to the vertical deflection system
(Y-input) of the CRT. The horizontal deflection system provides the
voltage for moving the beam horizontally. It has a sawtooth generator or a time-base generator and a synchronization circuit. The time
base generator produces a sawtooth waveform (see figure 14.3(b)) for
horizontal deflection of the electron beam. The purpose of the synchronization circuit is to start the horizontal sweep at a specific instant, with
respect to the waveform under observation. It synchronizes two types
of deflections so that horizontal deflection starts at the same point of
the input vertical signal each time it sweeps. In addition to the internal
sweep, there is a provision for external horizontal input (X-input). The
operation of vertical section and horizontal section are independent of
each other.
Cathode ray tube and its various components are discussed in the
following section.
276
14.2. Cathode ray oscilloscope
279
Vv
0
T/4
3T/4
T/2
T
t
(a) Voltage signal applied to vertical deflection plate
Vh
0
T/4
t
T/2 3T/4 T
(b) Voltage signal applied to horizontal deflection plate
Vv
0 T/4
T/2
3T/4
T
Vh
(c) Waveform displayed on CRO
Figure 14.3: Voltages applied to deflection plates and displayed waveform
279
14.3. Sensors and actuators
Quantity being Measured
281
Input Device
(Sensor)
Resistive thermometers
Thermocouple
Output Device
(Actuator)
Thermistor
p-n junction
LDR
Fan
Heater
Temperature
Lights & Lamps
Photodiode
Light Level
LED’s & Displays
Phototransistor
Fibre Optics
Solar Cell (Photo voltaic)
Strain Gauge
Lifts & Jacks
Pressure Switch
Force/Pressure
Electromagnetic
Piezoelectric
Vibration
Load Cells
Potentiometer
Motor
Encoders
Position
Solenoid
Opto-switch
Panel meters
Speed
LVDT Motor
Tacho-generator
Opto-coupler
Doppler Effect Sensors
AC and DC Motors
Stepper Motor
Brake
Loudspeaker
Microphone
Sound
Ultrasonic transducers
Piezo-electric Crystal
Buzzer
Table 14.1: Common Transducers
14.3.1.1
Temperature sensors
The most commonly used temperature sensors are resistance thermometers, thermocouples, thermistors, and p-n junction. They can be used
for the measurement of temperature.
281
Signal
Conditioner 1
Sensor 2
Signal
Conditioner 2
.....
.....
Sensor 1
Sensor N
289
Multiplexer
14.5. Data acquisition systems
Buffer
amplifier
Sample
and hold
Signal
Conditioner N
ADC
Computer
Figure 14.5: Block diagram for a data acquisition system
Data acquisition is the process of taking analog information from
a number of sources and converting into digital form for further processing. It consists of several stages including sampling of the signal, analog to digital conversion, multiplexing, etc. The block diagram
for data acquisition system is shown in Figure 14.5. The elements of
a data acquisition system include sensors, signal conditioning units,
multiplexer, buffer amplifier, sample and hold circuit, Analog to Digital Converter (ADC) and a computer.
Sensors convert the input signal into electrical signals. The sensors
are connected via some signal conditioning units to a data acquisition
system. Signal conditioners are used to increase the quality of the sensor output to a desired level before analog-to-digital conversion. Multiplexer is used to connect a number of analog signals, one at a time,
to a common channel. The function of buffer amplifier is to provide a
signal in a range close to but not exceeding the full input voltage range
of the ADC. The sample and hold maintains a fixed input value during
the short conversion time of the ADC. ADC produces digital output
corresponding to the input.
289
Chapter 15
Radio communication
15.1
Introduction
The purpose of a communication system is to transmit informationbearing signals through a communication channel. Three basic blocks
in any communication system are: 1) Transmitter 2) Channel and 3)
Receiver.
The transmitter puts the information from the source onto the channel. The channel is the medium connecting the transmitter and the
receiver and the transmitted information travels through this channel
until it reaches the destination. The original message signals usually
contain frequencies in the low frequency or audio frequency range.
Therefore, some form of frequency-band shifting (converting to high
frequency range) is necessary in order to make the signals suitable for
transmission. This shifting in the range of frequencies is achieved by
the process known as modulation.
The figure 15.1 depicts the elements of a communication system
viz., transmitter, transmission channel and receiver. Each part plays a
particular role in signal transmission, as explained below.
The transmitter processes the input signal to produce a suitable
transmitted signal suited to the characteristics of the transmission channel.
295
Chapter 16
Radar and Navigation
16.1
Introduction
Radar is an acronym for Radio Detection and Ranging. It is an electronic system used to detect, locate or measure the velocity of targets.
It collects information about distant objects or targets by sending electromagnetic waves to them and thereafter analyzing reflected waves or
the echo signals from the objects. Radar can detect static or mobile
objects in various conditions such as darkness, rain, fog and snow. The
frequencies used by radar lies in the upper UHF and microwave range.
The basic principle of radar can be explained with the help of the
block diagram as shown in figure 16.1. It consists of a transmitter and a
receiver, each connected to a directional antenna. The transmitter generates high power modulated signal and transmits through the antenna.
The duplexer allows the use of a single antenna for transmission and
reception and also separates transmitter and receiver from each other.
During transmission, the duplexer disconnects the receiver and connects the transmitter to the antenna.
The antenna radiates electromagnetic waves and these waves strike
on a distant target which can reflect (echo) some of energy back to the
same antenna. After transmission, the duplexer connects the antenna
with the receiver and disconnects the transmitter. Then echo signals
from the target are received by the receiver and processed to extract the
required information. By noting the time taken for the signal to reach
309
310
Chapter 16. Radar and Navigation
the target and echo signal to return back, the distance of the target can
be calculated. The direction of the received echo signal gives an idea
about the angular position of the target. It is also possible to detect the
height, speed and direction of a moving target.
itted
sm
Tran
Transmitter
rning
Retu
Duplexer
l
a
sign
Target
l
a
sign
Transmitter/receiver
Antenna
Reciever
Figure 16.1: Basic block diagram for radar
The display systems of radar provide the range information such as
azimuth, altitude and distance of the target. Commonly used displays
are Plan position Indicator (PPI)and Amplitude Scope (A Scope).
16.2
Radar equation
Basic radar range equations is given below.
R=
CT
2
(16.1)
where
R = Range.
C = Velocity of electromagnetic waves.
T = Time elapsed between transmission and reception of signal.
Consider the Figure 16.2
310
16.5. Navigational aids and systems
16.5
315
Navigational aids and systems
Navigation is the process of finding and controlling the movement of
a vehicle from one place to another. The position of an aircraft or ship
can be found by using radio navigational aids. This is achieved by
the installation of radio transmitters and receivers at known locations
on the earth’s surface as well as at aircraft or ship which will work
in conjunction with those on earth. Navigational aids include bouys,
beacons, lightships, radio beacons, fog signals etc.
Navigational aids
• Bouys are floating objects anchored at bottom. Their shape and
colour convey the message how to navigate around them.
• Beacons are structures permanently fixed to sea bed or land
Electronic navigation systems
• Instrument Landing System (ILS)
Some applications related to remote sensing and military, aircrafts are controlled without pilots in it. ILS enables take off,
flying and landing with the electronic systems on ground and air
borne.
• Ground Controlled Approach (GCA)
GCA is a system which assists the pilot to take off, fly and land
the aircraft. This helps the pilot to land the aircraft even in hazardous atmospheric conditions such as fog, haze, snow, rain etc.
• Radio Direction Finder (RDF)
RDF is used to find the direction of radio signal source. Direction of the electromagnetic signal is detected by the directional antenna. This over the horizon system helps the navigating ships.
• Long Range Navigation (LORAN)
It is a terrestrial navigational system using low frequency radio
transmitters that use the time interval between the radio signals
315
Chapter 17
Advanced communication
Systems
17.1
Introduction
In the chapters 15 and 16, we had a brief review on radio communication and radar systems. In this chapter, advanced communication
systems such as Microwave communication, Satellite Communication,
Optical communication and Cellular communication systems are discussed.
17.2
Microwave communication
Microwaves are electromagnetic waves of very short wavelength (in
the order of a few cm). Their frequencies lie in the range 1 GHz
to 1000 GHz (1 GHz = 109 Hz). Their short wavelengths make microwaves ideal for use in radio and television broadcasting. Communication using microwaves whose wavelengths are very short is called
microwave communication. Microwave communication is a category
of radio communication which deals with radiation of electromagnetic
waves from one point to another through free space. Useful frequency
range for microwave communication lies between 300 MHz and 150
317
318
Chapter 17. Advanced communication Systems
f1
Baseband
signal
f2
Repeater
Transmitter
Receiver
Baseband
signal
Figure 17.1: Basic block diagram for microwave communication system
GHz. Microwave communication system is line of sight (LOS) in nature limited by horizon due to earth’s curvature.
Microwave communication system is classified into two broad categories namely analog and digital. Analog microwave communication
systems are widely used. The analog system employs analog transmission techniques such as FM modulation and analog multiplexing
technique.
17.2.1
Microwave frequency bands
Designation
UHF
L Band
S Band
C Band
X Band
Ku Band
K Band
Ka Band
Frequency range
300 MHz - 1 GHz
1-2 GHz
2-4 GHz
4-8 GHz
8-12 GHz
12-18 GHz
18-27 GHz
27-40 GHz
Table 17.1: Microwave frequency bands
17.2.2
Microwave communication system
A microwave system consists of a terminal transmitter, a number of
repeater stations and a terminal receiver station (see Figure 17.1). The
functions of each blocks are explained below.
318
322
Chapter 17. Advanced communication Systems
Transponders
Satellite
Uplink
Solar panel
Downlink
36000 km
Earth
station
Earth surface
Earth
station
Figure 17.5: Satellite communication system
A transponder is a combination of receiver, amplifier and transmitter. Receiver in the transponder amplifies the uplink signal and converts it into another frequency downlink frequency. The block diagram
for the transponder is shown in Figure 17.6.
Transmitter/receiver
Antenna
Diplexer
Receiver
Signal
Processing
Transmitter
Figure 17.6: Block diagram for transponder
322
332
Chapter 17. Advanced communication Systems
Cell 2
Cell 7
Cell 3
Cell 1
Cell 6
Cell 2
Cell 7
Cell 4
Cell 5
Cell 3
Cell 2
Cell 7
Cell 1
Cell 6
Cell 4
Cell 3
Cell 1
Cell 5
Cell 6
Cell 4
Cell 5
Figure 17.13: Illustration of frequency reuse concept. Cells with the same
name use the same set of frequencies. A small cluster is outlined in bold and
replicated over the coverage area. In this example, cluster size N = 7 and
frequency reuse factor is 1/7 since each cell contains one-seventh of the total
number of available channels.
Consider a cellular system which has a total of S duplex channels1 available for use. If each cell is allocated a group of K channels
(K < S) and if S channels are divided among N cells into unique
and disjoint channel groups with each have the same number of channels, the total number of available radio channels can be expressed as
S = KN . The N cells which collectively use the complete set of
available frequencies is called a cluster.
The cells can be grouped in clusters of 7, 12 and 19 etc. to form a
repetitive pattern. If a cluster is replicated M times within the system,
the total number of duplex channels C, can be used as measure of
1
Two way communication by using the same channel
332
342
Chapter 17. Advanced communication Systems
A two channel CDMA system is shown in Figure 17.18. m(t) and
c(t) represent message and PN sequence respectively.
Advantages of CDMA
1. Increased cellular communications security.
2. Simultaneous conversations possible.
3. Increased efficiency, meaning that the carrier can serve more
subscribers.
4. Smaller phones.
5. Low power requirements and little cell-to-cell coordination needed
by operators.
6. Extended reach-beneficial to rural users situated far from cells.
17.6.4
Comparison of GSM and CDMA
A comparison between CDMA and GSM is given in table 17.2.
1.
2.
3.
4.
5.
6.
7.
CDMA
Based on spread spectrum
technique.
Improved privacy and
security.
Less probability of error
and hence high voice quality.
1.25 MHz bandwidth per
carrier
Available operating frequency
450, 800, 1900 MHz.
Using RUIM Card
(Removable User Identity
Module).
Soft/Softer hand-off
(make before break)
GSM
1. Based on TDMA
technique
2. Less secure.
3. High probability of error
and hence less voice quality.
4. 200kHz bandwidth
per carrier.
5. Available operating frequency
900, 1800, 1900 MHz
6. Using SIM Card
(Subscriber Identity
Module).
7. Hard hand-off
(break before make)
Table 17.2: Comparison between CDMA and GSM
342
17.7. General packet Radio Service (GPRS)
17.7
343
General packet Radio Service (GPRS)
GPRS is a packet based communication services for wireless communication. GPRS is a step towards 3G and is often referred to 2.5G. In
packet based communication data is split into packets, that are transmitted and then reassembled at the receiving end. This technique makes
much more efficient use of the available channel capacity compared to
circuit switching. In circuit switching, a circuit is switched permanently to a particular user. The idle time, during which there is no
data transmission, in circuit switching systems is effectively utilized in
packet switching.
17.7.1
Features of GPRS
Important features of GPRS are discussed below.
1. Speed One of the benefits of GPRS technology is that it offers
a much higher data rate than with GSM.
2. Packet switched operation Unlike GSM which uses circuit
switched techniques, GPRS technology uses packet switching in
line with the Internet. This makes far more efficient use of the
available capacity.
3. Always on connectivity It offers an ’Always On’ capability.
When using circuit switched techniques, charges are based on
the time a circuit is used, i.e., how long the call is. For packet
switched technology charges are for the amount of data carried.
4. More applications The packet switched technology combined
with the higher data rates opens up many more possibilities for
new applications.
17.7.2
GPRS services
GPRS services are defined to fall in one of two categories: Point to
Point (PTP) and Point to Multipoint (PTM) services. In PTP services,
packets are sent from a single source to a single destination. The PTM
343
17.7. General packet Radio Service (GPRS)
345
COMBINED FIRST AND SECOND SEMESTER B.TECH
(ENGINEERING) DEGREE EXAMINATION, MAY 2010
(2009 admissions)
EN 09.107 - BASICS OF ELECTRICAL, ELECTRONICS AND
COMMUNICATION ENGINEERING
Time : Three hours
Maximum:70 marks
Answer all questions in Part A, any two from Part B and
all from part C
Section I (Basics of Electrical Engineering)
Part A
Answer all questions
1. A coil of 500 turns is linked by a flux of 0.4 mWb. If the flux is
reversed in 0.01 second, find the e.m.f induced in the coil.
(2 marks)
2. What are the advantages and disadvantages of induction motors?
(2 marks)
3. A resistance of 12 Ω, an inductance f 0.15 H and a capacitor of
100 µF are connected in series across a 100 V, 50 Hz supply.
Calculate the impedance.
(1 mark)
Part B
Answer any two questions
4. Using kirchoff’s law, find the current through 10 Ω resistor.
2Ω
5Ω
20 V
10 Ω
345
8V
346
Chapter 17. Advanced communication Systems
5. Derive EMF equation of dc generator.
6. Explain the principle of operation of synchronous generator.
(2 × 5 = 10 marks)
Part C
7.
(a)
i. State and explain Faraday’s laws of electromagnetic
induction.
(5 marks)
ii. Compare electric and magnetic circuits.
(5 marks)
or
(b)
8.
i. Derive form factor and peak factor of a sine wave.
(5 marks)
ii. Three coils each of resistance 6 Ω and inductive reactance 8 Ω are joined in delta across 400 V, 3-phase
lines. Calculate the line current and power absorbed.
(2 marks)
(a) Explain the construction and principle of operation of single phase transformer.
or
(b)
i. Explain the construction details of d.c generator.
ii. Explain the principle of operation of induction motor.
(10 marks)
Section II
(Basics of Electronics and Communication Engineering)
Part A
Answer all questions
1. What are the advantages and disadvantages of negative feedback?
(2
marks)
346
17.7. General packet Radio Service (GPRS)
347
2. Write RADAR equation.
(1 mark)
3. What is meant by frequency reuse technique ?
(2 marks)
Part B
Answer any two questions
4. Explain briefly about various noises in amplifier.
5. Simplify the following Boolean Expression an implement using
only NAND gates.
(2 marks)
Y = A B.C + A B C + A B C + ABC
(2 × 5 = 10 marks)
6. Explain the principle of GSM.
Part C
7.
(a)
i. Explain the concept of differential amplifier.
(5
marks)
ii. Compare TTL and CMOS logic
(3 marks)
iii. List the characteristics of Op-Amp.
(2 marks)
or
(b) Explain the working of CRO with neat block diagram.
(10 marks)
8.
(a) Draw the block diagram of superheterodyne receiver and
explain.
(10 marks)
or
(b)
i. Explain the basic principle of cellular communication.
(5 marks)
ii. Write short note on GPRS technology.
(2 marks)
347
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