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Basics of Electrical, Electronics and Communication Engineering

K. A. NAVAS Asst.Professor in ECE Govt. Engineering College Thrissur-9 [emailprotected]

T. A. Suhail Lecturer in ECE Al-Ameen Engineering College Shoranur-2 [emailprotected]

Rajath Publishers 28/450-A, Club Road, Girinagar South, Kadavanthra, Kochi-682020

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:[emailprotected]

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

iii

iv 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

Contents 1

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

. . . . . . .

1 1 6 7 8 9 10 11

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 . . . . . . . . . . . . . .

. . . . . . .

17 17 18 19 21 21 22 24

. . . . . . .

33 33 34 34 35 35 36 36

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 . . . . . . . . . . . . . . .

. . . . . . .

xii

CONTENTS 3.8 3.9 3.10 3.11 3.12 3.13

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) . . . . . . . . . . . .

xii

. . . . . . . . . . . . . . . . .

. . . . . . . . . . . . . . . . . .

36 37 37 38 40 42 43 44 44 45 47 48 48 48 50 51 52 53

. . . . . . . . . . . . . . . . .

59 59 59 63 70 71 73 73 75 77 79 81 84 86 89 90 90 91

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

. . . . . .

. 91 . 97 . 98 . 102 . 103 . 105

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 . . . . . .

. . . . . . . . . . .

107 107 107 108 109 110 110 111 113 114 118 120

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 . . . . . . . .

. . . . . . .

125 125 126 127 129 130 131 131

. . . . . . .

135 135 136 136 138 142 144 144

4.15 4.16 4.17 4.18 4.19 5

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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

. . . . . . .

xiv

CONTENTS 7.8

. . . . . . .

145 145 146 147 152 155 157

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 . . . . . . . . . .

159 159 159 160 160 162 164 165 167

Synchronous generators 9.1 Introduction . . . . . . 9.1.1 Construction . 9.2 Principle of operation . 9.2.1 EMF equation

7.9

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 . . .

. . . . . . .

168

. . . .

171 171 171 174 176

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 . . . . . . . . . . . . . . . . .

. . . . .

179 179 179 180 181 183

. . . .

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

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 . . . . . . . . . . . . . . . .

193 193 194 195 196 197 197 201 202 203 205 205 206 208 209 211 211 212 214 216 217 217 220 221 221 222 223 223 223 224 224 227 228 229 230 231 232

xvi

CONTENTS 12.16.3 Crystal oscillators

. . . . . . . . . . . . . . . 232

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 . . . . . . . . . . . . . . . . . .

235 235 236 238 240 244 245 247 248 248 248 249 253 254 257 259 260 262 264 264 268 270 270 273

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 . . . . .

275 275 275 277 278 280 280 281 283 284

xvi

. . . . . . . . .

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 . . . . . . . . . . . . . . . . . . . . . .

284 285 285 286 286 287 287 287 288 288 290 291 291 293 293

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 . . . . . . . . .

. . . . . . . . . . .

295 295 297 298 301 302 303 304 304 305 305 306

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 . . . . . .

. . . . . .

309 309 310 311 312 313 314

xvii

. . . . . .

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

. . . . . . . . . . . . . . . . . . . . . . . . . . . . .

317 317 317 318 318 320 321 323 324 324 325 327 327 328 329 330 331 333 335 336 337 337 338 338 341 342 343 343 343 344

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=

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.

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

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.

1.7. Open circuit voltage and short circuit current

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

Circuit

VOC B

ISC

(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.

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

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

i1 i3

Figure 2.1: KCL

+i1 + i2 − i3 − i4 = 0

2.1. Kirchoff’s Laws

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 +

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.

Chapter 2. Kirchoff’s laws

Β Α

Ι (a) Rise in voltage +E

−

(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.

Β Α

−

(a) Fall in voltage -V

(b) Rise in voltage +V

Figure 2.3: Sign of battery emf R2

R1 + V1 E1

+ V2 _

+ _

Figure 2.4: KVL Illustration of KVL Consider the figure 2.4 which shows a single loop circuit in which KVL

Chapter 2. Kirchoff’s laws

Example 5 Find the loop currents in the electric circuit shown in Figure 2.13. 2Ω

5Ω

I2 5V

+ −

1Ω

2Ω

10 V

+ −

3Ω

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

(2.10)

2.4. Source transformation

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

+ − 50 V

20 Ω I

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 .

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

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

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

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.

Chapter 4. Single Phase AC Circuits Φ

Slip rings

Figure 4.1: Generation of sinusoidal emf

(a) Maximum flux linkage (Φm ) when θ = 0◦

φm cosθ

(b) Flux linkage = Φm cos θ

Figure 4.2: Flux linkage when coil rotates in a magnetic field

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

θ=0

θ = 360

θ = 180

θ = 270

Figure 4.4: Position of coil and induced emf

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

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.

4.12. AC through series R-C circuit

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 =

VR= IR

φ VC = IXC

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

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.

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

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

G M

Galvanometer

Figure 7.2: A simple loop generator

136

7.3. Simple loop generator

137

D D

C C

a b

(a)

emf

180

270

360

(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

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

xo =Axi

Feedback circuit

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 B

A.B = AB

A B

A.B

A A.B =A+B

A 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

Figure 13.18:

Q = AB + (A + 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 + 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

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

(a) Voltage signal applied to vertical deflection plate

Vh 0

T/4

T/2 3T/4 T

(b) Voltage signal applied to horizontal deflection plate

0 T/4

T/2 3T/4

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

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

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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

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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.

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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

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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

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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.

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

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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

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17.7. General packet Radio Service (GPRS)

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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

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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)

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)

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17.7. General packet Radio Service (GPRS)

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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)

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