CONTENTS
1.
INTRODUCTION ............................................................................ 1.3
1.1
1.2
1.3
1.4
1.5
1.6
1.7
1.8
1.9
1.10
1.11
1.12
1.13
2.
Functional elements of measurement system
1.4
1.1.1 Example for the concept of measurement system ...... 1.6
Classification of instruments used in instrumentation system 1.7
Performance characteristics ..................................................... 1.11
1.3.1 Static characteristics ................................................... 1.11
1.3.2 Dynamic characteristics ............................................. 1.17
Errors in measurements ........................................................... 1.18
Chaotic errors .......................................................................... 1.20
Operational errors ................................................................... 1.20
Limiting errors ......................................................................... 1.20
Static calibration of instruments .............................................. 1.23
Dynamic analysis of instruments ............................................ 1.26
Statistical evaluation of measurement data and errors ............1.39
Standards.................................................................................. 1.54
Summary .................................................................................. 1.69
Short questions and answers ................................................... 1.71
ELECTRICAL AND ELECTRONIC INSTRUMENTS ............... 2.3
2.1
Introduction ............................................................................. 2.3
2.2
Essentials of indicating instruments ........................................ 2.4
2.2.1
2.2.2
2.2.3
2.3
Deflecting Torque....................................................... 2.4
Controlling Torque ..................................................... 2.5
Damping Torque......................................................... 2.9
Types of analog ammeters and voltmeters .............................. 2.12
2.3.1
Moving iron type instruments .................................... 2.13
2.3.1.1 Attraction type MI instruments .................. 2.13
2.3.1.2 Repulsion type MI instruments
2.15
2.3.1.3
General Torque equation of MI instruments2.16
2.3.1.4
2.3.1.5
Errors in MI instruments ............................ 2.18
Advantages and disadvantages of MI
Instruments .................................................. 2.19
2.3.2
PMMC instrument ...................................................... 2.20
2.3.2.1 Construction and working .......................... 2.20
2.3.3
2.3.2.2
Torque equation ........................................... 2.21
2.3.2.3
Advantages and disadvantages of PMMC
instruments .................................................. 2.22
Dynamometer type instruments................................... 2.22
2.3.3.1
2.3.3.2
Construction and working ........................... 2.22
Torque equation for Electrodynamometer
instruments .................................................. 2.24
2.3.3.3
2.3.3.4
Errors in dynamometer type instruments ... 2.27
Advantages and disadvantages of
Dynamometer type instruments .................. 2.27
2.4
Extension of instrument range ................................................. 2.28
2.4.1
Shunts ......................................................................... 2.28
2.4.1.1 Requirements of shunt ................................ 2.28
2.4.1.2
2.4.1.3
2.4.2
2.5
Multipliers .................................................................. 2.30
2.4.2.1
2.4.2.2
Requirements of multiplier ........................ 2.30
Multiplier resistance for D.C meters .......... 2.31
2.4.2.3
Multiplier resistance for a.c meters ............ 2.31
Digital Voltmeters (DVM) ...................................................... 2.32
2.5.1
2.5.2
Ramp type DVM ......................................................... 2.35
Integrating (Dual Slope) type DVM ........................... 2.37
2.5.3
2.5.4
Potentionmetric type DVM ........................................ 2.41
Successive approximation type DVM ........................ 2.42
2.5.5
Automation in voltmeters ........................................... 2.45
2.5.6
2.6
Resistance of d. shunt ............................. 2.29
Shunt for a.c instruments ............................ 2.29
2.5.5.1
Automatic polarity indication ................... 2.45
2.5.5.2
Automatic ranging and decimal
point positioning ..................................... 2.45
2.5.5.3
Automatic Zeroing ..................................... 2.47
2.5.5.4
Display and decoders .................................. 2.48
Accuracy of DVM ....................................................... 2.49
Wattmeters............................................................................... 2.51
2.6.1 Wattmeter connection .................................................. 2.52
2.6.2
Electrodynamometer wattmeter .................................. 2.54
2.7
2.8
2.6.3
Deflecting torque ......................................................... 2.55
2.6.4
Errors in dynamometer wattmeters ............................. 2.56
2.6.5
Low power factor wattmeter (dynamometer type) ...... 2.57
2.6.6
Induction wattmeters ................................................... 2.58
2.6.7
Three phase wattmeter................................................. 2.61
Energy Meters ......................................................................... 2.62
2.7.1
Single phase induction energy meter.......................... 2.62
2.7.2
Errors in energy meter and adjustments ..................... 2.65
2.7.3
Three phase energy meters ........................................ 2.66
Instrument Transforms ............................................................ 2.68
2.8.1
Current Transformer (C.T)............................................ 2.68
2.8.1.1 Construction and working C.T .................... 2.68
2.8.1.2 Errors in C.T ................................................ 2.70
2.8.1.3 Effect of open circuited secondary ............. 2.71
2.8.1.4
2.8.2
2.8.3
Advantage of C.T over shunt ....................... 2.72
Potential Transformers (P.T) ...................................... 2.72
2.8.2.1
Construction and working of P.T ................ 2.72
2.8.2.2
2.8.2.3
Errors in P.T ................................................. 2.73
Advantage of P.T over Multipliers
2.74
Advantages of Instrument transformers
(Both C.T and P.T) ...................................................... 2.74
2.8.4
2.9
Use of C.T and P.T for power measurement ............... 2.75
Frequency Meters .................................................................... 2.75
2.9.1
Mechanical resonance (Vibrating need) type
frequency meter ........................................................... 2.76
2.10
2.9.2
Electrical resonance type frequency meter ................. 2.77
2.9.3
Weston (Moving iron) frequency meter ..................... 2.80
2.9.4
Digital frequency meter .............................................. 2.81
Phase meters ............................................................................ 2.82
2.10.1 Single phase dynamometer power factor meter ......... 2.82
2.10.2 Three phase dynamometer power factor meter .......... 2.84
2.10.3 Phase sequence indicators (Three Phase Meters) ....... 2.86
2.10.3.1 Rotating type phase sequence indicator ..... 2.86
2.10.3.2 Static type phase sequence indicator .......... 2.87
2.10.4 Electronic phase meter ............................................... 2.89
2.11
Magnetic Measurements.......................................................... 2.90
2.11.1 Flux meter................................................................... 2.91
2.11.2 Measurement of Flux Density(B) ............................... 2.93
2.11.3 Measurement of Magnetising Force(H) ..................... 2.95
2.11.4 Magnetic Potentiometer ............................................. 2.96
2.11.5 Measurement of Leakage factor with Flux meter ...... 2.98
2.12
Determination of B-H Curve ................................................... 2.99
2.12.1 Method of Reversals ................................................... 2.99
2.12.2 Step by step method .................................................... 2.100
2.13
Measurement of Iron Losses ................................................... 2.101
2.13.1 Methods for measurement of iron losses .................... 2.103
2.13.1.1 Wattmeter method
2.103
2.13.1.2 Bridge method .................................................... 2.105
2.13.1.3 A.C. Potentiometer method ................................... 2.110
3.
2.14
2.15
Problems .................................................................................. 2.111
Summary .................................................................................. 2.116
2.16
Short Question and answer ..................................................... 2.119
SIGNAL CONDITIONING AND BRIDGES.................................. 3.3
3.1
Introduction ............................................................................. 3.3
3.2
Need for signal conditioning ................................................... 3.3
3.3
Signal conditioning element .................................................... 3.3
3.4
D.C signal conditioning system............................................... 3.4
3.5
A.C signal conditioning system............................................... 3.5
3.6
Instrumentation amplifiers ...................................................... 3.6
3.7
Op-amp (Operational Amplifier)............................................. 3.8
3.7.1
3.7.2
3.7.3
Block diagram of Op-amp.......................................... 3.8
Ideal Op-amp .............................................................. 3.8
Op-amp characteristics ............................................... 3.9
3.8
Buffer amplifier ....................................................................... 3.13
3.9
Differential amplifier ............................................................... 3.14
3.10
3.11
Charge amplifier ...................................................................... 3.20
Filters.........................................................................................3.21
3.11.1 Need for filters ........................................................... 3.21
3.12
3.11.2 Types of filters ........................................................... 3.22
D.C. Bridges ............................................................................ 3.28
3.12.1 Wheatstone bridge...................................................... 3.28
3.13
3.12.2 Carey-Foster Slide wire bridge .................................. 3.33
3.12.3 Kelvin Double bridge ................................................. 3.40
A.C. Bridges ............................................................................ 3.42
3.13.1 Maxwell’s inductance - capacitance bridge ............... 3.46
3.13.2 Hay’s bridge 3.48
3.13.3 Anderson’s bridge................................................................................ 3.50
3.13.4 Owen’s bridge ............................................................ 3.53
3.13.5 Schering bridge .......................................................... 3.54
3.13.6 Wien’s bridge ............................................................. 3.57
3.14
Grounding Techniques ............................................................ 3.64
3.14.1 Difference between Safety Guard and Signal Ground 3.65
3.14.2
Ground Loops and Ground Currents..................... 3.65
3.14.3 Common-mode and Series-mode Voltages.................. 3.67
3.14.4. Protecting the Measuring
Leads from Parasitic Voltages.
3.69
3.14.4.1 Shielding Techniques..............................3.69
3.14.4.2. Isolation Techniques.............................. 3.71
3.14.4.3 Common Mode Rejection Ratio(CMRR)....... 3.72
3.14.4.4 Floating Guard............................................... 3.74
3.14.4.5. Doubly Shielded Cables................................. 3.75
4.
3.15
Summary ................................................................................3.75
3.16
Short question & answers ...................................................... 3.77
TELEMETRY AND DATA PRESENTATION ............................ 4.3
4.1
Introduction ............................................................................ 4.3
4.2
General telemetry system ....................................................... 4.3
4.3
D.C telemetering system ........................................................ 4.4
4.3.1
4.3.2
4.3.3
4.4
Voltage telemetering system ..................................... 4.4
Current telemetering system ..................................... 4.5
Position telemetering system .................................... 4.7
A.C Telemetry ........................................................................ 4.9
4.5
4.6
4.7
4.8
4.9
4.10
4.11
4.12
4.13
4.14
4.15
4.4.1
Amplitude modulation .............................................. 4.9
4.4.2
Frequency modulation ............................................... 4.10
4.4.3
Phase modulation ...................................................... 4.12
Pulse telemetry
4.13
4.5.1
PAM (Pulse Amplitude Modulation) ........................ 4.13
4.5.2
PDM (Pulse Duration Modulation) ........................... 4.14
4.5.3
PPM (Pulse Position Modulation)............................. 4.15
4.5.4 PCM (Pulse Code Modulation) ................................. 4.16
Transmission channels ........................................................... 4.16
Multiplexing ........................................................................... 4.18
4.7.1 Frequency division multiplexing .............................. 4.18
4.7.2 Time division multiplexing ....................................... 4.19
Data Presentation .................................................................... 4.20
Display devices....................................................................... 4.20
4.9.1 Seven segment display .............................................. 4.20
4.9.2 LED (Light emitting diode) ...................................... 4.21
4.9.3 LCD (Liquid crystal diode) ...................................... 4.22
4.9.4 Nixie tubes ................................................................ 4.24
Recorders ................................................................................ 4.25
4.10.1 Strip chart recorder .................................................... 4.26
4.10.2 X-Y recorder ............................................................. 4.27
4.10.3 Magnetic tape recorders ............................................ 4.28
4.10.4 Methods of recording in magnetic tape recorder ...... 4.31
4.10.5 Digital tape recorders ................................................ 4.39
Cathode Ray Oscilloscope (CRO) .......................................... 4.45
Cathode Ray Tube (CRT)....................................................... 4.47
4.12.1 Electron Gun...............................................................
4.48
4.12.2 Electrostatic and Magnetostatic focusing.................. 4.49
4.12.3 Electrostatic and Electromagnetic deflection ............ 4.53
4.12.4. Post Deflection Acceleration (PDA) ........................ 4.60
4.12.5 Effect of beam transit time and frequency limitations
4.62
4.12.6 Screen for CRTs ....................................................... 4.62
4.12.7 Graticules.................................................................. 4.64
Digital storage oscilloscope.................................................... 4.65
Summary ................................................................................. 4.68
Short question & answers
4.70
5.
TRANSDUCERS AND DATA ACQUISITION SYSTEMS ....... 5.3
5.1
Introduction ............................................................................ 5.3
5.2
Selection of transducer..............................................................5.4
5.3
Classification of transducers .................................................. 5.4
5.4
Resistive transducer ................................................................ 5.6
5.4.1
5.4.2
5.12
POTS (Potentiometers)............................................. 5.7
Strain gauges ............................................................ 5.10
5.4.2.1 Type of strain gauges ............................... 5.13
5.4.2.2 Measurement of strain using bridges........ 5.19
5.4.2.3 Temperature compensation....................... 5.20
5.4.2.4 Strain gauge type load cell....................... . 5.21
5.4.3. Resistance thermometer........................................... 5.22
5.4.4
Thermistors ............................................................... 5.24
5.5
Inductive Transducer .............................................................. 5.27
5.5.1
Linear Variable Differential Transformer (LVDT) . 5.27
5.6
Capacitive Transducer ............................................................ 5.29
5.6.1
Transducer using change in Area of plates ............. 5.30
5.6.2
Transducer using change in Distance between plates5.32
5.6.3
Differential Arrangement ........................................ 5.33
5.6.4
Transducer using change in Dielectric constant ...... 5.34
5.6.5
Frequency response of capacitive transducers ........ 5.36
5.7
Piezoelectric transducer .......................................................... 5.38
5.7.1
Equivalent Circuit of Piezoelectric Transducer....... 5.41
5.8
Electromagnetic transducers................................................... 5.44
5.9
Thermoelectric transducer ...................................................... 5.45
5.9.1
Thermocouples ....................................................... 5.45
5.10 Opticial transducer ................................................................. 5.46
5.11 Encoders ................................................................................. 5.48
5.11.1
Optical encoders ..................................................... 5.49
5.11.2
Resistive digital encoders ....................................... 5.50
5.11.3
Shaft encoders
5.51
D/A Converters .................................................................................. 5.52
5.13 A/D Converters....................................................................... 5.55
5.14 Sample and Hold circuit ......................................................... 5.57
5.15 Data acquisition systems ........................................................ 5.58
5.15.1 Analog Data Acquisition system ............................. 5.58
5.16
5.17
5.18
6.
5.15.2 Digital Data Acquisition system.............................. 5.60
Problems ................................................................................. 5.62
Summary ................................................................................. 5.81
Short question and answers .................................................... 5.83
PROCESS INSTRUMENTATION.................................................. 6.3
6.1
Introduction ............................................................................. 6.3
6.2
Measurement of pressure......................................................... 6.3
6.3
Measurement of temperature ................................................... 6.10
6.4
Measurement of speed ............................................................. 6.17
6.5
Measurement of acceleration................................................... 6.22
6.6
Measurement of flow............................................................... 6.25
6.7
Measurement of liquid level .................................................... 6.30
6.8
Measurement of sound ............................................................ 6.35
6.8.1 Sound level meter....................................................... 6.36
6.8.2 Microphones ............................................................... 6.36
6.9
Measurement of PH ................................................................. 6.38
6.10
General outline of instrumentation
6.11
6.12
system in thermal power plants. ............................................. 6.40
Summary .................................................................................. 6.46
Short question & answers
6.48