Anderson N.A. - Instrumentation for Process Measurement and Control (1998).pdf

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THIRD EDITION
for
NORMAN
A. ANDERSON
CHILTON COMPANY
PENNSYLVANIA
RAONaR,
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CONTENTS
Preface
SECTION
I FEEDBACK
PROCESS
CONTROL
1
1 Introduction
to Process
Control
1
Types of Processes 5 Processes with More Than One Capacity and Resis-
tance 6 Dead Time 6 Measurement 7 Symbols 1.0 The Feedback
Loop 1.0 Feedback Control 1.4 ControIling the Process 1.4 Selecting
ControIler Action 1.6 Upsets 1.7 Process Characteristics and ControIl-
ability 1.7 Controller Responses 1.8 On/Off Control 1.9 Proportional
Action 20
Integral Action (Reset) 23
Derivative Action 25
Selecting
the ControIler 27
Conclusion 29
Questions 30
2 Process/Pressure
Measuring
Instruments
33
What Is Pressure? 33
Units of Measurement 35
Pressure Measure-
ment 35
The Pascal 36
Bar Versus Pascal 37
Gauge, Absolute, and
Differential Pressure 37
Understanding the Effects of Gravity 38
Gravity-
Dependent Units 38
Gravity-Independent Units 39
Pressure Stan-
dards 39
Plant Instruments That Measure Pressure Directly 44
Bell
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vi
CONTENTS
Instrument 44
Slack .or Limp-Diaphragm 44
Pressure Gauges 46
Liquid or Steam Pressure Measurement 48
Seals and Purges 48
Pulsa-
tion Dampener 48
Metallic Bellows 49
Pressure Transmitters 52
Sig-
nal Transmissions 52
Pneumatic Recorders and Indicators 53
Mechanical
Pressure Seals 55
Calibration Techniques 59
Field Standard 59
Port-
able Pneumatic Calibrator 59
Force-Balance Pneumatic Pressure Trans-
mitter 60
Pneumatic Relay 62
Principle of Operation 63
Absolute
Pressure Transmitter 64
Questions 65
3 Level and Density Measurements 69
Level Measurement Methods 69 Float-and-Cable 70' Displacement
(Buoyancy) 71 Head or Pressure 73 Capacitance 78 Conductance 79
Radiation 79 Weight 79 Ultrasonic 80 Thermal 81 Density Mea-
surement Methods for Liquids and Liquid glumes 81 Hydrostatic Head 82
Radiation 84 Vibration 84 Temperature Eft'ects and Considerations 84
Dift'erential Pressure Transmitter 85
Questions 87
4 Flow Measurement 90
Constriction or Differential Head Type 91
Primary Devices 94
Secondai-y
Devices 99
Relating Flow Rate to Differential 100
Effect of Temperature
on Flow Rate 103
Variable Area Meters (Rotameter) 109
Open-Channel
Flow Rate Measurements 109
Primary Devices 110
Installation and
Selection Considerations 116
Velocity Flowmeters 117
Magnetic Flow-
meter 117
Vortex Flowmeter 121
Turbine Flowmeter 122
Other Flow-
meters 123
Conclusion 124
Questions 124
5 Temperature and Humidity Measurements
126
Temperature 126
Filled Thermal Systems 128
Electrical Systems 130
Thermocouples 130
Resistance Thermal Detectors 139
Thermistors 144
Humidity Measurements 144
Questions 148
6 Analytical Measurements 151
Electrical Conductivity 151
Types of Calibration 154
Calibration in
Conductivity 154
Calibration in Terms of Concentration of
Electrolyte
155
Polarization 156
Cell Construction 156
Electrodeless
Conductivity Measurements 157
Hydrogen Ion Activity (pH) 159
Ioniza-
tion or Dissociation 159
The pH Scale 161
Measurement of pH-The
Glass Electrode 164
Reference Electrode 165
Temperature Compensa-
tion 168
Reading the Output of the pH Electrodes 169
pH Control 170
Summary 172
Oxidation-Reduction Potential 172
Ion-Selective Measure-
ment 173
Chromatography 174
Capacitance 175
References 176
Questions 176
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