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Contents
Module 1
Fundamentals of process measurement.
OBJECTIVES……………………………...............................................................................
7
1.0
INTRODUCTION ........................................................................................................
10
1.1
PRESSURE MEASUREMENT ...................................................................................
10
1.1.1
General Theory ........................................................................................................
10
1.1.2
Pressure Scales........................................................................................................
10
1.1.3
Pressure Measurement ............................................................................................
10
1.1.4
Common Pressure Detectors....................................................................................
12
1.1.5
Differential Pressure Transmitters ............................................................................15
1.1.6
Strain Gauges............................................. .............................................................16
1.1.7
Capacitance Capsule .................................... ..........................................................17
1.1.8
Impact of Operating Environment ……………………….............................................18
1.1.9
Failures and Abnormalities .......................................................................................19
1.2
FLOW MEASUREMENT...............................................................................................20
1.2.1
Flow Detectors ..........................................................................................................20
1.2.2
Square Root Extractor...............................................................................................28
1.2.3
Density Compensating Flow Detectors .....................................................................32
1.2.4
Flow Measurement Errors..........................................................................................34
1.3
LEVEL MEASUREMENT .............................................................................................35
1.3.1
Level Measurement Basics .......................................................................................35
1.3.2
Three Valve Manifold................................................................................................36
1.3.3
Open Tank Measurement..........................................................................................38
1.3.4
Closed Tank Measurement .......................................................................................39
1.3.5
Bubbler Level Measurement System ........................................................................44
1.3.6
Effect of Temperature on Level Measurement ..........................................................46
1.3.7
Effect of Pressure on Level Measurement ................................................................49
1.3.8
Level Measurement System Errors............................................................................49
1.4
TEMPERATURE MEASUREMENT..............................................................................51
1.4.1
Resistance Temperature Detector (RTD)..................................................................51
1.4.2
Thermocouple (T/C) ..................................................................................................54
1.4.3
Thermal Wells............................................................................................................56
1.4.4
Thermostats...............................................................................................................57
REVIEW
QUESTIONS - EQUIPMENT ..............................................................................61
Module
2 - CONTROL
2.0
INTRODUCTION .........................................................................................................66
2.1
BASIC CONTROL PRINCIPLES .................................................................................66
2.1.1
Feedback Control.......................................................................................................68
2.1.2
Feedforward Control..................................................................................................68
2.1.3
Summary ...................................................................................................................68
2.2
ON/OFF CONTROL .....................................................................................................69
2.2.1
Summary ...................................................................................................................70
2.3
BASIC PROPORTIONAL CONTROL ..........................................................................71
2.3.1
Summary ...................................................................................................................73
2.4
Proportional Control .....................................................................................................74
2.4.1
Terminology...............................................................................................................74
2.4.2
Practical Proportional Control ...................................................................................74
2.4.3
Summary ...................................................................................................................81
2.5
Reset of Integral Action.................................................................................................81
2.5.1
Summary ...................................................................................................................85
2.6
RATE OR DERIVATIVE ACTION ................................................................................85
2.6.1
Summary ...................................................................................................................90
2.7
MULTIPLE CONTROL MODES....................................................................................90
2.8
TYPICAL NEGATIVE FEEDBACK CONTROL SCHEMES……………………………..91
2.8.1
Level Control ............................................................................................................91
2.8.2
Flow Control ..............................................................................................................92
2.8.3
Pressure Control........................................................................................................93
2.8.4
Temperature Control..................................................................................................94
REVIEW
QUESTIONS - CONTROL ..................................................................................95
Module 3 Analog electronic instrumentation
3.1 4 to 20 mA
analog current signals…………………………………………………………98
3.2 Relating 4
to 20 mA signals to instrument variables …………..………………………101
3.2.1 Example
calculation: controller output to valve ……………………………………...101
3.2.2 Example
calculation: flow transmitter………………………..………………………..102
3.2.3 Example
calculation: temperature transmitter…………………..……………………103
3.2.4 Example
calculation: pH transmitter ………………………………..…………………103
3.2.5 Example
calculation: reverse-acting I/P transducer signal…………….……………104
3.2.6
Graphical interpretation of signal ranges……………………………………...………105
3.3 Controller
output current loops …………………………………………………………..107
3.4 4-wire
(“self-powered”) transmitter current loops ………………………………………109
3.5 2-wire
(“loop-powered”) transmitter current loops ……………………………………..110
3.6 Troubleshooting
current loops …………………………………………………………...112
3.6.1 Using a
standard milliammeter to measure loop current ………………………...…114
3.6.2 Using a
clamp-on milliammeter to measure loop current ……………………..……116
3.6.3 Using
“test” diodes to measure loop current …………………………………..……..117
3.6.4 Using
shunt resistors to measure loop current ………………………………………119
3.6.5
Troubleshooting current loops with voltage measurements……………………...…120
3.6.6 Using
loop calibrators ……………………………………………………..…………....124
3.6.7 NAMUR
signal levels ………………………….………………………………………..129
Module 4
Digital data acquisition and networks
4.1
Digitization of analog quantities………………………………………………………….131
4.1.1 Resolution
……………………………………………………………..………………...131
4.1.2 Sampling
rate ……………………………………………………………...…………….136
4.2 Digital
data communication theory ………………………………………………………138
4.2.1 Serial
communication principles ………………………………………...…………….140
4.2.2 Physical
encoding of bits ……………………………………………………….………143
4.2.3
Communication speed ……………………………………………………………….…146
4.2.4 Data frames
……………………………………………………………………………...148
4.2.5 Channel
arbitration………………………………………………………………………157
4.2.6 Code
sets ………………………………………………………………………………..163
4.2.7 The OSI
Reference Model …………………………………………………..…………166
4.3 EIA/TIA-232,
422, and 485 networks ……………………………………………………168
4.3.1
EIA/TIA-232 ……………………………………………………………………….……..170
4.3.2
EIA/TIA-422 and EIA/TIA-485………………………….……………...……………….173
4.4 Ethernet
networks……………………………………………………………….…………180
4.4.1
Repeaters (hubs)…………………………………………………………………….…. 181
4.4.2 Ethernet
cabling ………………………….………………………………………………183
4.4.3 Switching
hubs………………………………………………………………………….. 186
4.5 Internet
Protocol (IP)………………………….……………………………………………188
4.5.1 IP
addresses……………………………………………………………………………..189
4.5.2
Subnetworks and subnet masks…………………………………………………….…193
4.5.3 IP
version 6 ……………………………………………………………………..……….196
4.5.4 DNS……………………………………………………………………………...….........196
4.5.5
Command-line diagnostic utilities………………………………………………..…….197
4.6
Transmission Control Protocol (TCP) and User Datagram Protocol (UDP) ……..…199
4.7 The HART
digital/analog hybrid standard……………………………………………….201
4.7.1 HART
multidrop mode…………………………………………………………………..208
4.7.2 HART
multi-variable transmitters ………………………………………………..........209
4.8 Modbus…………………………………………………………………………………...…210
4.8.1 Modbus
data frames…………………………………………………………………….210
4.8.2 Modbus
function codes and addresses……………….………………………………212
4.8.3 Modbus
function command formats …………………………………………………..213
Module 5 Smart
Transmitter
5.1 Definitions ……………………………………………………….………..……………..220
5.2.1
Selection, Calibration and installation
…………………………………………….….224
5.2.2
Reference Condition Accuracy …………………...…………………………………..225
5.2.3
Thermal errors………………………………………………………………..…………225
5.2.4
Application specific errors ………………………………...……………………………225
5.2.5 Analog
units ………………………………………………………………..……………226
5.2.6
Calibration………………………………………………………………………………..228
5.2.7
Calibration Equipment………………………………………………………..…………105
5.3
Calibrating Hart Transmitters …………………………..………………………………..234
5.3.1 Calibration
concepts………………………………………… …………………………234
5.3.2 Error
Calculation …………………………..……………………………………………..235
5.3.3 HART fundamentals…………………………….…………………….……….………..238
5.3.4
Calibrating a Conventional Instrument……………………………………...…………240
5.3.5
Calibrating HART Instrument ………………………………………….....……………240
5.3.6 HART
Calibration Requirement ………………………………...……………………..242
5.3.7
Calibrating the Input Section ………………………………………..…………………243
5.3.8 Calibrating
the Output Section…………………………………………………………243
5.3.9 Testing
overall Performance ………………………………………………..…………243
5.3.10 Effect
of Damping on test Performance……………………………. ………………244
5.3. 11
Operations that are Not proper Calibration………………...……………… ………244
5.3.5
Calibrating HART Instrument …………………………………………….....…………240
5.3.6 HART
Calibration Requirement ………………………………...……………………..242
5.3.7
Calibrating the Input Section …………………………………………..………….……243
5.3.8 Calibrating
the Output Section…………………………………………………………243
5.3.9 Testing
overall Performance ………………………………………………..…………243
5.3.10 Effect
of Damping on test Performance……………………… …… ………………244
Module 6 Progress of International Standardization of
Fieldbus…………………….248
6.1.1 what is
Fieldbus………………………………..…………………………………………249
6.1.2 Progress
of Fieldbus Standardization……...........................................................250
6.1.2
Recognition as a Standardization Work Item ……………..………..…………………250
6.2 Process of
Standardization...……………………………………………………………251
6.2.1 Fieldbus
Standard Specifications……………..…………………..…………………….252
6.2.2 IEC/ISA
Standard Specifications…………………………………..……………………252
6.3 Features
of Fieldbus ………………………………………………..………………….…253
6.3.1
Comparison with Conventional Communication………………………………………148
6.3.2 Reduced
Wiring Cost ……..……………………………………..……………………..256
6.3.3
Multi-drop Conn …………….………………………………….……………………….256
6.3.4
Multivariable Detection and Transmission………………..…..……………………….256
6.3.5 Fieldbus
Communication Systems ……..…………………...……………………….257
6.3.6 Improved
Transmission Accuracy…………….…………………..…………………….256
6.3.7 Removing
Error Factors……………………………………………..………………….258
6.3.8 Enhanced
Data Transmission ……..……………..………………...………………….257
6.3.9
Distributed Functions…………………………………………………….……..………..260
6.3.10
Fieldbus Communication Systems
……..……………………………...…………….257
6.3.11
Interoperability…………….……………………………………………..…………….261
Appendix A : Application of Smart
Devices in Fiscal and Custody Transfer of Natural Gas
Energy Measurement Using Flow Computers and
Chromatography………………262
Appendix B : Application of Smart
Devices Maintenance and Calibration
Using 744 Process Calibrator for
Calibration of HART Field Instrumentation……272
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