Contents
1 Pressure measurement 1
1.1 Pressure and its units of measurement 1
1.1.1 Common units
1.1.1 Pressure of gases 1
1.1.2 Pressure of liquids 2
1.2 Types of pressure 3
1.2.1 Absolute pressure 3
1.2.2 Atmospheric air pressure 3
1.2.3 Pressure difference, differential pressure 3
1.2.4 Atmospheric pressure difference, overpressure 4
1.3 Common methods for measuring pressure 5
1.3.1 Direct pressure measuring instruments 5
1.3.1.1 Pressure measuring instruments with liquid column 5
• U-tube manometer 6
• lnclined-tube manometer 6
• Multiple liquid manometer 7
• Float-type manometer 7
1.3.1.2 Pressure balances with liquid separation 7
1.3.1.3 Piston-type pressure measuring instruments 9
• Piston-type pressure measuring instruments
• with spring-loaded piston 9
• Dead-weight pressure measuring instruments 9
1.3.2 Indirect pressure measurement instruments 11
1.3.2.1 Pressure measuring instruments with flexible elements 11
1.3.2.2 Electrical pressure sensors and pressure measuring instruments 13
• Sensor types with strain gauges 13
• Strain gauge transmission principles 21
• Diaphragm conversion 21
• Sensor principles with displacement measurement 22
• Other sensor principles 25
• Sensor principles for inspection and calibration systems 26
1.4 Pressure measuring instruments with
flexible measuring elements 30
1.4.1 Flexible measuring elements 31
1.4.1.1 Bourdon tubes 31
1.4.1.2 Diaphragm measuring elements 41
• Diaphragms 42
• Capsules 46
VIII
1.4.1.3 Bellows 48
1.4.2 Movements 48
1.4.3 Dials and pointers 52
1.4.4 The case 54
1.4.4.1 Connection positions 54
1.4.4.2 Design types 55
• Modular design of commercial pressure measuring instruments 55
• Modular design for industrial measuring instruments 56
• Forged cases for liquid filling 57
1.4.4.3 Vibration damping by liquid filling 58
• Resonant frequencies and amplitudes 58
• Resistance to resonance 59
• Investigation of various instrument types 60
1.4.4.4 Safety of pressure measuring instruments 63
1.4.5 Electrical and pneumatic accessories 66
1.4.5.1 Alarm contacts 66
• Direct contacts 66
• Indirect contacts 68
1.4.5.2 Transmitters 69
• Potentiometric transmitter 69
• Capacitive transmitters 69
1.4.6 Special flexible element pressure measuring instruments 72
1.4.6.1 Pressure measuring instruments for absolute and differential pressure 72
• Differential pressure measuring instrument with diaphragm 73
• Absolute pressure measuring instrument with diaphragm 73
• Absolute pressure measuring instrument with capsule 74
1.4.6.2 Pressure measuring instruments with high overload capability 75
1.4.6.3 Pressure measuring instruments and pressure transducers for
ultrapure gases 76
1.4.6.4 Gas density monitors for SF6 systems 77
1.4.7 Special designs and optional accessories 79
1.4.7.1 Pressure measuring instruments for oxygen and acetylene 79
1.4.7.2 Calibration with other pressure media 79
1.4.7.3 Bourdon tube with tip bleed 79
1.4.7.4 Bourdon tube with filling 80
1.4.7.5 Extension of the lower scale range (retard scale) 80
1.4.7.6 Dual scales 80
1.4.7.7 Scales for direct measurement of force 80
1.4.7.8 Temperature scale 81
1.4.7.9 Scales with compensation for difference in levels 82
1.4.7.10 Luminous dials 83
1.4.7.11 Mark pointers 83
1.4.7.12 Drag pointers 83
1.4.7.13 Suppressed zero 83
1.4.7.14 Extended pointer shaft 84
1.4.7.15 Safety glass 84
1.4.7.16 Special protection during shipment 84
1.4.8 Measurement data and standards concerning applications 84
1.4.8.1 Full scale range and maximum operating range 84
15494_INTRO.P65 8 7/18/01, 18:28
IX
1.4.8.2 Accuracy of the indication 85
1.4.8.3 Process fluids 86
1.4.8.4 Environmental conditions 87
1.5 Pressure transducers, pressure measuring
converters and pressure transmitters with
analog and digital circuits 90
1.5.1 Definition of a pressure transducer 90
1.5.1.1 Pressure transducers and their specifications 92
1.5.1.2 Pressure measuring converters 92
1.5.1.3 Technical data and their definition 93
• Measuring range / measuring span 93
• Overload pressure range 93
• Burst pressure 93
• Power supply 93
• Output signal (analog, digital) 94
• Response time 94
• Accuracy and conformity error 95
• Hysteresis 95
• Temperature ranges 96
• Compensated temperature range 96
• Types of electrical connection 96
1.5.1.4 Pressure transmitters 96
1.5.1.5 Differential pressure transmitter 97
1.6 Diaphragm seals 100
1.6.1 Diaphragm seal characteristic 101
1.6.2 Displacement volume and control volume 102
1.6.3 Practical applications 102
1.6.4 Response time 102
1.6.5 Computer-aided selection of diaphragm seals 103
1.6.6 WIKA diaphragm seal systems 104
1.6.6.1 Diaphragm seals 104
1.6.6.2 INLINE SEAL™ diaphragm seals 105
1.6.6.3 Capsule diaphragm seals 106
1.6.7 Summary 106
1.7 Selection, installation and initial operation 107
1.7.1 Checklist for selecting a pressure measuring instrument 107
1.7.2 Installation and operating instructions for pressure measuring instruments 111
1.7.2.1 Accessories for the measuring point and attachments for pressure
measuring instruments 109
1.7.2.2 Shut-off devices 110
1.7.2.3 Mounting the measuring instrument in position 110
1.7.2.4 Damping the measuring system 110
1.7.2.5 Temperature considerations 110
X
1.7.2.6 Chemical seals / Protective buffers 110
1.7.2.7 Protective devices 110
1.7.2.8 Measuring arrangements 111
1.7.2.9 Installation and start-up 112
1.7.2.10 Operation 112
1.7.2.11 Storage 113
1.7.2.12 Hazardous process fluids 113
1.7.3 Certification and testing 113
1.7.3.1 Certification of material tests 113
1.7.3.2 Calibration 114
2 Thermometry
2.1 Introduction to thermometry 119
2.1.1 Historical development of the thermometer 120
2.1.2 Historical development of the temperature scales 121
121
2.2 Principles and definitions of
temperature measurement 122
2.2.1 The thermodynamic temperature scale 123
2.2.2 Temperature and its units 124
2.2.3 The International Temperature Scale (ITS-90) 125
2.2.4 Measuring principles and sensors for temperature measurement 129
2.2.4.1 Measuring principles on the basis of thermal expansion of substances 129
2.2.4.2 Electrical temperature sensors 131
• Metal resistance thermometers 131
• Thermocouples 132
• Semiconductor sensors 135
• Radiation thermometers (pyrometers) 139
2.2.4.3 Additional temperature measuring techniques 140
• Optical measuring methods 140
• Crystal oscillator temperature sensors 142
• Acoustic measuring methods 143
• Temperature indicators 144
• Thermal noise thermometers 144
• Capacitive temperature sensors 145
• Inductive temperature sensors 146
2.3 Industrial direct-contact thermometers 148
2.3.1 Temperature measurement with direct-contact thermometers 148
2.3.2 Temperature measurement in liquids and gases 149
2.3.2.1 Installation conditions of thermometers 149
• Thermometer installation in pipes 149
• Thermometer installation in tanks or cylinders 150
• Thermometer installation in steam pipes 150
• Thermometer installation in flue gas ducts 151
15494_INTRO.P65 10 7/18/01, 18:28
XI
2.3.2.2 Mechanical load 151
• Static loading by the hydrostatic pressure 151
• Dynamic loading of a thermowell exposed to flow 152
• Vibration load 153
2.3.2.3 Chemical resistance 155
• Resistance in oxidizing atmosphere 155
• Resistance in cases of oxygen deficiency
and in reducing atmosphere 155
• Resistance in aqueous media 155
2.3.2.4 Commonly used materials for thermowell 156
2.3.2.5 Standardized thermometers 157
• Standardized thermowells 158
• Standardized connection heads 161
2.3.3 Temperature measurement in solid bodies and on surfaces 162
2.3.3.1 Thermometer installation in solid bodies 162
2.3.3.2 Temperature measurement on surfaces 163
2.4 Temperature measurement variables 164
2.4.1 Heat transfer from the process to the thermometer 164
2.4.1.1 Thermal conductivity of substances 164
2.4.1.2 Heat transfer resistance at interfaces and phase boundaries 165
2.4.1.3 Transfer of heat by radiation 171
2.4.2 Immersion depth of the thermometer 174
2.4.3 Self-heating of electrical thermometers 175
2.5 Time response of contact thermometers 177
2.5.1 Time response in the water model 177
2.5.2 RC models for description of the dynamic behavior of thermometers 177
2.5.2.1 Thermometer with exponential transient response and the RC model 177
2.5.2.2 Basic circuit of R-C model in temperature measurement 179
2.5.3 Characteristic values for the time response 181
2.6 Industrial expansion thermometers 184
2.6.1 Glass thermometers 184
• Construction and types 184
• Parameters, errors and measuring uncertainties 187
2.6.2 Dial thermometers 190
2.6.2.1 Stem-type expansion thermometer 190
2.6.2.2 Bimetallic thermometers 192
• Construction and basic types 192
• Design of bimetals 193
• Parameters, errors and error limits 195
• Applications and technical designs 197
2.6.2.3 Spring thermometers 198
• Liquid spring thermometers 199
• Vapour pressure spring thermometer 202
• Gas pressure spring thermometers 203
15494_INTRO.P65 11 7/18/01, 18:28
XII
2.7 Electrical thermometers for
industrial applications 208
2.7.1 Platinum resistance thermometers 208
2.7.1.1 Construction of a platinum resistance thermometer 208
2.7.1.2 Platinum measuring resistors 209
• Ceramic measuring resistors 210
• Glass measuring resistors 210
• Film measuring resistors 211
2.7.1.3 Circuitry 212
2.7.1.4 Types of construction 213
• Industrial resistance thermometers with measuring elements 213
• Application-rated resistance thermometers 214
2.7.1.5 Measuring uncertainties of platinum resistance thermometers 217
• Self-heating error 217
• Instability and aging 217
• Effect of the insulation resistance 217
2.7.1.6 Standardization of industrial platinum resistance thermometers 218
2.7.2 Thermocouples 218
2.7.2.1 Construction of a thermocouple 219
2.7.2.2 Circuitry 219
2.7.2.3 Thermocouple pairings 219
2.7.2.4 Extension cables and compensating cables 221
2.7.2.5 Reference point compensation 221
2.7.2.6 Types of thermocouple design 221
• Technical thermocouples with measuring inserts 221
• Application-specific thermocouples 222
2.7.2.7 Measuring uncertainties of thermocouples 224
• Errors due to aging 224
• Errors due to inhomogeneities 225
• Errors due to the reference point and compensating cable 225
• Errors due to galvanic currents and faulty insulation resistance 226
2.7.2.8 Standardization and validation 227
• Basic value sets and tolerance classes 227
• Validability of thermocouples 228
2.8 Outlook and development trends for industrial
temperature measurement 229
3 Process engineering requirements for the
measurement of pressure and temperature 231
15494_INTRO.P65 12 7/18/01, 18:28
XIII
3.1 Signal processing and transmission in the
measurement chain 231
3.1.1 Transducer signal conversion 232
3.1.1.1 Basic measuring methods for electrical sensors 232
• Resistance 232
• Voltage 232
• Frequency conversion method 233
3.1.1.2 Basic functions of transducers 234
3.1.1.3 Analog transmitter or transducer 236
3.1.1.4 Digital transmitter or transducer 237
• Frequency analog-digital conversion 237
• Parallel analog-digital conversion 238
• Approximation analog-digital conversion 238
• Integrative analog-digital conversion 239
• Design of a digital transmitter 241
3.1.2 Standardized analog signal transmission 243
3.1.2.1 Voltage transmission 243
3.1.2.2 Current signal transmission 243
3.1.3 Digital signal transmission 246
3.1.3.1 Standardized electrical digital interfaces 246
• Serial interfaces 246
• Digital parallel interfaces 248
3.1.3.2 Field bus systems 249
• Reference model OSI (Open System Interconnection) 249
3.1.4 Signal processing and evaluation 250
3.1.4.1 Analog and digital indicators 250
• Analog indicating systems 250
• Digital indicating systems 252
3.1.4.2 Stored program controllers (SPC) 253
3.1.4.3 Loop controllers 254
3.1.4.4 Computer-aided evaluation 255
3.2 Calibration 256
3.2.1 Introduction to calibration technology 256
3.2.1.1 Calibration, validation and adjustment 256
3.2.1.2 Calibration traceability 256
3.2.1.3 Uncertainty of measurement when calibrating 257
3.2.2 Calibrating pressure measuring instruments 258
3.2.2.1 Calibrating with deadweight tester 259
• Calibrating pressure gauges with low measurement uncertainty
260
3.2.2.2 Calibrating with the quartz Bourdon tube controller 260
• The quartz Bourdon tube manometer as working standard 260
• Calibrating pressure transmitters 261
3.2.2.3 Calibrating with mobile calibration units 261
3.2.2.4 Error explanations for calibrating pressure gauges 262
3.2.3 Calibrating temperature measurement instruments 263
15494_INTRO.P65 13 7/18/01, 18:28
XIV
3.2.3.1 Calibration by fixed points 264
• Standard resistance thermometer conforming with ITS-90 264
• Fixed point calibration 266
• Resistance measuring bridges 267
3.2.3.2 Calibrating by comparison measurement 268
• Calibrating in thermostatic baths 268
• Calibrating in dry block calibrators 272
• Calibration in temperature block calibrators 274
3.2.3.3 Error observations for thermometer calibrating 275
3.2.4 Calibrating result documentation 277
3.3 Electromagnetic compatibility 278
3.3.1 Basic physical definitions 278
3.3.1.1 Basic definition of EMC 278
3.3.1.2 Voltage interference 278
3.3.1.3 Current interference 278
3.3.1.4 Electromagnetic waves 279
• Frequency ranges of electromagnetic waves 279
3.3.1.5 Types of coupling for electromagnetic interference 279
• Physical couplings 279
• Normal mode and common-mode interference 279
3.3.2 EMC standards and regulations 280
3.3.3 Breakdown of measuring methods by defined interference 282
3.3.3.1 Radiated field 282
3.3.3.2 Bursts 283
3.3.3.3 ESD 284
3.3.3.4 Surge 284
3.3.3.5 Voltage interruption/voltage fluctuation 285
3.3.3.6 Conducted high frequency irregularities 286
3.3.3.7 Overhead power frequency interference (hum) 286
3.3.3.8 Residual ripple 287
3.3.3.9 Emitted interference radiation 287
3.3.4 Demands on equipment behavior in industry 287
3.3.4.1 Equipment behavior classification when exposed to interference 288
3.3.4.2 The CE symbol 288
3.4 Explosion protection on electrical measuring devices 293
3.4.1 Basic terms and definitions 293
3.4.1.1 Historical development 293
3.4.1.2 Basic terms of physics 294
3.4.1.3 Standards and regulations 295
• Technical characteristic safety parameters 296
• Types of protection 297
3.4.2 Design rules for intrinsic explosion protected measuring devices 300
3.4.2.1 Electrical regulations 300
• Minimum ignition energy 300
• Power limitation 300
• Energy storage limitation 301
15494_INTRO.P65 14 7/18/01, 18:28
XV
3.4.2.2 Design rules 302
• Distance conditions 302
• Materials and material properties 302
3.5 Chemical resistance 304
4 Appendix and tables 307
4.1 National and international standards and
specifications 307
4.1.1 Pressure measuring instruments with an elastic
measuring element and accessories 307
4.1.1.1 German standards and specifications 307
4.1.1.2 International standards and specifications 312
4.1.1.3 Non-German standards and specifications 312
4.1.2 Flanges, connections and fittings 319
4.1.2.1 German standards and specifications 319
4.1.2.2 Non-German standards 323
4.1.3 Electrical measuring instruments and pressure gauges 327
4.1.3.1 German standards and specifications 327
4.1.4 Thermometers, temperature gauges and accessories 329
4.1.4.1 German standards and specifications 329
4.1.4.2 International standards and specifications 332
4.1.4.3 Non-German standards 333
4.1.5 Electrical temperature measuring instruments 338
4.1.5.1 German standards 338
4.1.5.2 International standards 340
4.1.5.3 Non-German standards 340
4.1.6 Further standards and specifications concerning general 342
measuring systems 342
4.1.6.1 German standards and specifications 342
4.1.6.2 International standards and specifications 345
4.1.6.3 Non-German standards 346
4.1.7 Standards and specifications with contents applying to safety 346
4.1.8 Further information is to be found in: 348
4.1.9 Contact addresses for standards and specifications 349
4.2 Tables and overviews 352
4.2.1 Tables of legal units 352
4.2.2 Conversion factors for commonly used pressure units 357
4.2.2.1 SI units - Technical units (metric) 357
4.2.2.2 SI units - Technical units (inch based) 358
4.2.2.3 Technical units (metric) - Technical units (inch based) 359
15494_INTRO.P65 15 7/18/01, 18:28
XVI
4.2.3 Refrigerants 360
4.2.4 pH values of various solutions at 68∞ F 362
4.2.5 Boiling and melting point of various process fluids at 29.92 "Hg 363
4.2.6 Density of process fluids 364
4.2.7 Types of enclosure for cases (NEMA and IP) 366
4.2.8 Common materials of pressure gauges 368
4.2.9 Comparison of corrosion-resistant steels between
international standards 370
4.2.10 Corrosion resistance table 371
4.2.11 WIKA part numbering system for mechanical pressure gauges 398
4.3 Legend of symbols used 400
4.4 Abbreviations 409
4.5 Literature, sources 411
4.6 Index 417
Related:
INSTRUMENT ENGINEERS' HANDBOOK-VOLUME I
INSTRUMENT ENGINEER'S HANDBOOK-VOLUME II
Measurement and Instrumentation Principles
0 comments:
Post a Comment