Electrical Temperature Measurements - with thermocouples and resistance thermometers
Electrical Temperature Measurement.pdf
Electrical Temperature Measurement with thermocouples and resistance thermometers
Matthias Nau
Contents
1 Electrical temperature measurement7
1.1 Contact temperature measurement7
1.2 Non-contact temperature measurement . 8
1.2.1 Total radiation pyrometer8
1.2.2 Spectral pyrometer9
1.2.3 Band radiation pyrometer9
1.2.4 Radiation density pyrometer . 9
1.2.5 Distribution pyrometer . 9
1.2.6 Ratio pyrometer9
2 The concept of temperature11
2.1 The historical temperature scale11
2.2 The fixed temperature points15
2.3 The temperature scale according to ITS-9015
3 Thermocouples19
3.1 The thermoelectric effect19
3.2 Thermocouples . 23
3.3 Polarity of the thermoelectric emf23
3.4 Action on break and short circuit24
3.5 Standardized thermocouples25
3.5.1 Voltage tables27
3.5.2 Deviation limits . 28
3.5.3 Linearity30
3.5.4 Long-term behavior30
3.6 Selection criteria32
3.6.1 Type T (Cu-Con)33
3.6.2 Type J (Fe-Con)33
3.6.3 Type E (NiCr-Con)33
3.6.4 Type K (Ni-CrNi)33
3.6.5 Type N (NiCrSi-NiSi)34
3.6.6 Types R, S and B . 34
3.7 Standard compensating cables35
3.7.1 Color codes of compensating cables36
3.8 Connection of thermocouples . 37
3.9 Construction of thermocouples . 40
3.10 Mineral-insulated thermocouples . 40
3.11 Troubleshooting42
3.11.1 Possible connection errors and their effects:43
4 Resistance thermometers45
4.1 The variation of resistance with temperature45
4.2 Platinum resistors45
4.2.1 Calculating the temperature from the resistance47
4.2.2 Deviation limits . 49
4.2.3 Extended tolerance classes50
4.3 Nickel resistors . 51
4.3.1 Deviation limits . 51
4.4 Connection of resistance thermometers52
4.4.1 2-wire arrangement52
4.4.2 3-wire arrangement53
4.4.3 4-wire arrangement53
4.4.4 2-wire transmitter54
4.5 Construction55
4.5.1 Ceramic resistance sensors55
4.5.2 Glass resistance sensors . 55
4.5.3 Foil sensors57
4.5.4 Thin-film sensors . 57
4.6 Long-term behavior of resistance thermometers59
4.7 Errors in resistance thermometers60
4.7.1 Effect of the cable60
4.7.2 Inadequate insulation resistance . 60
4.7.3 Self-heating61
4.7.4 Parasitic thermoelectric emfs62
5 The transfer function63
6 Heat conduction error . 67
6.1 Measures to reduce the heat conduction error69
7 Calibration and certification71
7.1 Calibration71
7.2 Calibration services72
7.3 Certification . 73
8 Fittings and protection tubes . 75
8.1 Construction of electrical thermometers . 75
8.1.1 Terminal heads to DIN 43 72976
8.2 DIN standard thermometers and protection tubes77
8.3 Application-specific thermometers . 80
8.3.1 Resistance thermometers for strong vibration . 80
8.3.2 Resistance thermometers for the food industry81
8.3.3 Resistance thermometers for heat meters . 82
8.4 Demands on the protection tube83
8.4.1 Metallic protection tubes . 84
8.4.2 Protection tubes for melts85
8.4.3 Organic coatings . 86
8.4.4 Ceramic protection tubes87
8.4.5 Ceramic insulation materials . 88
8.4.6 Special materials . 88
8.5 Operating conditions of protection tubes89
8.5.1 Protection tube materials with melts . 90
8.5.2 Resistance to gases91
9 Explosion-proof equipment . 93
9.1 Types of ignition protection95
9.1.1 Intrinsic safety “i” protection to EN 50 02095
9.1.2 Temperature probes and explosion protection . 95
9.2 The intrinsically safe circuit96
9.3 Interconnection of electrical equipment96
10 The measurement uncertainty101
10.1 The measurement process . 102
10.2 The simplistic approach: uncertainty interval . 102
10.3 The GUM approach: standard measurement uncertainty103
10.3.1 The rectangular distribution . 105
10.3.2 The triangular distribution . 105
10.3.3 The normal distribution106
10.4 Determining the measurement uncertainty to GUM106
10.5 Industrial practice: expanded measurement uncertainty106
10.6 Uncertainty components of a temperature measurement system107
11 Appendix115
11.1 Summary of steel types and their various designations115
11.2 Formulae for temperature conversion . 116
11.3 Voltage tables for thermocouples118
11.3.1 Iron - Constantan (Fe-Con) J119
11.3.2 Iron - Constantan (Fe-Con) L122
11.3.3 Copper - Constantan (Cu-Con) T . 123
11.3.4 Copper - Constantan (Cu-Con) U . 124
11.3.5 Nickel Chromium - Nickel (NiCr-Ni) K . 125
11.3.6 Nickel Chromium - Constantan (NiCr-Con) E . 130
11.3.7 Nicrosil - Nisil (NiCrSi-NiSi) N . 132
11.3.8 Platinum Rhodium - Platinum (Pt10Rh-Pt) S136
11.3.9 Platinum Rhodium - Platinum (Pt13Rh-Pt) R141
11.3.10 Platinum Rhodium - Platinum (Pt30Rh-Pt6Rh) B . 146
11.4 Reference values for Pt 100151
11.5 Reference values for Ni 100154
12 Standards and literature . 155
12.1 Standards155
12.2 Literature156
Index157
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