techniques for approximating the international temperature ... - BIPM

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158 temperature is measured with the desired accuracy with another thermometer (mercury-in- glass thermometer or resistance thermometer) or by realization of a fixed-point temperature (ice point or water triple point, see Sec. 9.4). 18.6 Calibration of Base-Metal Thermocouples The calibration of a thermocouple consists of the determination of its emf at a sufficient number of known temperatures, some of which can be fixed points, so that with some accepted means of interpolation its emf will be known over the entire temperature range in which it is to be used. In comparison to the situation with noble-metal thermocouples (Sec. 9.5), the number of calibration points necessary with base-metal !thermocouples to reach their limit of accuracy will be greater because of the more complex emf-temperature relationships and because more factors can influence the deviation of the real thermocouple characteristics from the reference table or polynomial values. Because of this the methods of interpolating between the calibration points become of prime importance for interpolation accuracies approaching 0.1 K [ASTM (1981)]. For lower accuracies comparatively simple methods of calibration will usually suffice (comparison with a standard thermometer in an isothermal environment). The errors in calibration are of two sorts: those influencing the observations at the calibration points and those arising from the interpolation between the calibration points. The influence of the first can be reduced by use of well-designed equipment and careful techniques. The recommended method to reduce the second error is to fit the differences between the observed calibration values and the values obtained from standard reference tables, i.e. the deviation of the real characteristics of the thermocouple from the nominal one. In order to determine the mean deviation curve the application of least-squares fitting is useful, but in several cases a graphical interpolation method will be sufficient (Sec. 9.5). Typical accuracies to be expected with the various thermocouples if calibrated using fixed points are given in Table 18.6, and when calibrated by comparison techniques are given in Table 18.7. The interpolation formulae used to generate the standard reference tables are given in Appendix F. No such formulae have yet been internationally agreed upon for the tungsten-rhenium types.
159 Table 18.6: Accuracies Attainable with Thermocouples using Fixed Point Techniques [ASTM (1981 )]. Type Temperature Calibration Calibration total uncer- range (°C) points uncertainty tainty of at observed interpolated points (K) values (K) _________________________________________________________________________ S or R 0... 1100 Zn,Sb,Ag,Au 0.2 0.3 S or R 0...1100 Sn,Zn,AI,Ag,Cu 0.2 0.3 B 600...1100 AI,Ag,Au 0.2 0.5 E 0... 870 Sn, Zn, AI 0.2 0.5 J 0...760 Sn,Zn,AI 0.2 1.0 K 0...1100 Sn,Zn,AI,Ag,Cu 0.2 1.0 N 0... 1100 Sn, Zn, AI, Ag, Cu 0.2 1.0 W/Re 1000 ... Au, Ni, Pd, Pt, Rh 0.5 ... 2.7 ... ...2000 ...5.0 ...7.0 _________________________________________________________________________ Table 18.7: Accuracies Attainable with Thermocouples using Comparison Techniques in Laboratory Furnaces [ASTM (1981 )]. Type Temperature Calibration Calibration total uncer- range (°C) points uncertainty tainty of at observed interpolated points (K) values (K) _________________________________________________________________________ S or R 0...1100 every 100 K 0.3 0.5 B 600... 1100 " " " 0.3 0.5 E 0... 870 " " " 0.5 0.5 J 0... 760 " " " 0.5 1.0 K 0...1100 " " " 0.5 1.0 N 0... " " " 0.5 1.0 _________________________________________________________________________
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BUREAU INTERNATIONAL DES POIDS ET M
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TECHNIQUES FOR APPROXIMATING THE IN
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iv W(100 °C) = 1.385 (exact value
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Centre for Quantum Metrology Nation
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2. Type J viii a) temperature range
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c) temperature range from 1664.5 °
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xii
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xiv Acknowledgments This monograph
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xvi 3.3.2 Melting Points of Gold (1
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xviii 11.3 Thermal Contact 111 11.4
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1 1. Introduction The Comité Consu
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3 thermometers except in special ex
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5 The accuracies with which tempera
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Table 1.1: Summary of Some Properti
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PART 1: TECHNIQUES AND THERMOMETERS
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11 Fig. 2.1: One form of apparatus
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13 Fig. 2.3: Flow cryostat, shown w
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15 Fig. 2.4: Stirred liquid bath fo
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17 contained within a cylindrical c
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19 Fig. 2.5: Schematic drawing of a
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21 device SRM 767 [Schooley et al.
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23 Table 3.1 : Current Best Estimat
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25 The widely-used, but not very re
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28 fraction of sample melted) can g
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30 Fig. 3.2a: Apparatus for the cal
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32 Fig. 3.3: Sealed cell for realiz
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34 Final readings of the thermomete
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36 temperatures differ (usually) sy
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38 Fig. 3.4: Cross sectional drawin
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40 Fig. 3.5: Miniature graphite bla
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42 4. Germanium Resistance Thermome
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44 Fig. 4.3: Example of the Π-type
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46 Fig. 4.4: Differences between dc
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48 - conversely, p-doped thermomete
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50 Fig. 4.6: Effect of a radio-freq
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52 that it will not be subject to m
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ln R n = ∑ i= 0 54 ⎛ ln T - P
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56 Fig. 5.1: Resistance (Ω) and s
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58 thermometer wires) caused a more
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60 6. Vapour Pressure Thermometry*
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62 transitions, but it could be app
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n ∑ i= 2 64 L x [ Π − k ] P =
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66 Fig. 6.3: Diagram at constant pr
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68 Fig. 6.4: Schematic construction
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70 Fig. 6.6: Use of an evacuated ja
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72 Following this, the connecting t
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74 Fig. 6.9: (c) N2, CO, Ar, O2, CH
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76 the Weber-Schmidt equation [Webe
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78 Table 6.1: Temperature values (K
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80 into the bulb (hydrous ferric ox
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82 Fig. 6.12: Effect on the vapour
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84 the remaining liquid increases.
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86 Curie constant (C⊥ is about 0.
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8.1 General Remarks 88 8. Platinum
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90 For a group of 45 thermometers h
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92 More recently, Seifert [(1980),
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94 For thermometers with W(4.2 K) <
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96 after 500 h at 1700 °C in air,
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98 normally extends about 50 cm bac
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100 inhomogeneities result from the
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9.5 Approximations to the ITS-90 10
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104 10. Infrared Radiation Thermome
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106 almost negligible. The final ac
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Page 130 and 131: 110 Fig. 11.1: Resistance-temperatu
Page 132 and 133: 112 Table 11.1: Typical Time Consta
Page 134 and 135: 114 calibration after each cool-dow
Page 136 and 137: 116 12. Carbon-Glass Resistance The
Page 138 and 139: 118 Fig. 12.1: Resistance-temperatu
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Page 142 and 143: 122 2 BT V = E0 − − CT ln ( DT)
Page 144 and 145: 124 Fig. 15.1: Principal features o
Page 146 and 147: 126 For a thermometer graduated abo
Page 148 and 149: 128 rise decreases with time but in
Page 150 and 151: 130 Fig. 16.1: (a) Fabrication of I
Page 152 and 153: 132 capillaries of a twin- (or four
Page 154 and 155: 134 advised to choose the thermomet
Page 156 and 157: 136 Fig. 16.6: Distribution of the
Page 158 and 159: 138 and between different thermomet
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Page 164 and 165: 144 Fig. 16.8: Tolerances for indus
Page 166 and 167: 146 Stability on thermal cycling is
Page 168 and 169: 18.2.1 Type T Thermocouple 148 With
Page 170 and 171: 150 within ± 0.5 to 0.7 percent. T
Page 172 and 173: 152 insulation even though it be af
Page 174 and 175: 154 Table 18.4: Recommended Sheath
Page 176 and 177: 156 In the case of the Types K and
Page 180 and 181: 160 19. Thermometry in Magnetic Fie
Page 182 and 183: 162 Type of Sensor T(K) Magnetic Fl
Page 184 and 185: 164 be noted that these lower tempe
Page 186 and 187: 166 Fig. 19.2: The change in calibr
Page 188 and 189: 168 Carbon-glass thermometers (Chap
Page 190 and 191: Ancsin, J. and Phillips, M.J. (1984
Page 192 and 193: 172 Berry, R.J. (1972): The Influen
Page 194 and 195: 174 Brodskii, A.D. (1968): Simplifi
Page 196 and 197: 176 Crovini, L., Perissi, R., Andre
Page 198 and 199: Hudson, R.P. (1972): Principles and
Page 200 and 201: 180 Lengerer, B. (1974): Semiconduc
Page 202 and 203: 182 OIML (1985): International Reco
Page 204 and 205: 184 Rusby, R.L. (1975): Resistance
Page 206 and 207: 186 Seifert, P. and Fellmuth, B. (1
Page 208 and 209: 188 Ween, S. (1968): Care and Use o
Page 210 and 211: 190 Fig. A.1: Differences between t
Page 212 and 213: National Institute of Metrology P.O
Page 214 and 215: 194 Appendix C Some Suppliers of Va
Page 216 and 217: 196 Appendix D Calculations Relativ
Page 218 and 219: 198 4. The calculation of the numbe
Page 220 and 221: 200 Appendix F Interpolation Polyno
Page 222 and 223: - temperature range from 0 °C to 1
Page 224 and 225: 204 where: d0 = 0; d5 = -3.17578007
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