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10 2. Uniform-Temperature Enclosures Calibration of thermometers requires uniform-temperature enclosures. All of the apparatuses described here to produce such enclosures may be constructed in the laboratory, or, alternatively, may be obtained commercially. The latter tend to be more costly and to provide poorer, although adequate, uniformity. For comparison calibrations, the uncalibrated thermometer and the laboratory standard are mounted in such a way as to be in good mutual thermal contact, as in a solid metal block or a stirred liquid. Significant errors can be avoided by proper attention to immersion depths, heat transfer along thermometer leads, thermal time lags, thermometer self-heating, temperature differences within the enclosure, radiation exchange with the environment, and so on. The type of enclosure used depends upon the temperature range involved. 2.1 1 K TO 300 K Several apparatuses that serve for the calibration of thermometers have been described. The temperature stability and uniformity of the apparatuses depend upon both their thermal design and the quality of the associated temperature controller. One that is simple, that has worked extremely well for calibrating capsule PRTs, and that can be used with germanium (Ge) or rhodium-iron (RhFe) resistance thermometers is shown in Fig. 2.1. A small copper block with holes for four thermometers is surrounded by two concentric copper radiation shields in an insulated container which is open at the bottom. The container hangs by a thin-walled metal tube in a liquid helium dewar. To prevent heat transfer along the thermometer leads, the latter pass through insulated holes in the copper block and one of the shields. Heaters are wound on both the block and the shields, and the temperature difference between them is measured with differential thermocouples. The block is cooled to liquid helium temperatures and the liquid is then blown out of the insulated container, leaving helium gas at atmospheric pressure therein. The liquid helium remaining in the dewar provides the necessary cooling. The block is heated to, and then maintained at, each desired temperature in turn, the shield temperatures being adjusted to be that of the block by a servo-control. The apparatus requires no vacuum feed-throughs for the leads and the thermometers rapidly reach equilibrium as a result of the good thermal contact between the block and the thermometer provided by the helium gas. With this system a PRT can be calibrated to within 1 mK.
11 Fig. 2.1: One form of apparatus used at NRC for calibration of resistance thermometers from 4.2 K to 273.15 K: A, metal cover; B, copper shields; C, copper block; D, expanded polystyrene; E, capsule PRT; F, liquid helium. An alternative procedure that is also widely used is to place the thermometers in a copper block that is enclosed within suitable radiation shields in an evacuated cryostat as shown in Fig. 2.2 (see, for example, Rusby et al. (1972), Compton and Ward (1975), or Besley and Kemp (1977)). Details of operation are given in the suggested references. It is sometimes useful to design the cryostat in a modular way to allow for the use of a single apparatus for different experiments. This may be facilitated by the incorporation of a cylindrical re-entrant well in the tube connecting the cryostat chamber to the part of the apparatus that is at room temperature. In this way, different modules, designed for different experiments, can be interchanged from the top flange, without one's having to disassemble the cryostat itself [see Pavese (1981 )]. For temperatures above 4 K, it is also possible to use closed-cycle refrigerators, so avoiding conventional liquid refrigerants and allowing convenient and faster operation. The thermal design of measuring modules for such a system is similar to that of a flow cryostat (Fig. 2.3) [Blanke and Thomas (1979)], but care must be taken to prevent mechanical - vibrations from adversely affecting the thermometer.
Page 1 and 2: BUREAU INTERNATIONAL DES POIDS ET M
Page 3 and 4: TECHNIQUES FOR APPROXIMATING THE IN
Page 5 and 6: iv W(100 °C) = 1.385 (exact value
Page 7 and 8: Centre for Quantum Metrology Nation
Page 9 and 10: 2. Type J viii a) temperature range
Page 11 and 12: c) temperature range from 1664.5 °
Page 13 and 14: xii
Page 15 and 16: xiv Acknowledgments This monograph
Page 17 and 18: xvi 3.3.2 Melting Points of Gold (1
Page 19 and 20: xviii 11.3 Thermal Contact 111 11.4
Page 21 and 22: 1 1. Introduction The Comité Consu
Page 23 and 24: 3 thermometers except in special ex
Page 25 and 26: 5 The accuracies with which tempera
Page 27 and 28: Table 1.1: Summary of Some Properti
Page 29: PART 1: TECHNIQUES AND THERMOMETERS
Page 33 and 34: 13 Fig. 2.3: Flow cryostat, shown w
Page 35 and 36: 15 Fig. 2.4: Stirred liquid bath fo
Page 37 and 38: 17 contained within a cylindrical c
Page 39 and 40: 19 Fig. 2.5: Schematic drawing of a
Page 41 and 42: 21 device SRM 767 [Schooley et al.
Page 43 and 44: 23 Table 3.1 : Current Best Estimat
Page 45: 25 The widely-used, but not very re
Page 48 and 49: 28 fraction of sample melted) can g
Page 50 and 51: 30 Fig. 3.2a: Apparatus for the cal
Page 52 and 53: 32 Fig. 3.3: Sealed cell for realiz
Page 54 and 55: 34 Final readings of the thermomete
Page 56 and 57: 36 temperatures differ (usually) sy
Page 58 and 59: 38 Fig. 3.4: Cross sectional drawin
Page 60 and 61: 40 Fig. 3.5: Miniature graphite bla
Page 62 and 63: 42 4. Germanium Resistance Thermome
Page 64 and 65: 44 Fig. 4.3: Example of the Π-type
Page 66 and 67: 46 Fig. 4.4: Differences between dc
Page 68 and 69: 48 - conversely, p-doped thermomete
Page 70 and 71: 50 Fig. 4.6: Effect of a radio-freq
Page 72 and 73: 52 that it will not be subject to m
Page 74 and 75: ln R n = ∑ i= 0 54 ⎛ ln T - P
Page 76 and 77: 56 Fig. 5.1: Resistance (Ω) and s
Page 78 and 79: 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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108 11. Carbon Resistance Thermomet
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110 Fig. 11.1: Resistance-temperatu
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112 Table 11.1: Typical Time Consta
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114 calibration after each cool-dow
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116 12. Carbon-Glass Resistance The
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118 Fig. 12.1: Resistance-temperatu
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120 14. Diode Thermometers Diodes c
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122 2 BT V = E0 − − CT ln ( DT)
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124 Fig. 15.1: Principal features o
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126 For a thermometer graduated abo
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128 rise decreases with time but in
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130 Fig. 16.1: (a) Fabrication of I
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132 capillaries of a twin- (or four
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134 advised to choose the thermomet
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136 Fig. 16.6: Distribution of the
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138 and between different thermomet
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140 therefrom) can then be used wit
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142
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144 Fig. 16.8: Tolerances for indus
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146 Stability on thermal cycling is
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18.2.1 Type T Thermocouple 148 With
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150 within ± 0.5 to 0.7 percent. T
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152 insulation even though it be af
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154 Table 18.4: Recommended Sheath
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156 In the case of the Types K and
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158 temperature is measured with th
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160 19. Thermometry in Magnetic Fie
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162 Type of Sensor T(K) Magnetic Fl
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164 be noted that these lower tempe
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166 Fig. 19.2: The change in calibr
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168 Carbon-glass thermometers (Chap
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Ancsin, J. and Phillips, M.J. (1984
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172 Berry, R.J. (1972): The Influen
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174 Brodskii, A.D. (1968): Simplifi
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176 Crovini, L., Perissi, R., Andre
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Hudson, R.P. (1972): Principles and
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180 Lengerer, B. (1974): Semiconduc
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182 OIML (1985): International Reco
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184 Rusby, R.L. (1975): Resistance
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186 Seifert, P. and Fellmuth, B. (1
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188 Ween, S. (1968): Care and Use o
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190 Fig. A.1: Differences between t
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National Institute of Metrology P.O
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194 Appendix C Some Suppliers of Va
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196 Appendix D Calculations Relativ
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198 4. The calculation of the numbe
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200 Appendix F Interpolation Polyno
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- temperature range from 0 °C to 1
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204 where: d0 = 0; d5 = -3.17578007
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