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22 3.1.1.3 Realization of Superconductive Fixed Points In Table 3.1 the ST-temperatures on the ITS-90 of the six metals Cd, In, AI, In, Pb, and Nb are listed*. The uncertainties given include the temperature measurement uncertainties assigned for the available experimental data, the non-uniqueness of the EPT-76, the differences of the T C 76 values published for high-quality samples of different origin and different parameters, and the effect on the ST-temperatures of the various factors that can be expected to influence the parameters of the investigated samples. In the application of superconductive fixed points the dependence of the ST-temperature on detection techniques has to be taken into consideration [Nara (1984)]. The mutual inductive technique is most effective because of its relative ease of application, the minimum stress transmitted to the sample, and the negligible sample contamination [Soulen and Colwell (1971 )]. Thermal anchoring of the samples and of the electrical leads is critical for the observation of nonhysteretic and reproducible transitions [Schooley et al. (1980) and Schooley and Soulen (1982)]. Because of the absence of latent heat, a high-quality adiabatic cryostat is necessary for accurate T C measurements. To check that the thermal conditions are adequate, the difference between the ST-temperature values obtained with increasing and decreasing the temperature of the sample through the transition range should always be measured. The temperature should then be stabilized at the mid-point of the transition before thermometer calibrations are carried out. Furthermore, external magnetic fields (earth's magnetic field and measuring field) can have an influence of a few mK on the ST-temperatures; the effect can be corrected for, or, more comfortably, compensated for. 3.1.2 Standard Reference Materials In contrast to the foregoing fixed point definition, the temperature value assigned to a standard reference material (SRM) is a device-temperature, i.e. the device reproduces precisely a temperature value which has been determined by calibration but which, within stated limits, is characteristic only of the individual device. The boundary between a SRM and a fixed point may be ill-defined as the specifications of a SRM can be so strict that the value assigned is the same as that of the physical state, within a comparable uncertainty. For example, below 10 K, several superconductive transitions may be used as fixed points. _________________________________________________________________________ * Note that the temperatures in Table 3.1 are slightly different from those used with the reference material NBS-SRM 767; the latter are given in Table 3.2.
23 Table 3.1 : Current Best Estimates of Superconductive Transition Temperatures and of the Total Uncertainties of the Estimate [Fellmuth and Maas (1987)] , Element TC90/ K Cd 0.5200 ± 0.0030 Zn 0.8500 ± 0.0030 AI 1.1810 ± 0.0025 In 3.4145 ± 0.0025 Pb 7.1997 ± 0.0025 Nb 9.2880 ± 0.0025 Table 3.2: Temperatures Assigned to Superconductive Fixed Points in the NBS (now NIST) Fixed-Point Devices *T C Substance Width Reproducibility (1 standard deviation) ( K) (mK) (mK) 0.0160 °W 0.7 ± 0.2 0.0230 °Be 0.2 0.1 0.0990 °lr 0.8 0.1 0.1605 °AuAI2 0.3 0.1 0.2065 °Auln2 0.4 0.15 0.5190 +Cd 0.5-8.0 0.3 0.8510 +Zn 2.5-10 0.4 1.1796 +AI 1.5-4.0 0.4 3.4145 +In 0.5-2.5 0.2 7.1996 +Pb 0.6-2.0 0.2 °SRM 768 [Schooley and Soulen (1982)] +SRM 767 [Schooley et al. (1980)] * T90 above 0.5 K.
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 and 30: PART 1: TECHNIQUES AND THERMOMETERS
Page 31 and 32: 11 Fig. 2.1: One form of apparatus
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: 21 device SRM 767 [Schooley et al.
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
Page 80 and 81: 60 6. Vapour Pressure Thermometry*
Page 82 and 83: 62 transitions, but it could be app
Page 84 and 85: n ∑ i= 2 64 L x [ Π − k ] P =
Page 86 and 87: 66 Fig. 6.3: Diagram at constant pr
Page 88 and 89: 68 Fig. 6.4: Schematic construction
Page 90 and 91: 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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