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46 Fig. 4.4: Differences between dc and ac (30 Hz) calibrations for typical germanium thermometers from Minneapolis Honeywell (upper hatched group, 250 to 1250 Ω at 4.2 K), Lake Shore Cryotronics (lower hatched group, 500 Ω at 4.2 K), and CryoCal (dashed curve, 500 Ω at 4.2 K) [after Anderson and Swenson (1978)]. 4.3.2 Resistance/Temperature Characteristics and Sensitivity Typical examples of the variation of resistance (R) with T for commercial germanium thermometers are shown in Fig. 4.5. The resistance at 1 K can be as high as 10 6 Ω and at 100 K as low as 1 Ω, but these are extreme values. For a typical thermometer suited to the temperature range 1 K to 30 K, R ranges from 1000 Ω at 4.2 K to less than 10 Ω at 77 K. The sensitivity (dR/dT) at 4.2 K is about -500 Ω K -1 . In practice the power dissipated in the sensor must be much less than 1 µW, corresponding to a maximum current of 30 µA with a 1000 Ω thermometer, or a voltage across the sensor of 30 mV (see Section 4.4.1 and Fig. 4.8). In order to measure temperatures near 4 K to within 0.01 % (0.5 mK), that would require instrumentation having microvolt resolution. Even lower sensor voltages are desirable, 2 to 4 mV being usual. Commonly, a potentiometric method is used to measure the resistance because of the high resistances involved. At every temperature the current is adjusted to maintain the voltage across the potential terminals as high as compatible with self-heating. This allows one to take advantage of the maximum sensitivity provided by the equipment. Where this procedure is inconvenient, a constant measuring voltage can be used over a wide range and correction made for self- heating (see Sec. 4.4.1).
47 Fig. 4.5: Some typical resistance versus temperature response curves for germanium thermometers. At very low temperatures the resistance can easily surpass 10 5 Ω so that the measuring current will be of the order of tens of nanoamperes if the power dissipated is to remain tolerable; the tolerable leakage current due to lack of insulation or from the measuring instrument itself must be much smaller. That necessitates a measuring system with excellent signal-to-noise ratio. The very large sensitivity and its rapid change with temperature has both advantages (high precision of measurement) and disadvantages (rather small practical temperature range for any one thermometer). The complicated behaviour of R and 1 dR R dT as functions of temperature, resulting from changes in the conduction mechanism in germanium, prevents their being expressed by simple functions. On the other hand, since both the resistivity and its temperature coefficient are strongly influenced by doping, one can obtain thermometers especially adapted to particular uses. For example: - n-doped thermometers have a relatively smoothly-changing sensitivity, and so a fairly wide temperature range.
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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
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 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 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
Page 92 and 93: 72 Following this, the connecting t
Page 94 and 95: 74 Fig. 6.9: (c) N2, CO, Ar, O2, CH
Page 96 and 97: 76 the Weber-Schmidt equation [Webe
Page 98 and 99: 78 Table 6.1: Temperature values (K
Page 100 and 101: 80 into the bulb (hydrous ferric ox
Page 102 and 103: 82 Fig. 6.12: Effect on the vapour
Page 104 and 105: 84 the remaining liquid increases.
Page 106 and 107: 86 Curie constant (C⊥ is about 0.
Page 108 and 109: 8.1 General Remarks 88 8. Platinum
Page 110 and 111: 90 For a group of 45 thermometers h
Page 112 and 113: 92 More recently, Seifert [(1980),
Page 114 and 115: 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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