techniques for approximating the international temperature ... - BIPM

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4 The tungsten strip-filament lamp mentioned in the preceding paragraph is not itself a thermometer, but acts as a transfer device. The lamp is calibrated with a standard optical pyrometer in terms of spectral radiance temperature at a particular wavelength versus current, and this calibration is subsequently transferred to another pyrometer. For a calibration using fixed points (which has been called a secondary realization, but this term is not recommended), the thermometer is calibrated at a number of such points (that may include both defining and secondary fixed points) and temperatures are interpolated between fixed points according to a functional (usually an empirical) relationship that experience has shown will generate values of temperature on the ITS-90 to within some specified degree of accuracy. Secondary fixed points are fixed points that are not used in the definition of the ITS-90, but which have been well-characterized, and the temperatures of which have been carefully determined on the ITS-90. Bedford et al. (1984) give recommended values of temperatures, together with an assessment of their uncertainties, for a large number of secondary fixed points. The values of temperature, which are on the IPTS-68, can be converted to the ITS-90 using the tables included here in Appendix A. A thermometric reference material might, in some circumstances, also be used in the sense of a secondary fixed point. Caution should be exercised, however, in the use of thermometric reference materials, which differ in principle from fixed points. A fixed point (whether primary or secondary) is a phase transition temperature of a substance of extremely high purity; any two samples of the substance will exhibit precisely the same transition temperature, so long as the experimental apparatus (furnace, cryostat) is properly designed and the thermometer is in temperature equilibrium with the sample. A thermometric reference material, on the other hand, is simply a batch of certified material from which samples can be drawn; a sample of this material, when used according to a specific recipe, undergoes a phase transition at a temperature that has been previously measured and certified with a calibrated thermometer. The material need not be especially pure, and the assigned transition temperature applies only to the particular lot from which the sample is drawn. Another lot of nominally the same substance may have a different transition temperature. In this monograph the many references to secondary fixed points should not be construed as being applicable to reference materials. A thermometric sealed cell, depending upon its construction, can be used either in the sense of a fixed point or of a reference material [Pavese (1980), (1986)]. If a reference material is used as a fixed point, the value of temperature associated with it should be that given by the supplier.
5 The accuracies with which temperatures may be referred to the ITS-90 as a result of a comparison calibration or a calibration with fixed points are comparable; if anything, the former is the more accurate except near the fixed point temperatures unless many fixed points are used. It is difficult to make any single statement regarding the limits of accuracy that may apply. As a rough guide, the largest uncertainty for any technique described herein will be ± 0.05 K below 100 K, ± 0.2 K near and above room temperature, ± 0.5 K up to 1000 °C, and ± 1 to 2 K above. Many of the techniques, of course, may give substantially better results than this. In Table 1.1 are listed all of the thermometers discussed in this monograph, their temperature ranges under various conditions, and typical associated uncertainties. The ITS-90 became the officially-recognized International Temperature Scale on January 1, 1990. In this monograph there are a few unavoidable references to its predecessor, the IPTS-68. Furthermore, there are undoubtedly users of this monograph who are measuring temperatures with thermometers calibrated on the IPTS-68. We emphasize that any temperature T68 (or t68) can be converted to its equivalent value of T90 (or t90) by use of the tables given here in Appendix A. Similarly, any previous edition of the ITS can be used to approximate the ITS-90 to within the combined accuracies of the associated conversion tables. This monograph is divided into two parts. Part 1 includes those methods and thermometers that are considered to be best suited for directly approximating the ITS-90, and the associated calibration techniques. Part 2 deals with a number of thermometers that are important because they are widely used or are used for special purposes, but that are in general less accurate than those of Part 1, and for which temperatures measured with them must still be traced to the ITS-90. Thus, for example, approximations based upon SPRTs are described in Part 1 but treatment of industrial platinum resistance thermometers (IPRTs) is relegated to Part 2 because, although IPRTs are in wide use, they are as a class not accurate enough for approximating the ITS-90 directly in the sense defined here. International specifications for IPRTs and standard thermocouple reference tables as developed for use with the IPTS-68 are included herein. At the time of writing, corresponding specifications and tables with respect to the ITS-90 had not yet been published. Approximate equivalents can be obtained using the tables in Appendix A. There is, naturally, a degree of overlap between the material contained herein and that in "Supplementary Information for the ITS-90" [CCT (1990)]. Methods for highly accurate fixed point realizations, for example, are described in some detail there, so will
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: 3 thermometers except in special ex
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 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
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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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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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