techniques for approximating the international temperature ... - BIPM

More documents

Recommendations

Info

38 Fig. 3.4: Cross sectional drawing of a miniature graphite crucible for thermocouple calibrations (dimensions are in millimetres) [Tischler and Koremblit (1982)]. The tightly-fitting crucible lid has a small perforation to vent occluded gases that are released as the temperature is raised. For calibration, the thermocouple with the crucible attached is placed in a small- diameter, fused-silica tube through which a slow flow of nitrogen is maintained to protect against oxidation of the graphite. The silica tube in turn is inserted into a conventional furnace at the appropriate temperature with the silica tube extending to room temperature. The furnace power is then increased so that the furnace equilibrium temperature will be slightly (typically 1 K to 5 K) higher than the melting temperature of the ingot and the melting transition is recorded. Following this, the furnace power is reduced so that the temperature will equilibrate at an equal amount below the transition temperature and the freezing transition is recorded. A typical transition plateau lasts about 20 min. Depending upon the rate of change of furnace temperature, and upon the difference between furnace temperature and transition temperature, the temperature of the freezing plateau will be significantly lower than that of the melting plateau because of the relatively small latent heats, large heat transfer, and effect of pressure on the ingot due to surface tension. Let VP be the thermocouple emf at the temperature of the plateau, VF the emf when the thermocouple has equilibrated at the furnace temperature following the transition, and VT the emf at the true transition temperature. On a plot of VF vs VP, the intersection of a line joining the points corresponding to melting (VPm ) and freezing (VPf ) with the line VF = VP gives the desired emf VT, which is usually reproducible to about ± 1 µV and accurate to ± 0.3 K. It is likely almost as accurate to take for VT the mean of the melt and freeze emfs.
39 With some deterioration in accuracy (± 0.5 K), a simpler method is not to stabilize the furnace temperature close to the transition temperature, but to let it pass through at a relatively high rate. For Cu, Sb, Pb, Sn, In take VT = VPm from the melt; the large amount of undercooling makes VP from the freeze unreliable. For Au, Ag, In, and Cd take VT = (V Pm + VPf)/2, or VT = VPm, which will be almost the same. For AI it is necessary to take VT = (VPm + VPf)/2. Variations of this technique are described by Tischler and Anteneodo (1986) where the freezing point is a permanent part of the thermocouple. Other workers are applying miniature fixed points for the calibration of standard-welded and metal-sheathed thermocouples. 3.4 Fixed Points for Pyrometry 3.4.1 Blackbody Furnaces Infrared pyrometers (monochromatic or broad-band) must be calibrated against blackbodies. If modest accuracy is sufficient, it is possible to use semi-miniature furnaces as opposed to those recommended for highest accuracy [CCT (1990)]. Sakuma and Hattori (1982a) have designed furnaces of this sort that are in moderately wide use. A graphite blackbody crucible 4 cm diameter, 6.5 cm long, with a 1 cm aperture (Fig. 3.5) is encapsulated in a stainless-steel cylinder which carries the furnace heater, either embedded in grooves parallel to the axis or wound around the circumference. The steel cylinder extends beyond the blackbody aperture for better temperature uniformity, and includes a stainless-steel disk with a 6 mm aperture covering the front of the blackbody. Argon flows through the steel capsule to prevent oxidation of the graphite. This steel cylinder containing the crucible and furnace heater is mounted in an alumina tube that is surrounded by suitable radiation shields and thermal insulation (Fig. 3.6). The whole furnace is 10 cm diameter by 25 cm long, and is attached to a temperature-control unit consisting of a SCR power regulator, an on-off temperature controller, and indicators. A monitoring thermocouple is attached to the steel capsule. With the main power switch on and the regulator switch off, the furnace is maintained about 10°C above the freezing point of the metal in the blackbody. Then, with the regulator switch on, the crucible cools at a pre-determined rate through the freezing transition. The freezing plateau lasts about 10 min and is accurate to within about - 0.1 ± 0.1 K. Such a furnace is available for each of the metals Cu, Ag, AI, Sb, and Zn.
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 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 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
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) <
Page 116 and 117:
96 after 500 h at 1700 °C in air,
Page 118 and 119:
98 normally extends about 50 cm bac
Page 120 and 121:
100 inhomogeneities result from the
Page 122 and 123:
9.5 Approximations to the ITS-90 10
Page 124 and 125:
104 10. Infrared Radiation Thermome
Page 126 and 127:
106 almost negligible. The final ac
Page 128 and 129:
108 11. Carbon Resistance Thermomet
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
Page 140 and 141:
120 14. Diode Thermometers Diodes c
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
Page 160 and 161:
140 therefrom) can then be used wit
Page 162 and 163:
142
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 178 and 179:
158 temperature is measured with th
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
show all

techniques for approximating the international temperature ... - BIPM

Create successful ePaper yourself

Delete template?

Save as template?