techniques for approximating the international temperature ... - BIPM
techniques for approximating the international temperature ... - BIPM techniques for approximating the international temperature ... - BIPM
28 fraction of sample melted) can give information regarding impurities in the melting substance (see Section 6.3.6). In addition, the lifetimes of these fixed points is at least of the order of decades; no changes of the reproduced temperatures have yet been observed in about a dozen years. Sealed cells offer many advantages for disseminating and approximating the ITS-90. They provide the possibility of a whole set of defining and secondary fixed points spanning a wide temperature range, instead of just the triple point of water, for checking the stability of thermometers. For small changes in thermometer calibration, they allow retrieval of a calibration. Furthermore, calibration procedures can be simplified and still maintain good accuracy. The cells also allow dissemination of fixed points (rather than calibrated thermometers) for ITS-90 maintenance. The sealed cell is well adapted to the cryogenic range and hence, in particular, to the calibration of capsule-type thermometers in adiabatic cryostats. However, the technique has also been applied to the calibration of long-stem SPRTs in the range from the triple point of argon to the triple point of indium [Bonnier (1975), Bonnier and Moser (1983), Ancsin and Phillips (1984)] under heat-flow conditions. Apparatuses that have been used successfully are illustrated in Figs. 3.2a, b. Sealed cells are also commonly used for calibrations of resistance thermometers or thermocouples at metal freezing points to temperatures as high as the freezing point of copper (1085 °C). The crucibles used are essentially the same as those for non-sealed operation [CCT (1990)]. A national standardizing laboratory usually constructs its own sealed cells, but the procedure is moderately difficult; they are also available commercially. The sealed cell usually consists of enclosing the crucible in a purged, sealed, silica envelope having a re-entrant well close-fitted within the crucible well. Care should be taken to ensure that the pressure of the inert gas filling is such as to give closely one atmosphere pressure during the melting or freezing transition. A typical sealed cell (for the copper freezing point [Crovini et al. (1987)]) is shown in Fig. 3.3. (See also Sections 3.2 and 3.3; see, for example, [Bonnier and Moser (1983)] for discussion of general techniques and especially for filling of the crucible.) 3.2 Fixed Points -50 °C to 630 °C 3.2.1 Ice Point (0 °C) For many measurements with platinum resistance thermometers and for all measurements with thermocouples (or with liquid-in-glass thermometers) an ice point, rather than a water triple point, is sufficiently accurate [Thomas (1934)].
29 Fig. 3.1: Different approaches with sealed cells: a) thermometers inserted in a well A of the block C protruding inside the cell D [IMGC design, see Pavese et al. (1984)]; b) thermometers inserted in a block C, where one or more cells D (each containing a different substance) can be screwed on at E [Pavese (1987)]; c) thermometers inserted as in a), but the cell itself has many compartments, each containing a different substance (B is the sealing system of the cell: indium gasket or pinch-weld tube) [Bonnier and Hermier (1982)]; d) another multicompartment cell with sample chambers (C1 - C6) of copper coils surrounding the thermometer well [PAMI design, see Pavese et al. (1984)]; e) as in a) but with a screw seal to allow for refilling and with thin horizontal copper baffles in the sample chamber to improve thermal contact between thermometer and sample [Ancsin (1982)].
- 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 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
- 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
29<br />
Fig. 3.1: Different approaches with sealed cells: a) <strong>the</strong>rmometers inserted in a well A of <strong>the</strong><br />
block C protruding inside <strong>the</strong> cell D [IMGC design, see Pavese et al. (1984)]; b)<br />
<strong>the</strong>rmometers inserted in a block C, where one or more cells D (each containing a<br />
different substance) can be screwed on at E [Pavese (1987)]; c) <strong>the</strong>rmometers<br />
inserted as in a), but <strong>the</strong> cell itself has many compartments, each containing a<br />
different substance (B is <strong>the</strong> sealing system of <strong>the</strong> cell: indium gasket or pinch-weld<br />
tube) [Bonnier and Hermier (1982)]; d) ano<strong>the</strong>r multicompartment cell with sample<br />
chambers (C1 - C6) of copper coils surrounding <strong>the</strong> <strong>the</strong>rmometer well [PAMI design,<br />
see Pavese et al. (1984)]; e) as in a) but with a screw seal to allow <strong>for</strong> refilling and<br />
with thin horizontal copper baffles in <strong>the</strong> sample chamber to improve <strong>the</strong>rmal<br />
contact between <strong>the</strong>rmometer and sample [Ancsin (1982)].
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