techniques for approximating the international temperature ... - BIPM
techniques for approximating the international temperature ... - BIPM techniques for approximating the international temperature ... - BIPM
18 end; and an inert buffer gas (helium) is maintained over the working fluid (sodium) vapour, the buffer-gas pressure being externally controlled by conventional techniques. The furnace temperature can be changed from one level to another by changing the buffer-gas pressure; re-equilibration at the new level is rapid, typically within a few tenths of a kelvin in 20 minutes for a 50 K change. A standard pressure and temperature feedback control system allows the temperature to be controlled at a given level to within a few mK. The response to small pressure changes is very rapid, the speed being determined more by the temperaturesensor response than the heat-pipe response. Temperature uniformity within the furnace to within a few mK is possible. With sodium as the working fluid, the heat-pipe furnace is operable from about 550 °C to 1100 °C; with potassium, from about 400 °C to 950 °C. Another type of furnace used for the calibration of thermocouples is the electric tube furnace, shown schematically in Fig. 2.5 [Dauphinee (1955)]. The cylindrical Nichrome furnace tube about 3 cm in diameter and 50 cm long forms part of a one-turn secondary of a high-power transformer, and is resistively heated by the high ac secondary current. A silica tube is placed inside the furnace tube, and the thermocouples to be calibrated are inserted inside this with their tips welded or otherwise physically joined together. The furnace is uninsulated so its temperature can be changed very rapidly. A typical calibration run with Pt10Rh/Pt thermocouples takes 2 hours from ambient to 1100 °C and down again. This high speed is possible because the absolute emfs of the unknown and the standard need not be simultaneously known, but only the slowly-changing difference between them. Typically, with Pt10Rh/Pt calibrations for example, this difference when the furnace is heating will have slightly different values from when it is cooling, but it can be shown that the mean of the two is the same as the steady-state difference. With (even slightly) dissimilar base-metal thermocouples, the furnace temperature must be stabilized at the desired calibration points before the emfs are measured. In this furnace there is really no constant temperature zone, but this does not matter so long as the small volume around the welded tips is isothermal.
19 Fig. 2.5: Schematic drawing of a fast-response electric tube furnace for thermocouple calibrations [Dauphinee (1955)].
- 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: 17 contained within a cylindrical c
- 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
- 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
19<br />
Fig. 2.5: Schematic drawing of a fast-response electric tube furnace <strong>for</strong> <strong>the</strong>rmocouple<br />
calibrations [Dauphinee (1955)].
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