techniques for approximating the international temperature ... - BIPM
techniques for approximating the international temperature ... - BIPM techniques for approximating the international temperature ... - BIPM
122 2 BT V = E0 − − CT ln ( DT) . (14.2) T + T Equation (14.2) fits experimental data to better than ± 15 mK below 54 K and ± 25 mK above 90 K. 0 With silicon diode thermometers, the complete range must be fitted in two sections, omitting a small range around 20 K where the thermometer cannot be used because of the afore-mentioned sharp change in slope. On either side of this critical region the V versus T characteristic is smooth, allowing non-critical fitting with simple polynomials. The fitting equations require a dozen or more calibration points, suitably spaced in temperature, in each range. An accuracy within ± 0.05 K cannot be obtained from calibration at a smaller number of fixed points. No general statement can be made regarding the stability of diode thermometers. Selected ones can be as stable as ± 0.01 K on thermal cycling but much larger instabilities can occur unpredictably. In zero magnetic field and below 20 K, diodes show high sensitivity associated with a readily-measurable voltage (millivolts in 1-2 V).
123 15. Liquid-in-Glass Thermometry Even though the liquid-in-glass thermometer is used much less frequently today than formerly, it is still a very commonly used device. Although it is normally an instrument of only moderate accuracy, the very best of them, when used with sufficient attention to detail, have millikelvin capability over a narrow temperature range. Amongst its advantages are easy portability, independence of auxiliary equipment, low cost, compatibility with most environments, moderate ruggedness, and wide range (it has been used to measure temperatures as low as 70 K and as high as 1000 °C, but its most frequent use is within the range -40 °C to 250 °C). Disadvantages include a large sensing element, impossibility for continuous or automatic readout, long time constant, awkward dimensions, secular changes, and hysteresis (except for special types). The components of a ypical liquid-in-glass thermometer are shown in Fig. 15.1. These include: Bulb: The reservoir for containing most of the thermometric liquid. Stem: The glass tube having a capillary bore along which the liquid moves with changes in temperature. Auxiliary Scale: A narrow-temperature-range scale for reading a reference temperature (usually the ice point). It should be marked as for the main scale (below). If the main scale range includes the reference temperature no auxiliary scale is supplied. Contraction Chamber: An enlargement of the capillary bore between the auxiliary and main scales, or between the reservoir and the main scale, to limit the length of the capillary (and hence the thermometer). Immersion Line: A line marking the depth to which a partial-immersion thermometer should be immersed. Main Scale: An engraved, etched, or otherwise permanently attached scale with welldefined, narrow graduation lines against which the height of the liquid in the capillary is measured. There may be a colored backing material for better visibility of the lines. The main scale is graduated in fractions or multiples of degrees Celsius. If its range incorporates the reference temperature, it is the only scale.
- 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 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
123<br />
15. Liquid-in-Glass Thermometry<br />
Even though <strong>the</strong> liquid-in-glass <strong>the</strong>rmometer is used much less frequently today than<br />
<strong>for</strong>merly, it is still a very commonly used device. Although it is normally an instrument of only<br />
moderate accuracy, <strong>the</strong> very best of <strong>the</strong>m, when used with sufficient attention to detail, have<br />
millikelvin capability over a narrow <strong>temperature</strong> range. Amongst its advantages are easy<br />
portability, independence of auxiliary equipment, low cost, compatibility with most<br />
environments, moderate ruggedness, and wide range (it has been used to measure<br />
<strong>temperature</strong>s as low as 70 K and as high as 1000 °C, but its most frequent use is within <strong>the</strong><br />
range -40 °C to 250 °C). Disadvantages include a large sensing element, impossibility <strong>for</strong><br />
continuous or automatic readout, long time constant, awkward dimensions, secular changes,<br />
and hysteresis (except <strong>for</strong> special types).<br />
The components of a ypical liquid-in-glass <strong>the</strong>rmometer are shown in Fig. 15.1.<br />
These include:<br />
Bulb: The reservoir <strong>for</strong> containing most of <strong>the</strong> <strong>the</strong>rmometric liquid.<br />
Stem: The glass tube having a capillary bore along which <strong>the</strong> liquid moves with changes<br />
in <strong>temperature</strong>.<br />
Auxiliary Scale: A narrow-<strong>temperature</strong>-range scale <strong>for</strong> reading a reference <strong>temperature</strong><br />
(usually <strong>the</strong> ice point). It should be marked as <strong>for</strong> <strong>the</strong> main scale<br />
(below). If <strong>the</strong> main scale range includes <strong>the</strong> reference <strong>temperature</strong> no<br />
auxiliary scale is supplied.<br />
Contraction Chamber: An enlargement of <strong>the</strong> capillary bore between <strong>the</strong> auxiliary and<br />
main scales, or between <strong>the</strong> reservoir and <strong>the</strong> main scale, to limit<br />
<strong>the</strong> length of <strong>the</strong> capillary (and hence <strong>the</strong> <strong>the</strong>rmometer).<br />
Immersion Line: A line marking <strong>the</strong> depth to which a partial-immersion <strong>the</strong>rmometer<br />
should be immersed.<br />
Main Scale: An engraved, etched, or o<strong>the</strong>rwise permanently attached scale with welldefined,<br />
narrow graduation lines against which <strong>the</strong> height of <strong>the</strong> liquid in<br />
<strong>the</strong> capillary is measured. There may be a colored backing material <strong>for</strong><br />
better visibility of <strong>the</strong> lines. The main scale is graduated in fractions or<br />
multiples of degrees Celsius. If its range incorporates <strong>the</strong> reference<br />
<strong>temperature</strong>, it is <strong>the</strong> only scale.
Change language