Abstract
We used absolute primary acoustic gas thermometry (AGT) to calibrate a Pt–Co resistance thermometer on the thermodynamic temperature scale by measuring the speed of sound in helium at a temperature T* chosen to be near the temperature of the triple point of neon, T Ne. Prior to the present AGT, the Pt–Co thermometer was used with a neon triple-point cell as part of an interlaboratory comparison. Taken together, the results of the interlaboratory comparison and the present AGT redetermined the thermodynamic temperature T Ne = (24.555 15 ± 0.000 24) K. This new value of T Ne is consistent with other recent determinations obtained with various primary methods. After completing the AGT thermodynamic calibration, we used the Pt–Co thermometer to link T* to the temperature ratios measured by single-pressure refractive-index gas thermometry (SPRIGT) in a different laboratory. (Gao et al 2020 Metrologia 57 065006) Now, the T*-linked SPRIGT system can calibrate other thermometers on the thermodynamic temperature scale T in the range 5 K ⩽ T ⩽ T Ne without using the international temperature scale ITS-90. At most temperatures in this range, the uncertainties of the T*-linked SPRIGT system are smaller than those of the ITS-90 systems used by National Metrology Institutes to calibrate resistance thermometers.
Highlights
Using the techniques of primary acoustic gas thermometry (AGT), [1, 2] we measured the thermodynamic temperature of the triple point of neon and obtained the result: TNe = (24.555 15 ± 0.000 24) K. (All uncertainties reported in this work are one standard uncertainty corresponding to a 68% confidence level.) As shown in table 1 and figure 1, the present result for TNe is consistent, within combined uncertainties, with other recent determinations of TNe [3,4,5,6]
After completing and analyzing the results of the AGT work, we obtained a thermodynamic calibration of one particular platinum–cobalt (Pt–Co) resistance thermometer, which was transferred to the TIPC-LNE Joint Laboratory of the Chinese Academy of Sciences, where—by September 2019—it was installed in the single-pressure refractive-index gas thermometry (SPRIGT) system to calibrate that system at TNe
The sum in quadrature of all the uncertainties in table 5 is 0.16 mK. This is the uncertainty of calibrating the Pt–Co thermometer using the present AGT at a thermodynamic temperature near TNe
Summary
In figure 1, two literature values of TNe are based on refractive-index gas thermometry (RIGT) [5, 6] and one is based on dielectric constant gas thermometry (DCGT) [4] These values of TNe were obtained during wide-range measurements of the differences T − T90 and their estimated uncertainties u(T − T90). After completing and analyzing the results of the AGT work, we obtained a thermodynamic calibration of one particular platinum–cobalt (Pt–Co) resistance thermometer, which was transferred to the TIPC-LNE Joint Laboratory of the Chinese Academy of Sciences, where—by September 2019—it was installed in the SPRIGT system to calibrate that system at TNe. As discussed in [7], the uncertainty of the TNe-linked SPRIGT system was 0.16 mK at TNe where it was dominated by imperfections in the AGT and resistance thermometry. We briefly describe the AGT and our measurements while emphasizing the features that dominate our uncertainty budget
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