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Primary Acoustic Thermometry From 217 K to 303 K



Michael R. Moldover, S J. Boyes, A R. Goodwin, Christopher W. Meyer


We report new values for the difference (T T90) between Kelvin thermodynamic temperatures T and ITS-90, the International Temperature Scale of 1990. The new data span the range 217 K {less then or equal to} T 303 K with standard uncertainties of 0.6 mK. A detailed description of the measurements and their analysis is in press [1]. The new values of (T-T90) were obtained by measuring the speed-of-sound in argon contained in the same spherical acoustic resonator that had been used at NBS to redetermine the universal gas constant R[2]. The largest component of the uncertainty resulted from choosing among models to extrapolate the speed-of-sound data to zero pressure. At the triple point of mercury, (Tm - T90 ) = (-2.3 0.6) mK; at the triple point of gallium, (Tg - T90) = (4.6 0.6)mK. The new value of Tg is (4.3 0.8) mK larger than previously obtained with this apparatus. We suspect that the earlier value of Tg is erroneous because a virtual leak at Tg progressively contaminated the argon used in that work. This suggestion is supported by new acoustic data taken when the resonator was filled with xenon. Fortunately, the virtual leak did not affect the redetermination of R [1,2]. The present work resulted in many suggestions for improving primary acoustic thermometry to achieve sub-millikelvin uncertainties over a wide temperature range.
Proceedings Title
Proceedings of the TEMPMEKO '99 Symposium
Conference Dates
June 1-3, 1999
Conference Location
Delft, NL
Conference Title
Symposium on Temperature and Thermal Measurement in Industry and Science


acoustic resonator, acoustic thermometry, gas thermometry, primary thermometry, speed-of-sound, thermometry


Moldover, M. , Boyes, S. , Goodwin, A. and Meyer, C. (1999), Primary Acoustic Thermometry From 217 K to 303 K, Proceedings of the TEMPMEKO '99 Symposium, Delft, NL (Accessed April 22, 2024)
Created April 1, 1999, Updated February 17, 2017