Determination of T–T90 from 234 K to 303 K by acoustic thermometry with a cylindrical resonator

Abstract

The determination of the differences (T–T90) between the thermodynamic temperature T and the international temperature scale of 1990 (ITS-90) T90, is important for an evaluation of the approximation to T by T90. Such evaluations are necessary for the potential revision of ITS-90. A number of efforts have been devoted to the determination of (T–T90) by the acoustic gas thermometry (AGT) using spherical or quasi-spherical resonators. We report in this paper a new study in the temperature range from 234 K to 303 K using AGT in argon with a cylindrical resonator. Piezo-electric acoustic transducers were used to measure the acoustic resonant frequencies. The resonant frequencies of the transverse magnetic microwave modes of the cavity were measured using straight probe antennas. This work further illustrates the high performance of the microwave resonant procedure to measure the thermal expansion of a cylindrical cavity at different temperatures and pressures. The (T–T90) measurements, with standard uncertainties in the range from 0.5 mK to 0.8 mK, agree well with the existing data from AGT with spherical or quasi-spherical resonators. We believe that cylindrical acoustic gas thermometry, with an uncertainty comparable with that using spherical or quasi-spherical resonators but simpler mechanical assembly, has the potential for accurate measurements of (T–T90) at higher temperatures.