Deviation of Temperature Determined by ITS-90 Temperature Scale from Thermodynamic Temperature Measured by Acoustic Gas Thermometry at 79.0000 K and at 83.8058 K

Refractive index gas thermometry between 13.8 K and 161.4 K

“…These estimates, which span the temperature interval comprised between the triple point of hydrogen near 13.8 K and the triple point of xenon near 161.4 K, were obtained using gaseous helium and neon as thermometric substances. Our results are found in good agreement with other recent determinations [3][4][5][6][7][8][9][10] of (T − T 90 ) obtained with several different primary thermometry methods in an overlapping temperature range.…”

“…Geometrical shape factors ε 1 (left plot) and ε 2 (right plot) which define the deviation of the internal geometrical shape of the resonator from that of a perfect sphere. The small recorded variation of these parameters as a function of pressure up to 370 kPa for two test temperatures at 25 K and 83 K indicate that geometrical corrections for the microwave eigenfrequencies recorded in this work can be safely neglected in the simple correction model described by equation (10).…”

“…Models and experimental verifications are also available to account for the perturbing effect of waveguides and holes [25], (Left) Relative differences between frequency ratios of TM and TE modes at 13.8 K corrected for skin effect using equation (10) or alternatively uncorrected. (Right) Relative differences between frequency ratios of TM and TE modes at 161 K corrected for skin effect using equation (10) or alternatively by using the experimentally fitted halfwidth of each mode. Geometrical shape factors ε 1 (left plot) and ε 2 (right plot) which define the deviation of the internal geometrical shape of the resonator from that of a perfect sphere.…”

“…The simple correction model of equation (10) assumes that the resistive and reactive components of the microwave surface impedance of copper are equal, and does not account for the complications introduced by the anomalous skin effect taking place at low temperature and high frequency [24]. Evidence of these anomalies was revealed by the systematic frequency dependence of ρ Cu estimated from various modes.…”

“…Also, the consequences of any alternative correction to account for skin effect perturbations from that represented by equation (10) would have minor consequences. In fact, as evidenced in figure 8, even without correction of the experimental frequencies, the resulting change in the estimated frequency ratios f m (0, T)/ f m (p, T) would be relatively less than 3 ppb in the worst case and thus irrelevant given the present uncertainty context.…”