CCT KEY COMPARISON NO 1 (CCT-K1): REALISATIONS OF THE ITS-90, 0.65 K TO 24.5561 K, USING RHODIUM-IRON RESISTANCE THERMOMETERS

摘要

At its meeting in 1996 the CCT initiated five Key Comparisons to test the equivalence of realisations of the ITS-90 between National Measurement Institutes. CCT-K1 covers the temperature range from 0.65 K to 24.5561 K, in which the ITS-90 is defined by specified vapour-pressure equations for ~3He (0.65 K to 3.2 K) and ~4He (1.25 K to 5.0 K) and interpolation equations for a constant-volume gas thermometer (ICVGT) using ~3He or ~4He (3 K to 24.5561 K). The comparison was carried out using rhodium-iron resistance thermometers from the seven participating laboratories represented by the authors. The measurements were made in two experiments at NPL, which also coordinated the comparison. Measurements were made at 43 temperatures over the range. The results presented are taken from the report in which a graph of differences is plotted relative to the weighted means at each temperature as the agreed baseline. These means are taken as the Key Comparison Reference Values, but without attaching any special significance to them with respect to a 'best realisation' of the ITS-90. The differences and uncertainties, and the degrees of equivalence between the NMIs, will be documented in Appendix B of the BIPM Key Comparison Database, so allowing the relevant Calibration and Measurement Capabilities to be validated for Appendix C.