Final report of APMP.T-S7: APMP regional comparison of Co-C eutectic melting point using Pt/Pd thermocouples

Abstract

A regional supplementary comparison on the Co-C eutectic point (1324 °C in ITS-90) was carried out in APMP involving five NMIs: KRISS (Korea), NIM (China), NMIJ (Japan), NMIA (Australia) and NPLI (India). The comparison was done through a round robin style with two Pt/Pd thermocouples having greatly different thermoelectric inhomogeneity (± 0.0196 % and ± 0.132 % at 1324 °C), which were made by the pilot laboratory (KRISS). Both were calibrated twice, before and after the circulation by the pilot laboratory. As a reference value, the weighted mean was adopted since the Birge ration criterion was safely satisfied. The participants were asked to supply the temperature profile of the furnace used to realize the Co-C point in order to estimate the uncertainty due to thermoelectric inhomogeneity. Results from all laboratories were consistent with the reference value within the calculated uncertainties. Birge number of 0.2 to 0.3 and En number less than 0.5 were obtained, meaning that the comparison successfully demonstrated the use of Pt/Pd thermocouple to compare the calibration capabilities of participating laboratories at the melting temperature of Co-C eutectic point regardless of the amount of thermoelectric inhomogeneity. It was verified that the calibration uncertainty level of {(0.2 °C ~ 0.3 °C) + ucell} (k = 2) can be obtained at the Co-C eutectic melting point by means of Pt/Pd thermocouple having a small inhomogeneity of about 0.02 %. Main text To reach the main text of this paper, click on Final Report. Note that this text is that which appears in Appendix B of the BIPM key comparison database kcdb.bipm.org/. The final report has been peer-reviewed and approved for publication by the CCT, according to the provisions of the CIPM Mutual Recognition Arrangement (CIPM MRA).