Bilateral Comparison of Type S and Pt/Pd Thermocouples between KRISS and NRC

KRISS and NRC have conducted a comparison to examine the equivalence of thermocouple calibrations carried out in their respective facilities. Type S and Pt/Pd thermocouples having a common welded junction were calibrated at the metal fixed‐points of Sn, Zn, Al, and Ag through five cycles at each NMI. The immersion properties in the fixed‐point cells were also investigated. For the type S thermocouple, the differences were less than the equivalent of 0.15 °C at all fixed points. The equivalent temperature differences for the Pt/Pd thermocouple were within 0.04 °C from the Sn point to the Al point, but a difference of 0.32 °C was obtained at the Ag point. This difference may be attributed to the 12 μV value for the thermoelectric inhomogeneity of the Pt/Pd thermocouple as revealed by the immersion profiles. The comparison confirmed that the fixed‐point thermocouple calibrations carried out by the two NMIs are in good agreement, though the results appear limited by the less‐than‐ideal thermoelectric inhomogeneity of the thermocouples employed.