Investigation of Co–C cells to improve thermocouple calibration

Abstract

An intercomparison of the melting temperatures of four Co–C eutectic fixed-point cells by using two Pt/Pd thermocouples was performed. The cells are usable for the calibration of thermocouples and were constructed in the participating laboratories of PTB, NPL, LNE and NMIJ/AIST. The measurements were performed in four different high-temperature furnaces but by applying the same measurement procedure. In spite of slightly different cell designs and different material sources the melting temperatures of the investigated Co–C cells agreed very well within their expanded uncertainties of k = 2. Furthermore, the mean maximum difference of the melting temperatures of the four Co–C cells measured in different laboratories by using different furnaces and Pt/Pd thermocouples was found to be of the order of 85 mK (2 µV).