Comparison of Co–C and Pd–C Eutectic-Point Cells for Thermocouple Calibration Between LNE-Cnam and NMIJ

Abstract

Evaluation of the melting temperatures of two Co-C and two Pd-C eutectic-point cells were performed using three Pt/Pd thermocouples constructed at LNE-Cnam and NMIJ. During the comparison of cells, Pt/Pd thermocouples were evaluated at the Ag fixed point, at which their drifts and inhomogeneity represented differences within 0.03 • C and 0.14 • C, respectively. One Co-C cell and one Pd-C cell were designed and constructed at LNE-Cnam, while one Co-C cell and one Pd-C cell were designed and constructed at NMIJ. In spite of differences in cell design and in materials sources, melting points of Co-C and Pd-C eutectic-point cells realized using LNE-Cnam high-temperature furnace agreed within approximately 0.02 • C and 0.01 • C, respectively. Furthermore, the realizations of the Pd-C eutectic point at LNECnam and NMIJ agreed within a temperature equivalent of approximately 0.11 • C. The uncertainty of the realization was estimated to be approximately 0.14 • C (k = 2), with a major contribution from the inhomogeneity of the thermocouple.

Comparison of Co–C Eutectic-Point Cells for Thermocouple Calibration Between SP and NMIJ

“…The temperature differences between the melting temperatures of Cell SP−L and Cell NMIJ−L were found to be 0.05 • C and 0.04 • C using the Pt/Pd thermocouples and the Co-C cell, respectively, as transfers. The expanded uncertainty (k = 2) was from 0.04 • C to 0.05 • C. These temperature differences were small enough, within 0.1 • C, and agree with the results reported in previous research [3,4] as described in Sect. 1.…”

“…As recently reported, several laboratories performed and reported a comparison for thermocouples at the melting temperature of Co-C cells [2][3][4], and it was found that the difference of the measured melting temperature of the Co-C cells was within 0.1 • C in spite of slightly different cell designs and different material sources. On the other hand, since the Co-C eutectic point is not a defined fixed point on the International Temperature Scale of 1990 (ITS-90) [5], the melting temperature of the Co-C cell for thermocouple calibration needs to be determined by using a calibrated radiation thermometer.…”

“…Since the SP local thermocouples or the NMIJ local thermocouples were only used at SP or NMIJ, respectively, the uncertainty contribution due to inhomogeneity of the thermocouple can be excluded when the immersion length of each thermocouple and temperature profile to which they were exposed is fixed during comparison measurements. In addition, before comparisons, several Pt/Pd thermocouples were used as monitoring thermocouples to measure temperature profiles of furnaces and to investigate the heat flowing along the thermocouple stem during the melting described in [4].…”

“…3a, b, error bars show the expanded uncertainties, 2u c . The combined measurement uncertainties, u c , at the melting point of the Co-C cells were calculated as follows by the equation described in [4]:…”

A pan-European investigation of the Pt-40%Rh/Pt-20%Rh (Land–Jewell) thermocouple reference function

“…Above 1000 °C, LNE-Cnam have a series of high temperature fixed-points (HTFPs) up to a temperature of 1500 °C suitable for thermocouple calibration, as well as a number of HTFPs up to a temperature of 1953 °C which are used for radiation thermometry but can be adapted for thermocouple calibration [19,[33][34][35][36][37][38]. However, due to technical problems with the furnace used for realizing these fixed points, the LNE-Cnam measurements in this article were restricted to the wire bridge calibrations using Pd and Pt points, and the freezing point of silver using a conventional tube furnace.…”