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Recently, the eutectic points are being studied by many national institutes, and considered being useful for the calibration laboratories in industry to improve their uncertainty of thermocouple calibration at high temperature. To conduct a cooperative research for investigation on the reliability of thermocouple calibration in industry at high temperature, a working group has been established within the Japan Society for the Promotion of Science (JSPS). AIST and nine domestic laboratories participated to this working group. In this working group, thermocouple comparison measurements were performed at around 1300 °C in nine laboratories by using two Pt/Pd thermocouples and one type R thermocouple following calibration at Co-C eutectic point. It was found that the uncertainties of calibration at around 1300°C in industry would be improved by utilizing the calibration at Co-C eutectic point.

A copper freezing-point furnace and four copper freezing-point cells were constructed in our institute. The furnace was consisted of one main heater and two end-heaters. The copper freezing-point cells were open type cells with high-purity graphite crucibles that contained copper of 99.9999% purity. The uncertainty in realizing freezing-point for thermocouple calibration was evaluated using the Pt/Pd thermocouples. The main sources of the uncertainty investigated were reproducibility of the plateau, the temperature distribution in the cell and the impurity effect of the metal. The combined standard uncertainty was estimated to be 20.2mK.

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