Development and Evaluation of a Co-C Eutectic-Point Cell for Thermocouple Calibration.

The cobalt-carbon (Co-C) eutectic point at $$1324\,^{\circ }\hbox {C}$$ has in previous studies proved to be suitable as a reference for thermocouple calibration above $$1100\,^{\circ }\hbox {C}$$ . For types S, R, and B, it fills the gap between the copper point and the palladium point, and for Pt/Pd thermocouples, it extends the range from the copper point. This work describes the implementation of the Co-C reference point at the Technical Institute of Sweden (SP). A Co-C cell was developed and manufactured at SP in a collaboration project with the National Metrology Institute of Japan (NMIJ). The principle of the cell is a hybrid design with double walls, both for the outer crucible and the inner thermometer well, with graphite foil between the walls. To evaluate the performance of the developed cell (SP cell), a comparison between the SP cell and another cell, manufactured and provided from the National Physics Laboratory (NPL) in England, is performed using Pt/Pd thermocouples as transfer standards. The comparison showed very good agreement, with differences below 40 mK, using the same furnace and two different thermocouples. The expanded uncertainty $$(k=2)$$ for the comparison was estimated to be 70 mK. [ABSTRACT FROM AUTHOR]