Development and Long-Term Stability Assessment of Co-C Eutectic Fixed Point for Thermocouple Thermometry

The long-term stability assessment on the Co-C eutectic fixed point cell indigenously developed at CSIR-National Physical Laboratory, India is presented. Metal-carbon eutectic fixed points are promising candidates for the direct traceability to high-temperature thermometry and radiometry. The acceptance of any fixed point as a temperature reference cell depends on its repeatability, reproducibility, and long-term stability. In this paper, we report the detailed investigations on development and realization of Co-C cell and comparison of successive 3-year data to evaluate the long-term stability and robustness of cell. We assigned melting transition temperature to Co-C cell by using Type-S thermocouple, calibrated on ITS-90 fixed points. The cell has been subjected for 270h of melt-freeze cycle since its construction in 2014 and exhibits excellent thermo-mechanical stability. The Co-C melting transition temperature and measurement uncertainty were estimated by using the same Type-S thermocouple, for 3years from 2015 to 2017, and overall drift for the cell was estimated to be 0.1 degrees C, after normalizing the drift of the thermocouple