No.7（2012）11.Uncertainty evaluation on cobalt-carbon eutectic point for thermocouple calibration

Haruhiko Numajiri, Masashi Sasaki, Hiromasa Mizuno

  The metal-carbon eutectic points were proposed as new temperature standards and put into practice by the National Metrology Institute of Japan, National Institute of Advanced Industrial Science and Technology (NMIJ/AIST). The cobalt - carbon (Co-C) eutectic point (1324˚C), a metal-carbon eutectic point, has become the new standard for the thermocouple calibration between the freezing point of copper (1084.62˚C) and the melting point of palladium (1554˚C in air).
  We realized the Co-C eutectic point using an electric furnace with an open type cell and the thermocouple calibration uncertainty is evaluated using platinum versus palladium (Pt/Pd) thermocouples in our laboratory. Factors influencing measurement uncertainty are as follows: the determination of the inflection point in the melting plateau, the repeatability of the melting plateau, surrounding temperature effects and heat flux influence on the cell. The combined standard uncertainty is estimated to be 13.8 mK.

Keywords
Thermocouple, Cobalt – carbon eutectic point, Uncertainty

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