Validation of the fixed-point realization of the thermocouple scale using a radiation thermometer in the temperature range between the freezing points of Ag and Pd

We have developed a blackbody comparison system to validate the fixed-point realization of the thermocouple temperature scale using the radiation thermometry scale. Platinum/palladium, type S and type B thermocouples were calibrated at the fixed points of Ag, Cu, Fe-C, Co-C and Pd (only for type B). The radiation thermometer used was an LP4 linear pyrometer operating at a central wavelength of 650 nm. To assign the Fe-C eutectic melting temperature in our laboratory, a radiometric Fe-C cell was fabricated, and its melting temperature was determined as (1154.0 +/- 0.1) degrees C with k = 2. Two scales were compared from 962 degrees C to 1555 degrees C in the blackbody comparison system. The two scales were consistent within 0.5 degrees C up to 1400 degrees C, but the discrepancy for the type B thermocouple increased to 2.3 degrees C at 1554.8 degrees C. The thermocouple and radiometric scales realized at our laboratory were in agreement up to the freezing temperature of Pd within the measurement uncertainty.