Comparison of nickel–carbon and iron–carbon eutectic fixed point cells for the calibration of thermocouples

Abstract

Three nickel–carbon (Ni–C) and three iron–carbon (Fe–C) eutectic fixed points cells of a new design, meeting the requirements for reliable applications and being suitable for the calibration of thermocouples, were constructed at PTB and Inmetro. Their melting temperatures were compared by using the high-temperature furnace of PTB (HTF-R) and two platinum/palladium (Pt/Pd) thermocouples. The measured emfs of the Ni–C eutectic fixed point cells at the inflection points of the melting curves agree within a temperature equivalent of about 0.29 °C, compared with an agreement of about 0.09 °C found for the Fe–C cells. Additional comparison measurements of two Fe–C eutectic fixed point cells in a second high-temperature furnace (HTF-M, Inmetro) demonstrate the applicability of the Fe–C eutectic cells as transfer standards for the dissemination of temperatures.