Investigation of differently designed Pd–C eutectic fixed-point cells for the calibration of thermocouples

Abstract

An interlaboratory comparison of the melting temperatures of three palladium–carbon (Pd–C) eutectic fixed-point cells of different designs and usable for the calibration of thermocouples was performed at NIM. Two Pt/Pd thermocouples were constructed for this particular purpose. One of the Pd–C eutectic cells is of conventional design and size; the two other cells are miniature fixed-point cells of different designs. The melting temperature of the conventional cell, PdC1-NIM, was slightly higher than the melting temperatures of the miniature cells by about 160 mK (PdCM2 of PTB) and 290 mK (PdC2-NIM). The melting temperatures of the two miniature Pd–C cells agree within their measurement uncertainties for k = 2 of about 135 mK. Furthermore, a new aspect of leakage effects often observed in the use of Pd–C cells is presented.