Abstract. We present an emf-temperature reference function for platinum versus palladium (Pt/Pd) thermocouples in air for the range 0 °C to 1500 °C. The reference function is based on the International Temperature Scale of 1990 (ITS-90) and has an expanded uncertainty (coverage factor of two) of less than the equivalent of 11 mK for temperatures up to 1050 °C and rising smoothly to approximately 0.3 K at 1500 °C. The reference function is based on a set of Pt/Pd thermocouples of exceptional stability and homogeneity constructed from Pt and Pd wire of very high purity (99.999% mass fraction and 99.997% mass fraction, respectively). Experimental results are presented on the thermoelectric stability of Pt/Pd thermocouples at high temperatures and on the calibration of Pt/Pd thermocouples based on this reference function.

Print publication: Issue 5 (October 1998)