New Reference Functions for Platinum-13% Rhodium versus Platinum (Type R) and Platinum-30% Rhodium versus Planinum-6% Rhodium (Type B) Thermocouples Based on the ITS-90

摘要

The Comite Consultatif de Thermometrie requested its Working Group 2 to collaborate with national laboratories in the production of new reference tables and functions for thermocouples based on the International Temperature Scale of 1990 (ITS-90). Pursuant to this recommendation, NPL and NIST have obtained data on type B and type R thermocouples relative to the ITS-90. Thermocouples obtained from several sources have been compared in the range -50 degrees C to 1070 degrees C against platinum resistance thermometers that were calibrated in accordance with the ITS-90 to 962 degrees C, with an extrapolation to 1070 degrees C. The thermoelectric voltages of the thermocouples were also determined at the freezing points of indium, tin, cadmium, zinc, aluminum, silver and gold. From the results of these measurements, polynomials giving the thermoelectric voltages as a function of t90 have been developed for type R thermocouples. Results for type B thermocouples will be addressed.