Stability study of simple high precision Pt-Au thermocouples to measure temperatures to 1000 deg C

摘要

A new design of a simple and robust Pt-Au thermocouple for high precision temperature measurement has been developed by NMIA. As these thermocouples are made from pure elements (platinum and gold), they do not suffer from the oxidation and hysteresis that limit the performance of the commonly used Type R or S thermocouples. The calibration stability and mechanical robustness of 3 Pt-Au thermocouples was assessed up to 960 deg C after 500 hours of heat treatment at 900 deg C and 50 thermal cyclings between ambient and 900 deg C. They are found to be reproducible to +-10 mK without any mechanical failure and can be used in both vertical and horizontal furnaces. These thermocouples can be calibrated by NMIA with an expanded uncertainty of +-32 mK at 960 deg C at a 95percent confidence limit, which is far better than conventional type R or S thermocouples, and comparable to platinum resistance thermometers. This thermocouple is proposed as more-accurate replacement, over the temperature range of 0-1000 deg C, for the commonly used type R or S thermocouples, as industrial transfer standard, in a robust form familiar to industrial calibration laboratories.