Thermoelectric Scanning Study of Pt/Pd and Au/Pt Thermocouples up to 960 °C with a Pressure Controlled Sodium Heat‐Pipe

The performance of the Gold/Platinum (Au/Pt) thermocouple and the Platinum/Palladium (Pt/Pd) thermocouple has received considerable study and it is found that stability of these thermocouples approaches that of Standard Platinum Resistance Thermometers. However there is still some question on the uncertainties due to the different temperature profiles of the furnaces. In this paper results of the measurements on thermal emf variations by means of thermoelectric scanning are reported. Scanning is carried out in a pressure controlled heat pipe at 960 °C over 475 mm along the thermocouples. A Au/Pt thermocouple and three Pt/Pd thermocouples were tested. Pt/Pd thermocouples were subjected to 1000 hours exposure to 1200 °C in different furnaces. As the portion of thermocouple wire previously exposed to around 750 °C crossed the top of the heat‐pipe, a 0.4 K apparent temperature drop was detected. It is found that with this thermoelectric scanning method, the effect of accumulated heat treatment on the Pt/Pd th...