Study of the Instability of Noble Metal Thermocouples in Vacuum

Abstract

Thermoelectric instabilities of noble metal thermocouples and individual thermoelements (platinum, rhodium, iridium, platinum-rhodium, and iridium-rhodium alloys) have been studied in vacuum in the temperature range 800 to 1600°C. These studies are an extension of previous work performed in oxidizing and neutral atmospheres. As in that work, the principal source of instability was found to be contamination of the thermoelements by impurities from ceramic protection tubes. Thermocouple errors associated with this contamination are reported and compared with the previous data.