Abstract
The design and performance of platinum resistance thermometers are evaluated for periods of up to 5000 h exposure between 1050 °C and 1100 °C. These thermometers are designed as interpolation instruments for the International Practical Temperature Scale (IPTS). Long term stability and high temperature insulation resistance measurements were of particular interest, and after an initial 500 h of high temperature exposure, drift rates measured at 0 °C were as low as 0.002 °C per 100 h.
Insulation resistance was inferred from measurements between the sensing element and a fifth lead wire adjacent to and insulated from the element. An electrical analog was used to establish the correlation between this measurement and the true shunting resistance due to electrical leakage at high temperatures. These measurements suggest that the sensing element resistance could be increased up to a factor of two or three without causing errors greater than 0.001 °C due to insulation effects, thereby reducing the sensitivity requirements on null detectors.