Metal sheathed mineral insulated thermocouples used for measurement of exhaust gas temperature in turbines and aircraft engines are usually not replaced after initial installation. Therefore, the change in calibration of these thermocouples during service is of interest. In this paper, two 5,000 hour stability tests were conducted on some standard and non-standard thermocouples in the laboratory in air atmosphere at 538°C, the mid temperature for gas turbine application and at 875°C, near the high end of aircraft engine applications. A comparison is made on calibration changes between laboratory and actual environment. Future work involving extension of the 875°C beyond 5,000 hours, laboratory testing in reducing atmospheres and insitu testing is proposed.

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