What is the relationship between the service life and degradation of thermocouples?

In practical application, prefabricated thermocouples usually have protective tubes and are only used with bare wires in special circumstances. Therefore, in most cases, the lifespan of the protective tube determines the lifespan of the thermocouple. It is necessary to collect and accumulate data on the practical application status of thermocouples over a long period of time in order to give accurate results. Thermocouples are commonly used temperature sensors in scientific research and production. Despite their simple structure, significant measurement errors can still occur if not taken seriously during use. Here, specific discussions will be conducted on the selection of temperature measurement points for simple questions that may arise during application. The main reasons for errors in thermocouple penetration depth, response time, thermal radiation, and thermal impedance will also be identified. Precautions for thermocouple heterogeneity, operating atmosphere, insulation resistance, selective oxidation of K-type thermocouples, K-state and armored thermocouple shunt errors will also be pointed out.

Degradation and lifespan of thermocouples

The so-called degradation of thermocouples refers to the phenomenon of aging and degeneration of thermocouples after use. Thermocouples made of metals or alloys gradually grow their internal grains at high temperatures. The alloy contains a small amount of impurities, and its orientation or shape will also change, and it will also react to the recovery or oxidizing gases in the surrounding environment. Along with the above changes, the thermoelectric potential of the thermocouple will also undergo extremely sensitive changes. Therefore, the deterioration of thermocouples is inevitable.

The degradation of thermocouples is a quantitative process, which is difficult to quantify and will vary with the type, diameter, operating temperature, atmosphere, and time of the thermocouple. The service life of a thermocouple refers to the time when the thermocouple deteriorates beyond the allowable error limit, or even breaks and cannot be used.