Metallic and Ceramic Thin Film Thermocouples for Gas Turbine Engine Applications

Hot section temperatures in gas turbine engines can reach 1500 degrees C, an environment in which implementing sensors for in situ measurement is rather difficult. Therefore, there is a need to develop instrumentation for these turbine engines that can survive the harsh conditions. Thin film instrumentation is targeted for this purpose because it is non-invasive to the physical and thermodynamic properties of the engine components. Type-S and type-K thin film and wire thermocouples are currently being utilized for surface temperature measurement during the testing phase of gas turbine engines. These metallic thin film thermocouples suffer from drift and degradation due to microstructural changes and oxidation. Therefore, thin film thermocouples based alternatively on platinum: palladium and indium oxynitride: indium tin oxynitride, as well as their oxide counterparts, have been developed and proved to be more stable than conventional type-S and type-K thin film thermocouples operating in these high temperature (> 1000 degrees C) oxidizing environments. Furthermore, the metallic and ceramic thin film thermocouples described within this paper exhibited remarkable stability and have drift rates similar to bulk (wire) thermocouples operating in the same temperature range.