HIGH TEMPERATURE SENSORS FOR SMALL GAS TURBINES

The report describes an experimental program performed to generate technology on high temperature sensor concepts for small gas turbines. Major emphasis was placed on the definition of material systems needed for transducers with long life, good reliability, and fast response for sensing turbine inlet temperatures in the range of 2200 to 2500F with transients to 3000F. The technology related to three types of sensors was considered thermocouples, resistive devices, and radiation pyrometers. Inherent material problems with resistive devices at temperatures above 1600F limited the experimental program on this concept. Thermocouple and radiation sensors were studied extensively, resulting in several promising approaches. Two types of thermocouple probes were found to have potential application to turbine engines. A proposed protected thermocouple junction offers best reliability and durability, but has relatively slow response to changes in gas temperature. A suggested exposed Pt- Rh junction has much improved response rate however, the reliability and durability are much less than the protected junction. Five commercial radiation pyrometers were evaluated and one concept chosen as having, by far, the greatest potential for application to turbine engines. The sensor employs a silicon p-n junction photovoltaic detector. The sensor demonstrated microsecond response, good accuracy, and good reliability as long as the environmental temperature for the silicon chip was kept below 250F and the window was maintained clean. A unique air-collimator lens was devised which acts as an interface between the turbine gas path and the sensor window.