A self-compensated ceramic strain gage for use at elevated temperatures

Abstract

A ceramic thin film strain gage has been developed for static strain measurements at temperatures up to 1400°C. These thin film sensors are ideally suited for in situ strain measurement in harsh environments, such as those encountered in the hot sections of gas turbine engines. However, the wide bandgap semiconductor used as the active strain elements in these devices also exhibited a large temperature coefficient of resistance (TCR). Thus, to reduce the apparent strain or thermally induced strain in these static strain sensors to an acceptable level, a novel self-compensation scheme was demonstrated using thin film platinum resistors placed in series with the active strain element. A mathematical model was developed and design rules were established for the self-compensated circuitry using this approach. Close agreement between the model and actual static strain results have been achieved using this approach, and reliable static strain measurements have been made over an extended temperature range.