High-stability capacitance strain gauge for use at extreme temperatures

A new type of strain gauge is described, intended to have high stability at temperatures up to 650°C. It is based on the variation of capacitance between two electrodes mounted at the crowns of arched strips, the flexure of the strips changing with small variations in the separation of their feet. The performance of the gauge at high temperatures has been studied at length; uncertainties in strain measurement of only a few parts in 106 arise over long periods and many cycles of temperature or stress. The practical problems associated with making measurements in the field of small capacitances (about 1 pF) are discussed, and are shown not to be too severe. A typical result from a field trial is quoted.