Some factors affecting long‐term stability of strain measurements using metal foil gauges

Abstract

The stability of long‐term strain measurements is very much dependent on the correct selection of techniques, materials and equipment for the conditions under which the measurements are to be taken.Temperature effects are also a major factor. Temperature‐induced changes in resistance of the Wheat‐stone bridge completion and balancing components can result in an output signal indistinguishable from that produced by change of gauge resistance due to surface strain. The signal conditioning and readout equipment can also be affected by temperature and become an additional source of instability.The term ‘instability’, in strain gauging, generally refers to ‘zero drift’ and random deviations of readings when the loading conditions are stationary. In particular it refers to those situations where a measurement system has been balanced and measurements have been taken with a particular load condition which cannot be repeated to re‐check the original zero.In this paper the major sources of instability are identified and recommendations are made as to how best to obtain long‐term stability of strain measurements using metal foil gauges.Information on principal error sources in strain measurement systems using metal foil gauges is included for completeness and because an appreciation of these sources is also vitally important.