ON A GENERAL METHOD OF COMPENSATION IN STRAIN GAUGE WORK

If gauges or rosettes identical with those used in testing are affixed to a compensating bar under known stresses and of the same material as the test piece, the required stresses are obtained directly in terms of the known compensating stress and of the measured resistance changes. Cross‐sensitivity, gauge factor and constants of elasticity of the test piece cancel out and errors due to inaccurate assumptions for their values are avoided. If the test strains, elastic or non‐elastic, are required and the elastic compensating strain is known, Poisson's ratio of the compensator enters into the evaluation. A region of the test piece where stresses or strains are known may serve as a compensator. One compensating rosette or two single compensating gauges suffice for any number of identical testing gauges. Initial zero balance may not always be needed and special circuits facilitate evaluation, which lends itself to simple self‐contained automation. An analogue unit suggested for incorporation in a strain meter allows direct display of principal stresses and directions from rosette measurements.