Effect of pressure on electrical resistance strain gages

The pressure effect is defined as the indicated strain response minus the expected response of a strain gage under hydrostatic pressure. The problem is that the expected strain response only considers the strains at the test surface and neglects the grid compression perpendicular to this surface. In this paper, this effect will be included in the analysis, and a simple equation is derived relating the pressure effect to the grid compressibility. The relation is tested by comparing predictions with literature data. It turns out that for most constantan gages the pressure effect is about 0.55 mu epsilon/MPa and is independent of the grid design. Furthermore, it is shown that the alternative way of calculating the pressure effect from gage factor and transverse sensitivity (using Bridgman factors) does not compare well with measurements.