Mercury-in-rubber (whitney) strain gauge

Abstract

Mercury-in-rubber strain gauges are used in plethysmography for determining changes in the volume of various parts of the body from changes in their girth. Temperature also affects the output of the gauge, but a temperature compensating element is required only infrequently. Error resulting from the change in resistance due to the change in temperature of the gauge becomes negligible if the gauge is allowed to reach thermal equilibrium with the skin or organ surface before measurement. When there are simultaneous rapid changes in skin temperature, ambient temperature, and blood flow, use of temperature compensated gauges improves accuracy of measurements. The accompanying equations and nomograms simplify design of temperature compensating networks from easily obtainable materials, e.g., copper, constantan, nichrome, and nickel.