Strain gauge

A strain gauge is a device used to measure deformation (strain) of an object. The most common type of strain gauge consists of a flexible backing which supports a metallic foil pattern etched onto the backing. As the object is deformed, the foil pattern is deformed, causing its electrical resistance to change. This resistance change, usually measured using a Wheatstone bridge circuit, can be used to calculate the exact amount of deformation by means of the quantity known as the gauge factor.

The gauge factor of a strain gauge relates strain to change in electrical resistance. The gauge factor <math>GF<math> is defined by the formula <math>GF=\frac{\Delta R/R_G}{\epsilon}<math> where <math>R_G<math> is the resistance of the undeformed gauge, <math>\Delta R<math> is the change in resistance caused by strain, and <math>\epsilon<math> is strain.

For measurements of small strain, semiconductor strain gauges are often preferred over foil gauges. A semiconductor gauge usually has a larger gauge factor than a foil gauge. Semiconductor gauges tend to be more expensive, more sensitive to temperature changes, and are more fragile than foil gauges.