A strain gauge (alternatively: strain gage) is a device used to measure deformation (strain) of an object. Invented by Edward E. Simmons and Arthur C. Ruge in 1938, the most common type of strain gauge consists of an insulating flexible backing which supports a metallic foil pattern. The gauge is attached to the object by a suitable adhesive, such as cyanoacrylate^[1]. As the object is deformed, the foil is deformed, causing its electrical resistance to change. This resistance change, usually measured using a Wheatstone bridge, is related to the strain by the quantity known as the gauge factor.

The gauge factorGF is defined as where R_G is the resistance of the undeformed gauge, ΔR is the change in resistance caused by strain, and ε is strain. For metallic foil gauges, the gauge factor is usually a little over 2^[2]. For a single active gauge and three dummy resistors, the output v from the bridge is where BV is the bridge excitation voltage.

Foil gauges typically have active areas of about 2-10 mm in size. With careful installation, the correct gauge, and the correct adhesive, strains up to at least 10% can be measured.

This article is based on the article Strain gauge from the free encyclopedia Wikipedia and is distributed under The GNU Free Documentation Licence.