The scope of the strain gage principle

The 50-year-old strain-gage principle has found widespread application in the measurement of dynamometric quantities; i.e., sensors for force/mass, pressure, torque, or acceleration. It further plays an important role in the measurement of such geometric quantities as displacement and level. About 50% of all sensors (by value) rely on the strain-gage principle. A very important second application of strain gages is the experimental stress analysis of structural parts. The piezoresistive effect can be described by a gage factor k resulting from a geometric effect plus a stress-induced modulation of the electric-field charge transport. These gage factors range from near 2 in metals to more 100 in semiconductors. On this basis, a broad spectrum of sensors can be realized, reaching from the especially tailored super-precision transfer-load cell (maximum error 2*10/sup -5/, diameter 25 cm, price $25000) down to a mass-produced tiny monolithic silicon pressure sensor (error 1%, diameter 6 mm, price $5).<>