Strain gauges

Strain gauges are used to sense strain. They are passive transducers where the variation in electrical resistance in wires is used to sense the strain produced by a force on the wires. The important types of strain gauges are wire strain gauges, foil strain gauges and semiconductor strain gauges. Four types of wire strain gauges are Grid type, Rossette type, Torque type and Helical type. Foil strain gauges are extension of the resistance wire strain gauge. Here strain sensing is achieved through a metal foil. The typical materials used for foil construction are nichrome, constantan, isoelastic, nickel and platinum. The advantages of foil strain gauges are greater dissipation capacity, larger surface area, possibility of large scale fabrication, higher operating temperature range and better bonding. In cases, where high gauge factor is required, semiconductor strain gauges are preferred. The basic principle employed here is piezo resistive effect. Germanium and Silicon are the preferred semiconducting materials. By using simple temperature compensation methods, even microstrains can be measured by semiconductor strain gauges.