Data Acquisition Web

The first bonded, metallic wire-type strain gage was developed in 1938. The metallic foil-type strain gage consists of a grid of wire filament of approximately 0.025 mm thickness, bonded directly to the strained surface by a thin layer of epoxy resin. When a load is applied, the resulting change in surface length is communicated to the resistor and the corresponding strain is measured in terms of the electrical resistance of the foil wire, which varies linearly with strain.

Each strain gage material has its characteristic gage factor, resistance, temperature coefficient of gage factor, thermal coefficient of resistivity, and stability. Unfortunately, the most desirable strain gage materials are the most sensitive to temperature and age. For short duration tests, this may not be a concern, but for continuous industrial measurement, one must include temperature and drift compensation. Typical materials are Constantan, Nichrome V, platinum alloys, Isoelastic, Karma-type alloy wires, foils, or semiconductor materials. The most popular are copper-nickel alloys and nickel-chromium alloys.