Strain Gauge

Strain is a dimensionless measurement that is a ratio of the change in length to the original length of an object. Therefore, a positive strain is the result of stretching a material and negative strain is the result of compression. Stress is a measurement of the force applied divided by the initial cross-sectional area of an object, or the internal resisting capacity of an object.

A Strain gauge (sometimes referred to as a Strain gage) is a sensor whose resistance varies with applied force; It converts force, pressure, tension, weight, etc., into a change in electrical resistance which can then be measured. When external forces are applied to a stationary object, stress and strain are the result.

Each strain gauge is composed of a metal foil insulated by a flexible substrate. The two leads pass a current through the gauge, and as the surface of the object being measured stretches or contracts, the change in resistance is measured. This change in resistance is proportional to the change in length on the surface of the object being tested. Strain gauges work by measuring the change in electrical resistance across a thin conductive foil. The gauge factor (or “gage factor”) is the sensitivity of the strain gauge (usually 2). It converts the change in resistance to the change in length.