Hot Tip #24 – Stain Gauge

How does the strain gauge on my tunnel loading conveyor work?

The strain gauge is one of the most widely used strain measurement sensors. It is a resistive elastic unit whose change in resistance is a function of applied strain.

Where R is the resistance, e is the strain, and S is the strain sensitivity factor of the gage material (gage factor in some books).
Among strain gages, an electric resistance wire strain gage has the advantages of lower cost and being an established product. Thus it is the most commonly used type of device. Other types of strain gages are acoustic, capacitive, inductive, mechanical, optical, piezo-resistive, and semi-conductive.

A wire strain gage is made by a resistor, usually in metal foil form, bonded on an elastic backing. Its principle is based on the fact that the resistance of a wire increases with increasing strain and decreases with decreasing strain, as first reported by Lord Kelvin in 1856.

When the strain gage is attached and bonded well to the surface of an object, the two are considered to deform together. The strain of the strain gage wire along the longitudinal direction is the same as the strain on the surface in the same direction.