Strain Gauge

Overview

Strain gauges are simple sensors that can be used to measure forces. They consist peice of conducting material that changes resistance as it is stretched in a given direction. The diagram below shows this:

Circuitry

Typically, the change in resistance of the strain gauge is very small. In order to accurately measure this small change, special circuitry is needed. For this, a wheatstone bridge configuration is usually employed. There are variants on how this circuit can be arranged; two are presented below.

The first configuration is the simplest method. The wheatstone bridge measures small imbalances in the resistances. Here it is comparing the strain gauge resistance to $R_{3}$, which has a resistance equal to the resistance of the unstretched strain gauge. The other two resistors should have similar values.

Next is a more advanced circuit used for measuring strain in both directions. Two strain gauges are used, and must be positioned carefully, as shown in the second figure.

References

• http://www.allaboutcircuits.com/vol_1/chpt_9/7.html/strain_gauges