# 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 ${\displaystyle R_{3}}$, 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.

### Example Usage

The FX1901 is an inexpensive 1% strain gauge that can be used for a variety of applications. It is available for about \$30 and comes in 10, 25, 50, and 100 lbf models

Here is an example set up circuit with amplifier amp and tuning potentiometer:

Ensure that the power lines are very stable, it is suggested that in noisy environments, a DC-DC converter, power regulator(L78L05) and large power capacitors are used to ensure clean signal. In more ideal environments, a simple capacitor across the power lines should be sufficient.