How do the Strain Gauges Work?
When a force is applied to a structure, the length of the structure changes. Strain measures this change of length. The strain gauge is glued to the structure being tested, so any distortion of the structure will also cause a distortion of the strain gauge. As the strain gauge contains conducting material – often a pattern of metal foil – the distortion results in a change in the resistance of the gauge. By measuring the change in resistance we can measure the strain. Easily said – but how is resistance to be measured? Generally through a “Wheatstone bridge” arrangement. This has 4 arms, arranged in a square. Each arm generally contains either a resistor of known resistance, or a strain gauge – strain gauges will occupy 1, 2 or 4 of the arms. Taking the case of 1 strain gauge in the Wheatstone bridge – a quarter bridge arrangement. Power lines are connected to opposite corners of the bridge, lets call them A and C, providing an excitation voltage. The measurement is made across the oth
