Strain Guage

Strain is defined as the amount of deformation in a body due the applied force.  The Strain gauge is a thin layer of metal in the form of a foil and mounted on a flexible strip.  The strip is mounted on the specimen whose strain is to be measured.  The mounting of the strain gauge of the specimen is done through a special adhesive to ensure that the strain of the specimen is accurately transferred to the strain gauge.

When the specimen is subjected to a force, it elongates.  This elongation is also transferred to the strain gauge which is mounted on the specimen.  This changes the resistance of the gauge which is measured as the amount of deformation.

Since the value of the change is resistance is very small, conventional methods of measuring the resistances cannot be used.

Hence, a Wheatstone bridge excited by an external power supply is used, the resistance of the strain gauge is one arm of the Wheatstone Bridge.