The strain gauge has been in use for many years and is the fundamental sensing element for many types of sensors including pressure sensors, load cells, torque sensors, position sensors, et cetera.
In order to explain a strain gauge and its working, we need to first define strain.
Strain is what happens as a result of stress. If a material is stressed by a force, it often changes shape and gets a little bit longer (if you've pulled it apart) or shorter (if you've pushed it together). Therefore, strain is defined as the change in length the force produces divided by the material's original length.
A Strain Gauge is a passive transducer that converts a mechanical elongation or displacement produced due to a force into its corresponding change in resistance R, inductance L, or capacitance C.
It is basically used to measure the strain in a work piece. If a metal piece is subjected to a tensile stress, the metal length will increase and thus will increase the electrical resistance of the material. Similarly, if the metal is subjected to compressive stress, the length will decrease, but the breadth will increase. This will also change the electrical resistance of the conductor
Following is a basic diagram of a bonded strain gauge –
Application in Load Measurement –
In engineering, designing anything from a car engine or a bridge to a wind turbine or an airplane wing requires measurement of stress that will be inflicted by the load. Strain gauge simplifies this process by providing accurate data and the engineer does not have to rely on intuition or guesswork.