The principle of electrical strain gauge is based on measurement of change in some electrical characteristics such as, resistance, capacitance or inductance. In general, resistance type strain gauges are used. It is proportional to strain applied on test specimen. It works on principle of change in resistance of wire with change in strain; resistance is measured by using Wheatstone bridge. The output of Wheatstone bridge can be calibrated to give strain.
Advantages of Electrical Strain Gauges
- Simple in construction.
- Strain gauges can be calibrated in terms of quantities, such as, force, displacement, pressure and acceleration.
- Very sensitive.
- Linearity.
- They provide good output for indicating and recording purposes.
- Inexpensive and reliable.
CLASSIFICATION OF ELECTRICAL STRAIN GAUGES
Electrical strain gauges are classified according to,
- Bonding
Bonded strain gauge
The name “bonded gauges” is given to strain gauges, which are glued to a large structure under stress, i.e. specimen.
Unbonded strain gauge
Unbonded gauges are cemented. They are simply screwed at desired location, so that, they can be detached or dismantled and can be again attached or assembled for repetitive times, as and when required.
- Construction
- Wire type bonded strain gauge
- Foil type bonded strain gauge
- Semiconductor type bonded strain gauge
SELECTION CRITERIA FOR STRAIN GAUGES
Selection of suitable strain gauge is done by considering,
- Size of strain gauge, i.e. availability of space.
- Location, where the strain gauge is to be mounted.
- High gauge resistance.
- Sensitivity.
- Environmental conditions, at which, strain measurement is to be done.
- Cost
- Requirement of protection – Needed or not.
- Strain limits of measurements.
