Strain Gauge

• Strain Gauge is a device used to measure strain on an object.
• As the object is deformed, the foil is deformed, causing its electrical resistance to change.
• This resistance change, usually measured using a Wheatstone bridge, is related to the strain by the quantity known as the gauge factor.

• A strain gauge is a sensor whose resistance varies with applied force.
• It converts force, pressure, tension, weight, etc., into a change in electrical resistance which can then be measured.

Construction

• The strain gauge has resistive elements.
• It can be connected in half-bridge and full-bridge type.
• It has various types as following:

1. Bonded and un-bonded metal wire type
2. Wire type
3. Foil type
4. Frame type
5. Sheath type

Operation

• When the load or weight is acting on the strain gauge element, it deforms.
• The deformation in element causes the change in resistance of it. As per the balance and unbalance condition of the bridge, the voltmeter shows the output voltage.
• The output voltage is proportional to the change in resistance of the strain gauge elements and that change in resistance is proportional to the weight acting on it. 
• Therefore, the output voltage vary with the weight.
• The fixed dc voltage source is required for this operation.

Advantages

• High sensitivity to input
• Low cost
• Small size
• Simple control
• Fast response
• Available in wide range

Dis-advantages

• Errors
• They are affected by external vibrations and temperature

Applications

• In weight measurement applications
• In die cutting applications
• In some medical applications
• As a Load Cell
• In torque meters
• In diaphragm pressure gauge
• In accelerometers
• In flow meters