There are many types of strain gauges available like capacitance type, impedance  type, mechanical type etc. But the most commonly used among these is the resistance type strain gauges.

 

When a force is applied to a structure, the length of the structure changes. Strain is the ratio of this change in dimension to the original, and strain gauges are used to measure it. As the strain gauge is glued to the structure, any distortion will also cause a distortion of the strain gauge. The gauge contains conducting material and the distortion therefore results in a change in its resistance. By measuring this change in resistance we can measure the strain.

Applications

• Any change in strains, may it be shear tensile or compressive, can be measured by using these strain gauges. There are different types of strain gauges for different applications and material.

Codes

• BS 6888 (UK)
• NAS 942 (USA)
• VDI/VDE 2635

Methodology

• The surface is where strain gauge has to be placed is marked, grinded and cleaned properly.
• Araldite is used to make the surface smooth and finished.
• The Strain-Gauge is glued using the special adhesive for gauges to adhere.
• The required connections depending on the bridge to be used are made using the dummy gauge and the core wire. Dummy gauge block is clamped to the surface near to the strain-gauge.
• All connections are made using a switcher units(in case of multiple gauges) and the readout instruments.
• When all the instruments are in place readings can be taken. These strain gauges must be calibirated to the change in temperature.

Limitations

• The strain gauges must be calibirated for temperature changes that affect the strain gauge measurements.
• Before taking any readings it is neccasary to attach a shunt and measure the change in strain. If the change is not consistent the readings will be significantly affected.