strain gauges - course materials

Strain Gauges

Strain Gauge• A strain gauge (or strain gage) is a device used to

measure strain on an object. Invented by Edward E. Simmons and Arthur C. Ruge in 1938, the most common type of strain gauge consists of an insulating flexible backing which supports a metallic foil pattern. The gauge is attached to the object by a suitable adhesive, such as cyanoacrylate.[1] 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.

How they work

• An excitation voltage is applied to input leads of the gauge network, and a voltage reading is taken from the output leads. Typical input voltages are 5 V or 12 V and typical output readings are in millivolts.

What about changes in temperature?

• Most strain gauges are made from a constantan alloy. Various constantan alloys and Karma alloys have been designed so that the temperature effects on the resistance of the strain gauge itself cancel out the resistance change of the gauge due to the thermal expansion of the object under test.

Non Temperature Compensated Gauge

• Strain gauges that are not self-temperature-compensated (such as isoelastic alloy) can be temperature compensated by use of the dummy gauge technique. A dummy gauge (identical to the active strain gauge) is installed on an unstrained sample of the same material as the test specimen.

The sample with the dummy gauge is placed in thermal contact with the test specimen, adjacent to the active gauge. The dummy gauge is wired into a Wheatstone bridge on an adjacent arm to the active gauge so that the temperature effects on the active and dummy gauges cancel each other

Wheatstone Bridge

Principles of the Wheatstone Bridge

• https://www.youtube.com/watch?v=Y3-Mhil1uzY

• <iframe width="420" height="315" src="https://www.youtube.com/embed/Y3-Mhil1uzY" frameborder="0" allowfullscreen></iframe>

• https://www.youtube.com/watch?v=3rOvQ3qFZpI

• <iframe width="420" height="315" src="https://www.youtube.com/embed/3rOvQ3qFZpI" frameborder="0" allowfullscreen></iframe>

Temperature Correction of Strain Gauges

• https://www.youtube.com/watch?v=nb7NETKtvYQ&index=4&list=PLD0zKK4lStDY6k8TzeOv9FVt-gdj9kNUc

• <iframe width="560" height="315" src="https://www.youtube.com/embed/nb7NETKtvYQ?list=PLD0zKK4lStDY6k8TzeOv9FVt-gdj9kNUc" frameborder="0" allowfullscreen></iframe>

Strain Gauge Amp• https://www.youtube.com/watch?v=s

b0SA2fbXhw

• <iframe width="560" height="315" src="https://www.youtube.com/embed/sb0SA2fbXhw" frameborder="0" allowfullscreen></iframe>

Strain Gauge Data Logger

Structural Strain

Measuring Strain on Coke Can

• Strain Gage Rosette/ Thin walled pressure vessel

• https://www.youtube.com/watch?v=SCuH3AnZgFU

• <iframe width="420" height="315" src="https://www.youtube.com/embed/SCuH3AnZgFU" frameborder="0" allowfullscreen></iframe>

Strain Gauge Basics• https://www.youtube.com/watch?v=GmFV

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