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Wheatstone Bridge Strain Gauge
Wheatstone bridge strain gauge circuits are used extensively inside pressure transducers to convert mechanical stress into an electrical output signal.
The basic circuit consists of four resistive elements which are connected together into a diamond shaped configuration. Typically all 4 resistive elements are active strain gauges to maximise sensitivity of the pressure sensor but in some cases 2 fixed resistors are used with 2 strain gauges instead.
Two strain gauges are located on a pressure sensing diaphragm where they will be stretched along their width and the other two are located where they will be stretched along their length.
The simplest way to achieve this is to mount all four strain gauges onto the surface of a circular diaphragm in a radial configuration 90 degrees apart all pointing in the same direction.
The two strain gauges that are pointing tangentially will be stretched across their width reducing resistance. The two strain gauges that are pointing perpendicularly will be stretched along their length increasing resistance.
The strain gauges that increase in resistance are connected directly opposite each other in the diamond shaped wheatstone bridge circuit and likewise for the two strain gauges that decrease in resistance.
If a voltage is dropped across two opposite points of the Wheatstone bridge circuit a voltage difference can be measured between the other 2 circuit points which will vary with applied pressure.
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Site Last Updated: 12/05/08
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