Strain is the amount of deformation of a body due to an applied force. More specifically, strain (ε) is defined as the fractional change in length, as shown in Figure 1.
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Figure 1. Definition of Strain
Strain can be positive (tensile) or negative (compressive). For each type of bridge configuration, the calculation formula will be different.
Sample Calculation: Using a quarter bridge circuit, you can use the formula below to calculate the strain ε where the Vo/Vex ratio is the input voltage (-25mV/V and +25mV/V) to calculate both maximum positive and negative strains and GF is the Gage Factor given by the sensor manufacturer.
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Figure 2. Quarter-Bridge Circuit
In this example, for a given GF of 2, it will result in both equations :
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And after a few manipulations: