1046-Converting output value to strain without calibration

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1046-Converting output value to strain without calibration

Postby clearwater304 » Wed Jul 31, 2013 7:16 am

I have a project where I will be attaching strain gages to an object to calculate strain on certain parts of the design. I want to know the strain value at this location within about 5% accuracy. I've found this equation to convert voltage into strain, but I'm not sure how it correlates to the output value of the phidgetbridge:
(Differential Voltage)=(Number of Active Arms)*((Gage Factor)/4)*(Strain)*(Excitation Voltage)

Is the bridge value:
1. Differential Voltage (Assuming this is the load value minus the unloaded value)
2. (Differential Voltage)/(Excitation Voltage)
3. (Differential Voltage)/((Excitation Voltage)*1000)
4. Or Some other value entirely

I've run a cantilever beam test to try and correlate the voltage to strain but no matter what values I put in, my strain is way off from what it should be. I have a full bridge strain gage which should have two active arms on the test. The Gage Factor for the strain gage is 2.14. At the location I am measuring strain, the strain should be .000686. With the formula mentioned using the differential voltage as the bridge value, I get the strain to be .0739.

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