How can I measure the pressure from my strain gauge?

I bought a strain gauge from RS components, and I want to find out how can I get the pressure from the measured voltage on the strain gauge. I managed to the Wheatstone bridge and supply it with a voltage as Vex.

Based on this document, the manufacturer will provide the conversion formula but on the PDF manual here is what I only found. Can someone help me or supply any reference on how can I compute the pressure?

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A strain gauge will change its resistance based on physical deformation. The amount of force (or pressure) that makes that deformation depends entirely on the material it is bonded to.
– Andy aka
Sep 14 ’14 at 16:48

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It can only be calibrated when you’ve constructed your pressure gauge (bonded the strain gauge to a deforming disk etc.). You’ll need to amplify the change in voltage (using a suitable amplifier) and see what outputs you get for a given (known) pressure.
– JIm Dearden
Sep 14 ’14 at 18:24

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Temperature compensation is important with a sensor like this. Maxim Integrated’s MAX1458 (an older part but still available I think) used a constant-current source (instead of a constant-voltage source) to drive the Wheatstone bridge, then inferred the temperature from the common-mode voltage. Calibration requires applying known pressures at known temperatures, then fitting a curve that approximates the physical input that corresponds to that output. In production, each individual sensor must be calibrated because of manufacturing variances.
– MarkU
Sep 14 ’14 at 21:50

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2 Answers
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You will probably need to calibrate it yourself. Put some known stresses on it and see what it does. I used to work in industrial automation, and every one of the scales had to be calibrated in-place when empty and with at least one test weight before it would even be close to accurate.

I think you can use microcontroller for example AVR ATMEGA 16 and then use ADC(Analog to digital converter) pins and then you measure voltage at your minimum pressure and call it 0
and max pressure 255 then you have 256 degree of pressure you can display on LCD.
(sorry for my bad english)

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