strain-gagevoltagewheatstone-bridge
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?
The required specs on the DAC may result in a higher cost than necessary - I suggest using a voltage divider and adding a small trim voltage to it. That would be two precision resistors of equal value and a higher value resistor from the DAC output. For example, you could use 4.99K (2 pcs) and one 249K to give an adjustment range of about +/-1%.
One flaw in your circuit is that the gain varies with the absolute value of the load cell resistors. If you use an instrumentation amp or connect the load cell to the non inverting input you can avoid that issue.
simulate this circuit – Schematic created using CircuitLab
You may be seeing thermal EMFs, as well as thermal drift of the resistors.
Blowing hot air with a hot air gun is not the way to test a circuit like that. Use a proper environmental chamber with a fan inside and control the air flow over the board (maybe with a bit of foam). You may have to wait an hour or two for the temperature to stabilize. The hot air gun will lead to wrong conclusions. You may see dynamic changes that even out as the gradients disappear.
Do not have anything on the board that dissipates a lot of power (I assume you are doing this).
Leaded resistors can be a bit less prone to change from external mechanical forces. Try flexing the board a bit and see if your reading changes. Chances are this is not your problem, but it's worth a check.
Best Answer
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.