I am playing around with a strain gauge that I pulled out of an old scale. It is a three wire strain gauge and I have determined from the resistances between the wires that it acts like a potentiometer, the middle wire acting as the wiper. My problem is occuring when I wire up the wheatstone and then to a LM324N op amp. The wheatstone is figured out (I get 0V across the 'sense' nodes when the strain gauge has no load applied). I can't seem to get a proper output on the op amp. With a gain of 65 I get Vout = 8V with no fluctuation when the strain gauge is compressed. Vout remains at 8V even when I unplug the two sense wires and the resistors from the op amp, which makes no sense (no pun intended) to me. I've attached my circuit and would appreciate any insight to this problem. Thanks!

 

Why your op-amp has two inputs?

The op-amp inverting input should only have the two resistors, nothing else.

 

hmm Not sure what I was thinking. Problem has been fixed. thanks!