The main reason for instrumentation amplifiers is to amplify the difference between the two inputs. The voltage that the difference is riding on (+2.5V, in your case) is called the common mode voltage. If you look at the datasheets, you will find a spec for common mode rejection. The bigger this number is, the better the amplifier will "ignore" the common mode voltage.The difference between the two inputs (Vin) or the difference between the V and GND?
If I used an INA122 would I be able use a single supply and read 0v at no difference?
You should not be getting 9V if your bridge is balanced. Are you using precision resistors in your bridge?So the circuit is working, I have to turn the gain to about G=2200 to get good results...the output is at 9V unloaded and I get up to 11V with 500lbs of load. I can't go any further because the output will max out under 500lbs. Is there any way to get better resolution?
I missed that. The comment about SG1 andSG3 being the active gauges threw me, but I suppose that means that the other two are oriented orthogonally to the direction of strain.I believe the bridge is a strain gauge, meaning that all four resistors in the bridge are strain gauges.