I'm not sure if this is the correct place to ask this, but here goes. I have build an opamp ciruit to amplify the signal from a force transducer. This is working fine, but the problem that I am having is that if someone walks around it different spots, my steady state level will change by almost 50mV or sometimes more. I have removed the transducer and shorted the diff inputs of the opamp to ground through a resister and I get the same effect. I have grounded the gnd 0V rail to earth along with the transducer as well. I have used caps near the opamp but still no luck. I have a Tektronix TDS2014 for which I am analyzing the signal and if I touch the probe wire, the output level of the opamp will go up 20 or 30 millivolts. These are brand new scope probes and I have tried four of them, they all do the same thing, so I am ruling them out.
Is there a way that I can elliminate this. I need to get acturate reading into my process, but whenever someone moves, this level moves up and interferes with the signal. I am using a TI INA126 Differiential op amp with a gain of 1000.
I have even tried placing the entire circuit inside a grounded wire screen cage and I still get the same effect. I also know that it is not vibration being transmitted to the transducer because of the above forementioned removal of transducer and replacing with resister to ground.
Thanks,
James