A single ended earth grounded data-acq. board on the left in the below illustration has inputs coupled by BNC cables coming from force transducer amplifiers A1, A2, A3, A4 as shown on the right:
If no BNC is hooked up, when I measure the voltage between any BNC connector terminal to earth I read around 100VAC by a multimeter. But by using low impedance setting of the multimeter I verified that this is stray voltage aka ghost voltage.
Since I measure this stray voltage between BNC inner pin to earth and BNC outer pin to earth, I guess this stray voltage is in phase both terminals of the BNC.
There is no direct ground loops in the system i.e the amplifiers'/sources' grounds are not earthed. During data acquisition sometimes I see noise coming and going for some seconds sometimes, and I was suspicious of capacitive coupling.
My questions are:
1-) The data-acquisition max input voltage is +-10VDC. Would this stray voltage be problem in this case? Is it exceeding maximum common mode range? Because the moment I hook up the reading are okay. But Im not sure is this stray voltage still have side effects.
2-) Is this configuration is more susceptible to error in readings than in differential ended inputs? How would diff ended. connection eliminate the noise caused by stray voltages?