Hi every one, I have a HP 34401a meter that is causing some issues with a high impedance sensor input. when I place only the ground wire ( black ) to the input circuit ground, the sensor reading jumps quiet dramatically, this does not happen if i place only the Red wire. I have tried an AMPROBE 30XR-A with no issues, but it is not sensitive enough for this. can any one think of why this could happen. I can provide schematics of the input circuitry if needed, the sensor input is connected to an instrumentation amp. many thanks.