GROUND LOOPS
REFERENCE > ADVANCED TECHNIQUES >

What is a Ground Loop?
If your computer is at ground G1, and the instruNet device is at ground G2, and the device under test is at ground G3; and these 3 grounds vary by several milliVolts (as noted here), then attaching a wire between G2 and G3 (e.g. the common (-) wire within the cable that attaches your sensor to instruNet), then current will flow on that wire, and this current will induce a voltage drop along that wire.

How can I determine if this is causing a problem?
If you are working with low level signals (e.g. < 100mV) and the readings are eradic or incorrect, your problem might be related to high frequencies between grounds, induced by a ground loop.

What to do about it ?
Please see Dealing with High Frequecies between Grounds, which in effect, is very similar to the ground loop issue.