Noise Caused by Ground Loops
When measuring voltages in circuits where the multimeter and the DUT are referenced to a common earth
ground, a "ground loop" is formed. As shown below, any voltage difference between the two ground ref-
erence points (Vground) causes current to flow through the measurement leads. This causes noise and off-
set voltage (usually power–line related), which are added to the measured voltage.
The best way to eliminate ground loops is to isolate the multimeter from earth by not grounding the input
terminals. If the multimeter must be earth–referenced, connect it and the DUT to one common ground
point. Also connect the multimeter and DUT to the same electrical outlet whenever possible.
Measurement Tutorial
164
Keysight Truevolt Series Operating and Service Guide
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