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Measurement Tutorial
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
reference points (Vground) causes current to flow through the measurement leads. This causes noise and
offset 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.
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Keysight Truevolt Series Operating and Service Guide
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