7Measurement Tutorial
278 Keysight 34420A User’s Guide
Noise Caused by Ground Loops
When measuring voltages in circuits where the meter and the device-under-test
are both referenced to a common earth ground, a “ground loop” is formed. As
shown below, any voltage difference between the two ground reference points
(V
ground
) causes a current to flow through the LO measurement lead. This causes
an error voltage, V
L
, which is added to the measured voltage.
To minimize ground loop errors:
–If V
ground
is a dc voltage, keep R
L
small compared to R
i
.
–If V
ground
is an ac voltage, keep R
L
small compared to Z, and set the meter’s
integration time (NPLC) to 1 or greater. See page 71.
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