Noise Caused By Magnetic Loops; Noise Caused By Ground Loops - DATATEC EDU34450A Guia Del Usuario

The figure below shows a Common Mode Rejection (CMR) circuit:

Noise Caused by Magnetic Loops

If you are making measurements near magnetic fields, take caution to avoid inducing voltages in the measurement
connections. You should be especially careful when working near conductors carrying large currents. Use twisted-
pair connections to the instrument to reduce the noise pickup loop area, or dress the test leads as close together as
possible. Loose or vibrating test leads will also induce error voltages. Tie down test leads securely when operating
near magnetic fields. Whenever possible, utilize magnetic shielding materials or increase the distance from
magnetic sources.

Noise Caused by Ground Loops

When measuring voltages in circuits where the instrument and the device-under-test are both referenced to a
common earth ground, a ground loop is formed. As shown in figure below any voltage difference between the two
ground reference points (V ) causes a current to flow through the measurement leads. This causes noise and
ground
offset voltage (usually power-line related), which are added to the measured voltage.
100 Keysight EDU34450A User's Guide