Keysight U2741A Guide D'utilisation page 50

3 Measurement Tutorial
Noise caused by magnetic loops
If you are making measurements near magnetic fields, it is a good practice to
avoid inducing voltages in the measurement connections. Conductor carrying
high current is one common source of magnetic field. You can use twisted-pair
cable connections to the digital multimeter to reduce the noise pickup loop area,
or place the test leads as close together as possible. Loose or vibrating test leads
will also induce error voltages. Tie test leads securely when operating near
magnetic fields. Whenever possible, use magnetic shielding materials or increase
the distance from magnetic sources to minimize this error.
Noise caused by ground loops
When measuring voltages in circuits where the digital multimeter and the device
under test are both referenced to a common earth ground, a ground loop is
formed. As shown in
reference points (V
leads. This gives rise to noise and offset voltage (usually power-line related),
which are added to the measured voltage.
50
Figure 3-2, any voltage difference between the two ground
) will cause a current to flow through the measurement
ground
Keysight U2741A User's Guide