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3
Measurement Tutorial
50
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
Figure 3-
2, any voltage difference between the two ground
reference points (V
ground
through the measurement leads. This gives rise to noise and
offset voltage (usually power- line related), which are added
to the measured voltage.
) will cause a current to flow
U2741A User's Guide
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