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3
Measurement Tutorial
62
Make sure the digital multimeter and the AC source are
connected to the same electrical outlet whenever possible.
You should also minimize the area of any ground loops that
cannot be avoided. A high- impedance source is more
susceptible to noise pickup than a low- impedance source.
You can reduce the high- frequency impedance of a source by
placing a capacitor in parallel with the digital multimeter's
input terminals. You may have to experiment to determine
the correct capacitor value for your application.
Most extraneous noise is not correlated with the input
signal. You can determine the error as shown below
(Equation
4):
Voltage Measured
Correlated noise, while rare, is especially detrimental.
Correlated noise always adds directly to the input signal.
Measuring a low- level signal with the same frequency as the
local power line is a common situation that is prone to this
error.
2
2
=
V
+
Noise
in
(4)
U2741A User's Guide
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