
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 Ri
.
•
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.
R
L
=
Lead Resistance
R
i
=
Multimeter Isolation
Resistance
C
i
=
Multimeter Isolation
Capacitance
V
ground
=
Ground Noise Voltage
I
=
V
ground
caused current flow
=
V
ground
R
L
+
Z
Z
=
R
i
∗
Z
C
i
R
i
+
Z
C
i
V
L
=
I
∗
R
L
Ideal
Meter
7
Chapter 7 Measurement Tutorial
Measurement Techniques and Sources of Error
253
Содержание 34420A
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Страница 13: ...1 Quick Start ...
Страница 31: ...2 Front Panel Operation ...
Страница 55: ...3 Features and Functions ...
Страница 117: ...4 Remote Interface Reference ...
Страница 200: ...5 Error Messages ...
Страница 213: ...6 Application Programs ...
Страница 245: ...6 Chapter 6 Application Programs Microsoft Excel Macro Example 245 ...
Страница 246: ...Chapter 6 Application Programs Microsoft Excel Macro Example 246 ...
Страница 247: ...7 Measurement Tutorial ...
Страница 274: ...8 Specifications ...
Страница 279: ...Dimensions Chapter 8 Specifications 34420A Nano Volt Micro Ohm Meter 280 ...
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