Keysight 34972A - Page 274

7Tutorial
274 Keysight 34970A/34972A User’s Guide
Where:
R
L
= Lead resistance
R
i
= DMM isolation resistance
C
i
= DMM isolation capacitance
V
ground
= Ground noise voltage
I = Current flow caused by V
ground
=
Z ≈ Z
Ci
= ≈ 10 MΩ at 50 or 60 Hz
V
L
=
To minimize ground loop errors:
–If V
ground
is a DC voltage, keep R
L
small compared to R
i
.
–If V
ground
is an AC voltage, keep R
L
small compared to Z, and set the DMM’s
integration time to 1 PLC or greater (see page 133 for a discussion of
integration time).
DMM
HI
LO
R
L
R
L
V
ground
I
V
test
» C
i
250 pF
R
i
>10 GW
V
ground
R
L
Z+
--------------------
1
2πfC
-------------
IR
L
×