Agilent Technologies 34420A User Manual

Common Mode Rejection (CMR)
Ideally, a meter is completely isolated from earth-referenced circuits.
However, there is finite resistance and capacitance between the meter’s
input LO terminal and earth ground. If the input terminals are both
driven by an earth referenced signal, V
f
, then a current will flow through
R
S
and create a voltage drop V
L
as shown below.
Any resulting voltage, V
L
, will appear as an input to the meter. As the
value of R
S
approaches 0, so does the error. Additionally, if V
f
is at the
power line frequency (50 Hz or 60 Hz), the noise can be greatly reduced
by setting the meter’s integration time (NPLC) to 1 or greater.
See page 252.
V
f
= Common Mode Float voltage
R
S
= LO Lead Resistance
R
i
= Meter Isolation Resistance
C
i
= Meter Isolation Capacitance
Z
i
= Parallel Impedance of R
i
+ C
i
Error ( V
L )
=
V
f
x R
S
R
S
+ Z
Ideal
Meter
Chapter 7 Measurement Tutorial
Measurement Techniques and Sources of Error
254

Agilent Technologies 34420A Specifications

General

Brand	Agilent Technologies
Model	34420A
Category	Multimeter
Language	English