Agilent E1412A Multimeter Application Information
27
Rejecting Power
Line Noise
Voltages
A desirable characteristic of integrating analog-to-digital (A/D) converters
is their ability to reject spurious signals. The integrating techniques reject
power-line related noise present with a dc signal on the input. This is called
normal mode rejection
or
NMR
. Normal mode noise rejection is achieved
when the multimeter measures the average of the input by “integrating” it
over a fixed period. If you set the integration time to a whole number of
power line cycles (
PLC
s) these errors (and their harmonics) will average out
to approximately zero.
The E1412A provides three A/D integration times (1, 10 and 100PLCs) to
reject power line frequency noise (and power-line frequency harmonics).
Power line frequency defaults to 60Hz unless you specifically set it to 50Hz
with the
CAL:LFR
command. The multimeter determines the proper
integration time based on which power line frequency is set. Table 2-2
shows the noise rejection achieved with various configurations. Select a
longer integration time for better resolution and increased noise rejection.
Common Mode
Rejection (
CMR
)
Ideally, a multimeter is completely isolated from earth-referenced circuits.
However, there is finite resistance between the multimeter's input LO
terminal and earth ground as shown below. This can cause errors when
measuring small voltages which are floating relative to earth ground.
Table 2-2. Noise Rejection
Power Line
Cycles (PLCs)
Integration Time
NMR
60Hz
(50Hz)
0.02
400
s
(400
s)
NONE
0.2
3ms
(3ms)
NONE
1
16.7ms
(20ms)
60dB
10
167ms
(200ms)
60dB
100
1.67sec
(2sec)
60dB
Summary of Contents for Agilent E1412A
Page 2: ......
Page 10: ...8 Contents Notes...
Page 14: ...12 Notes...
Page 15: ...13 Notes...
Page 16: ...14 Notes...
Page 26: ...24 Agilent E1412A Multimeter Module Setup Chapter 1 Notes...
Page 194: ...192 Agilent E1412A Multimeter Error Messages Appendix B Notes...
Page 201: ...Index 199 Index Agilent E1412A User s Manual and SCPI Programming Guide...