
Keysight E1412A Digital Multimeter User Guide
xxxiii
DC Voltage Measurements
Keysight E1412A Multimeter Application Information
device-under-test. This effect becomes evident for a source resistance of greater
than 100k
, or when the multimeter's operating temperature is significantly
greater than 30°C.
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 3 shows the noise rejection
achieved with various configurations. Select a longer integration time for better
resolution and increased noise rejection.
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 E1412A
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