Section 8. Operation
FIGURE 74: Ac Power Noise Rejection Techniques
Ac Noise Rejection on Small Signals
The CR800 rejects ac power line noise on all voltage ranges except mV5000 and
mV2500 by integrating the measurement over exactly one full ac cycle before A-
to-D
(p. 489) conversion as listed in table Ac Noise Rejection on Small Signals (p. 317).
Ac Noise Rejection on Small Signals
1
Ac Power Line
Frequency
Measurement
Integration Duration
CRBasic Integration
Code
60 Hz 16.667 ms
_60Hz
50 Hz 20 ms
_50Hz
1
Applies to all analog input voltage ranges except mV2500 and mV5000.
Ac Noise Rejection on Large Signals
If rejecting ac-line noise when measuring with the 2500 mV (mV2500) and 5000
mV (mV5000) ranges, the CR800 makes two fast measurements separated in time
by one-half line cycle. A 60 Hz half cycle is 8333 µs, so the second
measurement must start 8333 µs after the first measurement integration began.
The A-to-D conversion time is approximately 170 µs, leaving a maximum input-
settling time of approximately 8160 µs (8333 µs – 170 µs). If the maximum
input-settling time is exceeded, 60 Hz line-noise rejection will not occur. For 50
Hz rejection, the maximum input settling time is approximately 9830 µs (10,000
µs – 170 µs). The CR800 does not prevent or warn against setting the settling
time beyond the half-cycle limit. Table Ac Noise Rejection on Large Signals
(p.
317)
lists details of the half-cycle ac-power line-noise rejection technique.
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