Campbell CR3000 Micrologger, Руководство оператора

Страница: 390 / 644

Section 8. Operation
390
FIGURE 91: Ac Power Noise Rejection Techniques
Ac Noise Rejection on Small Signals
The CR3000 rejects ac power line noise on all voltage ranges except mV5000 and
mV1000 by integrating the measurement over exactly one full ac cycle before A-
to-D
(p. 529)
conversion as listed in table Ac Noise Rejection on Small Signals
(p. 341).
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 mV1000 and mV5000.
Ac Noise Rejection on Large Signals
If rejecting ac-line noise when measuring with the 1000 mV (mV1000) and 5000
mV (mV5000) ranges, the CR3000 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 CR3000 does not prevent or warn against setting the settling
time beyond the half-cycle limit. Table Ac Noise Rejection on Large Signals
(p.
341)
lists details of the half-cycle ac-power line-noise rejection technique.