Campbell CR800 Series - Ac Noise Rejection on Small Signals 1; Ac Noise Rejection on Large Signals 1

Section 8. Operation
355
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.
Ac Noise Rejection on Large Signals
1
Ac-Power Line
Frequency
Measurement
Integration
Time
CRBasic
Integration
Code
Default
Settling
Time
Maximum
Recommended
Settling Time
2
60 Hz 250 μs • 2
_60Hz
3000 μs 8330 μs
50 Hz 250 μs • 2
_50Hz
3000 μs 10000 μs
1
Applies to analog input voltage ranges mV2500 and mV5000.
2
Excitation time and settling time are equal in measurements requiring excitation. The CR800 cannot excite VX
excitation terminals during A-to-D conversion. The one-half-cycle technique with excitation limits the length of
recommended excitation and settling time for the first measurement to one-half-cycle. The CR800 does not
prevent or warn against setting a settling time beyond the one-half-cycle limit. For example, a settling time of up
to 50000 µs can be programmed, but the CR800 will execute the measurement as follows:
1. CR800 turns excitation on, waits 50000 µs, and then makes the first measurement.
2. During A-to-D, CR800 turns off excitation for ≈170 µs.
3. Excitation is switched on again for one-half cycle, then the second measurement is made.