CR1000 Manual - Campbell Scientific

Section 8. Operation
Figure 88: Ac power line noise rejection techniques
ac Noise Rejection on Large Signals
If rejecting ac-line noise when measuring with the 2500 mV (mV2500) and 5000
mV (mV5000) ranges, the CR1000 makes two fast measurements separated in time
by one-half line cycle (see figure ac Power Line Noise Rejection Techniques (p. 285)
). A 60-Hz half cycle is 8333 µs, so the second measurement must start 8333 µs
after the first measurement integration began. The A/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 CR1000 does
not prevent or warn against setting the settling time beyond the half-cycle limit.
Table ac Noise Rejection on Large Signals (p. 285) lists details of the half-cycle acpower
line-noise rejection technique.
Table 56. ac Noise Rejection on Large Signals
Applies to analog input voltage ranges mV2500 and mV5000.
ac Power Line
Frequency
Measurement
Integration
Time
CRBasic
Integration
Code
Default
Settling
Time
Maximum
Recommended
Settling Time*
60 Hz 250 μs x 2 _60Hz 3000 μs 8330 μs
50 Hz 250 μs x 2 _50Hz 3000 μs 10000 μs
*Excitation time and settling time are equal in measurements requiring excitation. The CR1000 cannot excite VX / EX excitation
channels during A/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 CR1000 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 CR1000 will execute
the measurement as follows:
1. CR1000 turns excitation on, waits 50000 µs, and then makes the first measurement.
285