Campbell Scientific CR3000 Micrologger - Manual (Page 290)

Section 8. Operation
290
8.1.2.7.1 ac Power Line Noise Rejection
Grid or mains power (50 or 60 Hz, 230 or 120 Vac) can induce electrical noise at
integer multiples of 50 or 60 Hz. Small analog voltage signals, such as
thermocouples and pyranometers, are particularly susceptible. CR3000 voltage
measurements can be programmed to reject (filter) 50-Hz or 60-Hz related noise.
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 ac cycle before A/D
conversion as illustrated in table ac Noise Rejection on Small Signals
(p. 290)
and
the full cycle technique of figure ac Power Line Noise Rejection Techniques
(p.
290).
Table 57. ac Noise Rejection on Small Signals
Applies to all analog input voltage ranges except mV1000 and mV5000 .
ac Power Line Frequency
Measurement Integration
Duration CRBasic Integration Code
60 Hz 16.667 ms _60Hz
50 Hz 20 ms _50Hz
Figure 91: Ac power line noise rejection techniques
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 (see figure ac Power Line Noise Rejection Techniques
(p. 290)
). 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