Campbell Scientific CR3000 CR3000 Micrologger - Page 290

Section 8. Operation 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. Measurement Integration ac Power Line Frequency 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 290