Campbell Scientific CR1000KD CR800 and CR850 Measurement and Control Systems - Page 280
ac Power Line Noise Rejection
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Section 8. Operation duration. Consequently, noise at 1 / (integer multiples) of the integration duration is effectively rejected by an analog integrator. table CRBasic Measurement Integration Times and Codes (p. 280) lists three integration durations available in the CR800 and associated CRBasic codes. If reversing the differential inputs or reversing the excitation is specified, there are two separate integrations per measurement; if both reversals are specified, there are four separate integrations. Table 54. CRBasic Measurement Integration Times and Codes Integration Time (ms) CRBasic Code Comments 250 µs 250 Fast integration 16.667 ms _60Hz Filters 60-Hz noise 20 ms _50Hz Filters 50-Hz noise 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. CR800 voltage measurements can be programmed to reject (filter) 50-Hz or 60-Hz related noise. 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 ac cycle before A/D conversion as illustrated in table ac Noise Rejection on Small Signals (p. 280) and the full cycle technique of figure ac Power Line Noise Rejection Techniques (p. 281). Table 55. ac Noise Rejection on Small Signals Applies to all analog input voltage ranges except mV2500 and mV5000. Measurement Integration ac Power Line Frequency Duration CRBasic Integration Code 60 Hz 16.667 ms _60Hz 50 Hz 20 ms _50Hz 280
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