Section 8. Operation
280
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.
ac Power Line Frequency
Measurement Integration
Duration CRBasic Integration Code
60 Hz 16.667 ms
_60Hz
50 Hz 20 ms
_50Hz
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