The magnitude of the frequency response of an analog integrator is a SIN(x)/x
shape, which has notches (transmission zeros) occurring at 1/(integer multiples) of
the integration duration. Consequently, noise at 1/(integer multiples) of the
integration duration is effectively rejected by an analog integrator. 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 59. Analog Measurement Integration
Integration Time (ms)
Integration Parameter
Argument
Comments
0 to 16000 µs
0 to 16000
250 µs is considered fast and
normally the minimum
16.667 ms
_60Hz
Filters 60 Hz noise
20 ms
_50Hz
Filters 50 Hz noise
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. CR1000 voltage
measurements can be programmed to reject (filter) 50 Hz or 60 Hz related noise.
Noise is rejected by using a signal integration time that is relative to the length of
the ac noise cycle, as illustrated in the figure Ac Power-Line Noise Rejection
Techniques
(p. 316).
FIGURE. Ac power line noise rejection techniques -- 8 10 30
Figure 83. Ac-Power Noise-Rejection Techniques
The CR1000 rejects ac power line noise on all voltage ranges except mV5000 and
mV2500 by integrating the measurement over exactly one full ac cycle before A-
316
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