Specifications

Section 4. Sensor Support
4-8
4.2.5 Integration
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Measurement Noise Problems” available at www.campbellsci.com.
The CR1000 incorporates circuitry to perform an analog integration on
voltages to be measured prior to the A/D conversion. 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. TABLE
4
.2-4 lists three integration durations available in the CR1000 and associated
CRBASIC codes. If reversing the differential inputs or reversing the excitation
is specified, there will be two separate integrations per measurement; if both
reversals are specified, there will be four separate integrations.
TABLE 4.2-4. CRBASIC Measurement Settling Time
and Integration 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.
4.2.5.1 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. CR1000 voltage
measurements can be programmed to reject (filter) 50 or 60 Hz related noise.
4.2.5.1.1 AC Noise Rejection on Small Analog Signals
The CR
1000 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 4.2-5 and the full cycle technique
of
FIGURE 4.2-1.
TABLE 4
.2-5. AC Noise Rejection Integration on Voltage Ranges
Except mV5000 and mV2500
AC Power Line
Frequency
Measurement
Integration Duration
CRBASIC Integration
Code
60 Hz 16.667 ms _60Hz
50 Hz 20 ms _50Hz