Campbell Scientific CR9000X Measurement and Control System - Manual (Page 118)

Section 3. CR9000X Measurement Details
OS returned Filter Order and Integration:
The integration and Sinc filter order that a given CR9058E is using can be
determined through RTDaq's terminal mode window (Datalogger/Terminal
Emulator). Click on "Open Terminal". Next, hit Enter several times until the
CR9000> prompt is returned. Type in "4" and enter. The CR9058Es' slot
numbers, integration times, and Sinc filters will be returned.
Example 3.2.1: Given a scan rate of 2 seconds (2000000 microseconds),
what integration time and sinc-n filter order should be used in a
CR9058 to provide 60 Hz rejection? It is desired to filter out higher
order frequencies (higher than 60 Hz) as well. Input reversal and open
thermocouple checking should be used.
The AvailTime is computed by these steps:
Start with the Scan Interval (2,000,000 uSec) with the following
adjustments:
Subtract off 1520 microseconds because range code v2C is used.
(=1998480)
Divide by 2, subtract 420 microseconds because input reversal is used.
(=998820)
Subtract off another 1320 microseconds. (997500)
AvailTime = ((2,000,000 -1520)/2 - 420) - 1320 = 997,500 micro-
seconds
For 60 Hz rejection, the integration time should be a multiple of 1/60 seconds
(16667 microseconds) and the integration step size (96 microseconds). The
smallest number that meets this criteria is 300,000 microseconds. Given the
AvailTime of 997,500 microseconds, we could select 300,000 or 600,000 or
900,000 microseconds for the integration period.
Solving for the Filter Order using Eq. 3.2.2, setting the NumberofSamples to
680 (max) and using an IntegTime of 300,000 uSec (minimum value for this
example), results in a maximum Filter Order of 1.
Eq. 3.2.3 also shows that any integration time greater than 32,640
microseconds results in a filter order of 1. In order to utilize all of the available
time, we decide to use the 900,000 micro-second integration time. The
measurement instruction would look like:
'VoltDiff( Dest, Reps, Range, ASlot, DiffChan, RevDiff, Settle, Integ, Mult, Offset)
VoltDiff(IBlk18(), 10, v2c, 8, 1, 1, 0, 900000, 1.0, 0 )
3.3 CR9052 Filter Module Measurements
Each CR9052 module has six differential analog measurement channels with
programmable input ranges from ±20 mV to ±5 V. Each channel has its own
programmable-gain instrumentation amplifier, pre-sampling analog filter, and
sigma-delta analog-to-digital converter.
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