Campbell Scientific CR5000 Measurement and Control Module - Manual (Page 76)

Section 3. CR5000 Measurement Details
3-22
background calibration will be disabled (even if the scan is not executed).
The calibrate instruction is described in Section 7.
The self calibration does not take place if there is not enough time to run it or if
the calibrate instruction is in the CR5000 program and never executed.
Without the self calibration the drift in accuracy with temperature is about a
factor of 10 worse. For example, over the extended temperature range (-40 to
85
°
C) the accuracy specification is approximately 0.1% of reading. If the self
calibration is disabled, the accuracy over the range is approximately 1% of
reading. Temperature is the main factor causing a calibration shift and the
need for the self calibration. If the temperature of the CR5000 remains the
same there will be little calibration drift with the self calibration disabled.
The time constant for the background calibration (at the 4 second rate) is
approximately 36 seconds. This allows the CR5000 to remain calibrated
during fairly rapid temperature changes. In cases of extreme temperature
change, such as bringing a vehicle from equilibrium in a chamber at -30
°
C out
into a hot Arizona day, it may be worthwhile to override the background
calibration by running the calibration instruction in the scan with the
measurements.
Another case where using the calibration instruction makes sense is where
there is not time for the background calibration in the normal scan but the
program can periodically stop making measurements and run the calibration
instruction in a separate scan.