Campbell Scientific CR5000 Measurement and Control Module - Manual (Page 142)

Section 7. Measurement Instructions
7-16
Calibrate (Dest, AllRanges)
The Calibrate instruction places the CR5000 self calibration under program
control. Placing the Calibrate instruction in the program disables the automatic
self calibration that is normally run in the background (Section 3.8).
The Calibrate parameters are optional and are only used to place the results of
the calibration in a variable array. With no parameters the Calibrate instruction
does not return data.
Parameter
& Data Type Enter
Dest
Array
If present the array must contain at least 60 elements (more if excitation is used in the
program. With no parameters no data are returned.
AllRanges
Constant
Option to calibrate ranges not being used. Dest must be entered before AllRanges
parameter
Alpha Code Value Result
False =0 Calibrate only Voltage ranges used in program
True ≠0 Calibrate all Voltage ranges
In most cases the background calibration is adequate and the
calibrate instruction should not be used in the program.
There are three valid situations for using the Calibrate instruction:
1) With the normal set of measurements there is not time for the Calibration
to run in the background but the program can periodically stop making
measurements and run the calibration in a separate scan.
2) The CR5000 will experience extremely rapid temperature change and the
Calibration instruction is run to update the calibration before each set of
measurements.
3) The program is run by a repair technician specifically to get the results of
the calibration. (Calibration values are also available in the status table
without running a special program.)
If there is not enough time leftover in a fast scan for the background calibration
to run, the message: “Warning when Fast Scan x is running background
calibration will be disabled.” will be returned when the program is compiled (x
is the number of the fast scan where the first fast scan entered in the program is
1, the next scan is 2, etc.) If you see this message you have the options of
letting the scan run without any calibration (if the temperature remains
constant there will be little shift, Section 3.8), reducing the number of
measurements or the time it takes to make them (e.g., shorten the integration),
or periodically changing to a different scan to run the calibration.
In cases of rapid temperature change, such as bringing a vehicle from
equilibrium at -30
°C to a hot Arizona day, running the Calibration instruction
in the program can improve the accuracy of the measurements. It has to be a
rapid change to require this; the background calibration filters new readings
and has a time constant (63% response to a step change) of approximately 36
seconds. When the calibration instruction is run in the program the calibration
is completely updated each time the instruction is run.
NOTE