Specifications

Section 7. Measurement Instructions
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.
Range
Constant
Option to calibrate ranges not being used. Dest must be entered before Range 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.
NOTE
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 CR3000 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.
Unless the Range option is selected, the calibrate instruction only measures the
range and integration combinations that occur in the measurements in the
program. For the 250 µs and zero integration calibrations multiple
measurements are averaged for the calibration values. The 250 µs integration
calibration averages five measurements and the zero integration calibration
averages ten measurements.
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