CR1000 Manual - Campbell Scientific

Section 7. Installation
7.8 Programming Resource Library
This library of notes and CRBasic code addresses a narrow selection of CR1000
applications. Consult a Campbell Scientific applications engineer if other
resources are needed.
7.8.1 Calibration Using FieldCal() and FieldCalStrain()
Calibration increases accuracy of a sensor by adjusting or correcting its output to
match independently verified quantities. Adjusting a sensor's output signal is
preferred, but not always possible or practical. By using the FieldCal() or
FieldCalStrain() instruction, a linear sensor output can be corrected in the
CR1000 after the measurement by adjusting the multiplier and offset.
When included in the CR1000 CRBasic program, FieldCal() and
FieldCalStrain() can be engaged through a support software calibration wizard (p.
449). Help for using the wizard is available in the software. A more arcane
procedure can be executed though the CR1000KD Keyboard / Display Display or
the numeric monitor in any version of datalogger support software. The numeric
monitor procedure is used in the examples below to clearly illustrate the workings
of the calibration functions.
7.8.1.1 CAL Files
Calibration data are stored automatically, usually on the CR1000 CPU: drive, in
CAL files. These data become the source for calibration factors when requested
by the LoadFieldCal() instruction. A CAL file is created automatically on the
same CR1000 memory drive and given the same name (with .cal extension) as the
program that creates and uses it. For example, the CRBasic program file
CPU:MyProg.cr1 generates the CAL file CPU:MyProg.cal.
CAL files are created if a program using FieldCal() or FieldCalStrain() does not
find an existing, compatible CAL file. Files are updated with each successful
calibration with new multiplier and offset factors. Only if the user creates a datastorage
output table with the SampleFieldCal() instruction will a calibration
history be recorded.
Note CAL files created by FieldCal() and FieldCalStrain() differ from files
created by the CalFile() instruction (File Management (p. 515) ).
7.8.1.2 CRBasic Programming
Field calibration functionality is utilized through either:
• FieldCal() — the principal instruction used for non-strain gage type sensors.
For introductory purposes, use of one FieldCal() instruction and a unique set
of FieldCal() variables for each sensor to be calibrated is recommended. Use
of variable arrays is permitted for more advanced applications.
or,
• FieldCalStrain() — the principal instruction used for strain gages measuring
microstrain. Use of one FieldCalStrain() instruction and a unique set of
FieldCalStrain() variables for each sensor to be calibrated is recommended.
Use of variable arrays is permitted for more advanced applications,
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