Campbell Scientific LoggerNet Datalogger Support Software - Manual (Page 559)

Appendix F. Calibration and Zeroing
those two conditions. For future measurements (unknowns), a linear response
will be used based on the line defined by those two points.
To perform a two-point multiplier and offset calibration, use an argument of 2
(the number two) for the calibration type in the FieldCal instruction of your
CRBasic program. The Calibration Wizard can be used to calculate and apply
the two different known conditions while the program is running in the
datalogger.
F.3.4 Two-Point Multiplier Only Calibration
Two-point multiplier only calibration uses a linear fit technique against two
different known value conditions of the sensor’s measurement, but only the
slope value (multiplier) is calculated and changed. The offset is unaffected by
this calibration. The sensor is placed into the first condition, and the known
value for that condition is provided to the datalogger program. One or more
measurements in that first condition occur, and then the datalogger informs the
user that the second known condition should be applied to the sensor. When
that condition is applied, the second known value is provided to the datalogger,
and the datalogger measures the second condition. After completing the
measurement of the second point condition, a best fit of the two points is
calculated, resulting in a slope value (m value or multiplier) with the offset
assumed to be zero. Thus the simple form y=mx is a representation of the fit,
where m is the new multiplier value.
To perform a two-point multiplier only calibration, use an argument of 3 (the
number three) for the calibration type in the FieldCal instruction of your
CRBasic program. The Calibration Wizard can be used to calculate and apply
the two different known conditions while the program is running in the
datalogger.
F.4 Performing a Manual Calibration
F.4.1 How to Use the Mode Variable for Calibration Status and
Control
To perform a manual calibration (without use of the LoggerNet Calibration
Wizard) on a FieldCal enabled program running in a datalogger, it is necessary
to understand the function of the mode variable that is used as an argument of
the FieldCal instruction.
In a CRBasic calibration program, a mode variable is declared and associated
with a particular FieldCal instruction, thereby associating it with the
measurement to be calibrated.
Most values of the mode variable represent the status of the calibration for that
affected measurement. A few values of the mode variable are set by the user of
the datalogger to instruct the program to proceed with calibrations.
F-5