Watlow Electric Revision 5 - Manual (Page 32)

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5.8 SCALING AND CALIBRATION
Since a computer is used to display the reading and load the setpoints, a
mathematical step can be used to convert measurements and setpoints to
engineering units and correct for known sensor calibration errors.
For example, the ANAFAZE SYSTEM 32 does all thermocouple calculations in
degrees F since this provides almost twice the resolution of degrees C. If degrees
C display and setpoints are desired the computer makes the F to C conversion as
data is received from the ANAFAZE SYSTEM 32 and converts the setpoints from
C to F as they are sent to the controller.
In a similar manner, linear sensors can be converted to engineering units and
adjusted for known calibration errors with a conversion step. For a linear sensor
two outputs can be measured (x1 and x2) and converted into engineering units (y1
and y2) using the standard formula:
y = mx + b
where m = (y2 - y1)/(x2 - x1)
and b = y2 - mx2 or b = y1 - mx1
The same conversion formula can be used to convert the desired setpoint into a
percentage of full scale which allows the ANAFAZE SYSTEM 32 to control to
the actual measured signals while the computer displays the measurements and
setpoints in engineering units. This approach eliminates the need for
potentiometers and other analog adjustments on each input channel.
The ANASOFT-32 software for the IBM PC and compatible computers includes
these scaling functions as part of the menu driven program. Please consult
ANAFAZE for additional information.