Instruction Manual

4.11 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 8 PID 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 8 PID 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 8 PID 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 PID 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.

4.12 RTD INPUTS

RTD's can be connected in different configurations including bridge circuits, three wire

and four wire -- please request a copy of the ANAFAZE RTD application bulletin.