Watlow CAS - Manual (Page 85)

Appendix: Linear Scaling Examples
CAS User’s Guide 75
Appendix: Linear Scaling
Examples
Example 1
Situation
A pressure sensor that generates a 4-20 milliamp signal is connected to
the CAS. The specifications of the sensor state that it generates 4
milliamps at 0.0 PSI and 20 mA at 50.0 PSI.
Setup
The sensor is connected to a channel input set up with a resistor scaling
network to produce 60 millivolts at 20 mA. (See the Inputs section of
Chapter 2: Installation for more information on scaling networks.)
The sensor measures PSI in tenths, so the appropriate display format is -
999.9 to +3000.0.
This table shows the input readings.
The scaling values are therefore:
PV
Displayed
Sensor Input Reading (%FS)
50.0 psi 20 100%
0.0 4 100% x (4ma/20ma) = 20%
Parameter Low Value High Value
Process Value (PV) 0.0 psi 50.0 psi
Input Reading (RDG) 20.0 100.0