Watlow CAS200 - Manual (Page 100)

Chapter 6: Linear Scaling Examples CAS200 User’s Guide
88 Watlow Anafaze
Example 1: 4-20mA Sensor
Situation
A pressure sensor that generates a 4-20 milliamp signal is
connected to the scanner. The specifications of the sensor
state that it generates 4mA at 0.0 pounds per square inch
(psi) and 20mA at 50.0 psi.
Setup
The sensor is connected to a loop input set up with a
resistor scaling network to produce 60 millivolts at 20mA.
The INPUT TYPE for the loop is let to LINEAR. The sensor
measures psi in tenths, so the DISP FORMAT is set to
-999.9 TO +3000.0.
Table 6.1 Input Readings
The scaling values set up in the SETUP LOOP INPUT menu
are shown in Table 9.2.
Table 6.2 Scaling Values
Process
Variable
Displayed
Sensor
Input
Reading, Percent of
Full Scale (%FS)
50.0 psi 20mA 100%FS
0.0 psi 4mA 100% x (4mA/20mA) = 20%FS
Parameter Prompt Value
High Process Variable HIGH PV 50.0 psi
High Sensor Reading HIGH RDG 100.0%FS
Low Process Variable LO PV 0.0 psi
Low Sensor Reading LO RDG 20.0%FS