Watlow CAS - Manual (Page 62)

52 CAS User’s Guide
Setup
Linear Scaling Menus
The linear scaling menus appear under the Setup Channel Inputs main
menu. Linear scaling is available for linear and pulse inputs only. It lets
you scale the "raw" input readings (readings in millivolts or hertz) to the
engineering units of the process variable.
NOTE
The linear scaling menus will only be present if you set the chan-
nel’s input type to Linear (or, for some menus, to Pulse).
For linear inputs, the input reading is in percent (-16.6 to 100%)
representing the -10 to 60 mV input range of the CAS. For pulse inputs,
the input reading is in hertz (cycles per second.) The scaling function is
defined by two points on a conversion line, the high PV and the low PV.
High PV is the high end of the input in engineering units, and the low
PV is the low end. The engineering units of the process variable can be
any arbitrary units.
The example below shows a high PV of 20 PSI and a low PV of 0 PSI.
The high reading is the high end of the input signal (where 60mV =
100%).
Before you enter the values that determine the two points for the
conversion line, you must choose an appropriate display format. The
CAS has six characters available for process variable display; select the
setting with the desired number of decimal places before and after the
decimal point. Use a display format that matches the range and
resolution of the process variable. The display format you choose is
used for the setpoint, alarms, deadband, and alarm deviation.
Process
Variable
InputR eading
20 PSI
0 PSI
0%
0 m V
100%
60 m V
Lo
R dg
Lo PV
H iPV
H i
R dg