Watlow Series 988 - Manual (Page 147)

9.10 WATLOW Series 988 User’s Manual Enhanced Software Features, Chapter 9
Enhanced Software
Duplex
Requirements
The duplex control feature requires enhanced software and a process out-
put.
Overview
Certain systems require that a single process output control both heating
and cooling outputs. A Series 988 controller configured with enhanced
software and a process output can function as two separate outputs. With
a 4 to 20mA output the heating output will operate from 12 to 20mA (0 to
+100 percent) and the cooling output will operate from 12 to 4mA (0 to -
100 percent). In some cases this type of output is required by the device
that the 988 controls, such as a three-way valve that opens one way with
a 12 to 20mA signal and opens the other way with a 4 to 12mA signal.
This feature reduces the overall system cost by using a single output to
act as two outputs.
NOTE:
Duplex applications
require a special
valve.