Watlow CLS - Manual (Page 157)

Appendix B: Enhanced Process Control
149
Setpoint Differential
Selectable Values: From the ratio loop PV minimum reading to the
maximum reading.
NOTE
Ratio control cannot be used on the same control loop as
Cascade control; however, both features may be used in the
same multi-loop controller.
Remote Analog setpoint
The Remote Analog Setpoint (Remote SP) is set up identically to the
Ratio control. If you wish to use a Remote SP, an analog input from one
of the control loops is typically connected to an external current or
voltage source, which can be defined as Linear. All other input types are
also usable as Remote SP inputs.
The loop which contains the Remote SP input is the “Master loop“, and
the Ratio control parameters are set up as outlined in the Ratio control
section of this appendix.
Differential Control
Differential control is a function you enable through the Ratio control
feature, which allows a process to be controlled at a difference to
another process. You enable the Differential control by setting the Ratio
value to 1.0 and adjusting the differential to accommodate the desired
offset.
LOOP PROCESS UNITS
ALARM SETPOINT STATUS OUT%
02 RATIO CONTROL
SP DIFF.? 0