Dual Pid - Watlow Controls 988 Series Manual

Dual PID Sets
Requirements
The Series 988 controller needs the enhanced software option to use dual
PID sets.
Overview
Standard software units have a single set of PID parameters. Units with
enhanced software can use two independent sets of heat/cool PID para-
meters, PID A [PidA] and PID B [Pidb]. To enable dual PID, enter the
Global Menu and set the algorithm prompt [ALgO] to dual PID [Pid2].
This second set of PID parameters enables the controller to switch
between two sets of PIDs, to compensate for changes in the system
characteristics. This need can arise from a variety of circumstances, such
as significant set point changes (controlling at 250, then controlling at
750), operating a furnace with half a load versus a full load of steel,
changing the speed of a conveyor through a curing oven or using different
materials in an extruder.
Series 988 controllers can be configured to switch between PID A and PID B
based on a process value, a set point value or the event input status.
• At [Pid2] PID 2 Crossover Selection (Global Menu) select what will
cause the switch:
• [Proc] Crossover Process Value, (input 1), PIDs will switch
based on the crossover process value;
• [StPt] Crossover Set Point (1) Value, PIDs will switch at the
crossover set point value, PID A used below the crossover
point and PID B above;
• [``no] no crossover.
• At [`Ei1] Event Input 1 or [`Ei2] Event Input 2 select [`Pid]:
• PID A is used when the event input switch is open;
• PID B when the event input switch is closed.
(Note: One event input is standard on all units, a second event input is an
option.)
WATLOW Series 988 Enhanced Software Features
9