Marathon Computer AACC 2000 - Manual (Page 62)

Marathon Monitors Inc.
AACC 2000 Carbon Nov. 1, 1997
62
Gain scheduling
Gain scheduling is the automatic transfer of control between one set of PID values and
another. In the case of the AACC 2000 controllers, this is done at a presettable process
value. It is used for the more difficult to control processes which exhibit large changes
in their response time or sensitivity at, for example, high and low process variables, or
when heating or cooling.
The AACC 2000 has two sets of PID values. You can select the active set from either a
digital input, or from a parameter in the PID list, or you can transfer automatically in gain
scheduling mode. The transfer is bumpless and will not disturb the process being
controlled.
To use gain scheduling, follow the steps below:
Step1: Enable in configuration level
Gain scheduling must first be enabled in
Configuration level. Goto the
Inst Conf list,
select the parameter
Gsch, and set it to YES.
Step 2: Set the transfer point
Once gain scheduling has been enabled, the
parameter
G.SP will appear at the top of the
Pid list in FuLL access level. This sets the
value at which transfer occurs. PID1 will be
active when the process value is below this
setting and PID2 when the process value is
above it. The best point of transfer depends on
the characteristics of the process. Set a value
between the control regions that exhibit the
greatest change
Step 3: Tuning
You must now set up the two sets of PID values. The values can be
manually set, or automatically tuned as described earlier in this chapter.
When tuning automatically you must tune twice, once above the switching
point G.SP and again below the switching point. When tuning, if the
process value is below the transfer point G.SP the calculated values will
automatically be inserted into PID1 set and if the process value is above
G.SP, the calculated values will automatically be inserted into PID2 set.
Gsch
YES
G.SP
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