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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:
Gsch
YES
G.SP
350
Step 3: Tuning
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
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.
AACC 2000 Carbon | 62 | Nov. 1, 1997 |