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3.5.2 Optimization after start-up or at the set-point
The two methods are optimization after start-up and at the set-point.
As control parameters are always optimal only for a limited process range,
various methods can be selected dependent of requirements. If the process
behaviour is very different after start-up and directly at the set-point, parameter
sets 1 and 2 can be optimized using different methods. Switch-over between
parameter sets dependent of process status is possible (see page 25).
Optimization after start-up: (see page25 )
Optimization after start-up requires a certain separation between process value
and set-point. This separation enables the controller to determine the control
parameters by evaluation of the process when lining out to the set-point.
This method optimizes the control loop from the start conditions to the set-point,
whereby a wide control range is covered.
We recommend selecting optimization method "Step attempt after start-up"
with tunE = 0 first. Unless this attempt is completed successfully, we
recommend a "Pulse attempt after start-up".
Optimization at the set-point: (see page 18)
For optimizing at the set-point, the controller outputs a disturbance variable to the
process. This is done by changing the output variable shortly. The process value
changed by this pulse is evaluated. The detected process parameters are
converted into control parameters and saved in the controller.
This procedure optimizes the control loop directly at the set-point. The advantage
is in the small control deviation during optimization.
3.5.3 Selecting the method ( ConF/ Cntr/ tunE)
Selection criteria for the optimization method:
tunE = 0
tunE = 1
tunE = 2
Sufficient set-point reserve:
inverse controller: (with process value < set-point- (10% of rnGH - rnGL)
direct controller:
Step attempt after start-up
Condition:
The controller outputs 0% correcting variable or Y. L o and waits, until the process
is at rest (see start-conditions on page 16).
Subsequently, a correcting variable step change to 100% is output.
8800 process controller
Step attempt after start-up
sufficient set-point reserve is
provided
always step attempt after
start-up
(with process value > set-point + (10% of rnGH - rnGL)
- tunE = 0 and sufficient set-point reserve provided or
- tunE = 2
17
Pulse attempt after start-up
sufficient set-point reserve is
provided
Operation
Optimization at the set-point
sufficient set-point reserve is not
provided
sufficient set-point reserve is not
provided
Self-tuning
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