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 ).
Optimization after start-up: (see page 18)
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 then recommend
a “Pulse attempt after start-up”.
Optimization at the set-point: (see page 19)
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.
3.5.6 Selecting the method ( ConF/ Cntr/ tunE)
Selection criteria for the optimization method:
Step attempt after start-up Pulse attempt after start-up Optimization at the set-point
tunE = 0 sufficient set-point reserve is provided sufficient set-point reserve is not
provided
tunE = 1 sufficient set-point reserve is provided sufficient set-point reserve is not
provided
tunE = 2 Only step attempt after start-up required
Sufficient set-point reserve:
inverse controller:(with process value < set-point- (10% of rnGH - rnGL)
direct controller: (with process value > set-point + (10% of rnGH - rnGL)