14
VCS – Viscosity Controller
4.6
Manual optimization
An optimum adaptation of the control parameters (P, I, D) is necessary in order to balance an appearing
deviation as quickly, non-oscillating and exactly as possible, according to the given operating conditions.
Generally these adjustments require a lot of professional knowledge that cannot be replaced
by this brief information.
The following information is for help purpose only:
P = proportional band Xp (%):
lower value = longer impulses, more sensitive reaction
higher value = shorter impulses, less sensitive reaction
Examples: - Oscillating temperature without distinct initial overshot: Xp too low;
- The setpoint is reached very slowly after initial exceeding: Xp too high.
I = integral action time Tn (min):
lower value = shorter impulse gaps, faster balancing
higher value = longer impulse gaps, slower balancing
Examples: - the set value is reached very slowly without overshooting: Tn too high;
- high initial overshot followed by fading oscillation: Tn too low.
D = rate time Tv (min):
increases the controller reaction in case of fast actual value or setpoint alterations
(adjust only if necessary). Higher values cause higher increase
Empirical dimensioning of Xp / Tn / Tv
Based on the actual value curves, the control loop can be re-optimized:
-
:
Actual value is only slowly approaching the set point.
Setting rule:
Increase proportional component. If this leads to an improvement, then reduce the integration time.
This repeat to one satisfactory regulator result is achieved.
-
: Actual value slowly approaches the set point with slight oscillations.
Setting rule:
Increase proportional component. If this leads to an improvement, then reduce the
-
: Actual value approaches the set point without significant overshoot.
Optimal controller behavior for processes that do not allow overshoot.
-
: Actual value is approaching the set point with a slight muted overshoot.
Optimal controller behavior for fast control and compensation of Interference components.
()
Setting rule
: The first overshoot should not be 10% of the setpoint step exceed.
-
: Actual value approaches the setpoint quickly, but oscillates far over. The Vibrations are
damped and thus just barely stable
Setting rule:
reduce proportional component. If this is an improvement leads, then increase the integration time.
This repeat to one satisfactory regulator result is achieved.
Summary of Contents for Viscosity VC312
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