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Supplementary information
Type 8792, 8793 REV.2
26.3 Adjustment rules for PID controllers
The Type 8793 control system comes with a self-optimization function for the structure and parameters of
the integrated process controller. The PID parameters determined can be viewed via the operating menu and
empirically re-optimized as desired.
The regulatory literature includes a series of adjustment rules which can be used in experimental ways to
determine a favorable setting for the controller parameters. To avoid incorrect settings, always observe the
conditions under which the particular adjustment rules have been drawn up. Apart from the properties of the
controlled system and the controller itself, the aspect whether a change in the disturbance variable or command
variable is to be corrected plays a role.
26.3.1 Adjustment rules according to Ziegler and Nichols (oscillation
method)
With this method the controller parameters are adjusted on the basis of the behavior of the control circuit at
the stability limit. The controller parameters are first adjusted so that the control circuit starts to oscillate. The
occurring critical characteristic values suggest a favorable adjustment of the controller parameters. A prereq-
uisite for the application of this method of course is that the control circuit may be oscillated.
Procedure
→
Set controller as P-controller (i.e. Tn = 999, Tv = 0), first select a low value for Kp
→
Set required set-point value
→
Increase Kp until the control variable initiates an undamped continuous oscillation.
The proportionality coefficient (amplification factor) set at the stability limit is designated as K
crit
. The resulting
oscillation duration is designated as T
crit
.
Progress of the control variable at the stability limit
X
Time
Tcrit t
Actual value
Figure 77:
Progress of the control variable PID
english
Summary of Contents for 8792
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