Controller With Additional Functions For Cascade Control; Cascade Control - bürkert 1110 Bedienungsanleitung

DIGITAL INDUSTRIAL CONTROLLER
5.6

Controller with additional functions for cascade control

5.6.1 Cascade control

In a cascade control, two control loops are interlinked so that one control loop (the
main control loop) is superimposed on the other (the auxiliary control loop). We
therefore speak of a double control loop (Figure 13).
PVd 1
SP1
W1 Xd1
+
-
Sollwert-
Setpoint
geber
generator
Figure 13: Cascade control
The controlled system is split into the two subsystems F
variable PV1 is measured on the subsystem F
PV2 is measured on the subsystem F
The auxiliary control loop consists of the auxiliary controller F
F . The setpoint for the auxiliary control loop is given by the output variable CO1 of
S2
the main controller F
auxiliary control loop and the subsystem F
specified as SP1.
A prerequisite for interaction between the two control loops is that the auxiliary
control loop must have a faster time response than the main control loop, i.e. the
essential delays are encountered in the sub-loop F
the subsystem F
disturbances Z1 influencing the subsystem F
loop.
Example:
Control of the temperature in a tank heated with hot steam can be mentioned as an
example of a cascade control. A fast auxiliary control loop for control of the
hot steam flow rate is superimposed on the slow temperature control loop with the
main controller F
CO1 PVd2
Y1 Xd2
F R1 F R2
F R1 F R1
+
-
Hilfsregler
Hauptregler
Main controller Auxiliary
controller
Hilfsregelkreis
Auxiliary control loop
Hauptregelkreis
Main control loop
.
S2
, which constitutes the main control loop together with the
R1
are balanced out by the faster auxiliary control loop and
S2
.
R1
Z2 Z2
CO2 PV2
Y2 X2
F S2
F S2
Teilstrecke 2 Teilstrecke 1
Subsystem 2 Subsystem 1
and F
S1 S2
and the auxiliary controlled variable
S1
and the subsystem
R2
. The setpoint of the main control loop is
S1
. Disturbances Z2 influencing
S1
are balanced out by the main control
S1
Z1 Z1
PV1 X1
F S1
F R1
. The controlled
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