Examples Of Applied Control Types; Cascade Control - Omron SYSMAC CS Series Operation Manual

Examples of Applied Control Types

5-2

Examples of Applied Control Types

Control purpose
Suppression of disturbance (on secondary
loop)
Adaptation to dead time from secondary
through to primary loop
Suppression of disturbance (on primary loop)
Suppression of disturbance (on primary and
secondary loops)
Suppression of disturbance (on primary and
secondary loops)
Adaptation to mutual interaction between pro-
cesses
Adaptation to dead time
Adaptation to changes in dead time
Note
5-2-1

Cascade Control

This section shows examples of applied control types when controlling special
control targets.
As the function blocks of the Loop Controller can be combined as desired
(excluding restrictions on the number of function blocks according to function
block address), use this feature to build a control system suited to your partic-
ular control requirements.
The following table shows the relationship between example control types cor-
responding to special control targets and the purpose of the control.
Control type example
Cascade control
Feedforward control
Cascade + feedforward control
Non-interacting control (a type of
feedforward control)
Sample PI control
Dead time compensation
Variable sample cycle control
"Special control targets" here refer to the following.
• Processes having a prolonged dead time
• Processes whose dynamic or static characteristics change
• Processes whose dynamic characteristics are not the "regular dead time
+ first-order lag"
• Processes whose non-linearity of dynamic or static characteristics are
large
• Processing involving a large number of variables and strong mutual inter-
action
However, design your system taking into consideration the possibility that the
control target cannot be completely controlled by this Loop Controller (take
into consideration that functions for observing the characteristics of the con-
trol target are required).
In the following instances, input the MV of PID1 on the primary loop and the
Remote Set Point of PID2 on the secondary loop, and connect the PLC in
series. This configuration is referred to as "cascade control."
• When there are two controllable processes, and the process to be con-
trolled is one of the processes (PV of primary loop)
• When the other (primary loop) can be controlled by controlling the other of
the two (secondary loop)
• When there is disturbance on the other process (secondary loop), or
when there is dead time until the effect of change on the other (secondary
loop) operated terminal appears in the PV of the other (primary loop)
Section 5-2
Section
5-2-1 Cascade Control
5-2-2 Feedforward Control
5-2-1 Cascade Control/5-2-2
Feedforward Control
5-2-2 Feedforward Control
5-2-3 Sample PI Control
5-2-4 Dead Time Compensation
5-2-4 Dead Time Compensation
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