Control Response At Different Feedback Structures - Siemens SIMATIC S7-1200 Function Manual

Principles for control

2.6 Control Response at Different Feedback Structures

Response to disturbances
The setpoint is influenced by disturbance variables. The controller has to eliminate the
resulting control deviations in the shortest time possible. The response to disturbances is
improved by minimizing fluctuation of the process value and the time required to reach the
new setpoint.
x Process value
w Setpoint
①
Influencing a disturbance variable
Disturbance variables are corrected by a controller with integral action. A persistent
disturbance variable does not reduce control quality because the control deviation is
relatively constant. Dynamic disturbance variables have a more significant impact on control
quality because of control deviation fluctuation. The control deviation is eliminated again only
by means of the slow acting integral action.
A measurable disturbance variable can be included in the controlled system. This inclusion
would significantly accelerated the response of the controller.
2.6 Control Response at Different Feedback Structures
Control behavior of controllers
A precise adaptation of the controller to the time response of the controlled system is
decisive for the controller's precise settling to the setpoint and optimum response to
disturbance variables.
The feedback circuit can have a proportional action (P), proportional-derivative action (PD),
proportional-integral action (PI), or proportional-integral-derivative action (PID).
If step functions are to be triggered by control deviations, the step responses of the
controllers differ depending on their type.
28
Function Manual, 03/2017, A5E35300227-AC
PID control