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DIGITAL INDUSTRIAL CONTROLLER
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The purpose of a follow-up control is to slave the controlled variable PV1 as exactly
as possible to another variable, the command variable, which varies in time. Either a
process variable PV2 originating from a system F
S2
or a different variable with a
given time progression can be used as the command variable (Figure 9).
Figure 9: Follow-up control
The controller of a follow-up control configuration must be designed so as to arrive
at a good response to setpoint changes with a short settling time and well-
attenuated stabilisation.
Example:
Let us take a power steering system as an example of a follow-up control. The
command variable PV2 for the angle of the wheel (controlled variable PV1) is
specified by the position of the steering wheel.
5.4 Controller with additional functions for follow-up control
5.4.1 Follow-up control (external set-point input)
5.4.2
External setpoint controller
structure
The
external setpoint
controller structure highlighted in Figure 10 is obtained by
appropriately configuring the overall structure. It is based on PID controller 2. PID
controller 1 is not used. Input 1 is used for the control variable PV1, while the
command variable is applied to input 2 as the external setpoint.
In this controller structure, the binary input can be used to switch between the
external setpoint and the setpoint SP1.
Z
SP=
PV2
F
S
F
R
Controller
Controlled system
Setpoint
generator
F
S2
PVd
PV1
CO
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