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10. Closed-loop control functions
Closed-loop control is a process in which the variable to be
controlled (controlled variable x) is permanently monitored and
compared with the reference variable (or preset value). The
result of this comparison influences the controlled variable for
adjustment to the reference variable.
Exact information on the steady-state behaviour and on the
dynamic behaviour of the controlled system is required for
selecting a suitable controller. In most cases the characteristics
are experimentally found and can hardly be influenced.
We distinguish between three types of controlled systems.
Controlled systems with
compensation
In a controlled system with compensation control variable x is
moving towards a new final value (steady state). Important in
these controlled systems is the gain (transfer coefficient K
S
).
The smaller the gain the better the system can be controlled.
These controlled systems are called P(roportional) systems.
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