En
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28
Closed-loop control
In a closed-loop control, the controlled variable is
measured and the result, the actual setpoint, is sent
to the controller. The actual value is compared with
the setpoint. Then the manipulated variable is
calculated in order to bring the controlled variable
back to the setpoint. Opposite to the open-loop
control, a check is constantly performed to see
whether the required result occurs. Any deviations
will be corrected. A closed-loop control is meaningful
if the disturbance variables are unknown or subject
to large variation. The closed-loop control ensures
that the setpoint is retained.
Fig. 36
Closed-loop control
T
M
03
70
92
17
13
Closed-loop
controller
Final control
element
Controlled
variable
Disturbance
variable
Control
factor
Manipulated
variable
Setpoint
Control
process
Measuring
element
Actual value of
Controlled variable
