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7/26/2019 Example Close-loop System
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- Basic Elements of ControlSystems -
FREDERICK UNIVERSITY CYPRUS
AMEM 326
Lecturer: Dr. Sotiris Omirou
Basic Elements of an open-loop system
Controlelement
Correctionelement
Process
input output
controller
signal expectedto producerequired output
controlledvariable
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Example (1) of an open-loop system
An electric fire used to heat a room
Controlled variable:
Control element:
Correction element:
Process:
room temperaturethe operator
the switch and the fire
the room
Identify the subsystems in an open-loop controlledspeed motor
Controlled variable:
Control element:Correction element:
Process:
motor speed
the operatorthe switch
the motor
Example (2) of an open-loop system
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Basic Elements of a closed-loop system
Controlelement
Correctionelement
Process
input outputcontroller
reference value controlledvariable
measurementelement
error signal
+
-
feedback
comparison element
Comparison element
Controlelement
Correctionelement
Process
input outputcontroller
reference value controlled
variable
measurementelement
error signal
+
-
feedback
comparison element
Compares the reference value with the measured valueand produces an error signal
Error = reference measured value
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Control element
Controlelement
Correctionelement
Process
input outputcontroller
reference value controlledvariable
measurementelement
error signal
+
-
feedback
comparison element
This element decides what action to take when itreceives an error signal
Correction element
Controlelement
Correctionelement
Process
input outputcontroller
reference value controlled
variable
measurementelement
error signal
+
-
feedback
comparison element
This element is used to produce a change in the processto remove the error and is often called an actuator
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Process element
Controlelement
Correctionelement
Process
input outputcontroller
reference value controlledvariable
measurementelement
error signal
+
-
feedback
comparison element
The process or plant is the system of which a variable isbeing controlled
Measurement element
Controlelement
Correctionelement
Process
input outputcontroller
reference value controlled
variable
measurementelement
error signal
+
-
feedback
comparison element
This produces a signal related to the variable beingcontrolled and provides the signal fed back to thecomparison element to determine if there is an error
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Feedback
Controlelement
Correctionelement
Process
input outputcontroller
reference value controlledvariable
measurementelement
error signal+
_
feedback
comparison element
The feedback can be either positive or negative:
Error signal = reference value + feedback
Error signal = reference value - feedback
Example (1) of a closed-loop system
An electric fire used to heat a room with a thermometer indicating the current room temperature
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Example (1) of a closed-loop system (cont)
Controlled variable:
Reference value:
Comparison element:
Error signal:
Control element:
Correction element:
Process:
Measuring device:
the room temperature
the operatorthe difference between measured andrequired temperature
the operator
the required room temperature
the hand of the operator
the room
the thermometer
Example (2) of a closed-loop system
The automatic control of water level in a tank
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Example (2) of a closed-loop system (cont)
Controlled variable:
Reference value:
Comparison element:
Error signal:
Control element:
Correction element:
Process:
Measuring device:
Water level in tank
the leverthe difference between the actual andinitial setting of the lever positions
the pivoted lever
Initial setting of lever position
the flap opening or closingthe water supply
water in the tank
the floating ball and lever
Example (4) of a closed-loop system
Driving a car
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Example (4) of a closed-loop system (cont)
Controlled variable:
Reference value:
Comparison element:
Error signal:
Control element:
Correction element:
Process:
Measuring device:
direction of the car along the road
the driverthe difference between the actual andrequired directions
the driver
the required direction along the road
the hands on the steering wheel
the vehicle dynamics
visual observation
Control of direction
Example (4) of a closed-loop system (cont)
Controlled variable:
Reference value:
Comparison element:Error signal:
Control element:
Correction element:
Process:
Measuring device:
speed of the car along the road
the driverthe difference between the actual andrequired speeds
the driver
the required speed along the road
the foot on the pedals
the vehicle dynamics
visual observation
Control of speed
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Example (5) of a closed-loop system
Maintenance of the liquid level in a container
Example (5) of a closed-loop system (cont)
Controlled variable:
Reference value:
Comparison element:
Error signal:
Control element:
Correction element:
Process:
Measuring device:
level of liquid in the tank
the workman
the difference between the actual andrequired levels
the workman
the required level
the valve
the water in the container
visual observation of thegauge glass