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