SYSTEM
A system is an arrangement, set or collection of things connected in such a manner as to perform a specific task. A system consists of a sequence of components in which each component has some cause as input and its effect will be on its output. Broadly it is a sequential set of cause and effects. Each system may have a large number of subsystems.
CONTROL SYSTEM
Control system is an arrangement of physical components connected in such a manner as to command, direct or regulate itself or another system. Control systems may classified as
1> Open loop control system
2> Closed loop control system.
OPEN LOOP CONTROL SYSTEM
In this control system action is independent of the desired output. The actual signal depends only on the input command and output has no control over it.
FEATURES
> lower cost
> lower accuracy
> good stability
> easily buildable
Input command is the sole factor responsible for providing the control action , control adjustment depends upon the judgement and estimate of human being, presence of nonlinearities cause malfunctioning and any change in system component cannot be taken care of automatically.
EXAMPLES:
>Automatic toaster
>electric watch
>automatic washing machine etc.
CLOSED LOOP CONTROL SYSTEM
In such a system control action is somehow dependent on the output. In this system the controlled output is fedback through a feedback element and compared with the reference input. Thus the actuating signal is the difference of desired output and reference input.
FEATURES
> Complicated and costlier
> higher accuracy
> less stable
change in the system component is automatically taken care of ,it is accurate even in the presence of nonlinearities , the control adjustment is dependent on the output and feedback element and the control action is provided by the difference of the input command and the corresponding output.
EXAMPLES
> liquid level control system ,
> traffic signal system,
> temperature control of a room.
The essentials of such control are
1> an error detecting device
2> an amplifier
3> an error correcting device.
each element serves a functional purpose in matching the regulated or controlled quantity to the reference quantity .
FEEDBACK
Feedback is that property of a closed loop control system which allows the output or some other controlled variable of the system , to be compared with the input to the system, so that the appropriate control action may be formed as some function of the output and input.
A feedback is said to exist in a system if the cause and effect between variables is interrelated.
CHARACTERISTICS OF FEEDBACK
> Increased bandwidth
> Increased accuracy
> reduced sensitivity to disturbances
> reduced distortions and nonlinearities
> tendency towards oscillations or instability
TERMINOLOGY
The terms used in closed loop control system are defined below
> COMMAND: The command is the input which is varied by some means external to and independent of the feedback control system
> REFERENCE INPUT: The reference input is a signal established as a standard of comparison for a feedback control system by virtue of its relation to the command input.
> ACTUATING INPUT(or signal): This is the reference input minus the primary feedback and provides for corrective action.
> SYSTEM ERROR: The system error is th ideal value of the controlled variable minus the value of the final controlled variable.
> CONTROLLED VARIABLE: It is a variable which is to be controlled
> CONTROL ELEMENTS: The control elements comprise of the feedback
and the elements which when employed give the actuating signal and regulate the output.
>DISTURBANCE: A disturbance is an undesired input signal which affects the value of the controlled output.
SERVOMECHANISM
A system is an arrangement, set or collection of things connected in such a manner as to perform a specific task. A system consists of a sequence of components in which each component has some cause as input and its effect will be on its output. Broadly it is a sequential set of cause and effects. Each system may have a large number of subsystems.
CONTROL SYSTEM
Control system is an arrangement of physical components connected in such a manner as to command, direct or regulate itself or another system. Control systems may classified as
1> Open loop control system
2> Closed loop control system.
OPEN LOOP CONTROL SYSTEM
In this control system action is independent of the desired output. The actual signal depends only on the input command and output has no control over it.
FEATURES
> lower cost
> lower accuracy
> good stability
> easily buildable
Input command is the sole factor responsible for providing the control action , control adjustment depends upon the judgement and estimate of human being, presence of nonlinearities cause malfunctioning and any change in system component cannot be taken care of automatically.
EXAMPLES:
>Automatic toaster
>electric watch
>automatic washing machine etc.
CLOSED LOOP CONTROL SYSTEM
In such a system control action is somehow dependent on the output. In this system the controlled output is fedback through a feedback element and compared with the reference input. Thus the actuating signal is the difference of desired output and reference input.
FEATURES
> Complicated and costlier
> higher accuracy
> less stable
change in the system component is automatically taken care of ,it is accurate even in the presence of nonlinearities , the control adjustment is dependent on the output and feedback element and the control action is provided by the difference of the input command and the corresponding output.
EXAMPLES
> liquid level control system ,
> traffic signal system,
> temperature control of a room.
The essentials of such control are
1> an error detecting device
2> an amplifier
3> an error correcting device.
each element serves a functional purpose in matching the regulated or controlled quantity to the reference quantity .
FEEDBACK
Feedback is that property of a closed loop control system which allows the output or some other controlled variable of the system , to be compared with the input to the system, so that the appropriate control action may be formed as some function of the output and input.
A feedback is said to exist in a system if the cause and effect between variables is interrelated.
CHARACTERISTICS OF FEEDBACK
> Increased bandwidth
> Increased accuracy
> reduced sensitivity to disturbances
> reduced distortions and nonlinearities
> tendency towards oscillations or instability
TERMINOLOGY
The terms used in closed loop control system are defined below
> COMMAND: The command is the input which is varied by some means external to and independent of the feedback control system
> REFERENCE INPUT: The reference input is a signal established as a standard of comparison for a feedback control system by virtue of its relation to the command input.
> ACTUATING INPUT(or signal): This is the reference input minus the primary feedback and provides for corrective action.
> SYSTEM ERROR: The system error is th ideal value of the controlled variable minus the value of the final controlled variable.
> CONTROLLED VARIABLE: It is a variable which is to be controlled
> CONTROL ELEMENTS: The control elements comprise of the feedback
and the elements which when employed give the actuating signal and regulate the output.
>DISTURBANCE: A disturbance is an undesired input signal which affects the value of the controlled output.
SERVOMECHANISM
