CONTROL SYSTEM
*Basic of control system*
>System:-A system is arrangement of component that act together
and perform desired work.
Input----System----Output
>Control system:-Control system means to regulate, Direct command the
system so as to obtain the desired objective.
>Transfer system:-Laplace transform of output to the Laplace transform of
input is called transfer function.
Transfer system=Laplace of output
Laplace of input
*Classification
of control system*
>Open loop or non-feedback system:-When the output
quantity is non-feedback to the input quantity, The control system is called
open loop control system.
Input---controller-----process-----output
^Advantage:-
1. Low cost, simple in construction
and
design.
2. Easy to maintain.
3. System is stable.
^Disadvantage:-
1. Less accuracy and
accurate depend upon calibration.
2. Inaccurate result are
obtained with parameter variation.
^Example:-
1. Traffic light.
2. Bread toaster.
3. Washing machine.
>Closed loop or feedback or
automatic control system:-When the output
quantity of control system is feedback to the input quantity, the control
system is called closed loop.
^Advantage:-
-Accuracy is more.
-Output is less
sensitive to parameter changing.
-Non-linear distortion
are less.
-Bandwidth is increase.
^Disadvantage:-
-Tendency toward
oscillator.
-Complicated design.
-More expensive.
-Stability problem.
*Feedback
is two types*
1.Negative:-Amplifier, Gain will be reduced.
2.Positive:-Oscillator, Gain will be
increased.
*Effect of feedback*
1. Feedback can reduce
the effect of noise and disturbance.
2. Due to feedback
system is more accurate.
3. Sensibility may increase
[efficiency].
*Functional block diagram of control*
The diagram which
represents the function of the system is called functional block diagram of
control system. The physical diagram may be differing from each other.
*Dead
time*
Dead time is the amount
of time that it takes for your process variable to start changing after your
value changes.
If you were taking a
shower, the dead time is the amount of time it would take for you to feel a
change in temperature after you have adjusted the hot or cold water.
*Lag time*
Lag time is the amount
of time after the dead time that the process variable takes to move 63.3% of
its final value after a step change in value position lag time is also called a
capacity element.
*Self regulating process*
Self regulating process
are process that are inherently self regulating .Self regulating process have
built in feedback characteristics that cause the process to tend toward self
regulating.
*Non self regulating
process*
A non self regulating
process is one where the process does not tend towards self regulation. These processes
have no self regulating feedback characteristics and will tend toward being
unstable if not controlled externally.
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Open loop operation |
Close loop operation |
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Its performance accuracy depends
upon its calibration. |
It has inherent accuracy
due to feedback. |
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It is a simple system. |
System is complex. |
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More stable. |
Less stable. |
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Presence of non-linearity’s
cause malfunctioning. |
Effect of non-linearity can be minimized by selecting proper reference signal. |
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