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CONTENTS
1- Open Loop System
2- Feed Back Concepts
3- Close Loop System
4- Automatic And Manual Control System (With Example)
5- Representing Of Control System
6- Transfer Function And Block Diagram
7- Signal Flow Diagram And Mason’s Theorem
8- State Variables Diagram
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CONTENTS
9- Transition Matrix.
10- Solution Of State Variable By Computer.
11- System Response (With Step, Ramp And Exponential Input)
And Time Response.
12- Construction Of Control Systems (Potentiometers, Dc Motor,
Alternative Motor).
13- System Stability (Routh-herth Method, Graphic Standard,
Nyquist Standard, Nichols, Bode Diagram And Root Locus.
12- Computer Applications
Of Stability.
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Advanced control engineering, roland s. burns
Control engineering, neil munro
CONTROL SYSTEM DESIGN, Graham C. Goodwin, Stefan F.
Graebe& Mario E. Salgado
Analog & digital control system design, chi-Tsong chen
Control Systems And Control Systems Engineering With Classical
and Modern Techniques And Advanced Concepts Control,
wikibooks
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Control System Design Guide, George Ellis
Introduction To Control Engineering, Ajit K. Mandal
Analysis And Design Of Control System Using Matlab,
Roa V.Dukkipati
Modern Control Engineering, Third Addition, Katsuhico
Ogata
Analysis And Control Of Linear Systems, Philippe De
Larminat
Or Any Control System Books
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A system is a combination of components that act
together and perform a certain objective. A system is
not limited to physical ones. The concept of the
system
can
be
applied
to
abstract,
dynamic
phenomena such that encountered in economic. The
word system should be interpreted to imply physical,
biological, economic and so on.
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In general, a system may be defined as a collection of
matter, parts, components or procedure which are
included within some specified boundary as shown in
figure (1). A system may have any number of inputs
and outputs.
system
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In control engineering, the way in which the system
outputs respond in changes to the system inputs (i.e
system response) is very important. The control
system design engineer will attempt to evaluate the
system response by determining
model
a mathematical
for the system. Knowledge of the system
inputs , together with the mathematical model, will
allow the system outputs to be calculated.
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It is conventional refer to the system being controlled
as the plant, and this; as with other elements, is
represented by a block diagram. Some inputs, the
engineer will have direct control over, and can be used
to control the plant outputs. These are known as
control inputs. There are other inputs over which the
engineer has no control, and these will tend to deflect
the plant outputs from their desired values. These are
called disturbance inputs.
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In the case of the ship shown in figure (2), the rudder
and engines are the control inputs, whose values can
be adjusted to control certain outputs, for example
heading and forward velocity. The wind, waves and
current are disturbance inputs and will induce errors
in outputs (called control variables) of position,
heading and forward velocity . In addition, the
disturbances will introduce increased ship motion
(roll, pitch and heave) which
again is not desirable. 10
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ship
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+
-
plant
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Those systems in which the output has no effect on
the control action are called open-loop control
systems. In other word, in an open-loop control
system the output is neither measured nor feed back
for comparison with the input.
Example:
Washing machine, soaking washing, and rinsing in the
washer operate on the a time basis. the machine does
not measure the output signal. That is, the cleanliness
of the clothes.
In any open-loop control system the output is not
compared with the reference
input.
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Thus, to each reference input there corresponds a
fixed operating condition; as a result, the accuracy of
the system depends on calibration. In the presence of
disturbances, an open-loop control system will not
perform desired task.
Open-loop control can used, in practice, only if the
relationship between output and input is known and if
there are neither internal nor external disturbances.
Note that, any control system the operate on a time
basis is open-loop. For instance, the traffic control by
means of signals operated on a time basis is another
example of open-loop control
system.
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We can say that, represents and open-loop control
system and is used for very simple application. The
main problem with open-loop control is that the
controlled variable is sensitive to changes in
disturbance inputs.
Example:
If a gas fire switched on in a room, and the
temperature climbs to 20˚ C, it will remain at that
value unless there is a disturbance. This could be
caused by leaving a door to the room open. Or
alternatively, by a change in out side temperature.
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A system that maintains a prescribed relationship
between output and the reference input by comparing
them and using the difference as a means of control is
called a feed back control system. Previous example is
best to be here, by measuring the actual room
temperature and comparing it with the reference
temperature (desired temperature), the thermostat
turns the heating or cooling equipments on or off in
such away as to ensure that the room temperature
remains at a comfortable level regardless of the
outside conditions.
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Feed back control systems are not limited to
engineering but can be found in various
nonengineering fields as well. The human body, for
instance, is a highly advanced feed back control
system. Both body temperature and blood pressure
are kept constant by means physiological feed back. In
fact, feed back performs a vital function; it makes the
human body relatively insensitive to external
disturbances thus enabling it to function properly in a
changing environment.
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Feed back control systems are often referred to as
closed-loop control systems. In practice, the terms
feed back control and close-loop are used
interchangeably. In a closed-loop control system the
error signal, which is the difference between the input
signal and the feed back signal (which may be the
output signal itself or a function of the output signal
and its derivatives and/or integrals), is fed to
controller so as to reduce the error and bring the
output of the system to a desired values. The terms
closed-loop control always implies the use feed back
control action in order to
reduce system error.
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Forward Path
+
-
plant
controller
Measured
value
sensor
Feed back Path
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specifications
Closed-loop
External Disturbances
& Internal Variations in
system parameters
Accuracy of component
Relatively insensitive
stability
stability is a major problem ,
overcorrect error cause
oscillations of constant or
changing amplitude
Open-loop
Sensitive
Possible to use inaccurate and use accurate
inexpensive components to
components
obtain the accurate control of
given plant
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Is easier to build
because system
stability is not a major
problem
20
Number of component
more
less
Cost and power
higher
lower
To obtain other differences refer back to references
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The physical realization of system to control room
temperature is shown in figure below, the output
signal from temperature sensing device as
thermocouple (?) or a resistance thermometer is
compared with the desired temperature. Any
difference or error causes the controller to send a
control signal to the gas solenoid valve which
produces a linear movement of the valve stem. Thus
adjusted the gas flow of gas to the burner of the gas
fire. The desired temperature is usually obtained from
manual adjustment of a potentiometer
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Steady conditions will exist when actual and desired
temperatures are the same, and the heat input
exactly balances the heat loss through the wall of the
building .
The system can operate in two modes:
Proportional control: here the linear movement of
the valve stem is proportional to the error. This
provides a continues modulation of the heat input to
the room producing very precise temperature control.
This used for applications where temperature control,
of say better than 10 C , is required (i.e hospital,
industrial standard room, ….) where accuracy is more
important than cost.
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On – Off control: also called thermostatic or bangbang control, the gas valve is either fully open or fully
closed, the heater is either on or off. This form of
control produces an oscillation of about 2 or 3o C of
the actual temperature about desired temperature,
but is cheap to implement and is used for law cost
applications (i.e. domestic heating systems).
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