block diagram for control systems
Post on 16-Jul-2015
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Block Diagram Representation of Control Systems
By MSc. Student Mohammed AboAjmaa
1By Mohammed AboAjmaa SDU
Dr. Selçuk ComlekçiA COURSE OFFERED BY
T.C Suleyman Demirel University
College of Engineering Electronic And Communications Eng. Department
What is Block Diagram
A bock diagram is pictorial representation of the functionsperformed by each component and of the flow signals . In a blockdiagram all system variables are linked to each other throughfunctional block, the functional block is a symbol for themathematical operation on the input signal to the block thatproduces the output. A block diagram is high-level type of flowchart.It is useful tool in designing new processes or improving existingprocesses.
2By Mohammed AboAjmaa SDU
3By Mohammed AboAjmaa SDU
Note: Team members who construct a block diagram must have a clear understanding of how the process operates.
Examples about Block Diagram
1- 522113 xaxax
2- 112211 nnn xaxaxax
Draw the Block Diagrams of the following equations:
4By Mohammed AboAjmaa SDU
An open-loop controller is a type of controller thatcomputes its input into a system using only thecurrent state and its model of the system. Acharacteristic of the open-loop controller doesn’tuse feedback to determine if its output has achieved thedesired goal of the input. This means that the systemdoesn’t observe the output of the
processes.
Open-loop control system
GH(s)= Open-loop transfer function
5By Mohammed AboAjmaa SDU
6By Mohammed AboAjmaa SDU
Ex:
A digital camera is used to take a photograph, it istransferred to the computer where processing of thepicture takes place and finally a printout isproduced. This is a open system because no attemptis made to improve the picture. If the person takingthe picture decides to improve the final printoutusing graphics software he has to change to closedloop system by adding
controller.
Closed-loop Control Systems
Feedback control systems are often referred to as closed-loopcontrol systems. In practice, the term feedback control andclosed-loop control are used interchangeably. In a feedbackcontrol system the actuating error signal is the differencebetween the input signal and the feedback signal (which may bethe output signal itself or a function of output signal and itsderivative or integration). The feedback is a fed to the controllerso as to reduce the error and bring the output of the system to adesired value. The term closed-loop control always mean the useof feedback control action in order to reduce system
error.
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The General Form Of Feedback Control System
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Characteristic Equation
The control ratio is the closed loop transfer function of the system:
)()(1
)(
)(
)(
sHsG
sG
sR
sC
The denominator of closed loop transfer function determines the characteristic equation of the system:
Which given by: 0)()(1 sHsG
9By Mohammed AboAjmaa SDU
For the above system The behavior depends on the value of gain (K).
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Ex: Weather Station:
INPUT:The heat from the sun causes
the temperature sensor to produce data and this is sent
to the computer.
PROCESS:Data is received by the
computer and it is processed. The processed data is displayed on the
monitor as a graph.
OUTPUT:The temperature levels are printed out. This is one form of output.
FeedbackThe temperature is continuouslymonitored and this is called feedback.As long as the sensor works, thecomputer processes and the printerprints out - feed back is taking place.
12By Mohammed AboAjmaa SDU
Reduction techniques
The aim of reduction technique is to simplify the block diagram and get transfer function.
C(s)
R(s)=?
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Reduction techniques procedure
:1. Combining blocks in cascade or in parallel
1G2G
21GG
1G
2G
21 GG
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2. Moving a summing point behind a block:
G G
G
:3. Moving a summing point ahead of a block
G G
G
1
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4. Moving a pickoff point behind a block:
G G
G
1
5. Moving a pickoff point ahead of a block:
G G
G
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6. Eliminating a feedback loop:
G
H
G
1H
G
G
1
GH
G
1
17By Mohammed AboAjmaa SDU
Find the transfer function of the following block diagrams:
2G 3G1G
4G
1H
2H
)(sY)(sR
18By Mohammed AboAjmaa SDU
Sol:1-
2-
19By Mohammed AboAjmaa SDU
3-
4-
5-
)()(1
)(
)(
)(
32413242121
3241
GGGGGGGHHGG
GGGG
sR
sY
20By Mohammed AboAjmaa SDU
Thanks For Listening
21By Mohammed AboAjmaa SDU
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