Basic elements in control systems

Mr. C.S.Satheesh, M.E.,
Basic elements in control systems
System
Types of Control Systems
Open Loop Control Systems
Closed Loop Control Systems
Difference Between Open loop & Closed loop Control Systems

1. Basic elements in control systems
Presented by
Mr.C.S.Satheesh, M.E.,
Assistant Professor, Department of EEE,
MuthayammalEngineering College (Autonomous),
Namakkal(Dt), Rasipuram–637408
MUTHAYAMMAL ENGINEERING COLLEGE
(An Autonomous Institution)
(Approved by AICTE, New Delhi, Accredited by NAAC, NBA & Affiliated to Anna University),
Rasipuram -637 408, NamakkalDist., Tamil Nadu, India.

2. Why do we study the control system?
Todesigncontrollersforasystembasedonitsownproperties.
Itisthebasisforensuringthateveryautomaticsystemperformsits
ordainedtaskaccurately,efficientlyandquickly(optimally)despite
beingsubjectedtovaryingenvironmentalconditions.
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3. Purpose of control system
Acontrolsystemmanages,commands,directs,orregulatesthe
behaviorofotherdevicesorsystemsusingcontrolloops.
Itcanrangefromasinglehomeheatingcontrollerusinga
thermostatcontrollingadomesticboilertolargeIndustrialcontrol
systemswhichareusedforcontrollingprocessesormachines.
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4. System
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Whenanumberofelementsorcomponentsareconnectedina
sequencetoperformaspecificfunction,thegroupthusformedis
calledsystem

5. Control systems
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Acontrolsystemisasystem,whichprovidesthedesiredresponseby
controllingtheoutput.Thefollowingfigureshowsthesimpleblockdiagramofa
controlsystem.

6. Contd…
Here,thecontrolsystemisrepresentedbyasingleblock.Since,theoutputis
controlledbyvaryinginput,thecontrolsystemgotthisname.
Wewillvarythisinputwithsomemechanism.Inthenextsectiononopenloop
andclosedloopcontrolsystems,wewillstudyindetailabouttheblocksinside
thecontrolsystemandhowtovarythisinputinordertogetthedesired
response.
Types of Control Systems:
 Open Loop Control Systems
 Closed Loop Control Systems
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7. Open loop control systems
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Thefollowingfigureshowstheblockdiagramoftheopenloopcontrol
system.
Inopenloopcontrolsystems,outputisnotfed-backtotheinput.So,the
controlactionisindependentofthedesiredoutput.
Here,aninputisappliedtoacontrolleranditproducesanactuatingsignal
orcontrollingsignal.Thissignalisgivenasaninputtoaplantorprocess
whichistobecontrolled.So,theplantproducesanoutput,whichis
controlled.Thetrafficlightscontrolsystemwhichwediscussedearlierisan
exampleofanopenloopcontrolsystem.

8. Closed loop control systems
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9. Contd…
Inclosedloopcontrolsystems,outputisfedbacktotheinput.So,the
controlactionisdependentonthedesiredoutput.
Theerrordetectorproducesanerrorsignal,whichisthedifference
betweentheinputandthefeedbacksignal.Thisfeedbacksignalis
obtainedfromtheblock(feedbackelements)byconsideringtheoutput
oftheoverallsystemasaninputtothisblock.Insteadofthedirect
input,theerrorsignalisappliedasaninputtoacontroller.
So,thecontrollerproducesanactuatingsignalwhichcontrolstheplant.
Inthiscombination,theoutputofthecontrolsystemisadjusted
automaticallytillwegetthedesiredresponse.Hence,theclosedloop
controlsystemsarealsocalledtheautomaticcontrolsystems.Traffic
lightscontrolsystemhavingsensorattheinputisanexampleofa
closedloopcontrolsystem.
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10. Difference Between Open loop & Closed loop
Control Systems
S.NoOpen Loop Control Systems Closed Loop Control Systems
1.Control action is independent of
the desired output.
Control action is dependent of the desired
output.
2.Feedback path is not present.Feedback path is present.
3.These are also called asnon-
feedback control systems.
These are also called asfeedback
control systems.
4.Easy to design. Difficult to design.
5.These are economical. These are costlier.
6.Inaccurate. Accurate.
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11. References :
A.Nagoorkani, Control Systems,
RBA Publications.
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12. Thank You
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