Distributed control system PPT 1 2 3 4 5

PLC AND HARDWARE

1. DCS Vs PLC
ThemostbasicdifferencebetweenaPLCandaDCSis
thatPLCsweredesignedtoreplacerelay-basedcontrols
andanalogequipment,controllingonemachine.
DCS,ontheotherhand,areusedtocontrolentireplants,
buildings,orprocessesthatarevastandinterconnected.

2. Distributed control system
Adistributedcontrol
system(DCS)isaplatform
forautomatedcontroland
operationofaplantor
industrialprocess.
ADCScombinesthe
followingintoasingle
automatedsystem:human
machineinterface(HMI),
logicsolvers,historian,
commondatabase,alarm
management,and a
commonengineeringsuite.

3. DCS

5. DCSOperator
Control
Panel
Main
Control
Computer
Operator
Control
Panel
Archival
Data
Storage
Supervisory (host)
Computer
PROCESS
Local
Computer
Local
Computer
Local
Computer
Local Display Local Display
Data highway
To other Processes To other Processes
Local data acquisition and
control computers

6. DCS Elements-1
•LocalControlUnit:Thisunitcanhandle8to16individualPID
loops.
•DataAcquisitionUnit:Digital(discrete)andanalogI/Ocan
behandle.
•BatchSequencingUnit:Thisunitcontrolsatimingcounters,
arbitraryfunctiongenerators,andinternallogic.
•LocalDisplay:Thisdeviceprovidesanalogdisplaystations,
andvideodisplayforreadout.
•BulkMemoryUnit:Thisunitisusedtostoreandrecall
processdata.

7. DCS Elements-2
•GeneralPurposeComputer:Thisunitisprogrammedbya
customerorthirdpartytoperformoptimization,advance
control,expertsystem,etc
•CentralOperatorDisplay:Thisunittypicallycontainseveral
consolesforoperatorcommunicationwiththesystem,and
multiplevideocolorgraphicsdisplayunits
•DataHighway:Aserialdigitaldatatransmissionlink
connectingallothercomponentsinthesystem.Itallowfor
redundantdatahighwaytoreducetheriskofdataloss
•LocalareaNetwork(LAN)

13. Need for DCS
•DCSisasystemofsensors,controllers,and
associatedcomputersthataredistributedthroughouta
plant.
•Eachoftheseelementsservesauniquepurposesuch
asdataacquisition,processcontrol,aswellasdata
storageandgraphicaldisplay.
•Theseindividualelementscommunicatewitha
centralizedcomputerthroughtheplant’slocalarea
network–oftenreferredtoasacontrolnetwork.

14. Example
•DCSatapowerplantmightautomaticallyincrease
generationcapacityinordertokeepupwithchanging
demandforelectricityduringhotSummerdaysand
thendecreaseitasoutdoortemperaturescool
overnightanddemandsubsides.
•WhereasaPLCcouldadjustasingleunitoperation,
theDCScanmakeadjustmentstoeachofaplant’s
manyinteractingunitoperations.

16. How is a DCS Used?
•Asthe‘centralbrain’oftheplanttheDCSmakes
automateddecisionsbasedonproductiontrendsit
seestheminreal-timethroughoutaplant.
•WhileDCSsareusedacrosstheprocesscontrol
industriestosupervisecomplexproductionprocesses,
theyaremorewidelydeployedatlarge,continuous
manufacturingplantssuchasthoseinthe
petrochemicalindustry.

17. •WiththehelpofaDCStheseandothermanufactures
canefficientlycoordinateadjustmentsinatop-down
fashionusingacentralizednetworkofcomputers.
•InstructionsfromtheDCSaredeployedthroughouta
plantandfedtoindividualcontrollers.
•WhenconfiguredappropriatelytheDCScanimprove
safetywhilealsoenhancingproductionefficiency.

18. What Makes the DCS so
Important?
•Acomparisonoftwoplantsmayhelptoillustratethe
importanceoftheDCS.
•First,imagineasmallmunicipalwastewater
treatmentfacilitythatemploysadozencontrolloops.
•Theplant’sengineeringstaffcaneasilykeepa
mindfuleyeontheperformanceofsuchalimited
numberofcontrollers.
•Next,imaginealargerefinerythatoperates10,000
highlydynamicandinteractingcontrolloops.

19. •Whilecoordinatingcontrolatthetreatmentfacilityis
relativelyeasy,thetaskoforchestratingcontrolatthe
refinerycanbeoverwhelmingwithouttheuseofa
DCS.
•Overtheyears,thelinebetweenDCSandPLChas
blurred.WhiletheDCShastraditionallybeenthe
onlysolutionforachievingsafeandefficientplant-
widecontrol,advancementinprocessingcapabilities
hasallowedthePLCtorapidlytakeongreater
responsibility.

20. Advantages of DCS
•Accessalargeamountofrealtimeinformation
fromthedatahighway.
•Monitoringtrendsofpastprocessconditions.
•Readilyinstallnewon-linemeasurements
togetherwithlocalcomputers.
•Alternatequicklyamongstandardcontrol
strategiesandreadcontrollerparametersin
software.
•Asightfullengineercanusetheflexibilityofthe
frameworktoimplementhislatestcontroller
designideasonthehostcomputer.

21. DCS Vendors
•Honeywell
•Fisher-Rosemont
•Baily
•Foxboro
•Yokogawa
•Siemens

22. DCS Applications