基于单片机的火灾探测和监控系统外文文献翻译xWord格式.docx

基于单片机的火灾探测和监控系统外文文献翻译xWord格式.docx

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Typicaldetectorvoltageoutputlevels

Detectorcondition

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detectoroutputvoltageiswelldefined

fromthepAtothemArange（say,fromamere15pAinthedonnantmodeto60mA）intheactivemode.Inmanydetectorsthe

given in Table l. The more sensitive theisused:

acoincidencetechnique

detector,themoresusceptibleitistofalsealarms.Inordertocontrolthe

detectorprecisely,eitherofthefollowingmethodscanbebuiltintothedetector,orafilteringtechniquesuchthatalogiccircuitbecomesactiveonlyifxalarmsaredetectedwithinatimeperiodT.Thedetectiontechniquedependsgreatlyonthelocationandplantbeingprotected;

smokedetectorsareusedforsleepingareas,infraredorultravioletradiationareusedwhenflammableliquidsarebeinghandled,heatdetectorsareusedforfiresuppressionorextinguishingsystems.Ingeneral,lifeandpropertyprotectionhavedifferentapproaches.

Alarmdevices,apartfromtheusualaudibleorvisiblealarms,mayincorporatesolidstatesoundreproductionandemergencyvoicecommunicationorprintersthatrecordtime,date,locationandotherinformationrequiredbythestandardcodeofpracticeforfireprotectionforcomplexplants.Heaviside[4]hasanexcellent

reviewofalltypesofdetectorsandextinguishersystems.

LIControlphilosophyanddivisionoflabour

Ourcontrolphilosophyisimplementedhierarchically.Threelevelsofsystemhierarchyareimplemented,withtwolevelsofdecisionmaking.Thereisnocommunicationbetweenequipmentonthesamelevel.Interactionbetweenlevelsoccursbyupwardstransferofinformationregardingthestatusofthesubsystemsanddownwardstransferofcommands.ThisisshowninFig.1whereatlevel1isthe

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centralstationmicrocomputerandistheultimatedecisionmaker（whennotinmanualmode）.Atlevel2arethelocalcontrollers,whichresideinthelocalstations.Atlevel3aretheactualdetectorsandactuators.Amanualmodeofoperationisprovidedatalllevels.

Informationregardingthestatusofalldetectorsistransmittedonaperareabasistothelocalcontrollers.Theirinformationiscondensedandtransmittedupwardtothecentralmicrocomputer.Transferofstatusisalwaysunidirectionalandupwards-Transferofcommandsisalwaysunidirectionalanddownwards,withexpansionatthelocalcontrollevel.Thisapproachpreservesthestrictrulesofthehierarchyforexactmonitoringdetectionandalarmsystemsassociatedwithhighriskplants.

Theclassificationofthetwolayersofcontrolsisbaseduponlayersofdecisionmaking,withrespecttothefactsthat

（a）Whenthedecisiontimecomes,themakingandimplementationofadecisioncannotbepostponed

（b）Thedecisionshaveuncertainty

（c）Itwillisolatelocaldecisions（e.g.locallywemighthaveanalarmalthough

theremaybeafaultwiththesystem）

2Generalhardware

I:

Fig.2depictsourdesigninthesimplestofforms.Thesystemusesanopenpartylineapproachwithfourconductorcablesgoinginaloopsharedbyalltheremotedevicesandthecontrolpanel.Thisapproachissimpleinconceptandiseconomicallyfeasible.However,onemajordisadvantageisthedependencyonasinglecableforpowerandsignaling.Incaseswherereliabilityisofextremeimportance,twooreventhreecablestaking different

routesthroughoutthesystemmaybeconnectedinparallel.Fig.3givesthedrivercircuitryrequiredtoderiveanexpandablebus.Thisdesigntakesadvantageofrecentadvancesinthesinglechipmicrocomputertechnologytoreducetheinterfacebetween

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thecentralstationandthelocalstations.

2.1Centralcontroltask

Acentralunitprovidesacentralizedpointtomonitorandcontrolthesystem

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activities.Inthesystemtobedescribedthecentralcontrolunitservesafivefoldpurpose.

（i）Itreceivesinformationfromthelocalstationsandoperatesthealarmsandotheroutputdevices.

（ii）Itnotifiestheoperatorincaseofsystemmalfunction.

（iii）Itprovidesanoverallsystemcontrolmanualandautomatic.（iu）Itprovidesasystemtestpointoflocalstationsanditself.

（u）Itprovidesacentralpointforobservation,learningandadaptation.

2.2Localstations

Thelocalstationscantakelocaldecisionsregardingrecognitionofarisksituation,andactindependentlyonlocalaffairs.Inthistechniquewedependon'

load-typecoordination^,e.g.thelowerlevelunitsrecognizetheexistenceofotherdecisionunitsonthesamelevel;

thecentralorthetoplevelprovidesthelowerunitswithamodeloftherelationshipbetweenitsactionandtheresponseofthesystem.

Itisevidentthatapowerfulmachineisrequiredatthisstagesothatalltherequiredfunctionscanbeimplemented.Theavailabilityofthenewgenerationofmicrochipsmakesthisarchitectureafeasiblesolution.

Asinglechipmicrocomputerwaschosenoverdiscretedigitalandanaloguedevicestointerfacetothefielddevicesandtothecentralmicrocomputer.Thisisthemainreasonthatpreviouslythisapproachwasnotfeasible.

Inselectingthemicrocomputerforthelocalstations,thecriterionwastherequirementforachipwhichcontainsthemostintegrationoftheanalogueanddigitalportsrequiredfortheinterfaceandtheutilizationofCMOStechnologyowingtoremotenessofthelocalstations.ThechoicewastheMotorola68HC11A4,forthefollowingreasons:

（a）ItisCMOStechnology;

thisreducespowerconsumption.

（b）IthasaUARTonboard;

thisfacilitatesserialcommunication.

（e）Ithasana/dconverteronboard;

thiseliminatesanexternalA/D.

（d）Ithas4KofROM,256bytesofRAM,512bytesofEERROMwith401/0linesanda16bittimer;

thissatisfiedallourmemoryand1/0requirementsatthelocalstationside.

3Systemimplementation

Thelocalstation:

Fig.3istheblockdiagramofthecircuitusedtoutilizethe

MC68HC11A4asaremotefiredetectingcircuitwhileFig.4illustratesthesame

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TRANSMISSION Fig.5Closrrfloo.coMtctums

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circuitinanexpandedform.Itcanbeseenthatthesinglemicrocontrollercanbeusedtomonitormorethanonedetector,thusreducingsystemcost.

Thelooppowersupply,whichisusuallybetween28and26V,isfurtherregulatedbya5V100mAmonolithiclowpowervoltageregulatortosupplypowertothemicrocontroller.Theonboardoscillator,coupledwithanexternalcrystalof2.4576MHz,suppliesthemicrocontrollerwithitstimingsignalwhichisdividedinternallybyfourtoyieldaprocessorfrequencyof614.4kHz,whichisanevenmultipleoftheRS232[7]baudrategenerator.InthisSectiontheterm'

supervisedinputoroutput9willbeusedtomeanthatthefunctioninquestionismonitoredforopen-andshort-circuitconditionsinadditiontoitsothernormalfunctions.MoreinformationcanbefoundinReference9.

4Mainloop

Fig.7Mainloopflowchart

5Conclusion

Thispaperdescribesthedevelopmentofalargescalefiredetectionandalarmsystemusingmulti-singlechipmicrocomputers.Thearchitectureusedisatwo-levelhierarchyofdecisionmaki