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毕业设计(论文)-金属管件气密性检测装置的控制系统设计

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编号:9744309    类型:共享资源    大小:12.70MB    格式:RAR    上传时间:2018-03-24 上传人:好资料QQ****51605 IP属地:江苏
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金属管 气密性 检测 装置 控制系统 设计
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毕业设计(论文)-金属管件气密性检测装置的控制系统设计,金属管,气密性,检测,装置,控制系统,设计
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PROGRAMMABLELOGICCONTROLLERAPROGRAMMABLELOGICCONTROLLERPLCORPROGRAMMABLECONTROLLERISADIGITALCOMPUTERUSEDFORAUTOMATIONOFELECTROMECHANICALPROCESSES,SUCHASCONTROLOFMACHINERYONFACTORYASSEMBLYLINES,AMUSEMENTRIDES,ORLIGHTINGFIXTURESPLCSAREUSEDINMANYINDUSTRIESANDMACHINESUNLIKEGENERALPURPOSECOMPUTERS,THEPLCISDESIGNEDFORMULTIPLEINPUTSANDOUTPUTARRANGEMENTS,EXTENDEDTEMPERATURERANGES,IMMUNITYTOELECTRICALNOISE,ANDRESISTANCETOVIBRATIONANDIMPACTPROGRAMSTOCONTROLMACHINEOPERATIONARETYPICALLYSTOREDINBATTERYBACKEDORNONVOLATILEMEMORYAPLCISANEXAMPLEOFAREALTIMESYSTEMSINCEOUTPUTRESULTSMUSTBEPRODUCEDINRESPONSETOINPUTCONDITIONSWITHINABOUNDEDTIME,OTHERWISEUNINTENDEDOPERATIONWILLRESULT1HISTORYTHEPLCWASINVENTEDINRESPONSETOTHENEEDSOFTHEAMERICANAUTOMOTIVEMANUFACTURINGINDUSTRYPROGRAMMABLELOGICCONTROLLERSWEREINITIALLYADOPTEDBYTHEAUTOMOTIVEINDUSTRYWHERESOFTWAREREVISIONREPLACEDTHEREWIRINGOFHARDWIREDCONTROLPANELSWHENPRODUCTIONMODELSCHANGEDBEFORETHEPLC,CONTROL,SEQUENCING,ANDSAFETYINTERLOCKLOGICFORMANUFACTURINGAUTOMOBILESWASACCOMPLISHEDUSINGHUNDREDSORTHOUSANDSOFRELAYS,CAMTIMERS,ANDDRUMSEQUENCERSANDDEDICATEDCLOSEDLOOPCONTROLLERSTHEPROCESSFORUPDATINGSUCHFACILITIESFORTHEYEARLYMODELCHANGEOVERWASVERYTIMECONSUMINGANDEXPENSIVE,ASELECTRICIANSNEEDEDTOINDIVIDUALLYREWIREEACHANDEVERYRELAYIN1968GMHYDRAMATICTHEAUTOMATICTRANSMISSIONDIVISIONOFGENERALMOTORSISSUEDAREQUESTFORPROPOSALFORANELECTRONICREPLACEMENTFORHARDWIREDRELAYSYSTEMSTHEWINNINGPROPOSALCAMEFROMBEDFORDASSOCIATESOFBEDFORD,MASSACHUSETTSTHEFIRSTPLC,DESIGNATEDTHE084BECAUSEITWASBEDFORDASSOCIATESEIGHTYFOURTHPROJECT,WASTHERESULTBEDFORDASSOCIATESSTARTEDANEWCOMPANYDEDICATEDTODEVELOPING,MANUFACTURING,SELLING,ANDSERVICINGTHISNEWPRODUCTMODICON,WHICHSTOODFORMODULARDIGITALCONTROLLERONEOFTHEPEOPLEWHOWORKEDONTHATPROJECTWASDICKMORLEY,WHOISCONSIDEREDTOBETHE“FATHER“OFTHEPLCTHEMODICONBRANDWASSOLDIN1977TOGOULDELECTRONICS,ANDLATERACQUIREDBYGERMANCOMPANYAEGANDTHENBYFRENCHSCHNEIDERELECTRIC,THECURRENTOWNERONEOFTHEVERYFIRST084MODELSBUILTISNOWONDISPLAYATMODICONSHEADQUARTERSINNORTHANDOVER,MASSACHUSETTSITWASPRESENTEDTOMODICONBYGM,WHENTHEUNITWASRETIREDAFTERNEARLYTWENTYYEARSOFUNINTERRUPTEDSERVICEMODICONUSEDTHE84MONIKERATTHEENDOFITSPRODUCTRANGEUNTILTHE984MADEITSAPPEARANCETHEAUTOMOTIVEINDUSTRYISSTILLONEOFTHELARGESTUSERSOFPLCS2DEVELOPMENTEARLYPLCSWEREDESIGNEDTOREPLACERELAYLOGICSYSTEMSTHESEPLCSWEREPROGRAMMEDIN“LADDERLOGIC“,WHICHSTRONGLYRESEMBLESASCHEMATICDIAGRAMOFRELAYLOGICTHISPROGRAMNOTATIONWASCHOSENTOREDUCETRAININGDEMANDSFORTHEEXISTINGTECHNICIANSOTHEREARLYPLCSUSEDAFORMOFINSTRUCTIONLISTPROGRAMMING,BASEDONASTACKBASEDLOGICSOLVERMODERNPLCSCANBEPROGRAMMEDINAVARIETYOFWAYS,FROMLADDERLOGICTOMORETRADITIONALPROGRAMMINGLANGUAGESSUCHASBASICANDCANOTHERMETHODISSTATELOGIC,AVERYHIGHLEVELPROGRAMMINGLANGUAGEDESIGNEDTOPROGRAMPLCSBASEDONSTATETRANSITIONDIAGRAMSMANYEARLYPLCSDIDNOTHAVEACCOMPANYINGPROGRAMMINGTERMINALSTHATWERECAPABLEOFGRAPHICALREPRESENTATIONOFTHELOGIC,ANDSOTHELOGICWASINSTEADREPRESENTEDASASERIESOFLOGICEXPRESSIONSINSOMEVERSIONOFBOOLEANFORMAT,SIMILARTOBOOLEANALGEBRAASPROGRAMMINGTERMINALSEVOLVED,ITBECAMEMORECOMMONFORLADDERLOGICTOBEUSED,FORTHEAFOREMENTIONEDREASONSNEWERFORMATSSUCHASSTATELOGICANDFUNCTIONBLOCKWHICHISSIMILARTOTHEWAYLOGICISDEPICTEDWHENUSINGDIGITALINTEGRATEDLOGICCIRCUITSEXIST,BUTTHEYARESTILLNOTASPOPULARASLADDERLOGICAPRIMARYREASONFORTHISISTHATPLCSSOLVETHELOGICINAPREDICTABLEANDREPEATINGSEQUENCE,ANDLADDERLOGICALLOWSTHEPROGRAMMERTHEPERSONWRITINGTHELOGICTOSEEANYISSUESWITHTHETIMINGOFTHELOGICSEQUENCEMOREEASILYTHANWOULDBEPOSSIBLEINOTHERFORMATS21PROGRAMMINGEARLYPLCS,UPTOTHEMID1980S,WEREPROGRAMMEDUSINGPROPRIETARYPROGRAMMINGPANELSORSPECIALPURPOSEPROGRAMMINGTERMINALS,WHICHOFTENHADDEDICATEDFUNCTIONKEYSREPRESENTINGTHEVARIOUSLOGICALELEMENTSOFPLCPROGRAMSPROGRAMSWERESTOREDONCASSETTETAPECARTRIDGESFACILITIESFORPRINTINGANDDOCUMENTATIONWEREVERYMINIMALDUETOLACKOFMEMORYCAPACITYTHEVERYOLDESTPLCSUSEDNONVOLATILEMAGNETICCOREMEMORYMORERECENTLY,PLCSAREPROGRAMMEDUSINGAPPLICATIONSOFTWAREONPERSONALCOMPUTERSTHECOMPUTERISCONNECTEDTOTHEPLCTHROUGHETHERNET,RS232,RS485ORRS422CABLINGTHEPROGRAMMINGSOFTWAREALLOWSENTRYANDEDITINGOFTHELADDERSTYLELOGICGENERALLYTHESOFTWAREPROVIDESFUNCTIONSFORDEBUGGINGANDTROUBLESHOOTINGTHEPLCSOFTWARE,FOREXAMPLE,BYHIGHLIGHTINGPORTIONSOFTHELOGICTOSHOWCURRENTSTATUSDURINGOPERATIONORVIASIMULATIONTHESOFTWAREWILLUPLOADANDDOWNLOADTHEPLCPROGRAM,FORBACKUPANDRESTORATIONPURPOSESINSOMEMODELSOFPROGRAMMABLECONTROLLER,THEPROGRAMISTRANSFERREDFROMAPERSONALCOMPUTERTOTHEPLCTHOUGHAPROGRAMMINGBOARDWHICHWRITESTHEPROGRAMINTOAREMOVABLECHIPSUCHASANEEPROMOREPROM3FUNCTIONALITYTHEFUNCTIONALITYOFTHEPLCHASEVOLVEDOVERTHEYEARSTOINCLUDESEQUENTIALRELAYCONTROL,MOTIONCONTROL,PROCESSCONTROL,DISTRIBUTEDCONTROLSYSTEMSANDNETWORKINGTHEDATAHANDLING,STORAGE,PROCESSINGPOWERANDCOMMUNICATIONCAPABILITIESOFSOMEMODERNPLCSAREAPPROXIMATELYEQUIVALENTTODESKTOPCOMPUTERSPLCLIKEPROGRAMMINGCOMBINEDWITHREMOTEI/OHARDWARE,ALLOWAGENERALPURPOSEDESKTOPCOMPUTERTOOVERLAPSOMEPLCSINCERTAINAPPLICATIONSREGARDINGTHEPRACTICALITYOFTHESEDESKTOPCOMPUTERBASEDLOGICCONTROLLERS,ITISIMPORTANTTONOTETHATTHEYHAVENOTBEENGENERALLYACCEPTEDINHEAVYINDUSTRYBECAUSETHEDESKTOPCOMPUTERSRUNONLESSSTABLEOPERATINGSYSTEMSTHANDOPLCS,ANDBECAUSETHEDESKTOPCOMPUTERHARDWAREISTYPICALLYNOTDESIGNEDTOTHESAMELEVELSOFTOLERANCETOTEMPERATURE,HUMIDITY,VIBRATION,ANDLONGEVITYASTHEPROCESSORSUSEDINPLCSINADDITIONTOTHEHARDWARELIMITATIONSOFDESKTOPBASEDLOGIC,OPERATINGSYSTEMSSUCHASWINDOWSDONOTLENDTHEMSELVESTODETERMINISTICLOGICEXECUTION,WITHTHERESULTTHATTHELOGICMAYNOTALWAYSRESPONDTOCHANGESINLOGICSTATEORINPUTSTATUSWITHTHEEXTREMECONSISTENCYINTIMINGASISEXPECTEDFROMPLCSSTILL,SUCHDESKTOPLOGICAPPLICATIONSFINDUSEINLESSCRITICALSITUATIONS,SUCHASLABORATORYAUTOMATIONANDUSEINSMALLFACILITIESWHERETHEAPPLICATIONISLESSDEMANDINGANDCRITICAL,BECAUSETHEYAREGENERALLYMUCHLESSEXPENSIVETHANPLCSINMORERECENTYEARS,SMALLPRODUCTSCALLEDPLRSPROGRAMMABLELOGICRELAYS,ANDALSOBYSIMILARNAMES,HAVEBECOMEMORECOMMONANDACCEPTEDTHESEAREVERYMUCHLIKEPLCS,ANDAREUSEDINLIGHTINDUSTRYWHEREONLYAFEWPOINTSOFI/OIEAFEWSIGNALSCOMINGINFROMTHEREALWORLDANDAFEWGOINGOUTAREINVOLVED,ANDLOWCOSTISDESIREDTHESESMALLDEVICESARETYPICALLYMADEINACOMMONPHYSICALSIZEANDSHAPEBYSEVERALMANUFACTURERS,ANDBRANDEDBYTHEMAKERSOFLARGERPLCSTOFILLOUTTHEIRLOWENDPRODUCTRANGEPOPULARNAMESINCLUDEPICOCONTROLLER,NANOPLC,ANDOTHERNAMESIMPLYINGVERYSMALLCONTROLLERSMOSTOFTHESEHAVEBETWEEN8AND12DIGITALINPUTS,4AND8DIGITALOUTPUTS,ANDUPTO2ANALOGINPUTSSIZEISUSUALLYABOUT4“WIDE,3“HIGH,AND3“DEEPMOSTSUCHDEVICESINCLUDEATINYPOSTAGESTAMPSIZEDLCDSCREENFORVIEWINGSIMPLIFIEDLADDERLOGICONLYAVERYSMALLPORTIONOFTHEPROGRAMBEINGVISIBLEATAGIVENTIMEANDSTATUSOFI/OPOINTS,ANDTYPICALLYTHESESCREENSAREACCOMPANIEDBYA4WAYROCKERPUSHBUTTONPLUSFOURMORESEPARATEPUSHBUTTONS,SIMILARTOTHEKEYBUTTONSONAVCRREMOTECONTROL,ANDUSEDTONAVIGATEANDEDITTHELOGICMOSTHAVEASMALLPLUGFORCONNECTINGVIARS232ORRS485TOAPERSONALCOMPUTERSOTHATPROGRAMMERSCANUSESIMPLEWINDOWSAPPLICATIONSFORPROGRAMMINGINSTEADOFBEINGFORCEDTOUSETHETINYLCDANDPUSHBUTTONSETFORTHISPURPOSEUNLIKEREGULARPLCSTHATAREUSUALLYMODULARANDGREATLYEXPANDABLE,THEPLRSAREUSUALLYNOTMODULAROREXPANDABLE,BUTTHEIRPRICECANBETWOORDERSOFMAGNITUDELESSTHANAPLCANDTHEYSTILLOFFERROBUSTDESIGNANDDETERMINISTICEXECUTIONOFTHELOGIC4PLCTOPICS41FEATURESTHEMAINDIFFERENCEFROMOTHERCOMPUTERSISTHATPLCSAREARMOREDFORSEVERECONDITIONSSUCHASDUST,MOISTURE,HEAT,COLDANDHAVETHEFACILITYFOREXTENSIVEINPUT/OUTPUTI/OARRANGEMENTSTHESECONNECTTHEPLCTOSENSORSANDACTUATORSPLCSREADLIMITSWITCHES,ANALOGPROCESSVARIABLESSUCHASTEMPERATUREANDPRESSURE,ANDTHEPOSITIONSOFCOMPLEXPOSITIONINGSYSTEMSSOMEUSEMACHINEVISIONONTHEACTUATORSIDE,PLCSOPERATEELECTRICMOTORS,PNEUMATICORHYDRAULICCYLINDERS,MAGNETICRELAYS,SOLENOIDS,ORANALOGOUTPUTSTHEINPUT/OUTPUTARRANGEMENTSMAYBEBUILTINTOASIMPLEPLC,ORTHEPLCMAYHAVEEXTERNALI/OMODULESATTACHEDTOACOMPUTERNETWORKTHATPLUGSINTOTHEPLC42SYSTEMSCALEASMALLPLCWILLHAVEAFIXEDNUMBEROFCONNECTIONSBUILTINFORINPUTSANDOUTPUTSTYPICALLY,EXPANSIONSAREAVAILABLEIFTHEBASEMODELHASINSUFFICIENTI/OMODULARPLCSHAVEACHASSISALSOCALLEDARACKINTOWHICHAREPLACEDMODULESWITHDIFFERENTFUNCTIONSTHEPROCESSORANDSELECTIONOFI/OMODULESISCUSTOMISEDFORTHEPARTICULARAPPLICATIONSEVERALRACKSCANBEADMINISTEREDBYASINGLEPROCESSOR,ANDMAYHAVETHOUSANDSOFINPUTSANDOUTPUTSASPECIALHIGHSPEEDSERIALI/OLINKISUSEDSOTHATRACKSCANBEDISTRIBUTEDAWAYFROMTHEPROCESSOR,REDUCINGTHEWIRINGCOSTSFORLARGEPLANTS43USERINTERFACEPLCSMAYNEEDTOINTERACTWITHPEOPLEFORTHEPURPOSEOFCONFIGURATION,ALARMREPORTINGOREVERYDAYCONTROLASIMPLESYSTEMMAYUSEBUTTONSANDLIGHTSTOINTERACTWITHTHEUSERTEXTDISPLAYSAREAVAILABLEASWELLASGRAPHICALTOUCHSCREENSMORECOMPLEXSYSTEMSUSEAPROGRAMMINGANDMONITORINGSOFTWAREINSTALLEDONACOMPUTER,WITHTHEPLCCONNECTEDVIAACOMMUNICATIONINTERFACE44COMMUNICATIONSPLCSHAVEBUILTINCOMMUNICATIONSPORTS,USUALLY9PINRS232,BUTOPTIONALLYEIA485ORETHERNETMODBUS,BACNETORDF1ISUSUALLYINCLUDEDASONEOFTHECOMMUNICATIONSPROTOCOLSOTHEROPTIONSINCLUDEVARIOUSFIELDBUSESSUCHASDEVICENETORPROFIBUSOTHERCOMMUNICATIONSPROTOCOLSTHATMAYBEUSEDARELISTEDINTHELISTOFAUTOMATIONPROTOCOLSMOSTMODERNPLCSCANCOMMUNICATEOVERANETWORKTOSOMEOTHERSYSTEM,SUCHASACOMPUTERRUNNINGASCADASUPERVISORYCONTROLANDDATAACQUISITIONSYSTEMORWEBBROWSERPLCSUSEDINLARGERI/OSYSTEMSMAYHAVEPEERTOPEERP2PCOMMUNICATIONBETWEENPROCESSORSTHISALLOWSSEPARATEPARTSOFACOMPLEXPROCESSTOHAVEINDIVIDUALCONTROLWHILEALLOWINGTHESUBSYSTEMSTOCOORDINATEOVERTHECOMMUNICATIONLINKTHESECOMMUNICATIONLINKSAREALSOOFTENUSEDFORHMIDEVICESSUCHASKEYPADSORPCTYPEWORKSTATIONS45PROGRAMMINGPLCPROGRAMSARETYPICALLYWRITTENINASPECIALAPPLICATIONONAPERSONALCOMPUTER,THENDOWNLOADEDBYADIRECTCONNECTIONCABLEOROVERANETWORKTOTHEPLCTHEPROGRAMISSTOREDINTHEPLCEITHERINBATTERYBACKEDUPRAMORSOMEOTHERNONVOLATILEFLASHMEMORYOFTEN,ASINGLEPLCCANBEPROGRAMMEDTOREPLACETHOUSANDSOFRELAYSUNDERTHEIEC611313STANDARD,PLCSCANBEPROGRAMMEDUSINGSTANDARDSBASEDPROGRAMMINGLANGUAGESAGRAPHICALPROGRAMMINGNOTATIONCALLEDSEQUENTIALFUNCTIONCHARTSISAVAILABLEONCERTAINPROGRAMMABLECONTROLLERSINITIALLYMOSTPLCSUTILIZEDLADDERLOGICDIAGRAMPROGRAMMING,AMODELWHICHEMULATEDELECTROMECHANICALCONTROLPANELDEVICESSUCHASTHECONTACTANDCOILSOFRELAYSWHICHPLCSREPLACEDTHISMODELREMAINSCOMMONTODAYIEC611313CURRENTLYDEFINESFIVEPROGRAMMINGLANGUAGESFORPROGRAMMABLECONTROLSYSTEMSFBDFUNCTIONBLOCKDIAGRAM,LDLADDERDIAGRAM,STSTRUCTUREDTEXT,SIMILARTOTHEPASCALPROGRAMMINGLANGUAGE,ILINSTRUCTIONLIST,SIMILARTOASSEMBLYLANGUAGEANDSFCSEQUENTIALFUNCTIONCHARTTHESETECHNIQUESEMPHASIZELOGICALORGANIZATIONOFOPERATIONSWHILETHEFUNDAMENTALCONCEPTSOFPLCPROGRAMMINGARECOMMONTOALLMANUFACTURERS,DIFFERENCESINI/OADDRESSING,MEMORYORGANIZATIONANDINSTRUCTIONSETSMEANTHATPLCPROGRAMSARENEVERPERFECTLYINTERCHANGEABLEBETWEENDIFFERENTMAKERSEVENWITHINTHESAMEPRODUCTLINEOFASINGLEMANUFACTURER,DIFFERENTMODELSMAYNOTBEDIRECTLYCOMPATIBLE5PLCCOMPAREDWITHOTHERCONTROLSYSTEMSPLCSAREWELLADAPTEDTOARANGEOFAUTOMATIONTASKSTHESEARETYPICALLYINDUSTRIALPROCESSESINMANUFACTURINGWHERETHECOSTOFDEVELOPINGANDMAINTAININGTHEAUTOMATIONSYSTEMISHIGHRELATIVETOTHETOTALCOSTOFTHEAUTOMATION,ANDWHERECHANGESTOTHESYSTEMWOULDBEEXPECTEDDURINGITSOPERATIONALLIFEPLCSCONTAININPUTANDOUTPUTDEVICESCOMPATIBLEWITHINDUSTRIALPILOTDEVICESANDCONTROLSLITTLEELECTRICALDESIGNISREQUIRED,ANDTHEDESIGNPROBLEMCENTERSONEXPRESSINGTHEDESIREDSEQUENCEOFOPERATIONSPLCAPPLICATIONSARETYPICALLYHIGHLYCUSTOMIZEDSYSTEMSSOTHECOSTOFAPACKAGEDPLCISLOWCOMPAREDTOTHECOSTOFASPECIFICCUSTOMBUILTCONTROLLERDESIGNONTHEOTHERHAND,INTHECASEOFMASSPRODUCEDGOODS,CUSTOMIZEDCONTROLSYSTEMSAREECONOMICDUETOTHELOWERCOSTOFTHECOMPONENTS,WHICHCANBEOPTIMALLYCHOSENINSTEADOFA“GENERIC“SOLUTION,ANDWHERETHENONRECURRINGENGINEERINGCHARGESARESPREADOVERTHOUSANDSORMILLIONSOFUNITSFORHIGHVOLUMEORVERYSIMPLEFIXEDAUTOMATIONTASKS,DIFFERENTTECHNIQUESAREUSEDFOREXAMPLE,ACONSUMERDISHWASHERWOULDBECONTROLLEDBYANELECTROMECHANICALCAMTIMERCOSTINGONLYAFEWDOLLARSINPRODUCTIONQUANTITIESAMICROCONTROLLERBASEDDESIGNWOULDBEAPPROPRIATEWHEREHUNDREDSORTHOUSANDSOFUNITSWILLBEPRODUCEDANDSOTHEDEVELOPMENTCOSTDESIGNOFPOWERSUPPLIES,INPUT/OUTPUTHARDWAREANDNECESSARYTESTINGANDCERTIFICATIONCANBESPREADOVERMANYSALES,ANDWHERETHEENDUSERWOULDNOTNEEDTOALTERTHECONTROLAUTOMOTIVEAPPLICATIONSAREANEXAMPLEMILLIONSOFUNITSAREBUILTEACHYEAR,ANDVERYFEWENDUSERSALTERTHEPROGRAMMINGOFTHESECONTROLLERSHOWEVER,SOMESPECIALTYVEHICLESSUCHASTRANSITBUSSESECONOMICALLYUSEPLCSINSTEADOFCUSTOMDESIGNEDCONTROLS,BECAUSETHEVOLUMESARELOWANDTHEDEVELOPMENTCOSTWOULDBEUNECONOMICVERYCOMPLEXPROCESSCONTROL,SUCHASUSEDINTHECHEMICALINDUSTRY,MAYREQUIREALGORITHMSANDPERFORMANCEBEYONDTHECAPABILITYOFEVENHIGHPERFORMANCEPLCSVERYHIGHSPEEDORPRECISIONCONTROLSMAYALSOREQUIRECUSTOMIZEDSOLUTIONSFOREXAMPLE,AIRCRAFTFLIGHTCONTROLSPROGRAMMABLECONTROLLERSAREWIDELYUSEDINMOTIONCONTROL,POSITIONINGCONTROLANDTORQUECONTROLSOMEMANUFACTURERSPRODUCEMOTIONCONTROLUNITSTOBEINTEGRATEDWITHPLCSOTHATGCODEINVOLVINGACNCMACHINECANBEUSEDTOINSTRUCTMACHINEMOVEMENTSPLCSMAYINCLUDELOGICFORSINGLEVARIABLEFEEDBACKANALOGCONTROLLOOP,A“PROPORTIONAL,INTEGRAL,DERIVATIVE“OR“PIDCONTROLLER“APIDLOOPCOULDBEUSEDTOCONTROLTHETEMPERATUREOFAMANUFACTURINGPROCESS,FOREXAMPLEHISTORICALLYPLCSWEREUSUALLYCONFIGUREDWITHONLYAFEWANALOGCONTROLLOOPSWHEREPROCESSESREQUIREDHUNDREDSORTHOUSANDSOFLOOPS,ADISTRIBUTEDCONTROLSYSTEMDCSWOULDINSTEADBEUSEDASPLCSHAVEBECOMEMOREPOWERFUL,THEBOUNDARYBETWEENDCSANDPLCAPPLICATIONSHASBECOMELESSDISTINCTPLCSHAVESIMILARFUNCTIONALITYASREMOTETERMINALUNITSANRTU,HOWEVER,USUALLYDOESNOTSUPPORTCONTROLALGORITHMSORCONTROLLOOPSASHARDWARERAPIDLYBECOMESMOREPOWERFULANDCHEAPER,RTUS,PLCSANDDCSSAREINCREASINGLYBEGINNINGTOOVERLAPINRESPONSIBILITIES,ANDMANYVENDORSSELLRTUSWITHPLCLIKEFEATURESANDVICEVERSATHEINDUSTRYHASSTANDARDIZEDONTHEIEC611313FUNCTIONALBLOCKLANGUAGEFORCREATINGPROGRAMSTORUNONRTUSANDPLCS,ALTHOUGHNEARLYALLVENDORSALSOOFFERPROPRIETARYALTERNATIVESANDASSOCIATEDDEVELOPMENTENVIRONMENTS6DIGITALANDANALOGSIGNALSDIGITALORDISCRETESIGNALSBEHAVEASBINARYSWITCHES,YIELDINGSIMPLYANONOROFFSIGNAL1OR0,TRUEORFALSE,RESPECTIVELYPUSHBUTTONS,LIMITSWITCHES,ANDPHOTOELECTRICSENSORSAREEXAMPLESOFDEVICESPROVIDINGADISCRETESIGNALDISCRETESIGNALSARESENTUSINGEITHERVOLTAGEORCURRENT,WHEREASPECIFICRANGEISDESIGNATEDASONANDANOTHERASOFFFOREXAMPLE,APLCMIGHTUSE24VDCI/O,WITHVALUESABOVE22VDCREPRESENTINGON,VALUESBELOW2VDCREPRESENTINGOFF,ANDINTERMEDIATEVALUESUNDEFINEDINITIALLY,PLCSHADONLYDISCRETEI/OANALOGSIGNALSARELIKEVOLUMECONTROLS,WITHARANGEOFVALUESBETWEENZEROANDFULLSCALETHESEARETYPICALLYINTERPRETEDASINTEGERVALUESCOUNTSBYTHEPLC,WITHVARIOUSRANGESOFACCURACYDEPENDINGONTHEDEVICEANDTHENUMBEROFBITSAVAILABLETOSTORETHEDATAASPLCSTYPICALLYUSE16BITSIGNEDBINARYPROCESSORS,THEINTEGERVALUESARELIMITEDBETWEEN32,768AND32,767PRESSURE,TEMPERATURE,FLOW,ANDWEIGHTAREOFTENREPRESENTEDBYANALOGSIGNALSANALOGSIGNALSCANUSEVOLTAGEORCURRENTWITHAMAGNITUDEPROPORTIONALTOTHEVALUEOFTHEPROCESSSIGNALFOREXAMPLE,ANANALOG010VINPUTOR420MAWOULDBECONVERTEDINTOANINTEGERVALUEOF032767可编程逻辑控制器可编程逻辑控制器(PLC)或可编程序控制器是用于机电过程自动化的数字计算机,例如控制机械厂生产线、游乐设施或照明装置。可编程控制器在许多工业和机器中使用。与通用的计算机不同的是,PLC是专为多个输入和输出管理,扩展温度范围、不受电磁噪音影响、抗震动和冲击所设计。控制器的操作程序通常存储在电池供电或非易失性的内存中。PLC是实时的系统,因为系统产生的输出结果必须在有限的时间内回馈到输入,否则会导致错误操作。1历史PLC发明是针对于美国汽车制造行业的需要。可编程逻辑控制器最初通过了在软件版本更换硬连线的控制板生产模式更改时的汽车工业。在PLC之前,控制、程序化和安全联锁逻辑制造汽车是使用上百或上千的继电器、凸轮计时器、鼓定序仪和专用的闭环控制器来完成的。在每年更新模型等设施转变过程是非常耗时并且成本高昂的,这是因为电工需要单独地再接电线给每个中转。在1968年GMHYDRAMATIC(自动输电分局)发布通用汽车公司的提议,电子替代布线中继系统。获奖的提案来自贝得福得,马萨诸塞的贝得福得同事。第一个PLC选定084,因为它是贝得福得同事的第八十四个项目。贝得福得同事建立了一家新的公司致力开发、生产、销售,和服务这一新产品MODICON,代表模块化数字控制器。迪克莫利,被认为是PLC之父,他是从事该项目的人之一。1977年古尔德电子公司当前所有者收购法国施耐德电气公司同德国公司AEG并售予该品牌为MODICON。084模型之一首次被设在北部安多弗的MODICON总部马萨诸塞州。这是专门为通用汽车服务的,并且经过了近二十多年的不间断服务。直至984出现,MODICON使用的84名字才在其产品范围中结束。汽车工业仍是PLC的最大用户之一。2发展早期的可编程控制器是设计来取代继电器逻辑系统。这些可编程控制器的“阶梯逻辑”是与继电器逻辑示意图非常类似的。选择此程序表示法的目的是为了减少对现有技术人员的培训需求。其他早期的可编程控制器使用指令列表编程,基于一个堆栈编程逻辑求解器进行求解。现代可编程控制器在各种各样的方式可以被编程,从梯形逻辑语言到更加传统的编程语言例如BASIC和C语言。另一个方法是状态逻辑,被设计的一种非常高级编程语言根据状态转换图的可编程控制器编程。很多早期可编程控制器没有可编程终端的逻辑图形表示法,逻辑反而是被描绘成一系列在一些版本的布尔格式的逻辑表达式,类似于布尔代数。随着编程码发展,由于上述原因它变成更常见的梯形逻辑语言。更新的格式如国家逻辑和功能块(这是类似的逻辑描述使用数字逻辑集成电路时的方式)的存在,但它们仍没有梯形逻辑语言流行。一个主要原因是可编程控制器解决问题用一个可预测和重复的序列的逻辑,并且梯形逻辑语言可以用其他格式让程序员(写逻辑)的人看到逻辑的时间,所有问题更加容易地程序化。21编程早期的PLC,到80年代中期,都是用专有的编程版或专用编程终端,往往有专门的功能键,代表各种PLC程序逻辑元件。程序存储在盒式磁带盒上。由于缺少的内存容量很少用于打印设备。最古老的可编程控制器使用的是非易失性磁核心内存。最期PLC在个人计算机上使用应用软件编程。计算机连接到PLC通过以太网RS232,RS485或RS422缆线连接。编程软件允许输入梯式逻辑编程。通常,软件提供了用于调试和故障排除的功能,例如在操作过程中或通过仿真的逻辑部分PLC软件突出显示当前状态。该软件将上传和下载PLC程序以便备份和恢复。在某些型号的PLC中虽然程序写入一个可移动的芯片,如EEPROM或EPROM,但该方案还是得从个人电脑传输到PLC编程版。3功能PLC的功能经过多年的发展,包括连续的继电器控制,运动控制,过程控制,分布式控制系统和网络。一些现代PLC的数据处理,存储,处理能力和通信能力相当于台式电脑。PLC编程结合远程I/O硬件,一台通用台式计算机允许在某些应用中重叠使用某一可编程控制器。在重工业中PLC被认为没有这些桌面计算机为主的逻辑控制器的实际性强,因为PLC在台式计算机系统中运行不是很稳定,并且,因为台式计算机硬件没有被设计成耐温度、湿气、振动和耐用作为可编程控制器的处理器。除桌面基于逻辑的硬件局限之外,例如WINDOWS操作系统不适合自己的确定性逻辑的执行,结果是PLC逻辑不可能总是对规定逻辑变化的输入状态与极端性预计的时间一致。尽管如此,这样桌面逻辑被应用在较不重要情况,像实验室自动化和小型设施中使用该应用程序的要求不高,因为他们的价格一般都远远低于昂贵的PLC。在最近数年,小产品称为PLR(可编程逻辑继电器),并且因为名字相似,变得更常见并被接受。这些很像PLC已经应用于轻工业,它只有少部分的输入/输出(例如一些真实的输入输出信号)参与,低成本,很理想。这些小设备尺寸和形状比较普通地几位制造商制作,并且由更大的PLC制作商来填满他们低端产品规格。俗名包括PICO控制器、纳米PLC和其他的小控制器。多数这些控制器有在8到12数字输入、4到8数字输出,多达2个模拟输入。尺寸通常是4英寸宽、3英寸高、3英寸深。大多数这样的设备有一个小邮票大小的液晶屏幕来观看简化梯子逻辑的输入/输出点(只有一小部分程序被可见于给定的时间)和状况,并且这些屏幕由一个电磁四通摇臂按钮操纵加上四个不同的用于浏览和编辑的逻辑电钮,类似于录像机遥控按钮。控制器大多数有一个小插座为通过连接RS232或RS485到个人计算机,以便程序员可能为编程使用简单的窗口应用而不是被迫使用微小的LCD和电钮。不像普通PLC,通常是模块化,大大扩展,控制器通常不会取模块化并且不是可扩展的,但是他们提供稳健设计的确定性和执行逻辑的价值比PLC少。4可编程序控制器PLC41未来发展从其他计算机来看,主要区别是可编程控制器具有特殊条件(例如,灰尘、湿、热、冷)和具有广泛的输入/输出(I/O)安排的设施。这些是连接PLC的传感器和执行器。可编程控制器是读取限制开关、模拟过程变量(如温度和压力)以及位置复杂的定位系统。有些人利用机器系统来查看光源与照明。执行器使可编程控制器操作电子电机、气动或液压缸、磁继电器、电磁线圈的模拟输出。输入/输出的安排可以建立一个简单的可编程控制器、或可编程序控制器可以用外部的I/O模块连接插入的计算机网络。42系统规模一个小的PLC是固定数量的输入和输出生成的连接。如果基础模型具有足够的I/O通常可扩展。模块化可编程控制器有一个机箱(也称为机架)在其中放置具有不同的功能模块。处理器和I/O模块的选择被定制为特定的应用程序。几个机架可以有一个单个的处理器,可能会有成千上万的输入和输出。一种特殊的高速串行I/O环节是机架减少多个线路使用分布式离散处理器。43使用界面可编程控制器的配置、报警报告或日常控件可能需要与人进行交互。一个简单的系统可能使用按钮和指示灯与用户进行交互。可以用图形触摸屏文本显示。更复杂的系统使用PLC通过通信接口连接到一台计算机上安装的编程和监测软件来使用。44通信可编程控制器被建于通常的9针RS232,也可以选择485或以太网的通信端口由环境影响评估。协议、BACNET或东方是通常作为通信协议之一包含其中。其它选项包括各项如构架或现场总线。在自动化
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本文标题:毕业设计(论文)-金属管件气密性检测装置的控制系统设计
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