VIRTUAL INSTRUMENTATION AND DISTRIBUTED MEASUREMENT SYSTEMS

REVIEWS-LETTERS-REPORTS

VIRTUALINSTRUMENTATIONANDDISTRIBUTEDMEASUREMENTSYSTEMS

ViktorSmieˇsko—KarolKov´aˇc

∗

Thedevelopmentanduseofprogrammablemeasurementsystemshavebeenwidelyexplored.Thepossibilityofmodifying

themeasurementproceduresimplybychangingthealgorithmexecutedbythecomputer-basedarchitecturewithoutreplacingthehardwarecomponentsmakestheexperimentalactivityeasier.Virtualmeasurementsystemshavebeenintroducedtosimplifythedesign,implementationanduseofprogrammablemeasurementsystemsbyadoptingavisualinterface.Networkinghasalsobeenintroducedsuccessfullyinmeasurementtointerconnectdifferentinstrumentsanddataprocessingsitesintoadistributedmeasurementsystem(DMS).IndustriesthatdevelopanduseDMSaremigratingawayfromproprietaryhardwareandsoftwareplatformsinfavourofopensystemsandstandardizedapproaches.

Keywords:virtualinstrumentation,distributedmeasurementsystem,remoteandnetworkedmeasurement,intercon-nectbuses.

1INTRODUCTION

Formanyyearselectronicinstrumentshavebeeneasilyidentifiedproducts.Althoughtheyrangedinsizeandfunctionality,theyalltendedtobebox-shapedobjectswithacontrolpanelandadisplay.Stand-aloneelectronicinstrumentsareverypowerful,expensiveanddesignedtoperformoneormorespecifictasksdefinedbythevendor.However,theusergenerallycannotextendorcustomizethem.Theknobsandbuttonsontheinstrument,thebuilt-incircuitry,andthefunctionsavailabletotheuser,allofthesearespecifictothenatureoftheinstrument.Inaddition,specialtechnologyandcostlycomponentsmustbedevelopedtobuildtheseinstruments,makingthemveryexpensiveandhardtoadapt.

WidespreadadoptionofthePCoverthepasttwentyyearshasgivenrisetoanewwayforscientistsandengi-neerstomeasureandautomatetheworldaroundthem.OnemajordevelopmentresultingfromtheubiquityofthePCistheconceptofvirtualinstrumentation.Avirtualinstrumentconsistsofanindustry-standardcomputerorworkstationequippedwithoff-the-shelfapplicationsoft-ware,cost-effectivehardwaresuchasplug-inboards,anddriversoftware—whichtogetherperformthefunctionsoftraditionalinstruments.Todayvirtualinstrumentationiscomingofage,withengineersandscientistsusingvirtualinstrumentsinliterallyhundredsofthousandsofappli-cationsaroundtheglobe,resultinginfasterapplicationdevelopment,higherqualityproductsandlowercosts.Virtualinstrumentsrepresentafundamentalshiftfromtraditionalhardware-centredinstrumentationsys-temstowardssoftware-centredsystemsthatexploitthecomputingpower,productivity,displayandconnectivitycapabilitiesofpopulardesktopcomputersandworksta-tions.

AlthoughPCandintegratedcircuittechnologiesexpe-riencedsignificantadvancesinthepasttwodecades,itis

thesoftwarethatmakespossiblebuildingvirtualinstru-mentsonthisfoundation.Engineersandscientistsarenolongerlimitedbytraditionalfixed-functioninstruments.Nowtheycanbuildmeasurementandautomationsys-temsthatsuitexactlytheirspecificneeds.

2THECONCEPTIONOFVIRTUALINSTRUMENT

Usuallyinstrumentationmanufacturersprovidespe-cificfunctionstogivenarchitectureandfixedinterfacesformeasuringdevices,andthuslimittheapplicationdo-mainofthesedevices.Inactualusemuchtimeisrequiredforadjustingthemeasuringrangeandforsavinganddoc-umentingtheresults.

Theadventofmicroprocessorsinthemeasurementandinstrumentationfieldsproducedrapidmodificationsofmeasuringdevicetechnology,soonfollowedbytheappearanceofcomputer-basedmeasurementtechniques.Conceptualmodelofearly-computerizedinstrumentationisgiveninFig.1.

Asingleusercontrolsthesystem,whichrunsexclu-sivelyonapieceofhardware.Thereisasinglecontrolstructure,whichisformedbythecombinationoftheuserandtheprogramthatcontrolsthemultipledevicesat-tachedtotheinstrumentationbus.Themainchallengesarethedevicecouplingandtheprogrammingmodels.Themeasurementconsistsofthreeparts,asshowninFig.2,acquisitionofmeasurementdataorsignals,conditioningandprocessingofanalysisofmeasurementsignalsandpresentationofdata.

Theconceptofvirtualinstrumentisfrequentlyusedinindustrialmeasurementpractice,butnotalwayswithpreciselythesamemeaning.Forsomepeople,virtualin-strumentsarebasedonstandardcomputersandrepre-sentsystemsforstorage,processingandpresentationof

∗DepartmentofMeasurement,SlovakUniversityofTechnology,Ilkoviˇcova3,81219Bratislava,Slovakia

c2004FEISTUISSN1335-3632󰀁

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PROGRAMUSERDEVICEDRIVERINSTRUMENTATIONBUSDEVICE1DEVICE2DEVICEnPROCESSFig.1.Conceptualmodelofearlycomputerizedinstrumentation

SIGNALSACQUISITIONANDINSTRUMENTCONTROLPRESENTATIONPROCESSINGORANALYSISFig.2.Thediagramofmeasurementprocess

ADDEDHARDWAREPCADDEDSOFTWARESIGNALGENERATIONDATAPROCESSINGDATAPRESENTATIONDATAACQUISITIONFig.3.Thegeneralconceptionofvirtualinstrument

measurementdata.Forothers,avirtualinstrumentisacomputerequippedwithsoftwareforavarietyofusesin-cludingdriversforvariousperipherals,aswellasanaloguetodigitalanddigitaltoanalogueconverters,representinganalternativetoexpensiveconventionalinstrumentswithanaloguedisplaysandelectronics.Bothviewsaremoreorlesscorrect.Acquisitionofdatabyacomputercanbeachievedinvariouswaysandforthisreasontheunder-standingofthearchitectureofthemeasuringinstrumentbecomesimportant.

AvirtualinstrumentcanbedefinedasanintegrationofsensorsbyaPCequippedwithspecificdataacquisi-tionhardwareandsoftwaretopermitmeasurementdataacquisition,processinganddisplay.

AvirtualinstrumentcanreplacethetraditionalfrontpanelequippedwithbuttonsanddisplaybyavirtualfrontpanelonaPCmonitor.Virtualinstrumentsarea

meansofintegrationofthedisplay,controlandcentral-izationofcomplexmeasurementsystems.

Industrialinstrumentationapplications,however,re-quirehighrates,longdistances,andmulti-vendorin-strumentconnectivitybasedonopenindustrialnetworkprotocols.

Inordertoconstructavirtualinstrumentitisnec-essarytocombinethehardwareandsoftwareelementswhichshouldperformdataacquisitionandcontrol,dataprocessinganddatapresentationinadifferentwaytotakemaximumadvantageofthePC.Itseemsthatinthefuturetherestrictionsofinstrumentswillmovemoreandmorefromhardware.SuchageneralconceptionofvirtualinstrumentationispresentedinFig.3.

ThevendorofvirtualinstrumentcanusetheserialcommunicationbasedonRS-232standardortheparallelcommunicationbasedonGPIBstandard(knownalsoasHP-IB,IEEE488.1-2orIEC625.1-2),PCbus,orVXI-bus(VMEeXtensionforInstrumentation).Themaincategoriesofvirtualinstruments:

a)Graphicalfrontpanelonthecomputerscreentocon-trolthemodulesorinstruments

a1)controlledmoduleisplug-inDAQboard,

a2)controlledinstrumentisbasedonGP-IBboard,a3)controlledinstrumentisconnectedviaserialport,a4)controlledinstrumentisVXI-board(orsystem).b)Graphicalfrontpanelwithnophysicalinstrumentsatallconnectedtothecomputer.Instead,thecomputeracquiresandanalysesthedatafromfilesorfromothercomputersonanetwork,oritmayevencalculateitsdatamathematicallytosimulateaphysicalprocessoreventratherthanacquiringactualrealworlddata.TothePCconnectionsaccordingtopointa)thefol-lowingprocessmeasuringdevicesareattached:–Sensors

–GP-IBinstruments–Serialinstruments–VXIinstruments

Thisstructureisaresultofinternationalstandardizationallowingmorefreedominusingboardsandinstrumentsfromvariousmanufactures.

Themainrepresentativefeaturesofvirtualinstru-mentsdescribingtheirfunctionalityarefollowing:

–Enhancingtraditionalinstrumentfunctionalitywithcomputers;

–Openingthearchitectureofinstruments;

–Widespreadrecognitionandadoptionofvirtualinstru-mentsoftwaredevelopmentframeworks.

3BASICCOMPONENTSOFVIRTUALINSTRUMENTS

Thebasiccomponentsofallvirtualinstrumentsin-cludeacomputerandadisplay,thevirtualinstrumentsoftware,abusstructure(thatconnectsthecomputerwiththeinstrumenthardware)andtheinstrumenthard-ware.

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PCDAQGP-IBSERIALMXIBOARDBOARDPORTBOARDSENSORS„SERIAL“INSTRUMENTSGP-IBVXIINSTRUMENTSINSTRUMENTSPROCESFig.4.StructureofthePC-basedinstrumentationhardware

3.1ComputerandDisplay

Thecomputerandthedisplayaretheheartofvirtualinstrumentsystems.Thesesystemsaretypicallybasedonapersonalcomputerorworkstationwithahigh-resolutionmonitor,akeyboard,andamouse.Itisimpor-tantforthechosencomputertomeetthesystemrequire-mentsspecifiedbytheinstrumentationsoftwarepackages.RapidtechnologicaladvancementsofPCtechnologyhavegreatlyenhancedvirtualinstrumentation.MovingfromDOStoWindowsgavetoPCusersthegraphi-caluserinterfaceandmade32-bitsoftwareavailableforbuildingvirtualinstruments.Theadvancesinprocessorperformancesuppliedthepowerneededtobringnewap-plicationswithinthescopeofvirtualinstrumentation.Fasterbusarchitectures(suchasPCI)haveeliminatedthetraditionaldatatransferbottleneckofolderbuses(ISA).ThefutureofvirtualinstrumentationistightlycoupledwithPCtechnology.3.2Software

Ifthecomputeristheheartofthevirtualinstrumentsystems,thesoftwareistheirbrain.Thesoftwareuniquelydefinesthefunctionalityandpersonalityofthevirtualinstrumentsystem.Mostsoftwareisdesignedtorunonindustrystandardoperatingsystemsonpersonalcom-putersandworkstations.Softwareimplementedcanbedividedintoseverallevels,whichcanbedescribedinahierarchicalorder.

Registerlevelsoftware

Register-levelsoftwarerequirestheknowledgeofinnerregisterstructureofthedevice(DAQboard,RS232in-strument,GP-IBinstrumentorVXImodule)forenteringthebitcombinationtakenfromtheinstructionmanualinordertoprogrammeasurementfunctionsofthede-vice.Itisthehardestwayinprogramming.Theresultingprogramisstronglyhardwaredependentanditisrarelyexecutableonsystemswithdifferenthardware.

Driverlevelsoftware

Oneofthemostimportantcomponentsinmeasure-mentsystemstodayisthedevicedriversoftware.Device

driversperformtheactualcommunicationandcontroloftheinstrumenthardwareinthesystem.Theyprovideamedium-leveleasy-to-useprogrammingmodelthaten-ablescompleteaccesstocomplexmeasurementcapabili-tiesoftheinstrument.

Inthepastprogrammersspentasignificantamountoftimewritingthissoftwarefromscratchforeachinstru-mentofthesystem.Today,instrumentdriversaredeliv-eredasmodular,off-the-shelfcomponentstobeusedinapplicationprograms.Severalleadingcompaniesformed(in1988)theInterchangeableVirtualInstrument(IVI)Foundation.TheIVIFoundationwasformedtoestablishformalstandardsforinstrumentdriversandtoaddressthelimitationsoftheformerapproaches.High-leveltoolsoftware

Currentlythemostpopularwayofprogrammingisbasedonthehigh-leveltoolsoftware.Witheasy-to-usein-tegrateddevelopmenttools,designengineerscanquicklycreate,configureanddisplaymeasurementsinauser-friendlyform,duringproductdesign,andverification.Themostknown,populartoolsareasfollows:

•LabVIEW(LaboratoryVirtualInstrumentEngineer-ingWorkbench)—isahighlyproductivegraphicalpro-gramminglanguageforbuildingdataacquisitionandin-strumentationsystems.Tospecifythesystemfunction-alityoneintuitivelyassemblesblockdiagrams—anat-uraldesignnotationforengineers.Itstightintegrationwithmeasurementhardwarefacilitiesrapiddevelopmentofdataacquisition,analysisandpresentationofsolutions.•LabWindows/CVI(CforVirtualInstrumentation)—isaWindowsbased,interactiveANSICprogrammingenvironmentdesignedforbuildingvirtualinstrumenta-tionapplications.Itdeliversadrag-and-dropeditorforbuildinguserinterfaces,acompleteANSICenvironmentforbuildingtestprogramlogic,andacollectionofauto-matedcodegenerationtools,aswellasutilitiesforbuild-ingautomatedtestsystemsandmonitoringapplicationsoflaboratoryexperiments.ThemainpowerofCVIliesinthesetoflibraries.

•HPVEE(Hewlett-Packard’sVisualEngineeringEn-vironment)—allowsgraphicalprogrammingforinstru-mentationapplications.ItisakindofVisualEngineeringEnvironment,aniconicprogramminglanguageforsolv-ingengineeringproblems.Italsoprovidesanopportunitytogather,analyzeanddisplaydatawithoutconventional(text-based)programming.

•TestPoint—isaWindowsbasedobject-orientedsoft-warepackagethatcontainsextensiveGPIBinstrumentandDAQboardsupport.Itcontainsanovelstate-of-theartuserinterfacethatiseasytouse.Objects,called“stocks”areselectedanddraggedwithamousetoawork

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area(panel).Logicflowiseasilyestablishedwithapointanddragactionlist.TestPointtakesadvantageofeveryMicrosoftWindowsfeatures.

•MeasurementStudio—isameasurementtoolfordataacquisition,analysis,visualizationandInternetconnec-tivity.ThisdevelopmenttoolhelpsyoubuildyourtestsystembyintegratingintoyourexistingMicrosoftcom-piler.MeasurementStudioprovidesacollectionofcon-trolsandclassesdesignedforbuildingvirtualinstrumen-tationsystemsinsideVisualBasicorVisualC++.WithMeasurementStudioyoucanconfigureplug-indataac-quisitionboards,GPIBinstruments,andserialdevicesfrompropertypageswithoutwritinganycode.Withuserinterfacecomponentsyoucanconfigurereal-time2Dand3Dgraphs,knobs,meters,gauges,dials,tanks,ther-mometers,binaryswitches,andLEDs.WithpowerfulIn-ternetcomponents,youcansharelivemeasurementdataamongapplicationsviatheInternet.

SCPI—Standardcommandsforprogrammableinstruments

SCPIisnotasoftwaretoolasareformersystems,butitisaneffectiveaidenablingeasystandardisedcontrolofprogrammableinstruments.SCPIdecreasesdevelopmenttimeandincreasesareadabilityoftestprograms.SCPIprovidesaneasyunderstandablecommandset,guaran-teesawell-definedinstrumentbehaviourunderallcondi-tions,whichpreventsunexpectedinstrumentbehaviour.AlthoughIEEE488.2isusedasbasisofSCPI,itdefinesprogrammingcommandsthatwecanusewithanytypeofhardwareorcommunicationlink.Ithasanopenstruc-ture.TheSCPIConsortiumcontinuesinaddingcom-mandsandfunctionalitytotheSCPIstandard.

Real-timeandembeddedcontrolhasbeenlongthedomainofspecialisedprograms.Advancesinindustry-standardtechnologiesincludingmorereliableoperatingsystems,morepowerfulprocessorsandcomputer-basedreal-timeengineeringtoolsareintroducingnewlevelsofcontrolanddeterminismtovirtualinstrumentation.Thispresentsnewopportunitiesforscientiststotakeonin-creasinglysophisticatedreal-timeandembeddeddevelop-ment.SoftwarescalesacrossdevelopmentonthePCintodevelopmentinreal-timeandembeddedapplications.Sci-entistsandengineerscanmoveintonewapplicationareaswithoutasteeplearningcurvebecausethesoftwareitselfevolvestoincorporateemergingcomputertechnologies.3.3InterconnectBuses

Fourtypesofinterconnectbusesdominatetheindus-try:theserialconnection(serialport),theGPIB,thePCbusandVXIbus.

Serialport.SerialcommunicationbasedonRS-232standardisthesimplestwayofusingacomputerinmea-surementapplicationsandcontrolofinstruments.SerialcommunicationisreadilyavailableviatheserialportofanyPCanditislimitedindatatransmissionrateanddis-tance(upto19.2Kbytes/sec,recently115Kbytes/sec,

and15m)anditallowsonlyonedevicetobeconnectedtoaPC.

GPIB.Itwasthefirstindustrystandardbusforconnect-ingcomputerswithinstrumentation.AmajoradvantageofGPIBisthattheinterfacecanbeembeddedontherearofastandardinstrument.Thisallowsdualuseoftheinstrument:asastand-alonemanualinstrumentorasacomputer-controlledinstrument.Becauseofthisfea-ture,thereareawidevarietyofhigh-performanceGPIBinstrumentstochoosefrom.TheGPIBoffersaflexiblecablethatconnectsaGPIBinterfacecardinthecom-putertoupto15instrumentsoveradistanceofuptotwentymeters.Theinterfacecardcomeswithsoftwarethatallowstransmissionofcommandstoaninstrumentandreadingofresults.EachGPIBinstrumentcomeswithadocumentedlistofcommandsforinitiatingeachfunc-tion.Typically,thereisnoadditionalsoftwaredeliveredwiththeinstrument.GPIBhasamaximumdatarateof1Mbytes/sandtypicaldatatransfersarebetween100and250Kbytes/s.Itdependsontheresponseofthemea-suredsubject.

PC-bus.WiththerapidacceptanceoftheIBMper-sonalcomputerintestandmeasurementapplications,therehasbeenacorrespondinggrowthofplug-ininstru-mentationcardsthatareinsertedintospareslots.How-ever,high-accuracyinstrumentsrequiresignificantcir-cuitboardspacetoachievetheirintendedprecision.Be-causeofthelimitedprintedcircuitboardspaceandcloseproximitytosourcesofelectromagneticinterference,PCbusinstrumentstendtobeoflowerperformancethanGPIBinstrumentsbutalsooflowercost.ManyaresimpleADCs,DACs,anddigitalI/Ocards.PCbusinstrumen-tationisbestsuitedforcreatingsmall,inexpensiveacqui-sitionsystemswheretheperformanceisnotofparamountimportance.Sincethesecardsplugdirectlyintothecom-puterbackplaneandcontainnoembeddedcommandin-terpreterasfoundinGPIBinstruments,personalcom-puterplug-incardsarenearlyalwaysdeliveredwithdriversoftwaresothattheycanbeoperatedfromapersonalcomputer.Thissoftwaremayormaynotbecompati-blewithothervirtualinstrumentsoftwarepackages,soitisrecommendedtocheckwiththevendorsbeforehand.Mostdataacquisitionboardsaremultifunctional,ietheyacceptbothanalogueanddigitalsignals.Theseplug-indataacquisitionboardsgainwiderandwideracceptanceduetotheirlowpriceandhighflexibilityobtainedfromtheassociatedsoftware.

VXIbus.Inthelateeighties,theVMEeXtensionforInstrumentation(VXI)standardallowedcommunicationamongunitswithtransferover20Mbytes/secondbe-tweenVXIsystems.VXIinstrumentsareinstalledinarackandarecontrolledby,andcommunicatedirectlywith,aVXIcomputer.TheseVXIinstrumentsdonothavebuttonsorswitchesfordirectlocalcontrolanddonothavelocaldisplaytypicalintraditionalinstruments.Itisanopen-systeminstrumentarchitecturethatcom-binesmanyoftheadvantagesofGPIBandcomputerbackplanebuses.VXIbusinstrumentsareplug-inmod-ulesthatareinsertedintospeciallydesignedcardcages

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GPIBControllerToanotherGPIBinstrumentVXIMainframeGPIBINSTINSTRAMVXI#1#...INSTCPU2#3Fig.5.AVXIbussystemcontrolledbyGPIB

VXIMainframe

PC

INSTINSTRAM

T#1

...#2

...INSTINS#3#4

Fig.7.AVXIbussystemcontrolledbyanembeddedVXIbus

computerinsertedintothemainframe

knownas“mainframes”.Mainframesincludepowersup-plies,aircoolingequipmentandbackplanecommunica-tionforthemodules.TheVXIbusisuniqueinthatitcombinesacomputerbackplanebasedontheVME-busforhigh-speedcommunicationandoffersaqualityEMCenvironmentthatallowshigh-performanceinstrumenta-tionsimilartothatfoundinGPIB.Asaresult,muchmorecompactmeasuringsystemscanbebuilt.

TherearethreewaystocommunicatebetweenthecomputerandtheVXIbusinstruments.

a)ThefirstmethodisbyusingGPIB.Inthiscase,aGPIBtoVXIbusconvertermoduleispluggedintotheVXIbusmainframeandastandardinterfacecablecon-nectsitandtheGPIBinterfacecardinthecomputer.TheadvantagesanddisadvantagesofthistechniqueareverysimilartoapureGPIBdesign.Thissystemtendstobeeasytoprogram,butdataspeedsarelim-itedtoGPIBspeeds.However,becausetheinternaldataspeedswithintheVXIbusmainframecanexceed10Mbytes/s,oftenahigh-speedapplicationissolvedbylocalhigh-speedacquisitionandprocessingoccur-ringwithinthemainframeandhighlevelresultstrans-fertothecomputeroverGPIB.Figure5showsanex-ampleofVXIbussystemusingGPIB.

b)Thesecondtechniqueistouseahigher-speedinter-connectbusbetweentheVXIbusmainframeandthecomputer.Themostcommonimplementationofthisisahigh-speedflexible-cableinterfaceknownasMXIbus.AsinGPIB,anMXIbusinterfacecardandsoftwareareinstalledonthecomputerandacableattachesittoanMXIbustoVXIbusconvertermoduleintheVXIbusmainframe.MXIbusisessentiallyanimplementationoftheVXIbusonaflexiblecable.Thismeansthatthe

MXIVXIMainframeUNKINSTINSTRAMINSTCPUMXI#1#2...#3VXIFig.6.AVXIbussystemcontrolledoverahigh-speedMXIbus

cable

conversionstoVXIbusaresimpleandfast,bringingMXIbusperformancewithinafactorof2orsoofna-tiveVXIbusspeeds.TheadvantageofMXIbusisthatitallowstheuseofoff-the-shelfcomputerstocommu-nicatewithVXIbusinstrumentsataspeedconsider-ablyhigherthanGPIB.AdisadvantageisthattheMXIbuscablecanbethickandunwieldy,andthereissomelossofdata-transferbandwidthduetothecon-version.Figure6showsanexampleVXIbussystemusingMXIbus.

c)ThethirdwayistoinsertpowerfulVXIbuscomputersdirectlyintotheVXIbusmainframe.VXIbuscomput-erstendtoberepackagedversionsofindustrystandardpersonalcomputersandworkstationsthatrunindus-trystandardoperatingsystemsandsoftware.Thead-vantageofthistechniqueisthatitpreservesthefullcommunicationsperformanceofVXIbus.Thedisad-vantageisthatthechoiceofVXIbuscomputerswillalwaysbeasubsetofthechoiceofstandardindustrycomputers.VXIbuscomputertechnologywilltypicallylagbehindtheperformanceoftheindustryasawhole,offerfeweralternativeconfigurationsandbepricedatapremiumduetoitslowervolume.Figure7showsanexampleVXIbussystemusinganembeddedcomputer.3.4InstrumentHardware

Theprecedingsubsectiononinterfacesalsotouchesontheattributesfoundineachoftherespectiveinstrumenthardwareproducts.Onenoteisworthtoberepeated:Virtualinstrumentationnevereliminatestheinstrumenthardwarecompletely.Tomeasuretherealworldtherewillalwaysbesomesortofmeasurementhardware,sensor,transducerandconditioningcircuit,butthephysicalformfactorofthisinstrumentationmaycontinuetoevolve.

4DISTRIBUTEDMEASUREMENTSYSTEMS

Thepresenttrendininterconnectedmeasurementsys-temsistoextendtheareacoveredbytheinterconnectedsystemsinthegeographicalscale.Thissetsafurtherlimit

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FILETERMINALTERMINALTERMINALSERVER123LANCONTROLLERCONTROLLERCONTROLLERCONTROLLERGPIBDAQRS232VXIMXIGPIBRS232ININSTSTINSTRUMENTINSTRUMENTINSTRUMENTRRMXIU123UMEM...NENVXITT45Fig.8.Blockdiagramofdistributedmeasurementsystembased

onLAN

DISPLAYFILESFTPINTERNETDATAEXPLORERSOCKETURLCONTROLLFig.9.ThearchitectureofadistributedsystembasedonInternet

totheuseofsuchsystems.Asinthecaseoflargeandcom-plexplants,astructurednetworkedmeasurementsystemcanbeadoptedbyscalingitsusetothegeographicalarea.Thegeographicalprocesstobemonitoredandcontrolledispartitionedintocellsthatcanbedealtwithbyasin-gleprocessingunitoragroupoflocallyconnectedunits.Geographicallydistributedunitsareconnectedbyageo-graphicalcomputernetworkintoadistributedmeasure-mentsystem.Inthiscasecommunicationdelaysusuallycannotbeneglected.Thisisevenmorerelevantifthetraf-ficinthecomputernetworkisnotnegligibleduetothenumberofcomputersconnectedandtheamountofcom-munications,especiallyifapubliccomputernetworkisusedtorealisetheinterconnectionsamongthemeasuringprocessingunits.

Itseemsthatinthenearfuturelocalnetwork(LAN)canbeconsideredasakindofmeasurementbus,fromtheviewpointofmeasurementandcontrolsystems.AtypicalexampleofsuchasystemincludingvariousvirtualinstrumentsispresentedinFig.8.Itcanbeconsideredasafirststeptoawider,Internetbasedtechnology.Inthelastfewyearsasurprisinglyrapidgrowthoffastandreliablecommunicationnetworkshasallowedaneasyinterchangeofinformationandcommandsbetweencom-putersbothconnectedtolocalnetworksandconnectedtofarawaysiteofwideareanetworks(WAN),suchastheInternet.Thus,networkservicesandprogrammableinstrumentationnowpermitthedevelopmentofmeasure-mentlaboratoriesdistributedonawidegeographicalareaandsimultaneouslyavailabletoseveralusersvariouslylo-catedintheterritory.

CommonInternet-basedsoftwarecanbeusedtopro-videeasydatamigrationbetweenvariouscommunication

pathways.Multi-computerprocessingsystemsareeffec-tiveincreatingcomplexsystemsbyovercominglimita-tionsofasinglecomputerconcernedwiththeoverallcom-putingpowerorthenumberofsignalstobeacquiredandprocessed.

StandardsoftwarelanguagessuchasCandJavacanbeusedwithoff-the-shelfdevelopmenttoolstoimplementtheembeddednetworknodeapplicationsandtheweb-basedapplicationsrespectively.InternetbasedTCP/IPprotocols,Ethernettechnologyand/orDataSocketscanbeusedtodesignthenetworkinginfrastructure,Fig.9.DataSocketisasoftwaretechnologyforWindowsthatmakessharingallmeasurementsacrossanetwork(remoteWebandFTPsites)aseasyaswritinginformationtoafile.ItusesURLstoaddressdatabythesamewayweuseURLinaWebbrowsertospecifyWebpages.DataSocketincludedwithanysoftwaretoolisidealwhensomeonewishestocompletecontroloverthedistributionofthemeasurementbutdoesnotwanttolearntheintricaciesoftheTCP/IPdatatransferprotocols.

Inalltypesofnetworkedanddistributedmeasurementsystemspresentedabove,real-timeoperationandcon-straintsarecriticalissuestobeconsideredduringsystemdesigntoensurethecorrectsystemoperation.

Withdistributedmeasurementsystemonecantakere-motemeasurements,distributeaprogram’sexecution,orpublishmeasurementdataovertheInternet.Theevolvedhardwareandsoftwaretechnologiesprovideuserswiththetoolstheyneedforeasybuildingofapowerfuldis-tributedsystem.

Bypublishingyourmeasurementorautomationap-plicationovertheInternetreal-timedatacanbeviewedbyusersonremotecomputers.Withapplicationdevelop-mentenvironmentsWebserversareavailablesoyoucanpublishauserinterfacetotheInternet.Withoutanyad-ditionalprogrammingyoucanpublishyourfrontpanelasaWebpagesousersacrosstheInternetcanviewthesepanelsrunningwithinanystandardWebbrowser.

Applicationshaveoneormoremeasurementnodesphysicallyseparatedfromthecomputerthatiscon-trollingthemandcollectingdata.Remotemeasure-mentapplicationsoftenrequirehighspeedstreamingofdataandseveralclientsconnectedtoasinglemeasure-ment.ForstreamingmeasurementdataacrossanetworkDataSocketprovidesyouwithaneasy-to-useinterface.UsingDataSocketyoucaneasilystreamanykindofmea-surementdataacrossalocalareanetworkortheInter-nettoseveralclientprograms.BothWebserversandDataSocketprovideasimpleandconvenientwaytopub-lishyourmeasurementdata.

5CONCLUSIONS

Virtualinstrumentationisfuelledbyever-advancingcomputertechnologyanditoffersthepowerofcreatinganddefiningsomeone’sownsystembasedonanopenframework.Thecombinationofcomputerperformance,graphicalsoftware,andmodularinstrumentationhasled

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[13]TAN,K.K.—SOH,C.Y.:InstrumentationontheInternet,

EngineeringScienceandEducationJournalIEE10No.2(2001),61–67.

[14]FERRERO,A.—PIURI,V.:ASimulationToolforVirtual

LaboratoryExperimentsinaWWWEnvironment,Proc.IEEEConf.onInstrumentationandMeasurementTechnology,St.Paul,Minnesota,USA,18–21May1998,1,102–107.

[15]SCPI:StandardCommandsforProgrammableInstruments,ver-sion1991.0,May1991.[16]ni.com/dvi.

ˇ´C,ˇK.—KAZICKA,ˇ[17]SMIESKO,V.—KOVAR.:VXI-busasa

ToolforDynamicTesting,Proc.Int.Conf.CATE93,Brno,1993,283–287.

ANSI/IEEEStd.488.1—1987,IEEEStandardDigitalInterfaceforProgrammableInstrumentation.

ANSI/IEEEStd.488.2—1987,IEEEStandardCodes,Formats,ProtocolsandCommonCommands.

ˇSMIESKO,V.:SomePropertiesofVXISysteminRelationtoHP-IB,ProceedingsPreciseMeasurementinArmy.Brno,1991,68–71.

VXI-busSystemSpecification,Revision1.3,Tektronix.

´SOVˇ´I.—SMIESKO,ˇˇONDRAA,V.—SETNICKA,V.:Contri-butiontotheEfficiencyofGPIBInstrumentation.In:Measure-mentScienceReview.Vol.1,No.1,2001,59–62.

HELSEL,R.:VisualProgrammingforPHVEE,PrenticeHallPTR,1997.

HPVEEforWindowsUserManual,Hewlett-PackardCorp.,1993.

LabWindows/CVIUserManual,NationalInstr.Corp.,Austin1994.

TestPointDemoSystem,KeithleyInstruments,1992.

EREN,H.—NICHOLS,W.J.—WONGSO,I.:TowardsanInternet-BasedVirtual-WireEnvironmentwithVirtualInstru-mentation.IEEEInstrumentationandMeasurement,Confer-ence,Budapest,Hungary,May21–23,2001,817–820.

JASENEK,J.:SensorswithDistributedParametersontheBasisofPOTDR,JournalofElectr.Eng53No.9/s(2002),101-106,PresentedatXVI-thInternationalConferenceEMFM,Bratislava,Sept.11-13,2002.

ˇ´SOVˇ´I.—SMIESKO,ˇKAZICKA,R.,ONDRAA,V.:Improving

totheemergenceofvirtualinstruments,whicharesub-stantiallydifferentfromtheirphysicalancestors.Virtual

instrumentsaremanifestedindifferentformsrangingfromgraphicalinstrumentpanelstocompleteinstrumentsystems.Modularinstrumentationbuildingblocksarebe-comingmoreprevalentintheindustryandareallow-inguserstodevelopcapabilitiesunattainableusingtra-ditionalinstrumentarchitectures.Despitethesechangeshowever,themeasurementparadigmremainsunaltered.Thismightbetheproperplatformforthenewdevelop-ment.

Thetrendinvirtualinstrumentationincreasinglyinte-gratesthemeasurementsystemsintomorecomplexmoni-toringandcontrolsystemsdistributedoverdifferent(pos-siblygeographicallydistant)locations.Theremotein-strumentationcontrolisbecomingpopularsincethenet-workshavebecomereliableandworldwideandalmosteverynewinstrumentembedsprogrammablecapabilities.Thepasthasshownthatunlessproperstandardsareavailable,diversificationduetoad-hocsolutionswillslowtheprogressinthefield.Thus,itseemsaproperchal-lengeforthefuturetostartthinkingofstandardizationofvirtualinstrumentationanddistributedmeasurementsystems.

References

[18][19][20]

[21][22]

[23][24][25][26][27]

[1]CRISTALDI,L.—FERRERO,A.—PIURI,V.:Programmable

Instruments,VirtualInstrumentsandDistributedMeasure-mentSystems.IEEEInstrumentation&MeasurementMaga-zine,Sep.,1999,20–27.

[28]

[2]BAICAN,R.—NESCULESCU,D.:AppliedVirtualInstrumen-tation,WITPress,Boston,2000.

[3]GOLDBERG,H.:WhatisVirtualInstrumentation?IEEE

Instrumentation&MeasurementMagazine,December2000,

[29]10–13.

theAT&MSParameters,J.ElectricalEngineering46No.7

[4]SPOEDLER,H.J.W.:VirtualInstrumentsandVirtualEn-(1995),261–2.

vironments.IEEEInstrumentation&MeasurementMagazine,

´SOVˇ´I.—SETNICKA,ˇˇ[30]ONDRAA,V.—SMIESKO,V.:Auto-Vol.2,1999,14–19.

thmatedInstrumentationApplication.In:12InternationalSci-ˇˇP.:MeasurementontheThreshold[5]SMIESKO,V.—KUKUCA,

entificConference“R´adioelektronika2002”,Bratislava,SlovakoftheThirdMillennium,J.ElectricalEngineering52No.7-8

Republic,14–16May2002,182–185.

(2001),240–243.

[6]TRUCHARD,J.:FutureofVirtualInstrumentation,NIWeek,Received17October20032002.

ViktorSmieˇsko(Prof,Ing,CSc)wasborninZlatovce,[7]DES-JARDIN,L.:VirtualInstrumentsandtheRoleofSoft-ware.ElectronicInstrumentHandboock.McGraw-Hill,1995,Czechoslovakia,in1948.Hegraduatedwithhonorsin1970

44.1–44.14.andreceivedtheCSc(PhD)degreeattheFacultyofElec-[8]GALWAS,B.A.—RAK,R.J.:VirtualLaboratory—aFu-tricalEngineering,SlovakTechnicalUniversity.CurrentlyisturePartoftheNewWeb-BasedModelofUndergraduateEngi-FullProfessorforInstrumentationattheFacultyofElectricalneeringStudiesDevelopedbyWarsawUniversityofTechnology.EngineeringandInformationTechnology,SlovakUniversityJointIMEKOTC-1&XXXIVMKMConference2002,Wroclaw,

ofTechnology.Hisresearchinterestsareintheareasofauto-8-12September,2002.

matedinstrumentationandelectromagneticcompatibility.

[9]McCONNELL,E.:TheFutureofVirtualInstrumentation.Sen-KarolKov´aˇc(Doc,Ing,CSc)wasborninBratislava,Slo-sors,July1997,237–240.

vakiaonJune9,1952.HereceivedtheIng(MSc)degreewith

[10]EPPLER,B.:ABeginnersGuidetoSCPI,Addison-Wesley

honorsin1976andtheCSc(PhD)degreeinelectricalengi-PublishingCompanyInc.,1999.

neeringfromtheFacultyofElectricalEngineeringoftheSlo-[11]BERTOCCO,M.—FERRARIS,F.—OFFELLI,C.—PARVIS,

M.:AClient-ServerArchitectureforDistributedMeasurementvakTechnicalUniversity,Bratislava.Since1976hehasbeenSystems,IEEETransactionsonInstrumentationandMeasure-withtheDepartmentofMeasurementoftheFacultyofElec-tricalEngineeringandInformationTechnology,SlovakUni-ment47No.5(1998),1143–1148.

[12]LEE,K.B.—SCHNEEMAN,R.D.:Internet-BasedDistributedversityofTechnology,nowasAssociateprofessorforElectric

MeasurementSystemandControlApplication,IEEEInstru-Measurement.Hisresearchinterestsareintheareaofcom-mentation&MeasurementMagazine,June1999,23–27.putermodellingandmeasurementofESDpulseprocesses.