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1、2VirtualInstrumentsandSoftSensors2.1VirtualInstrumentsInthischapter,theconceptsofvirtualinstruments(VIs)andofsoftsensorswillbeintroducedinsomedetail.Inparticular,wewillcommenceinthissectionwithanintroductiontoVIs,tofocusinthenextoneonsoftsensors,thatarethemaintopicofthebo
2、ok.VIscanbeconsideredasawiderclassthansoftsensors.Infact,softsensorsfocusontheprocessofestimationofanysystemvariableorproductqualitybyusingmathematicalmodels,substitutingsomephysicalsensorsandusingdataacquiredfromsomeotheravailableones.Fortheirpart,VIsarebasedonsoftwareth
3、atperformsanyofthetypicalactionsinvolvedinameasurementand/orcontrolproblem,byexploitingavailableinstrumentation,computersandsoftware.Thisactioncaneitherinvolve,ornot,modelingcapabilitiestypicalofsoftsensors.VIsaretheresultoftherapiddiffusionthathastakenplaceinthelast20yea
4、rsoflow-costWindows-basedpersonalcomputers,Macs,andworkstationsinanyengineeringapplicationfield,alongwithperformingsoftware(Foster,1998).Theyrepresentanalternativeparadigmtotraditionalinstrumentsandallowusbothtocustomizethemeasuringfacilitycapabilitiestouserapplicationand
5、totakecontrolofthewaymeasurementresultsareusedandpresented.TheflexibilityofVIsisobtainedbysoftwarethatisusedtotransformacollectionoffacilitiesintothecustomizedinstrumentationsuitableforthemeasurementtaskofinterest.Also,theuseofsoftwareallowstheadaptation,atdifferenttimes,
6、oftheavailableresourcestonewmeasuringproblemsinsuchawayastoadaptthemeasuringsystemtonewscenarios,andhencetobetterexploitavailableresources.16SoftSensorsforMonitoringandControlofIndustrialProcessesThreemainfunctionalblockscanberecognizedinanyinstrument,andallofthemhavebeen
7、affectedbychangesintroducedbytheintroductionofVIs(Combs,1999):•measurement;•computation;•userinterface.Asregardsmeasurement,thisistheveryfirstactionthatameasuringsystemperformsontheobservedvariable,inordertoextractsomekindofmeaningfulsignal.Signalsextractedfromrealplantsa
8、reanaloginnature,whilethemajorityofmoderninstrumentationisdigital.Ananalogtodigital(A/D)converte
