经典外文翻译底土的土壤结构和饱和导水率毕业论文设计文档格式.docx
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Low-costprogrammablepulsegeneratorforparticletelescopecalibration
Abstract
Inthispaperwepresentanewcalibrationsystemforparticletelescopesincludingmultipulsegeneratoranddigitalcontroller.Thecalibrationsystemgeneratessynchronizedpulsesofvariableheightforeverydetectorchannelonthetelescope.ThecontrolsystemisbasedonacommercialmicrocontrollerlinkedtoapersonalcomputerthroughanRS-232bidirectionalline.Theaimofthedeviceistoperformlaboratorycalibrationofmulti-detectortelescopespriortocalibrationataccelerator.Thistaskincludesevaluationoflinearityandresolutionofeachdetectorchannel,aswellascoincidencelogic.TheheightsofthepulsessenttothedetectorsareobtainedbyMonteCarlosimulationoftelescoperesponsetoaparticlefluxofanydesiredgeometryandcomposition.ElsevierScienceB.V.Allrightsreserved.
Toassureacorrectinterpretationofdataobtainedwithscientificinstrumentsonboardsatellites,aswellastocomparethesedatawiththoseofsimilarinstruments,athoroughpre-flightcalibrationisrequired.Forsolarandcosmicrayparticletelescopes,thiscalibrationisusuallycarriedoutintwosteps:
first,acalibrationofeachindividualdetectorusingradioactivesourcesandstandardnuclearinstrumentation(NIMorCAMACmodules),followingbyafinaltestofthewholetelescopeperformedinaparticleacceleratorsite.Thesuccessofcalibrationonacceleratorrequiresthat,priortotheexperiences,alldetectorsandelectronicsparameter(polarizationvoltages,amplifiergainsandshapingtimes,thresholds,etc.)havenearlydefinitivevalues.Hereweproposeacheapandsimplepre-calibrationprocedurebasedonanewsystemthatwehavecalledProgrammablePulseGenerator(PPG).ThePPGdevelopedinourlaboratoryhasbeendesignedforaspecificinstrument,afour-detectorcosmicraytelescope,butitcaneasilybemodifiedforsimilarexperiments.
Thestandardcalibrationprocedureforindividualdetectorsandtheirelectronicchainsconsistsofintroducingpulsesofknownamplitudescomingfromapulsegenerator,togetherwiththepulsesreleasedinthedetectorbyparticlescomingfromaradioactivesource.However,thesestandardpulsegeneratorsdopresentseverallimitations:
Thepulseamplitudemustbesetmanually.Thus,togeneratethepulsesthatdifferentparticleswithdifferentenergieswouldreleaseonthedetectors,itisnecessarytochangethepulseheightseverytime.
Standardpulsegeneratorsonlyprovideoneoutputsignal,soeitherseveralmodulesareneededtocalibrateacompletetelescope,oritisnecessarytosplitthesingleoutputinordertogetseveralsignals.Itisdifficulttocheckthecoincidencelogicbecausethefoursignalsarenotindependent.
Toovercomethesedifficulties,pulsegeneratorsofprogrammableamplitudeandratehavebeenproposed.Abdel-Aal[1]presentedaprogrammablerandompulsegeneratorwheretheheightandseparationofindividualpulsesarecontrolledbysoftware.Butinhisschemethepulsesarereleaseddirectlyfromadigital-to-analogconverter(DAC),thushavingthetemporalcharacteristicsoftheDACoutput.Ourpurposeistogeneratevariableheightanalogpulseswithsimilarshapetothatreleasedbynucleardetectors.
Thelow-costPPGpresentedhereisintendedtointroduceeverydetectorchannel,thepulsesreleasedbyanyparticlefluxsupposedtobeencounteredbytheinstrumentonrealexperiments(inourcase,onouterspaceenvironment).Theproposedpre-calibrationschemeissketchedinthediagramofFig1.Forabignumberofsimulatedevents,theenergysignalsreleasedatthedifferentdetectorsofthetelescopearestoredonapersonalcomputer(PC).Foreachindividualevent,theenergysignaldataaresentthroughabidirectionalRS-232-ClinetothePPG,whichtransformstheresultsofthesimulationintorealpulsesandsendsthemtotherealinstrument.
Fig1
2PPGdescription
ThedesignofthePPGisdividedintotwofunctionalmodules:
digitalelectronicsandanalogelectronics,whoseblockdiagramsareenclosedindashedboxesshowninFig2.ThedataarrivingatthedigitalmodulefromthePCaresentto12bitDAC.TheDACoutputvoltagesaretransformedintheanalogmoduleintosuitablepulses,readytobeintroducedintothetestinputoftherelateddetectorchannelofthetelescope.
AnaloganddigitalmodulesaredescribedwithsomedetailinSections2.1and2.2.InSection2.3wedescribesomenoiseproblemsrelatedwiththemicrocontroller,andthewaywefoundtosolvethem.
2.1Analogmodule
Thismodulemustbecapableofproducingsignalpulsessimilartothosegeneratedinthedetectorsbythepassageofenergeticchargedparticles,whoseshapecanbedescribedbythefollowingfunction:
(1)
Therelevantsignalparametersarethepulseheighto