WELMEC 7.1--Development of Software Requirements

WELMEC7.1Issue2WELMECEuropeancooperationinlegalmetrologyInformativeDocumentDevelopmentofSoftwareRequirementsMay2005WELMECWG7WELMEC7.1,Issue22WELMECEuropeancooperationinlegalmetrologyWELMECisacooperationbetweenthelegalmetrologyauthoritiesoftheMemberStatesoftheEuropeanUnionandEFTA.ThisdocumentprovidesbackgroundinformationtotheWELMECGuide7.2“SoftwareGuide(MeasuringInstrumentsDirective2004/22/EC)”.ThelatterisoneofanumberofGuidespublishedbyWELMECtoprovideguidancetomanufacturersofmeasuringinstrumentsandtoNotifiedBodiesresponsibleforconformityassessmentoftheirproducts.TheGuidesarepurelyadvisoryanddonotthemselvesimposeanyrestrictionsoradditionaltechnicalrequirementsbeyondthosecontainedinrelevantECDirectives.Alternativeapproachesmaybeacceptable,buttheguidanceprovidedinthisdocumentrepresentstheconsideredviewofWELMECastothebestpracticetobefollowed.Publishedby:WELMECSecretariatBEVArltgasse35A-1160ViennaAustriaTel:[phone]Fax:[phone]E-mail:[e-mail]:(SUPPORTINGWELMEC7.2)SOFTWAREEXAMINATIONBASEDONTHEMEASURINGINSTRUMENTSDIRECTIVECONTENTSForeword51Introduction61.1BackgroundandScope61.2Conception62Terminology82.1Programcode82.2LegallyRelevantSoftware82.3ChangesofSoftware102.3.1Unintentionalchanges102.3.2Intentionalchanges(corruption,misuse)withsimplecommonsoftwaretools102.3.3Intentionalchanges(corruption,misuse)withspecialsophisticatedsoftwaretools102.4ProtectionofSoftware112.4.1Protectedsoftware112.4.2Audittrail112.5Interfaces122.5.1Hardwareinterface122.5.2Protectiveinterface122.5.3Softwareinterface122.5.4Protectivesoftwareinterface122.6Datasecurity133EssentialSoftwareRequirements144DefinitionofLevels164.1SoftwareProtectionLevel164.2SoftwareExaminationLevel(TypeExaminationorDesignExamination)174.3DegreeofSoftwareConformity175TechnicalFeaturesofMeasuringInstrumentsandSystems195.1HardwareConfiguration195.2UserInterface(Shell)195.3SoftwareLoading195.4SoftwareStructure205.5SoftwareEnvironment205.6FaultDetection205.7LongtermStorageofMeasurementValues205.8Measuringprinciple20WELMECWG7WELMEC7.1,Issue246InterpretationoftheEssentialSoftwareRequirementsforSelectedMeasuringInstrumentsandSystems226.1ExampleA:SimpleStand-AloneMeasuringInstrument226.1.1DescriptionoftheInstrument226.1.2LegalClassification236.1.3TechnicalClassification246.1.4InterpretationoftheEssentialSoftwareRequirements246.2ExampleB:PC-based,ModularComplexMeasuringSystem306.2.1DescriptionoftheSystem306.2.2LegalClassification316.2.3TechnicalClassification326.2.4InterpretationoftheEssentialSoftwareRequirements327ReferencesandOtherLiterature478Revisionsofthisdocument48WELMECWG7WELMEC7.1,Issue25FOREWORDThisreviseddocumentisintendedtoprovideinformationaboutthedevelopmentofsoftwarerequirementsbasedontheMeasuringInstrumentsDirective.UptothepublicationoftheMIDinApril2004thisGuidehasbeenusedasabasisfornationaltypeapprovalsinsomeEuropeancountries.Thereforetheresponsibleworkinggroup7“Software”hasdecidedonits9thmeeting,8October2004nottowithdrawthisGuidebuttokeepitasaninformativedocumentwithupdatedcrossreferencestothefinalMIDtextandtobringitinlinewiththenewWELMECSoftwareGuide7.2.ForsoftwareexaminationandsoftwaretestingofMIDinstrumentsWELMEC7.1,Issue2,shallnotbeapplied.InsteadWELMECGuide7.2istherecommendedWELMECdocumentthatshouldbeusedforMIDconformityassessmentsofsoftwarecontrolledinstruments.WELMECWG7WELMEC7.1,Issue261Introduction1.1BackgroundandScopeTheMeasuringInstrumentsDirective(MID)[1]willcontainEssentialrequirements(AnnexI)formeasuringinstrumentsusedforlegalpurposes.Someoftheseessentialrequirementscanbedirectlyappliedtothesoftwarecontrollingtheseinstruments,otherstobothhardwareandsoftwareofameasuringinstrument.IthasbeentheexperienceduringthedevelopmentoftheMIDthatthesekindsofessentialrequirementsneedauniforminterpretationwithregardtosoftware,inordertoavoidanunequaltreatmentofcustomersbythevariousEuropeanNotifiedBodies.AfterpublicationofthenewWELMECSoftwareGuide7.2theGuideinhandhasonlyinformativecharacter.IthasbeenrevisedinordertoadaptittothefinalMIDtextandtheresultsoftheEUGrowthNetworkMID-Software.Thelistofsignificantchangesfromthepreviousissueisgiveninthelastchapter8.Guide7.1(aswellas7.2)trytomakethereaderawareofthefactthatonlytestingthemetrologicalperformanceofaninstrumentwithoutespeciallytakingcareofthesoftwarecontrollingthisinstrumentisinmanycasesnolongeradequateformodern,microprocessor-controlledorevenPC-basedmeasuringinstruments,asitissubstantiallythesoftwareanditsintegritythatdeterminesthemetrologicalpropertiesandreliabilityofaninstrument.AstheGuidecoversverydifferentcategoriesofmeasuringinstrumentsitcangiveonlythebasicsofsoftwareexamination.ItisintendedtobesuccessivelyamendedbyspecificannexesforeachkindofmeasuringinstrumentsimilartothespecificannexescontainedintheMID.ThisGuideisintendedtosupportauniformsoftwareexaminationinEuropeandtomaketheresultofanexaminationestimableforthemanufacturer.Theguideis,however,notmandatory,evenforthoseinstrumentsthatarecoveredbytheMID.1.2ConceptionThegu