Which one, SIL or PL? - Troax

Both IEC 62061 (SIL) and ISO 13849-1 (PL) specify requirements for the design and implementation of safety-related control systems of ... Skiptomaincontent BLOG Whichone,SILorPL? 2021-02-12 • 5 minread Whenasafetyfunctionisrequiredforriskreductionasafetycontrolsystemisengineeredandimplementedtoperformthatfunction.Standardsanddirectivescanbeajungle.So,ifyouareanengineer,integrator,orbuildmachines,whatdoyouhavetofollow? TWOMACHINERYAPPLICATIONSTANDARDS Therearetwomachineryapplicationstandardsthatengineerscanutilizetodesigntheirsafetycontrolsystem.ThereisIEC62061:2005whichisusedtodeterminetheSILforelectrical,electronic,andprogrammableelectronicsystems,andISO13849-1:2015whichisusedtodeterminethePLofthesafety-relatedpartsofthecontrolsysteme.g.mechanical,electrical,pneumatic,orhydraulic. ‘’WhichoneshouldIuse?’’isusuallythequestionthatwearefrequentlyasked–whichIwillattempttoanswer.BothIEC62061(SIL)andISO13849-1(PL)specifyrequirementsforthedesignandimplementationofsafety-relatedcontrolsystemsofmachinery.Themethodsdevelopedineachstandardaredifferentbut,whencorrectlyapplied,canachieveacomparablelevelofriskreduction. COMPARISONOFTHESTANDARDS Thetwostandardsclassifysafety-relatedcontrolsystemsthatimplementsafetyfunctionsintolevelsthataredefinedintermsoftheirprobabilityofdangerousfailureperhour. ISO13849-1hasfivePerformanceLevels(PL’s)a,b,c,d,ande;whileIEC62061hasthreeSafetyIntegrityLevels(SIL’s)1,2,and3. IfwecomparethetechnicalrequirementsbetweenIEC62061(SIL)andISO13849-1(PL)andconsideringthefollowingaspects: Terminology. Riskestimationandperformanceallocation Safetyrequirementsspecification Systematicintegrityrequirements. Diagnosticfunctions Softwaresafetyrequirements Wecandrawthefollowingconclusion:Safety-relatedcontrolsystemscanbedesignedtoachieveacceptablelevelsoffunctionalsafetyusingeitherofthetwostandards.Thisisachievedbyintegratinganon-complexSRECS(safety-relatedelectricalcontrolsystem)subsystemsorSRP/CS(safety-relatedpartsofacontrolsystem)designedinaccordancewithIEC62061(SIL)andISO13849-1(PL),respectively.  BothstandardscanalsobeusedtoprovidedesignsolutionsforcomplexSRECSandSRP/CS.Thisisachievedbyintegratingelectrical,programmable,orelectronicsubsystemsdesignedinaccordancewithIEC61508. SOWECANUSEEITHER…WHICHONEDOWEUSETHEN? Theselectionanduseofeitherstandardmaystillnotbeclear,thereforethefollowingconsiderationsmayhelpinattemptingtodeterminetheuseofeitherIEC62061(SIL)orISO13849-1(PL). Previousexperience|Previousknowledgeandexperienceinthedesignofmachinerysafety-relatedcontrolsystemsbasedupontheconceptofcategoriesdescribedpreviouslyinISO13849-1:1999canmeanthattheuseofISO13849-1:2006ismoreappropriate. Othermediathanelectrical|Safety-relatedcontrolsystemsbaseduponmediaotherthanelectricalcanmeanthattheuseofISO13849-1(PL)ispossiblymoreappropriate. Customerrequirements|Customerrequirementstodemonstratethesafetyintegrityofamachinesafety-relatedcontrolsystemintermsofaSILcanmeanthattheuseofIEC62061ismoreappropriate. ExistingmachineryusingSIL|Safety-relatedcontrolsystemsofmachineryusedin,forexample,theprocessindustries,whereothersafety-relatedsystems(suchassafetyinstrumentedsystemsinaccordancewithIEC61511)arecharacterizedintermsofSILs,canmeanthattheuseofIEC62061ismoreappropriate. THEMOSTFREQUENTLYUSEDSTANDARDTODAY ItisgenerallyacceptedthatthemajorityofindustryusesISO13849-1(PL)becausethemachinebuilderswerepreviouslyusingEN954-1,whichhavenaturallymigratedtoISO13849-1(PL).ThisisreinforcedbyasurveyillustratedbelowthatwascarriedoutbythejointworkinggroupofISO/TC199–IEC/TC44,whichatthetimewasconsideringthemergingofIEC62061andISO13849-1. WHATNEXT? Therewasaprojecttomigratethetwostandardsintoone,butduetothetimelinetocompletetheprojectrunningoverandsignificantdisagreementtheprojectwasterminated.BothIEC62061(SIL)andISO13849-1(PL)arecurrentlyinrevisionandareexpectedtobereleasedsometimein2021. Itislikelythattheselectioncriteriadeterminingtheuseofeitherstandardwillbecomeevenhardertodetermine. CONCLUSION IcanrecommendyoureadtheexistingTechnicalReport(IEC/TR62061-1:2010)which,althoughdated,providesfurtherinformationandwillcontinuetoprovidefurtherupdateshereontheproposedcontentsofIEC/TS62061-1(GuidelinesontheapplicationofIEC62061)andfurthernewsonthecontentsoftherevisionsofIEC62061andISO13849-1. Itwouldbepreferableiftherewasonlyonestandard,butforthetimebeing,youmayhavetousethemboth. PS-WHYARESTANDARDSIMPORTANT? Standardsnotonlyhelpinprovidingapresumptionofconformity,whichcamesharplyintofocuswiththe‘’JamesElliottruling’’. Butalsoprovidethecatalystforinnovation,andcontributeinexcessof€40billiontotheeconomicgrowthfortheEU,detailedintheimagebelowfromarecentEuropeanUnionworkshop:  THEWRITER DavidAndrewMain-Readehasbeeninvolvedinthefieldoffunctionalsafetyinexcessofthirtyyears.HerepresentsBSIasanexpertonavarietyofInternationalandNationalstandards(IEC,ISO,CENELEC,andBS)andisaTÜVRheinlandFSExpertandhasspentovertwentyyearswithRockwellAutomationastheirGlobalstandardsspecialist. Standards Troax MakingYourWorldSafe