EN ISO 13849-1: Performance Level (PL) - Pilz

The greater the risk, the higher the requirements of the control systems. The hazardous situation is classified into five levels, known as Performance ... ENISO13849-1:PerformanceLevel(PL) Thegreatertherisk,thehighertherequirementsofthecontrolsystems.Thehazardoussituationisclassifiedintofivelevels,knownasPerformanceLevels(PL),fromPL"a"(low)toPL"e"(high).TherequiredPLisdeterminedandassignedaspartoftheriskassessmentinaccordanceENISO13849-1. ENISO13849-1/-2:Safetyofmachinery–Safety-relatedpartsofcontrolsystems AsthesuccessortoEN954-1,ENISO13849-1isthemainsafetystandardforthedesignofsafety-relatedcontrolsystemsformachinery. PerformanceLevel IncontrasttothepreviousstandardEN954-1,whichtookadeterministic(reproducible)approach,ENISO13849-1isbasedonaprobabilisticapproachtoassessingsafety-relatedcontrolsystems. Aswellasdealingwithelectrical,electronicandprogrammableelectronicsystems,thestandardalsoconsidersothercontroltechnologies,suchasfluidpowerforexample TheprovencategoriesfromEN954-1havebeenretained,butsafety-relatedpropertiesarealsoassessedquantitativelythroughstatisticalcalculationmethods.APerformanceLevelisdetermined,basedonthecategories.Thisisdescribedbythefollowingparameters: Category(structuralrequirement) Meantimetodangerousfailure(MTTFd) Diagnosticcoverage(DC)and Commoncausefailure(CCF)   ENISO13849-2Safetyofmachinery-Safety-relatedpartsofcontrolsystems Byvalidationwemeananevaluatedexamination,includinganalysisandtestingofthesafetyfunctionsandcategoriesofsafety-relatedpartsofcontrolsystems.   ApplicabilityofEN954-1 InprincipleEN954-1lostitspresumptionofconformitywiththeMachineryDirective2006/42/ECon31.12.2011,soactuallyitmaynolongerbeappliedinaconformityassessmentprocedurefor2006/42/EC.   Exception:Inindividualproductstandardsforspecificmachinetypes(e.g.machinetools),applicationisstillpermittedundertwoconditions: 1)EN954-1mustbenotedinthenormativereferenceswiththeissuedate EN954-1:1996 Example:EN12417:2001+A2:2009Machinetools–Safety–Machiningcentres 2)EN954-1andENISO13849-1arebothlistedinparallelinthenormativereferenceswiththeissuedate EN954-1:1996andENISO13849-1:2006 Example:ENISO23125:2015–Machinetools–Safety–Turningmachines ​ Reachyourgoalinsixsteps TheintroductionofENISO13849-1hasalsoresultedinnewproceduralrequirementsformachinedesign.Thedesignofsafety-relatedpartsofcontrolsystemsisaniterativeprocess,whichiscompletedinseveralsteps. Step1-Definetherequirementsofthesafetyfunctions Thisisthemostimportantstep.Firstofall,therequiredpropertiesmustbedefinedforthesafetyfunctions.Forsafetygateguardingonamachine,forexample,hazardousmovementsmustbeshutdownwhenthesafetygateisopened.Itmustnotbepossibleforthemachinetorestartwhilethesafetygateisopen. Step2-DeterminetherequiredPerformanceLevel(PL) Thegreatertherisk,thehighertherequirementsofthecontrolsystem.Thecontributionofreliabilityandstructurecanvarydependingonthetechnologyused.Thelevelofeachhazardoussituationisclassifiedinfivestagesfrom"a"to"e".With"a"thecontrolfunction'scontributiontoriskreductionislow,withPL"e"it'shigh.TheriskgraphcanbeusedtodeterminetherequiredPerformanceLevel(PLr)forthedescribedsafetyfunction. Severityofinjury(S) S1=Slight(normallyreversible)injury S2=Serious(normallyirreversible)injury,includingdeath Frequencyand/orexposuretoahazard(F) F1=Seldomtolessoftenand/orexposuretimeisshort F2=Frequenttocontinuousand/orexposuretimeislong Possibilityofavoidinghazardorlimitingharm(P) P1=Possibleunderspecificconditions P2=Scarcelypossible Step3–Designandtechnicalimplementationofthesafetyfunctions The"safetygateinterlock"safetyfunctiondescribedinStep1isrealisedthroughcontrolmeasures.ThesafetygateinterlockisimplementedusingacodedproximityswitchsuchasthePSENcode.Thisprovidestheoptiontoconnectseveralsafetygatesinserieswithoutreducingtheeffectivenessofthemonitoringfunctions.What'smore,codingalsoofferscomprehensivemanipulationprotection.ThesensorsareevaluatedusingamultifunctionalsafetysystemsuchasthePNOZmulti.Thedriveisshutdownviatwocontactorswithpositive-guidedcontacts. Step4–Determineandevaluatetheperformancelevel TodeterminetheachievedPerformanceLevel,thesafetyfunctionisseparatedintosensor,logicandactuator.Eachofthesesubsystemscontributestothesafetyfunction.AllthenecessaryperformancedataisavailableforPilzcomponents.Pilzprovidesauser-friendlycalculationtool(PAScal)forthispurpose. Step5–Verification ThisstepdeterminestheextenttowhichtheachievedPerformanceLevelmatchestherequiredPerformanceLevel.TheachievedPLmustbegreaterthanorequaltothePLrrequiredfromtheriskassessment.Thismeansa"greenlight"forthemachinedesign. Step6–Validation Alongsidethepurelyqualitativerequirementsforthedesignofsafetysystems,itisalsoimportanttoavoidsystematicfailures.Thishappensduringvalidation. Doyourequirefurtherinformation?Pleasereadchapter3.7!TheEnglishSafetyCompendiumoffersknowledgearoundmachinesafety. 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