best practices in profibus network diagnostics - softing · pdf filebest practices in profibus...

PROFIBUS is the digital fieldbus technology with the highest distribution worldwide, providing advantages for all types of applications.

Even with proper installation, however, the operating reserves of the fieldbus communication will progressively decrease and, in the end, may lead to severe communication failures causing immediate production downtimes and considerable financial losses. Thus it is essential to continuously keep an eye on the PROFIBUS network. This task is supported by appropriate diagnostic tools.

This White Paper discusses the state-of-the-art of diagnosing PROFIBUS networks and provides helpful hints for avoiding a communication breakdown and resulting unplanned production downtimes.

Best Practices in PROFIBUS Network Diagnostics

EXECUTIVE SUMMARY

WHITE PAPER

White Paper

Table of Contents

1 Introduction .......................................................................................................................................... 1

2 PROFIBUS Overview .............................................................................................................................. 2

3 Diagnosing a PROFIBUS Network .......................................................................................................... 8

3.1 Physical Analysis of PROFIBUS DP Networks ..................................................................................... 9

3.1.1 Cable Test ..................................................................................................................................... 9

3.1.2 Topology Scan ............................................................................................................................ 11

3.1.3 Quality Index .............................................................................................................................. 12

3.1.4 Signal-to-NoiseRatio .................................................................................................................. 13

3.1.5 Rise Time .................................................................................................................................... 14

3.1.6 Signal Waveform in Oscilloscope Display .................................................................................... 15

3.2 Physical Analysis of PROFIBUS PA Networks .................................................................................... 16

3.2.1 DC Voltage Measurement .......................................................................................................... 16

3.2.2 Signal Voltage ............................................................................................................................. 16

3.2.3 BitRateDeviation ...................................................................................................................... 16

3.2.4 Polarity ....................................................................................................................................... 16

3.3 Logical Analysis of PROFIBUS Networks .......................................................................................... 17

3.3.1 Baud Rate ................................................................................................................................... 17

3.3.2 Live List ...................................................................................................................................... 17

3.3.3 NetworkInformation .................................................................................................................. 18

3.3.4 PROFIBUSMasterInformation ................................................................................................... 18

3.3.5 PROFIBUSSlaveInformation ...................................................................................................... 19

3.3.6 Frame Analysis ........................................................................................................................... 19

4 Approaches for Analyzing a PROFIBUS Network ................................................................................. 20

4.1 General Notes on Analyzing a PROFIBUS Network .......................................................................... 20

4.2 InterpretingtheQualityIndex ......................................................................................................... 20

4.3 Use Case: Acceptance of a PROFIBUS Network ............................................................................... 22

4.4 UseCase:TroubleshootingaPROFIBUSNetwork ............................................................................ 23

4.4.1 TroubleshootingaWorkingPROFIBUSNetwork ......................................................................... 23

4.4.2 TroubleshootingaNon-WorkingPROFIBUSNetwork ................................................................. 24

White Paper

5 Analysis Tools for PROFIBUS Networks ................................................................................................ 25

5.1 MobilePROFIBUSDiagnosticsTool .................................................................................................. 25

5.2 PROFIBUSDiagnosticsSoftware ...................................................................................................... 26

5.3 StationaryPROFIBUSDiagnosticsTool ............................................................................................. 27

6 Summary ............................................................................................................................................. 29

7 TerminologyRelatedtoPROFIBUSDiagnostics .................................................................................... 32

8 AboutSofting ...................................................................................................................................... 36

9 Authors ............................................................................................................................................... 37

10 References .......................................................................................................................................... 37

11 List of Figures ...................................................................................................................................... 38

12 List of Tables ....................................................................................................................................... 38

Best Practices in PROFIBUS Network Diagnostics 1

1 Introduction

Availableformorethan20years,thePROFIBUSstandardtodayoffersamaturedigitalfieldbustechnology.Itisusedinfactoryaswellasprocessautomationapplicationsandcanalsobefoundinhybridindustrieslikefoodandbeveragesorpharmaceuticals.Inaddition,PROFIBUSisalsoapplicableinothermarketslikebuildingautomationandrailwayapplications.PROFIBUSisthustheonlyfieldbustechnologyservingallthesedifferentapplicationareas.

AccordingtothePROFIBUS&PROFINETInternational(PI)associationabout53.7millionPROFIBUSdevicesweresoldbytheendof2015andthisnumberisstillgrowingrapidly.ThislargeinstalledbasesuggestsPROFIBUSasaleadingfieldbustechnologywhichdefinitelywillberelevantforyears,ifnotdecades,tocome.Consequently,PROFIBUSinstallationscanbefoundallovertheworld,oftencomprisingseveralthousand devices.

AsPROFIBUSactsasthecommunicationbackboneofproductionplants,itsreliableoperationisessentialforoptimalplantproductivity.Nonetheless,applicationmalfunctionscanbeexperiencedduringcommis-sioningaswellasoperationandoften,besidesperipheralfaults,thisbehavioriscausedbyphysicalfaults.Due to the fact that PROFIBUS is a very mature and robust technology, the causes of these failures typically arenotadeeptechnicalissue.Rather,therealproblemoftenissimplyafaultyconnectororanincorrectbustermination.

However,findingtherootofanobservedfaultybehaviorisnotalwaysaneasyfeat:Forinstance,thePROFIBUScommunicationmayonlymalfunctionoccasionallyorerrorsmaybedetectedinseeminglyunrelatedpartsoftheoverallnetwork.Also,earthingfaultsmaybeslowlydamagingthefieldbusoperation,creatingageneraldistrustintheoverallnetwork.

VarioustypesoftoolsareavailablefordetectingPROFIBUSmalfunctions.Theyprovideawiderangeoffunctionalityforconductingcabletests,electricalsignalanalysisandlogicalnetworkanalysis.ThisWhitePaperdiscussesthedifferentmeasurementsthatcanbeperformedforaPROFIBUSnetworkanddescribesthebestpracticestokeepthefieldbusupandrunningthroughoutthecompletecommunicationlifecycleandtoavoidexpensiveunplannedproductiondowntimes.

AsextensivedocumentationregardingthecorrectinstallationofaPROFIBUSnetworkisavailable,thistopicis not addressed in this White Paper.

White Paper


2 PROFIBUS Overview

PROFIBUS(PROcess FIeld BUS)isaworldleadingfieldbuscommunicationstandardinautomationtech-nology.Itsupportsthedigitaldataexchangewithinanetworkusingasinglebuscable,resultinginahighdatatransmissionreliability.Basedonnumerousprotocolextensions,itprovidessolutionsforawiderangeofapplicationareasincludingmanufacturingandprocessautomation(seeFigure 1).

Figure 1: DifferentMarketSegmentsSupportedbyPROFIBUS (Source:PROFIBUS&PROFINETInternational)

In1993,thePROFIBUSDecentralizedPeripherals(DP)standardwasreleased,focusingonthesimpleandfastdeterministiccommunicationbetweencontrollersandremoteI/Ofielddevices(sensorsandactuators).

InthedifferentapplicationareasPROFIBUStypicallyusestheEIA-485transmissiontechnologyasthephysicallayerunlessitisnotapplicableduetospecificrequirements(e.g.powersupplytothefielddevicesviathebuscable,heavyinterference,orlongdistances).EIA-485isbasedonashieldedcoppercablewithapairoftwistedwiresprovidinganimpedanceof150Ω.Itallowstheconnectionofupto126stationstoone PROFIBUS DP network1,supportingalinearbustopology.Forensuringadefinedbusidlevoltage(alsocalled“quiescentlevel”)onthetransmissionlineswhilenoframesarebeingexchangedandformini-mizingthelinereflections,eachendofaPROFIBUSDPsegmentisconnectedtoaterminator.Transmis-sionratesfrom9.6KBit/sto12MBit/saresupported.PROFIBUSDPenablesthenon-reactivecouplingandde-couplingofstationsandtheincrementalcommissioningoftheoverallPROFIBUSnetwork.Inparticular,thisallowsthesubsequentexpansionofthenetworkwithoutaffectingstationsalreadyinoperation.

1 APROFIBUSnetworkincludingmorethan32stationshastobestructuredinsegmentsusingrepeaters.Eachsegmentmaycontainupto32stations,includingtherepeater(s).Thecombinationoftheindividualsegmentscanbe seen as one logical PROFIBUS network.

White Paper


ThePROFIBUSDataLinkLayerisdefinedbytheFieldbusDataLink(FDL)protocol.WithinthisprotocolaTokenPassingmethoddefinesthenetworkaccess(seeFigure 2).Itdifferentiatesbetweenmasterstations(stationscontrollingthedataexchangeviathefieldbus)andslavestations(sensorsandactuatorsrespondingtoindividualreadrequestsorreceivingdataviathefieldbus)andcontrolsthetimeslotsoftheindividual masters.2Basedonthismaster/slavetechnology,thefieldbusisaccessedandthereliabledataexchangebetweenPROFIBUSstationsisperformed.

ThePROFIBUSDPstandarddefinesdifferentversions.ThePROFIBUSDP-V0versionprovidesthebasicfunctionalityofthecommunicationprotocol,including,inparticular,cycliccommunicationanddevice-,module-andchannel-specificdiagnosticsforquickfaultlocalization(bothforcommunicationfaultsaswellasapplication-specificerrors,e.g.“ExcessTemperature”or“ShortCircuitonOutput”).ThePROFIBUSDP-V1versionsupplementsthePROFIBUSDP-V0versionwithfunctionalityforacycliccommunication,i.e.supportingtasksofintelligentstations,suchasparameterization,operation,monitoring,alarmhandling,andmaintenance.ForthispurposePROFIBUSDP-V1definestheonlineaccesstofieldbusstationsviaengi-neeringtools.IncomparisontoPROFIBUSDP-V1,thePROFIBUSDP-V2versionprovidesextendedfunction-ality,includingtimesynchronization,isochronousreal-timefunctionalityasrequiredfordrivecontrolaswellastime-stampingandslave-to-slavecommunication.

PROFIBUSDPdefinesdifferentdevicetypeswhicharedescribedinTable 1.

2 Thetimeslotsoftheindividualmastersaredefinedaspartofthe(offline)configurationprocess.Theuserhastoensurethateverymasterreceivesatimeslotwhichislongenoughtoperformallitscommunicationtasksandthatallthedataexchangebetweentheindividualmastersandthevariousslavesisperformedinreal-timewithminimaltimeoverhead.

White Paper


PROFIBUS DP Device Type

Description

PROFIBUS DP Master Class 1

ThePROFIBUSDPMasterClass1controlsthecommunicationprocessforexchangingprocessvalueswithindividualslavesusingthedefinedcycliccommandsduringtheconfiguredtimeslots.3

Typical PROFIBUS DP Master Class 1 devices include controllers and PCs.

PROFIBUS DP Master Class 2

ThePROFIBUSDPMasterClass2accessesthefieldbusbyusingacyclicservices.4Theseallowtheconfigurationandparameterizationofintelligentfielddevices.

Engineering and operator panels typically act as PROFIBUS DP Master Class 2.

PROFIBUS DP Slave ThePROFIBUSDPSlaveisaperipheraldevicethatreadsinputinformationandsendsoutputinformationtotheperiphery.Theamountofsupportedinputandoutputinformationdependsonthedevice;amaximumof246Bytes of input data and 244 Bytes of output data can be processed.

Table 1: PROFIBUS DP Device Types34

DifferentnetworkarchitecturesaresupportedbasedonthePROFIBUSDPdevicetypesfromTable 1, providingahighflexibility.Thesearchitecturesinclude:

• Single Master Network Hereonlyonemasterstation(PROFIBUSDPMasterClass1)isconnectedtothePROFIBUSDPnetworkduringoperation.Whileacontrolleractsasthecentralcontrolunit,theindividualslavesareconnectedtothefieldbusatremotelocations. Thesinglemasternetworkprovidestheshortestfieldbuscycletime.

• MultiMasterNetwork Hereseveralmasterstations(PROFIBUSDPMasterClass1andPROFIBUSDPMasterClass2,respec-tively)areconnectedtothePROFIBUSDPnetwork.Theseeitherbuildindividuallyindependentsub-networks,eachconsistingofonePROFIBUSDPMasterClass1andtheappropriateslaves,ortheyincludeadditionalstationsfordevelopmentanddiagnostics.Whileallmasterscanreadtheinputandoutputvaluesoftheslaves,onlythePROFIBUSDPMasterClass1stationconfiguredforthisslaveisallowedtowritetheoutputvaluesofaparticularslave.

Figure 2showsaPROFIBUSDParchitectureexampleillustratingthedataexchangeofonePROFIBUSDPMasterClass1stationandonePROFIBUSDPMasterClass2stationbasedontheTokenPassingmethod.

3 ThePROFIBUSDPMasterClass1canalsouseacyclicservicesasdefinedbytheMasterSlaveAcyclicCommunicationofClass1(MSAC_C1).

4 TheseservicesaredefinedbytheMasterSlaveAcyclicCommunicationofClass2(MSAC_C2).DespitethenameacyclicservicescanbeperformedbythePROFIBUSDPMasterClass2onaregulartimebase,e.g.forprovidingdataas required by a SCADA system.

White Paper


Figure 2: CyclicandAcyclicPROFIBUSDPCommunication (Source:PROFIBUS&PROFINETInternational)

ThecapabilitiesofindividualPROFIBUSdevicesaredescribedbytheGeneralStationDescription(GSD)andtheElectronicDeviceDescription(EDD)files.TheGSDfilecontainsthekeydataofanindividualPROFIBUSdevice,informationaboutitscommunicationcapabilitiesand,e.g.diagnosticvalues.ItsuppliesalltheinformationnecessaryforthecyclicexchangeofmeasuredvaluesandmanipulatedvariablesbetweenthefielddeviceandthePROFIBUSmaster,andsupportstheconfigurationofthePROFIBUSnetwork.TheEDDprovidesadditionalinformationdescribingapplication-specificfunctionsandtheparametersofcomplexfielddevices.Itcomprisesadescriptionofthedevicecapabilitiesexchangedacyclically,includinggraphics-basedoptions,anddeviceinformationsuchasorderdata,materials,maintenanceinstructions,etc.5

In1996,thePROFIBUSProcessAutomation(PA)applicationprofilewasreleased.ItusesthePROFIBUSDPcommunicationtechnologyandespeciallyaddressesprocessautomationneeds.PROFIBUSPAissuitableforuseinhazardousandpotentiallyexplosiveareas(Exzones0and1).Thus,incontrarytousingthetransmis-sion technology EIA-485 for PROFIBUS DP networks, the data transfer in PROFIBUS PA networks typically isperformedbasedonManchesterCodedBusPowered(MBP)6, which is capable of supplying power to theindividualfielddevicesviathebuswire.Asaconsequence,thewiringoverheadcanbereducedsignifi-cantly.PROFIBUSPArequiresapassivelineterminationateachendofthenetwork.

5 EDDfilesareprimarilyusedinPROFIBUSProcessAutomation(PA)applications.6 The Manchester Coded Bus Powered transmission technology has been developed and standardized independently

ofthePROFIBUScommunicationandaddressesthedemandsofprocessautomation.MBPisusedbyotherfieldbusesaswell,e.g.byFOUNDATION™ Fieldbus H1.

White Paper


MBPcommunicationrequiresonly8Bitsforencodingacharacter.7 Thus, PROFIBUS PA meets the require-mentsforamuchsimplerandsaferinstallationandincorporatesallthebenefitsofdigitaltransmissionrightdowntothefielddevice.PROFIBUSPAalsosupportsintrinsicallysafeapplicationsprovidingexplosionprotectionbylimitingthepowersuppliedbythebusortheinstallationcomponentsinthefield.Itiswidelyusedinchemical,oil,andgasindustryapplications.TheMBPtransmissiontechnologybasicallysupportsavarietyofdifferenttopologies,includinglinearandsimpletreestructures.Inpractice,the“Trunk&SpurTopology”(seeFigure 3)hasestablisheditselfasthede-factostandard,asitisparticularlyclearandwelllaidout.Thankstothetechnicallymatureinstallationtechnologies available on the market, it also exhibits a high degree of robustness. The overall length of a segmentmaynotexceed1,900m,andthelengthofthespursinintrinsicallysafeapplicationsislimitedto30mandmustbetakenintoaccountwhencalculatingtheoveralllength.PROFIBUS PA is based on the PROFIBUS DP-V1 version. It uses the PROFIBUS DP protocol at a data transfer rateof31.25KBit/sandisconnectedtoaPROFIBUSDPnetworkbyusingacouplingdevicesuchasasegmentcoupleroralink.PROFIBUSDPthenactsasabackbonenetworkfortransmittingprocesssignalstothe controller.

Figure 3: Trunk & Spur Technology Used by PROFIBUS PA and Coupling of PROFIBUS PA Segments to PROFIBUS DP8 (Source:PROFIBUS&PROFINETInternational)

7 Incomparison,standardPROFIBUSDPusestheserialUARTNRZ(Non-Return-to-Zero)communication,whichisbased on 11 Bit character encoding.

8 Asanalternative,thebarriercanalsobeimplementedwithinthesegmentcouplingdevice.Herenobarriersarerequiredwithinthefielddistributors,butlesselectricalpowerisavailable.

White Paper


ThePROFIBUSPAapplicationprofiledefinesfunctionsandparametersforprocesscontroldevices,suchastransmitters,actuators,valves,andanalyzers.Thesefunctionsandparametersareusedtoadaptthedevicestotherespectiveapplicationandprocessconditions.ThefunctionsarebasedonFunctionBlocks,andtheassociatedparametersareclassifiedasinput,output,andinternalparameters.ThePROFIBUSPAapplicationprofilealsodetermineshowthevariousservicesofthePROFIBUScommunicationprotocolareused. This means, for example, that process data that is exchanged cyclically is based on a standard format foralldevices.Inadditiontothemeasuredvalueand/ormanipulatedmeasurementvalue,thisformatalsofeaturesastatussupplyinginformationaboutthequalityofthevalueandpossiblelimitviolations.Ittherebyprovidesthefoundationforharmonizedapplications,simplifiedengineering,deviceexchange-abilityandincreasedreliabilitybymeansofstandardizeddiagnosticinformation.

ThelatestversionV3.02ofthePROFIBUSPAapplicationprofileespeciallyaddressesuserrequestsforcomprehensivediagnosticandstatusinformationaswellastherequirementsofsystem-orientedassetmanagementforfielddeviceswithinprocessautomationapplications.

White Paper


3 Diagnosing a PROFIBUS Network

APROFIBUSnetworkisaverysensitivetransmissionsystemwithtransfercharacteristicsintheVHFrange,especiallywhenusinghightransferratesof1.5MBit/sorhigher.ItisthereforeimportanttostrictlyfollowthePROFIBUS&PROFINETInternationalinstallationguidelineswhensettingupaPROFIBUSnetwork.

Anydeviationfromanoptimallyinstalledbuslinehasanegativeimpactonthetransmissionbehavior.Inaddition,anyimproperlyinstalledconnector,illegalspurcableortransitionbetweentwodifferentcabletypeschangestheimpedanceatthatlocationandcausesreflectionsthatdeterioratethesignal.

Toovercomethisvulnerability,thePROFIBUSstandarddefinesaveryrobustcommunicationsystemforexchangingdatabetweenPROFIBUSMastersandSlaves.Itscommunicationcapabilitiesincludespecificrobustnessfeatures,whichensureareliablecommunicationwithoutlossofcontrolandcorruptdataevenwhencommunicationerrorsoccur.APROFIBUSnetworkinstallationaccordingtothestandardthussupportsacommunicationoperatingreserve.

EachPROFIBUSframecontainssomeredundantinformation(paritybits,framechecksequence,specificstartandenddelimiters)providingbiterrordetectioncapabilitiesuptoHammingDistance4.If,bythosemeans,thereceivingstationdetectsanerror,itdoesnotrespondandthuscausesthesendertorepeattheframe(uptoseventimesdependingonthenetworkconfiguration).

TheexistenceofthatoperatingreservewithinaPROFIBUSnetwork,however,mayresultinthestatusindi-catorsshowingacorrectmodeofoperationattheindividualcontrollersanddevicesofthenetwork.Thisfact can lead a user to assume that the network is working properly, even if this is not true. Only when the rateofdatacorruptionreachesacriticalthresholdwillthefaultbecomevisibletotheuser.Atthisstage,however,thecommunicationhastypicallyalreadystoppedandcausedproductiondowntime.

ByanalyzingthePROFIBUScommunicationinmoredetail,aprogressivedecreaseoftheoperatingreservesforthebuscommunicationcanbeidentifiedbeforethecommunicationstopsworking.Assoonastheuserisawareofthisdecrease,correctiveactioncanbetakentoavoidunplanneddowntime.

This chapter discusses the various types of PROFIBUS DP and PROFIBUS PA network analyses, including the physicalmeasurementofthePROFIBUScable,theelectricalsignalanalysisaswellasthecommunicationanalysisatthePROFIBUSframelevel.AsthephysicallayerdiffersbetweenPROFIBUSDPandPROFIBUSPA,differentanalysismethodshavetobeappliedhere(seeSections3.1 and 3.2,respectively).ThePROFIBUSframelevel,however,isidenticalforbothprotocols,allowinguseofthesamelogicalanalysismethodsforcommunicationinPROFIBUSDPaswellasPROFIBUSPAnetworks(seeSection3.3).

Additionalchapterswillthenprovidesomehintsonhowtocombinetheindividualdiagnosismethodseffi-cientlytoperformanoverallanalysisofPROFIBUSnetworksatdifferentstagesofthePROFIBUSinstallationlifecycle,e.g.duringcommissioningofaPROFIBUSnetworkoraspartofpreventivemaintenanceactions(seeChapter4).Chapter5givesanoverviewaboutdifferenttypesoftoolsthatareavailableonthemarketfor analyzing PROFIBUS networks.

White Paper


3.1 Physical Analysis of PROFIBUS DP Networks

The physical analysis of PROFIBUS DP networks is performed at segment level. It comprises measurements of the PROFIBUS cables used, including the bus terminators, as well as the electrical signals of the EIA-485 transmissiontechnology.ThetestsconductedrefertothephysicallayerofaPROFIBUScommunication.

ThephysicalanalysismeasurementsmakeuseofthedifferentialsignalmechanismdefinedfordatatransferwithinPROFIBUSDP.Theactualdatasignalistransferredviatwosignallines(linesAandB)invertedtoeachother.ForPROFIBUSDPcommunicationthedifferentialvoltagedefiningthedifferencebetweenthetwosignallinesAandBisinterpreteddigitally,eitherrepresentingalogic0orlogic1signal.Anyfaultsoccurringherecanpreventacorrectdetectionofthecommunicationbitstream.

The most commonly used connector for PROFIBUS DP is the 9-pin D-sub connector. Pin 8 is used for line A,pin3forlineB.IndividualPROFIBUSstationsareconnectedusingonlythesetwolinesviaatwistedpaircableprovidingashieldinaddition.Thus,aPROFIBUScableconnectsjustthesetwopins.

Thegoalofthephysicalanalysisisthecreationofageneralbusstatusstatement.Forthispurpose,thesignalsonthePROFIBUSlinearerecordedatdifferentlocationsandtimes.Theserecordsarecomparedandanalyzed to detect and locate physical problems that may lead to bus faults.

ThephysicalanalysisofPROFIBUSDPnetworksconsistsofdifferenttypesofmeasurements.Theyarediscussedinthefollowingsections.

3.1.1 Cable Test

ThecabletestprovidesafirstindicationofthephysicalstatusofaPROFIBUSinstallation.Itdetectscablingfaults,whichmaycausesporadicandnon-reproducibleerrorsduetointerferencesusceptibilityorevencommunicationmalfunctions.

The cable test examines the cabling and the terminators of PROFIBUS segments by means of Time Domain Reflection(TDR)measurements.Itdeterminesthecablesegmentlength,scansforunwantedreflectionsonthelineandverifiestheproperterminationofthecable.Thuscablingerrorslikeshortcircuitsandbrokenwires or shields can be found.

In detail, the cable test allows to detect the following cabling faults:

• Wire or shield breakage• Crossed wires• Short circuits between the PROFIBUS signal lines A and B• Short circuits between the PROFIBUS signal lines A or B and the shield• Branch lines• Inhomogeneous line segments• Incorrect and non-powered terminators

White Paper


The cable test is performed at either end of the PROFIBUS segment. It consists of three steps that have to be successively completed: First, the cable test is carried out on the open cable without terminators at either end of the segment. This step helps to detect the cable segment length, to check the proper instal-lationofthecableandtodeterminewhethernon-conformantterminatorsorresistorshavebeeninstalled.Next,thecableistestedtogetherwiththeterminatorattheother(remote)endoftheline.Thistestidenti-fiesadefectivebusterminatoraswellasamissingsupplyvoltageforthisbusterminator.Inthethirdstep,the cable test is performed with the terminators connected at both ends of the PROFIBUS segment. The successful pass of all these steps is a sign that the cabling has been properly installed.Incaseofafaultanerrordescriptionand,ifpossible,thedistancefromthetestlocationaredisplayedaspartofthecabletest(seeFigure 4 and Figure 5).Thisinformationcanbeusedfortroubleshooting.

Figure 4: PROFIBUS Cable Test Results (Whiletheleftscreenshotshowsthesuccessfulpassoftheopencableteststep,therightscreenshotindicatesaterminatorerrorattheremoteendofthecable.)

Figure 5: Detailed Results from PROFIBUS Cable Test

ThecabletestrequiresthatthereisnoPROFIBUSDPMaster(e.g.controller)inthenetwork.Itcanbeperformed regardless of whether PROFIBUS DP Slaves are connected and powered or not.

White Paper


3.1.2 Topology Scan

ThetopologyscancanbeusedasanindicationofwhetherthecablingofthesegmentswithinaPROFIBUSnetwork has been set up correctly.9 In the test a PROFIBUS Master simulator is connected directly to a poweredterminatorateitherendofthenetwork.ThePROFIBUSMastersimulatoraddresseseachexistingstationandmodifiesthecableimpedancewhilethestationisanswering,thuscausingreflectionsonthebus.Thetimedifferencebetweentheoriginalandthereflectedsignalcanbeusedtocalculatethedistancetothemeasuredstation.Basedontheresults,thesequenceaswellasthedistancesofallpassivePROFIBUSSlavesfromthePROFIBUSMastersimulatoraredetermined(seeFigure 6).

Figure 6: TopologyScanResultIndicatingaHealthyPROFIBUSNetwork

ThetopologyscanrequiresthatnoPROFIBUSMasterstation,suchasacontrolleroranMPIpanel,isactivein the PROFIBUS network during the measurement.10Toidentifytheoveralltopologyincludingtheindi-vidualPROFIBUSMasters,therelativedistanceofeachmasterfromthetestlocationhastobeenteredmanuallyafterthetopologyscan.

9 A successful performance of the topology scan requires a properly installed segment cable that is free of unwanted reflections.AnyfailureduringthetopologyscansuggestsafaultyPROFIBUScablinginstallation.

10 AsaPROFIBUSMastersimulatorisusedinsteadofregularPROFIBUSMastersduringthetopologyscan,adifferentnetworkloadandcommunicationbehaviorapply.ThusthissetupcannotbeusedtoexaminethenetworkloadaswellasthetimingbehavioroftheactualPROFIBUScommunication.

White Paper


For a plausibility check the topology scan can be repeated from the other end of the PROFIBUS network. If thetwotestsarelargelycomparable,thetestresultsarelikelytobecorrect.Propercableinstallationandphysical health of the PROFIBUS network11 can thus be assumed.

3.1.3 Quality Index

The quality index12 combines an assessment of the voltage level and the signal waveform into a general statementaboutthephysicaltransmissionqualityofthePROFIBUScommunicationfortheindividualstationsinthenetwork.ThequalityindexsummarizesdifferenttypesofinformationdescribingthequalityofaPROFIBUSnetwork,includingvoltagemeasurementsandthecalculatedresultsforrisetime,over-shootsandundershootsaswellasleveldropscausedbyreflections.Thequalityindexisbasedonawaveformscanwith16samplesperbit.Thefirst3scansandthelast3scansofeachbitrelatetotheedges(riseandfalltime)whilethe10scansinthemiddleareusedtoevaluatethesignal quality.Tocalculatethequalityindex,thePROFIBUScommunicationisanalyzedforeachstation.Areferencevoltageisiterativelyadjustedinseveralstepstowardsafinalvalueforwhichtherearelessthan20viola-tions(glitches,edgeandlevelerrors)per1,000transferredbitsfromaparticularPROFIBUSstation.Inotherwords,thequalityindexcanbeseenastheheightofarectanglethatcanbeplacedintheinner10/16ofabit without touching the signal waveform. As soon as the reference voltage has been determined, the test captures the number of glitch, edge and level errors that occurred at that voltage. Thus,permanentsignaldistortionscausedbythetransmissionlineitself(e.g.reflections,signal“rounding”duetolow-passbehavior)haveadirectimpactontheresultingqualityindex,whereassporadicdistur-bancescausedbyexternalelectromagneticdisturbancesarenotincludedinthequalityindex.Sporadicdisturbancesthatconcernlessthan2%ofthebitsdonotaffectthequalityindex,either.Figure 7showsanexampleofthequalityindexdisplayforagiventestlocation,indicatingthequalityindexofeachstationwithinthePROFIBUSnetwork.

11 A key requirement to ensure the physical health of a PROFIBUS network is that bus terminators are powered andconnectedatbothbusends.Inaddition,allcablesofthePROFIBUSnetworkhavetobeconnectedcorrectly.Longdead-endbranches,significantdifferencesinthecabletypes,incorrectormissingbusterminatorsaswellasadditionalPROFIBUSconnectorsthatarenotconnectedreducethequalityofthePROFIBUSnetwork.

12 The PROFIBUS signal quality index is a criterion for assessing the physical quality of an electrical signal during the PROFIBUScommunication.IthasbeendefinedbySoftingandisusedwithintheSoftingPROFIBUSdiagnostictools.

White Paper


Figure 7: QualityIndexBarGraphofAllStationsShowingGoodOperationalState (Thetesttoolisconnectedtostation2.Atthistestlocationthequalityindexofstation2isveryhigh.Thebarsaresortedintopologicalorder.Thefartherawayastation,theloweritsqualityindex.)

Bymonitoringthequalityindexforanextendedduration,fluctuationsinthequalityindexofasignal,e.g. during the course of a day or week, can be found. The long-term monitoring of the quality index, for instance,allowstodetectelectromagneticdisturbanceswhicharecausedbymachinesoperatedonlytemporarily,orwhichoccurduringthemachinerystart-up,e.g.atshiftchange.Inaddition,voltageorclimaticfluctuations(liketemperatureorcondensationchanges)inthecourseofadayorweekcanbeidentifiedaswell.

Aswiththetopologyscan(seeSection3.1.2)itisrecommendedtoperformthequalityindexmeasurementfrom both ends of the PROFIBUS network. Network problems can then be located by comparing the results.

Section4.2givestipsonhowtoanalyzeaqualityindexdiagramrecordedatdifferenttestlocations.

3.1.4 Signal-to-NoiseRatio

Thesignal-to-noiseratioindicatesthefrequencyofdeviationsfromtheidealsignalwaveform.Thesedevia-tionscanhaveexternalcauses(electromagneticdisturbances)orresultfromdetrimentaleffectsinthecabling(reflections,damping)ordefectivebusdriversinthestations.Disturbancescanalsobecoupledintothebusthroughastation.Evensporadicdisturbancesaredetectedusingthesignal-to-noiseratio.

Thesignal-to-noiseratioreferstotheminimumvoltagedifferencebetweenthelogic0levelandthelogic1levelofthePROFIBUSsignal.Itisdefinedbytheinterference-freerangeofthedifferentialvoltage(seeFigure 8)andindicatesthelevelofvulnerabilityofthePROFIBUScommunicationtodisturbancesataspecificstationwithinthePROFIBUSnetwork.

White Paper


Figure 8: DefinitionofSignal-to-NoiseRatioWithinPROFIBUSSignal

Thesignal-to-noiseratioisdeterminedbyadaptingthereferencevoltageduringteniterationsperformedovertenframesofthetestedstation.DuringthesestepsanyinterferenceofthePROFIBUSsignalthatexceedsthehigherorlowerlimitoftheactualreferencevoltageduringtheevaluationperiodleadstoacontinuousadaptationofthereferencevoltageuntilthefinalvalueisreached.Asaresult,disturbancesdirectlyinfluencethemeasuredsignal-to-noiseratio.

3.1.5 Rise Time

Therisetime(alsocalled“edgesteepness”)isanotherimportantaspectinthephysicalanalysisofaPROFIBUSDPnetwork.Thistestexaminesthetransitionsbetweenthelogic0levelandthelogic1levelofthePROFIBUSsignalandviceversa.Flattenededgesreducethetimeduringwhichtheappropriatevoltageisappliedconstantlyattherequiredlevel.InanextremecasethissituationmaypreventthereceivermodulesinPROFIBUSdevicestocorrectlydecodethetransmissionsignal,thusresultingintransmissionerrors. As a rule of thumb the appropriate voltage has to be constantly applied at the required level for at leastonehalfbittime.Todeterminetherisetime,thresholdvoltagevaluesaredefinedat10%and90%ofthedifferencebetweenthelogic0levelandthelogic1levelofthePROFIBUSsignal.Thetimerequiredforthedifferentialvoltagetochangebetweenthesetwothresholdvaluesismeasuredforbothrisingandfallingedges.TheresultingrisetimeandfalltimeindicatehowcloseaPROFIBUSsignalistotheidealsquarewaveform.TheelectricalpropertiesrelatedtotheuseoflongerPROFIBUScablesoradatatransmissionathigherbaudratescausea“rounder” signal waveform due to the damping at high frequencies.

White Paper


Figure 9: BeispielanzeigefürdieFlankensteilheitbeiderPROFIBUS-Kommunikation

3.1.6 Signal Waveform in Oscilloscope Display

AnotherwaytoanalyzetheelectricalsignalofaPROFIBUSDPcommunicationistousetheoscilloscopedisplay, which shows the voltage signal waveform for line A and line B. The display is based on user-select-abletriggersforrecordingthesignalofarelevantframe.Thesignalwaveformallowstodetectdistortionsofthesignalvoltagewaveformaswellasreflectionsonthecableresultingfromanincorrectlyinstalledcableorphysicalfaultswithinthenetwork.Thepositionofthereflectionsinthedisplayaswellastheirlengthgiveanindicationofthedistancebetweentheinterferencelocationandthecurrenttestlocation.

Therearedifferentmodeswhichprovideadditionalmeansfordetectingdisturbances:Whilethestandardmode compares the signals on line A and line B, the other two modes allow comparing line A and line B, respectively,withthegroundlevel.Thisfunctionalityenablesthedetectionofdisturbancesthataffectthetwosignalwiresinthesamewayandthuscannotbedetectedusingthedifferentialvoltage.

Byanalyzingthevoltagesignalwaveform,variouscablingissuescanbeidentified.Forinstance,atransientsignaldipmayrefertotheuseofspurcableswhilealongreflectionandsignaldipmayindicatetheuseofsignificantlydifferentcabletypes.Otherproblems,suchasshortcircuitsorfaultsinthebustermination,canalsobedetected.Inaddition,thevoltagesignalwaveformprovidesanindicationofanunwantedloador an increased resistance between line A and line B.

Thesignalwaveformallowsamoreaccurateidentificationofdifferentfaultcausesthanispossibleusingcondensedtestresultslikethequalityindex(seeSection3.1.3)orthesignal-to-noiseratio(seeSection3.1.4).Thedetailedinterpretationofthesignalwaveform,however,requiresexperienceandexpertise.

White Paper


3.2 Physical Analysis of PROFIBUS PA Networks

The physical analysis of PROFIBUS PA networks is performed at segment level.

It comprises various measurements of PROFIBUS cables and electrical signals in PROFIBUS PA networks using the Manchester Coded Bus Powered transmission technology. The tests conducted refer to the physicallayerofaPROFIBUScommunication.

APROFIBUSPAsegmentprovidespowertotheconnectedstations.Forthis,a“powerconditioner”appliesa DC voltage of up to 32 V to the bus line. At the far end of the segment a minimum voltage of 9 V is requiredforproperoperation.ThePROFIBUSframesaretransmittedasasymmetricACsignalontopoftheDCsupplyvoltageofroughly900mVpeak-to-peak.WhenaPROFIBUSPAstationtransmitsaframe,itmodulatesitscurrentconsumptionofatleast10mAaccordingtotheManchesterencodingschemeandthusgeneratesanACsignalcarryingtheinformationoftheframe.Duetoalow-passfilterinthepowerconditionertheACsignalisnoteliminatedbythevoltageregulationinthepowersupply.

ThephysicalanalysisofPROFIBUSPAnetworksconsistsofdifferenttypesofmeasurements.Theyarediscussedinthefollowingsections.Theindividualphysicalanalysismethodscanbecombinedforanoverallsegment check to assess the physical health of the connected PROFIBUS PA segment.

3.2.1 DC Voltage Measurement

The DC voltage measurement determines the DC voltage of the connected PROFIBUS PA segment. PROFIBUSPAsegmentsmayhavealengthofupto1900m.Aseachstationdrawsatleast10mAfromthebus, there is a voltage drop along the line. The standard requires a supply voltage in the range from 9 V to 32Vatanybuslocation.IfthemeasuredDCvoltageislessthanauser-configurablelimit(typically9V)anerror is displayed.

3.2.2 Signal Voltage

ThesignallevelofthemodulatedACsignalismeasuredforeachstationandgivesanindicationofthesignal quality. The nominal range is 700 mV to 1000 mV peak-to-peak.

3.2.3 BitRateDeviation

Thebitratedeviationfromthenominalvalueof31.25KBit/sismeasuredforeachstation.Thestandardrequiresadeviationlessthan0.2%.

3.2.4 Polarity

Thismeasurementdetectsthepolarityofthecommunicationsignalforeachstation.

White Paper


3.3 Logical Analysis of PROFIBUS Networks

AsthePROFIBUScommunication(PROFIBUSDPaswellasPROFIBUSPA)takesplaceacrosstheindividualsegments within the overall network, the logical analysis is performed at network level.

PROFIBUSDPandPROFIBUSPAbothusethesameprotocol,whichallowstheapplicationofthesamemethodsforanalyzingbothnetworksatalogicalcommunicationlevel.ThefocusisonmonitoringthePROFIBUScommunicationinordertoassessthelogicalstateofthePROFIBUSnetworkandtheconnectedstationsfromtheacquiredinformation.ThelogicalanalysisofPROFIBUSnetworksallowstoidentifyparameterandconfigurationerrorsintheindividualPROFIBUSstationsaswellastoanalyzethePROFIBUSdata, error frames and retries.

ThelogicalanalysisofPROFIBUSnetworksindicatesthatthePROFIBUScommunicationisworkingproperlyifnounwantedeventslikediagnosticmessages,errorframes,retries,etc.occurduringstandarddataexchangebetweenPROFIBUSMastersandPROFIBUSSlaves.However,thePROFIBUScommunicationisfaulttolerantanddoesnotrequireaperfectelectricalsituation.

ThissectiondescribesdifferentaspectsofanalyzingthecommunicationinaPROFIBUSnetwork.

3.3.1 Baud Rate

PROFIBUSDPsupportsavarietyoftransmissionratesintherangefrom9.6KBit/sto12MBit/s.Thus,thefirststepinanylogicalnetworkanalysisistodeterminetheactualtransmissionrate.

Typically,atoolforperformingthelogicalanalysisofPROFIBUSnetworksisabletoautomaticallydetectthebaudrateused.Thisisonlypossible,however,ifthereistrafficonthePROFIBUSnetwork.Otherwisethetransmission rate to be used for the logical network analysis has to be set manually. Specifying a baud rate thatdiffersfromtheoneactuallyusedinthePROFIBUSnetworkwillresultindetectingmanyframeerrors.The logical analysis of PROFIBUS networks cannot be carried out correctly, either, in that case.

3.3.2 Live List

Oncethebaudrateisset,themonitoredPROFIBUScommunicationcanbeusedtoscanforPROFIBUSstationsconnectedtothenetwork.Allstationsparticipatinginthecommunicationareincludedinthelivelist.

Foragraphicalpresentationofthelivelist,thepurelistofconnectedPROFIBUSstationscanbeextendedbyadditionalstationinformation,suchastheassignedPROFIBUSstationaddress,thedetectedstationstatusorfurtherdetailslikethedevicenamegiveninthestation’sGSDfile.Anexampleofalivelistisshown in the middle window shown in Figure 10.

White Paper


3.3.3 NetworkInformation

ThenetworkinformationprovidesanoverviewaboutthestatusofthePROFIBUScommunicationmonitoredinthePROFIBUSnetwork.Thedetailsavailableatthislevelinclude,forexample,theminimum/average/maximumbuscycledurationsaswellasthenumberofobservedretryframes,diagnosticmessagesandrestartsofPROFIBUSstations(derivedfromtheidentificationofparameterizationframes).AnexampleofthedisplayednetworkinformationcanbeseeninFigure 10.

Figure 10: NetworkInformationDisplay

3.3.4 PROFIBUSMasterInformation

ThePROFIBUSMasterinformationsummarizesthespecificcharacteristicsoftheindividualPROFIBUSMasters available in the PROFIBUS network. They are derived from the analysis of the logged PROFIBUS communication.

ThePROFIBUSMasterinformationincludestheindividualstationaddressesusedbythePROFIBUSMasterswithinthePROFIBUSnetworkaswellasthecurrentoperatingstates.Adistinctionismadebetweentheregulardataexchange,thestoppedoperationwithoutanycyclicdataexchangeaswellasthestateinwhichinputdataisreadbutnooutputdataiswrittenandwhichmaycausePROFIBUSSlavestoswitchtothefail-safestateifthisstateissupported.Furthermore,thePROFIBUSMasterinformationcomprisesthefollowing:thecurrentpollcycledefinedbythedurationofthecompletesetofcycliccommunicationframesexchangedbetweenthePROFIBUSMasterandallthePROFIBUSSlaves;theidletimeresultingfrom33bittimesplusanadditionaldelaydependingontheactualbusparameters;andtheslottimederivedfromthetimingbehaviorofthevariousPROFIBUSstations.

White Paper


3.3.5 PROFIBUSSlaveInformation

AllthePROFIBUSDPversions(PROFIBUSDP-V0throughtoPROFIBUSDP-V2)definediagnosticinformationontheslave,includingstandarddiagnosticsaswellasdevice-specificdiagnostics.

ThelogicalanalysisofthePROFIBUScommunicationdeliversverydetailedinformationontheindividualPROFIBUSSlaves,includinggeneralinformationabouteachPROFIBUSSlave.Iftheslave´sidentificationnumber is recorded, it is possible to provide vendor and device model details. The contents of the respec-tiveGSDfilecanalsobeusedtodisplaymeaningfuldiagnosticmessagesorthevendoranddevicemodel.Inaddition,informationaboutthecyclicinputandoutputaswellastheacyclicdataofthisdevicecanbeshown.

IfaPROFIBUSSlaveis(re-)startedduringtheanalysisperiod,thePROFIBUSMastersendsaparameteriza-tionframetothisslave.Theparametersgiveninthisframeincludeaminimumsetofparametersdefinedbythestandardaswellasadditionalapplication-specificparameters.Todecodetheseparameters,theappropriateGSDfileforthePROFIBUSSlavehastobeavailable.

Inresponsetoa(re-)startedPROFIBUSSlavethePROFIBUSMastercheckstheconfigurationbytransmittingaconfigurationframe.Theconfigurationinformationinthisframeisdisplayed.FormodularI/Odevicesthisinformationcanbeaccompaniedbyadditionaldetailsontheindividualmodulestructure,whichisobtainedfromtheappropriateGSDfile,ifavailable.WhenthePROFIBUSSlaveisrunningstable,however,noconfig-urationinformationisprovided.

IfanerrororanexceptionoccurswithinaPROFIBUSSlave,theslavenotifiesthePROFIBUSMasterofthissituationbysettingthediagnosticflagaspartofacyclicresponse.ThePROFIBUSMasterthengathersadditionalinformationontheerrororexceptionfromtheslavebyusingthePROFIBUSGetDiagservice.Individualerrorsandexceptionsthathaveoccurredduringtheanalysisperiodcanbelisted.

ThediagnosticinformationderivedfromthePROFIBUScommunicationcanbedividedintothreegroups:Device-specificdiagnosticinformationisbasedonafreelydefineddevice-specificbytestring,whichrequiresthedeviceGSDfilefordecoding.Theidentifier-specificdiagnosticinformationdescribesindi-vidualfaultsthathaveoccurredwithacertainsetofI/Odata,e.g.foraspecificmodule.Identifier-specificdiagnosescanbefurtherdetailedusingchannel-specificdiagnoses,whichindicateanerrortypeforeachI/Ochannel.Frequentlyoccurringerrortypesarepre-definedinthePROFIBUSstandardwhileothererrortypescanbespecifiedbythedevicemanufacturerbyassigningtextintheassociatedGSDfile.ThePROFIBUSDP-V1standarddefinesadditionaldiagnosticmessages,e.g.foraddingandremovingremoteI/Omodules.

3.3.6 Frame Analysis

FramesequencescanberecordedduringthelogicalanalysisofthePROFIBUScommunication.Forstartingandstoppingtherecording,varioustriggerconditionsareavailable.Framefilterscanbeappliedwhilerecordingoratalaterstagewhenanalyzingtherecordedframes.Filterconditionsarebasedonselectedstationaddressesand/orservices.Allrecordedframescontaintimestampswitharesolutionof10nstoallowfortiminganalysis.Therecordedframesarepresentedinadecodeddisplayformatfordetailedanalysesondifferentprotocollayers.

White Paper


4 Approaches for Analyzing a PROFIBUS Network

4.1 General Notes on Analyzing a PROFIBUS Network

When analyzing a PROFIBUS network some general points should be kept in mind.13

Likeallelectricallines,PROFIBUScableshaveohmicresistance,capacitanceandinductance.Inaddition,thebusdriversofthebusstationsareohmicandcapacitiveloads.Therefore,thevoltagelevelsandthesignalwaveformdeterminedatdifferentlocationsonthesamePROFIBUSnetworkcandiffersignificantly.

Furthermore, crossed wires or interrupted lines cause a failure of the PROFIBUS network from the fault locationonwards.Corrodedcontactsinconnectorscansignificantlyweakenthesignalfromthefaultlocationonwards.

Tofindthesefaults,itisrecommendedtomeasurethesignalqualityatdifferentlocationsonthebus,atleastatbothlineends.IfaPROFIBUSnetworkcomprisesmultiplesegmentsconnectedthroughrepeaters,each segment has to be measured separately.

OnewaytofindthecauseofanobservedproblemistodividethecompletePROFIBUSnetworkintosmallersegments and to test these using a PROFIBUS Master simulator. While this approach only allows to test the PROFIBUS network step by step, it is a reliable way to locate physical issues.

4.2 InterpretingtheQualityIndex

AkeycriterioninanalyzingandassessingaPROFIBUSnetworkisthequalityindex(seeSection3.1.3).Themeasuredqualityindexdependsonthestationtypeandtheoveralllengthofthecurrentlytestedcablesegment.

IftheoveralllengthofthePROFIBUSnetworkisrelativelyshortandthebushasbeenrecentlyinstalledandcommissioned,allmeasuredqualityindexesshouldbesignificantlyabove4,00014. For a longer segment, the quality index will decrease with increasing distance. A lower measured quality index can also be observed for tests taken from the other end of the PROFIBUS cable, if the baud-rate dependent maximum cable length has not been exceeded.

Ameasuredqualityindexbelow2,500alwaysindicatesdefectivecablingand/orconnectorsorincorrectnetwork terminators.

WhileaPROFIBUSinstallationwithameasuredqualityindexof1,000maystillberunning,theoperatingreservesforthebuscommunicationaredefinitelyalmostdepletedandthenoiseimmunityisverylow,resultinginsporadicfaults.

13 Ingeneral,itisimportanttounderstandthatallPROFIBUSdiagnostictoolsinfluencethePROFIBUStransmissionbehavior.Thisappliesparticularlytotheindividualtestlocations,i.e.thelocationwherethediagnostictoolisconnectedtothefieldbus.

14 TheSoftingqualityindexrangesbetween0and5,000.AgradualdeteriorationofthequalityindexesofthePROFIBUSstationsfromthetestlocationtotheremoteendofthefieldbusisstandardbehaviorandcausedbythecable’sresistivity.AlongcablelengthincombinationwitholderEIA-485driversmayresultinaqualityindexoflessthan4,000,whichinthiscaseisnotanindicationofPROFIBUSproblems.

White Paper


ForevaluatingthequalityindexofthevariousstationswithinaPROFIBUSnetworkitisrecommendedtocombinethequalityindexmeasurementwiththetopologyscan(seeSection3.1.2)andtoreviewthequalityindexoftheindividualstationsintopologicalorder.15

Ifastationshowsalowqualityindexwhilethequalityindexoftheneighboringstationisatanormallevel,thecauseisusuallyrelatedtothatstation.ForinstancetheremaybeaproblematthePROFIBUSconnector.Ontheotherhand,ifacompletegroupofneighboringstationsshowsalowqualityindex,thecauseisrelatedtothePROFIBUScablingbetweenthelaststationwithagoodqualityindexandthefirststationwithabadqualityindex.HereitisagoodideatorepeatthePROFIBUSanalysisfromtheotherendofthebuslineandtocomparetheresults.Ifasignificantdropinthequalityindexcanbeseenatthesamelocationwhenmeasuringfrombothsides,thecontactresistanceistoohighthere.IfthelocationofthequalityindexdropdiffersbetweenthemeasurementsfromthetwoendsofthePROFIBUSline,awirebreakandaninterruptionofthefieldbusareaprobablecause.

Agradualdeteriorationofthequalityindexesfromthetestlocationtotheremoteendofthebusisbasicallynormalandcausedbytheresistivity.Anexcessivedropinthequalityindex,however,indicatesapoor transmission behavior of the bus.

Iftestsperformedatdifferentlocationsshowconsiderablequalityindexdifferences,thecausemaybereflectionsduetodifferentcabletypes,spurcablesorconnectorsaswellasmissingbusterminators.Theerrorcausecanbefoundnearthetestlocationthatdeliveredtheworstqualityindexresults(seeFigure 11).

Figure 11: Example of the Quality Index Measured from Either End of the PROFIBUS Segment (Heretheterminatingresistorismissingatthebeginningofthebus,nearstation2.)

15 Incaseofcabledefectsorunwantedreflectionsonthecable,thetopologyscanwillnotdeliverreliableresults.Inthiscasetheuserhastomanuallysorttheindividualstationsintopologicalorder.

White Paper


4.3 Use Case: Acceptance of a PROFIBUS Network

AfterinstallationtheacceptanceofaPROFIBUSnetworkisaveryimportantsteptodocumentthestatusofthePROFIBUSnetworkataninitialstagebeforestartingthedailyproduction.Thenetworkstatustestresults that are documented during the acceptance test are very useful for verifying the proper perfor-manceofthePROFIBUSnetworkaftermaintenanceactivities.

Thecabletest(seeSection3.1.1)canbeusedasafirsttestduringtheinstallationandcommissioningphaseofaPROFIBUSnetwork.TheinstallercandirectlychecktheassembledcablesystemafterlayingthecableandscrewingtogetherthePROFIBUSconnectors.VeryofteninstallationandcommissioningofthePROFIBUScableareperformedbydifferentfieldservicepersonnel.InthiscasethepersoninchargeofcommissioningthePROFIBUSnetworkcancarryoutcabletestinginordertoverifythatthePROFIBUScablesegments have been properly installed. It is also a good idea to create a test report containing detailed informationaboutthetestedcablesegmentsduringtheacceptanceofaPROFIBUSnetwork.

AnotherindicatorofahealthyPROFIBUSnetworkistheresultofatopologyscan(seeSection3.1.2).ThesuccessfuldetectionofthecorrectPROFIBUSnetworktopologyprovesthatthephysicalnetworkinstalla-tion,includingproperterminationatbothends,hasbeenperformedcorrectlyandthatthecablesegmentisfreeofunwantedreflections.

Thenextstepistorunanetworkanalysisbasedonthenetworkinformation(seeSection3.3.3).InthistestthePROFIBUSnetworktrafficisloggedforsometime(i.e.longerthan10minutes)andcheckedforretryframes.AlownumberofretryframesindicatesthatthePROFIBUShasbeenconfiguredcorrectlyandthatthe individual PROFIBUS Slaves are working properly and are correctly connected to the network.16

ThequalityindexoftheindividualPROFIBUSstationsisdeterminednext(seeSections3.1.3 and 4.2).BesidestakingasnapshotofthequalityindexoftheindividualPROFIBUSstationsitisalsoimportanttoperformthismeasurementoveraprolongedperiodoftimetobeabletodetectfluctuationsofthecommu-nicationqualityduringthisperiod.Thetestshouldrunforatleastoneproductioncycleinordertoensurethateverycomponentwhichcouldaffectthequalityindexhasbeentested(e.g.trailingcablesandslidingcontactsweremoved).Thisstepalsomonitorsthesignalwaveform(seeSection3.1.6)bymeansoftheoscilloscopefunctiontocheckthesignalvoltageofthePROFIBUSstations.

Inthelaststepalong-termanalysisisconductedoverseveralhourstoascertainthecommunicationqualityofthePROFIBUSphysicsaswellasthePROFIBUScommunication(e.g.bycheckingthenumberofcommu-nicationfaults,retryframes,etc.).

16 Therequirementsregardingamaximumtolerablenumberofretrieswithinacertaintimeperiodstronglydependontheapplication.Inslowlyrunningcontrolsystems(e.g.watertreatment)withlongreactiontimes,theoccurrenceofretrieshashardlyanyimpactontheapplication.Ontheotherhand,infastrunningcontrolsystems(e.g.bottlingplants)orinfeedbackcontrolsystems,theoccurrenceofretriesmayhaveaconsiderableimpactontheoperationalavailabilityandstabilityoftheapplication.Herethereshouldbenoretryframesduringacceptanceofanetwork.However,withinsystemsrunninginanelectromagneticallypollutedenvironment,retriesmightbeinevitable.

White Paper


Figure 12: Detailed Test Report Summarizing the Results of a PROFIBUS Network Acceptance Test

The result of a PROFIBUS network acceptance test is documented in a formal report comprising the networkanalysisresults.Thecontentsofthetestreportcanbeadaptedwithaconfigurationtooltosuitindividualneeds(seeFigure 12).

4.4 UseCase:TroubleshootingaPROFIBUSNetwork

The individual measurement methods described in Chapter 3helptotroubleshootatleastpartiallyworkingPROFIBUS networks as well as PROFIBUS networks that are not working properly any longer or that sporadi-callyorcontinuouslystopworking.

4.4.1 TroubleshootingaWorkingPROFIBUSNetwork

AnincreasingnumberofcommunicationproblemsthatoccurduringtheregularoperationofaPROFIBUSnetworkareasignthatthequalityofthePROFIBUSinstallationhasdeterioratedsincethetimeofitsinitialinstallation.TroubleshootinghelpstoidentifyandlocatetheweakpointsinthePROFIBUSinstallationandtriggertargetedmaintenanceactionsforimprovingtheoverallqualityofthePROFIBUSnetworkandrestoring its original quality level.

Thecabletest(seeSection3.1.1)isausefulmethodfordetectingcablefaultsduetowornPROFIBUScablecomponents,suchasadefectivetrailingcableorbrokencablewires.

ThefirststepintroubleshootingaPROFIBUSnetworkthatisstillworkingistoacquirethenetworkinfor-mation(seeSection3.3.3).Iftestresultsareavailablefromprevioustroubleshootingactivitiesoraccep-tancetests,theyshouldbecomparedwiththecurrentresultsinordertofindfurtherclues.Inthisstep,thePROFIBUSnetworktrafficisloggedforsometime(i.e.longerthan10minutes)andcheckedforretryframes.AlargenumberofretryframessuggeststhatthePROFIBUSnetwork’soperatingreservesforthebuscommunicationhavedecreasedcomparedtotheinitialstatusandthatthePROFIBUScommunicationisin a state of growing instability.

White Paper


Thenthequalityindex(seeSections3.1.3 and 4.2)isdeterminedforeachstation.Toobtainageneraloverview,thismeasurementisperformedoverafewminutesattwoorthreedifferentlocationswithineachcablesegmentofthePROFIBUSnetwork.Forstationswithlowqualityindexes,theoscilloscopeviewcanbeusedforfurtheranalysis(seeSection3.1.6).LowsignallevelsinthemiddleofeachbitindicatefaultyEIA-485transceiversorincreasedresistanceintheconnectororcable,whereasanydeviationfromtherectangularshapeiscausedbyirregularcapacitiveorinductiveloads.

Theoccurrenceofretryframes,restarts/parameterizationsandframeerrorsaswellastheobservationoflowqualityindexesorasignalwaveformthatdoesnotrepresentcorrectPROFIBUScommunicationbehaviorareimportantcluestoidentifyaPROFIBUScommunicationproblem,finditscausewithinthenetworkanddeterminetheappropriatemaintenanceactions.

OncompletionofthemaintenanceworkitisrecommendedtoperformthesetoftroubleshootingactionsrecommendedforaPROFIBUSnetworkacceptancetest(seeSection4.3).ThisensuresreliablePROFIBUScommunication.

4.4.2 TroubleshootingaNon-WorkingPROFIBUSNetwork

IfthePROFIBUSnetworkisnotworkinganylonger,theavailableoperatingreserveshavedecreasedtoapointwherePROFIBUScommunicationisnolongerpossible.

ThefirststepthereforeistobringthePROFIBUSnetworkintoastatewheretheindividualtroubleshootingactionsdescribedinChapter3canbecarriedout.ThiscanusuallybeachievedbysubdividingtheaffectedPROFIBUSsectionintoindividualworkingPROFIBUSsubsegmentsandbyperformingtheindividualstepsdescribedinSection4.4.1 for each of these subsegments.

The division of a PROFIBUS network typically disconnects the PROFIBUS Master from the individual PROFIBUSstationsinthesubsegment.ItisthusrecommendedtoconnecttheMastersimulatortotherelevantPROFIBUSsegmentinordertorunaphysicalanalysisofthebus(suchasqualityindex,risetime,signal-to-noiseratio,topologyorthecableitself).17

17 AstheMastersimulatordoesnotactasaregularPROFIBUSDPMaster,theinformationprovidedintheprotocolviewwillonlybeoflimitedusewhentheMastersimulatorisactive.

White Paper


5 Analysis Tools for PROFIBUS Networks

Toaccommodatethewidevarietyofusecases,differentanalysistoolsareavailablefortroubleshootingaPROFIBUSnetwork.Thischapterintroducestheindividualtoolsandexplainstheirfunctionality.

5.1 MobilePROFIBUSDiagnosticsTool

DesignedfortroubleshootingaPROFIBUSnetworkdirectlyonsiteintheproductionplant,amobilediag-nosticstool18providesacomprehensivesetoffunctionality,asdescribedinChapter3. It is used during setupandcommissioningofthePROFIBUSnetworkaswellasfortroubleshooting,andcanalsobeusedforlaboratory tests.

Figure 13: MobileToolforPROFIBUSNetworkDiagnostics

ThetoolprovidesfunctionalityfortestingthePROFIBUScablesandtheelectricalsignals,andforperformingthelogicalnetworkanalysis.WithitspowerfulfunctionalitythemobilediagnosticstoolthuscombinesthephysicalanalysisofPROFIBUSDP(seeSection3.1)andPROFIBUSPA(seeSection3.2)networksaswellasthelogicalPROFIBUSanalysis(seeSection3.3)inonecompactunit.

18 ThemobilediagnosticstooldescribedinthissectionreferstotheSoftingPROFIBUSTester5(BC-700-PB)product.

White Paper


Duetothevarietyofdiagnosticcasessupportedbythemobilediagnosticstool,itseaseofuseisaveryimportantprerequisite.Inadditiontoanintuitive,simple-to-useoperatorinterface,pushbuttons,agraphicalcolordisplayandacontext-sensitivehelpsystem,amobiledevicealsohastofeatureastand-alonemodeforusewithoutaPCornotebooksothatitcanbeeasilytakentotheindividualtestlocationswithintheplant.Batterysupporteliminatestheneedforapoweroutlet.Thefunctionalityiscomple-mentedbytheabilitytologdatawhileworkingremotelyintheplant.Afullsetofvisualizationcapabilitiesforpresentingthetestresultsinaclearandeasy-to-understandmannercompletethefunctionality.

ThemobilediagnosticstoolsupportsacceptancetestingofinstalledPROFIBUSnetworksaswellaspreven-tivemaintenanceactivities.ItallowstheoptimizationofPROFIBUSinstallationsandthedetaileddocumen-tationoftheinstalledstatus.

5.2 PROFIBUSDiagnosticsSoftware

ThePROFIBUSdiagnosticssoftware19runsonPChardwareandextendsthefunctionalityofthemobilePROFIBUSdiagnosticstool(seeSection5.1).Thedataloggedinthemobiledeviceduringthediagnos-ticssession(s)canbeaccessedandanalyzedindetailbymakingoptimaluseofthegraphicalcapabilitiesprovidedbythisenvironment.ThePROFIBUSdiagnosticssoftwareisthusanessentialcomponentofanoverallPROFIBUSdiagnosticsconcept.

Basedontheloggedanalysisdata,thePROFIBUSdiagnosticssoftwareprovidesthevarioussignalandlogicalanalysiscapabilitiesfortestingPROFIBUSnetworksasdescribedinChapter3. It addresses the full rangeofcommissioningandtroubleshootingrequirementsforaPROFIBUSinstallation.AnexampleoftheinformationprovidedbythePROFIBUSdiagnosticssoftwareisshowninFigure 14.

19 ThedescriptionofthePROFIBUSdiagnosticssoftwareisbasedontheSoftingPROFIBUSDiagnosticsSuite.

White Paper


Figure 14: PROFIBUSDiagnosticsSoftwareAllowingDetailedAnalysisofRecordedPROFIBUSFrames

ThePROFIBUSdiagnosticssoftwareoffersadditionaldiagnosticfunctionalitycomparedtothemobilePROFIBUSdiagnosticstool.Forinstance,thePROFIBUSdiagnosticssoftwarecanbeusedfor:

• Scanning the PROFIBUS topology• Analyzingframesbyusingtriggerandfilterconditions• EvaluatingthetestsperformedwiththemobilePROFIBUSdiagnosticstool• Analyzingthesignalwaveformbyusingoscilloscopefunctionality

AnotherpowerfulfeatureofthePROFIBUSdiagnosticssoftwareisthepossibilitytocarryoutquicktests(i.e.anautomatedsequenceofbasictests),whichprovideacomprehensiveoverviewofthenetworkstatus–atthepushofabutton,inlessthanoneminute.Alltheinformationisshowninplaintextonthesoft-ware’suserinterfaceusingthecontentoftherespectiveGSDfilesoftheconnectedPROFIBUSstations.

ThecomprehensivefunctionalityalsosupportstheuseofthePROFIBUSdiagnosticssoftwareinacceptancetests.Forthis,thesoftwareprovidesaspecialfeatureforgeneratingatestreportasshowninFigure 12.

5.3 StationaryPROFIBUSDiagnosticsTool

Astationarydiagnosticstool20(seeFigure 15)isdesigned,inparticular,forthelong-termdiagnosisofthePROFIBUScommunicationwithinanetwork.ItlogsandanalyzesthecompletePROFIBUStrafficoveralongertimeframe.Thestationarydiagnosticstoolisespeciallysuitablefordetectingcommunicationproblemswiththehelpofcontinuousmonitoring–withouttheneedforengineersonsite.

20 ThestationarydiagnosticstooldescribedinthissectionreferstotheSoftingTHLINKPROFIBUSproduct.

White Paper


Figure 15: StationaryToolforAnalyzingthePROFIBUSTraffic

Thekeyadvantageofastationarydiagnosticstoolisthatitallowsthecontinuousanalysisofthenetwork,includingthemeasurementofthePROFIBUScycletimesandthedetectionofcriticalevents,suchasthenumberofframeretries,messageretransmissionsandrestartsofPROFIBUSstations,aswellasdevicefaults(seedetailsdescribedinSection3.3)anddiagnosticmessages.Thisdataisusedforderivinginforma-tionabouttheactualdecreaseofoperatingreservesforthebuscommunicationatastageatwhichthePROFIBUSnetworkitselfisstillworkingproperly.

InadditiontothesimpledisplayofOKorBADoperatingstates,thestationarydiagnosticstoolalsoprovidesaccesstologgedinformationaboutthePROFIBUScommunication.ThisinformationcantypicallybeaccessedthroughanintegratedwebserverconnectedviaEthernettoacentralmonitoringandoperatingstation,whicheliminatestheneedforon-siteinspections.

ThestationarydiagnosticstoolisinstalledbyconnectingittothePROFIBUSnetworkinserieswiththeother devices. It requires no changes to the bus addresses and the control program.

White Paper


6 Summary

AsadigitalfieldbusPROFIBUSprovidesverystablecommunicationcapabilities.Itisimportanttounder-stand,however,thattheoriginalstatusatthetimeofthenetworkinstallationwillnotremaininitscurrentstatethroughoutthecompletelifecycle.TheoperatingreservesforthePROFIBUScommunicationwillratherdecreasecontinuouslyandmaintenanceactivitieswillberequiredinordertocounteracttheagingofthePROFIBUScommunicationandpreventage-relateddowntimes.

Thus,itisessentialtocontinuouslyobservethecurrentstatusofthePROFIBUSinstallationandtoscheduletheappropriatemaintenanceactivitiespriortotheoccurrenceofexpensivedowntimesoftheplantduetomalfunctioningPROFIBUScommunication.Anextensivesetofanalysiscapabilitiesareavailableforthistask, including the physical analysis of electrical signals within PROFIBUS DP and PROFIBUS PA networks. In addition,thePROFIBUScommunicationcanbeanalyzedatlogicallevel.Asummaryofallthesepossibilitiescan be found in Table 2.

White Paper


AnalysisFunctionLife Cycle Phase SupportedDiagnosticsTools

Acceptance Test

Troubleshooting

Mobile(Stand Alone)

Mobile(PCBased) Stationary

PROFIBUS DP Cable Test

X X

PROFIBUS DP Topology Scan

X X X

PROFIBUS DP Quality Index

X X X X

PROFIBUS DP Signal-to-NoiseRatio

X X

PROFIBUS DP Rise Time

X X

PROFIBUS DP Signal Waveform

X X X X

PROFIBUS PA DC Voltage Measurement

X X X X

PROFIBUS PA Signal Voltage Measurement

X X X X

PROFIBUS PA BitRateDeviation

X X X X

PROFIBUS PA Polarity

X X X

PROFIBUS DP BaudRateDetection

X X X

Live List X X X

NetworkInformation X X X X X

PROFIBUS MasterInformation

X X X X

PROFIBUS SlaveInformation

X X X X

Frame Analysis X X X X X

Table 2: UsageofDifferentPROFIBUSDiagnostics

White Paper


Theavailablesetofdiagnosticfunctionalityisdesignedtosuitthedifferenttasksthatneedtobeaccom-plishedoverthelifecycleofaPROFIBUSinstallation.Ontheonehand,itcanbeusedtoensureproperPROFIBUSinstallationbeforestartingthenetworkoperation.MobilePROFIBUSdiagnosticstoolsareidealforthistask.Ontheotherhand,thePROFIBUSnetworkdiagnosticssupporttheearlydetectionofexistingPROFIBUScommunicationproblemswithinarunningplant.ThechallengehereistocontinuouslymonitorthecurrentPROFIBUSinstallationstatusandtotriggertheappropriatemaintenanceactionspriortoexpensivebreakdowns.Consequently,thisapplicationareafocusesontheuseofstationaryPROFIBUSdiagnosticstools.

Insummary,theindividualPROFIBUSdiagnosticcapabilitiesdiscussedinthisWhitePapersafeguardahighavailabilityandoperatingreserveofPROFIBUSnetworksthroughouttheirlifecycle.However,usingtherightdiagnosticproceduresintherightsituationisjustasessentialasin-depthPROFIBUSexpertise.OnlythiscombinationensuresthattherightactionistakenattherighttimetokeepthePROFIBUSnetworkupandrunningatalltimes,withoutanyproblems.

White Paper


7 TerminologyRelatedtoPROFIBUSDiagnostics

Baud Rate Datatransmissionrate(1Baud=1Bit/s)PROFIBUSDPsupportsdifferenttransmissionratesintherangefrom9.6KBit/sto12MBit/s.PROFIBUS PA is based on the Manchester Coded Bus Powered (MBP) trans-missiontechnologysupportingafixeddatatransmissionrateof31.25KBit/s.

Bit Time TimeneededfortransmittingonebitThe Bit Time depends on the Baud Rate.

Bus Cycle PROFIBUScommunicationduringacompleteTokencirculationThe bus cycle includes all PROFIBUS frames sent between the start of the cyclicPROFIBUScommunicationperformedbyonePROFIBUS Master and the followingstartofthecyclicPROFIBUScommunicationbythesamePROFIBUS Master.InamultimastersystemthebuscyclecoversthecompletesetofthecyclicPROFIBUScommunicationperformedbetweentheindividual PROFIBUS Masters and all PROFIBUS Slaves.

DifferentialVoltage Voltage between the EIA-485signallinesA(pin8)andB(pin3)TheDifferentialVoltageisdigitizedbytheindividualPROFIBUSstationsintologic1orlogic0informationforeachindividualBit Time.TheDifferentialVoltage refers to a momentary snapshot and changes permanently.

Edge Error Bit for which the edge Rise Time and Fall Time of the Differential Voltage is morethan6/16thoftheBit TimeAnEdgeErroristheresultofinsufficientRise Timewhentransmittingabit.

EIA485 OSImodelphysicallayerelectricalspecificationofatwo-wire,half-duplex,multipointserialconnectionEIA-485specifiesadifferentialformofsignaling.Thedataisconveyedbythedifferencebetweenthewires’voltages.Onepolarityofvoltageindicateslogic 1, the reverse polarity indicates logic 0.EIA-485 is the most commonly used physical layer in PROFIBUS DP networks.EIA-485 has been formerly known as RS-485 or RS485.

EvaluationPeriod 10/16thoftheBit Timearoundthebitcenter(EIA-485 transceiver-sample point),withinwhichtheSignal-to-Noise Ratio is measured

Fall Time Time required for a PROFIBUS signal to change from the logic 1 level to the logic 0 level21

21 ThefalltimeismeasuredbytheSoftingPROFIBUSDiagnosticsToolswitharesolutionof1/16thofthebittime.

White Paper


Glitch Error Bit for which the measured Differential Voltage is less than the current Refer-ence Voltageforatleast2/16thoftheBit Time and then recoversGlitchErrorsaretheresultofovershootsandundershootswhentransmittinga bit.

Idle State Busconditionbetweentwosuccessiveframes,eitherbetweenaresponseframe and the request frame of the subsequent message cycle or between a request frame for which no response frame is returned and the next request frameIn the Idle State no EIA-485transmitterofanystationisactive.ThevoltagelevelduringtheIdleStateisensuredbythebustermination.

Illegal Frame Frame not conformant to IEC 61158-3

Level Error Bit for which the measured Differential Voltage does not reach the current Reference VoltageLevelErrorsaretheresultofvoltagedipswhentransmittingabit.

Logical Analysis Analysis of a PROFIBUS network at the Data Link Layer of the PROFIBUS com-municationThe Logical Analysis is based on the analysis of individual PROFIBUS frames. It is performed at the PROFIBUS network level.For a full analysis of a PROFIBUS network the Logical Analysis has to be complemented by a Physical Analysis.

Manchester Coded Bus Powered (MBP)

OSImodelphysicallayerelectricalspecificationofdigitalbit-synchronousdatatransmissionbasedonatwistedtwo-wire,bidirectionalconnectionMBPiswidelyusedforfieldbusesintheprocessindustry.The MBP transmission technology provides a data transmission rate of 31.25 KBit/sandperformsatleastonetransitionbetweenthelogic0levelandthelogic1levelorviceversafortransmittingonebit.Itrequires8bitsforencod-ing a character.MBPiscapableofsupplyingpowertotheindividualfielddevicesviathebuswire.PROFIBUS PA uses MBP transmission technology.MBP is standardized in IEC 61158-2.

White Paper


Message Cycle SmallestelementaryPROFIBUScommunicationunitA Message Cycle consists of a request frame sent by a PROFIBUS Master to anotherPROFIBUSstationplusthecorrespondingresponseoracknowledge-ment frame.ThetimingofaPROFIBUSmessagecyclehastorespecttheIdleTimeaswellastheminimumstationdelaytimedefinedfortheindividualPROFIBUS station.Only PROFIBUS MastershavetherighttoinitiateaMessageCycleaslongthey possess the Token.

Physical Analysis Analysis of a PROFIBUS network at the physical layer of the PROFIBUS com-municationThe Physical Analysis combines the measurement of PROFIBUS cables includ-ing the Terminators and the measurement of electrical signals. It is per-formed at the PROFIBUS segment level.For a full analysis of a PROFIBUS network the Physical Analysis has to be complemented by a Logical Analysis.

PROFIBUS Master ActivebusstationcoordinatingtheaccesstothebusUsuallyacontrolleractsasthePROFIBUSMaster.Inaddition,SCADAstationsor MPI panels may act as PROFIBUS Masters. PROFIBUSsupportstheuseofone(singlemastersystem)orseveral PROFIBUSMasters(multimastersystem)withinonenetwork.

PROFIBUS Segment SectionofthePROFIBUSnetworkterminatedonbothlineendsusinga poweredresistorcombination(Terminator)A repeater which is either inserted between line ends or else connected to onelineendalsoconstitutesasegmenttermination.

PROFIBUS Slave Busstationwhichasaruleonlysendstothebusuponrequestbythe PROFIBUS Master(e.g.digitalI/O)

Quality Index ValueindicatingthequalityofthePROFIBUScommunicationforaspecificPROFIBUSstationbyassessingthevoltagelevelaswellasthesignalwave-formTheQualityIndexisdeterminedbythefinalvalueoftheReference Voltage, whichisdefinedbyatotalnumberof20Glitch Errors, Edge Errors and Level Errorswhiletransmitting1,000bitsto/fromanindividualstation.

Reference Voltage Differential Voltagewhichismodifiediterativelyaccordingtoaspecific algorithmtowardsafinalvalue,whichthendefinestheQuality Index and the Signal-to-Noise Ratio

White Paper


Retry Frame PROFIBUS Request Frame sent again by the PROFIBUS Master if the PROFIBUSstationhasnottransmittedtherequestedresponseoracknow-ledgement frame within the Slot Time

Rise Time Time required for a PROFIBUS signal to change from the logic 0 level to the logic 1 level22

Signal-to-NoiseRatio Maximum of the interference-free range of the Differential Voltage deter-mined during the Evaluation PeriodoftheframesforaspecificPROFIBUSstationVoltage drops during the Evaluation Period are not taken into account if they arelessthan1/16oftheBit Time.TheSignal-to-NoiseRatioisdeterminedbythefinalvalueoftheReference VoltageatwhichnointerferencewiththePROFIBUSsignaloccursafterevaluatingtenframesofaspecificstation.

Slot Time MaximumwaitingtimebetweensendingthePROFIBUSrequestframeandthecompletereceptionofthefirstbitoftherequestedresponseoracknow-ledgement frame

Terminator TerminationatbothendsofaPROFIBUSsegmentTheTerminatorpreventsreflectionsbyprovidingthecorrectimpedanceatbothendsofthePROFIBUSsegment.Inaddition,theTerminatorensuresaDifferential Voltage of approximately 1.1 V during the Idle State.

Token Frame(SD4)whichisexchangedbetweentheindividualactivestations (PROFIBUS Masters)inaround-robinfashiontoinitiatetheindividual PROFIBUScommunicationandthuscontrolaccesstothePROFIBUSnetworkOnlythestationpossessingtheTokenisallowedtostartaMessage Cycle.In a single master system the Token is passed from the PROFIBUS Master to itself.

22 TherisetimeismeasuredbytheSoftingPROFIBUSDiagnosticsToolswitharesolutionof1/16thofthebittime.

White Paper


8 AboutSofting

TheSoftingIndustrialAutomationsegmentispartoftheSoftinggroupfoundedin1979.

SoftingIndustrialAutomationisaglobalspecialistinindustrialcommunicationtechnologiessuchasfield-busesandIndustrialEthernet.Withover35yearsofexperience,Softing’sIndustrialAutomationbusinessunitsdeliverconnectivity,diagnosticproducts,andservicestocustomersinthefactoryandprocessauto-mationindustry.

SoftinghasbeenworkingonthePROFIBUStechnologysincethestartoftheinitialPROFIBUSprojectlaunchedin1987.SincethenSoftinghasbeendeeplyinvolvedinthedevelopmentofvariouskindsofPROFIBUSproducts.Today,theSoftingPROFIBUSofferingisproven-in-useinawidevarietyofapplicationsby a large number of manufacturers and users around the world.

Softing’sgreattechnicalPROFIBUSexpertiseandexperienceresultingfromimplementingavastnumberoffield-provenproductsandsuccessfulcustomer-specificprojectshasalsoledtothedevelopmentofefficientPROFIBUSdiagnostictoolsthatarewidelyusedinthemarket.TheseproductssupportmobileaswellasstationaryanalysesandincludepowerfulPROFIBUSdiagnosticsoftware.AsaresulttheSoftingproductsofferacomprehensivesetoffunctionalityfordetectingandsolvingthedifferenttypesofPROFIBUSproblems.TocomplementthisrangeofproductsSoftingalsoofferstrainingsfortroubleshootingPROFIBUSnetworksandperformson-siteoperationsforanalyzingandsolvingindividualdetectedPROFIBUSproblems.

TheSoftingproductsaretailoredtotherequirementsofsystemintegrators,devicevendors,machineandequipmentmanufacturers,orendusersandareknownfortheireaseofuseandfunctionaladvantages.

SoftingIndustrialAutomationGmbH Richard-Reitzner-Allee 6 85540 Haar Germany Phone: +49 89 45 656 -340 Fax: +49 89 45 656 -488 E-Mail: [email protected] industrial.softing.com

White Paper

mailto:info.automation%40softing.com?subject=PROFIBUS%20Diagnosis

http://industrial.softing.com/en/startpage.html


9 Authors

Dr. Hans Endl Product Management SoftingIndustrialAutomationGmbH Haar(nearMunich),Germany

Georg Süss OperationalMarketing SoftingIndustrialAutomationGmbH Haar(nearMunich),Germany

10 References

• PROFIBUSDiagnosticsSuite GettingStartedManual Version 2.11, Revision May 31, 2013 SoftingIndustrialAutomationGmbH,May2013

• The Insider’s Guide to Maintaining PROFIBUS Networks AnintroductiontocommonPROFIBUSproblems,theirlocationandrectification Hitex Development Tools Available at: http://www.hitex.co.uk/fileadmin/uk-files/downloads/softing/Maintaining_profibus_3.pdf (asofJune16,2016)

• PROFIBUSInstallationGuidelineforCommissioning Version 1.0.2, Order No. 8.032 PROFIBUS&PROFINETInternational,November2006

• QualityofProfibusInstallations Max Felser, Bern University of Applied Sciences WFCS2006,6thIEEEInternationalWorkshoponFactoryCommunicationSystems, June27-30,2006,ConferenceCenterTorinoIncontra,Torino,Italy Available at: http://www.felser.ch/download/FE-TR-0601.pdf (asofJune16,2016)

White Paper

http://www.hitex.co.uk/fileadmin/uk-files/downloads/softing/Maintaining_profibus_3.pdf

http://www.felser.ch/download/FE-TR-0601.pdf


11 List of Figures

12 List of Tables

Table 1: PROFIBUS DP Device Types ..................................................................................................... 4

Table2: UsageofDifferentPROFIBUSDiagnostics .............................................................................. 30

Figure1: DifferentMarketSegmentsSupportedbyPROFIBUS .............................................................. 2

Figure2: CyclicandAcyclicPROFIBUSDPCommunication ..................................................................... 5

Figure 3: Trunk & Spur Technology Used by PROFIBUS PA and Coupling of PROFIBUS PA Segments to PROFIBUS DP ...................................................................................................... 6

Figure 4: PROFIBUS Cable Test Results ................................................................................................. 10

Figure 5: Detailed Results from PROFIBUS Cable Test .......................................................................... 10

Figure6: TopologyScanResultIndicatingaHealthyPROFIBUSNetwork ............................................. 11

Figure7: QualityIndexBarGraphofAllStationsShowingGoodOperationalState ............................. 13

Figure8: DefinitionofSignal-to-NoiseRatioWithinPROFIBUSSignal .................................................. 14

Figure9: BeispielanzeigefürdieFlankensteilheitbeiderPROFIBUS-Kommunikation .......................... 15

Figure10: NetworkInformationDisplay ................................................................................................ 18

Figure 11: Example of the Quality Index Measured from Either End of the PROFIBUS Segment ............21

Figure 12: Detailed Test Report Summarizing the Results of a PROFIBUS Network Acceptance Test ......23

Figure13: MobileToolforPROFIBUSNetworkDiagnostics .................................................................... 25

Figure14: PROFIBUSDiagnosticsSoftwareAllowingDetailedAnalysisofRecordedPROFIBUSFrames .27

Figure15: StationaryToolforAnalyzingthePROFIBUSTraffic ............................................................... 28

White Paper

best practices in profibus network diagnostics - softing · pdf filebest practices in profibus...

Documents