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Lifecycle planning for your DCSBy Mitch Cochran, Process Control Solutions LLC

Theadventofthedistributedcon-trol system (DCS) in the1980sbroughtpowerplantcontrolintothe digital age, combined the

formerlyseparatefunctionsofcontroland data acquisition, and enabledprocess data to be integrated withenterprise-wide business-manage-mentdata.Inthe1990s,DCSsuppli-ers further enhanced their systems,movingawayfromproprietaryhard-wareandsoftware,andtowardmoreinter-operable, standards-basednetworks. Net result: Today’s DCSis a reliable, user-friendlyproduct that dominatesthe controls sector of theelectric-power industry.

Butallproducts,nomat-ter how dominant, havea finite lifecycle. This isparticularlytrueformicro-processor-based products.Owner/operators of DCSs,therefore, eventually mustaddresssuchlifecycleplan-ning problems as lack ofmanufacturer support,shortage of spare parts,andprocessorcapacitylim-itations.Lifecycleplanningalso involvesevaluationofbudgetary constraints aswellascorporatestrategiesregarding future expan-sion.

This article discusseslifecycle planning for oneof the most popular DCSs in NorthAmerica—the WDPF (for Westing-house Distributed Processing Fam-ily), manufactured by Emerson Pro-cess Management’s Power & WaterSolutions unit, Pittsburgh, Pa. Notethat Emerson purchased the formerWestinghouse Process Control Divwhen Siemens AG acquired thatcompany’s power generation busi-ness. Intent here is to help ownersof any make and model DCS decidehow long they should retain theirexistingcontrolsystem,andatwhatpointtheyshouldmaketheleaptoanewsystem—usingtheWDPFasanexample.

WDPF maintenanceTheWDPFcontrol systemhasbeenon the market since the mid 1980s,and is approaching the end of itsproduct lifecycle (Fig1).That’snotaknock against the product. That’s afactestablishedbythemanufacturer’sproduct-support policy. Emerson’spolicyistoprovideaminimumof10yearsofproductsupport.Thefollow-ingdefinitionsfromtheoriginalequip-mentmanufacturer(OEM)apply:n “Current products” are the most

up-to-date products offered withpublished pricing, normal leadtimes,andcompletesupport.Cur-rentproductsarerecommendedfornewinstallations.

n “Active products” have been func-tionallyreplacedby“currentprod-ucts,” but remain available withpublished pricing, normal leadtimes, and complete support.Active products are intended forexpansion of existing systems.Transitionto“activeproduct”sta-tus marks the start of the 10-yrproduct-supportcommitment.

n “Maintained products” gener-allyarenotavailableforpurchase.

Supportisavailable,butisfocusedstrictly on maintenance—replace-mentparts,repairs,andfieldser-vice. Emerson encourages ownersofproductsinthiscategorytoiniti-atetheirlifecycleplanning.

n “Retired products” are no longeravailable for purchase. Supportis limited, slower, more costly,and subject to material availabil-ity.Transitionto“retiredproduct”statusmarkstheendofthe10-yrproduct-supportcommitment.TheWDPFcontrolsystemisclas-

sified as a “maintainedproduct,” and is quicklyapproaching “retired prod-uct” status. At the man-agement level, therefore,WDPFusersshouldbeask-ingthemselves:Howlong—andatwhatO&Mcost—canI maintain my DCS? Howmuch—and in what year—shouldIbudgetforasystemupgrade?

At the technician level,usersshouldbeasking:Aremy system backups com-pleteanduptodate?WhatcanIdo tobeprepared fora software server crash?WherecanIgetrefurbishedWDPF parts? Could I ben-efit from having a plantsimulator?WhatcanIdotoalleviate memory capacitylimitations?

System backups. Topreventthelossofcriticalconfigurationsoftwareduring a hardware or software fail-ure,WDPFsystemsmustbebackedupproperly.Recoveringfromahard-diskcrashonanoperatorWEStationis routine maintenance, requiringonlyablankharddriveandthe“bootnet–install”procedurefromtheSoft-wareLoadKitU0-8001-2.x.

The software server, however, isthe most critical drop in the WDPFsystem, since all other drops areloaded from the software server. Sorecovering from a hard-disk crashonthesoftwareserverisamuchbig-ger deal. This requires Solaris and

1. Even the most reliable DCS eventually needs to be upgraded, because of such problems as lack of OEM sup-port and shortage of spare parts

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WDPF Release CD-ROMs, back-uptapes, third-party licenses, variouscustom files and drivers, and more.Manytimes,ifproperback-upshavenot been maintained, recovery froma hard-disk crash on the softwareserver cannot be accomplished com-pletely.

The solution: Maintain a “hot-spare”backupharddriveforthesoft-ware server. With this action, eventhe worst-case scenario—recoveryfrom a software server hard-drivefailure—becomes routine mainte-nance.

SerialinterfaceQLCcardscontainconfigurationfiles inbattery-backedRAMmemory.Thesefilesalsomustbe backed up to storage media, incaseaQLCcardfails.

The WDPF is not self-document-ing. Therefore, all logic drawings—knownas“SAMA”drawingsbecausethey follow theScientificApparatusMakers Assn standards—must bemaintained. An “as-built” drawingreview may be needed, in order tobringyourdrawingsup-to-date.

All of these maintenance tasksshouldbeperformed,ataminimum,during an annual inspection of theWDPF system. At this time, pre-ventive maintenance also should beconducted on the WDPF hardware,to prevent dust, soiling, or normal

wear-and-tear from impairing sys-tem reliability. The annual inspec-tion also should include housekeep-ing tasks for the Unix file system,and documentation of processormemory.

Capacity limitations oftheWDPFsystem can hamper system opera-tion and maintenance by makingit impossible to add or modify DCScontrollogic,alarming,ormonitoringfunctions.Lackofavailabledatabasespace in the distributed process-ing units (DPUs) and in the datahighwaysystemIDs—referred toasSIDs—arethemostcommoncapacityproblemsencounteredwithaWDPFcontrolsystem.

OneactionthatfreesupdatabasememoryiscleanupoftheDPUs.Thisworkdoesnotrequireanyadditionalhardware,andmostofitcanbedoneoffsite so that plant downtime isminimized. The cleanup procedureidentifiesanddeletesunusedpointsand obsolete logic. It also identifiesalarmablepointsthatcouldbemovedtoanemptyDPU.Atotalplantout-ageisnotrequiredtoaccomplishthistask.

Anotheroptiontoalleviatecapac-ity limitations is to add anotherDPU processor to the system. EachDPU comprises 120 kilobytes (kB)of database space to which alarms

fromotherDPUscouldbere-located.Adding a DPU with cabinet and Q-Crates makes it possible to relocateI/O points and control functionsfromotherDPUs,aswellasmovingalarms.

Rebuildingthesystempointdirec-tory can alleviate the problem ofSIDsbeing“maxedout.”Inadditionto identifying and deleting unusedpointsandobsoletelogic,pointbroad-cast frequencies will be optimized.Preliminary steps can be performedoffsiteontheDPUsourcecode,butatotalplantoutageofonetotwodaysisrequiredtoloadthemodifiedDPUsource code and rebuild the systempointdirectory.

Hardware maintenance. Severaloptionsareavailabletousers,whenitcomestohardwaremaintenanceoftheWDPFsystem.SupportfromtheOEMincludes:n Emerson Sure-Serve Contracts.

The OEM of fers repair andexchange services designed toaccommodate varying needs anddeliveryrequirements.

n Standard Repair and Return.Under this traditional scenar-io, customers return items forinspection, test, and repair. It isEmerson’sobjectivetoserviceandreturnall company-manufactureditemswithin30daysofreceipt.

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n 24-Hour Exchange. This optionis designed to address customerneeds in the event of an emer-gencyorothercriticalsituation.Areplacement item will be shippedwithin 24 hours of receiving themalfunctioning part. This level ofservicecanbeprovidedonlyforin-stockitems.

n Advance Replacement allows forcriticalsituationswhereyoumusthave a replacement item dis-patchedimmediately.Onceyoucallforthisserviceandyourpurchaseorder or credit card is received,a refurbished part, if available,willbeshippedtoyou.Youwillberesponsible to ship your service-ableitembacktoEmersonwithin30days.Users also can tap several non-

OEMsuppliersofWDPFspareparts.Forexample,SunMicrosystemsandHP parts—including RAM (randomaccessmemory),harddrives,HPopti-caldrivesandopticaldiscs,Ultra-5,and Sparc-5 machines—can be pur-chased from Sun resellers. Theseparts also can frequently be foundon E-Bay. Used hardware—includ-ingdata-highwayinterface(DTBox)and DPU hardware—is availablefromresellersorcustomerswhohaverecently upgraded from WDPF. Forinstance,DeepSouthHardwareSolu-

tions LLC, Osyka, Miss, buys andsellssurplusWDPFpartsforpower-plantandturbinecontrolsystems.

Advanced simulators areinvalu-able tools for plant operator train-ing.InadditiontolearningthebasicDCS windowing functions, traineescan gain familiarity with normaloperatingprocedures—suchasplantstartup and shutdown—and abnor-mal plant situations—such as feed-pump trips, gas-turbine runbacks,andsoon.

Simulators also can serve as avaluable maintenance tool. Forexample, I&C technicians can usethem to build or maintain compe-tency in such tasks as loop checks,instrument calibrations, and testinglogic modifications prior to actualimplementation on the DCS. Final-ly, because the simulator runs onstandard control-system hardware,it can double as a “hot-spare” partsbin,thusimprovingDCSavailabilitywhen critical—and increasingly dif-ficulttoobtain—partsfail.

Time to upgradeDespitethebesteffortsofthemainte-nancecrew,acomputer-basedcontrolsystemeventuallybecomesobsolete,and must be replaced. For WDPFusers, replacement options include

migrationtoOvationretainingtheQ-LineI/O,oratotalsystemretrofittoanotherDCStechnology—suchastheSiemensT3000,Foxboro,Bailey,andHoneywell.Acomprehensivecontrol-system assessment will help usersdecidewhenit’stimetoupgrade.Theassessmentmightinclude:n System capacity evaluation—an

evaluation of DPU memory andsystempointdirectorycapacity.

n Interviews with O&M personnel.Aquestionnaireisausefultooltoquickly assess the system hard-ware configuration. Interviewswith operators and maintenancestaff can help identify specificareasthatneedimprovement.

n Analysisofhistoricaldata.Opera-tions logs and historical data canbeusedtoidentifyareaswherethecontrolsystemshouldbeoptimizedorupgradedtoimproveplantavail-ability,efficiency,oremissions.

n The Emerson System AssessmentTool. End-users and owners ofWDPF systems can access Emer-son’s automated assessment tool,availableonthewebatwww.wdpf-users.com,forhelpwiththeirDCSlifecycleplanning.Ovation option. Somepowerpro-

ducersaredoingawaywiththethree-letter acronym that has for decadesdominated process control (DCS), in

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favorof the two-letteracronymthatdominates the retail and residentialworld—PC. Emerson seems to havecarriedthisconceptthefarthest,withitsOvationproduct.

First released in1997,Ovation isa fully PC-based powerplant controlsystem that eliminates proprietaryoperatingschemesandvendor-specif-ic hardware. According to Emerson,Ovation reduces the risk of obsoles-cence often associated with propri-etary control systems, and providesbetter and more accessible informa-tion than is available through thetypicalDCS.

For users of existing WDPF sys-tems,anupgrade toOvation canbeaccomplishedviaacompleteredraw,or by using Emerson’s “migrationtool”whichcansimplifyandspeeduptheupgrade.The36-MWSanGabrielMillPlant,Pomona,Calif, forexam-ple, completed its conversion fromWDPFtoOvationduringashutdownlastingonlyoneweekend.

The automated migration toolenablesownersofWDPFsystemstoupgrade to theOvationsystemwithminimal re-engineering and systemretuning(Fig2).Thetoolquicklycon-vertsWDPFgraphicsandlogiccodestoOvation’sopenarchitecture,avoid-ing the lengthy outages needed forthetypicalmodernizationproject.

Migration to the Ovation systemalso can provide enhanced systemfunctionality and process efficien-cy while reducing risks related tocomponent obsolescence. If you areconsidering upgrading your WDPFsystem to Ovation, here are generalanswerstoacoupleofthequestions

you’relikelytoask:Question 1: What are the pros

and cons of the migration tool, ver-susacompleteredraw?Answer:Themigration tool converts the WDPFDPU source code directly into Con-trol Builder Sheets and database,forimportintoOvation.Aone-to-onechange-outofDPUsisrequired.Also,some upfront work may be requiredto get the DPU source code into aformat that the migration tool willaccept. The migration tool offers awell-provedmigrationpath,andisagoodoptionifdocumentationislack-ing,or ifscheduleorbudgetarycon-straintsdictate thepaceof theDCSupgrade.

Bycontrast,the“redraw”isexactlywhat its name implies. The pointdatabase is generated from theWDPFas-builtterminationlistsandQ-Line I/O documentation, and theControl Builder Sheets are redrawnto match the as-built WDPF SAMAlogicdrawings(Fig3).

Performing a complete redraw ismoreexpensivebecauseof theaddi-tional software engineering that’srequired. Two DPUs—which arelocatedside-by-sideandperformthesamefunction—canbecombinedintoonecontrollerbothtohelpoffsetthehigheroverallcostofaredrawprojectand to improve control-system reli-ability. A redraw project also offersseveraladvantagesoveramigrationproject, which should be consideredinyourevaluation.Theseinclude:n More readable SAMA logic. With

themigrationtool, logic isbrokenup into small bites in order tomatchWDPFexecutionorder,and

signallinescriss-crossthesheetinavisuallyconfusingway.

n Bettercontrol-systemlogicreview.Withthemigrationtool,acompre-hensive design review is not per-formed.

n Designmodificationseasilycanbeintegrated as part of the upgradeprocess.

n Simulation testing can be per-formed.To compare the costs of a migra-

tion versus a redraw, users mayrequest separate quotes from Emer-son—oneforastraightmigrationandtheotherforare-draw.Anadditionalquotefromathird-partyDCSconsul-tantmayberequiredfortheas-builtdocumentation and/or simulationdevelopment.

Question 2: Which operatingsystem should I choose—Solaris orWindows? Answer: Solaris usersoftenarefamiliarwithUnixandcon-cernedaboutnetworksecurity,whileWindowsuserswanteasyconnectiv-ity to the plant local area network(LAN) and inexpensive, off-the-shelfcomputer parts. Other benefits ofSolaris include easy recovery fromhard-drive failures—with the “bootnet–install” option—and X-Window-ing capability—via HummingbirdExceed.Ontheotherhand,Windowshas Expanded Engineering Toolboxfunctions,whichareexcellent.

Ovation redraw projectA typical WDPF-to-Ovation redrawproject includes the following ele-ments:n Plant walk-down and drawing

collection. A thorough review ofthe DCS process graphics is per-formed,inconjunctionwithaplantwalk-down, to gain familiaritywith the plant systems. Masterred-linedrawings (SAMA,P&IDs,electricalschematics)arecollected.Also, the WDPF software serverconfiguration, along with customtrend groups and any third-partysoftware licenses—such as forApplix, optical drives, and print-ers—isdocumentedandbackedupforfuturereference.

n As-builtSAMAlogicdrawingsarethestartingpointforthesoftwaredesign.Logicdrawingsareextract-edfromDPUsourcecode.

n As-built termination lists and Q-Line Card slot assignments andaddressing documentation willbe generated and validated. Thisinformation is entered into theOvation DBID Tool (DatabaseInitial Definition) to generate theinitialOvationpointdatabase.

n Network layout/Ovation system

2. PC-based process control is a DCS upgrade option—one particularly well-suited for WDPF users because of Emerson’s “migration tool” that upgrades to the Ovation system with a minimum of re-engineering and system retuning

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architecture design. Fiberopticruns between buildings and tur-bine enclosures provide isolationfrom electromagnetic interferenceand eliminate grounding issues.The 10-BaseT connections makefor flexible system architecture.Thenumberandphysicallocationsoffiberrunsandnetworkswitchesmustbedetermined.

n Ovation hardware order. Basedon the WDPF system hardware,software design requirements,and Emerson’s recommended net-work layout, the Ovation systemhardwareordercanbeplaced.TheQ-Line I/O hardware need not bereplaced,onlythehuman-machineinterfacesandtheDPUmulti-buschassisandpowersupplies.

n Spare parts are more economicalifcompletecontrollerupgradekitsarespecified, rather than individ-ualparts.Also,a simulatorusingOvationhardwarecoulddoubleasa“hot-spare”partsbin.

n WEStationgraphics.NewerWDPFsystems with WEStation graph-ics require no additional graphicswork. Older WDPF systems with“classicgraphics”requirearedrawoftheprocessgraphics.

n Simulator design. A simulatormodelwillbedevelopedinordertodebugtheOvationsoftware.

n Finaldesignreview.Basedontheinterviews with O&M personnel,reviewofhistoricaldata,andlogicreview, control-logic modificationsoradditionstoimproveplantreli-ability, efficiency, or emissionsare reviewed and included in thesoftware design. Any additions ormodificationstothelogicmayneedtobereflectedintheI/Otermina-tion lists and process graphics aswell.

n Software submittal to Emerson.Alldocumentation,alongwiththeSoftwareServerbackuptape,willbesubmittedtoEmersonandusedto implement the Ovation soft-ware.

n Softwarevalidationtesting.Atotalplant simulator model facilitatesdebugging of the software designand implementation. The “loop-backstimulator”readstheoutputsfromthecontrolsystem,simulatesthe process response, and writesthe inputs to the control system.A detailed test procedure is aninvaluable tool that helps maxi-mizesimulationtimeandensuresthatnothing ismissed.While thepurpose of the simulation test isto validate the software design,maintaining the simulator at theplant for operator training andasan engineering toolmay bean

attractive option. This could bedone with “virtual controllers” orusingactualOvationhardware.

Installation, commissioningForbothredrawandmigrationproj-ects, the installation of Ovation’sfiberopticnetwork canbe completedpriortotheplantoutageinwhichthetotalsysteminstallationoccurs.Afterallsystemsarelockedoutandtaggedout,theDPUprocessors,powersup-plies,WEStations,andWDPFHigh-wayInterfaceBoxesareremovedandthe Ovation controllers and WESta-tions are installed and downloaded.With proper planning, a WDPF-to-Ovation upgrade can be completedduring a normal gas-turbine com-bustor inspectionoutage—evenonalarge2×1combined-cycleplant.

Commissioning activities are sub-ject to many factors—such as priceof fuel and dispatch requirements.Some “hot” commissioning activitiesinclude: pre-start simulations, falsefire, first sync, load-ramp tuning,and load rejections. Documentationand closeout of the upgrade projectincludes point database backup,software serverbackup to tape, andprinting the as-built control builderlogic. ccj oh

3. A redraw project is an alternative to “migrating” to the Ovation system. It typically is more expensive because of the additional software engineering that’s required, but its benefits include more readable SAMA logic drawings and a better control-system logic review