servo valve calibration.docx
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servovalvecalibration
servovalvecalibration
Postedby ESKAY
on19May,2013-4:
16pm
DearCSAandAll,
Iwouldliketocalibratethedistillatefuel65FPservo,throthe"calibrate"modefacilityinMk6system.[GEFr5Mk6control].Unlike,theGasservovalvecalibration,wherewesettheservovalveoutputvaluesthro"manual"setpointandthencomparetheerrorwiththeLVDTfeedback.Howcanwemakeuseofthisprocedureforthe65FPservo,wherewehaveNOLVDTforthefeedbackandthereisNOstem(scalemarking)onthe65FPservotoseethemovementoftheservo?
WehaveonlyFlowdividerasthefeedbackandourturbinedon'thavetheauxiliarypumpandneedtoruntheturbinein"crank"modeforthecalibrationwithinlimitedtime.Pleaseguidemefortheproperandeffectivecalibrationofthedist.fuelsystem.
Thanks..
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PostedbyBobJohnstonon19May,2013-7:
09pm
It'sdifficultIknow,reallytheonlywaytocheckisdoa"dummyfire"withnosparkplugsandquicklycheckthefuelflowatacoupleofManualFSRpoints.Runatrendofthemajorcriteriaatthesametimeandyoucanthenreview.
GivethemachineabitofaCrankaftertestingandbeforefiringtogetridoftheexcessfuel.
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Postedby CSA
on20May,2013-6:
23am
ESKAY,
Thisideaof"calibratingservo-operateddevices"onGE-designheavydutygasturbinesisa HUGE myth.It'ssimply notpossible tocalibrateanythingotherthanLVDTfeedback.EvenwhenGEfieldpersonnelsaytheyare"calibrating"theSRVortheGCVortheIGVsortheLFBV(LiquidFuelBypassValvetheyare NOT. TheyareonlycalibratingtheLVDTfeedbackfromthosedevices.Thereiszero effectontheservoortheservo-valveoutputstabilityafter"calibration";theonlythingthatchangesistheLVDTfeedbackcalibration.
Fullstop.
Period.
It'ssimplyimpossibletosendapositionreferencetoadevicethathasnopositionfeedbackandexpectthatdevicetogotosomeposition,orwhattheSpeedtronicbelievesthatpositiontobeifthereisnopositionfeedback.
So,don'tbelieveeverythingyouhearpeoplesaywhoseemtobeknowledgeableaboutGESpeedtroniccontrolsystems,becausetheyquiteoftendon'tsaywhattheymean,andtheyquiteoftendon'tknowwhattheyaresaying.Especiallywhentheyaretalkingaboutelectro-hydraulicservo-valves.
Ifyouarehavingproblem(s)withcontrolofliquidfuel,telluswhattheproblem(s)are,whatyouhavedonetotroubleshoottheproblem,andwhattheresultsofyourtroubleshootingwere.Thenwecantrytohelpyouwithresolvingyourproblem,orwithunderstandingtheliquidfuelsystemanditscomponents.
AsBobJohnstonsays,ifyoudon'thaveanACmotor-drivenAuxiliaryHydraulicPumpthenyouaregoingtohavetocranktheunittoestablishhydraulicpressure--justaswithanyotherhydraulically-operateddevice.
TherehavebeensomeverycreativepeoplewhohaveusedtheDCmotor-drivenHydraulicRatchetPumptoprovidehydraulicpressuretothehydraulicsystem,butittakessometemporarytubingre-work.AndIdon'tbelievetheHydraulicRatchetPumpoutputisfilteredverywellsotherecanbecontaminationofservosand/orservofiltersifthat'susedforthatpurposewithoutproperfiltration.Also,thepressureoftheHydraulicRatchetPumpisnotadjustableandislikelynotthesameastheMainHydraulicPump,noristheflow-rateoutputoftheHydraulicRatchetPumpanywherenearthatoftheMainHydraulicPump.Itworksforacrudecheckofsystemoperation,butforanythingmorethanthatitisnecessarytocranktheunittogetpressurefromtheAccessoryGear-drivenMainHydraulicPumpifthereisnoACmotor-drivenAuxiliaryHydraulicPump.
TheliquidfuelcontrolvalvesofmostGE-designheavydutygasturbinesaredesignedtocontrolflow-rateusingfeedbackfromtheliquidfuelflowdivider.Theflowcontrolvalveispositionedatwhateveropening/closingitneedstobeatinordertomakethescaledfeedbackfromthespeedpick-upsontheliquidfuelflowdividerequaltotheliquidfuelflow-ratereference(foraMarkVI,thatsignalnameisusuallyFQR,andtheflow-ratefeedbackisusuallyFQLorFQLMorFQLM1).
EvenforLFBVswithLVDTs,theLVDTsarejusttherefor"stability";themaincontrol"loop"fortheliquidfuelsystemisflow-rateusingtheliquidfuelflowdividerfeedback.
ToproperlycalibrateLVDTfeedbackitisnecessarytophysicallymeasurethepositionofthedevicewiththeLVDTs--somethingmostpeopleneverdoonGE-designheavydutygasturbineswhen"calibrating"LVDTfeedback.MostoftheLFBVsonnewerGEFrame5sdonothavevalvestemsorplugsthatarevisiblesoit'snotevenpossibletoverifythepositionofthevalveplug.
Again,ifyouarehavingproblemswithliquidfueltelluswhattheyare,whatyou'vedone,andwhattheresultsofwhatyou'vedonewere.Ifyouonlyrunliquidfueloccasionallyandyouhavetroublestransferringfromgasfueltoliquidfuel,ortroublestartingonliquidfuelthentheLFBVisnottheproblem--norwouldthe"calibration"oftheLVDTsontheLFBVbetheproblem.
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Postedby CSA
on20May,2013-1:
41pm
ESKAY,
Ithoughtwe'dbeenoverthisbefore....
Nothinghaschangedsincethen.
Nothing.
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Postedby ESKAY
on21May,2013-1:
33pm
DearCSA,
Thanksfordirectingmetotheoldthread,forthesameissueofcalibratingthe65FPservovALVE.
AsyouhavefurtherclarifiedthatthereisNOwaytocalibratethefunctionalityof65FPservo,otherthanrunningtheturbineindistillatemodeandandviewthetrendandvarioussignalsinsertedintothewatchwindowtoanalysetheproblem,ifany.Assuch,wehaveNOprobleminthedistillatefuelmodeoperation.Iwouldliketogettheknowledgeaboutcalibratingthedist.fuelservo,incase,ifitisrequired.Thanksfortheadviceandyouracknowledgement/quickresponse.
Wishingyou..Regards..
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Postedby ESKAY
on22May,2013-12:
21pm
DearCSAsir,
Icouldnotfindtheanswerthrothe"search"facilityORearlierthreadsregardingmyclarificationonMk4servocalibration,whichwasrejectedbyoneofyourmoderator.
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IFOLLOWEDTHEPROCEDUREGIVENINTHEMANUAL,butIhavecertainissues.OnthecalibrationdisplayforSRVANDGCV,whileGDAJisvaried,withL4X1-L4X-L3adj-L20FGX1-L3GCV(forGCV)-L3GRV(fortheSRV)-forcedto"1",withAUX.HydraulicoilpumpswitchedON.IfindtheSRVservovalvestrokingfromitsdatum(closed)positiontoitsfullopenpositionwithGDAJsetat-0.30andaboveandviceversa.WhereasforGCV,theSERVOdoesnotliftatall.IsittheJDAJhexa-decimalvalue,automaticallychangestoeither13OR12withtheFORCEENTERisactivatedORJDAJvaluechangeisNOTrequired.WhatmustbethevalueforLOCATELOWandLOCATEHIGH,normallysetfortheservo?
(forGCV/SRV).WhyitisNOTpossibletoholdtheSRVatanyfixedvalueofGDAJ?
WhereamIwrong?
Pleasehelpsolvetheprobleminservocalibration.
Iseekyourkindhelp/adviceatyourearliest,sir.
Thanks..Withregards..
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Postedby CSA
on22May,2013-2:
28pm
ESKAY,
Isenseyourfrustration.I,too,foracoupleofyearsasanewGEemployeewasunderthemistakenbeliefthatliquidfuelbypassvalves--indeed,anyservo-operateddeviceonaGE-designheavydutygasturbine--required"calibration."Itwasn'tuntilIreallythoughtaboutandunderstoodwhatcalibrationis,inageneralsense,andwhatis--orcanbe--calibratedonaGE-designheavydutygasturbinewithservo-operateddevicesthatitreallybecamecleartome.
Iwasonlyreferringyoutoapreviouspostinwhichyouasked,essentially,thesamequestion:
Howto"calibrate"aservo,specificallyaservo-operatedliquidfuelbypassvalvewhichdoesNOThaveLVDTsforpositionfeedback.
Whenusingthe"Calibrate"featureofaSpeedtronicturbinecontrolsystemonaservo-operateddevice,the>>ONLY<<"thing"thatiscalibratedisLVDT (position) feedback.IFTHEREARENOLVDTs,THEN>>NOTHING<Theservoisnot"calibrated."
Thevalve(orIGVs)arenot"calibrated."
OnlyLVDTfeedbackfromadevicewithanelectro-hydraulicservo-valveiscalibratedusingthe"Calibrate"featureofaSpeedtronicturbinecontrolsystem.
RegardlessiftheSpeedtronicisaMarkIV,MarkV,MarkVI,orMarkVIe. IftherearenoLVDTsontheservo-operateddevicethennothingcanbecalibrated.
"Calibration"ofaservo-operateddevicewithLVDTsforpositionfeedbackistheprocessofconvertingthevoltagefeedbackfromtheLVDT(s)toposition,inpercentofratedstroke(travel)ofthedevice(or,inthecaseofIGVs,degreeofangleofopening).
Ifthe0%strokeoccursat0.700VACRMSvoltagefeedback,andthe100%strokeoccursat3.500VACRMS(thevaluesareforexemplarypurposes ONLY),thentheoffset(or"zero")forthefeedbackvoltageis0.700VACRMS,andthegain(or"span")forthefeedbackis0.028VACRMSperpercentstroke.TheSpeedtroniccalculatestheoffsetandgaininternallyafterdeterminingthevaluesduringacalibration;thereisnooperatorortechnicianactionrequir