Siemens LMV52.240B1 - How the O 2 Is Measured with the QGO20 Sensor and PLL52 Module

TechnicalInstructions  LMVSeries
DocumentNo.LV5‐1000
Section6 Page26SCCInc.


IfonlytheO
2
alarmfunctionistobeuse dand theO
2
trimhasnotbeencommissioned,afewkey
parametersmustbeset.Theseare:

1. O2MaxValue‐settothemaximumsafe%O
2
(wet)forallpoints.
2. O2Alarmcurve‐entertheminimumsafe%O
2
(wet)foreachpoint.
3. TauLow‐FireOEM‐thedelaytimeoftheburner/boileratlowfire
4. TauHigh‐FireOEM‐thedelaytimeoftheburner/boilerathighfire
5. OptgMode‐settoO2Limiter

IftheO
2
trimhasnotbeencommissioned,itwillbenecessarytomanuallyenterTauLow‐FireOEMand
TauHigh‐FireOEM.TheseTautimesdonothavetobeasaccurateasiftheO
2
trimwasbeingused.
ThesecanbemanuallytimedbyusingtheO
2
readingontheAZL(recommended),ortypicalvaluescan
beused.HigherturndownburnerswillproducelongerlowfireTautimes.Typically,fora5‐to‐1
turndownburner,TauLow‐FireOEMisbetween10‐20seconds.TauHigh‐FireOEMistypically4
secondsorless.
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HowtheO
2
isMeasuredwiththeQGO20SensorandPLL52Module
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TheQGO20isaZirconiumtypesensorthatisheatedtoapproximately1292°F.Thehightemperatures
allowoxygentodiffusethroughtheZirconiumcellandproduceamilli‐voltsignal.Thismilli‐voltsignalis
referredtoastheNernstVoltage.TheNernstVoltagethatisproducedforagiven%O
2
isdependenton
theconcentrationofoxygenandthetemperatureof theZirconiumcell.ThePLL52modulereads both
theNernstVoltageandthetemperatur eoftheZirconiumcell.Withthisinformation,the%O
2
canbe
accuratelydeterminedandsentbacktotheLMV52overCANbus.
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Aswellastakingthemilli‐voltsignalsandconvertingthesetoCANbusdata,thePLL52alsoservesasthe
controllerfortheZirconiumcell'sheatingelement.ThePLL52isalsoaplacetoconnectthecombustion
airtemperaturesensorandthestackgastemperaturesensor.
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Threemilli‐voltsignalsoriginateintheQGO20:
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1. NernstVoltagefromtheZirconiumoxideO
2
cell terminalsB1andM
2. O
2
cellthermocouplesignalterminalsB2andM
3. Coldjunctionthermocouplecompensation  terminals G2andU3
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Thesethreemilli‐voltsignalsbetweentheQGO20andthePLL52mustberuninaseparateconduitand/
orashieldedcable.
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SeeSection2forcompletedetailsonwiringtheQGO20tothePLL52.
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HighvoltagewiresarealsoconnectedfromthePLL52totheQGO20fortheheater.Itisveryimportant
thatthesewiresareruninaseparateconduitawayfromthemilli‐voltsignals.
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NOTE:NeverconnecttheQGO20heaterdirectlytolinevoltage!Permanentdamagewillresulttothe
heatingelementandthesensor.HighvoltagewiresfortheheatertotheQGO20mustcomefromthe
PLL52module.SeeSection2formoreinformation.
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Also,duetopossibleinterferenceonthemilli‐voltsignals,thePLL52mustbeinstalledwithin30feetof
theQGO20.
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