Siemens LMV52.240B1 - Page 195

LMVSeriesTechnicalInstructions 
DocumentNo.LV5‐1000
SCCInc. Page23 Section6
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NumberTauSuspend‐Thelengthoftimeaftermainflamelight‐offthatisrequireduntilanaccurate,
representativeO
2
valueisreadbytheO
2
sensor.Basically,thetimeittakestoreplacealloftheairin
theboilerwithproductsofcombustion.Thisparameterisamultiplierthatistakentimesthedelaytime
atlowfire(TauLow‐Fire)todeterminethelengthofwaitingtimebeforearepresentativeO
2
valueis
measuredandtheO
2
trimcanengage.

IfTauLow‐Firewasreadtobe5secondsduringO
2
ControlCurvecommissioning,and
NumberTauSuspendissetto10,thentheO
2
trimwouldengage50secondsaftermainflamelight‐off.
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Asettingof10willworkforalmostallapplications,andwillbeconservativeformost.Highernumbers
(morewaitingtime)aremoreconservativeandlowernumbersarelessconservative. 
Menupath:Params&Display>O2Contr/Alarm>GasSettings>Startmode
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Startmode‐Thisdetermineshowtheburnertransitionsfromlight‐offtoengagingtheO
2
trim.Twoof
themodes,“IgnLoadTC”and“IgnPtWithTC”,requireacombustionairtemperaturesensor.
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Immediatelyaftermainflamelight‐off,theO
2
sensordoesnothaveavalidreadingsincethegaspathof
theboilerisfullofair.Someburnerdesigns,mostnotablyultra‐lowNOxmeshburners,requiresome
typeofcompensationatlight‐offtoensureflamestabilitybeforetheO
2
sensorhasavalidreading.Four
optionsareavailable:

1. Standard‐Burnerwillmodulaterightafterlight‐off,notwaitingfortheO
2
trimtoengage.O
2
trim
willengageafterthetimedefinedbyNumberTauSuspendexpiresattheburner’scurrentload.
2. IgnLoadTC‐Thiswillvarytheignitionpositions(specialpositions)oftheactuatorsbasedonthe
combustionairtemperatureandalsobasedonadefinedloadnumber(parameterLoadofIgnition).
Thisalsowilldrivethe"temperaturecompensated"actuatorstoPoint2(orwhicheverpointis
definedbypa
rameterStartPointOp).TheburnerwillbeheldinPhase60atPoint2(orwhichever
pointisdefinedbyparameterStartPointOp)untilthetimedefinedbyNumberTauSuspendexpires.
TheburnerwillthenbereleasedtomodulatewiththeO
2
trimactive.
3. IgnPtWithTC‐Thiswillnotvarytheignitionpositions(specialpositions)oftheactuatorsbasedon
thecombustionairtemperature.Itwilldrivetheactuatorsfromthetemperature‐compensatedset
ignitionpositionstoPoint2(orwhicheverpointisdefinedbyparameterStartPointOp).Theburner
willbeheldinPhase60atPoint2(orwhicheverpointisdefinedbyparameterStartPointOp)unt
il
thetimedefinedbyNumberTauSuspendexpires.Theburnerwillthenbereleasedtomodulatewith
theO
2
trimactive.
4. IgnPtWoutTC‐Similarto“IgnPtWithTC”,butlessaccuracyduetothelackofacombustionair
sensor.

Onburnerswithawideflamestabilityb and,suchastraditionalnozzlemixingburners withlittleorno
FGR,aStartModesettingof“standard”typicallyworkswell.Onburnerswithamorenarrowflame
stabilityband(lowandultra‐lowNOxmeshburners),“IgnPtWithTC”typicallyworkswell.
Menupath:Params&Display>O2Contr/Alarm>GasSettings>Startmode 
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