XITRON XT2640 - Page 36

XT2640OperatingManual 13July2016 Page36of187
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IfNORMALisselectedthenthetouchpanelisusedforturningtheXT2640onandoff.Afterapowerinterruptionthe
XT2640willremainoffuntilmanuallyturnedon.
IfAUTO‐ONisselectedthenthetouchpanelcanbeusedtoturntheXT2640onandoff,buttheXT2640willalsopoweron
whenpowerisfirstapplied.AfterapowerinterruptiontheXT2640willturnon.
IfALWAYSONisselectedthentheXT2640isalwaysturnedonifpowerisapplied.
Recommendations:
Forbench‐topuseNORMALisrecommended
Foruseinafixedsystem(e.g.arack)theneitherAUTO‐ONorALWAYSONisrecommended
12.3.1.2 SELECTINGANAUTOZ EROPREFERENCE
TheAUTOZERObuttonallowsyoutoselectiftheXT2640occasionallychecksiftheDCzeroesrequireadjustingforchangesinthe
operatingenvironment.
IfONisselectedthentheXT2640willoccasionally(everyfewminutesinatypicalenvironment)adjustits’DCzeroesto
trackanychangestotheenvironment.Thisincursa20msgapbetweenmeasurementsonceeveryfewminutesinatypical
environment(a99.99%signalcaptureprobabilityfornon‐recurringtransientslasting<20ms).Notethatthissetting
cannoteffectSCOPEactions(e.g.inrushcurrentdetection);onceaSCOPEtriggerdetectionisinitiatedthenDCzero
adjustmentsareautomaticallydisableduntilcompleted.
IfOFFisselectedthentheDCzeroeswillslightlychangeiftheenvironmentchanges,howeverthetransientsignalcapture
probabilityis100%.
Recommendations:
InalmostallapplicationsthiswillbesettoON.OnlyselectOFFifyouareconcernedaboutanominally0.01%probabilityof
notcapturingnon‐recurringtransientsignaleventslastinglessthan20ms.
12.3.1.3 SELECTINGAVARPOL ARITYPREFERENCE
TheVARPOLARITYbuttonallowsyoutoselectthemeaningofthepolarityofallVARresults.
If+LEADisselectedthenapositiveVARresultindicatesthatcurrentisleadingthevoltage.
If+LAGisselectedthenapositiveVARresultindicatesthatcurrentislaggingthevoltage.
Recommendations:
Formostapplicationstheuseofthe+LEADsettingisrecommended.
Note:
MathematicallyVARhasusuallybeendescribedasthe‘sine’relationshiptothephaseshiftofthecurrentrelativetothe
voltagesoresultinginapositiveVARindicatingaleadingcurrent,butincertainindustriestheoppositeconventionisused
whereapositiveVARindicatesalaggingcurrent.
Bydefinitionlead/lagisindicatedbythepolarityofVARandnotbyanyothermeasurementresult.Showinglead/lagby
thepolarityofPFisincorrectbuthashistoricallybeendoneasaresultoflimitationsinsimplerVAWmeters.TheXT2640
doesnotfollowthishistoricaluseofthepolarityofPFbutinsteadusesthemathematicalpolarityforPF(notethatPF=W/
VA,soPFhasthepolarityofWatts).
12.3.1.4 SELECTINGAΣVAORΣVARPREFERENCE
TheΣVAorΣVARbuttonallowsyoutoselectthemethodbywhichtotalVAandtotalVARresults(i.e.theresultsforanentireVPA)
arecomputed.
IfΣ(VAR)isselectedthen–
TotalVAR=Σ(VAR).
TotalVAiscomputedusing(totalVA)
2
=(Σ(W))
2
+(Σ(VAR))
2

IfΣ(VA)isselectedthen–
TotalVARiscomputedusing(totalVAR)
2
=(totalVA)
2
‐(Σ(W))
2
.
TotalVAforeachVPAdependsontheWIRINGselectionforeachVPA:‐
3ø3w(2ch): totalVA=(Σ(VA))*(√3)/2
Otherwise: totalVA=Σ(VA)
Recommendations:
IfyouhavepreviouslyusedtheΣ(VA)method(whichisusedbysomeothermanufacturersofPowerAnalyzers)thenitis
recommendedtousethatsetting.OtherwisetheΣ(VAR)shouldbeselectedasitmatchesthemathematicalapproach.
Note:
SincethisselectionaffectsthetotalVAresults,thisselectionalsoaffectsthetotalPFresults.
Onlyforpuresinewavevoltagesandcurrentswiththeexpectedphaseshiftbetweenthevoltagesandaperfectlybalanced
loadistherenodifferenceintheresultsbetweentheseselections.
12.3.1.5 SELECTINGAFREQSPEEDPREFERENCE
TheFREQSPEEDbuttonallowsyoutoselecthowquicklytheXT2640measuresandrespondstochangesinthefundamental
frequency.
IfFASTisselectedthentheXT2640measuresthefundamentalfrequencyusingthefastestpossiblemeasurementperiod
(andtheleastresolution)andwillrespondasquicklyaspossibletochangesdetected.IfconfiguredforLForVLFoperation
bytheLF/PERIODsettingintheMEASCONFIGscreenforaVPAandaifchangeinfundamentalfrequencyof>1%occurs