XITRON XT2640 - Configuration Recommendations; Recommended FREQ SPEED System Preference; Recommended MEAS CONFIG Settings

XT2640OperatingManual 13July2016 Page79of187
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16.3 CONFIGURATION RECOMMENDATIONS
16.3.1 RECOMMENDED FREQSPEED SYSTEMPREFERENCE
ThissettingiscontainedintheSYSCONFIG–PREFERENCESscreen.
InmostcasestheNORMALsystempreferencesettingforFREQSPEEDisrecommendedforPWMapplications.
IftheloadisavariablespeedmotorandfastchangesinspeedarelikelytooccurthensettingtheFREQSPEEDpreferencetoFAST
shouldbeconsidered.InthiscaseyoushouldalsoconsiderusingashortLF/PERIODsettingintheMEASCONFIGforthatVPA.
Iftheloadisamotorbeingoperatedatanominallyfixedspeedandthemodulationfrequencyhassignificantjittersuchasisoften
causedbymotorjitterorbythebeatbetweenthemodulationandcarrierfrequenciesofthePWMsignalsthentheSLOWsetting
shouldbeconsidered.Thiscanbeofparticularimportancewhenviewingharmonicsresultsasthebeatfrequenciesbetweenthe
modulationandcarrierfrequencieshavethemaximumeffectonthoseresults.
16.3.2 RECOMMENDED MEAS CONFIGSETTINGS
SettingsnotdescribedherearenotaffectedbythesignalshavingPWMcontentsonospecificrecommendationsareneeded.
16.3.2.1 LF/PERIODSETTING 
GenerallythereisnoPWMspecificprecautionregardingthissetting.Howeveryoushouldconsiderthatthissettingnotonlyaffects
themeasurementperiod(andsotheupdaterate)butalsosetstheminimumfrequencymeasurablebytheXT2640,whichcanbeof
importancewhenusingavariablemodulationfrequency(e.g.avariablespeedmotordrive).
Ifitisimportantthatthemeasurementresultstracksignificantrapidchangesinmodulationfrequencyorothermeasurement
resultsthenthisshouldbesetforasfastofaLF/PERIODsettingaspossiblefortheminimummodulationfrequencytobemeasured.
16.3.2.2 FUNDSETTING
Iftheloadisinductive(suchasamotor)thentheCURRENTsettingshouldbeused;onlyifthereisnoloadortheloadisnot
inductiveshouldtheVOLTAGEsettingbeused.IfeithertheCURRENTorVOLTAGEsettingisusedthenthemaximumfrequency
enteredshouldbeaslowaspossible,atorslightlyabovethemaximumexpectedmodulationfrequencyandbelow½theminimum
expectedcarrierfrequency.
Iftheamountofmodulationisverylow,particularlyifVOLTAGEisselected,thentheXT2640mightnotbeabletoextractthe
modulationfrequencyfromtheselectedsignalandinthosecasesyoushouldselectaFIXEDsettingandenterafrequencyequalto
themodulationfrequency.Thefrequencyenteredwillneedtobechangedifthemodulationfrequencyischanged.
16.3.2.3 BANDWIDTHSETTING
TherearetwopossiblemethodsofconfiguringthebandwidthofmeasurementsofPWMbasedsignals,eachmethodhasits’merits.
1.
Usingawidebandwidthformeasurements.Ifitisdesirabletoensurethatallnon‐harmonicmeasurements(suchas
voltage,currentandpower)containthesignalcontentwithaswideofabandwidthaspossiblethentheBANDWIDTH
settingshouldbesettoUNFILTERED.Allnon‐harmonicmeasurementsmadebytheXT2640willthenincludeallsignal
contentwithinthebandwidthcapabilitiesofthespecificchannelsinstalledintheunit.Becausethevoltagemeasurement
includesthecarrierfrequencycontentthemeasurementresultsforvoltage,VA,PFandVARmightbesignificantlydifferent
fromthosewhichyoumayexpect;howeverthisensuresthatthepowerresultscontainallofthepowerintheloadby
includingmotorlossesathighfrequenciesandsoyieldsthebestpossibleaccuracyforefficiencyandpowerloss
measurements.
2.
Usingarestrictedbandwidthformeasurements.Ifitisdesirabletoonlyincludethemodulationfrequencycontent(andits’
harmonics)inthemeasuredvoltage,VA,PFandVARthenBANDWIDTHshouldbesettoUSERandafrequencyentered
whichislessthan½ofthelowestexpectedPWMcarrierfrequencybutabovethatofthehighestexpectedmodulation
frequency.IntheXT2640theeffectofsuchsignificantfilteringisgenerallynegligibleonthemeasurementresultaccuracy
andhasthepossibleadvantageofyieldingtheexpectedvoltage,VA,PFandVARresults;howeverthepowerresultswillnot
containmotorlossesathighfrequencies.
Note:
SignalscapturedusingtheSCOPEVIEWscreenarealsoaffectedbythissetting.
TheuseoftheAUTO‐TRACKsettingforBANDWIDTHisnotrecommendedinPWMapplicationsunlesstheHARMONICS
settingissettolessthan1/6
th
oftheminimumexpectedvaluefortheratiobetweenthemodulationandcarrier
frequencies.
Theapparentdifferenceinthevoltageandrelatedmeasurementsbetweenthebandwidthselectionsdescribedaboveisa
resultofthedifferenceinthemeasuredsignalcontent,thisisnotspecifictotheXT2640.
a.
TheRMSvoltageincludesbothcarrierandmodulationcomponents,sotheresultantvoltagemeasurement=
√(V
carrier
2
+V
modulation
2
).
b.
TypicallytheRMScurrentisunaffectedasitincludesverylittlecarriercomponentbecauseofaninductiveload.
c.
TypicallythisdoesnotaffectWattsandrelatedmeasurements(e.g.efficiency)otherthanincludinganycarrier
frequencylossesintheloadsinceWattsmeasurementsonlyincludefrequencycomponentswhicharepresentin
bothvoltageandcurrentsignals.
d.
TypicallyV,VAandVARwillbemuchhigherandPFwillbemuchlowerformeasurementswithanunrestricted
bandwidththanthosemeasurementsforjustthemodulationcomponent.Thisisjustbecauseofthecarrier
frequencycontentofthesignalsthemselvesasdescribedina)above.