XITRON XT2640 - Vpa Measurements; VPA Fundamental Frequency; VPA Amplitude Measurements; Data Collection

XT2640OperatingManual 13July2016 Page162of187
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VoltageandcurrentRMS(thesquarerootoftheaveragesquaredsampleinthemeasurementperiod).
Watts(theaverageofthevoltageandcurrentsamplesmultipliedtogetherinthemeasurementperiod)
Harmonicamplitudeandphaseanalysisofthevoltageandcurrentsamples(usingFourierTransforms).Thisanalysisisonly
performedifa)thefundamentalfrequencyisknown,andb)youhaveconfiguredforatleast1harmonictobeanalyzed.
FormulationoftheCycleViewdatafromallsamplesinthemeasurementperiod.Cycleviewplaceseverysamplefromthe
measurementperiodatthecorrectphasetobuildasinglecycleformedfromallcyclespresentduringthemeasurementperiod.This
usestheresultsoftheharmonicanalysisatthefundamentaltopositionthesamplescorrectlyanditusesthefundamentalfrequency.
Spectralanalysisofthevoltageandcurrentsamples(usingFourierTransforms).Thisanalysisisonlyperformedifconfigured.
Dcurrentoptiononly(ifconfiguredforauto‐range):
AtanytimeduringameasurementperiodiftherangeispresentlytheLOrangeandthecurrentisatleastclosetooverload
thentheHIrangeisimmediatelycommandedinthischannelandtherelevantsamplingcontroliscommandedtostarta
newmeasurementperiodhoweverallchannelsintheaffectedVPAarecommandedtonotdiscardtheexistingpeakresults
whenstartingthismeasurementperiod.
IfattheendofthemeasurementperiodtherangeispresentlytheHIrangebutallsampleswithinthemeasurementwere
belowalevelindicatingthattheLOrangemaybeused,thentheLOrangeiscommandedpriortostartingthenext
measurementperiod.
25.5 VPA MEASUREMENTS
25.5.1 VPAFUNDAMENTALFREQUENCY
EachVPAprovidesafundamentalfrequencytoitsassociatedsamplingcontrolasdeterminedbytheFUNDconfigurationsettingin
theVPA;thismaybebymeasurement,byconfiguration,orfromanotherVPA.
IfthefundamentalfrequencyismeasuredthenthisisfromthevoltageorcurrentinthelowestnumberedchannelintheVPAand
usesthefollowingmethod‐
Thisisperformedbymeasurementoftheperiodbetweenzerocrossingsoftheoutputofadigitalband‐passfilterwhichusesthe
configuredsamplesfromthechannel.
Hysteresisisemployedonthezerocrossingdetectiontopreventnearfundamentalsignalcomponentsfromcreatingfalse
zerocrossingdetections.
Becausethefilteringisband‐passthefrequencyisestablishedregardlessofanyDCsignalcontent.
Thelowfrequencycorneroftheband‐passfilterissetbytheLF/PERIODsettingfortheVPA.
Thehighfrequencycorneroftheband‐passfilteriscontinuouslyadjustedtomatchthemeasuredfrequency.The
maximumcornerfrequencyofthisfilterislimitedbytheFUNDsettingoftheVPA.
Tocorrectlydetecttheedgesofthewaveformtheremustbeatleast3samplesineachcycle,thusthemaximummeasurable
frequencyisjustover80kHzforL,AandSchanneltypes,orjustover305kHzforWchanneltypes.
25.5.2 VPAAMPLITUDE MEASUREMENTS
ForeachoftheVPAsthefollowingmeasurementsareperformeddependingontheWIRINGconfigurationoftheVPA.
Nx1ø TherearenoVPAmeasurementsperformed.
2ø3w Measurementsofthedifferencebetweenthetwochannelvoltages(thisproducestheresultsforøAB
data)andmeasurementsofthesumofthetwochannelcurrents(thisproducestheresultsforNdata).
3ø3w(2ch) Measurementsofthedifferencebetweenthetwochannelvoltages(thisproducestheresultsforøAB
data)andmeasurementsofthesumofthetwochannelcurrents(thisproducestheresultsforøCdata).
3ø3w(3ch) Measurementsofthedifferencebetweeneverypairofchannelvoltages(thisproducestheresultsfor
øAB,øACandøBCdata).
3ø4w Measurementsofthedifferencebetweeneverypairofchannelvoltages(thisproducestheresultsfor
øAB,øACandøBCdata)andmeasurementsofthesumofthethreechannelcurrents(thisproducesthe
resultsforNdata).
VPAmeasurementsareasub‐setofthechannelvoltage/currentmeasurements–
DC(theaverageofthesamplesinthemeasurementperiod).
Peak(thehighestmodulussampleinthemeasurementperiod).
Rectified(theaveragemodulussampleinthemeasurementperiod).
RMS(thesquarerootoftheaveragesquaredsampleinthemeasurementperiod).
25.6 DATACOLLECTION
ThiscollectstogetherthemeasurementresultsfromtheChannelandVPAMeasurementstoprovideallfinalmeasurementresults.
Inmanycasesthisinvolvesmorethanoneactualmeasurementresultwithcalculationsperformedtoproduceeachfinalresult.All
finalmeasurementresultsarecontinuouslycalculatedandhavetheconfiguredresponsefilteringimposed,thoseresultsarethen
heldasrequiredifyouhavecommandedtoholdmeasurements.Inthismannerallresponsefilteredresultshavethecorrectand
linearresponsefilteringcharacteristics.
Examplesoffinalresultscomputationsinclude–