XITRON XT2640 - Page 91

XT2640OperatingManual 13July2016 Page91of187
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Wchanneltype:75‐600Vrms.
VoltageCrestFactor:Solelylimitedbyamaximumpeakvoltageof1750Vpk.
CurrentandCurrentCrestFactor:Anycurrentinthefollowingrangeforeachcurrentoption(thechanneltypedoesnot
affecttherangesallowed)‐
Hcurrentoption:3mA‐30Arms.Crestfactorlimitedtothelowerof100oramaximumpeakcurrentof200Apk.
Dcurrentoption(HIrangeselection):2.5mA‐20Arms.Crestfactorlimitedtothelowerof100oramaximumpeakcurrent
of150Apk.
Dcurrentoption(AUTOrangeselection):0.7mA‐20Arms.Crestfactorlimitedtothelowerof100oramaximumpeak
currentof150Apk.
Dcurrentoption(LOrangeselection):0.7mA‐0.265Arms.Crestfactorlimitedtothelowerof100oramaximumpeak
currentof1Apk.
NotethatEN61000‐3‐2disregardsallharmonics<5mArmsinapplyingassessmentlimits(seeclause6.2.3.4),soinpractice
itisreasonabletoassumethatthereisnorequirementtoassessEUTswithanRMSloadcurrent<5mAasinthatcaseall
theharmonicassessmentresultswouldbedisregarded.
TotalPowerFactor:Anytotalpowerfactorintherange0.0001‐1.0.
FundamentalPowerFactor:Anyfundamentalpowerfactorintherange0.01‐1.0(forEN61000‐3‐2classesC(tbl3)andD
only,thereisnofundamentalpowerfactorrangelimitationfortheotherclassesorforEN61000‐3‐12).
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Power:Onlylimitedbythevoltage,currentandpowerfactorlimitationsstatedabove.
18.1.5.1 EXTER NALCURRENTMEASUREMENTS
TheuseofexternalcurrentdeviceswithaXT2640foranyEN61000‐3‐2compliancetestingisnotneededandshouldnotbeused
(unlessthecurrentoptionintheXT2640isX).
18.1.5.1.1 UsingExter nalCurrentShunts
IfnecessaryforEN61000‐3‐2,andasisoftenneededforEN61000‐3‐12toaccommodateitscurrentrequirements,theuseof
externalshuntsincombinationwiththeXcurrentoptionintheXT2640isrecommended.
Therequirementsforexternalshunts,whenneededforcompliancewithEN61000‐3‐2,‐12andEN61000‐4‐7standards,areas
follows–
TheresistanceoftheshuntmustbesuchthattheRMSvoltageacrosstheshuntis<0.15Vrmsatthemaximumexpected
currentdrawoftheEUT.ThisisarequirementofEN61000‐4‐7clause5.1,howeverthatrequirementmaybeconsidered
tobeoverriddenbybothEN61000‐3‐2and‐12asdiscussedinsection18.1.1.
Thepowerhandlingcapabilityoftheshuntanditsabilitytodissipateheatinyouruseofitmustbesuchthatthereisless
than1%differencebetweenitsvalueatlowcurrentsandthatatthemaximumexpectedEUTcurrent.
Theinductanceoftheshuntmustbe<10nHpermΩresistanceoftheshunt.Notethatresistorswhichareclaimedtobe
“non‐inductive”alwayshavesomeinductancesoyoushouldconsulttheshuntresistordatasheetforamaximum
inductancevalue;ifnoneisavailablethentheshuntshouldnotbeusedforthispurpose.“Classical”DCshuntsgenerallydo
notmeetthisrequirement,theuseof“folded”orcoaxialshuntsisrecommended.Youshouldalsoconsiderthatsinceshunt
inductancewillalwaysincreasethemeasurementresultsforhighorderharmonics,soiftheEUTispassingthe
requirementswiththeshuntbeingusedthenitwouldalsopass(possiblywithawidermargin)witha“perfect”shunt.
TheroutingofthevoltagesensewiringfromtheshunttotheXT2640shouldbesuchthatitalterstheapparentimpedance
oftheshuntat2kHzbylessthan1%.Thisgenerallymeansthatthevoltagesensewiringmustbeacloselytwistedpair
(notacoaxialcable)ofthingagewires(26awgorthinnerisrecommended)andthatitisroutedatright‐anglestothe
currentwiringforadistanceofatleast1footfromtheshuntanditscurrentcarryingwiring.Theroutingofthewiringis
verydependentonmanyfactors,someexperimentationshouldbeexpected.Generallyyoucandetectifthewiringisa
problembysimplychangingitandnotinganychangestotheveryhighorderharmonicsmeasurements,butthisassumes
thattheloadhassufficientsuchharmoniccontentandthatitisnotalsoaffectedbythechangestothewiringrouting.You
shouldnotethatthiseffectcaneitherraiseorlowerhighorderharmonicmeasurements,socancausefalsepassingor
failingindicationsonaEUT.
Youshouldconsidertheoperatingenvironmentoftheshunt.Lowresistanceshuntstypicallyhaveahightemperature
coefficientofresistancewhichwilllimittheirabilitytobeusedwithaccuracyinapoorlycontrolledenvironment.
Theshuntmustbemountedandprotectedsuchastoomaintainasafeenvironment.Theshuntisoperatingatanunsafe
voltagesoyoumustensurethatthereissufficientmechanicalshieldingtoensurethatobjectssuchasdefinedbyEN61010‐
1cannottouchanylivevoltagepartoftheshunt.
18.1.5.1.2 UsingExter nalInd uctiveTyp eCurrentTr ansduc ers
Externalinductivetypecurrenttransducerssuchascoilorhall‐effecttypesaregenerallynotrecommendedasfewmeetthe
requirements.Thereareafewsuchdeviceswhichdomeettherequirementshowever,somaybecarefullyconsidered.The
importantfeaturesofsuchadeviceare‐
Accuracy.Anoverallaccuracyof1%(aftercalibrationoftheinput:outputratio)isrequired.Youshouldalsoconsiderthe
relianceofthedeviceonthepositionofthecurrentcarryingwirewithinitsaperture;oftenthisisasubstantialeffectat
theseaccuracylevels.
Distortion.Thisisoftenthedominantfactorindecidingonadevice.EN61000‐4‐7requiresthatharmonicsmeasurements
bemadetowithin0.15%ofthefundamentalateachharmonicuptothe40
th
,soitisrecommendedthatthedevicehaveat
leasttwicethislevelofperformanceastypicallythereareothereffectswhicharenotapparentwheninitiallychoosingsuch
adevice.Note,however,thatthelimitsallowedforharmonicsinEN61000‐3‐12aremuchlargerthanthisandsoyou
shouldalsoconsiderwhetherusinglowerperformancetransducersthanthismightbeapplicable.