Isolated Current and Voltage Measurement Using …

1 FILTER FERRITE BEADGNDR = 3m Ohm+5V_ISO1 GND_ISO1 GND_ISO4CH 1 MSP430FR5869CH 2CH 3CH 4CH 5CH 612 BIT SARIRIYIBVRVYVBUARTINTERFACE+EXPANSION I/OJTAGINTERFACELED(x2)COMMS/ IO(Connector)JTAG(Connector)LEDVDD_2 FILTER FERRITE BEADAMC1100 GAIN 8(Iso. Amp)ISO POWER 1+5V_ISO1-5V_ISO1 GND_ISO1 ISO POWER 2+5V_ISO2-5V_ISO2 GND_ISO2 ISO POWER 3+5V_ISO3-5V_ISO3 GND_ISO3 VDD_2 = +5V_ISO4 JUMPER (MSP430 [ ] or ADS131 [ ] EVM INTERFACE)ISO POWER 4+5V_ISO4-5V_ISO4 GND_ISO4 GNDVDD_2+5V_ISO1-5V_ISO1+/- 250 mVAMC1100 GAIN 8(Iso. Amp)AMC1100 GAIN 8(Iso. Amp)AMC1100 GAIN 8(Iso. Amp)110/ 230 VTERMINALBLOCKTERMINALBLOCKTERMINALBLOCK R = MOhmR = KOhmCH 1 ADS131E08-EVM-PDKCH 2CH 3CH 4CH 5CH 624 BIT Delta-SigmaVDD_2 = 1 OPTION 2 NOTE: FILTER, FERRITE BEAD are optionalSN6501(Transformer Driver)5V_CNTLGNDGND_ISOTLV70450( LDO)TPS7A3001( LDO)+5V_ISO-5V_ISOISO POWERW urth750342354( : )VDD_25V_CNTLTPS7A6533( LDO)GNDPOWER VTI DesignsIsolatedCurrentand VoltageMeasurementUsingFullyDifferential IsolationAmplifierDesignOverviewDesignFe aturesThis TI designdemonstratesusingthe AMC1100-Voltageand CurrentMeasurementUsing.

2 BasedAFEto measurevoltageand Channel-IsolatedCurrentInputsand Groupdesigndetailsmeasuringvoltageinputs in an input-to-IsolatedVoltageInputsBasedon AMC1100 Fixed-outputisolationconfigurationand measuringcurrentGain,FullyDifferentialAm plifiersinputsin a channel-to-channelisolationconfiguration . Provisionto Interfaceto ADS131E08 ADC,Multi-This designalso demonstratespowerisolation,whichChannelS imultaneousSampling,24-Bit,Delta-makesth e designa completesubsystemto measureSigma( ), and EVMfor PerformanceTestingisolatedvoltagesand AFEcan be used OnboardShuntfor ThreeCurrentInputsandin applicationsthat requirereplacingCTs with ThreeVoltageInputsShuntsand potentialdividersare availableonboardtodirectlyconnectcurrent and Low-SideSupplyConfigurableto V or 5 VAMC1100isolationamplifiershavea low nonlinearity AccuracyPerformanceOverFull-ScaleInputer rorand an accuracyof < (175-mVRMS)

3 For Currentand Voltage < to 100%DesignResources IsolatedPowerSupplyGeneratedUsingSN6501 ToolFolderContainingDesignFilesTransform erDriverTIDA-00555 AMC1100 ProductFolder Can Be Interfacedto MCUWithAMC1100 Low-SN6501 ProductFolderSideSupplyConfiguredto VTLV704 ProductFolderFeaturedApplicationsTPS7A30 ProductFolderTPS7A6533-Q1 ProductFolder Portableand AdvancedPowerQualityAnalyzerCSD17571Q2 ProductFolder ProtectionRelays,IEDs,and FaultRecordersADS131E08 EVM-PDKToolFolderMSP430FR5869 ProductFolderASKOur E2E ExpertsWEBENCH CalculatorToolsAn IMPORTANTNOTICEat the end of this TI referencedesignaddressesauthorizeduse, intellectualpropertymattersand otherimportantdisclaimersand August2015 IsolatedCurrentand VoltageMeasurementUsingFullyDifferential IsolationAmplifierSubmitDocumentationFee dbackCopyright 2015, infrastructureapplicationsincludeprotect ion,control,and the gridinfrastructureend applicationsare multifunctionprotectionrelays,transforme rand motormonitoringsystems,powerqualityanaly zers,and be rack-mounted(AC mainsoperated)or portable(batteryoperated).

4 The portablesystemshaverequirementsfor separate(individual)and fully galvanically-isolatedchannelsto measurethe AC-DCvoltageand intelligentelectronicdevices(IEDs)that receiveanalogsignalsfromthe secondaryside of currenttransformers(CTs)and voltagetransformers(VTs).The relaysdetectwhetheror not theprotectedunit is in a trip signalis sent by protectiverelaysto the circuitbreakerstodisconnectthe faultycomponentsfromthe powersystem,if categorizedbasedon the equipmenttype protected,suchas generators,transmissionlines,transformer s,and protectionrelayhas the followingfunctionalblocks: CPU Digitalsignalprocessor(DSP)for processinganaloginputfromCT or VT DigitalI/O DC analogI/O Powersupply CommunicationsThe analoginputrequirementsincludethe following: Currentand voltageinputs Secondaryof CT, secondaryof potentialdivider Numberof currentand voltagechannelsfor protectionrelays 4 to 16 channels Measurementaccuracy 1%Accuratelymeasuringcurrentand voltageis a criticalrequirementfor the functionof a voltageis measuredusinga potentialtransformeror potentialdivider(multipleseriesresistors in adivider).

5 Usinga potentialdividerreducesthe boardsize and improveslinearityperformanceincomparison to a potentialdivider-basedvoltagemeasurement is limitedin that itdoesnot providethe isolationthat requiredfor systemsthat are expectedto conformto commonlyusedto currentinputhas a widedynamicrangein comparisonto the systemperformancedependson the type of the key currentsensorrequirementsare: Measurementaccuracy fromDC to 400 Hz Drift with time,frequency,and temperature Linearityand phaseshift Saturation Reliability Cost Size Safety( isolation )and electromagneticcompatibility(EMC)perform anceTo achievethe requiredperformancestandardslistedabove, selectCTs with a higherlevelof VoltageMeasurementUsingFullyDifferential IsolationTIDUA58 August2015 AmplifierSubmitDocumentationFeedbackCopy right 2015, usingCTs are that they providegalvanicisolation,havelow powerloss,and are notaffectedby the associateddisadvantagesof usingCTs is that theytendto be bulkyand expensiveif the userrequiresa aredisadvantageousto multifunctionprotectionrelayplatforms,wh ichare requiredto affectthe performanceof CTs becausethey saturatethe CTsduringfault conditions.

6 Whenhigh a magneticfield or frequentexposureto overloadsreducesthe usablelife of the alternativeto usingCTs to measurecurrentis low-valuemetalstripsmadewith Manganin shuntperformancefollowsmostof the havelimitationsin that they do not haveisolation,whichis requiredfor use in followingoptionsdetailthe differentisolationmethodsavailable:Input -to-outputisolation: In this case,all channelsare referencedto the isolationamplifiersrequirepowersupplieso n bothsidesof the : In this case,eachinputchannelis referencedto the isolationamplifiersrequireseparatepowers upplieson the inputside of the isolationbarrierand cansharea commonpowersupplyon the inputscan be appliedin the followingconfigurations:Single-ended:The lowestcost configurationis a single-ended,unbalanced, inputworkswell with afloatingsourcethat has relativelylow IN+ terminalimpedanceto groundmustbe high in comparisonto the sourcedifferentialimpedanceto ground-referencedsources,this type of inputimpliesthat the signaland instrumentgroundsmustbe twovoltagesare typicallynot the same,but if the levelsare closeto eachotherand the signalis relativelylarge,the usercan makethe.

7 Differentialinputamplifiersare mostcommonlyusedin measurementsystemsbecausethey provideahigh gain for the algebraicdifferencebetweentheirtwo inputsignalsor voltages,but a low gain for thevoltagescommonto anothermeansof reducingnoisein differentialinputis balancedbecausethe gainsand impedancesof thetwo inputsare the directlyconnectedto ground,so a differentialinputcan deal withsingle-ended-groundedor ,thereis a limit to the maximumsignalthat eachinputcan handlebecausethe amplifiersare referencedto August2015 IsolatedCurrentand VoltageMeasurementUsingFullyDifferential IsolationAmplifierSubmitDocumentationFee dbackCopyright 2015, voltageinputsare attenuatedby the onboardpotentialdividersand theseinputsdemonstratethefollowingin Table1:Table1. VoltageMeasurementPARAMETERSDESCRIPTIONV oltageinputsprovidinginput-to-outputThre efully-differentialisolationamplifiersar e usedto measurethe providinginput-to-One DC-DCconverteris usedto generatethe samepoweroutputisolationsupplyis connectedto all threeisolationamplifierson the is a groupisolatedreference,whichmeansthat all of the amplifierssharea currentinputsare appliedacrossthe onboardshuntand demonstratesthe followingin Table2:Table2.

8 CurrentMeasurementPARAMETERSDESCRIPTIONC urrentinputsprovidingchannel-to-Threeful ly-differentialisolationamplifiersare usedto measurethe providingchannel-to-ThreeseparateDC-DCco nvertersare usedto generatethe high-voltageside its own isolatedfromall followinglist detailsthe stepsfor interfacingthe isolationamplifierto the ADC:(A) Isolationamplifierof the common-modeDC output:The usercan configurethe isolationamplifierfor common-modeoutputwith the 3-V or 5-V low-sidesupply(outputside).(B) Interfaceto delta-sigmaADCADS131E08:A provisionto interfacethe amplifieroutputto a TI delta-sigmamodulatoris ADS131E08devicethe common-modevoltageisconfiguredto V.(C) Interfaceto MCU:An onboardMCUwith a 12-bitdifferentialinputhas ,the common-modevoltageis configuredto VoltageMeasurementUsingFullyDifferential IsolationTIDUA58 August2015 AmplifierSubmitDocumentationFeedbackCopy right 2015, SystemSpecifications2 Key SystemSpecificationsTable3.

9 DesignRequirementsSERIALNUMBERPARAMETERS SPECIFICATIONS1 Isolatedcurrentinputs(withonboardshunt)T hreeIsolatedvoltageinputs(withonboardpot ential2 Threedivider)3 MeasurementfrequencyDC, 50 Hz, 60 Hz4 Currentmeasurementaccuracy< ,for 5% to 100%of AMC1100inputfull scale5 Voltagemeasurementaccuracy< ,for 5% to 100%of AMC1100inputfull scaleAmplifieroutputinterface Option1 (withoutput6 Interfacedto ADS131E08common-modevoltageset to , typical)Amplifieroutputinterface Option2 (withoutput7 MSP430FR5869common-modevoltageset to , typical)8DC powersupplyinput5-V DC9 PowersupplyIsolated5 V and 5 V, VOptionto select5-V ADCor August2015 IsolatedCurrentand VoltageMeasurementUsingFullyDifferential IsolationAmplifierSubmitDocumentationFee dbackCopyright 2015,TexasInstrumentsIncorporatedFILTER FERRITE BEADGNDR = 3m Ohm+5V_ISO1 GND_ISO1 GND_ISO4CH 1 MSP430FR5869CH 2CH 3CH 4CH 5CH 612 BIT SARIRIYIBVRVYVBUARTINTERFACE+EXPANSION I/OJTAGINTERFACELED(x2)COMMS/ IO(Connector)JTAG(Connector)LEDVDD_2 FILTER FERRITE BEADAMC1100 GAIN 8(Iso.)

10 Amp)ISO POWER 1+5V_ISO1-5V_ISO1 GND_ISO1 ISO POWER 2+5V_ISO2-5V_ISO2 GND_ISO2 ISO POWER 3+5V_ISO3-5V_ISO3 GND_ISO3 VDD_2 = +5V_ISO4 JUMPER (MSP430 [ ] or ADS131 [ ] EVM INTERFACE)ISO POWER 4+5V_ISO4-5V_ISO4 GND_ISO4 GNDVDD_2+5V_ISO1-5V_ISO1+/- 250 mVAMC1100 GAIN 8(Iso. Amp)AMC1100 GAIN 8(Iso. Amp)AMC1100 GAIN 8(Iso. Amp)110/ 230 VTERMINALBLOCKTERMINALBLOCKTERMINALBLOCK R = MOhmR = KOhmCH 1 ADS131E08-EVM-PDKCH 2CH 3CH 4CH 5CH 624 BIT Delta-SigmaVDD_2 = 1 OPTION 2 NOTE: FILTER, FERRITE BEAD are optionalSN6501(Transformer Driver)5V_CNTLGNDGND_ISOTLV70450( LDO)TPS7A3001( LDO)+5V_ISO-5V_ISOISO POWERW urth750342354( : )VDD_25V_CNTLTPS7A6533( LDO)GNDPOWER TIDA-00555 FunctionalBlockDiagram6 IsolatedCurrentand VoltageMeasurementUsingFullyDifferential IsolationTIDUA58 August2015 AmplifierSubmitDocumentationFeedbackCopy right 2015,TexasInstrumentsIncorporatedIsolati onBarrier oscillatorRXTXTXR etiming and3rdorderactivelow-pass FullyDifferentialIsolationAmplifierThe AMC1100is a precisionisolationamplifierwith an outputseparatedfromthe inputcircuitryby asilicondioxide(SiO2)