Temperature Sensor Interface Module for …

1 400 300 200 100 01002003004005006007008009001000 Error (SC) Temperature (SC) C002 Measure ADC Error in SC Target specification for -200SC to +850SC TI DesignsTemperatureSensorInterfaceModulef or ProgrammableLogicControllers(PLC)SPACERT I DesignsTI Designsprovidethe foundationthat you needDesignFeaturesincludingmethodology,t estingand designfiles to Two DifferentSensorInputChannels:quicklyeval uateand customizethe Designs K-TypeThermocoupleInputwith CJChelpyouaccelerateyourtime to market. Compatibleto 2-, 3-, or 4-WireRTDP robesDesignResources RatiometricMeasurementfor RTD MeasurementAccuracyfor Thermocouple 1 CToolFolderContainingDesignFilesTIDA-000 18 ADS1220 ProductFolder MeasurementAccuracyfor RTD CLM5017 ProductFolder SensorOpenCircuit/SignalOut-of-RangeDete ctionLM5069 ProductFolder DigitalIsolationfor I/O ControllerInterfaceISO7141 CCProductFolder 24 V 20%InputPowerSupplyOperationISO1540 ProductFolder IEC-61000-4-4:EFT Up to 1 KV at 5 KHz onTPS71533 ProductFolderSignalPortsTPS7A4901 ProductFolderTCA6408 AProductFolder IEC-61000-4-2:ESDUp to 4-KVContactand 8-KVLM94022 ProductFolderAir DischargeLMP275 ProductFolder IEC-61000-4-5.

2 SurgeUp to 1-KVLine-EarthTS5A23159 ProductFolder(CM)on SignalPortsSPACERF eaturedApplications ProgrammableLogicControllers FactoryAutomationand ProcessControlASKOur AnalogExperts PortableInstrumentationWebBench CalculatorTools DataAcquisitionSystems IndustrialRoboticsMeasuredErrorof RTDI nputacrossTemperatureRangeof -200 C to 850 CAll trademarksare the propertyof May 2014 TemperatureSensorInterfaceModulefor ProgrammableLogicControllers(PLC)SubmitD ocumentationFeedbackCopyright 2014,TexasInstrumentsIncorporatedDesignS pecificationsand IMPORTANTNOTICEat the end of this TI referencedesignaddressesauthorizeduse, intellectualpropertymattersand otherimportantdisclaimersand FeaturesTable1 showsthe designspecificationsof theTemperatureSensorInterfaceModulefor ProgrammableLogicControllers(PLC) FEATURESI nputsTwo channelsK-Typesthermocouple2-, 3-, and 4-wirePT100 RTDprobesSensorTypes(HardwaresupportsRTD swith resistanceup to 2 k , whereasexistingTIVAMCU softwareisimplementedfor PT100 RTDonly)For thermocouplechannel: C; Overthe entireTC temperatureRange: 200 C toOverallMeasurementAccuracy1372 C(excludingsensorerrors)For RTDchannel: C.

3 Overthe entireRTDtemperatureRange: 200 C to 850 CFor CResolutionFor CColdJunctionCompensationOn-boardlocalte mperaturesensorIC(CJC)TypeColdJunctionCo mpensation0 C to 60 CTemperatureRangeMeasurementTypeRatiomet ricfor RTDPT100 RTD( 200 C to 850 C) and Thermocouple( 200 C to 1372 C) lookuptablesSensorLinearInterpolationimp lementedin TIVA MCUsoftwareModuleCalibrationADC s offsetand gain calibrationPowerSupplyRange18 V to 32-VDCI solation250-VDC (Continuous),Basicisolation1500-VAC for one minuteESDI mmunityIEC 61000-4-2:4 kV contactdischarges,8 kV air dischargesEFT ImmunityIEC 61000-4-4: 1 kV at 5 kHz on signalportsSurgeTransientImmunityIEC 61000-4-5: 1 kV line-earth(CM)on signalportsOperatingTemperatureRange0 C to 60 CStorageTemperature 40 C to 85 CTemperature,SurroundingAir60 C50-pinconnectorpluggabletoPLCI/O ModuleFront-EndControllerUsinga Tiva C SeriesARM Cortex -M4 MCU(TIDU191)Connector(s)4-pinscrewtermin alblockfor 2-, 3-, and 4-wireRTDprobes2-pindedicatedK-typetherm ocoupleconnectorFormFactor(L x W) x (Smallindustrialformfactor)2 TemperatureSensorInterfaceModulefor ProgrammableLogicControllersTIDU271 May 2014(PLC)SubmitDocumentationFeedbackCopy right 2014, sole objectiveof this referencedesignis to focuson the completecircuitdesignguidelinesthat helpengineersand systemarchitectsto develophigh precisiontemperaturemeasurementsolutions using24-bit delta-sigmaADCand mostwidelyusedtemperaturesensorslike thermocouplesand ResistanceTemperatureDetectors(RTDs).

4 This referencedesignaddressessensorsignalcond itioning,thermocouplecold junctioncompensation,ratiometricmeasurem enttechniquefor RTDs,recommendedsoftwareflow,sensorlinea rization,sensordiagnostics,transientprot ection,PCBlayout,and otherpracticaldesignconsiderationsfor achievinghigh-precisionrobustdesignfor TemperatureSensorInterfaceModuleis a fully isolateddesignwhichis essentialfor signalchainand powerline galvanicisolationbarrierbetweenthe host controllerside and the measurementside havebeenachievedusingdigitalisolatorsand a flybacktransformer, heartof this referencedesignis the ADS1220device,a 24-bitdelta-sigmaADC,whichprovidesa high resolution,high integration,low noise,and low cost completesensoranalogfront-endforDC designis also suitableto interfacewith differenttypesof boardspace,reducesdesignefforts,reducest ime to market,and demonstratesotherTI products,suchas hot swapand in-rushcurrentlimitcontroller,isolatedFl y-Buck controller,low noiseLDO,digitalisolators,localtemperatu resensors,analogswitchand I2C to GPIO expanderthat can be usedin the ,externalprotectioncircuitryis circuitryhas beensuccessfullytestedand verifiedfor compliancewith regulatoryIEC61000-4standards:EFT,ESD,an d standardIEC61000-4is necessaryto ensurethat the designnot only survivesbutalso performsas intendedin harshor the relevantdesignfiles like Schematics,BOM,LayerPlots,AltiumFiles,Ge rber,and TIVA C-SeriesMCUsoftwareare executablewith an easy-to-useGraphicalUserInterface(GUI).

5 Usersmay downloadthe files at BlockDiagramof TemperatureSensorInterfaceModulefor PLC3 TIDU271 May 2014 TemperatureSensorInterfaceModulefor ProgrammableLogicControllers(PLC)SubmitD ocumentationFeedbackCopyright 2014, TemperatureSensorInterfaceModuleprovides two differentialinputchannelsto take measurementsfromtwo channelsupports2-, 3-, and designusesa singleADS122024-bitdelta-sigmaADCwithan externalTS5A23159dual channel2 x 1 multiplexerswitchesthe twodifferentialanaloginputsto sharethe host controllercommunicateswith TCA6408A- I2 Cto the GPIO expanderoveran I2C bus, crossingthe isolationbarriervia the routeone of the two inputsto the inputchannelselectionis donein signalcomingin or goingout of the moduleis protectedagainsthigh voltagefast transientevents,whichare oftenexpectedin protectioncircuitrymakesuse of TVSand temperaturesensors(especiallythermocoupl es)produceoutputin the millivoltrange,whichmakessensorsproneto RC low-passdifferentialand commonmodefiltersare usedon eachanaloginputbeforeit reachesthe filterseffectivelyeliminatesany high frequencynoisepickupwhichmay be designprovidestwo localtemperaturesensorICs to sensethe cold junction(or referencejunction) a multi-gainanalogoutputtype temperaturesensorfed to ADS1220afterpassingthrougha low passfilter and one additionalTS5A23159dual channel2 x 1 is the TMP275,whichis a two-wiredigitaloutputtemperaturesensordi rectlyinterfacedto the I2C datareadysignal(DRDY)fromADS1220reportst he conversionstatus,whichconnectsto the GPIOpin of TCA6408A,configuredas convertedsensordata,the host controllerpollsfor the datareadystatuslatchedinsidethe inputport registerof TCA6408 Aoverthe I2C ProgrammableLogicControllersTIDU271 May 2014(PLC)

6 SubmitDocumentationFeedbackCopyright 2014, Operation5 Theoryof OperationTemperatureis one of the the mostessentialfactorthatneedscontinuousme asurement,monitoring,and controlin variousprocessesin ,industrydemandsaccurate,repeatable,and reliablemeasurementof Temperature ,becausetemperaturecan havesignificantimpacton productcost,quality,efficiencyand temperaturesensorsmeasuretemperatureby sensingsomechangein materialphysicalcharacteristicsas a functionof availablein a widevarietysuchas: Thermocouple ResistanceTemperatureDetector(RTD) Thermistor SemiconductorTemperatureSensorICTable2. Comparisonof DifferentTemperatureSensorsRESISTANCESEM ICONDUCTORTHERMOCOUPLETEMPERATURETHERMIS TORTEMPERATUREDETECTOR(RTD)SENSORICR ange 270 C to 2000 C 200 C to 850 C 50 C to 300 C 55 C to 200 CChangingPhysicalVoltageResistanceResist anceVoltageor currentCharacteristicExcitationSelf-powe redCurrentexcitationCurrentexcitationPow erSupply( A)CostLowHighLow to moderateLowResponseMediumto fastMediumMediumto fastMediumto fastAccuracyLessBestGoodBetterRepeatabil ityReasonableExcellentFair to GoodGoodto excellentVeryhigh (CanwithstandRuggednessLessHighMediumhig h shockand vibration)Amplification,Filtering,ColdLe adCompensation,Powersupply,Self-SpecialR equirementsjunctioncompensation,Lineariz ationFilteringcontainedLinearizationLow (40 V per C for K-Sensitivityat 20 CMediumVeryhighHigh(Typically10 mV/ C)Type)Self-HeatingNoVerylow to lowHighVerylow to lowLeadWireResistanceNot a problemProblematicNot a problemNot a problemInterchangeabilityGoodExcellentPo orto fairBetterStableoverlong period.

7 CPoorGoodper yearNoiseSusceptibilityHighMediumLowMedi umLinearityFairGoodPoor(Logarithmic)Good Smallto mediumbut limitedSizeSmallto largeMediumto smallSmallto mediumpackagechoicesAmongdifferenttypeso f temperaturesensors,the mostfrequentlyusedonesin industrialapplicationsarethermocouplesan d resistancetemperaturedetectors(RTDs).5 TIDU271 May 2014 TemperatureSensorInterfaceModulefor ProgrammableLogicControllers(PLC)SubmitD ocumentationFeedbackCopyright 2014,TexasInstrumentsIncorporated5 V5 2F5 2 FCDIFCCM2 CCM1RF1RF2RB1RB2 Low Drift OscillatorReference MuxPrecision Temp SensorAIN0 AIN1 AIN2 AIN3 SCLKCSAVDDAVSSDOUT/DRDYDIND eviceDRDYDGNDREFP0 REFN0 Internal ReferenceCLK10 A mAMuxDVDDPGA24-bit ADCD igital Filter and SPI InterfaceTheoryof ThermocoupleMeasurementCircuitUsingADS12 206 TemperatureSensorInterfaceModulefor ProgrammableLogicControllersTIDU271 May 2014(PLC)SubmitDocumentationFeedbackCopy right 2014,TexasInstrumentsIncorporated()HOTCO LDVSTTD = Backto Basics NOTE.

8 Any conductorsubjectedto thermalgradientwill generatea voltagebetweenits simplemetalbar producesa voltagewhenthereis a temperaturedifferencebetweenthe two the hot end are morethermallyagitatedthanthe electronsat the morethermallyagitatedelectronson the hot end beginto diffusetowardsthe redistributionofelectronscreatesa negativechargeat the coolerend and an equalpositivechargeat the electrostaticvoltagebetweenthe two opencircuitvoltageproducedin thisway is knownas SeebeckVoltage. The phenomenonis calledthe SeebeckEffect . The SeebeckEffectwas first discoveredby GermanscientistThomasJohannSeebeckin a singlemetalbar is will also producethe sameSeebeckVoltage,cancellingeachotheran d resultingin 0 V at the ,a singlewire doesnot formas a thermocoupleis formedwhentwo dissimilarmetalsare bondedtogetherelectricallyto formtwo junctionsas shownin VoltageDevelopedDue to TemperatureGradientFigure4. ThermocoupleThe magnitudeand directionof opencircuitvoltagedevelopedbetweenthe two endsis proportionalto thetemperaturedifference,as shownin Figure4 and Equation1.

9 (1)whereS is theSeebeckcoefficientorthermoelectricsen sitivityWhendesigningwith thermocouples,it is importantto understandthat thermocouplesare producea positiveor a negativevoltage,dependingon whetheror not themeasuredtemperatureis higheror lowerthanthe systemtemperature, May 2014 TemperatureSensorInterfaceModulefor ProgrammableLogicControllers(PLC)SubmitD ocumentationFeedbackCopyright 2014,TexasInstrumentsIncorporatedTheoryo f mostmisunderstoodimportantpointabouta thermocoupleis that virtuallyno voltageis developedatthe junctionis basicallyan electricalbondbetweentwo metalswhichcompletethe circuit,sothat currentflow can take developedacrosseachwire as temperaturechanges,asshownin Figure5. The voltagedifferenceis observedat the measuringend,becausetwo Thermocoupleand DevelopedVoltageDependingon the requiredtemperaturerange,vibrationresist ance,chemicalresistance,responsetime,and installationand equipmentrequirements,the designercan choosethe availablein differentcombinationsof metalsand calibrationsas givenin Typesof ThermocoupleTYPETYPEETYPEKTYPEJTYPERTYPE STYPETN ickel 10%Nickel 10%ChromiumPlatinum 13%,Platinum 10%,JunctionChromiumIron versusCopperversusversusNickelRhodiumver susRhodiumverusMaterialversusConstantanC onstantan 5% AluminumPlatinum( )Platinum( )ConstantanSiliconSeebeckCoefficient62 V/ C40 V/ C62 V/ C7 V/ C7 V/ C40 V/ Cat 20 CTemperature 100 C to0 C to 1370 C0 C to 760 C0 C to 1450 C0 C to 1750 C 160 C to 400 CRange1000 CHighResistancetoStandardforCryogenicoxi dationandOftenusedinGeneralGeneralHigher calibrationfor theuse.

10 Non-corrosion,differentialApplicationpur poseSensitivitymeltingpointofmagneticuse calibrationmeasurementsgoldpurposes8 TemperatureSensorInterfaceModulefor ProgrammableLogicControllersTIDU271 May 2014(PLC)SubmitDocumentationFeedbackCopy right 2014, OperationEachthermocouplesensorhas its own sensitivity( V/ C), a temperaturerange,and a nonlinearvoltagecurveoverthat temperaturerange,dependingon its metalsand nonlinearovertheiroperatingtemperaturera nges,as can be seenin ThermocoupleOutputas a Functionof TemperatureThe Seebeckcoefficientis a nonlinearfunctionof temperatureand causesthe outputvoltagesofthermocouplesto be a best practice,alwayschoosea thermocouplehavinglessvariationin its TemperatureversusSeebeckCoefficient9 TIDU271 May 2014 TemperatureSensorInterfaceModulefor ProgrammableLogicControllers(PLC)SubmitD ocumentationFeedbackCopyright 2014,TexasInstrumentsIncorporatedTheoryo f (CJC)A thermocouplemeasuresthe temperaturedifferencebetweenhot and cold measurethe absolutetemperatureat one junctionas illustratedin Figure8.