mg8g/mg8e paramagnetic oxygen analyzers · a magnetic wind oxygen analyzer is characterized by...

TechnicalInformation

Contents1. Introduction...................................................................................................22. TypesandApplicationsofOxygenAnalyzers..........................................3

2.1 ParamagneticOxygenAnalyzers....................................................................... 32.1.1 MagneticProportionalFlowRateMethod............................................ 4

2.1.2 MagneticWindMethod......................................................................... 4

2.1.3 MagneticForceMethod(DumbbellType)............................................ 6

2.1.4 MagneticForceMethod(PressureSensorType)................................. 6

2.2 ElectrochemicalOxygenAnalyzers................................................................... 72.2.1 ZirconiaSystem.................................................................................... 7

2.2.2 ElectrodeSystem.................................................................................. 9

2.3 AbsorptionSpectroscopyOxygenAnalyzer.....................................................102.3.1 TunableDiodeLaserSpectroscopy(TDLS)Method......................... 10

2.4 ApplicationsofOxygenAnalyzersbyMeasurementPrinciple.................... 112.5 OxygenAnalyzerSelectionFlowchart............................................................ 12

3. MG8G/MG8EFeatures.............................................................................. 134. MG8G/MG8ESystemConfigurationandSensorConstruction........... 14

4.1 SystemConfiguration....................................................................................... 144.2 SuitableApplicationsforMG8G/MG8EParamagneticOxygenAnalyzers.. 154.3 SensorConstruction......................................................................................... 16

5. EffectsofInterferenceGas....................................................................... 195.1 MeasurementofOxygen(O2)inthePresenceofInterferenceGases........ 195.2 DataonEffectsofInterferenceGases............................................................. 205.3 InterferenceGasCompensation...................................................................... 21

6. Characteristics(MG8ETestData)............................................................ 226.1 ResponseCharacteristic................................................................................... 226.2 FlowCharacteristics.......................................................................................... 226.3 AttitudeError...................................................................................................... 236.4 EffectsofAtmosphericPressureandLong-termDrift.................................. 23

RevisionInformation........................................................................................... 24

MG8G/MG8EParamagneticOxygenAnalyzers

TI11P03A05-01E

TI11P03A05-01E©CopyrightSep.2009(YK)2ndEditionOct.2012(YK)

YokogawaElectricCorporation2-9-32,Nakacho,Musashino-shi,Tokyo,180-8750JapanTel.:81-422-52-5617 Fax.:81-422-52-6792

2

AllRightsReserved.Copyright©2009,YokogawaElectricCorporation TI11P03A05-01E

1.Introduction

1. IntroductionTheMG8G/MG8EParamagneticOxygenAnalyzerscanmeasuretheoxygenconcentrationinagasmixturewithhighprecision.Theydothisbasedontheprinciplethatoxygenisaparamagneticmaterial(magneticallysusceptible).Unlikezirconiaoxygenanalyzers,theMG8G/MG8Eanalyzerscanalsomeasure the oxygen concentration in a flammable gas mixture.

The MG8G/MG8E Paramagnetic Oxygen Analyzers use a magnetic proportional flow rate sensor that was developedbyYokogawatoimprovetheperformanceofitsmagneticwindsensors.Thishasthefollowingfeatures:

• Cleanauxiliarygas(N2) flows past the sensor in the detection unit without coming into contact with the samplegas,ensuringlong-termmeasurementstabilityevenwhencorrosiveorcontaminatedgasismeasured.

• Thermistors with high sensitivity and fast response times directly detect changes in the flow rate of the auxiliarygas,achievinga90%responsewithin3seconds.

• Therearenomovingparts,ensuringexcellentresistancetovibrationandshock.

• Aninterference-gascompensationfunctionensuresaccuratemeasurementsevenwhenflammablebackgroundgaseswithmagneticproperties(havingamuchlowerlevelofmagneticsusceptibilitycomparedtooxygen)arepresent.

• Excellentindicatingstabilityinthevicinityofzeromakesitsuitableforlow-concentrationmeasurements(e.g.forsafetycontrol).

Thistechnicalinformationdocument(TI11P03A05-01E)waspreparedwiththepurposeofhelpingusersunderstandandmakethebestuseofthesefeaturesoftheMG8G/MG8EParamagneticOxygenAnalyzers.Itdescribesthemeasurementmethodsusedbyvarioustypesofoxygenanalyzersaswellastheirfeaturesandapplications,thedesignandoperationoftheMG8G/MG8EParamagneticOxygenAnalyzers,andtheeffectsandcharacteristicsofinterferencegases.

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32.TypesandApplicationsofOxygenAnalyzers

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2. TypesandApplicationsofOxygenAnalyzers

Oxygen,whichmakesupabout21%oftheair,isanessentialelementincombustionandcellularrespiration.Sinceoxygenisinvolvedinvarioustypesofchemicalprocesses,themeasurementandcontroloftheoxygenconcentrationareveryimportantforcontrollingtheseprocesses.

Therearevariousmethodsformeasuringtheoxygenconcentration,andthemajorityofthesefallintothetwofollowingroughcategories:(1)methodsthatusetheparamagneticpropertyofoxygen,(2)methodsthatusetheelectrochemicalpropertyofoxygen,and(3)methodsthatusetheabsorptionspectroscopyofoxygen.

2.1 ParamagneticOxygenAnalyzersFigure2.1comparestheparamagneticpropertiesofoxygenandothergases,andonlyoxygenexhibitsvery high magnetic susceptibility; most other gases have a relatively weak attraction to magnetic fields.

Nitrogenmonoxide(NO)alsoexhibitsafairlystrongmagneticsusceptibility;however,eveninexhaustgasesitsconcentrationisapproximatelyonly100ppm,whichissolowthatitsparamagneticpropertycanbeignored.

F0201.ai

Relative values of various gases assuming the bulk magnetic susceptibility of oxygen is 100

+21.6

Cl2CO2

NH3

CH4

N2O

N2

+6.2

+43.8

H2

C2H2

C2H4

+100

–0.128

–0.613

–0.575

–0.575

–0.376

–0.113

–0.37

–0.85

–0.42

NO2

Air

NO

O2

Figure2.1 RelativeBulkMagneticSusceptibilitiesofGasses

Paramagneticoxygenanalyzersusethefollowingmethods

(1) Magnetic proportional flow rate method(2) Magneticwindmethod(3) Magneticforcemethod(dumbbelltype)(4) Magneticforcemethod(pressuresensortype)

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2.1.1 MagneticProportionalFlowRateMethod

Exhaust gasSample + auxiliary gas

Thermistors

Magnet

Auxiliary gasSample gas

B

A

F0202.ai

Figure2.2 MagneticProportionalFlowRateSensor

AsshowninFigure2.2,asamplegasisintroducedfromthesensor’ssamplegasinletanddividedintotwostreamsinthering-shapedgasflowpath.Anauxiliarygasisintroducedfromtheauxiliarygasinletanddividedintotwostreams,AandB,whichflowtowardsthering-shapedgasflowpath.Athermistorisinstalled in each of these streams to determine their flow rates, and a magnet generates a magnetic field in streamB.

When a sample gas contains oxygen, the oxygen is drawn into the magnetic field, thereby decreasing the flow rate of auxiliary gas in stream B. The difference in the flow rates for streams A and B is proportional to theoxygenconcentrationofthesamplegas.Thisdifferenceisdeterminedandoutputbythethermistors.TheMG8G/MG8EParamagneticOxygenAnalyzersusethismethod.

A magnetic proportional flow rate oxygen analyzer is characterized by fast response and strong resistance tovibrationandshock.Furthermore,thethermistorsdonotcomeincontactwiththesamplegas,therebyensuringlong-termmeasurementstabilityevenwhencorrosiveorcontaminatedgasismeasured.

2.1.2 MagneticWindMethodThismethodwasdevelopedalongtimeagoandusesmanydifferenttypesofmeasurementcells.

Figure2.3showstwocylindricalchamberswithopposingconicallyshapedmagneticpolesthathaveflattopsandareseparatedbyaglass-coatedring-shapedheatingwireelement.Thechamberontheleftisthemeasurementchamber.Whenasamplegasisintroducedintothischamber,oxygenisdrawntowardtheheatingwire,wherethemagneticfieldisstrongest.Heatedbythewire,theoxygenlosesitsmagneticsusceptibilityandispushedupwardsbycoolergascomingfromthelowerpartofthechamber.Inthisway,aso-calledmagneticwindisgeneratedinthemeasurementchamber,anditsintensityisproportionaltotheoxygenconcentrationinthesamplegas.

Thetemperatureoftheheatingwireisrelatedtothecoolingeffectofthemagneticwind,andtothethermalconductivity, density, specific heat, and viscosity of the gas surrounding the heating wire.

Compensationisperformedwiththereferencechamber,whichisidenticalinconstructiontothemeasurement chamber, with the exception that no magnetic field is created. The two heating wires form a Wheatstonebridge,andtheresistancechangeisdetectedasachangeinthevoltage.

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Heatingelement

Sample gas

Measurementchamber

Reference chamber

Magneticwind

Magnet

Magnet

Heatingelement

Naturalconvection

Bridgeammeter

F0203.ai

vol%O2

Figure2.3 ExampleofConstructionofMagneticWindOxygenAnalyzer (withCylindricalMeasurementChamber)

Figure2.4showsameasurementcellwitharing-shapedgaspath.Athinglasstubewithaheatingwirewoundarounditprovidesadirectpaththroughthecenterofthecircularpath.Themagneticpoleofapermanentmagnetisplacedtotheleftofthecenterofthistube.Asamplegascontainingoxygenisattracted to the strongest part of the magnetic field generated by this magnet. When the oxygen is heated bythetube’sheatingwire,itlosesitsmagnetizationandispushedoutbycoolergasenteringfromtheleftsideofthetube;thus,amagneticwindpassingfromlefttorightisgeneratedinthetube.

Amagneticwindoxygenanalyzerischaracterizedbystrongresistancetovibrationandshock;ontheotherhand,sinceitsdetectionmethodreliesonthethermalconductivityofgas,itissusceptibletorapidchangesintheambienttemperatureandchangesinthegascomposition.Furthermore,measurementscanbeaffectedbythecontaminationofthesamplegasthroughcontactwiththesensorunit.

Ｎ

Ｓ

ＰＯ

Ｍ

mA

vol％O2

Sample gas

Ｏ2

Bridgeammeter

F0204.ai

Figure2.4 ExampleofConstructionofMagneticWindOxygenAnalyzer (withRing-shapedMeasurementChamber)

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2.1.3 MagneticForceMethod(DumbbellType)Figure2.5showsadumbbell-shapedobjectwithlowmagneticsusceptibilitythatissuspendedfromaplatinumorquartzwirewithinamagneticfield.Whenasamplegascontainingoxygenisguidedtothevicinityofthedumbbell,theoxygenisattractedtothepointofmaximummagneticfieldstrength,causingtheballsonthedumbbelltodeflectslightlyinanoppositedirection.Thetwistingofthesuspensionwireisdetected using a light source and a reflector that is attached to the center of the wire. The signal causes a current to flow through an excitation coil to correct the deflection. The current is proportional to the oxygen concentration.

Thismethodischaracterizedbyawidedynamicrangeandisnotinfluencedmuchbythepresenceofbackgroundgases.Thedownsideisthatithaslessresistancetovibrationandmechanicalshockandissusceptibletocontaminationandcorrosion.

Suspending wire

Dumbbell

Excitationcoil

Magnetic poleReflector

Photo sensors

Lightsource Vol%O2

F0205.ai

Figure2.5 MagneticForceMethod(dumbbelltype)

2.1.4 MagneticForceMethod(PressureSensorType)Whentwogasescomeintocontactinamagneticfield,adifferentialpressureisgeneratedthatisproportionaltothedifferenceinthemagneticsusceptibilitiesofthegases.Providingthattheoxygencontentoftheauxiliarygas(referencegas)remainsataconstantlevel,theoxygenconcentrationofthesamplegascanbedeterminedbymeansofthedifferentialpressure.Sincealternatingcurrentallowsforeasierdetectionandamplificationofsignals,amagneticfieldiscreatedusinganelectromagnetthatisintermittentlyexcited.Acondensermicrophonesensorormicroflowsensorthatisusedininfraredgasanalyzersisusedtodetectsmallvoltages.Figure2.6illustratesthismethod.

Althoughthismethodrequiresanauxiliarygas,itisaffectedrelativelylittlebybackgroundgasesandhasafastresponsetime.

Electromagnet Restrictor

Sample gas

Auxiliary gas

Small pressure sensor

F0206.ai

P

Figure2.6 MagneticForceMethod(pressuresensortype)

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2.2 ElectrochemicalOxygenAnalyzers2.2.1 ZirconiaSystem

(1) OxygenConcentrationCellAzirconiaceramicthathasbeenstabilized,forexample,bycalciumoxide(CaO)oryttriumoxide(Y2O3),isasolidelectrolytethatisconductiveonlytooxygenionswhenitisheatedtoahightemperature.

Figure2.7showsazirconiaelementwithaporousplatinumelectrodeattachedoneachside.Whentheelectrodesareexposedtoagasthatcontainsoxygen,thefollowingreactionsoccurbetweentheelectrodes,withthezirconiaelementservingasaseparator:

P1side(cathode): O2+4e-->2O2-

P2side(anode): 2O2--->O2+4e

ThismeansthatoxygenmoleculesgainelectronsandbecomeoxygenionsatelectrodeP1,givingitahigherpartialoxygenconcentration.TheseionstravelthroughthezirconiaelementtoelectrodeP2,creatinganoxygenconcentrationcell.Here,electronsarereleasedtoformoxygenmolecules,givingitalowerpartialoxygenconcentration.Thesereactionsbetweentheelectrodesgenerateanelectromotiveforce(E),whichisrepresentedbythefollowingNernstequation:

E=- RT ln P24F P1

R:gasconstant

T:absolutetemperature

F:Faradayconstant

WhentheP1sideisexposedtoareferencegas(e.g.air)andtheP2sideisexposedtoasamplegas,theoxygenconcentrationinthesamplegascanbedeterminedbymeasuringtheelectromotiveforcethatisgenerated.

Gas of high oxygen concentration

P1 Electrode (cathode)

Zirconia element

Electrode (anode)P2

Gas of low oxygen concentration

F0207.ai

Figure2.7 OxygenConcentrationCell

TheZR402/ZR202ZirconiaOxygenAnalyzers,theAV550GAveragingConverter,theZS8Explosion-proofOxygenAnalyzerandtheOX400LowConcentrationOxygenAnalyzerusethismethod.

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(2) LimitingCurrentSystemAsshowninthefigure2.8,iftheflowofoxygenintothecathodeofazirconiaelementheatedtohightemperatureislimited,thereappearsaregionwherethecurrentbecomesconstantevenwhentheappliedvoltageisincreased.Thislimitedcurrentisproportionaltotheoxygenconcentration.

F0208.ai

Gas diffusion hole

Diffusionchamber

Anode Current

Zirconia, or solid electrolyte

O2

O2 Cathode

Figure2.8 LimitingCurrentSystem

TheOX100/OX102OxygenAnalyzersusethismethod.

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2.2.2 ElectrodeSystemFigure2.9showstheinteriorofanelectrodeoxygenanalyzer.Ajelly-likeelectrolyteisappliedtothegoldcathode and silver anode, over which a thin Teflon membrane is stretched that is only permeable to oxygen. Whenavoltageof0.5Vto0.8Visappliedbetweentheelectrodes,apolarographiclimitingcurrentthatisproportionaltotheoxygenconcentrationcanbedetected.

Agalvaniccelloxygenanalyzerusesanelectrodesystemwiththiskindofseparatingmembrane.Withthismethod,anelectrode(cathode)madeofanoblemetalsuchasgoldorsilverandanelectrode(anode)madeofabasemetalsuchasleadarelocatedintheelectrolyte,whichisincontactwiththeairthroughtheseparatingmembrane.Thisseparatingmembraneisonlypermeabletooxygen.Thepermeatedoxygencausesanoxidationreactionatthecathodeandgeneratesapotentialwhenanadditionalresistorisconnectedtobothelectrodes.Theoxygenconcentrationcanbedeterminedbymonitoringthegeneratedcurrent.

Thedownsideofthismethodisthatthelifeofthesensorcellislimitedbybeingincontactwiththeairevenwhenmeasurementisnotbeingperformed,soperiodicreplacementisrequired.Anotherproblemisthatanegativedriftoccurswhentheanalyzerisoperatedcontinuously.Therefore,thisanalyzerisnotsuitableforcontinuousmeasurementsoveralongperiodoftime.However,itiscompactandcostsrelativelylittle,soitisusedasaportableanalyzer.

Silver electrode (+)

Electrolyte jelly

Gold electrode (-)ThermistorTeflon membraneTeflon membrane F0209.ai

Figure2.9 SeparatingMembraneElectrodeforMeasuringOxygenConcentration

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2.3 AbsorptionSpectroscopyOxygenAnalyzer2.3.1 TunableDiodeLaserSpectroscopy(TDLS)Method

OperationalPrincipleTDLSmeasurementsare basedonabsorptionspectroscopy.TDLSAnalyzeroperatesbymeasuringtheamountoflaserlightthatisabsorbed(lost)asittravelsthroughthegasbeingmeasured.InthesimplestformaTDLSanalyzerconsistsofalaserthatemitsinfraredlight,opticallensestofocusthelaserlightthroughthegastobemeasuredandthenontoadetector,thedetector,andelectronicsthatcontrolthelaserandtranslatethedetectorsignalintoasignalrepresentingthegasconcentration.Gasmoleculesabsorblightatspecificwavelengths,calledabsorptionlines.ThisabsorptionfollowstheBeer-LambertLaw.

I=I0•e-E・G・L

whereIistheradiationintensityafterabsorption

I0istheinitialradiationintensity

E is the extinction coefficient

Gisthegasconcentration

andListhepathlengthofthemeasurementarea

UsingaTunableDiodeLaserasalightsourceforspectroscopyhasthefollowingbenefits:• Sensitivity.ApplicationDependant.Sub-PPMinsomeapplications.

• Selectivity.Thenarrowlinewidthofthelaserisabletoresolvesingleabsorptionlines.Thisprovidesmorechoicesofaparticularpeaktouseformeasurement,usuallyallowingoneisolatedpeaktobeused.

• Power.Diodelasershavepowerrangingfrom0.5mWto20mW.Also,beinghighlycoherentthisallowsmeasurementinopticallythickenvironments(highparticulateloading).

• Monochromatic. No dispersive element (filter, etc.) required. Light source itself is selective.

• Tunable.Wavelengthcanbesweptacrosstheentireabsorptionfeature,thisallowsresonant(peak)andnonresonant(baseline)measurementduringeveryscan.Bymeasuringthebaselineandpeak,power at the detector can fluctuate rapidly by large amounts without affecting the measurement. This isusefulforhighparticulateapplications.

TheTDLS200andtheTDLS220(ExtractiveType)TDLSAnalyzersusethismethod.

Photo detector(Photo diode)Laser diode

Optical path

Laser beam

Process gas stream F0210.ai

Photo detector(Photo diode)Laser diode

Optical path

Laser beam

Process gas stream F0210.ai

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2.4 ApplicationsofOxygenAnalyzersbyMeasurementPrinciple

Table 2.1 shows which oxygen analyzer types are suitable for specific applications and industries.

Table2.1OxygenAnalyzerApplications,byAnalyzerType

Analyzertype Zirconia Magnetic Laser

Yokogawa’smodelZR202GZR22G

+ZR402G

ZR202SZR22S

+ZR402G

OX400OX100OX102

MG8G MG8E TDLS200

Application:Boiler/combustionfurnaceAllindustrytypes A BElectricpower A BOil/petrochemical A A BPulp/paper A B

Application:HeatingfurnaceOil/petrochemical A A BIronandsteel,nonferrousmetal A B BCeramic A B B

Application:ProcessqualityandsafetycontrolOil/petrochemical A APulp/paper C BOther(Ironandsteeletc.) B B A B

RemarksCombustion control, (C: humidity measurement)

Explosion-proof type

Built into device Quality control, combustion control

Explosion-proof type, safety and quality control

Combustion,safety control

A:MostsuitableB/C:Suitable

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2.5 OxygenAnalyzerSelectionFlowchart

*1

For semiconductor or electronic component manufacturing process

For combustioncontrol or

process control

With samplingDirect in-situ

Explosion-proofconstruction

required?

Explosion-proofconstruction

required?

YES or NO

Oxygen Analyzer

Flammable gas included?

NO

NO

YES

YES

OX400 or OX100 or OX102

MG8ETDLS200

Explosion-proof typeNote 2

Note 1

Paramagnetic Oxygen AnalyzersLaser Analyzers

MG8G

General-purpose type

Application

Sampling method

ZR22S+ZO21P+ZR402G

ZR22G+ZR402Gor ZR202G

ZR22G+ZO21P+ZR402G

ZR22G+AV550G

ZR22S+ZR402Gor ZR202S

Note 1: If a flammable gas makes up 0.5 % or less of the gas mixture, select “NO.”Note 2: All of these instruments must be ordered with the custom order process.Note 3: The ZR402G converter must not be installed in a hazardous area.Note 4: Max. of 8 points for measurement and averaging.Note 5: Optical path averagingNote 6: The ZO21P is a high temperature probe adapter.

Averaging measurement ?

NO

NONO

YES

Explosion-proofconstruction required?

YES

YES

YES

NO

Zirconia Oxygen Analyzers

Gas temperature 700°C or less?

Gas temperature 700°C or less?

Laser Analyzers

TDLS200

Note 3 Note 3, Note 6 Note 6

Note 2

Note 4Multi-points measurementand averaging Note 5

Line averaging

Averaging method

*1

Note 2

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133.MG8G/MG8EFeatures

3. MG8G/MG8EFeatures

uHighlyReliableandEasytoMaintain•Thesensorisdesignedsothatitdoesnotcomeintocontactwiththesamplegas(seesection4.3).Long-

termmeasurementstabilityisensuredevenwhencorrosiveorcontaminatedgasismeasured.

•Thelackofanymovingpartsensuresexcellentresistancetovibrationandshock.

•TheMG8Eisexplosion-proof(ExdIIBT4X).

uHighStabilityandFastResponse•Themainpartofthesensorunitincludingthemeasurementcellisinahousingwhereaconstant

temperatureismaintained.Thisminimizesanyeffectonthesamplegasbytheambienttemperatureandalsopreventsdraining,therebyassuringstablemeasurement.

•Highlysensitivethermistorswithfastresponsetimesdirectlydetecttheflowrateofauxiliarygases,ensuringa90%responsewithinthreeseconds.

•Excellentindicatingstabilityinthevicinityofzeromakesthesensorsuitableforlowconcentrationmeasurement(e.g.forsafetycontrol).

•Aninterference-gascompensationfunctionensuresaccuratemeasurementevenwhenparamagneticbackground gases (including flammable gases) are present.

uConverterwithaWealthofConvenientFunctions•Easycalibration

Allyouneedtodotocalibratetheunitisintroduceacalibrationgaswithazerooxygenconcentrationandpressthecalibrationbutton,thenrepeattheprocedurewiththegascontainingapre-determinedoxygen.Tosavetime,automaticcalibrationmodecanbeselected.Furthermore,anoutputfunctionthatdrivesasolenoidvalvetoswitchbetweenzeroandspanisprovidedasastandardfeature.

•Richself-diagnosticfunctions

Cell,measurementunittemperature,analogunit,digitalunit,andmemoryfailurescanbedetected.Ifafailureisdetected,theFAILlamplightsandamessageisdisplayed.Furthermore,iftheauxiliarygaspressurefallsbelowthesetpoint,contactoutputisactivated.

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4.MG8G/MG8ESystemConfigurationandSensorConstruction

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4. MG8G/MG8ESystemConfigurationandSensorConstruction

4.1 SystemConfiguration

Figure 4.1 shows the basic system configuration of the MG8G/MG8E Paramagnetic Oxygen Analyzers.

Thepre-treatmentunitvariesdependingonthedeviceandapplication,soallpre-treatmentunitshavetobecustom-ordered.

F0401.ai

Analog output (4 to 20 mA DC)Contact output(abnormal)(maintenance)(range selection answerback)(Hi / Lo alarm)

Gas outlet

Filter

Flowmeter

MG8G/MG8E

Needle valve

Needle valve

Pressurereducing valve

Pressurereducingvalve

Pressuremeter

Pressure reducing valve

Auxiliary gas N2

Zero gas N2

Span gas O2+N2

Samplegas

Water feedWater drainSteam inlet

Steam outletPower supply

Pre-treatmentunit

or Instrument air

P

Figure4.1 MG8G/MG8EOxygenAnalyzerSystemConfiguration

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4.2 SuitableApplicationsforMG8G/MG8EParamagneticOxygenAnalyzers

TheMG8GParamagneticOxygenAnalyzerisforgeneraluseandtheMG8EParamagneticOxygenAnalyzer is for explosion-proof applications. The MG8E has been certified by the TIIS* to meet the Ex d IIB T4Xstandard.

* Technology Institution of Industry Safety, Japan

ThefollowingtableshowstheapplicablecriteriaoftheMG8GandMG8E.

Table4.1ApplicabilityCriteriaofMG8ParamagneticOxygenAnalyzers(InstallationEnvironmentandMeasuredGas)

MG8OxygenAnalyzer

ApplicableRange

InstallationSite SampleGas

HazardousArea

Non-hazardous

Area*2

ClassAandBhazardousgases*1

orMixedgasesoflessthan4%hydrogen

Mixedgasesof4to100%hydrogen

ClassChazardousgas*1,

excludinghydrogen*3

Atmosphere SampleGas Atmosphere SampleGas Atmosphere SampleGas

MG8Eusedasexplosion-proof(Ex d IIB T4X*4)

0-1to25%O2(Notapplicablefor21-25%O2)

OK OK OK OK NA NA NA NA

MG8Eusedasnon-explosion-proof 0-1to25%O2 NA OK NA OK NA OK NA NA

MG8Gusedasnon-explosion-proof 0-5to25%O2 NA OK NA OK NA NA NA NA

NA:Notapplicable

*1: Refer to the Users Guide to Installing Explosion-proof Electrical Apparatus at Plants, issued by the Technology Institution of IndustrialSafety,Japan.

*2: The definition of the non-hazardous area is followed by the description in the Users Guide to Installing Explosion-proof ElectricalApparatusatPlants,issuedbytheTechnologyInstitutionofIndustrialSafety,Japan:Asanon-hazardousareaisconsidered a place where no occurrence of explosive gas atmospheres is guaranteed by the foreperson and confirmed by awrittendocument.

*3: Acetylene, carbon disulfide, hydrogen, and ethyl nitrate.*4: Ex d IIB T4X (a)Structure:Explosion-proof (b) Scope of area: Industrial sites and hazardous areas in office buildings. May not be used in hazardous locations in

mines. (c)Scopeofsamplegasorvapor: (c-1)ClassAandBhazardousgasesorvapor (c-2)Gasorvaporwithignitiontemperatureof135°Corgreater (c-3) Hydrogen concentration must be below 4%. Not applicable for gases containing acetylene, carbon disulfide

andethylnitrate. (d)Operatingconditions (d-1)Beforeopeningthecover,removepowerandmakesureofnon-hazardousatmospheres. (d-2)Donotuseformeasuringoxygenconcentrationofgasesotherthanthosecontainingairoroxygen

equivalent to or less than air, or those mixed with flammable gas or vapor.

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4.3 SensorConstructionThe MG8G/MG8E Paramagnetic Oxygen Analyzers use a magnetic proportional flow rate sensor that was developedbyYokogawa.Thissensorhashighsensitivityandthesamefastresponsetimeofazirconiasensor,anditsconstructionprovideshighresistancetovibrationandshock.

Inaddition,thesensor’sthermistorsdonotcomeintodirectcontactwiththesamplegas,therebyensuringlong-termmeasurementstabilityevenwhencorrosiveorcontaminatedgasismeasured.

(1) ConstructionandOperatingPrincipleFigure4.2showstheconstructionofthering-shapedsensor.

• AsamplegasentersfromthesamplegasinletandisdividedintostreamsAandA’inthering-shapedgaspath.

• AnauxiliarygasentersfromtheauxiliarygasinletandisdividedintostreamsBandB’,whichthenpassthroughathermistorthatispositionedineachofthegaspaths.Thesethermistorsdetecttheflow rates of the auxiliary gasses.

• Theauxiliarygasstreamsthenenterthering-shapedpathatpointsDandE,wheretheymeetwiththe sample gasses and flow in direction C toward an outlet.

• AstrongmagneticfieldiscreatedatpointD,wherestreamBoftheauxiliarygasentersthering-shapedpath.Ifthesamplegascontainsoxygen,theoxygenisattractedtoandconcentratedinthemagnetic field at point D. The oxygen thus restricts the flow of auxiliary gas at point D, which alters the ratio of flow rate B to flow rate B’. This change in the ratio is proportional to the oxygen concentration, anditisdetectedwiththethermistorsandoutput.

Sample gas + auxiliary gas Auxiliary gas

Sample gas

Magnet

Magnet

Auxiliary gas inlet

Sensorthermistors

Sample gas inlet

Samplegas

Auxiliary gas

Magnet

Sample gas + auxiliary gas outlet

Sample gas + auxiliary gas

F0402.ai

B

B‘

CD

E

A

A‘

Figure4.2 MagneticProportionalFlowRateSensor

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(2) SensorUnitGasPathTheMG8G/MG8EParamagneticOxygenAnalyzersachievestablemeasurementbyavarietyofmeans.(SeeFigure4.3.)

• Themainpartofthesensorunit,includingthecell,iscontainedwithinahousing.Insidethishousingaconstanttemperatureismaintainedtoensurethatthegastemperatureisnotaffectedbychangesintheambienttemperature.

• Inordertostabilizethetemperaturewithinthishousing,anintegralcomputationfunctionhasbeenadded.

• Measureshavealsobeentakentopreventfluctuatingindicationscausedbychangesinthesampleand auxiliary gas flow rates.

(a)BypassUnit(onlyavailablewiththeMG8E)The horizontal axis represents the flow rate of the sample gas entering the paramagnetic oxygen analyzer, andtheverticalaxisrepresentstheflowrateofthesamplegasenteringthecell.Ifthesamplegasentersthe paramagnetic oxygen analyzer at a slow rate, all the gas flows into the cell. If the rate exceeds 235 ml/min, the excess portion flows into the bypass unit.

(b)SampleGasPre-heatingUnit(onlyavailablewiththeMG8E)Thesensorunithousingiskeptataconstant55°C.Thetemperatureofthesamplegasenteringthehousingisusuallylessthan55°C.Anychangeinthesamplegastemperaturecanchangethemeasurementcelltemperatureandaffectitsoutput.

Beforethesamplegasentersthemeasurementcell,theMG8EParamagneticOxygenAnalyzerpassesitthroughapre-heatingunitinordertobringitclosetothetemperaturemaintainedinsidethesensorunithousing.

(c)StabilizingFlowRateofAuxiliaryGasTheauxiliarygasisnitrogen(N2).TheMG8G/MG8EParamagneticOxygenAnalyzersdeterminetheoxygen concentration using the ratio of the flow rates for this nitrogen gas; therefore, it is essential to keep the flow rate constant. This is done by means of capillary restriction resistance.

(d)PressureSwitch(onlyavailablewiththeMG8E)If the auxiliary gas flow is disrupted while the paramagnetic oxygen analyzer is operating, the output signal overshootsthescale.Topreventthisfromoccurring,apressureswitchontheprimarysideoftheauxiliarygaslineregulatoractivatesanalarmtonotifytheoperatorthatpreventiveactionshouldbetaken.

(e)TemperatureControlforSensorUnitHousing(onlyavailablewiththeMG8E)Toguardagainstdisturbancessuchasvoltagefluctuations,anintegralcomputationfunctionhasbeenaddedthatmakesitpossibletocontrolthetemperaturetowithin0.005°C.Furthermore,themeasurementcelltemperatureiscontrolledduringthewarm-upphasebycapturingthecelltemperature(summingofthesignalsfromtheleftandrightthermistors)andincreasingtheheatertemperatureifthecelltemperatureislow,thengraduallyloweringtheheatertemperatureasthecelltemperaturerises.

(f)CompensationforAtmosphericPressureError(onlyavailablewiththeMG8E)Equippedwithanatmosphericpressure-compensationsensorasstandard,atmosphericpressureerrorcanbecompensated.

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(3) BlockDiagramofOxygenAnalyzerGasPathinSensorUnit

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Explosion-proofhousing wall

Sensor unithousing

Bypass unit

Capillary tube

Sample gas pre-heating unit

Regulator

Pressure switch

Pressure gauge

Flame arrestor

Flame arrestor0 to 200 kPa

Sample gas inlet Auxiliary gas (N2) inlet Gas outlet

Note: A pressure sensor for compensating for atmospheric pressure changes is installed in the electrical circuit.

Measurement Cell

P

100 to600ml/min

235 ml/min

300 to 800 ml/min 35 ml/min 335 to 835 ml/min

Figure4.3BlockDiagramofMG8EGasPathinSensorUnit

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Flow

rate

of g

as fl

owin

g in

to c

ell (

ml/m

in)

Setting range of sample gas flow rate

Flow rate of sample gas flowing into MG8E (ml/min)

240

220

200

180

160

140

120

100100 200 300 400 500 600 700 800 900 10000

Figure4.4FlowCharacteristicsofMG8EBypassUnit

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195.EffectsofInterferenceGas

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5. EffectsofInterferenceGas

5.1 MeasurementofOxygen(O2)inthePresenceofInterferenceGases

ThefollowingtableindicateswhentheMG8Eanalyzercanbeusedtomeasureoxygen(O2)inthepresenceofinterferencegases.

No. Typeofindustry InterferencegascomponentsMeasuringrange(%)

Remarks0–1 0–2 0–5

1Petrochemical

H2: 35%, CO2: 7%, N2: B A A A Note 12 C3: 0 – 5%, C4: 5 – 10%, N2: B — A A Note 1, off gas3 Oil H2: 10 – 40%, C1: 20 – 30%, C2: 15 – 30%, N2: B A A A Note 1, to flare stack4

Chemical

VCM (C2H3C1) + Air A A A5 C4H10 + Air — A A Note 26 CH4: 50%, C2H4: 25%, CO2: 4%, Ar: 15% A A A7 C4H10: 20%, O2: 6%, N2: B A A A8 H2 +O2 A A A Note 1, electrolytic plant9

Iron and steelH2: 75%, N2: 25% + Air — A A Note 1

10 (H2: 45%, CH4: 17%, CO: 16%, CO2: 4%) + Air — A A Note 111 Electric power (H2: 30%, CO2: 36%, CH4: 4%) + Air — A A Note 1, fuel cell

12 Environmental sewage CH4: 55%, CO2: 39% + Air A A A Digestion gas

13 Nuclear power He + O2 A A A Note 2A:Measurementispossiblewhentheeffectoftheinterferencegasiswithin±0.02%O2or±1%ofspan,whicheverishigher.Note 1: Auxiliary gas flow rate: 55 ml/minNote2:PleasecontactuswhenC4H10is50vol%ormore,orwhennuclearpower(He+O2)istobemeasured.

TestingMethod(1)Adjustthezerobalancewiththeinterferencegasandnitrogen(N2)gas.

(2)PerformcalibrationwiththeO2/N2gasandobtainthedeviationfromtheO2/interferencegas.

CAUTIONTheinformationintheabovetableappliesonlytoclassAandBhazardousgasesorvaporsandtogasmixtures that are less than 4% hydrogen gas, in which cases the analyzer must be used as specified in the explosion-proof specification.

Theanalyzercannotbeusedtomeasuretheoxygenconcentrationingasesorvaporscontainingacetylene,carbondisulfide,orethylenenitrate.Furthermore,theexplosion-proofcertificationdoesnotapplytoNos.1,3,8,9,10,and11intheabovetable.

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5.2 DataonEffectsofInterferenceGasesThefollowingdataonamixtureofinterferencecomponentsandO2isfromananalyzerthathasbeencalibratedwithN2andO2+N2.

Theoxygenconcentrationcanbemeasuredwithin±2%ofspan.

O2+CO2(92%)+N2(8%)

Range:0to1vol%O2

Auxiliary gas flow rate: 35 ml/min

2 3 4 5

11 20 43234 5

6 7 8 9 101

O2(0.89%)+CO2(92.0%)+N2(7.11%)

N2

O2(0.89%)+N2(99.11%)

O2(0.59%)+CO2

(92.0%)+N2(7.41%)

1%(5V)

O2(0.59%)+N2(99.41%)

0%(1V)

O2=0.59%

O2=0.89%

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3 min

Figure5.1DataExampleofEffectsofInterferenceGases

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5.3 InterferenceGasCompensationMG8G/MG8EParamagneticOxygenAnalyzersmakeuseoftheparamagneticpropertyofoxygen(magneticsusceptibility,i.e.theabilitytobecomemagnetizedinthepresenceofanexternallyappliedmagneticfield)tomeasuretheoxygenconcentration.Gasesotherthanoxygenmayalsoexhibitthischaracteristic,althoughtheywillnotbenearlyasmagneticallysusceptibleasoxygen.Accordingly,processgaseswithvaryinglevelsofmagneticsusceptibilitycaninterferewithandcauseerrorsinthemeasurementoftheoxygenconcentration.

Errorssuchasthesethatarecausedbytheparamagneticpropertyofprocessgasesmaybesignificantwithlowoxygenconcentrationsintherangeof0%to1%;however,theMG8G/MG8EParamagneticOxygenAnalyzersareabletocanceloutthisinterferenceerrorbasedonthedifferenceindensityofasamplegasandareferencegas.AsshowninFigure5.2,asamplegasisdividedintostreamsAandA’inthering-shapedgaspath.Anauxiliarygas(N2) enters at the center of the sensor unit and flows left and right instreamsBandB’.AmagneticfieldisappliedatpointDwheretheauxiliarygasentersthering-shapedpath.Eveniftheauxiliarygasdoesnotcontainoxygen,thepresentofparamagneticgasessuchasN2willaffecttheratiooftheauxiliarygasflowratesinstreamsBandB’,resultinginanerror.Thiserrorcanbecompensatedbychangingthecellangle(cellattitude).

Forexample,ifcarbondioxide(CO2),whichhasalowermagneticsusceptibilitythannitrogen(N2),passesthroughthemeasurementcell,theanalyzerwillreadanegativevalue.IfthecellistiltedasshowninFigure5.3,theflowrateoftheauxiliarygastowardstreamB’willincreaseduetothehigherdensityoftheCO2.Thiswillchangetheflowrate,therebycancelingoutthenegativedeviation.Thechangeintheauxiliarygasflowrateduetothemagneticsusceptibilityofthegasiscancelledoutbychangingthemeasurementcellangle,whichaltersthedensityandcausesachangeintheauxiliarygasflowrate.Inthisway,theinterferenceerrorcanbecompensatedfor.

Priortoshipmentfromthefactory,eachMG8G/MG8EParamagneticOxygenAnalyzerreceivesafinaltuninginwhichthemeasurementcellangle(attitude)isadjustedbasedonthemagneticcharacteristicsanddensityofthecustomer’ssamplegas.Thiscellangleisstoredintheanalyzer’smemory.

Wheninstallingtheanalyzer,rotatetheadjustmentknobuntilthebubbleinthebuilt-inbubblelevelisatthecenterposition.Thisbringsthemeasurementcelltothecorrectangle.

A‘

A

B

B‘

CD

E

Auxiliary gas inlet

Sensorthermistors

Sample gas inlet

Samplegas

Auxiliary gas

Sample gas + auxiliary gas outlet

Sample gas + auxiliary gas

Magnet

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Figure5.2DiagramofMeasurementCell

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Auxiliary gas inlet

Sample gas stream A

Magnet

Magnet

Sample gas inlet

Sensor thermistor

Auxiliary gas stream B

Sample gas stream A’

Auxiliary gas stream B’

Angleadjustment

Figure5.3ViewofMeasurementCellCross-section

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6.Characteristics(MG8ETestData)

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6. Characteristics(MG8ETestData)

6.1 ResponseCharacteristicResponsetime:90%responsewithin6seconds(fromthegasinletoftheoxygenanalyzer)

Responsecheckdata: Range:0%to1vol%O2

Zerogas:N2(99.999%),Spangas:N2+O2(0.978%)

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Paramagnetic Oxygen Analyzer

Paramagnetic oxygen analyzer

Exhaust gasSwitching cock

Zero gasSpan gas

Samplegasflowrate(ml/min)

Zero ➞ Span Span ➞ ZeroDead time(sec) 90% response(sec) Dead time(sec) 90% response(sec)

300 3.2 1.6 3.3 1.5600 2.9 1.5 2.6 1.5900 2.2 1.6 2.2 1.4

Note:Theanalyzerreadingwillreacha100%responsein10seconds(Yokogawa’spreviousmodel:30to50seconds)

6.2 FlowCharacteristicsSpecifications of flow characteristic testing

Range:0to1vol%O2


Zerogas:N2,Spangas:O2(0.975%)+N2

<Testresult:±0.2%ofspan>

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(ml/min)

(ml/min)

700

610

350

510610

500

300

600

4.880

0.9968

1.0008

0.99710.9973

4.874

4.886

4.882

1% 0%(5 V) (1 V)

(0)

(0)(0)

Flow rate Output

Flow rate Output

(+0.20% of span)

(-0.20% of span)

(+0.10% of span)

(+0.10% of span)

<Span> <Zero>

1 min

(V DC)

(V DC)

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236.Characteristics(MG8ETestData)

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6.3 AttitudeErrorTestingthatshowshowchangesintheattitudeoftheoxygenanalyzeraffecttheindicatedvalue

Range:0to2vol%O2

Zerobalance:CO(65%)+H2(4.5%)+CO2andN2

Samplegas: Zerogas:N2,Spangas:O2(1.61%)+N2

Sample gas flow rate: 600 ml/min


Attitudechange(1°increaseinangle)Front Back Left Right

Zero gas -0.02% of span -0.001% of span -0.137% of span -0.095% of spanSpan gas -0.04% of span -0.25% of span -0.216% of span

*In the case of 0 to 1% O2range: Vicinityofzero:0.2%/1°ofspan(Yokogawa’spreviousmodel:about10%/1°ofspan) Vicinityofspan:0.4%/1°ofspan

6.4 EffectsofAtmosphericPressureandLong-termDrift

1050

0 168 336 504

0 168 336 504

5

4

3

2

1

0

-1

-2

-3

-4

-5

5

4

3

2

1

0

-1

-2

-3

-4

-5

1000

950

900

850

800

1050

1000

950

900

850

800

Effects of Atmospheric Pressure

Specification: ±1% of span/10 hPa

Specification: ±2% of span

0.12% of span/10 hPa

Long-term Drift

Zero pointSpan point

Atm

osph

eric

pre

ssur

e (h

Pa)

Atm

osph

eric

pre

ssur

e (h

Pa)

Pressure

Zero point

Span point

Pressure

Span

Span

Zero

Zero

1 week

1 week

Time (hr)

Time (hr)

Error (%)

Error (%)

1st week: 1.2% of span2nd week: 0.5% of span3rd week: 0.3% of span

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RevisionInformationTitle : MG8G/MG8EParamagneticOxygenAnalyzersManualnumber: TI11P03A05-01E

Sep.2009/1stEditionNewlypublished

Oct.2012/2ndEditionOverallrevision

Oct.30,2012-00

mg8g/mg8e paramagnetic oxygen analyzers · a magnetic wind oxygen analyzer is characterized by...

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