SpectralSpectral irradianceirradiance and and highhightemperaturetemperature measurementsmeasurements

SS--108.4010108.4010LicenciateLicenciate coursecourse in in measurementmeasurement

sciencescienceMaija OjanenMaija Ojanen

SpectralSpectral irradianceirradiance

SpectralSpectral irradianceirradiance

•• HowHow muchmuch radiantradiant fluxflux hitshits a a certaincertainsurfacesurface elementelement??

dAdE Φ

=

where dΦ is the radiant flux coming to surface element dA

SpectralSpectral irradianceirradiance

Receiving surface element Emitting surface element

SpectralSpectral radianceradiance

•• HowHow muchmuch an an infinitesimalinfinitesimal surfacesurfaceelementelement radiatesradiates into an into an infinitesimalinfinitesimal solidsolidangleangle divideddivided byby solidsolid angleangle and and projectionprojectionsurfacesurface

•• ””BrightnessBrightness” of the ” of the sourcesource

SpectralSpectral radianceradiance

ωθ ddAdL

11

2

cosΦ

=Radiance 22

21cosr

dAd θω =

SpectralSpectral radianceradiance and and Planck’sPlanck’s lawlaw

•• AccordingAccording to to Planck’sPlanck’s lawlaw, , idealideal blackbodyblackbodyhashas spectralspectral radianceradiance of of

⎥⎦

⎤⎢⎣

⎡−⎟⎠⎞

⎜⎝⎛

′=

1exp

)()(25

1

Tc

BcEc

λλ

λελ

RadianceRadiance metermeterLens

Detector

Focal plane

SpectroradiometerSpectroradiometerCollecting lens

Source

Input slit

Mirrors

Detector

SpectralSpectral irradianceirradiance scalescale realizationrealization

•• Standard Standard lamplamp•• FilterFilter radiometerradiometer, , whichwhich consistsconsists ofof

–– TrapTrap detectordetector ((threethree photodiodesphotodiodes))–– CalibratedCalibrated apertureaperture–– InterferenceInterference filterfilter–– TemperatureTemperature controllercontroller

•• CurrentCurrent--toto--voltagevoltage converterconverter + + digitaldigitalmultimetermultimeter

MeasurementMeasurement setupsetup

Standard Standard lamplamp

TrapTrap detectordetector

•• ThreeThree photodiodesphotodiodes–– EgEg. . SiSi, , GeGe, , InGaAsInGaAs

•• The The lightlight reflectsreflects fivefivetimestimes fromfrom oneone diodediodeto to anotheranother

•• The The photocurrentsphotocurrents arearesummedsummed

•• The The backwardbackwardreflectionreflection is is smallsmall

MeasurementMeasurement procedureprocedure

•• The The photocurrentphotocurrent of the of the lamplamp is is measuredmeasured at at differentdifferent wavelengthswavelengths usingusing bandpassbandpass filtersfilters

•• TheoreticalTheoretical photocurrentphotocurrent i is i is calculatedcalculated fromfrom

A=ApertureA=Aperture areaarea, , E=spectralE=spectral irradianceirradiance, , R=powerR=powerresponsivityresponsivity of the of the detectordetector and and ττ= = transmittancetransmittance of of the the filterfilter

λλτλλλ

dREAi kckc ∫= )()()(,

MeasurementMeasurement procedureprocedure

•• The The emissivityemissivity of the of the lamplamp is set to is set to initializationinitialization valuevalue

•• The The differencedifference betweenbetween theoreticaltheoretical and and measuredmeasured currentcurrent is is minimizedminimized iterativelyiterativelybyby adjustingadjusting temperaturetemperature in in Planck’sPlanck’s lawlaw

⎥⎦

⎤⎢⎣

⎡−⎟

⎠⎞

⎜⎝⎛

′=

1exp

)()(25

1

Tc

BcEc

λλ

λελ

ApplicationsApplications

•• DetectingDetecting holesholes in in ozoneozone layerlayer–– MeasurementsMeasurements of the UV of the UV radiationradiation thatthat

reachesreaches the the EarthEarth

•• RadiationRadiation protectionprotection measurementsmeasurements•• RemoteRemote sensingsensing

HighHigh temperaturetemperaturemeasurementsmeasurements

HighHigh temperaturetemperature measurementsmeasurements

•• DifficultiesDifficulties to to measuremeasure withwith traditionaltraditionalresistanceresistance sensorssensors, , thermistorsthermistors and and thermalthermal elementselements as the as the highhigh temperaturetemperaturemightmight damagedamage the the sensorsensor

Non-contactmeasurementsneeded

NonNon--contactcontact measurementmeasurement devicesdevices

•• PyrometersPyrometers ((relativerelative))•• FilterFilter radiometersradiometers ((absoluteabsolute))

PyrometerPyrometer

•• PyrometerPyrometer–– ComparesCompares radiatorradiator and and referencereference–– SensitiveSensitive to to misalignmentmisalignment

1

2

1−

⎥⎦

⎤⎢⎣

⎡

⋅−=

λ

λ

ζλ

,

,lncal

pheff

cal II

cTT

Iph,λ = measured photocurrent, c2 = 1.4388·10-2 Km = second radiation constant, λeff = effective wavelength of the filter, TCal = reference temperature, ICal = reference current, ζ = kετρk = attenuation factor of the filter, ε = emissivity, τ = transmittance of the filter and ρ = reflectance of the optical components.

ExamplesExamples of of pyrometerspyrometers

ConstructionConstruction of IKE LP3 of IKE LP3 linearpyrometerlinearpyrometer

FilterFilter radiometerradiometer

•• For For absoluteabsolute temperaturetemperature measurementsmeasurements, , similarsimilar filterfilter radiometersradiometers cancan bebe usedused as in as in spectralspectral irradianceirradiance measurementsmeasurements–– FilterFilter passbandspassbands in in nearnear--infraredinfrared regionregion–– TypicallyTypically lowerlower signalsignal levelslevels

CalibrationCalibration

•• International International temperaturetemperature scalescale (ITS(ITS--90) 90) defineddefinedfromfrom 156.59 156.59 °°CC to 961.78 to 961.78 °°C C usinusing g freezingfreezingpointspoints of of differentdifferent materialsmaterials: : –– Indium 156.59 Indium 156.59 °°CC–– TinTin 231.92 231.92 °°CC–– ZincZinc 419.53 419.53 °°CC–– Aluminium 660.323 Aluminium 660.323 °°CC–– SilverSilver 961.78 961.78 °°C C

CalibrationCalibration

•• Calibrations against fixed point cells (Calibrations against fixed point cells (egeg. . AluminiumAluminium, silver, copper , silver, copper 1084.62 1084.62 °°C)C)

•• AboveAbove 961.78 961.78 °°C (silver point) scale is C (silver point) scale is purely extrapolatedpurely extrapolated

•• Pyrometer calibration?Pyrometer calibration?–– Quality assurance neededQuality assurance needed

•• Eutectic cells above copper Eutectic cells above copper

EutecticEutectic cellscells

•• EutecticEutectic metalmetal--carboncarbon cellscells cancan provideprovidefixedfixed pointspoints thatthat areare higherhigher thanthan freezingfreezingpointpoint of of coppercopper

•• EgEg. . PtPt/C (1737 /C (1737 °°CC, Rh/C (1657 , Rh/C (1657 °°C)C), , ReRe/C /C (2474 (2474 °°C)C)

EutecticEutectic cellscells

•• ReproducibilityReproducibility importantimportant!!–– AllowsAllows comparisonscomparisons betweenbetween differentdifferent

institutesinstitutes–– AvoidingAvoiding contaminationcontamination in in fabricationfabrication

•• HighHigh metalmetal puritypurity•• MaterialMaterial addedadded in argon in argon filledfilled gloveglove bagbag•• FillingFilling meltsmelts carriedcarried out out underunder argonargon•• CheramicCheramic oror disposabledisposable toolstools

StructureStructure of a of a fixedfixed pointpoint cellcell

ApplicationsApplications

•• MetalMetal industryindustry•• ExhaustExhaust gasgas temperaturetemperature measurementsmeasurements•• ……

QuestionsQuestions??