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??