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Appendix
54 MarathonSeriesFA/FR
11Appendix
11.1DeterminationofEmissivity
Emissivityisameasureofanobject’sabilitytoabsorbandemitinfraredenergy.Itcanhaveavalue
between0and1.0.Forexamplea mirrorhasanemissivityof 0.1,whiletheso‐called“Blackbody“
reachesanemissivityvalueof1.0.Ifahigherthanactualemissivityvalueis
set,theoutputwillread
low,providedthetargettemperatureisaboveitsambienttemperature.Forexample,ifyouhaveset
0.95andtheactualemissivityis0.9,thetemperaturereadingwillbelowerthanthetruetemperature.
Anobject’semissivitycanbedeterminedbyoneofthefollowingmethods:
1. DeterminetheactualtemperatureofthematerialusinganRTD(PT100),athermocouple,orany
othersuitablemethod.Next,measuretheobject’stemperatureandadjustemissivitysettinguntil
thecorrecttemperaturevalueisreached.Thisisthecorrectemissivityforthemeasuredmaterial.
2. Ifpossible,applyflatblackpaint
toaportionofthesurfaceoftheobject.Theemissivityofthe
paintmustbeabove0.98.Next,measurethetemperatureofthepaintedareausinganemissivity
settingof0.98.Finally,measurethetemperatureofanadjacentareaontheobjectandadjustthe
emissivityuntilthesame
temperatureisreached.Thisisthecorrectemissivityforthemeasured
material.
11.2TypicalEmissivityValues
Thefollowingtableprovidesabriefreferenceguidefordeterminingemissivityandcanbeusedwhen
oneoftheabovemethodsisnotpractical.Emissivityvaluesshowninthetableareonlyapproxima te,
sinceseveralparametersmayaffecttheemissivityofamaterial.Theseincludethefollowing:
1. Temperature
2. Angle
ofmeasurement
3. Geometry(plane,concave,convex)
4. Thickness
5. Surfacequality(polished,rough,oxidized,sandblasted)
6. Spectralrangeofmeasurement
7. Transmissivity(e.g.thinfilmsplastics)