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Appendix
12.2TypicalEmissivityValues
Thefollowingtableprovidesabriefreferenceguidefordetermining
emissivityandcanbeusedwhenoneoftheabovemethodsisnot
practical.Emissivityvaluesshowninthetableareonlyapproximate,
since several parameters may affect the emissivity of a material.
Theseincludethefollowing:
1. Temperature
2. Angle
ofmeasurement
3. Geometry(plane,concave,convex)
4. Thickness
5. Surfacequality(polished,rough,oxidized,sandblasted)
6. Spectralrangeofmeasurement
7. Transmission(e.g.thinfilmsplastics)
To optimize surface temperature measurements, consider the
followingguidelines:
• Determinetheobjectemissivityusingtheinstrumentwhichis
alsotobeusedfor
themeasurements.
• Avoid reflections by shielding the object from surrounding
temperaturesources.
• For higher temperature objects use instruments with the
shortestwavelengthpossible.
• Fortranslucentmaterialssuchasplasticfoilsorglass,assure
thatthebackgroundisuniformandlowerintemperaturethan
theobject.
• Mountinstrumentperpendicular
tosurface ifpossible.Inall
cases,donotexceedanglesmorethan30°fromincidence.