Product Description
10 Rev. E2 04/2011 Marathon MR
2.1.3 Low or Changing Emissivities
If the emissivities in both wavelengths (colors) were the same, as they would be for any blackbody
(emissivity = 1.0) or greybody (emissivity < 1.0 but constant), then their ratio would be 1, and target
emissivity would not be an influence. However, in nature there is no such thing as a greybody. The
emissivity of all real objects changes with wavelength and temperature, at varying degrees, depending
on the material.
When emissivity is uncertain or changing, a 2-color sensor can be more accurate than a 1-color
instrument as long as the emissivity changes by the same factor in both wavelength bands. Note,
however, that accurate measurement results are dependent on the application and the type of material
being measured. To determine how to use 2-color sensors with your application when uncertain or
changing emissivities are a factor, please contact your sales representative.
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