Message Board Thread - "emissivity when taking images at an angle"

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emissivity when taking images at an angle AMP 11/15/2005
I have an application where I will be taking images of a printed circuit assembly that is installed inside an instrument. Due to how the board is installed, the camera will have to be at an angle to the board. How will that impact the emissivity values and thus the temperature reading? At what angle can I assume emissivity values haven't changed? Thank you.
Re:emissivity when taking images at an angle Manuel 11/16/2005
Hi AMP..

body Emissivity will not be affected, energy does. remember from Level I, The energy of the body will be the sum of emited, Reflected and Conducted energy.

if try to avoid that warmer or cooler ambients which can reflects or conducts energy to the board i guess this will help your readings..

my two cents..

Re:emissivity when taking images at an angle Gary Orlove 11/16/2005
The figure below shows the directional emittance for a number of material types. Note that some materials are approximately lambertian up to 50 or 60° viewing angle. This means that one, as a rule of thumb, need not bother about the directional influence on the emittance for viewing angles less than say 55°. Clean metals are exceptions from this rule.

Diffuse grey radiators have naturally a certain amount of reflectance. Incident radiation on such a surface is reflected diffusely, i.e. scattered back in all directions within the hemisphere as opposed to specularly reflecting surfaces that reflect in one direction only according to the reflection law for mirrors. Many smooth, more or less shiny surfaces have a certain degree of specular reflection, which tends to increase with increasing viewing angle.

Gary Orlove
Infrared Training Center

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