Understanding Infrared Thermography Reading 3

■ Aiming Normal to the Target
Aiming normal (perpendicular) to the target surface or as close as possible to
normal is important because the effective emissivity of a target surface is
partially dependent on the surface texture. It stands to reason, then, that if the
surface is viewed at a skimming angle, the apparent texture will change, the
effective emissivity will change greatly and the measurement will be affected
by misleading reflections. These can result in cold errors as well as hot errors.
A safe rule is to view the target at an angle within 30 degrees of normal
(perpendicular). If the target emissivity is very high this can be increased to
as high as a 60 degree angle if necessary.
Note:
where: θ angle from normal
θ = 30º
θ = 60º where Ɛ is high
Charlie Chong/ Fion Zhang