7. Emissivity
For an infrared temperature measurement, the different surface
conditions must be minded, as these have an influence on the
measurement result. The emission factor describes the characteristics of
the reflectivity of materials. The duller and darker the object is, the more
accurate the measurement will be.
The outer surface of very shiny, reflective or transparent objects distorts
the measurement result. It is here recommended to color the targeting
surface in dull- black or to attach a dull-black tape on it, which you can
use as measurement surface after the temperature harmonized.
Most organic, painted or oxidized surfaces have an emissivity of 0.95, so
this instrument is fixed to this value.
The following table shows the emission factors of various materials:
Material
Condition
Temperature-Range
Emissivity-
factor (ɛ)
Aluminium
polished
50°C … 100°C
0.04 ... 0.06
Raw surface
20°C … 50°C
0.06 ... 0.07
oxidized
50°C ... 500°C
0.2 ... 0.3
Aluminium oxide,
Aluminium powder
normal Temperature
0.16
Brass
matt
20°C ... 350°C
0.22
oxidized at 600°C
200°C ... 600°C
0.59 ... 0.61
Polished
200°C
0.03
Wrought with
sandpaper
20°C
0.2
Bronze
polished
50°C
0.1
porous and raw
50°C ... 150°C
0.55
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