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Operating instructions CellaTemp PK / PKF / PKL xx
16 Ways to determine emissivity
Technical literature or operating manuals often contain data on the emissivity of
various materials� This information should be used with caution, however� It is
important to know for which temperature and which wavelength the emissivity
value is applicable� Furthermore, the stated emissivity values were obtained under
ideal conditions� In actual practice, the total emissivity of the target object will vary,
depending on the amount of extraneous radiation transmitted through the object
from the background or reflected onto the object from the foreground�
The emissivity can be determined using one of the following methods:
Contact measurements
Measure the temperature with a contact thermocouple and measure the surface
temperature with a pyrometer� Adjust the emissivity coefficient on the pyrometer
until both devices show the same temperature� When measuring with the thermo-
couple, make sure to have good thermal contact and low heat dissipation�
Using a reference emissivity coefficient
Apply matte black colour to a part of the surface to be measured� This part has an
emissivity of 94 %� At first, measure the temperature of the coloured part� Then
make a comparative measurement right next to the coloured part and adjust the
emissivity on the pyrometer until it displays the previous measurement reading
again�
16.1 Emissivity coefficient tables
List of emissivity coefficients of different materials in %�
Model
PK 11 / PK 12 / PK 14 / PK 18 / PKL 11
Wavelength λ
8 - 14 μm
„Black body“
100
Aluminium oxide
76
Asphalt
90���98
Baking oven, dark colour
96
Concrete
55���65
Bitumem (roofing paper)
96
