ISR 12-LO
•
IGAR 12-LO Operating Manual
Settings / Parameter Descriptions
•
26
4.6
Emissivity
ε
/
emissivity slope K
Emissivity
(ε)
setting only in mono mode.
Emissivity slope setting (K =
ε
1
/
ε
2
) only in ratio mode.
For a correct measurement it is necessary to adjust the emissivity. This
emissivity is the relationship between the emission of a real object and the
emission of a black body radiation source (this is an object which absorbs all
incoming rays and has an emissivity of 100%) at the same temperature.
Different materials have different emissivities ranging between 0% and 100% (settings at the
pyrometer between 0.1 to 1, equivalent to 10 to 100%). Additionally, the emissivity is
depending on the surface condition of the material, the spectral range of the pyrometer and
the measuring temperature. The emissivity setting of the pyrometer must be adjusted
accordingly. Typical emissivity values of various common materials for the two spectral ranges of
the instruments are listed below. The tolerance of the emissivity values for each material is
mainly dependent on the surface conditions. Rough surfaces have higher emissivities.
In ratio mode (2-color mode) the pyrometer is measuring simultaneously with
2 sensors in adjacent wavelengths. It calculates the temperature by ratioing
the radiation intensities of the two wavelengths. This ratio technique
eliminates a number of factors that degrade the accuracy of a conventional
single-color instrument e.g. measurement independent of emissivity in wide
areas, unaffected by dust in the field of view, unaffected by dirty viewing windows or lenses,
etc. In some cases, the emissivities of the two wavelengths can differ so that it is necessary to
correct the ratio of the two emissivities (
ε
1
/
ε
2
) to get a correct temperature reading. This
correction can be done with the emissivity slope setting K. The K-factors of metals are normally
higher than 1. For a correct measuring result it is recommended to make a comparison test, e.g.
with a thermocouple probe. Then the K-factor must be corrected until the pyrometer shows the
same temperature value.
Emissivity values and emissivity slope values of various common materials are listed below:
Measuring object
Emissivity
ε
(at 0.9 µm)
Emissivity
ε
(at 1.6 µm)
Emissivity slope K
“Black body furnace“
1
1
1
Steel heavily scaled
0.93
0.85 to 0.9
1
Steel rolling skin
0.88
0.8 to 0.88
1.00 to 1.01
Steel, molten
0.3
0.2 to 0.25
Slag
0.85
0.8 to 0.85
1
Chromium, bright
0.28 to 0.32
0.25 to 0.3
Brass oxidized (tarnished)
0.65 to 0.75
0.6 to 0.7
Bronze, blank
0.03
0.03
Copper, oxidized
0.88
0.7 to 0.85
Zinc
0.58
0.45 to 0.55
Nickel
0.22
0.15 to 0.2
Gold, Silver, bright
0.02
0.02
Porcelain glazed
0.6
0.6
1
Porcelain rough
0.8 to 0.9
0.8 to 0.9
1
Graphite
0.8 to 0.92
0.8 to 0.9
1.01
Chamotte
0.45 to 0.6
0.45 to 0.6
1
Earthenware, glazed
0.86 to 0.9
0.8 to 0.9
1
Brick
0.85 to 0.9
0.8 to 0.9
1
Soot
0.95
0.95
1
Settings:
10%
. . .
100%
Settings:
0.8
. . .
1.2
