Keller ITS CellaPort PT 120, Руководство по эксплуатации, Страница: 41 / 72

Operating manual PT 11x, 12x,13x
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20 Theory of Non-Contact Temperature Measurements
All materials radiate thermal energy in all states of aggregation above
absolute zero. This radiation is mainly caused by atomic or molecular
oscillations. The intensity of this infrared radiation is a measure for the
temperature of the radiating body. A pyrometer detects this radiation
and displays it as a temperature value.
20.1 Emissivity
The intensity of the radiation not only depends on the temperature but
also on the radiation properties of the material you want to measure. The
ability of a body to emit infrared radiation is expressed by a material con-
stant called
Emissivity coefficient or just emissivity.
This coefficient lies between 0...100 %. A body with ideal radiation (black
body) has a coefficient of 100 %. Materials with the same temperature
but with lower radiation intensity have coefficients lower than 100 %. Ex-
act temperature readings can only be obtained when the emissivity coef-
ficient of the target is correctly adjusted on the pyrometer. The pyrometer
then automatically compensates for the lower radiation.
For non-contact measurements the CellaPort uses the intensity of the
infrared radiation at a certain wavelength.
It is necessary to configure the CellaPort to the respective emissivity co-
efficient of the measuring object. An incorrectly set emissivity coefficient
leads to wrong temperature readings. Below is a table showing emissivi-
ty coefficients for various materials.