Siemens Ardoptix PT 140 AF1, Operating Manual, Page: 48 / 68

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Operating manual
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22 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.
22.1 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
Ardoptix uses the intensity of the in-
frared radiation at a certain wavelength.
It is necessary to configure the
Ardoptix to the respective emissivity coef-
ficient 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.