Each body with a temperature above the absolute zero (-273.15°C = 0 Kelvin) emits an electromagnetic Radiation from its surface, which is proportional to its intrinsic temperature. A part of this so-called intrinsic Radiation is infrared Radiation, which can be used to measure a body’s temperature. This Radiation penetrates the atmosphere. With the help of a lens the beams are Focused on a detector element, which generates an electrical signal proportional to the Radiation. The signal is amplified and transformed into an output signal proportional to the object temperature. The measuring value may be shown in a display or transfered as analog output signal, which supports an easy connection to control systems of the process management.