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9 Basics of Infrared Thermometry
Depending on the temperature each object emits a certain amount of infrared radiation. A change in the
temperature of the object is accompanied by a change in the intensity of the radiation. For the measurement
of “thermal radiation” infrared thermometry uses a wave-length ranging between 1 µm and 20 µm.
The intensity of the emitted radiation depends on the material. This material contingent constant is described
with the help of the emissivity which is a known value for most materials (►10 Emissivity).
Infrared thermometers are optoelectronic sensors. They calculate the surface temperature on the basis of
the emitted infrared radiation from an object. The most important feature of infrared thermometers is that
they enable the user to measure objects contactless. Consequently, these products help to measure the
temperature of inaccessible or moving objects without difficulties. Infrared thermometers basically consist of
the following components:
▪ lens
▪ spectral filter
▪ detector
▪ electronics (amplifier/ linearization/ signal processing)
The specifications of the lens decisively determine the optical path of the infrared thermometer, which is
characterized by the ratio Distance to Spot size.
The spectral filter selects the wavelength range, which is relevant for the temperature measurement. The
detector in cooperation with the processing electronics transforms the emitted infrared radiation into electrical
signals.
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