Basics
Measurement of Infrared Temperature
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3 Basics
3.1 Measurement of Infrared Temperature
All surfaces emit infrared radiation. The intensity of this infrared radiation changes according to the temperature of
the object. Depending on the material and surface properties, the emitted radiation lies in a wavelength spectrum
of approximately 1 to 20 µm. The intensity of the infrared radiation (heat radiation) is dependent on the material.
For many substances, this material-dependent constant is known. This constant is referred to as the emissivity
value.
Infrared cameras are optical-electronic sensors. These sensors are sensitive to the emitted radiation. Infrared
cameras consist of a lens, spectral filter, sensor array, and an electronic signal processing unit. The task of the
spectral filter is to select the wavelength spectrum of interest. The sensor converts the infrared radiation into an
electrical signal. The connected electronics processes this signal for further analysis. The intensity of the emitted
infrared radiation is thereby used to determine the temperature of the target. Since the intensity of the infrared
radiation is dependent on the material, the appropriate emissivity can be selected on the sensor.
The biggest advantage of the infrared camera is its capability for the contactless determination of target surface
temperatures. Consequently, surface temperatures of moving or hard to reach objects can be easily measured.
3.2 Emissivity of Target Object
To determine the emissivity of the target object, see section 9.4
is low, measured results could be falsified by interfering infrared radiation from background objects (such as
heating systems, flames, fireclay bricks, etc. located close beside or behind the target object). This type of problem
can occur when measuring reflective surfaces and very thin materials, such as plastic film and glass.
This measurement error can be reduced to a minimum, if care is taken during installation and the camera is
shielded from these reflecting radiation sources.
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