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Basics
3 Basics
3.1 Measurement of Infrared Temperature
Everything emits an amount of infrared radiation according to its surface temperature. The intensity of
the 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. It is referred to as "emissivity value", see
appendix, see section .9.2
Typical Emissivity
Values, page 55.
Infrared thermometers are optical-electronic sensors. These sensors are able to detect "radiation of
heat". Infrared thermometers are made up of a lens, a spectral filter, a sensor, 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 parameter. The connected electronics generate electrical
signals for further analysis. As the intensity of the emitted infrared radiation is dependent on the
material, the required emissivity can be selected on the sensor.
The biggest advantage of the infrared thermometer is its ability to measure in the absence of contact.
Consequently, surface temperatures of moving or hard to reach objects can easily be measured.
3.2 Distance and Spot Size
The desired spot size on the target will determine the maximum measurement distance and the
necessary focus length of the optical module. To avoid erroneous readings the target spot size must
contain the entire field of view of the sensor. Consequently, the sensor must be positioned so the field
of view is the same as or smaller than the desired target size. For a list indicating the available focus
models and their parameters see Figure 2:
Optical Diagrams
page 11.
best
good
incorrect
Background
Target greater than spot size
Target greater equal to spot size
Target smaller than spot size
Figure 8: Proper Sensor Placement
XR
15
Rev. B2 Feb 2017
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