Basics; Measurement Of Infrared Temperature; Distance And Spot Size; Ambient Temperature - RayTek TX Operating Instructions Manual

Basics

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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
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:
Target greater than spot size

3.3 Ambient Temperature

The sensing head is designed for measurements in ambient temperatures between 0°C and 70°C (32 to
160°F). In ambient conditions above 70°C (160°F), a water or air cooled housing is available to extend
the operating range to 120°C (250°F) with air cooling and to 175°C (350°F) with water cooling. When
using the water cooled housing, it is strongly recommended to use the supplied air purge collar to
avoid condensation on the lens. In ambient conditions up to 315°C (600°F), the ThermoJacket housing
should be used.
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Typical Emissivity Values, Seite 37.
Optical Diagrams
Best
Target greater equal to spot size
Figure 3: Proper Sensor Placement
Rev. O 06/2011
on page 10.
Good Incorrect
Target smaller than spot size
Background
TX