Basics
MI3
21
4
Basics
4.1
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 thermometers are optical-electronic sensors. These sensors are sensitive to the emitted
radiation. 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 signal. The signal processing electronics
analyze the electrical signal and convert it into a temperature measurement. 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 temperature without
touching an object. Consequently, surface temperatures of moving or hard to reach objects can easily
be measured.
4.2
Emissivity of Target Object
To determine the emissivity of the target object see section 19.1
If emissivity 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 particular care is taken during installation
and the sensing head is shielded from these reflecting radiation sources.
4.3
Ambient Temperature
The sensing head is suited for the ambient temperatures up to 120°C (248°F) for the standard heads
and up to 180°C (356°F) for the LTH heads. The sensing head can operate in ambient temperatures up
to 200°C (392°F) with the air-cooling accessory.
4.4
Atmospheric Quality
If the lens gets dirty, infrared energy will be blocked and the instrument will not measure accurately.
It is good practice to always keep the lens clean. The Air Purge Jacket helps keep contaminants from
building up on the lens. If you use air purging, make sure a filtered air supply with clean dry air at the
correct air pressure is installed before proceeding with the sensor installation.
4.5
Electrical Interference
To minimize electrical or electromagnetic interference or “noise”, please be aware of the following:
•
Mount the unit as far away as possible from potential sources of electrical interference, such as
motorized equipment, which can produce large step load changes.
•
Use shielded wire for all input and output connections.
•
To avoid current equalizations, make sure that a sufficient potential equalization is realized
between the sensing head and metal housing of the communication box.
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