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Infrared Basics

Infrared Basics
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when temperature matters BASIC PRINCIPLES of non-contact temperature measurement

Physical principles Physical principles when temperature matters With our eyes we see the world in visible light. Although visible light makes up only a small part of the radiation spectrum, the invisible light covers most of the remaining spectral range. The radiation of invisible light carries much more additional information. The infrared temperature measurement system Optics Sensor Infrared System The advantages of non-contact temperature measurement are obvious – it supports: • Temperature measurements of moving or overheated objects and of objects in hazardous surroundings • Very fast...

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Physical principles If you point the measuring device on this hole, you can declare the temperature emitting from inside as black radiation which you can use for calibrating your measuring device. In reality, simple systems use surfaces, which are covered with pigmented paint and show absorption and emissivity values of 99 % within the required wavelength range. Usually, this is sufficient for calibrations of actual measurements. when temperature matters Radiation principles of a black body The radiation law by Planck shows the basic correlation for non-contact temperature measurements: It...

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Physical principles when temperature matters Thermal detectors Pyroelectric detectors Quantum detectors With these detectors, the temperature of the sensitive element changes due to the absorption of electromagnetic radiation. The temperature chance causes a modification of the temperature-dependent property of the detector, which is electrically analyzed and serves as a measure for the absorbed energy. The illustration shows the basic construction of a pyroelectric detector. This sensitive element consists of pyroelectric material with two electrodes. As a result of the temperature change...

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Emissivity and temperature measurement when temperature matters Temperature measurement of plastics Transmission rates of plastics vary according to wavelength. They react inversely proportional to the thickness, whereas thin materials are more transmissive than thick plastics. Optimal measurements can be carried out with wavelengths, where transmissivity is almost zero. Independent of the thickness. Polyethylene, polypropylene, nylon and polystyrene are non-transmissive at 3.43 µm; polyester, polyurethane, PTFE, FEP and polyamide are non-transmissive at 7.9 µm. For thicker and pigmented...

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Emissivity and temperature measurement when temperature matters Environmental influences Calibration of infrared thermometers [1] [2] The chart below shows that the transmissivity of air strongly depends on the wavelength. Areas of high damping alternate with areas of high transmissivity – the so-called atmospheric windows. The transmissivity in the long-wave atmospheric window (8 – 14 µm) is constantly high, whereas, due to the atmosphere, there are measurable reductions in the shortwave area, which may lead to false results. Typical measuring windows are 1.1 … 1.7 µm, 2 … 2.5 µm and 3 … 5...

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Emissivity and temperature measurement when temperature matters Optics, sighting techniques and electronics of infrared pyrometers Construction of the infrared thermometers Lenses and windows The measuring chain begins with an optical system – usually consisting of lens optics. The lens receives the emitted infrared energy from a measuring spot and focuses it onto a detector. Measurements based on this technology can only be correct, if the measuring object is bigger in size than the detector spot. The distance ratio describes the size of the measuring spot at a specific distance. It is...

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when temperature matters Optics, sighting techniques and electronics of infrared pyrometers Window Materials / Properties The table presents a comparative overview of various window materials Windows with anti-reflection coating have significantly higher transmissivity (up to 95 %). The transmission loss can be corrected with transmissivity adjustment on the window, providing that the manufacturer has specified transmissivity for the corresponding wavelength range. Otherwise, it must be experimentally determined with an infrared thermometer and a reference source. The new double laser...

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Optics, sighting techniques and electronics of infrared pyrometers In order to correctly display spot size, optical sighting systems were developed with size marking in the crosshairs, which enable precise targeting. Since laser pyrometers are significantly easier and safer than contact thermometers, engineers have tried to mark the spot size with laser sighting techniques independently from the distance – according to the distance-spot-size ratio in the diagram. Outputs and interfaces (analog and digital). As an example: pluggable, digital interface modules of the electronic box Two warped...

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Infrared cameras and applications Infrared cameras and applications when temperature matters Seeing localized hotspots thereby allowing weaknesses in our environment to be detected has always been the fascinating aspect of modern thermal imaging. Not least due to the constantly more effective methods of manufacturing the IR optical image sensors, infrared cameras have undergone a drastic improvement in their price/performance ratio. Focal Plane Array (FPA) Detector element Temperature measurement The devices have become smaller, more robust, and with lower energy consumption. For some time...

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Infrared cameras and applications In the past USB was a purely office communication interface. The widespread use of this interface standard compared to FireWire initiated numerous developments, which have considerably improved the industrial capabilities of the interface and therefore the usability of USB 2.0 devices. Due to the development of constantly more powerful, smaller and at the same time lower cost laptops, netbooks, tablet PCs and smartphones, it is now possible to use their • Large displays for showing thermal images, Optimized Li-ion batteries for power supply, Computing power...

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