There are many advantages to using infrared thermometers to measure temperature. For instance, fast response times (ms range) gives users more information in a fixed time period. It also allows objects that move, rotate or vibrate to be measured and makes light work of temperatures up to 3000°C, where contact probes have a shortened lifespan. Non-contact measurement also means no surface contamination or influence of the thermal conductivity of a probe.
Every form of matter with a temperature above absolute zero emits infrared radiation due to the internal mechanical movement of its molecules. The intensity of this movement depends on the temperature of the object and since the molecule movement represents charge displacement, electromagnetic radiation is emitted as photons. The spectrum of this radiation ranges from 0,7 to 1000 μm wavelength, but the usable infrared spectrum range for temperature measurement is only 0,7 to 14 μm.
To ensure accurate and repeatable measurements however, users must bear some considerations in mind. Always choose an IR device with optics tuned for the correct wavelength in order to focus maximum energy onto the detector. A rule of thumb is that for temperatures up to 600°C, use the general 8-14 μm wavelength. There are a few exceptions which call for special units of glass tuned to 5 &um;m, also certain plastics have specific wavelengths. Users should bear in mind that the ability to view the object under measurement by direct line-of-sight is important, as is protecting the optics of infrared thermometers against dust and condensation. In general, IR thermometers measure only surface temperatures and the ability of objects to emit thermal radiation depends on the type of material and particularly on the surface finish.
New developments in IR temperature measurement
Recently the IR sensor market has seen two new trends emerge:
* IR thermometers are significantly lower in cost. The most expensive parts of an infrared thermometer are the lenses and detectors. New lens technology and mass production of IR detectors for consumer products have resulted in lower prices for these two important components.
* IR sensors have become smaller in size. In the past, the measurement of low temperatures made it necessary to use lenses with relatively large diameters in order to capture enough emitted energy. Progress in detector technology together with improved low noise analogue preamplifier techniques have helped reduce the dimensions of the IR sensing head dramatically. The newer sensors with their better response characteristics require less energy to retrieve a usable signal, as a result lenses can have smaller diameters.
R&C Instrumentation reports that its range of IR units from Raytek and Ircon cover the temperature range from -50 to 3000°C. Scanners from both companies can be supplied as complete applications packages together with software that can be customised for many different industrial applications. Continual innovation and new product developments will ensure that solutions are always available as user requirements become more demanding.
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