Pyrometer Series Metis MQ utilizes lead sulphide and Metis MB lead selenide detectors with filtered spectral response at relative short infrared wavelengths, and they are therefore often used to measure metal surfaces above 75°C (Metis MQ) or above 50° (Metis MB). The emissivity of these surfaces decreases with an increase wavelength, so they offer much better performance than other pyrometers with similar low zero scale temperatures, but with longer wavelength response.
Other major advantages are the lower sensitivity for changes in emissivity at shorter wavelengths, the small spot sizes, the fast response time and the digital signal processing which allow the pyrometer to operate within very wide temperature ranges. This makes these units preferable for many other applications, too. Optical and electronic parts are housed in a rugged IP65, extruded aluminium casting to operate in harsh industrial environments.
The infrared energy radiated by the target is centered via focusable (Metis MQ) or fixed focus lenses (Metis MB) directly on the detector. The focusing feature gives you control of the cone of vision and offers the possibility to measure either a small spot (focused) or the average of a bigger spot (out of focus). Fixed focus lenses with larger diameter collect more infrared energy and therefore result in smaller spot sizes.
The lenses are made of quartz glass (Metis MP23 and MP25) or calcium fluoride CaF2 (Metis MB) which are highly transparent in their spectral regions. If additional windows are necessary, they must offer similar optical characteristics.
The detector is sensitive to infrared radiation in an area called the cone of vision. For full scale temperatures up to 700°C the cone of vision diameter in front of the lens is about 16 mm and about 9 mm for full scale temperatures above. This area has to be kept free from any intervening objects. The spot size diameter for distances not given in the chart can be calculated by interpolation.