The small and handy device for determining fine dust concentrations provides an annularly constructed measurement chamber with assigned Wood's tubes, a supply and measuring electronic system constructed in two parts with an analog part and a digital part, as well as a microprocessor, produced using C-MOS technology, and assigned DC/DC converters control modules for generating the required operating voltages. All the dust located in the measuring volume is illuminated by means of a monochromatic illuminating device in the wavelength region of 800-1000 nm, in order to guarantee perfect dust assessment of the fine, airborne dust which can get into the lungs. The scattered light of the particles is measured at an angle of exactly 70 DEG . The use of an exact measuring angle and the guidance of the illuminating and measuring beam by the use of lenses, diaphragms and suitable Wood's tubes renders it possible in the case of punctiform imaging of the measuring beam on a receiver to obtain a measuring chamber with a design that is very small, low in noise and streamlined. By minimising the energy requirement of the electronic system, it is possible to reduce the space requirement for the required accumulator, so that the latter can also be installed in the apparatus. The internal cycles during measurement, the measured value processing and the measured value display are controlled by a microprocessor which has a low power requirement. IMAGE
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