Abstract: To increase the dynamic range when testing the particle size distribution of aerosols, the invention proposes a method whereby particles are detected in two measuring volumes connected in series in the measuring channel, whereby in particular the total number of particles flowing through the measuring channel passes through one measuring volume while only a smaller number of particles passes through the other measuring volume. A device appropriate therefor provides for a first measuring volume (MV1) to be located immediately downstream of an inlet nozzle (4) for the aerosol and having a surface perpendicular to the flow direction of the aerosol, said surface corresponding to the surface of the end of the inlet nozzle and for a second measuring volume to be provided downstream of the first measuring volume at a distance therefrom, the cross section of said second measuring volume perpendicular to the flow direction of the aerosol being smaller than the cross section of the measuring channel.

Abstract: For simplifying the optical measurement of a particle flow in a fluid and in particular for eliminating errors, in a device for measuring a particle flow in a fluid with at least one illumination system having a diaphragm and at least one receiver system having a diaphragm, the invention provides for a diaphragm (6a, 11a) to have an aperture (6, 11) with an edge (6b, 11b) constructed convexly towards the interior of the diaphragm aperture (6, 11). According to a method, the particle flow is illuminated and/or observed through a diaphragm aperture with an edge constructed convexly towards its interior and the maximum intensity of the particle flying through a first optical measuring range is measured and account is only taken of the particle if the intensity on flowing through a second measuring range exceeds a specific minimum percentage of the maximum intensity measured for this particle.