Optics: measuring and testing – For size of particles – By particle light scattering
Patent
1997-01-13
1998-11-24
Font, Frank G.
Optics: measuring and testing
For size of particles
By particle light scattering
356338, 356340, 356342, 250564, 250574, 340630, 340638, 340555, G01N 2100, G01N 1502, G08B 1710
Patent
active
058415343
DESCRIPTION:
BRIEF SUMMARY
FIELD OF THE INVENTION
The invention relates to an apparatus for measuring the light scatter by particles suspended in a carrier medium for determining the density, the size or the size distribution of the particles.
BACKGROUND OF THE INVENTION
Besides measuring the light absorption, measuring the light scatter is a generally known method to detect suspended particles in air but also in other gases or also in transparent liquids like, for example water and to determine the density, the size or the size distribution of the particles. In this, light from a monochromatic or polychromatic light source is directed towards the carrier medium. The beam of light hits the particles suspended in the carrier medium and is absorbed afterwards preferably in a light trap. If the beam of light hits a particle, the particle deflects a small portion of the light, as a so-called scattered light, out of its original direction. A light sensitive receiver measures the intensity of the scattered light. The spatial intersection region which is covered both by the beams of light from the light source and the angle of view of the receiver is called light-scattering center here.
JP 4-260 197 A in US-periodical: Patent Abstracts of Japan, Section P, Vol 17/No. 48 (1993) P-1477 shows an apparatus in which beams of light pulsed chronologically one after another are directed from two light sources towards a common light-scattering center for determining the size (diameter) of particles suspended in a carrier medium. A common receiver is associated with both light sources, the axis of the receiver is pointed at the light -scattering center. The two light sources can be arranged in such a way that they emit their beams of light at different angles to the axis of the receiver.
Both light sources are arranged in such a way that the receiver receives the scattered light in forward direction. The signals supplied by the common receiver are supplied to an evaluating device having a control device for the timing of the pulsed beams of light one after another.
It remains open whether and, should it be, how the carrier medium flows or is guided. Additionally, the device is depicted in a way in that no special housing is provided, so that problems which are associated with the occurrence of light scattered at an inner wall of a housing and/or the accuracy of the measurement which is hence affected are consequently not mentioned.
DE 38 31 654 A1 shows and describes an optical smoke alarm with a strongly light absorbing measuring chamber. With little effort it shall be avoided that the scattered radiation caused by fouling of the measuring chamber leads to a false alarm. To this end, a additional second light sensitive receiver is employed in a housing-like measuring chamber, the view field of the second receiver is pointed at a surface area of the measuring chamber which is illuminated by one of the light sources. With this second receiver a comparative value is determined which corresponds to the level of fouling of the housing increasing with time, and which is appropriately taken into account in the control circuitry to eliminate the negative effects of a changing scatter radiation background in the housing on the accuracy of the measurement.
DE 33 34 545 A1 also shows an optical smoke alarm having two light sources which are arranged symmetrically to the axis of a receiver and which emit their beams of light at an acute angle to the axis of the receiver, so that the scattered light is received as backward radiation here. The two light sources and the receiver are contained in a housing having two openings through which the beams of lights from the light sources can emerge, so that the problem of wandering reflected scatter light radiation is thus solved without using lots of diaphragms. The carrier medium with the particles can also be fed into the housing through one of the openings.
Further apparatus have been described by Bol, Roth und Wurzbacher "Erfassung und Untersuchung kolloider Luft- und Abwasserverunreinigungen durch Streulichtme
REFERENCES:
patent: 4397557 (1983-08-01), Herwig et al.
patent: 4607915 (1986-08-01), Cole
patent: 4906978 (1990-03-01), Best et al.
patent: 5231378 (1993-07-01), Dennis et al.
patent: 5440145 (1995-08-01), Cole
patent: 5587790 (1996-12-01), Nagashima
Font Frank G.
Gerhard Lorenz Innovative Technik + Messgeratebau
Vierra-Eisenbey Jason D.
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