Optics: measuring and testing – For size of particles – By particle light scattering
Reexamination Certificate
2000-03-22
2001-08-28
Font, Frank G. (Department: 2877)
Optics: measuring and testing
For size of particles
By particle light scattering
C356S335000, C356S337000, C356S338000
Reexamination Certificate
active
06281972
ABSTRACT:
FIELD OF ART
The present invention relates to a method and apparatus for measuring particle size distribution of particles suspended in a gas with great ease and high precision.
BACKGROUND ART
As an apparatus for classifying particles suspended in a gas by their electric mobilities, one is disclosed in the Journal of Aerosol Science, Vol. 16, pp. 443-452, “Aerosol Classification by Electric Mobility” by E. O. Knutson and K. T. Whitby (Reference 1).
The prior art classifying apparatus per se can only classify particles by their electric mobilities. However, by connecting the condensation nucleus type counter device disclosed in “Aerosol Technology” (Wiley Interscience 1982), p. 262 by W. C. Hinds (Reference 2) to the aforementioned apparatus for classifying particles by their electric mobilities and counting the number of the classified particles at various electric mobility values, it is possible to measure electric mobility distribution with high precision.
In the Journal of Aerosol Science Vol. 9, pp. 41-54 (1978), “Determination of the Aerosol Size Distribution from the Mobility Distribution of the Charged Fraction of Aerosol” by W. A. Hoppel (Reference 3), there is described a data processing method for converting the electric mobility distribution obtained as described above into particle size distribution.
However, the data processing method relates to a method for solving a problem falling in the category of so-called inverse problems. Owing to the nature of such problems, there are cases where no solution exists and where the uniqueness or stability of a solution is not assured. For these reasons, there are some cases that fail to measure particle size distribution or give rise to a large error in the particle size distribution measured.
Examples of methods for directly measuring particle size distribution of particles suspended in a gas include the light-scattering method using a light-scattering type automatic particle counter prescribed by JIS-B-9921 (Reference 4), the method using an impactor, described in “Applied Aerosol Technology” (Yokendo, 1984), p. 262 by Mikiji Takahashi (Reference 5) and the aerosol beam method described in “Applied Aerosol Technology” (Yokendo 1984) p. 264 by Mikiji Takahashi (Reference 6).
However, these methods for the direct measurement of particle size distribution have difficulty in measuring a particle size distribution with high precision.
In view of the above, an object of the present invention is to provide a measuring method and a measuring apparatus that can measure particle size distribution of particles suspended in a gas with precision higher than that obtained in the conventional methods of measuring particle size distribution by obtaining particle sizes from the electric mobility and number of charges of individual particles without using any analytical means.
DISCLOSURE OF THE INVENTION
In order to attain the object described above, the method for measuring particle size distribution according to the present invention is characterized by classifying particles suspended in a gas according to their electric mobilities, then using a particle size measuring method to directly obtain approximate values of particle sizes, obtaining the number of charges on the particles from the electric mobilities and the approximate particle sizes thus obtained, and determining the precise particle sizes from the number of charges thus obtained and the electric mobilities.
An apparatus for measuring particle size distribution according to the present invention is characterized by comprising an electric mobility classifying section that comprises an outside electrode, an inside electrode and an annular cylindrical hollow portion defined by the outside and inside electrodes, a particle size measuring section disposed under the electric mobility classifying section for measuring approximate particle sizes, and a guide frame that allows the electric mobility classifying section and the annular cylindrical hollow section to communicate with each other; supplying from above a sample gas containing charged particles under measurement into the cylindrical hollow section of the electric mobility classifying section to classify the particles according to their electric mobilities; supplying the gas containing the classified particles into the the particle size measuring section via the guide frame to directly obtain approximate particle sizes; obtaining the number of charges of the particles from the approximate particle sizes; and determining precise particle sizes from the number of charges and the electric mobilities.
Since the present invention determines particle sizes from the electric mobilities according to which particles are classified and the number of charges, as described above, it enables measurement of particle size distribution with high precision.
REFERENCES:
patent: 4633714 (1987-01-01), Mazumder et al.
patent: 5296910 (1994-03-01), Cole
Ebara Kensei
Shin Shoichiro
Font Frank G.
Japan as represented by Director General of Agency of Industrial
Oblon & Spivak, McClelland, Maier & Neustadt P.C.
Punnoose Roy M.
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