Patent EP-0990888-A2 (EP)
Inventor: YAMAGUCHI TETSUJI
IPC: G01N15/02
Filed: 1999-09-28
Abstract: The present invention provides a particle size distribution measurement
apparatus (1) and a particle size distribution analysis method capable of
obtaining a highly accurate particle size distribution (Ft(D)) in view of
conditions at the time of measurement including information obtained
depending on measurement conditions and particle sizes, capable of enhancing
the accuracy of calculating the particle size distribution (Ft(D)) and improving
reproducibility without performing complicated operation processing and
allowing a user to freely change the number of divisions and display widths for
operation and display sections within a display range. 
     An apparatus (1) for measuring a particle size distribution (Ft(D))
according to the present invention includes a light source (3) directing a laser
light to particles (2b) which are dispersed into a solvent (2a) and which are
making a Brownian motion; a detector (8) converting an interference light (Li)
caused by Doppler-shifted scattered light by the particles (2b) into an electric
detection signal (D(t)); an operation unit (14) obtaining an intermediate
function (S(f)) by processing the detection signal (D(t)); and a processing unit
(16) subjecting the intermediate funtion (S(f)) to inverse problem and thereby
calculating a particle size distribution (Ft(D)), includes a data selecting unit
(15) provided between the operation unit (14) and the processing unit (16), for
selecting data from all data regions in the intermediate function (S(f)) at
appropriate intervals and creating a data table S(f 1,2,3..n )) used in inverse
problem. 
     A method for analyzing a particle size distribution according to the
present invention includes the steps of directing a laser light to particles (2b)
which are dispersed into a solvent (2a) and which are making a Brownian
motion; converting an interference light (Li) caused by Doppler-shifted
scattered light by the particles (2b) into an electric detection signal (D(t));
processing the detected signal (D(t)) to obtain an intermediate function (S(f));
and subjecting the intermediate function (S(f)) to inverse problem and thereby
calculating a particle size distribution (Ft(D)), includes furtheron, while
presetting an assumed particle size distribution (F(D)), calculating frequency
characteristics (S(f)) of the detection signal (D(t)) and setting the frequency 
characteristics (S(f)) as measured frequency characteristics; calculating
frequency characterics of Lorenzian function having a half width obtained by a
Stokes-Einstein expression from measurement conditions in accordance with
particle sizes (D 1 -D 8 ) and setting the frequency characteristics of Lorenzian
function as operation frequency characteristics (S 1 -S 8 ); calculating a response
function (P(f,D)) indicating a light intensity with respect to particle size (D1 -
D8) based on the operation frequency characteristics (S 1 -S 8 ) for every
frequency (f); calculating the frequency characteristics (Sc(f)) based on
assumed values in the assumed particle size distribution (F(D)) for every
frequency (f) using the response function (P(f,D)) as a weight: correcting the
assumed particle size distribution in accordance with a rate of a difference (r 0 )
between the frequency characteristics (Sc(f)) based on the assumed values and
the measured frequency characteristics (S(f)); repeating the processing steps
using the corrected assumed particle size distribution (F'(D)); determining, as
a true particle size distribution (Ft(D)), the assumed particle size distribution
(F(D)) when the rate of the difference (r 0 ) between the frequency characteristics
(Sc(f)) based on the assumed values and the measured frequency
characteristics (S(f)) falls within a predetermined range.