Optics: measuring and testing – For size of particles
Reexamination Certificate
1999-10-08
2001-06-26
Font, Frank G. (Department: 2877)
Optics: measuring and testing
For size of particles
C356S336000, C356S337000
Reexamination Certificate
active
06252658
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a particle size distribution measuring apparatus which detects a diffraction/scattering light generated by irradiating a laser beam onto a dispersing particle group, and measures a particle (grain) size distribution of the particle group on the basis of an intensity signal of the scattered light obtained by the detection.
2. Description of Related Art
In a particle size distribution measuring apparatus using a diffraction or scattering phenomenon of light by particles, an intensity distribution of diffraction light or scattering light, that is, a relationship between a diffraction or scattering angle and a light intensity is measured, and then, this measured result is subjected to operational processing based on a Fraunhofer diffraction theory or Mie scattering theory, and thereby, a particle size distribution of a sample particle is calculated (computed). The aforesaid particle size distribution measuring apparatus has been used for research and development of raw materials in a mining industrial field such as the cement or ceramic industry, and in ceramics, in particular.
In the development of new materials in the ceramic and polymer fields, a demand has been recently made to measure micro particles in a sub-micron region, and therefore, efforts have been made to develop instruments which can measure not only relatively large particles, but also particles in a sub-micron region.
An example of a particle size distribution measuring apparatus is disclosed in Japanese Examined Patent Publication (Kokoku) No. 6-43950.
FIG. 4
is a view schematically showing a construction of the particle size distribution measuring apparatus disclosed in the above publication. In
FIG. 4
, a reference numeral
41
denotes a sample cell comprising a transparent container which contains a liquid (hereinafter, referred to as a sample solution)
42
prepared by dispersing a particle group of a target specimen for measurement in a medium liquid. A laser beam source
43
which is located on one side (rear side) of the cell
41
provides an enlarged parallel laser beam
44
from a beam expander (not shown) so as to irradiate the cell
41
.
A collective (condenser) lens
45
is located on the other side (front side) of the cell
41
, and a ring detector
46
is arranged on a focal position of the collective lens
41
. The ring detector
46
is constructed in such a manner that a plurality of photo-sensors having a ring or semi-ring like light receiving surface having mutually different radius are coaxially arranged around an optical axis of the collective lens
45
. Further, the ring detector
46
receives light scattered/diffracted at a relatively small angle off of the optical axis of the laser beam
44
which has been diffracted or scattered by the particles in the cell
41
for each scattering angle, and then, measures each respective light intensity.
An optical detector group
47
for wide-angle scattering light detects each light scattered/diffracted at a relatively large angle of the laser beam
44
which has been diffracted or scattered by the particles in the cell
41
for each scattering angle. Further, the optical detector group
47
for wide-angle scattering light is composed of the collective lens
45
and a plurality of photo-sensors
48
to
53
which are located at an angle different from the ring detector
46
, and can detect a wide-angle scattering light which exceeds a predetermined angle by particles in the cell
41
, in accordance with each located angle. More specifically, the photo-sensors
48
to
51
detect a forward scattering light, the photo-sensor
52
detects a side scattering light, and the photo-sensor
53
detects a backward scattering light.
A reference numeral
54
denotes a pre-amplifier for amplifying an output of the photo-sensors constituting the above ring detector
46
, reference numerals
55
to
58
individually denote pre-amplifiers for amplifying each output of the photo-sensors
48
to
51
for forward scattering light, and reference numerals
59
and
60
individually denote pre-amplifiers for output of the photo-sensor
52
for side scattering light and the photo-sensor
53
for backward scattering light. A multiplexor
61
successively captures each output of the pre-amplifiers
54
to
60
, and successively transmits the output to an A/D converter
62
, and a computer
63
functions as a processor to which an output of the A/D converter
62
is inputted.
The computer
63
stores a program for processing the outputs converted into a digital signal (the digital data relative to light intensity) of the ring detector
46
and photo-sensor
48
to
53
on the basis of a known Fraunhofer diffraction theory or Mie scattering theory and determining a particle size distribution of the particle group.
In the aforesaid particle size distribution measuring apparatus, when sample liquid
42
is contained in the cell
41
, the laser beam
44
is irradiated on the sample cell
41
from the laser beam source
43
and the laser beam
44
is diffracted or scattered by particles contained in the cell
41
. Of the diffraction light or the scattering light, a light having a relatively small scattering angle is imaged on the ring detector
46
by means of the collective lens
45
. In this case, the photo-sensor arranged on the outer peripheral side of the ring detector
46
receives a light having a larger scattering angle while the photo-sensor arranged on an inner peripheral side thereof receives light having a smaller scattering angle. Thus, a light intensity detected by the outer peripheral side photo-sensor reflects a particle quantity having a smaller particle size, and a light intensity detected by the inner peripheral side photo-sensor reflects a quantity of sample particle having a larger particle size. The light intensity detected by each photo-sensor is converted into an analog electric signal, and further, is inputted to the multiplexor
61
via the pre-amplifier
54
.
On the other hand, of the laser beam
44
diffracted or scattered by the particles, a relatively large scattering angle light, which is not converged by the collective lens
45
, is detected by means of the photo-sensors
48
to
53
, and then, the light intensity distribution is measured. In this case, the photo-sensors
48
to
51
for forward scattering light, the photo-sensor
52
for side scattering light and the photo-sensor
53
for backward scattering light, successively detect scattering light from a particle having a small particle (grain) size. A light intensity detected by each of these photo-sensors
48
to
53
is converted into an analog electric signal, and then, is inputted to the multiplexor
61
via pre-amplifiers
55
to
60
.
In the multiplexor
61
, measurement data from the ring detector
46
and photo-sensors
48
to
53
, that is, the analog electric signal is successively captured in a predetermined order. Then, the analog electric signal captured by the multiplexor
61
is made into a serial signal, and is successively converted into a digital signal by means of the A/D converter
62
, and further, is inputted to the computer
63
. The computer
63
processes light intensity data for each scattering angle obtained by each of the ring detector
46
and the photo-sensors
48
to
53
on the basis of a Fraunhofer diffraction theory and a Mie scattering theory.
As seen from the above description, in such a particle size distribution measuring apparatus, the light intensity distribution of the scattering light having a large particle size range is measured by means of the ring detector
46
while the light intensity distribution of the wide-angle scattering light having a small particle size range is measured by means of the photo-sensors
48
to
53
. Then, the outputs of these ring detector
46
and photo-sensors
48
to
53
are processed by means of the computer
63
, so that a particle size distribution of a particle group can be determined over a wide range from a relatively large par
Igushi Tatsuo
Ito Toshiya
Sakai Yukio
Togawa Yoshiaki
Font Frank G.
Horiba Ltd.
Nguyen Sang H.
Price and Gess
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