JPH07260669A - Grain size distribution measuring device - Google Patents

Abstract

PURPOSE:To select the grain size distribution of particle group distributed over a wide area by selecting the grain size distribution based on the light scattering method with the aid of a light scattering phenomena generating at the time when scattering and flying particle group is irradiated by a light. CONSTITUTION:Diffracted/scattered lights of less than specified forward angle among diffracted/scattered lights of a particle group are condensed by a lens 4 and their intensity distribution is measured by an array sensor 5. At the same time, forward, side and backward scattered lights exceeding the specified angle among the scattered lights of the particle group are measured by optical sensors 6-8 installed separately from the sensor 5. In this case, the digital conversion data outputted from the sensor 5 and sensors 6-8 are picked up into a calculation part 13 through a common A/D converter 11, and they are used as a unified vector component for scattered light intensity, thus calculating the data by using a preset conversion factor matrix for converting a scattered light intensity distribution vector into a grain size distribution vector and obtaining the grain size distribution of particle group at one time.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a particle size distribution measuring device based on a so-called light scattering method, which utilizes a light scattering phenomenon which occurs when particles of particles in a dispersed flying state are irradiated with light, and particularly particles having a wide distribution. The present invention relates to a particle size distribution measuring device suitable for measuring a particle size distribution of a group.

[0002]

2. Description of the Related Art In a particle size distribution measuring apparatus using Mie's scattering theory or Fraunhofer diffraction theory,
The diffracted / scattered light from the particle group to be measured is collected using a lens to form a diffracted / scattered image on the light receiving surface of an array sensor such as a ring detector, and the spatial intensity distribution of the diffracted / scattered light from the output. Those having a structure for obtaining the above and converting it into a particle size distribution are mainly put into practical use.

Further, conventionally, diffracted / scattered light from a group of particles to be measured is incident on the end faces of optical fibers arranged at a predetermined angle from each other, and an optical sensor is provided at the other end of each optical fiber. Other structures have also been proposed.

Here, a general-purpose particle size distribution measuring device is generally required to have a very wide measuring range ranging from submicron to several thousand and several hundred μm. The reason why the former method using an array sensor such as a ring detector occupies the mainstream in practical machines is that in the case of large particles, the scattered light changes drastically within a very narrow forward angle range (scattering angle near 0 °). However, with array sensors such as ring detectors, diffraction /
This is because the portion corresponding to the scattering angle of about 0 ° can be divided into very fine parts, and the light intensity in this region where the change is sharp can be measured with high resolution and continuously. On the other hand, in the method using the optical fiber, the scattering angle is 0
Since it is impossible to subdivide the vicinity of the above-mentioned degree and the area of the end face of the optical fiber that is the light-introducing end is a small circle, compared to the structure using an array sensor such as a ring detector, There is also a problem that the amount of light that leads to is not secured.

As described above, a method using an array sensor such as a ring detector is advantageous especially for measuring a large-diameter particle, but since the array sensor such as a ring detector is generally manufactured from a silicon wafer, its size is large. There is a restriction on the size, and the measurement limit of the diffraction / scattering angle is about 40 ° or less in front. Here, when measuring small particles, especially submicron particles, the change depending on the scattering angle of scattered light becomes slow as a whole, and the overall change including not only the front but also the side and the back is performed. Need to be detected.

Therefore, in order to cover a wide measuring range as described above in a device using an array sensor such as a ring detector, one scattered light with an angle larger than about 40 ° ahead is separately provided. Alternatively, it has been put into practical use to provide a plurality of optical sensors and measure the light intensity thereof. In this case, the intensity of scattered light at a large angle becomes weaker, so an optical sensor that measures this should normally be brought closer to the particle to be measured, and use a sensor with a large light-receiving area because the change is slow as described above. Is common.

In an apparatus in which an array sensor such as a ring detector is combined with another optical sensor, conventionally, the array sensor and the other sensor are different types of sensors, and only the array sensor is used. Since the characteristic or spatial commonality between the sensors is lost, in the conventional device of this type, the outputs from the array sensor and the other sensor are digitally converted by separate A / D converters. Then, the data of the diffraction / scattered light intensity distribution by the array sensor is converted into a particle size distribution, and the data of the scattered light intensity distribution by other sensors is converted into a separate particle size distribution. Finally, by combining the two, the particle size distribution of the entire measured particle group is obtained.

[0008]

By using an array sensor such as a ring detector, it is possible to measure the diffracted / scattered light at a small front angle with a high resolution by using an array sensor such as a ring detector. With the conventional wide-range particle size distribution measuring device that is also capable of measuring submicron particles by using the above optical sensor, the intensity distribution pattern of the front minute angle scattering (diffraction) light and other front, side and It is treated completely differently from the intensity distribution pattern of scattered light, and the theoretical basis is ambiguous in that the particle size distributions obtained separately based on the respective data are connected later, and an accurate particle size distribution is obtained. There is no guarantee that That is, it is difficult for the conventional particle size distribution measuring device to accurately measure a wide range of particle size distribution. Further, since the A / D converter is provided for each sensor, the number of parts is increased and the size of the entire device is increased.

The present invention has been made in view of the above points, and an object thereof is to provide a particle size distribution measuring apparatus capable of accurately measuring a wide range of particle size distribution.

[0010]

In order to achieve the above object, the present invention provides an intensity distribution of diffracted / scattered light by a particle group obtained by irradiating a particle group in a dispersed flying state with a parallel light flux. In a device for measuring the particle size distribution of particle groups by measurement, a lens that collects diffracted / scattered light of a predetermined angle or less out of the diffracted / scattered light by the particle group and the diffracted light that is condensed by the lens / An array sensor for detecting the intensity distribution of scattered light, and of the scattered light by the particle group, any of forward scattered light, side scattered light, and back scattered light that exceeds the above angle is made incident and its intensity is detected 1
The output of each of the plurality of optical sensors and the array sensor and the optical sensor is taken in through a common A / D converter, and the respective data are integrated into a component of a scattered light intensity distribution vector. And a calculation means for calculating the particle size distribution of the particle group at once by an operation using a preset conversion coefficient matrix for converting the scattered light intensity distribution vector into the particle size distribution vector from the data. It is characterized by

[0011]

When the particles are irradiated with light such as laser light, a spatial intensity distribution pattern of diffracted / scattered light is generated, and this pattern changes depending on the size of the particles. When a particle group in which particles of various sizes are mixed is irradiated with light, the light intensity distribution pattern generated from the particle group is a superposition of diffracted / scattered light from each particle.

When this is expressed by a vector and a matrix, r = Af. Here, r is a light intensity distribution vector and f is a particle size distribution vector. A is the particle size distribution vector f
Is a coefficient matrix for converting into the light intensity distribution vector r.
In the actual calculation method, the component (element) of r is
Light intensity data detected by an array sensor or light sensor at a scattering angle.

Therefore, all the data of the front minute angle scattered / diffracted light and the other front scattered light, side scattered light and back scattered light by the array sensor and another optical sensor are unified into a light intensity distribution vector. There is no theoretical contradiction of treating it as an element of r, and by using such r and obtaining the conversion matrix A (described later), the components of the particle size distribution vector f can be obtained all at once.

[0014]

DESCRIPTION OF THE PREFERRED EMBODIMENTS The drawings are block diagrams of embodiments of the present invention.

Laser light emitted from the laser light source 1 is applied to the flow cell 2. In the flow cell 2, a suspension 3 in which a group of particles to be measured is dispersed in a medium is flown in a direction perpendicular to the paper surface, and the irradiated laser light is scattered or diffracted by the particles.

A lens 4 is arranged in front of the flow cell 2 in the traveling direction of the irradiation laser light, and a ring detector 5 is arranged in front of it in the focal position thereof. The ring detector 5 is formed by concentrically arranging a plurality of photosensors each having a ring-shaped or semi-ring-shaped light receiving surface whose radius is different from each other around the optical axis of the lens 4.
40 ° out of scattered / diffracted light by particles in the flow cell 2
Light having a scattering / diffraction angle within is collected by the lens 4 on the ring detector 5.

Around the flow cell 2, there are, for example, three optical sensors 6 at different angles from the lens 4 and the detector 5.
7 and 8 are arranged to detect the intensities of the forward scattered light, the side scattered light and the back scattered light of a predetermined angle exceeding 40 ° by the particles in the flow cell 2 according to the respective arrangement angles. You can

The output signals from the respective elements of the ring detector 5 and the respective photosensors 6, 7 and 8 are guided to the A / D converter 11 via the preamplifier 9 and the multiplexer 10, respectively, and are sequentially digital-converted, and then input. It is taken into the arithmetic unit 13 via the output interface 12.

The calculation unit 13 includes a CPU 13a and a ROM 13
b, a RAM 13c, and the like, and is mainly configured by a computer system. Light intensity data from each element in the ring detector 5 and each optical sensor 6, 7, 8 is RA.
It is taken into M13c and using these data, ROM
The particle size distribution of the particles to be measured can be calculated all at once by the conversion formula described later written in 13b. A printer 14 and a CRT 15 that print and display the calculation result of the particle size distribution are connected to the calculation unit 13.

Next, a method of calculation in the calculation unit 13 will be described. Particles of different sizes are mixed in the flow cell 2, and the intensity distribution pattern of scattered / diffracted light due to these particles is a superposition of scattered / diffracted light from each particle. = Af ... (1) However,

[0021]

[Formula 1]

[0022]

[Formula 2] Is. r is a light intensity distribution vector, and its element r _i
(I = 1, 2, ..., M) is the intensity of the front minute angle scattered / diffracted light detected by each element of the ring detector 5. r _i (i = m + 1, m + 2, ..., P)
Is the front, side, detected by the optical sensors 6, 7, and 8.
This is the intensity of backscattered light. f is a particle size distribution vector. The particle size distribution range is finite, and this range is divided into n,
The inside of each divided section is represented by one particle diameter D _j . The element f _{j of} f (j = 1, 2, ..., N) is the amount of particles corresponding to the particle diameter D j. A is the particle size distribution f,
It is a coefficient matrix for converting into a light intensity distribution r. Element a of A
_{i, j} (i = 1,2, ... m, m + 1, ...
The physical meaning of p; j = 1, 2, ..., N) is the incident light intensity of the light diffracted / scattered by the particle group having the particle diameter D _{j and} the unit particle amount to the i-th element. The numerical value of a _{i, j} can be theoretically calculated based on the wavelength of the light source, the polarization component, the arrangement of the optical system, and the like. For this, the Fraunhofer diffraction theory is used when the particle diameter is sufficiently larger than the wavelength of the laser light serving as the light source.

However, when the particle diameter is in the submicron region which is about the same as or smaller than the wavelength of laser light, it is necessary to use the Mie scattering theory. The Fraunhofer diffraction theory can be considered to be an excellent approximation of the Mie scattering theory, which is effective in the case of forward small angle scattering when the particle size is sufficiently larger than the wavelength.

In the equations (1) to (3), the intensity distribution pattern of the front minute angle scattered light condensed by the lens 4 and the other intensity patterns of the front, side and back scattered light are unified. , And based on these equations, a wide range of particle size distributions can be calculated and obtained all at once. This calculation method is generally inverse problem (inverse problem)
There are various methods. For example, when the least squares method is used, the particle size distribution (vector) f can be calculated by the following equation (4) based on the equation (1).
f = (A ^T A) ^-1 A ^T r ···
(4) where _AT is the transposed matrix of A and () ^-1 represents the inverse matrix. On the right side of the equation (4), as described above, each element of the light intensity distribution (vector) r is the light intensity detected by the ring detector 5 and the optical sensors 6, 7, 8 placed in front, side, and rear. And the coefficient matrix A is obtained by using Fraunhofer diffraction theory or Mie scattering theory,
Since it can be calculated in advance, the particle size distribution (vector) can be obtained by executing the calculation of equation (4) using those known data.
f will be obtained all at once. By the way, based on the same idea as described above, a method of measuring a particle size distribution with a wider range and high resolution will be described. That is, the wavelength of the light source,
Consider a case where the measurement conditions such as the polarization component and the arrangement of the optical system (focal length of the lens 4, arrangement of the sensor and detector, etc.) are changed.

It is assumed that, under a certain measurement condition (provisionally, condition k), a total of p _k of incident light amount data is obtained for the light intensity distribution patterns of the front minute angle scattered light and the front, side, and back scattered light. .

If the measurement conditions are different, the light intensity distribution (vector) and the coefficient matrix are different even if the particle size distribution (vector) is the same.

Assuming that the light intensity distribution vector under the measurement condition k is r _k and the coefficient matrix is A _k , the relationship of r _k = A _k f ··· (5) holds as in (1). Same sample (same particle size distribution)
On the other hand, if the intensity distribution pattern of the scattered light is measured q times under different measurement conditions, they can be combined and expressed by the following equation (6).

R ′ = A′f (6) where

[0029]

[Formula 3] Is. Where r _k (k = 1, 2, ..., Q)
Is itself a vector, and A _k (k = 1, 2, ...
..., q) is itself a matrix. Therefore, r '
Is a (p ₁ + p ₂ + ... _Pk + ... _Pq ) next vector, and A'is (p ₁ + p ₂ + ... _Pk + ...
... p _q ) × n-order matrix.

If the light intensity distribution patterns obtained under a plurality of different measurement conditions by such a method are handled in a unified manner,
Similar to the formula (1), a more wide range, high resolution and more accurate particle size distribution can be calculated and obtained all at once by the method of the formula (4). Therefore, in the embodiment shown in the drawings, the wavelength and polarization component of the light source 1 can be changed, and the arrangement of the optical system (focal length of the lens 4, arrangement of the detector 5, sensor 6, etc.) can be made variable. This can be achieved by

In this case, the light source is not limited to the laser light source, and a plurality of single wavelength lights extracted from the halogen light source can be used. The measurement conditions can also be changed by changing the polarization component of the light with a polarization filter.

Further, the mechanism for changing the focal length of the condenser lens for the front minute angle scattered light can be realized not only by changing the lens but also by adopting a zoom lens.

Furthermore, in the present invention, in addition to the arrangement of the detector and the scattered light condensing lens as in the above-mentioned embodiment, the lens is arranged between the flow sails as a light source. It is needless to say that the invention can be similarly applied to the one using an optical system called so-called inverse Fourier transform.

[0034]

As described above, according to the present invention,
Intensity distribution pattern of front minute angle scattered light measured by a condenser lens and array sensor, and intensity distribution pattern of front, side and back scattered light exceeding the above angle by an optical sensor separately arranged Treats and as a unified
By using this, the particle size distribution is measured all at once by the transformation coefficient matrix, so compared to the conventional method of connecting the separately calculated particle size distributions later, a wider range of particle size distributions can be more accurately and It becomes possible to measure with resolution, and since the output from each sensor is taken in by a common (one) A-D converter, the entire device can be made compact.

[Brief description of drawings]

FIG. 1 is a diagram showing a schematic configuration of a particle size distribution measuring apparatus which is an embodiment of the present invention.

[Explanation of symbols]

 1 ... Laser light source 2 ... Flow cell 3 ... Suspension 4 ... Lens 5 ... Ring detector 6, 7, 8 ... Optical sensor 9 ... Preamplifier 11 ... A / D converter 13 ... Calculation unit

Claims (1)

[Claims] 1. An apparatus for measuring a particle size distribution of a particle group by measuring an intensity distribution of diffracted / scattered light by the particle group, which is obtained by irradiating a particle group in a dispersed flying state with a parallel light flux. Of the diffracted / scattered light by the group, a lens that condense the diffracted / scattered light of a predetermined angle forward, an array sensor that detects the intensity distribution of the diffracted / scattered light that is condensed by the lens, and the scatter by the particle group Of the light, one or a plurality of optical sensors that detect the intensity of any of forward scattered light, side scattered light, and back scattered light that exceeds the angle, and the outputs of the array sensor and the optical sensor. Each output is taken in through a common AD converter, each data is used as a component of a unified scattered light intensity distribution vector, and from that data,
A particle size distribution characterized by comprising calculation means for calculating the particle size distribution of particle groups all at once by calculation using a conversion coefficient matrix set in advance for converting the scattered light intensity distribution vector into a particle size distribution vector. measuring device.