JP3282580B2 - Laser diffraction / scattering particle size distribution analyzer - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

The present invention relates to a laser diffraction / scattering type particle size distribution measuring apparatus, and more particularly to a particle size distribution measuring apparatus suitable for measuring a particle size distribution of a low concentration sample.

[0002]

2. Description of the Related Art In a laser diffraction / scattering type particle size distribution measuring apparatus, the spatial intensity distribution of diffraction / scattered light obtained by irradiating a laser beam to a group of particles to be measured dispersed in a medium is measured. The measurement result is converted into a particle size distribution based on Mie's scattering theory or Fraunhofer diffraction theory.

The principle of a particle size distribution measuring device based on the laser diffraction / scattering method will be described below. FIG. 1 shows a basic configuration of a particle size distribution measuring apparatus using this method.

When a dispersed particle group P to be measured is irradiated with a laser beam from a laser light source 1, it is spatially diffracted.
A scattered light intensity distribution pattern results. Of these, the light intensity distribution pattern of the forward scattered light is condensed by the condensing lens 3, and a ring-like diffraction /
Create a scattered image. On this detection surface, a ring detector 4 in which ring-shaped or semi-ring-shaped light-sensitive portions having different radii are arranged concentrically is placed, and a light intensity distribution of a diffraction / scattered image is detected. The side scattered light and the back scattered light are detected by the side scattered light sensor 5 and the back scattered light sensors 6 and 6, respectively.

[0005] The light intensity distribution pattern thus obtained varies depending on the size of the particles. Since particles having different sizes are mixed in an actual sample, a light intensity distribution pattern generated from a particle group is obtained by superimposing diffraction / scattered light from each particle.

When this is expressed by a matrix,

[0007]

(Equation 1)

[0008] However,

[0009]

(Equation 2)

S (vector) is a light intensity distribution vector. The element s _i (i = 1, 2, ‥, m) is the amount of incident light detected by each light receiving element of the ring detector 4, the side scattered light sensor 5, and the back scattered light sensors 6, 6.

Q (vector) is the particle size distribution (frequency distribution%)
Vector. The particle size range to be measured (maximum particle size; x ₁ , minimum particle size x _{n + 1} ) is divided into n, and each particle size section is [x _j , x _{j + 1} ] (j = 1, 2, ‥, n)
And An element q _j of q (vector) is a particle amount corresponding to the particle section [x _j , x _{j + 1} ]. Normally,

[0012]

(Equation 3)

The normalization (normalization) is performed so that A is a coefficient matrix for converting a particle size distribution (vector) q into a light intensity distribution (vector) s. A element a _{i, j} (i = 1,2, ‥, m, j = 1,2, ‥,
The physical meaning of n) is the i of the light diffracted and scattered by the particle group of the unit particle amount belonging to the particle diameter section [x _j , x _{j + 1} ].
This is the amount of light incident on the th element.

The numerical values of a _{i, j} can be theoretically calculated in advance. For this, the Fraunhofer diffraction theory is used when the particle diameter is sufficiently larger than the wavelength of the laser light serving as a light source. However, in the submicron region where the particle diameter is about the same as or smaller than the wavelength of the laser light, it is necessary to use Mie scattering theory. The Fraunhofer diffraction theory can be considered to be an excellent approximation of the Mie scattering theory that is effective when the particle diameter is sufficiently large compared to the wavelength in forward small angle scattering.

In order to calculate the elements of the coefficient matrix A using Mie scattering theory, it is necessary to set the absolute refractive index (complex number) of the particles and the medium (medium liquid) in which the particles are dispersed. Instead of setting the absolute refractive index of each particle, the relative refractive index (complex number) between the particle and the medium may be set.

Now, an equation for obtaining the least square solution of the particle size distribution (vector) q based on the equation (1) is derived.

[0017]

(Equation 4)

Is obtained. On the right side of the equation (6), each element of the light intensity distribution (vector) s is represented by the ring detector 4, the side scattered light sensor 5, and the back scattered light sensor 6, 6.
Is a numerical value detected by. The coefficient matrix A can be calculated in advance using the Fraunhofer diffraction theory or the Mie scattering theory. Therefore, if the calculation of the expression (6) is performed using the known data, it is apparent that the particle size distribution (vector) q can be obtained.

The principle of measuring the particle size distribution based on the laser diffraction / scattering method has been described above. This is one example of a method of calculating the particle size distribution, and there are various other variations. Also, there are various variations in types and arrangements of sensors and detectors.

In this specification, the coefficient matrix A is basically defined as a conversion coefficient. However, shown in (6)

[0021]

(Equation 5)

Can be used as a conversion coefficient. Therefore, here, the conversion coefficients are all derived from the coefficient matrix A and used for the particle size distribution calculation.

[0023]

According to the particle size distribution measurement based on the laser diffraction / scattering method, the particle concentration suitable for the measurement is in the range of several tens ppm to several hundred ppm, and is as low as 10 ppm or less. It is difficult to accurately measure the particle size distribution of a sample of concentration.

That is, the data of the diffraction / scattered light measured by the laser diffraction / scattering method includes diffraction / scattered light from impurities other than the measurement target contained in the medium, and disturbance light from the optical system such as a cell. And noise components caused by various factors such as electrical noise. Also, when the sample has a low concentration, the diffracted and scattered light is weaker than that of a normal sample. If the particle size distribution is calculated using the light intensity distribution data of light as it is, a very large error will occur. For example, particle size distribution data may be obtained as if particles exist in a particle diameter range where particles do not actually exist, that is, a ghost peak may occur (see FIG. 6).

An object of the present invention is to provide a laser diffraction / scattering type particle size distribution measuring device capable of accurately measuring the particle size distribution of a sample having a low concentration of 10 ppm or less.

[0026]

In order to achieve the above object, a laser diffraction / scattering type particle size distribution measuring apparatus of the present invention comprises:
The dispersed particle group to be measured is housed in a cell, the spatial intensity distribution of the diffracted / scattered light obtained by irradiating the cell with laser light is measured, and the measured particle group is measured based on the light intensity distribution data. In a laser diffraction / scattering type particle size distribution measuring device that obtains a particle size distribution, it is configured to measure the spatial intensity distribution of the diffracted / scattered light using a cell having a long optical path length in a region where the laser light passes, It is characterized by having an arithmetic processing means for performing smoothing on the light intensity distribution data obtained by the measurement and calculating the particle size distribution using the data after the processing.

In the present invention, a cell having a long optical path length means that the optical path length of a normal cell is 1 cm or less,
A cell having an optical path length much longer than that, for example, an optical path length of 3 cm or more.

The operation of the present invention will be described below. First, in the particle size distribution measurement based on the laser diffraction / scattering method, if the diffraction / scattered light does not include a noise component (or is small and negligible), the light intensity as illustrated in FIG. Distribution data is obtained, and the particle size distribution data calculated using the distribution data is as shown in FIG.

On the other hand, the light intensity distribution data in the case where the noise component is included in the diffracted / scattered light is data as illustrated in FIG. 5, and the light intensity distribution data including the noise component is used as it is to obtain the particle size. When you calculate the distribution data,
Data as shown in FIG. 6 is obtained, and a ghost peak appears in the particle size distribution data.

Here, the light intensity distribution data shown in FIG.
That is, when smoothing is performed on the light intensity distribution data in the case where the diffraction / scattered light includes a noise component, the processed data becomes light intensity distribution data as illustrated in FIG. The particle size distribution data calculated using this is shown in FIG.
, That is, data in which the occurrence of a ghost peak does not appear.

Therefore, even if a noise component is included in the light intensity data of the diffracted / scattered light, it is possible to avoid an error in the particle size distribution data due to the adverse effect of the noise component by performing the smoothing on the data. .

However, when the noise component is further large, the intensity itself of the diffracted / scattered light emitted from the particles must be increased. For this purpose, it is necessary to increase the number of particles irradiated with laser light. As a solution to this, in the present invention, a cell having a long optical path length is used for measuring the diffracted / scattered light. The operation will be described below.

First, as shown in FIG. 9A, when a normal concentration sample (10 ppm to 100 ppm) is measured using a normal cell (with an optical path length of 1 cm or less) S 1, diffraction of an appropriate intensity is performed. -Scattered light is obtained.

Next, when a low-concentration (10 ppm or less) sample is measured using the cell S1 having the same optical path length, FIG.
As shown in (B), since the number of particles irradiated with the laser beam is smaller than that in the case of the normal density, the intensity of the diffracted / scattered light is weakened. Therefore, in this case,
The influence of noise components increases, making accurate particle size distribution measurement difficult.

On the other hand, as shown in FIG. 9 (C), when a sample is accommodated in a cell S2 having a long optical path length and diffraction / scattered light is measured, even if the concentration of the sample is low, a normal cell is used. Since more particles can be irradiated with laser light than S1, the intensity of the measured diffracted / scattered light increases. As a result, the S / N is greatly improved.

From the above, the laser diffraction / scattering type particle size distribution measuring apparatus of the present invention can accurately measure the particle size distribution of a sample having a low concentration of 10 ppm or less. It can be used for particle size distribution measurement of pollutants in rivers and oceans, monitoring of protozoa in tap water and its water source, and the like.

[0037]

Embodiments of the present invention will be described below with reference to the drawings.

FIG. 2 is a block diagram showing the configuration of the embodiment of the present invention. First, in this embodiment, the measurement of the diffracted / scattered light is performed by using a very long cell having an optical path length of 3 cm or more in a region through which the laser beam passes as the cell 2 containing the sample.

In FIG. 2, the output light from the laser light source 1 is applied to the sample in the cell 2 in a state of being converged into a parallel light beam by the collimator lens 1a. Of the diffracted and scattered light generated by this, the forward light enters the ring detector 4 via the condenser lens 3 and its light intensity is detected. Further, the scattered light to the side enters the side scattered light sensor 5, and the scattered light to the rear enters the back scattered light sensors 6 and 6, and the respective light intensities are detected.

An output signal from each light receiving element of the ring detector 4 and each output signal of the side scattered light sensor 5 and the back scattered light sensors 6 and 6 are output from a preamplifier 7 and an A / A
The data is taken into the arithmetic processing unit 9 via the D converter 8.

The arithmetic processing unit 9 is actually composed mainly of a computer and its peripheral devices, and operates based on an installed program. FIG. 2 is a block diagram for each function based on the program. I have.

The arithmetic processing unit 9 includes the ring detector 4 and each of the optical sensors 5 and 6 fetched through the A / D converter 8.
Storage unit 9a for storing light intensity distribution data from
And a smoothing processing unit 9b for performing smoothing on the light intensity distribution data in the data storage unit 9a, and the grain size distribution of the sample using the data after the processing is described by the above-described equations (1) to (6). And a particle size distribution calculation unit 9c that calculates based on the particle size distribution.

Further, the arithmetic processing unit 9 is connected to a display 10 for displaying light intensity distribution data of diffraction / scattered light and calculation results of particle size distribution.

In the above embodiment of the present invention, the light intensity distribution data of the diffracted and scattered light measured by the ring detector 4, the side scattered light sensor 5, and the back scattered light sensors 6 and 6 are used as they are, Instead of calculating the distribution, the measured data is subjected to smoothing, and the particle size distribution is calculated using the light intensity distribution data after this processing (see FIG. 7). Noise components generated by various factors such as diffraction / scattered light from impurities and disturbance light from an optical system such as a cell can be removed, and errors such as ghost peaks can be avoided (see FIG. 8). ).

In addition, since the sample is accommodated in the cell 2 (3 cm or more) whose optical path length is much longer than that of a normal cell and the diffraction and scattered light are measured, even if the concentration of the sample is low, The number of particles irradiated with the laser light can be increased, and the intensity of the diffracted / scattered light emitted from the particles increases.

Therefore, according to the present embodiment, even if the sample has a low concentration (10 ppm or less), its particle size distribution can be accurately measured.

In the embodiment of the present invention, a cell for a gas medium or a cell for a liquid medium can be used as the cell 2 for storing a sample. When a cell for a gaseous medium is used, the apparatus of the present embodiment can be used for measuring the particle size distribution of pollutants in the atmosphere, and when a cell for a liquid medium is applied, rivers and oceans can be used. It can be used for particle size distribution measurement of pollutants, monitoring of protozoa in tap water and its water source, and the like.

[0048]

As described above, according to the present invention, the spatial intensity distribution of the diffracted / scattered light is measured using a cell having a long optical path in the region through which the laser beam passes, and the measurement is performed by the measurement. Since the light intensity distribution data is smoothed and the particle size distribution is calculated using the processed data, the particle size distribution of a low-concentration sample of 10 ppm or less can be accurately measured. This makes it possible to measure the particle size distribution of objects that were not possible in the past, such as particle size distribution measurement of pollutants in the atmosphere, particle size distribution measurement of pollutants in rivers and oceans, monitoring of protozoa in tap water and its water source, etc. It can be expected to help in finding clues to solve various environmental problems and various public health difficulties.

[Brief description of the drawings]

FIG. 1 is an explanatory diagram of a basic particle size distribution measuring device using a laser diffraction / scattering method.

FIG. 2 is a block diagram showing a configuration of an embodiment of the present invention.

FIG. 3 is a graph showing an example of light intensity distribution data of diffracted / scattered light when the diffracted / scattered light does not include a noise component.

FIG. 4 is a graph showing an example of particle size distribution data when a noise component is not included in diffraction / scattered light.

FIG. 5 is a graph showing an example of light intensity distribution data of diffracted / scattered light when the diffracted / scattered light contains a noise component.

FIG. 6 is a graph showing an example of particle size distribution data when a diffraction / scattered light includes a noise component.

FIG. 7 is a graph showing an example of data obtained by performing smoothing on light intensity distribution data of diffracted / scattered light including a noise component.

FIG. 8 is a graph showing an example of particle size distribution data obtained using smoothed light intensity distribution data.

FIG. 9 is a diagram illustrating the operation of the present invention.

[Explanation of symbols]

 REFERENCE SIGNS LIST 1 laser light source 1 a collimator lens 2 cell 3 condenser lens 4 ring detector 5 side scattered light sensor 6 back scattered light sensor 7 preamplifier 8 A / D converter 9 arithmetic processing unit 9 a data storage unit 9 b smoothing processing unit 9 c particle size distribution Arithmetic unit 10 Display

Continuation of front page (58) Field surveyed (Int.Cl. ⁷ , DB name) G01N 15/02 G01N 15/14

Claims (1)

(57) [Claims] 1. A group of particles to be measured in a dispersed state is accommodated in a cell, and a spatial intensity distribution of diffraction / scattered light obtained by irradiating the cell with laser light is measured, and based on the light intensity distribution data. A laser diffraction / scattering type particle size distribution measuring device that obtains the particle size distribution of the particles to be measured is configured to measure the spatial intensity distribution of the diffracted / scattered light using a cell with a long optical path in the area where the laser light passes. A laser diffraction / characteristic processing means for performing smoothing on the light intensity distribution data obtained by the measurement and calculating the particle size distribution using the processed data.
Scattering type particle size distribution analyzer.