JPH0640058B2 - Particle size distribution measuring device - Google Patents

Description

The present invention relates to a laser diffraction / scattering type particle size distribution measuring device.

<Prior Art> In a particle size distribution measuring apparatus using a laser diffraction / scattering method, a particle size distribution of a particle group to be measured is calculated from an intensity distribution of diffracted / scattered light generated by irradiating a particle group to be measured with laser light. Is calculated.

That is, when the particle group is irradiated with laser light, an intensity distribution pattern of diffracted / scattered light corresponding to the size of the particles included in the particle group is generated.

This light intensity distribution pattern is condensed by the lens,
A diffraction / scattering image is formed at the position of the focal length, and this image is detected by placing a ring detector in which a plurality of photo-detecting elements having light receiving surfaces having different radii are concentrically arranged at the focal position. The side scattered light is detected by a side scattered light sensor placed separately from the ring detector.

This light intensity pattern changes depending on the size of the particles, but since the actual sample contains particles with various sizes and different diameters, the light intensity patterns generated from the particle groups are different from each other. Is a superposition of the diffracted / scattered light from the particles.

If this is expressed in a matrix, Becomes

However, Are as shown below.

here Is a light intensity distribution spectrum. The element r _i (i = 1,
2, ... M) is the amount of incident light detected by each element of the ring detector and the side scattered light sensor.

Is a particle size distribution (frequency distribution%) vector. The particle size distribution range is finite, the range is divided into n, and the maximum value is d _1,
The minimum value is d _{n + 1} . Each divided section [d _j ,
[d _{j + 1} ] is represented by one particle diameter D _j (j = 1, 2, ... N). The element f of f (j = 1,2, ... n) is the particle diameter D _j
Is the amount of particles corresponding to.

Normally, normalization is performed so that Σf _j = 100 (%) (4).

Is the particle size distribution (vector) The light intensity distribution (vector) Is a coefficient matrix to be converted into.

The physical meaning of the elements a _{i, j} (i = 1,2, ... m, j = 1,2, ... n) of is the light diffracted / scattered by the particle group of the unit particle amount of the particle diameter D _j. Is the amount of incident light on the i-th element of.

The numerical value of a _{i, j} can be theoretically calculated.

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

In addition, using Mie scattering theory, In order to calculate the factor of, it is necessary to set the refractive index of the particles and the liquid medium in which they are dispersed, as described above.

Now, based on equation (1), the particle size distribution Derivation of the formula for the least squares solution of Is obtained. However, Is the transposed matrix of, and () ^-1 represents the inverse matrix.

Light intensity distribution on the right side of equation (5) Each element of is the numerical value detected by the ring detector and the side scattered light sensor, and the coefficient matrix Can be calculated in advance using Fraunhofer diffraction theory or Mie scattering theory, so if the calculation of Eq. (5) is executed using these known data, the particle size distribution can be calculated. It is clear that

The above is the basic measurement principle of the laser diffraction / scattering method, but the one shown here is an example of the calculation method of the particle size distribution, and there are various other variations. Also, there are various variations in the types and arrangements of the sensors and detectors.

<Problems to be Solved by the Invention> By the way, in the conventional particle size distribution measuring apparatus as described above, a wide measuring range (for example, 0.1 to 200 μ in one range) is used.
m), when the particle size distribution measurement is performed, if the actual distribution range of the sample particles is on the smaller side of this measurement range, for example, about 0.5 to 2 μm as shown in FIG. The larger one, for example, 150 ~
A ghost peak G, which should not exist, may appear at a particle size of 200 μm.

This is due to the detection error of the light intensity distribution and the calculation error associated with the particle size distribution calculation, but the measurement results show that such particles actually exist.

The purpose of the present invention is to eliminate such ghost peaks, for example, not a passive measure such as applying an appropriate distribution function, but using light intensity distribution to eliminate ghost peaks based on the measurement principle, Moreover, it is an object of the present invention to provide a particle size distribution measuring device capable of performing accurate and efficient particle size distribution calculation without performing unnecessary calculation due to the presence of this ghost peak.

<Means for Solving the Problems> A configuration for achieving the above object will be described with reference to the basic conceptual diagram shown in FIG. 1. According to the present invention, a laser beam L is applied to a particle group S in a dispersed state. In a device having a detection optical system a for detecting the intensity distribution of the diffracted / scattered light D generated by irradiation, and a calculation means b for calculating the particle size distribution of the particle group based on a predetermined algorithm from the intensity distribution detection result, The maximum particle size estimating means c for obtaining the size of the maximum particle existing in the particle group from the intensity distribution of the detected diffraction / scattered light is provided, and the calculating means b is estimated by the maximum particle size estimating means c from the above-mentioned algorithm. It is characterized in that the calculation is performed by excluding the part relating to the range of the particle size exceeding the maximum particle size.

<Operation> In the case of a relatively large particle having a size of 10 μm or more, it is possible to determine which element of the ring detector the peak value of the light intensity distribution pattern of a specific particle diameter corresponds to by using Fraunhofer diffraction theory. .

The maximum particle size estimating means c of the present invention estimates the presence or absence of the above-mentioned large particles from the detection result of the diffraction / scattered light intensity distribution pattern, that is, the light intensity incident on each element of the ring detector, and Based on this, when converting the light intensity distribution to the particle size distribution, unnecessary calculation of the portion corresponding to the non-existing particle diameter is not performed, so that no ghost peak appears in the calculation result, and the calculation efficiency is improved.

<Embodiment> FIG. 2 is an overall configuration diagram of an embodiment of the present invention.

An inlet and an outlet are formed in the flow cell 1 in a direction orthogonal to the paper surface, and a sample suspension in which a sample particle group is uniformly dispersed in a liquid medium is allowed to flow inside the inlet and the outlet.

On one side of the flow cell 1, a laser light source 2 and a collimator 3 for converting its output light into a parallel light flux having a predetermined cross-sectional area are arranged, and the parallel laser light passing through the collimator 3 suspends the sample in the flow cell 1. The liquid is irradiated.

A condensing lens 4 and a ring detector 5 placed on the focal plane of the condensing lens 4 are disposed on the side opposite to the laser light source 2 with the flow cell 1 interposed therebetween, and the diffraction / scattered light by the sample particles in the flow cell 1 is ring-shaped. A diffraction / scattering image is formed on the light receiving surface of the detector 5. The ring detector 5 is a concentric array of a plurality of ring-shaped optical sensors having different radii, and the light intensity of each diffraction / scattering angle is measured by each sensor. The intensity of scattered light having a large scattering angle is measured by the side scattered light sensor 6 placed on the side of the cell 1.

The output of the ring detector 5 and the output of the side scattered light sensor 6 are taken into the computer 7 via an amplifier, an AD converter, etc. (neither is shown).

In the computer 7, the particle size distribution is calculated from the interleaved / scattered light intensity distribution data by the ring detector 5 and the side scattered light sensor 6 based on the above equation (5). Before performing the calculation, the maximum particle diameter existing in the sample particle group is estimated from the diffraction / scattered light intensity distribution data as shown below. The problem here is the particle size range of 10 μm or more as described above, and this estimation is performed from the output of each sensor of the ring detector 5.

In the Fraunhofer diffraction theory, whether or not particles having a diameter of 10 μm or more can be confirmed using the following equation (6).

πDs / λf = 1.375 (6) Here, D is the particle diameter, s is the detector radius at which the peak value appears, λ is the wavelength of the irradiation laser light, and f is the focal length of the condenser lens 4.

That is, first, it is determined whether or not each sensor output data of the ring detector 5 exceeds a certain threshold value (0 or a detection error range). Then, the sensor radius of the output below this threshold and the outermost (maximum radius) sensor radius is s
Then, the particle diameter D corresponding to it is determined using the equation (6). Accordingly, it can be considered that there are no large particles having a particle diameter D or more.

That is, it is theoretically calculated that the peak value of the light intensity distribution pattern of the w-th largest particle (particle diameter D _W ) appears at the position of the detector radius corresponding to the v-th sensor from the inside of the ring detector 5. be able to. Then, when the light intensity incident on the vth sensor from the inside is 0 or within the detection error range, it is estimated that there are no particles in the particle size range (D _{1 to} D _w ) from the largest to the wth. it can.

Considering this estimation result, equation (1) becomes Becomes

However, Are as shown below.

Is. Therefore, the formula for converting the diffraction / scattered light intensity distribution into the particle size distribution is Can be

By using the equation (10), the ghost peak can be removed, and at the same time, the dimension of the matrix and the vector is smaller than that of the equation (5), so that the calculation time is shortened.

<Effects of the Invention> As described above, according to the present invention, the diffraction of particle groups /
From the scattered light intensity distribution data, estimate the maximum particle size of the particles that exist in the particle group, and based on the estimation result, remove the part for the nonexistent particles from the calculation formula for calculating the particle size distribution, and perform the calculation. Since it is performed, even if the particle size distribution of the sample particles is unevenly distributed in the smaller one, the ghost peak does not appear in the larger one as in the past, and the calculation for unnecessary parts is excluded, so the calculation time is reduced. It is possible to shorten the time or improve the calculation accuracy by using the same calculation time.

[Brief description of drawings]

 FIG. 1 is a basic conceptual diagram showing the configuration of the present invention, FIG. 2 is an overall configuration diagram of an embodiment of the present invention, and FIG. 3 is an explanatory diagram of a ghost peak. 1 ... Flow cell 2 ... Laser light source 3 ... Collimator 4 ... Condensing lens 5 ... Ring detector 6 ... Side scattered light sensor 7 ... Computer

Claims (1)

[Claims] 1. A detection optical system for detecting an intensity distribution of diffracted / scattered light generated by irradiating a dispersed particle group with a laser beam, and a particle size of the particle group based on a predetermined algorithm from the intensity distribution detection result. An apparatus having an arithmetic means for calculating a distribution comprises a maximum particle diameter estimating means for determining the size of the maximum particle existing in the particle group from the intensity distribution of the detected diffracted / scattered light, and the arithmetic means comprises the algorithm described above. The particle size distribution measuring apparatus is configured to perform the calculation by excluding a portion related to a particle diameter range exceeding the maximum particle diameter estimated by the maximum particle diameter estimating means.