JPH0224533A - Apparatus for measuring distribution of grain size - Google Patents

Abstract

PURPOSE:To reduce measuring errors by selecting a conversion coefficient which is suitable for measuring conditions among a plurality of conversion coefficients which are computed based on a plurality of relative refractive indexes beforehand, and computing the distribution of grain sizes. CONSTITUTION:Laser light emitted from a laser light source 1 is magnified through a collimator lens 2. The parallel luminous flux of the laser light is projected on a flow cell 3. The incident light beams inputted into the same element of a detector 6 are only the light beams whose scattering angles are very close. The output signal from each element represents the light intensity signal for every scattering angle. The distribution of the scattering light intensities is obtained form the output signal from every element. An operating part sends the digital conversion data of the distribution of the scattering light intensities from the detector 6 into a RAM 13. The distribution of the grain sizes of specimen grains is computed by using a converting expression which is written in a ROM 12. A selecting switch 16 is operated before the measurement. The optimum coefficient is selected out of a plurality of conversion coefficient matrixes A within the ROM 12 in correspondence with the actual relative refractive index between the grains to be measured and a medium.

Description

DETAILED DESCRIPTION OF THE INVENTION <Industrial Application Field> The present invention relates to a particle size distribution measuring device based on the so-called light scattering method, which utilizes the light scattering phenomenon that occurs when particles are irradiated with light.

<Prior art> Conventionally, most of the devices that measure the particle size or particle size distribution of a sample by irradiating particles in a medium with a parallel light beam and utilizing the diffraction or scattering phenomenon of light by the particles are based on the Fraunhofer diffraction phenomenon. . When determining particle size using this diffraction phenomenon, it is theoretically difficult to measure on the submicron order of 1 μm or less. Therefore, scattering theory (Mie's theory) is used to measure samples with such small particle sizes.

By the way, in Mie's theory, in order to determine the relationship between the intensity distribution of scattered light (the relationship between the scattering angle and the light intensity) and the particle diameter, the relative refractive index of the medium and the particle is required. Therefore, M i
Conventional measurement devices using e-theory either fix this refractive index to an average value in advance and calculate the particle size distribution from the scattered light intensity distribution, or the measurer inputs the refractive index and then inputs the refractive index. Either method is used to calculate the particle size distribution using the refractive index obtained.

<Problems to be Solved by the Invention> Among conventional apparatuses that employ a method in which the refractive index is fixed at an average constant value, it is natural that the refractive index of the sample particles varies depending on the apparatus. There is a problem that accurate measurements cannot be made if there is a large difference from a fixed value.

On the other hand, those that use a method that allows the measurer to input the refractive index do not have the above-mentioned problem, but the M
The theoretical formula for ie is extremely complicated, and if the particle size distribution was calculated from the step of substituting the refractive index, the calculation would take a considerable amount of time, resulting in a long measurement time. Furthermore, a high-performance computer is required to be attached to the device, which increases the cost.

The present invention has been made in view of these points, and aims to provide a particle size distribution measuring device that can perform measurements in a short time without using a high-performance computer, and has less measurement error.

<Means for Solving the Problems> In order to achieve the above object, the present invention provides a storage means for storing a plurality of conversion coefficients obtained in advance using a plurality of relative refractive indices, and A selection means for selecting any one of them is provided, and the scattered light intensity distribution is converted into a particle size distribution using the selected conversion coefficient.

Particle size distribution is calculated using a conversion coefficient determined in advance based on Mie's theory, and the measuring device itself is
Complex calculations based on IE theory can be omitted.

Here, the conversion coefficient to be used can be selected from a plurality of conversion coefficients obtained using a plurality of relative refractive indices, so that the operator can select the most appropriate one according to the sample to be measured during measurement. This makes it possible to reduce errors.

<Embodiment> FIG. 1 is a block diagram of an embodiment of the present invention, and FIG. 2 is a front view of the light-receiving surface of the detector 6.

Laser light emitted from a laser light source 1 is expanded by a collimator lens 2 and is irradiated onto a flow cell 3 as a parallel beam of light.

A suspension 4 in which sample particles are dispersed in a medium is flowing inside the flow cell 3, and the irradiated laser light is scattered by the particles.

A lens 5 is disposed behind the flow cell 3, and a detector 6 is disposed further behind the lens 5 at its focal position, and these measure the intensity distribution of light scattered by particles. .

That is, as shown in FIG. 2, the detector 6 has a plurality of photo-electrical conversion elements concentrically arranged around the optical axis of the irradiated laser beam and each having a half-ring-shaped light-receiving surface with a different radius. This is a so-called ring detector. As shown in FIG. 3, the light scattered by the particles has the same scattering angle ψ and is incident on the detector 6 at the same radius r by the action of the lens 5.

Therefore, the light incident on the same element of the detector 6 is lost.

There is only light with very close scattering angles, and the output signal from each element represents a light intensity signal for each scattering angle, and the scattered light intensity distribution can be obtained from the output signal for each element.

The output signals from each element of the detector 6 are guided to the A-D converter 9 via the preamplifiers 7...7 and the multiplexer 8, where they are sequentially converted into digital signals, and then sent to the arithmetic unit via the input/output interface 10. be included.

The calculation unit is mainly composed of a computer system equipped with CPU II, R2M17, RAM13, etc.
The digital conversion data of the scattered light intensity distribution by the detector 6 is stored in the RAM 13, and the particle size distribution of the sample particles is calculated using the conversion formula written in the ROM 12, which will be described later. , that is, multiple conversion coefficients are written.

The computer system includes a printer 14 and a CRT.
15 and a selection switch 16 for selecting any one of the plurality of conversion coefficients in the ROM 12. Then, the CPU I f is configured to convert the scattered light intensity distribution data taken into the RAM 13 into a particle size distribution using the conversion coefficient selected by the selection switch 16, and output the result to the printer 14 or CRT 15. ing.

Next, a method of converting the scattered light intensity distribution to the particle size distribution will be explained.

Mie's theoretical formula is as follows.

If the scattered light intensity per particle is ■, and the linearly polarized component whose vibration direction of the incident light is perpendicular to the observation plane and the linearly polarized component whose direction is parallel to the observation plane are Ih and I/, respectively, then 1= (on r +I//)/2 ... is expressed as (1), where γ is the angle between the incident angle direction and the observation direction, Po
1 is a Legendre multiplication function.

Also, in equation (2), Here, i is an imaginary unit (~r7 units).

N, , D, , N2 and D2 in equation (3) are α
If β is a particle size parameter and β is a dimensionless parameter, then

The particle size parameter α is “=2πr/λ (5) where r is the particle radius and λ is the incident light wavelength, and the dimensionless parameter β is as follows, where m is the relative refractive index. β=mα (6).

(4) In 2, , where JH5゜I7□ is a half-7 cell function.

From the above Mie theoretical formula, the light intensity I for the angle γ is:
Once the particle diameter r and relative refractive index m are determined, it can be uniquely calculated.

It is expressed as Here, D is a particle size (diameter), ψ is a scattering angle, and has a relationship with γ in Mie's equation as ψ=180′γ. In addition, 1(ψ) is the intensity distribution of the scattering angle, f (D
) is the particle size distribution. Furthermore, K (ψ, D) is the scattered light intensity per unit particle amount calculated from Mie's equation.

The range of particle size distribution is finite, the range is divided into n parts, and each divided section is represented by one particle diameter, and the intensity distribution is also measured by m elements of the detector 6. Then, equation (8) can be approximated as shown in equation (9) below.

l(ψ,)=ΣK(ψi+D,), f(D j
) ...(9) J'1 where i = 1.2...m, j = 1.2...n
It is.

Since equation (9) is linear, it can be expressed as 7=Af self...αl using vectors and matrices, and when this is solved for the particle size distribution, f = (A' A) - 'A ' 1 ・9.・0
It becomes υ.

Here, A is a coefficient matrix by K(ψ□, D,) and Mie
The formula O can be obtained by calculating the position and area of each element on the detector 6 and the diameter of each particle. If A is determined according to the measurement conditions, the scattered light intensity distribution! can be measured and immediately converted into particle size distribution f using equation (4).

In determining A from the formula of Mte, it is necessary to determine the relative refractive index m in addition to the above-mentioned device elements.

Now, in the embodiment of the present invention, a plurality of conversion coefficient matrices A are calculated in advance assuming a plurality of relative refractive indices m, and these are written in the ROM 12.

As a result, the measurer operates the selection switch 16 prior to measurement and selects the most appropriate one from among the plurality of conversion coefficient matrices A in the ROM 12 according to the actual relative refractive index between the particle to be measured and the medium. By selecting one of these, it is possible to obtain particle size distribution measurement results with less error.

The selection method using the selection switch 16 includes a method in which an actual relative refractive index is input and the CPU 11 selects a conversion coefficient calculated using a refractive index closest to that refractive index, and a method in which the CPU 1l selects a conversion coefficient calculated using a refractive index closest to the actual relative refractive index, and a method in which the names of sample particles and medium are input. By doing this, CPLIII selects a preset conversion coefficient according to the input combination, or because particle density and refractive index are correlated, by inputting the particle density, CPLIII selects the optimal conversion coefficient. In each of the above methods, the CPU II does not select the conversion coefficients based on the input information, but the measurer selects them based on a separately prepared table, etc. , it is also possible to adopt a method of directly inputting the selection results.

Figure 4 is a graph showing an example of measuring the particle size distribution by dispersing the same sample particles in the same medium and changing the refractive index used in the calculation, and also shows the measurement results by the sedimentation method (light transmission method). It is something. In this example, alumina (AltOi) was used as the sample particles and water (HtO) was used as the medium. Moreover, 1.6 and 2.0 were used as the absolute refractive index of the alumina particles (the absolute refractive index of water is 1.33, so the relative refractive index m is approximately 1.2 and 1.5).

As is clear from this example, compared to the measurement results obtained by the sedimentation method, which is assumed to be close to the true particle size distribution of the sample particles, the results using a refractive index of 1.6 show that the particle size deviates significantly to the smaller side. In contrast, the results using a refractive index of 2.0 are closer to the true particle size distribution. It should be noted here that the particles used for particle size distribution measurement are generally substances with an average absolute refractive index of about 1.6 to 1.7, and water is used as the medium. This means that there are many things to do. Therefore, it can be seen that in the conventional apparatus which fixes the relative refractive index m, a value of about 1 or 2 is adopted, and a considerable error occurs when measuring the above-mentioned sample.

In addition, in the above embodiment, the case was explained in which the lens 5 and the ring-shaped detector 6 were used as the optical system for measuring the intensity distribution of scattered light, but the present invention is not limited to this.
A photo-electric conversion element and a pick-up slot are scanned around a cylindrical flow cell without using a lens, and the intensity of light incident on the element at each scanning position is sequentially measured. A so-called scanning method or the like can also be employed.

<Effects of the Invention> As explained above, according to the present invention, a particle size distribution can be determined by selecting a conversion coefficient suitable for measurement conditions from among a plurality of conversion coefficients calculated in advance based on a plurality of relative refractive indices. Since the refractive index is configured to be able to be calculated, measurement errors can be reduced compared to conventional devices that perform calculations with the refractive index fixed at a constant value.

Moreover, since the particle size distribution is calculated using coefficients calculated in advance based on Mie's theoretical formula, the measurement (calculation) time is shortened, there is no need to use a high-performance computer, and the cost is low. It is achievable at a reasonable price.

[Brief explanation of the drawing]

Fig. 1 is a configuration diagram of an embodiment of the present invention, Fig. 2 is a front view of the light-receiving surface of the detector 6, Fig. 3 is an illustration of scattered light by particles, and Fig. 4 is particle size distribution measurement according to an embodiment of the present invention. It is a graph showing an example of the results. 1... Laser light source 2... Collimator lens 3... Flow cell 5... Lens 6... Detector 9... A-D converter 11... CPU 12... ROM 13... RAM 16... Selection switch Patent applicant: Shimadzu Corporation Agent
Patent Attorney Nishi 1) Arata

Claims (1)

[Claims] A measurement optical system that measures the intensity distribution of scattered light by the particles by irradiating the sample particles dispersed in the medium with a parallel light beam; In an apparatus equipped with an arithmetic means for calculating a particle size distribution, a storage means for storing a plurality of conversion coefficients determined in advance using a plurality of relative refractive indices, and a selection for selecting any one of the plurality of conversion coefficients. have the means,
A particle size distribution measuring device, wherein the calculation means is configured to convert the scattered light intensity distribution into a particle size distribution using a selected conversion coefficient.