JPH0228537A - Device for measuring particle size distribution - Google Patents

Abstract

PURPOSE:To accomplish accurate measurement in the wide range of particle size by synthesizing plural light intensity distributions measured by using plural condensing lenses to one light intensity distribution with an arithmetic operation and obtaining a particle size distribution by using the synthesized light intensity distribution. CONSTITUTION:Laser light projected from a laser light source 1 irradiates a flow cell 3 through a collimator lens 2. Sample suspension 4 is made to flow in the cell 3 and the projected light is diffracted or scattered in an angle in accordance with the diameter of particle. The light intensity distribution can be detected by a photodetector 8 through three condensing lenses 5a-5c, set on the optical axis of irradiating light by a lens driving mechanism 6, whose focal distances are different from one another. After outputs from the respective photoelectric conversion elements of the photodetector 8 are respectively amplified by pre-amplifier 12, they are incorporated in a computer system 15 through a multiplexer 13 and an A/D conversion part 14. In the system 15, data from the photodetector 8 is incorporated in a RAM 153 and the particle size distribution is calculated to be displayed on a CRT 154.

Description

DETAILED DESCRIPTION OF THE INVENTION <Industrial Application Field> The present invention relates to a particle size distribution measuring device that utilizes a diffraction phenomenon or a light scattering phenomenon that occurs when particles in a dispersed state are irradiated with light.

<Prior art> A particle size distribution measuring device that utilizes the phenomenon of light diffraction or scattering by particles measures the intensity distribution of diffracted light or scattered light (the relationship between the diffraction angle or scattering angle and light intensity), and then uses Fraunhofer diffraction to measure the intensity distribution (the relationship between the diffraction angle or scattering angle and light intensity). Alternatively, the particle size distribution is calculated by performing arithmetic processing based on the theory of Mie scattering.

To measure the intensity distribution of diffracted light or scattered light, a diffraction image or scattered image is usually formed at the focal point using a condensing lens, and the light intensity distribution of the image is measured using a ring detector or a photodiode array. This is done by detecting it with a detector.

By the way, in the method of measuring particle size distribution that utilizes such a phenomenon, in general, when the particle size is lpm or more, the Fraunhofer diffraction theory is mainly used, and when the particle size is smaller than that, the light intensity distribution is calculated based on the particle size using the Mie scattering theory. In order to measure particles with large diameters, it is necessary to measure light with a small diffraction angle with high precision, and in order to measure particles with small diameters, it is necessary to measure light with a small diffraction angle It is necessary to measure light with a large angle).

Therefore, conventionally, the intensity distribution has been measured by appropriately changing the focal length of the condensing lens depending on the size of the particles to be measured. In other words, when the particle size distribution of sample particles is expected to be on the relatively small diameter side, a lens with a short focal length is used, and when the particle size distribution is expected to be on the relatively large diameter side, a lens with a long focal length is used. It is used to measure the intensity distribution.

In addition, the detector used is a ring detector, for example, with a large diameter so that a wide range of particle size distributions can be measured at once, and with a high resolution so that it can detect light with minute diffraction angles. are doing.

Furthermore, the light beam irradiated onto the sample is narrowed down to an extremely narrow beam in order to detect diffracted light at minute angles.

<Problems to be Solved by the Invention> In the method of measuring by changing the condensing lens according to the particle size of the sample particles, it is difficult to obtain high resolution according to the particle size distribution when the particle size distribution range is relatively narrow. Although measurement is possible and effective, it is not possible to measure samples with particle size distribution over a wide range.

It is possible to widen the measurement range to some extent with the above method by increasing the detection range (angle, diameter for a ring detector) of the detector or narrowing down the luminous flux, but both have limits in terms of accuracy. Moreover, the cost is also high.

An object of the present invention is to provide a particle size distribution measuring device that can measure samples with a wide range of particle size distributions with high precision without using a detector with a large detection range.

Means for Solving the Problems> In order to achieve the above object, the present invention includes a plurality of condensing lenses having different focal lengths, and measures the light intensity distribution using each of the condensing lenses. In addition, a calculation means is provided for combining the obtained plurality of light intensity distributions into one light intensity distribution by a correction calculation, and the particle size distribution is calculated from the combined light intensity distribution.

Effect> As shown in Fig. 3, the condensing lens 5 with a short focal length
If diffracted light (scattered light) is focused using a, the distribution of light at large angles can be measured with high precision, but the resolution of the distribution of light at small angles is low. Conversely, if the light is focused using the focusing lenses 5b to 5C having a long focal length, the distribution of light at small angles can be measured with high resolution, but the light at large angles cannot be measured.

When diffracted light (scattered light) is focused on the detector 8 using each of the focusing lenses 5a to 5C and its intensity distribution is measured, the measurement results are shown in FIGS. The obtained light intensity distribution measurement results make effective use of the detection ability of the detector 8 in the angular range corresponding to the focal length of each of the condensing lenses 5a to 5C, and these results are, for example, Mutual strength at angles ψ2 and ψ3 ■
, 2 and ■, 2 degrees, and Ibff and Ic3 are corrected and synthesized so that they match, a high-resolution light intensity distribution can be obtained over a wide angle range of O to ψ1.

<Example> FIG. 1 is a block diagram of an embodiment of the present invention.

A laser beam emitted from a laser light source 1 is converted into a parallel beam having a predetermined cross section by a collimator lens 2 and is irradiated onto a flow cell 3 .

A sample suspension 4 in which sample particles are dispersed in a medium is flowing inside the flow cell 3, and the irradiated light is diffracted or scattered at an angle depending on the diameter of the particles.

At the rear of the flow cell 3, three condensing lenses 5a, 5b, and 5C having mutually different focal lengths are selectively arranged. That is, each of the condensing lenses 5a to 5c is
The lens driving mechanism 6 is configured to selectively set one of them on the optical axis of the irradiated light.

The lens drive mechanism 6 includes a rack 61 that supports each of the lenses 5a to 5C and is movable, and a pinion gear 62 that meshes with the rack 61. The monitor 63 is configured to include a motor 63 that rotates the pinion gear 62, and the like, and the monitor 63 is driven based on instructions from a computer system 15, which will be described later.

Here, a protrusion 64 is formed on the rack 61, and along the moving direction of the rack 61, each lens 5a,
Position detectors 7a, 7b and 7C are arranged at a pitch corresponding to the arrangement pitch of 5b and 5c. The computer system 15 detects each detector 7 by the projection 64 arriving at the position where the position detector 7a, 7b or 7c is disposed.
It is configured to detect that each condensing lens 5a, 5b, or 5c is located on the optical axis by a detection signal output from a, 7b, or 7C.

Now, the intensity distribution of the light focused by any one of the focusing lenses 53 to 5C is detected by the photodetector 8 positioned at the focusing surface, that is, the focal position of the used lens.

The photodetector 8 is a so-called ring detector in which, for example, a plurality of photoelectric conversion elements each having a ring-shaped light-receiving surface having different radii are arranged concentrically around the optical axis, and the diffraction (scattering) angle Since large light enters the outer element and small light enters the inner element, the output of each element represents a light intensity signal for each diffraction (scattering) angle, and based on this, the intensity of the diffracted (scattered) light is calculated. distribution can be obtained.

Further, the photodetector 8 is supported on a cart 9 that is displaced by a detector drive mechanism 10 in order to move it to each of the above-mentioned focal positions.

The detector drive mechanism 10 includes a guide 101. It is composed of a wire 102, pulleys 103 to 106, and a motor 107. The guide 101 carries a cart 9 and extends in the optical axis direction, and a wire 102 is connected to the cart 9. This wire 102 is tensioned by pulleys 103-106,
It is driven by a motor 107 via a pulley 103. The motor 107 is driven and controlled based on instructions from the computer system 15. Protrusion 9 on trolley 9
1 is provided, and position detectors 11a, llb, and llc are provided along the guide 101 at positions corresponding to the focal positions of the respective condensing lenses 5a, 5b, and 5c. The computer system 15 includes a position calculator 11a, flb or 1. Protrusion 91 at the location of lc
The arrival of each detector 11a, llb or l
It is configured to detect that the photodetector 8 is located at the focal position of each of the condensing lenses 5a, 5b, or 5C based on the detection signal output from the lc.

The output of each photoelectric conversion element of the photodetector 8 is amplified by a preamplifier 12-12, and then sequentially guided to an A-D converter 14 via a multiplexer 13, where it is digitally converted and input into a computer system 15. It will be done.

The computer system 15 includes a CPU 151° ROM 1
52. In addition to the RAM 153, a CPU 151 that displays particle size distribution measurement results, etc. It is equipped with a keyboard 155 for inputting measurement conditions, system startup commands, etc., and an input/output interface 156 for connecting with various external devices, and based on the program written in the ROM 152,
Data from the photodetector 8 is stored in the RAM 15 while controlling each part.
3, the particle size distribution can be calculated and displayed on the CRT 15.

FIG. 2 is a flowchart showing the gist of the contents of the program written in the ROM 152, and the operation will be explained below with reference to this diagram.

When a start command is given after setting measurement conditions, etc., first, the condensing lens 5a is selected and positioned on the optical axis.

At the same time, the photodetector 8 is positioned on the focal point of this lens 5a. In this state, light intensity distribution data from the photodetector 8 is collected and stored in the RAM 153.

Next, the condensing lens 5b is positioned on the optical axis by driving the motor 62, and the photodetector 8 is positioned at the focal point of the lens 5b by driving the motor 107. In this state, light intensity distribution data is similarly collected and stored in the RAM 153.

Thereafter, the condensing lens 5c is further selected, and with the photodetector 8 positioned at the focal position of this lens 5C, light intensity distribution data is similarly collected and stored in the RAM 153.

The three types of light intensity distribution data obtained through the above operations are combined into one light intensity distribution by a correction calculation. The synthesis method is shown below.

FIG. 3 is a diagram showing changes in the relationship between the diffraction (scattering) angle and the image height (radius of arrival of light on the detection surface) due to differences in the focal lengths of the condensing lenses 5a to 5C.

As shown in the same figure (al), a lens 5a with a short focal length
When using , the light at an angle of ψ1 is projected on the photodetector 8 at a position rl, and the light at an angle ψ2 is projected at the same position < rat. On the other hand, if a lens 5b with a longer focal length is used as shown in FIG. It is projected onto the vessel 8. If a lens 5C with an even longer focal length is used, as shown in the same figure (C1),
The light at the small angle ψ3 is projected onto the position Tc3, and the light at the angle O to ψ3 is magnified and enters the photodetector 8.

FIG. 4 shows an example of a graph representing the light intensity distribution measurement results obtained using each of the condensing lenses 58 to 5C as described above. In this figure, (al, (b) and ゛(C)
1 shows the light intensity distribution when the same sample was measured using condensing lenses 5a, 5b, and 5C, respectively. (
The distributions between 0-911□ and O~ψ in Figure 81 have been expanded to become (b1 diagram and +01 diagram).In other words, (intensity 1.! in Figure 81) +
The intensity tbz in figure b1 is the same angle ψ2
Since the light is the same, the intensity should be equal, so
For example, if the sensitivity of the photodetector 8 is corrected (taking into account the sensitivity of the photodetector 8 so that the values of ■ and t in the bJ diagram are equal to The data of ψ2 to ψ in the (b) diagram can be connected. Furthermore, since ψ in the (b) diagram and ψ3 in the (C1 diagram) are also lights at the same angle, Ib3 and Tc3 have the same value. By correcting the entire data in Figure (C1) in the same way so that ■. in Figure +01 becomes equal to Ib3 in Figure (b1) after the above correction, (Figure 81, (b) and (C1 It becomes possible to connect the data of ψ, ψ2, ψ2 to ψ3, and ψ3 to O in the figure, and three types of data can be combined into one light intensity distribution data.

The light intensity distribution data thus synthesized is then converted into a particle size distribution and displayed on the CRT 155.

The conversion method to particle size distribution is known, and an outline thereof is shown below.

The light intensity distribution with respect to the diffraction (scattering) angle is l(ψ).

The particle size distribution function is f(D), and the diffraction per unit particle amount calculated theoretically from the Fraunhofer or Mie equation (
If the intensity of the scattered (scattered) light is K(ψ, D), the relationship between the diffracted (scattered) light and the particle size distribution is! (ψ) =j':'K (ψ
, D)・f (D) dD−...(]).

Now, it is assumed that the intensity distribution of diffracted (scattered) light is measured by a finite m number of photoelectric conversion elements, and that the particle size distribution also has a finite range and is divided into n parts, each of which has a division interval of 1.
Assuming that the particle size is represented by one particle size, equation (1) can be approximated as follows. Since this equation (2) is linear, when expressed as a vector and a matrix, it becomes J=Af (3). Solving this for f, f= (A'A)-'A' J----- (4)
becomes. Note that here, A is a coefficient matrix based on K (a, D), A' is a transposed matrix, and ()-' is an inverse matrix.

Using this equation (4), the particle size distribution f can be determined from the measurement results of the light intensity distribution l. In the embodiment of the present invention, the above-mentioned combined light intensity distribution data is used as l.

Since the light intensity distribution obtained by synthesis includes light intensity information in a wide angle range from ψ1 to around 0° with high resolution, the obtained particle size distribution also has a correspondingly high resolution and can be used to analyze fine particles. It has a wide particle size range up to coarse particles.

Incidentally, in order to achieve such measurement results using light intensity distribution data from a single lens as in the past, the resolution of the photodetector 8 must be extremely high. That is, for example, to achieve this using the lens 5a shown in FIG. It is necessary to arrange a large number of elements.In other words, it is necessary to have the same performance as the element group between 0 and rb2 in FIG. 3(b) between 0 and r and z. or (C)
When using the lens 5b or 5c shown in the photodetector 8
needs to be extremely large, both of which are unrealistic.

In addition, in the above embodiment, an example was shown in which three condensing lenses were provided, but the number may be any number greater than or equal to two, and the order of the lenses used may be arbitrary. Of course. Further, changing the lens and moving the photodetector do not need to be performed automatically, and may be configured to be manually positioned by the measurer. Furthermore, as the photodetector, in addition to a ring detector, a photodiode array may be used, or a method of scanning a photomultiple may also be used.

<Effects of the Invention> As explained above, according to the present invention, a plurality of light intensity distributions measured using each of a plurality of condensing lenses are combined into one light intensity distribution by calculation, and after the combination, Since the particle size distribution is determined using the light intensity distribution, it is possible to measure the light intensity distribution with high resolution over a wide angular range, and therefore, it is possible to obtain a highly accurate particle size distribution over a wide particle size range. Moreover, there is no need for a detector with a large measurement range (large light-receiving area) or a detector with high positional resolution, and the above effects can be achieved without increasing costs.

[Brief explanation of the drawing]

FIG. 1 is a configuration diagram of an embodiment of the present invention, FIG. 2 is a flowchart showing the contents of the program written in the ROM 152, and FIG. 3 is a diffraction ( FIG. 4 is a graph showing an example of measuring the light intensity distribution using each of the condensing lenses 5a to 5C. 1...'...Laser light source 2...Collimator lens 3...
...Flow cell 4...Sample suspension 5a, 5b, 5c...Condensing lens 6...Lens drive mechanism 8... ...Photodetector 10...Detector drive mechanism 13...Multiplexer 14...A-D converter

Claims (1)

[Claims] In a device that measures the intensity distribution of diffracted light or scattered light obtained by irradiating sample particles dispersed in a medium with a parallel light beam, and calculates the particle size distribution of sample particles from the measurement results, multiple devices with different focal lengths are used. Equipped with a condensing lens,
Each of the plurality of condensing lenses is used to condense the diffracted light or scattered light and the intensity distribution thereof can be sequentially measured. What is claimed is: 1. A particle size distribution measuring device, comprising a calculation means for combining the intensity distribution measurement results of 1 to 1 into a single intensity distribution by a predetermined correction calculation, and configured to calculate a particle size distribution from the combined intensity distribution.