JP2001330551A - Particle measuring instrument - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a particle measuring instrument capable of highly accurately measuring the sizes of individual particles on a one-by-one basis without conducting calibration in particular, with a wide measurement range and with high resolution. SOLUTION: A measurement optical system (a condensing lens 3, a ring detector 4, a photomultiplier 5 for sideway scattering light detection, and a photomultiplier 6 for backward scattering light detection) is disposed to measure the space intensity distribution of diffracted/scattered light obtained by irradiating one particle in a flow cell 2 with a laser beam. A computation means (computer 11) is provided for finding the size of the particle from the intensity distribution of diffracted/scattered light. The diameter of the particle is found based on Mie's theory of scattering or Fraunhofer's theory of diffraction by using the refraction factor of the measured particles and that of a medium with the particles dispersed. This enables particle diameters to be measured with a wide measurement range and with high resolution.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a particle measuring device, and more particularly, to a particle measuring device capable of determining the size of individual particles in a suspension or aerosol one by one.

[0002]

2. Description of the Related Art As a device for detecting the presence or absence of particles in a liquid or a gas and for determining the size of each particle, devices such as a particle counter and a dust counter are known. I have.

In this type of apparatus, generally, a suspension or aerosol containing particles to be measured is flowed into a sample cell, and the flow is irradiated with laser light, and the flow is converted into a sheath flow or a fine flow. By
A sample is traversed in the irradiated laser light one by one, and a set of light-collecting optical system and an optical sensor are arranged close to the sample cell, for example, on the side in the traveling direction of the laser light. Then, by detecting the scattered light of the laser light by the particles to be measured, the presence of the particles is detected, or the size of the particles is detected. In addition, in order to improve the detection accuracy, one set of condensing optical systems and optical sensors are arranged on each side on both sides with respect to the traveling direction of the laser light,
Alternatively, a pair of condensing optical systems and optical sensors are arranged one by one in front and rear besides the side, and the presence and size of particles are similarly detected using the sum and average value of each sensor output. Also known are those described in, for example, JP-A-63-1953.
No. 6, JP-A-61-35335).

[0004]

In the above-mentioned conventional particle counter, etc., since the intensity of scattered light is simply measured, the structure is simple and inexpensive, but the particle size is small. Is to determine the approximate size of the particles on the assumption that it is correlated with the sum of the detected intensities of scattered light by one or at most two or three optical sensors placed at appropriate places. For particles having a particle resolution of 10 μm or more, there is almost no resolution of the particle diameter, furthermore, calibration is required, and for particles different from the particles used for calibration, However, there is a problem that the reliability of the measurement result is low.

The present invention has been made in view of such circumstances, and it has been found that the size of each individual particle can be measured over a wide measurement range and with high resolution without performing calibration. Another object of the present invention is to provide a particle measuring device capable of measuring with high accuracy.

[0006]

In order to achieve the above object, a particle measuring apparatus according to the present invention comprises a flow cell for passing a suspension or aerosol in which particles to be measured are dispersed in a liquid or a gas. A laser light irradiation optical system for irradiating the particles in the flow cell with laser light, a measurement optical system for measuring the spatial intensity distribution of diffraction / scattered light obtained from one particle by the irradiation of the laser light, and the measurement thereof It is characterized by having an arithmetic means for obtaining the size of the particle from the spatial intensity distribution of the diffracted / scattered light obtained by the optical system.

The present invention does not determine the size of a particle from the intensity of the scattered light obtained by irradiating the particle with laser light, but the spatial intensity distribution of the diffracted and scattered light by one particle is Mie scattering. By utilizing the theory or the Fraunhofer diffraction theory, the size of each particle is obtained from the spatial intensity distribution pattern of the diffracted / scattered light, thereby achieving the intended purpose.

That is, Mie's scattering theory or Fraunhofer diffraction theory is that the pattern of the spatial intensity distribution of the diffraction / scattered light by a particle depends on the particle size of the particle. This is the theory applied to the device. In this laser diffraction / scattering particle size distribution measuring device, the particles to be measured are dispersed in a medium or gas to form a suspension or an aerosol,
The spatial intensity distribution of the diffracted / scattered light obtained by irradiating the suspension or the aerosol with laser light, that is, the diffracted / scattered light by a plurality of particle groups is measured. And from the measurement result of the spatial intensity distribution of the diffraction and scattered light,
The particle size distribution of the particle group is obtained by calculation based on Mie's scattering theory or Fraunhofer diffraction theory. In a laser diffraction / scattering type particle size distribution measuring apparatus to which Mie's scattering theory or Fraunhofer diffraction theory is applied, if the refractive index of a medium (liquid or gas) and a particle to be measured is known, the spatial intensity distribution of the diffracted / scattered light is determined. An accurate particle size distribution can be obtained from the measurement results.

According to the present invention, instead of the particle size distribution of the particle group, the individual size of the particle is determined from the spatial intensity distribution of the diffracted / scattered light obtained by irradiating each particle with laser light. If the refractive index of the particle to be measured and the refractive index of the liquid or gas in which the particle is dispersed are known, the size of the particle can be determined from the spatial intensity distribution of diffraction / scattered light by the particle. Can be calculated accurately, and the particle size can be calculated using simpler calculations than the calculation using matrix calculation in a laser diffraction / scattering type particle size distribution analyzer in which the spatial intensity distributions of diffraction / scattered light from multiple particle groups overlap. Can be accurately determined.

According to the particle measuring apparatus of the present invention, the size of the particle is not determined from the magnitude (pulse height) of the detection signal of the scattered light as in the prior art, but the spatial intensity of the diffracted / scattered light is used. Since the particle diameter is determined from the distribution pattern, there is also an advantage that the particle diameter is hardly affected by fluctuations of the light source and sensitivity drift of the sensor.

[0011]

Embodiments of the present invention will be described below with reference to the drawings. FIG. 1A is a block diagram showing a configuration diagram of an embodiment of the present invention, and FIG.
3 is a schematic front view of the ring detector 4. FIG. The laser light source 1 includes, for example, a semiconductor laser, a condenser lens, a collimator lens, and the like, and can irradiate the flow cell 2 with parallel laser light. This laser light source 1
Has a large output compared to that used in a laser diffraction / scattering type particle size distribution analyzer, and is considered so that even a single particle will have a certain degree of intensity of diffraction / scattered light from it. I have.

The flow cell 2 is made of an optically transparent material, and has a flow path orthogonal to the optical axis of the laser light from the laser light source 1. Is flowed at a relatively low concentration of the suspension. Here, the inner diameter dimension forming the flow path of the flow cell 2 is very small, and the flow is made into a sheath flow as necessary, so that the laser light emitted from the laser light source 1 can be simultaneously irradiated with two or more particles. Is designed not to cross.

On the opposite side of the flow cell 2 from the laser light source 1, a ring detector 4 is disposed on the optical axis of the irradiated laser light via a condenser lens 3. As shown in FIG. 1B, the ring detector 4 has a plurality of light-receiving surfaces P, which are ring-shaped or semi-ring-shaped or have quarter-rings and have different radii, and are arranged concentrically. It is a light detector. Therefore, the ring detector 4 receives, through the condenser lens 3, diffracted and scattered light within a predetermined angle range in front of the particles in the flow cell 2, and outputs related to the amount of light incident on each light receiving surface. After being amplified and digitized by the data sampling circuit 10 having the corresponding amplifier and A / D converter,
Captured by the computer 11.

A photomultiplier tube 5 for measuring the side scattered light and a photomultiplier for measuring the back scattered light are provided at an appropriate angle to the side and the rear (the laser light source 1 side) of the flow cell 2. A tube 6 is arranged. These photomultiplier tubes 5 and 6 have slits S arranged on their light incident surfaces, and this sensor configuration detects weak side scattered light and back scattered light by one particle with high sensitivity. be able to. The outputs of the photomultiplier tubes 5 and 6 for detecting these side and back scattered light are also amplified and digitized by the sampling circuit 10, and then taken into the computer 11.

The data of the amount of light incident on each light receiving surface of the ring detector 4 and the data of the amount of light incident on the photomultiplier tube 56 for detecting the side scattered light and the back scattered light are diffracted by one particle as a whole. It represents the spatial intensity distribution of the scattered light. Here, the data sampling circuit 10 amplifies and digitizes the output related to the amount of light incident on each light receiving surface of the ring detector 4 and the output of the side scattered light sensor 5 and the back scattered light sensor 6 at minute intervals. In the computer 11, while one particle traverses the laser beam, each light amount measurement data is integrated,
The spatial intensity distribution of the diffraction / scattered light by one particle is obtained. This is because the irradiation laser light has a spatial intensity distribution and, when the particles are not spherical, a pattern different from the diffraction / scattering theory is exhibited, so that these effects are reduced.

The computer 11 determines the size of the particle from the spatial intensity distribution of the diffracted / scattered light obtained as described above. This method can be obtained from Mie's scattering theory or Fraunhofer diffraction theory without calibration if the refractive index of the medium and the refractive index of the particles to be measured are known in advance. More specifically, when the above-mentioned respective refractive indices are known, the angle of the first peak of the spatial intensity distribution of the diffracted / scattered light, that is, in the spatial intensity distribution pattern of the diffracted / scattered light, The angle at which the first peak is seen from the smaller side correlates with the particle size. The relationship between the angle of the first peak and the particle diameter must be accurately determined in advance by a calculation based on the well-known Mie scattering theory or Fraunhofer diffraction theory if the refractive indices of the medium and the particles to be measured are known. Can be. Therefore, in the computer 11, every time one particle crosses the laser beam, the size of the particle can be obtained with high resolution from the spatial intensity distribution data of the diffracted / scattered light. The determined size of each individual particle is displayed on the display 12.
, And can be printed on the printer 13.

Here, in the above embodiment, 1
In order to measure the spatial intensity distribution of the diffracted / scattered light by the individual particles, the output power of the laser light source 1 is increased compared to that used in the laser diffraction / scattering type particle size distribution measuring device, and the ring detector is used. 4 enables measurement of forward diffracted and scattered light, and for side and back scattered light weaker than forward diffracted and scattered light, photomultiplier tubes 5 and 6 provided with slits S are used. Although the measurement is possible, if the output power of the laser light source 1 cannot be increased due to the type of the particle to be measured, forward diffraction / scattered light can also be measured using a photomultiplier tube. Good. In this case, since the photomultiplier tube cannot arrange individual light receiving surfaces close to each other like a ring detector, it is necessary to use the following optical system. FIG. 2 schematically shows an example of the configuration.

In the example of FIG. 2, forward diffracted and scattered light from particles to be measured in the flow cell 2 is diffused by the diffusing lens 21. Then, in front of the diffusion lens 21 in the traveling direction of the laser beam, different distances from the optical axis are provided around the optical axis of the diffusion lens 21, and therefore, at positions of different diffraction and scattering angles, A plurality of photomultiplier tubes 22a, 22b,... Are arranged, and each of the photomultiplier tubes 22a, 22b, ... has an arc shape having a radius equal to the distance from the optical axis of the diffusion lens 21. Slit RS
Attach. With such a configuration, the diffusion lens 21
Are arranged concentrically with respect to the optical axis of the center, and light passing through each slit RS is detected by each of the photomultiplier tubes 22a, 22b,.... .

According to the above configuration, the forward diffracted / scattered light measured by the condenser lens 3 and the ring detector 4 in the above example is spatially spread by the diffusion lens 21 and then arranged on a concentric circle. Through the arc-shaped slits RS having different radii from each other.
.., and can be measured with high sensitivity without increasing the output power of the laser light source 1.

Further, in the above embodiment, an example was shown in which the suspension in which the particles to be measured were dispersed in the medium was irradiated with laser light, but the present invention is not limited to this.
Of course, the particles to be measured may be dispersed in a gas to form an aerosol, and the aerosol may be irradiated with a laser beam to measure the diffraction and scattered light from the particles to be measured.

[0021]

As described above, according to the present invention, the spatial intensity distribution of the diffracted / scattered light obtained by irradiating the individual particles flowing in the state of a suspension or aerosol in the flow cell with laser light is obtained. One or two or three optical sensors arranged at appropriate positions such as a conventional pulse counter to measure the particle size from the intensity distribution based on Mie's scattering theory or Fraunhofer diffraction theory Compared to the case where the size of the particle is obtained from the sum of the intensity detection results of the scattered light, not only the resolution of the particle diameter is remarkably improved, but also the refractive index of the particle to be measured and the medium is known. Thus, an accurate particle size can be obtained in a wide particle size range without performing calibration.
As a result, it has become possible to detect biological particles such as algae and fungi that could not be detected by the conventional particle counter.

[Brief description of the drawings]

FIG. 1A is a block diagram showing a configuration of an embodiment of the present invention, and FIG. 1B is a schematic front view of a ring detector 4 thereof.

FIG. 2 is a schematic view showing a configuration of an optical system for measuring forward diffraction and scattered light according to another embodiment of the present invention.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Laser light source 2 Flow cell 3 Condensing lens 4 Ring detector 5 Photomultiplier tube (for side scattered light detection) 6 Photomultiplier tube (for backscattered light detection) 10 Data sampling circuit 11 Computer 12 Display 13 Printer 21 Diffusion Lens 22a, 22b ··· Photomultiplier tube P Light receiving surface S Slit RS Arc-shaped slit

Claims (1)

[Claims] 1. A flow cell through which a suspension or aerosol in which particles to be measured are dispersed in a liquid or a gas passes therethrough, a laser light irradiation optical system for irradiating the particles in the flow cell with laser light, and the laser light. Measurement optical system that measures the spatial intensity distribution of diffracted and scattered light obtained from a single particle by irradiation of light, and determines the size of the particle from the spatial intensity distribution of diffracted and scattered light obtained by the measuring optical system A particle measuring device comprising a calculation means.