JP3301658B2 - Method and apparatus for measuring particle size of fine particles in fluid - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method and an apparatus for measuring the particle size of fine particles in a fluid. More specifically, a novel method capable of detecting fine particles present as an insoluble substance in a test fluid such as pure water or ultrapure water and measuring the particle size, and an apparatus for performing the method. Regarding the configuration.

[0002]

2. Description of the Related Art As a method of detecting fine particles in a fluid, there is a method of detecting light attenuation due to a shadow of fine particles passing on the optical axis of a parallel light beam, and a method of detecting fine particles collected from a test fluid by filtering with a membrane filter. A method of observing with an electron microscope, a method of irradiating a test fluid with light and converting scattered light generated by fine particles into an electric signal by a photomultiplier tube or the like have been proposed,
It has also been implemented.

[0003] Among the various methods described above, the first method has a detection limit of about 1 µm and cannot detect submicron particles. The second method takes more than half a day for one observation work,
It is not suitable for practical use in manufacturing sites. Third
The method requires a large-sized high-power laser and a high-sensitivity photodetector such as a photomultiplier tube, so the size of the device becomes huge and it must be extremely expensive. Technology is required.

As described above, expensive and precise equipment is required for detecting submicron particles, and its operation is not easy. However, there is an increasing need for fine particle detection technology in many fields, such as industrial use of ultrapure water instead of chlorofluorocarbon in consideration of environmental protection.

On the other hand, the present applicant has proposed, as Japanese Patent Application No. 4-56418, a completely novel particle detection method and apparatus which can detect ultrafine particles with an extremely simple configuration based on a new principle. I have.

Generally, a parallel beam exhibits Fraunhofer diffraction due to the presence of fine particles in the beam. Here, "diffraction" is defined as "a general term for various phenomena that cannot be explained by the straightness of light", and is described by the Huygens-Fresnel principle in which light is a wave. However, Fraunhofer diffraction is a phenomenon that occurs when the radius of the fine particles is larger than the wavelength of light. When the radius of the fine particles is smaller than the wavelength of light, the diffraction angle increases and interference cannot occur with a parallel beam, so scattering occurs. Is treated as

That is, according to the Fraunhofer diffraction theory based on parallel light, the spread angle Δθ due to diffraction when the light shield is a fine particle is Δθ = 1.22λ with respect to the fine particle diameter D = 2r.
/ D. Therefore, as the diameter of the light-shielding fine particles becomes smaller, the spread angle Δθ becomes larger, and when D = 0.78λ, the spread angle Δθ becomes 90 degrees. This divergence angle is considered to be the limit of the detection of fine particles by diffraction, and actually, a diffraction image of fine particles having a particle size of 0.52 μm or less with respect to the incident wavelength λ = 0.67 μm cannot be easily obtained experimentally.

On the other hand, in the method proposed in Japanese Patent Application No. 4-56418, when fine particles are present near the focal point of a focused light beam focused by a focusing lens, the particle size is smaller than the wavelength of light. It utilizes the phenomenon that the diffraction angle becomes small even for fine particles and an observable diffraction image is generated. in this way,
It was confirmed that a diffraction image of particles having a particle size of 0.1 μm, which was conventionally difficult, was obtained. Also, this method has a particle size of 0.1μ
Needless to say, it is effective for fine particles of m or more. Further, this method has an extremely important industrial advantage that it can be implemented by a combination of an inexpensive semiconductor laser and a photodiode, and can detect submicron particles with high sensitivity and high accuracy.

[0009]

SUMMARY OF THE INVENTION An object of the present invention is to apply the above-mentioned new principle to not only detection of fine particles but also to a novel method capable of measuring the particle size of the detected fine particles, and a novel method thereof. It is intended to provide a device for performing.

[0010]

According to the present invention, there is provided a method for measuring the particle size of fine particles contained in a test fluid, wherein a light beam from a coherent light source is applied to a test fluid flowing at a predetermined flow rate. Immediately after the light is condensed at a predetermined focal point, the test fluid is irradiated to the test fluid, and a pair of a pair of laser light beams are arranged at a predetermined interval in an optical path of the light beam on a plane perpendicular to the optical axis of the light beam. Receiving the light beam by the photoelectric conversion element, detecting a first measurement value correlated with the particle diameter of the fine particles contained in the test fluid from at least one output of the photoelectric conversion element, Detecting a second measurement value correlated with the passing position of the fine particle based on a time difference of detection by
There is provided a method for measuring the particle size of fine particles in a test fluid, the method including a process of extracting the particle size of the fine particles by correcting with a measured value.

According to the present invention, there is provided a light source for generating a coherent light beam, an optical system for converging the light beam to a predetermined focal point, and an apparatus immediately after the focal point. A substantially transparent liquid flow path for irradiating the test fluid flowing at a predetermined flow rate with the light beam, and in a light path of the light beam on a plane perpendicular to the optical axis of the light beam. A pair of photoelectric conversion elements, each of which converts a change in a light beam caused by the presence of fine particles contained in the test fluid into an electric signal, and outputs a pair of photoelectric conversion elements from at least one output of the photoelectric conversion elements. First detection means for extracting a signal value correlated with the particle diameter of the fine particles, second detection means for extracting a time difference between changes in outputs of the pair of photoelectric conversion elements, and detection values of the first detection means. Correction is made by the detection value of the second detection means Particle diameter measuring apparatus of the fine particles in the test fluid is provided, characterized in that it comprises a positive means.

[0012]

In the particle diameter measuring method according to the present invention, an optical change generated in the convergent beam due to the presence of the fine particles in the test fluid is detected by the photoelectric conversion element, and a signal value correlated with the fine particle diameter is extracted. On the other hand, by using a pair of photoelectric conversion elements, passage position information of the fine particles is obtained, and the signal value is corrected to specify the size of the fine particles.

That is, as described later in detail, an optical phenomenon that occurs when fine particles contained in the test fluid crosses the convergent light beam changes in correlation with the size of the fine particles. Therefore, in the method according to the present invention, the particle size of the fine particles is extracted by detecting the optical change of the convergent light beam by the photoelectric conversion element.

However, since the test fluid actually passes through a flow path having a certain thickness, it depends on whether the test fluid passes through a position close to the light source or a position far from the light source inside the flow path. The detection result on the photoelectric conversion element side changes. Therefore, the method according to the present invention utilizes the fact that the light beam irradiated on the fluid under test is a convergent beam, and requires a pair of photoelectric conversion elements to allow the fine particles to cross the convergent light beam. The passage position of the fine particles is detected by measuring the time.

The method according to the present invention as described above can be carried out by a simple apparatus using an inexpensive semiconductor laser and a photodiode, while quickly and easily measuring the particle size of submicron-level fine particles. can do.

Hereinafter, the present invention will be described more specifically with reference to Examples, but the following disclosure does not limit the technical scope of the present invention in any way.

[0017]

FIG. 1 is a conceptual diagram of a particle measuring apparatus using the principle of the present invention.

As shown in FIG. 1, the apparatus comprises a semiconductor laser 1 as a coherent light source, an optical system 2 for converging a light beam B generated by the semiconductor laser 1, and an optical system 2
And a pair of photoelectric conversion elements 4a and 4b that receive the light beam B.
Here, the optical cell 3 is configured to allow the test fluid to flow at right angles to the optical axis of the light beam B,
The photoelectric conversion elements 4a and 4b are arranged at predetermined intervals along an array direction parallel to the flow direction of the test fluid. The outputs of the photoelectric conversion elements 4a and 4b are input to the time difference detection circuit 6 via the signal processing circuits 5a and 5b. On the other hand, the output of the photoelectric conversion element 4a is also input to the diffraction image detection circuit 7.

FIG. 2 is a diagram showing a three-dimensional layout of the apparatus shown in FIG. 1 by its main members.

As shown in FIG. 1, the photoelectric conversion elements 4a, 4a
Each of b is actually a photoelectric conversion element array formed from a plurality of photoelectric conversion elements arranged horizontally, and can detect a diffraction image generated in the light beam B by the fine particles as a change in the received light power. it can. Since the peak value of the change in the received light power changes in accordance with the particle diameter of the fine particles, the particle diameter of the fine particles can be measured from the output signal value of the photoelectric conversion element. Since the function of each of the photoelectric conversion elements 4a and 4b is to detect a diffraction image generated in transmitted light,
In particular, there is no need to have high sensitivity or high resolution. In addition, a single photodiode can be used in principle as the photoelectric conversion element. However, by using a photodiode array and a signal processing circuit described later, the S / N ratio is high and processing is easier. A detection signal can be generated.

FIG. 3 is a diagram showing the operation of the photoelectric conversion elements 4a and 4b and a configuration example of the signal processing circuits 5a and 5b shown in FIG.

That is, as shown in FIG. 3 (a), due to the presence of the fine particles, the light beam B is diffracted, and correspondingly, the light intensity distribution by the diffraction image is generated on the light receiving surface of the photoelectric conversion element. . Here, the photodiode array is adjusted so that an output signal is in an initial state (for example, “zero”) in a state where light is uniformly applied to each element. On the other hand, for example, when a photodiode array of four elements is used, a circuit including a plurality of differential amplifiers as shown in FIG. 3B is used as a signal processing circuit. Here, the outputs of the respective photodiode elements are coupled to the respective inputs a to d of the respective differential amplifiers, and a state in which exactly the same output signal is output from the four elements, that is, the respective photoelectric conversion elements receive light. The values of the respective resistance elements are set so that the output signal e becomes a standard state (for example, "zero") when the optical powers are all equal.

The signal processing circuit configured as described above
Since the difference generated between each pair of inputs of the differential amplifier is accumulated and output, the signal component of the output of the light receiving element array is emphasized as a result, and the S / N ratio of the detection signal is improved. Perform the function.

FIG. 4A is a graph showing the correlation between the detection signal value output through the above-described signal processing circuit and the particle diameter of the fine particles. However, the detection signal value detected here is only a relative value that changes depending on the passing position of the fine particles, as described below.

As described above, the particle size measuring apparatus according to the present invention has a pair of photoelectric conversion element arrays spaced from each other. Therefore, as shown in FIG. 4B, when the fine particles cross the light beam B, a time difference T occurs between the signal outputs from the photoelectric conversion element arrays 4a and 4b. The time difference T corresponds to the time required for the fine particles in the test fluid to cross the light beam. That is, as shown in FIG. 1, when the fine particles pass through the passing position X on the side closer to the light source and when they pass through the passing position Y on the far side from the light source, the fine particles are transported to the test fluid flowing at a constant flow velocity. The time required for the fine particles to traverse the light beam varies. Therefore,
The passing position of the fine particles can be known from the corresponding peak value of each output signal of the photoelectric conversion element arrays 4a and 4b, for example, the time difference T between the maximum peak values.

Using the passing position information thus detected, the detection signal value having a correlation with the above-mentioned particle diameter is corrected, and a signal output corresponding to the absolute value of the particle diameter of the fine particles can be obtained.

A semiconductor laser can be used as the coherent light source 1. The shorter the oscillation wavelength, the higher the detection sensitivity. In addition, this measuring device operates even when the light source has a relatively low output. In experiments conducted by the present inventors, effective detection was possible even with a semiconductor laser having an output of 1 mW or less, specifically, 0.2 mW.

In the optical cell 3, at least the light receiving surface and the transmitting surface of the focused light are made of a material transparent to the wavelength of the light beam B. It is also preferable to provide, for example, a laminar flow plate so that turbulence does not occur in the flow of the test fluid containing the fine particles. Further, by using a combination of a collimator lens and a convergent lens as the optical system 2, a convergent light beam as shown in the figure can be obtained.

[Experimental Example] With the configuration shown in FIG.
The particle size of the fine particles was measured under the following conditions.

[0030]

[Table 1]

When measurement was performed on the test fluid under the above conditions, the value of the output signal was 1: 3: 5 (relative value).
This particle size measurement method was confirmed to be effective. Therefore, the absolute value of the particle size can be easily known by calibrating the apparatus with fine particles having a known particle size.

[0032]

As described in detail above, the method according to the present invention is a completely novel method capable of quickly and easily measuring the particle size of submicron-level fine particles.

Further, this method can be carried out by a simple apparatus using an inexpensive semiconductor laser and a photodiode, and can be preferably used for a wide range of applications.

[Brief description of the drawings]

FIG. 1 is a diagram schematically showing a basic configuration of a measuring device according to the present invention.

FIG. 2 is a diagram showing a specific configuration example of a measuring device according to the present invention, using its main components.

FIG. 3 is a diagram illustrating an operation of the photoelectric conversion element and a configuration example of the signal processing circuit illustrated in FIG. 1;

FIG. 4 is a diagram for explaining the operation of the device shown in FIG. 1;

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 ... Semiconductor laser, 2 ... Optical system, 3 ... Optical cell, 4a, 4b ... Photoelectric conversion element, 5a, 5b ... Signal processing circuit, 6 ... Time difference detection circuit, 7 ... Diffraction image detection circuit

Claims (6)

(57) [Claims] 1. A method for measuring the particle size of fine particles contained in a test fluid, wherein a light beam from a coherent light source is focused on a predetermined focus on the test fluid flowing at a predetermined flow rate. Immediately thereafter, the test fluid is irradiated to the test fluid, and the light beam is irradiated by a pair of photoelectric conversion elements arranged at a predetermined interval in the optical path of the light beam on a plane perpendicular to the optical axis of the light beam. Receiving a first measurement value correlated with the particle size of the fine particles contained in the test fluid from at least one output of the photoelectric conversion element, and detecting the passage of the fine particles based on a time difference between detections by the pair of photoelectric conversion elements. Detecting a second measurement value correlated with the position, and correcting the first measurement value with the second measurement value to extract a particle diameter of the fine particle; Particle size measurement method. 2. The method according to claim 1, wherein each of said pair of photoelectric conversion elements is a photoelectric conversion element array including a plurality of photoelectric conversion elements linearly arranged in an arrangement direction parallel to each other. A method for measuring the particle size of fine particles in a test fluid, wherein each of the pair of photoelectric conversion element arrays detects scattering or diffraction generated in the light beam by the fine particles. 3. An apparatus for implementing the method according to claim 1 or 2, comprising a light source for generating a coherent light beam, and an optical system for converging the light beam to a predetermined focal point. Right after the focal point, a substantially transparent liquid flow path for irradiating the test fluid flowing at a predetermined flow rate with the light beam, and on a plane perpendicular to the optical axis of the light beam, A pair of photoelectric conversion elements arranged at predetermined intervals in an optical path of the light beam, each converting a change in the light beam caused by the presence of fine particles contained in the test fluid into an electric signal; First detection means for extracting a signal value correlated with the particle diameter of the fine particles from at least one output; second detection means for extracting a time difference between changes in the outputs of the pair of photoelectric conversion elements; The detection value of the second detection means A particle diameter measuring device for fine particles in a test fluid, comprising: a correcting means for correcting the particle diameter. 4. The device according to claim 3, wherein each of said pair of photoelectric conversion elements is a photoelectric conversion element array including a plurality of photoelectric conversion elements linearly arranged in an arrangement direction parallel to each other. An apparatus for measuring the particle size of fine particles in a test fluid, wherein each of the pair of photoelectric conversion element arrays detects scattering or diffraction generated in the light beam by the fine particles. 5. The signal processing circuit according to claim 4, wherein said first and second detecting means include a differential amplifier for extracting a mutual difference between outputs of said photoelectric conversion elements. A particle size measuring device configured to receive an output of the photoelectric conversion element array via the photoelectric conversion element array. 6. An apparatus according to claim 3, wherein said light source is a semiconductor laser,
A particle size measuring device, wherein the photoelectric conversion element is a photodiode or a photodiode array.