JPH09196842A - Fi value measuring method and device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To measure an FI(falling index) value accurately and simply. SOLUTION: An optical beam from a coherent light source 1 is converged by an optical system 2, and a flow 3 of fluid including fine perticles is passed near the focus of the converged beam of light, and the diffracted light by the fine perticles in the fluid is detected by a photo-detector 4 installed on the light path on the side opposite to the light source about the flow of the fluid including fine perticles and is transduced into electric signals. The FI value of the fluid is determined by subjecting the obtained electric signals to a specified processing.

Description

Detailed Description of the Invention

[0001]

TECHNICAL FIELD The present invention relates to a fluid FI (Fouli).
The present invention relates to a completely new method capable of accurately and simply measuring the ng Index) value, and a configuration of a FI value measuring device to which the method is applied.

[0002]

2. Description of the Related Art Turbidity is used as a typical measure for evaluating so-called water quality. Turbidity is a scale for measuring the concentration of mainly solid impurities present in a test liquid, and is measured by several methods as described below. (1) A method of observing the turbidity of the sample with the naked eye and determining the turbidity by comparing with a standard solution. Method (3) Method of irradiating the sample with light with a wavelength of around 660 nm and calculating the turbidity from the intensity of light scattered by particles in the sample

However, in the above-mentioned (1) visual turbidity measuring method, the measuring range is about 1 to 10 degrees, and it is practically impossible to measure turbidity as low as 1 degree or less. Further, also in the turbidity measuring method using transmitted light of the above (2), the amount of transmitted light extinction is small for a sample with low turbidity, and it is said that the measuring range is 5 degrees or more. Further, in the turbidity measuring method by the amount of scattered light of the above (3), the blank value becomes high due to scattered light and stray light due to water molecules, so that the measuring range is eventually set to about 1 to 5 degrees. In addition to this, a method for measuring transmitted scattered light turbidity using an integrating sphere has been proposed, but at present, the lower limit of the measurement range is 0.2 degree. Therefore, for example, like filtered water using a reverse osmosis membrane or a hollow fiber membrane, the turbidity is 0.1.
It was impossible to evaluate the water quality at a level equivalent to sub-degree.

Therefore, when a high degree of turbidity evaluation is required, a more straightforward water quality standard called FI value is used. That is, the FI value is a value obtained by filtering the test liquid under a predetermined condition using a membrane filter having a predetermined specification, and measuring the time required to filter a predetermined amount of the test liquid,
Usually, it is measured under the following conditions.

(1) Effective diameter 42.7 mm (nominal diameter 47 mm: HA
WP047, Type HA) 0.45 μm Maybren filter, and (2) under the pressure of 2.1 kg / cm ² G.
The time t ₁ during which 500 cc is filtered is measured, and (3) 15 minutes after the start of pressurization, the time t ₂ during which 500 cc of the test solution is filtered is measured, and (4) in the above process. The obtained values t ₁ and t ₂ are calculated according to the following formula to obtain a PI value: PI
(15 minutes, 2.1KG) = (1-t ₁ / t ₂ ) × 100 (%),
(5) Further, the FI value is obtained by the following formula: FI (15 minutes,
2.1KG) = PI / 15

However, the evaluation based on the FI value is based on a very convenient definition, and the current measurement method cannot be used in actual water quality control unless a sufficient margin is taken into consideration for the measurement value. Further, since it cannot be used for the purpose of continuously monitoring the FI value on-site or on the line, the industrial application range is narrow.

[0007]

As described above, the FI value obtained by the conventional measuring method is not always an objective evaluation method, and its range of use is limited.

Therefore, the present invention is a method for measuring an FI value that can be used in a field requiring a precise evaluation in a particularly clean region such as a fluid, particularly filtered water using a reverse osmosis membrane or a hollow fiber membrane. Is intended to provide. Further, it is also one of the objects of the present invention to provide an FI value measuring device capable of implementing this evaluation method.

[0009]

BEST MODE FOR CARRYING OUT THE INVENTION According to the present invention, a light beam from a coherent light source is once focused on a predetermined focal point to form a radial light beam, and a fluid whose FI value is to be measured is emitted near the focal point. The light-dark distribution of the light beam that is caused to pass through the beam and is diffracted by fine particles in the fluid is detected by a photodetector arranged on the optical path of the light beam on the side opposite to the light source with respect to the fluid. A FI value measuring method for a fluid is provided, which is characterized in that the FI value of the fluid is obtained based on a change in the electric signal.

As an apparatus for carrying out the method according to the present invention, according to the present invention, a coherent light source, an optical system for condensing light from the coherent light source, and a light beam condensed by the optical system are provided. An optical cell that is arranged near the focal point and through which the sample liquid flows, a photodetector that is arranged on the optical path of the light beam and on the opposite side of the optical cell from the light source of the light beam, and this light An FI value measuring device comprising an electric circuit for measuring the number of fine particles in a fluid from an electric signal from a detector, and means for converting an output signal of the electric circuit into a signal corresponding to the FI value. Provided.

The FI value measuring method according to the present invention is based on the finding that the FI value and the measured value obtained by a predetermined method described later have an extremely high correlation. However, although the detection principle of the present invention cannot be completely explained theoretically at present, the following explanation is tried.

When fine particles are present in the parallel beam, Fraunhofer diffraction development produces a light-dark distribution having a specific pattern in the projected image of the parallel beam. here,
"Diffraction" is defined as "a general term for various phenomena that cannot be explained by the straightness of light", but is generally explained by the Huygens-Fresnel principle based on the wave nature of light. However, this Fraunhofer diffraction development appears only when the radius of the fine particles is larger than the wavelength of light, and is a physical phenomenon used in particle size distribution analyzers and the like.

Diffraction can be considered as a kind of scattering, and is generally explained by Mie scattering theory derived from Maxwell's electromagnetic equation. However, Mie scattering theory is generally complicated in handling. Is an approximation from the relationship between the particle radius r and the incident wavelength λ (Rayleigh scattering when r <λ, Mie scattering when r is close to λ, Mie scattering when r> λ Fraunhofer diffraction). However, when the radius of the fine particles is equal to or less than the wavelength of light, it is treated as mere scattering. This is because when the radius of the particles becomes about the wavelength of light, the particles behave as if they act as a point light source and cause scattering, and the diffraction angle becomes large, so that interference cannot occur with parallel beams.

Here, in the Fraunhofer diffraction theory by parallel light as shown in FIG. 2, the spread angle Δθ due to diffraction when the light shield is fine particles is Δθ = 1.22λ / D, where D = 2r is the diameter of the fine particles. It is represented by. Therefore, the smaller the diameter of the fine particles to be shielded, the larger the spread angle Δθ of diffraction becomes, and when D = 0.78λ, the spread angle becomes just 90 degrees. Usually, this divergence angle is considered to be the detection limit in the diffraction type fine particle detection device, and therefore, when the incident wavelength λ = 0.67 μm, the detectable particle size is 0.52 μm. In fact, experimentally, it is not easy to obtain a diffraction pattern with a particle size smaller than the wavelength.

However, according to the method of the present invention, when fine particles are present in the vicinity of the focal point of a diffused beam diffusing from a specific focal point, the diffraction angle is sufficient even for fine particles having a particle size smaller than the wavelength of light. It becomes smaller, and the presence of fine particles can be easily detected from the distribution of light and dark in the projected image of the beam. Further, by receiving the light beam including the diffraction distribution as described above by the light receiving element array and converting it into an electric signal, an electric signal having an extremely strong correlation with the FI value of the test liquid can be obtained.

Further, the FI value measuring method according to the present invention can be carried out by using an inexpensive laser (light source) with a small output and an inexpensive photodiode (detector), as will be specifically described later. Therefore, there is an industrially very important advantage that the measuring device becomes inexpensive and the on-site handling becomes simple.

Hereinafter, the present invention will be described in more detail with reference to examples, but the following disclosure is merely an example of the present invention and does not limit the technical scope of the present invention.

[0018]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS FIG. 1 is a diagram showing the basic configuration of a FI value measuring apparatus capable of carrying out the method according to the present invention.

As shown in the figure, this apparatus is produced by a laser 1 which is a coherent light source, a converging optical system 2 for converging the emitted light of the laser 1 to a predetermined focal point, and a converging optical system 2. An optical cell 3 for circulating the test liquid near the focal point of the diffused light beam and a light receiving element array 4 for receiving the light beam after passing through the optical cell 3 are provided.

In the above-mentioned FI value measuring device, the light source can be constructed by using the inexpensive semiconductor laser 1, and is constructed as a collimated light source by the collimator lens. Also, as the light receiving element array 4, a commercially available product using a photodiode can be preferably used. Further, as the converging optical system 2, a relatively simple optical lens or the like can be used.

Although not shown, the signal output from the light-receiving element array 4 is connected to a microcomputer system, a general-purpose information processing device or the like via an A / D converter or an appropriate interface. . In these processing devices, the detected light intensity signal or diffraction image signal is converted into a processable electric signal. The structure and operation of this type of device are readily available from the market, and detailed description thereof is omitted.

In the FI value measuring device configured as described above, the coherent light is emitted from the light source 1 through the optical system 2 to the test liquid flowing in the optical cell 3. still,
Any laser oscillator 1 can be used, but the shorter the oscillation wavelength, the higher the detection sensitivity. In the experiments conducted by the inventors up to the present time, the output is 1 m.
It could be effectively used even with a semiconductor laser of W or less, specifically 0.2 mW. Further, it is advantageous to select the focal lengths of the condensing system and the optical lens 2 depending on the size of the fine particles contained in the test liquid. Specifically, when the particle size contained in the test liquid is about 0.2 μm, it is preferable to use a lens having a focal length of about 10 mm.

In the optical cell 3, at least the light receiving surface and the transmitting surface for the focused light need to be transparent. Since this optical cell does not need to worry about stray light, it can have a simple structure.However, a means for preventing turbulence in the flow of the test fluid containing fine particles, such as a laminar flow plate, is provided in the optical cell. It is preferable to provide it. Also, in an actual device, the optical system 2 is positionally adjusted so that the focused light emitted from the laser 1 can be focused at a certain position with respect to the optical cell 3, for example, the center of the optical cell. It is preferable to appropriately provide means. The photodetector 4 is for detecting a diffracted image hidden in the transmitted light, and the requirement for sensitivity is low. Therefore, although a single photodiode can be used in principle, it is preferable to use a photodiode array in practice. This photodiode array is advantageously arranged perpendicular to the direction of the flow containing the particles to be detected and also perpendicular to the optical axis.

FIG. 3 is a conceptual diagram for explaining the principle of the FI value measuring device measuring method according to the present invention.

As shown in the figure, when the test liquid is irradiated with convergent light, a focused light diffraction image (light intensity distribution) appears even for fine particles having a particle size smaller than the wavelength of light. By detecting the diffraction image with the light receiving element, the presence of fine particles in the test liquid can be accurately detected. Therefore, by counting the number of particles in the test liquid, it is possible to obtain a measurement value having a strong correlation with the FI value of the test liquid.

In an actual device, in order to improve the SN ratio of the photodetector 4, the signals of the respective elements of the photodiode array are superposed in multiple stages using a differential amplifier, and when fine particles do not pass, That is, the electric signal in the state where the light uniformly hits each element of the photodiode array
It is preferable that an electric signal corresponding to the characteristics (number, size, etc.) of the particles is generated when the light quantity changes in any of the elements due to the focused light diffraction image.

Example 1 The device shown in FIG. 1 was manufactured according to the specifications shown in Table 1 below.

[0028]

[Table 1]

Next, the FI value measuring device A according to the present invention described above.
And the conventional FI value measuring device B were used to compare the measurement results in the procedure as shown in FIG. That is, as shown in FIG. 4 (a), tap water was collected as a test liquid, and the FI value was measured by the method of the present invention and the conventional method before and after filtration with a filter. Further, as shown in FIG. 4 (b), the FI value of industrial water was also measured by each measuring method. FIG. 5 shows the measurement results. As can be seen from the figure, the measured value obtained by the method according to the present invention has an extremely strong correlation with the FI value measured by the conventional method.

[0030]

As described above in detail, the FI value measuring method according to the present invention can continuously measure the FI value without collecting the test liquid. Further, since it can be easily carried out by using inexpensive members, the industrial application range is extremely wide.

[Brief description of drawings]

FIG. 1 is a conceptual diagram of an FI value measuring device using the principle of the present invention.

FIG. 2 is a diagram showing Fraunhofer diffraction development when fine particles are present in a parallel beam.

FIG. 3 is a conceptual diagram for explaining the principle of the FI value detection method according to the present invention.

FIG. 4 is a diagram conceptually showing an evaluation method of the FI value measuring device according to the present invention.

FIG. 5 is a graph showing a correlation between a measurement result obtained by the FI value measuring device according to the present invention and an evaluation result by FI value measurement.

[In the figure]

 1 laser 2 lens 3 optical cell 4 photodetector

Claims (5)

[Claims] 1. A light beam from a coherent light source is once focused on a predetermined focal point to form a radial light beam,
A fluid whose FI value is to be measured is passed through a radial light beam in the vicinity of the focal point, and the light-dark distribution of the light beam generated by diffraction by fine particles in the fluid is measured on the opposite side of the fluid from the light source. A FI value measuring method characterized in that the FI value of the fluid is obtained based on a change in the electric signal detected by a photodetector arranged on the optical path of the light beam and converted into an electric signal. 2. A coherent light source, an optical system for condensing light from the coherent light source, and a flow of a fluid which is disposed near the focal point of the light beam condensed by the optical system and which contains fine particles inside. The passing optical cell, the photodetector arranged on the optical path of the light beam and on the opposite side of the optical cell from the light source of the light beam, and the number of fine particles in the fluid from the electric signal from the photodetector. An FI value measuring device comprising: an electric circuit for measuring the electric field and means for converting an output signal of the electric circuit into a signal corresponding to the FI value. 3. The device according to claim 2, wherein the light source is a semiconductor laser and the photodetector is a photodiode. 4. The device according to claim 2 or 3, wherein the optical system is a lens. 5. The device according to claim 2, wherein the photodetector is a photodiode array arranged perpendicular to the flow direction of the fluid and perpendicular to the optical axis. A device characterized by being.