JPH058980B2 - - Google Patents

Description

Detailed Description of the Invention [Industrial Application Field] The present invention is a particle measuring device, more specifically, a particle measuring device that irradiates a laser beam into a fluid, detects scattered light from fine particles floating in the liquid, and measures the particle size. The present invention relates to a particle measuring device that measures characteristics of particles such as particle size and number of particles.

[Conventional technology] Conventionally, there is a known technology for measuring characteristics such as particle size and number of particles within a measurement area by making light incident on the measurement area and measuring the amount of transmitted light and scattering characteristics. .

For example, this technique is also used to measure impurity particles in pure water, but the measurement is difficult because the fine particles in pure water have small diameters and are only sparsely present. Therefore, in order to increase the intensity of scattering from particles, conventional methods have focused the incident light flux from a laser light source, etc. on a small area, provided a high-intensity measurement area, and received the scattered light from particles passing through this area. is used.

In a particle measuring device that irradiates particles with a laser beam and analyzes the scattered light from the particles, it is important to determine how to set the measurement portion through which the particles pass.

In particular, the shape of the incident laser beam constituting the particle detection area, the passing direction of the particles, and the setting method of the mask provided in the part that receives the scattered light from the particles are important when determining the particle size from the scattered light of the particles to be detected. Since it depends directly on the radial resolution, various measures have been taken.

[Problems to be solved by the invention] Conventionally, since the particles to be measured are relatively large, up to 0.2 μm, the scattered light from the particles is strong, and even when measuring particles in pure water, the scattered light from the pure water is There is no need to increase the convergence of the laser beam in order to distinguish it from the background light consisting of particles, etc., and to do so, it is necessary to reduce the size of the mask that sets the effective diameter of the beam that constitutes the particle detection area to the full width at half maximum. do not have.

However, in order to detect particles of 0.1 μm or smaller separately from background light, the laser beam is focused to about 10 μm to form a particle detection region, and the length of the detection region in the optical axis direction is also limited to the same extent. This makes it necessary to suppress the background light intensity. To achieve this, a mask with a slit aperture of about 10 μm is installed at the imaging position of the light receiving lens that captures the scattered light. It is not easy to constantly maintain the optimal position in the environment, even if mechanical precision is improved. Especially when considered as an online continuous measurement system,
It is conceivable that the imaging position of the scattered light may move on the mask surface due to daily changes in the temperature of the surrounding atmosphere or thermal distortion or vibration caused by a built-in heat source such as a laser light source.

Therefore, an object of the present invention is to provide a particle measuring device that can set the mask position to an optimal position and perform stable scattered light measurement even when external disturbances such as temperature changes and vibrations occur. .

[Means for Solving the Problems] In order to solve the above-mentioned problems, the present invention uses photoelectric detection to detect the position of a mask having a slit that forms an aperture in the imaging plane of the light-receiving lens through the slit. We adopted a configuration that controls movement so that the intensity signal of background light in the scattered light output from the device is maximized.

[Function] In such a configuration, the mask on the imaging surface of the light receiving lens that sets the detection range of the particle detection area formed at the focal point of the laser beam is automatically controlled, and the mask It can be adjusted so that the full width at half maximum of the laser beam is captured as the detection area, and the position of the mask in the scattered light receiving system can always be automatically set to the optimal position.

[Example] Hereinafter, the present invention will be described in detail according to an example shown in the drawings.

In FIG. 1, the reference numeral 10 is a quadrangular prism-shaped measurement cell.
An inflow pipe 12 through which a sample liquid 22 such as pure water containing 3.3 flows in, and an outflow pipe 13 through which the sample liquid 22 is discharged from the inside of the measurement cell 10 are provided. An elliptical incident laser beam 2 from a laser light source (not shown)
1 is generated, and a uniform flow shown by arrow A is formed so that the particles pass through the converging point 21a perpendicularly to the laser optical axis. This uniform flow is caused by the inflow pipe 12
This can be achieved by stabilizing the flow rate flowing into the measurement cell 10 from the source.

Scattered light 24 from the particles passing through the condensing point 21a along with this flow is imaged by the light receiving lens 25 onto the mask 26, and the scattered light restricted by the slit 26a reaches the photoelectric detector 27. Measurements are taken. An actuator 28 is provided to move the mask, as described below.

Usually, a laser beam has a Gaussian light intensity distribution, and the same applies to the elliptical beam 21 used in the present invention. That is, as shown in FIG. 2, the intensity 21' of the light beam attenuates as it moves away from the center. For example, if the large circle in the figure is set at a position where the light intensity becomes 1/e ² of the center intensity, the intensity of the small circle changes so that it becomes a position where the light intensity becomes 1/2 of the center intensity. Now, the diameter of this small circle is called the full width at half maximum.

With such a luminous flux, if the particle detection area 35 is not limited, there is a possibility that particles passing through the base where the intensity of the luminous flux is weak will be detected, resulting in poor particle size resolution.

Therefore, in order to limit the field of view of the luminous flux to the full width at half maximum E seen from the direction A, an optical arrangement as shown in FIGS. 1 and 2 is adopted. In addition, particle detection area 3
The direction in which the particles pass through 5 is such that the cross-sectional area in the plane perpendicular to the passing direction is large, that is, the first
Set in direction A in Figures 2 and 2.

In FIG. 2, if the optical axis adjustment is properly performed, the particle detection area 35 set by the slit 26a will be within the shaded area in the figure, and the field of view width E will be the center of the elliptical beam 21. It will be located in

In this way, when the adjusted positional relationship between the mask and the laser beam is disrupted by the action of an external force, the actuator 28 is driven by the control system described below to recover the misalignment.

The photoelectric pulses corresponding to the scattered light output from the photoelectric detector 27 are integrated by the sampling unit 29 for each unit sampling time, and the count value for each sampling becomes time series data.
The data is stored in the time-series data memory 33 of the microcomputer (CPU) 30 via the time-series data writing unit 32. If the photodetector used is a photomultiplier tube for counting photons suitable for detecting weak light, this stored data has fluctuations based on the probability law of the photon detection process. Therefore, in order to obtain the average light intensity received by the mask 26, moving average processing is performed on the data in the memory, and the data is used as control data for the drive circuit 31. The microcomputer 30 is connected to a memory (ROM) that stores programs and a work area memory (RAM) 34 that processes data.

Next, the operation of the apparatus configured as described above will be explained using the flowcharts shown in FIGS. 4 to 6.

In FIG. 1, an elliptical laser beam 21 is focused on a focal point 21a to form a particle detection area 35 as shown in FIG. 2, and a sample liquid 22 containing fine particles 23 is caused to flow in the direction A. Fine particles 2 are generated by laser light.
The scattered light 24 scattered from the light receiving lens 2
5. The light is received by the photoelectric detector 27 through the slit 26a. The photoelectric pulses corresponding to the scattered light outputted from the photoelectric detector 27 are integrated every unit sampling time via the sampling unit 29, and are stored in the time series data memory 33 as described above.
is memorized. In this case, moving average processing is performed to determine the average light intensity received by the mask 26.
This method is illustrated in FIG. step
In S1 to S3, the memory address n is incremented, k pieces of data are transferred from the n-th data from the memory 33, k pieces of data are taken in, and an averaging operation is performed on the k pieces of data. This averaged data is stored in the memory 33 again in step S5.
Return to the th data. The total number of data is M
This is repeated until n>M-k+1 (step S6), and the moving average processing of the time series data is performed.

During such particle measurement, the optical axis of the incident laser beam 21 and the center of the slit 26a are both aligned with the light receiving lens 2.
Even if it is adjusted to a position that intersects the optical axis of No. 5, this adjustment may be deviated due to external forces such as temperature changes, heat generation from the light source, or vibrations. Here, FIG. 3a shows a state in which the adjustment is correct, and FIG. 3b shows a state in which the adjustment has deviated. As shown in figure b, if the adjustment is off,
The field of view width E, which is limited by the slit 26, is shifted from the center of the laser beam, and the particle detection area becomes part D. This means that the low light density area at the base of the laser beam is used, and the intensity of the scattered light from the particles is weak. Eventually, it was confirmed that small particles had been detected. Furthermore, the particle size at the detection limit also increases, and the detection ability decreases.

Here, it is suitable for the scattered light from the particle detection area used for detecting deviation to have a continuous component proportional to the volume of the particle detection area, such as from water molecules in pure water, which occasionally passes through the particle detection area. Since the scattered light from the particles becomes a strong pulse-like signal, it is not suitable as a shift detection signal. However, in an example where the particles present are sparse, such as in the case of measuring particles in ultrapure water, the average measured value of time series data including scattered light of particles may be used as the control data.

Therefore, when the mask 26 is moved by the actuator 28, the intensity output of the background light at that mask position and its position are stored in memory, the mask position where the background light output is maximum is found, and the mask position is moved to that position. Move the mask. By performing this automatic mask position adjustment operation at regular intervals,
The particle detection area 35, which is limited by the position of the slit in the mask, can always be kept in alignment with the center of the laser beam. This makes it possible to maintain particle size resolution and particle detection ability at a constant level.

The control flow implementing this method is illustrated in FIGS. 5 and 6.

First, background light data is extracted using the method shown in FIG. In step T1, initial values are set, and in steps T2 and T3, n is incremented, data at address n in the memory 33 is read, and the value is set to L. This data value L and a threshold value L2 for extracting background light are compared in the comparator 30a in the microcomputer 30 (step T4). Data smaller than L2 is taken as background light, and in step T5, the number P of background light data and the sum S of background light data values are determined. This is n
Repeat until >M-k+1 (step
T6), average value of the calculated values in step T7 = S/P
seek.

Subsequently, automatic mask correction is performed based on the algorithm shown in FIG.

First, in step R1, the reference position x of the mask 26 is initialized (x=0), and the position number (maximum value M) m of the mask 26 is initialized (M=0). Subsequently, in step R2, via the drive circuit 31,
The mask position is moved by driving the actuator 28. Set the mask movement step to Δx
Then, the mask position x becomes x=Δx·m.
Next, in step R3, the average count value of the background light in the mask x is determined. This is found in the flow shown in Figures 4 and 5, and =S/P
This value is used in step R4,
It is stored in the mth memory in R13. This process is continued until the mask position reaches the maximum value M (step R5).

When the mask position reaches the maximum value M or more, it moves to d and performs control to find the optimal mask position P. In step R6, the optimum position P, mask position number m, and constant L3 are each set to 0.
Increment the mask position m (step
R7), through the background light memory in step R8,
Read the average count value of the m-th background light. Subsequently, in step R9, the comparator 30b of the microcopy computer compares the value of and the value of L3. If it is larger than L3, it is judged as the optimal position, and in step R10, L3=, P=m is set. On the other hand, if it is smaller than L3, step R11 is set.
Then, the above steps are repeated until the mask position reaches the maximum value M. When the mask position reaches the maximum value, actuator 2 is activated in step R12.
8 to move the mask 26 to the position determined by x=Δx·P. At this position, the intensity of the background light in the scattered light is at its maximum, resulting in the adjusted condition shown in FIG. 3a.

The optical axis deviation of the laser beam discussed above can be expected also in the depth direction shown as F in Figure 2 and in the optical axis direction of the irradiation laser (perpendicular to the page), but the depth determined by the slit Because the directional spread is large and the diameter of the laser beam near the focal point is not abrupt, it can be handled more leniently than in any of the field width directions.
Therefore, the misalignment correction direction has been discussed only in the field width direction.

Furthermore, in the embodiments described above, the actuator 28 does not necessarily need to be attached to the mask 26, and the purpose can be achieved even if it is attached to the light receiving lens 25, the irradiation optical system, or the light source section. In this case, the actuator may be provided so that the image of the irradiated light moves within the imaging plane in a direction perpendicular to the slit direction of the mask.

[Results] As explained above, according to the present invention, the position of the mask in the scattered light receiving system, which is installed for the purpose of increasing the particle size resolution of particles passing through the particle detection area, is always set at the optimal position. This enables stable scattered light measurement even when disturbances such as humidity changes or vibrations occur.

[Brief explanation of the drawing]

FIG. 1 is a perspective view showing the schematic configuration of the device of the present invention;
Figure 2 is a configuration diagram showing the particle measurement method, Figure 3a is an explanatory diagram showing the state when the mask is in the optimal position, Figure 3b is an explanatory diagram when the mask is shifted from the optimal position, and Figure 4 is FIG. 5 is a flowchart showing the moving average processing of time series data, FIG. 5 is a flowchart showing the extraction of background light data, and FIG. 6 is a flowchart showing the flow of the automatic mask position correction algorithm. 10...Measurement cell, 21...Laser beam, 23
...Fine particles, 24...Scattered light, 25...Light receiving lens, 26...Mask, 27...Photoelectric detector, 28
... Actuator, 35 ... Particle detection area.

Claims (1)

[Claims] 1. Irradiating a particle detection area in a fluid with a laser beam,
In a particle measuring device that receives laser scattered light from particles in a liquid by a photoelectric detector via a light receiving lens, and processes an output signal from the photoelectric detector to measure particle characteristics, a mask having a slit forming an opening at the slit; a driving means for driving the mask in a direction substantially perpendicular to the slit; and a driving means for sequentially moving the mask to detect scattering output from a photoelectric detector at each mask position. A storage means for storing the intensity output of background light in the light and its mask position; A means for finding a mask position where the intensity output is maximum and moving the mask to that mask position via the driving means. A particle measuring device characterized by: