JPH02114148A - Particulate measuring apparatus - Google Patents

Abstract

PURPOSE:To enable a highly accurate mask alignment by arranging a mask, an ND filter holder and a photoelectric detector. CONSTITUTION:An ND filter holder 9 is inserted between a mask 8 and a photoelectric detector 10. The holder 9 is provided with two ND filters A and B different in permeability at an opening thereof. Then, the holder 9 is turned with an actuator 9a so that any part of the filters A and B or a cavity C is movable with an optical path position. When the cavity C is inserted into an optical path, no dimering is performed. By selecting any of the filters A and B or the cavity C, an intensity of scattered light 6 inputted into the photoelectric detector 10 can be adjusted. In addition, the actuator 9a is controlled by a control section composed of a microprocessor, memory and the like.

Description

[Detailed Description of the Invention] [Industrial Application Field] The present invention relates to a particulate measuring device, in particular, a particle measuring device that irradiates a detection area in a medium with a laser beam, receives laser scattered light from particles in the medium with a photoelectric detector, The present invention relates to a particle measuring device that measures particle characteristics according to an output signal from a photoelectric detector.

[Prior Art] Optical measuring devices that utilize light scattering have been used as devices for measuring fine particles in media such as liquids and gases. In this type of device, particles are measured by evaluating the scattering state of light incident on the liquid or gas to be measured using a light receiving element. However, since the intensity of scattered light from particles is weak, It is common to adjust the polarization angle to obtain the strongest scattered light intensity signal.

[Problems to be Solved by the Invention] In addition, a technique is known that uses the so-called photon counting method, in which the scattered light intensity is digitally measured as the number of photons, to evaluate the scattered light intensity in particle diameter measurement. According to , it is less susceptible to electrical drift and noise than processing the scattered light intensity as an analog quantity, and can perform more accurate measurements, but when measuring particle diameters within a fairly wide range of particle diameters. If the dynamic range is set according to the small particle size range, extremely strong scattered light will occur in the large particle size range, and the intensity of the scattered light may not be within the dynamic range of the photoelectric detector.

Therefore, it is conceivable to perform light attenuation using an ND filter or the like so that the scattered light intensity always falls within the dynamic range of the photoelectric detector.

On the other hand, in order to reduce the influence of background light in the measurement area of particle scattered light, a structure is known in which an optical mask is provided in the light receiving system. A mechanism is also being considered that automatically adjusts the depth of the measurement area or the optical system of the light receiving system to be optimal. Such a structure of the mask alignment mechanism is described in Japanese Patent Application No. 173991/1982 by Kokuyo.

However, if an ND filter or the like is inserted into the light receiving system in order to reduce the scattered light to match the dynamic range of the photoelectric detector as described above, there is a risk that the automatic alignment mechanism described above may not operate accurately. .

SUMMARY OF THE INVENTION An object of the present invention is to solve the above problems and provide a particle measuring device that can handle a large particle diameter measurement range without adversely affecting the alignment of an optical mask.

[Means for Solving the Problems] In order to solve the above problems, in the present invention, a detection area in a medium is irradiated with laser light, and a photoelectric detector receives the scattered laser light from particles in the medium. In a particle measuring device that measures particle characteristics according to the output signal of a photoelectric detector,
A control means is provided for controlling the intensity of the scattered light input to the photoelectric detector so that the intensity of the scattered light is within a dynamic range of the photoelectric detector. At this time, the photoelectric detector includes an optical mask that limits the area where the scattered light intensity is measured, and a mask alignment mechanism that controls the position of the optical mask in the optical path of the light receiving system according to the output of the photoelectric detector. However, when the position of the optical mask is controlled by this mask alignment mechanism, a configuration is adopted in which a light amount that enables mask alignment is obtained even when the light is significantly reduced by the scattered light intensity control means.

[Operation] According to the above configuration, the scattered light intensity control means can select the scattered light intensity that is suitable for the dynamic range of the photoelectric detector that measures the scattered light intensity when measuring the particle size. When aligning an optical mask to limit the area where the scattered light intensity is measured, accurate mask alignment is possible even when the light is significantly reduced by the scattered light intensity control means.

[Embodiments] The present invention will be described in detail below based on embodiments shown in the drawings.

First, the basic structure of a particle measuring device employing the present invention will be explained with reference to FIG.

FIG. 1(A) shows the structure of an optical system and a control system of a particle measuring device employing the present invention.

In the figure, reference numeral 1 denotes a laser light source such as a semiconductor laser. A beam expander 2 and a condensing lens 3 are arranged on the optical axis of the output light of the laser light source 1, and the output laser beam 4 is condensed at a condensing point 5. Ru.

The condensing point 5 is set in a measurement region in a sample medium containing fine particles such as a liquid or gas (not shown).

At an angle of approximately 90 degrees to the direction of incidence of the laser beam 4,
Light receiving systems (7 to 10) for detecting side scattered light are arranged. Basically, the light receiving system includes an imaging lens 7 that focuses the scattered light 6 on the position of a mask 8, a mask 8, and a photoelectric detector 1.
Consists of 0. The mask 8 is used to make the scattered light component only at the focal point 5 enter the photoelectric detector 10 .

FIG. 1(B) shows an enlarged view of the vicinity of the condensing point 5. In FIG. 1(B), the shaded area H corresponds to the size and shape of the aperture of the mask 8 projected by the imaging lens 7. The scattered light of the particles passing through this region is set to be input to the photoelectric detector IO as optical information of the particles.

The basic structure shown so far is almost the same as that of the conventional device, but in this embodiment, the mask 8 and the photodetector 10 are
An ND filter holder 9 is inserted between them.

As shown in FIG. 2, the ND filter holder 9 is a rotary disc-shaped one, and has a plurality of circular openings, in which two ND filters of A% and B with different transmittances are held. It is provided. The ND filter holder 9 is rotated by the actuator 9a, and either the filter A% B5 or the cavity C (one of the openings) can be moved to the optical path position. No dimming occurs when cavity C is inserted into the optical path. That is, by selecting either the filter A%B or the cavity C, the intensity of the scattered light 6 input to the photoelectric detector 10 can be adjusted.

The actuator 9a is controlled by a control unit 100 composed of a microprocessor, memory, etc. based on a measurement procedure described later.

Note that the position of the mask 8 is determined by the arrows (up and down) in the figure by a known mask alignment mechanism under the control of the control unit 100.
shall be adjusted in the direction. This alignment is performed in a known manner, for example according to the output intensity of the photodetector 10.

The control unit 100 is a photoelectric detector! The particle diameter is calculated from the output data of O by the method described later, and output in a predetermined format to an output unit 10 consisting of a printer or a display. In this measurement procedure, the control unit 100 rotates the ND filter holder 9 via the actuator 9a. Note that the so-called photon counting method, in which the scattered light intensity is digitally measured as the number of photons, is used to evaluate the scattered light intensity in particle diameter measurement.

Here, problems when performing light attenuation using the ND filter holder 9 will be explained with reference to FIG.

FIG. 3(A) shows the depth d of the image formed by the imaging lens 7 of the mask 8 when the ND filter is not inserted between the mask 8 and the light-receiving surface of the photoelectric detector 10, and the measurement area H within this depth. The light intensity distribution H' obtained by the photoelectric detector 10 at
It shows.

As can be seen from FIG. 1(B), the measurement area traversed by the laser beam 4 has a visual field width W corresponding to the aperture width of the mask 8.
A particle measurement region H is formed.

On the other hand, in this measurement region H&:, the light intensity distribution that can be detected by the photoelectric detector 10 is extremely strong and has little fluctuation in the center of the laser beam 4, as indicated by the symbol H'. By moving the mask 8 in the vertical direction, the measurement area H of the light receiving system having the depth d can be positioned at the center of the laser beam 4.

However, when an ND filter is inserted into the optical path of the light receiving system to attenuate the light, the light intensity distribution obtained by the photoelectric detector 10 becomes highly fluctuating as indicated by symbol H' in FIG. 3(B).

Fluctuations in light intensity correspond to the quotient &/μ of the standard deviation of light intensity divided by the average value μ of light intensity, so the light intensity μ obtained by the photoelectric detector 10 decreases due to light attenuation by attaching an ND filter. Naturally, the fluctuation also increases, making it difficult to determine the optimal position of the mask 8 in response to changes in the output of the photoelectric detector 1°.

Therefore, in this embodiment, the control section 100 performs measurement control as shown in FIG. 4.

The control procedure shown in FIG. 4 is stored as a control program for the control section 100 in a ROM (not shown) connected to the control section 100.

When the start of measurement is instructed via an operation system (not shown),
In step S1 of FIG. 4, the control unit 100 causes the laser light source 1 to emit light, and the photoelectric detector 11 measures the light intensity in the measurement area.

First, as an initial state, in step S2, the ND filter holder 9 is rotated and set by the actuator 9a so that the cavity C is placed in the optical path of the light receiving system.

Next, in step S3, the photoelectric detector 1 is
Mask alignment control is performed to adjust the position of the mask 8 while monitoring the output of 0.

Subsequently, in steps S4 and S5, the intensity of scattered light from particles in the medium is measured by the photoelectric detector 10, and processing for selecting an appropriate ND filter is performed.First, in step S4, the output of the photoelectric detector 10 is checked, and the photoelectric detector 10 is It is determined whether the intensity of light incident on the detector 10 falls within the dynamic range of the photoelectric detector 10 when the ND filter A is attached. If this step is affirmed, the ND filter A is inserted into the optical path under the control of the actuator 9a in step S6.

In step S5, it is similarly determined whether the intensity of light incident on the photoelectric detector 10 falls within the dynamic range of the photoelectric detector 10 when the ND filter B is attached. If this step is affirmed, the ND filter B is inserted into the optical path under the control of the actuator 9a in step S8. If it is determined in step S5 that measurement is not possible even with ND filter B, the particle diameter is determined to be too large, and the process is terminated with an error in step S9.

When steps S6 and S8 are completed, the particle diameter is measured based on a known scattered light intensity evaluation in step S7.

Note that, as described above, the photon counting method is used to evaluate the scattered light intensity in the particle diameter measurement in step S7.

According to the above configuration, the intensity of the scattered light received by the photoelectric detector 10 is strong, and even when the light is significantly attenuated for measurement within a dynamic range, highly accurate mask alignment is possible.

Furthermore, the photon counting method is used to evaluate the scattered light intensity in particle size measurement, which is less susceptible to electrical drift and noise than when the scattered light intensity is processed as an analog quantity, allowing for more accurate measurements. Can be done.

Note that since the ND filter for light attenuation is a parallel plane plate, even if it is installed between the mask 8 and the photoelectric detector 10, there is no fear that the light flux to be measured will deviate from the light receiving surface of the photoelectric detector 10. In the above description, 2 ffl of AlB is used as the ND filter, but by selecting and using a larger number of filters, even when the transmittance is lower than that of B, highly accurate mask alignment is possible.

According to such a configuration, it is possible to form an appropriate light attenuation state according to the particle diameter to be measured, and to perform accurate measurement over a wide range of particle diameters.

[Effects of the Invention] As is clear from the above, according to the present invention, a detection area in a medium is irradiated with a laser beam, laser scattered light from particles in the medium is received by a photoelectric detector, and the detection area of the photoelectric detector is In a particle measuring device that measures particle characteristics according to an output signal, the intensity of the received scattered light is within the dynamic range of the photoelectric detector by providing means for controlling the intensity of scattered light input to the photoelectric detector. A control means is provided to adjust the intensity of the scattered light so that the intensity of the scattered light is within the range. At this time, an optical mask that limits the area where the photoelectric detector measures the scattered light intensity, and a mask alignment mechanism that controls the light reception of this optical mask and its position in the system optical path according to the output of the photoelectric detector are provided. When the position of the optical mask is controlled by this mask alignment mechanism, a configuration is adopted in which the scattered light intensity control means is controlled to obtain a scattered light intensity that enables mask alignment. By selecting the scattered light intensity suitable for the dynamic range of the photoelectric detector that measures the scattered light intensity when measuring the particle size using the light intensity control means, accurate particles can be obtained even when the particle size is large and the scattered light intensity is strong. Diameter measurements can be made. Furthermore, when aligning an optical mask that limits the area where the photoelectric detector measures the intensity of scattered light, even if the light is significantly reduced by the scattered light intensity control means, N
Since the rotation of the D filter holder provides a sufficient amount of light for mask alignment, there are excellent effects such as enabling highly accurate mask alignment.

[Brief explanation of the drawing]

FIG. 1(A) is an explanatory diagram showing the configuration of a particulate measuring device adopting the present invention, FIG. 1(B) is an explanatory diagram of the measurement area, and FIG. 2 is the configuration of the ND filter control system of FIG. 1. 3(A) and (B) are explanatory diagrams showing the influence of the ND filter on mask alignment, and FIG. 4 is an explanatory diagram showing the influence of the ND filter on mask alignment.
) is a flowchart showing the measurement control procedure of the control unit. 1... Laser light source 2... Beam expander 3
...Condensing lens 4...Laser beam 5...Focusing point 6...Scattered light 7...Imaging lens 8...Mask 9
...ND filter holder 10...Photoelectric detector A,
B... ND filter C... Cavity J 1 Ryu 1 Kei Sen 1 Miyagefu O-→--) 11 No. 4
figure

Claims (1)

[Claims] 1) Irradiating a detection area in a medium with a laser beam, receiving laser scattered light from particles in the medium with a photoelectric detector, and measuring particle characteristics according to the output signal of the photoelectric detector. In the particle measuring device, by providing means for controlling the intensity of scattered light input to the photoelectric detector, the intensity of the received scattered light is automatically controlled so as to fall within the dynamic range of the photoelectric detector. A particle measuring device featuring: 2) The photoelectric detector has an optical mask that limits the area in which the scattered light intensity is measured, and a mask alignment mechanism that controls the position of the optical mask in the optical path of the light receiving system according to the output of the photoelectric detector. 2. When the position of the optical mask is controlled by the mask alignment mechanism, the scattered light intensity control means controls the scattered light intensity so that mask alignment is possible. particulate measuring device.