JP2001174394A - Particle size distribution measuring device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To facilitate calibration in a particle size distribution measuring device. SOLUTION: A calibration light source 34 for irradiating at homogeneous illuminance is arranged for a detector 18 for detecting light scattered by a sample. The detector 18 is irradiated by the calibration light source 34 to measure an output from each light receiving element 20. The output is originally proportional to an area of the light receiving element 20. However, when dispersion is produced, a correcting coefficient for correcting the dispersion is determined for each section of the detector 18 corresponding to each light receiving element 20. In an actual particle size measurement of a sample, the correction with the correction coefficient is carried out for the output from each light receiving element 20. Further, the correction coefficient is periodically calculated, and when the coefficient varies largely, abnormality of the device is determined.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a particle size distribution measuring apparatus for measuring the particle size of a granular sample by measuring the intensity distribution of light radiated on the sample and scattered by the sample.

[0002]

2. Description of the Related Art When a particle dispersed at an appropriate concentration is irradiated with light, a scattering phenomenon occurs. It is known that the intensity distribution of the scattered light with respect to the scattering angle varies depending on the particle size (particle size) of the particles, and a particle size distribution measuring device that uses this to determine the particle size of the particulate sample is known.

A particle size distribution measuring device having the following basic configuration is known. That is, it has a laser light source for irradiating the sample with light and a detector having a plurality of light receiving elements for receiving light scattered by the sample. In addition, it has a condensing lens that condenses the light scattered by the sample at a predetermined position on the detector for each scattering angle. The plurality of light receiving elements of the detector are provided corresponding to a predetermined range of the scattering angle. This light receiving element outputs an electric signal according to the amount of light received. Therefore, if the output of each detector, that is, the output of each light receiving element is measured, the intensity distribution of the scattered light can be obtained, and the particle size of the sample can be obtained therefrom.

[0004] The photoelectric conversion efficiency of the light receiving element of the detector, that is, the output value of the electric signal with respect to the amount of received light varies from element to element. For example, even a light receiving element cut out from the same silicon wafer may have a variation of several percent. In addition, the shape of the light receiving element, the characteristics of a processing system for a signal from the light receiving element, and the like may vary. In order to eliminate errors due to these variations, the sensitivity is calibrated for each detector section corresponding to the light receiving element when the apparatus is assembled.

[0005]

As described above, at the time of assembling the apparatus, even if the sensitivity calibration is performed for each detector category, if the detector or the signal processing system circuit is replaced, Since there is a possibility that the characteristics of the parts before and after replacement may be different, it is necessary to perform sensitivity calibration again. Further, even if there is no replacement of parts, even if the characteristics change due to aging, re-calibration is required. On the other hand, it is difficult to perform the same calibration as at the time of assembly with the device installed, and in reality, it is common to remove the device and take it to the factory before performing calibration. There were problems such as the inability to measure the particle size and the increase in man-hours and cost. Further, even if the sensitivity changes due to a change over time, there is a problem that the detection is delayed and the measurement accuracy is reduced.

SUMMARY OF THE INVENTION The present invention has been made to solve the above-mentioned problem, and has as its object to provide a particle size measuring apparatus which can be easily calibrated.

[0007]

In order to solve the above-mentioned problems, a particle size distribution measuring apparatus according to the present invention is a method for irradiating a sample with a measuring light source which irradiates a sample with respect to a detector which detects light scattered by the sample. Separately, a calibration light source that emits light of a predetermined intensity is provided.

[0008] Based on the sensitivity of light from the calibration light source, calibration of the detector, correction of output, and monitoring of abnormality can be performed.

If the calibration light source irradiates the detector with uniform light, the output difference of each section of the detector based on this calibration light source will be a variation for each section. By setting a correction coefficient for each section so as to cancel out this variation and multiplying the output for each section at the time of measurement by this, the aforementioned variation can be eliminated or reduced. In addition, even if the calibration light source does not emit uniform light, if the illuminance distribution is known in advance, the uniform light is determined by determining a correction coefficient in consideration of the illuminance distribution. As in the case of irradiation, the influence of variation can be reduced.

[0010] The output of the detector or the correction coefficient with respect to the light from the calibration light source or the correction coefficient is measured periodically or at a necessary time, and a change with time of the measured value is monitored. And the occurrence of an abnormality in the signal processing system. Preferably, an output value or a correction coefficient at the time of reference as at the time of assembling the device is stored, and the stored value is compared with a measured value. When the difference becomes larger than a predetermined value, an abnormality is detected. Notify.

Also, the light source for calibration can change the amount of light,
Irradiation with a plurality of light amounts can be performed. According to this, it is possible to accurately correct the variation when the dynamic range of each section of the detector greatly differs.

[0012]

Embodiments of the present invention (hereinafter referred to as embodiments) will be described below with reference to the drawings. FIG.
It is a figure showing the schematic structure of the particle size distribution measuring device of this embodiment. The sample to be measured is placed in the scattering field 10 in an appropriately dispersed state. Further, the scattering field 10 may be a part of the pipe, and the sample may be flowing in the pipe. The sample placed in the scattering field 10 is irradiated with parallel rays from the laser light source 12 via the collimator 14. In the scattering field 10, light hitting the sample particles is scattered. The distribution of the scattered light, that is, the distribution of the light intensity at each angle (scattering angle) θ of the scattered light with respect to the irradiated light changes depending on the particle size of the sample. Distributed over a wide range. The light that has passed through the scattering field 10 passes through the condenser lens 16 and reaches the detector 18.
The condenser lens 16 is a lens that collects light at a predetermined position on the detector 18 for each scattering angle θ. That is, even if the light scattered by the particles at different positions in the scattering field 10 has the same scattering angle θ, the light condensing position on the detector 18 is the same.

FIG. 2 shows a detector 1 viewed from the light irradiation direction.
8 is shown. The detector 18 has a substantially sector shape as shown, and the tip O of the sector shape is
It is arranged so as to coincide with the center of the optical axis from the light source 12. Further, the light receiving element 20 is divided into a plurality of sections by a concentric circle centered on the tip O, and the light receiving element 20 is arranged for each section. Therefore, one light receiving element 20 has a shape that becomes a part of a ring. Due to this arrangement, a certain range of the scattering angle θ is condensed on one light receiving element 20. The light receiving element 20 is an element that outputs an electric signal according to the received light amount. Further, as shown in the figure, the area of the light receiving element 20 is narrow near the tip O and wide on the far side. This considers that the output of each light receiving element 20 is made as uniform as possible in response to the intensity distribution of the scattered light having a small scattering angle θ, that is, a distribution in which more light is collected near the tip O. It was done.

FIG. 3 shows a part of a processing system for an output signal of the light receiving element 20. The output of the light receiving elements 20 is amplified by preamplifiers 22 arranged one for each light receiving element 20, and sent to a multiplexer 24. In the multiplexer 24, the output of one light receiving element 20 is selectively sent to the amplifier 26, the output to be selected is switched, and the outputs of all the light receiving elements 20 are sequentially sent out. Returning to FIG. 1, the output of the amplifier 26 is sent to an arithmetic and control unit 30 through an A / D (analog / digital) converter 28, where the intensity distribution of the scattered light is Is calculated, and an operation relating to the particle size of the sample is performed. The measurement results and the like are sent to an output device 32 such as a printer or a display.

As shown in FIG. 1, in the present embodiment, a calibration light source 34 is disposed behind the condenser lens 16 and in front of the detector 18. The calibration light source 34 can irradiate the detector 18 with light with uniform illuminance. It is desirable that the position of the calibration light source 34 be as far as possible from the detector 18 in order to obtain uniform illuminance. As a result, it is preferable that the calibration light source 34 be disposed immediately after the condenser lens. By this irradiation, the output of the light receiving element 20 becomes proportional to the area. If the output of the light receiving element 20 deviates from this relationship, the photoelectric conversion efficiency of the light receiving element 20 or
It is considered that there is variation in the signal processing system such as the preamplifier 22. When such a variation occurs, the arithmetic and control unit 30 performs normalization so that the output of each light receiving element 20 is proportional to the area thereof, and determines a correction coefficient for each output. For example, an appropriate correction coefficient exceeding 1 is set for the light receiving element 20 considered to have a low output, and an appropriate correction coefficient less than 1 is set for the light receiving element 20 considered to be a high output. I do. The set correction coefficient is stored in the correction coefficient storage unit in the arithmetic and control unit 30. At the time of actual measurement, the output of each light receiving element 20 is multiplied by the correction coefficient so as to cancel out the variation of the detector corresponding to each light receiving element 20 for each section.

The determination of the correction coefficient is performed by the arithmetic and control unit 30.
Is executed periodically or as needed, and each time it is compared with a coefficient initially set in the arithmetic and control unit 30 or a reference coefficient. In this comparison, if these differences are larger than the predetermined value, the arithmetic and control unit 30 determines that some abnormality has occurred,
This is notified by the output device 32. The threshold value for this abnormality determination is determined by the difference between the currently calculated coefficient and the previous coefficient,
Or it can be determined corresponding to the ratio.

FIG. 4 shows an example of the configuration of the calibration light source 34. An LED (light emitting diode) 38 serving as an actual light source is embedded in an opaque housing 36. The light emitted from the LED 38 passes through a diffusion plate 42 arranged so as to cover the entire opening 40 of the housing 36 and is irradiated as uniform light.

As described above, when the calibration light source 34 irradiates the detector with uniform illuminance, the output of each light receiving element 20 is
It is proportional to its area. For this reason, at the time of calibration, depending on the position of the light receiving element 20, a light amount significantly different from that at the time of actual particle size measurement and an output is also different. Therefore, at the time of calibration, in the light receiving element 20 and the signal processing system,
It is also conceivable that the light intensity and the output may not be in a preferable range for measurement, for example, in a range where linearity can be obtained. At this time,
This can be dealt with by preparing two or more types of illuminance of the calibration light source 34. Two types of light sources for high illuminance and low illuminance may be used, and two equivalent light sources are prepared, and a difference in illuminance can be obtained by irradiating only one and irradiating both.

The light source for calibration uses the detector 1 with sufficiently uniform illuminance.
Even when the irradiation of No. 8 cannot be performed, it is possible to monitor the abnormality of the device by comparing with the previous measurement. In addition, at the time of assembly of the device, while performing the conventional calibration,
By measuring the output of the calibration light source and comparing these, the illuminance distribution of the calibration light source is determined in advance,
Can respond.

In monitoring changes over time, the output itself can be compared with the previously measured and calculated correction coefficient and the correction coefficient calculated at the present time. For example, at the time of assembling the device, the output of each section of the detector 18 by the calibration light source may be stored, and an abnormality may be determined by comparing the output with a similar measurement later.

The light source for calibration is not limited to the LED, and other light sources such as a halogen lamp can be used.
Further, irradiation may be performed using a predetermined wavelength component, for example, a wavelength component of the light source 12 using a bandpass filter.

Although the case where the calibration light source is fixed has been described above, the light source may be movable. That is, at the time of measurement, a position retracted from the optical path from the scattering field may be set, and at the time of calibration, the entire detector may be irradiated with light for calibration from a position at which almost the same illuminance is provided, for example, from the front of the detector.

[Brief description of the drawings]

FIG. 1 is a block diagram showing a schematic configuration of the present embodiment.

FIG. 2 is a diagram showing a configuration of a detector.

FIG. 3 is a diagram showing a configuration of a detector and a signal processing system.

FIG. 4 is a diagram showing a configuration of a calibration light source.

[Explanation of symbols]

10 scattering field, 12 light source, 16 condenser lens, 18
Detector, 20 light receiving element (classification of detector), 22 preamplifier (signal processing system), 30 arithmetic and control unit.

Claims (6)

[Claims] 1. A particle size distribution measuring device for measuring the particle size of a sample by measuring the scattering state of light applied to a dispersed granular sample, wherein a detector for detecting light scattered by the sample is applied to a sample. A particle size distribution measuring device having a calibration light source for irradiating light of a predetermined intensity separately from a measuring light source for irradiation. 2. The particle size distribution measuring device according to claim 1, wherein the detector is constituted by a plurality of light receiving elements, and has a section determined for each light receiving element, and the detector for the light from the calibration light source is provided. A particle size distribution measuring device, comprising: output correction means for obtaining variations in characteristics of each of the sections based on outputs of the sections of the detector, and correcting outputs of the respective sections based on the variations. 3. The particle size distribution measuring device according to claim 2, wherein the correction coefficient storage means for storing each correction coefficient calculated for each of the sections, the correction coefficient stored in the correction coefficient storage means and a current value. And an abnormality notifying means for notifying the difference when the difference is larger than a predetermined value. 4. The particle size distribution measuring device according to claim 1, wherein the detector is constituted by a plurality of light receiving elements, and has a section determined for each light receiving element. A particle size distribution measuring device, comprising: comparing the output of each of the detector sections with a previous output, and when the difference is larger than a predetermined value, notifying the abnormality of the difference. 5. The particle size distribution measuring device according to claim 2, wherein the calibration light source irradiates at least the detector with uniform light. 6. The particle size distribution measuring device according to claim 1, wherein said calibration light source is capable of irradiating light with a plurality of types of light amounts.