JPS62108386A - Particulate counter - Google Patents

Abstract

PURPOSE:To reduce a noise component, and to perform the measurement of a particulate by receiving two sets of scattered rays of light with two photodetectors, and performing a pulse-amplitude analysis after the signal outputs are multiplied at an analog multiplication circuit. CONSTITUTION:Irradiating light 2 from a laser light source 1 irradiates a fluid trickle 3, and two sets of scattered rays of light 4 and 4' emitted from the particulate are condensed at lenses 5 and 5' respectively, and are received at two sets of photomultipliers PMT 6 and 6'. The photodetecting signals of the PMTs 6 and 6' are amplified respectively at amplifiers 7 and 7', and are inputted to an analog multiplier 12. The output signal of the multiplier 12 is inputted to a counter 10 through a differential amplifier 9, and the count value of the counter 10 becomes a value that the pulse-amplitude analysis is applied on an input signal. Thus, by multiplying two waves including random signal noise with each other, a true signal overlapped simultaneously in each wave is separated from the noise and can be taken out.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Application of the Invention] The present invention relates to a particle counter that measures particles in a fluid.

[Background of the invention]

A light scattering type particle counter that measures the particles by detecting scattered light emitted by particles suspended in a fluid generally has a fifth particle counter.
It is configured as shown in the figure, and the irradiation light 2 from the light source 1
irradiates a stream 3 of fluid containing fine particles, and a part 4 of the scattered light from the fine particles is focused by a lens 5 and received by a photomultiplier tube (PMT) 6. Although FIG. 5 shows the case where a laser light source is used as the light source, the same applies when an incandescent lamp is used as the light source. 7 is an amplifier, 8 is a voltage source that provides a threshold value Vth, 9 is a voltage comparator, and 10 is a counter. The above P M T 6 is due to fluctuations between photoelectron emission and secondary electron emission. Generates so-called shot noise (N),
If the signal (S) due to the scattered light from the particles is weak, it will be buried in noise and cannot be detected. Figure 6 is an example of a waveform detected by PMT when a relatively large particle passes through the irradiation area, where the circle in the figure indicates the particle scattered light, and all other random waves other than the circle above are noise. . When the threshold value Vth is selected as shown by the broken line in FIG. 6, the number of particles can be determined by counting the signals exceeding the threshold value. In the waveform when the particle size of the particles is even smaller, as shown in FIG. 7, the height of the scattered light signal M from the particles approaches the noise signal.

Therefore, the signal M cannot be counted unless the threshold value Vth approaches the height of the noise. If the threshold value is brought close to noise in this way, there is a risk of erroneous counting, so generally the S/N ratio is set to a margin of 1.5 to 2 or more. The largest source of noise (N) is the shot noise contained in the DC component of the PMT output current, which is caused by a portion of the irradiated light reflecting off the inner surface of the detection cell and entering the PMT. In order to reduce the amount of light (called stray light), the structure of the detection cell and the prevention of reflection on the inner surface must be devised. FIG. 8 is a diagram showing the configuration of a so-called scanning-type light-scattering particle counter that oscillates irradiation light periodically at high speed. The light from the laser light source 1 is swung by a scanning oscillating mirror 11.

Fine particles 12 suspended in the fluid are irradiated. The part indicated by 13 in the figure is the detection space, and the lens 5° slit 1 is designed to detect only the scattered light from the detection space 1;
4. The light is focused through the lens 5' and received by the PMT 6, but the steps after the PMT 6 are the same as in the case of FIG. 3 above.

Since the wl measurement field is limited by the slit 14, scattered light from only the particles present in the detection space 13 can be received. In the above configuration, even if the particles are stationary, the laser beam is scanning at high speed, so the received light signal becomes a pulse. However, even if the detection space 13 is limited as described above, the stray light still exists. cannot be reduced below a certain point. In other words, since there is a limit to reducing the noise itself, it is difficult to measure even smaller particles unless the S/N ratio is improved through signal processing.

A light scattering particle measuring device is disclosed in the already well-known Japanese Utility Model Application Publication No. 58-138063. In this known example, as shown in FIG. 9, the scattered light scattered by the fine particles is received in equal amounts by two light receiving elements 6.6' arranged very close to each other, and the threshold value is 8.8'. When the threshold value is set to 1, the results of wave height analysis by voltage comparators 9 and 9', respectively, are analyzed by six measuring devices in which simultaneous signals are determined by an AND circuit 15. When trying to process a waveform by obtaining a signal, the voltage comparator 9, for example,
As shown in a), only signal C enters the AND circuit 15,
The voltage comparator 9' outputs a signal A as shown in FIG. 2(b).
, B, and D enter the AND circuit 15, the above AN
The output of the D circuit 15 becomes zero, and the waveform cannot be judged or processed.

[Purpose of the invention]

An object of the present invention is to obtain a particle counter with reduced noise components.

[Summary of the invention]

The particle counter of the present invention is a particle counter that measures the diameter and number of particles by irradiating light beams onto particles floating in a fluid, detecting scattered light from the particles, and collecting the particles with a condensing lens. Two light-receiving elements each receive two sets of scattered light, and the signal output of each light-receiving element is processed by an analog multiplication circuit.

After the multiplication, the noise component is reduced by providing means for analyzing the wave height.

[Embodiments of the invention] Next, embodiments of the present invention will be described with reference to the drawings.

FIG. 1 is a block diagram showing a first embodiment of a particle counter according to the present invention, FIG. 2 is an input and output waveform diagram of the analog multiplication circuit in the above embodiment, and FIG. 3 is a diagram showing a second embodiment of the present invention. FIG. 4 is a block diagram showing a third embodiment of the present invention. In FIG. 1, irradiation light 2 from a laser light source 1 irradiates a fluid trickle 3 containing suspended particles, and two sets of scattered lights 4, 4' emitted from the particles are transmitted to a lens 5.
5' and two photomultiplier tubes (PMT) 6.6'
The received light signals of each PM 76.6' are amplified by amplifiers 7.7' and input to the analog multiplier circuit]2. The light receiving systems 5 to 7 and 5' to 7' are the same, but are arranged at symmetrical positions with respect to the optical axis of the laser irradiation light 2. 10 is a counter.

When the respective inputs X and Y of the analog multiplier circuit 12 are input from the respective amplifiers 7' and 7, the analog multiplier 12 performs an operation such that -X-Y (k is a constant). FIG. 2 shows examples of signal waveforms of input X, input Y, and XY. In the figure, (a) is the waveform of x (shi), (
b) shows the waveform of Y (t), and (C) shows the waveform of XY.

Input X and large input are random signals arbitrarily generated by a computer, and are considered to correspond to noise of PMT6.6'. X・Y corresponds to the output of the analog multiplication circuit 12 (the value obtained by multiplying the values of X(t), YD) at each time), where A', B, C
, D, the scattered signals are X (t), Y (t
), and the magnitude of each signal is 0.5 (the minimum value of noise is O1, the maximum value is 1), and the magnitude of each signal is 0.5.
),.

The waveform when the signals are superimposed is indicated by a 0 mark.

As is clear from the figure, in the waveform of X (t), only the C signal can clearly separate the noise. In the Y(t) waveform, each of the A, B, and D signals can be separated from the noise, but the C signal is hidden by the noise and is difficult to separate. However, when looking at the X-Y waveform (c), A, B, C,
It is possible to separate all signals in D from noise. In this way.

By mutually multiplying two waves containing random signal noise, the true signal that is simultaneously superimposed in each wave can be separated from the noise and extracted.

In the second embodiment shown in FIG. 3, a laser beam from a laser light source is bent at right angles by a mirror 16 for changing the optical path, enters a vibration mirror 11 to form a scanning beam, and the scanning beam is converted to a scanning beam by a lens 17. After making them parallel, the floating particles 12 are irradiated, and the scattered light is transmitted to each PMT 6.6' through lenses 5, 5' and slits 14 and 14'.
It is receiving light. The signal processing system for the light-receiving signal is the same as that in the first embodiment, so it is omitted.

In the third embodiment shown in FIG. 4, scattered light emitted from a fluid stream 3 containing fine particles is focused by a single condensing lens 5 using a laser beam from a laser light source 1, and then a half mirror 18
splits each light into two parts, the transmitted light and the reflected light, and PM each light.
Light is received at T6 and 6'. 19 in the figure is an optical trap. The signal processing system for the received light signal is the same as that in the first embodiment, and is omitted in the figure.

Although each of the above embodiments uses laser light from a laser light source, it goes without saying that similar results can be obtained even when an incandescent lamp is used as the light source.

〔Effect of the invention〕

As described above, the particle counter according to the present invention irradiates light beams onto particles floating in a fluid, detects scattered light from the particles, and measures the diameter and number of particles. By providing two light-receiving elements that each receive two sets of scattered light condensed by an optical lens, and a means for multiplying the signal output of each light-receiving element by an analog multiplier circuit and then analyzing the wave height, noise components can be detected. Because it is possible to reduce the noise and separate the above signal from the noise,
It is possible to count even smaller particles.

[Brief explanation of drawings]

FIG. 1 is a block diagram showing a first embodiment of a particle counter according to the present invention, FIG. 2 is an input and output waveform diagram of the analog multiplication circuit in the above embodiment, and FIG. 3 is a diagram showing a second embodiment of the present invention. FIG. 4 is a configuration diagram showing the third embodiment of the present invention, FIG. 5 is a configuration diagram showing a conventional particle counter, and FIG. 6 is a configuration diagram showing a conventional particle counter. Figure 7 is a diagram showing an example of a detection waveform when a small particle passes through the irradiation area, Figure 8 is a configuration diagram of a scanning type light scattering particle counter, and Figure 9 is a diagram showing a detection waveform when a small particle passes through the irradiation area. FIG. 2 is a configuration diagram of a conventional example using an AND circuit for signal determination.

Claims (4)

[Claims] (1) In a particle counter that measures the particle size and number of particles by irradiating light beams onto particles floating in a fluid and detecting the scattered light from the particles, two sets of light beams focused by a condensing lens are used. A particle counter comprising two light receiving elements each receiving scattered light, and means for multiplying the signal output of each light receiving element by an analog multiplication circuit and then analyzing the wave height. (2) The fine particles according to claim 1, wherein the two sets of scattered lights are optically divided into two pieces of scattered light collected by one condensing lens. Counter. (3) The particle counter according to claim 1, wherein the two sets of scattered lights are respective scattered lights that are separately focused by two condenser lenses. (4) The scope of the claim characterized in that the scattered lights separately focused by the two focusing lenses have their focusing optical axes set at symmetrical angles with respect to the irradiation optical axis. The particulate counter described in Section 3.