JPH05149866A - Particle detector - Google Patents

Abstract

PURPOSE:To avoid the occurrence of a counting error in the case of the generation of a self noise, by receiving focused light with a plurality of optoelectric transducers, and by transmitting to count a pulse for detecting a particle, only where pulses for detecting scattered lights outputted from the respective elements are in a fixed time. CONSTITUTION:A focused light LA2 moves from one split optoelectric transducer 11A to the other one 11B separated respectively, and the signal is supplied to a circuit 12 for generating a counting pulse, delaying by the time lag TA for moving. Delay circuits 26, 27 supply an AND circuit 28 with a continuous pulse signal from the time of the pulse generation to the lapse of a fixed continuous time TB. The circuit 28 makes the logical operation of continuous pulse signals S14 and S24, and gives a circuit 13 for counting the number of particles the detecting signals S31 during the overlapping of continuous pulses, and the circuit 13 counts them. Counting errors can be reduced even where pulses overlap each other and self noises generate, by selecting the time TB longer than the time difference TA.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a particle detecting device, and more particularly to a so-called light scattering type particle detecting device for detecting the concentration of particles in a liquid which is a gas or a liquid, for example, using a light beam which is a laser beam. It is suitable for application.

[0002]

2. Description of the Related Art Conventionally, as a light scattering type particle detector, for example, when measuring the cleanliness of a clean room in a semiconductor manufacturing process, a sample air AIR flowing from an inflow side nozzle 1 as shown in FIG. The discharge-side nozzle 3 is configured to jet the particle-detecting light beam 2 composed of the following.

Particle PCL contained in the sample air AIR
Generates scattered light LA1 when it traverses the light beam 2, and causes the scattered light LA1 to be condensed by the condenser lens 4 onto the light receiving section 5 which is a photoelectric conversion element.

Thus, the light receiving section 5 includes a particle detection pulse P1 having a crest value corresponding to the light quantity of the scattered light LA1 and hence the particle diameter of the particle PCL as shown in FIG. 4A every time the particle PCL passes. A photoelectric conversion output S1 composed of a voltage signal is generated, and this photoelectric conversion output S1 is supplied to the amplification processing circuit unit 6.

When the voltage level of the photoelectric conversion output S1 exceeds a particle selection level K0 having a threshold voltage corresponding to a predetermined particle size D, the amplification processing circuit section 6 detects the voltage as shown in FIG. 4 (B). Generates pulse P2 and detects this pulse output S
The number 2 is given to the particle number counting unit 7 to count the number of particles contained in the unit volume of the sample air AIR passed through the particle number counting unit 7.

[0006]

However, in practice, noise N1 randomly generated in the photoelectric conversion element (this is called self-noise) is superimposed on the photoelectric conversion output S1 of the light receiving portion 5 formed of the photoelectric conversion element. For some reason, the level of the self-noise N1 is, as shown by the noise waveform N1 in FIG.
When it exceeds 0, the amplification processing circuit unit 6 generates a noise pulse PN1 as shown in FIG. 4B, and the particle number counting unit 7 may erroneously count.

The present invention has been made in consideration of the above points, and it is possible to sufficiently suppress the possibility that the particle count result will be erroneously counted even if self-noise occurs in the photoelectric conversion element. The present invention intends to propose a particle detection device according to the above.

[0008]

In order to solve such a problem, in the present invention, a plurality of photoelectric conversion elements 11A and 1A are used.
1B, the plurality of photoelectric conversion elements 11A and 11B are
The focused light LA2 of the scattered light LA1 generated when the particles PCL contained in the sample fluid AIR move in the particle detection light beam 2 are arranged so as to be sequentially adjacent in the moving direction according to the movement of the particles PCL. The photoelectric conversion element 11A or 11 and the light receiving unit 11 that sequentially outputs the scattered light detection pulses P11 and P12 each time the focused light LA2 passes.
Each time the scattered light detection pulse P11 or P12 is generated from B, the focused light LA2 is converted into a plurality of photoelectric conversion elements 11A and 11A.
Performing AND operation of the sustain pulses P31 and P32 with the sustain pulse forming means 26 and 27 respectively outputting the sustain pulses P31 and P32 having the predetermined duration TB equal to or longer than the time difference TA required to pass B. AND logic operation means 2 for sending out a particle detection pulse P41 having a pulse width corresponding to the time when the continuous pulses P31 and P32 outputted from the continuous pulse forming means 26 and 27 overlap with each other.
8 and pulse counting means 13 for counting the particle detection pulse P41.

[0009]

The converged light LA2 of the scattered light LA1 by one particle PCL is received by the plurality of photoelectric conversion elements 11A and 11B, and at the same time, scattered light detection sequentially output from each of the plurality of photoelectric conversion elements 11A and 11B is detected. Only when the pulses P11 and P12 are within the predetermined time TB, the logical product calculating means 28 sends out the particle detection pulse P41 and causes the pulse counting means 13 to count, whereby each photoelectric conversion element 11A or 11B. Even when self-noise N1 that exceeds the particle selection level K0 occurs in the above, it is possible to effectively avoid the occurrence of false counting, and thus the false counting is small, and the count value can be measured with high reliability. Can be realized.

[0010]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS An embodiment of the present invention will be described in detail with reference to the drawings.

In FIG. 1 in which parts corresponding to those in FIG. 3 are designated by the same reference numerals, 10 indicates a light scattering type particle detecting device as a whole, and a light receiving portion 11 is two divided photoelectric conversion elements 11A each of which is a photodiode. And 11B, the divided photoelectric conversion elements 11A and 11B are sequentially adjacent to each other in the direction in which the focused light LA2 obtained via the condenser lens 4 moves when the particle PCL moves in the particle detection light beam 2. It is arranged to do.

Thus, the particle PCL in the sample air AIR
Between the inflow side nozzle 1 direction and the outflow side nozzle 3 direction after the light beam has entered the light beam 2 and exits in the discharge side nozzle 3 direction.
The focused light LA2 of A1 moves from the divided photoelectric conversion element 11A to the divided photoelectric conversion element 11B on the light receiving surfaces of the divided photoelectric conversion elements 11A and 11B in accordance with the movement of the particle PCL, and as a result, the divided photoelectric conversion is performed. Elements 11A and 11B
2A and 2B, respectively, scattered light detection pulses P11 and P1 are generated which are temporally shifted by the movement time difference TA according to the movement of the focused light LA2.
A pair of photoelectric conversion output signals S11 and S21 including 2 are supplied to the counting pulse generating circuit 12, respectively.

The photoelectric conversion output signals S11 and S21 are amplified by the amplification circuits 20 and 21 of the counting pulse generation circuit 12, respectively.
Is supplied to the DC / AC separation circuits 22 and 23 via the DC line, and only the AC component contained in the photoelectric conversion output signals S11 and S21 is detected as shown in FIGS. 2 (A) and 2 (B).
12 and S22 are supplied to the comparison circuits 24 and 25.

Comparing circuits 24 and 25 detect the detection signal S12.
And S22 are compared with the particle size selection levels K1 and K2, respectively, and when the signal levels of the detection signals S12 and S22 exceed the particle size selection levels K1 and K2 as shown in FIGS. 2 (C) and 2 (D). The count pulse signals S13 and S23 including the count pulses P21 and P22 rising to the logic "1" level are supplied to the delay circuits 26 and 27, respectively.

The delay circuits 26 and 27, as shown in FIGS. 2 (E) and 2 (F), detect pulse signals S13 and S2.
3 when a pulse is generated, the continuous pulse signal S including the continuous pulses P31 and P32 which rises to the logic "1" level during the period from that time until the predetermined duration TB elapses.
14 and S24 are supplied to the AND circuit 28.

Here, the duration TB is the detection pulse signal S
When the detection pulses P21 and P22 corresponding to the scattered light detection pulses P11 and P12 are sequentially generated in 13 and S23, they are preselected to have a size slightly longer than the movement time difference TA that occurs between them, whereby one detection pulse P21
The leading edge portion of the sustain pulse P32 corresponding to the other detection pulse P22 temporally overlaps the trailing edge portion of the sustain pulse P31 corresponding to.

The logical product circuit 28 performs the logical product operation of the continuous pulse signals S14 and S24 to detect the particle which rises to the logic "1" level while the continuous pulses P31 and P32 overlap as shown in FIG. 2 (G). The particle detection signal S31 including the pulse P41 is given to the particle number counting circuit 13 to be counted.

In the above structure, when the particle PCL is carried by the sample air AIR, the irradiation position of the focused light LA2 on the light receiving portion 11 moves in accordance with the movement of the particle PCL, so that the divided photoelectric charges are generated. After the state where the conversion element 11A is irradiated is obtained, the divided photoelectric conversion element 11B is changed to the state where the divided photoelectric conversion element 11B is irradiated (FIGS. 2A and 2B).

Accordingly, the focused light LA2 is divided by the comparison circuits 24 and 25 of the counting pulse generation circuit 12 into the divided photoelectric conversion element 1.
Detection pulses P21 and P22 having a time difference TA corresponding to the time required to move from the 1A side to the divided photoelectric conversion element 11B are sequentially generated (FIG. 2 (C) and FIG. 2).
(D)).

Thus, the delay circuits 26 and 27 generate the sustaining pulses P31 and P32 having the durations TB which partially overlap each other (FIGS. 2E and 2).
(F)) As a result, the particle detection light beam 2 is directed to the particle PCL.
Pulse passes from the AND circuit 28 every time
By obtaining the particle detection pulse P41 having a pulse width corresponding to the overlap period of P1 and P32, the number of particles carried by the sample air AIR can be counted in the particle number counting circuit 13.

During such a particle detection operation, for example, at time tx in FIG. 2, pulse-shaped self-noise N2 (FIG. 2A) is generated in one of the divided photoelectric conversion elements 11A, for example. Noise pulse PN2 (Fig. 2
(C) is a detection pulse signal S obtained from the comparison circuit 24.
When mixed in 13, the continuous pulse PN3 (FIG. 2E) corresponding to the noise pulse PN2 is mixed in the continuous pulse signal S14 of the delay circuit 26.

However, at this time, no self-noise is generated in the other divided photoelectric conversion element 11B (FIG. 2 (B), FIG. 2 (D)), and therefore the other delay circuit 27 does not generate a continuous pulse ( FIG. 2 (F). Accordingly, the divided photoelectric conversion element 11 is included in the particle detection signal S31 of the AND circuit 28.
The false detection pulse based on the self-noise of A does not occur (FIG. 2 (G)).

According to the above construction, the focused light is caused to move on the divided photoelectric conversion elements 11A and 11B in accordance with the movement of the particle PCL, and at the same time, each photoelectric conversion output signal S1.
2 and S22, the durations TB of the duration pulses P31 and P32 generated on the basis of 2 and S22 are selected to be larger than the movement time difference TA of the focused light so that the durations TB overlap each other. Even if self-noise occurs in either one, it is possible to further reduce the probability of erroneous counting.

Actually, two divided photoelectric conversion elements 11 are used.
The probability that self-noise will occur in A and 11B at the same time is extremely small, and according to experiments, the divided photoelectric conversion elements 11A and 1B are
1B photoelectric conversion output signal S12 or S obtained from one side
Even if the ratio S / N of the white noise to the particle pulse of 22 was about 2, the miscount due to self-noise generated from the divided photoelectric conversion elements 11A and 11B could be suppressed to 1 or less per hour.

In the above embodiment, the light receiving section 11
However, the present invention is not limited to this, and various materials can be applied as the material of the light receiving portion 11 as long as they can generate a photoelectric conversion action. Further, in the above-described embodiment, the light receiving unit 11 has two
Although the case of division is described, the present invention is not limited to this, and two individual photoelectric conversion elements may be arranged side by side in the same direction as the direction in which particles pass.

Further, in the above embodiment, the light receiving section 1
Although the case where 1 is divided into 2 has been described, the present invention is not limited to this, and the photoelectric conversion element is divided into 3 or more divisions and the logic based on the photoelectric conversion output signal obtained from each division element. The product circuit 12 outputs the particle detection signal S31.
May be output.

[0027]

As described above, according to the present invention, the scattered light of the particle detection light beam applied to the sample fluid is converted into a plurality of particle detection pulse signals having a time difference according to the moving time of the particles, and the particles are moved. Self-noise is generated in each photoelectric conversion element by generating a plurality of continuous pulses having a longer duration than the time based on the particle detection pulse signal and obtaining a particle detection pulse corresponding to the overlapping portion of both. Even in such a case, it is possible to effectively prevent erroneous counting from occurring, and thus it is possible to realize a particle detection device with few erroneous counting and highly reliable measurement of the count value.

[Brief description of drawings]

FIG. 1 is a block diagram showing an embodiment of a light scattering type particle detection device according to the present invention.

FIG. 2 is a signal waveform diagram showing a waveform of an electric pulse generated in each signal.

FIG. 3 is a block diagram showing a conventional light-scattering particle detection device.

FIG. 4 is a signal waveform diagram showing a waveform of an electric pulse generated in a particle detection signal.

[Explanation of symbols]

2 ... Particle detection light beam (light beam), 10 ... Particle detection device, 11 ... Light receiving part, 11A, 11B ... Photoelectric conversion element (divided photoelectric conversion element), 13 ... Pulse counting means (number of particles) Counting circuit), 26, 27 ... Continuous pulse forming means (delay circuit), 28 ... Logical product calculating means (logical product circuit), LA1 ... Scattered light, LA2 ... Focused light, P11,
P12 ... Scattered light detection pulse, P31, P32 ... Continuous pulse, P41 ... Particle detection pulse, AIR ... Sample fluid (sample air), PCL ... Particle, TA ... Time difference, T
B ... Duration.

Claims (1)

[Claims] 1. A plurality of photoelectric conversion elements, wherein in the plurality of photoelectric conversion elements, focused light of scattered light generated when particles contained in a sample fluid move in a particle detection light beam is used. A light receiving portion which is arranged so as to be adjacent to each other in the direction of movement in accordance with the movement of the above, and which sequentially outputs a scattered light detection pulse each time the focused light passes through; Each time a pulse is generated, a continuous pulse forming means for outputting a continuous pulse having a predetermined duration longer than the time difference required for the focused light to pass through the plurality of photoelectric conversion elements, and a logical product of the continuous pulses AND operation means for transmitting a particle detection pulse having a pulse width corresponding to the time at which the continuous pulses output from the continuous pulse forming means overlap by executing the operation, and the particle detection means. Particle detector, characterized in that it comprises a pulse counting means for counting the pulses.