JPH0339635A - Particulate measuring instrument - Google Patents

Abstract

PURPOSE:To accurately detect even ultra fine particles (of <=0.07mum in particle size) by selecting and outputting only an output signal which exceeds a preset threshold value and has simultaneousness out of the output signals of two photodetectors 7 and 7'. CONSTITUTION:The photodetectors 7 and 7' are provided at positions of about + or -60 deg. to the optical axis of a light beam 1 opposite to the spherical part 4a of a flow cell 4. Light scattered by a fine particle in liquid to be measured is photodetected by the photodetectors 7 and 7' at the same time. A detection part extracts only signals which exceed the preset threshold value from the output signals of the photodetectors 7 and 7' by respective discriminating circuits and further selects and outputs only signals which have simultaneousness among them by a decision circuit. A counting circuit counts those signals and then the counted value corresponds to the quantity of fine particles larger than the particle size corresponding to the threshold value. Further, the threshold value is set in plural stages and signals exceeding the respective threshold values are counted respectively to find the difference between two optional counted values, thereby finding the distribution of the quantity of fine particles of size between the particle sizes corresponding to the two threshold values, i.e. particle size.

Description

[Detailed Description of the Invention] (Industrial Application Field) The present invention relates to an apparatus for measuring the number and particle size distribution of fine particles contained in liquids such as ultrapure water, ultra-superpure water, chemical solutions, and gases such as air. .

(Prior technology) For example, ultrapure water and ultra-superpure water used in semiconductor manufacturing processes are required to have an extremely high level of cleanliness. There is a number of fine particles inside. By the way, the number of fine particles contained in such ultrapure water or ultra-super pure water is only about a few per ml, but the particle size varies from large to small, and in recent years, the particle size has increased. It is required to be able to accurately detect even extremely small particles of about 0.05 to 0.1 μm.

Now, as a particulate measuring device, one that measures particulates contained in ultrapure water is available in "Ultra LSI Ultra Clean Technology Symposium Proceedings", pp. 27-40 (19
(1987).

This conventional device consists of a light source that generates a light beam, a flow cell placed on the optical axis of the light beam through which ultrapure water to be measured flows, and a light receiver placed opposite the flow cell. A light beam is irradiated onto the ultrapure water flowing through the flow cell, and the light scattered by fine particles in the ultrapure water is collected and received by a light receiver, and the fine particles are detected from the peak that appears in the output signal of the light receiver. The number and particle size distribution of the scattered light can be determined by comparing the peak of the output signal of the receiver with a preset threshold, and detecting the difference between Since this method is carried out by counting the peaks that occur, there is a problem in that it is difficult to measure fine particles with a particle size of 0.07βm or less. In other words, the peak of the output signal of the photoreceiver based on the scattered light of particles with a particle size of 0.07 μm or less is extremely low, so in order to capture such particles, the threshold value must be set based on the dark current of the photodetector, etc. It is necessary to lower the background level to the very limit, but if this is done, when noise is superimposed on the output signal of the receiver for some reason, the peak will be
It becomes impossible to distinguish whether it is caused by fine particles or noise.

(Problems to be Solved by the Invention) The purpose of the present invention is to solve the above-mentioned problems of conventional devices, and to be able to detect extremely accurately even fine particles with particle diameters of 0.07 μm or less. We are here to provide you with the equipment you need.

(Means for Solving the Problems) In order to achieve the above object, the present invention includes a light source that generates a light beam, a flow cell provided on the optical axis of the light beam, through which a fluid to be measured flows, and a flow cell that is provided on the optical axis of the light beam. 1 each at a position facing the flow cell and symmetrical with respect to the optical axis.
It has a total of two light receivers, each of which is individually provided, and a detection section that is connected to these two light receivers, and the detection section is connected to each of the two light receivers. established,
Out of the output signals of each of these photoreceivers, a total of two identification circuits extract only the output signals exceeding a preset threshold value, and these two identification circuits are connected to these two identification circuits. a determination circuit that selects and outputs only simultaneous output signals from among the output signals of the individual identification circuits;
The present invention provides a particle measuring device characterized by comprising a counter circuit that counts the output signal of the determination circuit.

In the above, a laser light source such as an argon laser is usually used as a light source that generates a light beam.

Further, a flow cell, which is provided on the optical axis of the light beam and through which the fluid to be measured flows, is made of a transparent material such as quartz glass. The shape may be cylindrical, such as a cylinder or a rectangular tube, but if one with a spherical part is used and the optical axis of the light beam is located at the center of the spherical part, the flow cell and the fluid to be measured are It is now possible to prevent light scattered by the interface between the flow cell and the air from entering the receiver, and it is now possible to efficiently receive only the light scattered by the particles passing through the center of the spherical part. This is preferable because the background level in the output signal of the photoreceiver is lowered and the S/N ratio is improved.

The light receiver has a photomultiplier, a phototransistor, or the like as a light receiving element. Then,
A total of two light receivers are provided, one in each position facing the flow cell and symmetrical with respect to the optical axis of the light beam. According to Mie's scattering theory, the smaller the angle between the optical axis and each light receiver, the greater the intensity of the scattered light by the particles, but if it becomes too small, the proportional relationship between the particle diameter of the particles and the intensity of the scattered light deteriorates. Therefore, it is most preferable to set the angle to 60° or around 60°.

The detection section includes a total of two identification circuits that are connected to two light receivers and extract only those output signals that exceed a preset threshold from among the output signals of each light receiver. , connected to these two identification circuits,
It includes a determination circuit that selects and outputs only simultaneous output signals from the output signals of these two discrimination circuits, and a counter circuit that counts the output signals of the determination circuit. Each of these circuits may be configured independently, or a microcomputer or the like may be collectively provided with the function of the detection section.

(Operation) While flowing the fluid to be measured through the flow cell, the flow cell is irradiated with a light beam from a light source. At this time, if the fluid to be measured contains particles, scattered light is generated when the particles cross the light beam, and the scattered light is simultaneously received by two light receivers.

Therefore, in the detection section, each identification circuit extracts only the output signal that exceeds a preset threshold value from among the output signals of each photoreceiver, and the determination circuit extracts only the output signal that exceeds a preset threshold.
Among the output signals of each discrimination circuit, output signals with simultaneity,
In other words, if only the output signals that appear simultaneously in two identification circuits at a certain time are selected and output, and the output signals are counted by a counter circuit, the counted value, that is, the output signal of the counter circuit will produce the following. This corresponds to the number of particles whose diameter is larger than the particle size corresponding to the set threshold value. In addition, if you set several thresholds in multiple stages, count the number of objects that exceed each threshold, and then calculate the difference between any two counted values, you can find the particles that correspond to the two thresholds. The number of fine particles with a size between
That is, the particle size distribution can be determined.

Embodiments In FIGS. 1 and 2, the device has a light source 2 generating a light beam 1. In FIG. Then, the optical axis 3 of the light beam 1
A flow cell 4 having a spherical part 4a through which the fluid to be measured flows, and an inlet pipe 4c and an outlet pipe 4b for the fluid to be measured are connected to the spherical part 4a.

Further, on the optical axis 3 between the light source 2 and the flow cell 4, a projecting lens 5 is provided to focus the light beam 1 on the center of the spherical portion 4a of the flow cell 4. Furthermore, optical axis 3
Above, on the opposite side of the light source 2 with respect to the flow cell 4, a beam block 6 is provided.

A light receiver 7 is provided opposite the spherical portion 4a of the flow cell 3 and at a position +60' with respect to the optical axis 3.

Similarly, another light receiver 7' is provided at a position 160° to the optical axis. These two receivers7.
The axis 7' is aligned with the center of the spherical portion 4a of the flow cell 4. On the axis, a light-receiving lens 8 and a pinhole 9 exist for the light receiver 7, and a light-receiving lens 8' and a pinhole 9- for the light receiver 7-.
are placed respectively.

On the other hand, as shown in FIG. 3, a detection section 10 is connected to the above-mentioned light receiver 7.7'. The photoreceiver 7 is connected to an identification circuit 101 having a function of setting an arbitrary threshold value (1, 1) and a voltage comparison function, and similarly, the photoreceiver 7' is connected to an identification circuit 102. . Further, these identification circuits 101 and 102 are connected to a determination circuit 103 having an AND function, further, the determination circuit 103 is connected to a counter circuit 104, and the counter circuit 104 is connected to an arithmetic circuit 105.

Further, the detection unit 10 detects a threshold value V + different from the above.
It is provided with identification circuits 106 and 107 having a h2 setting function and a voltage comparison function, and the identification circuit 106 is connected to the light receiver 7, and the identification circuit 107 is connected to the light receiver 7'. Further, these identification circuits 106 and 107 are connected to a determination circuit 108 having an AND function, further, the determination circuit 108 is connected to a counter circuit 109, and the counter circuit 109 is connected to the above-mentioned arithmetic circuit 105. .

In exactly the same way, the detection unit ↑0 has a further different threshold value V
+ h 3 setting function and a voltage comparison function.
The identification circuit 111 is connected to the light receiver 7'. Further, these identification circuits 110 and 111 are connected to a determination circuit 112, which is further connected to a counter circuit 113, and the counter circuit 113 is connected to the arithmetic circuit 105. That is, in the detection unit 10 in this embodiment, there are three sets of completely identical identification circuits, determination circuits, and counter circuits. As described in the section of the function, this is necessary when determining the particle size distribution, and the number of sets is not limited to three, but should be provided depending on the number of threshold stages to be set. In other words,
When it is desired to measure only the number of fine particles, it is sufficient to provide only one set of these.

To explain the operation of the above-mentioned device, first, the flow cell 4
Then, a fluid to be measured, such as ultrapure water, is continuously flowed from the inlet pipe 4C toward the outlet pipe 4b. Under this condition, the light beam 1 is irradiated from the light source 2 to the flow cell 4 .

The light beam 1 is most focused by the projection lens 5 at the center of the spherical part 4a of the flow cell 4, and then passes through the beam block 6.
is absorbed and quenched.

Now, if the fluid to be measured flowing through the flow cell 4 contains particulates, scattered light is generated when the particulates cross the light beam 1. Of this scattered light, only the light scattered by the particles passing through the center of the spherical part 4a of the flow cell 4 is received by the light receiver 7 via the light receiving lens 8 and the pinhole 9. The light is received by the light receiver 7' through the hole 9', and the intensity of each light is detected.

Since this intensity is related to the number and particle size distribution of fine particles as described above, these values can be determined from the output signal of the light receiver 7.7'.

That is, in FIG. 3, the output signal of the light receiver 7 is compared with a threshold value ■lh1 set in advance by the identification circuit 101,
Only output signals that exceed . Figure 4 (a
) and (b) show such operations, and the output signal of the light receiver 7 shown in (a) of the figure is
Threshold value V1. exceeds □, time 12.1. Only the signals at 0 and 0 are extracted, as shown in (b) of the same figure.
It can be changed to a logic signal of "1". Note that in the figure, V on the vertical axis is the magnitude of the output signal, and tl and t2 on the horizontal axis are time. In exactly the same way, the output signal of the photoreceiver 7' is compared with a preset threshold value V l h l by an identification circuit 102, and only those output signals exceeding the threshold value V1□ are taken out. Figure 4 (C),
(d) shows such an operation, and the output signal of the photoreceiver 7' shown in FIG. Only the output signals at times t3 and t□ are taken out and changed into logical signals of "O" and "1" as shown in (d).

In the determination circuit 103, the identification circuit 101.
102 output signals are logically ANDed. Therefore, the output signal of the determination circuit 103 is as shown in FIG.
As shown in e), only those at time tl have simultaneity, and if these are counted by the counter circuit 104, the counted value will show the number of particles. That is, in this example, among the output signals that appear exceeding the threshold V1□, only the output signal that appears at time tl and has simultaneity is based on the light scattered by the particles, and therefore does not have simultaneity. No, what appears at times t2 and t3 is noise.

Exactly the same thing as above occurs in the identification circuit 1 in which a threshold value V t h2 different from the threshold value V+ht is set.
06.107, determination circuit 108, and counter circuit 10
9, and also with a different threshold value V
Identification circuit 1■0.111 where Ih 3 is set,
This is also performed in the system of the determination circuit 112 and the counter circuit 113, and the output signals of the counter circuits 109 and 113 are sent to the arithmetic circuit 105 together with the output signal of the counter circuit 104 mentioned above.
sent to.

This arithmetic circuit 105 then performs the arithmetic operations described in the operation section from the output signals of the counter circuits 104, 109, and 113 based on three different threshold values to determine the particle size distribution.

(Effects of the Invention) In the device of the present invention, the detection section detects an output signal that exceeds a preset threshold value among the output signals of each of the two light receivers connected to each of the light receivers. A total of two identification circuits are connected to these two identification circuits, and from among the output signals of these two identification circuits, only the simultaneous output signals are selected and output. Since it is equipped with a judgment circuit that counts the output signal of this judgment circuit and a counter circuit that counts the output signal of this judgment circuit, the threshold value can be lowered to the very limit of the background level caused by the dark current of the photoreceiver, and the output of the photoreceiver can be reduced. Even if noise is superimposed on a signal for some reason, it is no longer possible to misidentify whether a peak is caused by particles or noise. Therefore, it becomes possible to accurately measure the number and particle size distribution of even fine particles whose particle diameter is 0.07 μm or less.

[Brief explanation of drawings]

1 to 3 are schematic diagrams of a particle measuring device according to an embodiment of the present invention, in which FIG. 1 is a perspective view, FIG. 2 is a plan view, and FIG. 3 is a circuit diagram. FIGS. 4(a) to 4(e) are graphs showing output signals from the detection section. 1: Light beam 2: Light source 3: Optical axis 4: Flow cell 4a: Spherical part 4b: Leading tube 4c: Introducing tube 5: Light projecting lens 6: Beam block 7: Light receiver 7-: Light receiver 8: Light receiving lens 8' : Light receiving lens 9: Pinhole 9'': Pinhole 10: Detection section 101: Identification circuit 102: Identification circuit 103: Judgment circuit 104: Counter circuit 105: Arithmetic circuit 106: Identification circuit 107: Identification circuit 108: Judgment circuit 109: Counter circuit 110: Identification circuit 111: Identification circuit 112: Judgment circuit 113: Counter circuit

Claims (1)

[Claims] A light source that generates a light beam, a flow cell through which a fluid to be measured is caused to flow, which is provided on the optical axis of the light beam, and one each provided at a position opposite to the flow cell and symmetrical with respect to the optical axis. In addition, there are a total of two receivers,
It has a detection section connected to these two light receivers,
The detection section is connected to the two light receivers and extracts only the output signals exceeding a preset threshold out of the output signals of each of the light receivers. a determination circuit that is connected to these two identification circuits and selects and outputs only simultaneous output signals from among the output signals of these two identification circuits; A particulate measuring device comprising: a counter circuit that counts output signals of the circuit.