Light-scattering dust particle counter

Abstract

A light-scattering dust particle counter. A scattering cavity collection light path uses two ellipsoidal mirrors which are arranged on two sides of a gas path and have reflective surfaces mounted opposing each other, so as to simultaneously collect two separate scattered light signals on two sides of a tested dust particle, and the collection range thereof can reach approximately twice that of a conventional particle counter. In terms of a signal processing scheme, the two scattered light signals are subjected to I / V conversion and amplification after respectively being received by a photoelectric detector, and an addition circuit or a field programmable gate array circuit is then used to perform synchronous superimposition on the two signals. Due to temporal synchronization, two pulse signals after being superimposed may achieve the effect of signal strength superimposition and enhancement, whereas noise is random and not temporally synchronized, and the noise after being superimposed only increases in frequency without a significant change in intensity, thereby achieving the effect of increasing a signal-to-noise ratio.

Description

A light scattering dust particle counter Technical Field

[0001] The present invention relates to a dust particle sensor, in particular to a light scattering dust particle counter, and belongs to the technical field of air cleanliness detection. Background Art

[0002] Particle counters are primarily used to measure the number and size distribution of dust particles per unit volume in clean environments. They are widely used in manufacturing enterprises and scientific research departments, including the electronics industry, pharmaceutical plants, semiconductors, optical and precision machining, plastics, paint spraying, hospitals, environmental protection, and testing laboratories. The semiconductor industry, in particular, places even stricter control on tiny dust particles during integrated circuit production, requiring the ability to detect particles as small as 0.1μm in diameter. This places high demands on the sensitivity of particle counters.

[0003] Invention US2004 / 0042008A1 proposes a counter solution capable of detecting particles as small as 0.1μm. The light source utilizes a high-power laser diode with a specific output power exceeding 1W. Due to the high power of the light source, the noise within the scattering cavity is also high. To reduce this noise, the invention incorporates a complex multi-stage extinction noise reduction structure along the laser irradiation direction. To collect the light signal, two parabolic reflectors arranged in opposing positions are used to collect the single-sided scattered light signal from the particles being measured. To ensure rapid and sufficient ventilation of the entire scattering cavity during detection, the air outlet of the air path is located in the middle area between the two reflectors.

[0004] This solution has the following shortcomings: ① The laser diode used is a specific mode or customized multi-mode laser, which is expensive. Due to its high power consumption, it needs to be combined with a complex cooling structure to ensure good heat dissipation of the laser; ② The laser output power is large, and complex noise reduction measures need to be taken from multiple aspects to control the optical noise to an appropriate range; ③ The scattered light collection range is small, and only the unilateral scattered light of the measured particle is collected, and the collection range is limited.

[0005] Summary of the Invention

[0006] In response to the above-mentioned existing problems, the present invention provides a light-scattering dust particle counter. The scattering cavity collection light path adopts two ellipsoidal reflectors with reflecting surfaces installed opposite to each other on both sides of the gas path. The scattered light signals on both sides of the measured dust particles are collected in two ways at the same time. The collection range can be about twice that of a conventional particle counter. In terms of signal processing scheme, the two scattered light signals are first received by photoelectric detectors respectively and then subjected to I / V conversion and amplification. Then, an adding circuit or a field programmable gate array circuit is used to synchronously superimpose the two signals. Since the two pulse signals are synchronized in time, the signal intensity will be superimposed and enhanced after superposition. However, the noise is random and not synchronized in time. After superposition, the noise only increases in frequency, and the intensity does not change significantly, thereby achieving the effect of improving the signal-to-noise ratio.

[0007] The technical solutions of the present invention are as follows:

[0008] A light scattering high-sensitivity dust particle counter is characterized in that it includes an optical path system and a signal processing system;

[0009] The optical system includes a laser diode 101, a laser collimating lens group 102, a cylindrical lens group 103, a first ellipsoidal reflector 104, a first photodetector 105, an extinction structure 106, a second ellipsoidal reflector 107 and a second photodetector 108;

[0010] The light emitted by the laser diode 101 is sequentially focused into a linear spot at the center of the photosensitive area after passing through the laser collimator 102 and the cylindrical lens assembly 103, and then reaches the extinction structure 106 after passing through the photosensitive area. The first ellipsoidal reflector 104 and the second ellipsoidal reflector 107 are arranged on both sides of the plane formed by the center line of the gas path and the optical axis of the excitation light path, and the two reflecting surfaces of the first ellipsoidal reflector 104 and the second ellipsoidal reflector 107 are arranged facing each other.

[0011] The first ellipsoidal reflector 104 and the second ellipsoidal reflector 107 are both provided with through holes at their axis as apertures. The two focal points of the first ellipsoidal reflector 104 are respectively located at the center of the photosensitive area and the central through hole of the second ellipsoidal reflector 107. The two focal points of the second ellipsoidal reflector 107 are respectively located at the center of the photosensitive area and the central through hole of the first ellipsoidal reflector 104. When the measured particle passes through the photosensitive area, it is irradiated and emits scattered light. The first ellipsoidal reflector 104 collects the scattered light of the measured particle in the photosensitive area and reflects it, and then it passes through the central through hole of the second ellipsoidal reflector 107 and reaches the photosensitive surface of the second photodetector 108. The second ellipsoidal reflector 107 collects the scattered light of the measured particle in the photosensitive area and reflects it, and then it passes through the central through hole of the first ellipsoidal reflector 104 and reaches the photosensitive surface of the first photodetector 105.

[0012] The signal processing system includes a first photodetector 105, a first preamplifier circuit 201, a first post-amplifier circuit 202, a second photodetector 108, a second preamplifier circuit 205, a second post-amplifier circuit 206, an adding circuit 203 and a comparison counting circuit 204;

[0013] The first photodetector 105 converts the received scattered light signal into a current signal. The current signal enters the first preamplifier circuit 201 and is converted into a voltage pulse signal. After passing through the first post-amplifier circuit 202, the voltage pulse amplitude is amplified to form a first pulse signal, which is recorded as h1. The second photodetector 108 receives the scattered light signal from the other side and passes it through the second preamplifier circuit 205 and the second post-amplifier circuit 206 in sequence to obtain an amplified second pulse signal, which is recorded as h2.

[0014] The two amplified pulse signals are superimposed in a time-synchronized manner by the adding circuit 203 to form a new pulse signal with a higher signal-to-noise ratio. The pulse amplitude of the signal is the sum of the amplitudes of the two signals.

[0015] The optical system operates as follows: Light emitted by the laser diode is parallelized by the laser collimator and then focused into a linear spot at the center of the photosensitive region by the cylindrical lens. When the particle being measured passes through the photosensitive region, it is illuminated and emits scattered light. After passing through the photosensitive region, the illumination beam continues on to the extinction structure, where it is mostly absorbed. A portion of the scattered light emitted by the particle being measured is collected and reflected by the first ellipsoidal reflector, passes through the central through-hole of the second ellipsoidal reflector, and reaches the second photodetector. Another portion is collected and reflected by the second ellipsoidal reflector, passes through the central through-hole of the first ellipsoidal reflector, and reaches the first photodetector.

[0016] The scattered light signal processing system includes a first photodetector, a first preamplifier circuit, a first post-amplifier circuit, a second photodetector, a second preamplifier circuit, a second post-amplifier circuit, an adder circuit, and a comparison and counting circuit. After receiving scattered light, the photodetector generally directly converts the light signal into a current signal of corresponding intensity. The adder circuit, which can time-synchronize the signal amplitudes of two pulse signals, can be implemented using hardware circuits, field-programmable gate arrays (FPGAs), or other computational circuits.

[0017] In the scattered light signal processing system, the two paths of scattered light are pre-amplified and post-amplified respectively according to the circuit method of the same principle, and then enter the adding circuit to realize signal superposition. Since the two pulse signals are synchronized in time, the superposition will form an effect of superimposed and enhanced signal strength. However, the noise is random and not synchronized in time. After superposition, the noise only increases in frequency, and the intensity does not change significantly, thereby achieving the effect of improving the signal-to-noise ratio.

[0018] Compared with the existing technology, this application can achieve the following technical effects:

[0019] 1. The scattered light collection range is large, and the light signals on both sides of the particle can be collected at the same time. The scattered light collection range is nearly twice that of a conventional particle counter;

[0020] 2. High signal-to-noise ratio, using signal synchronous superposition processing technology to add signal amplitudes without increasing noise;

[0021] 3. No specific high-power laser is required, and the instrument cost is low. At the same time, since the laser power is relatively low, the scattering noise inside the optical cavity is relatively low, and the noise reduction structure design is relatively simple. BRIEF DESCRIPTION OF THE DRAWINGS

[0022] FIG1 is a schematic diagram of the optical path system of the present application.

[0023] FIG2 is a schematic diagram showing the composition of the signal processing system of the present application.

[0024] FIG3 is a schematic diagram showing the principle of the signal processing method of the present application. DETAILED DESCRIPTION

[0025] The present invention will be further described below with reference to the accompanying drawings and embodiments, but the scope of protection of the present invention should not be limited thereto.

[0026] As shown in Figure 1, the optical path system of the present application consists of a laser diode 101, a laser collimating lens group 102, a cylindrical lens group 103, a first ellipsoidal reflector 104, a first photodetector 105, an extinction structure 106, a second ellipsoidal reflector 107, and a second photodetector 108.

[0027] The first ellipsoidal reflector 104 and the second ellipsoidal reflector 107 are both provided with through holes at their axis as apertures. The two focal points of the first ellipsoidal reflector 104 are located at the center of the photosensitive region and the central through hole of the second ellipsoidal reflector 107, respectively. The two focal points of the second ellipsoidal reflector 107 are located at the center of the photosensitive region and the central through hole of the first ellipsoidal reflector 104, respectively. The first ellipsoidal reflector 104 collects scattered light from the particles being measured in the photosensitive region and reflects it, which then passes through the central through hole of the second ellipsoidal reflector 107 and reaches the photosensitive surface of the second photodetector 108. The second ellipsoidal reflector 107 collects scattered light from the particles being measured in the photosensitive region and reflects it, which then passes through the central through hole of the first ellipsoidal reflector 104 and reaches the photosensitive surface of the first photodetector 105.

[0028] The first ellipsoidal reflector 104 and the second ellipsoidal reflector 107 are arranged on both sides of a plane formed by the center line of the gas path and the optical axis of the excitation light path, and the two reflective surfaces are arranged facing each other.

[0029] More preferably, the first photodetector 105 and the second photodetector 108 can be photodiodes, avalanche photodiodes or photomultiplier tubes with higher sensitivity.

[0030] The optical path system of the present application works as follows: the light emitted by the laser diode 101 becomes parallel light after passing through the laser collimator 102 group, and then passes through the cylindrical mirror group 103 to focus into a linear light spot at the center of the photosensitive area. When the measured particle passes through the photosensitive area, it will be illuminated and emit scattered light. After passing through the photosensitive area, the illumination light beam continues to move forward to the extinction structure 106 and most of it will be absorbed by the extinction structure. Of the scattered light emitted by the measured particle, a part is collected and reflected by the first ellipsoidal reflector 104, passes through the central through hole of the second ellipsoidal reflector 107, and reaches the second photodetector 108. The other part is collected and reflected by the second ellipsoidal reflector 107, passes through the central through hole of the first ellipsoidal reflector 104, and reaches the first photodetector 105.

[0031] The scattered light signal processing system of the present application includes a first photodetector 105, a first preamplifier circuit 201, a first post-amplifier circuit 202, a second photodetector 108, a second preamplifier circuit 205, a second post-amplifier circuit 206, an adding circuit 203, a comparison counting circuit 204, etc.

[0032] The first photodetector 105 converts the received scattered light signal into a current signal. The current signal enters the first preamplifier circuit 201 and is converted into a voltage pulse signal. After passing through the first post-amplifier circuit 202, the voltage pulse amplitude is further amplified to form a first pulse signal, which is recorded as h1. The second photodetector 108 receives the scattered light signal on the other side and passes it through the second preamplifier circuit 205 and the second post-amplifier circuit 206 in sequence to obtain an amplified second pulse signal, which is recorded as h2. The two amplified pulse signals are superimposed on each other in a time-synchronized manner by the adding circuit 203 to form a new pulse signal with a higher signal-to-noise ratio. As shown in FIG3 , the pulse amplitude of the signal is the sum of the amplitudes of the two signals. However, due to the time asynchronization, the noise only increases in frequency, but the noise amplitude does not increase.

Claims

1. A light scattering high-sensitivity dust particle counter, characterized in that: Including optical path system and scattered light signal processing system; The optical system includes a laser diode 101, a laser collimating lens group 102, a cylindrical lens group 103, a first ellipsoidal reflector 104, a first photodetector 105, an extinction structure 106, a second ellipsoidal reflector 107 and a second photodetector 108; The light emitted by the laser diode 101 is sequentially focused into a linear spot at the center of the photosensitive area after passing through the laser collimator 102 and the cylindrical lens assembly 103, and then reaches the extinction structure 106 after passing through the photosensitive area. The first ellipsoidal reflector 104 and the second ellipsoidal reflector 107 are arranged on both sides of the plane formed by the center line of the gas path and the optical axis of the excitation light path, and the two reflecting surfaces of the first ellipsoidal reflector 104 and the second ellipsoidal reflector 107 are arranged facing each other. The first ellipsoidal reflector 104 and the second ellipsoidal reflector 107 are both provided with through holes at their axis as apertures. The two focal points of the first ellipsoidal reflector 104 are respectively located at the center of the photosensitive area and the central through hole of the second ellipsoidal reflector 107. The two focal points of the second ellipsoidal reflector 107 are respectively located at the center of the photosensitive area and the central through hole of the first ellipsoidal reflector 104. When the measured particle passes through the photosensitive area, it is irradiated and emits scattered light. The first ellipsoidal reflector 104 collects the scattered light of the measured particle in the photosensitive area and reflects it, and then it passes through the central through hole of the second ellipsoidal reflector 107 and reaches the photosensitive surface of the second photodetector 108. The second ellipsoidal reflector 107 collects the scattered light of the measured particle in the photosensitive area and reflects it, and then it passes through the central through hole of the first ellipsoidal reflector 104 and reaches the photosensitive surface of the first photodetector 105. The scattered light signal processing system includes a first photodetector 105, a first preamplifier circuit 201, a first post-amplifier circuit 202, a second photodetector 108, a second preamplifier circuit 205, a second post-amplifier circuit 206, an adding circuit 203 and a comparison counting circuit 204; The first photodetector 105 converts the received scattered light signal into a current signal, which is then converted into a voltage pulse signal after entering the first preamplifier circuit 201. After passing through the first post-amplifier circuit 202, the voltage pulse amplitude is amplified into a first pulse signal, which is recorded as h1. The second photodetector 108 receives the scattered light signal from the other side and sequentially passes through the second preamplifier circuit 205 and the second post-amplifier circuit. After 206, the amplified second pulse signal is obtained, which is recorded as h2; The two amplified pulse signals are superimposed in a time-synchronized manner by the adding circuit 203 to form a new pulse signal with a higher signal-to-noise ratio. The pulse amplitude of the signal is the sum of the amplitudes of the two signals.

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