Patent Publication Number: US-10768091-B2

Title: Particle counting method and system

Description:
CROSS REFERENCE TO RELATED APPLICATION 
     The present application claims the priority of Chinese patent application CN 201710235740.7, filed on Apr. 12, 2017, which is hereby incorporated herein by reference in its entirety. 
     TECHNICAL FIELD OF THE INVENTION 
     The present disclosure belongs to the field of particle optical detection, and in particular, relates to a particle counting method and system. 
     BACKGROUND OF THE INVENTION 
     Optical particle counters are currently the primary detection tool for most industrially controlled particle contamination. Classifying by particle sizes, particles includes 5 μm particles, 2 μm particles, 1 μm particles, 0.5 μm particles, 0.2 μm particles, 0.1 μm particles, 0.05 μm particles, and even smaller, nano-sized particles. 
     Optical particle counters currently used to detect micron-sized particles (above 2 μm) are based on the principle of the light blockage method. As shown in  FIGS. 1 and 2 , the existing light-blockage particle counter comprises a light source  201 , an optical component  202 , a flow cell  203 , a photoelectric detector  204 , a preamplifier  205 , a comparator  206 , and a counter  207 . By means of the optical component  202  (including a convex lens, a cylindrical mirror, etc.), the circular spot generated by the light source  201  is converted into a line spot to be irradiated on the flow channel  208  within the flow cell  203 , thereby forming a linear detection area  210 , and then when the particles  200  pass through the detection area, scattered light is generated to be irradiated on the photoelectric detector  204  to generate current pulse signals  211  and  212  having different amplitudes and pulse widths, and then the current pulse signals are converted into voltage pulse signals via the preamplifier  205 , and then into digital signals  213  and  214  via the comparator  206 , which are input into the counter  207 , and the counter  207  screens and counts the pulse signals according to the amplitudes of the pulse signals.  FIG. 3  is a view showing a pulse signal scattered by particles passing through the detection area  210  in the flow cell  203  obtained by the existing particle counting system based on the light blockage method, which visually shows the conversion process of optical signals to electrical signals during the particle detection process in the light-blockage particle counter system. 
     The existing light-blockage particle counter converts the light emitted by the light source into a line light source through the optical component, and the main purpose thereof is to make the light source distribute uniformly in the detection area, thereby ensuring the sensitivity and resolution of the detection. However, the optical structures of the existing optical particle counter and system are relatively complicated, have a low light source utilization rate, and only can utilize a part of the light beam converted by the optical module in the light source. 
     The optical particle counter for detecting sub-micron-sized and nano-sized particles (below 1 μm) is based on the principle of light scattering, and generally adopts a circular spot, which can improve the utilization rate of the light source, increase the scattered light intensity of the particles, and improve the sensitivity of the system. However, due to the uneven distribution of the optical density of the light source spot, the resolution and sensitivity of the system on particles are greatly reduced, which seriously affects the test accuracy of the system. 
     SUMMARY OF THE INVENTION 
     An objective of the present disclosure is to provide a particle counting method with strong universality, and high sensitivity and resolution. 
     Another objective of the present disclosure is to provide a particle counting system with a simple light path structure, and high sensitivity and resolution. 
     To achieve the above purposes, a technical solution employed by the present disclosure is as follows: 
     A particle counting method, comprises: 
     S1) generating a light channel for detecting particles; 
     S2) acquiring optical signals scattered by the particles passing through the light channel and converting the optical signals into pulse signals; 
     S3) according to the pulse signals, obtaining distances between closest positions which are closet to center of the light channel in paths along which the particles pass through the light channel and the center of the light channel; 
     S4) according to an optical density distribution of the light channel, compensating amplitudes of the pulse signals of the particles when passing through the closest positions such that the compensated amplitudes of the pulse signals of the particles are equal to amplitudes of pulse signals of particles with same particle diameters when passing through the center of the light channel; 
     S5) screening and counting the particles according to the compensated amplitudes of the pulse signals to realize counting of the particle with respective particle sizes. 
     Specifically, the light channel is perpendicular to paths through which the particles flow, and an optical density of the light channel is normally distributed in a section perpendicular to the paths through which the particles flow. 
     Specifically, the pulse signals are voltage pulse signals. 
     Further, S3) comprises: 
     Obtaining flow times of the particles passing through the light channel according to pulse widths of the voltage pulse signals due to that pulse widths of pulse signals are correlated with times that the particles pass through the light channel; 
     Obtaining flow paths of the particles flowing through the light channel according to flow velocities and the flow times of the particles; 
     Calculating first distances between closest positions to a center of the light channel, positions closest to the center of the light channel in the flow path are the closest positions. 
     Further, S4) comprises: 
     pulse voltage amplitudes of the particles at the closest positions are initial pulse voltage amplitudes, and pulse voltage amplitudes of the particles at the closest positions after compensation are compensated pulse voltage amplitudes; calculating, according to the distances and an optical density distribution function, compensation coefficients of the initial pulse voltage amplitudes required to be compensated according to the distances and an optical density distribution function, wherein the initial pulse voltage amplitudes are pulse voltage amplitudes of the particles at the closest positions; 
     obtaining the compensated pulse voltage amplitudes of the particles according to the compensation coefficient, wherein the compensated pulse voltage amplitudes are pulse voltage amplitudes of the particles at the closest positions after compensation. 
     The present disclosure further employs the following technical solution: 
     A particle counting system, utilizing the foregoing particle counting method, comprises: 
     a light source module for generating a light beam for detecting the particles; 
     a flow cell module having a flow channel through which the particles flows, the light beam being irradiated on the flow channel to form a light channel at the flow channel for detecting the particles; 
     an optical signal collecting and processing module configured to acquire scattered optical signals formed by the particles passing through the light channel, to convert the scattered optical signals into corresponding pulse signals, to compensate the pulse signals, and to screen and count the pulse signals. 
     Further, the light source module comprises a semiconductor laser for generating a laser beam irradiated on the flow channel to form the light channel at the flow channel which is perpendicular to the flow channel. 
     Further, the light source module further comprises a collimating lens disposed between the semiconductor laser and the flow cell module, and the laser beam is collimated by the collimating lens and then is irradiated on the flow channel to form a cylindrical light channel on the flow channel, and an optical density of the light channel is normally distributed. 
     Specifically, the optical signal collecting and processing module comprises a photoelectric detector, a preamplifier, an Analog to Digital converter sampling unit, and a micro control unit connected in sequence, 
     the photoelectric detector is used to convert the optical signals scattered by the particles into current pulse signals; 
     The preamplifier is used to convert the current pulse signals into voltage pulse signals; 
     The Analog to Digital converter sampling unit is used to convert the voltage pulse signals into digital signals; 
     The micro control unit is used to compensate, to screen and to count the digital signals. 
     Further, the photoelectric detector has a photodiode or a photomultiplier. 
     The above-mentioned orientation words, such as front, back, left, and right, are defined in terms of the orientation of the particle counting system during normal use. 
     The scope of the present disclosure is not limited to technical solutions specifically combined by the above technical features, and should encompass other technical solutions formed by any combination of the above technical features or the equivalent features thereof. For example, the technical solutions are formed by substituting between the above technical features and (but not limited to) the technical features with similar functions disclosed by the present disclosure. 
     Due to the use of the above technical solutions, the present disclosure has the following advantages over the prior art: The optical density of the particle entering the light channel at any angle is compensated to be equivalent to the optical density obtained at the center of the light channel, which ensures the pulse signal corresponding to the particle is only related to the particle size of the particle, and thus the particles with different particle sizes can be screened and counted according to the pulse signals. The particle counting method of the present disclosure has strong universality and high utilization of the light source, and greatly improves the sensitivity and resolution of the detection. The particle counting system of the present disclosure has a simple optical path structure, uniformly distributes the optical density of the light channel without complicated light paths, which reduces the processing difficulty of the flow cell. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is a schematic structure diagram of an existing particle counting system; 
         FIG. 2  is a schematic diagram of a light spot formed on the flow cell in the existing particle counting system; 
         FIG. 3  is a schematic diagram of signal conversion of the existing particle counting system; 
         FIG. 4  is a schematic structure diagram of a particle counting system of the present disclosure; 
         FIG. 5  is a schematic diagram of a light spot formed on the flow cell in the particle counting system of the present disclosure; 
         FIG. 6  is a schematic distribution diagram of the optical density of the light channel formed by the particle counting system of the present disclosure; 
     
    
    
     Wherein,  1 —light source module;  2 —flow cell module;  3 —optical signal collecting and processing module;  21 —flow channel;  31 —photoelectric detector;  32 —preamplifier;  33 —Analog to Digital converter sampling unit;  34 —micro control unit;  101 —light channel;  102 —closest position;  103 —optical density distribution curve;  104 —center. 
     DETAILED DESCRIPTION OF EXEMPLARY EMBODIMENTS 
     As shown in  FIG. 4  to  FIG. 6 , a particle counting system of the present disclosure, comprises: 
     a light source module  1 , the light source module  1  is for generating a light beam for detecting the particles  100 ; 
     a flow cell module  2 , the flow cell module  2  has a flow channel  21  through which the particles  100  flow, the light beam being irradiated on the flow channel  21  to form a light channel  101  at the flow channel  21  for detecting the particles  100 ; 
     an optical signal collecting and processing module  3 , the optical signal collecting and processing module  3  is configured to acquire scattered optical signals formed by the particles  100  passing through the light channel  101 , to convert the scattered optical signals into corresponding pulse signals, to compensate the pulse signals, and to screen and count the pulse signals. 
     In the present embodiment, the light source module  1  comprises a semiconductor laser for generating a laser beam and a collimating lens disposed between the semiconductor laser and the flow cell module  2 . The laser beam is collimated by the collimating lens and then irradiated on the flow channel  21  to form a cylindrical light channel  101  perpendicular to the flow channel  21  at the flow channel  21 . An optical density of the light channel  101  is normally distributed. 
     The optical signal collecting and processing module  3  comprises a photoelectric detector  31 , a preamplifier  32 , an Analog to Digital converter sampling unit  33 , and a micro control unit  34  connected in sequence. The photoelectric detector  31  is used to convert the optical signals scattered by the particles  100  into current pulse signals, and in the present embodiment, the photoelectric detector  31  has a photodiode or a photomultiplier. The preamplifier  32  is used to convert the current pulse signals into voltage pulse signals. The Analog to Digital converter sampling unit  33  is used to convert the voltage pulse signals into digital signals. The micro control unit  34  is used to compensate, to screen and to count the digital signals. 
     A particle counting method utilizing the particle counting system of the present disclosure is as follows: 
     A particle counting method, comprises: 
     S1) opening the light source module  1  to generate a light channel  101  on the flow channel  21  for detecting the particles  100 , the light channel  101  is perpendicular to paths through which the particles  100  flow, and an optical density of the light channel  101  is normally distributed in a plane perpendicular to the paths through which the particles  100  flow, and a distribution curve  103  of the optical density is shown in  FIG. 6 . The optical density distribution function is: 
     
       
         
           
             
               
                 
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     wherein, w 0  is an optical density at the center of the light channel; ρ and k are corresponding coefficients, and r is a distance to the center of the light channel  101 . 
     S2) acquiring voltage pulse signals corresponding to optical signals scattered by the particles  100  passing through the light channel  101 , specifically, 
     S21) acquiring the optical signals scattered by the particles  100  via the photoelectric detector  31  and converting the optical signals into current pulse signals; 
     S22) converting the current pulse signals into voltage pulse signals via the preamplifier  32 ; 
     S23) converting the voltage pulse signals into digital signals via the Analog to Digital converter sampling unit  33 . 
     S3) according to the voltage pulse signals, in the micro control unit  34 , obtaining distances between closest positions to center of the light channel  101  in paths along which the particles  100  pass through the light channel  101  and the center  104  of the light channel  101 , specifically, 
     S31) obtaining flow times of the particles  100  passing through the light channel  101  according to pulse widths of the voltage pulse signals due to that pulse widths of the voltage pulse signals are correlated with times that the particles  100  pass through the light channel  101 , and when the particles  100  pass through the light channel  101  in a speed v 0 , the pulse widths of the voltage pulse signals, i.e., the flow times are t 0 , 
     S32) obtaining flow paths of the particles  100  flowing through the light channel  101  according to flow velocities v 0  and the flow times t 0  of the particles  100 , lengths of which are:
 
 L 1= v   0   ×t   0   (2)
 
     S33) calculating first distances r 1  between closest positions  102  and center  104  of the light channel  101 , positions closest to the center  104  of the light channel  101  in the flow path are the closest positions  102 , and due to the light channel  101  is circle shaped in the plane perpendicular to the flow paths  21 , a radius thereof is R, 
     
       
         
           
             
               
                 
                   
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     then, 
     S4) according to the optical density distribution curve  103  of the light channel  101 , compensating amplitudes of the pulse signals of the particles  100  when the particles  100  pass through the closest positions to the center  104  of the light channel  101  in the paths along which the particles  100  pass through the light channel  101 , such that the compensated amplitudes of the pulse signals of the particles  100  are equal to amplitudes of pulse signals of particles  100  with the same particle diameters when passing through the center  104  of the light channel  101 , specifically: 
     S41) pulse voltage amplitudes of the particles  100  at the closest positions  102  measured by the particle counting system is initial pulse voltage amplitudes V 1 , and
 
 V 1= Mg×Φ 1= Mg×S 1× I 1  (4),
 
     wherein, Mg is a product of an amplification factor of the preamplifier  32  and a photoelectric conversion efficiency of the photoelectric detector  31 , Φ 1  is a luminous flux generated by the particles  100  passing through the closest position  102 , and S1 is an equivalent area of a scattered light generated by the particles  100 , and I 1  is an optical density at the closest position  102 , 
     center pulse voltage amplitudes V 0  of the particles  100  passing through the center  104  of the light channel are:
 
 V 0= Mg×Φ 0= Mg×S 1× I 0= Mg×S 1×ρ× w   0   (5);
 
     wherein, Φ 0  is a luminous flux generated by the particles  100  passing through the center  104  of the light channel  101 , I 0  is an optical density at the centers, ρ is a corresponding coefficient, and w 0  is an optical density at the center  104  of the light channel  101 . 
     S42) The compensated pulse voltage amplitudes are pulse voltage amplitudes of the particles  100  at the closest positions  102  after compensation, and calculating, according to the first distances and an optical density distribution function, compensation coefficients f of the initial pulse voltage amplitudes required to be compensated, 
     
       
         
           
             
               
                 
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     S43) Obtaining compensated pulse voltage amplitudes V of the particles  100  according to the compensation coefficient f. 
     
       
         
           
             
               
                 
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     S5) Screening and counting the particles  100  according to the compensated pulse signal amplitudes V to realize counting of particles  100  with respective particle sizes. 
     After compensation, it can ensure to obtain the same optical density as passing through the center  104  of the light channel  101  when the particles  100  enter into the light channel  101  at any angle, which greatly improves the sensitivity of the particle counting system and the utilization of the laser beam. 
     The particle counting method does not require a complicated optical path structure, and utilizes the optical density distribution function of the light source module  1  to compensate the light scattering signal by detecting the time t 0  of the particles passing through the light channel  101 , to achieve that the particles of the same size passing through the light channel  101  at any position can generate detectable signals of the same amplitude, which ensures that the acquired pulse signals corresponding to the particles  100  are only related to the particle sizes of the particles  100 , and thus can screen and count the particles of different particle sizes according to the pulse signals. 
     The particle counting system has a simple optical path structure, greatly improves sensitivity and resolution of the detection, is suitable for detecting gas-phase and liquid-phase insoluble particles, reduces the processing difficulty of the flow cell module  2 , and improves the utilization rate of the light source module  1 . 
     As above described, the present disclosure is explained according to the purpose thereof, but the present utility model is not limited to the above-mentioned embodiments and implement methods. Various variations and implementations can be made by the practitioners of the relative technical fields within the technical concept of the present disclosure.