CN113820256A - A method for measuring the particle size of air particles by time-of-flight method - Google Patents

Abstract

Translated fromChinese

本发明公开一种采用时间飞行法测量空气颗粒物粒径的方法，光纤偏振激光器发出的偏振激光光束经过渥拉斯通棱镜分束后经过平凸柱面镜，将平凸柱面镜的入瞳与渥拉斯通棱镜的出射面重合从而产生与主光线平行的两束厚度一致的光窗帘；光窗帘的两侧分别设置非球面反光镜、雪崩二极管光电探测器，粒子沿单方向运动且连续穿过两束光窗帘从而发生散射现象，非球面反光镜收集散射光，将散射光汇集到雪崩二极管光电探测器；本发明的优点是：本发明结构简单，使用光学器件数量少，后期机械结构设计简单，光路调整容易，测量精度高。最主要是聚光镜后面没有光学元件，聚光像差小，可形成达到衍射极限厚度的光窗帘。

The invention discloses a method for measuring the particle size of air particles by using a time-of-flight method. The polarized laser beam emitted by a fiber polarized laser is split by a Wollaston prism and then passes through a plano-convex cylindrical mirror, and the entrance pupil of the plano-convex cylindrical mirror is separated. Coinciding with the exit surface of the Wollaston prism to produce two light curtains with the same thickness parallel to the main ray; aspherical reflectors and avalanche diode photodetectors are respectively set on both sides of the light curtain, and the particles move in one direction and continuously The scattering phenomenon occurs through the two beams of light curtains, the aspherical reflector collects the scattered light, and the scattered light is collected into the avalanche diode photodetector; the advantages of the present invention are: the present invention has a simple structure, a small number of optical devices used, and a mechanical structure in the later stage. Simple design, easy adjustment of optical path, and high measurement accuracy. The most important thing is that there is no optical element behind the condenser, and the condenser aberration is small, which can form a light curtain with a diffraction-limited thickness.

Description

Method for measuring particle size of air particles by adopting time flight method

Technical Field

The invention relates to the field of air particulate matter testing, in particular to an optical system for air particulate matter testing.

Background

The current air particulate matter measurement method comprises the following steps: weighing method, photoresistance method, angle scattering method, beta-ray method, oscillation balance method, time flight method and the like, wherein the photoresistance method and the angle scattering method are optical principles, and the principles are simple and easy to realize. At present, the measurement range of the scattering method of the similar instruments at home and abroad is about 0.5-20 μm approximately, but the scattering method is interfered by the refraction coefficient and the rice scattering, and the measurement result has certain deviation from the actual measurement result. The aerodynamic diameter of the particles can be tested using the time-of-flight method. Aerodynamic diameter refers to the unit density (1 g/cm) of particles with the same settling velocity in air³) The assumed spherical particle diameter is independent of the geometric size, shape and density of the particles. The aerodynamic diameter is used to represent the size of the particle, since it is most closely related to the ability of the particle to penetrate the respiratory tract and to its deposition. The sedimentation rate of particles penetrating into alveoli must be lower than 0.003m/s, corresponding to the sedimentation rate of particles with a unit density of 7 μm in diameter, particles with an aerodynamic diameter of 10 μm or more generally cannot pass through the nasopharynx, and particles with an aerodynamic diameter of more than 50 μm can reach the mouth and nose with respiratory motion, but cannot be inhaled. In addition such large particles do not stay in the air too long. Most airborne dust is irregular in shape and can accumulate. The process of aggregating particles depends on aerodynamic properties and not on particle size. The soot particle diameter may exceed 15 μm, but it may be the same as the settling velocity of spherical particles with an aerodynamic diameter of 7 μm. Therefore, the aerodynamic diameter of the particles is of the greatest importance when evaluating them. The optical system for testing the air particles by the conventional time flight method has a complex structure; the used optical devices are more, and the manufacturing cost is high; the spherical condenser lens is followed by calcite and a concave cylindrical lens, which cause spherical aberration, so that a light curtain with a thickness up to the diffraction limit cannot be obtained.

Disclosure of Invention

The invention aims to provide a method for measuring the particle size of air particles by adopting a time flight method, wherein a polarized laser beam emitted by an optical fiber polarized laser passes through a plano-convex cylindrical mirror after being split by a Wollaston prism, and the entrance pupil of the plano-convex cylindrical mirror is superposed with the exit surface of the Wollaston prism so as to generate two light curtains with the same thickness parallel to a principal ray; the two sides of the light curtain are respectively provided with an aspheric surface reflector and an avalanche diode photoelectric detector, the particles move along a single direction and continuously pass through the two light curtains to generate a scattering phenomenon, the aspheric surface reflector collects scattered light and collects the scattered light to the avalanche diode photoelectric detector, the avalanche diode photoelectric detector detects two continuous scattered light pulses, the height of the scattered light pulses is in direct proportion to the scattering particle size of the particles, and the interval of the two continuous scattered light pulses is the movement time of the particles between the two light curtains; the avalanche diode photoelectric detector collects the peak value of the scattered light pulse height and converts the peak value through an AD (analog-to-digital converter), a singlechip connected with the AD converts the processed scattered light pulse height signal into a voltage value and the flight time of the particles between two light curtains and transmits the voltage value and the flight time to a PC (personal computer) end, and the PC compares the voltage value with a calibration curve to obtain the scatterometry and kinetic particle size value of the particles.

The curtain also comprises a 45-degree reflective mirror which is opposite to the light curtain, and a light trap device is arranged on the reflecting surface of the 45-degree reflective mirror.

The connecting line between the focal point of the non-spherical reflector and the avalanche diode photoelectric detector is vertical to the light curtain.

The height between the two light curtains is H +/-f t g (theta); in the formula, the focal length of the f-planoconvex cylindrical mirror and the beam splitting half angle of the theta-Wollaston prism are shown.

The invention has the advantages that: the invention has the advantages of simple structure, less used optical devices, simple later mechanical structure design, easy light path adjustment and high measurement precision. Most importantly, no optical element is arranged behind the condenser lens, the condensing aberration is small, and a light curtain with the thickness reaching the diffraction limit can be formed.

Drawings

FIG. 1 is a schematic perspective view of the present invention;

FIG. 2 is a schematic view of the X-Z plane of the present invention;

FIG. 3 is a schematic view of the Y-Z plane of the present invention;

FIG. 4 is a top view of FIG. 1;

in the figure, 1, a fiber polarization laser, 2, a Wollaston prism, 3, a plano-convex cylindrical mirror, 4, an optical trap, 5.45-degree reflectors, 6, an aspheric reflector, 7, an avalanche diode photoelectric detector, 8, particles and 9, an optical window curtain.

Detailed Description

The invention is described in detail below with reference to the accompanying drawings, as shown in the drawings, a polarized laser beam emitted by an optical fiber polarization laser 1 is split by a Wollastonprism 2 and then passes through a planoconvexcylindrical mirror 3, and an entrance pupil of the planoconvex cylindrical mirror is overlapped with an exit surface of the Wollaston prism so as to generate twolight curtains 9 parallel to a principal ray; the two sides of the light curtain are respectively provided with anaspheric surface reflector 6 and an avalanche diodephotoelectric detector 7, andparticles 8 move along a single direction and continuously pass through twolight curtains 9 so as to generate a scattering phenomenon; theaspheric surface reflector 6 collects scattered light, and the scattered light is collected to the avalanche diodephotoelectric detector 7. the avalanche diodephotoelectric detector 7 converts the light pulse into a voltage value and uploads the voltage value to the PC terminal.

In order to avoid influencing the detection of scattered light, the light curtain device further comprises a 45-degree reflector 5 opposite to the light curtain, and alight trap device 4 is arranged on the reflecting surface of the 45-degree reflector.

Preferably, the line between the focal point of the aspherical mirror and the avalanche diode photodetector is perpendicular to the optical curtain.

The height between the two light curtains is H +/-f t g (theta); in the formula, the focal length of the f-planoconvex cylindrical mirror and the beam splitting half angle of the theta-Wollaston prism are shown.

The principle of the invention is as follows: the particle moves along a single direction and continuously passes through the two light curtains to generate a scattering phenomenon, the aspheric surface reflector collects scattered light and collects the scattered light to the avalanche diode photoelectric detector, the avalanche diode photoelectric detector detects two continuous scattered light pulses, the height of the scattered light pulses is in direct proportion to the scattering particle size of the particle, and the interval of the two continuous scattered light pulses is the movement time of the particle between the two light curtains; the avalanche diode photoelectric detector collects the peak value of the scattered light pulse height and converts the peak value through an AD (analog-to-digital converter), a singlechip connected with the AD converts the processed scattered light pulse height signal into a voltage value and the flight time of the particles between two light curtains and transmits the voltage value and the flight time to a PC (personal computer) end, and the PC compares the voltage value with a calibration curve to obtain the scatterometry and kinetic particle size value of the particles.

The main beam enters the optical trap through a 45-degree mirror, thereby avoiding affecting the detection of scattered light.

The components of the invention: the optical fiber polarization laser, the Wollaston prism, the plano-convex cylindrical mirror, the optical trap, the 45-degree reflector, the aspheric reflector, the avalanche diode photoelectric detector and the like can adopt commercial products.

Claims (4)

Translated fromChinese

1.一种采用时间飞行法测量空气颗粒物粒径的方法，其特征在于：光纤偏振激光器发出的偏振激光光束经过渥拉斯通棱镜分束后经过平凸柱面镜，将平凸柱面镜的入瞳与渥拉斯通棱镜的出射面重合从而产生与主光线平行的两束厚度一致的光窗帘；光窗帘的两侧分别设置非球面反光镜、雪崩二极管光电探测器，粒子沿单方向运动且连续穿过两束光窗帘从而发生散射现象，非球面反光镜收集散射光，将散射光汇集到雪崩二极管光电探测器，雪崩二极管光电探测器检测到两个连续的散射光脉冲，散射光脉冲高度与粒子散射粒径成正比，两个连续的散射光脉冲的间隔即为粒子在两束光窗帘间的运动时间；雪崩二极管光电探测器采集散射光脉冲高度峰峰值并通过AD进行转换，与AD连接的单片机将处理后的散射光脉冲高度信号换算成电压值以及粒子在两束光窗帘间的飞行时间上传给PC端，PC通过与校准曲线进行比对进而得出颗粒的散射学及动力学粒径值。1. a method that adopts the time-of-flight method to measure the particle size of air particles, it is characterized in that: the polarized laser beam that the fiber polarized laser sends passes through the plano-convex cylindrical mirror after the Wollaston prism beam splitting, the plano-convex cylindrical mirror is The entrance pupil coincides with the exit surface of the Wollaston prism to produce two light curtains with the same thickness parallel to the main ray; aspherical reflectors and avalanche diode photodetectors are respectively set on both sides of the light curtain, and the particles move in a single direction. The aspherical mirror collects the scattered light and collects the scattered light into the avalanche diode photodetector, which detects two consecutive scattered light pulses, and the scattered light The pulse height is proportional to the particle size, and the interval between two consecutive scattered light pulses is the movement time of the particles between the two light curtains; the avalanche diode photodetector collects the peak-to-peak height of the scattered light pulses and converts them through AD. The single chip computer connected to AD converts the processed scattered light pulse height signal into voltage value and the flight time of the particles between the two beams of light curtains and uploads it to the PC. Kinetic particle size value.2.根据权利要求1所述的采用时间飞行法测量空气颗粒物粒径的方法，其特征在于：还包括与所述光窗帘的正对着的45度反光镜，45度反光镜的反射面设置光陷阱器。2. the method that adopts time-of-flight method to measure the particle size of air particles according to claim 1, it is characterized in that: also comprise the 45 degree reflective mirror that is opposite to described light curtain, the reflective surface of 45 degree reflective mirror is arranged light trap.3.根据权利要求1所述的采用时间飞行法测量空气颗粒物粒径的方法，其特征在于：非球面反光镜的焦点、雪崩二极管光电探测器之间的连线垂直于光窗帘。3. The method for measuring the particle size of airborne particles by the time-of-flight method according to claim 1, wherein the connecting line between the focus of the aspherical mirror and the avalanche diode photodetector is perpendicular to the light curtain.4.根据权利要求1所述的采用时间飞行法测量空气颗粒物粒径的方法，其特征在于：两束光窗帘之间的高度为H＝+/-f*tg(θ)；式中，f-平凸面柱面镜焦距，θ-渥拉斯通棱镜光束分离半角。4. the method that adopts time-of-flight method to measure the particle size of air particles according to claim 1, is characterized in that: the height between two beams of light curtains is H=+/-f*tg(θ); In the formula, f - Plano-convex cylindrical mirror focal length, θ-Wallaston prism beam splitting half angle.

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