A method for identifying particle size and detecting concentration of particulate matters

Abstract

The present application relates to the technical field of optical particle sensing, in particular to a particle size identification and concentration detection method. The method comprises: a laser emitted by a laser emits a laser beam which is first focused and then diverged by a lens; at least two photosensitive devices are distributed along the propagation direction of the laser beam with the laser focal point as a reference, including near-focal point and far-focal point devices, and the receiving surfaces of the devices are all directed towards the laser beam to collect scattered light; the scattered light signals of each device are collected, converted into current / voltage independently, amplified and then input into a processing unit; based on the characteristics that the near-focal point high irradiance preferentially captures small particle size scattered light and the far-focal point large beam diameter preferentially captures large particle size scattered light, a mapping relationship between particle size and channel is established; by calibrating the number concentration and mass concentration coefficient of each channel with standard particles, combined with linearization processing, the synchronous detection of PM1.0, PM2.5 and PM10 is realized, and the particle size identification accuracy and concentration measurement reliability are effectively improved.

Description

Technical Field

[0001] The present invention relates to the field of optical particle sensing technology, and more particularly to a method for particle size identification and concentration detection. Background Art

[0002] Existing typical solutions for measuring particle size using laser scattering technology mainly include two categories:

[0003] The first approach uses scattered light intensity to identify particle size. This approach works on the principle that, under the same conditions, larger particles of the same substance typically produce more scattered light than smaller particles. However, this approach has significant drawbacks: the absolute scattered light intensity at a single angle depends not only on particle size but also strongly on the stability of the laser light output power, the particle material (refractive index), shape, and color (absorption). This combination of interfering factors results in severely inaccurate particle size identification.

[0004] The second approach uses multi-angle detection. By placing multiple photodetectors with different scattering angles (e.g., forward, 90 degrees to the side, and backward) around the laser beam illumination area (usually with the laser focal point as a reference), the method exploits the differences in the spatial distribution of scattered light from particles of varying sizes for identification. However, this approach has inherent limitations: to prevent the laser from directly striking the detectors, the forward and backward detectors must be positioned away from the laser focal point, significantly attenuating the received signal strength. Improving accuracy requires increasing system complexity, which in turn drives up costs. Summary of the Invention

[0005] In view of this, the present invention provides a method for particle size identification and concentration detection, aiming to solve the problem of insufficient particle size identification accuracy of existing particle sensing technologies, and the low measurement accuracy when detecting large particle concentrations (including mass concentration and number concentration) due to insufficient particle size identification accuracy.

[0006] In order to achieve the above object, the present invention adopts the following technical solutions:

[0007] A method for particle size identification and concentration detection, characterized by comprising the following steps:

[0008] The laser emitted by the laser forms a laser beam that is focused first and then diverged after passing through the lens;

[0009] Taking the laser focus as a reference point, at least two photosensitive devices are distributed along the propagation direction of the laser beam, including a photosensitive device near the laser focus and a photosensitive device far from the laser focus;

[0010] The receiving surface of each photosensitive device faces the laser beam to collect scattered light;

[0011] Collect scattered light signals from each photosensitive device, and input them into the processing unit after independent signal conversion and processing;

[0012] Identify particle size based on the difference in scattered light capture rates between near and far focus positions for particles of different sizes;

[0013] The number concentration and mass concentration of particles are calculated based on the calibration parameters.

[0014] In a specific embodiment, the signal conversion and processing includes independent or time-division multiplexing current / voltage conversion, signal amplification, and analog-to-digital conversion of the multi-path scattered light signals.

[0015] In a specific implementation scheme, the particle size identification is specifically: by adjusting the position of the photosensitive device and the laser power, the capture rate of particles of different particle sizes in the corresponding photosensitive device channel reaches a peak value, and a mapping relationship between particle size and channel is established.

[0016] In a specific embodiment, the calibration parameter acquisition includes:

[0017] Use standard particles to test the response data of each channel under concentration gradient;

[0018] Collect the number concentration and mass concentration values ​​of the reference instrument in the corresponding particle size range;

[0019] The number concentration calibration coefficient and mass concentration calibration coefficient of each channel are calculated through linearization processing.

[0020] In a specific embodiment, the near-focus position utilizes the high irradiance characteristic to preferentially capture scattered light from small-sized particles, and the far-focus position utilizes the large beam diameter characteristic to preferentially capture scattered light from large-sized particles.

[0021] In a specific embodiment, the number of the photosensitive devices can be expanded, and the particle size recognition resolution can be improved by increasing the number of photosensitive devices distributed along the light beam direction.

[0022] In a specific embodiment, the method further includes a step of dynamically adjusting the laser power to expand the particle size detection range by adjusting the laser output power.

[0023] In a specific possible implementation scheme, the mass concentration detection includes the simultaneous calculation of PM1.0, PM2.5 and PM10.

[0024] In a specific possible implementation scheme, the position of the photosensitive device is optimized based on the target detection particle size range, so that the scattered light capture rate of particles of a specific particle size in the corresponding channel is significantly higher than that in other channels.

[0025] Compared with the prior art, the particle size identification and concentration detection method has the following beneficial effects:

[0026] The aerodynamic diameter of the microparticle can be accurately identified, and the mass concentrations of PM1.0, PM2.5 and PM10 can be calculated through the microparticle counting and mass concentration algorithm, and the accuracy of the mass concentrations of PM2.5 and PM1.0 can reach ±10%, and the accuracy of the mass concentration of PM10 can reach ±15% relative to the standard instrument. BRIEF DESCRIPTION OF DRAWINGS

[0027] In order to more clearly illustrate the technical solutions in the embodiments of the present application or the prior art, the drawings needed to be used in the embodiments or the prior art description will be briefly introduced as follows. Obviously, the drawings in the following description are only some embodiments of the present application, and other drawings can be obtained by those skilled in the art without creative labor on the basis of the provided drawings.

[0028] Figure 1 Embodiment 1 of the optical schematic diagram of the optical system of the present application.

[0029] Figure 2 The circuit block diagram of the circuit system of the present application.

[0030] Figure 3 The relationship between the particle size and the capture efficiency of the photosensitive device.

[0031] Figure 4 Embodiment 2 of the optical schematic diagram of the optical system of the present application.

[0032] Wherein 1-laser, 2-lens, 3-first photosensitive device, 4-second photosensitive device. DETAILED DESCRIPTION

[0033] The technical solutions in the embodiments of the present application will be described clearly and completely as follows. Obviously, the described embodiments are only some of the embodiments of the present application, but not all the embodiments. Based on the embodiments in the present application, all other embodiments obtained by those skilled in the art without creative labor fall within the scope of protection of the present application.

[0034] The particle size identification and concentration detection method described in the present invention is applied to the collection of scattered light from particles, and includes:

[0035] Construct the following optical system for scattered light collection; Figure 1 As shown, the laser light emitted by the laser 1 passes through the lens 2 and forms a laser light that is first focused and then diverged. With reference to the focus of the laser light, at least two photosensitive devices are arranged on the sides of the laser beam along the irradiation direction of the laser beam and distributed at different positions. For example, the first photosensitive device 3 is arranged near the laser focus, and the second photosensitive device 4 is arranged far from the laser focus. Figure 1 In the embodiment shown, the first photosensor 3 and the second photosensor 4 are arranged on the same side along the irradiation direction of the laser beam; the receiving surface of the photosensor faces the laser beam to collect scattered light; although Figure 1 The receiving surfaces of the photosensitive devices shown in the figure are parallel to the light beam emission axis, but they may not be parallel as long as the scattered light is effectively collected; the effective collection means that the efficiency of receiving scattered light is not affected. Figure 4 In another embodiment shown, the far laser focus is obtained by placing a reflector in the optical path after the laser focus. Reconstructing the optical path by the reflector can optimize the detection space, device layout, or scattered light collection strategy. The reflector can also extend the optical path, moving the far focus position away from the laser to avoid detector obstruction.

[0036] Figure 1 The two photosensitive devices are only examples, and more can be arranged as needed;

[0037] Exemplarily, the photosensitive device is a photodiode PD;

[0038] Exemplarily, the position of the photosensitive device and the laser power are adjustable to optimize the capture rate;

[0039] Construct the following circuit system for scattered light signal conversion and circuit processing; Figure 2 As shown, the circuit adopts a completely independent parallel processing method for multi-path scattered light signals. The specific process is as follows:

[0040] Photoelectric conversion: Each photosensitive device (such as Figure 1 The first photosensor 3 (photosensor 1) and the second photosensor 4 (photosensor 2) convert the scattered light signal (scattered light of the particle matter) into a current signal; Figure 2 The circuit system shown includes two scattered light collection channels;

[0041] I / U conversion (current / voltage conversion): The current signal of each channel is converted into a voltage signal through an independent I / U conversion module (such as I / U conversion 1 and I / U conversion 2);

[0042] Signal amplification: Each voltage signal is adjusted in amplitude through an independent amplification circuit (such as signal amplification 1 and signal amplification 2);

[0043] Analog-to-digital conversion and processing: The amplified signal is input into the microcontroller unit (MCU), where it is usually first converted into a digital signal by its built-in ADC (analog-to-digital converter) and then processed by the MCU.

[0044] For example, Figure 2 The circuit shown adopts an independent processing mode for multi-path scattered light signals, and can also be changed to a time division multiplexing mode similar to independent processing as needed. The specific implementation is based on the existing technology. Figure 2 Not shown and will not be described in detail.

[0045] The particle size (particulate matter size) recognition principle of the above optical system and circuit system is as follows:

[0046] There is a significant difference in the capture efficiency of scattered light from particles (of different particle sizes) between photosensors located near and far from the laser focal point. This difference stems from the change in the spatial characteristics of the laser beam. By adjusting the laser output power and the layout of the photosensitive tubes, particle size identification and particle concentration detection can be achieved:

[0047] Characteristics of near-focus area: Near the laser focus, the laser beam diameter is small, the energy is concentrated, and the irradiance reaches the maximum;

[0048] Laser beams have the smallest diameter and the highest irradiance, making them advantageous for capturing the weak scattered light from small particles. This is because small particles of the same material inherently have weak scattered light intensity, and high irradiance effectively improves their signal-to-noise ratio. However, this disadvantage is particularly true for large particles, which are sparsely distributed (low number concentration) at the same mass concentration. Consequently, the small beam diameter results in a very small number of captured scattered light events.

[0049] This feature is beneficial for capturing the scattered light of small-sized particles. The reason is that when the wavelength and output power of the laser light source remain unchanged, the smaller the particle size of particles of the same substance, the weaker the scattered light. Only when the laser beam illumination is large enough can the scattered light of small-sized particles be better captured.

[0050] On the contrary, this feature is not conducive to capturing scattered light from large-sized particles. The reason is that large particles are different from small particles. Under the same mass concentration conditions, the larger the particles, the lower the number per unit spatial volume (that is, the lower the number concentration). Since the laser beam is small, the amount (number) of scattered light generated must be extremely small, making it difficult to capture the scattered light from large particles.

[0051] Far-focus area characteristics: Far away from the focus, the laser beam diameter becomes larger, the energy becomes divergent, and the irradiance decreases;

[0052] The increased laser beam diameter and reduced irradiance make this characteristic particularly suitable for detecting large particles. The principle is that the strong scattered light from large particles compensates for the disadvantage of low irradiance, and the larger beam diameter increases the probability of interaction with large particles. Conversely, small particles are difficult to detect due to the weak scattered light and low irradiance.

[0053] Contrary to the reasons explained above, the farther away from the focal point, the more favorable it is for capturing scattered light from large-sized particles, that is, the greater the capture rate, while the capture rate for scattered light from small-sized particles is lower. That is:

[0054] The principle of low capture rate of scattered light of small-sized particles: the smaller the particle size, the weaker the scattered light of the particles. At this location, the irradiance is low, and the scattered light of the particles is even weaker. These two factors inevitably lead to the result that small-sized particles are difficult to detect.

[0055] The reason why the scattered light capture rate of large-sized particles is low is that for the same type of material, the larger the particles, the stronger the scattered light. This characteristic of strong scattered light makes up for the deficiency of low laser irradiance. At the same time, since the beam diameter here is large, this factor is conducive to capturing the scattered light of large particles.

[0056] By optimizing the position layout of the photosensitive device and the laser power configuration, a mapping relationship between the particle size and the photosensitive device channel can be established, thereby achieving particle size identification. Figure 3 shown.

[0057] On the basis of the above technical solution, the present invention further provides the following particle size identification, concentration calibration, and concentration measurement methods:

[0058] The particle size recognition method first determines the target particle size recognition resolution and selects the center particle size value of the particle size range. A multi-concentration gradient test is performed using standard particles to obtain the response data of each photosensitive device channel. The dominant channel with the highest capture rate is determined through analysis, and a mapping relationship between this channel and the corresponding particle size is established. If the capture rate difference between channels is not significant, optimization is performed by adjusting the photosensitive device position or laser power.

[0059] Exemplarily, the particle size identification step includes:

[0060] S1: Determine the resolution of particle size recognition, thereby determining the center particle size value of the minimum interval of particle size recognition

[0061] S2: Using standard particles of a certain size to perform testing, obtaining response data for each photosensitive device (hereinafter referred to as a detection channel) at different concentrations;

[0062] S3: Find the detection channel with the highest capture rate (largest signal) and associate it with the corresponding particle size identification channel. (Note: If the capture rate differences between channels are not significant, optimization can be achieved by adjusting the position of the photosensor and the laser power.)

[0063] The concentration calibration (or calibration) method is to synchronously collect the signal quantity of each channel when the ambient particulate matter concentration is stable; linearize the signal quantity in terms of number concentration and mass concentration respectively to obtain the linearized value of each channel; synchronously collect the precise number concentration value and mass concentration value of the reference particle size spectrometer in the corresponding particle size range; calculate and store the calibration coefficient of each channel: the number concentration calibration coefficient is the ratio of the reference number concentration to the channel linearization value, and the mass concentration calibration coefficient is the ratio of the reference mass concentration to the channel linearization value;

[0064] For example, taking two channels as an example, two independent photosensitive device detection nodes are set up. Channel 1 (near focus channel): the photosensitive device is located near the laser focus (high irradiance area), and channel 2 (far focus channel): the photosensitive device is located in the divergent beam area far from the focus (large spot diameter area). Each photosensitive device corresponds to an independent signal processing link. The concentration calibration steps include:

[0065] When the ambient particulate matter concentration is stable, the signal quantities P1 and P2 of each channel are collected, and then linear processing is performed on the number concentration and mass concentration respectively to obtain N C1 、N C2 Value and N M1 、N M2 value;

[0066] Collect the number concentration C and mass concentration M of the corresponding particle size range from the reference instrument (particle size spectrometer);

[0067] Calculate and store the calibration coefficients for each channel:

[0068] Concentration coefficient of each channel: K C1 =C1 / N C1 ;K C2 =C2 / N C2 ;

[0069] Mass concentration coefficient of each channel: K M1 =C1 / N M1 ;K M2 =C2 / N M2 ;

[0070] The concentration measurement method acquires the signal quantity of each channel in real time, obtains intermediate values through linearization processing of the number concentration and the mass concentration, calls the pre-stored calibration coefficient, multiplies the intermediate values of each channel by the corresponding calibration coefficient, respectively calculates the number concentration and the mass concentration of each particle size channel, and finally outputs the hierarchical mass concentration results of PM1.0, PM2.5 and PM10.

[0071] For example, the mass concentration result of the near-focus channel corresponds to PM1.0; the mass concentration result of the far-focus channel corresponds to PM10; and the PM2.5 mass concentration = near-focus channel result x a + far-focus channel result x b (a and b are weight coefficients determined through calibration).

[0072] The detection principles of the two channels are as follows:

[0073] The near-focus channel (special for small particle size detection) is located in the high irradiance region near the laser focus point, and its core advantage lies in capturing the weak scattered light of small particle matter (such as PM1.0).

[0074] High irradiance enhances weak signal: the laser beam diameter is smallest and the energy is most concentrated in this region, which can significantly improve the signal-to-noise ratio of small particle matter (weak intrinsic scattered light);

[0075] Limitation of small beam diameter: large particles are rare in the same mass concentration (low number concentration), and the small beam diameter leads to few captured scattering events, so it is not suitable for large particle detection.

[0076] The far-focus channel (special for large particle size detection) is located in the low irradiance region away from the focus point and is specially designed for efficient capture of large particle matter (such as PM10).

[0077] Large spot diameter improves capture probability: the divergent beam expands the action space and increases the chance of large particles passing through the laser region;

[0078] Strong scattered light compensates for low irradiance: the strong scattered light characteristics of large particles can offset the insufficient irradiance in the far-focus region, while small particles are difficult to be detected due to the weak scattered light and low irradiance.

[0079] By comparing the scattering light capture rate difference of the two channels:

[0080] When small particles pass through, the near-focus channel signal is significantly stronger than the far-focus channel;

[0081] When large particles pass through, the far-focus channel signal is significantly stronger than the near-focus channel;

[0082] Combined with the mapping relationship established by calibration (such as near-focus -> PM1.0 and far-focus -> PM10), particle size classification and concentration calculation are realized.

[0083] Exemplarily, the concentration measurement step includes:

[0084] Collect the signal quantities P1 and P2 of each channel, and then perform linearization processing on the number concentration and mass concentration respectively to obtain N C1 、N C2 Value and N M1 、N M2 value;

[0085] Read storage parameter K C1 , K C2 , K M1 , K M2 ;

[0086] Calculate the number concentration corresponding to each particle size channel: P C1 =K C1 *N C1 ;PC2=KC2*NC2;

[0087] Calculate the number concentration corresponding to each particle size channel: PM1=K M1 *N M1 ; PM2=K M2 *N M2 .

[0088] On the basis of the above technical solution, as an alternative, a dynamic adjustment function of laser power can be added. By adjusting the laser power, the capture efficiency of the channel for the corresponding particle size can be changed. Because the capture efficiency is affected by the combined factors of light irradiance and beam size, changing the laser output power, although it cannot change the beam size, can change the light irradiance of the beam at the position of the photosensor, thereby achieving the purpose of changing the capture efficiency for a certain particle size.

[0089] In order to expand the system's adaptability to detecting particles of different sizes, a dynamic adjustment function of laser power can be added. By dynamically adjusting the laser output power to change the light irradiance at the receiving position of the photosensor, the capture efficiency of particles of different sizes can be optimized. The specific solution is as follows:

[0090] Add laser power regulation circuit;

[0091] A laser power regulation circuit is added to the original system, which forms a closed-loop control with the laser source and microcontroller (MCU):

[0092] The laser power regulation circuit receives the control signal (such as PWM signal) output by the MCU and dynamically adjusts the output power of the laser source (for example, the power regulation range can be set to 5%-100% of the rated power according to demand);

[0093] The circuit includes a power detection feedback module that collects the current laser output power value in real time and transmits it back to the MCU to ensure power regulation accuracy (for example, the error can be set to ≤±3% based on the requirements of the specific test environment).

[0094] Control logic: Capture efficiency optimization based on light irradiance;

[0095] The MCU dynamically adjusts the laser power based on the signal feedback from each detection channel (such as the light intensity signal received by the photosensor). The core logic is as follows:

[0096] When a channel (such as the far-focus channel) detects that the signal is continuously saturated (exceeding the preset threshold, for example, 90% full scale, indicating that the signal intensity reaches 90% of the full scale), it is determined that the reflected / scattered light from particles in this area is too strong. At this time, the MCU reduces the duty cycle of the PWM signal (for example, from 50% to 20%), thereby reducing the laser output power.

[0097] When the signal of a certain channel is continuously weak (lower than the preset threshold, for example: 10% full scale, indicating that the signal strength is only 10% of the full scale), it is determined that the light irradiance is insufficient, and the MCU increases the PWM duty cycle to increase the laser output power;

[0098] Technical principle: By changing the light irradiance in the target area, the system can adapt to the response characteristics of particles of different sizes to light signals while keeping the geometric parameters of the light beam (such as beam diameter and divergence angle) unchanged. For example, large particles reflect / scatter light more strongly, so reducing the light irradiance can avoid signal saturation; small particles reflect / scatter light less strongly, so increasing the light irradiance can enhance signal recognition, thereby optimizing the capture efficiency of particles of different sizes.

[0099] For example, when the system detects frequent saturation of signals from large-sized particles (e.g., >10 μm) in the far-focus area:

[0100] The MCU reduces the laser power by 30% from the rated value through the power regulation circuit;

[0101] At this time, the physical parameters of the light beam, such as the divergence angle and diameter, remain unchanged, but the light irradiance at the receiving position of the photosensor decreases, and the intensity of the reflected / scattered light signal from large-size particles adapts accordingly to avoid saturation.

[0102] This mechanism optimizes the scattered light capture conditions of large-sized particles by dynamically adjusting the light irradiance, which helps to improve the detection efficiency of larger-sized particles and thus expands the system's detection adaptability to a large particle size range.

[0103] After adding the dynamic adjustment function of laser power, the system can optimize the capture efficiency of particles of different sizes by dynamically adjusting the light irradiance without changing the geometric characteristics of the light beam, thereby improving the detection adaptability of particles with multiple size distributions under complex working conditions.

[0104] The various embodiments in this specification are described in a progressive manner, and each embodiment focuses on the differences from other embodiments. The same and similar parts between the various embodiments can be referred to each other. The above description of the disclosed embodiments enables professionals and technicians in this field to implement or use the present invention. Various modifications to these embodiments will be apparent to professionals and technicians in this field, and the general principles defined herein can be implemented in other embodiments without departing from the spirit or scope of the present invention. Therefore, the present invention will not be limited to the embodiments shown herein, but will conform to the widest scope consistent with the principles and novel features disclosed herein.

Claims

1. A method for particle size identification and concentration detection, characterized in that: Including the following The laser emitted by the laser forms a laser beam that is focused first and then diverged after passing through the lens; Taking the laser focus as a reference point, at least two photosensitive devices are distributed along the propagation direction of the laser beam, including a photosensitive device near the laser focus and a photosensitive device far from the laser focus; The receiving surface of each photosensitive device faces the laser beam to collect scattered light; Collect scattered light signals from each photosensitive device, and input them into the processing unit after independent signal conversion and processing; The particle size is identified based on the difference in scattered light capture rates of particles of different sizes at the near and far focus positions. The near focus position utilizes the high irradiance characteristic to preferentially capture scattered light from small-sized particles, while the far focus position utilizes the large beam diameter characteristic to preferentially capture scattered light from large-sized particles. The number concentration and mass concentration of particles are calculated based on the calibration parameters.

2. The method for particle size identification and concentration detection according to claim 1, characterized in that: The signal conversion and processing includes independent or time-division multiplexing current / voltage conversion, signal amplification and analog-to-digital conversion of multi-path scattered light signals.

3. The method for particle size identification and concentration detection according to claim 1, characterized in that: The particle size identification is specifically as follows: by adjusting the position of the photosensitive device and the laser power, the capture rate of particles of different particle sizes in the corresponding photosensitive device channel reaches a peak value, and a mapping relationship between the particle size and the channel is established.

4. The method for particle size identification and concentration detection according to claim 1, characterized in that: The calibration parameter acquisition includes: Use standard particles to test the response data of each channel under concentration gradient; Collect the number concentration and mass concentration values ​​of the reference instrument in the corresponding particle size range; The number concentration calibration coefficient and mass concentration calibration coefficient of each channel are calculated through linearization processing.

5. The method for particle size identification and concentration detection according to claim 1, characterized in that: The number of photosensitive devices can be expanded, and the particle size recognition resolution can be improved by increasing the number of photosensitive devices distributed along the light beam direction.

6. The method for particle size identification and concentration detection according to claim 1, characterized in that: The method further includes a step of dynamically adjusting the laser power, and expanding the particle size detection range by adjusting the laser output power.

7. The method for particle size identification and concentration detection according to claim 1, characterized in that: The mass concentration detection includes the simultaneous calculation of PM1.0, PM2.5 and PM10.

8. The method for particle size identification and concentration detection according to claim 1, characterized in that: The position of the photosensitive device is optimized based on the target detection particle size range, so that the scattered light capture rate of particles of a specific particle size in the corresponding channel is significantly higher than that in other channels.

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