Stable air intake device for particle counter, dust particle counter, and gas sampling method

Abstract

This application provides a stable air intake device, a dust particle counter, and a gas sampling method for a particle counter, belonging to the field of particle counters. The stable air intake device includes: a main pipe for flowing sampling airflow driven by a negative pressure pump; a Venturi tube fixedly fitted inside the main pipe, the Venturi tube including a throat section and an expansion section, the expansion section being close to the air intake end of the main pipe and forming the input end of the Venturi tube; a gap is provided between the expansion section and the main pipe to allow the sampling airflow to pass through; the input end of the Venturi tube is connected to a clean air source; wherein the length of the main pipe is longer than the length of the Venturi tube, and the main pipe is connected to the sampling end of the particle counter. This application embodiment improves the flow stability of the sampling airflow and maintains a constant sampling flow rate through a dual-drive mechanism of main-path negative pressure suction combined with Venturi negative pressure ejection, reducing the sampling flow rate fluctuation rate of the dust particle counter and promoting the improvement of particle counting accuracy.

Description

Technical Field

[0001] This application relates to the field of dust particle detection technology, and in particular to a stable air intake device for a particle counter, a dust particle counter, and a gas sampling method. Background Technology

[0002] Dust particle counters are core instruments for clean environment monitoring, air quality management, and aerosol science research. They use the principle of optical scattering to accurately detect the size and number of suspended particles in a gas. Dust particle counters draw in airflow through a pump, but a drawback is the instability of the airflow, which can cause fluctuations. The accuracy of the counter is directly related to the flow rate; unstable airflow leads to fluctuations in the measured value, affecting the counting accuracy. Summary of the Invention

[0003] This application provides a stable air intake device, a dust particle counter, and a gas sampling method for a particle counter, to solve or alleviate one or more technical problems in the prior art.

[0004] As a first aspect of the embodiments of this application, the embodiments of this application provide a stable air intake device for a particle counter, comprising: The main pipeline is used to circulate the sampling airflow driven by the negative pressure air pump; The Venturi tube is fixedly installed inside the main pipeline. The Venturi tube includes a throat section and an expansion section. The expansion section is close to the air inlet end of the main pipeline and forms the input end of the Venturi tube. There is a gap between the expansion section and the main pipeline to allow the sampling gas flow. The input end of the Venturi tube is connected to a clean gas source. The main pipe is longer than the venturi tube and is connected to the sampling end of the particle counter.

[0005] In one embodiment, the venturi tube further includes an extension section near the expansion section, the extension section being located outside the main pipe; the stabilizing intake device further includes a first fixing fixture and a second fixing fixture, the first fixing fixture being used to fix the extension section and the second fixing fixture being used to fix the main pipe.

[0006] In one embodiment, a third fixing fixture is further included for fixing the venturi tube inside the main pipe; the third fixing fixture includes a collar and at least one support member, the collar being fitted inside the side wall of the main pipe, and the support member being fixedly connected to the expansion section of the venturi tube.

[0007] In one embodiment, the venturi tube, the third fixing fixture, and the main pipe are integrally formed.

[0008] In one embodiment, the minimum inner diameter of the throat segment is 1 / 10 to 1 / 3 of the maximum inner diameter of the expansion segment.

[0009] In one embodiment, the system further includes a first flow meter and a second flow meter. The first flow meter is disposed at one end of the expansion section away from the throat section and is used to detect the flow rate entering the venturi tube. The second flow meter is disposed between the venturi tube in the main pipeline and the sampling end and is used to detect the total flow rate entering the particle counter.

[0010] In one embodiment, a PID controller is also included to adjust the flow rate of the gas source based on the measurements of the first and second flow meters, such that the clean gas flow rate of the venturi tube is greater than the sampled gas flow rate.

[0011] In one embodiment, a pressure sensor is also included, which is disposed in the throat section of the venturi tube; the PID controller is a feedforward-feedback composite controller, whose feedforward control loop pre-adjusts the flow reference value of the clean gas source according to the measurement value of the second flow meter, and its feedback control loop simultaneously performs closed-loop correction according to the measurement values ​​of the first flow meter and the pressure sensor, so as to stabilize the throat negative pressure within a preset threshold range.

[0012] As a second aspect of the present application, the present application provides a dust particle counter, including a stable air intake device as described in any of the above embodiments.

[0013] As a third aspect of the embodiments of this application, this application provides a gas sampling method for a dust particle counter, applied to a dust particle counter in any of the above embodiments, including: Start the air pump and pump the sampling airflow into the main pipeline; A filtered clean airflow is pumped toward the Venturi tube, and when the clean airflow flows to the Venturi tube, a negative pressure is generated at its throat. The total airflow rate is detected in real time by the second flow meter, and the clean airflow rate flowing to the Venturi tube is detected in real time by the first flow meter. The difference between the total airflow rate and the clean airflow rate is calculated by the control unit, and this difference is determined as the sampling gas flow rate.

[0014] This application's embodiment employs the aforementioned technical solution, utilizing a dual-drive mechanism combining main-path negative pressure suction and Venturi negative pressure ejection to enhance the flow stability of the sampling airflow. When the airflow resistance at the sampling end fluctuates due to factors such as blockage or changes in ambient air pressure, the negative pressure generated at the throat of the Venturi tube can automatically compensate for this fluctuation, maintaining a constant sampling flow rate and reducing the sampling flow rate fluctuation rate of the dust particle counter. The stability of the sampling flow rate further promotes the improvement of particle counting accuracy, reducing particle overlap loss and miscounting caused by flow rate fluctuations.

[0015] The above overview is for illustrative purposes only and is not intended to be limiting in any way. In addition to the illustrative aspects, embodiments, and features described above, further aspects, embodiments, and features of this application will become readily apparent from the accompanying drawings and the following detailed description. Attached Figure Description

[0016] In the accompanying drawings, unless otherwise specified, the same reference numerals throughout the various drawings denote the same or similar parts or elements. These drawings are not necessarily drawn to scale. It should be understood that these drawings depict only some embodiments disclosed in this application and should not be construed as limiting the scope of this application.

[0017] Figure 1 A schematic diagram of a stable air intake device according to an embodiment of this application is shown.

[0018] Figure 2 A schematic diagram of a stable air intake device according to another embodiment of this application is shown.

[0019] Figure 3 Show Figure 2 A cross-sectional structural diagram of the third fixing fixture in the diagram.

[0020] Figure 4 A schematic diagram of a dust particle counter according to an embodiment of this application is shown.

[0021] Figure 5 A schematic flowchart of a gas sampling method according to an embodiment of this application is shown.

[0022] Explanation of reference numerals in the attached figures: 100: Main pipeline; 210: Expansion section; 220: Throat section; 230: Extension section; 240: Clean air source pump; 300: First flow meter; 400: Second flow meter; 600: Particle counter; 700: The first fixed fixture; 800: Second fixed fixture; 900: Third fixing fixture; 910: collar; 920: support component. Detailed Implementation

[0023] In the following description, only certain exemplary embodiments are briefly described. As those skilled in the art will recognize, the described embodiments can be modified in various ways without departing from the spirit or scope of this application. Therefore, the drawings and description are considered to be exemplary in nature and not restrictive.

[0024] This application provides a stable air intake device for a particle counter 600, such as... Figures 1 to 4 As shown, the stable air intake device includes a main pipe 100 and a venturi tube.

[0025] The main duct 100 is used to circulate the sampling airflow driven by a negative pressure air pump. The main duct 100 can be a circular tube with a uniform diameter, and its interior is used to circulate the sampling airflow driven by the negative pressure air pump. The main duct 100 can be made of medical-grade stainless steel, with the inner wall polished and the surface roughness Ra≤0.4μm to reduce airflow resistance and prevent particle adsorption. One end of the main duct 100 is connected to the sampling end (i.e., the air inlet) of the dust particle counter 600, and the other end is open. The sampling airflow enters the main duct 100 from the open end, carrying aerosol particles from the environment, and enters the optical detection chamber of the particle counter 600 through the main duct 100 under the suction action of the air pump.

[0026] The venturi tube is fixedly fitted inside the main pipe 100, and the two are arranged coaxially. The venturi tube includes a throat section 220 and an expansion section 210. The expansion section 210 is close to the air inlet end of the main pipe 100 and forms the input end of the venturi tube. A gap is provided between the expansion section 210 and the main pipe 100, which allows the sampling airflow of the main pipe to flow smoothly without being blocked by the venturi tube.

[0027] The inlet of the Venturi tube is connected to a clean air supply pump 240. This clean air supply pump 240 pumps in compressed air or clean nitrogen that has been filtered through a high-efficiency particulate air filter (HEPA or ULPA), with a particle concentration far lower than that of the sampling environment (e.g., reaching ISO Class 1 cleanliness). The clean air supply pump 240 pumps out a clean airflow, which is continuously introduced into the Venturi tube.

[0028] The main duct 100 is longer than the venturi tube. This design ensures that the venturi tube is entirely integrated inside the main duct 100, and that the main duct 100 has a sufficiently long straight section downstream of the venturi tube to fully develop the flow and further stabilize the airflow. The main duct 100 connects to the sampling end of the particle counter 600.

[0029] When the negative pressure air pump starts, a continuous negative pressure suction force is generated in the main pipeline 100, and the sampling airflow is drawn in through the annular gap. At the same time, the clean air source pump 240 introduces a clean airflow at a certain pressure into the venturi tube. When the clean airflow flows through the expansion section 210, the flow velocity gradually increases due to the gradual decrease in cross-sectional area; when it enters the throat section 220, the flow velocity reaches its maximum. According to Bernoulli's principle, after the clean airflow accelerates through the expansion section 210, it reaches its highest velocity at the throat section 220, and the pressure drops to its lowest, forming a local negative pressure zone. This negative pressure is transmitted to the main pipeline 100 through the outlet of the venturi tube, producing a suction or traction effect on the sampling airflow at the annular gap, making the flow velocity of the sampling airflow more stable and effectively suppressing airflow fluctuations caused by air pump pulsation or external environmental disturbances.

[0030] This embodiment of the application improves the flow stability of the sampling airflow through a dual-drive mechanism combining main-path negative pressure suction and Venturi negative pressure ejection. When the airflow resistance at the sampling end fluctuates due to factors such as blockage or changes in ambient air pressure, the negative pressure generated at the throat 220 of the Venturi tube can automatically compensate for the fluctuation, maintain a constant sampling flow rate, and reduce the sampling flow rate fluctuation rate of the dust particle counter 600. The stability of the sampling flow rate further promotes the improvement of particle counting accuracy and reduces particle overlap loss and false counting caused by flow rate fluctuations.

[0031] In one implementation, such as Figure 1 As shown, the venturi tube also includes an extension section 230, which is close to the expansion section 210 and is located outside the main pipe 100; the stabilizing intake device also includes a first fixing fixture 700 and a second fixing fixture 800, the first fixing fixture 700 being used to fix the extension section 230 and the second fixing fixture 800 being used to fix the main pipe 100.

[0032] The venturi tube is installed inside the main pipeline 100 and needs to be fixed with a fixture to form a stable structure.

[0033] In this embodiment, by extending the input end of the venturi tube to the outside of the main pipe 100 and fixing it independently, the axial movement or radial displacement of the venturi tube inside the main pipe 100 is avoided, ensuring that the annular gap between the expansion section 210 and the main pipe 100 is uniform.

[0034] This embodiment of the application uses a separate fixing structure for the venturi tube and the main pipe 100 to avoid the transmission of mechanical stress caused by equipment vibration or temperature changes, so that the relative position of the venturi tube and the main pipe 100 maintains higher accuracy, ensuring that the ratio of clean airflow to sampling airflow is stable in the long term and improving the air intake stability.

[0035] The structures of the first fixing fixture 700 and the second fixing fixture 800 can adopt various technical solutions that may be adopted by those skilled in the art or that may be adopted in the future.

[0036] In one embodiment, another method of securing the venturi tube within the main pipe 100 is provided, such as... Figure 2 As shown, the stabilizing air intake device also includes a third fixing fixture 900 for fixing the venturi tube inside the main pipe 100; the third fixing fixture 900 includes a collar 910 and at least one support member 920. The collar 910 is fitted inside the side wall of the main pipe 100, for example by interference fit or welding. The support member 920 is fixedly connected to the expansion section 210 of the venturi tube. The support member 920 is preferably three or four thin sheet-like structures evenly distributed in the circumferential direction, and its cross-section is designed to be streamlined to reduce obstruction to the sampling airflow.

[0037] In this embodiment, the third fixing fixture 900 achieves fixed fixing of the venturi tube within the main pipe 100 without relying on the extension section 230, resulting in a more compact structure, avoiding the generation of local eddies, and further improving intake stability.

[0038] In one embodiment, the venturi tube, the third fixing fixture 900, and the main pipe 100 are integrally molded using injection molding or 3D printing. This integral molding structure eliminates assembly errors, ensures coaxiality between the venturi tube and the main pipe 100, and avoids relative displacement caused by vibration.

[0039] The one-piece molded structure ensures that the width of the annular gap is highly consistent across the entire circumference, preventing flow deviation or eddies when the sampling airflow enters the annular gap. Eliminating flow deviation is particularly important for the dust particle counter 600: particles undergo non-uniform acceleration in flow deviation, resulting in inconsistent particle transit times through the optical detection area, which in turn causes fluctuations in the pulse signal amplitude and affects the accuracy of particle size determination.

[0040] Furthermore, the one-piece molding structure eliminates assembly gaps and fitting errors between components, preventing loosening or deformation that may occur during long-term use. Simultaneously, the one-piece molding flow channel surface is continuous and smooth, without steps or gaps, eliminating the possibility of particles depositing at these locations and re-entering the airflow, ensuring the consistent counting accuracy of the particle counter 600 during long-term operation.

[0041] The fixed structure provided in this application embodiment can ensure the uniformity of the annular gap, so that all particles pass through at basically the same speed, avoiding fluctuations in the amplitude of the pulse signal and affecting the accuracy of particle size determination.

[0042] In one embodiment, the minimum inner diameter D1 of the throat section 220 is 1 / 10 to 1 / 3 of the maximum inner diameter D2 of the expansion section 210. It can be understood that the minimum inner diameter of the throat section 220 is the side closer to the output end, and the maximum inner diameter of the expansion section 210 is the side closer to the input end. For example, the minimum inner diameter of the throat section 220 is 1 / 10, 1 / 9, 1 / 7, 1 / 5, 1 / 4, or 1 / 3 of the maximum inner diameter of the expansion section 210. By limiting the above parameters, the negative pressure effect of the clean airflow after flowing into the venturi tube can be guaranteed. When the throat diameter ratio is greater than 1 / 3, the negative pressure in the throat 220 is insufficient, resulting in a weak entrainment effect on the sampling airflow and an insignificant flow stabilization effect. When the throat diameter ratio is less than 1 / 10, the flow velocity in the throat 220 is too high. Although the negative pressure increases, the consumption of clean airflow increases sharply, and turbulence noise is easily generated in the throat 220. This can, in turn, transmit high-frequency pressure pulsations to the sampling airflow through air path coupling.

[0043] In one example, for a dust particle counter 600 with a sampling flow rate of 2.83 L / min (0.1 CFM), D1 is 2 mm and D2 is 10 mm, with a ratio of 1 / 5.

[0044] In one embodiment, the system further includes a first flow meter 300 and a second flow meter 400. The first flow meter 300 is disposed at one end of the expansion section 210 away from the throat section 220 and is used to detect the flow rate entering the venturi tube. The second flow meter 400 is disposed between the venturi tube and the sampling end of the main pipeline 100 and is used to detect the total flow rate entering the particle counter 600.

[0045] In one example, both flow meters can be thermal mass flow meters, which are characterized by fast response (≤100ms) and high accuracy (±1% of reading). The probe of the first flow meter 300 extends into the venturi tube, and the probe of the second flow meter 400 is embedded in the side wall of the main pipe 100. Both use non-invasive measurement and do not interfere with the airflow.

[0046] In one embodiment, a PID controller is also included to adjust the flow rate of the clean gas source based on the measurements of the first flow meter 300 and the second flow meter 400, such that the clean gas flow rate of the venturi tube is greater than the flow rate of the sampling gas.

[0047] In one example, let the total flow rate be Q_total and the clean air flow rate be Q_aux, then the sampled air flow rate Q_sample = Q_total - Q_aux. The PID controller can control Q_aux to be 10% to 30% larger than Q_sample.

[0048] In the dust particle counter 600, if the clean airflow rate is less than or close to the sampling airflow rate, the negative pressure generated by the Venturi throat 220 is insufficient to overcome the resistance of the sampling air path, and the sampling airflow will experience backflow or unstable "breathing" phenomenon.

[0049] This embodiment actively maintains Q_aux > Q_sample using a PID controller, ensuring the Venturi tube always operates in an "ejector" rather than a "suction" state, thereby forming a stable and reliable negative pressure source at the throat 220. Furthermore, this closed-loop monitoring method can promptly detect flow drift caused by filter blockage, pump aging, etc., and compensate and correct it through software algorithms, ensuring that particle counting is always calculated based on an accurate sampling volume, guaranteeing the long-term reliability of counting accuracy.

[0050] In one embodiment, a pressure sensor is also included, which is disposed in the throat section 220 of the venturi tube; the PID controller is a feedforward-feedback composite controller, whose feedforward control loop pre-adjusts the flow reference value of the clean air source according to the measurement value of the second flow meter 400, and its feedback control loop simultaneously performs closed-loop correction according to the measurement values ​​of the first flow meter 300 and the pressure sensor, so as to stabilize the throat negative pressure within a preset threshold range.

[0051] The pressure sensor can be a miniature piezoresistive or capacitive pressure sensor, and its range and accuracy are selected according to the actual negative pressure range (e.g., -10 kPa to 0 kPa).

[0052] The input to the feedforward control loop is the measured value from the second flow meter 400, which is the total airflow rate entering the particle counter. Since the sampled airflow rate equals the total airflow rate minus the clean airflow rate, when the total airflow rate shows a changing trend due to pump fluctuations or changes in sampling port resistance, the feedforward control loop can immediately adjust the clean air source's output flow rate reference value in advance based on this change. For example, when the second flow meter 400 detects an increasing trend in the total airflow rate, the feedforward control loop rapidly increases the set flow rate of the clean air source, thereby offsetting changes in throat negative pressure in advance and preventing large fluctuations in the sampled airflow rate.

[0053] The feedback control loop simultaneously receives the clean airflow rate measured by the first flow meter 300 and the throat pressure value measured by the pressure sensor 220, and performs closed-loop correction on the remaining deviation after feedforward control. The feedback control loop can use a standard PID algorithm to compare the clean airflow rate and the throat negative pressure value with their respective target ranges. For example, the target range for the clean airflow rate is 1.2 times the sampled airflow rate, and the throat negative pressure is stabilized at -2 kPa ± 0.2 kPa. The correction amount is calculated based on this and superimposed on the control signal output by the feedforward control to ultimately adjust the flow rate of the clean air source.

[0054] This application embodiment, by introducing throat negative pressure measurement and feedforward-feedback composite control, can further improve the ability of the stable air intake device to suppress interference such as air source fluctuations, air pump pulsation, and sampling port blockage, so that the particle counter can still obtain a constant sampling flow rate in complex environments, thereby ensuring the accuracy and repeatability of particle counting.

[0055] This application provides a dust particle counter 600, such as... Figure 4 As shown, the device includes a stable air intake device as described in any of the above embodiments. Specifically, the dust particle counter 600 also includes an optical detection cavity, a laser source, a photodetector, a signal processing circuit, and a negative pressure air pump. The sampling end of the main pipe 100 is connected to the sampling air inlet of the counter 600. The stable airflow, processed by the stable air intake device, enters the optical detection cavity. The airflow carrying particles passes through the focal spot area of ​​the laser beam. The scattered light generated by the particles is received by the photodetector and converted into electrical pulses. The signal processing circuit then performs particle counting and particle size classification.

[0056] The dust particle counter 600 employs the aforementioned stable air intake device to ensure a stable flow rate of the sampling airflow. The sampling airflow entering the optical detection cavity is stable, without pulsations or eddies, resulting in a more uniform particle distribution within the airflow and improved velocity consistency when passing through the laser beam. This reduces signal amplitude variations caused by flow rate fluctuations, thereby enhancing particle size resolution and counting accuracy. The particle counter 600 is particularly suitable for applications requiring extremely high measurement accuracy, such as pharmaceutical GMP certification and semiconductor cleanroom monitoring.

[0057] like Figure 5 As shown, this application embodiment also provides a gas sampling method for a dust particle counter 600, applied to any of the above embodiments of the dust particle counter 600, including: S510, start the air pump to pump the sampling airflow into the main pipeline 100; control the negative pressure air pump to start, generate a continuous negative pressure in the main pipeline 100, thereby pumping the sampling airflow into the main pipeline 100.

[0058] S520, a filtered clean airflow is pumped into the venturi tube. When the clean airflow reaches the venturi tube, a negative pressure is generated at its throat 220. This negative pressure acts on the sampling airflow in the main pipe 100 to form an auxiliary suction.

[0059] S530 uses a second flow meter 400 to detect the total airflow in real time, and a first flow meter 300 to detect the clean airflow flowing to the Venturi tube in real time.

[0060] S540 calculates the difference between the total airflow rate and the clean airflow rate through the control unit, and determines this difference as the sampling gas flow rate. That is, Q_sample = Q_total - Q_aux. The control unit uses this difference as a feedback signal to dynamically adjust the output flow rate of the clean gas source, so that Q_sample is stabilized near the target value (e.g., 2.83 L / min ± 2%).

[0061] The counting method provided in this application utilizes an indirect measurement approach, where "total flow rate - auxiliary flow rate = sampling flow rate," avoiding the increased flow resistance and particulate matter deposition problems that might arise from directly installing a flow sensor in the sampling gas path. Since the clean airflow is filtered clean gas, the first flow meter 300 is not contaminated by particulate matter, exhibiting good long-term stability. Simultaneously, closed-loop control maintains a constant sampling flow rate, ensuring that the dust particle counter 600 obtains a consistent sampling volume under different ambient air pressures and filter loads, thereby guaranteeing the accuracy of the count concentration (particles / m³) measurement.

[0062] In the description of this specification, it should be understood that the terms "center," "longitudinal," "transverse," "length," "width," "thickness," "upper," "lower," "front," "rear," "left," "right," "vertical," "horizontal," "top," "bottom," "inner," "outer," "clockwise," "counterclockwise," "axial," "radial," and "circumferential" indicate the orientation or positional relationship based on the orientation or positional relationship shown in the accompanying drawings. They are used only for the convenience of describing this application and simplifying the description, and do not indicate or imply that the device or element referred to must have a specific orientation, or be constructed and operated in a specific orientation. Therefore, they should not be construed as limitations on this application.

[0063] Furthermore, the terms "first" and "second" are used for descriptive purposes only and should not be construed as indicating or implying relative importance or implicitly specifying the number of technical features indicated. Thus, a feature defined as "first" or "second" may explicitly or implicitly include one or more of that feature. In the description of this application, "multiple" means two or more, unless otherwise explicitly specified.

[0064] In this application, unless otherwise expressly specified and limited, the terms "installation," "connection," "linking," and "fixing," etc., should be interpreted broadly. For example, they can refer to a fixed connection, a detachable connection, or an integral part; they can refer to a mechanical connection, an electrical connection, or a communication connection; they can refer to a direct connection or an indirect connection through an intermediate medium; they can refer to the internal communication of two components or the interaction between two components. Those skilled in the art can understand the specific meaning of the above terms in this application according to the specific circumstances.

[0065] In this application, unless otherwise expressly specified and limited, "above" or "below" the second feature can include direct contact between the first and second features, or contact between the first and second features through another feature between them. Furthermore, "above," "over," and "on top" of the second feature includes the first feature being directly above or diagonally above the second feature, or simply indicates that the first feature is at a higher horizontal level than the second feature. "Below," "below," and "under" the second feature includes the first feature being directly above or diagonally above the second feature, or simply indicates that the first feature is at a lower horizontal level than the second feature.

[0066] The foregoing disclosure provides many different implementations or examples for carrying out different structures of this application. To simplify the disclosure, specific examples of components and arrangements are described above. Of course, these are merely examples and are not intended to limit the scope of this application. Furthermore, reference numerals and / or letters may be repeated in different examples; such repetition is for simplification and clarity and does not in itself indicate a relationship between the various implementations and / or arrangements discussed.

[0067] The above description is merely a specific embodiment of this application, but the scope of protection of this application is not limited thereto. Any person skilled in the art can easily conceive of various variations or substitutions within the technical scope disclosed in this application, and these should all be included within the scope of protection of this application. Therefore, the scope of protection of this application should be determined by the scope of the claims.

Claims

1. A stable air intake device for a particle counter, characterized in that, include: The main pipeline is used to circulate the sampling airflow driven by the negative pressure air pump; A venturi tube is fixedly fitted inside the main pipe. The venturi tube includes a throat section and an expansion section. The expansion section is close to the air inlet end of the main pipe and forms the input end of the venturi tube. A gap is provided between the expansion section and the main pipe to allow the sampling gas flow. The input end of the venturi tube is connected to a clean gas source. The main pipe is longer than the venturi tube, and the main pipe is connected to the sampling end of the particle counter.

2. The stable air intake device according to claim 1, characterized in that, The venturi tube further includes an extension section located near the expansion section, the extension section being located outside the main pipe; the stabilizing intake device further includes a first fixing fixture and a second fixing fixture, the first fixing fixture being used to fix the extension section, and the second fixing fixture being used to fix the main pipe.

3. The stable air intake device according to claim 1, characterized in that, It also includes a third fixing fixture for fixing the Venturi tube inside the main pipe; the third fixing fixture includes a collar and at least one support member, the collar being sleeved inside the side wall of the main pipe, and the support member being fixedly connected to the expansion section of the Venturi tube.

4. The stable air intake device according to claim 3, characterized in that, The Venturi tube, the third fixing fixture, and the main pipe are integrally formed.

5. The stable air intake device according to any one of claims 1 to 4, characterized in that, The minimum inner diameter of the throat segment is 1 / 10 to 1 / 3 of the maximum inner diameter of the expansion segment.

6. The stable air intake device according to any one of claims 1 to 4, characterized in that, It also includes a first flow meter and a second flow meter. The first flow meter is disposed at one end of the expansion section away from the throat section and is used to detect the flow rate entering the venturi tube. The second flow meter is disposed in the main pipeline between the venturi tube and the sampling end and is used to detect the total flow rate entering the particle counter.

7. The stable air intake device according to claim 6, characterized in that, It also includes a PID controller for adjusting the flow rate of the gas source based on the measurements of the first flow meter and the second flow meter, so that the clean gas flow rate of the venturi tube is greater than the sampled gas flow rate.

8. The stable air intake device according to claim 7, characterized in that, It also includes a pressure sensor, which is installed in the throat section of the venturi tube; the PID controller is a feedforward-feedback composite controller, whose feedforward control loop pre-adjusts the flow reference value of the clean gas source according to the measurement value of the second flow meter, and its feedback control loop simultaneously performs closed-loop correction according to the measurement values ​​of the first flow meter and the pressure sensor, so as to stabilize the negative pressure in the throat within a preset threshold range.

9. A dust particle counter, characterized in that, Includes the stable air intake device as described in any one of claims 1 to 8.

10. A gas sampling method for a dust particle counter, characterized in that, The dust particle counter applied to claim 9 includes: Start the air pump and pump the sampling airflow into the main pipeline; A filtered clean airflow is pumped toward the Venturi tube, and a negative pressure is generated at the throat of the Venturi tube as the clean airflow passes through it. The total airflow rate is detected in real time by the second flow meter, and the clean airflow rate flowing to the Venturi tube is detected in real time by the first flow meter. The control unit calculates the difference between the total airflow rate and the clean airflow rate, and determines this difference as the sampling gas flow rate.

Images