CN113552048A - Particle counting method - Google Patents
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- CN113552048A CN113552048A CN202110845099.5A CN202110845099A CN113552048A CN 113552048 A CN113552048 A CN 113552048A CN 202110845099 A CN202110845099 A CN 202110845099A CN 113552048 A CN113552048 A CN 113552048A
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Abstract
The invention provides a particle counting method, which comprises the following steps: calibrating the photoelectric detection component; calibrating threshold voltages corresponding to particles with different particle sizes; and setting a comparison voltage value adjusted by a potentiometer of the particle channel based on the threshold voltage, comparing the output voltage of the photoelectric detection part with the comparison voltage value through a comparator, distinguishing the size of the particles and counting the number. The comparison voltage value of the comparator is adjusted through the potentiometer, so that counting can be efficiently and accurately completed, and the cost is low; the particle counter is calibrated and then is measured, the steps are simple, the deviation range of the final measurement result is greatly reduced, the method does not depend on a standard counter and a manual operation level, the measurement efficiency is high, the reliability is good, the realization is easy, and the further popularization and development of the measurement technology are facilitated.
Description
Technical Field
The invention belongs to the technical field of metering, and particularly relates to a particle counting method for metering by adopting an optical particle counter.
Background
The particle counting method commonly used at present is based on the mie scattering principle, and adopts a light scattering type laser particle counter to measure the number of dust particles in a single volume in a clean environment and the particle size distribution. Particle counting is widely applied to industries such as medicine, precision machinery and microorganism, and is also one of the main metering works of authorities such as epidemic prevention stations, disease control centers and quality supervision authorities. With the gradual implementation of the GMP certification system and the deep application of the particles in the aerosol in the disease transmission analysis, the influence of the quality of the particle counting method is also larger and larger. However, the accuracy, reliability and consistency of the existing particle counting method cannot completely meet the application requirements, and one of the important reasons is that the existing particle counter is not completely calibrated or is not effectively calibrated before being put into use. Before counting, a typical inspector uses a standard particle counter to calibrate the existing particle counting method, and manually and blindly adjusts the comparison voltage of comparators of different particle channels to make the particle channel counting be approximately the same as that of the standard particle counter. Then, one or more particles with unknown particle sizes are measured in a working area, the comparison voltage of a comparator needs to be manually adjusted for many times, and the whole particle counting efficiency is low due to the fact that the comparison with a standard counter is frequently carried out and the uncertainty is high, the reliability is difficult to improve, and the requirement of the measurement work cannot be met.
Therefore, there is a need to research an effective and feasible particle counting method to improve the accuracy and reliability of the metering work, so as to further promote the deep development and wide application of the metering technology.
Disclosure of Invention
The present invention is directed to solving some, all, or potential problems of the prior art described above and provides a particle counting method that employs a particle counter to test the particle size and distribution of airborne dust particles.
Some terms or principles that may be involved in the present invention are explained by way of example and not by way of limitation as follows:
mie scattering (Mie scattering), an optical phenomenon, is one case of scattering. When the size of the particles is close to or larger than the wavelength λ of the incident light, most of the incident light is scattered in the forward and vertical directions, which is called mie scattering.
Particle size (particulate size): the diameter of a certain scattering particle in the air is the diameter of the particle corresponding to the intensity of the scattered light, in mum.
Standard counter: and obtaining a satisfactory result through national organization comparison.
The metering principle of the particle counter is as follows: a photoelectric detection component is provided, and comprises an optical module and a photoelectric receiving module which are arranged in different directions. A working area is formed in an optical field output by the optical module, airflow of particles with certain concentration passes through the working area, light scattered by single particles through a Mie scattering collector is collected and then is projected onto a photosensitive element of the photoelectric receiving module, and energy is converted into a voltage pulse signal through a pre-amplification circuit. The voltage pulse signals are compared with threshold voltages of channels with different particle diameters to distinguish the size of the particle diameters and count the number of particles with different particle diameters.
The invention provides a particle counting method, which adopts a particle counter to count, wherein the particle counter comprises a photoelectric detection part, a main control board, a comparator and a potentiometer, wherein the comparator and the potentiometer are integrated on the main control board; the counting process comprises the following steps: s1, calibrating a photoelectric detection part; the photodetection component includes: the device comprises a laser, a photosensitive element and a preamplification circuit; s2, calibrating threshold voltages corresponding to particles with different particle sizes; s3, setting a particle channel according to the particle size, and setting a comparison voltage value adjusted by a potentiometer of the particle channel based on the threshold voltage corresponding to the particles with the particle size; s4, enabling the particle airflow to be detected to pass through a working area of the particle counter, comparing the output voltage of the photoelectric detection part with the comparison voltage value by using a comparator to distinguish the size of particles, and counting the number of the particles; step S1 includes calibrating the laser intensity in advance, setting the light path turning component in the working area, and calibrating the output voltage of the preamplifier circuit. The particle counter generally comprises a photoelectric detection component and a counting component, wherein the photoelectric detection component can be divided into an optical module and a photoelectric receiving module in two directions of a working area, namely, an output light beam of a laser in the optical module can not be projected to the photoelectric receiving module along a light path in one direction. If the photoelectric detection component needs to be effectively calibrated, on one hand, the light intensity of the laser light source in the working area needs to be calibrated because the light intensity of the particle counter in the working area is required to be uniform and the light intensity of each point in the whole working area is the same; on the other hand, a pre-amplification circuit of the photoelectric detection component needs to calibrate the electric signal after photoelectric conversion by the photosensitive element. In step S1, the light path turning component is set based on the same laser light source to perform calibration in an integrated manner, so that the light intensity of the laser light source in the working area meets the preset light intensity requirement after the laser light intensity is calibrated, and the light intensity of each particle count is kept in good consistency. Meanwhile, a laser light source is adopted for calibration, so that the calibration deviation accumulation is avoided, and the deviation can be reduced to the greatest extent. The light path turning element, such as a reflector or a combination of several reflectors, is used to turn the working beam and then irradiate the light-sensitive element for subsequent calibration, and the light path turning element may be correspondingly arranged in combination with the specific layout of the working area of the particle counter and the light-sensitive element to guide the working beam to the light-sensitive element. In the step S3, the potentiometer is set based on the threshold voltage to accurately set the comparative voltage values of different particle channels, so that the uncertainty of manual blind tuning is avoided; compared with a counting method of a standard counter, the counting method has the advantages that the efficiency is greatly improved, and counting results can be obtained more visually and rapidly.
Before the step S1, shaping the output beam of the laser to obtain a working beam; the light path structure for beam shaping comprises a lens, and the working beam is a flat-top beam.
The calibrating the laser light intensity comprises: calibrating the spot area size of the working light beam in the working area and the uniformity of light intensity distribution in the spots; the specific process comprises the following steps: acquiring spot information of the working light beam by using a laser spot collector, wherein the spot information comprises a spot image, and evaluating whether the spot size meets the requirement and whether the light intensity distribution in the spot is uniform according to the spot image; and adjusting the distance between the lens and the laser according to the evaluation result.
The specific process of calibrating the laser intensity further comprises the following steps: presetting a standard total value of the optical power of the working area, measuring the optical power of the working beam, and adjusting the optical power of the working area to be consistent with the standard total value based on the measurement result. By calibrating the optical power of the working beam, whether the light intensity of the working beam meets the actual particle counting requirement can be evaluated, and the consistency of the optical power of the laser light source after beam shaping is kept.
Calibrating the output voltage of the pre-amplifier circuit comprises: an attenuation sheet is additionally arranged between the light path turning element and the photosensitive element to weaken the light intensity of light spots irradiated on the photosensitive element; and adjusting the area of the light spot irradiating the photosensitive element by a light spot cutting clamp between the light path turning element and the photosensitive element. Because in some specific applications, the light intensity of the working light beam may exceed the bearable light intensity range of the photosensitive element, the setting of the attenuation sheet can adjust the light intensity of the light spot, and the risk that the working light beam directly irradiates the photosensitive element to damage the photosensitive element is effectively avoided. The light spot cutting clamp is arranged, so that the light spot area with specific requirements can be obtained, the practical application is better combined, and the flexibility of calibration work is improved. The attenuation sheet and the light spot cutting clamp can be set according to actual counting working conditions and a specifically adopted particle counter, or both the attenuation sheet and the light spot cutting clamp can be selected, and the method is not limited.
In step S2, the method includes collecting a waveform output by the preamplifier circuit through particles with a predetermined particle size in the working area, statistically analyzing a peak value of the waveform, and labeling a threshold voltage corresponding to the predetermined particle size.
The predicted particle size is at least 6, including 0.3 mu m, 0.5 mu m and 1.0 mu m; in step S3, at least 6 particle channels are set, and at least 6 comparative voltage values are adjusted by using a potentiometer.
And performing one-time statistical analysis on the peak value of the waveform, writing data obtained through the statistical analysis into a memory of a preset main control board, processing by a processor to obtain the threshold voltage, and giving a comparison voltage value adjusted by each channel potentiometer.
Adopting a virtual oscilloscope to statistically analyze the peak value of the waveform; the virtual oscilloscope is based on graphical programming software, including Labview. The virtual oscilloscope utilizes high-performance modular hardware and combines efficient and flexible software to complete various testing, measuring and automation applications. Wherein Labview is system engineering software designed specifically for testing, measurement and control applications, with fast access to hardware and data information.
In the process of calibrating the output voltage of the pre-amplification circuit, measuring the output voltage of the pre-amplification circuit by using a universal meter; when a plurality of particle counters are adopted for counting, the preamplifier circuit of each particle counter is provided with a potentiometer, and the potentiometer is adjusted to enable the output voltage of the preamplifier circuit of each particle counter to be consistent and equal to the design theoretical value of the output voltage of the photoelectric detection component. The universal meter is simple to operate, easy to configure, low in cost and convenient for finishing the calibration work. Based on the calibrated laser light intensity, the designed theoretical value of the output voltage of the photoelectric detection component is predictable and can also be obtained through theoretical calculation, the output voltage of the pre-amplification circuit of each particle counter is adjusted to be consistent with the designed theoretical value, the output voltage of the pre-amplification circuit of each particle counter is calibrated, the marked threshold voltage is more reliable, the comparison voltage value can be set more accurately, and the final counting result can be acquired more accurately.
Compared with the prior art, the invention has the main beneficial effects that:
the particle counting method does not completely depend on the existing standard counter for counting, counting can be efficiently and accurately completed through the combination of the potentiometer and the comparator, the cost is low, the efficiency is high, the counting is performed after the same laser light source is continuously calibrated, and the risk of generating errors is greatly reduced. The uncertainty of manual operation is avoided. By adopting the counting method, the consistency of results obtained by multiple particle counters through multiple counting is good; is very beneficial to the further popularization and development of the metering technology.
Drawings
Fig. 1 is a schematic diagram of a particle counter according to a first embodiment of the present invention.
Fig. 2 is a schematic process diagram of a particle counting method according to a first embodiment of the invention.
Fig. 3 is a schematic diagram of the calibrated laser intensity according to the first embodiment of the present invention.
Fig. 4 is a schematic view of a calibration tool for a photoelectric receiving module according to a first embodiment of the present invention.
Fig. 5 is a schematic diagram of the calibrated laser intensity in the second embodiment of the present invention.
Fig. 6 is a schematic view of a calibration tool in a second embodiment of the present invention.
Detailed Description
The technical solutions in the specific embodiments of the present invention will be clearly and completely described below, and it should be understood that the described embodiments are only a part of the embodiments of the present invention, and not all of the embodiments. All other embodiments, which can be derived by a person skilled in the art from the embodiments given herein without making any creative effort, shall fall within the protection scope of the present invention.
The above and/or additional aspects and advantages of the present invention will become apparent and readily appreciated from the following description of the embodiments, taken in conjunction with the accompanying drawings. In the figures, parts of the same structure or function are denoted by the same reference numerals, and not all parts shown are denoted by the associated reference numerals in all figures for reasons of clarity of presentation.
The operations of the embodiments are depicted in the following embodiments in a particular order, which is provided for better understanding of the details of the embodiments and to provide a thorough understanding of the present invention, but the order is not necessarily one-to-one correspondence with the methods of the present invention, and is not intended to limit the scope of the present invention.
It is to be noted that the flow charts and block diagrams in the figures illustrate the operational procedures which may be implemented by the methods according to the embodiments of the present invention. It should also be noted that, in some alternative implementations, the functions noted in the block may occur out of the order noted in the figures. For example, two blocks shown in succession may, in fact, be executed substantially concurrently, or the blocks may sometimes be executed in the alternative, depending upon the functionality involved. It is also noted that each block of the block diagrams and/or flowchart illustration, and combinations of blocks in the block diagrams and/or flowchart illustration, can be implemented by special purpose hardware-based systems which perform the specified functions or acts, or combinations of special purpose hardware and manual acts.
Example one
In the first embodiment of the present invention, as shown in fig. 1, the particle counter adopted in the first embodiment of the present invention is composed of an optical module for providing a working beam, a working area for performing detection, a photoelectric receiving module for performing optical signal receiving and conversion, a main control board integrated with a processor and a comparator, and a mechanical potentiometer electrically connected with the comparator. The optical module and the photoelectric receiving module are positioned in two directions of the working area; the working area is typically a photosensitive working area and a mie scattering collector. The optical module is internally provided with a laser serving as a laser light source and a power supply part thereof, and the output light intensity of the laser can be adjusted by adjusting the power supply of the laser; in this embodiment, a light path shaping structure including a plurality of lenses and a diaphragm is disposed near the output end of the laser, a gaussian spot of an output beam of the laser is shaped to obtain a working beam in the form of a flat-top beam, and the spots formed in the working area are flat-top homogenized. The lens is exemplified by a collimating lens, it should be noted that the light path shaping structure may also be designed accordingly according to the actual application requirement or the specific used particle counter structure, and may also include other optical lenses or optical elements, without limitation. The light from single particle through Mie scattering collector is collected by photoelectric receiving module, especially projected to photosensitive element. The photosensitive element of the embodiment is a photodiode, and has the advantages of small volume, fast response and good reliability. In other embodiments, other photosensitive elements such as phototriodes, etc. may be used, without limitation. The energy is converted into a voltage pulse signal through a pre-amplification circuit of the photoelectric receiving module, and the voltage pulse signal is compared with threshold voltages of different particle size channels to distinguish the size of the particle size, so that counting is realized.
In this embodiment, the particle counting method shown in fig. 2 includes: s1, calibrating a photoelectric detection part; s2, calibrating threshold voltages corresponding to particles with different particle sizes; s3, setting a particle channel according to the particle size, and setting a mechanical potentiometer to adjust a comparison voltage value of the particle channel based on a threshold voltage corresponding to the particle with the particle size; s4, enabling the particle airflow to be detected to pass through a working area, comparing the output voltage of the photoelectric detection part with a comparison voltage value by a comparator to distinguish the particle size, and counting the number; in step S1, the laser intensity is calibrated first, and then the optical path turning component is set in the working area to calibrate the output voltage of the preamplifier circuit.
In this embodiment, as shown in fig. 3, a laser spot collector is used in the process of calibrating the laser intensity, which exemplifies that a CCD camera arranged on a slide rail and adjustable in front and rear positions obtains spot images of a plurality of working light beams, and whether the spot size meets the requirements or not and whether the light intensity distribution in the spots is uniform or not is evaluated through the spot images. And if the non-uniformity exists, adjusting the distance between the lens in the light beam shaping structure in the optical module and the laser.
In this embodiment, as shown in fig. 4, the calibration fixture of this embodiment uses a surface mirror as the optical path turning element, and an attenuation sheet is additionally disposed on the optical path. In the embodiment, a plurality of particle counters are adopted for counting, a universal meter is adopted to measure the actual output voltage of the pre-amplification circuit in the process of calibrating the output voltage of the pre-amplification circuit, the pre-amplification circuit is provided with a mechanical potentiometer, and the mechanical potentiometer is adjusted to keep the output voltage of the pre-amplification circuit of each particle counter consistent. In this embodiment, the voltage is equal to the design theoretical value of the output voltage of the pre-amplification circuit of the photoelectric detection component under the calibrated laser intensity. The design theoretical value of the output voltage can be obtained by calculation. In general, the calibrated laser intensity is determined, the standard value of the photoelectric conversion rate of the photodiode of the particle counter is provided when the photodiode manufacturer leaves a factory, and the design theoretical value of the output voltage can be calculated according to the gain theory of the pre-amplifier circuit. For the sake of understanding, for example, it is known that the power of the working light beam is 0.8 μ W, the photoelectric conversion rate of the photodiode is 0.5A/W, the amplification gain of the pre-amplifier circuit is 5000000 Ω, and the theoretical value of the output voltage is 2V. When the operation is carried out on particle counting, the result obtained by the plurality of particle counters is good in consistency, the output voltage of the pre-amplification circuit is calibrated to be consistent with a theoretical calculated value, and the reliability of analysis of subsequent counting results is high. The potentiometers used in this embodiment are all mechanical potentiometers. A mechanical potentiometer is a three-terminal mechanically operated rotary analog device that can be used in a variety of electrical and electronic circuits. A mechanical potentiometer is a passive device that does not require a power source or additional circuitry to perform its basic linear or rotational position function. Mechanical potentiometers are very common, inexpensive and readily available. The traditional method is changed by combining the mechanical potentiometer and the comparator to implement particle counting, so that the equipment cost of the metering work is not increased, the labor cost is saved, and the reliability and consistency of counting results are improved. In some embodiments, the potentiometers used are all digital potentiometers, and the potentiometers are selected according to practical application, and are not limited.
In step S2, the waveform output by the preamplifier circuit is collected by using particles with a predetermined particle size in the working area of the particle counter for counting, the peak value of the waveform is statistically analyzed at one time, the peak value of the waveform is statistically analyzed by using the virtual oscilloscope, the data obtained by statistical analysis is written into the memory of the preset main control board, and the processor calls the data to calibrate the threshold voltage corresponding to each particle size channel, that is, the voltage value to be adjusted by the mechanical potentiometer of each channel is given. In the embodiment, a Labview acquisition system with a high-speed ADC board card is adopted to acquire the waveform output by the preamplifier circuit. For example: passing 0.3 mu m particles in a working area, collecting waveforms output by a pre-amplification circuit by using Labview, statistically analyzing the peak value of each waveform, and marking the threshold voltage of the 0.3 mu m particles; collecting waveforms output by a pre-amplification circuit through 0.5μm particles by using Labview, statistically analyzing the peak value of each waveform, and marking the threshold voltage of the 0.5μm particles; through 1.0 mu m particles, collecting waveforms output by a pre-amplification circuit by using Labview, carrying out statistical analysis on the peak value of each waveform, and then marking the threshold voltage of the 1.0 mu m particles. In the embodiment, the example of the software which adopts the virtual oscilloscope and is based on the graphical programming is Labview, which is not limited, but may also be other graphical programming software which can visually display various aspects of the application, including hardware configuration, measurement data and debugging. The particle counter is calibrated by a plurality of particles with preset particle sizes according to the number of particle size channels of the particle counter, and the number of the general preset particle sizes is at least 6. In this embodiment, a 6-channel particle counter may be configured to adjust 6 threshold voltages by using a mechanical potentiometer to realize counting of different channels.
Example two
The light intensity of the particle counter is required to be uniform, the light intensity of each point in the whole working area is the same, and the light intensity consistency of the optical module of each particle counter is required to be good. As shown in fig. 5, in this embodiment, the standard laser intensity is determined by using an optical power meter in addition to the CCD camera, a standard total value of the optical power of the working area is preset, the optical power of the working beam is measured, and the optical power of the working area is adjusted to be consistent with the standard total value based on the measurement result. And calculating the total power by adopting an optical power meter, and then adjusting the laser power supply. When a plurality of particle counters are used for counting, the power of the laser in each optical module after shaping is kept consistent by adopting the optical power meter.
Another main difference between the second embodiment and the first embodiment is that, as shown in fig. 6, the calibration tool further includes a spot cutting fixture additionally disposed between the attenuator and the photodiode. In the process of calibrating the output voltage of the pre-amplification circuit, the light spot area of the irradiated photodiode is adjusted through the light spot cutting clamp, and the light intensity of the irradiated photodiode is further adjusted through adjusting the light spot area.
For clarity of description, the use of certain conventional and specific terms and phrases is intended to be illustrative and not restrictive, but rather to limit the scope of the invention to the particular letter and translation thereof. The present invention has been described in detail, and the structure and operation principle of the present invention are explained by applying specific embodiments, and the above description of the embodiments is only used to help understanding the method and core idea of the present invention. It should be noted that, for those skilled in the art, it is possible to make various improvements and modifications to the present invention without departing from the principle of the present invention, and those improvements and modifications also fall within the scope of the claims of the present invention.
Claims (10)
1. A method of counting particles, comprising: counting by adopting a particle counter, wherein the particle counter comprises a photoelectric detection part, a main control board, a comparator and a potentiometer, wherein the comparator and the potentiometer are integrated on the main control board;
the counting process comprises the following steps:
s1, calibrating a photoelectric detection part of the particle counter; the photodetection component includes: the device comprises a laser, a photosensitive element and a preamplification circuit;
s2, calibrating threshold voltages corresponding to particles with different particle sizes;
s3, setting a particle channel of the particle counter according to the particle size, and setting a comparison voltage value adjusted by a potentiometer of the particle channel based on the threshold voltage corresponding to the particles with the particle size;
s4, enabling the particle airflow to be detected to pass through a working area of the particle counter, comparing the output voltage of the photoelectric detection part with the comparison voltage value by using a comparator to distinguish the size of particles, and counting the number of the particles;
step S1 includes calibrating the laser intensity in advance, setting the light path turning component in the working area, and calibrating the output voltage of the preamplifier circuit.
2. The particle counting method according to claim 1, characterized in that: before the step S1, shaping the output beam of the laser to obtain a working beam; the light path structure for beam shaping comprises a lens and a diaphragm, and the working beam is a flat-topped beam.
3. The particle counting method according to claim 2, characterized in that: the calibrating the laser light intensity comprises: calibrating the spot area size of the working light beam in the working area and the uniformity of light intensity distribution in the spots; the specific process comprises the following steps: acquiring light spot information of the working light beam by using a laser light spot collector, wherein the light spot information comprises a light spot image; evaluating whether the size of the light spot meets the requirement or not and whether the light intensity distribution in the light spot is uniform or not according to the light spot information; and adjusting the distance between the lens and the laser according to the evaluation result.
4. The particle counting method according to claim 3, wherein: the specific process of calibrating the laser intensity further comprises the following steps: presetting a standard total value of the optical power of the working area, measuring the optical power of the working beam, and adjusting the optical power of the working area to be consistent with the standard total value based on a measurement result.
5. The particle counting method according to claim 2, characterized in that: calibrating the output voltage of the pre-amplifier circuit comprises: an attenuation sheet is additionally arranged between the light path turning element and the photosensitive element to weaken the light intensity of light spots irradiating the photosensitive element; and adjusting the area of the light spot irradiating the photosensitive element by a light spot cutting clamp between the light path turning element and the photosensitive element.
6. The particle counting method according to any one of claims 1 to 5, wherein: in step S2, the method includes collecting a waveform output by the preamplifier circuit through particles with a predetermined particle size in the working area, statistically analyzing a peak value of the waveform, and labeling a threshold voltage corresponding to the predetermined particle size.
7. The particle counting method according to claim 6, wherein: in the process of calibrating the output voltage of the pre-amplification circuit, measuring the output voltage of the pre-amplification circuit by using a universal meter; when a plurality of particle counters are adopted for counting, the preamplifier circuit of each particle counter is provided with a potentiometer, and the potentiometer is adjusted to enable the output voltage of the preamplifier circuit of each particle counter to be consistent and equal to the design theoretical value of the output voltage of the photoelectric detection component.
8. The particle counting method according to claim 6, wherein: and performing one-time statistical analysis on the peak value of the waveform, writing the data obtained by the statistical analysis into a memory of the main control board, obtaining the threshold voltage by a processor, and giving a comparison voltage value adjusted by each channel potentiometer.
9. The particle counting method according to claim 6, wherein: adopting a virtual oscilloscope to statistically analyze the peak value of the waveform; the virtual oscilloscope is based on graphical programming software, including Labview.
10. The particle counting method according to claim 6, wherein: the predicted particle size is at least 6, including 0.3 mu m, 0.5 mu m and 1.0 mu m; in step S3, at least 6 particle channels are set, and at least 6 comparative voltage values are adjusted by using a potentiometer.
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