CN216160394U

CN216160394U - Portable aerosol particle size spectrometer

Info

Publication number: CN216160394U
Application number: CN202121348091.XU
Authority: CN
Inventors: 黄志煌; 刘俊杰; 骆新峥
Original assignee: Fujian Metrology Institute; National Institute of Metrology
Current assignee: Fujian Metrology Institute; National Institute of Metrology
Priority date: 2021-06-17
Filing date: 2021-06-17
Publication date: 2022-04-01
Anticipated expiration: 2031-06-17

Abstract

The utility model provides a portable aerosol particle size spectrometer which comprises a photoelectric sensor, a signal filtering and amplifying circuit, a high-speed comparator, a peak value storage circuit, a high-speed AD sampling circuit and a microprocessor, wherein the photoelectric sensor is connected with the signal filtering and amplifying circuit; the photoelectric sensor is connected with the signal input end of the signal filtering and amplifying circuit, the signal output end of the signal filtering and amplifying circuit is respectively connected with the high-speed comparator and the peak value storage circuit, the high-speed comparator is connected with the microprocessor, and the peak value storage circuit is connected with the microprocessor through the high-speed AD sampling circuit. By adopting the particle size spectrometer, the rapid sampling can be realized, the calculation accuracy of the particle concentration is improved, and the measurement of the particle size spectrum of atmospheric particles is realized.

Description

Portable aerosol particle size spectrometer

Technical Field

The utility model relates to the technical field of environmental monitoring, in particular to a portable aerosol particle size spectrometer.

Background

The aerosol is a mixed gaseous dispersion system composed of atmospheric, solid or liquid particles, and the size of the aerosol particles is nanometer and micron-submicron, usually between 10nm and 10 μm. The aerosol has the characteristics of small particle size, large area, strong activity, easy attachment of toxic and harmful substances and the like, the aerosol stays in the atmosphere for a long time, large-particle-size particles can be directly removed by nasal cavities and throats, the proportion of small-particle-size particles deposited in lungs and bronchus is correspondingly increased along with the reduction of the particle size, and then the small-particle-size particles enter blood circulation to cause diseases related to cardiopulmonary dysfunction. Due to the physical and chemical characteristics of the aerosol, the aerosol not only becomes a propagation carrier of epidemic situations such as novel coronavirus pneumonia and the like, but also harms human health, can destroy the ecological environment, and plays an important role in global climate change and regional atmospheric haze pollution formation.

Currently, particle detection in aerosol mainly refers to measurement of physical parameters, namely, the number, concentration and distribution of particle sizes of particles. The particle size distribution determines the characteristics of the aerosol, provides characteristics of the aerosol for researchers, and helps the researchers analyze the influence brought by the aerosol. Currently, the measurement of the particle size and the number concentration (particle number spectrum) of nano-sized and submicron-sized particles in aerosol is widely applied to various fields. Especially in environmental protection and meteorological research field, can obtain the source of atmospheric particulates according to the number spectral distribution characteristic of aerosol particle to provide the basis for administering particulate matter pollution. In addition, aerosol particle size spectrometers are also widely used in performance testing of related products, such as: the performance evaluation of the clean air quality of the air purifier, the filtering efficiency of the mask, the measurement of the particle size and the concentration of the automobile exhaust particles and the like need to be matched with a corresponding aerosol particle size distribution and quantitative concentration measurement system.

Currently, in the research on the particle size distribution of atmospheric particulates at home and abroad, the following common methods for measuring the particle size of the particulates mainly comprise: optical, aerodynamic and electrical measurements were made of the particles, respectively, for their optical equivalent diameter, aerodynamic diameter and electromigration diameter. Among them, the instrument for measuring by optical measurement method is an Optical Particle Counter (OPC) whose working principle is: the scattering occurs on the particles through laser irradiation, after the particles are focused by the reflector, the detector which forms a certain angle with the laser irradiation direction on the same horizontal plane receives scattered light pulse signals, and the particle number concentration and the particle size are measured according to the number and the strength of the pulse signals. The instrument for measuring by aerodynamics has an aerodynamic particle size spectrometer (APS) whose working principle is: according to the inertia property of the particles, the particles are classified according to the particle size by aerodynamics, and then the particle size and the concentration information of the particles are obtained by measurement. The method also has higher measurement accuracy, but also has the problems of complex instrument performance, high price, heavy equipment, strict use conditions and the like. An instrument utilizing an electrical measurement method is a scanning electromigration particle size spectrometer (SMPS), and the working principle of the SMPS is as follows: the diameter of the particulate matter obtained by measuring the electric mobility of the particulate matter is called as the electromigration diameter, the method can measure the concentration of the particulate matter efficiently, has high measurement precision, extremely prepared particle size and multiple stages, but has the problems of complex structure, high price and heavy instrument, radioactive substances are in a charge neutralizer in the instrument, and the equipment is difficult to popularize widely due to strict operation specifications.

Instrument based on optical particle counter of micron level is light and handy, and portable's advantage obtains comparatively extensive application at present, and optical particle counter passes through signal acquisition circuit and measures the intensity and the quantity mapping of the pulse signal that photoelectric sensor produced into aerosol granule particle diameter and concentration, and particle diameter distributes promptly, and its particle diameter passageway measurement principle is: the corresponding particle size channels screen, amplify, compare and count the signal amplitude of the signal received by the photoelectric sensor, the hardware measurement classification of each particle size gear of the existing optical particle counter is independent, the particle size channels mainly comprise a single channel (only one particle size is measured), a double channel (measuring two particle sizes) and a multi channel (generally 6 channels: 0.3 μm, 0.5 μm, 1.0 μm, 3.0 μm, 5.0 μm and 10 μm respectively), the particle size gear required by the particle size spectrometer at least actually meets more than 16 channels, the gear of the existing optical particle counter for particle size classification is at most 16 gears, the calculation of the number of actually required channels cannot be met, the measurement accuracy is influenced, and the particle counting concentration measurement is limited.

Disclosure of Invention

The utility model aims to solve the technical problem of providing a portable aerosol particle size spectrometer, which realizes quick sampling and provides accurate particle size classification and particle concentration calculation.

The utility model is realized by the following steps: a portable aerosol particle size spectrometer comprises a photoelectric sensor, a signal filtering and amplifying circuit, a high-speed comparator, a peak value storage circuit, a high-speed AD sampling circuit and a microprocessor;

the photoelectric sensor is connected with the signal input end of the signal filtering and amplifying circuit, the signal output end of the signal filtering and amplifying circuit is respectively connected with the high-speed comparator and the peak value storage circuit, the high-speed comparator is connected with the microprocessor, and the peak value storage circuit is connected with the microprocessor through the high-speed AD sampling circuit.

Further, the photoelectric sensor comprises a gas circuit cavity, a light path transmitting unit, a silicon photodiode, a concave mirror, a convex lens, a diaphragm and a light trap, wherein the light path transmitting unit is used for transmitting parallel laser beams, the laser beams generate scattered light through particles in the gas circuit cavity, the scattered light sequentially passes through the concave mirror, the convex lens and the diaphragm to the silicon photodiode, the silicon photodiode is used for receiving the scattered light, and the light trap is used for absorbing the laser beams.

Further, the light path emitting unit includes a laser and a lens group, the laser adopts a semiconductor red laser with power of 30mW and wavelength of 632nm, and a laser beam of the laser emits a parallel laser beam after passing through the lens group.

Furthermore, the signal filtering and amplifying circuit comprises a low-pass filtering circuit and a signal amplifying circuit, the photoelectric sensor converts the received scattered light into a pulse signal, then the noise is removed through the low-pass filtering circuit, and then the signal output range is adjusted to 0-12V through the signal amplifying circuit.

Furthermore, the particle size spectrometer also comprises a first voltage follower and a second voltage follower, the signal filtering and amplifying circuit is connected with the high-speed comparator through the first voltage follower, and the signal filtering and amplifying circuit is connected with the peak value storage circuit through the second voltage follower. The voltage follower is arranged, so that the effects of buffering, isolating and improving the carrying capacity of signals can be achieved, and the two paths of signals are prevented from interfering with each other.

Further, a digital-to-analog conversion circuit is connected between the microprocessor and the high-speed comparator, the digital-to-analog conversion circuit outputs a voltage value as a reference voltage of the high-speed comparator, the high-speed comparator outputs a pulse signal with a TTL level to the microprocessor when the voltage of the received pulse signal exceeds the reference voltage of the digital-to-analog conversion circuit, the high-speed comparator keeps outputting a low level when the voltage of the received pulse signal is lower than the reference voltage of the digital-to-analog conversion circuit, the microprocessor performs interrupt processing when receiving a pulse rising edge, performs an accumulation counting operation, and simultaneously starts the high-speed AD sampling circuit to perform peak value measurement of the pulse signal.

Furthermore, the peak value storage circuit comprises an amplification buffer operation circuit, an energy storage capacitor and an operational transconductance amplifier, wherein the energy storage capacitor is respectively connected with the amplification buffer operation circuit and the operational transconductance amplifier, the amplification buffer operation circuit is connected with the operational transconductance amplifier, when a control signal pin is at a high level, the energy storage capacitor is kept and reflected at an output end, the amplification buffer operation circuit charges the energy storage capacitor to realize voltage sampling, during sampling, the operational transconductance amplifier is closed, the energy storage capacitor keeps charging until the energy storage capacitor is charged to the maximum value of the input voltage, the peak voltage of the input signal is kept, at the moment, the voltage value collected by the high-speed AD sampling circuit is the peak voltage value of the pulse, when the control signal pin is at a low level, the operational transconductance amplifier is opened, the energy storage capacitor discharges outwards to complete a peak value holding time sequence, waiting for the arrival of the next pulse signal.

The utility model has the advantages that:

1. the aerosol particle size measuring device based on the optical method has small equipment volume and provides a portable measuring instrument;

2. the peak value of a pulse signal generated by the photoelectric sensor is collected through the high-speed AD chip, a corresponding voltage value is obtained, pulses are captured through the high-speed comparator to realize counting of the pulses, grading calculation of more particle size channels is realized through calibration and fitting, the calculation accuracy and efficiency of particle mass concentration are improved, and measurement of an atmospheric particulate particle size spectrum is realized.

Drawings

The utility model will be further described with reference to the following examples with reference to the accompanying drawings.

Fig. 1 is a schematic diagram of a logic structure of a portable aerosol particle size spectrometer according to the present invention.

FIG. 2 is a schematic view of a photoelectric sensor according to the present invention

Fig. 3 is a schematic diagram of a peak holding circuit according to an embodiment of the utility model.

Fig. 4 is a schematic diagram of a high-speed AD sampling circuit according to an embodiment of the utility model.

Fig. 5 is a schematic diagram of a digital-to-analog conversion circuit according to an embodiment of the utility model.

FIG. 6 is a schematic diagram of the pulse processing process of the present invention.

Fig. 7 is a schematic diagram illustrating a correspondence between voltage and particle size in 48 particle size channels divided by the portable aerosol particle size spectrometer according to an embodiment of the present invention.

Fig. 8 is a flow chart of the implementation of the measurement method of the portable aerosol particle size spectrometer of the present invention.

Fig. 9 is a graph showing the effect of particle size spectrum obtained in an example of the present invention for different particle size channels (the abscissa is the particle size channel, and the ordinate is the particle concentration).

Detailed Description

Referring to fig. 1 to 7, a portable aerosol particle size spectrometer of the present invention includes a photoelectric sensor, a signal filtering and amplifying circuit, a high-speed comparator, a peak storing circuit, a high-speed AD sampling circuit, and a microprocessor;

Preferably, as shown in fig. 2, the photoelectric sensor includes an air path cavity 21, an optical path emitting unit 22, a silicon photodiode 23, a concave mirror 24, a convex lens 25, a diaphragm 26 and a light trap 27, the optical path emitting unit 22 is configured to emit a parallel laser beam 28, the laser beam 28 passes through a particulate matter 29 in the air path cavity to generate scattered light, the scattered light sequentially passes through the concave mirror 24, the convex lens 25 and the diaphragm 26 to reach the silicon photodiode 23, the silicon photodiode 23 serves as a receiver for receiving the scattered light, and the light trap 27 is configured to absorb the laser beam. When the gas path cavity is used, gas to be detected can be sucked into the gas inlet of the gas path cavity through the vacuum pump and is discharged from the gas outlet of the gas path cavity. In the figure, the x-axis is the laser irradiation direction, the y-axis is the gas flow direction, the z-axis is the scattered light receiving direction, and the three directions are perpendicular to each other.

The optical path emitting unit 22 includes a laser 221 and a lens assembly 222, where the laser 221 is a semiconductor red laser with a power of 30mW and a wavelength of 632nm, and a laser beam of the laser emits a parallel laser beam after passing through the lens assembly 222.

Preferably, the signal filtering and amplifying circuit comprises a low-pass filtering circuit and a signal amplifying circuit, the photoelectric sensor converts the received scattered light into a pulse signal, then removes noise through the low-pass filtering circuit, and then adjusts the signal output range to 0-12V through the signal amplifying circuit.

Preferably, the particle size spectrometer further comprises a first voltage follower and a second voltage follower, the signal filtering and amplifying circuit is connected with the high-speed comparator through the first voltage follower, and the signal filtering and amplifying circuit is connected with the peak value storage circuit through the second voltage follower. The voltage follower is arranged, so that the effects of buffering, isolating and improving the carrying capacity of signals can be achieved, and the two paths of signals are prevented from interfering with each other.

Preferably, a digital-to-analog conversion (DAC) circuit is further connected between the microprocessor and the high-speed comparator, the digital-to-analog conversion (DAC) circuit outputs a voltage value as a reference voltage of the high-speed comparator, the high-speed comparator outputs a pulse signal of a TTL level to the microprocessor when the voltage of the received pulse signal exceeds the reference voltage of the digital-to-analog conversion (DAC) circuit, the high-speed comparator keeps outputting a low level when the voltage of the received pulse signal is lower than the reference voltage of the digital-to-analog conversion (DAC) circuit, the microprocessor performs interrupt processing when receiving a pulse rising edge, performs an accumulative counting operation, and simultaneously starts the high-speed AD sampling circuit to perform peak value measurement of the pulse signal.

Preferably, as shown in fig. 3, the peak value storing circuit includes an amplifying buffer operational circuit (SOTA), an energy storing capacitor (C2) and an Operational Transconductance Amplifier (OTA), the energy storing capacitor is respectively connected to the amplifying buffer operational circuit (SOTA) and the Operational Transconductance Amplifier (OTA), the amplifying buffer operational circuit (SOTA) and the Operational Transconductance Amplifier (OTA) are connected, when the control signal pin is at a high level, the energy storing capacitor is held and reflected at the output terminal, the amplifying buffer operational circuit charges the energy storing capacitor to realize voltage sampling, during the sampling period, the operational transconductance amplifier is turned off, the energy storing capacitor keeps charging until the energy storing capacitor reaches the maximum value of the input voltage, the peak voltage of the input signal is maintained, the voltage value acquired by the high-speed AD sampling circuit at this time is the peak voltage value of the pulse, when the control signal pin is at a low level, and the operational transconductance amplifier is started, the energy storage capacitor discharges outwards, a peak value holding time sequence is completed, and the arrival of the next pulse signal is waited.

Referring to fig. 1 to 9, the present invention provides a method for measuring a portable aerosol particle size spectrometer, the method comprising the following steps:

step 1, absorbing sample gas into the photoelectric sensor, wherein the photoelectric sensor generates a pulse signal when receiving scattered light of particles;

step 2, filtering and amplifying the pulse signal through a filtering and amplifying circuit;

step 3, dividing the pulse signal into two paths of independent original pulse signals through two voltage followers, and inputting the two paths of independent original pulse signals into a high-speed comparator and a peak value storage circuit respectively;

step 4, when the high-speed comparator receives that the voltage of an original pulse signal exceeds the reference voltage, outputting a pulse signal of TTL level to the microprocessor, when the voltage of the original pulse signal received by the high-speed comparator is lower than the reference voltage, the high-speed comparator always outputs low level, and the original pulse signal is integrated into a standard TTL level pulse signal through the high-speed comparator;

step 5, the TTL level pulse signal is connected to an IO interruption port of a microprocessor, the microprocessor is interrupted when a pulse rising edge comes, counting is accumulated, and meanwhile, a high-speed AD sampling circuit is started to measure the peak value of the pulse signal;

step 6, when the original pulse signal passes through a peak value storage circuit, prolonging the peak value time of the pulse signal, simultaneously carrying out analog-to-digital conversion through a high-speed AD sampling circuit, converting the voltage of the peak value of the pulse signal into a digital value, carrying out analog-to-digital conversion through the high-speed AD sampling circuit, collecting the peak value of the pulse signal, resetting the peak value storage circuit of the pulse signal after AD collection is finished, and waiting for the arrival of the next pulse signal;

and 7, matching and calculating the peak voltage and the corresponding number of the acquired signals and the particle size channels through an internal particle size grading algorithm of the microprocessor to obtain the particle concentration distribution condition of each particle size channel and draw a particle size spectrum, wherein the particle size channels preset the corresponding particle size ranges. As shown in fig. 6, graph a is the original pulse, and after filtering and amplifying, graph b is obtained, and then the number of pulse peaks corresponding to different particle size channels is calculated according to the particle size corresponding to different particle size channels, and graph c is obtained.

Preferably, the step 7 of "presetting the particle size range corresponding to the particle size channel" includes: six standard polystyrene particles of 0.3 μm, 0.5 μm, 1 μm, 3 μm, 5 μm, 10 μm and the like are used as standard substances, voltage values of pulse signal peaks corresponding to particle size channels of the particle size spectrometer are calibrated after atomization, peak voltage values corresponding to other 42 particle size channels are calculated through a fitting algorithm after calibration is completed, and the corresponding relation between 48 groups of particle sizes and the voltage values is obtained, as shown in fig. 7. For example, a maximum of 4096 particle size channel pulses can be collected by using a 12-bit high-speed AD, the voltage compression classification of the 4096 particle size channel pulses can be converted into the corresponding 48 groups of aerosol particle size distributions by an internal classification unit of the microprocessor, and the calculated concentration map of each particle size channel is output and displayed to a user, as shown in fig. 9.

Preferably, the step 7 further includes:

the mass concentration values of PM1.0, PM2.5 and PM10 are calculated from the particle size spectrum and by the following particle mass concentration formulas:

wherein M is_nRepresents the sum of the mass concentrations of n particle size channel particles, n represents the total number of particle size channels of the particle size,

represents the average radius of spherical particles in the ith size passage,

the average density of the particles in the ith particle size channel is expressed, assuming that the optical diameter of the corresponding channel is consistent with the kinetic diameter, for example, the average density value is 1g/cm³，N_iThe number of particles in the ith particle size channel is expressed;

and comparing the calculation result with the calculation results of standard PM1.0, PM2.5 and PM10 measuring devices to obtain a correction factor K of the concentration, and multiplying the particle concentration value calculated by the particle mass concentration formula by the correction factor K to obtain a corrected particle concentration value.

The aerosol particle size measuring device based on the optical method has small equipment volume and provides a portable measuring instrument; the method comprises the steps of irradiating laser on particulate matters to generate scattering, focusing the scattering on the particulate matters through a reflector, receiving scattered light pulse signals through a receiving unit, measuring the particle number concentration and the particle size according to the number and the intensity of the pulse signals, acquiring the peak value of the pulse signals generated by a photoelectric sensor by adopting a high-speed AD chip, obtaining the corresponding voltage value, capturing pulses by adopting a high-speed comparator to realize pulse counting, obtaining a particle size distribution diagram of actually required particle size channels by adopting a partial calibration and partial fitting mode, designing an inversion algorithm of the particle concentration by using an iterative recursive algorithm of the particle size diagram, obtaining the mass concentrations of PM10, PM2.5, PM1 and the like by calculation, obtaining a more accurate particle concentration value calculation formula by correction, and further improving the particle concentration detection accuracy of the instrument.

Although specific embodiments of the utility model have been described above, it will be understood by those skilled in the art that the specific embodiments described are illustrative only and are not limiting upon the scope of the utility model, and that equivalent modifications and variations can be made by those skilled in the art without departing from the spirit of the utility model, which is to be limited only by the appended claims.

Claims

1. A portable aerosol particle size spectrometer is characterized in that: the device comprises a photoelectric sensor, a signal filtering and amplifying circuit, a high-speed comparator, a peak value storage circuit, a high-speed AD sampling circuit and a microprocessor;

2. A portable aerosol particle size spectrometer as claimed in claim 1, wherein: the photoelectric sensor comprises a gas circuit cavity, a light path transmitting unit, a silicon photodiode, a concave mirror, a convex lens, a diaphragm and a light trap, wherein the light path transmitting unit is used for transmitting parallel laser beams, the laser beams generate scattered light through particles in the gas circuit cavity, the scattered light sequentially passes through the concave mirror, the convex lens and the diaphragm to the silicon photodiode, the silicon photodiode is used for receiving the scattered light, and the light trap is used for absorbing the laser beams.

3. A portable aerosol particle size spectrometer as claimed in claim 2, wherein: the light path emission unit comprises a laser and a lens group, the laser adopts a semiconductor red laser with the power of 30mW and the wavelength of 632nm, and a laser beam of the laser emits a parallel laser beam after passing through the lens group.

4. A portable aerosol particle size spectrometer as claimed in claim 1, wherein: the signal filtering and amplifying circuit comprises a low-pass filtering circuit and a signal amplifying circuit, the photoelectric sensor converts received scattered light into pulse signals, then the low-pass filtering circuit removes noise, and then the signal amplifying circuit adjusts the signal output range to 0-12V.

5. A portable aerosol particle size spectrometer as claimed in claim 1, wherein: the particle size spectrometer also comprises a first voltage follower and a second voltage follower, the signal filtering and amplifying circuit is connected with the high-speed comparator through the first voltage follower, and the signal filtering and amplifying circuit is connected with the peak value storage circuit through the second voltage follower.

6. A portable aerosol particle size spectrometer as claimed in claim 1, wherein: and a digital-to-analog conversion circuit is connected between the microprocessor and the high-speed comparator, and the digital-to-analog conversion circuit outputs a voltage value as a reference voltage of the high-speed comparator.

7. A portable aerosol particle size spectrometer as claimed in claim 1, wherein: the peak value storage circuit comprises an amplification buffer operation circuit, an energy storage capacitor and an operational transconductance amplifier, wherein the energy storage capacitor is respectively connected with the amplification buffer operation circuit and the operational transconductance amplifier, and the amplification buffer operation circuit is connected with the operational transconductance amplifier.