Photoacoustic trace gas intelligent detection system and method

Abstract

The invention relates to the technical field of trace gas detection, in particular to a photoacoustic trace gas intelligent detection system and method.A general control unit controls a gas flow circulation unit to be started, target gas to be detected is pumped into an inner cavity of a photoacoustic cell unit, and the pressure intensity of the inner cavity is made to be standard atmospheric pressure; a signal generator is controlled to generate PWM waveforms with set frequency and duty ratio, one PWM waveform drives an LED light source to generate a continuous light source and excite target gas in an inner cavity to generate periodic barometric disturbance after being modulated by a light source modulation unit, a signal processing unit converts a detected vibration signal into an electric signal, and the other PWM waveform serves as a reference signal, so that the periodic barometric disturbance is generated. A signal with a set frequency is separated from the electric signal, amplified, converted into a voltage signal and transmitted to a master control unit; converting the voltage signal into a voltage value, and generating the gas concentration of the target gas based on the voltage value; according to the invention, miniaturization and automatic control of photoacoustic trace gas detection are realized, and the cost is reduced.

Description

Technical Field

[0001] The present invention relates to the technical field of trace gas detection, and particularly to an intelligent photoacoustic trace gas detection system and method. Background Art

[0002] Trace gas detection has important applications in many fields such as environmental monitoring, industrial safety, medical diagnosis, and scientific research. Traditional gas detection methods mainly include electrochemical sensors, semiconductor gas sensors, gas chromatography, etc. However, these methods have certain limitations in terms of selectivity, sensitivity, stability, and portability.

[0003] In related technologies, spectroscopic analysis technology has been widely used in the field of gas detection due to its high selectivity, high sensitivity, and non-contact and non-destructive characteristics. Among them, photoacoustic spectroscopy (PAS) technology, as a highly sensitive trace gas detection method, has been widely used in environmental monitoring, industrial process control, medical diagnosis, and safety monitoring. Photoacoustic spectroscopy technology is based on the principle of photoacoustic effect, and realizes the detection of gas concentration by measuring the acoustic signal generated after the gas absorbs light energy.

[0004] Photoacoustic spectroscopy technology has many advantages compared with traditional spectroscopic technologies, including high sensitivity, zero background signal, linear response, and applicability to various gases. It can detect gas concentrations down to the ppb or even ppt level, and since only the absorbed light generates photoacoustic signals, background interference is greatly reduced. In addition, the photoacoustic signal intensity is linearly related to the gas concentration, which is convenient for quantitative analysis, and almost all gases have their characteristic absorption spectra, and can be effectively detected by selecting appropriate wavelengths. However, traditional photoacoustic spectroscopy systems generally have problems such as large volume, complex structure, and high cost. They mainly rely on lasers as light sources, require professional personnel for operation and maintenance, and are difficult to achieve portability and large-scale applications. Summary of the Invention

[0005] The purpose of the present invention is to provide an intelligent photoacoustic trace gas detection system and method, which can realize the miniaturization and automatic control of photoacoustic trace gas detection, and greatly reduce the cost.

[0006] To achieve the above purpose, the present invention provides the following technical solutions: In a first aspect, an embodiment of the present invention provides an intelligent photoacoustic trace gas detection system, which includes: a photoacoustic cell unit, a light source modulation unit, a signal processing unit, an air flow circulation unit, a master control unit, and a signal generator; The overall control unit is used to control the start of the air flow circulation unit, pump the target gas to be detected into the inner cavity of the photoacoustic cell unit, and make the pressure in the inner cavity be one standard atmosphere; and is used to control the signal generator to generate a PWM waveform with a set frequency and duty cycle. The PWM waveform is divided into two paths, and is used to convert the voltage signal sent by the signal processing unit into a voltage value, and generate the gas concentration of the target gas based on the voltage value. The light source modulation unit is used to modulate one path of the PWM waveform, drive the LED light source to generate a continuous light source, and excite the target gas in the inner cavity to generate periodic pressure disturbances. The signal processing unit is used to convert the detected vibration signal into an electrical signal, use the other path of the PWM waveform as a reference signal, separate the signal with the set frequency from the electrical signal, amplify it and then convert it into a voltage signal and send it to the overall control unit.

[0007] Preferably, the photoacoustic cell unit includes a photoacoustic cell main body, tower connectors arranged on the left and right sides of the photoacoustic cell main body, and panel covers arranged on the front and back sides of the photoacoustic cell main body. Through holes communicating with each other front and back are opened in the middle of the photoacoustic cell main body and the front and back panel covers. Ultraviolet quartz glass sheets are arranged on both sides of the front and back of the through holes, and rubber rings are used to seal both ends of the through holes. An inner cavity is vertically opened at the top of the photoacoustic cell main body.

[0008] Preferably, the light source modulation unit includes a first power amplifier and a voltage-controlled constant current source. Specifically, the light source modulation unit is used to sequentially perform power amplification and current stabilization on one path of the PWM waveform through the first power amplifier and the voltage-controlled constant current source, drive the LED light source to flash with a stable power and frequency, and modulate to generate a continuous light source; the LED light source includes two groups of LED array light sources, and the two groups of LED array light sources are symmetrically arranged on the front and back panel covers.

[0009] Preferably, the signal processing unit includes a photoacoustic signal sensor, a second power amplifier, a low-pass filter, and a phase-locked amplifier connected in sequence. The input end of the phase-locked amplifier is also connected to the signal generator. The photoacoustic signal sensor is arranged at the top end of the inner cavity. The photoacoustic signal sensor is used to collect the vibration signal of the target gas in the inner cavity and convert it into an electrical signal. The second power amplifier is used to amplify the electrical signal to obtain an amplified electrical signal. The low-pass filter is used to filter out the high-frequency noise in the amplified electrical signal and send the filtered low-frequency effective signal to the phase-locked amplifier; the center frequency of the low-pass filter is the set frequency. The lock-in amplifier is used to use another PWM waveform as a reference signal, separate the signal with a set frequency in the low-frequency effective signal, amplify it and then convert it into a voltage signal and input it into the master control unit.

[0010] Preferably, the air flow circulation unit includes a micro air pump and a solenoid valve respectively connected to the master control unit, and the micro air pump is connected to the pagoda joint of the photoacoustic cell unit through a hose.

[0011] Preferably, generating the gas concentration of the target gas based on the voltage value includes: Converting the voltage value into the concentration value of the target gas through a preset concentration inversion algorithm, and calibrating the concentration value into the gas concentration of the target gas according to a preset relative calibration algorithm of the device.

[0012] Preferably, converting the voltage value into the concentration value of the target gas through a preset concentration inversion algorithm includes: Obtain the voltage values corresponding to n different gas concentrations to obtain a set of data points, expressed as: , represents the nth voltage value, represents the gas concentration corresponding to the nth voltage value; Calculate the mean values of the voltage values and the gas concentrations in this set of data points through the following formula: , represents the mean voltage, represents the mean gas concentration; Calculate the variance of the voltage values through the following formula , as well as the covariance of the voltage values and the gas concentrations : ; Calculate the slope a and intercept b of the linear relationship line through the following formula: ; Establish a linear relationship formula between the concentration value y of the target gas and the voltage value x, that is ; Substitute the voltage value into the linear relationship formula to obtain the concentration value of the target gas.

[0013] Preferably, calibrating the concentration value into the gas concentration of the target gas according to a preset relative calibration algorithm of the device includes: Obtain the voltage values corresponding to two different gas concentrations, denoted as ; Calculate the gas concentrations corresponding to the current voltage value according to the linear relationship formula, and obtain two gas concentrations , ; Solve for the slope A and intercept B of the relative error according to the formula: ; Where: ; The calibrated relationship formula is ; Substitute the concentration value of the target gas into the relationship formula to obtain the gas concentration value of the target gas.

[0014] Preferably, the system further includes a human-machine interaction unit, and the human-machine interaction unit is used to display the gas concentration.

[0015] In a second aspect, an embodiment of the present invention provides a photoacoustic trace gas intelligent detection method, and the method includes the following steps: The master control unit controls the air flow circulation unit to start, pumps the target gas to be detected into the inner cavity of the photoacoustic cell unit, and makes the pressure in the inner cavity be one standard atmospheric pressure; The master control unit controls the signal generator to generate a PWM waveform with a set frequency and duty cycle. The PWM waveform is divided into two paths. One path of the PWM waveform is modulated by the light source modulation unit, and then drives the LED light source to generate a continuous light source, which excites the target gas in the inner cavity to generate periodic pressure disturbances. The signal processing unit converts the detected vibration signal into an electrical signal, and uses the other path of the PWM waveform as a reference signal, separates the signal with the set frequency from the electrical signal, amplifies it, and then converts it into a voltage signal and transmits it to the master control unit; The master control unit converts the voltage signal into a voltage value and generates the gas concentration of the target gas based on the voltage value.

[0016] The beneficial effects of the present invention are as follows: The present invention pumps the target gas to be detected into the inner cavity of the photoacoustic cell unit through the air flow circulation unit, and makes the pressure in the inner cavity be one standard atmospheric pressure; generates a PWM waveform with a set frequency and duty cycle through the signal generator, modulates one path of the PWM waveform through the light source modulation unit, drives the LED light source to generate a continuous light source, and excites the target gas to generate periodic pressure disturbances. The signal processing unit converts the vibration signal into an electrical signal, uses the other path of the PWM waveform as a reference, separates and amplifies the signal with a specific frequency in the electrical signal, and finally transmits the processed voltage signal to the master control unit to accurately calculate the target gas concentration, realizing efficient and accurate trace gas detection. The photoacoustic trace gas intelligent detection system and method provided by the present invention realize the miniaturization and automatic control of photoacoustic trace gas detection, and greatly reduce the cost. Description of the Drawings

[0017] To more clearly illustrate the technical solutions in the embodiments of the present invention or the prior art, the following will briefly introduce the drawings required in the embodiments. Obviously, the drawings in the following description are only some embodiments of the present invention. For those of ordinary skill in the art, without creative efforts, other drawings can be obtained based on these drawings.

[0018] Figure 1 is the overall framework diagram of the photoacoustic trace gas intelligent detection system in the embodiment of the present invention; Figure 2 is the structural schematic diagram of the photoacoustic cell unit in the embodiment of the present invention; Figure 3 is the framework diagram of the light source modulation unit in the embodiment of the present invention; Figure 4 is the framework diagram of the signal processing unit in the embodiment of the present invention; Figure 5 is the process schematic diagram of the master control unit and the human-computer interaction unit in the embodiment of the present invention; Figure 6 is the process schematic diagram of the photoacoustic trace gas intelligent detection method in the embodiment of the present invention. Specific Embodiments

[0019] The following will clearly and completely describe the concept, specific structure and technical effects generated by the present invention in combination with the embodiments and the drawings, so as to fully understand the purpose, solution and effect of the present invention. It should be noted that, without conflict, the embodiments in the present invention and the features in the embodiments can be combined with each other.

[0020] Most of the related technologies use lasers or tunable laser diodes. The driving circuits of such light sources are complex, with high power consumption and relatively high overall prices. Using a resonant photoacoustic cell as the gas container, although the obtained photoacoustic signal will be improved, the structure of the photoacoustic cell is complex, and the light source frequency needs to be matched, resulting in a complex overall structure, large volume and high sensitivity to the environment. The overall equipment is troublesome to maintain, the prices of each component are expensive, and the maintenance cost is high. It is necessary to bind devices such as computers for data analysis, the detection process is complex to operate, and the human-computer interaction logic is chaotic.

[0021] In recent years, the development of LED technology has brought revolutionary changes to photoacoustic spectroscopy systems. Compared with traditional laser sources, LED light sources have the advantages of significantly lower costs, smaller size, lower power consumption, longer life, and flexible wavelength selection. The price of LED light sources is only a few tenths of that of lasers of the same power. The small size is conducive to the miniaturization and portability of the system. The low power consumption is suitable for battery-powered portable devices, and the life span can usually reach more than 100,000 hours. In addition, LEDs with suitable wavelengths can be selected according to the absorption characteristics of different gases. Although LED light sources have limitations such as large spectral width and low power density, their advantages are still significant. In terms of photoacoustic cell design, non-resonant photoacoustic cells are ideal for portable devices due to their simple structure, easy manufacture and maintenance, insensitivity to environmental vibrations, good stability, wide response frequency range, and suitability for miniaturization and portability. Although their signal amplification factor is small, their sensitivity is usually lower than that of resonant photoacoustic cells under traditional designs.

[0022] With the rapid development of microelectronics, micromachining and signal processing technologies, miniaturization and portability of gas detection equipment has become a reality. This is mainly due to the design technology of micro photoacoustic cells, which optimizes the acoustic path to reduce the volume while maintaining good acoustic performance; the application of highly integrated electronic systems, using high-performance microcontrollers and application-specific integrated circuits; low-power design strategies, optimizing circuits and algorithms to extend battery life; and the optimization of human-computer interaction, simplifying the operation process and improving the overall user experience. The comprehensive application of these technologies makes portable photoacoustic spectroscopy gas detection equipment have practical value and market potential.

[0023] Traditional photoacoustic spectroscopy gas detection systems are mainly divided into several representative solutions. The first is the laser-driven resonant photoacoustic spectroscopy system, which uses a mid-infrared quantum cascade laser or a tunable diode laser as a light source, in conjunction with a Helmholtz resonant cavity or a cylindrical resonant cavity, and uses a high-sensitivity microphone or piezoelectric sensor for detection, and the signal processing relies on a phase-locked amplifier. Although this type of system has high sensitivity (up to ppb level), it is bulky (usually greater than 10 liters), expensive, and consumes a lot of power (usually greater than 50 watts). The other type is a system that combines Fourier transform infrared spectroscopy with photoacoustic detection. It uses a wide-spectrum infrared light source, a Fourier transform interferometer, and a multi-channel resonant photoacoustic cell to detect multiple gases at the same time, but the system is highly complex, bulky, and expensive.

[0024] Current representative miniaturization solutions include miniaturized photoacoustic spectroscopy devices based on quantum cascade lasers (QCLs). These devices use QCLs as high-power excitation light sources and combine them with highly sensitive piezoelectric sensors or micro-resonant photoacoustic cells to achieve highly sensitive detection of target gases by modulating the light source frequency. The advantage is that QCL light sources have high power and narrow spectral band characteristics, which can significantly increase the photoacoustic signal intensity and are suitable for detecting gases with extremely low concentrations. However, they also have disadvantages such as high cost, large volume, and high power consumption, making it difficult to achieve a fully portable design. Moreover, highly sensitive sensors require complex temperature control and signal processing algorithms. For example, in the medical field, such devices are used for breath analysis to detect the concentration of carbon monoxide or nitrous oxide, but their volume and cost limit their widespread application in mobile devices.

[0025] On the other hand, miniaturized devices based on quartz-enhanced photoacoustic spectroscopy (QEPAS) enhance the photoacoustic signal by reflecting the beam of the excitation light source multiple times (such as through echo plates or optical fibers) to extend the interaction path between light and gas. This technology usually combines micro piezoelectric sensors or fiber optic sensors. Its advantages are that it does not require a resonant photoacoustic cell, has a simple structure, is easy to miniaturize, and has relatively high sensitivity, making it suitable for detecting gases with extremely low concentrations. However, the disadvantages are that it requires precise control of the optical path alignment and beam stability, has certain requirements for the wavelength and power of the light source, and may require additional optical elements. In the field of environmental monitoring, QEPAS devices are used to detect the concentration of gases such as methane or ozone. They have relatively high sensitivity and selectivity, but have high requirements for the stability of the optical path.

[0026] Photoacoustic spectroscopy technology refers to the principle based on the photoacoustic effect. When light of a specific wavelength radiated by a light source is absorbed by gas molecules, the energy levels of the molecules transition. Subsequently, through a non-radiative relaxation process, the energy is converted into heat energy, resulting in a local temperature increase and the generation of a pressure wave. This acoustic signal can be detected by a microphone and is proportional to the gas concentration. Compared with traditional spectroscopic analysis methods, photoacoustic spectroscopy technology has the advantage of directly measuring the absorption signal rather than the transmission signal, enabling highly sensitive and selective gas detection.

[0027] To solve the technical problems in the background art, based on the photoacoustic spectroscopy technology, the present invention designs a synchronous dual-channel LED array light source collaborative modulation by using a low-cost and low-power LED as the light source, designs a resin integrally formed non-resonant micro photoacoustic cell, and obtains a high-sensitivity photoacoustic signal by means of an independently designed integrated two-stage signal processing architecture - a signal acquisition and amplification circuit and a phase-locked amplifier. Through the microcontroller and peripheral circuits of the independently designed program, an automatic control system with a three-layer architecture of the physical layer, application layer, and control layer for functions such as light source modulation, signal acquisition, data processing, and human-computer interaction is realized, so as to quickly and real-time obtain the concentration of a specific gas and realize the full automation of the detection and data processing process. The present invention is low in cost, overall miniaturized, and the automatic control system and the human-computer interaction logic are reasonably designed, which is conducive to promoting the productization and popularization of the photoacoustic gas detection technology.

[0028] Referring to Figures 1 to 5 , the present invention provides a photoacoustic trace gas intelligent detection system, and the system includes: a photoacoustic cell unit, a light source modulation unit, a signal processing unit, an air flow circulation unit, a master control unit, and a signal generator; The master control unit is used to control the start of the air flow circulation unit, pump the target gas to be detected into the inner cavity of the photoacoustic cell unit to make the pressure in the inner cavity be one standard atmospheric pressure; and is used to control the signal generator to generate a PWM waveform with a set frequency and duty cycle, the PWM waveform is divided into two paths, and is used to convert the voltage signal sent by the signal processing unit into a voltage value and generate the gas concentration of the target gas based on the voltage value; The light source modulation unit is used to modulate one path of the PWM waveform to drive the LED light source to generate a continuous light source to excite the target gas in the inner cavity to generate a periodic air pressure disturbance; The signal processing unit is used to convert the detected vibration signal into an electrical signal, use the other path of the PWM waveform as a reference signal, separate the signal with a set frequency from the electrical signal, amplify it and then convert it into a voltage signal and send it to the master control unit.

[0029] The photoacoustic trace gas intelligent detection system disclosed by the present invention is composed of six module units with a three-layer architecture, including: an air flow circulation unit, a light source modulation unit, a signal processing unit, and a photoacoustic cell unit at the physical layer; a general control unit at the control layer; and a human-computer interaction unit at the application layer. The working principle of this system is that in the micro photoacoustic cell unit of the air flow circulation, a dual-channel LED array light source with a fixed wavelength modulated according to a specific frequency is introduced, generating photoacoustic signals that are collected by sensor devices such as piezoelectric ceramics. The signal processing unit performs amplification and filtering on the two-stage signal processing architecture in the circuit to obtain preliminary photoacoustic electrical signals. All the above operations are automatically controlled by the general control unit at the control layer without human intervention. The obtained photoacoustic electrical signals are converted into digital signals by the general control unit and calculated according to the designed two-point dynamic calibration algorithm to eliminate signal distortion caused by hardware differences between devices, thereby inversely calculating the concentration of the target gas. It is fed back to the user by the human-computer interaction unit in a wired or wireless manner and automatically makes relevant response reactions. The present invention realizes full automation throughout the process, and the overall system has a small volume and low cost, facilitating wide installation to monitor the quality of the target gas and make responses.

[0030] Reference Figure 2 , in some embodiments, the photoacoustic cell unit includes a photoacoustic cell main body 100, tower connectors 200 arranged on the left and right sides of the photoacoustic cell main body 100, and panel covers 300 arranged on the front and back sides of the photoacoustic cell main body 100; Through holes communicating front and back are opened in the middle of the photoacoustic cell main body 100 and the front and back panel covers 300. Ultraviolet quartz glass sheets are arranged on both sides of the front and back of the through holes, and rubber rings are used to seal both ends of the through holes; An inner cavity 400 is vertically opened at the top of the photoacoustic cell main body 100.

[0031] Specifically, the photoacoustic cell unit is designed as a non-resonant photoacoustic cell. The main body and accessories are integrally formed by 3D printing with resin materials. Tower connectors 200 are left on both sides for accessing the air flow circulation unit; an opening is provided at the top of the photoacoustic cell main body 100, and the opening extends vertically downward to form an inner cavity 400; piezoelectric ceramics and other photoacoustic signal sensors are placed at the opening; the front and rear covers have the same specifications and are fixed to the photoacoustic cell main body 100 by M4 metal screws. One JGS1 ultraviolet quartz glass sheet is placed in front of and behind the middle through hole, and it is sealed with a nitrile O-ring to ensure the seal of the internal cavity. The maximum external side length of this photoacoustic cell unit is only 60 mm, and the internal cavity is a cylindrical shape with a diameter of 5 mm and a length of 20 mm. It has a small overall volume, is made of resin materials with low cost and light weight.

[0032] Reference Figure 3 , in some embodiments, the light source modulation unit includes a first power amplifier and a voltage-controlled constant current source; The light source modulation unit is specifically configured to sequentially amplify the power and stabilize the current of a PWM waveform through a first power amplifier and a voltage-controlled constant current source, drive the LED light source to flash with a stable power and frequency, and modulate to generate a continuous light source; the LED light source includes two groups of LED array light sources, and the two groups of LED array light sources are symmetrically arranged on the front and rear panel covers 300.

[0033] Specifically, the light source modulation unit is responsible for receiving the PWM waveform with a specific frequency and duty cycle generated by the signal generator controlled by the master control unit, amplifying the power and stabilizing the current through the first power amplifier and the voltage-controlled constant current source, thereby driving the LED light source to modulate with a stable power and frequency, so as to generate a modulated continuous light as the light source for the photoacoustic reaction. The LED light source has two groups, which are symmetrically arranged on the front and rear sides of the photoacoustic cell body 100. The same PWM waveform generated is modulated synchronously to keep the modulation of the two groups of LED light sources the same, forming the cooperation of the LED array dual-channel modulation to solve the defect of insufficient power of a single LED lamp.

[0034] Reference Figure 4 , in some embodiments, the signal processing unit includes a photoacoustic signal sensor, a second power amplifier, a low-pass filter, and a lock-in amplifier connected in sequence, and the input end of the lock-in amplifier is also connected to a signal generator; The photoacoustic signal sensor is arranged at the top of the inner cavity, and the photoacoustic signal sensor is used to collect the vibration signal of the target gas in the inner cavity and convert it into an electrical signal; The second power amplifier is used to amplify the electrical signal to obtain an amplified electrical signal; The low-pass filter is used to filter the high-frequency noise in the amplified electrical signal and transmit the filtered low-frequency effective signal to the lock-in amplifier; the center frequency of the low-pass filter is a set frequency; The lock-in amplifier is used to use another PWM waveform as a reference signal, separate the signal with the set frequency in the low-frequency effective signal, amplify it and then convert it into a voltage signal and transmit it to the master control unit.

[0035] Specifically, a piezoelectric ceramic or other photoacoustic signal sensor is used to collect the signal of the device, and the signal is preliminarily amplified by the second power amplifier. A low-pass filter with a fixed center frequency is used to filter the high-frequency noise, and only the low-frequency effective signal is transmitted to the lock-in amplifier. The lock-in amplifier uses the PWM waveform generated by the signal generator as a reference signal to separate and amplify the photoacoustic signal with the same frequency. On the one hand, the signal intensity can be directly queried through the computer via USB or LAN. On the other hand, the separated photoacoustic signal is secondarily amplified and transmitted to the master control unit as a voltage signal for further processing.

[0036] In some embodiments, the air flow circulation unit includes a micro air pump and a solenoid valve respectively connected to the master control unit, and the micro air pump is connected to the tower joint of the photoacoustic cell unit through a hose.

[0037] Specifically, the air flow circulation unit includes a micro air pump and a solenoid valve. The micro air pump is connected to the tower joint of the photoacoustic cell unit through a hose. The master control unit controls the states of the air pump and the solenoid valve. Before each detection of the photoacoustic signal, the master control unit controls the air flow circulation, so as to ensure that the internal gas is always consistent with the external environment when obtaining detection data, and realize the intelligent linkage control of the air flow circulation and the detection timing.

[0038] The photoacoustic cell unit designed by the present invention adopts the resin 3D printing one-piece forming process. The inner cavity size is only 5mm * 20mm. It adopts a non-resonant micro-structure. The overall structure is simple. The non-resonant design greatly reduces the requirement standard for the light source. The stable output of the LED power is realized through the independently designed constant current source. The designed LED array dual-channel cooperative modulation scheme can use multiple LED lights in combination to further enhance the light power and the photoacoustic signal; the two-stage signal processing architecture of the first power amplifier and the lock-in amplifier, plus the same-source and same-frequency dual-channel PWM wave to control the light source modulation and the reference signal of the lock-in amplifier, further reduces the phase noise; the two-stage dynamic calibration algorithm solves the problem of signal distortion caused by hardware differences between different devices.

[0039] The cost of the light source modulation unit used in the present invention is greatly reduced, the volume is greatly reduced, it can be integrated and miniaturized, and the power consumption is also well controlled; and the data accuracy obtained by the present invention is sufficient to meet various requirements. The whole set of system is easy to use and maintain, can be deployed in most environments and remotely monitor the data results, has a complete set of control systems and human-computer interaction logics, is convenient to operate, and has a high degree of intelligence. It is convenient for large-scale deployment and promotion without being limited to a specific laboratory environment.

[0040] In some embodiments, generating the gas concentration of the target gas based on the voltage value includes: Converting the voltage value into the concentration value of the target gas through a pre-set concentration inversion algorithm, and calibrating the concentration value into the gas concentration of the target gas according to a pre-set relative calibration algorithm of the device.

[0041] Specifically, the master control unit is the core of the control logic of all components, controlling the generation of clock signals and the control signal generator to generate PWM waveform signals, thereby controlling the light source modulation unit and providing a reference signal for the lock-in amplifier. By designing the light source modulation signal and the reference signal of the lock-in amplifier in the same source, the phase noise is reduced. The voltage signal of the photoacoustic signal separated by the lock-in amplifier is collected by the ADC module of the master control unit and converted into a digital signal, and the voltage signal is converted into the concentration value of the target gas through a pre-set concentration inversion algorithm. The power supply of all electronic components and the start and stop of the air flow circulation unit are controlled according to the self-designed program.

[0042] In some embodiments, the conversion of the voltage value into the concentration value of the target gas through a pre-set concentration inversion algorithm includes: Obtain the voltage values corresponding to n different gas concentrations to obtain a set of data points, expressed as: , represents the nth voltage value, represents the gas concentration corresponding to the nth voltage value; Calculate the mean values of the voltage values and gas concentrations in this set of data points through the following formula: , represents the mean voltage, represents the mean gas concentration; Calculate the variance of the voltage values through the following formula , as well as the covariance of the voltage values and gas concentrations : ; Calculate the slope a and intercept b of the straight line of the linear relationship through the following formula: ; Establish a linear relationship formula between the concentration value y of the target gas and the voltage value x, that is ; Substitute the voltage value into the linear relationship formula to obtain the concentration value of the target gas.

[0043] Specifically, the specific process of the concentration inversion algorithm is as follows: The voltage value of the photoacoustic signal collected by the ADC of the master control unit is positively correlated with the concentration of the target gas. Therefore, we can establish the relationship between the concentration of the target gas and the voltage value under laboratory conditions, and the program automatically calculates according to the following method after the controller obtains the voltage value.

[0044] First, obtain the voltage value data corresponding to n different gas concentrations, expressed as: , x represents the voltage value, and y represents the gas concentration corresponding to this voltage value; Calculate the mean values of the x and y values in this set of data points and , that is: , Calculate the variance of the x values and the covariance of the x and y values , ; Calculate the slope a and the y-intercept b of the straight line of the linear relationship, ; Finally, obtain the linear relationship formula between the target gas concentration y and the voltage value x, that is .

[0045] In some embodiments, calibrating the concentration value to the gas concentration of the target gas according to the preset device relative calibration algorithm includes: Obtain the voltage values corresponding to two different gas concentrations, denoted as ; Calculate the gas concentration corresponding to the current voltage value according to the linear relationship formula, and obtain two gas concentrations , ; Solve for the slope A and intercept B of the relative error according to the formula: ; Where: ; The relationship formula after calibration is ; Substitute the concentration value of the target gas into the relationship formula to obtain the gas concentration value of the target gas.

[0046] Device calibration algorithm: Since there are certain differences between the same components of different devices, this results in fluctuations in the concentration of the target gas and the finally detected voltage value on different devices. At this time, each device needs to be calibrated separately before leaving the factory to eliminate the numerical error caused by the differences in device components. The relative calibration algorithm is designed as the following scheme: First, obtain the voltage values corresponding to the device under two different gas concentrations (preferably one high concentration and one low concentration), denoted as , where x represents the voltage value and y represents the gas concentration corresponding to this voltage value; Calculate the gas concentration by calculating the current voltage value according to the linear relationship formula obtained under the previous laboratory conditions, and obtain , ; According to the formula , solve for the slope A and intercept B of the relative error, that is , ; The relationship formula after calibration is , where Y is the gas concentration value calculated according to the experimental fitting curve. After the second conversion of the relationship formula, the errors on different devices are further corrected, thereby eliminating the errors between devices.

[0047] Refer to Figure 5 , in some embodiments, the system further includes a human-computer interaction unit, and the human-computer interaction unit is used to display the gas concentration.

[0048] The human-computer interaction unit feeds back the gas concentration to the user through the human-computer interaction unit and takes corresponding processing measures according to the user's preset settings.

[0049] Refer to Figure 6 , the present invention provides an intelligent photoacoustic trace gas detection method, and the method includes the following steps: S100, the master control unit controls the air flow circulation unit to start, pumps the target gas to be detected into the inner cavity of the photoacoustic cell unit, and makes the pressure in the inner cavity be one standard atmospheric pressure; S200, the master control unit controls the signal generator to generate a PWM waveform with a set frequency and duty cycle. The PWM waveform is divided into two paths. One path of the PWM waveform is modulated by the light source modulation unit and then drives the LED light source to generate a continuous light source, exciting the target gas in the inner cavity to generate periodic pressure disturbances. The signal processing unit converts the detected vibration signal into an electrical signal, and uses the other path of the PWM waveform as a reference signal, separates the signal with the set frequency from the electrical signal, amplifies it and then converts it into a voltage signal and inputs it into the master control unit; S300, the master control unit converts the voltage signal into a voltage value and generates the gas concentration of the target gas based on the voltage value.

[0050] Specifically, the master control unit is designed and implemented based on STM32F407ZGT6. Taking the detection of the concentration of acetone in the target gas as an example, first, the program controls the start of the air flow circulation unit. The micro air pump runs and the solenoid valve opens, and the target gas is sucked into the inner cavity by the air pump. At this time, the inner cavity is at one atmosphere, and the solenoid valve is closed. The program of the master control unit controls the generation of a PWM waveform with a frequency of 10Hz and a duty cycle of 50%. The PWM waveform is divided into two paths. One path controls the flashing of the front and rear dual-channel LED array light sources through a power amplifier and a voltage-controlled constant current source. The LED array light source is a dual 4-light array light source with a luminous center wavelength of 275nm and a light power of about 100mw. The front and rear dual-group LED array light sources emit light in a coordinated and synchronous manner for modulation. The modulated continuous light source excites the target gas in the inner cavity to generate periodic air pressure disturbances, which are transmitted to the photoacoustic signal sensor installed at the top of the inner cavity through gas vibration. The photoacoustic signal sensor converts the detected vibration signal into an electrical signal, which is amplified by a second power amplifier of model AD620 and the high-frequency noise is filtered by a low-pass filter with a center frequency of 10Hz. The obtained low-frequency effective signal is transmitted into a lock-in amplifier. The second PWM waveform with the same frequency and the same source generated by the master control unit is used as the reference signal of the lock-in amplifier to separate the 10Hz acoustic signal, which is amplified twice and then transmitted to the ADC module of the master control unit. The chip of the master control unit collects and converts the electrical signal into a digital signal, and automatically calculates the obtained digital signal into the gas concentration according to the designed concentration inversion algorithm and the program of the device relative calibration algorithm. On the one hand, the master control unit displays the gas concentration result on the LCD screen through the SPI communication protocol for the user to view. On the other hand, the data can also be wirelessly transmitted to the terminal upper computer through Bluetooth or Wi-Fi protocols to realize remote monitoring and control by the user. And according to the pre-set operation logic, if the detected gas concentration is too high, other devices can be automatically controlled to react, such as turning on the ventilation fan and triggering the alarm device, etc.

[0051] It can be seen that the content in the above system embodiment is applicable to the method embodiment. The functions specifically implemented in the method embodiment are the same as those in the above system embodiment, and the beneficial effects achieved are also the same as those achieved in the above system embodiment.

[0052] The above is a specific description of the preferred embodiment of the present disclosure, but the present disclosure is not limited to the above implementation manner. Those skilled in the art can also make various equivalent deformations or substitutions without departing from the spirit of the present disclosure, and these equivalent deformations or substitutions are all included in the scope defined by the claims of the present disclosure.

Claims

1. A photoacoustic trace gas intelligent detection system, characterized in that: The system comprises: a photoacoustic cell unit, a light source modulation unit, a signal processing unit, an airflow circulation unit, a master control unit and a signal generator; The master control unit is used to control the start of the gas flow circulation unit to pump the target gas to be detected into the inner cavity of the photoacoustic cell unit so that the pressure of the inner cavity is a standard atmospheric pressure; and is used to control the signal generator to generate a PWM waveform with a set frequency and duty cycle, the PWM waveform is divided into two paths, and is used to convert the voltage signal sent by the signal processing unit into a voltage value, and generate the gas concentration of the target gas based on the voltage value; The light source modulation unit is used to modulate a PWM waveform to drive the LED light source to generate a continuous light source, and to stimulate the target gas in the inner cavity to generate periodic pressure disturbances; The signal processing unit is used to convert the detected vibration signal into an electrical signal, and use another PWM waveform as a reference signal to separate the signal of the set frequency from the electrical signal and convert it into a voltage signal after amplification to transmit it to the main control unit.

2. The system according to claim 1, characterized in that The photoacoustic cell unit comprises a photoacoustic cell body, pagoda joints arranged on the left and right sides of the photoacoustic cell body, and panel covers arranged on the front and rear sides of the photoacoustic cell body; A through hole connecting the front and the back is opened in the middle of the photoacoustic cell body and the front and rear side panel covers, and ultraviolet quartz glass sheets are arranged on the front and rear sides of the through hole, and rubber rings are used to seal the two ends of the through hole; An inner cavity is vertically opened on the top of the photoacoustic cell body.

3. The system according to claim 1, characterized in that The light source modulation unit includes a first power amplifier and a voltage-controlled constant current source; The light source modulation unit is specifically used to perform power amplification and current stabilization on a PWM waveform through a first power amplifier and a voltage-controlled constant current source in sequence, driving the LED light source to flash at a stable power and frequency, so as to modulate and generate a continuous light source; the LED light source includes two groups of LED array light sources, and the two groups of LED array light sources are symmetrically placed on the panel covers on the front and rear sides.

4. The system according to claim 1, characterized in that The signal processing unit comprises a photoacoustic signal sensor, a second power amplifier, a low-pass filter and a lock-in amplifier which are connected in sequence, and the input end of the lock-in amplifier is also connected to a signal generator; The photoacoustic signal sensor is arranged at the top of the inner cavity, and the photoacoustic signal sensor is used to collect the vibration signal of the target gas in the inner cavity and convert it into an electrical signal; The second power amplifier is used to amplify the electrical signal to obtain an amplified electrical signal; The low-pass filter is used to filter the high-frequency noise in the amplified electrical signal and transmit the filtered low-frequency effective signal to the phase-locked amplifier; the center frequency of the low-pass filter is the set frequency; The lock-in amplifier is used to use another PWM waveform as a reference signal, separate the signal of the set frequency from the low-frequency effective signal, amplify it, and convert it into a voltage signal to be transmitted to the main control unit.

5. The system according to claim 1, characterized in that The airflow circulation unit comprises a micro air pump and a solenoid valve respectively connected to the master control unit, and the micro air pump is connected to the pagoda connector of the photoacoustic cell unit through a hose.

6. The system according to claim 1, characterized in that The step of generating the gas concentration of the target gas based on the voltage value includes: The voltage value is converted into the concentration value of the target gas by a preset concentration inversion algorithm, and the concentration value is calibrated to the gas concentration of the target gas according to a preset device relative calibration algorithm.

7. The system according to claim 6, characterized in that The method of converting the voltage value into the concentration value of the target gas by using a preset concentration inversion algorithm includes: Obtain the voltage values ​​corresponding to n different gas concentrations and obtain a set of data points, expressed as: , represents the nth voltage value, Indicates the gas concentration corresponding to the nth voltage value; The mean of the voltage value and gas concentration in this group of data points is calculated by the following formula: , represents the mean voltage, Indicates the mean gas concentration; The variance of the voltage value is calculated by the following formula , and the covariance of voltage and gas concentration : ； The slope a and intercept b of the linear relationship line are calculated using the following formula: ； Establish a linear relationship between the concentration value y of the target gas and the voltage value x, that is, ; Substitute the voltage value into the linear relationship to obtain the concentration value of the target gas.

8. The system according to claim 7, characterized in that The step of calibrating the concentration value to the gas concentration of the target gas according to a preset relative calibration algorithm of the device includes: Get the voltage values ​​corresponding to two different gas concentrations, recorded as ; Calculate the gas concentration corresponding to the current voltage value according to the linear relationship and get two gas concentrations: , ; Solve the slope A and intercept B of the relative error according to the formula: ； in: ； The relationship formula after calibration is ; Substitute the concentration value of the target gas into the relationship formula to obtain the gas concentration value of the target gas.

9. The system according to claim 1, characterized in that The system also includes a human-computer interaction unit, which is used to display the gas concentration.

10. A photoacoustic trace gas intelligent detection method, characterized in that: The method comprises the following steps: The main control unit controls the airflow circulation unit to start, pumping the target gas to be detected into the inner cavity of the photoacoustic cell unit so that the pressure of the inner cavity is a standard atmospheric pressure; The master control unit controls the signal generator to generate a PWM waveform with a set frequency and duty cycle. The PWM waveform is divided into two paths. One PWM waveform is modulated by the light source modulation unit to drive the LED light source to generate a continuous light source, which excites the target gas in the inner cavity to generate periodic air pressure disturbances. The signal processing unit converts the detected vibration signal into an electrical signal, and uses the other PWM waveform as a reference signal to separate the signal of the set frequency from the electrical signal, amplify it, and convert it into a voltage signal to be transmitted to the master control unit. The main control unit converts the voltage signal into a voltage value, and generates a gas concentration of the target gas based on the voltage value.

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