A gas concentration detection device and method based on photoacoustic cell

Abstract

The present invention provides a gas concentration detection device and method based on a photoacoustic cell, comprising: a detection module, a sound source driving module and a data acquisition and processing module; the detection module comprises a resonant photoacoustic cell, an acoustic wave signal generating mechanism, an acoustic wave signal collecting mechanism, an air inlet and an air outlet are arranged on the inner wall of the resonant photoacoustic cell, the air inlet is connected to an air inlet pipeline, the air outlet is connected to an air outlet pipeline, the sound source driving module comprises a function generator and an acoustic wave generating driver, when the resonant photoacoustic cell is passed into the gas to be measured, the data acquisition and processing module generates an acoustic wave-frequency response curve based on the collected acoustic wave signal and the frequency signal output by the function generator, determines the resonant frequency, and calculates the concentration of the gas to be measured according to the functional relationship between the resonant frequency and the gas concentration. The present invention solves the problems of low efficiency and high cost when detecting gas concentration based on traditional photoacoustic spectroscopy technology.

Description

Technical Field

[0001] The present invention relates to the technical field of gas detection, and in particular to a gas concentration detection device and method based on a photoacoustic cell. Background Art

[0002] As science and technology continue to develop and advance in today's world, various toxic gases are also emitted. These problems have seriously troubled people's normal lives. Therefore, high-precision gas concentration detection technology has an increasingly important position in various fields. For example, in the field of atmospheric science and environmental monitoring, the increasing emissions of greenhouse gases have seriously damaged the current ecological environment. Therefore, it is necessary to monitor the concentration of trace gases in the atmosphere in real time to prevent further deterioration. For coal chemical companies, the demand for high-precision detection of gas concentration is even more obvious. By detecting the concentration of toxic gases generated in the production process, it is controlled to meet national safety emission standards. High-sensitivity gas concentration detection technology has been widely used in different fields such as industrial process control, medical diagnosis, atmospheric science and environmental monitoring.

[0003] There are many gas concentration detection methods on the market, including electrochemical sensing, Fourier infrared spectroscopy, chemiluminescence, etc. However, these methods cannot detect in real time and need frequent calibration. Compared with these gas concentration detection methods, the most widely used is the trace gas detection technology based on laser spectroscopy, which has the characteristics of high sensitivity, high selectivity, and fast response time. As a kind of laser spectroscopy technology, photoacoustic spectroscopy detects gas concentration by detecting the acoustic wave signal generated by the gas based on the photoacoustic effect. Its measurement principle is: first measure the resonance frequency of the photoacoustic cell, then adjust the modulation frequency of the laser and the demodulation frequency of the phase-locked amplifier to be strictly consistent with the resonance frequency, then the laser emits laser into the photoacoustic cell, and the laser interacts with the gas to be measured to generate a photoacoustic signal with a frequency equal to the laser modulation frequency, and then an acoustic-electric transducer is used to collect the acoustic wave signal in the photoacoustic cell, and finally the concentration of the gas in the photoacoustic cell is calculated by constructing a curve of the laser wavelength and the intensity of the acoustic wave signal. There is a major technical problem in traditional photoacoustic spectroscopy that limits its promotion and application: in traditional photoacoustic spectroscopy, when the composition or concentration of the gas in the photoacoustic cell changes, the resonant frequency of the photoacoustic cell will change accordingly. If the modulation frequency of the laser and the demodulation frequency of the phase-locked amplifier are not revised in time, the measurement results of the sensor based on this technology will be distorted, thereby causing the sensor to fail. Therefore, for traditional photoacoustic spectroscopy, it is necessary to calibrate the resonant frequency of the photoacoustic cell in real time, and it is necessary to repeatedly calibrate the modulation frequency of the laser and the demodulation frequency of the phase-locked amplifier based on the real-time resonant frequency of the photoacoustic cell obtained by calibration. The above calibration and adjustment process makes the gas concentration detection process of traditional photoacoustic spectroscopy complicated and cumbersome, affecting the efficiency of gas concentration detection. In addition, traditional photoacoustic spectroscopy faces the problem of needing to select a suitable laser according to the target gas to be detected, and the cost of the laser usually accounts for more than 50% of the total cost, which makes the cost of gas concentration detection high, limiting the application and development of traditional photoacoustic spectroscopy in the field of high-sensitivity detection of gas concentration. In order to solve the above scientific and technological problems, the present invention provides a real-time gas concentration detection device and method based on a photoacoustic cell and without a laser. Summary of the invention

[0004] The purpose of the present invention is to provide a gas concentration detection device and method based on a photoacoustic cell, so as to solve the problems of low efficiency and high cost when detecting gas concentration based on traditional photoacoustic spectroscopy technology.

[0005] To achieve the above object, the present invention provides the following solutions:

[0006] A gas concentration detection device based on a photoacoustic cell, comprising:

[0007] Detection module, sound source driving module and data acquisition and processing module.

[0008] The detection module includes a resonant photoacoustic cell; an acoustic wave signal generating mechanism and an acoustic wave signal collecting mechanism are arranged on the inner cavity wall of the resonant photoacoustic cell; the resonant photoacoustic cell is also provided with an air inlet and an air outlet; the air inlet is connected to an air inlet pipeline, and the air outlet is connected to an air outlet pipeline.

[0009] The sound source driving module includes a function generator and a sound wave generating driver.

[0010] The signal input end of the function generator is connected to the data acquisition and processing module; the signal output end of the function generator is connected to the signal input end of the sound wave generating driver, and the signal output end of the sound wave generating driver is connected to the signal input end of the sound wave signal generating mechanism; the signal output end of the sound wave signal collecting mechanism is connected to the signal input end of the data acquisition and processing module.

[0011] The data acquisition and processing module is used to determine the resonance frequency based on the sound wave signal collected and the sound wave-frequency response curve generated by the frequency signal output by the function generator after the gas to be measured is introduced into the resonant photoacoustic cell, and calculate the concentration of the gas to be measured according to the resonance frequency.

[0012] Optionally, the air inlet pipeline is provided with a first needle valve, an air circuit pressure indicator and an air circuit flow indicator; the air outlet pipeline is provided with a second needle valve; the first needle valve and the second needle valve are used to adjust the pressure and flow of the gas in the gas pipeline.

[0013] Optionally, a vacuum diaphragm pump is also provided on the air outlet pipeline.

[0014] Optionally, the data acquisition and processing module includes a preamplifier, a phase-locked amplifier and a controller; the signal input end of the preamplifier is connected to the signal output end of the acoustic signal collection mechanism, the signal output end of the preamplifier is connected to the signal input end of the phase-locked amplifier, the signal output end of the phase-locked amplifier is connected to the signal input end of the controller, and the signal output end of the controller is connected to the signal input end of the function generator; the synchronization signal input end of the phase-locked amplifier is connected to the synchronization signal output end of the function generator.

[0015] The preamplifier is used to amplify the sound wave signal output by the sound wave signal collecting mechanism.

[0016] The phase-locked amplifier is used to demodulate the amplified sound wave signal output by the preamplifier.

[0017] Optionally, the acoustic wave signal generating mechanism is arranged on a cavity wall corresponding to a center position of an inner cavity of the resonant photoacoustic cell.

[0018] Optionally, the acoustic wave signal generating mechanism and the acoustic wave signal collecting mechanism are respectively arranged on the cavity wall corresponding to the center position of the inner cavity of the resonant photoacoustic cell.

[0019] Optionally, the acoustic wave signal collecting mechanism and the acoustic wave signal generating mechanism are symmetrical along the axis of the resonant photoacoustic cell.

[0020] Optionally, the resonant photoacoustic cell comprises a first-order longitudinal mode resonant photoacoustic cell.

[0021] The first-order longitudinal mode resonant photoacoustic cell comprises a first buffer chamber, a second buffer chamber, an acoustic resonance cavity, the acoustic wave signal generating mechanism, and the acoustic wave signal receiving mechanism.

[0022] The first buffer chamber and the second buffer chamber are arranged on both sides of the acoustic resonance cavity and are communicated with the acoustic resonance cavity; the first buffer chamber is provided with the air inlet; and the second buffer chamber is provided with the air outlet.

[0023] The sound wave signal generating mechanism and the sound wave signal receiving mechanism are respectively arranged on the inner cavity wall corresponding to the center position of the acoustic resonance cavity, and the sound wave signal generating mechanism and the sound wave signal collecting mechanism are symmetrical along the axis of the resonant photoacoustic cell.

[0024] The present invention also provides a gas concentration detection method based on a gas concentration detection device of a photoacoustic cell, comprising:

[0025] The gas to be tested is introduced into the resonant photoacoustic cell, and the pressure and flow rate of the gas in the resonant photoacoustic cell are adjusted by using a first needle valve on the air inlet pipeline and a second needle valve on the air outlet pipeline until they remain stable.

[0026] The control function generator outputs square waves of different frequencies to drive the sound wave signal generating mechanism to generate sound wave signals of different frequencies.

[0027] The acoustic wave signal collecting mechanism is controlled to collect the acoustic wave signal in the resonant photoacoustic cell and convert the acoustic wave signal into an electrical signal.

[0028] The acoustic wave electric signal-frequency curve is drawn according to the acoustic wave electric signal and the frequency output by the function generator; the resonance frequency of the resonant photoacoustic cell is obtained according to the acoustic wave electric signal-frequency curve and the concentration of the gas to be measured is calculated according to the resonance frequency.

[0029] Optionally, drawing a sound wave electric signal-frequency curve diagram according to the sound wave electric signal and the frequency output by the function generator specifically includes:

[0030] Set the sweep frequency range and sweep step.

[0031] The acoustic wave electrical signal within the scanning frequency range is scanned based on the scanning step and the acoustic wave electrical signal-frequency curve graph is generated.

[0032] Determine whether the curve change trend in the acoustic wave electrical signal-frequency curve diagram is continuously rising or continuously falling.

[0033] If so, the scanning frequency range is increased, and the acoustic wave electrical signal output by the acoustic wave signal collecting mechanism is re-scanned.

[0034] If not, the current acoustic wave electrical signal-frequency curve diagram is output.

[0035] According to the specific embodiments provided by the present invention, the following technical effects are disclosed:

[0036] The present invention provides a gas concentration detection device and method based on a photoacoustic cell, comprising: a detection module, a sound source driving module and a data acquisition and processing module; the detection module comprises a resonant photoacoustic cell, an acoustic wave signal generating mechanism, an acoustic wave signal collecting mechanism, an air inlet and an air outlet are arranged on the inner cavity wall of the resonant photoacoustic cell, the air inlet is connected to an air inlet pipeline, the air outlet is connected to an air outlet pipeline, and the sound source driving module comprises a function generator and an acoustic wave generating driver; when the resonant photoacoustic cell is passed into the gas to be measured, the data acquisition and processing module generates an acoustic wave-frequency response curve based on the collected acoustic wave signal and the frequency signal output by the function generator, determines the resonant frequency, and calculates the concentration of the gas to be measured according to the resonant frequency. The present invention obtains a frequency-acoustic wave signal curve diagram under different acoustic wave frequencies by arranging an acoustic wave signal generating mechanism and an acoustic wave signal collecting mechanism on the inner cavity wall of the resonant photoacoustic cell, and can accurately determine the resonant frequency of the photoacoustic cell based on the curve diagram, and then accurately determine the gas concentration in the photoacoustic cell according to the functional relationship between the resonant frequency and the gas concentration. During the gas concentration detection process, the gas concentration is determined only based on the functional relationship between the resonance frequency and the gas concentration. There is no need for frequent real-time calibration of the resonance frequency and frequent real-time calibration of the laser modulation frequency and the phase-locked amplifier demodulation frequency in traditional photoacoustic spectroscopy technology, which greatly improves the efficiency of gas concentration detection. At the same time, since there is no need to use a laser, the cost of gas concentration detection is reduced, and the stability of the device during long-term operation is greatly improved. BRIEF DESCRIPTION OF THE DRAWINGS

[0037] In order to more clearly illustrate the embodiments of the present invention or the technical solutions in the prior art, the drawings required for use in the embodiments will be briefly introduced below. Obviously, the drawings described below are only some embodiments of the present invention. For ordinary technicians in this field, other drawings can be obtained based on these drawings without paying creative work.

[0038] Figure 1A schematic diagram of the structure of a gas concentration detection device based on a first-order longitudinal mode resonant photoacoustic cell provided in Example 1 of the present invention;

[0039] Figure 2 Schematic diagram of a photoacoustic cell with three resonance modes provided in Example 1 of the present invention;

[0040] Figure 3 The output frequency response curve diagram provided by Example 2 of the present invention;

[0041] Figure 4 This is a comparison chart of the experimental measurement results and the formula calculation results provided in Example 2 of the present invention.

[0042] Reference numerals:

[0043] 1-detection module, 111-first needle valve, 112-gas pressure display meter, 113-gas flow display meter, 114-second needle valve, 115-vacuum diaphragm pump, 121-air inlet, 122-air outlet, 123-first buffer chamber, 124-second buffer chamber, 125-acoustic resonance cavity, 126-acoustic signal collection mechanism, 127-acoustic signal generating mechanism, 2-function generator, 3-acoustic wave generating driver, 4-data acquisition and processing module, 41-preamplifier, 42-phase-locked amplifier, 43-controller. DETAILED DESCRIPTION

[0044] The following will be combined with the drawings in the embodiments of the present invention to clearly and completely describe the technical solutions in the embodiments of the present invention. Obviously, the described embodiments are only part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without creative work are within the scope of protection of the present invention.

[0045] The purpose of the present invention is to provide a gas concentration detection device and method based on a photoacoustic cell, by arranging an acoustic signal generating mechanism and an acoustic signal collecting mechanism on the inner wall of the resonant photoacoustic cell, so as to obtain a frequency-acoustic signal curve diagram under different acoustic frequencies, accurately determine the resonant frequency of the photoacoustic cell based on the curve diagram, and then accurately determine the gas concentration in the photoacoustic cell according to the functional relationship between the resonant frequency and the gas concentration. During the gas concentration detection process, the gas concentration is determined only according to the functional relationship between the resonant frequency and the gas concentration, without the need for frequent real-time calibration of the resonant frequency in traditional photoacoustic spectroscopy technology and frequent real-time calibration of the laser modulation frequency and the phase-locked amplifier demodulation frequency, which greatly improves the efficiency of gas concentration detection. At the same time, since no laser is needed, the stability of the device for long-term operation is greatly improved, and the cost required for gas concentration detection is also greatly reduced.

[0046] In order to make the above-mentioned objects, features and advantages of the present invention more obvious and easy to understand, the present invention is further described in detail below with reference to the accompanying drawings and specific embodiments.

[0047] Example 1

[0048] This embodiment provides a gas concentration detection device based on a photoacoustic cell, see Figure 1 , including: a detection module 1, a sound source driving module and a data acquisition and processing module 4.

[0049] The detection module 1 includes a resonant photoacoustic cell; an acoustic signal generating mechanism 127 and an acoustic signal collecting mechanism 126 are provided on the inner wall of the resonant photoacoustic cell. The acoustic signal collecting mechanism 126 is used to collect the acoustic signal output by the acoustic signal generating mechanism 127 and convert it into an electrical signal. The acoustic signal generating mechanism 127 has no positional limitation in the resonant photoacoustic cell, such as Figure 2 The photoacoustic cell structures in three resonance modes are shown respectively.

[0050] exist Figure 2 In the figure, the acoustic wave signal generating mechanism 127 and the acoustic wave signal collecting mechanism 126 can be set at the position of the black solid frame, or at the position corresponding to the dotted frame according to the needs. The acoustic wave signal generating mechanism 127 and the acoustic wave signal collecting mechanism 126 can be adjusted arbitrarily according to actual needs, and no limitation is made here. It should be noted that each resonant photoacoustic cell only includes one acoustic wave signal collecting mechanism 126 and one acoustic wave signal generating mechanism 127.

[0051] Since the sound wave in the resonant cavity is strongest at the center of the resonant cavity, the sound wave signal collection mechanism 126 in the resonant photoacoustic pool can be set on the cavity wall corresponding to the center of the acoustic resonant cavity, so that the sound wave signal in the resonant cavity can be fully collected, and the corresponding sound wave signal generation mechanism 127 can also be set on the cavity wall corresponding to the center of the acoustic resonant cavity. More specifically, the sound wave signal generation mechanism 127 and the sound wave signal collection mechanism 126 can also be set to be symmetrical along the axis of the resonant photoacoustic pool.

[0052] The acoustic signal generating mechanism 127 may be a buzzer, and the acoustic signal collecting mechanism 126 may be a microphone, which may be a condenser microphone. The specific structures of the acoustic signal generating mechanism 127 and the acoustic signal collecting mechanism 126 may be determined according to actual needs, and the buzzer and the microphone are only used as examples and do not have any limiting effect.

[0053] The resonant photoacoustic cell is also provided with an air inlet 121 and an air outlet 122; the air inlet 121 is connected to the air inlet pipeline, and the air outlet 122 is connected to the air outlet pipeline. In order to facilitate the adjustment of the gas flow and pressure during air inlet and air outlet, and to intuitively obtain the gas flow value and gas pressure value, a first needle valve 111, a gas circuit pressure display meter 112 and a gas circuit flow display meter 113 can be provided on the air inlet pipeline; a second needle valve 114 is provided on the air outlet pipeline. By adjusting the first needle valve 111 and the second needle valve 114, the pressure and flow of the gas in the gas pipeline can be adjusted to keep the pressure and flow in the gas pipeline stable. A vacuum diaphragm pump 115 can also be provided on the air outlet pipeline to evacuate the gas in the photoacoustic cell.

[0054] The resonant photoacoustic cell in this embodiment includes three resonance modes: angular, radial, and longitudinal. Figure 2 In the figure, (a) is the angular mode resonant photoacoustic cell; (b) is the longitudinal mode resonant photoacoustic cell; (c) is the radial mode resonant photoacoustic cell.

[0055] The sound source driving module includes a function generator 2 and a sound wave generating driver 3. When the sound wave signal generating mechanism 127 is selected as a buzzer, the sound wave generating driver 3 can be selected as a buzzer driver.

[0056] The signal input end of the function generator is connected to the data acquisition and processing module 4; the signal output end of the function generator 2 is connected to the signal input end of the sound wave generating driver 3, and the signal output end of the sound wave generating driver 3 is connected to the signal input end of the sound wave signal generating mechanism 127; the signal output end of the sound wave signal collecting mechanism 126 is connected to the signal input end of the data acquisition and processing module 4.

[0057] The data acquisition and processing module 4 includes a preamplifier 41, a phase-locked amplifier 42 and a controller 43; the data acquisition and processing module 4 is used to determine the resonance frequency based on the sound wave signal collected and the sound wave-frequency response curve generated by the frequency signal output by the function generator 2 after the gas to be measured is passed into the resonant photoacoustic cell, and calculate the concentration of the gas to be measured based on the resonance frequency.

[0058] The preamplifier 41 is used to amplify the acoustic signal output by the acoustic signal collecting mechanism 126. The amplification factor can be set by setting a suitable transimpedance preamplifier, which is usually set at 10 6 -10 8 The signal input end of the preamplifier 41 is connected to the signal output end of the acoustic signal collecting mechanism 126 , and the signal output end of the preamplifier 41 is connected to the signal input end of the phase-locked amplifier 42 .

[0059] The phase-locked amplifier 42 is used to demodulate the amplified sound wave signal output by the preamplifier 41. The signal output end of the phase-locked amplifier 42 is connected to the signal input end of the controller 43, and the signal output end of the controller 43 is connected to the signal input end of the function generator 2; the synchronization signal input end of the phase-locked amplifier 42 is connected to the synchronization signal output end of the function generator 2, and the connection between the synchronization signal end of the phase-locked amplifier 42 and the function generator 2 can ensure that the demodulation frequency of the phase-locked amplifier is consistent with the output frequency of the function generator, which is convenient for the subsequent generation of the sound wave signal-frequency curve.

[0060] The controller 43 may be a computer. If it is a computer, LabView software may be installed in the computer. The computer is connected to the function generator via a serial port line, and the frequency of the square wave signal at the output end of the function generator may be controlled by the LabView software in the computer.

[0061] The resonant photoacoustic cell may specifically be a first-order longitudinal mode resonant photoacoustic cell.

[0062] The structure of the first-order longitudinal mode resonant photoacoustic cell may include a first buffer chamber 123 , a second buffer chamber 124 , an acoustic resonance cavity 125 , an acoustic wave signal generating mechanism 127 and an acoustic wave signal collecting mechanism 126 .

[0063] The first buffer chamber 123 and the second buffer chamber 124 are disposed on both sides of the acoustic resonance cavity 125 and communicated with the acoustic resonance cavity 125 ; the first buffer chamber 123 and the second buffer chamber 124 can reduce airflow noise.

[0064] The first buffer chamber 123 is provided with an air inlet 121 , and the second buffer chamber 124 is provided with an air outlet 122 .

[0065] In a first-order longitudinal mode resonant photoacoustic pool, it can be required that the acoustic wave signal generating mechanism 127 and the acoustic wave signal receiving mechanism 126 are respectively arranged on the inner cavity wall corresponding to the center position of the acoustic resonance cavity 125, and the acoustic wave signal generating mechanism 127 and the acoustic wave signal collecting mechanism 126 are symmetrical along the axis of the resonant photoacoustic pool 125.

[0066] The detection device based on this embodiment realizes the principle of gas concentration detection: sound waves form standing waves in the acoustic resonance cavity of the resonant photoacoustic cell, the microphone collects the sound wave signal and converts it into an electrical signal, which is amplified by the preamplifier and transmitted to the phase-locked amplifier, which demodulates the signal and transmits it to the computer for processing to obtain the frequency of the resonant photoacoustic cell. When the sound wave frequency is the same as the acoustic resonance cavity frequency, resonance is formed, and the sound wave signal is the largest at this time. Therefore, sound waves of different frequencies are output through the buzzer to obtain a curve graph of the sound wave signal-frequency. When the signal amplitude in the curve graph obtained in the gas detection device of the present invention is the highest, the corresponding sound wave frequency is the resonant frequency of the resonant photoacoustic cell.

[0067] The speed of sound propagates at different speeds in different media. When the average molar mass of the mixed gas changes, the speed of sound will change accordingly, resulting in a change in the sound wave signal. The average molar mass of mixed gases of different concentrations is different, and the sound wave signal measured by the gas detection device of the present invention will also change accordingly, and the highest point of the signal amplitude in the curve graph will also change accordingly. According to the present invention, the gas detection device can detect the changing resonance frequency, and the concentration information of the gas to be tested with the concentration change can be inverted based on the changing resonance frequency.

[0068] In this embodiment, an acoustic wave signal generating mechanism and an acoustic wave signal collecting mechanism are arranged in the photoacoustic cell, and the following effects can be achieved: 1) no expensive laser devices and photoelectric detection devices with complicated operation steps are required, and compared with the laser absorption spectrum with a high degree of commercialization, the cost and operation simplicity of related equipment are greatly reduced; 2) compared with the traditional photoacoustic spectroscopy technology using the photoacoustic cell, there is no need to consider the frequency drift of the resonant photoacoustic cell (the resonant frequency changes with the change of the concentration and composition of the gas filled in the photoacoustic cell), and the steps of frequent calibration of the electrical parameters of the photoacoustic cell during the gas measurement process are avoided, and the error caused by calibration is avoided, so that the measurement results are more accurate and the measurement efficiency is high. 3) Compared with the traditional photoacoustic spectroscopy technology in the prior art, there is no need for optical collimation, thereby avoiding the restrictions of the reserved optical path and the light-through window in the photoacoustic cell structure design and preparation link, simplifying the structure of the detection device, providing convenience for the preparation of a compact small-volume photoacoustic cell, and saving the cost of the detection device. 4) A method of controlling the sound wave generating mechanism to emit sound wave signals of different frequencies through a function generator, and scanning the sound wave signal through a preset frequency scanning range to generate a sound wave signal-frequency curve graph, and regarding the sound wave frequency corresponding to the maximum amplitude of the sound wave signal in the curve graph as the resonant frequency. When the gas composition and concentration in the photoacoustic cell change, the highest point of the signal amplitude in the sound wave signal-frequency curve graph will also change accordingly. Therefore, the resonant frequency of the resonant photoacoustic cell obtained in this embodiment will change with the change of gas composition and concentration. The gas concentration detection device of this embodiment can be applied to the efficient detection of gases of different combinations and concentrations, and has broad application prospects.

[0069] Example 2

[0070] This embodiment provides a gas concentration detection method of a gas detection device based on a photoacoustic cell, comprising:

[0071] S1: The gas to be tested is introduced into the resonant photoacoustic cell, and the pressure and flow rate of the gas in the resonant photoacoustic cell are adjusted by using the first needle valve 111 on the air inlet pipeline and the second needle valve 114 on the air outlet pipeline until they remain stable.

[0072] S2: The controller 43 controls the function generator 2 to output square waves of different frequencies to drive the sound wave signal generating mechanism 127 to generate sound wave signals of different frequencies.

[0073] S3: Control the acoustic wave signal collecting mechanism 126 to collect the acoustic wave signals in the resonant photoacoustic cell and convert the acoustic wave signals into electrical signals.

[0074] S4: Draw an acoustic wave electric signal-frequency curve according to the acoustic wave electric signal and the frequency output by the function generator 2; obtain the resonant frequency of the resonant photoacoustic cell according to the acoustic wave electric signal-frequency curve and calculate the concentration of the gas to be measured according to the resonant frequency.

[0075] In step S4, a sound wave electric signal-frequency curve is drawn according to the sound wave electric signal and the frequency output by the function generator 2, specifically including:

[0076] Set the sweep frequency range and sweep step.

[0077] The acoustic wave electric signal within the scanning frequency range is scanned based on the scanning step and an acoustic wave electric signal-frequency curve diagram is generated.

[0078] Determine whether the curve change trend in the acoustic wave electrical signal-frequency curve diagram is continuously rising or continuously falling.

[0079] If so, the scanning frequency range is increased, and the acoustic wave electrical signal output by the acoustic wave signal collecting mechanism is scanned again.

[0080] If not, the current sound wave electrical signal-frequency curve diagram is output.

[0081] In order to facilitate those skilled in the art to understand the solution of this embodiment, Figure 1 The specific device structure describes the specific practical operation steps of the test:

[0082] 1) According to Figure 1 The device structure shown in the figure is to connect the detection device, turn on the vacuum diaphragm pump 115, and allow N2 to continuously flow into the resonant photoacoustic cell; manually adjust the first needle valve 111 and the second needle valve 114 to keep the pressure and flow rate of the gas path of the resonant photoacoustic cell stable;

[0083] 2) setting the parameters of the function generator 2, connecting the output end of the function generator 2 to the sound wave generating driver 3, and driving the sound wave signal generating mechanism 127 to generate sound waves;

[0084] 3) Open the LabView program in the controller 43 and set the frequency scanning range and scanning step.

[0085] The frequency scanning range can be determined by estimating a resonance frequency value according to the parameters of the resonance photoacoustic cell used before the experiment, and setting a suitable frequency scanning range according to the resonance frequency estimate value.

[0086] 4) The collected sound wave signal is converted into an electrical signal and output to the preamplifier 41, and the preamplifier 41 amplifies the signal by 10 6 After being multiplied, it is output to the lock-in amplifier 42;

[0087] 5) The lock-in amplifier 42 demodulates the received electrical signal and transmits it to the controller 43. In the LabView program in the controller 43, the demodulated signal is displayed on the LabView frequency response curve;

[0088] 6) According to the frequency response curve obtained in step 5), the frequency scanning range and scanning step in step 3) are adjusted, and steps 3) to 5) are repeated to obtain a frequency response curve diagram that can reflect the resonant frequency, that is, a relationship diagram between the acoustic wave signal and the frequency, such as Figure 3 As shown, Figure 3 This is the frequency response curve of the resonant photoacoustic cell under pure N2.

[0089] Wherein, adjusting the frequency scanning range may be to increase the frequency scanning range, such as Figure 3 As shown, if the frequency scanning range set in step 5) is set to 1750Hz-1800Hz, the desired resonant frequency does not exist in the frequency scanning curve, then it is necessary to increase the frequency scanning range to reacquire the sound wave signal until a frequency response curve that can reflect the resonant frequency is obtained. When there are obvious rising and falling curves in the frequency response curve obtained based on the adjusted frequency scanning range, the highest point in the complete frequency response curve can be obtained, and the frequency corresponding to the highest point is the resonant frequency of the resonant photoacoustic cell.

[0090] 7) The frequency corresponding to the strongest acoustic wave signal is the resonant frequency f of the resonant photoacoustic cell. jmq , the target gas concentration is calculated by the following formula.

[0091]

[0092] Where jmq is the number of vibration modes in the angular, longitudinal and radial directions, κ is the adiabatic index, R0 is the molar gas constant, T is the temperature, n is the type of mixed gas, M is the molar mass of the gas, and c is the relative humidity. n is the corresponding concentration of the gas, α jm It refers to the value of the mth extreme point of the j-order Bessel function (in units of π), R is the radius of the acoustic resonant cavity, and L is the effective length of the acoustic resonant cavity.

[0093] In particular, for the first-order longitudinal mode resonant photoacoustic cell, j = m = 0, q = 1, the above formula can be derived as:

[0094]

[0095] When the gas introduced into the resonant photoacoustic cell is pure N2, let n=1, M=28 in the above formula. On the premise of knowing the resonant frequency, the gas concentration of pure N2 can be inverted by the above formula.

[0096] To further verify the feasibility of the gas detection device of the present invention, 20% CH4:N2, 40% CH4:N2, 60% CH4:N2, 80% CH4:N2 and 100% CH4:N2 gases were introduced into the resonant photoacoustic cell respectively, and steps 1) to 7) were repeated under the condition of known gas concentration, so as to determine the actual measurement result of the resonant frequency based on the sound wave signal-frequency curve graph displayed by LabView. In addition, the known gas concentration was substituted into the relationship between gas concentration and resonant frequency to calculate the resonant frequency formula calculation result, as shown in FIG. Figure 4 The graph shows the actual measurement results of the resonance frequency and the calculation results of the resonance frequency formula. In the formula, n = 2, M1 = 16, M2 = 28. Figure 4 It can be seen that the experimental results are highly consistent with the calculated results, which proves that the method of controlling the sound wave generating mechanism to emit sound wave signals of different frequencies through a function generator, scanning the sound wave signal through a preset frequency scanning range, generating a sound wave signal-frequency curve, and regarding the sound wave frequency corresponding to the maximum amplitude of the sound wave signal in the curve as the resonant frequency is feasible, and thus determining the gas concentration based on the functional relationship between the resonant frequency and the gas concentration is also feasible.

[0097] The various embodiments in this specification are described in a progressive manner, and each embodiment focuses on the differences from other embodiments. The same or similar parts between the various embodiments can be referenced to each other.

[0098] The principles and implementation methods of the present invention are described in this article using specific examples. The description of the above embodiments is only used to help understand the method and core idea of ​​the present invention. At the same time, for those skilled in the art, according to the idea of ​​the present invention, there will be changes in the specific implementation methods and application scope. In summary, the content of this specification should not be understood as limiting the present invention.

Claims

1. A gas concentration detection device based on a photoacoustic cell, characterized in that: include: Detection module, sound source driving module and data acquisition and processing module; The detection module includes a resonant photoacoustic cell; an acoustic wave signal generating mechanism and an acoustic wave signal collecting mechanism are provided on the inner cavity wall of the resonant photoacoustic cell; the resonant photoacoustic cell is also provided with an air inlet and an air outlet; the air inlet is connected to an air inlet pipeline, and the air outlet is connected to an air outlet pipeline; The sound source driving module includes a function generator and a sound wave generating driver; The signal input end of the function generator is connected to the data acquisition and processing module; the signal output end of the function generator is connected to the signal input end of the sound wave generating driver, and the signal output end of the sound wave generating driver is connected to the signal input end of the sound wave signal generating mechanism; the signal output end of the sound wave signal collecting mechanism is connected to the signal input end of the data acquisition and processing module; The data acquisition and processing module includes a phase-locked amplifier; the phase-locked amplifier is used to demodulate the amplified sound wave signal output by the preamplifier; the phase-locked amplifier and the synchronization signal end of the function generator are connected to ensure that the demodulation frequency of the phase-locked amplifier is consistent with the output frequency of the function generator, so as to facilitate the subsequent generation of a sound wave signal-frequency curve diagram; The data acquisition and processing module is used to determine the resonance frequency based on the acoustic wave signal collected and the acoustic wave signal-frequency response curve generated by the frequency signal output by the function generator after the gas to be measured is introduced into the resonant photoacoustic cell, and calculate the concentration of the gas to be measured according to the functional relationship between the resonance frequency and the gas concentration; The resonant photoacoustic cell includes three resonance modes: angular, radial and longitudinal; The resonant photoacoustic cell operates in a first-order longitudinal mode, and the structure includes a first buffer chamber, a second buffer chamber, an acoustic resonance cavity, an acoustic wave signal generating mechanism and an acoustic wave signal collecting mechanism; the first buffer chamber and the second buffer chamber are arranged on both sides of the acoustic resonance cavity and are connected to the acoustic resonance cavity, the first buffer chamber is provided with an air inlet, and the second buffer chamber is provided with an air outlet, and the acoustic wave signal generating mechanism and the acoustic wave signal collecting mechanism are respectively arranged on the inner cavity wall corresponding to the center position of the acoustic resonance cavity; The frequency corresponding to the strongest acoustic wave signal is the resonant frequency f of the resonant photoacoustic cell. jmq , the target gas concentration is calculated by the following formula: Where jmq is the number of vibration modes in the angular, longitudinal and radial directions, κ is the adiabatic index, R0 is the molar gas constant, T is the temperature, n is the type of mixed gas, M is the molar mass of the gas, and c is the relative humidity. n is the corresponding concentration of the gas, α jm It refers to the value of the mth extreme point of the j-order Bessel function, in units of π, R is the radius of the acoustic resonant cavity, and L is the effective length of the acoustic resonant cavity.

2. The gas concentration detection device based on the photoacoustic cell according to claim 1 is characterized in that: The air inlet pipeline is provided with a first needle valve, an air path pressure indicator and an air path flow indicator; the air outlet pipeline is provided with a second needle valve; The first needle valve and the second needle valve are used to adjust the pressure and flow of the gas in the gas pipeline.

3. The gas concentration detection device based on the photoacoustic cell according to claim 2 is characterized in that: The air outlet pipeline is also provided with a vacuum diaphragm pump.

4. The gas concentration detection device based on the photoacoustic cell according to claim 1, characterized in that: The data acquisition and processing module also includes a preamplifier and a controller; The signal input end of the preamplifier is connected to the signal output end of the acoustic signal collecting mechanism, the signal output end of the preamplifier is connected to the signal input end of the lock-in amplifier, the signal output end of the lock-in amplifier is connected to the signal input end of the controller, and the signal output end of the controller is connected to the signal input end of the function generator; the synchronization signal input end of the lock-in amplifier is connected to the synchronization signal output end of the function generator; The preamplifier is used to amplify the sound wave signal output by the sound wave signal collecting mechanism.

5. The gas concentration detection device based on photoacoustic cell according to claim 1, characterized in that: The sound wave signal generating mechanism is arranged on the cavity wall corresponding to the center position of the inner cavity of the resonant photoacoustic cell.

6. The gas concentration detection device based on the photoacoustic cell according to claim 1, characterized in that: The acoustic wave signal generating mechanism and the acoustic wave signal collecting mechanism are respectively arranged on the cavity wall corresponding to the center position of the inner cavity of the resonant photoacoustic cell.

7. The gas concentration detection device based on the photoacoustic cell according to claim 5 or 6, characterized in that: The acoustic wave signal collecting mechanism and the acoustic wave signal generating mechanism are symmetrical along the axis of the resonant photoacoustic cell.

8. The gas concentration detection device based on photoacoustic cell according to claim 1, characterized in that: The acoustic wave signal generating mechanism and the acoustic wave signal collecting mechanism in the first-order longitudinal mode resonant photoacoustic cell are symmetrical along the axis of the resonant photoacoustic cell.

9. The gas concentration detection method of the gas concentration detection device according to any one of claims 1 to 8, characterized in that: include: Passing the gas to be tested into the resonant photoacoustic cell, and adjusting the pressure and flow rate of the gas in the resonant photoacoustic cell by using a first needle valve on the air inlet pipeline and a second needle valve on the air outlet pipeline until they remain stable; Controlling the function generator to output square waves of different frequencies to drive the sound wave signal generating mechanism to generate sound wave signals of different frequencies; Controlling the acoustic wave signal collecting mechanism to collect the acoustic wave signals of different frequencies in the resonant photoacoustic cell and converting the acoustic wave signals into electrical signals; The acoustic wave electric signal-frequency curve is drawn according to the acoustic wave electric signal and the frequency output by the function generator; the resonance frequency of the resonant photoacoustic cell is obtained according to the acoustic wave electric signal-frequency curve, and the concentration of the gas to be measured is calculated according to the functional relationship between the resonance frequency and the gas concentration.

10. The gas concentration detection method according to claim 9, characterized in that: The step of drawing a sound wave electric signal-frequency curve diagram according to the sound wave electric signal and the frequency output by the function generator specifically includes: Set the scanning frequency range and scanning step; Scan the acoustic wave electrical signal within the scanning frequency range based on the scanning step and generate the acoustic wave electrical signal-frequency curve graph; Determine whether the curve change trend in the acoustic wave electrical signal-frequency curve diagram is continuously rising or continuously falling; If yes, increase the scanning frequency range and rescan the acoustic wave electrical signal output by the acoustic wave signal collecting mechanism; If not, then the current acoustic wave electrical signal-frequency curve is output, wherein the frequency value corresponding to the maximum electrical signal is the resonance frequency of the photoacoustic cell.

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