A multi-gas synchronous detection device and method

Abstract

This application discloses a multi-gas synchronous detection device and method, relating to the field of multi-gas synchronous detection technology. The device includes a light source module, a photoacoustic signal detection module, and a data processing module. The photoacoustic signal detection module includes a photoacoustic cell, and the light source module includes multiple light source components, each corresponding to a gas to be detected. Each light source component generates excitation light and directs it into the channel of the photoacoustic cell containing the gas to be detected. The wavelength of the excitation light is modulated based on a sinusoidal signal of a preset frequency. The preset frequency is selected from half the fundamental frequency and half the higher-order overtones of the photoacoustic cell. Different light source components correspond to different preset frequencies. The photoacoustic cell determines the electrical signal corresponding to each gas to be detected based on the photoacoustic effect. The data processing module further demodulates the signal to obtain the gas concentration of each gas to be detected. This application can reduce the cost and complexity of multi-gas synchronous detection.

Description

Technical Field

[0001] This application relates to the field of multi-gas synchronous detection technology, and in particular to a simple multi-gas synchronous detection device and method based on a photoacoustic cell. Background Technology

[0002] In recent years, with the continuous advancement of science and technology, trace gas detection technology has played an increasingly important role in environmental monitoring, medical diagnosis, aerospace, and industrial applications. Photoacoustic spectroscopy for gas detection, as an emerging laser indirect absorption spectroscopy technique, has developed rapidly. This technology has the following significant characteristics: zero background signal (no signal output when there is no specific absorption), no wavelength selectivity (applicable to laser sources in all spectral bands from ultraviolet to terahertz), detection sensitivity positively correlated with excitation light power, and a wide linear response range (the linear response to the concentration of the gas to be detected covers at least three orders of magnitude). The photoacoustic signal detection module is one of the core components of photoacoustic spectroscopy gas detection technology. The photoacoustic signal detection module used in traditional photoacoustic spectroscopy gas detection technology is mainly a photoacoustic cell. Photoacoustic cells can be divided into two types: non-resonant and resonant. Non-resonant photoacoustic cells are usually used in conjunction with broadband infrared light sources and filters to detect various mixed gases. In contrast, resonant photoacoustic cells can form standing waves and amplify photoacoustic signals, thereby achieving high-sensitivity trace gas concentration inversion. They are mostly used in high-sensitivity gas concentration detection technologies. Due to their superior performance, resonant photoacoustic cells have attracted much attention from researchers.

[0003] The basic principle of photoacoustic spectroscopy gas detection technology is as follows: After the characteristic gas being detected absorbs the light emitted by the excitation light source, the molecules jump to a higher energy level. In the high energy level state, the molecules will undergo a collision relaxation process and jump from the high energy level to a lower energy level. The internal energy released during the jump process causes the local temperature of the characteristic gas to rise. This periodic temperature change generates sound waves, which are detected by the microphone inside the photoacoustic cell. The microphone converts the sound wave signal related to the gas concentration into an electrical signal, and the gas concentration is determined by analyzing the electrical signal.

[0004] However, traditional photoacoustic spectroscopy gas detection technology is mostly used for the detection of a single gas. Existing resonant photoacoustic cell multi-gas detection technology mainly includes the following three types: (1) Traditional resonant photoacoustic cell multi-gas detection technology generally uses time-division multiplexing technology to measure multiple gases in the same photoacoustic cell at intervals, which cannot achieve real-time synchronous detection of multiple gases. (2) Traditional resonant photoacoustic cell multi-gas detection technology uses multiple photoacoustic cells, each containing one gas. Multiple gases are detected synchronously through multiple photoacoustic cells, which greatly increases the cost of the detection device and the complexity of its construction. (3) Traditional resonant photoacoustic cell multi-gas detection technology is designed with photoacoustic cells containing multiple resonant cavities with similar frequencies to achieve synchronous detection of multiple gases at different resonant frequencies. However, the structure of the photoacoustic cell needs to be precisely designed to ensure the formation of multiple resonant cavities with similar frequencies, which greatly increases the cost of the detection device and the complexity of its construction.

[0005] In conclusion, addressing the issues of high cost, complex construction, and simultaneous detection of multiple gases in photoacoustic cell design is crucial. Summary of the Invention

[0006] The purpose of this application is to provide a multi-gas synchronous detection device and method, which can reduce the cost and complexity of multi-gas synchronous detection.

[0007] To achieve the above objectives, this application provides the following solution:

[0008] In a first aspect, this application provides a multi-gas synchronous detection device, which includes: a light source module, a photoacoustic signal detection module, and a data processing module;

[0009] The photoacoustic signal detection module includes a photoacoustic cell, which is a resonant photoacoustic cell, and the photoacoustic cell contains multiple gases to be detected.

[0010] The light source module includes multiple light source components, the number of which is the same as the number of gases to be detected, and each light source component corresponds one-to-one with a gas to be detected. The light source components are used to generate excitation light and incident the excitation light into the channel of the gas to be detected in the photoacoustic cell. The wavelength of the excitation light is modulated based on a sinusoidal signal of a preset frequency, and the wavelength of the excitation light varies within a preset wavelength range. The preset frequency is selected from half of the fundamental frequency and half of the higher-order overtones of the photoacoustic cell. Different light source components correspond to different preset frequencies, and the preset wavelength range is determined based on the absorption line of the gas to be detected.

[0011] The photoacoustic cell is used to generate photoacoustic signals based on the photoacoustic effect, which are generated by the interaction between excitation light and the gas to be detected. The photoacoustic signals are then converted to obtain the electrical signals corresponding to each gas to be detected.

[0012] The data processing module, connected to the light source module and the photoacoustic cell respectively, is used to demodulate the electrical signal corresponding to the gas to be detected based on the sinusoidal signal of the preset frequency, so as to obtain the gas concentration of each gas to be detected.

[0013] Optionally, the light source component includes: a first function generator, a second function generator, and an excitation light source. The signal output terminal of the first function generator is connected to the current modulation input terminal of the excitation light source, and the signal output terminal of the second function generator is connected to the current scanning input terminal of the excitation light source.

[0014] The first function generator is used to output a sinusoidal signal of a preset frequency to modulate the wavelength of the light output from the excitation light source;

[0015] The second function generator is used to output a triangular wave signal and control the voltage amplitude of the triangular wave signal so that the wavelength of the light output by the excitation light source varies within a preset wavelength range.

[0016] The excitation light source is used to output excitation light under the drive of the first function generator and the second function generator.

[0017] Optionally, the light source component further includes: a light source temperature controller, the output terminal of which is connected to the temperature control input terminal of the excitation light source;

[0018] The light source temperature controller is used to control the temperature of the output light from the excitation light source;

[0019] The excitation light source is used to output excitation light under the drive of the first function generator, the second function generator, and the light source temperature controller.

[0020] Optionally, the photoacoustic cell includes multiple channels, the number of channels being equal to the number of gases to be detected, with each channel corresponding to a gas to be detected. In this case, one channel contains one gas to be detected.

[0021] Optionally, the photoacoustic cell includes multiple channels, the number of channels being less than the number of gases to be detected. In this case, one channel can contain one or more gases to be detected, and multiple gases to be detected contained in the same channel will not react.

[0022] Optionally, when a channel contains multiple gases to be detected, the multi-gas synchronous detection device further includes a coupling optical fiber, through which the excitation light emitted by the light source components corresponding to the multiple gases to be detected contained in the channel is incident on the channel.

[0023] Optionally, the photoacoustic pool includes a first microphone and a second microphone, which are located inside the photoacoustic pool;

[0024] The first microphone is used to convert the photoacoustic signal corresponding to each gas to be detected, so as to obtain the noisy electrical signal corresponding to each gas to be detected.

[0025] The second microphone is used to convert the noise signal from the photoacoustic cell into a noise electrical signal;

[0026] The difference between the noisy electrical signal and the noise electrical signal corresponding to each gas to be detected is the electrical signal corresponding to each gas to be detected.

[0027] Optionally, the photoacoustic signal detection module also includes a three-dimensional adjustment frame; the photoacoustic cell is mounted on the three-dimensional adjustment frame, which is used to adjust the position of the photoacoustic cell so that each excitation light can be incident on the channel where the gas to be detected is located in the photoacoustic cell.

[0028] Optionally, the data processing module includes multiple lock-in amplifiers and a computer;

[0029] The number of lock-in amplifiers is the same as the number of light source components, and there is a one-to-one correspondence between the lock-in amplifiers and the light source components. The reference signal input terminal of the lock-in amplifier is connected to the synchronization signal output terminal of the first function generator in the light source component, the detection signal input terminal of the lock-in amplifier is connected to the signal output terminal of the photoacoustic cell, and the signal output terminal of the lock-in amplifier is connected to the signal input terminal of the computer. The lock-in amplifier is used to demodulate the electrical signal corresponding to the gas to be detected based on a sinusoidal signal of a preset frequency using the second harmonic demodulation method to obtain the second harmonic signal.

[0030] The computer is used to determine the gas concentration of the gas to be detected based on the second harmonic signal.

[0031] Secondly, this application provides a multi-gas synchronous detection method, applied to the multi-gas synchronous detection device described in any one of the above-mentioned methods, the multi-gas synchronous detection method comprising:

[0032] An excitation light incident command is issued based on the fundamental frequency and higher-order overtones of the photoacoustic cell. The excitation light incident command is used to control the light source component in the light source module to generate excitation light and incident the excitation light onto the channel of the gas to be detected in the photoacoustic cell. The wavelength of the excitation light is modulated based on a sinusoidal signal of a preset frequency, and the wavelength of the excitation light varies within a preset wavelength range. The preset frequency is selected from half of the fundamental frequency and half of the higher-order overtones of the photoacoustic cell. Different preset frequencies correspond to different light source components. The preset wavelength range is determined based on the absorption line of the gas to be detected.

[0033] Receive the electrical signal corresponding to each gas to be detected output by the photoacoustic cell;

[0034] The electrical signal corresponding to the gas to be detected is demodulated based on a sinusoidal signal of a preset frequency to obtain the gas concentration of each gas to be detected.

[0035] According to the specific embodiments provided in this application, this application has the following technical effects:

[0036] This application provides a multi-gas synchronous detection device and method, comprising: a light source module, a photoacoustic signal detection module, and a data processing module. The photoacoustic signal detection module includes a photoacoustic cell containing multiple gases to be detected. The light source module includes multiple light source components, each corresponding to a gas to be detected. The light source components generate excitation light and incident it onto the channel of the gas to be detected in the photoacoustic cell. The wavelength of the excitation light is modulated based on a sinusoidal signal of a preset frequency. The preset frequency is selected from half of the fundamental frequency and half of the higher-order overtones of the photoacoustic cell. Different light source components correspond to different preset frequencies. The photoacoustic cell generates a photoacoustic signal based on the photoacoustic effect, which is generated by the interaction between the excitation light and the gas to be detected. The photoacoustic signal is then converted to obtain an electrical signal corresponding to each gas to be detected. The data processing module demodulates the electrical signal corresponding to the gas to be detected based on the sinusoidal signal of the preset frequency to obtain the gas concentration of each gas to be detected. This application introduces the fundamental frequency and higher-order overtones of the photoacoustic cell and modulates the wavelength of the excitation light using different preset frequencies to detect each gas separately. This ensures that the detection process of each gas is independent and does not interfere with each other, enabling simultaneous detection of multiple gases. Moreover, it only requires one photoacoustic cell and does not require precise design of the photoacoustic cell, thereby reducing the cost and complexity of multi-gas simultaneous detection. Attached Figure Description

[0037] To more clearly illustrate the technical solutions in the embodiments of this application or the prior art, the drawings used in the embodiments will be briefly introduced below. Obviously, the drawings described below are only some embodiments of this application. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0038] Figure 1 This is a schematic diagram of the multi-gas synchronous detection device for simultaneously detecting CO2 and H2O gases provided in Embodiment 1 of this application.

[0039] Figure 2 This is a schematic diagram of the fundamental frequency and higher-order overtone signals of the photoacoustic cell provided in Embodiment 1 of this application after frequency sweeping.

[0040] Figure 3 This is a schematic diagram of the simultaneous detection of second harmonic signals of CO2 gas and H2O gas provided in Embodiment 1 of this application.

[0041] Figure 4This is a schematic diagram of the second harmonic signals of the CO2 laser and the H2O laser when only the CO2 laser is turned on and the H2O laser is turned off, as provided in Embodiment 1 of this application.

[0042] Figure 5 This is a schematic diagram of the second harmonic signals of the H2O laser and the CO2 laser when only the H2O laser is turned on and the CO2 laser is turned off, as provided in Embodiment 1 of this application.

[0043] Figure 6 This is a flowchart of a multi-gas synchronous detection method provided in Embodiment 2 of this application.

[0044] Reference numerals in the attached figures: 1-First excitation light source; 2-First function generator A; 3-Second function generator A; 4-First light source temperature controller; 5-Photoacoustic signal detection module; 6-Second excitation light source; 7-Second light source temperature controller; 8-First lock-in amplifier; 9-Second lock-in amplifier; 10-Computer; 11-Second function generator B; 12-First function generator B; 51-Photoacoustic cell. Detailed Implementation

[0045] The technical solutions of the embodiments of this application will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of this application, and not all embodiments. Based on the embodiments of this application, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of this application.

[0046] Example 1

[0047] To address the issues of high cost and complex setup in existing technologies for simultaneous multi-gas detection, as well as the inability of traditional photoacoustic cells to achieve simultaneous multi-gas detection, this embodiment aims to achieve simultaneous multi-gas detection using a photoacoustic cell with fewer devices. It mainly utilizes the fundamental frequency and multiple higher-order overtones of the resonant photoacoustic cell to achieve simultaneous multi-gas detection by combining frequency division multiplexing technology with traditional photoacoustic cells.

[0048] Specifically, this embodiment provides a simple multi-gas synchronous detection device, which includes a light source module, a photoacoustic signal detection module, and a data processing module.

[0049] The photoacoustic signal detection module includes a photoacoustic cell, which is a resonant photoacoustic cell containing multiple gases to be detected.

[0050] The light source module includes multiple light source components, the number of which is the same as the number of gases to be detected. Each light source component corresponds one-to-one with a gas to be detected. The light source components generate excitation light and direct it into the channel of the photoacoustic cell containing the gas to be detected (the gas corresponding to the light source component). The wavelength of the excitation light is modulated based on a sinusoidal signal of a preset frequency, and the wavelength varies within a preset wavelength range. The preset frequency is selected from half the fundamental frequency and half the higher-order overtones of the photoacoustic cell. Different light source components correspond to different preset frequencies, and the preset wavelength range is determined based on the absorption lines of the gases to be detected.

[0051] The photoacoustic cell is used to generate photoacoustic signals based on the photoacoustic effect, which are generated by the interaction between excitation light and the gas to be detected. The photoacoustic signals are then converted to obtain the electrical signals corresponding to each gas to be detected.

[0052] The data processing module, connected to the light source module and the photoacoustic cell respectively, is used to demodulate the electrical signal corresponding to the gas to be detected based on the sinusoidal signal of the preset frequency, so as to obtain the gas concentration of each gas to be detected.

[0053] In this embodiment, the light source module includes multiple light source components, all of which have identical structures. Each light source component includes a first function generator, a second function generator, and an excitation light source. The signal output terminal of the first function generator is connected to the current modulation input terminal of the excitation light source, and the signal output terminal of the second function generator is connected to the current scanning input terminal of the excitation light source. The function generator is a multi-waveform signal source capable of generating sine waves, square waves, triangular waves, sawtooth waves, and even arbitrary waveforms. It also possesses modulation functions, including amplitude modulation, frequency modulation, phase modulation, and pulse width modulation.

[0054] The first function generator is used to output a sine wave signal. By controlling the frequency of the sine wave signal, the wavelength of the light output from the excitation source is modulated. Specifically, the frequency of the sine wave signal is controlled to a preset frequency, which is half of the fundamental frequency or half of the higher-order overtone when the photoacoustic cell resonates. At this time, the first function generator is used to output a sine wave signal of the preset frequency to modulate the wavelength of the light output from the excitation source.

[0055] It should be noted that different light source components have different preset frequencies. For example, the output frequency of the first function generator of one light source component can be set to half of the fundamental frequency of the photoacoustic cell, and the output frequency of the first function generator of another light source component can be set to half of the higher-order overtones of the photoacoustic cell. Higher-order overtones include first-order overtones, second-order overtones, and so on. The fundamental frequency and higher-order overtones are obtained by setting the temperature and current of the excitation light source at the absorption line of a characteristic gas (randomly selected according to user needs), adjusting the frequency through the first function generator, adjusting the current through the second function generator, and adjusting the temperature through the light source temperature controller, continuously changing the frequency, and obtaining the resonant frequency of the photoacoustic cell through a first harmonic sweep.

[0056] The second function generator outputs a triangular wave signal. By controlling the voltage amplitude of the triangular wave signal, the wavelength of the excitation light source is scanned near the absorption line of the gas to be detected. That is, by changing the wavelength of the excitation light source, it is made to sweep across the absorption line of the gas to be detected. The specific scanning principle when the wavelength of the excitation light source scans near the absorption line of the gas to be detected is to ensure that the wavelength of the excitation light source slowly passes through the absorption line of the gas to be detected. At this time, the second function generator outputs a triangular wave signal and controls the voltage amplitude of the triangular wave signal to make the wavelength of the excitation light source change within a preset wavelength range. The preset wavelength range is determined based on the absorption line of the gas to be detected, specifically the numerical range near the absorption line of the gas to be detected, such as (absorption line - A, absorption line + A), where A is a preset value.

[0057] It should be noted that the absorption line of a gas refers to the characteristic wavelength absorbed by the gas when irradiated with light of a specific wavelength. These characteristic wavelengths correspond to the energy level transitions within the gas molecules. The spectrum of absorption at a specific wavelength is usually related to the type and concentration of the gas. By analyzing the absorption line of a gas, the composition and concentration of the gas can be inferred.

[0058] The excitation light source is used to output excitation light under the drive of the first function generator and the second function generator.

[0059] In this embodiment, the light source component further includes a light source temperature controller, the output terminal of which is connected to the temperature control input terminal of the excitation light source.

[0060] The light source temperature controller is used to control the temperature of the output light from the excitation light source. Specifically, the temperature control drive module inside the light source temperature controller controls the temperature of the output light from the excitation light source.

[0061] The excitation light source outputs excitation light under the drive of the first function generator, the second function generator, and the light source temperature controller. The wavelength of the excitation light is modulated based on a sinusoidal signal of a preset frequency, and the wavelength varies within a preset wavelength range. The preset frequency is selected from half of the fundamental frequency and half of the higher-order overtones of the photoacoustic cell. Different preset frequencies correspond to different light source components, and the preset wavelength range is determined based on the absorption line of the gas to be detected. The excitation light output from the excitation light source in each light source component is incident on the photoacoustic cell in the photoacoustic signal detection module.

[0062] In this embodiment, the photoacoustic cell includes multiple channels, the number of channels being equal to the number of gases to be detected, and each channel corresponds one-to-one with a gas to be detected. In this case, one channel contains one gas to be detected.

[0063] In this embodiment, the photoacoustic cell includes multiple channels, the number of which is less than the number of gases to be detected. In this case, one channel can contain one or more gases to be detected, and multiple gases to be detected contained in the same channel will not react.

[0064] When a channel contains multiple gases to be detected, the multi-gas synchronous detection device in this embodiment further includes a coupling optical fiber. The excitation light emitted by the light source components corresponding to the multiple gases to be detected contained in the channel is incident on the channel through the coupling optical fiber. That is, multiple excitation lights are coupled through the coupling optical fiber and then enter the same channel of the photoacoustic cell. It has been verified that the excitation light signal, photoacoustic signal and electrical signal will not change at this time.

[0065] The photoacoustic cell in this embodiment can be a differential photoacoustic cell with two microphones inside. One microphone is used to detect the photoacoustic signal of the gas to be detected, and the other microphone is used to detect the noise signal. Subtracting the noise signal from the photoacoustic signal can reduce the interference caused by the noise signal and improve the signal-to-noise ratio. Of course, the photoacoustic cell in this embodiment can also be a photoacoustic cell with only one microphone.

[0066] In this embodiment, the photoacoustic cell includes a first microphone and a second microphone, which are located inside the photoacoustic cell. The first microphone is used to convert the photoacoustic signal corresponding to each gas to be detected to obtain a noisy electrical signal corresponding to each gas to be detected. The second microphone is used to convert the noise signal of the photoacoustic cell to obtain a noisy electrical signal. The difference between the noisy electrical signal and the noisy electrical signal corresponding to each gas to be detected is the electrical signal corresponding to each gas to be detected.

[0067] In this embodiment, the photoacoustic signal detection module also includes a three-dimensional adjustment frame. The photoacoustic cell is mounted on the three-dimensional adjustment frame, which can be used to fix the photoacoustic cell to its position. Specifically, the three-dimensional adjustment frame can be adjusted in three directions (x-axis, y-axis, and z-axis). For example, the height of the photoacoustic cell and the distance between the excitation light source and the photoacoustic cell can be adjusted to facilitate collimated incident light, ensuring that each excitation light can be incident on the channel containing the gas to be detected in the photoacoustic cell. This achieves the goal of illuminating the channel corresponding to each gas in the photoacoustic cell with the excitation light corresponding to each gas. When adjusting the photoacoustic cell, after determining the incident angle of the excitation light propagation direction relative to the plane of the photoacoustic cell, the position of the photoacoustic cell relative to the excitation light source is adjusted using the three-dimensional adjustment frame. This ensures that the excitation light passes through the channel of the photoacoustic cell without contact, as long as the excitation light emitted by the excitation light source and the photoacoustic cell are on a straight line, allowing the excitation light to pass smoothly through the channel without obstruction.

[0068] In this embodiment, the data processing module includes multiple lock-in amplifiers and a computer.

[0069] The number of lock-in amplifiers is the same as the number of light source components, with a one-to-one correspondence between lock-in amplifiers and light source components. The reference signal input terminal of the lock-in amplifier is connected to the synchronization signal output terminal of the first function generator in the light source component (which is the light source component corresponding to the lock-in amplifier). The detection signal input terminal of the lock-in amplifier is connected to the signal output terminal of the photoacoustic cell. The signal output terminal of the lock-in amplifier (which can also be called the communication port of the lock-in amplifier) ​​is connected to the signal input terminal of the computer (which can also be called the communication port of the computer). The lock-in amplifier is used to demodulate the electrical signal corresponding to the gas to be detected based on a sinusoidal signal of a preset frequency using the second harmonic demodulation method to obtain the second harmonic signal.

[0070] The computer is used to determine the gas concentration of the gas to be detected based on the second harmonic signal.

[0071] In this embodiment, the signal output terminal of the photoacoustic cell is connected to the detection signal input terminal of the lock-in amplifier via a serial data line.

[0072] The following describes the operation of the multi-gas synchronous detection device provided in this embodiment, including the following steps:

[0073] (1) For each light source component, the excitation light source outputs excitation light under the drive of the first function generator, the second function generator and the light source temperature controller. The first function generator outputs a sine wave signal. By controlling the frequency of the sine wave signal, the wavelength of the excitation light output by the excitation light source is modulated. The second function generator outputs a triangular wave signal. By controlling the voltage amplitude of the triangular wave signal, the wavelength of the excitation light output by the excitation light source is scanned near the absorption line of the gas to be detected. The light source temperature controller controls the temperature of the excitation light output by the excitation light source.

[0074] (2) For each light source component, adjust the propagation direction of the output light of the excitation light source or adjust the position of the photoacoustic cell so that the output excitation light is incident into the channel in the photoacoustic cell that contains the gas to be detected corresponding to the excitation light, so as to ensure that multiple excitation lights are incident into different channels of the photoacoustic cell respectively.

[0075] (3) For each gas to be detected, after the excitation light interacts with the gas to be detected in the photoacoustic cell, the released energy causes the gas molecules and their spatial medium (i.e. the channel where the gas to be detected is located) to be periodically heated according to the laser modulation frequency (i.e. the preset frequency used to modulate the wavelength of the excitation light). Under the condition of a certain volume, the periodic temperature change of the gas will cause the corresponding pressure change, thereby generating a sound field effect. The acoustic signal (i.e. photoacoustic signal) can be sensed through a high-sensitivity microphone.

[0076] (4) For each gas to be detected, the microphone converts the photoacoustic signal into an electrical signal and transmits it to the detection signal input terminal of the lock-in amplifier via the serial data line. At the same time, the reference signal input terminal of the lock-in amplifier receives the synchronous sine wave signal provided by the first function generator in the light source component corresponding to the gas to be detected. The electrical signal is processed by the second harmonic demodulation method. Finally, the demodulation result is transmitted to the computer for processing through the communication port. The peak value of the second harmonic signal obtained after demodulation corresponds to the concentration information of the gas to be detected. The concentration information of the gas to be detected can be obtained by using the concentration calibration result (i.e., the correspondence between the peak value of the second harmonic signal and the concentration).

[0077] This embodiment discloses a simple multi-gas synchronous detection device, which includes a light source module, a photoacoustic signal detection module, and a data processing module. The light source module non-contactly incident multiple beams of excitation light onto the photoacoustic signal detection module. Each beam of excitation light reacts with its corresponding gas to be detected, generating a photoacoustic effect and thus producing an acoustic signal. The acoustic signal is detected by a microphone inside the photoacoustic cell and converted into an electrical signal. The data processing module processes the electrical signal to achieve gas concentration inversion. This embodiment uses the fundamental frequency and high-order overtones of a traditional photoacoustic cell to achieve multi-gas synchronous detection, which reduces the design cost of the photoacoustic cell, reduces the complexity of building a photoacoustic cell multi-gas detection device, and solves the problem that traditional photoacoustic cells cannot perform multi-gas synchronous detection, thus broadening the application of photoacoustic cells in the field of multi-gas synchronous detection.

[0078] Compared with the prior art, this embodiment has the following beneficial effects:

[0079] (1) When using traditional photoacoustic spectroscopy for multi-gas detection, multiple microphones are required to detect the photoacoustic signals of multiple resonant cavities. This multi-channel design has the same resonant frequency, which can cause other channels to cross-respond to a single laser. Moreover, multiple microphones also increase the complexity of the system. This embodiment uses a traditional photoacoustic cell to perform synchronous multi-gas detection through its fundamental frequency and higher-order overtones, thereby avoiding the cross-response caused by the same resonant frequency. Furthermore, only one microphone is needed to detect the photoacoustic signal, reducing the complexity of the system.

[0080] (2) When using traditional photoacoustic spectroscopy gas detection technology for multi-gas detection, a photoacoustic cell with only a single resonant cavity combined with time-division multiplexing technology can also be used for multi-gas detection, but this method cannot achieve true synchronous detection. In this embodiment, a traditional photoacoustic cell is used, and frequency division multiplexing technology is combined with its fundamental frequency and higher-order overtones to perform multi-gas detection, thereby achieving synchronous detection of multiple gases.

[0081] (3) This embodiment adopts the traditional photoacoustic cell design route. It does not require the design of multiple resonant cavities with similar frequencies to realize multi-gas detection. Instead, it uses the fundamental frequency and high-order overtones of the photoacoustic cell itself to perform multi-gas detection, which reduces the cost of photoacoustic cell design and the complexity of building photoacoustic cell multi-gas detection device.

[0082] (4) This embodiment does not require the design of multiple resonant cavities with similar frequencies to realize multi-gas detection. Instead, it uses the fundamental frequency and high-order overtones of the photoacoustic cell itself to detect multiple gases, which provides a new idea for multi-gas detection based on photoacoustic cell.

[0083] The following section will further describe the multi-gas synchronous detection device of this embodiment, taking the simultaneous detection of CO2 and H2O as an example:

[0084] like Figure 1 As shown, the device for simultaneous multi-gas detection based on the photoacoustic cell 51 includes: a light source module, a photoacoustic signal detection module 5, and a data processing module. The light source module includes two light source components. The first light source component includes a first excitation light source 1 (i.e., an H2O laser), a first function generator A2, a second function generator A3, and a first light source temperature controller 4. The second light source component includes a second excitation light source 6 (i.e., a CO2 laser), a first function generator B12, a second function generator B11, and a second light source temperature controller 7. The photoacoustic signal detection module 5 includes the photoacoustic cell 51. The data processing module includes a first lock-in amplifier 8, a second lock-in amplifier 9, and a computer 10. The signal output terminal of the first function generator A2 is connected to the current modulation input terminal of the first excitation light source 1. The synchronization signal output terminal of the first function generator A2 is connected to the reference signal input terminal of the first lock-in amplifier 8. The signal output terminal of the second function generator A3 is connected to the current scanning input terminal of the first excitation light source 1. The signal output terminal of the first light source temperature controller 4 is connected to the temperature control input terminal of the first excitation light source 1. The signal output terminal of the first function generator B12 is connected to the current modulation input terminal of the second excitation light source 6. The synchronization signal output terminal of the first function generator B12 is connected to the reference signal input terminal of the second lock-in amplifier 9. The signal output terminal of the second function generator B11 is connected to the current scanning input terminal of the second excitation light source 6. The signal output terminal of the second light source temperature controller 7 is connected to the temperature control input terminal of the second excitation light source 6. The signal output terminal of the photoacoustic cell 51 is connected to the detection signal input terminal of the first lock-in amplifier 8 and the detection signal input terminal of the second lock-in amplifier 9. The communication ports of the first lock-in amplifier 8 and the second lock-in amplifier 9 are connected to the communication port of the computer 10. The output light from the first excitation light source 1 and the output light from the second excitation light source 6 are respectively incident on the photoacoustic signal detection module 5.

[0085] In this embodiment, both the first excitation light source 1 and the second excitation light source 6 can be distributed feedback diode lasers, or quantum cascade lasers, terahertz light sources, etc., but are not limited to these.

[0086] In this embodiment, the signal output terminal of the photoacoustic cell 51 is connected to the detection signal input terminals of the first lock-in amplifier 8 and the second lock-in amplifier 9 via a serial data cable. The photoacoustic cell 51 is fixed on a three-dimensional adjustment frame, which facilitates the collimation of the optical path. The distance between the first excitation light source 1 and the second excitation light source 6 and the photoacoustic cell 51 can be adjusted to illuminate the two channels of the photoacoustic cell 51 respectively. The photoacoustic cell 51 selected in this embodiment is a differential photoacoustic cell with a fundamental frequency of 1.7kHz, a cavity length of 100mm, and a resonant cavity radius of 5mm.

[0087] like Figure 2 As shown, it is the result of frequency sweeping of the photoacoustic cell 51 using an H2O laser, which can determine the fundamental frequency and higher-order overtones of the photoacoustic cell 51.

[0088] After obtaining the fundamental frequency and higher-order overtones of the photoacoustic cell 51, the fundamental frequency, first-order overtones, and second-order overtones can be selected for multi-gas synchronous detection experiments. Here, only the fundamental frequency and first-order overtones are selected for the synchronous detection of CO2 and H2O gases, including the following steps:

[0089] (1) The first excitation light source 1 outputs a light beam under the control of the first function generator A2, the second function generator A3 and the first light source temperature controller 4. The first function generator A2 outputs a sine wave signal. By controlling the frequency of the sine wave signal, the wavelength of the light output by the first excitation light source 1 is modulated. Specifically, the output frequency value of the first function generator A2 is set to half of the fundamental frequency of the photoacoustic cell 51, i.e., 887.2Hz. The output voltage amplitude can be optimized according to the signal result. The second function generator A3 outputs a triangular wave signal. By controlling the voltage amplitude of the triangular wave signal, the wavelength of the light output by the first excitation light source 1 is continuously scanned near the absorption line of H2O gas. The scanning rate is set to 20mHz, and the wavelength of the light output by the first excitation light source 1 is ensured to slowly pass through the absorption line of H2O gas.

[0090] (2) The second excitation light source 6 outputs a light beam under the control of the first function generator B12, the second function generator B11, and the second light source temperature controller 7. The first function generator B12 outputs a sine wave signal. By controlling the frequency of the sine wave signal, the wavelength of the light output by the second excitation light source 6 is modulated. Specifically, the output frequency value of the first function generator B12 is set to half of the first overtone of the photoacoustic cell 51, i.e., 2.625kHz. The output voltage amplitude can be optimized according to the signal result. The second function generator B11 outputs a triangular wave signal. By controlling the voltage amplitude of the triangular wave signal, the wavelength of the light output by the second excitation light source 6 is continuously scanned near the absorption line of CO2 gas. The scanning rate is set to 20mHz, and the wavelength of the light output by the second excitation light source 6 is ensured to slowly pass through the absorption line of CO2 gas.

[0091] (3) Adjust the propagation direction of the excitation light output by the first excitation light source 1 and the second excitation light source 6, and incident the excitation light into the photoacoustic cell 51, wherein the two excitation lights pass through the two resonant cavities of the photoacoustic cell 51 respectively.

[0092] (4) After the two excitation beams interact with the gas to be detected in the photoacoustic cell 51, the released energy causes the gas molecules and their spatial medium to be periodically heated according to the frequency modulated by the laser. Under the condition of a certain volume, the periodic temperature change of the gas will cause the corresponding pressure change, thereby generating an acoustic signal. The photoacoustic signal can be sensed by a high-sensitivity microphone.

[0093] (5) The microphone converts the photoacoustic signal into an electrical signal, which is transmitted to the detection signal input terminal of the first lock-in amplifier 8 and the detection signal input terminal of the second lock-in amplifier 9 via a serial data line. At the same time, the reference signal input terminal of the first lock-in amplifier 8 receives the synchronization signal provided by the first function generator A2, and the reference signal input terminal of the second lock-in amplifier 9 receives the synchronization signal provided by the first function generator B12. The electrical signals are processed by the second harmonic demodulation method respectively. Finally, the demodulation result is transmitted to the computer 10 for processing through the communication port. The peak value of the second harmonic signal obtained after demodulation corresponds to the concentration information of the gas to be detected, and the concentration information of the gas to be detected can be obtained.

[0094] To further verify the sensitivity of the multi-gas synchronous detection device based on the photoacoustic cell 51 in this embodiment, experimental tests were conducted on the device under the same conditions, including photoacoustic signal detection with both lasers simultaneously and alternately activated. Figure 3 , Figure 4 and Figure 5 As can be seen, when only the CO2 laser is turned on and the H2O laser is turned off, the signal amplitude of the CO2 gas is not affected; similarly, when only the H2O laser is turned on and the CO2 laser is turned off, the signal amplitude of the H2O gas is also not affected.

[0095] The results show that using the fundamental frequency and higher-order overtones of the photoacoustic cell 51 for multi-gas synchronous detection, the photoacoustic signals between each demodulation frequency do not interfere with each other. This technology can be applied to multi-gas synchronous detection technology, and depending on the different experimental environment requirements, the other higher-order overtones of the photoacoustic cell 51 can be selected to be used simultaneously for multi-gas detection.

[0096] Example 2

[0097] This embodiment provides a method for simultaneous detection of multiple gases, applied to the simultaneous detection device for multiple gases described in Embodiment 1, such as... Figure 6 As shown, the multi-gas synchronous detection method includes:

[0098] S1: An excitation light incident command is issued based on the fundamental frequency and higher-order overtones of the photoacoustic cell; the excitation light incident command is used to control the light source component in the light source module to generate excitation light and incident the excitation light onto the channel of the gas to be detected in the photoacoustic cell; wherein, the wavelength of the excitation light is modulated based on a sinusoidal signal of a preset frequency, and the wavelength of the excitation light varies within a preset wavelength range, the preset frequency is selected from half of the fundamental frequency and half of the higher-order overtones of the photoacoustic cell, the preset frequency is different for different light source components, and the preset wavelength range is determined based on the absorption line of the gas to be detected.

[0099] S2: Receives the electrical signal corresponding to each gas to be detected output by the photoacoustic cell.

[0100] S3: Demodulate the electrical signal corresponding to the gas to be detected based on the sinusoidal signal of the preset frequency to obtain the gas concentration of each gas to be detected.

[0101] The technical features of the above embodiments can be combined in any way. For the sake of brevity, not all possible combinations of the technical features in the above embodiments are described. However, as long as there is no contradiction in the combination of these technical features, they should be considered to be within the scope of this specification.

[0102] This document uses specific examples to illustrate the principles and implementation methods of this application. The descriptions of the above embodiments are only for the purpose of helping to understand the methods and core ideas of this application. Furthermore, those skilled in the art will recognize that, based on the ideas of this application, there will be changes in the specific implementation methods and application scope. Therefore, the content of this specification should not be construed as a limitation of this application.

Claims

1. A multi-gas simultaneous detection device, characterized by, The multi-gas synchronous detection device comprises a light source module, a photoacoustic signal detection module and a data processing module; The photoacoustic signal detection module comprises a photoacoustic cell, and the photoacoustic cell is a resonant photoacoustic cell; the photoacoustic cell contains a plurality of gases to be detected; The light source module comprises a plurality of light source components, the number of the light source components is the same as the number of the gases to be detected, and the light source components correspond to the gases to be detected one by one; the light source components are used for generating excitation light and making the excitation light incident into a channel in which the gas to be detected is located in the photoacoustic cell; wherein the wavelength of the excitation light is modulated based on a preset frequency sinusoidal signal, and the wavelength of the excitation light changes in a preset wavelength range; the preset frequency is selected from half of a fundamental frequency and half of a high-order overtone frequency of the photoacoustic cell; the preset frequencies corresponding to different light source components are different; and the preset wavelength range is determined based on absorption lines of the gases to be detected; The photoacoustic cell is used for generating photoacoustic signals generated by interaction between the excitation light and the gases to be detected based on the photoacoustic effect, and converting the photoacoustic signals to obtain an electrical signal corresponding to each of the gases to be detected; The data processing module is connected with the light source module and the photoacoustic cell respectively, and is used for demodulating the electrical signal corresponding to each of the gases to be detected based on the preset frequency sinusoidal signal to obtain a gas concentration of each of the gases to be detected; The photoacoustic cell comprises a plurality of channels, the number of the channels is equal to the number of the gases to be detected, and the channels correspond to the gases to be detected one by one; in this case, one channel contains one gas to be detected; or the photoacoustic cell comprises a plurality of channels, the number of the channels is less than the number of the gases to be detected; in this case, one channel contains one or more gases to be detected, and the plurality of gases to be detected contained in the same channel do not react with each other; The photoacoustic signal detection module further comprises a three-dimensional adjusting frame; the photoacoustic cell is installed on the three-dimensional adjusting frame, and the three-dimensional adjusting frame is used for adjusting the position of the photoacoustic cell so that each excitation light can be incident into the channel in which the gas to be detected is located in the photoacoustic cell.

2. The multi-gas simultaneous detection apparatus according to claim 1, wherein The light source component comprises a first function generator, a second function generator and an excitation light source; a signal output end of the first function generator is connected with a current modulation input end of the excitation light source; and a signal output end of the second function generator is connected with a current scanning input end of the excitation light source; The first function generator is used for outputting a preset frequency sinusoidal signal to modulate the wavelength of light output by the excitation light source; The second function generator is used for outputting a triangular wave signal and controlling the voltage amplitude of the triangular wave signal to make the wavelength of the light output by the excitation light source change in a preset wavelength range; The excitation light source is used for outputting excitation light under the driving of the first function generator and the second function generator.

3. The multi-gas simultaneous detection apparatus according to claim 2, wherein The light source component further comprises a light source temperature controller; an output end of the light source temperature controller is connected with a temperature control input end of the excitation light source; The light source temperature controller is used for controlling the temperature of the light output by the excitation light source; The excitation light source is used for outputting excitation light under the driving of the first function generator, the second function generator and the light source temperature controller.

4. The multi-gas simultaneous detection apparatus according to claim 1, wherein When the channel contains multiple gases to be detected, the multi-gas synchronous detection device further comprises a coupling optical fiber, and the excitation light emitted by the light source components corresponding to the multiple gases to be detected in the channel is incident on the channel through the coupling optical fiber.

5. The multi-gas simultaneous detection apparatus according to claim 1, wherein The photoacoustic cell comprises a first microphone and a second microphone, and the first microphone and the second microphone are located inside the photoacoustic cell. The first microphone is configured to convert the photoacoustic signal corresponding to each gas to be detected to obtain a noisy electrical signal corresponding to each gas to be detected. The second microphone is configured to convert the noise signal of the photoacoustic cell to obtain a noise electrical signal. The difference between the noisy electrical signal corresponding to each gas to be detected and the noise electrical signal is the electrical signal corresponding to each gas to be detected.

6. The multi-gas simultaneous detection apparatus according to claim 2, wherein The data processing module comprises a plurality of lock-in amplifiers and a computer. The number of lock-in amplifiers is the same as the number of light source components, and the lock-in amplifiers correspond one-to-one to the light source components; the reference signal input end of the lock-in amplifier is connected to the synchronous signal output end of the first function generator in the light source component, the detection signal input end of the lock-in amplifier is connected to the signal output end of the photoacoustic cell, and the signal output end of the lock-in amplifier is connected to the signal input end of the computer; the lock-in amplifier is configured to demodulate the electrical signal corresponding to the gas to be detected based on a preset frequency sinusoidal signal using a second harmonic demodulation method to obtain a second harmonic signal; The computer is configured to determine the gas concentration of the gas to be detected based on the second harmonic signal.

7. A method for multi-gas simultaneous detection, applied to the multi-gas simultaneous detection device of any one of claims 1-6, characterized in that, The multi-gas synchronous detection method comprises: The excitation light emission instruction is based on the fundamental frequency and the high-order generic frequency of the photoacoustic cell; the excitation light emission instruction is used to control the light source components in the light source module to generate excitation light and to emit the excitation light to the channel in which the gas to be detected is located in the photoacoustic cell; wherein the wavelength of the excitation light is modulated based on a preset frequency sinusoidal signal, and the wavelength of the excitation light varies within a preset wavelength range, the preset frequency is selected from half of the fundamental frequency and half of the high-order generic frequency of the photoacoustic cell, the preset frequencies corresponding to different light source components are different, and the preset wavelength range is determined based on the absorption line of the gas to be detected; Receiving the electrical signal corresponding to each gas to be detected output by the photoacoustic cell; Demodulating the electrical signal corresponding to the gas to be detected based on a preset frequency sinusoidal signal to obtain the gas concentration of each gas to be detected.

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