Multi-gas synchronous detection device and method

Abstract

The invention discloses a multi-gas synchronous detection device and method, and relates to the technical field of multi-gas synchronous detection, the 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, the light source module comprises a plurality of light source parts, the light source parts are in one-to-one correspondence with to-be-detected gas, and the data processing module is connected with the photoacoustic cell; the light source components generate excitation light and emit the excitation light into a channel where to-be-detected gas is located in the photoacoustic cell, the wavelength of the excitation light is modulated based on a sine wave signal with a preset frequency, the preset frequency is selected from half of the fundamental frequency and half of the high-order overtone of the photoacoustic cell, and different light source components correspond to different preset frequencies; the photoacoustic cell determines an electric signal corresponding to each to-be-detected gas based on the photoacoustic effect, and the data processing module further demodulates the electric signal to obtain the gas concentration of each to-be-detected gas. According to the invention, the cost and construction complexity of multi-gas synchronous detection can be reduced.

Description

Technical Field

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

[0002] In recent years, with the continuous progress of science and technology, trace gas detection technology has played an increasingly important role in environmental monitoring, medical diagnosis, aerospace and industrial applications. As an emerging laser indirect absorption spectroscopy technology, photoacoustic spectroscopy gas detection technology has developed rapidly. This technology has the following significant features: zero background signal (no output signal when there is no specific absorption), no wavelength selectivity (applicable to laser sources in all spectral bands from ultraviolet to terahertz), detection sensitivity is positively correlated with the 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 the photoacoustic spectroscopy gas detection technology. The photoacoustic signal detection module used in traditional photoacoustic spectroscopy gas detection technology is mainly a photoacoustic cell. The photoacoustic cell can be divided into two types: non-resonant and resonant. The non-resonant photoacoustic cell is usually used in conjunction with a broadband infrared light source and a filter to be applied to the detection of a variety of mixed gases. In contrast, the resonant photoacoustic cell can form standing waves and amplify the photoacoustic signal, thereby achieving high-sensitivity trace gas concentration inversion. It is mostly used in high-sensitivity gas concentration detection technology. Due to its excellent performance, the resonant photoacoustic cell has attracted much attention from scientific 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 transition to a high energy level. In the high energy level state, the molecules undergo a collision relaxation process and transition from a high energy level to a low energy level. The internal energy released during the transition causes the local temperature of the characteristic gas to rise. This periodic temperature change generates sound waves and is 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 determines the gas concentration by analyzing the electrical signal.

[0004] However, traditional photoacoustic spectroscopy gas detection technology is mostly used for the detection of a single gas. The 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 perform interval measurements on multiple gases in the same photoacoustic cell, and cannot achieve real-time synchronous detection of multiple gases. (2) Traditional resonant photoacoustic cell multi-gas detection technology uses multiple photoacoustic cells, each of which contains one gas, and multiple gases are synchronously detected through multiple photoacoustic cells, which greatly increases the cost of the detection device and the complexity of the detection device construction. (3) Traditional resonant photoacoustic cell multi-gas detection technology designs a photoacoustic cell with multiple resonant cavities with similar frequencies to achieve synchronous detection of multiple gases at different resonant frequencies, but 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 the detection device construction.

[0005] In summary, it is crucial to solve the problems of high cost, complex construction and simultaneous detection of multiple gases in photoacoustic cell design. Summary of the invention

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

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

[0008] In a first aspect, the present application provides a multi-gas synchronous detection device, the multi-gas synchronous detection device comprising: 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 contains a plurality of gases to be detected;

[0010] The light source module includes a plurality of light source components, the number of which is the same as the number of 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 to generate excitation light, and irradiate the excitation light into the channel where the gas to be detected is located in the photoacoustic cell; wherein the wavelength of the excitation light is modulated based on a sinusoidal wave 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 high-order overtone 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 a photoacoustic signal generated by the interaction between the excitation light and the gas to be detected based on the photoacoustic effect, and convert the photoacoustic signal to obtain an electrical signal corresponding to each gas to be detected;

[0012] The data processing module is connected to the light source module and the photoacoustic cell respectively, and is used to demodulate the electrical signal corresponding to the gas to be detected based on a sinusoidal wave signal of a preset frequency 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 end of the first function generator is connected to the current modulation input end of the excitation light source, and the signal output end of the second function generator is connected to the current scanning input end of the excitation light source;

[0014] The first function generator is used to output a sine wave signal of a preset frequency to modulate the wavelength of the output light of 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 changes 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, wherein an output end of the light source temperature controller is connected to a temperature control input end of the excitation light source;

[0018] The light source temperature controller is used to control the temperature of the output light of 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 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.

[0021] Optionally, the photoacoustic cell includes multiple channels, and the number of channels is less than the number of gases to be detected. In this case, one channel contains 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 excitation light emitted by light source components corresponding to the multiple gases to be detected contained in the channel is incident on the channel.

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

[0024] 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;

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

[0026] 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.

[0027] Optionally, the photoacoustic signal detection module also includes a three-dimensional adjustment frame; the photoacoustic cell is installed on the three-dimensional adjustment frame, and the three-dimensional adjustment frame 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 a plurality of lock-in amplifiers and a computer;

[0029] The number of the phase-locked amplifiers is the same as the number of the light source components, and the phase-locked amplifiers correspond to the light source components one by one; the reference signal input end of the phase-locked amplifier is connected to the synchronization signal output end of the first function generator in the light source component, the detection signal input end of the phase-locked amplifier is connected to the signal output end of the photoacoustic cell, and the signal output end of the phase-locked amplifier is connected to the signal input end of the computer; the phase-locked amplifier is used to demodulate the electrical signal corresponding to the gas to be detected based on a sine wave signal of a preset frequency by using a second harmonic demodulation method to obtain a 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] In a second aspect, the present application provides a multi-gas synchronous detection method, which is applied to any of the multi-gas synchronous detection devices described above, and the multi-gas synchronous detection method includes:

[0032] An excitation light incident instruction is issued based on the fundamental frequency and high-order overtones of the photoacoustic cell; the excitation light incident instruction is used to control the light source component in the light source module to generate excitation light, and to incident the excitation light into the channel where the gas to be detected is located in the photoacoustic cell; wherein the wavelength of the excitation light is modulated based on a sinusoidal wave 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 high-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;

[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 the sinusoidal wave signal of the 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] The present application provides a multi-gas synchronous detection device and method, including: a light source module, a photoacoustic signal detection module and a data processing module, the photoacoustic signal detection module includes a photoacoustic cell, the photoacoustic cell contains multiple gases to be detected, the light source module includes multiple light source components, the light source components correspond to the gases to be detected one by one, the light source components are used to generate excitation light, and the excitation light is incident on the channel where the gas to be detected is located in the photoacoustic cell, the wavelength of the excitation light is modulated based on a sinusoidal wave signal of a preset frequency, the preset frequency is selected from half of the fundamental frequency and half of the high-order overtone of the photoacoustic cell, and different light source components correspond to different preset frequencies, the photoacoustic cell is used to generate a photoacoustic signal generated by the interaction between the excitation light and the gas to be detected based on the photoacoustic effect, and the photoacoustic signal is converted to obtain an electrical signal corresponding to each gas to be detected, and the data processing module is used to demodulate the electrical signal corresponding to the gas to be detected based on the sinusoidal wave signal of the preset frequency to obtain the gas concentration of each gas to be detected. The present application introduces the fundamental frequency and high-order overtones of the photoacoustic cell, uses different preset frequencies to modulate the wavelength of the excitation light, and detects each gas to be detected separately, thereby ensuring that the detection processes of each gas to be detected are independent of each other and do not interfere with each other. Multi-gas synchronous detection can be achieved, and only one photoacoustic cell is required, and there is no need for precise design of the photoacoustic cell, thereby reducing the cost and construction complexity of multi-gas synchronous detection. BRIEF DESCRIPTION OF THE DRAWINGS

[0037] In order to more clearly illustrate the embodiments of the present application 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 application. For ordinary technicians in this field, other drawings can be obtained based on these drawings without paying creative work.

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

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

[0040] Figure 3 This is a schematic diagram of the second harmonic signal for simultaneously detecting CO2 gas and H2O gas provided in Example 1 of the present application.

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

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

[0043] Figure 6 A method flow chart of a multi-gas synchronous detection method provided in Example 2 of the present application.

[0044] Figure markings: 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 phase-locked amplifier; 9-second phase-locked amplifier; 10-computer; 11-second function generator B; 12-first function generator B; 51-photoacoustic cell. DETAILED DESCRIPTION

[0045] The following will be combined with the drawings in the embodiments of the present application to clearly and completely describe the technical solutions in the embodiments of the present application. Obviously, the described embodiments are only part of the embodiments of the present application, not all of the embodiments. Based on the embodiments in the present application, all other embodiments obtained by ordinary technicians in this field without creative work are within the scope of protection of this application.

[0046] Example 1

[0047] In view of the problems of high cost and complex construction in the prior art for simultaneous detection of multiple gases, and the problem that traditional photoacoustic cells cannot achieve simultaneous detection of multiple gases, the present embodiment aims to achieve simultaneous detection of multiple gases in a photoacoustic cell using fewer devices, mainly utilizing the fundamental frequency and multiple high-order overtones of a resonant photoacoustic cell, thereby achieving simultaneous detection of multiple gases in combination with frequency division multiplexing technology while using only a traditional photoacoustic cell.

[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 comprises a photoacoustic cell, which is a resonant photoacoustic cell and contains a plurality of gases to be detected.

[0050] The light source module includes a plurality of light source components, the number of which is the same as the number of 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 to generate excitation light, and the excitation light is incident on the channel where the gas to be detected (the gas to be detected corresponding to the light source component) is located in the photoacoustic cell. The wavelength of the excitation light is modulated based on a sinusoidal wave 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 high-order overtone 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.

[0051] The photoacoustic cell is used to generate a photoacoustic signal generated by the interaction between the excitation light and the gas to be detected based on the photoacoustic effect, and convert the photoacoustic signal to obtain an electrical signal corresponding to each gas to be detected.

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

[0053] In this embodiment, the light source module includes a plurality of light source components, and the structures of the plurality of light source components are the same. The light source components include: a first function generator, a second function generator and an excitation light source, the signal output end of the first function generator is connected to the current modulation input end of the excitation light source, and the signal output end of the second function generator is connected to the current scanning input end of the excitation light source. The function generator is a multi-waveform signal source, which can generate sine waves, square waves, triangle waves, sawtooth waves and even arbitrary waveforms, and also has modulation functions, including amplitude modulation, frequency modulation, phase modulation and pulse width modulation.

[0054] The first function generator is used to output a sinusoidal wave signal, and the wavelength of the light output by the excitation light source is modulated by controlling the frequency of the sinusoidal wave signal. Specifically, the frequency of the sinusoidal wave signal is controlled to be a preset frequency, which is half of the fundamental frequency or half of the high-order overtone when the photoacoustic pool resonates. At this time, the first function generator is used to output a sinusoidal wave signal of a preset frequency to modulate the wavelength of the light output by the excitation light source.

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

[0056] The second function generator is used to output a triangular wave signal. By controlling the voltage amplitude of the triangular wave signal, the wavelength of the output light 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 output light of the excitation light source, it is swept across the absorption line of the gas to be detected. When the wavelength of the output light of the excitation light source is scanned near the absorption line of the gas to be detected, the specific scanning principle is: ensure that the wavelength of the output light of the excitation light source slowly passes through the absorption line of the gas to be detected. At this time, 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 output light of the excitation light source changes 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 exposed to light of a specific wavelength. These characteristic wavelengths correspond to energy level transitions within the gas molecules. The spectrum that absorbs a specific wavelength is usually related to the type and concentration of the gas. By analyzing the absorption line of the 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, and an output end of the light source temperature controller is connected to a temperature control input end of the excitation light source.

[0060] The light source temperature controller is used to control the temperature of the light output from the excitation light source, and specifically controls the temperature of the light output from the excitation light source through a temperature control driving module inside the light source temperature controller.

[0061] 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. At this time, the wavelength of the excitation light is modulated based on a sine wave 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 high-order overtone 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. The excitation light output by 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 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.

[0063] In this embodiment, the photoacoustic cell includes multiple channels, and the number of channels is less than the number of gases to be detected. At this time, one channel contains 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 of this embodiment also includes: a coupling optical fiber, and 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 beams of excitation light are coupled by the coupling optical fiber and then hit the same channel of the photoacoustic pool. It has been verified that the excitation light signal, photoacoustic signal and electrical signal will not change at this time.

[0065] The photoacoustic cell of this embodiment can be a differential photoacoustic cell, which has 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 of 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, and the first microphone and the second microphone 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, and the second microphone is used to convert the noise signal of the photoacoustic cell to obtain a noise electrical signal, and 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.

[0067] In this embodiment, the photoacoustic signal detection module also includes a three-dimensional adjustment frame, and the photoacoustic cell is installed on the three-dimensional adjustment frame. Specifically, the photoacoustic cell can be fixed on the three-dimensional adjustment frame. The three-dimensional adjustment frame is used to adjust the position of the photoacoustic cell, and specifically can be adjusted in three directions (x-axis, y-axis, and z-axis). For example, the height of the photoacoustic cell, the spacing between the excitation light source and the photoacoustic cell can be adjusted to facilitate the collimated incidence of the light path, so that each excitation light can be incident on the channel where the gas to be detected is located in the photoacoustic cell, and the excitation light corresponding to each gas to be detected is irradiated in the channel corresponding to each gas to be detected in the photoacoustic cell. When adjusting the photoacoustic cell, after determining the incident angle of the propagation direction of the excitation light relative to the plane where the photoacoustic cell is located, the position of the photoacoustic cell relative to the excitation light source is adjusted by the three-dimensional adjustment frame, so 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 in a straight line, the excitation light can pass through the channel smoothly without being blocked.

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

[0069] The number of the lock-in amplifiers is the same as the number of the light source components, and the lock-in amplifiers correspond to the light source components one by one. 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), and the lock-in amplifier is used to demodulate the electrical signal corresponding to the gas to be detected based on the sine wave signal of the preset frequency by 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 through a serial data line.

[0072] The working process of the multi-gas synchronous detection device provided in this embodiment is introduced below, which includes 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 sinusoidal wave signal. By controlling the frequency of the sinusoidal wave signal, the wavelength of the output light of 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 output light of 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 output light of 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 on the channel of the photoacoustic cell containing the gas to be detected corresponding to the excitation light, and ensure that multiple beams of excitation light are respectively incident on different channels of the photoacoustic cell.

[0075] (3) For each gas to be detected, after the excitation light interacts with the gas to be detected in the photoacoustic cell, the energy released causes the gas molecules to be detected and their spatial medium (i.e., the channel where the gas to be detected is located) to be periodically heated according to the frequency of laser modulation (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 trigger corresponding pressure changes, thereby generating a sound field effect. The acoustic signal (i.e., photoacoustic signal) can be sensed by a high-sensitivity microphone.

[0076] (4) For each gas to be detected, the microphone converts the photoacoustic signal into an electrical signal, which is transmitted to the detection signal input terminal of the phase-locked amplifier through the serial data line. At the same time, the reference signal input terminal of the phase-locked amplifier receives the synchronized sinusoidal wave signal provided by the first function generator in the light source component corresponding to the gas to be detected, and processes the electrical signal by the second harmonic demodulation method. The final demodulation result is transmitted to the computer through the communication port for processing. 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 corresponding relationship between the peak value of the second harmonic signal and the concentration).

[0077] The present 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 irradiates multiple beams of excitation light to the photoacoustic signal detection module. The multiple beams of excitation light react with the corresponding gases to be detected, respectively, and a photoacoustic effect occurs, thereby generating 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. The present embodiment uses the fundamental frequency and high-order overtones of the traditional photoacoustic cell itself to achieve multi-gas synchronous detection, which not only reduces the cost of the photoacoustic cell design, but also reduces the complexity of building the photoacoustic cell multi-gas detection device. It also solves the problem that multi-gas synchronous detection cannot be performed using the traditional photoacoustic cell, and broadens the application of the photoacoustic cell 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 gas detection technology for multi-gas detection, multiple microphones are required to detect the photoacoustic signals of multiple resonant cavities respectively. This multi-channel design structure has the same resonant frequency, which will cause other channels to have cross-responses to a single laser, and multiple microphones will also increase the complexity of the system. This embodiment uses a traditional photoacoustic cell to perform multi-gas synchronous detection through its fundamental frequency and high-order overtones, thereby avoiding the cross-response caused by the same resonant frequency, and 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. This embodiment uses a traditional photoacoustic cell, and combines frequency division multiplexing technology at its fundamental frequency and high-order overtones to perform multi-gas detection, thereby achieving synchronous detection of multiple gases.

[0081] (3) This embodiment adopts the design route of the traditional photoacoustic cell. There is no need to specially design multiple resonant cavities with similar frequencies to achieve multi-gas detection. Instead, the fundamental frequency and high-order overtones of the photoacoustic cell itself are used for multi-gas detection, which not only reduces the cost of the photoacoustic cell design, but also reduces the complexity of building a photoacoustic cell multi-gas detection device.

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

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

[0084] like Figure 1 As shown, the device for synchronous detection of multiple gases 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., 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., 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, and the data processing module includes a first lock-in amplifier 8, a second lock-in amplifier 9 and a computer 10. The signal output end of the first function generator A2 is connected to the current modulation input end of the first excitation light source 1, the synchronization signal output end of the first function generator A2 is connected to the reference signal input end of the first lock-in amplifier 8, the signal output end of the second function generator A3 is connected to the current scanning input end of the first excitation light source 1, and the signal output end of the first light source temperature controller 4 is connected to the temperature control input end of the first excitation light source 1. The signal output end of the first function generator B12 is connected to the current modulation input end of the second excitation light source 6, the synchronization signal output end of the first function generator B12 is connected to the reference signal input end of the second phase-locked amplifier 9, the signal output end of the second function generator B11 is connected to the current scanning input end of the second excitation light source 6, and the signal output end of the second light source temperature controller 7 is connected to the temperature control input end of the second excitation light source 6. The signal output end of the photoacoustic cell 51 is connected to the detection signal input end of the first phase-locked amplifier 8 and the detection signal input end of the second phase-locked amplifier 9, and the communication port of the first phase-locked amplifier 8 and the communication port of the second phase-locked amplifier 9 are connected to the communication port of the computer 10. The output light of the first excitation light source 1 and the output light of the second excitation light source 6 are respectively incident on the photoacoustic signal detection module 5.

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

[0086] In this embodiment, the signal output end of the photoacoustic cell 51 is connected to the detection signal input end of the first phase-locked amplifier 8 and the detection signal input end of the second phase-locked amplifier 9 through a serial data line. The photoacoustic cell 51 is fixed on a three-dimensional adjustment frame, which can facilitate the alignment of the optical path. The spacing between the first excitation light source 1 and the second excitation light source 6 and the photoacoustic cell 51 can be adjusted to achieve irradiation in two channels of the photoacoustic cell 51. 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 resonance cavity radius of 5mm.

[0087] like Figure 2 As shown, it is the result of sweeping the photoacoustic cell 51 using a H2O laser, and the fundamental frequency and high-order overtones of the photoacoustic cell 51 can be determined.

[0088] After obtaining the fundamental frequency and high-order overtones of the photoacoustic cell 51, the fundamental frequency, first-order overtones, second-order overtones and other high-order overtones can be selected to perform a multi-gas synchronous detection experiment. Here, only the fundamental frequency and the first-order overtones are selected to perform a CO2 gas and H2O gas synchronous detection experiment, 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 sinusoidal wave signal. By controlling the frequency of the sinusoidal 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 pool 51, that is, 887.2 Hz. 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 the H2O gas. The scanning rate is set to 20 mHz, and it is ensured that the wavelength of the light output by the first excitation light source 1 slowly passes through the absorption line of the 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 sinusoidal wave signal. By controlling the frequency of the sinusoidal 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-order frequency harmonic of the photoacoustic pool 51, that is, 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 it is ensured that the wavelength of the light output by the second excitation light source 6 slowly passes through the absorption line of CO2 gas.

[0091] (3) The propagation directions of the excitation lights output by the first excitation light source 1 and the second excitation light source 6 are adjusted, and the excitation lights are incident on 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 light beams interact with the gas to be detected in the photoacoustic cell 51, the released energy causes the gas molecules to be detected and their spatial medium to be periodically heated according to the frequency of laser modulation. Under the condition of a certain volume, the periodic temperature change of the gas will cause corresponding pressure change, thereby generating an acoustic signal, which can be sensed by a high-sensitivity microphone.

[0093] (5) The microphone converts the photoacoustic signal into an electrical signal, and transmits it to the detection signal input terminal of the first phase-locked amplifier 8 and the detection signal input terminal of the second phase-locked amplifier 9 through the serial data line. At the same time, the reference signal input terminal of the first phase-locked amplifier 8 receives the synchronization signal provided by the first function generator A2, and the reference signal input terminal of the second phase-locked 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. The final demodulation results are transmitted to the computer 10 through the communication port for processing. 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] In order to further verify the sensitivity of the multi-gas synchronous detection device based on the photoacoustic cell 51 of this embodiment, the device was experimentally tested under the same conditions, including photoacoustic signal detection with two lasers turned on simultaneously and alternately. Figure 3 , Figure 4 and Figure 5 It can be seen that 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 when the fundamental frequency and high-order overtones of the photoacoustic cell 51 are used for synchronous detection of multiple gases, the photoacoustic signals between the demodulated frequencies do not interfere with each other. This technology can be applied to the synchronous detection of multiple gases. According to different experimental environment requirements, the remaining high-order overtones of the photoacoustic cell 51 can be used simultaneously for multi-gas detection.

[0096] Example 2

[0097] This embodiment provides a multi-gas synchronous detection method, which is applied to the multi-gas synchronous detection device described in Embodiment 1. Figure 6 As shown, the multi-gas synchronous detection method includes:

[0098] S1: issuing an excitation light incident instruction based on the fundamental frequency and high-order overtones of the photoacoustic cell; the excitation light incident instruction is used to control the light source component in the light source module to generate excitation light, and incident the excitation light into the channel where the gas to be detected is located in the photoacoustic cell; wherein the wavelength of the excitation light is modulated based on a sinusoidal wave 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 high-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.

[0099] S2: Receive 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 wave signal of the preset frequency to obtain the gas concentration of each gas to be detected.

[0101] The technical features of the above embodiments may be combined arbitrarily. To make the description concise, 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 article uses specific examples to illustrate the principles and implementation methods of this application. The description of the above embodiments is only used to help understand the method and core ideas of this application. At the same time, for those skilled in the art, according to the ideas of this application, 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 this application.

Claims

1. A multi-gas synchronous detection device, characterized in that: 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 includes a photoacoustic cell, which is a resonant photoacoustic cell, and contains a plurality of gases to be detected; The light source module includes a plurality of light source components, the number of which is the same as the number of 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 to generate excitation light, and irradiate the excitation light into the channel where the gas to be detected is located in the photoacoustic cell; wherein the wavelength of the excitation light is modulated based on a sinusoidal wave 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 high-order overtone 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; The photoacoustic cell is used to generate a photoacoustic signal generated by the interaction between the excitation light and the gas to be detected based on the photoacoustic effect, and convert the photoacoustic signal to obtain an electrical signal corresponding to each gas to be detected; The data processing module is connected to the light source module and the photoacoustic cell respectively, and is used to demodulate the electrical signal corresponding to the gas to be detected based on a sinusoidal wave signal of a preset frequency to obtain the gas concentration of each gas to be detected.

2. The multi-gas synchronous detection device according to claim 1, characterized in that: The light source component comprises: a first function generator, a second function generator and an excitation light source, wherein the signal output end of the first function generator is connected to the current modulation input end of the excitation light source, and the signal output end of the second function generator is connected to the current scanning input end of the excitation light source; The first function generator is used to output a sine wave signal of a preset frequency to modulate the wavelength of the output light of the excitation light source; 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 changes within a preset wavelength range; The excitation light source is used to output excitation light under the drive of the first function generator and the second function generator.

3. The multi-gas synchronous detection device according to claim 2, characterized in that: The light source component also includes: a light source temperature controller, the output end of the light source temperature controller is connected to the temperature control input end of the excitation light source; The light source temperature controller is used to control the temperature of the output light of the excitation light source; 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.

4. The multi-gas synchronous detection device according to claim 1, characterized in that: The photoacoustic cell includes 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. At this time, one channel contains one gas to be detected.

5. The multi-gas synchronous detection device according to claim 1, characterized in that: The photoacoustic cell includes multiple channels, the number of which is less than the number of gases to be detected. At this time, one channel contains one or more gases to be detected, and multiple gases to be detected contained in the same channel will not react.

6. The multi-gas synchronous detection device according to claim 5, characterized in that: 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.

7. The multi-gas synchronous detection device according to claim 1, characterized in that: The photoacoustic cell includes 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 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 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.

8. The multi-gas synchronous detection device according to claim 1, characterized in that: The photoacoustic signal detection module also includes a three-dimensional adjustment frame; the photoacoustic cell is installed on the three-dimensional adjustment frame, and the three-dimensional adjustment frame 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.

9. The multi-gas synchronous detection device according to claim 2, characterized in that: The data processing module includes a plurality of lock-in amplifiers and a computer; The number of the phase-locked amplifiers is the same as the number of the light source components, and the phase-locked amplifiers correspond to the light source components one by one; the reference signal input end of the phase-locked amplifier is connected to the synchronization signal output end of the first function generator in the light source component, the detection signal input end of the phase-locked amplifier is connected to the signal output end of the photoacoustic cell, and the signal output end of the phase-locked amplifier is connected to the signal input end of the computer; the phase-locked amplifier is used to demodulate the electrical signal corresponding to the gas to be detected based on a sine wave signal of a preset frequency by using a second harmonic demodulation method to obtain a second harmonic signal; The computer is used to determine the gas concentration of the gas to be detected based on the second harmonic signal.

10. A multi-gas synchronous detection method, applied to the multi-gas synchronous detection device according to any one of claims 1 to 9, characterized in that: The multi-gas synchronous detection method comprises: An excitation light incident instruction is issued based on the fundamental frequency and high-order overtones of the photoacoustic cell; the excitation light incident instruction is used to control the light source component in the light source module to generate excitation light, and to incident the excitation light into the channel where the gas to be detected is located in the photoacoustic cell; wherein the wavelength of the excitation light is modulated based on a sinusoidal wave 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 high-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; Receive the electrical signal corresponding to each gas to be detected output by the photoacoustic cell; The electrical signal corresponding to the gas to be detected is demodulated based on the sinusoidal wave signal of the preset frequency to obtain the gas concentration of each gas to be detected.

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