Extended-range resonant photoacoustic cell for acetylene detection and detection method of extended-range resonant photoacoustic cell

Abstract

The invention relates to an extended-range resonant photoacoustic cell for acetylene detection and a detection method thereof, belongs to the technical field of partial discharge in a high-voltage insulating transformer, and provides the extended-range resonant photoacoustic cell for acetylene detection in order to solve the problem that a photoacoustic spectrum detection device is poor in sensitivity. Comprising a first buffer cavity, a second buffer cavity, a laser, four reflectors, a photoelectric detector and a controller which are arranged in a shell, and a resonance gas chamber is arranged between the first buffer cavity and the second buffer cavity so as to communicate the first buffer cavity with the second buffer cavity; the laser is located on one side of the first buffer cavity. The four reflectors are symmetrically arranged in the first buffer cavity and the second buffer cavity in pairs respectively; the photoelectric detector is used for detecting optical signals; the microphone is used for sound signals; the controller is used for processing the optical signal and the acoustic signal to obtain a detection result of the characteristic gas. The four reflectors not only can increase the absorbance, but also can realize continuous monitoring and improve the detection sensitivity.

Description

Technical Field

[0001] The invention relates to the technical field of partial discharge in high-voltage insulating transformers, and in particular to an extended-range resonant photoacoustic cell for acetylene detection and a detection method thereof. Background Art

[0002] The insulating oil inside large oil-immersed power transformers will gradually age and decompose into a small amount of hydrocarbon gas, such as acetylene (C 2 H 2 ), methane (CH 4 ) and carbon monoxide (CO). By detecting the volume fraction of these gases, the potential faults of the transformer can be analyzed and judged. At present, gas chromatography is mainly used for detection. This method has the disadvantages of consuming carrier gas, complex gas path and long-term unstable operation, which brings many inconveniences to operation and maintenance. Photoacoustic spectroscopy is a spectral technology based on the photoacoustic effect discovered by AGBell in 1880. When a light source in the molecular absorption band is irradiated on the sample, the sample molecules absorb light energy and transition to an excited state. The molecules in the excited state return to the ground state through collision relaxation. At the same time, the absorbed light energy is converted into the internal energy of the molecule, and the local temperature of the molecule increases. When the laser irradiated on the sample molecule is modulated, the local temperature of the molecule changes periodically, thereby generating periodic pressure changes, that is, sound waves. The relationship between the sound signal and the laser wavelength is recorded by an acoustic sensor such as a microphone, and the photoacoustic spectrum signal is obtained. It has the advantages of high sensitivity, strong stability and fast response speed. Since 2000, Kelman Company in the UK has applied photoacoustic spectroscopy technology to the detection of gas and micro-water in insulating oil, and developed a portable online monitoring system.

[0003] In the existing photoacoustic spectroscopy detection technology, in order to reduce the noise of the detection results, a dual-cavity differential photoacoustic cell is selected, that is, it has two sets of resonance cavities and buffer cavities of the same shape and size, with the same noise and opposite vibration phases. Through the differential operation of the dual-microphone signals, since only one reflector is set in the photoacoustic cell to increase the optical path, while obtaining a high signal-to-noise ratio detection result, it restricts the improvement of the gas absorbance in the gas chamber of the photoacoustic cell in the photoacoustic spectroscopy detection, so that the detection sensitivity is limited. Summary of the invention

[0004] In view of the problems existing in the prior art, the present invention provides an extended-range resonant photoacoustic cell for acetylene detection and a detection method thereof. By setting four reflectors to realize the circulation of laser signals in the photoacoustic cell and to increase the optical path of the laser signals, not only the absorbance can be increased, but also the detection of acetylene gas in the photoacoustic cell can be realized by continuous monitoring, thereby increasing the absorbance of characteristic gases and improving the sensitivity of photoacoustic spectrum detection of characteristic gases.

[0005] The present invention provides an extended-range resonant photoacoustic cell for acetylene detection, which comprises: shell; A first buffer chamber is arranged in the shell, and an air inlet window is provided at the top of the first buffer chamber and an optical window is provided at the side thereof, so that characteristic gas can enter the first buffer chamber through the air inlet window; A second buffer chamber is disposed in the housing, and the second buffer chamber is provided with an exhaust window so that the characteristic gas can be discharged from the second buffer chamber through the exhaust window; A resonant air chamber, disposed between the first buffer chamber and the second buffer chamber to connect the first buffer chamber and the second buffer chamber; A laser, the laser is located at one side of the first buffer cavity and outside the optical window, and provides laser light to generate a photoacoustic spectroscopy effect with a characteristic gas in the resonant gas chamber; Reflectors, wherein there are four reflectors, which are symmetrically arranged in pairs in the first buffer cavity and the second buffer cavity respectively, so that the laser emitted by the laser is reflected by the four reflectors, thereby doubling the optical path of the laser signal; A photodetector for detecting the optical signal of the photoacoustic spectroscopy effect; A microphone, located on the top of the resonant air chamber, for detecting the acoustic signal of the photoacoustic spectroscopy effect; The controller is connected to the laser, the photodetector and the microphone respectively, and is used to filter and amplify the electrical signal of the photodetector, perform negative feedback regulation on the laser to ensure the stability of the light source output, and process the detection signal obtained by the microphone to obtain the detection result of the characteristic gas.

[0006] When the characteristic gas enters the first buffer cavity, the resonant gas chamber and the second buffer cavity in sequence from the air inlet window, the laser emitted by the laser enters the first buffer cavity through the optical window, and is reflected by four mirrors to double the optical path of the laser signal, and generates a photoacoustic effect with the characteristic gas in the resonant gas chamber.

[0007] If the laser continuously emits laser signals, the temperature conditions of the detection environment will change. Therefore, the laser works at set time intervals, thereby obtaining discrete detection results at specific time intervals, and cannot obtain continuous detection results. The four reflectors can realize the circulation of laser signals in the photoacoustic cell. This setting can not only increase the absorbance, but also realize the continuous monitoring of acetylene gas detection in the photoacoustic cell. By setting up four reflectors, the optical path of the laser signal is increased, thereby increasing the absorbance of the characteristic gas, and realizing the improvement of the sensitivity of the characteristic gas photoacoustic spectrum detection.

[0008] Furthermore, the first buffer cavity and the second buffer cavity are symmetrically arranged on both sides of the resonant air chamber. The two buffer cavities should be arranged symmetrically. The symmetrical arrangement helps to obtain the maximum sound pressure signal at the characteristic frequency, thereby improving the sensitivity of the photoacoustic spectroscopy detection.

[0009] Furthermore, there are two resonant air chambers, which are arranged up and down to form an upper resonant air chamber and a lower resonant air chamber.

[0010] Furthermore, the microphone is installed on the center line of the outer side of the resonance air chamber and is level with the inner surface of the upper resonance air chamber.

[0011] The present invention provides a detection method, using the above-mentioned extended-range resonant photoacoustic cell for acetylene detection, comprising the following steps: Step 1, controlling characteristic gas (acetylene gas) to enter the first buffer chamber; Step 2, emit a laser signal, and adjust the laser signal so that it can be absorbed by the characteristic gas (i.e., the light beam is consistent with the absorption spectrum of acetylene gas molecules); Step 3, collecting the acoustic wave signal formed after the characteristic gas absorbs the laser signal and converts it; Step 4, demodulating the acoustic wave signal through a phase-locked amplifier to obtain characteristic gas photoacoustic spectrum detection results.

[0012] The sound wave signals converted from the gas molecules absorbing light energy in the photoacoustic cell are collected by a microphone installed in the center of the resonant cavity flush with the cavity wall. The sensitivity of the microphone is 50 mV / Pa.

[0013] Furthermore, the step 1 specifically includes: Step 1.1, adjust the angle of the reflector so that the laser emitted by the light source returns along the resonant gas chamber, while preventing the light from hitting the inner wall to reduce the noise introduced by absorption; In step 1.2, the photoacoustic cell is first filled with high-purity N2, and then with characteristic gas (acetylene gas with a volume fraction of 0.01%), and the rate is adjusted; the applied pressure of the extended-range resonant photoacoustic cell for acetylene detection is adjusted to be controlled at normal pressure conditions, and the temperature is controlled at room temperature (25°C).

[0014] Further, the specific process of step 2 is: Step 2.1, modulate the current injected into the laser by superimposing the triangular wave output by the function generator and the sine wave output by the phase-locked amplifier to obtain the modulation frequency, so that the wavelength of the output light source falls within the absorption peak range of the characteristic gas (acetylene absorption peak), and measure the photoacoustic signal multiple times to obtain the average value; the purpose of controlling the modulation frequency is to make the emitted light source better absorbed by the acetylene gas and improve the detection sensitivity; modulate the light source frequency before the light source is emitted; Step 2.2, change the working temperature of the laser to adjust the resonant frequency, use the resonance acoustic spectrum method to measure the actual resonant frequency of the photoacoustic cell in real time, and realize the negative feedback regulation of the resonant frequency, so that the working frequency can be accurately adjusted to the standard frequency of the laser in real time. The resonant frequency increases with the increase of temperature and decreases with the decrease of temperature. The changed temperature is the working temperature of the laser. Furthermore, in step 4, the acoustic wave signal is demodulated by a lock-in amplifier, and the specific process includes: Step 4.1, a reference signal is provided through a phase-locked amplifier, whose frequency is very close to the expected frequency of the acoustic signal and has a fixed phase relationship; after this reference signal is mixed with the obtained acoustic signal, a sum frequency and a difference frequency signal are generated through a mixer, and then the high-frequency component is filtered out through a low-pass filter, retaining the low-frequency difference frequency signal, where the difference frequency signal contains the amplitude and phase information of the acoustic signal; in this process, the real component (X) and the imaginary component (Y) are extracted respectively, which correspond to the amplitude and phase information of the acoustic signal respectively.

[0015] Step 4.2, measuring the amplitude and phase of the mixing signal by a lock-in amplifier to determine the amplitude and phase information of the acoustic wave signal; Step 4.3, further amplify the generated difference frequency signal through an amplifier to enhance the strength of the detection signal and make it suitable for subsequent processing.

[0016] Step 4.4, the amplified difference frequency signal is converted into a digital signal through the data acquisition card. The signal processed by the phase-locked amplifier will be input into the data acquisition card (DAQ). The data acquisition card converts the analog signal into a digital signal so that it can be read and processed by the computer. The data acquisition card realizes the conversion of analog signals to digital signals through the analog-to-digital converter (ADC) and has a certain resolution and sampling rate to provide data accuracy and data points.

[0017] Step 4.5, after processing, the photoacoustic spectrum detection results are obtained to extract useful information and conduct final data analysis.

[0018] The digital signal is stored in the memory of the data acquisition card and read, processed and analyzed by the computer. On the computer, various software tools and algorithms can be used to further process the signal, such as filtering, Fourier transform, spectrum analysis, etc., to extract useful information and perform final data analysis. The processed signal data can be used to display the amplitude, phase or other relevant parameters of the acoustic wave signal, thereby obtaining the results of photoacoustic spectroscopy detection.

[0019] In the photoacoustic spectroscopy detection system, the acoustic signal generated by the photoacoustic effect in the resonant gas chamber is usually very weak and may be drowned by noise, so a high-sensitivity microphone is used to collect the photoacoustic signal; after processing, it is ensured that the weak sound wave signal generated from the photoacoustic pool can be effectively detected and analyzed to achieve high-precision detection of gas components.

[0020] It can be seen from the above technical solutions that the present invention has the following advantages: (1) The invention solves the technical problem that a dual-cavity differential photoacoustic cell is selected to reduce the noise of the detection results. Since only one reflector is set in the photoacoustic cell to increase the optical path, while obtaining a high signal-to-noise ratio detection result, the improvement of the gas absorbance in the gas chamber of the photoacoustic cell in the photoacoustic spectroscopy detection is restricted, which limits the detection sensitivity.

[0021] (2) By setting a reflector in the resonant gas chamber, the optical path of the laser signal is increased, thereby increasing the absorbance of the characteristic gas. This design uses the principle of Beer-Lambert law to significantly improve the detection sensitivity, which is particularly important for the accurate detection of characteristic gases such as acetylene.

[0022] (3) The design of the left second buffer cavity effectively reduces the acoustic background noise and the noise caused by gas flow. This structural design helps to improve the signal-to-noise ratio of the system, ensuring high sensitivity while also obtaining high-quality detection results.

[0023] (4) The controller filters and amplifies the electrical signal transmitted by the photodetector, and uses the output end to perform negative feedback regulation on the laser to ensure the stability of the light source output. This design helps maintain the stability of the light source during photoacoustic spectroscopy detection and further improves the accuracy and reliability of detection. BRIEF DESCRIPTION OF THE DRAWINGS

[0024] In order to more clearly illustrate the embodiments of the present invention or the technical solutions in the prior art, the drawings required for use in the embodiments or the description of the prior art will be briefly introduced below. Obviously, the drawings described below are only some embodiments of the present invention. For ordinary technicians in this field, other drawings can be obtained based on these drawings without paying creative labor.

[0025] Figure 1 It is a schematic diagram of the structure of an extended-range resonant photoacoustic cell for acetylene detection; Figure 2 is a detection curve diagram of acetylene gas in specific embodiment 1 of the present invention; Figure 3 It is a low-sensitivity photoacoustic cell detection curve diagram; Figure 4This is a detection curve diagram of the extended-range resonant photoacoustic cell for acetylene detection of the present application; Among them, 1-housing; 2-laser; 3-optical window; 4-first buffer cavity; 5-air inlet window; 6-resonance air chamber; 6A-upper resonant air chamber; 6B-lower resonant air chamber; 7-microphone; 8-second buffer cavity; 9-exhaust window; 10-photodetector; 11-controller; 12-reflector. DETAILED DESCRIPTION

[0026] In order to make the purpose, features and advantages of the present invention more obvious and easy to understand, the technical solutions in the embodiments of the present invention will be clearly and completely described below in conjunction with the drawings in the embodiments of the present invention. Obviously, the embodiments described below are only part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without creative work are within the scope of protection of the present invention.

[0027] Example 1 like Figure 1 As shown, the present invention provides an extended-range resonant photoacoustic cell for acetylene detection, which comprises: Shell 1; A first buffer chamber 4 is arranged in the housing 1, and an air inlet window 5 is provided at the top of the first buffer chamber 4, and an optical window 3 is provided at the side thereof, so that characteristic gas can enter the first buffer chamber 4 from the air inlet window 5; A second buffer chamber 8 is disposed in the housing 1, and the second buffer chamber 8 is provided with an exhaust window 9 so that the characteristic gas can be discharged from the second buffer chamber 8 through the exhaust window 9; The resonant air chamber 6 is arranged between the first buffer chamber 4 and the second buffer chamber 8 to connect the first buffer chamber 4 and the second buffer chamber 8; A laser 2, the laser 2 is located at one side of the first buffer cavity 4 and outside the optical window 3, and provides laser light to generate a photoacoustic spectroscopy effect with the characteristic gas in the resonant gas chamber 6; The reflectors 12 include four reflectors 12, which are symmetrically arranged in pairs in the first buffer cavity 4 and the second buffer cavity 8, so that the laser emitted by the laser 2 is reflected by the four reflectors 12, thereby doubling the optical path of the laser signal; specifically, the first buffer cavity 4 is provided with two reflectors arranged opposite to each other, and the second buffer cavity 8 is provided with two reflectors arranged opposite to each other, and the reflectors 12 located in the first buffer cavity 4 and the reflectors 12 located in the second buffer cavity 8 are symmetrically arranged along the center line of the shell; the angle between the four reflectors 12 and the horizontal plane is 30-60°, and the angles between the four reflectors 12 and the horizontal plane are adjusted according to needs during use.

[0028] A photodetector 10, used to detect the optical signal of the photoacoustic spectroscopy effect; A microphone 7, located at the top of the resonant air chamber 6, for detecting the acoustic signal of the photoacoustic spectroscopy effect; The controller 11 is respectively connected to the laser 2, the photodetector 10, and the microphone 7, and is used to filter and amplify the electrical signal of the photodetector 10, and use the output end to perform negative feedback regulation on the laser 2 to ensure the stability of the light source output. At the same time, the detection signal obtained by the microphone 7 is processed to obtain the detection result of the characteristic gas.

[0029] When the characteristic gas enters the first buffer cavity 4, the resonant gas chamber 6 and the second buffer cavity 8 in sequence from the air inlet window 5, the laser emitted by the laser 2 is emitted into the first buffer cavity 4 through the optical window 3, and is reflected by four reflectors 12, so that the optical path of the laser signal is multiplied, and a photoacoustic effect is generated with the characteristic gas in the resonant gas chamber 6.

[0030] The shell 1 is made of a material with a larger wave impedance to make the photoacoustic cell, and the quality factor and the photoacoustic signal obtained under the same excitation are larger, such as pure iron, brass, and red copper, which are in the top three wave impedances. Brass is preferably used as the shell material of the photoacoustic cell, because its thermal conductivity is good enough, and the heat caused by the laser heating gas in the cell can be conducted out through the boundary, so that the temperature uniformity of the gas in the cavity is good enough, so as to have a larger quality factor.

[0031] The laser 2 is a tunable laser that combines a common laser with a certain tuning mechanism, so that the wavelength of the laser output can be adjusted within a certain range.

[0032] The optical window 3 is arranged in the first buffer cavity 4, so that the light source emitted by the laser can enter the gas chamber and produce a photoacoustic effect with the characteristic gas in the resonant gas chamber, thereby realizing photoacoustic spectrum detection of the characteristic gas; The optical window 3 is set according to the diameter of the light beam. In order to ensure the reliability of photoacoustic spectroscopy detection of characteristic gases, the diameter of the optical window should not exceed 90% of the light beam diameter. This design can ensure that the light beam will not have too much loss when passing through the optical window, and at the same time avoid the light beam being clipped in the aperture of the system, resulting in energy waste and possible damage.

[0033] The first buffer cavity 4 has an air inlet window at the upper end and an optical window at the left side. The characteristic gas enters the resonant gas chamber through the first buffer cavity, and the laser signal is incident on the resonant gas chamber through the optical window. The first buffer cavity and the second buffer cavity are symmetrically arranged on both sides of the resonant air chamber. The two buffer cavities should be arranged symmetrically. The symmetrical arrangement helps to obtain the maximum sound pressure signal at the characteristic frequency, thereby improving the sensitivity of photoacoustic spectroscopy detection.

[0034] Preferably, the first buffer cavity 4 and the second buffer cavity 8 are 70 mm long and 60 mm wide. The buffer cavity of this size can effectively reduce the acoustic background noise and improve the system signal-to-noise ratio. The design of rounded connection between the buffer cavity and the resonant cavity can reduce the noise impact caused by gas flow, thereby increasing the amplitude of the sound pressure signal and improving the detection sensitivity of the system.

[0035] The resonant air chamber 6 is connected to the first buffer chamber 4 and the second buffer chamber 8. The characteristic gas fills the first buffer chamber 4, the resonant air chamber 6 and the second buffer chamber 8 from the air inlet window 5 at the upper end of the first buffer chamber 4. The laser emitted by the laser 2 is injected into the resonant air chamber 6 through the optical window 3 set on the first buffer chamber 4. After being reflected by four reflectors 12, the optical path of the laser signal is doubled, and the laser signal and the characteristic gas in the resonant air chamber 6 produce a detectable photoacoustic effect.

[0036] There are two resonant air chambers 6, which are arranged up and down to form an upper resonant air chamber 6A and a lower resonant air chamber 6B. The two resonant cavities with exactly the same shape and size have the same noise. The incident laser signal is reflected by the reflector, which doubles the optical path of the laser signal and the photoacoustic signal, thereby improving the signal-to-noise ratio.

[0037] The microphone 7 is installed at the center of the outer side of the resonance air chamber and is level with the inner surface of the resonance air chamber to collect the sound signal generated by the photoacoustic effect in the resonance air chamber.

[0038] The second buffer chamber 8 is provided with an exhaust window 9 at the upper end, and the acoustic background noise can be reduced by the second buffer chamber 8. The first buffer chamber 4 and the second buffer chamber 8 are connected by the upper resonant air chamber 6A and the lower resonant air chamber 6B in a rounded corner connection manner to reduce the noise impact caused by the gas flow, thereby increasing the amplitude of the sound pressure signal and improving the detection sensitivity of the system.

[0039] The second buffer cavity 8 and the first buffer cavity 4 are completely consistent in size and shape.

[0040] The photodetector 10 is installed on the right side of the second buffer cavity 8, with its photosensitive surface facing the light output end of the photoacoustic cell. The photodetector 10 converts the received optical signal into an electrical signal and sends it to the controller 11 for data processing.

[0041] The controller 11 is connected to the laser 2, the microphone 7, and the photodetector 10, filters and amplifies the electrical signal received from the photodetector 10, and uses the output end to perform negative feedback regulation on the laser 2 to ensure the stability of the light source output; processes the detection signal transmitted by the microphone 7 to obtain the detection result of the characteristic gas.

[0042] Principle description: Based on the principle of the basic law of Beer-Lambert law: When a monochromatic light beam is irradiated on the surface of an absorbing medium, after passing through a medium of a certain thickness, the intensity of the transmitted light will be weakened because the medium absorbs part of the light energy. The greater the concentration of the absorbing medium and the greater the thickness of the medium, the more significant the weakening of the light intensity, and the relationship is:

[0043] in: A represents the absorbance of acetylene gas in the photoacoustic cell; Indicates the intensity of the incident light signal of the laser; Indicates the intensity of the light transmitted by acetylene gas in the photoacoustic cell; K represents the absorption coefficient of acetylene to laser signal in the photoacoustic cell; l represents the optical path length of the laser signal in the photoacoustic cell, usually in cm; c represents the concentration of acetylene gas in the photoacoustic cell, and the unit can be g / L or mol / L.

[0044] According to the above formula, the physical meaning of the Beer-Lambert law is that when a parallel monochromatic laser signal passes vertically through the acetylene gas in the photoacoustic cell, the absorbance A of the acetylene gas in the photoacoustic cell is proportional to the concentration c of the acetylene gas and the optical path l of the laser signal in the photoacoustic cell.

[0045] In order to improve the sensitivity of photoacoustic spectroscopy analysis of characteristic gases, reflectors are set at four relative positions in the buffer cavity. The installation angle of the reflectors meets the requirement of reflecting the laser signal to the next reflector. According to the Beer-Lambert law, the optical path of the laser signal is increased by adding reflectors, thereby increasing the absorbance of the characteristic gas and improving the sensitivity of photoacoustic spectroscopy detection of characteristic gases.

[0046] A certain concentration of acetylene gas is filled into the first buffer chamber 4 through the air inlet window 5. Under the action of air pressure, the acetylene gas gradually fills the resonance chamber 6 and the second buffer chamber 8. At this time, the exhaust window 9 is in a closed state. While the acetylene gas is filled into the air inlet window 5, the controller 11 adjusts the parameters of the laser 2 to emit a laser signal that meets the parameters of the resonance chamber and the absorption wavelength of the acetylene gas. The laser signal emitted by the laser 2 enters the air chamber through the optical window 3, enters the upper resonant air chamber 6A after passing through the first reflector 12 located near the laser 2, and is transmitted to the second reflector 12 located at the upper part of the second buffer chamber 8 through the upper resonant air chamber 6A. The laser signal reflected by the second reflector 12 is transmitted to the third reflector 12 located at the lower part of the second buffer chamber 8. The laser signal reflected by the third reflector 12 enters the lower resonant air chamber 6B, and the laser signal transmitted by the lower resonant air chamber 6B is transmitted to the fourth reflector 12 located at the upper part of the first buffer chamber 4. The laser signal reflected by the fourth reflector 12 is transmitted to the first reflector 12, and the laser signal is cyclically transmitted between the four reflectors 12. In this process, since the wavelength of the laser signal meets the absorption wavelength of acetylene gas, the laser signal and the acetylene gas generate a photoacoustic signal, which is picked up by the microphone 7, converted into an electrical signal and transmitted to the controller 11. The controller 11 processes and analyzes the signal transmitted by the microphone 7 and converts it into an electrical signal as follows: Figure 2 The method shown is presented to the user. During the continuous detection of acetylene gas, the photodetector 10 converts the received optical signal into an electrical signal and hands it over to the controller 11 for data processing. The controller 11 filters and amplifies the received electrical signal, and uses the output end to perform negative feedback regulation on the laser 2 to ensure the stability of the light source output. During the acetylene gas detection process, according to the Beer-Lambert law, the optical path of the laser signal is increased by adding a reflector, thereby increasing the absorbance of the characteristic gas and realizing the improvement of the sensitivity of the characteristic gas photoacoustic spectrum detection.

[0047] like Figure 3 and Figure 4 , the test curves generated by the low-sensitivity photoacoustic cell and the photoacoustic cell of this embodiment are compared under the same conditions, and it can be seen that the sensitivity is improved by 2.5 times. Comparison conditions: 0.01% acetylene gas is filled into the photoacoustic cell at a rate of 200 mL / min, the application pressure of the photoacoustic cell is controlled at normal pressure, and the temperature is controlled at 25°C.

[0048] Example 2 A detection method, using the extended-range resonant photoacoustic cell for acetylene detection of Example 1, comprises the following steps: Step 1, controlling the characteristic gas (acetylene gas) to enter the first buffer chamber 4 at a specific rate (for example, 200 mL / min) through a mass flow meter; the step 1 specifically includes: Step 1.1, adjust the angle of the reflector 12 so that the laser emitted by the light source returns along the resonant air chamber 6, while preventing the light from hitting the inner wall to reduce the noise introduced by absorption; In step 1.2, the photoacoustic cell is first filled with high-purity N2 for 5 minutes, and then filled with characteristic gas (acetylene gas with a volume fraction of 0.01%), and the rate is adjusted; the application pressure of the extended-range resonant photoacoustic cell for acetylene detection is adjusted to normal pressure conditions, and the temperature is controlled at room temperature (25°C).

[0049] Step 2, turn on the laser 2, send out a laser signal, and adjust the laser signal through the laser controller 11 and the function generator so that it can be absorbed by the characteristic gas (that is, the light beam is consistent with the absorption spectrum of the acetylene gas molecule); the specific process of step 2 is: Step 2.1, modulate the current injected into laser 2 by superimposing the triangular wave output by the function generator and the sine wave output by the phase-locked amplifier to obtain the modulation frequency, so that the wavelength of the output light source falls within the absorption peak range of the characteristic gas (acetylene absorption peak), and measure the photoacoustic signal multiple times to obtain the average value; the purpose of controlling the modulation frequency is to make the emitted light source better absorbed by acetylene gas and improve the detection sensitivity; modulate the light source frequency before the light source is emitted; Step 2.2, change the working temperature of laser 2 to adjust the resonance frequency, use the resonance acoustic spectrum method to measure the actual resonance frequency of the photoacoustic pool in real time, and realize the negative feedback regulation of the resonance frequency, so that the working frequency can be accurately adjusted to the standard frequency of laser 2 in real time.

[0050] Step 3, collecting the acoustic wave signal formed after the characteristic gas absorbs the laser signal and converts it; Step 4: demodulate the acoustic wave signal through a phase-locked amplifier, and then use an acquisition card to collect information to obtain the characteristic gas photoacoustic spectrum detection results. The specific process includes: Step 4.1, a reference signal is provided through a phase-locked amplifier, whose frequency is very close to the expected frequency of the acoustic signal and has a fixed phase relationship; after the reference signal is mixed with the acquired acoustic signal, a sum frequency and a difference frequency signal are generated through a mixer, and then the high-frequency component is filtered out through a low-pass filter, and the low-frequency difference frequency signal is retained, wherein the difference frequency signal contains the amplitude and phase information of the acoustic signal; Step 4.2, the amplitude and phase information of the acoustic wave signal are determined by measuring the amplitude and phase of the mixing signal through a phase-locked amplifier; in this process, the real component (X) and the imaginary component (Y) are extracted respectively, which correspond to the amplitude and phase information of the acoustic wave signal respectively.

[0051] Step 4.3, further amplify the generated difference frequency signal through an amplifier to enhance the strength of the detection signal and make it suitable for subsequent processing.

[0052] Step 4.4, the amplified difference frequency signal is converted into a digital signal through the data acquisition card. The signal processed by the phase-locked amplifier will be input into the data acquisition card (DAQ). The data acquisition card converts the analog signal into a digital signal so that it can be read and processed by the computer. The data acquisition card realizes the conversion of analog signals to digital signals through the analog-to-digital converter (ADC) and has a certain resolution and sampling rate to provide data accuracy and data points.

[0053] Step 4.5, after being processed by the algorithm in the controller 11, the amplitude and phase of the acoustic wave signal, i.e. the photoacoustic spectrum detection result, are obtained to extract useful information and perform final data analysis.

[0054] Among them, the algorithm in the controller processes the data collected by the data acquisition card as follows: S1: Based on the spectral characteristics of acetylene gas under the nitrogen background, spectral data containing the characteristic absorption peak of acetylene is simulated and simulated noise is added to simulate the data in the actual measurement process.

[0055] S2: Perform baseline correction on the simulated or actually collected spectral data to eliminate the baseline drift caused by instrument or environmental factors and ensure that the characteristic peak of acetylene gas is more obvious.

[0056] S3: Savitzky-Golay filtering noise reduction technology is used to smooth the data through polynomial fitting while retaining the shape of the acetylene characteristic peak to complete the processing of spectral data.

[0057] S4: Normalize the processed spectral data to standardize its numerical range to eliminate the range differences under different measurement conditions and facilitate subsequent quantitative analysis.

[0058] S5: Extract characteristic absorption peaks of acetylene gas from the normalized spectral data, and these characteristic peaks are associated with the concentration of acetylene gas.

[0059] S6: Based on the extracted characteristic absorption peak, a quantitative relationship model between acetylene gas concentration and absorption peak intensity is established to achieve accurate determination of acetylene gas concentration in oil.

[0060] S7: Output the concentration result of acetylene gas and compare it with the standard sample of known concentration to ensure the accuracy and reliability of the analysis result.

[0061] S8: The spectral data before and after processing and the analysis results of acetylene gas concentration are displayed in the form of charts to facilitate the observation and analysis of the detection effect of acetylene gas under the nitrogen background. The sound wave signal converted by the gas molecules in the photoacoustic cell after absorbing light energy is collected by a microphone installed in the center of the resonant cavity and flush with the cavity wall. The sensitivity of the microphone is 50 mV / Pa.

[0062] In the several embodiments provided in the present application, it should be understood that the disclosed devices and systems can be implemented in other ways. For example, the device embodiments described above are only schematic. For example, the division of the units is only a logical function division. There may be other division methods in actual implementation, such as multiple units or components can be combined or integrated into another system, or some features can be ignored or not executed. Another point is that the mutual coupling or direct coupling or communication connection shown or discussed can be through some interfaces, indirect coupling or communication connection of devices or units, which can be electrical, mechanical or other forms.

[0063] As described above, the above embodiments are only used to illustrate the technical solutions of the present invention, rather than to limit the same. Although the present invention has been described in detail with reference to the aforementioned embodiments, those skilled in the art should understand that the technical solutions described in the aforementioned embodiments may still be modified, or some of the technical features thereof may be replaced by equivalents. However, these modifications or replacements do not deviate the essence of the corresponding technical solutions from the spirit and scope of the technical solutions of the embodiments of the present invention.

Claims

1. An extended-range resonant photoacoustic cell for acetylene detection, characterized in that: It includes: shell; A first buffer chamber is arranged in the shell, and an air inlet window is provided at the top of the first buffer chamber and an optical window is provided at the side thereof, so that characteristic gas can enter the first buffer chamber through the air inlet window; A second buffer chamber is disposed in the housing, and the second buffer chamber is provided with an exhaust window so that the characteristic gas can be discharged from the second buffer chamber through the exhaust window; A resonant air chamber, disposed between the first buffer chamber and the second buffer chamber to connect the first buffer chamber and the second buffer chamber; A laser, the laser is located at one side of the first buffer cavity and outside the optical window, and provides laser light to generate a photoacoustic spectroscopy effect with a characteristic gas in the resonant gas chamber; Reflectors, wherein there are four reflectors, which are symmetrically arranged in pairs in the first buffer cavity and the second buffer cavity respectively, so that the laser emitted by the laser is reflected by the four reflectors, thereby doubling the optical path of the laser signal; A photodetector, used for detecting the optical signal of the photoacoustic spectroscopy effect, and for converting the optical signal into an electrical signal; A microphone, located on the top of the resonant air chamber, for detecting the acoustic signal of the photoacoustic spectroscopy effect; The controller is connected to the laser, photodetector and microphone respectively, and is used to filter and amplify the electrical signal generated by the photodetector, and to perform negative feedback regulation on the laser to ensure the stability of the light source output. At the same time, it processes the detection signal obtained by the microphone to obtain the detection result of the characteristic gas.

2. The extended-range resonant photoacoustic cell for acetylene detection according to claim 1, characterized in that: The first buffer cavity and the second buffer cavity are symmetrically arranged on both sides of the resonant air chamber.

3. The extended-range resonant photoacoustic cell for acetylene detection according to claim 1, characterized in that: There are two resonant air chambers, which are arranged up and down to form an upper resonant air chamber and a lower resonant air chamber.

4. The extended-range resonant photoacoustic cell for acetylene detection according to claim 3, characterized in that: The microphone is installed on the center line of the outer side of the resonance air chamber and is level with the inner surface of the upper resonance air chamber.

5. A detection method, using the extended-range resonant photoacoustic cell for acetylene detection according to any one of claims 1 to 4, comprising the following steps: Step 1, controlling characteristic gas to enter the extended-range resonant photoacoustic cell for acetylene detection; Step 2, sending out a laser signal, and adjusting the laser signal so that it can be absorbed by the characteristic gas; Step 3, collecting the acoustic wave signal formed after the characteristic gas absorbs the laser signal and converts it; Step 4: Process the acoustic wave signal to obtain characteristic gas photoacoustic spectrum detection results.

6. The detection method according to claim 5, characterized in that: The step 1 specifically includes: Step 1.1, adjust the angle of the reflector so that the laser emitted by the light source returns along the resonant gas chamber, while preventing the light from hitting the inner wall to reduce the noise introduced by absorption; Step 1.2, the photoacoustic cell is first filled with high-purity N2, then filled with characteristic gas, and the rate is adjusted; the application pressure of the extended-range resonant photoacoustic cell for acetylene detection is adjusted to be controlled at normal pressure conditions, and the temperature is controlled at normal temperature.

7. The detection method according to claim 5, characterized in that: Step 2 Specific process: Step 2.1, modulate the current injected into the laser by superimposing the triangular wave output by the function generator and the sine wave output by the phase-locked amplifier to obtain the modulation frequency, so that the wavelength of the output light source falls within the absorption peak range of the characteristic gas, and measure the photoacoustic signal multiple times to obtain the average value; Step 2.2, change the working temperature of the laser to adjust the resonance frequency, use the resonance acoustic spectrum method to measure the actual resonance frequency of the photoacoustic pool in real time, and realize negative feedback regulation of the resonance frequency.

8. The detection method according to claim 5, characterized in that: In step 4, the acoustic wave signal is demodulated by a lock-in amplifier, and the specific process includes: Step 4.1, a reference signal is provided through a phase-locked amplifier, and after the reference signal is mixed with the obtained sound wave signal, a sum frequency and a difference frequency signal are generated through a mixer, and then a high-frequency component is filtered out through a low-pass filter, and a low-frequency difference frequency signal is retained, wherein the difference frequency signal contains the amplitude and phase information of the sound wave signal; Step 4.2, measuring the amplitude and phase of the mixing signal by a lock-in amplifier to determine the amplitude and phase information of the acoustic wave signal; Step 4.3, further amplifying the generated difference frequency signal through an amplifier; Step 4.4, converting the amplified difference frequency signal into a digital signal; Step 4.5, after processing, the amplitude and phase of the sound wave signal are obtained.

Images