An SF 6 Decomposition product monitoring fiber optic photoacoustic gas sensor, system and method

Abstract

An SF6 decomposition product monitoring fiber optic photoacoustic gas sensor, system and method, belonging to the technical field of fiber optic sensing and measurement for the operation and maintenance of power transmission and transformation equipment, solves the problem of large airflow noise commonly existing in existing SF6 decomposition product gas detection schemes. The present invention designs two identical photoacoustic resonance tubes. The photoacoustic signal amplitudes in the two photoacoustic resonance tubes are the same and the phases are opposite, while the amplitudes and phases of the incoherent noise in the tubes are the same. Two cantilever beam sensors for detecting photoacoustic signals installed in the mounting holes of the cantilever beam sensors form a differential dual-tube photoacoustic cell structure with the two photoacoustic resonance tubes, which is beneficial to suppressing the influence brought by airflow noise. The designed diversion tube helps to disperse the SF6 gas flow flowing into and out of the photoacoustic resonance tubes, making the SF6 gas flow flowing into and out of the photoacoustic resonance tubes smoother, avoiding the noise caused by excessive flow, and at the same time reducing the flow noise generated by turbulence and vortices during the gas flow process.

Description

Technical Field

[0001] The present invention belongs to the technical field of optical fiber sensing and measurement for the operation and maintenance of power transmission and transformation equipment, and relates to a fiber optic photoacoustic gas sensor, system and method for monitoring SF 6 decomposition products. Background Art

[0002] Sulfur hexafluoride gas (SF 6 ) has stable chemical properties and excellent insulation properties, which makes it an ideal insulation and arc extinguishing medium and is widely used in the field of gas insulated equipment. When there are impurities or trace water and oxygen in the gas insulated equipment, sulfur hexafluoride gas will decompose into various toxic or corrosive gases during operation through faults such as partial discharge or local overheating. By detecting the decomposition products of sulfur hexafluoride such as H 2 S, SO 2 , CO, HF, etc., the degradation of the internal insulation performance of the equipment can be detected in time, so as to take corresponding measures for maintenance and avoid the occurrence of accidents. Therefore, in order to ensure the long-term, reliable and fault-free operation of gas insulated equipment, it is necessary to monitor the insulation status of the equipment in real time online.

[0003] Photoacoustic spectroscopy has become the mainstream of gas detection technology, with advantages such as high sensitivity, good selectivity, no background and fast response. Target gas molecules absorb laser light of a specific wavelength, transition from a low energy state to a high energy state, and return to the low energy state through non-radiative transitions, and this process is accompanied by the release of heat. Modulate the excitation light source at a certain frequency, and the gas molecules will release the absorbed light energy periodically through heat, resulting in periodic thermal expansion of the gas and generating sound waves. Traditional electrical acoustic sensors have too much noise, while fiber optic acoustic sensors are immune to electromagnetic interference. Therefore, a fiber optic acoustic sensor can be used to pick up acoustic wave information and convert it into an optical signal, and the concentration information of the gas can be obtained from the optical signal through a demodulation system. The literature Detection of SF 6 gas decomposition component H 2 S based on fiber-optic photoacoustic sensing. Sensors and Actuators B: Chemical, 2023, 378: 133174. proposed a highly sensitive fiber optic Fabry-Perot (F-P) photoacoustic gas detection system with anti-electromagnetic interference and intrinsically safe characteristics for quantitative analysis of the sulfur hexafluoride decomposition component H 2 S. However, sulfur hexafluoride has special physical properties, which are mainly reflected in its high gas density, resulting in too much gas flow noise, making it impossible to monitor the sulfur hexafluoride decomposition products in real time online. Summary of the Invention

[0004] The technical solution of the present invention is used to solve the problem of large airflow noise commonly existing in the existing sulfur hexafluoride decomposition product gas detection solutions.

[0005] The present invention solves the above technical problems through the following technical solutions:

[0006] The present invention provides a fiber optic photoacoustic gas sensor for monitoring SF 6 decomposition products, including: an intake buffer chamber, a differential double-tube photoacoustic cell structure, and an exhaust buffer chamber; the open end of the intake buffer chamber is hermetically connected to one side of the differential double-tube photoacoustic cell structure, and the other side of the differential double-tube photoacoustic cell structure is hermetically connected to the open end of the exhaust buffer chamber; one end of the intake cavity of the intake buffer chamber is provided with an excitation light source fiber collimator mounting hole, the other end of the intake cavity is open, and the intake hole processed on one side of the intake buffer chamber communicates with the intake cavity; two identical first photoacoustic resonance tubes and second photoacoustic resonance tubes, as well as a plurality of diversion tubes, are processed inside the differential double-tube photoacoustic cell structure. Two cantilever beam sensor mounting holes are symmetrically processed at the central positions on both sides of the differential double-tube photoacoustic cell structure for mounting cantilever beam sensors. The cantilever beam sensors respectively abut against the outer walls of the first photoacoustic resonance tube and the second photoacoustic resonance tube; one end of the exhaust cavity of the exhaust buffer chamber is closed, the other end of the exhaust cavity is open, and the exhaust hole processed on one side of the exhaust buffer chamber communicates with the exhaust cavity.

[0007] Preferably, the diameter of the diversion tube is larger than the diameter of the first photoacoustic resonance tube or the second photoacoustic resonance tube.

[0008] Preferably, the first photoacoustic resonance tube and the second photoacoustic resonance tube are symmetrically arranged about the xoz plane.

[0009] Further, the fiber optic photoacoustic gas sensor for monitoring SF 6 decomposition products of the present invention further includes: a fiber collimator, and the fiber collimator is installed in the excitation light source fiber collimator mounting hole.

[0010] Further, the fiber optic photoacoustic gas sensor for monitoring SF 6 decomposition products of the present invention further includes: two single-mode optical fibers, and the two single-mode optical fibers are respectively connected to the cantilever beam sensors installed in the first cantilever beam sensor mounting hole and the second cantilever beam sensor mounting hole.

[0011] The present invention also provides a method applied to the above-mentioned fiber optic photoacoustic gas sensor for monitoring SF 6 decomposition products, including the following steps:

[0012] 1) SF 6The decomposition products enter the gas cavity through the air inlet hole, flow into the outlet cavity through the first photoacoustic resonance tube, the second photoacoustic resonance tube and the diversion tube in the differential dual-tube photoacoustic cell structure, and then flow out through the air outlet hole;

[0013] 2) The excitation light is incident into the intake cavity through the fiber optic collimator. The excitation light excites the SF 6 decomposition product gas molecules in the intake cavity. Photoacoustic pressure waves are formed during propagation in the first photoacoustic resonance tube and the second photoacoustic resonance tube, and the photoacoustic pressure waves cause the cantilever beam of the cantilever beam sensor to vibrate;

[0014] 3) The probe light is input from two single-mode optical fibers. A Fabry-Perot cavity is formed between the end faces of the two single-mode optical fibers and the cantilever beam of the cantilever beam sensor. The reflected light from the end face of the single-mode optical fiber interferes with the reflected light from the cantilever beam. An instrument is used to demodulate the interference spectrum, thereby detecting the SF 6 concentration of the decomposition product.

[0015] The present invention also provides an SF 6 decomposition product monitoring fiber optic photoacoustic gas sensor system, including: a detection light source, an optical fiber coupler, an excitation light source, a high-speed spectrometer, a signal processing circuit, and a computer; the excitation light source is connected to the fiber optic photoacoustic gas sensor through a fiber optic collimator, the detection light source is connected to the optical fiber coupler through an optical fiber, the optical fiber coupler is connected to the fiber optic photoacoustic gas sensor by using two single-mode optical fibers respectively, the output end of the optical fiber coupler is connected to the input end of the high-speed spectrometer, the output end of the high-speed spectrometer is connected to the input end of the signal processing circuit, and the output end of the signal processing circuit is connected to the input end of the computer.

[0016] Further, the working process is as follows: The excitation light emitted by the excitation light source is incident into the fiber optic photoacoustic gas sensor to excite the gas molecules to be measured. The detection light emitted by the detection light source passes through the optical fiber coupler and then enters the fiber optic photoacoustic gas sensor through two single-mode optical fibers respectively for differential detection. The detected differential interference spectrum signal is transmitted to the high-speed spectrometer through the optical fiber coupler. The differential interference spectrum signal is processed by the signal processing circuit, and the processing result is displayed in the computer.

[0017] Preferably, the wavelength range of the high-speed spectrometer is 1525 nm - 1570 nm, and the sampling frame rate is greater than 10 kHz.

[0018] Preferably, the detection light source uses a broadband detection light source.

[0019] The advantages of the present invention are:

[0020] The fiber optic photoacoustic gas sensor of the present invention is designed with two identical photoacoustic resonance tubes. The amplitudes of the photoacoustic signals in the two photoacoustic resonance tubes are the same, but the phases are opposite, while the amplitudes and phases of the incoherent noise in the tubes are the same. The two cantilever beam sensors for detecting photoacoustic signals installed in the mounting holes of the cantilever beam sensor and the first photoacoustic resonance tube and the second photoacoustic resonance tube form a differential dual-tube photoacoustic cell structure, which is beneficial to suppressing the influence brought by airflow noise. The designed diversion tube helps to disperse the flow rate of the SF 6 gas flowing into and out of the first photoacoustic resonance tube and the second photoacoustic resonance tube, so that the flow rate of the SF 6 gas flowing into and out of the first photoacoustic resonance tube and the second photoacoustic resonance tube is smoother, avoiding the noise caused by excessive flow rate, and at the same time reducing the flow noise generated by turbulence and vortices during the gas flow process. Description of the Drawings

[0021] Figure 1 is the three-dimensional front perspective view of the SF 6 decomposition product monitoring fiber optic photoacoustic gas sensor in the first embodiment of the present invention;

[0022] Figure 2 is the front perspective view of the SF 6 decomposition product monitoring fiber optic photoacoustic gas sensor in the first embodiment of the present invention;

[0023] Figure 3 is the rear perspective view of the SF 6 decomposition product monitoring fiber optic photoacoustic gas sensor in the first embodiment of the present invention;

[0024] Figure 4 is the left perspective view of the SF 6 decomposition product monitoring fiber optic photoacoustic gas sensor in the first embodiment of the present invention;

[0025] Figure 5 is the right perspective view of the SF 6 decomposition product monitoring fiber optic photoacoustic gas sensor in the first embodiment of the present invention;

[0026] Figure 6 is the bottom perspective view of the SF 6 decomposition product monitoring fiber optic photoacoustic gas sensor in the first embodiment of the present invention;

[0027] Figure 7 is the sectional perspective view of the SF 6 decomposition product monitoring fiber optic photoacoustic gas sensor in the first embodiment of the present invention along the xoy plane;

[0028] Figure 8 is the SF 6Front elevation perspective view of the sectional view of the decomposed product monitoring fiber optic photoacoustic gas sensor along the xoy plane;

[0029] Figure 9 is the SF of the first embodiment of the present invention 6 Oblique perspective view of the sectional view of the decomposed product monitoring fiber optic photoacoustic gas sensor along the yoz plane;

[0030] Figure 10 is the SF of the first embodiment of the present invention 6 Front elevation perspective view of the sectional view of the decomposed product monitoring fiber optic photoacoustic gas sensor along the yoz plane;

[0031] Figure 11 SF of the first embodiment of the present invention 6 Comparison diagram of the noise when the decomposed product monitoring fiber optic photoacoustic gas sensor and the traditional fiber optic photoacoustic gas sensor measure the SF 6 Flow noise of decomposed products;

[0032] Figure 12 is the SF of the second embodiment of the present invention 6 Structural block diagram of the decomposed product monitoring fiber optic photoacoustic gas sensing system. Detailed implementation manners

[0033] To make the objectives, technical solutions and advantages of the embodiments of the present invention clearer, the technical solutions in the embodiments of the present invention will be clearly and completely described below in conjunction with the embodiments of the present invention. Obviously, the described embodiments are part of the embodiments of the present invention, rather than all of the embodiments. All other embodiments obtained by those of ordinary skill in the art based on the embodiments of the present invention without creative efforts shall fall within the protection scope of the present invention.

[0034] The technical solutions of the present invention will be further described below in conjunction with the accompanying drawings of the specification and specific embodiments:

[0035] Embodiment 1

[0036] As Figures 1 to 10 shown, the SF of the embodiment of the present invention 6 The decomposed product monitoring fiber optic photoacoustic gas sensor includes: an intake buffer chamber 41, a differential dual-tube photoacoustic cell structure 42, and an outlet buffer chamber 43; the open end of the intake buffer chamber 41 is hermetically connected to one side of the differential dual-tube photoacoustic cell structure 42, and the other side of the differential dual-tube photoacoustic cell structure 42 is hermetically connected to the open end of the outlet buffer chamber 43.

[0037] The intake buffer chamber 41 is a cuboid structure, and a cylindrical intake cavity 411 is machined inside along the x-axis center line direction of the cuboid. One end of the intake cavity 411 is provided with an excitation light source fiber collimator mounting hole 44, and the other end of the intake cavity 411 is open. The excitation light source fiber collimator mounting hole 44 is used to mount the fiber collimator. The excitation light emitted by the excitation light source is incident into the intake cavity 411 through the fiber collimator. An intake hole 45 is machined on one side of the intake buffer chamber 41, and the intake hole 45 communicates with the intake cavity 411.

[0038] The differential dual-tube photoacoustic cell structure 42 is a cuboid structure. A first photoacoustic resonance tube 421, a second photoacoustic resonance tube 422, a first diversion tube 423, and a second diversion tube 424 are machined along the x-axis direction of the cuboid. The first photoacoustic resonance tube 421, the second photoacoustic resonance tube 422, the first diversion tube 423, and the second diversion tube 424 are parallel to each other. Among them, the first photoacoustic resonance tube 421 and the second photoacoustic resonance tube 422 are symmetric about the xoz plane left and right, and the first diversion tube 423 and the second diversion tube 424 are symmetric about the xoy plane up and down; the structural dimensions of the first photoacoustic resonance tube 421 and the second photoacoustic resonance tube 422 are exactly the same, and the structural dimensions of the first diversion tube 423 and the second diversion tube 424 are exactly the same; the diameters of the first diversion tube 423 and the second diversion tube 424 are larger than the diameters of the first photoacoustic resonance tube 421 and the second photoacoustic resonance tube 422. Preferably, the diameters of the first diversion tube 423 and the second diversion tube 424 are twice the diameters of the first photoacoustic resonance tube 421 and the second photoacoustic resonance tube 422.

[0039] At the central positions on both sides of the differential dual-tube photoacoustic cell structure 42, a first cantilever beam sensor mounting hole 47 and a second cantilever beam sensor mounting hole 48 are symmetrically machined respectively. The first cantilever beam sensor mounting hole 47 and the second cantilever beam sensor mounting hole 48 are both used to mount the cantilever beam sensor, and the cantilever beams of the cantilever beam sensors are respectively in contact with the outer walls of the first photoacoustic resonance tube 421 and the second photoacoustic resonance tube 422.

[0040] The exhaust buffer chamber 43 is a cuboid structure, and a cylindrical exhaust cavity 431 is machined inside along the x-axis center line direction of the cuboid. One end of the exhaust cavity 431 is closed, and the other end of the exhaust cavity 431 is open. An exhaust hole 46 is machined on one side of the exhaust buffer chamber 43, and the exhaust hole 46 communicates with the exhaust cavity 431.

[0041] The SF of the embodiment of the present invention 6 The detection process of the photoacoustic gas sensor for monitoring the decomposition products is as follows:

[0042] Install the fiber collimator in the excitation light source fiber collimator mounting hole 44, and use two single-mode fibers to connect to the cantilever beam sensors installed in the first cantilever beam sensor mounting hole 47 and the second cantilever beam sensor mounting hole 48 respectively;

[0043] SF 6 The decomposition products enter the gas cavity 411 from the air inlet hole 45, and flow into the outlet cavity 431 through the first photoacoustic resonance tube 421, the second photoacoustic resonance tube 422, the first diversion tube 423, and the second diversion tube 424 in the differential dual-tube photoacoustic cell structure 42, and then flow out through the air outlet hole 46;

[0044] The excitation light is incident into the intake cavity 411 through the fiber collimator, and the excitation light excites SF 6 decomposition product gas molecules in the intake cavity 411. The excitation light irradiates the gas molecules to be measured, and these gas molecules will absorb the light energy and convert it into heat energy. The energy conversion process causes the gas molecules to rapidly heat up, and then a small pressure change is generated in the intake cavity 411. This pressure fluctuation converted from light energy propagates in the first photoacoustic resonance tube 421 and the second photoacoustic resonance tube 422 to form a photoacoustic pressure wave. The photoacoustic pressure wave causes the cantilever beam of the cantilever beam sensor to vibrate. At this time, the detection light is input from the two single-mode fibers, and a Fabry-Perot cavity is formed between the end faces of the two single-mode fibers and the cantilever beam of the cantilever beam sensor. The reflected light from the end face of the single-mode fiber interferes with the reflected light of the cantilever beam. By demodulating the interference spectrum with an instrument, the concentration of the decomposition products of SF 6 can be detected.

[0045] The principle of reducing the airflow noise of the SF 6 decomposition product monitoring photoacoustic gas sensor according to the embodiment of the present invention is analyzed as follows:

[0046] First of all, the SF 6 decomposition product monitoring photoacoustic gas sensor according to the embodiment of the present invention is structurally designed with a first photoacoustic resonance tube 421 and a second photoacoustic resonance tube 422. Since the sizes and shapes of the two photoacoustic resonance tubes are exactly the same, the amplitudes of the photoacoustic signals in the two photoacoustic resonance tubes are the same and the phases are opposite, while the amplitudes and phases of the incoherent noise in the tubes are the same; the two cantilever beam sensors for detecting photoacoustic signals installed in the first cantilever beam sensor mounting hole 47 and the second cantilever beam sensor mounting hole 48 and the first photoacoustic resonance tube 421 and the second photoacoustic resonance tube 422 form a differential dual-tube photoacoustic cell structure, which is beneficial to suppressing the influence brought by the airflow noise.

[0047] Secondly, since the SF 6 gas has a higher density than air, this characteristic of high density and large molecular weight makes the SF 6 gas generate more noise when flowing due to more frequent and intense collisions between molecules. SF6 The flow rate of the gas also affects the magnitude of the gas flow noise. Generally speaking, the greater the flow rate, the more intense the collisions and frictions between gas molecules, and the greater the resulting airflow noise. Therefore, reducing the gas flow noise is the key to achieving real-time on-line monitoring of the SF 6 decomposition products; in response to this problem, the first diversion tube 423 and the second diversion tube 424 designed for the SF 6 decomposition product monitoring photoacoustic gas sensor of the present invention embodiment help to disperse the SF 6 gas flow rate flowing into and out of the first photoacoustic resonance tube 421 and the second photoacoustic resonance tube 422, so that the SF 6 gas flow rate flowing into and out of the first photoacoustic resonance tube 421 and the second photoacoustic resonance tube 422 is smoother, avoiding the noise caused by too large a flow rate, and at the same time reducing the flow noise generated by the turbulence and vortices during the gas flow process.

[0048] As Figure 11 shown, in the fiber optic photoacoustic gas sensor without a diversion tube, the one-standard deviation noise of the gas is measured to be approximately equal to 1.2 pm, while after adding the diversion tube, the measured one-standard deviation noise can be reduced to approximately 0.17 pm, greatly reducing the flow noise.

[0049] Embodiment 2

[0050] As Figure 12 shown, the SF 6 decomposition product monitoring fiber optic photoacoustic gas sensing system of the present invention embodiment includes: a detection light source 1, an optical fiber coupler 2, an excitation light source 3, a fiber optic photoacoustic gas sensor 4, a high-speed spectrometer 5, a signal processing circuit 6, and a computer 7; the excitation light source 3 is connected to the fiber optic photoacoustic gas sensor 4 through an optical fiber collimator, the detection light source 1 is connected to the optical fiber coupler 2 through an optical fiber, the optical fiber coupler 2 is connected to the fiber optic photoacoustic gas sensor 4 respectively by two single-mode optical fibers, the output end of the optical fiber coupler 2 is connected to the input end of the high-speed spectrometer 5, the output end of the high-speed spectrometer 5 is connected to the input end of the signal processing circuit 6, and the output end of the signal processing circuit 6 is connected to the input end of the computer 7.

[0051] Preferably, the wavelength range of the high-speed spectrometer 5 is 1525 nm - 1570 nm, and the sampling frame rate is greater than 10 kHz; the detection light source 1 uses a broadband detection light source.

[0052] The working process of the SF 6 decomposition product monitoring fiber optic photoacoustic gas sensing system of the present invention embodiment is as follows:

[0053] The excitation light emitted by the excitation light source 3 is incident on the fiber optic photoacoustic gas sensor 4 to excite the gas molecules to be measured. After the detection light emitted by the detection light source 1 passes through the fiber optic coupler 2, it enters the fiber optic photoacoustic gas sensor 4 through two single-mode optical fibers respectively for differential detection. The detected differential interference spectral signal is transmitted to the high-speed spectrometer 5 through the fiber optic coupler 2, and the differential interference spectral signal is processed by the signal processing circuit 6, and the processing result is displayed in the computer 7.

[0054] The above embodiments are only used to illustrate the technical solutions of the present invention, rather than to limit it; although the present invention has been described in detail with reference to the foregoing embodiments, those of ordinary skill in the art should understand that: they can still modify the technical solutions recorded in the foregoing embodiments, or perform equivalent replacements on some of the technical features; and these modifications or replacements do not make the essence of the corresponding technical solutions deviate from the spirit and scope of the technical solutions of the embodiments of the present invention.

Claims

1. A fiber optic photoacoustic gas sensor for monitoring SF6 decomposition products, characterized in that: The open end of the air inlet buffer chamber is sealed and connected to one side of the differential double-tube photoacoustic pool structure, and the other side of the differential double-tube photoacoustic pool structure is sealed and connected to the open end of the air outlet buffer chamber; an excitation light source fiber collimator mounting hole is provided at one end of the air inlet cavity of the air inlet buffer chamber, and the other end of the air inlet cavity is open, and an air inlet hole processed on one side of the air inlet buffer chamber is connected to the air inlet cavity; two identical first and second photoacoustic resonance tubes and a plurality of guide tubes are processed in the differential double-tube photoacoustic pool structure, and the plurality of guide tubes are connected to the first and second photoacoustic resonance tubes. The second photoacoustic resonance tube is arranged in parallel, and two mounting holes for installing cantilever beam sensors are symmetrically processed at the center positions on both sides of the differential double-tube photoacoustic pool structure. The cantilever beam sensors are respectively abutted against the outer walls of the first photoacoustic resonance tube and the second photoacoustic resonance tube. The two cantilever beam sensors and the first and second photoacoustic resonance tubes constitute a differential double-tube photoacoustic pool structure; one end of the air outlet cavity of the air outlet buffer chamber is closed, and the other end of the air outlet cavity is open, and the air outlet hole processed on one side of the air outlet buffer chamber is connected to the air outlet cavity.

2. The optical fiber photoacoustic gas sensor for monitoring SF6 decomposition products according to claim 1 is characterized in that: The diameter of the flow guide tube is larger than the diameter of the first photoacoustic resonance tube or the second photoacoustic resonance tube.

3. The optical fiber photoacoustic gas sensor for monitoring SF6 decomposition products according to claim 1, characterized in that: The first photoacoustic resonance tube and the second photoacoustic resonance tube are arranged symmetrically with respect to the xoz plane.

4. The optical fiber photoacoustic gas sensor for monitoring SF6 decomposition products according to claim 1, characterized in that: Also includes: The optical fiber collimator is installed in the optical fiber collimator installation hole of the excitation light source.

5. The optical fiber photoacoustic gas sensor for monitoring SF6 decomposition products according to claim 1, characterized in that: The two single-mode optical fibers are respectively connected to the cantilever beam sensors installed in the first cantilever beam sensor installation hole and the second cantilever beam sensor installation hole.

6. A method for detecting the concentration of SF6 decomposition products using the SF6 decomposition product monitoring optical fiber photoacoustic gas sensor according to any one of claims 1 to 5, characterized in that: The following steps are involved: 1) SF6 decomposition products enter the gas cavity from the air inlet, flow into the gas outlet cavity through the first photoacoustic resonance tube, the second photoacoustic resonance tube and the guide tube in the differential double-tube photoacoustic cell structure, and then flow out through the air outlet; 2) The excitation light is incident into the air inlet cavity through the optical fiber collimator. The excitation light excites the gas molecules of the SF6 decomposition product in the air inlet cavity, propagates in the first photoacoustic resonance tube and the second photoacoustic resonance tube to form a photoacoustic pressure wave, which causes the cantilever beam of the cantilever beam sensor to vibrate; 3) The detection light is input from two single-mode optical fibers. The end faces of the two single-mode optical fibers and the cantilever beam of the cantilever beam sensor form a Fabry-Perot cavity. The reflected light from the end faces of the single-mode optical fibers interferes with the reflected light from the cantilever beam. The interference spectrum is demodulated by an instrument to detect the concentration of SF6 decomposition products.

7. An optical fiber photoacoustic gas sensing system for monitoring SF6 decomposition products, characterized in that: include: A detection light source, a fiber optic coupler, an excitation light source, a high-speed spectrometer, a signal processing circuit, and a computer; the excitation light source is connected to the fiber optic photoacoustic gas sensor according to any one of claims 1 to 5 through a fiber optic collimator, the detection light source is connected to the fiber optic coupler through an optical fiber, the fiber optic coupler uses two single-mode optical fibers to be respectively connected to the fiber optic photoacoustic gas sensor, the output end of the fiber optic coupler is connected to the input end of the high-speed spectrometer, the output end of the high-speed spectrometer is connected to the input end of the signal processing circuit, and the output end of the signal processing circuit is connected to the input end of the computer.

8. The optical fiber photoacoustic gas sensing system for monitoring SF6 decomposition products according to claim 7 is characterized in that: The working process is as follows: the excitation light emitted by the excitation light source is incident on the fiber optic photoacoustic gas sensor to excite the gas molecules to be measured. The detection light emitted by the detection light source passes through the fiber optic coupler and then enters the fiber optic photoacoustic gas sensor through two single-mode optical fibers for differential detection. The detected differential interference spectrum signal is transmitted to the high-speed spectrometer through the fiber optic coupler. The differential interference spectrum signal is processed by the signal processing circuit, and the processing result is displayed on the computer.

9. The optical fiber photoacoustic gas sensing system for monitoring SF6 decomposition products according to claim 7, characterized in that: The wavelength range of the high-speed spectrometer is 1525nm-1570nm, and the sampling frame rate is greater than 10kHz.

10. The optical fiber photoacoustic gas sensing system for monitoring SF6 decomposition products according to claim 7, characterized in that: The detection light source adopts a broadband detection light source.

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