Linear light spot multi-pass optical fiber photoacoustic gas sensor for gas insulation equipment

Abstract

The invention discloses a linear light spot multi-pass optical fiber photoacoustic gas sensor for gas insulation equipment, belongs to the technical field of sensing and measuring of operation and maintenance of power transmission and transformation equipment, and solves the problems that an existing optical fiber photoacoustic trace gas detection instrument is large in size and not beneficial to miniaturization. Modulated excitation light of the sensor enters a rectangular gas chamber with a high-reflectivity plano-concave reflector, and is reflected for multiple times in the gas chamber to form linear light spot distribution, so that a photoacoustic signal is generated; the probe light reflected by the tail end of the cantilever beam etched on the sound wave sensitive cantilever beam diaphragm, the end face of the tail end of the single-mode optical fiber and the reflected probe light generate a Fabry-Perot interference effect, so that the concentration of the gas is detected; the volume of the rectangular air chamber is greatly reduced, so that the size of the whole sensing probe is reduced, and the sensor has the advantages of small volume, high sensitivity, intrinsic safety and the like.

Description

Technical Field

[0001] The invention belongs to the field of sensing and measuring technology for operation and maintenance of power transmission and transformation equipment, and relates to a linear light spot multi-pass optical fiber photoacoustic gas sensor for gas insulation equipment. Background Art

[0002] Intelligent sensing is the core technology of the power Internet of Things. Real-time monitoring of the operating status of electrical equipment is an important means to ensure the safe operation of the power grid. Gas-insulated equipment adopts a fully enclosed structural design and is filled with sulfur hexafluoride gas with excellent insulation and arc extinguishing performance. It can greatly reduce the size of high-voltage electrical equipment and increase the transmission capacity. It has become a key equipment for ultra-high voltage transmission and urban power grids. When overheating or discharge failure occurs inside the gas-insulated equipment, sulfur hexafluoride decomposes to form low-fluorine sulfides. These low-fluorine sulfides react chemically with electrodes, insulating materials, gas impurities and moisture to produce a variety of highly toxic and highly corrosive decomposition derivatives. Monitoring the concentration of decomposition derivatives can accurately analyze and provide early warning of the type and severity of latent faults inside gas-insulated equipment. Trace gas detection technology plays an important role in many fields with its high sensitivity, high selectivity and wide applicability. The detection of SF6 decomposition derivatives such as hydrogen sulfide (H2S) and carbon monoxide (CO) is of great significance.

[0003] Photoacoustic spectroscopy gas detection technology is an indirect absorption spectroscopy technology. A beam of excitation light with a frequency (wavelength) within the absorption spectrum of the target gas molecules is used to irradiate the gas to be tested. Some gas molecules will absorb the energy of the excitation light and transition to a high-energy state. The excited gas molecules return to a low-energy state in the form of a non-radiative transition, and this process is accompanied by the release of heat. When the excitation light source is modulated at a certain frequency, the release of heat presents the same cycle. When the gas in the gas chamber of the photoacoustic cell undergoes periodic thermal expansion, sound waves with an amplitude proportional to the concentration of the gas to be tested are generated. Since the photoacoustic spectroscopy technology detects the sound signal generated by the gas absorbing light energy, there is no need for the detector to receive the transmitted light, avoiding the influence of interference factors such as light scattering and reflection in traditional spectroscopy. It has the advantages of high sensitivity, high precision, no background, and a wide range of applicable gases.

[0004] Although the traditional resonant multi-pass photoacoustic cell has the advantages of more light reflection times and long gas absorption path, it has problems such as large size of photoacoustic sensor, large gas consumption and long response time. Therefore, how to reduce the volume of the photoacoustic cell and miniaturize the device is still a major challenge. Summary of the invention

[0005] The technical solution of the present invention is used to solve the problem that the current optical fiber photoacoustic trace gas detection instrument has a large volume and is not conducive to miniaturization.

[0006] The present invention solves the above technical problems through the following technical solutions:

[0007] The present invention provides a linear light spot multi-pass optical fiber photoacoustic gas sensor for gas-insulated equipment, comprising: a sensor body (10), an incident end cover (20), and an output end cover (30); the incident end cover (20) is fixed to the incident end of the sensor body (10), and the output end cover (30) is fixed to the output end of the sensor body (10);

[0008] A rectangular air chamber (101) is provided inside the sensor body (10), and two gas diffusion holes (102) are symmetrically provided on two side surfaces of the sensor body (10), wherein the gas diffusion holes (102) connect the outside of the sensor body (10) with the rectangular air chamber (101) inside the sensor body (10);

[0009] The incident end and the exit end of the rectangular air chamber (101) are respectively provided with an annular groove, a first plano-concave reflector (40) is installed in the groove of the incident end, an incident hole (401) is provided on the first plano-concave reflector (40), a second plano-concave reflector (50) is installed in the groove of the exit end, and the concave surfaces of the first plano-concave reflector (40) and the second plano-concave reflector (50) are opposite and both are arranged toward the rectangular air chamber (101).

[0010] The incident end cover (20) is provided with a fiber collimator mounting hole (201), the central axes of the fiber collimator mounting hole (201) and the incident hole (401) coincide with each other, and the central axes are aligned with the incident port of the rectangular air chamber (101); the incident end cover (20) is provided with a single-mode fiber pinhole (202) and a reflection cavity (203) in sequence from the outside to the inside, and a round-shaped sound wave sensitive cantilever beam diaphragm (60) is pasted on the end of the reflection cavity (203); the central axes of the single-mode fiber pinhole (202), the reflection cavity (203) and the sound wave sensitive cantilever beam diaphragm (60) coincide with each other, and the central axes are aligned with the incident port of the rectangular air chamber (101);

[0011] An elliptical observation hole (301) is provided on the emission end cover (30), and the central axes of the observation hole (301), the second plano-concave reflector (50), the rectangular air chamber (101) and the first plano-concave reflector (40) coincide with each other.

[0012] Furthermore, when in use, the optical fiber collimator is installed in the optical fiber collimator installation hole (201), and the single-mode optical fiber pin is installed in the single-mode optical fiber pin hole (202). The incident light beam of the modulated excitation light is incident into the rectangular air chamber (101) through the optical fiber collimator and the incident hole (401) in sequence. The first plano-concave reflector (40) and the second plano-concave reflector (50) arranged at both ends of the rectangular air chamber (101) reflect the incident light beam of the modulated excitation light back and forth multiple times in the rectangular air chamber (101) to form a linear light spot. The gas to be measured in the rectangular gas chamber (101) absorbs the modulated excitation light, generates a photoacoustic effect, causes periodic thermal expansion of the gas, and then generates an acoustic signal, thereby causing the acoustic wave sensitive cantilever beam diaphragm (60) to generate forced vibration; the detection light passes through the single-mode optical fiber pinhole (202) and the reflection cavity (203) in sequence, and the detection light reflected by the end of the cantilever beam etched on the acoustic wave sensitive cantilever beam diaphragm (60) generates a Fabry-Perot interference effect with the end face of the single-mode optical fiber and the reflected detection light, thereby detecting the concentration of the gas.

[0013] Furthermore, the surface of the acoustic wave sensitive cantilever beam diaphragm (60) is plated with gold.

[0014] Furthermore, the reflectivity of the first plano-concave reflector (40) and the second plano-concave reflector (50) are both higher than 98%.

[0015] Furthermore, the detection light adopts broadband detection light, and the central wavelength of the broadband detection light is 1550nm and the bandwidth is 45nm.

[0016] The advantages of the present invention are:

[0017] The modulated excitation light of the sensor of the present invention enters a rectangular air chamber with a high-reflectivity plano-concave reflector, generates multiple reflections in the air chamber to form a linear light spot distribution, and generates a photoacoustic signal; the detection light reflected by the end of the cantilever beam etched on the sound wave sensitive cantilever beam diaphragm and the end face of the single-mode optical fiber and the reflected detection light generate a Fabry-Perot interference effect, thereby detecting the concentration of the gas; the rectangular air chamber greatly reduces the volume of the air chamber, thereby reducing the size of the entire sensor probe, and the sensor of the present invention has the advantages of small size, high sensitivity, intrinsic safety, etc.; the excitation light and the detection light are both transmitted by optical fiber, realizing an all-optical gas detection method. BRIEF DESCRIPTION OF THE DRAWINGS

[0018] Figure 1 It is a front view of the three-dimensional structure of a linear spot multi-pass optical fiber photoacoustic gas sensor for gas-insulated equipment according to an embodiment of the present invention;

[0019] Figure 2 It is a three-dimensional structural explosion diagram of a linear spot multi-pass optical fiber photoacoustic gas sensor for gas-insulated equipment according to an embodiment of the present invention;

[0020] Figure 3 It is a three-dimensional structural front view of a sensor body of a linear spot multi-pass optical fiber photoacoustic gas sensor for gas-insulated equipment according to an embodiment of the present invention;

[0021] Figure 4 is a projection view of the yoz plane of the sensor body of the linear spot multi-pass optical fiber photoacoustic gas sensor for gas-insulated equipment according to an embodiment of the present invention;

[0022] Figure 5 It is a half-section top view along the xoy plane of a three-dimensional structure front view of a linear spot multi-pass optical fiber photoacoustic gas sensor for gas-insulated equipment according to an embodiment of the present invention;

[0023] Figure 6 It is a half-section oblique view along the xoy plane of a front view of a three-dimensional structure of a linear spot multi-pass optical fiber photoacoustic gas sensor for gas-insulated equipment according to an embodiment of the present invention;

[0024] Figure 7 1 is a front view of an incident end cap of a linear spot multi-pass optical fiber photoacoustic gas sensor for gas-insulated equipment according to an embodiment of the present invention;

[0025] Figure 8 1 is a front view of an output end cap of a linear spot multi-pass optical fiber photoacoustic gas sensor for gas-insulated equipment according to an embodiment of the present invention;

[0026] Fig. 9 It is a half-section front view of the installation and use of a linear spot multi-pass optical fiber photoacoustic gas sensor for gas-insulated equipment according to an embodiment of the present invention;

[0027] Fig.10 Schematic diagram of linear light spot distribution of a linear light spot multi-pass optical fiber photoacoustic gas sensor for gas-insulated equipment according to an embodiment of the present invention;

[0028] Fig.11 This is a comparison diagram of photoacoustic signal values ​​of multiple reflections and single reflections of a linear light spot of a linear light spot multi-pass optical fiber photoacoustic gas sensor for gas-insulated equipment according to an embodiment of the present invention;

[0029] Fig.12 A relationship curve between the photoacoustic signal value measured by the linear spot multi-pass optical fiber photoacoustic gas sensor for gas-insulated equipment according to an embodiment of the present invention and the change in acetylene gas concentration. DETAILED DESCRIPTION

[0030] In order to make the purpose, technical solution and advantages of the embodiments of the present invention clearer, the technical solution in the embodiments of the present invention will be clearly and completely described below in combination with the embodiments of the present invention. Obviously, the described embodiments are 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.

[0031] The technical solution of the present invention is further described below in conjunction with the accompanying drawings and specific embodiments:

[0032] Embodiment 1

[0033] like Figure 1 and Figure 2 As shown, a linear spot multi-pass optical fiber photoacoustic gas sensor for gas-insulated equipment according to an embodiment of the present invention comprises: a sensor body (10), an incident end cover (20), and an output end cover (30); the sensor body (10) is a rectangular parallelepiped structure, and the incident end cover (20) and the output end cover (30) are both block structures matching the sensor body (10).

[0034] like Figure 3 to Figure 4 As shown, a flat rectangular air chamber (101) is provided inside the sensor body (10), and two gas diffusion holes (102) are symmetrically provided on two side surfaces of the sensor body (10), wherein the gas diffusion holes (102) connect the outside of the sensor body (10) with the rectangular air chamber (101) inside the sensor body (10).

[0035] like Figures 5 and 6 As shown, the incident end and the exit end of the rectangular air chamber (101) are respectively provided with an annular groove, a first plano-concave reflector (40) in the shape of a circular cake is installed in the groove at the incident end, an incident hole (401) is provided on the first plano-concave reflector (40), and a second plano-concave reflector (50) in the shape of a circular cake is installed in the groove at the exit end, the size of the groove matches the first plano-concave reflector (40) and the second plano-concave reflector (50), and the concave surfaces of the first plano-concave reflector (40) and the second plano-concave reflector (50) are opposite and are both arranged toward the rectangular air chamber (101).

[0036] like Figure 5 , Figure 6 , Figure 7As shown, the incident end cover (20) is fixed to the incident end of the sensor body (10) by screws, and a fiber collimator mounting hole (201) is provided on the incident end cover (20), and the central axes of the fiber collimator mounting hole (201) and the incident hole (401) coincide with each other, and the central axes are aligned with the incident port of the rectangular air chamber (101); a single-mode fiber pinhole (202) and a reflection cavity (203) are provided on the incident end cover (20) in sequence from the outside to the inside, and a round sound wave sensitive cantilever beam diaphragm (60) is pasted on the end of the reflection cavity (203); the central axes of the single-mode fiber pinhole (202), the reflection cavity (203) and the sound wave sensitive cantilever beam diaphragm (60) coincide with each other, and the central axes are aligned with the incident port of the rectangular air chamber (101).

[0037] like Figure 5 , Figure 6 , Figure 8 As shown, the output end cover (30) is fixed to the output end of the sensor body (10) by screws, and an elliptical observation hole (301) is provided on the output end cover (30), and the central axes of the observation hole (301), the second plano-concave reflector (50), the rectangular air chamber (101) and the first plano-concave reflector (40) coincide with each other.

[0038] The working process of the linear spot multi-pass optical fiber photoacoustic gas sensor for gas-insulated equipment according to the embodiment of the present invention is as follows:

[0039] like Fig. 9 As shown, when in use, the optical fiber collimator is installed in the optical fiber collimator installation hole (201), and the single-mode optical fiber pin is installed in the single-mode optical fiber pin hole (202). The incident light beam of the modulated excitation light passes through the optical fiber collimator and the incident hole (401) in sequence and is incident into the rectangular air chamber (101). The first plano-concave reflector (40) and the second plano-concave reflector (50) arranged at both ends of the rectangular air chamber (101) reflect the incident light beam of the modulated excitation light back and forth multiple times in the rectangular air chamber (101) to form a linear light spot distribution. The gas to be measured in the rectangular gas chamber (101) absorbs the modulated excitation light, generates a photoacoustic effect, causes periodic thermal expansion of the gas, and then generates an acoustic signal, thereby causing the acoustic wave sensitive cantilever beam diaphragm (60) to generate forced vibration; the detection light passes through the single-mode optical fiber pinhole (202) and the reflection cavity (203) in sequence, and the detection light reflected by the end of the cantilever beam etched on the acoustic wave sensitive cantilever beam diaphragm (60) generates a Fabry-Perot interference effect with the end face of the single-mode optical fiber and the reflected detection light, thereby detecting the concentration of the gas.

[0040] Preferably, the detection light adopts broadband detection light, and the central wavelength of the broadband detection light is 1550nm and the bandwidth is 45nm.

[0041] Preferably, the surface of the acoustic wave sensitive cantilever beam diaphragm (60) is plated with gold.

[0042] Preferably, the reflectivity of the first plano-concave reflector (40) and the second plano-concave reflector (50) are both higher than 98%.

[0043] The principle of the present invention is as follows:

[0044] The modulated excitation light is incident into the rectangular gas chamber (101), and after multiple reflections and back and forth propagation, the absorbed light energy causes the gas to be measured in the rectangular gas chamber (101) to undergo periodic thermal expansion, thereby generating a photoacoustic signal. According to the Lambert-Beer absorption law, the photoacoustic signal generated by gas absorption in the non-resonant photoacoustic cell can be obtained as follows:

[0045] S PA =αP0CFM S (1)

[0046] In the formula, α is the absorption coefficient of the gas to be measured, P0 is the effective excitation light power, C is the concentration of the gas to be measured, F is the cell constant, and M s Indicates the sensitivity of the acoustic sensor;

[0047] The cell constant F can be expressed by the following equation:

[0048]

[0049] In the formula, C p and C v are the isobaric specific heat capacity and isovolumetric specific heat capacity, respectively; Q is the quality factor of acoustic resonance; l represents the interaction distance between the gas to be measured and the incident laser; S is the cross-sectional area of ​​the photoacoustic tube; v g Indicates the speed of sound.

[0050] It can be deduced from formulas (1) and (2) that by reducing the cross-sectional area of ​​the photoacoustic tube and increasing the interaction distance between the gas and the incident light, the cell constant can be increased, thereby increasing the photoacoustic signal value.

[0051] In the multi-pass structure, after N reflections, the light spot position distribution can be described by the following equation:

[0052] x N =Usin(NФ+a) (4)

[0053] y N =Vsin(NФ+b) (5)

[0054] Where U and V are the boundary values ​​of the light spot in the x and y directions, a and b are the initial phases of the light spot in the x and y directions, and Φ is a constant.

[0055] When the initial phase meets the following conditions:

[0056] a=b±π (6)

[0057] The spot distribution equation can be expressed as:

[0058]

[0059] Formula (7) indicates that the light spot on the reflector will be distributed in a straight line.

[0060] Experiment and simulation

[0061] like Fig.10 As shown, the linear spot distribution generated by the linear spot multi-pass optical fiber photoacoustic gas sensor for gas-insulated equipment of the present invention has a smaller beam propagation space, which reduces the volume of the rectangular gas chamber and satisfies the multiple reflection conditions. By changing the position and angle of the incident light, the light is restricted to propagate within the axial plane in the rectangular gas chamber, and the spot distribution on the plano-concave reflector appears as a straight line. Compared with the traditional elliptical spot distribution, the required transmission space is smaller, which can reduce the volume of the photoacoustic cell gas chamber.

[0062] like Fig.11 As shown, the linear spot multi-pass optical fiber photoacoustic gas sensor for gas-insulated equipment of the present invention is compared with the gas detection signal value of a single reflection. For the same gas concentration, the linear spot multiple reflection signal value is 12.4 times that of the single reflection signal.

[0063] like Fig.12 As shown, the linear spot multi-pass fiber optic photoacoustic gas sensor for gas-insulated equipment of the present invention measures the photoacoustic signals of gases with different concentrations. It can be seen that the photoacoustic signal value has a good linear relationship with the gas concentration and has a high sensitivity (slope), so that it can have a large detection range, and the lowest detectable gas concentration reaches the ppb level.

[0064] In summary, compared with the traditional elliptical spot distribution pattern, the linear spot multi-pass fiber optic photoacoustic gas sensor for gas-insulated equipment of the present invention requires a smaller light transmission space. Therefore, designing the air chamber cross-section into a rectangle can meet the multiple reflection conditions, further reducing the cross-sectional area of ​​the photoacoustic tube, thereby reducing the air chamber volume and increasing the amplitude of the photoacoustic signal.

[0065] 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 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. A linear spot multi-pass optical fiber photoacoustic gas sensor for gas-insulated equipment, characterized in that: include: A sensor body (10), an incident end cover (20), and an output end cover (30); the incident end cover (20) is fixed to the incident end of the sensor body (10), and the output end cover (30) is fixed to the output end of the sensor body (10); A rectangular air chamber (101) is provided inside the sensor body (10), and two gas diffusion holes (102) are symmetrically provided on two side surfaces of the sensor body (10), wherein the gas diffusion holes (102) connect the outside of the sensor body (10) with the rectangular air chamber (101) inside the sensor body (10); The incident end and the exit end of the rectangular air chamber (101) are respectively provided with an annular groove, a first plano-concave reflector (40) is installed in the groove of the incident end, an incident hole (401) is provided on the first plano-concave reflector (40), a second plano-concave reflector (50) is installed in the groove of the exit end, and the concave surfaces of the first plano-concave reflector (40) and the second plano-concave reflector (50) are opposite and are both arranged toward the rectangular air chamber (101); The incident end cover (20) is provided with a fiber collimator mounting hole (201), the central axes of the fiber collimator mounting hole (201) and the incident hole (401) coincide with each other, and the central axes are aligned with the incident port of the rectangular air chamber (101); the incident end cover (20) is provided with a single-mode fiber pinhole (202) and a reflection cavity (203) in sequence from the outside to the inside, and a round-shaped sound wave sensitive cantilever beam diaphragm (60) is pasted on the end of the reflection cavity (203); the central axes of the single-mode fiber pinhole (202), the reflection cavity (203) and the sound wave sensitive cantilever beam diaphragm (60) coincide with each other, and the central axes are aligned with the incident port of the rectangular air chamber (101); An elliptical observation hole (301) is provided on the emission end cover (30), and the central axes of the observation hole (301), the second plano-concave reflector (50), the rectangular air chamber (101) and the first plano-concave reflector (40) coincide with each other.

2. The linear spot multi-pass optical fiber photoacoustic gas sensor for gas-insulated equipment according to claim 1, characterized in that: When in use, the optical fiber collimator is installed in the optical fiber collimator installation hole (201), and the single-mode optical fiber pin is installed in the single-mode optical fiber pin hole (202). The incident light beam of the modulated excitation light is incident into the rectangular air chamber (101) through the optical fiber collimator and the incident hole (401) in sequence. The first plano-concave reflector (40) and the second plano-concave reflector (50) arranged at both ends of the rectangular air chamber (101) reflect the incident light beam of the modulated excitation light back and forth multiple times in the rectangular air chamber (101) to form a linear light spot distribution. The gas to be measured in the rectangular gas chamber (101) absorbs the modulated excitation light, generating a photoacoustic effect, causing periodic thermal expansion of the gas, thereby generating an acoustic signal, thereby causing the acoustic wave sensitive cantilever beam diaphragm (60) to generate forced vibration; the detection light passes through the single-mode optical fiber pinhole (202) and the reflection cavity (203) in sequence, and the detection light reflected by the end of the cantilever beam etched on the acoustic wave sensitive cantilever beam diaphragm (60) generates a Fabry-Perot interference effect with the end face of the single-mode optical fiber and the reflected detection light, thereby detecting the concentration of the gas.

3. The linear spot multi-pass optical fiber photoacoustic gas sensor for gas-insulated equipment according to claim 1, characterized in that: The surface of the acoustic wave sensitive cantilever beam diaphragm (60) is plated with gold.

4. The linear spot multi-pass optical fiber photoacoustic gas sensor for gas-insulated equipment according to claim 1, characterized in that: The reflectivity of the first plano-concave reflector (40) and the second plano-concave reflector (50) are both higher than 98%.

5. The linear spot multi-pass optical fiber photoacoustic gas sensor for gas-insulated equipment according to claim 2, characterized in that: The detection light adopts wide-spectrum detection light, and the central wavelength of the wide-spectrum detection light is 1550nm and the bandwidth is 45nm.

Images