CN114076737B - Distributed online monitoring system and method based on optical fiber photoacoustic sensing - Google Patents
Distributed online monitoring system and method based on optical fiber photoacoustic sensing Download PDFInfo
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- 239000013307 optical fiber Substances 0.000 title claims abstract description 269
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- 230000005284 excitation Effects 0.000 claims abstract description 48
- 230000003287 optical effect Effects 0.000 claims description 73
- 239000004065 semiconductor Substances 0.000 claims description 34
- 239000012528 membrane Substances 0.000 claims description 29
- 238000001228 spectrum Methods 0.000 claims description 29
- 230000008859 change Effects 0.000 claims description 14
- 239000000835 fiber Substances 0.000 claims description 8
- 238000012545 processing Methods 0.000 claims description 5
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- 230000002269 spontaneous effect Effects 0.000 claims description 2
- 230000007704 transition Effects 0.000 description 8
- 238000010586 diagram Methods 0.000 description 5
- 230000000737 periodic effect Effects 0.000 description 5
- 238000003491 array Methods 0.000 description 4
- 230000005540 biological transmission Effects 0.000 description 4
- 238000004867 photoacoustic spectroscopy Methods 0.000 description 4
- 238000010521 absorption reaction Methods 0.000 description 3
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- 230000035945 sensitivity Effects 0.000 description 3
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- 230000005283 ground state Effects 0.000 description 2
- 238000003199 nucleic acid amplification method Methods 0.000 description 2
- 238000005070 sampling Methods 0.000 description 2
- 239000010963 304 stainless steel Substances 0.000 description 1
- 229910000589 SAE 304 stainless steel Inorganic materials 0.000 description 1
- 230000008602 contraction Effects 0.000 description 1
- 238000000295 emission spectrum Methods 0.000 description 1
- 230000007613 environmental effect Effects 0.000 description 1
- 230000005281 excited state Effects 0.000 description 1
- 238000005259 measurement Methods 0.000 description 1
- 238000012986 modification Methods 0.000 description 1
- 230000004048 modification Effects 0.000 description 1
- 238000010895 photoacoustic effect Methods 0.000 description 1
- 230000004044 response Effects 0.000 description 1
- 239000007787 solid Substances 0.000 description 1
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- 230000001360 synchronised effect Effects 0.000 description 1
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- G—PHYSICS
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- G01N—INVESTIGATING OR ANALYSING MATERIALS BY DETERMINING THEIR CHEMICAL OR PHYSICAL PROPERTIES
- G01N21/00—Investigating or analysing materials by the use of optical means, i.e. using sub-millimetre waves, infrared, visible or ultraviolet light
- G01N21/17—Systems in which incident light is modified in accordance with the properties of the material investigated
- G01N21/1702—Systems in which incident light is modified in accordance with the properties of the material investigated with opto-acoustic detection, e.g. for gases or analysing solids
- G01N2021/1704—Systems in which incident light is modified in accordance with the properties of the material investigated with opto-acoustic detection, e.g. for gases or analysing solids in gases
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Abstract
The invention discloses a distributed on-line monitoring system and a method based on optical fiber photoacoustic sensing, wherein the system comprises a plurality of groups of excitation light source devices with different wave bands, a group of detection light source devices, an optical fiber array and a plurality of groups of optical fiber photoacoustic sensing probes, wherein the laser light source devices emit laser light sources, the detection light source devices emit photoacoustic excitation light sources, each group of optical fiber photoacoustic sensing probes are arranged in different monitoring areas, one end of each group of optical fiber photoacoustic sensing probes is respectively connected with each excitation light source device through the optical fiber array, and the other end of each group of optical fiber photoacoustic sensing probes is respectively connected with the detection light source device through the optical fiber array; one group of the laser beams comprises a laser light source and a collimating lens, and the laser beams emitted by the laser light source are converged by the collimating lens and are coupled into the optical fiber array in a beam splitting way; the invention has the advantages that: the excitation light sources are more, the application scene is not limited, and the condition that the detection requirement of multi-component gas exists is met.
Description
Technical Field
The invention relates to the technical field of optical fiber acoustic wave sensing and photoacoustic spectroscopy, in particular to a distributed online monitoring system and method based on optical fiber photoacoustic sensing.
Background
The photoacoustic spectroscopy technology has become an effective means in the field of trace gas detection, and has the advantages of high sensitivity, no background detection, high response speed, no electromagnetic interference and the like. The main principle is based on the selective absorption of gas molecules and lambert-beer law, and the photoacoustic effect of gas can be mainly explained by three steps: 1. the gas molecules absorb the excitation light with a specific wavelength and transition from a ground state to an excitation state; 2. the excited state molecules transition back to the ground state without radiation, releasing heat, causing the surrounding gas to expand; 3. when the excitation light is modulated by a periodic signal, the gas also forms sound waves in a periodic expansion and contraction manner, the sound waves are detected by the microphone, and the detected photoacoustic signal and the gas concentration are in direct proportion. Therefore, improving the sensitivity of the microphone is an effective means for improving the sensitivity of the photoacoustic spectroscopy gas detection system. The optical fiber acoustic wave sensing is a new acoustic wave detection technology, and the basic principle is that light is used as a detection signal, and the change of physical quantities such as external temperature, strain, pressure and the like is sensed through an acoustic wave sensitive membrane and is reflected into the change of optical parameters, so that the detection of the external physical quantities is realized. The mode has the advantages of electromagnetic interference resistance, long-distance measurement, distributed detection and the like. The photoacoustic spectroscopy technology and the optical fiber acoustic wave sensing technology are combined to realize accurate detection of trace gas, and the method has the advantages of being passive and miniature, and is very suitable for gas detection in some narrow areas or in the special field of large-scale transformer equipment, such as serious electromagnetic interference, unlike other photoacoustic gas detection systems. Document Chen Ke, guo Min, liu shi, et al fiber-optic photoacoustic sensor for remote monitoring of gas micro-leakage J. Optics express,2019,27 (4): 4648-4659 reports a miniature optical fiber photoacoustic gas sensor, laser light is transmitted to a photoacoustic probe through an optical fiber to excite a photoacoustic signal, and the photoacoustic signal is detected by broad spectrum light to obtain a gas concentration. However, this method has the limitation of single excitation light source and fixed application scene, and cannot meet the requirement of multi-component gas detection.
Disclosure of Invention
The invention aims to solve the technical problems that the optical fiber photoacoustic sensing scheme in the prior art has the limitations of single excitation light source and fixed application scene, and cannot meet the condition of multi-component gas detection requirement.
The invention solves the technical problems by the following technical means: the distributed on-line monitoring system based on optical fiber photoacoustic sensing comprises a plurality of groups of excitation light source devices with different wavebands, a group of detection light source devices, an optical fiber array (15) and a plurality of groups of optical fiber photoacoustic sensing probes, wherein the laser light source devices emit photoacoustic excitation light sources, the detection light source devices emit wide-spectrum light for detecting photoacoustic signals, each group of optical fiber photoacoustic sensing probes are arranged in different monitoring areas, one end of each group of optical fiber photoacoustic sensing probes is respectively connected with each excitation light source device through the optical fiber array (15), and the other end of each group of optical fiber photoacoustic sensing probes is respectively connected with the detection light source devices through the optical fiber array (15); one of the excitation light source devices with different wave bands comprises a laser light source (5) and a collimating lens (17), the laser light source (5) emits laser beams with specific wavelengths, the laser beams are converged and coupled into the input ends of the optical fiber array (15) in a splitting way through the collimating lens (17), and the output ends of the optical fiber array (15) are connected with one end of each group of optical fiber photoacoustic sensing probes in a one-to-one correspondence mode.
According to the invention, the multiplex of the excitation light sources with different wave bands can realize the detection of multi-component gas, each group of optical fiber photoacoustic sensing probes are arranged in different monitoring areas, the gas detection of one monitoring area or the gas time-sharing detection of a plurality of monitoring areas is realized by selectively switching on one monitoring area or switching on the optical fiber photoacoustic sensing probes corresponding to the plurality of monitoring areas in a time-sharing manner, the whole system performs distributed detection, the excitation light sources are more, the application scene is not limited, and the condition that the detection requirement of multi-component gas exists is met.
Further, another group of the excitation light source devices with different wave bands comprises a laser driving circuit (16), a first semiconductor laser (1), an erbium-doped fiber amplifier (4) and a first optical switch (6), the laser driving circuit (16) drives the first semiconductor laser (1) to emit laser with specific wavelength into the erbium-doped fiber amplifier (4), the erbium-doped fiber amplifier (4) amplifies the optical power, the amplified laser enters the first optical switch (6), each output channel of the first optical switch (6) is connected with an input port of an optical fiber array (15) in a one-to-one correspondence mode, and each output end of the optical fiber array (15) is connected with one end of each group of optical fiber photoacoustic sensing probes in a one-to-one correspondence mode.
Still further, another group of the excitation light source devices with different wave bands further comprises a second semiconductor laser (2) and a second optical switch (3), the laser driving circuit (16) drives the first semiconductor laser (1) and the second semiconductor laser (2) to emit laser with specific wavelengths, the laser is transmitted to the second optical switch (3) through optical fibers respectively, and the second optical switch (3) controls the opening and the closing of two optical paths to enable one of the laser to enter the erbium-doped optical fiber amplifier (4).
Further, the detection light source device comprises an optical fiber broad spectrum light source (7), an optical fiber circulator (8), a third optical switch (9), a spectrometer (10) and an industrial personal computer (11), broadband light emitted by the optical fiber broad spectrum light source (7) is incident to the third optical switch (9) through the optical fiber circulator (8), output channels of the third optical switch (9) are respectively connected with the other ends of the optical fiber photoacoustic sensing probes in one-to-one correspondence, interference spectrums generated in the optical fiber photoacoustic sensing probes are returned to the third optical switch (9) from the optical fiber array (15) and are output to the spectrometer (10) through the optical fiber circulator (8), and the industrial personal computer (11) collects spectrums detected by the spectrometer (10) and performs signal processing and display.
Still further, the signal processing and display includes: demodulating the spectrum by adopting a high-speed spectrum demodulation method to obtain the dynamic cavity length of the interference cavity, obtaining the amplitude of the photoacoustic signal by measuring the cavity length change of the interference cavity, and obtaining and displaying the gas concentration according to the proportional relation between the amplitude of the photoacoustic signal and the gas concentration.
Further, the number of the optical fiber photoacoustic sensing probes is 3, namely a first optical fiber photoacoustic sensing probe (12), a second optical fiber photoacoustic sensing probe (13) and a third optical fiber photoacoustic sensing probe (14), the number of output ends of the optical fiber array (15) is greater than or equal to the number of the optical fiber photoacoustic sensing probes, and the first optical fiber photoacoustic sensing probe (12), the second optical fiber photoacoustic sensing probe (13) and the third optical fiber photoacoustic sensing probe (14) are respectively connected with one output end of the optical fiber array (15).
Furthermore, the first optical fiber photoacoustic sensing probe (12), the second optical fiber photoacoustic sensing probe (13) and the third optical fiber photoacoustic sensing probe (14) have the same structure and comprise an acoustic wave sensitive membrane (18), an air chamber (19), an optical fiber end face (20), an optical fiber collimator (21) and a shell (22), wherein the optical fiber end face (20) and the optical fiber collimator (21) are arranged in the shell (22) in parallel, the optical fiber end face (20) and the optical fiber collimator (21) have the same shape, one end of the optical fiber end face (20) extends out of the shell (22) to extend out of one optical fiber probe to be connected with a detection light source device through an optical fiber array (15), and one end of the optical fiber collimator (21) extends out of the shell (22) to be connected with an excitation light source device through the optical fiber array (15); the air chamber (19) comprises an optical acoustic tube and an air guide channel, wherein one end of the optical acoustic tube is horizontally arranged and is connected with the other end of the optical collimator (21), the air guide channel is vertically arranged, the upper end of the air guide channel is communicated with the other end of the optical acoustic tube, the lower end of the air guide channel is connected with the other end of the optical fiber end face (20), the right side of the air guide channel is provided with an acoustic wave sensitive membrane (18) in parallel, the acoustic wave sensitive membrane (18) is used as the right side face of the shell (22), the acoustic wave sensitive membrane (18) is provided with a cantilever structure, the cantilever structure is a rectangular groove with the free end facing downwards, and outside air to be detected is diffused into the air chamber (19) through a slot of the cantilever structure on the acoustic wave sensitive membrane (18).
Furthermore, the photoacoustic excitation light source is incident into the air chamber (19) through the optical fiber collimator (21) to excite a photoacoustic signal, and is detected by the acoustic wave sensitive membrane (18) arranged on the outer side of the air chamber (19), the free end of the cantilever beam structure of the acoustic wave sensitive membrane (18) and the optical fiber end face (20) form an optical fiber Fabry-Perot interference cavity, the photoacoustic signal enables the cantilever beam structure to vibrate to cause the length change of the Fabry-Perot interference cavity, and the detection of the photoacoustic signal is realized by detecting the cavity length change of the interference cavity.
The invention also provides a method for the distributed on-line monitoring system based on optical fiber photoacoustic sensing, wherein a plurality of groups of excitation light source devices with different wave bands respectively emit laser light sources with different wave bands, one wave band of laser light source detects a gas, one group of excitation light source devices is selectively connected or the plurality of groups of excitation light source devices are connected in a time-sharing manner to realize gas detection or multicomponent gas time-sharing detection, each group of optical fiber photoacoustic sensing probes is arranged in different monitoring areas, and one monitoring area or the optical fiber photoacoustic sensing probes corresponding to the plurality of monitoring areas are selectively connected in a time-sharing manner to realize gas detection of the monitoring area or gas time-sharing detection of the monitoring areas.
The invention has the advantages that:
(1) According to the invention, the multiplex of the excitation light sources with different wave bands can realize the detection of multi-component gas, each group of optical fiber photoacoustic sensing probes are arranged in different monitoring areas, the gas detection of one monitoring area or the gas time-sharing detection of a plurality of monitoring areas is realized by selectively switching on one monitoring area or switching on the optical fiber photoacoustic sensing probes corresponding to the plurality of monitoring areas in a time-sharing manner, the whole system performs distributed detection, the excitation light sources are more, the application scene is not limited, and the condition that the detection requirement of multi-component gas exists is met.
(2) The excitation light and the detection light of the photoacoustic signal are transmitted by the optical fiber, and the whole sensing structure does not contain an electrical element and has the electromagnetic interference resistance; and meanwhile, the long-distance transmission and low transmission loss characteristics of the optical fiber can realize long-distance telemetry. The detection mode is suitable for gas detection in the fields of transformers, environmental monitoring, safety monitoring and the like, and is a general monitoring system.
Drawings
Fig. 1 is a schematic structural diagram of a distributed online monitoring system based on optical fiber photoacoustic sensing disclosed in embodiment 1 of the present invention;
fig. 2 is a schematic structural diagram of an optical fiber photoacoustic sensing probe in a distributed online monitoring system based on optical fiber photoacoustic sensing disclosed in embodiment 1 of the present invention;
fig. 3 is a front view of a right side view, i.e., a cantilever structure, of an optical fiber photoacoustic sensing probe in the distributed online monitoring system based on optical fiber photoacoustic sensing disclosed in embodiment 1 of the present invention;
fig. 4 is a schematic structural diagram of a distributed online monitoring system based on optical fiber photoacoustic sensing disclosed in embodiment 2 of the present invention;
fig. 5 is a schematic structural diagram of a distributed online monitoring system based on optical fiber photoacoustic sensing disclosed in embodiment 3 of the present invention;
fig. 6 is a schematic structural diagram of a distributed online monitoring system based on optical fiber photoacoustic sensing disclosed in embodiment 4 of the present invention.
Detailed Description
For the purpose of making the objects, technical solutions and advantages of the embodiments of the present invention more apparent, the technical solutions in the embodiments of the present invention will be clearly and completely described in the following in conjunction with the embodiments of the present invention, and it is apparent that the described embodiments are some embodiments of the present invention, but not all embodiments. All other embodiments, which can be made by those skilled in the art based on the embodiments of the invention without making any inventive effort, are intended to be within the scope of the invention.
Example 1
As shown in fig. 1, a distributed online monitoring system based on optical fiber photoacoustic sensing includes multiple groups of excitation light source devices with different wavebands, a group of detection light source devices, an optical fiber array 15 and multiple groups of optical fiber photoacoustic sensing probes, wherein the laser light source devices emit photoacoustic excitation light sources, the detection light source devices emit wide spectrum light for detecting photoacoustic signals, each group of optical fiber photoacoustic sensing probes are placed in different monitoring areas, one end of each group of optical fiber photoacoustic sensing probes is connected with each excitation light source device through the optical fiber array 15, and the other end of each group of optical fiber photoacoustic sensing probes is connected with each detection light source device through the optical fiber array 15.
In this embodiment, each group of optical fiber photoacoustic sensing probes is placed in SF 6 Different areas in electrical equipment, SF 6 Electrical discharge generating H 2 S、SO 2 And the fault characteristic gas is equal, one of the excitation light source devices with different wave bands comprises a laser light source 5 and a collimating lens 17, and the detection light source device comprises an optical fiber broad spectrum light source 7, an optical fiber circulator 8, a third optical switch 9, a spectrometer 10 and an industrial personal computer 11. The laser source 5 emits ultraviolet light beam with specific wavelength to SO 2 The detection is carried out, the light beams are converged and split and coupled into the input ends of the optical fiber array 15 through the collimating lens 17, and the output ends of the optical fiber array 15 are respectively connected with one end of each group of optical fiber photoacoustic sensing probes in a one-to-one correspondence mode. Broadband light emitted by the optical fiber broadband light source 7 is incident to the third optical switch 9 through the optical fiber circulator 8, output channels of the third optical switch 9 are respectively connected with the other end of each group of optical fiber photoacoustic sensing probes in one-to-one correspondence, interference spectrums generated in each group of optical fiber photoacoustic sensing probes are returned to the third optical switch 9 from the optical fiber array 15 and are output to the spectrometer 10 through the optical fiber circulator 8, and the industrial personal computer 11 collects spectrums detected by the spectrometer 10 and performs signal processing and display. In this embodiment, a high-speed spectrum demodulation method is adopted to demodulate light to obtain a dynamic cavity length of an interference cavity, the amplitude of a photoacoustic signal is obtained by measuring the cavity length change of the interference cavity, and the gas concentration is obtained and displayed according to the proportional relation between the amplitude of the photoacoustic signal and the gas concentration.
The number of the optical fiber photoacoustic sensing probes is 3, namely a first optical fiber photoacoustic sensing probe 12, a second optical fiber photoacoustic sensing probe 13 and a third optical fiber photoacoustic sensing probe 14, the number of the output ends of the optical fiber array 15 is greater than or equal to that of the optical fiber photoacoustic sensing probes, and the first optical fiber photoacoustic sensing probe 12, the second optical fiber photoacoustic sensing probe 13 and the third optical fiber photoacoustic sensing probe 14 are respectively connected with one output end of the optical fiber array 15.
As shown in fig. 2 and fig. 3, the first optical fiber photoacoustic sensing probe 12, the second optical fiber photoacoustic sensing probe 13 and the third optical fiber photoacoustic sensing probe 14 have the same structure and each comprise an acoustic wave sensitive diaphragm 18, an air chamber 19, an optical fiber end face 20, an optical fiber collimator 21 and a housing 22, wherein the optical fiber end face 20 and the optical fiber collimator 21 are arranged in parallel in the housing 22, the optical fiber end face 20 and the optical fiber collimator 21 have the same shape, one end of the optical fiber end face 20 extends outwards from the housing 22 to be connected with a detection light source device through an optical fiber array 15, and one end of the optical fiber collimator 21 extends outwards from the housing 22 to be connected with an excitation light source device through the optical fiber array 15; the gas chamber 19 comprises an optical acoustic tube and an air guide channel, wherein one end of the optical acoustic tube is horizontally arranged and is connected with the other end of the optical collimator 21, the air guide channel is vertically arranged and the upper end of the air guide channel is communicated with the other end of the optical acoustic tube, the lower end of the air guide channel is connected with the other end of the optical fiber end face 20, the right side of the air guide channel is parallelly provided with an acoustic wave sensitive membrane 18, the acoustic wave sensitive membrane 18 serves as the right side face of the shell 22, the acoustic wave sensitive membrane 18 is provided with a cantilever structure 181, the cantilever structure 181 is a rectangular groove with a downward free end, outside gas to be detected is diffused into the gas chamber 19 through the slot of the cantilever structure 181 on the acoustic wave sensitive membrane 18, gaps among the gas chamber 19, the optical fiber end face 20, the optical collimator 21 and the shell 22 are filled with solids, wherein the volume of the gas chamber 19 is 60 mu L, the length of the optical fiber end face 20 is 10mm, the acoustic wave sensitive membrane 18 is a wafer made of 304 stainless steel, the diameter and the thickness are respectively 10mm and 5 mu m, the upper notch is 10 mu m, the cantilever structure 181 is respectively 1.6mm and 0.8mm, the free end face of the cantilever structure and the free end face 20F-P is 200 mu m. The working distance of the optical fiber collimator 21 is 80mm and is 10mm longer than the maximum length of the photoacoustic cell in the air chamber 19.
The photoacoustic excitation light source is incident into the air chamber 19 through the optical fiber collimator 21 to excite a photoacoustic signal, and is detected by the acoustic wave sensitive diaphragm 18 arranged on the outer side of the air chamber 19, the free end of the cantilever structure 181 of the acoustic wave sensitive diaphragm 18 and the optical fiber end face 20 form an optical fiber Fabry-Perot interference cavity, the photoacoustic signal enables the cantilever structure 181 to vibrate to cause the length change of the Fabry-Perot interference cavity, and the detection of the photoacoustic signal is realized by detecting the cavity length change of the interference cavity. Excitation light and detection light are transmitted through optical fibers and are incident into the first optical fiber photoacoustic sensing probe 12, the second optical fiber photoacoustic sensing probe 13 and the third optical fiber photoacoustic sensing probe 14 in a time sharing mode, the whole sensing structure does not contain electrical elements, the electromagnetic interference resistance is achieved, and the detection device is applicable to detection of large-scale electrical equipment such as transformer oil; the remote transmission of the optical fiber and the time division multiplexing of the multi-point probe realize the distributed network distribution monitoring and the remote telemetry.
The working process of the embodiment is as follows: first, the laser light source 5 emits laser beams with specific wavelengths, the laser beams are converged and collimated by the collimating lens 17, and the output laser beams are coupled into the optical fiber array 15 and respectively transmitted to the first optical fiber photoacoustic sensing probe 12, the second optical fiber photoacoustic sensing probe 13 and the third optical fiber photoacoustic sensing probe 14 at different positions. The gas molecules to be detected in the optical fiber photoacoustic sensing probe absorb laser energy and transition to a high energy level, the energy can be released through the non-radiative transition, the gas in the sensing probe is expanded, and the gas in the sensing probe is also periodically expanded with heat and contracted with cold due to the fact that laser is modulated by a periodic signal, sound pressure is formed, and the free end of the cantilever structure 181 of the acoustic wave sensitive membrane 18 in the sensing probe is pushed to periodically vibrate.
Then, the optical fiber broad spectrum light source 7 emits broad spectrum light, the broad spectrum light is incident to the input end of the third optical switch 9 through the optical fiber circulator 8, and the output broad spectrum light is respectively transmitted to the first optical fiber photoacoustic sensing probe 12, the second optical fiber photoacoustic sensing probe 13 and the third optical fiber photoacoustic sensing probe 14 through the other one of the optical fiber arrays 15 and irradiates the free end of the cantilever structure 181 on the acoustic wave sensitive diaphragm 18 in the sensing probe; the optical fiber end face 20 and the cantilever structure 181 of the acoustic wave sensitive membrane 18 in the sensing probe form a low-fineness optical fiber Fabry-Perot interference cavity, broad spectrum light is reflected by two surfaces of the interference cavity to form an interference spectrum, and the interference spectrum is transmitted to the third optical switch 9 through the optical fiber array 15 and is output to the spectrometer 10 through the optical fiber circulator 8; when the acoustic wave acts on the acoustic wave sensitive membrane 18, the length of the Fabry-Perot interference cavity is changed, and the interference spectrum peak value detected by the spectrometer 10 moves; the interference spectrum is collected by the industrial personal computer 11, the dynamic cavity length of the interference cavity is obtained by adopting a high-speed spectrum demodulation method, the amplitude of the photoacoustic signal is calculated by measuring the cavity length change of the interference cavity, and the industrial personal computer 11 obtains and displays the concentration of the gas to be measured according to the calibration coefficient. The high-speed spectrum demodulation method is a phase demodulation algorithm based on white light interference, and the change of the Fabry-Perot cavity length can be detected through fast Fourier transformation.
The laser light source 5 directly outputs laser beams through the collimating lens 17, the wavelength range of the outgoing laser beams is 300nm-5 mu m, and the laser beams can be coupled into optical fibers for long-distance transmission.
The third optical switch 9 is an optical fiber optical switch, and the number of optical switch channels is greater than or equal to the number of optical fiber photoacoustic sensing probes required by distributed detection.
The optical fiber broad spectrum light source 7 is a near infrared super radiation light emitting diode SLED or an amplified spontaneous radiation ASE light source, and the spectral width is larger than 20nm. In this example, the center wavelength is 1550nm and the spectral width is 60nm.
The spectrometer 10 is a high-speed spectrometer, the spectrum sampling rate and the pixel number are respectively greater than 5KHz and 128, and the working wavelength range is covered with the emission spectrum range of the optical fiber spectrum light source 7. In this embodiment, the spectrometer 10 has a spectral sampling rate and pixel count of 5KHz and 128, and operates in the 1510nm-1590nm wavelength range.
Example 2
As shown in fig. 4, embodiment 2 of the present invention differs from embodiment 1 in that another excitation light source device is provided: the excitation light source device comprises a laser driving circuit 16, a first semiconductor laser 1, an erbium-doped optical fiber amplifier 4 and a first optical switch 6, wherein the laser driving circuit 16 drives the first semiconductor laser 1 to emit near infrared laser into the erbium-doped optical fiber amplifier 4, the erbium-doped optical fiber amplifier 4 amplifies the optical power, the amplified laser enters the first optical switch 6, each output channel of the first optical switch 6 is connected with the input port of the optical fiber array 15 in one-to-one correspondence, and each output end of the optical fiber array 15 is connected with one end of each group of optical fiber photoacoustic sensing probes in one-to-one correspondenceAnd (5) connection. The first semiconductor laser 1 emits near infrared laser light to detect SF 6 H generated by electric discharge 2 S, S. The first semiconductor laser 1 is a near infrared DFB laser having a center wavelength of 1530 nm.
The working process of the embodiment is as follows: first, the laser driving circuit 16 drives the first semiconductor laser 1, so that the first semiconductor laser 1 emits near infrared laser light, the laser light output by the first semiconductor laser 1 is transmitted to the erbium-doped fiber amplifier 4, amplification of laser power is achieved, the amplified laser light is transmitted to the input end of the first optical switch 6, the output end of the first optical switch 6 is connected with the first optical fiber photoacoustic sensing probe 12, the second optical fiber photoacoustic sensing probe 13 and the third optical fiber photoacoustic sensing probe 14, and the output end of the first optical switch 6 is switched so that the laser light is transmitted to the first optical fiber photoacoustic sensing probe 12, the second optical fiber photoacoustic sensing probe 13 and the third optical fiber photoacoustic sensing probe 14 through one of the optical fiber arrays 15. The gas molecules to be detected in the probe absorb laser energy and transition to a high energy level, the energy can be released through non-radiative transition, the gas in the sensing probe is caused to expand, and the gas in the sensing probe is also periodically expanded with heat and contracted with cold due to the fact that laser is modulated by a periodic signal, sound pressure is formed, and the free end of the cantilever structure 181 of the acoustic wave sensitive membrane 18 in the sensing probe is pushed to periodically vibrate.
Finally, the optical fiber broad spectrum light source 7, the optical fiber circulator 8, the third optical switch 9, the spectrometer 10 and the industrial personal computer 11 are used for detecting and calculating the interference spectrum formed by the reflection of the broad spectrum light from the two surfaces of the optical fiber Fabry-Perot interference cavity with low fineness to the cantilever beam structure 181 of the acoustic wave sensitive membrane 18, so as to obtain the concentration of the gas to be detected, and the concentration is displayed, and the detection and demodulation processes of the interference spectrum are the same as those of the embodiment 1 and are not repeated herein.
The first semiconductor laser 1 is a wavelength tunable laser light source, is in butterfly-shaped package, and is coupled with an optical fiber to output laser, and the central wavelength of the laser is enabled to correspond to the absorption wavelength of the gas to be detected by changing the driving bias current.
The first optical switch 6 and the third optical switch 9 are optical fiber optical switches with the same model, the number of optical switch channels is equal, and the number of optical fiber photoacoustic sensing probes required by distributed detection is greater than or equal to the number of optical fiber photoacoustic sensing probes required by distributed detection.
Example 3
As shown in fig. 5, embodiment 3 of the present invention is different from embodiment 2 in that the excitation light source device further includes a second semiconductor laser 2 and a second optical switch 3, the laser driving circuit 16 drives the first semiconductor laser 1 and the second semiconductor laser 2 to emit near infrared laser light, and the near infrared laser light is transmitted to the second optical switch 3 through optical fibers respectively, and the second optical switch 3 controls the opening and closing of two optical paths, so that one of the two laser light enters the erbium-doped fiber amplifier 4. The first semiconductor laser 1 and the second semiconductor laser 2 are wavelength tunable laser light sources, butterfly packages and coupled optical fibers output laser light, and the central wavelength of the coupled optical fibers corresponds to the absorption wavelength of the gas to be detected by changing the driving bias current. The center wavelength of the optical fiber broad spectrum light source 7 is far away from the center wavelengths of the first semiconductor laser 1 and the second semiconductor laser 2. In comparison with example 2, the first semiconductor laser 1 was a near-infrared DFB laser having a center wavelength of 1530nm, and the second semiconductor laser 2 was a near-infrared DFB laser having a center wavelength of 1650.9nm, each having a power of 10mW.
Example 4
As shown in fig. 6, embodiment 4 is an excitation light source device according to embodiment 3 added to embodiment 1, so that the entire system includes 3 groups of excitation light source devices with different wavebands at the same time, and can detect SF in a time-sharing manner 6 Electrical discharge generating H 2 S and SO 2 。
The working procedure of example 4 is: first, the laser light source 5 emits ultraviolet light with a specific wavelength, the ultraviolet light is converged and collimated by the collimating lens 17, and the output laser beams are coupled into the optical fiber array 15 and respectively transmitted to the first optical fiber photoacoustic sensing probe 12, the second optical fiber photoacoustic sensing probe 13 and the third optical fiber photoacoustic sensing probe 14 at different positions. Then, the laser driving circuit 16 drives the first semiconductor laser 1 and the second semiconductor laser 2, so that the first semiconductor laser 1 and the second semiconductor laser 2 respectively emit near infrared light with specific wavelengths, the near infrared light output by the first semiconductor laser 1 and the second semiconductor laser 2 is respectively transmitted to the second optical switch 3, the two laser beams are transmitted to the erbium-doped optical fiber amplifier 4 in a time-sharing manner by controlling the opening and closing of two input ends of the second optical switch 3, the amplification of the laser power is realized, the amplified laser beams are transmitted to the input ends of the first optical switch 6, the output ends of the first optical switch 6 are respectively connected with the first optical fiber photoacoustic sensing probe 12, the second optical fiber photoacoustic sensing probe 13 and the third optical fiber photoacoustic sensing probe 14, and the laser beams are respectively transmitted to the first optical fiber photoacoustic sensing probe 12, the second optical fiber photoacoustic sensing probe 13 and the third optical fiber photoacoustic sensing probe 14 through one of the optical fiber arrays 15 by switching the output ends of the first optical switch 6. The gas molecules to be detected in the probe absorb laser energy and transition to a high energy level, the energy can be released through non-radiative transition, the gas in the sensing probe is caused to expand, and the gas in the sensing probe is also periodically expanded with heat and contracted with cold due to the fact that laser is modulated by a periodic signal, sound pressure is formed, and the free end of the cantilever structure 181 of the acoustic wave sensitive membrane 18 in the sensing probe is pushed to periodically vibrate.
Finally, the optical fiber broad spectrum light source 7 emits broad spectrum light to be incident to the input end of the third optical switch 9 through the optical fiber circulator 8, the output end of the third optical switch 9 is connected with the optical fiber photoacoustic sensing probe, the sequence of the optical fiber photoacoustic sensing probe is consistent with that of the first optical switch 6, the output end switching control is synchronous with that of the first optical switch 6, and the output broad spectrum light is respectively transmitted to the free ends of the cantilever beam structures 181 on the acoustic wave sensitive membranes 18 in the sensing probes through the other one of the multi-core optical fiber arrays 15 and respectively transmitted to the first optical fiber photoacoustic sensing probe 12, the second optical fiber photoacoustic sensing probe 13 and the third optical fiber photoacoustic sensing probe 14; the optical fiber end face 20 and the cantilever structure 181 of the acoustic wave sensitive membrane 18 in the sensing probe form a low-fineness optical fiber Fabry-Perot interference cavity, the two surfaces of the interference cavity reflect wide-spectrum light to form an interference spectrum, and the interference spectrum is transmitted to the third optical switch 9 through the multi-core optical fiber array 15 and is output to the spectrometer 10 through the optical fiber circulator 8; when the acoustic wave acts on the acoustic wave sensitive membrane 18, the length of the Fabry-Perot interference cavity is changed, and the interference spectrum peak value detected by the spectrometer 10 moves; the interference spectrum is collected by the industrial personal computer 11, the dynamic cavity length of the interference cavity is obtained by adopting a high-speed spectrum demodulation method, the amplitude of the photoacoustic signal is calculated by measuring the cavity length change of the interference cavity, and the industrial personal computer 11 obtains and displays the concentration of the gas to be measured according to the calibration coefficient.
The above embodiments are only for illustrating the technical solution of the present invention, and are not limiting; although the invention has been described in detail with reference to the foregoing embodiments, it will be understood by those of ordinary skill in the art that: the technical scheme described in the foregoing embodiments can be modified or some technical features thereof can be replaced by equivalents; such modifications and substitutions do not depart from the spirit and scope of the technical solutions of the embodiments of the present invention.
Claims (5)
1. The distributed online monitoring system based on the optical fiber photoacoustic sensing is characterized by comprising a plurality of groups of excitation light source devices with different wave bands, a group of detection light source devices, an optical fiber array (15) and a plurality of groups of optical fiber photoacoustic sensing probes, wherein the excitation light source devices emit laser light sources, the detection light source devices emit photoacoustic excitation light sources, each group of optical fiber photoacoustic sensing probes are arranged in different monitoring areas, one end of each group of optical fiber photoacoustic sensing probes is respectively connected with each excitation light source device through the optical fiber array (15), and the other end of each group of optical fiber photoacoustic sensing probes is respectively connected with the detection light source devices through the optical fiber array (15); one group of the excitation light source devices with different wave bands comprises a laser light source (5) and a collimating lens (17), the laser light source (5) emits laser beams with specific wavelengths, the wavelength range of the outgoing light of the laser light source (5) is 300nm-5 mu m, the beams are converged and split to be coupled into each input end of an optical fiber array (15) through the collimating lens (17), and each output end of the optical fiber array (15) is connected with one end of each group of optical fiber photoacoustic sensing probes in a one-to-one correspondence mode;
the other group of the excitation light source devices with different wave bands comprises a laser driving circuit (16), a first semiconductor laser (1), an erbium-doped fiber amplifier (4) and a first optical switch (6), and also comprises a second semiconductor laser (2) and a second optical switch (3), wherein the laser driving circuit (16) drives the first semiconductor laser (1) and the second semiconductor laser (2) to emit laser with specific wavelengths, the laser is respectively transmitted to the second optical switch (3) through optical fibers, and the second optical switch (3) controls the opening and the closing of two optical paths so that one laser enters the erbium-doped fiber amplifier (4); the erbium-doped optical fiber amplifier (4) amplifies optical power, amplified laser enters the first optical switch (6), output channels of the first optical switch (6) are respectively connected with input ports of the optical fiber array (15) in one-to-one correspondence, and output ends of the optical fiber array (15) are respectively connected with one ends of all groups of optical fiber photoacoustic sensing probes in one-to-one correspondence; the center wavelength of the first semiconductor laser (1) is 1530nm, and the center wavelength of the second semiconductor laser (2) is 1650.9 nm;
the number of the optical fiber photoacoustic sensing probes is 3, namely a first optical fiber photoacoustic sensing probe (12), a second optical fiber photoacoustic sensing probe (13) and a third optical fiber photoacoustic sensing probe (14), the number of output ends of the optical fiber array (15) is more than or equal to that of the optical fiber photoacoustic sensing probes, and the first optical fiber photoacoustic sensing probe (12), the second optical fiber photoacoustic sensing probe (13) and the third optical fiber photoacoustic sensing probe (14) are respectively connected with one output end of the optical fiber array (15); the first optical fiber photoacoustic sensing probe (12), the second optical fiber photoacoustic sensing probe (13) and the third optical fiber photoacoustic sensing probe (14) are identical in structure and comprise an acoustic wave sensitive membrane (18), an air chamber (19), an optical fiber end face (20), an optical fiber collimator (21) and a shell (22), the optical fiber end face (20) and the optical fiber collimator (21) are arranged in the shell (22) in parallel, the optical fiber end face (20) and the optical fiber collimator (21) are identical in shape, one end of the optical fiber end face (20) extends out of the shell (22) to extend out of one optical fiber probe to be connected with a detection light source device through an optical fiber array (15), and one end of the optical fiber collimator (21) extends out of the shell (22) to extend out of one optical fiber probe to be connected with an excitation light source device through the optical fiber array (15); the air chamber (19) comprises an optical acoustic tube and an air guide channel, wherein one end of the optical acoustic tube is horizontally arranged and is connected with the other end of the optical collimator (21), the air guide channel is vertically arranged, the upper end of the air guide channel is communicated with the other end of the optical acoustic tube, the lower end of the air guide channel is connected with the other end of the optical fiber end face (20), the right side of the air guide channel is provided with an acoustic wave sensitive membrane (18) in parallel, the acoustic wave sensitive membrane (18) is used as the right side face of the shell (22), the acoustic wave sensitive membrane (18) is provided with a cantilever structure (181), the cantilever structure (181) is a rectangular groove with a downward free end, and the external gas to be tested is diffused into the air chamber (19) through a slot of the cantilever structure (181) on the acoustic wave sensitive membrane (18);
the detection light source device comprises an optical fiber broad spectrum light source (7), an optical fiber circulator (8), a third optical switch (9), a spectrometer (10) and an industrial personal computer (11), broadband light emitted by the optical fiber broad spectrum light source (7) is incident to the third optical switch (9) through the optical fiber circulator (8), output channels of the third optical switch (9) are respectively connected with the other end of each group of optical fiber photoacoustic sensing probes in one-to-one correspondence, interference spectrums generated in each group of optical fiber photoacoustic sensing probes are returned to the third optical switch (9) from an optical fiber array (15) and are output to the spectrometer (10) through the optical fiber circulator (8), and the industrial personal computer (11) collects spectrums detected by the spectrometer (10) and performs signal processing and display.
2. A distributed on-line monitoring system based on optical fiber photoacoustic sensing according to claim 1, characterized in that the optical fiber broad spectrum light source (7) is a near infrared super radiation light emitting diode, SLED, or an amplified spontaneous radiation, ASE, light source.
3. A distributed online monitoring system based on fiber optic photoacoustic sensing of claim 1, wherein the signal processing and displaying comprises: demodulating the spectrum by adopting a high-speed spectrum demodulation method to obtain the dynamic cavity length of the interference cavity, obtaining the amplitude of the photoacoustic signal by measuring the cavity length change of the interference cavity, and obtaining and displaying the gas concentration according to the proportional relation between the amplitude of the photoacoustic signal and the gas concentration.
4. A distributed on-line monitoring system based on optical fiber photoacoustic sensing according to claim 3, characterized in that the photoacoustic excitation light source is incident into the air chamber (19) through the optical fiber collimator (21) to excite the photoacoustic signal, and is detected by the acoustic wave sensitive membrane (18) installed outside the air chamber (19), the free end of the cantilever structure of the acoustic wave sensitive membrane (18) and the optical fiber end face (20) form an optical fiber fabry-perot interference cavity, the photoacoustic signal causes the cantilever structure to vibrate to cause the fabry-perot interference cavity length change, and the detection of the photoacoustic signal is realized by detecting the cavity length change of the interference cavity.
5. The method of any one of claims 1-4, wherein the multiple groups of excitation light source devices with different wavebands respectively emit laser light sources with different wavebands, the laser light source with one waveband detects a gas, one group of excitation light source devices is selectively connected or the multiple groups of excitation light source devices are in time-sharing connection, one gas detection or multicomponent gas time-sharing detection is realized, each group of optical fiber photoacoustic sensing probes is arranged in different monitoring areas, and the optical fiber photoacoustic sensing probes corresponding to one monitoring area or the multiple monitoring areas are selectively connected or the optical fiber photoacoustic sensing probes corresponding to the multiple monitoring areas are in time-sharing connection, so that the gas detection of one monitoring area or the gas time-sharing detection of the multiple monitoring areas is realized, and the whole system performs distributed detection.
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