CN114076737A - 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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Abstract
The invention discloses a distributed online monitoring system and a distributed online monitoring 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, 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 devices through the optical fiber array; one group of the laser light sources comprises a laser light source and a collimating lens, and laser beams emitted by the laser light source are converged by the collimating lens and coupled into an optical fiber array in a splitting manner; the invention has the advantages that: and the number of excitation light sources is large, the application scene is not limited, and the condition of the multi-component gas detection requirement 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 detecting trace gases, 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. gas molecules absorb exciting light with specific wavelength and transition from a ground state to an excited state; 2. the molecules in the excited state are in non-radiative transition back to the ground state, and heat is released, so that surrounding gas is expanded; 3. when the exciting light is modulated by the periodic signal, the gas also forms sound waves by periodic expansion and contraction, the sound waves are detected by the microphone, and the detected photoacoustic signal is in direct proportion to the gas concentration. Increasing the sensitivity of the microphone is therefore an effective means of increasing the sensitivity of photoacoustic spectroscopy gas detection systems. 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 changes of external physical quantities such as external temperature, strain, pressure and the like are sensed through an acoustic wave sensitive membrane and are reflected into the changes of optical parameters, so that the detection of the external physical quantities is realized. The method has the advantages of electromagnetic interference resistance, remote measurement, distributed detection and the like. The photoacoustic spectroscopy technology and the optical fiber acoustic wave sensing technology are combined, accurate detection of trace gas is achieved, the method is different from other photoacoustic gas detection systems, has the advantages of being passive and micro, and is very suitable for gas detection in narrow areas or serious in electromagnetic interference, such as the gas detection in the special field of large-scale power transformation equipment. The document Chen Ke, Guo Min, Liu Shuai, et al fiber-optical photoacoustic sensor for remote monitoring of gas micro-leak [ J ] Optics express,2019,27(4):4648-4659 reports a miniature fiber photoacoustic gas sensor, laser light is transmitted through optical fiber to a photoacoustic probe to excite photoacoustic signal, and the photoacoustic signal is detected by broad spectrum light to obtain gas concentration. However, the method has the limitations 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 in the prior art, the optical fiber photoacoustic sensing scheme has the limitations of single excitation light source and fixed application scene, and the condition of the multi-component gas detection requirement cannot be met.
The invention solves the technical problems through the following technical means: a distributed online monitoring system based on optical fiber photoacoustic sensing 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 (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 multiple groups of 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 split and coupled to input ends of an optical fiber array (15) through the collimating lens (17), and 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 manner.
The invention can realize the detection of multi-component gas by multiplexing the excitation light sources with different wave bands, each group of optical fiber photoacoustic sensing probes is 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 connecting one monitoring area or connecting the optical fiber photoacoustic sensing probes corresponding to a plurality of monitoring areas in a time-sharing way, the whole system carries out distributed detection, the number of excitation light sources is more, the application scene is not limited, and the condition that the multi-component gas detection requirement exists is met.
Furthermore, another group of the excitation light source devices with the multiple groups of different wave bands comprises a laser driving circuit (16), a first semiconductor laser (1), an erbium-doped optical fiber amplifier (4) and a first optical switch (6), the laser driving circuit (16) drives the first semiconductor laser (1) to enable the first semiconductor laser to emit laser with a specific wavelength to enter the erbium-doped optical fiber amplifier (4), the erbium-doped optical fiber amplifier (4) amplifies optical power, the 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 a one-to-one correspondence mode, and 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.
Furthermore, another group of the excitation light source devices with the multiple groups of 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 wavelength, 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 the two optical paths, so that one laser beam enters the erbium-doped optical fiber amplifier (4).
Further, the detection light source device comprises an optical fiber wide 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 wide spectrum light source (7) enters the third optical switch (9) through the optical fiber circulator (8), output channels of the third optical switch (9) are respectively in one-to-one correspondence with the other end of each group of optical fiber photoacoustic sensing probes, interference spectra generated in each group of optical fiber sensing probes are returned to the third optical switch (9) from an optical fiber array (15) and output to the spectrometer (10) through the optical fiber circulator (8), and the industrial personal computer (11) collects spectra detected by the spectrometer (10) and performs signal processing and display.
Still further, the signal processing and displaying includes: and demodulating the spectrum by adopting a high-speed spectrum demodulation method to obtain the dynamic cavity length of the interference cavity, measuring the cavity length change of the interference cavity to obtain the amplitude of the photoacoustic signal, and obtaining and displaying the gas concentration according to the proportional relation between the amplitude of the photoacoustic signal and the gas concentration.
Furthermore, the number of the optical fiber photoacoustic sensing probes is 3, the optical fiber photoacoustic sensing probes are respectively 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 more 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 respectively comprise an acoustic wave sensitive membrane (18), an air chamber (19), an optical fiber end surface (20), an optical fiber collimator (21) and a shell (22), the optical fiber end surface (20) and the optical fiber collimator (21) are arranged in the shell (22) in parallel, the optical fiber end surface (20) and the optical fiber collimator (21) have the same shape, one end of the optical fiber end surface (20) extends out of the shell (22) to form an optical fiber probe, and the optical fiber probe is connected with the detection light source device through the optical fiber array (15), and one end of the optical fiber collimator (21) extends out of the shell (22) to form an optical fiber probe and is connected with the excitation light source device through the optical fiber array (15); air chamber (19) are including light sound pipe and air guide channel, light sound pipe level sets up and one end links up with fiber collimator (21) other end, and the vertical setting of air guide channel and the other end of upper end and light sound pipe communicate with each other, and the other end of lower extreme and fiber end face (20) links up, air guide channel right side parallel arrangement sound wave sensitive diaphragm (18), sound wave sensitive diaphragm (18) are as the right flank of shell (22), set up a cantilever beam structure on sound wave sensitive diaphragm (18), the cantilever beam structure is the decurrent rectangular channel of free end, and the outside gas that awaits measuring diffuses to air chamber (19) in through the line of a small of the seam of the cantilever beam structure on the sound wave sensitive diaphragm (18).
Furthermore, the photoacoustic excitation light source is incident into the air chamber (19) through the optical fiber collimator (21) to excite photoacoustic signals 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 signals enable the cantilever beam structure to vibrate to cause the change of the length of the Fabry-Perot interference cavity, and the detection of the photoacoustic signals is realized by detecting the change of the cavity length of the interference cavity.
The invention also provides a distributed online monitoring system method 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, the laser light source with one wave band detects one 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, so that the gas detection or the multi-component gas time-sharing detection is realized, 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 connecting one monitoring area or connecting the optical fiber photoacoustic sensing probes corresponding to the plurality of monitoring areas in a time-sharing manner, and the whole system carries out the distributed detection.
The invention has the advantages that:
(1) the invention can realize the detection of multi-component gas by multiplexing the excitation light sources with different wave bands, each group of optical fiber photoacoustic sensing probes is 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 connecting one monitoring area or connecting the optical fiber photoacoustic sensing probes corresponding to a plurality of monitoring areas in a time-sharing way, the whole system carries out distributed detection, the number of excitation light sources is more, the application scene is not limited, and the condition that the multi-component gas detection requirement 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 capability of resisting electromagnetic interference; meanwhile, the long-distance transmission and low transmission loss characteristics of the optical fiber can realize long-distance remote measurement. The detection mode is suitable for gas detection in the fields of transformers, environment monitoring, safety monitoring and the like, and is a universal 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 right side view, that is, a front view of 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 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 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 fiber photoacoustic sensing disclosed in embodiment 4 of the present invention.
Detailed Description
In order to make the objects, 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 with reference to the embodiments of the present invention, and it is obvious that the described embodiments are some embodiments of the present invention, but not all embodiments. All other embodiments, which can be derived by a person skilled in the art from the embodiments given herein without making any creative effort, shall fall within the protection scope of the present invention.
Example 1
As shown in fig. 1, a distributed online monitoring system based on optical fiber photoacoustic sensing 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 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 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 the detection light source devices through the optical fiber array 15.
In this embodiment, each group of optical fiber photoacoustic sensing probes is placed in the SF6Different zones, SF, in electrical equipment6Electrical discharge to produce H2S、SO2When fault characteristic gas exists, one of the excitation light source devices of the multiple groups of different wave bands comprises a laser light source 5 and a collimating lens 17, and the detection light source device comprises an optical fiber wide 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 light source 5 emits ultraviolet light beams with specific wavelength to SO2And detecting, wherein light beams are converged and split and coupled to each input end of the optical fiber array 15 through the collimating lens 17, and each output end of the optical fiber array 15 is respectively connected with one end of each group of optical fiber photoacoustic sensing probes in a one-to-one correspondence manner. Broadband light emitted by the optical fiber wide-spectrum light source 7 enters a third optical switch 9 through an 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 a one-to-one correspondence mode, interference spectra generated in each group of optical fiber photoacoustic sensing probes return to the third optical switch 9 from an optical fiber array 15 and are output to a spectrometer 10 through the optical fiber circulator 8, and an industrial personal computer 11 collects the spectra detected by the spectrometer 10 and performs signal processing and display. In the embodiment, a high-speed spectrum demodulation method is adopted to demodulate a spectrum to obtain the dynamic cavity length of the interference cavity, the amplitude of the 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 optical fiber photoacoustic sensing probe comprises 3 optical fiber photoacoustic sensing probes, 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, wherein the number of the 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.
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 of the first optical fiber photoacoustic sensing probe, the second optical fiber photoacoustic sensing probe 13, and the third optical fiber photoacoustic sensing probe 14 includes an acoustic wave sensitive membrane 18, an air chamber 19, an optical fiber end surface 20, an optical fiber collimator 21, and a housing 22, where the optical fiber end surface 20 and the optical fiber collimator 21 are arranged in parallel in the housing 22, the optical fiber end surface 20 and the optical fiber collimator 21 have the same shape, and one end of the optical fiber end surface 20 extends out of the housing 22 to form an optical fiber probe, and is connected to the detection light source device through the optical fiber array 15, and one end of the optical fiber collimator 21 extends out of the housing 22 to form an optical fiber probe, and is connected to the excitation light source device through the optical fiber array 15; the air chamber 19 comprises a photoacoustic tube and an air guide channel, the photoacoustic tube is horizontally arranged, one end of the photoacoustic tube is connected with the other end of the optical fiber 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 photoacoustic tube, the lower end of the air guide channel is connected with the other end of the optical fiber end face 20, the acoustic wave sensitive membrane 18 is arranged on the right side of the air guide channel in parallel, the acoustic wave sensitive membrane 18 is used as the right side face of the shell 22, a cantilever beam structure 181 is arranged on the acoustic wave sensitive membrane 18, the cantilever beam structure 181 is a rectangular groove with a downward free end, external gas to be detected is diffused into the air chamber 19 through a slot opening of the cantilever beam structure 181 on the acoustic wave sensitive membrane 18, gaps among the air chamber 19, the optical fiber end face 20, the optical fiber collimator 21 and the shell 22 are filled by adopting a solid, wherein the volume of the air chamber 19 is 60 muL, the length of the photoacoustic pool is 10mm, and the acoustic wave sensitive membrane 18 is a 304 stainless steel wafer, the diameter and the thickness are respectively 10mm and 5 μm, a cantilever beam structure 181 with a gap of 10 μm is carved on the diaphragm, the length and the width of the cantilever beam are respectively 1.6mm and 0.8mm, the free end of the cantilever beam structure 181 and the optical fiber end face 20 form a Fabry-Perot interference cavity, and the length of the static cavity is 200 μm. The working distance of the optical fiber collimator 21 is 80mm, which is larger than the maximum length of the photoacoustic cell in the air chamber 19 by 10 mm.
The photoacoustic excitation light source is incident into the air chamber 19 through the optical fiber collimator 21 to excite photoacoustic signals 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 181 of the acoustic wave sensitive membrane 18 and the optical fiber end face 20 form an optical fiber Fabry-Perot interference cavity, the photoacoustic signals enable the cantilever beam structure 181 to vibrate to cause changes of the length of the Fabry-Perot interference cavity, and the detection of the photoacoustic signals is realized by detecting the changes of the cavity length of the interference cavity. The excitation light and the detection light are transmitted through the 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 manner, the whole sensing structure does not contain an electrical element, has the anti-electromagnetic interference capability and can be suitable for detecting large electrical equipment such as transformer oil; the long-distance transmission of the optical fiber and the time division multiplexing of the multi-point probe realize the distributed network distribution monitoring and the long-distance remote measurement.
The working process of the embodiment is as follows: firstly, the laser light source 5 emits a laser beam with a specific wavelength, the laser beam is converged and collimated by the collimating lens 17, and the output laser beam is coupled into the optical fiber array 15 and 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 at different positions. The gas molecules to be detected in the optical fiber photoacoustic sensing probe absorb laser energy and are transited to a high energy level, the light energy releases energy through nonradiative transition, the gas in the sensing probe expands, the laser is modulated by periodic signals, so that the gas in the sensing probe also expands periodically with heat and contracts with cold to form sound pressure, and the free end of a cantilever beam structure 181 of an acoustic wave sensitive membrane 18 in the sensing probe is pushed to vibrate periodically.
Then, the wide-spectrum light emitted by the optical fiber wide-spectrum light source 7 is incident to the input end of the third optical switch 9 through the optical fiber circulator 8, and the output wide-spectrum 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 the other optical fiber array 15 and is irradiated to the free end of the cantilever structure 181 on the acoustic wave sensitive membrane 18 in the sensing probe; the optical fiber end face 20 and a cantilever beam structure 181 of the acoustic wave sensitive membrane 18 in the sensing probe form a low-fineness optical fiber Fabry-Perot interference cavity, two surfaces of the interference cavity reflect wide-spectrum light to form an interference spectrum, 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 sound waves act on the sound wave sensitive membrane 18, the length of a 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 can detect the change of the Fabry-Perot cavity length through fast Fourier transform.
The laser light source 5 directly outputs laser beams through the collimating lens 17, the light-emitting wavelength range 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 channels of the optical switch is greater than or equal to the number of optical fiber photoacoustic sensing probes required by distributed detection.
The optical fiber wide spectrum light source 7 is a near-infrared super-radiation light emitting diode SLED or an amplified spontaneous radiation ASE light source, and the spectrum width is more than 20 nm. In this embodiment, the center wavelength is 1550nm, and the spectrum width is 60 nm.
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 should cover the emission spectrum range of the optical fiber spectrum light source 7. In this embodiment, the spectrum sampling rate and the number of pixels of the spectrometer 10 are 5KHz and 128, and the operating wavelength range is 1510nm to 1590 nm.
Example 2
As shown in fig. 4, embodiment 2 of the present invention is different from embodiment 1 in that another excitation light source device is provided: the excitation light source device comprises a laser drive circuit 16, a first semiconductor laser 1, an erbium-doped fiber amplifier 4 and a first optical switch 6, wherein the laser drive circuit 16 drives the first semiconductor laser 1 to emit near-infrared laser to enter the erbium-doped fiber amplifier 4, and the near-infrared laser is doped into the erbium-doped fiber amplifier 4The erbium 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 a one-to-one correspondence manner, and 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 manner. The first semiconductor laser 1 is made to emit near-infrared laser light to enable detection of SF6H generated by electric discharge of electric appliance2And 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: firstly, the laser driving circuit 16 drives the first semiconductor laser 1 to make the first semiconductor laser 1 respectively emit near-infrared laser, the laser output by the first semiconductor laser 1 is transmitted to the erbium-doped fiber amplifier 4 to realize amplification of laser power, the amplified laser is transmitted to the input end of the first optical switch 6, the output end of the first optical switch 6 is 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 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 one of the optical fiber arrays 15 by switching the output end of the first optical switch 6. The gas molecules to be detected in the probe absorb laser energy and are transited to a high energy level, the light energy releases energy through radiationless transition, the gas in the sensing probe expands, and the gas in the sensing probe also expands periodically with heat and contracts with cold due to the fact that the laser is modulated by periodic signals, sound pressure is formed, and the free end of the cantilever beam structure 181 of the sound wave sensitive membrane 18 in the sensing probe is pushed to vibrate periodically.
Finally, the interference spectrum formed by reflecting the broad spectrum light from two surfaces of the low-fineness optical fiber fabry-perot interference cavity formed by the cantilever beam structure 181 of the acoustic wave sensitive membrane 18 is detected and calculated by 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 to obtain and display the concentration of the gas to be detected, the detection and demodulation process of the interference spectrum is the same as that in embodiment 1, and details are not repeated here.
The first semiconductor laser 1 is a wavelength-tunable laser source, is packaged in a butterfly manner, is coupled with an optical fiber to output laser, and has a central wavelength which is corresponding 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 of the same type, the number of optical switch channels is equal to or greater than the number of optical fiber photoacoustic sensing probes required by distributed detection.
Example 3
As shown in fig. 5, a difference of embodiment 3 of the present invention from embodiment 2 is 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, which is transmitted to the second optical switch 3 through optical fibers, respectively, and the second optical switch 3 controls the on and off of two optical paths, so that one of the laser light enters the erbium-doped fiber amplifier 4. The first semiconductor laser 1 and the second semiconductor laser 2 are wavelength-tunable laser sources, are packaged in a butterfly manner, are coupled with optical fibers to output laser, and have central wavelength corresponding to the absorption wavelength of the gas to be detected by changing the driving bias current. The central wavelength of the optical fiber wide spectrum light source 7 is far away from the central 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, and the power was 10mW each.
Example 4
As shown in fig. 6, embodiment 4 is the embodiment 1, in which the excitation light source device of embodiment 3 is added, so that the whole system simultaneously includes 3 groups of excitation light source devices with different wavebands, and the SF can be detected in a time-sharing manner6Electrical discharge to produce H2S and SO2。
The working process of the embodiment 4 is as follows: firstly, 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 beam is coupled into the optical fiber array 15 and 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 at different positions. Then, the laser driving circuit 16 drives the first semiconductor laser 1 and the second semiconductor laser 2 to make the first semiconductor laser 1 and the second semiconductor laser 2 respectively emit near infrared light with specific wavelength, 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, two laser beams are transmitted to the erbium-doped fiber amplifier 4 in a time-sharing manner by controlling the opening and closing of two input ends of the second optical switch 3 to realize the amplification of laser power, 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 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 output end of the first optical switch 6 is switched to make the laser light respectively transmitted to the first optical fiber photoacoustic sensing probe 12 through one optical fiber array 15, A second optical fiber photoacoustic sensing probe 13 and a third optical fiber photoacoustic sensing probe 14. The gas molecules to be detected in the probe absorb laser energy and are transited to a high energy level, the light energy releases energy through radiationless transition, the gas in the sensing probe expands, and the gas in the sensing probe also expands periodically with heat and contracts with cold due to the fact that the laser is modulated by periodic signals, sound pressure is formed, and the free end of the cantilever beam structure 181 of the sound wave sensitive membrane 18 in the sensing probe is pushed to vibrate periodically.
Finally, the wide-spectrum light emitted by the optical fiber wide-spectrum light source 7 enters the input end of a third optical switch 9 through an optical fiber circulator 8, the output end of the third optical switch 9 is connected with the optical fiber photoacoustic sensing probe and is consistent with the first optical switch 6 in sequence, the switching control of the output end is synchronous with the first optical switch 6, and the output wide-spectrum 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 another optical fiber array 15 and irradiates the free end of a cantilever beam structure 181 on an acoustic wave sensitive membrane 18 in the sensing probe; the optical fiber end face 20 and a cantilever beam structure 181 of the acoustic wave sensitive membrane 18 in the sensing probe form a low-fineness optical fiber Fabry-Perot interference cavity, two surfaces of the interference cavity reflect wide-spectrum light to form an interference spectrum, 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 sound waves act on the sound wave sensitive membrane 18, the length of a 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 examples are only intended to illustrate the technical solution of the present invention, but not to limit it; although the present 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 solutions described in the foregoing embodiments may still be modified, or some technical features may be equivalently replaced; and such modifications or substitutions do not depart from the spirit and scope of the corresponding technical solutions of the embodiments of the present invention.
Claims (10)
1. A distributed online monitoring system based on 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 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 (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 multiple groups of 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 split and coupled to input ends of an optical fiber array (15) through the collimating lens (17), and 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 manner.
2. The distributed on-line monitoring system based on optical fiber photoacoustic sensing according to claim 1, it is characterized in that the other group of the excitation light source devices with the plurality of groups of 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 enable the laser emitting specific wavelength to enter the erbium-doped optical fiber amplifier (4), the erbium-doped optical fiber amplifier (4) amplifies optical power, the 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 a one-to-one correspondence mode, and 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.
3. The distributed online monitoring system based on optical fiber photoacoustic sensing according to claim 2, wherein another of the excitation light source devices in the multiple groups of different wavelength bands 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 laser light with specific wavelength, and the laser light is transmitted to the second optical switch (3) through optical fibers, and the second optical switch (3) controls the on and off of two optical paths, so that one of the laser light enters the erbium-doped fiber amplifier (4).
4. The distributed on-line monitoring system based on optical fiber photoacoustic sensing according to claim 1, it is characterized in that the detection light source device comprises an optical fiber wide 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 wide-spectrum light source (7) enters a third optical switch (9) through an 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 a one-to-one correspondence mode, interference spectra generated in each group of optical fiber photoacoustic sensing probes return to the third optical switch (9) from an optical fiber array (15) and are output to a spectrometer (10) through the optical fiber circulator (8), and an industrial personal computer (11) collects the spectra detected by the spectrometer (10) and performs signal processing and display.
5. A distributed on-line monitoring system based on fiber optic photoacoustic sensing according to claim 4, characterized in that the fiber optic broad spectrum light source (10) is a near infrared super-radiation light emitting diode SLED or an amplified spontaneous emission ASE light source.
6. The distributed online monitoring system based on optical fiber photoacoustic sensing according to claim 4, wherein the signal processing and displaying comprises: and demodulating the spectrum by adopting a high-speed spectrum demodulation method to obtain the dynamic cavity length of the interference cavity, measuring the cavity length change of the interference cavity to obtain the amplitude of the photoacoustic signal, and obtaining and displaying the gas concentration according to the proportional relation between the amplitude of the photoacoustic signal and the gas concentration.
7. The distributed online monitoring system based on optical fiber photoacoustic sensing according to claim 1, wherein there are 3 optical fiber photoacoustic sensing probes, which are respectively 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 output ends 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 to one output end of the optical fiber array (15).
8. The distributed on-line monitoring system based on optical fiber photoacoustic sensing according to claim 7, it is characterized in that 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 respectively 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), an optical fiber end face (20) and an optical fiber collimator (21) are arranged in parallel in the shell (22), 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 form an optical fiber probe, the optical fiber probe is connected with the 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 form an optical fiber probe, and the optical fiber probe is connected with the excitation light source device through the optical fiber array (15); the gas chamber (19) comprises a photoacoustic tube and a gas guide channel, the photoacoustic tube is horizontally arranged, one end of the photoacoustic tube is connected with the other end of the optical fiber collimator (21), the gas guide channel is vertically arranged, the upper end of the gas guide channel is communicated with the other end of the photoacoustic tube, the lower end of the gas guide channel is connected with the other end of the optical fiber end face (20), the sound wave sensitive membrane (18) is arranged on the right side of the gas guide channel in parallel, the sound wave sensitive membrane (18) serves as the right side face of the shell (22), a cantilever beam structure (181) is arranged on the sound wave sensitive membrane (18), the cantilever beam structure (181) is a rectangular groove with a downward free end, and external gas to be measured is diffused into the gas chamber (19) through a slot opening of the cantilever beam structure (181) on the sound wave sensitive membrane (18).
9. The distributed online monitoring system based on optical fiber photoacoustic sensing according to claim 8, wherein the photoacoustic excitation light source is incident into the gas chamber (19) through the optical fiber collimator (21) to excite a photoacoustic signal, and is detected by the acoustic wave sensitive membrane (18) installed outside the gas chamber (19), the free end of the cantilever beam structure of the acoustic wave sensitive membrane (18) and the end face (20) of the optical fiber form a fiber fabry-perot interference cavity, the photoacoustic signal vibrates the cantilever beam structure to cause the change of the length of the fabry-perot interference cavity, and the detection of the photoacoustic signal is realized by detecting the change of the length of the interference cavity.
10. The method for distributed on-line monitoring system based on fiber optic photoacoustic sensing according to any one of claims 1 to 9, 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 one gas, one gas detection or the time-sharing detection of multiple gas components is realized by selectively switching on one of the excitation light source devices or the multiple groups of excitation light source devices in time-sharing mode, each group of fiber optic photoacoustic sensing probes is placed in different monitoring areas, the gas detection in one monitoring area or the gas time-sharing detection in multiple monitoring areas is realized by selectively switching on one of the monitoring areas or switching on the fiber optic photoacoustic sensing probes corresponding to multiple monitoring areas in time-sharing mode, and the whole system performs distributed detection.
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