CN114264611A - Photoacoustic spectrum detection system based on optical fiber sensing - Google Patents
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Abstract
The invention is suitable for the technical field of oil gas detection, and provides an optical-acoustic spectrum detection system based on optical fiber sensing, which comprises an ultra-narrow-band optical fiber laser, a first optical isolator, piezoelectric ceramics and a second optical isolator, wherein the piezoelectric ceramics are also connected with a signal driving module, and the optical-acoustic spectrum detection system further comprises an optical fiber coupler, an optical fiber circulator, a triplexer, an acoustic sensing unit, a first Faraday optical rotation mirror, a second Faraday optical rotation mirror, a photoelectric detector, a collection card and a computer signal processing unit. According to the invention, the gas detection sensitivity is improved and the trace concentration detection of the gas is realized in an optical fiber sensing mode.
Description
Technical Field
The invention belongs to the technical field of oil gas detection, and particularly relates to a photoacoustic spectroscopy detection system based on optical fiber sensing.
Background
The gas detection principle in the photoacoustic spectroscopy oil is the photoacoustic effect of gas, namely, the gas absorbs a light source with a specific wavelength to generate a sound effect, and then the sound effect is amplified through an acoustic resonance structure, and the intensity of sound information is detected to reflect the concentration of the gas.
The laser photoacoustic spectroscopy oil-gas online monitoring system disclosed in application number CN201911032515.9 comprises an oil-gas separation unit, a gas-liquid separation unit and a gas-liquid separation unit, wherein the oil-gas separation unit is used for sampling dissolved gas in transformer oil and separating oil from gas; the gas path unit is connected with the oil-gas separation unit and used for conveying the sample gas after oil-gas separation; the photoacoustic detection unit is connected with the gas circuit unit, generates pulsed light by modulating a laser light source, generates sound waves after sample gas absorbs the pulsed light, detects the intensity of the sound waves by a microphone, and stores sound wave data; and the field control unit is connected with the oil-gas separation unit and the photoacoustic detection unit and used for transmitting field data to the workstation.
The microphone is a traditional detection mode of the photoacoustic spectrum to the resonance sound, needs to be electrified to work, is easily interfered by an electromagnetic field, and has limited sensitivity due to the influence of the aging degree of the diaphragm. The advantages of high sensitivity, electromagnetic interference resistance and the like of the existing optical fiber sensing are gradually reflected, and the optical fiber sensing acoustic detection device is applied to various industries, so that the optical fiber sensing acoustic detection device suitable for photoacoustic spectroscopy gas detection is manufactured by mainly adopting the principle of optical fiber sensing, the gas detection sensitivity is improved, and the purpose of trace gas detection is realized.
Disclosure of Invention
In view of the above problems, the present invention aims to provide a photoacoustic spectroscopy detection system based on optical fiber sensing, which aims to solve the above technical problems.
The invention adopts the following technical scheme:
the optoacoustic spectrum detection system comprises an ultra-narrow band optical fiber laser, a first optical isolator, piezoelectric ceramics and a second optical isolator which are connected in sequence, the piezoelectric ceramics are further connected with a signal driving module, the optoacoustic spectrum detection system comprises an optical fiber coupler, an optical fiber circulator, three couplers, an acoustic sensing unit, a first Faraday optical rotation mirror and a second Faraday optical rotation mirror, and further comprises a photoelectric detector, an acquisition card and a computer signal processing unit, wherein the photoelectric detector and the acquisition card are connected in a four-way and one-to-one correspondence manner, all the acquisition cards are connected to the computer signal processing unit, the optical fiber coupler is provided with an input end and two output ends, the input end of the optical fiber coupler is connected to the second optical isolator, two output ends of the optical fiber coupler are respectively connected to the optical fiber circulator and the first optical fiber circulator in a corresponding manner, and the optical fiber circulator is provided with three ports, the three ports are connected to the optical fiber coupler, the three couplers and the second path of photoelectric detector respectively in sequence, one side of each of the three couplers is divided into three paths which are connected to the optical fiber circulator, the third path of photoelectric detector and the fourth path of photoelectric detector respectively, the other side of each of the three couplers is divided into two paths which are connected to the acoustic sensing unit and the second Faraday rotation mirror respectively, and the acoustic sensing unit is further connected to the first Faraday rotation mirror.
Furthermore, four acquisition cards correspond to four photodetectors one by one, wherein signals output by the first acquisition card are reference signals p4, and signals output by the second acquisition card to the fourth acquisition card are fluctuation signals p1-p3 respectively; the processing procedure of the computer signal processing unit is as follows:
subtracting the reference signal p4 from the fluctuation signals p1-p3 to obtain three paths of difference signals D1-D3, and meanwhile, taking the average value D of the difference signals D1-D3;
subtracting the average value D from the three paths of difference signals D1-D3 respectively to obtain three paths of intermediate signals a, b and c, and performing differential calculation on the three paths of intermediate signals a, b and c respectively to obtain corresponding obtained signals D, e and f;
calculating three-way signals A51 ═ a (e-f), A52 ═ b (f-d), A53 ═ c (d-e), and summing the three-way signals A51-A53 to obtain a first signal N;
calculating the square values of the three intermediate signals a, b and c respectively, and then summing to obtain a second signal M;
and performing integration processing after calculation according to the N/M, and then demodulating the sound signal through a high-pass filter.
The invention has the beneficial effects that: the conventional photoacoustic spectrum detection device mainly adopts a microphone to realize the detection of photoacoustic signals, but the sensitivity of the microphone cannot be continuously improved, and the detection capability of gas trace concentration is limited.
Drawings
FIG. 1 is a schematic diagram of a photoacoustic spectroscopy detection system based on fiber sensing according to an embodiment of the present invention;
fig. 2 is a schematic diagram of a processing procedure of a computer signal processing unit according to an embodiment of the present invention.
Detailed Description
In order to make the objects, technical solutions and advantages of the present invention more apparent, the present invention is described in further detail below with reference to the accompanying drawings and embodiments. It should be understood that the specific embodiments described herein are merely illustrative of the invention and are not intended to limit the invention.
In order to explain the technical means of the present invention, the following description will be given by way of specific examples.
Fig. 1 shows a structure of a photoacoustic spectroscopy detection system based on optical fiber sensing according to an embodiment of the present invention, and only the relevant portions of the photoacoustic spectroscopy detection system according to an embodiment of the present invention are shown for convenience of illustration.
As shown in fig. 1, the photoacoustic spectrometry detection system based on optical fiber sensing provided in this embodiment includes an ultra-narrow band optical fiber laser 1, a first optical isolator 2, a piezoelectric ceramic 3, and a second optical isolator 4, which are connected in sequence, the piezoelectric ceramic 4 is further connected to a signal driving module 10, the photoacoustic spectrometry detection system includes an optical fiber coupler 5, an optical fiber circulator 6, a triplexer 7, an acoustic sensing unit 8, a first faraday rotator 9, a second faraday rotator 11, a photodetector 14, an acquisition card 12, and a computer signal processing unit 13, wherein the photodetector 14 and the acquisition card 12 are connected in four ways and in one-to-one correspondence, all the acquisition cards 12 are connected to the computer signal processing unit 13, the optical fiber coupler 5 has an input end and two output ends, the input end of the optical fiber coupler 5 is connected to the second optical isolator 4, two output ends of the optical fiber coupler 5 are respectively and correspondingly connected to the optical fiber circulator 6 and the first photo detector (i.e., PD4 'shown in the figure), the optical fiber circulator 6 has three ports, sequentially three ports are respectively connected to the optical fiber coupler 5, the third coupler 7 and the second photo detector (i.e., PD 1' shown in the figure), one side of the third coupler is divided into three paths and is respectively connected to the optical fiber circulator 6, the third photo detector (i.e., PD2 'shown in the figure) and the fourth photo detector (i.e., PD 3' shown in the figure), the other side is divided into two paths and is respectively connected to the acoustic sensing unit 8 and the second faraday rotation mirror 11, and the acoustic sensing unit 8 is further connected to the first faraday rotation mirror 9.
The working principle of the system is as follows:
the acoustic sensing unit is integrated into the photoacoustic cell, and the acoustic sensing unit and the photoacoustic cell can be designed into an integrated form. The gas in the detection oil is pumped into the photoacoustic cell, then the photoacoustic cell is irradiated by laser collimation, the gas in the photoacoustic cell generates sound waves with specific frequency after absorbing pulse laser, and the parameters of the sound waves are related to the concentration of the gas. Meanwhile, the laser signal is input into the acoustic sensing unit, and the sound wave can affect the output optical signal of the acoustic sensing unit, so that the original sound signal can be demodulated by finally analyzing the output optical signal of the acoustic sensing unit. The original sound signal after amplification is extracted by the demodulation system, and the acoustic signal is measured by adopting a phase-locked amplification mode, so that the measurement of the gas concentration is realized. The system also realizes the processing of the sound signals in a mode of phase-locked amplification and the like based on the principle, which is the prior art and is not described herein again.
Specifically, light source output light of the ultra-narrow band fiber laser is input into PLZ piezoelectric ceramics for modulation through a first optical isolator (for preventing reflected light), the modulation is driven through a signal driving module, then the light source output light is output through a second optical isolator (for preventing reflected light), the light source output light is divided into two paths through a fiber coupler, one path is collected through reference light which does not participate in sensing, and the reference light is collected through a first path of photoelectric detector and a first path of collection card; the other path of light is divided into the optical fiber sensing unit through the circulator and the three-three optical fiber couplers in sequence; in the figure, three couplers output two divided beams of light, one path of light is used as signal light and is subjected to acoustic sensing signal pickup through an acoustic sensing unit, then the signal light is reflected through a first Faraday rotator, the other path of light is used as reference light and is not subjected to any processing (simple sound insulation is needed in the test), the two paths of light are reflected through a second Faraday rotator, the two paths of light are evenly divided into three paths through the three couplers, the phases of the three paths of light signals are 180 degrees, the first path of light returns to the second path of photodetector through an optical fiber circulator, and the other two paths of light are respectively output to the third and fourth paths of photodetectors to form three paths of signal light in total. And finally, performing photoelectric conversion on the four paths of photoelectric detectors, acquiring the converted four paths of acquisition cards, inputting acquired signals into a computer signal processing unit, demodulating through an optical fiber demodulation algorithm, and extracting acoustic signals.
The four acquisition cards correspond to the four photoelectric detectors one by one, wherein signals output by the first acquisition card are reference signals p4, and signals output by the second acquisition card to the fourth acquisition card are fluctuation signals p1-p3 respectively; as shown in fig. 2, the processing procedure of the computer signal processing unit is as follows:
s1, subtracting the reference signal p4 from the fluctuation signals p1-p3 respectively to obtain three paths of difference signals D1-D3, and meanwhile, taking the average value D of the difference signals D1-D3.
Subtracting the reference signal p4 from p1-p3 to obtain an effective three-way difference signal:
according to formula (1), one can obtain (D1+ D2+ D3)/3 ═ D;
wherein A is the signal amplitude, the composite signal
Comprises a signal phi s to be measured and a system inherent initial phase
Environmentally induced phase shift
The requirement of this embodiment is the to-be-detected acoustic signal.
And S2, subtracting the average value D from the three difference signals D1-D3 respectively to obtain three intermediate signals, namely a, b and c, and performing differential calculation on the three intermediate signals a, b and c respectively to obtain corresponding obtained signals D, e and f.
After subtracting the average value D from D1-D3, respectively, there are:
then, differentiating the equation (2) with respect to time to obtain:
s3, calculating three-way signals a51 ═ a (e-f), a52 ═ b (f-d), and a53 ═ c (d-e), and summing three-way signals a51-a53 to obtain a first signal N.
Subtracting the results obtained by the formula (3) two by two, then cross-multiplying, and finally summing to obtain:
and S4, calculating the square values of the three paths of intermediate signals a, b and c respectively, and summing to obtain a second signal M.
S5, the signal is integrated after being calculated according to N/M, and then demodulated by a high-pass filter.
Then calculating M value and N/M value, and integrating N/M value with time to obtain
According to
Values, filtered by high-pass filtering
And
finally, the signal to be measured is obtained
I.e. a sound signal.
The above description is only for the purpose of illustrating the preferred embodiments of the present invention and is not to be construed as limiting the invention, and any modifications, equivalents and improvements made within the spirit and principle of the present invention are intended to be included within the scope of the present invention.
Claims (2)
1. The utility model provides a optoacoustic spectrum detecting system based on optical fiber sensing, a serial communication port, optoacoustic spectrum detecting system includes the super narrow band fiber laser, first optoisolator, piezoceramics, the second optoisolator that connect in order, piezoceramics still is connected with signal drive module, optoacoustic spectrum detecting system includes optical fiber coupler, optic fibre circulator, three couplers, acoustics sensing element, first Faraday optical rotatory mirror and second Faraday optical rotatory mirror, still includes photodetector, collection card and computer signal processing unit, wherein photodetector, collection card all have four ways and the one-to-one connection, all collection cards all are connected to computer signal processing unit, optical fiber coupler has an incoming end and two outgoing ends, optical fiber coupler's incoming end is connected to second optoisolator, optical fiber coupler's two outgoing ends correspond respectively and are connected to optic fibre circulator and first photoelectric detector all the way, the optical fiber circulator is provided with three ports, the three ports are connected to the optical fiber coupler, the three couplers and the second path of photoelectric detector in sequence, one side of each of the three couplers is divided into three paths to be connected to the optical fiber circulator, the third path of photoelectric detector and the fourth path of photoelectric detector, the other side of each of the three couplers is divided into two paths to be connected to the acoustic sensing unit and the second Faraday rotation mirror, and the acoustic sensing unit is further connected to the first Faraday rotation mirror.
2. The photoacoustic spectrometry system according to claim 1, wherein four acquisition cards are respectively associated with four photodetectors, wherein the signal output from the first acquisition card is a reference signal p4, and the signals output from the second acquisition card to the fourth acquisition card are respectively a fluctuation signal p1-p 3; the processing procedure of the computer signal processing unit is as follows:
subtracting the reference signal p4 from the fluctuation signals p1-p3 to obtain three paths of difference signals D1-D3, and meanwhile, taking the average value D of the difference signals D1-D3;
subtracting the average value D from the three paths of difference signals D1-D3 respectively to obtain three paths of intermediate signals a, b and c, and performing differential calculation on the three paths of intermediate signals a, b and c respectively to obtain corresponding obtained signals D, e and f;
calculating three-way signals A51 ═ a (e-f), A52 ═ b (f-d), A53 ═ c (d-e), and summing the three-way signals A51-A53 to obtain a first signal N;
calculating the square values of the three intermediate signals a, b and c respectively, and then summing to obtain a second signal M;
and performing integration processing after calculation according to the N/M, and then demodulating the sound signal through a high-pass filter.
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