CN111337453A - Multipoint gas concentration detection method and detection device for eliminating dynamic loss influence - Google Patents

Multipoint gas concentration detection method and detection device for eliminating dynamic loss influence Download PDF

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CN111337453A
CN111337453A CN202010289930.9A CN202010289930A CN111337453A CN 111337453 A CN111337453 A CN 111337453A CN 202010289930 A CN202010289930 A CN 202010289930A CN 111337453 A CN111337453 A CN 111337453A
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collimator
gas
detected
gas chamber
chamber
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王宗良
钱思宇
于元芳
田存伟
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Liaocheng University
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    • 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
    • G01N21/25—Colour; Spectral properties, i.e. comparison of effect of material on the light at two or more different wavelengths or wavelength bands
    • G01N21/31—Investigating relative effect of material at wavelengths characteristic of specific elements or molecules, e.g. atomic absorption spectrometry
    • G01N21/39—Investigating relative effect of material at wavelengths characteristic of specific elements or molecules, e.g. atomic absorption spectrometry using tunable lasers
    • G—PHYSICS
    • G01—MEASURING; TESTING
    • 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
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    • G—PHYSICS
    • G01—MEASURING; TESTING
    • G01N—INVESTIGATING OR ANALYSING MATERIALS BY DETERMINING THEIR CHEMICAL OR PHYSICAL PROPERTIES
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    • G01N21/01—Arrangements or apparatus for facilitating the optical investigation
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    • G—PHYSICS
    • G01—MEASURING; TESTING
    • 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
    • G01N21/25—Colour; Spectral properties, i.e. comparison of effect of material on the light at two or more different wavelengths or wavelength bands
    • G01N21/31—Investigating relative effect of material at wavelengths characteristic of specific elements or molecules, e.g. atomic absorption spectrometry
    • G01N21/39—Investigating relative effect of material at wavelengths characteristic of specific elements or molecules, e.g. atomic absorption spectrometry using tunable lasers
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Abstract

The invention discloses a multipoint gas concentration detection method and a multipoint gas concentration detection device for eliminating dynamic loss influence, wherein each gas chamber to be detected is connected with a photoacoustic cell with the same type in parallel as a reference gas chamber, the gas concentration of the reference gas chamber is known, second harmonic signals output by the two gas chambers are used as a ratio, the linear relation between the gas concentration of the gas chamber to be detected and the ratio of the second harmonic signals of the two gas chambers can be seen through the ratio, and the concentration information of the gas chamber to be detected can be directly obtained from the gas concentration of the reference gas chamber and the ratio of the second harmonic signals of the two gas chambers by utilizing the relational expression. The method can realize multi-point gas concentration detection and eliminate the influence of optical fiber bending loss and the influence of absorption loss of the first to-be-detected gas chamber on the second to-be-detected gas chamber, the first to-be-detected gas chamber and the second to-be-detected gas chamber on the front-end gas chamber during gas concentration detection of the third reference gas chamber.

Description

Multipoint gas concentration detection method and detection device for eliminating dynamic loss influence
Technical Field
The invention relates to the technical field of gas concentration detection, in particular to a multipoint gas concentration detection method and a multipoint gas concentration detection device for eliminating dynamic loss influence.
Background
The optical fiber gas sensing technology is a technology with wide prospect in the sensing field at present, the optical fiber gas sensor has specific application in a plurality of industries due to the advantages of high sensitivity, high precision, high response speed and the like, and particularly, in recent years, the explosion events of chemical plants are frequent, and a large amount of toxic and harmful gases seriously threaten the ecological environment and the human health, so that the detection of some harmful trace gases is particularly important for ensuring the safety of human beings. Moreover, in mining, oil and gas transmission pipeline, some enterprise operation workshops to some trace gas's detection, not only require high accuracy, still require to realize distributed multiple spot and detect to this safety in the guarantee operation, but at the in-process that multiple spot gas detected, receive external environment and self influence easily and produce the optical fiber loss, cause the gas detection precision low.
The optical fiber loss is an important mark of the optical fiber transmission quality, the factors causing the optical fiber loss are many, in the multi-point gas detection, dynamic loss caused by light bending and absorption of a detection air chamber at the front end of a series air chamber can gradually weaken the intensity of light after an optical signal is transmitted through the optical fiber, meanwhile, the optical signal can also gradually weaken, and the detection precision and stability are influenced because a background signal in the output signal of a subsequent phase-locked amplifier is overlarge.
Disclosure of Invention
The invention provides a multipoint gas concentration detection method and a multipoint gas concentration detection device which are reasonable in structural design, simple to operate and capable of effectively eliminating dynamic loss influence, and aims to overcome the defects in the prior art.
In order to achieve the purpose, the invention adopts the technical scheme that:
a multipoint gas concentration detection method for eliminating dynamic loss influence comprises the following steps:
(a) firstly, two waveforms output by a signal generator are superposed to form modulated light and laser beams emitted by a laser collimator, the laser beams are connected with a first coupler and divided into two beams, the two beams respectively enter a first air chamber to be detected and a first reference air chamber through a first collimator and a second collimator and then pass through a photoacoustic resonant cavity, the modulated light is absorbed by gas, sound waves generated by photoacoustic effect generate resonance on the wall of the photoacoustic resonant cavity, so that sound wave signals are enhanced, the signals are detected by a microphone, and the microphone converts the sound signals into electric signals to be output;
(b) the laser beam is collected by a third collimator and connected with a second coupler to be divided into two beams again, the two beams respectively enter a second gas chamber to be tested and a second reference gas chamber through a fifth collimator and a sixth collimator and then pass through the photoacoustic resonant cavity, the modulated light is absorbed by gas, the acoustic wave generated by the photoacoustic effect generates resonance on the wall of the photoacoustic resonant cavity, the acoustic wave signal is detected by a microphone, and the microphone converts the acoustic signal into an electric signal to be output;
(c) the laser beam is collected by a seventh collimator and connected with a third coupler to be divided into two beams again, the two beams respectively enter a third gas chamber to be tested and a third reference gas chamber through a ninth collimator and a tenth collimator and then pass through the photoacoustic resonant cavity, the modulated light is absorbed by gas, the acoustic wave generated by the photoacoustic effect generates resonance on the wall of the photoacoustic resonant cavity, the acoustic wave signal is detected by a microphone, and the microphone converts the acoustic signal into an electric signal to be output;
(d) the microphones of the first to-be-detected air chamber, the second to-be-detected air chamber, the third to-be-detected air chamber and the first reference air chamber, the second reference air chamber and the third reference air chamber are connected with the analog switch and used for controlling the signal output of each light path; the other end of the analog switch is connected with a pre-amplification circuit, a current signal is converted into a voltage signal, the voltage signal is extracted by a phase-locked amplifier, and finally a harmonic signal is collected by a data acquisition system and transmitted to a computer for data processing.
(e) The ratio of the collected harmonic signals of the first gas chamber to be detected and the first reference gas chamber is used for obtaining the linear relation between the gas concentration of the gas chamber to be detected and the ratio of the second harmonic signals of the two gas chambers, and the concentration information of the first gas chamber to be detected can be directly obtained from the gas concentration of the first reference gas chamber and the ratio of the second harmonic signals of the two gas chambers by using the relational expression; the ratio of the harmonic signals of the second air chamber to be detected and the second reference air chamber is made, and the concentration information of the second air chamber to be detected can be directly obtained from the gas concentration of the second reference air chamber and the ratio of the second harmonic signals of the two air chambers; then, the harmonic signals of the third air chamber to be detected and the third reference air chamber are used as a ratio, and the concentration information of the third air chamber to be detected is obtained according to the gas concentration of the third reference air chamber and the ratio of the second harmonic signals of the two air chambers; the multi-point gas concentration detection can be realized, and the influence of the bending loss of the optical fiber and the influence of the absorption loss of the front-end gas chamber caused by the first gas chamber to be detected on the second gas chamber to be detected, the first gas chamber to be detected and the second gas chamber to be detected on the gas concentration detection of the third reference gas chamber can be eliminated.
Further, the two waveforms output by the signal generator in the step (a) are sine wave and sawtooth wave.
Further, in order to ensure the signal intensity of the air chamber to be measured, the splitting ratios of the first coupler, the second coupler and the third coupler in the steps (a) - (c) are all 99: 1, namely the light beam entering the gas chamber to be measured is 99 percent, and the light beam entering the reference gas chamber is 1 percent.
The invention also provides a multipoint gas concentration detection device for eliminating dynamic loss influence, which is designed for realizing the detection method and comprises a signal generator, a voltage adder, a laser transmitter, a first coupler, a second coupler, a third coupler, an analog switch, a pre-amplification circuit, a phase-locked amplifier, a data acquisition system and a computer system, the signal output end of the signal generator is connected with the synchronous signal input end of the voltage adder, the synchronous signal output end at the other end of the signal generator is connected with the phase-locked amplifier, the output end of the voltage adder is connected with the laser transmitter, the output end of the laser transmitter is connected with a first coupler, the first coupler divides the light path into a first light path and a second light path according to a fixed coupling ratio, the first light path is provided with a first gas chamber to be measured containing unknown concentration information, and the second light path is provided with a first reference gas chamber containing fixed concentration information; a first collimator is arranged on the side wall of the first air chamber to be measured, and a third collimator is arranged on the other side wall corresponding to the first collimator; a second collimator is arranged on the side wall of the first reference air chamber, and a fourth collimator is arranged on the other side wall corresponding to the second collimator; the first gas chamber to be detected is connected with a second coupler through a third collimator, the second coupler divides output light from the first gas chamber to be detected into a third light path and a fourth light path according to a fixed coupling ratio, the third light path is provided with a second gas chamber to be detected containing unknown concentration information, the fourth light path is provided with a second reference gas chamber containing fixed concentration information, a fifth collimator is arranged on the side wall of the second gas chamber to be detected, and a seventh collimator is arranged on the other side wall corresponding to the fifth collimator; a sixth collimator is arranged on the side wall of the second reference air chamber, and an eighth collimator is arranged on the other side wall corresponding to the sixth collimator; the second gas chamber to be measured is connected with a third coupler through a seventh collimator, the third coupler divides the output light of the second gas chamber to be measured into a fifth light path and a sixth light path according to a fixed coupling ratio, the fifth light path is provided with a third gas chamber to be measured containing unknown concentration information, the sixth light path is provided with a third reference gas chamber containing fixed concentration information, the side wall of the third gas chamber to be measured is provided with a ninth collimator, and the other side wall corresponding to the ninth collimator is provided with an eleventh collimator; a tenth collimator is arranged on the side wall of the third reference air chamber, and a twelfth collimator is arranged on the other side wall corresponding to the tenth collimator; the photoacoustic cell comprises a first air chamber to be detected, a second air chamber to be detected, a third air chamber to be detected, a first reference air chamber, a second reference air chamber and a third reference air chamber, and is characterized in that the first air chamber to be detected, the second air chamber to be detected, the third air chamber to be detected, the first reference air chamber, the second reference air chamber and the third reference air chamber are photoacoustic cells with the same model and size, a photoacoustic resonant cavity and a microphone are arranged in the photoacoustic cells, the photoacoustic resonant cavity is cylindrical, the first air chamber to be detected, the second air chamber to be detected, the third air chamber to be detected, the microphone of the first reference air chamber, the second reference air chamber and the third reference air chamber are connected with an analog switch, the signal output end of the analog switch is connected with a pre-amplification circuit, the output end of the.
Further, the laser emitter is a butterfly-shaped distributed feedback semiconductor laser.
Furthermore, the first air chamber to be tested and the first reference air chamber, the second air chamber to be tested and the second reference air chamber, and the third air chamber to be tested and the third reference air chamber are respectively encapsulated by shells, so that the fixing is convenient; and each air chamber is provided with an air inlet and an air outlet.
Further, the laser beam of the first optical path enters the first gas chamber to be measured through the first collimator, passes through the photoacoustic resonant cavity of the first gas chamber to be measured, and is collected by the third collimator; and the laser beam of the second light path enters the first reference gas chamber through the second collimator, passes through the photoacoustic resonant cavity of the first reference gas chamber, and is collected by the fourth collimator.
Further, the laser beam of the light path three enters the second gas chamber to be measured through the fifth collimator, passes through the photoacoustic resonant cavity of the second gas chamber to be measured, and is collected by the seventh collimator; and the laser beam of the light path four enters the second reference gas chamber through the sixth collimator and passes through the photoacoustic resonant cavity of the second reference gas chamber, and the laser beam is collected by the eighth collimator.
Further, the laser beam of the optical path five enters the third air chamber to be tested through the ninth collimator, passes through the photoacoustic resonant cavity of the third air chamber to be tested, and is collected by the eleventh collimator; and the laser beam of the light path six enters the third reference gas chamber through the tenth collimator, passes through the photoacoustic resonant cavity of the third reference gas chamber and is collected by the twelfth collimator.
Compared with the prior art, the invention has the beneficial effects that:
the invention provides a multipoint gas concentration detection method for eliminating dynamic loss influence, which is characterized in that a ratio of collected harmonic signals of a first gas chamber to be detected and a first reference gas chamber is made, so that the linear relation between the gas concentration of the gas chamber to be detected and the ratio of second harmonic signals of two gas chambers can be obtained, and the concentration information of the first gas chamber to be detected can be directly obtained from the gas concentration of the first reference gas chamber and the ratio of the second harmonic signals of the two gas chambers by utilizing the relational expression. And (4) making a ratio of the second gas chamber to be detected and the second reference gas chamber harmonic signal, and solving the concentration information of the second gas chamber to be detected according to the gas concentration of the second reference gas chamber and the ratio of the second harmonic signal of the two gas chambers. And then, the ratio of the harmonic signals of the third air chamber to be detected and the third reference air chamber is made, and the concentration information of the third air chamber to be detected can be obtained according to the gas concentration of the third reference air chamber and the ratio of the second harmonic signals of the two air chambers. The multi-point gas concentration detection can be realized, and the influence of the bending loss of the optical fiber and the influence of the absorption loss of the front-end gas chamber caused by the first gas chamber to be detected on the second gas chamber to be detected, the first gas chamber to be detected and the second gas chamber to be detected on the gas concentration detection of the third reference gas chamber can be eliminated. The method has more advantages in technology, has high feasibility, and can greatly improve the measurement precision in multi-point gas detection.
By providing the multipoint gas detection method for eliminating the dynamic loss, the linear relation between the gas concentration of the gas chamber to be detected and the ratio of the second harmonic signals of the two gas chambers is obtained, and the multipoint gas concentration detection device for eliminating the influence of the dynamic loss is designed. The stability of whole system detection is improved, higher practical value has very high feasibility to measurement accuracy in the multiple spot gas detection can be improved greatly.
Drawings
Fig. 1 is a schematic structural diagram in an embodiment of the present invention.
In the figure: 1-signal generator, 2-voltage adder, 3-laser emitter, 4-first coupler, 5-second coupler, 6-third coupler, 7-analog switch, 8-preamplification circuit, 9-phase-locked amplifier, 10-data acquisition system, 11-computer system, 12-light path I, 13-light path II, 14-first gas chamber to be measured, 15-first reference gas chamber, 16-first collimator, 17-second collimator, 18-third collimator, 19-fourth collimator, 20-light path III, 21-light path IV, 22-second gas chamber to be measured, 23-second reference gas chamber, 24-fifth collimator, 25-sixth collimator, 26-seventh collimator, 27-an eighth collimator, 28-a fifth light path, 29-a sixth light path, 30-a third gas chamber to be measured, 31-a third reference gas chamber, 32-a ninth collimator, 33-a tenth collimator, 34-an eleventh collimator, 35-a twelfth collimator, 36-a photoacoustic resonant cavity, 37-a microphone, 38-a shell, 39-a gas inlet and 40-a gas outlet.
Detailed Description
The technical solutions in the embodiments of the present invention will be clearly and completely described below with reference to the drawings in the embodiments of the present invention, and it is obvious that the described embodiments are only a part of the embodiments of the present invention, and not all of the 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.
Referring to fig. 1, a method for detecting a multipoint gas concentration without dynamic loss influence includes the following steps:
(a) firstly, two waveforms output by a signal generator are superposed to form modulated light and laser beams emitted by a laser collimator, the laser beams are connected with a first coupler and divided into two beams, the two beams respectively enter a first air chamber to be detected and a first reference air chamber through a first collimator and a second collimator and then pass through a photoacoustic resonant cavity, the modulated light is absorbed by gas, sound waves generated by photoacoustic effect generate resonance on the wall of the photoacoustic resonant cavity, so that sound wave signals are enhanced, the signals are detected by a microphone, and the microphone converts the sound signals into electric signals to be output;
(b) the laser beam is collected by a third collimator and connected with a second coupler to be divided into two beams again, the two beams respectively enter a second gas chamber to be tested and a second reference gas chamber through a fifth collimator and a sixth collimator and then pass through the photoacoustic resonant cavity, the modulated light is absorbed by gas, the acoustic wave generated by the photoacoustic effect generates resonance on the wall of the photoacoustic resonant cavity, the acoustic wave signal is detected by a microphone, and the microphone converts the acoustic signal into an electric signal to be output;
(c) the laser beam is collected by a seventh collimator and connected with a third coupler to be divided into two beams again, the two beams respectively enter a third gas chamber to be tested and a third reference gas chamber through a ninth collimator and a tenth collimator and then pass through the photoacoustic resonant cavity, the modulated light is absorbed by gas, the acoustic wave generated by the photoacoustic effect generates resonance on the wall of the photoacoustic resonant cavity, the acoustic wave signal is detected by a microphone, and the microphone converts the acoustic signal into an electric signal to be output;
(d) the microphones of the first to-be-detected air chamber, the second to-be-detected air chamber, the third to-be-detected air chamber and the first reference air chamber, the second reference air chamber and the third reference air chamber are connected with the analog switch and used for controlling the signal output of each light path; the other end of the analog switch is connected with a pre-amplification circuit, a current signal is converted into a voltage signal, the voltage signal is extracted by a phase-locked amplifier, and finally a harmonic signal is collected by a data acquisition system and transmitted to a computer for data processing.
(e) The ratio of the collected harmonic signals of the first gas chamber to be detected and the first reference gas chamber is used for obtaining the linear relation between the gas concentration of the gas chamber to be detected and the ratio of the second harmonic signals of the two gas chambers, and the concentration information of the first gas chamber to be detected can be directly obtained from the gas concentration of the first reference gas chamber and the ratio of the second harmonic signals of the two gas chambers by using the relational expression; the ratio of the harmonic signals of the second air chamber to be detected and the second reference air chamber is made, and the concentration information of the second air chamber to be detected can be directly obtained from the gas concentration of the second reference air chamber and the ratio of the second harmonic signals of the two air chambers; then, the harmonic signals of the third air chamber to be detected and the third reference air chamber are used as a ratio, and the concentration information of the third air chamber to be detected is obtained according to the gas concentration of the third reference air chamber and the ratio of the second harmonic signals of the two air chambers; the multi-point gas concentration detection can be realized, and the influence of the bending loss of the optical fiber and the influence of the absorption loss of the front-end gas chamber caused by the first gas chamber to be detected on the second gas chamber to be detected, the first gas chamber to be detected and the second gas chamber to be detected on the gas concentration detection of the third reference gas chamber can be eliminated.
Further, the two waveforms output by the signal generator in the step (a) are sine wave and sawtooth wave.
Further, in order to ensure the signal intensity of the air chamber to be measured, the splitting ratios of the first coupler, the second coupler and the third coupler in the steps (a) - (c) are all 99: 1, namely the light beam entering the gas chamber to be measured is 99 percent, and the light beam entering the reference gas chamber is 1 percent.
The invention also provides a multipoint gas concentration detection device for eliminating the influence of dynamic loss, which is designed for realizing the detection method and comprises a signal generator 1, a voltage adder 2, a laser transmitter 3, a first coupler 4, a second coupler 5, a third coupler 6, an analog switch 7, a pre-amplification circuit 8, a lock-in amplifier 9, a data acquisition system 10 and a computer system 11, wherein the signal output end of the signal generator 1 is connected with the synchronous signal input end of the voltage adder 2, the synchronous signal output end at the other end of the signal generator 1 is connected with the lock-in amplifier 9, the output end of the voltage adder 2 is connected with the laser transmitter 3, the output end of the laser transmitter 3 is connected with the first coupler 4, the first coupler 4 divides the light path into a first light path 12 and a second light path 13 according to a fixed coupling ratio, the first light path 12 is provided with a first gas chamber to be detected 14 containing unknown concentration information, the second light path 13 is provided with a first reference gas chamber 15 containing fixed concentration information; a first collimator 16 is arranged on the side wall of the first air chamber to be measured 14, and a third collimator 18 is arranged on the other side wall corresponding to the first collimator 16; a second collimator 17 is arranged on the side wall of the first reference gas chamber 15, and a fourth collimator 19 is arranged on the other side wall corresponding to the second collimator 17; the first gas chamber to be measured 14 is connected with the second coupler 5 through the third collimator 18, the second coupler 5 divides the output light from the first gas chamber to be measured 14 into a third light path 20 and a fourth light path 21 again according to a fixed coupling ratio, the third light path 20 is provided with a second gas chamber to be measured 22 containing unknown concentration information, the fourth light path 21 is provided with a second reference gas chamber 23 containing fixed concentration information, the side wall of the second gas chamber to be measured 22 is provided with a fifth collimator 24, and the other side wall corresponding to the fifth collimator 24 is provided with a seventh collimator 26; a sixth collimator 25 is arranged on the side wall of the second reference gas chamber 23, and an eighth collimator 27 is arranged on the other side wall corresponding to the sixth collimator 25; the second gas chamber to be measured 22 is connected with the third coupler 6 through the seventh collimator 26, the third coupler 6 divides the output light of the second gas chamber to be measured 22 into a fifth light path 28 and a sixth light path 29 again according to a fixed coupling ratio, the fifth light path 28 is provided with a third gas chamber to be measured 30 containing unknown concentration information, the sixth light path 29 is provided with a third reference gas chamber 31 containing fixed concentration information, a ninth collimator 32 is arranged on a side wall of the third gas chamber to be measured 30, and an eleventh collimator 34 is arranged on the other side wall corresponding to the ninth collimator 32; a tenth collimator 33 is arranged on the side wall of the third reference gas chamber 31, and a twelfth collimator 35 is arranged on the other side wall corresponding to the tenth collimator 33; the first to-be-measured air chamber 14, the second to-be-measured air chamber 22 and the third to-be-measured air chamber 30, the first reference air chamber 15, the second reference air chamber 23 and the third reference air chamber 31 are photoacoustic cells with the same type and size, a photoacoustic resonant cavity 36 and a microphone 37 are arranged in the photoacoustic cells, the photoacoustic resonant cavity 36 is cylindrical, the microphones 37 of the first to-be-measured gas chamber 14, the second to-be-measured gas chamber 22, the third to-be-measured gas chamber 30, the first reference gas chamber 15, the second reference gas chamber 23 and the third reference gas chamber 31 are connected with the analog switch 7, the signal output end of the analog switch 7 is connected to the preamplifier circuit 8, the output end of the pre-amplification circuit 8 is connected with a phase-locked amplifier 9, the signal extracted by the phase-locked amplifier 9 is collected and processed by a data collection system 10, and the signal output end of the data collection system 10 is connected to a computer system 11.
Further, the laser emitter 3 is a butterfly-shaped distributed feedback semiconductor laser.
Further, the first to-be-tested air chamber 14 and the first reference air chamber 15, the second to-be-tested air chamber 22 and the second reference air chamber 23, and the third to-be-tested air chamber 30 and the third reference air chamber 31 are respectively packaged by using a shell 38, so that the fixing is facilitated; each air chamber is provided with an air inlet 39 and an air outlet 40.
Further, the laser beam of the first optical path 12 enters the first gas chamber to be measured 14 through the first collimator 16, passes through the photoacoustic resonant cavity 36 of the first gas chamber to be measured 14, and is collected by the third collimator 18; the laser beam of the second optical path 13 enters the first reference gas cell 15 through the second collimator 17, passes through the photoacoustic resonant cavity 36 of the first reference gas cell 15, and is collected by the fourth collimator 19.
Further, the laser beam of the light path three 20 enters the second gas chamber 22 to be measured through the fifth collimator 24, passes through the photoacoustic resonant cavity 36 of the second gas chamber 22 to be measured, and is collected by the seventh collimator 26; the laser beam of the optical path four 21 enters the second reference gas cell 23 through the sixth collimator 25, passes through the photoacoustic resonant cavity 36 of the second reference gas cell 23, and is collected by the eighth collimator 27.
Further, the laser beam of the optical path five 28 enters the third gas chamber to be measured 30 through the ninth collimator 32, passes through the photoacoustic resonant cavity 36 of the third gas chamber to be measured 30, and is collected by the eleventh collimator 34; the laser beam in the optical path six 29 enters the third reference gas cell 31 through the tenth collimator 33, passes through the photoacoustic resonant cavity 36 of the third reference gas cell 31, and is collected by the twelfth collimator 35.
The multipoint gas concentration detection method for eliminating the dynamic loss influence divides the second harmonic amplitude of the gas chamber to be detected and the second harmonic amplitude of the reference gas chamber, theoretical derivation can show that the gas concentration of the gas chamber to be detected and the ratio of the second harmonic signals of the two gas chambers are in a linear relation, and the concentration information of the gas chamber to be detected can be directly obtained from the gas concentration of the reference gas chamber and the ratio of the second harmonic signals of the two gas chambers by utilizing the relational expression. The multipoint optical fiber gas sensing system is connected well, and gas to be measured is filled into the gas chamber.
When multipoint gas sensing detects, the photoacoustic signal is collected and transmitted through signal processing units at all levels, and the second harmonic of the signal is extracted through a phase-locked amplifier, wherein the formula of the second harmonic can be expressed as follows:
S2f＝Sm·CFP·cos(ψ)·H2(v0)
wherein, S2F is a second harmonic signal extracted by the lock-in amplifier, Sm is microphone sensitivity, C is target gas concentration, F is photoacoustic cell response frequency, P is input optical power, ψ is phase difference between the lock-in amplifier and laser amplitude modulation, and H2(cm-1) is the size of the second harmonic obtained by fourier cosine series expansion of the absorption profile at the center of the target gas absorption line.
In the transmission process, the influence of self or external environment always generates optical fiber bending loss, optical fiber insertion loss and the influence of the absorption of the front-end air chamber on the gas detection of the rear air chamber. The most direct embodiment of the dynamic loss of the part is that the incident laser energy is weakened and the optical power is attenuated. The second harmonic signal extracted by the lock-in amplifier is also attenuated.
The invention provides a multipoint gas concentration detection method for eliminating dynamic loss in an optical fiber sensing system, namely, each gas chamber to be detected is connected with a photoacoustic cell with the same type and size in parallel and serves as a reference gas chamber, and the two gas chambers are filled with the same gas with different concentrations, wherein the concentration of the reference gas chamber is known. The second harmonic ratio formula extracted from the two air chambers can be expressed as:
Figure BDA0002450023600000111
when Sm.F.cos (psi) ═ omega, the above formula can be simplified to
Figure BDA0002450023600000112
When the models of the photoacoustic cell and the microphone are not changed and the phase difference between the phase-locked amplifier and the laser amplitude modulation is not changed artificially, the sensitivity Sm of the microphone, the response frequency F of the photoacoustic cell and the phase difference psi between the phase-locked amplifier and the laser amplitude modulation are not changed, namely the parameter omega can be changed into a constant value, the lambda is the ratio of the gas chamber to be measured and the reference gas chamber omega, namely the lambda is also a constant
Figure BDA0002450023600000113
The two photoacoustic cells are connected in parallel and are connected through the optical fiber coupler, the splitting ratio of the optical fiber coupler is β: theta, the optical power is I before passing through a coupling area, laser divides an optical path into two paths through the coupler, the two optical paths respectively enter the air chamber to be measured and the reference air chamber, because the bending degree and the length of the optical fiber are different, after the coupling area is split, two beams of laser reach the two air chambers through the two optical fibers, the optical power loss ratio from the coupling area to the two air chambers is I: j respectively, and the optical power ratio reaching the two air chambers has the following relation:
Figure BDA0002450023600000114
the laser enters the two air chambers from the coupling area, the dynamic loss of the laser is mainly influenced by the bending degree and the length of the optical fiber, the two air chambers are packaged by the shell, the influence of the bending of the optical fiber before entering the shell on the two air chambers is the same, and the interference of the external environment on the two air chambers can be effectively reduced, namely, the bending loss is mainly influenced by the bending loss of the section of the optical fiber which reaches the two air chamber collimators after entering the shell, the bending degree and the length of the section of the optical fiber which is separated from the two air chambers are fixed, so the loss ratio i: j is a fixed ratio, and meanwhile, the splitting ratio β: theta of the coupler is also a fixed value:
Figure BDA0002450023600000121
at this time η is a constant value
By substituting the formulae (3), (4) and (5) into the formula (1)
Figure BDA0002450023600000122
In the relation, the second harmonic signals of the gas chamber to be measured and the reference gas chamber can be selectively output by the analog switch, and are obtained by the phase-locked amplifier, the gas concentration of the reference gas chamber B is known, and the concentration of the gas chamber A to be measured can be obtained, and the formula (6) can be transformed to obtain:
Figure BDA0002450023600000123
the linear relation between the gas concentration of the gas chamber to be measured and the ratio of the second harmonic signals of the two gas chambers can be seen in the formula, the concentration information of the gas chamber to be measured can be directly obtained from the gas concentration of the reference gas chamber and the ratio of the second harmonic signals of the two gas chambers by utilizing the relation,
the optical power loss effect caused by front-end air chamber absorption can also be eliminated by the formula (7) because of the beer-Lambert law Iout＝Iin·e-αCL，IoutIs the transmitted light intensity, IinThe front ends of the second gas chamber to be measured and the second reference gas chamber pass through the same light path, and the light path enters the first gas chamber to be measured through the first coupler and then passes through the second gas chamber to be measuredThe coupler enters a second gas chamber to be tested and a second reference gas chamber. The light path has an absorption loss influence on a second air chamber to be detected and a second reference air chamber after passing through the first air chamber to be detected. The optical power is reduced, and the absorption loss influence caused by the first air chamber to be detected is the same, so that the absorption loss influence on the second air chamber to be detected and the second reference air chamber is the same, and the absorption loss components of the second air chamber to be detected and the second reference air chamber are directly reduced by a ratio method in the formula (7), so that the absorption loss influence is eliminated. For the third air chamber to be tested and the third reference air chamber, the front ends of the third air chamber to be tested and the third reference air chamber pass through the same light path, and the light path enters the first air chamber to be tested through the first coupler, then enters the second air chamber to be tested through the second coupler, and finally reaches the third air chamber to be tested and the third reference air chamber. The light path has an absorption loss influence on a third air chamber to be detected and a third reference air chamber at the rear end after passing through the first air chamber to be detected and the second air chamber to be detected. The optical power is reduced, because the absorption losses of the first air chamber to be detected and the second air chamber to be detected are all the absorption losses caused by the first air chamber to be detected and the second air chamber to be detected, the absorption losses of the third air chamber to be detected and the third reference air chamber are all the same, and then through a ratio method in the formula (7), the absorption loss components of the second air chamber to be detected and the second reference air chamber are directly reduced, so that the influence of the absorption losses is eliminated.
According to the formula (7), the gas concentration value of the gas chamber to be detected is only related to the ratio of the second harmonic signal of the two gas chambers and the concentration value of the reference gas chamber, if the gas concentration value of the reference light path gas chamber is fixed, the gas concentration of the gas chamber to be detected can be obtained according to the collected ratio of the second harmonic signal of the gas chamber to be detected and the second harmonic signal of the reference gas chamber, and the analog switch can be used for controlling the output of multiple paths of signals, so that the multi-point gas detection is. Meanwhile, the optical power loss influence and optical power fluctuation caused by optical fiber bending and front end air chamber gas absorption can be eliminated.
In multi-point gas detection, the method can eliminate dynamic influences including optical fiber bending loss, gas chamber absorption loss and the like, and achieves high measurement precision and long detection distance. Meanwhile, the number of the connecting optical fibers is reduced, the detection stability of the whole system is improved, and the method has the advantages of low cost and high practical value.
Although embodiments of the present invention have been shown and described, it will be appreciated by those skilled in the art that changes, modifications, substitutions and alterations can be made in these embodiments without departing from the principles and spirit of the invention, the scope of which is defined in the appended claims and their equivalents.

Claims (9)

1. A multipoint gas concentration detection method for eliminating dynamic loss influence is characterized by comprising the following steps:
(a) firstly, two waveforms output by a signal generator are superposed to form modulated light and laser beams emitted by a laser collimator, the laser beams are connected with a first coupler and divided into two beams, the two beams respectively enter a first air chamber to be detected and a first reference air chamber through a first collimator and a second collimator and then pass through a photoacoustic resonant cavity, the modulated light is absorbed by gas, sound waves generated by photoacoustic effect generate resonance on the wall of the photoacoustic resonant cavity, so that sound wave signals are enhanced, the signals are detected by a microphone, and the microphone converts the sound signals into electric signals to be output;
(b) the laser beam is collected by a third collimator and connected with a second coupler to be divided into two beams again, the two beams respectively enter a second gas chamber to be tested and a second reference gas chamber through a fifth collimator and a sixth collimator and then pass through the photoacoustic resonant cavity, the modulated light is absorbed by gas, the acoustic wave generated by the photoacoustic effect generates resonance on the wall of the photoacoustic resonant cavity, the acoustic wave signal is detected by a microphone, and the microphone converts the acoustic signal into an electric signal to be output;
(c) the laser beam is collected by a seventh collimator and connected with a third coupler to be divided into two beams again, the two beams respectively enter a third gas chamber to be tested and a third reference gas chamber through a ninth collimator and a tenth collimator and then pass through the photoacoustic resonant cavity, the modulated light is absorbed by gas, the acoustic wave generated by the photoacoustic effect generates resonance on the wall of the photoacoustic resonant cavity, the acoustic wave signal is detected by a microphone, and the microphone converts the acoustic signal into an electric signal to be output;
(d) the microphones of the first to-be-detected air chamber, the second to-be-detected air chamber, the third to-be-detected air chamber and the first reference air chamber, the second reference air chamber and the third reference air chamber are connected with the analog switch and used for controlling the signal output of each light path; the other end of the analog switch is connected with a pre-amplification circuit, a current signal is converted into a voltage signal, the voltage signal is extracted by a phase-locked amplifier, and finally a harmonic signal is collected by a data acquisition system and transmitted to a computer for data processing.
(e) The ratio of the collected harmonic signals of the first gas chamber to be detected and the first reference gas chamber is used for obtaining the linear relation between the gas concentration of the gas chamber to be detected and the ratio of the second harmonic signals of the two gas chambers, and the concentration information of the first gas chamber to be detected can be directly obtained from the gas concentration of the first reference gas chamber and the ratio of the second harmonic signals of the two gas chambers by using the relational expression; the ratio of the harmonic signals of the second air chamber to be detected and the second reference air chamber is made, and the concentration information of the second air chamber to be detected can be directly obtained from the gas concentration of the second reference air chamber and the ratio of the second harmonic signals of the two air chambers; then, the harmonic signals of the third air chamber to be detected and the third reference air chamber are used as a ratio, and the concentration information of the third air chamber to be detected is obtained according to the gas concentration of the third reference air chamber and the ratio of the second harmonic signals of the two air chambers; the multi-point gas concentration detection can be realized, and the influence of the bending loss of the optical fiber and the influence of the absorption loss of the front-end gas chamber caused by the first gas chamber to be detected on the second gas chamber to be detected, the first gas chamber to be detected and the second gas chamber to be detected on the gas concentration detection of the third reference gas chamber can be eliminated.
2. The method according to claim 1, wherein the two waveforms outputted from the signal generator in step (a) are sine wave and sawtooth wave.
3. The method according to claim 1, wherein in order to ensure the signal strength of the gas cell to be tested, the splitting ratios of the first coupler, the second coupler and the third coupler in steps (a) - (c) are all 99: 1, namely the light beam entering the gas chamber to be measured is 99 percent, and the light beam entering the reference gas chamber is 1 percent.
4. A multipoint gas concentration detection device for eliminating dynamic loss influence is characterized by comprising a signal generator, a voltage adder, a laser transmitter, a first coupler, a second coupler, a third coupler, an analog switch, a pre-amplification circuit, a phase-locked amplifier, a data acquisition system and a computer system, the signal output end of the signal generator is connected with the synchronous signal input end of the voltage adder, the synchronous signal output end at the other end of the signal generator is connected with the phase-locked amplifier, the output end of the voltage adder is connected with the laser transmitter, the output end of the laser transmitter is connected with a first coupler, the first coupler divides the light path into a first light path and a second light path according to a fixed coupling ratio, the first light path is provided with a first gas chamber to be measured containing unknown concentration information, and the second light path is provided with a first reference gas chamber containing fixed concentration information; a first collimator is arranged on the side wall of the first air chamber to be measured, and a third collimator is arranged on the other side wall corresponding to the first collimator; a second collimator is arranged on the side wall of the first reference air chamber, and a fourth collimator is arranged on the other side wall corresponding to the second collimator; the first gas chamber to be detected is connected with a second coupler through a third collimator, the second coupler divides output light from the first gas chamber to be detected into a third light path and a fourth light path according to a fixed coupling ratio, the third light path is provided with a second gas chamber to be detected containing unknown concentration information, the fourth light path is provided with a second reference gas chamber containing fixed concentration information, a fifth collimator is arranged on the side wall of the second gas chamber to be detected, and a seventh collimator is arranged on the other side wall corresponding to the fifth collimator; a sixth collimator is arranged on the side wall of the second reference air chamber, and an eighth collimator is arranged on the other side wall corresponding to the sixth collimator; the second gas chamber to be measured is connected with a third coupler through a seventh collimator, the third coupler divides the output light of the second gas chamber to be measured into a fifth light path and a sixth light path according to a fixed coupling ratio, the fifth light path is provided with a third gas chamber to be measured containing unknown concentration information, the sixth light path is provided with a third reference gas chamber containing fixed concentration information, the side wall of the third gas chamber to be measured is provided with a ninth collimator, and the other side wall corresponding to the ninth collimator is provided with an eleventh collimator; a tenth collimator is arranged on the side wall of the third reference air chamber, and a twelfth collimator is arranged on the other side wall corresponding to the tenth collimator; the photoacoustic cell comprises a first air chamber to be detected, a second air chamber to be detected, a third air chamber to be detected, a first reference air chamber, a second reference air chamber and a third reference air chamber, and is characterized in that the first air chamber to be detected, the second air chamber to be detected, the third air chamber to be detected, the first reference air chamber, the second reference air chamber and the third reference air chamber are photoacoustic cells with the same model and size, a photoacoustic resonant cavity and a microphone are arranged in the photoacoustic cells, the photoacoustic resonant cavity is cylindrical, the first air chamber to be detected, the second air chamber to be detected, the third air chamber to be detected, the microphone of the first reference air chamber, the second reference air chamber and the third reference air chamber are connected with an analog switch, the signal output end of the analog switch is connected with a pre-amplification circuit, the output end of the.
5. The multipoint gas concentration detection device for eliminating the dynamic loss influence according to claim 4, wherein the laser emitter is a butterfly distributed feedback semiconductor laser.
6. The multipoint gas concentration detection device for eliminating the dynamic loss influence according to claim 4, wherein the first to-be-detected gas chamber and the first reference gas chamber, the second to-be-detected gas chamber and the second reference gas chamber, and the third to-be-detected gas chamber and the third reference gas chamber are respectively encapsulated by shells for being fixed conveniently; and each air chamber is provided with an air inlet and an air outlet.
7. The multipoint gas concentration detection apparatus for eliminating the dynamic loss influence according to claim 4, wherein the laser beam of the first optical path enters the first gas chamber to be measured through the first collimator, passes through the photoacoustic resonant cavity of the first gas chamber to be measured, and is collected by the third collimator; and the laser beam of the second light path enters the first reference gas chamber through the second collimator, passes through the photoacoustic resonant cavity of the first reference gas chamber, and is collected by the fourth collimator.
8. The multipoint gas concentration detection apparatus for eliminating the dynamic loss influence according to claim 4, wherein the laser beam of the optical path three enters the second gas chamber to be tested through a fifth collimator, passes through the photoacoustic resonant cavity of the second gas chamber to be tested, and is collected by a seventh collimator; and the laser beam of the light path four enters the second reference gas chamber through the sixth collimator and passes through the photoacoustic resonant cavity of the second reference gas chamber, and the laser beam is collected by the eighth collimator.
9. The multipoint gas concentration detection apparatus for eliminating the dynamic loss influence according to claim 4, wherein the laser beam of the optical path five enters the third gas chamber to be tested through a ninth collimator, passes through the photoacoustic resonant cavity of the third gas chamber to be tested, and is collected by an eleventh collimator; and the laser beam of the light path six enters the third reference gas chamber through the tenth collimator, passes through the photoacoustic resonant cavity of the third reference gas chamber and is collected by the twelfth collimator.
CN202010289930.9A 2020-04-14 2020-04-14 Multipoint gas concentration detection method and detection device for eliminating dynamic loss influence Pending CN111337453A (en)

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Cited By (2)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
CN111829968A (en) * 2020-07-09 2020-10-27 长沙矿山研究院有限责任公司 Multi-stage transient dynamic performance measuring device of laser gas concentration measuring sensor
CN112461765A (en) * 2020-10-16 2021-03-09 南京南智先进光电集成技术研究院有限公司 Gas concentration measuring system and method based on photoacoustic spectrometry

Cited By (3)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
CN111829968A (en) * 2020-07-09 2020-10-27 长沙矿山研究院有限责任公司 Multi-stage transient dynamic performance measuring device of laser gas concentration measuring sensor
CN111829968B (en) * 2020-07-09 2024-04-23 长沙矿山研究院有限责任公司 Multistage transient dynamic performance measuring device of laser gas concentration measuring sensor
CN112461765A (en) * 2020-10-16 2021-03-09 南京南智先进光电集成技术研究院有限公司 Gas concentration measuring system and method based on photoacoustic spectrometry

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