CN1904659A - Method and apparatus for sensing methane concentration based on optical fiber Bragg raster - Google Patents
Method and apparatus for sensing methane concentration based on optical fiber Bragg raster Download PDFInfo
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- CN1904659A CN1904659A CN 200610052880 CN200610052880A CN1904659A CN 1904659 A CN1904659 A CN 1904659A CN 200610052880 CN200610052880 CN 200610052880 CN 200610052880 A CN200610052880 A CN 200610052880A CN 1904659 A CN1904659 A CN 1904659A
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Abstract
The invention relates to a method for optical fiber Prague grating used in methane thickness sensor and the device to realize the method. The FBG sensor connects to broad band light source through optical fiber circulator, and reflecting light connects to optical fiber coupler through optical fiber circulator. The input of photodiode connects to one end of 3-dB optical fiber coupler, and the output end of photodiode connects to data acquisition card that is connected to FFT analyzer. The other end of 3-dB optical fiber coupler connects to two optical fiber collimator. Two reflecting mirrors are set corresponding to two optical fiber collimators and one could control the movement by step motor. The invention is suited for multiple spot methane thickness high accuracy measurement.
Description
Technical field
The invention belongs to technical field of optical fiber sensing, particularly a kind of Fiber Bragg Grating FBG equipment of being applied to the method for sensing methane concentration and realizing this method.
Background technology
At sensory field of optic fibre, (fiber bragg grating FBG) because it is very responsive to temperature, stress, variations in refractive index, and becomes very important senser element in the industry to Fiber Bragg Grating FBG.The centre wavelength of FBG reflectance spectrum is directly proportional with the effective refractive index of fiber core layer, and the effective refractive index of fiber core layer is subjected to extraneous temperature, stress influence, and the variation of therefore measuring the centre wavelength of FBG reflectance spectrum just can obtain the variation of ambient temperature.
The conventional catalyst oxidizing process is utilized the oxidation reaction of methyl hydride catalyzed oxidation element catalytic methane and oxygen, and chemical energy is converted into heat energy, measures variation of temperature by thermistor, thereby obtains the methane concentration value.This method measuring accuracy is higher, but treatment circuit is complicated, is subjected to outside electromagnetic interference easily, influences accuracy of measurement; And treatment circuit needs the power supply power supply, the potential safety hazard of existence generation electric spark.In addition, this method is unfavorable for realizing distributed sensing.
Summary of the invention
The present invention is exactly at the deficiencies in the prior art, on the basis of conventional catalyst oxidizing of methylene sensing method, has proposed a kind of solution of the sensing methane concentration based on Fiber Bragg Grating FBG, and the equipment of realizing this method is provided simultaneously.
Method of the present invention may further comprise the steps:
1, selects the wideband light source of wavelength coverage covering Fiber Bragg Grating FBG reflection kernel wavelength for use, strip of light wide region 20～60nm; The light that light source sends is got to by circulator on the FBG array of FBG sensor series connection of the individual different reflection kernel wavelength of n (n 〉=2), the FBG sensor is pressed close to methyl hydride catalyzed oxidation element and is placed, the effect of methyl hydride catalyzed oxidation element is to be temperature variation with the methane concentration change transitions, when FBG environment methane concentration of living in changes, equidirectional variation takes place in environment temperature thereupon, therefore the effective refractive index of fiber core layer changes, and causes the reflection kernel wavelength of FBG to drift about.The reflection kernel wavelength of FBG is:
λ＝2n·Λ (1)
Wherein n represents the effective refractive index of fiber core layer, and Λ represents FBG sensor grating constant.
2, the transducing signal that reflects of FBG enters a 3-dB fiber coupler through a circulator, and the 3-dB fiber coupler is divided into aplanatic two bundles with light signal; The aplanatic flashlight of two bundles incides on the catoptron by optical fiber collimator respectively and reflects coupled back into optical fibers; Move by the position of controlling one of them catoptron, change the relative light path between the two paths of signals light.The Doppler shift produce owing to moving of catoptron is:
f＝2v/λ (2)
Wherein v represents the speed that catoptron moves, and λ represents the signal light wavelength.
3, two paths of signals light converges interference in the 3-dB coupling mechanism, interference signal is converted into electric signal through an arm of 3-dB coupling mechanism by photodiode, by the data collecting card collection, enter the fast fourier transform analyser (Fast Fourier Transform, FFT).F in (2) formula can be read by the fft analysis instrument, the wavelength X of flashlight can be obtained thus.
The equipment of realizing such scheme is: the FBG sensor is connected with the wideband light source light signal by optical fiber circulator, and reflected light is connected with the fiber coupler light signal by optical fiber circulator.The input end of photodiode is connected with an end light signal of 3-dB fiber coupler, and photodiode output is electrically connected with data collecting card.Capture card is electrically connected with the fft analysis instrument.The other end of 3-dB fiber coupler is connected with two optical fiber collimator light signals respectively, and corresponding two optical fiber collimator positions are provided with two catoptrons, and one of them catoptron moves by its position of step motor control.Methyl hydride catalyzed oxidation element adopts ripe existing product.
The present invention is applicable to the methane concentration high-acruracy survey of multiple spot.Adopt the FBG sensor of a plurality of different reflection kernel wavelength can realize the multiplexing of a plurality of sensors, realize quasi-distributed sensing.In addition, because the optical signals Optical Fiber Transmission is to the long-range regulating mechanism of separating, so solved being subject to electromagnetic interference (EMI), having the problem of hidden danger of electric fuse of original electricity disposal system.
Description of drawings
Fig. 1 is an one-piece construction synoptic diagram of the present invention.
Embodiment
As shown in Figure 1, wideband light source 1 is connected with the 1. end light signal of optical fiber circulator 2, and the 2. end of optical fiber circulator 2 is connected with FBG sensor 3 light signals.Methyl hydride catalyzed oxidation element 4 is connected with FBG sensor 3 positions.3. the end of optical fiber circulator 2 is connected with fiber coupler 5 light signals.The input end of photodiode 9 is connected with an end light signal of 3-dB fiber coupler 5, and the output terminal of photodiode 9 is electrically connected with data collecting card 10.Data collecting card 10 is electrically connected with fft analysis instrument 11.The other end of 3-dB fiber coupler 5 is connected with two optical fiber collimator 6 light signals respectively, and corresponding two optical fiber collimator 6 positions are provided with two catoptrons 7, and one of them catoptron moves by stepper motor 8 its positions of control.Above-mentioned FBG sensor 3 is placed on the measured point as the sensing methane concentration device, wideband light source 1 and signal demodulation part are all in monitoring center, broadband light enters FBG sensor 3 by single-mode fiber, passes flashlight back monitoring center by single-mode fiber again and carries out signal demodulation and processing.
Selecting wavelength coverage for use is 60nm (can cover the broadband of Fiber Bragg Grating FBG reflection kernel wavelength) light source, the light that light source sends is got to the FBG sensor array by optical fiber circulator and is listed, the FBG sensor is pressed close to methyl hydride catalyzed oxidation element and is placed, the effect of methyl hydride catalyzed oxidation element is to be temperature variation with the methane concentration change transitions, when FBG environment methane concentration of living in changes, equidirectional variation takes place in environment temperature thereupon, therefore the effective refractive index of fiber core layer changes, and causes the reflection kernel wavelength of FBG to drift about.The reflection kernel wavelength of FBG is:
λ＝2n·Λ (1)
Wherein n represents the effective refractive index of fiber core layer, and Λ represents FBG sensor grating constant.
The transducing signal that FBG reflects enters a 3-dB fiber coupler through a circulator, and the 3-dB fiber coupler is divided into aplanatic two bundles with light signal; The aplanatic flashlight of two bundles incides on the catoptron by optical fiber collimator respectively and reflects coupled back into optical fibers; Move by the position of controlling one of them catoptron, change the relative light path between the two paths of signals light.The Doppler shift produce owing to moving of catoptron is:
f＝2v/λ (2)
Wherein v represents the speed that catoptron moves, and λ represents the signal light wavelength.
Two paths of signals light converges interference in the 3-dB coupling mechanism, interference signal is converted into electric signal through an arm of 3-dB coupling mechanism by photodiode, by the data collecting card collection, enters FFT (FastFourier Transform) analyser.F in (2) formula can be read by the fft analysis instrument, the wavelength X of flashlight can be obtained thus.
Claims (2)
1, based on the method for the sensing methane concentration of Fiber Bragg Grating FBG, it is characterized in that this method may further comprise the steps:
(1) select for use wavelength coverage to cover the wideband light source of Fiber Bragg Grating FBG reflection kernel wavelength, strip of light wide region 20～60nm; The light that light source sends is got to by circulator on the FBG array of FBG sensor series connection of n different reflection kernel wavelength, n 〉=2; The FBG sensor is pressed close to methyl hydride catalyzed oxidation element and is placed, the effect of methyl hydride catalyzed oxidation element is to be temperature variation with the methane concentration change transitions, when FBG environment methane concentration of living in changes, equidirectional variation takes place in environment temperature thereupon, therefore the effective refractive index of fiber core layer changes, cause the reflection kernel wavelength of FBG to drift about, the reflection kernel wavelength of FBG is:
λ＝2n·Λ (1)
Wherein n represents the effective refractive index of fiber core layer, and Λ represents FBG sensor grating constant;
(2) transducing signal that reflects of FBG enters a 3-dB fiber coupler through a circulator, and the 3-dB fiber coupler is divided into aplanatic two bundles with light signal; The aplanatic flashlight of two bundles incides on the catoptron by optical fiber collimator respectively and reflects coupled back into optical fibers; Move by the position of controlling one of them catoptron, change the relative light path between the two paths of signals light, because the mobile Doppler shift that produces of catoptron is:
f＝2v/λ (2)
Wherein v represents the speed that catoptron moves, and λ represents the signal light wavelength;
(3) two paths of signals light converges interference in the 3-dB coupling mechanism, and interference signal is converted into electric signal through an arm of 3-dB coupling mechanism by photodiode, by the data collecting card collection, enters the fast fourier transform analyser; Read f in (2) formula by the fourier transform analysis instrument, obtain the wavelength X of flashlight thus.
2, adopt the employed equipment of claim 1 method, it is characterized in that the FBG sensor is connected with the wideband light source light signal by optical fiber circulator in this equipment, reflected light is connected with the fiber coupler light signal by optical fiber circulator; The input end of photodiode is connected with an end light signal of 3-dB fiber coupler, and photodiode output is electrically connected with data collecting card; Capture card is electrically connected with the fft analysis instrument; The other end of 3-dB fiber coupler is connected with two optical fiber collimator light signals respectively, and corresponding two optical fiber collimator positions are provided with two catoptrons, and one of them catoptron moves by its position of step motor control.
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| CNB2006100528802A CN100392454C (en) | 2006-08-10 | 2006-08-10 | Method and apparatus for sensing methane concentration based on optical fiber Bragg raster |
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| CNB2006100528802A CN100392454C (en) | 2006-08-10 | 2006-08-10 | Method and apparatus for sensing methane concentration based on optical fiber Bragg raster |
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Cited By (3)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| CN101046450B (en) * | 2007-04-19 | 2010-05-19 | 山东科技大学 | Fiber grating process and equipment for detecting methane |
| CN101632013B (en) * | 2007-03-09 | 2011-11-02 | 三菱电机株式会社 | Optical fiber sensor |
| CN111812060A (en) * | 2020-06-19 | 2020-10-23 | 中国矿业大学 | Methane concentration detection system |
Family Cites Families (3)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| CN2559981Y (en) * | 2002-02-08 | 2003-07-09 | 武汉理工大学 | Optical fibre gas-sensitive sensing measuring apparatus |
| CN1176390C (en) * | 2003-04-28 | 2004-11-17 | 浙江大学 | Palladium film hydrogen sensing device based fibre-optical grating temperature non-responsiveness |
| CN100483107C (en) * | 2005-11-22 | 2009-04-29 | 重庆工学院 | Distributed microstructure optical fiber gas sensing system and sensing method |
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Cited By (3)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| CN101632013B (en) * | 2007-03-09 | 2011-11-02 | 三菱电机株式会社 | Optical fiber sensor |
| CN101046450B (en) * | 2007-04-19 | 2010-05-19 | 山东科技大学 | Fiber grating process and equipment for detecting methane |
| CN111812060A (en) * | 2020-06-19 | 2020-10-23 | 中国矿业大学 | Methane concentration detection system |
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