CN100483107C - Distributed microstructure optical fiber gas sensing system and sensing method - Google Patents

Abstract

The invention discloses a distributed micro-structure optical fiber marsh gas sensing system and sensing method. The system is formed by a wind-band light source, a wide-band couple, an initial short period optical fiber grating, multiply series connecting single negative micro-structure optical fiber marsh gas sensors, an optical fiber link circuit, an optical fiber spectrum demodulator and a computer, wherein the single negative micro-structure optical fiber marsh gas sensor is formed by a short period optical fiber grating and two long period optical fiber gratings. The method is that it orientates the temperature factor and the sensing factor of each sensor; it then measures the marsh gas density of each sensing point.

Description

Distributed microstructure optical fiber gas sensing system and method for sensing

Technical field

The invention belongs to Fibre Optical Sensor, aerochemistry, safety technique field, be specifically related to a kind of distributed microstructure optical fiber gas sensing system and method for sensing that obtains methane gas concentration.

Background technology

Aspect mining safety, for a long time, great especially big coal mining accident all over the world takes place often, and dead and wounded number is many then reaches hundreds of people.Each major accident is all brought huge property loss, brings the loss that can't retrieve especially for industrial life, has all caused threat for family and society.The one of the main reasons of coal mining accident is the blast that high concentration gas causes, coal mine gas from explosion all often takes place in the whole world.At present, to effective monitoring and control or a global problem of gas, people have dropped into great amount of manpower and financial resources are studied this problem, but produce little effect.It is effective ways of evading these serious accidents that the environment of coal mine and the course of work are carried out Monitoring and Controlling, the wherein most important also most importantly Detection ﹠ Controling of gas (major component is a methane) gas concentration.Firedamp sensor is the critical equipment of the mine gas comprehensive regulation and hazard prediction, is subjected to people's extensive attention.

Firedamp sensor is a kind of gas sensor.The sensor that can detect methane gas mainly contains metal oxide semiconductor sensor, catalytic combustion type sensor and the absorption sensor of optical fiber that came out in 1962, has been widely used in the detection and the warning of coal gas, liquefied petroleum gas (LPG), rock gas and mine gas gas.Catalytic combustion type gas sensor is divided into direct catalytic combustion type and catalytic Contact combustion-type, this sensor highly sensitive, and low price is suitable for rugged surroundings; Its deficiency is that anti-high dense impact property is poor, and poor stability needs frequent adjustment, and the life-span is short, and the response time is longer, has serious potential safety hazard.In addition, the firedamp sensor that utilizes optical fiber to realize mainly comprises absorption firedamp sensor of optical fiber air chamber and fast travelling waves of optical fibre firedamp sensor.The absorption firedamp sensor of optical fiber air chamber is made of two optical fiber and two concave mirrors; Its advantage is can remote measurement, electric insulation, no potential safety hazard; Its shortcoming is that sensor bulk is big, complex structure, and the Distributed Detection difficulty, higher to the sensing environmental requirement, vibrationproof is poor.The covering that the fast travelling waves of optical fibre firedamp sensor is removed multimode optical fiber with the method for chemical corrosion or abrasion forms; The advantage of this sensor is simple to operate, and measuring speed is fast, the sensor-based system Miniaturizable; The shortcoming of its existence mainly is that the making of sensor is loaded down with trivial details and very difficult, and signal noise is very big, and measuring accuracy is not high, and the structure relative complex of sensor-based system needs high pressure voltage divider system and cooling system.

The gas sensing system close with the present invention is based on the absorption firedamp sensor of air chamber and a kind of distribution type fiber-optic gas sensing system of forming.The optic fibre light path of this sensor-based system part comprises an input optical fibre A, a photoswitch B (comprising optical fiber end G), returns optical fiber C1～C16 (each sensor has and returns optical fiber) with a plurality of Fibre Optical Sensor S1～S16 (mostly being 16 at present most) of optical fiber series connection, many as shown in Figure 1; Each sensor of series connection comprises fiber optical circulator (D1～D16), through mode gas absorption chamber (E1～E16) and short period fiber grating (F1～F16).Its sensing principle is: light is by the input end (end 1) of fiber optical circulator in Optical Fiber Transmission to a sensor, and from holding 2 to output to the through mode gas absorption chamber, be transferred to a short period fiber grating in the optical fiber again, the light of part wavelength is reflected back toward the through mode gas absorption chamber; The light that sees through this gas absorption chamber once more is transferred to the end 2 of fiber optical circulator, and passes through another root Optical Fiber Transmission to photoswitch from its end 3, and photoswitch output light is to Photodetection system; Light is absorbed by wherein gas during through the through mode gas absorption chamber at twice, measures the concentration of methane gas by the uptake of measuring light; Each sensor is only got the light intensity of a narrow band light, and different sensors is selected the light of different arrowbands for use, so just can realize the Distributed Detection of methane gas.The advantage of this sensor is can remote measurement, electric insulation, no potential safety hazard.Its shortcoming is the cost height (price of fiber optical circulator is very expensive) of (1) each sensor, (2) the big and complex structure (need) of sensor bulk with fiber optical circulator and through mode gas absorption chamber, (3) (each sensor needs an independently optical fiber to the Distributed Detection difficulty, it is very difficult to connect up), (4) to sensing environmental requirement higher (needing dustproof), vibrationproof is poor, (5) use the inconvenient (inwall that needs frequent cleaning through mode gas absorption chamber, and this is pretty troublesome thing), (6) can not eliminate environment temperature and the influence (can not obtain the temperature information of sensing point, and only obtain the intensity signal of each sensor) of interference to measuring.These are not enough and defective remains new technology and method and overcome and improvement.

Summary of the invention

Purpose of the present invention just is at the prior art above shortcomings, and a kind of distributed microstructure optical fiber gas sensing system and method for sensing that obtains methane gas concentration is provided.The structure of this sensor-based system, assembling and debugging are simple, build large-scale distributed gas and temperature sensing network easily; The complete fiberize of each transducing part in the sensor-based system, volume is little, and is simple in structure, and cost is lower, and Distributed Detection is easy, and is not high to the sensing environmental requirement, easy to use, and cleaning is than being easier to, and vibrationproof is good.Its method for sensing can detect gas density and temperature simultaneously, can eliminate the interference on temperature, light source and the light path, and test result is reliable and stable.

Technical scheme of the present invention is as follows:

This distributed microstructure optical fiber gas sensing system includes wideband light source, optical fiber, wide-band coupler, initial short period fiber grating, optical fiber link, fiber spectrum detuner and computing machine; Wideband light source is connected to an input end of wide-band coupler by optical fiber, the output terminal of wide-band coupler is connected to initial short period fiber grating by optical fiber, the other end of initial short period fiber grating is connected to the front end of optical fiber link by optical fiber, another input end of wide-band coupler is connected to the optic fibre input end of fiber spectrum detuner by optical fiber, and the FPDP of fiber spectrum detuner is connected to computing machine by data interface bus (as standard data interfaces such as USB, RS232,485, GPIB); Each single lens reflex type microstructure optical fiber gas sensor in the optical fiber link places tested methane gas.Wherein, optical fiber link is to be in series by optical fiber by two or more single lens reflex type microstructure optical fiber gas sensors, when connecting such sensor adjacent, the rear end of previous sensor links to each other with the front end of a back sensor, the front end of previous sensor is as the front end of optical fiber link, spacing in the same optical fiber link between the short period fiber grating reflection kernel wavelength of any two sensors is greater than half of corresponding two short period fiber grating reflection wavelength band three dB bandwidth sums, and the spacing between the short period fiber grating reflection kernel wavelength of any adjacent two sensors is less than 2 times of corresponding two short period fiber grating reflection wavelength band three dB bandwidth sums; The spectrum of wideband light source comprises one or more absorbing bands of methane gas; Spacing in the centre wavelength of initial short period fiber grating and the optical fiber link between the short period fiber grating reflection kernel wavelength of any sensor is greater than half of the reflection wavelength band three dB bandwidth sum of initial short period fiber grating and other any short period fiber grating.

Each single lens reflex type microstructure optical fiber gas sensor in the optical fiber link, it be on optical fiber at a distance of certain distance with two long period fiber grating, as two coupling mechanisms, the resonance of these two long period fiber grating coupling centre wavelength, bandwidth are close with coupling efficiency, and their wave resonance strap is positioned at the absorbing band (being that the strong absorbing band 1120～1150nm band of near infrared or 1150～1170nm band or 1640～1680nm band or 2350～2390nm are with) of methane gas (major component is a methane).Distance between two long period fiber grating is 5-800mm, and the coupling efficiency of its central wavelength is greater than 99%, and the three dB bandwidth of wavelength is greater than 7nm, coupling efficiency greater than 99% wavelength bandwidth greater than 3nm.Part or whole section fibre cladding between two long period fiber grating expose, and do not have plastics protection overlay.Outside two long period fiber grating with a short period fiber grating, the coupling efficiency of this short period fiber grating is greater than 90%, its resonance centre wavelength near the resonance centre wavelength of long period fiber grating, to the spacing of the resonance centre wavelength of long period fiber grating less than 1/4th of the wavelength bandwidth of long period fiber grating coupling efficiency 99%; The short period fiber grating to the distance of adjacent long period fiber grating greater than 0.5mm (ultimate range can reach tens kilometers).The rear end of one end of short period fiber grating as sensor arranged, and the other end is as front end.

In order to protect single lens reflex type microstructure optical fiber gas sensor; two long period fiber grating have been made above-mentioned; fibre cladding; be with a protective sleeve outside this section sensing section optical fiber of a short period fiber grating; aperture is arranged on the protective sleeve; optical fiber is pasted on the protective sleeve with solidifying glue at both ends near protective sleeve; at the both ends of protective sleeve a transition buffer cover is arranged respectively; one ventilative dustproof thin layer is arranged outside protective sleeve; sign has the front-end and back-end of sensor on the surface at protective sleeve two ends, and identifies the coupling centre wavelength that the short-and-medium period optical fiber grating of this sensor is arranged.

The distributed sensing process of this sensor-based system is: the light of light source is transferred to initial short period fiber grating by optical fiber and wide-band coupler, initial short period fiber grating reflects the interior light of its strap to wide-band coupler, and the light transmission of its commplementary wave length is to optical fiber link; In optical fiber link, the short period fiber grating of each single lens reflex type microstructure optical fiber gas sensor returns the reflection of the light in its corresponding coupled wavelength band, this reflected light has comprised the flashlight of correspondence position methane gas, the light of its commplementary wave length will be transferred to other single lens reflex type microstructure optical fiber gas sensor of back, and the light reflection in again that it is the corresponding short period fiber grating coupled wavelength band of the single lens reflex type microstructure optical fiber gas sensor of back is returned and as the flashlight of its methane gas; The short period fiber grating of different single lens reflex type microstructure optical fiber gas sensors has different coupled wavelength bands, and the light of different optical wavelength is returned in reflection, so the spectral information of different wave length band has been represented the methane gas concentration and the temperature information of diverse location.In each single lens reflex type microstructure optical fiber gas sensor, (1) the resonance wavelength band of two long period fiber grating and a short period fiber grating is all in the absorbing band of methane gas, when the light in the fiber cores in the corresponding wavelength band arrived a long period fiber grating, the light in the Resonant Wavelengths of Long Period Fiber Gratings band was coupled in the fibre cladding and transmits; (2) total reflection takes place and produces evanescent wave in the light in the fibre cladding on the contact interface of fibre cladding and methane gas, and evanescent wave passes fibre cladding and enters methane gas and absorbed by methane gas; (3) penetration depth of evanescent wave is relevant with the concentration of methane gas with absorbed luminous energy, and the evanescent wave that influenced by gas density returns fibre cladding, continues to produce total reflection and evanescent wave at other point, and is absorbed and influence by methane gas; (4) when the light of fibre cladding arrives second long period fiber grating, be coupled in the fiber cores again and transmit; (5) light arrives second short period during fiber grating, and the light of this short period fiber grating resonance central wavelength is reflected; The light that is reflected back toward is coupled to fibre cladding once more when arriving second long period fiber grating, produce repeatedly total reflection, evanescent wave at the contact interface of fibre cladding and methane gas again, absorbed by methane gas and return fibre cladding.The light that returns fibre cladding is coupled to fiber cores again when arriving first long period fiber grating once more, and is transferred to detection system or unit as flashlight.The flashlight that the short period fiber grating reflection of each sensor turns back to wide-band coupler in initial short period fiber grating and the optical fiber link is transferred to the fiber spectrum detuner, computing machine obtains the catoptrical spectroscopic data of each short period fiber grating (comprising its wavelength and amplitude) by the fiber spectrum detuner, and calculates the methane gas concentration and the temperature at each single lens reflex type microstructure optical fiber gas sensor place.The flashlight that each short period fiber grating that obtains at computing machine reflects has comprised intensity and centre wavelength information, and the centre wavelength of its flashlight is only relevant with temperature, can determine temperature thus; And strength information is subjected to the influence of methane gas concentration, calculates the concentration of methane gas with signal light intensity, and proofreaies and correct the measured value of methane gas concentration with the temperature value that obtains.Like this, this sensor-based system just can obtain along the gas density and the measured temperature of each sensor distribution on the optical fiber link.

The method for sensing that this distributed microstructure optical fiber gas sensing system obtains methane gas concentration is: the concentration and the temperature information of the methane gas at each each sensor place of single lens reflex type microstructure optical fiber gas sensor senses on the optical fiber link, the fiber spectrum detuner obtains the reflected spectrum data (comprising wavelength and amplitude data) of each sensor simultaneously and is transferred to computing machine, and computing machine calculates the temperature and the concentration measurement of each sensor place methane gas according to these spectroscopic datas; Its concrete steps are: step 1 is to demarcate the temperature coefficient k of each single lens reflex type microstructure optical fiber gas sensor on the optical fiber link ₁[i], sensitivity coefficient k ₂[i], correction coefficient k ₃[i] and primary constant a ₀[i] ([] and numeric representation sequence number wherein, it is the sequence number that i in the square bracket represents each single lens reflex type microstructure optical fiber gas sensor in the optical fiber link, from the front end of optical fiber link to the rear end sort ascending in regular turn, the sequence number of sensor is 1 foremost, the sequence number of rearmost end sensor is N; I also represents the sequence number of each short period fiber grating in the sensor-based system, the sequence number of initial short period fiber grating is 0, the sequence number of the short period fiber grating from i the single lens reflex type microstructure optical fiber gas sensor that the optical fiber link front end begins is i, i=0,1,2,3.....N, following sequence number i is identical therewith): (1) at first is the data that need use when obtaining calibration coefficient: (a) in the optical fiber link each single lens reflex type microstructure optical fiber gas sensor to be placed in temperature simultaneously be reference temperature T ₀And gas density is in 0 the gas box, and catoptrical amplitude of short period fiber grating and centre wavelength that computing machine obtains initial short period fiber grating and each single lens reflex type microstructure optical fiber gas sensor are respectively I ₀[i] and λ ₀[i], i=0,1,2,3.....N; (b) in the optical fiber link each single lens reflex type microstructure optical fiber gas sensor to be placed in temperature simultaneously be reference temperature T ₀And gas density is reference concentration C ₁Gas box in, the catoptrical amplitude of short period fiber grating that computing machine obtains initial short period fiber grating and each single lens reflex type microstructure optical fiber gas sensor is respectively I ₁[i], i=0,1,2,3.....N; (c) in the optical fiber link each single lens reflex type microstructure optical fiber gas sensor to be placed in temperature simultaneously be that catoptrical amplitude of short period fiber grating and centre wavelength that computing machine obtains initial short period fiber grating and each single lens reflex type microstructure optical fiber gas sensor are respectively I in 0 the gas box for demarcating temperature T r gas density ₂[i] and λ _r[i], i=0,1,2,3.....N; (d) in the optical fiber link each single lens reflex type microstructure optical fiber gas sensor to be placed in temperature simultaneously be reference concentration C for demarcating temperature T r gas density ₁Gas box in, the catoptrical amplitude of short period fiber grating that computing machine obtains initial short period fiber grating and each single lens reflex type microstructure optical fiber gas sensor is respectively I ₃[i], i=0,1,2,3.....N.(2) after obtaining above-mentioned data, computing machine is according to the temperature coefficient k of each single lens reflex type microstructure optical fiber gas sensor on the optical fiber link in these these sensor-based systems of data computation ₁[i], sensitivity coefficient k ₂[i], correction coefficient k ₃[i] and primary constant a ₀[i], i=0,1,2,3.....N, its concrete computing formula is as follows:

(a) the temperature coefficient k of i single lens reflex type microstructure optical fiber gas sensor in the optical fiber link ₁[i] is

$k_1\left[i\right]=\frac{T_r-T_0}{{\mathrm{\λ}}_r\left[i\right]-{\mathrm{\λ}}_0\left[i\right]}$

Wherein, Tr demarcates temperature, T ₀It is reference temperature;

I is the sequence number of each single lens reflex type microstructure optical fiber gas sensor, i=1,2,3......N;

λ ₀[i] is that temperature is that T0 and gas density are 0 o'clock i catoptrical centre wavelength of short period fiber grating;

λ _r[i] is that temperature is that Tr and gas density are 0 o'clock i catoptrical centre wavelength of short period fiber grating;

(b) the sensitivity coefficient k of i single lens reflex type microstructure optical fiber gas sensor in the optical fiber link ₂[i] is

$k_2\left[i\right]=\frac{{\mathrm{<figure-callout\; id="1"\; label="C"\; filenames="C200510057393E00191.png,C200510057393E00192.png"\; state="\{\{state\}\}">C</figure-callout>}}_1}{\ln \left\{\frac{I_3\left[i\right]I_2[i-1]}{I_3[i-1]I_2\left[i\right]}\right\}}$

Wherein, C ₁It is the reference concentration of timing signal methane gas;

I=1,2,3......N, the sequence number of expression single lens reflex type microstructure optical fiber gas sensor;

I ₃[i] is that temperature is that demarcation temperature T r and gas density are C ₁The time i the catoptrical amplitude of short period fiber grating, I ₃[i-1] is i-1 catoptrical amplitude of short period fiber grating this moment;

I ₂[i] is that temperature is that demarcation temperature T r and gas density are 0 o'clock i catoptrical amplitude of short period fiber grating, I ₂[i-1] is i-1 catoptrical amplitude of short period fiber grating this moment;

(c) the correction coefficient k of i single lens reflex type microstructure optical fiber gas sensor in the optical fiber link ₃[i] is

$k_3\left[i\right]=\frac{{\mathrm{<figure-callout\; id="1"\; label="C"\; filenames="C200510057393E00191.png,C200510057393E00192.png"\; state="\{\{state\}\}">C</figure-callout>}}_1\ln \left\{\frac{I_1\left[i\right]I_3[i-1]}{I_1[i-1]I_3\left[i\right]}\right\}}{(T_r-T_0)\ln \left\{\frac{I_2[i-1]I_3\left[i\right]}{I_2\left[i\right]I_3[i-1]}\right\}}$

Wherein, C ₁It is the reference concentration of timing signal methane gas;

Tr demarcates temperature, T ₀It is reference temperature;

I=1,2,3......N, the sequence number of expression single lens reflex type microstructure optical fiber gas sensor;

I ₃[i] is that temperature is that Tr and gas density are C ₁The time i the catoptrical amplitude of short period fiber grating, I ₃[i-1] is i-1 catoptrical amplitude of short period fiber grating this moment;

I ₂[i] is that temperature is that Tr and gas density are 0 o'clock i catoptrical amplitude of short period fiber grating, I ₂[i-1] is i-1 catoptrical amplitude of short period fiber grating this moment;

I ₁[i] is that temperature is T ₀And gas density is C ₁The time i the catoptrical amplitude of short period fiber grating, I ₁[i-1] is i-1 catoptrical amplitude of short period fiber grating this moment;

(d) the primary constant a of i single lens reflex type microstructure optical fiber gas sensor in the optical fiber link ₀[i] is

$a_0\left[i\right]=\frac{{\mathrm{<figure-callout\; id="1"\; label="C"\; filenames="C200510057393E00191.png,C200510057393E00192.png"\; state="\{\{state\}\}">C</figure-callout>}}_1\ln \left\{\frac{I_0\left[i\right]}{I_0[i-1]}\right\}}{\ln \left\{\frac{I_2\left[i\right]I_3[i-1]}{I_2[i-1]I_3\left[i\right]}\right\}}$

Wherein, C ₁It is the reference concentration of timing signal methane gas;

I=1,2,3......N, the sequence number of expression single lens reflex type microstructure optical fiber gas sensor;

I ₃[i] is that temperature is that demarcation temperature T r and gas density are C ₁The time i the catoptrical amplitude of short period fiber grating, I ₃[i-1] is i-1 catoptrical amplitude of short period fiber grating this moment;

I ₂[i] is that temperature is that demarcation temperature T r and gas density are 0 o'clock i catoptrical amplitude of short period fiber grating, I ₂[i-1] is i-1 catoptrical amplitude of short period fiber grating this moment;

I ₀[i] is that temperature is reference temperature T ₀And gas density is 0 o'clock i catoptrical amplitude of short period fiber grating, I ₀[i-1] is i-1 catoptrical amplitude of short period fiber grating this moment;

Step 2 be the test methane gas concentration and temperature: (1) at first, each single lens reflex type microstructure optical fiber gas sensor distributed earth in the optical fiber link places tested methane gas, this computer-chronograph obtains the catoptrical amplitude of each short period fiber grating from the spectroscopic data that the fiber spectrum detuner obtains and centre wavelength is respectively I[i] and λ [i], i=0,1,2,3......N; (2) then, calculate the temperature variation at each sensor place, i single lens reflex type microstructure optical fiber gas sensor place is with respect to the temperature variation Δ T[i of reference temperature in the optical fiber link] be

ΔT[i]＝k ₁[i]{λ[i]-λ ₀[i]}

Wherein, i=1,2,3......N, the sequence number of expression single lens reflex type microstructure optical fiber gas sensor;

k ₁[i] is the temperature coefficient of i single lens reflex type microstructure optical fiber gas sensor obtaining of timing signal;

λ ₀[i] is that temperature is reference temperature T in the calibration process ₀The time i the catoptrical centre wavelength of short period fiber grating;

I the catoptrical centre wavelength of short period fiber grating that λ [i] obtains when being test;

(3) calculate the methane gas concentration that distributes along each sensor on the optical fiber link at last, the methane gas concentration C [i] at i single lens reflex type microstructure optical fiber gas sensor place is in the optical fiber link that distributed microstructure optical fiber gas sensing system calculates:

$C\left[i\right]=k_2\left[i\right]\ln \left\{\frac{I\left[i\right]}{I[i-1]}\right\}+k_3\left[i\right]\mathrm{\&Delta;T}\left[i\right]+a_0\left[i\right]$

Wherein, i=1,2,3......N, the sequence number of expression single lens reflex type microstructure optical fiber gas sensor, the distributing position of corresponding different sensors;

k ₂[i], k ₃[i] and a ₀[i] is respectively sensitivity coefficient, correction coefficient and the primary constant of i single lens reflex type microstructure optical fiber gas sensor obtaining of timing signal, obtained by the calibration process of step 1;

Δ T[i] be the temperature variation of i single lens reflex type microstructure optical fiber gas sensor place the time calculating of test with respect to reference temperature;

I[i] i catoptrical amplitude of short period fiber grating when being test;

I[i-1] i-1 catoptrical amplitude of short period fiber grating when being test.

Like this, just measured the methane gas concentration that distributes along each sensor on the optical fiber link after obtaining spectroscopic data, its measured value is subjected to the influence disturbed on temperature, light source and the light path less.

The advantage of this distributed microstructure optical fiber gas sensing system and method for sensing:

The advantage of this distributed gas sensing system and method for sensing is: the single lens reflex type microstructure optical fiber gas sensor in (1) this sensor-based system is to realize on one section complete optical fiber, its Stability Analysis of Structures, volume is little, vibrationproof is good, measurement range wide (can reach 0～17%), anti-high dense impact property is good, and the reaction time is fast, and the life-span is long, do not need frequent adjustment sensor, do not have the gas absorption air chamber, working service is convenient, and the cleaning of dust is simply easy, electric insulation, do not burn, be perfectly safe, no potential safety hazard; (2) Distributed Detection of gas in this sensor-based system and method for sensing can be realized on a large scale, system wiring is simple, and whole cost is low, also can realize remote measurement, and non-relay telemeter distance can reach more than 10 kilometers, and the regularity of algorithm is strong, calculates simpler; (3) this sensor-based system can obtain the concentration and the temperature distribution information of methane gas simultaneously, and its method for sensing has been eliminated the influence that districution temperature is measured the respective sensor gas density.

Description of drawings

Fig. 1 is the absorption gas sensing system structural drawing of distribution type fiber-optic air chamber;

Fig. 2 is the single lens reflex type microstructure optical fiber gas sensor construction figure that this patent relates to;

Fig. 3 is the distributed microstructure optical fiber gas sensing system structural drawing that this patent relates to;

Fig. 4 is the local refinement figure of the distributed microstructure optical fiber gas sensing system that relates to of this patent.

Embodiment

Further specify the present invention below in conjunction with accompanying drawing:

Referring to Fig. 2; the structure of the single lens reflex type microstructure optical fiber gas sensor in this sensor-based system has: optical fiber coating 1, fibre cladding 2, fiber core 3, long period fiber grating LPFG1 4, long period fiber grating LPFG2 5; short period fiber grating 6, protective sleeve 7; dust filters thin layer 8; solidify glue 9, transition buffer cover 10.Wherein, fiber optic materials is quartzy, is removing two long period fiber grating that are provided with the about 20mm of length on one section optical fiber of plastic protective coating; These two long period fiber grating are at a distance of 10cm, and their coupling centre wavelength all is 1160nm, and its three dB bandwidth is 10nm, and the coupling efficiency of its central wavelength is 99.7%, and its coupling efficiency is 3.5nm greater than 99% wavelength bandwidth; Outside these two long period fiber grating, be provided with a short period fiber grating, this short period fiber grating is 4mm to the distance of adjacent long period fiber grating, and its length is 5mm, and its coupling efficiency is 95%, its 3dB wavelength bandwidth is 0.4nm, and its resonance centre wavelength is 1160.7nm; Fibre cladding between two long period fiber grating exposes, and the fibre cladding at all the other places has plastic protective coating; Outside this section optical fiber that two long period fiber grating and a short period fiber grating are arranged, be provided with a protective sleeve; aperture is arranged on the protective sleeve; optical fiber is pasted on the protective sleeve with solidifying glue at both ends near protective sleeve; be provided with a transition buffer cover respectively at the both ends of protective sleeve; outside protective sleeve, be provided with a ventilative dustproof thin layer; in this segment protect cover outside surface sign near the short period fiber grating " rear end " and " 1160.7nm " arranged, identifying at the outside surface of the protective sleeve other end has " front end ".According to above-mentioned similar composition structure, reconstruct two single lens reflex type microstructure optical fiber gas sensors in addition, the structure and parameter of the structure of these two single lens reflex type microstructure optical fiber gas sensors and parameter thereof and above-mentioned single lens reflex type microstructure optical fiber gas sensor is basic identical, its difference is: two long period fiber grating coupling centre wavelengths of one of them single lens reflex type microstructure optical fiber gas sensor are 1161nm, the resonance centre wavelength of its short period fiber grating is 1161.7nm, in the protective sleeve outside surface sign near the short period fiber grating " rear end " and " 1161.7nm " is arranged; And the coupling centre wavelength of two long period fiber grating of another single lens reflex type microstructure optical fiber gas sensor is 1162nm; the resonance centre wavelength of its short period fiber grating is 1162.7nm, in this segment protect cover outside surface sign near the short period fiber grating " rear end " and " 1162.7nm " is arranged.After having constituted these three single lens reflex type microstructure optical fiber gas sensors, sign there be " rear end " of the single lens reflex type microstructure optical fiber gas sensor of " 1160.7nm " have " front end " of the single lens reflex type microstructure optical fiber gas sensor of " 1161.7nm " to link to each other with sign by optical fiber, sign had " rear end " of the single lens reflex type microstructure optical fiber gas sensor of " 1161.7nm " have " front end " of the single lens reflex type microstructure optical fiber gas sensor of " 1162.7nm " to link to each other with sign by optical fiber again.So just constituted the optical fiber link of being made up of three single lens reflex type microstructure optical fiber gas sensors (N=3), it is the front end of this optical fiber link that sign has " front end " of the single lens reflex type microstructure optical fiber gas sensor of " 1160.7nm ".

Referring to Fig. 3, the structure of this sensor-based system has: wideband light source A, optical fiber B1～B4, wide-band coupler Cw, a plurality of single lens reflex type microstructure optical fiber gas sensor S1～S _NThe optical fiber link of forming, and fiber spectrum detuner D, computing machine E.Its constructive method is: the about 1160nm of centre wavelength, the wideband light source A of the about 40nm of bandwidth is connected to the input end of wide-band coupler Cw by optical fiber B1, the output terminal of wide-band coupler Cw is connected to the end of initial short period fiber grating G0 by optical fiber B3, the other end of initial short period fiber grating G0 is connected to the front end (promptly indicating the front end of the single lens reflex type microstructure optical fiber gas sensor of " 1160.7nm ") of optical fiber link by optical fiber B4, another input end of wide-band coupler Cw is connected to fiber spectrum detuner D by optical fiber B2, and (its wavelength resolution is 0.01nm, can survey minimum amplitude is-70dBm, the Wavelength demodulation time is 1 second) optic fibre input end, the data output end of fiber spectrum detuner D is connected to computing machine by the gpib interface bus.The resonance centre wavelength of initial short period fiber grating GO is 1159.7nm, and its reflectivity (resonance coupling efficiency) is 90%, and the three dB bandwidth of its coupled wavelength band is 0.4nm.In this distributed microstructure optical fiber gas sensing system, the light of light source is transferred to initial short period fiber grating by optical fiber and wide-band coupler, near its 1159.7nm wavelength light is reflexed to the fiber spectrum detuner by initial short period fiber grating, as the initial reference signal of light source and light path, the light transmission at its commplementary wave length place each single lens reflex type microstructure optical fiber gas sensor to the optical fiber link; In each sensor of optical fiber link, the light of long period fiber grating coupled wavelength band (comprising its centre wavelength) will be through the reflection of the absorption of coupling, total reflection and the evanescent wave effect thereof of two long period fiber grating, methane gas, short period fiber grating, coupling and process such as absorption more again, and wherein the light of short period fiber grating central wavelength will turn back to wide-band coupler and be transferred to the fiber spectrum detuner; Like this, three sensors reflex to only 1160.7nm, the 1161.7nm of fiber spectrum detuner and near the light of three narrow wavelength bands the 1162.7nm wavelength on the optical fiber link, the amplitude of these three narrow wavelength band light is subjected to the influence of the gas density of correspondence position, and the centre wavelength of its narrow wavelength band light is subjected to Temperature Influence; Fiber spectrum detuner D obtains the catoptrical spectroscopic data of each sensor on initial short period fiber grating and the optical fiber link, and is sent to computing machine E by the GPIB data-interface; Computing machine obtains these spectroscopic datas, identify near 1159.7nm, 1160.7nm, 1161.7nm and the 1162.7nm wavelength narrow band light with sequence number 0,1,2,3 respectively, again temperature and the methane gas concentration that calculates three sensor correspondence positions according to the light intensity and the centre wavelength of these four narrow band light.

The method for sensing that present embodiment obtains distribution methane gas concentration is: the methane gas concentration and the temperature information of three diverse locations of three single lens reflex type microstructure optical fiber gas sensor senses on the optical fiber link, fiber spectrum detuner obtain initial short period fiber grating and three sensors near 1159.7nm, 1160.7nm, 1161.7nm and 1162.7nm wavelength reflected spectrum data and be transferred to computing machine; Computing machine identifies near 1159.7nm, 1160.7nm, 1161.7nm and the 1162.7nm wavelength narrow band light respectively with sequence number i=0,1,2,3, again the temperature that calculates three sensor correspondence positions according to the light intensity and the centre wavelength of these four narrow band light and the measured value of methane gas concentration.Its concrete steps are: step 1 is to demarcate the temperature coefficient k of three sensors ₁[i], sensitivity coefficient k ₂[i], correction coefficient k ₃[i] and primary constant a ₀[i] (i=1,2,3): it is reference temperature T that three single lens reflex type microstructure optical fiber gas sensors in (1) optical fiber link are placed in temperature simultaneously ₀=10 ℃ and gas density are in 0 the gas box, and computing machine obtains that the light intensity and the centre wavelength of narrow band light is respectively I near 1159.7nm, 1160.7nm, 1161.7nm and the 1162.7nm wavelength ₀[i] and λ ₀[i], i=0,1,2,3; (2) to be placed in temperature simultaneously be reference temperature T to three single lens reflex type microstructure optical fiber gas sensors in the optical fiber link ₀=10 ℃ and gas density are in 4% the gas box, and computing machine obtains that the light intensity of narrow band light is respectively I near 1159.7nm, 1160.7nm, 1161.7nm and the 1162.7nm wavelength ₁[i], i=0,1,2,3; (3) to be placed in temperature simultaneously be in 0 the gas box for demarcating r=25 ℃ of gas density of temperature T to three single lens reflex type microstructure optical fiber gas sensors in the optical fiber link, and computing machine obtains that the light intensity and the centre wavelength of narrow band light is respectively I near 1159.7nm, 1160.7nm, 1161.7nm and the 1162.7nm wavelength ₂[i] and λ _r[i], i=0,1,2,3; (4) to be placed in temperature simultaneously be in 4% the gas box for demarcating r=25 ℃ of gas density of temperature T to three single lens reflex type microstructure optical fiber gas sensors in the optical fiber link, and computing machine obtains that the light intensity of narrow band light is respectively I near 1159.7nm, 1160.7nm, 1161.7nm and the 1162.7nm wavelength ₃[i], i=0,1,2,3; The aforementioned demarcation temperature coefficient of the above-mentioned data substitution k that (5) will obtain ₁[i], sensitivity coefficient k ₂[i], correction coefficient k ₃[i] and primary constant a ₀The computing formula of [i] obtains the temperature coefficient k of three single lens reflex type microstructure optical fiber gas sensors on the optical fiber link ₁Ii], sensitivity coefficient k ₂[i], correction coefficient k ₃[i] and primary constant a ₀[i] (i=1,2,3).Step 2 is gas densities of three sensor punishment cloth on the measuring fiber link: three sensors of (1) optical fiber link are distributed in the methane gas of three diverse locations, light intensity and centre wavelength that computing machine obtains near the narrow band light of 1159.7nm, 1160.7nm, 1161.7nm and 1162.7nm wavelength are respectively I[i] and λ [i], i=0,1,2,3; (2) according to the computing formula in aforementioned when test, and the part spectroscopic data that obtains of step 1, the coefficient k of three sensors ₁[i], k ₂[i], k ₃[i] and primary constant a ₀[i] (i=1,2,3) calculates on the optical fiber link three sensor places with respect to reference temperature T ₀=10 ℃ temperature variation Δ T[i] (i=1,2,3), calculate on the optical fiber link methane gas concentration C [i] (i=1,2,3) of three sensor punishment cloth again.So just obtain the measured value of the methane gas concentration of three single lens reflex type microstructure optical fiber gas sensor punishment cloth on the optical fiber link.The concentration resolution of this sensor-based system can be less than 0.1%, and temperature resolution is 1 ℃, and the space distribution distance between the sensor can be less than 15cm, and its Measuring Time can be less than 2 seconds.

Claims (5)

1, a kind of distributed microstructure optical fiber gas sensing device is characterized in that: it comprises wideband light source, wide-band coupler, initial short period fiber grating, optical fiber link, fiber spectrum detuner and computing machine; Wideband light source is connected to an input end of wide-band coupler by optical fiber, the output terminal of wide-band coupler is connected to initial short period fiber grating by optical fiber, initial short period fiber grating is connected to the front end of optical fiber link by optical fiber, another input end of wide-band coupler is connected to the optic fibre input end of fiber spectrum detuner by optical fiber, and the FPDP of fiber spectrum detuner is connected to computing machine by the data-interface line; Optical fiber link is in series by optical fiber by two or more single lens reflex type microstructure optical fiber gas sensors; Single lens reflex type microstructure optical fiber gas sensor comprises two long period fiber grating separated by a distance on the optical fiber and a short period fiber grating outside these two long period fiber grating, these two long period fiber grating have close coupling centre wavelength, bandwidth and coupling efficiency, the resonance wavelength band of these two long period fiber grating is all in the absorbing band of methane gas, fibre cladding between these two long period fiber grating exposes, and the reflection kernel wavelength of this short period fiber grating is near the resonance centre wavelength of long period fiber grating; The interval of the reflection kernel wavelength of any two the short period fiber gratings in initial short period fiber grating and each single lens reflex type microstructure optical fiber gas sensor short period fiber grating is greater than half of the three dB bandwidth sum of corresponding two short period fiber grating reflection wavelength bands.

2, distributed microstructure optical fiber gas sensing device according to claim 1, it is characterized in that: each single lens reflex type microstructure optical fiber gas sensor in the optical fiber link is by the order series connection of the increasing or decreasing of its short period fiber grating reflection kernel wavelength, the rear end of previous single lens reflex type microstructure optical fiber gas sensor is connected with the front end of a back single lens reflex type microstructure optical fiber gas sensor, and the interval of the reflection kernel wavelength of any adjacent two the short period fiber gratings in initial short period fiber grating and each single lens reflex type microstructure optical fiber gas sensing short period fiber grating is less than 2 times of the three dB bandwidth sum of corresponding two short period fiber grating reflection wavelength bands; In the single lens reflex type microstructure optical fiber gas sensor, distance between two long period fiber grating is 5-800mm, the coupling efficiency of long period fiber grating central wavelength is greater than 99%, the long period fiber grating coupling efficiency is at least 3nm greater than 99% wavelength bandwidth, the short period fiber grating arrives the distance of adjacent long period fiber grating greater than 0.5mm, short period fiber grating coupling efficiency is greater than 90%, short period fiber grating centre wavelength to the spacing of long period fiber grating coupling centre wavelength less than 1/4th of the wavelength bandwidth of long period fiber grating 99% coupling efficiency.

3, distributed microstructure optical fiber gas sensing device according to claim 1 and 2; it is characterized in that: outside each single lens reflex type microstructure optical fiber gas sensor that has comprised two long period fiber grating, fibre cladding and short period fiber gratings on the optical fiber link, be with a protective sleeve; on each protective sleeve aperture is arranged; the sensor fibre section is pasted on the protective sleeve with solidifying glue at both ends near protective sleeve; at the both ends of protective sleeve a transition buffer cover is arranged respectively, ventilative dustproof thin layer is arranged outside protective sleeve.

4, a kind of method for sensing, it has utilized distributed microstructure optical fiber gas sensing device as claimed in claim 1 or 2, it is characterized in that: the methane gas concentration and the temperature information of each each sensing point of single lens reflex type microstructure optical fiber gas sensor senses on the optical fiber link, fiber spectrum detuner obtain initial short period fiber grating and each single lens reflex type microstructure optical fiber gas sensor reflects the spectroscopic data that returns and is transferred to computing machine; Computing machine is according to the spectroscopic data and the recursion relative ratio method of each short period fiber grating, with the reference signal of the catoptrical amplitude of the previous short-and-medium period optical fiber grating of single lens reflex type microstructure optical fiber gas sensor, calculate the temperature and the concentration of the methane gas at a back single lens reflex type microstructure optical fiber gas sensor place as a back single lens reflex type microstructure optical fiber gas sensor; Its concrete steps are: temperature coefficient, sensitivity coefficient, correction coefficient and the primary constant of demarcating each single lens reflex type microstructure optical fiber gas sensor on the optical fiber link earlier, be to test and calculate the temperature variation of described each single lens reflex type microstructure optical fiber gas sensor place then, test and calculate the methane gas concentration of each measured point at last again with recursion relative ratio method with respect to reference temperature; Computing formula when its demarcation and test is respectively:

(1) the temperature coefficient k of i single lens reflex type microstructure optical fiber gas sensor in the optical fiber link ₁[i] is

$k_1\left(i\right)=\frac{T_r-T_0}{{\mathrm{\&lambda;}}_r\left[i\right]-{\mathrm{\&lambda;}}_0\left[i\right]}$

Wherein, Tr demarcates temperature, T ₀It is reference temperature;

[] and numeric representation sequence number wherein, value in [] both can have been represented the sequence number of initial short period fiber grating and single lens reflex type microstructure optical fiber gas sensor, the sequence number that also can represent the reflected light bands of a spectrum of initial short period fiber grating and the short-and-medium period optical fiber grating of single lens reflex type microstructure optical fiber gas sensor, the sequence number of initial short period fiber grating is 0, begin in regular turn incrementally the short period fiber grating of each single lens reflex type microstructure optical fiber gas sensor is numbered 1 from the front end of optical fiber link, 2,3.....N, N is a single lens reflex type microstructure optical fiber gas number of sensors in the optical fiber link, i=0,1,2,3......N, as follows; I=1,2,3......N in this formula;

λ ₀[i] is that temperature is T ₀And gas density is 0 o'clock i catoptrical centre wavelength of short period fiber grating;

λ _r[i] is that temperature is that Tr and gas density are 0 o'clock i catoptrical centre wavelength of short period fiber grating;

(2) the sensitivity coefficient k of i single lens reflex type microstructure optical fiber gas sensor in the optical fiber link ₂[i] is

$k_2\left[i\right]=\frac{C_1}{\ln \left\{\frac{I_3\left[i\right]I_2[i-1]}{I_3[i-1]I_2\left[i\right]}\right\}}$

Wherein, C ₁It is the reference concentration of timing signal methane gas;

I=1,2,3......N, the sequence number of expression single lens reflex type microstructure optical fiber gas sensor or short period fiber grating wherein and reflected light bands of a spectrum thereof;

I3[i] be that temperature is that demarcation temperature T r and gas density are C ₁The time i the catoptrical amplitude of short period fiber grating, I ₃[i-1] is i-1 catoptrical amplitude of short period fiber grating this moment;

I ₂[i] is that temperature is that demarcation temperature T r and gas density are 0 o'clock i catoptrical amplitude of short period fiber grating, I ₂[i-1] is i-1 catoptrical amplitude of short period fiber grating this moment;

(3) the correction coefficient k of i single lens reflex type microstructure optical fiber gas sensor in the optical fiber link ₃[i] is

$k_3\left[i\right]=\frac{C_1\ln \left\{\frac{I_1\left[i\right]I_3[i-1]}{I_1[i-1]I_3\left[i\right]}\right\}}{(T_r-T_0)\ln \left\{\frac{I_2[i-1]I_3\left[i\right]}{I_2\left[i\right]I_3[i-1]}\right\}}$

Wherein, C ₁It is the reference concentration of timing signal methane gas;

Tr demarcates temperature, T ₀It is reference temperature;

I=1,2,3......N, the sequence number of expression single lens reflex type microstructure optical fiber gas sensor or short period fiber grating wherein and reflected light bands of a spectrum thereof;

I ₃[i] is that temperature is that Tr and gas density are C ₁The time i the catoptrical amplitude of short period fiber grating, I ₃[i-1] is i-1 catoptrical amplitude of short period fiber grating this moment;

I ₂[i] is that temperature is that Tr and gas density are 0 o'clock i catoptrical amplitude of short period fiber grating, I ₂[i-1] is i-1 catoptrical amplitude of short period fiber grating this moment;

I ₁[i] is that temperature is T ₀And gas density is C ₁The time i the catoptrical amplitude of short period fiber grating, I ₁[i-1] is i-1 catoptrical amplitude of short period fiber grating this moment;

(4) the primary constant a of i single lens reflex type microstructure optical fiber gas sensor in the optical fiber link ₀[i] is

$a_0\left[i\right]=\frac{C_1\ln \left\{\frac{I_0\left[i\right]}{I_0[i-1]}\right\}}{\ln \left\{\frac{I_2\left[i\right]I_3[i-1]}{I_2[i-1]I_3\left[i\right]}\right\}}$

Wherein, C ₁It is the reference concentration of timing signal methane gas;

I=1,2,3......N, the sequence number of expression single lens reflex type microstructure optical fiber gas sensor or short period fiber grating wherein and reflected light bands of a spectrum thereof;

I ₃[i] is that temperature is that demarcation temperature T r and gas density are C ₁The time i the catoptrical amplitude of short period fiber grating, I ₃[i-1] is i-1 catoptrical amplitude of short period fiber grating this moment;

I ₂[i] is that temperature is that demarcation temperature T r and gas density are 0 o'clock i catoptrical amplitude of short period fiber grating, I ₂[i-1] is i-1 catoptrical amplitude of short period fiber grating this moment;

I ₀[i] is that temperature is reference temperature T ₀And gas density is 0 o'clock i catoptrical amplitude of short period fiber grating, I ₀[i-1] is i-1 catoptrical amplitude of short period fiber grating this moment;

(5) when test, i single lens reflex type microstructure optical fiber gas sensor place is with respect to the temperature variation Δ T[i of reference temperature in the optical fiber link] be

ΔT[i]＝k ₁[i]{λ[i]-λ ₀[i]}

Wherein, i=1,2,3......N, the sequence number of expression single lens reflex type microstructure optical fiber gas sensor or short period fiber grating wherein and reflected light bands of a spectrum thereof;

k ₁[i] is the temperature coefficient of i single lens reflex type microstructure optical fiber gas sensor obtaining of timing signal;

λ ₀[i] is that temperature is reference temperature T in the calibration process ₀The time i the catoptrical centre wavelength of short period fiber grating;

I the catoptrical centre wavelength of short period fiber grating that λ [i] obtains when being test;

When (6) testing, the tested methane gas concentration C [i] at i single lens reflex type microstructure optical fiber gas sensor place is in the optical fiber link that distributed microstructure optical fiber gas sensing system calculates:

$C\left[i\right]=k_2\left[i\right]\ln \left\{\frac{I\left[i\right]}{I[]-1)}\right\}+k_3\left[i\right]\mathrm{\&Delta;T}\left[i\right]+a_0\left[i\right]$

Wherein, i=1,2,3......N, the sequence number of expression single lens reflex type microstructure optical fiber gas sensor or short period fiber grating wherein and reflected light bands of a spectrum thereof;

k ₂[i] is the sensitivity coefficient of i single lens reflex type microstructure optical fiber gas sensor obtaining of timing signal;

k ₃[i] is the correction coefficient of i single lens reflex type microstructure optical fiber gas sensor obtaining of timing signal;

a ₀[i] is the primary constant of i single lens reflex type microstructure optical fiber gas sensor obtaining of timing signal;

I[i] i catoptrical amplitude of short period fiber grating when being test;

I[i-1] i-1 catoptrical amplitude of short period fiber grating when being test;

Δ T[i] be the temperature variation of i single lens reflex type microstructure optical fiber gas sensor place the time calculating of test with respect to reference temperature.

5, a kind of method for sensing, it has utilized distributed microstructure optical fiber gas sensing device as claimed in claim 3, it is characterized in that: the methane gas concentration and the temperature information of each each sensing point of single lens reflex type microstructure optical fiber gas sensor senses on the optical fiber link, fiber spectrum detuner obtain initial short period fiber grating and each single lens reflex type microstructure optical fiber gas sensor reflects the spectroscopic data that returns and is transferred to computing machine; Computing machine is according to the spectroscopic data and the recursion relative ratio method of each short period fiber grating, with the reference signal of the catoptrical amplitude of the previous short-and-medium period optical fiber grating of single lens reflex type microstructure optical fiber gas sensor, calculate the temperature and the concentration of the methane gas at a back single lens reflex type microstructure optical fiber gas sensor place as a back single lens reflex type microstructure optical fiber gas sensor; Its concrete steps are: coefficient and primary constant are ended in temperature coefficient, sensitivity coefficient, the school of demarcating each single lens reflex type microstructure optical fiber gas sensor on the optical fiber link earlier, be to test and calculate the temperature variation of described each single lens reflex type microstructure optical fiber gas sensor place then, test and calculate the methane gas concentration of each measured point at last again with recursion relative ratio method with respect to reference temperature; Computing formula when its demarcation and test is respectively:

(1) the temperature coefficient k of i single lens reflex type microstructure optical fiber gas sensor in the optical fiber link ₁[i] is

$k_1\left(i\right)=\frac{T_r-T_0}{{\mathrm{\&lambda;}}_r\left[i\right]-{\mathrm{\&lambda;}}_0\left[i\right]}$

Wherein, Tr demarcates temperature, T ₀It is reference temperature;

[] and numeric representation sequence number wherein, value in [] both can have been represented the sequence number of initial short period fiber grating and single lens reflex type microstructure optical fiber gas sensor, the sequence number that also can represent the reflected light bands of a spectrum of initial short period fiber grating and the short-and-medium period optical fiber grating of single lens reflex type microstructure optical fiber gas sensor, the sequence number of initial short period fiber grating is 0, begin in regular turn incrementally the short period fiber grating of each single lens reflex type microstructure optical fiber gas sensor is numbered 1 from the front end of optical fiber link, 2,3.....N, N is a single lens reflex type microstructure optical fiber gas number of sensors in the optical fiber link, i=0,1,2,3......N, as follows; I=1,2,3......N in this formula;

λ ₀[i] is that temperature is T ₀And gas density is 0 o'clock i catoptrical centre wavelength of short period fiber grating:

λ _r[i] is that temperature is that Tr and gas density are 0 o'clock i catoptrical centre wavelength of short period fiber grating;

(2) the sensitivity coefficient k of i single lens reflex type microstructure optical fiber gas sensor in the optical fiber link ₂[i] is

$k_2\left[i\right]=\frac{C_1}{\ln \left\{\frac{I_3\left[i\right]I_2[i-1]}{I_3[i-1]I_2\left[i\right]}\right\}}$

Wherein, C ₁It is the reference concentration of timing signal methane gas;

I=1,2,3......N, the sequence number of expression single lens reflex type microstructure optical fiber gas sensor or short period fiber grating wherein and reflected light bands of a spectrum thereof;

I ₃[i] is that temperature is that demarcation temperature T r and gas density are C ₁The time i the catoptrical amplitude of short period fiber grating, I ₃[i-1] is i-1 catoptrical amplitude of short period fiber grating this moment;

I ₂[i] is that temperature is that demarcation temperature T r and gas density are 0 o'clock i catoptrical amplitude of short period fiber grating, I ₂[i-1] is i-1 catoptrical amplitude of short period fiber grating this moment;

(3) the correction coefficient k of i single lens reflex type microstructure optical fiber gas sensor in the optical fiber link ₃[i] is

$k_3\left[i\right]=\frac{C_1\ln \left\{\frac{I_1\left[i\right]I_3[i-1]}{I_1[i-1]I_3\left[i\right]}\right\}}{(T_r-T_0)\ln \left\{\frac{I_2[i-1]I_3\left[i\right]}{I_2\left[i\right]I_3[i-1]}\right\}}$

Wherein, C ₁It is the reference concentration of timing signal methane gas;

Tr demarcates temperature, T ₀It is reference temperature;

I=1,2,3......N, the sequence number of expression single lens reflex type microstructure optical fiber gas sensor or short period fiber grating wherein and reflected light bands of a spectrum thereof;

I ₃[i] is that temperature is that Tr and gas density are C ₁The time i the catoptrical amplitude of short period fiber grating, I ₃[i-1] is i-1 catoptrical amplitude of short period fiber grating this moment;

I ₂[i] is that temperature is that Tr and gas density are 0 o'clock i catoptrical amplitude of short period fiber grating, I ₂[i-1] is i-1 catoptrical amplitude of short period fiber grating this moment;

I ₁[i] is that temperature is T ₀And gas density is C ₁The time i the catoptrical amplitude of short period fiber grating, I ₁[i-1] is i-1 catoptrical amplitude of short period fiber grating this moment;

(4) the primary constant a of i single lens reflex type microstructure optical fiber gas sensor in the optical fiber link ₀[i] is

$a_0\left[i\right]=\frac{C_1\ln \left\{\frac{I_0\left[i\right]}{I_0[i-1]}\right\}}{\ln \left\{\frac{I_2\left[i\right]I_3[i-1]}{I_2[i-1]I_3\left[i\right]}\right\}}$

Wherein, C ₁It is the reference concentration of timing signal methane gas;

I=1,2,3......N, the sequence number of expression single lens reflex type microstructure optical fiber gas sensor or short period fiber grating wherein and reflected light bands of a spectrum thereof;

I ₃[i] is that temperature is that demarcation temperature T r and gas density are C ₁The time i the catoptrical amplitude of short period fiber grating, I ₃[i-1] is i-1 catoptrical amplitude of short period fiber grating this moment;

I ₂[i] is that temperature is that demarcation temperature T r and gas density are 0 o'clock i catoptrical amplitude of short period fiber grating, I ₂[i-1] is i-1 catoptrical amplitude of short period fiber grating this moment;

I ₀[i] is that temperature is reference temperature T0 and gas density is 0 o'clock i catoptrical amplitude of short period fiber grating, I ₀[i-1] is i-1 catoptrical amplitude of short period fiber grating this moment;

(5) when test, i single lens reflex type microstructure optical fiber gas sensor place is with respect to the temperature variation Δ T[i of reference temperature in the optical fiber link] be

ΔT[i]＝k ₁[i]{λ[i]-λ ₀[i]}

Wherein, i=1,2,3......N, the sequence number of expression single lens reflex type microstructure optical fiber gas sensor or short period fiber grating wherein and reflected light bands of a spectrum thereof;

k ₁[i] is the temperature coefficient of i single lens reflex type microstructure optical fiber gas sensor obtaining of timing signal;

λ ₀[i] is that temperature is reference temperature T in the calibration process ₀The time i the catoptrical centre wavelength of short period fiber grating;

I the catoptrical centre wavelength of short period fiber grating that λ [i] obtains when being test;

When (6) testing, the tested methane gas concentration C [i] at i single lens reflex type microstructure optical fiber gas sensor place is in the optical fiber link that distributed microstructure optical fiber gas sensing system calculates:

$C\left[i\right]=k_2\left[i\right]\ln \left\{\frac{I\left[i\right]}{I[i-1)}\right\}+k_3\left[i\right]\mathrm{\&Delta;T}\left[i\right]+a_0\left[i\right]$

Wherein, i=1,2,3......N, the sequence number of expression single lens reflex type microstructure optical fiber gas sensor or short period fiber grating wherein and reflected light bands of a spectrum thereof;

k ₂[i] is the sensitivity coefficient of i single lens reflex type microstructure optical fiber gas sensor obtaining of timing signal;

k ₃[i] is the correction coefficient of i single lens reflex type microstructure optical fiber gas sensor obtaining of timing signal;

a ₀[i] is the primary constant of i single lens reflex type microstructure optical fiber gas sensor obtaining of timing signal;

I[i] i catoptrical amplitude of short period fiber grating when being test;

I[i-1] i-1 catoptrical amplitude of short period fiber grating when being test;

Δ T[i] be the temperature variation of i single lens reflex type microstructure optical fiber gas sensor place the time calculating of test with respect to reference temperature.

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