CN100468049C - Detection method for Optical-fiber transmitting infrared absorption type methane gas - Google Patents
Detection method for Optical-fiber transmitting infrared absorption type methane gas Download PDFInfo
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- CN100468049C CN100468049C CN 200710017792 CN200710017792A CN100468049C CN 100468049 C CN100468049 C CN 100468049C CN 200710017792 CN200710017792 CN 200710017792 CN 200710017792 A CN200710017792 A CN 200710017792A CN 100468049 C CN100468049 C CN 100468049C
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Abstract
This invention discloses one fiber transmission infrared absorptive firedamp gas test method based on micro split device, which uses wide band infrared light, flash grating, transmission fiber, absorptive chamber, photo electricity detector and signal process circuit, wherein, the light from LED source to get center wave for 1331 nm thin light source through flash grating into incidence fiber transmission and into absorptive chamber full of firedamp gas; the emit light sends through polymer lens coupled to exit fiber then to photo electricity detector and signal process circuit based on gas infrared absorptive rules of Beer-Lambert gas to get gas chamber gas concentration through testing gas chamber infrared attenuate.
Description
Technical field:
The present invention relates to a kind of detection method of methane gas, particularly a kind of detection method of infrared absorption type methane gas of Optical Fiber Transmission.
Background technology
Methane (CH
4) be flammable explosive gas, be the principal ingredient of coal-mine gas, biogas, rock gas, be a kind of important chemical material, concentration 5.3%～15% o'clock in atmosphere has explosivity.Gas accident is one of main threat of Safety of Coal Mine Production, is the great difficult problem of puzzlement mining industry always, brings tremendous loss to the country and people.Simultaneously, methane still causes one of the principal ingredient of " greenhouse effect ", and the year corrosion for a long time of city gas tube also is a big hidden danger of urban safety.Therefore, the methane detection system of developing a kind of safe and reliable, high sensitivity, essential safety has practical and great social effect and economic worth.
The detection method of methane gas has multiple according to the difference of pick-up unit, as catalytic combustion type, semiconductor-type, biological formula, electrochemical oxidation formula, optical interference formula etc.The infrared absorption type methane gas detection method of Optical Fiber Transmission has the incomparable advantage of many other sensing detection method, big, the anti-electromagnetic interference (EMI) of, dynamic range fast, burn-proof and explosion prevention, be difficult for poisoning as response speed, and available fiber transmission realizes remote measurement etc., is particularly suitable for the strong-electromagnetic field environment and such as the application under the rugged surroundings of mine etc.
Document " design and the experimental study of fiber optics formula methane gas sensor " (Zhang Jingchao, University On The Mountain Of Swallows, in April, 2006) a kind of infrared absorption type methane gas detection method has been proposed, it adopts DFB LD light source (distributed feedback type semiconductor laser), Ring-down chamber to absorb air chamber, small echo denoising and harmonic detecting technique, though it can obtain very high accuracy of detection, but this method will adopt semiconductor laser, because laser instrument itself is just very expensive, therefore it is very high to detect cost, and degree of being practical is very low.Defectives such as in addition, also there is absorption air chamber structure relative complex in this method, and data processing is loaded down with trivial details.
Summary of the invention:
Technical matters to be solved by this invention is to improve the low deficiency of cost height, degree of being practical of the near infrared light fiber detecting method of above-mentioned based semiconductor laser instrument, a kind of detection method of the Optical Fiber Transmission infrared absorption type methane gas based on little optical splitter is provided, and its detection to methane gas has characteristics simple and easy, with low cost, easy to use.
For reaching above purpose, the present invention takes following technical scheme to be achieved:
A kind of detection method of infrared absorption type methane gas of Optical Fiber Transmission, it is characterized in that, comprise and adopt a broadband infrared light source, one to have little optical splitter of blazed grating, an absorption air chamber, a photodetector and a signal processing circuit and form optic testing system;
Described broadband infrared light source is concentrated the narrow-band light source that obtains under the methane adsorption peak by the blazed grating beam split of little optical splitter, the narrow-band light source that is obtained is transferred to the absorption air chamber by being coupled into incident optical, adopt spherical lens that narrow-band light source is collimated into directional light at the incident end that absorbs air chamber, after focusing on, the emergent light that the GRIN Lens of the exit end through absorbing air chamber will be carried the concentration of methane gas signal directly is coupled into outgoing optical fiber, and transferring to photodetector, emergent light is converted to electric signal by photodetector with light signal and inputs to signal processing circuit again.
In the such scheme, the blazed grating of described little optical splitter adopts silicon low-light sheet to make, and its reflecting surface is made zigzag fashion; Described GRIN Lens has tail optical fiber; Described air chamber is made non-removable structure; Described broadband infrared light source is to adopt near the infrared LED of centre wavelength 1331nm.
The absorption methane gas detection method of Optical Fiber Transmission of the present invention compared with prior art, has the following advantages:
1. no longer need to adopt expensive laser instrument light splitting technology, and adopt near the infrared LED light source of centre wavelength 1331nm, in conjunction with little optical splitter of the little blazed grating of silicon that adopts MEMS (MEMS (micro electro mechanical system)) fabrication techniques.Under situation of making in enormous quantities, high conformity, and single average unit cost is very low, as 2200 yuan one of semiconductor laser, can be controlled in 300 yuan and adopt the blazed grating beam split to produce cost in batches, and the serviceable life of LED will be much larger than the life-span of semiconductor laser.
2. adopt the little blazed grating of silicon can from wideband light source, catch to such an extent that need the narrow-band light source of wavelength, change the blazing angle θ of blazed grating, can obtain different centre wavelength, and then can realize that a cover system detects multiple gases concentration, and not only can only detect methane gas.
3. absorb air chamber incident end and adopt the spherical lens collimation, exit end adopts the GRIN Lens of magnetic tape trailer fibre to focus on, and being made of one structure, and reflection and interaction noise are little, simple in structure.
4. make full use of proven technique and product in the present optical fiber telecommunications system,, realize online remote measurement by the optical fiber low-loss transmission, and responsive probe part essential safety.
Description of drawings
Fig. 1 is the light channel structure synoptic diagram that the present invention is based on the infrared absorption type Optical Fiber Detection System of Methane Gas of little optical splitter.Wherein, 3 is incident optical; 5 are outgoing optical fiber.
Fig. 2 is the light-dividing principle synoptic diagram of little optical splitter among Fig. 1.Wherein, 10 is diaphragm; 11 is condenser lens; 12 is collimation lens; 13 is blazed grating.
Fig. 3 is the structural drawing of the absorption air chamber among Fig. 1.
Fig. 4 is the light-dividing principle figure of blazed grating among Fig. 2.
Embodiment:
As shown in Figure 1 to Figure 3, the present invention adopts a broadband infrared light source 1 (can comprise temperature control and Current Control link), one to have little optical splitter 2, incident and the outgoing optical fiber 3 of blazed grating 13 and 5, absorption air chambers 4, a photodetector 6 and signal processing circuit 7 composition test macros.The stable light source of broadband infrared light source 1 output through temperature and Current Control, the narrow band light that obtains specific wavelength via little optical splitter 2 is coupled into incident optical 3, these incident optical 3 other ends link to each other with absorption air chamber 4 incident end spherical lenses 8, GRIN Lens 9 tail optical fibers that absorb air chamber 4 exit ends are connected with outgoing optical fiber 5, outgoing optical fiber 5 other ends connect photodetector 6, and photodetector 6 connects signal processing circuit 7.Wherein, broadband infrared light source 1 can adopt near the infrarede emitting diode LED of centre wavelength 1331nm, and incident and outgoing optical fiber 3,5 can adopt the single mode silica fibre, and photodetector 6 can adopt photodiode.
Little optical splitter 2 comprises a diaphragm 10, these diaphragm 10 both sides are respectively arranged with condenser lens 11 and collimation lens 12, blazed grating 13 is for adopting the little blazed grating of silicon of MEMS fabrication techniques, and its reflecting surface is a zigzag fashion, and is oppositely arranged on collimation lens 12 parallel light emergences one side.Principle of the present invention is to utilize blazed grating 13 beam split concentrate to obtain narrow-band light source to realize the infrared absorption method measurement methane gas 1331nm wavelength under.Through the sawtooth reflecting surface beam split after the condenser lens 11 of little optical splitter 2 focuses on the back to be parallel beam by diaphragm 10 collimated lens 12 collimations of infrared light that the stable wideband light source 1 of the output of temperature and current-modulation sends by blazed grating 13, obtain the narrow-band light source of centre wavelength at 1331nm, the narrow-band light source centre wavelength that is obtained overlaps with the methane gas near ir absorption peaks, transfer to the absorption air chamber 4 that is full of methane gas through incident optical 3, the parallel air chamber 4 that passes behind air chamber 4 incident end spherical lenses 8 collimations, the emergent light that carries concentration of methane gas information directly is coupled into outgoing optical fiber 5 at air chamber 4 exit ends after GRIN Lens 9 focuses on, be converted into electric signal through photodetector 6 again, obtain testing results through signal processing circuit 7, promptly can obtain concentration of methane gas in the air chamber 4 by detecting the infrared light attenuation that sees through air chamber 4.
Transmission-type of the present invention absorbs air chamber 4 and adopts spherical lens 8 at the incident end light from incident optical 3 incidents to be collimated, adopt the light of 9 pairs of output air chambers of GRIN Lens of magnetic tape trailer fibre to focus at exit end, directly be coupled into outgoing optical fiber 5, whole air chamber 4 can be made of one structure, this air chamber structure is simple, aligning and coupling are convenient, and coupling efficiency is higher.(comprising collimation and coupling focusing block, coupling efficiency 〉=74.6%)
Infrared absorption is based on the Beer-Lambert law, suc as formula (1), through conversion as the formula (2).
I＝I
0exp(-αLc) (1)
c＝ln(I
0/I)/αL (2)
In the formula: I is the luminous energy that photodetector 6 receives; I
0It is the narrow-band light source energy that obtains through blazed grating 13; α is methane gas absorption coefficient under this wavelength; L absorbs light path; C is tested concentration of methane gas.By formula (2) as seen, at incident light energy I
0, under the certain situation of absorption coefficient, absorption light path L, measure outgoing luminous energy I (also being the energy that photodetector 6 receives) and just can obtain tested concentration of methane gas.
For example, methane is the near infrared light of 1331nm at wavelength, and its absorption coefficient is a constant, α=5.4m
-1, air chamber length (absorption light path) L=0.2m, I
0=242.7 μ W, I=241.3 μ W can get gas concentration c=0.5% by following formula calculating.
The light-dividing principle of blazed grating 13 as shown in Figure 4.Among the figure, N is the normal direction of bottom surface; D is a grating constant; N is the normal direction of the face that glitters;
Be the angle of incident ray with the face normal direction of glittering;
Be emergent light and bottom surface normal direction angle; θ is a blazing angle; I is an incident light; I ' is an emergent light.
(there is not the zero level principal maximum of the chromatic dispersion a big chunk in the projectile energy that accounted for transmission grating, remaining energy is assigned on the positive and negative principal maximum at different levels again, cause that grade spectral line that chromatic dispersion is arranged that is used for analyzing only to be assigned to very little energy) difference, blazed grating 13 can focus on light intensity near the m level blaze wavelength λ the m level spectrum, as long as λ satisfies:
dsin(2θ)＝mλ (3)
So, can grating be applicable on certain grade of spectrum of a certain specific band by the design of blazing angle θ and grating constant d.Below provide a concrete embodiment of calculating: processing blazing angle θ is 4 °, grating constant d is the blazed grating 13 of 50 μ m, the angle of control incident light i is 87 °, through blazed grating 13 beam split, just can obtain to test the infrared light of the required 1331nm of methane concentration on main is inferior.
Claims (1)
1. the detection method of the infrared absorption type methane gas of an Optical Fiber Transmission, it is characterized in that, comprise and adopt a broadband infrared light source, one to have little optical splitter of blazed grating, an absorption air chamber, a photodetector and a signal processing circuit and form optic testing system;
Described broadband infrared light source is concentrated the narrow-band light source that obtains under the methane adsorption peak by the blazed grating beam split of little optical splitter, the narrow-band light source that is obtained is transferred to the absorption air chamber by being coupled into incident optical, adopt spherical lens that narrow-band light source is collimated into directional light at the incident end that absorbs air chamber, after focusing on, the emergent light that the GRIN Lens of the exit end through absorbing air chamber will be carried the concentration of methane gas signal directly is coupled into outgoing optical fiber, and transferring to photodetector, emergent light is converted to electric signal by photodetector with light signal and inputs to signal processing circuit again; It is characterized in that the blazed grating of described little optical splitter adopts silicon low-light sheet to make, its reflecting surface is made zigzag fashion; Described spherical lens, GRIN Lens and absorption air chamber are made incorporate structure.
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| CN102768188A (en) * | 2012-07-30 | 2012-11-07 | 山东建筑大学 | Medical equipment |
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