CN103776794A - Methane gas sensing equipment - Google Patents
Methane gas sensing equipment Download PDFInfo
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- CN103776794A CN103776794A CN201210416717.5A CN201210416717A CN103776794A CN 103776794 A CN103776794 A CN 103776794A CN 201210416717 A CN201210416717 A CN 201210416717A CN 103776794 A CN103776794 A CN 103776794A
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Abstract
The invention relates to methane gas sensing equipment which comprises an infrared broadband light source, a tunable Fabry-Perot filter, a gas sampling chamber, a photoelectric detection device and a drive control and data analysis system, wherein two design schemes of the tunable Fabry-Perot filter are adopted as follows: the first design scheme is mainly and technically characterized in that the Fabry-Perot filter comprises a first band-pass filter, a liquid crystal phase modulator, a second band-pass filter and a driving source; the liquid crystal phase modulator is arranged in a Fabry-Perot cavity formed by the first band-pass filter and the second band-pass filter; the driving source realizes the tuning function of the filters through controlling the valid refractive index of a liquid crystal material in the Fabry-Perot cavity; the main difference between the main technical features of the second design scheme and that of the first design scheme is as follows: the first band-pass filter and the second band-pass filter are respectively replaced by a long wave-pass phase step type filter and a short wave-pass phase step type filter, and the long wave-pass phase step type filter and the short wave-pass phase step type filter have different cut-off frequencies.
Description
Technical field
The invention belongs to photoelectricity gas sensing technical field, especially a kind of methane gas sensing equipment that has adopted tunable fabry-perot filter.
Background technology
Infrared-gas sensing technology is that a kind of near infrared spectrum based on gas with various molecule is selected absorption characteristic, utilizes gas concentration and absorption intensity relation (lambert-Bill Lambert-Beer law) to differentiate the gas sensing technology of gas composition definite its concentration.It is widely used as having compared with electric chemical formula, catalytic combustion type, semiconductor-type etc. with other classification gas sensing technology, long service life, highly sensitive, good stability, be applicable to that gas is many, cost performance is high, maintenance cost is low, can on-line analysis etc. series of advantages, therefore, be widely used in the fields such as petrochemical complex, metallurgical industry, industrial and mineral exploitation, atmospheric pollution detection, agricultural, health care.Along with the development of semiconductor laser technology, in all kinds of infrared-gas sensing technologies, adopt the gas sensing technology of tunable laser, in recent years, obtained application more and more widely.Than the technology of utilizing broadband infrared light source and narrow band pass filter, this technology has low drift and the feature such as anti-interference, provides more stable and accurate gas concentration to detect.But, the high-quality tunable laser of this Technology Need, therefore, price comparison costliness.Another kind of feasible technology is the technology that adopts broadband infrared light source and tunable narrow-band optical filter, and stability and the precision comparable with the gasmetry that adopts tunable laser technology also can be provided.
In all kinds of wave filter technologies, traditional optical method F-P etalon is a kind of narrow-band filtering device that utilizes multiple-beam interference principle to make, and mainly contains two types: a kind of is airspace, and a kind of is optical glass interval.The multiple-beam interference effect of the high reflectance institute forming method Fabry-Perot-type cavity by multilayer dielectric film on two logical light faces, can realize the multi-wavelength narrow-band filtering output in broad spectrum, and have that stable performance, clear aperature are large, luminous power damage threshold is high, simple in structure and the characteristic such as cost is low, therefore, be widely used in all kinds of laser instruments, optical gauge and photoconductive fiber communication apparatus.
For the Fabry-Perot etalon of airspace, can by change the incident angle of light carry out tuning, but the tuning range of this method is very little; Also can adopt the chamber progress row of using mechanical means (as step motor) to change Fabry-Perot etalon tuning, this method can realize large tuning range, but tuning precision is low, and high to the accuracy requirement of mechanical part, and stability is bad.In addition, adopt PZT piezoelectric ceramics (lead zirconate titanate) technology long by the chamber of change Fabry-Perot etalon, can improve tuning precision and speed, but be difficult for accomplishing miniaturization, and driving circuit is also more complicated; Change the temperature of etalon and also can realize in a big way tuning, still, the shortcoming of the method is that speed is slow.Meanwhile, the filtering output characteristics of simplex method F-P etalon is the multimode output that a light frequency is spaced apart Free Spectral Range.
Summary of the invention
The object of the invention is to overcome the deficiencies in the prior art, utilize broadband infrared light source and tunable fabry-perot filter and photodetector etc. to realize high stability, the gas concentration of high precision and low price detects.Described tunable fabry-perot filter be by liquid crystal phase-modulator be placed in the chamber of Fabry-Perot etalon, realize the linearly polarized light signal to seeing through fabry-perot filter continuously, fast and precise light frequency tuning function, and two reflectings surface of Fabry-Perot-type cavity are set to bandpass filter or phase step type wave filter and realize the arrowband single-mode output of fabry-perot filter according to the Free Spectral Range that the transmission bandwidth of the transmission bandwidth of described bandpass filter or described phase step type wave filter arranges Fabry-Perot-type cavity.
The present invention solves existing technical matters and takes following technical scheme to realize:
A kind of methane gas sensing equipment comprises an infrared wideband light source, a tunable fabry-perot filter, a gas sampling chamber, Electro-Optical Sensor Set and driving is controlled and data analysis system, the driving of described photodetector and signal receiving circuit and control circuit and data analysis system, the light being sent by described infrared wideband light source is first by after tunable fabry-perot filter, by being received by described the first Electro-Optical Sensor Set behind described gas sampling chamber, carried out the absorption spectrum of detected gas to carry out data analysis and obtain by described control circuit and data analysis system the concentration of this gas.
And, described tunable fabry-perot filter comprises the first bandpass filter, liquid crystal phase-modulator, the second bandpass filter and drive source, liquid crystal phase-modulator is arranged in the chamber of the fabry-perot filter being made up of the first bandpass filter and the second bandpass filter, realizes the tuber function of wave filter by liquid crystal phase-modulator in control Fabry-Perot-type cavity.
And, the first described bandpass filter and the second bandpass filter are a kind of bandpass filter of the multilayer dielectric film arranging on the inside surface of optically transparent material and have identical transmission bandwidth, can be according to the acutance coefficient of transmitted light is arranged to different reflectivity in the passband of described bandpass filter, this reflectivity is arranged between 80% to 98%, arrange 100% or approach 100% reflectivity beyond the passband, and on the outside surface of optically transparent material, optical anti-reflective film is set.
And, the center of the first described bandpass filter and the absorption spectrum of the center of the passband of the second bandpass filter and the gas of required detection is identical or approach identical, the width of this passband is according to the requirement of gas test precision is determined, be set to 2 nanometers between 5 nanometers, the Free Spectral Range of described fabry-perot filter should be greater than described passband width, and making through the light signal of described tunable narrow-band optical filter is single-mode optics signal.
And, described tunable fabry-perot filter comprises a long-pass step filter, liquid crystal phase-modulator, short-pass step filter and drive source, liquid crystal phase-modulator is arranged in the chamber of the fabry-perot filter being made up of described long-pass step filter and described short-pass step filter, realizes the tuber function of wave filter by controlling liquid crystal phase-modulator in described Fabry-Perot-type cavity.
And, described long-pass step filter and short-pass step filter are a kind of optical filters of the multilayer dielectric film arranging on the inside surface of optically transparent material, described long-pass step filter has 100% or approach 100% reflectivity for the light that is less than cutoff frequency, and described short-pass step filter has 100% or approach 100% reflectivity for the light that is greater than cutoff frequency; Can be according to the acutance coefficient of transmitted light be arranged to different reflectivity in the passband of described long-pass step filter and short-pass step filter, this reflectivity is arranged between 80 and 98%, and on the outside surface of optically transparent material, optical anti-reflective film is set.
And, the cutoff frequency of described long-pass step filter is less than the cutoff frequency of described short-pass step filter, formed the passband width of described fabry-perot filter by the cutoff frequency of described long-pass step filter and the cutoff frequency of described short-pass step filter, the width of this passband is according to the requirement of gas test precision is determined, be arranged on 2 nanometers between 5 nanometers, the center of the center of this passband and the absorption spectrum of the gas of required detection is identical or approach identical, the Free Spectral Range of described tunable fabry-perot filter is greater than its free transmission range, making through the light signal of described tunable narrow-band optical filter is single-mode optics signal.
And what described liquid crystal phase-modulator adopted is nematic phase type liquid crystal material, the thickness of liquid crystal material is several microns to tens microns.
And described tunable fabry-perot filter drive source is that a kind of frequency is about 2KHz, voltage amplitude can be at the square-wave signal of modulating of zero to positive and negative 5 volts, and the modulating frequency of voltage amplitude be 10 kilo hertzs or more than.
And, described control circuit and data analysis system comprise a system take digital signal processor and embedded software as core, for controlling driving and the signal receiving circuit of the drive source of described tunable fabry-perot filter, described photodetector and receiving extraneous control signal and output signal, to realize the absorption spectrum of described infrared-gas sensing equipment to detected gas and the measuring ability of concentration.
And the size of described gas sampling chamber, according to the factor such as concentration and precision that will detect gas is determined, is generally several centimetres to hundreds of centimeter length.
And the output of described infrared wideband light source is linearly polarized light, its optical axis is consistent with the optical axis of described tunable fabry-perot filter, and spectral width exceedes 5 nanometers, and centre wavelength equals or the approaching gas absorption spectra Dai center of surveying.
And the central homology wavelength of described tunable fabry-perot filter is arranged on 1.65 microns, or 2.3 microns, or 3.3 microns, or approach above-mentioned several wavelength.
Advantage of the present invention and good effect are:
The present invention is reasonable in design, by broadband infrared light signal being carried out to the tuning scanning of continuous, quick and accurate frequency spectrum, make its see through tunable narrow-band wave filter only one can be tuning fast narrowband optical signal, realize the accurate detection to detecting gas absorption spectra and gas concentration in conjunction with photodetector etc.
That the present invention has is simple in structure, machinery-free moving-member, stable and reliable for performance, cost is low, size is little, be easy to install and the feature such as production, can meet for the reliability service requiring under the little and extreme working environment of size, can be widely used in the fields such as petrochemical complex, metallurgical industry, industrial and mineral exploitation, atmospheric pollution detection, agricultural, health care.
Accompanying drawing explanation
Fig. 1 is the schematic diagram of a common law F-P etalon;
Fig. 2 is the structural representation of liquid crystal phase-modulator;
Fig. 3 is that the phase place of light transmission liquid crystal phase-modulator is with the change curve schematic diagram of extra electric field;
Fig. 4 is the driving electric signal schematic diagram of liquid crystal phase-modulator;
Fig. 5 is a kind of structural representation of tunable Fabry-Perot-type wave filter;
Fig. 6 is the schematic diagram of bandpass filter;
Fig. 7 is the schematic diagram of long wave pass;
Fig. 8 is the schematic diagram of short wave-pass filter;
Fig. 9 is the transmitted spectrum schematic diagram of common law F-P etalon;
Figure 10 is the transmitted spectrum schematic diagram of tunable Fabry-Perot-type wave filter;
Figure 11 is schematic diagram of the present invention;
Figure 12 is the schematic diagram of system control of the present invention and data analysis system.
Embodiment
Below in conjunction with accompanying drawing, the embodiment of the present invention is further described.
Fig. 1 has provided the schematic diagram of a kind of common Fabry-Perot (Fabry-Perot) light standard tool 100.The material of this Fabry-Perot light standard tool 100 generally uses to resemble near infrared and visible light wave range and melts quartz or the such optical glass of BK7, the refractive index of supposing material is n, two logical light faces 2 and 4 all plate highly reflecting films, its reflectivity is R, thickness is h, and light, to approach the incident angle incident of zero degree, only has the 2nh=m of meeting λ, could see through etalon, wherein m is the level time of transmitted light.The Free Spectral Range FSR of light standard tool 100
1can be expressed as: Δ λ=λ
2/ (2nh), or with frequency representation: Δ ν=c/ (2nh), wherein c is the light velocity.The crest frequency of transmitted light can be expressed as: ν=mc/ (2nh), and wherein m is order of interference, the frequency bandwidth of transmitted light can be expressed as:
Δ ν
1/2(FWHM)=c (1-R)/(2nhR
1/2), wherein c is the light velocity.
Can find out the Free Spectral Range FSR of light standard tool 100 from above-mentioned two formula
1with thickness be that h is inversely proportional to.The refractive index of supposing material is n=1.5, realize FSR
1=100GHz, 1 millimeter of thickness h ≈.Free Spectral Range FSR
1larger, its thickness is just less.After the material of etalon and thickness are determined, the frequency bandwidth of transmitted light is main relevant with reflectivity R, and reflectivity is higher, and (finesse) is less for frequency broadband or acutance.The feature of the transmitted spectrum of Fabry-Perot (Fabry-Perot) light standard tool is that the bandwidth of each transmission spectrum can be accomplished very narrow, the frequency interval of transmitted spectrum equates and the non-constant width of optical frequency bandwidth, generally can cover optical frequency bands of a spectrum more than 100 nanometers, as shown in Figure 9.
Because the general liquid crystal material as photoelectric device has high resistivity, therefore, can be considered to desirable dielectric substance.Owing to forming the orderly orientation of molecule and the form of extension elongation, liquid crystal has anisotropic dielectric characteristic and mono-symmetry, and as a uniaxial crystal, the direction of its optical axis is consistent with the oriented of molecule.When under the effect of liquid crystal molecule at external electrical field, can form electric dipole.Under the moment loading forming at electric dipole, make the orientation of liquid crystal molecule turn to the direction of electric field, can, by changing the power of electric field, change the direction of the optical axis of liquid crystal.Therefore, can utilize this characteristic of liquid crystal to make optical phase modulator, tunable optic filter or other photoelectric devices, as photoswitch and light intensity modulator etc.The thickness of the general liquid crystal rete as photoelectric device is several microns to tens microns.The present invention utilizes just liquid crystal, under electric field action, the refractive index of linearly polarized light is produced to this characteristics design of change and forms.
Fig. 2 is the structural representation of a liquid crystal phase-modulator 200, comprises outer optically transparent material 12 and 24, transparent electrode layer 16 and 26, and separation layer 19 and liquid crystal layer 18. generally plate optical anti-reflective films in the inside and outside both side surface 5 and 7 of optically transparent material 12 and 24.Two transparency electrodes 16 of liquid crystal phase tuner are connected with driving circuit 14 with 26, the driving signal being produced by driving circuit forms and drives electric field between two transparency electrode retes, utilize the effective refractive index n of electric field change Fabry-Perot intraluminal fluid crystalline substance, regulate light frequency ν and the Free Spectral Range of the transmitted light of fabry-perot filter.Fig. 3 has provided a thickness and has been about the nematic phase type liquid crystal of 10 microns at 2KHz, and amplitude peak is (driving signal as shown in Figure 4) under the driving of square-wave voltage of 5 volts of +/-, to optical wavelength be 1550 nanometer optical wave phase places change be related to schematic diagram.The maximum light phase that can realize approximately 2 π postpones.
It shown in Fig. 5, is the first structure of tunable fabry-perot filter, tunable fabry-perot filter 300 comprise the first bandpass filter 10, liquid crystal phase-modulator 200, the second bandpass filter 20 and driving circuit 14, the first bandpass filter 10 and the second bandpass filter 20 be respectively the outside surface 8 of optically transparent material 9 and 23 and 22 or inside surface 11 and 21 on plate multilayer dielectric film and realize.The first bandpass filter 10 and the second bandpass filter 20 have identical filtering characteristic, as shown in Figure 6, and at free transmission range ν
1with ν
2between (filtering interval 32), reflectivity is R, reflectivity is higher, transmitted spectrum approximately narrow (generally, for the application of gas sensing, this reflectivity, between 80% to 98%, for other application, arranges as requested specially), is less than ν
1(filtering interval 30) or be greater than ν
2(filtering interval 34) reflectivity is 100% or approaches 100%, and modern coating technique can accomplish to be greater than 100 nanometers this passband frequency spectrum scope.
The first Design of Bandpass scheme: as plated bandpass filter multilayer dielectric film on the outside surface 8 and 22 at optically transparent material 9 and 23, the length in forming method Fabry-Perot-type (Fabry-Perot) chamber is D between two wave filters 10 and 20
1.The second Design of Bandpass scheme: as plated bandpass filter multilayer dielectric film on the inside surface 11 and 21 at optically transparent material 9 and 23, the length in forming method Fabry-Perot-type (Fabry-Perot) chamber is D between two wave filters 10 and 20
2, obviously, due to D
1be greater than D
2.The Free Spectral Range of the fabry-perot filter that therefore, the first Design of Bandpass scheme can realize is less than the second design proposal.Certainly, also can between the inner side of optically transparent material 12 and 24 and transparent electrode layer 16 and 26, directly plate multilayer thin-film-filter realizes, like this, due to the thickness very little (several microns to tens microns) of liquid crystal, therefore, can realize the larger tunable fabry-perot filter of intrinsic Free Spectral Range (i.e. the Free Spectral Range of the tunable optic filter when without extra electric field), but wave filter manufacture difficulty is larger.
Take above-mentioned the first Design of Bandpass scheme as example, in Fig. 5, the light beam 6 that incides wave filter 300 is a branch ofly to propagate along z direction, polarization axle is the linearly polarized light of x direction, identical with the optical axis direction of liquid crystal phase-modulator 200, the refractive index of supposing light transparent materials is n, at free transmission range ν
1with ν
2between, only have the 2nD of meeting
1the light of+Γ=m λ could see through etalon, and wherein m is the level time of transmitted light.The Free Spectral Range FSR of wave filter 300
2for: Δ λ=λ
2/ (2nD
1+ Γ), or with frequency representation:
?Δ ν=c/ (2nD
1+ Γ), wherein c is the light velocity, and Γ representative changes by refraction the light path that incident light is produced by liquid crystal under DC Electric Field, and the crest frequency of transmitted light can be expressed as: ν=mc/ (2nD
1+ Γ), wherein m is order of interference, transmission light frequency broadband can be expressed as:
Δ ν (FWHM)=c (1-R)/((2nD
1+ Γ) R
1/2), wherein c is the light velocity.
According to above-mentioned formula, tunable fabry-perot filter 300, for the linearly polarized light that approaches zero degree incident, is supposed n=1.5, D
1=1 millimeter, λ=1550 nanometer, the tuning range that can obtain the transmitted light crest frequency of about 150GHz (is about the intrinsic Free Spectral Range FSR of wave filter 300
21.5 times).Comparatively speaking, according to formula above, the change in the frequency band broadband to Free Spectral Range Δ ν and transmitted light is much smaller.The transmitted spectrum schematic diagram of tunable fabry-perot filter as shown in figure 10.Usually, for the application of pure gas sensing, need tuning bandwidth to be about 2 to 5 nanometer range, therefore, require the length in fabry-perot filter chamber to be about between 0.5 millimeter to 0.25 millimeter, directly plate multilayer thin-film-filter in the inner side of optically transparent material 12 and 24 or between transparent electrode layer 16 and 26 and realize than being easier to.
Usually, for the application of pure gas sensing, need tuning bandwidth to be about 2 to 5 nanometer range, therefore, require the length in fabry-perot filter chamber to be about between 0.5 millimeter to 0.25 millimeter, directly plate multilayer thin-film-filter in the inner side of optically transparent material 12 and 24 or between transparent electrode layer 16 and 26 and realize than being easier to.
As can be seen here, tunable fabry-perot filter 300, under the effect of extra electric field, can be realized the tuning of transmitted light crest frequency in a big way and substantially not change transmission light frequency broadband and Free Spectral Range.This characteristic is for many application of tunable fabry-perot filter 300, as it is significant to be applied to laser instrument and frequency spectrum instrument etc.Similarly, also can do identical analysis to the second Design of Bandpass scheme.At free transmission range ν
1with ν
2between spectrum region in addition 30 and 34, because the reflectivity of bandpass filter 10 and 20 is 100% or approaches 100%, therefore, the filtered device 300 of this part incident light has stoped.
Can be found out by above analysis, as the intrinsic Free Spectral Range FSR of wave filter 300
2be greater than free transmission range ν
2-ν
1time, only have a mould to see through wave filter 300; Work as FSR
2be less than free transmission range ν
2-ν
1, and be greater than (the ν of 0.5 times
2-ν
1) time; only have 2 moulds to see through wave filter 300. therefore; after the free transmission range of the first bandpass filter 10 and the second bandpass filter 20 is determined; can be by intrinsic Free Spectral Range FSR be set; realize in this free transmission range the single mode of wave filter 300 or 2 and 2 tunable outputs with patrix.Due to Fig. 6 demonstration is the filter characteristic of a desirable wave filter, in fact, above-mentioned bandpass filter is between spectrum region 30 and 32, when 32 and 34 transition, can not a saltus step, but exist between a zone of transition, therefore, in the time that the free transmission range of the first bandpass filter 10 and the second bandpass filter 20 is set, also to consider above-mentioned factor.
For free transmission range ν
2-ν
1larger situation, as be greater than 50 nanometers, the manufacture difficulty of bandpass filter 10 and bandpass filter 20 is larger, particularly, as requires between spectrum region little situation between 30 and 32,32 and 34 zone of transition, and difficulty is larger.For this reason, designed the second structure of tunable fabry-perot filter: this structure adopts a kind of phase step type wave filter.This project organization has used two phase step type wave filters with different filter ranges to replace respectively the first bandpass filter 10 and the second bandpass filter 20.As shown in Figure 7, be a long-pass phase step type wave filter, light frequency is greater than ν
1light to have reflectivity be R, and light frequency is less than ν
1light to have reflectivity be 100% or approach 100%, replace bandpass filter 10 by this long wave pass.Shown in Fig. 8 is a short-pass phase step type wave filter, and light frequency is less than ν
2light to have reflectivity be R, and light frequency is greater than ν
2light to have reflectivity be 100% or approach 100%, by this short wave-pass filter replacement bandpass filter 20, obviously, the structure of this use long-pass and short-pass phase step type wave filter is identical to the function of wave filter 300 with the design proposal of above-mentioned use bandpass filter.
This uses the advantage of the second structure of long-pass and short-pass phase step type wave filter to be: (1) relatively easily realizes large free transmission range (ν
2-ν
1), (2) relatively easily realize smaller from by the end of passband or the frequency spectrum transition from passband to rejection zone, because wave filter 300 has the reversibility of symmetry and light path, therefore, above-mentioned two phase step type wave filters are exchanged, do not affect the performance of wave filter 300.
Figure 10 is schematic diagram of the present invention.A kind of methane gas sensing equipment 400 comprises an infrared wideband light source 40, tunable fabry-perot filter 300 and drive source 50 thereof, gas sampling chamber 44, methane gas 46 in gas sampling chamber 44, photodetector 48, and one control and data analysis system, as shown in figure 11, this system comprises driving and the signal receiving circuit 52 of photodetector 48, control circuit and data analysis system 54, the bandwidth of infrared wideband light source 40 should be greater than 5 nanometers, and its centre frequency equals or approaches the centre frequency of the absorption spectrum of methane, the centre frequency of the infrared absorption spectrum of methane is at 1.65 microns, 2.3 micron, near 3.3 microns.Because the infrared absorption spectrum bandwidth of methane is considerably beyond the passband width of tunable fabry-perot filter 300, therefore, the spectral centroid frequency of infrared wideband light source 40 and the centre of homology frequency of tunable fabry-perot filter 300 are as long as just can meet the accuracy of detection of gas near at above-mentioned several absorption spectrums center.
The collimated light beam being produced by infrared wideband light source 40 enters gas sampling chamber 44 after seeing through tunable fabry-perot filter 300, its output intensity is detected and is obtained by photodetector 48 respectively, in the time that drive source 50 is tuning to tunable fabry-perot filter 300, the gas absorption light signal that sees through gas sampling chamber 44 is detected and obtains and pass through driving and signal receiving circuit 52 by photodetector 48, then is carried out data analysis and obtained the concentration of institute's methane-containing gas 46 in gas sampling chamber 44 by control circuit and data analysis system 54.According to lambert-Bill Lambert-Beer law, the concentration of gas 46 is higher, is absorbed stronglyer, sees through the light intensity of gas sampling chamber 44 more weak.The length of gas sampling chamber 44 depends on the concentration of surveyed gas, the factors such as gas absorption intensity and required measuring accuracy, and General Requirements is the several centimetres of scopes to hundreds of centimetre.In order to guarantee maximum measuring accuracy, General Requirements is at set free transmission range (ν
2-ν
1) in, from ν
2to ν
1tuning frequency be 10KHz or more than, requiring the output of drive source 50 to have frequency is 2KHz, amplitude is in zero square wave voltage signal of modulating to 5 volts of +/-, amplitude zero to peaked modulating frequency 10K or more than, as shown in Figure 4.
The present invention requires the only linearly polarized light of output of infrared wideband light source 40, and the optical axis of its optical axis and tunable fabry-perot filter 300 is in same direction.
It is emphasized that above-mentioned explanation only plays demonstration and describes, is not an in detail exhaustively explanation, is not intended to limit the present invention on described concrete form yet.Through description above, all may occur many changes of the present invention and variation.Selected concrete enforcement is only used to better explain the application in principle of the present invention and reality.This explanation can make the people who is familiar with this field can better utilize the present invention, designs according to actual needs different concrete enforcement and changes accordingly.
Claims (13)
1. a methane gas sensing equipment, it is characterized in that: comprise an infrared wideband light source, a tunable fabry-perot filter, a gas sampling chamber, Electro-Optical Sensor Set and driving is controlled and data analysis system, the driving of described photodetector and signal receiving circuit and control circuit and data analysis system, the light being sent by described infrared wideband light source is first by after tunable fabry-perot filter, by being received by described the first Electro-Optical Sensor Set behind described gas sampling chamber, carried out the absorption spectrum of detected gas to carry out data analysis and obtain by described control circuit and data analysis system the concentration of this gas.
2. a kind of methane gas sensing equipment according to claim 1, it is characterized in that: described tunable fabry-perot filter comprises the first bandpass filter, liquid crystal phase-modulator, the second bandpass filter and drive source, liquid crystal phase-modulator is arranged in the chamber of the fabry-perot filter being made up of the first bandpass filter and the second bandpass filter, realizes the tuber function of wave filter by liquid crystal phase-modulator in control Fabry-Perot-type cavity.
3. according to the tunable fabry-perot filter described in claim 1 and 2, it is characterized in that: the first described bandpass filter and the second bandpass filter are a kind of bandpass filter of the multilayer dielectric film arranging on the inside surface of optically transparent material and have identical transmission bandwidth, can be according to the acutance coefficient of transmitted light is arranged to different reflectivity in the passband of described bandpass filter, this reflectivity is arranged between 80% to 98%, arrange 100% or approach 100% reflectivity beyond the passband, and on the outside surface of optically transparent material, optical anti-reflective film is set.
4. according to the tunable fabry-perot filter described in claim 1 and 2, it is characterized in that: the center of the first described bandpass filter and the absorption spectrum of the center of the passband of the second bandpass filter and the gas of required detection is identical or approach identical, the width of this passband is according to the requirement of gas test precision is determined, be set to 2 nanometers between 5 nanometers, the Free Spectral Range of described fabry-perot filter should be greater than described passband width, and making through the light signal of described tunable narrow-band optical filter is single-mode optics signal.
5. tunable fabry-perot filter according to claim 1, it is characterized in that: comprise a long-pass step filter, liquid crystal phase-modulator, short-pass step filter and drive source, liquid crystal phase-modulator is arranged in the chamber of the fabry-perot filter being made up of described long-pass step filter and described short-pass step filter, realizes the tuber function of wave filter by controlling liquid crystal phase-modulator in described Fabry-Perot-type cavity.
6. according to the tunable fabry-perot filter described in claim 1 and 5, it is characterized in that: described long-pass step filter and short-pass step filter are a kind of optical filters of the multilayer dielectric film arranging on the inside surface of optically transparent material, described long-pass step filter has 100% or approach 100% reflectivity for the light that is less than cutoff frequency, and described short-pass step filter has 100% or approach 100% reflectivity for the light that is greater than cutoff frequency; Can be according to the acutance coefficient of transmitted light be arranged to different reflectivity in the passband of described long-pass step filter and short-pass step filter, this reflectivity is arranged between 80 and 98%, and on the outside surface of optically transparent material, optical anti-reflective film is set.
7. according to the tunable fabry-perot filter described in claim 1 and 5, it is characterized in that: the cutoff frequency of described long-pass step filter is less than the cutoff frequency of described short-pass step filter, formed the passband width of described fabry-perot filter by the cutoff frequency of described long-pass step filter and the cutoff frequency of described short-pass step filter, the width of this passband is according to the requirement of gas test precision is determined, be arranged on 2 nanometers between 5 nanometers, the center of the center of this passband and the absorption spectrum of the gas of required detection is identical or approach identical, the Free Spectral Range of described tunable fabry-perot filter is greater than its free transmission range, making through the light signal of described tunable narrow-band optical filter is single-mode optics signal.
8. according to the tunable fabry-perot filter described in claim 1,2 and 5, it is characterized in that: what described liquid crystal phase-modulator adopted is nematic phase type liquid crystal material, and the thickness of liquid crystal material is several microns to tens microns.
9. a kind of methane gas sensing equipment according to claim 1, it is characterized in that: described tunable fabry-perot filter drive source is that a kind of frequency is about 2KHz, voltage amplitude can be at the square-wave signal of modulating of zero to positive and negative 5 volts, and the modulating frequency of square-wave voltage amplitude be 10 kilo hertzs or more than.
10. a kind of methane gas sensing equipment according to claim 1, it is characterized in that: described control circuit and data analysis system comprise a system take digital signal processor and embedded software as core, for controlling driving and the signal receiving circuit of the drive source of described tunable fabry-perot filter, described photodetector and receiving extraneous control signal and output signal, to realize the absorption spectrum of described infrared-gas sensing equipment to detected gas and the measuring ability of concentration.
11. a kind of methane gas sensing equipments according to claim 1, is characterized in that: the size of described gas sampling chamber, according to the factor such as concentration and precision that will detect gas is determined, is generally several centimetres to hundreds of centimeter length.
12. a kind of methane gas sensing equipments according to claim 1, it is characterized in that: the output of described infrared wideband light source is linearly polarized light, its optical axis is consistent with the optical axis of described tunable fabry-perot filter, spectral width exceedes 5 nanometers, and centre wavelength equals or the approaching gas absorption spectra Dai center of surveying.
13. a kind of methane gas sensing equipments according to claim 1, is characterized in that: the central homology wavelength of described tunable fabry-perot filter is arranged on 1.65 microns, or 2.3 microns, or 3.3 microns, or approach above-mentioned several wavelength.
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| CN201210416717.5A CN103776794A (en) | 2012-10-28 | 2012-10-28 | Methane gas sensing equipment |
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| CN201210416717.5A CN103776794A (en) | 2012-10-28 | 2012-10-28 | Methane gas sensing equipment |
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Application publication date: 20140507 |