CN101424629A - Optical fibre grating sensor - Google Patents
Optical fibre grating sensor Download PDFInfo
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- CN101424629A CN101424629A CNA2008102322381A CN200810232238A CN101424629A CN 101424629 A CN101424629 A CN 101424629A CN A2008102322381 A CNA2008102322381 A CN A2008102322381A CN 200810232238 A CN200810232238 A CN 200810232238A CN 101424629 A CN101424629 A CN 101424629A
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- wavelength
- fiber
- light signal
- fiber grating
- methane concentration
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Abstract
The invention relates to a fiber grating sensor which comprises a light source, optical fibers, a probe and a fiber grating, wherein the fiber grating is mounted on the optical fibers in a measuring point, is used for monitoring the change of a methane concentration, and is plated with metal platinum. The fiber grating sensor is characterized in that a probe light signal output by a light source is injected from the incident ends of the optical fibers, and the wavelength of probe light is not in a selective function wavelength brand of the fiber grating and forms a preset wavelength difference value with the selective function wavelength band. When the monitored methane concentration changes to a quantitative value, the selective function wavelength band of the fiber grating in the measuring point at least drifts away to the preset wavelength difference value so that the selective function wavelength band is crossed and overlapped with a probe light signal wavelength brand. At the time, the wavelength band in the measuring point generates a certain reflection or dissipation of the probe light signal, the probe detects the intensity change of the probe light signal at the emergent ends so as to probe the change of the methane concentration.
Description
Affiliated technical field
The present invention relates to a kind of fiber-optic grating sensor, is to survey the sensor that methane gas changes by optical fiber and fiber grating, and this equipment belongs to field of sensing technologies.
Background technology
Methane (CH4) is the principal ingredient of mine gas, rock gas, biogas and multiple liquid fuel, is the important raw material of industry and the combustion gas of daily life, and it also is a flammable explosive gas, and what explode in atmosphere is limited to 5.3% down, on be limited to 15.0%.Simultaneously also be considered to one of topmost gas of greenhouse effect, it is reported that CH4 absorption infrared capable is 15-30 a times of CO2, occupies 15% of whole greenhouse contribution amount.The concentration of CH4 is annual approximately with 1% speed increment in the air.Therefore in time detect generation source, source of leakage and the concentration of CH4 gas, industrial and mineral safe operation, personal safety and environmental protection are had crucial effect." safety regulations in coal mine " also expressly provided and will be carried out multiple spot, real-time high Precision Detection to the methane content in the colliery.
The methane measuring method that extensively adopts mainly contains catalytic oxidation and optical method at present.Wherein catalytic oxidation utilizes catalyst methane and oxygen generation oxidation reaction, and chemical energy is converted into heat energy, measures variation of temperature by thermistor, thereby obtains the methane concentration value.This method generally can only reach 0.1% measuring accuracy, and circuit part is subjected to outside electromagnetic interference easily, influences accuracy of measurement; Owing to need the power supply power supply, the potential safety hazard of sending electric spark arranged; Sensor poisons easily, to the poor selectivity of gas, be prone to wrong report, and system needs frequent calibration; This method also is unfavorable for realizing distributed measurement.Optical method is divided into two kinds of absorption and interfere types again, and they have utilized the relation of methane infrared absorption characteristic and methane concentration and optical index existence respectively.Interferometric sensor needs frequent adjustment, is subject to the interference of other gases, its reliability and less stable; Spectral absorption formula measuring method is measured sensitivity owing to need increase light path by the method for geometrical optics to improve, so integration is relatively poor relatively, and realizes that the distributed measurement difficulty is very big.
The fiber-optic grating sensor that grew up in recent years has unrivaled advantage with respect to conventional sensors, it is highly sensitive, response is fast, dynamic range greatly, is not subjected to electromagnetic interference (EMI), corrosion-resistant, volume is little, can realize that the long Distance Transmission of signal and field conduct remote measurement, sensing head can put into rugged surroundings, simple in structure, working stability is reliable and be easy to form optical fiber network sensing system.But what adopt at present is that wide light source adds accurate Wavelength demodulation device and realizes, its equipment complexity, and the maintenance cost height can't satisfy the actual needs of a lot of productive lifes.
Summary of the invention
The present invention is directed to the deficiencies in the prior art, proposed a kind of measuring accuracy height, be easy to the methane sensing equipment based on Fiber Bragg Grating FBG integrated and encapsulation.
For this reason, the present invention proposes a kind of fiber-optic grating sensor, comprise light source, optical fiber, detector and be placed in the fiber grating that methane changes that is used for that is positioned at measurement point on the optical fiber, it is characterized in that:
One this fiber grating surface is coated with layer of metal platinum,
The detection light signal of one light source output injects from an end that is called the incident end of optical fiber, and the wavelength of surveying light signal and has the preset wavelength difference with described selectively acting wavelength not in the selectively acting wavelength band of fiber grating,
One when monitored methane variation reaches certain value, be positioned at the preset wavelength difference that the selectively acting wavelength band of the fiber grating of measurement point has drifted about above-mentioned at least, thereby make this selectively acting wavelength band cover the part of described detection wavelength of optical signal band at least, at this moment, the fiber grating of this measurement point is just to certain reflection or dissipation of having surveyed light signal generating, promptly survey the part reflection or the dissipation of light signal, thereby other end exit end at the incident end of optical fiber, then detect the variation of transmitted light, thereby detect the variation of methane.
The present invention surveys to be monitored a kind of fiber-optic grating sensor that methane changes, be to be coated with layer of metal platinum on the fiber grating surface, its thickness is the 1-5 micron, the platinum film layer is as catalyzer, under the effect of catalyzer, methane in the gas to be measured and airborne oxygen generation oxidation reaction are emitted heat, temperature raises near making platinum film, cause fiber grating also to change thereupon, thereby make fiber grating generation axial strain, cause fiber grating selectively acting wavelength band position excursion, if variation has taken place near the methane of being monitored a fiber grating, and the variation that takes place has reached the degree that we are concerned about, at this moment the selectively acting wavelength band of the fiber grating preset wavelength difference of having drifted about at least, thereby make this selectively acting wavelength band cover a part of surveying the wavelength of optical signal band at least, at this moment, the fiber grating of this measurement point is just to certain reflection or dissipation of having surveyed light signal generating, promptly survey the part reflection of light signal or dissipate, detector detects the variation of transmitted light, this explanation has stress to exist, thereby may detect the variation of corresponding methane.
In actual engineering, we usually only need obtain the data that a part of methane changes, just can reach our target, in the methane warning system in the scene of a needs monitoring methane concentration, to be not more than 0.05% o'clock methane concentration we press for understanding, we only need to set a monitoring, alarming concentration, as 0.1% methane concentration, then as the fiber grating that is coated with metal platinum on the optical fiber of sensor, measure this fiber grating when 0.1% methane concentration the selectively acting wavelength band and choose a wavelength as the wavelength of surveying light signal, select light source according to this wavelength then, the described fiber grating of metal platinum that is coated with is when the methane concentration that is not more than at 0.05% o'clock, its selectively acting wavelength band has wavelength difference with the wavelength of the detection light signal of selecting, this sensor is installed in the place of monitoring, under normal conditions, the environment methane concentration is when the methane concentration that is not more than at 0.05% o'clock, the detection light signal that injects sensor fiber loss less passed through optical fiber and fiber grating, can record intensity at the detector of the exit end of optical fiber through light signal, and as benchmark, have only when the methane concentration of measurement point near or when reaching 0.1% methane concentration, the fiber grating selectively acting wavelength band that is coated with metal platinum of this measurement point will drift about and with the wavelength band juxtaposition of surveying light signal, and to surveying suitable reflection or the dissipation of light signal generating, at this moment, can monitor obvious variation on the detector through the intensity of light signal, thereby triggered the methane concentration alert if, reached the purpose of monitoring.
Under actual engineering specifications, a value of only monitoring methane concentration usually is not enough, so the different a plurality of detection light signals of wavelength can be set, just can monitor a plurality of values of methane concentration, the trend that changes of measurement point methane concentration as can be seen simultaneously is so that better monitoring.
Description of drawings:
Fig. 1 is the reflectance spectrum of a Bragg grating of expression, the spectrum of a detection light signal and both graphs of a relation;
Fig. 2 is the transmitted spectrum of a long period fiber grating of expression, the spectrum of a detection light signal and both graphs of a relation;
Fig. 3 is the structured flowchart of the fiber-optic grating sensor of relevant first embodiment of the present invention of expression;
Fig. 4 is the structured flowchart of the fiber-optic grating sensor of relevant second embodiment of the present invention of expression;
Fig. 5 is the structured flowchart of the fiber-optic grating sensor of relevant the 3rd embodiment of the present invention of expression;
Among the figure: 3,3a, 3b, 3n one light source,
9a, 9b one optical branching device,
5 one are coated with the fiber grating of metal platinum
6,6a, 6b, 6n one photo-detector,
7 one optical fiber,
8 one photoswitches,
10a, 10b, 10n one fixed wave filter.
Embodiment
Curve 1 among Fig. 1 has schematically shown the reflectance spectrum of a Bragg grating, λ
1And λ
2Be respectively the lower limit and the upper limit wavelength of this Bragg grating reflection wavelength, all wavelength all are the wavelength that Bragg grating can reflect in these two wavelength, are called the reflection wavelength band here.Curve 2 has schematically shown a spectrum of surveying light signal, λ
3And λ
4Be respectively the lower edge and the upper edge wavelength of this detection light signal, λ
2And λ
3Between distance be exactly that described preset wavelength is poor.
Curve 11 among Fig. 2 has schematically shown the transmitted spectrum of a long period fiber grating, λ
1And λ
2Be respectively the lower limit and the upper limit wavelength of this long period fiber grating coupling attenuation wavelength, long period fiber grating all has decay to all wavelength in these two wavelength, is called the dissipation wavelength band here.Curve 2 has schematically shown a spectrum of surveying light signal, λ
3And λ
4Be respectively the lower edge and the upper edge wavelength of this detection light signal, λ
2And λ
3Between distance be exactly that described preset wavelength is poor.
First embodiment
Fig. 3 is the structured flowchart of the fiber-optic grating sensor of expression first embodiment.The fiber-optic grating sensor of first embodiment by light source 3, photo-detector 6, be positioned at measurement point and be used to monitor fiber grating that is coated with metal platinum 5 and the optical fiber 7 that methane concentration changes and constitute.Connect with optical fiber between each parts.
Detection light signal from light source 3 outputs, the wavelength of surveying light signal is not in the selectively acting wavelength band of the fiber grating 5 that is coated with metal platinum, and default wavelength difference arranged with it, survey light signal by optical fiber 7 and fiber grating 5, and detect the intensity of surveying light signals by photo-detector 6, at monitored methane concentration no change or change when not reaching the degree that we are concerned about, the wavelength of surveying light signal is not at the selectively acting wavelength band of the fiber grating that is coated with metal platinum 5 that is positioned at measurement point, be that fiber grating 5 is not to surveying light signal reflection or consume, at this moment to detect be zero-decrement substantially light signal to photo-detector 6, and with this intensity as benchmark, when the methane concentration of monitored point changes to the degree of our care, the selectively acting wavelength band that is positioned at the fiber grating that is coated with metal platinum 5 of the described measurement point described preset wavelength difference of having drifted about at least, at this moment described selectively acting wavelength band has covered a part of surveying the wavelength of optical signal band at least, this fiber grating 5 is just to suitable reflection or the dissipation of having surveyed light signal generating, at this moment photo-detector 6 detects the intensity of surveying light signal obvious variation, thereby detects the variation of methane concentration.
Second embodiment
Fig. 4 is the structured flowchart of the fiber-optic grating sensor of expression second embodiment.The fiber-optic grating sensor of second embodiment by light source 3a, light source 3b, light source 3n, photo-detector 6, photoswitch 8, be positioned at measurement point and be used to monitor fiber grating that is coated with metal platinum 5 and the optical fiber 7 that methane concentration changes and constitute.Connect with optical fiber between each parts.
From light source 3a, light source 3b, the detection light signal of the different wave length of light source 3n output, the wavelength of surveying light signal is not all in the selectively acting wavelength band of the fiber grating 5 that is coated with metal platinum, and different preset wavelength differences arranged with it, photoswitch 8 can select the detection light signal of Different Light by optical fiber 7 and fiber grating 5, arrive photo-detector 6, at this moment to detect be zero-decrement substantially light signal to photo-detector 6, and with this intensity as benchmark, the variation of monitored methane concentration can cause the drift of the selectively acting wavelength band of the fiber grating 5 that is coated with metal platinum, when preset wavelength difference that the selectively acting wavelength band has drifted about different, we can detect the Strength Changes of the different detection light signal of input, so just can detect a plurality of values that methane concentration changes.
The 3rd embodiment
Fig. 5 is the structured flowchart of the fiber-optic grating sensor of expression the 3rd embodiment.The fiber-optic grating sensor of the 3rd embodiment by light source 3a, light source 3b, light source 3n, wave filter 10a, wave filter 10b, wave filter 10n, photo-detector 6a, photo-detector 6b, photo-detector 6n, optical branching device 9a, optical branching device 9b, be positioned at measurement point and be used to monitor fiber grating that is coated with metal platinum 5 and the optical fiber 7 that methane concentration changes and constitute.Connect with optical fiber between each parts.
From light source 3a, light source 3b, the detection light signal of the different wave length of light source 3n output, the wavelength of surveying light signal is not all in the selectively acting wavelength band of fiber grating 5, and different preset wavelength differences arranged with it, survey light signal by optical branching device 9a, again by optical fiber 7, fiber grating 5 and optical branching device 9b, enter into different detectors by different wave filters respectively, each wave filter and light source are one to one, and only allow the detection light signal of corresponding wavelength to pass through, other detection filtered optical signal is fallen, and when methane concentration do not changed each intensity of surveying light signal as benchmark, the variation of monitored methane concentration can cause the drift of the selectively acting wavelength band of the fiber grating 5 that is coated with metal platinum, when the selectively acting wavelength band has drifted about described different preset wavelength difference, will cause the variation of different detection light signal strengths, all detection light signals see through optical fiber 7 and optical branching device 9b, enter into different detectors by different wave filters respectively, detector will be at this moment each intensity of surveying light signal and corresponding benchmark strength ratio, we just can detect a plurality of values of methane concentration variation like this.
As seen, the method according to detection of the present invention is simpler than the method for prior art.
Certainly, the present invention is not limited to the embodiment that the front is introduced, and we can replace whole device with another kind of equivalent arrangements, and do not exceed scope of the present invention.
Claims (2)
1. fiber-optic grating sensor, comprise light source, optical fiber, detector and be placed on the optical fiber be positioned at measurement point be used to monitor the fiber grating that methane concentration changes, it is characterized in that:
One this fiber grating surface is coated with layer of metal platinum,
The detection light signal of one light source output injects from an end that is called the incident end of optical fiber, and the wavelength of surveying light signal and has the preset wavelength difference with described selectively acting wavelength not in the selectively acting wavelength band of fiber grating,
One when monitored methane concentration variation reaches certain value, be positioned at the preset wavelength difference that the selectively acting wavelength band of the fiber grating that is coated with metal platinum of measurement point has drifted about above-mentioned at least, thereby make this selectively acting wavelength band cover the part of described detection wavelength of optical signal band at least, at this moment, the fiber grating of this measurement point is just to certain reflection or dissipation of having surveyed light signal generating, promptly survey the part reflection of light signal or dissipate, detector detects the variation that the optical fiber exit end is surveyed light signal strength, thereby detects the variation of described methane concentration.
2. a kind of fiber-optic grating sensor according to claim 1, it is characterized in that: a plurality of light sources inject a plurality of detection light signals from an end that is called the incident end of optical fiber, its wavelength is not all in described reflection wavelength band, and have different preset wavelength differences, thereby can detect a plurality of values that the measurement point methane concentration changes with reflection wavelength.
Priority Applications (1)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| CNA2008102322381A CN101424629A (en) | 2008-11-12 | 2008-11-12 | Optical fibre grating sensor |
Applications Claiming Priority (1)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| CNA2008102322381A CN101424629A (en) | 2008-11-12 | 2008-11-12 | Optical fibre grating sensor |
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| Publication Number | Publication Date |
|---|---|
| CN101424629A true CN101424629A (en) | 2009-05-06 |
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| Application Number | Title | Priority Date | Filing Date |
|---|---|---|---|
| CNA2008102322381A Pending CN101424629A (en) | 2008-11-12 | 2008-11-12 | Optical fibre grating sensor |
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|---|---|
| CN (1) | CN101424629A (en) |
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2008
- 2008-11-12 CN CNA2008102322381A patent/CN101424629A/en active Pending
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Open date: 20090506 |