CN102997044B - Method and system for resisting polarization fading of natural gas pipe leakage detecting sensor group - Google Patents
Method and system for resisting polarization fading of natural gas pipe leakage detecting sensor group Download PDFInfo
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Abstract
The invention discloses a method and system for resisting polarization fading of a natural gas pipe leakage detecting sensor group. A special modulated signal generating module and a laser form a light source, and a 2*2 coupler and a Faraday rotatormirror form a leakage sonic sensor with a Michelson structure; the sensor with the structure is arranged on a pipe body at a certain interval, adjacent sensors form a sensor group, and each sensor is connected in parallel between a transmitting optical fiber and a returning optical fiber through a light beam splitter and a light beam combiner; and two arms of each sensor are not equal in length, two Faraday rotatormirrors serve as reflecting mirrors of each sensor, the rotation angle is 45 degrees, and the polarization state change of reflecting light just counteracts the polarization state change of incident light, so that the visibility of signals of the sensors and the sensor groups is kept the highest. The phenomenon of polarization inducing signal fading of the interferometer is overcome, the sensitivity and accuracy of leakage detection are improved, the false alarm rate is reduced, and the method and the system are not easily affected by environment factors.
Description
Technical field
The present invention is a kind of anti-polarization decay method and system of gas pipeline leakage detecting sensor group.Relate to the measurement of mechanical vibration, measurement and the piping system technical field of impact.
Background technology
At present, the pipeline overall length of building up in the world reaches 2,500,000 kilometers, and having exceeded railway total kilometrage becomes the main means of transportation of world energy sources, and the oil product of developed country and oil producing area, the Middle East transports all realizes channelization.China's pipeline has also obtained very fast development in recent years, overall length also exceedes 70,000 kilometers, begun to take shape across thing, stretch from the north to the south, cover the whole nation, be communicated with the overseas large general layout of energy pipe network, pipeline transportation becomes the major way of the allotment conveying of the strategic energy such as oil gas.
Pipeline, due to cross-regional wide, is subject to the reason such as disaster, third party's breakage in installation, has caused more pipe leakage accident to occur.External pipe safety situation also allows of no optimist very much, and natural gas line big bang occurs San Bruno city on September 9th, 2010 of the U.S., and blast causes long 51 meters a, hollow place of wide 9 meters on road surface.The pipeline of approximately 8 meters of one segment lengths, 76 centimetres of diameters is exploded heaven, flies out about 30 meters far away, and causes large-range fire disaster, causes 4 people's death, and 3 people are missing, and at least 52 people are injured, 4 hectares of burnt areas, and tens of houses are burnt.People's safety, environmental consciousness significantly promote in recent years, are also more and more paid attention to as the pipeline transportation safety problem of high risk industries.
In proven technique, only have sound wave monitoring method comparatively effective for natural gas line leakage at present, but in order to improve the accuracy of real-time to leakage monitoring and leak source location, must on pipeline, add the layout density of large sensor, increase corresponding power supply, communication facilities simultaneously, cause system cost and installation and maintenance costly.
Along with the development of sensing technology is external as the companies such as U.S. CSI, ATMOSI, European TER have carried out the research of SCADA leakage monitoring system, Sensornet company has also developed the leakage monitoring system based on distributed optical fiber temperature sensor, and portioned product has also been applied for patent protection at home; The units such as domestic University Of Tianjin, Tsing-Hua University, China Renmin People's Liberation Army Office Support Engineering Academy also further investigate the leakage monitoring method of pipeline.
Patent CN200410020046.6 discloses a kind of distribution type fiber-optic method for monitoring leak from oil gas pipe and monitoring device based on principle of interference.This monitoring system requires to lay side by side an optical cable at Near Pipelines along pipeline, utilizes the Fiber optic micro-vibration sensor of optical fiber composition in optical cable.Patent CN200620119429, CN200610113044.0 are the pipeline leakage monitor based on Sagnac fibre optic interferometer, and patent CN200610072879.6 is a kind of pipeline leakage monitor and method based on distributed optical fiber acoustic sensing technology.
" sensor and micro-system " the 26th the 7th phase of volume " the gas pipe line leakage detection method based on distributed fiberoptic sensor " discloses a kind of gas pipe line leak detecting device and method based on distributed fiberoptic sensor, it is installing optical fibres sensor on the pipeline body with certain intervals, the vibration wave signal that continuous real-time monitoring is propagated along pipeline body, the vibration wave signal gathering is carried out to analyzing and processing, comprise type identification and vibration source location, wherein type identification is whether to belong to leak type by the extraction and analysis of vibration wave feature is differentiated to it, propagate into the position at the time delay definite vibration of the velocity of propagation on pipeline body wave source place in conjunction with vibration wave of adjacent several Fibre Optical Sensors according to vibration wave simultaneously, the light intensity signal of sensor output is realized the determining of position of leakage point after opto-electronic conversion.
CN1837674A discloses a kind of pipeline leakage testing device and method based on distributed optical fiber acoustic sensing technology.
US2006/0225507A1 discloses a kind of pipeline leakage testing device and method based on distributed fiberoptic sensor.
Above-mentioned technology all belongs to distributed optical fiber sensing monitoring method.But such technical monitoring is subject to the impact of the interference incident that pipeline occurs while leakage, have very high system false alarm rate, and antijamming capability is poor.
Summary of the invention
The object of the invention is to invent a kind of sensitivity and accuracy is high, false alarm rate is low, be not subject to the anti-polarization decay method and system of the gas pipeline leakage detecting sensor group based on Fibre Optical Sensor of such environmental effects.
In view of above-mentioned a few class Leak Detection, the sensitivity that monitoring technology exists is low, false alarm rate is high, be subject to the problems such as such environmental effects, the present invention is to provide the quasi-distributed leakage vibration monitoring of a kind of high sensitivity based on Fibre Optical Sensor method and system, adopt high sensor to make micro-leakage to occur when pipeline, when the leakage primary stages such as seepage, monitored in time, and in conjunction with the time domain of incident of leakage, frequency domain character effectively reduces and disturbs the system false alarm rate causing, this technical scheme has overcome poor accuracy in monitoring technology before this and the deficiency of mounting process complexity, make related maintenance personnel can take in time counter-measure, avoid causing larger security incident.
Thereby the natural gas line leakage system with the sensitivity of high leakage vibrating sensing is to have realized the raising of the induction sensitivity of interferometer to vibration signal by the length of increase interferometer two pickup arms and space length, at the intelligent identification technology that has adopted leakage signal aspect the inhibition that Environmental Random Vibration is disturbed, random accidental vibration and sudden, continuation leakage signal are effectively distinguished, and the leakage signal time delay of simultaneously obtaining in conjunction with adjacent multiple sensors, the location of having realized more accurately leakage point.
Optical fiber in the common communications optical cable of utilization and oil and gas pipes laying in one ditch is as transmitting and passback optical fiber, pipeline is revealed to Fibre Optical Sensor to be connected between transmitting-receiving Transmission Fibers by Optical multiplexing technology is parallel with one another, form light circuit, pipeline is revealed Fibre Optical Sensor and is arranged on pipeline, the optical fiber sensing system that formation can monitoring pipe road acoustic vibration.Utilize light source to reveal Fibre Optical Sensor scanning to each pipeline, reveal the distribution situation of Fibre Optical Sensor according to pipeline to the photoelectric conversion signal demodulation, the extraction that gather, the vibration information of realizing each pipeline leakage Fibre Optical Sensor obtains, detect analysis conduit and reveal Fibre Optical Sensor signal and judged whether that pipeline leakage event occurs, reveal Fibre Optical Sensor according to adjacent pipeline and detect that the time delay of arrival of signal realizes the location to leak point.
After pipe leakage, can produce the sound wave of each frequency range, the shorter ultrasound wave of wavelength ratio apart from sound source not far position just gradually by Absorption of Medium, and wavelength is shorter, attenuation by absorption also faster, only have the distant of low-frequency sound wave and infrasonic wave propagation, can propagate a few km to tens kms.Adopt in the system of infrasonic sensor being installed compared with long pipeline two ends because available signal frequency range is narrower, to the accurate positioning effect of leakage signal not enough at present.
The anti-polarization decay method of gas pipeline leakage detecting sensor group is that the sensor of a Michelson interferometer structure is installed at a certain distance on pipeline body, by the sensor of several Michelson interferometer structures by beam splitter and bundling device and be connected in launching fiber and passback optical fiber between; Two arms of Michelson interferometer are not isometric, each Michelson interferometer uses two faraday rotation mirrors as catoptron, the anglec of rotation is 45 degree, catoptrical polarization state is changed and just in time offset the polarization state variation of incident light, thereby make the visibility of interferometer remain maximum.
Adopt optical fiber Michelson interferometer as leaking sonic detection sensor, the light intensity signal of its output can be write as after opto-electronic conversion:
V
0∝1+Vcos(φ
s+φ
n+φ
0)+V
n(1)
Wherein, V
0be the voltage signal of output, V is the visibility of interferometer, V
ncircuit additional noise, φ
sserve as reasons and leak the phase difference signal that vibration wave causes, be the leakage vibration wave signal that will survey, φ
0for the initial phase of interferometer, be a constant, φ
nfor the low frequency wonder of phasic difference, be a Uncertainty, change with temperature and external environment impact.Can realize and leak vibration wave signal psi by the demultiplexing technology matching with modulation of source mode
sobtain, and to this signal psi
sthe time delay that arrives corresponding sensor estimates, having realized vibration wave source in conjunction with vibration wave along the speed v of pipe transmmision is determining of leakage point position.
In fact, in Michelson interferometer optical fiber with the corresponding refractive index n of two polarization modes
xand n
yunequal, simultaneously because micro-curved, the distortion of optical fiber, the variation of environment temperature make n
xand n
yrandom variation, causes optical fiber output polarization state random variation, is reflected in interference signal visibility V random variation between 0～1, and this phenomenon is the polarization inducement signal fade-out of interferometer.This phenomenon will cause the reduction of sensor detection sensitivity and signal to noise ratio (S/N ratio) and unstable, for eliminating polarization decay, adopt faraday rotation mirror method, before two catoptrons of common Michelson interferometer, respectively add a Faraday rotator and form faraday rotation mirror, the anglec of rotation is 45 degree, catoptrical polarization state is changed and just in time offset the polarization state variation of incident light, thereby make the visibility of interferometer remain 1.
In formula (1), due to low-frequency disturbance φ
nrandom variation, and amplitude is large, is subject to φ
nvariable effect, the signal to noise ratio (S/N ratio) of system output is changing, and as sin φ
n=0 o'clock, the complete blanking of signal, this be called the phase fading phenomenon of interferometer.
In order to eliminate polarization decay phenomenon, adopt phase carrier technology to detect leakage acoustic signals.Specific as follows:
While making Michelson interferometer, make interferometer two arms not isometric, two arm length difference are Δ L;
Using sawtooth signal as modulation signal, frequency is the twice of leaking sound wave frequency span, be applied to the adjustable laser instrument of optical frequency, laser instrument output optical frequency is according to the synchronous laser changing of saw wave modulator signal, be input to Michelson interferometer, because two arms are not isometric, laser by two arms will produce delay inequality, thereby the two bundle laser that participate in interfering are except sawtooth wave falling edge, the optical frequency in other moment is poor is a constant, therefore, the interference signal of interferometer output is the cosine signal of an approximate single-frequency, angular frequency
0two arm length difference Δ L are directly proportional to interferometer, and Δ L is larger, and interference signal frequency is higher; The linear superposition that the interference signal of sensor group output is several approximate simple signals, its frequency spectrum is several discrete spectral lines, spectral line amplitude stabilization is constant;
Use bandpass filter to carry out filtering to interference signal, filter center frequency is interference signal centre frequency, and bandwidth is identical with saw wave modulator signal frequency.The carrier signal that can obtain this interferometer after filtering, is used cosine and the sinusoidal signal demodulation identical with carrier signal predominant frequency, and phase fading problem that can erasure signal, obtains original leakage acoustic signals.
The formation of the anti-polarization decay system of this gas pipeline leakage detecting sensor group is shown in Fig. 1, and it comprises light source, light path system and circuit part; A Fibre Optical Sensor is installed at a certain distance on pipeline body, multiple Fibre Optical Sensors form a Fibre Optical Sensor group, each Fibre Optical Sensor group shares a launching fiber and is connected with light source, and each Fibre Optical Sensor group is used a passback optical fiber to be connected with photodetector; Photodetector output connects signals collecting and processing module, and signals collecting and processing module output connect microcomputer by external interface.Through the processing of signals collecting and processing module, the sensor group signal mixing based on frequency division multiplexing mode has been realized the demultiplexing of each sensor in sensor group, obtains original leakage vibration wave signal.
Send laser by light source, realize after beam splitting through transmission light path, part light is transferred to the Fibre Optical Sensor group being arranged on duct wall, Fibre Optical Sensor group is picked up after the leakage vibration signal and noise of pipe transmmision, again be transmitted back to the photodetector of system through transmission light path, carry out leakage signal demodulation and discriminance analysis by signals collecting and processing module, and leakage signal is carried out to time delay and estimate to realize the location to leakage point.
Described Fibre Optical Sensor adopts optical fiber Michelson interferometer, in the time making, makes interferometer two arms not isometric as the Michelson interferometer that leaks sonic detection sensor, and two arm length difference are Δ L; By 2 × 2 coupling mechanisms and two faraday rotation mirror formations that the anglec of rotation is 45 degree;
Described signals collecting and processing module comprise that signal condition unit, signal gathering unit, processing unit, terminal show and external interface; The signal of photodetector output is connected in series signal condition unit, signal gathering unit and processing unit successively, and processing unit output has terminal to show and external interface; Processing unit comprises leakage signal identification circuit and state event location circuit.
Light source forms (seeing Fig. 4) by the adjustable laser instrument of optical frequency and dedicated modulation signal generating module, has the D/A output of the modulation signal generation module of frequency adjustment, amplitude adjusted and the sawtooth wave/selection of falling sawtooth wave input to connect the input of laser instrument; Use modulation signal module to produce required sawtooth wave or the signal of falling saw wave modulator, by the D/A output in modulation signal generation module, be applied to the continuous laser that on laser instrument, exportable optical frequency changes according to sawtooth wave or the rule of falling sawtooth wave.
When optical frequency is pressed after the laser injection of sawtooth wave or the rule of falling sawtooth wave variation, the interference signal carrier wave of each interferometer output is the cosine signal of approximate single-frequency, this interference signal is as the carrier signal of leaking acoustic signals, the arm length difference difference of interferometer, corresponding interference signal carrier frequency, can be by the carrier signal of different interferometers separately by filtering method also by difference.
Wherein as shown in Figure 5, it is mainly by operational amplifier U7, Distributed Feedback Laser U8, operational amplifier U9 and 2 triode Q4, Q5 group for modulation of source circuit; The 7 termination VDC of U7, after connecting with diode D8, capacitor C 41 after 6 terminating resistor R18, connect again with the circuit of capacitor C 38 parallel connections, after 6 terminating resistor R19, meet VDC, connect again the ground that is connected in series to of diode D4, D5, D6, D7 simultaneously, 4,7,8,9,10 end ground connection, 3 ends are ground connection after resistance R 17,2 ends and the end that meets U8; 1, the 14 end ground connection of U8,12 ends are through capacitor C 34 ground connection, 5,11 termination VDC, 4 termination PDne, 6 termination TEC+, 3 ends connect the collector of triode Q4 after choking coil L3 connects with resistance R 20, and 3 ends connect the collector of triode Q5 after choking coil L3 connects with resistance R 21 simultaneously; Between 1,2 ends of U9 after parallel resistance R22 and capacitor C 39 by 1 terminating resistor R25 to 6 ends, Pdne connecting resistance R30 again resistance in series R27 connects 3 ends of U9, connect the resistance R 30 and the ground connection of connecting after potentiometer resistance R31, resistance R 32, capacitor C 43 three's parallel connections of Pdne simultaneously, 5 ends meet VREF through resistance R 24, and 7 ends connect capacitor C 45 to ground through resistance R 28 and 8 ends altogether through resistance R 26; Pick out the base stage through diode D11, D12 to Q4 from the upper end of capacitor C 45, base stage connects capacitor C 44 to ground simultaneously, connects also arrive ground through diode D10 with resistance R 29 simultaneously, and the base stage of Q4 connects the base stage of Q5, and the grounded emitter of Q4, Q5;
Described light path system is a Michelson interferometer to be installed at a certain distance on pipeline as pipe leakage sonic sensor, the laser that simultaneously laser instrument sends by with pipeline laying in one ditch optical cable in an Optical Fiber Transmission (being called launching fiber), when laser arrives near each sensor, be divided into two bundles by beam splitter, beam of laser is injected sensor input end, another beam of laser passes to next sensor by launching fiber, by that analogy; Every 2-10 adjacent sensor is divided into one group, and in group, the interference signal of each sensor, by combiner device access passback optical fiber, transfers back to equipment receiving end; The length of the launching fiber on pipeline between adjacent two sensors and passback optical fiber is all greater than 1/2 of laser instrument coherent length, and the supplying with optical fiber of curtailment prevents from occurring between sensor signal cross-talk;
Each sensor group is used a passback optical fiber, and whole like this sensing light path needs a launching fiber, and passback number of fibers is identical with sensor group quantity;
Due to the arm length difference difference of the sensor in every group, launching fiber, passback fiber lengths between neighboring sensors are all greater than 1/2 of laser instrument coherent length, in can guarantee group, the frequency of each sensor output interference signal be different, between group inner sensor, does not interfere.
Described signals collecting and processing module comprise that signal condition unit, signal gathering unit, processing unit, terminal show and external interface; The signal of photodetector output is connected in series signal condition unit, signal gathering unit and processing unit successively, and processing unit output has terminal to show and external interface;
The interference light signal of each sensor group is converted to electric signal by photoelectric conversion module, the corresponding opto-electronic conversion passage independently of each sensor group;
The interference signal that signals collecting and processing module gather each sensor group is digital signal, due to each interferometer signal carrier frequency difference in group, and do not interfere between each interferometer, namely between each interferometer signal, do not crosstalk, can the carrier signal of each sensor in group thoroughly be separated by the method for bandpass filtering;
Bandpass filtering obtains after the carrier signal of each sensor, by phase generated carrier modulation and demodulation technology, demodulates original leakage acoustic signals;
Analyze the delay inequality of the leakage acoustic signals that adjacent two sensors detect, in conjunction with sound wave transmission speed in pipeline, the location that can realize leakage point;
The formation of described signals collecting and processing module is shown in Fig. 8, and it comprises signal condition unit, signal gathering unit, processing unit, display terminal and external interface; Wherein as shown in Figure 9, it is mainly made up of operational amplifier U14, photoelectric diode U15 signal condition element circuit; 1,5,8 ends of U15 are unsettled, 3,4 end ground connection, and 2 ends connect 6 ends after resistance R 39, capacitor C 60 the two parallel connection, and 6 ends connect 3 ends of U14,8 ends of 7 termination U14 through resistance R 43; The 4 end ground connection of U14,5 ends are unsettled, and 6,7 ends meet AD_VINI altogether, 1 termination AD_OUT mouth, 2 ends are through resistance R 42 ground connection, the two parallel connection of connecting resistance R40 between 1,2 ends, capacitor C 59.
The present invention is based on faraday rotation mirror method, realize the anti-polarization decay of the interference signal of each sensor in sensor group and group, visibility and the signal to noise ratio (S/N ratio) of sensor and sensor group interference signal are improved and have stablized, thereby greatly improve the multiplexing quantity of sensor group inner sensor, reduce the usage quantity of optical fiber, detect in keeping system under the prerequisite of effect, reduced system complex degree and cost.
Utilize with the common communications optical fibre in optical cable of oil and gas pipes laying in one ditch respectively as sending and receiving Transmission Fibers, pipe leakage Fibre Optical Sensor is connected between transmitting-receiving Transmission Fibers by Optical multiplexing technology is parallel with one another, form light circuit, it is along the line that pipe leakage Fibre Optical Sensor is evenly laid in pipeline, and formation can be monitored the optical fiber sensing system of pipe leakage vibration.Utilize light source to each pipe leakage Fibre Optical Sensor scanning, based on faraday rotation mirror method, realize the anti-polarization decay of the interference signal of a sensor in sensor group and group, visibility and the signal to noise ratio (S/N ratio) of sensor and sensor group interference signal are improved and have stablized, use photoelectric conversion module that the interference light signal of each sensor group is converted to electric signal, the corresponding opto-electronic conversion passage independently of each sensor group, the interference signal that is gathered each sensor group by signals collecting and processing module is digital signal, and can the carrier signal of each sensor in group thoroughly be separated by the method for bandpass filtering, by phase generated carrier modulation and demodulation technology, demodulate original leakage vibration wave signal, analyze the delay inequality of the leakage vibration wave signal that adjacent several sensor detects, in conjunction with vibration wave transmission speed in pipeline, the location that can realize leakage point.Thereby the multiplexing modulation-demodulation technique of application multisensor has improved the multiplexing quantity of sensor group inner sensor greatly, reduce the usage quantity of optical fiber, detect in keeping system under the prerequisite of effect, reduce system complex degree and cost.
The present invention has overcome and causes Michelson interferometer sensor detection sensitivity and signal to noise ratio (S/N ratio) to reduce and unsettled interferometer polarization inducement signal fade-out, makes sensitivity and accuracy raising, the false alarm rate reduction detecting based on the gas pipeline leakage of Fibre Optical Sensor and is not subject to such environmental effects.
Brief description of the drawings
Fig. 1 monitoring system of fiber optical sensing natural gas pipeline
The sensing light path connection diagram that Fig. 2 gas pipeline leakage detects
Fig. 3 Michelson interferometer structural representation
The modulation principle figure of Fig. 4 optical frequency adjustable type light source
Fig. 5 modulation of source circuit diagram
Fig. 6 leaks vibration wave demodulation principle block diagram
Fig. 7 light path adapter structure and transmission index path
Fig. 8 signals collecting and processing module structural drawing
Signal condition element circuit figure in Fig. 9 signals collecting and processing module
Wherein 1,1-1 ..., 1-n-beam splitter 2,2-1 ..., 2-n-Fibre Optical Sensor
3,3-1 ..., 3-n-combiner device 4,5,6,7,8,9-time delay optical fiber
Embodiment
In conjunction with the accompanying drawings and embodiments the present invention is further described, but should limit the scope of the invention with this.
Embodiment. as depicted in figs. 1 and 2, it comprises light source, light path system and circuit part to the formation of this example; On pipeline body, every 1.5km, a Fibre Optical Sensor is installed, 10 sensors are installed altogether, front 5 sensors and rear 5 sensors form respectively a sensor group, each Fibre Optical Sensor group shares a launching fiber and is connected with light source, and each Fibre Optical Sensor group is used a passback optical fiber to be connected with photodetector; Photodetector output connects the signals collecting and the processing module that comprise leakage signal identification and state event location function, and described signals collecting and processing module comprise that signal condition unit, signal gathering unit, processing unit, terminal show and external interface; The signal of photodetector output is connected in series signal condition unit, signal gathering unit and processing unit successively, and processing unit output has terminal to show and external interface.Signals collecting and processing module output connect microcomputer by external interface.Through the processing of signals collecting and processing module, the sensor group signal mixing based on frequency division multiplexing mode has been realized the demultiplexing of each sensor in sensor group, obtains original leakage vibration wave signal.
Sensor adopts the interferometer of Michelson-structure, and the faraday rotation mirror that two anglecs of rotation of each interferometer use are 45 degree is as catoptron.The present embodiment has been made 10 Michelson interferometer sensors, is divided into two groups, every group of 5 sensors, and arm length difference is respectively 5m, 7.5m, 10m, 12.5m, 15m;
By two sensors according to Fig. 2 and be connected in launching fiber and passback optical fiber between, two sensor groups share launching fibers, each independent passback optical fiber that uses;
Inject from launching fiber the laser that optical frequency changes with sawtooth wave, from photoelectric conversion module receiving sensor group interference signal for passback optical fiber, use bandpass filter to interference signal filtering, obtain the carrier signal of each sensor.Known by testing, sensor group and filtered sensor carrier signal amplitude stabilization are constant, and the sensor signal after demodulation is stable, and signal to noise ratio (S/N ratio) is substantially constant; And being replaced by common Michelson interferometer, the Michelson interferometer of above-mentioned use faraday rotation mirror obtains Mach-Zehnder interferometer, even if only connect 1 or 2 interferometers between launching fiber and passback optical fiber, sensor group and filtered sensor signal amplitude also all become unstable.
Described light source is a kind of special light source system of modulation /demodulation, forms (seeing Fig. 4) by the adjustable laser instrument of optical frequency and dedicated modulation signal generating module; Modulation signal generation module adopts digital form to realize, calculate according to wave mode, signal amplitude, frequency parameter the modulation signal segment that obtains one-period by digital form, then export by digital-to-analog conversion (D/A) mode, the modulated-analog signal of output is connected on laser instrument, wherein select sawtooth wave or the signal type of falling saw wave modulator by parameter configuration, capable of regulating signalization amplitude, direct current biasing and frequency; Sawtooth wave or the be to the maximum ± 5V of the requirement of falling sawtooth signal amplitude of the output of modulation signal generation module, frequency is 200KHz to the maximum; The laser that laser instrument after modulation output optical frequency changes with modulation signal synchronous waveform, is input in sensing light path, can realize multiplexing, the signal carrier that forms multiple sensors of sensor;
Wherein as shown in Figure 5, it is mainly by operational amplifier U7, Distributed Feedback Laser U8, operational amplifier U9 and 2 triode Q4, Q5 group for modulation of source circuit; The 7 termination VDC of U7, after connecting with diode D8, capacitor C 41 after 6 terminating resistor R18, connect again with the circuit of capacitor C 38 parallel connections, after 6 terminating resistor R19, meet VDC, connect again the ground that is connected in series to of diode D4, D5, D6, D7 simultaneously, 4,7,8,9,10 end ground connection, 3 ends are ground connection after resistance R 17,2 ends and the end that meets U8; 1, the 14 end ground connection of U8,12 ends are through capacitor C 34 ground connection, 5,11 termination VDC, 4 termination PDne, 6 termination TEC+, 3 ends connect the collector of triode Q4 after choking coil L3 connects with resistance R 20, and 3 ends connect the collector of triode Q5 after choking coil L3 connects with resistance R 21 simultaneously; Between 1,2 ends of U9 after parallel resistance R22 and capacitor C 39 by 1 terminating resistor R25 to 6 ends, Pdne connecting resistance R30 again resistance in series R27 connects 3 ends of U9, connect the resistance R 30 and the ground connection of connecting after potentiometer resistance R31, resistance R 32, capacitor C 43 three's parallel connections of Pdne simultaneously, 5 ends meet VREF through resistance R 24, and 7 ends connect capacitor C 45 to ground through resistance R 28 and 8 ends altogether through resistance R 26; Pick out the base stage through diode D11, D12 to Q4 from the upper end of capacitor C 45, base stage connects capacitor C 44 to ground simultaneously, connects also arrive ground through diode D10 with resistance R 29 simultaneously, and the base stage of Q4 connects the base stage of Q5, and the grounded emitter of Q4, Q5;
The formation of described signals collecting and processing module is shown in Fig. 8, and it comprises signal condition unit, signal gathering unit, processing unit, display terminal and external interface; Wherein as shown in Figure 9, it is mainly made up of operational amplifier U14, photoelectric diode U15 conditioning unit circuit; 1,5,8 ends of U15 are unsettled, 3,4 end ground connection, and 2 ends connect 6 ends after resistance R 39, capacitor C 60 the two parallel connection, and 6 ends connect 3 ends of U14,8 ends of 7 termination U14 through resistance R 43; The 4 end ground connection of U14,5 ends are unsettled, and 6,7 ends meet AD_VINI altogether, 1 termination AD_OUT mouth, 2 ends are through resistance R 42 ground connection, the two parallel connection of connecting resistance R40 between 1,2 ends, capacitor C 59; Wherein operational amplifier U14 selects AD8572, and photoelectric diode U15 selects OPA380AID.
The anti-polarization decay method of this gas pipeline leakage detecting sensor group is the laser instrument formation light source that uses dedicated modulation signal generating module and have optical frequency modulation, is built the leakage sonic sensor of Michelson structure by 2*2 coupling mechanism and faraday rotation mirror; The sensor of this structure is installed at a certain distance on pipeline body, and several adjacent sensors are as a sensor group; Each sensor by beam splitter and bundling device and be connected in launching fiber and passback optical fiber between, the sensor of all the sensors group is all linked into same launching fiber, and different sensors group is used separately a passback optical fiber; Two arms of Michelson interferometer sensor are not isometric, each sensor uses two faraday rotation mirrors as catoptron, the anglec of rotation is 45 degree, catoptrical polarization state is changed and just in time offset the polarization state variation of incident light, thereby make the visibility of sensor and sensor group signal remain maximum.
This example is through test of many times, prove in the present invention to be effective for the anti-polarization decay technology of sensor group and group inner sensor, greatly improve sensitivity and the stability of system detection signal, thereby also improved the multiplexing quantity of sensor group inner sensor, reduced reuse cost.
Claims (6)
1. an anti-polarization decay system for gas pipeline leakage detecting sensor group, it comprises light source, light path system and circuit part; A Fibre Optical Sensor is installed at a certain distance on pipeline body, multiple Fibre Optical Sensors form a Fibre Optical Sensor group, each Fibre Optical Sensor group shares a launching fiber and is connected with light source, and each Fibre Optical Sensor group is used a passback optical fiber to be connected with photodetector; Photodetector output connects signals collecting and processing module, and signals collecting and processing module output connect microcomputer by external interface;
Send laser by light source, realize after beam splitting through transmission light path, part light is transferred to the Fibre Optical Sensor group being arranged on duct wall, Fibre Optical Sensor group is picked up after the leakage vibration signal and noise of pipe transmmision, again be transmitted back to the photodetector of system through transmission light path, carry out leakage signal demodulation and discriminance analysis by signals collecting and processing module, and leakage signal is carried out to time delay and estimate to realize the location to leakage point;
It is characterized in that: described sensor adopts the interferometer of optical fiber Michelson-structure, and interferometer two arms are not isometric, and two arm length difference are Δ L; In sensor group, the arm length difference of each Michelson interferometer is all not identical, and the arm length difference of the Michelson interferometer in different sensors group is identical; The faraday rotation mirror that optical fiber Michelson interferometer is 45 degree by a 2*2 coupling mechanism and two anglecs of rotation forms;
Described light source is made up of the adjustable laser instrument of optical frequency and dedicated modulation signal generating module; There is the D/A output of the modulation signal generation module of frequency adjustment, amplitude adjusted and the sawtooth wave/selection of falling sawtooth wave input to connect the input of laser instrument; Use modulation signal module to produce required sawtooth wave or the signal of falling saw wave modulator, by the D/A output in modulation signal generation module, be applied on laser instrument and export optical frequency according to the continuous laser of sawtooth wave or the rule of falling sawtooth wave variation, the stack of the multiple approximate single-frequency cosine signal that the interference signal of sensor group output is amplitude stabilization; The modulation of source main circuit of dedicated modulation signal generating module will be made up of operational amplifier U7, Distributed Feedback Laser U8, operational amplifier U9 and 2 triode Q4, Q5; The 7 termination VDC of U7, the first connecting resistance R18 of 6 ends of U7, connect afterwards after a parallel circuit ground connection again, this parallel circuit comprises two branch roads, and wherein one route diode D8 and capacitor C 41 series connection form, another route capacitor C 38 forms, after the 5 terminating resistor R19 of U7, meet VDC, 5 ends of U7 connect being connected in series to of diode D4, D5, D6, D7 simultaneously again, the 4 end ground connection of U7,3 ends of U7 ground connection after resistance R 17,2 ends of U7 connect 2 ends of U8; 1, the 14 end ground connection of U8,12 ends of U8 are through capacitor C 34 ground connection, 5, the 11 termination VDC of U8, the 4 termination PDne of U8, the 6 termination TEC+ of U8,3 ends of U8 connect the collector of triode Q4 after choking coil L3 connects with resistance R 20, and 3 ends of U8 connect the collector of triode Q5 after choking coil L3 connects with resistance R 21 simultaneously; 2 ends of U9 connect 1 end that is connected U9 after the parallel circuit being formed with capacitor C 39 by resistance R 22, also contact resistance R25 of parallel circuit simultaneously that formed by resistance R 22 and capacitor C 39, be connected to afterwards 6 ends of U9, PDne connecting resistance R30 connects 3 ends of U9 again after resistance in series R27, simultaneously, the resistance R 30 that meets PDne also connects the parallel circuit being made up of resistance R 31, resistance R 32, capacitor C 43 threes, ground connection more afterwards, 5 ends of U9 meet VREF through resistance R 24, and 7 ends of U9 connect capacitor C 45 to ground through resistance R 28 and 8 ends of U9 altogether through resistance R 26; Pick out the base stage through diode D11, D12 to Q4 from the upper end of capacitor C 45, base stage connects capacitor C 44 to ground simultaneously, connects also arrive ground through diode D10 with resistance R 29 simultaneously, and the base stage of Q4 connects the base stage of Q5, and the grounded emitter of Q4, Q5.
2. the anti-polarization decay system of a kind of gas pipeline leakage detecting sensor group according to claim 1, is characterized in that described signals collecting and processing module comprise that signal condition unit, signal gathering unit, processing unit, terminal show and external interface; Photodetector output is connected in series signal condition unit, signal gathering unit and processing unit successively, and processing unit output has terminal to show and external interface; Processing unit comprises leakage signal identification circuit and state event location circuit.
3. the anti-polarization decay system of a kind of gas pipeline leakage detecting sensor group according to claim 1, it is characterized in that described light path system is a Michelson interferometer to be installed at a certain distance on pipeline as pipe leakage sonic sensor, the laser that simultaneously laser instrument sends by with pipeline laying in one ditch optical cable in an Optical Fiber Transmission that is called launching fiber, when laser arrives near each sensor, be divided into two bundles by beam splitter, beam of laser is injected sensor input end, another beam of laser passes to next sensor by launching fiber, by that analogy, every 2-10 adjacent sensor is divided into one group, and in group, the interference signal of each sensor, by combiner device access passback optical fiber, transfers back to equipment receiving end, the length of the launching fiber on pipeline between adjacent two sensors and passback optical fiber is all greater than 1/2 of laser instrument coherent length, and the supplying with optical fiber of curtailment prevents from occurring between sensor signal cross-talk, each sensor group is used a passback optical fiber, and whole sensing light path only has a launching fiber, and passback number of fibers is identical with sensor group quantity.
4. the anti-polarization decay system of a kind of gas pipeline leakage detecting sensor group according to claim 1, is characterized in that described signals collecting and processing module comprise signal condition unit, signal gathering unit, processing unit, display terminal and external interface; The signal of photodetector output is connected in series signal condition unit, signal gathering unit and processing unit successively, and processing unit output has terminal to show and external interface.
5. the anti-polarization decay system of a kind of gas pipeline leakage detecting sensor group according to claim 4, is characterized in that described signal condition element circuit is mainly made up of operational amplifier U14, photoelectric diode U15; 1,5,8 ends of U15 are unsettled, 3, the 4 end ground connection of U15, and 2 ends of U15 connect by connecing 6 ends after resistance R 39 and capacitor C 60 the two parallel circuit that form again, and 6 ends of U15 connect 3 ends of U14 through resistance R 43,8 ends of the 7 termination U14 of U15; The 4 end ground connection of U14,5 ends are unsettled, and 6,7 ends meet AD_VINI altogether, the 1 termination AD_OUT mouth of U14,2 ends of U14 are through resistance R 42 ground connection, the two parallel circuit of connecting resistance R40 between 1,2 ends of U14, capacitor C 59.
6. the anti-polarization decay method of the anti-polarization decay system of the gas pipeline leakage detecting sensor group described in a right to use requirement 1, it is characterized in that installing at a certain distance the sensor of the not isometric Michelson interferometer structure of two arm on pipeline body, several adjacent sensors are as a sensor group, each sensor by beam splitter and bundling device and be connected in launching fiber and passback optical fiber between;
Adopt optical fiber Michelson interferometer as leaking sonic detection sensor, the light intensity signal of its output is write as after opto-electronic conversion:
V0∝1+Vcos(φs+φn+φ0)+Vn
Wherein, V0 is the voltage signal of output, V is the visibility of interferometer, and Vn is circuit additional noise, and φ s serves as reasons and leaks the phase difference signal that vibration wave causes, be the leakage vibration wave signal that will survey, the initial phase that φ 0 is interferometer, is a constant, the low frequency wonder that φ n is phasic difference, be a Uncertainty, change with temperature and external environment impact; Can realize and leak obtaining of vibration wave signal psi s by the demultiplexing technology matching with modulation of source mode, and the time delay that this signal psi s arrives corresponding sensor is estimated, adopt faraday rotation mirror method, before two catoptrons of common Michelson interferometer, respectively add a Faraday rotator, the anglec of rotation is 45 degree, catoptrical polarization state is changed and just in time offset the polarization state variation of incident light, thereby make the visibility of interferometer remain maximum;
Two arms as the Michelson interferometer of sensor are not isometric, and two arm length difference are Δ L, using sawtooth signal as modulation signal, frequency is the twice of leaking sound wave frequency span, be applied to the adjustable laser instrument of optical frequency, laser instrument output optical frequency is according to the synchronous laser changing of saw wave modulator signal, be input to Michelson interferometer, laser by two arms will produce delay inequality, thereby the two bundle laser that participate in interfering are except sawtooth wave falling edge, the optical frequency in other moment is poor is a constant, the interference signal of interferometer output is the cosine signal of an approximate single-frequency, angular frequency 0 is directly proportional to interferometer two arm length difference Δ L, Δ L is larger, interference signal frequency is higher, the linear superposition that the interference signal of sensor group output is several approximate simple signals, its frequency spectrum is several discrete spectral lines, spectral line amplitude stabilization is constant,
Use bandpass filter to carry out filtering to sensor group interference signal, filter center frequency is the centre frequency of sensor group inner sensor interference signal, and bandwidth is identical with saw wave modulator signal frequency; After filtering, can obtain the carrier signal of this sensor, signal amplitude is stable.
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| CN102997054A (en) * | 2011-09-14 | 2013-03-27 | 中国石油天然气集团公司 | System for resisting polarization fading of natural gas pipe leakage detecting sensor group |
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