CN102997044A - 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 pipe-line system technical field of impact.
Background technique
At present, the pipeline overall length of building up in the world reaches 2,500,000 kilometers, and having surpassed the 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 is also above 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 transport becomes the major way of the allotment conveying of the strategic energy such as oil gas.
Pipeline is subjected to the reasons such as natural disaster, third party's breakage in installation owing to cross-regional wide, has caused more pipe leakage accident to occur.External pipe safety situation also allows of no optimist very much, and the natural gas line big bang occurs in U.S. San Bruno city on September 9th, 2010, and blast causes long 51 meters, wide 9 a meters hollow place on the road surface.The pipeline of about 8 meters of one segment length, 76 centimetres of diameters is exploded the Heaven, flies out about 30 meters far away, and causes large-range fire disaster, causes 4 people dead, 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.
Only have the sound wave monitoring method comparatively effective for natural gas line leakage in the ripe technology at present, but in order to improve the real-time of leakage monitoring and the accuracy of leak source location, the layout density that must add at pipeline large sensor, increase simultaneously corresponding power supply, communications equipment, cause system cost and installation and maintenance costly.
Along with the development of sensory technique has been carried out the research of SCADA leakage monitoring system such as companies such as U.S. CSI, ATMOSI, European TER abroad, 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 optical fiber in the optical cable to form a Fiber optic micro-vibration sensor.Patent CN200620119429, CN200610113044.0 are the pipeline leakage monitor based on the Sagnac fibre optic interferometer, and patent CN200610072879.6 is a kind of pipeline leakage monitor based on distributed optical fiber acoustic sensing technology and method.
" sensor and micro-system " the 7th phase of the 26th volume " based on the gas pipeline leakage detection method of distributed fiberoptic sensor " discloses a kind of gas pipeline leak detecting device and method based on distributed fiberoptic sensor, it is to have installing optical fibres sensor on the pipeline body of certain intervals, the vibration wave signal that continuous real-time monitoring is propagated along pipeline body, the vibration wave signal that gathers is carried out analysing and processing, comprise type identification and vibration source location, wherein whether type identification is for to belong to leak type by the extraction and analysis of vibration wave feature being differentiated it, the time lag that simultaneously propagates into adjacent several optical fiber transducers according to vibration wave determines that in conjunction with the velocity of propagation of vibration wave on pipeline body the position at vibration wave source place, the light intensity signal of sensor output realize position definite of leakage point after photoelectric 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 the distributed optical fiber sensing monitoring method.But such technical monitoring is subject to the impact of the interference incident that pipeline occurs when leaking, have very high system's false alarm rate, and antijamming capability is relatively poor.
Summary of the invention
The objective of the invention is to invent that a kind of sensitivity and degree of accuracy are high, false alarm rate is low, be not subject to the anti-polarization decay method and system based on the gas pipeline leakage detecting sensor group of Fibre Optical Sensor of such environmental effects.
In view of above-mentioned a few class Leak testtion, 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 provides the quasi-distributed leakage vibration monitoring of a kind of high sensitivity based on Fibre Optical Sensor method and system, adopt high sensor so that can little leakage occur when pipeline, the leakages such as seepage were in time monitored during the primary stage, and in conjunction with the time domain of incident of leakage, frequency domain character effectively reduces and disturbs the system's false alarm rate that causes, this technological scheme has overcome poor accuracy in the monitoring technology before this and the deficiency of mounting process complexity, so that the related maintenance personnel can in time take counter-measure, avoid causing larger security incident.
Thereby the natural gas line leakage system with the sensitivity of high leakage vibrating sensing has realized the raising of interferometer to the induction sensitivity of oscillating signal by the length and the space length that increase interferometer two pickup arms, at the intelligent identification technology that has adopted leakage signal aspect the inhibition that Environmental Random Vibration is disturbed, at random accidental vibration and sudden, persistency leakage signal have effectively been distinguished, and in conjunction with the leakage signal time delay that adjacent a plurality of sensors obtain simultaneously, 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 emission and passback optical fiber, pipeline is revealed optical fiber transducer to be connected between the transmitting-receiving transmission fiber by Optical multiplexing technology is parallel with one another, form light circuit, pipeline is revealed optical fiber transducer and is installed on the pipeline, but forms the optical fiber sensing system of monitoring pipe road acoustic vibration.Utilize light source that each pipeline is revealed optical fiber transducer scanning, reveal photoelectric conversion signal demodulation, the extraction of distribution situation to gathering of optical fiber transducer according to pipeline, the vibration information of realizing each pipeline leakage optical fiber transducer obtains, the detection analysis conduit is revealed the optical fiber transducer signal and has been judged whether that pipeline leakage event occurs, and reveals optical fiber transducer according to adjacent pipeline and detects the time delay of arrival realization of signal to the location of leak point.
Can produce the sound wave of each frequency range behind the pipe leakage, just gradually by Absorption of Medium, and wavelength is shorter in the not far position of distance sound source for the short ultrasound of wavelength ratio, 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 at present and the system of infrasonic sensor is being installed because the available signal frequency range is narrower than the long pipeline two ends, to the accurate positioning effect of leakage signal not enough.
The anti-polarization decay method of gas pipeline leakage detecting sensor group is that the sensor of a Michelson interferometer structure is installed on pipeline body at a certain distance, by the sensor of several Michelson interferometer structures by beam splitter and bundle-mixer 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 reflector, angle of swing is 45 degree, and the polarization state that makes catoptrical polarization state variation just in time offset incident light changes, thereby makes the visibility of interferometer remain maximum.
Adopt the optical fiber Michelson interferometer as leaking the sonic detection sensor, the light intensity signal of its output can be write as after photoelectric 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
nThe circuit additional noise, φ
sServe as reasons and leak the phase difference signal that vibration wave causes, be the leakage vibration wave signal that to survey, φ
0Being the initial phase of interferometer, is a constant, φ
nBeing the low frequency wonder of phase difference, is a Uncertainty, changes with temperature and external environment impact.Can realize leaking the vibration wave signal psi by the demultiplexing technology that is complementary with the modulation of source mode
sObtain, and to this signal psi
sThe time lag that arrives corresponding sensor estimates, realized that along the speed v of pipe transmmision to the vibration wave source be determining of leakage point position in conjunction with vibration wave.
In fact, in the Michelson interferometer optical fiber with the corresponding refractive index n of two polarization modes
xAnd n
yUnequal, simultaneously because the variation of little curved, the distortion of optical fiber, ambient temperature makes n
xAnd n
yChange at random causes optical fiber output polarization state change at random, is reflected in interference signal visibility V change at random 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 and unstable, for eliminating polarization decay, adopt the faraday rotation mirror method, namely before two reflectors of common Michelson interferometer, respectively add a Faraday rotator and consist of faraday rotation mirror, angle of swing is 45 degree, the polarization state that makes catoptrical polarization state variation just in time offset incident light changes, thereby makes the visibility of interferometer remain 1.
In the formula (1), because low-frequency disturbance φ
nChange at random, and amplitude is large, is subjected to φ
nVariable effect, the signal to noise ratio of system's output is changing, and as sin φ
n=0 o'clock, the complete blanking of signal, this namely is called the phase fading phenomenon of interferometer.
In order to eliminate the polarization decay phenomenon, adopt the phase carrier technology to detect the leakage acoustic signals.Specific as follows:
When making Michelson interferometer, make interferometer two arms not isometric, two arm length difference are Δ L;
With sawtooth signal as modulation signal, frequency is for leaking the twice of sound wave frequency bandwidth, be applied to the adjustable laser of optical frequency, the laser that laser output optical frequency changes synchronously according to the 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 the sawtooth wave falling edge, other optical frequencies constantly are poor to be 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 with interferometer, and Δ L is larger, and the interference signal frequency is higher; The interference signal of sensor group output is the linear superposition of several approximate simple signals, and its frequency spectrum is several discrete spectral lines, and the spectral line amplitude stabilization is constant;
Use band-pass filter that interference signal is carried out filtering, the filter center frequency is the interference signal CF center frequency, and bandwidth is identical with the saw wave modulator signal frequency.Can obtain the carrier signal of this interferometer after the filtering, use cosine and the sinusoidal signal demodulation identical with the carrier signal main frequency, but the phase fading problem of erasure signal obtain original leakage acoustic signals.
The formation of the anti-polarization decay system of this gas pipeline leakage detecting sensor group is seen Fig. 1, and it comprises light source, light path system and circuit part; An optical fiber transducer is installed on pipeline body at a certain distance, a plurality of optical fiber transducers consist of an optical fiber transducer group, each optical fiber transducer group shares a launching fiber and is connected with light source, and each optical fiber transducer group uses a passback optical fiber to be connected with photodetector; Photodetector output connects signals collecting and puocessing module, and signals collecting and puocessing module output connect microcomputer by external interface.Through the processing of signals collecting and puocessing module, the sensor group signal that mixes based on the frequency division multiplexing mode has been realized the demultiplexing of each sensor in the sensor group, obtains original leakage vibration wave signal.
Send laser by light source, after the transmission light path realizes beam splitting, part light is transferred to the optical fiber transducer group that is installed on the tube wall, the optical fiber transducer group is picked up behind the leakage oscillating signal and noise of pipe transmmision, again be transmitted back to the photodetector of system through the transmission light path, carry out leakage signal demodulation and discriminance analysis by signals collecting and puocessing module, and leakage signal is carried out time delay estimate that realization is to the location of leakage point.
Described optical fiber transducer adopts the optical fiber Michelson interferometer, when making, makes interferometer two arms not isometric as the Michelson interferometer that leaks the sonic detection sensor, and two arm length difference are Δ L; By 2 * 2 Couplers and two faraday rotation mirror formations that angle of swing is 45 degree;
Described signals collecting and puocessing 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 recognition circuit and state event location circuit.
Light source consists of (seeing Fig. 4) by optical frequency adjustable laser and dedicated modulation signal generating module, has the D/A of the modulation signal generation module of frequency adjustment, amplitude adjusted and the sawtooth wave/selection of falling sawtooth wave input to export the input that connects laser; Use the modulation signal module to produce required sawtooth wave or the signal of falling the saw wave modulator, by the output of the D/A in the modulation signal generation module, be applied to the continuous laser that exportable optical frequency changes according to sawtooth wave or the rule of falling the sawtooth wave on the laser.
Press the laser injection of sawtooth wave or the rule of falling sawtooth wave variation when optical frequency after, 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 of interferometer is different, corresponding interference signal carrier frequency can be separated the carrier signal of different interferometers by filtering method also with difference.
Wherein the modulation of source circuit as shown in Figure 5, it is mainly by operational amplifier U7, Distributed Feedback Laser U8, operational amplifier U9 and 2 triode Q4, Q5 groups; The 7 termination VDC of U7, connect again with the circuit of capacitor C 38 parallel connections after connecting with diode D8, capacitor C 41 behind the 6 terminating resistor R18, meet VDC behind the 6 terminating resistor R19, connect again simultaneously the ground that is connected in series to of diode D4, D5, D6, D7,4,7,8,9,10 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 are through choke coil L3 and the collector electrode that meets triode Q4 after resistance R 20 is connected, and 3 ends are through choke coil L3 and the collector electrode that meets triode Q5 after resistance R 21 is connected simultaneously; Between 1,2 ends of U9 after shunt resistor R22 and the capacitor C 39 by 1 terminating resistor R25 to 6 ends, Pdne connecting resistance R30 again series resistors R27 connects 3 ends of U9, the ground connection of connecting after the resistance R 30 that meets simultaneously Pdne and potentiometer resistance R31, resistance R 32, the capacitor C 43 three's parallel connections, 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 with resistance R 29 through diode D10 simultaneously and also arrives ground, and the base stage of Q4 connects the base stage of Q5, and the grounded-emitter connection of Q4, Q5;
Described light path system is a Michelson interferometer to be installed at a certain distance as the pipe leakage sonic sensor on pipeline, simultaneously the laser that sends of laser by with pipeline laying in one ditch optical cable in an optical fibre transmission (being called launching fiber), when laser arrives near each sensor, be divided into two bundles by beam splitter, beam of laser is injected the sensor input end, another Shu Jiguang passes to next sensor by launching fiber, by that analogy; Every 2-10 adjacent sensor is divided into one group, and the interference signal of each sensor transfers back to the equipment receiving terminal by combiner device access passback optical fiber in the group; The length of the launching fiber on the pipeline between adjacent two sensors and passback optical fiber all is greater than 1/2 of laser coherent length, and supplying with optical fiber of curtailment prevents from occuring between the 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 the passback number of fibers is identical with sensor group quantity;
Because the arm length difference of the sensor in every group is different, launching fiber between the adjacent sensors, passback fiber lengths are all greater than 1/2 of laser coherent length, the frequency of each sensor output interference signal is different in can the assurance group, does not interfere between the group inner sensor.
Described signals collecting and puocessing 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;
Photoelectric conversion module is converted to electrical signal with the interference light signal of each sensor group, the corresponding photoelectric conversion passage independently of each sensor group;
The interference signal that signals collecting and puocessing module gather each sensor group is digital signal, because each interferometer signal carrier frequency is different in the group, and do not interfere between each interferometer, namely do not crosstalk between each interferometer signal, the carrier signal of each sensor is thoroughly separated in can will organizing by the method for bandpass filtering;
After bandpass filtering obtains the carrier signal of each sensor, by the phase generated carrier modulation and demodulation technology, demodulate 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 puocessing module is seen Fig. 8, and it comprises signal condition unit, signal gathering unit, processing unit, video terminal and external interface; Wherein the signal condition element circuit as shown in Figure 9, it mainly is comprised of operational amplifier U14, photoelectric diode U15; 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, and 1 termination AD_OUT mouth, 2 ends be 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 the faraday rotation mirror method, realize the anti-polarization decay of the interference signal of each sensor in sensor group and the group, improve and stablized visibility and the signal to noise ratio of sensor and sensor group interference signal, thereby greatly improved the multiplexing quantity of sensor group inner sensor, reduced the usage quantity of optical fiber, detect in keeping system under the prerequisite of effect, reduced system complex degree and cost.
The common communications optical fibre in optical cable of utilization and oil and gas pipes laying in one ditch is respectively as the sending and receiving transmission fiber, the pipe leakage optical fiber transducer is connected between the transmitting-receiving transmission fiber by Optical multiplexing technology is parallel with one another, form light circuit, it is along the line that the pipe leakage optical fiber transducer evenly is laid in pipeline, and formation can be monitored the optical fiber sensing system of pipe leakage vibration.Utilize light source to each pipe leakage optical fiber transducer scanning, based on the faraday rotation mirror method, realize the anti-polarization decay of the interference signal of a sensor in sensor group and the group, improve and stablized visibility and the signal to noise ratio of sensor and sensor group interference signal, use photoelectric conversion module that the interference light signal of each sensor group is converted to electrical signal, the corresponding photoelectric conversion passage independently of each sensor group, the interference signal that is gathered each sensor group by signals collecting and puocessing module is digital signal, and the carrier signal of each sensor is thoroughly separated in can will organizing by the method for bandpass filtering, by the 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 use the multiplexing quantity that the multiplexing modulation-demodulation technique of multisensor has improved sensor group inner sensor greatly, reduced the usage quantity of optical fiber, detect in keeping system under the prerequisite of effect, reduced system complex degree and cost.
The present invention has overcome and causes Michelson interferometer sensor detection sensitivity and signal to noise ratio to reduce and unsettled interferometer polarization inducement signal fade-out, makes sensitivity and degree of accuracy raising, the false alarm rate reduction that the gas pipeline leakage based on Fibre Optical Sensor detects and is not subject to such environmental effects.
Description of 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 puocessing module structural drawing
Signal condition element circuit figure in Fig. 9 signals collecting and the puocessing module
Wherein 1,1-1 ..., 1-n-beam splitter 2,2-1 ..., the 2-n-optical fiber transducer
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 specified, but should not limit protection scope of the present invention with this.
Embodiment. the formation of this example as depicted in figs. 1 and 2, it comprises light source, light path system and circuit part; On pipeline body, every 1.5km an optical fiber transducer is installed, 10 sensors are installed altogether, front 5 sensors and rear 5 sensors consist of respectively a sensor group, each optical fiber transducer group shares a launching fiber and is connected with light source, and each optical fiber transducer group uses a passback optical fiber to be connected with photodetector; Photodetector output connects signals collecting and the puocessing module that comprises leakage signal identification and state event location function, and described signals collecting and puocessing 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 puocessing module output connect microcomputer by external interface.Through the processing of signals collecting and puocessing module, the sensor group signal that mixes based on the frequency division multiplexing mode has been realized the demultiplexing of each sensor in the sensor group, obtains original leakage vibration wave signal.
Sensor adopts the interferometer of Michelson-structure, and it is that 45 faraday rotation mirrors of spending are as reflector that each interferometer uses two angle of swing.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;
With two sensors according to Fig. 2 and be connected in launching fiber and passback optical fiber between, two sensor groups share launching fibers, each independently uses one to return optical fiber;
Inject the laser that optical frequency changes with sawtooth wave from launching fiber, with photoelectric conversion module receiving sensor group interference signal, use band-pass filter to interference signal filtering from passback optical fiber, obtain the carrier signal of each sensor.By test as can be known, sensor group and filtered sensor carrier signal amplitude stabilization are constant, and the sensor signal after the demodulation is stable, and signal to noise ratio is substantially constant; And being replaced by common Michelson interferometer, the Michelson interferometer of above-mentioned use faraday rotation mirror obtains the Mach-Zehnder interferometer, even 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, and laser and the dedicated modulation signal generating module adjustable by optical frequency consist of (seeing Fig. 4); Modulation signal generation module adopts digital form to realize, namely calculate the modulation signal segment that obtains one-period by digital form according to wave mode, signal amplitude, frequency parameter, then export by digital-to-analog conversion (D/A) mode, the modulated-analog signal of output is connected on the laser, wherein select sawtooth wave or the signal type of falling the saw wave modulator, capable of regulating signalization amplitude, direct current biasing and frequency by parameter configuration; Sawtooth wave or the requirement of falling the sawtooth signal amplitude of the output of modulation signal generation module are to the maximum ± 5V, and frequency is 200KHz to the maximum; Laser after modulation output optical frequency is input in the sensing light path with the laser that the modulation signal synchronous waveform changes, and can realize multiplexing, the signal carrier that forms a plurality of sensors of sensor;
Wherein the modulation of source circuit as shown in Figure 5, it is mainly by operational amplifier U7, Distributed Feedback Laser U8, operational amplifier U9 and 2 triode Q4, Q5 groups; The 7 termination VDC of U7, connect again with the circuit of capacitor C 38 parallel connections after connecting with diode D8, capacitor C 41 behind the 6 terminating resistor R18, meet VDC behind the 6 terminating resistor R19, connect again simultaneously the ground that is connected in series to of diode D4, D5, D6, D7,4,7,8,9,10 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 are through choke coil L3 and the collector electrode that meets triode Q4 after resistance R 20 is connected, and 3 ends are through choke coil L3 and the collector electrode that meets triode Q5 after resistance R 21 is connected simultaneously; Between 1,2 ends of U9 after shunt resistor R22 and the capacitor C 39 by 1 terminating resistor R25 to 6 ends, Pdne connecting resistance R30 again series resistors R27 connects 3 ends of U9, the ground connection of connecting after the resistance R 30 that meets simultaneously Pdne and potentiometer resistance R31, resistance R 32, the capacitor C 43 three's parallel connections, 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 with resistance R 29 through diode D10 simultaneously and also arrives ground, and the base stage of Q4 connects the base stage of Q5, and the grounded-emitter connection of Q4, Q5;
The formation of described signals collecting and puocessing module is seen Fig. 8, and it comprises signal condition unit, signal gathering unit, processing unit, video terminal and external interface; Wherein the conditioning unit circuit as shown in Figure 9, it mainly is comprised of operational amplifier U14, photoelectric diode U15; 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, and 1 termination AD_OUT mouth, 2 ends be 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 formation light source that uses the dedicated modulation signal generating module and have the optical frequency modulation, is made up the leakage sonic sensor of Michelson structure by 2*2 Coupler and faraday rotation mirror; The sensor of this structure is installed on pipeline body at a certain distance, and several adjacent sensors are as a sensor group; Each sensor by beam splitter and bundle-mixer and be connected in launching fiber and passback optical fiber between, the sensor of all the sensors group all is linked into same launching fiber, and the 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 reflector, angle of swing is 45 degree, the polarization state that makes catoptrical polarization state variation just in time offset incident light changes, thereby makes the visibility of sensor and sensor group signal remain maximum.
This example is through test of many times, proved that the anti-polarization decay technology for sensor group and group inner sensor is effective among the present invention, greatly improve sensitivity and the stability of system's testing signal, thereby also improved the multiplexing quantity of sensor group inner sensor, reduced reuse cost.
Claims (10)
1. the anti-polarization decay method of a gas pipeline leakage detecting sensor and sensor group, it is characterized in that on pipeline body, installing at a certain distance the sensor of the not isometric Michelson interferometer structure of two arm, several adjacent sensors are as a sensor group, each sensor by beam splitter and bundle-mixer and be connected in launching fiber and passback optical fiber between;
Adopt the optical fiber Michelson interferometer as leaking the sonic detection sensor, the light intensity signal of its output is write as after photoelectric conversion:
V
0∝1+Vcos(φ
s+φ
n+φ
0)+V
n
Wherein, V
0Be the voltage signal of output, V is the visibility of interferometer, V
nThe circuit additional noise, φ
sServe as reasons and leak the phase difference signal that vibration wave causes, be the leakage vibration wave signal that to survey, φ
0Being the initial phase of interferometer, is a constant, φ
nBeing the low frequency wonder of phase difference, is a Uncertainty, changes with temperature and external environment impact; Can realize leaking the vibration wave signal psi by the demultiplexing technology that is complementary with the modulation of source mode
sObtain, and to this signal psi
sThe time lag that arrives corresponding sensor is estimated, adopt the faraday rotation mirror method, namely before two reflectors of common Michelson interferometer, respectively add a Faraday rotator, angle of swing is 45 degree, the polarization state that makes catoptrical polarization state variation just in time offset incident light changes, thereby makes the visibility of interferometer remain maximum.
2. the anti-polarization decay method of a kind of gas pipeline leakage detecting sensor group according to claim 1 is characterized in that:
Two arms as the Michelson interferometer of sensor are not isometric, and two arm length difference are Δ L;
With sawtooth signal as modulation signal, frequency is for leaking the twice of sound wave frequency bandwidth, be applied to the adjustable laser of optical frequency, laser output optical frequency is input to Michelson interferometer according to the laser that the saw wave modulator signal changes synchronously, and the laser by two arms will produce delay inequality, thereby the two bundle laser that participate in interfering are except the sawtooth wave falling edge, other optical frequencies constantly are poor to be a constant, and 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 with interferometer, and Δ L is larger, and the interference signal frequency is higher; The interference signal of sensor group output is the linear superposition of several approximate simple signals, and its frequency spectrum is several discrete spectral lines, and the spectral line amplitude stabilization is constant;
Use band-pass filter that sensor group interference signal is carried out filtering, the filter center frequency is the CF center frequency of sensor group inner sensor interference signal, and bandwidth is identical with the saw wave modulator signal frequency; Can obtain the carrier signal of this sensor after the filtering, signal amplitude is stable.
3. a right to use requires the anti-polarization decay system of a kind of gas pipeline leakage detecting sensor group of 1 described method, it is characterized in that it comprises light source, light path system and circuit part; An optical fiber transducer is installed on pipeline body at a certain distance, a plurality of optical fiber transducers consist of an optical fiber transducer group, each optical fiber transducer group shares a launching fiber and is connected with light source, and each optical fiber transducer group uses a passback optical fiber to be connected with photodetector; Photodetector output connects signals collecting and puocessing module, and signals collecting and puocessing module output connect microcomputer by external interface;
Send laser by light source, after the transmission light path realizes beam splitting, part light is transferred to the optical fiber transducer group that is installed on the tube wall, the optical fiber transducer group is picked up behind the leakage oscillating signal and noise of pipe transmmision, again be transmitted back to the photodetector of system through the transmission light path, carry out leakage signal demodulation and discriminance analysis by signals collecting and puocessing module, and leakage signal is carried out time delay estimate that realization is to the location of leakage point.
4. the anti-polarization decay system of a kind of gas pipeline leakage detecting sensor group according to claim 3 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; The arm length difference of each Michelson's interferometer is all not identical in the sensor group, and the arm length difference of the Michelson's interferometer in the different sensors group is identical; The optical fiber Michelson interferometer is that 45 faraday rotation mirrors of spending consist of by a 2*2 Coupler and two angle of swing.
5. the anti-polarization decay system of a kind of gas pipeline leakage detecting sensor group according to claim 3 is characterized in that described signals collecting and puocessing 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 recognition circuit and state event location circuit.
6. the anti-polarization decay system of a kind of gas pipeline leakage detecting sensor group according to claim 3 is characterized in that described light source is made of optical frequency adjustable laser and dedicated modulation signal generating module; There is the D/A of the modulation signal generation module of frequency adjustment, amplitude adjusted and the sawtooth wave/selection of falling sawtooth wave input to export the input that connects laser; Use the modulation signal module to produce required sawtooth wave or the signal of falling the saw wave modulator, export by the D/A in the modulation signal generation module, be applied to the continuous laser that the output optical frequency changes according to sawtooth wave or the rule of falling the sawtooth wave on the laser, the interference signal of sensor group output is the stack of a plurality of approximate single-frequency cosine signal of amplitude stabilization.
7. the anti-polarization decay system of a kind of gas pipeline leakage detecting sensor group according to claim 6 is characterized in that the modulation of source main circuit of dedicated modulation signal generating module will be by operational amplifier U7, Distributed Feedback Laser U8, operational amplifier U9 and 2 triode Q4, Q5 groups; The 7 termination VDC of U7, connect again with the circuit of capacitor C 38 parallel connections after connecting with diode D8, capacitor C 41 behind the 6 terminating resistor R18, meet VDC behind the 6 terminating resistor R19, connect again simultaneously the ground that is connected in series to of diode D4, D5, D6, D7,4,7,8,9,10 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 are through choke coil L3 and the collector electrode that meets triode Q4 after resistance R 20 is connected, and 3 ends are through choke coil L3 and the collector electrode that meets triode Q5 after resistance R 21 is connected simultaneously; Between 1,2 ends of U9 after shunt resistor R22 and the capacitor C 39 by 1 terminating resistor R25 to 6 ends, Pdne connecting resistance R30 again series resistors R27 connects 3 ends of U9, the ground connection of connecting after the resistance R 30 that meets simultaneously Pdne and potentiometer resistance R31, resistance R 32, the capacitor C 43 three's parallel connections, 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 with resistance R 29 through diode D10 simultaneously and also arrives ground, and the base stage of Q4 connects the base stage of Q5, and the grounded-emitter connection of Q4, Q5.
8. the anti-polarization decay system of a kind of gas pipeline leakage detecting sensor group according to claim 3, it is characterized in that described light path system is a Michelson interferometer to be installed at a certain distance as the pipe leakage sonic sensor on pipeline, simultaneously the laser that sends of laser by with pipeline laying in one ditch optical cable in an optical fibre 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 the sensor input end, another Shu Jiguang passes to next sensor by launching fiber, by that analogy; Every 2-10 adjacent sensor is divided into one group, and the interference signal of each sensor transfers back to the equipment receiving terminal by combiner device access passback optical fiber in the group; The length of the launching fiber on the pipeline between adjacent two sensors and passback optical fiber all is greater than 1/2 of laser coherent length, and supplying with optical fiber of curtailment prevents from occuring between the sensor signal cross-talk; Each sensor group is used a passback optical fiber, and whole sensing light path only has a launching fiber, and the passback number of fibers is identical with sensor group quantity.
9. the anti-polarization decay system of a kind of gas pipeline leakage detecting sensor group according to claim 3 is characterized in that described signals collecting and puocessing module comprise signal condition unit, signal gathering unit, processing unit, video 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.
10. the anti-polarization decay system of a kind of gas pipeline leakage detecting sensor group according to claim 9 is characterized in that described signal condition element circuit mainly is comprised of operational amplifier U14, photoelectric diode U15; 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, and 1 termination AD_OUT mouth, 2 ends be through resistance R 42 ground connection, the two parallel connection of connecting resistance R40 between 1,2 ends, capacitor C 59.
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