CN102313141A - Optical fiber vibration sensing system for pipeline leakage detection - Google Patents
Optical fiber vibration sensing system for pipeline leakage detection Download PDFInfo
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Abstract
The invention relates to an optical fiber vibration sensing system for pipeline leakage detection, which belongs to the technical field of optical fiber sensing and comprises a light source, a 3*3 optical fiber coupler, a first delay optical fiber, a first 2*2 optical fiber coupler, a second 2*2 optical fiber coupler, a sensing optical fiber, a second delay optical fiber, a third 2*2 optical fiber coupler and an optical detector. The optical fiber vibration sensing system is based on the Sagnac interference principle, the detection sensitivity and the stability of the sensing system are improved through adopting the introduction of fixed phase bias into the 3*3 optical fiber coupler, and the power of light returning the detector is enhanced through adding the optical fiber environment formed by the 2*2 optical fiber couplers, so the signal-to-noise ratio of the detector is improved, and the sensing distance is increased. The optical fiber vibration sensing system has the characteristics that the structure is simple, the sensitivity is high, and the stability is good. The optical fiber vibration sensing system can realize the real-time leakage detection on the transmission pipeline.
Description
Technical field
The invention belongs to technical field of optical fiber sensing, relate to the pipeline leakage testing technology, specifically be meant a kind of distributed optical fiber vibration sensing system whether pipeline is revealed that is used to detect.
Background technique
Traditional pipeline leakage testing technology is difficult to realize in practical application in real time, accurate monitoring.Along with the development of optical fiber sensing technology, the distributing optical fiber sensing technology also progressively is applied to the line leakage field, and it has real-time, highly sensitive, the characteristics that traditional line leakage technology is not had such as is easy to lay.The distributed optical fiber vibration sensing technology is the new technology that development in recent years is got up, and it has made full use of the characteristics that optical fiber self " biography " and " sense " unite two into one.
Distributed optical fiber sensing system is divided into quasi-distributed and complete distributed two big types: quasi-distributed and complete distributed optical fiber sensing system.
The quasi-distributed optical fiber sensed system mainly refers to the sensed system based on Fiber Bragg Grating FBG, and the Chen Zhi of China University Of Petroleum Beijing proposition such as grade and University of Electronic Science and Technology Rao Yun river just utilizes fiber Bragg grating sensor to carry out oil and gas pipes monitoring and optical fiber invasive system.But because on an optical fiber, generally can only be connected in series 15 Bragg gratings; At most can not be above 30; Therefore it is too many for the oil and gas pipes that length reaches tens of kilometers, to detect blind spot, can not realize distributed measurement, can only be called the quasi-distributed optical fiber sensed system.
Fully the distribution type fiber-optic measurement comprises: optical time domain reflection type distributed optical fiber sensing system and based on the optical fiber sensing system of Sagnac (Sagnac) principle of interference.Optical time domain reflection type distributed fiberoptic sensor is that back-scattering light is surveyed; And the backscattering light intensity is very faint; This just requires light source must be that the burst pulse light source of superhigh power (thanks to Kong Li; Rao Yunjiang; Ran Cengling. based on high-power
optical time domain reflectometer optical fiber distributed type sensed system [J] towards the narrow linewidth single mode fiber laser. the optics journal; 2002,28 (3): 569-572.), this has increased the cost of whole system undoubtedly greatly; The detectivity of optical time domain reflection type distributed fiberoptic sensor is very low; Usually need scattered light is carried out weighted mean up to ten thousand times for improving sensitivity; In the weighted mean process; The optical fiber state need remain unchanged, and destruction is a time-varying process, so optical time domain reflection type distributed fiberoptic sensor can not be used for the detection and the location of destruction.In order to overcome the shortcoming of optical time domain reflectometer; Someone has proposed the optical fiber sensing system based on the Sagnac principle of interference; Characteristics based on the optical fiber sensing system of Sagnac principle of interference are that the two-way light walk that interferes is same light path, and therefore less demanding to the coherent length and the Polarization Control of light path, light path structure is simple; Be convenient to adjustment; Structurally have great advantage (E.Udd, Distributed fiber optic strain sensor based on the Sagnac and Michelson interferometers [J] Smart Structures and Materials, 1996:105-110.).But in the various Sagnac optical fiber sensing systems of existing technology bibliographical information; In order to improve the detection sensitivity of system; Usually in light path, adopt piezoelectric constant (PZT) phase-modulator to introduce phase bias (optical fiber is wrapped on the piezoelectric constant, makes optical fiber produce deformation and then generation phase shift offset) through the ceramic piezoelectric effect of PZT.PZT phase-modulator ratio is easier to regulate; But the piezoelectric modulus of piezoelectric constant has small variation in the process of change in voltage; It is certain non-linear that to be elongation have with the variation of voltage; And possibly there is instability in control circuit and optical fiber winding structure, and therefore, there is certain unstability in the phase control of this kind method.In addition, because the PZT phase-modulator needs Control of Voltage, be an Active Device, this has increased the complexity of system architecture undoubtedly and has been unfavorable for reducing cost.
Summary of the invention
The present invention provides a kind of pipeline leak detection to use optical fiber vibration sensing system; This sensed system is to having the improvement based on the optical fiber sensing system of Sagnac principle of interference now, introducing detection sensitivity and stability that stationary phase is setovered and improved sensed system through adopting 3 * 3 FON Fiber Optic Couplers; The optic fibre environment that is made up of 2 * 2 FON Fiber Optic Couplers through increase strengthens the luminous power of return detector, thereby improves signal to noise ratio, the increase distance sensing of prober.Have characteristics simple in structure, highly sensitive, good stability.
Technological scheme of the present invention is following:
A kind of pipeline leak detection is used optical fiber vibration sensing system; As shown in Figure 1, comprise that light source 1,3 * 3 FON Fiber Optic Couplers 2, first postpone optical fiber the 3, the one 2 * 2 FON Fiber Optic Coupler the 4, the 22 * 2 FON Fiber Optic Coupler 5, sensor fibre 6, second postpones optical fiber the 7, the 32 * 2 FON Fiber Optic Coupler 8 and photodetector 9; In 3 * 3 FON Fiber Optic Couplers 2; First input end connects optical fiber 11 through first and links to each other with the output terminal of light source 1; The 3rd input end connects optical fiber 12 through second and links to each other with the input end of photodetector 9; First output terminal postpones optical fiber 3 through first and links to each other with the first input end of the one 2 * 2 FON Fiber Optic Coupler 4, and the 3rd output terminal connects optical fiber 13 through the 3rd and links to each other with second input end of the one 2 * 2 FON Fiber Optic Coupler 4, and second input end and second output terminal are vacant; First output terminal of the one 2 * 2 FON Fiber Optic Coupler 4 links to each other with an end of sensor fibre 6, and the end that the other end of sensor fibre 6 and second postpones optical fiber 7 links to each other, and the other end of the second delay optical fiber 7 links to each other with the first input end of the 32 * 2 FON Fiber Optic Coupler 8; Two output terminal interconnection of the 32 * 2 FON Fiber Optic Coupler 8, its second input end is vacant; In the 22 * 2 FON Fiber Optic Coupler 5, first input end connects optical fiber 14 through the 4th and links to each other with second output terminal of the one 2 * 2 FON Fiber Optic Coupler 4, two output terminal interconnection, and second input end is vacant.
Working principle of the present invention is:
As shown in Figure 1, the outer surface of the sensor fibre in the sensed system along pipe laying in pipeline, during system works, the path of propagation of light has four in the system:
Path a: the light by light source 1 sends is exported by first output port of 3 * 3 FON Fiber Optic Couplers 2 behind the first connection optical fiber, 11,3 * 3 FON Fiber Optic Couplers 2; Then successively through first postpone optical fiber the 3, the one 2 * 2 FON Fiber Optic Coupler 4, sensor fibre 6, second postpones optical fiber 7 back entering the 32 * 2 FON Fiber Optic Coupler 8; Return through the 32 * 2 FON Fiber Optic Coupler 8 again; And postpone optical fiber 3,3 * 3 FON Fiber Optic Couplers 2 and be connected optical fiber 12 with second through the second delay optical fiber 7, sensor fibre the 6, the one 2 * 2 FON Fiber Optic Coupler 4, first successively, finally get into photodetector 9;
Path b: the light by light source 1 sends is exported by first output port of 3 * 3 FON Fiber Optic Couplers 2 behind the first connection optical fiber, 11,3 * 3 FON Fiber Optic Couplers 2; Then successively through first postpone optical fiber the 3, the one 2 * 2 FON Fiber Optic Coupler 4, sensor fibre 6, second postpones optical fiber 7 back entering the 32 * 2 FON Fiber Optic Coupler 8; Return through the 32 * 2 FON Fiber Optic Coupler 8 again; And connect optical fiber 13,3 * 3 FON Fiber Optic Couplers 2 and be connected optical fiber 12 with second through the second delay optical fiber 7, sensor fibre the 6, the one 2 * 2 FON Fiber Optic Coupler the 4, the 3rd successively, finally get into photodetector 9;
Path c: the light by light source 1 sends is exported by the 3rd output port of 3 * 3 FON Fiber Optic Couplers 2 behind the first connection optical fiber, 11,3 * 3 FON Fiber Optic Couplers 2; Then successively through the 3rd connect optical fiber the 13, the one 2 * 2 FON Fiber Optic Coupler 4, sensor fibre 6, second postpones optical fiber 7 back entering the 32 * 2 FON Fiber Optic Coupler 8; Return through the 32 * 2 FON Fiber Optic Coupler 8 again; And connect optical fiber 13,3 * 3 FON Fiber Optic Couplers 2 and be connected optical fiber 12 with second through the second delay optical fiber 7, sensor fibre the 6, the one 2 * 2 FON Fiber Optic Coupler the 4, the 3rd successively, finally get into photodetector 9;
Path d: the light by light source 1 sends is exported by the 3rd output port of 3 * 3 FON Fiber Optic Couplers 2 behind the first connection optical fiber, 11,3 * 3 FON Fiber Optic Couplers 2; Then successively through the 3rd connect optical fiber the 13, the one 2 * 2 FON Fiber Optic Coupler 4, sensor fibre 6, second postpones optical fiber 7 back entering the 32 * 2 FON Fiber Optic Coupler 8; Return through the 32 * 2 FON Fiber Optic Coupler 8 again; And postpone optical fiber 3,3 * 3 FON Fiber Optic Couplers 2 and be connected optical fiber 12 with second through the second delay optical fiber 7, sensor fibre the 6, the one 2 * 2 FON Fiber Optic Coupler 4, first successively, finally get into photodetector 9.
In path a, b, c and d; Have only path b identical with the light path of path d, this two-way light finally interferes at 3 * 3 FON Fiber Optic Couplers, 2 places, and converts optical signal into electrical signal by photodetector 9; Further electrical signal is separated mediation signal conversion again, can confirm the position of leak point.
Detection (location) principle of concrete leakage point can be described as: as shown in Figure 1; If when leakage accident takes place in the L place of pipeline 10; Can cause the vibration at sensor fibre 6 corresponding position P places, thereby cause that the phase place of propagates light changes in the optical fiber, though b is identical with the light path of the two-way light of path d propagation along the path; But they are through the asynchronism(-nization) of oscillating point P; Therefore the phase change of the caused two-way light of oscillating signal is also different, between the two-way light certain phase difference is arranged, and just can confirm the position in oscillating point through the phase change of real-time detection two-way optical interference signal.
In the t moment, the two-way light that b and path d propagate along the path interferes at 3 * 3 FON Fiber Optic Couplers, 2 places, and interference signal is:
Wherein: P
0Be the detection of optical power that light source 1 is sent, τ postpones 3 needed times of optical fiber, i.e. τ=n for surveying light through first
EffL
2/ c (n
EffBe the effective refractive index of optical fiber, c is the light velocity, L
2Be the length of the first delay optical fiber 3); T is that light comes and goes oscillating point P and sensor low order end 8 needed times of the 32 * 2 FON Fiber Optic Coupler, i.e. T=2n
EffX/c (x is the distance of oscillating point P to system's low order end the 32 * 2 FON Fiber Optic Coupler 8), the detection light that 2 π/3 are sent for light source 1 is from the phase difference (phase bias of promptly being introduced by 3 * 3 FON Fiber Optic Couplers) of the two-beam of first and second output terminal output of 3 * 3 FON Fiber Optic Couplers;
Serve as reasons and be applied to the phase change (ω that the vibration source on the sensor fibre 6 causes
sFrequency for vibration source), exist
Be under the situation of small-signal, formula (1) but abbreviation be:
Its AC compounent is:
τ
TPropagate the needed time of one-period for the light that b or path d along the path propagate, τ in sensed system (postpones the length L of optical fiber 3 by first
2Confirm) confirm after, τ
TBe definite value.The amplitude of AC compounent is:
Because oscillating signal is a broadband signal, certainly exist the alternating component P of the feasible output of some frequency components signal
ω s=0, that is:
sin(ω
sτ/2)cos(ω
sT/2)＝0 (5)
Work as ω
sτ/2=N π perhaps
Light intensity is zero when (N is a natural number), and this moment, corresponding frequency was called " zero frequency ".Can know that by formula (5) " zero frequency " exists certain corresponding relation with the position of oscillating point P, promptly just can confirm the position of oscillating point P through seeking " zero frequency ".In addition, sin (ω
sτ/2) item also can influence the signal to noise ratio of sensed system, if sin is (ω
sτ/2) value is smaller, and phase difference also can be less, and signal can be more weak, also just is not easy to extract interference signal.Therefore, should select the L of appropriate length
2, make sin (ω
sτ/2) in the wide frequency range of oscillating signal, keep higher value, to improve the signal to noise ratio of sensor.For the ease of detecting, come oscillating point P is positioned with first " zero frequency ", passing through type (5) can be extrapolated:
By first " zero frequency " of the detected interference signal of prober, just in formula (6), " zero frequency " that when k=1, calculates, derivation can get, and oscillating point P apart from the distance of sensor fibre 6 low order ends the 32 * 2 FON Fiber Optic Coupler 8 is:
Core of the present invention is created point and is:
1, the effect of 3 * 3 FON Fiber Optic Couplers is that (in 3 * 3 FON Fiber Optic Couplers: the phase difference between first output terminal and second output terminal is π/3 to the biasing of introducing stationary phase; Phase difference between second output terminal and the 3rd output terminal is π/3; Phase difference between first output terminal and the 3rd output terminal is 2 π/3), thus guarantee that sensed system has higher sensitivity and stability.
2, two of the 22 * 2 FON Fiber Optic Coupler output terminals directly link to each other, and constitute an optic fibre environment, can promote the luminous power that turns back to photodetector 9, to improve the signal to noise ratio of sensed system.
To sum up, the invention has the beneficial effects as follows: pipeline leak detection provided by the invention is used optical fiber vibration sensing system, introduces detection sensitivity and stability that stationary phase is setovered and improved sensed system through adopting 3 * 3 FON Fiber Optic Couplers; The optic fibre environment that is made up of 2 * 2 FON Fiber Optic Couplers through increase strengthens the luminous power of return detector, thereby improves signal to noise ratio, the increase distance sensing of prober.Have characteristics simple in structure, highly sensitive, good stability.
Description of drawings
Fig. 1 is the structural representation of pipeline leak detection provided by the invention with optical fiber vibration sensing system.Wherein 1 is that light source, 2 is that 3 * 3 FON Fiber Optic Couplers, 3 are that the first delay optical fiber, 4 is that the one 2 * 2 FON Fiber Optic Coupler, 5 is the 22 * 2 FON Fiber Optic Couplers, the 6th, and sensor fibre, 7 is that the second delay optical fiber, 8 is the 32 * 2 FON Fiber Optic Couplers, the 9th, photodetector, the 10th, and measurand (can be pipelines such as gas transmission, oil, water), 11 is that the first connection optical fiber, 12 is that the second connection optical fiber, 13 is that the 3rd connection optical fiber, 14 is the 4th connection optical fiber.
Fig. 2 is by the time-domain diagram of pipeline leak detection provided by the invention with the interference signal that optical fiber vibration sensing system obtained.
Fig. 3 is by the frequency domain figure of pipeline leak detection provided by the invention with the interference signal that optical fiber vibration sensing system obtained.
Embodiment
As shown in Figure 1; Our water pipe replaces petroleum pipeline to test, and the length of testing the used first delay optical fiber 3 is 3km, and the length of sensor fibre 6 is 10km; Water pipe 10 leak L are 7km apart from the horizontal equivalent of sensor fibre 6 low order ends the 32 * 2 FON Fiber Optic Coupler 8; Be oscillating point P apart from the distance of sensor fibre 6 low order ends the 32 * 2 FON Fiber Optic Coupler be 7km, the time-domain diagram for sensing (interference) signal that obtains shown in Figure 2, shown in Figure 3 is that transducing signal shown in Figure 2 is through Fourier transformation; Frequency domain figure behind wavelet transformation and the denoising can see more clearly that first " zero frequency " is positioned at f
NullNear=the 7.158kHz,, get c=3.0 * 10 according to formula (7)
8M/s, n
Eff=1.5, calculating can get x=6985m.Absolute error is 15m, and relative error is 0.2%.
Claims (1)
1. a pipeline leak detection is used optical fiber vibration sensing system, comprises that light source (1), 3 * 3 FON Fiber Optic Couplers (2), first postpone optical fiber (3), the one 2 * 2 FON Fiber Optic Coupler (4), the 22 * 2 FON Fiber Optic Coupler (5), sensor fibre (6), second delay optical fiber (7), the 32 * 2 FON Fiber Optic Coupler (8) and the photodetector (9); In 3 * 3 FON Fiber Optic Couplers (2); First input end connects optical fiber (11) through first and links to each other with the output terminal of light source (1); The 3rd input end connects optical fiber (12) through second and links to each other with the input end of photodetector (9); First output terminal postpones optical fiber (3) through first and links to each other with the first input end of the one 2 * 2 FON Fiber Optic Coupler (4), and the 3rd output terminal connects optical fiber (13) through the 3rd and links to each other with second input end of the one 2 * 2 FON Fiber Optic Coupler (4), and second input end and second output terminal are vacant; First output terminal of the one 2 * 2 FON Fiber Optic Coupler (4) links to each other with an end of sensor fibre (6); The end that the other end of sensor fibre (6) and second postpones optical fiber (7) links to each other, and the other end of the second delay optical fiber (7) links to each other with the first input end of the 32 * 2 FON Fiber Optic Coupler (8); In the 32 * 2 FON Fiber Optic Coupler (8), two output terminal interconnection, second input end is vacant; In the 22 * 2 FON Fiber Optic Coupler (5), first input end connects optical fiber (14) through the 4th and links to each other with second output terminal of the one 2 * 2 FON Fiber Optic Coupler (4), two output terminal interconnection, and second input end is vacant.
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| CN104456088B (en) * | 2014-10-22 | 2017-03-01 | 北京工业大学 | Linear type Sagnac monitoring pipeline safety system based on 3 × 3 bonders |
| CN107991229A (en) * | 2017-11-24 | 2018-05-04 | 冷兴友 | A kind of pipe fitting welding detection vibrations equipment |
| CN110231409A (en) * | 2019-06-21 | 2019-09-13 | 华中科技大学 | A kind of detection method and system of underground piping damage |
| CN110514287A (en) * | 2019-08-19 | 2019-11-29 | 南京邮电大学 | Based on single mode-less fundamental mode optical fibre coupler vibrating sensor |
| CN112066270A (en) * | 2020-09-14 | 2020-12-11 | 贵州电网有限责任公司 | Method and device for monitoring leakage of distributed optical fiber built-in water pipeline |
| CN113188050A (en) * | 2021-03-05 | 2021-07-30 | 华新燃气集团有限公司 | Pipeline cleaner positioning method based on linear Sagnac distributed optical fiber vibration sensing |
| CN114324494A (en) * | 2021-12-07 | 2022-04-12 | 中国科学院物理研究所 | Semiconductor film gas sensor |
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| CN104456088B (en) * | 2014-10-22 | 2017-03-01 | 北京工业大学 | Linear type Sagnac monitoring pipeline safety system based on 3 × 3 bonders |
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| CN114324494A (en) * | 2021-12-07 | 2022-04-12 | 中国科学院物理研究所 | Semiconductor film gas sensor |
| CN114324494B (en) * | 2021-12-07 | 2024-04-09 | 中国科学院物理研究所 | Semiconductor film gas sensor |
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Application publication date: 20120111 |