CN105651373A - Two-point synchronous vibration measuring method based on polarization optical time-domain reflection technology - Google Patents
Two-point synchronous vibration measuring method based on polarization optical time-domain reflection technology Download PDFInfo
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- CN105651373A CN105651373A CN201610032900.3A CN201610032900A CN105651373A CN 105651373 A CN105651373 A CN 105651373A CN 201610032900 A CN201610032900 A CN 201610032900A CN 105651373 A CN105651373 A CN 105651373A
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- G01H—MEASUREMENT OF MECHANICAL VIBRATIONS OR ULTRASONIC, SONIC OR INFRASONIC WAVES
- G01H9/00—Measuring mechanical vibrations or ultrasonic, sonic or infrasonic waves by using radiation-sensitive means, e.g. optical means
- G01H9/004—Measuring mechanical vibrations or ultrasonic, sonic or infrasonic waves by using radiation-sensitive means, e.g. optical means using fibre optic sensors
Abstract
The invention discloses a two-point synchronous vibration measuring method based on a polarization optical time-domain reflection technology. The method comprises the steps of: inputting a plurality of continuous optical pulses to obtain back scattering optical signals, performing Fourier transform on the variation of optical intensity of the back scattering signals with time at each position, and finding out the position of a first oscillation point and the frequency of the oscillation point from a frequency spectrum of the back scattering signals; and then calculating a phase of the frequency signal at the position of each optical fiber behind the first oscillation point through a result obtained by the Fourier transform, and positioning a second synchronous vibration signal through the comparison of phase changes. According to the invention, a sensing system does not need to be improved, a simple and basic POTDR sensing system is used to measure the position of the second synchronous vibration point; in the case of multipoint vibration, the position of second synchronous vibration is analyzed for the vibration at each frequency, and no mutual interference exists between the different frequencies; and the method is also suitable for the synchronous vibration with a certain frequency spectrum width.
Description
Technical field
The present invention relates to technical field of optical fiber sensing, particularly a kind of based on the method measuring 2 once per revolution vibrations in polarized light time domain reflection technology.
Background technology
Optical fiber sensing technology is the brand-new technology developed from 20 century 70s, and along with fibre-optic practical and optical communication technique development, optical fiber sensing technology is with the attitude fast development of diversification. When light transmits in a fiber, owing to optical fiber is by the impact of the environmental factors such as external disturbance, temperature, strain, displacement, the parameter such as the polarization state of optical signal, power, wavelength, phase place can change. By these parameters of light in detection fiber, it is possible to obtain the change information of optical fiber surrounding, thus realizing sensing.
When a branch of short light pulse incides optical fiber, it is along spread fiber and is dispersed into all directions, a part of scattering light along fiber-optic transfer and returns to incidence end, and this some scattered light is called that rayleigh backscattering light, back rayleigh scattering light carry sensor fibre along the line by the information of disturbance. It is through in monitoring optical fiber the characteristic of back rayleigh scattering light based on the optical time domain sensing technology of Rayleigh scattering and realizes a kind of sensing technology of distributed sensing.
Polarized light time domain reflection technology be through detection back rayleigh scattering light polarization state realize sensing a kind of optical time domain reflection technology. 1980, Rogers proposed the thought of polarized light time domain reflection technology (POTDR), and its ultimate principle is as shown in Figure 1. The light that laser instrument sends is become pulsed light by after acousto-optic modulator modulation, it is amplified to after certain power through erbium-doped fiber amplifier and is incided testing fiber by circulator, back rayleigh scattering light in transmitting procedure is returned by circulator, by being received by a photoelectric detector after polarization beam apparatus analyzing. When optical fiber is subject to external disturbance, in optical fiber, the polarization state of light will change. Simultaneously as there is back rayleigh scattering when light pulse is transmitted in a fiber, therefore by the change of detector detection backscattering polarization state, the optical fiber information by disturbance just can be obtained.
When transmitting in a fiber due to light, the change of polarization state be have successional. For traditional POTDR method for sensing, first disturbance point can mask the impact of subsequent perturbations for the impact of the polarization state of light in optical fiber, so POTDR measures multipoint disturbance and has certain difficulty. Especially for once per revolution vibration, owing to also cannot be distinguished by once per revolution vibration from frequency domain, so differentiation and location to multiple once per revolution vibration points are the difficult problems needing emphasis to solve in POTDR sensor-based system.
Summary of the invention
The technical problem to be solved is to overcome the deficiencies in the prior art to provide a kind of based on the method measuring 2 once per revolution vibrations in polarized light time domain reflection technology, the present invention is without improving sensor-based system, it is possible to adopt the POTDR sensor-based system on simple basis to measure the position of second once per revolution vibration point; The position of second once per revolution vibration of the vibration of each frequency when multiple spot vibrates, can be analyzed, will not interfere with each other between different frequency.
The present invention solves above-mentioned technical problem by the following technical solutions:
According to the present invention propose a kind of based in polarized light time domain reflection technology measure 2 once per revolution vibrations method, comprise the following steps:
Step one, T injection N group light pulse at the same time in optical fiber, obtain the backward scattered POTDR signal of N group; Backward scattered for this N group POTDR signal every n group continuously in chronological order is done cumulative mean, obtainsPOTDR signal after group is average; Wherein,Interval T comes and goes optical fiber required time, f more than light pulsesFor default measurable peak frequency,For rounding downwards;
Step 2, step one is obtainedPOTDR signal after group is average is sequentially arranged and the alignment of opsition dependent information, obtain the time dependent backscatter signal in each position in optical fiber, time dependent for each position backscatter signal is carried out fast fourier transform FFT process, and try to achieve power spectrum, and then obtain the frequency spectrum of the backscatter signal of each position on optical fiber, from this frequency spectrum, obtain the position L of the vibration in first oscillation point1And the frequency f of vibration;
The coefficient of the frequency content f of each position that step 3, FFT obtain is respectively provided with the form of a+bi, utilizesCalculating obtains the phase place change profile along fiber lengths of the frequency content that frequency is f respectively; Wherein, i represents that imaginary unit, a represent the real part of this frequency content coefficient, and b represents imaginary part;
The phase place change of the frequency content that frequency is f of each position backscatter signal after step 4, first oscillation point of contrast, the position that phase place is undergone mutation is the position of second once per revolution vibration point.
As of the present invention a kind of based on the further prioritization scheme of method measuring 2 once per revolution vibrations in polarized light time domain reflection technology, also including presetting a power threshold, in frequency spectrum step 2 obtained, signal power is rejected less than the point of this power threshold.
As of the present invention a kind of based on the further prioritization scheme of method measuring 2 once per revolution vibrations in polarized light time domain reflection technology, more than described power threshold is more order of magnitude greater than the spectrum power of noise.
As of the present invention a kind of based on the further prioritization scheme of method measuring 2 once per revolution vibrations in polarized light time domain reflection technology, when vibration signal is the wideband vibration with certain spectral range, the frequency spectrum obtained from step 2 selects multiple frequency content, calculate the phase place change along optical fiber each position of each frequency content respectively, finally by the phase place change information cumulative mean of each frequency content, the catastrophe point again through contrast phase place realizes the location to second wideband homogenous frequency signal position.
A kind of based on the method measuring multiple spot once per revolution vibration in polarized light time domain reflection technology, employing said method, by analyzing the position of second once per revolution vibration of the vibration of each frequency, thus measuring multiple spot vibration.
The present invention adopts above technical scheme compared with prior art, has following technical effect that
(1) present invention back scattering optical signal under multiple continuous print light pulses input, then the light intensity of each position backscatter signal is done Fourier transformation over time, from the frequency spectrum of backscatter signal, find the position in first oscillation point and the frequency in this oscillation point; The result obtained again through Fourier's change calculates the phase place obtaining this frequency signal each fiber position after first oscillation point, by contrasting the change of phase place, it is achieved the location to second once per revolution vibration signal;
(2) present invention is without improving sensor-based system, it is possible to adopt the POTDR sensor-based system on simple basis to measure the position of second once per revolution vibration point; The position of second once per revolution vibration of the vibration of each frequency when multiple spot vibrates, can be analyzed, will not interfere with each other between different frequency; Once per revolution vibration for there being one fixed width is equally applicable.
Accompanying drawing explanation
Fig. 1 is the Experimental equipment adopting the method to analyze 2 once per revolution vibrations.
Fig. 2 is the POTDR signal of experiment collection spectrogram after Fourier transformation.
Fig. 3 is the map of magnitudes of the same frequency component of the backscatter signal of each point on optical fiber.
Fig. 4 is the result of the phase information of the once per revolution vibration of extracting directly.
Fig. 5 is the result of the phase information after optimizing.
Fig. 6 be the signal of two frequencies of 10-11HZ phase-accumulated average after result.
Detailed description of the invention
Below in conjunction with accompanying drawing, technical scheme is described in further detail:
Step one, experimental provision as shown in Figure 1 can be adopted, 1000 groups of light pulse signals that interval is 100us are sent by laser instrument, it is the optical fiber of 2400m that light pulse signal is entered total length by 2 mouthfuls after entering circulator, on optical fiber, 1000m place and 2100 meters of have added the vibration of two same frequencys (10-11Hz) respectively, and rear orientation light then by obtaining the transducing signal of 1000 groups of POTDR after an analyzer after circulator 3 mouthfuls. Measurable peak frequency f is preset according to realitysFor 100HZ, according toTaking n=25, pulse interval T=100us comes and goes optical fiber required time more than light pulse simultaneously. Do, by every for these 1000 groups of signals 25 groups, the noise once on average reducing in signal, obtain 40 groups average after signal.
Step 2, by obtain average after 25 groups of signals be sequentially arranged and opsition dependent information alignment, the backscatter signal (interval of change is nT) over time of each point can be obtained, time dependent for each position signal carries out fast Fourier transform (FFT) process, and seek power spectrum, the frequency spectrum of the backscatter signal of each point on optical fiber can be obtained, as shown in Figure 2. Can show that from frequency spectrum the frequency of once per revolution vibration is at about 11Hz. The amplitude of component that frequency is 11HZ is taken out along the distribution of optical fiber and obtains curve S, as shown in Figure 3, it is possible to be accurately positioned out the position in first oscillation point at 1000 meters of.
The coefficient of the frequency content f of each position that step 3, FFT obtain is respectively provided with the form of a+bi, utilizesCalculating obtains the phase place change profile along fiber lengths of the frequency content that frequency is f respectively; Wherein, i represents that imaginary unit, a represent the real part of this frequency content coefficient, and b represents imaginary part;Fig. 4 is the result of the phase information of the once per revolution vibration of extracting directly, without the phase place of the composition of the frequency f of backscatter signal after first oscillation point optimized with the change of fiber position. In sensing at POTDR, optical fiber having some polarization insensitive points and exists, cause that the backscatter signal intensity of these positions and noise signal are on an order of magnitude, therefore the phase place analyzed of these positions is inaccurate.
Step 4, for curve S, we take 0.24 times of the signal maximum in curve S is threshold value, is considered as bad point for signal amplitude in curve S less than the point of this threshold value. The phase place at the phase place of the composition of frequency f bad point place along the distribution of fiber lengths is covered with the phase value of the previous point of bad point. Finally give the phase place of composition of the POTDR signal intermediate frequency rate 11HZ after optimizing along the distribution of optical fiber, it appeared that phase place is held essentially constant after vibrating at first from this curve, the sudden change that phase place occurs after the vibration of second same frequency occurs, follow-up present irregular change, judge that the position of second once per revolution vibration point is near 2100 meters accordingly.
Fig. 5 is after the polarization insensitive point that a selected threshold value filters on optical fiber, the phase place change of the composition of the frequency f of the backscatter signal of each position obtained.
Step 5, repetition said method, obtain the phase place distribution with fiber lengths of the component that frequency is 10HZ, and by the PHASE DISTRIBUTION cumulative mean of 10HZ and 11HZ, the result obtained is as shown in Figure 6.
When measuring multiple spot vibration, by analyzing the position of second once per revolution vibration of the vibration of each frequency, will not interfere with each other between different frequency.
Therefore in POTDR, the method is adopted, it is possible to effectively orienting the position of second same frequency vibration in each oscillation point, measurement POTDR being tested to multiple spot vibration has certain meaning.
Above content is in conjunction with concrete preferred implementation further description made for the present invention, it is impossible to assert that specific embodiment of the invention is confined to these explanations. For general technical staff of the technical field of the invention, without departing from the inventive concept of the premise, it is also possible to make some simple deductions or replacement, protection scope of the present invention all should be considered as belonging to.
Claims (5)
1. one kind based in polarized light time domain reflection technology measure 2 once per revolution vibrations method, it is characterised in that comprise the following steps:
Step one, T injection N group light pulse at the same time in optical fiber, obtain the backward scattered POTDR signal of N group; Backward scattered for this N group POTDR signal every n group continuously in chronological order is done cumulative mean, obtainsPOTDR signal after group is average; Wherein,Interval T comes and goes optical fiber required time, f more than light pulsesFor default measurable peak frequency,For rounding downwards;
Step 2, step one is obtainedPOTDR signal after group is average is sequentially arranged and the alignment of opsition dependent information, obtain the time dependent backscatter signal in each position in optical fiber, time dependent for each position backscatter signal is carried out fast fourier transform FFT process, and try to achieve power spectrum, and then obtain the frequency spectrum of the backscatter signal of each position on optical fiber, from this frequency spectrum, obtain the position L of the vibration in first oscillation point1And the frequency f of vibration;
The coefficient of the frequency content f of each position that step 3, FFT obtain is respectively provided with the form of a+bi, utilizesCalculating obtains the phase place change profile along fiber lengths of the frequency content that frequency is f respectively;Wherein, i represents that imaginary unit, a represent the real part of this frequency content coefficient, and b represents imaginary part;
The phase place change of the frequency content that frequency is f of each position backscatter signal after step 4, first oscillation point of contrast, the position that phase place is undergone mutation is the position of second once per revolution vibration point.
2. according to claim 1 a kind of based on the method measuring 2 once per revolution vibrations in polarized light time domain reflection technology, it is characterized in that, also including presetting a power threshold, in frequency spectrum step 2 obtained, signal power is rejected less than the point of this power threshold.
3. it is according to claim 2 a kind of based on the method measuring 2 once per revolution vibrations in polarized light time domain reflection technology, it is characterised in that more than described power threshold is more order of magnitude greater than the spectrum power of noise.
4. according to claim 1 a kind of based on the method measuring 2 once per revolution vibrations in polarized light time domain reflection technology, it is characterized in that, when vibration signal is the wideband vibration with certain spectral range, the frequency spectrum obtained from step 2 selects multiple frequency content, calculate the phase place change along optical fiber each position of each frequency content respectively, finally by the phase place change information cumulative mean of each frequency content, the catastrophe point again through contrast phase place realizes the location to second wideband homogenous frequency signal position.
5. one kind based in polarized light time domain reflection technology measure multiple spot once per revolution vibration method, it is characterized in that, adopt the method described in any one in claim 1-4, by analyzing the position of second once per revolution vibration of the vibration of each frequency, thus measuring multiple spot vibration.
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| CN106767961A (en) * | 2016-12-20 | 2017-05-31 | 南京大学 | A kind of method and device for eliminating polarized light time domain reflection instrument signal fadeout |
| CN110388948A (en) * | 2019-08-05 | 2019-10-29 | 长飞光纤光缆股份有限公司 | Distributed temperature, vibration while detection sensor based on multi-core optical fiber |
| CN111765960A (en) * | 2020-07-23 | 2020-10-13 | 国网山西省电力公司太原供电公司 | Method for extracting seismic signals of OPGW (optical fiber composite overhead ground wire) optical cable based on distributed optical fiber sensing |
| CN111780857A (en) * | 2020-06-05 | 2020-10-16 | 南京曦光信息科技有限公司 | Multi-point disturbance positioning detection method of P-OTDR system based on harmonic accumulation |
| CN112556823A (en) * | 2020-12-08 | 2021-03-26 | 武汉理工光科股份有限公司 | Oil-gas pipeline cleaner ball-clamping positioning monitoring method and device based on distributed optical fiber sensing |
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Cited By (6)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| CN106767961A (en) * | 2016-12-20 | 2017-05-31 | 南京大学 | A kind of method and device for eliminating polarized light time domain reflection instrument signal fadeout |
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| CN110388948A (en) * | 2019-08-05 | 2019-10-29 | 长飞光纤光缆股份有限公司 | Distributed temperature, vibration while detection sensor based on multi-core optical fiber |
| CN111780857A (en) * | 2020-06-05 | 2020-10-16 | 南京曦光信息科技有限公司 | Multi-point disturbance positioning detection method of P-OTDR system based on harmonic accumulation |
| CN111765960A (en) * | 2020-07-23 | 2020-10-13 | 国网山西省电力公司太原供电公司 | Method for extracting seismic signals of OPGW (optical fiber composite overhead ground wire) optical cable based on distributed optical fiber sensing |
| CN112556823A (en) * | 2020-12-08 | 2021-03-26 | 武汉理工光科股份有限公司 | Oil-gas pipeline cleaner ball-clamping positioning monitoring method and device based on distributed optical fiber sensing |
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