CN204881836U - Fiber grating earthquake sounds sensing probe - Google Patents

Abstract

The utility model provides a fiber grating earthquake sounds sensing probe, including optic fibre, the low light level bars of warbling, the spring, the quality piece, the low light level bars of warbling, the barrel, spring one end is connected with the quality piece, the other end and the barrel connect, optic fibre one end is glued with the quality piece, and the other end is glued with the barrel. Two gratings of warbling have the same reflectance spectrum, the reflectivity is less than 1% antiradar reflectivity grating to arrange outside the strain sensor workspace, in order to avoid the grating stress influence of originally experiencing.

Description

A kind of fiber grating ground sound sensing probe

Technical field

The utility model relates to sensor technical field, in particular to a kind of fiber grating ground sound sensing probe.

Background technology

Geosound of debris flow refers to that rubble flow is in flow process, and the particle be mingled with can collide with massif on the way, produces the vibration with characteristic frequency, and this vibration is propagated along ditch bank rock and just produced geosound of debris flow.Early warning can be carried out to rubble flow by Monitoring Debris Flow ground sound, strive for the time of preventing and reducing natural disasters to greatest extent, effectively reduce the degree of casualty loss.But the by comparison monitoring of seismic wave, the ground sound intensity that rubble flow produces is low, and decline is fast in the communication process of shallow layer surface, and maximum propagation distance about 100 meters, remarkable frequency is at about 100Hz.Traditional electronic vibration sensor obtains application in geosound of debris flow monitoring, but there is larger difficulty in laying and maintenance.The characteristics such as optical fiber sensing technology has high sensitivity, is easy to multipoint multiplexing, electromagnetism interference, passive remote monitoring, gain great popularity in the vibration monitoring of complex environment.In order to reliable Monitoring Debris Flow ground acoustical signal, require that Fibre Optical Sensor has very high sensitivity (detectable acceleration is less than 0.1g), natural frequency is higher than about 250Hz.In addition, because the source of most of rubble flow has uncertainty with sending out, in order to accurate forecast and outburst and the Evolution Regularity of studying rubble flow, need to lay sensor in a large number in the region that may break out, this multiplexing quantity to sensor, sensitivity, monitoring distance and real-time are proposed very high requirement.Existing " point type " fiber-optic grating sensor fiber grating is fixed on (as semi-girder) in physical construction, vibrating sensing is realized by physical construction conduction, its sensitivity can meet the requirement of geosound of debris flow monitoring substantially, but be difficult to carry out multiplexing on a large scale, not easily lay in wide scope; Distributed Optical Fiber Sensing Techniques is (as optical fiber Brillouin sensing device (BOTDA), fiber Raman sensor (DTS) can meet the requirement of monitoring on a large scale preferably, but the transducing signal detected is weak, need to extract signal by jumbo data processing, real-time is not good.

In order to promote sensitivity and the multiplexing capacity of optical fibre vibration sensor, realize to geosound of debris flow on a large scale, high reliability is monitored, some researchists introduce optical fiber water and listen the sensing solutions of meter (see " Liu Yuliang, He Jun etc. the progress [J] of fiber optic seismic ripple detection. laser and optoelectronics progress .2009, 11:21 ~ 28. "), DFB Fiber laser technology is adopted to convert vibration change the change of wavelength to, this wavelength variations is amplified again by the demodulation of non-equilibrium Michelson fiber-optic interferometer, realize highly sensitive ground sound sensing, but the program needs to inscribe high reflectance grating on Active Optical Fiber, complicated process of preparation, the limited amount of reusable sensor, and system constructing cost is high, rarely has the relevant report in civil area application.Other optical fiber sensing technology, such as optical fiber optical grating Fabry-Perot (FFP) interferometer etc., be difficult to amplify transducing signal in area of light, sensitivity improving is very limited, and system complex, practicality is not strong.Therefore, develop high sensitivity, the by force novel ground sonic transducer of multiplexing capacity and there is significant application value.

Summary of the invention

Technical problem to be solved in the utility model is to provide a kind of fiber grating ground sound sensing probe and system, the advantages such as this apparatus structure is simple, easy to make, highly sensitive, flexible configuration.

The technical scheme that the utility model is taked is:

A kind of fiber grating ground sound sensing probe, comprise optical fiber, spring, mass, cylindrical shell, be provided with spring, mass in cylindrical shell, spring one end is connected with mass, and the spring other end is connected with cylindrical shell; Optical fiber one end and mass cementing, the optical fiber other end and cylindrical shell cementing.

Described optical fiber is inscribed and has the first chirp grating, the second chirp grating, described first chirp grating, the second chirp grating are positioned near the cementing point of optical fiber, outside strain sensing workspace.

Described first chirp grating, the second chirp grating have identical reflective spectral property, and reflectivity is lower than 1%.

Distance between mass top to inner barrel end face is L, changes the distance L between described mass and described cylindrical shell, can change the sensitivity of sensing probe.

A kind of fiber grating ground sound sensor-based system, comprise LASER Light Source, electrooptic modulator, optical circulator, Transmission Fibers and a kind of ground sound sensing probe, the first port of described optical circulator connects LASER Light Source; Second port of optical circulator connects Transmission Fibers; Described Transmission Fibers is connected in series multiple described ground sound sensing probe; 3rd port of optical circulator connects described photodetector; The data collecting card that photodetector is changed with band A/D is connected; First port of described time delay module connects electrooptic modulator; Second port of time delay module connects the external trigger port of described data collecting card; Described computing machine is connected with the control port of time delay module; Computing machine is connected with the output port of data collecting card.

The operation wavelength of described LASER Light Source is positioned at the reflectance spectrum scope of the chirp grating of described ground sound sensing probe.

The method for sensing of a kind of fiber grating ground sound sensor-based system, the continuous light of light source is after electrooptic modulator modulation, form light pulse, light pulse enters optical circulator, enter described ground sound sensing probe again, form the interference pulse signal of reflection in each probe positions, then enter photodetector through optical circulator, the change of light signal is converted to the change of electric signal.Time delay module trigger data acquisition card gathers, and send the digital signal containing phase place change information to computing machine, computing machine calls phase demodulation algorithm, and the phase place change of discriminating digit signal, demodulates Vibration Parameter.

Described ground sound sensing probe is connected in series by optical fiber, described time delay module produces the controlled pulse of two-way time delay, drive described electrooptic modulator and described data collecting card, carry out difference acquisition and processing based on the time delay difference of diverse location Shangdi sound sensing probe reflection coherent pulse light signal on single fiber, realize multiple spot time division multiplex.

A method for sensing for fiber grating ground sound sensor-based system, is applied to rubble flow monitoring.

Work and the principle of multiplexing of fiber grating ground sound sensor-based system are as follows:

The light that LASER Light Source sends is injected into single fiber Michelson interference sensor through circulator, assuming that chirp grating (2) and chirp grating (6) reflection coefficient are R ₀, the light intensity of laser is I ₀, then chirp grating (2) reflected light is I ₀* R ₀, transmitted light is I ₀* (1-R ₀).When transmitted light incides on chirp grating (6), the intensity of reflected signal is I ₀* (1-R ₀) * R ₀, reflected signal by the intensity after chirp grating (2) is: I ₀* (1-R ₀) ²* R ₀.Then the intensity ratio of chirp grating (2) and chirp grating (6) two bundle back light is: 1:(1-R ₀) ².

For reflectivity lower than 1% low light level grid, the multiple reflections between two gratings is very limited on the impact of interference fringe, can be approximated to be constant power two-beam.Two-beam is the reflected light of same LASER Light Source, has the identical direction of propagation and stable phase differential, therefore can produce two-beam interference, meet the condition of Michelson interference, therefore have:

I _D≈2R ₀*I ₀*{1+cos[4πn _effL/λ+φ _r]}(1)

In formula, I _dfor the light intensity of two-beam interference, L is the distance between two gratings, φ _rit is the phase differential between two gratings.When optical fiber between two gratings is subject to external disturbance, the phase differential change △ φ of interference signal:

$\mathrm{\Δ}\mathrm{\φ}\≈\frac{4\mathrm{\π}}{\mathrm{\λ}}n\mathrm{\Δ}L\≈\frac{4\mathrm{\π}}{\mathrm{\λ}}n*L*0.78*\mathrm{\Δ}\mathrm{\ϵ}---\left(2\right)$

From formula (2), after the wavelength of light source is determined, the interferometric phase variation factor of two beam interferometer light is directly related with grating space L.Grating distance is longer, and the sensitivity of phase place change is higher.Research shows, the phase place of common grating is changed to:

${\mathrm{\Δ\φ}}_{FBG}\≈\frac{4\mathrm{\π}}{\mathrm{\λ}}n*d*0.78*\mathrm{\Δ}\mathrm{\ϵ}---\left(3\right)$

In formula, d is the length of grating.The length of most of grating at several millimeter, and Distance Theory between Michelson interference sensor two gratings is determined by the coherent length of LASER Light Source.Comparison expression (2) and (3) known, under same strain parameter, the remolding sensitivity monochromatic light grid height L/d of single fiber Michelson interference sensor is doubly.Such as, assuming that the length of grating is 6mm, the brachium L of Michelson interference sensor is 180mm, then the sensitivity of system can improve 30 times!

When the ground sound sensing probe of reality makes, in order to ensure grating itself by the impact of stress, thus cause phase place variation error, beyond stress workspace grating being encapsulated in respectively optical fiber.In addition, according to the requirement of different geosound of debris flow, can improve the length of sensing probe physical construction, between flexible grating, stress burst length L changes the sensitivity of probe.

Multiplexing for Multi probe, low light level grid time-division multiplex technology can be adopted, namely select the weak preparing grating probe of warbling of co-wavelength, multiple probe is connected in series successively.When vibration monitoring, time delay module produces the pulse of two-way time delay programmable regulating, drive described electrooptic modulator and described data collecting card respectively, the coherent pulse light signal time delay reflected due to the ground sound sensing probe on diverse location is different, by regulating the time delay value of time delay module, capture card is triggered when target probe reflected signal arrives, and capture card gathers current demand signal and processes, and the signal of other positions probe reflection will be isolated.Based on the method, by preset different time delay value, the vibration signal of each probe can be detected successively, realize multi-probe time division multiplex.And the extraction of preset time delay value, can when system electrification, by the scanning to whole fibre circuit, the intensity location in conjunction with optical grating reflection signal obtains and preserves, without the need to human configuration.The multiplexing capacity of system is directly related with selecting the reflectivity of grating, such as, selects the preparing grating of reflectivity 1% to pop one's head in, and its multiplexing quantity can be suitable with the wavelength division multiplex scheme (WDM) of traditional high reflectance grating.When optical grating reflection rate drops to 0.01%, single operation window reusable 500 sensing probes.Therefore, the sensor-based system of this utility model both can realize highly sensitive sensing, again can according to the requirement of concrete monitoring target or application scenarios, and the parameter such as reflectivity, time delay of adjustment grating, realizes the multiplexing on a large scale of sensing probe, have splendid adaptability.

Compared with prior art, the beneficial effects of the utility model are:

1, interference structure is simple, highly sensitive.Adopt typical piston type vibrating sensing structure, in an optical fiber, realize double grating interfere, turn process without the need to carrying out special envelope to grating, physical arrangement is simple; Utilize the Michelson interference of weak chirped grating reflection light, remolding sensitivity monochromatic light grid height L/d doubly.

2, low light level grid manufacture craft is ripe.Antiradar reflectivity chirp grating directly can be prepared on ordinary optic fibre, is especially applicable to wire-drawer-tower technique and makes grating, only need require to carry out grating inscription according to line space design in fiber drawing process, be easy to suitability for industrialized production;

3, system flexibility is strong, can according to application scenarios flexible configuration.Namely the sensitivity of probe according to concrete application scenario flexible design, can design different grating space length to regulate the sensitivity of interferometer; Multiplexing quantity of popping one's head in can be expanded by regulating the reflectivity of grating, and segmentation continues; The position of probe also can be selected arbitrarily, without the need to specific installation.

Accompanying drawing explanation

Fig. 1 is the structural representation adopting double grating to form the utility model sensing probe;

Fig. 2 is the structural drawing adopting the utility model sensor to form time division multiplex sensor-based system;

In figure: 1-optical fiber, the 2-the first chirp grating, 3-spring, 4-mass, 5-cylindrical shell, the 6-the second chirp grating, 7-LASER Light Source, 8-electrooptic modulator, 9-optical circulator, 10-Transmission Fibers, 11-ground sound sensing probe, 12-photodetector, 13-data collecting card, 13-time delay module, 14-computing machine.

Embodiment

Below in conjunction with accompanying drawing, specific embodiment of the utility model is described in further detail:

Fiber grating ground of the present utility model sound sensing probe structure as shown in Figure 1, comprises optical fiber 1, the first chirp grating 2, spring 3, mass 4, the second chirp grating 6, cylindrical shell 5.Mass 4 is suspended from cylinder inboard wall, and cylindrical shell 5 center top is provided with entrance hole, and optical fiber 1 is introduced by the entrance hole of cylindrical shell 5, and after mass 4, the leadout hole that the other end is offered at the bearing of cylindrical shell 5 is drawn.Spring 3 one end is connected with mass 4, and spring 3 other end is connected with cylindrical shell 5; Optical fiber 1 one end and mass 4 cementing, optical fiber 1 other end and cylindrical shell 5 cementing.

First chirp grating 2, second chirp grating 6 is low light level grid of warbling.Chirp grating has wider reflectance spectrum, can guarantee not by the impact of the factors such as temperature, to the usable reflection of incident laser under complex environment; Low light level grid have strong time division multiplex ability, and the convenient probe made carries out multiplexing on a large scale according to actual needs.

Optical fiber 1 is inscribed the first chirp grating 2, second chirp grating 6, first chirp grating 2, second chirp grating 6 and have identical reflective spectral property, reflectivity is the distance between 0.1%, two gratings is 180mm.The sensitivity of geosound of debris flow detection requirement sensing reaches 0.1g, close to the lower limit of common grating sensor, the distance designed between two gratings is 180mm, and sensitivity can promote 30 times (about 14dB), geosound of debris flow detection requirement can be met preferably, and there is preferably economy.

First chirp grating 2, second chirp grating 6 is positioned near the cementing point of optical fiber, outside strain sensing workspace, to avoid the affected by force of grating own, thus produces uncertain impact to phase place change.

A kind of fiber grating geosound of debris flow time division multiplex sensor-based system of the present utility model as shown in Figure 2, comprise LASER Light Source 7, electrooptic modulator 8, optical circulator 9, Transmission Fibers 10, ground sound sensing probe 11, photodetector 12, with the data collecting card 13 of A/D conversion, time delay module 14, computing machine 15.First port of optical circulator 9 connects LASER Light Source 7; Second port of optical circulator 9 connects Transmission Fibers 10; Transmission Fibers 10 is connected in series multiple ground sound sensing probe 11; 3rd port of optical circulator 9 connects states photodetector 12; The data collecting card 13 that photodetector 12 is changed with band A/D is connected; First port of time delay module 14 connects electrooptic modulator 8; The external trigger port of the second port connection data capture card 13 of time delay module 14; Computing machine 15 is connected with the control port of time delay module 14; Computing machine 15 is connected with the output port of data collecting card.

When the transducer system equipment of this utility model runs, narrow-linewidth laser light source sends the continuous light power signal of about 10dBm, and the operation wavelength of LASER Light Source 7 is positioned at the reflectance spectrum scope of the first chirp grating 2, second chirp grating 6.The continuous light of light source is adjusted after 8 systems through electrooptic modulator, form the light pulse being greater than 50ns, light pulse enters optical circulator 9, enter ground sound sensing probe 11 again, the interference pulse signal of reflection is formed in each probe positions, photodetector 12 is entered again through optical circulator 9, the change of light signal is converted to the change of electric signal, now, trigger data acquisition card 13 after time delay gathers, and change into digital signal and send computing machine 15 to, computing machine 15 calls PGC phase demodulation algorithm, the phase place change of discriminating digit signal, demodulates Vibration Parameter.

Ground sound sensing probe 11 is connected in series by optical fiber, described time delay module 14 produces the pulse of two-way time delay programmable regulating, drive described electrooptic modulator 8 and described data collecting card 13, time delay difference based on diverse location Shangdi sound sensing probe reflection coherent pulse light signal carries out difference acquisition and processing, realizes multiple spot time division multiplex.

Time delay module 14 etc. involved by the utility model, has had application in optical time domain reflection, large-capacity fiber grating sensing field, and the correlation technique of phase demodulation modules, listen in meter etc. at water and obtain widespread use.Just enumerate part implementation at this, concrete describing is not done to the detail characteristic of module again.

Core of the present utility model is the feature for geosound of debris flow monitoring, introducing is warbled the highly sensitive sensing probe of low light level grid Michelson interference fabrication techniques, and in conjunction with the stronger time division multiplex ability of low light level grid, structure can the fiber Bragg grating sensor network laid of multiplexing, wide area on a large scale, has a good application prospect.

Claims (3)

1. a fiber grating ground sound sensing probe, comprise optical fiber (1), spring (3), mass (4), cylindrical shell (5), spring (3), mass (4) is provided with in cylindrical shell (5), it is characterized in that, spring (3) one end is connected with mass (4), and spring (3) other end is connected with cylindrical shell (6); Optical fiber (1) one end and mass (4) cementing, optical fiber (1) other end and cylindrical shell (6) cementing; The upper inscription of described optical fiber (1) has the first chirp grating (2), the second chirp grating (6), and described first chirp grating (2), the second chirp grating (6) are positioned near the cementing point of optical fiber, outside strain sensing workspace.

2. a kind of fiber grating ground sound sensing probe according to claim 1, is characterized in that: described first chirp grating (2), the second chirp grating (6) have identical reflective spectral property, and reflectivity is lower than 1%.

3. fiber grating ground according to claim 1 sound sensing probe, it is characterized in that: the distance between mass (4) top to cylindrical shell (5) inside top surface is L, change the distance L between described mass (4) and described cylindrical shell (5), the sensitivity of sensing probe can be changed.