CN102156213A - Fiber bragg grating current measurement method based on birefrigent effect - Google Patents

Abstract

The invention discloses a fiber bragg grating current measurement method based on birefrigent effect, belonging to the technical field of sensors and measurement. Devices used for the method comprise a broadband light source (11), a fiber coupler (12), a sensing fiber bragg grating (13), a support optical fiber (20), a permanent magnet (14), silicon slices (15 and 16), a magnet coil (17), a support (18), a drive current control unit (19), a spectrometer (19), a spectrometer (21) a spectrum analyzing unit (22) and an output and display unit (23). The method has the characteristics that the current measurement is realized on the basis of the principle that the sensing fiber bragg grating generates the birefrigent effect under the action of radial electromagnetic force so as to present two reflectance spectrums with different polarization states and the difference of the central wavelengths of the two reflectance spectrums is in direct proportion to the radial electromagnetic force; and as the differential measurement method is adopted, the temperature crossing sensitive problem of the fiber bragg grating sensing signals is solved.

Description

A kind of fiber Bragg grating current measuring method based on birefringence effect

Technical field

The present invention relates to a kind of fiber Bragg grating current measuring method, belong to sensor and field of measuring technique.

Background technology

Current measurement techniques is in electric system and electronic technology field has a wide range of applications and important meaning.At present, the research of current measurement techniques has been become one of focus, and wherein provide solution preferably for current measurement based on the current sense technology of optical fiber.

The physical influence of fibre optic current sensor institute foundation has a variety of, mainly contains electromagnetic induction, Faraday magnetooptical effect, thermal effect (temperature mode), inverse piezoelectric effect, magnetic-type, magnetostrictive effect etc.Fibre optic current sensor based on electromagnetic induction adopts traditional current transformer or hollow mutual inductor (Rogowski coil) sampling transmission line choke, utilize the active device modulation technique, with optical fiber as signalling channel, the light signal of high-pressure side conversion is passed to ground carry out signal Processing, thereby obtain the device of measured signal.Since still adopt the conventional current sensor to make sensing head in the system, can only be as a kind of transition scheme of electromagnetic type current sensor to full optical fibers current sensor.

(Min-Cheol Oh, Jun-Kyu Seo, Kyung-Jo Kim, Hoon Kim, Jun-Whee Kim, and Woo-Sung Chu, Optical current sensors consisting of polymeric waveguide components, JOU RNAL OF LIGHTWAVE TECHNOLOGY, 28 (12), 2010) proposition is to work as linearly polarized light by being in the homogeneous isotropic medium in the external magnetic field based on the current sensor of Faraday magnetooptical effect, and when the direction of propagation of light is consistent with outer magnetic field direction, the effect that the linear polarization polarization surface will rotate.

Based on the fibre optic current sensor of thermal effect (temperature mode), inverse piezoelectric effect, magnetic-type, magnetostrictive effect all is because the effect of electric current makes optical fiber or fiber grating is stressed or produce displacement (length changes) essentially, thereby the principle of utilizing fibre optic interferometer principle or fiber grating to detect strain or temperature realizes the detection of electric current.

The heat that thermal effect (temperature mode) fibre optic current sensor is based on the electric current generation makes the optical fiber thermal expansion, and length increases; The inverse piezoelectric effect fibre optic current sensor is that it will produce deformation when adding certain voltage to piezoelectric ceramics, from but fiber lengths increase.More than two kinds of principles all can constitute interference-type optical fiber current sensor or fiber Bragg grating current sensor respectively.

The Fibre Optical Sensor that utilizes magnetic force to detect electric current can be divided into two classes, one class is (Heredero R L, De Caleya R F, Guerrero H, et al.Micro-machined optical fiber current sensor.APPLIED OPTICS, 38 (25), 1999) magnetic force that proposes produces displacement, make the changing of interference cavity long hair of optical fiber FP interference sensor, thereby realization current detecting, another kind of is (Yong Zhao, Qing-yao Meng, Kun Chen.Novel current measurement method based on fiber Bragg grating sensor technology.SENSORS AND ACTUATORS A:PHYSICAL, what 126,2006) propose makes the ferromagnetic material that is in the magnetic field be subjected to that magneticaction is moved or deformation based on surveying magnetic field that electric current produces, causes fiber grating to produce strain, influence the fiber grating reflectance spectrum, thereby electric current is detected.The direction that this fiber Bragg grating current sensor applies electromagnetic force is axial along fiber grating, makes the skew of fiber grating reflection wavelength.

The magnetostrictive effect fibre optic current sensor generally is fixed on optical fiber on the magnetostriction materials, and magnetostriction materials place magnetic field.Magnetostriction materials are flexible to change fiber lengths, thereby the light path in the optical fiber changes, and causes the variation of light phase, utilizes the interferometric method detected phase to change and can measure by measuring magnetic field, and then can get tested current value.Perhaps (Deborah Reilly, Andrew J.Willshire, Grzegorz Fusiek, Pawel Niewczas, and James R.McDonald, A fiber-Bragg-grating-based sensor for simultaneous AC current and temperature measurement, IEEE SENSORS JOURNAL, 6 (6), 2006) propose to make and be fixed on that fiber grating is stretched on the magnetostriction materials, by detection fiber grating reflection wavelength amount of movement, can obtain the size of tested electric current.The shortcoming of this type optical fiber current sensor is owing to adopt direct bonding method, so there is load effect in the location for paste, and along with the increase of electric current, hysteresis effect can occur, is difficult to overcome.

Summary of the invention

The objective of the invention is to not only in order to overcome the weak point of prior art, have also that cost is low, the simple advantage of signal demodulating method, simultaneously, also solved the temperature cross sensitivity problem of fiber-optic grating sensor measuring-signal.

Technical scheme of the present invention is as follows:

A kind of current measuring method, mainly comprise a fiber grating radial load sensing unit, the electromagnetic force generation device, light source, fiber coupler, spectrometer, spectroscopy unit, output and display unit, it is characterized in that: described current measuring method mainly is to utilize a sensor fibre grating to realize the radial load measurement, described fiber grating radial load sensing unit is by a sensor fibre grating, one section support optical fiber and up and down two silicon chips with smooth surface form, optical fiber is parallel is placed between two silicon chips for described sensor fibre grating and support; Described electromagnetic force generation device is by a permanent magnet, a support and a drive current controller of twining solenoid is formed, described permanent magnet be fixed on go up in described up and down two silicon chips silicon chip above, the support that is wound with solenoid be fixed on lower silicon slice below, described drive current controller links to each other with solenoid by lead; Described light source links to each other with sensor fibre grating one end by described fiber coupler, output terminal through fiber coupler after the measuring-signal of sensor fibre grating reflects through self links to each other with spectrometer, the output signal of spectrometer is sent to spectroscopy unit by signal wire, is further handled by output and display unit.

Of the present inventionly utilize sensor fibre grating to realize that radial load measures, be to utilize the sensor fibre grating to produce birefringence effect under the radial electromagnetic force effect and two reflectance spectrums with different polarization states occur, the principle that the difference of these two reflectance spectrum centre wavelengths is directly proportional with radial electromagnetic force realizes.

Technical characterictic of the present invention also is: the described timbering material that is wound with solenoid is plastics, and is interior through being of a size of 15mm, highly is 100mm.Described one section material, diameter and sensor fibre grating that supports optical fiber is identical, and removes their surface coating layer.

The present invention has following characteristics: 1. adopted the differential wave disposal route, avoided the temperature cross sensitivity problem of fiber grating measuring-signal; 2. signal transmission attenuation is low, and is undistorted, is fit to telemeasurement; 3. measuring sonde part electrical isolation, the security of system are good.

Description of drawings

Fig. 1 is the fiber Bragg grating current measuring principle synoptic diagram based on birefringence effect provided by the invention.

Fig. 2 is not tested simultaneously electric current of coil turn and FBG output wavelength difference graph of a relation in the electromagnetic force generation device of the present invention.

Fig. 3 is not tested simultaneously electric current of air gap and FBG output wavelength difference graph of a relation in the electromagnetic force generation device of the present invention.

Fig. 4 is not tested simultaneously electric current of solenoid area and FBG output wavelength difference graph of a relation in the electromagnetic force generation device of the present invention.

Tested electric current and the sensor fibre grating wavelength difference graph of relation of Fig. 5 for utilizing the present invention to realize after the selecting system parameter.

The sensor fibre optical grating reflection spectrum change figure when tested electric current changes that Fig. 6 utilizes the present invention to realize.

(a) measured current I=0

(b) measured current I=0.3A

(c) measured current I=0.5A

Embodiment

The fiber Bragg grating current measuring method that the present invention proposes, accompanying drawings is as follows:

The fiber Bragg grating current measuring system as shown in Figure 1, sensor fibre grating and one section support optical fiber and are placed on (benefit of doing like this is to make that the sensor fibre grating is stressed evenly) between two silicon chips at a certain distance, two optical fiber have identical materials and diameter.Being equipped with permanent magnet on last silicon chip, is the support that is wound with solenoid below the lower silicon slice.The light of wideband light source output is sent to the sensor fibre grating through coupling mechanism, and the light signal with specific reflection wavelength is received by spectroanalysis instrument by coupling mechanism.When not applying tested electric current, spectroanalysis instrument can only monitor the light signal with a reflection peak.When tested electric current is applied in the solenoid, coil current will produce magnetic field, and permanent magnet is subjected to the electromagnetic force effect in magnetic field, and the optical fiber under it is produced radial load, make the sensor fibre grating produce radial strain, i.e. birefringent phenomenon.Because on mutually orthogonal both direction, the result of linear birefringence effect makes the sensor fibre grating produce two reflection peaks, and along with the increase that adds tested electric current, electromagnetic force increases, the birefringence effect that the sensor fibre grating of pressurized produces is more obvious, causes the reflectance spectrum of two kinds of orthogonal polarisation state to be separated from each other all the more.By detection to the wavelength separated amount, promptly, can learn the size of tested electromagnetic force by detecting the poor of two orthogonal polarisation state reflected light crests, because electromagnetic force and electric current to be measured have definite corresponding relation, thereby realized measurement to electric current.

According to the fiber mode theory as can be known, under temperature-resistant situation, when having only radial force to act on optical fiber, it (is the wavelength difference detection method owing to what finally adopt, so even there is axial strain in fact, that the axial stress of optical fiber is assumed to be zero, also can in measurement result, be eliminated), at this moment, will cause the additional birefringent phenomenon of optical fiber, be exactly that this birefringent phenomenon has caused two kinds of additional orthogonal polarization modes.Therefore, if on a fiber grating, apply radial load, will cause the separation of the reflectance spectrum of two kinds of polarization states.The difference of the polarization mode wavelength separated amount of these two quadratures can be expressed as:

${\mathrm{\&Delta;\&lambda;}}_{B,y}-{\mathrm{\&Delta;\&lambda;}}_{B,x}=\frac{\mathrm{F\&Lambda;}}{\mathrm{\&pi;}{\mathrm{RE}}_1{L}_1}\left\{{\mathrm{<figure-callout\; id="0"\; label="n"\; filenames="HSA00000457862600012.png"\; state="\{\{state\}\}">n</figure-callout>}}_{0,x}^3\right[p_{12}(3-v_1)-p_{11}(1+{3v}_1)]-n_{0y}^3[p_{11}(3+v_1)-p_{12}(1+{5v}_1)\left]\right\}---\left(1\right)$

In the formula, Λ is the grating cycle, and F is for being L along length ₂The external force of optical fiber effect, R is the radius of fibre cladding, n _{0, x}And n _{0, y}Be respectively the initial effective refractive index on two orthogonal directionss, p ₁₁And p ₁₂Elasto-optical coefficient for optical fiber; E ₁And v ₁Be respectively the Young's modulus of elasticity and the Poisson ratio of optical fiber.

As seen the amount of movement difference of the wavelength under two polarization states of fiber grating is directly proportional with radial load.

Because electric current can produce magnetic field, size of current and magnetic field exist corresponding relation, and permanent magnet can produce electromagnetic force under the action of a magnetic field, if can convert the variation of electric current to be measured to electromagnetic force by certain device, and this power radially is applied on the fiber grating, then can utilize above-mentioned principle to realize the measurement of electric current.Concrete scheme that this paper proposes and structure are as shown in Figure 1.Wherein, constitute spiral tube structure by solenoid and permanent magnet, the energising back produces magnetic flux in magnetic circuit, and to permanent magnet generation electromagnetic attraction, permanent magnet is under the electromagnetic attraction effect, direction along the magnetic line of force moves a little distance, and working gas gap is reduced, thereby produces mechanical motion trend.At this moment electromagnetic attraction F can be tried to achieve by energy equilibrium, as shown in Equation (2)

$F=\frac{{\mathrm{dW}}_m}{\mathrm{d\&delta;}}---\left(2\right)$

In the formula, d δ is the distance that permanent magnet moves under electromagnetic attraction F effect, dW _mIt is the variable quantity that is stored at magnetic energy in the magnetic system.

Ignore the fringing of magnetic flux on the air gap, and notice that the displacement of permanent magnet has only changed the magnetic energy of storing in the air gap, writes out:

$W_m=\frac{1}{2}{\mathrm{\&mu;}}_0{H}^2\mathrm{s\&delta;}=\frac{1}{2}{\mathrm{\&mu;}}_0{\left(\frac{\mathrm{\&Psi;}}{s{\mathrm{\&mu;}}_0}\right)}^2\mathrm{s\&delta;}=\frac{1}{2}\frac{{\mathrm{\&Psi;}}^2\mathrm{\&delta;}}{{\mathrm{s\&mu;}}_0}---\left(3\right)$

In the formula, H is the magnetic field intensity of air-gap field,

Ψ is the air-gap flux amount, and s is the cross-sectional area of air gap, can simplify and think solenoid cross-sectional area, μ ₀Be the magnetic permeability in the vacuum, W _mBe the magnetic energy of air gap, δ is the distance that air gap reduces.

Then according to formula (3), formula (2) can be written as:

$F=\frac{{\mathrm{dW}}_m}{\mathrm{d\&delta;}}=\frac{1}{2}\frac{{\mathrm{\&Psi;}}^2}{{\mathrm{s\&mu;}}_0}---\left(4\right)$

According to the magnetic circuit correlation theorem, the pass that can get air gap magnetic flux Ψ and electric current is

$\mathrm{\&Psi;}\&ap;\frac{{\mathrm{\&mu;}}_0\mathrm{NIs}}{\mathrm{\&delta;}}---\left(5\right)$

In the formula, N is a coil turn.

Then convolution (4) and formula (5) can get electromagnetic attraction and be:

$F=\frac{1}{2}\frac{{{\mathrm{\&mu;}}_{0}s\left(\mathrm{NI}\right)}^2}{{\mathrm{\&delta;}}^2}---\left(6\right)$

After obtaining the expression formula of electromagnetic attraction, promptly set up the relation of electromagnetic attraction and electric current to be measured.Like this, with formula (6) substitution formula (1), get final product the wavelength difference of two polarization states of fiber grating and the relation of electric current, as shown in the formula:

$\mathrm{\&Delta;\&lambda;}=\frac{{\mathrm{\&mu;}}_0{\mathrm{sN}}^2{I}^2}{{2\mathrm{\&delta;}}^2{L}_2}\frac{\mathrm{\&Lambda;}}{\mathrm{\&pi;}{\mathrm{RE}}_1}\left\{{\mathrm{<figure-callout\; id="0"\; label="n"\; filenames="HSA00000457862600012.png"\; state="\{\{state\}\}">n</figure-callout>}}_{0,x}^3\right[p_{12}(3-v_1)-p_{11}(1+{3v}_1)]-{\mathrm{<figure-callout\; id="0"\; label="n"\; filenames="HSA00000457862600012.png"\; state="\{\{state\}\}">n</figure-callout>}}_{0,y}^3[p_{11}(3+v_1)-p_{12}(1+{5v}_1)\left]\right\}---\left(7\right)$

Wherein, note wavelength difference Δ λ=Δ λ _{B, y}-Δ λ _{B, x}For specific device, s, N, δ, L ₂Be constant, under the known situation of optic fibre characteristic parameter, Δ λ ∝ I as can be known then ²When electric current passed through, the electromagnetic force that solenoid produces made the sensor fibre grating be subjected to the radial stress effect, and pairwise orthogonal reflection of polarization wavelength separated amount increases.Strength of current is big more, and fractional dose is many more, therefore utilizes electromagnetic force that sensor fibre grating wavelength branch deviation is changed, and can come the size of sensory current intensity.

Known permeability of vacuum μ ₀=4 π * 10 ^-7H/m, sensor fibre grating periods lambda=0.5355 μ m, the radius R of fibre cladding=62.5 μ m, the Young's modulus of elasticity E of optical fiber ₁=7 * 10 ¹⁰Pa, the effective refractive index n that fibre core is initial _Eff=1.43, the elasto-optical coefficient p of optical fiber ₁₁=0.121, p ₁₂=0.270, the Poisson ratio v of optical fiber ₁=0.17.

Below some structural parameters in the measuring system are done simulation analysis to the influence of measurement characteristics.

If s=10 ^-4m ², δ=2 * 10 ^-3M, L ₂=1.5 * 10 ^-2M.

As shown in Figure 2, when the solenoid number of turn less relatively (N=900), electric current changes the electromagnetic force effect that causes, and that sensor fibre grating two polarization state reflection wavelengths are separated is not obvious.Increase with the solenoid number of turn, the electromagnetic force effect increases thereupon, and two polarization state reflection wavelengths move difference to be increased gradually.But when the number of turn increased, the solenoid volume can increase thereupon, and manufacture craft also can corresponding complexity, and the electric current energy consumption increases.Therefore, compromise is considered, selected number of turn N=1500.

Determining to select parameter s=10 under the N=1500 situation ^-4m ², L ₂=1.5 * 10 ^-2M.As shown in Figure 3, when the number of turn certain (N=1500), by the height of adjusting air gap electromagnetic force is increased, the effect of wavelength separated is more obvious, can also continue to increase simultaneously current measurement sensitivity.But the height that reduces air gap also can increase the difficulty of manufacture craft.In conjunction with actual conditions, width of air gap is δ=10 ^-3Do not consider when m is following.Select easily δ=1.5 * 10 of realization ^-3M.

Determining under the N=1500 situation δ=1.5 * 10 ^-3M, L ₂=1.5 * 10 ^-2M.As shown in Figure 4, in the number of turn certain (N=1500) and certain (δ=1.5 * 10 of air gap ^-3M) time, by adjusting the solenoid area electromagnetic force is increased, thereby the wavelength separated amount is increased.This kind method more easily realizes, again in conjunction with actual conditions, so select s=3.14 * 10 ^-4m ²

Because the length L of optical fiber in magnetic field ₂Variation range is little, and is not obvious to the influence of electromagnetic force size, so do not consider as adjustable parameters.

To sum up, select parameter: N=1500, s=3.14 * 10 ^-4m ², δ=1.5 * 10 ^-3M, L ₂=1.5 * 10 ^-2M.Provided final tested electric current and two kinds of polarization mode reflection wavelengths of sensor fibre grating difference relation curve as shown in Figure 7.

As shown in Figure 5, along with the increase of tested electric current, the difference of two kinds of polarization mode reflection wavelengths of sensor fibre grating increases, and measures sensitivity and improves.After tested electric current was greater than 0.7A, measurement characteristics had good linearity, at this moment, measured sensitivity and can reach 2nm/A.If the resolution of wavelength pick-up unit can reach 1pm, can tell the current change quantity of 0.5mA.

Build preliminary system experimental device according to Fig. 1, recorded in tested electric current increase process the situation of change of spectrum by spectroanalysis instrument, from Fig. 6 as seen, when tested electric current is 0, there is not this moment birefringence effect to produce, have only a reflection peak in the sensor fibre grating reflection spectrum; When tested electric current increases, because the sensor fibre grating is subjected to birefringence effect, and two polarization modes appear, these two polarization modes reflection wavelength situation separated from one another occurs, and electric current are big more along with the increase of electromagnetic force, separate obviously more, be consistent with theoretical analysis result.

Claims (4)

1. current measuring method, mainly comprise a fiber grating radial load sensing unit, the electromagnetic force generation device, light source, fiber coupler, spectrometer, spectroscopy unit, output and display unit, it is characterized in that: described current measuring method mainly is to utilize a sensor fibre grating (13) to realize the radial load measurement, described fiber grating radial load sensing unit is by a sensor fibre grating (13), and one section is supported optical fiber (20) and two silicon chips (15 with smooth surface up and down, 16) form described sensor fibre grating and support that optical fiber is parallel to be placed between two silicon chips; Described electromagnetic force generation device is by a permanent magnet (14), a support (18) and a drive current controller (19) of twining solenoid (17) is formed, described permanent magnet be fixed on go up in described up and down two silicon chips silicon chip above, the described support that is wound with solenoid be fixed on lower silicon slice below, described drive current controller links to each other with solenoid by lead; Described light source (11) links to each other with sensor fibre grating one end by described fiber coupler (12), output terminal through fiber coupler after the measuring-signal of sensor fibre grating reflects through self links to each other with spectrometer (21), the output signal of spectrometer is sent to spectroscopy unit (22) by signal wire, then is output with display unit (23) to handle.

2. according to the described current measuring method of claim 1, it is characterized in that: the described sensor fibre grating (13) that utilizes is realized the radial load measurement, be to utilize the sensor fibre grating to produce birefringence effect under the radial electromagnetic force effect and two reflectance spectrums with different polarization states occur, the principle that the difference of these two reflectance spectrum centre wavelengths is directly proportional with radial electromagnetic force realizes.

3. according to the described current measuring method of claim 1, it is characterized in that: described support (18) material that is wound with solenoid (17) is plastics, and is interior through being of a size of 15mm, highly is 100mm.

4. according to the described current measuring method of claim 1, it is characterized in that: described one section material, diameter and sensor fibre grating (13) that supports optical fiber (20) is identical, and removes their surface coating layer.

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