CN103411633A - Multi-physical quantity measurement signal recognition method based on FBG (Fiber Bragg Grating) sensor - Google Patents

Abstract

A multi-physical quantity measurement signal recognition method based on an FBG (Fiber Bragg Grating) sensor comprises the following steps: two FBG sensors are respectively placed symmetrically on an upper surface and a lower surface of an equal-strength cantilever arm, so as to measure and isolated a wavelength drift which is caused by three parameters of acceleration, temperature and pressure; an FBG image acquisition method based on a CMOS image sensor is used and the CMOS image sensor is used to capture an FBG facula, so that wavelength recognition of the FBG sensor is transformed into facula image recognition; and a pixel position and time multiplex is used to distinguish different facula images produced by the FBG sensor, so that a multi-facula image can be accurately recognized and positioned. The multi-physical quantity measurement signal recognition method based on the FBG sensor can isolate and recognize three different parameters; the CMOS is combined with the time division multiplexing technology to accurately demarcate the FBG facula image; the wavelength shift variation is converted to detection of displacement changes of the facula image; the multi-point and multi-parameter information can be recognized; and the practical significance for popularization and application of the large-scale FBG sensor network is realized.

Description

Many physical quantities signal recognition method based on the FBG sensor

Technical field

The invention belongs to FBG sensing measurement field, relate to the many signal analysis identifications to the FBG sensor, especially relate to a kind of signal recognition method of many physical quantities based on the FBG sensor.

Background technology

The essence of blipology is that sensing grating (FBG) reflectance spectrum is carried out to Real-Time Monitoring, analyzes the position of centre wavelength.Namely need signal is become to electric signal from light signal, then from electric signal, transfer the process of digital signal to.The prior art shortcoming has: the one, light signal is processed, it is the trace analysis of the foveal reflex wavelength of sensor, the most direct detecting instrument of fiber-optic grating sensor foveal reflex wavelength is spectrometer, but the spectrometer price is high, the output display of information is not directly perceived, is difficult to meet the needs of practical application; The 2nd, wavelength information is converted into to electric signal in order to process output, and insensitive to wavelength during the photoelectric detector receiving optical signals, the FBG reflectance spectrum is similar to and sees gaussian shaped profile as simultaneously, it is narrower that reflected light signal has live width, the characteristics such as power is low, the 3rd, many physical quantitys are detected simultaneously, also can't realize.In a word up to the present, also do not have a kind of recognition technology can meet simultaneously high resolving power, multiparameter, multipoint multiplexing detection and the not high practical requirement of cost.

Summary of the invention

In order to overcome above-mentioned the deficiencies in the prior art, the object of the present invention is to provide a kind of signal recognition method of many physical quantities based on the FBG sensor, can separate and identify the multiparameter micro-signal, and the Intellisense information identifying method, realize simultaneously, accurately measuring multiparameter.

To achieve these goals, the technical solution used in the present invention is:

Many physical quantities signal recognition method based on the FBG sensor, comprise the steps:

1). multi-parameter signals separates: employing is placed two FBG sensors in the upper and lower two surface symmetries of equal strength overarm arm and is measured and isolate the wave length shift caused due to acceleration, three parameters of temperature and pressure;

2). adopt the FBG image acquisition method based on cmos image sensor, utilize cmos image sensor to catch the FBG hot spot, the identification of the wavelength of FBG sensor is converted into to light spot image identification;

3). to many light spot images precise marking and location: adopt location of pixels and time division multiplex to distinguish the light spot image that different FBG sensors produce, due to light source according to pulse mode work, the corresponding different delay of each light pulse and different FBG sensor, by receiving also recording light pulse, determine time delay value, demarcate different FBG according to time delay value; After front and back two width figure light spot image ownership are determined, more relatively by same FBG, do not produce between light spot image and change in the same time, determine thus the variation of measurand.

Described step 1) medium tenacity semi-girder refers on this semi-girder the sectional area difference apart from stiff end different distance place.

Described step 2) in, FBG image acquisition method is by identification and gathers the shift offset that in the CMOS light spot image, hot spot occurs, it is the pixel-shift amount that facula position occurs, and then displacement pixel-shift value is converted into to the wavelength variations value, finally draw the relation between measured physical quantity changing value and spot displacement pixel-shift amount.

Compared with prior art, the invention solves the STRESS VARIATION cross-infection phenomenon that FBG sensor for temperature, pressure and acceleration change cause; Can separate simultaneously and identify three different parameters, by adopting CMOS to carry out accurately, demarcate the FBG light spot image in conjunction with time-division multiplex technology, realization becomes wave length shift to detect the light spot image change in displacement, this method can not only be identified multiple spot, multiparameter information, and is of practical significance to applying large-scale FBG sensing network.

The accompanying drawing explanation

Fig. 1 is the theory diagram structural representation of the measuring system of sensor-based system of the present invention, and black arrow means incident light, and dotted arrow means reflected light.

Fig. 2 is sensing unit schematic diagram of the present invention.

Embodiment

Below in conjunction with accompanying drawing, the present invention is described in further details.

The object of the invention is based on many physical quantities of FBG sensor sensor-based system, and work out a kind of energy and separate and identify the multiparameter micro-signal, and the Intellisense information identifying method, realize simultaneously, accurately measuring multiparameter.

Signal identification is mainly to adopt CMOS to demarcate in conjunction with time-division multiplex technology the hot spot that different FBG produce, and then obtains the wavelength variations that each physical quantity variation causes.

As shown in Figure 2, sensor-based system mainly comprises sensing unit and measuring system.Sensing unit as shown in Figure 1, comprise an end be fixed on equi intensity cantilever on fixture, be placed on the equi intensity cantilever other end mass, be arranged on semi-girder stiff end and a symmetrical FBG sensor and the 2nd FBG sensor that is positioned at the semi-girder upper and lower surface, be arranged on fixture and near the 3rd FBG sensor on the fixture close to very from the semi-girder stiff end, realize multimetering, can use a plurality of sensing units; Measuring system comprises ASE light source, 1*3 coupling mechanism, 1*2 coupling mechanism, collimating mirror, the hot spot that glitters, cmos image sensor and computing machine computer.Wherein equi intensity cantilever is the triangle semi-girder, and mass is arranged on the joint place of two hypotenuses of equi intensity cantilever, and mass can be selected spheroid.

Signal identification of the present invention mainly comprises following content:

1) multi-parameter signals separation method: adopt at upper and lower two surface two the FBGs sensors of symmetrical placement of equal strength overarm arm and measure and isolate due to acceleration, the wave length shift that three parameters of temperature and pressure cause.

2) multi-parameter signals acquisition method: adopt the FBG image acquisition method based on cmos image sensor, utilize cmos image sensor to catch the FBG hot spot, effectively the identification of the wavelength of FBG sensor is converted into to light spot image identification.FBG image acquisition method is exactly identification and gathers the shift offset that in the CMOS light spot image, hot spot occurs, the pixel-shift amount of namely facula position generation, and then displacement pixel-shift value is converted into to the wavelength variations value, finally draw the relation between measured physical quantity changing value and spot displacement pixel-shift amount.

3) many light spot images precise marking, localization method: every width figure has a plurality of FBG hot spots, because many FBGs can not produce a plurality of hot spots in the same time, the characteristics such as these light spot shape sizes, light intensity are basically identical, is not which produced in the same time by same FBG these hot spots of how to confirm? because measure physical quantities changes, only to cause light spot image occurrence positions change slightly, need the displacement calculating amount just need know which light spot image is produced by same FBG, need to know the time dependent one-to-one relationship of these light spot images and FBG.Propose to adopt location of pixels and time-division multiplex technology to distinguish the light spot image that different fbg produce for this reason.According to pulse mode work, the corresponding different delay of each light pulse and different FBG, determine time delay value by receiving also recording light pulse, demarcates different FBG according to time delay value due to light source.After front and back two width figure light spot images ownership determine, more relatively by same FBG, do not produce between light spot image and change in the same time, determine that measurand changes.Concrete survey sheet as shown in Figure 2.

Measuring principle of the present invention is as follows:

A.CMOS imageing sensor principle:

According to blazed grating formula: l (sin θ+sin θ _k=k λ (1)

Getting differential obtains: $\mathrm{\Δ}{\mathrm{\θ}}_k=\frac{k}{l\×\cos {\mathrm{\θ}}_k}---\left(2\right)$

Wherein l is pitch, and θ is incident angle, θ _kFor angle of diffraction, k is diffraction progression, and λ is lambda1-wavelength.

CMOS shows that the hot spot displacement is: Δ x=f * tg Δ θ _k(3)

By (2) and (3), can be obtained: $\mathrm{\Δx}=f\×\frac{k}{l\×\cos {\mathrm{\θ}}_k}\mathrm{\Δ\λ}---\left(4\right)$

Wherein, Δ x is the facula deviation amount, and f is the condenser lens angle, Δ θ _kFor the angle of diffraction variable quantity, again according to cmos imaging principle formula: Δ x=p * Δ p (5)

P is Pixel Dimensions, and Δ p is the pixel-shift number,

By (4) and (5), can be obtained: $\mathrm{\Δ\λ}=\frac{p\×l\×\cos {\mathrm{\θ}}_k}{\mathrm{fk}}\mathrm{\Δp}---\left(6\right)$

Here f=10cm, k=1, p=42mm,

θ _k=45 °, finally can obtain If show, detect the FBG hot spot and move 1 pixel, mean that the FBG grating wavelength has changed 25pm

B. temperature survey

When environment temperature changed Δ T, the grating cycle caused by thermal expansion effects changed

ΔΛ＝α×Λ×ΔT (8)

With the effective refractive index caused by thermo-optic effect, be changed to

Δn _eff＝n _eff×ξ×ΔT (9)

According to formula (1), (2), (9) and (10) finally can obtain:

Δλ _BT＝λ _B×(α+ξ)ΔT (10)

In formula:

α is thermal expansivity,

$\mathrm{\ξ}=\frac{1}{n_{\mathrm{eff}}}\frac{{\∂n}_{\mathrm{eff}}}{\∂T}$ For thermo-optical coeffecient.

In conjunction with formula (7), finally can obtain $\frac{\mathrm{\Δp}}{\mathrm{\ΔT}}=\frac{{\mathrm{\λ}}_B\×(\mathrm{\α}+\mathrm{\ξ})}{25}\×{10}^9---\left(11\right)$

C. pressure survey:

Assumed stress changes only makes the refractive index of FBG and physical length change, and the change of FBG length causes because the ambient pressure variation causes the FBG axial stress to change.

When environmental pressure changes Δ P,

Δλ _B＝2ΛΔn _eff+2n _effΔΛ (12)

Namely

${\mathrm{\Δ\λ}}_{\mathrm{BP}}={\mathrm{\λ}}_B(\frac{1}{\mathrm{\Λ}}\frac{\∂\mathrm{\Λ}}{\∂P}+\frac{1}{n}\frac{\∂n}{\∂P})\mathrm{\ΔP}---\left(13\right)$

According to axial stress, change the wave length shift formula caused:

${\mathrm{\Δ\λ}}_B={\mathrm{\λ}}_B\{1-\frac{{n_{\mathrm{eff}}}^2}{2}[P_{12}-\mathrm{\υ}(P_{11}+P_{12})\left]\right\}\×\mathrm{\ΔS}---\left(14\right)$

But with the Hu law

$\frac{L-L_0}{L_0}=\frac{F}{\mathrm{EA}}---\left(15\right)$

Can obtain

$\frac{\mathrm{\ΔL}}{L}=-\frac{(1-2\mathrm{\υ})P}{E}---\left(16\right)$

$\frac{\mathrm{\Δn}}{n}=\frac{{n_{\mathrm{eff}}}^{2}P}{2E}(1-2\mathrm{\υ})(2p_{12}+p_{11})---\left(17\right)$

Therefore can obtain:

${\mathrm{\Δ\λ}}_{\mathrm{BP}}={\mathrm{\λ}}_B[-\frac{(1-2\mathrm{\υ}}{E}+\frac{{n_{\mathrm{eff}}}^2}{2E}(1-2\mathrm{\υ})(2p_{12}+p_{11})]\mathrm{\ΔP}---\left(18\right)$

In conjunction with formula (7), can obtain $\frac{\mathrm{\Δp}}{\mathrm{\ΔP}}=\frac{{\mathrm{\λ}}_B[-\frac{(1-2\mathrm{\υ}}{E^{\′}}+\frac{{n_{\mathrm{eff}}}^2}{2E^{\′}}(1-2\mathrm{\υ})(2p_{12}+p_{11})]}{25\×{10}^{-12}}---\left(19\right)$

Wherein: For unit pressure, change the hot spot pixel side-play amount caused

P ₁₁And p ₁₂For bullet light component of tensor (Pockel coefficient),

υ is the Poisson ratio of fiber optic materials,

S is that axial stress changes,

E is elastic modulus,

L ₀With L, be respectively FBG and change front and back length,

F and A are respectively the suffered external force of FBG and lifting surface area.

D. acceleration analysis:

Because the strain that uniform cross section overarm arm diverse location produces is unequal, this proposes high requirement to the accurate location of placing sensor.Design equi intensity cantilever for this reason, its feature is the sectional area difference apart from stiff end different distance place, when mass ball M being placed on to the joint place of two hypotenuses of beam, when the system acceleration changes Δ a, the top of beam is subject to (F=g+ Δ power a), can guarantee strain stress equal and opposite in direction (quality of ignoring the arm of hanging oneself from a beam) everywhere on beam, structural drawing as shown in Figure 1.

$\mathrm{\ϵ}=\frac{6\mathrm{FL}}{{\mathrm{EBh}}^2}---\left(20\right)$

Wherein:

E is the Chang Shi modulus of semi-girder material,

L is the total length of semi-girder,

B is the bottom width of semi-girder,

H is the thickness of beam.

According to the deflection formula of equi intensity cantilever end, the equivalent spring rigidity K that can obtain beam is:

$K=\frac{{\mathrm{EBh}}^3}{{6L}^3}---\left(21\right)$

Due to the inertial force effect, overarm and mass ball are in vibrational state, and the equation of motion and system simple harmonic oscillation formula according to mass can obtain:

My+Ky＝-Ma _g (22)

$Y\≈\frac{A_g}{{\mathrm{\ω}}_0^2}---\left(23\right)$

Wherein:

Y is the relative displacement of mass ball and system,

Y is the displacement amplitude of end mass ball,

A _gFor the acceleration amplitude,

For the natural frequency of system,

According to F=KY, finally can draw:

$\mathrm{\Δ}{\mathrm{\λ}}_{\mathrm{Bg}}=\frac{{36\mathrm{ML}}^4}{E^2{B}^2{h}^5}\mathrm{\Δa}---\left(24\right)$

In conjunction with formula (7), can obtain $\frac{\mathrm{\Δp}}{\mathrm{\Δa}}=\frac{{36\mathrm{ML}}^4}{E^2{B}^2{h}^5\×25\×{10}^{-12}}---\left(25\right)$

A concrete application example, the arm of hanging oneself from a beam is attached to fixture for example on the drilling well head, arm is very thin when hanging oneself from a beam, and a FBG sensor FBG1 and the 2nd FBG sensor FBG2 are positioned at apart from two surfaces of the very near and symmetrical upper underbeam of stiff end, when the 3rd FBG sensor is fixed on the very near drilling well head of distance overarm arm, can think that the wave length shift that a FBG sensor and the 2nd FBG sensor cause because temperature and pressure changes equates, and the wave length shift equal and opposite in direction that acceleration change causes, opposite direction.And the 3rd FBG sensor only is subject to the wave length shift caused due to temperature variation, and these three sensors are identical because of the wave length shift that temperature variation causes.

It is exactly that acceleration change causes that the twice of wavelength variations value is designated as Δ λ that first sensor deducts the second sensor ₁, first sensor adds that the second sensor is exactly that the temperature and pressure co-variation causes that the twice of wavelength variations value is designated as Δ λ ₂, the 3rd sensor is to only have the wave length shift that temperature variation causes to be designated as Δ λ ₃, Δ λ ₂-2* Δ λ ₃For changing, pressure causes the wave length shift value.

It is steel that system adopts semi-girder, length L=50mm, bottom width B=30mm, thickness h=1mm, Young modulus E=208GPa.The mass M of beam-ends mass=0.3 kilogram.In experiment, adopt the reflection wavelength of 850nm, ASE makes light source.

The light that ASE sends reaches optical fiber FBG through coupling mechanism, the Wavelength matched light of those and FBG is reflected back, through coupling mechanism and reach collimating mirror, collimating mirror becomes directional light to light, and reach blazed grating, the light of blazed grating diffraction different wave length is to diverse location, the line focus lens converge on cmos image sensor, be shown as different light spot images, and light spot image is delivered to computer and with demarcating the hot spot algorithm, analyze and identify, finally find out the relation between light spot image change in displacement and wave length shift variation.

In experiment, be 125 μ m without coating FBG diameter, three FBGs sensors are coated with respectively different materials, and the coating of different-thickness prevents that sensor is subject to physical damage on the one hand, perhaps avoid noise and error, the more important thing is in order to improve the sensitivity of FBG sensor.

So the invention solves the STRESS VARIATION cross-infection phenomenon that FBG sensor for temperature, pressure and acceleration change cause.

Claims (5)

1. based on many physical quantities signal recognition method of FBG sensor, it is characterized in that, comprise the steps:

1). multi-parameter signals separates: employing is placed two FBG sensors in the upper and lower two surface symmetries of equal strength overarm arm and is measured and isolate the wave length shift caused due to acceleration, three parameters of temperature and pressure;

2). adopt the FBG image acquisition method based on cmos image sensor, utilize cmos image sensor to catch the FBG hot spot, the identification of the wavelength of FBG sensor is converted into to light spot image identification;

3). to many light spot images precise marking and location: adopt location of pixels and time division multiplex to distinguish the light spot image that different FBG sensors produce, due to light source according to pulse mode work, the corresponding different delay of each light pulse and different FBG sensor, by receiving also recording light pulse, determine time delay value, demarcate different FBG according to time delay value; After front and back two width figure light spot image ownership are determined, more relatively by same FBG, do not produce between light spot image and change in the same time, determine thus the variation of measurand.

2. the signal recognition method of the many physical quantities based on the FBG sensor according to claim 1, is characterized in that, described step 1) medium tenacity semi-girder refers on this semi-girder the sectional area difference apart from stiff end different distance place.

3. the signal recognition method of the many physical quantities based on the FBG sensor according to claim 1 and 2, is characterized in that, described equi intensity cantilever is the triangle semi-girder, at the joint place of two hypotenuses of equi intensity cantilever, mass is set.

4. the signal recognition method of the many physical quantities based on the FBG sensor according to claim 1, is characterized in that, in described step 1):

The wave length shift pass caused due to acceleration is:

Wherein,

For unit acceleration, change the hot spot pixel side-play amount caused, Δ λ is wave length shift, and Δ a is acceleration change, M is the quality of mass, and L is the total length of semi-girder, and E is the Chang Shi modulus of semi-girder material, B is the bottom width of semi-girder, and h is the thickness of semi-girder;

The wave length shift pass caused due to temperature is:

Wherein,

For unit temperature, change the hot spot pixel side-play amount caused, Δ λ is wave length shift, and Δ T is temperature variation, λ _BFor lambda1-wavelength, α is thermal expansivity,

For thermo-optical coeffecient;

The wave length shift pass caused due to pressure is:

Wherein,

For unit pressure, change the hot spot pixel side-play amount caused, Δ λ is wave length shift, and Δ P is that pressure changes, λ _BFor lambda1-wavelength, p ₁₁And p ₁₂For bullet light component of tensor, υ is the Poisson ratio of fiber optic materials, and S is that axial stress changes, and E ' is elastic modulus.

5. the signal recognition method of the many physical quantities based on the FBG sensor according to claim 1, it is characterized in that, described step 2) in, FBG image acquisition method is by identification and gathers the shift offset that in the CMOS light spot image, hot spot occurs, it is the pixel-shift amount that facula position occurs, and then displacement pixel-shift value is converted into to the wavelength variations value, finally draw the relation between measured physical quantity changing value and spot displacement pixel-shift amount.

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