CN105258716A - L-shaped fiber grating sensor and application thereof - Google Patents

Abstract

The invention relates to a high-sensitivity fiber grating temperature sensor having relatively good strain crosstalk resistance capability and provides a material heat expansion coefficient measurement method based on the fiber grating sensor. For improving temperature measurement sensitivity of the fiber grating sensor, an L-shaped temperature sensitization structure is provided. A fiber grating is fixed in a free state on the L-shaped temperature sensitization structure. Tail ends of a transverse support arm and a vertical support arm of the structure are respectively designed to have a slope, the slopes have same inclination angles and are on one same inclination line, and the slopes are used for fixing the fiber grating sensor. The measurement sensitivity mainly depends on a material heat expansion coefficient and geometric dimensions of the L-shaped temperature sensitization structure. For measuring the material heat expansion coefficient, on the basis of the L-shaped sensitization packaging structure, two L-shaped sensitization packaging structures are merged to form a similar inverted L-shaped structure, structure deformation characteristics can be figured out in a back-stepping mode according to center wavelength offset of the fiber grating caused temperature change, and thereby the heat expansion coefficient of the measured material can be calculated.

Description

L shape fiber-optic grating sensor and application thereof

Technical field

The present invention relates to a kind of L shape fiber-optic grating sensor and application thereof, belong to Fiber Bragg Grating technology field.

Background technology

Fiber grating (FBG) has the two-parameter sensing characteristics of temperature and strain, but its temperature control is relatively low.The naked grating of reflection wavelength near 1550nm, temperature control coefficient only has about 10pm/ DEG C, often cannot meet the requirement of high-acruracy survey.For improving fiber-optic grating sensor sensitivity of thermometry, many scholars have done large quantifier elimination in temperature sensitizing.There is people to be directly pasted onto by FBG on the large polymkeric substance of coefficient of thermal expansion abroad, its temperature control coefficient is largely increased.But when measuring like this, on the one hand, fiber grating cannot the change of direct sense ambient temperature, on the other hand, object grating when thermal expansion is also subject to covering the unstable additive factor impacts such as the cementing stress on its surface, and this will affect ambient temperature measurement precision and response time.Therefore need to study new temperature enhanced package form, improve temperature measurement accuracy, shield the impact of extraneous stress disturbing factor from structural design angle.

Material expansion coefficient is one of hot physical property of material, it is the key character amount of exosyndrome material characteristic, in engineering design, exact instrument manufacture, material welding and processing, there is important references to be worth, significant in Practical Project and fundamental research to the measurement of material expansion coefficient.Have a lot to the measuring method of the linear expansion coefficient of sample in various temperature range of different materials and size, common methods is as capacitance method, Mechanical Method and optical method.Often kind of measurement means all has different features, and applicable material is also variant.Particularly when strong-electromagnetic field environment and some complex mechanical structure inside carry out hot expansibility measurement, the applying working condition of some general measuring methods cannot be met, cause measuring accuracy to reduce.Therefore, need to study a kind of new material thermal expansivity monitoring that there is stronger anti-electromagnetic interference capability, be convenient to remote online monitoring, only need to utilize measured material, just can realize the monitoring of its thermal expansivity, without the need to by other auxiliary material as the right method of thermal expansivity marked ratio.

Summary of the invention

The object of the present invention is to provide a kind of high sensitivity L shape fiber-optic grating sensor for measuring tempeature, this L shape fiber-optic grating sensor is also used for the measurement of material thermal expansion coefficient widenable to inverted T shape structure.

Technical scheme: a kind of L shape fiber-optic grating sensor, is characterized in that: comprise L shape matrix and fiber grating, and wherein L shape matrix is made up of horizontal support arm and vertical support arm, and wherein horizontal support arm and vertical leg extremities have the slope be located along the same line; Above-mentioned fiber grating is fixed on L shape matrix, and has four point of fixity with L shape matrix, is followed successively by the first point of fixity, the second point of fixity, the 3rd point of fixity, the 4th point of fixity; Wherein the first point of fixity, the second point of fixity are positioned on the slope of above-mentioned horizontal support arm, and the 3rd point of fixity, the 4th point of fixity are positioned on the slope of above-mentioned vertical support arm; The grating section of fiber grating is positioned between the second point of fixity and the 3rd point of fixity; Between above-mentioned first point of fixity and the second point of fixity, the fiber grating of the 3rd point of fixity and the 4th point of fixity is slack strand.

Utilize the method for L shape fiber-optic grating sensor measuring tempeature change described in claim 1, it is characterized in that: use following formula

$\frac{\mathrm{\Δ}\mathrm{\λ}}{\mathrm{\λ}}=(\mathrm{\α}+\mathrm{\ζ})\mathrm{\Δ}T+(1-P_e){\mathrm{\ϵ}}_T$

${\mathrm{\ϵ}}_T=\frac{\sqrt{{(l_2+{\mathrm{\α}}_1{l}_2\mathrm{\Δ}T)}^2+{(l_1+{\mathrm{\α}}_1{l}_1\mathrm{\Δ}T)}^2}-\sqrt{l_1^2+{l_2}^2}}{\sqrt{l_1^2+{l_2}^2}}$

Wherein: Δ λ is the center wavelength shift amount that grid region causes, and λ is fiber-optic grating sensor centre wavelength, and α is optical fiber coefficient of thermal expansion, and ζ is optical fiber thermo-optical coeffecient, and Δ T is temperature variation, P _efor optical fiber valid elastic-optic constants, α ₁the material thermal expansion coefficient of L shape structure, l ₁vertical arm length, l ₂it is horizontal arm length.

When variation of ambient temperature, by the effect to fiber bragg grating center wavelength skew generation two aspects.That belonging to L shape structure, vertical length between support arm and horizontal leg extremities will change due to the thermal expansion effects of material on the one hand, the spacing of the point of fixity making to lay respectively on vertical support arm belonging to L shape structure and horizontal leg extremities slope also changes by this thereupon, and then directly causing axial tension suffered by therebetween fiber grating to change thereupon, this axial tension is actual is caused by the thermal force that causes due to variation of ambient temperature.On the other hand, the fiber grating being in vacant state, simultaneously also by the change of direct feeling environment temperature, is subject to thermo-optic effect impact and screen periods is changed.The advantage of this temperature sensitizing version is: one is that belonging to L shape structure, vertical support arm and horizontal support arm all can be out of shape because temperature variation produces in vertical and horizontal direction respectively, and this changes directly causing the spacing of the point of fixity be positioned on its slope.And this distance change is more remarkable compared to L shape structure expanded by heating effect in a single direction, therefore contributes to improving unit temperature and change influence power to axial force suffered by grating.Two be in vacant state fiber grating by the change of direct feeling environment temperature, not only contribute to improving temperature-responsive speed, gluing liquid can also to be shielded in other adherent structures to the disturbing factor in grating grid region.

The fixed point being positioned at the fiber grating both sides on vertical support arm belonging to L shape structure and horizontal leg extremities slope axially arranges one section of lax transition section region along fiber grating separately more laterally, for shielded from external stresses crosstalk, equally again point of fixity is set respectively so that these two sections lax transition section regions are fixing on vertical support arm and horizontal leg extremities slope at lax transition section areas outside.Effectively shielding and isolation are carried out in the stress crosstalk can may introduced to external world by the lax transition section region arranged in both sides, fiber grating grid region.

Utilize the inverted T-shaped fiber-optic grating sensor of L shape fiber-optic grating sensor composition described in claim 1, it is characterized in that: two L shape fiber-optic grating sensor compositions, two L shape fiber-optic grating sensors are form back-to-back, and are integrated, and entirety presents inverted T-shaped structure.

Utilize inverted T-shaped fiber-optic grating sensor described in claim 3 to measure the method for material thermal expansion coefficient, it is characterized in that comprising following process:

Step 1: measurement mechanism is put in temperature control box and heats;

Step 2: adopt optical patchcord to be connected on (FBG) demodulator by fiber grating, so that the center wavelength shift situation of Real-Time Monitoring fiber grating;

Step 3: along with temperature increases, treat geodesic structure expanded by heating, belonging to inverted T-shaped structure, the distance of vertical support arm and horizontal leg extremities changes, and will produce the axial force along fiber grating.This axial force and temperature acting in conjunction cause fiber bragg grating center wavelength to offset.Same environment residing for the fiber grating laying respectively at inverted T-shaped structure both sides, can cancel out each other because suffered temperature action is identical, can calculate the axial strain that object produces because of expanded by heating like this, and then derive the thermal expansivity of material, concrete formula is:

${\mathrm{\α}}_S=\frac{{\mathrm{\Δ\λ}}_1-{\mathrm{\Δ\λ}}_2}{K_{\mathrm{\ϵ}}\mathrm{\λ}\mathrm{\Δ}T}$

Wherein: α _sfor the coefficient of thermal expansion of detected materials, K _εfor the strain sensitivity of fiber-optic grating sensor, Δ λ ₁for the center wavelength shift amount that grating grid region 1 causes, Δ λ ₂for the center wavelength shift amount that grating grid region 2 causes, K _εfor the strain sensitivity of fiber-optic grating sensor, λ is fiber-optic grating sensor centre wavelength, and Δ T is temperature variation.

Accompanying drawing explanation

Fig. 1 is L shape fiber-optical grating temperature sensor sensitization structure figure, Fig. 2 is the structural drawing that inverted T-shaped fiber-optic grating sensor measures material thermal expansion coefficient, Fig. 3 is fiber-optical grating temperature sensor resistance to stress crosstalk structural drawing, Fig. 4 is L shape fiber-optical grating temperature sensor sensitization structure geometric graph, and Fig. 5 monitors the inverted T-shaped construction geometry figure of material expansion coefficient.

Number in the figure title: the larger material of 1---thermal expansivity; 2---fiber grating; 3,4---slope; 5,7,8,10---point of fixity; 6,9---relaxes transiting section fiber; 11,12---fiber grating extension line; 13---fiber Bragg grating (FBG) demodulator; 14---rigid elongate strip thin slice; l ₁---L shape fiber-optical grating temperature sensor indulges the length of support arm; l ₂---the length of the horizontal support arm of L shape fiber-optical grating temperature sensor; l ₃---the length of the right one side of something of the horizontal support arm of inverted T-shaped structure; Δ l ₃---the length changed after the right half of expanded by heating of the horizontal support arm of inverted T-shaped structure; l ₄---inverted T-shaped structure indulges the length of support arm; Δ l ₄---the length that inverted T-shaped structure changes after indulging support arm expanded by heating; Length between l---inverted T-shaped structure horizontal support arm right-hand member and vertical support arm top; L '---the length between-inverted T-shaped structure horizontal support arm right-hand member and vertical support arm top after expanded by heating.

Embodiment

Be described in detail below in conjunction with the technical scheme of accompanying drawing to invention:

1, L shape fiber-optical grating temperature sensor sensitization structure, is respectively designed to have identical inclination angle at the horizontal support arm of L shape structure and vertical leg extremities and is positioned at slope (3) on same oblique line, (4).Fiber grating is fixed on the horizontal support arm of material and the slope of vertical support arm with free state.

Along with test environment temperature variation, fiber grating can not only experience the center wavelength shift because thermo-optic effect causes, also will be subject to the fiber grating two ends point of fixity distance change caused because of thermal expansion of belonging to structure horizontal support arm and vertical support arm and the responsive to axial force that causes, this axial force also will cause raster center wavelength shift.The size of this axial force depends primarily on the change of test environment temperature, the material thermal expansion coefficient of structure and L-type sensitization structure physical dimension.By adjusting these parameters, the adjustment to optical fiber grating temperature measurement sensistivity and range can be realized.

That the spacing of indulging support arm and horizontal leg extremities belonging to L shape structure will change due to expanded by heating on the one hand, and then the spacing laying respectively at point of fixity (7), (8) on L shape structure slope is changed thereupon, this also changes directly causing axial force suffered by therebetween fiber grating, and this axial force is actual is caused by the thermal force that causes due to variation of ambient temperature.On the other hand, the fiber grating being in vacant state, by the change of direct feeling environment temperature, is subject to thermo-optic effect impact and screen periods is changed.Therefore the temperature variant approximate relation of fiber bragg grating center wavelength side-play amount can be obtained:

$\frac{\mathrm{\Δ}\mathrm{\λ}}{\mathrm{\λ}}=(\mathrm{\α}+\mathrm{\ζ})\mathrm{\Δ}T+(1-P_e){\mathrm{\ϵ}}_T$

Wherein, ${\mathrm{\ϵ}}_T=\frac{\sqrt{{(l_2+{\mathrm{\α}}_1{l}_2\mathrm{\Δ}T)}^2+{(l_1+{\mathrm{\α}}_1{l}_1\mathrm{\Δ}T)}^2}-\sqrt{l_1^2+{l_2}^2}}{\sqrt{l_1^2+{l_2}^2}}$

Wherein: α is optical fiber coefficient of thermal expansion, ζ is optical fiber thermo-optical coeffecient, P _efor optical fiber valid elastic-optic constants, α ₁the material thermal expansion coefficient of L shape structure, l ₁the length at top, l ₂the length of bottom.

2, the fiber-optical grating temperature sensor structural design of resistance to stress crosstalk, be fixed on rigid elongate strip thin slice by fiber grating two ends in lax mode, the fixed point in grating both sides axially arranges one section of relaxation area for shielded from external stresses crosstalk along thin bar separately more laterally.For reducing the curvature in fiber slack transition section region and optical fiber grating sensing region to greatest extent, optical fiber should be ensured with sine wave in rigid elongate strip thin slice layout.

3, on L-type sensitized reaction basis described in feature 1, propose two L-type sensitized reaction to merge the structure forming a kind of similar inverted T shape, measure for material thermal expansion coefficient.Tested structure is designed to inverted T shape version, and two ends and vertical leg extremities about the horizontal support arm as substrate are designed to the slope with certain angle of inclination respectively.Two fiber-optic grating sensors are pasted in inverted T shape structure both sides respectively according to described resistance to stress crosstalk encapsulating structure form.Wherein a fiber grating FBG2 is in complete relaxed state, only can experience temperature variation.Another fiber grating FBG1 is then in tension.Along with test environment temperature variation, the fiber grating being in tension can not only experience the center wavelength shift because thermo-optic effect causes, also this fiber grating two ends point of fixity distance be subject to because material heat expansion causes is changed the responsive to axial force caused, this axial force also will cause raster center wavelength shift.Subtracted each other by the center wavelength shift amount that tension is corresponding with two fiber gratings of relaxed state, the impact of variation of ambient temperature can be eliminated, and then obtain the fiber grating axial force change because deformation that temperature variation suffered by structure produces causes.Suffered by fiber grating, axial force changes the center wavelength shift amount situation caused, can anti-pushing-out structure deformation behaviour, and then calculates the material thermal expansion coefficient of tested inverted T shape, and computing method are as follows:

The formula that fiber grating pair strain and temperature respond simultaneously is:

$\frac{\mathrm{\Δ}\mathrm{\λ}}{\mathrm{\λ}}=(\mathrm{\α}+\mathrm{\ζ})\mathrm{\Δ}T+(1-P_e){\mathrm{\ϵ}}_T$

Wherein α is optical fiber coefficient of thermal expansion, and ζ is optical fiber thermo-optical coeffecient; P _efor optical fiber valid elastic-optic constants, Δ T is the variation range of temperature.Shown in Fig. 5, the center wavelength shift amount formula that the fiber-optic grating sensor FBG1 being in tension and the fiber-optic grating sensor FBG2 being in relaxed state is corresponding is respectively:

$\frac{{\mathrm{\Δ\λ}}_1}{\mathrm{\λ}}=K_T\mathrm{\Δ}T+K_{\mathrm{\ϵ}}{\mathrm{\ϵ}}_T$

$\frac{{\mathrm{\Δ\λ}}_2}{\mathrm{\λ}}=K_T\mathrm{\Δ}T$

Can calculate according to geometrical scale:

${\mathrm{\ϵ}}_T=\frac{l^{\′}-l}{l}=\frac{\sqrt{{\left(l_{3+}{l}_3{\mathrm{\α}}_S\mathrm{\Δ}T\right)}^2+{\left(l_{4+}{l}_4{\mathrm{\α}}_S\mathrm{\Δ}T\right)}^2}-\sqrt{{l_3}^2+{l_4}^2}}{\sqrt{{l_3}^2+{l_4}^2}}={\mathrm{\α}}_S\mathrm{\Δ}T$

And then calculate material expansion factor alpha _scomputing formula be:

${\mathrm{\α}}_S=\frac{{\mathrm{\Δ\λ}}_1-{\mathrm{\Δ\λ}}_2}{K_{\mathrm{\ϵ}}\mathrm{\λ}\mathrm{\Δ}T}$

This method adopts two homogeneity fiber gratings as Sensitive Apparatus, by inverted T-shaped structure, can offset the impact of variation of ambient temperature, can facilitate the thermal linear expansion coefficient directly measuring material.

Claims (4)

1. a L shape fiber-optic grating sensor, it is characterized in that: comprise L shape matrix (1) and fiber grating (2), wherein L shape matrix (1) is made up of horizontal support arm and vertical support arm, and wherein horizontal support arm and vertical leg extremities have the slope be located along the same line; Above-mentioned fiber grating (2) is fixed on L shape matrix (1), and have four point of fixity with L shape matrix (1), be followed successively by the first point of fixity (5), the second point of fixity (7), the 3rd point of fixity (8), the 4th point of fixity (10); Wherein the first point of fixity (5), the second point of fixity (7) are positioned on the slope of above-mentioned horizontal support arm, and the 3rd point of fixity (8), the 4th point of fixity (10) are positioned on the slope of above-mentioned vertical support arm; The grating section of fiber grating (2) is positioned between the second point of fixity (7) and the 3rd point of fixity (8); Between above-mentioned first point of fixity (5) and the second point of fixity (7), the fiber grating (2) of the 3rd point of fixity (8) and the 4th point of fixity (10) is slack strand.

2. utilize the method for L shape fiber-optic grating sensor measuring tempeature change described in claim 1, it is characterized in that:

Use following formula

${\mathrm{\ϵ}}_T=\frac{\sqrt{{(l_2+{\mathrm{\α}}_1{l}_2\mathrm{\Δ}T)}^2+{(l_1+{\mathrm{\α}}_1{l}_1\mathrm{\Δ}T)}^2}-\sqrt{l_1^2+{l_2}^2}}{\sqrt{l_1^2+{l_2}^2}}$

Wherein: Δ λ is the center wavelength shift amount that grid region causes, and λ is fiber-optic grating sensor centre wavelength, and α is optical fiber coefficient of thermal expansion, and ζ is optical fiber thermo-optical coeffecient, and Δ T is temperature variation, P _efor optical fiber valid elastic-optic constants, α ₁the thermal expansivity of material, l ₁vertical arm length, l ₂it is horizontal arm length.

3. utilize the inverted T-shaped fiber-optic grating sensor of L shape fiber-optic grating sensor composition described in claim 1, it is characterized in that: two L shape fiber-optic grating sensor compositions, two L shape fiber-optic grating sensors are form back-to-back, and are integrated, and entirety presents inverted T-shaped structure.

4. utilize inverted T-shaped fiber-optic grating sensor described in claim 3 to measure the method for material thermal expansion coefficient, it is characterized in that: use following formula

${\mathrm{\α}}_S=\frac{{\mathrm{\Δ\λ}}_1-{\mathrm{\Δ\λ}}_2}{K_{\mathrm{\ϵ}}\mathrm{\λ}\mathrm{\Δ}T}$

Wherein: α _sfor the coefficient of thermal expansion of detected materials, K _εfor the strain sensitivity of fiber-optic grating sensor, Δ λ ₁for the center wavelength shift amount that grating grid region 1 causes, Δ λ ₂for the center wavelength shift amount that grating grid region 2 causes, K _εfor the strain sensitivity of fiber-optic grating sensor, λ is fiber-optic grating sensor centre wavelength, and Δ T is temperature variation.