CN102313523B - Sensitivity calibration method of fiber Bragg grating strain sensor - Google Patents

Abstract

The invention, which belongs to the measuring technology, relates to a sensitivity calibration method of a fiber Bragg grating strain sensor. In the invention, a four-point-bending equal-strength beam is used to calibrate a fiber Bragg grating strain sensor sensitivity. The method is characterized by: determining a position where the fiber Bragg grating is pasted on a standard beam; installing the standard beam on a fixed platform and using a standard beam fulcrum to support the standard beam on the platform; adjusting loading points of a loading beam so as to achieve uniform force on the standard beam; connecting the fiber Bragg grating sensor with a fiber Bragg grating demodulation device; applying a transverse force which is perpendicular to an axis on a midpoint of the loading beam, wherein an effect direction of the transverse force is superposed with a longitudinal symmetrical plane of the standard beam; applying load on the standard beam; using the fiber Bragg grating demodulation device to record wavelength change of the fiber Bragg grating; then calculating the strain of a beam surface and a sensitivity coefficient of the fiber Bragg grating so as to realize calibration. By using the method of the invention, uniform loading can be achieved; the uniform and stable force of the fiber Bragg grating can be guaranteed; a reliable parameter can be provided for technology research and measurement of the fiber Bragg grating sensor.

Description

A kind of fiber Bragg grating strain sensor Sensitivity Calibration method

Technical field

The invention belongs to measuring technique, relate to a kind of scaling method of fiber Bragg grating strain sensor sensitivity.

Background technology

At present, modern structure health monitoring is more and more subject to the extensive attention of society with diagnosis, and fiber-optic grating sensor is also expanded to aerospace field from bridge, tunnel, building, earthquake etc. for monitoring structural health conditions.The fast development of fiber-optic grating sensor is also to require more and more higher for measuring accuracy.For the fiber grating sensitivity of using, be now all the coefficient providing according to supplier, belong to UNIVERSAL COEFFICIENT, degree of accuracy is low, in measuring accuracy during high or changes in environmental conditions, and the change of coefficient has had influence on the result of measurement.

Up to the present, for the demarcation of light grating strain transducer sensitivity, also there is no a kind of i.e. reliable more accurate scaling method again, and accurate sensitivity is to guarantee the accuracy of measurement result and repeatable important parameter.

Summary of the invention

Object of the present invention: provide a kind of loading even, the fiber Bragg grating strain sensor Sensitivity Calibration method that precision is high.

Technical solution of the present invention: a kind of fiber Bragg grating strain sensor Sensitivity Calibration method, it comprises the steps,

Step 1: Standard Beam is provided;

Step 2: determine the position that fiber grating is pasted on Standard Beam;

Step 3: installation code beam in stationary platform, is used Standard Beam fulcrum that Standard Beam is supported on platform;

Step 4: adjust the load(ing) point on loading beam, make on Standard Beam stressed even;

Step 5: fiber grating is connected with fiber Bragg grating (FBG) demodulator;

Step 6: do the transverse force perpendicular to axis at loading beam mid point, its effect overlaps with longitudinal symmetrical plane of Standard Beam;

Step 7: imposed load on Standard Beam;

Step 8: use fiber Bragg grating (FBG) demodulator to record the wavelength variations of fiber grating;

Step 9: utilize formula (2) to calculate the strain on Standard Beam surface,

Wherein, Standard Beam surface strain: $\mathrm{\ϵ}=\±\frac{\mathrm{Mh}}{2\mathrm{EI}}=\±\frac{12\mathrm{\ω}\·h}{{3l}^2-{4a}^2}---\left(2\right),$

Utilize formula (4) to calculate fiber grating sensitivity coefficient:

Wherein, the curved segment moment of flexure such as M is Standard Beam, I is the moment of inertia of Standard Beam xsect, h is the thickness of Standard Beam, and E is the elastic modulus of Standard Beam material, and l is the distance between two Standard Beam fulcrums, a be Standard Beam fulcrum to the distance between load(ing) point, ω is the amount of deflection of Standard Beam midpoint.

Fiber grating sticks between two load(ing) points of Standard Beam.

Described loading beam by stage casing stressed, and Standard Beam stressed be two sections stressed.

Standard Beam is arranged in stationary platform by Standard Beam fulcrum, and described loading beam is carried on Standard Beam by load(ing) point, and top loads and is directly carried on loading beam.

The invention has the beneficial effects as follows: fiber Bragg grating strain sensor Sensitivity Calibration method of the present invention adopts one-piece construction symmetric design, the normal stress that has guaranteed beam, is uniformly distributed along width by linear distribution along depth of section.Utilize 4 curved beam of uniform strengths to fiber Bragg grating strain sensor sensitivity demarcate, top loads and is exerted all one's strength and be uniformly distributed by loading beam, two ends by loading beam namely load in fiber grating region of living in to Standard Beam active section again, it loads evenly, guaranteed that fiber grating is stressed evenly, stable, for technical study and the measurement of fiber-optic grating sensor provides parameter reliably, there is the advantages such as simple to operate, reliable and stable, for the development of using and surveying sensing technology of fiber Bragg grating strain sensor provides, provide powerful support for.

Accompanying drawing explanation

Fig. 1 loads the structural representation of demarcating in fiber Bragg grating strain sensor Sensitivity Calibration method of the present invention;

Fig. 2 is that fiber Bragg grating strain sensor Sensitivity Calibration method of the present invention loads schematic diagram,

Wherein, 1-stationary platform, 2-Standard Beam fulcrum, 3-Standard Beam, 4-load(ing) point, 5-loading beam, 6-top load.

Embodiment

Below by embodiment, the present invention is described in further detail:

Fiber Bragg grating strain sensor Sensitivity Calibration method of the present invention utilize 4 curved beam of uniform strengths to fiber Bragg grating strain sensor sensitivity demarcate.

Refer to Fig. 1, it is that the loading calibration system of fiber Bragg grating strain sensor Sensitivity Calibration method of the present invention comprises that stationary platform 1, Standard Beam fulcrum 2, Standard Beam 3, fiber grating active section, load(ing) point 4, loading beam 5, top load 6.Wherein, described stationary platform 1 is fixed part, and stationary platform area is larger, for bringing convenience to measurement.Standard Beam is arranged in stationary platform 1 by Standard Beam fulcrum 2, and the size of described Standard Beam and material can change as required.Meanwhile, the position of Standard Beam fulcrum 2 in stationary platform can regulate according to the size of Standard Beam, uses Standard Beam fulcrum that Standard Beam is supported on platform.Described loading beam 5 is carried on Standard Beam 3 by load(ing) point 4, and top loading 6 is carried on loading beam 5, adjusts as required the load(ing) point on loading beam, mixes up load(ing) point stressed even to guarantee on Standard Beam.Fiber grating sticks between two load(ing) points 4, and is connected to fiber Bragg grating (FBG) demodulator by optical fiber.

At loading beam mid point, do the transverse force perpendicular to axis, its effect overlaps with longitudinal symmetrical plane of Standard Beam, only has moment of flexure and without shearing, go out the suffered stress of Standard Beam with optical fiber grating measuring in fiber grating is pasted section.Wherein, Standard Beam is supported on fiber grating between load(ing) point.

Refer to Fig. 2, it is that fiber Bragg grating strain sensor Sensitivity Calibration method of the present invention loads schematic diagram.According to the mechanics of materials can obtain on beam between load(ing) point etc. curved segment stress be:

$\mathrm{\σ}=\frac{\mathrm{My}}{I}=\frac{24E\·\mathrm{\ω}\·y}{{3l}^2-{4a}^2}---\left(1\right)$

So, the strain in Standard Beam upper and lower surface is:

$\mathrm{\ϵ}=\±\frac{\mathrm{Mh}}{2\mathrm{EI}}=\±\frac{12\mathrm{\ω}\·h}{{3l}^2-{4a}^2}---\left(2\right)$

Wherein:

M is the curved segment moments of flexure such as Standard Beam, and I is the moment of inertia of Standard Beam xsect, the thickness that h is Standard Beam, E is the elastic modulus of Standard Beam material, l is the distance between two Standard Beam fulcrums, a be Standard Beam fulcrum to the distance between load(ing) point, ω is the amount of deflection of Standard Beam midpoint.

According to optical fibre Bragg optical grating strain sensing principle:

ε＝K _TΔλ (3)

K wherein _tfor the ga(u)ge factor of fiber grating, Δ λ is the drift value of center sensor wavelength.

So required sensitivity coefficient is:

$K_T=\frac{12\mathrm{\ω}\·h}{({3l}^2-{4a}^2)\mathrm{\Δ\λ}}---\left(4\right)$

The present invention utilize 4 curved beam of uniform strengths to fiber Bragg grating strain sensor sensitivity demarcate, during real work, at loading beam mid point, do the transverse force perpendicular to axis, fiber grating is pasted section pure bending is occurred, with optical fiber grating measuring, go out the suffered stress of Standard Beam, its concrete steps are as follows again:

Step 1: design provides Standard Beam;

Step 2: determine the position that fiber grating is pasted on Standard Beam;

Step 3: installation code beam in stationary platform, is used Standard Beam fulcrum that Standard Beam is supported on platform;

Step 4: adjust the load(ing) point on loading beam, guarantee on Standard Beam stressed even;

Step 5: fiber-optic grating sensor is connected with fiber Bragg grating (FBG) demodulator;

Step 6: do the transverse force perpendicular to axis at loading beam mid point, its effect overlaps with longitudinal symmetrical plane of Standard Beam;

Step 7: imposed load on Standard Beam;

Step 8: use fiber Bragg grating (FBG) demodulator to record the wavelength variations of fiber grating;

Step 9: utilize formula (2) to calculate the strain on Standard Beam surface, utilize formula (4) to calculate the sensitivity coefficient of fiber grating.

Wherein, described 4 curved loading equipemtns are high temperature strain gauge Performance Testing machine GY-700; Fiber Bragg grating (FBG) demodulator is SM130 type.

The present invention utilize 4 curved beam of uniform strengths to fiber Bragg grating strain sensor sensitivity demarcate, top loads is exerted all one's strength and is uniformly distributed by loading beam, more namely loads in fiber grating region of living in to Standard Beam active section by the two ends of loading beam.And fiber grating is pasted and to be only had moment of flexure in section and without shearing, pure bending only occurs, with optical fiber grating measuring, go out the suffered stress of Standard Beam.Wherein Standard Beam is stressed be two sections stressed, and the loading beam that applies power is stressed by stage casing, has so just avoided loading inhomogeneous, has guaranteed that fiber grating is stressed evenly, stable.And integrally-built symmetric design, the normal stress that has guaranteed beam, is uniformly distributed along width by linear distribution along depth of section, for technical study and the measurement of fiber-optic grating sensor provides parameter reliably, there is the advantages such as simple to operate, reliable and stable, there is larger actual application value.

Claims (4)

1. a fiber Bragg grating strain sensor Sensitivity Calibration method, is characterized in that, comprise the steps,

Step 1: Standard Beam is provided;

Step 2: determine the position that fiber grating is pasted on Standard Beam;

Step 3: installation code beam in stationary platform, is used two Standard Beam fulcrums that Standard Beam is supported on platform;

Step 4: loading beam is carried on Standard Beam by two load(ing) points, adjusts the load(ing) point on loading beam, makes on Standard Beam stressed even;

Step 5: fiber grating is connected with fiber Bragg grating (FBG) demodulator;

Step 6: do the transverse force perpendicular to axis at loading beam mid point, its effect overlaps with longitudinal symmetrical plane of Standard Beam;

Step 7: the two ends by loading beam are to Standard Beam active section imposed load;

Step 8: use fiber Bragg grating (FBG) demodulator to record the wavelength variations of fiber grating;

Step 9: utilize formula (1) to calculate the strain on Standard Beam surface,

Wherein, Standard Beam surface strain: $\mathrm{\ϵ}=\±\frac{\mathrm{Mh}}{2\mathrm{EI}}=\±\frac{12\mathrm{\ω}\·h}{{3l}^2-{4a}^2}---\left(1\right),$

Utilize formula (2) to calculate fiber grating sensitivity coefficient:

Wherein, the curved segment moment of flexure such as M is Standard Beam, I is the moment of inertia of Standard Beam xsect, h is the thickness of Standard Beam, and E is the elastic modulus of Standard Beam material, and l is the distance between two Standard Beam fulcrums, a be Standard Beam fulcrum to the distance between load(ing) point, ω is the amount of deflection of Standard Beam midpoint.

2. fiber Bragg grating strain sensor Sensitivity Calibration method according to claim 1, is characterized in that: fiber grating sticks between two load(ing) points on Standard Beam.

3. fiber Bragg grating strain sensor Sensitivity Calibration method according to claim 1 and 2, is characterized in that: described loading beam is stressed by stage casing, and Standard Beam stressed be that two ends are stressed.

4. fiber Bragg grating strain sensor Sensitivity Calibration method according to claim 3, it is characterized in that: Standard Beam is arranged in stationary platform by Standard Beam fulcrum, described loading beam is carried on Standard Beam by load(ing) point, and top loads and is directly carried on loading beam.

Images