CN201535667U - Double tube fiber Bragg grating strain sensor insensitive to temperature change - Google Patents

Abstract

The utility model relates to a double tube fiber Bragg grating strain sensor insensitive to temperature change. The sensor adopts the key structure that two metal tubes are used for encapsulation, wherein the inner tube is fixed at two ends of the outer tube through threads, the fiber Bragg grating is fixed in the inner tube through adhesive, and the fiber Bragg grating is in optical connection with a signal processing device. In case of ambient temperature change, the outer tube expands outwardly along the axial direction and the free end of the inner tube expands inwardly along the axial direction, the thermal dilatation of the fiber Bragg grating caused by temperature change and Bragg wavelength displacement caused by photo-thermal effect are compensated through utilizing the difference value between the thermal expansion coefficients of the outer tube and the inner tube. The utility model adopts the mechanical compensation mode to realize temperature compensating effect only with one fiber Bragg grating, thereby guaranteeing the precision of strain measurement of the fiber Bragg grating in practical application.

Description

A kind of to the insensitive double hose fiber Bragg Grating Strain Sensor of temperature variation device

Technical field

The utility model relates to photoelectron measuring element technical field, and is specifically a kind of to the insensitive double hose fiber Bragg Grating Strain Sensor of temperature variation device.

Background technology

Strain transducer is to determine the deformation of object or as a kind of senser element of other parameters of function of strain.Because unique electrical insulating property is given the anti-electromagnetic interference capability (EMI) of optical fiber Bragg raster and at the intrinsic safety of inflammable and explosive occasion, in recent years rapidly based on the strain measurement scheme development of optical fiber Bragg raster.Because optical fiber Bragg raster to responsive to temperature, can be subjected to the interference of temperature inevitably when therefore detecting strain, must carry out temperature compensation.

The at present typical and immediate fiber Bragg Grating Strain Sensor device of the utility model is that thermometal strain transducer based on aluminum pipe, indium steel pipe is (referring to document: Wu Chuanfu, Liu Youxin, " fiber Bragg grating strain sensor temperature compensation solution ", " infrared ", 2006 (4), VOL.27, No.4).This sensor carries out laminate packaging by the semicircle sleeve pipe of indium steel and aluminium, outermost layer and innermost layer are semicircle indium steel pipe, the middle layer is semicircle aluminum pipe, and pipe end is adhesively fixed, and will apply the two ends that prestressed fiber grating is adhesively fixed on ectonexine indium steel pipe.Because the outer tube of this sensor uses hard brittle material indium steel, may cause under the bigger situation of strain damaging, and adopt the complicated encapsulating structure of three layers of pipe, influenced strain sensing sensitivity, and this sensor the time only considered temperature compensation under the non-measurement state in design, do not consider the influence of the thermal expansivity of measurand to optical fiber Bragg raster.

Summary of the invention

The purpose of this utility model be to provide a kind of on the structure compensates to the interference of sensing grating strain measurement, ensure the measuring accuracy of optical fiber Bragg raster in actual strain detects to the insensitive double hose fiber Bragg Grating Strain Sensor of temperature variation device.

The purpose of this utility model is achieved in that the insensitive double hose fiber Bragg Grating Strain Sensor of temperature variation device, the encapsulation of employing bimetal pipe, the two ends of optical fiber Bragg raster are pasted between two interior pipes with holes, pipe was fixed in the threaded outer tube of inwall two ends by screw thread in outer wall was threaded, and outer tube is fixed on the tested structure by the mode of bolt by fixed orifice.

Pipe was made by the bigger material of thermal expansivity in outer wall was threaded, and interior pipe is thicker; The threaded outer tube of inwall adopts the thermal expansivity materials with smaller to make, and outer tube is thinner.

When temperature raises, outer tube outwards expands vertically, the pipe free end inwardly expands vertically in the screw thread with holes, utilize the difference between the thermal expansivity of inner and outer pipe, the Bragg wavelength-shift that optical fiber Bragg raster thermal expansion that compensation causes because of temperature fluctuation and photo-thermal effect are taken place only obtains the applied stress effects of strain in the Bragg of optical fiber Bragg raster wavelength-shift.

The main performance of this sensor: double hose packaged fiber Bragg grating strain transducer belongs to the mechanical compensation structure to the insensitive technology of temperature variation, relies on the interaction of inner and outer pipe to make optical fiber Bragg raster not be acted upon by temperature changes.

The pass of the displacement of the centre wavelength of optical fiber Bragg raster and strain and temperature variation is:

$\frac{{\mathrm{\Δ\λ}}_B}{{\mathrm{\λ}}_B}=(1-p_e)\mathrm{\Δ\ϵ}+({\mathrm{\α}}_f+\mathrm{\ξ})\mathrm{\ΔT}---\left(1\right)$

P in the formula _eBe effective elasto-optical coefficient, α _fBe the thermal expansivity of optical fiber, ξ is the thermo-optical coeffecient of optical fiber.If introduce strain and temperature-sensitivity coefficient S _εAnd S _T, and with S _εAnd S _TSubstitution formula (1), then

$\frac{{\mathrm{\Δ\λ}}_B}{{\mathrm{\λ}}_B}=S_{\mathrm{\ϵ}}\mathrm{\Δ\ϵ}+S_T\mathrm{\ΔT}---\left(2\right)$

The utility model is the difference of utilizing between the thermal expansivity of inner and outer pipe, offsets optical fiber Bragg raster because the deformation that thermal expansion and photo-thermal effect take place, thereby solves the influence of temperature variation to the optical fiber Bragg raster peak wavelength.Can get thus

$\frac{{\mathrm{\&Delta;\&lambda;}}_B}{{\mathrm{\&lambda;}}_B}=S_{\mathrm{\&epsiv;}}[\mathrm{\&Delta;\&epsiv;}+\frac{2{\mathrm{\&alpha;}}_2{l}_2-{\mathrm{\&alpha;}}_1{l}_1}{{\mathrm{<figure-callout\; id="3"\; label="l"\; filenames="H2009201119629E00011.png"\; state="\{\{state\}\}">l</figure-callout>}}_3}\mathrm{\&Delta;T}]+S_T\mathrm{\&Delta;T}=S_{\mathrm{\&epsiv;}}\mathrm{\&Delta;\&epsiv;}+[S_{\mathrm{\&epsiv;}}\frac{2{\mathrm{\&alpha;}}_2{l}_2-{\mathrm{\&alpha;}}_1{l}_1}{{\mathrm{<figure-callout\; id="3"\; label="l"\; filenames="H2009201119629E00011.png"\; state="\{\{state\}\}">l</figure-callout>}}_3}+S_T]\mathrm{\&Delta;T}---\left(3\right)$

α in the formula ₁Be the thermal expansivity of outer tube, α ₂Be the thermal expansivity of interior pipe, l ₁Be the length of outer tube, l ₂Be the free-ended length of interior Guan Yiduan, l ₃Length for the optical fiber in the pipe in being fixed in.

Because the optical fiber Bragg raster that is packaged in the bimetal tube is insensitive to temperature variation, then in the formula (3)

$[S_{\mathrm{\&epsiv;}}\frac{2{\mathrm{\&alpha;}}_2{l}_2-{\mathrm{\&alpha;}}_1{l}_1}{{\mathrm{<figure-callout\; id="3"\; label="l"\; filenames="H2009201119629E00011.png"\; state="\{\{state\}\}">l</figure-callout>}}_3}+S_T]\mathrm{\&Delta;T}=0$

Therefore the displacement of the centre wavelength of optical fiber Bragg raster is only relevant with strain variation,

$\frac{\mathrm{\&Delta;}{\mathrm{\&lambda;}}_B}{{\mathrm{\&lambda;}}_B}=(1-P_e)\mathrm{\&Delta;\&epsiv;}=(1-P_e)\frac{\mathrm{\&sigma;}}{E}---\left(4\right)$

Compare with the fiber Bragg Grating Strain Sensor device of existing three layers of pipe encapsulation, the beneficial effects of the utility model are: sensor adopts two-layer pipe, when temperature variation, the influence of the off-set value of fiber grating Bragg wavelength in the internal pipe of temperature variation has been eliminated in the interaction of inner and outer pipes, ensured that optical fiber Bragg raster also can normal use in the bigger occasion of temperature, and can guarantee the system accuracy of strain measurement.And when the size design of inner and outer pipes that the outer tube design is very thin, interior pipe is very thick, by managing in the synchronous turn, the tightness and the effect temperature compensation of the optical fiber in the pipe in being fixed in is finely tuned.Because should become sensor only adopts two-tube encapsulation, inner and outer pipes is with being threaded, so simple in structure.

Description of drawings

Fig. 1 is a double hose fiber Bragg Grating Strain Sensor device structural representation of the present utility model.

Each label is represented among the figure: pipe in the 1-outer wall is threaded, 2-fixed orifice, the threaded outer tube of 3-inwall, 4-optical fiber Bragg raster, pipe in 5-is with holes, 6-optical fiber.

Embodiment

As shown in Figure 1, double hose fiber Bragg Grating Strain Sensor device of the present utility model is made up of the threaded interior pipe 1 of outer wall, fixed orifice 2, the threaded outer tube 3 of inwall, optical fiber Bragg raster 4 and optical fiber 6, interior pipe 5 with holes; The two ends of optical fiber Bragg raster 4 are pasted between two interior pipes 5 with holes, and pipe 1 was fixed in the threaded outer tube of inwall 3 two ends in outer wall was threaded, and bolt is fixed on outer tube 3 on the tested structure by fixed orifice 2.

Pipe 1 was made by the bigger material of thermal expansivity in outer wall was threaded, and interior pipe is thicker.The threaded outer tube 3 of inwall adopts the thermal expansivity materials with smaller to make, and outer tube is thinner.When temperature raises, outer tube 3 outwards expands vertically, interior pipe 1 free end inwardly expands vertically, utilize the difference between the thermal expansivity of inner and outer pipe, offset the deformation of optical fiber Bragg raster 4, thereby compensates is to the influence of the peak wavelength shift value of optical fiber Bragg raster owing to thermal expansion and photo-thermal effect generation.

The two-tube embodiment of being encapsulated as that makes with copper, stainless steel material:

1. two-tube size is as follows: outer tube material is elected the 45# steel as, and external diameter is got 10mm, and internal diameter is got 9mm, length 114mm; Inner tube material is elected copper as, and external diameter is got 9mm, and internal diameter is got 4mm, and two segment length are respectively 42mm.

2. press accompanying drawing 1 configuration experiment.

3. obtain the Bragg wavelength of optical fiber Bragg raster with the fiber grating analyser.

4. the Theoretical Calculation result shows: when the initial Bragg wavelength of optical fiber Bragg raster is 1550nm, and S _ε=1-p _e=0.784 μ ε ^-1, S _T=α _f+ ξ=7.35 * 10 ^-6℃ ^-1, this double hose fiber Bragg Grating Strain Sensor system sensitivity is 1.2152pm/ μ ε.

Claims (3)

1. one kind to the insensitive double hose fiber Bragg Grating Strain Sensor of temperature variation device, it is characterized in that by outer wall threaded in pipe (1), fixed orifice (2), the threaded outer tube of inwall (3), optical fiber Bragg raster (4) and optical fiber (6), with holes in pipe (5) form; The two ends of optical fiber Bragg raster (4) are pasted between two interior pipes with holes (5), and pipe (1) was fixed in the threaded outer tube of inwall (3) two ends in outer wall was threaded, and bolt is fixed on outer tube (3) on the tested structure by fixed orifice (2).

2. according to claim 1 to the insensitive double hose fiber Bragg Grating Strain Sensor of temperature variation device, it is characterized in that outer wall threaded in the pipe (1) make by the bigger material of thermal expansivity.

3. according to claim 1 to the insensitive double hose fiber Bragg Grating Strain Sensor of temperature variation device, it is characterized in that the threaded outer tube of inwall (3) adopts the thermal expansivity materials with smaller to make.

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