CN100353167C - Sensing device for optical fiber optical grating flow speed - Google Patents

Abstract

The present invention relates to a sensing device which can carry out high precision real-time monitoring and measurement on the parameters of various fluids, such as flow rate, flow quantity, etc., and can be widely used in various fields, such as building construction, spaceflight aviation, ocean detection, scientific research, etc. The sensing device is mainly composed of a hermetic expansion pipe, a fiber grating, a split ring, an optical fiber, etc. The present invention is characterized in that a designed flowrate-pressure pipe has two positions with different flow rate, and flow rate is converted into pressure by the flowrate-pressure pipe so as to carry out sensing and monitoring. When fluids penetrate through the flowrate-pressure pipe, pressure difference exists inside and outside the hermetic expansion pipe which then expands or shrinks along the axial direction, the split ring is driven to be compressed or stretched, and the central wavelength of the fiber grating is caused to drift finally. Under the condition of constant operating ambient temperature, highly sensitive parameters such as flow rate, flow quantity, etc. can be sensed and monitored by using corresponding formulas according to the drift quantity of the central wavelength. The sensing device uses the fiber grating as a primary sensing unit, and has the advantages of simple structure, novel method and high measuring precision.

Description

Sensing device for optical fiber optical grating flow speed

Technical field

The present invention relates to a kind of sensing device, monitoring and measurement in the time of carrying out high-precision real to parameters such as various flow rate of fluid, flows, can be widely used in numerous areas such as building structure, space flight and aviation, hydrospace detection and scientific research, belong to a kind of Dynamic Non-Destruction Measurement of novelty.

Background technology

Fiber grating is a kind of emerging photonic device that occurs in the recent period, and it is a kind of space periodicity index distribution that forms in fiber core.This periodic structure can change and control the dissemination of light wave in optical fiber.Fiber-optic grating sensor is by fiber grating being imbedded backing material and inside configuration or sticked on its surface, make it to parameter sensitivity to be measured, and the size and the direction of coming sensing parameter to be measured by the variation of optic fiber grating wavelength and bandwidth.Combine with the fiber-optic grating sensor array and with wavelength-division multiplex and time division multiplex system, can realize the multiple spot monitoring properties of materials (as temperature, strain, pressure, displacement, speed, acceleration etc.).Fiber grating sensing technology has been widely used in numerous areas such as building structure, space flight and aviation, hydrospace detection and scientific research, belongs to a kind of Dynamic Non-Destruction Measurement of novelty.

The present invention is a kind of fiber bragg grating sensing device that can carry out high-precision sensing to flow velocity, flow etc.Result for retrieval shows, does not still adopt fiber grating to realize the patent report of flow velocity, sensing flux at present.

Summary of the invention

The objective of the invention is to disclose a kind of structure of fiber bragg grating sensing device, parameters such as the flow velocity of its energy convection cell, flow carry out high-precision sensing.The present invention is the sensing primitive with the fiber grating, have precision height, anti-electromagnetic interference (EMI), can be long-range and advantage such as multiple spot distributed measurement monitoring.

Sensing principle of the present invention

At first, utilize flow velocity-pressure pipe, can be converted into pressure to the flow velocity in its pipe by it; Then, design corresponding fiber bragg grating pressure sensing mechanism sensing pressure; According to the anti-flow speed value that pushes away in obtaining managing of the pressure size of measuring.Be primarily characterized in that: utilize flow velocity-pressure pipe that flow velocity is converted to pressure, then by fiber bragg grating pressure sensing mechanism sensing and monitoring.

Technical scheme of the present invention: sensing device for optical fiber optical grating flow speed, it comprises flow velocity-pressure pipe, its characteristics are levied and are: conduit 7 couples together both by the flow velocity-pore a of pressure pipe 1 top and the pore c of airtight cylinder 3 respectively, conduit 8 couples together both by the flow velocity-pore b of pressure pipe top and the pore d of airtight cylindrical center respectively, and and the airtight draw-tube 2 of airtight cylindrical center communicates, inverted split ring 5 is on airtight cylinder interior right side, respectively by connecting rod 9 and 10 and airtight draw-tube and airtight cylinder be connected and fixed, fiber grating 4 writes on the optical fiber 6, and be pasted on the side of split ring, one end of optical fiber 6 is unsettled, and the other end passes airtight cylinder.

According to Bernoulli equation, intraductal pressure is relevant with flow velocity, and flow velocity is big more, and pressure is more little.There are the two different in flow rate V of place in flow velocity-pressure pipe pipe ₁, V ₂, the pressure P at this two place ₁, P ₂Also different, there is a pressure difference Δ P, can characterize flow velocity with pressure difference Δ P.Can get flow velocity V by fluid continuity equation and Bernoulli equation ₁With flow velocity V ₂Between pressure difference Δ P can be expressed as:

$\mathrm{\&Delta;P}=P_1-{\mathrm{<figure-callout\; id="2"\; label="P"\; filenames="C20051001589700071.png"\; state="\{\{state\}\}">P</figure-callout>}}_2=\mathrm{\&kappa;\&rho;}{\mathrm{<figure-callout\; id="1"\; label="V"\; filenames="C20051001589700071.png"\; state="\{\{state\}\}">V</figure-callout>}}_1^2+C=\mathrm{\&kappa;\&rho;}{V}^2+C$ (1)

κ and the coefficient that flow velocity-the pressure tubular construction is relevant in the formula, ρ is the density of fluid, C is a constant, V=V ₁Be flow rate of fluid.Can see flow velocity V from (1) formula ₁With flow velocity V ₂Between square being directly proportional of pressure difference Δ P and flow velocity V.Be that flow velocity V measurement can be converted to pressure difference Δ P measurement, pressure difference Δ P then can measure by fiber bragg grating pressure sensing mechanism.

Fiber bragg grating pressure sensing mechanism mainly is made up of airtight draw-tube, airtight cylinder, fiber grating, split ring, optical fiber.Airtight draw-tube elasticity coefficient is very little, can only in axial direction stretch, and an end of airtight draw-tube is pasted on an end of airtight cylinder.Split ring lies against in the airtight cylinder, and the semi-circular arch of split ring is connected and fixed by connecting link and airtight draw-tube and airtight cylinder respectively.Fiber grating is pasted on the split ring side, and optical grating axial and split ring parallel sided.Optical fiber one end is unsettled, and the other end passes airtight cylinder.When having pressure difference inside and outside the airtight draw-tube, draw-tube will elongate or shorten along axial direction, thereby opening endless tube semi-circular arch place is under pressure or pulling force, and then fiber grating be stretched or compression, by the variation of grating centre wavelength, can record the inside and outside pressure difference of airtight draw-tube.A conduit couples together flow velocity-pressure pipe and airtight cylinder by the flow velocity-pore a of pressure pipe top and the pore c of airtight cylinder respectively, another root couples together both by the flow velocity-pore b of pressure pipe top and the pore d of airtight cylindrical center respectively, and communicate with the airtight draw-tube 2 of airtight cylindrical center, the upwards inside and outside pressure difference of airtight slip-tube shaft this moment equals flow velocity V ₁With flow velocity V ₂Between pressure difference Δ P, and Δ P is corresponding with flow velocity, therefore can record the size of flow velocity by the variation of grating centre wavelength.

Under steady temperature, split ring is under the tensile force f effect, and fiber grating centre wavelength will be drifted about to shortwave

$\mathrm{\&Delta;\&lambda;}=\frac{12{\mathrm{\&mu;}}_1{\mathrm{\&lambda;}}_0(1-p_e)d}{E{a}^{3}b}\&CenterDot;(\frac{a}{2}-\frac{{\mathrm{<figure-callout\; id="2"\; label="a"\; filenames="C20051001589700071.png"\; state="\{\{state\}\}">a</figure-callout>}}^2}{12d})F$ (2)

Wherein a is a split ring straight beam width, and b is a straight beam thickness, and split ring semi-circular arch radius is r, and moment loading is a distance between external force F and straight beam center line apart from d=r+a/2, p _eEffective elasto-optical coefficient for optical fiber is about 0.22, and E is the Young modulus of split ring material, λ ₀Be the centre wavelength of fiber grating, μ ₁Be split ring strain transmission factor, it is relevant with factors such as backing material and stickup situations.And F=Δ PS, Δ P is the inside and outside pressure difference of airtight draw-tube, S is the cross-sectional area of draw-tube.At this moment

$\mathrm{\&Delta;\&lambda;}=\frac{12{\mathrm{\&mu;}}_1{\mathrm{\&lambda;}}_0(1-p_e)d}{E{a}^{3}b}\&CenterDot;(\frac{a}{2}-\frac{{\mathrm{<figure-callout\; id="2"\; label="a"\; filenames="C20051001589700071.png"\; state="\{\{state\}\}">a</figure-callout>}}^2}{12d})\mathrm{\&Delta;PS}=\frac{12\mathrm{\&kappa;}{\mathrm{\&mu;}}_1{\mathrm{\&mu;}}_2{\mathrm{\&lambda;}}_0(1-p_e)\mathrm{\&rho;dS}}{E{a}^{3}b}(\frac{a}{2}-\frac{{\mathrm{<figure-callout\; id="2"\; label="a"\; filenames="C20051001589700071.png"\; state="\{\{state\}\}">a</figure-callout>}}^2}{12d}){\mathrm{<figure-callout\; id="2"\; label="V"\; filenames="C20051001589700071.png"\; state="\{\{state\}\}">V</figure-callout>}}^2+\mathrm{\&Omega;}$ (3)

Wherein $\mathrm{\&Omega;}=\frac{12{\mathrm{\&mu;}}_1{\mathrm{\&lambda;}}_0(1-p_e)\mathrm{dCS}}{E{a}^{3}B}-(\frac{a}{2}-\frac{a^2}{12d}),$ μ ₂Correction factor for this sensing device.

Know easily that from (3) formula fiber grating centre wavelength drift value Δ λ and square of flow velocity are linear, so we can utilize the grating wavelength coding techniques to measure flow rate of fluid.In addition, from following formula as can be known, optic fiber grating wavelength drift value Δ λ is relevant apart from the structure of d, straight beam width a, thickness b and flow velocity-pressure pipe with moment loading.The parameter of improving flow velocity-pressure pipe and split ring can further improve sensing sensitivity.

And flow W is the product of flow velocity V and flow velocity-pressure pipe cross-sectional area s, i.e. W=sV.

The invention has the beneficial effects as follows, be the sensing primitive with the fiber grating, features simple structure, method novelty, measuring accuracy height.Based on the advantage of fiber grating itself, this sensor also have anti-electromagnetic interference (EMI), corrosion-resistant, be suitable for working under the rugged surroundings such as inflammable and explosive High Temperature High Pressure and can be long-range and advantage such as multiple spot distributed measurement.

Description of drawings

Fig. 1 is the sensing device for optical fiber optical grating flow speed structural representation.

Fig. 2 is measurement mechanism figure of the present invention.

Fig. 3 is the typical light spectrogram of the present invention in the certain flow rate scope.

Fig. 4 is a centre wavelength drift value of the present invention and the graph of a relation of corresponding flow velocity.

Wherein: 1 flow velocity-pressure pipe, 2 airtight draw-tubes, 3 airtight cylinders, 4 fiber gratings, 5 split rings, 6 optical fiber, 7 conduits, 8 conduits, 9 connecting links, 10 connecting links, 11 fluid intakes, 12 fluid egress points, 13 fiber couplers, 14 light sources, 15 photo-detectors, V ₁, V ₂Flow rate of fluid in flow velocity-pressure pipe pipe, a. pore, b. pore, c. pore, d. pore.

Embodiment

Below in conjunction with accompanying drawing embodiments of the present invention are further specified:

Fig. 1 is the sensing device for optical fiber optical grating flow speed structural representation, and Fig. 2 is measurement mechanism figure.

Technical scheme of the present invention: sensing device for optical fiber optical grating flow speed, it comprises flow velocity-pressure pipe, its characteristics are levied and are: conduit 7 couples together both by the flow velocity-pore a of pressure pipe 1 top and the pore c of airtight cylinder 3 respectively, conduit 8 couples together both by the flow velocity-pore b of pressure pipe top and the pore d of airtight cylindrical center respectively, and and the airtight draw-tube 2 of airtight cylindrical center communicates, inverted split ring 5 is on airtight cylinder interior right side, respectively by connecting link 9 and 10 and airtight draw-tube and airtight cylinder be connected and fixed, fiber grating 4 writes on the optical fiber 6, and be pasted on the side of split ring, one end of optical fiber 6 is unsettled, and the other end passes airtight cylinder.With flow velocity-pressure pipe 1 and airtight cylinder 3 horizontal positioned.Fiber grating 4 is pasted on the side of split ring 5, and the connected mode of split ring 5 and conduit as mentioned above.The light that light source 14 sends arrives fiber gratings 4 and reflects through fiber coupler 13, and reflected light incides photo-detector 15 once more through fibre optic grating coupler 13.

Described V ₁, V ₂Be different flow velocity in flow velocity-pressure pipe pipe, flow velocity-pressure pipe is by material such as glass, polymkeric substance, metal, alloys.

Described airtight draw-tube can only stretch vertically, and it is made by organic polymer, aluminum foil material.

Described fiber grating is the Fiber Bragg Grating FBG or the long period fiber grating of glass, plastics.

Described split ring is made by organic polymer or the metal material of medium Young modulus 1000MPa～4000MPa.

Described optical fiber is single-mode fiber.

The operating ambient temperature of sensing device for optical fiber optical grating flow speed is between-20 ℃～70 ℃.

Embodiment

Flow velocity-pressure pipe selects for use glass to make.

Airtight draw-tube selects for use the aluminium foil pipe to make.

Airtight cylinder and split ring select for use organic glass (Young modulus is about 2500Mpa) to make.

Fiber grating is to select for use quartzy single-mode fiber, employing uv-exposure technology and phase mask method to write to make the Fiber Bragg Grating FBG that forms or adopt the amplitude mask method to write the long period fiber grating that system forms.Fiber grating sticks on split ring straight beam side.Optical fiber is quartzy single-mode fiber; Fiber coupler is 2 * 2 or 1 * 2 fiber coupler.

Light source is selected wideband light source or tunable optical fiber laser for use; Photo-detector is selected fiber spectrometer for use.

The internal diameter 26.5mm of the flow velocity of actual fabrication-pressure pipe, the internal diameter 11.0mm of throat.S=9.5 * 10 are amassed in the effective cross section of draw-tube ^-3m ², used fiber grating is a Fiber Bragg Grating FBG, and its length is about 12mm, and centre wavelength is about 1562nm, and peak value is greater than 7dB.Split ring is made by organic glass (Young modulus is about 2500Mpa), and its radius is r=60.0mm, the long L=40.0mm of straight beam, and straight beam width a=4.42mm, thickness b=2.60mm, moment loading is apart from d=62.2mm.

Under constant room temperature, this sensing device is carried out the flow-velocity sensing test, its measurement mechanism synoptic diagram is as shown in Figure 3.Fig. 4 is the typical light spectrogram of this sensing device in the certain flow rate scope.Show that through repeatedly testing the flow velocity sensing dynamic range of this sensing device is 0.051～0.147m/s, and the flow velocity of distinguishable at least 0.0003m/s.As far as we know, this is the optimal value of being reported at present.Improve the parameter of flow velocity-pressure pipe and fiber bragg grating pressure sensing mechanism, the sensitivity that can further improve the flow velocity sensing.

As previously described, by respective formula, can also carry out the high-precision sensing of fluid flow.In the practical application, light signal is converted to electric signal, carries out data processing with computing machine again, the flow velocity of sensing monitoring in real time, flow by photoelectric commutator.

Claims (7)

1, a kind of sensing device for optical fiber optical grating flow speed, it comprises flow velocity-pressure pipe, it is characterized in that: upper conduit (7) couples together flow velocity-pressure pipe (1) and airtight cylinder (3) by the flow velocity-pore a of pressure pipe (1) top and the pore c of airtight cylinder (3) respectively, downcomer (8) couples together flow velocity-pressure pipe (1) and airtight cylinder (3) by the flow velocity-pore b of pressure pipe top and the pore d of airtight cylindrical center respectively, and the airtight draw-tube (2) of downcomer (8) and airtight cylindrical center communicates, inverted split ring (5) is on airtight cylinder interior right side, be connected and fixed with airtight draw-tube and airtight cylinder by left connecting rod (9) and right connecting rod (10) respectively, fiber grating (4) writes on the optical fiber (6), and be pasted on the upper side of split ring, one end of optical fiber (6) is unsettled, and the other end passes airtight cylinder.

2, sensing device for optical fiber optical grating flow speed according to claim 1 is characterized in that: flow velocity V with pore a corresponding position flows through in flow velocity-pressure pipe ₁With the flow velocity V that flows through with pore b corresponding position ₂Be different flow velocity in flow velocity-pressure pipe pipe, flow velocity-pressure pipe is by glass, polymkeric substance, metal or alloy material.

3, sensing device for optical fiber optical grating flow speed according to claim 1 is characterized in that: described airtight draw-tube can only stretch vertically, and it is made by organic polymer or aluminum foil material.

4, sensing device for optical fiber optical grating flow speed according to claim 1 is characterized in that: described fiber grating is the Fiber Bragg Grating FBG or the long period fiber grating of glass or plastics.

5, sensing device for optical fiber optical grating flow speed according to claim 1 is characterized in that: described split ring is made by organic polymer or the metal material of medium Young modulus 1000Mpa～4000MPa.

6, sensing device for optical fiber optical grating flow speed according to claim 1 is characterized in that: described optical fiber is single-mode fiber.

7, sensing device for optical fiber optical grating flow speed according to claim 1 is characterized in that: the operating ambient temperature of described sensing device is between-20 ℃～70 ℃.

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