CN101750183A - Fiber grating pressure sensor - Google Patents
Fiber grating pressure sensor Download PDFInfo
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- CN101750183A CN101750183A CN200810227868A CN200810227868A CN101750183A CN 101750183 A CN101750183 A CN 101750183A CN 200810227868 A CN200810227868 A CN 200810227868A CN 200810227868 A CN200810227868 A CN 200810227868A CN 101750183 A CN101750183 A CN 101750183A
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Abstract
The invention provides a fiber grating pressure sensor. The sensor comprises a cantilever beam, a first elastic membrane and a fiber, wherein the cantilever beam is provided with a first end and a second end, the first end is fixed, and the second end is in the cantilever state; the first elastic membrane is fixedly connected with a first support pillar facing the cantilever beam; the end of the first support pillar abuts against one side of the second end of the cantilever beam; the fiber is provided with a fiber grating; and the fiber grating is fixedly connected with the cantilever beam. The fiber grating pressure sensor of the invention can effectively reduce the size of the fiber in the stressed direction, and thus, can be used for pressure measurement in narrow space. In addition, the invention can also be provided with a second elastic membrane, and thus, can be used for directly measuring the differential pressure signal by using the combined actions of the first elastic membrane and the second elastic membrane on the cantilever beam.
Description
Technical field
The present invention relates to a kind of pressure, liquid level, flow measuring and controlling device that is applied to fields such as petrochemical complex, water conservancy, Aeronautics and Astronautics, automobile, medical treatment, specifically, relate to a kind of fiber bragg grating pressure sensor.
Background technology
Sensor is the important technology basis of new technology revolution and information society, becomes one of commodity that sold well most on the international market since the mid-80.In the last few years, in seven big class sensors such as power, heat, voltage, magnetic, gas, wet, light, enjoyed favor with the Fibre Optical Sensor in the optical sensor especially.Optical fiber sensing technology is a field of the guided wave photon technology of photon and beared information transmission.Photon technology is the technology of photonics and electronics be combined into.Along with science and technology development, much more superior than the speed capabilities and the spatial content of electronics as the photon of information carrier.Photo response speed is than the individual order of magnitude of electronics Senior Three, and characteristics such as the high parallel processing capability of photon and high information rate make it have potentiality far above electronic information capacity and processing speed, will promote the development of optical information and photonic computer.
Various electrical sensors are used for such as local measurement such as oil gas jar, oil gas well, oil gas pipe, have unsafe factor (under the interference of down-hole rugged environment such as high temperature, high pressure, burn into electromagnetism etc. can't operate as normal).And fiber-optic grating sensor is highly suitable for application in the rugged surroundings because of its intrinsic safety.
Fiber-optic grating sensor have such as anti-electromagnetic interference (EMI), low-loss, flexible, volume is little, outside in light weight, cost is low, corrosion-resistant, waterproof, fire prevention etc. the are intrinsic advantage, important measurement parameters such as temperature and stress are had the high measuring accuracy and the linearity, and sufficient measurement range.
Existing fiber grating pressure sensitizing sensor mainly contain following several [Song Lina. Fiber Bragg Grating Temperature pressure sensing technology research. Northwest University's master thesis, 2008.6.]:
(1) fibre optic compression sensor 10 of polymkeric substance embedding fiber grating pressure enhanced sensitivity is modal fiber-optic grating sensor, and its structure as shown in Figure 1.This sensor uses particular polymer material 101 that the fiber grating (FBG) 102 of optical fiber 104 is packaged in the metal sleeve 103, because the elastic modulus of the modular ratio bare fibre of particular polymer material 101 is little, pressure is had higher response; Therefore, the strain that produces under identical stress will increase, and the increase of strain will cause that the relative variation of centre wavelength increases, and so then realizes the enhanced sensitivity of counter stress.In order to eliminate in the encapsulation process owing to polymer cure contraction and polymkeric substance and bonding and fricative the warbling of fiber grating of casing wall, at metal sleeve precoating one deck soft elastic material.Fiber grating pressure-responsive sensitivity through encapsulation is 0.036nm/MP, is 12 times of bare optical fibers and bare optical gratings 0.003nm/MPa, and pressure measurement range can reach more than the 40MP.
But, this kind fibre optic compression sensor is owing to be to adopt polymkeric substance to realize enhanced sensitivity, its resistance to elevated temperatures is very poor, and for reaching higher sensitivity, need polymkeric substance and optical fiber that long contact length is arranged, though thereby make thin but its size of this kind fibre optic compression sensor in the optic fibre force direction be length dimension generally more than 7cm, can't be used for the pressure survey of small space.And this kind Fibre Optical Sensor can only be used for measured pressure signal, and can not be used for measure differences in pressure.
(2) cylindrical drum-piston type fibre optic compression sensor 20, its structure as shown in Figure 2.In a piston cylinder operator that is combined into by hydrostatic column (cylindrical drum 201) and piston 202, charge into gas, a valve 203 is arranged, charge into the amount of gas in order to control at the left end of cylindrical drum 201.When ambient pressure makes cylindrical drum 201 and piston 202 relative motions, will make the fiber grating (FBG) 205 of optical fiber 204 produce strain, bragg wavelength is moved.For reducing to rub and the leakage of gas when preventing piston 202 motions, between cylindrical drum 201 and piston 202, scribble lubricating oil.In order to make fiber grating 205 in measurement range, keep extended state, make fiber grating 205 produce certain prestrain before the measurement earlier.The sensitivity of this fiber grating pressure sensitization structure can reach 1078.8nm/MPa, is 3.515 * 10 of bare fibre
5Doubly.
This kind fiber grating pressure sensitizing sensor, can be by changing the initial parameter of the body of inflating in the cylindrical drum 201, come the sensitivity and the measurement range of modifier, but there are the following improvements that wait: satisfying under the highly sensitive condition on the one hand, just can not satisfy its measurement range, its measurement range only is 0-0.0045MPa; The sensor of this structure relatively is applicable to the sensing measurement of air pressure under the low pressure, hydraulic pressure on the other hand, when temperature variation is big, because gas is subjected to Temperature Influence bigger, the sensor of this moment not only changes responsive to pressure, and, need carry out temperature during use and go quick or compensation the temperature variation sensitivity; In addition, owing to need to guarantee the mobile space of piston 202, this sensor generally more than 10cm, can not be used for the pressure survey of small space in the size (length dimension) of optic fibre force direction; And this sensor can not seal, and can not be applied to have in corrosive gas or the liquid; At last, this sensor can not be measured two pressure differentials in the space.
(3) fiber bragg grating pressure sensor 30 of metal tube combination pressure enhanced sensitivity, its structure as shown in Figure 3.This sensor is to use a physical construction hydrodynamic pressure to be converted to the optical fiber axial strain with some levels.This structure tool sensing pipe 301 and stay pipe 302, the grating 304 of optical fiber 303 is pasted between sensing pipe 301 and the stay pipe 302, sensing pipe 301 is used to experience the pressure of fluid, when fluid enters sensing pipe 301, sensing pipe 301 will be stretched and the grating 304 that is pasted between sensing pipe 301 and the stay pipe 302 also is stretched accordingly, thereby grating 304 foveal reflex wavelength are drifted about, get final product the size of perception fluid pressure by the monitoring wavelength change.
This kind sensor is subjected to the influence of structure and sensing pipe 301 elastic modulus, in order to obtain the bigger relative movement distance of sensing pipe 301 and stay pipe 302, need bigger size, the size of the optic fibre force direction of this sensor is generally more than 10cm, its size is bigger, is unfavorable for the pressure survey in small space.In addition, this sensor is had relatively high expectations to process technology, the cost height.And this sensor also can only detected pressures, can not measure differences in pressure.
(4) fiber bragg grating pressure sensor 40 of corrugated tube and ladder beam fiber grating pressure enhanced sensitivity, its structure as shown in Figure 4.This kind fiber bragg grating pressure sensor is to experience pressure by corrugated tube 401, and the grating 403 that passes to optical fiber 402 by other mechanisms produces the enhanced sensitivity device of strain.As ladder beam-corrugated tube fiber bragg grating pressure sensor, fiber grating 403 is sticked on the ladder beam 404, be installed in again in the closed container 405, on closed container 405 walls corrugated tube 401 is housed, the mobile terminal of corrugated tube 401 links to each other with ladder beam 404.When ambient pressure acts on the corrugated tube 401, will form centre-point load on the ladder beam 404, make beam generation deformation, thereby cause that fiber grating 403 produces strain longitudinally, and cause the bragg reflection peak wavelength to change.The sensitivity of this kind ladder beam-corrugated tube fiber bragg grating pressure sensor can reach 8.73nm/MPa, is 7455 times of bare optical fibers and bare optical gratings.But, generally be lower than 10MPa, so the withstand voltage scope of this fiber bragg grating pressure sensor can not be higher than 10MPa because corrugated tube 401 is own withstand voltage not high.
This kind sensor is subjected to the influence of corrugated tube processing technology and sensitivity, and the size of corrugated tube 401 is bigger, makes the size (gauge) of optic fibre force direction of this sensor not be thinner than 6cm, can not be used for the pressure survey of small space.And, owing to adopt the ladder beam structure, can not eliminate the fiber grating chirp, can cause the distorted signals of measurement, sensitivity is measured in influence.In addition, the corrugated tube 401 direct application of forces are given ladder beam 404, and by carriage, friction force is not bigger, make sensitvity constraint.And this sensor also can only measured pressure signal, can not detect the pressure differential signal in two spaces.
In sum, existing fiber bragg grating pressure sensor all exists size sensor bigger, can not be used for small space, and the problem of the pressure differential signal of energy measurement different spaces not.
Therefore, be necessary to provide a kind of new fiber-optic grating sensor structure, overcome the above-mentioned defective that the existing fiber grating pressure sensor exists.
Summary of the invention
The objective of the invention is to, a kind of fiber bragg grating pressure sensor is provided, it adopts flexible sheet and cantilever beam structure, can effectively dwindle the size of optic fibre force direction, thereby can be used for the pressure survey of small space.
The present invention also aims to, a kind of fiber bragg grating pressure sensor is provided, it is the gaging pressure difference signal directly.
Above-mentioned purpose of the present invention can adopt following technical scheme to realize: a kind of fiber bragg grating pressure sensor, and it comprises:
Semi-girder has first end and second end, and wherein first end is fixed, and second end is in cantilever position;
First flexible sheet, it is fixedly connected with first fore-set towards described semi-girder, and the end of this first fore-set contacts mutually with a side of second end of described semi-girder;
Optical fiber, it has fiber grating, and this fiber grating is fixedly connected on the semi-girder.
In an optional embodiment of the present invention, described fiber bragg grating pressure sensor also comprises: second flexible sheet, itself and first flexible sheet are oppositely arranged, and being fixedly connected with second fore-set towards semi-girder, opposite side relative with a side of first fore-set on second end of this second fore-set and described semi-girder contacts mutually.
In an optional example of the present invention, described fiber-optic grating sensor also includes housing, and this housing is formed with containing cavity, and is formed with first mounting groove on hull outside, has first through hole that is communicated in described containing cavity in the bottom of this first mounting groove; Described semi-girder is arranged in the containing cavity of described housing, first end of this semi-girder is fixedly supported on the housing, the sealing of described primary diaphragm periphery is installed on first mounting groove of housing, and described first fore-set passes first through hole of described first mounting groove bottom and contacts mutually with second end of described semi-girder.
In an optional example, described hull outside also is provided with second mounting groove on the position relative with first mounting groove, is provided with second through hole that is communicated in described containing cavity in the bottom of this second mounting groove; The sealing of described secondary diaphragm periphery is installed on described second mounting groove, and described second fore-set passes described second through hole and contacts mutually with described semi-girder.
In the present invention, described first fore-set is provided with miniature bearing, and described first fore-set contacts second end in described semi-girder by this miniature bearing.
In the present invention, described second fore-set is provided with miniature bearing, and described second fore-set contacts second end in described semi-girder by this miniature bearing.
Utilize this miniature bearing, be subjected to transverse force at fore-set and do the time spent, this fore-set can carry out small rolling on semi-girder, thereby greatly reduces the friction between fore-set and the semi-girder, thereby can improve the accuracy of measuring when carrying out pressure survey.
In the present invention, described semi-girder is an equi intensity cantilever.Adopt this equal strength semi-girder, can effectively eliminate the fiber grating chirp, improve and measure sensitivity.
In the present invention, described fiber grating is pasted and fixed on the semi-girder.
In the present invention, be provided with the support portion in the containing cavity of described housing, first end of described semi-girder is supported on this support portion, and a briquetting is pressed on first end of semi-girder, and be fixed on the support portion, thereby first end of semi-girder is pressed abd fixed on the described support portion by securing member.In this example, can be provided with on the described briquetting for what optical fiber passed and wear groove.
In the present invention, described first flexible sheet is made by stainless steel material.Described second flexible sheet is also made by stainless steel material.
In the present invention, described semi-girder is made by beryllium-bronze material.
In the present invention, be formed with annular flange portion at the edge of described first flexible sheet, the outside of this annular flange portion and described first mounting groove are tightly connected together, thereby realize being tightly connected of first flexible sheet and first mounting groove.
In the present invention, be formed with annular flange portion at the edge of described second flexible sheet, the outside of this annular flange portion and described second mounting groove are tightly connected together, thereby realize being tightly connected of second flexible sheet and second mounting groove.
In the present invention, for making things convenient for the assembling in housing of semi-girder and fiber grating, described housing comprises main casing and is packaged on the capping of main casing end, is formed with the hole of passing through for described optical fiber in described capping, adopts polymeric seal between described capping and the optical fiber.
Adopt said structure of the present invention, effect of the present invention is significant: 1) because the present invention adopts flexible sheet and semi-girder to realize the enhanced sensitivity of fiber grating, the size of flexible sheet can be done very for a short time, thereby make fiber bragg grating pressure sensor of the present invention can do very thinly in the size of optic fibre force direction (thickness direction of housing), for example its thickness can be thinned to 12mm, thereby help being installed in the small space, come the pressure of small space is carried out pressure survey.And, fiber bragg grating pressure sensor of the present invention can be according to the needs of measurement environment, realize also can realizing the change of measurement range large-area measurement, thereby make that its application is more extensive by the thickness that changes flexible sheet and semi-girder by the size of sensor outer housing.2) because fiber-optic grating sensor of the present invention is equipped with two flexible sheets in hull outside, these two flexible sheets can pass to semi-girder by fore-set with pressure respectively, the compressing semi-girder is to the little side shifting of pressure, fiber grating can this deformation of perception, thereby make fiber bragg grating pressure sensor of the present invention can measure the pressure differential signal of two different spaces or the same space dynamic environment.3), thereby make sensor good corrosion resistance be arranged to rugged surroundings because sensor outer housing of the present invention can will form an air locking.And sensor internal is measured used fiber grating, can resist electromagnetic interference (EMI), and low-loss, volume is little, in light weight, cost is low, corrosion-resistant, waterproof fireproofing etc.
Description of drawings
Fig. 1 is the fiber bragg grating pressure sensor structural representation of existing encapsulation type packaged fiber grating;
Fig. 2 is existing cylindrical drum-piston type optical fibre grating pressure sensor structure synoptic diagram;
Fig. 3 is existing metal tube combined fiber bragg grating pressure sensor structural representation;
Fig. 4 is existing corrugated tube and ladder beam fiber bragg grating pressure sensor structural representation;
Fig. 5 faces structural representation for the fiber bragg grating pressure sensor of embodiments of the invention 1;
Fig. 6 is the A-A sectional structure synoptic diagram of Fig. 5;
Fig. 7 is the mathematical analysis structural representation of equi intensity cantilever of the present invention;
Fig. 8 is the mechanical structure synoptic diagram of the fiber bragg grating pressure sensor of embodiments of the invention 1;
Fig. 9 is the fiber grating reflection wavelength of sensor I of experimental example of embodiments of the invention 1 and the variation relation synoptic diagram of load-carrying;
Figure 10 is the fiber grating reflection wavelength of sensor II of experimental example of embodiments of the invention 1 and the variation relation synoptic diagram of load-carrying;
Figure 11 is an application examples synoptic diagram of the embodiment of the invention 1;
Figure 12 faces structural representation for the fiber bragg grating pressure sensor of the embodiment of the invention 2;
Figure 13 is the B-B sectional structure synoptic diagram of Figure 12.
Embodiment
Embodiment 1
As Fig. 5-Figure 10 shows that synoptic diagram of the fiber-optic grating sensor 50 of present embodiment.As Fig. 5, shown in Figure 6, the fiber-optic grating sensor 50 of present embodiment comprises: semi-girder 51, first flexible sheet 521, first fore-set 531, second flexible sheet 522, second fore-set 532 and optical fiber 54.Wherein, semi-girder 51 has first end 511 and second end, 512, the first ends 511 are fixing, and second end 512 is in cantilever position; Described first fore-set 531 is fixedlyed connected with first flexible sheet 521, and stretch out towards described semi-girder 51, the end of this first fore-set 531 contacts mutually with a side of second end 512 of described semi-girder 51, thereby the radial pressure that first flexible sheet 521 is subjected to passes to semi-girder 51; Secondary diaphragm 522 is arranged on the position relative with primary diaphragm 521, second fore-set 532 is fixedly connected on second flexible sheet 522, and also stretch out towards semi-girder 51, the opposite side that this second fore-set 532 is relative with the side with first fore-set 531 on described semi-girder 51 second ends 512 contacts mutually, thereby the radial pressure that will be subjected to the secondary diaphragm 522 of primary diaphragm 521 opposite sides also passes to semi-girder 51, and optical fiber 54 has fiber grating, and this fiber grating is fixedly connected on the semi-girder 51.During use, with first flexible sheet 521 and second flexible sheet 522 be arranged at two different spaces or the same space dynamic environment in, the primary diaphragm 521 of semi-girder 51 both sides, when secondary diaphragm 522 is under pressure, respectively pressure is passed to the relative both sides of second end 512 of semi-girder 51 by first fore-set 531 and second fore-set 532, second end 512 of compressing semi-girder 51 is to the little side shifting of pressure, be fixed on fiber grating on the semi-girder 51 and perceive this deformation of semi-girder 51, output signal changes, thereby measures the pressure differential signal in two different spaces or the same space dynamic environment.
In the present embodiment, owing to be to adopt first flexible sheet 521, second flexible sheet 522 and semi-girder 51 to realize the enhanced sensitivity of optical fiber 54, the size of first flexible sheet 521 and second flexible sheet 522 can be done very for a short time, thereby make fiber bragg grating pressure sensor 50 of the present invention be subjected to the size of force direction can do very thinly at optical fiber 54, for example its thickness can be thinned to 12mm, thereby can be placed in the small space, the pressure differential of small space is measured.And, the fiber bragg grating pressure sensor of present embodiment can be according to the needs of measurement environment, realize the change of measurement range by the thickness that changes first flexible sheet 521, second flexible sheet 522 and semi-girder, also can realize large-area measurement, thereby make its range of application more extensive by the size that increases first flexible sheet 521 and second flexible sheet 522.
As Fig. 5, shown in Figure 6, in an object lesson of present embodiment, described fiber-optic grating sensor 50 also includes housing 55, this housing 55 is formed with containing cavity 550, and on the relative position in housing 55 outsides, being formed with first mounting groove 551 and second mounting groove 552 respectively, described first flexible sheet 521 and second flexible sheet 522 periphery sealing respectively are installed on this first mounting groove 551 and second mounting groove 552.Have first through hole 553 and second through hole 554 that is communicated in described containing cavity 550 respectively in the bottom of this first mounting groove 551 and second mounting groove 552; Described semi-girder 51 is arranged in the containing cavity 550 of described housing 55, first end 511 of this semi-girder 51 is fixedly supported on the housing 55, first fore-set 531 that is fixedly connected on primary diaphragm 521 passes first through hole 553 of described first mounting groove 551 bottoms and contacts mutually with a side of second end 512 of described semi-girder 51, thereby the radial pressure that primary diaphragm 521 is subjected to is passed to second end 512 of semi-girder 51; Second fore-set 532 that is fixedly connected on secondary diaphragm 522 passes described second through hole 554 and contacts mutually with the opposite side of second end 512 of described semi-girder 51, thereby the radial pressure that secondary diaphragm 522 is subjected to is passed to second end 512 of semi-girder 51.
In an example of present embodiment, can be provided with miniature bearing 561 on described first fore-set 531, this first fore-set 531 contacts second end 512 in described semi-girder 51 by this miniature bearing 561.Also can be provided with miniature bearing 562 on described second fore-set 532, this second fore-set 532 contacts second end 512 in described semi-girder 51 by this miniature bearing 562.Like this, utilize this miniature bearing 561,562, be subjected to transverse force and do the time spent at first fore-set 531, second fore-set 532, this first fore-set 531 and second fore-set 532 can carry out small rolling by miniature bearing 561,562 on semi-girder 51, thereby greatly reduce the friction between first fore-set 531, second fore-set 532 and the semi-girder 51, improve the accuracy when carrying out the pressure differential measurement.
In the object lesson of embodiment, for the linearity that the grating wavelength that guarantees sensor fibre 54 in measurement range drifts about, avoid fiber grating to produce chirp, as shown in Figure 5, described semi-girder 51 can adopt equi intensity cantilever, measures sensitivity and accuracy to improve.Wherein, if non-uniform beam designs to such an extent that make maximum on each cross section of beam all reach the permissible stress value of material, then such beam just is called the beam of uniform strength.
In an optional example of the present invention, as Fig. 5, shown in Figure 6, in the containing cavity 550 of described housing 55, be provided with support portion 556, first end 511 of described semi-girder 51 is supported on this support portion 556, one briquetting 557 is pressed on first end 511 of semi-girder 51, and briquetting 557 is fixed on the support portion 556, thereby first end 511 of semi-girder 51 is pressed abd fixed on the described support portion 556 by securing member 558.In this example, can be provided with on the described briquetting 557 for what optical fiber 54 passed and wear groove 5571.
In an object lesson of present embodiment, described first flexible sheet 521, second flexible sheet 522 and housing 55 can be made by stainless steel material.Described first fore-set 531 can be processed with first flexible sheet, 521 one.Described second fore-set 531 can be processed with second flexible sheet, 521 one.Described semi-girder 51 can be made by beryllium-bronze material, and the elastic modulus of this kind material is relatively little, and it is relatively good that deformation recovers.The fiber grating of described optical fiber 54 can be pasted and fixed on the semi-girder 51.
In the object lesson of embodiment, the edge of described first flexible sheet 521, second flexible sheet 522 can be formed with annular flange portion 5211,5221 respectively, the outside of this annular flange portion 5211 and described first mounting groove 551 are tightly connected together, thereby realize being tightly connected of first flexible sheet 521 and first mounting groove 551; The outside of this annular flange portion 5221 and described second mounting groove 552 are tightly connected together, thereby realize being tightly connected of second flexible sheet 522 and second mounting groove 552.
In the present embodiment, owing to be to adopt flexible sheet and semi-girder to realize the enhanced sensitivity of fiber grating 54, do not need as existing cylindrical drum-piston type optical fibre grating pressure transducer 30 and metal tube combined fiber bragg grating pressure sensor 40, to need relative motion, thereby housing 55 can be after installing each parts, form air locking, thereby make 50 pairs of rugged surroundings of fiber-optic grating sensor of the present invention that good corrosion resistance be arranged.In the present embodiment, for making things convenient for semi-girder 51 and the assembling of fiber grating 54 in housing 55, described housing 55 comprises main casing 581 and is packaged on the capping 582 of main casing 581 ends, in described capping 582, be formed with the hole 583 that the tail optical fiber for described optical fiber 54 passes through, adopt polymeric seal between the tail optical fiber of described capping 582 and optical fiber 54, thereby make this fiber bragg grating pressure sensor 50 after assembling, form air locking.
Further specify the fiber bragg grating pressure sensor 50 of the measure differences in pressure of present embodiment below by theoretical analysis and experimental example.
The strain fiber grating through the encapsulation of overstress enhanced sensitivity in the present embodiment sticks on the equi intensity cantilever 51; With first flexible sheet 521 and 522 sealings of second flexible sheet, this primary diaphragm 521 is respectively with first fore-set 531 with secondary diaphragm 522 and closely contacts with equi intensity cantilever 51 with second fore-set 532 in housing 55 both sides; Both sides primary diaphragm 521, secondary diaphragm 522 will not be subjected to displacement to the direction of semi-girder 51 pressure that is subjected to when both sides simultaneously, compressing equi intensity cantilever 51 produces deformation to the little side shifting of pressure, the fiber grating 54 foveal reflex wavelength change that this deformation causes, thus it is poor to carry out detected pressures by (FBG) demodulator.
At first the foveal reflex wavelength X B of fiber grating can be determined by Prague (Bragg) formula of fiber grating: λ
B=2n
EffΛ
B(1)
As seen λ
BDepend on two factors: effective refractive index n
EffWith the grating periods lambda
B, the variation of any one factor all can cause λ
BChange.When stress during, can cause Λ simultaneously in fiber grating
BVariation and the n that causes by elasto-optical effect
EffVariation, its expression formula is:
Δ λ in the formula
BBe the fiber grating reflection wavelength variable quantity that stress causes, ε is the dependent variable of fiber grating, P
eBe the effective elasto-optical coefficient of optical fiber.
In order to guarantee the linearity of sensor fibre grating wavelength drift in measurement range, avoid fiber grating to produce chirp, therefore sensor of the present invention has adopted the equi intensity cantilever structure.Equi intensity cantilever 51 as shown in Figure 7, equi intensity cantilever 51 is an isosceles triangle, thick h, base b
0, long L, the width b (x) at its x place is:
b(x)=b
0(1-x/L)????????????????????????(3)
The amount of deflection at equi intensity cantilever x place is under extraneous stress:
F is vertically downward the concentrated stress of external influence at the x place of equi intensity cantilever 51, E
1Be the elastic modulus of material, I
0=b
0h
3/ 12 is the moment of inertia of the xsect of O point place equi intensity cantilever 51.
Locate the amount of deflection maximum in the summit of equi intensity cantilever 51 as can be known by formula (4):
The strain at the place, summit of equi intensity cantilever 51 is:
In order to adapt to rugged environment, sensor of the present invention needs sealing, to guarantee the sensing characteristics of equi intensity cantilever 51 and fiber grating, so taked flexible sheet (first flexible sheet 521 and second flexible sheet 522) hermetically-sealed construction.As a concrete example, first flexible sheet 521 and second flexible sheet 522 all adopt the fixing circular film of periphery, wherein the center amount of deflection y of circular film in this is analyzed
cExpression formula is:
Can get diaphragm and be subjected to pressure P formula:
μ is the Poisson ratio of stainless steel membrane sheet material in the formula, and t is a stainless steel diaphragm thickness, E
2Be the elastic modulus of diaphragm material, R is the circular film radius.The principle of work of the fiber bragg grating pressure sensor 50 of the measure differences in pressure in the present embodiment is: flexible sheet is experienced ambient pressure, and pass to equi intensity cantilever 51 by fore-set, the deformation of equi intensity cantilever 51 drives the fiber grating generation deformation of optical fiber 54, is got place, the summit deflection formula of equi intensity cantilever like this by formula (2), (5), (6):
In wushu (6) the substitution formula (2), get the stressed f formula of equi intensity cantilever single face:
P
1S-P
2S-f
1-f
2-f＝0????????????????????????(11)
Substitution formula (8), (9) and (10):
(P
1-P
2)S＝f
1+f
2+f
Δ P is the both sides pressure difference of the sensor 50 of present embodiment in the formula, is this sensor Specifeca tion speeification.
What sensor 50 adopted is the equi intensity cantilever of stainless steel diaphragm and beryllium-bronze material, two kinds of different sensors of diaphragm thickness have been designed, first flexible sheet 521, second flexible sheet, 522 thickness are the abbreviation sensor I of 0.3mm, and first flexible sheet 521, second flexible sheet, 522 thickness are the abbreviation sensor II of 0.4mm.Each parameter of formula (12) is:
(1) stainless steel diaphragm: elastic modulus E
2=206GPa, sensor I diaphragm thickness t=0.3mm, sensor II diaphragm thickness t=0.4mm, Poisson ratio μ=0.3, circular film radius R=14mm, the effective lifting surface area S=7.85 of diaphragm * 10
-5m
2(surface of contact of counterweight and sensor is the circle of diameter 1cm in the experiment);
(2) equi intensity cantilever 51: base b
0=6mm, thick h=0.4mm, elastic modulus E
1=128GPa, beam length L=30mm;
(3) fiber grating 54: the effective elasto-optical coefficient P of optical fiber
e=0.22, sensor I fiber grating foveal reflex wavelength X
B=1559.192nm, sensor II fiber grating foveal reflex wavelength X
B=1555.099nm.
Data are brought formula (12) into
,
Sensor I
Sensor II
Sensor one side zero load in the experiment, opposite side is placed the different counterweight (surface of contact of counterweight and sensor is the circle of diameter 1cm) of mass M, produce different pressure difference Δ P thus, according to formula (13) and (14) and fiber grating foveal reflex wavelength data, we obtain the mathematical relation of sensor wavelength signal and counterweight quality:
Sensor I
λ＝-3.9668×10
-5M+1559.192????????????????????(15)
Sensor II
λ＝1.6707×10
-5M+1555.099?????????????????????(16)
Wherein M is a counterweight quality afterburning in the experiment, and unit is g, and λ is a sensor fiber optical grating reflection wavelength, and unit is nm.
The semi-girder of sensor is selected the equi intensity cantilever 51 of beryllium-bronze material for use, size sensor: long 62mm, wide 30mm, high 12mm; To diaphragm thickness is that the technical feature of two kinds of sensors of 0.3mm and 0.4mm is tested the relation between its load-carrying and the wavelength variations such as Fig. 9 and Figure 10 respectively.
By Fig. 9 and Figure 10 as seen, the two sensors wavelength is the better linearity relation with the variation of pressure differential (load-carrying), meets theoretical formula (12).Sensor I linearity less than 150N with greater than 1000N the time is relatively poor as can be seen, the linearity and stability better (being the best effort scope of this sensor) between pressure differential 1500N to 10000N; The matched curve of Fig. 9 straight line is:
λ＝-8.0×10
-5M+1559.654????????????????????????(17)
Slope-8.0 * 10
-5, being negative value, the fiber grating of sensor is subjected to force compresses in the illustrative experiment; Table 1 has provided the strain-responsive data of this sensor, this shows that this sensor performance is good, and its negative strain is the stressed compressed result of fiber grating.
Table 1. sensor I is to the strain-responsive data of different pressures difference
| Pressure/g | ??138.5 | ??238.5 | ??338.5 | ??438.5 | ??538.5 | ??638.5 | ??738.5 | ??838.5 | ??938.5 | ??1038.5 |
| Stress/μ ε | ??-1.27 | ??-9.50 | ??-21.14 | ??-26.96 | ??-29.87 | ??-35.69 | ??-37.69 | ??-40.90 | ??-46.11 | ??-48.82 |
Sensor II curve totally is in line, and partial data departs from, and as seen its sensitivity is low, is fit to rough measure pressure differential signal, is not suitable for precision measurement; The matched curve of Figure 10 straight line is:
λ＝1.0×10
-5M+1163.756????????????????(18)
Slope is 1.0 * 10
-5, the stressed stretching of fiber grating of this sensor in the experiment of symbol positive value specifies.
Stress and foveal reflex wavelength change curve when also having measured sensor in the experiment and in water, applying the different flow hydraulic impact, the relaxation time of finding sensor I is short, response speed is fast, and pressure and flow are had good linear response, can be used for precisely and dynamically measuring; And the relaxation time of sensor II is quite grown (greater than 20 seconds), is fit to static rough measure occasion.
By formula (15) and (17) and (16) and (18) more as can be known, some difference of theoretical value and experiment value (corresponding slope is inconsistent), but slope differences within error range, this has also proved the reliability of this sensor.Its source of error is: do not consider the gluing coefficient of fiber grating, and stainless steel diaphragm processing is meticulous inadequately etc.
An application examples below by the fiber bragg grating pressure sensor 50 of a present embodiment further specifies the application of present embodiment in measure differences in pressure.
As shown in figure 11, the outside seepage of pipeline 7 damaged back pipeline liquids, the fiber-optic grating sensor 50 of highly sensitive present embodiment can be put into, two flexible sheets (first flexible sheet 521, second flexible sheet 522) are during over against leak 71, because liquid leakage, second flexible sheet 522 is subjected to hydraulic shock power, so in first flexible sheet 521 and second flexible sheet, the 522 same environment of living in but stressed different, this fiber-optic grating sensor 50 just can be experienced and this pressure differential, thereby can further analyze this leak 71 situations.
Embodiment 2
As Figure 12, Figure 13 is the structural representation of the fiber-optic grating sensor 60 of present embodiment.The basic structure of present embodiment is identical with embodiment 1 with principle of work, the key distinction of itself and embodiment 1 is, in the present embodiment, only is provided with a flexible sheet (for example only having first flexible sheet 621), thereby energy measurement pressure signal only, and can not the gaging pressure difference signal.
As shown in Figure 12 and Figure 13, the fiber-optic grating sensor 60 of present embodiment comprises: semi-girder 61, first flexible sheet 62, first fore-set 63 and optical fiber 64.Wherein, semi-girder 61 has first end 611 and second end, 612, the first ends 611 are fixing, and second end 612 is in cantilever position; Described first fore-set 63 is fixedlyed connected with first flexible sheet 62, and stretch out towards described semi-girder 61, the end of this first fore-set 63 contacts mutually with a side of second end 612 of described semi-girder 61, thereby the radial pressure that first flexible sheet 62 is subjected to passes to semi-girder 61; And optical fiber 64 has fiber grating, and this fiber grating is fixedly connected on the semi-girder 61.During use, the primary diaphragm 62 of semi-girder 61 1 sides is under pressure, this pressure passes to a side of second end 612 of semi-girder 61 by first fore-set 63, second end 612 of compressing semi-girder 61 moves to opposite side, be fixed on fiber grating on the semi-girder 61 and perceive this deformation of semi-girder 61, output signal changes, thus measured pressure signal.
In the present embodiment, owing to be to adopt first flexible sheet 62 and semi-girder 61 to realize the enhanced sensitivity of the fiber grating of optical fiber 64, the size of first flexible sheet 62 can be done very for a short time, thereby make fiber bragg grating pressure sensor 60 of the present invention be subjected to the size of force direction can do very thinly at optical fiber 64, for example its thickness can be thinned to 12mm, thereby can be placed in the small space, the pressure of small space is measured.And, the fiber bragg grating pressure sensor 60 of present embodiment can be according to the needs of measurement environment, realize the change of measurement range by the thickness that changes first flexible sheet 62 and semi-girder 61, also can realize large-area measurement, thereby make its range of application more extensive by the size that increases first flexible sheet 62.
As shown in Figure 12 and Figure 13, in an object lesson of present embodiment, described fiber-optic grating sensor 60 also includes housing 65, this housing 65 is formed with containing cavity 650, and being formed with first mounting groove 651 in housing 65 outsides, the 62 periphery sealings of described first flexible sheet are installed on this first mounting groove 651.Has first through hole 653 that is communicated in described containing cavity 650 respectively in the bottom of this first mounting groove 651; Described semi-girder 61 is arranged in the containing cavity 650 of described housing 65, first end 611 of this semi-girder 61 is fixedly supported on the housing 65, first fore-set 63 that is fixedly connected on primary diaphragm 62 passes first through hole 653 of described first mounting groove 651 bottoms and contacts mutually with a side of second end 612 of described semi-girder 61, thereby the radial pressure that primary diaphragm 62 is subjected to is passed to second end 612 of semi-girder 61.
In an example of present embodiment, as shown in figure 13, can be provided with miniature bearing 661 on described first fore-set 63, this first fore-set 63 contacts second end 612 in described semi-girder 61 by this miniature bearing 661.Like this, utilize this miniature bearing 661, be subjected to transverse force at first fore-set 63 and do the time spent, this first fore-set 63 can carry out small rolling by miniature bearing 661 on semi-girder 61, thereby greatly reduce the friction between first fore-set 63 and the semi-girder 61, improve the accuracy when carrying out pressure survey.
In the object lesson of embodiment, in order to guarantee the linearity of sensor fibre grating wavelength drift in measurement range, avoid fiber grating to produce chirp, as shown in Figure 5, described semi-girder 51 can adopt equi intensity cantilever, improve to measure sensitivity and accuracy with this equal strength semi-girder.Wherein, if non-uniform beam designs to such an extent that make maximum on each cross section of beam all reach the permissible stress value of material, then such beam just is called the beam of uniform strength.
In an optional example of the present invention, as shown in figure 13, in the containing cavity 650 of described housing 65, be provided with support portion 656, first end 611 of described semi-girder 61 is supported on this support portion 656, one briquetting 657 is pressed on first end 611 of semi-girder 61, and briquetting 657 is fixed in (as shown in figure 12) on the support portion 656, thereby first end 611 of semi-girder 61 is pressed abd fixed on the described support portion 656 by securing member 658.In this example, similar with embodiment 1, can be provided with on the described briquetting 657 for what fiber grating passed and wear groove 6571 (as shown in figure 12).
In an object lesson of present embodiment, similar with embodiment 1, described first flexible sheet 62 and housing 65 can be made by stainless steel material, and described first fore-set 63 can be processed with first flexible sheet, 62 one.Described semi-girder 61 can be made by beryllium-bronze material, and the elastic modulus of this kind material is relatively little, and it is relatively good that deformation recovers.The fiber grating of described optical fiber 64 can be pasted and fixed on the semi-girder 61.
In the object lesson of embodiment, as shown in figure 13, the edge of described first flexible sheet 62 can be formed with annular flange portion 621, the outside of this annular flange portion 621 and described first mounting groove 651 are tightly connected together, thereby realize being tightly connected of first flexible sheet 62 and first mounting groove 651.
In the present embodiment, owing to be to adopt flexible sheet and semi-girder to realize the enhanced sensitivity of fiber grating 54, do not need as existing cylindrical drum-piston type optical fibre grating pressure transducer 30 and metal tube combined fiber bragg grating pressure sensor 40, to need relative motion, thereby housing 65 can be after installing each parts, form air locking, thereby make 60 pairs of rugged surroundings of fiber-optic grating sensor of the present invention that good corrosion resistance be arranged.In the present embodiment, for making things convenient for semi-girder 61 and the assembling of fiber grating 64 in housing 65, described housing 65 comprises main casing 681 and is packaged on the capping 682 of main casing 681 ends, in described capping 682, be formed with the hole 683 that the tail optical fiber for described fiber grating 64 passes through, adopt polymeric seal between described capping 682 and the tail optical fiber, thereby make this fiber-optic grating sensor 60 after assembling, form air locking.
Foregoing description of the present invention only is exemplary attribute, and the various distortion that therefore do not depart from main idea of the present invention ought to be within the scope of the present invention.These distortion should not be regarded as departing from the spirit and scope of the present invention.
Claims (16)
1. fiber bragg grating pressure sensor, it comprises:
Semi-girder has first end and second end, and wherein first end is fixed, and second end is in cantilever position;
First flexible sheet, it is fixedly connected with first fore-set towards described semi-girder, and the end of this first fore-set contacts mutually with a side of second end of described semi-girder;
Optical fiber, it has fiber grating, and this fiber grating is fixedly connected on the semi-girder.
2. fiber bragg grating pressure sensor as claimed in claim 1, it is characterized in that, described fiber bragg grating pressure sensor also comprises: second flexible sheet, itself and first flexible sheet are oppositely arranged, and being fixedly connected with second fore-set towards semi-girder, this second fore-set contacts mutually with the opposite side relative with a side of first fore-set on described semi-girder second end.
3. fiber bragg grating pressure sensor as claimed in claim 1 or 2, it is characterized in that, described fiber bragg grating pressure sensor also includes housing, this housing is formed with containing cavity, and on this hull outside, be formed with first mounting groove, have first through hole that is communicated in described containing cavity in the bottom of this first mounting groove; Described semi-girder is arranged in the containing cavity of described housing, first end of this semi-girder is fixedly supported on the housing, the sealing of described primary diaphragm periphery is installed on first mounting groove of housing, and described first fore-set passes first through hole of described first mounting groove bottom and contacts mutually with second end of described semi-girder.
4. fiber bragg grating pressure sensor as claimed in claim 3 is characterized in that, described hull outside also is provided with second mounting groove on the position relative with first mounting groove, is provided with second through hole that is communicated in described containing cavity in the bottom of this second mounting groove; The sealing of described secondary diaphragm periphery is installed on described second mounting groove, and described second fore-set passes described second through hole and contacts mutually with described semi-girder.
5. fiber bragg grating pressure sensor as claimed in claim 1 is characterized in that, described first fore-set is provided with miniature bearing, and described first fore-set contacts second end in described semi-girder by this miniature bearing.
6. fiber bragg grating pressure sensor as claimed in claim 2 is characterized in that, described second fore-set is provided with miniature bearing, and described second fore-set contacts second end in described semi-girder by this miniature bearing.
7. fiber bragg grating pressure sensor as claimed in claim 1 or 2 is characterized in that, described semi-girder is an equi intensity cantilever.
8. fiber bragg grating pressure sensor as claimed in claim 1 or 2 is characterized in that described fiber grating is pasted and fixed on the described semi-girder.
9. fiber bragg grating pressure sensor as claimed in claim 3, it is characterized in that, in the containing cavity of described housing, be provided with the support portion, first end of described semi-girder is supported on this support portion, one briquetting is pressed on first end of semi-girder, and be fixed on the support portion, thereby first end of semi-girder is pressed abd fixed on the described support portion by securing member.
10. fiber bragg grating pressure sensor as claimed in claim 9 is characterized in that, described briquetting is provided with for what described optical fiber passed and wears groove.
11. fiber bragg grating pressure sensor as claimed in claim 1 is characterized in that, described first flexible sheet is made by stainless steel material.
12. fiber bragg grating pressure sensor as claimed in claim 2 is characterized in that, described second flexible sheet is made by stainless steel material.
13. fiber bragg grating pressure sensor as claimed in claim 1 or 2 is characterized in that, described semi-girder is made by beryllium-bronze material.
14. fiber bragg grating pressure sensor as claimed in claim 3, it is characterized in that, in the present invention, edge at described first flexible sheet is formed with annular flange portion, the outside of this annular flange portion and described first mounting groove are tightly connected together, thereby realize being tightly connected of first flexible sheet and first mounting groove.
15. fiber bragg grating pressure sensor as claimed in claim 4, it is characterized in that, edge at described second flexible sheet is formed with annular flange portion, the outside of this annular flange portion and described second mounting groove are tightly connected together, thereby realize being tightly connected of second flexible sheet and second mounting groove.
16. fiber bragg grating pressure sensor as claimed in claim 3, it is characterized in that, described housing comprises main casing and is packaged on the capping of main casing end, is formed with the hole of passing through for described optical fiber in described capping, adopts polymeric seal between described capping and the optical fiber.
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