CN111473733A - Ultra-large range fiber grating displacement sensor and measuring method - Google Patents

Ultra-large range fiber grating displacement sensor and measuring method Download PDF

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Publication number
CN111473733A
CN111473733A CN202010332638.0A CN202010332638A CN111473733A CN 111473733 A CN111473733 A CN 111473733A CN 202010332638 A CN202010332638 A CN 202010332638A CN 111473733 A CN111473733 A CN 111473733A
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China
Prior art keywords
fiber grating
stress
rim plate
pull rope
grating
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CN202010332638.0A
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Inventor
崔洪亮
程立耀
于淼
王忠民
罗政纯
杨先进
杨先勇
吴崇坚
郑志丰
杨悦
张耀鲁
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Zhuhai Renchi Photoelectric Technology Co ltd
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Zhuhai Renchi Photoelectric Technology Co ltd
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    • G—PHYSICS
    • G01—MEASURING; TESTING
    • G01B—MEASURING LENGTH, THICKNESS OR SIMILAR LINEAR DIMENSIONS; MEASURING ANGLES; MEASURING AREAS; MEASURING IRREGULARITIES OF SURFACES OR CONTOURS
    • G01B11/00—Measuring arrangements characterised by the use of optical techniques
    • G01B11/02—Measuring arrangements characterised by the use of optical techniques for measuring length, width or thickness
    • G—PHYSICS
    • G01—MEASURING; TESTING
    • G01B—MEASURING LENGTH, THICKNESS OR SIMILAR LINEAR DIMENSIONS; MEASURING ANGLES; MEASURING AREAS; MEASURING IRREGULARITIES OF SURFACES OR CONTOURS
    • G01B9/00—Measuring instruments characterised by the use of optical techniques
    • G01B9/02—Interferometers
    • G01B9/02015—Interferometers characterised by the beam path configuration
    • G01B9/02023—Indirect probing of object, e.g. via influence on cavity or fibre
    • G—PHYSICS
    • G01—MEASURING; TESTING
    • G01B—MEASURING LENGTH, THICKNESS OR SIMILAR LINEAR DIMENSIONS; MEASURING ANGLES; MEASURING AREAS; MEASURING IRREGULARITIES OF SURFACES OR CONTOURS
    • G01B9/00—Measuring instruments characterised by the use of optical techniques
    • G01B9/02—Interferometers
    • G01B9/02015—Interferometers characterised by the beam path configuration
    • G01B9/02029—Combination with non-interferometric systems, i.e. for measuring the object
    • G01B9/02031—With non-optical systems, e.g. tactile
    • G—PHYSICS
    • G01—MEASURING; TESTING
    • G01D—MEASURING NOT SPECIALLY ADAPTED FOR A SPECIFIC VARIABLE; ARRANGEMENTS FOR MEASURING TWO OR MORE VARIABLES NOT COVERED IN A SINGLE OTHER SUBCLASS; TARIFF METERING APPARATUS; MEASURING OR TESTING NOT OTHERWISE PROVIDED FOR
    • G01D5/00—Mechanical means for transferring the output of a sensing member; Means for converting the output of a sensing member to another variable where the form or nature of the sensing member does not constrain the means for converting; Transducers not specially adapted for a specific variable
    • G01D5/26—Mechanical means for transferring the output of a sensing member; Means for converting the output of a sensing member to another variable where the form or nature of the sensing member does not constrain the means for converting; Transducers not specially adapted for a specific variable characterised by optical transfer means, i.e. using infrared, visible, or ultraviolet light
    • G01D5/32—Mechanical means for transferring the output of a sensing member; Means for converting the output of a sensing member to another variable where the form or nature of the sensing member does not constrain the means for converting; Transducers not specially adapted for a specific variable characterised by optical transfer means, i.e. using infrared, visible, or ultraviolet light with attenuation or whole or partial obturation of beams of light
    • G01D5/34—Mechanical means for transferring the output of a sensing member; Means for converting the output of a sensing member to another variable where the form or nature of the sensing member does not constrain the means for converting; Transducers not specially adapted for a specific variable characterised by optical transfer means, i.e. using infrared, visible, or ultraviolet light with attenuation or whole or partial obturation of beams of light the beams of light being detected by photocells
    • G01D5/353—Mechanical means for transferring the output of a sensing member; Means for converting the output of a sensing member to another variable where the form or nature of the sensing member does not constrain the means for converting; Transducers not specially adapted for a specific variable characterised by optical transfer means, i.e. using infrared, visible, or ultraviolet light with attenuation or whole or partial obturation of beams of light the beams of light being detected by photocells influencing the transmission properties of an optical fibre
    • G01D5/35306—Mechanical means for transferring the output of a sensing member; Means for converting the output of a sensing member to another variable where the form or nature of the sensing member does not constrain the means for converting; Transducers not specially adapted for a specific variable characterised by optical transfer means, i.e. using infrared, visible, or ultraviolet light with attenuation or whole or partial obturation of beams of light the beams of light being detected by photocells influencing the transmission properties of an optical fibre using an interferometer arrangement
    • G01D5/35309—Mechanical means for transferring the output of a sensing member; Means for converting the output of a sensing member to another variable where the form or nature of the sensing member does not constrain the means for converting; Transducers not specially adapted for a specific variable characterised by optical transfer means, i.e. using infrared, visible, or ultraviolet light with attenuation or whole or partial obturation of beams of light the beams of light being detected by photocells influencing the transmission properties of an optical fibre using an interferometer arrangement using multiple waves interferometer
    • G01D5/35316—Mechanical means for transferring the output of a sensing member; Means for converting the output of a sensing member to another variable where the form or nature of the sensing member does not constrain the means for converting; Transducers not specially adapted for a specific variable characterised by optical transfer means, i.e. using infrared, visible, or ultraviolet light with attenuation or whole or partial obturation of beams of light the beams of light being detected by photocells influencing the transmission properties of an optical fibre using an interferometer arrangement using multiple waves interferometer using a Bragg gratings

Abstract

The utility model provides an ultra-large range fiber grating displacement sensor and measuring method, the sensor includes the casing, sets up the winding device in the casing, winding device includes the rim plate of two different wheel footpaths at least, is big rim plate and little rim plate respectively, and the pivot of two rim plates is connected and is makeed the linkage of little rim plate when big rim plate rotates, and big rim plate twines and connects first stay cord, the second stay cord is connected in the winding of little rim plate, and the second stay cord is connected with stress fiber grating. The displacement measuring distance is increased to the order of tens of meters by using winding devices of different radii. The wide range setting of the structural feature of this disclosed sensor receives the restriction of device size less, has reduced the preparation degree of difficulty of device, is favorable to using widely of device. The method can be applied to real-time online monitoring of large-range displacement such as landslide, soft soil foundation settlement, structural health and the like.

Description

Ultra-large range fiber grating displacement sensor and measuring method
Technical Field
The disclosure relates to the related technical field of photoelectron measuring devices, in particular to a super-large-range fiber grating displacement sensor and a measuring method.
Background
The statements in this section merely provide background information related to the present disclosure and may not necessarily constitute prior art.
The landslide refers to the action and phenomenon that a certain part of rock and soil on a mountain slope moves integrally to the lower part of the slope along a certain soft structural surface or structural belt by generating shearing displacement under the action of gravity including the gravity of the rock and soil and the dynamic and static pressure of underground water. The continuous scouring of surface water bodies such as earthquakes, rainfall and snow melting, scouring and soaking of surface water, rivers and the like to slope toe; unreasonable human engineering activities such as digging slope toe, loading on the upper part of the slope body, blasting, storing and draining water in a reservoir, mining and the like can induce landslide, and the landslide can be induced by the actions such as tsunami, storm surge, freeze thawing and the like. Some landslides occur at a time slightly later than the time of induction of the contributing factor, so long-term continuous monitoring is the best method of prevention. The soft soil foundation is defined as a soft soil layer with low strength and high compression amount, and most of the soft soil layer contains certain organic substances. Because the soft soil has low strength and large sinking amount, great harm is often brought to road engineering or large-scale building engineering. In the health detection of large building structures, the structures are easy to generate large deformation under the load action. Both of these situations require long term continuous monitoring.
The existing detection method has the characteristics of small volume, corrosion resistance, electromagnetic interference resistance, easiness in networking and multiplexing and the like, so that the fiber bragg grating is more and more emphasized in the field of sensors. The inventor finds that the conventional detection method based on the fiber bragg grating displacement sensor has the general measuring range within 20mm, and the measuring distance is larger and can reach 1-2 meters. The limitation of the existing fiber grating displacement sensor structure and the increase of the measuring range can greatly increase the manufacturing difficulty and the sensor volume, for example, patent application No. 201410209172.X, the patent name is an ultra-large-range fiber grating displacement sensor and a measuring method, if the measuring range is increased, the manufacturing difficulty and the sensor volume can be greatly increased, and the long-term stable measurement of the sensor is not facilitated.
Disclosure of Invention
In order to solve the problems, the disclosure provides an ultra-large range fiber grating displacement sensor and a measuring method, and displacement measuring distance is increased to the magnitude of dozens of meters by adopting winding devices with different radiuses. The method can be applied to real-time online monitoring of large-range displacement such as landslide, soft soil foundation settlement, structural health and the like.
In order to achieve the purpose, the following technical scheme is adopted in the disclosure:
the first aspect of the disclosure provides a super large range fiber grating displacement sensor, including the casing, set up the winding device in the casing, winding device includes the rim plate of two different wheel footpaths at least, is big rim plate and little rim plate respectively, and the pivot of two rim plates is connected and is makeed big rim plate linkage when rotating, and first stay cord is connected to big rim plate, the second stay cord is connected to little rim plate, and the second stay cord is connected with stress fiber grating.
The first aspect of the disclosure provides a measuring method based on the ultra-large range fiber grating displacement sensor, which includes the following steps:
calibrating wavelength lambda of temperature compensation fiber gratingWAnd stressWavelength lambda of fiber gratingB；
Acquiring the measured wavelength variation of the stress fiber grating and the temperature compensation grating in real time;
calculating the temperature variation according to the wavelength variation of the temperature compensation grating;
and calculating the displacement to be measured according to the temperature variation and the wavelength variation of the stress fiber grating.
Compared with the prior art, the beneficial effect of this disclosure is:
(1) according to the wheel disc winding device, the wheel discs with different wheel diameters are arranged, the variable quantity of the first pull rope is reduced to the variable quantity of the second pull rope according to the proportion of the wheel diameters, and when the first pull rope is stretched outwards, the large wheel disc and the small wheel disc are driven to rotate to drive the second pull rope to wind; the scale of the wheel disc can be set, the range of the sensor is improved, the displacement measurement of the ultra-large range is realized, and the displacement can reach more than dozens of meters at least. The wide range setting of the structural feature of this disclosed sensor receives the restriction of device size less, has reduced the preparation degree of difficulty of device, is favorable to using widely of device.
(2) According to the method, the temperature compensation treatment is carried out on the measurement data of the stress fiber grating through the temperature compensation grating, so that the wavelength drift amount of the stress fiber grating is only influenced by the stress action; the accuracy of system detection is further improved.
Advantages of additional aspects of the disclosure will be set forth in part in the description which follows, or may be learned by practice of the disclosure.
Drawings
The accompanying drawings, which are included to provide a further understanding of the disclosure, illustrate embodiments of the disclosure and together with the description serve to explain the disclosure and not to limit the disclosure.
Fig. 1 is a cross-sectional view in a front view of a sensor of embodiment 1 of the present disclosure;
FIG. 2 is a top view of a sensor of embodiment 1 of the present disclosure;
fig. 3 is an external view of a sensor of embodiment 1 of the present disclosure;
FIG. 4 is a schematic structural diagram of a small wheel disc according to embodiment 1 of the present disclosure;
wherein: 1. the optical fiber cable winding device comprises a winding device body 1-1, a groove 2, a second pull rope 3, a tension spring 4, a stress ring 5, a first fixing screw 6, a gasket 7, a stress optical fiber grating 8, a temperature compensation grating 9, an optical fiber 10, an optical cable joint 11, an optical cable 12, a limiting block 13, a fixing pull ring 14, a first pull rope 15, a second fixing screw 16, a fixing piece 18, a shell 19, a third fixing screw 20, a fixing terminal 21 and a fourth fixing screw.
The specific implementation mode is as follows:
the present disclosure is further described with reference to the following drawings and examples.
It should be noted that the following detailed description is exemplary and is intended to provide further explanation of the disclosure. Unless defined otherwise, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this disclosure belongs.
It is noted that the terminology used herein is for the purpose of describing particular embodiments only and is not intended to be limiting of example embodiments according to the present disclosure. As used herein, the singular forms "a", "an" and "the" are intended to include the plural forms as well, and it should be understood that when the terms "comprises" and/or "comprising" are used in this specification, they specify the presence of stated features, steps, operations, devices, components, and/or combinations thereof, unless the context clearly indicates otherwise. It should be noted that, in the case of no conflict, the embodiments and features in the embodiments in the present disclosure may be combined with each other. The embodiments will be described in detail below with reference to the accompanying drawings.
Example 1
In the technical scheme disclosed in one or more embodiments, as shown in fig. 1 and 2, an ultra-large range fiber grating displacement sensor comprises a shell 18 and a winding device 1 arranged in the shell 18, wherein the winding device 1 at least comprises wheel discs with two different wheel diameters, namely a large wheel disc and a small wheel disc, rotating shafts of the two wheel discs are connected to enable the small wheel disc to be linked when the large wheel disc rotates, the large wheel disc is wound and connected with a first pull rope 14, the small wheel disc is wound and connected with a second pull rope 2, and the second pull rope 2 is connected with a stress fiber grating 7. The outlet end of the first pull cord 14 is used for connecting a detection object or a detection point.
In the embodiment, by arranging wheel discs with different wheel diameters, the variation of the first pull rope 14 is proportionally reduced to the variation of the second pull rope 2 according to the proportion of the wheel diameters, and when the first pull rope 14 is stretched outwards, the large wheel disc and the small wheel disc are driven to rotate to drive the second pull rope 2 to wind; the scale of the wheel disc can be set, the range of the sensor is increased, the measurement of the displacement of the ultra-large range is realized, and the displacement can reach more than dozens of meters at least.
In some embodiments, it is realized that the rotating shafts of the two wheel discs are connected to each other, so that the small wheel disc is linked when the large wheel disc rotates, the connecting manner of the rotating shafts of the two wheel discs may be any manner, optionally, may be a coaxial arrangement, the large wheel disc and the small wheel disc are fixedly arranged on the same rotating shaft, and the rotating shaft is fixedly arranged in the housing through the bearing connection fixing member 16.
Alternatively, the fixing member 16 may be provided as a support rod or a support shaft, and fixed to the housing by a third fixing screw 19.
As a structure that can realize, the mode that the pivot of two rim plates is connected can be for gear connection, and big rim plate and steamboat dish rotatable respectively fix in casing 18, and the first gear and the coaxial rotation of first gear of the pivot connection of big rim plate, the second gear is connected in the pivot of steamboat dish and the coaxial rotation of second gear, and the meshing of the tooth portion of first gear and second gear realizes that two rim plate pivots are connected. The range can be determined by the gear ratio and the ratio of the wheel diameter of the gear to the wheel disc. The gear diameter is adjusted, and the gear is used as a middle connecting structure to realize fine adjustment of the measuring range under the gear proportion.
In some embodiments, the first cord 14 is wound in a direction opposite to the second cord 2 such that when the two pulleys rotate, the first cord 14 and the second cord 2 are wound in one side and wound out the other side.
Optionally, the second pull rope 2 and the first pull rope 14 are both steel wire ropes, the steel wire ropes have high tensile strength, fatigue resistance and impact toughness, the thin steel wire ropes can also achieve high tensile strength, and the thin steel wire ropes can be set to be thin steel wire ropes, so that measurement errors of displacement are reduced.
In some embodiments, the second pulling rope 2 is connected with the stress fiber grating 7 through the stress ring 4, the stress fiber grating 7 is adhered on the stress ring 4, and the deformation direction of the stress fiber grating 7 is consistent with the stress direction of the stress ring 4. The use of the stress ring 4 can convert the tension to be measured into micro-strain suitable for fiber grating measurement. The deformation direction of the stress fiber grating 7 is consistent with the stress direction of the stress ring, so that the fiber grating can better capture the strain amount generated by the stress ring 4.
Optionally, the stress ring 4 is connected to the second pull rope 2 through an extension spring 3. Extension spring 3 is used for turning into the displacement volume tensile, provides wire rope's resilience force through using extension spring 3, when realizing a wide range measurement, has realized retrenching of wire rope resilience structure, and extension spring converts the displacement volume of awaiting measuring after will scaling down into the pulling force to the stress ring simultaneously. The tension spring 3 of this embodiment may be selected from a 304 stainless steel tension spring having a wire diameter of 1.2, an outer diameter of 22mm and a length of 450 mm.
When the thin steel wire as the second pulling rope 2 pulls the extension spring, the extension spring 3 converts the displacement variation of the thin steel wire into a pulling force acting on the stress ring; extension spring 3 provides resilience force and is used for withdrawing of wire rope simultaneously, when selecting extension spring's specific parameter, should guarantee that extension spring 3's tensile volume is enough long, and the pulling force size should guarantee to play wire rope's resilience effect, and when wire rope did not receive outside pulling force to influence promptly, spring 3 can stimulate coaxial reel and withdraw the wire rope that stretches out.
The stress ring 4 is mainly used for converting the tensile force of the spring into the stress acting on the stress fiber grating 7, and when the tensile force of the extension spring 3 acting on the stress ring 4 changes, the stress applied to the stress fiber grating 7 adhered on the stress ring 4 also changes; the parameters of the stress ring 7 are selected to ensure that the tensile force of the tension spring 3 cannot cause the stress fiber grating on the stress ring to break, i.e. the strain amount of the stress ring 7 does not exceed the detection range of the stress fiber grating.
The two sides of the stress ring 4 can be provided with fixing holes which are respectively used for fixing the stress ring 4 on the shell 18 and connecting the extension spring 3, and the round mouth of the stress ring 4 is required to be vertically downward when the stress ring 4 is installed, so that the stress ring 4 is prevented from generating deformation due to self gravity. The material of the stress ring 4 of the embodiment can be spring steel, and the size can be selected from the inner diameter of 20mm, the outer diameter of 23mm and the height of 15 mm; a small hole of approximately 2mm in diameter may be provided on each side of the stress ring.
As a further improvement, a temperature compensation grating 8 can be further included, and the temperature compensation grating 8 and the stress fiber grating 7 are connected with the same optical fiber 9 and arranged in the shell 18 at a position close to the stress fiber grating 7. The temperature compensation grating 8 and the stress fiber grating 7 respectively collect data through different light paths in the optical fiber 9. The temperature compensation grating 8 is mainly used for carrying out temperature compensation treatment on the stress fiber grating 7 to ensure that the wavelength drift amount of the stress fiber grating is only influenced by stress; the temperature compensation grating 8 is always in a state of not being stressed and only influenced by temperature change.
Optionally, a gasket 6 may be further disposed between the stress ring 4 and the fixing point of the housing 18, and is used to increase the distance between the stress ring and the housing, and to leave a space for the stress fiber grating 7 adhered to the stress ring 4; this embodiment may use a shim with a thickness of 15 mm.
Optionally, the stress ring 4 and the housing 18 may be fixed by a threaded connection, and a first fixing screw 5 is provided to fix the stress ring 4 on the housing so that the stress ring does not move along with the extension of the extension spring; the first fixing screw of this embodiment may be a screw with a diameter of 2mm and a length of 20 mm.
Optionally, the temperature compensation grating 8 and the stress fiber grating 7 are mainly used for transmission of optical signals; the present embodiment may use corning single mode fiber, and the model may be g.652d.
In order to realize the transmission of the sensor sensing data, the sensor sensing data can be connected to the data acquisition equipment and the light source through optical fibers, optionally, an optical cable joint 10 is arranged on the shell 18, the optical cable joint 10 is connected with an optical cable 11, the optical cable is connected with an optical fiber 9, and the optical cable 11 is mainly used for protecting the optical fiber and realizing the long-distance transmission of optical signals; this embodiment may use an outdoor optical cable having a diameter of 8 mm. The cable joint is used to connect the cable to the sensor housing and this embodiment may be a waterproof flange joint of M8.
In other embodiments, a stopper 12 may be further provided to limit the first pull cord 14 from being fully retracted; the limiting block 12 is disposed at a wire outlet of the first pulling rope 14 on the housing 18, or the limiting block 12 may be fixed at a position on the first pulling rope 14 close to the end of the first pulling rope. When the measurement calibration is performed, the variation is measured with the position of the stopper 14 as the displacement starting point.
In order to conveniently fix a measured object or a point to be measured, a fixing device, which can be a fixing pull ring 13, can be arranged at the tail end of the first pull rope 14, and the fixing pull ring 13 is mainly used for connecting a steel wire rope with the point to be measured; the pull ring 13 of the present embodiment may be made of stainless steel.
The fixing mode of the first pull rope 14 and the large wheel disc and the fixing mode of the second pull rope and the small wheel disc can be selected according to the size of the wheel diameter, and the fixing mode can be realized, when the size of the wheel surface of the wheel disc meets the requirement of fixing a screw, the second fixing screw 15 can be fixedly arranged with the wheel disc, when the wheel diameter is smaller, the middle position of the wheel disc with the structure shown in figure 4 can be provided with the groove 1-1, and the pull ropes are arranged in the groove 1-1. The reel of this embodiment may have a radius ratio of 150, a small reel radius of 1mm, a large reel radius of 150mm, and a slot 1-1 in the middle of the small reel for holding the thin wire.
Optionally, the structure of the casing 18 may be a frame structure or a fully-enclosed structure, the fully-enclosed structure may protect the internal sensor, the fully-enclosed structure may adopt a structure of upper and lower casings, and the upper and lower casings are fixedly connected by a fourth fixing screw 21.
Alternatively, as shown in fig. 3, a fixed terminal 20 may be disposed outside the housing, and the sensor of the present embodiment is fixedly disposed at the position of the measurement point through the fixed terminal 20.
The embodiment can select to use the casing of length 44cm, width 33cm height 8cm, and the setting of inside rim plate and stay cord just can have sufficient space that sets up, and it is thus clear that the sensor device volume of this embodiment is less, portable is favorable to using widely.
Example 2
The embodiment provides a method for measuring an ultra-large range fiber grating displacement sensor based on embodiment 1, which includes the following steps:
s1 calibrating wavelength lambda of temperature compensation fiber gratingWWavelength lambda of stress fiber gratingB；
S2, acquiring the measured wavelength variation of the stress fiber grating 7 and the temperature compensation grating 8 in real time;
s3, calculating the temperature variation according to the wavelength variation of the temperature compensation grating 8;
s4, calculating the displacement S to be measured according to the temperature variation and the wavelength variation of the stress fiber grating 7.
The displacement can be calculated more simply and conveniently based on the device structure of the embodiment, and rapid measurement can be realized.
Optionally, in step 4, according to the temperature variation and the wavelength variation of the stress fiber grating 7, a calculation formula for calculating the displacement S to be measured may be:
Δλ＝KS·KF·K·S·λB(1-Pe)+λB(α+ζ)ΔT (1-10)
wherein, KS、KF、KAre all constant terms. KsIs the ratio of the circumferences of the small wheel disc and the large wheel disc, KFThe elastic coefficient of the tension spring 3, KThe strain sensitivity coefficient of the strain ring 4 is α, zeta is the thermal expansion coefficient of FBG material, DeltaT is the temperature variation, LambdaBThe bragg wavelength of the fiber bragg grating 7; pe＝neff 2[P2-μ(P1+P2)]2, the effective elastic-optical coefficient of the material of the fiber Bragg grating 7 is shown, wherein P1And P2Is the elasto-optic coefficient of the FBG material; mu is the Poisson's ratio, n, of the material of the fiber Bragg grating 7effTo activateThe effective refractive index at which light propagates within the optical fiber.
In this embodiment, a fiber bragg grating is specifically adopted, and the principle of measuring strain by the fiber bragg grating is as follows: fiber bragg gratings (FBGs for short) are optical sensors that are inscribed in the center of a standard, single-mode optical fiber in a spatially varying manner using intense ultraviolet laser light. Short wavelength ultraviolet photons have sufficient energy to break the highly stable silica binder, destroy the structure of the fiber and slightly increase its refractive index. Interference between two successive laser beams or between the fiber and its mask produces strong spatial periodic variations in the uv light, which results in a corresponding periodic variation in the refractive index of the fiber. The grating formed in the region of the fiber where this change occurs will become a wavelength selective mirror image: light travels down the fiber and reflects at each slight change, but these reflections produce destructive interference at most wavelengths and continue along the fiber. However, within a particular narrow band of wavelengths, useful interference can occur that can travel back down the fiber.
Bragg wavelength lambdaBIt can be calculated by:
λB＝2neffΛ (1-1)
in the formula: n iseffEffective refractive index for laser propagation in the fiber, Λ the period of the Bragg gratingBIs Λ and neffAs a function of (c).
λ is the temperature change Δ T of the environment when the fiber Bragg grating FBG is not affected by the external force fieldBDrift occurs, and the relationship between the amount of drift and the temperature change can be written as:
ΔλB＝λB(α+ζ)ΔT (1-2)
wherein α is the thermal expansion coefficient of the FBG material, ζ is the thermo-optic coefficient of the FBG material, and Δ T is the temperature variation.
When the ambient temperature is constant, the FBG is subjected to the action of an external force field, lambdaBDrift occurs, and the drift amount is:
Δλ＝λB(1-Pe)Δ (1-3)
in the formula: delta is the stress variation; pe＝neff 2[P2-μ(P1+P2)][ 2 ] represents the effective elasto-optic coefficient of the FBG material, where P1And P2Is the elasto-optic coefficient of the FBG material; μ is the poisson ratio of the FBG material.
λ when strain and temperature act on the FBG at the same timeBDrift occurs, and the drift amount is:
Δλ＝λB(1-Pe)Δ+λB(α+ζ)ΔT (1-4)
based on the device structure of embodiment 1, during this embodiment actual measurement, big rim plate radius is R, and the radius of little rim plate is R, can obtain the ratio K of the circumference of little rim plate and big rim plateSComprises the following steps:
Figure BDA0002465517220000111
setting the displacement of the point to be measured relative to the sensor as S, the winding amount of the second pull rope 2 can be obtained, that is, the elongation X of the tension spring 3 is:
X＝S·KS(1-6)
since the forces are opposite, when the tension applied to the tension spring is X, the variation Δ F of the applied force applied to the stress ring 4 can be determined as follows:
ΔF＝KF·X (1-7)
wherein, KFThe elastic coefficient of the tension spring 3.
When the stress ring is subjected to an acting force Δ F, the stress variation Δ of the stress fiber grating on the stress ring 4 is:
Δ＝K·ΔF (1-8)
wherein, KIs the strain sensitivity coefficient of the strain ring 4.
The relation between the wavelength variation delta lambda of the stress fiber grating and the displacement S to be measured can be obtained by combining the formulas (1-2), (1-3), (1-4), (1-5), (1-6), (1-7) and (1-8):
Δλ＝KS·KF·K·S·λB(1-Pe)+λB(α+ζ)ΔT (1-10)
wherein, KS、KF、KAre all constant terms. KSIs the ratio of the circumferences of the small wheel disc and the large wheel disc, KFThe elastic coefficient of the tension spring 3, KThe strain sensitivity coefficient of the strain ring 4 is α, zeta is the thermal expansion coefficient of FBG material, DeltaT is the temperature variation, LambdaBThe bragg wavelength of the fiber bragg grating 7; pe＝neff 2[P2-μ(P1+P2)]2, the effective elastic-optical coefficient of the material of the fiber Bragg grating 7 is shown, wherein P1And P2Is the elasto-optic coefficient of the FBG material; mu is the Poisson's ratio, n, of the material of the fiber Bragg grating 7effIs the effective index of refraction for the laser light to propagate within the fiber.
To illustrate the accuracy of the measurements of the method of this example, actual measurements were made. In step S1, calibrating the wavelength of the grating, wherein the temperature compensation fiber grating is 1545.545 nm; the stress fiber grating was 1556.500 nm.
Stretching the sensor fixing ring outwards by a distance of 15 meters to obtain a real-time stress fiber grating value, wherein the temperature compensation fiber grating 8 is 1545.545nm, and the stress fiber grating 7 is 1558.800 nm; namely the drift amount of the temperature compensation fiber grating is 0; substituting into the formula Δ λW＝λW(α + ζ) Δ T, the temperature change amount Δ T may be obtained as 0.
The measured wavelength change amount Δ λ of the stress fiber grating is 1558.800-1556.500-1.5 nm and the temperature change amount Δ T obtained in step S3 is 0, and the wavelength change amount Δ λ is substituted into the formula Δ λ KS·KF·K·S·λB(1-Pe)+λB(α + ζ) Δ T, the measured displacement S is 15 meters, and the system measurement value matches the actual displacement, which illustrates that the measurement method and the measurement apparatus of embodiment 1 can accurately measure large displacements.
The above description is only a preferred embodiment of the present disclosure and is not intended to limit the present disclosure, and various modifications and changes may be made to the present disclosure by those skilled in the art. Any modification, equivalent replacement, improvement and the like made within the spirit and principle of the present disclosure should be included in the protection scope of the present disclosure.
Although the present disclosure has been described with reference to specific embodiments, it should be understood that the scope of the present disclosure is not limited thereto, and those skilled in the art will appreciate that various modifications and changes can be made without departing from the spirit and scope of the present disclosure.

Claims (10)

1. A super-large range fiber grating displacement sensor is characterized in that: including the casing, set up the winding device in the casing, winding device includes the rim plate of two different wheel footpaths at least, is big rim plate and little rim plate respectively, and the pivot of two rim plates is connected and is makeed the linkage of big rim plate when rotating, and first stay cord is connected to big rim plate, the second stay cord is connected to little rim plate, and the second stay cord is connected with stress fiber grating.
2. The ultra-large range fiber grating displacement sensor of claim 1, wherein: the large wheel disc and the small wheel disc are fixedly arranged on the same rotating shaft, and the rotating shaft is fixedly arranged in the shell through a bearing connecting and fixing piece.
3. The ultra-large range fiber grating displacement sensor of claim 1, wherein: the mode that the pivot of two rim plates is connected is gear connection, and big rim plate and steamboat dish are rotatable respectively to be fixed in the casing, and the first gear and the coaxial rotation of first gear that the pivot of big rim plate is connected, and the second gear is connected in the pivot of steamboat dish and the coaxial rotation of second gear, and the meshing of first gear and the gear part of second gear realizes that two rim plate pivots are connected.
4. The ultra-large range fiber grating displacement sensor of claim 1, wherein: the winding direction of the first pull rope is opposite to that of the thin steel wire, so that when the two wheel discs rotate, one side of the first pull rope and the other side of the second pull rope take up wires, and the other side of the first pull rope and the second pull rope pay off wires;
or the second pull rope and the first pull rope are both steel wire ropes.
5. The ultra-large range fiber grating displacement sensor of claim 1, wherein: the connection mode of the second pull rope connected with the stress fiber grating is connected through a stress ring, the fiber grating is adhered to the stress ring, and the deformation direction of the stress fiber grating is consistent with the stress direction of the stress ring.
6. The ultra-large range fiber grating displacement sensor of claim 5, wherein: the stress ring is connected with the second pull rope through an extension spring.
7. The ultra-large range fiber grating displacement sensor of claim 5, wherein: and a gasket is arranged between the stress ring and the fixed point of the shell.
8. The ultra-large range fiber grating displacement sensor of claim 1, wherein:
the temperature compensation grating and the stress fiber grating are connected with the same optical fiber and arranged in the shell at a position close to the stress fiber grating;
or the tail end of the first pull rope is provided with a fixing device for connecting the first pull rope with the point to be measured;
or the shell further comprises a limiting block, and the limiting block is arranged at the wire outlet of the first pull rope on the shell, or the limiting block is fixed at a position, close to the tail end of the first pull rope, on the first pull rope.
9. The method for measuring the ultra-large range fiber grating displacement sensor according to any one of claims 1 to 8, which is characterized by comprising the following steps:
calibrating wavelength lambda of temperature compensation fiber gratingWWavelength lambda of stress fiber gratingB；
Acquiring the measured wavelength variation of the stress fiber grating and the temperature compensation grating in real time;
calculating the temperature variation according to the wavelength variation of the temperature compensation grating;
and calculating the displacement S to be measured according to the temperature variation and the wavelength variation of the stress fiber grating.
10. The measurement method according to claim 9, characterized by: the calculation formula for calculating the displacement S to be measured is as follows:
Δλ＝KS·KF·K·S·λB(1-Pe)+λB(α+ζ)ΔT
wherein, KS、KF、KAre all constant terms. KSIs the ratio of the circumferences of the small wheel disc and the large wheel disc, KFThe elastic coefficient of the tension spring 3, Kα is the thermal expansion coefficient of FBG material, zeta is the thermo-optic coefficient of FBG material, Delta T is the variation of temperature and lambdaBIs the Bragg wavelength of the fiber Bragg grating; pe＝neff 2[P2-μ(P1+P2)]2, effective elasto-optic coefficient of fiber Bragg grating material, wherein P1And P2Is the elasto-optic coefficient of the FBG material; mu is the Poisson's ratio, n, of the fiber Bragg grating materialeffIs the effective index of refraction for the laser light to propagate within the fiber.
CN202010332638.0A 2020-04-24 2020-04-24 Ultra-large range fiber grating displacement sensor and measuring method Pending CN111473733A (en)

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