CN116697917B - Adjustable long gauge length optical fiber distributed strain monitoring device and monitoring and installing method thereof - Google Patents
Adjustable long gauge length optical fiber distributed strain monitoring device and monitoring and installing method thereof Download PDFInfo
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- CN116697917B CN116697917B CN202310480294.1A CN202310480294A CN116697917B CN 116697917 B CN116697917 B CN 116697917B CN 202310480294 A CN202310480294 A CN 202310480294A CN 116697917 B CN116697917 B CN 116697917B
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- 238000012544 monitoring process Methods 0.000 title claims abstract description 34
- 239000013307 optical fiber Substances 0.000 title claims abstract description 31
- 238000012806 monitoring device Methods 0.000 title claims abstract description 28
- 238000000034 method Methods 0.000 title claims abstract description 13
- 239000000835 fiber Substances 0.000 claims abstract description 113
- 238000009434 installation Methods 0.000 claims abstract description 15
- 238000004519 manufacturing process Methods 0.000 claims abstract description 13
- 229920000642 polymer Polymers 0.000 claims abstract description 5
- 238000003825 pressing Methods 0.000 claims description 35
- 239000011248 coating agent Substances 0.000 claims description 18
- 238000000576 coating method Methods 0.000 claims description 18
- 201000010099 disease Diseases 0.000 claims description 12
- 208000037265 diseases, disorders, signs and symptoms Diseases 0.000 claims description 12
- 238000005259 measurement Methods 0.000 claims description 11
- 230000003287 optical effect Effects 0.000 claims description 11
- 238000005516 engineering process Methods 0.000 claims description 10
- 230000005540 biological transmission Effects 0.000 claims description 8
- 239000004642 Polyimide Substances 0.000 claims description 6
- 238000004873 anchoring Methods 0.000 claims description 6
- 229920001721 polyimide Polymers 0.000 claims description 6
- 238000006073 displacement reaction Methods 0.000 claims description 5
- 230000035945 sensitivity Effects 0.000 claims description 5
- 239000011152 fibreglass Substances 0.000 claims description 4
- 229920000058 polyacrylate Polymers 0.000 claims description 3
- 230000003014 reinforcing effect Effects 0.000 claims description 3
- 238000010276 construction Methods 0.000 abstract description 6
- 230000036541 health Effects 0.000 abstract description 4
- 238000004806 packaging method and process Methods 0.000 abstract description 2
- 238000010586 diagram Methods 0.000 description 5
- 230000008859 change Effects 0.000 description 4
- 229910001220 stainless steel Inorganic materials 0.000 description 3
- 238000004026 adhesive bonding Methods 0.000 description 2
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- 239000010935 stainless steel Substances 0.000 description 2
- 230000009471 action Effects 0.000 description 1
- 230000009286 beneficial effect Effects 0.000 description 1
- 238000004891 communication Methods 0.000 description 1
- 238000001514 detection method Methods 0.000 description 1
- 230000000694 effects Effects 0.000 description 1
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Classifications
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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
- G01B11/16—Measuring arrangements characterised by the use of optical techniques for measuring the deformation in a solid, e.g. optical strain gauge
- G01B11/18—Measuring arrangements characterised by the use of optical techniques for measuring the deformation in a solid, e.g. optical strain gauge using photoelastic elements
Abstract
The invention relates to the technical field of structural health strain monitoring, in particular to an adjustable long gauge length optical fiber distributed strain monitoring device and a monitoring and installing method thereof. The invention solves the problems that the manufacturing process of the traditional distributed long-gauge fiber grating strain sensor is complex, the consistency is difficult to control, the prestress and the gauge length are difficult to adjust and the like through the detachable structure capable of accurately adjusting the prestress, and the problems that the bare fiber packaging range of the traditional distributed long-gauge fiber grating strain sensor is small and the strain of the sensor is uneven are solved through the matched construction of the polymer-coated sensing grating string structure and the detachable structure capable of accurately adjusting the prestress, so that the distributed fiber strain sensor which has a simple structure, is easy to manufacture and install and can accurately adjust the prestress is suitable for large-area economic installation and distributed strain monitoring of large-scale structural engineering.
Description
Technical Field
The invention relates to the technical field of structural health strain monitoring, in particular to an adjustable long-gauge-distance optical fiber distributed strain monitoring device and an installation method thereof.
Background
At present, the health monitoring of large-scale structural engineering such as high-speed bridges is lack of a targeted sensing technology. The existing on-line monitoring sensor is mainly based on an electronic strain gauge, generally has a short measurement length, cannot realize distributed measurement, and cannot cover the whole domain of a monitoring target. The integral safety monitoring and disaster early warning of structure can be realized only by large-area arrangement, but the cost and the construction difficulty are very high, and the local concentrated strain condition after construction easily exceeds the measuring range of the sensor, so that the adjustment cost and the difficulty are high. Therefore, the large engineering structure has large size and larger randomness of the damage position, and effective damage information is difficult to obtain by adopting the traditional 'point' type sensor for local detection.
The optical fiber sensor is easy to realize distributed measurement and mainly comprises an optical fiber distributed strain sensor based on a Brillouin scattering sensing technology and a distributed strain sensor based on an optical fiber Bragg grating. Although the optical fiber distributed strain sensor based on the Brillouin scattering sensing technology can realize distributed measurement, the optical fiber distributed strain sensor has low measurement accuracy, slow speed measurement and incapability of dynamic measurement, and can easily cause optical fiber stretch-break to local large strain such as cracks. Wu Zhishen et al [ Wu Zhishen, li Suzhen ] distributed long gauge fiber bragg grating strain sensor and method of manufacturing same [ P ]. Jiangsu province: CN100417963C,2008-09-10 ] proposes a distributed long gauge length fiber bragg grating strain sensor for health detection and monitoring of structural facilities and a manufacturing method thereof, the strain sensor is formed by connecting a plurality of long gauge length fiber bragg grating strain sensors in series, fusion of structural whole information and local information in the health monitoring process is realized, local damage diagnosis of a large-scale structure such as crack monitoring of a concrete structure and reinforcement corrosion and structural whole performance evaluation is realized, high-precision test under the condition of tiny strain such as environmental vibration is realized, and the problems of low installation cost, stability and durability of the sensor are solved. However, the manufacturing process of a single long gauge length sensor is complex, the consistency is difficult to control, the encapsulation range of the bare optical fiber is small, the strain of the sensor is uneven, the prestress and the gauge length are difficult to adjust, and the problems that local large strain easily exceeds the measurement range and the like exist. Zhang Hao in 2019 [ Zhang Hao, zhong Zhixin, yang Shaogong, liu Kai, shang Xiaoyang ] a combined long gauge length fiber grating strain sensor with accurately adjustable prestressing force [ P ]. Jiangsu province: CN209559136U,2019-10-29 provides a combined long gauge length fiber bragg grating strain sensor with accurately adjustable prestress, which solves the technical problems that the elastic modulus of the packaging structure material of the existing strain sensor is not matched with the elastic modulus of the soil body to be measured, the packaging structure and the soil body to be measured cannot cooperatively deform, and thus the monitoring precision is inaccurate. However, the sensor has a complex structure and a complex manufacturing process, and the distributed sensor is difficult to realize.
Therefore, there is still a need for a distributed optical fiber strain sensor with simple structure, easy fabrication and installation, and accurate adjustment of pre-stress, which is suitable for large-area economical installation and distributed strain monitoring in large-scale structural engineering, and realizes monitoring coverage of the whole area and accurate monitoring of local disease strain.
Disclosure of Invention
The invention aims to provide an adjustable long-gauge-length optical fiber distributed strain monitoring device, which solves the problems that the manufacturing process of the traditional distributed long-gauge-length optical fiber grating strain sensor is complex, the consistency is difficult to control, the prestress and the gauge length are difficult to adjust and the like through a detachable structure capable of accurately adjusting the prestress, and solves the problems that the bare optical fiber packaging range of the traditional distributed long-gauge-length optical fiber grating strain sensor is small and the strain of the sensor is uneven through the cooperation construction of a polymer-coated sensing grating string structure and the detachable structure capable of accurately adjusting the prestress, so that the distributed optical fiber strain sensor which has the advantages of simple structure, easy manufacture and installation and capability of accurately adjusting the prestress is realized, and is suitable for large-area economic installation and distributed strain monitoring of large-scale structural engineering.
The invention provides an adjustable long gauge length optical fiber distributed strain monitoring device, comprising:
the sensing grating string comprises a plurality of sensing fiber gratings connected in series and is used for sensing strain in a distributed mode; the sensing grating is connected with the transmission optical cable and the fiber bragg grating demodulator in series;
connecting devices are arranged on two sides of each sensitive fiber bragg grating;
the connecting device consists of a pressing sheet and a base, wherein the cross section of the base is'The section of the tablet is # -, and the cross section of the tablet is # ->The lower surfaces of the horizontal ends of the two ends of the pressing sheet are attached to the upper horizontal surfaces of the two ends of the base; the pressing sheet of the connecting device comprises a V-shaped groove; the base of the connecting device is provided with a trapezoid protruding structure, and the V-shaped groove of the pressing sheet and the trapezoid of the base are provided with a trapezoid protruding structureThe protruding structures are matched; a gap is reserved between the V-shaped groove and the trapezoid protruding structure;
the connecting device is fixed on a mounting base, and the section of the mounting base is "A "type; the mounting base is fixed on a monitored object;
the connecting device is fixed between the two vertical plates of the mounting base;
the base of connecting device both sides have the locating hole, and are located the U type inslot between two risers of mounting base, install adjusting screw on two risers of mounting base, adjusting screw's position cooperates with the locating hole on the base.
Further, the bottom of the inner side of the V-shaped groove of the pressing sheet of the connecting device is provided with a rough pattern, and the top of the protruding structure of the base of the connecting device is provided with a rough pattern so as to clamp the sensing grating string.
Further, bolt mounting seats are respectively machined on the front side surface and the rear side surface of the mounting base and are used for mounting bolts so that the mounting base is fixed on a monitored monitoring object, and small contact surface mounting is guaranteed.
Further, through holes and threaded holes are respectively machined in the corresponding positions of the pressing sheet and the base, and the pressing sheet and the base are fixedly connected through screws.
Furthermore, the sensing grating string is made of a single-mode fiber with polyimide coating, fiber gratings with different wavelengths are directly manufactured through the coating at different positions at equal intervals by a femtosecond laser continuous inscription technology, and then glass fiber reinforced plastics are coated.
Further, the sensing grating string is made of a single-mode fiber with polyacrylate or polyimide coating, and is made by directly manufacturing a weak reflection fiber grating array through the coating at different positions at equal intervals through a femtosecond laser continuous inscription technology, and then coating a polymer reinforcing layer; correspondingly, the fiber bragg grating demodulator is replaced by a weak reflection fiber bragg grating array demodulator.
The invention also provides an installation method of the adjustable long gauge length optical fiber distributed strain monitoring device, which comprises the following steps: the method comprises the following steps:
the first step, assembling a connecting device, connecting a pressing sheet with a base through a screw, enabling the pressing sheet to be in a loose state, enabling a sensing grating string to pass through a V-shaped groove of the pressing sheet and slide in the V-shaped groove of the pressing sheet;
secondly, mounting the mounting base on the surface of the monitored target according to the position of the anchored sensing grating string, wherein the mounting mode comprises structural adhesive bonding or bolt fixing;
thirdly, installing the connecting device on the installation base, fixing the connecting device on the installation base through matching the adjusting screw with the positioning hole, and clamping the connecting device on the sensing grating string through rotating the screw connected with the upper pressing sheet and the base;
and fourthly, connecting the sensing grating with a transmission optical cable and a fiber grating demodulator in series, and adjusting the positions of four adjusting screws according to the monitoring of the fiber grating demodulator so as to adjust the pretightening force of the sensitive fiber grating to reach a set value.
The invention also provides a monitoring method of the adjustable long gauge length optical fiber distributed strain monitoring device, which comprises the following steps:
the first step: monitoring crack diseases generated at any position of the monitored bridge girder through a distributed strain monitoring device of the distributed long gauge optical fiber;
and a second step of: the strain epsilon of the fiber grating can be obtained by detecting the wavelength variation delta lambda of the sensitive fiber grating through the fiber grating demodulator, so that the relative displacement delta of the anchoring end can be obtained according to the known gauge lengthLThus can be according to deltaLEstimating the total seam width of the seam disease between the gauge lengths;
the formula used is as follows:
strain of sensitive fiber gratingεCan be expressed as:
wavelength variation of the sensitive fiber bragg grating is:
wherein:p e is the elasto-optical coefficient of the optical fiber,λ B is the center wavelength of the fiber bragg grating,K T is the temperature sensitivity coefficient delta of the fiber bragg gratingTIs the ambient temperature variation;
and a third step of: when the local crack disease of the monitored object is about to reach the sensitive fiber bragg grating range of the corresponding position, the connecting devices and the mounting bases on the two sides of the sensitive fiber bragg grating of the corresponding position are adjusted, the pretightening force of the sensitive fiber bragg grating is changed, and the monitoring can be continued.
Further, during monitoring, the last connecting device of the last sensitive fiber bragg grating of the sensing grating string is in a loose state, so that the last sensitive fiber bragg grating of the sensing grating string monitors the temperature to perform temperature compensation.
The beneficial technical effects of the invention are as follows:
(1) The invention does not need to manufacture a single long gauge length sensor, realizes distributed long gauge length strain sensing through simple installation of the whole series of fiber bragg gratings, greatly simplifies the structure and the production process, improves the production efficiency, improves the monitoring consistency, reduces the cost and is suitable for large-scale use.
(2) The invention can adjust the prestress in the installation process, properly adjust the gauge length according to the construction condition, greatly improve the flexibility and has strong adaptability to the complex structural conditions of engineering monitoring.
(3) The invention can adjust the prestress after construction, thereby realizing a large number of sensitive fiber gratings on a series of fiber gratings in a denser wavelength division multiplexing mode, solving the problem of overscan of partial sensitive fiber gratings due to insufficient multiplexing interval caused by local stress concentration and effectively improving multiplexing scale.
(4) The invention is easy to disassemble and assemble, can reserve the connecting device and the mounting base, replaces the sensing grating string, and has high maintenance and replacement performance. Meanwhile, the sensing grating strings and the connecting device can be reused, and the use cost is reduced when a plurality of engineering structures are monitored.
Drawings
In order to more clearly illustrate the embodiments of the present invention or the technical solutions in the prior art, the drawings that are needed in the description of the embodiments or the prior art will be briefly described, and it is obvious that the drawings in the description below are some embodiments of the present invention, and other drawings can be obtained according to the drawings without inventive effort for a person skilled in the art.
FIG. 1 is a schematic diagram of an adjustable long gauge fiber optic distributed strain monitoring device;
FIG. 2 is a schematic diagram of a connection device of an adjustable long gauge fiber optic distributed strain monitoring device;
FIG. 3 is a schematic view of the mounting base of an adjustable long gauge fiber optic distributed strain monitoring device;
fig. 4 is a schematic diagram of an adjustable long gauge length optical fiber distributed strain monitoring device provided by the invention installed at the bottom of a highway bridge.
Fig. 5 is a schematic view of a mounting base structure with a bolt mounting base according to the present invention.
In the figure: sensing a grating string 100, and sensing a fiber grating 101;
a connecting device 200, a pressing sheet 201; a base 202; a positioning hole 203;
a mounting base 300, an adjusting screw 301, a bolt mounting base 302;
a transmission optical cable 400;
fiber grating demodulator 500.
Detailed Description
The following description of the embodiments of the present invention will be made apparent and fully in view of the accompanying drawings, in which some, but not all embodiments of the invention are shown. All other embodiments, which can be made by those skilled in the art based on the embodiments of the invention without making any inventive effort, are intended to be within the scope of the invention.
In the description of the present invention, it should be noted that the directions or positional relationships indicated by the terms "center", "upper", "lower", "left", "right", "vertical", "horizontal", "inner", "outer", etc. are based on the directions or positional relationships shown in the drawings, are merely for convenience of describing the present invention and simplifying the description, and do not indicate or imply that the devices or elements referred to must have a specific orientation, be configured and operated in a specific orientation, and thus should not be construed as limiting the present invention. Furthermore, the terms "first," "second," and "third" are used for descriptive purposes only and are not to be construed as indicating or implying relative importance.
In the description of the present invention, it should be noted that, unless explicitly specified and limited otherwise, the terms "mounted," "connected," and "connected" are to be construed broadly, and may be either fixedly connected, detachably connected, or integrally connected, for example; can be mechanically or electrically connected; can be directly connected or indirectly connected through an intermediate medium, and can be communication between two elements. The specific meaning of the above terms in the present invention will be understood in specific cases by those of ordinary skill in the art.
Example 1
Referring to fig. 1, a schematic diagram of an adjustable long gauge length optical fiber distributed strain monitoring device capable of accurately adjusting prestress according to the present invention includes: a sensing grating string 100, including a plurality of serially connected sensitive fiber gratings 101, for sensing strain in a distributed manner; the sensing grating string 100 is connected with the transmission optical cable 400 and the fiber bragg grating demodulator 500;
referring to fig. 2, a connection device 200 is installed at both sides of a single sensitive fiber grating 101, the connection device 200 is composed of a pressing piece 201 and a base 202, and the pressing piece 201 and the base 202 clamp a designated position between adjacent gratings of the sensing grating string 100 through mechanical cooperation and are convenient for anchoring. The base 202 has a cross-section of'Type ofThe section of the tablet 201 is%>"shape", the lower surface of the horizontal end of the two ends of the said tablet 201 is laminated with the upper horizontal plane of the two ends of the base 202; the pressing piece 201 of the connecting device 200 comprises a V-shaped groove; the base 202 of the connecting device 200 is provided with a trapezoid protruding structure, and the V-shaped groove of the pressing piece 201 is matched with the trapezoid protruding structure of the base 202; a gap is reserved between the V-shaped groove and the trapezoid protruding structure; positioning holes 203 are further formed on two sides of the base 202.
Referring to fig. 3, the connection device 200 is fixed on a mounting base 300, and the cross section of the mounting base 300 is "The two vertical plates of the installation base 300 are provided with U-shaped groove structures, and the installation base 300 is fixed on a monitored object; and adjusts the pre-tightening state of the sensing grating string 100 in cooperation with the connection device 200. The riser is mounted with an adjustment screw 301.
Referring to fig. 5, bolt mounting seats 302 are formed on both sides of the mounting base 300, and are used for mounting bolts to fix the mounting base on a monitored object, so as to ensure that a small contact surface is mounted.
The sensing grating string 100 comprises a plurality of sensing grating strings 100 with different wavelengths, in this embodiment, the sensing grating string 100 is made of a single mode fiber with polyimide coating, and fiber gratings with different wavelengths are directly manufactured through the coating at different positions with equidistant intervals by a femtosecond laser continuous writing technology, and then are coated with glass fiber reinforced plastic.
In this embodiment, the distance interval between the fiber gratings is 1 m, the fiber wavelength interval is 2.4 nm, 16 fiber gratings are total from 1528 nm to 1564nm, the total length is 15 m, and the bandwidth of the sensitive fiber grating 1013 dB is 0.3 nm-0.5 nm. The thickness of the outer coating glass fiber reinforced plastic is 0.5 and mm, and the diameter is 1.25 and mm. Optical cable connectors are manufactured at two ends of the sensing grating string 100 and can be connected with the transmission optical cable 400.
Referring to fig. 2 and 3, the connection device 200 includes a pressing piece 201 and a base 202. The pressing piece 201 is of a V-shaped groove structure and is made of stainless steel sheets in a punching mode, and rough patterns are formed in the bottom of the inner side of the V-shaped groove. The base 202 has a trapezoid protruding structure and is manufactured by cutting stainless steel wires. The top of the protruding structure is provided with a rough pattern. The protruding structure of the base 202 is matched with the V-shaped groove contained in the pressing piece 201 to clamp the sensing grating string 100.
In this embodiment, the diameter of the cylindrical cavity formed by the trapezoidal protruding structure of the base 202 and the V-shaped groove contained in the pressing piece 201 is 1. 1 mm smaller than the diameter of the sensing grating string 100 by 1.25 mm, and the sensing grating string 100 is clamped by press fit. Two positioning holes 203 are formed on two sides of the base 202 of the connecting device 200, and are cylindrical counter bores. The corresponding positions of the pressing piece 201 and the base 202 are respectively provided with a through hole and a threaded hole, so that the pressing piece 201 and the base 202 can be conveniently connected through screws.
Referring to fig. 3, the mounting base 300 has a U-shaped groove structure, which is formed by cutting a stainless steel wire, and has an inner side length slightly longer than that of the base 202, and has a screw hole through which the adjusting screw 301 is mounted, at a position corresponding to the positioning hole 203 of the base 202.
Referring to fig. 4, a schematic diagram of an adjustable long gauge length optical fiber distributed strain monitoring device capable of accurately adjusting prestress provided by the invention is installed at the bottom of a highway bridge, and the installation method comprises the following steps:
in a first step, the connection device 200 is assembled, the presser piece 201 is connected with the base 202 by a screw, the presser piece 201 is in a loose state, and the sensor grating string passes through the groove of the presser piece 201 and can slide in the V-shaped groove of the presser piece 201.
And secondly, mounting the mounting base 300 on the surface of the monitored target according to the position of the anchored sensing grating string 100 in a structural adhesive bonding or bolt fixing mode.
Third, the connecting device 200 is mounted on the mounting base 300, and the connecting device 200 is fixed by matching the adjusting screw 301 with the positioning hole 203; the connection device 200 is clamped to the sensor grating string by screws connected to the base 202 through the upper clamping plate 201.
Fourth, the sensing grating is connected to the light transmission and fiber grating demodulator 500, and the positions of the four adjusting screws 301 are adjusted according to the monitoring of the fiber grating demodulator 500, so as to adjust the pretightening force of the sensitive fiber grating 101 to reach the set value.
Referring to fig. 4, the working principle of the adjustable long gauge length optical fiber distributed strain monitoring device capable of accurately adjusting prestress provided by the invention is as follows:
by lengthening the gauge length of the sensitive fiber grating 101, the two ends adopt the anchoring mode of the connecting device 200 and the mounting base 300 to enable the sensitive fiber grating 101 to measure the average strain of the structure in the gauge length range, thereby establishing the relation between the strain and the displacement of the two ends, and realizing the association of macro-micro information to achieve the purpose of damage coverage. Any sensitive fiber bragg grating 101 in the embodiment is generally designed to be 1 m in gauge length, the coverage area is far larger than that of a traditional point strain gauge, the strain measurement precision can reach 1 mu epsilon, the output of the strain measurement precision can reflect physical quantity changes in a certain area or characteristic scale of a structure, a sensing grating string is formed by wavelength division multiplexing of the sensitive fiber bragg gratings 101, a plurality of long gauge length sensing units are connected in series to form a network, the association of macro-micro information can be realized, the purpose of damage coverage of the whole length is achieved, and the strain measurement precision is suitable for safety monitoring of large-scale large civil engineering structures.
Referring to fig. 4, crack diseases are generated at any position of the monitored bridge girder, the distributed strain monitoring device of the long gauge length optical fiber can monitor the strain change of the corresponding sensitive optical fiber grating 101, and the average strain change condition between the two anchoring end mounting bases 300 corresponding to the crack diseases can be reduced.
Assume that the gauge length of the sensor isLIn this example, 1 m. Relative displacement delta of anchor end mounting base 300LLength from gauge length ofLIs in tension with the sensing grating of (2)FElongation under action deltalEqual. Strain of sensitive fiber grating 101εCan be expressed as:
the wavelength variation of the sensitive fiber grating 101 is:
wherein:p e is the elasto-optical coefficient of the optical fiber,λ B is the center wavelength of the fiber bragg grating,K T is the temperature sensitivity coefficient delta of the fiber bragg gratingTIs the ambient temperature variation.
In a temperature stable environment, the strain epsilon of the fiber grating can be obtained by detecting the wavelength variation delta lambda of the sensitive fiber grating 101 through the fiber grating demodulator 500, so that the relative displacement delta of the anchoring end can be obtained according to the known gauge lengthLThus can be according to deltaLThe total seam width of the inter-gauge crack disease was estimated.
Since the optical fiber is sensitive to both strain and temperature changes, temperature is also an important factor affecting the sensitivity of the fiber bragg grating sensor. In the environment of temperature change, a fiber grating temperature sensor is also added to monitor the environment temperature in real time, and the temperature sensitivity coefficient of the fiber grating is also addedK T And calibrating, and performing temperature compensation on the environmental temperature parameter monitored in real time by adding the fiber bragg grating temperature sensor at a proper position so as to eliminate the influence of temperature change. In this embodiment, the last connection device 200 of the last sensitive fiber bragg grating 101 of the sensing grating string 100 is in a relaxed state and insensitive to strain, so that the last sensitive fiber bragg grating 101 of the sensing grating string 100 monitors the temperature to perform temperature compensation.
In this embodiment, when the local crack disease of the monitored object is about to reach the measuring range of the sensitive fiber bragg grating 101 at the corresponding position, the connection device 200 and the mounting base 300 on both sides of the sensitive fiber bragg grating 101 at the corresponding position are adjusted, and the pretightening force of the sensitive fiber bragg grating 101 is changed, so that the monitoring can be continued.
Implementation of the embodiments example 2
In this embodiment, the sensing grating string includes a single-mode fiber with a polyacrylate or polyimide coating, and is manufactured by directly manufacturing a weak reflection fiber grating array through the coating at different positions with equal distance intervals by using a femtosecond laser continuous writing technology, and then coating a polymer reinforcing layer. In a corresponding manner, the fiber grating demodulator 500 is replaced with a weak reflection fiber grating array demodulator.
The monitoring object of the monitoring device provided by the invention is not limited to monitoring of structural crack diseases, monitoring of other structural health strains, and monitoring of dynamic strains caused by vibration, dynamic load and the like, and is also in the monitoring range.
Finally, it should be noted that: the above embodiments are only for illustrating the technical solution of the present invention, and not for limiting the same; although the invention has been described in detail with reference to the foregoing embodiments, it will be understood by those of ordinary skill in the art that: the technical scheme described in the foregoing embodiments can be modified or some or all of the technical features thereof can be replaced by equivalents; such modifications and substitutions do not depart from the spirit of the invention.
Claims (8)
1. An adjustable long gauge length optic fibre distributing type strain monitoring device, its characterized in that: comprising the following steps:
the sensing optical grating array comprises a sensing optical grating array (100), wherein the sensing optical grating array (100) comprises a plurality of sensitive fiber gratings (101) which are connected in series and are used for sensing strain in a distributed mode; the sensing grating string is connected with a transmission optical cable (400) and a fiber bragg grating demodulator (500);
connecting devices (200) are arranged on two sides of any single sensitive fiber bragg grating (101), and one connecting device is shared between adjacent sensitive fiber bragg gratings (101) to form distributed measurement;
the connecting device (200) is composed of a pressing sheet (201) and a base (202), and the cross section of the base (202) is 'shaped like a Chinese character'"the section of the tablet (201) is>The lower surfaces of the horizontal ends of the two ends of the pressing piece (201) are attached to the upper horizontal surfaces of the two ends of the base (202); the pressing piece (201) of the connecting device (200) comprises a V-shaped groove; the base (202) of the connecting device (200) is provided with a trapezoid protruding structure, and the V-shaped groove of the pressing sheet (201) is matched with the trapezoid protruding structure of the base (202); a gap is reserved between the V-shaped groove and the trapezoid protruding structure;
the connecting device (200) is fixed on a mounting base (300), and the cross section of the mounting base (300) is' shaped "A "type; the mounting base (300) is fixed on a monitored object;
the connecting device (200) is fixed between U-shaped grooves surrounded by two upright plates of the mounting base (300);
positioning holes (203) are formed in two sides of a base (202) of the connecting device (200), the positioning holes are located in U-shaped grooves between two vertical plates of the mounting base (300), adjusting screws (301) are mounted on the two vertical plates of the mounting base (300), and the positions of the adjusting screws (301) are matched with the positioning holes (203) on the base (202);
the wavelength interval of the sensitive fiber bragg gratings (101) of the sensing grating string (100) is 2nm-2.5 nm, and the 3dB bandwidth of the sensitive fiber bragg gratings (101) is 0.3 nm-0.5 nm;
the sensing grating string (100) is manufactured by directly manufacturing fiber gratings at different positions at equal intervals through a coating by using a single-mode fiber and a femtosecond laser continuous inscription technology;
the strain monitoring device is characterized in that the sensitive fiber bragg grating (101) is subjected to long gauge length, and the two ends of the sensitive fiber bragg grating (101) are anchored by adopting a connecting device (200) and a mounting base (300) so that the sensitive fiber bragg grating (101) measures average strain of a structure in a gauge length range;
the last connecting device (200) of the last sensitive fiber bragg grating (101) of the sensing grating string (100) is in a loose state and insensitive to strain, so that the last sensitive fiber bragg grating (101) of the sensing grating string (100) monitors temperature to perform temperature compensation.
2. The adjustable long gauge fiber optic distributed strain monitoring device of claim 1, wherein: the bottom of the inner side of the V-shaped groove of the pressing sheet (201) of the connecting device (200) is provided with a rough pattern, and the top of the protruding structure of the base (202) of the connecting device (200) is provided with a rough pattern so as to clamp the sensing grating string.
3. The adjustable long gauge fiber optic distributed strain monitoring device of claim 1, wherein: bolt mounting seats (302) are respectively machined on two sides of the mounting base (300) and are used for mounting bolts to enable the mounting base to be fixed on a monitored monitoring object, and small contact surface mounting is guaranteed.
4. The adjustable long gauge fiber optic distributed strain monitoring device of claim 1, wherein: through holes and threaded holes are respectively machined in the positions corresponding to the pressing piece (201) and the base (202), and the pressing piece and the base are fixedly connected through screws.
5. The adjustable long gauge fiber optic distributed strain monitoring device of claim 1, wherein: the sensing grating string (100) is manufactured by directly manufacturing fiber gratings with different wavelengths through the coating at different positions at equal distance through a single mode fiber with polyimide coating and then coating glass fiber reinforced plastic by a femtosecond laser continuous inscription technology.
6. The adjustable long gauge fiber optic distributed strain monitoring device of claim 1, wherein: the sensing grating string is manufactured by directly manufacturing a weak reflection fiber grating array through a coating at different positions at equal intervals by a single mode fiber with polyacrylate or polyimide coating through a femtosecond laser continuous inscription technology, and then coating a polymer reinforcing layer; correspondingly, the fiber bragg grating demodulator (500) is replaced by a weak reflection fiber bragg grating array demodulator.
7. A method of installing an adjustable long gauge fiber optic distributed strain monitoring device as claimed in any of claims 1-6 wherein: the method comprises the following steps:
firstly, assembling a connecting device (200), connecting a pressing sheet (201) with a base (202) through a screw, enabling the pressing sheet (201) to be in a loose state, and enabling a sensing grating string to pass through a V-shaped groove of the pressing sheet (201) and slide in the V-shaped groove of the pressing sheet (201);
secondly, mounting the mounting base (300) on the surface of a monitored target according to the position of the anchored sensing grating string (100) in a bolt fixing mode;
thirdly, installing the connecting device (200) on the installation base (300), fixing the connecting device (200) on the installation base (300) through matching of the adjusting screw (301) and the positioning hole (203), and clamping the connecting device (200) to the sensing grating string through rotating the screw connected with the base (202) through the upper pressing piece (201);
fourthly, connecting the sensing grating with the transmission optical cable (400) and the fiber bragg grating demodulator (500) in series, and adjusting the positions of the four adjusting screws (301) according to the monitoring of the fiber bragg grating demodulator (500), so as to adjust the pretightening force of the sensitive fiber bragg grating (101) to reach a set value.
8. A method of monitoring an adjustable long gauge fiber optic distributed strain monitoring device as claimed in any one of claims 1-6 wherein: the method comprises the following steps:
the first step: the method comprises the steps that crack diseases generated at any position of a monitored bridge girder are monitored through a distributed strain monitoring device of a distributed long-gauge optical fiber;
and a second step of: detecting the wavelength variation delta of the sensitive fiber grating (101) by a fiber grating demodulator (500)λCan obtainStrain of fiber gratingεThereby according to a known gauge lengthLObtaining the relative displacement delta of the anchoring endlThus can be according to deltalEstimating the total seam width of the seam disease between the gauge lengths;
the formula used is as follows:
strain of sensitive fiber grating (101)εCan be expressed as:
the wavelength variation of the sensitive fiber grating (101) is:
wherein:p e is the elasto-optical coefficient of the optical fiber,λ B is the center wavelength of the fiber bragg grating,K T is the temperature sensitivity coefficient delta of the fiber bragg gratingTIs the ambient temperature variation;
and a third step of: when the local crack disease of the monitored object is about to reach the measuring range of the sensitive fiber bragg grating (101) at the corresponding position, the connecting devices (200) and the mounting base (300) at the two sides of the sensitive fiber bragg grating (101) at the corresponding position are adjusted, the pretightening force of the sensitive fiber bragg grating (101) is changed, and the monitoring can be continued.
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