阅读说明：本技术 一种多点串联式分布式光纤位移传感器及其测量系统 (Multipoint serial distributed optical fiber displacement sensor and measuring system thereof ) 是由 董永康 徐金龙 巴德欣 李惠 于 2020-08-28 设计创作，主要内容包括：本发明提出一种多点串联式分布式光纤位移传感器及其测量系统,将分布式传感光纤黏贴于变截面悬臂梁上下表面,形成位移传感器,利用变截面悬臂梁端部位移变化与其上下表面传感光纤应变变化之间的传感关系,实现对悬臂梁端部位移的测量。传感器的位移测量精度和量程可以调节,并且单个位移传感器可以实现多方向位移测量。本发明介绍的位移传感器可通过一根光纤进行多点串联,使用高空间分辨率长距离分布式光纤应变传感系统测量所有串联测点的位移变化,形成超多测点的长距离同步位移监测系统。本发明能够满足大型土木工程结构对长距离、超多测点和高精度的位移测量需求,并且造价成本合理,系统结构简单,便于实施。(The invention provides a multipoint tandem type distributed optical fiber displacement sensor and a measuring system thereof.A distributed sensing optical fiber is adhered to the upper surface and the lower surface of a variable cross-section cantilever beam to form a displacement sensor, and the displacement of the end part of the cantilever beam is measured by utilizing the sensing relation between the displacement change of the end part of the variable cross-section cantilever beam and the strain change of the sensing optical fiber on the upper surface and the lower surface of the variable cross-section cantilever beam. The displacement measurement precision and the measuring range of the sensor can be adjusted, and the single displacement sensor can realize multi-direction displacement measurement. The displacement sensor can be connected in series at multiple points through one optical fiber, and a high-spatial-resolution long-distance distributed optical fiber strain sensing system is used for measuring displacement changes of all series-connected measuring points, so that a long-distance synchronous displacement monitoring system with more than multiple measuring points is formed. The invention can meet the requirements of large civil engineering structure on long-distance, ultra-multiple measuring points and high-precision displacement measurement, and has the advantages of reasonable manufacturing cost, simple system structure and convenient implementation.)

1. A multipoint serial distributed optical fiber displacement sensor is characterized in that: the strain sensor comprises 1 distributed strain sensing optical fiber (1), an adhesive (2), n variable cross-section cantilever beams (3), 2 cantilever beam bases (4), n measuring range base plates (5) and 2 fixed bases (6); n is a positive integer greater than or equal to 1; distributed strain sensing optical fiber (1) is pasted in the upper and lower surface of variable cross section cantilever beam (3) through gluing agent (2), the root of variable cross section cantilever beam (3) is fixed with a cantilever beam base (4), and on another cantilever beam base (4) was lapped to the tip to between tip and another cantilever beam base (4) through journey backing plate (5) bed hedgehopping, 2 cantilever beam base (4) are respectively through corresponding unable adjustment base (6) are fixed with being surveyed the structure.

2. The distributed fiber optic displacement sensor of claim 1, wherein: the cantilever part of the variable cross-section cantilever beam (3) is in a triangular plate shape, the plate thickness t is constant, and the cross-section width b (x) at the position of the cantilever length x needs to satisfy b (x) k (L-x), wherein k is constant, and L is the total length of the cantilever part of the variable cross-section cantilever beam (3).

3. The distributed fiber optic displacement sensor of claim 2, wherein: distributed strain sensing optical fiber (1) uses gluing agent (2) to paste in the upper and lower surface of variable cross section cantilever beam (3) along the straight line, and the specific position is the perpendicular line of tip summit to the base of the partial triangle-shaped board that becomes cross section cantilever beam (3) and encorbelments, distributed strain sensing optical fiber (1) and variable cross section cantilever beam (3) coordinate the deformation.

4. The distributed fiber optic displacement sensor of claim 1, wherein: the end part of the variable cross-section cantilever beam (3) is lapped on the measuring range base plate (5), the length dL between the lapping position and the top point of the end part of the variable cross-section cantilever beam (3) is preferably not more than 5% of the overhanging length L of the variable cross-section cantilever beam (3), namely dL is not more than 0.05L.

5. The distributed fiber optic displacement sensor of claim 1, wherein: displacement measurement sensitivity coefficient k of distributed optical fiber displacement sensor_dIs constant, the expression is k_d＝|_t-_bI/w, wherein w represents the displacement variation of the lapping position of the end part of the variable cross section cantilever beam (3) and the measuring range base plate (5) in the direction vertical to the variable cross section cantilever beam (3),_trepresenting the strain variation of the distributed strain sensing optical fiber (1) on the upper surface of the variable cross-section cantilever beam (3),_brepresenting the strain variation of the distributed strain sensing optical fiber (1) on the lower surface of the variable cross-section cantilever beam (3),_tand_bhas opposite sign of strain_t-_bI represents the sum of the strain variation of the distributed strain sensing optical fiber (1) on the upper surface and the lower surface of the variable cross-section cantilever beam (3); at known k_dBy measuring_t-_bAnd according to the relation w ═ non-calculation_t-_b|/k_dAnd calculating to obtain the change of w of the distributed optical fiber displacement sensor, thereby realizing displacement measurement.

6. The distributed fiber optic displacement sensor of claim 5, wherein: displacement measurement sensitivity coefficient k of distributed optical fiber displacement sensor_dThe relation between the geometrical parameters of the cantilever beam (3) with the variable cross section is k_d＝(t+d)/(L-dL)²Wherein t represents the thickness of a triangular plate of an overhanging part of the variable cross-section cantilever beam (3), d represents the diameter of the distributed strain sensing optical fiber (1), L is the total length of the overhanging part of the variable cross-section cantilever beam (3), dL is the length between the lap joint position and the top point of the end part of the variable cross-section cantilever beam (3), and the distributed optical fiber displacement sensor can customize a displacement measurement sensitivity coefficient k by adjusting t, d, L and dL four parameters_d。

7. The distributed fiber optic displacement sensor of claim 6, wherein: when the distributed optical fiber displacement sensor is in an initial state, the contact surfaces of the 2 cantilever beam bases (4) and the variable cross-section cantilever beams (3) are at the same horizontal height, the end parts of the variable cross-section cantilever beams (3) are heightened through the measuring range base plate (5), namely, the tilting height of the end parts of the variable cross-section cantilever beams (3) and the measuring range base plate (5) is equal to the thickness of the measuring range base plate (5) in the initial state.

8. The distributed fiber optic displacement sensor of claim 7, wherein: the measuring range of the distributed optical fiber displacement sensor is s ═ d₁,d₂) Wherein d is₁＝-t_d，d₂＝max(|_t-_b|)/k_d，t_dRepresents the thickness of the span plate (5), max (& lt & gt_t-_b|) represents the maximum strain variation sum, max (& gt_t-_bI) is determined by the elastic strain limit of the material of the variable cross-section cantilever beam (3), k_dThe displacement measurement sensitivity coefficient of the distributed optical fiber displacement sensor can be adjusted by adjusting t_d、max(|_t-_bI) and k_dThe three parameters customize the sensor range.

9. A multipoint serial distributed optical fiber displacement sensor measuring system is characterized in that: the measuring system comprises a plurality of multipoint series-connected distributed optical fiber displacement sensors according to any one of claims 1 to 8, the distributed optical fiber displacement sensors are sequentially connected in series through one distributed strain sensing optical fiber (1) to form a measuring system, the distributed strain sensing optical fibers (1) on all the series-connected distributed optical fiber displacement sensors form a complete optical fiber loop and are connected into the high-spatial-resolution distributed optical fiber strain measuring system, the strain distribution change of the whole distributed strain sensing optical fiber (1) is measured through the high-spatial-resolution distributed optical fiber strain measuring system, the strain change of the distributed strain sensing optical fiber (1) on the upper surface and the lower surface of each series-connected distributed optical fiber displacement sensor variable-section cantilever beam (3) is obtained at the same time, and the strain change of the upper surface and the lower surface of each variable-section cantilever beam (3) and the end part of each variable-section cantilever beam (3) are lapped and connected with each other And obtaining the displacement measurement result of each distributed optical fiber displacement sensor by the linear relation between the displacement variable quantities of the positions to form a set of multipoint serial distributed optical fiber displacement measurement system.

10. The measurement system of claim 9, wherein: the high spatial resolution distributed optical fiber strain measurement system is a Brillouin time domain analysis system with high spatial resolution, a Brillouin frequency domain analysis system with high spatial resolution or a Rayleigh light frequency domain reflection system with high spatial resolution; the Brillouin time domain analysis system with the high spatial resolution comprises a differential double-pulse Brillouin time domain analysis system and a pre-pumping pulse Brillouin time domain analysis system.

Technical Field

The invention belongs to the technical field of optical fiber sensing, and particularly relates to a multipoint serial distributed optical fiber displacement sensor and a measuring system thereof.

Background

The displacement change of the civil engineering structure is an important representation of the change of the structural state, and the acquisition of the displacement information of the civil engineering structure has important significance for analyzing the structural mechanical behavior, monitoring the structural disease development and evaluating the structural safety state. However, civil engineering structures have the characteristics of large volume, long distance, complex structure, many key positions, small displacement change and the like, structures such as bridges, tunnels, railways, roads, oil and gas pipelines and the like have the possibility of generating structural diseases in the whole length range of a design service period, and the displacement change displayed at the early stage of the structural diseases is usually in millimeter order. Therefore, when civil engineering structure safety monitoring is carried out, the more the number of displacement monitoring points is, the longer the covering distance is, the higher the measurement precision is, the easier the structural damage can be found as early as possible, the more the measures for timely taking remediation and maintenance are facilitated, and the more the structural safety risk can be effectively reduced.

At present, displacement sensors commonly used in civil engineering structure safety monitoring are mainly of the following types: the fiber bragg grating displacement sensor, the stay wire type displacement sensor, the LVDT displacement sensor, the laser displacement sensor and the like. For example, in a fiber grating displacement sensor disclosed in patent CN108955540A, a fiber grating is used as a sensing element, a mechanical linkage is used to convert the measured displacement into a strain change of the fiber grating, and the displacement is measured by measuring a strain signal of the fiber grating. For another example, a cascade hybrid stay wire displacement sensor introduced in the utility model CN204831201U uses a stay wire and a gear transmission device to convert the measured displacement into the signal change of an internal angle sensor, and realizes the measurement of the displacement based on the linear relationship between the two. The common disadvantage of the displacement sensors is that a displacement measurement system with ultra-long distance and ultra-multiple measuring points cannot be formed within a reasonable cost tolerance range, and the requirement of civil engineering structure monitoring for acquiring displacement information of a large number of key positions cannot be met.

For example, for a pull-wire displacement sensor, an LVDT displacement sensor and a laser displacement sensor, each sensor usually needs to be equipped with a data transmission line separately to connect with a data acquisition instrument and occupy a data acquisition channel, and due to the limitation of the number of the data acquisition channels of the instrument, the number of the accessible sensors is small. In addition, along with the increase of the covering distance of the sensors, the total length of the data transmission line is multiplied by the number of the sensors, and the transmission loss of the sensing signals is increased, so that the operability and the total cost of the displacement measurement system which forms an ultra-long distance and a plurality of measuring points in the actual civil engineering monitoring are not reasonable.

For the fiber grating displacement sensor, although a plurality of sensors can be connected in series through one optical fiber and data acquisition is carried out simultaneously, the number of gratings which can be connected in series through one optical fiber is limited, and is generally not more than dozens. In addition, because the fiber grating displacement sensors need to be connected through optical fiber fusion or flange plate butt joint, each connection point generates a certain degree of optical signal transmission loss, the number of the optical fiber connection points is increased along with the increase of the number of the sensors, the number of the optical fiber connection points is also increased, obvious signal attenuation is generated through accumulation, and the number of the fiber grating displacement sensors which can be connected in series is further limited. In addition, the fiber grating sensor has high cost, and besides a precise mechanical transmission device, gratings need to be engraved on the optical fiber, so that the total cost of the displacement monitoring system is too high due to the large use of the fiber grating sensor, and the fiber grating sensor does not meet the reasonable cost requirement of engineering monitoring.

Disclosure of Invention

The invention aims to solve the problems of small quantity of measuring points, short covering distance, overhigh cost of a plurality of measuring points and the like of a displacement sensing system in the monitoring of the existing civil engineering structure, and provides a multipoint serial distributed optical fiber displacement sensor and a measuring system thereof.

The invention is realized by the following technical scheme, and provides a multipoint tandem type distributed optical fiber displacement sensor which comprises 1 distributed strain sensing optical fiber 1, an adhesive 2, n variable cross-section cantilever beams 3, 2 cantilever beam bases 4, n measuring range base plates 5 and 2 fixed bases 6; n is a positive integer greater than or equal to 1; distributed strain sensing optical fiber 1 is pasted on the upper surface and the lower surface of variable cross section cantilever beam 3 through gluing agent 2, the root of variable cross section cantilever beam 3 is fixed with a cantilever beam base 4, and the tip is lapped on another cantilever beam base 4 to between tip and another cantilever beam base 4 through the lift of distance backing plate 5, 2 cantilever beam base 4 is respectively through corresponding unable adjustment base 6 is fixed with the structure under test.

Furthermore, the cantilever portion of the variable cross-section cantilever beam 3 has a triangular plate shape, the plate thickness t is constant, and the cross-sectional width b (x) at the cantilever length x position needs to satisfy b (x) k (L-x), where k is constant and L is the total length of the cantilever portion of the variable cross-section cantilever beam 3.

Further, the distributed strain sensing optical fiber 1 is adhered to the upper surface and the lower surface of the variable cross-section cantilever beam 3 along a straight line by using an adhesive 2, the specific position is a vertical line from the top point of the end part of the triangular plate of the overhanging part of the variable cross-section cantilever beam 3 to the bottom edge, and the distributed strain sensing optical fiber 1 and the variable cross-section cantilever beam 3 deform in a coordinated manner.

Furthermore, the end part of the variable cross-section cantilever beam 3 is lapped on the measuring range backing plate 5, and the length dL between the lapping position and the top point of the end part of the variable cross-section cantilever beam 3 is preferably not more than 5% of the overhanging length L of the variable cross-section cantilever beam 3, namely dL is less than or equal to 0.05L.

Further, the displacement measurement sensitivity coefficient k of the distributed optical fiber displacement sensor_dIs constant, the expression is k_d＝|_t-_bI/w, wherein w represents the displacement variation of the lapping position of the end part of the variable cross section cantilever beam 3 and the measuring range backing plate 5 in the direction vertical to the variable cross section cantilever beam 3,_trepresenting the amount of strain change of the distributed strain sensing optical fiber 1 on the upper surface of the variable cross-section cantilever beam 3,_brepresenting the strain variation of the distributed strain sensing optical fiber 1 on the lower surface of the variable cross-section cantilever beam 3,_tand_bhas opposite sign of strain_t-_bI represents the sum of the strain variation of the distributed strain sensing optical fiber 1 on the upper surface and the lower surface of the variable cross-section cantilever beam 3; at known k_dBy measuring_t-_bAnd according to the relation w ═ non-calculation_t-_b|/k_dAnd calculating to obtain the change of w of the distributed optical fiber displacement sensor, thereby realizing displacement measurement.

Further, the displacement measurement sensitivity coefficient k of the distributed optical fiber displacement sensor_dThe relation between the geometrical parameters of the variable cross-section cantilever beam 3 is k_d＝(t+d)/(L-dL)²Wherein t represents the thickness of the triangular plate of the overhanging part of the variable cross-section cantilever beam 3, d represents the diameter of the distributed strain sensing optical fiber 1, L is the total length of the overhanging part of the variable cross-section cantilever beam 3, dL is the length between the lap joint position and the top point of the end part of the variable cross-section cantilever beam 3, and the distributed optical fiber displacement sensor can customize the displacement measurement sensitivity coefficient k by adjusting t, d, L and dL four parameters_d。

Further, when the distributed optical fiber displacement sensor is in an initial state, the contact surfaces of the 2 cantilever beam bases 4 and the variable-section cantilever beam 3 are at the same horizontal height, the end part of the variable-section cantilever beam 3 is heightened through the measuring base plate 5, that is, the tilting height of the lap joint position of the end part of the variable-section cantilever beam 3 and the measuring base plate 5 is equal to the thickness of the measuring base plate 5 in the initial state.

Further, the measuring range of the distributed optical fiber displacement sensor is s ═ d (d)₁,d₂) Wherein d is₁＝-t_d，d₂＝max(|_t-_b|)/k_d，t_dRepresents the thickness of the span plate 5, max (& gt_t-_b|) represents the maximum sum of the strain changes, max (#) of the distributed strain sensing optical fiber 1 on the upper surface and the lower surface of the variable cross-section cantilever beam 3 in the relative positive displacement direction relative to the initial state_t-_bI) is determined by the elastic strain limit of the material of the variable cross-section cantilever beam 3, k_dThe displacement measurement sensitivity coefficient of the distributed optical fiber displacement sensor can be adjusted by adjusting t_d、max(|_t-_bI) and k_dThe three parameters customize the sensor range.

The invention also provides a measuring system of the multipoint tandem type distributed optical fiber displacement sensor, the measuring system comprises a plurality of the multipoint tandem type distributed optical fiber displacement sensors, the mode that the distributed optical fiber displacement sensors form the measuring system is that the distributed optical fiber displacement sensors are sequentially connected in series through a distributed strain sensing optical fiber 1, the distributed strain sensing optical fibers 1 on all the distributed optical fiber displacement sensors connected in series form a complete optical fiber loop and are connected into the high-spatial resolution distributed optical fiber strain measuring system, the strain distribution change of the whole distributed strain sensing optical fiber 1 is measured through the high-spatial resolution distributed optical fiber strain measuring system, and simultaneously the strain change of the distributed strain sensing optical fibers 1 on the upper surface and the lower surface of each distributed optical fiber displacement sensor variable-section cantilever beam 3 connected in series is obtained, and obtaining a displacement measurement result of each distributed optical fiber displacement sensor according to a linear relation between the strain change of the upper surface and the lower surface of the variable cross-section cantilever beam 3 and the displacement change of the lapping position of the end part of the variable cross-section cantilever beam 3, thereby forming a set of multi-point serial distributed optical fiber displacement measurement system.

Further, the high spatial resolution distributed optical fiber strain measurement system is a brillouin time domain analysis system with high spatial resolution, a brillouin frequency domain analysis system with high spatial resolution or a rayleigh optical frequency domain reflection system with high spatial resolution; the Brillouin time domain analysis system with the high spatial resolution comprises a differential double-pulse Brillouin time domain analysis system and a pre-pumping pulse Brillouin time domain analysis system.

The invention has the beneficial effects that: a plurality of distributed optical fiber displacement sensors can be connected in series through a distributed sensing optical fiber to form a complete optical signal channel, and the ultra-long distance coverage of displacement measurement and the information acquisition of ultra-multiple measuring points are realized by utilizing the ultra-low signal transmission loss of optical fiber signals and the advantages of ultra-long sensing distance, distributed measurement, high durability, high spatial resolution and the like of the distributed optical fiber strain sensing technology. In addition, each distributed optical fiber displacement sensor can customize displacement measurement direction, quantity, measuring range and displacement sensitivity according to the monitoring target requirement, has excellent engineering structure adaptability, and can be widely applied to various related fields of large-scale civil engineering structure displacement monitoring. In addition, all the serially connected displacement sensors only occupy one data acquisition channel, synchronous measurement can be realized, the system is simple in structure and good in expandability, the displacement sensors can meet the requirements of long-distance, multi-measuring-point and high-precision displacement measurement of large-scale civil engineering structures, the overall manufacturing cost is reasonable, the serially connected system is simple in structure, temperature compensation is avoided, synchronous measurement can be realized, and the displacement measurement precision and the measuring range of the sensors can be customized and adjusted.

Drawings

Fig. 1 is a schematic structural diagram of a multipoint tandem distributed optical fiber displacement sensor according to the present invention, which is used for measuring unidirectional displacement;

FIG. 2 is a schematic structural diagram of a multi-point tandem distributed optical fiber displacement sensor according to the present invention for bidirectional displacement measurement;

fig. 3 is a schematic structural diagram of a multipoint tandem distributed optical fiber displacement sensor measurement system according to the present invention.

Detailed Description

The technical solutions in the embodiments of the present invention will be described clearly and completely with reference to the accompanying drawings in the embodiments of the present invention, and it is obvious that the described embodiments are only a part of the embodiments of the present invention, and not all of the embodiments. All other embodiments, which can be derived by a person skilled in the art from the embodiments given herein without making any creative effort, shall fall within the protection scope of the present invention.

With reference to fig. 1 to 3, the present invention provides a multipoint tandem distributed optical fiber displacement sensor, which includes 1 distributed strain sensing optical fiber 1, an adhesive 2, n variable cross-section cantilever beams 3, 2 cantilever beam bases 4, n measuring pads 5 and 2 fixing bases 6; n is a positive integer greater than or equal to 1; the distributed strain sensing optical fiber 1 is adhered to the upper surface and the lower surface of the variable cross-section cantilever beam 3 through an adhesive 2, the root of the variable cross-section cantilever beam 3 is fixedly connected with a cantilever beam base 4, and the connection mode can be adhesive 2 or bolt and nut connection; the end part is lapped on the other cantilever beam base 4, the distance between the end part and the other cantilever beam base 4 is increased by a distance cushion plate 5, and 2 cantilever beam bases 4 are respectively fixed with a structure to be measured through the corresponding fixed bases 6. The displacement measurement mechanism of the distributed optical fiber displacement sensor is that the displacement change of the end part of the variable cross-section cantilever beam 3 is measured by measuring the strain change of the distributed strain sensing optical fiber 1 and then measuring the displacement change of the end part of the variable cross-section cantilever beam 3 by utilizing the linear relation between the displacement change of the end part of the variable cross-section cantilever beam 3 and the strain change of the upper surface and the lower surface of the variable cross-section cantilever beam.

One distributed optical fiber displacement sensor can simultaneously measure the displacement in n directions. When n is 1, the displacement sensor can measure the displacement change in 1 direction (the direction perpendicular to the plane of the variable-section cantilever beam 3); when n is 2, the displacement sensor can measure the displacement change in 2 directions (the vertical direction of the plane where the two variable-section cantilever beams 3 are respectively located); by analogy, the number of the variable cross-section cantilever beams 3 and the number of the measuring range backing plates 5 can be continuously increased according to the number of the target displacement directions, so that the number of the displacement directions which can be measured by a single distributed optical fiber displacement sensor is increased.

When the unidirectional displacement measurement is carried out, the quantity of the variable cross-section cantilever beam 3 and the measuring range base plate 5 is 1 (as shown in figure 1), and the test displacement sensor can only measure the displacement perpendicular to the variable cross-section cantilever beam 3. When the bidirectional displacement measurement is carried out, the structure of the displacement sensing is changed into the structure shown in fig. 2, the basic structure of the sensor is unchanged, and the change is that 3 to 2 variable cross-section cantilever beams are added and respectively fixed on two surfaces of a cantilever beam base 4, the number of corresponding range base plates 5 is also increased to 2, the variable cross-section cantilever beams are fixed on two surfaces of the cantilever beam base 4 on the other side, and the end parts of the corresponding variable cross-section cantilever beams 3 are heightened. At this time, the displacement sensor can measure the displacement direction perpendicular to the two variable cross-section cantilever beams 3, and therefore bidirectional displacement measurement can be carried out. By analogy, the number of the variable cross-section cantilever beams 3 and the measuring range base plates 5 can be increased, the number of the surfaces of the cantilever beam bases 4 can be correspondingly increased, and the number of the displacement directions which can be measured by the displacement sensor can be further increased.

The distributed strain sensing optical fiber 1 used by the distributed optical fiber displacement sensor is a single-mode non-polarization-maintaining quartz optical fiber or a single-mode polarization-maintaining quartz optical fiber.

The adhesive 2 used by the distributed optical fiber displacement sensor is acrylate adhesive, epoxy resin adhesive or ultraviolet curing adhesive.

The cantilever part of the variable cross-section cantilever beam 3 is in a triangular plate shape, the plate thickness t is constant, and the cross-section width b (x) at the position of the cantilever length x needs to satisfy b (x) k (L-x), wherein k is constant, and L is the total length of the cantilever part of the variable cross-section cantilever beam 3.

The distributed strain sensing optical fiber 1 is adhered to the upper surface and the lower surface of the variable cross-section cantilever beam 3 along straight lines by using an adhesive 2, the specific position is a vertical line from the top point of the end part of the triangular plate of the overhanging part of the variable cross-section cantilever beam 3 to the bottom edge, and the distributed strain sensing optical fiber 1 and the variable cross-section cantilever beam 3 deform in a coordinated manner.

The end part of the variable cross-section cantilever beam 3 is lapped on the measuring range base plate 5, and the length dL between the lapping position and the top point of the end part of the variable cross-section cantilever beam 3 is preferably not more than 5% of the overhanging length L of the variable cross-section cantilever beam 3, namely dL is less than or equal to 0.05L.

The displacement measurement sensitivity coefficient (sensor sensitivity coefficient for short) of the distributed optical fiber displacement sensor is defined as the sum of the strain variation of the distributed strain sensing optical fiber 3 on the upper surface and the lower surface of the variable cross-section cantilever beam 3 caused when the lap joint position of the end part of the variable cross-section cantilever beam 3 and the measuring range base plate 5 generates unit displacement variation vertical to the direction of the variable cross-section cantilever beam 3, and the displacement measurement sensitivity coefficient k of the distributed optical fiber displacement sensor_dIs constant, the expression is k_d＝|_t-_bI/w, wherein w represents the displacement variation of the lapping position of the end part of the variable cross section cantilever beam 3 and the measuring range backing plate 5 in the direction vertical to the variable cross section cantilever beam 3,_trepresenting the amount of strain change of the distributed strain sensing optical fiber 1 on the upper surface of the variable cross-section cantilever beam 3,_brepresenting the strain variation of the distributed strain sensing optical fiber 1 on the lower surface of the variable cross-section cantilever beam 3,_tand_bhas opposite sign of strain_t-_bI represents the sum of the strain variation of the distributed strain sensing optical fiber 1 on the upper surface and the lower surface of the variable cross-section cantilever beam 3; at known k_dBy measuring_t-_bAnd according to the relation w ═ non-calculation_t-_b|/k_dAnd calculating to obtain the change of w of the distributed optical fiber displacement sensor, thereby realizing displacement measurement.

Displacement measurement sensitivity coefficient k of distributed optical fiber displacement sensor_dThe relation between the geometrical parameters of the variable cross-section cantilever beam 3 is k_d＝(t+d)/(L-dL)²Wherein t represents a variable cross-section cantilever beam 3Choose partial triangular plate thickness, d represents the diameter of distributed strain sensing optic fibre 1, and L is the total length of the part of encorbelmenting of variable cross section cantilever beam 3, and dL is the length apart from the tip summit of variable cross section cantilever beam 3 in overlap joint position, distributed optical fiber displacement sensor can be through adjusting t, d, L, dL four item parameter customization displacement measurement sensitivity coefficient k_d。

When the distributed optical fiber displacement sensor is in an initial state, the contact surfaces of the 2 cantilever beam bases 4 and the variable cross-section cantilever beam 3 are at the same horizontal height, the end part of the variable cross-section cantilever beam 3 is heightened through the measuring range base plate 5, namely, the tilting height of the lap joint position of the end part of the variable cross-section cantilever beam 3 and the measuring range base plate 5 is equal to the thickness of the measuring range base plate 5 in the initial state.

Defining the displacement direction of the cantilever part of the variable cross-section cantilever beam to restore to a plane as a relative negative displacement direction, and the displacement direction of the cantilever part of the variable cross-section cantilever beam to tilt as a relative positive displacement direction, wherein the measuring range (simply referred to as sensor measuring range) of the distributed optical fiber displacement sensor is s ═ d (d ═ d₁,d₂) Wherein d is₁＝-t_d，d₂＝max(|_t-_b|)/k_d，d₁Is a negative real number, representing the measurement range of relative negative displacement, d₂Is positive real number and represents the measurement range of relative positive displacement, t_dRepresents the thickness of the span plate 5, max (& gt_t-_b|) represents the maximum sum of the strain changes, max (#) of the distributed strain sensing optical fiber 1 on the upper surface and the lower surface of the variable cross-section cantilever beam 3 in the relative positive displacement direction relative to the initial state_t-_bI) is determined by the elastic strain limit of the material of the variable cross-section cantilever beam 3, k_dThe displacement measurement sensitivity coefficient of the distributed optical fiber displacement sensor can be adjusted by adjusting t_d、max(|_t-_bI) and k_dThe three parameters customize the sensor range. The material of the variable cross-section cantilever beam 3 used by the displacement sensor needs to have good elasticity, and comprises polycarbonate plastic, polymethyl methacrylate plastic and modified plastic thereof, and also comprises iron, aluminum, copper, titanium and alloy materials thereof.

The invention also provides a multi-point tandem type distributed optical fiber displacement sensor measuring system, as shown in figure 3, the measuring system comprises a plurality of multi-point tandem type distributed optical fiber displacement sensors, the mode of the measuring system formed by the plurality of distributed optical fiber displacement sensors is that the plurality of distributed optical fiber displacement sensors are sequentially connected in series through one distributed strain sensing optical fiber 1, the distributed strain sensing optical fibers 1 on all the distributed optical fiber displacement sensors connected in series form a complete optical fiber loop and are connected into the high spatial resolution distributed optical fiber strain measuring system, the strain distribution change of the whole distributed strain sensing optical fiber 1 is measured through the high spatial resolution distributed optical fiber strain measuring system, and simultaneously the strain change of the distributed strain sensing optical fibers 1 on the upper surface and the lower surface of each distributed optical fiber displacement sensor variable cross-section cantilever beam 3 connected in series is obtained, and obtaining a displacement measurement result of each distributed optical fiber displacement sensor according to a linear relation between the strain change of the upper surface and the lower surface of the variable cross-section cantilever beam 3 and the displacement change of the lapping position of the end part of the variable cross-section cantilever beam 3, thereby forming a set of multi-point serial distributed optical fiber displacement measurement system.

The high spatial resolution distributed optical fiber strain measurement system is a Brillouin time domain analysis system (BOTDA) with high spatial resolution, a Brillouin frequency domain analysis system (BOFDA) with high spatial resolution or Rayleigh optical frequency domain reflection systems (OFDR and OBR) with high spatial resolution; the Brillouin time domain analysis system with high spatial resolution comprises a differential double-pulse Brillouin time domain analysis system (DPP-BOTDA) and a pre-pumping pulse Brillouin time domain analysis system (PPP-BOTDA), and the used distributed optical fiber strain measurement system is better than 20cm in spatial resolution and is better than 5cm in sampling interval. The number of the welding points or connection points of the distributed strain sensing optical fiber 1 is required to be as small as possible, and the bending radius of the optical fiber is required to be as large as possible at the position needing to be bent, so that the propagation loss of optical signals is reduced, and the sensing distance which can be covered by a system is increased.

When the actual engineering monitoring is carried out, the displacement measurement precision, the displacement range and the displacement direction quantity required by a monitoring target are determined according to the specific requirements of an engineering structure. Firstly, according to the requirement of displacement measurement precision, determining the displacement sensorThe geometrical size of the cantilever beam 3 with variable cross section is k_d＝(t+d)/(L-dL)²Wherein k is_dThe sensor sensitivity coefficient is represented, t represents the thickness of a triangular plate of the overhanging part of the variable cross-section cantilever beam 3, d represents the diameter of the distributed strain sensing optical fiber 1, L is the total length of the overhanging part of the variable cross-section cantilever beam 3, and dL is the length between the lap joint position and the top point of the end part of the variable cross-section cantilever beam 3. k is a radical of_dThe displacement measurement precision is directly determined, namely the displacement measurement precision of the distributed optical fiber displacement sensor can be customized by adjusting t, d, L and dL four parameters. Secondly, determining the material of the variable cross-section cantilever beam 3 and the thickness of the range backing plate 5 according to the displacement measurement range requirement. The distributed optical fiber displacement sensor has a measuring range (simply referred to as sensor measuring range) of s ═ d₁,d₂) Wherein d is₁＝-t_d，d₂＝max(|_t-_b|)/k_d，d₁Is a negative real number, representing the measurement range of relative negative displacement, d₂Is positive real number and represents the measurement range of relative positive displacement, t_dRepresents the thickness of the span plate 5, max (& gt_t-_b|) represents the maximum sum of the strain changes, max (#) of the distributed strain sensing optical fiber 1 on the upper surface and the lower surface of the variable cross-section cantilever beam 3 in the relative positive displacement direction relative to the initial state_t-_bI) is determined by the elastic strain limit of the material of the variable cross-section cantilever beam 3, k_dIs the sensor sensitivity coefficient. Therefore, t can be adjusted_d、max(|_t-_bI) and k_dThe three parameters (i.e., the material of the variable cross-section cantilever beam 3 and the thickness of the span plate 5) customize the sensor span. Thirdly, according to the requirement of the number of the displacement measurement directions, the number of the variable cross-section cantilever beams 3 and the number of the range backing plates 5 are determined, and the number and the direction of the surfaces of the cantilever beam bases 4 are reasonably adjusted, so that the variable cross-section cantilever beams 3 are perpendicular to the displacement direction of the measurement target, and the corresponding displacement measurement is carried out.

The multipoint serial distributed optical fiber displacement sensor and the measuring system thereof provided by the invention are introduced in detail, the principle and the implementation mode of the invention are explained by applying specific examples, and the description of the examples is only used for helping to understand the method and the core idea of the invention; meanwhile, for a person skilled in the art, according to the idea of the present invention, there may be variations in the specific embodiments and the application scope, and in summary, the content of the present specification should not be construed as a limitation to the present invention.