CN115265470A - Fiber Bragg grating settlement sensor with high resolution - Google Patents

Abstract

The invention discloses a fiber Bragg grating sedimentation sensor with high resolution, comprising a water storage shell and an encapsulation shell, a diaphragm is arranged spaced apart between the water storage shell and the encapsulation shell; The water outlet valve, the water inlet valve and the water blocking valve are arranged on both sides of the water storage shell; a ring is arranged in the encapsulation housing, the top of the ring is arranged with a first force transmission rod connected with the diaphragm, and the bottom of the ring is arranged with a pass through A second dowel rod fixed by screws to the bottom surface of the inner side of the encapsulation shell, a first fiber fixing groove and a second fiber fixing groove are arranged on both sides of the ring, and fiber Bragg gratings are arranged in the first fiber fixing groove and the second fiber fixing groove , the part of the fiber Bragg grating protruding from the encapsulation shell is sheathed with an optical fiber sheath; the bottom of the encapsulation shell is provided with a ventilation valve. The sensor has low cost and good reliability.

Description

A Fiber Bragg Grating Subsidence Sensor with High Resolution

technical field

The invention relates to the technical field of optical fiber sensor devices, in particular to an optical fiber Bragg grating settlement sensor with high resolution.

Background technique

Civil engineering structures will induce settlement and deformation of the structure under the combined action of various factors such as soft soil foundation, improper operation of water interception and drainage, excessive load, and failure of design and construction standards to meet the specification requirements. If the settlement deformation is too large, it exceeds the national standard specification The set danger threshold will lead to the occurrence of devastating accidents such as the collapse of engineering structures in severe cases. The settlement is measured by using a total station or a level to regularly record each measuring point, but real-time monitoring of the structure cannot be realized. In order to protect the safe operation of civil engineering structures, it is imperative to promote dynamic acquisition, continuous real-time, strong anti-interference ability, and good stability automatic deformation monitoring technology.

Fiber Bragg grating has the advantages of small size, wavelength coding, quasi-distributed measurement, convenient networking and good reliability in automatic deformation monitoring. In addition, compared with traditional photoelectric static level and capacitive static level, fiber Bragg The anti-electromagnetic interference characteristics of the grating enable it to serve in harsh environments for a long time.

The radial pressure sensitivity of the bare fiber Bragg grating is only -4.33pm/MPa, which cannot be directly applied to water pressure measurement. Therefore, it is necessary to design a corresponding sensitivity enhancement structure and packaging shell to achieve high-precision measurement of water pressure changes at the measurement point , and then according to the principle of the connecting pipe, the designed fiber Bragg grating settlement sensor is arranged at the reference point and each monitoring point, and the settlement sensor can be sensitive to the change of water level pressure reflected by the settlement deformation. To accurately identify the corresponding water level changes, the measurement system based on settlement sensors can be widely used in engineering fields such as bridge deflection deformation, railway track settlement, tunnel convergence deformation, uneven settlement of buildings and uplift of underground comprehensive pipe gallery.

Contents of the invention

The purpose of the present invention is to provide a fiber Bragg grating settlement sensor with high resolution to realize the monitoring of settlement phenomena.

In order to solve the above technical problems, the present invention provides a technical solution: a fiber Bragg grating subsidence sensor with high resolution, including a water storage shell and an encapsulation shell, and the water storage shell and the encapsulation shell are spaced apart There is a diaphragm; the top of the water storage shell is provided with a water outlet valve, and the two sides of the water storage shell are provided with a water inlet valve and a water blocking valve; a ring is provided in the packaging shell, and the top of the ring is provided with a first valve connected to the diaphragm. A dowel bar, the bottom of the ring is provided with a second dowel bar that is detachably fixed to the bottom surface of the inner side of the packaging case, and the first fiber fixing groove and the second fiber fixing groove are arranged on both sides of the ring, and the first fiber fixing groove Fiber Bragg gratings are arranged in the groove and the second fixed fiber groove, and the part of the fiber Bragg grating extending out of the packaging casing is covered with an optical fiber sheath; a vent valve is arranged at the bottom of the packaging casing.

According to the above solution, the first dowel bar and the second dowel bar are distributed vertically and symmetrically with respect to the center of the ring, and the first fiber-fixing groove and the second fiber-fixing groove are horizontally symmetrically distributed relative to the center of the ring.

According to the above scheme, the fiber Bragg grating is fixed in the first fiber-fixing groove and the second fiber-fixing groove by bonding.

According to the above solution, the bottom of the second dowel bar is in the shape of a trapezoidal boss, and the bottom surface of the second dowel bar is provided with a threaded hole for connecting the packaging shell and the second dowel bar to be fixed with the packaging shell by screws.

According to the above scheme, the water outlet valve, the water inlet valve and the water blocking valve are all fixed to the water storage shell through threaded connection.

According to the above solution, the ventilation valve is fixed to the packaging shell through threaded connection.

According to the above scheme, the initial central wavelength of the fiber Bragg grating is 1530-1560 nm, the length of the grating area is 10-15 mm, and the intensity of reflected light is not lower than 95% of the intensity of incident light.

According to the above scheme, the materials of the first dowel bar, the second dowel bar, the first fiber-fixing groove, the second fiber-fixing groove and the ring are obtained through integrated mechanical processing of the first kind of alloy which is homogeneous; The sheet, the water storage shell and the packaging shell are made of a homogeneous second type alloy.

According to the above scheme, the first type of alloy is 4J36 Invar alloy steel, and the second type of alloy is 316 stainless steel.

According to the above scheme, the structural size of the ring satisfies the following relationship,

Wherein Pe is the elasto-optic coefficient of the fiber Bragg grating, α _Λ is the thermal expansion coefficient of the fiber Bragg grating, α _{n is} the thermo-optic coefficient of the fiber Bragg grating, r is the radius of the ring, c is the first dowel and the second The length of the dowel bar, α ₁ and α ₂ are the thermal expansion coefficients of the first type alloy and the second type alloy, respectively.

The beneficial effects of the present invention are: the traditional optical fiber Bragg grating settlement sensor is designed with a buoy structure, and must be open to communicate with the atmosphere. The designed ring and diaphragm structure have good isolation from the atmosphere, and do not need to replenish water frequently. At the same time, when subjected to the liquid pressure in the cavity, the fiber Bragg grating is always in a state of tension, making the sensor highly reliable.

Furthermore, the sensor only uses a section of fiber Bragg grating, and utilizes the difference in the thermal expansion coefficient of metal materials to realize the temperature self-compensation of the sensor. Compared with the traditional solution of using two fiber Bragg gratings for measurement and temperature compensation, it reduces the manufacturing cost of the sensor.

Description of drawings

Fig. 1 is a cross-sectional view of a fiber Bragg grating settlement sensor with high resolution according to an embodiment of the present invention.

Figure 2 is a partially enlarged view of Figure 1;

Fig. 3 is a cross-sectional force and size schematic diagram of a circular ring according to an embodiment of the present invention;

Fig. 4 is a flow chart of evaluating the effective resolution of a fiber Bragg grating settlement sensor with high resolution according to an embodiment of the present invention;

Fig. 5 is a schematic diagram of an application of a fiber Bragg grating settlement sensor with high resolution in settlement monitoring according to an embodiment of the present invention.

In the figure: 101-fiber Bragg grating, 102-ring, 103-first dowel, 104-second dowel, 105-first fiber fixing groove, 106-second fiber fixing groove, 107-fiber protection Set, 108-diaphragm, 109-water storage shell, 110-encapsulation shell, 111-water outlet valve, 112-water inlet valve, 113-water blocking valve, 114-breather valve, 115-screw, 2-water level pressure, 3-Liquid storage tank, 4-Fiber Bragg grating settlement sensor at the reference point, 5-Fiber Bragg grating settlement sensor located before the settlement of the monitoring point, 6-Fiber Bragg grating settlement sensor located after the settlement of the monitoring point, 7-Signal transmission multiple Core optical cable, 8-connected water pipe, 9-terminal signal collection and analysis table.

Detailed ways

In order to make the purpose, technical solutions and advantages of the embodiments of the present disclosure clearer, the technical solutions of the embodiments of the present disclosure will be clearly and completely described below in conjunction with the accompanying drawings of the embodiments of the present disclosure. Apparently, the described embodiments are some of the embodiments of the present disclosure, not all of them. Based on the described embodiments of the present disclosure, all other embodiments obtained by persons of ordinary skill in the art without creative effort fall within the protection scope of the present disclosure.

Referring to Fig. 1 and Fig. 2, a fiber Bragg grating subsidence sensor with high resolution includes a water storage case 109 and an encapsulation case 110, and a diaphragm 108 is arranged between the water storage case 109 and the encapsulation case 110 The top of the water storage shell 109 is provided with a water outlet valve 111, and the two sides of the water storage shell 109 are provided with a water inlet valve 112 and a water blocking valve 113; The first dowel 103 connected to the diaphragm 108, the bottom of the ring 102 is provided with the second dowel 104 fixed to the inner bottom surface of the package housing 110 by screws 115, and the first fiber fixing groove 105 is arranged on both sides of the ring 102 With the second fiber-fixing groove 106, the fiber Bragg grating 101 is arranged in the first fiber-fixing groove 105 and the second fiber-fixing groove 106, and the part of the fiber Bragg grating 101 that protrudes from the package housing 110 is covered with a fiber sheath 107; A ventilation valve 114 is provided at the bottom of the casing 110 .

The fabrication and assembly process of the sensor is as follows:

The material of the first dowel 103, the second dowel 104, the first fiber-fixing groove 105, the second fiber-fixing groove 106 and the ring 102 is homogeneous 4J36 Invar alloy steel, the diaphragm 108, The material of the water storage shell 109 and the packaging shell 110 is homogeneous 316 stainless steel, the material selection of the optical fiber sheath 107, the water outlet valve 111, the water inlet valve 112, the water blocking valve 113, the ventilation valve 114, and the screw 115 can refer to National or industry standards.

The ring 102, the first dowel bar 103, the second dowel bar 104, the first fiber fixing groove 105, and the second fiber fixing groove 106 are processed by integrated machining, which must be processed by wire electric discharge cutting. To ensure its dimensional accuracy, a trapezoidal boss is provided at the bottom of the second dowel 104, and a threaded hole is provided at the bottom of the boss for connection with the package housing 110, the optical fiber sheath 107, the diaphragm 108, the water storage housing 109, The packaging shell 110, the water outlet valve 111, the water inlet valve 112, the water blocking valve 113, the ventilation valve 114, and the screw 115 are processed in a conventional manner. external thread.

First use 0.1mol/L sodium hydroxide solution to remove the oil stains on the surface of parts 102-115 during machining, and then add 10% dilute nitric acid solution, ring 102, first dowel 103, second dowel 104, and A solid fiber slot 105, a second solid fiber slot 106, an optical fiber sheath 107, a diaphragm 108, a water storage shell 109, a packaging shell 110, a water outlet valve 111, a water inlet valve 112, a water blocking valve 113, and a ventilation valve 114 1. Screw 115 is placed in a beaker, and the metal oxide on the surface of the parts is cleaned. After cleaning, the metal core is wiped with 75% alcohol solution. After cleaning, the sensor must be prevented from being polluted.

Pre-assemble all parts except a fiber Bragg grating 101 in the settlement sensor (including the ring 102, the first dowel bar 103, the second dowel bar 104, the first fiber-fixing slot 105, the second fiber-fixing slot 106, Optical fiber sheath 107, diaphragm 108, water storage shell 109, packaging shell 110, water outlet valve 111, water inlet valve 112, water blocking valve 113, ventilation valve 114, screw 115), observe that there is no obvious gap between the above parts After the assembly error, the diaphragm 108 and the first dowel 103 are connected by laser welding.

The selected fiber Bragg grating 101 has an initial central wavelength value between 1530 and 1560 nm, and the length of the grating area is 10 to 15 mm, thereby increasing the reflectivity of the grating and making the reflected light intensity reach 95% of the incident light intensity. Paste the fiber Bragg grating Before 101, it should be subjected to high temperature aging and cyclic aging work. The coating layer of the fiber Bragg grating 101 is stripped, and only the cladding and core of the optical fiber are kept. The length of the coating layer is equal to the diameter of the ring 102, The sum of 1/2 of the length of the first fiber fixing groove 105 and 1/2 of the length of the second fiber fixing groove 106 .

Before pasting the fiber Bragg grating 101, use absolute ethanol to wipe the optical fibers on both sides. When pasting the fiber Bragg grating 101, apply 1000 micro-strain pre-stretching to it, and the corresponding wavelength shift is about 1.2nm. Place the fiber Bragg grating 101 on 353ND glue is dripped into the first fiber fixing groove 105 and the second fiber fixing groove 106, wherein the A component and B component of the 353ND glue are evenly mixed in a ratio of 10:1, and the wavelength value of the fiber Bragg grating 101 is observed during the pasting process .

Place the ring 102 pasted with the fiber Bragg grating 101 in the package housing 110, the pigtails at both ends of the fiber Bragg grating 101 pass through the fiber sheath 107 of the package housing 110, and use Kraft K-0243 thread glue and the inner hexagon Screws 115 are used to connect the ring 102 and the package housing 110 , and then access protective devices such as optical fiber lead-out sleeves and jumpers.

The water outlet valve 111, water inlet valve 112 and water blocking valve 113 are installed on the water storage housing 109 in a threaded manner using Kraft K-0243 thread glue and nylon gasket. The function of the water outlet valve 111 is to drain the connection shown in Fig. Air in the sensor system, so that water can fill the water storage housing 109 of each settlement sensor, the ventilation valve 114 is installed on the bottom of the packaging housing 110 in a threaded connection with Kraft K-0243 thread glue, and the ventilation valve 114 The function is to make the part below the diaphragm 108 of the sedimentation sensor consistent with the atmospheric pressure of the outside world.

The diaphragm 108 and the packaging shell 110 are connected by laser welding. The water storage shell 109 is installed on the packing shell 110 by threaded connection with Kraft K-0243 thread glue. Please avoid touching the diaphragm as much as possible during the operation. In area 108, record the center wavelength of the fiber Bragg grating 101 at this time, complete the production of the fiber Bragg grating settlement sensor, and finally carry out the high and low temperature cycle aging work to release the assembly stress generated during the production process of the settlement sensor.

Referring to Fig. 3, if the ring 102 is installed in the encapsulation housing 110 of the subsidence sensor, the ring needs to be in contact with the first dowel 103, the second dowel 104, and the diaphragm 108 that are in contact with each other when deformed by temperature changes. And the package housing 110 performs deformation coordination. The material of the ring 102, the first dowel 103 and the second dowel 104 in the settlement sensor is homogeneous 4J36 Invar alloy steel, and the material of the packaging shell 110 and the diaphragm 108 is homogeneous 316 stainless steel, 4J36 The coefficient of thermal expansion of Invar alloy steel is less than that of 316 stainless steel.

The temperature self-compensation principle is as follows:

When the overall external temperature rises, the central wavelength will increase because the fiber Bragg grating 101 is sensitive to temperature, and the ring 102 will elongate in the horizontal direction under the effect of thermal expansion and contraction, and the fiber Bragg grating 101 will be sensitive to strain. The central wavelength of the fiber Bragg grating 101 pasted on the first fiber-fixing groove 105 and the second fiber-fixing groove 106 increases, and the increase in temperature will cause the overall thermal expansion and deformation of the settlement sensor, causing the ring 102 to be stretched in the vertical direction. The stretching in the vertical direction will cause the compression of the ring 102 in the horizontal direction, so that the central wavelength of the fiber Bragg grating 101 will be reduced. By setting the appropriate structural size of the ring 102, that is, the temperature self-compensation model of the ring 102, the The resulting changes in the center wavelength of the fiber Bragg grating 101 can cancel each other out, realizing the temperature self-compensation function of the settlement sensor, and analyzing it in the same way when the overall external temperature decreases.

The function of the first dowel 103 and the second dowel 104 is to transmit the forced displacement and deformation applied to the ring 102 by the diaphragm 108 and the bottom of the packaging case 110, because the first dowel 103 and the second dowel 104 The cross-sectional size of is larger than the cross-sectional size of the ring 102, so it can be considered that the above-mentioned forced displacement deformation is completely transmitted to the ring 102.

The strain change Δε and temperature change ΔT acting on the fiber Bragg grating 101 will cause the center wavelength λ _B of the fiber Bragg grating 101 to linearly shift, and the change relationship can be expressed as:

Δλ _B /λ _B ＝(1-P _e )Δε+(α _Λ +α _n )ΔT

In the formula, Δλ _B is the wavelength variation of the fiber Bragg grating 101, and Pe, α _Λ and α _n are the elasto _- optic coefficient, thermal expansion coefficient and thermo-optic coefficient of the fiber Bragg grating 101, respectively.

Assuming that the radius of the ring 102 is r, the expansion or contraction deformation Δr′ of the ring 102 made of 4J36 material under the temperature change ΔT satisfies:

Δr'=α _4J36 ·r·ΔT

Correspondingly, the wavelength variation Δλ _B of the fiber Bragg grating 101 corresponding to the above formula is:

Δλ _B ＝(1-P _e )α _4J36 ·λ _B ·ΔT

The central wavelength offset of the fiber Bragg grating 101 at the temperature change ΔT:

Δλ _B ＝(α _Λ +α _n )·λ _B ·ΔT

Correspondingly, when the temperature changes ΔT, the length change Δl′ between the bottom of the package housing 110 of the subsidence sensor and the diaphragm 108 satisfies:

Δl'=α ₃₁₆ (2r+2c)·ΔT

In the formula, r is the radius of the ring, and c is the length of the first dowel bar and the second dowel bar;

Since the thermal expansion coefficient α _4J36 of 4J36 Invar alloy steel is smaller than the thermal expansion coefficient α ₃₁₆ of 316 stainless steel, the difference between the above formula and the free expansion deformation of 4J36 Invar alloy Δl=α _4J36 (2r+2c)ΔT is:

Δl'-Δl=(α ₃₁₆ -α _4J36 )(2r+2c)·ΔT

The above formula can be understood as the boundary condition of forced tensile displacement applied at both ends of the top of the first dowel 103 and the bottom of the second dowel 104, so that the vertical direction of the ring 102 is stretched, correspondingly, the circular The horizontal direction of the ring 102 is compressed, and the amount of compression in the horizontal direction of the ring 102 is Δ1 _level . Due to the symmetry of the ring structure, the vertical stretching of the ring 102 is numerically equal to the amount of compression in the horizontal direction. Therefore, the amount of compression in the horizontal direction of the ring 102 is:

Δl _level = (α ₃₁₆ −α _4J36 )(2r+2c)·ΔT

Correspondingly, the wavelength variation Δλ _B of the fiber Bragg grating 101 corresponding to the above formula is:

Combining the following three formulas,

Δλ _B ＝(1-P _e )α _4J36 ·λ _B ·ΔT

Δλ _B ＝(α _Λ +α _n )·λ _B ·ΔT

Let Δλ _B = 0 in the above formula, that is, the temperature self-compensation model of the ring 102 structure in the fiber Bragg grating settlement sensor is obtained. In order to realize its temperature self-compensation function, the structure size of the ring 102 needs to meet:

In the temperature self-compensation model, Pe, α _Λ and α _n are the elasto-optic coefficient, thermal expansion coefficient and thermo-optic coefficient of the fiber Bragg grating 101 respectively, _r is the radius of the ring 102, c is the first dowel 103 and the second The lengths of the second dowel 104, α _4J36 and α ₃₁₆ are the thermal expansion coefficients of 4J36 Invar alloy steel and 316 stainless steel, respectively.

The water level pressure measurement principle of the fiber Bragg grating subsidence sensor is as follows:

When the water storage housing 109 is filled with water, the water level pressure 2 on the diaphragm 108 is transmitted from the first dowel 103 to the ring 102, and the vertical direction of the ring 102 is compressed so that the horizontal direction stretches, which in turn causes the diaphragm 108 to stick to the The fiber Bragg gratings 101 on the first fiber-fixing groove 105 and the second fiber-fixing groove 106 generate tensile strain, so that the central wavelength of the fiber Bragg grating 101 shifts.

In this embodiment, the sensitivity coefficient of the subsidence sensor is defined as S, the variation of the water level pressure is ΔP, and the variation of the central wavelength of the fiber Bragg grating 101 pasted on the first fiber-fixing groove 105 and the second fiber-fixing groove 106 is defined as Δλ above The relationship between the three is:

In order to obtain the designed fiber Bragg grating subsidence sensor, it is necessary to pass a sensitivity test, so as to obtain a linear relationship between the variation of the central wavelength shift of the fiber Bragg grating 101 and the variation of water level pressure.

The sensitivity test method is described as follows:

Connect the water inlet valve 112 of the fiber Bragg grating subsidence sensor after packaging to a silicone hose with a diameter of 8 mm, connect the silicone hose at the end of the water inlet valve 112 to the liquid storage tank, close the water blocking valve 113, and drain the water to the liquid storage tank. Open the water outlet valve 111 of the settlement sensor before injecting pure water into the tank, until the water outlet valve 111 floods, then shake the bubble position of the silicone hose of the water inlet valve 112, close the water outlet valve 111 after the inspection is completed, and then inject a small amount into the liquid storage tank Pure water until the fiber Bragg grating 101 wavelength is about 0.5nm higher than that before the test system is installed.

The sensitivity test of the fiber Bragg grating settlement sensor is carried out at room temperature. The data sampling frequency of the fiber grating demodulator is set to 5Hz. The pressure corresponding to the height of the water level is the step length, and the water level pressure loading-unloading test cycle is carried out 3 times, and the wavelength drift of the fiber Bragg grating 101 is recorded in real time.

Obtain the real-time curves of the loading-unloading wavelength of the fiber Bragg grating settlement sensor for 3 times, take the average value of the wavelength drift corresponding to each water level pressure value in the 3 repeated experiments, and perform the least squares method to fit, so as to obtain the optical fiber The sensitivity S of the Bragg grating settlement sensor.

The settlement sensor is based on the principle of connecting pipes to monitor the change of water level and pressure. There are many factors that affect its resolution. In order to prove that the fiber Bragg grating settlement sensor has high resolution performance, dichotomy, non-repeated two-factor variance analysis and correlation analysis are used. Statistical methods are used to analyze the test data of the fiber Bragg grating settlement sensor, so as to obtain its effective resolution.

Referring to Fig. 4, load the water level pressure with a value of n to the fiber Bragg grating settlement sensor, record the wavelength data of the fiber Bragg grating 101 at this time, and then perform average value processing on this data to obtain the wavelength shift compared with the initial state The above process is loaded continuously for 8 to 10 times, and the non-repeated two-factor analysis of variance is used to test whether the change of water volume and different sensors have a significant impact on the wavelength drift. The significance level α is set to 0.01. The level meets the requirements and then conducts correlation analysis. The linear correlation threshold is 0.9. If the sensor linear correlation is greater than the threshold, it proves that the fiber Bragg grating subsidence sensor can distinguish the small change of the water level pressure with a value of n, and then adopts the dichotomy method to input the water level Adjust the pressure to half or n/2, repeat the above criteria, and judge whether the sensor can still distinguish.

Correspondingly, if the sensor cannot distinguish the slight change of the water level pressure with value n, adjust the input water level pressure to a multiple of 2n, repeat the above criterion, judge whether the sensor can still distinguish, repeat the above criterion, and so on.

A specific case is used to further illustrate the effective resolution method of the fiber Bragg grating settlement sensor:

The resolution test experiment of the fiber Bragg grating settlement sensor was carried out at room temperature. One end of the silicone hose with a diameter of 8mm was connected to the water inlet valve 112 of the four packaged fiber Bragg grating settlement sensors, and the other end was connected to the Three-way joints, and then use silicone hoses with a diameter of 8mm to connect each three-way joints and the liquid storage tank 3, thus forming a complete set of connector system. All air bubbles.

The selected liquid storage tank has a cross-sectional area of 8000mm2, so 8mL of water corresponds to a water level of 1mm. Use a graduated cylinder or syringe to continuously input 8mL of water into the liquid storage tank 3, and the total loaded water volume is 64mL. Record 4 optical fibers The central wavelength of the Bragg grating settlement sensor is averaged for the central wavelength data. The results of the non-repeated two-factor variance analysis show that the F value is 190.45. When the significance level α is 0.01, the F _α value is 3.36, and the linear correlation is as high as 0.99, which is greater than The linear correlation threshold is 0.9, indicating that the sensor can effectively distinguish the change of water level height of 1mm, and then load 4mL of water into the above system, the corresponding water level height is 0.5mm, repeat the above experimental steps, the results of non-repetitive two-factor analysis of variance show that the F value is 10.46 , greater than the F _α value when the significance level α is 0.01, but the linear correlation is only 0.68, which is lower than the linear correlation threshold of 0.9, indicating that the sensor cannot effectively distinguish the water level change of 0.5 mm.

In the fiber Bragg grating settlement sensor with high resolution of this embodiment, the basis for measuring the multi-point settlement deformation of the structure is the principle of semi-closed connecting pipes. The settlement sensor measures the water level pressure change caused by the settlement change of each measuring point, and then according to the water pressure - The displacement relationship can get the settlement value of each measuring point.

The expression of the connecting pipe principle is: After injecting homogeneous liquid into several groups of containers with interconnected bottoms, when the liquid is not flowing, even if the water level of each container changes slightly, the liquid level of each container in the connecting pipe system will always remain the same. Keep on the same level, as shown in Figure 5, the semi-closed connecting pipe is to directly connect the connected container with each fiber Bragg grating settlement sensor (comprising the fiber Bragg grating settlement sensor 4 at the reference point, the fiber optic Bragg grating settlement sensor located at the monitoring point before the settlement). The grating settlement sensor 5 and the diaphragm 108 of the optical fiber Bragg grating settlement sensor 6 after the monitoring point has settled are connected to each other to measure the liquid pressure change caused by the settlement change of each measuring point, and then according to the hydraulic pressure-displacement relationship, the pressure of each measuring point can be obtained. settlement value.

As shown in Figure 5, in the application process of actual settlement measurement, a complete set of settlement deformation monitoring system consists of a liquid storage tank 3, i (i≥2) fiber Bragg grating settlement sensors (including reference point fiber Bragg grating settlement sensors 4. The fiber Bragg grating settlement sensor 5 located before the settlement of the monitoring point, the settlement sensor 6) of the fiber Bragg grating located after the settlement of the monitoring point, the signal transmission multi-core optical cable 7, the connecting water pipe 8, and the terminal signal acquisition and analysis instrument 9. If If the on-site wind speed of the settlement measurement is high or the air pressure at each settlement measuring point is unstable, a connecting air pipe should also be added (for example, when monitoring the deflection of a bridge erected at a high altitude in a canyon, a connecting air pipe must be installed to keep the partial air pressure below the diaphragm of each settlement sensor consistent) .

Since the liquid level of the liquid storage tank 3 needs to be connected to the atmosphere so as to keep the air pressure consistent, the phenomenon of water evaporation will inevitably occur, so that the water pressure on the diaphragm 108 of all fiber Bragg grating settlement sensors in the settlement deformation monitoring system will change. Each measuring point shows a trend of uplift deformation. Therefore, when monitoring the settlement of each pier in practical applications, as shown in Figure 5, one settlement reference point must be selected to arrange the settlement sensor (that is, the FBG settlement sensor 4 at the reference point), and the rest of the FBG settlement sensors (including The monitoring value of the fiber Bragg grating settlement sensor 5 located before the settlement of the monitoring point and the settlement sensor 6 of the fiber Bragg grating located after the settlement of the monitoring point must be subtracted from the value of the reference point, thereby avoiding the change of the settlement data caused by water evaporation.

The relative settlement of the monitoring point (including the FBG settlement sensor 5 before the settlement of the monitoring point and the FBG settlement sensor 6 after the settlement of the monitoring point) relative to the reference point (that is, the FBG settlement sensor 4 of the reference point) _Δui is:

In the formula: λ ₁ ' and λ ₁ are the real-time and initial values of the central wavelength of the fiber Bragg grating 101 at the reference point, respectively, and λ _i ' and λ _i are the real-time and initial values of the central wavelength of the fiber Bragg grating 101 at the monitoring point , S ₁ and S _i are the sensitivity coefficients of the fiber Bragg grating settlement sensor at the reference point and the monitoring point, respectively.

The ring 102 in the fiber Bragg grating settlement sensor with high resolution of this embodiment can realize the temperature self-compensation function of a single fiber Bragg grating, so there is no need to install a temperature compensation grating. The traditional buoy-type structure settlement sensor must be open to communicate with the atmosphere. In practical applications, the evaporation of water is relatively large. Compared with it, the present invention has better isolation from the atmosphere, and the water outlet of the fiber Bragg grating settlement sensor is closed during application. After the valve 111 and the water blocking valve 113, the amount of water evaporation is very small, and there is no need for frequent water replenishment, which can realize long-term settlement monitoring of the structure.

The above is only an embodiment of the present invention, and does not limit the patent scope of the present invention. Any equivalent structure or equivalent process conversion made by using the description of the present invention and the contents of the accompanying drawings, or directly or indirectly used in other related technologies fields, all of which are equally included in the scope of patent protection of the present invention.

Claims (10)

1. A fiber Bragg grating subsidence sensor with high resolution is characterized in that: it comprises a water storage housing and an encapsulation housing, and a diaphragm is arranged between the water storage housing and the encapsulation housing; the top of the water storage housing A water outlet valve is provided, and water inlet valves and water blocking valves are provided on both sides of the water storage shell; a ring is set in the packaging shell, the top of the ring is provided with a first dowel connected to the diaphragm, and the bottom of the ring is provided with a There is a second dowel bar that is detachably fixed to the bottom surface of the inner side of the package shell. The first and second fiber fixing grooves are arranged on both sides of the ring, and the first fiber fixing groove and the second fiber fixing groove are set in the first fiber fixing groove and the second fiber fixing groove. There is a fiber Bragg grating, and the part of the fiber Bragg grating extending out of the packaging casing is covered with an optical fiber sheath; the bottom of the packaging casing is provided with a vent valve. 2. The fiber Bragg grating settlement sensor with high resolution according to claim 1, characterized in that: the first dowel rod and the second dowel rod are vertically symmetrically distributed with respect to the center of the ring, and the first solid fiber The grooves and the second fiber-fixing grooves are distributed horizontally and symmetrically with respect to the center of the ring. 3. The fiber Bragg grating settlement sensor with high resolution according to claim 1, wherein the fiber Bragg grating is fixed in the first fiber-fixing groove and the second fiber-fixing groove by bonding. 4. The fiber Bragg grating settlement sensor with high resolution according to claim 1, characterized in that: the bottom of the second dowel bar is in the shape of a trapezoidal boss, and the bottom surface of the second dowel bar is provided with a threaded hole for connecting The encapsulation shell and the second dowel rod are fixed to the encapsulation shell by screws. 5. The fiber Bragg grating subsidence sensor with high resolution according to claim 1, characterized in that: the water outlet valve, the water inlet valve and the water shutoff valve are all fixed to the water storage shell by threaded connection. 6. The fiber Bragg grating subsidence sensor with high resolution according to claim 1, characterized in that: the ventilation valve is fixed to the package casing by screw connection. 7. The fiber Bragg grating settlement sensor with high resolution according to claim 1, characterized in that: the initial center wavelength of the fiber Bragg grating is 1530-1560 nm, the length of the grating area is 10-15 mm, and the intensity of the reflected light is not low 95% of the incident light intensity. 8. The fiber Bragg grating settlement sensor with high resolution according to claim 1, characterized in that: the first dowel rod, the second dowel rod, the first solid fiber groove, the second solid fiber groove and the ring The materials are all made of homogeneous first type alloy through integrated mechanical processing; the diaphragm, water storage shell and packaging shell are made of homogeneous second type alloy. 9. The fiber Bragg grating settlement sensor with high resolution according to claim 1, characterized in that: the first type of alloy is 4J36 Invar alloy steel, and the second type of alloy is 316 stainless steel. 10. The fiber Bragg grating settlement sensor with high resolution according to claim 8, characterized in that: the structural size of the ring satisfies the following relationship,

Wherein Pe is the elasto-optic coefficient of the fiber Bragg grating, α _Λ is the thermal expansion coefficient of the fiber Bragg grating, α _{n is} the thermo-optic coefficient of the fiber Bragg grating, r is the radius of the ring, c is the first dowel and the second The length of the dowel bar, α ₁ and α ₂ are the thermal expansion coefficients of the first type alloy and the second type alloy, respectively.

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