Calibration device and test method of fiber bragg grating pipeline deformation sensor

Abstract

The invention discloses a fiber bragg grating pipeline deformation sensor calibration device and test method, and the device comprises a fiber bragg grating pipeline expansion strain sensor, an expansion cylinder, a propulsion cone, a fixed column, a cross beam, a screw rod, a high-precision electronic displacement meter, a supporting frame, a first fixed frame plate, a second fixed frame plate, a bottom plate, a comparison femtosecond fiber bragg grating, and a fiber bragg grating demodulator. The fiber bragg grating pipeline expansion strain sensor comprises a femtosecond fiber bragg grating, a flexible sensitized structure body, a first mounting block, a second mounting block and an iron wire, the expansion cylinder is used for simulating a pipeline, and the fiber bragg grating pipeline expansion strain sensor is assembled on the simulated pipeline and can monitor the expansion strain of the simulated pipeline. Based on the structural characteristics of the fiber bragg grating and the fiber bragg grating multiplexing technology, the fiber bragg grating pipeline expansion strain sensor can realize distributed monitoring of the expansion state of the pipeline, and can measure and monitor the expansion dependent variable of the simulated pipeline in real time.

Description

Technical Field

[0001] The present invention belongs to the technical field of fiber optic sensing monitoring, and particularly relates to a calibration device and a testing method for a fiber Bragg grating pipeline deformation sensor. Background Art

[0002] Pipeline deformation monitoring is very important in fields such as major equipment and fluid transportation. Through real-time monitoring of deformation, the changes in fluid velocity, pressure, and flow rate can be reflected, and abnormal changes and deformations can be detected in a timely manner. This plays a crucial role in their safety assessment and operation and maintenance, and also helps to optimize the design of the pipeline system. At present, pipeline deformation measurement technologies are constantly developing and progressing. In the early stage, methods such as manual visual inspection and periscope monitoring were often used to monitor the pipeline condition. Using simple tools for pipeline monitoring has the advantages of convenience, speed, and low cost, and has been widely used in pipeline detection. However, the monitoring of pipelines mainly focuses on the situation after an accident or a problem occurs, resulting in a certain degree of lag. In addition, traditional pipeline monitoring methods rely heavily on the work experience of staff, and most of the monitoring equipment used is expensive and not easy to carry. With the continuous progress of monitoring technology, pipeline monitoring has transitioned from manual to intelligent machines.

[0003] At present, the main methods for pipeline deformation monitoring at home and abroad include pipeline closed-circuit television method, negative pressure wave method, infrared thermal imaging method, and some methods relying on acoustic principles for monitoring. However, these methods have limitations, such as limited measurement distance, high equipment price, inaccurate measurement, difficult installation, etc., and it is difficult to meet the requirements of modern industry for high-precision and real-time measurement and may miss detections. The pipeline deformation detectors known so far can be roughly divided into 3 types: The first type is the aluminum disc type deformation detector. The advantages of this type of detector are simple structure and good passability. The disadvantages are that it can only record the maximum deformation amount and has relatively low measurement accuracy. This type of detector is still widely used in the internal detection process due to its high passability, low risk, and low cost. The second type is the angle-coded multi-channel deformation detector. The advantages of this type of detector are high radial detection accuracy and good passability. The disadvantage is that the cost is relatively high. Due to its high detection accuracy and high passability, this type of detector has become the most commonly used type of deformation detector in pipeline deformation detection. The third type is the strain type deformation detector. The advantages of this type of detector are simple structure and high passability, but this technology has not been truly put into industrial on-site detection. Based on the basic principle of fiber Bragg grating and using the method of strain type deformation, a calibration device and a testing method for a fiber Bragg grating pipeline deformation sensor are provided, which can greatly improve the radial detection accuracy. Summary of the Invention

[0004] Aiming at the deficiencies of the prior art, the present invention provides a calibration device and a test method for a fiber Bragg grating pipeline deformation sensor. By assembling the fiber Bragg grating pipeline deformation sensor onto the pipeline, the expansion strain of the pipeline can be monitored. Based on its structural characteristics and fiber Bragg grating multiplexing technology, the fiber Bragg grating pipeline deformation sensor can achieve distributed monitoring of the pipeline expansion state, realizing real-time measurement and monitoring of pipeline deformation. This technology features high precision, long-distance transmission, and strong anti-interference ability, greatly improving the accuracy and reliability of pipeline deformation measurement.

[0005] To solve the above problems, the technical solutions provided by the present invention are as follows:

[0006] The embodiment of the present invention provides a calibration device for a fiber Bragg grating pipeline deformation sensor, including a deformation transfer component and a deformation measurement component; the deformation transfer component includes an expansion cylinder (7), a propulsion cone (8), a fixed column (9), a cross beam (10), a screw (11), a first fixed frame plate (14), a second fixed frame plate (15), and a bottom plate (16); the third connection thread hole group (9-1) of the fixed pile (9) and the thread holes of the bottom plate (16) are assembled with 9 bolts; the first connection thread hole group (7-1) at the lower end of the expansion cylinder (7) and the fourth connection thread hole group (9-2) on the side of the fixed column (9) are assembled with 4 bolts; the fastening thread hole group on the right side of the first fixed frame plate (14) and the sixth connection thread hole group (10-2) on the left side of the cross beam (10) are fixed by four bolts; the fastening thread hole group on the left side of the second fixed frame plate (15) and the seventh connection thread hole group (10-3) on the right side of the cross beam (10) are fixed by four bolts, and the screw (11) is passed through the fifth connection thread hole group (10-1) of the cross beam (10) and screwed into the second connection thread hole group (8-1) of the propulsion cone (8) to fix the screw (11), the cross beam (10), and the propulsion cone (8) together;

[0007] The deformation measurement component includes a fiber Bragg grating pipeline expansion strain sensor (6), a high-precision electronic displacement gauge (12), and a support frame (13); the bottom of the support frame (13) and the bottom plate (16) are assembled and fixed together with bolts. The high-precision electronic displacement gauge (12) is passed through the pore at the top of the support frame (13), and the circular structure at the bottom of the high-precision electronic displacement gauge (12) just touches the flat circular tabletop at the upper end of the bolt (11). The fiber Bragg grating pipeline expansion strain sensor (6) is precisely sleeved on the side of the expansion cylinder (7) to measure the volume expansion of the expansion cylinder (7).

[0008] In a preferred embodiment of the present invention, the fiber Bragg grating pipeline expansion strain sensor (6) includes a femtosecond fiber Bragg grating (1), a flexible sensitized structure body (2), a first mounting block (3), a second mounting block (4), and a wire (5); the coating layers of the parts of the fiber on both ends of the femtosecond fiber Bragg grating (1) are removed and fixed in the capillary steel pipe grooves (2-2) at both ends of the flexible sensitized structure body (2) with an adhesive; the grating area of the femtosecond fiber Bragg grating (1) is suspended and arranged in the exact middle position of the sensitized structure (2-1) of the flexible sensitized structure body (2), and the femtosecond fiber Bragg grating (1) needs to be pre-stretched before being fixed with the adhesive; the first mounting block (3) and the second mounting block (4) are inserted from the thinner end of the flexible sensitized structure body (2), and the cavities of the first mounting block (3) and the second mounting block (4) are of a stepped structure, which plays a role in limiting the flexible sensitized structure body (2); the first mounting block (3) and the second mounting block (4) are connected to the wire (5) through two through-hole groups of the first mounting block (3) and the second mounting block (4), and are fixed with machine screws through 4 wire fastening threaded hole groups on the front surfaces of the first mounting block (3) and the second mounting block (4).

[0009] In a preferred embodiment of the present invention, the expansion cylinder (7) is a cylindrical ring structure, and the first connection threaded hole group (7-1) at the bottom of the expansion cylinder (7) includes 8 threaded holes, and the 8 threaded holes are evenly distributed in a circumferential array manner.

[0010] In a preferred embodiment of the present invention, the propulsion cone (8) is a frustum structure, a second connection threaded hole group (8-1) is provided at the center of the propulsion cone (8), and 4 through-hole groups (8-2) are arranged at the same time for reducing weight; the radius of the lower end of the propulsion cone (8) is smaller than the radius of the expansion cylinder (7), and it is in close contact with the expansion cylinder (7).

[0011] In a preferred embodiment of the present invention, the fixed column (9) is a cylindrical structure, a third connection threaded hole group (9-1) is machined at the bottom of the fixed column (9), the third connection threaded hole group (9-1) includes 9 through holes, and the 9 through holes are arranged in a cross shape, and 4 fourth connection threaded hole groups (9-2) are arranged in a circumferential array on the side surface of the fixed column 9.

[0012] In a preferred embodiment of the present invention, the cross beam (10) is a cuboid structure, a fifth connection threaded hole group (10-1) is provided at the center of the cross beam (10), which is correspondingly connected to the screw rod (11) and allows the screw rod (11) to pass through; there are evenly distributed sixth connection threaded hole groups (10-2) and seventh connection threaded hole groups (10-3) on the left and right sides of the cross beam (10).

[0013] In a preferred embodiment of the present invention, pores are formed above the support frame (13) for clamping the high-precision electronic displacement gauge (12), and the height and angle can be adjusted.

[0014] In a preferred embodiment of the present invention, the deformation measurement component includes a comparison femtosecond fiber grating (17) and a fiber grating demodulator (18); the comparison femtosecond fiber grating (17) is wound around the expansion cylinder (7) in one circle, and the intersection is fixed with quick-drying AB glue; the femtosecond fiber grating (1) of the fiber grating pipeline expansion strain sensor (6), the comparison fiber grating (17) and the fiber grating demodulator (18) are connected by jumpers, and the fiber grating demodulator (18) saves data in real time to test the strain response performance of the fiber grating pipeline expansion strain sensor (6) and the comparison fiber grating (17) and the sensitivity difference between them. By testing and comparing the response performance of the fiber grating pipeline expansion strain sensor (6) and the comparison fiber grating (17), the calibration test of the fiber grating pipeline deformation sensor is completed.

[0015] The embodiment of the present invention provides a calibration test method for a fiber grating pipeline deformation sensor, which is realized by using a calibration device for a fiber grating pipeline deformation sensor as described in the above embodiment, and includes the following steps:

[0016] Step 1: After the calibration device is assembled, the fixed pile (9) is fixed at the bottom of the calibration device, and the expansion cylinder (7) and the propulsion cone (8) connected to the fixed pile (9) will no longer move relative to each other after being assembled and aligned; the first fixed frame plate (14) is fixed on one side of the calibration device, and the second fixed frame plate (15) is fixed on the other side of the calibration device. The cross beam (10) connected to the frame plate and the screw (11) on the cross beam (10) will no longer move relative to each other after being assembled and adjusted in position.

[0017] Step 2: When the propulsion cone (8) is rotated, the displacement feed changes. The measuring rod of the high-precision electronic displacement gauge (12) is always in perpendicular contact with the platform above the screw (11), and the reading of the high-precision electronic displacement gauge (12) begins to change, which can show the displacement change of the propulsion cone (8) sinking; the expansion cylinder (7) begins to expand uniformly in all directions. Since the structural characteristics of the propulsion cone have been calibrated, the relationship between the feed and the perimeter change of the expansion cylinder (7) can be inferred according to geometric and mechanical formulas, and then the information on the volume expansion change of the expansion cylinder (7) can be obtained.

[0018] Step 3: The volume change of the expansion cylinder (7) is transmitted as the strain of the iron wire 5. A comparative femtosecond fiber grating (17) is set, horizontally wound around the expansion cylinder (7) for one circle, and fixed at the intersection with quick-drying AB glue, which can reflect the deformation and expansion amount of one circle of the expansion cylinder (7). The fiber grating pipeline expansion strain sensor (6) that always adheres tightly to the expansion cylinder (7) is affected by external strain, and the central wavelength of the fiber grating shifts. Furthermore, the corresponding relationships among the displacement feed amount, the pipeline volume deformation and expansion amount, and the fiber grating wavelength change amount can be established, so as to perform calibration. The entire calibration test scheme is in a constant-temperature laboratory environment. The materials contacted by the fiber grating pipeline expansion strain sensor (6) and the comparative fiber grating (17) are the same, which can eliminate the influence of temperature on both of them.

[0019] Step 4: Use jumpers to connect the femtosecond fiber grating (1) of the fiber grating pipeline expansion strain sensor (6), the comparative fiber grating (17), and the fiber grating demodulator (18). Adjust the high-precision electronic displacement gauge (12) to zero at the position where the expansion cylinder (7) just starts to deform. Set the high-precision electronic displacement gauge (12) from 0 mm to -1 mm, and then keep it at -0.1 mm, -0.2 mm, -0.3 mm, -0.4 mm, -0.5 mm, -0.6 mm, -0.7 mm, -0.8 mm, -0.9 mm, -1.0 mm for at least 30 s respectively to achieve a stable test effect, and use the fiber grating demodulator (18) to save data in real time, so as to test the strain response performance of the fiber grating pipeline expansion strain sensor (6) and the comparative fiber grating (17) and the sensitivity difference between them. By testing the response performance of the fiber grating pipeline expansion strain sensor (6) and the comparative fiber grating (17), the calibration test of the fiber grating pipeline deformation sensor is completed.

[0020] Compared with the prior art, the embodiment of the present invention provides a calibration device and a test method for a fiber grating pipeline deformation sensor, which have the following beneficial effects: (1) The fiber grating pipeline expansion strain sensor adopts a sensitized structure in design, which plays a sensitizing effect, concentrates the deformation amount of one circle on the cross section of the pipeline on the flexible sensitized structure of the sensor, and can better monitor the strain caused by the pipeline expansion change. (2) The structure of the simulated pipeline expansion device proposed by the present invention is simple. It converts the expansion amount information of the pipeline into the change of the advancing rotation cone feed amount, and represents the fuzzy expansion amount change through relatively intuitive digital changes, so as to realize the measurement of the simulated pipeline expansion. (3) The accuracy is relatively high. The present invention uses a scale with a very low graduation value for measurement, can more accurately control the amount of the feed, and obtains a more practical measurement and calibration result. Description of the Drawings

[0021] To more clearly illustrate the technical solutions in the embodiments or the prior art, the following will briefly introduce the drawings required for the description of the embodiments or the prior art. Obviously, the drawings in the following description are only some embodiments of the invention. For those of ordinary skill in the art, without creative efforts, other drawings can be obtained based on these drawings.

[0022] Figure 1 Schematic diagram of the overall structure of a calibration device for a fiber Bragg grating pipeline deformation sensor provided by an embodiment of the present application.

[0023] Figure 2 Rear view of a calibration device for a fiber Bragg grating pipeline deformation sensor provided by an embodiment of the present application.

[0024] Figure 3 Schematic diagram of measuring the simulated pipeline volume expansion amount by a calibration device for a fiber Bragg grating pipeline deformation sensor provided by an embodiment of the present application.

[0025] Figure 4 Schematic diagram of the arrangement of the fiber Bragg grating and the deformation sensor in the actual calibration experiment of a calibration device for a fiber Bragg grating pipeline deformation sensor provided by an embodiment of the present application.

[0026] Figure 5 Partial structural cross-sectional view of a fiber Bragg grating pipeline expansion strain sensor with a sensitivity enhancement effect for measuring the pipeline volume expansion amount provided by an embodiment of the present application.

[0027] Figure 6 Overall schematic diagram of a fiber Bragg grating pipeline expansion strain sensor with a sensitivity enhancement effect for measuring the pipeline volume expansion amount provided by an embodiment of the present application.

[0028] Figure 7 Schematic diagram of the structure of a sensitized structure body provided by an embodiment of the present application.

[0029] Figure 8 Schematic diagram of the structure of a first mounting block provided by an embodiment of the present application.

[0030] Figure 9 Schematic diagram of the structure of an expansion cylinder provided by an embodiment of the present application.

[0031] Figure 10 Schematic diagram of the structure of a propulsion cone provided by an embodiment of the present application.

[0032] Figure 11 Schematic diagram of the structure of a fixing column provided by an embodiment of the present application.

[0033] Figure 12 Schematic diagram of the structure of a cross beam provided by an embodiment of the present application.

[0034] Figure 13 This is a comparison experimental data graph of the fiber Bragg grating and the pipeline expansion strain sensor obtained from the pipeline volume expansion calibration experiment provided by the embodiment of the present application.

[0035] Figure 14 This is a repeatability experimental data graph obtained from the pipeline volume expansion calibration experiment provided by the embodiment of the present application.

[0036] Description of the drawings: Femtosecond fiber Bragg grating 1, flexible sensitized structure 2, first mounting block 3, second mounting block 4, iron wire 5, fiber Bragg grating pipeline expansion strain sensor 6, expansion cylinder 7, propulsion cone 8, fixing column 9, cross beam 10, screw 11, high-precision electronic displacement gauge 12, support frame 13, first fixed frame plate 14, second fixed frame plate 15, bottom plate 16, comparison femtosecond fiber Bragg grating 17, fiber Bragg grating demodulator 18. Flexible sensitized structure 2-1, U-shaped groove 2-2, cavity 3-1, through-hole group 3-2, iron wire fastening threaded hole group 3-3, first connection threaded hole group 7-1, second connection threaded hole group 8-1, through-hole group 8-2, third connection threaded hole group 9-1, fourth connection threaded hole group 9-2, fifth connection threaded hole group 10-1, sixth connection threaded hole group 10-2, seventh connection threaded hole group 10-3. Detailed implementation manners

[0037] Next, the technical solutions in the embodiments of the present application will be clearly and completely described in conjunction with the drawings in the embodiments of the present application. Obviously, the described embodiments are only a part of the embodiments of the present application, rather than all the embodiments. Based on the embodiments of the present application, all other embodiments obtained by those skilled in the art without making creative efforts belong to the scope of protection of the present application. When referring to the "upper", "lower", "front", "rear", "left", "right", etc. used for the installation position or direction of the structure or components in this embodiment, they are based on the orientation of the given drawings. They are only for convenience of description to distinguish the relative positions of the components or directions, and do not represent the orientation when the calibration device or components in this embodiment are used.

[0038] In recent years, the fiber Bragg grating sensing technology has developed rapidly. Using light as the sensing output signal, the signal is stable, anti-interference, and the signal can be transmitted over a very long distance with very little attenuation. The sensor has good stability and durability, and is very suitable for long-term and real-time safety monitoring. It has broad application prospects in the field of operation and maintenance safety monitoring of major projects. With the development of technology, the pipeline deformation measurement technology has gradually been applied to actual projects. The embodiment of the present invention provides a new pipeline expansion measurement device and measurement method, aiming to solve the technical problems of complex structure, resource waste, inconvenient installation, and low accuracy existing in the current existing pipeline measurement field.

[0039] Specifically, as Figure 1 , Figure 2 , Figure 3 and Figure 4 shown, an embodiment of the present invention provides a calibration device for an optical fiber grating pipeline deformation sensor, including a deformation transmission part assembly and a deformation measurement part assembly. The deformation transmission part assembly includes an expansion cylinder 7, a propulsion cone 8, a fixed column 9, a cross beam 10, a screw rod 11, a first fixed frame plate 14, a second fixed frame plate 15 and a bottom plate 16. The third connection thread hole group 9-1 of the fixed pile 9 and the thread hole of the bottom plate 16 are assembled with 9 bolts. The first connection thread hole group 7-1 at the lower end of the expansion cylinder 7 and the fourth connection thread hole group 9-2 on the side of the fixed column 9 are assembled with 4 bolts. The fastening thread hole group on the right side of the first fixed frame plate 14 and the sixth connection thread hole group 10-2 on the left side of the cross beam 10 are fixed by four bolts. The fastening thread hole group on the left side of the second fixed frame plate 15 and the seventh connection thread hole group 10-3 on the right side of the cross beam 10 are fixed by four bolts. The screw rod 11 is passed through the fifth connection thread hole group 10-1 of the cross beam 10 and screwed into the second connection thread hole group 8-1 of the propulsion cone 8 to fix the screw rod 11, the cross beam 10 and the propulsion cone 8 together. The expansion cylinder 7 in this embodiment simulates a pipeline.

[0040] The deformation measurement part assembly includes an optical fiber grating pipeline expansion strain sensor 6, a high-precision electronic displacement gauge 12 and a support frame 13. The bottom of the support frame 13 and the bottom plate 16 are assembled and fixed together with bolts. The high-precision electronic displacement gauge 12 is passed through the pore at the top of the support frame 13. The circular structure at the bottom of the high-precision electronic displacement gauge 12 just touches the flat circular tabletop at the upper end of the bolt 11. The optical fiber grating pipeline expansion strain sensor 6 is precisely sleeved on the side of the expansion cylinder 7 for measuring the volume expansion of the expansion cylinder 7.

[0041] As Figure 5 , Figure 6 , Figure 7 and Figure 8As shown, two optical fibers are respectively led out from both ends of the fiber Bragg grating pipeline expansion strain sensor 6 for measuring the volume expansion of the pipeline. The fiber Bragg grating pipeline expansion strain sensor 6 includes a femtosecond fiber Bragg grating 1, a flexible sensitized structure body 2, a first mounting block 3, a second mounting block 4 and a wire 5. The coating layers of the partial optical fibers at both ends of the femtosecond fiber Bragg grating 1 are removed and fixed in the capillary steel pipe grooves 2-2 at both ends of the flexible sensitized structure body 2 with an adhesive, and the adhesive is preferably epoxy resin. The grating area of the femtosecond fiber Bragg grating 1 is suspended and arranged at the exact middle position of the sensitized structure 2-1 of the flexible sensitized structure body 2, and the femtosecond fiber Bragg grating 1 needs to be pre-stretched before being fixed with the adhesive. The first mounting block 3 and the second mounting block 4 are inserted into the thinner end of the flexible sensitized structure body 2. The cavities of the first mounting block 3 and the second mounting block 4 are of a stepped structure, which plays a role in limiting the flexible sensitized structure body 2. The first mounting block 3 and the second mounting block 4 are connected to the wire 5 through two through hole groups of the first mounting block 3 and the second mounting block 4, and are fixed with machine screws through four wire fastening threaded hole groups on the front surfaces of the first mounting block 3 and the second mounting block 4. Refer to Figure 8 , a cavity 3-1 and two through hole groups 3-2 are arranged on the side surface of the first mounting block 3, and two wire fastening threaded hole groups 3-3 are arranged on the front surface of the first mounting block 3. The structures of the first mounting block 3 and the second mounting block 4 are similar or the same.

[0042] Installation and fixation of the fiber Bragg grating pipeline expansion strain sensor 6: Adjust the length and angle of the wire 5, insert it into the sensor mounting block, and at the same time adjust the fastening machine screw on the front surface of the mounting block. After the installation and assembly are completed, the installation position of the sensor needs to be adjusted to ensure that it is in a horizontal state and closely fits the surface of the pipeline. Then, by adjusting the angles and positions of the two side fixing frame plates, ensure that the center of the circular platform at the bottom of the screw 11 and the center of the propulsion cone 8 are in the same vertical direction, and both the cross beam 10 and the propulsion cone 8 remain in the horizontal direction. Adjust the opening angle and length of the support frame 13 to ensure that the high-precision electronic displacement gauge 12 is in the vertical direction, and the top of the circular structure at the bottom of the high-precision electronic displacement gauge 12 is located at the center of the circular platform of the screw 11. The cross beam 10, the screw 11, the high-precision electronic displacement gauge 12, the first fixing frame plate 14, and the second fixing frame plate 15 do not move relative to each other after the assembly and calibration of the position.

[0043] The working principle of the fiber Bragg grating pipeline expansion strain sensor 6 is as follows: Place the fiber Bragg grating pipeline expansion strain sensor on the pipeline. To ensure a tight connection between the fiber Bragg grating pipeline expansion strain sensor and the pipeline and better transmit strain, the length of the iron wire 5 and the tightness of the machine screw can be adjusted to better fix and fit the pipeline. When the pipeline expands, the radial force generated causes the iron wire to deform. The fiber Bragg grating sensor assembled on the pipeline is affected by the external strain, and the central wavelength of the fiber Bragg grating drifts. The strain of the iron wire is reflected by the change in the wavelength of the fiber Bragg grating sensor. In the laboratory, a calibration test is conducted on the sensor. Fix the pipeline equipped with the fiber Bragg grating sensor, change the volume change of the pipeline through the calibration device, obtain the wavelength drift at different expansion states, and through data processing, obtain the relationship between the pipeline volume change and the wavelength drift of the fiber Bragg grating pipeline expansion strain sensor. In practical applications, the actual wavelength drift of the fiber Bragg grating pipeline expansion strain sensor obtained is used to inversely deduce the pipeline volume change state at the location of the fiber Bragg grating pipeline expansion strain sensor through the functional relationship obtained by calibration. Based on the fiber Bragg grating multiplexing technology, multiple fiber Bragg grating sensors are arranged along the axial direction of the pipeline to conduct distributed monitoring of the entire state of the pipeline.

[0044] The measurement principle of the present invention is as follows:

[0045] When the ambient temperature is constant, for a fiber Bragg grating with an initial central wavelength of λ B the wavelength drift Δλ B and the axial strain Δε it receives are related as follows:

[0046]

[0047] where Pe is the effective photoelastic coefficient of the optical fiber, and at room temperature, Pe is approximately equal to 0.22.

[0048] The steel wire fixed to the outer wall of the pipeline by precision set screws. Under the action of a uniform internal pressure P, the surface strain ε of the pipeline eq generates a tensile force F on both sides of the sensitization axis through linear coupling. The overall equivalent stiffness coefficient k of the calibration device eq is related to the axial length and the size of the hollow shaft, and the expression is:

[0049] F = k eq ·X (2);

[0050] The tensile force F on both sides of the sensitization structure generates an axial displacement ΔX in the structure. Since the sensing steel wire and the sensitization structure have different equivalent stiffness coefficients, the equivalent strain ε of the sensor can be obtained from the tensile strain monitored by the FS-FBG sensor eq :

[0051]

[0052] where k sen and k st represent the equivalent stiffness coefficients of the sensitization structure and the steel wire respectively. Substituting the equation into (4), the relationship between the pipeline volume change rate and the FS-FBG strain can be derived:

[0053]

[0054] From the above equation, the theoretical relationship between the pipeline volume change and the fiber Bragg grating wavelength change Δλ B can be obtained. There is a good corresponding relationship between the load F on the bolt and the fiber Bragg grating wavelength change Δλ B . Before actual application, it is necessary to further calibrate the fiber Bragg grating pipeline expansion strain sensor. By continuously changing the pipeline volume change through the calibration device and simultaneously monitoring the wavelength change of the fiber Bragg grating pipeline expansion strain sensor, the measurement function relationship between the volume change and the fiber Bragg grating wavelength change Δλ B is established. During actual application, according to the wavelength drift of the fiber Bragg grating at different positions of the pipeline and combined with the measurement function, the pipeline state at that location can be inversely calculated.

[0055] As Figure 9 shown, the expansion cylinder 7 is a cylindrical ring structure. The first connection thread hole group 7-1 at the bottom of the expansion cylinder 7 contains 8 thread holes, and these 8 thread holes are evenly distributed in a circumferential array manner. The bottom end of the expansion cylinder 7 in this embodiment is fixed, and there are four centrally symmetric notches at its upper end, and a part of it is also transversely cut at a certain distance from the bottom, which can enable the entire expansion cylinder 7 to expand naturally under the action of an external force.

[0056] As Figure 10 shown, the propulsion cone 8 is a frustum-shaped structure. A second connection thread hole group 8-1 is provided at the center of the propulsion cone 8, and four through-hole groups 8-2 are arranged at the same time to reduce the weight; the radius of the lower end of the propulsion cone 8 is smaller than the radius of the expansion cylinder 7 and is in close contact with the expansion cylinder 7.

[0057] As Figure 11 shown, the fixing column 9 is a cylindrical structure. A third connection thread hole group 9-1 is machined at the bottom of the fixing column 9. The third connection thread hole group 9-1 contains 9 through holes, and these 9 through holes are arranged in a cross shape. Four fourth connection thread hole groups 9-2 are arranged in a circumferential array on the side of the fixing column 9.

[0058] As Figure 12As shown in the figure, the cross beam 10 has a cuboid structure. At the center of the cross beam 10, there is a fifth connecting threaded hole group 10-1, which is correspondingly connected to the screw rod 11 and allows the screw rod 11 to pass through. On the left and right sides of the cross beam 10, there are evenly distributed sixth connecting threaded hole groups 10-2 and seventh connecting threaded hole groups 10-3.

[0059] Figure 2 Combined with Figure 1 , the lower end of the screw rod 11 is connected to the propulsion cone 8, and the threaded part is connected and fixed to the cross beam 10. The upper end is a flat circular tabletop. The high-precision electronic displacement gauge 12 is composed of an electronic displacement dial and a measuring rod. There is a spherical structure at the bottom measuring rod. The support frame 13 generally has a rectangular column structure. There are pores on the upper part of the support frame 13 for clamping the high-precision electronic displacement gauge 12, and the height and angle can be adjusted. The first fixed frame plate 14 has a cuboid structure, is placed on the left tabletop and fixed. There are evenly distributed threads on the right side corresponding to the left side of the cross beam 10. The second fixed frame plate 15 has the same structure and parameters as the first fixed frame plate 14. The evenly distributed threads on the left side correspond to the right side of the cross beam 10. The fixed bottom plate 16 has the same structure and parameters as the first fixed frame plate 14. The evenly distributed threads on the upper side correspond to the lower side of the fixation.

[0060] After the assembly is completed, by adjusting the extension length and angle of the support frame 13, the position of the high-precision electronic displacement gauge 12 can be controlled. Before the expansion strain measurement starts, the bottom of the thimble of the high-precision electronic displacement gauge 12 just contacts the flat tabletop on the screw rod 11, and it is ensured that the movement range is always at the center position of the upper circular tabletop of the screw rod 11. The propulsion cone 8 and the expansion cylinder 7 are always in contact with each other. Appropriate lubricant can be applied when necessary to ensure that the smoothness of their contact remains unchanged.

[0061] As Figure 3 and Figure 4 shown, the components of the deformation measurement part include a comparative femtosecond fiber grating 17 and a fiber grating demodulator 18. The comparative femtosecond fiber grating 17 is wound around the expansion cylinder 7 for one circle, and the intersection points are fixed with quick-drying AB glue. The femtosecond fiber grating 1 of the fiber grating pipeline expansion strain sensor 6, the comparative fiber grating 17 and the fiber grating demodulator 18 are connected by jumpers. The fiber grating demodulator 18 saves data in real time, so as to test the strain response performance of the fiber grating pipeline expansion strain sensor 6 and the comparative fiber grating 17 and the sensitivity difference between them. By testing the response performance of the comparative fiber grating pipeline expansion strain sensor 6 and the comparative fiber grating 17, the calibration test of the fiber grating pipeline deformation sensor is completed.

[0062] The embodiment of the present invention also provides a calibration test method for a fiber grating pipeline deformation sensor, which is realized by using the calibration device of a fiber grating pipeline deformation sensor in the above embodiment. Among them, it includes the following steps:

[0063] Step 1: After the calibration device is assembled, the fixed pile 9 is fixed to the bottom of the calibration device. After the expansion cylinder 7 and the propulsion cone 8 connected to the fixed pile 9 are assembled and aligned, there is no relative movement between them; the first fixed frame plate 14 is fixed to one side of the calibration device, and the second fixed frame plate 15 is fixed to the other side of the calibration device. After the cross beam 10 connected to the frame plate and the screw 11 on the cross beam 10 are assembled and adjusted to the correct position, there is no relative movement between them;

[0064] Step 2: When the propulsion cone 8 rotates, the displacement feed changes. The measuring rod of the high-precision electronic displacement gauge 12 is always in perpendicular contact with the upper platform of the screw 11. The reading of the high-precision electronic displacement gauge 12 starts to change, which can show the displacement change of the propulsion cone 8 sinking; the expansion cylinder 7 starts to expand evenly in all directions. Since the structural characteristics of the propulsion cone have been calibrated, the relationship between the feed and the perimeter change of the expansion cylinder 7 can be inferred according to geometric and mechanical formulas, and then the information on the volume expansion change of the expansion cylinder 7 can be obtained;

[0065] Step 3: The volume change of the expansion cylinder 7 is transmitted as the strain of the iron wire 5. The comparison femtosecond fiber grating 17 is set and horizontally wound around the expansion cylinder 7 for one circle, and fixed at the intersection with quick-drying AB glue, which can reflect the deformation and expansion amount of one circle of the expansion cylinder 7. The fiber grating pipeline expansion strain sensor 6 that always adheres to the expansion cylinder 7 is affected by the external strain, and the center wavelength of the fiber grating shifts. Then, the corresponding relationship between the displacement feed, the simulated pipeline volume deformation and expansion amount, and the fiber grating wavelength change amount can be established, so as to carry out calibration. The entire calibration test scheme is in a constant-temperature environment in the laboratory. The materials contacted by the fiber grating pipeline expansion strain sensor 6 and the comparison fiber grating 17 are the same, which can eliminate the influence of temperature on both;

[0066] Step 4: Use jumpers to connect the femtosecond fiber grating 1 of the fiber grating pipeline expansion strain sensor 6, the comparison fiber grating 17, and the fiber grating demodulator 18. Adjust the high-precision electronic displacement gauge 12 to zero at the position where the expansion cylinder 7 just starts to deform. Set the high-precision electronic displacement gauge 12 from 0 mm to -1 mm, and then keep it at -0.1 mm, -0.2 mm, -0.3 mm, -0.4 mm, -0.5 mm, -0.6 mm, -0.7 mm, -0.8 mm, -0.9 mm, -1.0 mm for at least 30 s respectively to achieve a stable test effect, and use the fiber grating demodulator 18 to save data in real time to test the strain response performance of the fiber grating pipeline expansion strain sensor 6 and the comparison fiber grating 17 and the sensitivity difference between them; by testing the response performance of the fiber grating pipeline expansion strain sensor 6 and the comparison fiber grating 17, the calibration test of the fiber grating pipeline deformation sensor is completed.

[0067] As Figure 13 andFigure 14 As shown, the corresponding curve of the fiber Bragg grating pipeline expansion strain sensor 6 is the pipeline deformation sensor, and the corresponding curve of the comparison fiber Bragg grating 17 is the FBG. When simulating the expansion deformation of the pipeline device, the wavelength change amounts of both the fiber Bragg grating pipeline expansion strain sensor 6 and the comparison fiber Bragg grating 17 have good linearity with the feed displacement amount, and under the same feed displacement condition, the wavelength change amount of the fiber Bragg grating pipeline expansion strain sensor 6 is larger than that of the fiber Bragg grating 17. Furthermore, it can be concluded that under the same strain condition, the wavelength change amount of the fiber Bragg grating pipeline expansion strain sensor 6 is larger and the sensitivity is higher. The test was repeated three times, and the error of the test results was small and within a reasonable range to prove the feasibility and rationality of the simulated pipeline expansion deformation calibration device and the calibration method.

[0068] Although the present invention has been disclosed above with preferred embodiments, the above preferred embodiments are not intended to limit the present invention. Those of ordinary skill in the art can make various modifications and alterations without departing from the spirit and scope of the present invention. Therefore, the protection scope of the present invention is subject to the scope defined by the claims.

Claims

1. A calibration device for a fiber Bragg grating pipeline deformation sensor, characterized in that: The invention comprises a deformation transmission part assembly and a deformation measurement part assembly; the deformation transmission part assembly comprises an expansion cylinder (7), a thrust cone (8), a fixing column (9), a cross beam (10), a screw rod (11), a first fixing frame plate (14), a second fixing frame plate (15) and a bottom plate (16); the third connecting threaded hole group (9-1) of the fixing pile (9) and the threaded holes of the bottom plate (16) are assembled with 9 bolts, the first connecting threaded hole group (7-1) at the lower end of the expansion cylinder (7) and the fourth connecting threaded hole group (9-2) on the side of the fixing column (9) are assembled with 4 bolts; the The fastening threaded hole group on the right side of a fixed frame plate (14) and the sixth connecting threaded hole group (10-2) on the left side of the cross beam (10) are fixed by four bolts; the fastening threaded hole group on the left side of the second fixed frame plate (15) and the seventh connecting threaded hole group (10-3) on the right side of the cross beam (10) are fixed by four bolts, and the screw rod (11) is passed through the fifth connecting threaded hole group (10-1) of the cross beam (10) and screwed into the second connecting threaded hole group (8-1) of the propulsion cone (8), so as to fix the screw rod (11), the cross beam (10) and the propulsion cone (8) together; The deformation measurement component comprises a fiber Bragg grating pipeline expansion strain sensor (6), a high-precision electronic displacement meter (12) and a support frame (13); the bottom of the support frame (13) and the bottom plate (16) are assembled and fixed together by bolts, and the high-precision electronic displacement meter (12) is passed through the hole at the top of the support frame (13). The circular structure at the bottom of the high-precision electronic displacement meter (12) just contacts the flat circular table at the upper end of the bolt (11). The fiber Bragg grating pipeline expansion strain sensor (6) is precisely sleeved on the side of the expansion cylinder (7) to measure the volume expansion of the expansion cylinder (7).

2. The calibration device of a fiber Bragg grating pipeline deformation sensor according to claim 1, characterized in that: The fiber Bragg grating pipeline expansion strain sensor (6) comprises a femtosecond fiber Bragg grating (1), a flexible sensitizing structure (2), a first mounting block (3), a second mounting block (4) and an iron wire (5); the coating layer of part of the optical fibers at both ends of the femtosecond fiber Bragg grating (1) is removed, and the fibers are fixed to the capillary steel tube grooves (2-2) at both ends of the flexible sensitizing structure (2) with an adhesive; the grating area of ​​the femtosecond fiber Bragg grating (1) is suspended and arranged in the middle of the sensitizing structure (2-1) of the flexible sensitizing structure (2), and the femtosecond fiber Bragg grating (1) needs to be pre-stretched before being fixed with the adhesive; The first mounting block (3) and the second mounting block (4) are inserted from the thinner end of the flexible sensitizing structure (2); the cavities of the first mounting block (3) and the second mounting block (4) are stepped structures, which play a role in limiting the flexible sensitizing structure (2); the first mounting block (3) and the second mounting block (4) are connected to the iron wire (5) through two through hole groups of the first mounting block (3) and the second mounting block (4), and are fixed by four iron wire fastening threaded hole groups on the front of the first mounting block (3) and the second mounting block (4) through machine screws.

3. The calibration device of a fiber Bragg grating pipeline deformation sensor according to claim 2, characterized in that: The expansion cylinder (7) is a cylindrical ring structure, and the first connection threaded hole group (7-1) at the bottom of the expansion cylinder (7) comprises 8 threaded holes, and the 8 threaded holes are evenly distributed in a circular array.

4. The calibration device of a fiber Bragg grating pipeline deformation sensor according to claim 3, characterized in that: The propulsion cone (8) is a truncated cone-shaped structure. The center of the propulsion cone (8) is provided with the second connecting threaded hole group (8-1), and four through-hole groups (8-2) are arranged at the same time to reduce weight. The radius of the lower end of the propulsion cone (8) is smaller than the radius of the expansion cylinder (7), and is in close contact with the expansion cylinder (7).

5. The calibration device of a fiber Bragg grating pipeline deformation sensor according to claim 4, characterized in that: The fixing column (9) is a cylindrical structure, and the bottom of the fixing column (9) is processed with the third connecting threaded hole group (9-1), and the third connecting threaded hole group (9-1) includes 9 through holes, and the 9 through holes are arranged in a cross-shaped manner. The side of the fixing column 9 is provided with 4 fourth connecting threaded hole groups (9-2) distributed in a circumferential array.

6. The calibration device of a fiber Bragg grating pipeline deformation sensor according to claim 5, characterized in that: The crossbeam (10) is a rectangular parallelepiped structure. A fifth connecting threaded hole group (10-1) is provided at the center of the crossbeam (10), which is correspondingly connected to the screw rod (11) and allows the screw rod (11) to pass through; and a sixth connecting threaded hole group (10-2) and a seventh connecting threaded hole group (10-3) are evenly distributed on the left and right sides of the crossbeam (10).

7. The calibration device of a fiber Bragg grating pipeline deformation sensor according to claim 6, characterized in that: A hole is provided on the top of the support frame (13) for clamping the high-precision electronic displacement meter (12), and the height and angle can be adjusted.

8. The calibration device of a fiber Bragg grating pipeline deformation sensor according to claim 7, characterized in that: The deformation measurement component comprises a comparison femtosecond fiber grating (17) and a fiber grating demodulator (18); the comparison femtosecond fiber grating (17) is wound around the expansion cylinder (7) and fixed at the intersection with quick-drying AB glue; the femtosecond fiber grating (1) of the fiber grating pipeline expansion strain sensor (6), the comparison fiber grating (17) and the fiber grating demodulator (18) are connected by jumper wires, and the fiber grating demodulator (18) stores data in real time, so as to test the strain response performance of the fiber grating pipeline expansion strain sensor (6) and the comparison fiber grating (17) and the sensitivity difference between them, and complete the calibration test of the fiber grating pipeline deformation sensor by testing and comparing the response performance of the fiber grating pipeline expansion strain sensor (6) and the comparison fiber grating (17).

9. A calibration test method for a fiber Bragg grating pipeline deformation sensor, implemented by using a calibration device for a fiber Bragg grating pipeline deformation sensor as claimed in claim 8, characterized in that: The following steps are involved: Step 1, after the calibration device is assembled, the fixed pile (9) is fixed to the bottom of the calibration device, and the expansion cylinder (7) and the thrust cone (8) connected to the fixed pile (9) no longer move relative to each other after being assembled and calibrated; the first fixed frame plate (14) is fixed to one side of the calibration device, and the second fixed frame plate (15) is fixed to the other side of the calibration device, and the crossbeam (10) connected to the frame plate and the screw (11) on the crossbeam (10) no longer move relative to each other after being assembled and adjusted; Step 2, when the propulsion cone (8) is rotated, the displacement feed amount changes, the measuring rod of the high-precision electronic displacement meter (12) is always in vertical contact with the platform above the screw (11), and the reading of the high-precision electronic displacement meter (12) begins to change, which can show the displacement change amount of the propulsion cone (8) sinking; the expansion cylinder (7) begins to expand uniformly in all directions. Since the structural characteristics of the propulsion cone have been calibrated, the relationship between the feed amount and the change amount of the circumference of the expansion cylinder (7) can be inferred based on geometric and mechanical formulas, and then the information on the change amount of volume expansion of the expansion cylinder (7) can be obtained; Step 3, the volume change of the expansion cylinder (7) is transferred as the strain of the iron wire 5, and a comparison femtosecond fiber grating (17) is set, which is horizontally wound around the expansion cylinder (7) and fixed at the intersection with quick-drying AB glue, so as to reflect the deformation and expansion of the expansion cylinder (7) in one circle. The fiber grating pipeline expansion strain sensor (6) always close to the expansion cylinder (7) is affected by the external strain, and the central wavelength of the fiber grating is shifted, so that the corresponding relationship between the displacement feed amount, the pipeline volume deformation expansion amount and the fiber grating wavelength change amount can be established, so as to perform calibration; the entire calibration test scheme is in a constant temperature environment of the laboratory, and the fiber grating pipeline expansion strain sensor (6) and the comparison fiber grating (17) are in contact with the same material, which can eliminate the influence of temperature on both. Step 4, using jumper wires to connect the femtosecond fiber Bragg grating (1), the comparison fiber Bragg grating (17) and the fiber Bragg grating demodulator (18) of the fiber Bragg grating pipeline expansion strain sensor (6), adjusting the high-precision electronic displacement meter (12) to zero value at the position where the expansion cylinder (7) just begins to deform, setting the high-precision electronic displacement meter (12) from 0 mm to -1 mm, and then respectively at -0.1 mm, -0.2 mm, -0.3 mm, -0.4 mm, -0.5 mm, -0.6 mm, -0.6 mm, -0.7 mm, -0.8 mm, -0.9 mm, -10 mm, -11 mm, -12 mm, -13 mm, -14 mm, -15 mm, -16 mm, -17 mm, -18 mm, -19 mm, -20 mm, -21 mm, -22 mm, -23 mm, -24 mm, -25 mm, -26 mm, -27 mm, -28 mm, -29 mm, -30 mm, -31 mm, -32 mm, -33 mm, -34 mm, -35 mm, -36 mm, -37 mm, -38 mm, -39 mm, -40 mm, -41 mm, -42 mm, -43 mm, -44 mm, -45 mm, -46 mm, -47 mm, -48 mm, -49 mm, -50 mm, -51 mm, -52 mm, -53 mm, -54 mm, -55 mm, -56 mm, -57 mm, -58 mm, -59 mm, -60 mm, -61 mm, -62 mm, -63 mm, -64 mm, -65 mm, -66 mm, -67 mm, -68 mm, -69 mm, -70 mm, -71 mm, -72 mm, -73 mm 7mm, -0.8mm, -0.9mm, -1.0mmf are respectively maintained for at least 30 seconds to achieve a stable test effect, and a fiber Bragg grating demodulator (18) is used to save data in real time, thereby testing the strain response performance of the fiber Bragg grating pipeline expansion strain sensor (6) and the comparison fiber Bragg grating (17) and the difference in sensitivity between them; by testing the response performance of the fiber Bragg grating pipeline expansion strain sensor (6) and the comparison fiber Bragg grating (17), the calibration test of the fiber Bragg grating pipeline deformation sensor is completed.

Images