A device and method for measuring relative displacement of V-shaped macro-bend optical fiber

Abstract

The application discloses a V-shaped macro-bending optical fiber relative displacement speed measuring and early warning device and method, which comprises a V-shaped displacement conversion mechanism, a fixed radius guide, a sensing optical fiber, a light source, a photoelectric conversion and signal conditioning module, a microcontroller and an LCD. The relative movement of two monitoring points of a bridge changes the V-shaped angle and the effective macro-bending length of the sensing optical fiber, causing the change of output light intensity and voltage. The microcontroller samples at a fixed time, identifies the start and end of displacement events, converts the start and end voltages into displacement according to a calibration relationship, calculates the average speed of the events according to the ratio of displacement difference and duration, displays the voltage, displacement, time and speed on the LCD, and outputs an alarm when the threshold is exceeded. The device does not need an external oscilloscope on site and is suitable for monitoring the seismic, vehicle impact and wind-induced response of a support, a expansion joint and adjacent beam sections.

Description

Technical Field

[0001] This invention relates to the fields of fiber optic sensing, embedded measurement, and bridge structural health monitoring, specifically to a V-shaped macro-bend fiber optic relative displacement velocity measurement and early warning device and method. Background Technology

[0002] Under the influence of earthquakes, vehicle impacts, heavy traffic, wind loads, temperature changes, bearing aging, and uneven foundation settlement, bridges may experience relative displacement and vibration between the beam and bearings, between the beam and piers, on both sides of expansion joints, and between adjacent beam segments. Excessive relative displacement amplitude, rapid changes, multiple collisions within a short period, or residual displacement after an event may increase the risk of bearing slippage, failure of limiting devices, damage to expansion joints, beam end collisions, and beam collapse. Continuous monitoring of critical connections and timely display of displacement and velocity facilitates risk warnings and rapid post-disaster inspections by operational personnel. This monitoring is used to identify existing structural responses in the bridge and is not intended to predict the timing of earthquakes.

[0003] Existing bridge displacement monitoring methods include resistive or inductive displacement sensors, wire displacement gauges, laser ranging, visual measurement, satellite positioning, and fiber Bragg grating sensors. Some electrical sensors require power supply near the measurement point and lightning and electromagnetic protection; visual and laser methods are affected by line of sight, pollution, and installation space; fiber Bragg grating methods typically require wavelength demodulation equipment. In the laboratory, intensity-modulated fiber optic sensors often rely on oscilloscopes or industrial control computers to observe voltage waveforms. These devices are bulky, consume a lot of power, and are expensive, making them unsuitable for long-term, multi-point deployment on bridge sites.

[0004] Sensing schemes based on fiber macrobending loss change the output light intensity by altering the fiber's bending state through mechanical structures. Existing technologies have disclosed twisted-pair macrobending radial coupling structures, microbending tooth structures, spring or elastic base bending structures, and displacement sensing structures with fixed-diameter circular grooves and gear racks. These structures differ from the articulated V-shaped double arms, fixed-radius guides in the rotation area, and embedded event speed measurement terminals used in this invention.

[0005] The initial prototype used a V-shaped structure formed by two arms, capable of generating detectable photoelectric voltage changes under reciprocating motion excitation. Early methods of fixing the optical fiber with tape or binding clips resulted in issues such as random sharp bends, localized pressure, slippage, and fiber optic cable traction. Using an oscilloscope directly only allowed for waveform observation and could not create a displacement and velocity measurement terminal suitable for independent field operation. Therefore, it was necessary to integrate the controlled macro-bending sensing structure, signal range conditioning, microcontroller-based timing sampling, displacement calibration, event start / stop recognition, velocity calculation, and LCD display into a single unit. Summary of the Invention

[0006] The purpose of this invention is to provide a V-shaped macro-bend fiber relative displacement velocity measurement and early warning device and method, which converts the relative motion between two monitoring points on a bridge into a controlled macro-bend state change of the sensing fiber, and uses an embedded terminal to complete signal acquisition, displacement conversion, event velocity calculation, display and early warning without an external oscilloscope.

[0007] To achieve the above objectives, the technical solution of the present invention is as follows:

[0008] A V-shaped macro-bend fiber optic relative displacement velocity measurement and early warning device includes: a first mounting component and a second mounting component, respectively used to connect a first monitoring point and a second monitoring point on a bridge; a first support arm, a second support arm, and a rotating connector, wherein the first support arm and the second support arm form a V-shaped displacement conversion mechanism with a variable included angle through the rotating connector; a fixed-radius guide component, disposed at or near the rotating connector; a sensing fiber, arranged along the first support arm and the second support arm and passing around the fixed-radius guide component, forming a controlled macro-bend section at the fixed-radius guide component; a light source, a photoelectric conversion module, a signal conditioning module, a microcontroller, and an LCD display module, wherein the light source is optically connected to the input end of the sensing fiber, the photoelectric conversion module is optically connected to the output end of the sensing fiber, and the signal conditioning module is connected between the photoelectric conversion module and the microcontroller. Between the analog-to-digital conversion interfaces; wherein, the relative motion between the first monitoring point and the second monitoring point drives the angle change of the V-shaped displacement conversion mechanism, causing at least one of the contact center angle, effective macrobending length and contact state of the sensing optical fiber on the fixed radius guide to change; the microcontroller is configured to collect photoelectric voltage according to a preset sampling period, record the event start voltage and start time when the photoelectric voltage change exceeds the event trigger threshold, record the event termination voltage and termination time when the photoelectric voltage continuously and stably reaches a preset stabilization time, convert the event start voltage and event termination voltage into start displacement and termination displacement respectively according to the calibration relationship, calculate the event average relative displacement velocity by dividing the absolute value of the difference between the start displacement and the termination displacement by the event duration, and control the LCD display module to display the monitoring results.

[0009] The fixed-radius guide is a cylindrical guide post or guide wheel, with an arc groove on its outer circumference; the arc groove is used to limit the axial movement of the sensing optical fiber along the fixed-radius guide, and the bottom and edge of the groove are continuous and smooth transition surfaces.

[0010] A first optical fiber constraint and a second optical fiber constraint are respectively provided on both sides of the controlled macrobend section. The first optical fiber constraint is used to fix the position of the sensing optical fiber, and the second optical fiber constraint is connected to the pre-tightening adjustment component so that the sensing optical fiber keeps in contact with the fixed radius guide within the monitoring range. A pigtail stress relief component is provided on the outer side of the first optical fiber constraint and the second optical fiber constraint.

[0011] The signal conditioning module includes at least one of a buffer circuit, an amplifier circuit, a low-pass filter circuit, a voltage divider circuit, and a limiting protection circuit, used to adjust the output signal of the photoelectric conversion module to the input range allowed by the analog-to-digital conversion interface of the microcontroller; when performing voltage division or gain conversion, the microcontroller restores the sampled voltage to the photoelectric voltage corresponding to the calibration relationship according to a preset range coefficient.

[0012] The microcontroller is an STM32F407ZG microcontroller, installed on the Zhengdian Atom STM32F407ZG Explorer development board; the analog-to-digital conversion interface is the ADC channel of a 12-bit analog-to-digital converter, with the input pin being the ADC and the reference voltage being 3.3 V; the microcontroller forms a 1 ms time base through the TIM6 timer, and displays the photoelectric voltage, event displacement difference, event duration, and average relative displacement velocity of the event through a 480×320 pixel TFT-LCD display module.

[0013] The microcontroller performs multiple analog-to-digital conversions on each sampling point and takes the average value; the event trigger threshold is the absolute value of the difference between adjacent sampling photoelectric voltages, and the event termination condition is that the absolute value of the difference between adjacent sampling photoelectric voltages is continuously lower than the event trigger threshold for a preset stabilization time.

[0014] It also includes at least one of an alarm module and a communication module; when at least one of the relative displacement, the average relative displacement velocity of the event, the duration of the event, or the frequency of the event exceeds the corresponding threshold, the microcontroller controls the alarm module to output an audible, visual, or switch alarm, and / or sends the measurement point number, event time, displacement, and velocity through the communication module.

[0015] A bridge relative displacement velocity measurement and early warning system, wherein the first and second mounting components are respectively installed between the bridge beam and the support or pier, on both sides of the expansion joint, between adjacent beam segments, or on both sides of the limiting component; multiple of the devices are connected to an embedded terminal on site through independent acquisition channels, optical switches or multi-channel photoelectric conversion modules, and the embedded terminal on site sends monitoring data to a remote management platform.

[0016] The method of using a V-shaped macro-bend fiber optic relative displacement velocity measurement and early warning device includes the following steps:

[0017] The first step is to establish the calibration relationship between the photoelectric voltage and the relative displacement between the two monitoring points on the bridge, and to obtain the V-shaped structure angle θ.

[0018] The second step involves using the V-shaped structure angle θ and the effective rotation radius L = 70 mm to inversely calculate the displacement S = 70sin(πθ / 180).

[0019] The third step is to collect photoelectric voltage according to the preset sampling period and perform range restoration, digital filtering and baseline correction.

[0020] Fourth step: When the change in adjacent sampled photoelectric voltage exceeds the event trigger threshold, record the event start voltage U1 and the start time t1;

[0021] Fifth step: When the photoelectric voltage continuously stabilizes for a preset stabilization time, record the event termination voltage U2 and the termination time t2;

[0022] The sixth step is to obtain the initial displacement S1 and the final displacement S2 corresponding to U1 and U2 respectively according to the calibration relationship, and calculate the average relative displacement velocity v of the event according to v=|S2-S1| / (t2-t1);

[0023] The seventh step involves displaying the photoelectric voltage, displacement difference, event duration, and average relative displacement velocity of the event on the LCD, and outputting a warning message when the preset indicators exceed the threshold.

[0024] In one calibration implementation, the unit of the photoelectric voltage U after range restoration is mV, the unit of the V-shaped structure angle θ is degrees, and the unit of the relative displacement S is mm. The relative displacement is obtained by S = 70sin(πθ / 180).

[0025] In a verification embedded embodiment, the STM32F407ZG Explorer development board from Zhengdian Atom is used. The main control device is an STM32F407ZG. The ADC channel receives the conditioned photoelectric signal through the ADC pin. TIM6 provides a 1 ms time base. The TFT-LCD displays the photoelectric voltage, displacement difference, event duration, and velocity. The oscilloscope is only used for calibration and comparison during the R&D phase and is not an essential component of the field device.

[0026] The invention may also include a preload adjustment module, a pigtail stress release module, an alarm module, and a communication module. The alarm threshold is determined by the specific bridge's design allowable values, operation and management requirements, and health baseline.

[0027] The beneficial effects of this invention are as follows:

[0028] Controlled macro-bending paths offer better assembly repeatability than random bending; the V-shaped rotation structure eliminates the need for slide rails, reducing friction and jamming; the microcontroller directly performs sampling, timing, displacement conversion, and velocimetry, replacing the on-site oscilloscope; the LCD can display event results locally; fiber optic sensing points are suitable for environments with electromagnetic interference and long-distance cabling; the device can be used for monitoring earthquake, impact, vehicle, and wind-induced responses in bridge bearings, expansion joints, adjacent beam segments, and limiting components. Attached Figure Description

[0029] Figure 1 A schematic diagram of the overall structure of the V-shaped macro-bend fiber optic relative displacement velocity measurement and early warning device;

[0030] Figure 2 A schematic diagram of the controlled macrobending state of the sensing fiber when the V-shaped displacement conversion mechanism is in two included angle states;

[0031] Figure 3 This is a schematic diagram of a partial structure of a fixed-radius guide component and an arc groove;

[0032] Figure 4 A schematic diagram of the fiber optic constraint, pre-tightening, and pigtail stress relief structure;

[0033] Figure 5 This is a schematic diagram of the device installed between the bridge beam and the supporting structure.

[0034] Figure 6 This is a block diagram showing the connection between the optical sensor and the embedded speed measurement display terminal.

[0035] Figure 7 This is a schematic diagram of the photoelectric signal conditioning and analog-to-digital conversion connection;

[0036] Figure 8 This is a schematic diagram of the LCD display interface;

[0037] Figure 9 Flowchart of the method for calculating the average relative displacement velocity of an event;

[0038] Figure 10 This is a schematic diagram of a multi-point monitoring network for bridges.

[0039] In the diagram: 1-First mounting component; 2-Second mounting component; 3-First support arm; 4-Second support arm; 5-Rotating connector; 6-Fixed radius guide; 7-Sensing fiber optic cable; 8-First fiber optic constraint component; 9-Second fiber optic constraint component; 10-Pigtail stress relief component; 12-Protective housing; 13-Light source; 14-Photoelectric conversion module; 15-Signal conditioning module; 16-Microcontroller; 17-Analog-to-digital converter; 18-Timer; 19-Storage module; 20-LCD display module; 21-Alarm module; 22-Communication module; 23-Bridge beam; 24-Support; 25-Pier; 26-Power supply module; 27-Button module; 28-Data interface; 29-Connecting rod; 30-Multi-channel acquisition module. Detailed Implementation

[0040] The present invention will be further described below with reference to the accompanying drawings and embodiments. The embodiments are used to illustrate the technical solutions and are not intended to limit the scope of protection. Fiber optic connections, structural anchoring, waterproof sealing, and power circuits not specifically described can employ conventional techniques in the art.

[0041] Example 1: V-shaped controlled macrobending sensing structure. See also Figures 1 to 4 The first arm 3 and the second arm 4 are made of metal sheets, fiber-reinforced composite materials, or engineering plastic sheets, and the two arms form a V-shaped structure through a rotating connector 5. A fixed-radius guide 6 is located in the rotating area, and its outer circumference is provided with a continuous arc groove. The sensing optical fiber 7 is arranged along the first arm 3, passes around the fixed-radius guide 6, and then leads out along the second arm 4. The first optical fiber constraint 8 fixes the position of the sensing optical fiber, the second optical fiber constraint 9 can be connected to the pre-tightening adjustment structure, and the pigtail stress release component 10 isolates the movement of the external pigtail. In this embodiment, the physical prototype does not have an angle limiting block or a limiting screw. Figure 1 and Figure 2 The drawing is based on the actual structure of the completed prototype.

[0042] A verification prototype uses a cylindrical guide with a diameter of 4 mm and a tight-buffered optical fiber with a mechanical outer diameter of approximately 1 mm. The nominal bending radius of the sensing fiber's centerline is approximately 2.5 mm. The prototype underwent four load-unload cycles at angles of 4°, 8°, 12°, 16°, 20°, and 24°, with 4°–20° considered as the primary unsaturated sensitive region. The average relationship across the four cycles in the direction of increasing angle is U = -0.001105θ² + 0.178080θ + 1.338, with an average curve determination coefficient R² of 0.9957; the relationship in the direction of decreasing angle is U = 0.004520θ² + 0.068830θ + 1.664, with an average curve determination coefficient R² of 0.9884. The average coefficients of variation for the sensitive regions in both directions are approximately 3.04% and 5.18%, respectively, and the normalized maximum hysteresis is approximately 10.29%. These data illustrate the optional necessity of establishing directional correlation calibration relationships.

[0043] Local optical field simulations with a fixed arc angle of 60° showed that as the bending radius decreased from 4 mm to 1 mm, the estimated macro-bending loss increased from approximately 0.0632 dB to approximately 0.1934 dB, illustrating the trend of enhanced optical field leakage due to small-radius macro-bending. The simulation results do not directly correlate with the photoelectric conversion voltage.

[0044] Example 2: Photoelectric conversion and range conditioning. See also Figure 6 and Figure 7 The light source 13 can be a 1550 nm DFB light source or other stable light sources adapted to the sensing fiber. The photoelectric conversion module 14 converts the output light intensity of the sensing fiber 7 into voltage. The signal conditioning module 15 may include operational amplifier buffer, adjustable gain, RC low-pass filter, resistor voltage divider, and clamping limiter. For cases where the output of the photoelectric conversion module may exceed 3.3 V, the voltage input to the ADC is limited to 0–3.3 V by reducing the photoelectric gain or using voltage divider limiting, and the calibration voltage is restored in software using the range factor. Unlimited voltages exceeding the allowable range must not be directly input to the microcontroller.

[0045] Example 3: Embedded speed measurement display terminal. See also Figures 6 to 9 The system utilizes the STM32F407ZG Explorer development board from Zhengdian Atom, with the target device in Keil 5 being the STM32F407ZGTx and the processor core being a Cortex-M4. The photoelectric signal, after signal conditioning, is input to the ADC channel. The analog-to-digital converter 17 uses a 12-bit resolution and a 3.3V reference voltage, and can continuously convert 10 times per sampling point and take the average value. The TIM6 timer 18 is set to an interrupt period of 1 ms to generate an event timestamp. The LCD display module 20 uses a 480×320 pixel display area to plot the real-time voltage waveform and displays the current photoelectric voltage U, event displacement difference dS, event duration T, and event average velocity V in the display area.

[0046] After the program powers on, it first reads the initial voltage to avoid misinterpreting the power-on transition from 0 V to the operating voltage as a displacement event. Let the current sampled voltage be Ui and the previous sampled voltage be Ui-1. When |Ui-Ui-1| is greater than the event trigger threshold H, the voltage before the edge is recorded as U1, and the start time t1 is recorded. In the event state, if |Ui-Ui-1| is still greater than H, the program waits again for the stable region. When the time for |Ui-Ui-1| to be no greater than H reaches the stability confirmation time Ts, the time of first entering the stable region is taken as t2, and the termination voltage U2 is recorded. Thus, the speed calculation does not include the stability confirmation waiting time.

[0047] One implementation of the program sets the sampling time base to 1 ms, the LCD refresh cycle to 10 ms, the average number of times per sampling point to 10, the event trigger threshold H to 10 mV, and the stabilization confirmation time Ts to 200 ms. These parameters can be adjusted according to photoelectric noise and the bridge response frequency; patent protection is not limited to these values.

[0048] Example 4: Embedded implementation of calibration formula for the electrical engineering competition. Under specific prototype and calibration conditions, the photoelectric voltage U after range restoration is expressed in mV, and the V-shaped structure angle θ is expressed in degrees. The following formula is used for conversion: The relative displacement S is in mm, using S=70sin(πθ / 180). The program calculates S1=f(U1) and S2=f(U2) respectively, and then calculates the average relative displacement velocity v=|S2-S1| / (t2-t1), where t1 and t2 are in seconds, and v is in mm / s. The program performs domain protection before taking the square root, and disables division when the duration is zero to avoid invalid results.

[0049] The above formula is used for embedded verification of a specific prototype. After the bridge is installed on-site, if the effective length of the outrigger, installation eccentricity, or the pre-tensioning state of the connecting rod or fiber changes, it should be recalibrated using known relative displacements, and the new function coefficients or lookup table data should be written into storage module 19. For devices with significant directional hysteresis, two sets of calibration relationships can be stored separately for angle increase and angle decrease, and the corresponding relationship can be selected based on short-term trends.

[0050] Example 5: Bridge bearing monitoring. See also Figure 5 The first mounting component 1 is fixed to the bridge beam 23 or the upper bearing plate, and the second mounting component 2 is fixed to the lower bearing plate of the bearing 24, the cap beam, or the pier 25. The connecting rod 29 can be connected by a ball joint, a flexible hinge, or an oblong hole to compensate for displacement in non-measuring directions and installation errors. The device can be set up along the longitudinal, transverse, or vertical directions of the bridge, and each individual sensing unit mainly measures the relative motion in its arrangement direction.

[0051] The microcontroller 16 compares displacement, velocity, duration, and event frequency with thresholds. Under normal conditions, the LCD displays real-time values; when a monitored threshold is exceeded, the status character changes or an indicator light illuminates; when a warning threshold is exceeded, the alarm module 21 issues an audible and visual signal or a switch signal, and the communication module 22 sends the measurement point number, event time, displacement, and velocity. Thresholds are set based on bridge design allowable values, site baselines, and operational management requirements. This device monitors and provides risk warnings for bridge responses caused by earthquakes, vehicle impacts, wind-induced vibrations, or bearing slippage; it is not used to predict the timing of natural disasters.

[0052] Example 6: Expansion Joint and Beam End Monitoring. The first mounting component 1 and the second mounting component 2 are installed on both sides of the expansion joint or adjacent beam segments, respectively. A protective housing 12 is installed below or to the side of the expansion joint and includes drainage and maintenance structures. The device records joint width events, rapid collision displacements, and residual displacements after the events. For continuous, slow displacements, periodic displacement conversion can be used; for rapid events, an event start-stop velocity measurement method is used.

[0053] Example 7: Multi-point monitoring. See also Figure 10 Sensing units are installed at multiple supports, expansion joints, and limiting components. These multiple sensing units can be connected to a field embedded terminal via independent fiber optic channels, optical switches, or a multi-channel photoelectric conversion module 30. The field terminal displays local results and transmits monitoring data to a remote management platform via wired or wireless communication. In the event of a communication interruption, event data can be temporarily stored in the storage module 19.

[0054] Example 8: Application Boundaries of Oscilloscopes. During the R&D and calibration phases, oscilloscopes can be used in conjunction with embedded terminals to synchronously acquire and verify waveforms, sampling periods, and threshold settings. In formal field monitoring, the microcontroller 16, timer 18, analog-to-digital converter 17, and LCD display module 20 constitute an independent acquisition and display terminal, without the oscilloscope as a necessary component.

Claims

1. A V-shaped macro-bend optical fiber relative displacement velocity measurement and early warning device, characterized in that, include: The first mounting component (1) and the second mounting component (2) are used to connect the first monitoring point and the second monitoring point of the bridge, respectively; the first support arm (3), the second support arm (4) and the rotating connector (5) form a V-shaped displacement conversion mechanism with a variable included angle through the rotating connector (5); the fixed radius guide (6) is set at the rotating connector (5) or its adjacent area; the sensing fiber (7) is arranged along the first support arm (3) and the second support arm (4) and passes around the fixed radius guide (6), forming a controlled macro-bend section at the fixed radius guide (6); the light source (13), the photoelectric conversion module (14), the signal conditioning module (15), the microcontroller (16) and the LCD display module (20) are connected, the light source (13) is optically connected to the input end of the sensing fiber (7), the photoelectric conversion module (14) is optically connected to the output end of the sensing fiber (7), and the signal conditioning module (15) is connected to the input end of the sensing fiber (7). Between the photoelectric conversion module (14) and the analog-to-digital conversion interface of the microcontroller (16); wherein, the relative motion between the first monitoring point and the second monitoring point drives the angle change of the V-shaped displacement conversion mechanism, causing at least one of the contact center angle, effective macrobending length and contact state of the sensing fiber (7) on the fixed radius guide (6) to change; the microcontroller (16) is configured to collect photoelectric voltage according to a preset sampling period, record the event start voltage and start time when the photoelectric voltage change exceeds the event trigger threshold, record the event termination voltage and termination time when the photoelectric voltage continuously and stably reaches a preset stable time, convert the event start voltage and event termination voltage into start displacement and termination displacement respectively according to the calibration relationship, calculate the event average relative displacement velocity by dividing the absolute value of the difference between the start displacement and the termination displacement by the event duration, and control the LCD display module (20) to display the monitoring results.

2. The V-shaped macro-bend optical fiber relative displacement velocity measurement and early warning device as described in claim 1, characterized in that, The fixed radius guide (6) is a cylindrical guide post or guide wheel, and its outer circumference is provided with an arc groove; the arc groove is used to limit the movement of the sensing fiber (7) along the axial direction of the fixed radius guide (6), and the bottom and edge of the groove are continuous and smooth transition surfaces.

3. The V-shaped macro-bend optical fiber relative displacement velocity measurement and early warning device as described in claim 1, characterized in that, A first fiber optic constraint (8) and a second fiber optic constraint (9) are respectively provided on both sides of the controlled macrobend section. The first fiber optic constraint (8) is used to fix the position of the sensing fiber, and the second fiber optic constraint (9) is connected to the pre-tightening adjustment component so that the sensing fiber (7) remains in contact with the fixed radius guide (6) within the monitoring range. A pigtail stress release component (10) is provided on the outside of the first fiber optic constraint (8) and the second fiber optic constraint (9).

4. The V-shaped macro-bend optical fiber relative displacement velocity measurement and early warning device as described in claim 1, characterized in that, The signal conditioning module (15) includes at least one of a buffer circuit, an amplifier circuit, a low-pass filter circuit, a voltage divider circuit, and a limiting protection circuit, used to adjust the output signal of the photoelectric conversion module (14) to the input range allowed by the analog-to-digital conversion interface of the microcontroller (16); when performing voltage division or gain conversion, the microcontroller (16) restores the sampled voltage to the photoelectric voltage corresponding to the calibration relationship according to the preset range coefficient.

5. The V-shaped macro-bend optical fiber relative displacement velocity measurement and early warning device as described in claim 1, characterized in that, The microcontroller (16) is an STM32F407ZG microcontroller, which is installed on the STM32F407ZG Explorer development board of Zhengdian Atom; the analog-to-digital conversion interface is the ADC channel of a 12-bit analog-to-digital converter, the input pin is ADC, and the reference voltage is 3.3 V; the microcontroller (16) forms a 1 ms time base through the TIM6 timer, and displays the photoelectric voltage, event displacement difference, event duration and event average relative displacement velocity through a 480×320 pixel TFT-LCD display module.

6. A V-shaped macro-bend optical fiber relative displacement velocity measurement and early warning device as described in claim 1 or 5, characterized in that, The microcontroller (16) performs multiple analog-to-digital conversions on each sampling point and takes the average value; the event trigger threshold is the absolute value of the difference between adjacent sampling photoelectric voltages, and the event termination condition is that the absolute value of the difference between adjacent sampling photoelectric voltages is continuously lower than the event trigger threshold for the preset stabilization time.

7. The V-shaped macro-bend optical fiber relative displacement velocity measurement and early warning device as described in claim 1, characterized in that, It also includes at least one of an alarm module (21) and a communication module (22); when at least one of the relative displacement, the average relative displacement velocity of the event, the duration of the event or the frequency of the event exceeds the corresponding threshold, the microcontroller (16) controls the alarm module (21) to output an audible, visual or switch alarm, and / or sends the measurement point number, event time, displacement and velocity through the communication module (22).

8. A bridge relative displacement velocity measurement and early warning system, characterized in that, Includes at least one device as described in any one of claims 1 to 7; the first mounting component (1) and the second mounting component (2) are respectively disposed between the bridge beam (23) and the support (24) or the pier (25), on both sides of the expansion joint, between adjacent beam segments or on both sides of the limiting component; multiple devices are connected to the field embedded terminal through independent acquisition channels, optical switches or multi-channel photoelectric conversion modules, and the field embedded terminal sends monitoring data to the remote management platform.

9. A method of using a V-shaped macro-bend optical fiber relative displacement velocity measurement and early warning device, characterized in that, The steps are as follows: The first step is to establish the calibration relationship between the photoelectric voltage and the relative displacement between the two monitoring points on the bridge, and to obtain the V-shaped structure angle θ. The second step involves using the V-shaped structure angle θ and the effective rotation radius L = 70 mm to inversely calculate the displacement S = 70sin(πθ / 180). The third step is to collect photoelectric voltage according to the preset sampling period and perform range restoration, digital filtering and baseline correction. Fourth step: When the change in adjacent sampled photoelectric voltage exceeds the event trigger threshold, record the event start voltage U1 and the start time t1; Fifth step: When the photoelectric voltage continuously stabilizes for a preset stabilization time, record the event termination voltage U2 and the termination time t2; The sixth step is to obtain the initial displacement S1 and the final displacement S2 corresponding to U1 and U2 respectively according to the calibration relationship, and calculate the average relative displacement velocity v of the event according to v=|S2-S1| / (t2-t1); The seventh step involves displaying the photoelectric voltage, displacement difference, event duration, and average relative displacement velocity of the event on the LCD, and outputting a warning message when the preset indicators exceed the threshold.

10. The method of using the V-shaped macro-bend optical fiber relative displacement velocity measurement and early warning device as described in claim 9, characterized in that, The unit of the photoelectric voltage U after range restoration is mV, the unit of the V-shaped structure angle θ is degrees, and the unit of the relative displacement S is mm. The relative displacement is obtained by S = 70sin(πθ / 180).

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