Strain performance testing device of distributed strain optical cable

Abstract

The utility model relates to a strain performance testing device for a distributed strain optical cable, and belongs to the technical field of optical fiber monitoring technologies. Comprising a test bench, the test bench is provided with a fixed adjusting rack and a movable adjusting rack, the fixed adjusting rack and the movable adjusting rack are respectively provided with a clamp, a to-be-tested optical cable is fixed between the two clamps, and two ends of the to-be-tested optical cable are electrically connected with a tester through a connection jumper wire; the movable adjusting frame moves on the test bed through the movable driving mechanism, so that the movable adjusting frame is close to or far away from the fixed adjusting frame to load or unload the to-be-tested optical cable; a displacement digital display meter is arranged on the movable adjusting frame and is used for displaying the displacement amount of the to-be-measured optical cable on the movable adjusting frame; the fixed adjusting frame is provided with a displacement dial indicator, and the displacement dial indicator is used for displaying the offset of the to-be-measured optical cable on the fixed adjusting frame. The test precision can reach the sensor level, the operation is simple and convenient, and the test efficiency is greatly improved.

Description

A strain performance testing device for distributed strain optical cables Technical Field

[0001] This utility model relates to a strain performance testing device for distributed strain optical cables, belonging to the field of optical fiber monitoring technology. Background Technology

[0002] In recent years, with the rapid development of my country's national economy, structural safety has received increasing attention from all sectors of society for large-scale projects involving national welfare and people's livelihood. From the perspective of structural safety, the need for monitoring the health and safety of various structures in pipelines, tunnels, bridges, and other engineering projects is becoming increasingly prominent. Due to its suitability for long-distance continuous monitoring, fiber optic distributed strain monitoring technology has been widely used in structural health monitoring. This technology is based on Brillouin optical time-domain reflectometry, injecting short pulse light and continuous probe light from both ends of the optical fiber. By measuring the frequency change of the stimulated Brillouin scattering light in the fiber, strain information at various points along the fiber axis can be obtained. Distributed strain monitoring technology utilizes the Brillouin scattering effect of light in the optical fiber, allowing monitoring points along the entire fiber to monitor the structural strain information of corresponding parts of the structure. The stress of the structure itself is calculated based on the structural elastic modulus and other relevant information. For long-distance structural safety monitoring, for the same density of monitoring cross-sections, distributed strain monitoring based on fiber optic sensing technology is more economical and cost-effective.

[0003] Distributed strain monitoring technology uses three dimensions for data (time, test distance, and strain value). Compared with traditional point-based two-dimensional data analysis and processing (time and strain value), the data processing is more difficult. However, due to the detailed and dense data, it is beneficial for performing correlation data analysis on the entire structure of continuous long-distance projects, and can more intuitively reflect the overall structural safety and health status of the project.

[0004] As a special type of strain monitoring sensor, strain-sensitive optical cables, a key component in distributed strain monitoring, currently lack relevant national and industry standards. For testing and calibration of their strain performance, the common practice is to use optical cable tensile testing equipment for quantitative tensile testing. However, because this equipment is primarily designed for testing the maximum tensile force or breaking force of communication optical cables, the loading and unloading forces are large and the speeds are fast. Furthermore, the equipment typically uses guide wheel winding for clamping at both ends, with the cable fixed by lateral friction on the wheels. This results in an overly bulky setup, numerous interference factors along the cable route, and an inability to meet sensor-level testing and analysis requirements, thus failing to obtain test results economically and quickly. Summary of the Invention

[0005] The technical problem to be solved by this utility model is to provide a strain performance testing device for distributed strain optical cables, which is simple to operate, improves testing efficiency, and achieves sensor-level testing accuracy. The optical cable clamping section is limited to a short distance, making the stress zoning of the optical cable under test clear, and the test curve can more accurately reflect the stress state of each part of the optical cable, so as to facilitate further in-depth analysis.

[0006] The technical solution adopted by this utility model to solve the above problems is as follows: a strain performance testing device for distributed strain optical cables, including a test bench, on which a fixed adjustment frame and a movable adjustment frame are provided. Clamps are respectively provided on the fixed adjustment frame and the movable adjustment frame. The optical cable to be tested is fixed between the clamps, and both ends of the optical cable to be tested are electrically connected to the tester via jumpers. The movable adjustment frame moves on the test bench via a moving drive mechanism, causing the movable adjustment frame to move closer to or further away from the fixed adjustment frame, thereby loading or unloading the optical cable to be tested. A displacement digital display is provided on the movable adjustment frame, which is used to display the displacement of the optical cable to be tested on the movable adjustment frame. A displacement dial indicator is provided on the fixed adjustment frame, which is used to display the offset of the optical cable to be tested on the fixed adjustment frame.

[0007] The moving drive mechanism includes a horizontally arranged lead screw, through which a moving adjustment frame is threadedly connected. A pulley is respectively provided on one end of the lead screw and the output end of the gear reducer. A transmission belt is sleeved between the two pulleys. The input end of the gear reducer is connected to the motor through a coupling.

[0008] The clamp includes a lower half-screw and an upper half-screw that mate with each other to form a half-screw. The half-screw has a central cavity through which the optical cable under test passes. Two clamping plates are respectively provided on the optical cable under test and are located at both ends of the cavity. Fastening nuts are screwed onto both ends of the half-screw and abut against the clamping plates. Rotating the fastening nuts causes them to press against the clamping plates and push them toward the cavity. The half-screw also has two adjusting nuts, which are threadedly connected to the half-screw. Rotating the adjusting nuts in the same direction causes the half-screw to move, thereby stretching the optical cable under test.

[0009] The clamp is a conical structure, and the clamp includes an upper clamp and a lower clamp that fit together.

[0010] The fixed adjustment frame is equipped with a stretching unit, which includes two spaced-apart stretching blocks. The two stretching blocks are movably mounted on the fixed adjustment frame and are fixedly connected by a horizontally arranged connecting rod. A clamp is provided on one of the stretching blocks. The fixed adjustment frame is equipped with a handle, and the lead screw of the handle is horizontally rotated on the fixed adjustment frame, with the end of the lead screw fixedly connected to another stretching block. Rotating the handle moves the lead screw within the fixed adjustment frame, pushing the stretching unit to move horizontally along the fixed adjustment frame, thereby achieving quantitative stretching of the optical cable located within the fixed adjustment frame.

[0011] Compared with existing technologies, the advantages of this invention are as follows: A strain performance testing device for distributed strain optical cables; this testing device is modified based on a sensor calibration platform, achieving sensor-level testing accuracy, and is easy to operate, significantly improving testing efficiency. The clamping section of the optical cable under test is limited to a short distance, clearly defining the stress zones of the cable, allowing the test curve to more accurately reflect the stress state of each part of the cable for subsequent in-depth analysis. By precisely determining the zero-point and ultimate tensile position, the testing process is limited to the linear variation range of the optical cable strain curve, enabling more accurate and effective data acquisition. Attached Figure Description

[0012] Figure 1 is a schematic diagram of a strain performance testing device for a distributed strain optical cable according to an embodiment of the present invention;

[0013] Figure 2 is a schematic diagram of the optical cable strain / length test curve;

[0014] Figure 3 is a schematic diagram of the explosion of the clamp in Figure 1;

[0015] Figure 4 is a schematic diagram of the assembly of the fixture in Figure 1;

[0016] In the diagram: 1. Test bench; 2. Fixed adjustment frame; 3. Moving adjustment frame; 4. Fixture; 5. Optical cable under test; 6. Tester; 7. Pulley; 8. Lead screw; 9. Digital displacement display; 10. Displacement dial indicator; 11. Transmission belt; 12. Gear reducer; 13. Coupling; 14. Motor; 15. Left fixture affected section; 16. Right fixture affected section; 17. Middle effective section; 18. Fastening nut; 19. Upper clamp; 20. Lower clamp; 21. Adjusting nut; 22. Upper plate of Haval screw; 23. Lower plate of Haval screw; 24. Upper bushing; 25. Lower bushing; 26. Connecting jumper; 27. Handle; 28. Tension block; 29. ​​Connecting rod. Detailed Implementation

[0017] The present invention will be further described in detail below with reference to the accompanying drawings and embodiments.

[0018] As shown in Figure 1, the strain performance testing device for a distributed strain optical cable in this embodiment includes a test bench 1. The test bench 1 is equipped with a fixed adjustment frame 2 and a movable adjustment frame 3. The fixed adjustment frame 2 is fixed to the test bench 1 by positioning bolts. A moving drive mechanism drives the movable adjustment frame 3 to move along the test bench 1, causing the movable adjustment frame 2 to move closer to or further away from the fixed adjustment frame 2. Clamps 4 are respectively provided on the fixed adjustment frame 2 and the movable adjustment frame 3, and the optical cable 5 to be tested is fixed within the clamps 4. Both ends of the optical cable to be tested are electrically connected to the testing instrument 6 via jumper cables 26. A displacement digital display 9 is provided on the movable adjustment frame 3, and a displacement digital display 10 is used to display the displacement of the optical cable to be tested mounted on the movable adjustment frame. A displacement dial indicator 10 is provided on the fixed adjustment frame 2, and a displacement dial indicator 10 is used to display the offset of the optical cable to be tested mounted on the fixed adjustment frame 2. Due to the tension of the movable adjustment frame 3, the clamp 4 on the fixed adjustment frame 2 has a slight directional offset. To ensure test accuracy, the actual displacement of the optical cable under test should be based on the difference between the displacement display 9 and the displacement dial gauge 10. The fixed adjustment frame 2 is equipped with a tensioning unit, which includes two spaced-apart tension blocks 28. The two tension blocks 28 are mounted on the fixed adjustment frame 2 and are fixedly connected by a horizontally arranged connecting rod 29. A clamp is mounted on one tension block 28. The fixed adjustment frame is equipped with a handle 27, whose lead screw is horizontally screwed onto the fixed adjustment frame 2 and fixedly connected to another tension block. Rotating the handle moves the lead screw within the fixed adjustment frame, pushing the tensioning unit horizontally along the fixed adjustment frame to achieve quantitative tensioning of the optical cable within the fixed adjustment frame.

[0019] The aforementioned moving drive mechanism includes a horizontally arranged lead screw 8, through which a moving adjustment frame 3 is threadedly connected. One end of the lead screw 8 and the output end of the gear reducer 12 are respectively equipped with pulleys 7, and a transmission belt 11 is sleeved between the two pulleys 7. The input end of the gear reducer 12 is connected to a motor 14 via a coupling 13. The motor 14 drives the gear reducer 12 to rotate, which in turn drives the pulleys 7 and the transmission belt 11 to rotate, causing the lead screw 8 to rotate, thereby driving the moving adjustment frame 3 to move and load / unload the optical cable 5 under test on the moving adjustment frame 3.

[0020] As shown in Figures 3 and 4, the clamp 4 includes two mating lower half-screw plates 23 and an upper half-screw plate 22, forming a half-screw. The half-screw has a central cavity through which the optical cable under test passes. Two clamping plates are fitted onto the optical cable 5, located at opposite ends of the cavity. Fastening nuts 18 are screwed onto both ends of the half-screw, abutting against the clamping plates. Rotating the fastening nuts 18 causes them to press against the clamping plates and push them into the cavity, thus fixing the optical cable 5 within the half-screw. Two adjusting nuts 21 are also provided on the half-screw, threadedly connected to it. Rotating the two adjusting nuts 21 in the same direction moves the half-screw, thereby causing the optical cable under test to move synchronously, i.e., the cable is stretched. The half-screw is fixed to the fixed adjustment frame 2 or the movable adjustment frame 3 by bushings.

[0021] The aforementioned clamping piece is a conical structure, comprising an upper clamping piece 19 and a lower clamping piece 20 that engage with each other. The aforementioned bushing comprises an upper bushing 24 and a lower bushing 25 that engage with each other.

[0022] The optical cable under test is fixed by the movable adjustment frame 3 and the fixed adjustment frame 2. The actual displacement is accurately measured based on the readings of the displacement digital display and the displacement dial gauge. The optical cable under test is clamped by a fixture, and longitudinal friction is applied to achieve maximum tensile force transmission. The test method in this application refers to the test and calibration methods of sensors. Based on this, and considering the differences in structural rigidity between strain gauge optical cables and point sensors, the linearity and repeatability issues are fully considered in the development of the test method. A method for determining the test zero point and the limit position is proposed to ensure the accuracy of the test data.

[0023] The method for determining the zero point in strain testing includes the following steps:

[0024] a. After the two ends of the optical cable to be tested are clamped and fixed, the readings of the displacement digital display and dial gauge are cleared to zero. The strain data of the optical cable under relaxed and tensile conditions are scanned using a strain gauge.

[0025] Relaxed state (when the optical cable under test is relaxed to the point where it just touches the table surface, it is recorded as position A);

[0026] Tightened state (no slippage at the clamp, no loosening of the optical cable, marked as position B);

[0027] b: At position B, the length of the optical cable under test between the two clamps should be measured and recorded as L, and the tensile reading should be C. 显 (The displacement display value is X, the displacement dial indicator value is Y, and C) 显 =XY).

[0028] c: Import the strain data txt files scanned at positions A and B into an Excel spreadsheet for calculation. Select the center position of the fixture (1-2m) as the effective segment (according to the graph, try not to select the stress segment data near the fixture), and calculate the average strain value of each data point in the effective segment (denoted as S0 and S1 respectively).

[0029] d: Substitute the total tensile length L and the average strain values ​​S1 and S0 into the following formula to calculate the actual tensile amount C of the optical cable. 实 :

[0030] C 实 = (S1-S0)*10 -6 *L

[0031] Where: S1 and S0 are in µɛ, and L and C are in mm;

[0032] e: Calculate C0, C 0= (C) 显 - C 实 )+k,

[0033] Where k is a correction constant, which is taken as 1.5 mm based on the experience of multiple tests, and C0 is the test zero point for subsequent tensile cycle tests.

[0034] A method for testing the strain performance of a distributed strain optical cable includes the following steps:

[0035] Step 1: Before the test, the optical cable to be tested should be left to stand for more than 24 hours in an environment with a room temperature of 25±3℃ and a humidity of ≤85%.

[0036] Step 2: Cut a 20m length of the optical cable to be tested and place it on the test bench. The surface of the optical cable to be tested should be smooth and straight, and there should be no defects such as damage, cracks, uneven thickness, or twisting.

[0037] Step 3: After aligning the positions of the fixed and movable adjustment frames, the optical cable under test is fixed to both frames using two clamps. The straight-line distance between the midpoints of the two clamps is 5000±100mm. Since the lateral clamping force of the clamps has a certain influence on the strain of the optical cable under test, based on experience, the affected area is approximately 1.5m long extending from the clamp. According to the equipment's spatial positioning accuracy requirements, the minimum unaffected section length should be 2m. Due to the limitation of the test bench length, the optical cable under test is appropriately set to 5m in length. This allows for the discarding of data from the two ends of the optical cable, using only the data from the middle effective section, thus ensuring the accuracy of the test data.

[0038] Step 4: Mark the surface of the optical cable under test at the exit of the two clamps, close to the edge of the clamps, with self-adhesive paper to determine whether the optical cable under test slips during the test. If a gap is found between the self-adhesive paper and the edge of the clamp during the test, it indicates that slippage has occurred.

[0039] Step 5: Strip appropriate lengths of optical fiber from both ends of the optical cable under test, and connect the two optical fibers to the optical fiber input interface of the tester through jumper cables.

[0040] Step 6: Start the strain testing software and scan to detect the length and reference strain data of the optical cable under test.

[0041] Step 7: Set the motor speed and direction of rotation. The motor drives the gear reducer, causing the pulley and transmission belt to rotate. The lead screw then rotates slowly and uniformly, with a rotation speed set to within 10 seconds per revolution. This moves the moving adjustment frame away from the fixed adjustment frame, straightening and tightening the optical cable under test between the two clamps. Start the strain testing software and scan again to detect the strain data of the optical cable under test. Using the test bench as a reference, a difference of less than 5mm between the height of the midpoint of the optical cable under test and the height of the top surface of the clamp is considered as tension.

[0042] Step 8: Determine the test zero point according to the strain test zero point determination method, move the center point of the optical cable under test between the two clamps to the test zero point, and clear the data on the displacement digital display and displacement dial indicator to zero.

[0043] Step Nine: Slowly and uniformly rotate the handle to stretch the optical cable under test to the maximum strain limit position according to the tensile test requirements. Let it stand for at least 10 minutes and observe the changes in the displacement dial gauge. After stabilization, observe whether slippage occurs at the marked point on the clamp. If slippage occurs, remark the clamp and adjust the test plan to lower the limit until slippage does not occur. The maximum strain limit position is determined according to the different optical cable structural performances; the maximum strain limit position is different for different optical cables.

[0044] Step 10: Slowly and evenly rotate the handle in the opposite direction to release the load to the test zero position.

[0045] Step 11: Repeat steps 9 and 10 in sequence, at least 3 times. When the data on the displacement dial indicator is basically stable and no longer changing, and the clamp markings do not slip, the formal testing of the optical cable under test can begin.

[0046] Step 12: Starting from the test zero point, load or unload step by step according to the set step distance. When each step distance is reached, use the strain monitoring software in the tester to scan and save the strain data, and record the readings of the displacement display and displacement dial gauge.

[0047] The process of gradually stretching from the test zero position to the maximum limit position is the loading process, which should be divided into 6-8 steps. The process of returning from the maximum limit position to the test zero position is the unloading process. A complete loading and unloading process is called one stretching cycle.

[0048] Step 13: Each standard test should consist of at least 3 tensile cycles. Each tensile cycle should be performed as consecutively as possible, with an interval of no more than 1 hour between each tensile cycle. The room temperature should be kept constant during the test.

[0049] Step Fourteen: After the test is completed, save the test data. As shown in Figure 2, the test data can be exported to data analysis and processing software. To eliminate the influence of clamp pressure on the strain test results, the sections of the optical cable under test affected by the clamps at both ends should be excluded: the left clamp-affected section 15 and the right clamp-affected section 16. The distance between the left clamp-affected section and the right clamp-affected section is not less than 1.5m from the corresponding side clamp. Only the data of the effective middle section 17 between the left clamp-affected section 15 and the right clamp-affected section 16 is selected for corresponding analysis and calculation. The calculation formula refers to the sensor standard specifications, see Table 2.

[0050] In step twelve above, each time the maximum limit position or test zero position is reached, if reverse loading or unloading is required, the maximum limit position or test zero position should be slightly exceeded before turning the handle in the opposite direction to proceed with the next loading or unloading process.

[0051] Based on the structural performance of the optical cable under test, a corresponding test plan was developed, determining key requirements such as the maximum displacement, the number of loading and unloading cycles, and the displacement at each step of loading and unloading, and relevant tests were conducted accordingly. When the displacement reached each step position, a Brillouin strain temperature tester (BOFDA) was used to perform a full-line scan test, and the relevant data were recorded and saved.

[0052] After the test was completed, various strain performance indicators were calculated and analyzed according to the relevant data and the calculation formulas specified in the sensor standard (see Table 2). The calculation formulas were executed in accordance with the standards of "DL / T 1736-2017 Basic Technical Conditions for Fiber Bragg Grating Instruments" (hereinafter referred to as Standard 1) and "JJF 1305-2011 Calibration Specification for Linear Displacement Sensors" (hereinafter referred to as Standard 2).

[0053] Table 2

[0054]

[0055]

[0056] The testing apparatus described in this application is a modification of a sensor calibration platform, achieving sensor-level testing accuracy while being easy to operate and significantly improving testing efficiency. The clamping section of the optical cable under test is confined to a short distance, clearly defining the stress zones within the cable. This allows the test curve to more accurately reflect the stress state of each part of the cable, facilitating subsequent in-depth analysis. By precisely determining the zero-point and ultimate tensile strength positions, the testing process is limited to the linear variation range of the optical cable strain curve, enabling the acquisition of more accurate and effective data.

[0057] In addition to the above embodiments, this utility model also includes other implementation methods. All technical solutions formed by equivalent transformation or equivalent substitution should fall within the protection scope of the claims of this utility model.

Claims

1. A strain performance testing device for a distributed strain optical cable, characterized in that: The test bench includes a fixed adjustment frame and a movable adjustment frame, each equipped with a clamp. The optical cable under test is fixed between the clamps, and both ends of the optical cable are electrically connected to the tester via jumpers. The movable adjustment frame moves on the test bench via a moving drive mechanism, moving closer to or further away from the fixed adjustment frame to load or unload the optical cable under test. The movable adjustment frame is equipped with a displacement digital display, which displays the displacement of the optical cable under test on the movable adjustment frame. The fixed adjustment frame is equipped with a displacement dial indicator, which displays the offset of the optical cable under test on the fixed adjustment frame.

2. The strain performance testing device of a distributed strain optical cable according to claim 1, characterized in that: The fixed adjustment frame is equipped with a stretching unit, and a clamp is fixed to the stretching unit; a handle is screwed onto the fixed adjustment frame, and the handle screw is fixedly connected to the stretching unit. Rotating the handle drives the stretching unit to move along the fixed adjustment frame to perform quantitative stretching on the optical cable to be tested.

3. The strain performance testing device for a distributed strain optical cable according to claim 1, characterized in that: The moving drive mechanism includes a horizontally arranged lead screw, through which a moving adjustment frame is threadedly connected. A pulley is respectively provided on one end of the lead screw and the output end of the gear reducer. A transmission belt is sleeved between the two pulleys. The input end of the gear reducer is connected to the motor through a coupling.

4. The apparatus for testing strain performance of a distributed strain optical cable according to claim 1, wherein: The clamp includes a lower half-screw and an upper half-screw that mate with each other to form a half-screw. The half-screw has a central cavity through which the optical cable under test passes. Two clamping plates are respectively provided on the optical cable under test and are located at both ends of the cavity. Fastening nuts are screwed onto both ends of the half-screw and abut against the clamping plates. Rotating the fastening nuts causes them to press against the clamping plates and push them toward the cavity. The half-screw also has two adjusting nuts, which are threadedly connected to the half-screw. Rotating the adjusting nuts in the same direction causes the half-screw to move, thereby stretching the optical cable under test.

5. The apparatus for testing strain performance of a distributed strain optical cable according to claim 4, wherein: The clamp is a conical structure, and the clamp includes an upper clamp and a lower clamp that fit together.

6. The strain performance testing device for a distributed strain optical cable according to claim 1, characterized in that: The fixed adjustment frame is equipped with a stretching unit, which includes two spaced-apart stretching blocks. The two stretching blocks are movably mounted on the fixed adjustment frame and are fixedly connected by a horizontally arranged connecting rod. A clamp is provided on one of the stretching blocks. The fixed adjustment frame is equipped with a handle, and the lead screw of the handle is horizontally rotated on the fixed adjustment frame, with the end of the lead screw fixedly connected to another stretching block. Rotating the handle moves the lead screw within the fixed adjustment frame, pushing the stretching unit to move horizontally along the fixed adjustment frame, thereby achieving quantitative stretching of the optical cable located within the fixed adjustment frame.

Images