Strain monitoring system based on coaxial cable

Abstract

The utility model relates to a strain monitoring system based on coaxial cables. The strain monitoring system comprises two coaxial cable sensors which are respectively connected with ports of a vector network analyzer; the coaxial cable sensors are respectively laid along the length direction of the object to be measured, and each coaxial cable sensor is provided with two reflection points; wherein the reflection points of the head end and the tail end of one coaxial cable sensor are fixed, the reflection point of the head end of the other coaxial cable sensor is fixed, and the reflection point of the tail end can move along the length direction of an object to be measured; the vector network analyzer is used for transmitting microwaves to the two coaxial cable sensors through the ports and collecting the time difference delta t of the reflected microwaves. Through the two coaxial cable sensors, the deformation of the two coaxial cable sensors under the conditions of temperature, temperature and external force is measured according to the reflection time of microwaves, the large deformation of the oil and gas pipeline is monitored, and temperature compensation is considered at the same time. The device is simple in structure, convenient to use, high in efficiency, good in effect, high in practicability and wide in applicability, and obtained data is simple and easy to process.

Description

Technical Field

[0001] The utility model relates to a strain monitoring system, in particular to a strain monitoring system based on a coaxial cable, and belongs to the technical field of structural health monitoring. Background Art

[0002] In the field of oil and gas pipeline strain monitoring, commonly used monitoring methods include monitoring solutions using vibrating-wire strain gauges and fiber optic sensing solutions based on BOTDA (Brillouin optical time-domain analysis) and BOTDR (Brillouin optical time-domain reflectometry). The monitoring solution of vibrating-wire strain gauges is point sensing, which is economical and applicable when there are fewer monitoring points; the fiber optic sensing solution is distributed sensing, which is suitable for engineering projects that need to monitor multiple monitoring points over long distances.

[0003] Both the vibrating-wire strain gauge monitoring solution and the fiber optic sensing solution have a significant drawback, that is, the strain range that can be measured is relatively small. The maximum strain range that a typical vibrating-wire strain gauge can monitor is ±5000 microstrain. The maximum strain range that a fiber optic sensing solution can monitor is limited by the fiber optic material itself. Generally speaking, the strain range that a glass optical fiber can withstand is ±20,000 microstrain. Beyond this range, the fiber optic will break. Therefore, the maximum strain range that a fiber optic sensing solution can monitor is generally ±20,000 microstrain.

[0004] In the strain monitoring project of oil and gas pipelines, due to engineering requirements, the oil and gas pipelines may work in a large deformation state, and the strain they bear exceeds the range of ±20000 microstrain. At this time, the solution of using vibrating wire strain gauges or optical fiber sensors can no longer monitor the strain of oil and gas pipelines.

[0005] Therefore, it is necessary to provide a strain monitoring system using a coaxial cable with temperature compensation. Summary of the invention

[0006] In order to solve the deficiencies of the prior art, the utility model aims to provide a strain monitoring system using a coaxial cable with temperature compensation.

[0007] In order to achieve the above objectives, the utility model adopts the following technical solutions:

[0008] A coaxial cable-based strain monitoring system includes two coaxial cable sensors respectively connected to ports of a vector network analyzer;

[0009] The coaxial cable sensors are laid along the length direction of the object to be measured, and are each provided with two reflection points;

[0010] The reflection points at the head end and the end of one of the coaxial cable sensors are fixed, and the reflection point at the head end of the other coaxial cable sensor is fixed, and the reflection point at the end end can be moved along the length direction of the object to be measured;

[0011] The vector network analyzer is used to transmit microwaves to two coaxial cable sensors through a port and collect the time difference Δt of reflected microwaves.

[0012] The two coaxial cable sensors mentioned above have the same length, both l .

[0013] Furthermore, the above l 1-8m.

[0014] The microwave frequency emitted by the above-mentioned vector network analyzer is 50MHz to 4GHz.

[0015] The end reflection point of the other coaxial cable sensor is moved along the length direction of the object to be measured via a pulley.

[0016] The above-mentioned vector network analyzer is connected to a data reading device, and the data reading device is connected to a cloud computer via a wireless module;

[0017] The cloud computer is used to calculate the time difference of the reflected microwave according to the formula (Δ t 1 –Δ t 2 ) / Δ t 0 Calculate the strain; where Δ t 0 is the time difference from the initial moment when the coaxial cable sensor is installed, Δ t 1 and Δ t 2 is the time difference of monitoring time.

[0018] The above-mentioned object to be tested includes an oil and gas pipeline.

[0019] The reflection point of the above coaxial cable sensor is a cavity serially connected to the coaxial cable. The cavity is cylindrical, the outer shell of the cavity is connected to the outer conductor of the coaxial cable, and the middle part passes through the inner conductor of the coaxial cable.

[0020] The utility model is beneficial in that:

[0021] The utility model discloses a coaxial cable-based strain monitoring system, which uses two coaxial cable sensors to measure the deformation of the two coaxial cable sensors under the conditions of temperature, temperature and external force by microwave reflection time, so as to monitor the large deformation of the oil and gas pipeline and take temperature compensation into consideration at the same time.

[0022] The coaxial cable-based strain monitoring system of the utility model has a simple structure, is easy to use, obtains simple and easy-to-process data, has high efficiency, good effect, and has strong practicality and wide applicability. BRIEF DESCRIPTION OF THE DRAWINGS

[0023] Figure 1 Schematic diagram of the strain monitoring system.

[0024] Figure 2 A cross-sectional view showing a schematic structural diagram of a coaxial cable.

[0025] The meanings of the marks in the accompanying drawings are as follows: 1. coaxial cable, 2. first coaxial cable sensor, 3. cavity, 4. oil and gas pipeline, 5. second coaxial cable sensor, 6. pulley, 7. vector network analyzer, 8. port A, 9. port B, 10. data cable, 11. data acquisition instrument, 12. cloud calculator, 13. battery and solar power supply equipment, 14. wire, 101. sheath, 102. outer conductor, 103. insulator, 104. inner conductor, 301. shell structure. DETAILED DESCRIPTION

[0026] The present invention is described in detail below with reference to the accompanying drawings and specific embodiments.

[0027] A coaxial cable-based strain monitoring system is composed of a vector network analyzer 7, two coaxial cable sensors (a first coaxial cable sensor and a second coaxial cable sensor), a power supply device, a data reading device, and a cloud (remote) computer.

[0028] The coaxial cable sensor consists of a coaxial cable and a cavity; the coaxial cable 1 is composed of a sheath 101, an outer conductor 102, an insulator 103, and an inner conductor 104 from the outermost layer to the innermost layer. Along the same length direction, two metal cavities are connected in series on the coaxial cable. The cavity is cylindrical. The outer shell 301 of the cavity is connected to the outer conductor 102 of the coaxial cable, and the middle part passes through the inner conductor 104 of the coaxial cable. The two cavities connected in series constitute a reflection point. The length between the cavities is the length of the coaxial cable sensor. l Preferably it is 1-8m.

[0029] The first coaxial cable sensor 2 and the second coaxial cable sensor 5 are connected to the A port and the B port of the vector network analyzer respectively. The first coaxial cable sensor and the second coaxial cable sensor are laid along the length direction of the oil and gas pipeline respectively. Among them, the first end cavities of the first and second coaxial cable sensors are fixed on the oil and gas pipeline, the terminal cavity of the first coaxial cable sensor is fixed on the oil and gas pipeline, and the terminal cavity of the second coaxial cable sensor can move along the length direction on the oil and gas pipeline 4 through the pulley 6. The terminal cavities of the first and second coaxial cable sensors are aligned.

[0030] The vector network analyzer 7 emits microwaves from the A port 8 and the B port 9 respectively, the microwave frequency is preferably 2-4 GHz, and collects the time difference Δt of the reflected microwaves, specifically:

[0031] The microwave emitted from port A 8 passes through the two fixed cavities 3 of the fixed first coaxial cable sensor 2 to form two reflection peaks. The time difference between the two reflection peaks is the initial time when the sensor is installed. T n When Δ t 0 , and the subsequent monitoring time is T n+1 The time difference is Δ t 1 , according to the relationship that Δt is proportional to length, (Δ t 1 –Δ t 0 ) contains the pseudo strain information at this moment, that is, the change information of the oil and gas pipeline under the influence of stress and temperature.

[0032] The microwave emitted from port B 9 passes through a fixed cavity 3 and a movable cavity 3 of the movable second coaxial cable sensor 5 and also forms two reflection peaks. The time difference between the two reflection peaks is the initial time when the sensor is installed. T n When Δ t 0 , in the subsequent monitoring state time T n+1 The time difference is Δ t 2 , (Δ t 2 –Δ t 0 ) contains the change information affected by temperature. That is, the pulley makes the second coaxial cable sensor not affected by the length direction force; if the oil and gas pipeline itself is stretched by the external force, it will not stretch the coaxial cable with the pulley. The coaxial cable with the pulley can only sense the temperature change, but not the force change of the oil and gas pipeline.

[0033] The reading device is connected to the vector network analyzer via a data line 10 and is connected to the cloud computer 12 via a wireless module, and feeds back the Δ obtained by the vector network analyzer to the cloud computer. t 0 , Δ t 1 , Δ t 2 .

[0034] According to the change in length / length = strain, the cloud calculator uses the time difference of the reflected microwave feedback according to the formula (Δ t 1 –Δ t 2 ) / Δt 0 Calculate the strain; where Δ t 0 is the time difference from the initial moment when the coaxial cable sensor is installed, Δ t 1 and Δ t 2 For monitoring T n+1 The time difference of the moment.

[0035] The battery and solar power supply device 13 supplies power to the vector network analyzer 7 and the data acquisition device 11 through the wire 14 .

[0036] The coaxial cable adopted by the utility model can reach a measuring range of ±150,000 microstrain as a strain monitoring system, and is suitable for monitoring large deformation of oil and gas pipelines.

[0037] Coaxial cable is widely used for signal transmission in the communication field. It is an electromagnetic wave transmission medium like optical fiber and has a similar waveguide mechanism. The light waves propagating in the optical fiber and the microwaves propagating in the coaxial cable are both electromagnetic waves. The only difference between the two is the different frequency bands of the electromagnetic waves. Since the tensile and compression performance of coaxial cable is far superior to that of optical fiber, the mechanism of optical fiber sensing can be implemented on coaxial cable to achieve large strain monitoring. Similar to optical fiber sensing, when coaxial cable is used for strain monitoring, the measured microwave signal is not only affected by the strain at the point to be measured, but also by the temperature change at the point to be measured.

[0038] The utility model manufactures two cavity structures at both ends of a section of a coaxial cable to manufacture two microwave reflection points. When the strain and temperature of the two reflection points change, the distance between the two points will change, and the time difference of microwave reflection at the two points will also change. By calculating this time difference, the strain and temperature change data can be measured, thereby realizing a coaxial cable strain monitoring system with temperature compensation, and realizing the monitoring of large strains of oil and gas pipelines.

[0039] The above shows and describes the basic principle, main features and advantages of the utility model. Those skilled in the art should understand that the above embodiments do not limit the utility model in any form, and any technical solution obtained by equivalent replacement or equivalent transformation falls within the protection scope of the utility model.

Claims

1. A strain monitoring system based on coaxial cable, characterized in that: It includes two coaxial cable sensors respectively connected to ports of a vector network analyzer; The coaxial cable sensors are laid along the length direction of the object to be measured, and are each provided with two reflection points; The reflection points at the head end and the end of one of the coaxial cable sensors are fixed, and the reflection point at the head end of the other coaxial cable sensor is fixed, and the reflection point at the end end can be moved along the length direction of the object to be measured; The vector network analyzer is used to transmit microwaves to two coaxial cable sensors through a port and collect the time difference Δt of reflected microwaves.

2. The strain monitoring system according to claim 1, characterized in that: The two coaxial cable sensors have the same length, both l .

3. The strain monitoring system according to claim 2, characterized in that: Said l 1-8m.

4. The strain monitoring system according to claim 1, characterized in that: The microwave frequency emitted by the vector network analyzer is 50 MHz to 4 GHz.

5. The strain monitoring system according to claim 1, characterized in that: The end reflection point of the other coaxial cable sensor is moved along the length direction of the object to be measured via a pulley.

6. The strain monitoring system according to claim 1, characterized in that: The vector network analyzer is connected to a data reading device, and the data reading device is connected to a cloud computer via a wireless module; The cloud computer is used to calculate the time difference of the reflected microwave according to the formula (Δ t 1–Δ t 2) / Δ t 0 calculation strain; where Δ t 0 is the time difference when the coaxial cable sensor is installed, Δ t 1 and Δ t 2 is the time difference of monitoring time.

7. The strain monitoring system according to claim 1, characterized in that: The object to be tested includes an oil and gas pipeline.

8. The strain monitoring system according to claim 1, characterized in that: The reflection point of the coaxial cable sensor is a cavity serially connected to the coaxial cable. The cavity is cylindrical, the outer shell of the cavity is connected to the outer conductor of the coaxial cable, and the middle part passes through the inner conductor of the coaxial cable.

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