Tension screening technology for communication cables based on wave propagation and distributed acoustic sensing

Abstract

It is a tension screening technology for communication cables based on wave propagation and distributed acoustic sensing (DAS) that first determines the position of utility poles related to optical fiber cables using wave propagation technology and obtains the tension. Vibration data generated from mechanical impacts on utility poles is converted into an image indicating the position of the utility poles using an edge detection algorithm. Advantageously, by using the edge detection method and wave propagation analysis of the present invention to obtain the tension, the tension of the optical fiber cable can be measured quickly, reliably, and accurately.

Description

Technical Field

[0001] This application generally relates to distributed fiber optic sensing (DFOS) systems, methods, structures, and related technologies. More particularly, it relates to tension screening techniques for electrical communication cables based on wave propagation and distributed acoustic sensing (DAS).

Background Art

[0002] Most modern optical fiber communication networks include aerial cables suspended from utility poles. The tension experienced by the installed optical fiber cable changes over time. Cable tension variations often lead to a decline in the structural performance of the structures supporting the optical fiber cable. Therefore, telecommunication service providers need to monitor the tension of aerial optical fiber cables to ensure reliable telecommunication services.

[0003] Conventional tension monitoring methods use a tensiometer to accurately measure the correct tension of an optical fiber cable. In operation, the tensiometer is clamped to the optical fiber cable or wire rope, measures the deflection, and converts the measured deflection into a tension measurement value. In this conventional method, it is necessary to install tensiometers between multiple poles of the optical fiber cable where tension measurement is required. Such procedures are expensive, time-consuming, and require a significant amount of time by technicians.

Summary of the Invention

[0004] Aspects of the present disclosure directed to tension screening techniques for electrical communication cables based on wave propagation and distributed acoustic sensing (DAS) provide advancements in the art.

[0005] In contrast to the prior art, from a first perspective, the technology of the present invention uses the communication optical fiber cable itself as a sensing medium to provide rapid tension screening of the communication optical fiber cable along the route and real-time tension screening / judgment along the entire route of the optical fiber cable.

[0006] From another perspective, the technology of the present invention can be summarized by the following process. (1) Integrate a DFOS system equipped with an interrogator with the route of the target telecommunication optical fiber cable, thereby making the entire route of the optical fiber cable an optical fiber sensor. (2) A field technician applies a mechanical impact to the utility pole from which the optical fiber cable is suspended. The impact has a time interval of t0. A machine learning process determines the wave velocity related to the impact. (4) Use wave propagation theory to determine the tension.

[0007] In operation, the existing optical fiber cable provides vibration sensing over its entire length without the need for an external power source or a communication channel for data transfer or control. Sensing over the entire length of the optical fiber cable is performed with extremely high accuracy and sensitivity from one end of the optical fiber cable.

[0008] To determine the tension of the cable along the cable, first determine the position of the utility pole relative to the optical fiber cable and adopt wave propagation technology to obtain the tension. The vibration data generated from the mechanical impact on the utility pole is converted into an image that provides the location of the utility pole using an edge detection algorithm. Advantageously, by using the edge detection method and wave propagation analysis of the present invention to obtain the tension, the tension of the optical fiber cable can be measured quickly, reliably, and accurately.

Brief Description of the Drawings

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Figure 1(A)

Figure 1(B)

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Figure 2

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Figure 3

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Figure 4

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Figure 5

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Figure 6

DETAILED DESCRIPTION OF THE INVENTION

[0015] The following merely exemplifies the principles of the present disclosure. Therefore, it should be understood by those skilled in the art that various configurations embodying the principles of the present disclosure, which are not explicitly described or illustrated herein, can be devised.

[0016] Furthermore, all examples and conditional terms listed herein are for the sole purpose of facilitating the understanding of the concepts provided by the inventors to promote the principles of the present disclosure and the technology, and should not be construed as being limited to the specifically recited examples and conditions.

[0017] Furthermore, all descriptions in this specification regarding the principles, aspects, and embodiments of the present disclosure, as well as the specific examples thereof, are meant to include both the equivalents of their structures and functions. Further, such equivalents are meant to include both currently known equivalents and equivalents developed in the future, i.e., elements developed that achieve the same function regardless of their structure.

[0018] Thus, for example, those skilled in the art will understand that any block diagram in this specification is a conceptual diagram specifically showing a circuit that realizes the principle of the present disclosure.

[0019] In this specification, unless otherwise specified, the drawings including figures are not drawn at an exact scale.

[0020] As additional background, note that a distributed fiber optic sensing system interconnects an optoelectronic integrator to an optical fiber (or cable) and converts the optical fiber into an array of sensors distributed along the optical fiber. In practice, the fiber becomes the sensor, and the interrogator generates / injects laser light energy into the fiber to sense / detect events along the fiber.

[0021] As those skilled in the art will understand and recognize, DFOS technology can be utilized to continuously monitor vehicle movement, human traffic, excavation work, seismic activity, temperature, structural integrity, liquid and gas leaks, and many other conditions and activities. It is used worldwide to monitor power plants, communication networks, railways, roads, bridges, borders, critical infrastructure, onshore and offshore power and pipelines, and downhole applications in oil, gas, and enhanced geothermal power generation. The advantage of distributed fiber optic sensing is that it is not restricted by line-of-sight or remote power access constraints and can be deployed in continuous lengths exceeding 30 miles while sensing / detecting at any point along its end-to-end length depending on the system configuration. Therefore, the cost per sensing point over long distances is far beyond that of competing general technologies.

[0022] Distributed optical fiber sensing measures the change in "backscattering" of light that occurs within an optical sensing fiber when the sensing fiber encounters environmental changes such as events of vibration, strain, or temperature change. As described above, the sensing fiber functions as a sensor over its entire length, providing real-time information regarding the physical / environmental surroundings and the integrity / security of the fiber. Further, distributed optical fiber sensing data identifies the exact location of events and conditions occurring along or near the sensing fiber.

[0023] A schematic diagram illustrating a general arrangement and operation of a distributed optical fiber sensing system advantageously incorporating artificial intelligence / machine learning (AI / ML) analysis is exemplified in FIG. 1(A). Referring to FIG. 1(A), it is observed that an optical sensing fiber is connected to an interrogator. Although not shown in detail, the interrogator may include an encoded DFOS system that can adopt a configuration of a coherent receiver known in the art as shown in FIG. 1(B).

[0024] As is well known, modern interrogators are systems that generate an input signal to the optical sensing fiber and detect / analyze the reflected / scattered and received signal. The received signal is analyzed to generate an output indicating the environmental conditions that occurred along the fiber. The received backscattered signal is caused by reflections within the fiber such as Raman backscattering, Rayleigh backscattering, and Brillouin backscattering.

[0025] As is understood, modern DFOS systems include an interrogator that periodically generates an optical pulse (or any encoded signal) and inputs it into the optical fiber. The input optical pulse signal is transmitted along the optical fiber.

[0026] At positions along the fiber, a small portion of the signal is backscattered / reflected and returned to and received by the interrogator. The backscattered / reflected signal conveys information that the interrogator uses for detection, such as a change in power level indicating mechanical vibration.

[0027] The received backscattered signal is converted into the electrical domain and processed by an interrogator. Based on the input time of the pulse and the time when the signal is detected, the interrogator determines from which position along the optical sensing fiber the received signal comes and can sense the movement at each position along the optical sensing fiber. The method of classification may be further used to detect and identify events or other environmental conditions including acoustic and / or vibration and / or heat along the optical sensing fiber.

[0028] As described above, the systems and methods according to the present disclosure employ distributed fiber optic sensing (DFOS) / distributed acoustic sensing (DAS) / distributed vibration sensing (DVS), and collect vibration data from an optical fiber sensor cable at least partially supported by utility poles. To obtain the tension of the optical fiber cable, wave propagation techniques and edge detection methods are utilized. Advantageously, existing optical fiber communications that transmit live traffic may also serve as DFOS sensors over their entire length without adding power or communication channels. Monitoring of the vibration behavior along the entire length of the optical fiber sensor cable can be performed from one end. As will be described in more detail, the method of the present invention employs wave propagation techniques to obtain the tension of the optical fiber sensor cable. In determining the wave velocity, our method first determines the positions of the utility poles along the optical fiber sensor cable where the cable is suspended. Vibration data resulting from mechanical shocks applied to the utility poles are detected / received by the DFOS system and converted into an image for identifying the positions of the utility poles by edge detection techniques. Thereafter, the tension acting on the optical fiber sensor cable is determined.

[0029] FIG. 2 is a schematic diagram showing an exemplary system and method for screening the tension of an electrical communication cable according to an aspect of the present disclosure, and shows the overall structure according to the present disclosure.

[0030] As shown in the figure, the state where consecutive utility poles are suspending a telecommunication cable is shown. As described above, this cable becomes an optical fiber sensor by adding a DOFS / DAS system including an interrogator and an analyzer. As shown in the figure, the DAS performs data collection, and then determines the position of the utility pole and the wave velocity in the subsequent analysis. Such determination is used to determine the tension along the optical fiber sensor cable by a visualization operation. When used uniformly, the system of the present invention provides tension screening. As shown in the figure, the tension screening system of the present invention includes a data collection operation, a data processing operation, and a data reporting operation.

[0031] Consider a scenario where an engineer applies five mechanical shocks to a utility pole suspending an optical fiber sensor cable at time intervals t 0 (t 0 (t > 5 s). Due to this mechanical shock, the utility pole vibrates.

[0032] The vibrating utility pole generates vibrations in the optical fiber sensor cable, and these vibrations are detected by the DAS data collection operation. As is well known, DAS vibration sensing can detect / collect mechanical vibrations in an optical fiber sensor cable with a resolution of about 50 cm up to a range of about 100 km. Advantageously, such mechanical sensing is provided by existing optical fiber communication cables that are already deployed or optical fiber communication cables that transmit live communication traffic.

[0033] The received raw vibration signal is preprocessed to identify the position of the pole and obtain the wave velocity. Such a signal is generally depicted as a waterfall image, and such a waterfall image is converted to grayscale.

[0034] Figure 3 is a schematic block diagram showing an exemplary flowchart of a process according to an aspect of the present disclosure.

[0035] During visualization, the tension in each section of the fiber optic sensor cable along the path is shown. The derivation of the tension acting on the fiber optic sensor cable is as follows.

[0036] Consider a mass component Δx from a cable of length l. The mass component is in static equilibrium, and the tensions F T acting on both sides of the mass component are equal in magnitude and opposite in direction.

[0037] The tensions F T acting on the string in the positive and negative x-directions are approximately constant and independent of position and time. Since the x-components of the tensions cancel each other out, the resultant force is equal to the sum of the y-components of the forces, as shown in FIG. 4, which is a schematic diagram showing the static equilibrium of the cable mass under the tension according to the aspects of the present disclosure. Continuing to refer to this figure, the following can be understood.

Number

Number

[0038] The resultant force on the small mass component can be written as follows.

Number

[0039] Using Newton's second law, the resultant force is equal to mass × acceleration.

Number

[0040] FIG. 5 is a schematic force diagram showing exemplary forces acting on a cable element according to aspects of the present disclosure.

[0041] F TDivide by Δx and take the limit as Δx approaches zero.

Math

[0042] Recall that the linear wave equation is as follows.

Math

[0043] Therefore, it becomes as follows.

Math

[0044] That is, the tension acting on the cable becomes as follows.

Math

[0045] Data collection. Connect the DAS to the target path and record the hammer strike data for each pole. The low vibration data recorded from the hammer strike is shown as a waterfall image. Such a waterfall image obtained from the hammer strike result on the utility pole generally shows a "V" shape. The position in the image corresponding to the tip of the "V" is the position of that utility pole relative to the optical fiber sensor cable. As those skilled in the art will understand and recognize, such distance determination is different from, for example, GPS position information that has nothing to do with the optical fiber sensor cable. (Apply edge detection algorithm for pole position identification)

[0046] To show the edges of the waterfall image, perform Canny edge detection. The Canny edge detection algorithm includes the following operation process.

[0047] (1) Grayscale conversion. Convert the color image to grayscale.

[0048] (2) Noise removal. Apply Gaussian blur with image convolution operation technology to smooth the grayscale image and reduce noise. The kernel size is determined by the expected blur effect. The following formula shows the kernel of a Gaussian filter of size (2k + 1) × (2k + 1).

Equation

[0049] (3) Gradation calculation. In a grayscale image, edges correspond to changes in pixel intensity. By calculating the gradient of the image using an edge detection operator, the intensity and direction of the edges can be detected.

[0050] (4) Non-maximum suppression. Non-maximum suppression is applied to the gradient intensity matrix to find the pixels with the maximum value at the edges.

[0051] (5) Two thresholds. The two thresholds identify three types of pixels: high-intensity pixels, low-intensity pixels, and other pixels that contribute to the final edges.

[0052] (6) Edge tracking by hysteresis. Based on the thresholding results, hysteresis can convert low-intensity pixels to high-intensity pixels if at least one of the surrounding pixels of the pixel being processed is a high-intensity pixel. (Wave velocity and tension calculation)

[0053] Once the "V"-shaped edge is determined, the wave velocity can be calculated from the processed waterfall image

Equation

[0054] FIG. 6 is a schematic diagram showing exemplary features of a system and method according to an aspect of the present disclosure.

[0055] Here, the present disclosure has been shown using several specific examples, but those skilled in the art will recognize that the present teachings are not limited thereto. Therefore, the present disclosure should be limited only by the claims appended hereto.

Claims

1. A method for screening the tension of an optical communication cable using distributed fiber optic sensing / dispersed acoustic sensing (DFOS / DAS), comprising: an optical sensor fiber at least partially suspended from a plurality of utility poles; an optical interrogator configured to generate an optical pulse, input the generated optical pulse into the optical sensor fiber, and receive a backscattered signal from the optical sensor fiber for optical communication with the optical sensor fiber; an analyzer configured to collect and analyze the backscattered signal, generate a waterfall image to identify the positions of the utility poles, determine the wave velocity of vibrations propagating through the optical sensor fiber, and determine the tension of the optical sensor fiber; comprising the above-described distributed fiber optic sensing / dispersed acoustic sensing (DFOS / DAS) system; operating the DFOS / DAS while applying a mechanical shock to a plurality of the utility poles; generating a color waterfall image from the backscattered signal resulting from the mechanical shock; determining the positions of the utility poles that have received the mechanical shock along the optical sensor fiber; determining the wave velocity of the vibrations propagating through the optical sensor fiber due to the mechanical shock; and determining the tension of the optical sensor fiber.

2. The method according to claim 1, further comprising applying a Canny edge detection operation to the color waterfall image generated from the backscattered signal resulting from the mechanical shock.

3. The method according to claim 2, further comprising converting the color waterfall image into a grayscale image.

4. The method according to claim 3, further comprising applying Gaussian blur involving an image convolution operation to smooth the grayscale image.

5. The method according to claim 4, further comprising determining the wave velocity of the vibrations propagating through the optical sensor fiber from the smoothed grayscale image, and determining the tension within the optical sensor fiber from the determined wave velocity.

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