Distributed optical fiber monitoring sensing optical cable damage positioning method

Abstract

The invention discloses a distributed optical fiber monitoring sensing optical cable damage positioning method, and relates to the technical field of distributed optical fiber monitoring. The method comprises the following steps: carrying out preliminary measurement on a sensing optical cable by using an OTDR (Optical Time Domain Reflectometer), and judging whether the optical cable is damaged or not and the preliminary measurement distance of a damage point when the optical cable is damaged; judging whether the bare fiber is welded or not according to the distance threshold value, carrying out OTDR secondary measurement, and recording the light attenuation condition and the secondary measurement distance of each damage point according to the measurement result; according to the light attenuation condition, the damage points are divided into two types of severe attenuation or fiber breaking damage and medium and below attenuation damage, and the final damage point position is positioned in a targeted mode. According to the invention, monitoring can be carried out through combined use of existing equipment of the distributed optical fiber monitoring project, and other equipment does not need to be purchased separately. Moreover, the optical cable damage positioning precision can reach one meter, the invested positioning cost is low, the effect is good, and the method is also suitable for damage positioning of other communication optical cables.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of distributed optical fiber monitoring, in particular to a distributed optical fiber monitoring sensing optical cable damage positioning method. BACKGROUND

[0002] Distributed optical fiber sensing technology has been widely used in the monitoring of various linear engineering, such as oil and gas pipelines, long-distance power transmission, border control and other engineering. For underground engineering such as buried pipelines and buried cables, the sensing optical cable is often buried with the engineering object underground. In the process of laying and maintaining the sensing optical cable, it often faces the problem of difficult positioning of damage location. The sensing optical cable is buried underground, and the long redundant distance caused by the large number of cable coils brings great difficulty to the positioning of optical cable damage.

[0003] At present, OTDR optical time domain reflectometer is often used to judge the damage distance of the optical cable. Due to the ranging error of dozens of meters, combined with the lack of positioning function, it often leads to an increase in the area of ground maintenance excavation, resulting in a large amount of coordination and compensation costs, and low efficiency in finding and repairing, which causes the distributed optical fiber monitoring system to be unable to operate effectively for a long time. In addition, there are optical cable breakage finding devices with positioning function on the market, but they cannot locate non-breakage damage, and need to purchase expensive equipment or entrust third parties for on-site technical services, which cannot use the existing equipment of the distributed optical fiber monitoring project to locate, resulting in high cost. SUMMARY

[0004] The purpose of the present application is to provide a distributed optical fiber monitoring sensing optical cable damage positioning method, which aims to solve or improve at least one of the above technical problems.

[0005] To achieve the above purpose, the present application provides the following scheme: A distributed optical fiber monitoring sensing optical cable damage positioning method, comprising: using an OTDR optical time domain reflectometer to preliminarily measure the sensing optical cable, to determine whether the optical cable has damage and the preliminary measurement distance of the damage point when there is damage; setting a distance threshold, if the preliminary measurement distance is less than or equal to the distance threshold, then splicing a segment of bare optical fiber of a predetermined length at the starting point and performing OTDR secondary measurement, if the preliminary measurement distance is greater than the distance threshold, then directly performing OTDR secondary measurement; recording the optical attenuation and the secondary measurement distance of each damage point according to the OTDR secondary measurement result; dividing the damage points into two categories of "serious attenuation or breakage damage" and "moderate and below attenuation damage" according to the optical attenuation; for serious attenuation or breakage damage, using a Rayleigh DAS demodulator to measure, and combining the field knocking and DAS FBE signal to locate the final damage point position; For medium and below attenuation damage, the Stokes light curve is measured by using the Raman DTS demodulator to determine the cable distance of the damage point, and then combined with the DAS demodulator and the field knocking to finally determine the position of the damage point.

[0006] Optionally, the distance threshold is set to 500 meters, and the preset length is not less than 2 kilometers.

[0007] Optionally, the division standard of the optical attenuation is that the optical attenuation less than 0.3 dB is small attenuation, the optical attenuation between 0.3 dB and 1.0 dB is medium attenuation, and the optical attenuation greater than 1.0 dB or the fiber break is serious attenuation.

[0008] Optionally, the measurement method for serious attenuation or fiber break damage specifically includes: connecting the starting point of the optical cable to the DAS demodulator to obtain the light intensity curve, determining the demodulation stable starting point and the corresponding blind area distance L0; reciprocally knocking along the optical cable near the secondary measurement distance of the damage point obtained in the OTDR secondary measurement; judging the channel where the damage point is located according to the FBE value change displayed by the DAS demodulator, and calculating the accurate distance L of the damage point L = L1-L0, wherein L1 is the optical cable distance corresponding to the channel of the damage point.

[0009] Optionally, the measurement method for medium and below attenuation damage specifically includes: connecting the starting point of the optical cable to the Raman DTS demodulator for measurement to obtain the Stokes light curve; determining the blind area of the medium and below attenuation damage point of the sensing optical cable according to the position of the serious attenuation or fiber break in the starting part of the curve, and recording the blind area distance M0; determining the damage point distance M1 according to the attenuation part in the curve, and calculating the accurate distance M = M1-M0; finding the corresponding channel in the DAS demodulator according to the calculated M value, and confirming the final damage point position by combining the field knocking and the FBE value change.

[0010] Optionally, the field knocking method is that for the buried optical cable, a hammer is used to knock the ground surface at a frequency of 1 time / s; and for the overhead optical cable, a small wooden stick is used to knock the optical cable or the support at a frequency of 1 time / s.

[0011] Optionally, the damage points are sequentially searched and repaired from near to far according to the distance starting point.

[0012] Optionally, the process of finding the corresponding channel in the DAS demodulator according to the calculated M value is: Measure the frequency band energy FBE value of the optical cable under ambient noise conditions without impact, and calculate the optical cable distance N = L0 + ( M1 - M0), and find the corresponding channel based on the optical cable distance.

[0013] According to specific embodiments provided by the present invention, the present invention discloses the following technical effects: This invention discloses a method for locating damage in distributed optical fiber monitoring sensing cables. The method includes using an OTDR (Optical Time Domain Reflectometer) to perform preliminary measurements on the sensing cable, determining whether damage exists and, if so, the initial distance to the damage point; determining whether to splice bare fibers based on a distance threshold, and performing a secondary OTDR measurement; recording the optical attenuation and the secondary measurement distance for each damage point based on the measurement results; classifying the damage points into two categories based on the optical attenuation: "severe attenuation or fiber breakage damage" and "moderate or lower attenuation damage," and then specifically locating the final damage point. This invention can utilize only the OTDR commonly used in optical cable laying, and the Raman DTS demodulator and Rayleigh DAS demodulator commonly used in distributed optical fiber monitoring. By combining these devices, the accuracy of damage location in sensing optical cables is greatly improved, the damage finding process is accelerated, and repair and compensation costs are saved. Furthermore, this method is also applicable to damage location in other buried or overhead communication optical cables. Attached Figure Description

[0014] To more clearly illustrate the technical solutions in the embodiments of the present invention or the prior art, the drawings used in the embodiments will be briefly introduced below. Obviously, the drawings described below are only some embodiments of the present invention. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0015] Figure 1 This is the overall flowchart for the distributed optical fiber monitoring and sensing cable damage localization of this invention; Figure 2 This is a schematic diagram illustrating the determination of the demodulation stabilization starting point based on the DAS light intensity curve according to the present invention. Figure 3 This is a schematic diagram illustrating the use of an OTDR to record the number and approximate distance of optical cable damage according to the present invention; Figure 4 This is a schematic diagram illustrating the method for locating severe damage to optical cables based on the intensity of DAS acoustic signals according to the present invention; wherein, Figure 4 (a) is a schematic diagram of the DAS sound wave signal intensity when not struck; Figure 4 (b) Schematic diagram of DAS acoustic signal intensity during reciprocating striking; Figure 5 This is a schematic diagram illustrating the method for determining the optical cable damage distance based on the DTS Stokes curve according to the present invention; wherein, Figure 5(a) is a schematic diagram of the overall distribution of the Stokes curve; Figure 5 (b) is a magnified local curve diagram of the suspected damaged area; Figure 6 This is a schematic diagram illustrating the method for locating moderate to severe damage in optical cables based on the intensity of DAS acoustic signals according to the present invention; wherein, Figure 6 (a) is a schematic diagram of the DAS sound wave signal intensity distribution curve under ambient noise conditions without impact; Figure 6 (b) is a schematic diagram of the DAS acoustic signal intensity response obtained after reciprocating tapping near the estimated damage point. Detailed Implementation

[0016] The technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0017] The purpose of this invention is to provide a method for locating damage to distributed optical fiber monitoring and sensing cables, aiming to solve or improve at least one of the above-mentioned technical problems.

[0018] To make the above-mentioned objects, features and advantages of the present invention more apparent and understandable, the present invention will be further described in detail below with reference to the accompanying drawings and specific embodiments.

[0019] This invention provides a method for locating damage to distributed optical fiber monitoring and sensing cables, comprising: An OTDR (Optical Time Domain Reflectometer) was used to perform preliminary measurements on the sensing optical cable to determine whether the cable was damaged and, if so, the initial distance to the damaged point.

[0020] A distance threshold is set. If the initial measured distance is less than or equal to the distance threshold, a bare optical fiber of a preset length is spliced ​​at the starting point and a second OTDR measurement is performed. If the initial measured distance is greater than the distance threshold, a second OTDR measurement is performed directly.

[0021] Record the light decay status and the secondary measurement distance of each damage point based on the secondary measurement results of the OTDR.

[0022] Based on the light decay, the damage points are divided into two categories: "severe attenuation or fiber breakage damage" and "moderate or lower attenuation damage".

[0023] For severe attenuation or fiber breakage damage, a Rayleigh DAS demodulator is used for measurement, and the final damage point is located by combining on-site tapping and the FBE signal of the DAS. As a specific implementation method, the specific implementation process of this step includes: Connect the optical cable starting point to the DAS demodulator, obtain the light intensity curve, determine the demodulation stabilization starting point and the corresponding dead zone distance L0; tap the optical cable repeatedly near the secondary measurement distance of the damage point obtained in the OTDR secondary measurement; determine the channel where the damage point is located based on the FBE value change displayed by the DAS demodulator, and calculate the accurate distance of the damage point L = L1 - L0, where L1 is the optical cable distance corresponding to the channel of the damage point.

[0024] For attenuation damage of moderate to low level, a Stokes curve is measured using a Raman DTS demodulator to determine the distance of the damaged fiber optic cable. This is then combined with a DAS demodulator and on-site tapping to pinpoint the final damage location. As a specific implementation method, this step includes the following steps: Connect the optical cable starting point to the Raman DTS demodulator for measurement to obtain the Stokes curve; determine the dead zone of the moderate to low attenuation damage point in the sensing optical cable based on the severe attenuation or fiber breakage location at the beginning of the curve, and record the dead zone distance M0; determine the damage point distance M1 based on the attenuation part in the curve, and calculate the accurate distance M = M1 - M0; find the corresponding channel in the DAS demodulator based on the calculated M value, and confirm the final damage point location by combining on-site tapping and FBE value changes.

[0025] The process of finding the corresponding channel in the DAS demodulator based on the calculated M value is as follows: the frequency band energy FBE value of the optical cable under ambient noise conditions without impact is measured, and the optical cable distance N = L0 + ( M1 - M0) is calculated. The corresponding channel is then found based on the optical cable distance.

[0026] Based on the above technical solution, the following specific embodiments are provided.

[0027] In this embodiment, an OTDR (Optical Time Domain Reflectometer) is used to initially determine the location of damage to the sensing optical cable. For short distances, a section of optical fiber needs to be spliced ​​to lengthen the fiber space and reduce testing errors. For long distances, no splicing is required.

[0028] Using an OTDR (Optical Time Domain Reflectometer) to initially determine the light attenuation level and approximate distance, the search is conducted in two ways: the first is for severely attenuated points, and the second is for points with moderate to low attenuation. The search methods differ for these two scenarios.

[0029] The first type of severe attenuation point locator involves fewer steps. First, locate the fiber optic channel corresponding to the attenuation point. Then, have personnel tap the channel on-site to see which channel reacts the most. Based on this, determine the exact location of the damage point and calculate the exact fiber optic cable distance from the damage point.

[0030] The second method, locating attenuation points below medium level, involves more steps. Like the first method, using only a DAS device is insufficient to accurately locate these attenuation points because they are not clearly distinguishable on the DAS FBE plot. This method combines DTS equipment, using the Stokes curve to first determine the precise distance to each attenuation point. Then, the DAS device is used to locate the corresponding channel based on the precise distance, and finally, the exact location is determined by tapping on-site.

[0031] Since previous damage points can cause distance errors in subsequent damage point location and testing, it is recommended to start from the starting point and search for and repair damage points one by one to avoid this error.

[0032] Therefore, see Figure 1 When damage is detected in the sensing optical cable, step S1 first uses an OTDR (Optical Time Domain Reflectometer) for preliminary assessment. Step S2: If the damage point is within 500 meters of the starting point, step S3: Splice a bare optical fiber of more than 2 kilometers in length at the starting point to extend the cable for easier testing. Step S4: If the damage point is more than 500 meters from the starting point, do not splice the bare optical fiber; directly connect the OTDR. Step S5: Use the OTDR again for measurement, recording the number of optical attenuations and the approximate distance corresponding to each attenuation point.

[0033] For detailed steps S5, please refer to [link / reference]. Figure 3 The attenuation status and approximate distance of each element are determined from the OTDR (Optical Time Domain Reflectometer) measurement results. In the example, S51 represents the attenuation curve, S52 represents low attenuation (below 0.3 dB), S53 represents medium attenuation (0.3~1.0 dB), and S54 represents severe attenuation (above 1.0 dB) or fiber breakage. The attenuation level can be determined based on the allowable values ​​of the distributed fiber optic monitoring system; in this example, 0.3 dB and 1.0 dB are used as the dividing values. Low and medium attenuation may be distributed in multiple locations along the optical cable, especially common in directly buried optical cables.

[0034] See Figure 1 Step S6 locates the points of severe optical attenuation or fiber breakage damage in the sensing optical cable. Step S7 connects the starting point of the optical cable (including bare fiber) to the Rayleigh DAS demodulator for measurement. Step S8 uses the light intensity curve measured by the DAS demodulator to determine the stable demodulation starting point.

[0035] For detailed steps S8, please refer to [link / reference]. Figure 2In the example, S81 is the light intensity curve. At the very beginning of the curve, the light intensity signal usually exhibits obvious instability, oscillation, or anomalies, reflecting that the interferometer has not yet reached a stable state. The boundary point S82 where the curve fluctuates stably is found, and this boundary point is taken as the starting point for demodulation stabilization. The optical cable distance L0 corresponding to S82 is used as the blind zone to determine the location of severe light attenuation or fiber breakage damage in the sensing optical cable.

[0036] See Figure 1 Step S9: Send personnel to the vicinity of the location identified in Step S5 as having severe optical attenuation or fiber breakage in the sensing optical cable and repeatedly tap along the cable route. If it is a buried optical cable, use a hammer to tap the ground at a frequency of once per second; if it is an overhead optical cable, use a small wooden stick to tap the optical cable or its support at a frequency of once per second. Step S10: Determine the location of severe optical attenuation or fiber breakage in the optical cable based on the FBE value.

[0037] For detailed steps S10, please refer to [link / reference]. Figure 4 ,like Figure 4 (a) In the example, S101 represents the typical frequency band energy (FBE) value of the optical cable under ambient noise conditions without impact. The FBE value reflects the intensity of the DAS acoustic signal. Here, the width of each column represents the length of a channel. S102 represents the channel location with an abnormally low FBE value. Figure 4 (b) In step S9, the optical cable is repeatedly tapped along its path near the point of severe optical attenuation or fiber breakage until the point S101 is reached. At this point, the value of S101 increases to the level of S103, which is much higher than the FBE value of nearby points. At this time, the value of channel S102 next to S101 remains relatively small. The point corresponding to channel S102 is S104, and the optical cable distance corresponding to point S104 is L1. Then L = L1 - L0 (L0 is the dead zone distance of the point of severe optical attenuation or fiber breakage) is the accurate optical cable distance from the point of severe optical attenuation or fiber breakage to the starting point of the optical cable. The channel S102 next to channel S101 found by tapping in step S9 is the point of severe optical attenuation or fiber breakage in the optical cable. Thus, the location of the point of severe optical attenuation or fiber breakage in the optical cable is completed.

[0038] See Figure 1 Step S12 locates points of medium to low optical attenuation in the sensing optical cable. Step S13 connects the starting point of the optical cable (including bare fiber) to a Raman DTS demodulator for measurement to obtain the DTS Stokes curve. Step S14 determines the accurate optical cable distance to the point of optical cable damage based on the DTS Stokes curve.

[0039] For details on step S14, please refer to [link / reference]. Figure 5 ,like Figure 5(a) In the example, S141 is the Stokes curve. First, by observing the large attenuation at the beginning of the curve, the corresponding point S142 is found. This is the optical loss point of the DTS equipment's optical switch or plug. The optical cable distance corresponding to point S142 is M0, which serves as the blind zone for determining the medium and lower optical attenuation damage points in the sensing optical cable. S143 is the medium and lower optical attenuation portion shown by the Stokes curve. For example... Figure 5 (b) shows the S144 curve obtained by magnifying part S143. The point corresponding to the end of the falling segment of the S144 curve is S145, and the optical cable distance M1 corresponds to point S145. Then M = M1-M0 (M0 is the blind zone distance of the point with medium or lower optical attenuation damage) is the accurate optical cable distance from the point with medium or lower optical attenuation damage of the sensing optical cable to the starting point of the optical cable.

[0040] See Figure 1 Steps S7, S8, and S9 are described above. Step S15 determines the location of moderate to low optical attenuation damage in the optical cable based on the FBE value.

[0041] For detailed steps S15, please refer to [link / reference]. Figure 6 ,like Figure 6 (a) In the example, S151 is the typical frequency band energy FBE value of the optical cable under ambient noise conditions without impact. For example... Figure 6 (b) Calculate the optical cable distance N = L0 + (M1 - M0) to find the point S152 corresponding to the optical cable distance N. Point S152 corresponds to channel S153. In step S9, tap along the optical cable route near the point of moderate or lower optical attenuation damage in the sensing optical cable until the value of S153 increases significantly and is much higher than the FBE value of nearby points. At this point, the point tapped in step S9 is the point of moderate or lower optical attenuation damage in the sensing optical cable. Thus, the search for the point of moderate or lower optical attenuation damage in the sensing optical cable is completed.

[0042] As a further implementation method, first locate the damage point closest to the starting point of the optical cable, repair it, and then locate the next damage point further away, and so on.

[0043] The various embodiments in this specification are described in a progressive manner, with each embodiment focusing on the differences from other embodiments. The same or similar parts between the various embodiments can be referred to each other.

[0044] This document uses specific examples to illustrate the principles and implementation methods of the present invention. The descriptions of the above embodiments are only for the purpose of helping to understand the core ideas of the present invention. Furthermore, those skilled in the art will recognize that, based on the ideas of the present invention, there will be changes in the specific implementation methods and application scope. Therefore, the content of this specification should not be construed as a limitation of the present invention.

Claims

1. A method for locating damage to a distributed optical fiber monitoring sensor cable, characterized in that, include: An OTDR (Optical Time Domain Reflectometer) was used to perform preliminary measurements on the sensing optical cable to determine whether the cable was damaged and, if so, the initial distance to the damage point. Set a distance threshold. If the initial measured distance is less than or equal to the distance threshold, then splice a bare optical fiber of a preset length at the starting point and perform a second OTDR measurement. If the initial measured distance is greater than the distance threshold, then directly perform a second OTDR measurement. Record the optical attenuation and the secondary measurement distance of each damage point based on the secondary measurement results of the OTDR; Based on the optical decay situation, the damage points are divided into two categories: "severe attenuation or fiber breakage damage" and "moderate and lower attenuation damage". For severe attenuation or fiber breakage damage, Rayleigh DAS demodulators are used for measurement, and the final damage point is located by combining on-site tapping and the FBE signal of DAS. For moderate and lower attenuation damage, the Stokes curve is measured using a Raman DTS demodulator to determine the distance of the optical cable from the damage point. Then, the DAS demodulator and on-site tapping are used to locate the final damage point.

2. The method for locating damage to distributed optical fiber monitoring and sensing cables according to claim 1, characterized in that, The distance threshold is set to 500 meters, and the preset length is not less than 2 kilometers.

3. The method for locating damage to distributed optical fiber monitoring and sensing cables according to claim 1, characterized in that, The criteria for classifying optical decay are as follows: optical decay less than 0.3dB is considered small decay, optical decay between 0.3dB and 1.0dB is considered medium decay, and optical decay greater than 1.0dB or fiber breakage is considered severe decay.

4. The method for locating damage to distributed optical fiber monitoring and sensing cables according to claim 1, characterized in that, The measurement methods for severe attenuation or fiber breakage specifically include: Connect the optical cable starting point to the DAS demodulator, obtain the light intensity curve, and determine the demodulation stabilization starting point and the corresponding dead zone distance L0. The damage point obtained in the secondary OTDR measurement was repeatedly struck along the optical cable near the secondary measurement distance. Based on the FBE value change displayed by the DAS demodulator, determine the channel where the damage point is located, and calculate the accurate distance of the damage point L = L1 - L0, where L1 is the optical cable distance corresponding to the channel of the damage point.

5. The method for locating damage to distributed optical fiber monitoring and sensing cables according to claim 1, characterized in that, The measurement method for moderate and lower attenuation damage specifically includes: The optical cable starting point is connected to a Raman DTS demodulator for measurement to obtain the Stokes curve. Based on the location of severe attenuation or fiber breakage at the beginning of the curve, determine the blind zone of the sensing optical cable with medium or lower attenuation damage points, and record the blind zone distance M0. Determine the distance M1 from the damage point based on the attenuation region in the curve, and calculate the accurate distance M = M1 - M0; Based on the calculated M value, the corresponding channel is located in the DAS demodulator. The final location of the damage point is confirmed by combining the on-site tapping and the change in FBE value.

6. The method for locating damage to distributed optical fiber monitoring and sensing cables according to claim 1, characterized in that, The on-site striking method is as follows: for buried optical cables, use a hammer to strike the ground surface at a frequency of 1 time per second; for overhead optical cables, use a small wooden stick to strike the optical cable or support at a frequency of 1 time per second.

7. The method for locating damage to distributed optical fiber monitoring and sensing cables according to claim 1, characterized in that, The damaged points are located and repaired sequentially from the nearest to the farthest point from the starting point.

8. The method for locating damage to distributed optical fiber monitoring and sensing cables according to claim 5, characterized in that, The process of finding the corresponding channel in the DAS demodulator based on the calculated M value is as follows: Measure the frequency band energy FBE value of the optical cable under ambient noise conditions without impact, and calculate the optical cable distance N = L0 + ( M1 - M0), and find the corresponding channel based on the optical cable distance.

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