A method for locating damage of a distributed optical fiber monitoring sensing optical cable

Abstract

The application discloses a kind of distributed optical fiber monitoring sensing optical cable damage location method, it is related to distributed optical fiber monitoring technical field.The method includes: using OTDR optical time domain reflectometer to carry out preliminary measurement to sensing optical cable, it is judged whether optical cable exists damage and the preliminary measurement distance of damage point when existing damage;According to distance threshold value, it is judged whether bare optical fiber is fused, and OTDR secondary measurement is carried out, according to the measurement result record optical fading and the secondary measurement distance of each damage point;According to the optical fading, damage point is divided into two categories of " serious attenuation or broken fiber damage " and " moderate and below attenuation damage ", and the position of final damage point is positioned specifically.The application can be monitored by combined use of existing equipment of distributed optical fiber monitoring project itself, without separately purchasing other equipment.And, the optical cable damage location precision of the application can reach one meter, the positioning cost is low, the effect is good, and it is also applicable to the damage location of other communication optical cable.

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 monitoring various linear projects, such as oil and gas pipelines, long-distance power transmission, border control and other projects. For underground projects such as buried pipelines and buried cables, the sensing optical cable is often buried underground together with the project object. In the process of laying and maintaining the sensing optical cable, it often faces the problem of locating the damage position. 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 the optical cable damage.

[0003] Currently, 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:

[0006] A distributed optical fiber monitoring sensing optical cable damage positioning method, comprising:

[0007] 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;

[0008] Setting a distance threshold, if the preliminary measurement distance is less than or equal to the distance threshold, a segment of bare optical fiber of a predetermined length is spliced at the starting point and OTDR secondary measurement is performed, if the preliminary measurement distance is greater than the distance threshold, OTDR secondary measurement is directly performed;

[0009] According to the OTDR secondary measurement result, record the optical attenuation and the secondary measurement distance of each damage point;

[0010] According to the optical attenuation, the damage points are divided into two categories: "serious attenuation or breakage damage" and "moderate and below attenuation damage";

[0011] For serious attenuation or fiber breakage damage, use Rayleigh DAS demodulator to measure, combined with field knocking and DAS FBE signal positioning to determine the final damage point position;

[0012] For moderate and below attenuation damage, use Raman DTS demodulator to measure the Stokes light curve, determine the cable distance of the damage point, and then combine DAS demodulator and field knocking to locate the final damage point position.

[0013] Optionally, the distance threshold is set to 500 meters, and the preset length is not less than 2 kilometers.

[0014] Optionally, the division standard of the optical attenuation is: optical attenuation less than 0.3 dB is small attenuation, optical attenuation between 0.3 dB and 1.0 dB is moderate attenuation, and optical attenuation greater than 1.0 dB or fiber breakage is serious attenuation.

[0015] Optionally, the measurement method for serious attenuation or fiber breakage damage specifically includes:

[0016] Connect the starting point of the optical cable to the DAS demodulator to obtain the light intensity curve, determine the demodulation stable starting point and the corresponding blind area distance L0;

[0017] Knock along the optical cable around the secondary measurement distance of the damage point in the OTDR secondary measurement;

[0018] According to the FBE value change displayed by the DAS demodulator, determine the channel where the damage point is located, and calculate the accurate distance L = L1- L0 of the damage point, where L1 is the cable distance corresponding to the damage point channel.

[0019] Optionally, the measurement method for moderate and below attenuation damage specifically includes:

[0020] Connect the starting point of the optical cable to the Raman DTS demodulator for measurement to obtain the Stokes light curve;

[0021] Determine the blind area of the moderate and below attenuation damage point of the sensing optical cable according to the serious attenuation or fiber breakage position of the starting part of the curve, and record the blind area distance M0;

[0022] Determine the damage point distance M1 according to the attenuation part in the curve, and calculate the accurate distance M = M1- M0;

[0023] According to the calculated M value, find the corresponding channel in the DAS demodulator, and confirm the final damage point position combined with field knocking and FBE value change.

[0024] Optionally, the field knocking method is: for buried optical cable, use a hammer to knock the ground surface at a frequency of 1 time / s; for overhead optical cable, use a small wooden stick to knock the optical cable or support at a frequency of 1 time / s.

[0025] Optionally, the damage points are searched and repaired in order from near to far according to the distance from the starting point.

[0026] Optionally, the process of finding the corresponding channel in the DAS demodulator according to the calculated M value is as follows:

[0027] The FBE value of the optical cable under the condition of ambient noise without knocking is measured, and the optical cable distance N = L0+ (M1-M0) is calculated, and the corresponding channel is found according to the optical cable distance.

[0028] According to the specific embodiments provided by the application, the following technical effects are disclosed:

[0029] The application discloses a distributed optical fiber monitoring sensing optical cable damage positioning method, which comprises the following steps: using an OTDR (Optical Time Domain Reflectometer) to perform preliminary measurement on a sensing optical cable, judging whether the optical cable is damaged and the preliminary distance of a damage point when the optical cable is damaged; judging whether a bare optical fiber is fusion spliced according to a distance threshold value, and performing secondary measurement on the OTDR, recording optical attenuation and secondary measurement distance of each damage point according to a measurement result; dividing the damage points into two categories, i.e., "serious attenuation or fiber breakage damage" and "moderate and below attenuation damage", according to the optical attenuation, and positioning the final damage point position. The application can only use the OTDR (Optical Time Domain Reflectometer) commonly used in optical cable laying work, the Raman DTS demodulator and the Rayleigh DAS demodulator commonly used in distributed optical fiber monitoring, and through the combination of the above-mentioned devices, the sensing optical cable damage positioning precision is greatly improved, the sensing optical cable damage searching progress is accelerated, and the maintenance and compensation cost expenditure is saved. Meanwhile, the method is also applicable to the damage positioning of other buried or overhead communication optical cables. BRIEF DESCRIPTION OF DRAWINGS

[0030] In order to more clearly illustrate the technical solutions in the embodiments of the present application or the prior art, the following will briefly introduce the drawings needed to be used in the embodiments. Obviously, the drawings in the following description only constitute some embodiments of the present application, and for those skilled in the art, other drawings can also be obtained without creative labor.

[0031] Figure 1 The figure is a general flow chart of the distributed optical fiber monitoring sensing optical cable damage positioning of the present application.

[0032] Figure 2 The figure is a schematic diagram of determining the demodulation stable starting point according to the DAS light intensity curve of the present application.

[0033] Figure 3 The figure is a schematic diagram of recording the optical cable damage quantity and approximate distance using the OTDR of the present application.

[0034] Figure 4 Fig. 1 is a schematic diagram of the present application for judging the location of serious damage of an optical cable according to the DAS acoustic wave signal intensity; wherein, Figure 4 (a) is a schematic diagram of the DAS acoustic wave signal intensity when not knocking; Figure 4 (b) is a schematic diagram of the DAS acoustic wave signal intensity when reciprocating knocking is performed;

[0035] Figure 5 Fig. 2 is a schematic diagram of the present application for judging the damage distance of an optical cable according to the DTS Stokes light curve; wherein, Figure 5 (a) is a schematic diagram of the overall distribution of the Stokes light curve; Figure 5 (b) is a schematic diagram of the local curve after zooming in on the suspected damage area;

[0036] Figure 6 Fig. 3 is a schematic diagram of the present application for judging the location of moderate or below damage of an optical cable according to the DAS acoustic wave signal intensity; wherein, Figure 6 (a) is a schematic diagram of the DAS acoustic wave signal intensity distribution curve under the condition of ambient noise when not knocking; Figure 6 (b) is a schematic diagram of the DAS acoustic wave signal intensity response obtained after reciprocating knocking near the estimated damage point. DETAILED DESCRIPTION

[0037] The technical solutions in the embodiments of the present application will be clearly and completely described below with reference to the drawings in the embodiments of the present application. Obviously, the described embodiments are only part of the embodiments of the present application, rather than all the embodiments. Based on the embodiments in the present application, all other embodiments obtained by those of ordinary skill in the art without creative labor fall within the scope of the present application.

[0038] The purpose of the present application is to provide a distributed optical fiber monitoring sensing optical cable damage positioning method, aiming to solve or improve at least one of the above technical problems.

[0039] In order to make the above purposes, characteristics and advantages of the present application more obvious and easy to understand, the present application will be further described in detail below with reference to the drawings and specific embodiments.

[0040] The present application provides a distributed optical fiber monitoring sensing optical cable damage positioning method, comprising:

[0041] The OTDR optical time domain reflectometer is used to perform preliminary measurement on the sensing optical cable, to judge whether the optical cable has damage and the preliminary measurement distance of the damage point when there is damage.

[0042] A distance threshold is set, if the preliminary measurement distance is less than or equal to the distance threshold, a segment of bare optical fiber of a preset length is spliced at the starting point and OTDR secondary measurement is performed, if the preliminary measurement distance is greater than the distance threshold, OTDR secondary measurement is directly performed.

[0043] According to the OTDR secondary measurement result, record the optical attenuation condition and the secondary measurement distance of each damage point.

[0044] According to the optical attenuation condition, divide the damage points into two categories: "serious attenuation or fiber breakage damage" and "moderate and below attenuation damage".

[0045] For the serious attenuation or fiber breakage damage, use the Rayleigh DAS demodulator to measure, and combine the field knocking and the DAS FBE signal to locate the final damage point position. As a specific implementation, the specific implementation process of this step includes:

[0046] Connect the starting point of the optical cable to the DAS demodulator, obtain the optical intensity curve, determine the demodulation stable starting point and the corresponding blind area distance L0; knock along the optical cable near the secondary measurement distance of the damage point obtained in the OTDR secondary measurement; according to the FBE value change displayed by the DAS demodulator, judge the channel where the damage point is located, and calculate the accurate distance L = L1- L0 of the damage point, where L1 is the optical cable distance corresponding to the damage point channel.

[0047] For the moderate and below attenuation damage, use the Raman DTS demodulator to measure to obtain the Stokes light curve, judge the damage point optical cable distance, and then combine the DAS demodulator and the field knocking to locate the final damage point position. As a specific implementation, the specific implementation process of this step includes:

[0048] Connect the starting point of the optical cable to the Raman DTS demodulator for measurement to obtain the Stokes light curve; determine the blind area of the moderate and below attenuation damage point in the sensing optical cable according to the serious attenuation or fiber breakage position of the starting part of the curve, and record the blind area distance M0; determine the damage point distance M1 according to the attenuation part in the curve, and calculate the accurate distance M = M1- M0; find the corresponding channel in the DAS demodulator according to the calculated M value, and confirm the final damage point position by combining the field knocking and the FBE value change.

[0049] 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 the condition of no knocking and environmental noise, and calculate the optical cable distance N = L0+ ( M1- M0), and find the corresponding channel according to the optical cable distance.

[0050] Based on the above technical solutions, the following specific embodiments are provided.

[0051] In this embodiment, the OTDR optical time domain reflectometer is used to preliminarily judge the damage position of the sensing optical cable. For the short distance, a section of optical fiber is spliced to lengthen the space of the optical fiber and reduce the test error. For the long distance, the lengthening is not needed.

[0052] Use OTDR optical time domain reflectometer to preliminarily judge the optical decay condition and the approximate distance, and find in two cases. The first is a serious attenuation point, and the second is a moderate or below attenuation point. The finding methods of the two cases are different.

[0053] The first serious attenuation point finding step is less. First, find the optical fiber channel corresponding to the attenuation point, and then knock on the site by personnel to see which channel reacts, thereby determining the accurate damage point position and calculating the accurate damage point cable distance.

[0054] The second moderate or below attenuation point finding step is more. If the moderate or below attenuation point is found in the first case, it cannot be found accurately by using only one DAS device, because the moderate or below attenuation point cannot be distinguished on the FBE graph of the DAS. This method combines the DTS device, uses the Stokes light curve to find the accurate distance of each attenuation point, and then replaces the DAS device to find the corresponding channel through the accurate distance, and then finds the accurate site position by knocking on the site.

[0055] Because the previous damage point will cause a distance error in the subsequent damage point finding test, in order to avoid this error, it is recommended to find and repair the damage points from the starting point.

[0056] Therefore, referring to Figure 1 When the sensing optical cable is found to be damaged, step S1 first uses the OTDR optical time domain reflectometer to preliminarily judge, step S2 is within 500 meters from the starting point, step S3 is to splice a length of 2 kilometers or more of bare optical fiber at the starting point of the optical cable to lengthen the optical cable to be positioned for convenient testing, step S4 is more than 500 meters from the starting point, and step S5 is to connect the OTDR optical time domain reflectometer directly. Step S5 uses the OTDR optical time domain reflectometer to measure again, and records the optical decay amount and the approximate distance corresponding to each optical decay point in detail.

[0057] Step S5 is detailed, referring to Figure 3 Find and record the optical decay condition and the approximate distance from the OTDR optical time domain reflectometer measurement result. In the example, S51 is the optical decay curve, S52 is a small attenuation (0.3 dB or less), S53 is a moderate attenuation (0.3-1.0 dB), and S54 is a serious attenuation (1.0 dB or more) or a broken fiber. The degree of attenuation can be determined according to the allowable value of the distributed optical fiber monitoring system. In this example, 0.3 dB and 1.0 dB are used as the dividing values. Small attenuation and moderate attenuation can be distributed in multiple places of the optical cable, especially for direct-buried optical cables.

[0058] Referring to Figure 1, step S6 is for finding the serious optical attenuation or fiber breakage point of the sensing optical cable, step S7 is for connecting the starting point of the optical cable (including bare fiber) to the Rayleigh DAS demodulator for measurement, and step S8 is for determining the stable starting point of demodulation by using the light intensity curve measured by the DAS demodulator.

[0059] For details of step S8, see Figure 2 , in the example, S81 is the light intensity curve, and at the beginning of the curve, the light intensity signal usually shows obvious instability, oscillation or abnormality, reflecting that the interferometer has not reached a stable state. The demarcation point S82 of the stable fluctuation of the curve is found, the demarcation point S82 is taken as the stable starting point of demodulation, and L0 corresponding to the demarcation point S82 is taken as the blind area for determining the serious optical attenuation or fiber breakage point of the sensing optical cable.

[0060] For details of step S10, see Figure 1 , step S9 is for sending personnel to the vicinity of the serious optical attenuation or fiber breakage point of the sensing optical cable to knock along the optical cable route back and forth, using a hammer to knock the ground surface at a frequency of 1 second 1 time for a buried optical cable, or using a small wooden stick to knock the optical cable or the optical cable support at a frequency of 1 second 1 time for an overhead optical cable. Step S10 is for determining the serious optical attenuation or fiber breakage point according to the FBE value.

[0061] For details of step S10, see Figure 4 , for example Figure 4 (a) In the example, S101 is the frequency band energy FBE value of the optical cable under the condition of no knocking and environmental noise, and the FBE value reflects the strength of the DAS sound wave signal. Each column width represents a channel length, and S102 is the abnormal FBE low value channel point. Figure 4 (b) As shown in step S9, knock along the optical cable route near the serious optical attenuation or fiber breakage point of the sensing optical cable until the position of S101 is reached, and the value of S101 increases to the extent of S103, that is, the FBE value is much higher than that of the nearby point. At this time, the value of S102 beside S101 remains small, S102 corresponds to point S104, and the optical cable distance corresponding to point S104 is L1. Then L = L1- L0 (L0 is the blind area distance of the serious optical attenuation or fiber breakage point) is the accurate optical cable distance from the serious optical attenuation or fiber breakage point of the sensing optical cable to the starting point of the optical cable. The S102 channel beside the S101 channel found by knocking in step S9 is the serious optical attenuation or fiber breakage point of the sensing optical cable, and thus the search for the serious optical attenuation or fiber breakage point of the sensing optical cable is completed.

[0062] For details of step S10, see Figure 1, step S12 is for searching the middle and below light attenuation point in the sensing optical cable, step S13 connects the start point of the optical cable (including bare fiber) to the Raman DTS demodulator for measurement, and obtains the DTS Stokes light curve. Step S14 determines the accurate optical cable distance of the optical cable damage point according to the DTS Stokes curve.

[0063] Step S14 is described in detail in Figure 5 , as shown in Figure 5 (a) In the example, S141 is the Stokes light curve. First, the corresponding point S142 is found by observing the large attenuation of the initial part of the curve, which is the DTS device optical switch or plug optical loss point. The optical cable distance corresponding to the point S142 is M0, which is the blind area for determining the middle and below light attenuation damage point in the sensing optical cable. S143 is the middle and below light attenuation part reflected in the Stokes light curve. As shown in Figure 5 (b) The S143 part is enlarged as shown, and the S144 curve is obtained. The end of the descending segment of the S144 curve corresponds to the point S145, and the optical cable distance M1 corresponding to the point S145. Then M = M1-M0 (M0 is the blind area distance of the middle and below light attenuation damage point) is the accurate optical cable distance of the middle and below light attenuation damage point from the start point of the sensing optical cable.

[0064] Refer to Figure 1 , steps S7, S8 and S9 are described above. Step S15 determines the middle and below light attenuation damage point in the optical cable according to the FBE value.

[0065] Step S15 is described in detail in Figure 6 , as shown in Figure 6 (a) In the example, S151 is the frequency band energy FBE value of the optical cable under the condition of no knocking and environmental noise. As shown in Figure 6 (b) The optical cable distance N = L0+ (M1-M0) is calculated as shown, the point S152 corresponding to the optical cable distance N is found, and the S153 channel corresponding to the point S152 is found. Step S9 repeatedly knocks along the optical cable route near the middle and below light attenuation damage point in the sensing optical cable until the S153 value increases a lot and is much higher than the FBE value of the nearby point. At this time, the point knocked by step S9 is the middle and below light attenuation damage point in the sensing optical cable. Thus, the search for the middle and below light attenuation damage point in the sensing optical cable is completed.

[0066] As a further implementation, the damage point closest to the start point of the optical cable is searched first, and then the next damage point far away is searched after the first damage point is repaired, and so on.

[0067] Each embodiment in the specification is described in a progressive manner, and each embodiment focuses on the difference from other embodiments. The same and similar parts between each embodiment can be referred to each other.

[0068] The principles and implementations of the present application are described in the specific examples herein, and the above examples are only used to help understand the core idea of the present application; at the same time, for those skilled in the art, according to the idea of the present application, the specific implementation and application range will be changed. In view of the above, the content of the specification should not be understood as a limitation of the present application.

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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