Trough sensing system, trough, and method for measuring physical quantities using sensing cable

Abstract

To provide an improved novel trough sensing system and a trough for a cable each of which enables, for example, a sensing cable to secure required reliability, and enables the sensing cable to secure required detection sensitivity, and a method for measuring physical quantity using the sensing cable.SOLUTION: A trough sensing system comprises, for example, a sensing cable including an optical fiber transmitting an optical signal, a trough which is made of material including a synthetic resin material and in which the sensing cable is housed, and a measuring instrument measuring a physical quantity at a portion, housed in the trough, of the sensing cable based upon the optical signal from the optical fiber. The physical quantity may be a physical quantity corresponding to vibration, a physical quantity corresponding to strain, temperature, etc. The sensing cable also may be fixed at least partly to the trough.SELECTED DRAWING: Figure 1

Description

[Technical Field]

[0001] The present invention relates to a trough sensing system. ,to This invention relates to a method for measuring physical quantities using a rough and a sensing cable. [Background technology]

[0002] Conventionally, cable troughs that enclose cables such as power transmission cables and communication cables and protect the cables from water, soil, etc. have been known (Patent Documents 1 and 2). Cable troughs are installed, for example, along roads or railway tracks, and are buried underground together with the cables or laid on the ground surface.

[0003] Meanwhile, optical fiber sensing has been developed that observes changes in strain, vibration, and temperature along the length of an optical fiber by observing backscattered light generated in the optical fiber by light propagating through the optical fiber (Non-Patent Document 1). Furthermore, methods for measuring strain and vibration distributions have been proposed, such as detecting backscattered Brillouin light (Non-Patent Documents 2, 3, and 4) and detecting Rayleigh scattered light (Non-Patent Document 5). Furthermore, a method using fiber Bragg gratings (FBG) has also been proposed as a method for measuring strain and vibration using optical fiber (Non-Patent Document 6).

[0004] Also, a configuration is known in which a sensing cable laid along a railway track is directly buried underground without using a cable trough (Non-Patent Document 7). [Prior art documents] [Patent documents]

[0005] [Patent Document 1] Japanese Patent Application Publication No. 09-70129 [Patent Document 2] Japanese Patent Application Laid-Open No. 2004-282976 [Non-patent literature]

[0006] [Non-Patent Document 1] Kazuo Hotate, "Optical Fiber Sensor," Laser Research, Vol. 41, No. 5, pp. 307-314, May 2013 [Non-patent document 2] H. Ohno, H. Naruse, M. Kihara, and A. Shimada, “Industrial Applications of the BOTDR Optical Fiber Strain Sensor” Optical Fiber Technology 7, 45-64 2001. [Non-patent document 3] Y. Mizuno, W. Zou, Z. He, and K. Hotate, “Proposal of Brillouin optical correlation-domain reflectometry (BOCDR)” OPTICS EXPRESS Vol. 16, No. 16 12148-12153 2008. [Non-patent document 4] K. Hotate, T. Hasegawa, “Measurement of Brillouin Gain Spectrum Distribution along an Optical Fiber Using a Correlation-Based Technique-Proposal, Experiment and Simulation”, IEICE TRANS. ELECTRON., Vol., E83-C, No.3 405-412 2000. [Non-patent document 5] K. Nishiguchi “Phase unwrapping for fiber-optic distributed acoustic sensing” Proceedings of the 47th ISCIE International Symposium on Stochastic Systems Theory and Its Applications Honolulu, Dec. 5-8, 2015. [Non-patent document 6] Takanori Saito, Kenichi Nakamura, Masaru Koshihara, Hiroshi Furukawa, "High-Performance FBG Sensor Monitor," IEICE Technical Report OFT2011-42 (2011-10) [Non-Patent Document 7] Fiber Optic Sensing Association, “Installation Considerations for Rail” Official document of the FOSA Technology Committee March 2018. [Non-patent document 8] X. Bao, DJ Webb and DA Jackson, “32km Distributed Temperature Sensor Based on Brillouin Loss in an Optical Fiber,” Optics Letters, vol. 18, no. 18, p.1561, September 1993. [Non-Patent Document 9] Ryuji Nagai, Keiichi Hashiba, and Jinglong Tang, "Recent Applications of Optical Fiber Temperature Distribution Measurement Devices," IEICE Technical Report OFT2019-37 (2019-10) Summary of the Invention [Problem to be solved by the invention]

[0007] However, if an optical fiber cable is buried directly underground as in Non-Patent Document 7, corrosion of the cable coating may damage the optical fiber inside and increase transmission loss.

[0008] Therefore, one of the objects of the present invention is to provide an improved new trough sensing system, a cable trough, and a method for measuring a physical quantity using a sensing cable, which, for example, makes it possible to ensure the required reliability of the sensing cable and to ensure the required detection sensitivity by the sensing cable. [Means for solving the problem]

[0009] The trough sensing system of the present invention includes, for example, a sensing cable including an optical fiber that transmits an optical signal, a trough made of a material including a synthetic resin material and that houses the sensing cable, and a measuring instrument that measures a physical quantity at the portion of the sensing cable that is housed in the trough based on the optical signal from the optical fiber.

[0010] In the trough sensing system, the physical quantity may be at least one of a physical quantity corresponding to vibration and a physical quantity corresponding to strain.

[0011] In the trough sensing system, the physical quantity may be temperature.

[0012] In the trough sensing system, the sensing cable may be at least partially fixed to the trough.

[0013] The trough sensing system may include an elastic member that elastically presses the sensing cable against the trough or a member fixed to the trough.

[0014] In the trough sensing system, the sensing cable may be fixed to the trough at a plurality of spaced apart locations.

[0015] In the trough sensing system, the sensing cables may be fixed to the trough at intervals equal to or less than the distance resolution of the measuring device.

[0016] In the trough sensing system, the sensing cables may be fixed to the trough at intervals of 5 m or less.

[0017] In the trough sensing system, the sensing cable may be positioned, in a cross section intersecting the longitudinal direction within the trough, closer to the input end of the vibration input to the trough than to the end opposite the input end.

[0018] The trough sensing system may include a cable separate from the sensing cable housed within the trough, and the sensing cable may be positioned closer to the end of the vibration input side to the trough than the separate cable in a cross section intersecting the longitudinal direction within the trough.

[0019] The trough sensing system may include a cable separate from the sensing cable housed within the trough, the trough being buried underground, and the sensing cable being positioned above the separate cable.

[0020] In the trough sensing system, the trough has a body with an opening that is open on the upper side and a lid that covers the opening from above, and the sensing cable may be fixed to the body at a position closer to the lid than the lower end of the body.

[0021] In the trough sensing system, the trough may have a body with an opening that is open on the upper side and a lid that covers the opening from above, and the sensing cable may be fixed to the lid.

[0022] In the trough sensing system, the measuring device may measure the physical quantity by detecting backscattered light contained in the optical signal.

[0023] In the trough sensing system, the optical fiber may be provided with an attenuation section that attenuates, by 60 dB or more, reflected light that is input from one end of the optical fiber in the longitudinal direction and reflected at the other end.

[0024] In the trough sensing system, the attenuating section may be a non-reflective end that deflects light in a direction away from the one end.

[0025] In the trough sensing system, the backscattered light may be Brillouin scattered light.

[0026] In the trough sensing system, the backscattered light may be Rayleigh scattered light.

[0027] In the trough sensing system, the core included in the optical fiber may include a fiber Bragg grating core in which the refractive index varies periodically in the longitudinal direction.

[0028] In the trough sensing system, the core included in the optical fiber may include a plurality of fiber Bragg grating cores arranged discretely in the longitudinal direction.

[0029] In the traffic sensing system, the measuring device may measure the physical quantity based on a component of a specific frequency band extracted from the optical signal.

[0030] In the traffic sensing system, the specific frequency band may be equal to or greater than 60 [Hz] and equal to or less than 100 [Hz].

[0031] The trough sensing system may include a weight disposed in the trough.

[0032] In the trough sensing system, the measuring instrument may have an event discrimination unit that discriminates, based on a measurement result of the physical quantity, an event that has occurred at a position in the sensing cable where a change in the physical quantity has occurred.

[0033] In the traffic sensing system, the event determination unit may determine the event by data analysis using machine learning.

[0034] The trough sensing system of the present invention includes, for example, a trough, a sensing cable housed within the trough and at least partially fixed to the trough, the sensing cable including an optical fiber that transmits an optical signal, and a measuring instrument that measures a physical quantity at a portion of the sensing cable housed within the trough based on the optical signal from the optical fiber.

[0035] The cable trough of the present invention is, for example, a trough that accommodates a sensing cable and has a fixing portion that fixes the sensing cable.

[0036] In the cable trough, the fixing portion may be a plurality of fixing portions spaced apart in the longitudinal direction.

[0037] The cable trough may comprise a weight attached to the trough that changes the natural frequency of the trough relative to when the weight is not provided.

[0038] A method for measuring a physical quantity using a sensing cable of the present invention includes, for example, a step of receiving an optical signal from an optical fiber included in a sensing cable housed in a trough, and a step of measuring a physical quantity at a portion of the sensing cable housed in the trough based on the received optical signal. [Effects of the Invention]

[0039] According to the present invention, for example, it is possible to provide an improved and novel trough sensing system, a cable trough, and a method for measuring a physical quantity using a sensing cable, which can ensure the required reliability of the sensing cable and the required detection sensitivity by the sensing cable. [Brief explanation of the drawings]

[0040] [Figure 1] FIG. 1 is an exemplary schematic diagram illustrating the configuration of a sensing system according to the first embodiment. [Figure 2] FIG. 2 is an exemplary schematic perspective view (including a partial cross section) of the sensing system according to the embodiment. [Figure 3] FIG. 3 is an exemplary schematic cross-sectional view of the sensing system of the embodiment, taken along a line intersecting the longitudinal direction thereof. [Figure 4] FIG. 4 is an exemplary schematic perspective view showing a part of the internal structure of a trough included in the sensing system of the embodiment. [Figure 5] FIG. 5 is an exemplary schematic cross-sectional view of a sensing optical fiber cable included in the sensing system of the embodiment. [Figure 6] FIG. 6 is an exemplary schematic cross-sectional view of a sensing system according to a first modification of the first embodiment, taken along a line intersecting the longitudinal direction. [Figure 7] FIG. 7 is an exemplary schematic cross-sectional view of a sensing system according to a second modification of the first embodiment, taken along a line intersecting the longitudinal direction. [Figure 8] FIG. 8 is an exemplary schematic cross-sectional view of a part of a trough and a sensing optical fiber cable included in a sensing system according to a third modified example of the first embodiment. [Figure 9] FIG. 9 is an exemplary schematic cross-sectional view of a part of a trough and a sensing optical fiber cable included in a sensing system according to a fourth modified example of the first embodiment. [Figure 10] FIG. 10 is an exemplary schematic cross-sectional view of a sensing optical fiber cable included in a sensing system according to a fifth modified example of the first embodiment. [Figure 11] FIG. 11 is an exemplary schematic diagram showing the configuration of a sensing system according to a sixth modified example of the first embodiment. [Figure 12] FIG. 12 is an exemplary schematic diagram illustrating the configuration of the sensing system according to the second embodiment. [Figure 13] FIG. 13 is an exemplary schematic diagram illustrating the configuration of a sensing system according to the third embodiment. [Figure 14] FIG. 14 is an exemplary schematic diagram illustrating the configuration of a sensing system according to the fourth embodiment. [Figure 15] FIG. 15 is an exemplary schematic diagram illustrating the configuration of a sensing system according to the fifth embodiment. [Figure 16] FIG. 16 is an exemplary schematic block diagram showing the configuration of a measuring device included in the sensing system of the fifth embodiment. [Figure 17] FIG. 17 is an exemplary schematic diagram illustrating the configuration of a sensing system according to the sixth embodiment. [Figure 18] FIG. 18 is an exemplary schematic cross-sectional view showing the configuration of a portion of the sensing system of the seventh embodiment, illustrating a state in which the trough is laid on the ground near the railway. [Figure 19] FIG. 19 is an exemplary schematic cross-sectional view showing the configuration of a part of the sensing system of the seventh embodiment, illustrating a state in which the trough is buried in the ground near the railway line. [Figure 20] FIG. 20 is an exemplary schematic cross-sectional view showing the configuration of a portion of the sensing system of the eighth embodiment, illustrating a state in which the trough is laid on the ground near a road. [Figure 21] FIG. 21 is an exemplary schematic cross-sectional view showing the configuration of a part of the sensing system of the eighth embodiment, illustrating a state in which the trough is buried in the ground near a road. [Figure 22] FIG. 22 is an exemplary schematic cross-sectional view intersecting the longitudinal direction of a sensing system having a trough to which a weight is attached according to a modified example of the embodiment. [Figure 23] FIG. 23 is an exemplary schematic cross-sectional view intersecting the longitudinal direction of a sensing system having a trough to which a weight is attached according to another modified example of the embodiment. [Figure 24] FIG. 24 is an exemplary schematic cross-sectional view intersecting the longitudinal direction of a sensing system having a trough to which a weight is attached according to yet another modified example of the embodiment. [Figure 25] FIG. 25 is a flowchart showing an example of a processing procedure for measurement and event discrimination in the sensing system of the embodiment. DETAILED DESCRIPTION OF THE INVENTION

[0041] Exemplary embodiments and modifications of the present invention are disclosed below. The configurations of the embodiments and modifications shown below, as well as the actions and results (effects) brought about by these configurations, are merely examples. The present invention can also be realized by configurations other than those disclosed in the following embodiments and modifications. Furthermore, according to the present invention, it is possible to obtain at least one of the various effects (including derivative effects) obtained by the configurations.

[0042] The following embodiments have similar components, and in the following description, the same reference numerals will be used to designate the similar components, and redundant explanations may be omitted.

[0043] In the drawings, the X direction is represented by an arrow X, the Y direction is represented by an arrow Y, and the Z direction is represented by an arrow Z. In each cross section intersecting with the X direction, the X, Y, and Z directions intersect and are perpendicular to each other. The X direction may be referred to as the longitudinal direction of the trough 10, the Y direction may be referred to as the width direction of the trough 10, and the Z direction may be referred to as the height direction of the trough 10. The trough 10 is often installed so that the Z direction is upward, but the Z direction does not necessarily have to face upward. In addition, although each drawing illustrates a configuration in which the trough 10 extends straight, this is not limited thereto. In reality, the trough 10 may bend up and down depending on the elevation of the location where it is laid or buried, or may bend along a road or railroad. In addition, in each drawing, the cross section of the cable or optical fiber may be indicated by simple hatching.

[0044] [First embodiment] FIG. 1 is a schematic cross-sectional view showing the configuration of a sensing system 1 of a first embodiment. The sensing system 1 of this embodiment includes a trough 10, a sensing optical fiber cable 20, and a measuring instrument 100. The trough 10 houses the sensing optical fiber cable 20. In other words, the sensing optical fiber cable 20 is routed within the trough 10. The measuring instrument 100 receives an optical signal transmitted through at least one sensing optical fiber 21 in the sensing optical fiber cable 20, measures a physical quantity at a portion of the sensing optical fiber cable 20 housed within the trough 10 based on the received optical signal, and measures vibrations and sounds occurring around the trough 10 corresponding to the physical quantity. The physical quantity measured by the sensing system 1 is, for example, a physical quantity representing vibration, a physical quantity representing strain, temperature, etc. The sensing optical fiber cable 20 is an example of a sensing cable.

[0045] Fig. 2 is a perspective view of the sensing system 1. Fig. 3 is a cross-sectional view of the sensing system 1 taken along a plane intersecting the longitudinal direction. Fig. 4 is a perspective view showing a part of the internal structure of the trough 10.

[0046] As shown in FIGS. 2 to 4, the trough 10 includes a body 11 and a lid 12. Also, as shown in FIG. 3, the body 11 includes a plate-like bottom wall 11a extending with a substantially constant width and a substantially constant thickness, and two plate-like side walls 11b extending with a substantially constant height and a substantially constant thickness in the height direction from both widthwise ends of the bottom wall 11a. The two side walls 11b are substantially parallel. The body 11 includes an opening 11c that opens in the Z direction. In other words, the body 11 has a groove-like shape with a substantially U-shaped cross section, including the opening 11c that opens in the Z direction. The opening 11c extends in the longitudinal direction with a substantially constant width. The opening 11c is covered by the lid 12. The lid 12 has a plate-like shape extending with a substantially constant width and a substantially constant thickness. The lid 12 and the bottom wall 11a are substantially parallel. With this configuration, the trough 10 forms a storage chamber R as a linearly extending closed space having a substantially rectangular cross-sectional shape. In addition to the sensing optical fiber cable 20, cables other than the sensing optical fiber cable 20, such as an optical fiber cable 30 for communication and a metal cable 40 for power supply, are stored within the storage chamber R. The sensing optical fiber cable 20 is an example of a sensing cable. In this embodiment, a spacer 13 is provided between the body 11 and the lid 12, and a connecting member 14 that supports the lid 12 and the spacer 13 is provided on the side wall 11b of the body 11, but the spacer 13 and the connecting member 14 are not essential. The shape and structure of the trough 10 can be implemented with various other configurations.

[0047] The trough 10 is made of a material, such as a material containing synthetic resin, that is capable of transmitting vibrations, sound, external forces, etc. acting on the trough 10 from the outside to the sensing optical fiber cable 20 inside the trough 10, or a material that can transmit them more suitably.

[0048] Furthermore, in this embodiment, the sensing optical fiber cable 20 is fixed to the trough 10 so that external vibrations and the like are transmitted to the sensing optical fiber cable 20 without being attenuated.

[0049] 3 is a cross-sectional view of the sensing optical fiber cable 20 at a position where it is fixed to the trough 10 by the mounting member 16. As shown in FIG. 3, the sensing optical fiber cable 20 is supported by a support member 15 fixed to the side wall 11b of the trough 10, and is sandwiched between the support member 15 and the mounting member 16 fixed to the support member 15, thereby being fixed to the support member 15, the mounting member 16, and ultimately to the trough 10. The support member 15 and the mounting member 16 may be fixed to the trough 10 by fasteners such as screws, or by welding or fusion bonding. The support member 15 and the mounting member 16 are examples of fixing parts.

[0050] As shown in FIG. 3 , the sensing optical fiber cable 20 is positioned closer to the upper end 10b of the lid 12 than the lower end 10a of the bottom wall 11a, and is fixed to the side wall 11b of the body 11. The sensing optical fiber cable 20 is also positioned closer to the end 10b than the communication optical fiber cable 30 and the metal cable 40. With this configuration, when vibrations or forces are input from the end 10b in a cross section intersecting the longitudinal direction, attenuation of the input vibrations or forces by the trough 10, the optical fiber cable 30, the metal cable 40, etc. can be suppressed, thereby further improving the detection sensitivity of the sensing optical fiber cable 20. The end 10b is an example of an end on the vibration or force input side. It has been experimentally confirmed that this arrangement is more effective when the trough 10 is buried in the ground G, as shown in FIG. 2 . In this case, at least a portion of the lid 12 of the trough 10 may be exposed above the ground G, or the trough 10 may be buried underground without being exposed above the ground G.

[0051] 4, the sensing optical fiber cable 20 is at least partially fixed to the trough 10. In this embodiment, the sensing optical fiber cable 20 is, for example, partially fixed to the trough 10 at a plurality of locations spaced apart at intervals S in the longitudinal direction. In this case, it is preferable that the interval S in the longitudinal direction be equal to or less than the distance resolution in the measurement of the measuring instrument 100 (for example, equal to or less than 5 m).

[0052] Fig. 5 is a cross-sectional view of the sensing optical fiber cable 20 of the first embodiment. As shown in Fig. 5, in the first embodiment, the sensing optical fiber cable 20 includes a tension member 22 extending in the longitudinal direction at the center of the cross section, a sensing optical fiber 21 and other optical fibers 23 arranged to surround the periphery of the tension member 22 and extending in the longitudinal direction, and a coating 24 surrounding the outer periphery. The sensing optical fiber cable 20 may include two or more sensing optical fibers 21. The sensing optical fiber cable 20 may also include a coated conductor that transmits electrical signals or power, instead of the optical fiber 23, or a dummy fiber that does not transmit signals, power, or the like. The sensing optical fiber 21 and other optical fibers 23 may also extend in a multiple spiral shape around the tension member 22.

[0053] The above-mentioned sensing optical fiber 21 may be a single-mode optical fiber conforming to G.652, G.653, G.654, G.655, G.656, or G.657 specified by the International Telecommunication Union.

[0054] Next, the operating principle of the sensing system 1 of the first embodiment will be described.

[0055] 1, the sensing optical fiber cable 20 is connected to a port 100a of the measuring instrument 100, thereby optically connecting a sensing optical fiber 21 included in the sensing optical fiber cable 20 to an optical system inside the measuring instrument 100. The signal light output from the measuring instrument 100 is transmitted within the sensing optical fiber 21.

[0056] Acoustic waves and vibration waves generated around the trough 10 are transmitted to the trough 10 and further transmitted through the trough 10 to the sensing optical fiber 21 housed within the trough 10. This causes the sensing optical fiber 21 to expand and contract, changing the core refractive index. This change in the core refractive index changes the backscattered light characteristics relative to the signal light.

[0057] In backward Rayleigh scattering, the wavelength of the light does not change, but the phase and intensity of the light change.

[0058] When measuring Rayleigh scattered light, a distributed acoustic sensor (hereinafter referred to as DAS) can be used. DAS is described in Non-Patent Document 5.

[0059] When using a DAS, the measuring instrument 100 outputs pulsed signal light, which is input to the sensing optical fiber 21.

[0060] In the sensing optical fiber 21, Rayleigh scattered light is generated along the longitudinal direction due to the signal light. The Rayleigh scattered light is transmitted through the sensing optical fiber 21 in the direction opposite to the traveling direction of the signal light, and is input from the sensing optical fiber 21 to the measuring instrument 100.

[0061] When a vibration wave or an acoustic wave is generated around a certain point in the longitudinal direction of the sensing optical fiber 21, the phase and intensity of the light in the Rayleigh scattering that occurs in the sensing optical fiber 21 at that point changes depending on the expansion and contraction of the sensing optical fiber 21.

[0062] In addition, in the embodiment for detecting Rayleigh scattered light, the sensing optical fiber 21 can be an optical fiber having a core in which a fiber Bragg grating (hereinafter referred to as FBG) whose refractive index changes periodically in the longitudinal direction is continuously formed over the entire length.

[0063] The measuring instrument 100 can detect the vibration wave or acoustic wave acting on the sensing optical fiber 21 from the change in the phase or intensity of the received Rayleigh scattered light.

[0064] In backward Brillouin scattering, the wavelength of light changes and the Brillouin frequency also changes.

[0065] When measuring Brillouin scattered light, the principles of Brillouin optical time domain reflectometry (hereinafter referred to as BOTDR) or Brillouin optical correlation domain reflectometry (hereinafter referred to as BOCDR) can be used. BOTDR is described in Non-Patent Document 2, and BOCDR is described in Non-Patent Document 3.

[0066] When using a BOTDR, the measuring instrument 100 outputs pulsed signal light, which is input to the sensing optical fiber 21.

[0067] When using BOCDR, the measuring instrument 100 outputs a signal light whose frequency is sinusoidally modulated. The signal light is input to the sensing optical fiber 21.

[0068] Unlike the case of the DAS described above, when a BOTDR or BOCDR is used, Brillouin backscattered light generated in the longitudinal direction due to the signal light is observed from the sensing optical fiber 21. In this case, the measuring instrument 100 detects the frequency components of the Brillouin scattered light and detects changes in strain occurring in the optical fiber.

[0069] In this way, the measuring instrument 100 can detect the vibration wave or acoustic wave acting on the sensing optical fiber 21 at each position in the longitudinal direction by detecting the backscattered light due to Rayleigh scattering or Brillouin scattering.

[0070] [First Modification] Fig. 6 is a cross-sectional view of the sensing system 1 according to a first modified example of the first embodiment. As shown in Fig. 6, the sensing optical fiber cable 20 may be fixed to the lid 12. Even with this configuration, when vibration or force is input from the end 10a of the lid 12, it is possible to reduce attenuation factors in the transmission path of the vibration or force from the lid 12 to the sensing optical fiber cable 20, thereby further improving the detection sensitivity of the sensing optical fiber cable 20.

[0071] [Second Modification] Fig. 7 is a cross-sectional view of a sensing system 1 according to a second modification of the first embodiment. As shown in Fig. 7, the sensing optical fiber 21 may be included in a communication optical fiber cable 30 together with other communication optical fibers (not shown). In this case, the communication optical fiber cable 30 is also the sensing optical fiber cable 20, and is an example of a sensing cable. Furthermore, the optical fiber cable 30 including the sensing optical fiber 21 may be fixed to the bottom wall 11a or the side wall 11b of the trough 10 by a mounting member 16. With such a configuration, the same effects as those of the above-described embodiment and modifications can be obtained.

[0072] [Third Modification] Fig. 8 is a cross-sectional view of a part of the trough 10 and the sensing optical fiber cable 20 in a third modified example of the first embodiment. As shown in Fig. 8, the sensing system 1 may include an elastic member 17 that elastically presses the sensing optical fiber cable 20 against the trough 10 or a support member 15 that is a member fixed to the trough 10. With this configuration, the sensing optical fiber cable 20 can be more reliably brought into close contact with the trough 10 or a member fixed to the trough 10, and vibrations and forces can be more easily transmitted from the trough 10 to the sensing optical fiber cable 20.

[0073] [Fourth Modification] Fig. 9 is a cross-sectional view of a portion of the trough 10 and the sensing optical fiber cable 20 of a fourth modified example of the first embodiment. As shown in Fig. 9, the elastic member 17 may elastically press the sensing optical fiber cable 20 against the support member 15 and the mounting member 16. Although not shown, the elastic member 17 may also elastically press the sensing optical fiber cable 20 only against the mounting member 16. With this configuration, the same effect as in the third modified example can be obtained. Furthermore, in this case, since the elastic member 17 presses the sensing optical fiber cable 20 toward the input side of the vibration or force, the vibration or force is more easily transmitted to the sensing optical fiber cable 20.

[0074] [Fifth Modification] Fig. 10 is a cross-sectional view of a sensing optical fiber cable 20 according to a fifth modified example of the first embodiment. As shown in Fig. 10, the sensing optical fiber cable 20 has a tension member 22 and a plurality of optical fibers 25 arranged so as to surround the periphery of the tension member 22, and at least one of the plurality of optical fibers 25 may be used as the sensing optical fiber 21. Note that each of the optical fibers 25 may be covered with a coating.

[0075] [Sixth Modification] Fig. 11 is a schematic configuration diagram of a sensing system 1 according to a sixth modified example of the first embodiment. As shown in Fig. 11, when the sensing optical fiber cable 20 has two sensing optical fibers 21, the two sensing optical fibers 21 may be optically connected at an end 20a of the sensing optical fiber cable 20 on the opposite side from the measuring instrument 100.

[0076] In this case, the signal light sent from the measuring instrument 100 is transmitted through the sensing optical fiber 21 that travels back and forth within the sensing optical fiber cable 20, and vibration at one point in the longitudinal direction of the sensing optical fiber cable 20 affects Rayleigh scattering at two points in the series of sensing optical fibers 21.

[0077] Therefore, in this configuration, the obtained distribution data of the vibration wave or acoustic wave is folded back and averaged, thereby making it possible to obtain measurement results with reduced noise.

[0078] Furthermore, although not shown, further noise reduction can be achieved by optically connecting more sensing optical fibers 21 and folding them back at both longitudinal ends of the sensing optical fiber cable 20 so that they travel back and forth multiple times within the sensing optical fiber cable 20.

[0079] As explained above, in the above-mentioned embodiments and variants, by surrounding the sensing optical fiber cable 20 (sensing cable) with a trough 10 made of a material including a synthetic resin material, the required reliability of the sensing optical fiber cable 20 can be ensured, and by transmitting vibrations and external forces from outside the trough 10 to the sensing optical fiber cable 20 via the trough 10, the required detection sensitivity of the sensing optical fiber cable 20 can be ensured.

[0080] Furthermore, in the above-described embodiments and variants, since the sensing optical fiber cable 20 is fixed to the trough 10, the detection sensitivity of the sensing optical fiber cable 20 can be increased compared to when it is not fixed to the trough 10.

[0081] [Second embodiment] FIG. 12 is a schematic configuration diagram of a sensing system 1A of the second embodiment. As shown in FIG. 12, FBGs 21f are arranged discretely in the longitudinal direction of a sensing optical fiber 21A of this embodiment, for example, at predetermined intervals. As described in Non-Patent Document 6, the reflection wavelength of an FBG changes in response to expansion and contraction. Therefore, when FBGs 21f are arranged discretely in the longitudinal direction of the sensing optical fiber 21, the FBGs 21f of the sensing optical fiber 21 expand and contract in response to vibrations or sound generated around the trough 10, changing the reflection wavelength. In this case, the measuring instrument 100 can measure the vibrations or sound acting on the sensing optical fiber 21 based on the change in the wavelength of the light reflected by the FBGs 21f.

[0082] [Third embodiment] 13 is a schematic configuration diagram of a sensing system 1B of the third embodiment. As shown in FIG. 13, a non-reflection end 21b is provided at an end 21a of the sensing optical fiber 21 of this embodiment on the side opposite the measuring instrument 100. The non-reflection end 21b reduces reflection at the end of the sensing optical fiber 21 and is an example of an attenuation section. The non-reflection end 21b can be realized, for example, as an end face obtained by cutting the end 21a at an angle and deflecting light in a direction away from the end on the measuring instrument 100 side, a member added to the end 21a made of a material with a higher refractive index than the core, or a member that absorbs or attenuates light.

[0083] The signal light input from the measuring device 100 to the sensing optical fiber 21 is reflected at the end 21a and attenuated by the non-reflection end 21b provided at the end 21a.

[0084] Generally, the intensity of Rayleigh scattered light and Brillouin scattered light generated in an optical fiber is small; in the case of Rayleigh scattered light, it is about 60 dB smaller than the input signal light, and in the case of Brillouin scattered light, it is about 75 dB smaller than the input signal light.

[0085] A light-receiving element (not shown) provided in the measuring instrument 100 for receiving Rayleigh scattered light or Brillouin scattered light detects such weak light. Therefore, if the intensity of the light reflected by the end 21a of the sensing optical fiber 21 is high, the photoelectric conversion level of the light-receiving element may become saturated or the light-receiving element may be destroyed. In this regard, according to this embodiment, the reflected light can be attenuated by the non-reflecting end 21b, so that such undesirable phenomena can be avoided.

[0086] In addition, it has been found that in the above configuration, the attenuation of the reflected light at the non-reflection end 21b is preferably about 60 dB.

[0087] [Fourth embodiment] Fig. 14 is a schematic configuration diagram of a sensing system 1C of the fourth embodiment. As shown in Fig. 14, in this embodiment, as in the sixth modified example (see Fig. 11), the sensing optical fiber cable 20 has two sensing optical fibers 21, and the two sensing optical fibers 21 are optically connected at an end 20a of the sensing optical fiber cable 20 on the opposite side from the measuring instrument 100.

[0088] However, in this embodiment, two ends 21c and 21d of sensing optical fiber 21 on the measuring device 100 side are connected to ports 100a and 100b of measuring device 100, respectively.

[0089] The measuring device 100 detects backscattered light by Brillouin optical correlation domain analysis (hereinafter referred to as BOTDA) or Brillouin optical time domain analysis (hereinafter referred to as BOCDA). BOTDA is described in Non-Patent Document 8, and BOCDA is described in Non-Patent Document 4.

[0090] When BOTDA is used, continuous signal light (indicated by the solid arrow in Figure 14) is input to the sensing optical fiber 21 from port 100a of the measuring instrument 100, and pulsed excitation light (indicated by the dashed arrow in Figure 14) is input to the sensing optical fiber 21 from port 100b.

[0091] On the other hand, when BOCDA is used, frequency-modulated signal light is input from port 100a to the sensing optical fiber 21, and pulsed excitation light is input from port 100b to the sensing optical fiber 21. In this case, the signal light is modulated with a sine wave of a frequency equivalent to the Brillouin frequency shift (Stokes shift) of the sensing optical fiber 21 that is the measurement target.

[0092] The signal light output from port 100a and input to end 21c is output from end 21d via sensing optical fiber 21 and input to port 100b of the measuring instrument 100. On the other hand, the excitation light output from port 100b and input to end 21d is output from end 21c via sensing optical fiber 21 and input to port 100a of the measuring instrument 100.

[0093] During transmission, the excitation light causes Brillouin scattering along the longitudinal direction of the sensing optical fiber 21, and the signal light is Brillouin amplified. The Brillouin amplified signal light is input to the port 100b of the measuring instrument 100.

[0094] The measuring instrument 100 obtains the amount of frequency change from the frequency components of the Brillouin amplified signal light, and calculates the strain distribution in the longitudinal direction of the sensing optical fiber 21 from this value.

[0095] In this case too, the signal light sent from the measuring instrument 100 is transmitted through the sensing optical fiber 21 that travels back and forth within the sensing optical fiber cable 20, and vibration at one point in the longitudinal direction of the sensing optical fiber cable 20 affects Brillouin scattering at two points in the series of sensing optical fibers 21.

[0096] Therefore, in this embodiment as well, the obtained distribution data is folded and averaged, thereby making it possible to obtain measurement results with reduced noise.

[0097] [Fifth embodiment] Fig. 15 is a schematic configuration diagram of a sensing system 1D of the fifth embodiment. As shown in Fig. 15, in this embodiment, similar to the fourth embodiment (see Fig. 14), the sensing optical fiber cable 20 has two sensing optical fibers 21, and the two sensing optical fibers 21 are optically connected at an end 20a of the sensing optical fiber cable 20 on the opposite side from the measuring instrument 100D.

[0098] Also in this embodiment, two ends 21c and 21d of sensing optical fiber 21 on the measuring device 100 side are connected to ports 100a and 100b of measuring device 100, respectively.

[0099] 16 is a block diagram showing the configuration of measuring device 100D. As shown in FIG. 16, in this embodiment, measuring device 100D includes light source 101, couplers 102a and 102b, light receiving element 103, time fluctuation detection unit 104, and fluctuation frequency detection unit 105.

[0100] The signal light output from the light source 101 is split by the coupler 102a. One of the signal lights split by the coupler 102a is input to the sensing optical fiber 21 from the port 100a, and the other is input to the coupler 102b.

[0101] The signal light output from the end 21d of the sensing optical fiber 21 is input to the coupler 102b via the port 100b. The coupler 102b multiplexes the signal light branched by the coupler 102a with the signal light from the port 100b that has passed through the sensing optical fiber 21. The light-receiving element 103 converts the signal light multiplexed by the coupler 102a into an electrical signal.

[0102] The time variation detection unit 104 detects the change over time in the intensity of the signal light (signal waveform), and the variation frequency detection unit 105 analyzes the frequency components by performing a fast Fourier transform on the signal waveform.

[0103] Through the above-described steps, the measuring instrument 100D can measure the temporal changes in vibrations and sounds occurring throughout the entire sensing optical fiber cable 20, as well as their frequency components.

[0104] Although the fifth embodiment is a system for detecting transmitted light rather than backscattered light, it can be used in combination with the first to fourth embodiments, which detect backscattered light. In this case, each embodiment may be provided with a separate measuring instrument 100, and may be realized using another sensing optical fiber 21 in the sensing optical fiber cable 20.

[0105] [Sixth embodiment] Fig. 17 is a schematic configuration diagram of a sensing system 1E of the sixth embodiment. As shown in Fig. 17, in this embodiment, similar to the fifth embodiment (see Fig. 15), the sensing optical fiber cable 20 has two sensing optical fibers 21. However, as shown in Fig. 17, in this embodiment, the end portions 21a of these two sensing optical fibers 21 are not connected to each other.

[0106] In this embodiment, the measuring instrument 100 has the function of detecting vibrations and sound by detecting backscattered light, as in the first to third embodiments, and also has the function of measuring the temperature distribution in the longitudinal direction of the sensing optical fiber 21.

[0107] In addition to BOTDR and BOCDR, a Raman optical time domain reflectometer (hereinafter referred to as ROTDR) can be used to measure the temperature distribution in the longitudinal direction of the sensing optical fiber 21. ROTDR is described in Non-Patent Document 9.

[0108] The measuring instrument 100 inputs signal light for detecting vibrations and sound and signal light for detecting temperature into separate sensing optical fibers 21, and can measure temperature as well as vibrations and sound based on backscattered light obtained from the sensing optical fiber 21 in response to the signal light. The measuring instrument 100 can calculate the temperature distribution in the longitudinal direction of the sensing optical fiber 21.

[0109] According to this embodiment, it is possible to measure temperature as well as vibration and sound.

[0110] [Seventh embodiment] 18 and 19 are cross-sectional views showing a part of the sensing system 1 of the seventh embodiment, which includes a trough 10 provided along a railway line 1001. Fig. 18 shows the state where the sensing system is installed on the ground G near the railway line 1001, and Fig. 19 shows the state where the sensing system is buried underground near the railway line 1001.

[0111] In this configuration, vibrations generated on the track 1001 due to the passage of a train or the like propagate to the surrounding area. The vibrations propagate to the trough 10 installed near the track 1001, causing the trough 10 to vibrate. The measuring instrument 100 receives an optical signal transmitted by a sensing optical fiber 21 housed in the trough 10, and measures the vibrations based on the received optical signal. Note that the vibrations measured by the sensing system 1 are not limited to vibrations caused by the running of a train, and various vibrations caused by, for example, falling rocks, the passage of a vehicle at a railroad crossing, the intrusion of animals or humans onto the tracks, etc. can also be measured.

[0112] [Eighth embodiment] 20 and 21 are cross-sectional views showing a part of the sensing system 1 of the eighth embodiment, which includes a trough 10 provided along a road 1002. Fig. 20 shows the state where the sensing system 1 is laid on the ground G near the road 1002, and Fig. 21 shows the state where the sensing system 1 is buried underground near the road 1002.

[0113] In this configuration, vibrations generated on the road 1002 due to the passage of a vehicle or the like propagate to the surrounding area. The vibrations propagate to the trough 10 installed near the road 1002, causing the trough 10 to vibrate. The measuring device 100 measures the vibrations based on an optical signal transmitted by the sensing optical fiber 21 housed in the trough 10. Note that the vibrations measured by the sensing system 1 are not limited to vibrations generated by the running of a vehicle.

[0114] [Findings gained through experiments] The inventors conducted an experiment in which a trough 10 containing a sensing optical fiber 21 was buried near a road 1002, and vibrations generated when a person, bicycle, automobile, etc. passed through the road 1002 were measured from the optical signals transmitted through the sensing optical fiber 21. For comparison, vibrations were also measured under the same conditions when a sensing optical fiber cable 20 having a sensing optical fiber 21 was directly buried near the road 1002 without using the trough 10. The following phenomena were confirmed through such comparative experiments. [1] In measurements based on the optical signal of the sensing optical fiber 21 housed in the trough 10, higher frequency vibrations were detected compared to when the sensing optical fiber cable 20 was directly buried in the ground G. At lower frequencies, noise is large and the S / N ratio may be low. In other words, according to the sensing systems 1, 1A to 1E of the above embodiments in which the sensing optical fiber 21 (sensing optical fiber cable 20) is housed in the trough 10, it may be possible to improve the vibration detection sensitivity compared to when the sensing optical fiber 21 is not housed in the trough 10. [2] Measurements based on the optical signal of the sensing optical fiber 21 housed in the trough 10 detected vibrations in the same frequency band regardless of the object passing through. This indicates that natural vibrations may occur in the trough 10 when vibrations are transmitted from the vibration source, and that the natural vibrations may be detected by the sensing optical fiber 21 (sensing optical fiber cable 20). In this case, it is possible to further increase the vibration detection sensitivity by adjusting the specifications of the trough 10, such as the material, shape, and structure. In experiments, the frequency band in question was between 60 Hz and 100 Hz.

[0115] [Modification with weight attached to the trough] 22 to 24 are cross-sectional views of the sensing system 1 showing examples (modifications) in which a weight 18 is attached to adjust the vibration of the trough 10. In the example of FIG. 22, the weight 18 is attached to the side wall 11b, in the example of FIG. 23, the weight 18 is attached to the lid 12, and in the example of FIG. 24, the weight 18 is attached to the support member 15. By attaching the weight 18 to the trough 10 in this way, the vibration frequency and vibration mode of the trough 10 can be adjusted to appropriate values ​​compared to when the weight 18 is not attached, thereby further increasing the detection sensitivity of vibration and sound by the sensing optical fiber 21 (sensing optical fiber cable 20). The weight and attachment position of the weight 18 are appropriately set depending on the target vibration, the specifications of the trough 10, and the like. The weight 18 may be molded integrally with each member during the manufacturing of the member, or may be attached to each member using a fastener such as a screw, an adhesive, or the like.

[0116] [Processing Procedure] 25 is a flowchart showing the processing procedure performed by the sensing system 1 of the above embodiment. Note that similar processing can be performed in the above-described modified examples and the sensing systems 1A to 1E of other embodiments.

[0117] First, the measuring instrument 100 emits and receives light (S1). That is, in S1, the measuring instrument 100 outputs an optical signal and receives signal light and excitation light from the sensing optical fiber 21 to which the optical signal has been input.

[0118] Next, the measuring instrument 100 measures a physical quantity by the above-described method based on the optical signal received from the sensing optical fiber 21 (S2). The physical quantity acquired in S2 may be, for example, a physical quantity representing vibration, a physical quantity representing sound, a physical quantity representing strain, or temperature, or may be a physical quantity calculated from a predetermined correlation based on these measured physical quantities.

[0119] Next, measuring instrument 100 discriminates the event (S3). In S3, the computer included in measuring instrument 100 acquires output parameters for input parameters based on, for example, a trained model stored as a program in a storage unit, and discriminates the event based on the output parameters. Here, discriminable events include, for example, an object corresponding to a measured physical quantity, the object's speed, position, etc. Examples of objects that are the subject of an event include humans, animals, vehicles (bicycles, automobiles, railroad cars, etc.), and natural objects (falling rocks, etc.). The computer included in measuring instrument 100 is an example of an event discrimination unit. Note that, in S3, an object that is the subject of an event not classified by a previous trained model, i.e., a new object different from previously classified objects, may be classified. Furthermore, the trained model can be obtained by machine learning using training data in which measurement data measured using sensing system 1 is associated with a label indicating the corresponding event. A deep learning method such as a neural network can be used as the machine learning method.

[0120] Next, measuring instrument 100 performs machine learning based on the measured data, physical quantities, and determined events (S4), and updates or stores the results of the machine learning in the trained model (S5). Note that updating is a process of deleting a portion of past data corresponding to new data, and storing is a process of adding new data to past data without deleting it.

[0121] While the above describes exemplary embodiments and modifications of the present invention, these are merely examples and are not intended to limit the scope of the invention. The above embodiments and modifications can be implemented in various other forms, and various omissions, substitutions, combinations, and modifications can be made without departing from the spirit of the invention. Furthermore, the specifications of each configuration, shape, and the like (structure, type, direction, model, size, length, width, thickness, height, number, arrangement, position, material, etc.) can be modified as appropriate. [Explanation of symbols]

[0122] 1, 1A to 1E: Sensing system 10...Trough 10a...end 10b...end 11...Body 11a...Bottom wall 11b…Side wall 11c…Aperture 12…Lid 13...Spacer 14...Connecting member 15...Support member (fixed part) 16...Mounting member (fixing part) 17...Elastic member 18... Weight 20...Sensing optical fiber cable (sensing cable) 20a...End 21, 21A...Sensing optical fiber (optical fiber) 21a...end 21b…Non-reflection end 21c...end 21d...end 21f…FBG 22...Tension member 23...Optical fiber 24...Sheathing 25...Optical fiber 30...Fiber optic cable 40...Metal cable 100,100D…Measuring instrument 100a...Port 100b...port 101…Light source 102a... Coupler 102b... Coupler 103...Light receiving element 104...Time variation detection unit 105...Fluctuation frequency detection unit 1001...Railway 1002…road G...ground R…Containment room S...Spacing X…direction Y...direction Z…direction

Claims

1. a trough made of a material including a synthetic resin material; a sensing cable received within the trough and at least partially secured to the trough, the sensing cable including an optical fiber for transmitting an optical signal; a measuring instrument that measures a physical quantity that changes in the trough or around the trough at a portion of the sensing cable that is fixed to the trough based on the optical signal from the optical fiber; and Equipped with A trough sensing system in which the sensing cable is positioned, in a cross section intersecting the longitudinal direction within the trough, closer to the input end of the vibration input to the trough than to the end opposite the input end.

2. a trough made of a material including a synthetic resin material; a sensing cable received within the trough and at least partially secured to the trough, the sensing cable including an optical fiber for transmitting an optical signal; a measuring instrument that measures a physical quantity that changes in the trough or around the trough at a portion of the sensing cable that is fixed to the trough based on the optical signal from the optical fiber; and a cable separate from the sensing cable housed in the trough; Equipped with A trough sensing system in which the sensing cable is positioned closer to the end of the vibration input side to the trough than the other cable in a cross section intersecting the longitudinal direction within the trough.

3. a trough made of a material including a synthetic resin material; a sensing cable received within the trough and at least partially secured to the trough, the sensing cable including an optical fiber for transmitting an optical signal; a measuring instrument that measures a physical quantity that changes in the trough or around the trough at a portion of the sensing cable that is fixed to the trough based on the optical signal from the optical fiber; and a cable separate from the sensing cable housed in the trough; Equipped with The trough is buried in the ground; A trough sensing system, wherein the sensing cable is positioned above the other cable.

4. a trough made of a material including a synthetic resin material; a sensing cable received within the trough and at least partially secured to the trough, the sensing cable including an optical fiber for transmitting an optical signal; a measuring instrument that measures a physical quantity that changes in the trough or around the trough at a portion of the sensing cable that is fixed to the trough based on the optical signal from the optical fiber; and Equipped with The trough has a body having an opening that is open on the upper side and a lid that covers the opening from above, A trough sensing system, wherein the sensing cable is fixed to the body at a position closer to the lid than the lower end of the body.

5. a trough made of a material including a synthetic resin material; a sensing cable received within the trough and at least partially secured to the trough, the sensing cable including an optical fiber for transmitting an optical signal; a measuring instrument that measures a physical quantity that changes in the trough or around the trough at a portion of the sensing cable that is fixed to the trough based on the optical signal from the optical fiber; and Equipped with The trough has a body having an opening that is open on the upper side and a lid that covers the opening from above, The trough sensing system, wherein the sensing cable is fixed to the lid.

6. 6. The trough sensing system according to claim 1, wherein the physical quantity is at least one of a physical quantity corresponding to vibration and a physical quantity corresponding to strain.

7. 7. The trough sensing system according to claim 1, wherein the physical quantity is a temperature.

8. The trough sensing system according to any one of claims 1 to 7, further comprising an elastic member that elastically presses the sensing cable against the trough or against a member fixed to the trough.

9. The trough sensing system according to claim 7 or 8, wherein the sensing cable is fixed to the trough at a plurality of spaced apart locations.

10. The trough sensing system according to claim 9 , wherein the sensing cables are fixed to the trough at intervals equal to or less than the distance resolution of the measuring device.

11. The trough sensing system according to claim 10 , wherein the sensing cables are fixed to the trough at intervals of 5 m or less.

12. 12. The trough sensing system according to claim 1, wherein the measuring device measures the physical quantity by detecting backscattered light contained in the optical signal.

13. 13. The trough sensing system according to claim 12, wherein the optical fiber is provided with an attenuation section that attenuates by 60 dB the light that is input from one end of the optical fiber in the longitudinal direction and reflected at the other end.

14. The trough sensing system of claim 13 , wherein the attenuating portion is a non-reflective end that deflects light away from the one end.

15. The trough sensing system according to any one of claims 12 to 14, wherein the backscattered light is Brillouin scattered light.

16. The trough sensing system according to any one of claims 12 to 14, wherein the backscattered light is Rayleigh scattered light.

17. The trough sensing system according to any one of claims 13 to 16, wherein the core included in the optical fiber includes a fiber Bragg grating core whose refractive index changes periodically in the longitudinal direction.

18. The trough sensing system according to any one of claims 13 to 16, wherein the core included in the optical fiber includes a plurality of fiber Bragg grating cores arranged discretely in the longitudinal direction.

19. 17. The traffic sensing system according to claim 1, wherein the measuring device measures the physical quantity based on a component of a specific frequency band extracted from the optical signal.

20. 20. The trough sensing system according to claim 19, wherein the specific frequency band is equal to or greater than 60 [Hz] and equal to or less than 100 [Hz].

21. The trough sensing system according to any one of claims 1 to 19, comprising a weight provided in the trough.

22. A trough sensing system as described in any one of claims 1 to 21, wherein the measuring instrument has an event discrimination unit that discriminates an event that occurred at a position in the sensing cable where a change in the physical quantity occurred based on the measurement result of the physical quantity.

23. The traffic sensing system according to claim 22 , wherein the event determination unit determines the event by data analysis using machine learning.

24. Trough and a sensing cable received within the trough and at least partially secured to the trough, the sensing cable including an optical fiber for transmitting an optical signal; a measuring instrument that measures a physical quantity that changes in the trough or around the trough at a portion of the sensing cable that is fixed to the trough based on the optical signal from the optical fiber; and Equipped with A trough sensing system in which the sensing cable is positioned, in a cross section intersecting the longitudinal direction within the trough, closer to the input end of the vibration input to the trough than to the end opposite the input end.

25. The trough included in the trough sensing system according to any one of claims 1 to 24, Made of materials including synthetic resin materials, A housing for housing the sensing cable; A trough having a fixing portion for fixing the sensing cable.

26. 26. The trough of claim 25, wherein the fastening portion is a plurality of longitudinally spaced fastening portions.

27. 27. The trough of claim 25 or 26, comprising a weight provided in the trough that changes the natural frequency of the trough relative to when the weight is not provided.

28. A method for measuring a physical quantity that changes in the trough or around the trough using the sensing cable included in the trough sensing system according to any one of claims 1 to 24, receiving the optical signal from the optical fiber included in the sensing cable partially secured to the trough; measuring a physical quantity at a portion of the sensing cable housed in the trough based on the received optical signal; A method for measuring a physical quantity, comprising:

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