JP4011196B2 - Optical fiber sensor - Google Patents

Description

[0001]
BACKGROUND OF THE INVENTION
The present invention relates to an optical fiber sensor.
[0002]
[Prior art]
In order to avoid the occurrence of disasters due to erosion on riverbanks and coasts, it is necessary to perform frequent patrols to grasp the progress of erosion. However, since the survey is dependent on humans and the efficiency is low, in recent years, a technique for measuring the erosion state automatically and in real time has been studied.
For example, in a technique using an acoustic sounding device, a riverbank or a coastal position is detected using reflection of ultrasonic waves by an appropriately installed sounding sounding device that is not affected by erosion. This method can automatically and in real time measure the erosion status of riverbanks and coasts. However, in order to measure over a wide area of riverbanks and coasts, it is necessary to install many expensive acoustic measuring instruments. The cost becomes enormous.
[0003]
Japanese Laid-Open Patent Publication No. 8-75595 proposes a sensor that detects anomalies in the ground using an optical fiber sensor (hereinafter referred to as “optical fiber sensor”). It can be considered to install and detect the presence or absence of erosion. For example, the optical fiber sensor is installed in a borehole formed along the scouring direction of a river or ocean at the shore or coast, and the Raman of light incident on the optical fiber extending along the borehole is installed. It is conceivable to detect anomalies by measuring the temperature change of the optical fiber by measuring the backscattered light due to scattering. In the optical fiber, the Raman scattering of the incident light changes depending on the temperature change. Therefore, when the backscattered light due to the Raman scattering is measured, the presence or absence of abnormality can be determined from the change in the received light intensity of the backscattered light with the measuring instrument. Therefore, anomalies can be detected when the intensity of backscattered light measured by the measuring instrument changes due to the temperature difference between the erosion of the riverbank and coast and when the erosion occurs and the optical fiber touches the water. The distance from the measuring instrument to the abnormal part can be specified from the elapsed time until the reception of the backscattered light.
[0004]
[Problems to be solved by the invention]
However, in optical fiber sensors using Raman scattering, it is necessary to ensure a temperature difference between normal and abnormal conditions, and there is a concern that abnormalities cannot be detected in natural environments such as riverbanks and coasts. . In view of the above problem, for example, it is conceivable to keep the optical fiber temperature constant by using a heater or the like. However, since the cost increases, if a large number of optical fiber sensors are installed over a wide range, the cost becomes enormous. Such a problem occurs. Furthermore, in order to detect the temperature change of the optical fiber from the backscattered light due to the Raman scattering, a complicated and expensive device is required, which is expensive.
In addition to the erosion on the riverbank and the coast, the optical fiber sensor is required to be used as various contact-type sensors. There was a problem that versatility was low.
[0005]
The present invention has been made in view of the above problems,
(A) The cost can be reduced.
(B) By detecting the breakage or bending of the optical fiber, the abnormality can be detected easily and reliably.
(C) In addition to avoiding natural disasters, it has high versatility as a contact-type sensor
An object is to provide an optical fiber sensor.
[0006]
[Means for Solving the Problems]
  In the invention of claim 1, a plurality of connected, Each has a cylindrical shapeUnit (15, 31, 41, 51) and an optical fiber (16) communicating with these units, and the light connected between these units is bent by an external force between adjacently connected units. It is configured to detect that a fiber is broken or bent by measuring reflected light or backscattered light incident on the optical fiber from an optical pulse tester (9), and is connected adjacently. Optical fibers communicated between the unitsWhen the adjacent connected units are bent, they break with the optical fiber.It is fixed to each unit by restraining means (49, 59), and an extra length (16a) of the optical fiber is secured for each unit,The extra length of the optical fiber is housed in the cylindrical unit,The optical fiber sensor is characterized in that, when the unit is bent, the optical fiber is integrally displaced together with each unit to be broken or bent.
[0007]
In this optical fiber sensor, while the unit connection state is maintained (normal), the optical transmission performance of the optical fiber communicated with these units is ensured, and the adjacent units are bent by an external force. When the optical fiber connected between these units breaks or a sharp bend that affects the optical transmission characteristics occurs, the reflected light generated at the break point of the optical fiber or the bent position occurs. Backscattered light is observed by an optical pulse tester, and an optical fiber abnormality can be detected from a position away from the unit installation position.
In this optical fiber sensor, the optical fiber is fixed to each adjacent unit by the restraining means. Therefore, when the unit is bent, the optical fiber fixed to the unit is integrated with the unit. The optical fiber communicated between these units easily breaks or suddenly bends. For this reason, when an external force exceeding the load required for bending between the units (hereinafter referred to as “folding load”) is applied, the optical fiber is easily and reliably broken or bent, and the action of the external force can be reliably detected. . In addition, since the break point and the bending position of the optical fiber are detected, it is not necessary to secure a temperature difference as in the conventional optical fiber sensor using changes in Raman scattering due to temperature changes, and high versatility is obtained. In addition, the configuration is simple and the cost can be reduced.
[0008]
Anomalies in the optical fiber are detected by irradiating a light pulse (for example, laser pulse light) from the optical pulse tester into the optical fiber and observing the backscattered light or the reflected light due to Fresnel reflection. When the optical fiber sensor is installed (before the optical fiber is broken), a normal state can be confirmed when an optical pulse is incident on the optical fiber by an optical pulse tester. For example, if the end of the optical fiber communicating with the unit is made a non-reflective end, the reflected light is not detected in the normal state (when the optical fiber is not broken or bent), but when the optical fiber is broken, The breakage of the optical fiber can be detected by observing the backscattered light from the breaking point and the reflected light by Fresnel reflection. When the optical fiber connected to the unit is configured to reflect the incident light from the optical pulse tester by changing it to another wavelength, the reflected light of a specific wavelength can be detected under normal conditions, but the optical fiber is broken or bent or When the optical fiber expands and contracts, the reflected light in the same wavelength band as the incident light is observed, so that breakage, bending, and expansion / contraction of the optical fiber can be detected.
[0009]
As described above, various configurations can be adopted as the configuration of the end portion of the optical fiber communicating with the unit as long as it is a configuration that enables discrimination between the normal time and the abnormal time by the optical pulse tester. If the extra length of the optical fiber is secured for each unit, it is possible to check whether there is an abnormality in the optical fiber without special processing such as a non-reflective end on the end of the optical fiber communicating with the unit. . That is, when light enters the optical fiber from the optical pulse tester, the elapsed time from the incident to the reception of the reflected light varies depending on whether there is an abnormality in the optical fiber. Can be confirmed. In the test using the optical pulse tester, the distance from the abnormal point to the optical pulse tester can be detected by detecting the elapsed time from the incident light to the optical fiber until the reflected light or backscattered light is received. If the extra length of the optical fiber is secured for each unit, the separation distance from the optical pulse tester to the abnormal part of the optical fiber will be specified in units, and the part where the external force is applied will be more detailed. It becomes possible to specify.
[0010]
  The optical fiber sensor according to claim 2 is characterized in that in the optical fiber sensor according to claim 1, the extra length (16a) of the optical fiber is wound around the side surface (24) of the main body of the unit.
  Also,Claim3The optical fiber sensor according to claim 1.Or 2In the optical fiber sensor described above, the restraining means is a sheath tube that communicates between adjacently connected units, and when the unit is bent, the sheath tube is broken and stored in the sheath tube. The optical fiber is also ruptured. The sheath tube is formed from a fragile material such as glass or resin. Further, in the sheath tube, the optical fiber is constrained and stored so as not to allow the displacement of the optical fiber, and the optical fiber is easily broken as the sheath tube is broken. When fixing optical fibers to adjacent units connected by individual restraining means, it is necessary to ensure that the optical fibers are broken or bent by bringing the units close to each other. When the fiber is accommodated in the sheath tube, the optical fiber can be easily broken even if there is a gap between adjacent units, and the degree of freedom of the configuration of the optical fiber sensor is improved.
[0011]
  Claim4The optical fiber sensor according to claim 1.1 to 3 itemsThe optical fiber sensor described above is characterized by comprising a rotation restricting means for restricting relative rotation between adjacently connected units. The rotation restricting means restricts relative rotation between adjacently connected units and allows the units to be bent by an external force. When the relative rotation between adjacently connected units is restricted by the rotation restricting means, twisting or breaking of the optical fiber communicated so as to pass between the units is restricted, and the workability and installation work of this optical fiber sensor are restricted. Improves. Further, the rotation restricting means may be configured to allow relative rotation between the units after the installation of the optical fiber sensor is completed.
[0012]
DETAILED DESCRIPTION OF THE INVENTION
A first embodiment of an optical fiber sensor of the present invention will be described below with reference to FIGS.
In FIG. 1, the optical fiber sensor 1 of the present embodiment is installed by being inserted into a bored hole 3 having a length of several meters formed on a river bank 2. The optical fiber sensor 1 includes a plurality of connected units 15, 15... And an optical fiber 16 communicated with the units 15, 15. The optical fiber 16 is connected via a branch cable 5, an optical closure 6, and an optical cable 7 to a detection unit 8 that is installed apart from the river bank 2.
[0013]
The detection unit 8 includes an optical pulse tester 9 (OTDR: Optical Time Domain Reflectometer), a computer 10 that controls the optical pulse tester 9, and a plurality of optical lines branched from the optical cable 7 via the optical termination box 12. And a selector 11 for selecting an optical line on which the optical pulse output from the optical pulse tester 9 is incident. As the optical cable 7, for example, one having several hundred cores is adopted, and the optical pulse from the optical pulse tester 9 is incident on the optical line selected by the selector 11 and transmitted through the optical cable 7. It is transmitted to the target optical fiber sensor 1 through the connected branch cable 5.
In the optical closure 6, a plurality of branch cables 5 can be connected to one optical cable 7, and the optical pulse tester 9 is selected by selecting an optical line to be connected to the optical pulse tester 9 by the selector 11. The branch cable 5 and the optical fiber sensor 1 on which the light pulse is incident can be easily selected. Moreover, the number of the optical closures 6 connected to the optical cable 7 may be plural. For example, the optical closures 6 are installed at a plurality of locations of the optical cable 7 laid over several tens of kilometers, and each optical closure 6 has an optical cable. It is also possible to connect a plurality of branch cables 5 and the optical fiber sensor 1 to 7.
As the optical cable 7, the existing communication optical cable is also used, so that the cost can be greatly reduced.
[0014]
In FIG. 1, the boring hole 3 is an inclined shaft, but can also be a horizontal shaft.
In FIG. 1, the lower end of the borehole 3, which is a tilt shaft, is set lower than the water level of the river 13 in the vicinity of the river 13, and the upper end of the borehole 3 is positioned farther from the river 13 than the lower end. Without being limited, it is also possible to make the lower end of the borehole 3 higher than the water level of the river 13. The optical fiber sensor 1 housed in the boring hole 3 is suspended from a fixing box 14 installed near the upper end of the boring hole 3 and supported at a predetermined position in the boring hole 3. When the riverbank 2 is eroded and the borehole 3 is broken, the water flow of the river 13 comes into contact with the optical fiber sensor 1.
In the case of a horizontal pit, one end of a borehole formed so as to stop (close) or break through the river 13 at the riverbank 2 is positioned in the vicinity of the river 13 and a fixing box near the other end separated from the river 13 14 is installed to support the optical fiber sensor 1 in the borehole. The fixing box 14 is installed in the vicinity of the other end of the boring hole by using a vertical shaft such as a manhole formed by excavating from the river bank 2 or a horizontal shaft for laying the optical cable 7 underground.
In any of the bore holes, it is preferable that the optical fiber sensor 1 is stably supported by filling with a filler. Further, since the optical fiber sensor 1 detects the collapse of the mass of the riverbank 2 due to the erosion of the river 13, when applying the optical fiber sensor 1 that does not involve contact with the water of the river 13, any of the boreholes The formation position may be anywhere on the riverbank 2 as long as it is affected by the collapse of the river 13 due to erosion, and the height of the river 13 with respect to the water level is irrelevant.
As shown in FIG. 1, when the borehole 3 is formed so as to be lower than the water level of the river 13 and the optical fiber sensor 1 is installed at a position lower than the water level of the river 13, when the erosion collapse of the riverbank 2 occurs, It is also possible to adopt a configuration in which the fiber sensor 1 is directly exposed to the water flow of the river 13 and the erosion of the riverbank 2 is detected by bending between the units 15 and 15 by the force acting from the water flow of the river 13.
[0015]
FIG. 2 is a front view showing the optical fiber sensor 1, and FIG. 3 is an exploded perspective view showing the unit 15.
In FIG. 3, the unit 15 includes a cylindrical unit body 17 and a cylindrical exterior body 18 attached to the outside of the side surface of the unit body 17. Each of the unit main body 17 and the exterior body 18 is formed of a lightweight and waterproof material such as plastic or vinyl chloride. Between adjacent units 15 and 15, a joint recess 19 b is formed by forming a joint protrusion 19 a protruding from the flange portion 20 a of one unit 15 on the flange portion 20 b of the other unit 15 (see FIG. 2). The connection state is maintained by being inserted into and fitted in. Further, as shown in FIG. 2, the joint recess 19b is fitted with a thin wall-shaped strength holding projection 19c projecting from the joint projection 19a to reinforce the connection state between the units 15 and 15. Therefore, this makes it possible to ensure the transportability of the optical fiber sensor 1 and the installation workability to the boring hole 3.
As shown in FIG. 3, the strength holding projection 19c regulates the relative rotation between the units 15 and 15 and also functions as the rotation regulating means according to claim 3, so that the light before being installed in the boring hole 3 can be used. In the fiber sensor 1, there is no fear that the optical fiber 16 communicated so as to pass between the units 15 and 15 is twisted, and the optical transmission characteristics of the optical fiber 16 can be maintained.
[0016]
Optical fiber grooves 21 a and 21 b for inserting the optical fiber 16 are communicated with the flange portions 20 a and 20 b at both axial ends of the unit main body 17 on the same straight line along the central axis of the unit main body 17. The optical fiber grooves 21a and 21b of all the connected unit bodies 17 communicate with each other on the same straight line.
The optical fiber 16 has a surplus length 16a between the optical fiber grooves 21a and 21b. The extra length 16a is accommodated so as to be wound around the side surface 24 of the unit main body between the flanges 20a and 20b. 3 is a radius maintaining means for maintaining the radius of curvature of the optical fiber 16 drawn into the side surface 24 of the unit main body so as not to affect the optical transmission characteristics.
The extra length 16 a wound around the unit main body side surface 24 is sandwiched between the unit main body side surface 24 and the exterior body 18 attached to the outside of the unit main body side surface 24. The exterior body 18 is attached to the unit main body side surface 24 with an urging force by its own elasticity, and the extra length 16a wound around the unit main body side surface 24 is pressed by the exterior body 18 so as not to cause unnecessary bending or the like.
[0017]
Further, the optical fiber grooves 21a and 21b, the space between the unit main body 17 and the exterior body 18 and the like are made waterproof by using an O-ring (not shown), a waterproof gel material, or the like. Further, in the optical fiber grooves 21a and 21b, the optical fiber 16 is fixed by a restraining means 25 such as an adhesive having a waterproof property, and the waterproof property is achieved. The portion of the optical fiber 16 that is communicated between the units 15 and 15 is also waterproofed with an adhesive or the like. Thus, in the optical fiber sensor 1, the waterproof property of the optical fiber 16 is ensured reliably and the optical transmission characteristic of the optical fiber 16 is maintained.
The optical fiber 16 is bonded and fixed to each of the end portion (flange portion 20a) of one adjacent unit 15 and the end portion (flange portion 20b) of the other unit 15 by an adhesive employed as the restraining means 25. Therefore, even if the units 15 and 15 are relatively displaced, the units 15 and 15 are restrained so as not to leave the optical fiber grooves 21a and 21b. The restraining means 25 is not limited to an adhesive, and various configurations can be adopted as long as the optical fiber 16 can be restrained to the unit 15.
The optical fiber 16 is connected to the optical fiber on the branch cable 5 side by a fixing box 14 (see FIG. 1), and is connected to the detection unit 8 through the optical cable 7.
[0018]
When the optical fiber sensor 1 is installed in the boring hole 3, the strength holding protrusion 19 c is cut and then the optical fiber sensor 1 is inserted into the boring hole 3. Before the strength holding projection 19c is cut, the bending strength between the units 15 and 15 is ensured, and the optical fiber 16 is prevented from being broken or bent, and has excellent transportability, but after the strength holding projection 19c is cut, The bending strength between the units 15 and 15 is reduced, and the unit 15 is easily bent.
[0019]
The outer surface of the optical fiber sensor 1 accommodated in the boring hole 3 is brought close to the inner surface of the boring hole 3, the river bank 2 is eroded by the river 13, and the mass of the river bank 2 collapses, and at the same time, the optical fiber sensor unit 15 at the boundary portion of the collapsed mass. 15 and the optical fiber 16 communicated between these units 15 and 15 is also broken and broken or bent. At this time, since the optical fiber 16 is restrained by the units 15 and 15 by the restraining means 25, the glass optical fiber 16 is easily broken or bent when the units 15 and 15 are bent.
[0020]
Since the test for checking whether the optical fiber 16 is broken or bent is performed at any time by the optical pulse tester 9, the optical fiber related to the optical fiber 16 can be detected by detecting the broken or bent (abnormal part) of the optical fiber 16. It is found that erosion has occurred at the location where the sensor 1 is installed.
The detection unit 8 automatically selects an optical line to be tested by the selector 11 and tests the presence / absence of an abnormal portion of the optical line related to each optical fiber sensor 1 while sequentially switching the connection to the optical pulse tester 9. Therefore, even when a large number of optical fiber sensors 1 are installed in a wide range, erosion of the river bank 2 can be quickly detected for all the installation positions of the optical fiber sensors 1. Since the presence or absence of an abnormal portion of the optical fiber 16 is tested for each optical line selected by the selector 11, it is easy to identify the eroded portion when the breakage of the optical fiber 16 is detected.
In addition, since an abnormal portion of the optical fiber 16 is detected, it is easier to detect erosion than a configuration in which erosion is detected from a change in Raman scattering, and the analysis relating to the detection is also easy, and a complicated analyzer. The cost can be reduced.
When the erosion of the river bank 2 further progresses, the bending between the units 15 and 15 occurs again and the optical fiber 16 becomes short, the broken or bent portion of the optical fiber 16 is detected in the same manner as when the first broken portion is detected. The progress of erosion can be grasped. This is not limited to the present embodiment, but is common to various optical fiber sensors according to the present invention, and the same applies to optical fiber sensors described in the following embodiments.
[0021]
The optical pulse tester 9 can test the optical line related to each optical fiber 16 at any time, thereby confirming the normality of the entire optical line including the optical cable 7 and the like. In addition, in the optical test by the optical pulse tester 9, when an abnormality (breaking of the optical fiber 16, etc.) is detected in the optical path between the optical pulse tester 9 and the optical fiber sensor 1, reflected light or backscattered light is emitted. Since an abnormal point or the like can be identified from the time until it reaches the pulse tester 9 and its strength, maintenance is easy, which contributes to a reduction in maintenance costs.
[0022]
Furthermore, according to this optical fiber sensor 1, since the extra length 16a of the optical fiber 16 is secured for each unit 15, the position of the abnormal portion of the optical fiber 16 in the specific optical fiber sensor 1 is specified in units of 15 units. it can.
The extra length 16a is secured about several meters, and when an optical line test is performed by the optical pulse tester 9, an abnormal portion of the optical fiber 16 can be specified in units of 15 units. Thereby, the abnormal part of the optical fiber 16 can be specified, and at the same time, the degree of erosion of the river bank 2 can be grasped by the detection unit 8.
The length of the extra length 16a is the elapsed time until the reflected light or backscattered light that is generated when the optical pulse incident from the optical pulse tester 9 reaches the breaking position of the optical fiber 16 returns to the optical pulse tester 9, Different for each unit 15. Therefore, the length of the extra length 16a is in accordance with the optical test accuracy of the optical pulse tester 9, and may be short if the measurement accuracy of the optical pulse tester 9 is high, and sufficient if the measurement accuracy of the optical pulse tester 9 is low. Secure.
[0023]
Further, in order to surely cause the optical fiber 16 to break or bend between the adjacent unit main bodies 17 and 17, the optical fiber sensor is formed so that the optical fiber grooves 21a and 21b are on the downstream side of the water flow of the river 13. 1 is installed in the boring hole 3 and when the unit 15 is bent, the unit 15 may be relatively displaced so that the unit 15 rotates about the boundary between the optical fiber grooves 21a and 21b. preferable. As a result, the units 15 and 15 are bent, and when the optical fiber 16 restrained by each unit 15 is displaced integrally with the unit 15, the optical fiber 16 is bent sharply around the boundary between the optical fiber grooves 21a and 21b. As a result, breakage and bending occur easily and reliably, and erosion detection accuracy is improved.
If the optical fiber sensor 1 is installed in a direction other than that described above, the optical fiber 16 is less likely to be broken or bent even if the unit 15 is bent. Therefore, this optical fiber sensor 1 has a bending directionality, and a high detection accuracy can be obtained for an external force in a specific direction. For external forces in other directions, the detection accuracy is low, and malfunctions due to causes other than the collapse of the lump on the river bank 2 are reduced.
[0024]
When the optical fiber sensor 1 is installed in the boring hole 3, if the strength holding projections 19 c are left in a partial state without being completely cut, the size or the like of the connecting portion can be adjusted to adjust the unit 15. , Folding strength between 15 can be adjusted. If the bending strength between the units 15 and 15 is increased, the optical fiber 16 is prevented from being carelessly broken and broken. For example, when the river bank 2 is soft ground, it is caused by deformation of the ground other than erosion. There is no fear of the optical fiber 16 being broken or bent.
That is, if the units 15 and 15 are easily broken, the units 15 and 15 may be broken even when they are in contact with the inner wall of the boring hole 3 when the optical fiber sensor 1 is installed. It is necessary to carefully insert the optical fiber sensor 1 into the boring hole 3, and the installation workability is lowered. However, if the bending resistance between the units 15 and 15 is increased by the strength-holding protrusion 19c, the insertion work into the boring hole 3 can be efficiently advanced without causing bending between the units 15 and 15, Even a long optical fiber sensor 1 can be efficiently inserted into the boring hole 3.
Further, if the riverbank 2 is soft ground, the riverbank 2 is deformed by the vibration generated by the construction in the vicinity and the borehole 3 is deformed, and the units 15 and 15 are caused by causes other than the collapse of the riverbank 2 due to erosion. However, if the strength of bending between the units 15 and 15 is increased by the strength retaining projection 19c, it is possible to prevent the units 15 and 15 from being broken when the river bank 2 is deformed. Thus, it is possible to prevent the optical fiber 16 from being broken or bent due to causes other than the collapse of the riverbank 2.
[0025]
Next, an optical fiber sensor according to a second embodiment of the present invention will be described with reference to FIGS.
FIG. 4 is a front view showing the optical fiber sensor 30. 4, this optical fiber sensor 30 includes units 31, 31... Connected on the same straight line, and optical fibers 16 communicated with these units 31, 31. It is installed in the boring hole 3 in the same manner. The optical fiber 16 is connected to the detector 8 via the fixing box 14, the branch cable 5, the optical closure 6, and the optical cable 7 as in the first embodiment.
[0026]
FIG. 5 is an exploded perspective view showing the unit 31.
In FIG. 5, the unit 31 includes a cylindrical unit main body 32 and disc-shaped lids 33 and 34 that are removably screwed to the axial end of the unit main body 32. The unit main body 32 and the lids 33 and 34 are both made of a waterproof and lightweight material such as plastic or vinyl chloride.
The lid 33 screwed to one end of the unit body 32 in the axial direction includes a circular protrusion 33b protruding from the central portion of the outer surface 33a, and an optical fiber hole 33c penetrating through the radial central portion including the circular protrusion 33b. It has.
As shown in FIG. 6, the lid 34 screwed to the other axial end of the unit main body 32 includes a circular concave portion 34b having a recessed central portion of the outer surface 34a, and an optical fiber hole 34c penetrating the radial central portion. And.
[0027]
As shown in FIG. 4, when the lids 33 and 34 are screwed onto the unit main body 32, the optical fiber hole 33c of the lid 33 and the optical fiber hole 34c of the lid 34 communicate with each other on the same straight line.
Further, in the optical fiber sensor 30, between the units 31 and 31 connected adjacently, the circular protrusion 33 b of the lid 33 of one unit 31 is formed on the circular recess 34 b of the lid 34 of the other unit 31. The connection state between the units 31 and 31 is ensured by fitting. The projecting dimension of the circular protrusion 33b and the depth dimension of the circular recess 34b are both about several millimeters, and an external force such as a water flow of the river 13 acts between the circular protrusion 33b and the circular recess 34b fitted to each other. Then, the fitting state is easily released, and the units 31 and 31 are easily bent.
[0028]
When the circular protrusion 33b and the circular recess 34b are fitted, the optical fiber holes 33c and 34c are communicated. The optical fiber 16 communicates with all the units 31 over the entire length of the optical fiber sensor 30 by communicating with the optical fiber holes 33c and 34c. Further, in the optical fiber holes 33c and 34c, the optical fiber 16 is fixed by a restraining means (not shown) such as an adhesive, and waterproofing is achieved. For this reason, when the lids 33 and 34 are screwed and fixed to the end portions of the unit body 32 in the axial direction, the water tightness in the unit body 32 is secured.
[0029]
As in the case of the optical fiber sensor 1 shown in FIG. 1, the optical fiber sensor 30 installed in the boring hole 3 has a space between the units 31, 31 at the boundary portion of the collapsed mass when the riverbank 2 erodes the riverbank 2 and collapses the mass. The optical fiber 16 communicated between the units 31 and 31 is broken or bent. Therefore, when the optical pulse tester 9 detects the breakage or bending of the optical fiber 16, erosion of the river bank 2 is detected. As in the first embodiment, the optical fiber 16 is tested for any optical line connected to the detection unit 8 by the selector 11 and connected to the detection unit 8 as in the first embodiment. Even if there are a large number of optical fiber sensors 30, the optical fiber sensor 30 related to the optical fiber 16 is identified by detecting an abnormal portion of the optical fiber 16, and the optical fiber 16 in the identified optical fiber sensor 30 is identified. An abnormal location is specified in units of 31 units, and an erosion location, degree, and the like of the river bank 2 are specified.
The improvement in the maintainability of the optical line from the optical pulse tester 9 to the optical fiber sensor 30 is the same as in the first embodiment.
[0030]
Between the fitted circular protrusion 33b and the circular recess 34b, the optical fiber 16 communicated with the optical fiber holes 33c and 34c is fixed to the circular protrusion 33b or the circular recess 34b by the restraining means. Since the units 31 and 31 are constrained so as not to be separated even if they are bent, when the units 31 and 31 are bent and relatively displaced, the optical fiber 16 is also displaced following the units 31 and easily and easily. The optical fiber 16 is surely broken or bent.
[0031]
Moreover, in this optical fiber sensor 30, since the connection state between the units 31 and 31 is ensured by fitting the circular protrusions 33b and the circular recesses 34b, both the units 31 and 31 are not bent. There is no direction. In addition, since the optical fiber 16 is communicated on the central axis between the adjacent units 31 and 31, when the bending occurs between the units 31, 31, the optical fiber 16 is broken or bent regardless of the direction of the bending. . Accordingly, the unit 31 can be easily bent with a small load against an external force from any direction.
For example, when the water flow of the river 13 is strong, a lump that collapses from the riverbank 2 due to erosion collapses in the horizontal direction while being pushed away by the water flow of the river 13 instead of vertically downward, and the optical fiber sensor also has a horizontal direction of the river 13. There are cases in which external force acts on. In this case, in the optical fiber sensor having the folding directionality, the folding direction is matched with the collapse direction (downward) of the clot, so that erosion of the river bank 2 may not be detected. However, in the optical fiber sensor 30 that does not have the folding directionality, the bending between the units 31 and 31 occurs with certainty regardless of the collapse direction of the mass, and erosion can be detected. Moreover, since the installation direction of the optical fiber sensor 30 in the borehole 3 is free, the effect of improving the installation workability in the borehole 3 can be obtained.
Needless to say, the bending resistance between the units 31 and 31 can be adjusted by adjusting the shape of the circular protrusions and circular recesses fitted to each other to adjust the fitting force.
[0032]
Next, an optical fiber sensor 40 according to a third embodiment of the present invention will be described with reference to FIGS.
As shown in FIG. 7, the optical fiber sensor 40 of the present embodiment includes units 41, 41... Connected in large numbers, and an optical fiber 16 communicated with these units 41, 41. Similar to the fiber sensor 1, it is installed in the borehole 3. The optical fiber 16 is connected to the detector 8 via the fixing box 14, the branch cable 5, the optical closure 6, and the optical cable 7 as in the first embodiment.
[0033]
FIG. 9 is a perspective view showing the unit 41.
The unit 41 includes a cylindrical unit main body 42 and an exterior body 44 that is mounted on the outer side surface 43 of the axially central portion of the unit main body 42. The unit main body 42 and the exterior body 44 are both made of a lightweight material that can ensure waterproofness such as plastic and vinyl chloride. The exterior body 44 has a C-shaped cross section and is stably attached to the side surface 43 of the unit body with its own elastic force.
[0034]
Both the optical fiber groove 46 formed in the flange portion 45 at one axial end of the unit body 42 and the optical fiber groove 48 formed in the flange portion 47 at the other axial end extend along the axial direction of the unit main body 42. And located on the same straight line. The optical fiber grooves 46 and 48 (of the unit main body 42) of all the connected units 41, 41... Communicate on the same straight line.
Between the units 41 and 41 connected adjacently, the flange portion 45 of one unit 41 and the flange portion 47 of the other unit 41 are brought into contact with each other, and the optical fiber grooves 46 and 48 are communicated. The optical fiber 16 is communicated through a sheath tube 49 (glass tube) that is housed and fixed so as to pass to the optical fiber grooves 46 and 48 that are communicated with each other.
As the sheath tube, various configurations other than the glass tube can be adopted as long as waterproofness can be ensured. In the case of a glass tube, a linear expansion coefficient close to that of the optical fiber 16 can be obtained, so that there is no fear of damaging the optical fiber 16 even when the temperature at the installation site is changed, and the optical transmission characteristics of the optical fiber 16 are maintained over a long period of time. be able to.
[0035]
Further, between the abutted flange portions 45 and 47, pin holes (not shown) formed in the wedge-shaped divided portion 47a provided so that the pins 45a and 45b protruding from the flange portion 45 can be divided into the flange portion 47 are provided. ) To prevent relative rotation around the central axis of the units 41 and 41. Further, the flange portions 45 and 47 that are in contact with each other maintain a connected state by winding a water-soluble tape 41a made of paper or the like from the outside. The water-soluble tape 41a is preferably bonded and fixed with an adhesive such as water-soluble starch paste.
Since the optical fiber groove 48 of the flange portion 47 is formed in a portion other than the split portion 47 a of the flange portion 47, the housing position of the sheath tube 49 stored in the optical fiber groove 48 is the split portion in the flange portion 47. It is not affected by the attachment / detachment of 47a.
The pins 45a and 45b and the water-soluble tape 41a function as rotation restricting means according to claim 3.
[0036]
A surplus length 16 a secured around the optical fiber 16 is wound around the unit main body side surface 43, and the surplus length 16 a is pressed by being sandwiched by an exterior body 44 attached to the unit main body side surface 43 from the outside. On the unit main body side surface 43, a radius of curvature greater than a prescribed value that can maintain the optical transmission characteristics by bending the optical fiber 16 along the elastic pad 43a attached in the vicinity of the optical fiber grooves 46 and 48 is secured. A pair of elastic pads 43a are disposed opposite to both sides of the optical fiber groove 46 or 48, an elastic cushion 43b made of sponge or the like is disposed between the opposed elastic pads 43a and 43a, and the optical fiber 16 is bent. Is not going to be abrupt.
[0037]
The boundary between the flanges 45 and 47 of the unit main body 42 and the exterior body 44 is all waterproofed by an adhesive or a gel material and prevents water from entering the exterior body 44. The extra length 16a wound around the side surface 43 is protected from water so that there is no concern that the light transmission characteristics will be adversely affected by water immersion.
Since the portion of the optical fiber 16 that is not protected by the outer casing 44 is protected by the sheath tube 49, the entire length of the optical fiber 16 of the optical fiber sensor 40 is reduced by the outer casing 44 and the sheath tube 49. It is protected from flooding and the optical transmission characteristics are maintained.
[0038]
In this optical fiber sensor 40, before and during installation in the boring hole 3, the engagement between the pins 45a and 45b and the pin holes and the connection state between the adjacent units 41 and 41 are stabilized by the water-soluble tape 41a and the like. Thus, it is possible to secure the transportability and the installation workability to the borehole 3.
[0039]
In a normal state (before erosion of the river bank 2), the division part 47a is housed in the flange part 47 and is restricted from protruding from the flange part 47 by the water-soluble tape 41a wound around the flange parts 45 and 47 from the outside. However, the river bank 2 is eroded by the water flow of the river 13, the optical fiber sensor 40 installed in the borehole 3 is exposed to the water flow, and the water-soluble tape 41a is melted. 47 (see reference numeral 47a of the phantom line in FIG. 8). At this time, between the units 41 and 41 connected adjacently, the connection state between the flange portion 45 of one unit 41 and the split portion 47a of the other unit 41 is ensured by the pins 45a and 45b. Only the sheath tube 49 and the optical fiber 16 housed in the sheath tube 49 bear the coupling force between the flange portion 47 other than the split portion 47a and the flange portion 45. The acting displacement force acts on the sheath tube 49 and the optical fiber 16 in a concentrated manner. Therefore, when the water flow of the river 13 directly acts on the optical fiber sensor 40, the sheath tube 49 is easily broken even by a weak force, the unit 41, 41 is bent, and the optical fiber 16 is also broken. Since the optical fiber 16 has an outer diameter that substantially matches the inner diameter of the sheath tube 49 and is restrained so as not to float in the sheath tube 49, the optical fiber 16 is easily and reliably broken when the sheath tube 49 is broken. .
[0040]
When the divided portion 47a is freely displaceable with respect to the flange portion 47, the portion other than the divided portion 47a of the flange portion 47 and the flange portion 45 of another unit 41 are substantially in point contact in the vicinity of the sheath tube 49. The unit 41 can be bent by an external force from any direction, and the optical fiber sensor 40 is not bent.
For this reason, for example, even when the water flow of the river 13 is obstructed by an obstacle and does not directly act on the optical fiber sensor 40 when the river bank 2 is eroded, the optical fiber 16 is broken by the collapse of the river bank 2 due to erosion or the like. As a result, erosion can be reliably detected. In addition, since the orientation of the optical fiber sensor 40 in the borehole 3 is thereby free, the effect of improving the installation workability in the borehole 3 can be obtained.
[0041]
As the water-soluble tape 41a and the adhesive for fixing the water-soluble tape 41a, it is preferable to employ a material that can be naturally decomposed, and this prevents the river 13 from being contaminated even if it is dissolved in water.
If buried in the borehole 3 for a long time, the water-soluble tape 41a corrodes and loses the binding force between the units 41 and 41, and the bending strength between the units 41 and 41 becomes almost zero. Even if the optical fiber sensor 40 is only exposed by erosion, the unit 41 and 41 are bent by the weight of the unit 41, and the erosion of the riverbank 2 can be detected more sensitively.
In addition, the water-soluble tape 41a made of a biodegradable material has no fear of contaminating the river bank 2 due to corrosion.
[0042]
When the optical pulse tester 9 detects the breakage of the optical fiber 16, the erosion of the river bank 2 is detected. The test of whether or not the optical fiber 16 is broken in the detection unit 8 is performed at any time for all optical lines connected to the detection unit 8 by the selector 11 as in the first embodiment. Even if there are a large number of optical fiber sensors 40 connected, the optical fiber sensor 40 related to the optical fiber 16 is specified by detecting the breakage of the optical fiber 16. In addition, in the optical fiber sensor 40, the extra length 16a of the optical fiber 16 is sufficiently secured inside each unit 41, and the broken portion of the optical fiber 16 can be specified in units of units 41. The degree of erosion of the riverbank 2 can be grasped by the detection unit 8 in units of 41 units.
The improvement in maintainability of the optical line from the optical pulse tester 9 to the optical fiber sensor 40 is the same as in the first embodiment.
[0043]
Next, an optical fiber sensor 50 according to a fourth embodiment of the present invention will be described with reference to FIGS.
As shown in FIG. 10, the optical fiber sensor 50 of the present embodiment includes units 51, 52... Connected in large numbers, and an optical fiber 16 communicated with these units 51, 51. Similar to the fiber sensor 1, it is installed in the borehole 3. The optical fiber 16 is connected to the detector 8 via the fixing box 14, the branch cable 5, the optical closure 6, and the optical cable 7 as in the first embodiment.
[0044]
FIG. 11 is a perspective view showing the unit 51.
The unit 51 includes a cylindrical unit main body 52 and an exterior body 54 that is mounted on the outer side surface 53 of the axially central portion of the unit main body 52. The unit main body 52 and the exterior body 54 are both made of a lightweight material that can ensure waterproofness such as plastic and vinyl chloride. The exterior body 54 has a C-shaped cross section and is stably attached to the side surface 53 of the unit main body with its own elastic force.
[0045]
The optical fiber groove 56 formed in the flange portion 55 at one end in the axial direction of the unit body 52 and the optical fiber groove 58 formed in the flange portion 57 at the other end in the axial direction both extend along the axial direction of the unit body 52. And located on the same straight line.
Between the units 51 and 51 connected adjacently, the flange portion 55 of one unit 51 and the flange portion 57 of the other unit 51 are brought into contact with each other, and the optical fiber grooves 56 and 58 are communicated with each other. The optical fiber 16 is communicated through a sheath tube 59 (glass tube) that is housed and fixed so as to pass to the fiber grooves 56 and 58. As the sheath tube, various configurations other than the glass tube can be adopted as long as waterproofness can be ensured. In the case of a glass tube, a linear expansion coefficient close to that of the optical fiber 16 can be obtained, so that there is no fear of damaging the optical fiber 16 even when the temperature at the installation site is changed, and the optical transmission characteristics of the optical fiber 16 are maintained over a long period of time. be able to.
[0046]
Further, between the abutted flange portions 55 and 57, pins 55a, 55b and 55c projecting from the flange portion 55 are connected to pin grooves 57a and 57b formed on the flange portion 57 (pin grooves corresponding to the pins 55c are unit grooves). 51, which is located on the back side of the drawing sheet (not shown) to prevent relative rotation around the central axis of the units 51 and 51.
The pins 55a, 55b, 55c and the pin grooves 57a, 57b function as rotation restricting means according to claim 3.
When the sheath tube 59 is broken, the optical fiber 16 is broken and broken. When a break of the optical fiber 16 is detected by the optical pulse tester 9 of the detector 8, it is detected that an external force is applied to the optical fiber sensor 50 and the unit 51, 51 is bent.
[0047]
The pins 55a, 55b, and 55c protrude radially outward from the ring-shaped flange portion 55 and are inserted into the pin grooves 57a and 57b of the flange portion 57. The two pins 55a and 55b are disposed on both sides of the optical fiber groove 56, and another pin 55c is disposed to face the optical fiber groove 56 in the diameter direction of the flange portion 55, and all the pins 55a, 55b, 55c is parallel. For this reason, the adjacent units 51 and 51 are not easily rotated around the axis centering on the diameter of the flange portion 55 connecting the optical fiber groove 56 and the pin 55c, and have a high bending strength, but the pins 55a and 55b are the center. It is easy to rotate in and out of the flange portion 55, and in and out of the flange portion 55 with the pin 55c as the center, and the bending of the units 51 and 51 has directionality.
As shown in FIG. 10, all the units 51, 51... Are connected so that the optical fiber grooves 56, 58 are on the same straight line, and the bending directions between all the units 51, 51 are aligned. If the direction of easy bending of the units 51, 51 of the optical fiber sensor 50 installed in the borehole 3 is adapted to the direction of the water flow of the river 13, the presence or absence of erosion can be detected sensitively.
[0048]
The unit body side surface 53 is wound with a surplus length 16a secured to the optical fiber 16, and the surplus length 16a is pressed by an exterior body 54 attached to the unit body side surface 53 from the outside. On the side surface 53 of the unit main body, a radius of curvature that is greater than a prescribed value that ensures optical transmission characteristics by bending the optical fiber 16 along the elastic pad 60 attached in the vicinity of the optical fiber grooves 56 and 58 is secured.
Since the boundary between the flanges 55 and 57 of the unit main body 52 and the exterior body 54 is all waterproof by an adhesive or a gel material and prevents water from entering the interior of the exterior body 54, the unit body The extra length 16a wound around the side surface 53 is protected from water so that there is no concern that the light transmission characteristics will be adversely affected by water immersion.
Since the portion of the optical fiber 16 that is not protected by the outer casing 54 is protected by the sheath tube 59, the entire length of the optical fiber 16 of the optical fiber sensor 50 is reduced by the outer casing 54 and the sheath tube 59. It is protected from flooding and the optical transmission characteristics are maintained.
[0049]
In this optical fiber sensor 50, before and during installation in the boring hole 3, the connection state between the adjacent units 51 and 51 is maintained by the engagement between the pins 55a, 55b and 55c and the pin grooves 57a and 57b. Transport workability and installation workability to the boring hole 3 can be secured.
[0050]
When the riverbank 2 is eroded by the water flow of the river 13 and the clod collapses, the unit 51, 51 at the boundary of the collapsible clod is bent, the sheath tube 59 is broken, and the optical fiber 16 is also broken and broken. The optical fiber 16 has an outer diameter that substantially matches the inner diameter of the sheath tube 59, is constrained to be non-floatable in the sheath tube 59, and the optical fiber 16 is easily and reliably broken when the sheath tube 59 is broken. 2 erosion can be reliably detected.
Further, by adjusting the diameter of the pins 55a, 55b, 55c and the size of the pin grooves 57a, 57b, the bending load required for the bending between the units 51, 51 can be easily adjusted, and the strength of the water flow of the river 13 can be adjusted. Yes.
[0051]
When the optical pulse tester 9 detects the breakage of the optical fiber 16, the erosion of the river bank 2 is detected. The test of whether or not the optical fiber 16 is broken in the detection unit 8 is performed at any time for all optical lines connected to the detection unit 8 by the selector 11 as in the first embodiment. Even when there are a large number of optical fiber sensors 50 connected, by detecting the breakage of the optical fiber 16, the installation position of the optical fiber sensor 40 related to the optical fiber 16, that is, the erosion location of the river bank 2 is specified. The
In this optical fiber sensor 50, the extra length 16a of the optical fiber 16 is sufficiently secured inside each unit 51, and the broken portion of the optical fiber 16 can be specified in units of units 51. The degree of erosion of the riverbank 2 can be grasped by the detection unit 8.
The improvement in maintainability of the optical line from the optical pulse tester 9 to the optical fiber sensor 50 is the same as in the first embodiment.
[0052]
In each of the above-described embodiments, the detection of the erosion of the river bank 2 is targeted. However, the optical fiber sensor of the present invention can be used as a debris flow and landslide detection sensor, various embankment slopes and cut slope failure detection sensors, and the like. The detection target is not limited.
In addition, the configuration of the optical fiber sensor of the present invention is not limited to the above-described embodiments. For example, the configuration for maintaining the connection state between the units of the optical fiber sensor in the initial installation state is appropriately changed. It goes without saying that it is possible.
[0053]
【The invention's effect】
As described above, according to the optical fiber sensor of the first aspect, when a plurality of connected units are bent by an external force, the optical fiber communicated so as to pass between the units is broken or bent (abnormal part). Is sure to occur,
(A) By detecting an abnormal portion of this optical fiber with an optical pulse tester, it is possible to easily and reliably detect that an external force having a magnitude exceeding the bending load between the units is applied.
(B) The configuration is simple, and the effect of the load can be detected for a number of optical fiber sensors by a single optical pulse tester, and the cost can be reduced.
(C) Even if a large number of optical fiber sensors are connected to the optical pulse tester, the optical fiber sensor in which the optical fiber is broken or bent can be easily identified.
(D) An optical line abnormality from the optical pulse tester to the optical fiber sensor can be detected at any time by the optical pulse tester, and the abnormal part can be easily identified, so that maintenance is facilitated.
(E) If the extra length of the optical fiber is ensured for each unit, an excellent effect is obtained such that an abnormal portion of the optical fiber can be detected in units and the portion to which the load is applied can be specified with high accuracy.
[0054]
According to the optical fiber sensor of the second aspect, when the adjacent units are bent, the sheath pipe communicated between these units is broken, and the optical fiber housed in the sheath pipe is also reliably broken. The location where the load is applied can be detected more reliably, and the separation distance between the units can be set according to the dimensions of the sheath tube, and an excellent effect is obtained in that the degree of freedom in design is improved.
[0055]
According to the optical fiber sensor of the third aspect of the present invention, the optical fiber sensor is provided with a rotation restricting means for restricting relative rotation between adjacently connected units, and is passed between the units when the optical fiber sensor is transported or installed. Since the twisting and breaking of the optical fiber communicated with each other can be controlled, an excellent effect of improving the workability of transportation and installation is obtained.
[Brief description of the drawings]
FIG. 1 is an overall view showing an installation state of an optical fiber sensor according to a first embodiment of the present invention.
FIG. 2 is a front view showing the optical fiber sensor according to the first embodiment of the present invention.
3 is an exploded perspective view showing a unit constituting the optical fiber sensor of FIG. 2; FIG.
FIG. 4 is a front view showing an optical fiber sensor according to a second embodiment of the present invention.
5 is an exploded perspective view showing a unit constituting the optical fiber sensor of FIG. 4; FIG.
6 is a perspective view showing a lid of the unit shown in FIG. 4. FIG.
FIG. 7 is a front view showing an optical fiber sensor according to a third embodiment of the present invention.
8 is a rear view of the optical fiber sensor of FIG. 7. FIG.
9 is an exploded perspective view showing a unit constituting the optical fiber sensor of FIG. 7; FIG.
FIG. 10 is a front view showing an optical fiber sensor according to a fourth embodiment of the present invention.
11 is an exploded perspective view showing a unit constituting the optical fiber sensor of FIG.
[Explanation of symbols]
DESCRIPTION OF SYMBOLS 1, 30, 40, 50 ... Optical fiber sensor, 9 ... Optical pulse tester, 15, 31, 41, 51 ... Unit, 16 ... Optical fiber, 25 ... Restraint means (adhesive), 41a ... Rotation restriction means (water-soluble) 45a, 45b ... rotation restriction means (pin), 49 ... restraint means, sheath tube (glass tube), 55a, 55b, 55c ... rotation restriction means (pin), 57a, 57b ... rotation restriction means (pin groove) ), 59... Restraining means, sheath tube (glass tube).

Claims (4)

A plurality of connected units (15, 31, 41, 51) each having a cylindrical shape and an optical fiber (16) communicating with these units are bent by an external force between adjacently connected units. Detecting that the optical fiber communicated between these units is broken or bent by measuring reflected light or backscattered light incident on the optical fiber from the optical pulse tester (9). Each unit is configured by a restraining means (49, 59) that is configured as described above, and breaks together with the optical fiber when the optical fiber communicated between the adjacently connected units is bent between the adjacently connected units. fixed to said securing extra length of the optical fiber for each unit (16a), an extra length of the optical fiber having a cylindrical shape Housed in serial unit, optical fiber sensors which the optical fiber with each unit when between the unit is bent, characterized in that the adapted cause breakage or bending displaced integrally (1,30,40 50).  The optical fiber sensor according to claim 1, wherein the extra length (16a) of the optical fiber is wound around the side surface (24) of the main body of the unit.  The restraint means is a sheath tube (49, 59) communicating between adjacent units, and when the unit is bent, the sheath tube is broken and the light stored in the sheath tube 3. The optical fiber sensor according to claim 1, wherein the fiber is also broken.  A rotation restricting means (41a, 45a, 45b, 55a, 55b, 55c, 57a, 57b) for restricting relative rotation between adjacently connected units is provided. An optical fiber sensor according to item.

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