JP2017110921A - Cable diagnosis system and sensing cable - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a system capable of efficiently diagnosing whether or not moisture exists inside a coated cable, and a degree thereof if that exists.SOLUTION: A sensing cable 10 is equipped with an optical fiber 15 provided on a surface of a cable body portion whose outer peripheral surface is coated by a coating layer. A tube is fixed on the surface of the cable body portion, and the optical fiber 15 is inserted into the tube without being fixed. The optical fiber 15 is formed with an FBG, light emitted from an interrogator 30 is reflected by the FBG, and it wavelength is computed. Wavelength change is converted into temperature (temperature change) inside the cable in a monitoring device 40. From features showing in a temperature change curve, the presence/absence and a degree of moisture inside the cable are diagnosed.SELECTED DRAWING: Figure 5

Description

  The present invention relates to a cable diagnostic system, and more particularly to a system for diagnosing a moisture (wetting) state in a coated cable. The present invention also relates to a sensing cable suitable for a cable diagnostic system.

  In recent years, structural health monitoring that attaches sensors to a structure and periodically diagnoses the state of the structure has attracted attention because of the need for efficient maintenance and management of the structure.

  Among the structures, bridges built on rivers, straits, etc. are equipped with multiple cables for hanging bridge girders. When the cable is corroded by moisture, its yield strength decreases. The condition of the cable must be diagnosed regularly.

  Patent Document 1 discloses a cable used for a suspended structure such as a cable-stayed bridge, in which an optical fiber is provided along the length direction. Patent Document 1 describes that the humidity distribution inside a cable is measured using an optical fiber.

JP 2007-297777 A

  In order to minimize the corrosion of cables used outdoors, including cables for suspending bridge girder bridges, cover the surface so that water and air do not touch the wire strands that make up the cable directly. It is common to do. However, water may enter the cable during the installation of the cable, or water may enter the cable due to deterioration or damage to the coating. In this case, water vaporization due to an increase in the outside air temperature during the day and condensation due to a decrease in the outside air temperature during the night are repeated inside the cable, and the inside of the cable remains moist. Moisture inside the cable causes corrosion of the wire as described above.

  An object of the present invention is to make it possible to efficiently diagnose whether or not moisture is present in a coated cable and, if present, the degree thereof.

  In the cable diagnostic system according to the present invention, an optical fiber in which a fiber Bragg grating is formed without being fixed to the cable along the longitudinal direction of the cable inside the cable whose outer peripheral surface is covered with a coating layer. A sensing cable provided; a light source that generates incident light incident on the optical fiber; a light receiving element that receives reflected light from the fiber Bragg grating; and a light receiving signal output from the light receiving element. An interrogator having a wavelength calculation device for calculating the wavelength of reflected light by a fiber Bragg grating, conversion means for converting data representing the wavelength of reflected light output from the interrogator into data representing temperature, and representing the wavelength of the reflected light The data or the data representing the temperature Characterized in that it comprises recording means for recording, and a monitoring device comprising a temperature change curve generating means for generating a temperature variation curve based on the data representative of the temperature over a predetermined time period, the I. The monitoring device may include a display device for displaying the temperature change curve.

  A fiber Bragg grating (hereinafter also referred to as FBG) formed on an optical fiber changes the period of the diffraction grating and changes the wavelength of light reflected by the FBG regardless of strain or temperature. Here, the sensing cable used in the cable diagnosis system according to the present invention is provided with an optical fiber provided with FBG without being fixed to the cable inside the cable. The strain is not transmitted or difficult. Therefore, the wavelength of the reflected light by the FBG can be changed depending strongly on the temperature change. In other words, the temperature change inside the cable at the location where the FBG is located can be accurately grasped based on the wavelength change of the reflected light by the FBG.

  The cable can be used as a cable for suspending a structure, for example, a bridge. For example, a plurality of wire strands are bundled in a circular cross section. A parallel wire cable in which a plurality of wire strands are bundled in parallel may be used, or a twisted wire cable in which a plurality of wire strands are twisted. The optical fiber is provided in the coating layer together with the cable. The optical fiber may be provided so as to extend linearly along the longitudinal direction of the cable, or may be provided in a spiral shape so as to be wound around the outer peripheral surface of the cable. The cable used outdoors changes its internal temperature due to changes in temperature.

  The interrogator includes a light source, a light receiving element, and a wavelength calculation device. Incident light generated by the light source enters the optical fiber, and reflected light from the FBG formed on the optical fiber is received by the light receiving element. The wavelength of the light reflected by the FBG is calculated by the wavelength calculation device using the output light reception signal. As described above, when a temperature change occurs inside the cable where the FBG is located, the wavelength of the reflected light calculated by the wavelength calculation device changes.

  Data representing the wavelength of reflected light by the FBG is converted into data representing temperature in the monitoring device. The deviation from the relative temperature, not the absolute temperature, but the relative temperature, for example, the temperature at the start of diagnosis (measurement), is calculated by data conversion. As described above, since the optical fiber according to the present invention is provided inside the cable without being fixed to the cable, even if the cable is distorted, the wavelength of the reflected light from the FBG does not change. Data representing the wavelength of reflected light can be accurately converted to data representing temperature.

  Data representing the wavelength of reflected light from the FBG over a predetermined period of time, for example, one day to several days, is acquired and recorded over time, whereby the temperature change of the FBG from one day to several days can be obtained. A temperature change curve is generated from the temperature change of the FBG. Data representing the wavelength of reflected light may be recorded, or data representing temperature may be recorded. Of course, both data can be recorded.

  The temperature change curve is completely different depending on the specific heat of air and water when there is no moisture in the cable (dry state) and when there is moisture (wet state). By observing a temperature change curve representing the temperature change of the FBG over a predetermined time, the presence or absence of moisture inside the cable can be diagnosed.

  In one embodiment, the monitoring device includes temperature gradient calculation means for differentiating the temperature change curve to calculate a temperature gradient. The temperature gradient calculated by differentiating the temperature change curve (the slope of the temperature change curve) depends on the amount of moisture present in the cable as well as in the presence and absence of moisture in the cable. Change. By using not only the temperature change curve described above but also the temperature gradient, it is possible to accurately diagnose the presence or absence of moisture inside the cable and the degree to which moisture is present.

  Preferably, the monitoring device includes a determination unit that determines the presence or absence and the degree of moisture in the cable using at least one of the temperature change curve and the temperature gradient. The feature quantity (feature value) that appears in the temperature change curve and the temperature gradient is used to determine the presence and degree of moisture inside the cable.

  Preferably, a plurality of fiber Bragg gratings having different diffraction grating periods are formed in the optical fiber at intervals in the longitudinal direction of the optical fiber. The presence or absence and degree of moisture inside the cable at each of a plurality of locations in the longitudinal direction of one cable can be diagnosed.

  In the sensing cable according to the present invention, an optical fiber having a fiber Bragg grating is provided without being fixed to the cable along the longitudinal direction of the cable inside the cable whose outer peripheral surface is covered with a covering layer. It is characterized by. The wavelength change of the reflected light due to the FBG is not caused by the strain, that is, only the temperature change can be captured by the wavelength change.

  In one embodiment, the cable includes a cable main body portion in which a plurality of wire strands are bundled in a circular cross section, and a covering layer provided on the outer peripheral surface of the cable main body portion. An elongated hollow tube is fixed, and the optical fiber having an outer diameter smaller than the hollow inner diameter of the tube is passed through the tube. It is possible to prevent the distortion of the cable body from being transmitted to the optical fiber.

  Preferably, a filament tape is wound around the outer peripheral surface of the cable main body, and the covering layer is provided on the outer peripheral surface of the filament tape. The shape of the sensing cable can be stabilized.

  In another embodiment, a plurality of fiber Bragg gratings having different diffraction grating periods are formed in the optical fiber at intervals in the longitudinal direction of the optical fiber. Wavelength changes at each of a plurality of locations in the longitudinal direction of a single cable can be acquired.

  As described above, according to the present invention, it is possible to efficiently diagnose whether or not moisture is present inside the coated cable, and if so, to what extent.

It is a front view which shows a part of cable stayed bridge roughly. It is a cross-sectional view of a sensing cable. It is a front view of a sensing cable. It is a cross-sectional view of the optical fiber passed through the tube. A block diagram showing the electrical configuration of the interrogator is shown along with the optical fiber and monitoring device. It is a flowchart which shows the flow of a process of a monitoring apparatus. It is a graph which shows a temperature change curve. The graph of a temperature change curve is expanded and shown. (A)-(C) are the graphs which show the gradient value of a temperature change curve.

  FIG. 1 is a front view schematically showing a part of a cable-stayed bridge spanned on both banks of a river or a strait.

  The cable-stayed bridge 1 is composed of a tower 2 erected, a bridge girder 3 spanning both banks, and a plurality of sensing cables 10. The tower 2 is erected on both sides of the bridge girder 3 (one tower 2 is shown in FIG. 1), and the bridge girder 3 passes between the two towers 2. From the tower 2 to the bridge girder 3, a plurality of sensing cables 10 are stretched diagonally from the left and right sides of the tower 2. One end of the sensing cable 10 is fixed to the tower 2 and the other end is fixed to the bridge girder 3. The bridge girder 3 is supported in a well-balanced manner by a plurality of sensing cables 10 obliquely stretched to the left and right of the tower 2.

  The sensing cable 10 that supports the bridge girder 3 includes an optical fiber 15 therein (details of the structure of the sensing cable 10 will be described later). The length of the optical fiber 15 is longer than the length of the main body of the sensing cable 10 (cable main body 11 to be described later) connecting the tower 2 and the bridge girder 3, and the light emitted from the lower end of the sensing cable 10 The fiber 15 is wound along the bridge girder 3 and collected in one place. Each of the plurality of optical fibers 15 collected in one place is connected to an interrogator 30 described later. The interrogator 30 may be installed only when diagnosing the cable, or may be permanently installed at an appropriate place on the cable-stayed bridge 1 or in the vicinity of the cable-stayed bridge 1.

  FIG. 2 is a cross-sectional view of the sensing cable 10. FIG. 3 shows a front view of the sensing cable 10 by omitting a filament tape and a coating layer to be described later.

  The sensing cable 10 includes a cable main body 11 in which a plurality of wire wires 12 having a circular cross section are bundled in a substantially circular cross section, and a filament tape 13 wound spirally around the outer peripheral surface of the cable main body 11 without a gap. A coating layer 14 covering the outer peripheral surface of the filament tape 13, an optical fiber 15, and a tube 16 through which the optical fiber 15 is passed.

  The cable body 11 is configured by bundling a plurality of wire strands 12 having a diameter of 7 mm, for example. The wire strand 12 is a steel wire whose surface is plated with zinc. Although the number of wire strands 12 is determined according to the required strength of the cable body 11, the cable body 11 is generally composed of tens to hundreds of wire strands 12. In order to increase the tensile strength, a plurality of wire strands 12 may be twisted together at a twist angle of about 3 °.

  A gap (space) formed by adjacent wire strands 12 is formed in the longitudinal direction of the cable body portion 11 on the surface of the cable body portion 11 configured by bundling a plurality of wire strands 12. The elongated tube 16 is bonded (fixed) to the cable body 11 using this gap. The tube 16 is provided in the entire longitudinal direction of the cable body 11. An optical fiber 15 is passed through the tube 16. The optical fiber 15 is provided in the entire longitudinal direction of the cable main body 11 and has a length sufficient to come out from the lower end of the sensing cable 10 and connect to the interrogator 30 as described above.

  FIG. 4 shows an enlarged cross section of the tube 16 and the optical fiber 15 passing through the tube 16.

  The optical fiber 15 includes a quartz glass or plastic core 15A disposed in the center thereof, a quartz glass or plastic clad 15B provided on the outer circumferential surface of the core 15A, and a resin coated on the outer circumferential surface. And a coating layer 15C. The refractive index of the cladding 15B is smaller than the refractive index of the core 15A, and the light incident on the core 15A propagates through the core 15A while repeating total reflection. The tube 16 is made of polyimide and has an inner diameter of, for example, 600 μm. On the other hand, the outer diameter of the optical fiber 15 passed through the tube 16 is, for example, 125 μm, and the optical fiber 15 is loosely passed through the tube 16. Since the optical fiber 15 is not fixed to the cable main body 11, even if the cable main body 11 expands and contracts (even if it is distorted), the expansion and contraction is not transmitted to the optical fiber 15.

  2 and 3, the filament tape 13 is spirally wound around the outer peripheral surface of the cable body 11, so that the circular shape of the cable body 11 is maintained. The tube 16 through which the optical fiber 15 is passed is also located inside the filament tape 13 together with the cable body 11.

  The outer peripheral surface of the filament tape 13 is covered with high-density polyethylene having a thickness of several mm to form a coating layer 14. The covering layer 14 is made of, for example, press-fitted high-density polyethylene that has been softened (fluidized) by being heated and softened into the tubular body while the cable body 11 around which the filament tape 13 is wound is inserted and moved. Then, the high density polyethylene is attached to the outer peripheral surface of the filament tape 13, and the outer shape of the attached high density polyethylene is adjusted through a die or the like and cooled.

  FIG. 5 is a block diagram showing the electrical configuration of the interrogator 30 together with the optical fiber 15 connected to the interrogator 30 and the monitoring device 40. The interrogator 30 is connected to all of the plurality of optical fibers 15 provided inside each of the plurality of sensing cables 10 constituting the cable-stayed bridge 1, but in FIG. , One optical fiber 15 is shown connected.

  The interrogator 30 includes a light source 31, a light receiving module 32, a wavelength calculation device 33, an optical circulator 34, an optical connection terminal 35, and a USB (Universal Serial Bus) connection terminal 36.

  Light of a predetermined wavelength band is emitted from the light source 31. For example, a semiconductor laser that emits light having a wavelength band of 80 nm from 1510 nm to 1590 nm is used as the light source 31. Light from the light source 31 enters the optical fiber 15 connected to the optical connection terminal 35 via the optical circulator 34.

  Of the optical fiber 15, a plurality of fiber Bragg gratings (hereinafter referred to as FBGs) having different diffraction grating periods are arranged at intervals in a portion disposed inside the sensing cable 10 covered with the coating layer 14. It is formed with a gap. Although three FBG1 to FBG3 are shown in FIG. 5, the number of FBGs and the interval between the FBGs can be arbitrarily set.

  The FBG is a diffraction grating formed on the core 15A of the optical fiber 15, and reflects light having a wavelength (Bragg wavelength) twice the period of the diffraction grating. For example, FBG1 is formed on the core 15A of the optical fiber 15 so as to reflect light having a center wavelength of 1528 nm, FBG2 reflecting light having a center wavelength of 1535 nm, and FBG3 reflecting light having a center wavelength of 1538 nm.

  Reflected light from the FBGs 1 to 3 is received by the light receiving module 32 via the optical circulator 34 and is photoelectrically converted here. An electrical signal output from the light receiving module 32 is given to the wavelength calculation device 33.

  The wavelength calculation device 33 is a device (circuit) that calculates the wavelength of light reflected by the FBGs 1 to 3 from the electrical signal output from the light receiving module 32. The wavelength calculation unit 33 calculates the wavelength of the reflected light from the three FBG1 to FBG3 having different periods. Data representing the wavelength of the reflected light calculated by the wavelength calculation device 33 is given to the monitoring device 40 through a USB cable connected to the USB connection terminal 36.

  The monitoring device 40 is typically a personal computer and includes a CPU (Central Processing Unit), a memory, a hard disk, a keyboard, a display device, and the like. The monitoring device 40 is connected to the interrogator 30 when diagnosing the sensing cable 10. However, the monitoring device 40 may be always connected to the interrogator 30 and may be connected to the interrogator 30 by wireless connection instead of using a USB cable (in this case, the interrogator 30 and the monitoring device 40). Each is provided with a wireless communication device). In any case, data representing the wavelength of the reflected light from the FBGs 1 to 3 is given from the interrogator 30 to the monitoring device 40, and predetermined processing is executed in the monitoring device 40 as described below.

  The optical fiber 15 undergoes thermal expansion / contraction due to temperature. Since the diffraction grating interval (period) in the FBG formed in the optical fiber 15 changes due to thermal expansion / contraction, the wavelength of reflected light in the FBG changes according to temperature. By obtaining the correspondence between the temperature change and the wavelength change in advance using the optical fiber 15 to be used, the temperature change in the FBG can be calculated from the wavelength change of the reflected light calculated by the wavelength calculation device 33.

  As an example, the correspondence between temperature change and wavelength change is 0.01015 nm / ° C. That is, when there is a change of 1 ° C., the wavelength of the reflected light changes by about 0.01 nm. Conversely, if the wavelength of the reflected light changes by 0.01 nm, it means that a 1 ° C. change has occurred in the FBG. If the wavelength of the reflected light changes to the long wavelength side, it means that the temperature of the FBG has risen. Conversely, if the wavelength of the reflected light changes to the short wavelength side, it means that the temperature of the FBG has fallen. To do.

  The optical fiber 15 also expands and contracts (strains) when an external force is applied. However, as described above, since the optical fiber 15 is loosely passed through the tube 16 (FIG. 4), even if the cable main body 11 is expanded or contracted, it is not transmitted to the optical fiber 15. Therefore, the optical fiber 15 (FBG) provided in the sensing cable 10 can efficiently capture the wavelength change caused by the temperature change.

  FIG. 6 is a flowchart showing a process flow of the monitoring device 40.

  As described above, the monitoring device 40 receives data representing the wavelength of reflected light from the FBG calculated by the wavelength calculation device 33 of the interrogator 30 (step 51). Data representing the wavelength of the reflected light in time series is sequentially input to the monitoring device 40.

  The monitoring device 40 executes a process of converting data representing the wavelength (change) of the reflected light from the FBG given from the wavelength calculation device 33 into a temperature change in the FBG (step 52). Data representing the correspondence between the temperature change and the wavelength change described above is stored in advance in the hard disk of the monitoring device 40, and this is used for the conversion process. The data representing the correspondence between the temperature change and the wavelength change may be obtained by programming a mathematical formula or a lookup table.

  Data representing the time-series FBG temperature change calculated by the conversion is used, and a curve representing the temperature change of the FBG (hereinafter referred to as a temperature change curve) is displayed on the display screen of the display device of the monitoring device 40. (Step 53).

  Fig. 7 shows the temperature change curves of FBG1 to 3 over a period of 3 days (259,200 seconds) with changes in the outside air temperature. The vertical axis shows the temperature difference (° C) and the horizontal axis shows time (s). Yes. The vertical axis shows the difference (temperature difference) from the reference temperature, where the temperature at the start of measurement is the reference temperature (0 ° C.).

  In FIG. 7, the solid line is a temperature change curve measured by the FBG 1 provided in a healthy part (dry place where moisture is not included), and the alternate long and short dash line is provided in a small water-containing part (a part with low wetness). The temperature change curve measured by the FBG 2 and the broken line respectively show the temperature change curve measured by the FBG 3 provided in a portion having a large water content (a portion where the degree of wetness is large). The degree of water content was reproduced by changing the number of times water (mist) was sprayed on the cable body 11 in the experiment. Specifically, a state where water is sprayed once onto the cable body 11 of the sensing cable 10 from which the covering layer 14 and the filament tape 13 are removed and lightly moistened is referred to as “a small water-containing portion” (small wetness). ), And a state where the water is sprayed several times and is extremely wetted is defined as “a large water-containing part” (large wetness).

  Focusing on the daily temperature change, it can be seen that the temperature difference between the highest temperature and the lowest temperature is greatly different between the healthy part and the water-containing part. For example, paying attention to the temperature change of FBGs 1 to 3 on the first day (0 second to 86,400 seconds), the temperature difference between the water-containing parts (one-dot chain line (FBG2) and broken line (FBG3)) was about 20 ° C. On the other hand, the temperature difference of the healthy part (solid line (FBG1)) is only about 15 ° C. By paying attention to the temperature difference of the temperature change curve, the presence or absence of moisture inside the sensing cable 10 can be diagnosed.

  FIG. 8 shows an enlarged view of the temperature change curve shown in FIG. 7 immediately after the start of measurement (from 0 second to 10,000 seconds).

  Immediately after the start of measurement, the time required for the temperature of the healthy part (FBG1) to rise and a temperature change of, for example, + 7 ° C. was about 3800 seconds (solid line). On the other hand, the time required for the temperature of the water-containing part (FBG2, FBG3) to rise and the temperature change of + 7 ° C. to occur similarly was about 5000 seconds or longer (dashed line and broken line). The presence or absence of moisture inside the sensing cable 10 can also be diagnosed by paying attention to the rate of temperature change immediately after the start of measurement.

  Further, in FIGS. 7 and 8, when focusing on the gradient (gradient) of the temperature change curve, a large gradient appears in the temperature change curve (solid line) of the healthy region (FBG1), whereas the water-containing region (FBG2, 2). It can be seen that the gradient of the temperature change curve of the healthy part does not appear in the temperature change curve (one-dot chain line, broken line) of FBG3). Furthermore, when the temperature change curve (dashed line) of the small water-containing part (FBG2) is compared with the temperature change curve (dashed line) of the large water-containing part (FBG3), the large water-containing part (dashed line) It can be seen that the gradient of the temperature change curve is smaller. That is, by paying attention to the gradient value of the temperature change curve, it is possible to accurately diagnose not only the presence / absence of moisture inside the sensing cable 10 but also the degree thereof.

  FIGS. 9A to 9C show the gradient values (temperature gradients) of the temperature conversion curves for each of FBG1, FBG2, and FBG3 shown in FIG. 7 (the gradient calculation time interval is 60 seconds). The temperature gradients shown in FIGS. 9A to 9C are calculated by differentiating the temperature change curves for the FBGs 1 to 3 shown in FIG. 7 (steps 54 and 55).

  As described above, the temperature change curve of the healthy part includes a relatively large gradient. Therefore, for example, if the maximum value of the temperature gradient (which may be the maximum value of the absolute value) is used as a feature value (feature value) and the maximum value of the temperature gradient exceeds a predetermined threshold, the part is a healthy part. It can be determined. Referring to FIG. 9A, the maximum value of the temperature gradient calculated from the temperature change curve for FBG1 exceeds 0.5. On the other hand, referring to FIGS. 9B and 9C, the maximum value of the temperature gradient for FBG2 and FBG3 does not exceed 0.5. For example, the threshold value may be set to 0.5, and if the maximum value of the temperature gradient exceeds 0.5, the monitoring device 40 may automatically determine that the site is healthy.

  Comparing FIG. 9 (B) and FIG. 9 (C), it can be clearly seen from the gradient curve that the maximum gradient value decreases when the water content is large. As described above, if the maximum value of the temperature gradient is equal to or less than the predetermined threshold value, it is determined that water is present inside the monitoring cable 10. Further, the smaller the maximum value of the temperature gradient, the greater the degree of water content. This may be automatically determined by the monitoring device 40. Thus, the temperature change curve and the temperature gradient calculated from the temperature change curve can be used to automatically determine the presence and degree of water inside the monitoring cable 10.

  The graphs shown in FIGS. 7, 8, and 9 </ b> A to 9 </ b> C can be displayed on the display screen of the display device of the monitoring device 40. That is, the graph shown in FIG. 7 records data representing the wavelength of reflected light given from the interrogator 30 to the monitoring device 40 for a predetermined time, and based on the data representing the correspondence between temperature change and wavelength change. What is necessary is just to convert into a temperature change. Of course, instead of the data representing the wavelength of the reflected light, data representing the converted temperature may be recorded for a predetermined time. The graph shown in FIG. 8 can be displayed by enlarging the graph shown in FIG. The graph shown in FIG. 9 can be created by differentiating the temperature change curve shown in FIG. By using the graphs of FIGS. 7, 8 and 9 displayed on the display screen, it is possible to diagnose whether or not moisture is contained in the sensing cable 10 and the degree thereof. Further, as described above, if data representing the slope value of the temperature conversion curve shown in FIG. 9 is used, the presence / absence and the degree of moisture inside the sensing cable 10 are automatically determined using one or more threshold values. Can be determined. Since one sensing cable 10 is provided with a plurality of FBGs, it is possible to grasp the portion of the sensing cable 10 that contains moisture.

10 Sensing cable
11 Cable body
12 Wire strand
13 Filament tape
14 Coating layer
15 optical fiber
16 tubes
30 Interrogator
31 Light source
32 Receiver module
33 Wavelength calculator
34 Optical circulator
40 Monitoring device

Claims (9)

A sensing cable provided with an optical fiber in which a fiber Bragg grating is formed without being fixed to the cable along the longitudinal direction of the cable inside the cable whose outer peripheral surface is covered with a covering layer; ,
A light source that generates incident light incident on the optical fiber, a light receiving element that receives light reflected from the fiber Bragg grating, and a light reception signal that is output from the light receiving element are used to determine the wavelength of light reflected by the fiber Bragg grating. An interrogator equipped with a wavelength computing device for computing;
Conversion means for converting data representing the wavelength of reflected light output from the interrogator into data representing temperature, recording means for recording data representing the wavelength of reflected light or data representing the temperature over a predetermined time, and predetermined time A monitoring device comprising temperature change curve generating means for generating a temperature change curve based on data representing a temperature over a range of temperatures;
Cable diagnostic system equipped with. The monitoring device
A temperature gradient calculating means for differentiating the temperature change curve to calculate a temperature gradient;
The cable diagnostic system according to claim 1. The monitoring device
Determination means for determining the presence and degree of moisture inside the cable using at least one of the temperature change curve and the temperature gradient;
The cable diagnostic system according to claim 2. A plurality of fiber Bragg gratings having different diffraction grating periods are formed in the optical fiber at intervals in the longitudinal direction of the optical fiber.
The cable diagnostic system according to any one of claims 1 to 3. The cable is a bridge parallel wire cable or a stranded wire cable in which a plurality of wire strands are bundled in a circular cross section.
The cable diagnostic system according to any one of claims 1 to 4. An optical fiber having a fiber Bragg grating is provided without being fixed to the cable along the longitudinal direction of the cable inside the cable whose outer peripheral surface is covered with a covering layer.
Sensing cable. The above cable
A cable main body in which a plurality of wire strands are bundled in a circular cross section, and a covering layer provided on the outer peripheral surface of the cable main body,
An elongated hollow tube is fixed to the surface of the cable body,
The optical fiber having an outer diameter smaller than the hollow inner diameter of the tube is passed through the tube.
The sensing cable according to claim 6. Filament tape is wrapped around the outer peripheral surface of the cable body,
The coating layer is provided on the outer peripheral surface of the filament tape,
The sensing table according to claim 7. A plurality of fiber Bragg gratings having different diffraction grating periods are formed in the optical fiber at intervals in the longitudinal direction of the optical fiber.
The sensing cable according to any one of claims 6 to 8.

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