Monitoring system

Abstract

Provided is a monitoring system that makes it possible to reduce the frequency of replacement of a sensor attached to a monitored object. One example of a monitoring system according to the present invention comprises: a vibrating string sensor (8) that is attached to a monitored object comprising a water pipe line or a bridge and outputs an electric signal corresponding to the vibration of a built-in vibrating string (8g) when the vibration string (8g) is allowed to vibrate freely; and a determination unit (34b) whereby the state of the monitored object is determined on the basis of a peak frequency that is obtained by performing frequency analysis of measurement data related to the electric signal output from the vibrating string sensor (8) and is within a second frequency range not including a first frequency range including the natural frequency of the vibrating string (8g).

Description

surveillance system

[0001] The present invention relates to a monitoring system for monitoring the condition of water pipelines, bridges, and the like.

[0002] Monitoring the condition of water pipelines, bridges, etc. is important for carrying out maintenance inspections of these structures.

[0003] For example, Patent Document 1 describes the configuration of a water leak detection system that detects water leaks by installing a sensor terminal consisting of a vibration sensor and a terminal device in an exposed portion of a water pipe buried in the ground. Here, the exposed portion of the water pipe is considered to be the location of a manhole, but if the distance between the two nearest manholes is long and the leak is located far away from the manhole location, it becomes difficult to detect the leak.

[0004] Furthermore, Patent Document 2 describes a bridge pier soundness evaluation system that evaluates the soundness of bridge piers. This system focuses only on the peak of the Fourier spectrum obtained from vibrations measured by a vibration sensor installed on the top (top surface) of the pier, and considers the frequency at which the peak is shown to be the natural frequency. Then, if the natural frequency exceeds a threshold value, the pier is evaluated as stable, and if the natural frequency is below the threshold value, the pier is evaluated as unstable.

[0005] JP 2020-76646 A JP 2007-271402 A

[0006] The vibration sensors used in Patent Documents 1 and 2 have a lifespan of about several years, and when the lifespan is reached, the vibration sensors must be replaced. If the replacement frequency is high, the replacement work increases and becomes uneconomical.

[0007] The present invention has been made to solve the above-mentioned problems, and aims to provide a monitoring system that can reduce the frequency of replacing sensors attached to monitored objects.

[0008] In order to achieve the above-mentioned object, a monitoring system according to one aspect of the present invention comprises a vibrating string sensor attached to a monitored object consisting of a water pipeline or a bridge, and which outputs an electrical signal corresponding to the vibration of the built-in vibrating string when the vibrating string is allowed to vibrate freely, and a judgment unit which judges the state of the monitored object based on a peak frequency obtained by frequency analysis of the measurement data of the electrical signal output from the vibrating string sensor, the peak frequency being within a second frequency range that does not include a first frequency range that includes the natural frequency of the vibrating string.

[0009] According to this configuration, the frequency of the monitored object can be measured by the peak frequency within the second frequency range, and the state of the monitored object can be determined based on this frequency. The vibration string sensor used here has fewer electrical components such as resistors than vibration sensors such as acceleration sensors that generally detect vibrations, has high moisture resistance, and has a long life. Therefore, the frequency of replacement of the vibration string sensor can be reduced compared to vibration sensors.

[0010] The monitored object may be a water pipeline, and the judgment unit may be configured to judge whether the water pipeline is in a state of having a water leakage defect based on whether the peak frequency obtained by frequency analysis of the measurement data of the electrical signal output from the vibrating string sensor is within the second frequency range.

[0011] With this configuration, vibrations caused by a water leak in a water pipeline can be detected by the peak frequency within the second frequency range, and the presence or absence of a peak frequency within the second frequency range can be used to determine whether the water pipeline is experiencing a water leak, thereby detecting the water leak. Compared to vibration sensors commonly used for water leak detection, vibration string sensors have fewer electrical components such as resistors, are highly moisture-resistant, and have a long lifespan. Therefore, the frequency of replacement of vibration string sensors can be reduced compared to vibration sensors. Furthermore, vibration sensors commonly used for water leak detection are not highly moisture-resistant and are therefore typically installed in exposed portions of water pipelines, such as manholes, rather than buried underground. Therefore, for example, if the distance between the nearest two manholes is long, they may not be able to detect water leaks. In contrast, vibration string sensors have high moisture resistance, so installing one or more vibration string sensors even in water pipelines buried underground can reliably detect water leaks.

[0012] The vibrating string sensor may be attached to the outer wall of the straight pipe section of the water pipeline, and the vibrating string sensor may be positioned so that the vibrating string of the vibrating string sensor intersects with the center line of the straight pipe section when viewed from a direction overlapping with the straight pipe section.

[0013] According to this configuration, by installing multiple vibration string sensors in the straight pipe section of the underground water pipeline, it is possible to install multiple vibration string sensors at appropriate distances, which makes it possible to reliably detect water leaks. Also, since vibrations caused by water leaks in the water pipeline are thought to easily propagate in the circumferential direction of the water pipeline, by arranging the vibration string sensor so that the vibrating string of the vibration string sensor intersects with the center line of the straight pipe section when viewed from the direction overlapping the straight pipe section, it becomes easier to detect water leak defects.

[0014] The water pipeline has a first pipe, a second pipe, and an expansion and contraction flexible pipe joint including a cylindrical sleeve, and is configured such that the first pipe and the second pipe are connected by the expansion and contraction flexible pipe joint, and a first sensor housing has a first cylinder one end attached to a first pipe position that is a predetermined position of the first pipe, and a first cylinder holder one end attached to a first reference position of the sleeve and the other end movable in a telescopic manner relative to the other end of the first cylinder, and is equipped with a first measuring tool having the vibrating string sensor built in such that the natural frequency of the vibrating string changes in accordance with a change in distance between the first pipe position and the first reference position, and a second sensor housing has a second cylinder one end attached to a second pipe position that is a predetermined position of the second pipe, and a second cylinder holder one end attached to a second reference position of the sleeve and the other end movable in a telescopic manner relative to the other end of the second cylinder, and is equipped with a first measuring tool having the vibrating string sensor built in such that the natural frequency of the vibrating string changes in accordance with a change in distance between the second pipe position and the second reference position The measuring device may further include a second measuring tool having the vibrating string sensor built in so that the vibration frequency changes, and a displacement calculation unit, wherein the displacement calculation unit calculates a first distance change amount, which is the amount of change in the distance between the first piping position and the first reference position, based on a peak frequency obtained by frequency analysis of measurement data of an electrical signal output from the vibrating string sensor of the first measuring tool, the peak frequency being within the first frequency range, and calculates a second distance change amount, which is the amount of change in the distance between the second piping position and the second reference position, based on a peak frequency obtained by frequency analysis of measurement data of an electrical signal output from the vibrating string sensor of the second measuring tool, the peak frequency being within the first frequency range, and calculates the displacement of the first piping relative to the expansion flexible pipe joint based on the first distance change amount, and calculates the displacement of the second piping relative to the expansion flexible pipe joint based on the second distance change amount.

[0015] According to this configuration, vibration string sensors are used as sensors provided in the first and second measuring tools, and measurement data obtained from the output of the vibration string sensors is used to detect water leakage defects and to calculate the displacement of the first and second pipes relative to the expansion flexible pipe joint. Therefore, there is no need to provide separate sensors for detecting water leakage defects and for calculating the displacement, which is economical.

[0016] The monitored object may be a bridge, and the judgment unit may be configured to judge that the health of the bridge is lower when the peak frequency within the second frequency range obtained by frequency analysis of the measurement data of the electrical signal output from the vibrating string sensor is smaller than the standard value of the bridge's natural frequency.

[0017] According to this configuration, the standard value of the bridge's natural frequency is the value when the bridge is in a healthy state with no deterioration, and the peak frequency within the second frequency range is the measured value of the bridge's natural frequency. The smaller this measured natural frequency is from the standard value, the lower the bridge's health is determined to be, and the bridge's health can be evaluated. Compared to vibration sensors generally used to measure bridge natural frequencies, vibrating string sensors have fewer electrical components such as resistors, are highly moisture-resistant, and have a long lifespan. Therefore, the frequency of replacement of vibrating string sensors can be reduced compared to vibration sensors.

[0018] The bridge is constructed by combining a plurality of components including a first component and a second component adjacent to each other, and the sensor storage device has a tube having one end attached to a first position which is a predetermined position of the first component and a tube holder having one end attached to a second position which is a predetermined position of the second component and the other end which moves in a telescopic manner relative to the other end of the tube, and is equipped with a measuring tool having the vibrating string sensor built in so that the natural frequency of the vibrating string changes in accordance with changes in the distance between the first position and the second position, and further equipped with a displacement calculation unit, wherein the displacement calculation unit calculates the amount of change in the distance between the first position and the second position based on a peak frequency obtained by frequency analysis of measurement data of the electrical signal output from the vibrating string sensor, the peak frequency being within the first frequency range.

[0019] According to this configuration, a vibrating string sensor is used as the sensor provided in the measuring tool, and measurement data obtained from the output of the vibrating string sensor is used to evaluate the soundness of the bridge and to calculate the amount of change in distance between the first position of the first component and the second position of the second component. This eliminates the need to provide separate sensors for evaluating the soundness of the bridge and calculating the amount of change, which is economical.

[0020] The first and second components may be a parapet and a bridge girder of an abutment of the bridge, two adjacent bridge girders of the bridge, or an abutment or pier to which an upper shoe of a movable bearing fixed to the underside of a bridge girder of the bridge and a lower shoe of the movable bearing are fixed.

[0021] The present invention has the above-described configuration and has an effect of providing a monitoring system that can reduce the frequency of replacing sensors attached to a monitored object.

[0022] FIG. 1 is a schematic diagram showing the overall configuration of a monitoring system in a first embodiment. FIG. 2 is a schematic diagram showing the internal configuration of a first measuring tool. FIG. 3 is a diagram showing the amplitude spectrum of an electrical signal output from a vibrating string sensor when a test is conducted in which the vibrating string is allowed to freely vibrate while the vibrating string sensor is stationary. FIG. 4 is a diagram showing the amplitude spectrum of an electrical signal output from the vibrating string sensor when a test is conducted in which the vibrating string sensor is vibrated at 1000 Hz while the vibrating string is allowed to freely vibrate. FIG. 5 is a side view showing an example of the state of a water pipeline a predetermined time after the installation of an expansion flexible pipe joint and a measuring device. FIG. 6 is a schematic diagram showing the configuration of a monitoring system in a second embodiment as viewed from the side. FIG. 7 is a schematic diagram showing a measuring tool attached to a water pipeline of the monitoring system shown in FIG. 6 as viewed from above. FIG. 8 is a schematic diagram showing the internal configuration of a vibrating string sensor used in the second embodiment. FIG. 9 is a schematic diagram showing an example of a bridge, which is a monitored object in a third embodiment. FIG. 10 is a schematic diagram showing an example of a measuring tool attached to a bridge support shown in FIG. 9. Fig. 11 is a cross-sectional view of the bearing shown in Fig. 10 in a direction perpendicular to the bridge axis. Fig. 12 is a schematic diagram showing an example of a monitoring system in a third embodiment. Fig. 13 is a schematic diagram showing an example of a monitoring system in a fourth embodiment.

[0023] Preferred embodiments of the present invention will be described below with reference to the drawings. Note that, in the following, identical or corresponding elements throughout the drawings will be designated by the same reference numerals, and redundant description thereof may be omitted. Furthermore, the drawings are schematic illustrations of the respective components for ease of understanding, and the shapes, dimensional ratios, and the like may not be accurately depicted. Furthermore, the present invention is not limited to the following embodiments. Therefore, the numerical values ​​of frequencies and the like exemplified below are merely examples, and the present invention is not limited to these numerical values.

[0024] 1 is a schematic diagram showing the general configuration of a monitoring system according to a first embodiment. The object to be monitored in this monitoring system is a water pipeline having a first pipe 1, a second pipe 2, and an expansion flexible joint 3. This water pipeline is configured such that the first pipe 1 and the second pipe 2 are connected by the expansion flexible joint 3.

[0025] The first pipe 1, the second pipe 2, and the expansion flexible pipe joint 3 are buried underground. The first and second pipes 1, 2 are composed of flange portions 1a, 2a inserted into the expansion flexible pipe joint 3 and main pipes 1b, 2b connected to the flange portions 1a, 2a. The expansion flexible pipe joint 3 has a cylindrical sleeve 4 and ring-shaped seal members 5, 6 disposed at both ends of the sleeve 4. The seal members 5, 6 are disposed so that a gap is formed between the outer peripheral wall surfaces of the first pipe 1 and the second pipe 2 and the inner peripheral surface of the sleeve 4. The first pipe 1 and the second pipe 2 are connected to the sleeve 4 through this gap to allow tilting, bending, and the like. The first pipe 1 and the second pipe 2 are connected to the sleeve 4 via the seal members 5, 6 so as to be freely expandable and contractible in the axial direction of the sleeve 4. The sleeve 4 is composed of a rigid pipe body, but may also be composed of a flexible pipe body.

[0026] The monitoring system in the first embodiment includes a measuring device 11, an observation device 33A, and a monitoring device 35A.

[0027] The measuring device 11 includes a plurality of first measuring tools 12 and a plurality of second measuring tools 13. The first measuring tool 12 is configured by a first sensor holder S1 comprising a first tube 19 and a first tube holder 20, and a vibration string sensor 21 built into it. The second measuring tool 13 is configured by a second sensor holder S2 comprising a second tube 23 and a second tube holder 24, and a vibration string sensor 21 built into it. While only one first measuring tool 12 and one second measuring tool 13 are shown in FIG. 1 , in this example, for example, four first measuring tools 12 are disposed at equal intervals in the circumferential direction of the sleeve 4 of the expansion flexible pipe joint 3 and the first and second pipes 1 and 2, and similarly, for example, four second measuring tools 13 are disposed at equal intervals in the circumferential direction. The number of each of the first and second measuring tools 12 and 13 may be one or two, but three or more is preferred. Furthermore, when a plurality of first and second measuring tools 12 and 13 are provided, they do not need to be spaced equally apart in the circumferential direction as long as their circumferential positions can be specified. In other words, a plurality of first measuring tools 12 may be arranged at different circumferential positions on the sleeve 4, and a plurality of second measuring tools 13 may be arranged at different circumferential positions on the sleeve 4.

[0028] An annular plate-shaped annular portion 26 is disposed on the outer periphery of the first piping position 15 of the first piping 1, and an annular plate-shaped annular portion 27 is disposed on the outer periphery of the first reference position 16 of the sleeve 4. Similarly, an annular plate-shaped annular portion 28 is disposed on the outer periphery of the second piping position 17 of the second piping 2, and an annular plate-shaped annular portion 29 is disposed on the outer periphery of the second reference position 18 of the sleeve 4.

[0029] The annular portions 26 and 27 have mounting portions 37 for mounting the first measuring tool 12, and the annular portions 28 and 29 have mounting portions 37 for mounting the second measuring tool 13.

[0030] In the first measuring tool 12, one end of the first tube 19 is attached to the attachment portion 37 of the annular portion 26 via the universal joint 30, and thus the one end of the first tube 19 is attached to the first piping position 15 via the universal joint 30 and the annular portion 26. One end of the first tube holder 20 is attached to the attachment portion 37 of the annular portion 27 via the universal joint 30, and thus the one end of the first tube holder 20 is attached to the first reference position 16 via the universal joint 30 and the annular portion 27. The other end of the first tube holder 20 is configured to be movable in a telescopic manner relative to the other end of the first tube 19, and the first sensor holder S1 expands and contracts in accordance with changes in the distance between the first piping position 15 and the first reference position 16.

[0031] In the second measuring tool 13, one end of the second tube 23 is attached to the attachment portion 37 of the annular portion 28 via the universal joint 30, and thus the one end of the second tube 23 is attached to the second piping position 17 via the universal joint 30 and the annular portion 26. One end of the second tube holder 24 is attached to the attachment portion 37 of the annular portion 29 via the universal joint 30, and thus the one end of the second tube holder 24 is attached to the second reference position 18 via the universal joint 30 and the annular portion 29. The other end of the second tube holder 24 is configured to be movable in a telescopic manner relative to the other end of the second tube 23, and the second sensor holder S2 expands and contracts in accordance with changes in the distance between the second piping position 17 and the second reference position 18.

[0032] FIG. 2 is a schematic diagram showing the internal configuration of the first measuring tool 12. The vibrating string sensor 21 includes a housing 21h, a shaft 21s, a vibrating string 21g, two coils 21c, and a spring 21b. The housing 21h has a bottomed cylindrical shape with a cylindrical portion and a bottom portion closing the base end of the cylindrical portion. The bottom portion of the housing 21h is fixed to the inner surface of one end of the first tube 19 using an appropriate member 41. The shaft 21s is arranged so as to be freely insertable into the tip end of the housing 21h. One end of the vibrating string 21g is fixed to the inner bottom portion of the housing 21h, and the other end of the vibrating string 21g is fixed to one end of the shaft 21s via the spring 21b. The other end of the shaft 21s is fixed to the other end of the first tube holder 20 using an appropriate member 42. Furthermore, two coils 21c are arranged within the housing 21h facing each other at positions close to the center of the vibrating string 21g.

[0033] The vibrating string sensor 21 outputs an electrical signal corresponding to the vibration of the built-in vibrating string 21g when the vibrating string 21g is allowed to vibrate freely. For example, by passing a pulse current from an observation device 33A installed on the ground to the coil 21c via a sensor cable 32 buried underground, a magnetic field is instantaneously generated, attracting the vibrating string 21g to the coil 21c and then releasing it, causing the vibrating string 21g to vibrate freely. At this time, an AC voltage is generated in the coil 21c by electromagnetic induction, and the resulting electrical signal is sent to the observation device 33A via the sensor cable 32.

[0034] The internal configuration of second measuring tool 13 is similar to that of first measuring tool 12, and therefore a description thereof will be omitted. The natural frequency of vibrating string 21g of vibrating string sensor 21 in first measuring tool 12 changes in accordance with a change in the distance between first piping position 15, where first measuring tool 12 is attached, and first reference position 16. Furthermore, the natural frequency of vibrating string 21g of vibrating string sensor 21 in second measuring tool 13 changes in accordance with a change in the distance between second piping position 17, where second measuring tool 13 is attached, and second reference position 18.

[0035] The observation device 33A is configured using, for example, a microcontroller or the like, and has a frequency analysis unit 34a, a determination unit 34b, a displacement calculation unit 34c, etc. When, for example, a periodic inspection is performed, the observation device 33A passes a pulse current through the coil 21c of the vibrating string sensor 21 of each of the plurality of first measuring tools 12 and the plurality of second measuring tools 13 at a predetermined timing, and then measures the electrical signal output from the vibrating string sensor 21 for a predetermined time, and detects a peak frequency by performing FFT (Fast Fourier Transform) or the like on the measurement data of the electrical signal for this predetermined time in the frequency analysis unit 34a.

[0036] Furthermore, in the observation device 33A, the determination unit 34b performs a water leakage determination process based on the detected peak frequency, and the displacement calculation unit 34c performs a displacement calculation process.

[0037] In the water leakage determination process by the determination unit 34b, it is determined whether the water pipeline equipped with the first and second pipes 1 and 2 and the expansion flexible pipe joint 3 has a water leakage defect depending on whether the peak frequency detected by the frequency analysis unit 34a is within a second frequency range (Rf2) that does not include a first frequency range (Rf1) that includes the natural frequency of the vibrating string 21g.

[0038] Furthermore, in the displacement calculation process by the displacement calculation unit 34c, the displacement of the first pipe 1 relative to the expansion flexible pipe joint 3 is calculated based on the peak frequencies detected by the frequency analysis unit 34a and within a first frequency range (Rf1) including the natural frequency of the vibrating chord 21g, and the displacement of the second pipe 2 relative to the expansion flexible pipe joint 3 is also calculated. This will be described in detail later.

[0039] The first frequency range (Rf1) and the second frequency range (Rf2) will now be described with reference to Fig. 3 and Fig. 4. Fig. 3 shows the amplitude spectrum of the electrical signal output from the vibrating string sensor 21 when a test is conducted in which the housing 21h and shaft 21s of the vibrating string sensor 21 are fixed to a test stand, the test stand is stationary, and a pulse current is passed through the coil 21c to cause the vibrating string 21g to vibrate freely. Fig. 4 shows the amplitude spectrum of the electrical signal output from the vibrating string sensor 21 when a test is conducted in which the housing 21h and shaft 21s of the vibrating string sensor 21 are fixed to a test stand, the test stand is vibrating at 1000 Hz, and a pulse current is passed through the coil 21c to cause the vibrating string 21g to vibrate freely.

[0040] The first frequency range Rf1 is a frequency range for displacement measurement that includes the natural frequency of the vibrating string 21g of the vibrating string sensor 21, e.g., 1500 to 3000 Hz. Meanwhile, the second frequency range Rf2 is a frequency range in which water pipelines vibrate due to water leakage. For example, in the case of stainless steel pipes, it is known that water leakage can cause vibrations in the range of 400 to 1200 Hz. Therefore, the second frequency range Rf2 is set to a range of 400 to 1200 Hz, assuming a stainless steel pipe. However, this range is not limited to this. In the example shown in FIG. 4, the test stand to which the vibrating string sensor 21 is fixed is vibrated at 1000 Hz to simulate vibrations due to water leakage. Thus, the second frequency range Rf2 is set to a range that does not include the natural frequency of the vibrating string 21g and does not overlap at all with the first frequency range Rf1.

[0041] In Fig. 3 , there is no peak frequency within the second frequency range Rf2, whereas in Fig. 4 , there is a peak frequency within the second frequency range Rf2. That is, Fig. 3 shows the test results simulating a state in which there is no water leakage defect in the water pipeline, while Fig. 4 shows the test results simulating a state in which there is a water leakage defect in the water pipeline. As shown in Fig. 4 , when the test stand to which the vibrating string sensor 21 is attached is vibrated at 1000 Hz to simulate vibration due to a water leak, a peak frequency appears at 1000 Hz within the second frequency range Rf2 in the amplitude spectrum of the electrical signal output from the vibrating string sensor 21. Furthermore, although not shown, when the test stand is vibrated at 500 Hz and 700 Hz, for example, in the same manner as in the test shown in Fig. 4 , peak frequencies appear at 500 Hz and 700 Hz within the second frequency range Rf2 in the amplitude spectrum of the electrical signal output from the vibrating string sensor 21. That is, vibrations caused by water leakage can be detected by the appearance of peak frequencies within the second frequency range Rf2 in the amplitude spectrum of the electrical signal output from the vibrating string sensor 21. Note that although Figures 3 and 4 show examples of amplitude spectra in which the vertical axis represents amplitude, peak frequencies can also be detected in the same way using power spectra in which the vertical axis represents the square of the amplitude.

[0042] The vibrating string sensor 21 here is originally intended to measure displacement based on a peak frequency within the first frequency range Rf1, but in this embodiment, the judgment unit 34b performs a water leakage judgment process to determine whether or not there is a water leakage defect based on whether or not a peak frequency exists within the second frequency range Rf2.

[0043] In the vibrating string sensor 21, the peak frequency within the first frequency range Rf1 corresponds to the natural frequency of the vibrating string 21g. Here, the total length of the vibrating string sensor 21 is the distance from the base end of the housing 21h (the bottom of the housing 21h described above) to the tip end of the shaft 21s (the other end of the shaft 21s described above). In the case of the first measuring tool 12, the total length of the vibrating string sensor 21 also expands or contracts in accordance with the expansion or contraction of the first sensor holder S1. When the distance between the first piping position 15 in the first piping 1 and the first reference position 16 of the sleeve 4 of the expansion flexible pipe joint 3 increases, thereby expanding the length of the first sensor holder S1, the total length of the vibrating string sensor 21 also expands accordingly. When the total length of the vibrating string sensor 21 expands, the tension of the vibrating string 21g increases, and the natural frequency increases. Conversely, when the distance between the first piping position 15 and the first reference position 16 becomes shorter and the length of the first sensor housing S1 becomes shorter, the overall length of the vibrating string sensor 21 also becomes shorter accordingly, and the natural frequency of the vibrating string 21g becomes lower. Therefore, by pre-storing the initial value of the natural frequency of the vibrating string 21g of the first measuring tool 12 when the measuring device 11 is initially installed, it is possible to calculate the first distance change (V1), which is the change in the distance between the first piping position 15 and the first reference position 16, based on the subsequent change in the natural frequency of the vibrating string 21g.

[0044] The case of the second measuring tool 13 is similar to that of the first measuring tool 12, and the initial value of the natural frequency of the vibrating string 21g of the second measuring tool 13 at the time when the measuring device 11 is first installed is stored in advance, and the second distance change amount (V2), which is the change in the distance between the second piping position 17 and the second reference position 18, can be calculated based on the subsequent change in the natural frequency of the vibrating string 21g.

[0045] Therefore, the displacement calculation unit 34c calculates a first distance change amount V1, which is the amount of change in distance between the first pipe position 15 in the first pipe 1 and the first reference position 16 of the sleeve 4 of the expansion flexible pipe joint 3, using a predetermined calculation formula with a variable being the peak frequency within the first frequency range Rf1 obtained from the measurement data of the output of the first measuring tool 12. Furthermore, the displacement calculation unit 34c calculates a second distance change amount V2, which is the amount of change in distance between the second pipe position 17 in the second pipe 2 and the second reference position 18 of the sleeve, using a predetermined calculation formula with a variable being the peak frequency within the first frequency range Rf1 obtained from the measurement data of the output of the second measuring tool 13. Note that the position data on the sleeve 4 of the expansion flexible pipe joint 3 for the first reference position 16 and the second reference position 18 are known.

[0046] At an actual construction site, the expansion flexible pipe joint 3 and the measuring device 11 are arranged, for example, in the following procedure. First, the soil is excavated, and the first pipe 1 and the second pipe 2 are connected using the expansion flexible pipe joint 3. Four first measuring tools 12 and four second measuring tools 13 are attached between the annular portions 26, 27, 28, and 29 that are provided in advance on the first pipe 1, the second pipe 2, and the expansion flexible pipe joint 3. The four first measuring tools 12 and the four second measuring tools 13 are arranged, for example, at angular intervals of 90 degrees in the circumferential direction. Note that the angular intervals are not limited to 90 degrees, and it is sufficient that the angular positions in the circumferential direction at which each of the first and second measuring tools 12 and 13 is arranged are known.

[0047] Here, when the expansion flexible pipe joint 3 and the measuring device 11 are initially installed, the first pipe 1 and the second pipe 2 are connected in a straight line by the expansion flexible pipe joint 3 so that their respective axes (center lines) 1C, 2C are on the same straight line. When the expansion flexible pipe joint 3 and the measuring device 11 are initially installed in this way, there is no expansion or contraction or inclination of the first pipe 1 and the second pipe 2 with respect to the sleeve 4 of the expansion flexible pipe joint 3, so the four first distance change amounts V1 obtained from the measurement data of the outputs of the vibration string sensors 21 of the four first measuring tools 12 and the four second distance change amounts V2 obtained from the measurement data of the outputs of the vibration string sensors 21 of the four second measuring tools 13 are zero. In addition, in this example, the first and second measuring tools 12, 13 are arranged so that the vibrating string 21g of the vibrating string sensor 21 built into each of them is parallel to the axes 1C, 2C of the first and second pipes 1, 2 and the axis (center line) of the sleeve 4 of the expansion flexible pipe joint 3.

[0048] Fig. 5 is a side view showing an example of the state of a water pipeline when a predetermined time has elapsed since the installation of the expansion flexible pipe joint 3 and the measuring device 11. Fig. 5 shows a state in which the axis 1C of the first pipe 1 and the axis 2C of the second pipe 2 are misaligned, causing the expansion flexible pipe joint 3 to tilt.

[0049] In the observation device 33A, the displacement calculation unit 34c calculates the first distance change amount V1 and the second distance change amount V2 as described above based on the peak frequency within the first frequency range Rf1 obtained by frequency analysis of the measurement data after a predetermined time has elapsed since the installation of the expansion flexible pipe joint 3 and the measuring device 11.

[0050] Here, the multiple first distance change amounts V1 are calculated from measurement data obtained by multiple first measuring tools 12 disposed at different circumferential positions of the expansion flexible pipe joint 3 and the first piping 1, so the degree of expansion and inclination of the first piping 1 relative to the expansion flexible pipe joint 3 can be calculated from the multiple first distance change amounts V1 according to a predetermined calculation formula. For example, since the multiple first distance change amounts V1 indicate the first distance change amounts V1 at the attachment locations of the respective first measuring tools 12, the expansion amount (expansion length) and inclination direction of the first piping 1 can be determined by combining this with position data of the angle on the circumference of the sleeve 4 to which each first measuring tool 12 is attached. The same applies to the multiple second distance change amounts V2.

[0051] Therefore, the displacement calculation unit 34c calculates the displacement of the first pipe 1 and the second pipe 2 relative to the expansion and contraction flexible pipe joint 3. As the displacement, four first distance change amounts V1 at different positions on the circumference of the sleeve 4 of the expansion and contraction flexible pipe joint 3 are used to calculate the amount of expansion and contraction of the first pipe 1 relative to the sleeve 4 and the tilt angle of the first pipe 1 relative to the axis (center line) of the sleeve 4, and similarly, four second distance change amounts V2 are used to calculate the amount of expansion and contraction of the second pipe 2 relative to the sleeve 4 and the tilt angle of the second pipe 2 relative to the axis of the sleeve 4. The expansion and contraction amount of the first pipe 1 is, for example, the amount of deviation of the end of the first pipe 1 on the axis 1C of the sleeve 4 that is connected to the sleeve, and the expansion and contraction amount of the second pipe 2 is, for example, the amount of deviation of the end of the second pipe 2 on the axis 2C of the sleeve 4 that is connected to the sleeve.

[0052] Furthermore, the displacement calculation unit 34c can calculate the axial deviation d (Figure 5), which is the deviation between the axis 1C of the first pipe 1 and the axis 2C of the second pipe 2, from the inclination angle of the first pipe 1 with respect to the axis of the sleeve 4 of the expansion and contraction flexible pipe joint 3 and the inclination angle of the second pipe 2 with respect to the axis of the sleeve 4.

[0053] The observation device 33A wirelessly transmits the leak detection result and calculation results such as the displacement of the first pipe 1 and the second pipe 2 relative to the expansion flexible pipe joint 3 to a remote monitoring device 35A. The monitoring device 35A is configured, for example, by a server installed in a monitoring center. The monitoring device 35A also has a display device, and can display the leak detection result and calculation results received from the observation device 33A on the display device.

[0054] The monitoring center staff can check whether there is a leak in the water pipeline. The center staff also determines whether the expansion / contraction amounts of the first pipe 1 and the second pipe 2, which are the calculation results, exceed the allowable expansion / contraction amount, for example, 200 mm, and whether the axial misalignment amount d exceeds the allowable axial misalignment amount, for example, 100 mm. If the calculation results show that the expansion / contraction amounts or the axial misalignment amount exceed the allowable expansion / contraction amount, the center staff determines whether to replace the expansion / contraction flexible pipe joint 3 with a new expansion / contraction flexible pipe joint or repair the expansion / contraction flexible pipe joint 3 using a pipe joint repair device. If the calculation results show that the expansion / contraction amounts or the axial shift amount do not exceed the allowable expansion / contraction amount, the center staff can confirm that the expansion / contraction flexible pipe joint 3 can be used continuously.

[0055] As described above, it is possible to detect the positional relationship of the first pipe 1 and the second pipe 2 with respect to the expansion flexible pipe joint 3. As a result, it becomes possible to accurately determine whether or not the expansion flexible pipe joint 3 needs to be repaired or replaced.

[0056] The frequency analysis unit 34a, the determination unit 34b, and the displacement calculation unit 34c may be provided in the monitoring device 35A, rather than in the observation device 33A. In this case, measurement data for a predetermined time of the electrical signals output from the vibrating string sensors 21 of each of the plurality of first measuring tools 12 and the plurality of second measuring tools 13 may be transmitted from the observation device 33A to the monitoring device 35A.

[0057] In this embodiment, a vibrating string sensor 21 is used as the sensor provided in the first measuring tool 12 and the second measuring tool 13, and measurement data obtained from the output of the vibrating string sensor 21 is used to detect water leakage defects and calculate the displacement of the first piping 1 and the second piping 2 relative to the expansion flexible pipe joint 3, so there is no need to provide separate sensors for detecting water leakage defects and for detecting the above-mentioned displacement, which is economical.

[0058] Furthermore, the vibration string sensor 21 has fewer electrical components such as resistors, is more moisture-resistant, and has a longer lifespan than vibration sensors such as acceleration sensors. While the lifespan of a vibration sensor is only a few years, the lifespan of the vibration string sensor 21 exceeds 10 years. Therefore, the frequency of replacement of the vibration string sensor 21 can be reduced compared to vibration sensors.

[0059] In addition, in the water leakage determination process, if a peak frequency exists within the second frequency range Rf2 in the amplitude spectrum of the measurement data obtained from the output of at least one of the multiple vibration string sensors 21 provided on the multiple first measuring tools 12 and the multiple second measuring tools 13, it may be determined that the water pipeline is in a state of having a water leakage defect.

[0060] In addition, the measurement data used in the leak detection process may be measurement data obtained from the output of some of the multiple vibrating string sensors 21 provided on the multiple first measuring tools 12 and the multiple second measuring tools 13.

[0061] In this embodiment, the first and second measuring tools 12 and 13 are installed in a state in which the axes 1C and 2C of the first and second pipes 1 and 2 are collinear, as shown in Fig. 1, but this is not limiting. For example, the first and second measuring tools 12 and 13 may be installed in a state in which the axis 1C of the first pipe 1 and the axis 2C of the second pipe 2 are misaligned, as shown in Fig. 5.

[0062] Second Embodiment Fig. 6 is a schematic side view of the configuration of a monitoring system in a second embodiment, and Fig. 7 is a schematic top view of a measuring tool attached to a water pipeline of the monitoring system shown in Fig. 6. The monitored object in this monitoring system is a water pipeline buried underground. This monitoring system monitors the condition of the water pipeline. Specifically, it monitors whether the water pipeline has a water leakage defect.

[0063] The monitoring system in the second embodiment includes a measuring tool 7, an observation device 33B, and a monitoring device 35B. The measuring tool 7 includes a vibrating string sensor 8 and a protective tube 31 that covers the vibrating string sensor 8. The measuring tool 7 is attached to the outer wall of a straight pipe section 10 of a water pipeline via an appropriate mounting member 36. As shown in FIG. 7 , the measuring tool 7 is attached to the outer wall of the straight pipe section 10 so that the vibrating string 8g of the vibrating string sensor 8 intersects (orthogonal in this example) the center line 10C of the straight pipe section 10 in a plan view. Note that although the vibrating string sensor 8 is disposed directly above the straight pipe section 10 here, it may also be disposed on the side of the straight pipe section 10, for example. In other words, the vibrating string sensor 8 is disposed so that the vibrating string 8g of the vibrating string sensor 8 intersects the center line 10C of the straight pipe section 10 when viewed from a direction overlapping the straight pipe section 10. Note that the measuring tool 7 may also be configured without the protective tube 31.

[0064] 8 is a schematic diagram showing the internal configuration of the vibrating string sensor 8. The vibrating string sensor 8 includes a housing 8h, a vibrating string 8g, two coils 8c, and a spring 8b. The housing 8h is cylindrical with both ends closed. One end of the vibrating string 8g is fixed to one end inside the housing 8h, and the other end of the vibrating string 8g is fixed to the other end inside the housing 8h via the spring 8b. In addition, two coils 8c are arranged inside the housing 8h facing each other at positions close to the center of the vibrating string 8g.

[0065] 2 , the vibrating string sensor 8 outputs an electrical signal corresponding to the vibration of the built-in vibrating string 8g when the vibrating string 8g is allowed to freely vibrate. For example, by passing a pulse current from an observation device 33B installed on the ground to the coil 8c via a sensor cable 32 buried underground, a magnetic field is instantaneously generated, attracting the vibrating string 8g to the coil 8c and then releasing it, causing the vibrating string 8g to vibrate freely. At this time, an AC voltage is generated in the coil 8c by electromagnetic induction, and the resulting electrical signal is sent to the observation device 33B via the sensor cable 32.

[0066] The observation device 33B is configured using, for example, a microcontroller or the like, and has a frequency analysis unit 34a, a determination unit 34b, etc. In the observation device 33B, for example, when a periodic inspection is performed, a pulse current is passed through the coil 8c of the vibrating string sensor 8 of the measuring tool 7 at a predetermined timing, and then the electrical signal output from the vibrating string sensor 8 is measured for a predetermined time, and the measurement data of the electrical signal for this predetermined time is subjected to FFT (Fast Fourier Transform) or the like in the frequency analysis unit 34a to detect a peak frequency. The determination unit 34b performs a water leakage determination process based on this detected peak frequency.

[0067] In the water leakage determination process by the determination unit 34b, whether or not the water pipeline including the straight pipe section 10 has a water leakage defect is determined based on whether or not the peak frequency detected by the frequency analysis unit 34a is within a second frequency range (Rf2) that does not include a first frequency range (Rf1) that includes the natural frequency of the vibrating string 8g. The observation device 33B wirelessly transmits this water leakage determination result to a remote monitoring device 35B. The monitoring device 35B is configured, for example, by a server installed in a monitoring center. The monitoring device 35B also has a display device and can display the water leakage determination result received from the observation device 33B on the display device. Staff at the monitoring center can confirm whether or not there is a water leakage in the water pipeline.

[0068] The frequency analysis unit 34a and the determination unit 34b may be provided in the monitoring device 35B instead of in the observation device 33B. In this case, measurement data for a predetermined time of the electrical signal output from the vibrating string sensor 8 of the measuring tool 7 may be transmitted from the observation device 33B to the monitoring device 35B.

[0069] The vibration string sensor 8 used in this embodiment has fewer electrical components such as resistors, is more moisture-resistant, and has a longer lifespan than vibration sensors generally used for water leak detection. While the lifespan of a vibration sensor is only a few years, the lifespan of the vibration string sensor 8 exceeds 10 years. Therefore, the frequency of replacement of the vibration string sensor 8 can be reduced compared to vibration sensors.

[0070] Furthermore, vibration sensors generally used for water leak detection are not highly moisture-resistant, and therefore are usually installed in exposed portions of water pipelines, such as manholes, and are not buried underground. Therefore, for example, if the distance between the two nearest manholes is long, water leaks may not be detected. In contrast, the vibration string sensor 8 is highly moisture-resistant, and therefore can be installed in the straight pipe section 10 buried underground, as in this embodiment. By installing multiple vibration string sensors 8 at appropriate distances, water leaks can be reliably detected.

[0071] Because vibrations caused by water leakage in a water pipeline are thought to easily propagate in the circumferential direction of the water pipeline, the measuring tool 7 is attached to the outer wall of the straight pipe section 10 so that the vibrating string 8g of the vibrating string sensor 8 intersects, or more preferably is perpendicular to, the center line 10C of the straight pipe section 10 when viewed from a direction where the vibrating string sensor 8 overlaps with the straight pipe section 10. This makes it easier to detect water leakage defects. As described above, it is preferable to arrange the measuring tool 7 so that the vibrating string 8g of the vibrating string sensor 8 intersects the center line 10C of the straight pipe section 10, but it is also acceptable to arrange the measuring tool 7 so that the vibrating string 8g of the vibrating string sensor 8 is parallel to the center line 10C of the straight pipe section 10.

[0072] A commercially available vibrating string sensor for measuring temperature or fluid pressure may be used as the vibrating string sensor 8. For example, when a vibrating string sensor for measuring temperature is used, the temperature can be calculated based on the peak frequency within a first frequency range (Rf1) that includes the natural frequency of the vibrating string built into the vibrating string sensor. Alternatively, a vibrating string sensor for measuring strain may be used as the vibrating string sensor 8.

[0073] Furthermore, instead of the measuring tool 7 equipped with the vibrating string sensor 8, a first measuring tool 12 equipped with the vibrating string sensor 21 of the first embodiment may be used. In this case, both longitudinal end portions of the first measuring tool 12, i.e., the end of the first tube 19 to which the universal joint 30 is attached and the end of the first tube holder 20 to which the universal joint 30 is attached in Fig. 1, are attached to the straight pipe section 10 via appropriate mounting members. In this case, the universal joints 30 on both sides may be omitted.

[0074] In the first and second embodiments, in one inspection, the observation devices 33A, 33B may acquire measurement data of the electrical signals output from the vibrating string sensors 21, 8 multiple times over a predetermined period of time, the frequency analysis unit 34a may detect a peak frequency for each of the acquired measurement data, and the determination unit 34b may perform a water leak determination process based on this. In this case, the determination unit 34b may be configured to determine that there is a water leak defect in the water pipeline if it determines that there is a water leak defect in all of the multiple water leak determination processes corresponding to the multiple measurement data. This prevents erroneous detection of a water leak defect.

[0075] In the first embodiment described above, the first and second measuring tools 12, 13 are used to detect the displacement of the first and second pipes 1, 2 relative to the expansion flexible pipe joint 3 and to detect water leakage defects, but this is not limiting. For example, the first and second measuring tools 12, 13 may be used only to detect the displacement of the first and second pipes 1, 2 relative to the expansion flexible pipe joint 3, and a water leakage defect detection measuring tool similar to the measuring tool 7 or the first measuring tool 12 described in the second embodiment may be provided separately from the first and second measuring tools 12, 13 for detecting water leakage defects. This water leakage defect detection measuring tool may be attached to the expansion flexible pipe joint 3 so that the vibrating string of the vibration string sensor built into it is parallel to the axis of the expansion flexible pipe joint 3, or may be attached so that it is not parallel. Furthermore, the water leakage defect detection measuring tool may be attached to the first and second pipes 1, 2 so that it is parallel to the axis of the first and second pipes 1, 2, or may be attached so that it is not parallel. Furthermore, the leakage defect detection measuring tool may be attached to any component constituting the water pipeline. For example, the leakage defect detection measuring tool may be attached to a flange, a valve, a bent pipe portion, or the like other than the first and second pipes 1 and 2 and the expansion flexible pipe joint 3, which are straight pipe portions.

[0076] Third Embodiment A monitoring object in a monitoring system according to a third embodiment is a bridge. Fig. 9 is a schematic diagram showing an example of a bridge.

[0077] The bridge shown in Figure 9 is configured by combining multiple components such as abutments 101, 102, a pier 103, bridge girders 104, 105, and bearings 106 to 109. This bridge has a pier 103 between two abutments 101, 102 on both sides, with a bridge girder 104 spanning between one abutment 101 and the pier 103, and a bridge girder 105 spanning between the other abutment 102 and the pier 103. The bridge girder 104 is supported by bearings 106, 107 installed on the abutment 101 and the pier 103, and the bridge girder 105 is supported by bearings 109, 108 installed on the abutment 102 and the pier 103. The abutments 101, 102 have lower footings 101c, 102c, vertical walls 101b, 102b on the footings, and parapets 101a, 102a which are portions that protrude upward from the vertical walls.

[0078] Expansion devices 111, 112, and 113 are installed in the gap between the parapet 101a of the abutment 101 and the bridge girder 104, the gap between two adjacent bridge girders 104 and 105, and the gap between the parapet 102a of the abutment 102 and the bridge girder 105. In addition, a bridge fall prevention device 115 is attached between the two bridge girders 104 and 105.

[0079] Furthermore, in this embodiment, measuring tools 121, 122, and 123 are attached via appropriate mounting members between the parapet 101a of the abutment 101 and the bridge girder 104, between the two bridge girders 104 and 105, and between the parapet 102a of the abutment 102 and the bridge girder 105. These measuring tools 121, 122, and 123 are attached to the ends or sides in the width direction of the bridge that are not passageways for vehicles or the like.

[0080] Moreover, Fig. 10 is a schematic diagram showing an example of a measuring tool attached to the bridge bearing shown in Fig. 9. Fig. 11 is a cross-sectional view of the bearing shown in Fig. 10 in a direction perpendicular to the bridge axis.

[0081] 10 and 11 is a movable bearing, and has an upper shoe 51 fixed to the underside of the bridge girder 105, and a lower shoe 52 fixed on the vertical wall 102b of the abutment 102. A stainless steel plate is fixed to the underside of the upper shoe 51, and an intermediate member 53 consisting of a sliding plate 54 such as a Teflon (registered trademark) plate, an intermediate plate 55, a rubber plate 56, and a seal ring 57 is arranged between the stainless steel plate on the underside of the upper shoe 51 and the lower shoe 52. The intermediate plate 55 and the rubber plate 56 are arranged in a cylindrical recess 52c provided in the lower shoe 52.

[0082] The lower shoe 52 has a pair of side sections 52a that face each other in the direction perpendicular to the bridge axis, which is a direction perpendicular to the bridge axis direction, and guide blocks 52b with an L-shaped cross section are fixed to both of these side sections 52a with bolts. The upper shoe 51 has a pair of side sections 51a that face the pair of side sections 52a of the lower shoe 52 from the inside, and has a pair of protrusions 51b that protrude in the direction perpendicular to the bridge axis from both ends of each side section 51a. The range R1 between the pair of protrusions 51b is the range within which the side sections 52a of the lower shoe 52 can move relative to the upper shoe 51 in the bridge axis direction.

[0083] In this embodiment, a measuring tool 124 is attached between the upper shoe 51 of the movable bearing 109 and the vertical wall 102b of the abutment 102, and an observation device 33C4 corresponding to the measuring tool 124 is installed on the vertical wall 102b. Note that, if the bearing 106 is a movable bearing similar to the bearing 109, the measuring tool 124 may be attached between the upper shoe 51 of the movable bearing 106 and the vertical wall 101b of the abutment 101, and an observation device 33C4 corresponding to the measuring tool 124 may be installed on the vertical wall 101b. Also, if the bearings 107, 108 are movable bearings similar to the bearing 109, the measuring tool 124 may be attached between the upper shoes 51 of the movable bearings 107, 108 and the pier 103, and an observation device 33C4 corresponding to the measuring tool 124 may be installed on the pier 103.

[0084] 12 is a schematic diagram showing an example of a monitoring system according to the third embodiment. The monitoring system according to the third embodiment includes the above-described measuring tools 121-124, four observation devices 33C1-33C4 corresponding to the measuring tools 121-124, and a monitoring device 35C. In this example, the system includes four measuring tools 121-124, but it may also include at least one of the measuring tools. The monitoring device 35C is configured, for example, by a server installed in a monitoring center or the like, and includes a frequency analysis unit 34A, a determination unit 34B, and a displacement calculation unit 34C.

[0085] The measuring tools 121 to 124 are similar to the first measuring tool 12 in the first embodiment shown in Fig. 2. That is, each of the measuring tools 121 to 124 is configured by incorporating a vibrating string sensor 21 in a sensor housing S1 consisting of a tube 19 and a tube holder 20.

[0086] In the measuring tool 121, one end of a tube 19 is attached via an appropriate mounting member to a first position P11 of the parapet 101a (first component) of the abutment 101. One end of a tube support 20 is attached via an appropriate mounting member to a second position P21 of the bridge girder 104 (second component). The other end of the tube support 20 is movable in a telescopic manner relative to the other end of the tube 19, and the natural frequency of the vibrating string 21g changes in accordance with a change in the distance L1 between the first position P11 and the second position P21.

[0087] In addition, in the measuring tool 122, one end of the tube 19 is attached to a first position P12 of the bridge girder 104 (first component) via an appropriate mounting member. One end of the tube support 20 is attached to a second position P22 of the bridge girder 105 (second component) via an appropriate mounting member. The other end of the tube support 20 is movable in a telescopic manner relative to the other end of the tube 19, and the natural frequency of the vibrating string 21g changes in accordance with a change in the distance L2 between the first position P12 and the second position P22.

[0088] Furthermore, in the measuring tool 123, one end of the tube 19 is attached to a first position P13 of the bridge girder 105 (first component) via an appropriate mounting member. One end of the tube support 20 is attached to a second position P23 of the parapet 102a (second component) of the abutment 102 via an appropriate mounting member. The other end of the tube support 20 is movable in a telescopic manner relative to the other end of the tube 19, and the natural frequency of the vibrating string 21g changes in accordance with changes in the distance L3 between the first position P13 and the second position P23.

[0089] 10 , in the measuring tool 124, one end of the tube 19 is attached to a first position P14 of the vertical wall 102b (first component) of the abutment 102 via an appropriate mounting member. One end of the tube support 20 is attached to a second position P24 of the upper shoe 51 (second component) of the movable bearing 109 via an appropriate mounting member. The other end of the tube support 20 is movable in a telescopic manner relative to the other end of the tube 19, and the natural frequency of the vibrating string 21g changes in response to changes in the horizontal distance L4 between the first position P14 and the second position P24.

[0090] The measuring tools 121 to 124 may be attached so that their longitudinal directions are reversed. That is, the measuring tools 121 to 124 may be attached so that the positions of the tube 19 and the tube receiver 20 of the sensor housing S1 are reversed left to right in Figures 10 and 12.

[0091] The observation devices 33C1 to 33C4 are configured using, for example, a microcontroller, and when performing periodic inspections, for example, they pass a pulse current through the coil 21c of the vibrating string sensor 21 of the corresponding measuring tool 121 to 124 at a predetermined timing, then measure the electrical signal output from the vibrating string sensor 21 for a predetermined period of time, and transmit the measurement data of the electrical signal for this predetermined period of time to the monitoring device 35C.

[0092] In monitoring device 35C, frequency analysis section 34A performs FFT (Fast Fourier Transform) or the like on the measurement data received from each of monitoring devices 35C1 to 35C4 to detect each peak frequency.

[0093] Furthermore, in the monitoring device 35C, the determining unit 34B evaluates the soundness of the bridge based on each peak frequency detected by the frequency analyzing unit 34A. An example of this evaluation method will be described.

[0094] The evaluation unit 34B evaluates the soundness of the bridge based on the peak frequencies (f2) detected by the frequency analysis unit 34A and located within a second frequency range (Rf2) that does not include a first frequency range (Rf1) that includes the natural frequency of the vibrating string 21g, and the standard value (fs) of the bridge's natural frequency. Here, the first frequency range Rf1 is set to, for example, a range of 1500 to 3000 Hz, and the second frequency range Rf2 is set to, for example, a range of 0.1 to 30 Hz. The standard value (fs) of the bridge's natural frequency is the natural frequency calculated from waveforms recorded by impact vibration testing or the like when the bridge was in a sound condition (e.g., at the time of completion).

[0095] Then, the judgment unit 34B calculates the judgment index k as k=f2 / fs, and determines the judgment rank according to, for example, the following (1) to (4).

[0096] (1) If k<0.7, the judgment rank is determined to be Rank A1. In this case, there is a dangerous deformation due to an abnormal external force, and it can be determined that repairs and reinforcement are necessary by referring to other investigation results.

[0097] (2) If 0.7≦k<0.85, the judgment rank is determined to be rank A2. In this case, it can be determined that it is necessary to grasp the progress of the decrease in natural frequency, etc.

[0098] (3) If 0.85≦k<1.0, the judgment rank is determined to be rank B. In this case, it can be determined that there are few problems at present.

[0099] (4) If 1.0≦k, the judgment rank is determined as rank S. In this case, the current state can be judged as healthy.

[0100] In this way, the smaller the judgment index k, i.e., the smaller the peak frequency f2 is compared to the standard value fs of the bridge's natural frequency, the lower the bridge's soundness is judged to be (the greater the degree of deterioration of the bridge). The peak frequency f2 is the measured value of the bridge's current natural frequency.

[0101] The judgment unit 34B calculates the evaluation result of the bridge soundness (judgment index k and judgment rank) in the manner described above.

[0102] In addition, the displacement calculation unit 34C of the monitoring device 35C calculates the change in the distance L1 between the first position P11 and the second position P21 based on the peak frequency (f11) detected in the frequency analysis unit 34A based on the measurement data from the observation device 33C1 corresponding to the measuring tool 121, and which is within a first frequency range (Rf1) that includes the natural frequency of the vibrating string 21g.

[0103] In addition, the displacement calculation unit 34C calculates the amount of change in the distance L2 between the first position P12 and the second position P22 based on the peak frequency (f12) detected in the frequency analysis unit 34A based on the measurement data from the observation device 33C2 corresponding to the measuring tool 122, and which is within a first frequency range (Rf1) that includes the natural frequency of the vibrating string 21g.

[0104] In addition, the displacement calculation unit 34C calculates the change in the distance L3 between the first position P13 and the second position P23 based on the peak frequency (f13) detected in the frequency analysis unit 34A based on the measurement data from the observation device 33C3 corresponding to the measuring tool 123, and which is within a first frequency range (Rf1) that includes the natural frequency of the vibrating string 21g.

[0105] Furthermore, the displacement calculation unit 34C calculates the amount of change in the distance (horizontal distance) L4 between the first position P14 and the second position P24 shown in FIG. 10 based on the peak frequency (f14) detected in the frequency analysis unit 34A based on the measurement data from the observation device 33C4 corresponding to the measuring tool 124, and which is within a first frequency range (Rf1) that includes the natural frequency of the vibrating string 21g.

[0106] The monitoring device 35C is equipped with a display device, and can display on the display device the evaluation results of the bridge soundness by the determination unit 34B and the calculation results by the displacement calculation unit 34C. Staff at the monitoring center can plan future countermeasures and the like based on the evaluation results of the bridge soundness and the calculation results by the displacement calculation unit 34C.

[0107] In this embodiment, a vibrating string sensor 21 is used as a sensor provided in the measuring tools 121-124, and measurement data obtained from the output of the vibrating string sensor 21 is used to evaluate the bridge's soundness and calculate the amount of change in the distances L1-L4 between the first position of the first component and the second position of the second component. This eliminates the need to provide separate sensors for evaluating the bridge's soundness and calculating the amount of change, which is economical. Note that in this embodiment, each of the measuring tools 121-124 is installed so that the longitudinal direction of the vibrating string sensor 21 is aligned with the bridge axis direction. However, depending on installation space and other factors, the longitudinal direction of the vibrating string sensor 21 may be installed in a direction other than the bridge axis direction.

[0108] Furthermore, the vibrating string sensor 21 has fewer electrical components such as resistors, is more moisture-resistant, and has a longer lifespan than vibration sensors typically used to measure the natural frequency of bridges. While the lifespan of a vibration sensor is only a few years, the vibrating string sensor 21 has a lifespan of over 10 years. Therefore, the frequency of replacement of the vibrating string sensor 21 can be reduced compared to vibration sensors.

[0109] The frequency analysis unit 34A, determination unit 34B, and displacement calculation unit 34C may be provided in each of the observation devices 33C1 to 33C4, rather than in the monitoring device 35C. In this case, the evaluation results of the bridge soundness by the determination unit 34B and the calculation results by the displacement calculation unit 34C may be transmitted from each of the observation devices 33C1 to 33C4 to the monitoring device 35C.

[0110] 13 is a schematic diagram showing an example of a monitoring system according to a fourth embodiment. The monitoring object in this monitoring system is a bridge, and the bridge shown in FIG. 9 will be used as an example for explanation.

[0111] The monitoring system in the fourth embodiment includes measuring tools 71-73, three observation devices 33D1-33D3 corresponding to the measuring tools 71-73, and a monitoring device 35D. In this example, three measuring tools 71-73 are included, but at least one of the measuring tools may be included. The monitoring device 35D is configured, for example, by a server installed in a monitoring center or the like, and includes a frequency analysis unit 34A and a determination unit 34B.

[0112] Measuring devices 71-73 are similar to the measuring device 7 shown in Figures 6 and 7 in the second embodiment, and are equipped with, for example, a vibrating string sensor 8 for measuring temperature or fluid pressure. That is, each of measuring devices 71-73 is configured by incorporating a vibrating string sensor 8 in a protective tube 31. Measuring device 71 is attached to the vertical wall 101b of the abutment 101 via an appropriate mounting member, and an observation device 33D1 corresponding to measuring device 71 is installed on the vertical wall 101b. Measuring device 72 is attached to the pier 103 via an appropriate mounting member, and an observation device 33D2 corresponding to measuring device 72 is installed on the pier 103. Measuring device 73 is attached to the vertical wall 102b of the abutment 102 via an appropriate mounting member, and an observation device 33D3 corresponding to measuring device 73 is installed on the vertical wall 102b. It is also possible for each of the measuring tools 71 to 73 to be configured without the protective tube 31. Furthermore, each of the measuring tools 71 to 73 may be installed so that the longitudinal direction of the vibrating string sensor 8 is the same as the bridge axis direction, or so that the longitudinal direction of the vibrating string sensor 8 is not the same as the bridge axis direction. Furthermore, a vibrating string sensor for measuring strain may be used as the vibrating string sensor 8. Furthermore, measuring tools similar to the measuring tools 71 to 73 may be installed on a fixed bearing, or may be installed across two components that do not displace, such as between a fixed bearing and an abutment.

[0113] The observation devices 33D1 to 33D3 are configured using, for example, a microcontroller, and when conducting periodic inspections, for example, they pass a pulse current through the coil 8c of the vibrating string sensor 8 of each corresponding measuring tool 71 to 73 at a predetermined timing, then measure the electrical signal output from the vibrating string sensor 8 for a predetermined period of time, and transmit the measurement data of the electrical signal for this predetermined period of time to the monitoring device 35D.

[0114] In the monitoring device 35D, the frequency analysis unit 34A performs FFT (Fast Fourier Transform) or the like on the measurement data received from each of the monitoring devices 35D1 to 35D3 to detect each peak frequency.

[0115] Furthermore, in the monitoring device 35D, the judgment unit 34B evaluates the bridge's soundness based on each peak frequency detected by the frequency analysis unit 34A. The judgment unit 34B evaluates the bridge's soundness based on a peak frequency (f2) detected by the frequency analysis unit 34A that is within a second frequency range (Rf2) that does not include a first frequency range (Rf1) that includes the natural frequency of the vibrating string 8g, and the standard value (fs) of the bridge's natural frequency. Here, the second frequency range Rf2 is set to, for example, a range of 0.1 to 30 Hz. The bridge's soundness is evaluated in the same manner as the judgment unit 34B of the monitoring device 35C in the third embodiment. Detailed explanations are omitted here. The lower the peak frequency f2 is compared to the standard value fs of the bridge's natural frequency, the lower the bridge's soundness (the greater the degree of deterioration).

[0116] The monitoring device 35D is equipped with a display device, and can display the bridge soundness evaluation results obtained by the judgment unit 34B on the display device. Based on the bridge soundness evaluation results, the monitoring center staff can plan future countermeasures, etc.

[0117] The vibrating string sensor 8 used in this embodiment has fewer electrical components such as resistors, is more moisture-resistant, and has a longer lifespan than vibration sensors generally used to measure the natural frequency of bridges. While the lifespan of a vibration sensor is about several years, the vibrating string sensor 8 has a lifespan of more than 10 years. Therefore, the frequency of replacement of the vibrating string sensor 8 can be reduced compared to vibration sensors.

[0118] The frequency analysis unit 34A and the determination unit 34B may be provided in each of the observation devices 33D1 to 33D3, rather than in the monitoring device 35D. In this case, the results of the bridge soundness evaluation by the determination unit 34B may be transmitted from each of the observation devices 33D1 to 33D3 to the monitoring device 35D.

[0119] Furthermore, instead of the measuring tools 71 to 73 equipped with the vibrating string sensor 8, a first measuring tool 12 equipped with the vibrating string sensor 21 in the first embodiment may be used. In this case, both longitudinal end portions of the first measuring tool 12, i.e., the end of the first tube 19 to which the universal joint 30 is attached and the end of the first tube support 20 to which the universal joint 30 is attached in Fig. 1, are attached to the upper surfaces of the vertical wall 101b of the abutment 101, the pier 103, and the vertical wall 102b of the abutment 102 via appropriate mounting members. In this case, the universal joints 30 on both sides may be omitted.

[0120] In the third embodiment, the measuring tools 121-124 incorporating the vibrating string sensor 21 are used as measuring tools for calculating the amount of change in the distances L1-L4 and for evaluating the bridge soundness, but this is not limited to this. For example, the measuring tools 121-124 may be used only for calculating the amount of change, and a separate measuring tool incorporating a vibrating string sensor may be installed for evaluating the bridge soundness. The measuring tools for evaluating the bridge soundness may be the measuring tools 71-73 in the fourth embodiment, or, as described above, the first measuring tool 12 equipped with the vibrating string sensor 21 in the first embodiment may be used instead of the measuring tools 71-73.

[0121] From the above description, many modifications and other embodiments of the present invention will be apparent to those skilled in the art. Therefore, the above description should be construed as illustrative only and is provided for the purpose of teaching those skilled in the art the best mode for carrying out the present invention. Details of the structure and / or function thereof may be substantially changed without departing from the spirit of the present invention.

[0122] The present invention is useful as a monitoring system or the like that can reduce the frequency of replacing sensors attached to a monitored object.

[0123] S1 First sensor storage device (sensor storage device) S2 Second sensor storage device 1 First pipe 2 Second pipe 3 Expansion flexible pipe joint 4 Sleeve 8, 21 Vibration string sensor 10 Straight pipe section 12 First measuring tool 13 Second measuring tool 15 First pipe position 16 First reference position 17 Second pipe position 18 Second reference position 19 First tube (tube) 20 First tube holder (tube holder) 23 Second tube 24 Second tube holder 34b, 34B Determination unit 34c, 34C Displacement calculation unit 51 Upper shoe of movable support 52 Lower shoe of movable support 101, 102 Abutment 101a, 102a Abutment parapet 103 Pier 104, 105 Bridge girder 106 to 109 Bearings 121 to 124 Measuring tool

Claims

1. A monitoring system comprising: a vibrating string sensor attached to a monitored object consisting of a water pipeline or a bridge, which outputs an electrical signal corresponding to the vibration of the built-in vibrating string when the vibrating string is allowed to vibrate freely; and a determination unit which determines the state of the monitored object based on peak frequencies obtained by frequency analysis of measurement data of the electrical signal output from the vibrating string sensor, the peak frequencies being within a second frequency range that does not include a first frequency range that includes the natural frequency of the vibrating string.

2. The monitoring system of claim 1, wherein the monitored object is a water pipeline, and the determination unit determines whether the water pipeline is in a state of having a water leakage defect based on whether a peak frequency obtained by frequency analysis of measurement data of the electrical signal output from the vibrating string sensor is within the second frequency range.

3. The monitoring system of claim 2, wherein the vibrating string sensor is attached to the outer wall of the straight pipe section of the water pipeline, and the vibrating string sensor is positioned so that the vibrating string of the vibrating string sensor intersects with the center line of the straight pipe section when viewed from a direction overlapping the straight pipe section.

4. The water pipeline comprises a first pipe, a second pipe, and an expandable flexible joint including a cylindrical sleeve, the first pipe and the second pipe being connected by the expandable flexible joint; a first sensor holder having a first tube with one end attached to a first pipe position, which is a predetermined position of the first pipe, and a first tube holder with one end attached to a first reference position of the sleeve and the other end moving in a telescopic manner relative to the other end of the first pipe, is provided with a first measuring tool with a built-in vibration string sensor so that the natural frequency of the vibrating string changes in accordance with changes in the distance between the first pipe position and the first reference position; and a second sensor holder having a second tube with one end attached to a second pipe position, which is a predetermined position of the second pipe, and a second tube holder with one end attached to a second reference position of the sleeve and the other end moving in a telescopic manner relative to the other end of the second pipe, is provided with a second measuring tool with a built-in vibration string sensor so that the natural frequency of the vibrating string changes in accordance with changes in the distance between the second pipe position and the second reference position.

3. The monitoring system according to claim 2, further comprising a displacement calculation unit, which calculates a first distance change amount, which is the amount of change in distance between the first piping position and the first reference position, based on a peak frequency obtained by frequency analysis of measurement data of the electrical signal output from the vibrating string sensor of the first measuring tool, the peak frequency being within the first frequency range, and calculates a second distance change amount, which is the amount of change in distance between the second piping position and the second reference position, based on a peak frequency obtained by frequency analysis of measurement data of the electrical signal output from the vibrating string sensor of the second measuring tool, the peak frequency being within the first frequency range, and calculates the displacement of the first piping relative to the expansion flexible pipe joint based on the first distance change amount, and calculates the displacement of the second piping relative to the expansion flexible pipe joint based on the second distance change amount.

5. The monitoring system of claim 1, wherein the monitored object is a bridge, and the judgment unit judges that the health of the bridge is lower when the peak frequency within the second frequency range obtained by frequency analysis of the measurement data of the electrical signal output from the vibrating string sensor is smaller than the standard value of the bridge's natural frequency.

6. The monitoring system according to claim 5, wherein the bridge is constructed by combining a plurality of components including a first component and a second component adjacent to each other, and the monitoring system further comprises a measuring device having a vibrating string sensor built in to a sensor housing having a tube with one end attached to a first position that is a predetermined position of the first component and a tube holder with one end attached to a second position that is a predetermined position of the second component and the other end moving in a telescopic manner relative to the other end of the tube, and further comprises a displacement calculation unit, wherein the displacement calculation unit calculates the amount of change in the distance between the first position and the second position based on a peak frequency obtained by frequency analysis of measurement data of the electrical signal output from the vibrating string sensor, the peak frequency being within the first frequency range.

7. The monitoring system according to claim 6, wherein the first and second components are a parapet and a bridge girder of an abutment of the bridge, two adjacent bridge girders of the bridge, or an upper shoe of a movable bearing fixed to the underside of a bridge girder of the bridge and an abutment or pier to which the lower shoe of the movable bearing is fixed.

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