JP2014182101A - Strain measurement method and strain measurement device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a strain measurement method and a strain measurement device that enable strains on multiple points to be suitably measured.SOLUTION: There is provided a strain measurement method that enables strains on multiple points to be measured by using FBG sensors 2, when there is present such an optical fiber laying condition that a curvature radius satisfying total reflection condition between a core and a cladding in an optical fiber cannot be ensured. The strain measurement method includes the steps of: demultiplexing light from a light source 1 by a first wavelength divider 4 and irradiating the plurality of FBG sensors 2 corresponding to each wavelength band of the first wavelength divider 4 with light from the light source 1; and demultiplexing respective reflected light beams from the FBG sensors 2 by a second wavelength divider 5 and measuring strains by the plurality of FBG sensors 2, on the conditions that the total reflection condition between the core and the cladding in the optical fiber laid from the light source 1 to the FBG sensors 2 is satisfied and that loss in optical intensity in the optical fibers present at a waveguide of both the optical intensity radiated from the light source 1 upon the FBG sensors 2 and the optical intensity reflected from the FBG sensor 2 is minimized.

Description

  The present invention relates to a strain measuring method and a strain measuring apparatus that measure multi-point strain.

  In general, an electric resistance strain gauge is used as a method and apparatus for measuring strain. However, in recent years, FBG (Fiber Bragg Grating) sensors, which are optical fiber sensors excellent in light weight, electromagnetic interference resistance, and explosion resistance, have come to be used. The FBG sensor has a property of strongly reflecting a specific wavelength called a Bragg wavelength. The Bragg wavelength changes with strain and temperature, and has good linearity with respect to strain change and temperature change.

  In addition, when measuring strain at multiple points using an FBG sensor, multiple FBG sensors are generally arranged in series (chained) on a single optical fiber, and the installation efficiency is improved by simplifying the FBG sensor measurement line. (For example, see Patent Documents 1 to 3).

JP 2006-138757 A JP 2011-43379 A JP 2011-163941 A Japanese Patent No. 5090289 Nakajima Tomio, Arakawa Norihiro, "High-speed dynamic strain measurement technology using FBG sensor", IIC REVIEW No.38, pp. 37-44 (2007), IHI inspection and measurement publication

  However, an optical fiber in which a plurality of FBG sensors are arranged in series (chains) and a radius of curvature that satisfies the total reflection condition between the optical fiber core and the clad cannot be secured for the optical signal propagating in the optical fiber core. When placed in the laying condition, the optical signal in the core leaks to the outside through the cladding at the optical fiber portion having a small radius of curvature, and the intensity of the optical signal transmitted through the optical fiber core is attenuated. There was a problem. It is known that a general single mode optical fiber cannot satisfy the total reflection condition between the optical fiber core and the clad when the radius of curvature is smaller than 30 mm. Even in a single mode optical fiber that can make the radius of curvature smaller, it is only about 15 mm in radius of curvature that the total reflection condition between the core and the clad can be satisfied.

  In such a case, a configuration in which FBG sensors are arranged in parallel as shown in FIG. The configuration in which the FBG sensors are arranged in parallel uses an optical passive element called an optical coupler. The optical coupler fulfills two functions of dividing the optical signal intensity propagated through one or a plurality of optical fibers into two or more optical fibers and consolidating them into one optical fiber. In the case of FIG. 3, the light emitted from the light source is split through the optical circulator, and further split by the optical coupler while maintaining the wavelength band irradiated by the light source to irradiate each FBG sensor. Furthermore, the reflected light from the FBG sensor is recombined by an optical coupler and guided to a wavelength measuring device via an optical circulator.

  However, as a method for measuring the Bragg wavelength of the FBG sensor, as shown in FIG. 3 of Patent Document 1 and Patent Document 4, an optical coupler is disposed between the optical circulator and the FBG sensor and an optical filter is used (Non-Patent Document 1). In the measurement principle, the optical signal intensity irradiated to each FBG sensor decreases according to the optical intensity division ratio of the optical coupler (for example, 50%: 50% when dividing into two FBG sensors). The intensity of the optical signal incident on the optical filter for measurement also decreases with the light intensity division ratio of the optical coupler. In addition, the optical intensity division ratio of the optical coupler is smaller than when the FBG sensors are connected in series. Here, FIGS. 7A and 7B show the FBG reflected light spectrum and the case where an optical coupler is used (division ratio 50%), and show that the optical signal intensity of the optical coupler is reduced. Yes. In addition, the vertical axis | shaft of Fig.7 (a) is a logarithmic scale axis | shaft display, and the vertical axis | shaft of FIG.7 (b) is a linear scale axis | shaft display.

  In the strain measurement method using the FBG sensor described in Non-Patent Document 1, the wavelength band of the reflected light from the FBG sensor is sufficiently narrower than the wavelength band of the optical filter described in Non-Patent Document 1, and the optical The measurement principle is to consider it as a line spectrum (mathematically a δ function) considering the relationship between the transmittance, reflectance and wavelength of the filter.

  However, in the method of Non-Patent Document 1, the optical signal incident on the optical filter for measuring strain is not limited to the narrowband light centered on the Bragg wavelength from the FBG sensor, Since optical connectors such as optical circulators and optical couplers and weak broadband light due to Fresnel reflection from the fusion splice (see Fresnel reflection in Fig. 7 (a)), the reflected light intensity of the FBG sensor is The reduction in size causes a problem that the influence of broadband light due to Fresnel reflection that is relatively weak with respect to the intensity of reflected light from the FBG sensor increases. At this time, the influence of the Fresnel reflection intensity increases in the light intensity transmitted and reflected through the optical filter for measuring strain. Therefore, when there is a part where the radius of curvature of the optical fiber cannot satisfy the total reflection condition between the core and the clad, if an optical coupler is used to divide the optical signal between the FBG sensor and the optical circulator, a broadband Due to the effect of Fresnel reflection, the measurement principle using the reflected light spectrum of the FBG sensor as a line spectrum cannot be satisfied, and the measurement accuracy of the Bragg wavelength is reduced. This is the same effect as a decrease in the reflectance of the FBG sensor.

  In general, the reflectance of the FBG sensor is higher as the grating length is longer, and if the FBG sensor is about 15 mm, a reflectance of 99% can be obtained. However, when the grating length is shortened to about 1 mm or 2 mm from the condition of the subject, the reflectance decreases from about 50% to about 60%. Therefore, when optical signal intensity division by an optical coupler is applied to an FBG sensor with a short grating length, if the optical coupler division ratio is 50%, it is equivalent to the fact that the reflectivity of the FBG is reduced from 25% to 30%. Furthermore, since the optical coupler divides light in the entire irradiation wavelength band of the light source, the wavelength band of Fresnel reflection is similar to the irradiation light spectrum of the light source and has a wide band. Therefore, the precondition that the reflected light of the FBG sensor, which is the principle of strain measurement by the FBG sensor of Non-Patent Document 1, is a line spectrum may not be sufficiently satisfied.

  The present invention has been made in view of the above circumstances, and an optical fiber in which a radius of curvature that satisfies the total reflection condition between the optical fiber core and the clad cannot be secured for an optical signal propagating in the optical fiber core. It is an object of the present invention to provide a strain measuring method and a strain measuring apparatus capable of suitably measuring multi-point strains by an FBG sensor even when laying conditions exist.

The strain measurement method of the present invention, when there is an optical fiber laying condition that can not secure a radius of curvature that satisfies the total reflection condition between the optical fiber core and the clad for the optical signal propagating in the optical fiber core, A strain measurement method for measuring strains at multiple points using an FBG sensor,
A plurality of FBG sensors and optical fibers attached to the site under the above conditions and arranged in parallel, a first wavelength divider arranged between the light source and the plurality of FBG sensors, and reflection from the plurality of FBG sensors A second wavelength divider disposed on the light side,
Light that divides light from the light source into a plurality of optical fibers by a first wavelength divider, irradiates light from the light source to a plurality of FBG sensors corresponding to each wavelength band, and lays between the light source and the FBG sensor The total reflection condition between the fiber core and the cladding is always satisfied, and the light intensity loss in the optical fiber in the waveguide of the light intensity irradiated to the FBG sensor from the light source and the light intensity reflected from the FBG sensor is minimized. In this condition, each reflected light from the FBG sensor is demultiplexed by the second wavelength divider, and distortions by a plurality of FBG sensors are measured.

  Here, the difference between the wavelength divider and the optical coupler will be described. The optical coupler is an optical passive element that divides or couples the light intensity. The most common optical coupler divides an optical signal transmitted through one optical fiber into two 50%: 50% optical fiber paths. Such an optical coupler is called a 1 × 2 optical coupler. A generally available optical coupler includes a 1 × 4 optical coupler that divides an optical signal transmitted through one optical fiber into four optical fibers by 25%. On the other hand, the wavelength divider demultiplexes an optical signal transmitted through one optical fiber according to the wavelength band of light. The best optically known wavelength divider is a triangular prism. However, since fiber optic technology transmits digital signals, a continuous wavelength divider (which is commonly referred to as a spectroscope) is not used, and as shown in FIG. In order to prevent signal interference, a dielectric thin film optical filter having a wavelength band and a chirp FBG having a wide transmission band are used. Dielectric thin film optical filters have insertion loss when irradiating an optical signal, and cannot be wavelength-divided with the optical intensity of 100% of the original optical signal, but the optical signal intensity is half that of an optical coupler. There is no such thing as. Such wavelength division of an optical signal is generally used as wavelength division multiplexing (WDM) in optical fiber communication. However, when an FBG sensor is used as a strain sensor or a temperature sensor, the FBG sensor can be connected in series (in a chain) as described in the prior art. It is often done. However, in the actual structure, as described in the present invention, it may be difficult to lay the optical fiber so as to satisfy the total reflection condition between the optical fiber core and the clad in all the FBG sensors. In such a case, as described above, an optical coupler is generally used.

  The strain measurement method of the present invention can be applied when there is an optical fiber laying condition with a radius of curvature that cannot satisfy the total reflection condition between the optical fiber core and the clad for the optical signal propagating in the optical fiber core. preferable.

  In the strain measurement method of the present invention, the portion of the optical fiber laying condition that has a radius of curvature that cannot satisfy the total reflection condition between the optical fiber core and the clad with respect to the optical signal propagating in the optical fiber core includes a narrowed portion, a bent portion At least one of a part, a curved part, a folded part, a peripheral part of a rod-like body, and the like.

The strain measuring device of the present invention, when there is an optical fiber laying condition that can not ensure a radius of curvature that satisfies the total reflection condition between the optical fiber core and the clad for the optical signal propagating in the optical fiber core, A strain measuring device that measures multi-point strains by FBG sensors,
A plurality of FBG sensors and optical fibers attached to the site under the above conditions and arranged in parallel, a first wavelength divider arranged between the light source and the plurality of FBG sensors, and reflection from the plurality of FBG sensors A second wavelength divider disposed on the light side,
Light that divides light from the light source into a plurality of optical fibers by a first wavelength divider, irradiates light from the light source to a plurality of FBG sensors corresponding to each wavelength band, and lays between the light source and the FBG sensor The total reflection condition between the fiber core and the cladding is always satisfied, and the light intensity loss in the optical fiber in the waveguide of the light intensity irradiated to the FBG sensor from the light source and the light intensity reflected from the FBG sensor is minimized. The reflected light from the FBG sensor is demultiplexed by the second wavelength divider, and distortions by a plurality of FBG sensors are measured.

The strain measuring device of the present invention has an optical fiber laying condition in which there is an optical fiber laying condition with a radius of curvature that cannot satisfy the total reflection condition between the optical fiber core and the clad for an optical signal propagating in the optical fiber core. A strain measuring device that measures strain by an FBG sensor,
A plurality of FBG sensors and optical fibers, which are attached to the light source and the part under the above-mentioned conditions,
An optical circulator for controlling the direction of light guiding from the light source;
A first wavelength divider that demultiplexes light from the optical circulator into a plurality of optical fibers and outputs the demultiplexed light to a plurality of FBG sensors;
Reflected light from a plurality of FBG sensors, after passing through the first wavelength divider and the optical circulator, a second wavelength divider that demultiplexes and outputs,
A plurality of optical filters corresponding to the light demultiplexed by the second wavelength divider;
A transmitted light side photoelectric converter that receives transmitted light from the optical filter;
A reflected light side photoelectric converter that receives reflected light from the optical filter.

  In the strain measuring apparatus of the present invention, when there is an optical fiber laying condition that has a radius of curvature that cannot satisfy the total reflection condition between the optical fiber core and the clad for the optical signal propagating through the optical fiber core, When an optical fiber is arranged from the wavelength divider to the FBG sensor corresponding to each wavelength band of the first wavelength divider, the optical fiber is composed of a plurality of parallel fibers and has a curvature larger than the radius of curvature. It is preferable to lay with a radius.

  In the strain measuring apparatus of the present invention, the portion of the optical fiber laying condition having a radius of curvature that cannot satisfy the total reflection condition between the optical fiber core and the clad with respect to the optical signal propagating in the optical fiber core includes a narrowed portion, a bent portion At least one of a part, a curved part, a folded part, a peripheral part of a rod-like body, and the like.

  According to the strain measurement method and the strain measurement apparatus of the present invention, the optical fiber laying condition is such that a radius of curvature that satisfies the total reflection condition between the optical fiber core and the clad cannot be secured for the optical signal propagating in the optical fiber core. Even in the case of a subject that requires the use of multiple FBG sensors, multiple FBG sensors are arranged and mounted in parallel using the first wavelength divider, and parallel FBG sensors The configuration of the first wavelength divider and the second wavelength divider can suppress the reduction of the reflected light intensity of the FBG sensor and can suitably measure multi-point distortion.

It is a block diagram which shows the example of embodiment of this invention. It is a conceptual diagram which shows an example at the time of constructing the embodiment of this invention in the site | part of the optical fiber installation conditions. FIG. 3 is an arrow view in the III-III direction of FIG. 2. It is a conceptual diagram which shows the other example at the time of constructing the embodiment of this invention in the site | part of the optical fiber installation conditions. It is a conceptual diagram which shows an example at the time of arrange | positioning an FBG sensor in series and laying in the site | part of the optical fiber laying conditions. It is a conceptual diagram which shows the other example at the time of arrange | positioning an FBG sensor in series and laying in the site | part of the optical fiber laying conditions. (A) is a spectrum diagram showing Fresnel reflection in the case where the vertical axis is a logarithmic scale axis display, the FBG reflected light spectrum is used, and an optical coupler is used (division ratio 50%). (B) The vertical axis is a linear scale axis display, and is a spectrum diagram showing the FBG reflected light spectrum and the case where an optical coupler is used (division ratio 50%). It is a related figure which shows the transmittance | permeability and wavelength of an ideal wavelength divider.

  Hereinafter, an exemplary embodiment for carrying out the strain measuring method and strain measuring apparatus of the present invention will be described with reference to FIG.

  The strain measurement method and the strain measurement apparatus according to the embodiment are configured so that an optical fiber laying condition in which a radius of curvature that satisfies a total reflection condition between an optical fiber core and a clad cannot be secured for an optical signal propagating in the optical fiber core. Is applied as a multi-point strain measurement.

  Here, the optical fiber laying condition is a condition including a radius of curvature that cannot satisfy the total reflection condition between the optical fiber core and the clad for the optical signal propagating in the optical fiber core. Further, the site of the optical fiber laying condition is at least one of a narrowed portion, a bent portion, a curved portion, a folded portion, a peripheral portion of the rod-like body, and the like. One example of representing such a state is a case where four FBG sensors 2 are bonded in the axial direction of a measurement object A having a rod-like body as shown in FIG. At this time, when the periphery and the end side of the rod-shaped body are surrounded by the obstacle S, when the FBG sensor 2 is connected in series, a portion Fs having an extremely small radius of curvature of the optical fiber 12 is generated. Similarly, as another example, there are obstacles S ′ both above and below the vertical end of the measurement object A ′ as shown in FIG. 6, so that they are in the vicinity of both obstacles S ′. In some cases, four FBG sensors 2 are bonded in the vertical direction and the horizontal direction of the measurement object A ′, and strains in the vertical direction and the horizontal direction are measured. At this time, if the FBG sensor 2 is connected in series, a portion Fs having an extremely small radius of curvature of the optical fiber 12 is generated.

  In order to prevent the generation of the portion Fs having a small radius of curvature in FIGS. 5 and 6, as a specific example of the laying of the optical fiber, an FBG sensor is used for a measuring object A of a rod-shaped body as shown in FIGS. 2 and the optical fiber 12 are arranged in parallel. As another specific example of the laying of the optical fiber, there is one in which the FBG sensor 2 and the optical fiber 12 are arranged in parallel with respect to the vertical direction and the horizontal direction of the measurement object A ′ as shown in FIG. The FBG sensor 2 and the optical fiber 12 of FIGS. 2 and 3 are laid so as to satisfy the total reflection condition of the optical signal between the core and the clad of the optical fiber from the first wavelength divider 4 of FIG.

  The strain measurement method and strain measurement apparatus of the embodiment include a light source 1, a plurality of FBG sensors 2 arranged in parallel, an optical circulator 3 that controls the direction of light guided from the light source 1, and an optical circulator 3. A first wavelength divider 4 that demultiplexes and outputs the light from the plurality of FBG sensors 2; a second wavelength divider 5 that demultiplexes and outputs the reflected light from the plurality of FBG sensors 2; The plurality of optical filters 6 corresponding to the light demultiplexed by the second wavelength divider 5, the transmitted light side photoelectric converter 7 that receives the transmitted light from the optical filter 6, and the reflected light from the optical filter 6 A reflected light side photoelectric converter 8 and a transmitted light side photoelectric converter 7 and a data processor 9 connected to the reflected light side photoelectric converter 8 are provided.

  The light source 1 continuously outputs broadband light, and the broadband light includes all the Bragg wavelengths of the FBG sensor 2. An optical fiber 10 on the light source side is arranged between the light source 1 and the optical circulator 3 so as to guide broadband light to the optical circulator 3, and between the optical circulator 3 and the first wavelength divider 4. The optical fiber 11 on the intermediate side is arranged so as to guide broadband light from the optical circulator 3 to the first wavelength divider 4.

  The FBG sensor 2 is formed in the optical fiber 12 on the measurement side. The optical fiber 12 on the measurement side is composed of a plurality of parallel fibers bonded to a predetermined part (four in FIG. 1), and is arranged in a parallel state under optical fiber laying conditions. Moreover, the optical fiber 12 on the measurement side is branched from the first wavelength divider 4, and each optical fiber 12 on the measurement side ensures a radius of curvature that can satisfy the total reflection condition between the optical fiber core and the clad. Or arranged in a straight line. Here, the radius of curvature that can satisfy the condition of total reflection between the optical fiber core and the clad is 30 mm or more in the case of a general single mode optical fiber. 2 and 3, when the FBG sensor 2 is arranged on the measuring object A of the rod-shaped body, a plurality of FBG sensors 2 (four in FIG. 3) are disposed along the circumferential direction of the rod-shaped body. ing.

  The optical circulator 3 guides the light from the light source 1 to the FBG sensor 2 via the first wavelength divider 4 and reflects the reflected light from the FBG sensor 2 via the first wavelength divider 4. The light is guided to the second wavelength divider 5.

The first wavelength divider 4 demultiplexes the light of the light source 1 with a plurality of wavelengths so as to correspond to the plurality of FBG sensors 2. Here, when an optical coupler is used instead of the wavelength divider, the light of the light source 1 is demultiplexed by the light intensity, so that the signal-to-noise ratio of the signal is lowered, and the weak broadband light such as Fresnel reflection is adversely affected. . More specifically, the wavelength divider has a light insertion loss of about -1 dB (20.5%), whereas the 50:50 optical coupler has a light loss including a loss of an optical connector or the like. Becomes about -4 dB (-1 dB is insertion loss, division ratio is -3 dB, 60.2%). Since the unit of light intensity is milliwatt or microwatt, the decibel display of light loss is calculated by 10 × log ₁₀ (output light intensity / input light intensity).

  The second wavelength divider 5 is connected to the optical circulator 3 via a reflection-side optical fiber 13, has substantially the same function as the first wavelength divider 4, and is reflected by the plurality of FBG sensors 2. The reflected light is demultiplexed at a plurality of wavelengths so as to correspond to the plurality of reflected lights.

  The optical filter 6 is connected to the second wavelength divider 5 via a filter-side optical fiber 14 and is composed of a plurality of (four in FIG. 1) dielectric thin film optical filters, and has a second wavelength. Each of them corresponds to the wavelength band of the light demultiplexed by the splitter 5.

  The transmitted light side photoelectric converter 7 is connected to the optical filter 6 via the transmitted light side optical fiber 15 so as to convert the transmitted light from the optical filter 6 into an electrical distortion signal. The reflected light side photoelectric converter 8 is connected to the optical filter 6 via an optical fiber 16 on the reflected light side. The output voltages of the transmitted light side photoelectric converter 7 and the reflected light side photoelectric converter 8 correspond to the transmittance and the reflectance of the optical filter 6, and the output voltage of the transmitted light side photoelectric converter 7 and the reflected light side photoelectric conversion. It is possible to know the Bragg wavelength of the FBG sensor from the output voltage of the detector 8 on the premise that the reflected light width of the FBG sensor is processed with a line spectrum, and as a result, it is possible to know the strain change of the subject. It has become.

  The data processor 9 is connected to the transmitted light side photoelectric converter 7 and the reflected light side photoelectric converter 8 via a transmission path 17 such as an optical fiber or an electric cable. And the distortion signal is received from the reflected light side photoelectric converter 8. Here, the data processor 9 includes a measurement unit and a data recording unit, and may include other signal processing functions. The data processor 9 does not receive the signals of all the transmitted light side photoelectric converters 7 and the reflected light side photoelectric converters 8 but may receive a desired signal as necessary, or may be divided individually. May be.

  The operation of the embodiment for carrying out the present invention will be described below.

  When measuring multi-point strain in a portion of the optical fiber laying condition that has a radius of curvature that cannot satisfy the total reflection condition between the optical fiber core and the clad, a plurality of optical fibers 12 including the FBG sensor 2 are prepared as a preparation stage. It is laid by adhesive means such as optical connector connection, fusion connection and mechanical splice. Here, the optical fiber 12 secures a radius of curvature that satisfies the total reflection condition between the optical fiber core and the clad under the optical fiber laying condition, or is arranged in a straight line, and from the light source 1 to the FBG sensor 2. The optical fiber 12 in the optical fiber 12 in the waveguide satisfies the total reflection condition between the core and the clad of the optical fiber 12 to be laid and has the light intensity irradiated from the light source 1 to the FBG sensor 2 and the light intensity reflected from the FBG sensor 2. Light intensity loss is minimized.

  In the measurement stage, broadband light is emitted from the light source 1 and is incident on the first wavelength divider 4 via the optical circulator 3. Next, in the first wavelength divider 4, the light is demultiplexed for each wavelength band, demultiplexed into a plurality of optical fibers 12, and incident on the FBG sensor 2 at the tip of each optical fiber 12. Here, the first wavelength divider 4 demultiplexes the light from the light source 1 for each wavelength band, and irradiates the plurality of FBG sensors 2 corresponding to each wavelength band with the light of the light source 1.

  The reflected light reflected from each FBG sensor 2 becomes one optical signal via the first wavelength divider 4 and is guided to the second wavelength divider 5 by the optical circulator 3. In the second wavelength divider 5, the reflected light is demultiplexed so as to correspond to the plurality of FBG sensors 2 and is incident on the plurality of optical filters 6.

  In the optical filter 6, transmitted light and reflected light are generated, and the transmitted light is incident on the transmitted light side photoelectric converter 7 and the reflected light is incident on the reflected light side photoelectric converter 8. Next, the transmitted light side photoelectric converter 7 converts the transmitted light into a voltage signal and sends it to the data processor 9, and the reflected light side photoelectric converter 8 converts the reflected light into a voltage signal and sends it to the data processor 9. The data processor 9 obtains a plurality of Bragg wavelengths from the respective voltage signals. Here, the processing of the data processor 9 may be one that continuously measures the Bragg wavelength or may be processed by adding necessary conditions.

  Thus, according to the embodiment, the optical fiber laying in which the radius of curvature satisfying the total reflection condition between the optical fiber core and the clad cannot be secured for the optical signal propagating in the optical fiber core. Even in the case of a subject in which conditions exist and it is necessary to use a plurality of FBG sensors 2, a plurality of FBG sensors 2 are arranged and attached in parallel by the first wavelength divider 4, With the configuration of the parallel FBG sensor 2, the first wavelength divider 4, and the second wavelength divider 5, the reduction of the reflected light intensity of the FBG sensor 2 can be suppressed, and multipoint distortion can be suitably measured.

In the strain measuring device of the embodiment,
A light source 1;
A plurality of FBG sensors 2 and optical fibers 12 which are attached to a part under optical fiber laying conditions and arranged in parallel;
An optical circulator 3 for controlling the direction of light guided from the light source 1;
A first wavelength divider 4 that demultiplexes the light from the optical circulator 3 and outputs the demultiplexed light to a plurality of FBG sensors 2;
A second wavelength divider 5 for demultiplexing and outputting the reflected light from the plurality of FBG sensors 2 via the first wavelength divider 4 and the optical circulator 3;
A plurality of optical filters 6 corresponding to the light demultiplexed by the second wavelength divider 5;
A transmitted light side photoelectric converter 7 that receives transmitted light from the optical filter 6;
When the reflected light side photoelectric converter 8 that receives the reflected light from the optical filter 6 is provided, even if the optical fiber laying condition exists, a plurality of FBG sensors 2 are arranged in parallel and easily attached, The configuration of the parallel FBG sensor 2, the first wavelength divider 4, and the second wavelength divider 5 can suppress the reduction of the reflected light intensity of the FBG sensor 2, and can measure multipoint distortion more suitably. .

  In the embodiment, the portion of the optical fiber laying condition that has a radius of curvature that cannot satisfy the total reflection condition between the optical fiber core and the clad with respect to the optical signal propagating in the optical fiber core includes a narrowed portion, a bent portion, and a curved portion. Even at least one of the peripheral portion, the folded portion, and the peripheral portion of the rod-shaped body, the reduction of the reflected light intensity of the FBG sensor 2 can be further suppressed, and multi-point strain can be measured very suitably.

  Note that the strain measuring method and strain measuring apparatus of the present invention are not limited to the above-described embodiments, and it is needless to say that various changes can be made without departing from the scope of the present invention.

1 Light source
2 FBG sensor 3 Optical circulator 4 First wavelength divider 5 Second wavelength divider 6 Optical filter 7 Transmitted light side photoelectric converter 8 Reflected light side photoelectric converter 12 Optical fiber

The strain measuring device of the present invention has an optical fiber laying condition in which there is an optical fiber laying condition with a radius of curvature that cannot satisfy the total reflection condition between the optical fiber core and the clad for an optical signal propagating in the optical fiber core. A strain measuring device that measures strain by an FBG sensor,
A light source;
A plurality of FBG sensors and optical fibers attached to the site under the conditions and arranged in parallel;
An optical circulator for controlling the direction of light guiding from the light source;
A first wavelength divider that demultiplexes light from the optical circulator into a plurality of optical fibers and outputs the demultiplexed light to a plurality of FBG sensors;
Reflected light from a plurality of FBG sensors, after passing through the first wavelength divider and the optical circulator, a second wavelength divider that demultiplexes and outputs,
A plurality of optical filters corresponding to the light demultiplexed by the second wavelength divider;
A transmitted light side photoelectric converter that receives transmitted light from the optical filter;
A reflected light side photoelectric converter that receives reflected light from the optical filter ,
When there is an optical fiber laying condition with a radius of curvature that cannot satisfy the total reflection condition between the optical fiber core and the clad for an optical signal propagating in the optical fiber core, the first wavelength divider when we arranged optical fibers to FBG sensors corresponding to each wavelength band of the wavelength splitter, the optical fiber is made of a plurality of parallel, are laid with a radius of curvature greater than the radius of curvature shall It is.

Claims (7)

When there is an optical fiber laying condition that does not ensure a radius of curvature that satisfies the total reflection condition between the optical fiber core and the clad for the optical signal propagating in the optical fiber core, the multipoint distortion caused by the FBG sensor is reduced. A strain measurement method for measuring,
A plurality of FBG sensors and optical fibers attached to the site under the above conditions and arranged in parallel, a first wavelength divider arranged between the light source and the plurality of FBG sensors, and reflection from the plurality of FBG sensors A second wavelength divider disposed on the light side,
Light that divides light from the light source into a plurality of optical fibers by a first wavelength divider, irradiates light from the light source to a plurality of FBG sensors corresponding to each wavelength band, and lays between the light source and the FBG sensor Satisfy the total reflection condition between the core and clad of the fiber, and minimize the light intensity loss in the optical fiber in the waveguide of the light intensity irradiated from the light source to the FBG sensor and the light intensity reflected from the FBG sensor A strain measuring method characterized in that each reflected light from the FBG sensor is demultiplexed by the second wavelength divider, and strains by a plurality of FBG sensors are measured.   2. The method according to claim 1, wherein an optical fiber laying condition having a radius of curvature that does not satisfy a total reflection condition between the optical fiber core and the clad exists for an optical signal propagating in the optical fiber core. Strain measurement method.   Optical fiber laying conditions where the radius of curvature does not satisfy the total reflection condition between the optical fiber core and the clad for the optical signal propagating in the optical fiber core are constricted, bent, curved, folded, rod-shaped The strain measuring method according to claim 1, wherein the strain measuring method is at least one of a peripheral part of the body. When there is an optical fiber laying condition that does not ensure a radius of curvature that satisfies the total reflection condition between the optical fiber core and the clad for the optical signal propagating in the optical fiber core, the multipoint distortion caused by the FBG sensor is reduced. A strain measuring device for measuring,
A plurality of FBG sensors and optical fibers attached to the site under the above conditions and arranged in parallel, a first wavelength divider arranged between the light source and the plurality of FBG sensors, and reflection from the plurality of FBG sensors A second wavelength divider disposed on the light side,
Light that divides light from the light source into a plurality of optical fibers by a first wavelength divider, irradiates light from the light source to a plurality of FBG sensors corresponding to each wavelength band, and lays between the light source and the FBG sensor Satisfy the total reflection condition between the core and clad of the fiber, and minimize the light intensity loss in the optical fiber in the waveguide of the light intensity irradiated from the light source to the FBG sensor and the light intensity reflected from the FBG sensor A strain measuring apparatus, characterized in that each reflected light from the FBG sensor is demultiplexed by the second wavelength divider, and the strain by a plurality of FBG sensors is measured. Strain that measures strain with a multipoint FBG sensor when there is an optical fiber laying condition with a radius of curvature that does not satisfy the total reflection condition between the optical fiber core and the clad for the optical signal propagating in the optical fiber core A measuring device,
A light source;
A plurality of FBG sensors and optical fibers attached to the site under the conditions and arranged in parallel;
An optical circulator for controlling the direction of light guiding from the light source;
A first wavelength divider that demultiplexes light from the optical circulator into a plurality of optical fibers and outputs the demultiplexed light to a plurality of FBG sensors;
Reflected light from a plurality of FBG sensors, after passing through the first wavelength divider and the optical circulator, a second wavelength divider that demultiplexes and outputs,
A plurality of optical filters corresponding to the light demultiplexed by the second wavelength divider;
A transmitted light side photoelectric converter that receives transmitted light from the optical filter;
A strain measurement apparatus comprising: a reflected light side photoelectric converter that receives reflected light from the optical filter.   When there is an optical fiber laying condition with a radius of curvature that cannot satisfy the total reflection condition between the optical fiber core and the clad for an optical signal propagating in the optical fiber core, the first wavelength divider When the optical fiber is arranged up to the FBG sensor corresponding to each wavelength band of the wavelength divider, the optical fiber is composed of a plurality of parallel fibers and laid with a radius of curvature larger than the radius of curvature. The strain measurement apparatus according to claim 4 or 5, wherein   Optical fiber laying conditions where the radius of curvature does not satisfy the total reflection condition between the optical fiber core and the clad for the optical signal propagating in the optical fiber core are constricted, bent, curved, folded, rod-shaped The strain measuring device according to any one of claims 4 to 6, wherein the strain measuring device is at least one of a peripheral portion of the body.

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