JPH11223513A - Strain measuring device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To accurately detect narrow range strain. SOLUTION: A gauge body 2 is constituted of optical fiber by forming a round path 13 where linear measurement parts 12 are arranged mutually in parallel together with a curvature 11 with radius of curvature having very small transmission attenuation of light pulse and the linear measurement part 12 formed in measuring gauge length L and by winding the round path 13 a plurality of turns on the plane shifting the position so that the total length of the curvature 11 and the linear measurement part 12 is over a linear proper gauge length capable of measuring average strain by this optical fiber. The gauge body 2 is fixed on the measuring plane 1 of the measuring object so that the linear measurement part 12 goes along the strain direction.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a BOTDA for measuring backscattered light (Brillouin scattering) of an optical pulse generated by stress applied to an optical fiber and detecting distortion of a structure or the like.
The present invention relates to a strain measuring device using an optical fiber by a method.

[0002]

2. Description of the Related Art Conventionally, an optical pulse is input to an optical fiber,
Japanese Patent Application Laid-Open No. 61-104235 discloses a strain measurement system using an optical fiber that measures the backscattered light of an optical pulse generated by the distortion of an optical fiber to detect the distortion of an object to be measured. There has been proposed a strain measuring method for measuring a strain distribution in an optical cable by mounting a fiber core. Japanese Patent Application Laid-Open No. 4-86510 discloses that an optical fiber is wound around a reinforcing bar of a structure, thereby fixing the optical fiber to the structure, and forming a bent portion to generate a scattering loss. There has been proposed a device for measuring the distortion of the light. In such a strain measurement system, an OTDR (Optical Domain) that time-resolves a signal of backscattered light when an optical pulse is incident on an optical fiber.
Reflectometry) method is used, but in this measurement system, the natural Brillouin scattered light power generated in the optical fiber is very weak and difficult to measure. Therefore, as shown in FIG. 3, pulse light (pump light) and continuous (CW) light (probe light) are emitted from one end (or both ends) of the optical fiber.
BOTDA (Brillouin Optical-Fiber Time) using stimulated Brillouin scattering interaction between both signals
Domain Analysis) method has been proposed.

[0003]

However, according to the above configuration, the shortest gauge length (distance resolution) of the optical fiber capable of detecting the loss due to the backscattered light depends on the performance of the strain measuring instrument. In the range of 0 to 2.5 m, only the average strain of the optical fiber having a length of 2.0 to 2.5 m can be measured. When measuring the strain of the structure, the gauge length is 2.0 to 2.5 m.
When the distance is 2.5 m, there is a problem in that it is not possible to perform a detailed measurement in a range less than that, and it is not possible to measure a distortion with high accuracy to specify a place.

An object of the present invention is to provide a distortion measuring method and apparatus capable of solving the above problems and detecting a distortion in a narrower range with high accuracy.

[0005]

According to a first aspect of the present invention, an optical pulse is input to an optical fiber fixed to an object to be measured by a strain measuring device, and light generated by the distortion of the optical fiber. A strain measuring apparatus using an optical fiber for measuring distortion of an object to be measured by measuring backscattered light of a pulse. Part and a straight line measuring part formed to the length of the measuring gauge, forming a circuit path in which the straight line measuring parts are arranged in parallel to each other, and displacing the circuit path on a plane and winding it a plurality of times. By this, the total length of the curved portion and the straight line measuring portion is configured to be equal to or longer than the straight line specific gauge length capable of measuring the average strain by the optical fiber, and the straight line measuring portion is measured along the strain direction. Measurement plane In which fixed.

[0006] According to the above configuration, the gauge body is formed by winding the optical fiber having a length equal to or more than the intrinsic gauge length multiple times on the orbital path including the curved portion and the linear measuring portion. When this occurs, the optical fiber of the linear measuring unit expands and contracts, and this distortion can be measured as backscattered light.Therefore, the distortion occurring in a narrow range of the measuring gauge length of the linear measuring unit can be measured accurately, Measurement accuracy of strain due to fiber can be improved.

According to a second aspect of the present invention, in addition to the above-described configuration, a plurality of gauge bodies formed continuously in series are arranged, and light pulses are emitted at the ends of the gauge bodies and the backscattered light is received. It is connected to a strain measuring device for measuring the strain of the optical fiber.

[0008] According to the above configuration, when a large structure has a plurality of measurement points, the plurality of measurement points can be measured at once by connecting the gauge bodies attached to the measurement plane in series. The apparatus can be simplified.

According to a third aspect of the present invention, when the gauge bodies are connected to each other by using the connector, the influence of the fluctuation of the light pulse by the connector on the intermediate optical fiber cable led from the gauge body to the connector. A pre-length portion having a length that does not reach the fluctuation of the light pulse by the main body is formed.

According to the above configuration, if the scattering by the connector increases, the measured value is likely to be inaccurate due to the influence of the scattering of the gauge body. However, the intermediate cable is provided with a pre-length portion to increase the length of the intermediate cable. This ensures accurate measurement even if the amount of scattering of the connector is large.

[0011]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS Here, an embodiment of a distortion measuring device according to the present invention will be described with reference to FIGS.

As shown in FIG.
A distortion measuring device for measuring distortion of a measurement plane 1 provided at a plurality of locations of a large structure to be measured.
, A plurality of gauge bodies 2 made of optical fibers, each of which is attached to the gauge body 2, an intermediate optical fiber cable (hereinafter referred to as an intermediate cable) 3 derived from the gauge body 2, and an intermediate cable 3
4 for connecting each gauge body 2 in series via
In the vicinity of the connector 4 of the intermediate cable 3, the connector 4
When a large amount of scattered light (not limited to Brillouin scattered light) is large, an extra length loop 3a, which is an extra length portion provided to eliminate the influence of the gauge body 4 on the scattered light, and the gauge body 2 are connected in series. BO connected to end intermediate cable 3b
And a TDA measuring device (strain measuring device) 5. In addition,
A plurality of gauge bodies 2 can be formed and arranged continuously in series without the connector 4.

As shown in FIG. 1, the gauge main body 2 is formed by an optical fiber with a bending portion 11 having a bending radius r, r 'having a very small amount of light pulse transmission attenuation, and a length longer than the measurement gauge length L. With the straight line measuring unit 12, a substantially elliptical orbital path 13 in which the straight line measuring unit 12 is arranged in parallel with each other.
Is formed, and the spiral path 13 is displaced on the plane and spirally wound a plurality of times, so that the total length of the optical fibers of the bending portion 11 and the linear measuring portion 12 reduces the average distortion caused by this optical fiber. It is configured to be longer than the measurable intrinsic gauge length.

Due to the characteristics of the BOTDA measuring instrument 5, the intrinsic gauge length of this optical fiber is, for example, 2.0 to 2.5 m, and therefore the total length of the optical fiber of the gauge body 2 needs to be 2.5 m or more. The length L of the straight line measuring unit 12
Is set to 100 mm or more in this case.
If the total length is about 300 mm, the number of turns is 8 to 1
0, but preferably the total length of the optical fiber is 4.0.
By securing about m, more accurate measurement becomes possible. The bending radius r (r <r ') of the bending portion 11 is set to a set value such that the light pulse has no transmission loss due to the bending of the light propagation path and the attenuation is negligibly small for measurement. For example, it is desirable that the radius of curvature r = 15 mm or more.

In the gauge body 2, the gauge body 2 is fixed to a measurement plane 1 of an object to be measured along a direction in which a straight line measuring section 12 is distorted, and both ends of the straight line measuring section 12 apply pretension. It is fixed to the measurement plane 1 via the mounting plate 21 which is held and adhered and fixed, and the straight line measurement unit 12 is also adhered and fixed to the measurement plane 1 over the entire length.

The strain measured here includes a compression strain and an expansion strain, and the pretension is for detecting the compression strain satisfactorily. The upper limit thereof is within a range not exceeding the strength of the optical fiber. The lower limit is a range in which possible compressive strain can be covered, and in this case, tension may be applied so that a prestrain of 0.1% is generated. The scattered light due to the bending of the curved portion 3 is considered at the time of measurement as the intrinsic scattering amount of the gauge.

When the scattered light of the connector 4 is large at the connection between the intermediate cables 3, the measured value of the scattered light of the gauge body 4 may be affected, and the accuracy of the distortion detection value may be reduced. Here, it is considered that the influence is not exerted by securing the length by winding the optical fiber a plurality of times by, for example, a loop of about 10 m by the pre-length loop 3a. Although the pre-length loop 3a is formed in the intermediate cable 3, the pre-length loop 3a is not limited to the loop shape, but may be any as long as the length is small with little distortion.

The BOTDA measuring device 5 is composed of a measuring section including a laser light source and a light receiving circuit, and an arithmetic processing section including a computer. In the above configuration, BOTDA
The laser pulse emitted from the laser light source of the measuring instrument 5 is
It is sequentially sent from the end intermediate cable 3b to the gauge body 2 connected in series, the amount of scattered light is measured by the light receiving circuit of the BOTDA measuring instrument 5, and the amount of distortion of the optical fiber in the time axis (distance) is measured by the arithmetic processing unit. Is done. Thereby, the distortion of the gauge length L at the mounting position of the gauge main body 2 at a predetermined position is accurately measured. Also intermediate cable 3
In the case where large scattering occurs in the connector 4 of the connection part, even if a large attenuation appears at the position (distance) of the connector 4,
Since the length of the optical fiber is ensured by the pre-length loop 3a, the measurement accuracy of the gauge body 2 does not decrease.

According to the above configuration, in the conventional strain measuring apparatus, it is not possible to accurately measure the strain in a narrow range due to the large intrinsic gauge length. By winding an optical fiber having a length equal to or more than the corresponding length a plurality of times into an oval shape and bonding and fixing the straight line measuring portion 12 to the measurement plane 1, a narrow range of the measuring gauge length L corresponding to the length of the straight line measuring portion 12 can be obtained. Distortion can be detected with high accuracy.

Further, a plurality of gauge bodies 2 are connected in series via a connector 4 along one optical fiber (intermediate cable 3), and the gauge bodies 2 are mounted on a plurality of measurement planes 1 so as to cover a wide area. Multi-point measurement is possible, and the work of measurement preparation and removal can be greatly reduced. Further, even when the amount of scattered light from the connector 4 is large and the distance between the connector 4 and the gauge body 2 is short, the extra length loop 3a
Is provided, the measured value of the gauge body 2 is not affected by the connector 4.

In the above embodiment, each connector 4
Although one gauge body 2 is interposed therebetween, a plurality of gauge bodies 2 formed in series between the connectors 4 may be interposed.

[0022]

As described above, according to the first aspect of the present invention, an optical fiber having a length equal to or greater than the intrinsic gauge length is wound a plurality of times on a circuit path including a curved portion and a linear measuring portion. By turning the gauge body, if the measurement plane is distorted, the optical fiber of the linear measurement part expands and contracts, and this distortion can be measured as backscattered light. The strain occurring in a narrow range can be accurately measured, and the accuracy of measuring the strain caused by the optical fiber can be improved.

According to the second aspect of the present invention, when a large structure has a plurality of measurement points, the gauge bodies attached to the measurement plane are connected in series to measure the plurality of measurement points at once. And the device can be simplified.

According to the third aspect of the invention, when the scattering by the connector increases, the scattering of the gauge body is affected and the measured value tends to be inaccurate. By ensuring a long length, accurate measurement is possible even when the amount of scattering of the connector is large.

[Brief description of the drawings]

FIG. 1 is a front view of a gauge main body showing an embodiment of a strain measuring device according to the present invention.

FIG. 2 is a configuration diagram showing the distortion measuring device.

FIG. 3 is an explanatory diagram showing a distortion measurement method according to the BOTDA method.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Measurement plane 2 Gauge main body 3 Intermediate optical fiber cable 3a Preliminary loop 4 Connector 5 BOTDA measuring instrument 11 Bending part 12 Straight line measuring part 13 Circuit path 21 Mounting plate

 ──────────────────────────────────────────────────続 き Continuing from the front page (72) Masayuki Tanigawa 1-89, Minamikohoku, Suminoe-ku, Osaka-shi, Osaka Prefecture Inside Hitachi Zosen Corporation (72) Inventor Teruhisa Ishihara 1-chome, Minamikohoku, Suminoe-ku, Osaka-shi, Osaka No. 7-89 Hitachi Zosen Corporation (72) Inventor Yoshiko Ikuta 1-89 Minami Kohoku, Suminoe-ku, Osaka City, Osaka Prefecture Inside Hitachi Zosen Corporation

Claims (3)

[Claims] 1. An optical fiber for inputting an optical pulse to an optical fiber fixed to an object to be measured by a strain measuring device, measuring backscattered light of the optical pulse caused by the distortion of the optical fiber, and detecting the distortion of the object to be measured. A strain measuring device using a linear measuring unit, wherein a gauge body is formed by an optical fiber, a curved portion having a curved radius with a very small optical pulse transmission attenuation amount, and a straight line measuring unit formed to a measuring gauge length. Is formed in parallel with each other, and by winding this loop several times with the position shifted on the plane, the total length of the curved portion and the straight line measuring portion is increased by the average distortion caused by this optical fiber. The strain measuring device is configured to have a length equal to or longer than a straight line specific gauge length capable of measuring, and the straight line measuring unit is fixed to a measurement plane of an object to be measured along a strain direction. 2. A plurality of gauge bodies continuously formed in series are arranged, and a strain measuring device that emits light pulses, receives backscattered light, and measures strain of an optical fiber is connected to an end thereof. 2. The distortion measuring device according to claim 1, wherein: 3. When the gauge bodies are connected to each other by using a connector, the influence of the light pulse fluctuation by the connector on the intermediate optical fiber cable led from the gauge body to the connector affects the fluctuation of the light pulse by the gauge body. 3. The strain measuring apparatus according to claim 2, wherein a pre-length portion having a length less than the length is formed.