JPH1164392A - Optical fiber applied measuring instrument - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an optical fiber application measuring instrument capable of precise measurement and excellent in long period reliability. SOLUTION: As an optical fiber for an optical fiber sensor 8, a single mode fiber always provided with optical activity even in a state without a magnetic field is adopted and the optical fiber itself is a (span) fiber twisted at a manufacturing step. An optical fiber for the sensor 8 is composed of a core part 30 for propagating light, a clad layer 31 and a coating layer 32 successively provided at its outer peripheral and is mechanically twisted to the right at a loading step. As the polarizing surface of light is averaged by rotation when light is propagated within the sensor 8, nonuniformity of the inside of the sensor 8 in terms of light is eliminated to realize highly precise measurement without the deterioration of sensitivity.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an optical measuring instrument for measuring a physical quantity by utilizing a change in the characteristics of light.
The present invention relates to an optical measuring instrument having an improved configuration of an optical fiber sensor.

[0002]

2. Description of the Related Art Conventionally, there has been proposed an optical fiber applied measuring instrument for measuring a physical quantity by light. In particular, the optical fiber current measuring device arranges an optical fiber as a sensor in close proximity to a conductor through which a current to be measured flows, and passes linearly polarized light through the sensor to measure the angle of rotation of the Faraday effect caused by the current to be measured. Things.

FIG. 8 shows an example of a conventional optical fiber current measuring device as disclosed in U.S. Pat. S. It is a block diagram showing the optical fiber current measuring device described in Japanese Patent No. 3,605,013. As shown in FIG. 8, the optical fiber current measuring device includes a laser 1, a polarizer 2, a transmitting fiber 3, an optical fiber sensor (optical guide) 3 ', a conductor to be measured 4, an analyzer 5, an optical detector 6, The optical fiber sensor 3 ′ is configured such that an optical fiber for a sensor is arranged close to the conductor 4 to be measured so as to be wound therearound.

The light emitted from the laser 1 serving as a light source is
The light is converted into linearly polarized light by the polarizer 2, and guided to the optical fiber sensor 3 ′ through the light transmitting fiber 3. A magnetic field is generated by the current I flowing through the conductor to be measured 4, and this magnetic field causes light propagating in the optical fiber sensor 3 ′ to
Optical rotation based on the Faraday effect occurs. After passing through the optical fiber sensor 3 ′, the light is guided to the analyzer 5 through the light transmitting fiber 3, and only the light component in the direction of the analyzer 5 passes and is guided to the photodetector 6. When the current amount I changes, the Faraday rotation angle changes in accordance with the change, so that the light amount after passing through the analyzer 5 changes, and the output of the photodetector 6 changes accordingly. Therefore, by measuring the output of the photodetector 6, the current amount I can be obtained. The obtained result is displayed by the display device 7 also serving as a signal processor.

[0005]

However, in the conventional optical fiber current measuring device as shown in FIG.
Due to the birefringence induced in the optical fiber by winding the sensor optical fiber around the conductor to be measured,
There is a problem that the sensitivity of the sensor optical fiber is reduced and the measurement result fluctuates due to an external environment such as temperature. In addition, in order to use it in a power system, it is necessary to secure not only high-precision measurement but also long-term reliability.

[0006] Such a problem is not limited to the optical fiber current measuring device, and various physical quantities of the object to be measured can be measured by utilizing a change in light passing through an optical fiber sensor arranged near the object to be measured. It is also present in various fiber optic applied meters configured to measure.

The present invention has been proposed to solve such problems of the prior art, and an object of the present invention is to provide an optical fiber-based measuring instrument capable of performing high-accuracy measurement and having excellent long-term reliability. To provide.

[0008]

According to a first aspect of the present invention, there is provided an optical fiber sensor disposed near an object to be measured, and an optical fiber sensor for generating light for measurement. A light source to be sent to the sensor, a detector for detecting light emitted from the sensor, a coupling optical system for optically coupling the sensor with the light source and the detector, and a signal processing unit for processing a signal from the detector In an optical fiber applied measuring instrument for measuring a physical quantity by a change in the characteristics of light, a fiber having optical rotatory power even in the absence of a magnetic field is used as the optical fiber sensor.

According to the first aspect of the present invention, by using an optical fiber having optical rotation at all times even in the absence of a magnetic field as the optical fiber sensor, when the light propagates through the optical fiber sensor, the polarization plane of the light Are rotated and averaged by rotation, so that non-uniformity inside the optical fiber sensor viewed from the light is reduced. As a result, the effect of linear birefringence induced in the optical fiber and causing non-uniformity can be suppressed, and highly accurate measurement can be realized.

According to a second aspect of the present invention, in the optical fiber applied measuring device according to the first aspect, as the optical fiber for the optical fiber sensor, an optical fiber twisted at a manufacturing stage is used, and the optical fiber is further twisted at a mounting stage. It is characterized by being arranged in addition to the above.

According to the second aspect of the present invention, an optical fiber having a small amount of birefringence can be obtained by using a spun fiber twisted in a manufacturing stage. That is, the spun fiber is manufactured by drawing while rotating a preform as a fiber raw material, so that there is no asymmetry of the fiber core portion generated at the time of manufacturing the fiber, and a fiber having a small birefringence can be realized. In this case, since the optical fiber is twisted at a high temperature in the manufacturing stage, almost no stress is generated inside the fiber, the optical fiber has almost no optical rotation.

However, even if such a homogeneous optical fiber is used, if the optical fiber has a curvature in the mounting stage, birefringence is induced in the optical fiber due to the curvature, and the optical fiber becomes substantially non-uniform. Become. On the other hand, in the present invention, by forming the optical fiber sensor by further twisting the optical fiber at the mounting stage, it is possible to generate stress in the twisting direction and impart optical rotation to the propagating light. .

Therefore, when the light propagates in such an optical fiber sensor, the polarization plane of the light is rotated and rotated by the rotation, so that the polarization plane is averaged, thereby eliminating the non-uniformity inside the optical fiber sensor as viewed from the light. And high-accuracy measurement can be realized without lowering the sensitivity.

According to a third aspect of the present invention, there is provided the first or second aspect.
In the optical fiber applied measuring device, the cladding outer diameter of the optical fiber for the optical fiber sensor is 2r (μ).
m), assuming that the number of turns of the optical fiber around the object to be measured is m (turns), the torsion rate n _t (turns / m) applied to the optical fiber in the mounting stage is n _t ≦ (125 / 2r) (8.0-log ₁₀ m).

According to the third aspect of the present invention, the value of the torsion rate n _t (times / m) added to the optical fiber for the optical fiber sensor in the mounting stage is determined by the cladding outer diameter 2r (μm).
By specifically defining m), it is possible to suppress a decrease in life due to mechanical strength due to torsion and to improve long-term reliability.

According to a fourth aspect of the present invention, in the optical fiber applied measuring device of the first, second or third aspect, the birefringence amount of the entire length of the optical fiber for the optical fiber sensor is a relationship between the number of twists and the birefringence amount. Is characterized in that the number of twists is set so as to have one of values near 0 ° and near an extreme value.

According to the fourth aspect of the present invention, since the total length of the optical fiber for the optical fiber sensor is near 0 ° or near the extreme value, the change in sensitivity becomes small even when the external environment such as temperature changes. , High accuracy can be maintained.

According to a fifth aspect of the present invention, there is provided an optical fiber applied measuring instrument according to any one of the first to fourth aspects,
The direction of the polarization plane of the light incident on the optical fiber sensor is +45 with respect to the plane on which the optical fiber is disposed.
°, + 135 °, -45 °, or -135 °.

According to the fifth aspect of the invention, by twisting the optical fiber sensor, the degree of averaging of the birefringence induced in the fiber can be increased, and as a result, the twist can be reduced with a small amount of twist. Since the amount of change in sensitivity can be reduced, a reduction in life can be suppressed, and high accuracy can be maintained.

The invention according to claim 6 is the invention according to claim 4 or 5.
In the optical fiber applied measuring device described above, a quartz fiber is used as the optical fiber for the optical fiber sensor, and the number of twists N (times) over the entire length of the optical fiber is 3.5M-1 ≦ N ≦ 3.5M + 1 (M is other than 0) Is a value satisfying the following.

According to the invention of claim 6, the number of twists N over the entire length of the quartz fiber for the optical fiber sensor is provided.
By specifically defining (times), the rotation angle of the polarization plane of the light due to the twist can be made an integral multiple of around 90 °, so that the birefringence amount of the entire length of the optical fiber for the optical fiber sensor is obtained. Can be set near 0 °. Therefore, even if the external environment such as temperature changes, the amount of change in sensitivity is reduced without lowering the sensitivity.
High accuracy can be maintained.

According to a seventh aspect of the present invention, in the optical fiber applied measuring device of the fourth aspect, a quartz fiber is used as the optical fiber for the optical fiber sensor, and the number of twists N (times) over the entire length of the optical fiber is | N | = 1.75 + 3.5M (M is a positive integer).

According to the seventh aspect of the present invention, the number of twists N over the entire length of the quartz fiber for the optical fiber sensor is provided.
By specifically defining (times), the amount of birefringence can be made an extreme value. Therefore, even if the external environment such as the temperature changes, the change amount of the sensitivity becomes small, so that high accuracy can be maintained.

According to an eighth aspect of the present invention, there is provided an optical fiber applied measuring instrument according to any one of the first to seventh aspects,
When the average bending radius of the optical fiber for the optical fiber sensor is R (m), the number of turns of the optical fiber around the object to be measured is m, and the wavelength of light is λ,
The outer diameter 2r (μm) of the cladding of this optical fiber is (r / 62.5) ² ≦ (80 / 2mπR / 3.8) (R
/0.25) ² (λ / 0.8).

According to the invention of claim 8, the cladding outer diameter of the optical fiber for the optical fiber sensor is 2r (μm).
With the average bending radius R (m) of the optical fiber and the number of turns m,
And by specifically defining the wavelength λ of light, birefringence due to bending can be reduced,
Accuracy can be increased.

According to a ninth aspect of the present invention, there is provided an optical fiber applied measuring instrument according to any one of the first to eighth aspects,
When the average bending radius of the optical fiber for the optical fiber sensor is R (m) and the number of turns of the optical fiber around the object to be measured is m, the cladding outer diameter 2r (μm) of the optical fiber is 2r / 125 ≦ (8.0−log ₁₀ m) × 2mπR /
It is a value that satisfies 3.5.

According to the ninth aspect of the invention, the cladding outer diameter of the optical fiber for the optical fiber sensor is 2r (μm).
Is specifically defined with respect to the average bending radius R (m) of the optical fiber and the number of turns m, so that even if the bending radius R of the optical fiber is small, the birefringence due to bending can be reduced, and the twisting at the mounting stage can be achieved. Since the reduction in the life based on the mechanical strength can be suppressed, accuracy and long-term reliability can be improved.

According to a tenth aspect of the present invention, in the optical fiber applied measuring instrument according to any one of the first to ninth aspects, the optical fiber for the optical fiber sensor applies a torsional stress to at least a core portion thereof. It is an optical fiber provided with a new coating layer.

According to the tenth aspect of the present invention, the twist can be fixed by providing a new coating layer after applying a torsional stress to at least the core portion of the optical fiber sensor. Therefore, entanglement of the optical fiber due to twisting is eliminated, and mounting is facilitated, and the effect of linear birefringence induced in the optical fiber and causing non-uniformity is suppressed by optical rotation of light due to twisting stress. Therefore, highly accurate measurement can be realized.

The invention according to claim 11 is the invention according to claims 1 to 10
In the optical fiber applied measuring device according to any one of the above, the optical fiber for the optical fiber sensor, torsion stress is applied to at least its core portion, at least both ends are fixed, and a protective outer jacket is provided. Characterized in that it is an optical fiber provided with a pipe.

According to the eleventh aspect of the present invention, the optical fiber sensor is provided with a protective pipe as a jacket outside the optical fiber sensor with at least both ends fixed by applying a torsional stress to at least the core portion. The effects of linear birefringence induced during
It can be suppressed by optical rotation of light due to torsional stress. Therefore, high-precision measurement can be realized, deterioration of the optical fiber itself can be prevented, and long-term reliability can be ensured.

The twelfth aspect of the present invention provides the first to eleventh aspects.
In the optical fiber applied measuring device according to any one of the above, the present invention is applied to current measurement using the Faraday effect.

According to the twelfth aspect of the present invention, by applying the optical fiber measuring instrument according to the first to eleventh aspects having the above-described excellent effects to current measurement utilizing the Faraday effect, high accuracy is achieved. An optical fiber current measuring instrument capable of performing accurate measurement and having excellent long-term reliability can be realized.

[0034]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS A plurality of embodiments in which an optical fiber applied measuring device according to the present invention is applied to an optical fiber current measuring device will be described below with reference to FIGS.

[1. First Embodiment] [1-1. FIG. 1 shows, as a first embodiment of the present invention, one embodiment of an optical fiber current measuring device to which each of the second and twelfth aspects of the present invention is applied. As shown in FIG. 1, in the optical fiber current measuring device of the present embodiment, the optical fiber sensor 8
Are arranged so as to surround the conductor 4 to be measured.

As shown in FIG. 1, the optical fiber current measuring device according to the present embodiment is roughly divided into a sensor optical unit 9,
It comprises a signal processing unit 10 and a transmission fiber unit 11.

The signal processing unit 10 includes a light source 12 that generates measurement light, a detector 13 that detects two lights from the sensor optical unit 9 and converts the two lights into an electric signal corresponding to the intensity.
A signal processing circuit 14 that performs arithmetic processing on the signal obtained by the detector 13 and an output terminal 15 that outputs a processing result are provided. The light source 12 is constituted by a laser diode or a super luminescent diode.

The transmission fiber unit 11 includes a light transmission fiber 16 for transmitting light from the light source 12 in the signal processing unit 10 to the sensor optical unit 9, and two detection fibers in the signal processing unit 10 from the sensor optical unit 9. And two light receiving fibers 17 for transmitting light to the container 13.

On the other hand, the sensor optical unit 9 is
a and an optical fiber sensor section 18b. The coupling optical unit 18a includes four lenses 19 to 22,
It comprises a polarizer 23, two beam splitters 24 and 25, and two analyzers 26 and 27. Here, of the four lenses 19 to 22, the first lens 19
Is used to convert the light from the light transmitting fiber 16 into a parallel beam, and the second lens 20 receives the light from the optical fiber sensor 18b and receives the light emitted from the optical fiber sensor 18b. Used to
The third and fourth lenses 21 and 22 are used for condensing the parallel beams and entering the respective light receiving fibers 17.

The polarizer 23 is used to convert the light into linearly polarized light in a 45-degree direction with respect to the horizontal direction (the plane on which the optical fiber sensor 8 is disposed), and the two beam splitters 24 and 25 convert the light into the linearly polarized light. Each of them is used to split transmitted light and reflected light according to the incident direction. The two analyzers 26 and 27 transmit orthogonally polarized x and y by transmitting light of linearly polarized light in the horizontal and vertical directions, respectively.
Each is used to extract each polarization component of the direction.

In this case, the coupling optical unit 18a transmits the light from the light transmitting fiber 16 to the first lens 19 and the polarizer 2
3. The light is sent to one end of the optical fiber sensor section 18b via the first beam splitter 24 and the second lens 20.

The light in the reflection direction from the optical fiber sensor section 18b passes through the second lens 20,
, And is transmitted to the second beam splitter 25 to be split into light in two directions. The one split light is transmitted to the first light receiving fiber 1 via the first analyzer 26 and the third lens 21.
7 The other split light is transmitted through the second analyzer 27 and the fourth lens 22 to the other light receiving fiber 1.
7

On the other hand, the optical fiber sensor section 18b is composed of an optical fiber sensor 8 composed of an optical fiber wound around the conductor 4 through which the current to be measured flows by an integral multiple of 1 or more. 8 has a reflective end 28 at the end thereof. Here, a case where a highly reliable quartz fiber is used as the optical fiber for the optical fiber sensor 8 will be described, but the present invention is not particularly limited to the quartz fiber. Also, the reflection end 2 of the optical fiber sensor 8
Numeral 8 reflects the light propagating in the optical fiber sensor 8, returns the light again into the optical fiber sensor 8, and propagates the light in the opposite direction. At this time, by using the reflection end 28, the input end and the output end of the optical fiber completely coincide with each other. In the drawing, reference numeral 29 indicates such an input / output end, and the input / output end 29 is housed in a structure. The input / output end 29, which is both ends of the optical fiber sensor 8, and the above-mentioned reflection end 28 are arranged close to each other.

[1-2. Configuration of Optical Fiber Sensor] FIG. 2 is an explanatory diagram showing details of the optical fiber sensor 8. As an optical fiber for the optical fiber sensor 8,
A single mode fiber that always has optical rotation even in the absence of a magnetic field is employed, and the optical fiber itself is a (span) fiber twisted in a manufacturing stage. The optical fiber for the optical fiber sensor 8 is composed of a core portion 30 through which light propagates, a cladding layer 31 and a coating layer 32 provided sequentially on the outer periphery thereof, and is mechanically twisted rightward in the mounting stage. I have.

[1-3. Current Measurement] The current measurement of the conductor 4 to be measured by the optical fiber current measuring device of FIG. 1 having the above configuration is performed as follows. First, light emitted from the light source 12 of the signal processing unit 10 is transmitted to the light transmitting fiber 16.
Is transmitted to the coupling optical system 18a of the sensor optical unit 9 through the optical path.

The light from the light transmitting fiber 16 is converted into a parallel beam by the first lens 19, converted into linearly polarized light by the polarizer 23, and then transmitted through the first beam splitter 24 to be converted into a second beam. And is incident on the starting end of the optical fiber sensor section 18b.

The light that has entered the optical fiber sensor section 18b propagates through the optical fiber sensor 8 and is reflected by the reflection end 28, and then returns to the optical fiber sensor 8 again, and propagates in the opposite direction to the coupling optical system 18a. From the incident end, which is the start end of. In this case, the optical fiber sensor unit 1
The polarization plane of the light passing back and forth in 8b rotates due to the Faraday effect induced by the measured current flowing through the conductor 4 to be measured.

The light emitted from the optical fiber sensor 8 is converted into a parallel beam by the second lens 20 of the coupling optical system 18a, then reflected by the first beam splitter 24, and is reflected by the second beam splitter 25. It is split into light in two directions.

In this case, one of the split beams from the second beam splitter 25 passes through the third lens 21 and the light receiving fiber 17 after the first analyzer 26 extracts the polarization component in the x direction. Then, it is sent to one detector 13 of the signal processing unit 10. Further, the other split light is obtained by extracting the polarization component in the y direction by the second analyzer 27.
The light is sent to the other detector 13 via the fourth lens 22 and the light receiving fiber 17.

In this way, the light of the polarization components in the x direction and the y direction is sent to each detector 13 and these detectors 13
The signals of the respective polarization components obtained in (1) are sent to the signal processing circuit 14 where they are subjected to arithmetic processing, and the obtained processing results, that is, the measurement results, are output from the output terminal 15.

[1-4. Operation of Optical Fiber Sensor] The signal flow in the optical fiber current measuring device shown in FIG. 1 has been described above. In particular, the optical fiber sensor 8 has a uniform core portion 30 and an optical fiber sensor 8 because of its configuration. As light propagates, the plane of polarization of the light rotates.
This will be described below.

First, the optical fiber for the optical fiber sensor 8 is a single mode fiber that always has optical rotation even in the absence of a magnetic field, and the optical fiber itself is twisted by drawing while rotating the preform in the manufacturing stage. Core (30) produced during fiber fabrication because
Is eliminated and the amount of birefringence is reduced (<2 ° / m). That is, the core portion 30 is made uniform.

When the optical fiber is bent, a main axis of birefringence is generated in the bending direction, that is, the direction in which the optical fiber is arranged (x-axis) and the direction perpendicular thereto (y-axis). Cause. On the other hand, the optical fiber sensor 8 is mechanically twisted rightward even in the mounting stage.
The light propagating inside rotates. That is, in FIG. 2, when light in a linear direction propagates in the axial direction (z-axis direction) of the optical fiber sensor 8, points A and B
The direction of the polarization plane at the point is shown, and since the optical fiber is twisted, the polarization plane of the light rotates at an angle θ at the point B as compared with the point A. The optical fiber is
A similar effect can be obtained even when the motor is twisted mechanically to the left.

As described above, when light propagates inside the optical fiber sensor 8, the light is averaged due to the rotation of the polarization plane of the light, so that the non-uniformity inside the optical fiber sensor 8 as viewed from the light can be eliminated. And high-accuracy measurement can be realized without lowering the sensitivity. Since the optical rotation due to the torsional stress has a fixed ratio to the amount of twist, if the amount of twist is known in advance, the amount of optical rotation can be obtained, and the Faraday effect due to the magnetic field generated by the current 4 to be measured can be obtained. Can be separated. In particular, in the present embodiment, since the optical path is reciprocated using the reflecting mirror 28, the amount of optical rotation due to twisting is reversed in the going and returning directions, and is canceled out. Has the advantage that it can be measured.

Therefore, according to the embodiment, as a result of imparting optical rotation to the optical fiber, the non-uniformity inside the fiber can be eliminated, so that highly accurate current measurement can be realized.

[2. Second Embodiment] As a second embodiment according to the present invention, one embodiment of an optical fiber current measuring device to which the inventions of claims 3 and 12 are applied will be described below. In this embodiment,
Since this corresponds to a modification of the above-described first embodiment, a description of a configuration equivalent to that of the first embodiment will be omitted.

That is, in this embodiment, the amount of twist applied to the optical fiber of the optical fiber sensor 8 as shown in FIG. 1 is specified to improve long-term reliability. In particular, the life of the optical fiber sensor 8 is important for applying the optical fiber current measuring device for the power system.

First, the lifetime t _{s of} the optical fiber twisted in the mounting stage is expressed by the following equation (1).

Ln (t _s / t _pe1 ) = ln (P _f / L · N _p1 ) −ln (b) −n · ln (σ _s / σ _p1 ), b = ln (1 + N _p2 / N _p1 ) / Ln ｛1+ (σ _p2 ) ⁿ · t _pe2 / (σ _p1 ) ⁿ · t _pe1 … (1) In the equation (1), each parameter is a parameter of the strength test of the optical fiber twisted at the manufacturing stage. Represents. t _pe1 and t _pe2 are the first and second proof test times,
P _f is the failure probability, L is the fiber length, N _p1 and N _p2 are 1,
The number of breaks per unit length during the second proof stress test,
σ _p1 and σ _p2 are the stresses at the time of the first and second proof stress tests, and n is the slope obtained by the dynamic fatigue test.

Σ _s is the stress during actual use and is equal to the maximum principal stress of the fiber. That is, it is expressed as follows.

Σ _s = [σ _zmax + ｛(σ _zmax ) ² + 4G ² θ ²
r ² ｝ ^1/2 ] / 2 where G is the transverse elastic coefficient, θ is the twist angle per unit length, and r is the outer radius of the cladding layer of the optical fiber.
Σ _zmax is the maximum stress of bending, and is expressed by the following equation.

Σ _zmax = {r / (R + r)} E where R is the bending radius of the fiber and E is the Young's modulus.

More specifically, a quartz fiber is used as an optical fiber for an optical fiber sensor, and a breakage probability P _f = 1
0 ^-5 , outer radius of cladding of optical fiber r = 62.5μ
m, the bending radius of the fiber was 0.5 m, and the number of windings was m = 1, and a strength test was performed. As a result, n = 20 and t _pe1 = 1.
2 (s), b = 0.0492, σ _p1 = 3.196 × 10
^s (Pa), N _p1 = 1.43 (co / m), E = 7.2 ×
10 ¹⁰ (N / m ² ), G = E / ｛2 · (1 + 0.
2) The result was obtained. Then, when this result was substituted into the above equation (1), the dependency of the fiber breaking life on the number of twisting of the fiber was obtained as shown in FIG. As is apparent from FIG. 3, the torsion rate was 8 turns / m.
In the following manner, a mechanical life of 25 years or more required for an electric power system can be secured.

More specifically, the probability of fracture P _f = 10 ^-5
In order to secure a mechanical life of 25 years or more, the following conditional expression is required by further simplifying the expression (1). That is, when the outer diameter of the clad of the optical fiber for the optical fiber sensor is 2r (μm) and the number of turns of the optical fiber around the object to be measured is m (turns), the twisting ratio n added to the optical fiber in the mounting step is n _{If t} (times / m) satisfies the following expression (2), a life of 25 years or more can be secured with a breakage probability P _f = 10 ⁻⁵ .

[0062]

(Equation 4) The equation (2) indicates that the bending radius of the fiber R ≦ 0.
This is a necessary condition that is satisfied when the distance is 5 m, and when R> 0.5 m, the life can be further extended. By the way, if the condition of FIG. 3 is substituted, n _t ≦ 8.0 (times / m)
= 16.0π (radian / m), which is consistent with the result of FIG.

Therefore, by applying a twist to the optical fiber that satisfies the condition of the expression (2), the optical fiber becomes homogeneous, so that highly accurate measurement can be realized and long-term reliability is improved. Can be.

[3. Third Embodiment] As a third embodiment according to the present invention, in particular, one embodiment of an optical fiber current measuring device to which the inventions according to claims 4 to 7 and the invention according to claim 12 are applied. A description will be given next. Note that this embodiment corresponds to a modification of the above-described first embodiment, and a description of a configuration equivalent to that of the first embodiment will be omitted.

That is, in the present embodiment, in the optical fiber sensor 8 as shown in FIG. 1, the birefringence amount of the entire length of the optical fiber is near 0 ° or near the extreme value in the relationship between the number of twists and the birefringence amount. The number of twists is set as described above to ensure high accuracy.

FIG. 4 shows the relationship between the number of twists over the entire length of the optical fiber and the amount of birefringence (arbitrary scale) in the quartz fiber. At this time, the polarization plane of the light incident on the optical fiber sensor 8 is +4 with respect to the direction in which the optical fiber is arranged.
It is around 5 ° (equivalent results are around + 135 °, -45 °, and -135 °). Here, the neighborhood is ± 2
A range of 2.5 ° is shown, but the effect is even greater in the range of ± 10 °. The relationship between the twist amount ξ and the rotation light amount ω in the quartz fiber is expressed by the following equation.

Ω = 0.073ξ (radian) The coefficient 0.073 slightly changes depending on the temperature. Here, between the number of twists N (times) and the amount of twist ξ, ξ =
There is a 2πN relationship. The condition that the amount of twist と す る is set to be a multiple of 3.5 times is expressed by the following equation (3).

2π (3.5M−1) ≦ ξ (= 2πN) ≦ 2π (3.5M + 1) (3) In the equation (3), M is a positive integer, and ξ
A negative value indicates a leftward twist. If the amount of twist ξ is defined as shown in the equation (3), the amount of rotation ω is (π / 2)
M is substantially equal to M, and the birefringence over the entire length of the optical fiber is close to 0 ° as shown in FIG.

When the current value is low, there is a relationship between the sensitivity S of the optical fiber current measuring device and the amount of birefringence δ as expressed by the following equation (4).

S = sin δ / δ (4) Therefore, if the amount of birefringence δ is near 0 °, highly sensitive and highly accurate measurement can be performed. Further, even if the amount of optical rotation slightly changes due to a change in temperature, the sensitivity S hardly changes and the temperature stability is excellent because the amount of birefringence is close to 0 °.

In FIG. 4, the number of twists N (times)
Is near the value obtained by adding 1.75 to a multiple of 3.5 times, and is expressed by the following equation (5).

| N | = 1.75 + 3.5M (5) In the equation (5), M is a positive integer.
If the number of twists N is defined so as to be close to satisfying the expression (5), that is, within ± 1, as shown in FIG.
The birefringence amount is near the extreme value. In this case, the sensitivity S of the measuring instrument
Is slightly reduced, but since the amount of birefringence is near the extreme value, there is little change in sensitivity even if the amount of rotation changes slightly due to a temperature change.

As described above, the birefringence of the optical fiber sensor is set to a value close to 0 ° or to an extreme value in the relationship between the number of twists and the amount of birefringence. A highly accurate measuring instrument which is hardly affected can be realized. Also, the direction of the plane of polarization of light incident on the optical fiber sensor (the direction of linearly polarized light) is + 45 ° and +135 with respect to the plane on which the optical fiber is arranged.
By setting the angle in the vicinity of °, -45 °, or -135 °, the amount of change in sensitivity can be reduced with a small amount of twist, and a reduction in life can be suppressed.

[4. Fourth Embodiment] Next, as a fourth embodiment of the present invention, one embodiment of an optical fiber current measuring instrument to which each of the inventions according to claims 8 and 12 is applied will be described. In this embodiment,
Since this corresponds to a modification of the above-described first embodiment, a description of a configuration equivalent to that of the first embodiment will be omitted.

That is, in this embodiment, the cladding outer diameter 2r (μm) of the optical fiber sensor 8 as shown in FIG.
By defining the average bending radius R (m) and the number of turns m of the optical fiber, and the wavelength λ of the light,
The purpose is to improve the accuracy by reducing birefringence due to bending.

First, an optical fiber sensor 8 having a cladding outer diameter of 2r (μm) has an average bending radius R around the conductor 4 to be measured.
When installed in (m), the amount of birefringence Δβ (° / m) due to bending induced in the optical fiber is given by the following (6)
It is expressed by an equation.

Δβ = | (πEc / λ) (r / R) ² × (180 / π) | (6) where E is Young's modulus (= 7.75 × 10 ⁹ kg / m ²⁾
(Quartz)) and c are photoelastic constants (= −3.5 × 10 ⁻¹¹ m)
² / kg), and λ is the wavelength of light. FIG. 5 shows that r = 62.
The relation between the average bending radius R and the amount of birefringence Δβ in the case of 5 μm is shown. From FIG. 5, it can be seen that the smaller the average bending radius R (m), the larger the amount of birefringence Δβ and the lower the sensitivity of the optical fiber sensor 8.

Accordingly, assuming that the amount of birefringence over the entire length of the optical fiber sensor 8 is δ (°) and the number of turns of the optical fiber sensor 8 around the conductor 4 to be measured is m, the following equation is obtained from the above equation (6). Can be

Δ = 3.8 × (0.25 / R) ² (r / 6
2.5) ² (0.8 / λ) × 2mπR In this case, since the sensitivity S of the optical fiber sensor 8 is expressed by the above equation (4), in order to keep the measurement accuracy within ± 1%, δ It is desirable that ≦ 0.35 radian = 20 °. 4, when the number of twists over the entire length of the optical fiber is set to about 3.5 or more, the amount of birefringence becomes 1/4 or less as compared with the case where the number of twists is zero. Therefore, if the fiber parameters are set so as to suppress the amount of birefringence induced by bending to 20 ° × 4 = 80 ° or less, the measurement accuracy of ± 1% can be easily satisfied.

Therefore, the parameters of the optical fiber sensor 8 according to the present embodiment are set so as to satisfy the condition shown in the following equation (7).

[0075]

(R / 62.5) ² ≦ (80 / 2mπR / 3.8) (R / 0.25) ² (λ / 0.8) (7) In this equation (7), R = 0.1 (m), m = 10 (times),
Substituting λ = 0.8 (μm), the outer radius r of the cladding of the optical fiber sensor is 45 μm or less.

Also, R ≧ 0.25 (m), m = 1
(Times), when λ = 1.3 (μm) and r <40 (μm), δ <3 °, and even if the number of twists over the entire length of the optical fiber is zero, a predetermined accuracy can be satisfied. further,
If this is twisted about 3.5 turns or more over the entire length of the optical fiber, δ <0.75 °, sensitivity S> 0.999997 can be realized, and an ultra-high-precision optical fiber current measuring device can be realized.

Therefore, according to the present embodiment, the amount of birefringence over the entire length of the optical fiber can be greatly reduced by using the parameters of the optical fiber sensor 8 that satisfies the expression (7). The accuracy of the vessel can be increased.

[5. Fifth Embodiment] As a fifth embodiment according to the present invention, one embodiment of an optical fiber current measuring instrument to which each of the inventions of claims 9 and 12 is applied will be described below. In this embodiment,
Since this corresponds to a modification of the above-described first embodiment, a description of a configuration equivalent to that of the first embodiment will be omitted.

That is, in this embodiment, the cladding outer diameter 2r (μm) of the optical fiber sensor 8 as shown in FIG.
Is defined with respect to the average bending radius R (m) and the number of turns m of the optical fiber, the amount of birefringence over the entire length of the optical fiber is reduced, the accuracy is increased, and the reduction in mechanical life is suppressed to ensure long-term reliability. It enhances the character.

The condition for ensuring the mechanical life required for the power system is as follows:
Torsion ratio n added to the mounting stage for optical fiber
_t (times / m) was specified. In order to reduce the birefringence amount over the entire length of the optical fiber to a certain value, as shown in FIG.
Twist more than 5 turns.

Therefore, if the average bending radius of the optical fiber sensor 8 is R (m), the following equation is established.

## EQU12 ## (125 / 2r) (8.0-log ₁₀ m) ×
2mπR ≧ 3.5 That is, the optical fiber sensor 8 satisfies the following expression (8).

[0082]

2r / 125 ≦ (8.0−log ₁₀ m) × 2mπR / 3.5 (8) where r is the outer radius (μm) of the cladding of the optical fiber,
m is the number of turns (turns) of the optical fiber around the conductor 4 to be measured. In this equation (8), m = 1 (times), R =
Substituting 0.05 (m) gives r ≦ 45 (μm).

Therefore, according to the present embodiment,
By using the optical fiber sensor 8 that satisfies the expression (8), even when the bending radius of the optical fiber sensor 8 is small, the amount of birefringence over the entire length of the optical fiber can be reduced, and the mechanical life due to twisting at the mounting stage. Therefore, an optical fiber current measuring instrument excellent in accuracy and long-term reliability can be realized.

Further, as a modified example of this embodiment,
The condition of the cladding outer diameter 2r of the formula (8) and the cladding outer diameter 2r of the formula (7) described in the fourth embodiment are explained.
r, the outer radius r of the cladding of the optical fiber sensor 8 is less than 40 μm (80 μm
Less). According to this configuration, it is possible to realize an optical fiber current measuring device that is further highly accurate and has excellent long-term reliability.

[6. Sixth Embodiment] FIG. 6 is a diagram showing one embodiment of an optical fiber current measuring device to which each of the inventions according to the tenth and twelfth aspects is applied, particularly as a sixth embodiment of the present invention. FIG. 4 is an explanatory view showing details of an optical fiber sensor, particularly; In this embodiment,
Since this corresponds to a modification of the above-described first embodiment, a description of a configuration equivalent to that of the first embodiment will be omitted.

That is, in the present embodiment, FIG.
As shown in FIG. 5, torsion stress is applied to these portions by twisting the core portion 30, the cladding layer 31, and the coating layer 32 of the optical fiber sensor 8, and the twisting occurs around the coating layer 32. Is fixed by an external coating layer 33 of acrylic or the like newly provided.

With this configuration, the entanglement of the optical fiber due to the twist can be prevented, the mounting becomes easy, and the influence of the linear birefringence induced in the optical fiber and causing the non-uniformity is reduced. Can be suppressed by optical rotation of light due to stress.

As described above, according to the present embodiment, the core layer 30 of the optical fiber sensor 8 moves from the coating layer 3
By applying a torsional stress to up to two portions and providing an outer coating layer 33 around the portion to fix the torsion, an extremely easy-to-handle and high-precision optical fiber current measuring device can be realized. In addition, it is not always necessary to apply a torsional stress to the entire portion from the core portion 30 to the coating layer 32, and by applying at least a torsional stress to the core portion 30, similarly excellent effects can be obtained. .

[7. Seventh Embodiment] FIG. 7 is a diagram showing one embodiment of an optical fiber current measuring device to which each of the inventions according to the eleventh and twelfth aspects is applied, as a seventh embodiment of the present invention. FIG. 4 is an explanatory view showing details of an optical fiber sensor, particularly; In this embodiment,
Since this corresponds to a modification of the above-described first embodiment, a description of a configuration equivalent to that of the first embodiment will be omitted.

That is, in the present embodiment, FIG.
As shown in FIG. 7, the sixth embodiment is characterized in that the torsion stress is applied to these portions by twisting the core portion 30, the cladding layer 31, and the coating layer 32 constituting the optical fiber of the optical fiber sensor 8. This is the same as the embodiment, but the method of fixing this torsion is different. In the present embodiment, the torsion is fixed by connectors 34 for fixing both ends of the optical fiber sensor 8, and a protective pipe 35 serving as a jacket is provided outside the optical fiber sensor 8. Also, connectors 3 at both ends
At least one of the four is provided with a torsion fixture 36 for fixing after adjusting the torsion. further,
Although not shown, a guide for the optical fiber sensor 8 may be provided partially or entirely in the pipe 35.

With this configuration, after passing the optical fiber sensor 8 through the pipe 35, the number of twists over the entire length of the optical fiber sensor 8 can be easily determined by rotating one connector 34. Therefore, the entanglement of the optical fiber due to the twist can be prevented, the mounting becomes easy, the number of twists can be easily adjusted in the mounting stage, and the straight line which is induced in the optical fiber and causes the non-uniformity. The influence of birefringence can be appropriately suppressed by optical rotation of light due to appropriate torsional stress.

As described above, according to the present embodiment, the coating layer 3 extends from the core 30 of the optical fiber sensor 8.
2, a torsion stress is applied to both ends of the optical fiber sensor 8, and a pipe 35
Is provided, it is possible to realize a highly accurate optical fiber current measuring device which is very easy to handle, can prevent deterioration of the optical fiber sensor 8 itself, and can be easily adjusted at the mounting stage.

It is not always necessary to apply a torsional stress to the entire portion from the core portion 30 to the coating layer 32. By applying at least a torsional stress to the core portion 30, similarly excellent effects can be obtained. Things. Further, the means for fixing both ends of the optical fiber sensor 8 is not limited to the configuration of the connector 34 or the torsion fixing tool 36, and the specific configuration can be appropriately selected. The general configuration can be appropriately selected.

[8. Other Embodiments] The present invention
The present invention is not limited to the above-described embodiment, and various other modifications can be made within the scope of the present invention. For example, as described in the above embodiment, the present invention is particularly effective for an optical fiber current measuring instrument, and is more suitable for an electric power system in view of long-term reliability. The present invention can be similarly applied to applied measuring instruments, and can obtain excellent effects.

Further, in the above-described embodiment, a case where a quartz fiber is used as the optical fiber sensor has been particularly described. However, the present invention is not limited to this, and other various materials such as lead glass may be used. In this case, an effect equivalent to that of the above-described embodiment can be obtained. In particular, the above (1)
The condition of the mechanical life described in the formula is valid for all optical fiber sensors, regardless of the presence or absence of torsion, using optical fiber parameters that satisfy the optical fiber life t _s ≧ 25 years under this condition with respect to mechanical stress, When applied to power systems or other uses,
All of their applications are within the scope of the present invention.

[0096]

As described above, according to the present invention,
By imparting optical rotation to an optical fiber for an optical fiber sensor, the homogeneity with respect to light in the optical fiber can be improved, so that an optical fiber applied measuring instrument capable of performing highly accurate measurement can be provided. In particular, by applying an appropriate twist to an optical fiber, it is possible to provide an optical fiber applied measuring instrument that can perform highly accurate measurement and has excellent long-term reliability.

[Brief description of the drawings]

FIG. 1 is a configuration diagram showing an optical fiber current measuring device according to a first embodiment of the present invention.

FIG. 2 is an explanatory diagram showing details of the optical fiber sensor of FIG. 1;

FIG. 3 is a graph showing the relationship between the torsion ratio and the life of an optical fiber sensor according to a second embodiment of the present invention.

FIG. 4 is a graph showing the relationship between the number of twists and the amount of birefringence over the entire length of an optical fiber sensor according to a third embodiment of the present invention.

FIG. 5 is a graph showing a relationship between a bending diameter and an amount of birefringence per unit length of an optical fiber sensor according to a fourth embodiment of the present invention.

FIG. 6 is an explanatory diagram showing details of an optical fiber sensor according to a sixth embodiment of the present invention.

FIG. 7 is an explanatory diagram showing details of an optical fiber sensor according to a seventh embodiment of the present invention.

FIG. 8 is a configuration diagram showing an example of a conventional optical fiber current measuring device.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 4 ... Conductor to be measured 8 ... Optical fiber sensor 9 ... Sensor optical part 10 ... Signal processing part 11 ... Transmission fiber part 18a ... Coupling optical part 18b ... Optical fiber sensor part 30 ... Core part 31 ... Cladding layer 32 ... Coating layer 33 ... Outside Coating layer 34 ... Connector 35 ... Pipe 36 ... Torsion fixture

 ────────────────────────────────────────────────── ─── Continuing on the front page (72) Inventor Yuji Mizutani 2121 Naoyo, Asahi-machi, Mie-gun, Mie Prefecture Inside of Mie Plant, Toshiba Corporation (72) Inventor Ken Sato 2-1 Ukishima-cho, Kawasaki-ku, Kawasaki-shi, Kawasaki, Kanagawa Prefecture Inside Toshiba Hamakawasaki Plant (72) Inventor Toru Uenishi 2-1 Ukishima-cho, Kawasaki-ku, Kawasaki-shi, Kanagawa Prefecture Inside Toshiba Hamakawasaki Plant (72) Inventor Sakae Ikuta 3-2-18 Okusawa, Setagaya-ku, Tokyo Toshiba Substation Equipment Technology Co., Ltd. (72) Inventor Takeshi Yokota 1-1-1, Shibaura, Minato-ku, Tokyo Inside Toshiba Corporation Head Office (72) Inventor Hideki Noda 1-1-1, Shibaura, Minato-ku, Tokyo Stock Company Toshiba head office

Claims (12)

[Claims] 1. An optical fiber sensor disposed near an object to be measured, a light source that generates light for measurement and sends the light to the sensor, a detector that detects light emitted from the sensor, and the sensor A coupling optical system that optically couples a light source and a detector, and a signal processing unit that processes a signal from the detector; and an optical fiber applied measuring device that measures a physical quantity by changing a characteristic of light. An optical fiber-applied measuring instrument characterized in that an optical fiber having optical rotation is always used even in the absence of a magnetic field, as an optical fiber for a sensor. 2. An optical fiber twisted in a manufacturing stage is used as an optical fiber for the optical fiber sensor.
2. The optical fiber applied measuring instrument according to claim 1, wherein the optical fiber is further twisted and arranged at a mounting stage. 3. When the outer diameter of the cladding of the optical fiber for the optical fiber sensor is 2r (μm) and the number of turns of the optical fiber around the object to be measured is m (times), the optical fiber is mounted on the optical fiber. The torsion ratio n _t (times / m) added to the step is a value satisfying n _t ≦ (125 / 2r) (8.0-log ₁₀ m).
An optical fiber applied measuring instrument as described. 4. The twisting is performed so that the birefringence amount of the entire length of the optical fiber for the optical fiber sensor has one of a value near 0 ° and a value near an extreme value depending on the relationship between the number of twists and the amount of birefringence. 4. The optical fiber applied measuring instrument according to claim 1, wherein the number is set. 5. The direction of the plane of polarization of light incident on the optical fiber sensor is + 45 °, + 135 °, −45 °, or −1 with respect to the plane on which the optical fiber is disposed.
The optical fiber applied measuring device according to any one of claims 1 to 4, wherein the angle is set to around 35 °. 6. A quartz fiber is used as the optical fiber for the optical fiber sensor, and the number of twists N (times) over the entire length of the optical fiber is 3.5M-1 ≦ N ≦ 3.5M + 1 (M is an integer other than 0). 6. A value satisfying the following:
An optical fiber applied measuring instrument as described. 7. A quartz fiber is used as the optical fiber for the optical fiber sensor, and the number of twists N (times) over the entire length of the optical fiber satisfies | N | = 1.75 + 3.5M (M is a positive integer). The optical fiber applied measuring device according to claim 4, wherein the value is within ± 1 of the value. 8. The optical fiber for the optical fiber sensor has an average bending radius of R (m), the number of turns of the optical fiber around the object to be measured is m, and the wavelength of light is λ.
In this case, the outer diameter of the cladding of the optical fiber is 2r.
(Μm) is (r / 62.5) ² ≦ (80 / 2mπR / 3.8) (R
/0.25) ² (λ / 0.8), wherein the optical fiber-applied measuring instrument according to any one of claims 1 to 7, wherein: 9. When the average bending radius of the optical fiber for the optical fiber sensor is R (m) and the number of turns of the optical fiber around the object to be measured is m,
The outer diameter 2r (μm) of the cladding of this optical fiber is 2r / 125 ≦ (8.0-log ₁₀ m) × 2mπR /
The optical fiber applied measuring instrument according to any one of claims 1 to 8, wherein the value satisfies 3.5. 10. The optical fiber for an optical fiber sensor according to claim 1, wherein a new coating layer is provided after applying a torsional stress to at least a core portion of the optical fiber. The optical fiber applied measuring instrument according to any one of the above. 11. The optical fiber for an optical fiber sensor applies a torsional stress to at least a core portion thereof.
The optical fiber applied measuring instrument according to any one of claims 1 to 10, wherein the optical fiber is an optical fiber provided with a protective pipe serving as a jacket outside at least at both ends fixed. . 12. The optical fiber applied measuring instrument according to claim 1, wherein the measuring instrument is applied to current measurement utilizing the Faraday effect.