JPH0949776A - Optical cable and pressure measuring system - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an optical cable being capable of being used for a pressure sensor without necessity of a special structure with low loss without restriction in an installing position. SOLUTION: The optical cable comprises an optical fiber core wire 1 coated with resin, a fiber 2 longitudinally attached to the wire 1 or twisted and a sheath 3 of thin film plastic covering the periphery of the fiber 2. In this case, at least part of the resin coating of the wire 1 is brought into contact with the inner wall of the sheath 3 in a sectional shape, and hence the wire 1 is eccentrically deviated in the sectional direction with respect to the circular sheath 3 to be contained.

Description

Detailed Description of the Invention

[0001]

TECHNICAL FIELD The present invention relates to an optical cable and a pressure measuring system.

[0002]

2. Description of the Related Art Conventionally, a pressure sensor using an optical fiber or an optical cable has been known. This type of pressure sensor focuses on the fact that optical loss increases when pressure is applied to the optical fiber. It uses an optical fiber having elasticity, and uses a so-called microbend, which is a minute bend of the optical fiber. and so on.

FIG. 5 is a cross-sectional view of a first prior art optical fiber. In the figure, 21 is a core and 22 is a clad. This conventional technique is disclosed in, for example, Japanese Patent Laid-Open No. 6-229846.
It is known from the official gazette.

This optical fiber is a plastic optical fiber in which silicone rubber is used for the core 21 and silicone rubber or elastomer whose refractive index is lower than that of the core 21 is used for the clad 22, and this optical fiber itself is used as a pressure sensor. It is a thing. Since this optical fiber has elasticity, the amount of light transmission changes when it is deformed. A light source is provided at one end of the optical fiber and a light receiving body is provided at the other end, and the switch can be operated by changing the amount of received light.

However, in this embodiment, since there is no protective coating on the optical fiber, the use environment is limited to an environment that is less susceptible to external damage. Moreover, since the core 21 is made of silicone rubber, the transmission loss of the optical fiber is relatively high.
There is a problem that it is not suitable for measuring pressure in a long distance section of m or more.

FIG. 6 is a sectional view of a second prior art optical cable. In the figure, 31 is a strength member, 32 is a spacer,
33 is an optical fiber core wire, 34 is a press winding, and 35 is a jacket. This prior art is, for example, the actual Kaihei 6-1083.
It is known from Japanese Patent Publication No. 4 and the like.

This optical cable comprises a tensile strength member 3 having a circular cross section.
A plurality of concave spacers 32 having a rough surface are provided on the outer peripheral surface of 1, and the optical fiber core wires 33 are housed on each of them.
A press winding 34 having a rough surface on the optical fiber core wire 33
Is lapped and the outer cover 35 is extruded and coated on the outer cover. When lateral pressure is applied to the optical fiber core wire 33, microbends are generated and transmission loss increases. By sandwiching this optical cable with a pressure detection plate and supplying light from a light source to one end of a plurality of optical fiber core wires 33 via an optical demultiplexer, and connecting an optical power meter to the other end, a pressure detection plate is provided. The pressing direction and magnitude of the applied pressure can be measured.

However, in this embodiment, if a silica-based optical fiber is applied to the optical fiber core wire 33, it is possible to reduce the loss, but since the plurality of optical fiber core wires 33 are used, the outer diameter of the optical cable is small. In addition, a special spacer 32 and a press winding 34, which are roughened so as to easily generate microbends in the optical fiber core wire 33, are required. Further, since the strength member 31 is a steel wire, there is a problem that it is difficult to use it in a flammable environment or an explosive environment.

[0009]

SUMMARY OF THE INVENTION The present invention has been made in view of the above-mentioned circumstances and can be used for a pressure sensor, has no restrictions on the installation location, has a low loss, and requires a special structure. An object of the present invention is to provide an optical cable that does not include the optical cable and a pressure measurement system that uses the optical cable.

For example, although the pressure of a fluid can be estimated by calculation, it is extremely difficult to actually measure the pressure distribution over a long distance in a small-diameter conduit. However, the optical cable of the present invention can be easily installed even in such a small-diameter conduit, the pressure and pressure distribution at the installation location can be measured, and the optical cable can also be used in a flammable dangerous material. Further, the pressure measuring system of the present invention can measure the pressure in a long distance section from a remote place.

[0011]

According to a first aspect of the present invention, there is provided an optical cable in which a fiber sheath is twisted or longitudinally attached to an optical fiber core wire having a resin coating and a plastic jacket is applied to the optical fiber core wire. At least a part of the resin coating is in contact with the inner wall of the outer cover.

According to a second aspect of the present invention, there is provided an optical cable in which a fiber jacket is twisted or vertically attached to a plurality of optical fiber core wires having a resin coating and a plastic jacket is applied to the optical fiber core wires. At least a part of the resin coating of at least one of the optical fiber core wires in the core optical fiber core wire is in contact with the inner wall of the jacket.

According to a third aspect of the invention, in the optical cable according to the first or second aspect, the fiber body is twisted together.

According to a fourth aspect of the invention, in the pressure measuring system, the optical cable according to any one of the first to third aspects and the measuring means for measuring the optical loss of the optical cable are provided. The pressure applied to the optical cable and the pressure distribution are measured based on the loss.

According to a fifth aspect of the present invention, in the pressure measuring system according to the fourth aspect, the light passing through the optical cable is transmitted to the light receiver of the measuring means.

[0016]

1 is an explanatory view of an optical cable showing a first embodiment of the present invention, FIG. 1 (A) is a perspective view, and FIG. 1 (B) shows one section. FIG.
In the figure, 1 is an optical fiber core wire, 2 is a fiber body, and 3 is a jacket.

The first embodiment is an optical cable in which a fiber body 2 is vertically attached or twisted to a resin-coated optical fiber core wire 1 and the periphery thereof is covered with a thin film plastic jacket 3. At that time, as shown in FIG. 1 (B), by making at least a part of the resin coating of the optical fiber core wire 1 in contact with the inner wall of the jacket 3 in the cross-sectional shape, the optical fiber core wire 1 has a circular shape. It is stored so as to be eccentric with respect to the jacket 3 in the cross-sectional direction. The resin coating and inner wall are
In a part of the cross section of the optical cable, the contact state as shown in FIG. 1 (B) is sufficient, and it is not always necessary to keep the contact state in the longitudinal direction of the optical cable.

Various members or materials can be selected for the optical fiber core wire 1, the fibrous body 2 and the jacket 3 in accordance with the use environment. The optical fiber core wire 1 uses, for example, a silica glass fiber coated with an ultraviolet curable resin. As the fibrous body 2, inexpensive polypropylene fiber can be used when high strength is not required.
When using in a long installation or in an environment where tension is applied,
High Young's modulus tensile strength fibers such as aramid fibers can be used. These fibers may be bundled, for example, and the fiber bundle may be twisted in consideration of handling in manufacturing.

The outer cover 3 is made of thin-walled plastic and is made of vinyl chloride, polyamide resin, polyethylene or the like in view of its excellent workability in thin wall, flexibility after processing, and shrinkability against pressure. Is suitable. However, when the optical cable is used in a solvent, it is desirable to use a resin that is as strong as possible against chemical changes, such as a fluororesin.

Under atmospheric pressure, voids are maintained in the fibrous body 2 inside the jacket 3 and no external force is applied to the optical fiber core wire 1. However, when external pressure is applied, the jacket 3 is a thin plastic. Therefore, the fiber body 2 is easily contracted, and the fiber body 2 is pressed against the optical fiber core wire 1. In this way, the external pressure is transmitted to the optical fiber core wire 1 via the fibrous body 2 as a contracting force. here,
Since the optical fiber core wire 1 is eccentrically housed with respect to the circular outer jacket 3 in the cross-sectional shape, the optical fiber core wire is housed in a concentric circle with the outer jacket as described later with reference to FIG. As compared with existing optical fiber cords for communication, the contracting force due to pressure application is applied non-uniformly to the optical fiber core wire 1.

This non-uniform contracting force presses the rough surface created by the fibrous body 2 against the optical fiber core wire 1, so that minute bending, so-called microbending, easily occurs. The transmission loss of the optical fiber core wire 1 increases in the portion where the microbending occurs, and it is possible to detect the increase of the pressure by measuring the increase of the transmission loss. When the bending of the optical fiber core wire 1 becomes large, bending loss occurs even in the case of uniform bending.

There are two methods for measuring the optical loss. The first method is a method of injecting light from one end of the optical fiber core wire 1, receiving light passing through the optical fiber core wire 1 at the other end, and measuring the fluctuation of the optical power.

The second method is a method in which light is made incident from one end of the optical fiber core wire 1 and reflected light which is reflected in the middle of the optical fiber core wire 1 and returns is measured. The means for measuring the reflected light is OTDR (Optical Time Dom).
It is known as an ain Reflectometer). This OTDR detects the backscattered light returning to the incident end side of the Rayleigh scattered light generated when the refractive index of the core of the optical fiber has a minute fluctuation.

If there is a transmission loss in the middle of the optical fiber, the inclination of the reflected light changes. Since the transmission loss of the optical fiber core wire 1 increases in the portion where the microbending occurs, it is possible to detect the increase in pressure by measuring the change in the inclination of the reflected light. Further, since the position where the optical loss is increased can be specified, it is possible to measure the pressure distribution of the environment where this optical cable is installed.

In such an optical cable, a microbend easily occurs in response to the application of pressure, so that the transmission loss of the optical fiber core wire 1 is sensitively increased, and the pressure fluctuation can be sensitively measured.

In addition, a thin plastic jacket usually has 4
Since the structure only accommodates the optical fiber core wire 1 and the fiber body 2 coated with the ultraviolet curable resin having an outer diameter of 00 μm or less,
Since the structure can have a small diameter with an outer diameter of slightly less than 1 mm and is highly flexible, it can be installed in a thin tube that is usually difficult to measure. The fibrous body 2 and the outer cover 3 effectively function as a damage protection layer of the optical fiber core wire 1.

When used in a solvent, even if the jacket 3 is dissolved, if the fluid is not adversely affected, the optical cable can be replaced and used when the sensing ability is impaired. Even if the optical cable is replaced, the cost burden is reduced because the cost of this optical cable is lower than that of the conventional product. If an existing optical cable is installed inside the pipe and the new optical cable is pulled into the pipe and laid, the existing optical cable can be tied to the new optical cable and used as a lead wire, so replacement is easy and the replacement cost is kept to a minimum. be able to.

By using this optical cable not only as a sensor but also by lengthening the optical cable and directly connecting it to the photodetector of the measuring instrument so that the light passing through the optical cable is converted into an electric signal by this photodetector. This optical cable can be used as it is as a lead wire connecting between the measuring device and the sensor section at the measuring point. In addition, even when connecting to the sensor using a separate lead wire, it is possible to use an optical fiber for communication in this lead wire and directly connect it to the optical cable as a pressure sensor by fusion or an optical connector. No conversion equipment is required.

Therefore, measurement from a remote place becomes easy. Further, since it is possible to measure the pressure between the measured object and the measurement system without interposing an electric device or a conductor,
It is possible to minimize the adverse effect of the induced current or the like on the object to be measured and the measurement data.

In particular, when a silica glass fiber is used for the optical fiber core wire 1, the silica glass fiber is excellent in low loss, as is generally used for communication, and therefore, it has a long distance of several km or more. It is possible to construct a measurement system that measures the pressure over the section of from a remote location.

FIG. 2 is an explanatory view of an optical cable showing a second embodiment of the present invention, FIG. 2 (A) is a perspective view, and FIG. 2 (B) is an explanatory view showing one section. . In the figure,
The same parts as those in FIG.

The optical cable of this embodiment differs from the optical cable of the first embodiment described with reference to FIG. 1 in that a plurality of optical fiber cores 1 are accommodated, but other points are the same. Is. An optical cable in which a fiber body 2 is longitudinally attached or twisted to a resin-coated 6-core optical fiber core wire 1 and the periphery thereof is covered with a thin-film plastic jacket 3. The optical fiber core has at least one core in cross section. By disposing at least a part of the resin coating of the wire 1 in contact with the inner wall of the outer jacket 3, the optical fiber core wire 1 is eccentrically stored in the cross-sectional direction with respect to the circular outer jacket 3.

In the example illustrated in FIG. 2, six optical fiber core wires 1 are used, and in the sectional view of FIG. 2B, they are arranged point-symmetrically and surrounded by the six optical fiber core wires 1. The fibrous body 2 is arranged in the central portion. The optical fiber core wire 1 is 6
It does not have to be the core, and even if this central portion is made hollow, the seventh optical fiber core wire 1 is arranged, or a non-metallic tensile member having the same diameter as the optical fiber core wire 1 is used. You may arrange.

The resin coating and the inner wall may be in a contact state as shown in FIG. 2B in a partial cross section of the optical cable, and it is not necessary to keep the contact state in the longitudinal direction of the optical cable. Moreover, it is not necessary that the resin coating of the specific optical fiber core is always in contact with the inner wall.

In order to measure pressure using the optical cable of this embodiment, only one optical fiber core wire 1 is used,
The remaining optical fiber core wire 1 is used as a spare core wire. Also,
If the tip of the first optical fiber core wire of one core is connected to the tip of the second optical fiber core wire 1 of another core, the light passes through the second optical fiber core wire to the insertion end side of the light. Come back. Therefore, even when the light is inserted from one end of the optical fiber core and the light emitted from the emission end is received and the loss is measured, the measurement can be performed at the position on the insertion end side. As a result, it is not necessary to install measuring instruments at both ends of the optical cable or to take out the emitting end of the optical cable from the object to be measured.

Further, the light returning to the insertion end side through the second optical fiber core wire is returned to the distal end side through the third optical fiber core wire, and further to the tip end of the fourth optical fiber core wire here. When connected, the light returns to the insertion end side again through the fourth optical fiber core wire. In this way, by connecting at both ends of the tip and the insertion end, the number of cores of the optical fiber connected in series is increased, and if the number of cores used as a sensor is increased, the increase in loss due to pressure will increase the connected optical fiber. Since it is proportional to the number of hearts, the sensing ability as a sensor can be enhanced.

[0037]

EXAMPLE In the optical cable according to the first embodiment described with reference to FIG. 1, a silica single mode optical fiber core having an outer diameter of 250 μm, which uses an ultraviolet curable resin, is used as the optical fiber core fiber 1. Tens of denier tensile strength fibrous bodies were used for the body 2, and a plastic coating jacket 3 having a thickness of several hundreds of μm was applied to finish the outer diameter to about 0.9 mm.

FIG. 3 is a sectional view of a conventional optical cable as a comparative example of the present invention. In the figure, 11 is an optical fiber core wire, 12 is a tensile strength fiber body, and 13 is a jacket. This optical cable has been conventionally used, and an optical fiber core wire 11 having an outer diameter of 900 μm and using nylon as the outermost sheath is provided with a tensile strength fiber body 12 of several thousand denier around this, and several hundred μm. Thick plastic jacket 13
And an outer diameter of about 2 mm, which is a structure similar to the present invention.

The optical cable of the example of the present invention and the optical cable of the comparative example each having a length of 40 m were subjected to a water pressure of 100 atm. As a result, no change in loss was observed in the comparative example, whereas in the example of the present invention, the change in loss was about 6 dB, indicating that sufficient pressure was sensed.

FIG. 4 is a chart showing the measurement of the embodiment of the present invention by the OTDR method. In the figure, the horizontal axis is the distance from the insertion end of the optical cable, and the vertical axis is the transmission loss of the optical fiber core. In the pressure applying section over 40 m, there is a loss increase of 6 dB after the pressure is applied, and the inclination of this transmission loss characteristic line represents the loss of the optical fiber core wire. Since this slope is a straight line, it can be seen that the portion receiving pressure shows a uniform increase in loss. Since the horizontal axis of this chart indicates the distance, the pressure distribution of the measured environment can be specified by measuring the relationship between the loss increase and the distance.

[0041]

As is apparent from the above description, according to the first aspect of the invention, in the optical cable, at least a part of the resin coating of the optical fiber core wire contacts the inner wall of the jacket. Therefore, when pressure is applied to the optical cable, the jacket is contracted and the fiber body is pressed against the optical fiber core wire. At this time, since the optical fiber core wires are stored so as to be unevenly decentered in the cross-sectional direction, the fibrous body is unevenly pressed against the optical fiber core wire, and the fibrous body functions as a rough surface. Therefore, there is an effect that it is possible to easily generate microbending in the optical fiber core wire, increase the transmission loss of the optical fiber core wire, and realize a pressure sensor capable of sensitively measuring fluctuations in pressure.

Moreover, the structure is simple and the materials used are small,
Since the manufacturing is simple, the manufacturing cost can be reduced. Since it is possible to reduce the diameter, it is highly flexible, and sufficient strength can be realized, so that it can be installed in a narrow tube or the like, which is usually difficult to measure. Moreover, since all the constituent members are non-metallic structures made of non-metallic materials and do not use electricity during measurement, it is safe to measure the pressure of dangerous flammable fluids such as petroleum, and it is safe to monitor pipelines and detect abnormal points. It can also be used for identification.
Further, even if the outer cover is dissolved, if it does not adversely affect the fluid, it can be used while being replaced when the sensing ability is impaired.

According to the second aspect of the present invention, at least a part of the resin coating of at least one optical fiber among the plurality of optical fibers is in contact with the inner wall of the outer cover. Therefore, in addition to the effect described in claim 1 described above, the effect obtained by accommodating a plurality of optical fiber core wires is also exhibited.

For example, it is possible to apply only one optical fiber core wire to the pressure measurement and use the remaining optical fiber core wire as a spare core. Also, if the tip of one optical fiber core is connected to another one optical fiber core, even if light from the output end is required for loss measurement, it can be measured only at the insertion end side, and the measuring instrument Need not be installed at both ends and the emission end of the optical fiber core wire needs to be taken out from the object to be measured. Furthermore, if the number of cores connected at both ends of the optical fiber core is increased and the number of cores used as a pressure sensor is increased, the increase in loss due to pressure is doubled by the number of cores, so it is possible to enhance the sensing ability as a pressure sensor. Is.

According to the third aspect of the present invention, since the fibrous body is twisted, the fibrous body does not have to be scattered during the production, and the manufacturability is improved.

According to the invention set forth in claim 4, according to claim 1,
(3) The optical cable according to any one of (1) to (3) and the measuring means for measuring the optical loss of the optical cable, and the pressure and pressure distribution received by the optical cable are measured based on the optical loss, so that the optical fiber core wire can be easily There is an effect that the micro-bending can be generated, the transmission loss of the optical fiber core wire can be increased, and the pressure fluctuation can be sensitively measured.

Particularly, as a measuring means for measuring the optical loss,
When using a means that measures the light that is incident from one end of the optical fiber and that is returned by reflection in the fiber, the position of the loss increase can be specified, so the pressure distribution of the environment where the sensor is installed can be determined. Can be measured.

According to the invention described in claim 5, since the light passing through the optical cable is transmitted to the light receiver of the measuring means, a converting device for connection is not required, and the measurement from a remote place is easy. There is an effect that. Further, since the pressure can be measured without passing through an electric device or a conductor between the device under test and the measurement system, it is possible to minimize the adverse effect of the induced current or the like on the device under test and the measurement data. it can.

When the optical cable is not only used as a sensor but is lengthened and is directly connected to the light receiver of the measuring device, this optical cable is used as it is as a lead wire connecting the measuring device and the sensor section at the measuring point. be able to. In particular, when a silica fiber is used as the optical fiber, it is excellent in terms of low loss and versatility of the measurement system.

[Brief description of drawings]

FIG. 1 is an explanatory view of an optical cable showing a first embodiment of the present invention, FIG. 1 (A) is a perspective view, and FIG.
FIG. 3 is an explanatory view showing one section.

FIG. 2 is an explanatory diagram of an optical cable showing a second embodiment of the present invention, FIG. 2 (A) is a perspective view, and FIG.
FIG. 3 is an explanatory view showing one section.

FIG. 3 is a cross-sectional view of an optical cable as a comparative example of the invention.

FIG. 4 is a diagram of a chart of an example of the present invention measured by the OTDR method.

FIG. 5 is a cross-sectional view of a first prior art optical fiber.

FIG. 6 is a cross-sectional view of a second prior art optical cable.

[Explanation of Codes] 1 ... Optical fiber core wire, 2 ... Fiber body, 3 ... Outer sheath, 21 ... Core, 22 ... Clad, 31 ... Tensile strength body, 32 ... Spacer, 33 ... Optical fiber core wire, 34 ... Press winding , 35 ...
Jacket.

Claims (5)

[Claims] 1. An optical cable in which a plastic jacket is applied to a fiber body twisted or vertically attached to an optical fiber core wire having a resin coating, and at least a part of the resin coating is provided in the jacket. An optical cable characterized by being in contact with the inner wall. 2. An optical cable in which a fiber sheath is twisted or vertically attached to a plurality of optical fiber core wires having a resin coating and a plastic jacket is applied to the optical fiber core wires of the plurality of core fibers. At least a part of the resin coating of at least one core of the optical fiber is in contact with the inner wall of the jacket. 3. The optical cable according to claim 1, wherein the fibrous body is twisted together. 4. The optical cable according to any one of claims 1 to 3, and a measuring means for measuring an optical loss of the optical cable, and a pressure and a pressure distribution received by the optical cable based on the optical loss. A pressure measurement system characterized by measuring. 5. The light passing through the optical cable is transmitted to a light receiver of the measuring means.
The pressure measurement system described in.