JPH02183131A - Optical fiber sensor - Google Patents

Abstract

PURPOSE:To enable detection of the generation of a temperature change and a position where it occurs by arranging an optical fiber so built up integral with a energizing member to be bent at the same part in response to a local contraction of the energizing member as caused with the temperature change. CONSTITUTION:An optical fiber 1 and an energizing member 2 are connected together with an adhesive at joints 31-35 at a specified interval X. The member 2 is made of a material having a negative linear expansion coefficient to a thermal change. The optical fiber 1 is also connected to an optical fiber analyzer 4 at one end thereof. Now, for example, when sections 33-34 are heated by one reason or another, the member 2 contracts in these sections and is reduced by DELTAX. On the other hand, the linear expansion coefficient of the optical fiber 1 is positive and hence, the optical fiber 1 is drawn by the member 2 and caused to bend in these sections. As a result, in the optical fiber 1, a propagation loss worsens sharply in the sections 33-34 where this bending occurs and a step C is displayed at positions of the sections 32-34 as done by the analyzer 4 thereby enabling the determining of where a thermal change occurs in a long detecting section simultaneously.

Description

DETAILED DESCRIPTION OF THE INVENTION FIELD OF INDUSTRIAL APPLICATION The present invention relates to thermal sensors. More specifically, the present invention relates to a completely new configuration of a heat-sensitive sensor using an optical fiber, which allows a detection unit to be installed over a long distance and which is capable of detecting a heat detection position in a remote location.

BACKGROUND OF THE INVENTION One of the most widely used sensors is a thermal sensor. Typical heat sensing sensors include thermocouples, thermistors, and bimetals, which are configured to output the detected amount of heat change based on changes in electrical resistance or changes in electrical quantity such as switching on and off. .

That is, thermocouples utilize the phenomenon that an electromotive force is generated when heat is applied to the junction of dissimilar metals.

In addition, thermistors are made of Mn, Co, Ni, Fe, [
This method takes advantage of the large temperature coefficient of electrical resistance of oxide composite sintered bodies such as u. Bimetals are made by bonding metals with different coefficients of linear expansion to each other, and use the fact that the bonded metal plates warp when heated to control switches and variable resistors.

Problems to be Solved by the Invention The various heat-sensitive sensors described above are used for various purposes depending on their characteristics, but a problem common to all conventional heat-sensitive sensors is that one sensor There is a problem that the detectable area is limited to a narrow range.

That is, the area that can be detected by one heat-sensitive sensor is only the vicinity of the detection section of each sensor. Therefore, if thermal monitoring is to be carried out over the entire length of laid cables, pipelines, etc., it is necessary to arrange a very large number of heat sensing sensors.

Furthermore, in such an application, if one were to try to identify the location of a thermal change that should be detected, it would be necessary to connect each of the outputs of the numerous sensors placed to a specific monitoring station, which is difficult to do in practice. It must be said that this is unrealistic considering the scale of the facility that would require such a use.

Known heat-sensitive sensors that can constitute a long detection section include:
There is also known thermal paper (thermo label), which is a sheet coated with a special synthetic resin or pigment that develops or changes color when heated. However, since such a thermal sensor outputs heat detection with its own color change, it is still virtually impossible to detect heat detection from a remote location.

SUMMARY OF THE INVENTION Therefore, an object of the present invention is to provide a novel heat-sensitive sensor that solves the above-mentioned problems of the prior art, is capable of sensing heat over a long distance, and is also capable of detecting the position where heat is detected even in a remote location. Our goal is to provide the following.

Means for Solving the Problems According to the present invention, there is provided a biasing member configured to contract the linear length of a portion exposed to a specific temperature change in response to a specific temperature change; an optical fiber configured integrally with the biasing member so that the same portion is bent in response to local contraction of the biasing member caused by the change, and backscattering light propagating through the optical fiber. An optical fiber sensor is provided, which is configured to detect the occurrence and the position of the temperature change by observation using a loss measurement method.

As will be described later, the working optical fiber can continuously detect changes in the propagation loss of light propagating through the fiber from the input end to the output end. The heat sensing sensor according to the present invention utilizes the characteristics of such optical fibers.

That is, when light propagates through an optical fiber, it causes backscattering called Rayleigh scattering at various parts of the fiber. By detecting this backscattering level on the time axis, it is possible to continuously measure how light propagating through the optical fiber is attenuated due to propagation loss at each part of the optical fiber. This is called backscattering loss measurement method.
An optical fiber analyzer (OTDR) is known as a device for implementing this method.

When observing the state of propagating light in a normal optical fiber using an optical fiber analyzer, the propagating light attenuates smoothly and continuously from the input end toward the output end. However, if there is some kind of fault in the middle of the optical fiber and the propagation loss of the optical fiber locally increases at that location, a gradual drop in level will appear on the optical fiber analyzer at the location where the fault has occurred. Therefore, in the optical fiber sensor according to the present invention, an optical fiber and a biasing member are combined to cause a local increase in propagation loss to the optical fiber when a temperature change occurs within the measurement area. It is configured to apply a physical quantity.

That is, in the heat sensing sensor according to the present invention, the optical fiber is also deformed by, for example, being bent due to the contraction caused by the thermal change of the biasing member, and the propagation loss of the optical fiber caused by this deformation is measured by the backscattering loss measurement method. It is detected by

As an example, a configuration of a biasing member that bends an optical fiber due to thermal changes will be described.

A simple method for bending an optical fiber is, for example, twisting the optical fiber with a material that has a negative coefficient of linear expansion against temperature changes. That is, the optical fiber itself has a very small positive coefficient of linear expansion, and its length hardly changes even when the temperature increases. Therefore, in a sensor obtained by twisting a fiber-shaped biasing member with a negative coefficient of linear expansion and an optical fiber, the biasing member contracts as the temperature rises, and the difference in line length between the biasing member and the optical fiber causes light to emit light. The extra length of the fiber is bent, and the propagation loss of the optical fiber increases at that portion. In addition, as a material with a negative coefficient of linear expansion, LCP
(liquid crystal polymer plastic), a single wire of a plastic superstretched body, etc. can be exemplified.

A similar effect can also be achieved by using a shape memory alloy that memorizes a given shape at high temperatures and, even if deformed at low temperatures, returns to its original shape when heated to high temperatures again. That is, a member is memorized into a shape such as a coil shape, which is shorter in length than the original shape of the member, and this is stretched at a low temperature and then twisted with an optical fiber to produce a sensor.

When heat of a predetermined temperature or higher is applied to the optical fiber sensor thus obtained, the biasing member regains its memorized coiled shape and its overall length is shortened.

Therefore, bending occurs in the optical fibers twisted together.

In addition, as shape memory alloys, titanium (T) and nickel (
T1Ni alloy, which is an alloy with N1), is widely known. The transformation temperature of this alloy can be controlled by the Ni content, so if multiple shape memory alloy-optical fiber twisted heat sensing sensors with different component ratios are installed, the applied temperature can be controlled in stages. It is also possible to judge. Furthermore, by combining it with a spring or other shape memory alloy wire at a critical temperature, it is possible to create something that automatically restores its initial state after the heat to be detected disappears.

Furthermore, it can also be realized by keeping the coil spring in an extended state with a spacer member that softens, collapses, disappears, or melts due to the heat to be detected, and then couples this to the optical fiber. In this case, the spacer only needs to change its dimensions in response to some change, so it is not limited to heat, but also radiation,
A sensor capable of detecting ultraviolet rays, organic solvents, etc. can be easily constructed.

In addition to the above-mentioned twisting method, the biasing member and the optical fiber can be coupled together by a simple method such as gluing the optical fiber and the biasing member at a predetermined interval. You should choose.

The present invention will be described in more detail below with reference to the drawings, but the following disclosure is only one example of the present invention and does not limit the technical scope of the present invention in any way.

Embodiment FIGS. 1(a) and 1(5) are diagrams illustrating the basic configuration of an optical fiber sensor according to the present invention. As will be described later, FIG. 1(a) shows the initial state of the optical fiber sensor, and FIG. 1(a) shows the heat detection state of the optical fiber sensor.

The device shown in FIG. 1(a) consists of an optical fiber 1 and a biasing member 2.
and at a predetermined interval X at a connecting point 3. ~ 35 and are connected with adhesive. The biasing member 2 is made of a material having a negative coefficient of linear expansion with respect to thermal changes, and the optical fiber 1 has one end coupled to an optical fiber analyzer 4.

The state shown in FIG. 1(a) is the initial state, so to speak.
The optical fiber 1 and the biasing member 2 are linear with each other. In this state, the optical fiber analyzer has peaks A and B at both ends, as shown in Figure 1(a).
The optical power is observed to gradually decrease by one unit between the two. Here, what appears as a gentle slope in section a is the normal propagation characteristic of this optical fiber.

Note that the peaks A and B appearing at both ends are caused by Fresnel reflection at the input end and output end of the optical fiber, and in reality, it is preferable to remove them to prevent saturation of the light receiving element of the analyzer. . Specifically, this can be eliminated by using a directional coupler or providing a gate for coupling between the optical fiber 1 and the optical fiber analyzer 4.

In the optical fiber sensor device configured as described above, for example, when the sections 33 to 34 are heated for some reason, the biasing member 2 having a negative coefficient of linear expansion contracts in this section, and the length of that section is reduced. Decreased by ΔX. On the other hand, the coefficient of linear expansion of the optical fiber 1 is positive, so the coefficient of linear expansion of the optical fiber 1 is positive.
is pulled by the biasing member and bends in this section. Then, the optical fiber 1 is bent in the section 3. -3. Since the propagation loss deteriorates rapidly in the section 33, as shown by the optical fiber analyzer 4 in FIG.
-3. A step C is displayed at a position corresponding to .

In this way, if the optical fiber sensor according to the present invention is used, it is possible to simultaneously detect not only a thermal change but also where in a long detection section a thermal change occurs.

FIGS. 2(a) to 2(d) are diagrams illustrating the manufacturing method and structure when a shape memory alloy is used as the biasing member.

First, as shown in FIG. 2(a), the shape memory alloy wire 22
Shape memory alloy wire 2 is formed into a coil shape of length X at high temperature.
2 to memorize this shape. Subsequently, as shown in FIG. 2 et al., the shape memory alloy wire 22 is cooled to a low temperature state and then stretched to form a straight line having a length Y.

The linear shape memory alloy wire 22 thus obtained is used as a biasing member to be bonded and bonded to the optical fiber 1 at a predetermined distance y, as shown in FIG. 2(C). The optical fiber 1 is the first
It is coupled to an optical fiber analyzer 4 in the same way as the device shown in the figure. Moreover, a coil spring 23 with the other end fixed at a predetermined position is coupled to one end of the shape memory alloy wire 22.

In the optical fiber sensor configured as above, the second
As shown in FIG. 2(d), when the area 3□-3° is heated, the shape memory alloy wire 22 recovers the shape shown in FIG. 2(a) and becomes a coil. becomes, section 32
-3. decrease the distance by Δy.

Therefore, the optical fiber coupled thereto is the section 32-3.
．． , which increases the propagation loss in this section. The method for detecting the increased propagation loss is exactly the same as the device shown in FIG. 1, so a description thereof will be omitted.

Note that the stiffness of the shape memory alloy in a low temperature state is less than 1/3 of that of the shape recovery, and by setting an appropriate spring constant for the coil spring 23, the stiffness of the shape memory alloy in a low temperature state can be restored to its original state when the temperature in the section 32-3 decreases again. Return to a straight line like this.

Furthermore, FIGS. 3(a), 3(b) are diagrams showing other configuration examples of the biasing member.

That is, as shown in FIG. 3(a), the biasing member 30 of this optical fiber sensor is composed of a coil spring 32 and a spacer 31 sandwiched between the coil spring 32 at a predetermined interval. Although the optical fiber 1 is bonded to the coil spring 32 in predetermined sections, it should be noted that in the section where the spacer 31 is sandwiched, the optical fiber 1 is bonded to the coil spring 32 which is in an extended state to a length of 2.

Now, in the optical fiber sensor configured as described above, section 3. -32 is heated, the spacer 31 in this section dissolves and the coil spring 32 returns to its free length. Therefore, the optical fiber coupled to this section 31-3
Bending at □ increases propagation loss. The method for detecting this increase in propagation loss is the same as that of the apparatus shown in FIGS. 1 and 2, so a description thereof will be omitted.

Although this embodiment has been described as a heat-sensitive sensor, by making the biasing member have a positive coefficient of linear expansion, it can also be configured as a sensor that detects a local temperature drop.

Production Example An optical fiber sensor according to the present invention was actually produced using a shape memory alloy wire as a biasing member.

The shape memory alloy wire used as the biasing member is a TI wire with a diameter of 0.31Ilfflφ that has the property of recovering its shape at 80°C.
It is a NI-based shape memory alloy wire.

500 m of this shape memory alloy wire was kept at 100° C. and wound around a jig to form a coil having a diameter of 5 mmφ.

Subsequently, after cooling this to room temperature, the shape memory alloy wire was stretched until it became a straight line, and this was used as a biasing member.

On the other hand, the optical fiber used was a single mode optical fiber in which a bare optical fiber with a diameter of 0.25 mm was coated with an ultraviolet curable resin. The shape memory alloy wire used as a biasing member as described above and this optical fiber were arranged at a pitch of 30.
The fibers were twisted together to form an optical fiber sensor. The transmission loss of the optical fiber in this state is 1.3 wavelength
It was 0.45 dB/km in μm.

After connecting one end of the optical fiber sensor fabricated as described above to an optical fiber analyzer, store it at any location at 90°C.
When hot water was poured over the fiber, the shape memory alloy returned to its original coiled shape, causing the optical fiber to bend. At this time, on the optical fiber analyzer, 0.0
A step difference corresponding to a level drop of 6 to 0.2 dB was observed. Further, when the coiled portion was returned to its original straight state after returning to room temperature, the step on the optical fiber analyzer disappeared. Furthermore, when this was repeated, the level difference as described above appeared with good reproducibility. On the other hand, 75-70℃
No change was observed in the area where boiling water was poured.

As described in detail, if the optical fiber sensor according to the present invention is used, the detection section can be continuously arranged over a long distance, and when a thermal abnormality is detected,
Its position can also be detected. Such characteristics are
This is due to the unique configuration of the optical fiber sensor according to the present invention, which could not be achieved at all with conventional heat-sensitive sensors.

The optical fiber sensor according to the present invention is advantageous for equipment that needs to continuously detect thermal abnormalities over a long period of time, such as cable pipes for communication, electric power, etc., water supply pipes, oil supply pipes, etc. It can be used for.

The optical fiber itself is unguided and chemically stable, and
Since the biasing member can be selected from a wide range depending on the required detection temperature range, etc., this optical fiber sensor can be used in a wide range of application fields.

[Brief explanation of the drawing]

FIGS. 1(a) and 1(a) are diagrams schematically showing a configuration example of an optical fiber sensor according to the present invention and its operation, and FIGS. FIGS. 3(a) and 3(b) are diagrams illustrating still another configuration example of the optical fiber sensor and its operation according to the present invention; FIGS. It is. (Main reference numbers) 1°14 optical fiber, 2.22.30...Biasing member (resin), 4...Optical fiber analyzer, 23.32...Coil spring, 31...Spacer, Patent Applicant: Sumitomo Electric Industries, Ltd.

Claims (1)

[Scope of Claims] (1) A biasing member configured to shrink the linear length of a portion exposed to a specific temperature change, and An optical fiber is configured integrally with the biasing member so that the same portion is bent in response to local contraction of the biasing member, and the light propagating through the optical fiber is observed by a backscattering loss measurement method. An optical fiber sensor characterized in that the optical fiber sensor is configured to detect the occurrence and the position of occurrence of the temperature change. (2) The optical fiber sensor according to claim 1, wherein the biasing member is made of a material having a negative coefficient of linear expansion with respect to temperature. (4) The fiber target sensor according to claim 1, wherein the biasing member is a coil spring biased to an extended state longer than its free length by a member that softens or dissolves due to the heat to be detected. . (6) The optical fiber sensor according to any one of claims 1 to 4, wherein the biasing member and the optical fiber are twisted together to form a twisted yarn. (7) The biasing member and the optical fiber are bonded to each other with an adhesive at predetermined intervals in a linear direction. Optical fiber sensor.