JP2900769B2 - Temperature detecting optical fiber and method of manufacturing the same - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a temperature detecting optical fiber used for detecting the temperature of a long linear object such as an electric wire and a method of manufacturing the same.

[0002]

2. Description of the Related Art Various means have been developed as means for detecting the temperature of an object to be detected. When the object to be detected is a long linear object, a so-called lumped constant type temperature sensor such as a semiconductor temperature sensor is used. In order to detect the temperature of a long linear object by a sensor in the longitudinal direction, a plurality of temperature sensors must be arranged along the long linear object, and a large number of temperature sensors are required. Since the circuit for processing the output of the temperature sensor is also complicated, the overall configuration is complicated, and there is a problem that a malfunction is likely to occur due to the influence of noise.

Therefore, as a means suitable for detecting the temperature of a long linear object, a distributed constant type temperature sensor using an optical fiber has been proposed. It detects the change in backscattered light due to the rise in fiber temperature and detects abnormal temperature etc. of a linear long object.In this case, the change is detected because the backscattered light from the optical fiber is weak in the first place. This requires a complicated and expensive detection means.

On the other hand, as a means for detecting a temperature using an optical fiber, a temperature-sensitive coloring layer that changes color with temperature is provided on the outer periphery of the core of the optical fiber as described in Japanese Utility Model Publication No. 62-3761. Has been done.

That is, as shown in FIGS. 6A and 6B,
An optical fiber 1 is formed by providing a thermosensitive coloring layer 1b on the outer periphery of the core 1a, providing a cladding 1c on the outer periphery of the thermosensitive coloring layer 1b, and further providing a sheath 1c on the outer periphery. Light from a white light source or the like is incident thereon, and a change in the wavelength of light emitted from the optical fiber is detected by an attenuating effect due to absorption of light of a specific wavelength by the temperature-sensitive coloring layer 1b that has developed color.

[0006]

However, if the thermosensitive coloring layer 1b is provided on the outer periphery of the core 1a as described above, it is not necessary to detect weak light as much as backscattered light, but since light loss is large, There is also a limit on the optical transmission distance of the optical fiber, and if the long linear object that is the object of temperature detection is too long, the light emitted from the optical fiber will be too weak to detect abnormal temperatures sufficiently. There is a point.

That is, as shown by the arrows in FIGS. 6A and 6B, the light incident on the optical fiber 1
Although the light propagates while being totally reflected at the boundary surface between the a and the cladding 1c, the light is reflected by the thermosensitive coloring layer 1b due to the presence of the thermosensitive coloring layer 1b, and at this time, a part of the light is absorbed (or absorbed). Since the optical fiber 1 is longer, the optical loss increases as the optical fiber 1 becomes longer.

Further, as shown in FIG. 7, it is described in the above-mentioned publication that a plurality of thermosensitive coloring layers 1e are provided in a stripe shape on the outer periphery of the core 1a. Since almost no light propagates without hitting,
Again, the light loss is large.

Accordingly, the present invention has been made to solve the above-described problems, and has been made to reduce optical loss, extend the optical transmission distance of an optical fiber, and extend the optical fiber over a longer length than before. It is an object to detect an abnormal temperature of a linear long object.

[0010]

SUMMARY OF THE INVENTION An optical fiber for temperature detection according to the present invention comprises a core having a color-changing core portion including a thermosensitive color-changing material at a central portion, and a clad provided on the outer periphery of the core. It is characterized by:

Further, as a method for producing the same, a core material containing a thermosensitive color-changing material is poured into a hollow pipe, and after the core material is cured, the hardened core material is taken out from the hollow pipe to form a color-changing core. Preferably, a core made of a core material is formed on the outer periphery of the discoloration core, and a clad is formed on the outer periphery of the core. A first step of forming a core by pouring a core material having a higher refractive index than the resin tube into a resin tube as a clad, and a thermochromic material for the core material in the resin tube after the first step It is effective to include a second step of forming a discoloration core portion by pouring in a mixture of the above.

Thereafter, the resin tube may be removed, and a material having a large difference in refractive index from the air layer or the core may be replaced with a clad.

[0013]

In the present invention, for example, when a color changing material from colorless to green at 100 ° C. is used as a thermochromic material, it is colorless at normal temperature. When the discolored core changes color to green due to a rise in temperature, light other than the green component of the white light is absorbed when passing through the discolored discolored core, and the color (wavelength) of the emitted light changes with respect to the incident light. I do.

On the other hand, when the red light is incident, the red light passing through the discoloration core changed to green is absorbed, so that the intensity of the emitted light is attenuated to be lower than the intensity of the incident light.

Therefore, the abnormal temperature of the long linear object can be detected by detecting the change in the color (wavelength) or the change in the intensity of the emitted light.

At this time, since the color-changing core is provided at the center of the core as compared with the case where the color-changing layer is provided on the outer periphery of the core as in the prior art, total reflection is performed at the core-cladding boundary surface without passing through the color-changing core. The amount of light that propagates by repeating is increased, the light loss due to absorption in the discoloration core is reduced, and the light transmission distance can be increased.

[0017]

FIG. 1 is a schematic sectional view of an embodiment of the present invention, FIG. 2 is a schematic configuration diagram showing the configuration of an apparatus to which the present invention is applied, and FIGS. 3 and 4 are operation explanatory diagrams.

In FIG. 2 showing an apparatus to which the present embodiment is applied, reference numeral 11 denotes an optical fiber disposed along a long linear object such as an electric wire (not shown), and reference numeral 12 denotes a light incident end of the optical fiber 11. The white light or the monochromatic light is provided to the optical fiber 11.
A light source 13 is provided at the light emitting end of the optical fiber 11 and outputs a light receiving signal corresponding to the intensity of the emitted light.

At this time, when the light source 12 is a monochromatic light source, a light emitting element such as a red LED or a green LED may be used.

The optical fiber 11 is configured in detail as shown in FIG. 1, and includes a core 11a and a core 11a.
And a color-changing core portion 11b including a thermosensitive color-changing material that changes color to a color in which light absorption easily changes with respect to a specific wavelength of light from the light source 12 due to a rise in temperature, and is provided on the outer periphery of the core 11a. It comprises a clad 11c and a sheath 11d provided on the outer periphery of the clad 11c.

At this time, when the color-changing core portion 11b containing the thermosensitive color-changing material is formed only at the central portion of the core 11a, as a first step, for example, a cladding 11c made of a fluorine-based resin having an inner diameter of 2 mm and an outer diameter of 3 mm is used. Using a syringe to pour transparent silicone into the resin tube as the core 1
After forming 1a, as a subsequent second step, silicone containing a thermosensitive color changing material may be poured into the resin tube using a syringe to form the color changing core 11b.

At this time, as shown in FIG. 3 (a), the silicone A poured into the resin tube in the first step is subjected to friction on the inner wall surface of the tube, and it is difficult for the silicone A to proceed. As shown in FIG. 3 (b), the poured silicone B containing the thermochromic material proceeds smoothly in the portion corresponding to the center of the core 11a, and as a result, the structure shown in FIG. 1 is obtained.

However, in the first and second steps, since the same silicone is poured, there is no boundary between the silicone A containing no thermochromic material and the silicone B containing the thermochromic material after the silicone is cured.

After the second step, the resin tube may be removed and a material having a large difference in refractive index from the air layer or the core 11a may be replaced with the clad 11c.

By the way, the combination of the light from the light source 12 and the thermosensitive color changing material is preferably, for example, as shown in Table 1. The light source 12 emits monochromatic light such as red light, green light and yellow light in addition to white light. It is preferable to use the thermosensitive color changing material which is capable of developing, discoloring and erasing at high temperatures as shown in Table 1.

[0026]

[Table 1]

Table 1 shows the colors of the emitted light before and after the color change and the amount of the emitted light when the color of the thermosensitive color changing material changes (for example, from colorless to red) when the incident light of each color is used. In particular, the amount of emitted light indicates a change in the amount of light after the color change with reference to the state before the change in color. For example, “green small” indicates that the light amount of the green component is smaller than before the change, and “green large”. "Indicates that the light amount of the green component increases from before the change.

In Table 1, "before change" means a state at normal temperature, and "after color change" means a state at a high temperature of, for example, 60 ° C. or more.

As the material of the thermosensitive color changing material dispersed in the core 11a of the optical fiber 11, a material whose light absorption changes before and after the color change in relation to the light source 12 may be selected. When there is, it is desirable that those which reversibly change from colorless or red etc., which do not normally absorb in the wavelength region, to green or black or other colors in which red light is absorbed,
Specifically, the materials shown in Table 2 may be used, and as shown in Table 2, as a material that changes from colorless to red when heated to a high temperature, PSD-R (fluoran leuco compound), lauryl gallate, and toluene are used. It may be used, but it is not particularly limited to the materials shown in Table 2.

[0030]

[Table 2]

By the way, a study will be made on a range in which the incident light to the optical fiber 11 does not pass through the discoloration core portion 11b at the center of the core 11a when propagating through the optical fiber 11. FIG.
As shown in (a) and (b), the point P0 is set to a position where light is incident using the light source 12 or other light guides,
Point P1 is the position where the ray at the maximum angle that does not hit the discoloration core 11b first strikes the outer wall of the core 11a, point P2 is the position where the ray at the minimum angle that does not strike the discoloration core 11b first strikes the outer wall of the core 11a, Assuming that the point O is the center of the core 11a, r is the radius of the discoloration core 11b, R is the radius of the core 11a, and d is the distance from the center O to the light incident position P0, the incident angle δ of the incident light is given by Given by Here, φ and θ in Expression 1 are given by Expression 2 and Expression 3, respectively.

[0032]

(Equation 1)

[0033]

(Equation 2)

[0034]

(Equation 3)

By rearranging equations (1) to (3), the incident angle δ is expressed as shown in equation (4).
Speaking of the circle in the cross section of the optical fiber 11 shown in (c), the incident angle δ is φ ≦ δ ≦ (π−θ), (π + θ) ≦ δ ≦
When it is in the range of (2π−φ), light propagates without passing through the discoloration core 11b.

[0036]

(Equation 4)

As described above, when the color-changing core portion 11b containing the thermosensitive color-changing material is formed only at the central portion of the core 11a, light can propagate without passing through the color-changing core portion 11b specified by the incident angle δ in the above equation (4). The light that propagates without passing through the color-changing core portion 11b is increased due to the formation of the color-changing core portion 11b. As a result, the optical transmission distance of the optical fiber 11 can be extended, and it becomes possible to detect an abnormal temperature of a long linear object over a longer length than before, and furthermore, an environment with a lot of electromagnetic noise. It can be used under the environment where there is a danger of explosion.

As another embodiment, as shown in FIG. 5, a plastic optical fiber 15 is used as an optical fiber, and a portion of the core of the plastic optical fiber 15 having a length L corresponding to a temperature detection range. However, the above-mentioned thermochromic material may be dispersed, and in this case, there is an advantage that a temperature rise in an unnecessary part is not detected as compared with that shown in FIG.

Further, as another method of forming the discoloration core 11b, a material containing a thermosensitive discoloration material in a core material such as silicone is poured into a hollow pipe such as a glass tube or a vinyl chloride pipe. After hardening, the hardened core material is taken out from the hollow pipe to form a discoloration core 11b, and a core 1 made of a core material is formed around the outer periphery of the discoloration core 11b.
1a, and then a clad 11 is formed around the core 11a.
c may be formed.

[0040]

As described above, according to the temperature detecting optical fiber of the present invention, since the color-changing core containing the thermosensitive color-changing material is formed only at the center of the core, the light propagating without passing through the color-changing core is formed. Increases the optical loss, increases the optical transmission distance of the optical fiber compared to the past, enables the detection of abnormal temperatures of long linear objects, and the abnormal temperature of electric wires etc. It can be used in an environment with a lot of electromagnetic noise or an environment where there is a possibility of explosion, and its application range is wide.

Further, an optical fiber having a discoloration core at the center of the core can be manufactured by the method according to the second or third aspect.

[Brief description of the drawings]

FIG. 1 is a schematic sectional view of one embodiment of the present invention.

FIG. 2 is an overall schematic configuration diagram of one embodiment.

FIG. 3 is an operation explanatory diagram of one embodiment.

FIG. 4 is an operation explanatory diagram of one embodiment.

FIG. 5 is a schematic view of another embodiment.

FIG. 6 is a schematic view of a conventional example.

FIG. 7 is an operation explanatory diagram of a conventional example.

[Explanation of symbols]

 Reference Signs List 11 optical fiber 11a core 11b discoloration core 11c clad 15 plastic optical fiber

──────────────────────────────────────────────────続 き Continued on the front page (58) Field surveyed (Int.Cl. ⁶ , DB name) G02B 6/02 G01K 11/12

Claims (3)

(57) [Claims] 1. An optical fiber for temperature detection, comprising: a core having a discoloration core containing a thermosensitive discoloring material at a central portion; and a cladding provided on an outer periphery of the core. 2. A core material containing a thermosensitive color-changing material is poured into a hollow pipe, and after the core material is cured, the hardened core material is taken out of the hollow pipe to form a color-changing core, and then the color-changing core is formed. Forming a core made of a core material on the outer periphery of the core, and forming a clad on the outer periphery of the core. 3. A first step of forming a core by pouring a core material having a higher refractive index than the resin tube into a resin tube as a clad; and forming the core material in the resin tube after the first step. A second step of forming a color-changing core portion by pouring a mixture containing a thermo-sensitive color-changing material into the optical fiber.