JPH06109556A - Optical fiber low temperature sensor - Google Patents

Abstract

(57) [Summary] [Purpose] It can be used repeatedly over a long period of time, is lightweight, can be easily installed, and accurately detects when it has dropped below a predetermined temperature. [Structure] The optical fiber is coated with a coating material having a residual shrinkage of 0.6% or more.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a temperature sensor, and in particular, it is lightweight, easy to install, can be repeatedly used for a long period of time, and can detect a temperature lower than a predetermined temperature. The present invention relates to an optical fiber low temperature sensor.

[0002]

2. Description of the Related Art In a modern house, the floor plan of each room is standardized to some extent with the development of a unit construction method, which facilitates design and construction. Also, in recent years, the number of rooms has increased with the spread of two-family homes where two parents and children live together,
While the total floor area of the building is increasing, each room has an independent floor plan. Although these modern houses use new building materials, not all non-combustible materials are used, but mainly wooden structures. However, unlike modern office buildings, these modern houses do not have sprinklers and do not have sufficient disaster prevention equipment.

An abnormal temperature rise at a specific location may be accompanied by a risk of alteration of surrounding objects or ignition of surrounding objects. If such an abnormal temperature rise occurs, it may occur quickly. It is necessary to detect changes in the situation, avoid these dangers in advance, and take rapid repair measures for abnormal places. Once a fire occurs in a wooden house, the building often burns down unless it can be extinguished during the initial fire extinguishing stage. Therefore, in recent years, in order to prevent the occurrence of fire due to an abnormal temperature rise, it is required to detect an abnormal temperature rise in a specific room or each room in advance.

In order to detect this abnormal temperature rise in advance, a temperature sensor utilizing the optical fiber itself has been developed in recent years. This is because it is possible to reliably detect an abnormal temperature when the local temperature rises abnormally even if the heat detection line is extended in every corner by using the transmission loss of the optical fiber and becomes long. Has become. A temperature sensor utilizing this optical fiber is used for measuring the temperature distribution in the length direction by measuring the fluorescence reflection type optical fiber temperature sensor as shown in FIG. 7 and the backscattered light of the optical fiber as shown in FIG. There is a demand for distributed fiber optic temperature sensors.

[0005]

However, in the conventional temperature sensor using the optical fiber, compared with the conventionally used optical fiber and the transmission system, the temperature sensor using the fluorescent reflection type has a part of the sensor. There is a problem in that the glass composition must be significantly changed or a new part must be added.

Further, in the conventional temperature sensor using the optical fiber, since the backscattered light of the optical fiber is measured, a complicated measuring system is required, and the cost of the temperature measuring system increases. have.

The present invention provides an optical fiber low temperature sensor which can be repeatedly used over a long period of time, is lightweight, is easy to install, and can easily and accurately detect a temperature lower than a predetermined temperature. The purpose is to do.

[0008]

In order to achieve the above object, the optical fiber low temperature sensor of the present invention comprises an optical fiber core wire coated with a coating material having a residual shrinkage of 0.6% or more. It will be.

Then, it is preferable to obtain a residual shrinkage of 0.6% or more by forming irregularities on the surface of the optical fiber strand.

Alternatively, a residual shrinkage rate of 0.6% or more can be obtained by forming irregularities on the outer surface of the nipple to give a residual stress to the coating material coated on the surface of the optical fiber element wire. preferable.

[0011]

The temperature sensor is constructed by first coating the spun optical fiber with a thermosetting resin, then drying it in a drying oven, and coating the optical fiber formed by coating the plastic material with the coating material. At this time, use the one in which unevenness is formed on the surface of the optical fiber wire, or use the extrusion die having the unevenness on the inner surface of the nipple to coat the surface of the optical fiber wire with the coating material. Then, a residual stress is given and a residual shrinkage ratio of 0.6% or more is given. A heat detection cable formed by coating an optical fiber with a coating material whose contraction rate changes in accordance with a change in temperature is stretched around the temperature detection location. When the temperature lowers below a predetermined temperature at any place where the heat detection cable is stretched around, the coating material coating the optical fiber causes thermal contraction. Then, a large external force is applied to the optical fiber due to lateral pressure, and a slight bending (microbending) occurs in the optical fiber. This slight bending of the optical fiber increases the transmission loss of the optical fiber. Therefore, the intensity of the optical signal emitted from the optical signal intensity measuring instrument connected to the other end of the optical fiber is lower than the intensity of the optical signal incident from the optical signal incident instrument connected to one end of the optical fiber. To do. An abnormal low temperature is detected by measuring the intensity of the optical signal emitted from this optical signal intensity measuring device.

[0012]

EXAMPLES Examples of the present invention will be described below. FIG. 1 shows an embodiment of an optical fiber low temperature sensor according to the present invention.

In the figure, 1 is an optical fiber low temperature sensor, and 2 is an optical fiber. The optical fiber 2 includes a core having a high refractive index portion and a clad having a low refractive index portion, and has a concentric circle structure in which the clad surrounds the core. This optical fiber 2 usually uses a concentric platinum double crucible, in which a core is placed in the center crucible and a glass serving as a clad is placed in the outer crucible and melted, and a drawing line is drawn at the same time from a nozzle aligned with the central axis. The thermosetting resin is first coated and dried, and the primary coating resin is coated with a plastic material. As the optical fiber 2, it is possible to use a normal fiber such as a multimode fiber, a single mode (SM) fiber, a graded index (GI) fiber, a step index (SI) fiber.

A coating material 3 is formed in a tube shape and covers the optical fiber 2. The covering material 3 is made of a heat-shrinkable synthetic resin. For the coating material 3, a thermoplastic resin of pomiamide, polyester or polyurethane (Young's modulus of 100 kg / mm 2 or more) is used. The coating material 3 is coated so as not to tighten the optical fiber 2.

The heat shrinkage of a synthetic resin is a phenomenon in which when a polymer solid having a stretching history is heated, a rapid shrinkage occurs in a certain temperature range. The abrupt shrinkage of the synthetic resin that occurs when heated is such that the internal state of the polymer solid that has been fixed in the stretched state at the temperature that causes the thermal contraction of the synthetic resin by the heat applied from the outside. This occurs because the composition state is unfrozen and tries to return to a state in which it is stable when tension due to stretching is not working. The rapid shrinkage of the synthetic resin occurs near the glass transition temperature in the amorphous polymer and near the melting point in the crystalline polymer.

The non-crystalline polymer is also called an amorphous polymer and is a polymer substance having no recognized crystal structure, for example, a polymer such as polyvinyl acetate or polyethylene by radical polymerization. This non-crystalline polymer includes a polymer having an irregular structure (copolymer, branched polymer, etc.) in general, or a polymer having bulky side chains and not having a regular structure.

The crystalline polymer is a polymer substance such as polyethylene, nylon, etc. which has a clear crystal structure by X-ray diffraction. Since this polymer compound has a long chain, it does not crystallize 100%, and the crystallinity (ratio of crystallized molecules) changes depending on the crystallization conditions, heat treatment, etc. There are various crystalline polymers ranging from poorly polymerized polymers to linear polyethylene having a crystallinity of 80 to 90%.

The residual shrinkage rate of the coating material 3 is maintained at 0.6% or more. As described above, when the residual shrinkage rate of the covering material 3 is set to 0.6% or more, the covering material 3 is, as shown in FIG.
Although an increase in light transmission loss is not recognized with a rise in temperature, the light transmission loss increases in a low temperature range, particularly, below 5 ° C., for example. This is at a specific temperature (eg 5
This is due to the occurrence of minute bending (microbending) in the optical fiber 2 when the temperature becomes lower than (° C.). When microbending occurs in this optical fiber 2, the optical fiber 2
The optical signal incident from one end of the optical fiber causes reflection, and this reflection causes an increase in transmission loss of the optical signal. The transmission loss of this light exceeds 0 ℃ and is even lower (minus temperature range).
It increases as it becomes. Therefore, the temperature can be detected by measuring the increase amount of this transmission loss of light.

The residual shrinkage rate of the coating material 3 depends on the shrinkage amount in the longitudinal direction when a sample (for example, 100 mm in length) of a manufactured optical fiber core wire is heated (100 ° C., 1 Hr) and then cooled. Desired. That is, the shrinkage rate is obtained by the following equation 1.

[0020]

[Formula 1] As an example of applying a residual shrinkage ratio of 0.6% or more to the covering material 3, as shown in FIG. 3, unevenness 21 is provided on the surface of the optical fiber 2, and the optical fiber 1 provided with the unevenness 21 is attached to the nipple 60. The coating material 3 is run inside and the coating material 3 is coated with a heat-shrinkable synthetic resin extruded from between the die 50 and the nipple 60. By providing the unevenness 21 on the surface of the optical fiber 2 as described above, the residual shrinkage rate of 0.6% or more can be applied to the coating material 3.

Alternatively, as an example of applying a residual shrinkage ratio of 0.6% or more to the coating material 3, as shown in FIG.
No. 0 has an uneven surface 61 on the outer surface, the optical fiber 1 travels in the nipple 60, and heat is extruded from between the die 50 and the nipple 60 having the uneven surface 61 on the outer surface of the tip portion. The covering material 3 is covered with a contractible synthetic resin. As described above, by providing the unevenness 61 on the outer surface of the tip portion of the nipple 60, the interface between the optical fiber 2 and the covering material 3 covered with the unevenness can be made uneven and a residual shrinkage ratio of 0.6% or more can be applied. it can.

FIG. 5 shows a temperature detecting system for an optical fiber low temperature sensor according to the present invention.

In the figure, 10 is O-TDR (Optical).
In the Time Domein Reflect Meter, the optical signal incident from one end of the optical fiber is reflected by the minute bending (microbending) of the optical fiber, and the increase in the transmission loss of the optical signal due to this reflection is changed to the CRT in the time domain. It is a measuring instrument (time domain optical pulse reflectometer) for displaying. A low temperature sensor is configured by connecting the optical fiber low temperature sensor 1 to the O-TDR 10. This O
-Optical fiber low temperature sensor 1 connected to TDR10
Shall be installed at a place to be monitored so that it does not drop below the specified temperature.

Next, the operation of this embodiment will be described.
Now, the temperature inside a building (for example, a greenhouse) in which the optical fiber low temperature sensor 1 is installed has fallen below a predetermined temperature (for example, 5 ° C.) due to an abnormality in the temperature controller, etc. When the temperature decreases, the heat shrink member 3 covering the optical fiber 2 of the optical fiber low temperature sensor 1 contracts due to the temperature decrease due to the abnormality of the temperature controller. When the heat-shrinkable member 3 contracts, the heat-shrinkable member 3 applies a lateral pressure to the optical fiber 2. When a large lateral pressure is applied to the optical fiber 2 by the heat-shrinkable member 3, the optical fiber 2 is slightly bent (microbending).
The transmission loss of the optical fiber 2 increases due to this slight bending (micro bending). That is, the transmission loss of the optical fiber 2 rapidly increases when the heat-shrinkable member 3 contracts due to a decrease in the room temperature due to an abnormality in the temperature controller.

Therefore, an optical signal is made incident from one end of the optical fiber 2 by a light generator (not shown), propagates through the optical fiber 2 and is emitted from the other end of the optical fiber 2. By measuring the intensity, it is possible to obtain measurement data indicating how much the temperature of the room is decreasing. At this time, the O-TDR is provided at one end of the optical fiber 2.
If the measurement by 10 is performed, the increase amount of loss and its position can be immediately obtained by the display of the CRT as shown in FIG.

By changing the material of the heat-shrinkable member 3, the shrinkage rate of the heat-shrinkable member 3 with respect to heat is changed, and the detected temperature can be freely set.

[0027]

Since the present invention is configured as described above, it has the following effects.

Since the optical fiber core is coated with a coating material having a residual shrinkage of 0.6% or more, it can be repeatedly used for a long period of time, is lightweight and easy to lay, and has a predetermined temperature. It is possible to easily and accurately detect a decrease below.

Since the residual shrinkage ratio of 0.6% or more is obtained by forming the unevenness on the surface of the optical fiber element wire,
It is possible to easily manufacture a low temperature sensor that generates microbending when the temperature becomes lower than a predetermined temperature.

Further, since the residual shrinkage of 0.6% or more is formed on the outer surface of the nipple and the coating material coated on the surface of the optical fiber element has residual stress, the temperature is kept below the predetermined temperature. Then, a low temperature sensor that generates microbending can be easily manufactured.

[Brief description of drawings]

FIG. 1 shows an embodiment of an optical fiber low temperature sensor according to the present invention, and is an overall perspective view in which a part of an optical fiber is sectioned.

FIG. 2 is a characteristic diagram showing a state of an increase in optical transmission loss with respect to temperature of an optical fiber according to the present invention.

FIG. 3 is a diagram showing a method for manufacturing an optical fiber low temperature sensor according to the present invention.

FIG. 4 is a diagram showing another method for manufacturing the optical fiber low temperature sensor according to the present invention.

5 is a system configuration diagram using the optical fiber low temperature sensor shown in FIG.

FIG. 6 is a diagram showing measurement results by the optical fiber low temperature sensor shown in FIG.

FIG. 7 is a sectional view showing a conventional fluorescence reflection type optical fiber temperature sensor.

FIG. 8 is an overall configuration diagram of a conventional distributed optical fiber temperature sensor.

[Explanation of symbols]

1 ………………………………………………………… Optical fiber low temperature sensor 2 …………………………………………………… Optical Fiber 3 ………………………………………………………… Coating material 10 ……………………………………………… OT
DR 21,61 ……………………………………………… Concave and convex 50 …………………………………………………… Die 60 ……………… ………………………………………nipple

Claims (3)

[Claims] 1. The residual shrinkage of the optical fiber is 0.6%.
An optical fiber low temperature sensor formed by coating the above coating materials. 2. The optical fiber low temperature sensor according to claim 1, wherein the residual shrinkage ratio of 0.6% or more is obtained by forming irregularities on the surface of the optical fiber strand. 3. The residual shrinkage ratio of 0.6% or more is obtained by forming unevenness on the outer surface of the nipple to give a residual stress to the coating material coated on the surface of the optical fiber element wire. The optical fiber low temperature sensor according to claim 1.