JP3458631B2 - Optical fiber physical quantity sensor - Google Patents

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an optical fiber physical quantity sensor in which a sensor section is formed in an optical fiber, and light is guided from the sensor section by the optical fiber. The present invention relates to an optical fiber physical quantity sensor having improved mechanical durability such as earthquake resistance.

[0002]

2. Description of the Related Art Various contact-type sensors for detecting physical quantities such as temperature, strain, and stress are known. As a sensor using electricity, a sensor used for measuring temperature includes a thermistor or thermocouple whose electric resistance changes with temperature, and a sensor used for measuring strain has a strain gauge whose electric resistance changes due to strain. An optical fiber thermometer that measures the temperature by incorporating the amount of light from a temperature-sensitive fluorescent material into an optical fiber as a measuring device that uses a sensor whose optical characteristic amount changes according to the physical quantity, is formed inside the waveguide core. When a strain is applied to the grating (grating), the reflected light wavelength changes due to a change in the lattice spacing, and thus there is a fiber Bragg grating type strain gauge which measures the amount of strain.

[0003]

When performing multi-point measurement using an electric sensor, it is necessary to dispose a sensor at each measurement point and connect a power supply line and a signal line to each sensor. The measuring system becomes large and the cost becomes high. Further, the electric sensor is easily influenced by the electric environment, and there is a possibility of malfunction due to, for example, electromagnetic noise. Further, the electric sensor cannot be brought into contact with the object to be measured which is required to have electrical insulation.

The optical sensor does not have the drawbacks of the electric sensor as described above and is suitable for remote measurement because of the small transmission loss of the optical fiber. However, the optical fiber has low mechanical strength because the material is glass or plastic. Therefore, the measurement system using such an optical sensor has a problem of mechanical durability, especially seismic resistance. For example, a sensor unit whose optical characteristic amount changes according to a physical quantity is formed at the tip of an optical fiber, and this sensor unit is brought into contact with an object to be measured, and the optical fiber is connected from the sensor unit to a detector of the optical characteristic amount. In a sensor with a lead that guides light, when the sensor part vibrates with the object to be measured because the object to be measured vibrates, stress concentrates on the boundary between the lead part and the sensor part, and the optical fiber near the boundary. May break.

Therefore, an object of the present invention is to provide an optical fiber physical quantity sensor that solves the above-mentioned problems, enables accurate measurement, and has improved mechanical durability such as earthquake resistance.

[0006]

In order to achieve the above-mentioned object, the present invention provides a sensor section in which the optical characteristic quantity changes according to a physical quantity such as temperature and strain, at the tip of the optical fiber, An optical fiber physical quantity sensor that measures a physical quantity of an object to be measured from a light characteristic amount of the guided light as a lead section that guides light from the sensor section, and the sensor section is an object to be measured through at least a fixing agent such as resin. The lead part with a protective material such as metal , and
The elastic modulus between the cover and the protective material is smaller than that of the above fixing agent.
Fill the buffer part with a buffer material,
It is large near and small at far .

The protective material may be fixed to the object to be measured.

The sensor section and the protective material may be inserted into the object to be measured, and the periphery of the sensor section may be filled with the fixative.

[0009]

[0010]

[0011]

BEST MODE FOR CARRYING OUT THE INVENTION Hereinafter, embodiments of the present invention will be described in detail with reference to the accompanying drawings.

As shown in FIG. 1, in the optical fiber physical quantity sensor of the present invention, a sensor portion 21 whose optical characteristic quantity changes according to a physical quantity such as temperature or strain is formed at the tip of the optical fiber core wire 2. The optical fiber core wire 2 from the sensor portion 21 to the detector of the optical characteristic amount (not shown) is a lead portion 22 that guides the measurement light. The periphery of the lead portion 22 is covered with the protective material 3. As the protective material 3, a material having an elastic modulus larger than that of the optical fiber core wire 2 is used. Here, a SUS tube is used as the protective material 3.

A cylindrical insertion hole 4 (indicated by a dotted line inside the object to be measured) is formed in the object to be measured 1 in conformity with the shape of the protective material 3, and the sensor part 21 and the protective portion are protected in the insertion hole 4. The tip of the material 3 is inserted. The tip of the protective material 3 (indicated by a broken line inside the object to be measured) is inserted partway into the insertion hole 4, and the light forming the sensor portion 21 (indicated by a solid line) is located ahead of the tip of the protective material 3. Only the fiber core wire 2 is inserted. The fixative 5 is embedded in the insertion hole space (the space indicated by the dotted line) around the sensor portion 21. This fixative 5
Is a resin that is post-cured, such as an epoxy resin, and is flexible at the time of filling, but the sensor unit 21 can be integrated with the DUT 1 by curing thereafter. In this way, the sensor section 21 is integrally fixed to the DUT 1 by being embedded with the fixative 5, and
The protective material 3 is fixed to the DUT 1 by being inserted into the insertion hole 4.

In the space formed between the protective material 3 and the optical fiber core wire 2 of the lead portion 22 (the space shown by the broken line),
The buffer 7 made of gel is filled on the side close to the sensor unit 21. The buffer 7 has a smaller elastic modulus than the fixing agent 5. In addition, this buffer 7
The elastic modulus may be continuously or stepwise changed such that the elastic modulus increases as the distance from the sensor unit 21 increases and the elastic modulus decreases as the distance from the sensor unit 21 increases.

In the sensor of FIG. 1, first, since the sensor portion 21 is fixed to the object to be measured 1 with the fixing agent 5 and integrated, the physical quantity such as temperature and strain of the object to be measured 1 is measured by the sensor. The physical quantity of the DUT 1 is effectively transmitted to the portion 21, and the physical quantity of the DUT 1 can be accurately measured. In this embodiment, since the sensor unit 21 is inserted into the DUT 1, the optical characteristic amount of the sensor unit 21 changes according to the change in the physical quantity inside the DUT. A physical quantity measuring instrument (not shown) is connected to the side of the lead section 22 opposite to the sensor section 21, a probe light is sent from this physical quantity measuring instrument, and characteristics such as wavelength and quantity of light returned to the physical quantity measuring instrument. By measuring the quantity, the physical quantity of the DUT 1 can be measured.

Further, since the periphery of the lead portion 22 is covered with the protective material 3 having a larger elastic modulus than the optical fiber core wire 2 and the protective material 3 is fixed to the DUT 1, the lead portion 2 is conventionally used.
The stress concentrated on the boundary between the sensor 2 and the sensor portion 21 is dispersed in the length direction of the protective material 3, and the stress locally applied is relaxed. This enhances the mechanical strength of the sensor,
The durability is improved.

Since the buffer 7 having a smaller elastic modulus than the fixing agent 5 is filled between the lead portion 22 and the protective material 3,
Even when the sensor part 21 vibrates together with the DUT 1, the lead part 22 near the sensor part easily follows the vibration of the sensor part 21, and the stress applied to the boundary between the lead part 22 and the sensor part 21 is relaxed. Furthermore, if the elastic modulus of the buffer 7 decreases as the distance from the sensor portion 21 increases, the stress can be dispersed without being concentrated. This improves the seismic resistance of the sensor.

Next, as shown in FIG. 2, in another embodiment of the optical fiber physical quantity sensor of the present invention, a U groove 8 for fitting the protective material 3 into the surface of the DUT 1 is dug, and the U groove 8 is formed. Groove 8
Protective material 3 is fitted in. The sensor section 21 is in contact with the surface of the DUT 1. The protective material 3 is fixed to the DUT 1 by a fastener 6. The sensor section 21 is fixed to the surface of the DUT 1 with a fixing agent 5 such as resin. The other structure is similar to that of FIG. Therefore,
In this sensor, the physical quantity of the surface of the DUT 1 is the sensor unit 2
1, the physical quantity of the surface of the object to be measured can be accurately measured, and the stress is dispersed. Therefore, the durability and the earthquake resistance are excellent.

Although the two embodiments have been described above, the present invention is not limited to this, and the same effect can be obtained as long as the requirements described in the claims are satisfied. For example, in the case of FIG. 1, the protective material 3 is inserted partway into the insertion hole 4 and the sensor portion 21 is exposed at the tip thereof, but the protective material 3 may be provided up to the tip of the sensor portion 21. This way,
The optical fiber core wire is not damaged when the sensor unit 21 is mounted on the DUT 1. In this case, the tip of the protective member 3 is filled with a fixing agent for fixing the sensor unit 21 integrally with the protective member 3, and thereby the physical quantity of the DUT 1 is efficiently transmitted to the sensor unit 21. be able to.
Further, in the case of FIG. 1, the buffer 7 is used as the protective material 3 and the lead portion 22.
Although it is filled only in the space near the sensor portion 21 in the space between and, it may be filled over the entire length of the lead portion 22. In this case, vibration is applied to the protective material 3 covering the lead portion 22. Even in the case of, the vibration applied to the optical fiber core wire 2 of the lead portion 22 can be mitigated.

[0020]

The present invention exhibits the following excellent effects.

(1) Physical quantities such as temperature and strain of the object to be measured are effectively transmitted to the sensor section, and the physical quantity of the object to be measured can be accurately measured.

(2) Since the stress is relieved, the mechanical strength of the sensor is increased and the durability is improved.

[Brief description of drawings]

FIG. 1 is a perspective view of an optical fiber physical quantity sensor showing an embodiment of the present invention.

FIG. 2 is a perspective view of an optical fiber physical quantity sensor showing another embodiment of the present invention.

[Explanation of symbols]

1 DUT 2 Optical fiber core 3 protective materials 4 insertion holes 5 fixative 7 buffer 8 U groove 21 Sensor part 22 Lead

Continuation of the front page (56) Reference JP-A-7-324986 (JP, A) JP-A-8-201186 (JP, A) JP-A-5-296736 (JP, A) JP-A-6-221931 (JP , A) (58) Fields surveyed (Int.Cl. ⁷ , DB name) G01L 1/24 G01B 11/16 G01K 11/12

Claims (3)

(57) [Claims] 1. A sensor section, whose optical characteristic quantity changes according to a physical quantity such as temperature and strain, is formed at the tip of an optical fiber, and the optical fiber is used as a lead section for guiding light from the sensor section.
In an optical fiber physical quantity sensor that measures a physical quantity of an object to be measured from an optical characteristic quantity of guided light, the sensor unit is fixed to the object to be measured through at least a fixing agent such as a resin, and the periphery of the lead portion is metal. Cover it with a protective material such as
The elastic modulus between the cord and the protective material is higher than that of the fixing agent.
Fill a small buffer, and adjust the elastic modulus of the above buffer to the sensor section.
An optical fiber physical quantity sensor characterized in that it is made larger at a position closer to and smaller at a distance . 2. The optical fiber physical quantity sensor according to claim 1, wherein the protective material is fixed to an object to be measured. 3. The optical fiber physical quantity sensor according to claim 1, wherein the sensor section and the protective material are inserted into an object to be measured, and the periphery of the sensor section is filled with the fixative.