JPH0350215B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to a liquid detection sensor capable of detecting the presence of a liquid such as oil or water from a remote location using an optical fiber.

"Prior Art" Conventionally, liquid detection sensors that detect liquid over long distances have been provided with structures shown in FIGS. 7, 8, and 9, respectively. FIG. 7 shows an example of an optical fiber sensor with a partially peeled cladding type, in which reference numeral 1 denotes a core and 2 denotes a cladding. In this optical fiber sensor, a detection part 3 is formed by peeling off a part of the cladding 2. When a liquid 4 adheres to the detection part 3, the refractive index changes from the refractive index of air to that of the liquid. This results in a loss,
This is how the liquid is detected.

FIG. 8 shows an example of a clad refractive index variable type optical fiber sensor, in which reference numeral 5 indicates a core and 6 indicates a cladding. This optical fiber sensor detects liquid by causing a loss due to a change in the refractive index of the cladding 6 due to the liquid 7 adhering to and infiltrating the sensing portion.

FIG. 9 shows an example of an evanescent type optical fiber sensor with an eccentric core, in which reference numeral 8 indicates a core and 9 indicates a cladding. This optical fiber sensor uses the absorption of evanescent waves by the adhering liquid and the conversion into radiation mode by making the core 8 eccentric to the vicinity of the surface of the cladding 9 and actively generating evanescent waves. The liquid is detected by generating a loss in the liquid.

"Problems to be Solved by the Invention" By the way, the above optical fiber sensor for liquid detection has the following disadvantages.

Regarding the optical fiber sensor shown in Fig. 7,
It is necessary to peel off a portion of the cladding 2 to expose the surface of the core 1, so if the core 1 is made of glass or the like, it is easy to get scratched and break during peeling or construction when processing the sensor part. Easy to do. Further, when the core 1 is made of synthetic resin, although sufficient strength can be obtained, the refractive index is high and there is a complaint that liquids with a low refractive index cannot be detected. Furthermore, such an optical fiber sensor inherently has a large transmission loss due to its structure, making detection over a long distance difficult.

Regarding the optical fiber sensor shown in Fig. 8,
Since the refractive index of the cladding 6 in the detection section changes only between the curvature index of the cladding 6 in a state where the liquid 7 is not infiltrated and the refractive index of the liquid 7, it is difficult to detect a liquid with a low refractive index. Have difficulty. In addition, in order to shorten the detection time, it is necessary to reduce the thickness of the cladding 6 to several μm or less to reduce the time for the liquid 7 to infiltrate. However, reducing the thickness of the cladding 6 in this way reduces transmission loss. This increases the difficulty of detection over long distances.

For the optical fiber sensor shown in Figure 9,
When using it, it is necessary to peel off the coating (not shown) that serves as a buffer layer provided on the outer periphery of the clad 9, and like the one shown in FIG. 7, it is easily damaged and broken during construction.

In addition, regarding these optical fiber sensors,
In both cases, liquids are detected using the surface properties of the optical fiber itself, so there is a problem of poor reliability over a long period of time due to a decrease in sensitivity due to contamination of the sensor surface. There is.

"Means for Solving the Problems" In the liquid detection sensor of the present invention, a swelling material that swells due to infiltration of liquid is disposed on the outer periphery of the tension member, a recess is provided on the outer periphery of the swelling material,
The above problem is solved by attaching an optical fiber to the recess and disposing a restraining member on the outer periphery of the swelling material to restrain the optical fiber in the recess.

"Function" According to the liquid detection sensor of the present invention, a swelling material is disposed on the outer periphery of the tension member, a recess is provided on the outer periphery of the swelling material, and an optical fiber is attached to the recess, and Since a restraining member is provided to restrain the optical fiber in the recess, when it comes into contact with liquid, the swelling material infiltrates and swells, but the swelling material and the optical fiber are restrained by the restraining member. Because of this, stress is generated and deformation occurs in the optical fiber. Therefore, power loss occurs in the liquid detection sensor, and by observing this power loss in the detection system, the location of the liquid to be detected is detected.

Embodiment FIG. 1 is a diagram showing a first embodiment of the liquid detection sensor of the present invention. Reference numeral 10 in the figure is a tension member, and this tension member 10 is made of FRP, steel wire, or the like. A swelling material 11 that swells due to infiltration of liquid is placed on the outer periphery of the tension member 10 in an extrapolated state. As the swelling material 11, when the liquid to be detected is oil, ethylene propylene rubber or the like is used, and when the liquid to be detected is water, a mixture formed by molding and vulcanizing a water-swellable resin and chloroprene rubber is used. Further, this swelling material 11 has four grooves (recesses) 12 formed on its outer periphery.

These grooves 12 are arranged in parallel at equal intervals in the circumferential direction of the swelling material 11 and are spirally formed, and each of the grooves 12 accommodates an optical fiber strand 13 therein. Attached in condition. Further, on the swelling material 11 to which the optical fibers 13 are attached, the optical fibers 13 are placed in grooves 1.
2...A coil 14 for restraining and fixing is inserted inside. With such a configuration, the optical fiber wires 13 are restrained by the coils 14 and formed in the grooves 12.
Fixed inside. Here, optical fiber strand 1
As the material 3, an ordinary optical fiber wire coated with a silicone resin, an ultraviolet curable resin, or the like, or an optical fiber wire whose outer periphery is further coated with nylon, etc. are used. In addition, as the coil 14, a coil made of steel wire, a flexible spiral tube, etc. can be used, and it is also possible to use one made of synthetic resin, in which case it will not be affected by electromagnetic induction or lightning strikes. .

A reinforcing mesh 15 made of metal or reinforcing fiber is coated on the swelling material 11 on which the coil 14 is inserted.

In order to detect liquid using a liquid detection sensor having such a configuration, the sensor is connected to a detection system to be described later and is set at a location to be detected. Then, in the sensor, the swelling material 11 infiltrates and swells when it comes into contact with the liquid, but the swelling material 11 and the optical fibers 13...
4, stress is generated and the optical fiber strands 13 are bent into a spiral shape. This causes a power loss in the liquid detection sensor, and this power loss is observed by an optical pulse tester (OTDR) of the detection system, thereby detecting the location of the liquid to be detected. Here, even if the liquid to be detected exists in multiple locations,
Since the OTDR can observe power loss at multiple locations, the locations of each liquid to be detected are detected separately.

Next, a detection system using the liquid detection sensor of the present invention will be explained with reference to FIGS. 2 and 3.

FIG. 2 is a diagram showing an example of a detection system, in which reference numeral 20 is a pulse generator that determines the observation period, and 21 is a diagram that uses pulses from the pulse generator 20.
A sawtooth generator that generates a CRT27 sweep signal, 22
is an electrical/optical converter that converts electrical signals into optical signals,
23 is a directional coupler for guiding the power of backscattered light to a detector for observation; 24 is an optical/electrical converter for converting an optical signal into an electrical signal; 25 is an amplifier;
6 is an averaging circuit, and 28 is a liquid detection sensor of the present invention.

In the detection system having such a configuration, the optical signal output from the electric/optical converter 22 is incident on the optical fiber wire of the liquid detection sensor 28 via the directional coupler 23. This optical signal propagates through the optical fiber, but if the liquid detecting sensor 28 is infiltrated with liquid, a portion of the optical signal is radiated out of the optical fiber at this point. To explain this state using FIG. 3, before the liquid is detected, the power S attenuates as time passes, that is, as the distance increases. When liquid infiltrates any point of the liquid detection sensor 28, a power loss PL of a certain level difference occurs at time _T1 corresponding to that position. This is because the optical signal is radiated out of the optical fiber by the microbend at the point where the liquid has infiltrated into the liquid detection sensor 28, and the transmitted power is attenuated in a stepwise manner, resulting in the power S of the backscattered light.
This is because it also attenuates in steps. The sudden high level at time T ₂ is due to Fresnel reflection at the end of the optical fiber in the liquid detection sensor 28 .

In addition, in the above detection system, the case where the power S of the backscattered light is displayed on the CRT 27 and detected by visual judgment has been explained, but it is also possible to automatically detect the power loss PL using a computer etc. and issue an alarm. be.

FIG. 4 is a diagram showing a second example of the liquid detection sensor of the present invention. In FIG. 4, the same elements as those shown in FIG. 1 are given the same reference numerals, and their explanations will be omitted.

The difference between the liquid detection sensor shown in FIG. 4 and the one shown in FIG. 1 is that in the liquid detection sensor shown in FIG. This is because a plurality of strands are attached to the member 10 in a twisted state. In the liquid detection sensor shown in FIG. 4, six swelling wires 16 are twisted together and attached to the outer periphery of the tension member 10, and optical fibers are inserted into recesses 17 formed between the swelling wires 16. Element wire 13...
It is attached in a stored state. Further, a coil 14 is extrapolated onto the swelling wire 16 to which the optical fiber wires 13 are attached, and a reinforcing mesh 15 is further coated thereon.

Even with a liquid detection sensor configured like this,
By connecting and using the above-mentioned detection system, the position where liquid is present can be detected in the same manner as the liquid detection sensor shown in FIG.

FIG. 5 is a diagram showing a third example of the liquid detection sensor of the present invention.

The liquid detection sensor shown in FIG. 5 differs from those shown in FIGS. 1 and 4 in that the swelling material 11 in the liquid detection sensor shown in FIG. 5 is made of a double-core wire. . In the liquid detection sensor shown in FIG. 5, three bi-core wire rods 18 made of a swelling material are twisted together and attached to the outer periphery of the tension member 10. These two-core wire rods 18 have recesses 19 in the middle part of their respective outer peripheral surfaces.
are formed, and optical fiber wires 13 are housed in recesses 19 on the side opposite to the tension member 10, that is, on the outer peripheral side. Further, the coil 14 is extrapolated onto the double-core wire rod 18 to which the optical fiber wire 13 is attached,
Furthermore, a reinforcing mesh 15 is coated on this.

Even with a liquid detection sensor configured like this,
It has the same effect as the liquid detection sensor shown in FIGS. 1 and 4.

In the liquid detection sensor shown in FIG. 5, a tension member may be inserted into the two-core wire rod 18 as necessary, since in that case the tensile strength etc. will be further strengthened. Improves workability.

(Test Example) A liquid detection sensor of the present invention was manufactured, and an operation test was conducted using it.

The fabricated liquid detection sensor had the configuration shown in FIG. 4, and the tension member 10 was made of FRP with an outer diameter of 5 mm. Swelling line 16 has an outer diameter of 1 mm.
A graded index steel wire coated with ethylene propylene rubber and having an outer diameter of 5 mm as a whole was used, and the optical fiber wire 13 was coated with ultraviolet curable urethane acrylate and had an outer diameter of 0.3 mm. Optical fibers of 50/125 multimode optical fibers were used and twisted together at a pitch of 500 mm. The restraining coil 14 has an outer diameter of 2 mm.
A stainless steel wire was wound with an inner diameter of 15 mm and a pitch of 4 mm, and a reinforcing mesh 15 made of a steel wire with an outer diameter of 0.5 mm was covered thereon to form a sensor.

Using kerosene with a refractive index of n=1.438 as the liquid to be detected, we conducted an operation test by immersing the sensor in this kerosene.
A loss increase of 0.45 dB occurred in about 120 minutes, and was saturated with a loss increase of almost 1 dB in about 300 minutes.

From these results, the measurement range of OTDR is approximately
Since it was 20 dB, it was confirmed that simultaneous multi-point detection is possible.

In addition, when detecting using an automatic judgment device, since the accuracy of OTDR is 0.01 dB, the detection level can be set to 0.2 dB considering the margin for noise, etc., so the above power loss is sufficient to detect the target liquid. It was found that it could be detected.

"Effects of the Invention" As explained above, the liquid detection sensor of the present invention detects the presence of liquid by deforming the optical fiber when the liquid infiltrates into the swelling material, which causes loss. Therefore, the presence of the liquid to be detected can be detected regardless of the magnitude of the refractive index of the liquid to be detected, and by providing a restraining member along the entire line, the entire length can be used as a detection section.

In addition, since the optical fiber itself does not need to be specially modified, communication wire can be used, and transmission loss can be kept low, making detection over long distances possible. By peeling off a portion of the material, production costs can be reduced since no special process is required.

Furthermore, since the surface properties of the optical fiber are not utilized as in the conventional method, there is no decrease in sensitivity due to contamination, and long-term reliability can be obtained.

Furthermore, since the optical fiber is used as an optical fiber wire covered with a coating material, inconveniences such as damage and breakage during construction can be prevented, and workability can be improved.

In addition, since the optical fiber wire is attached to the concave part of the outer periphery of the expansion material, almost no external force acts on the optical fiber wire under normal conditions, so the transmission loss of the optical fiber under normal conditions can be reduced to a low level. It is possible to increase the responsiveness and sensitivity during liquid detection, and to manufacture a homogeneous liquid detection sensor with uniform detection characteristics with good reproducibility.

[Brief explanation of drawings]

1 to 6 are diagrams relating to the liquid detection sensor of the present invention, in which FIG. 1 is a schematic configuration diagram showing a first embodiment of the liquid detection sensor of the present invention, and FIG. 2 is a diagram showing the liquid detection sensor of the present invention. A schematic configuration diagram showing an example of a detection system suitably used when using the sensor,
FIG. 3 is a graph for explaining the mechanism for detecting the presence of liquid by the detection system shown in FIG. 2, and FIG.
FIG. 5 is a schematic configuration diagram showing a third embodiment of the liquid detection sensor of the present invention, FIG. 6 is a graph showing the results of an operation test, and FIG.
9 through 9 are schematic configuration diagrams showing examples of conventional liquid detection sensors. 10... Tension member, 11... Swelling material, 12... Groove, 13... Optical fiber wire, 14
... Coil, 16 ... Swelling wire, 17, 19 ... Concave portion, 18 ... Two-core wire rod.

Claims (1)

[Claims] 1. A swelling material that swells due to liquid infiltration is placed on the outer periphery of the tension member, a recess is provided on the outer periphery of the swelling material, an optical fiber is attached to the recess, and the swelling material is A liquid detection sensor characterized in that a restraining member for restraining an optical fiber wire in a recess is disposed on the outer periphery.