JPH0338539B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to a liquid sensor that optically senses the presence or absence of a liquid such as oil.

[Description of prior art]

Recently, oil leak accidents have been occurring frequently at oil storage bases, petrochemical plants, etc., and highly reliable liquid detectors are required due to legal regulations to detect such accidents early. There is.

One such liquid sensor is an optical waveguide type sensor. This consists of an optical waveguide formed in a transparent substrate, an exposed part of the optical waveguide that is exposed on the substrate surface between the input and output ends of the optical waveguide, and an exposed area that is wider than this exposed part. A coating layer made of silicone resin and having a refractive index smaller than that of the optical waveguide is disposed on a transparent substrate so as to cover the optical waveguide.

By optically connecting both ends of the above sensor to a light source and a photodetector via optical fibers and placing the sensor at the location where you want to detect oil leakage, it is possible to detect a state where no oil leakage has occurred, i.e. When no oil is attached to the liquid sensor, the light propagating in the optical waveguide is totally reflected at the boundary between the silicone resin coating layer and the optical waveguide, and propagates to the output end with low loss. However, when oil with a high refractive index adheres to the liquid sensor and infiltrates into the coating layer, the refractive index of the coating layer resin increases. As a result, the propagating light is emitted to the outside without being totally reflected at the boundary between the optical waveguide and the coating layer, and the amount of light propagating to the output end is reduced compared to before being infiltrated with oil.

Therefore, oil leakage can be detected by monitoring changes in the amount of light received by the photodetector connected to the waveguide sensor.

[Problem that the invention seeks to solve]

In the conventional optical sensor mentioned above, it takes a very long time for the silicone resin of the coating layer to infiltrate and its refractive index to increase. There was a problem in that it took a long time to process and the detection was delayed.

Particularly in the case of highly viscous liquids, a detection delay of several hours may occur.

Also, depending on the type of liquid to be detected, the refractive index of the silicone resin coating layer may not increase much due to its infiltration. For example, in the case of heavy oil C, the refractive index of the silicone resin increases by only about 0.5%, whereas conventional There was also the problem that the structured sensor could not detect heavy oil C and had a narrow range of application.

[Means to solve problems]

An optical waveguide having a higher refractive index than the surrounding area is provided in a flat substrate with a part thereof exposed on the substrate surface, and the exposed portion of the optical waveguide and the adjacent substrate surface connected thereto are coated with a continuous porous material. and optically connect the optical waveguide to a light source and a photodetector to form a sensor.

The coating layer made of the continuous porous material mentioned above can be made of various materials such as synthetic resins and ceramics, but if the liquid to be detected is oil, it is desirable to have water repellency to prevent false detection due to moisture penetration. In particular, fluorinated ethylene resins such as tetrafluorinated ethylene resins are suitable. In addition, in order to ensure that the liquid to be detected penetrates into the coating layer as quickly as possible due to the capillary action of continuous pores, the coating layer should be crimped to the light guide in a non-adhesive state rather than through optical contact. is desirable.

[Action of the invention]

When a liquid to be detected such as oil adheres to the coating layer of the sensor, since the coating layer is a continuous porous material, the liquid quickly penetrates through the pores by capillary action and reaches the surface of the light guide, causing no blockage under normal conditions. Since the refractive index at the outer surface of the light guide increases compared to when it is in contact with the atmosphere, the critical angle of total reflection at the interface increases, and the amount of light leaking from the light guide to the outside increases accordingly.

As a result, the amount of light emitted from the light guide decreases, and by monitoring changes in the amount of received light with a photodetector, it is possible to know whether the liquid is attached.

〔Example〕

The present invention will be described in detail below based on embodiments shown in the drawings.

FIGS. 1 and ₂ are _a perspective view and a side sectional view of a liquid sensor according to the present invention.
An optical waveguide 12 is formed having a refractive index n ₂ larger than that of n 2 .

The optical waveguide has a single path near the input end and near the output end, and two branch paths 12C and 12C in the middle.
It is branched into.

The optical waveguide 12 near the input end 12A and the output end 12B is completely embedded in the substrate 11, but the branch path 12C extends over almost the entire length of the exposed portion 12D exposed on the surface 11A of the substrate 11. I have it. The exposed portion 12D of the waveguide and the substrate surface 11A connected to the exposed portion 12D are both covered with a coating layer 13. This coating layer 13
consists of a sheet of continuous porous material, such as a continuous porous material of tetrafluoroethylene resin. This porous material covering layer 13 is manufactured separately and placed on the surface of the substrate 11, and is crimped to the substrate by, for example, fixing it at the end portion with an elastic fastener (not shown). An optical fiber 15 is connected to the input end 12A side of the waveguide 12.
One end of the fiber 15 is connected and the other end of the fiber 15 is connected to a light source.

Further, one end of another optical fiber 15 is connected to the output end 12B of the waveguide 12, and the other end is connected to a photodetector. The light that comes out from the light source, enters the waveguide 12, and propagates is also totally reflected at the exposed waveguide portion 12D and propagates, and is emitted to the optical fiber 15 on the output side with low loss.

If the liquid to be detected such as oil with a high refractive index is in the coating layer 1,
3, it penetrates into the coating layer 13 through continuous pores, reaches the exposed waveguide surface 12D, and wets this surface.

As a result, the exposed surface 12 in contact with the liquid to be detected
At D, the propagating light is not totally reflected, the amount of light propagating through the waveguide 12 decreases, and the amount of received light detected by the photodetector decreases, so if changes in light amount are monitored electrically, Adhesion of the detection liquid can be detected.

Further, as in the illustrated example, the coating layer 13 is applied to the waveguide 1.
If it is provided so as to cover not only the substrate surface 2D but also the substrate surface 11A that is connected to the exposed surface 12D, the liquid to be detected such as oil that adheres to the coating layer 13 in a portion away from the exposed portion 12D will also have continuous pores. Through exposed part 12D
Since the optical waveguide 12 is branched into two branch paths 12C and 12C, oil leakage can be detected over a much wider area than the width of the waveguide 12.

FIG. 3 shows a second embodiment of the invention.

In this example, the optical waveguide 12 in the translucent substrate 11 is a bent path that repeatedly moves near and far at a constant angle ψ with respect to the substrate surface, and the bent portions at regular intervals are exposed on the surface 11A of the substrate 11. An exposed portion 12D is formed. The exposed portions 12 are spaced apart from each other.
D... are covered with a common covering layer 13 made of a continuous porous material.

With this structure, the incident angle of light incident on the exposed surface 12D is reduced by ψ, so that it is possible to detect the attachment of a liquid having a smaller refractive index than in the structure of the first embodiment.

In other words, in the first embodiment, it is difficult to detect a liquid with a refractive index smaller than n ₁ of the substrate, but in the second embodiment, by setting the angle ψ to an appropriate value, the refractive index is smaller than n ₁ . can also sense liquids with a small refractive index. Furthermore, if the number of exposed surfaces 12D is increased, the change in the amount of light becomes larger, and the detection sensitivity increases. FIG. 4 shows another embodiment using a self-focusing light guide.

This example has a distribution in which the refractive index is maximum on the central axis and gradually decreases toward both sides in the width direction in the glass or plastic flat base material 21 by a method such as an ion diffusion method, a CVD method, or a copolymerization method. A semi-cylindrical waveguide 12 is integrally embedded with the exposed portion 12D aligned with the plate surface 21A of the base material 21, and is further embedded in the surface of the substrate 21 so as to cover the exposed portion 12D and the portion of the waveguide 12. It has a structure in which a covering layer 13 of a continuous porous material similar to the above embodiment is provided with a width _W2 wider than the width _{W1 ,} preferably twice or more of W1.

According to the above structure, even if the liquid to be detected adheres to the outside of the exposed waveguide portion 12D in the width direction, it is captured by the coating layer 13, and the liquid reaches the coated portion on the exposed portion 12D by penetration of the liquid. FIG. 5 shows an embodiment in which a single mode optical waveguide is used as the light guide of the sensor. A covering layer 13 made of a continuous porous material is provided.

Single mode optical fibers 15A and 15B are coupled to opposite sides of the sensor having the above structure, respectively,
Single mode light is made to enter the waveguide 22 through one optical fiber 15A, and light emitted from the waveguide is received by the fiber 15B.

In the above structure, when oil adheres to the surface of the coating layer 13, the oil quickly penetrates into the coating layer 13 and reaches the surface of the waveguide 22. As a result, the proportion of the evanescent wave 23 leaking out of the single mode light passing through the waveguide 22 increases, and the proportion of the light absorbed by the oil also increases.

Therefore, since the amount of light emitted from the exit of the waveguide 22 is reduced, oil leakage can be detected.

In this way, since detection is performed based on changes in the amount of evanescent waves seeping out from a single mode optical waveguide, it is necessary to control the incident angle of light into the waveguide within a fixed angle range, as in the case of using a multimode optical waveguide. No machining is required, making production easier.

In addition, when multicomponent glass, quartz glass, or plastic is used as the substrate material for configuring the sensor, ion exchange method, flame hydrolysis method used for manufacturing optical fibers, etc. Optical waveguides can be formed by using well-known techniques such as photopolymerization.

Further, the refractive index distribution in the vertical cross section of the single mode optical waveguide may be uniform or may have a slope. Further, the optical waveguide may be formed by methods other than those described above, such as vapor deposition, sputtering, ion implantation, and thermal diffusion. Figure 6 shows sensor 1
4 shows a device for actually detecting oil leaks. First, sensors 14 are placed at locations in the oil tank 24 where oil leakage is likely to occur, and these sensors 14 are connected in series or in parallel via optical fibers 15. Optical fiber 15 at the sidemost end
The light from the light source 25 is input to the optical fiber 15, and the light emitted from the optical fiber 15 at the other end is transmitted to the photodetector 26.
Detect with. Then, the electric signal from the photodetector 26 is transmitted to the alarm 2 through an amplifier 27 and a comparator 28.
Leads to 9. If the backscattering method, which is used to measure the connection loss of optical fiber connectors and the transmission loss of optical fibers, is used in combination, it is possible to not only detect oil leaks, but also to know the location of oil leaks.

Although the above description deals with sensing oil, any liquid that can penetrate into the pores of the coating layer 13 can be sensed without being limited to oil.

Specific numerical examples are shown below.

In the example shown in Fig. 4, an optical glass with a refractive index of 1.51 is used as the substrate, and a two-stage electric field ion exchange method is used to create a material in which the maximum refractive index is 1.53 and the refractive index gradually decreases from the center to the outer periphery. A graded index optical waveguide with a gradient was formed. Then, a separately manufactured continuous porous polytetrafluoroethylene resin sheet with a specific gravity of 0.68 and a thickness of 0.035 mm was placed on the substrate surface including the exposed surface of the waveguide, and the sheet and the substrate were pinched together at the edges. The sheet was then pressure-bonded to the substrate surface.

A light source and a photodetector are connected to the waveguide input end and output end of the above sensor via optical fibers, and while measuring the amount of light emitted from the waveguide, the coating layer of the sensor is coated with heavy oil A, B, and C. When a few drops of each were applied, the results were 0.5dB, 1.25dB, and
There was a change in light intensity of 0.98 dB, and oil adhesion could be detected. In addition, the time required for detection was 1 to 2 in each case.
It took an extremely short time, less than a minute.

〔Effect of the invention〕

In the liquid sensor according to the present invention, since a continuous porous material is used for the coating layer forming the detection surface, it is possible to detect the liquid on the surface of the light guide, compared to conventional ones that utilize the phenomenon of oil infiltration into the coating layer silicone resin itself. The speed at which the liquid arrives is extremely fast, and the response speed from when the liquid to be detected adheres to the sensor until it is sensed by the photodetector is fast, and highly safe detection can be performed.

In addition, since the optical waveguide is created in a flat substrate and the coating layer of the continuous porous material described above is provided to cover the exposed portion of the optical waveguide and the surface of the substrate adjacent to the exposed portion of the optical waveguide, the width of the exposed portion of the waveguide is Even if the liquid to be detected, such as oil, adheres to the outside of the optical fiber, it will be captured by the coating layer, and the liquid will reach the coating on the exposed part of the optical waveguide due to penetration of the liquid. The effective detection area can be made wider than when a solid coating is provided.

If the diameter of the optical fiber is increased to widen its detection area, the cross-sectional area of the transmitted light path will also increase, which will increase the sensitivity limit light leakage loss.In other words, the sensitivity of the sensor will decrease, but this According to the invention, there is a great advantage that the substantial sensing area can be expanded while the diameter of the light guide path remains the same.

[Brief explanation of drawings]

Fig. 1 is a perspective view showing a first embodiment of the present invention, Fig. 2 is a sectional view of the same side, Fig. 3 is a side sectional view showing a second embodiment of the invention, and Fig. 4 is a sectional view of the same side. FIG. 5 is a side sectional view showing a fourth embodiment of the present invention, and FIG. 6 is a schematic diagram showing an oil leak alarm system using a sensor according to the present invention. 11... Transparent substrate, 12... Optical waveguide, 12
A...Incidence end, 12B...Output end, 12C...Branch path, 12D...Exposed portion, 13...Continuous porous coating layer, 14...Sensor, 15, 15A, 15B...
...Optical fiber, 24... Oil tank, 25... Light source, 26... Photodetector, 27... Amplifier, 28...
Comparator, 29... Alarm.

Claims (1)

[Claims] 1. An optical waveguide having a higher refractive index than the surrounding area is provided in a flat substrate with a part of the optical waveguide exposed on the substrate surface, and the exposed portion of the optical waveguide and the adjacent substrate surface connected thereto are A liquid sensor covered with a coating layer made of a continuous porous material, the optical waveguide being optically connected to a light source and a photodetector.