JPH1073509A - Liquid detecting sensor and liquid detecting system using the same - Google Patents

Abstract

PROBLEM TO BE SOLVED: To obtain a liquid detecting sensor by which the contact of an optical fiber with a liquid to be detected, is detected with good accuracy over a long distance without a need of explosionproof measures by a method wherein the outer circumference of the optical fiber comprising a core and a clad is provided with a liquid-contact-response-material layer as well as an optical transmission loss and backscattering light are changed. SOLUTION: A quartz optical fiber 1 is composed of an optical fiber strand in which a core 1a is covered with a clad 1b and in which a protective layer 1c is executed additionally. The protective layer 1c is composed of three layers of, e.g. a primary coating, a buffer layer and a secondary coating. A liquid-contact-response-material layer 2 can be constituted of various materials according to a liquid to be detected. However, the layer is contracted when it comes into contact with the liquid to be detected, and a side pressure or a microbend can be given directly to the optical fiber without using a lock material layer. Consequently, when a change in the optical transmission loss of the optical fiber 1 due to it is monitored by an optical-transmission-loss measuring means, the existence of the liquid to be detected and its position can be detected over a long distance. In addition, when materials according to various liquids to be detected are selected, the effective function of a liquid detecting sensor can be displayed.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a liquid detection sensor for detecting the presence, presence, and location of electrolyte solutions such as acids, alkalis and salts, and other liquids stored in tanks or transported by pipeline. More particularly, the present invention relates to a liquid detection sensor that detects an optical transmission loss and a change in backscattered light caused by the presence of a liquid using an optical fiber, and a liquid detection system using the same. It is about.

[0002]

2. Description of the Related Art Conventionally, a liquid detection sensor for detecting a liquid such as an electrolyte solution and a liquid detection system using the same detect a decrease in insulation resistance between parallel electrode wires due to the presence of a liquid to be detected. (For example, Japanese Utility Model
No. 71741), an electric or electrochemical change caused by the presence of a liquid to be detected, such as one that detects a potential difference caused by the presence of an electrolyte solution between parallel electrode wires made of different metals (for example, see Japanese Patent Publication No. 2-36888). There is something to detect. However, the electrical system requires explosion-proof measures, and the accuracy decreases as the detection section becomes longer. And electrochemical systems are difficult to detect over long distances. Therefore, there is no need for explosion-proof measures, and as a sensor that can be detected over a long distance, by covering the outer periphery of the optical fiber with a member that expands due to the presence of water or oil, and by providing a means for restraining the expansion, There is one that detects a change in the intensity of the scattered light (for example, see Japanese Patent Application Laid-Open No. 63-266340).
However, there is no proposal for detecting a liquid other than water or oil, for example, an electrolyte solution. Further, none of the systems has been proposed which can distinguish between the liquid to be detected and other liquids and the liquid to be detected. However, recently, the necessity of storing and transporting various kinds of liquids including electrolyte solutions of acids, alkalis, and the like and transporting them by pipeline over a long distance has been increasing, and in many cases, detection of various liquids is required for safety measures. .

[0003]

SUMMARY OF THE INVENTION The present invention has been made to meet the above-mentioned demands, and the inventions according to claims 1 and 2 do not require explosion-proof measures, can be accurately detected over long distances, Moreover, it is an object of the present invention to provide a liquid detection sensor that can respond by selecting a material according to various types of liquids to be detected.

A third object of the present invention is to provide, in addition to the objects of the first and second aspects of the present invention, a liquid detection sensor capable of detecting a liquid to be detected and a specific liquid other than the liquid.

The invention described in any one of claims 4 to 7 provides, in addition to the objects of the inventions described in claims 1 and 2, a liquid detection sensor suitable for detecting an electrolyte solution, particularly an acidic solution or an alkaline solution. Make it an issue.

A seventh aspect of the present invention is to provide a liquid detection sensor capable of distinguishing and detecting an acidic liquid and an alkaline liquid in addition to the objects of the fifth or sixth invention.

According to an eighth aspect of the present invention, there is provided a liquid detection system capable of easily detecting the presence and / or position of a liquid to be detected by using the liquid detection sensor according to any one of the first to seventh aspects. Make it an issue.

[0008]

According to a first aspect of the present invention, there is provided an optical fiber having a core and a clad, wherein the optical fiber has a liquid contact responsive material layer on an outer periphery thereof. It is made of a liquid contact material that contracts when it comes into contact with the liquid to be detected. When the liquid-contact responding material layer comes into contact with the liquid to be detected, the liquid-contact responding material layer contracts and gives strain to the optical fiber due to lateral pressure or microbending, so that light transmission loss and backscattered light change. The optical fiber only needs to have at least a core and a clad, but a glass fiber having a protective layer is preferable because it is easy to handle.

According to a second aspect of the present invention, an optical fiber having a core and a clad is provided with a liquid-contact responding material layer and an outer coat layer sequentially around the optical fiber, and the liquid-contact responding material layer contracts when it comes into contact with the liquid to be detected. The outer layer is liquid-tight and soluble or liquid-resistant and liquid-permeable to the liquid to be detected. When the liquid to be detected comes into contact with the outer layer, the liquid to be detected is dissolved in the liquid to be detected or is permeable to the liquid, so that the liquid to be detected is introduced inside and comes into contact with the liquid contact responding material layer. When the liquid contact material layer comes into contact with the liquid to be detected, the liquid contact material shrinks and gives strain to the optical fiber due to lateral pressure or myrobend, so that light transmission loss and backscattered light change.

According to a third aspect of the present invention, in the liquid detection sensor according to the second aspect, the liquid contact responsive material layer contracts when it comes into contact with the liquid to be detected and expands when it comes into contact with another specific liquid. It is characterized in that the outer layer is made of a liquid responsive material, and the outer layer is made of a restraining member that restrains the expansion of the liquid contact material layer. When in contact with the liquid to be detected, the liquid contact material contracts and gives lateral pressure or microbend to the optical fiber, and when it comes into contact with other specific liquids, it expands and is constrained by the restraining material, causing distortion in the optical fiber due to lateral pressure or microbend In both cases, the optical transmission loss and the backscattered light change, and the response of the liquid contact material layer differs between the liquid to be detected and the other specific liquid.

According to a fourth aspect of the present invention, in the liquid detection sensor according to any one of the first to third aspects, the liquid contact material layer is made of an electrolyte gel which contracts when it comes into contact with an electrolyte solution. I do. The liquid contact material layer is made of an electrolyte gel that contracts when it comes into contact with the electrolyte solution, and applies a side pressure or a microbend to the optical fiber, thereby increasing optical transmission loss. Note that the electrolyte gel is a gel containing both or both of an anion group and a cation group, and when they come into contact with an electrolyte solution, those groups dissociate in the solution to become anions or cations. The degree of dissociation depends on the ion concentration of the electrolyte solution.

According to a fifth aspect of the present invention, in the liquid detection sensor according to the fourth aspect, the liquid contact material layer is made of a pH-sensitive gel that contracts when it comes into contact with an acidic liquid or an alkaline liquid. The liquid-contacting material layer is made of a pH-sensitive gel that contracts when it comes into contact with an acidic liquid or an alkaline liquid, and gives strain to the optical fiber due to lateral pressure or microbending, so that light transmission loss and backscattered light change. The pH-sensitive gel is an electrolyte gel in which the degree of dissociation of the anion group and / or the cation group depends on the pH value of the electrolyte solution.

According to a sixth aspect of the present invention, in the liquid detection sensor according to the fifth aspect, the liquid contact responsive material layer responds to an acidic liquid or an alkaline liquid as a liquid to be detected by an alkaline liquid opposite thereto. Alternatively, it is characterized by being made of a pH-sensitive material that is maintained unless it comes into contact with an acidic liquid. Since the liquid contact responding material layer keeps contracted in response to the acidic liquid or the alkaline liquid, the detection is easy and reliable.

According to a seventh aspect of the present invention, in the liquid detection sensor according to the fifth or sixth aspect, the liquid contact responsive material layer contracts when it comes into contact with an acidic liquid or an alkaline liquid, and conversely, an alkaline liquid or an acidic liquid. It is characterized by comprising a pH-sensitive gel which expands when it comes into contact with the gel. The liquid contact material layer has a different response between the acidic liquid and the alkaline liquid, so that it is easy to distinguish whether the liquid to be detected is an acid or an alkali.

According to an eighth aspect of the present invention, there is provided a liquid detection sensor according to any one of the first to seventh aspects and an optical transmission loss measuring device for measuring an optical transmission loss thereof or an optical pulse incident on the liquid detection sensor. And an optical pulse tester for measuring scattered light. The presence or absence and / or position of the liquid to be detected can be easily detected by monitoring the light transmission loss or backscattered light change of the liquid detection sensor using an optical transmission loss measuring device or an optical pulse tester that measures backscattered light. can do. The optical pulse tester for measuring the backscattered light has an OT for measuring the light intensity of the backscattered light.
DR (Optical Time Domain Re)
BOTDA (Brida) for measuring the frequency shift of Brillouin scattered light among the backscattered light
llouin Optical-Fiber Time
Domain Analysis) device is included.
The change in the backscattered light referred to here means a change in the intensity of the backscattered light, a difference between the frequency of the incident light and the frequency of the Brillouin scattered light, and the like.

[0016]

Embodiments of the present invention will be described with reference to the drawings. 1 and 2 are perspective views showing an embodiment of a liquid detection sensor according to the present invention. FIG. 1 shows a case where there is no outer layer, and FIG. 2 has an outer layer. Indicates that the outer layer is liquid-tight, and FIG. 2B shows that the outer layer is liquid-permeable. In FIG. 1, a liquid detection sensor 10 has a liquid contact material layer 2 provided on the outer periphery of a quartz glass optical fiber 1, and a quartz optical fiber 1 has a clad 1b on a core 1a.
And an optical fiber strand coated with a protective layer 1c. Although details of the protective layer 1c are not shown, the protective layer 1c includes, for example, three layers of a primary coating, a buffer layer, and a secondary coating. The liquid contact material layer 2 can be made of various materials according to the liquid to be detected as described later. However, since it contracts when it comes into contact with the liquid to be detected, side pressure or micro pressure is directly applied to the optical fiber without using a restricting material layer. Bend can be given. Therefore, if the change in the optical transmission loss of the optical fiber 1 due to this is monitored by the optical transmission loss measuring means, the presence of the liquid to be detected can be detected.

In FIG. 2, the liquid detection sensor 10 is formed by sequentially providing a liquid contact responding material layer 2 and a coating layer 3 or 4 on the outer periphery of a quartz glass optical fiber 1. The jacket layer 3 in FIG.
It is a liquid-tight and soluble in the liquid to be detected, for example, a plastic in which the soluble in the liquid to be detected is coated on the outer periphery of the liquid contact material layer. The outer layer 3 is made of, for example, a polyester resin. When the outer layer 3 comes into contact with an acidic liquid, the outer layer 3 is dissolved, so that the acidic liquid penetrates into the inside and comes into contact with the liquid contact responsive material layer 2. However, since the liquid detection sensor 10 is liquid-tight as long as it does not come into contact with an acidic liquid, there is an advantage that when the liquid detection sensor 10 is used outdoors, it does not malfunction due to rainwater.

The coating layer 4 shown in FIG. 2B is a liquid-resistant and liquid-permeable one, for example, an acid-resistant polyethylene yarn braided on the outer periphery of the liquid-contact responding material layer. Since the acid-resistant polyethylene yarn does not dissolve or deteriorate in the acidic liquid, it can be reused and continuously used as it is.
In addition, since the liquid is permeable, the acidic liquid is applied to the outer layer 4.
To come into contact with the liquid contact responding material layer. Instead, rainwater also enters the inside of the liquid detection sensor, so that the liquid contact responding material layer 2 must not respond to water.

Next, various liquid contact responding materials will be specifically described. For example, an electrolyte gel that contracts due to an acidic liquid includes styrene / divinylbenzene / sulfonic acid copolymer. Further, as an electrolyte gel that contracts due to a salt or an alkaline liquid, there is a styrene-divinylbenzene copolymer. Both swell when in contact with water. When such an electrolyte gel is used as a liquid contact material, the presence of the electrolyte gel can be easily detected because the gel shrinks with an electrolyte solution such as an acid, an alkali, and a salt. Even when used outdoors without a cover layer, it does not shrink due to water and does not malfunction due to rainwater. However, since it swells with water, if it comes into contact with the liquid to be detected in that state, it may not immediately contract. In the case where the outer layer 3 which is liquid-tight and water-resistant and dissolves in the liquid to be detected is provided, water does not come into contact with the liquid-contact responding material layer, so that the liquid-contact responding material layer 2 does not swell. In addition, a liquid-permeable and liquid-permeable outer layer 4 that is to be detected.
Is provided, the water-permeable material layer 2
Swells, but its expansion is restrained by the envelope layer 4, so that the presence of water can also be detected. As will be described later, when the liquid contact material layer contracts due to the liquid to be detected, and when the liquid contact material layer expands and is constrained by the jacket layer having a specific configuration, the lateral pressure on the optical fiber and the microbend are different. Are different from each other, the change characteristic of the light intensity of the backscattered light with respect to the distance from the light source is, for example, OTDR2.
By measuring at 0, the electrolyte solution and water can be distinguished and detected.

Further, an amphoteric electrolyte gel as a liquid contact material,
For example, using polyacrylonitrile gel fiber, pH
It contracts when it comes into contact with the acidic liquid of No. 3, and expands when it comes into contact with the alkaline liquid having a pH of 11. Moreover, the change in the fiber length is maintained even if the pH of the electrolyte solution in contact changes, and a hysteresis as shown in FIG. 3 is drawn. Therefore, when a polymer material containing polyacrylonitrile gel fiber is used as the liquid contact responding material layer, for example, after swelling at a pH value of 11, the degree of swelling is maintained even if it rains and the pH value decreases, so Is detected. Then, when it comes into contact with the acidic liquid and reaches pH 3, it contracts, and the lateral pressure on the optical fiber 1 once becomes zero. When the contact with the acidic liquid of pH 3 is further continued, an increase in lateral pressure due to contraction is detected. in this way,
Since it contracts when it comes into contact with an acidic liquid and expands when it comes into contact with an alkaline liquid, it can be detected separately by measuring the distance-light intensity characteristic of the backscattered light with the OTDR 20.

As a liquid contact responding material that responds to liquids other than the electrolyte solution, for example, PAA-PVA gel contracts when it comes into contact with acetone and swells when it comes into contact with water, which is useful for detecting acetone.

Next, an embodiment of the liquid detection system of the present invention using the above liquid detection sensor 10 will be described with reference to FIG. In FIG. 4, the liquid detection system 30 includes the liquid detection sensor 10 and the OTDR 20. The OTDR 20 includes a pulse oscillator 11, a sawtooth oscillator 12 that generates a sweep signal of a CRT 18 by a pulse from the pulse oscillator 11, an electrical / optical converter 13,
A directional coupler 14 for splitting the backscattered light, an optical / electrical signal converter 15, an amplifier 16, an averaging circuit 17,
T18, a connection optical fiber 19 for transmitting the pulse signal converted into an optical pulse by the electrical / optical converter 13 to the liquid detection sensor 10 and the optical / electrical converter 15 via the directional coupler 14. , An optical fiber connector 19a for connecting the liquid detection sensor 10 and the connection optical fiber 19, and the like.

FIG. 5 is a characteristic diagram showing a change in the light intensity of the backscattered light according to the distance from the starting end S of the liquid detection sensor 10 measured by the OTDR 20 of the liquid detection sensor detection system 30. When an optical pulse signal is sent to the optical fiber 1 of the liquid detection sensor 10, in a normal state,
As shown in FIG. 5A, the light intensity P of the backscattered light linearly decreases according to the length of the light that has passed through the optical fiber 1. At the starting end S of the liquid detection sensor 10 of the distance L _X, when the detection target liquid is in contact, wetted response material layer 2 is the contraction of that portion, distortion occurs because the lateral pressure or microbending is applied to the optical fiber 1 . Therefore, before detection
_The light intensity which was _X1 is reduced to P _X2 , causing a loss of ΔP _X. Therefore, the position of the liquid to be detected is OTDR
The information is displayed on the CRT 20 or as a numerical value via a separately provided computer. In addition, when the liquid contact material layer 2 swells due to a non-detection target liquid such as rainwater, a light transmission loss similarly occurs. In this case, the outer layer is a braid of the braid 4 as shown in FIG. If you leave rough density causes a difference in the resulting how losses between the portion and the unconstrained portion that is constrained expansion of the wetted response material layer 2, the distance L _X somewhat gently nonlinearly light around the Strength decreases. If this pattern is confirmed in advance by an experiment, it will be detected and the type of liquid will be known.

In the above example, the OTDR is used for detecting the position of the liquid to be detected, but the BOT is used as an optical pulse tester.
Devices using a DA device are also included in the present invention. If only the presence or absence of the liquid to be detected is detected, for example, an optical transmission loss measuring device including a light source and an optical power measuring device may be used. In addition, a jacket layer 4 for restraining the expansion of the liquid contact material layer 2
Is not limited to the braid as shown in FIG. 2 (b), and a string made of a liquid-resistant material to be detected may be wound around the outer periphery of the liquid-contact responding material layer 2. Any material may be used as long as it has a portion that is in contact with the liquid contact responding material layer 2 and a portion that is not in contact. In this case, microbending is likely to occur in the optical fiber 1, and the optical transmission loss and the change in backscattered light increase, so that the detection accuracy is improved. Further, in the above example, the optical fiber 1 is an optical fiber having the protective layer 1c. However, the optical fiber 1 may be further coated with nylon, or may be composed of only the core and the clad. Nylon coating makes handling easier, but detection sensitivity is slightly reduced. In the case of a core and a clad, the liquid contact material layer 2 also serves as the protective layer 1c, and it is necessary to select a suitable material.

[0025]

According to the first aspect of the present invention, the liquid-contact responsive material layer contracts when it comes into contact with the liquid to be detected, and applies lateral pressure or microbend to the optical fiber, so that the optical transmission loss of the optical fiber increases. By detecting the increase in the loss, there is an effect that a linear liquid detection sensor capable of detecting the presence of the detection target liquid over a long distance can be obtained at low cost.

According to the second aspect of the present invention, in addition to the effect of the first aspect of the present invention, a protective effect of the outer layer is added. Moreover, the outer layer is soluble or permeable to the liquid to be detected,
Since the detection target liquid is introduced into the inside, there is an effect that the detection target liquid can be detected.

According to a third aspect of the present invention, in addition to the effect of the second aspect of the present invention, when the liquid-contacting member comes into contact with the liquid to be detected, the liquid-contact responsive material contracts to apply a lateral pressure or a microbend to the optical fiber. When in contact with a specific liquid, it expands and is constrained by the constraining material to apply lateral pressure and microbend to the optical fiber.In either case, the optical transmission loss increases, or the backscattered light changes, and the liquid to be detected and other Since the response of the liquid contact responsive material layer differs between the specific liquid and the specific liquid, it is possible to detect the liquid separately.

The invention according to claim 4 has the effect that in the invention according to any one of claims 1 to 3, the liquid contact material layer is made of an electrolyte gel, so that the detection of the electrolyte solution is easy and reliable.

According to a fifth aspect of the present invention, in the fourth aspect of the present invention, since the liquid contact material layer is made of a pH-sensitive gel, an effect of easily and reliably detecting an acidic liquid or an alkaline liquid is obtained.

According to a sixth aspect of the present invention, in the invention of the fifth aspect, the state in which the liquid contact material layer contracts in response to the acidic liquid or the alkaline liquid does not come into contact with the opposite alkaline liquid or the acidic liquid. As long as the detection is maintained, the effect of easy and reliable detection is achieved.

According to the seventh aspect of the invention, in addition to the effect of the fifth or sixth aspect, the liquid contact material layer has a different response between the acidic liquid and the alkaline liquid, so that the liquid to be detected is different. This has the effect that it is easy to distinguish between an acid and an alkali.

According to an eighth aspect of the present invention, in addition to the effects of the first aspect, a change in the optical transmission loss of the liquid detection sensor is monitored by an optical transmission loss measuring device, or the change is monitored. By monitoring the change in the scattered light with the optical pulse tester, it is possible to easily detect the presence and / or the existence position of the liquid to be detected.

[Brief description of the drawings]

FIG. 1 is a perspective view showing an embodiment of a liquid detection sensor of the present invention.

FIG. 2 is a perspective view showing an embodiment of the liquid detection sensor of the present invention.

FIG. 3 is a response characteristic diagram of an ampholyte gel, which is an example of a liquid contact material, with respect to the pH of a liquid to be detected.

FIG. 4 is a block diagram of the liquid detection system of the present invention.

FIG. 5 is a characteristic diagram showing a change in light intensity of backscattered light according to a distance of a liquid detection sensor measured by an optical pulse tester.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Optical fiber 2 Wetted-response material layer 3, 4 Jacket layer 10 Liquid detection sensor 20 Optical pulse tester 30 Liquid detection system

Claims (8)

[Claims] An optical fiber having a core and a clad is provided with a liquid-contact responsive material layer on an outer periphery thereof, wherein the liquid-contact responsive material layer is made of a liquid-contact responsive material that contracts when it comes into contact with a liquid to be detected. Liquid detection sensor. 2. An optical fiber having a core and a clad, comprising a liquid contact responding material layer and a coating layer sequentially provided on an outer periphery of the optical fiber, wherein the liquid contact responding material layer is made of a liquid contact responding material that contracts when it comes into contact with a liquid to be detected. A liquid detection sensor, wherein the outer layer is liquid-tight and soluble or liquid-resistant and liquid-permeable with respect to a liquid to be detected. 3. The liquid detection sensor according to claim 2, wherein the liquid contact responsive material layer is made of a liquid contact responsive material that contracts when it comes into contact with the liquid to be detected and expands when it comes into contact with another specific liquid. The liquid detection sensor, wherein the outer layer is formed of a restraining member that restrains expansion of the liquid contact material layer. 4. The liquid detection sensor according to claim 1, wherein the liquid contact material layer is made of an electrolyte gel that contracts when it comes into contact with an electrolyte solution. 5. The liquid detection sensor according to claim 4, wherein the liquid contact responding material layer is made of a pH-sensitive gel that contracts when it comes into contact with an acidic liquid or an alkaline liquid. 6. The liquid detection sensor according to claim 5, wherein the liquid contact responding material layer does not come into contact with the opposite alkaline liquid or acidic liquid in a state in which it responds to an acidic liquid or an alkaline liquid as a liquid to be detected. A liquid detection sensor comprising a pH-sensitive gel that is maintained as long as possible. 7. The liquid detection sensor according to claim 5, wherein the liquid contact material layer contracts when it comes into contact with an acidic liquid or an alkaline liquid, and expands when it comes into contact with an alkaline liquid or an acidic liquid. A liquid detection sensor comprising a sensitive gel. 8. A liquid detection sensor according to claim 1, and an optical transmission loss measuring device for measuring an optical transmission loss thereof, or an optical pulse is incident on said liquid detection sensor to measure backscattered light. Liquid detection system consisting of an optical pulse tester.