Patent Description:
The disclosure relates to discovering and locating leakages of petroleum products or other fluids, such as organic or inorganic solvents, alcohols, acids or bases. Some of detectors used for this purpose include swellable materials, which noticeably swell on absorbing a particular fluid. When the liquid or vapor to be detected contacts the swellable material, it swells due to absorption of the fluid. The swollen structural element may press together or, to the contrary, separate other elements of an electrical sensor resulting in a detectable event. The swellable material may be conductive, and the conductivity may noticeably change when the material is swollen.

<CIT> provides an elongated detecting element for leaks of petroleum products. The sensor includes a copolymer which swells or dissolves on contact with petroleum products. Accordingly, the sensor loses its conductivity. However, a leakage cannot be discriminated from a physical break of the sensor.

<CIT> describes an elongated element composed of an insulated conductor covered with a swellable element. Additional detection wires may be used for sensing the presence or absence of electric current in the swellable portion. While capable of detecting the presence of hydrocarbons, such sensor does not allow for discriminating between a sensor break and a leakage alarm. <CIT> is an improvement of the sensor described in <CIT> as it allows the discrimination of breaks and leak alarms by introducing a third conductor. However, such structure is more complex and needs the use of a specialized three-terminal management module.

<CIT> teaches a device with two elongated conductors helically wrapped around a support core. A swellable, conductive polymer member surrounds the conductors. In the presence of a fluid, the swellable material remains conductive and, by swelling, forms a conductive bridge between the two elongated conductors.

While a variety of sensors are available on the market, there is still a need for further improvement.

The instant disclosure provides an elongated sensor having a proximal end and a distal end, and an inner portion therebetween, for detecting the presence of a fluid, the sensor comprising: a first conductor extending from the proximal end to the distal end of the sensor; and,
a second conductor extending from the proximal end to the distal end of the sensor, isolated from the first conductor in the inner portion of the sensor, comprising: a swellable conductor, wherein at least a portion of the swellable conductor is swollen when the portion is in contact with the fluid and the electrical conductance of the portion is at least <NUM> times less when the portion is in contact with the fluid than when absent contact with the fluid, and a subsidiary conductor is in direct contact with the swellable conductor in the inner portion of the sensor and in electrical contact with the first conductor at the distal end of the sensor, the swellable conductor is at least <NUM>% more swellable than the subsidiary conductor, and a ratio of the conductance of the subsidiary conductor to the conductance of the swellable conductor in absence of contact with the fluid is in the range of <NUM> to <NUM>; wherein the first conductor is at least partially covered with an isolative jacket for electrically isolating the first conductor from the second conductor in the inner portion of the sensor.

The disclosure also provides an elongated sensor having a proximal end and a distal end, and an inner portion therebetween, for detecting the presence of a fluid, the sensor comprising: a first conductor extending from the proximal end to the distal end of the sensor; and,
a second conductor extending from the proximal end to the distal end of the sensor, comprising: a swellable conductor, wherein at least a portion of the swellable conductor is swollen when the portion is in contact with the fluid and the electrical conductance of the portion is at least <NUM> times less when the portion is in contact with the fluid than when in absence of contact with the fluid, and a subsidiary conductor in direct contact with the first conductor and the swellable conductor in the inner portion of the sensor.

One aspect of the disclosure relates to a sensor cable comprising an elongated sensor and a termination resistor connected in parallel to a swellable conductor of the elongated through an insulated conductor which is an integral part of the sensor. Optionally, the outer surface of the sensor is covered with an elastic non-conductive overcoat permeable for the target liquid but impervious to the water and other fluids that shall not be detected.

Another aspect of the disclosure relates to a sensor cable comprising a multiplexer, a shared conductor, and a plurality of sensor cables, in which each of the plurality of sensor cables has a first terminal and a second terminal, the first terminals are connected to the shared conductor, the second terminals each connected to an individual conductor, and the individual conductors are multiplexed at the multiplexer.

One aspect of the disclosure relates to an elongated sensor having a proximal end and a distal end, and an inner portion therebetween, for detecting the presence of a fluid, the sensor comprising a hybrid swellable conductor. comprising a swellable conductor, wherein at least a portion of the swellable conductor is swollen when the portion is in contact with the fluid and the electrical conductance of the portion is at least <NUM> times less when the portion is in contact with the fluid than when absent contact with the fluid. The hybrid conductor further comprises a subsidiary conductor in direct contact with the swellable conductor in the inner part of the sensor. A ratio of the conductance of the subsidiary conductor to the conductance of the swellable conductor when absent contact with the fluid is in the range of <NUM> to <NUM>.

Exemplary embodiments will now be described in conjunction with the drawings in which:.

Some of conventional sensors for detection fluids, such as liquids or vapors, include a conductor formed of a swellable material with conductive particles dispersed therein. On contact with a fluid to be detected, the material swells so that the conductive particles separate from each other making the material non-conductive. Accordingly, an electric circuit formed by the sensor and power supply is broken. However, the interruption of the electric current caused by a leakage cannot be discriminated from e.g. a physical snap of the sensor.

The instant disclosure relates to a hybrid swellable conductor, also referred herein as a composite conductor, formed of a swellable conductor and a subsidiary conductor, connected in parallel and in permanent direct electric contact with one another along most of their length. The swellable conductor includes a swellable non-conductive or barely conductive material with a conductive admixture dispersed therein.

On contact with the fluid to be detected, the swellable conductor expands and the swollen material may lose its electrical conductivity or the conductivity becomes very low. However, the subsidiary conductor remains conductive and enables electric current through the sensor, including non-swollen and still conductive portion(s) of the swellable conductor. Preferably, a conductance of the subsidiary conductor is less than that of the swellable layer in its non-swollen state. When a portion of the swellable layer is swollen, the subsidiary conductor diverts part of the electric current to non-swollen portion(s) of the swellable layer. The relative increase of the resistance is less than that with a simple sensor with only a swellable layer and absent a subsidiary conductor indirect contact with the swellable layer along the sensor. A sensor with the hybrid conductor as disclosed herein may provide the same degree of sensitivity as a conventional sensor having the same swellable conductor without a subsidiary conductor. However, when a sensor is in contact with the liquid of interest, no electric current may be detected in a sensor without a subsidiary conductor, while a sensor with the composite conductor still has an electric current through the sensor, indicating that the sensor is intact and operational.

Furthermore, the composite conductor makes it possible to determine the location of a leakage. The subsidiary conductor and non-swollen portion(s) of the swellable conductor form a resistor network, and its resistance depends on the location of the leak. Therefore, the location may be determined based on resistance measurement(s).

Moreover, using the composite conductors allows for adjusting an alarm level, wherein an alarm may be configured so as to exclude small leaks and low changes in resistance of the sensor.

This disclosure provides a variety of sensors using the composite conductor for detecting a leakage and simultaneously indicating that the sensor is operational, and/or for detecting the location of the leak. Each sensor is designed for detecting one or more particular fluids, e.g. hydrocarbon liquids and vapors, gasoline, water, synthetic solvents, solvents extracted from natural products, turpentine, limonene, alcohols, acids or bases. Materials for the composite conductor are chosen on consideration of their interaction with the particular fluid(s).

With reference to <FIG>, an elongated sensor <NUM> for detecting the physical presence of a particular fluid has a proximal end <NUM>, a distal end <NUM>, and an inner portion <NUM> therebetween. The sensor <NUM> includes a first conductor <NUM> extending from the proximal end <NUM> to the distal end <NUM>. The first conductor <NUM> may be formed of one or more conductive metals or alloys, such as copper, silver, gold, aluminum, iron, nickel, cobalt, or any combination or alloys including other metals. The first conductor <NUM> is substantially inert, i.e. it does not swell and its conductivity does not change dependent on the presence of the fluid to be detected.

The sensor <NUM> also includes a second conductor <NUM> extending from the proximal end <NUM> of the sensor to the distal end <NUM>. The second conductor <NUM> is a composite conductor as discussed above.

The second conductor <NUM> includes a swellable conductor <NUM>. It swells when absorbing the fluid; a swollen portion loses its conductivity or the conductivity becomes significantly reduced. For certainty, the specific conductivity in a swollen portion drops at least <NUM> times in comparison with the non-swollen state, i.e. when absent contact with the fluid. In other words, the electrical conductance of the portion is at least <NUM> times less when the portion in contact with the fluid than when absent contact with the fluid. More preferably, the electrical conductance of the portion is at least <NUM> times less than when absent contact with the fluid.

The swellable conductor may be formed of one or more swellable materials with conductive admixture dispersed therein. When a portion of the swellable conductor absorbs the fluid, at least a portion of the swellable conductor swells, and the conductive particles start to separate or distance from each other. Accordingly, the electrical resistance of that portion increases at least <NUM> times and, preferably, at least <NUM> times. The swollen portion may completely lose its conductivity.

A suitable swellable material may be a polymer, an elastomer, or a mixture thereof. The list of suitable materials includes a natural or synthetic rubber, silicone, a thermoplastic elastomer, a styrenic polymer or elastomer, and vinyl polymer or elastomer. The conductive admixture may include carbon or metal powder, carbon or metal fibres, and/or nanotubes. Other materials and admixtures may be used if the conductance of the resulting swellable conductor significantly drops when a portion of the conductor absorbs the fluid. The swellable materials may also be mixed with non-swellable materials, in order to adjust the rate of swelling and/or to improve the mechanical or chemical properties of the swellable conductor.

It is desirable for the the sensor <NUM> be reusable after a duration time, e.g. after the swellable conductor is rinsed and/or dried to remove the fluid.

The second conductor <NUM> further includes a subsidiary conductor <NUM>, not sensitive or barely sensitive to the presence of the target fluids to be detected. Preferably, the subsidiary conductor <NUM> is substantially inert, i.e. it does not swell on contact with the fluid to be detected. However, if the subsidiary conductor <NUM> is swellable on contact with the fluid to be detected, the swellable conductor <NUM> is at least <NUM>% more swellable (in terms of volume ratio) than the subsidiary conductor <NUM>, and preferably - at least <NUM>% more swellable. The conductor <NUM> never completely losses its conductivity when in contact with target fluid.

The subsidiary conductor <NUM> may include one or more base materials such as a polymer, elastomer or a mixture thereof. The list of suitable materials includes a fluoropolymer, an elastomer, a polyolefin, a polyamide, and a polyimide. Conductive admixture should be added to those materials so as to enable the conductivity of the subsidiary conductor <NUM>. The conductive admixture may include carbon or metal powder, carbon or metal fibers, and/or nanotubes. Though it is not necessary, a same admixture material may be used in the swellable conductor <NUM> and the subsidiary conductor <NUM>. Thin metal or alloy wires or conductive film deposition on isolated elongate element as well as layers of graphene, carbon nanotubes, etc., are also suitable. The subsidiary conductor <NUM> may include an insulated elongate element covered with a deposited film of conductive particles such as metal or metal alloy, carbon black, carbon fibres, graphene, or nanotubes of carbon; the film may be also coated onto the first conductor <NUM> covered with an isolator.

In one embodiment, the subsidiary conductor <NUM> includes an intrinsically conducting polymer, such as polyacetylene, polyaniline, polypyrrole, etc. In another embodiment, the subsidiary conductor <NUM> is made of carbon fibers, as a bundle, a tow or a yarn. The subsidiary conductor <NUM> may be a thin metal film, e.g. with a thickness in the range from <NUM> to <NUM> deposited on, and covering fully or partially a non-conductive support, e.g. the isolating layer over the first conductor <NUM>.

Depending on the application, some materials can be used as swellable for one group of fluids and as non-swellable for another group of target fluids. For instance, silicone elastomers can be used as swellable material for hydrocarbons and as non-swellable for alcohols. In other words, the materials used in the sensor predefine one or more fluids which may be detected using the sensor.

The subsidiary conductor <NUM> provides a relatively weak electrical connection between the swellable conductor <NUM> and the first conductor <NUM>. Preferably, the electrical conductance of the subsidiary conductor <NUM> is at least <NUM> times lower than the conductance of the first conductor <NUM>. If the proximal end of the sensor <NUM> is connected to a power supply, the first conductor <NUM> loops the electric circuit and returns electric current to the proximal end of the sensor. Consequently, using a highly conductive first conductor reduces losses and heating of the sensor. However, the first conductor <NUM> may be formed of the materials suitable for the subsidiary conductor <NUM>, and the sensor may be arranged as a loop.

The conductance of the subsidiary conductor <NUM> should be comparable with the conductance of the swellable conductor <NUM> when it is not swollen. Otherwise, e.g. if a highly conductive copper wire were used instead of the subsidiary conductor described herein, the impact of the swellable conductor <NUM> would be negligible, and the device would essentially lose its leakage detector capability. The conductance of the subsidiary conductor <NUM> is in the range of <NUM> to <NUM> times of the electrical conductance of the swellable conductor <NUM> in its non-swollen state, and more preferably in the range of <NUM> to <NUM> times.

The first conductor <NUM> is electrically isolated from the second conductor <NUM> at least in the inner portion <NUM> of the sensor <NUM>. The constituents of the second conductor <NUM>, the swellable conductor <NUM> and the subsidiary conductor <NUM>, are in direct and permanent contact with one another, at least in the inner portion <NUM> of the sensor <NUM>.

At the distal end <NUM> of the sensor <NUM>, the first conductor <NUM> is in electrical contact with the subsidiary conductor <NUM>. A coupler may be used at the distal end <NUM> for electric coupling of the first conductor <NUM> and the subsidiary conductor <NUM>, and optionally the swellable conductor <NUM>. Alternatively, the subsidiary conductor <NUM> and the first conductor <NUM> may be bound together at the end <NUM>, e.g. spliced, or one may be coated onto another, or they may be integral and formed of a same material, though the two conductors are electrically isolated from one another everywhere but the distal end of the sensor.

At the proximal end <NUM>, a first connector may be connected to the first conductor <NUM>, and a second connector may be connected to the subsidiary conductor <NUM>. The second connector may also be connected to the swellable conductor <NUM>, or to both conductors <NUM> and <NUM>. The first and second connectors are for coupling the sensor to a resistance measurement device.

The swellable conductor <NUM> may cover only a portion of the subsidiary conductor <NUM>, in particular, missing the proximal and/or distal end of the subsidiary conductor <NUM> and, thus, not connected to the coupler at the distal end of the sensor and the second connector at the proximal end of the sensor.

Optionally, the sensor <NUM> includes an insulative jacket permeable to the fluid.

With reference to <FIG>, a sensor <NUM> is an embodiment of the sensor <NUM>. The first conductor may be a metal wire <NUM>. An isolative jacket <NUM> at least partially covers the first conductor <NUM> for electrically isolating the first conductor <NUM> from the second conductor in the inner portion <NUM> of the sensor.

The second conductor may include a subsidiary conductive jacket <NUM> at least partially covering the isolative jacket <NUM>. A swellable conductive jacket <NUM> at least partially covers the subsidiary jacket <NUM> and isolative jacket <NUM>. Preferably, the swellable jacket <NUM> is at least <NUM>% more swellable than the subsidiary jacket <NUM>, and more preferably - at least <NUM>% more swellable. Optionally, the sensor <NUM> includes an insulative jacket <NUM> permeable to the target fluid; the jacket <NUM> is shown in <FIG> but not in <FIG>.

Preferably, in the inner portion of the sensor, the jackets <NUM>, <NUM> and <NUM> completely cover one another. However, any of the jackets may cover underlying layers only partially. For example, the swellable jacket <NUM> and the subsidiary jacket <NUM>, each may be arranged in the form of one or more longitudinal stripes, one jacket over another, along the isolated wire <NUM>&<NUM>, between the proximal and distal ends of the sensor.

With reference to <FIG>, the first conductor <NUM> may be a wire in the harness of the second conductor <NUM>, or a conductive stripe on the surface of the second conductor <NUM>, isolated therefrom. The cross section of the sensor is not necessarily round; it may be flat, oval, square, etc. Other configurations are, of course possible.

The purpose of these structures is to leave the sensitive swellable material exposed to the target fluid while maintaining the conductivity of the sensor element, albeit decreased. When the conductive sensitive material contacts the fluid of interest, the material begins to absorb the fluid and swells, thereby losing its conductivity, at least partially. From the point of view of the user, the electrical resistance of the sensor will increase to a finite and measurable value, and this increase will be a function of the length of the detector element in direct contact with the fluid. In case of presence of fluid in contact with the detector element, the conductivity of the latter will not be lost completely. In the event of a break of the subsidiary conductive jacket <NUM> or its support (the insulated electrical wire <NUM>&<NUM>), the conductivity between the two terminals will be lost completely and the measurement device will indicate an open circuit.

With reference to <FIG>, a sensor <NUM> is an embodiment of the sensor <NUM>. The first conductor is a metal wire <NUM> with an isolative jacket <NUM> at least partially covering the first conductor <NUM> for electrically isolating the first conductor from the second conductor in the inner portion of the sensor. The second conductor includes a subsidiary conductive jacket <NUM> in the form of longitudinal stripes partially covering the isolative jacket <NUM>. A swellable conductive jacket <NUM> at least partially covers the subsidiary jacket <NUM> and isolative jacket <NUM>. Optionally, the sensor <NUM> includes an insulative jacket <NUM> permeable to the fluid. Portions of the sensor <NUM> between the stripes <NUM> may be filled with the material of the swellable conductive jacket <NUM>; in other words, the swellable conductive jacket <NUM> may be in direct contact with portions of the isolative jacket <NUM> not covered by the subsidiary conductive jacket <NUM>. Preferably, the swellable jacket <NUM> is at least <NUM>% more swellable than the subsidiary jacket <NUM>, and more preferably - at least <NUM>% more swellable.

In one embodiment, the first and second conductors are planar, as well as an isolator therebetween. <FIG> illustrate cross-sections of sensors <NUM> and <NUM> which are embodiments of the sensor <NUM>. The sensors include planar first conductor <NUM>, isolators <NUM>, subsidiary conductors <NUM>, swellable conductors <NUM>, and optional elastic insulative jacket <NUM> permeable to the target fluid.

Preferably, the isolators between the first and second conductors, such as the isolators <NUM> (<FIG> and <FIG>), <NUM> (<FIG>), <NUM> (<FIG>), and <NUM> (<FIG>) are non-swellable. The first conductor together with the isolator may form a conventional isolated wire.

With reference to <FIG>, a sensor <NUM> is an embodiment of the sensor <NUM>. The sensor <NUM> includes a first conductor <NUM>, an isolator <NUM>, a subsidiary conductor <NUM>, a swellable conductor <NUM>, an optional insulative jackets (not shown) permeable to the target fluid, and couplers <NUM> and <NUM>, at the proximal and distal ends of the sensor, respectively. At the distal end, the coupler <NUM> couples the second conductor, formed of the swellable conductor <NUM> and the subsidiary conductor <NUM>, with the first conductor <NUM>.

<FIG> provides equivalent schematics for normal and abnormal operation of the sensor <NUM> illustrated by the sensor <NUM>. R1 and R3 are resistance values for portions of the sensor <NUM> not affected by the fluid. R2a is an abnormal resistance of the sensor part in contact with the fluid, shown in the drawing as a central part of the sensor. In normal operation, that portion has resistance R2n, which is less than the abnormal resistance R2a. The total resistance of the sensor when no fluid is present is R(total, normal)=R1+R2n+R3. The total resistance of the sensor when in contact with the fluid is R(total, alarm)=R1+R2a+R3, which is greater than R(total, normal), though a finite value. In case the sensor is physically broken, its resistance is infinitively high.

Advantageously, the sensor <NUM> allows for discriminating between a cable break and the presence of a leak, and also indicative of the size of a swollen part.

With reference to <FIG> and <FIG>, the composite conductor <NUM> may be formed of a carbon fiber tow <NUM> at least partially coated with a swellable material <NUM> such as described for the swellable conductor <NUM>. <FIG> represents a simple and easy to manufacture layout of the sensor <NUM> where the subsidiary and preferably non-swellable conductor is made of readily available carbon fiber tow. The composite conductor illustrated in <FIG> may be joined to an isolated return wire, not shown in <FIG>, making the design illustrated in <FIG>, so that the composite conductor and the return wire may be connected to a measuring device at the proximal end of the sensor (left in the drawing).

The carbon fiber tow may also be placed in parallel to an insulated conductor to obtain a conductive stripe as presented in <FIG>.

With reference to <FIG>, an elongated sensor <NUM> for detecting the presence of a particular fluid has a proximal end <NUM>, a distal end <NUM>, and an inner portion <NUM> therebetween. The sensor <NUM> includes a first conductor <NUM> extending from the proximal end <NUM> to the distal end <NUM> of the sensor. The first conductor <NUM> may be formed of the same conductive metals and/or alloys, as the conductor <NUM> (<FIG>).

The sensor <NUM> further includes a second conductor <NUM> extending from the proximal end <NUM> to the distal end <NUM> of the sensor. The second conductor <NUM> is a composite conductor. It is formed of a swellable conductor <NUM> and a subsidiary conductor <NUM>, which operate the same way and may be formed of the same materials as the conductors <NUM> and <NUM> (<FIG>), respectively.

The swellable conductor <NUM> swells and is at least <NUM> times less conductive when infiltrated with the fluid than when absent contact with the fluid. More preferably, the specific conductivity in a swollen portion of the swellable conductor is at least <NUM> times less than when absent contact with the fluid. The subsidiary conductor <NUM> is in permanent direct contact with the first conductor <NUM> and swellable conductor <NUM> in the inner portion <NUM> of the sensor <NUM>.

Advantageously, the sensor <NUM> allows for discriminating between a cable break and the physical presence of a leak, and also indicative of the size of a swollen part. Additionally, the sensor <NUM> allows identifying the location of a leak, which is an important feature for elongated sensors, especially for buried applications.

It is desirable for the sensor <NUM> be reusable after a duration time, e.g. after the swellable conductor is rinsed and/or dried to remove the fluid.

In one embodiment of the sensor <NUM>, the first and second conductors are planar, as in the embodiment of the sensor <NUM> illustrated in <FIG>, with the exception that the isolators <NUM> are absent in accordance with the description of the sensor <NUM> (<FIG>).

The sensor <NUM> may be connected to a measuring system at the sensor's proximal end, as illustrated in <FIG>, wherein a sensor <NUM> is an embodiment of the sensor <NUM> and is used as an example of the sensor <NUM>. The sensor <NUM> includes a first terminal <NUM>, which may be a first connector or a wire end wherein the first connector may be attached or integral. The first terminal <NUM> is connected to a first conductor <NUM> at a proximal end <NUM> of the sensor.

The sensor <NUM> includes a second terminal <NUM>, which may be a second connector or a wire end wherein the second connector may be attached or integral. The second terminal <NUM> may be connected to a second conductor <NUM>&<NUM> through a coupler <NUM> at the proximal end <NUM> of the sensor. The coupler <NUM> may be integral with the terminal <NUM>.

At the distal end <NUM> of the sensor, two connectors (not shown) may be attached to the first and second conductors the same way as at the proximal end <NUM>. Instead <FIG> shows a return conductor <NUM> coupled to the first conductor <NUM> at the distal end <NUM> of the sensor and extending to the proximal end <NUM> of the sensor, and another return conductor <NUM> coupled by the coupler <NUM> to the second conductor at the distal end <NUM> of the sensor and extending to the proximal end <NUM> of the sensor, so that two more terminals <NUM> and <NUM> become available at the proximal end <NUM> of the sensor. The terminals <NUM> and <NUM> may be connectors or wire ends wherein connectors may be attached or integral. The return conductor <NUM> may be an extension of the first conductor <NUM>, though it needs to be isolated from the first and second conductors. Alternatively, the return conductor <NUM> may be coupled to the first conductor <NUM> using a coupler, not shown. It is also possible to have the return conductor <NUM> joined to the first conductor <NUM> by splicing, etc. The use of the return conductor <NUM> and the terminal <NUM> is optional as the electrical resistance of the first conductor <NUM> is low. Measuring the resistance of first conductor <NUM> allows the determination of the length of sensor in case of leak as it is not affected by the presence of fluids.

Each of the return conductors <NUM> and <NUM> may be an isolated wire or a metal stripe on an insulative jacket. With reference to <FIG>, a sensor 610A is an embodiment of the sensor <NUM>. The first conductor is a metal wire 620A. The subsidiary conductor forms a subsidiary jacket 650A at least partially covering the first conductor 620A, and the swellable conductor forms a swellable jacket 640A at least partially covering the subsidiary jacket 650A. One or more of return conductors 645A and 646A are stripes on the surface of an insulative jacket 660A, extending from the distal end of the sensor to the proximal end of the sensor, preferably in the longitudinal direction or possibly as spirals, and are covered with an insulative jacket <NUM>. The jackets 660A and <NUM> are permeable to the target fluid and may be made of a same insulative material.

With reference to <FIG>, a sensor <NUM> is an embodiment of the sensor <NUM>. The first conductor may be a metal wire <NUM>. The subsidiary conductor forms a subsidiary jacket <NUM> at least partially covering the first conductor <NUM>, and the swellable conductor forms a swellable jacket <NUM> at least partially covering the subsidiary jacket <NUM>.

Preferably, the swellable jacket <NUM> is at least <NUM>% more swellable than the subsidiary jacket <NUM>, and more preferably - at least <NUM>% more swellable. Optionally, the sensor <NUM> includes an insulative jacket <NUM> permeable to the fluid.

With reference to <FIG> and <FIG> and a fluid to be detected, the preferable embodiments include the first conductors <NUM> and <NUM> made of metals and/or alloys, the swellable conductors <NUM> and <NUM> - of swellable non-conductive materials with conductive admixture dispersed therein, and the subsidiary conductors <NUM> and <NUM> - of non-swellable or slightly swellable materials with conductive admixture dispersed therein, or of intrinsically conducting polymers. The subsidiary conductors <NUM> and <NUM> are preferably substantially non-swellable. However, if they swell on contact with the fluid, the swellability (a ratio of a volume of a swollen material to its volume in non-swollen state) of the swellable conductors <NUM> and <NUM> is preferably at least <NUM>% greater and, more preferably, at least <NUM>% greater than the swellability of the subsidiary conductors <NUM> and <NUM>. For the swellable conductors <NUM> and <NUM>, the specific conductivity in a swollen portion drops at least <NUM> times in comparison with the non-swollen state, and more preferably - at least <NUM> times. In other words, the electrical conductance of the portion is at least <NUM> times less when the portion in contact with the fluid than when absent contact with the fluid. More preferably, the electrical conductance of the portion is at least <NUM> times less than when absent contact with the fluid. Preferably, the electrical conductance of the subsidiary conductors <NUM> and <NUM> is at least <NUM> times lower than the conductance of the first conductors <NUM> and <NUM>. The conductance of the subsidiary conductors <NUM> and <NUM> is preferably in the range of <NUM> to <NUM> times the conductance of the swellable conductors <NUM> and <NUM> in the non-swollen state, and more preferably - in the range of <NUM> to <NUM> times. Preferably, the first conductor <NUM> or <NUM> serves as a central support wire, while other conductors form jackets at least partially surrounding the first conductor.

With reference to <FIG>, the operation of the sensor <NUM> is discussed using the sensor <NUM> as an example.

<FIG> provides equivalent schematics for normal operation of the sensor <NUM> when the particular fluid is absent. Numerals <NUM> to <NUM> indicate the four terminals <NUM>-<NUM> (<FIG>), respectively. Rs is a distributed resistance of the swellable conductor <NUM>. Rns is a distributed resistance of the subsidiary conductor <NUM>. Rc is a distributed resistance of the first conductor <NUM>.

<FIG> relate to the presence of a leakage caused by contact with the fluid targeted by the sensor somewhere in the central portion of the sensor. A portion <NUM> of the swellable conductor <NUM> is swollen because it has been infiltrated with the fluid. The schematics in <FIG> shows an increased resistance in the swollen portion. <FIG> relate to a physical break in the sensor. Numerals <NUM> to <NUM> indicate the four terminals <NUM>-<NUM> (<FIG>), respectively.

Providing electrical power to the sensor and measuring the resistance between the ends <NUM> and <NUM>, <NUM> and <NUM>, <NUM> and <NUM>, <NUM> and <NUM>, <NUM> and <NUM>, one can identify the presence and location of a leakage or break. The resistance of the conductor <NUM> being very low compared to the resistance of <NUM> and <NUM>, there would be no need for additional measures as <NUM> to <NUM> will give substantially the same result as <NUM> to <NUM>. However, measuring <NUM> to <NUM> (or <NUM> to <NUM>) can be used for better precision in the location determination. A simplified measuring procedure for determining the location of the leak is illustrated in <FIG>.

Compared to the conductance of the swellable conductor <NUM>, the conductance of the substantially non-swellable subsidiary conductor <NUM> is lower by several magnitudes, creating a weak parallel connection between the first conductor <NUM> and the swellable conductor <NUM>. The first conductor <NUM> exhibits high conductance, preferably at least <NUM> times higher than that of the subsidiary conductor <NUM>. The combination of the first conductor <NUM> having a high conductance and the substantially non-swellable subsidiary conductor <NUM> having a low conductance creates a hybrid non-swellable conductor, with electrical resistance of a constant and known value. Measuring the electrical resistance in the sensor <NUM> between terminals <NUM> and <NUM> is equivalent to connecting a measuring device to the terminals of the sensor <NUM> (<FIG>); and discriminating between leaks and breaks is achieved the same way.

The hybrid non-swellable conductor <NUM>&<NUM> allows additional features by incorporating terminals <NUM> and <NUM>. In particular, the length of the sensor can be determined by measuring the electrical resistance between the terminals <NUM> and <NUM>. Since the conductance of first conductor <NUM> is much higher than that of the second conductor <NUM>&<NUM> the resistance between the terminals <NUM> and <NUM> will not be affected by the status (alarm or normal) of the swellable layer <NUM>.

The local expanding of the swellable conductor creates a discontinuity in the distributed resistances network and can be advantageously used to locate a leakage along the sensor by measuring the electrical resistance between the terminals <NUM> and <NUM>, between <NUM> and <NUM>, and/or between <NUM> and <NUM>. In case of physical damage to the sensor, the location of a break can be determined by measuring the electrical resistance between the terminals <NUM> and <NUM>, and/or between <NUM> and <NUM>. The locations may be determined based on the Ohm Law using techniques known for resistor networks, or the sensor may be experimentally calibrated.

The aforedescribed sensors may be used in conditions where sensor may enter in contact with conductive media or non-target conductive fluids are naturally present, so nuisance alarms may be generated. Then the sensor needs a non-conductive coating permeable for the target fluid such as the jackets <NUM>, <NUM>, <NUM>, 660A, <NUM>, and that coating should provide electrical isolation between the sensor and the external solid particles or fluids. The isolative jacket may be swellable and/or elastic in order to allow the expansion of the swellable conductor underneath. Preferably, the elastic non-conductive overcoat is permeable for the target liquid but impervious to the water and other fluids that shall not be detected. In one embodiment, the non-conductive coating is made from the same swellable material as the one used for the manufacturing of the swellable conductors, such as conductors <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, and through the same manufacturing operation such as over- molding, extrusion/coextrusion, etc., but without adding conductive particles, or by using low concentration of conductive particles that do not create conductivity in the base material.

In one embodiment, the electrical connection between the swellable layer and the first conductor is made through openings in the insulation of the central conductor that are filled during the manufacturing process with a swellable material, and this creates regular "bridges" for the electrical current and thus the same features as with a non-swellable layer are obtained. With reference to <FIG>, a sensor <NUM> includes a swellable conductor <NUM>; suitable materials are the same as for the swellable conductor <NUM> (<FIG>). Adjacent to the swellable conductor <NUM> is an insulative layer <NUM> formed of an electric isolator and having gaps <NUM> filled with the swellable material thus connecting the swellable conductor <NUM> with the first conductor <NUM> which may be made of the same materials as the first conductor <NUM>. The sensor <NUM> optionally includes additional conductors <NUM> and a protective coating (not shown).

<FIG> illustrates equivalent schematics for the sensor <NUM>, wherein Rs - distributed resistance of swelling layer, Rns - resistances created by local contact between swellable layer and central conductor, and Rc - distributed resistance of central conductor.

<FIG> provides electrical schematics of an elongated sensor cable <NUM> for detection of non-conductive liquids or vapors that does not fall within the scope of the present invention.

The sensor cable <NUM> includes an elongated combination sensor with a swellable element <NUM>, and a resistor <NUM>. The elongated combination sensor has a proximal end and a distal end, and an inner portion therebetween. The combination sensor includes a first conductor extending from the proximal end to the distal end of the sensor and an elongated swellable conductor <NUM> extending from the proximal end to the distal end of the sensor, isolated from the first conductor in the inner portion of the sensor. At least a portion of the swellable conductor <NUM> is swollen when the portion is in contact with the fluid, and a conductance of the portion is at least <NUM> times less when the portion is in contact with the fluid than when absent contact with the fluid. With reference to <FIG>, the combination sensor may include a first conductor 120A, an isolator 125A, a swellable conductive jacket 140A, which is an embodiment of the swellable conductor <NUM>, and an optional elastic or swellable non-conductive jacket (not shown). The conductor 120A, isolator 125A, and swellable conductive jacket 140A have the same properties as the conductor <NUM>, isolator <NUM>, and the swellable conductive jacket <NUM> (<FIG>), respectively. With reference to <FIG>, the combination sensor may include a first conductor 320A, an isolator 325A, a swellable conductive jacket 340A, which is an embodiment of the swellable conductor <NUM>, and a protective elastic or swellable jacket 310A; the elements have the same properties as the conductor <NUM>, isolator <NUM>, the swellable jacket <NUM>, and the coating <NUM> (<FIG>), respectively. The first conductor shown as conductor 120A (<FIG>) or conductor 320A (<FIG>) is an isolated conductor; it may be isolated with an isolating jacket, such as the jacket <NUM> or <NUM>. The first conductor is an integral part of the combination sensor. The integral isolated conductor is a conductor that cannot be easily detached from the combination sensor. In case of mechanical damage of the elongated combination sensor, this conductor will be damaged as well, which allows to discriminate leaks from breaks. The inclusion of the resistor in parallel to the swellable conductor ensures that the conductance of the combination sensor is not completely lost when the swellable conductor is swollen when in contact with the target fluid. When the combination sensor is cut or broken, the connection to the termination resistor is lost as well and the total conductance is zero.

A passive termination resistor <NUM> with a resistance value of Rtm is connected locally in parallel to the swellable conductor <NUM> also referred herein as a sensor element <NUM>. A termination resistor <NUM> is electrically connected to both ends of the swellable elongated sensor <NUM>; to one end - through the first conductor which is an electrically isolated conductor mechanically integral with the sensor. The elongated sensor element <NUM> has a resistance value of Rs. The sensor <NUM> and resistor <NUM> form a composite resistor with an equivalent total resistance Rtot = Rs II Rtm, or Rtot = (Rs x Rtm)/(Rs + Rtm). Two conductors <NUM> and <NUM> may be wired through an optional two-wire jumper cable to a measurement device <NUM> used to determine the presence of the non-conductive fluid. Alternatively, the conductor <NUM> and/or <NUM> can be embedded into the swellable sensor element <NUM>. The device <NUM> may be a simple two-terminal ohmmeter or another suitable device.

In case of physical contact of the sensor element with non-conductive liquid or vapor <NUM>, the sensor starts swelling, its resistance increases.

Let the nominal resistance of the sensor element <NUM> at normal status be Rsn and Rtm be the resistance of the termination resistor <NUM>, so by measuring the equivalent resistance, the status of the sensor element <NUM> can be easily deducted from the following dependences:.

At the measurement side, a detection threshold can be defined for the leakage alarm, so nuisance alarms due to small contaminations can be avoided.

The resistance value of the terminal resistor <NUM> can be advantageously used to trim the sensitivity of the sensor element <NUM>. As the total resistance determined by the measuring device is equivalent to the parallel connection of two resistances, a lower value for the termination resistor <NUM> will limit the total resistance increase in case of swelling of the sensor element <NUM> where the conductivity is not completely lost (the presence of vapor or viscous liquid from previous contamination). In case of a contact with the target liquid, the swelling of the sensor element <NUM> will be such that its conductance will be completely lost and the total resistance Rsn II Rtm will go beyond the detection threshold of the measurement device.

Another useful feature of the termination resistor <NUM> is that it can compensate for the nominal sensor element resistance deviation due to manufacturing, temperature effects, residual contamination after detection of heavy hydrocarbons, etc. It is extremely useful in case of retrofit or replacement of an existing sensor system where the new sensor may present a nominal resistance different from the nominal resistance of the old sensor and the alarm system with fixed threshold may go into a leakage alarm or an in integrity alarm in case of break/short. The total resistance can be easily adjusted using the termination resistor <NUM>, which can be with fixed or adjustable resistance value. The terminal resistor <NUM> may also have other features, for instance a temperature coefficient with a different sign but same magnitude as that of the swelling conductive sensor element <NUM>, so it can compensate for the total resistance seen from ohmmeter should the sensor element resistance experience temperature dependence. Other compensation features can be achieved with different kinds of termination resistors.

The termination resistor <NUM> can be of any suitable kind, discrete film or wire wound resistor, or a distributed resistor made of high-resistance alloy wire, extruded conductive ceramic or plastic elongated element, etc. The use of elongated elements <NUM> and <NUM> with constant resistivity allows an automatic match of the value Rtm of the termination resistor <NUM> to the corresponding nominal resistance Rsn of the sensor element <NUM>, so the ratio Rtm to Rsn will remain the same with different lengths of sensor cable <NUM>.

The termination resistor <NUM> may be formed of any suitable combination of resistors connected in series, in parallel or in a combined series/parallel connection.

The termination resistor <NUM> can be embedded into a removable/replaceable end terminator, for easy testing and adjustment of the resistance of the element <NUM>. The end terminator may also include a series resistor and an optional switch for simulating leakage alarms without the application of fluids on the sensor cable.

The sensor cable may optionally contain other conductors for additional functions as power supply of measuring equipment, spare wires, combination of separate sensor elements for different target fluids, etc..

The value Rtm of the termination resistor <NUM> can be in the range of <NUM> to <NUM>,<NUM>,<NUM> times the nominal resistance Rsn of the sensor element <NUM>, with preferred a range of <NUM> to <NUM>,<NUM>.

The use of only two terminals for a sensor element allows simplified multiplexing along a sensor cable as shown in <FIG>. One of the terminals of each sensor is connected to a common reference, in some instances an available ground potential can be used.

<FIG> illustrates electrical schematics of a multiplexed multi-section sensor cable <NUM> for detection of non-conductive liquids or vapors. In the multi-section sensor cable <NUM>, the conductor <NUM> serves as a common, reference conductor for all sectional sensors. Each sensor element <NUM> (<NUM><NUM>, <NUM><NUM>,. , <NUM>N) may be an embodiment of the sensor <NUM> (<FIG>), an embodiment illustrated in <FIG> or <FIG>, or only the swellable conductor <NUM> (<FIG>). It has a separate terminal resistor <NUM> (<NUM><NUM>, <NUM><NUM>,. , <NUM>N) and electrical connection to the ohmmeter <NUM> through the common conductor <NUM>, as first terminal, and a connection through an individual conductor <NUM> (<NUM><NUM>, <NUM><NUM>,. , <NUM>N), as a selectable second terminal. The multiplexor <NUM> connects one by one the individual sensor sections to the ohmmeter <NUM>. In other words, the sensor cable <NUM> includes a multiplexer <NUM>, a shared conductor <NUM>, and a plurality of sensor cables, each including a sensor <NUM> and a resistor <NUM> and having a first terminal and a second terminal, the first terminals are connected to the shared conductor <NUM>, the second terminals each connected to an individual conductor <NUM>, and the individual conductors <NUM> are multiplexed at the multiplexer <NUM>. The sensor <NUM> may be used for detection of conductive fluids, if coated with a protective coating which acts as an electrical isolator.

Other multiplexing structures are possible, for instance using simple diodes very efficient matrix multiplexing can be built for an economic multi-sensor topology.

The sensor cables <NUM> and <NUM> contain only passive parts. They are durable and can withstand exposure to high-energy electric pulses without damage. The use of elongated sensors and sensor cables provide an efficient way for monitoring pipes, tanks, generators, etc., allowing for detection of leaking products from any point of the monitored equipment.

The aforedescribed sensors and sensor cables may be used as follows.

Large storage tanks may leak through corroded walls or tank bottom. Continuous monitoring based on leakage detection system is used in order to prevent large releases of hazardous fluids in the environment and loss of valuable product. One of the most frequently used detection systems is based on discriminating sensor cables that detect the physical presence of hydrocarbons or other target fluids while ignoring the water. Very often, during maintenance or normal operation, small quantities of hydrocarbons are released in the immediate vicinity of the tank and are absorbed by the soil. These residues are not considered as leaks but when they enter in contact with the sensors, a nuisance alarm may be generated and then the sensor has to be cleaned or replaced. The proposed sensors and sensor cables eliminate the frequent nuisance alarms by providing indication of the size of the contaminated sensor portion and straight-forward implementation of adjustable alarm threshold.

Leaking products from petrol stations may quickly contaminate the environment, damage the adjacent properties, and pose severe risk to the human life. Timely leakage detection of unwanted releases is an important part in the monitoring of such facilities. For instance, a leaking fuel dispenser may quickly cover a large area and constitutes a severe fire hazard. A leaking underground storage tank may contaminate the ground water and poison the soil of the neighboring properties. Reliable detection is an important part of the safe operation of petrol stations. During refueling, small quantities of liquid hydrocarbons are often released and may enter in contact with the sensors generating a nuisance alarm. These nuisance alarms will impact the normal operation of petrol stations. The proposed sensors and sensor cables eliminate the frequent nuisance alarms by providing indication of the size of the contaminated sensor portion. Insignificant quantities of products may be ignored while providing a warning about the contamination of the sensor.

It is practically impossible to supervise pipeline sections crossing water bodies by patrolling or aerial surveillance. Leaking pipelines release product that will float on the surface of the water and may quickly contaminate drinking water sources and wildlife habitat. Similar threats are found in harbors, marinas, etc. Hazardous fluid release in the water may pose a severe risk for the navigation, the human life and the environment. The water bodies may be contaminated by residual hydrocarbons from navigation, recreational activities, etc. A thin film of hydrocarbon is formed on the water surface and this film will trigger a nuisance alarm by the polymer-absorption sensor. The proposed novel sensors and sensor cables allow to set a minimum thickness of a hydrocarbon film which, if in contact with the hydrocarbons, that will trigger an alarm for a very reliable detection of large release of hazardous fluids.

A variety of liquid organic chemicals (e.g., oils, crude oil, refined petroleum products, gasoline, kerosene, organic solvents, and the like) are transported through buried pipelines. Leaks from these tanks and pipelines can contaminate ground water and cause extensive environmental damage. Further, leaks are difficult to detect and often are not detected until extensive environmental damage has already occurred. One method of detection has been to run a cable adjacent to the underground pipeline. However, very often and especially in urban environment, small quantities of hydrocarbons from other sources, such as vehicle leaks, motor or hydraulic oil pollution from pipeline maintenance, residual hydrocarbons from pipeline installing machines, etc., may enter in contact with the sensor cable and trigger a nuisance alarm leading to very costly excavation and leakage search. The proposed elongated sensors and sensor cables eliminate the false alarms by providing indication of the size of the contaminated sensor portion. Insignificant quantities of products may be ignored while providing a warning about the contamination of the sensor.

Advantageously, several elongated sensors or sensor cables, e.g. used for different fluids, may be used together. With reference to <FIG>, a bundled sensor cable may include a first sensor <NUM> for detection of a first group of fluids, a second sensor <NUM> for detection of a second group of fluids, optional return conductors <NUM>, and a protective braid <NUM> made of an insulating material permeable for the fluids of both groups.

Claim 1:
An elongated sensor (<NUM>, <NUM>) having a proximal end (<NUM>) and a distal end (<NUM>), and an inner portion (<NUM>) therebetween, for detecting the presence of a fluid, the sensor comprising:
a first conductor (<NUM>, <NUM>) extending from the proximal end (<NUM>) to the distal end (<NUM>) of the sensor (<NUM>, <NUM>); and,
a second conductor (<NUM>, <NUM>&<NUM>) extending from the proximal end (<NUM>) to the distal end (<NUM>) of the sensor (<NUM>, <NUM>), isolated from the first conductor (<NUM>, <NUM>) in the inner portion (<NUM>) of the sensor (<NUM>, <NUM>), comprising:
a swellable conductor (<NUM>, <NUM>), wherein at least a portion of the swellable conductor (<NUM>, <NUM>) is swollen when the portion is in contact with the fluid, and wherein a conductance of the portion is at least <NUM> times less when the portion is in contact with the fluid than when absent contact with the fluid, and
a subsidiary conductor (<NUM>, <NUM>) in direct contact with the swellable conductor (<NUM>, <NUM>) in the inner portion of the sensor (<NUM>, <NUM>) and in electrical contact with the first conductor (<NUM>, <NUM>) at the distal end (<NUM>) of the sensor (<NUM>, <NUM>), the swellable conductor (<NUM>, <NUM>) is at least <NUM>% more swellable than the subsidiary conductor (<NUM>, <NUM>), and a ratio of the conductance of the subsidiary conductor (<NUM>, <NUM>) to the conductance of the swellable conductor (<NUM>, <NUM>) in absence of contact with the fluid is in the range of <NUM> to <NUM>;
wherein the first conductor (<NUM>, <NUM>) is at least partially covered with an isolative jacket (<NUM>) for electrically isolating the first conductor (<NUM>, <NUM>) from the second conductor (<NUM>, <NUM>&<NUM>) in the inner portion (<NUM>) of the sensor (<NUM>, <NUM>).