GB2572130A

GB2572130A - System and method for detecting and locating dielectric variations

Info

Publication number: GB2572130A
Application number: GB1801496.9A
Authority: GB
Inventors: Cannazza Giuseppe; De Benedetto Egidio; Crowther Jonathan; Nosko Vladimir; Maria Cataldo Andrea
Original assignee: Sensor Group Ltd
Current assignee: Sensor Group Ltd
Priority date: 2018-01-30
Filing date: 2018-01-30
Publication date: 2019-09-25
Also published as: GB201801496D0; WO2019150105A1

Abstract

A system for detecting and locating dielectric variations caused by liquids using time domain reflectometry (TDR). The system comprises a sensing element 1, a sensing element head (8, fig 1), a measuring unit (2, fig 1) and a processing unit (3, fig 1). The sensing element head (8, fig 1) is connected to the sensing element 1 and has a coaxial section 10, a sensing section and a nonconductive shield 11 enclosing both the coaxial section 10 and the sensing section. The sensing section comprises a first wire conductor operable to act as a signal conductor 16, wherein the sensing section is alongside the coaxial section 10 and spaced apart from the coaxial section 10 by an intermediate portion. The coaxial section 10 comprises an inner conductor 13, an insulating dielectric 14, and an outer shield conductor 15.

Description

System and method for detecting and locating dielectric variations

The present invention relates to a system and a method for detecting and locating dielectric variations, and in particular to using reflectometry to detect and locate dielectric variations caused by liquids in proximity of a sensing element.

Time domain reflectometry (TDR) can be used for monitoring purposes in many different applications. TDR-based monitoring solutions rely on measurement of a material’s dielectric variations, for detecting and locating faults, anomalies, liquid leaks or other variations caused by impedance changes occurring along a probe ora sensing cable. Such impedance changes can be caused, for example, by local variations of the dielectric permittivity of the medium through which the TDR signal propagates or by local deformation of the geometry of the propagating structure. As a consequence, the reflected TDR signal can be associated to the aforementioned variations and to the corresponding distance length.

Several patents that relate to exploiting TDR use a sensing cable with a coaxial configuration, in which the space between the outer conductor and the inner conductor is filled with a liquidabsorbent material. The dielectric variation is sensed when the liquid permeates the absorbent material. For example, in US5410255, a method and apparatus for detecting and locating fluid leaks, particularly liquid leaks, and for determining whether the leaking liquid being detected is a non-conductive liquid (e.g. a hydrocarbon) or a conductive liquid (e.g. water) utilizes a composite detection cable having a pair of insulated conductors and a pair of uninsulated conductors. Pulses are applied to the insulated conductors and leaks are detected and located through TDR measurement. Then, the resistance between the uninsulated conductors is measured to determine whether or not the leak is conductive.

In US5134377, a leak detection system and method are disclosed in which an electrical circuit uses TDR techniques to monitor one or more leak detection cables for impedance changes which are caused when a cable is contacted by a leaking liquid. Also in this case, a coaxial configuration is used for the sensing cable, and at least one layer of the coaxial cable is fluid permeable.

In US5015958, elongate sensors comprising conductive polymers, in which an event (such as a leak) is detected when the event causes two conductors to become electrically connected, thus creating a system in which the connection point can be located by measuring the potential drop from one end of one of the conductors (called the locating member) to the connection point. Also, this system employs a coaxial cable configuration, although it does not use TDR.

In US6696974 B1, a cable composed of material capable of conducting light, sound, or electricity is inserted by appropriate means into a material to be examined. The objective is to detect displacement or deformation of the material by detecting displacement and deformation of the sensor cable system. Monitoring is conducted by attaching an appropriate test instrument to said cable that utilizes time domain reflectometry techniques. Also in this case, the invention resorts to a coaxial cable configuration for use with electrical time domain reflectometry.

In US 6956381 B2, a flexible probe for TDR-based soil moisture content measurements is described. The method uses flat, flexible, waveguides attached to a flexible sleeve filled with a filling material which press the flexible waveguides against an irregularly shaped interior borehole wall. This method should allow measuring soil water content at different depths from the surface, but it requires the multi-level installation of soil moisture probes to any desired depth from land surface (i.e., the used probes are in fact local probes; hence, a multitude of probes must be installed to retrieve a soil moisture content profile).

In US6114857A, a system and method for in-situ monitoring of corrosion in a conduit which carries fluids that have corrosive effects on the materials utilized for the conduit and/or equipment disposed in the conduit are describe. A cable of sufficient length having a conductor that is susceptible to the corrosive effects of the fluids in the conduit is deployed along a length of the conduit. The conductor is exposed to the fluid continuously or at selected spaced apart locations. The distance of each of the exposed locations from an accessible end is known. The cable may be a single conductor cable or a twisted pair of wires, each having a known impedance per unit length.

The cable is exposed to its surrounding environment continuously or at selected spaced apart locations. Also, the cable terminates at a known end. Nevertheless, as described above, most of these patents resort to an elongated sensing cable with coaxial configuration, wherein the space between the outer and the inner conductors is filled with a liquid-permeable material (as in US5134377) or the cross-sections of the sensor cable is changed due to external pressure.

Some of the aforementioned patents employ a single-conductor configuration or to a twistedpairconfiguration. In all of the systems and methods described in these patents, however, it is always necessary to know the length of the sensing cable. Additionally, the use of a coaxial configuration for dielectric sensing purposes means that the external metallic shield and the structural layers interposed between the two conductors must be perforated or permeable in order to allow the penetration of the liquid or material to be sensed. The adoption of the coaxial configuration as a dielectric sensing cable means that its basic structure must be modified, for example by including some multiple permeable layers within the construction of the cable, which consequently, complicates the fabrication process and increases related costs.

In addition, due to the wide variety of liquids or materials to be sensed it is necessary to construct a wide variety of slightly different cable configurations which are used in one or another situation (e.g. cables that are specific to the detection of: water; or, certain chemicals I petrochemicals). Furthermore, once leakage has been detected by such cables the affected area of the cable requires a “physical reset” achieved by cleaning, drying, or insertion of a new section of cable, which adds further cost and complication to the operation and maintenance of any associated system.

The necessity for a “physical reset” of sensing cables has also precluded their use in situations where their very burial causes a false positive (e.g. detection of water when buried in the ground occurs due to its burial in the ground) and where the need to exhume a cable for resetting where this would add further disruption and cost to rectification of the item being monitored.

Several patents also report the ability to detect leaks from containment or fluid retaining structures; however these all try to exploit the electrically non-conductive nature of the lining material. This is achieved by various means using either point sensors, sheet sensors, or even cable sensors all with varying degrees of success but always limited to the monitoring of containments within non-electrically conductive lining systems limiting their deployment to situations where plastic and bituminous geomembranes, or liquid applied coatings are also deployed. This means that it was hitherto impossible to monitor/detect and locate leakage from rubber geomembranes, clays, bentonites, concretes and metals which are all electrically conductive for the purposes of this type of leak detection and location.

The object of the present invention generally relates to an apparatus, applications and to the relevant methodology for detecting and locating dielectric variations caused by liquids in proximity of elongated sensing elements.

According to the present invention, there is provided a system and method as set forth in the appended claims. Other features of the invention will be apparent from the dependent claims and the description, which follows.

According to a first aspect of the invention, there is provided a system for detecting and locating dielectric variations caused by liquids using time domain reflectometry, TDR, comprising a sensing element, a sensing element head, a measuring unit and a processing unit, wherein the sensing element head is connected to the sensing element, the sensing element having a coaxial section, a sensing section and a non-conductive shield enclosing both the coaxial section and the sensing section, wherein the sensing section comprises a first wire conductor for acting as a signal conductor, and wherein the sensing section is alongside the coaxial section and spaced apart from the coaxial section by an intermediate portion, and wherein the coaxial section comprises an inner conductor, an insulating dielectric, and an outer shield conductor,

The sensing element may be capable of detecting any liquid type. This provides the advantage that only one form of sensing element is required. The system may be capable of detecting and locating dielectric variations caused by liquids in proximity to but not necessarily in contact with the sensing element.

The system may be capable of detecting leakage from electrically conductive containment materials, without the need for the addition of non-conductive waterproofing geomembranes, or liquid applied coatings. This is because it is not necessary in the case of the invention to detect the flow of liquid through a material because the leak is detected by reference to changes in the environment into which the leakage flows where the sensing element has been deployed. Due to the nature of the present invention this means that monitoring, detection and location is achievable whether the containment material is electrically conductive or not.

The sensing element may be an elongate element. The sensing element may be at least several metres long. The sensing element may be at least one kilometre long, or may be several kilometres long. The sensing section may be substantially parallel to the coaxial section.

The outer shield conductor may act as a reference ground conductor for the sensing section. The coaxial section may be a distance-calibrator for TDR measurements and may be for determining the length of the installed sensing element. The coaxial section may be used to transmit data. The inner conductor of the coaxial section may be used as a measuring conductor. The functionality of the coaxial section may be manually selectable, by connecting the coaxial section using male-female connectors, and/or by hardwiring the coaxial section to adjacent sensing elements. The functionality of the coaxial section may be remotely selectable, for example by automation or direct remote control over a network of devices connected by the coaxial section by way of multiplexors provided within a measuring unit. Alternatively, the coaxial section may be used only for distance calibration.

The sensing section may comprise a second wire conductor, operable to act as a ground conductor. The second wire conductor may be alongside the first wire conductor, and the second wire conductor may be insulated from the first wire conductor. The second wire conductor may be substantially parallel to the first wire conductor. The feature of the second wire conductor advantageously enables the coaxial section to be used for data transmission or network interconnectivity, which enables a permanent monitoring network to be provided where conductors of the coaxial section allow communication between permanently installed measuring units connected to sensing elements without the need for subscription data services provided by mobile telecommunication networks, or satellite.

The non-conductive shield may be semi-rigid. The non-conductive shield may be formed of a plastics material. The non-conductive shield may comprise a region with a flattened crosssectional profile in an intermediate portion between the sensing section and the coaxial section.

The sensing element may comprise an external absorbent material enclosing the coaxial section, the sensing section and the non-conductive shield. The absorbent material may be a non-woven geotextile or a sponge. The absorbent material may facilitate a local concentration of the liquid and may simultaneously highlight the TDR response variation caused by lowdielectric liquids flowing from the external medium towards the sensing element. For example, the low-dielectric liquid may be oil spilled from a leaking pipe, and the external medium may be soil.

When the external absorbent material is not present, the system may be used for detecting and locating water-like liquids with higher dielectric permittivity.

The sensing element head may be connected to an end of the sensing element and may comprise an ID device for generating an identification code of the sensing element. The identification code may be a unique identification code. The ID device may thereby allow a univocal association between the code and any information about the sensing element, for example length, geotagging, locations, installation date, etc.

The sensing element head may comprise a three-pin sensing element connector for connecting to the inner conductor of the coaxial section, the outer shield conductor of the coaxial section, and the first wire conductor of the sensing section respectively.

The measuring unit may comprise a power supply, a TDR module comprising an electromagnetic signal generator and a sampling and acquisition device. The gain and width of an electromagnetic signal generated by the electromagnetic signal generator may be tuneable, for example according to a distance of the sensing element to be analysed. The generated signal may be in the range of radio-microwave frequencies. The power supply may be an internal battery or an external solar panel, or other power supply means. The sampling and acquisition device may sample and acquire the reflected signal.

The measuring unit may comprise a electronic module for managing the components of the system. The measuring unit may interface the hardware to the processing unit through a data communication protocol, so as to implement a measurement method.

The measuring unit may further comprise an electronic module head. The electronic module head may permit switching and connection with the sensing element head. The electronic module head may comprise switch means for switching the propagation of a TDR signal so that the TDR signal propagates along the coaxial section or the sensing section. The switching means may comprise a first switch connectable to the coaxial section and a second switch connectable to the sensing section.

The electronic module head may comprise an ID reading chip for reading the ID code generated by the ID device.

The processing unit may be an industrial computer, a PLC, PC, laptop, smartphone, tablet or similar. The processing unit may be for processing acquired data through the procedure described in the measurement method and managing control software through a data communication protocol.

According to another aspect of the invention, there is provided a sensing element for a TDRbased system of detecting and locating dielectric variation. The sensing element may comprise any of the features described above in relation to the sensing element of the first aspect of the invention.

According to another aspect of the invention, there is provided a TDR-based method for detecting and locating dielectric variations, comprising providing the sensing element with a sensing head inside a material of which dielectric variations are to be detected, located or monitored, determining a length of the sensing element, obtaining a reference TDR output, acquiring a TDR output along the sensing element, and identifying a dielectric variation based on a comparison of the reference TDR output and the acquired TDR output.

The distal end of the sensing element may be left open or may be sealed with a protective cap. Alternatively, the distal end may be permanently or temporarily connected to another sensing element, either directly, for example by plugs or splices, or through a measuring unit, which may provide a boosting of an incoming TDR signal, or may provide communication and switching that may achieve a network of measuring units. The network of measuring units may be capable of varying the aggregate length of the sensing element by connection of a plurality of sensing elements together. The network of measuring units and sensing elements may be capable of communication with a central control entity.

The sensing element length may be unknown. The determining the length of the sensing element may comprise determining, through TDR measurement on the coaxial cable, the apparent length of the coaxial section. The method may comprise propagating a TDR signal along the coaxial section. Because the propagation velocity of the TDR signal in the coaxial section is constant and it only depends on its a-priori known constitutive and geometric characteristics (i.e. cross-sectional geometry and the dielectric permittivity of the insulating dielectric), it is possible to accurately evaluate the actual length of the coaxial section which is the same of the sensing element.

The obtaining the reference TDR output may comprise carrying out a TDR measurement on the sensing section in a normal operating condition wherein no dielectric variations are present.

The acquiring a TDR output may comprise carrying out a TDR measurement on the sensing section when dielectric variations may be present. Carrying out a TDR measurement on the sensing section may comprise propagating a TDR signal along the sensing section.

The method may comprise determining a location of the dielectric variation based on the determined length of the sensing element and the comparison of the reference TDR output and the acquired TDR output.

The method of measurement employed by the present invention enables the deployment of a common sensing element in a plethora of circumstances whereby the measurement of the environment can provide information about of the efficacy of the process under test, or the change of an environment due to infiltration.

The system and method according to the invention may be applied to: leak detection and location; soil water content monitoring; heap leach chemical distribution in the mining industry; monitoring, detection and location of changes in pollutant levels appearing in the ground; and in monitoring structures for damp, water or other liquid infiltrations.

For example, the system and method according to the invention may be used in heap leach mining for monitoring chemicals placed onto leach pads for the purpose chemical extraction of precious and semi-precious minerals. Heap leach mining requires the spreading of chemicals onto a formation of crushed rocks. The chemicals dissolve the desired mineral (e.g. cyanide dissolves gold, copper and uranium) from the rocks, then due to the effect of gravity (having combined themselves with the mineral in question) the solution flows to the bottom of the formation where it is collected and processed to reclaim the mineral from the solution. The cost and environmental impact of this type of mining is directly proportional to the efficiency of the leaching and collection processes. The leaching process can be improved by the deployment of sensing elements according to the invention within the formation to ensure that the optimal amount of chemicals is distributed and maintained within the formation.

The system and method according to the invention may be used in agriculture by monitoring soil water content in agricultural cultivations, The soils may be monitored to ensure even distribution of exactly the right quantity of water, to this end the present invention can be deployed within automated system to add further water to specifically to zones where dryness is evident whilst avoiding waste of water on zones that remain sufficiently humid for the specific requirement of the plant life in question.

Conversely the normal environmental conditions of the earth / ground can be monitored using the system and method according to the invention for ongoing normality where the presence of particular substance would be dangerous or a hindrance to the use of that land, or where it would be advantageous to prove that contamination has not taken place for example adjacent to a particularly hazardous process.

The system and method according to the invention may be used in structures and buildings where the presence of damp I rising damp; water ingress; and/or other liquid infiltrations would be beneficial to prevent damage to the structure building itself or to protect its contents I inhabitant from the impact of such ingress.

The system and method according to the invention may be used in storage tanks (water, fuels, chemicals) where the sensing element can wrapped around the tank in concentric rings where they can monitor, detect and locate leakage from tanks made from any material whether buried or above ground.

A further application of the system and method according to the invention includes monitoring, detecting and locating leaks in containment facilities, many of which are constructed either on or within the earth and being lined with a various materials either singularly or as a plurality (plastic geomembrane, bituminous geomembrane, liquid applied membrane coatings, rubber geomembrane, clay, bentonite, concrete, metal etc) and which are used for: storage tanks (water, fuels, chemicals); ponds; dykes; embankments; dams; canals; tailings; and/or leach pads.

The system and method according to the invention may be used in monitoring, detecting and locating leaks in new pipe installations carrying any liquids whether buried, placed on the ground, or suspended above the ground and/or existing pipe installations carrying any liquids whether buried, placed on the ground, or suspended above the ground.

The system and method may be capable of detecting leakage from pipes installed underwater (which may be below a water table level, rather than below free water) by enclosing the pipe and the sensing element in one-way moisture transfer fabric which would allow the flow from the leakage towards the surrounding water, but not the reverse flow. This would make the sensing element sensitive only to the liquid leaking from the pipe and insensitive to the surrounding water or water table. The above system, wherein a pipe-to-be-monitored and the sensing element are enclosed in a one-way moisture transfer fabric, which makes the sensing element sensitive only to liquid leaking from the pipe and insensitive to possible surrounding water, which may be water forming part of a water table..

The sensing element may also be installed inside sewer pipes and it can be used to detect clogging of the pipes by detecting dielectric variations due to the presence of materials other than liquid sewage.

The sensing element may also be installed inside pipes, in which case it may be used to detect clogging of the pipes by detecting dielectric variations due to the presence of unwanted materials other than liquid, such as sewage sediments, porous-like materials, waste-materials and/or fatbergs etc.

For a better understanding of the invention, and to show how embodiments of the same may be carried into effect, reference will now be made, by way of example only, to the accompanying diagrammatic drawings, in which:

Figure 1 shows a system for detecting and locating dielectric variations;

Figure 2 shows a section view of a first example of a sensing element of the system of figure 1;

Figure 3 shows a perspective, partially cut-away view of the first example of the sensing element;

Figure 4 shows the components and connections of an electronic module head and sensing element head of the system of figure 1; and

Figure 5 shows a section view of a second example of a sensing element.

As depicted in Figure 1, the system for detecting and locating dielectric variations caused by liquids comprises a sensing element 1; a sensing element head 8; a measuring unit 2; and a processing unit 3.

In turn, the measuring unit 2 comprises a TDR module 4; a power supply module 5; an electronic module 6 for managing the system (optionally with possibility of storing the acquired data in a database 9) and an electronic module head 7.

The TDR module 4 may be a commercial portable unit which comprises a signal generator (typically a voltage step-like or a pulse, having an equivalent bandwidth in the range of radiomicrowave frequencies) and a sampling and acquisition device. The pulse generator generates an electromagnetic pulse signal whose gain and width can be tuned according to the sensing element distance to be analysed. The sampling and acquisition device samples and acquires the reflected signal.

The processing unit 3 may be an industrial computer, a PC, laptop, smartphone, tablet or similar. The processing unit 3 processes the acquired data through dedicated control software. The power supply module 5 may be an internal battery, or an external power source such as a solar panel. Finally, the electronic module 6 manages all the components of the system, to interface the measuring unit 2 to the processing unit 3 and to permit switching and connection with the sensing element head 8.

A first example of the sensing element 1, shown in figures 2 and 3, is an elongated element. The cross-sectional configuration of the sensing element 1 is depicted in Figure 2 (dimensions not to scale). The sensing element 1 comprises a coaxial section 10, a sensing section parallel to and separated from the coaxial section 10, and an external non-conductive semirigid shield 11 enclosing both the coaxial section 10 and the sensing section. The sensing element 1 in figure 2 also comprises an external absorbent material 12, however this feature is optional, and other examples of sensing elements may not include this feature.

The coaxial section 10 comprises an inner conductor 13, an insulating dielectric 14, and an outer shield conductor 15. The coaxial section serves as a distance-calibrator for TDR measurements.

The sensing section comprises a wire conductor acting as a signal conductor 16. The signal conductor 16 may be a triple-wire conductor. The outer shield conductor 15 of the coaxial section 10 acts as reference ground conductor for the sensing section.

The external non-conductive semi-rigid shield 11 has a cross-sectional profile having a reduced flattened thickness in the intermediate portion between the two sections, which may form lobes at opposite sides of the intermediate portion. The external non-conductive semirigid shield 11 is formed of a plastics material.

The external absorbent material 12 may be a non-woven geotextile or a sponge. The coaxial section 10, sensing section and external semi-rigid shield 11 may be enclosed by the absorbent material 12.

Fig. 4 shows the components and connections of the electronic module head 7 and of the sensing element head 8. As detailed in Fig. 4, the sensing element head 8 comprises a threepin sensing element connector 17 and an ID device 19 generating a unique identification code. The electronic module head 7 includes two switches 22a, 22b and an ID reading chip 18, wherein the ID reading chip 18 reads the unique ID code generated by the ID device 19.

The sensing element head 8 allows a twofold connection. First it allows the connection between the sensing element 1 and the electronic module head 7 through three connection pins (i.e. one for connecting the inner conductor 13 of the coaxial section 10, one for connecting the outer shield grounded connector 15 and one for connecting the signal conductor 16). Secondly, it allows the connection between the ID device 19 and the ID reading chip 18, through two separate pins 20 and 21, for connection to the power and ground, respectively.

The TDR-based measurement method employs the afore-described system and includes four main steps being initialization, distance calibration, reference measurement and control measurement.

The initialization step comprises:

a) Installing the sensing element 1 equipped with the sensing element head 8 inside the material whose dielectric variations are to be detected or monitored. For example, in the application related to leak detection in pipes, the sensing element 1 can be placed parallel to the pipe whose leaks must be detected or monitored. The sensing element length may be unknown and its distal end may be left open or sealed with a protective cap.

b) Connecting the sensing element head 8 to the electronic module head 7 and the measuring unit 2 to the processing unit 3. The ID reading chip 18 reads the unique ID code generated by the ID device 19. The ID code, which is associated to the sensing element 1, is acquired by and stored in the processing unit 3. Therefore, any information about the sensing element, such as specific characteristics, geo-tagging, location, installation date, etc., is associated to the unique ID code generated by the ID device 19.

Distance calibration leads to the determination of the elongated sensing element 1 length, which can be also in the order of the kilometres. To this end, the switch 22a is positioned to contact the inner conductor 13 of the coaxial section 10. In this configuration, a TDR signal is propagated along the coaxial section 10. From the TDR measurement output, the apparent length of the coaxial section 10 is determined as the distance between the two reference points associated to the element connector 17 and to the distal end of the sensing element 1, respectively. Because the propagation velocity of the TDR signal in the coaxial section 10 is constant and it only depends on its a-priori known constitutive and geometric characteristics (i.e. cross-sectional geometry and the dielectric permittivity of the insulating dielectric 14), it is possible to accurately evaluate the actual length of the coaxial section 10 which is the same of the sensing element 1. This distance calibration procedure is practically performed through the multiplication between the a-priori known propagation velocity factor and the apparent length of the coaxial section 10 (according to the state- of-the-art literature related to TDR). This value is stored and associated to the ID code previously generated.

The reference measurement step relates to TDR measurement along the sensing section of the sensing element 1 for acquiring and storing a TDR output corresponding to a normal operating condition; i.e. no dielectric variations are present in the medium portion along sensing element 1. To this end the switch 22b is positioned to contact the signal conductor 16 of the sensing section. In this configuration, the outer shield conductor 15 acts as a reference ground for the signal conductor 16 and a TDR measurement is carried out. This data is stored in the processing unit 3, associated with the ID code and used as a reference to which compare the subsequent TDR data performed in the control measurement step.

The control measurement step relates to TDR measurement along the sensing section of the sensing element 1 for acquiring and storing a TDR output corresponding to the possible presence of dielectric variations in the medium portion along sensing element 1. In case some dielectric variations are present, the TDR measurement output will exhibit local variations with respect to the reference data previously acquired in step 3 (typically local minima in the TDR displayed measurement) and, thanks to distance calibration procedure performed in the previous step, the actual distances corresponding to these dielectric variations can be accurately determined by comparing the reference and control measurement data.

It is worth noting that the presence of an external absorbent material 12 in the sensing element 1 has twofold function. On one hand, it facilitates a local concentration of the liquid and, consequently, the corresponding effect of the dielectric variation can be emphasized in the TDR control measurement. As an additional effect, when the sensing element is installed or buried in a medium different from air, the absorbent material, which has a relative dielectric permittivity close to that of the air (i.e. approximately lower than 1.5), acts also as a physical separator between the sensing section portion and the external medium surrounding the sensing element. As a consequence, the TDR detection of the dielectric variations caused by low-dielectric liquids (such as oil, petroleum, etc. with a relative dielectric permittivity of approximately 2), can be more accurately detected. Should the absorbent material not be present, the effect introduced by low- dielectric materials would be masked by the dielectric effect of the medium (such as soil, sand, etc.) having a similar dielectric permittivity value.

On such basis, in another example of a sensing element, the sensing element can be realized without the external absorbent material 12 and thus the system can be used for detecting and locating water-like liquids with higher dielectric permittivity.

Furthermore, in another example of a sensing element 101, shown in Figure 5, to increase the sensitivity of the sensing element with or without any external absorbent material, the sensing section comprises two parallel conductors 116, 122 mutually insulated and distanced through an intermediate portion with a reduced flattened thickness. One of the conductors 116, 122 may be for the signal and the other of the conductors 116, 122 for the ground reference. The addition of a further conductor 116 advantageously enables the coaxial part 110 to be used after the initial set up process (where it measures the length of the sensing element) for data transmission which enables a permanent monitoring network to be provided where conductors 113, 115) of the coaxial part will allow communication between the permanently installed measuring units connected to sensing elements. This may reduce or eliminate the need for mobile data, GSM, WIFI, or other separate wired or wireless network (or internet) connection. Multiple sensing elements may be connected together to form a daisy-chain type of network architecture, or may employ other network geometries as may be suited to the application of the invention. The network of sensing elements may include measuring units and may include TDR modules and may be installed inline, connected together by the coaxial parts. The network of sensing elements may comprise multiplexor switching devices to switch the functionality of the coaxial parts between discrete lengths of the sensing element.

The sensing element itself may be installed during the original construction irrespective of the application in question, usefully however the sensing element may be pulled inside a pipe during a slip lining process whereby the sensing element can remain between the existing pipe and the slip lining, providing monitoring of the effectiveness and continued integrity of the existing pipe and its slip lining.

Underground pipes that are located in cold climates, often have a pre-existing heating element installed wrapped around the pipe. It is possible by heating the element and then surveying using infra-red camera, to assess the length of the cable by virtue of its rake around the pipe and the diameter of the pipe itself. This information would permit the use of the heating element as a sensing element when connected correctly to the measuring unit described herein.

Attention is directed to all papers and documents which are filed concurrently with or previous to this specification in connection with this application and which are open to public inspection with this specification, and the contents of all such papers and documents are incorporated herein by reference.

All of the features disclosed in this specification (including any accompanying claims, abstract and drawings), and/or all of the steps of any method or process so disclosed, may be combined in any combination, except combinations where at least some of such features and/or steps are mutually exclusive.

Each feature disclosed in this specification (including any accompanying claims, abstract and drawings) may be replaced by alternative features serving the same, equivalent or similar purpose, unless expressly stated otherwise. Thus, unless expressly stated otherwise, each feature disclosed is one example only of a generic series of equivalent or similar features.

The invention is not restricted to the details of the foregoing embodiment(s). The invention extends to any novel one, or any novel combination, of the features disclosed in this specification (including any accompanying claims, abstract and drawings), or to any novel one, or any novel combination, of the steps of any method or process so disclosed.

Claims

1. A system for detecting and locating dielectric variations caused by liquids using time domain reflectometry, TDR, the system comprising a sensing element, a sensing element head, a measuring unit and a processing unit, wherein the sensing element head is connected to the sensing element, the sensing element having a coaxial section, a sensing section and a non-conductive shield enclosing both the coaxial section and the sensing section, wherein the sensing section comprises a first wire conductor operable to act as a signal conductor, wherein the sensing section is alongside the coaxial section and spaced apart from the coaxial section by an intermediate portion, and wherein the coaxial section comprises an inner conductor, an insulating dielectric, and an outer shield conductor,

2. The system according to claim 1, wherein the sensing section further comprises a second wire conductor, operable to act as a ground conductor, the second wire conductor being alongside the first wire conductor, and the second wire conductor being insulated from the first wire conductor.

3. The system according to claim 1 or claim 2, wherein the non-conductive shield is semirigid.

4. The system according to any preceding claim, wherein the non-conductive shield comprises a region with a flattened cross-sectional profile in the intermediate portion between the sensing section and the coaxial section.

5. The system according to any preceding claim, wherein the sensing element comprises an external absorbent material enclosing the coaxial section, the sensing section and the nonconductive shield.

6. The system according to claim 5, wherein the external absorbent material comprises non-woven geotextile or a sponge.

7. The system according to any preceding claim, wherein the sensing element head comprises an ID device for generating an identification code of the sensing element.

8. The system according to any preceding claim, wherein the sensing element head comprises a three-pin sensing element connector for connecting to the inner conductor of the coaxial section, the outer shield connector of the coaxial section, and the first wire conductor of the sensing section respectively.

9. The system according to any preceding claim, wherein the measuring unit comprises a power supply, a TDR module comprising an electromagnetic signal generator and a sampling and acquisition device.

10. The system according to claim 9, wherein gain and/or width of an electromagnetic signal generated by the electromagnetic signal generator can be tuned according to a distance of the sensing element to be analysed.

11. The system according to claim 9 or claim 10, wherein the power supply is an internal battery or an external solar panel.

12. A TDR-based method for detecting and locating dielectric variations, comprising providing a sensing element with a sensing head inside a material of which dielectric variations are to be detected, located or monitored, determining a length of the sensing element, obtaining a reference TDR output, acquiring a TDR output along the sensing element, identifying a dielectric variation based on a comparison of the reference TDR output and the acquired TDR output.

13. The method according to claim 12, wherein the determining the length of the sensing element comprises determining, through TDR measurement on the coaxial section, the apparent length of the coaxial section, wherein it is possible to evaluate the actual length of the coaxial section which is the same as that of the sensing element..

14. The method according to claim 12 or claim 13, wherein the obtaining the reference TDR output comprises carrying out a TDR measurement on the sensing section in a normal operating condition wherein no dielectric variations are present.

15. The method according to any of claims 12 to 14, wherein the acquiring a TDR output comprises carrying out a TDR measurement on the sensing section.

16. The method according to any of claims 12 to 15, further comprising determining a location of the dielectric variation based on the determined length of the sensing element and the comparison of the reference TDR output and the acquired TDR output.

17. A sensing element for a system for a TDR-based system of detecting and locating dielectric variation, the sensing element comprising a coaxial section, a sensing section and a non-conductive shield enclosing both the coaxial section and the sensing section, wherein the sensing section comprises a first wire conductor operable to act as a signal

5 conductor, wherein the sensing section is alongside the coaxial section and spaced apart from the coaxial section by an intermediate portion, and wherein the coaxial section comprises an inner conductor, an insulating dielectric, and an outer shield conductor.

10

18. The system according to any one of claims 1 to 11, wherein a pipe-to-be-monitored and the sensing element are enclosed in a one-way moisture transfer fabric, which makes the sensing element sensitive only to liquid leaking from the pipe and insensitive to possible surrounding water.