NO20151324A1

NO20151324A1 - System and method for detecting moisture

Info

Publication number: NO20151324A1
Application number: NO20151324A
Authority: NO
Inventors: Ivar Granheim; Matthias Meyer; Mensudin Dzubur
Original assignee: Nexans
Priority date: 2015-10-06
Filing date: 2015-10-06
Publication date: 2017-04-07

Description

System and method for detecting moisture

Technical field

The present invention relates to a system and a method for detecting moisture, including water.

More particularly, the invention relates to a system for detecting and localizing moisture, comprising a sensor cable, including at least two elongated, electrical conductors separated by a material which is electrically insulating in dry conditions, the sensor cable being electrically connected to a time domain reflectometry monitoring device. The invention also relates to a method for detecting moisture, wherein such a sensor cable is used.

Background

There is a general need for detecting moisture. For instance, there is a need for detecting moisture due to unwanted water intrusion in fixed constructions such as residential or industrial buildings, or along pipelines, e.g. thermically insulated pipelines. Such detection may be crucial in order to avoid water damage to structures and equipment, to prevent corrosion, formation of fungus, formation of ice, etc.

In the present specification, the term moisture should be understood as the presence of a liquid, including water, and/or vapour, including water vapour.

US-2012/0126838 relates to an electrical detection cable for detecting moisture. This cable makes it possible to detect water intrusion in an elongated area where the cable is installed, for instance along a wall or under a roof covering in a building.

Other moisture detection cables in the background art make it possible not only to detect moisture, but also to localize a moisture intrusion's or incidence's position along the cable. For instance, WO-2004/102174 describes a system for monitoring a substrate for moisture penetration. The system includes a plurality of electrical conductors which are connected to a monitoring device via an interface. The conductors are woven into a ribbon-like carrier made of fibrous material, e.g. mineral fibres, glass fibres, textile fibres or a blend of fibres, which is electrically insulating in dry conditions. The system is capable of detecting moisture penetration along the electrical conductors. In an embodiment, the monitoring device is a time domain reflectometry (TDR) monitoring device, which enables the system to determine the location along the electrical conductors where the moisture penetration has tåken place.

Summary of the invention

There is a need for providing an improved system for detecting and localizing moisture, of the type mentioned in the introduction.

In particular, there is a need for providing such a system which provides appropriate protection to the electrical conductors while also providing appropriate responsivity to moisture.

The invention has been defined by the system as set forth in independent claim 1 and the method as set forth in independent claim 8. Advantageous embodiments are set forth in the dependent claims.

In an aspect, a system for detecting and localizing moisture has been provided. The system comprises a sensor cable which is electrically connected to a time domain reflectometry monitoring device, wherein the sensor cable includes at least two elongated, electrical conductors that are separated by a material which is electrically insulating in dry conditions, wherein the electrical conductors are embedded in an elongated element made of the material, the material being a polymer material håving a water absorption, according to ISO 62:2008 at 23 °C, in the range of 0.2 to 12.

In another aspect, a method for detecting moisture has been provided. The method comprises providing a sensor cable, including at least two elongated, electrical conductors that are separated by a material that is electrically insulating in dry conditions, wherein the electrical conductors are embedded in an elongated element made of the material, the material being a polymer material håving a water absorption, according to ISO 62:2008 at 23 °C, in the range of 0.2 to 12; connecting the sensor cable to a time domain reflectometry monitoring device; performing a time domain reflectometry analysis by the time domain reflectometry monitoring device; and establishing detection of moisture along the sensor cable by means of a result of the time domain reflectometry analysis.

The arrangement of embedding the electrical conductors in the elongated element made of such a material, leads to a system wherein the sensor cable may be non-porous and/or non-fibrous, as opposed to the background art system wherein the conductors are woven into a ribbon-like carrier made of fibrous material. This has, i.a., the effect of providing appropriate protection to the electrical conductors while also providing appropriate responsivity to moisture. Also, the sensor cable used in the system may be more easily deployed, and it may be manufactured in a more cost-effective way.

Brief description of the drawings

The present invention will be described in further details with reference to the enclosed figures:

Figure 1 is a schematic block diagram illustrating a system for detecting and localizing moisture. Figure 2 is a schematic block diagram illustrating an exemplary cross section of a sensor cable used in the system. Figure 3 is a schematic flow chart illustrating an exemplary method for detecting moisture. Figure 4 is a first graphic diagram illustrating TDR signals obtained by use of the invention. Figure 5 is a second graphic diagram illustrating TDR signals obtained by use of the invention. Figure 6 is a third graphic diagram illustrating TDR signals obtained by use of the invention.

Figure 7 is a graphic diagram illustrating properties of example materials.

Detailed description

The present invention will be discussed in further detail with reference to the enclosed drawings. It should be noted that the drawings and the detailed description illustrate some possible embodiments, given by way of non-limiting examples.

Figure 1 is a schematic block diagram illustrating a system 100 for detecting moisture.

The system comprises a sensor cable 110, which includes two elongated, electrical conductors 120, 130 that are separated by a material 140 which is electrically insulating in dry conditions. In other embodiments, more than two electrical conductors may be used.

As used herein, dry conditions may e.g. represent a state where no water vapor in air, surrounding a humidity sensor, has condensed on the surface of the sensor, or when the relative humidity (RH) is below 50 %, taking into consideration that a higher RH will condensate on the surface of the polymer covering and during time migrate into the polymer covering, but dependent on the surrounding temperature.

The length of the sensor cable 110 may e.g. be between 10 m and 300 m. Other lengths are also possible.

At its proximate end, the sensor cable 110 is electrically connected to a time domain reflectometry (TDR) monitoring device 150. The TDR monitoring device 150 may be a time domain reflectometer.

At its distant end, the sensor cable 110 may be open-ended, i.e. non-terminated. Alternatively, the sensor cable 110 may be terminated at its distant end by a terminating device 160 as illustrated. The terminating device 160 may be provided as a short-circuit of the conductors 120, 130. Alternatively, the terminating device 160 may be an impedance element with a predetermined impedance, e.g. a resistor.

Time-domain reflectometry or TDR is a measurement technique used to determine characteristics of electrical lines by observing reflected waveforms. The TDR monitoring device 150 is configured to propagate an incident signal, in the form of a step or impulse of electric energy, into the sensor cable 110. Subsequently, the TDR monitoring device is configured to observe the energy reflected by the sensor cable 110.

The TDR monitoring device 150 may further be configured to analyze the magnitude, duration and shape of the reflected waveform. By such analysis, the nature of the impedance variation in the sensor cable 110 can be determined. In particular, moisture along the sensor cable 110 may be detected. Also, the location of moisture along the sensor cable may be determined. Even a plurality of locations of moisture along the sensor cable, separated by areas of no moisture, may be determined.

Generally, the reflections from the sensor cable 110 will have the same shape as the incident signal, but their sign and magnitude depend on the change in impedance level. If there is a step increase in the impedance, then the reflection will have the same sign as the incident signal; if there is a step decrease in impedance, the reflection will have the opposite sign. A step decrease in impedance may be the result of moisture along the sensor cable, e.g. due to presence or intrusion of water.

The TDR monitoring device 150 may further be configured to compare a result of a first resulting waveform with a result of a second resulting waveform. The first resulting waveform may represent the TDR signal obtained under predetermined, advantageously dry conditions of the sensor cable, e.g. acquired during an initial calibration TDR procedure. The second resulting waveform may represent the TDR signal obtained under a monitoring condition, wherein moisture is to be detected.

The TDR monitoring device 150 may be selected from a range of regular TDR monitoring devices that are normally used for other purposes, e.g. for detecting short-circuits or open-circuits in electrical conductors or cables. Alternatively, the TDR monitoring device 150 may be specifically designed for the present purpose. The TDR-setup may be configured in dependency of the dielectric properties of the insulating material, the conductor sizes, thickness of the insulating material and the distance between the conductors.

The electrical conductors 120, 130 in the sensor cable 100 are embedded in an elongated element made of the material 140 that is electrically insulating in dry conditions.

The material 140 that surrounds the electrical conductors 120, 130 comprises a polymer material håving a water absorption, according to ISO 62:2008 at 23 °C, in the range of 0.2 to 12. More advantageously the water absorption, according to ISO 62:2008 at 23 °C, may be in the range 1 to 5.

Water absorption should in the context of the present disclosure be understood to be determined according to the ISO 62:2008 standard "Plastics - Determination of water absorption", at temperature +23 °C. In the sense of ISO 62:2008, water absorption may be measured as a percentual increase in weight of a material after exposure to water under specified conditions. In particular, water absorption (in weight%) of a test specimen of the material should be understood as the percentual increase in weight of an initially dry test specimen when it has been immersed in distilled water at temperature +23 °C for 24 hours.

In any of the above examples, the polymer material may advantageously include polyamide.

In a preferred, detailed example, the polymer material includes polyamide PA 12.

Alternatively, polyamides such as PA 12, PA 612, PA 610, PA 6, PA 66, or PA 46 may be used as the polymer material. Also, a blend of two or more of the above-mentioned materials may be used. Other possible useful polymer materials may include thermoplastic polyurethanes (TPUs), polyether TPU-based thermoplastic elastomers and/or other thermoplastic elastomers.

Still alternatively, certain types of polyamides may be used as the polymer material, for instance those mentioned in table 1 below. As shown in the table, the material may be selected with a view to desired water absorption and other material properties such as melting temperature.

The elongated element in which the electrical conductors of the sensor cable are embedded, may be a flexible, bendable coating, insulation, sheath or jacket that covers the electrical conductors. Hence, the embedded element may be understood as a polymer covering, or a coating, insulation, sheath or jacket that covers the electrical conductors along their entire length or along a substantial part of their length. This arrangement leads to a system wherein the electrical conductors of the sensor cable may be separated by a non-porous and/or homogenous substance, as opposed to the background art system of WO-2004/102174, wherein the conductors are woven into a ribbon-like carrier made of fibrous material. This has, i.e., the effect of providing appropriate protection to the electrical conductors while also providing appropriate responsivity to moisture. Also, the sensor cable used in the system may be more easily handled and deployed, it may be more robust, and the sensor cable may be manufactured in a more cost-effective way.

Figure 2 is a schematic block diagram illustrating an exemplary cross section of a sensor cable used in the system.

The illustrated sensor cable includes two parallel conductors. Each conductor includes a metallic core and a material which is electrically insulating in dry condition, that surrounds and separates the metallic cores, in such a way that the conductors' metallic cores are embedded in the material. Each metallic core may e.g. be made of copper, tin-coated copper, nickel-coated copper, aluminium, or another metal or alloy, or another electrically conductive, flexible material.

A range of suitable alternatives for the material that surrounds and separates the conductors has been specified above with reference to figure 1.

The distance 210 between the axes of the conductors, as illustrated in figure 2, may for instance be about 2.7 mm. It should be understood that this distance 210 may be varied according to the intended specific use and circumstances. The distance may, e.g., be between 1 mm and 8 mm.

The thickness 220 of the material that surrounds and separates the conductors may for instance be about 0,7 mm. It should be understood that this thickness 220 may be varied according to the intended specific use and circumstances. The-thickness may, e.g., be between 0,3 mm and 2 mm.

The diameter 230 of each conductor core may for instance be about 1,1 mm.

This diameter 230 may likewise be varied according to the intended specific use and circumstances, and may, e.g., be between 0,4 mm and 3 mm.

The diameter 240 of each insulated conductor may for instance be about 2,6 mm. This diameter 240 may also be varied according to the intended specific use and circumstances, and may, e.g., be between 1 mm and 8 mm.

The parallel, insulated conductors are joined together laterally by means of an elongate portion of the same material that surrounds and separates the conductors. The width 250 of this elongate material portion may for instance be about 0.15 mm. This width 250 may be varied according to the intended specific use and circumstances, and may, e.g., be between 0.05 mm and 5 mm.

The total width 260 of the sensor cable may for instance be about 5,3 mm.

This width 260 may likewise be varied according to the intended specific use and circumstances, and may, e.g., be between 2 mm and 15 mm.

Although the conductor cores and the surrounding material layer in which the conductor cores are embedded have been illustrated to have circular cross sections, it should be appreciated that other cross sections are also possible, including oval, square, triangular, rectangular, and others.

Figure 3 is a schematic flow chart illustrating an exemplary method for detecting moisture.

The method starts at the initiating step 310.

First, at the providing step 320, a sensor cable 110 is provided. The sensor cable 110 may, e.g. be of a type as disclosed in the present specification, e.g. as disclosed above with reference to figures 1 and 2. The providing step 320 may, e.g. include deploying or otherwise arranging the sensor cable 110 at a suitable location where detection of moisture is desired, e.g. in a fixed construction such as a building, along a pipeline, or the like.

Then, in the connecting step 330, the sensor cable 110 is electrically connected to a time domain reflectometry monitoring device, TDR monitoring device, 150. The TDR monitoring device may e.g. be of a type as disclosed in the present specification, e.g. as disclosed above with reference to figures 1 and 2.

Subsequently, the optional time domain reflectometry calibrating step 340 is performed. This calibrating step is typically performed at the first performance of the method, in order to establish initial values for the TDR data, when the sensor cable is deployed under dry conditions. In other cases, the calibrating step 340 may be omitted and the method may instead proceed to the analysis step 350.

The calibrating step 340 may be performed both to calibrate the TDR-instrument according to the charateristies of the sensor cable and with regards to the installation conditions of the sensor cable.

After the calibrating step 340, or if the calibrating step is omitted, after the connecting step 330, the method proceeds at the analysis step 350, which includes performing a time domain reflectometry analysis by the time domain reflectometry monitoring device 150.

The analysis step 350 includes the substep of establishing detection of moisture along the sensor cable by means of a result of the time domain reflectometry analysis.

The analysis step 350 may also include a substep of localizing at least one location of moisture along the sensor cable by means of the result of the time domain reflectometry analysis.

The analysis step 350 may also include comparing a result of a first resulting waveform with a result of a second resulting waveform. The first resulting waveform may represent the TDR signal obtained under predetermined, advantageously dry conditions of the sensor cable, e.g. acquired during an initial calibration TDR procedure. The second resulting waveform may represent the TDR signal obtained under a monitoring condition, wherein moisture is to be detected.

Detected moisture may be established when the difference between the first and second waveform exceeds a particular limit value. One or more positions associated with moisture along the sensor cable may be identified as the TDR position for which the first and second waveform exceeds the particular limit value. Such a limit value may e.g. be set by straightforward experiments.

Figures 4, 5, and 6 are graphic diagrams illustrating TDR signals obtained by use of the invention. A system for detecting and localizing moisture, as disclosed in the present specification, has been used. A Polyamid 12 based polymer compound has been selected as the material that surrounds and separates the conductors of the sensor cable. The length of the sensor cable was about 28 meters.

Figure 4 is a first diagram illustrating TDR signals obtained by use of the invention.

The diagram shows the TDR signal, or TDR reflection, as a function of distance along the sensor cable (in meters). The first graph 410 represents a signal obtained under dry conditions along the sensor cable, e.g. when the sensor cable is surrounded by dry air. The second graph 420 represents a signal obtained in a situation where the sensor cable is affected by immediate contact with water at approx. 16 meter, measured from the sensor cable's proximate end, i.e. at the TDR monitoring device. A detection of water/another liquid material will cause a negative amplitude/TDR-signal. As can be seen, there is a distinct difference between the first graph 410 representing the dry conditions, and the second graph 420 representing the wet/moist condition. Hence, based on the TDR result, moisture may be detected at a position about 16 meters from the proximate end of the sensor cable. To identify more exactly the distance to where the moi sture/water is evident, the TDR-instrument could be connected to the other end of the sensor-cable.

Figure 5 is a second graphic diagram illustrating TDR signals obtained by use of the invention.

The diagram shows the TDR signal, or TDR reflection, as a function of distance along the sensor cable (in meters). The first graph 510 represents a signal obtained under dry conditions along the sensor cable, e.g. when the sensor cable is surrounded by dry air. The second graph 520 represents a signal obtained in a situation where the sensor cable has just been affected by immediate contact with water at approx. 16 meter, measured from the sensor cable's proximate end, i.e. at the TDR monitoring device. The third graph 530 represents a corresponding TDR signal obtained four days after the recording of the second graph 520. As can be seen, there is an increased difference between the second graph 520 representing the newly occured wet/moist condition and the third graph 530, representing the "four days old" wet/moist condition. This is due to absorption of water into the material that surrounds and separates the conductors in the sensor cable, and in which the conductors are embedded.

Figure 6 is a third graphic diagram illustrating TDR signals obtained by use of the invention.

The diagram shows the TDR signal, or TDR reflection, as a function of distance along the sensor cable (in meters). The first graph 610 represents a signal obtained under dry conditions along the sensor cable, e.g. when the sensor cable is surrounded by dry air. The second graph 620 represents a signal obtained in a situation where the sensor cable has been affected by non-direct contact with water, i.e. with surrounding humid air at relative humidity of 85% at room temperature (23 °C), for three weeks. Then the sensor cable has been affected by normal, ambient conditions, with surrounding humid air at relative humidity of 40-50% at room temperature (23 °C), for one week. As can be seen, the sensor cable regenerates after one week in normal, ambient conditions, back to the initial TDR signal 610.

Figure 7 is a graphic diagram illustrating properties of example materials that may be used as the material 140 that surrounds and separates the electrical conductors in the sensor cable 110, and in which the conductors are embedded.

Various polyamide types are illustrated. Their water absorption values (according to ISO 62:2008 at 23 °C) are shown at the horizontal axis, and their melting points are shown at the vertical axis. Note that figure 7 includes data that may relate to glass fiber reinforced polymers, and glass fiber reinforcement is not necessarily used in the present system and method. Hence these values should merely serve as indicative data for water absorption tendencies.

Materials which exhibit a water absorption coefficient of 0.2 to 12 weight-%, in the sense of ISO 62:2008 at 23 °C, are useful as the material 140 that surrounds and separates the electrical conductors in the sensor cable 110. These material types include PA 11, PA 12, PA 612, PA 610, PA 6, PA 66, PA 46, PA6/66, PA6I/6T and TPUs. Among these materials, PA 12, PA 612, PA 610, PA 6, PA 66, PA 46, and TPUs are more preferred.

Both the degree of water/moi sture absorption and the dielectric properties of the polymer insulation material may be dependent of the selection of the polymer insulation material. By such a selection it is possible to vary and optimize the degree of water/moisture absorption and as such the magnitude of the TDR-reflection-signal during time of water/moisture contact.

Dependent of the application and the sensor-cable installation length and the temperature and chemical environment the sensor is going to be used, it is possible to choose between different polymer insulation materials with different water/moisture absorption and their dielectric properties to achieve an optimized sensor installation with regards to TDR-reflection signal strength. Operating temperatures along the sensor cable installation, in particular maximum and minimum operating temperatures along the sensor cable installation, may also be a consideration in the selection of the insulation material.

Typical Dk/Dielectric constant for a suitable polymer insulation material or compounds may, e.g. be in the range of 2 to 10 (according to DIN 53483).

The invention has been described with reference to detailed, exemplary embodiments. The scope of the invention has been set forth in the claims.

Claims

1. System (100) for detecting and localizing moisture, comprising a sensor cable (110) which is electrically connected to a time domain reflectometry monitoring device (150), wherein the sensor cable (110) includes at least two elongated, electrical conductors (120, 130) that are separated by a material (140) which is electrically insulating in dry conditions, wherein the electrical conductors (120, 130) are embedded in an elongated element made of the material (140), the material (140) being a polymer material håving a water absorption, according to ISO 62:2008 at 23 °C, in the range of 0.2 to 12.

2. System according to claim 1, wherein the polymer material has a water absorption, according to ISO 62:2008 at 23 °C, in the range of 1 to 5.

3. System according to one of the claims 1-2, wherein the polymer material comprises polyamide, thermoplastic polyurethane (TPU), polyether TPU-based thermoplastic elastomers and/or any combination thereof.

4. System according to claim 3, wherein the polyamide is polyamide PA 12.

5. System according to one of the claims 1-4, wherein the length of the sensor cable is between 10 m and 300 m.

6. System according to one of the claims 1-5, wherein the sensor cable is terminated by a terminating device (160).

7. Method for detecting moisture, comprising providing a sensor cable (110), including at least two elongated, electrical conductors (120, 130) that are separated by a material (140) that is electrically insulating in dry conditions, wherein the electrical conductors (120, 130) are embedded in an elongated element made of the material (140), the material being a polymer material håving a water absorption, according to ISO 62:2008 at 23 °C, in the range of 0.2 to 12; connecting the sensor cable (110) to a time domain reflectometry monitoring device (150); performing a time domain reflectometry analysis by the time domain reflectometry monitoring device; and establishing detection of moisture along the sensor cable by means of a result of the time domain reflectometry analysis.

8. Method according to claim 7, wherein the polymer material has a water absorption, according to ISO 62:2008 at 23 °C, in the range of 1 to 5.

9. Method according to one of the claims 7-8, wherein the polymer material comprises polyamide, thermoplastic polyurethane (TPU), polyether TPU-based thermoplastic elastomers and/or any combination thereof.

10. System according to claim 9, wherein the polyamide is polyamide PA 12.

11. Method according to one of the claims 7-10, wherein the step of performing a time domain reflectometry analysis includes localizing at least one location of moisture along the sensor cable by means of the result of the time domain reflectometry analysis.

12. Method according to one of the claims 7-11, wherein the step of performing a time domain reflectometry analysis includes comparing a result of a first resulting waveform with a result of a second resulting waveform.

13. Method according to one of the claims 7-12, wherein the step of performing a time domain reflectometry analysis is preceded by a time domain reflectometry calibrating step.