IL128755A

IL128755A - Device for detecting and locating leakage fluids in sealing systems

Info

Publication number: IL128755A
Application number: IL12875597A
Authority: IL
Original assignee: Progeo Monitoring Gmbh
Priority date: 1996-09-10
Filing date: 1997-09-10
Publication date: 2001-05-20
Also published as: EP0925490B1; ATE210285T1; IL128755A0; AU721004B2; WO1998011414A1; DE19638734C2; EP0925490A1; CA2265711A1; DE59705693D1; DE19638734A1; JP2001506745A; AU4549197A

Abstract

The invention concerns a device for detecting and locating leakage fluids in sealing systems, said device being characterized by a single-layer flat structure (4) which comprises electrically conductive particles and/or fibres and is disposed all-over the exterior of a sealing region to be monitored. The flat structure comprises an area-specific electrical resistance which, when wetted with an electrically conductive fluid, decreases in the region of the wetting and, when wetted with an electrically non-conductive fluid, increases in the region of the wetting. The flat structure (4) is further provided with a plurality of measuring contacts (5, 6) which are connected via one or a plurality of bus transmission lines to a measuring and evaluating arrangement (9) by means of which the electrical resistance of the flat structure (4) and/or the potential distribution can be measured in relation to a counter electrode disposed on the interior of the sealing region to be monitored, and a variation in the local resistance distribution and/or potential distribution within the flat structure (4) can be determined.

Description

DEVICE FOR DETECTING AND LOCATING LEAKAGE FLUIDS IN SEALING SYSTEMS 15 September 1998 DEVICE FOR DETECTING AND LOCATING LEAKAGE FLUIDS SEALING SYSTEMS The present invention relates to a device for detecting and locating both electrically conductive and electrically non-conductive leakage fluids in sealing systems .

DE 69014264 T2 describes a method for detecting leakages in an insulation layer which for example is installed below a waste dump to protect the groundwater against contaminated leakage water from the-. waste dum . In this, a first and a second geotextile material are arranged, said geotextile materials being separated from each other by a further insulation layer. Wove-h into the two geotextile materials are electrically-conductive, essentially parallel -aligned threads, with the geotextile materials being arranged in such a way that the conductive threads of the first geotextile material form an angle of preferably 90° with the conductive threads of the second geotextile material. This known process is characterised in that the conductive threads are combined in pairs, with the spacing between the pairs being further apart than the thread spacing in the pair. In order to detect a leakage, the electrical voltage and/or the resistance between two conductive threads forming a pair is determined. The location of the leakage can thus be established by cross-position fixing.

This known method has the disadvantage in that detection of a leakage is ensured only if the conductive threads are woven into the geotextile materials with narrow spacing between said threads . For if the conductive threads are spaced relatively wide apart, and if only a small amount of liquid leaks from a defective position in the insulation layer, then bridging of the conductive threads by the liquid leaking out, and thus detection of the damage, is not ensured in every case. Since in addition, it cannot be assumed that damage always only relates to the inner insulation layer but, especially with damage occurring in the construction phase, very often also relates to the insulation layer between the two geotextile materials comprising the conductive threads itself, under certain circumstances, leakage liquid can enter the ground without such damage being detected.

If however the spacing of the parallel conductive threads is selected so narrow as to really^ensure detection of a leakage, then the number of measuring contacts which must be connected to the conductive threads is accordingly high. However, this requires very considerable effort resulting in relatively high production costs of such leakage detection and location systems.

Furthermore it would be desirable if a device were available which would enable the detection not only of electrically conductive leakage fluids such as for example leakage water, but also electrically non-conductive leakage fluids such as for example heating oil.

From EP 0372697 A2 a sensor for the detection of oil leaks is already known. However, the known sensor is not suitable for the detection of leakage water or other aqueous leakage fluids because it comprises a resistor surrounded by an encasing made of a porous water-repellent resin, and is itself formed from a porous, water-repellent resin comprising electrically conductive carbon particles, said carbon particles comprising a water-repellent layer.

Furthermore, from US 5 191 785 a device for identifying and locating a leakage of electrically conductive fluids in the inner liner of a vessel Shaving a laminated wall structure is known. A graphite veil is mounted between the interior layer of the vessel made from an electrically non-conductive material and the outer shell of the vessel, said graphite veil comprising several measuring electrodes. In addition, the device comprises a main electrode arranged within the vessel in such a way that it is in permanent contact wijth the electrically conductive fluid contained therein. To detect and locate any leakage in the interior layer of the vessel, a voltage difference is consecutively applied to various electrode pairs and measured against the main electrode, with a leakage in the electrically non-conductive interior layer of the vessel practically representing an intermediate measuring tap on a long resistor, formed by a section of the graphite veil located between a pair of electrodes. However, detection and location of a leakage of electrically non-conductive fluids is not possible with this known device. 3a Based on this state of the art, it is the object of the present invention to provide a device of the type mentioned in the introduction which ensures safe detection of leakages in sealing systems both in the case of conductive and non-conductive leakage fluids, and which in addition can be produced economically.

According to the invention, this object is met by a device of the initially mentioned type characterised by a sheetlike structure comprising electrically conductive particles and/or fibres, said structure being arranged all over the. exterior of a sealing area to be monitored, and comprising an area-specific electrical resistance; said resistance decreasing in the area of wetting when wetted with an electrically conductive liquid, and said resistance increasing in the area of wetting when wetted with an electrically non-conductive liquid; with the sheetlike structure comprising an array of measuring contacts which are connected to a measuring and evaluation device by way of one or several bus transmission lines; by means of which measuring and evaluation device the electrical resistance of the sheetlike structure can be measured and a change in the local resistance distribution within the sheet-like structure can be determined. 4 aroa to bo monitored;—and a change of the local rcaiot-anco diotribution and/or potential diatribution within the ohoetlikc otr cturc can be determined.

With the device according to the invention, containers as well as sealing systems can be reliably monitored for leakage of both electrically conducting and nonconducting fluids, with even small quantities of leakage being detectable. The number of measuring contacts required for this is comparatively small so that the device according to the invention is relatively economical to realise. The use of the bus transmission line or lines also contributes to this. Furthermore, the device according to the invention makes it possible to exactly locate the place of damage, consequently the respective leakage can be repaired in a selective way and at justifiable cost . The number and spacing of the measuring contacts are suitably to be selected in such a way that the resistance distributio in the sheetlike 5 The measuring and evaluation device can measure the electrical resistance of the sheetlike structure either continuously or at specified times. In addition L gsxsi preferably made on the basis of a nonwoven fibre fabric or a fine, grid-like net structure, is preferably made in such a way that electrical conduction takes place between any points in the sheetlike structure, essentially via the surface of the particles and/or fibres.

According to a further advantageous Embodiment, the outside of the sheetlike structure /is provided with a liquid- impermeable layer. This arrangement is particularly advantageous if the sealing system to be monitored is situated in the ground and one has to expect that groundwater and/or surface water will impinge on the sheetlike structure thus possibly leading to a change in the electrical resistance of the sheetlike structure.

A further advantageous embodiment provides for at least one counter electrode which is located within the ooaling oyotcrn or in the ground outside the sealing system. In this way if there is a liquid- impermeable layer on the inoidc or outside of the sheetlike structure it can be detected whether the layer is intact or damaged.

- - According to another advantageous embodiment of the invention, the measuring contacts for coupling to the sheetlike structure comprise a contact surface made of conductive foam material, preferably conductive polyurethane foam. In this way a perfect coupling to the sheetlike structure is achieved, with said coupling being easy to produce. This applies in particular when using polyurethane foam material, which due to its high raicro-deformability and at the same time superior conductivity, is able to contact the sheetlike structure with a low transition resistance between a metallic contact surface of the measuring contact and the sheetlike structure.

A further preferred embodiment of the invention is characterised in that the measuring contacts are arranged spread out on the sheetlike structure. In this way more exact location of leakages can be achieved because, due to the two-dimensional evaluation of the measuring results, position fixing of the damage- is not solely limited to segments situated between^ the measuring contacts arranged at the periphery^of the sheetlike structure, but with increased accuracy can also take place between the measuring contacts spread out on the sheetlike structure.

For interrogating the measuring contacts, preferably a hybrid analog-digital bus system is provided whose digital and analog lines are series-connected, with switches at the measuring contacts being able to be activated via the digital part of the bus, said switches connecting the analog signal and data lines to the respective measuring contact. 7 Below, the invention is illustrated in more detail by means of a drawing showing one embodiment . In the drawing Figure 1 is a diagrammatic illustration of a tank shown in a section view, wherein the tank comprises a device according to the invention; Figure 2 is a top view of the tank and the dev according to the invention of Figure re¬ Figure 3 is a perspective view of a section of a sheetlike structure of the device according to the invention; are various views of a serial coupling element for producing a measuring*' contact on the sheetlike structure.

Figures 1 and 2 show a tank 1 in which a water-endangering liquid 2, such as e.g. heating oil or fuel, is stored. Reference 3 designates the lockable filling aperture of the tank 1.

All over the bottom and the sides of the tank 1, there is a sheetlike structure 4 which, preferably based on a nonwoven fibre fabric, comprises electrically-conductive particles and/or fibres. The sheetlike structure 4 is made in such a way that electrical conduction takes place between any points in the sheetlike structure 4, 8 essentially across the surface of the particles or fibres.' The specific resistance of the conductive particles or fibres and their mass per unit of area are matched in such a way that the sheetlike structure 4 has an area-specific electrical resistance; said resistance decreases in the area of wetting when wetted with an electrically conductive liquid, and said resistance increases in the area of wetting when wetted with an electrically non-conductive liquid.

The sheetlike structure 4, at its upper edge surrounding the tank, comprises an array of measuring contacts 5 to 8, between which the electrical resistance of the sheetlike structure can be measured at any time by means of an automatic measuring and evaluation device 9. The measuring contacts 5 to 8 are arranged in pairs, with the individual pairs on the one hand forming parallel measuring taps and on the other hand intersecting measuring taps . The number and spacing of the measuring taps is selected in such a way that ^the resistance distribution for the entire area otf the sheetlike structure 4 can be determined with adequate local resolution .

As an alternative to, or in addition to, the arrangement shown in the drawing, the measuring contacts can also be arranged spread out in a matrix- like arrangement, in specified locations on the sheetlike structure (sec Fig. 4- The measuring contacts 5 to 8 shown in Figures 1 and 2 are connected to the measuring and evaluation device 9 via bus transmission lines 11 to 14. A hybrid analog-digital bus system is used which does not require expensive analog-digital conversion at the measuring taps. - 9 - Via the digital part of the bus, switches at the measuring contacts are activated, said switches connecting the analog signal and data lines to the measuring contact .

The measuring and evaluation device comprises a display device (not shown) , for example in the form of a monitor, by way of which the location or the coordinates of any leakage are displayed. Furthermore, the measuring and evaluation device 9 comprises a signal device (not shown) which signals any leakage by an acoustic and/or visual alarm signal. Moreover, the measuring and evaluation device 9 comprises a modem 15 for remote transfer of the acquired measuring data.

If the resistance distribution of the sheetlike structure 4 is known prior to filling the tank 1, i.e. without leakage fluid impinging on the sheetlike structure 4, then by comparing the resistance distribution measured at a later time with the first measured resistance distribution, any occurrence of a leakage can be detected by local increase or decrease of resistance values. In this way, any change of resistance values is at first limited to the area which is moistened by liquid, thus locating the leakage is possible.

Since it cannot be ruled out that the leakage fluid will spread in the monitored area or below a seal to be monitored, thus rendering exact position fixing no longer possible, the number of measuring cycles of the measuring and evaluation device is set sufficiently high to ensure that the resistance distribution is established immediately after the first appearance of the leakage - 10 - fluid, before the liquid has spread out over a larger area .

Figure 3 shows a diagrammatic marginal section of a sheetlike structure 4 according to the invention. It can be noted that the sheetlike structure 4 comprising electrically conductive particles and/or fibres, has at its margin a connection element 5 forming a measuring contact. Furthermore, on its outside, the sheetlike structure 4 comprises a liquid- impermeable layer 10, for example a plastic layer.

The application of the device according to the invention is not solely limited to leakage monitoring of containers and sealing systems but is in particular also suitable for monitoring pipelines carrying water-endangering liquids. For this purpose, the sheetlike structure 4 shown in Figure 4 is produced in, or .cut to, strip shapes or lengths of material. / i To produce an extensive sheetlike structure, several lengths of material can be adjoined, maintaining a certain overlap, for example 5 cm. To achieve good contact in the area of overlap it is advantageous if the segment of the sheetlike structure overlapping on the top or outside, is placed with a longitudinal fold onto the longitudinal margin of the segment below, and that along the margin of overlap, both segments are held together by adhesive tape. In this, the segments can be 2 m or 4 m wide . 11 Fig .—4—ia a diagrammatic view of an embodiment where thg device according to the invention is used for monitoring a sealing membrane 16 of a flat roof for any leakage. The sheetlike structure 4 which is preferably producea from nonwoven fibre fabric is arranged below the ssaling membrane 16 to be monitored (shown partially cut away) and on one side comprises an array of measuring contacts 17 in a matrix-like arrangement. The sheetlike structure 4 acts as an effective sensor surfa e over the entire area. In order to detect any leakage, on top of the roof sealing membrane at least one counter electrode 18 is arranged. If the sealing membrane 16 is intact, then the resistance measured between one of the measuring contacts 17 and the counter elect-rode 18 is very high. By contrast, if rain wab¾r enters as a result of a leakage, the resistance of )6xe. sheetlike structure 4 is low in the area of moistening. By sequential interrogation of the individual measuring contacts 17, the leakage in the roof seal 16 car quickly be located. -Below.-'the sheetlike structure 4, a further seal 20 as we&l as at least one further counter electrode 21 can bd provided as an additional protection for the roof structure 19 below aaid chcctlikc atructurc.

Figures #A to ic show a lateral view (Fig. #A) , a top view (Fig. &B) and a bottom view (Fig. pC) of a preferred embodiment of a measuring contact module 17 to be arranged on the sheetlike structure. The contact surface of the module 17 comprises a conductive polyurethane foam material. In this way a good contact between the measuring points and the sheetlike structure is achieved. Both in the digital and in the analog lines of the bus system the measuring positions are series -connected and together with the circuit electronics and a contact - - surface 22 are sealed in the module case 23 made of epoxy resin. / 10 September 1997 ABSTRACT Described is a device for detecting and locating leakage fluids in sealing systems, characterised by a single-layer sheetlike structure (4) comprising electrically conductive particles and/or fibres, said structure being arranged all over the exterior of a sealing area to be monitored. The sheetlike structure comprises an area-specific electrical resistance which decreases in the area of wetting when wetted with an electrically conductive liquid, and said resistance increases in the area of wetting when wetted with an electrically non-conductive liquid. The sheetlike structure (4) also comprises an array of measuring contacts (5, 6) which are connected to a measuring and evaluation device (9) by way of one or several bus transmission ^lines; by means of said measuring and evaluation device the electrical resistance of the sheetlike structure (4) and/or the potential distribution can be measured in relation to a counter electrode arranged on the inside of the sealing area to be monitored, and any change of the local resistance distribution and/or potential distribution within the sheetlike structure (4) can be determined.

Figure 1 has been provided for publication with the abstract .

Claims

PCT/DE97/02045 13 MY/ab 96561WO 24 April 1998 Amended Claims

1. A device for detecting and locating both electrically conductive and electrically non-conductive leakage fluids in sealing systems, c h a r a c t e r i s e d by a sheetlike structure (4) comprising electrically conductive particles and/or fibres, said structure being arranged all over the exterior of a sealing area to be monitored, and comprising an area-specific electrical resistance; said resistance decreasing in the area of wetting when wetted with an electrically conductive liquid, and said resistance increasing in the area of wetting when wetted with an electrically non-conductive liquid; with the sheetlike structure comprising an array of measuring contacts (5, 6, 7, 8; 17) which are connected to a measuring and evaluation device (9) by way of one or several bus transmission lines (11,^12, 13, 14); by means of which measuring and evaluation device the electrical resistance of the sheetlike structure (4) can be measured continuously or at predetermined times and a change of the local resistance distribution within the sheetlike structure (4) can be determined.

2. A device according to claim 1, characterised in that the sheetlike structure (4) comprises particles and/ or fibres made of metal and/or conductive carbon.

3. A device according to claim 1 or 2, characterised in that electrical conduction takes place between any points in the sheetlike structure (4) , essentially via the surface of the particles and/or fibres . 14

4. A device according to one of the preceding claims, characterised in that on the outside the sheetlike structure (4) comprises a liquid-impermeable layer (10) .

5. A device according to one of the preceding claims, characterised in that means are provided by which a constant measuring current can be sent across at least part of the sheetlike structure, so that the voltage distribution in the sheetlike structure (4) in which current flows, can be determined by means of the measuring contacts (5, 6, 7, 8; 17) .

6. A device according to one of the preceding claims, c h a r a c t e r i s e d in that furthermore at least one counter electrode is provided which is locatable outside the sealing area to be monitored; with the potential distribution in relation to the counter electrode being measurable and a change in the potential distribution being determinable by the measuring and evaluation device (9) .

7. A device according to one of the preceding claims, characterised in that each of the measuring contacts (5, 6, 7, 8; 17) comprises a contact surface made of conductive foam material for coupling to the sheetlike structure (4) .

8. A device according to one of the preceding claims, characterised in that the measuring contacts (5, 6, 7, 8; 17) are arranged spread out, preferably in a matrix- like arrangement. 15

9. A device according to one of the preceding claims, characterised in that for interrogating the measuring contacts (5, 6, 7, 8; 17) a hybrid analog-digital bus system is provided whose digital and analog lines are series -connected, with switches at the measuring contacts being able to be activated via the digital part of the bus, said switches connecting the analogue signal and data lines to the respective measuring contact (5, 6, 7, 8; 17) . r Dr. Shlomo Law 124