MOISTURE PRESENCE ALARM SYSTEM

Abstract: A moisture presence alarm system has a sensor system which extends over an area to be monitored and a detector device which receives signals from the sensor system. This has spatially separated conductors in conductive contact with a moisture absorbent material. The position of the leak is determined by selective interrogation of pairs of conductors. The conductors may be in an orthogonal matrix (A1...X1; A2...X2), each conductor (10, 11) being associated with a moisture absorbent strip (12, 13).

Description: Moisture Presence Alarm System This invention relates to a moisture presence alarm εysterr, in particular for the roofs of buildings, but also for other purposes such aε beneath a swimming pocl. Particularly modern flat roofs are prone to rainwater leakage which can have very serious effects even if the leakage is only slight. Not only can the fabric of the building be damaged, wood become rotten and plaster be damaged, but, when business premises are involved, the consequential losses due to disruption caused by reinstatement and repair can be substantial. Moreover, if the building houses sensitive equipment, such as computers, this may be physically damaged and the disruption caused oy repairs can be even greater. As previously described moisture may be detected by placing an array of wires in contact with a moisture absorbent mat or pad, and detecting a change in resistance between pairs of wires which lie in proximity. Such an arrangement is placed beneath the waterproof roof covering, and connected to a suitable electrical or electronic detecting and monitoring unit. Alarm systems have been known (DE-PS 36650, US-PS 450244) in which changes of impedance between two conductor nets have been used to signal a moisture leak. US-PS 4110945 discloses locating the position of a leak within an area to be monitored by separately positioning a number of detectors at specific points in the area. However, the latter system is expensive if the number of detectors is large enough to make location accurate. The invention aims to provide a system which is cheap and simple to install and easy to monitor, while enabling a high degree of discrimination as to the location of a leak. Accordingly, the invention proposes a moisture leaκ alarm system having a sensor system which extends over an area tc be monitored, and a detector device which receives signals from the sensor system, the latter comprising spatially separated conductors in conductive contact with a moisture absorbent material, characterised in that the sensor system comprises a plurality of pairs of conductors and detects changes in electrical conditions between said pairs, the position of any leak within said area being determined by selective interrogation of the respective pairs of conductors . In a preferred form, the sensor system comprises two sets of conductors, one above the moisture absorbing material and the other below, each set being parallel and orthogonal to the other set, so that one conductor of each set forms a conductor pair at each crossing point. The invention also includes an electrical conductor comprising a moisture absorbent strip carrying on one side a single conductor in the form of a tape applied to the strip so as to be in conductive contact therewith. In addition, the invention proposes a method of installing a leak alarm system comprising the steps of applying to an extended surface to be monitored a plurality of conductors, and connecting thereto a detector device for receiving signals from the conductors, characterised in that a firt set of conductors is adhered in parallel lines in one direction across the surface, and a second set of conductors each one itself attached to a moisture absorbent strip is adhered in parallel lines across the surface transverse to the first with the strip in each case lying between the conductors of the first and second sets. In order that the invention shall be clearly understood, several exemplary embodiments thereof will now be describee with reference to the attached drawings, in which: Fig.l shows a moisture leak alarm sensor system; Fig.2 shows a cross-section through a wire crossing point of the sensor system laid in a roof; Fig.3 shows a cross-section of an electrical conductor strip; and Fig.4 shows a plan view of a roof with a different form of sensor system. Figure 1 shows a matrix of longitudinal wires identified Al , Bl,...Xl, and transverse wires identified A2, B2,...X2, position on a roof surface before the waterproof covering e.g. tiles or felt, is put on. The wires 10,11 in each case are uninsulated and are attached, e.g. by gluing, to a strip of moisture absorbent material 12,13 along its centre line. The material 12,13 may be similar to bandage, or any other suitable material, provided it can absorb moisture. It has also the function of allowing easier handling of the wire, and it can be itself stuck to the roof surface to keep the wires in place. The strip with wire attached is provided for use in rolls. Each wire at one end is ready for connection to the monitoring circuit, and the other end is free. The matrix spacing and size is chosen to match the size of the area to be monitored and the degree of accuracy required in pinpointing any moisture. Every crossing point represents a detector location (576 in the present example). Figure 2 shows a section through such a crossing point, to a much larger scale. The roof surface 15 has the longitudinal wire 10 on its strip 12 lying upon it. The strip may be glued to the surface. At right angles and above this is the transverse wire 11 on its strip 13. The whole matrix is then covered by the waterproof roofing material, represented by layers 16,17. In the event of a leak occurring, the moisture will come in contact with the strip 12 and/or 13 and be absorbed. It will then travel through the material until it reaches an area of strip 13 which lies directly between wires 10 and 11. This breaks down the insulation between the two and the leak can then be detected as conduction between at least two crossing wires of the matrix. It can be seen that the material strip 12 is not essential, but may help the moisture to reach the crossing point more quickly. The terminations of the wires Al to Xl, A2 to X2 are carried to a detector unit. The latter 'reports' by a cable or radio connection to a master control unit which may include a modem for carrying out an immediate alarm call by telephone. Wires Al to Xl can be supplied in turn with +12V. For each one, the voltage is measured in turn on wires A2 to X2. If the voltage is other than OV, there must be conduction at the crossing point of the two wires involved, thus pinpointing moisture there. An alarm signal is then transmitted to the master unit. The switching of the voltage and sensing connections sequentially through all possible combinations is preferably effected under software control. An additional check can be included in the sequencing, by reducing voltage on wires Al to Xl to OV and checking that no alarm signal occurs. Any alarm occurring is indicated as the number of the matrix crossing point on an LED display of the master control unit. In a modification, provision may be made for connections tc both ends of conductors so that a continuity check can be performed. In addition to the moisture detector array, there may be a number of pressure sensitive pads included, either with separate wiring or wired to the matrix, under the roof finish. These can be used to detect unauthorised access to the roof. Also, more than one detector array may be provided, for example below a further impermeable layer, so as to detect condensation within a building. In practice, a wire adhered to an absorbent strip is not the easiest material to produce or handle, and the wire tends to be unduly thick. A better alternative is a metallic tape attached along an absorbent strip. An example of such a conductor is shown in Figure 3. A porous or fibrous strip 20 (seen in cross-section) has along its top surface a conductor tape 21 which is in direct contact with that surface. This is held in place by a cover layer 22 with an adhesive layer 23, in practice an adhesive tape. For assembly purposes, the conductor tape 21 may itself be in the form of a metallised adhesive tape stuck adhesive-to-adhesive to the cover layer 22. The cover layer 22 protects and strengthens the conductor tape. A further possibility is to use an absorbent strip which is of close enough texture to receive a conductive coating deposited directly upon it by any suitable means, for example vacuum deposition, solder dip, or a continuous printing process using an aluminium or graphite paint. The first (lowermost) set of parallel conductors can most simply be provided by an adhesive tape in which the adhesive is on the lower side and a conductive layer is on the upper side. The moisture absorbent strip may use any material, such as cotton, jute, cellulose or synthetic material. It should be rot and vermin proof, so synthetic fibres e.g. glass-fibre, are attractive for this purpose. It will most commonly be fibrous. Depending on the spacing required between conductors two or more discrete parallel conductors may be applied to a single base strip. With appropriate dimensioning, base strips could be laid abutting side by side to cover a whole surface. Given a suitably bulky material, this could provide a full insulating layer over the surface for additional heat insulation. In an improvement of the system, the master control unit can be pre-set so that a certain level of conductivity at any node will be ignored, thus forming a threshold below which a leak alarm will not be generated. This may be applied to the whole roof area, to a certain lesser area, or to a particular node or nodes. This is useful when a matrix has been installed in a new building which is itself still drying out. During that period, there may be sufficient 'internal' moisture to trigger the system, so a higher threshold can be set. In an extreme case, there could be a short at one node, so the unit can be set to ignore all signals from that node. This would save the need to repair the matrix at that point. The systems described are of utility not just for roofs, but also for intermediate floors of a building, for swimming pools, and for other purposes. Figure 4 shows a somewhat different arrangement, in which rather less discrimination as to the leakage point is possible. A moisture leak alarm arrangement 30 is provided beneath a flat roof having a tank room 31, rooflights 32 and a gutter 33 with an outlet 34. As shown, the sensor system comprises nine separate detector units 40, identified by the letters A-H and J, each having a detector/transmitter 20. Each detector 20 is connected to two conductors, respectively indicated by solid and broken lines 41, 42 covering a defined area of the roof. Extending underneath the whole of each detector unit 40 is a water absorbent or blotting pad which when moist, electrically short circuits the conductors to produce an alarm condition. The conductors are of stainless steel so that they are not corroded by moisture. Each transmitter 20 is essentially controlled by a single chip controller, which consists of a timer counter registers, Rom/Eprom and a small amount of Ram. Approximately every six hours the timer output goes to a high level (eg plus 5 volts), which will turn on the microprocessor circuitry. At this stage the microprocessor simply updates a register, which is held in the internal Ram. After incrementing the value in this register, it tests to see if the required time duration is up. As an example, if the alarm is required to come on every 24 hours, then when the value in the register equals 8 (8 x 3 hours) it will turn the detector on. If the time is not up, then it resets the timer chip, and then puts itself back into the stop mode. When an alarm is detected the microprocessor executes a certain program which reads the unit number, turns on the transmitter, blows an indicator flashbulb and turns an O 89/00681 oscillator circuit on and off in such a sequence as to transmit the unit number to a display on the central receiver. After doing all this, the microprocessor resets its counter register, and then resets the timer chip. There can be up to 1024 transmitter units for each receiver. However, only 1000 units are used in practice, since the other unit members are used as synchronization, to ensure that the correct information is sent by the transmitter units, and one is used as a Test Channel. If an alarm is not detected then the device resets itself again. The central receiver unit detects the code sent by the transmitter and after error checking it turns on an alarm and indicates the number of the unit indicating the alarm, on a three digit LED display. Also information can be transmitted directly onto a computer. Provision may be made for receiving signals from two adjacent units, which tends to show that the leak lies at or near the boundary of the areas monitored by those units. The indicator flashbulb is conveniently mounted within the housing 10 of the transmitter 20. It enables a person repairing the roof to quickly confirm which transmitter initiated the alarm; moreover it provides a back-up indication should the display fail at the receiver unit. As an alternative, wire connections are employed throughout instead of the radio signals as previously described and the - entire arrangement is mains powered. All the links are under the waterproof roof covering and the central receiver unit acts as a controller for the entire system. The controller communicates with each of up to 250 individuial slave transmitters via a 3-core screened cable. The screen is used as the OV supply to the slaves, whilst the other 3 are +5V, and the two differential communication lines. The controller sends a unique code to each one of the slaves in turn, and then interogates them to see if an alarm has occurred. If no alarm has occurred on any of the units, then the controller waits until a specified time has elapsed and it again interrogates the slaves. If an alarm is detected then the slave number will appear on a 3 digit LED display on the controller and a buzzer will also be activated.

Claims: CLAIMS 1. A moisture presence alarm system having a sensor system which extends over an area to be monitored, and a detector device which receives signals from the sensor system, the latter comprising spatially separated conductors in conductive contact with a moisture absorbent material, characterised in that the sensor system comprises a plurality of pairs of conductors and detects changes in electrical conditions between said pairs, the position of any leak within said area being determined by selective interrogation of the respective pairs of conductors. 2. A system as claimed in claim 1 wherein the sensor system comprises two sets of conductors, one above the moisture absorbing material and the other below. 3. A system as claimed in claim 2 wherein each set of conductors is parallel and orthogonal to the other, one conductor of each set forming a conductor pair at their respective crossing point. 4. A system as claimed in claim 3 wherein the moisture absorbent material is in the form of a strip which carries a conductor on one surface thereof. 5. A system as claimed in claim 4 wherein the strip is rot- proof 6. A system as claimed in claim 4 or 5 wherein the conductor has the form of a tape applied to the strip so as to be in conductive contact therewith. 7. A system as claimed in claim 1 wherein the conductor & pairs lie adjacent one another on the same side of the moisture absorbent strip, and each pair covers a specific section of said area to be monitored. 5 8. A system as claimed in any preceding claim wherein the detector device can be pre-set with a threshold in respect of the signal from any specific conductor pair so that spurious leak signals can be eliminated. 10 9. An electrical conductor comprising a moisture absorbent strip carrying on one side a single conductor in the form of a tape applied to the strip so as to be in conductive contact therewith. 15 10. A conductor as claimed in claim 9 wherein the conductor is held to the strip by an adhesive cover layer. 11. A conductor as claimed in claim 9 wherein the conductor 20 tape is deposited directly on the strip by metallic deposition. 12. A conductor as claimed in claim 9 wherein the tape is of synthetic plastics carrying a deposit of metal. 25 13. A conductor as claimed in any of claims 9 to 12 wherein the strip has adhesive on the side opposite to the conductor. 14. A method of installing a moisture presence alarm system comprising the steps of applying to an extended surface to be monitored a plurality of conductors, and connecting thereto a detector device for receiving signals from the conductors, characterised in that a first set of conductors is positioned in parallel lines in one direction across the surface, and a second set of conductors is positioned in parallel lines across the surface transverse to the first, the conductors of one of the two sets being held in each case along a moisture absorbent strip which comes to lie between the conductors of the first and second sets. 15. A method as claimed in claim 14 wherein the other set of conductors is attached to a moisture absorbent strip.

Inventors: DARLING JOHN EDWARD, DARLING, JOHN, EDWARD
Applicants: AQUAVEYOR SYSTEMS LTD, AQUAVEYOR SYSTEMS LTD.
Application year: 1988
Main classification: G01M3
IPC codes: E04D13, G01M3