Communications: electrical – Condition responsive indicating system – Specific condition
Patent
1990-01-19
1990-10-23
Orsino, Joseph A.
Communications: electrical
Condition responsive indicating system
Specific condition
324557, 73 40, G08B 2100
Patent
active
049655540
DESCRIPTION:
BRIEF SUMMARY
This invention relates to a moisture presence alarm system, in particular for the roofs of buildings, but also for other purposes such as beneath a swimming pool.
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 by repairs can be even greater.
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. Other systems locate leaks by calculating the distance along a pair of wires to the point where a conductivity change has occurred.
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 leak 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 first set of generally parallel conductors extending in one direction on one side of the moisture absorbent material, and a second set of generally parallel conductors arranged transversely of said direction on the other side of the material, wherein the conductors of at least one set are attached to moisture absorbent strips, and wherein the conductors are electrically independent, forming a matrix such that each conductor of each set forms a conductor pair at their respective crossing points and the conductors are narrow compared with the spacing between them; and in that the detector device 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.
Preferably, each electrical conductor comprises 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 order that the invention shall be clearly understood, several exemplary embodiments thereof will now be described with reference to the attached drawings, in which:
FIG. 1 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; and
FIG. 3 shows a cross-section of an electrical conductor strip.
FIG. 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 respectively 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 pinp
REFERENCES:
patent: 4110945 (1978-09-01), Sheahan
patent: 4404516 (1983-09-01), Johnson, Jr.
"Plant Moisture-Detector is Self-Checking", Electric World, Jun. 15, 1972, pp. 34-35.
"Dissolving Paper Triggers Leak Sensor", Machine Design, Feb. 10, 1972, p. 115.
Hofsass Jeffery A.
Orsino Joseph A.
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