Patent Grant
7151461
1. Field of Invention
The invention relates to the field of security systems, and more particularly to a contact tamper switch for detecting attempts to tamper with components of a security system.
2. Description of Related Art
In the field of security systems it is known to provide some means to detect attempts to tamper with the system, for example as an attempt to disable or defeat it. In particular, unauthorized access to system components may be presumed as attacks on the system. In particular, components of the security system may be accessible by potential intruders while the security system is in an unarmed state. As an example, the system component may be located in a room open to the public during normal hours, while the security system is unarmed.
In one embodiment, a circuit board, for example a printed circuit board (PCB), as an element of a security system component, is provided with a pressure-sensitive switch. A cover or enclosure of the security system component can act on the switch when the cover or enclosure is closed. Alternately or additionally, a pressure-sensitive switch may act on the surface the security system component is mounted to. Opening the cover or enclosure, and/or removing the system component from the surface it is mounted to, releases the pressure on the switch, which then changes state to indicate the presumed attack.
This approach has certain drawbacks, however. Among these is the localized pressure on the switch causing uneven stress in the PCB and/or the enclosure or cover. This may lead to fracture or failure with repeated opening and closing of the switch, cover, and/or enclosure. Alternately, the material of the enclosure, for example plastic, may deform or ‘creep’ due to long term closure of the switch. Accordingly, the pressure sensitive switch may no longer be reliably closed due to the material creep. Additionally, the surface to which the system component is mounted may be uneven, and not provide a reliable surface to actuate the pressure sensitive switch.
An alternate tamper detection means comprises a reed switch and magnet arrangement. The reed switch changes state in proximity of the magnet, and the two are located in proximity with one another when the component is mounted to the wall and/or the cover or enclosure are closed. When the moved away from the magnet, typically by opening the cover or enclosure, the reed switch changes state to indicate the presumed attack. At least one drawback of this arrangement is the vulnerability of the reed switch. If a larger magnetic field with the proper polar orientation is placed in the vicinity of the reed switch, the reed switch will not detect loss of proximity with the magnet, which indicates the component may have been disturbed as part of a presumed attack.
Therefore, in order to overcome these and other drawbacks in the prior art, an improved tamper detection switch is desirable. Provided according to the present invention is a tamper detection switch, disclosed primarily for use in an enclosure of a security system component. The enclosure has a base and a cover that may be repositioned relative to the base. One of the cover and the base holds a conductive magnetic element free to translate within a predetermined range generally perpendicular to the respective cover or base. The other of the cover and the base holds at least two ferrous metal contacts of an open tamper circuit in proximity of a conductive magnetic element. In the closed position the conductive magnetic element bridges the ferrous contacts and closes the tamper circuit. Attempts to tamper with the enclosure separate the ferrous contacts from the conductive magnetic element, opening the tamper circuit and signaling a possible attack.
In further refined embodiments, the conductive magnetic element comprises one of a ferrous metal and an electromagnet, either in the shape of a cylindrical disk or a torus. In yet a further embodiment, the cover and base are secured to one another by one or more of a fastener, a snap fit, a friction fit, a mechanical hinge, a living hinge, or other means.
In further embodiments, the ferrous contacts may be mounted on a circuit board, the circuit board being positioned by the cover in its closed position to locate the two ferrous contacts in proximity of the base. The ferrous contacts may be secured to a cover by a snap fit, fastener, adhesive, solvents, friction fit, or other means. In yet a further embodiment, the base comprises a cage separable from the base, the conductive magnetic element being captured by the cage.
These and other features, benefits and advantages of the present invention will be made apparent with reference to the following specification and accompanying figures, wherein like reference numerals refer to like structures across the several views, and wherein:
Referring now to
The circuit board 14 includes a tamper detection circuit 16. The tamper detection circuit 16 is open between two ferrous contacts, 18, 20. In this context, ferrous contacts shall include contacts comprising a ferrous material as at least part therefore, for example ranging from ferrous material throughout to merely as a coating. Ferrous contacts 18, 20 are provided extending at least from a side of the circuit board 16 facing the base 12. In alternate embodiments, the tamper detection circuit may be located elsewhere in the component 11, or elsewhere in the security system generally, provided it is in communication with the ferrous contacts 18, 20. Additionally, one skilled in the art will recognize that the circuit board 14 itself is not essential, and any structure suitable to hold the ferrous contacts 18, 20 will suffice.
Base 12 includes a cage 22 for holding a conductive magnetic element 24. Cage 22 may be integral with the base 12, or as illustrated in the Figures, it may be a separable component independently mounted to the underlying surface 30. The conductive magnetic element may include a ferrous material having relatively low resistivity, or an electromagnet, similarly having low resistivity. Alternately or additionally, the conductive magnetic element may comprise one of a variety of low conductivity magnetic rare earth metals, ceramic, or alloy of aluminum, nickel and cobalt (sometimes termed ‘alnico’), to which a conductive, e.g., metallic, coating or plating is applied. Though many shapes of conductive magnetic element 24 are acceptable, in the exemplary embodiment it is cylindrical, as a disk or a torus. The cage 22 can by generally in the shape of the conductive magnetic element 24, or at least operative to prevent significant lateral movement or tilting of the conductive magnetic element 24. The conductive magnetic element 24 is free to move perpendicular to the base 12 and/or the circuit board 14, within a range permitted by stops 26. Additionally, stops 27 may be provided beneath the conductive magnetic element 24 to limit its downward axial movement. Alternately, if convenient with the mounting of the circuit board 14, the cage 22 may have a lower height dimension such that stops 27 are unnecessary in view of the underlying surface 30. Even so, they may still be provided for convenience in manufacturing and installation.
The operation of the magnetic contact tamper switch will now be described.
Referring now to
Additional protection is provided where, as in the illustrated embodiment, the cage 22 is separate from the base 12 and independently mounted to the underlying surface 30. In that case, where an intruder were to attack by attempting to remove the base 12 from the underlying surface 30, the cage 22, and consequently the magnetic element 24, would remain secured to the surface 30, and the tamper circuit 16 would be broken, indicating a potential attack.
In an alternate embodiment, the magnetic tamper switch 10 may be mounted within the component 11 in an inverted fashion. That is, the cage 22 and conductive magnetic element 24 may be provided on a cover 13, while the tamper switch are held by the base 12.
The present invention has been described herein with reference to certain exemplary and/or preferred embodiments. Certain alterations or modification may be apparent to those skilled in the art, in light of the present disclosure, without departing from the scope of the invention. These embodiments are meant to be illustrative, and not limiting, on the scope of the present invention, which is defined with reference to the appended claims.
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|---|---|---|---|
| 4296394 | Ragheb | Oct 1981 | A |
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| Number | Date | Country | |
|---|---|---|---|
| 20060092020 A1 | May 2006 | US |
