Detector for detecting vibrations

• US 6,069,560 A
• Filed: 02/28/1998
• Issued: 05/30/2000
• Est. Priority Date: 08/30/1995
• Status: Expired due to Term

• Current Assignee: Covial Device AB
• Original Assignee: Covial Device AB
• Inventors: Larsson, Roland
• Primary Examiner(s): TONG, NINA C
• Application Number:
  US09/029,492
• Time in Patent Office: 822 Days
• Field of Search: 340/566, 340/540, 340/683, 340/669, 340/529, 73/654, 73/514.31, 324/207.2, 324/207.15, 324/207.23, 280/735
• US Class Current: 340/540
• CPC Class Codes: G01H 11/02 by magnetic means, e.g. reluctance

Abstract

A security system having a vibration detector that senses vibration in any direction is disclosed. The vibration detector includes two or three detector elements that each have a magnet, and a coil or Hall-effect device that produces a signal in response to changes in a magnetic field in the vibration detector caused by movement of a magnet. The magnet in each detector element is mounted for reciprocating movement in one or more planes about a rest position. Each magnet is held temporarily in the rest position by springs. When three elements are used, the magnets are mounted on journalled shafts or on plate-like springs for reciprocal movement in directions that are at right angles to each other. When only two elements are used, the magnets are mounted on an elongate spring of substantially circular cross section so that the axial dimensions of the springs are at right angles to each other for reciprocating movement in all directions along a respective curved surface coinciding with a plane that is perpendicular to the axial dimension of the spring.

Claims

1. A detector system for a security device adapted for detecting vibration of an object in any of three mutually perpendicular directions, said detector system comprising:

a detector array including a plurality of detector devices, each detector device having a magnet supported for executing reciprocating movements in relation to a rest position, said magnets producing respective magnetic fields,

a respective restraining means operationally associated with each magnet to support the respective magnet from the object, said restraining means holding said respective magnet in said rest position temporarily; and

electrical means operationally associated with said detector devices for emitting an electric signal in response to a change in the magnetic fields produced by movement of said magnets relative to said electrical means,

said restraining means of the magnets of the detector devices providing free movement in space of the magnets collectively in three mutually perpendicular directions to enable the electrical means to produce said electrical signal in response to vibration of the object in any of the three mutually perpendicular directions.

2. The detector system as claimed in claim 1, wherein said plurality of detector devices are three in number and the reciprocal movements of the magnets of the three detector devices are mutually perpendicular.

3. The detector means as claimed in claim 2, wherein said magnets of the detector devices are supported for oscillating movement about three mutually perpendicular axes.

4. The detector means as claimed in claim 2, wherein said magnets of said detector devices are supported for linear reciprocating movement along three mutually perpendicular axes.

5. The detector system as claimed in claim 2, wherein each said detector device comprises a coil having a longitudinal axis coincident with an axis of linear reciprocal movement of the respective magnet, said magnet having north and south magnetic poles disposed along said axis for movement relative to said coil, said coil providing an electrical signal to said electrical means in response to a change in the magnetic field produced by movement of said magnet relative to said coil.

6. The detector system as claimed in claim 1, wherein each said detector device comprises a Hall-effect device adjacent to a respective magnet for sensing movement of said magnet.

7. The detector system as claimed in claim 6, wherein said restraining means comprises a plate-like element having one end supported from the object and its other end being free and attached to a respective one of said magnets, said one end being pivotably supported to the object for movement about a respective one of said mutually perpendicular axes, so as to support said magnet for oscillating movement about said one end.

8. The detector system as claimed in claim 1, further comprising a signal analyzer for detecting a change in said electric signal emitted by said electrical means in response to movement of at least one of said magnets.

9. The detector means as claimed in claim 8, wherein said change in said signal is a change in a amplitude or frequency.

10. The detector system as claimed in claim 1, comprising a casing for said security device, said detector system being included in said casing, said object comprising a door into which said casing is mountable, said casing including an optical device for permitting visual inspection from one side of the door to the other.