High security balanced-type, magnetically-actuated proximity switch

Abstract

A magnetically-actuated, proximity switch system for use in physical security monitoring systems, machinery control systems and the like, including a stationary assembly and an actuator assembly moveable relative thereto. The stationary assembly includes at least two electrically-interconnected magnetic reed switches and at least two interacting permanent biasing magnets disposed in a predetermined physical relationship. The magnets are arranged to have opposing polarity orientations which produce a resultant interactive magnetic field. Each reed switch is biased in a magnetically actuated state by its orientation and position within that field. The actuator assembly in turn includes at least two permanent actuating magnets arranged to produce a number of apparent magnetic poles corresponding to the number of apparent (or consequent) poles produced by the permanent biasing magnets and in opposition thereto. Thereby, the permanent magnet resultant interactive field is altered, thereby overcoming the effect of the permanent biasing magnets when the stationary assembly and the actuator assembly are in a predetermined relative physical relationship. The number of apparent poles is odd, and they are interactive so that the stationary assembly advantageously cannot be deceived or defeated using only a single permanent external magnet. A ferrous metal slug can be provided between the two bias magnets to aid in adjusting the positioning of the components to yield the desired performance and to magnetically short out a powerful individual magnet that could be eternally positioned in the center of the bias magnets in an attempt to defeat the device. A U-shaped ferrous metal shield can be used as an outer enclosure for the switch module.