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Magnetic switch has a ball

01 November, 2002

Magnetic switch has a ball

A US company has developed a magnetically operated switch which, it claims, is the first significant improvement in two-wire magnetic switches in 50 years. The Magnasphere technology, which is protected by six patents, is said to offer many advantages over conventional devices such as proximity sensors, Hall effect switches, reed switches and mercury tilt switches.

At the heart of the new switch is a spherical magnet. This is held in a stainless steel housing which is sealed with a ferromagnetic cap containing a cylindrical contacting electrode, from which it is insulated. In the normally open position, the magnetic sphere is attracted to the ferromagnetic portion of the cap, away from the electrode. The switch can be held in any orientation and will stay open.

When an actuator magnet approaches the switch from the end opposite the electrode, it attracts the sphere which snaps into position at the end of the case, closing the circuit between the case and the central electrode. The activation zone is far smaller than that of a reed switch, and a magnet outside the zone will pull the sphere away from the electrode, thus opening the switch and limiting the possibility of tampering. The actuating magnet can be of either pole.

The tiny (5.8mm diameter) switch is not affected by electromagnetic interference or by extremes of temperature, and can thus be installed inside equipment such as motors. It can be used in volatile atmospheres and the contacts will not weld if a high voltage is placed across them.

The operating air gap is nominally around 12mm for a neodymium magnet, or 1.6-3.1mm for a ferrous metal actuator. The switch`s operating life is said to be at least 300,000 cycles with a 250mA resistive load.

Because the Magnasphere responds to ferrous metals, it can be used as a direct replacement for inductive proximity switches. It can also replace Hall effect switches, delivering a similar performance without needing a power source.




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