Magnetics

How Reed Switches are used with a Permanent Magnet

Using Reed Switches in a sensing environment, one generally uses a magnet for actuation. It is important to understand this interaction clearly for proper sensor functioning. Sensors may operate in a normally open mode, a normally closed mode or a latching mode.

In the normally open mode, when a magnet is brought toward the Reed Switch (or vice versa) the reed blades will close. When the magnet is withdrawn the reed blades will open. With the normally closed sensor, bringing a magnet to the Reed Switch the reed blades will open, and withdrawing the magnet, the reed blades will re-close. In a latching mode the reed blades may be in either an open or closed state. When a magnet is brought close to the Reed Switch the contacts will change their state. If they were initially open, the contacts will close. Withdrawing the magnet the contacts will remain closed. When the magnet is again brought close to the Reed Switch, with a changed magnetic polarity, the contacts will now open. Withdrawing the magnet the contacts will remain open. Again, reversing the magnetic polarity, and bringing the magnet again close to the Reed Switch the contacts will again close and remain closed when the magnet is withdrawn. In this manner, one has a latching sensor or a bi-stable state sensor.

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Reed Switch used with Permenent Magnet