Reed Switches

A reed switch is basically two contacts sealed inside a glass envelope which can be closed or opened by a magnetic field being applied... either by a magnet or a coil.

As the contacts are sealed they are remarkably long lasting, within their rated operating parameters.

They are used mostly for small signal switching as the contacts are sealed and don't suffer from corrosion, except by the usual pitting caused by current flow.

John.

The only caveat with reed switches is that they can become slightly magnetic and develop a "memory" after many, many cycles, and therefor should not be used for systems that are guaranteed to preserve someone's physical safety, such as on a machine guard. Other than that, they are a nice, simple, and reliable switching device for low-voltage circuits.

Ing. Robert Forbus

Well they are used in Cardiac Pacemakers I have designed usually infant mortality failure.

hi. whats the magnetic switch for? its function? thanx.

I think if you will picture the mouthpiece on a double reed wind instrument, like an oboe, and you picture a contactor on each one, facing the contactor on the other, and they are held apart--or together--until they are opened, or closed, magnetically by a separate circuit, when you get some idea of the inner workings. And why a read switch is called a reed switch (or called reeds in a relay). If you haven't seen such an instrument, the reeds in a harmonica or accordian would make for a similar comparison.

So it's called reed swith because the switch arms are reeds or something that resembles reeds. I believe an other main advantage is that they can be made small and actuated precisely with very little current force.

Reed switches are hermetically sealed contacts, operated by an external magnet.The standard reed switch will respond to either north or south polarity.There are also north-seeking and south seeking reed switches, which as the name implies, are only operated with the proper polarity magnetic field present.There are mercury-wetted contacts that last virtually forever.(Hundreds of millions of operations).Common applications are low current, such as intrusion sensors (burglar, etc), revolution counters, wire guided robots, even level controls.Some even have built in resistors and or diodes for loop supervision.

Hope this helps

Obenay N. Pebvk

I would like to add that these reed switches can be operated by ac magnetically induced fields and so do not exhibit any 'memory' effect.....

The polarity of the magnetic field for a basic reed switch doesn't matter.....

UNLESS the reed switch assembly contains a biasing magnet which the external magnetic field must overcome......

Most reed swtches do not have this magnet fitted as standard.

John.