Reed Switch working | How Reed Switch Works

This page describes Reed Switch working operation. It mentions how Reed Switch works along with its construction and circuit symbol.

What is Reed Switch?:
• It is magnetically activated mechanical switch.
• It consists of two metallic contacts enclosed in a small enclosure usually glass capsule.
• The contacts are magnetic and move in response to a magnetic field. Permanent magnet is needed to activate the switch.
• There are two types of reed switches viz. SPST and SPDT. Most common one is SPST which is either normally open or normally closed type. The bistable version is also available.

Reed Switch structures

The figure-1 depicts two most commonly used reed switch structures viz. make type and change over type.

Reed Switch working | How Reed Switch Works

Reed Switch working

Let us understand Reed switch working operation with respect to its application as an alarm system which is triggered by intruder entering the home/office building.
➤In this system, magnet is attached to a door or window and reed switch is attached to the frame very close to the magnet. Both magnet and reed switch are enclosed in sealed plastic enclosure.
➤Here as long as the door/window is closed, magnet activates the reed switch. It is known as "normally closed" condition.
➤When the door/window is opened by stranger or some intruder, magnet part moves away from the reed switch part. As a result, contacts relax and circuit is broken. As a result alarm is triggered.
➤Reed switches are commonly supplied with axial leads. Hence they can be connected in series. Hence any one switch is opened, alarm is triggered.

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