Reed Relays and
Electronics India Limited
Manufacturer of Reed Switches, Reed Sensors and Reed-based products
Reed Relays and Electronics India Limited Incorporated in 1971

Reed Sensor

A reed sensor is a device built using a reed switch with additional functionality or features, for example, to withstand higher shock, easier PCB mounting, additional intelligent circuitry, biased contact states, etc.

Reed Sensor (Wikipedia)
(from top) Single-pole reed switch, four-pole reed switch and single-pole reed relay. Scale in centimeters.
Reed switch, contact detail.
Commonly-used circuit symbol
Operation of the reed switch

The reed switch is an electrical switch operated by an applied magnetic field. It was invented at Bell Telephone Laboratories in 1936 by Walter B. Ellwood. In its simplest and most common form, it consists of a pair of ferromagnetic flexible metal reeds contacts in a hermetically sealed glass envelope. The contacts are usually normally open, closing when a magnetic field is present, or they may be normally closed and open when a magnetic field is applied. The switch may be actuated by an electromagnetic coil, making a reed relay, or by bringing a permanent magnet near the switch. When the magnetic field is removed, the reeds in the reed switch return to their original position.

The reed is the metal part inside the reed switch envelope that is relatively thin and wide to make it flexible. It somewhat resembles part of some reed plants. The term "reed" may also include the external wire lead as well as the internal part.

An example of a reed switch application is to detect the opening of a door, when used as a proximity switch for a security alarm.

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