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Reed Switch

img_reed

The Reed Switch is an electrical switch that operates in response to an applied magnetic field. It was invented by Walter B. Ellwood of Bell Telephone Laboratories in 1936 and patented in the United States on June 27, 1940, under patent number 2264746.

Principle of Operation

The reed switch operates on a straightforward principle. Two metal reeds, typically made of iron and nickel, are sealed within a glass tube, overlapping at their endpoints but separated by a small gap of just a few microns. The glass tube is filled with a high-purity inert gas, such as nitrogen, or, in some cases, is vacuum-sealed to enhance high-voltage performance.

The reeds function as magnetic flux conductors. When no magnetic field is applied, the reeds remain separated. When exposed to a magnetic field generated by a permanent magnet or an electromagnetic coil, the magnetic flux induces opposite polarities at the reeds’ endpoints. If the magnetic force exceeds the natural spring tension of the reeds, they come into contact, closing the circuit. Once the magnetic field weakens or disappears, the reeds’ inherent elasticity causes them to separate, opening the circuit again.

This simple yet effective mechanism makes the reed switch highly reliable for various applications requiring magnetic field-triggered switching.

img_reed_sche

Example