Reed switch structure and operation: The form A reed switch comprises of two ferromagnetic reeds placed with a gap in between and hermetically sealed in a glass tube. The glass tube is filled with an inert gas, (nitrogen), or a vacuum to prevent the oxidation of the contacts. The surfaces of the reed contacts are plated with metals from the platinum group such as rhodium, ruthenium, palladium or iridium either by electroplating or sputtering.
The reed switch is operated by the magnetic field of an energized coil or a permanent magnet which induces north (N) and south (S) poles on the reeds. The reed contacts are closed by this magnetic attractive force. When the magnetic field is removed, the reed elasticity causes the contacts to open the circuit.
Reed switch actuation: In all systems, magnet and reed switch must be brought to within a specific proximity of each other. This distance will vary in accordance with the sensitivity of the reed switch, the amount of lead that is cropped and the strength of the magnet. As the lead is cut the switch sensitivity decreases as there is less ferromagnetic material to attract the magnet flux. When the magnet is close enough, the normally open contacts will close, when the magnet is removed the contacts will open. The relative distance for operation is always less than that for a release.
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