The Reed relay consists of a reed switch placed inside a coil. When a current flows through the coil, a magnetic field is formed. This field makes the contacts inside the reed switch close(or open if it is a normaly closed switch). The reed relay has a long life timeand the contacts has low variation in contact resistance and low bounce. The relays need only about 10mA of current to close and can be driven directly by most logic ICs. Older reed switches used mercury as contact material. Modern reed relays uses the more environmentaly friendly ruthenium or rhodium.

Reed relays is not much used any more, but might be found in some older public access branch exchanges.

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