A relay is an electromagnetic switching device consisting of an armature which is moved by an electromagnet to operate one or more switch contacts.
Some advantages of relays are that they provide amplification and isolation and are straightforward. They can switch difficult voltages (e.g. RF or high-powered AC) with complete isolation and no worries about level translation.
Relay disadvantages, compared to solid-state switching, include power efficiency, noise (both mechanical and electrical, including "contact bounce"), size, speed, and reliability. Analog switches are commonly used instead of relays in signal switching applications.
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