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Control Devices
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RELAYS
A relay is simply a remote-control switch, which uses a small amount
of current to control a large amount of current. A typical relay has
both a control circuit and a power circuit. Relay construction
contains an iron core, electromagnetic coil, and an armature (moveable
contact set). There are two types of relays: normally open (shown
below) and normally closed (NOT shown). A Normally open (N.O.)
relay has contacts that are "open" until the relay is energized
while a normally closed (N.C.) relay has contacts that are "closed"
until the relay is energized.
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