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Electromechanical relays are devices that
complete or interrupt a circuit by physically moving
electrical contacts into contact with each other. A relay
involves two circuits: the energizing circuit and the
contact circuit. The coil is on the energizing side and the
relay contacts are on the contact side. When a relay coil is
energized, current flow through the coil creates a magnetic
field. Whether in a DC unit, where the polarity is fixed, or
in an AC unit where the polarity changes 120 times per
second, the basic function remains the same: the magnetic
coil attracts a ferrous plate, which is part of the
armature. One end of the armature is attached to the metal
frame that is formed so that the armature can pivot, while
the other end opens and closes the contacts. Relay contacts
are designed, built and specified for the type of
application for the relay. No single voltage and current
rating applies to a given set of contacts under all
circumstances. Contact the relay manufacturer for guidance
if your requirements are unusual or the specifications seem
incomplete.
Relay-type choices available for electromechanical relays
include general-purpose relay, machine control or heavy-duty
relay, reed relay, and aerospace or MIL-Spec relay.
General-purpose relays operate with AC or DC current, at
common voltages and they can control currents ranging from
2A to 30A. A heavy-duty relay is used to control starters
and other industrial components. Reed relays are capable of
switching industrial components such as solenoids,
contactors and starter motors. An aerospace or MIL-spec
relay meets appropriate military specifications or is
intended for aerospace applications. Mounting choices for
electromechanical relays include PC board, socket or plug-in
style, bracket or flange mount, and DIN rail. |
