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A
latching relay has two relaxed states (bistable).
These are also called 'keep' or 'stay' relays. When
the current is switched off, the relay remains in
its last state. This is achieved with a solenoid
operating a ratchet and cam mechanism, or by having
two opposing coils with an over-center spring or
permanent magnet to hold the armature and contacts
in position while the coil is relaxed, or with a
remnant core. In the ratchet and cam example, the
first pulse to the coil turns the relay on and the
second pulse turns it off. In the two coil example,
a pulse to one coil turns the relay on and a pulse
to the opposite coil turns the relay off. This type
of relay has the advantage that it consumes power
only for an instant, while it is being switched, and
it retains its last setting across a power outage. |
