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.