Priniciples of Electromechanical Relay Operation
3.24 Introduction to Polarized Relays
A polarized relay is one that responds to the polarity as well as the
magnitude of the energizing current. One way of accomplishing this type of
operation is by connecting a blocking diode, either in series or in shunt,
with the coil of a conventional dc relay. When the energizing voltage is of
the correct polarity, operation takes place as in a conventional relay; with
opposite polarity applied voltage there is no response.