Two=part signal generating remote control relay - provides difference frequency, obtained from control signal and generated tone, to indicate presence of control signal

摘要

A control relay is operated by a control signal in the form of a preset frequency signal superimposed on the power supply network voltage. The control signal is detected by generating a second signal at a frequency such that mixing the two produces a very low frequency difference signal whose pressure signals the reception of the control signal. The second signal is provided by a generator which produces the signal at an initial first frequency different to that of the control signal during a first part of the latter and then at a second different frequency during a second part of the control signal period to trigger the relay. A detector passes the second frequency to trigger the relay after it has detected the first part of the control signal.