Electric alarm device for sensing signal over power distribution system

Claim 1

IN AN ELECTRIC ALARM DEVICE FOR SOUNDING AN ALARM IN RESPONSE TO A SIGNAL AT AN ALARM FREQUENCY SUPERIMPOSED ON THE REGULAR A.-C. SUPPLY LINE, THE COMBINATION COMPRISING A CONSTANTLY DRIVEN A.-C. MOTOR, A CAM SWITCH, A CLUTCH INTERPOSED BETWEEN THE MOTOR AND THE CAM SWITCH, A RESONANT RELAY HAVING AN INPUT CIRCUIT COUPLED TO THE SUPPLY LINE FOR RESPONSE TO THE ALARM SIGNAL AND HAVING OUTPUT CONTACTS, SAID CAM SWITCH INCLUDING NORMALLY CLOSED CONTACTS SO ARRANGED THAT WHEN THE CAM IS DRIVEN FROM A START POSITION TO A SAMPLING POSITION THE RESONANT RELAY INPUT CIRCUIT IS MOMENTARILY OPENED TO DROP OUT THE RESONANT RELAY, SAID CAM SWITCH FURTHER HAVING NORMALLY OPEN CONTACTS FOR SETTING UP AN AUXILIARY CIRCUIT TO THE CLUTCH TO MAINTAIN THE CLUTCH ENERGIZED DURING THE PERIOD OF DROP-OUT, BIASING MEANS FOR DISENGAGING THE CLUTCH AND FOR RESTORING THE CAM TO ITS START POSITION UPON FAILURE OF THE RESONANT RELAY TO RECLOSE AFTER ITS MOMENTARY OPENING DUE TO ABSENCE OF THE ALARM SIGNAL FROM THE SUPPLY LINE, AND ALARM MEANS ACTUATED BY THE CAM SWITCH UPON TRAVERSAL OF THE SAMPLING POSITION AND UNTIL THE CAM IS DRIVEN BACK TO ITS STARTING POSITION.