Rotor resistance control circuit for reversible a.-c. motors

Claim 1

IN COMBINATION; A REVERSIBLE A.-C. MOTOR HAVING A ROTOR WINDING, A STATOR WINDING, IMPEDANCE MEANS CONNECTED TO SAID ROTOR WINDING, AND A PLUGGING RELAY FOR CHANGING THE VALUE OF SAID IMPEDANCE MEANS RESPONSIVE TO A PLUGGING CONDITION; SAID PLUGGING RELAY COMPRISING COMPARATOR CIRCUIT MEANS CONNECTED TO SAID STATOR WINDING AND SAID ROTOR WINDING, A RELAY COIL CONNECTED TO SAID COMPARATOR CIRCUIT MEANS, AND RELAY CONTACTS FOR SAID RELAY COIL OPERATIVELY CONNECTED TO SAID IMPEDANCE MEANS; SAID RELAY CONTACTS BEING OPERABLE FROM A FIRST TO A SECOND POSITION FOR CHANGING THE VALUE OF SAID IMPEDANCE MEANS FROM A FIRST VALUE TO A SECOND VALUE; SAID RELAY CONTACTS BEING IN SAID FIRST POSITION WHEN SAID RELAY COIL IS DEENERGIZED AND BEING MOVED TO SAID SECOND POSITION WHEN SAID RELAY COIL IS ENERGIZED; SAID RELAY COIL BEING NORMALLY DEENERGIZED BY SAID COMPARATOR MEANS WHEN THE VOLTAGE OF SAID STATOR EXCEEDS THE VOLTAGE OF SAID ROTOR; SAID RELAY COIL BEING ENERGIZED RESPONSIVE TO THE ROTOR VOLTAGE EXCEEDING SAID STATOR VOLTAGE; SAID COMPARATOR MEANS COMPRISING A FIRST RECTIFIER MEANS CONNECTED TO SAID STATOR WINDING, A SECOND RECTIFIER CONNECTED TO SAID ROTOR WINDING AND A RESISTOR MEANS CONTINUOUSLY CONNECTED IN PARALLEL WITH SAID FIRST RECTIFIER AND IN SERIES WITH SAID SECOND RECTIFIER AND SAID RELAY COIL; SAID RECTIFIERS BEING CONNECTED IN SERIES OPPOSITION TO ONE ANOTHER.