Means for monitoring the operating speed of a motor

Claim 1

MEANS FOR MONITORING THE OPERATING SPEED OF AN ELECTRIC MOTOR NORMALLY OPERATING AT A SELECTED MAXIMUM SPEED RELATIVE TO THE FREQUENCY OF AN ALTERNATING CURRENT SOURCE, AND SAID MOTOR HAVING A PLURALITY OF FIELD WINDINGS ENERGIZED FROM SAID ALTERNATING CURRENT SOURCE; SAID MONITORING MEANS COMPRISING A BRIDGE CIRCUIT INCLUDING AT LEAST ONE OF SAID FIELD WINDINGS IN AN ARM THEREOF, AND ELECTRICAL INPUT LINES TO SAID BRIDGE CIRCUIT OPERATIVELY CONNECTED TO SAID ALTENATING CURRENT SOURCE, OUTPUT LINES FROM SAID BRIDGE CIRCUIT, AND ELECTRICAL CONDITION INDICATOR MEANS OPERATIVELY CONNECTED TO SAID OUTPUT LINES, SAID BRIDGE CIRCUIT BEING SO ARRANGED AS TO BE NORMALLY BALANCED UPON OPERATION OF SAID ELECTRIC MOTOR AT SAID SELECTED SPEED, AND UPON THE MOTOR OPERATING AT A SLOWER SPEED THAN SAID SELECTED SPEED THE IMPEDANCE OF THE FIELD WINDINGS OF SAID MOTOR MAY BE EFFECTIVELY CHANGED SO AS TO UNBALANCE THE BRIDGE CIRCUIT WHEREUPON THE ELECTRICAL CONDITION INDICATOR MEANS BECOMES EFFECTIVE TO INDICATE SAID SLOWER SPEED CONDITION OF THE MOTOR.