Elevator control including a common transmission circuit with a threshold circuit for each car to determine its availability to answer calls

Claim 1

A GROUP SUPERVISORY CONTROL SYSTEM FOR A GROUP OF ELEVATOR CARS ARRANGED TO SERVE A PLURALITY OF FLOORS COMPRISING, IN COMBINATION, MEANS FOR REGISTERING CALLS, A CALL TRANSMISSION CIRCUIT COMMON TO A PLURALITY OF ELEVATOR CARS OF SAID GROUP AND CORRESPONDING TO THE PATH OF THE CARS CONNECTED TO SAID CALL REGISTERING MEANS, A UNIDIRECTIONAL CONDUCTIVE DEVICE HAVING A FORWARD VOLTAGE DROP IN SAID TRANSMISSION CIRCUIT FOR EACH POSITION CORRESPONDING TO A FLOOR ALONG THE PATH OF THE CARS, MEANS FOR SUPPLYING A SUBSTANTIALLY CONSTANT DIRECT CURRENT TO SAID TRANSMISSION CIRCUIT AT POINTS CORRESPONDING TO REGISTERED CALLS, CURRENT SENSING MEANS FOR EACH CAR CONNECTED TO SAID TRANSMISSION CIRCUIT AT POINTS CORRESPONDING TO THE POSITION OF THE CAR, SAID SENSING MEANS BEING ADAPTED TO DRAIN CURRENT FROM SAID CIRCUIT IN A MAGNITUDE WHICH IS A FUNCTION OF THE AVAILABILITY OF THE CAR TO ANSWER CALLS WHEREBY THE SENSING MEANS OF THE AVAILABLE CAR MOST PROXIMATE A POINT CORRESPONDING TO A REGISTERED CALL ALTERS THE CURRENT IN SAID TRANSMISSION CIRCUIT FROM SAID POINT TO THE SENSING MEANS OF OTHER CARS, AND MEANS FOR STARTING EACH CAR IN RESPONSE TO THE ACCEPTANCE OF CURRENT CORRESPONDING TO A CALL BY ITS SENSOR.