Abstract: A control system for a revolving door includes an ultrasonic sensor having multiple sensor heads. The door has a housing and multiple movable compartments formed by door wings. The sensors emit energy waves into the housing in bursts, then receive echoes from any objects, including people, in the compartments. The sensors are activated when the door is activated by an authorized user. A controller stores a binary "echo" or "no echo" signal in memory in response to an emitted energy wave. The system determines a maximum height of an object or person in a compartment, then measures the total amount of time that it detects something above a selected percentage of the maximum height. When this time reaches a predetermined amount, the system interprets that as "piggybacking" (two individuals in one compartment). The system also interprets signals that go above, drop below, and then rise above the selected percentage again as piggybacking.

Abstract: A control system for a revolving door includes an ultrasonic sensor having multiple sensor heads. The door has a housing, and multiple moveable compartments formed by door wings attached to and radially extending from a rotatable axis. The sensors emit energy waves into the housing in bursts, then receive echoes from any objects, including people, in the chambers. The sensors are activated when the door is activated by an authorized user. A controller stores a binary "echo" or "no echo" signal in memory in response to an emitted energy wave. The memory is formed by multiple arrays, each array having a column associated with a particular sensor and used for storing echo signals from a particular ultrasonic burst. Each bit in a column represents incremental ranges of objects from the sensor head, and the controller stores the "echo" or "no echo" signal in an appropriate bit based on the elapsed time from the preceding burst.