| 摘要 |
<p>PROBLEM TO BE SOLVED: To correctly know a number of persons in a room by providing two ultrasonic transceivers on a ceiling near an entrance, measuring time since ultrasonic waves are emitted until reflected waves are received and comparing the measured time. SOLUTION: Ultrasonic transceivers 1a, 1b are provided on a ceiling near an entrance with a distance in a right-angled direction to the entrance. Ultrasonic waves emitted from the transceivers 1a, 1b toward a floor are reflected on the floor, a person or the like and received by the transceivers 1a, 1b, respectively. Measuring devices 2a, 2b measure time from emission to reception, and output to output terminals 3a, 3b. The respective outputs are applied to a comparator 4. The comparator 4 compares both outputs, and outputs the results to an external output terminal 5. By monitoring a change in outputs from the external output terminal 5, a person coming in/out of a room can be identified, and by observing entrance/remove of the room from an empty state, the number of persons in the room can be known.</p> |
