| 摘要 |
PURPOSE:To exactly detect a distance for a moving car in a travelling forward side by projecting a supersonic wave of a different frequency from a forward moving car at which a supersonic wave projected toward the forward side in an advancing direction is received toward a rear car. CONSTITUTION:A moving car A2 of a forward side projects a supersonic wave of second frequency f2 from a second transmission sensor S4 toward another moving car A1 of a rear side as the moving car A1 of the rear side is approached within a set distance and a second receiving sensor S3 provided for the rear side of the body receives the supersonic wave of first frequency f1. When the moving car A1 receives the second frequency f2, a counter 10 is stopped and measures elapsed time till the supersonic wave of the second frequency f2 is received after the supersonic wave of the first frequency f1 is projected. Since the elapsed time corresponds to the distance between two moving cars A1, A2, according to this elapsed time the distance up to the moving car A2 of the forward side can be detected.
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