PURPOSE: To perform reliable detection of approach of a moving object in a position spaced away by a given distance.
CONSTITUTION: Two sensors 11 and 21 to detect a sound wave propagating through a rail 10 when a moving object is run over rails 10 are provided. The two sensors 11 and 21 are arranged along the rail 10 and in a position spaced away by a distance being an odd number times as long as 1/4 of a wavelength λof a sound wave of detecting frequency. A delay circuit 14 is located in a manner to delay from the output of the one 11 of the two sensors by a time equivalent to λ/4. By adding an output from the delay circuit 14 and an output from the other 21 of the two sensors, detecting sensitivity in the one direction in which the moving object approaches is maximized and detecting sensitivity in a direction reverse to the one direction is minimized.
SUGIURA HIROSHI
FUKUCHI TETSUO
MEIKO KENSETSU KK
SYST GIKEN KK