| 摘要 |
<p>PROBLEM TO BE SOLVED: To prevent erroneous detection by encoding a signal sent out of an ultrasonic loudspeaker in a pulse shape. SOLUTION: An ultrasonic wave signal generated by an ultrasonic wave generating circuit 1 is converted into a gate in an ultrasonic wave gate circuit 3 by a gate signal of a gate pulse generating circuit 2, and becomes a pulse-like encoded signal. A reflected signal from a train 5 to be detected which is emitted in a space from an ultrasonic loudspeaker 4, is received by an ultrasonic microphone 6, and is inputted to a delay time detecting and pattern discriminating circuit 7. A delayτof this signal to the emitting timing is time corresponding to a distance between the ultrasonic loudspeaker 4→the train 5 to be detectedζthe ultrasonic microphone 6, and when a code pattern of its signal is the.same as a signal outputted from the ultrasonic loudspeaker 4, a train detecting signal is outputted from the output end 8. When an input signal is not inputted to the ultrasonic microphone 6 or the delayτis fairly different from time corresponding to a distance up to reception from emission of an ultrasonic wave or the code pattern does not coincide with an output signal, the train detecting signal is not outputted.</p> |
