| 摘要 |
PURPOSE:To detect level variation and to detect whether or not there is a mobile body by detecting the difference in amplitude between two pulses obtained by sampling a reflected wave at constant intervals of time. CONSTITUTION:An oscillator 1 sends an acoustic wave outside the audio frequency range to a body to be detected by using an acoustic wave radiator 2. Its reflected wave is passed through a sound collector 3 and level-adjusted by an automatic gain adjusting amplifier 4. The output of the amplifier 4 is sampled by an A/D converter 5 and the amplitude value at the moment of the sampling becomes a digital value, which is supplied to an amplitude difference detector 6. The detector 6 extracts the difference between two sampled values which succeed in terms of time and supplies the absolute amplitude difference signal to an absolute crest value detector 7. Even if the crest value is negative, the detector 7 inverts it to a positive value and outputs the inverted value. This crest value is held by a crest value holding circuit 8 and supplied to a comparator 9. This crest value is compared 9 and when it exceeds a reference value, a comparison output is generated, thereby detecting the mobile body.
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