| 摘要 |
<p>Ultrasonic double-sheet detecting system in which the frequency of the ultrasonic source is tuned to the natural frequency of the total system in the circumstances as things are. When no sheet-like object is present in the detecting system this system is in a situation comparable with proximities between microphone and loud speaker, and the frequency of the oscillator is tuned thereto. When a sheet-like object is present that situation is replaced by a comparator situation between the phases of the oscillator and of the ultrasonic signal receiver.</p> |
