| 摘要 |
<p>The embodiment of the invention disclosed herein is directed to a sensing device for determining the passage of high velocity, relatively small articles such as seeds being planted through high volume automatic planting apparatus used by farmers. The sensing device has a pair of spaced apart ultrasonic transducer elements, one acting as a transmitter and the other acting as a receiver. The driving circuit for the transmitting transducer has a feedback path coupled to the receiving amplifier of the receiving transducer. The pair of transducers, together with their respective driving and receiving circuits, form a closed loop oscillator circuit which includes the air gap between the transmitting and receiving elements. The spacing between the transmitting and receiving elements is maintained an integral number of half wavelengths to provide maximum sensitivity to high velocity small articles passing therebetween.</p> |
