| 摘要 |
<p>METHOD AND APPARATUS FOR ULTRASONIC MATERIAL LEVEL CONTROL A method and apparatus for material level control in which an ultrasonic transducer is mounted at the top of a material tank and is directed to transmit pulses downwardly toward and receive echo pulses reflected upwardly from the upper surface of a stored material. The echo signals from eight successive long-range pulses are digitized and then integrated according to apparent surface distance so that the sum of the true echo signals returned from the material surface is substantially greater than the sum of random noise signals for each transmitted pulse. An ultrasonic transducer is also disclosed in which a piezoelectric crystal is bonded to a flat diaphragm with the neutral bending axis of the crystal/diaphragm combination being within the bonding agent. The diaphragm is then pressed into the open end of a hollow shell to tune transducer resonant frequency, and a mixture of RTV and sand is cured within the shell to tune the transducer Q.</p> |
