| 摘要 |
A transmitting transducer is mounted on the outside wall of a vessel and supplies bursts of ultrasonic energy. If liquid is present, the energy is coupled to the other side of the vessel. Otherwise, the energy is attenuated. A receiving transducer (which may be the same as the transmitting transducer) is positioned to receive the ultrasonic energy if liquid is present. It is gated to be active only when such energy should arrive in the presence of liquid. The receiving transducer therefore generates an electrical signal indicating presence or absence of liquid in the vessel at the level at which the transducers are mounted.
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