| 摘要 |
An ultrasonic, echo-ranging instrument for measuring liquid level, the instrument including a transducer dispoed at a fixed position directly above the liquid surface. The transducer is excited to emit periodic pulses which are intercepted by the liquid surface as well as by a reference point a fixed distance from the transducer to produce both reference and liquid echo pulses that are returned to the transducer and detected thereby. The respective transit times of the reference echo and the liquid echo pulses are determined, and the ratio between these transit times is computed to provide an output representing the level of liquid. To ensure accurate readings, the reference echo and liquid echo pulses from the transducer are fed to a single automatic gain control circuit whose operation is time shared. Time sharing of the AGC is effected by means of a microcomputer which in the reference mode enables the AGC to effect gain control of the reference echo pulse during a time slot or window that is closed shortly after the first reference pulse is received regardless of its amplitude, the AGC thereafter being enabled in the liquid mode to effect gain control of the liquid echo pulse.
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