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Time-shaped AGC for ultrasonic liquid level meter of the echo-ranging type

  • US 4,578,997 A
  • Filed: 07/30/1984
  • Issued: 04/01/1986
  • Est. Priority Date: 01/04/1982
  • Status: Expired due to Term
First Claim
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1. An ultrasonic echo-ranging system to measure the level of a liquid in an open channel or other liquid container located in a gaseous environment subject to changes which affect the velocity of acoustic propagation;

  • said sytem comprising;

    A. an ultrasonic transducer disposed at a fixed position directly above the liquid;

    the gaseous environment therebetween determining the velocity of ultrasonic energy propagated therethrough;

    B. means to excite the transducer to emit periodic pulses of ultrasonic energy which are directed toward the surface of the liquid and reflected from this target to produce liquid echo pulses which return to the transducer and are detected thereby;

    C. reference means at a fixed point relative to the transducer to intercept energy emitted from said transducer and return it to the transducer to produce reference echo pulses;

    D. receiver means coupled to the transducer to derive therefrom at different times said reference echo pulses and said liquid echo pulses, said receiver means including automatic gain control means responsive to said pulses to produce output pulses of constant amplitude representing the reference pulses and output pulses of constant amplitude representing the liquid pulses, said automatic gain control means being constituted by a single automatic gain control circuit which is enabled during a first time slot subsequent to the emission of a transducer pulse to operate on the received reference echo pulse and during a later second time slot to operate on the received liquid echo pulse whereby the operation of the circuit is time shared;

    E. measuring means responsive to said output pulses to measure the time elapsed between the emitted transducer pulse and a subsequent reference echo pulse to determine the reference transit time, and to measure the time elapsed between the emitted transducer pulse and a subsequent liquid echo pulse to determine the target transit time; and

    F. a computer coupled to the measuring means to calculate the ratio of the reference and target transit times and to yield an output representing the level of the liquid independent of change sin the gaseous environment.

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