Ultra-sound Liquid Level Meter
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.
An ultrasonic echo-ranging system in which acoustic energy is propagated at a velocity that depends on a gaseous environment subject to changes which affect the velocity of acoustic propagation to measure a liquid level in an open channel or other liquid container located in said gaseous environment, said system comprising:
(A) an ultrasonic transducer having a diverging radiation field pattern 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 a side path in the radiation pattern of said transducer to intercept energy emitted form said transducer and return it to the transducer to produce reference echo signals, each signal being constituted by a series of pulses of varying amplitude, said series including a first pulse;
(D) receiver means coupled to the transducer to derive therefrom at different times said reference echo signals and said liquid echo pulses, said receiver means including automatic gain control means responsive to said liquid echo pulses and said reference echo signals to produce output pulses of constant amplitude representing the reference echo signals and said liquid echo pulses, said automatic gain control means being constituted by a single automatic gain control which is enabled during a first time slot subsequent to the emission of a transducer pulse to operate on the received reference echo signal and during a later second time slot to operate on the received liquid echo pulse whereby the operation of the control is time shared;
(E) measuring means responsive to the output pulses to measure the time elapsed between the emitted transducer pulse and a subsequent reference echo signal 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 transmit time;
(F) a microcomputer coupled to the measuring means to calculate a ratio existing between the reference and target transit times and to yield an output representing the level of the liquid independent of changes in the gaseous environment, said time slots being created by said computer which is so programmed to control said automatic gain control after a predetermined time interval during which several cycles of ultrasonic energy pulses are emitted by the transducer and are detected thereby, to define a reference time window which is closed a predetermined interval after the first pulse in the series thereof in the reference signal is received regardless of its amplitude, and a subsequent liquid echo pulse window to admit the liquid echo pulse.