Acoustic current meter

An acoustic current meter for measuring a component of a velocity of a flow of liquid, comprising:

• two transducers positioned so that acoustic energy emitted by each of the transducers travels along an acoustic path therebetween and impinges upon the other transducer, each transducer including terminals for applying a signal thereto to cause the transducer to emit acoustic signals and for providing a transducer output signal representative of an acoustic signal received by the transducer;
• means for periodically applying an A.C. signal of a first frequency to both transducers concurrently to cause the transducers to periodically emit bursts acoustic energy of the predetermined frequency;
• and
• means, responsive to output signals produced by each transducer in response to acoustic energy emitted by the other transducer, for comparing the phase of the transducer output signals and for providing an output signal representative of the phase difference therebetween, including:
• means for heterodyning each transducer output signal with a signal of a second frequency to provide two difference frequency signals;
• and
• means for comparing the phases of the difference frequency signals, and
• wherein the impedance presented to each transducer during periods when it is emitting acoustic signals is substantially equal to the impedance presented to that transducer during periods when it is receiving acoustic signals.

A system for measuring a component of the velocity of a flow of liquid and for providing an output signal representative of the component of the velocity, comprising:

• at least two transducers positioned so that acoustic energy emitted by each of the transducers travels along an acoustic path therebetween and impinges upon the other transducer, each transducer including terminals for applying a signal thereto to cause the transducer output signal representative of an acoustic signal received by the transducer;
• a transmit oscillator for providing an output signal of a first frequency;
• means for periodically applying the transmit oscillator output signal to each of the transducers to cause the transducers to emit a burst of acoustic energy;
• a reference oscillator for producing an output signal at a second frequency different from the first frequency by a difference frequency;
• first and second signal processing channels respectively associated with the first and second transducers for processing output signals produced by the associated transducer in response to acoustic signals received thereby, each signal processing channel including;
• means, responsive to the output signal from the associated transducer and to the reference oscillator output signal, for producing an intermediate signal at the difference frequency having a phase which is representative of the phase of the acoustic signal received by the associated transducer;
• and
• means for comparing the phases of the intermediate signals from the first and second processing channels and for producing a signal representative of the phase difference therebetween to provide a representation of the velocity component of the liquid flow being measured;
• and
• wherein the impedance present to each transducer during periods when it is emitting acoustic signals is substantially equal to the impedance presented to that transducer during periods when it is receiving acoustic signals.

A system for measuring a component of the velocity of a flow of liquid and for providing an output signal representative of the velocity component, comprising:

• at least two transducers positioned so that acoustic energy emitted by each of the transducers travels along an acoustic path therebetween and impinges upon the other transducer, each transducer including terminals for applying a signal thereto to cause the transducer to emit acoustic signals and for providing a transducer output signal representative of an acoustic signal received by the transducer;
• a transmit oscillator for providing an output signal of a first frequency;
• means for periodically applying the transmit oscillator output signal to each of the transducers during successive transmit intervals to cause each of the transducers to emit bursts of acoustic energy, the burst occurring at a repetition frequency;
• a reference oscillator for producing an output signal at a second frequency different from the first frequency by a difference frequency, the difference frequency being such that one cycle of the difference frequency extends over a plurality of transmit intervals;
• first and second signal processing channels respectively associated with the first and second transducers for processing output signals produced by the associated transducer in response to acoustic signals received thereby, each signal processing channel including:
• means, responsive to the output signal from the associated transducer and to the reference oscillator output signal, for producing an intermediate signal at the difference frequency having a phase which is representative of the phase of the acoustic signal received by the associated transducer;
• and
• means for comparing the phases of the intermediate signals from the first and second processing channels and for producing a signal representative of the phase difference therebetween to provide a representation of the velocity component of the liquid flow being measured.