Phase modulation, ultrasonic flowmeter

Claim 1

An apparatus for measuring the volumetric flow rate of a fluid in a closed conduit having turbulent flow comprising: two loop-circuits each including: a transmitting transducer formed to be attached externally to to a fluid carrying conduit; a tunable oscillator for supplying an ultrasonic signal to be transmitted through said conduit by said transmitting transducer, said tunable oscillator being tuned to a higher frequency for one of said loop-circuits than for the other; a receiving transducer formed to be attached externally to said conduit at a point diametrically opposite said transmitting transducer, for receiving the ultrasonic signal transmitted by said transmitting transducer, said first and second transducers in each loop-circuit being arranged such that their respective ultrasonic signals are transmitted in anti-parallel directions through said conduit; a bandpass filter connected to said receiving transducer; a limiting preamplifier for amplifying and symmetrically clipping the output signal of said bandpass filter; a phase demodulating circuit connected to said limiting preamplifier; a clipping circuit connected to said tuned oscillator and said phase demodulating circuit for supplying a symmetrically clipped synchronizing signal to said phase demodulation circuit; a voltage divider connected to the output of the phase demodulation circuit in the loop-circuit having the higher frequency, for balancing the amplitude difference between the output signals of said loop-circuits; a differential amplifier connected to the balanced outputs of said loop-circuits; an output bandpass filter connected to the output of said differential amplifier, whereby a demodulated, filtered, and time-varying signal having zero mean value is produced which is related to fluid flowrate with respect to its RMS amplitude; and an RMS voltmeter for measuring the RMS value of the amplitude of said demodulated, filtered, time-varying signal.

Claim 2

An apparatus for measuring the volumetric flow rate of a fluid in a closed conduit having turbulent flow comprising: two loop-circuits each including: a transmitting transducer formed to be attached externally to to a fluid carrying conduit; a tunable oscillator for supplying an ultrasonic signal to be transmitted through said conduit by said transmitting transducer, said tunable oscillator being tuned to a higher frequency for one of said loop-circuits than for the other; a receiving transducer formed to be attached externally to said conduit at a point diametrically opposite said transmitting transducer, for receiving the ultrasonic signal transmitted by said transmitting transducer, said first and second transducers in each loop-circuit being arranged such that their respective ultrasonic signals are transmitted in anti-parallel directions through said conduit; a bandpass filter connected to said receiving transducer; a limiting preamplifier for amplifying and symmetrically clipping the output signal of said bandpass filter; a phase demodulating circuit connected to said limiting preamplifier; a clipping circuit connected to said tuned oscillator and said phase demodulating circuit for supplying a symmetrically clipped synchronizing signal to said phase demodulation circuit; a voltage divider connected to the output of the phase demodulation circuit in the loop-circuit having the higher frequency, for balancing the amplitude difference between the output signals of said loop-circuits; a differential amplifier connected to the balanced outputs of said loop-circuits; an output bandpass filter connected to the output of said differential amplifier, whereby a demodulated, filtered, and time-varying signal having zero mean value is produced which is related to fluid flowrate with respect to its RMS amplitude; and an RMS voltmeter for measuring the RMS value of the amplitude of said demodulated, filtered, time-varying signal.

Claim 14

An apparatus for measuring the volumetric flowrate of a fluid in a closed conduit having turbulent flow, said apparatus comprising: means for exciting ultrasonic transducers to transmit ultrasonic signals at preselected frequencies; a pair of loop-circuits each including: a transmitting transducer formed to be attached externally to the conduit and operatively connected to said exciting means; a receiving transducer formed to be attached externally to the conduit at a point diametrically opposite said transmitting transducer for receiving the ultrasonic signal transmitted by said transmitting transducer, said transmitting and receiving transducers in each loop-circuit being arranged such that their respective ultrasonic signals are propagated in anti-parallel directions through the conduit; a bandpass filter operatively connected to said second transducer for passing a preselected band of frequencies about the frequency of the ultrasonic signal received by said second transducer; and a limiting preamplifier operatively connected to said bandpass filter for amplifying and symmetrically clipping the output signal of said bandpass filter; means for combining and phase demodulating the output signals from said loop circuits; and a second bandpass filter operatively connected to said combining and phase demodulating means for passing a preselected band or frequencies, whereby a demodulated, filtered, and time-varying signal having zero mean value is produced which is linearly related to fluid flow velocity with respect to either its RMS amplitude or mean zero-crossing frequency.

Claim 15

An apparatus for measuring the volumetric flowrate of a fluid in a closed conduit having turbulent flow, said apparatus comprising: means for exciting ultrasonic transducers to transmit ultrasonic signals at preselected frequencies; a pair of loop-circuits each including: a transmitting transducer formed to be attached externally to the conduit and operatively connected to said exciting means; a receiving transducer formed to be attached externally to the conduit at a point diametrically opposite said transmitting transducer for receiving the ultrasonic signal transmitted by said transmitting transducer, said transmitting and receiving transducers in each loop-circuit being arranged such that their respective ultrasonic signals are propagated in anti-parallel directions through the conduit; a bandpass filter operatively connected to said second transducer for passing a preselected band of frequencies about the frequency of the ultrasonic signal received by said second transducer; and a limiting preamplifier operatively connected to said bandpass filter for amplifying and symmetrically clipping the output signal of said bandpass filter; means for combining and phase demodulating the output signals from said loop circuits; and a second bandpass filter operatively connected to said combining and phase demodulating means for passing a preselected band or frequencies, whereby a demodulated, filtered, and time-varying signal having zero mean value is produced which is linearly related to fluid flow velocity with respect to either its RMS amplitude or mean zero-crossing frequency.