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Abstract

A Doppler flowmeter which utilizes a single crystal immersed in the flow stream directing energy in a direction parallel with the flow direction. The crystal is fed by an oscillator at a single frequency corresponding to an ultrasonic vibrational mode for the crystal. The crystal also detects reflected acoustic wave energy with the input and output signals being electrically combined in the crystal. An electrical discriminator circuit is able to separate a multi-spectral Doppler signal from the crystal by phase cancellation of the transmitted signal. The recovered signal is fed to a tunable state variable filter which establishes a ninety degree phase shift with the incoming multi-spectral signal. This phase shifted signal is combined with the incoming multi-spectral signal in a phase lock loop with an output of the loop used to clock the state variable filter. Another output is a synthesized Doppler frequency representative of the mean Doppler frequency.

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First Claim