Importance

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Abstract

A flowmeter for measuring the mass flow of a fluid stream, such as air, in a duct includes a sensor and electronic circuitry. The sensor includes a drag surface mounted to or forming part of an oscillatory element and mounted in the fluid stream for flow-damped oscillation. The oscillatory element is stimulated by a drive transducer and a pickup transducer senses the flow-damped oscillations. An intermediate circuit terminates the drive at a certain peak amplitude and measures the time interval required for the amplitude of the flow-damped oscillations to decay a predetermined amount. That interval is indicative of the fluid mass flow. The sensor may be a cantilevered beam. The beam may also be disposed behind a shroud and include a drag plate extending upstream of the shroud therefrom. The sensor may be a beam constrained to torsional oscillation about a longitudinal axis. The transducers are piezoelectric devices mounted on a beam in proximity with its neutral axis.

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First Claim