| 摘要 |
A Doppler-type ultrasonic flowmeter whose transmitting transducer is excited by an oscillator to project into the meter pipe a diverging beam of ultrasonic energy. The projected beam is reflected by contaminants carried by the fluid lying within the zone in which the projected beam intersects a reception beam converging toward a receiving transducer which picks up the reflected energy. The transmitted signal is mixed with the Doppler signal yielded by the receiving transducer to yield positive and negative beats which are applied to a low-pass filter from which is extracted a band of negative beat frequencies representing the disparate flow velocities of the contaminants within the zone dictated by the prevailing velocity profile of the fluid. This band is subjected to spectral analysis to determine the velocities of the contaminants and their relative percentages, from which the flow profile of the fluid being metered is calculated to ascertain the mean flow velocity thereof. |
