| 摘要 |
A transmitting electro-mechanical transducer is energized by electric pulses at a low frequency (typically several hertz to several kilohertz) to provide corresponding pulses of movement in the fluid. The fluid movement displaces a volume of the fluid in one direction and the motion of that fluid, when combined with the surrounding fluid, produces a fluid rotation which is sustained for a sufficient period of time, to be detected at a later time as an acoustic signal. A known distance downstream of the transmitting transducer, a receiving transducer detects the rotating volume of fluid. From the distance between the transmitting and receiving transducers and the time interval between their transmitted and detected signals, the fluid flow rate can be determined. The transmitting and receiving transducers can interchange their functions so that the difference in the time intervals is used to determine fluid flow rate. The transmitting transducer may also be energized with single pulses, a burst of pulses, or a continuous wave of pulses so that various methods, including phase detectors, may be used to determine the time difference between the received and transmitted, or reference signal, for providing a fluid flow rate signal.
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