| 摘要 |
<p>A fluid flow meter and, more especially, an airflow meter having fast response and very high resolution uses piezoelectric transducers (A,B) operating near resonance to pass ultrasonic signals upstream and downstream alternately in a flow passage (10). Transmission signals continue longer than the propagation time to the receiver so that the phase of the received signals can be compared to the transmission signals. The difference of upstream and downstream phase differences is a measure of the air velocity while the sum of those phase differences is useful to determine air temperature. These values along with an air pressure sensor (20) reading are combined to determine mass airflow through the passage (10). The acoustic transducers (A,B) are operated near resonance to optimize signal-to-noise ratio. Readings from the initial reception period of each transducer are ignored to avoid the effects of ringing of the transducer (A,B) from each previous transmission cycle and to allow the received signal to build up resonance with the acoustic signal.</p> |
