| 摘要 |
An ultrasonic transmitter is disposed on one wall inside the air induction tube of an internal combustion engine and an ultrasonic receiver is disposed on the opposite wall, downstream of the transmitter. A second transmitter-receiver pair is similarly located, but with the positions of transmitter and receiver reversed. Thus, the signals from one transmitter travel generally with the air flow, whereas the signals from the second transmitter travel generally against the air flow. Since the travel time of the signals depends on the velocity of the flowing air, the frequencies of signals from the two receivers are different and this difference is used to determine the air velocity and, hence, the air flow rate.
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