| 摘要 |
An acoustic flow meter has two transducers spaced along a fluid flow path which emit ultrasonic signals in opposite directions. Each signal is detected by the other transducer than the one it was sent from. The transmitted signals have exactly equal amplitudes and are either in phase with each other or exactly out of phase with each other. The signals travel at different speeds in the upstream and down stream directions, so the received signals are no longer in a pre-determined phase relationship. In the case of in-phase signals, one of the received signals is subtracted from the other to form a resulting new signal. In the case of anti-phase signals (as in figure), the received signals are added together to make a new signal. The amplitude of the new signal is related to the flow rate due to constructive or deconstructive interference when the received signals are combined. The flow rate can be calculated from the amplitude of this signal, therefore allowing simpler circuitry to be used than in conventional flow meters. |
