| 摘要 |
PROBLEM TO BE SOLVED: To eliminate a measurement error due to the 1.5 reciprocation noise following the reflected waves, and to reduce consumed electric current. SOLUTION: A flow velocity and a flow rate are obtained by repeating, a plurality of repetitions (n-times), an operation for receiving ultrasonic waves and then transmitting ultrasonic wave again in forward direction and reverse direction. The repetition in one direction is executed as follows. In the first two repetitions, the reception and transmission are executed at the same time. In the next two repetitions, after the reception, the next transmission is executed with a time lag of a half cycle period t of the ultrasonic wave. Such operations are alternately repeated two times. Thus, an apparent total arrival time is measured and a time lag due to the half-cycle period is compensated to obtain the correct arrival time for calculating the flow velocity and flow rate. Effects of the 1.5 reciprocation noise shown by dashed lines are eliminated by the n-times repetitions.
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