| 摘要 |
PROBLEM TO BE SOLVED: To provide an ultrasonic flow meter which ensures accuracy required in a flow measuring system and achieves low cost. SOLUTION: The ultrasonic flow meter 1 includes a pair of ultrasonic transmitting and receiving elements 2a, 2b within a flow channel 3 through which fluid GF flows on the upstream side and downstream side thereof, repeats the transmission of a measuring ultrasonic wave in a predetermined flow measuring period T, each time the measuring ultrasonic wave is received, controls the oscillation frequency of a measuring ultrasonic wave to be transmitted next time so that it has a lock wave number predetermined between the pair of ultrasonic transmitting and receiving elements 2a, 2b, and calculates a flow on the basis of the oscillation frequency controlled within the flow measuring period T. An oscillation circuit for ultrasonic wave oscillation is a ring oscillator circuit 34. By changing power supply voltage to be supplied to delay elements 341, 342 constituting the ring oscillator circuit 34, the oscillation frequency of the ring oscillator circuit 34 is controlled. COPYRIGHT: (C)2010,JPO&INPIT
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