| 摘要 |
PROBLEM TO BE SOLVED: To solve a problem in which, when determining propagation time of ultrasonic waves, a difference is generated between the waveforms received on the upstream side and the downstream side, in a part where reception amplitude is relatively large and is detected as an error in the propagation time. SOLUTION: In the system, a reception means 35 amplifies a reception signal, and a reception point memory means 38 stores the latest reception point data, by overwriting and updating the signal level until it reaches a predetermined value (Vref). Since overwriting and updating are stopped when it reaches the Vref, a zero-crossing point prior to a trigger level being set as a reception point, and thus power-saving operation due to the propagation time measurement with fewer errors and the reduced measurement time can be attained. COPYRIGHT: (C)2008,JPO&INPIT
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