| 摘要 |
PROBLEM TO BE SOLVED: To prevent the occurrence of a difference in received waveforms between upstream and downstream sides of a portion comparatively high in amplitude in calculating a period of time during which ultrasonic waves propagate, and the detection of such a difference as an error in propagation time. SOLUTION: A received signal is amplified by receiving means 35, and until the level of signal reaches a predetermined value (Vref), reception point memory means 38 sequentially stores latest reception point data in a plurality of memory sections. The average of a plurality of predetermined zero-cross points before Vref is used as a reception point. This makes it possible to measure a propagation time with few errors such as up-and-down offsets and to realize power-saving operation by shortening a measuring time. COPYRIGHT: (C)2009,JPO&INPIT
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