| 摘要 |
PROBLEM TO BE SOLVED: To solve a problem in finding the propagation time of an ultrasonic wave that a difference arises between a waveform received on the upstream side and one on the downstream side in a portion where a received amplitude is comparatively large and that the difference is to be detected as an error in propagation time. SOLUTION: A received signal is amplified by a reception means 35 while a receiving point storing means 38 causes the latest receiving point data to be stored in order in a plurality of storage parts until the level of the signal reaches a previously determined value (Vref). The average value of a plurality of zero crossing points in the vicinity of Vref can be used as a reception point, making it possible to measure the propagation time with errors reduced such as an upper or lower offset and to materialize power saving operation through the shortening of measurement time. COPYRIGHT: (C)2009,JPO&INPIT
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