| 摘要 |
PROBLEM TO BE SOLVED: To obtain a noise filtering method in which a noise at a frequency band identical to that of ultrasonic waves can be filtered out surely by a method wherein peak values of respective waveforms by detecting and recording a specific signal a plurality of numbers of times are compared at a prescribed timing and a minimum value is extracted. SOLUTION: A specific signal S from which a noise is to be filtered out is detected a plurality of numbers of times, e.g. twice, and waveforms of respective detected signals S1, S2 are recorded. Then, peak values of the respective waveforms of the respective detected signals S1, S2 are compared at a prescribed timing, a minimum value is extracted, and a signal S4 is obtained. In the signal S4, a minimum peak value out of effective components e1, e2 which are generated in the respective detected signals S1, S2 at an identical timing, i.e., the effective component e2, is left. In addition, noise components a1, a2 in the respective detected signals S1, S2 are generated at different timings. As a result, when the noise components a1, a2 are compared at an identical timing so as to extract the smaller noise component, a peak value 0 in which the noise components a1, a2 are not contained is extracted, and the noise components a1, a2 are filtered out. |
