The best scanning time is about 74 seconds. On continuing observation, the scanninginterval should be a little longer and it will not lose the time of observation.
扫描开始时间应以74秒前后为佳，持续观察时，扫描间隔时间宜长，且不会错过观察时机。
2
Effect distribution curves of scanninginterval and defect sizes on detecting results are obtained by experiment, and it can supply references to detect defect sizes reasonably.
通过实验，给出了缺陷尺寸和扫描间隔等因素对检测结果影响的分布曲线，为合理提取缺陷尺寸提供了参考。
3
The white noise scanning test was conducted before the shaking table test and repeated at every interval of each test to obtain the law of the basic frequency vary with the time.