For studying the effect of frequency in the coupled signals on fault diagnosis, the differential method for the third⁃order cumulant of coupled signals is adopted. The complex third⁃order cumulant has different definition forms, and different forms conclude different information. So, based on the 1 12 dimensional spectrum, the fault is diagnosed for the third⁃order cumulant respectively before and after differential. The experimental results show that, the increased frequency item in the third⁃order cumulant after differential produces impacts on the result of fault di⁃agnosis, and the degree of such impact is relevant to the differential times. Therefore, the correct rate of fault diag⁃nosis can be raised by changing the differential times of the third⁃order cumulant.%为了研究耦合信号中的频率信息对故障诊断的影响，采取对耦合信号的三阶累积量进行微分处理的方法。根据复数三阶累积量具有不同的定义形式，并且定义形式不同，其包含的耦合信息也不相同，同时借助112维谱，分别对微分前后的复数三阶累积量进行故障诊断。实验结果表明：微分后三阶累积量中所增加的频率信息对故障诊断的结果产生了影响，并且这种影响的程度与微分次数有关。因此，可以通过改变对三阶累积量的微分次数提高故障诊断正确率。
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