水轮机转子材料晶粒粗大，易导致超声检测信噪比低，实际检测容易漏检、误判。为了解决这一问题，对水轮机转子材料制成的试块采集了超声检测信号，对信号进行了经验模态分解和Hilbert变换，提取出包含有用信息的IMF分量，进行了信号的重构，重构后的信号信噪比有最高可达两倍的不同程度的提高。同时着眼于实时监测，确定了适合HHT重构信号降噪方法的最佳采样频率为探头频率的40倍。

The coarseness of crystalline grains in water turbine material decreases the UT signal SNR, which leads to undetected fault or misjudgment in actual UT testing. To solve this problem, UT signals was collected from a test block which is made of the same material as water turbine rotor. After the signals were processed by EMD and Hilbert transform, IMFs that include information of defects were chosen to rebuild signal. SNR was increased up to 2 times. The best sampling frequency, 40 times as the probe center frequency, for real time UT testing was determined considering SNR and calculation quantity.