Abstract: In order to resolve the no physical meaning negative frequency phenomena in Hilbert transform, the instantaneous frequency directed calculation method based on the local mean decomposition is researched. The steps of phase unwrap is presented. The direct method is compared with the direct quadrature. Because direct method and direct quadrature are equal in mathematics and have the same calculating result, direct method and direct quadrature can be thought as the same method. Direct method is also compared with the Hilbert transform, Teager energy method. Simulation and experimental results show that the direct method well reflects the signal phase modulation phenomenon, there is no obvious boundary distortion, and the instantaneous frequency is always positive. The direct method is applied in the analysis of rotating machinery vibration signals and a good result is achieved.

Key words: Directed method, Fault diagnosis, Hilbert transform, Instantaneous frequency, Local mean decomposition, Teager energy method