Modulated signal detection method for fault diagnosis

Envelope analysis is a dominant approach in detecting modulated fault signals in rotating machinery. The Hilbert transform is a popular method used to obtain envelopes. However, envelopes based on the Hilbert transform are only suitable for narrowband signals. Signals are usually filtered before envelope demodulation, which leads to the challenging issue of filter selection. A modulated fault signal detection method using the upper and lower envelopes of the signals is proposed. This method can demodulate the modulated fault signals directly from the raw data, which can include wideband and narrowband signals. The proposed method uses a simple algebraic operation instead of a transform function, so it is convenient in practical applications. It is tested with some simulated signals and some real-measured data. The test results show that the method can effectively demodulate a modulated fault signal directly from the raw data.