Research on vortex signal processing based on double-window relaxing notch periodogram

The vortex flowmeter is widely used in industries because of its many advantages. However, there is a problem when it works at low flowrate. The useful vortex signal is weak and easily drowned by noises, especially the harmonic noise whose frequency band generally lies in the vortex frequency band. Thus it is hard to pick out the vortex signal from noises. In order to solve the problem, the classical relaxing notch periodogram method and its algorithm on single-frequency signal estimation are first discussed. On the basis of them, the double-window relaxing notch periodogram with twice FFT is proposed. Hanning window is applied to frequency estimation and triangular window is used in amplitude estimation. The practicability of the improved method is proved by both simulations and experiments on practical signals. It is indicated that the method can not only retrieve the useful vortex signal exactly but also extend the lower measurement limit of vortex flowmeter.