Demodulation algorithm of low coherent heterodyne interference signal for axial clearance measurement of rotating machinery

Abstract

The time-domain low coherent heterodyne interference axial clearance measurement method has the challenges of small range and low precision in the clearance measurement of rotating machinery. An axial clearance demodulation algorithm based on the windowed power spectrum density transform (WPSD) is proposed. Based on the characteristics of low coherent heterodyne interference signal, the relationship model between window width and rotating structure motion parameters (amplitude of axial clearance change, rotor speed) is constructed, and the optimal window width mathematical model is obtained. The axial clearance measurement experiments are completed under different axial clearance measurement distances based on an experimental clearance platform, different rotor speeds and different axial clearance variation amplitudes. The experimental results show that the absolute error of the axial clearance reconstruction signal is less than 17 μm and the relative error is less than 4.8 % when the axial clearance measurement distance is 2.1 mm ∼ 11.3 mm, the rotor speed is in the range of 6000 rad/min ∼ 12000 rad/min, and the variation of axial clearance is in the range of 150 μm ∼ 350 μm. The experimental and simulation results are basically consistent.