This paper proposes a time-varying amplitude frequency monitoring method based on sliding window FFT of sub-synchronous oscillation to identify the time-varying modal parameters of the oscillating signals on-line. Firstly. windowed interpolation methods are used to reduce the spectral leakage and fence effect. and decrease the FFT identification errors. https://www.roneverhart.com/LiftMaster-PPWR-copyright-Wiegand-Receiver-with-Security-2-0-Technology/