Detection of induction motor operation condition by acoustic signal

This paper offers a new method to measure the operational condition of the induction motor. The acoustic signal is measured for analysis. It can not only still be detected normally when other signals can´t, but it also has the function of motor fault monitoring when it combines with a monitoring system completely. It makes signal sampling more convenient and easier, and also expands the functions and items of monitoring. The way of this method includes the following steps: firstly, the acoustic signal must be transformed into a spectrum by fast Fourier transform; secondly, the first band of the spectrum must be analyzed, and the peak frequency of this band calculated; thirdly, peak frequency-speed relation must be established; fourthly, the unknown speed with Lagrange polynomial must be calculated. From these steps, the method has a high degree of accuracy, and could detect induction motor speed and power.