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.