Selected data analysis techniques for equipment monitoring using drive's control signals

Variable speed drives are becoming the method of choice for powering AC motors in many industrial applications. They allow for flexible speed control, substantial energy savings, and reduced stress during motor start-up, all of which lead to lower lifecycle costs for the shaft line. Modern drives, in order to perform their controlling function, are equipped with sensors, hardware and software to measure or compute a number of signals (for example, current, torque, speed, frequency, power, flux, etc.). This data is available and can be used for diagnostic purposes. These signals can be analyzed for their spectral content, used for monitoring the operating point, for examining cyclic processes, etc. The data is freely available, but the format, quality and quantity are determined by the hardware. Furthermore, variable speed drives change the output frequency to follow desired process parameters. This work presents selected methods for handling these difficulties and turning them to our advantage. Some examples of these methods application to industrial data are presented. These results prove that a variable speed drive can be a valuable source of diagnostic data not only for the drive itself, but also for the entire driven process.