Method to determine rpm of direct current electric motor; involves low pass filtering of motor current signal and computing difference values between successive minimum and maximum of filtered signals

摘要

The method involves low pass filtering and differentiating the motor current signal. Difference values between successive minimum and maximum values of the differentiated, filtered motor current signals are computed and stored within a determined time interval. A ripple is determined from the difference values of the interval. Interval lengths are matched according to previously identified ripples.