Detecting Speed Fluctuations in D.C. Electric Motors Using a Radio Frequency Antenna Technique

This paper describes how the radio frequency (RF) signals generated during the mechanical commutation process in a D.C. electric motor can be used to estimate the motors rotational speed and also any oscillations in the motor speed. Amplitude and frequency modulated signals were added to the voltage supply of a D.C. electric motor to simulate fault conditions in the system. The R.F. signals generated during the commutation process were captured using a antenna which was interfaced to a high speed PCI interface card. The captured data was then processed using MATLAB. The results presented show the spectrums produced for a motor running at constant rotational speed and also with sinusoidal oscillations or fluctuations added to the motor rotational speed. Peaks in the spectrums are correlated to the motor speed and oscillations in the motor speed.