Rotating magnetic field based instantaneous angular speed measurement of low speed rotating machines

For early fault detection and health monitoring of low speed machines the instantaneous angular speed (IAS) measurement with high resolution and accuracy is required. The results show that IAS measurement is much more superior to the conventional methods i.e. analyzing acoustic waveforms, temperature variations, and vibrations etc. However accurate IAS measurement becomes very difficult due to slow and noisy response of the rotary transducers for low speed rotating machines. In the proposed technique, a fast rotating magnetic field (RMF) is used to measure the IAS for low-speed machines. An independent ac source is used to generate a balanced three-phase ac voltage, which is applied to the stator windings of a synchro whose rotor is coupled with the rotating member or rotor of a motor. The RMF in the air gap generates emf in the rotor of synchro whose frequency depends upon the slip speed. Since the RMF revolves at a speed, several times the speed of the rotating member or the rotor of motor, hence the IAS measurement becomes very fast and accurate. The proposed scheme is tested successfully for instantaneous change of speed within a range of 0 to 2 rpm.