A contact-less sensor for detecting low-frequency ripples of the load driven by a squirrel cage motor

Despite the well-known efficiency of the conventional MCSA (Motor Current Signature Analysis) technique for detecting the occurrence of load torque ripples by monitoring of sidebands close to the supply frequency, many other rotor faults produce this same spectral signature leading the user to be faced with a confusing situation. The aim of this paper is to propose an alternative that could overcome this major drawback. The experimental results conducted on a laboratory test-rig have revealed that the spectral signature of the emf induced at the terminals of a search coil placed near the motor frame may provide relevant information of diagnosis purpose, when the load torque oscillates at low frequencies.