Q: What are the causes of motor vibration and how to diagnose them using current signature analysis?
Answer
Motor vibration diagnosis via motor current signature analysis (MCSA): motor current spectrum reveals mechanical faults without speed sensors. Common fault signatures: (1) Rotor bar fault: sidebands around fundamental at 2x slip frequency (f_s = sf_s). (2) Static eccentricity: special frequency (fc) = (R +/- 1) x supply_freq where R = rotor slot count. (3) Bearing fault: characteristic defect frequencies – Ball Pass Frequency Outer Race (BPFO) BPFI (inner race) and ball spin frequency. (4) Stator winding fault: shorted turns show high 2x supply frequency component. (5) Misalignment: high 2x RPM and 1x RPM components. Implementation: (1) Acquire motor current via CT sensor and ADC. (2) Perform FFT (Hanning window 4096-point). (3) Compare spectrum to healthy baseline. Tools: AD4-MCSA (Analog Devices) or custom STM32 DSP implementation using CMSIS FFT. Set alarm thresholds: vibration > 4.5 mm/s RMS (ISO 10816-3). For online monitoring use continuous MCSA with embedded DSP.
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