1. Unwind Drive Cooling Fan Beat Frequency ©Bill Kilbey 2009

2. High 1x Cooling Motor/Fan Constant Speed Motor/fan sit on top of large variable speed motor, fan mounted directly on motor shaft The fan is subject to buildup of dirt/product 1x TS dominant with amplitudes increasing Attempt to balance was not successful – Varying amplitude 1mil pk-pk to 7mils pk-pk – Unstable phase ±100⁰

5. High 1x TS

6. High Resolution Spectrum

7. High Resolution Spectrum Zoom

8. Spectrum from other cooling fan

9. Calculations 1773.1 – 1769.3 = 3.8 RPM Delta (.063 Hz) The inverse of Diff. F1-F2 = T beat T beat = 15.8 secs. approx.

10. Time waveform beat on #2

11. Time waveform beat on #3

12. #2 PM Fan #3 PM Fan