Understanding Spectrum Resolution: Belt-Drive / Example 1

The FFT shown here displays data from 0 - 120kcpm. You have made the judgement that one of the peaks shown in the low-mid frequency range (< 12kcpm) is excessive. How reliably can you answer the following questions:

What is the source of any of the vibrations apparent in the <12kcpm range ? Entirely Unclear: As a belt-driven piece of equipment, there are 3 rotating components (motor, fan, belts) plus the same 2x line frequency we touched on in the direct-drive example. If you venture a guess as to the source of any particular peak, you have about a 1 in 3 or 4 chance of being correct - not the best of odds. Are you monitoring bearing defect frequency harmonics sufficiently ? Yes. With a machine running 1800, collecting an FFT to 120kcpm is sufficient to monitor the full range of frequencies in which bearing-related peaks will appear.

Summary: A spectrum really suited to bearing monitoring and low-mid frequency trending only - no specific frequencies are identifiable in the lower frequency ranges.Let's proceed with the same sequence of FFTs as shown in the previous example.