Determination of rpm based on scanning vibration spectral plot

A vibration analyzer for use in determining a nominal rotational speed of a rotating shaft, comprising:

• an input for sensing vibrational signal data at an unknown rotational speed of the shaft;
• a memory for storing the vibrational signal data;
• and
• a processor that executes instructions for:
• producing a spectral plot of the vibrational data,
• locating peaks in the spectral plot,
• scanning the spectral plot in predetermined rotational speed increments beginning at a first rotational speed and ending at a second rotational speed to provide a candidate rotational speed at each increment, and for each candidate rotational speed:
• identifying a predetermined number of associated harmonics,
• locating closest peaks in the spectral plot to the candidate rotational speed and its associated harmonics,
• measuring gaps between the located closest peaks and the candidate rotational speed, and
• recording a sum of the gaps,
• identifying one or more sums of the gaps that represent one or more local minimum gaps,
• summing peak sums associated with the one or more local minimum gaps, and
• selecting the candidate rotational speed that is associated with a maximum peak sum as the nominal rotational speed.