RPM associated with each FFT

Each FFT is linked to an RPM value used to place the FFT slice along the Y axis of the spectral map. However, during a single FFT range, the RPM can evolve because the working condition is a run up (or run down), but also because the rotating machine is vibrating. Several values of RPM correspond to the FFT (see red dashed line in following figure).

Figure 17: Oscillating RPM

To overcome the problem, the average RPM during start and end time of the FFT range is computed and used as the reference RPM.