Order Normalized Spectra

To obtain better order tracking resolution for data with large dynamic ranges, Rotate Plus can resample the data in the angle domain. This will obtain better resolution of order calculations at lower frequency ranges. The basic notion behind resampling into constant intervals in the angle domain is to achieve a constant angle resolution around the governing shaft and as such have the same data quality regardless of shaft speed. This feature is especially valuable when there is a large dynamic range in the shaft speed. In the example below, the shaft runs from 200 RPM to 1,400 RPM.

Below are two Spectrogram plots of data containing the same data. The top plot was generated with standard FFTs calculated in the time domain. Notice the poor definition of the orders at lower RPMs and the orders tend to "bleed" into one another at lower RPMs. In contrast, the lower plot was resampled in the angle domain. You can see that there is better resolution overall, especially at the lower RPMs.