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Remove Harmonics

Remove Harmonics creates a series of notch filters to remove specific frequencies from your signal.

Use Remove Harmonics, for example, if you are studying one rotating gear shaft in a gear box, and want to isolate it from the propagated effects of other gear shafts within the box. Also remove harmonics to filter out harmonically related signal components such as AC line components of 60 Hz, 120 Hz, and so forth.

Source Signal

Signal — Signal from which to remove harmonics. This signal can be an imported data signal such as a vibration signal, or a derived signal such as a TSA signal.

Filter Settings

Use the filter settings to specify the parameters that define the fundamental target frequency, notch bandwidth, and number of harmonics. The sample frequency Fs constrains the allowable combinations to the range [0 Fs/2]. Choose your settings so that the notch of your highest filtered harmonic falls completely within this range. Specifically, nf + bw/2 must fall within [0 Fs/2]. Here, n is the number of harmonics, f is the fundamental target frequency, and bw is the notch bandwidth.

  • Fundamental frequency — Choose the fundamental frequency based on your knowledge of the lowest harmonic frequency that you want to remove.

  • Notch bandwidth — Set the notch bandwidth:

    • Wide enough to remove sidebands and leakage around the target frequency along with the target frequency

    • Narrow enough that the notch does not filter out nearby harmonic information that you want to retain.

  • Number of Harmonics — Set the number of harmonics according to your knowledge of how much influence the higher harmonics have on your signal. You can try different harmonic levels and see how much influence they have on feature and computational performance.

The software stores the results of the computation in a new variable. The new variable name includes the source signal name with the suffix noharm.

For more information on notch – or stopband – filters, see butter.