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Filter TSA Signals

Apply filtering to a TSA signal to generate additional signals that isolate the response of specific components within a harmonically interrelated system such as a gearbox. These isolated signals can then be used for rotating machinery features that detect faults in specific physical components and locations.

Use TSA signal filtering only if shaft speeds are constant over time.

Signals to Generate

The filtered signals each retain a subset of the original TSA signal components. The TSA signal components are:

  • Primary shaft speed and specified higher-order harmonics (sh)

  • Gear meshing vibrations (fundamental frequencies and their higher-order harmonics) (gh)

  • Specified gear meshing sidebands (ss)

  • All other vibration components, including degradation, faults, noise, and unspecified gear-meshing sidebands and harmonics (ovc)

  • Difference signal — Contains ovc only. Computed by diff = tsa–(sh+gh+ss)

  • Regular signal — Computed by reg =sh+gh+ss

  • Residual signal — Contains ss and ovc. Computed by res=tsa–(sh+gh)

Speed Settings

  • Constant rotation speed (RPM) — Enter a constant rotation speed in RPM. This shaft speed applies to all members.

  • Nominal rotation speed (RPM) — Use an individual rotation speed for each member by selecting the condition variable that stores these values. You create this condition variable when you first compute the TSA signal if you select Compute nominal speed (RPM). For more information, see Time-Synchronous Averaging.

Filter Settings

  • Domain — Specify Order or Frequency.

    • Specify the order domain when you know the specific ratios between gear sizes in the gearbox. For example, if a gear rotates at three times the primary shaft speed, the order of the gear rotation is 3. Order is independent of absolute shaft speed.

    • Specify the frequency domain when you know the absolute frequencies of the rotating gears. For example, you might have a power spectrum whose peaks correspond to gear rotation.

  • Rotation orders or Frequencies (Hz) — Specify the order list or frequencies list for the known harmonics, in the form [o1 o2 o3 ...] for order domain and [f1 f2 f3 ....] for frequency domain. o1 and f1 both must represent the primary shaft speed, which produces the fundamental frequency.

  • Number of harmonics — Number of shaft and gear meshing frequency harmonics to be retained or filtered. This parameter includes the fundamental frequency represented by o1 or f1.

  • Number of sidebands — Number of sidebands to be retained (regular signal) or filtered (difference signal) from the order or frequency list. Modify Number of Sidebands to filter out known wideband frequency components around gear harmonics. As machines degrade, these wideband components typically grow. Filtering the known components at a given degradation state can improve detection sensitivity to further degradation.

The filter settings apply to all the filtered signals you select. If you want to apply a unique setting to each filtered signal, such as the Number of Sidebands setting, process the signals separately by selecting one filtered signal at a time.

Additional Information

The software stores the results of the computation in new variables. The new variable names include the source signal name with the suffix tsafilt.

For more information on filtered TSA signals, see: