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Rotating Machinery Features

The rotating machinery features describe aspects of gearbox machinery, where one primary shaft drives other rotating gears. The system is harmonically interrelated, and this interrelationship allows metrics that can not only detect, but also locate the source of the fault.

The statistical rotating machinery features are similar in nature to their general statistical counterparts in Signal Statistics. The remaining features were derived through research in the literature, and empirically determined to be effective for differentiating or isolating specific types of faults.

Signals to Use

  • TSA Signal — A time-synchronous averaged (TSA) signal is essential to calculating rotating machinery features. This option is read-only. You must select the TSA signal in the variable browser or the Time-Domain Features tab prior to selecting this feature option. To generate a TSA signal, use Filtering & Averaging > Time-Synchronous Averaging.

  • Difference Signal, Regular Signal — These filtered TSA signals provide the source for the specialized rotating machinery metrics. To generate these signals, use Filtering & Averaging > Filter TSA Signal.

Metrics Using TSA Signal

  • Root Mean Square (RMS) — Indication of the overall condition of the gearbox

  • Kurtosis — Indication of major peaks in the signal

  • Crest Factor (CF) — Peak-to-RMS ratio, which is an indication of gear damage in its early stages, especially where vibration signals exhibit impulsive traits

Metrics Using Difference Signal

  • Kurtosis (FM4) — Detect faults isolated to only a limited number of teeth in a gear mesh

  • Normalized 6th moment (M6A) — Indication of surface damage on the rotating machine components

  • Normalized 8th moment (M8A) — An improved version of the M6A indicator

Metrics Using Mixed Signals

  • Zero-order figure of merit (FM0) — Ratio of the standard deviations of the difference and regular signals, which is an indication of heavy wear and tooth breakage

  • Energy Ratio (ER) — Indication of heavy uniform wear, where multiple teeth on the gear are damaged

Additional Information

The software stores the results of the computation in new features. The new feature names include the source signal name with the suffix rotmac.

For information on using these metrics for evaluating rotating machinery, see Condition Indicators for Gear Condition Monitoring. For information on specific rotating metrics, see gearConditionMetrics.