Reducing Tachometer Jitter to Improve Gear Fault Detection



Eric Bechhoefer Dave He


Much research has been published on gear fault analysis techniques, almost all based on the time synchronous average (TSA). These include and are not limited to: residual analysis, energy operator, energy ratio, amplitude modulation, frequency modulation, sideband index, zeroorder figure of merit, etc. Because the TSA is based on tachometer zero cross times for a key phasor, the performance of these analyses is dependent on the quality of the tachometer data. The tachometer signal always has jitter, due to electrical noise, magnetic noise, or manufacturing spacing error of the tachometer target (e.g. gear tooth spacing). By implementing a novel zero phase filter to  reduce tachometer jitter, large improvements in the fault detection were observed. For a known gear fault, the separability, related to fault detection, increased from 10 to 25%.

How to Cite

Bechhoefer, E., & He, D. (2016). Reducing Tachometer Jitter to Improve Gear Fault Detection. Annual Conference of the PHM Society, 8(1).
Abstract 229 | PDF Downloads 79



time synchronous average, gear fault detection, tachometer, jitter, separation

Civil Aviation Authority, Report of the Helicopter Airworthiness Review Panel (HARP) of the Airworthiness Requirements Board, CAP 491 (1984).
Civil Aviation Authority, CAP 693 “Acceptable Means of Compliance Helicopter Health Monitoring CAA AAD 001-05-99 (1999)
Civil Aviation Authority, CAP 753, Helicopter Vibration Health (VHM) Guidance Material for Operators Utilizing VHM in Rotor and Rotor Drive Systems of Helicopters, (2012).
McFadden, P. A revised model for the extraction of periodic waveforms by time domain averaging. Mechanical Systems and Signal Processing 1 (1), 83-95, 1987.
Zakrajsek, J. Townsend, D., Decker, H. An Analysis of Gear Fault Detection Method as Applied to Pitting Fatigue Failure Damage. NASA Technical
Memorandum 105950, 1993.
Priebe, G, “Synchronous Averaging – the Trigger is Everything” 2003.
McInerny, S, Helicopter Drivetrain Vibration Condition Monitoring Algorithms, Gear Fault Data Set,, 2004.
Motion Systems Design, “Gears and Gear Drives”, MSD 2001.
Bechhoefer, E., Van Hecke, B., He, D., Processing for Improved Spectral Analysis, PHM Society Annual Forum, 2013.
Bechhoefer, E,. He, D., A Process for Data Driven Prognostics, MPFT, 2014.
Technical Research Papers