Downloaded from https://www.everyspec.com ADS-79D-HDBK example, only about 5% of the values should fall above the mean plus two standard deviations. 95 Appendix I discusses statistical processes, albeit for vibratory CBM algorithms. For off-aircraft limits, tentative alarm limits may be set with as few as 30 samples although the quality of the limits improve with larger populations. For laboratory data, 100‘s to 1000‘s of samples in a data set are generally available for like components. M.6.3.4 Exceedance Recording: Any exceedances should be recorded when each event occurs and flagged to the ground crew. M.6.4 Life Usage Monitoring:
Section G.7.3 in Appendix G encompasses life usage monitoring and applies to oil analysis utilizing laboratory, at-line testing, on-line sensors and manual observations. M.6.5 Anomalies and Faults: Fault detection methods discussed in Appendix G.6.2 apply to oil condition monitoring. Oil debris and condition data are analyzed to determine normal versus anomalous behavior. Condition indicators (CI) and health indicators (HI) should be developed to allow for sufficient time to schedule maintenance and prevent catastrophic failure. There are various diagnostic levels: a.
In electric chip detectors, a chip light is indicated when sufficient debris has collected to bridge a gap between two electrodes. b. AOAP limits, based on statistical analysis of large databases, indicate an abnormal increase in wear debris. c. Oil debris sensor (magnetic coil) limit algorithms are based on bearing faults from test rigs and component teardowns. An example algorithm is provided for rolling element bearings using an oil debris magnetic coil sensor. Note algorithms are also available for gears.
A spall is essentially a rectangular area of damage with some average thickness for the missing material where the width of the spall is proportional to bearing roller width and the length of the spall is a function of the bearing mean diameter and the angle of spall. In the case of a cylindrical rolling element, the rolling element width is the width of the roller. In the case of a spherical rolling element, the rolling element width is the diameter of the roller.
Thus, formulas may be derived to estimate bearing damage severity in terms of accumulated metallic wear debris counts or mass as functions of bearing geometry that include bearing pitch diameter, rolling element width, and number of rolling elements. 96 95 ASTM E2412-10, Standard Practice for Condition Monitoring of In-Service Lubricants by Trend Analysis Using Fourier Transform Infrared (FT-IR) Spectrometry. 96 ASTM D7685-11, Standard Practice for In-Line, Full Flow, Inductive Sensor for Ferromagnetic and Non- ferromagnetic Wear Debris Determination and Diagnostics for Aero Derivative and Aircraft Gas Turbine Engine Bearings. 257