Downloaded from https://www.everyspec.com ADS-79D-HDBK techniques to calculate rate trends from the very simple to the more complex. AOAP utilizes the rise-over-run trend. This rate trend takes the current sample minus the previous sample, divided by the usage metric, times the standard sample interval. For example moderate rate trends are typically set at 60% of alarm level and rapid trend rates are set at 90% of the alarm level. The usage metric and the standard sample interval metric must be the same units of measure, for example, hours. The rise-over-run trend calculation factors in equipment usage (Figure M-3) and is effective for continuous duty and intermittent duty machinery.
However, samples should be taken at or near the optimum sample interval. 78 79 FIGURE M-3 Example trend plot demonstrating rise–over–run: PPM versus operating hours On-line debris sensors typically use near-real-time cumulative trending (Figure M-4) to show the amount of mass removed and the rate of removal. 80 M.5.4.3 Maintaining Limits: Level and trend limits should be maintained to ensure they continue to reflect the rotorcraft condition. A regular interval for review should be established, for example every three years. In addition, limits should be reviewed after a significant change in component configuration.
For example, installation of finer filtration (less debris) or a new component with different metallurgy (different elements) will impact wear debris detection and analysis. 78 ASTM D7669-11, Standard Guide for Practical Condition Data Trend Analysis. 79 Toms, L and A. Toms., ―Machinery Oil Analysis - Methods, Automation & Benefits‖, 3rd Edition, STLE, Park Ridge, IL, 2008, ISBN: 978-0-9817512-0-7. 80 ASTM D7669-11, Standard Guide for Practical Condition Data Trend Analysis. 245