Downloaded from https://www.everyspec.com ADS-79D-HDBK debris (ferrous and non-ferrous) for their capture efficiency, and filters do not need to be analyzed as often as oil samples. 89 However, this test requires removing a filter. An instrument that performs these functions is utilized by the US Navy, Allied Forces and gas turbine OEMs. Individual particle analysis determines the specific alloy for every particle (e.g., M50) rather than just elements (e.g., iron, molybdenum, chromium and vanadium). With this method, particle detection and location is performed by camera or scanning electron microscope (SEM) and alloy identification of each particle is performed by XRF.
Particles may be obtained from a variety of sources such as magnetic chip detectors, filters, filter bowls, oil samples, etc. However, particles must be greater than 80 microns (abnormal wear size). For the SEM instrument, there is a significant cost and expertise to maintain the instrument and, although deployable, these instruments typically weigh 900+ lbs. To reduce the impact of this disadvantage to the military, lightweight versions utilizing the camera/XRF arrangement are being explored. 90 The above tests represent the most applicable off-aircraft, at-line tests available for rotorcraft.
The major advantage of at-line testing is the ability to provide immediate machine condition information. M.6.1.3 On-aircraft: On-aircraft, oil debris and oil condition monitoring provide the advantage of continuous real-time or near-real-time monitoring of wear and lubrication problems. On-aircraft oil sensors have minimal impact on system flow, provide direct results, and have little interference from outside influence. The disadvantages to on-aircraft sensors are the sensors must be fitted to the equipment and often are limited to one test per sensor e.g., wear debris.
For fluid condition and contamination, representative results are obtained by monitoring only a portion of the oil stream since it is the condition of the oil as a whole that is of interest. However, wear debris analysis may be misrepresented in partial flow scenarios due to flow dynamics of the wear particles. Consequently, wear debris should be measured by an in-line, full-flow sensor. Installation of an in-line monitoring sensor should not adversely influence the performance of a lubrication system: this can be a challenge in legacy rotorcraft. For new weapons systems, the sensor(s) should be built into the design.
Debris monitors should be placed before any lubrication pump(s) or filter(s). Examples are provided in the subsequent paragraphs of this section. M.6.1.3.1 On-aircraft Component Wear Monitoring: Several types of on-line and in-line sensors are available that detect metallic debris in the oil stream or portions of the oil stream and serve as indicators of component wear. Some sensors offer the earliest warning of bearing failures (magnetic coil) while others only provide last minute warning (chip detectors): Electric Chip Detectors create a magnetic field that attracts ferromagnetic debris particles.
The debris bridges a gap between two electrodes, which act as a switch closure for an 89 Humphrey, G. R., ― Filter Debris Analysis by Energy Dispersive X-Ray Fluorescence Applied to J52P408 Engines”, Denver X-Ray Conference , August 2007, Denver, CO. 90 Toms, A. M., Detecting Bearing and Gear Failures through At-Line Wear Debris Analysis”, MFPT April 2010, Huntsville, AL. 250