Downloaded from https://www.everyspec.com ADS-79D-HDBK alarm output. The device should be threaded directly into a lubrication system. These devices typically see between 30-60% of the oil flow, depending on design and location. Debris particles captured by the system should be removed for further inspection to determine the material type and possible wear mechanism. The switch nature of the Electric Chip Detector does not allow for debris trending and can cause excessive false positives by detecting insignificant debris build-up if not equipped with a metal fuzz burn-off mechanism. The Pulsed Electric Chip detector attempts to alleviate this problem.
A low energy current pulse clears fine debris away to reduce false positives. The number of pulses the unit outputs should be programmed into its memory. The pulses clear away fine debris, but the larger debris particles are still held onto. As with the conventional unit, the debris should be retained for further inspection. According to ADS-50, electronic chip debris monitors should be utilized on all oil-lubricated systems. Chip detectors are in widespread use on aircraft. Mesh Detector (screen) may also be used to provide a warning of ferrous and nonferrous conducting debris particles. Debris particles bridge the gap between strands to close a circuit.
Oil flow passes through the screen with minimal pressure drop. These screens are only good at detecting conductive particles (but the particle does not have to be ferrous, e.g. aluminum) and the particle size must be comparable to the screen hole size in order to complete the circuit. Induction Coil Sensors use a magnetic coil assembly to detect and categorize metallic particles by size and type (ferrous or non-ferrous). The minimum detectable particle size is determined by the bore size of the sensor. Currently, on-aircraft systems are designed to detect particles from 120 to 220 microns and up, depending on the diameter of the oil line.
The sensor consists of three coils surrounding the inside bore. Two coils create a magnetic field, and the third coil detects any disturbances in the field. Depending on the type and magnitude of the disturbance, the control unit determines the type of particle and the particle size. This type of sensor should be installed directly in the lube oil line and can be configured as an ―in-line‖ or ―on-line‖ configuration although SAE AIR 1828 recommends the full-flow, in-line configuration. Distribution of the particle sizes along with particle frequencies (rate) should be monitored and trended. The control unit also reports the total mass of ferrous material that has passed through the sensor.
This allows users to track the debris progression over time and to trend this information to determine the current state of the fluid wetted components. 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 where a redesign of the lubrication lines may be required. Induction coil, full-flow sensors are available and should be built into newer weapons systems. They are currently utilized on the F35 JSF (F135 engine and STOVL LiftFan), F22 Raptor (F119 engine) and a wide variety of industrial gearbox and gas turbine applications.
M.6.1.3.2 On-aircraft Fluid Condition and Fluid Contamination Monitoring: Several approaches are in development and testing for on-line oil quality and contamination sensors, although none are in widespread use and none are available for on-aircraft applications at this time. Examples of these fluid sensors are dielectric (capacitance), conductivity (resistance), impedance and infrared, which are discussed below: 251