A chip detector is an electronic instrument that attracts ferromagnetic particles such as iron chips. Chip detectors are frequently used in aircraft engine oil chip detection systems, where they can offer an early warning of imminent engine failure, thus greatly reducing the cost of an engine overhaul. This blog will provide an overview of chip detectors and their functions.
Chip detectors consist of small plugs that can be installed in an engine oil filter, oil sump, or aircraft drivetrain gearbox. Over time, engine wear and tear causes small metal chips to break loose from engine parts which then circulate in the engine oil, causing damage. A detector contains magnets incorporated into an electric circuit. Magnetic forces attract ferrous particles and collection of these particles continues until the insulated air gap between the magnets (in a two magnet configuration) or between the magnet and housing (in a single magnet configuration) is bridged, thereby cutting off the circuit. The result of this is an electronic signal for remote indication which activates a warning light on the instrument panel, indicating the presence of metal chips in the oil.
In applications with a self-closing valve/adapter, chip detectors can be positioned in the application through a bayonet or threaded interface. When the chip detector disengages from the valve, the valve closes, keeping any fluid loss from the system to a minimum.The chip detectors used on aircraft are inspected in every level of check. Inspection may also be done at specified intervals such as every 30 to 40 hours for an engine unit and 100 hours for an auxiliary power unit.
There are many advantages to using a chip detector. For one, no additional tools are needed to inspect and remove debris. Additionally, chip detectors enable BIT capability by integrating a resistor at the chip gap. Chip detectors utilize blade-type retention, which eliminates much of the wear associated with common ‘pin-in-slot’ type retention methods. Furthermore, strong magnet integrity provides high ferrous capture efficiency as well as significant retention.
To further increase capture efficiency, chip detectors are equipped with flow directional screens. In order to support resistor-based wire-fault, built-in-test functionality, chip detectors feature a circuit board integrated with the chip detector. Finally, chip detectors feature an electroless nickel plating for superior wear and corrosion protection, as well as an axial design which improves the detector’s capture efficiency and ease of chip removal.
To save weight, the chip detector assembly is primarily made from aluminum. There are five main parts of a chip detector’s construction: the flying lead, chip gap, ECD-to-valve- retention lugs, seals, and springs. The flying lead construction features three insulated conductors with an overbraid shield. The chip gap is the area where debris is held. An axial chip gap design is able to collect more debris than a radial type. Retention lugs are designed to FAA approval and are integrated in the valve body where they eliminate assembly errors and provide increased bearing area. The seals, usually o-rings, are used to seal the circuits and connections from oil. Lastly, the chip detector features stainless steel valve piston springs to assist in installation and operation.
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