Debris monitoring and analysis


The monitoring of debris particles in lubricating oils may be achieved using a variety of techniques.

The oldest and simplest is the use of a magnetic plug to collect and retain ferromagnetic debris. The particles collected may be examined externally as desired upon removal of the plug.

The requirement for on-line monitoring has led to the development of numerous electrical methods for detecting the presence of debris particles. Metallic particles may act as a switch by bridging a gap between magnetised electrodes or they may change the inductance of an electrical sensing coil. The degree of abrasion of a film resistor by metallic and non-metallic debris may also be monitored electrically to indicate the quantity of particles present in the surrounding fluid.

For analysis to take place the debris must be captured and retained. As outlined above, a magnetic plug may be used to collect the debris. Alternatively, very fine mesh filters, in removable cartridges, may be employed.  As well as achieving particle retention, such filters cause a pressure drop as they become clogged. Monitoring of this pressure change will give an indication of the rate of accumulation of debris.

Analysis of the debris particles is performed using either arc/spark-based equipment or, if more detailed information is required, by spectrometry. Spectrometry can achieve accurate multi-element analysis which may, given detailed knowledge of the machine, pinpoint very specifically the source of the debris particles.