Magnetic-Capacitive Wear Debris Sensor Plug for Condition Monitoring of Hydraulic Systems

This paper presents a new and efficient sensor for monitoring the presence of wear debris received by the storage tank in hydraulic systems. The proposed sensor plug employs a magnetic approach to attract the ferrous debris in the storage tank. A capacitive sensing scheme is employed in the same sensor plug to sense the presence of the debris accumulated on the plug. This combination of the magnetic and capacitive features in a single sensor for debris monitoring is new and it helps to realize a very sensitive sensor. The proposed sensor is designed in an ingenious way that the permanent magnet that is used to form the magnetic field in the vicinity of the sensor, to attract the debris towards the sensor, itself serves as one of the electrodes of the capacitive sensor. This approach improves the sensitivity and keeps the number of components in the sensor minimum. A prototype of the proposed sensor has been developed and tested. In the prototype, the change in capacitance of the sensor is measured using a high-resolution capacitance-to-digital converter. The sensor was tested after integrating it in a hydraulic test bed which has a controlled debris injection facility to the hydraulic circuit. The output of the sensor was found to be very sensitive to the typical ferrous debris that was introduced in the system. The proposed low-cost sensor will find applications in debris monitoring of underwater and land-based hydraulic systems.