Inductive-Capacitive Coulter Counting: Detection and Differentiation of Multi-Contaminants in Hydraulic Oil Using a Microfluidic Sensor

A microfluidic sensor based on the inductivecapacitive Coulter counting principle to detect multicontaminants in hydraulic oil is presented. The sensor consists of a silicon steel plate and a planar coil. The silicon steel plate makes the distribution of the magnetic flux more dense and uniform, thereby effectively improving the dection sensitivity. The experimental results show that the low-frequency alternating current should be used to detect ferromagnetic particles, and the high-frequency alternating current should be used to detect non-ferromagnetic particles. In inductance mode, the high-frequency excitation should be selected to identify smaller copper particles for comprehensive accuracy, and 30μm iron particles and 110μm copper particles were detected at 2.0MHz. In capacitance mode, the signal amplitude decreases with frequency, but the signal-tonoise ratio increases first with frequency and then decreases. There is the best capacitancedetection sensitivity at 0.7MHz, and 100μm water droplets and 160μm air bubbles were detected. As the core component of the portable oil detection device, this sensor can be used for health monitoring of mechanical equipment to prevent hydraulic system failure.