High-Throughput Sensor to Detect Hydraulic Oil Contamination Based on Microfluidics

Abstract

Based on the microfluidic technology, we designed a high-throughput sensor to detect the hydraulic oil contamination. The sensor has two working modes: inductance detection and capacitance detection. The inductance detection mode can detect ferromagnetic and non-ferromagnetic metal particles in the hydraulic oil. By changing the coil connection to switch to the capacitance detection mode, it can detect water droplets and air bubbles in the hydraulic oil. An annular microchannel is designed to increase the detection flow and to shorten the detection time. A pair of silicon steel sheets are built into the annular microchannel to collect the dispersed magnetic field in the detection area, which improves the accuracy in detecting ferromagnetic and non-ferromagnetic particles. Our experiments showed that the detection sensor is more stable when the plane coils have 20 turns. The magnetic field effect of the silicon steel sheet can improve the detection accuracy in inductance detection. Without the silicon steel sheet, the sensor can detect iron particles as small as 60–70 $\mu \text{m}$ with a signal-to-noise ratio (SNR) of 1.55 and copper particles as small as 150– $160~\mu \text{m}$ with an SNR of 1.35. With the silicon steel sheet, the sensor can detect iron particles as small as 60– $70~\mu \text{m}$ with an SNR of 3.42 and copper particles as small as 150– $160~\mu \text{m}$ with an SNR of 3.10. Capacitance detection can detect the water droplets of size 190– $200~\mu \text{m}$ and air bubbles of size 260– $270~\mu \text{m}$ .