Solid particles, water drops and air bubbles detection in lubricating oil using microfluidic inductance and capacitance measurements

The contaminants in lubricating oil can be used to judge the operating conditions of a machine, which can be divided into solid, liquid and gas depending on the form. Microfluidic devices based on the electrical technique are presented to detect ferrous metal particles, different kinds of non-ferrous metal particles, non-metallic particles, water drops and air bubbles. The ferrous metal particle and nonferrous metal particle can be detected by the inductance pulses and differentiated by the directions of inductance pulses based on the permeability of particles; a method that calculates the electrical conductivity of a particle is introduced to differentiate different kinds of nonferrous metal particles by measuring the inductance changes caused by the particles. Continuously and evenly distributed tiny ferromagnetic metal particles are introduced to detect non-metallic particles. Water drops and air bubbles can be detected by the capacitance pulses and differentiated by the directions of capacitance pulses.