A high sensitivity micro impedance sensor is presented for oil condition monitoring. The sensor consists of a microfluidic chip and a sensing unit. The sensing unit contains two solenoid coils and eight silicon steel tips, which can generate a highly focusing magnetic field. The micro impedance sensor can not only distinguish between ferromagnetic and non-ferromagnetic metal particles, but also water droplets and air bubbles in oil. The simulation results show that the magnetic induction is significantly improved due to the silicon steel tips, and the electric field intensity is also slightly enhanced. In the inductance experiments, the sensitivity is extremely improved based on magnetic focusing by silicon steel tips, iron particles with diameters down to $18\mu $ m and copper particles with diameters down to 75 $\mu \text{m}$ have been successfully detected by using the simple high sensitivity micro impedance sensor. In the capacitance experiments, the signal to noise ratio (SNR) of the micro impedance sensor with silicon steel tips is slightly improved; water droplets with diameters down to 100 $\mu \text{m}$ and air bubbles with diameters down to 200 $\mu \text{m}$ have been detected. The high sensitivity micro impedance sensor has been demonstrated to achieve the precise measurement of particle sizes and the accurate counting of microparticles.

A High Sensitivity Micro Impedance Sensor Based on Magnetic Focusing for Oil Condition Monitoring

A high sensitive multi-parameter micro sensor consisted of a microfluidic chip and a sensing unit is presented The sensing unit, which composed of a dual-coil and two silicon steel sheets, is embedded in the simple microfluidic chip with a straight microchannel structure The micro sensor can be used not only as an inductive sensor to distinguish between ferromagnetic and non-ferromagnetic metal particles, but also as a capacitive sensor to distinguish between water droplets and bubbles in hydraulic oil The simulation results show that both the magnetic field and the electric field of the sensing unit are enhanced under the effect of the silicon steel sheets In the experiments, the number of turns of the coil was optimized first, and then the comparative experimental results show that the detection amplitudes of both iron and copper particles were increased about four times compare with the sensing unit without silicon steel sheets, which verified the simulation results Using the simple micro sensor, without any complicated external circuits, in the inductance detection experiments, we demonstrate the successful detection of 33 μm iron particles and 90 μm copper particles in hydraulic oil; and in the capacitance detection experiments, we can detect 100 μm water droplets and 180 μm bubbles in hydraulic oil For both the inductance and capacitance detection, the results of particles with different sizes were in good agreement with the simulation results

A high sensitive multi-parameter micro sensor for the detection of multi-contamination in hydraulic oil

A high throughput and high sensitivity sensor for detection of oil metal debris is presented. The sensor is mainly composed of a planar coil, a ferrite core and a flat channel. The adoption of flat channel can increase the throughput without sacrifice of sensitivity. The comparative experiments show that the ferrite core not only eliminates the phenomenon of multiple pulse peaks for detecting individual metal particle in the flat channel, but also can improve the sensitivity of inductance detection and resistance detection. For detecting 130–140 $\mu \text{m}$ iron particles, the inductance amplitude and SNR (signal-to-noise ratio, the SNR is the amplitude divided by the interference noise) of sensor with ferrite core are 1.17 times and 1.22 times higher than those of sensor without ferrite core, respectively. For detecting 160–170 $\mu \text{m}$ copper particles, the inductance amplitude and SNR of sensor with ferrite core are 1.24 times and 1.28 times higher than those of sensor without ferrite core, respectively, and the resistance amplitude and SNR of sensor with ferrite core are 1.09 times and 1.07 times higher than those of sensor without ferrite core, respectively. In addition, the introduction of resistance detection can increase the ability of sensor to detect non-ferromagnetic metal particles. We can detect iron particles with diameter of $40~\mu \text{m}$ onwards and detect copper particles with diameter of $90~\mu \text{m}$ onwards using the sensor with ferrite core combined with inductance and resistance detection methods. This work improves the throughput of microfluidic high-precision detection, which can provide technical support for large-flow oil detection.

Oil Metal Debris Detection Sensor Using Ferrite Core and Flat Channel for Sensitivity Improvement and High Throughput

A novel inductive particle detection system was developed for a real-time monitoring of metals in airborne particles which cannot be measured using current commercial portable devices. The detection system consists of particle sampling, particle sensing, oil circulation sections and signal processing circuit. Airborne particles of different sizes enter the system and are classified according to their sizes in the particle sampling section. Particles larger than 5 µm are collected on the oil surface and passed through the particle sensing section along with the oil circulating throughout the system. The particle sensing section was realized using a 3D multilayer solenoid connected to a high-precision inductance meter. The performance of each section was first evaluated, and then the overall performance of the system was evaluated. The results show that ferrous and nonferrous metals in airborne particles can be detected and differentiated using proposed system with minimum detectable size of 5–10 µm for Fe and 50–60 µm for Cu particles. In addition, the number concentration of Fe particles was converted and compared with the reference number concentrations measured by high-precision commercial instrument, under the metal particle generation condition. The comparison results of the system show good agreement at concentrations within its detectable range, up to 200 #/L. The proposed system and design concept demonstrated here can be widely used for the real-time and extensive monitoring of airborne metal particles in industrial workplaces.

Inductive particle detection system for real-time monitoring of metals in airborne particles

Wear debris detection is an effective method to determine the running state of the machine. Recently, the planar inductor is commonly used to detect wear debris. The previous studies have found that the inductive signal would be varied while changing the position of wear debris pass through. However, the effect of position on the wear debris detection is not well understood. In this paper, a novel detection system in which the position of wear debris pass through could be adjusted precisely is designed. By changing the position in horizontal or vertical direction, the inductive signals of the wear debris were acquired. In the horizontal direction, the experimental results show that the amplitude of the inductive signal first increases and then decreases when the position changes from the center of the planar inductor to the outer. The maximum inductive signal appears when the wear debris pass through the edge of the inner coil, which is 20% higher than that for the center and much higher than that for the edge of outer coil. In the vertical direction, the signal decreases almost linearly when the position is away from the planar inductor. For every 0.1 mm step far away the planar inductor, the signal amplitude drops by approximately 10%. The variation trend of our experimental results is consistent with the numerical simulation results of magnetic intensity around the planar inductor.

https://www.mdpi.com/1424-8220/19/22/4961/pdf

The Effects of Position on the Wear Debris Detection with Planar Inductor.

Accurate detection of metallic wear debris is vital to avoid catastrophic failure of machine. An inductive metallic debris sensor in accordance with the theory of electromagnetism is presented to discuss the relationship between the sensitivity of inductive sensor and the position of microchannel inside the planar coil. Iron particles with 110–120µm in diameter are used in the experiment and the result demonstrate that the different position of microchannel does have influence on the sensitivity of planar coil. The sensitivity can be significantly improved when changing the position of microchannel, 130% increase in inductance amplitude could be got when the microchannel is near the edge of coil in contrast to near the center.

Research on the influence of different microchannel position on the sensitivity of inductive sensor

The influence of velocity of oil debris on the sensitivity in metal debris counting with microfluidic oil detection chip is reported in this paper. A microfluidic oil detection chip of a three-dimension solenoid with a micro channel crossing its center was presented in this paper. When measuring the inductance value of microfluidic oil detection chip caused by the oil debris, it can be found that the oil debris velocity affects the inductive pulse signal. Through experiments, the results show that the amplitude of inductance change is influenced by velocity of oil debris if the size and material of oil debris are known. With the increase of velocity of oil debris, the amplitude of inductive signal decreases. This result is important and has reference value for sizing oil debris and other particles by microfluidic oil detection chip.

Research on the influence of velocity on particle counting sensitivity of microfluidic oil detection chip

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Research on the influence of different microchannel position on the sensitivity of inductive sensor

Research on the influence of velocity on particle counting sensitivity of microfluidic oil detection chip