Inductive Debris Sensor Based on Dual-Excitation and Large-Diameter Flat Channel

Wear is one of the main reasons for the failure of mechanical equipment. The lubrication system is an important part of the mechanical equipment. And the wear debris in the lubricating oil contain important information such as the wear mechanism of the friction pair of the mechanical equipment and the type of wear failure. In view of the fact that traditional oil monitoring sensors cannot meet the requirements of high sensitivity and high throughput at the same time, this paper proposes an inductive sensor with dual-excitation and large-diameter flat flow channel. In the designed sensor structure, the dual-excitation structure can generate a stronger symmetrical gradient magnetic field than the single excitation structure, which improves the sensitivity of the sensor. Then, a large-diameter flat detection tube is arranged in the strong magnetic field area between the dual-excitation structure, which can effectively improve the flow and maintain a high sensitivity.

First, the structure of the sensor was introduced, and the theoretical mathematical model of the signal generated by the sensor was established. Then, the finite element analysis model of the sensor was established by using Ansys simulation software, and the magnetic field distribution laws of the single-excitation and dual-excitation structures in the xz plane and yz plane were respectively analyzed, and it was proved that the dual-excitation structure could produce a stronger symmetrical coupled magnetic field than the single excitation structure. In addition, the magnetic fields of the four structures of the single excitation with a circular pipe (SECP), single excitation with a flat pipe (SEFP), double excitation with a circular pipe (DECP) and double excitation with a flat pipe (DEFP) were compared and analyzed. It was found that the field strength generated by the double excitation with a flat tube structure was significantly better than that of the other three structures, and the peak value of the magnetic induction intensity was about 200% higher than that of the single excitation with circular tube structure.

In addition, the effects of the height and width of the large-diameter flat pipe on the magnetic field at the center of the pipe were respectively studied, and it was shown that increasing the height of the flat pipe makes the magnetic field of the sensor attenuate extremely fast, while increasing the width maked the magnetic field of the sensor attenuate slowly. Therefore, there were significant advantages to using flat tube as the flow path for the oil. Then, the influence of excitation current, the velocity and the spatial position of the debris in the pipeline on the signal was given, respectively.

Finally, an experimental platform for the detection of oil wear debris was built. Firstly, the debris of different sizes were used and the moving velocity of the sensor was changed to observe the debris signal. It was found that the amplitude of the debris signal increased with the increase of debris size and velocity, which was consistent with the finite element simulation analysis results. In addition, when the ferromagnetic wear debris of 25 μm were mixed into the lubricating oil and flow through the sensor, the inductive voltage generated by the induction coil contains obvious debris signals. The experimental results shown that the inductive sensor with dual-excitation and large-diameter flat flow channel designed in this paper could successfully detect the ferromagnetic debris of 25 μm in the flat pipe with an equivalent inner diameter of 28 mm, which could better meet the requirements of large flow and high sensitivity. Consequently, the sensor had certain engineering application value and could be used in some researches on analyzing tribological surfaces in the future.