To improve the wear monitoring accuracy of steel tribo-pairs, a ferromagnetic particle sensor that consists of a magnetic loop with two cylindrical magnetic poles and one magnetic housing is proposed. The induction coil is placed inside the magnetic poles to shield against external electromagnetic interference. The air gap is designed to 1 mm between the two magnetic poles, where a rotational symmetric high-gradient static magnetic field will be generated under constant direct current (dc) drive. The sine-wave-like signal of one period will be induced when one ferromagnetic particle flows through the sensor. The working principle of the sensor and the internal magnetic field distribution is explained by establishing a mathematical model and finite element analysis (FEA). Furthermore, the results about the effects of coil length and position show that the output voltage is not sensitive to the axial mounting positions of the induction coil, and a shorter inductive coil produces a larger output voltage. By the oil dynamic monitoring experiment, the sensor can distinguish 13- $\mu \text{m}$ ferromagnetic particles in an oil tube of 10-mm inner diameter. With its high sensitivity to ferromagnetic particles, the sensor is suitable for online wear monitoring of steel tribo-pairs.

中文翻译：

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基于旋转对称高梯度静磁场的铁磁磨损颗粒传感器

为了提高钢摩擦副的磨损监测精度，提出了一种铁磁颗粒传感器，该传感器由具有两个圆柱形磁极和一个磁性外壳的磁环组成。感应线圈放置在磁极内部，以屏蔽外部电磁干扰。两个磁极之间的气隙设计为 1 mm，在恒定直流 (dc) 驱动下将产生旋转对称的高梯度静磁场。当一个铁磁粒子流过传感器时，会感应出一个周期的正弦波状信号。通过建立数学模型和有限元分析（FEA）来解释传感器的工作原理和内部磁场分布。此外，线圈长度和位置影响的结果表明，输出电压对感应线圈的轴向安装位置不敏感，感应线圈越短，输出电压越大。通过油液动态监测实验，该传感器可以分辨出内径为10mm的油管中的13-$\mu\text{m}$铁磁颗粒。该传感器对铁磁颗粒具有高灵敏度，适用于钢摩擦副的在线磨损监测。