A Displacement Sensing Method Based on Permanent Magnet and Magnetic Flux Measurement

Abstract

This paper proposes a displacement sensing method based on magnetic flux measurement. A bridge-structured magnetic circuit, formed by permanent magnets and two ferromagnetic cores, is designed and discussed. The analyses of the equivalent magnetic circuit and three-dimensional finite element simulations showed that the magnetic flux density changes linearly with the reciprocal of the sum of a constant and the displacement. A prototype sensor of the bridge structure is developed that consists of four permanent magnets as excitation, a Hall sensor as reception, and two ferromagnetic cores as the connection. Experiments have validated the feasibility of this method. The measured results show a good linearity between the sensor’s output and the reciprocal of the sum of a constant and the displacement, with a correlation coefficient greater than 0.9995 across different measurement ranges. Additionally, the measured results significantly indicate that the proposed sensor is compatible with different ferromagnetic materials with a worst-case error of less than 5%. The proposed sensor has the advantages of low cost and good linearity; however, the test object is limited to ferromagnetic materials.

A Comprehensive Review of Steel Wire Rope Degradation Mechanisms and Recent Damage Detection Methods

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A method for compensation of permanent magnetic field perturbation (PMFP) testing signal based on lift-off measurement

“…where a, b, and k are constants. B c is the value of the permanent magnet bottom surface distance from the specimen lift-off is calculated from the value measured by Hall C [6].…”

“…In the realm of pulsed eddy current testing (PECT), Sreevatsan and George proposed a probe capable of concurrently detecting defects and lift-off [5]. Zhang, a member of Kang's research team, introduced a magnetic bridge displacement sensor that exhibits an inverse relationship between lift-off and measured value through the combination of a permanent magnet and an iron core [6]. In addition to conducting measurements and analysis of the lift-off during the testing process, furthermore, several researchers have devoted their efforts to mitigating the impact of lift-off on measurement signals [7][8][9].…”

Gap distance sensing for non-magnetic medium based on magnetoelectric effect under spatial separation condition

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