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Abstract

A device to detect the presence of particles, principally metallic particles, in fluid lines. The fluid to be sampled flows through a sensor coil which is flanked upstream and downstream by two field coils. The field coils are driven by a high frequency signal derived from a crystal oscillator and the upstream and downstream sections are wound in opposite directions such that the magnetic field from each section is cancelled out in the plane of the sense coil. When a ferromagnetic or conductive particle passes through the winding structure, the coupling in the sense coil is disturbed as the particle first interacts with the field in the upstream section of the field coil and later with the field in the downstream section of the field coil as it passes through the Sensor Coil Assembly (SCA). A characteristic signature is generated in the sense coil which results from the vector summation of these transient imbalance signals with the steady-state signal from the opposed field coils. Analysis of the phase of this signature can be used to detect and distinguish between the presence of ferromagnetic and non-ferromagnetic conductive particles. Since ferromagnetic and non-ferromagnetic conductive particles interact with the field via permeability and eddy current effects respectively, the transient phase signature has a characteristic lag-lead or lead-lag sequence depending on the nature of the particle.

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First Claim