Eddy-current type proximity sensor with closed magnetic circuit geometry

The eddy-current type proximity sensor is a noncontact type sensing device to detect the approach of a conductor by increase of coil resistance due to eddy-current loss. This paper proposes to add the cap-shaped magnetic flux shield at the top of the ferrite core for the actual sensor. In conventional proximity sensors, main magnetic flux path passes through the air between the target conductor and ferrite core. The proposed sensor, in contrast, has closed magnetic circuit geometry. This means that main magnetic flux path is almost completed by the core and the shield. Therefore, it is predicted that flux does not reach the target conductor and it causes debasement of sensing property. However, it is shown that the calculated results by finite element method and measured results of the sensing property of the proposed sensor is enhanced compared with the actual sensor. This paper quantitatively accounts the electromagnetisms of the proposed sensor from sensing property, flux distributions, and eddy-current loss in each part of the sensor body.