Extending the Linearity Range of Eddy-Current Displacement Sensor With Magnetoplated Wire

The ratio of the linearity range L
_o
to the coil diameter D of the ordinary eddy-current (EC) displacement sensor, L
_o
/D, is approximately 0.48. In conventional technology, the coil diameter needs to be increased to extend the measuring range of the EC displacement sensor. In this paper, we propose the use of magnetoplated wire (MPW) for the coil winding to improve the L
_o
/D ratio. An MPW is a copper wire whose circumference is plated with a magnetic thin film. We discuss the physical phenomena and impedance characteristics of the MPW coil and compare them with those of a coil that uses a conventional copper wire (COW). The L
_o
/D values of an EC sensor with an MPW coil and with a COW coil are 1.0 and 0.48, respectively. These results demonstrate the ability of the MPW coil to double L
_o
/D value over that of the COW coil