A Novel Eddy Current Method for Magnetic Plate Identification with Elimination of Lift-off Effect

Abstract

novel eddy current method for magnetic plate identification is presented. This method uses the magnetic property in low frequency and conductive property in high frequency of the magnetic plates. The frequency profiles are measured with a conventional impedance analyzer, as a function of lift-off, which represents the distance between the coil and magnetic plate. If a coil is placed to a magnetic plate, there is a cross frequency at which the measured value is as same as inductance of coil only. The measured value of cross frequency depends on the coil diameter, placed magnetic plate, not strongly depends on the liftoff. In this paper, identification of iron and nickel plates are successfully demonstrated. A discussion with an iron plate with nickel plating of 40 �m is also mentioned.

Evaluation of the Properties of Eddy Current Sensors Based on Their Equivalent Parameters

“…It is also important to properly select the frequency of the current exciting the coil since it affects not only the eddy currents penetration depth but also the metrological properties of the measuring instrument, including its sensitivity. Another important solution that needs to be implemented in the measuring instrument is the mechanism eliminating the influence of the lift-off effect [ 32 , 33 ] and the inaccuracy of the sensor position in relation to the tested element.…”