Design and implementation of functional measuring circuit for material-independent eddy current sensor

The characteristics of conventional eddy current sensor are dependent on the electromagnetic properties of the target materials. In this paper, according to the impedance vector projecting method, a measuring circuit with waveform generator, impedance to voltage converter, X/R orthogonal resolver, impedance normalizer, associated with nonlinear compensation is designed to eliminate the influence caused by different targets. Furthermore it is testified by experimental results that the design makes it possible to measure distance under different targets. The conclusions are shown that: (1) the impedance projecting method is useful in eliminating the influence caused by the electromagnetic properties of targets for eddy current sensor; (2) it is testified by experiment results that the measuring circuit designed can be used under six kinds of targets; (3) the nonlinearity of the circuit is 6%, and better nonlinearly compensation technology should be put forward to improve the linearity.