Enhancement of the sensitivity to EC coil impedance variations based on phase measurements

摘要

The estimation of eddy current (EC) coil impedance with high sensitivity is very important in many inspections especially when elevated operational frequencies and coils with low inductance are applied. For proper inspection results interpretation components of the coil impedance must be evaluated. In this paper new method for small impedance variations estimation based on phase measurement method is proposed. This technique is of particular important for processing the signal response of single coil (parametric) EC probe. It is possible to considerably reduce the effect of additive noise and amplitude variation by clipping the sine waveforms before measuring the phase shift. This shows a promise of enhanced sensitivity to small changes in real and imaginary components of the probe coil impedance. The next advantage of the phase method is the relaxed requirement for the Q factor of the resonant circuit, which includes the probe coil.