Physical Science, Measurement and Instrumentation, Management and Education, IEE Proceedings A

In eddy-current arrays employing large numbers of coil elements, a sensitive, fast measurement system employing the minimum of hardware components is required. A novel technique, which meets the above criteria and which is directly compatible with digital technology, is described. It relies on the generation of transient waveforms obtained when the initial current oscillation in the test coil is switched through a high resistive load. Amplitude and time measurements taken on these waveforms yield results which are sensitive to coil lift-off changes and flaw presence. The absolute coil impedance can also be found. An equivalent circuit is used to analyse the system transients, allowing a comparison to be made between the modelled waveforms and those obtained by experiment.