Portable Instrument for Eddy Currents Non-Destructive Testing based on Heterodyning Techniques

In this work an eddy current testing instrument employing heterodyning based measurements is presented. The instrument is composed of a portable computer and a dedicated electronic measurement circuitry to operate a specific type of probe. A DDS waveform generator and a transconductance amplifier are used to drive the probe with high amplitude currents and frequency up to 10 MHz. The probe output voltage is amplified up to 60 dB and down-converted to a lower intermediary frequency. The signal is converted into the digital domain and processed to compute the real and imaginary parts of the probe output voltage. The developed dedicated electronics were installed inside a rugged laptop computer to form a standalone instrument with post-processing and visualization capabilities. Electrical characterization and application results using the instrument and a particular eddy current probe are presented.