A New-Developed Multi-frequency Impedance Analyzing Instrument Used for Eddy Current Testing Based on DSP

As conventional multi-frequency eddy current impedance analyzer generally employs signal generator to compose multi-frequency excitation signal, separate multi-frequency signal with band-pass filter, PSD and phase-locked amplifier, and analyze multi-frequency operational factors with spectrum analyzer and switching circuit, which results in a complex structure design, high production cost and low detection resolution and reliability. This paper develops a high-performance multi-frequency impedance analyzing system (MFIA) for eddy current testing based on DSP and synchronous measurement strategy. The measuring system generates multi-frequency excitation waveform with minimum crest factor, implements FFT cross-spectral analysis of the excitation current and sensing voltage with software method, and calculate the sensor impedances in different harmonic components, which can separate parameters and suppress interferences effectively. Two-inductor network and U-cored eddy current sensor were fitted onto the circuit system respectively to carry out experiments. The results show that the system possesses a high detection resolution and reliability as well as good stability, which provides a favorable basis for designing intelligent multi-frequency impedance analyzer.