NDTnet 1998 Aug, Vol.3 No.8

Abstract

To digitally demodulate an eddy current signal, the main problem is to find out a 16 bit digitizer that is able to handle frequencies up to 10 MHz. A traditionnal approach is not able to digitize the signal using more than 10 bits.

The second problem is to simultaneously digitize up to 4 frequencies, without loosing any information, and without adding any noise.

The showed digitizer process is able to simultaneously manage 4 frequencies up to 10 Mhz with 16 bits resolution. The demodulation can then be digitally processed, achieving a 1% amplitude and 1° phase linearity.

Another advantage of the digital demodulation is the capability of more real time computation. For example, combinations between signals can be done in real time. As the complete instrument depends on a single clock source, there are no phase variations between channels. The consequence is a high quality of combinated signals.

Conclusion:
A digital demodulation is possible for simultaneous frequencies up to 10 MHz. The standard based architecture of the instrument allows any kind of real time processing including signal combination, signal recognition and noise reduction.

Fig. Digital demodulation - Instrument draft

Abstract Source:
Book of Abstracts, 7th European Conference on Non-Destructive Testing, 26-29 May 1998, ISBN: 87-986898-0-00

Full-Text Source:
Proceedings of the 7th European Conference on Non-Destructive Testing, 26-29 May 1998, ISBN:

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