Non-destructive eddy current test device using additive flux substractive flux switching

A non-destructive eddy current test device using additive flux/substractive flux switching, comprising:

• a control means for selecting either additive flux or subtractive flux operation;
• supplying means for supplying first and second excitation signals alternating at the same frequency but in phase opposition to one another;
• two analogous coils adjacent one another and electromagnetically coupled to a part under test so as to create two fluxes therein when excitation signals are supplied to said coils;
• feeding means controlled by said control means and connected to said supplying means and to said coils for feeding said excitation signals to said coils whereby each coil will have a terminal voltage corresponding to an impedance of the respective coil, said feeding means feeding said first excitation signal to said first coil and feeding either of said first or second excitation signals to said first coil in accordance with the selection by said control means;
• and
• measuring means connected to said coils for measuring the difference between the impedances of said first and second coils, by either adding or subtracting the terminal voltages of said first and second coils in accordance with the selection by said control means.