Andy G4JNT,
Having a "bend" in the transfer characteristic that changes with level
certainly means some non-linearity. If you look at spectra (in the
frequency domain) instead of RMS level (in the time domain), you may observe
what harmonics grow as the level is increased (assuming things get worse
with drive level). That would be one way to evaluate nonlinearity, but as
you want to use it for measurements then it would be irritating to need to
correct for self-distortion in the probe. One possible explanation is that
magnetostriction dynamically modulates the (micro) air gaps between EI
laminations?
Current transformers I have seen are invariably of toroidal construction.
That suggests that leakage reactance is part of the quality of making a good
current transformer, but leakage is "linear" and that alone would not
explain why you have a "bend" in the transfer characteristic using an EI
core. A toroidal core would seem to be less prone to magnetostriction
affects?
Have you got a toroidal transformer to try? There is no need to strip off
turns as it is fairly easy to arrange a 1 turn primary when the toroid has a
decent internal diameter ;-)
73, Bob ZL2CA
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