130627-2215 EDT
GoldDigger:
Power transformers are built with some comprimise on performance and cost, plus government regulations.
What this means is that a suitable ferromagnetic core is used to tightly couple the magnetic field of a primary to a secondary, and at nominal source voltage and frequency to run the core somewhat into saturation at the end of the volt-time integral in one direction. This causes a magnetizing current pulse to appear near the voltage zero crossing of the excitation. In my photos P6 and P7 you can see the pulse coincide with the negative slope voltage zero crossing. Unfortunately the P8 photo where there are both + and - current pulses does not have a reference voltage waveform for comparison.
To demagnetize a material you apply an AC magnetic field, and gradually reduce the excitation to zero. This keeps reducing the hysteresis curve, and approaches a zero residual flux when the excitation reaches zero. But just turning off excitation at a high flux level just leaves the core at some residual flux level.
By using a square loop material you can make a counter. Incrementally pulse the core in one direction. When saturation occurs, a pluse output can be generated.
References:
"Electric and Magnetic Fields", Stephen S. Attwood, 1949, John Wiley, Chapter 13.
"Electrical Circuits and Machinery", Hehre and Harness, 1942, John Wiley, page 262. Very nice plot.
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