Fred Abse wrote:
On Sat, 09 Jun 2012 20:37:02 -0800, Robert Baer wrote:

Basically, "BH" loop not seen; only a nice ellipse

You won't see a B-H loop that way.

On the X axis, you have current in the winding, that's fine. proportional
to H.

The Y axis is where it goes wrong:

Now, V = -L di/dt, or V proportional to d(phi)/dt

You want B (that is to say phi) on the Y axis.

You're seeing something proportional to dB/dt

Hence you need to integrate the voltage applied to the Y input.

Similar to how you'd use a Rogowski coil.

You're seeing what I'd expect to see with your test setup.

I do not think so; what is that pulse?
WRT percentage of time of sine drive, the pulse is in same position
and same width as seen from 0.5Hz to 500Hz; pops up at 5% of half-sine
time, jumps back down at 12% of half-sine time.

So, you might say that as the current drive increases, the core
eventually saturates and thereby the inductance goes toward zero, making
the voltage rise rapidly - that can explain the rise and top of the pulse.
BUT..why does it drop rapidly back after a pre-determined _increase_
of drive?
This is independent of frequency, so inductance, impedance are
meaningless arguments especially in the light of the frequency range
used for investigation.

Found a problem with my layout and resolved it.
Primary and secondary are identical - including the pulse.