sae140 wrote:
(snip)
> The third has me foxed, and is the reason why I've posted these images.
> Assuming that every other coil is a drive coil, I can see how each of
> these could be connected in series to achieve what would be in effect
> one single drive coil, albeit in four sections, but it is the
> remaining sensor windings which I don't quite understand. If opposing
> coil pairs were connected in series (phase/anti-phase) would this
> perform as well as the more conventional over-winding ?
>
> Any takers ?

The pairs of sensor windings have to be hooked up in series,
opposing, so that the induced voltages from the flux drive
windings cancels.

But if the core is also exposed to external flux that passes
through those two coils, the one that had external flux in
the same direction of the drive flux will see its core
saturate first (terminating the drive induced voltage
early), while the one that had the external flux opposing
the drive flux will see its core saturate a bit later, so
there will be that brief part of each half cycle when the
two sensor coil voltages will not be equal and opposite.
That sliver of mismatch is the output signal. The main
advantage to using a single surrounding sensor coil is that
the exact number of turns is not so important (only a
scaling effect on the output). Splitting the sensor coil up
into two separate coils connected in series requires an
exact turns count match or the induced drive voltages will
not cancel as the core flux swings from saturation to
saturation.

--
Regards,

John Popelish