Re: Floating Scopes

["Tesla list" <tesla-at-pupman-dot-com>]

Original poster: "Paul Nicholson by way of Terry Fritz <twftesla-at-qwest-dot-net>" <paul-at-abelian.demon.co.uk>

Ken wrote:
 > Is there any evidence that the currents from top of a
 > secondary to the top terminal of whatever capacitance a user
 > has will be any different than the ground current from bottom
 > of the secondary to earth?

Yes, the currents must differ if there is distributed
capacitance along the secondary (which there always is!).

Earlier this year, Terry Fritz accurately measured the
current profile of a secondary coil.  See

  http://www.abelian.demon.co.uk/tssp/tfcp260302/

 > maybe there is interesting capacitive coupling between the
 > secondary coil itself and the top terminal resulting in
 > currents that never have to even flow through the coil's
 > ground.

Yes, some current circulates through the secondary-to-topload
capacitance, thus never making it to the ground terminal.
This current, along with a similar circulating current moving
through the secondary-to-secondary capacitance, increases the
effective inductance of the secondary coil and raises the
location of max current somewhat above the base.

Jim Lux wrote:

 > A wireless LAN interface could also work,

Yes, could well do.  Up at 2.4GHz it might well work ok
despite all the RF interference.

Another approach, along the same lines might be to use
one of those little 2.4GHz FM TV transmitters. With a bandwidth
up to a few Mhz, it might be able to transfer the analogue
current signal with reasonable linearity.

The approach that is known to work is the current probe plus
fibre optic link, which Terry has put to good use on many
occasions.

Regards,
--
Paul Nicholson,
--