TSSP: List Archives

From: Paul
Date: Sat, 12 Oct 2002 23:27:21 +0100
Subject: Re: [TSSP] Top Voltage

Bart wrote:
> I have one of Terry's current sensors, so I can
> run the base lead through and set the scope to
> capture first breakout

Got anything to calibrate it with?  At least we don't
demand too much from the scope, just a peak reading to
better than 5%.

> When testing for "break-out" conditions, the gap arc voltage
> is the adjustment tool. The variacs allow us to ramp up to
> what ever is required to arc the gap, but the gap arc voltage
> sets the topvolts breakout potential.

Ok, I see.  Perhaps not so easy then to find the point
where it is only just beginning to break out.  Hopefully
the procedure for taking these measurements won't be too
hard, so that we can collect quite a few. 

It would also be very helpful to measure the secondary
Fres (with primary gap open) and the two mode frequencies
(with primary gap closed).  Not everyone is going to be able
to do this, and in those cases there will be some doubt that
we modeled the tuning correctly.  

Without frequency measurements, there could easily be 
another 5% error in converting the base current reading to 
a peak topvolts.  With frequency measurements the extra
error drops to around 1%, or the accuracy of the frequency
measurements, whichever is the worst.

I'm wondering if we should restrict to coils setup outdoors.
Perhaps the wrong time of year for most of us!  The thing is,
any doubt about the E-field around the top of the coil adds
directly to the error in the resulting breakout voltage.  The
presence of the ceiling is a big unknown quantity.  Likely    
not a problem for table top coils, or coils operated in a big
room.  The trouble is, even if a nearby wall or ceiling doesn't
add much in the way of extra C, it could nevertheless make
some redistribution of the topload charge, which is critical
to determining the location and size of the highest surface
field.  For example, a nearby wall might shift the charge to
one side of the topload by 30%, but only make 10% change to
the total charge, so we would see a 5% error in Fres but 
have a 30% error in breakout voltage.

Are we likely to still be able to find several coils with
this outdoor requirement?  Perhaps we should only trust
indoor measurements if the coil in question will breakout
equally readily in any direction from the toroid, indicating
that at least cylindrical symmetry of the E-field has been
obtained.

Wonder how many candidate systems that leaves within our
reach?  We want to get accurate figures, but going to far
will leave too few systems, so we won't get a clear
picture.  
--
Paul Nicholson,
--


Maintainer Paul Nicholson, paul@abelian.demon.co.uk.