Re: term understanding: voltage reversal.

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

Original poster: "Malcolm Watts" <m.j.watts-at-massey.ac.nz> 

Hi Jim,

On 19 Feb 2004, at 17:46, Tesla list wrote:

 > Original poster: Jim Lux <jimlux-at-earthlink-dot-net>
 >
 > At 08:02 AM 2/19/2004 -0700, you wrote:
 > >Original poster: "Dr. Resonance" <resonance-at-jvlnet-dot-com>
 > >
 > >
 > >Bert has a great point here.  A nice neat equation.  If you use a
 > >storage scope to see the primary discharge waveform you can find the
 > >nearly exact Q factor of your primary circuit.  Knowing the % voltage
 > >reversal you can solve the equation for effective Q factor.
 > >
 > >Another method is to observe the decrement (decay) factor which is
 > >related to circuit resistance.  You can use this information to
 > >determine effective dynamic Q factor was well.
 > >
 > >You fire the primary with and without the sec in place --- in a
 > >single shot mode.  Do not try this at high rep rates or the excessive
 > >Q without the sec will blow the cap.
 > >
 > >In a single shot mode you can compare the loaded and unloaded Q
 > >factor and thus determine the effective impedance of the primary
 > >looking into the secondary load. This information can also be used to
 > >determine the peak current in the primary and then compared to actual
 > >measurements with close agreement.
 >
 >
 > Based on the fact that the usual TC isn't a nice RLC, the relationship
 > between Q and VR isn't all that great anyway.  The standard formula
 > assumes an exponential decay, which would be the case if the losses
 > were resistive.  However, a big loss is the spark gap, which is hardly
 > a nice resistor.  I seem to recall someone coming up with some
 > measurements that showed a linear decay is more realistic.

Exactly right. The standard resistance-based equation for Q doesn't
apply to a circuit with a gas discharge path in it. I haven't yet
found a point where a linear decay in such a circuit becomes a log
decay with increasing series resistance either. I have found that the
normal log ringdown of an unloaded secondary dominates the shape of
the beat envelope if it is exceptionally lossy.

Malcolm

 > In any case, the VR is quite large on TC duty..
 >
 >
 >