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RE: Interesting Skin Depth Data

Hi Alex, Boris, Terry and All,

My statement was in general and aimed at the calculations of 
skin affect after an arc has formed, 
and not so much at the medical or human aspects.

The human flesh, muscle, nerve, vessel aspect is very complicated.
but then
I read many posts relating resonator frequency to feeling sensation of arc
with no mention of the vastly higher discharge arc frequency 
that may be the controlling mechanism for skin affect at the spark
discharge end.

I don't advocate drawing arcs to body parts though I've done my share.

What I've observed/felt:
Using a metal interface to the arc/corona from my hand:
As I approach from the greatest distance 
I experience the most severe "felt" arc affect,
i.e. I'm just getting close enough to draw corona.

Peak currents in the arc from my oscilloscope measurements 
are up to 22Apk for 2.5J increasing with increasing energy.

Peak currents IMHO are responsible for the uncomfortable muscle jerking
"feeling".

Additionally without a metal interface, 
High peak current causes high instantaneous
local heating at the point of arc contact with the flesh due to 
high epidermal contact resistance (I^2R) 
(and lots of voltage to overcome 'R' and dissipate peak power in it)

The nerves may be able to react to this due to, 
I believe, the thermal time constant affect, 
allowing nerves extended time to sense the event 
and/or with the peak current via muscular/vessel/nerve tissue 
if the rate of current rise is slow enough. 
(too fast and not enough time to react thus no feeling)

As I get closer to the Resonator (shorter arcs) 
the feeling becomes less severe until
at the resonator I feel little or nothing 
(usually nothing) due to the good contact (lower resistance)
while my body is conducting all the same peak current. 

Greater rep rates result in the body 
absorbing higher and higher average power,
and who wants to be a Dummy Load 
for a high voltage AC power supply ?
(gives new meaning to "dummy loads")

>TF: If you know the terminal capacitance, you can figure out the current
in the
>discharge spike.  However, it is probably a damped high frequency (maybe
>GHz) pulse so it gets messy.

You'd need to know the charge before and after the spike 
or how much is kept in the resonating system and 
how much was lost in the spike but peak currents/energies 
are much less in non-connected discharges (i.e. corona)
Only ground spikes dissipate all of it !

>TF: DC currents of a few amps flowing through the body are obviously in
the far
>lethal area. 

The fatality current figures are average or DC current.
I have never seen reference to maximum peak current for 500 nanoseconds.

Fast pulses may be attenuated, progressing more deeply into the body.

Warning, Don't risk contacting one of the slower fatality risk pulses !

I believe the rise/falltime and pulse width figure prominent. 
With fast and short pulses, human tissues appear to take more peak current
without the protection mechanisms complaining (no pain felt).

That is NOT to say there is no damage being done.

It would be nice to determine where irreversible damage begins (and degree)
as a function of rise/falltime, pulse width, peak current.....

Boris ???? aren't you working to establish this very thing ?

Alex: re:50/60HZ, I trust Brian's coil is/was well isolated from the power
mains.
Otherwise drawing arcs to the body can be dangerous due to the 
low resistance of the arc functioning as an efficient wire to conduct 
60 HZ currents but pulsed (better than not pulsed !)
at 120 Hz or higher if multiple half cycle gap conduction occurs.
60 HZ = 16.67mS = 16,667 uS = 16,667,000 nanosecond period 
Read above for my thoughts on contact resistance pain.

Regards, Dale
anxious to put to use those PP caps rcvd from TF. but am
Industry sponsor, FIRST robotics, Team #294
(neglecting TC'in)
(all my time last 2 mos helping design/build a robot for national competition)

-----Original Message-----
From: Tesla List [mailto:tesla-at-pupman-dot-com]
Sent: Saturday, March 11, 2000 9:58 AM
To: tesla-at-pupman-dot-com
Subject: Re: Interesting Skin Depth Data

Original Poster: "Alex Crow" <user-at-alexcrow.clara-dot-net> 

Dale,

If the arc event is of such high frequency, what is it that causes the pain
from
a power arc taken to the body, even via a small metal object? I was pulling
arcs
off Brian Basura's mini-twin with a car-key, and if you got too close and the
arc became brighter, there was a noticeable prickling and muscular
sensation. Is
this due to sharp pulses of one polarity from Ctop? The arc frequency might
become isolated from the ground as regards the Xl of the secondary, but the
conduction path is of low enough resistance to provide paths from all
transients
(and of course, as we know, potentially lethal 50Hz).

Alex

Tesla List wrote:

> Original Poster: "Dale Hall" <Dale.Hall-at-trw-dot-com>
> Hi all,
> The theory of using the resonator frequency may be perhaps
> flawed when doing skin affect analysis.
>
> Based upon my oscilloscope observations the
> frequency of an arc event is in the MHz range.
>
> The entire arc event is over in less that a microsecond (1MHz)
> The arc risetimes I've measured are in the order of
> ~25nS to ~100nS (~20MHz-5MHz) and some even higher freq.
>
> The resonator serves to provide charge to the Csec.
>
> The discharge of Csec generates the arc freq quite independent
> of the resonator ring up freq, for any one arc event.
>
> At 10-20 MHz arc oscillation, the ~30 MHy of the secondary
> represents good XL isolation from the arc (like a series choke).
>
> At 10-20Mhz the skin affect may well be more of a factor in the human case.