Re: [TCML] D'Arsanoval arc (discharge)

[David Dean <deano@xxxxxxxxxxxxxxxx>]

On Tuesday 19 May 2009 01:37:28 pm Dex Dexter wrote:
> Hi everybody,
>
> What kind of a high frequency arc it is?
> Is there some exact definition of it?
> I know it has something to do with tesla transformers,but I couldn't find
> useful info on it. Your help / explanation I'll appreciate.
> Thanks.
>
> Dex

Hi

In the latter part of the 19th century, and on into the early part of the 20th, 
there were some doctors and scientists who were looking into the medicinal 
effects of electric currents on the human body. Among the notable in this field 
were two french doctors, Jacques-Arsène d'Arsonval
 (http://en.wikipedia.org/wiki/Jacques-Arsène_d'Arsonval) and Paul Marie Oudin
(http://en.wikipedia.org/wiki/Paul_Oudin).

d'Arsonval and Tesla independently and simultaneously discovered that an 
alternating current having a frequency of 10kHz or more  produces no muscular 
contractions and does not affect the sensory nerves. This is called d'Arsonval 
current, also called Tesla current.

Though d'Arsonval's experiments ran the gamut from Galvanic currents (DC) to 
very high voltage very low current (as in Oudin coil), he is probably best 
known in the field of  electrophysiology for his work with moderate voltages 
and relatively high currents. He is credited with inventing apparatus used for 
diathermy and "bloodless surgery".

The term "d'Arsonval discharge" may be found in some old medical texts from 
around the 1920's era. This would be referring to the discharge from 
a "d'Arsonval apparatus", which is schematically the same as an Oudin coil, 
however the autotransformer would have a much lower turns ratio and be of 
heavier wire. I remember seeing a drawing and diagram of a "d'Arsonval 
apparatus" which was a flat spiral coil hanging from the wall.

A Tesla coil primary with "too many" turns can produce a d'Arsonval discharge 
from the outer turns of the primary to the strike rail or some other grounded 
object. I once had a Tesla coil with a primary that had 15 turns and tuned 
between 7 and 8. When I first hooked this coil up to my current SRSG, the gap 
was under the coil and the electrodes were made from a poor choice of brass 
alloy, one containing relatively high levels of zinc, and perhaps some lead, as 
it was a bearing alloy. When first firing up the coil using that gap, there 
were some weird "sheeting" like discharges between the outer turn of the 
primary and the spark gap. Once the gap had enough run time on it to "burn out" 
the excess zinc, lead, whatever metallic ions were being released, this 
phenomena subsided.

later
deano
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