Discharging CRT anode and capacitors on a VT52 DECscope

From: Dwight K. Elvey <dwight.elvey_at_amd.com>
Date: Thu May 27 17:53:37 2004

>From: "Tom Jennings" <tomj_at_wps.com>
>> On Wed, May 26, 2004 at 11:27:51PM +0000, jpero_at_sympatico.ca wrote:
>> > At science museum once saw a very tickish student girl walk off lexan
>> > platform by the big sphere HV generator depsite tech's warnings as
>> > she stepped off a looong 2 feet long arc... That 2 feet long HV arc must
be really packing
>> > of power.
>Merely in the interests of spawning another near-infinite regress on
>electron fundamentals...
>NO, it specifically had VERY LITTLE POWER, though a lotta voltage.
> P = E * I
>E= voltage, I= Current
>Probably as much POWER as a nine-volt battery or two. If it had much
>more, it would have been an unsafe display, as it's S.K.O.P. (*) to
>either not see, or ignore, or spite, safety warnings, and kid science
>museums certainly know that!

 There is quite enough energy in a normal 9 volt battery to
kill a person. It might need a little conversion but
the total amount of energy stored there is quite large.
I would suspect that there is several times less energy in
the large arc as in a 9 volt battery.
 The fact is, it is the current that kills. The voltage is
only needed to induce the current. Once one has enough current
across the heart, it makes little difference what the voltage
source was, so long as the current is sustained long enough
to do damage. Sure, you might also say that it is the total
energy that the heart takes in a given period of time. Still,
the voltage is relatively constant across the heart for any
given current.
 One might say there are two stages. One where the current
holds the heart long enough to kill and the other where
the total energy/time is large enough to damage tissue.
Still, dead is dead.
 As far as discharging CRT, the charge can come back after
some time. There are surface charges in the glass that
will tend to rebuild the charge after a simple discharge. Don't
trust a CRT unless a clip is connected from the second anode
to the conductive layer on the back. It ain't gonna kill you
from the shock but you might find a lot of glass where you
don't want it.
Received on Thu May 27 2004 - 17:53:37 BST

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