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Re: FLASHBACKS! not the groovy 60's!

Posted By: SVP Neon Equipment
Date: Friday, 31 October 2008, at 12:05 p.m.

In Response To: Re: FLASHBACKS! not the groovy 60's! (John Anderson)


Yes, there are differing views and opinions. But automated semiconductor manufacturing is hardly comparing apples to apples. In one situation the operator is very well isolated from the voltage during the process. In the other situation the operator is in *direct contact* with the process apparatus that the voltage may go through.

To each their own. But as you stated, people make mistakes and accidents do happen, usually at the most inopportune time. For me, in the latter situation above, I would much rather have a known excellent electrical insulator such as glass between me and a HV discharge than a known excellent electrical conductor such as metal.

Mark

> I realize there are differing views on metal
> vs. non-metal, grounding vs. ungrounded,
> etc. Here is my view:

> Every neon pumping system has conductive
> material in it at some point. To my
> knowledge, no-one has made an all-glass,
> non-conductive mechanical pump, or even a
> belt that doesn't become conductive once it
> absorbs crud and oil. If your pump plugs
> into the AC outlet, it's got substantial
> potential to ground, even if you leave off
> that "green" wire, and mount the
> belt-driven pump on insulators. Neutrals
> (white) almost always go back to the
> electrical panel ground in residential
> systems. In short, you cannot build a
> completely isolated system. If you have a
> direct drive pump, then you basically have a
> system ground - and you as the manifold
> operator are right in the middle where a
> flashback must pass through. Maybe you'll be
> lucky and remain isolated enough to avoid a
> discharge - but in my opinion you're taking
> a risk.

> Most neon manifolds are a hybrid of
> conductive and non-conductive materials.
> Glass manifolds, metal vacuum gauge heads,
> Robbin's metal filling valves, cylinders,
> turbo pumps, etc. At some point EVERY neon
> pumping system has conductive material a
> flashback can seek. If your bombarder is
> running off AC power from the line, you
> can't eliminate all potential to ground...
> even with a completely floating secondary.
> True, an HV discharge may bounce around to
> many points. But it's looking for a place to
> discharge its mother load. Take steps to
> ensure it's not you. As a human body
> contains mostly salty water, you can
> inadvertently become this path yourself
> unless you're suspended in air off the
> floor. And even then, there is substantial
> capacitive coupling to ground I would never
> take a chance on.

> Yes, an ungrounded metal manifold would be
> VERY dangerous. So would ungrounded metal
> filling valves. Should the bomber button
> accidentally engage, you could be toast! No
> conductive parts a human is likely to touch
> during bombarding should be ungrounded.
> Further, a well-grounded electrode placed
> between the manifold and the tube being
> pumped provides a path to ground should a
> flashback occur. Does it encourage
> flashbacks? That's not been my experience,
> except on pole-pigs wired as mid-point
> grounded units (a poor choice for neon use).
> Unless you can isolate every conductive
> object (including yourself) from potential
> to ground, you cannot guarantee YOU won't be
> the ground-return. Everyone makes mistakes -
> a simple mishap of touching a conductive
> part of your manifold while bombing
> shouldn't put you in a life-threatening
> position.

> Many neon pumping systems around the worlds
> operate safely with conductive metal
> components - even with all-metal valves
> (just to be clear, I'm a big fan of glass
> manifolds). At some point (of course) you
> have to make the transition to glass. Where
> this occurs should dictate your plan for
> safety grounding. Semiconductor
> manufacturers safely use high-current,
> high-frequency, high-voltage discharges all
> the time with metal systems during processes
> like vacuum deposition, and many others.
> How? They ground the metal systems well, and
> provide a conductive path before it passes
> by components humans touch.


SVP Neon Equipment

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