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Re: Concerned
I would try a small test using an AM radio as a detector first. It sort of
depends on what frequencies you are looking to shield and what your real
requirements are. Personally, I don't think most TC's put out enough RF
power to worry about at 5 meters away. The grounded chicken wire would
have a beneficial effect for safety though (it would make it hard to touch
the HV components), and it MIGHT help the EMI problem.
The problem with shielding is that it is hard to predict what happens.
There are models, but to do it with enough fidelity, it takes immense time
to define the configuration, and then an immenser time running on a
supercomputer to run the simulation. Alternately, you rely on experience
with similar systems and rules of thumb to get in the ballpark, then build
a prototype and test it. When the prototype bombs out, you get out the
copper foil, EMI gasket material, and start playing until it works.
For most applications and budgets, shielding is truly an art, not a
science.
So.. Go out and get that roll of chicken wire, get some 2x3 and knock
together a big framework in the driveway, string the chicken wire, and run
a test.
Let us all know what happens.
----------
> From: Tesla List <tesla-at-pupman-dot-com>
> To: tesla-at-pupman-dot-com
> Subject: Concerned
> Date: Tuesday, February 15, 2000 7:20 PM
>
> Original Poster: "Ted Rosenberg" <TRosen1-at-Tandy-dot-com>
>
> Jim: Now I am really concerned.
> My 6x24 coil is destined to be used in a Frankenstein lab setting in a
> Haunted House this October. I had planned to line the entire room with
> grounded chicken wire. There will be a good iron pipe ground looking for
the
> sparks a lot closer. But the chicken wire was going to prevent RFI to
most
> electronic devices possessed by patrons walking by...perhaps 15 feet from
> the display.
>
> Are you now suggesting this is a waste of time/effort?
>
> Ted
>
> -----Original Message-----
> From: Tesla List [mailto:tesla-at-pupman-dot-com]
> Sent: Monday, February 14, 2000 9:35 PM
> To: tesla-at-pupman-dot-com
> Subject: Re: Pacmakers and Tesla coils = bad??
>
>
> Original Poster: "Jim Lux" <jimlux-at-jpl.nasa.gov>
>
> However, building a GOOD Faraday cage is non trivial. Any wire that
> penetrates the surface (including the twists in the chicken wire) can
> provide a pathway for RF energy. The single best thing you can do is
> provide a good conductive counterpoise/ground underneath the coil so that
> the current induced by the RF field has somewhere "safe" to go (i.e. back
> into the other end of the coil).
>
>
> -----Original Message-----
> From: Tesla List <tesla-at-pupman-dot-com>
> To: tesla-at-pupman-dot-com <tesla-at-pupman-dot-com>
> Date: Monday, February 14, 2000 4:32 PM
> Subject: Re: Pacmakers and Tesla coils = bad??
>
>
> >Original Poster: rdgraaf-at-ocenl.nl
> >
> >There is a very simple solution: it's called a cage of Faraday...
> >Chicken wire will do the trick. Naturally this will cost some
> >performance, but hey what is more important? btw, will also protect
> >your own and your neighbours Hifi, TV, Computer, etc.!
> >
> >Ruud de Graaf
> >Holland
> >
> >
> >Date forwarded: Sun, 13 Feb 2000 20:14:02 -0700
> >Date sent: Sun, 13 Feb 2000 20:14:43 -0700
> >To: tesla-at-pupman-dot-com
> >Subject: Re: Pacmakers and Tesla coils = bad??
> >Forwarded by: tesla-at-pupman-dot-com
> >From: Tesla List <tesla-at-pupman-dot-com>
> >
> >> Original Poster: Terry Fritz <twftesla-at-uswest-dot-net>
> >>
> >> Hi Stan,
> >>
> >> WOW!!! When I was reading about pacemakers, it was implied that they
> >> could be accidently triggered by a number of things. I was not really
> >> "sure" a TC could do it but the things they described seemed like it
> would
> >> be very possible. However, this is proof that a 15/60 coil can
trigger
> the
> >> defibrillator types at 25 feet. The people that have these are warned
by
> >> their doctors what the jolt they give is like so they will be somewhat
> >> prepared. This is especially important if they are driving or
something
> >> (Mark mentioned that they would normally be unconscious, but perhaps
that
> >> can be programmed). Pacemakers can also be stunned into safe and
default
> >> modes if their logic detects something is wrong. This may go
unnoticed
> but
> >> they may not be able to operate as needed in such a fail safe state.
The
> >> equipment that "talks" to these pacemakers may be able to detect and
> count
> >> the number of times they are affected.
> >>
> >> There apparently are no official levels or standards of EM
interference
> >> for these things. Different brands appear to be affected more or
less.
> >> They are somewhat "hardened" against normal EMI but a Tesla coil is
> >> obviously quite abnormal in most EMI respects. CERN calls out 0.5mT
but
> I
> >> am not sure that is well based.
> >>
> >> http://www.cern.ch/CERN/SafetyGuide/Part3/42.Magnetic.html#warning
> >>
> >> It would be nice if we could come up with a "safe" distance or some
> >> maximum EM level but there appears to be no such data that would apply
to
> >> all manufacturers of pacemakers. It looks like the only thing we can
go
> by
> >> now is "Keep pacemakers FAR away from any TC!"
> >>
> >> Many thank for this very important post on this subject!
> >>
> >> Cheers,
> >>
> >> Terry
> >>
> >>
> >>
> >> At 09:15 PM 02/13/2000 -0500, you wrote:
> >> >I witnessed first-hand what a TC can do to a modern pacemaker. A
fellow
> >> >was about 20-25ft from a running 15/60 coil. It ran for maybe 30
> >> >seconds then suddenly he shook violently and dropped down on to his
> >> >knees. Apparently, the gap misfired or whatever and for a second the
> >> >frequency of the output was abnormal and triggered his pacemaker. If
I
> >> >remember right his delivered 5J. Whatever it delivered, it scared
the
> >> >holy heck out of me and was very painful for him. Fortunately, the
> >> >shock had no ill effects on his rhythm.
> >> >
> >> >Obviously this situation could have been disastrous. The TC could
have
> >> >triggered his pacemaker and sent his heart into an irregular beat, or
> >> >perhaps worse could have quietly destroyed his pacemaker and would
have
> >> >never been noticed until it failed to shock when it was really
needed.
> >> >
> >> >IMHO it's just not worth it. Keep pacemakers FAR away for any TC!
> >> >
> >> >-Stan
> >> >
> >> >Tesla List wrote:
> >> >>
> >> >> Original Poster: Terry Fritz <twftesla-at-uswest-dot-net>
> >> >>
> >> >> Hi Mark,
> >> >>
> >> >> I just want to thank you for adding this sort of expert addition to
> all
> >> >> this. I got onto this pacemaker thing by accident, but the stuff I
> saw
> >> >> really worried me!!
> >> >>
> >> >> Having a pacemaker zap someone would be sort of unpleasant.
However,
> >> >> having it do ANYTHING it is not supposed to be doing is a real
> concern.
> >> >> Tesla coils would be almost a worst case situation to find these
ultra
> >high
> >> >> tech gizmos dealing with.
> >> >>
> >> >> When they were just simply bipolar devices they were probably
pretty
> >immune
> >> >> to a lot of things. However, the are now really sophisticated and
> they
> >> >> could do a lot of harm if they were to get "confused". I think we
> need to
> >> >> be extra careful of these things now!
> >> >>
> >> >> Cheers,
> >> >>
> >> >> Terry
> >> >>
> >> >
> >>
> >
> >
> >
> >
>