EMP effects on mechanical watch movements -- Guy Macon

Discussion in 'General Electronics' started by Guy Macon, Jun 25, 2007.

  1. Guy Macon

    Guy Macon Guest

    Disclaimer: I designed an EMP simulator for the military, but this
    post is derived from publicly available information and does not
    contain any details of that design. I can say that this document:
    http://www.interferencetechnology.com/ArchivedArticles/lightning_and_transients/I96art07.htm
    pretty much matches what I know on the topic.

    Mark wrote:
    >
    >Guy Macon wrote:
    >
    >> The part that most people miss is that EMP is measured in volts
    >> per meter. a ten-meter-long conductor gets ten times the voltage
    >> as a one-meter-long conductor. A 1/10 meter one gets a tenth.
    >> This is really bad news for telephone systems and really good news
    >> for digital watches.

    >
    >Getting back again to my original inquiry, a mechanical watch has
    >some very thin and delicate parts in it, such as the hairspring.
    >
    >Let's assume a very thin wire 1mm in length, and the EMP pulse is
    >directed so that the full voltage is directed lengthways along the
    >wire.
    >
    >In the Wikipedia data I posted a link to in my prior message (the
    >data came from a Government study), I saw EMP of 50,000 V/m as being
    >possible on the ground from an exo-atmospheric detonation of a nuclear
    >warhead above the U.S. So for a 1mm long, very thin wire, we might see
    >as much as 50 volts applied across the wire for a brief moment. Could
    >this be enough to frapp that part?


    This is a very good question.

    The first step in answering it is to realize that the earth has already
    experienced many Nuclear EMPs, one of the largest being Starfish Prime
    in 1962; 1400 kilotons 400 km over Johnston Atoll, causing an artificial
    aurora borealis and effects in Hawaii. There were a lot of mechanical
    wristwatches and other precision mechanisms on the ship right below
    that EMP, and there were been no reports of failures. As an aside,
    many reports simply say "power outages in Hawaii." The actual effect
    was the simultaneous failure of 30 strings of series-connected
    streetlights in Oahu -- about 1% of Oahu's streetlights -- becauuse
    of blown fuses.

    Also in 1962, The USSR set off a 300 kiloton warhead 290 km over Dzhezkazgan.
    The EMP fused 570 km of overhead telephone line with a measured current of
    2,500 Amperes, started a fire at a Karaganda power plant, and shut down
    1,000-km of shallow-buried power cables. This is worse than the hawaii case
    because the lines were far longer, being on a continent and not an island.
    It didn't, however, destroy any mechanical wristwatches.

    The next step in answering this is to consider this quote:
    "this pulse is very roughly comparable to the electromagnetic
    fields radiated from a nearby lightning stroke"
    http://www.interferencetechnology.com/ArchivedArticles/lightning_and_transients/I96art07.htm?regid=
    Many people and lots of equipment have had near-misses from
    lightning strokes, and there have been no reports of mechanical
    damage to watches.

    Next, consider the logic of assuming that 50 volts on a watch part
    will cause damage but 50,000 volts of the person wearing it won't.
    (I have seen no claims that an EMP will electrocute everyone in
    it's range...) The reason for this is that a high voltage over
    a short duration has limited energy. This is true of EMP and of
    you touching a doorknob and getting a 50,000 volt shock.

    Also consider this from
    [ http://arxiv.org/ftp/physics/papers/0307/0307067.pdf ]

    "At least two kinds of EMP have been identified and studied extensively...
    One is an extremely fast pulse with a duration ~ 10-6 sec occurring at the
    beginning of a burst, which we call TEMP (tachy[fast]EMP). Since the TEMP
    was thought to have an electric field peak ~ 50 kV/m, ~ 10 to the 6 times
    greater than the much slower magnetohydrodynamic EMP (MHD EMP), it was
    expected that the TEMP would have a much bigger impact; and almost all the
    attention was focussed on TEMP. TEMP was anticipated to have devastating
    effects in electrically blacking out huge land masses; and much media
    coverage was given to this possibility. However, Rabinowitz showed that
    the impact of TEMP would be local rather than continental, and not be
    much greater than that of lightning. Later independent work by Millard,
    Meliopoulos, and Cokkinides reached similar conclusions. Consideration
    of the radiation reaction force and subtle relativistic effects indicate
    that 50 kV/m may not even be achievable for the preponderance of nuclear
    weapons that exist."

    So my conclusion is that EMP will not damage a mechanical watch movement
    if the wearer is far enough away to survive the nuclear blast.


    --
    G o o g l e F o o d : <http://www.guymacon.com> <http://www.guymacon.com/>
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    Guy Macon, Jun 25, 2007
    #1
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  2. Guy Macon

    neon

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    vultage can and will cream many evices including me quit w0rking with voltage on a wire and start thinking about current you maybe able to neasure 50kv but without the source behind is nill. exmple comb your hair with a plastic comb you end up with 5kv and get shocked kill somebody and they put 1000v to the chair and you cook. got the message?
     
    neon, Jul 24, 2007
    #2
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