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ElectroMagnetic Field

  1. Jun 15, 2008 #1
    Hi all,

    I am designing vending machine to be used outdoors in a train station.
    I am a mechanical engineer and i don't know much about electromagnetic fields.
    The fact is based on what I have read, in train stations in which the train is working with electric power, the power lines are high voltage and low frequency. and high voltage (probably generating high current) with low frequency will make a powerful electromagnetic field.

    1. is it true?
    2. if it is true, what effect does this powerful electromagnetic have? (i've read that one of the effects is that it affects or damages electrical boards and components inside other machines, but i also don't know whether its true or not)
    3. if it affects electrical components in my machine, how can i prevent it? should i use a specific material like stainless steel over mild steel or other materials? if so, does the thickness of the body matter?

    thank you all in advance,
  2. jcsd
  3. Jun 15, 2008 #2


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    You are asking about designing for EMP protection.
    You can probably find some information by searching on that topic.

    High voltage is used to keep the currents low.
    With straight wires and relatively low currents the magnetic fields are not likely to be that strong.
    Chances are that the random child with a permanent magnet toy will be more of a problem.
    However, I don't know the exact answer to this question.
  4. Jun 15, 2008 #3
    Dear Notime,

    Thanks for your reply, but i don get some parts of your answer:

    ""High voltage is used to keep the currents low."" ??? it will highly depend on the load i believe, isn't it?

    and Also Im not sure why but the electromagnetic filed is really considerable in train stations with electric power as the main source.

    EMP should be Electromagnetic pulse, right? is it the same as electromagnetic field? or is it a part of it? or??? im not familiar with this area at all.
  5. Jun 15, 2008 #4


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    Well P=EI.
    Since the load is concerned with power then increasing voltage decreases current required for the same power.
    Current in a conductor detemines the magnetic field.

    I am sure magnetic fields are measurable in a train station.
    Perhaps more so from the train motors.
    But unlike the child's toy magnet I have never seen metal objects move around because a train started up. So the child hitting your machine with their toy will probably induce greater current that the train will.

    If you have very sensitive circuits then either train or magnet could be a problem.
    EMP is, as you say, Electromagnetic pulse.
    This study area considers the effects of currents induced in your equipment by magnetic fields.
  6. Jun 16, 2008 #5
    If you wish to protect your circuits, you can simply enclose it in an electrically conductive material. This is the principle behind the Faraday cage.


    What specifically is your concern though? That EM fields will interfere with the electronic circuits in the vending machines? That the vending machines will experience a force from the high-voltage lines?
  7. Jun 16, 2008 #6


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    There are a number of immunity standards and tests that apply to various product families. Immunity to ESD (electrostatic discharge), immunity to powerline Surges, immunity to radiated EMI (electromagnetic radiation coming into your product, like from nearby radio sources), and immunity to conducted EMI (noise comes into your product over the powerline). To sell a product in Europe, for example, you must demonstrate at least the basic levels of immunity to these disturbances, in order to get a "CE" mark to sell your product:


    Other countries have similar regulations, although Europe is probably the most advanced in these requirements.

    Do some reading about the various EN 61000-4-x tests for immunity to interference, and then try to find a local test lab that does this kind of testing. They will be happy to answer your questions, and point you to hardware design resources that will help you design your machine to be robust in the real world.
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