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EMC - what to focus on?

  1. Aug 6, 2008 #1

    First i should apologies if this should have been posted in the homework sections but the three points that are automatically added to the post before writting doesn't really fit my question, so i decided to post it here.

    Then a little info about the situation might be in order.

    I'm a design engineering student and started on an internship 4 days ago at a company that makes laboratory equipment for protein identification. I've been given the assignment of designing a new cabinet/casing for one of their apparatus and have to take EMC into account.

    I cannot change the design/layout of any of the internal components, electrical or mechanical, i am only allowed to reposition them and so.

    From what i've read so far on EMC there are 3 main areas if you want to reduce EM radiation:
    *Coupling path

    Since i'm not allowed to change the design of the internal components, i'm thinking that i only have to focus on the coupling path and the only way to reduce the coupling path in this case is to use shielding, is this correct or are there other ways?
  2. jcsd
  3. Aug 6, 2008 #2
    What do you mean by EMC? There are a number of ways to deal electromagnetic radiation. Shielding is probably the cheapest, and the easiest to implement. By shielding I mean a faraday cage that encompasses the case. Another way of dealing with EM radiation is an active field cancelling system. What is the nature of your design? Is it to keep electromagnetic interference out of your box, or is it to keep your box from interfering with other processes outside of your box?
  4. Aug 6, 2008 #3
    I can say for sure that the main thing is to prevent the apparatus from interfering with other processes outside the box and that it should meet the regulations for household products. The current cabinet just barely passed the test for industrial products and although it's purely business to business they would like it to be legal for household products.

    I'm not sure about outside systems interfering with the apparatus but they haven't mentioned anything regarding that.
  5. Aug 6, 2008 #4


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    Staff: Mentor

    Sounds like you have some equipment that barely passes level "A" (for industrial environments), and you want to redesign the enclosure to pass level "B" (for home environments).

    So yes, you need to look at the shielding and gasketing of the new enclosure, and you will want to do some filtering on any cables or lines that go in and out of the enclosure. A classic book on the subject is "Noise Reduction Techniques in Electronic Systems" by Henry Ott. See if you can find a copy at your local technical library or bookstore, or just snag a copy off of Amazon.com.

    I googled EMC Shielding Gasketing, and got lots of useful hits. Here is the hit list:


    The gasketing is important, because your box will have to go together somehow, and the seams where it goes together need EMC gasketing in order to preserve the Faraday cage nature of the box. Otherwise, the seams with no good electrical continuity will serve as slot antennas, and your box will not serve as an effective shield.

    The filtering on the cables that go in and out of the box can be as simple as ferrite clamps, or as complex as T-filters explicitly connected to each signal line. What you use depends on the type of signal, its power level, and whether it can tolerate lowpass filtering to remove RF energy above 30MHz (where the radiated EMI scans typically start).

    I googled Ferrite EMC -- here's the hit list:

  6. Aug 7, 2008 #5
    Thank you very much berkeman that was a great reply it seems to have all the words/concepts i need to be aware of and even a book, thanks again!
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