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Using a computer to detect EMI?

  1. Aug 14, 2015 #1
    Hi all,

    I was wondering if a computer could be use to monitor the EMI on a house power line ? I have read a few papers on the subject, all of which proposing all sorts of devices, but I was wondering if it could be done directly by prompting a computer to monitor the electric flow through itself ?

    I don't know much about the subject but I'd like some tips on where to start looking.

    Thanks
     
  2. jcsd
  3. Aug 14, 2015 #2

    anorlunda

    Staff: Mentor

    EMI refers to radio waves in the air, not the current flowing through a device. Detecting it needs some kind of radio receiver.
     
  4. Aug 14, 2015 #3
    Thanks for the reply.

    The paper's abstract I got the information from seems to refer to noise measurable along electrical wiring:

    "In this paper, we describe LightWave, a sensing approach
    that turns ordinary compact fluorescent light (CFL) bulbs
    into sensors of human proximity. Unmodified CFL bulbs
    are shown to be sensitive proximity transducers when they
    are illuminated. This approach utilizes predictable
    variations in electromagnetic noise resulting from the
    change in impedance due to the proximity of a human body
    to the bulb. The electromagnetic noise can be sensed from
    any point along a home’s electrical wiring. This allows
    users to perform gestures near any CFL lighting fixture,
    even when multiple lamps are operational. Gestures can be
    sensed using a single interface device plugged into any
    electrical outlet. We experimentally show that we can
    reliably detect hover gestures (waving a hand close to a
    lamp), touches on lampshades, and touches on the glass part
    of the bulb itself. Additionally, we show that touches
    anywhere along the body of a metal lamp can be detected.
    These basic detectable signals can then be combined to
    form complex gesture sequences for a variety of
    applications. We also show that CFLs can function as more
    general-purpose sensors for distributed human motion
    detection and ambient temperature sensing."

    I'm a bit confused.
     
  5. Aug 14, 2015 #4

    anorlunda

    Staff: Mentor

    EMI stands for electromagnetic interference; such as if your computer intefered with cell phone reception.

    If it is proximity sensors that interest you, I suggest starting a new thread with a more appropriate title.
     
  6. Aug 14, 2015 #5

    tech99

    User Avatar
    Gold Member

    EMI means electro magnetic interference, and can be either "radiated" or "conducted". For the present application, I would guess that a radio receiver is coupled to the house wiring to monitor the noise characteristics from the CFL. To use a computer, it may be possible to couple to the wiring using a toroidal ferrite transformer, either on one wire or both, or to use a small coupling capacitor in conjunction with protective circuitry. A computer can be used as a radio receiver for low frequencies directly by using the sound card with spectrum analyser software, or by using a dongle to allow operation right up to microwaves. Bear in mind that if you use the power lead to the computer, it is likely to be very noisy due to the EMI from the computer itself. In fact, the domestic environment anywhere is now very polluted with EMI. Bear in mind that CFLs are being replaced by LEDs.
    .
     
  7. Aug 15, 2015 #6

    meBigGuy

    User Avatar
    Gold Member

    I agree that there is "radiated" and "conducted" EMI.

    There is nothing in a standard PC-like computer that will monitor, measure, or otherwise quantify powerline EMI. You need a conducted-EMI sensor of some sort connected to the computer in some way. You've researched that, I think, so I won't.
     
  8. Aug 17, 2015 #7
    Thank you for your comments. I was hoping I could use some of the computer's components to monitor conducted EMI but I think I will have to build the following:

     
  9. Aug 18, 2015 #8
    We do test our products to regulatory limits for both radiated and conducted emissions. The FCC's intent in both cases is to limit harmful interference with radio services (EMI). At the low frequencies of conducted emissions testing, the EUT itself is seldom large enough to contain a suitable antenna (low frequencies require long antennas). Instead, the conducted test ensures that the EUT does not launch signals onto power lines which can be harmful radiating antennas at low frequencies due to their length.

    The low end, 450KHz, is intended to protect the AM radio intermediate frequency of 455KHz. Historically, radiation at that frequency would bleed through old AM radios since only the antenna tuner had any rejection at that freq.

    In other words this is a shameful nit-pick on language: EMI is always radiated, but one of the tests for it involves measuring RF conducted onto power lines.
     
    Last edited: Aug 18, 2015
  10. Aug 18, 2015 #9

    sophiecentaur

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    Science Advisor
    Gold Member

    So do we ignore the interference that creeps its way into equipment down feed lines? I don't think that vulnerable equipment is able to distinguish between the two types (they are both Electromagnetic). 'Guided' interference may be a bit harder to detect and specify but it can be just as relevant. (It's the last one that people can manage to eliminate when it really matters.)
     
  11. Aug 19, 2015 #10
    You are right, we would absolutely care if noise creeps between pieces of equipment via feed lines and causes problems. We would not want to design such equipment or purchase it as a consumer. However, regulatory EMI testing does not address this.

    For example, a commercial stereo or TV may have many cables/wire connected up to it: RCA cables, USB cables, headphone cables, speaker wires etc. Conducted emissions testing is required on the AC mains cables and telecom cables (such as DSL), but not on the other cables. In other words, if a poorly designed CD player produces 540KHz noise on its audio-out RCA jack, and this interferes with AM reception within the attached stereo due to conducted coupling across the RCA cable, you would not be in violation of any regulatory requirements. This would be a product quality issue that the FCC would not care about any more than a poor quality RCA plug that broke apart after a few uses and prevented the system from working at all.

    The FCC is concerned with managing the electromagnetic spectrum. 540KHz on a 1 meter audio cable will not radiate, but launch it on a 5Km long overhead power line and now they care.
     
    Last edited: Aug 19, 2015
  12. Aug 19, 2015 #11

    sophiecentaur

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    Science Advisor
    Gold Member

    OK. I get it now. An Admin Anomaly. Lots of those in life. :smile:
     
  13. Aug 19, 2015 #12

    anorlunda

    Staff: Mentor

    If you make the definition of EMI too broad it becomes meaningless.

    As a power engineer, the worst types of interference I saw were:

    1. Electric arc funaces used to melt scrap metal. Interference was in the 60-360 Hertz range. One of them in Mexico caused compensating capacitor banks and transformers on the nearby grid to explode repeatedly and spectacularly.
      electric-arc-furnace-250x250.jpg
    2. An open pit mine drag bucket mining machine in Australia. That bucket's load was 40% of the total capacity of the local power grid. It cycled about once every180 seconds, i.e. 0.005 Hertz. It interfered violently with the water levels in the boiler drums in the power plant.http://www.touring-ohio.com/southeast/art/big-muskie.jpg [Broken]
    But in the normal use of the word EMI, neither of these qualifies. They are not RF frequencies.
     
    Last edited by a moderator: May 7, 2017
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