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EMF Detector made easy?

Discussion in 'Electronic Basics' started by Bryan, Mar 17, 2005.

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  1. Bryan

    Bryan Guest

    Hello one and all.

    I have been looking into building a "very" sensitive EMF detector due to
    issues with power lines in the area. I am sorry to say that I have no REAL
    idea on how to do it.
    I was also told that there is a way to build a device that would use Hall
    effect sensors to measure the earths magnetic field. It would be much more
    sensitive and would work if adjustable. I have yet to find a circuit design
    that will give a visual as well as audible measurement. An LED bar graph
    would be ok.
    Any good ideas on what I could build that would do this?

    Thanks for your help.

    Bryan
     
  2. Greetings, one.
    Then perhaps you have no real idea of the
    potential hazard, and rely on the morass
    of conflicting, often misconceived studies
    as the basis for deciding there is an issue.
    If I wanted to do that, I would probably use a
    simple coil pickup, followed by a high gain semi-
    narrowband 60 Hz filter in front of a PIC's or uP's
    A/D input, then implement a much narrower filter
    using DSP to pull what is likely to a small signal
    out of the noise.

    It would be easy to create any display you like
    using software and one pin per LED or even
    multiplex LEDs to drive more of them. For,
    example, at 1 nanoTesla, the red light could
    blink gently. At 1 microTesla, the bar would
    be fully on and blinking omenously. At higher
    levels, you could spell out "Run for you life!",
    You are welcome.
     
  3. Rich Grise

    Rich Grise Guest

    I'd say that if they're too low to detect except with specialized ultra-
    high sensitivity equipment, you're blowing smoke up your own ass.

    Cheers!
    Rich
     
  4. [System approach using uP cut.]
    Just to help promote this approach ahead of
    the other (as yet unseen) contenders ...

    With a little extra complexity in the coil and a
    few switches, it could also provide an arrow to
    indicate which direction the irradiated user ought
    to run. Otherwise, given the usual arrangements
    in the vicinity of power lines, he might run without
    gaining any *real* benefit from the effort.
     
  5. Bryan

    Bryan Guest

    Gosh Rich, thanks for the insight!
    What a pal!
     
  6. Robert Scott

    Robert Scott Guest

    Google "Fluxgate magnetic"


    -Robert Scott
    Ypsilanti, Michigan
     
  7. It's not difficult to build, you an use a ferrite loopstick with a lot
    of fine wire wound on it as the sensing probe. One of these is here.
    http://www.zen22142.zen.co.uk/Circuits/Misc/emf.htm

    Here's a meter using Hall effect sensors.
    http://my.execpc.com/~rhoadley/magmeter.htm
    http://my.execpc.com/~rhoadley/magmetr1.htm

    The big difficulty is calibrating it to a known standard. And they are
    not that expensive so there is no point in building one yourself.
    There are several companies that offer a calibrated EMF measurement
    meter for under a hundred dollars. Here's one with LEDs for under $25.
    Also the cellsensor mentioned below. http://www.lessemf.com/gauss.html
    Here's their main page
    http://www.lessemf.com/

    Two other inexpensive meters mentioned in a paragraph from a story found
    with google:
    "I brought an am radio to the office and it would be very noisy in that
    office but not in the other rooms and really bad near the wall and
    ceiling. I then went out and bought an emf meter (cellsensor, analog
    meter, single axis, $42.00) and measured very high readings only in that
    office and the hallway. It would blink and beep like crazy even on the
    high setting. I did much research and talked to other engineer friends
    who tell me it is unconceivable to have that much emf. So I bought a
    digital emf meter (A.W. Sperry EMF-200A, single axis, $60.00) and proved
    it. I was getting over 199 mg at the wall about 2" from the conduit
    behind sheetrock. It went off the scale about an inch from the wall."
     
  8. Luhan Monat

    Luhan Monat Guest

    Try Google: +"smoke detector" +anal
     
  9. Mark

    Mark Guest

    to start, think about this

    do you want to measure the ELECTRIC field at 60 Hz?

    or

    do you want to measure the MAGNETIC field at 60 Hz?

    that is two completly different measurments.

    Measuring an electomagnetic field implies you are in the far field
    meaning you are many wavelengths away from the source which at 60 Hz is
    several miles.

    Mark
     
  10. Bryan

    Bryan Guest

    I think I know how I am going to work this now.
    Thanks to everyone for their help. Well, almost everyone. For Rich I guess
    just a peice of advice.... Rich we all know that liquids conduct
    electricity. So, be carfulful next time you are around power supplies, and
    don't forget to wipe your chin! He will understand if he really cares.

    Cheers!
     
  11. Rich Grise

    Rich Grise Guest

    Well, an aluminum foil hat would be the cheapest solution.

    What "issues" do you have with power lines in the area? How sensitive
    does this detector have to be? I still say, if you can't detect something
    it's probably not worth worrying about very much.

    Thanks,
    Rich
     
  12. Absolutely. The OP clearly understands so little about the subject that
    advice on making a detector is futile.
    For 55 Hz, the distance is approximately 1000 km.
     
  13. A Proton Magnetometer for entertainment/nerd value or a Flux-Gate can
    measure the magnetic field component - *what for* and *how to calibrate* is
    for the user.

    Maybe easiest to buy?

    The Electric component can be seen in the dark when holding a flourescent
    tube at one end and the other closer to the wires - The 440 kV "SuperGrid"
    crossing Didcot, UK will light up the tube a fair bit.

    I did the experiment after getting small chocks while carrying a
    well-insulated child in a Nylon suit on my shoulders below the wires
    whenever child touched my head.

    Anyway - Electrometer is the word, I think.
     
  14. Rich Grise

    Rich Grise Guest

    You could check with some of the strawberry growers who are using the
    whole corridor under the hi-line alongside I-605. They might know
    something about the effects of power line induction.

    Good Luck!
    Rich
     
  15. GASP! You mean those strawberries we eat have been irradiated?!? Don't
    let the organic nuts know!

    People don't realize how much of an electrostatic field there is around
    those high tension lines. But it rapidly dissipates after a few scores
    of feet.
     
  16. ptaylor

    ptaylor Guest

    My girlfriend and I were once driving down a road with lots of
    high-tension lines above..(Going down LoLo Pass,on Mt.Hood,in Oregon,the
    wires were coming from the Bonneville dam.)
    And with the sun-roof open we could hear them hissing and buzzing..
    We noticed after a while we felt kind of "odd"..not really dizzy
    but,"wierd-headed"..
    We both noticed it,and I commented to her about it,and she had noticed
    it about the same time..
    The lines are pretty dang low in some places,I probably could have stood
    out of the sunroof,and raised my arm,and got an arc to jump to
    me,they're only like 15-20 feet overhead in places!!
    Wierd stuff.
     
  17. You were probably deceived by the lack of something to compare them to,
    and they were much higher than 20 feet. There is something like 800
    feet between towers, and the lines can sag somewhat, but they have to be
    certain heights above ground because of the high voltages, which can be
    a half million volts. The humdity in the air makes the crackling
    louder, but there's always some corona discharge when the voltages are
    that high.

    Check this out. Click on BIG Arcs and Sparks and D/L one and view it.
    http://www.teslamania.com/
     
  18. Mark

    Mark Guest

    why do you think it was the HT lines?

    maybe you should check your car for CO

    Mark
     
  19. ptaylor

    ptaylor Guest

    Yea,they probably were higher than 20 feet,but MAN they look LOW..
    It's funny when you see the wires up close,and realise that the "little"
    cables up there are like 4 inches diameter! (and there's 3 cables per
    conductor/phase,connected together with Y shaped pieces.) and those long
    glass insulators they're hanging from..they must be like 10 feet long!

    The crackling/hissing/buzzing noises are kinda freaky.
    I should go up there and take pics,or video or something..
    It's a creepy place! Desolate gravel "pits" on the side of the
    road,where people shoot off guns,and dump rubbish..
     
  20. I read in sci.electronics.design that Watson A.Name - "Watt Sun, the
    How close do you get to the overhead cables at the train station? Very
    close, in UK (3 m minimum, I believe) and they have 25 kV 50 Hz on them.
     
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