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seismograph

Discussion in 'Electronic Design' started by BeeJ, Nov 6, 2012.

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  1. BeeJ

    BeeJ Guest

    Looking for suggestions to create a seismograph that:
    is cheap; hardware < $100
    easy to build. no machining etc.
    sensitive (you tell me)
    rugged, can be moved easily
    ties to a laptop to record
    could use the mic audio input (I can write the code to graph).
    accuracy not important
    linear or log output
    about the size of a desktop PC or smaller.
    omnidirectional
     
  2. For $100 you could get a laser,some mirrors, photodiode and make an
    interferometer.
    (not easy though.)

    George H.
    Personally I think the OP needs to do more research.
     
  3. Tim Williams

    Tim Williams Guest

    With mK temperature regulation, perhaps.

    Say, Sloman has experience with those kinds of systems, perhaps a
    collaboration is in order?

    Tim
     
  4. miso

    miso Guest

    You can buy geophones new from RT Clark for not much more than the
    mystery surplus junk. You need to build a LNA.
    If you expect to "see" long distance earthquakes, you need very low
    frequency response. There are hacks to lower the resonance of the
    geophone with a negative resistor. Long distance sensing is teleseismic.
    Most geophones are for local shaking. That is where the negative
    resistor scheme comes into play.

    Check out this paper: RT Clark is cool. If you need some data not on the website, they will
    send it to you. They don't mind small orders.

    Right now they are at the SEG convention in Vegas.

    If you are going to use the geophone more like the manufacturers spec
    sheet, they will list a termination resistance. Be sure to at least
    consider the resistance of the low noise amp. These low noise op amp or
    instrumentation amps are quite low impedance all by themselves.

    There are plenty of designs on the internet for geophone amps, though
    none are particularly impressive. I just shake my head at the designs
    with jfet inputs since you will be plopping a resistor across the
    geophone anyway. LTC and AD have very low noise (thermal and 1/f) amps.

    I think I sound card will not work well. I'd suggest a DSA, but you want
    to go cheap. If you look at ebay item 261072944165, these sound cards
    come apart easily. Maybe you can mod one to go to lower frequency. They
    work find on linux and windows. The converter in the one I bought is
    from C-Media.
     
  5. Phil Allison

    Phil Allison Guest

    "Bee Jerkoff Fuckwit "

    ** What does this fucking idiot imagine he is going to detect ?

    Trucks driving down the street, people walking around in the next room,
    passing trains ??

    FFS - do NOT feed puerile trolls like this bloody imbecile.




    .... Phil
     
  6. RV Jones made a tiltometer/ seismograph with a capacitance
    micrometer.

    There's a graph showing the bi-daily tilt of his lab due to the nearby
    tides coming in and out.

    OK a quick scan to try and find what resolution he quotes...
    "Our best sensitivity gave an rms limit of 5x10^-12 mm for a recording
    time constant of 1 second. and our best stability a few times 10^-9
    mm per day."

    Wow! that was ~1970.

    George H.
     
  7. Parallel plate capacitor.

    http://bayimg.com/JAFKJaaek

    http://bayimg.com/jaFKkAAek

    I’m not sure if those pictures will come out.

    He says it took him a while (years) to report results because the
    electronics was mcuh better than the mechanicals that he was making.

    George H.
     
  8. Guest

    I wonder if one of those "magic" magnetic floating globes would move
    enough to
    actually detect, maybe even with a webcamera

    -Lasse
     

  9. No, sorry it's a three paddle C measurement. The middle paddle moves
    back and forth, relative to the two ends. The mica is just an
    insulator between the two outer paddles. Hey, spend some of Highlands
    profits and buy his book. I can almost guarantee that you'll enjoy
    it. (It’s the kind of read that you have to chew through slowly
    though.)

    George H.
     
  10. whit3rd

    whit3rd Guest

    The Electronic Goldmine geophones (I bought one) are vertical
    types, a spring-loaded magnet in a coil.
    Depends on amplifiers; generally, though wind noise (trees? Are
    you inside a building?) and road noise (or nearby herd critters)
    will be picked up.
    Not clear if your mic input is good at the earth-movement frequencies
    which are circa 1 Hz. Pro equipment uses FM modulation into analog tape
    recorders (or, it did when Mt. St. Helens was acting up).
    That means you need three axes of sensors; it'll cost ya. Horizontal
    sensors of the geophone type aren't a surplus item, to my knowledge.

    There have been multiple articles in Scientific American, in the
    (late, lamented) Amateur Scientist column; check out April 1996 and
    Sept 1975 and July 1979. The collected columns are available on
    CD-ROM
    <http://www.surplusshed.com/pages/item/m2071.html>
     
  11. I don't think you would want to detect movement, you would want to
    measure the changes in current required to keep it stable.
     
  12. Guest



    apparently it has four electro magnets inside controlling the hover
    I guess you could just hack into it and measure the currents

    -Lasse
     
  13. Guest

  14. miso

    miso Guest

    RT Clark sells a 3 component (X,Y,vertical) for $135. Like I said in my
    other post, don't screw with the surplus junk. New doesn't cost that
    much more, and you get specs and support.

    http://www.rtclark.com

    If the original poster wants to detect distant quakes, he is better off
    with a 4.5Hz model than a 10Hz natural frequency. The lower frequency
    geophones cost a bit more.

    RT Clark sells new geophones on ebay, though I don't think they are any
    cheaper than just calling them up and ordering what you want.

    All these geophones have spurious frequencies. That is something to take
    into account. That is why I really think buying surplus stuff like old
    geophones from mil surplus is the wrong way to go. They were used in
    intruder detection systems.
     
  15. Robert Baer

    Robert Baer Guest

    Use a dynamic mike..
     
  16. Syd Rumpo

    Syd Rumpo Guest

    On 06/11/2012 16:39, John Larkin wrote:

    There was an article in 'Wireless World' many years ago describing a
    capacitance tiltmeter using mercury. Two containers of Hg joined with a
    long flexible pipe with plates which you could adjust to sit just above
    the Hg. Very sensitive.

    There were also 'Mercury heave gauges' commercially available somewhat
    later for use in (vertical) ground movement monitoring, but I never saw
    one in real life.

    As for the OP, what do you need? A geophone for local events at 10Hz or
    so, or a seismometer for global events at 10mHz or so? There's a big
    difference.

    Cheers
     
  17. Guest

  18. gregz

    gregz Guest

    Adding mass to any microphone, speaker, record player pickup,.. I like the
    higher impedance of the pickups.

    Greg
     
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