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Discussion in 'Hobby Electronics' started by Don McKenzie, Aug 6, 2012.

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  1. Jon Kirwan

    Jon Kirwan Guest

    yeah. See:
    http://www.google.com/patents/US5835267

    My intent is to only use parts that a student can afford to
    buy and OWN at home. Not school equipment. Not access to
    expensive tools. Plain, simple, stuff. I have worked out a
    folding piece of cardstock paper that makes the box and has
    all the right angles set up for them, with baffles (also out
    of paper.) The DVD-RW is cheap and is a precision diffraction
    grating. The camera is cheap (blister-pack, $10 or less, at
    common grocery stores.) The merc-argon bulb is $8 to $12,
    depending. That's the ballpark I'm talking about. They build
    everything themselves, take it home, and own all of it.

    If you come up with a scheme that can align with the sun in a
    consistent fashion (without burning their poor eyes out),
    get's good data on the sky filtering and effects due to angle
    of incidence, uses a stop and baffles in the optical path
    that children make by hand using glue and scissors and a
    ruler, let me know.

    Think 12-year old and up.

    Jon
     
  2. Jon Kirwan

    Jon Kirwan Guest

    What I'm looking for would be analogous to using an ice bath
    for temperature calibration. In almost every way, temperature
    calibration is difficult. That is, everywhere except for ONE
    temperature. And there, it's easy and cheap and any idiot can
    do a decent job no matter how clumsy they may be. And single
    point temperature calibration is better than nothing at all.

    Kind of like that. It needs to be cheap and idiot proof. I'm
    not holding my breath. But that doesn't mean I've stopped
    looking, either. I just don't think it is in the cards, yet.

    Jon
     
  3. Geoff

    Geoff Guest

    Traceable intensity calibration even to 1%T is not easy. You
    could simply aquire some cheap pseudo neutral density filters
    such as cheap sunglasses, prefereably with a flat lens, and ask
    if you can scan with a local uni's Uv-Vis spectrometer, in
    either absorbance or %T mode.

    Then armed with a reference, you can do useful %T work. This
    assumes using a continuum type source though through your mono.
    (If your aim is to analyse the light itself rather than samples
    then disregard.)
     
  4. Jon Kirwan

    Jon Kirwan Guest

    I think 1% will be too difficult that way. I already know how
    hard that is to achieve, with good, accurate equipment and
    careful procedures. If I get within 1% of NIST as it is, I
    consider it very very accurate and very very lucky.

    I can't say I know exactly what you are suggesting -- too
    many specific possibilities arise in mind. You didn't address
    any of my points. So I need to leave it there.

    To do an intensity calibration, the students will have to do
    a much better job on the entrance slit. I've held off of the
    old 'pair of razor blades' idea. (Safety.) But I can
    resurrect it if I get in mind something useful to do and it
    seems practical.
    The intensity calibration setup I have is rather large right
    now and takes up a table. As I said, wavelength calibration
    is NOT a problem.

    We already use the sun as a source for transmission methods
    in a small box. A fluorescent yellow highlighter dipped a few
    times into distilled water, kept still transparent clear so
    very dilute, produces a beautiful green, for example. It does
    require a strong light source to be striking, so that's why
    the sun.

    DVD-RW is 1350 lines/mm or spaced by 0.74µm. The yellow
    spectral doublet of mercury at 577nm and 579nm is very
    visible to the eye and a lot of the solar Fraunhofer lines
    are also clearly discernable. Which is way better than I'd
    expected from cheap DVDs when I started doing this.

    Anyway, I will make some thoughts first and then maybe some
    attempts regarding the sun (in a few months time) and see
    where it takes me. I'll have to consider safety, consistency
    regardless of time of year, position of sun in sky, ... and
    work out a procedure students can achieve.

    Thanks,
    Jon
     
  5. Jon Kirwan

    Jon Kirwan Guest

    Yes, $30 is too much and so is requiring a computer. To start
    out, the students build a paper box and use a DVD and just
    their eyes. The DVD is far far less than $1. (20 cents?) The
    box is ONE sheet of cardstock (a few pennies.) The glue is
    Elmer's and doesn't need much. That's it. The DVD is the only
    tricky part. I just prefer the DVD-RW because it doesn't have
    a terrible blind spot in the red band (DVD-R absorbs heavily
    over a range in there.)

    Some students will then move on to the idea of a camera and
    using a computer to process the pixels. There is some work
    involved in that next step (I've already written all the
    wavelength calibration software, though.) Not all students go
    there. Most just stop at the box and use their eyes.
    I'll stick with the DVD-RW. 1350 lines/mm.

    Jon
     
  6. Jon Kirwan

    Jon Kirwan Guest

    P.S. I also see that the above $30 unit specs "better than
    3nm spectral resolution." I'm already getting much better
    than that, being able to easily separate 577nm and 579nm
    mercury doublet. Easily.

    Jon
     
  7. Jon Kirwan

    Jon Kirwan Guest

  8. OK. What is the final goal as a teaching experience and how will
    the difference between 0.1%, 1%, and 10% calibration affect
    the learning experience?

    1% solar calibration should not be too difficult. Set up
    a couple of baffles so that direct sunlight falls on a circle
    of known diameter on a piece of white card stock visible to
    the spectrometer. The spectrometer looks at this circle of
    light and reports a result.

    The alternative is to use your own light source and provide
    a sample of known reflectance and spectral characteristics.
    After calibration with that standard, the student can examine
    leaves, fabrics, minerals, etc, and get a pretty good estimate
    of their spectral reflectivity.

    Mark Borgerson




    Mark Borgerson
     
  9. Jon Kirwan

    Jon Kirwan Guest

    Yup, I also demontrate chlorophyll. I've been writing to
    scientists about this for such ideas.

    I could post up some pictures, I suppose.

    Jon
     
  10. Another good experiment might be to make up a chlorophyll
    solution---think spinach and rubbing alcohol in a blender,
    followed by a paper towel filter. (the paper towel filter
    will also produce quite a nice paper chromatogram under the
    right circumstances.)

    You will see some nice absorbtion spectra for the
    chlorophyll and other pigments, you should also see a strong
    fluorescence peak in the red when looking at right angles
    to the sunlight.
    Mark Borgerson
     
  11. Jon Kirwan

    Jon Kirwan Guest

     
  12. F Murtz

    F Murtz Guest

    Bart Simpson?
     
  13. LOL! Perhaps you should write to the engineers who design the
    instruments used by those scientists. Not all of them are regulars on
    C.A.E like myself.
    That wouuld be cool. I'm about to retire and might have some time to do
    more than read and respond on newsgroups.
    Mark Borgerson
     
  14. Jon Kirwan

    Jon Kirwan Guest

    Yeah, I noticed that too. His clock is hosed.

    Jon
     
  15. Wierd. I just changed from syncing with time.windows.com to
    time.nist.gov, and the time went from UCT to Pacific local.


    Mark Borgerson
     
  16. LOL! I just noticed that my clock is set to UCT. I often do this on
    purpose when comparing with data files that we always clock on UCT---it
    really helps when you have project files coming from the Gulf of Mexico,
    Oregon, 140W on the equator, and 80E in the Indian Ocean. I don't
    remember resetting it this time, but perhaps I reset it in an overdose
    of Olympic zeal.


    Mark Borgerrson
     
  17. The maritime museum in Greenwich would beg to disagree!

    I do have this computer set to check with an internet time
    server, so I'm not sure what is going on here.

    Mark Borgerson
     
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