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Cheap thermometer calibration technique?

Discussion in 'Electronic Equipment' started by DaveC, May 8, 2007.

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  1. Yes, but I don't know how you're going to get a matt finish on the
    water. More importantly perhaps, the ink might alter the boiling
    point.


    Best regards,
    Spehro Pefhany
     
  2. John Larkin

    John Larkin Guest

    My FLIR rep confirms: water is 0.98.

    John
     
  3. Tim Wescott

    Tim Wescott Guest

    The internal shutter is for NUC (Non-Uniform Correction) -- focal plane
    array sensors in general (even visible light) have gain and offset
    differences from one pixel to the next. Part of it is periodic with the
    internal structure of the chip or with polish marks. The rest is just
    purely random. Visible light sensors can be selected to eliminate this
    to some extent (pro video cameras have nonuniformity correction, but the
    camera manufacturers won't admit it). IR detectors can't, and the
    amount of nonuniformity in the uncooled detectors can be astonishing; as
    of five years ago it could be 100x as much as your intended signal.

    So every once in a while the shutter comes down, the internal logic
    recalibrates the NUC, and the camera continues on.

    There are only a few companies that actually manufacture imagers (FLIR
    Sweden is one). So many companies that "make" IR imagers are just
    plopping an OEM module made by someone else into their case.

    --

    Tim Wescott
    Wescott Design Services
    http://www.wescottdesign.com

    Posting from Google? See http://cfaj.freeshell.org/google/

    Do you need to implement control loops in software?
    "Applied Control Theory for Embedded Systems" gives you just what it says.
    See details at http://www.wescottdesign.com/actfes/actfes.html
     
  4. Doesn't 63/37 solder melt at 485° F at sea level?

    That would calibrate the thermocouple.

    The IR is a bit trickier as the surfaces you examine have differing
    emissivities.

    You likely have a calibrated instrument, but forget to shift for
    emissivity differences.

    For the IR to cal correctly, you need a "black body calibration source,
    which is typically an Aluminum ingot painted with IR paint.

    You can learn a lot here:

    http://www.mikroninfrared.com/App_Notes/Principles_of_IR.pdf

    These guys are the tops.
     
  5. Freezing point and melting point are also pressure related, and so they
    too vary.

    Also, water has a very low emissivity, and would be a very poor choice
    for a reading on the IR instrument.
     
  6. For his thermocouple. Not good choices for the IR device, however.

    The body temp thermometer is VERY accurate usually (mercury type), but
    you need a good black body source for the IR cal session.
     
  7. Very good call, Chuck.
    Not if the surface that got anodized was "shiny", as it were. A good
    black body source is aluminum (thick) as it conducts heat fairly evenly,
    but the ideal surface is a very matte finish, or even concentric rings
    cut into the face and then painted or anodized after a grit blast
    session.

    Shiny is bad, which is why water is bad, despite it also being a very
    good, even conductor of heat. The shiny surface reflects the IR back
    into the medium, hence reduced emissivity.
    You can find a fairly decent emissivity chart here, as well as a very
    good primer on the subject:

    http://www.mikroninfrared.com/App_Notes/Principles_of_IR.pdf
     
  8. Not really. It depends on the focal length of the instrument. Shiny
    surfaces do reflect a lot of their IR emissions back down into the medium
    however.

    A mirror finish of nearly anything yields results based on reflections,
    yet is still very dependent on the optical system utilized by the
    instrument.
    Not very much though... if at all. Surface quality is the most
    determinant factor, not "color".

    A sprinkling of copier toner would work better, but be much "messier".

    Is that a "messier function"? :-]
    Yes, but the underlying heat has to push through the tape medium, and
    there are losses.

    Any matte finish brings one closer to ideal. Flat black paint (very
    thin coat) is best.

    Take a look here for some really good facts:

    http://www.mikroninfrared.com/App_Notes/Principles_of_IR.pdf
     
  9. For the thermocouple, sure. Add some salt even. Not good for the IR
    tho.
    Boiling water is nebulous as one has to decide what "boiling" is, and a
    hearty boil can well be far above the boiling start point was/is.
    Top posting is utterly retarded, boy.


    You're a TOFU retard.
     

  10. Pointing at the finned side would yield better emissivity than the
    "smooth" side would.

    Anodized, extruded Al usually has a fairly shiny surface quality.

    The ideal black body source is a MATTE finish, so grit blasted Al with
    some matte black paint (very thin coat) would be best/better.

    Yields about a .97 Emissivity. The anodized Al (regardless of color)
    yields about ten full points lower, if not worse.

    Surface quality is a VERY important factor here.

    Have a look here for a bit more info. Even though you seem very
    knowledgeable about it, this should help.

    The ideal source, of course, is a cavity.

    http://www.mikroninfrared.com/App_Notes/Principles_of_IR.pdf
     

  11. Color isn't the issue. The surface of water is VERY reflective, so any
    IR the medium generates get reflect BACK into the medium. This is why
    water has such a poor emissivity.

    A matte finish Aluminum block/box filled with a known temp water
    (circulating) would likely be only a couple tenths of a degree off the
    water temp, and would allow the IR gun to be calibrated very well.
     

  12. Miles off the mark, as usual.
     

  13. You're nuts.
     

  14. And you are STILL a top posting Usenet RETARD!

    Do you not notice the conventions used by others or are you always
    deliberately fucking obtuse, boy?
     

  15. The term is matte.

    Water is a bad idea for the IR, and the color doesn't matter.

    The term for today is:

    SURFACE QUALITY

    http://www.mikroninfrared.com/App_Notes/Principles_of_IR.pdf
     
  16. Rich Grise

    Rich Grise Guest

    Borrow somebody's calibrated DVM that has a temp. probe. :)

    Cheers!
    Rich
     
  17. Lamey

    Lamey Guest


    You're a retarded dickheck who know nothing about which you speak.

    --
    Usenet lits score:
    GIT-R-DONE!
    #20 Usenet asshole
    #6 Lits Slut
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  18. Lamey

    Lamey Guest

    On Tue, 08 May 2007 17:44:25 -0700, The Great Attractor

    How's the tracking coming along retard?

    --
    Usenet lits score:
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  19. Hard to believe, but it is.

    Still, not a good source to cal IR with.

    Skin is about 0.96, but skin temp is always several degrees lower than
    internal body temp.

    A GOOD, NIST traceable black body source is only about 0.98

    1.0 is not achievable.
     
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