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I've got a problem for you ;-)

Discussion in 'CAD' started by Jim Thompson, Jan 27, 2004.

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  1. Jim Thompson

    Jim Thompson Guest

    I have a sandstone (American aboriginal) Indian carving with a clock
    and a bi-metal (rotating pointer) thermometer in it.

    I was able to find a replacement battery-powered clock mechanism.

    But I've had no luck with replacing the bi-metal thermometer.

    It's completely hosed... indicates 0 to +65 (°F) when the real range
    was 40 to 65 °F.

    I was pondering an electronic replacement with some kind of
    low-powered indicator (such as the fuel gauges in old GM products).

    Any ideas... design, procurement, etc.?

    Thanks!

    ...Jim Thompson
     
  2. I read in sci.electronics.design that Jim Thompson
    Isn't this a job for an LM 35? I don't know where you could get an LCD
    that simulates a pointer meter, though.
     
  3. There are some chips (eg. Philips) available to drive air-core
    indicator coils. Or you could probably scavenge a DC tachometer meter
    movement from somewhere. Then just one of those little National
    temperature sensor chips and an op-amp. It wouldn't operate for a year
    from a battery or anything, most meter movements need 100uA or so. A
    stepper motor would consume no power when not actually moving, that's
    one possibility. This kind of thing is used in some process control
    instrumentation becuase it will stand up to earthquakes (eg. for
    nuclear plants). Maybe an 4000 CMOS up/down counter, R2R ladder
    low-power DAC?

    Not to spoil your fun, but you can get 1-7/16" gold color bezel
    bimetal thermometers for just a few dollars.

    Best regards,
    Spehro Pefhany
     
  4. jmagerl

    jmagerl Guest

  5. Jim Thompson

    Jim Thompson Guest

    Spehro,

    I have a 6" pointer that indicates temperature over a 270° arc for
    -40°F to +120°F

    This is carved-in-stone out on the patio upon which you and your wife
    have set and is under the jurisdiction of the management ;-)

    Thus "hack" jobs are impermissible.

    I vaguely remember a thirty-year-ago project that used some kind of
    two-coil indicator (Stewart-Warner).

    These don't move when un-powered.

    What I had in mind is powering up every 15 minutes, apply power to the
    coils to set the current temperature, then sleep again for 15 minutes
    (or whatever is necessary).

    Temperature measurement has been a good chunk of my career... that's
    the easy part... getting the indicator mechanism will be a wee bit
    more difficult.

    Or maybe there's a bi-metal indicator out there that has adjustable
    end-points ??

    ...Jim Thompson
     
  6. Boris Mohar

    Boris Mohar Guest

    Pointer sticking at 0° ?
     
  7. Mark J.

    Mark J. Guest

    In news: (Jim Thompson):

    Heat up the bi-metal and temper/anneal/harden it? :)
     
  8. Jim Thompson

    Jim Thompson Guest

    [snip]

    Thanks for the tip! I have sent them an E-mail to see if they have a
    replacement mechanism.

    ...Jim Thompson
     
  9. Say no more. Hmm, okay given that, check out #5310 & 5353 here:
    http://www.branom.com/COMPANIES/taylor.html
    Stewart-Warner is *the* keyword for the raw movements themselves,
    AFAIUI.

    Drivers for this type of very linear indicator:

    http://www.semiconductors.philips.com/acrobat/applicationnotes/AN1761.pdf
    http://www.semiconductors.philips.com/acrobat/datasheets/SA5775A_3.pdf
    http://moon.feld.cvut.cz/hw/philips/acrobat/5027.pdf
    http://cache.national.com/ds/LM/LM1819.pdf (discontinued)
    http://www.nteinc.com/specs/1600to1699/pdf/nte1670.pdf
    http://www.onsemi.com/pub/Collateral/CS8190-D.PDF
    http://www.onsemi.com/pub/Collateral/CS4121-D.PDF

    Possible source for a movement (but looks more like 240° than 270°)
    http://cgi.ebay.com/ebaymotors/ws/eBayISAPI.dll?ViewItem&category=33679&item=2456769547
    I'll wager even more of mine, but this is about as easy as they come!
    Best regards,
    Spehro Pefhany
     
  10. Jim Thompson

    Jim Thompson Guest

    What's "0"? That's plus 40°F. I've not experienced 0°F EVER in
    Phoenix ;-)

    ...Jim Thompson
     
  11. Wrong repair paradigm. Unless the bimetal element has
    been heated or corroded so that it's incapable of reading
    correctly, it's just slipped a bit in its moorings. Look in
    the back for a little bitty adjustment screw with a locknut.

    Probably best to set it while the ambient temp is at its
    midrange.

    Mark L. Fergerson
     
  12. Note the "span" shift that Jim reports.. it's more than a "zero"
    offset.

    Best regards,
    Spehro Pefhany
     
  13. jim

    jim Guest

    i got a plate with a clock in the middle of it at the dollars stores and
    took the clock out of it to replace it inside someother piece of junk
    clock we have/had??? did never find any temperature stuff in the dollar
    stores, you might just throw it out if you cannot fix it or keep it in
    storage and your kids can throw it out when they have to go through your
    stuff...
     
  14. Chuck Harris

    Chuck Harris Guest

    Hi Jim,

    Although it is rare for a bimetal that isn't corroded to fail,
    you can get replacements for many different types from:

    http://www.slarose.com

    Let them know what the diameter, the temperature range, and the
    dial type (eg 270degree, 60 degree, etc..) and anything else you
    can think to describe, and they will let you know what matches.

    Typical price of these kinds of things is under $5.

    -Chuck Harris
     
  15. Bill Garber

    Bill Garber Guest

    : Hi Jim,
    :
    : Although it is rare for a bimetal that isn't corroded to fail,
    : you can get replacements for many different types from:
    :
    : http://www.slarose.com
    :
    : Let them know what the diameter, the temperature range, and the
    : dial type (eg 270degree, 60 degree, etc..) and anything else
    you
    : can think to describe, and they will let you know what matches.
    :
    : Typical price of these kinds of things is under $5.
    :
    : -Chuck Harris

    This ain't 1923, take a pic of the bimetal coil
    and email it to them. I'm sure if they see it they
    can match it much more readily.

    Bill @ GarberStreet Enterprizez };-)
    Web Site - http://garberstreet.netfirms.com
    Email -
    Remove - SPAM and X to contact me
     
  16. DarkMatter

    DarkMatter Guest


    There are a lot of them in regular Dept. stores in humi / temp
    combos.
     
  17. DarkMatter

    DarkMatter Guest


    As long as you can get the 270 degrees of arc, you could copy the
    scale from the procured unit to the unit in question. The needle will
    work, regardless of it's length (without extreme exaggerations that
    is).
     
  18. Some one does make a psueado LCD meter that has an analog look to it. Comes in colors too.
    But I can find it at the moment.

    I would stick with the mechanical style tho. Maybe check process control oriented distributors.
    Or even photo equipment suppliers (darkroom). You might find a suitable replacement that way.
    Even all stainless.

    Cheers
     
  19. Jim Thompson

    Jim Thompson Guest

    [snip]

    How ya going to do that in the front of a stone carving?

    I need a rotating pointer.

    ...Jim Thompson
     
  20. Jeff

    Jeff Guest

    A good stepper for this application could come from an old 3.5" floppy
    drive! Put a stop on the dial, rotate the stepper enough steps to rotate
    fully CCW from any postion, to set the pointer into a known pstion, and
    count the right number of steps CW to indicate the temperature. Have the
    pointer restet it's self every so often. It could be easily done with a AVR
    tiny, using the built in A/D to get a temperature reading, and a port to
    directly drive the stepper. The tempeature could be mapped in software, and
    few lines of code could control it.
    http://www.speff.com
     
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