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K type thermocouple, MAX31855K, Basic Stamp = stability/decoding issues. - Page 2 — Parallax Forums

K type thermocouple, MAX31855K, Basic Stamp = stability/decoding issues.

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Comments

  • kwinnkwinn Posts: 8,697
    edited 2014-08-21 09:41
    Subtract 25 from the reading then shift it right 2 bits. That removes the 24-26 offset and divides it by 4. If you want the fractional part of the reading use the 2 lsb's to determine if they are 0, .25, .5, or .75 before shifting the reading right.
  • Tracy AllenTracy Allen Posts: 6,664
    edited 2014-08-21 09:52
    Great! Stick to it long enough, and you'll be (hopefully) rewarded with that aha! moment.
    I ordered samples of the chip from Maxim to have on hand.

    The thermocouple count is signed 0.25 °C per bit, and the reference count is signed 0.625°C per bit.
    If I've got the shifts correct, then for temperatures >=0,

    degCouple = (TCtemp1 >> 2) / 4    ' Then display as xxx degC   
    
    degCinternal = TCtemp0 >> 4 * 5 / 8  ' Then display as xxx degC
    

    Note that you coule do the first one as a single >>4. The first shift by 2 isolates the temperature bits, and second shift by 2 scales to whole Celsius. If you want higher resolution, you can multiply the degCouple times 25 instead of divide by 4, then display as xxx.xx up to 655.25 °C.

    Your ice bath will work better if you put it in a thermos as a slush.
  • CuriousOneCuriousOne Posts: 931
    edited 2014-08-22 21:22
    Thanks a lot!

    Verified with boilling water and reading was around 96-97C, which is not bad, considerng I'm about 500 meters above sea level. Will do ice bath tests on monday.

    I've aquired laboratory burning oven (or it might be called differently, it is used for burning possibly dangerous biological waste before disposing). It can go up to 400C, heater is working, interior, door and sealings are OK, just temperature control system is gone, so I need to furbish a new one.
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