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Thermocouple kit using advanced code — Parallax Forums

Thermocouple kit using advanced code

Marc SchneiderMarc Schneider Posts: 5
edited 2007-04-16 08:53 in BASIC Stamp
Im currently using the advanced code for the thermocouple kit to output the temp on an lcd.· Right now it is working but im trying to make more decimals display. How would I go about altering this preogram to do this. thanks.

Comments

  • Skywalker49Skywalker49 Posts: 172
    edited 2007-04-12 19:56
    Hello Marc, does it make sense to display more decimals? I mean, you can try to display say 2nd decimal
    after the decimal point but if the sensor if not sensitive enough then it doesn't make sense.

    Ed
  • Marc SchneiderMarc Schneider Posts: 5
    edited 2007-04-14 18:57
    As of right now, there is no decimal places, just an integer.
  • Skywalker49Skywalker49 Posts: 172
    edited 2007-04-15 17:23
    Marc,

    in the documentation of the DS2760 Thermocouple kit is written:
    the Seebeck voltage from the thermocouple can be measured with an accuracy of 15.625 microvolts.

    Then if you check the look-up tables provided with the advanced code, the thermocouple gives approx. 40 microvolts per degree (C or F).
    As a result, the accuracy in degrees is even not 1/3 degree and so it doesn't make sense to display decimals.
    Degrees as whole numbers (integers) is the best you can get out of this scheme .. at least that is my interpretation.
    Anybody some more thoughts or experience with this device ?

    Ed
  • Marc SchneiderMarc Schneider Posts: 5
    edited 2007-04-16 02:27
    Thanks for the insight, I just thought I could read degree up to 1/8 of a degree decimal as stated in the Documentation.
  • Skywalker49Skywalker49 Posts: 172
    edited 2007-04-16 08:53
    Marc, the cold junction temperature is measured with 1/8 of a degree accuracy and is subtracted from the
    measured temperature. So this is an additional error of max 1/8 degree.

    The temp. of the junction has an accuracy of 15.625 microvolts. The ADC convertor has a resolution of 1 bit / 15.625 uV.
    Here the txt on the site of the chip manufacturer: http://www.sensorsmag.com/articles/0102/29/main.shtml
    With a full-scale range of ± 64 mV (LSB of 15.625 µV), the converter provides resolution better than 1°C,
    even with the lower output of a type K thermocouple.

    Agreed, it is better than 1°C but not good enough for 0.1°C

    Happy to discuss.
    Ed
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