PDA

View Full Version : Thermocouple kit using advanced code



Marc Schneider
04-13-2007, 12:07 AM
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.

Skywalker49
04-13-2007, 02:56 AM
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 Schneider
04-15-2007, 01:57 AM
As of right now, there is no decimal places, just an integer.

Skywalker49
04-16-2007, 12:23 AM
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 Schneider
04-16-2007, 09:27 AM
Thanks for the insight, I just thought I could read degree up to 1/8 of a degree decimal as stated in the Documentation.

Skywalker49
04-16-2007, 03:53 PM
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 V), the converter provides resolution better than 1C,
even with the lower output of a type K thermocouple.

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

Happy to discuss.
Ed