On Nov 7, 2007, at 5:45 PM, Paul Alfille wrote:
When you read the temperature (which should be the cold junction
temperature, not the thermocouple temperature) does it seem
accurate? (room temperature I presume).
Yes, I am able to read the cold junction temperature correctly.
In order to debug the problem, I wanted to focus on the code that
converts from mV to temperature. As you can see from the test
program I posted, I make the conversions with a 0.0C cold junction
temperature so it doesn't alter my measured temperature reading.
I'm not familiar with octave, so I don't know how you use it to
generate the coefficient list. Everything I've seen online with
thermocouples uses coefficients like:
c0 + c1 * x + c2 * x^2 + c3 * x^3 + c4 * x^4 + ... cn + x^n
The polycomp routine appears to do it a different way:
(x * (x * (x * a0 + a1) + a2) + a3)
I have come across lists of the first style, but it would be a little
tricky to convert from one to the other, I imagine (linear algebra to
solve?).
Regardless of the actual readings from the chip, I should be able to
test/exercise the polycomp() function and type_t data by calling it
with known voltages from a table and calculating the error between
the lookup value and the calculated value.
-Tom
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