I did some additional calculations to work out the raw value relationship with temperature. Rereading the book helped. He had me add a 2200 ohm resistor in order to mimic the R25 value of the LEGO sensor (12.2 instead of 10 kohm). So the R25 value I should be using in the equation is 12.2 -- which affects the results dramatically. Less dramatically, the beta value for the resistor I received was 3907, not 3750, so I fixed that, too. Not relying on the LEGO temperature calculation, I should be able to much more accurately do the math to calculate the correct temperature.
In that vein, I went ahead and further modified the calculations to affect reality. Instead of assuming an R25 of 12.2 kohms, I simply subtracted the 2200 ohm resistor from the measured value, and used that lower resistance to calculate the temperature with beta of 3907.
Tuesday, September 16, 2008
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