I'm using the voltage divider equation to solve for thermistor resistance. I have:
V_source = 4.9v V_therm = 2.95v R_known = 9kohm
I rearrange the equation so that it looks like:
R_therm = ((R_known * V_therm) / (V_source - V_therm));
And this results in a resistance value of approximately 13.6kohm, however, when I take the thermistor out of the circuit and measure its resistance directly (being sure not to touch it), the resistance measures ~11kohm. This 11kohm value makes more sense because it translates into an accurate temperature reading in Kelvins using the Steinhart-Hart equation. So, what am I doing wrong here?
edit: I know I'm converting the raw 10-bit ADC value to the
V_therm value properly, because it's exactly the same value that my multimeter shows.
Basically it seems like I need to let the Arduino run for a bit, heat the thermistor, cool it, then after a while it starts giving proper resistance readings. Is there a reason it doesn't work properly from the get-go and/or anything I can do about it? I'm using a TTC-103 10k thermistor.