I have one of those inside / outside digital thermometers that has the outside probe at the end of a long cable but somehow the cable was cut and the probe is gone forever. I assume it was probably some simple NTC resistor.
I have put a variable resistor in its place and recorded the temperatures it read as a function of the resistor value.
Ohm - - - TºC
95000 -31.0
92000 -30.0
51800 -21.4
27000 -10.0
8800 +11.0
5640 +19.8
4990 +22.2
4400 +25.0
3780 +27.8
3010 +32.3
1933 +40.7
1537 +44.5
I could spend an afternoon relearning about NTC curves and equations but maybe someone can help me out.
It looks like I need an NTC resistor of 4K4 at 25ºC.
Then there was some coefficient that defined the exponential resistance curve and that is where I get lost.
Anyone?
And, before anyone says it, yes, this is an academic exercise done for pleasure and not for profit. I know I can probably get a new digital thermometer cheaper than I can get the NTC resistor.
E.T.A.: I found some software that says it will calculate coefficients given the table of values but I do not know where to even start.
https://sourceforge.net/projects/thermistor/files/ http://thermistor.sourceforge.net/