# Calculate thermistor coefficents

paulie walnut
I'm using Visual Basic to graph data from a NTC thermistor and temperature sensor (via a DAC card). I want to calculate the thermistor coefficients R0 and B according to the equation (R0 should have subscript 0):
R = R0.e^B/T
T=absolute temperature
R=resistance

I have calculated ln(R) and 1/T but am unsure of how to calculate the coefficients. Any help would be greatly appreciated.

grzz
1st step is to take ln of both sides of the equation.

paulie walnut
Hi grzz, how can I take the ln of both sides if B is unknown?

grzz
R = R$_{o}$e$^{\frac{B}{T}}$

then

lnR = lnR$_{o}$ + B ($\frac{1}{T}$)

Compare with

y = c + mx

which is a straight line graph.

paulie walnut
Ok I think I'm getting there. So Ro is resistance at an arbitrary temperature eg. room temperature? So what is the first R?

grzz
R is the value of the resistance at temperature T (in Kelvin).

So one plots a graph of lnR on the vertical axis against 1/T on the horizontal axis and then the intercept on the R-axis will be .... and the slope of the graph will be ...

paulie walnut
Ok good stuff. I know that the slope is equal to B. Is R0 then equal to the intercept?

grzz
Ro = intercept on the R-axis.

paulie walnut
Thanks a million grzz!