# 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.

## Answers and Replies

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!