Calculate thermistor coefficents

  • #1

Main Question or Discussion Point

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

  • #2
993
13
1st step is to take ln of both sides of the equation.
 
  • #3
Hi grzz, how can I take the ln of both sides if B is unknown?
 
  • #4
993
13
R = R[itex]_{o}[/itex]e[itex]^{\frac{B}{T}}[/itex]

then

lnR = lnR[itex]_{o}[/itex] + B ([itex]\frac{1}{T}[/itex])

Compare with

y = c + mx

which is a straight line graph.
 
  • #5
Ok I think I'm getting there. So Ro is resistance at an arbitrary temperature eg. room temperature? So what is the first R?
 
  • #6
993
13
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 ...
 
  • #7
Ok good stuff. I know that the slope is equal to B. Is R0 then equal to the intercept?
 
  • #8
993
13
Ro = intercept on the R-axis.
 
  • #9
Thanks a million grzz!
 

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