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Re: graphical analysis menagerie (was: Need Ideas)



At 15:34 1/2/00 -0500, John D wrote:

... If you take
ordinary Allen-Bradley carbon resistors and cool them down, the resistance
depends on temperature. This makes them useful as secondary thermometers
in the range of roughly 77 Kelvin to maybe 10 milliKelvin. There is a
large range where the resistance is
exponential in the square root of temperature
to remarkably high precision. No kidding.
....
c) Even after you plot it on semi-log paper, you are left with something
(sqrt) that can't be well fitted by a polynomial (unless you transpose the
axes, which most people don't immediately do because they're stuck on the
idea that T is the *independent* variable)....

John's description possibly suggests the equation
Resistance = exp(k*sqrt(temperature))

Allen Bradley carbon composition resistors decrease in resistance with
temperature. So the scaling constant k is evidently negative.

Taking a sample A-B 0.27ohm resistor:
Temp (K) Res (ohms)
0.3 10^6
1 10^2
3 3
10 1
30 0.7
100 0.3 (from a graph of Rose-Innes's)

I don't have a curve fitting package here. Can someone else
fit this?


brian whatcott <inet@intellisys.net>
Altus OK