Bob,
I read your initial response to this thread; and I think that your
understanding of the situation is more complicated than it really is.
I snipped the following from your response:
> Nonetheless, you cannot possibly directly determine what the
temperature
> change of something as physically and geometrically complex as a
> connector, merely by factoring in what its resistance change is. Among
> other things, the solution is extremely non-linear and iterative.
Changing
> resistance will generate more heat, which will increase temperature,
which
> will generate even more heat ....and on and on! Add this to the fact
the
> resistance coefficient with temperature is itself non-linear, and you
can
The situation that you describe ..."changing resistance will generate more
heat..." is assuming that the heating in the conductor is due to current flow,
possibly as well as ambient changes. In the situation that you describe, you
have temperature changing (due to current flow), which increases resistance
(due to temperature change)... which increases temperature (due to increased
resistance) which increases resistance (due to increased temperature)... ...
I assume everyone gets the point of that train of thought, so I'll spare any
more cycles.
You are also assuming a complicated mechanical situation, such as a connector;
where there are interfaces, differing materials... many factors that would make
the math messy.
So, yes, I agree that your scenario could not possibly be described by a linear
equation.
However, I believe that the formulae that everyone is describing deal with the
change in resistance due to temperature alone. I would assume that one of the
conditions of using this formula is that the current flowing in the conductor
at the time of resistance measurement must be low enough to cause negligible
heating on its own.
Even with that, the equation is probably an approximation for small temperature
changes.
Your point is well taken: that is...know the limitations of any formula that
you apply.
To twist an old proverb: Believe half of what you see, none of what your hear
and about 10% of the formulae that can be reproduced by an ASCII email :-)
Chris Maxwell | Design Engineer - Optical Division
email [email protected] | dir +1 315 266 5128 | fax +1 315 797 8024
NetTest | 6 Rhoads Drive, Utica, NY 13502 | USA
web www.nettest.com | tel +1 315 797 4449 |
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