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Re: temperature jumps



This reminds me those noise induced (phase) transitions:
the heater timer acting a contol parameter of the system,
deciding the rate of heat transfer to volume of air in front
of the heater. I guess that, due to some mechanical effect
on the contacts, the temperature rises almost always in
the same amount, causing the sytem to show only two
states, namely dt=0 and dt=4 deg.
But then, this like the transitions between the two state
available to a bistable system. Ergodicity would then not
be broken, and we could not speak about a phase transition,
but just about a (noise induced) transition.

But this changes in an extended system where diffusion
takes place. This coupling between neighboring points
then allow an actual phase transition to happen.

I got the impression there was a whole wolume (in both
examples), altough surely small, where dT changed
uniformly, all points at the same time, did you meant this?

If it's not the case, then this system may
show a front invading this volume with dT=0, leaving
behind the new state dT=4. Did you observed something
like this?

Any comments?

Regards,
Miguel A. Santos
msantos@etse.urv.es

Karl Trappe wrote:

dQ = 0, dT = 4 degrees....sounds like a phase transition to me. Better
write it up quick. Check the slope. Is it 1st or 2nd order?...smile, Karl

I had a similar problem as a grad student. The heater timer used relay
contacts to turn on the heater. The contacts would occasionally stick,
causing the heater to stay on longer than the preset time. Voila, phase
transition! Of course, it would not repeat at the same temperature. I sure
learned that it pays to analyze your data promptly rather than take lots of
data to be analyzed later. One years worth of useless info... I'm betting
on similar causes. Karl


Every now and then a section of the curve is displaced upwards. For a period
of about 5 minutes the temperatures recorded are about 4 degrees higher,
then they drop back down to be once again consistent with earlier
measurements. Obviously a measurement problem. Does anyone know what
causes it?


I've seen behavior like that as well, and it was always due to an equipment
problem. Do all of your rigs do this, or just one? It sure sounds like a bad
connection somewhere. Another possibility is interference on the serial line.

JEG
__________________________________

John E. Gastineau john@gastineau.org KC8IEW
900 B Ridgeway Ave. http://gastineau.home.mindspring.com
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Dr. Karl I. Trappe Desk Phone: (512) 471-4152
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