[time-nuts] temperature stability basics

Bob Camp lists at rtty.us
Fri Nov 26 17:53:59 UTC 2010


Hi

The other answer is to let the temperature control electronics take care of the problem. If you are doing something inside that uses energy (like an oscillator) it have generate a heat rise through the insulation.

Bob

Sent from my iPhone

On Nov 26, 2010, at 2:24 AM, "beale" <beale at bealecorner.com> wrote:

> In an attempt to educate myself about temperature stability, I put a temperature sensor in a 1" cube of brass wrapped in plastic packing-type bubble wrap, and compared that with another sensor outside the bubble wrap, with the whole combination in a thin nylon case just to slow down direct air drafts. I put it on the bench in the office where the ambient temperature varies up and down by a few degrees over the day. I recorded both temperatures with milli-degree resolution.
> 
> Looking at the resulting plots, it looks like my thermal mass and thermal insulation on the "inside" sensor gives me only about a half  hour lag at most relative to the "outside" sensor (hard to say exactly, it doesn't look like a simple one-pole filter). Note, I am not attempting any kind of ovenized control as yet, just measuring some time constants.
> 
> I've read that plain bubble wrap has an "R value" of about 2 ft^2·°F·h/(BTU·in), while some types of rigid foam building insulation go up to R=8 (at least until the CFC gases used to blow the foam leak out). What is done in real instruments that need good thermal insulation? I assume dewar flasks are limited to aerospace applications.
> 
> Photo of the block prior to bubble wrap:
> http://picasaweb.google.com/bealevideo/2010_11_18TempExperiment
> 
> (live) plot of temperatures:
> http://www.pachube.com/feeds/12988
> 
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