[time-nuts] temperature stability basics

J. Forster jfor at quik.com
Fri Nov 26 16:08:14 UTC 2010


Thermos flasks were pretty common on early crystal oscillatots, including
GR, HP 107(?), and Sultzer at least.

-John

================


> 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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