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 _______________________________________________ time-nuts mailing list -- time-nuts@febo.com To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts and follow the instructions there.
