[time-nuts] Non electrical time-nuttery
djl at montana.com
Wed Jan 13 04:07:38 UTC 2010
not hard to visualize. If done that way, perhaps the two rods/tubes and the
bob should be stress relieved by liquid nitrogen treatment. Seems to work
for rifle barrels (one of my other time absorbers)
----- Original Message -----
From: "Lux, Jim (337C)" <james.p.lux at jpl.nasa.gov>
To: "Discussion of precise time and frequency measurement"
<time-nuts at febo.com>
Sent: Tuesday, January 12, 2010 5:14 AM
Subject: Re: [time-nuts] Non electrical time-nuttery
>>> BTW, Invar has a really low tempcoefficient, but tends to random
>>> shifts in its structure, yielding to abrupt length changes. Can't
>>> have everything, I suppose...
> That's what my friend trying to build the 1ppm pendulum found. He found
> that the standard technique is to build the pendulum out of two metals
> different CTE, arranged so that as the temperature changes, the center of
> mass of the pendulum stays the same.
> Imagine the long shaft of, say, 1 meter, with a CTE of 10 ppm/degree. You
> support the bob with a sleeve attached at the bottom of the main shaft of
> 30cm with a CTE of 30 ppm material (so the bob sits at 70cm from the
> As the temperature rises, the main shaft gets longer, but so does the
> sleeve, so it pushes the bob back to the proper location. (Wow, is this
> difficult to describe in words)
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