Re: Fused quartz pendulum - temperature coef
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Has anyone used quartz as the suspension flexure? It is very strong, and if thin enough, can be kept well below the brittle fracture limit.
On Tue, Apr 7, 2020 at 5:38 PM neil <njepsen@...
Yes Bepi - Matthus reports the results of what would have been a
very lengthy series of tests in his book. He used a FQ pendulum with
a brass bob and did a number of tests with different compensators
and different bob support positions. He heated the entire clock by
wrapping with an electric blanket, waiting a day or 2 then removing
the heat and measuring the step change in rate with a set change of
A few months ago I attempted to calculate the TC of my entire cast
iron bob, invar pendulum and phosphor bronze dual suspension, and
compensate with an aluminum spacer, but it was difficult to do in
the middle of summer with the daily high ambient temperatures in my
shop. I have since then dismantled the clock and purchased several
lengths of fused quartz tube ( the type used to make heater
elements). I'm right now in the process of building a new suspension
with soldered in place chops. I may do a You-tube video if the
motivation strikes. I will support the bob ( cast iron) in the
middle, use a glass spacer and set the compensator outside of the
Matthus also makes the same comment as you about supporting a cast
iron bob at the bottom, and not needing any further compensation,
but of course the suspension has as much if not more TC that the
entire pendulum rod, so getting it right is easier said than done.
On 8/04/2020 02:00 am, Bepi wrote:
On the subject of temperature sensitivity when I changed over to a
lead bob I noticed that the
original gray cast iron bob had, in principle, just the right
coefficient of expansion (1.08 10-5 ºC-1) and height to
compensate for an invar rod (1.21 10-6 ºC-1) when the two are
rigidly connected at the bottom of the bob. Does anybody know if
this design feature is typical of all synchronomes?
In principle for a given bob weight, one can always
compensate exactly for the pendulum temperature coefficient with
the right choice of materials and bob aspect ratio, so that the
problem changes from finding the smallest coefficient material to
the best known coefficient material. I would also be curious to
know if anybody has attempted to measure thermal expansion
experimentally with decent precision other than from period vs
natural ambient temperature fluctuations.
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