[time-nuts] Re: in-ground clock room

[Bill Beam]

On Wed, 08 Sep 2021 18:36:11 -0800, Bill Beam wrote:

>On Wed, 8 Sep 2021 18:54:03 -0700, Tom Van Baak wrote:

>>I am considering a below ground "clock room" away from the house. This 
>>will be for some low-drift quartz oscillators and also a couple of 
>>precision pendulum clocks. The goal is long-term, unattended, and very 
>>undisturbed operation.

>>For scale, assume the room is 1 meter +� 1 meter +� 2 meters deep. So 
>>that's vastly smaller than digging a basement, but much larger than 
>>drilling a 8 inch round pipe. Digging down gives some natural isolation 
>>and temperature regulation. A couple tons of concrete gives high 
>>stability vertical walls for the pendulum clocks.

>>If any of you have personal or professional experience with the design 
>>or construction of this sort of thing, especially experience with 
>>precast (utility) vaults or poured concrete, please let me know.

>>In case this gets too off-topic for time-nuts, off-list email to me is 
>>fine (tvb at leapsecond.com).

>>Thanks,
>>/tvb

>Tom,

>How long do you expect your proposed voult to go undisturbed?
>I have several pendulum clocks.  They are disturbed every couple of months
>by earth quakes.  By disturbed, I mean pendulum banging against the case walls....
>Any ground motion that can be felt will upset the clocks.  Often the clocks will
>signal an earth quake that is not felt.

>Good luck.

I spent a few years as a geotechnic/soils engineer and learned as others have pointed out
that a thermal wave of period one year and wave length of several meters propagates
downward thru the soil.  Peak amplitude of a few degrees can be expected near the surface.

Consider building an "oven" with the clock vault freely floating in a water-ice mixture.  This will
provide constant temperature (0C) and limited mechanical isolation from earth quakes.

But of course this will be expensive to operate.

As you know 'good' clocks require a lot of energy and generate a lot of entropy.

Protecting the quartz oscillators is much easier than protecting the pendulum clocks.




Bill Beam
NL7F