[time-nuts] Vibration isolation of quartz oscillators

[Dr. David Kirkby]

Dr David Kirkby Ph.D C.Eng MIET
Email: drkirkby at kirkbymicrowave.co.uk Web:
https://www.kirkbymicrowave.co.uk/
Kirkby Microwave Ltd (Tel 01621-680100 / +44 1621-680100)
Stokes Hall Lodge, Burnham Rd, Chelmsford, Essex, CM3 6DT.





On Sun, 28 Jun 2020 at 12:44, Tom Van Baak <tvb at leapsecond.com> wrote:

> About slabs and stability... Around the world there must be a hundred
> precision time labs, including official NMI (National Metrology
> Institute) labs that contribute to the calculation of UTC itself. You
> run into photos of these labs and their T&F gear on the web all the time
> when you search for time nutty stuff. Those of us with home labs -- even
> if just a few vintage frequency standards -- can relate.
>
> Anyone, one of my favorite lab photos is from VSL, the Dutch Metrology
> Institute. Photo attached. [1]
>
> Spend time time pan/zooming around the gear in the photo. The usual
> suspects: hp 105 quartz; TimeTech (I think); lots of SDI
> (Spectradynamics); also Truetime or Symmetricom stuff; maybe that's an
> old Tracor/Fluke VLF receiver on the far right (?); and of course lots
> of Stanford Research SR620 counters, the TIC still used by almost every
> time lab.
>
> But what really caught my eye was not just the four hp 5071A in the
> foreground but *how they are mounted* -- on top of massive granite blocks!
>

There's a picture of a granite block here, at a former place I used to work
as a student - EQD Aquila, the MODs calibration labs.

https://www.derelictplaces.co.uk/main/military-sites/14101-aquila-mod-testing-facility-bromley-march-2004-a.html#.XvirQuco9PY

about 60% of the way down the page. (Some of the pictures are quite
amusing, as well as some of scientific interest).

There's a couple of guys at my radio club used to work somewhere where a
milling machine was turning high precision device. I just phoned one to ask
what they used for anti-vibration, as I knew they took some precautions. He
said they had dug a hole about 2 m into the ground, above that was 600 mm
of "rubber", then 1.4 m of reinforced concrete. That used to stop lorries
messing up the work. That's a different sort of application.

I assume the OPs objects are quite large - not wrist watches. Otherwise, I
was wondering if an active damping system might be practical. They
certainly exist for laser tables

https://www.newport.com/n/active-vibration-damping

but I would imagine that for heavy 19" rack equipment, there would need to
be quite a bit of power consumed in such a system. I've never done any
calculations - just intuitively, I can't imagine that one could achieve
anything useful without some pretty big power amplifiers.

When I worked at UCL we had a laser table. Our department was near a main
road. The laser table had gas-filled "dampers", but apparently these made
the vibration problems worse rather than better, so the gas was removed. We
never had any active system.

Dave