[time-nuts] What interrupts aging?
preilley_454 at comcast.net
Sun Feb 5 19:19:59 EST 2017
I am curious: is the quartz in a high quality quartz crystal perfect?
That is; is the
crystalline lattice perfect, without flaws or impurities? I assume
that the quartz is
grown in a furnace, can we grow perfect quartz crystals?
On 2/5/2017 6:31 PM, Bob Camp wrote:
> Aging can be caused by many things. Stress on the blank (and can and leads and plating and …) is one
> source. There are good reasons to believe that quartz vs metal stress can take > 1 month to settle out
> to the 90% level. Particle (think borders down to atoms) equilibrium inside the can is another source.
> Adsorption / desorption rates on many of the likely candidates also run out into the > 1 month range.
> More or less — you can adsorb stuff in a few seconds that takes many weeks to desorb. Yes this is
> only the start of a very long list ….
> How long an interruption to stir things up? Does the oven go to full power after your interruption? If it
> does, things are likely to get tossed around and aging (or retrace or warmup or whatever you want to
> call it) is going to get going.
> Pile on top of this the fact that crystals are not the only thing that does aging like things. Capacitors
> have a fun characteristic known as dielectric absorption. Some (tantalums) have leakage that drops
> a LOT with time spent at temperature and voltage. Either way, bump the voltage and things move around
> for a while. Use the wrong caps and it can be quite a while.
> Next layer is keeping the OCXO at the same temperature. When a “normal” OCXO is sitting there on
> the bench, it’s in it’s own very specific temperate zone. Convection (and maybe other things) have acted
> over quite a while to set up that zone. Touch it / bump it / move it / blow on it …. you will change the
> temperature. Most likely you will change the gradient across the package. Rick wrote some papers
> back in the 90’s about why this really messes things up…. ( Again this is the start of a very long list …).
> It’s even longer if you have DAC’s and voltage references external to the OCXO.
> So yes, you can get aging a lot of ways. Knowing what is and what is not aging can get a bit complicated.
>> On Feb 5, 2017, at 3:11 PM, John Ackermann N8UR <jra at febo.com> wrote:
>> We know of OCXO that have been continuously running for years and have exceptional aging, supposedly as a result.
>> What does it take to interrupt that? A momentary loss of power? The oven cooling down? Some long period of off-time? Or, once the oscillator has baked in will it return to that low aging once it has been powered up and thermally stabilized?
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