[time-nuts] Quartz crystal aging and applied voltage

Bob Camp lists at rtty.us
Sun Jun 30 19:09:22 EDT 2013


Hi


On Jun 30, 2013, at 3:41 PM, Attila Kinali <attila at kinali.ch> wrote:

> On Sun, 30 Jun 2013 20:44:36 +0200
> Magnus Danielson <magnus at rubidium.dyndns.org> wrote:
> 
>>> Ions in the lattice are part of the crystal structure. When you "move"
>>> them by sweeping you put stress on the quartz. That stress may take a
>>> *long* time to relax out. Since there is now a defect in the lattice 
>>> (where the ion was) the stress may be relieved by an ion moving back to 
>>> that location.
> 
> That would make the aging even more severe.

Yes, swept quartz resonators tend to age more than an equivalent "normal" part. That assumes the normal part is made from high grade quartz.

> 
>>> Quartz is swept to reduce it's radiation sensitivity. That's a big deal if 
>>> you are going to put the oscillator in outer space or if you expect to
>>> need to use it when unexpected bright lights appear in the sky. Neither
>>> one is likely to be of interest in a typical basement lab. The levels
>>> involved also would drive you to radiation harden the rest of the
>>> oscillator circuit, not just the crystal.
> 
> Ok. From what i've read sofar, i thought that sweeping was mostly to
> improve aging.

I have never seen it used to improve aging.

> 
>> I don't agree that swept crystal has not been talked about. It is 
>> mentioned all over the precision crystal papers, it's there if you look 
>> for it.
> 
> Yes, sweeping is meantioned a lot, but i have so far not found any mention
> of aging due to DC voltage on a crystal.

It's not aging if it's a fixed bias. The easy way to have a fixed bias is to have zero volts on the resonator. Given that the effect is *very* small, any regulated bias in an oscillator should be fine.

> 
>> It however does not make much sense to discuss it for us, since 
>> we usually deal with complete oscillators and only rarely work with 
>> single crystals, and in that case very rarely of the quality where swept 
>> crystals occurs.
> 
> Well, i'd like to understand how crystal oscillators work, what their
> limits are and what has been done to push those limits. And sometimes
> weird questions pop into my mind :-)

Very little of what has been done or that could be done will be found in published papers ….


Bob

> 
> 
> Bob, Rick, thanks for the insights.
> 
> 			Attila Kinali
> 
> -- 
> The people on 4chan are like brilliant psychologists
> who also happen to be insane and gross.
> 		-- unknown
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