[time-nuts] Re: pulling some crystals

[glen english LIST]

yeah I certainly dont buy the 3 days at 105C based on my own 
research....  These are AT , by the way, FWIW.

Rick your point about not observing aging different for a 105C versus an 
80C xtal is telling. Today, it is hard to get xtal mfrs interested in 
the fussy crystals I want and only perhaps 100-200 per annum.  I am 
beginning to think I need to make a large automated test jig, or go 
about this a different way. Having a high PLL reference PD frequency is 
essential - 49MHz  or pref 98 MHz .

These dont have to be super stable over temperature-Â  since I disclipine 
that oscillator to an off-the-shelf cheap arse 10 MHz chip TCXOÂ  that 
costs $5Â  (1ppm is plenty ! ) .

*** Tweaking temperature to tweak frequency might just be useful. Of 
course, I am going to have to think about this, as the low end will be 
where the equipment temp can get to...

Looking at the temperature frequency curves for different angles cuts 
for 3OT crystals, for example, and my understanding of this stuff is 
rudimentary compared to a crystal expert :Â  A 0 second cut yields a 23 
ppm from 25 deg C to 87 deg C. at 70 deg C, in this graph this is +8ppm, 
IE the crystal might need to be cal-ed for 8ppm low.

DO you feel this might be an avenue to persue ? I certainly need to get 
some characteristic data first into my spreadsheets before I go off on this.

-glen


On 9/12/2023 3:03 pm, Richard (Rick) Karlquist wrote:
>
>
> On 12/7/2023 12:07 PM, glen english LIST wrote:
>>
>> All our crystals have undergo the process of preaging, also called 
>> "accelerated aging" (i.e. 3 days storage at +105 deg.C). This aging 
>> is equivalent to one year aging at normal temperature (according 
>> standard IEC 60122-1). The crystals produced for you had frequency 
>> shift after this preaging below 1.0 ppm, so it guaranties aging below 
>> 10 ppm after 10 years. The aging curve shows deceleration 
>> (saturation) in time.
>> Information to pulling parameter:
>
> This kind of discussion about "guaranteed aging" is completely at odds
> with everything I observed over many years working for HP.  The top
> HP experts on crystals never talked about crystals being so predictable.
> These experts were involved in inventing the SC cut, etc.
> They taught the rest of the industry how to make crystals.
> I personally observed many crystals aging vs time and vs temperature
> trying to "sort" out the good ones.  Crystals would be good for while, 
> then for no reason might drift in the opposite direction. I am
> especially skeptical of "3 days at 105 deg C is worth 10 years of
> aging."Â  The E1938A oscillator had an oven set point of around
> 105 degrees C.  It did not accelerate the aging compared to an
> 80 degree set point and certainly didn't accelerate it following
> a hockey stick curve.
>
> Rick