[time-nuts] crystal againg fit (was: Excel logarithmic function)
kb8tq at n1k.org
Thu Nov 24 18:20:37 EST 2016
There *has* been a lot of research into these functions. The Frequency Control
Symposium archives have at least a few dozen papers on the why and how
of the functions working. They are now behind a paywall for me so those who have
the luxury of access will have to dig for them on their own.
> On Nov 24, 2016, at 5:03 PM, Scott Stobbe <scott.j.stobbe at gmail.com> wrote:
> Sadly I don't think there is a concise answer to this, in reality you would
> make the decision on the fly depending on how much data you have and which
> model is the most well behaved.
> I think it's a really interesting topic to see some of what goes into an
> OCXO, a guaranteed limit on aging is one the many things.
> Part of the reason that information on the topic is somewhat is scattered,
> is if a commercial application genuinely needed 1e-12 stability for 100
> days free-running, the answer without hesitation would be atomic. Then as
> you dial back the long-term stability requirement how much NRE are you
> willing to spend; which is also why there doesn't seem to plenty of worked
> examples out there.
> On Thu, Nov 24, 2016 at 10:49 AM, Attila Kinali <attila at kinali.ch> wrote:
>> On Thu, 24 Nov 2016 08:16:08 -0500
>> Bob Camp <kb8tq at n1k.org> wrote:
>>> If you take the bad aging (out of spec) parts out of the pile, those are
>> the ones
>>> with the best fit. They have very pretty curves and they stick to those
>>> for a *long* time. They have a single dominant cause for their aging ( =
>> the defect).
>>> The rest of the parts have all of the causes bashed down by the process
>> so that
>>> over a 20 or 30 year span, there probably is no single dominant cause.
>> Then the question becomes: What would be a good fitting function for
>> the typical application of an OCXO that is regularly measured with
>> not too long time spans (e.g. GPSDO)? From the discussion it seems
>> that a second or third order Taylor would be sufficient to capture
>> aging for a span of 10-100 days.
>> Attila Kinali
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