John 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?
Short answer -- it all depends. But it usually takes much less than
you'd expect.
In my experience, supported by experimentation and by research into
published and credible anecdotal sources, the aging of quartz
oscillators often changes with little provocation (and in some cases,
none at all that one can tell from external observations). Sufficient
provocaton can include the oven cooling down, trimming the frequency,
physical shock (not necessarily very much -- sometimes just moving the
OCXO from one place to another and setting it down pretty gently), or
even a short loss of power. In short, *any* electrical or physical
disturbance.
The effects can range from a short period of settling with an asymptotic
slope back to the neighborhood of the previously-established aging rate,
all the way to beginning a completely new aging regime. Not
infrequently, even the sign of the aging rate changes. Further, any
given oscillator can react differently each time it is disturbed -- an
oscillator that previously settled quickly back to the neighborhood of
the previously-established aging may start a whole new aging regime the
next time it is disturbed.
That said, OCXOs may exhibit trends, behaving at least somewhat
consistently from one electrical disturbance to another (their reactions
to physical disturbances are always less consistent, IME).
Best regards,
Charles
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