[time-nuts] PRS-10 Warm-up Time, Calibrating/Adjusting, and long-term poweron

[JF PICARD]

A PRS10 with a long shelf life will need more than 10 months (not days !) to get its final drift. Its dépends of the homogeneity of the gas mixture (Rb85,87 and krypton) in the cell and a long non running time affects the mixture. After the end of this warm up period,  adjustement is time consuming as the drift is parabolic and the top of the parabole tends to flatten with the successive adjustements. You can get 1 or 2 x 10^-11 and the retrace  is in order of this magnitude after a couple of days without power. At this magnitude of adjustement you have to look at the barometric pressure to avoid false adjustements but the effect is little compared with the 5065A whose tube is much bigger (and with less noise...). The 5065A is a very good barometer but a little bit costly..



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On Fri, 3/8/19, Attila Kinali <attila at kinali.ch> wrote:

 Subject: Re: [time-nuts] PRS-10 Warm-up Time, Calibrating/Adjusting, and long-term poweron
 To: "Discussion of precise time and frequency measurement" <time-nuts at lists.febo.com>
 Date: Friday, March 8, 2019, 4:45 PM
 
 On Fri, 8 Mar 2019 06:31:48
 -0600
 Dana Whitlow <k8yumdoober at gmail.com>
 wrote:
 
 > The point here
 is that there are apparently a number of warm up drift
 > mechanisms operating, some of which take
 days to sensibly settle down.
 
 Longer. I know of one measurement, where the Rb
 had a kind of stable
 drift until it suddenly
 switched to another slope quite suddenly
 (within a few days) about half a year after
 power up.
 
 The aging
 mechanisms of Rb vapor cell standards are many and not
 all of them are well understood, much less
 controlled. Compared
 to that, an OCXO has
 "only" thermal stability of the oven, strain
 relaxation of the holder/crystal and
 deposition/removal of contaminants
 on the
 crystal surface. Ok, there are a couple more, but these
 three
 are the main contributors for most
 OCXO out there. While for the
 Rb vapor cell
 standard I could name you half a dozen just like that
 and I am far from being an expert on these.
 
 For those interested, John Vig
 wrote a couple of papers on the aging
 of
 OCXO in the 80s and 90s. The topic of Rb vapor cell aging is
 a lot
 more messy and I don't know
 whether there is any good paper that reviews
 the main contributors.
 
             Attila Kinali
 -- 
 It is upon moral qualities
 that a society is ultimately founded. All 
 the prosperity and technological sophistication
 in the world is of no 
 use without that
 foundation.
                  -- Miss
 Matheson, The Diamond Age, Neal Stephenson
 
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