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.. -------------------------------------------- On Fri, 3/8/19, Attila Kinali <attila@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@lists.febo.com> Date: Friday, March 8, 2019, 4:45 PM On Fri, 8 Mar 2019 06:31:48 -0600 Dana Whitlow <k8yumdoober@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 _______________________________________________ time-nuts mailing list -- time-nuts@lists.febo.com To unsubscribe, go to http://lists.febo.com/mailman/listinfo/time-nuts_lists.febo.com and follow the instructions there.