At the beginning of the E1938A project, I did some humidity tests on the 10811. It was fairly sensitive to humidity. I think I remember being able to get parts in 10^8 shift. The E1938A, having the bridge oscillator circuit, is completely insensitive to humidity and nearly so to temperature (10^-13 per degree C). It's aging is basically the same as the 10811, since the crystals are basically the same (different package).
Rick Karlquist N6RK Neville Michie wrote: > This is a theory that I have been thinking about for some time. > A possible physical process for crystal ageing is the desorption of > water from > surfaces in the oscillator circuit. > Most solid surfaces, particularly those with oxygen in the molecular > structure, > have at least a monolayer of water over the surface. > In high vacuum laboratory work you bake glassware at 300*C for 4 > hours in a > hard vacuum to remove this water to prevent future degassing. > > When you have an oven with air interchange to the ambient, the > humidity in the oven becomes very low. For example air at 20*C and > 65% RH > drops to 3.2% RH if heated to 80*C. (the vapour pressure of water is > still 1520 Pascals) > > Relative humidity is a good predictor of the amount of moisture > absorbed and adsorbed > by a solid. > The heating of the oven reduces the relative humidity, so much water > would leave a surface > on warm-up but the last of the water is tightly bound and to reach a > thermodynamic equilibrium under > these conditions is very slow. > > If the air at room temperature had the humidity reduced to 32.5%, > then the RH in the oven > would reduce to 1.6%, so the oscillator would still respond to the > change in humidity. > > The main evidence to support this theory is that it is a plausible > physical process with > slow enough time constants and known hysteresis that could explain > the days it takes > for my HP 10811A to return to the control voltage it formerly > required to be on frequency > after it has been allowed to cool down for 2 days. > The best experiment I can think of to prove this is to run the > oscillator in a paper bag until it is stable, > then trickle a flow of dry nitrogen into the bag for a day or two > and watch for oscillator drift as the humidity > in the oven drops to extremely low values. > It is a pity that I do not have bottled gas on tap any more. > cheers, Neville Michie > > On 16/02/2008, at 7:24 AM, Rick Karlquist wrote: > >> For ovenized crystals, any oven temperature change will >> cause aging to temporarily increase (and may change the >> direction as well). Restabilization may take an hour >> to a day, depending on how much the temperature was changed. >> We haven't noticed that powering up the oscillator or not >> makes a big difference. (This refers to leaving the oven >> on, and turning off the oscillator circuitry. This experiment >> This is a theory that I have been thinking about for some time.is >> easy to do on a 10811 since the supplies are separate.) >> Does that answer your question? >> >> Rick Karlquist N6RK >> >> >> [EMAIL PROTECTED] wrote: >>> Hi all, >>> the aging rate of crystals is known to be not constant. >>> Is there any known external cause affecting the rate, or it is only a >>> matter of casuality? >>> Thanks, >>> Antonio I8IOV >>> >>> >>> _______________________________________________ >>> time-nuts mailing list -- time-nuts@febo.com >>> To unsubscribe, go to >>> https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts >>> and follow the instructions there. >>> >>> >> >> >> >> _______________________________________________ >> time-nuts mailing list -- time-nuts@febo.com >> To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/ >> time-nuts >> and follow the instructions there. > > _______________________________________________ time-nuts mailing list -- time-nuts@febo.com To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts and follow the instructions there.