Re: [time-nuts] Aging rate of crystals
Aging is a composite of phenomena sometimes resulting in a negative rate and sometimes in a positive rate (most common). Some causes that haven't been mentioned in this thread are the slow release of stress in the crystalline structure created by shock or temperature excursion, and the diffusion of contact metalization into the crystal. A transistors gain can change with time and temperature, thus changing the phase shift and forcing the oscillating frequency to move up or down the phase plot of the crystal to compensate. Other changes in passive components can cause the same effect. I suppose one might also expect that atoms may be slowly shed from the bulk over time and (probably) increase the frequency. Somewhere, I have a NASA pub that describes a technique using Gamma Rays to accelerate aging so that later aging is much reduced, can't seem to find it now. I would guess that the radiation cause the stresses to relax. NASA was evidently interested because satellites experience a lot more radiation than we receive here on the surface and it probably caused a rapid frequency shift in otherwise unradiated crystals. I have two HP quartz oscillators that I've been running and logging for well over a decade. They run 24/7 and are on battery backup. The HP-103 shows about 6 parts in 10^-12/day and the HP-107 about 2 parts in 10^-13/day. I attribute this to steady temperature and solid mounting in a heavy rack. -Mike- At 03:41 PM 2/18/2008, you wrote: The long term aging rate is due entirely to the crystal, for all practical purposes, for any well designed oscillator circuit (or even a mediocre design). The aging of the crystal is basically not predictable. It's like the famous saying by J P Morgan when asked what the stock market will do: It will fluctuate. About the best you can do is test the aging for a few months and hope it won't get worse in the future. You have to be careful about getting an oscillator that simply got lucky during your aging test and put in much better than typical numbers. This can happen if the direction of aging changes (not unusual) in the middle of the aging test. You shouldn't overpromise aging compared to what you know your process can support. Other than holding the temperature constant, there is nothing else you need to do to get the best aging the crystal can do. If you get a lucky oscillator that has really good aging, it might continue to be really good, but there is no guarantee. Cheap crystals might have more predictable aging due to outgassing processes. However, this will be a large amount of aging. As you eliminate known causes of aging, it gets less predictable. Rick Karlquist N6RK [EMAIL PROTECTED] wrote: I learn from this discussion that the aging rate claimed by manufacturers would refer to the aging of the whole assembly, not the crystal alone. And for practical purposes that is correct. And even in the case of sealed assemblies, components other than the crystal itself may affect the overall measured drift. So my original question on this subject seems to lose any sense, because we will never be able to measure the aging of the crystal alone (if any, at this point) and hence variations in the aging rate either. Anyway some doubts of mine are not yet fully answered by this discussion, and I would appreciate your opinions. Given a good quality sealed OCXO running in constant ambient temperature, what kind of aging curve should one expect, a fluctuating one? (I understand that this might be the case, due to the interaction of known intrinsic aging factors having different timescales, as I've just learnt on this list. A regular curve would be hard to get). May it happen that fluctuations in frequency due to external causes such as tides, geomagnetic storms, or so, and not actually affecting the aging rate, are interpreted as fluctuations in the aging rate? I'm running a simple test comparing an OCXO (option 04E on a military Racal 1992 counter) to rubidium (LPRO), the counter being counting the LPRO. The test is running since about two weeks, and I started recording three days after power up. In the first days the OCXO showed a decreasing drift starting with some 3x10e-10 per day until it reached a stability within +/- 1x10e-10 in the last 5 days (that is, since 5 days back, the counters reads always the same value +/- the occasional uncertainty of the rightmost (11th) digit (10 seconds gate time). The OCXO specs are = 5x10e-10 per day. I didn't notice whether it is sealed, and won't check right now. I don't expect that the counter will always stay there, and I don't know what to think when the drift (aging rate?) will change. 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
Re: [time-nuts] Aging rate of crystals
I'm not familiar with the E1938, but the 10811, I believe is one of the small hi stab units that HP put into their higher end counters. It uses a single oven where the 103 and 107 used double ovens. Incidentally, the 103 uses a 1 MHz rock and the 107 uses a 5 MHz rock. -Mike- At 03:27 PM 2/19/2008, you wrote: Mike Fahmie wrote: Somewhere, I have a NASA pub that describes a technique using Gamma Rays to accelerate aging so that later aging is much reduced, can't seem to find it now. I would guess that the radiation cause the stresses to relax. NASA was evidently interested because satellites experience a lot more radiation than we receive here on the surface and it probably caused a rapid frequency shift in otherwise unradiated crystals. I remember some of the crystal gurus talking about this. I suspect it didn't pan out or everyone would be doing it. I also remember them saying that radiation causes color centers to appear. I have two HP quartz oscillators that I've been running and logging for well over a decade. They run 24/7 and are on battery backup. The HP-103 shows about 6 parts in 10^-12/day and the HP-107 about 2 parts in 10^-13/day. I attribute this to steady temperature and solid mounting in a heavy rack. -Mike- That's incredible Mike. I've never seen a 10811 or E1938 within a factor of 10 of the first number you gave, let alone the second. The second rate would be very respectible for a Rb standard. I believe those antique oscillators you have are using non-HP made xtals at 1 MHz (or 5 MHz at the most) in glass packages. While a steady temperature and solid mounting is great, it takes more than that to put up these kind of numbers. Congratulations, keep taking good care of those old war horses. I wish Len Cutler were still around to tell about it. He proudly keep a 107 prototype in his office. Len couldn't bring himself to design anything that wasn't a doomsday machine. Rick Karlquist, N6RK ___ 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.
Re: [time-nuts] Aging rate of crystals
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. ... At the beginning of the E1938A project, I did a bunch of characterization of 10811 oscillators. At the Santa Clara Division, we had first class environmental test chambers with heating, cooling, humidification, de-humidification, and nitrogen purge. The nitrogen was also available for fast cooling. The 10811 response to humidity was very rapid, like 10 or 15 minutes, almost as fast as the chamber itself could ramp. This occurred whether going from dry to humid or the other way around. I don't remember seeing any slow tails on the response. The immediate humidity response was on the order of a month of aging, so any humidity related aging effects would be masked. Rick Karlquist N6RK Rick, For these experiments did you remove the 10811 guts from the outer case? I realize the case is not sealed, but the air gap is very small; how could humidity get inside so rapidly? Did you look into /why/ the 10811 was humidity sensitive? The resonator and most individual board components are sealed, so that doesn't leave too much. Maybe the coarse tuning variable capacitor, which is exposed to air through its 2 mm hole? Do you know if most modern high-end OCXO, which are solder sealed, and which have no screwdriver tuning access hole, are immune from all humidity variations? /tvb ___ 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.
Re: [time-nuts] Aging rate of crystals
The long term aging rate is due entirely to the crystal, for all practical purposes, for any well designed oscillator circuit (or even a mediocre design). The aging of the crystal is basically not predictable. It's like the famous saying by J P Morgan when asked what the stock market will do: It will fluctuate. About the best you can do is test the aging for a few months and hope it won't get worse in the future. You have to be careful about getting an oscillator that simply got lucky during your aging test and put in much better than typical numbers. This can happen if the direction of aging changes (not unusual) in the middle of the aging test. You shouldn't overpromise aging compared to what you know your process can support. Other than holding the temperature constant, there is nothing else you need to do to get the best aging the crystal can do. If you get a lucky oscillator that has really good aging, it might continue to be really good, but there is no guarantee. Cheap crystals might have more predictable aging due to outgassing processes. However, this will be a large amount of aging. As you eliminate known causes of aging, it gets less predictable. Rick Karlquist N6RK [EMAIL PROTECTED] wrote: I learn from this discussion that the aging rate claimed by manufacturers would refer to the aging of the whole assembly, not the crystal alone. And for practical purposes that is correct. And even in the case of sealed assemblies, components other than the crystal itself may affect the overall measured drift. So my original question on this subject seems to lose any sense, because we will never be able to measure the aging of the crystal alone (if any, at this point) and hence variations in the aging rate either. Anyway some doubts of mine are not yet fully answered by this discussion, and I would appreciate your opinions. Given a good quality sealed OCXO running in constant ambient temperature, what kind of aging curve should one expect, a fluctuating one? (I understand that this might be the case, due to the interaction of known intrinsic aging factors having different timescales, as I've just learnt on this list. A regular curve would be hard to get). May it happen that fluctuations in frequency due to external causes such as tides, geomagnetic storms, or so, and not actually affecting the aging rate, are interpreted as fluctuations in the aging rate? I'm running a simple test comparing an OCXO (option 04E on a military Racal 1992 counter) to rubidium (LPRO), the counter being counting the LPRO. The test is running since about two weeks, and I started recording three days after power up. In the first days the OCXO showed a decreasing drift starting with some 3x10e-10 per day until it reached a stability within +/- 1x10e-10 in the last 5 days (that is, since 5 days back, the counters reads always the same value +/- the occasional uncertainty of the rightmost (11th) digit (10 seconds gate time). The OCXO specs are = 5x10e-10 per day. I didn't notice whether it is sealed, and won't check right now. I don't expect that the counter will always stay there, and I don't know what to think when the drift (aging rate?) will change. 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.
Re: [time-nuts] Aging rate of crystals
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 I like your theory, it has a marvelous macroscopic physical component to it. A way to run that test without any bottled gas would be start during a very humid spell (the stabilize things at a humid level; say 80% RH), then to put the crystal assembly into a sealable plastic container (Tupperware for US folks) with a bunch of silica gel or other desiccant. The humidity in the container will drop to well below 20%, and stay there until you open the container. That's a pretty decent range to work over. Tom Frank, KA2CDK ___ 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.
Re: [time-nuts] Aging rate of crystals
At the beginning of the E1938A project, I did a bunch of characterization of 10811 oscillators. At the Santa Clara Division, we had first class environmental test chambers with heating, cooling, humidification, de-humidification, and nitrogen purge. The nitrogen was also available for fast cooling. The 10811 response to humidity was very rapid, like 10 or 15 minutes, almost as fast as the chamber itself could ramp. This occurred whether going from dry to humid or the other way around. I don't remember seeing any slow tails on the response. The immediate humidity response was on the order of a month of aging, so any humidity related aging effects would be masked. Rick Karlquist N6RK Thomas A. Frank wrote: 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 I like your theory, it has a marvelous macroscopic physical component to it. A way to run that test without any bottled gas would be start during a very humid spell (the stabilize things at a humid level; say 80% RH), then to put the crystal assembly into a sealable plastic container (Tupperware for US folks) with a bunch of silica gel or other desiccant. The humidity in the container will drop to well below 20%, and stay there until you open the container. That's a pretty decent range to work over. Tom Frank, KA2CDK ___ 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.
