Hi Exact info on mass transfer is a bit complicated. A 5 MHz 5th overtone is a bit thicker and more massive than a 100 MHz 5th. Both are thicker (and more massive) than a 100 MHz fundamental. On top of that the blank is not equally sensitive to mass at all points on it’s surface. Finally, gold has a bit more mass than hydrogen. A layer of one is not quite the same as a layer of the other.
All that said, The standard “gee wiz” number is that 1 ppb is an atomic layer on a 5 MHz thrid. Given all of the hand waving, it’s a back calculated number based on calibrating the crystal with a thin film of gold (under these conditions …. on that design … calculated after XXX beers ...). Bob > On Nov 12, 2016, at 8:56 PM, Scott Stobbe <[email protected]> wrote: > > Those are wonderful plots :) > > I vaguely recall that a 1ppm frequency shift is approximately equivalent to > the mass transfer of one molecular layer of a crystal. So at some point > your counting atoms if there was no noise, thermal disturbance, mechanical > disturbance... > > On Sat, Nov 12, 2016 at 5:00 PM Tom Van Baak <[email protected]> wrote: > >> There were postings recently about OCXO ageing, or drift rates. >> >> I've been testing a batch of TBolts for a couple of months and it provides >> an interesting set of data from which to make visual answers to recent >> questions. Here are three plots. >> >> >> 1) attached plot: TBolt-10day-fit0-e09.gif ( >> http://leapsecond.com/pages/tbolt/TBolt-10day-fit0-e09.gif ) >> >> A bunch of oscillators are measured with a 20-channel system. Each >> frequency plot is a free-running TBolt (no GPS, no disciplining). The >> X-scale is 10 days and the Y-scale is 1 ppb, or 1e-9 per Y-division. What >> you see at this scale is that all the OCXO are quite stable. Also, some of >> them show drift. >> >> For example, the OCXO frequency in channel 14 changes by 2e-9 in 10 days >> for a drift rate of 2e-10/day. It looks large in this plot but its well >> under the typical spec, such as 5e-10/day for a 10811A. We see a variety of >> drift rates, including some that appear to be zero: flat line. At this >> scale, CH13, for example, seems to have no drift. >> >> But the drift, when present, appears quite linear. So there are two things >> to do. Zoom in and zoom out. >> >> >> 2) attached plot: TBolt-10day-fit0-e10.gif ( >> http://leapsecond.com/pages/tbolt/TBolt-10day-fit0-e10.gif ) >> >> Here we zoom in by changing the Y-scale to 1e-10 per division. The X-scale >> is still 10 days. Now we can see the drift much better. Also at this level >> we can see instability of each OCXO (or the lab environment). At this >> scale, channels CH10 and CH14 are "off the chart". An OCXO like the one in >> CH01 climbs by 2e-10 over 10 days for a drift rate of 2e-11/day. This is >> 25x better than the 10811A spec. CH13, mentioned above, is not zero drift >> after all, but its drift rate is even lower, close to 1e-11/day. >> >> For some oscillators the wiggles in the data (frequency instability) are >> large enough that the drift rate is not clearly measurable. >> >> The 10-day plots suggests you would not want to try to measure drift rate >> based on just one day of data. >> >> The plots also suggest that drift rate is not a hard constant. Look at any >> of the 20 10-day plots. Your eye will tell you that the daily drift rate >> can change significantly from day to day to day. >> >> The plots show that an OCXO doesn't necessarily follow strict rules. In a >> sense they each have their own personality. So one needs to be very careful >> about algorithms that assume any sort of constant or consistent behavior. >> >> >> 3) attached plot: TBolt-100day-fit0-e08.gif ( >> http://leapsecond.com/pages/tbolt/TBolt-100day-fit0-e08.gif ) >> >> Here we look at 100 days of data instead of just 10 days. To fit, the >> Y-scale is now 1e-8 per division. Once a month I created a temporary >> thermal event in the lab (the little "speed bumps") which we will ignore >> for now. >> >> At this long-term scale, OCXO in CH09 has textbook logarithmic drift. Also >> CH14 and CH16. In fact over 100 days most of them are logarithmic but the >> coefficients vary considerably so it's hard to see this at a common scale. >> Note also the logarithmic curve is vastly more apparent in the first few >> days or weeks of operation, but I don't have that data. >> >> In general, any exponential or log or parabolic or circular curve looks >> linear if you're looking close enough. A straight highway may look linear >> but the equator is circular. So most OCXO drift (age) with a logarithmic >> curve and this is visible over long enough measurements. But for shorter >> time spans it will appear linear. Or, more likely, internal and external >> stability issues will dominate and this spoils any linear vs. log >> discussion. >> >> So is it linear or log? The answer is it depends. Now I sound like Bob ;-) >> >> /tvb >> _______________________________________________ >> time-nuts mailing list -- [email protected] >> To unsubscribe, go to >> https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts >> and follow the instructions there. > _______________________________________________ > time-nuts mailing list -- [email protected] > To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts > and follow the instructions there. _______________________________________________ time-nuts mailing list -- [email protected] To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts and follow the instructions there.
