Hi This is your design, and under your control. Looking at one plot here or there and trying to guess what is going on is not a really good way to do this. The whole sub-thread we are on is simply a result of a “if it’s not crystal aging it can’t be anything else” comment way way back. My point here is that it *can* be something else and the list of things it *can* be is actually quite long. The voltage measurement stuff is simply one example out of at least a dozen and probably closer to a hundred possibles. Digging through all of those possible things is a lot of work. It’s work that can only be done “hands on” with a set of units and test gear. My first step would be to toss the setup into an environmental chamber and do some 48 hour temperature sweeps.
Aging is a “long term” drift. It goes on for years. Warmup is a very short term effect. It goes on for hours or days. Retrace is the process of re-settilitg to the previous long term aging line. It can take days / weeks / months depending on the oscillator. If you were buying the OCXO’s as an OEM, the specs you bought them to would be a function of what you asked for and how much you were willing to pay. It is unlikely that as an OEM you would have requirements on retrace and warmup, and aging. If you did have a spec it would be under fairly specific conditions (on power for three months, measure frequency, off power at XX C for 24 hours, on power again for 24 hours at YY C, measure delta frequency. That would cover warmup, but really says nothing about aging or retrace. Regardless of if an OCXO is spec’d for this or that issue or not, it experiences it. There are a lot of other things that OCXO’s do that many or may not be spec’d. When using one and digging into it, you have to deal with all the issues, regardless of if there is a spec or not. That assumes you want to dig in at this level. A *very* reasonable question is - what level do you want to dig into? That is why I bring up the good old “what is the goal?” question on a regular basis. Without a goal in mind, you will keep digging ever deeper. The number of issues you need to look into grows exponentially as you dig deeper. The time, learning, equipment, experiments, and number of test units each go up rapidly. It is work, equipment, and experiments that only apply to your design. It is not a piggyback process as you go deeper. Yes, that’s a bit of a long winded reply … sorry about that. Bob > On Nov 7, 2016, at 2:23 PM, Bob Stewart <[email protected]> wrote: > > Hi Bob, > > OK, given that, what is your view of the plot I presented? Let's remember > that I plotted this because I was trying to discover whether the EFC > circuitry has a time-related drift, or whether the DAC value drift I plotted > with the GPSDO locked to the GPS was caused by the OCXO. > > In one of your posts today, you talked about a long-term retrace lasting some > months. I've been using the term "aging". Has my choice of terms caused the > discussion to take a turn that it wouldn't have taken if I had used the term > "retrace"? The fact is that I don't know whether it's aging or retrace. I'm > not really clear on how to tell the difference. I'm especially handicapped > by not having the mfg specs for the OCXOs I use. It could be that I simply > haven't had the test unit under power for long enough to let the OCXO settle > out. And for sure when I added the test lead to the EFC (breaking a trace in > the process) there was enough off time to thoroughly insult the OCXO. > > Bob > > ----------------------------------------------------------------- > AE6RV.com > > GFS GPSDO list: > groups.yahoo.com/neo/groups/GFS-GPSDOs/info > > > From: Bob Camp <[email protected]> > To: Bob Stewart <[email protected]>; Discussion of precise time and frequency > measurement <[email protected]> > Sent: Monday, November 7, 2016 1:01 PM > Subject: Re: [time-nuts] Thermal impact on OCXO > > Hi > > Thermocouples in test leads are nasty because they operate on the temperature > delta rather than the absolute temperature. It’s the gradient you have to > worry about. > Until you have run out a few dozen sensors around your bench (or test > chamber) and > monitored them for a few days … you won’t believe just how little “point A” > has in common > with “point B”. > > Bob > > > On Nov 7, 2016, at 1:44 PM, Bob Stewart <[email protected]> wrote: > > > > -accidentally omitted timenuts from my reply to bob- > > Hi Bob, > > The data is at the 10uV level. As to whether I've plotted "data" or data, > > I can only report what I have. It seems to be consistent over the long > > run. I would expect to see something else if it were just noise. If the 4 > > attachments were strongly thermocoupled, wouldn't the data have a stronger > > correlation to temperature, rather than just to temperature transients? > > > > Bob ----------------------------------------------------------------- > > AE6RV.com > > > > GFS GPSDO list: > > groups.yahoo.com/neo/groups/GFS-GPSDOs/info > > > > From: Bob Camp <[email protected]> > > To: Bob Stewart <[email protected]> > > Cc: Discussion of Precise Time and Frequency Measurement > > <[email protected]> > > Sent: Monday, November 7, 2016 11:54 AM > > Subject: Re: [time-nuts] Thermal impact on OCXO > > > > Hi > > > > I would suggest you read the papers on the subject. They are out there. > > Even over a few days > > OCXO aging is likely to be non-linear ( => curved, not straight line). On > > an OCXO that is > > warming up, your are dealing with retrace rather than aging. This can have > > an impact for a > > few months after turn on. I have one unit in the basement that took 9 > > months to come out > > of retrace after being in storage for “a while”. It was an eBay item so no > > idea just how long > > the power off time was. > > > > Bob > > > > > >> On Nov 7, 2016, at 12:47 PM, Bob Stewart <[email protected]> wrote: > >> > >> Hi Bob, > >> > >> When you say that OCXOs don't age in a linear fashion, what does that > >> mean? IOW, is this a case where it's almost linear over a week, and the > >> non-linearity is only detectable when you consider the longer term? If > >> that's the case, then it seems reasonable to use the past 3 or so days of > >> data collection to project the near-term behavior; where near-term is less > >> than 3 days into the future. > >> > >> Bob > >> > >> ----------------------------------------------------------------- > >> AE6RV.com > >> > >> GFS GPSDO list: > >> groups.yahoo.com/neo/groups/GFS-GPSDOs/info > >> > >> > >> From: Bob Camp <[email protected]> > >> To: Bob Stewart <[email protected]>; Discussion of precise time and > >> frequency measurement <[email protected]> > >> Cc: Scott Stobbe <[email protected]> > >> Sent: Monday, November 7, 2016 6:08 AM > >> Subject: Re: [time-nuts] Thermal impact on OCXO > >> > >> Hi > >> > >> > >>> On Nov 5, 2016, at 10:43 PM, Bob Stewart <[email protected]> wrote: > >>> > >>> Hi Scott, > >>> D'oh. Thanks for the correction! Like I said, I don't do these > >>> calculations often. > >>> > >>> If as Bob Camp implies, the aging isn't from the OXCO, then I'm a bit > >>> stumped. I do have an op-amp in the EFC string with a voltage divider > >>> for gain. The resistors are Panasonic ERA-6AEDxxxV resistors. Mouser > >>> says they're temperature stable to 25PPM/C, but of course they don't > >>> mention an aging rate. I don't really see anything else, other than the > >>> OCXO, that is likely to be prone to a linear type of aging. > >> > >> OCXO’s don’t age in a linear fashion. At least 90% of them don’t. If you > >> dig into the FCS papers there are various > >> curves proposed as models. Mil-O-55310 has one of them as the “official” > >> approach. All of them have the basic > >> issue of mistakenly fitting to to short a time constraint. > >> > >> Bob > >> > >>> The aging rate appears to be stable from unit to unit, so naturally I > >>> considered the OCXO first. > >>> > >>> There is one other bit in the EFC string that might be controversial, but > >>> I don't see that it would be a candidate for the symptoms of aging. > >>> > >>> Bob > >>> ----------------------------------------------------------------- > >>> AE6RV.com > >>> > >>> GFS GPSDO list: > >>> groups.yahoo.com/neo/groups/GFS-GPSDOs/info > >>> > >>> From: Scott Stobbe <[email protected]> > >>> To: Bob Stewart <[email protected]> > >>> Cc: Discussion of Precise Time and Frequency Measurement > >>> <[email protected]> > >>> Sent: Saturday, November 5, 2016 9:19 PM > >>> Subject: Re: [time-nuts] Thermal impact on OCXO > >>> > >>> If your DAC spans the full EFC range than 1LSB is 1/2^20 ~ 1 PPM of the > >>> EFC range, and the EFC tuning range is 8/10E6 ~ 1 PPM full scale, so 1 > >>> LSB is ~1PPT. So, if everything else is stable the DAC code reflects > >>> changes solely due to the OCXO, which would be an aging of 24 PPT/day. > >>> On Sat, Nov 5, 2016 at 9:57 PM, Bob Stewart <[email protected]> wrote: > >>> > >>> Hi Scott, > >>> The 20 bits span about 6 volts. The EFC range spans about 8Hz (+/-4Hz). > >>> I don't do these calculations every day, but that's about 4.5PPT? > >>> Bob ------------------------------ ------------------------------ ----- > >>> AE6RV.com > >>> > >>> GFS GPSDO list: > >>> groups.yahoo.com/neo/groups/ GFS-GPSDOs/info > >>> > >>> > >>> > >>> From: Scott Stobbe <[email protected]> > >>> To: Bob Stewart <[email protected]>; Discussion of precise time and > >>> frequency measurement <[email protected]> > >>> Sent: Saturday, November 5, 2016 8:38 PM > >>> Subject: Re: [time-nuts] Thermal impact on OCXO > >>> > >>> I think that's a nice plot, it looks like you have stepped 160 LSB over 7 > >>> days or roughly 1 LSB per hour. With a 20bit dac you are trimming maybe 1 > >>> ppt/LSB to 4 ppt/LSB? In allan devation terms, the case of 1ppt/LSB, > >>> solely due to drift, you're at 1E-12 at 3600*sqrt(2) = 5000 s, in the > >>> case of 4ppt/hour your at 1E-12 at 1280 s. Seems reasonable. > >>> On Sat, Nov 5, 2016 at 2:47 PM, Bob Stewart <[email protected]> wrote: > >>> > >>> Oh dear. I attached the wrong file. Here's the correct one. > >>> ----------------------------- ------------------------------ ------ > >>> AE6RV.com > >>> > >>> GFS GPSDO list: > >>> groups.yahoo.com/neo/groups/ GFS-GPSDOs/info > >>> > >>> > >>> > >>> ______________________________ _________________ > >>> 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. > > _______________________________________________ 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.
