Re: [time-nuts] PRS-10 Warm-up Time, Calibrating/Adjusting, and long-term poweron
Moin, I'm sending this anwer to time-nuts as well (with permission of Taka) as this might be generally interesting. On Sat, 9 Mar 2019 04:23:27 + (UTC) Taka Kamiya wrote: > I am experiencing what you are talking about "live". > I have an experimental setup where PRS-10 is being steered by Trimble > Resolution-T. PRS-10 must be way off as it has been 3 hours and still has > not phase locked. (physics lock was established long ago) On LadyHeather, I > can see a graph with steady decline, and as I understand it, it represents > delta between the two. Rate of decline is starting to slow down, so it must > be approaching locking point. Once I see it locks, I will have to make few > hardware changes and restart it. I don't know what the PRS10 uses internally, but I wouldn't be surprised if they would just do a long time-constant PID loop. As most people will run a PRS10 continuously, having to wait a day or two for phase lock with a GPS source is not that much of an issue. > I am not in hurry to get it to lock. What I really want is a stable standard > once it is locked. I am actually testing 4 time standards at the same time: > one for each channel of scope. (Cs, Rb, GPSDRb, GPSDO) The winner will > become my house standard. I think you are making here a beginers mistake. You assume that there is one standard that fits all needs. But truth is, each standard has its uses and at different taus different standards will be the best one. If you are in the confortable position of running all of these standards at the same time, then I would do just that. Then you can use the one standard that is best for what you are doing when you need it. If you want to do it a bit more fancy, there are ways to build ensembles out of different style standards and to combine them in such a way, that always the best dominates the (in-)stability at a certain tau. E.g. [1] describes a decent way how to achieve this. > This is just a test run though. The real test > will begin after few weeks of warm up. I will have to come up with some kind > of recording system. This will be a challenge as none of the standards have > GPIB. I'm thinking of possibly taking a photograph of scope every hour for > days, so I can see the drift. If you have access to a TICC then you can use Timelab for it. Alternatively, anything that can produce timestamps or time differences of some kind is enough. You can then feed this to Timelab or Stable32 for further processing. > I have shot my foot so many times, it's full of holes now. Each hole is the proof of experience :-) Attila Kinali [1] "Composite clock: a new algorithm for servoing a VCO firstly to a hydrogen maser clock and then to a caesium clock", by Mbaye, Makdissi, Plantard, Vernotte, 2008, https://doi.org/10.1088/0026-1394/45/6/S12 -- 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.
Re: [time-nuts] PRS-10 Warm-up Time, Calibrating/Adjusting, and long-term poweron
Hi Ok, if you are concerned about 1 us and not to concerned about 100 ns, then there’s not a lot to set up. A standard that is good to 10 ns / s will do just fine. That’s 10 ppb and a “typical” OCXO in a counter will do just fine. Leave it on for a few days and set it to frequency. There are maybe a few hundred GPS module manufacturers out there. Going through all the in’s and out’s to fiddle with each one is a major task. There *are* timing grade GPS modules out there They are “good” in the 10’s of ns without any real crazy stuff. They are good in the single digit ns with some effort. Unless this is a very large volume product, just use one of the well known parts and move on. The uBlox M8T is a modern part that will easily meet your needs. Furuno and others make parts that are at least as good. Cost wise, you are <$50 for small volume and much less in large volume. I would not bother with a part that has not been designed to do timing. They can have bugs in them that only manifest at the worst moments. (like two months later in the field). At the very least, start with a known good part to get your setup going before you mess with any thing else. These devices (at least the timing ones) all have delay adjustments on them. You can zero out any cable delays. The same is true of a TBolt. You can set it’s PPS pulse to be early or late relative to GPS time (= no leap seconds, UTC has leap seconds). This adjustment also lets you come up with a *much* easier way to test your modules. Take the TBolt and set it to be 1 us early. Put the TBolt into channel A and the device you are testing into channel B on your counter. Measure the time between the two channels. You now don’t have to worry about the standard on the counter, it’s only running for one us. The TBolt is spec’d to be < +/- 100 ns of GPS all the time. They normally wobble around by < 10 ns. Lots of fun !!! Bob > On Mar 9, 2019, at 2:04 AM, Forrest Christian (List Account) > wrote: > > This seems like as good of a message to reply to as any. Thanks to > everyone who has replied so far - lots of good information, which is > right in the category of what I was looking for. > > Let me clarify what I'm hoping to measure. I apologize if some of > the terminology below is wrong, I'm still learning correct use of some > of the terms - I've tried to explain in a way where it is obvious what > I'm talking about even if the terms are slightly wrong. > > The GPS receivers I'm hoping to measure are used in an application > where the 1PPS is used to synchronize radio transmissions. Generally > one wants the pulse to be within a couple uS or so of the top of the > second.Older radios cared less, newer ones want it to be more > precise. Sorry about the soft spec, it unfortunately is what it is. > One note is that there is some expectation that there will be be > some fixed offset from the UTC second due to cable delays and the > like, so I'm less worried about a reasonably low fixed offset and > more about the variable (jitter) offset.I.E. 1uS +-100nS is > perfectly fine, 1uS +-1uS isn't so hot. > > In evaluating a new set of GPS receivers for this application, I'm > hoping to gather Pulse-to-Pulse delay figures for every pulse the GPS > receiver outputs over a week or so. I might end up repeating it in > various forms, including moving the GPS receiver into an > "environmental chamber" (aka modified chest freezer) to verify that > they still behave in low or high temperature - or if I can figure out > a reliable way to do so, to simulate various signal impairments such > as partial sky view. > > My intent is to then process the raw data to get a feeling for the > statistical nature of the 1PPS out of that particular GPS receiver. > For instance, how many pulses were outside the +-ns spec for the > receiver. What did the histogram of the in-spec pulses look like? > And so on. For some of the processing it's pretty obvious that I need > a clock source for the TICC which is going to be stable over the > entire period or else I'll end up measuring errors in the clock source > instead of the GPS receiver.It seems to me that if I'm looking for > a histogram supposedly confined to +-100nS, I'm probably going to want > to be able to measure around +-1nS with confidence. Much more than > that (0.1nS) seems a bit excessive, less than that (10nS) is too > coarse. > > Intuition and past experience implies that if I want to measure +-1nS > with confidence, I really need a slightly more accurate clock source > than the measurement itself. 0.1ppb over the measurement period seems > reasonable, 0.2ppb is probably good enough. I don't think I need > 0.02ppb. > > I replied in particular to Bob's message below since it seems to > confirm what I was thinking, even without me being verbose enough > about my application. It also sounds like powering this on for a day > or so before I start (or
Re: [time-nuts] PRS-10 Warm-up Time, Calibrating/Adjusting, and long-term poweron
This seems like as good of a message to reply to as any. Thanks to everyone who has replied so far - lots of good information, which is right in the category of what I was looking for. Let me clarify what I'm hoping to measure. I apologize if some of the terminology below is wrong, I'm still learning correct use of some of the terms - I've tried to explain in a way where it is obvious what I'm talking about even if the terms are slightly wrong. The GPS receivers I'm hoping to measure are used in an application where the 1PPS is used to synchronize radio transmissions. Generally one wants the pulse to be within a couple uS or so of the top of the second.Older radios cared less, newer ones want it to be more precise. Sorry about the soft spec, it unfortunately is what it is. One note is that there is some expectation that there will be be some fixed offset from the UTC second due to cable delays and the like, so I'm less worried about a reasonably low fixed offset and more about the variable (jitter) offset.I.E. 1uS +-100nS is perfectly fine, 1uS +-1uS isn't so hot. In evaluating a new set of GPS receivers for this application, I'm hoping to gather Pulse-to-Pulse delay figures for every pulse the GPS receiver outputs over a week or so. I might end up repeating it in various forms, including moving the GPS receiver into an "environmental chamber" (aka modified chest freezer) to verify that they still behave in low or high temperature - or if I can figure out a reliable way to do so, to simulate various signal impairments such as partial sky view. My intent is to then process the raw data to get a feeling for the statistical nature of the 1PPS out of that particular GPS receiver. For instance, how many pulses were outside the +-ns spec for the receiver. What did the histogram of the in-spec pulses look like? And so on. For some of the processing it's pretty obvious that I need a clock source for the TICC which is going to be stable over the entire period or else I'll end up measuring errors in the clock source instead of the GPS receiver.It seems to me that if I'm looking for a histogram supposedly confined to +-100nS, I'm probably going to want to be able to measure around +-1nS with confidence. Much more than that (0.1nS) seems a bit excessive, less than that (10nS) is too coarse. Intuition and past experience implies that if I want to measure +-1nS with confidence, I really need a slightly more accurate clock source than the measurement itself. 0.1ppb over the measurement period seems reasonable, 0.2ppb is probably good enough. I don't think I need 0.02ppb. I replied in particular to Bob's message below since it seems to confirm what I was thinking, even without me being verbose enough about my application. It also sounds like powering this on for a day or so before I start (or getting started and just throwing the first day's data away) might be reasonable to do and I don't need to let this thing run for months ahead of time to get to the accuracy I need. Of course, I'll do a bit of analysis on the data to try to verify that the unit isn't drifting. Out of curiosity, I'm also going to do some measurements on the couple of standalone OCXO's in my collection to see if either would be accurate enough for this particular measurement. The best one in my (admittedly limited) collection seems to be spec'd worse than I'd need, although I'm not sure how much aging it's done. None of them have seen any meaningful poweron time just because I've been too busy to play with them. I guess that at some point I should also up my game as far as good quality OCXO's since I do see how the right well-aged low-drift OCXO would probably be fine for this measurement. After reading everyone's response I'm still considering what to do as far as long-term runtime on the PRS10. I do know that I'm going to need this off and on for the next few months so once I get it in a permanent enclosure and get it powered up it will probably stay on continuously at least until I am done with this round of experiments, at which point it might get turned off with the hopes of extending it's service life. On Fri, Mar 8, 2019 at 8:06 AM Bob kb8tq wrote: > > Hi > > Some of this gets into just what you are trying to do. Cycle to cycle jitter > on the > PPS output of most GPS modules is in the “many ns” range. If sawtooth > correction > is not being applied, a measurement that is good to an accuracy of 1 ns / 5 = > 200 ps > would be plenty good enough. That is a 2x10^-10 (0.2 ppb) sort of accuracy. > > If you are looking at longer term effects, you may need better accuracy / > lower drift. > You can easily get past what a nice new 5071 can do heading down this road … > For > now let’s assume the target above is correct. > > The PRS-10 should be within 0.2 ppb within a few minutes after locking up. It > should > hold this sort of accuracy “on the shelf / power off” pretty much forever and > ever.
Re: [time-nuts] PRS-10 Warm-up Time, Calibrating/Adjusting, and long-term poweron
We have operated about 40 PRS10s over the past 20 years or so. These are all run continuously in benign environments and monitored via GPS time-transfer . Some have died after just over a year; others have operated for more than 12 years. A new one generally takes a few months to burn in, before its frequency drift stabilises to something like the specifications. They do not behave very predictably, showing sudden changes in frequency and so on. One exhibited frequent steps for a few years and then the problem went away. Trying to predict what they would do at the level of better than a few parts in 10^11 seems difficult. Cheers Michael On Sat, 9 Mar 2019 at 3:03 am, Attila Kinali wrote: > On Fri, 8 Mar 2019 06:31:48 -0600 > Dana Whitlow 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. > ___ 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.
Re: [time-nuts] PRS-10 Warm-up Time, Calibrating/Adjusting, and long-term poweron
> 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. What's going on there? Why/how does the mixture change? How does the mixture effect the frequency? If that is significant, how do they make the mixture at the factory accurately enough? Or is it small so they just tune around it? -- These are my opinions. I hate spam. ___ 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.
Re: [time-nuts] PRS-10 Warm-up Time, Calibrating/Adjusting, and long-term poweron
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 wrote: Subject: Re: [time-nuts] PRS-10 Warm-up Time, Calibrating/Adjusting, and long-term poweron To: "Discussion of precise time and frequency measurement" Date: Friday, March 8, 2019, 4:45 PM On Fri, 8 Mar 2019 06:31:48 -0600 Dana Whitlow 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. ___ 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.
Re: [time-nuts] PRS-10 Warm-up Time, Calibrating/Adjusting, and long-term poweron
今日は On Fri, 8 Mar 2019 14:09:20 + (UTC) Taka Kamiya via time-nuts wrote: > Why? Because nature of GPSDO and Rb, time constant is set to 2 to 3 hours. > (still experimenting) It takes few cycles of this to lock and stabilize. In > short, you'll be safe if you wait 24 to 48 hours. Rb modules are relatively > cheap. I really don't see a need to baby it. There are techniques to cut the "first lock time" down quite a bit. Most of them involve either switching of all the long time constant parts of the control loop or switching between different configurations (ie different multiplicative constants or even different topologies). The working principle of all is, that once you are reasonably close in frequency/phase, your long-time-constant loop will not have a large difference to work with and its internal state converges quickly to something close of what it should be. One very simple approach (which not always works) is to decompose your PI controller into a P and I part, and disable on startup the I part. Wait until the P part has gotten the error to something stable (not neccesarily small) then switch on the I term, with its internal state initialized to zero. A more sophisticated variant of this, uses an I part with a smaller time constant first to reduce the residual error, then estimates from its internal state the state of the real I part and switches over to that. Analysis of these dynamic loops can be a bit cumbersome and I recomend to read a good textbook on this topic before attempting to do something like this, as it's very easy to shot your foot. 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.
Re: [time-nuts] PRS-10 Warm-up Time, Calibrating/Adjusting, and long-term poweron
On Fri, 8 Mar 2019 06:31:48 -0600 Dana Whitlow 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.
Re: [time-nuts] PRS-10 Warm-up Time, Calibrating/Adjusting, and long-term poweron
Hi > On Mar 8, 2019, at 7:47 AM, Attila Kinali wrote: > > On Fri, 8 Mar 2019 01:18:45 -0700 > "Forrest Christian (List Account)" wrote: > >> 1) Assuming the PRS-10 has been off for a long time, how long should I >> plan on leaving this on for the 10Mhz to stabilize? I see the >> longest warmup time on the spec-sheet is 7 minutes - although this >> seems a lot shorter than I'd likely use in real life, I'm also not >> sure if there's much benefit to an excessively longer warmup time >> (like days), would like opinions on this. > > The warm-up time is from "I switched it on" to "there is a 10MHz signal > and it's 'stable'". I.e. at latest after 7 minutes you should be able > to use the ouptut of the PRS10. But keep in mind that the stable-after-warm-up > is not tha same as stable-for-a-time-nut. A Rb vapor cell standard has > a retrace (ie change of frequency after being switched on, for details see > John Vig's tutorial) of several weeks to a few months, depending on the > exact construction of the Rb cell, how long it has been in use and how > long it has been off. > > >> 2) Longer-term I'd like to use the 1PPS output from a Trimble >> Thunderbolt to calibrate the PRS10 and adjust if necessary just to >> trim out any aging drift on the PRS10. Initially I thought I was >> going to discipline the PRS10 on a continual basis with the >> Thunderbolt using the PPS input on the PRS10, but I've recently >> realized that leaving the PRS10 on permanently might not be the best >> option (see Question 3). So I'm looking for opinions on how to keep >> the PRS10 calibrated/adjusted. I.E. trim with the trimmer, adjust >> using digital commands, etc. > > Switching it on and off several times a month would be worse in > terms of longevity than having it running continuously. The vapor > cell itself is usually run between 60°C and 100°C and the Rb lamp > usually between 120°C and 170°C. As you can imagine, power cycling > gives a huge thermal strain on all the components. The inner construction > of the PRS10 is not optimized for power cycling but thermal insulation > of the sensitive components (see e.g. http://time.kinali.ch/Rb/PRS10/ ) > > So I would rather feed the PPS to the PRS10 directly and let itself > do the work. This will also give you an optimized control loop for > the performance of the PRS10 without you having to go through the > process of desiging and optimizing the loop. > > >> 3) As implied in #2, I was originally planning on leaving the PRS10 on >> a continuous basis. I've read a couple of things which imply that >> there is little benefit to doing so, and that every hour it's on >> consumes the lamp life. Assuming I only need the highly stable PRS10 >> source every few months for things like jitter measurements on 1PPS >> sources, is there any benefit to leaving the PRS10 on? > > If you want to do just jitter measurement, then I wouldn't use a Rb standard > but a stable OCXO instead. At averaging times below 1-10s an OCXO will beat > any Rb standard, even one that has an OCXO like the PRS10 (admittedly, it's > not a high quality OCXO but it's one none-the-less). An OCXO has a shorter > warm-up time (usually 2-3 minutes until stable, usually less than a day > until time-nuts-stable, less than a month until nutty-time-nut-stable). > > I personally, would use an OCXO as reference to the TICC (or TICCs?) > and use the PRS10 as an additional input to the TICC. This way you > can do a multi-way comparison between the GPSDOs and the Rb, removing > out the (in-)stability of the reference OCXO. > Putting some dimensions on this: A “telecom” Rb should be in the 0.01 ppb at one second (ADEV) range. It should improve by sqrt(tau) so at 100 seconds it will be at 0.001 ppb. It should improve some past that. Counting on 0.0001 ppb at 10,000 seconds …. not so much. A cheap / small OCXO may be at the same 0.01 ppb at 1 second level. An OCXO does not have a “predictable” improvement rate. You may have the same at 100 seconds as at 1 second. A very good (but maybe cheap … who knows …) OCXO could get you to 0.001 ppb at 1 second. You also could buy a few dozen to get one that actually does that. Testing could be involved to sort them out. Both the Rb and the OCXO have temperature stability specs on them. What those numbers are may be unknown on a surplus item. The “best case” claimed temperature stability on a telecom Rb is often better than the “best case” stability on your cheap OCXO. Indeed there are (rare) OCXO’s out there that get down to 0.0001 ppb at 1 second and hang in there out to 1,000 seconds. Finding one at all can be tough. Finding one cheap … you would have to be very lucky. Working out that you *do* have one will involve testing. Bob > > Beside those comments, you have not told us at what kind of performance > you are aiming at. There is a huge difference whether you need 1e-10 or > 1e-13 and whether you need it at 1s, 1ks or even 100ks averaging
Re: [time-nuts] PRS-10 Warm-up Time, Calibrating/Adjusting, and long-term poweron
I am experimenting with exactly the same thing. PRS-10 with Thunderbolt. PRS-10 takes about a day to stabilize. When physics lock happens, it has limited stability - which is mentioned in manual. Before I calibrated, I waited for 2 days. These movements are visible if you feed GPSDO into channel 1 of scope and set a trigger on it, and feed PRS-10 output to channel 2. For thunderbolt GPSDO, I am using a telecom unit, Nortel GPSTM modified with 1 pps output. PRS-10 can take this input and lock, but it takes 1 to 2 hours to lock up. I've tried 3 different GPSDO and they were all the same. When it locks on, it is still not stable. Why? Because nature of GPSDO and Rb, time constant is set to 2 to 3 hours. (still experimenting) It takes few cycles of this to lock and stabilize. In short, you'll be safe if you wait 24 to 48 hours. Rb modules are relatively cheap. I really don't see a need to baby it. --- (Mr.) Taka Kamiya I'm stuck in a wormhole Hello, worms! On Friday, March 8, 2019, 4:00:34 AM EST, Forrest Christian (List Account) wrote: Hopefully you'll all grace me with a few answers to a beginner time-nut question or two. I have a PRS-10 I've never used other than to power it on with a recently-acquired heatsink and verify that it seems to operate correctly and that the operational parameters don't seem out of tolerance. I would like to use this in the near future as a 10Mhz reference for a TAPR TICC which I'd like to use to measure the jitter performance of the PPS output of various consumer GPS receivers, the goal being to end up with a jitter histogram. So three interrelated questions: 1) Assuming the PRS-10 has been off for a long time, how long should I plan on leaving this on for the 10Mhz to stabilize? I see the longest warmup time on the spec-sheet is 7 minutes - although this seems a lot shorter than I'd likely use in real life, I'm also not sure if there's much benefit to an excessively longer warmup time (like days), would like opinions on this. 2) Longer-term I'd like to use the 1PPS output from a Trimble Thunderbolt to calibrate the PRS10 and adjust if necessary just to trim out any aging drift on the PRS10. Initially I thought I was going to discipline the PRS10 on a continual basis with the Thunderbolt using the PPS input on the PRS10, but I've recently realized that leaving the PRS10 on permanently might not be the best option (see Question 3). So I'm looking for opinions on how to keep the PRS10 calibrated/adjusted. I.E. trim with the trimmer, adjust using digital commands, etc. 3) As implied in #2, I was originally planning on leaving the PRS10 on a continuous basis. I've read a couple of things which imply that there is little benefit to doing so, and that every hour it's on consumes the lamp life. Assuming I only need the highly stable PRS10 source every few months for things like jitter measurements on 1PPS sources, is there any benefit to leaving the PRS10 on? -- - Forrest ___ 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. ___ 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.
Re: [time-nuts] PRS-10 Warm-up Time, Calibrating/Adjusting, and long-term poweron
Keep in mind that the 7 min "warmup time" of the PRS-10 is jut the time for the unit to get the physics package close enough to final temperature for the dithering loop to lock to the atomic transition. But based on measurements of current drawn by the oven(s), it takes more like an hour for the ovens to settle down very well. My own experiments with a well-used "telecom mod" PRS-10 suggest that it takes my unit more like 3 or 4 days to really settle down to its background frequency drift rate. This rate is specified as something like "< 5E-11 per month", which is frankly pretty awful. Mine seems to be better than spec, more like 2E-11 per month (frequency increasing over time). 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. I've been wondering about the issue of whether it's best to operate a PRS-10 only at times of need, or continuously, with respect to life. I posed the question direct;y to SRS, and they claim that it is better to leave it running all the time. My own "algorithm" has become "leave it on all the time" when I'm around and even remotely active with time-nuttery, but shut it down when I'm away on vacation. This is mostly out of concern for something going wrong with the power supply and burning the house down. Lightning storms are one such risk, for example. DanaK8YUM On Fri, Mar 8, 2019 at 3:00 AM Forrest Christian (List Account) < li...@packetflux.com> wrote: > Hopefully you'll all grace me with a few answers to a beginner > time-nut question or two. > > I have a PRS-10 I've never used other than to power it on with a > recently-acquired heatsink and verify that it seems to operate > correctly and that the operational parameters don't seem out of > tolerance. I would like to use this in the near future as a 10Mhz > reference for a TAPR TICC which I'd like to use to measure the jitter > performance of the PPS output of various consumer GPS receivers, the > goal being to end up with a jitter histogram. > > So three interrelated questions: > > 1) Assuming the PRS-10 has been off for a long time, how long should I > plan on leaving this on for the 10Mhz to stabilize? I see the > longest warmup time on the spec-sheet is 7 minutes - although this > seems a lot shorter than I'd likely use in real life, I'm also not > sure if there's much benefit to an excessively longer warmup time > (like days), would like opinions on this. > > 2) Longer-term I'd like to use the 1PPS output from a Trimble > Thunderbolt to calibrate the PRS10 and adjust if necessary just to > trim out any aging drift on the PRS10. Initially I thought I was > going to discipline the PRS10 on a continual basis with the > Thunderbolt using the PPS input on the PRS10, but I've recently > realized that leaving the PRS10 on permanently might not be the best > option (see Question 3). So I'm looking for opinions on how to keep > the PRS10 calibrated/adjusted. I.E. trim with the trimmer, adjust > using digital commands, etc. > > 3) As implied in #2, I was originally planning on leaving the PRS10 on > a continuous basis. I've read a couple of things which imply that > there is little benefit to doing so, and that every hour it's on > consumes the lamp life. Assuming I only need the highly stable PRS10 > source every few months for things like jitter measurements on 1PPS > sources, is there any benefit to leaving the PRS10 on? > > -- > - Forrest > > ___ > 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. > ___ 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.
Re: [time-nuts] PRS-10 Warm-up Time, Calibrating/Adjusting, and long-term poweron
On Fri, 8 Mar 2019 01:18:45 -0700 "Forrest Christian (List Account)" wrote: > 1) Assuming the PRS-10 has been off for a long time, how long should I > plan on leaving this on for the 10Mhz to stabilize? I see the > longest warmup time on the spec-sheet is 7 minutes - although this > seems a lot shorter than I'd likely use in real life, I'm also not > sure if there's much benefit to an excessively longer warmup time > (like days), would like opinions on this. The warm-up time is from "I switched it on" to "there is a 10MHz signal and it's 'stable'". I.e. at latest after 7 minutes you should be able to use the ouptut of the PRS10. But keep in mind that the stable-after-warm-up is not tha same as stable-for-a-time-nut. A Rb vapor cell standard has a retrace (ie change of frequency after being switched on, for details see John Vig's tutorial) of several weeks to a few months, depending on the exact construction of the Rb cell, how long it has been in use and how long it has been off. > 2) Longer-term I'd like to use the 1PPS output from a Trimble > Thunderbolt to calibrate the PRS10 and adjust if necessary just to > trim out any aging drift on the PRS10. Initially I thought I was > going to discipline the PRS10 on a continual basis with the > Thunderbolt using the PPS input on the PRS10, but I've recently > realized that leaving the PRS10 on permanently might not be the best > option (see Question 3). So I'm looking for opinions on how to keep > the PRS10 calibrated/adjusted. I.E. trim with the trimmer, adjust > using digital commands, etc. Switching it on and off several times a month would be worse in terms of longevity than having it running continuously. The vapor cell itself is usually run between 60°C and 100°C and the Rb lamp usually between 120°C and 170°C. As you can imagine, power cycling gives a huge thermal strain on all the components. The inner construction of the PRS10 is not optimized for power cycling but thermal insulation of the sensitive components (see e.g. http://time.kinali.ch/Rb/PRS10/ ) So I would rather feed the PPS to the PRS10 directly and let itself do the work. This will also give you an optimized control loop for the performance of the PRS10 without you having to go through the process of desiging and optimizing the loop. > 3) As implied in #2, I was originally planning on leaving the PRS10 on > a continuous basis. I've read a couple of things which imply that > there is little benefit to doing so, and that every hour it's on > consumes the lamp life. Assuming I only need the highly stable PRS10 > source every few months for things like jitter measurements on 1PPS > sources, is there any benefit to leaving the PRS10 on? If you want to do just jitter measurement, then I wouldn't use a Rb standard but a stable OCXO instead. At averaging times below 1-10s an OCXO will beat any Rb standard, even one that has an OCXO like the PRS10 (admittedly, it's not a high quality OCXO but it's one none-the-less). An OCXO has a shorter warm-up time (usually 2-3 minutes until stable, usually less than a day until time-nuts-stable, less than a month until nutty-time-nut-stable). I personally, would use an OCXO as reference to the TICC (or TICCs?) and use the PRS10 as an additional input to the TICC. This way you can do a multi-way comparison between the GPSDOs and the Rb, removing out the (in-)stability of the reference OCXO. Beside those comments, you have not told us at what kind of performance you are aiming at. There is a huge difference whether you need 1e-10 or 1e-13 and whether you need it at 1s, 1ks or even 100ks averaging times. 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.
Re: [time-nuts] PRS-10 Warm-up Time, Calibrating/Adjusting, and long-term poweron
> 1) Assuming the PRS-10 has been off for a long time, how long should I plan > on leaving this on for the 10Mhz to stabilize? I see the longest warmup > time on the spec-sheet is 7 minutes - although this seems a lot shorter than > I'd likely use in real life, I'm also not sure if there's much benefit to an > excessively longer warmup time (like days), would like opinions on this. Run the experiment. Collect some data from your GPS/PPS signals. Assume the GPS is correct and back compute the PRS-10 frequency. After you get everything sorted out, turn the PRS-10 off for a day, then collect data when you turn it back on and collect more data. After it has warmed up, the frequency will be stable. Look on your graph back toward the turnon time. Where can you see that the frequency differs from the stable value? It's warmed up a bit past that. -- These are my opinions. I hate spam. ___ 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.
