crystal aging and specifically OCXO aging - Page 1
Forum section: electronics / general

author: codeboy2k
author_rank: Super Contributor
timestamp: January 07, 2013, 04:05:57 pm
content: I'm thinking of buying an OCXO on eBay, specifically this one:http://www.ebay.com/itm/170923748997I have not designed with an OCXO before. The most I've ever designed with is the bog standard canned crystal oscillator or smt crystal, and I didn't really care about the accuracy or stability, because it was just running a micro or providing USB timing or Ethernet timing, and it didn't really matter, so I am not sure how to properly read the datasheet.http://www.isotemp.com/wp-content/uploads/2011/10/143-1000.pdfThe datasheet has a section on aging:2.2. Aginga. At time of shipment < ±5x10-10/dayb. After indefinite storagei. Daily < ±5x10-10 after 30 daysii. Yearly < ±1x10-7iii. 10 years < ±4x10-7My question is, is this aging data cumulative? being that it's on eBay should I just assume that I can't know it's true age andassume it's at least 10 years old or more (worst case)? and then does that mean it's < ±4x10-7 + (10yrs * ±1x10-7/year ) ??i.e < ±14 x10-7 or ±1.4ppm ?? If so, It's starting to become a prettybadclock .or is it just saying after 10 years its never going to be worse than ±4x10-7, final. (0.4ppm)What if it's actually 8 years old? should I use the Yearly aging figure, then it's (8yrs * ±1x10-7/year) = ±8x10-7.This is actually worse than the 10 year data... so I am confused.thanks !

author: Unknown
author_rank: Unknown
timestamp: January 07, 2013, 05:52:12 pm
content: The specs mean that after 10 years, it should be within 0.4 ppm. The specs mention indefinite storage, so after 8 years in the warehouse it should still meet those specs. I would expect it to be better after being turned on for 8 years, but there is no way to tell this from the specs.After 8 years it's probably going to be somewhere between 0.1 and 0.4 ppm worst case. Probably closer to 0.4 ppm. Aging is often specified as ppm drift * sqrt(time). This assumes its a truly random process (like diffusion). From the 1 year figure, you would estimate the 10 year figure to be 0.1 ppm * sqrt(10) = 0.3 ppm, which is quite close to the datasheet value.

author: AlfBaz
author_rank: Super Contributor
timestamp: January 07, 2013, 05:58:19 pm
content: Does it age if it hasn't ever been powered up?

author: Unknown
author_rank: Unknown
timestamp: January 07, 2013, 06:15:15 pm
content: Yes, though probably at a different (probably lower) rate than when turned on. The temperature is much lower, for example.

author: codeboy2k
author_rank: Super Contributor
timestamp: January 07, 2013, 08:45:20 pm
content: Quote from: alm on January 07, 2013, 05:52:12 pmThat's what I was expecting. Thanks.QuoteAha. The drift*sqrt(time) is an important piece of the puzzle to read the datasheet properly.So my theoretical 8 year old clock would be aboutGiven that it's an eBay part I'll probably just assume worst case 0.4 ppm and see how that fits into my application needs.

author: codeboy2k
author_rank: Super Contributor
timestamp: January 25, 2013, 06:42:56 pm
content: follow up... so I bought a few OCXOs on eBay, they arrived today, I've not had a chance to power them up yet, but here's a pic of what I bought.Does size matter?These three are different sizes, and each one has different significant figures in the output value.Does anyone have any comments on which of these are known to be any better than the others?Thanks!The large one:DESC: OFC/McCoy SC-CUT SINE 10 MHz OCXO CRYSTAL OSCILLATORMODEL: OSC92-100BFREQ: 10.000000 MHZmiddle one:DESC: CMAC 10MHz ocxo oscillator square wave sc-cutMODEL: STP2390CFREQ: 10 MHZsmall one:DESC: SC Cut Crystal 10MHZ ISOTEMP OCXO OSCILLATOR SQUARE WAVEMODEL: ISOTEMP OCXO143-141FREQ: 10.000 MHZ

author: ve7xen
author_rank: Super Contributor
timestamp: January 25, 2013, 08:35:08 pm
content: OFC: This is reported to be made by Isotemp and equivalent to OCXO134-10 from them. Not a bad part, 5ppb vs. temp from -30 to +60C, -105dBc @ 10Hz. It's also the oldest, so probably has aged the most, which means its aging rate will likely be very low now.CMAC: Can't find any information on this.ISOTEMP: Hard to say, the OCXO143 series spans a couple decades of performance, and the -141 seems to be a custom-spec part. It could be a little better than the OFC (1ppb vs. temp, 115dBc @ 10Hz), or it could be a lot worse. Given that it's square wave output it might be harder to implement well.I've received several OCXOs from eBay that were well off frequency (some 20ppm on a 5ppb part, and the EFC range insufficient to correct for it) and had poor stability as well (drift of some ppm with temp / time). Make sure you check them out before using.

author: saturation
author_rank: Super Contributor
timestamp: January 25, 2013, 09:39:50 pm
content: Oscillators vary in quality as you demonstrate, even among a type such as the ovenized set. For academic details, lots here and plow through the website, much is free:http://www.ieee-uffc.org/frequency_control/teaching.asp?name=vigtocThe OFC seems to be the best of the breed, and older aged crystals are better than young among the best makers, assuming it still works and was not abused in the reclamation. The downside is older ones [ decades] are closer to death too, but at an unknown time, but until then it functions as good as it will ever be.

author: codeboy2k
author_rank: Super Contributor
timestamp: January 26, 2013, 11:12:35 pm
content: Quote from: ve7xen on January 25, 2013, 08:35:08 pmthanks for the info, ve7xen.. (xen.. good call sign !) I saw your blog, I'm also planning to make a GPSDO like you wrote on your blog too.Along with these few OCXOs, I also ordered and received a Navman Jupiter TU60 GPS receiver. This one has the 10Khz correlated output so I am hoping to use that with the OCXO to make a GPSDO. provided, as you say, it's not out so much that it can't be pulled in.I wasn't pleased with what I received , the picture on the ebay sale shows a nice clean unit (of course!)what I got was sufficiently rusted to give me some initial worries. It would seem that it was previously in a pretty harsh environment outdoors. I just hope it still works and has life left in it.My goal is to have a decent 10Mhz reference on my bench, that I can use everywhere, so I can build a dual-slope ADC and perhaps get 7 or 8 digits from it, so I can have an accurate 10-12 digit frequency counter, so I can build an accurate DDS based function gen from it, so I can know my scope sweeps are timed accurately, etc.. etc.. there are so many uses for a good clock !after 25 years, I am retired from my day job as an engineer (hoping to freelance now) and just starting out with an empty home bench, so I am on a limited budget, and I'm planning to bootstrap my bench with stuff I build myself. The first thing I need is a decent clock. After that it's all gravy

author: codeboy2k
author_rank: Super Contributor
timestamp: January 27, 2013, 12:31:39 am
content: Quote from: saturation on January 25, 2013, 09:39:50 pmThanks saturation. Good link, I'll read it up.Seems like the OFC is the one I will start with.. It looks bent out of shape, that worries me a bit.My plan is to sync these 3 oscillators to a GPS receiver (as I said in my previous post, I have the Jupitor TU60 which has a GPS correlated 10Khz output).What I'd really like to do, but cannot because I don't have the equipment, is to warm these 3 oscillators up for 24 hours, then the next day take variance measurements for about tau=10^4 or 10^5 or so, and plot their Allen deviations over these tau. This will give me a baseline. Then, I want to connect them up to GPS and do it again. Hopefully they get can get down to better than 10e-13 or so while disciplined, as has been seen on the web blogs of many others who have tried this. Then I want to unplug them from the GPS signal for a week and see how they drift over 1 week. Maybe I'll know in only 24 hours..Alas, I don't have 1ps accurate counters at homeI could perhaps rent one good counter and do it sequentially, but it would be far better to be able to do them all at the same time with the same GPS signals.. but I don't want to rent 3 counters.

author: marshallh
author_rank: Unknown
timestamp: January 27, 2013, 12:56:50 am
content: See Agilent's various white papers on various subjects that may be related:http://www.home.agilent.com/agilent/application.jspx?cc=US&lc=eng&ckey=2232321&nid=-33080.0.00&id=2232321&cmpid=zzfindmetrology

author: codeboy2k
author_rank: Super Contributor
timestamp: January 27, 2013, 01:19:41 am
content: Quote from: marshallh on January 27, 2013, 12:56:50 amThanks marshall I will check it out.Also found some good practical information herehttp://www.ko4bb.com/Timing/index.phpand of course there's timenuts

author: saturation
author_rank: Super Contributor
timestamp: January 27, 2013, 01:47:03 pm
content: You're welcome. If you intend to do any time-nuts type stuff you'll need a good counter, time-nuts archives have many recommendation for models. Quartz tend to a wider spread short term vs Rb, but overall average is improved if ovenized, so you'll need to a counter at your lab to check the status of your oscillators routinely. Adjusting a quartz oscillator can create a deal of instability that could take many days to settle.http://www.ieee-uffc.org/frequency_control/teaching.asp?vig=vigcompQuote from: codeboy2k on January 27, 2013, 12:31:39 am