[time-nuts] Stable Watch Clocks

Tom Van Baak tvb at LeapSecond.com
Wed Dec 12 05:20:35 UTC 2012

Hi Simon,

Thanks for the URL. That's one of those tiny 6x2 mm crystals, 20 ppm crystals (ouch). The tempco (-0.034 ± 0.006 ppm/ T²) is excellent, though. Now, you can adjust rate; and temperature you can control. Notice they don't specify the stability, which is the key to timekeeping.

So I see a very interesting experiment/opportunity for you. Get one of these xtals and have it generate 1PPS. Then:
1) measure the accuracy (vs. spec)
2) confirm the tempco (vs. spec)
3) measure the stability (note: no spec given)
4) measure the daily or monthly or annual drift (vs. spec)

If you get one of these 32 kHz xtals, I'm happy to send you the other gear you need, if you have the time to do the experiment(s). You'll end up with some very nice plots and a wonderful article or series of articles for your electronics blog.

  ----- Original Message ----- 
  From: M. Simon 
  To: Tom Van Baak ; Discussion of precise time and frequency measurement 
  Sent: Tuesday, December 11, 2012 9:01 PM
  Subject: Re: [time-nuts] Stable Watch Clocks


  This quotes .038 ppm/C^2 delta T from the turn over point:


  The fly in the ointment is the aging rate of 5 ppm the first year (13ppb/day) and 3 ppm (8ppb/day) after. 

  I'm sure holding 1 degC is easy.  .1 C with some care and .01 C - my measuring eqpt ain't that good. So temperature ceases to be a problem. Is the other stuff workable?

  I would go with a 32KHz crystal for a "production" version to make it easy to multiply up to 10MHz. 


  Engineering is the art of making what you want from what you can get at a profit.

    From: Tom Van Baak <tvb at LeapSecond.com>
    To: Discussion of precise time and frequency measurement <time-nuts at febo.com> 
    Sent: Wednesday, December 12, 2012 3:55 AM
    Subject: Re: [time-nuts] Stable Watch Clocks

    > Typical 32KHz clock crystals are very stable in frequency if you can keep them 
    > close to the turnover temp. If you can hold 1 degC it is .04 ppm. 

    That's far better than I thought. Do you have a reference for this spec?

    I agree you might be able to make one accurate to 0.04 ppm, however briefly, but I've never seen one stable to 0.04 ppm. I mean, that's like 1 second a year.

    > I currently have no method for testing such a rig for stability. 

    Oh, the slipperly slope you are on. I have just the solution for you ...


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