[ntp:questions] NTP with GPS and RTC
david-taylor at blueyonder.co.uk.invalid
Sat Apr 27 13:56:15 UTC 2013
On 27/04/2013 09:13, David Woolley wrote:
> If the time error is low and bounded the frequency error does not
> necessarily have a low error bound. Simply polling fast and using a
> short loop time constant can give you a low error bound on the time, if
> the network delays are stable and the source is good.
Thanks, David. I just checked a power-down reboot of a Windows PC (for
replacement of a faulty card) with a PPS reference source, and the
jitter was down to its normal value within 20 minutes, and the offset
within 15 minutes. It was much more difficult to judge the time for the
frequency to stabilise, because there is so much variation with
temperature - perhaps it took 2 to 2.5 hours. Certainly not then 10
hours Bill has often stated.
Another warm PC which had a reboot this morning showed a 12 minute
jitter recovery time, 3 minutes for the offset to recover (about 50
microseconds typical) and you couldn't see any step in the frequency graph.
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