[ntp:questions] Trying to use Dimension 4 time keeper

David Lord snews at lordynet.org
Mon Sep 9 02:08:13 UTC 2013


W. eWatson wrote:
>  > Some settings that may be of interest.
>  >
>  > NTP servers
>  > server 0.us.pool.ntp.org iburst
>  > server 1.us.pool.ntp.org iburst
>  > server 2.us.pool.ntp.org iburst
>  > server 3.us.pool.ntp.org iburst
>  >
>  > ntp.drift contains
>  > 24.793
> 
> What about the above?  Does the user set the drift, and, if 24.793 is in 
> seconds, why so big?

Ntpd sets the drift value and keeps a record in the drift file
to be used next time ntpd is restarted.  Ntpd can take a long
while, hours rather than minutes, to establish a good valu for
the drift. Unless you really know what you are doing, you should
not tamper with the drift file.

> 
>  > Since the computer is obviously linked to the net, it is not necessary
>  > to go out there to check the time. You could do it against one of your
>  > local machines or whatever via the net.
> 
> How would that work?

Ntpd is both a client and a server so you only have to make sure
that you don't have a firewall blocking local access.

>  >
>  > What time accuracy do you need?
> 
> 0.1 seconds.
> 

A long while back the quality of the motherboard system clocks might
have been much better. A few of my 386/486 systems would be much
better than 1.0s/day without running ntpd/chronyd or similar. Add to
that they usually had a connector to select a remote system  clock
if needed (this then largely removes offset variation due to system
load but not due to ambient temperature changes).

If you can run ntpd on your Windows system you should get and
maintain  better than 0.01 s offsets. As the Meinberg install
suggests, you need to disable Windows time service in order to
effectively run ntpd. I've not tried SNTP for a long while, ie I was
running plain DOS, and often the logs showed no correction was needed
(ntp source would be my own server on a Linux, NetBSD or FreeBSD
system). My local systems without pps source has offsets within
200 us - 2 ms depending on ambient temperature changes. The pc with
gps/pps has mean offset 0.0-1.0 us, rms 4-5 us, maximum 27-37 us.



David



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