[ntp:questions] Re: Designing an NTP network for a research ships at sea...
marc at fordson.demon.co.uk
Mon Aug 25 00:06:48 UTC 2003
On Wed, 23 Jul 2003 13:03:20 -0400, "Val Schmidt"
<vschmidt at ldeo.columbia.edu> wrote:
>Thanks Everyone for the help.
>I have a few more questions.
>If I look at the timing errors involved in logging and time stamping NMEA
>position strings I might make an error diagram something like this:
> GPS Receiver/NMEA time error-> (~10ms)
> time to write serial data-> (~ns - maybe 1 sec)
> time to log serial data-> (~1ms)
> UTC to CPU offset-> (~100 ms with NTP
>NMEA driver - no PPS)
> *CPU TIMESTAMP*
>Do the estimates regarding nominal errors from each of these sources seem
>reasonable to everyone?
>Are there other sources of error that I've missed?
One gotcha that you might want to keep in mind -- make sure the GPS
receiver is not assuming a static installation. Some NTP drivers (eg.
Motorolla Oncore and MX4200) will set the receiver to an averaged
fixed position so it no longer has to navigate and can supply a
marginally more accurate time solution. No good, of course, on a boat
that's moving around.
For really accurate timing of your instruments, IRIG-B might fit the
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