[ntp:questions] how close to reference clock?

Markus Kühle markus.kuehle at t-online.de
Mon Dec 15 21:41:36 UTC 2003


hi,

we have a Meinberg GPS 167 with PPS and Linux system. Now my question:
How close is our lokal clock to the reference clock. Can i take the 
values from our PPS device or must I take the Generic?
Because the manual say that the local clock get a closenes to the gps 
with pps in 1 .. 10 nsec but the offset of this clock vary from -0.010 
to -0500.
Or can I take the offset from the pps device?
The main question is: what can I say about the accuracy of our lokal clock?
Or do you need other output to say it exactly?

Here some outputs:

ntpq -p:

Mon Dec  8 18:34:27 CET 2003
      remote           refid      st t when poll reach   delay   offset 
  jitter
==============================================================================
+GENERIC(0)      .GPS.            0 l   19   64  377    0.000   -0.103 
  0.073
oPPS(0)          .PPS.            0 l   31   64  377    0.000    0.001 
  0.004
------------------------------------------------------------------------------
Mon Dec  8 18:35:31 CET 2003
      remote           refid      st t when poll reach   delay   offset 
  jitter
==============================================================================
+GENERIC(0)      .GPS.            0 l   19   64  377    0.000   -0.137 
  0.034
oPPS(0)          .PPS.            0 l   31   64  377    0.000    0.001 
  0.004
------------------------------------------------------------------------------
Mon Dec  8 18:36:35 CET 2003
      remote           refid      st t when poll reach   delay   offset 
  jitter
==============================================================================
+GENERIC(0)      .GPS.            0 l   19   64  377    0.000   -0.538 
  0.402
oPPS(0)          .PPS.            0 l   29   64  377    0.000    0.001 
  0.004
------------------------------------------------------------------------------

the same as graph over days:
http://www.kloserver.de/globaltime/offset/offset2.png
http://www.kloserver.de/globaltime/offset/offset1.png

and the some outpus from ntptime:
Mon Dec 15 22:26:41 CET 2003
ntp_gettime() returns code 0 (OK)
   time c388a591.4e3f13f4  Mon, Dec 15 2003 22:26:41.305, (.305650720),
   maximum error 1887 us, estimated error 2 us, TAI offset -1073743576
ntp_adjtime() returns code 0 (OK)
   modes 0x0 (),
   offset 1.088 us, frequency -22.482 ppm, interval 256 s,
   maximum error 1887 us, estimated error 2 us,
   status 0x2107 (PLL,PPSFREQ,PPSTIME,PPSSIGNAL,NANO),
   time constant 6, precision 2.880 us, tolerance 496 ppm,
   pps frequency -22.482 ppm, stability 0.009 ppm, jitter 0.589 us,
   intervals 3579, jitter exceeded 7110, stability exceeded 103, errors 1.
------------------------------------------------------------------------------
Mon Dec 15 22:27:45 CET 2003
ntp_gettime() returns code 0 (OK)
   time c388a5d1.6b574f4c  Mon, Dec 15 2003 22:27:45.419, (.419301024),
   maximum error 1876 us, estimated error 2 us, TAI offset -1073743576
ntp_adjtime() returns code 0 (OK)
   modes 0x0 (),
   offset 0.992 us, frequency -22.481 ppm, interval 256 s,
   maximum error 1876 us, estimated error 2 us,
   status 0x2107 (PLL,PPSFREQ,PPSTIME,PPSSIGNAL,NANO),
   time constant 6, precision 2.880 us, tolerance 496 ppm,
   pps frequency -22.481 ppm, stability 0.007 ppm, jitter 0.677 us,
   intervals 3580, jitter exceeded 7110, stability exceeded 103, errors 1.
------------------------------------------------------------------------------
Mon Dec 15 22:28:49 CET 2003
ntp_gettime() returns code 0 (OK)
   time c388a611.885c3558  Mon, Dec 15 2003 22:28:49.532, (.532657856),
   maximum error 1870 us, estimated error 2 us, TAI offset -1073743576
ntp_adjtime() returns code 0 (OK)
   modes 0x0 (),
   offset 1.120 us, frequency -22.481 ppm, interval 256 s,
   maximum error 1870 us, estimated error 2 us,
   status 0x2107 (PLL,PPSFREQ,PPSTIME,PPSSIGNAL,NANO),
   time constant 6, precision 2.880 us, tolerance 496 ppm,
   pps frequency -22.481 ppm, stability 0.007 ppm, jitter 0.466 us,
   intervals 3580, jitter exceeded 7110, stability exceeded 103, errors 1.
------------------------------------------------------------------------------
Mon Dec 15 22:29:53 CET 2003
ntp_gettime() returns code 0 (OK)
   time c388a651.a4651f00  Mon, Dec 15 2003 22:29:53.642, (.642168480),
   maximum error 1882 us, estimated error 1 us, TAI offset -1073743576
ntp_adjtime() returns code 0 (OK)
   modes 0x0 (),
   offset 0.256 us, frequency -22.481 ppm, interval 256 s,
   maximum error 1882 us, estimated error 1 us,
   status 0x2107 (PLL,PPSFREQ,PPSTIME,PPSSIGNAL,NANO),
   time constant 6, precision 2.880 us, tolerance 496 ppm,
   pps frequency -22.481 ppm, stability 0.007 ppm, jitter 1.455 us,
   intervals 3580, jitter exceeded 7112, stability exceeded 103, errors 1.
------------------------------------------------------------------------------

thx for reading!
Markus Kühle




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