[time-nuts] TU30 jump second

Bo Hansen timenuts at rudius.net
Tue Apr 4 10:01:00 EDT 2017

Hi all

The data can be a bit hard to read in an email. So I will give it another try.

PC-time | Diff. | GPS-time | Diff.
011606.005 | 0.992 | 011604 |1
011607.013 | 1.008 | 011605 |1
011608.005 | 0.992 | 011607 |2 <--- The issue
011609.013 | 1.008 | 011608 |1
011610.004 | 0.991 | 011609 |1

I used a terminal program to log the NMEA data to a file and do the PC timestamp. Calculations were done in a spreadsheet by me. The PC-time is kept under control by Meinberg and also OK vs. <http://www.time.is> during the time of observation.

The PC-timestamp wobble is not the issue. It is a combination of the PC-time itself and the NMEA wobble. Nobody should expect the NMEA data to come at the same time every time relative to the 1 PPS. As Björn correctly points out it is always late and wobbles with processor load.

Sometimes the 2-something lag can last for many hours - I have seen more than 48 h.

The issue is the "seconds jump". The issue is not the relative difference between the PC-time and the GPS-time but the jump, e.g. using Tac32 reveals that the TU30 is always ~1200 ms late on in case of the "jump second" ~2300 ms late.

I wonder if it has anything to do with the Week 1024 Syndrome?

Indeed the TU30 is a old device. I guess some 30 years if not more looking at the components. F/W I have no idea.

The 10 kHz seems unaffected.


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