[ntp:questions] Assistance with PPS on Windows

unruh unruh at wormhole.physics.ubc.ca
Thu May 5 18:46:54 UTC 2011


On 2011-05-05, Chris Albertson <albertson.chris at gmail.com> wrote:
> The most simple explanation is that the PPS signal out of the clock is
> just about as poor as NTP is reporting it to be.  In other words
> everything is working fine.  Nothing is wrong with your cable or with
> NTP or with Windows.    Until some tests show otherwise I think it is
> best to assume the PPS signal going into the PC is close to how NTP is
> describing it.
>
> If you need better buy a GPS.  You can get setup with one that does
> works at the nanosecond level for under $100.

Uh, no. There is no way of getting the signal into the computer with
nanosecond accuracy. 1usec is about it. The interrupt service routines,
if you use a specialised driver for some interrupt driven card, will
take about 1usec to service the interrupt. Thus while the card may
deliver a pulse whose leading edge is within say 50ns of the correct
time that is irrelevant if the computer itself cannot respond fast
enough. 

But I agree, with a GPS you can get usec accuracy in the time delivered
for less than $100.



>
> On Thu, May 5, 2011 at 9:32 AM, Ken Link <klink at numberzero.org> wrote:
>> Assuming the Delay, Offset, and Jitter column units are msec, after
>> letting it run overnight and half of the next day I still see PPS with
>> 0 delay, 4.559 msec offset, and 3.123 msec jitter.
>>
>> The PPS source is the Meinberg TCR511PCI card, as seen here:
>> http://www.meinberg.de/english/products/tcr511pci.htm
>>
>




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