[ntp:questions] IEEE 1588 (PTP) at the nanosecond level?

Magnus Danielson magnus at rubidium.dyndns.org
Sun Mar 23 02:11:20 UTC 2014


On 21/03/14 16:17, Joe Gwinn wrote:
> Magnus,
>> Thus, another fairly severe environment.
> I have a personal war story from 1992:  At a Air Traffic Control center
> in Canada, one 19" cabinet had the green (safety ground) and white
> (power neutral) cables transposed.  This caused 2.3 Vrms at 180 Hz to
> appear between the VMEbus ground and the cabinet shell, with enough
> oomph to cause a small spark when oscilloscope probe grounding clip was
> connected to that VMEbus ground, this causing the system (and my heart)
> to crash.  If left connected, the ground clip became warm.  And how can
> ground generate a spark, even a small one?  Fixing the grounds dropped
> the offset to around ten millivolts.  The 180 Hz arose because the
> power supplies were single-phase capacitor-input, driven from the legs
> of three phase prime power.

Power neutral isn't really neutral when it takes a lot of beating.
Similarly, a grounding wire isn't doing much grounding as frequency goes up.

>>> That fails economically - might as well stick to IRIG.
>> Indeed. Doing 1 us level might be possible, going lower than that will
>> cause you more and more grey hairs one way or another.
> Well, now, this could be an advantage -- my hair is already gray, and
> more could be better.

Well, you may have younger colleagues which fails to have this 
advantage. I knew you would make the comment. :)

>>> There is a truism in the standards world, that it take three major
>>> releases (versions) of a standard for it to achieve maturity.  PTP is
>>> at version 2, so one more to go.
>> I'd say it depends on for what application. The trouble is when the
>> assumed applications increase at a quicker rate than the standard adapts
>> to handle them.
> It does, but having the market grow faster than the standards cycle can
> be the mark of success.

To some degree. Being perceived to be a solution isn't the same as it 
being a solution.

> By the way, development of the third revision of 1588 started in 2013.
> I joined what purported to be their reflector, but now that you mention
> it I haven't gotten any traffic -- Something must be wrong.  I will
> need to enquire.

They formally had their first session at the ISPCS in Lemgo.


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