[ntp:questions] Converting from Y-m-d h:m:s

Uwe Klein uwe_klein_habertwedt at t-online.de
Sun May 16 08:52:22 UTC 2010

Terje Mathisen wrote:
> Marc Leclerc wrote:
>> Hi,
>> I am looking to stay on true time, the real issue here in those
>> installation is not realy having the perfect time but that all the
>> device in the field have the same time. There are new ways to acheive
>> this such as IEEE 1588 but since no one is ready for this using GPS
>> device is our closest friend. But it's funny you asked, soon we will
>> tackel simple synchronous switching of breaker and then we'll have to
>> keep up with the AC cycles
> This is actually somewhat easier:
> You only need 8 or 10 ms accuracy to do this, in order to determine the 
> start of each 50 or 60 Hz cycle, then you phaselock your switch to the 
> AC cycles.

There is a (massive?) hitch.
The grid 24h average is held to the nominal frequency.

Shortterm frequency is load dependent.

so you need to sync all boxes to the _same_ zerocrossing in a
"variable frequency" domain with the help of a "true time" source.
not easy.


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