Controllogix Time Synchronization

[Lovell]

I am running into an issue with time synchronization between a 1756-L81E and 1756-L83E.
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L83E is the system time master. Enable Time Synchronization is checked.
L81E is a synchronized time slave. Enable Time Synchronization is checked.
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I have a DST instruction toggling Adjust for Daylight Savings time in the time master. It is currently checked.
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The time slave Adjust for Daylight Savings time is not changing with the master. It is currently NOT checked.
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. Time is in sync except it is an hour off while DST is happening.
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Do I need a DST instruction in both?
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Anyone have experience with this?

 

[JeremyM]

The TimeSync object has no knowledge of or bearing over DST. It deals in UTC.

DST is handled by the Logix WallClockTime object. Performing a GSV for its attributes, you can get the DateTime or LocalDateTime. The former is pure UTC (effectively governed by the TimeSync mechanism, when enabled), the latter is derived from UTC + Zone offset (hours and minutes) + DST offset (minutes, when DST is enabled).

You could set up a produce-consume block or message handler to "synchronize" the DST attribute between the two. This need not be deterministic since the LocalDateTime result is derived from the already-synchronized DateTime anyway.

I strongly encourage any and all timestamping you perform to be in UTC. It's universal and you only need to concern yourself with aspects of local time when presenting the data.

 

[Lovell]

I like that idea. I will GSV the ApplyDST from WALLCLOCK in time master and produce to the slave PLC. Then SSV the value to WALLCLOCK ApplyDST.

Thanks!