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Asked:20 Oct 2025

SIMATIC WinCC (TIA Portal): S7 series 1200 & Ktp900 Simple auto Duration Synchronisation uses Platform Duration

I've got a s7-1200 communicating  with a KTP900 basic and I've set the connection on the HMI for slave time synchronisation.  I've activated daylight saving on the PLC with uk time zone but have noticed that the HMI time does not change by an hour when it should. 
I've read the system time and local time into a DB so I can see that the local time is changing as it should in March and October but the time synchronisation on the HMI appears to use the system time.  I can't see a way to reconfigure this to sync the local time not the system time. Is there a work around or am I missing something. 

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Siemens Test Added an Answer on20 Oct 2025

S7-1200 & KTP900 Time Synchronization Issue

You've correctly identified a known behavior with S7-1200 and KTP900 Basic HMIs regarding time synchronization. The HMI, when set to 'Slave time synchronization', defaults to synchronizing with the PLC's system time, not the local time adjusted for daylight saving.

Unfortunately, there isn't a direct configuration option within the HMI to switch the synchronization source to the PLC's local time. The HMI uses the PLC system time for synchronization.

Workaround:

  • PLC Logic: Create a dedicated function block in the PLC to calculate and present the adjusted time (local time with DST) as a separate tag.
  • HMI Tag: Instead of synchronizing with the PLC's system time, have the HMI synchronize with this newly created tag containing the adjusted local time.

Further Information: Please refer to the following Siemens Support article for more details and a potential solution:

KTP400/600/700/900 Basic - Time synchronization with S7-1200/1500, daylight saving time not correct

Disclaimer: As Siemens Self Support, I provide information based on available resources in SiePortal. Always verify solutions in a test environment before implementation.

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