Why does the time interrupt start too late in SIMATIC PCS 7 during summer time?
If, as specified for SIMATIC PCS 7 V5.x, the local winter time is set on the CPU the whole year round, then after switchover to summer time, a configured time interrupt starts one hour too late. How do you prevent this?
In SIMATIC PCS 7 V5.x it is specified that the PLC is to be set to winter time the whole year round. Daylight saving changes are made in the OS. The local winter time must always be set in the PLC. More information is available in the PCS 7 readme, section 2.2. As the time is not changed in the CPU, the time interrupt occurs 1 hour too late during the summer.
The following alternatives are available:
- Setting the summer time on the PLC contrary to the guidelines contained in the SIMATIC PCS 7 Readme file.
- Using a SICLOCK time-of-day transmitter on the Ethernet. Time messages sent by SICLOCK and the CPU's HW CONFIG can be parameterized in such a way that the time-of-day in the CPU is switched to summer time.
- Using a C script to set the time-of-day in the CPU directly from the computer. A detailed description of this procedure is available in Entry ID: 786498.
In either case, a correction still has to be performed on the OS stations.
As WinCC assumes that the CPU is also set to winter time in summer, during the summer 1 hour is added to the time stamp for the messages on the PLC. However, if you also want to work with summer time on the PLC, this addition has to be prevented - see Entry ID: 7604251.
- Changing the program so that the time interrupt is executed at the right time during the summer, despite the fact that winter time is set on the PLC.
In order to do this, you have to reconfigure the time interrupt while the CPU is running. If you have perviously set 7:00 as the starting time, for example, then you must change the starting time to 6:00. You can use the SFC28 system function to reconfigure the time interrupt during CPU RUN. The reconfigured time interrupt then has to be restarted / activated with the SFC30 system function. It is up to you to ensure that the reconfiguration to summer time takes place at the right time (last weekend in March) and that winter time is also reset on time (last weekend in October).
In SIMATIC PCS 7 V6.0 onwards the time-of-day synchronization takes place by default with the GMT time zone. This means that the only option open to you is option 2). As far as the CET time zone is concerned, this means that the time-of-day has to be corrected accordingly by 1 hour in the winter and by 2 hours in the summer.