Hi guys,

I have encountered a very strange situation during investigation of a plant's trip. Examining event & alarm lists, I can clearly see that protection is activated for example at 23:44:50, and yet, when I place all relevant process quantities on the trend diagrams, I can read (via ruler) that sudden changes are recorded at for example 23:45:01, so there is about 10 sec or a bit more time difference. I didn't expect this, I can understand if the difference is 1 or 2 sec, but 10 seconds is a lot.

How to explain this? The system is PCS 7 v 9.0 SP3.

Does anyone have similar experience? How to know for sure what is the actual time of the trip? Based on my experience on other systems, event lists (SOE) are generally much more reliable and more accurate than analog trends, but differences are usually 1-2 seconds and not more.

The system doesn't have GPS time sync, but I think that is not important because difference is present inside PCS 7 system itself.

Do I need to check something else?

Thank you!

Hello Aden,

Regards

Hi, 

During event analysis, we should rely on alarm message which consists of more accurate timestamp.

Hence, all the digital signals and alarms should refer only the process alarm mesage. 

For the timestamp in trending, they normally compressed or round up to 5 seconds. For details, you need to check on the each individual tag Tag Logging settings. Normally swinging door might apply to make the archiving optimize.  

Search Swing door in this link. 

https://support.industry.siemens.com/cs/ww/en/view/109760739

In short, please refer to alarm message timestamp instead of trending timestamp. 

Hope it helps.