Understanding Exception and Compression Reporting for ACE Tags in OSIsoft PI

Understanding Exception and Compression Reporting for ACE Tags in OSIsoft PI

When working with OSIsoft PI, particularly with ACE (Advanced Computing Engine) tags, it's crucial to understand how exception and compression settings impact data storage and retrieval. Many users who implement ACE for calculation purposes often wonder if the parameters that regulate tag archiving behaviors apply to ACE tags like they do to standard PI tags. The answer is yes, ACE tags are subject to the same exception and compression settings as any other PI tags.

Exception and Compression Overview

Before diving into ACE tags specifically, let's revisit what exception and compression settings mean in the context of PI:

• Exception Settings: These are parameters set at the interface level that determine whether new data points should be sent to the PI Data Archive. The primary goal here is to filter out noise by only archiving significant changes. This is determined by the exception deviation, which is a threshold value specifying how much a data point must differ from the last archived point before it's stored.

• Compression Settings: Once data reaches the Data Archive, compression settings help reduce the amount of data stored without losing significant information. If consecutive data points are within a certain "compression deviation", the intermediate points are discarded, effectively "compressing" the data stream.

Applying These Settings to ACE Tags

ACE tags, while derived from computations rather than direct sensor inputs, adhere to the same principles:

1. Exception Reporting: Just as with standard tags, ACE-generated data undergoes the exception test. Despite the values being calculated, if a computed value differs from the last archived point by less than the exception deviation, it should, in theory, not be archived unless:

   • There's a configuration oversight.
   • The calculation logic explicitly dictates storage.
   • The reporting interface has specific settings bypassing this.

2. Compression Reporting: Once the data is entered into the PI Data Archive, compression settings manage its storage. The logic remains unchanged; if ACE outputs are sufficiently close (within the specified compression deviation), intermediate values get compressed out, saving space and reducing retrieval times.

Troubleshooting Unexpected Archiving

Users sometimes observe ACE tag values being archived even when within the exception dead band. This could be due to:

• Configuration Mismatches: Double-check the exception and compression settings for mismatches or errors.
• Setting Hierarchies: Ensure that there are no interface-level settings overriding the tag-level configurations.
• Calculation Logic: Review ACE calculation scripts to see if they have been programmed to force archiving beyond normal exception/compression logic.

Conclusion

In conclusion, exception and compression settings are indeed significant for ACE tags as they are for any other type of PI tag. Ensuring that these settings are appropriately configured helps maintain data integrity while optimizing storage resources. Understanding these mechanisms enables users to make informed decisions about data configuration and management within the PI System.