Troubleshooting Frozen Archive Tags in WinCC Tag Logging After CFC Changes

Archive tags appear frozen in WinCC OnlineTrendControl after modifying archiving attributes in CFC charts because a delta OS compilation does not reset runtime Tag Logging cache buffers when tag structures are deactivated. While changing block archiving settings in CFC does not require PLC chart compilation, WinCC Tag Logging requires a complete OS compilation with memory reset or a runtime archive cache reinitialization to realign internal archive IDs and resume logging for the remaining active tags.

Root Cause of Frozen Trend Values

When an automation engineer modifies the archive attributes on function block pins in SIMATIC CFC (switching pins from Long Term Archive to No Archive), compiling and downloading only changes to the OS frequently leaves Tag Logging runtime services out of synchronization.

SIMATIC WinCC Tag Logging manages data archiving via the CCAlgRtServer and CCTlgServer runtime subsystems. In PCS 7, cyclic and acyclic archive tags are generated directly from the CFC chart data blocks during OS compilation. When an archive attribute is removed, a delta compilation removes the tag from the configuration database but does not automatically flush or reorganize the active runtime Fast and Slow archive segments stored in Microsoft SQL Server. If an archive tag from the same CFC chart shares an internal channel acquisition block or cyclic logging schedule, the runtime logging service encounters orphaned internal acquisition handles. Consequently, the logging engine suspends acquisition on the remaining active tags in that group, causing flatlines or frozen trend displays in WinCC OnlineTrendControl.

Furthermore, downloading changes to the PLC (AS) is completely superfluous when modifying archive attributes. Archiving flags are strictly HMI compilation markers consumed by WinCC OS compilation tools; they alter no executable PLC code or data block layouts.

Procedure to Restore Tag Logging and Clear Archive Cache

To resolve frozen trend values and re-establish continuous data acquisition without corrupting historical database segments, execute the following corrective workflow:

Verify CFC Archive Attributes: Open SIMATIC Manager and verify that all target blocks have their archiving attributes configured correctly. Ensure that only required block I/O pins remain flagged for archiving.
Execute Complete OS Compilation with Memory Reset:
* Right-click the OS project in SIMATIC Manager and select Compile.
* In the OS Compilation Wizard, select Complete compilation instead of "Changes only".
* Check the option With memory reset to force the compilation wizard to rebuild the WinCC Tag Logging dictionary and eliminate orphaned acquisition pointers.
Reset WinCC Tag Logging Cache:
* Open the target OS project in WinCC Explorer.
* Open Tag Logging in WinCC Configuration Studio.
* Verify the Process Value Archives structure. Confirm that removed tags are completely deleted and that active tags possess valid acquisition cycles.
Perform Full OS Download or Reinitialize Runtime:
* If working in a redundant server pair, download the OS completely to the Standby OS Server first, verify archive activation, initiate redundancy switchover, and then download to the Master OS Server.
* In single-station systems, deactivate WinCC Runtime, restart the station operating system to terminate residual database engine locks, and reactivate WinCC Runtime.

Verification

In WinCC Runtime, open the process screen containing WinCC OnlineTrendControl. Confirm that trend curves for the remaining active tags update dynamically in real time.
Open WinCC Tag Logging and inspect the runtime status of archive tags. Ensure that acquisition cycles reflect the configured cycle times (e.g., 1 second, 5 seconds).
Open Windows Performance Monitor and inspect the WinCC Tag Logging counters (Process Values: Archived Values/sec) to ensure non-zero write throughput.
Review the WinCC diagnostic file CCTlgServer.log located in C:\Program Files (x86)\Siemens\WinCC\Diagnostics. Verify that no error codes such as 0x80004005 or acquisition timeout warnings are generated.

Limitations and Operational Precautions

Complete OS compilation with memory reset requires significant engineering workstation CPU time on large multiprojects.
Performing a full OS download requires stopping WinCC Runtime on a single station, causing a temporary loss of operator visualization. Always schedule full downloads during planned maintenance windows.
In redundant configurations, ensure that both OS servers complete their segment synchronization before validating trend curves. Never perform simultaneous complete downloads to both redundant servers.

Engineer FAQ

Do changes to CFC archive attributes affect the AS/PLC program?
No. CFC archiving properties (such as Long Term Archive) are WinCC HMI compilation metadata. Modifying them does not alter PLC memory, cycle time, or data blocks, making AS compilation and download unnecessary.
Why did some tags freeze while others continued archiving?
Tag Logging groups tags into acquisition packets based on common cycle rates and source AS connections. If a packet descriptor becomes corrupted due to a partial delta compilation, all tags assigned to that specific acquisition cycle or CFC chart block instance freeze.
Can frozen tags cause historical data loss?
Yes. During the time Tag Logging is frozen, values are not written to the active SQL Server database segments, creating irreversible gaps in historical trend analysis.

Technical References

SIMATIC PCS 7 OS Process Control System; WinCC Tag Logging Manual (A5E41356260-AA).
Siemens Industry Online Support Entry ID 109801081: PCS 7 Engineering System Compiling and Downloading Guide.
WinCC V7/V8 Configuration Studio Tag Logging Reference Architecture.