Configuring Short-Term Tag Logging vs Long-Term Archiving for APL Block Parameters in PCS 7

In SIMATIC PCS 7, the distinction between 'Archiving' and 'Long-term archiving' on Advanced Process Library (APL) block parameters dictates where and how historical process values are retained. Selecting 'Archiving' logs the parameter locally on the WinCC OS Server within cyclic circular SQL database segments—split into TagLoggingFast (acquisition cycles <= 1 minute) and TagLoggingSlow (acquisition cycles > 1 minute), with retention times configured in WinCC Tag Logging Archive Configuration (e.g., 1 to 7 days). Selecting 'Long-term archiving' flags the tag for streaming across the terminal bus via PH-Ready (CCCAPHServer) to SIMATIC Process Historian (PH) or a legacy Central Archive Server (CAS), where records are stored permanently in high-capacity enterprise databases.

Architectural Difference: Short-Term OS Logging vs Long-Term Archiving

In SIMATIC PCS 7, process value archiving is structured across two distinct architectural tiers to balance runtime performance with long-term data preservation:

1. Short-Term Archiving (Local OS Server Tag Logging)

Designed for real-time operator trend analysis, incident investigation, and shift reporting. Historical values are written directly by the WinCC OS Server to a local Microsoft SQL Server instance. Because disk storage on OS Servers is finite, data is stored in circular, FIFO (First-In, First-Out) database segments that automatically overwrite the oldest data once the allocated time or disk size limit is reached.

2. Long-Term Archiving (SIMATIC Process Historian / Central Archive Server)

Designed for multi-year regulatory compliance, enterprise batch reporting, and plant performance auditing. The PH-Ready component (CCCAPHServer) monitors local OS archive segments, compresses closed segment blocks, and streams them across the terminal bus to the centralized Process Historian server, where records are preserved indefinitely across expandable storage arrays.

TagLoggingFast vs TagLoggingSlow Mechanics and Segmentation

WinCC partitions local short-term tag archiving into two specialized database engines based on acquisition frequency:

TagLoggingFast

Acquisition Frequency: Cycles of 1 minute or less (e.g., 1 s, 2 s, 5 s, 10 s, 1 min).
Storage Optimization: Uses proprietary, high-speed binary delta-compression algorithms optimized for rapidly changing analog variables (e.g., pump discharge pressures, flow rates, motor currents).
Operational Role: Provides immediate, high-resolution trend displays on operator client stations.

TagLoggingSlow

Acquisition Frequency: Cycles of more than 1 minute (e.g., 2 min, 5 min, 10 min, 1 hour).
Storage Optimization: Designed for slowly drifting process values (e.g., large tank levels, ambient temperatures, daily production totalizers).
Operational Role: Minimizes SQL transaction overhead for tags that do not require second-by-second sampling.

Configuring Retention Periods and Segment Sizes in WinCC Explorer

To adjust the short-term retention duration on the WinCC OS Server:

Open WinCC Explorer on the OS Server or Engineering Station.
In the navigation tree, right-click Tag Logging -> Archive Configuration.
Select TagLoggingFast or TagLoggingSlow:
* Size of a single segment: Specifies the maximum disk size (e.g., 500 MB) or time period (e.g., 1 day) for individual SQL database files.
* Max. size of all segments: Specifies the total storage pool allocated for the archive (e.g., 20 GB).
* Time period covered by all segments: Specifies the total retention window (e.g., 7 days or 30 days).
When the maximum size or time limit is reached, WinCC detaches and deletes the oldest segment.
If 'Backup configuration' is enabled, detached segments are copied to an external network share before deletion.

Enabling Long-Term Archiving in Process Object View and CFC

To assign process variables to long-term archiving in bulk:

In SIMATIC Manager, open the target project and switch to Process Object View (View -> Process Objects).
Select the Parameters tab.
Locate the desired APL block parameters (e.g., MonAnL.PV_Out, PIDConL.MV, MotSpdCL.UserAna1).
In the Archive column, select from the dropdown:
* No archiving: Parameter is not logged.
* Archiving: Logged in local short-term Tag Logging only.
* Long-term archiving: Logged in local Tag Logging AND automatically forwarded to Process Historian.
In the Archive cycle column, select the desired sampling rate (e.g., 5 s or 1 min).
Execute a target compile: Right-click OS -> Compile -> Entire OS with 'With memory reset' to generate ProcessHistorian.cfg and update Tag Management.

Archiving Tier Comparison and Parameter Configuration Matrix

The following table summarizes the operational parameters, storage locations, and sizing rules for PCS 7 archiving tiers:

Parameter / FeatureTagLoggingFastTagLoggingSlowSIMATIC Process Historian (PH)Acquisition Cycle<= 1 minute (1 s – 60 s)> 1 minute (2 min – hours)Determined by OS Tag Logging cycleTypical Retention Time1 to 7 days7 to 30 days1 to 10+ years (Permanent)Storage TechnologyCircular SQL Segments (.mdf)Circular SQL Segments (.mdf)Central SQL Server + Store-and-ForwardHost WorkstationLocal WinCC OS ServerLocal WinCC OS ServerDedicated Process Historian ServerCFC / PO-View SettingArchiving (<= 1 min)Archiving (> 1 min)Long-term archivingPrimary ConsumerOS Client Real-Time TrendsOS Client Historical TrendsInformation Server & Enterprise Reports

Properly partitioning fast and slow archives prevents storage bottlenecks while preserving critical operational records.

Verification

To verify that tag archiving and retention are configured correctly:
1. In WinCC Explorer, open Tag Logging and verify that the target tag appears in the TagLoggingFast or TagLoggingSlow archive tree.
2. In WinCC Runtime, open a Trend Control, insert the archive tag, and verify that data points record continuously.
3. Inspect <Project_Dir>\ArchiveManager\TagLoggingFast in Windows Explorer; verify that individual .mdf database segments match the configured size and timestamp boundaries.
4. On the Process Historian server, open the Process Historian Management Console (PHMC) and confirm that tags flagged for 'Long-term archiving' actively increment the incoming transaction rate.

Limitations and Operational Precautions

Never allocate more than 80% of the OS Server's physical hard drive capacity to WinCC archive segments; running out of disk space halts SQL Server logging.
Avoid assigning excessive numbers of tags to 1-second acquisition cycles without operational justification, as high-frequency logging increases disk I/O load.
Modifying archive parameters from 'Archiving' to 'Long-term archiving' requires an OS compile and download to activate the changes on runtime servers.
Always validate final license quantities, archive tag packs, and MLFBs against the applicable Siemens catalog and authorized distributor quotation.

Engineer FAQ

What happens if a tag configured for 5-second archiving is assigned to TagLoggingSlow?

WinCC automatically routes tags based on their acquisition cycle. Any tag with an acquisition cycle of 1 minute or less is automatically handled by the TagLoggingFast engine, regardless of manual tree placement.

Can I extend short-term OS retention from 7 days to 6 months on the OS Server?

While technically possible if disk space permits, storing 6 months of high-frequency data locally can degrade OS client trend query responsiveness. Storing data beyond 30 days should be delegated to Process Historian.

What is the Central Archive Server (CAS)?

CAS was the predecessor to SIMATIC Process Historian used in PCS 7 V6.x and V7.x. Starting with PCS 7 V8.0, CAS was replaced by Process Historian with enhanced high-capacity time-series storage.

Technical References

Related Tags

Tag Logging
TagLoggingFast
TagLoggingSlow
Long-Term Archiving
Process Historian

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Configuring Short-Term Tag Logging vs Long-Term Archiving for APL Block Parameters in PCS 7