How to Resolve WinCC Archive Tags Flatlining with Uncertain Status After Download of Changes

To resolve the issue where specific analog archive tags (e.g., UserAna1 on MotSpdCL, MonAnL.PV_Out, or PIDConL.PV) stop archiving and flatline with an 'uncertain' quality code (16#40 or 16#4C) following a WinCC OS download of changes, engineers must resolve database schema lock conflicts and refresh the dynamic connection file. During a delta changes download, WinCC's Tag Logging Fast and Slow engines must dynamically reorganize database tables. If background archiving threads (CCAlgRtServer.exe, CCDataServer.exe) hold open locks, the new tag schema is not committed, causing affected archive tags to freeze while live online values continue updating. The immediate resolution requires restarting the OS runtime or deleting the temporary project connection file (<ProjectName>.dcf) and executing a full compile.

Mechanics of Tag Logging Schema Updates During Download of Changes

In SIMATIC PCS 7, downloading changes (Download Changes Only) allows engineers to deploy newly created CFC charts, block icons, and tag logging configurations without halting the plant's active WinCC OS Runtime.

During an OS delta download:
1. The Engineering Station transfers new database configuration records to the target OS Server.
2. The WinCC project manager notifies the Tag Logging runtime component (CCAlgRtServer.exe and CCDataServer.exe) that the tag logging schema has changed.
3. The Tag Logging engine must attach the new tags to the active circular archive segments (TagLoggingFast or TagLoggingSlow) and dynamically re-index the archive tables in Microsoft SQL Server.

Under normal conditions, this operation occurs in fractions of a second without interrupting active logging.

Root Causes: Database Schema Locks and .dcf File Corruption

When specific archive tags stop updating—flatlining as a horizontal line in trend displays and displaying an 'uncertain' or 'bad quality' icon (16#40 / 16#4C)—the failure originates from one of three conditions:

1. SQL Database Schema Lock Conflict

If the OS Server is experiencing heavy historical query traffic from OS Clients, WebNavigator sessions, or Process Historian data extraction, the active SQL database segment file is locked. The delta download cannot restructure the tag logging table, leaving the modified tag definitions disconnected from the archive engine.

2. Project Database Connection File (`.dcf`) Corruption

The file <Project_Name>.dcf located in the OS project directory caches internal database connection handles between WinCC Tag Management and SQL Server. If this file becomes corrupted or out of synchronization during delta downloads, newly compiled archive tags are improperly referenced.

3. Redundant Partner Desynchronization

In redundant OS server pairs, if Server A applies the changes cleanly but Server B encounters a network delay during redundancy update propagation, the synchronization manager suspends logging on the affected tags to prevent historical record divergence.

Step-by-Step Resolution: Runtime Restart and .dcf Regeneration

Follow this procedure to restore logging on flatlined tags:

Temporary Online Recovery (Single Server Restart)

On the affected redundant server (e.g., Server B), open WinCC Explorer and deactivate Runtime.
Wait until all WinCC processes close cleanly.
Reactivate Runtime on Server B.
The Tag Logging engine will rebuild its memory buffers from SQL Server, resynchronize with Server A, and resume archiving the flatlined tags immediately.

Permanent Project File Recovery (Deleting Corrupted .dcf)

If restarting runtime fails to restore tag logging:
1. Deactivate WinCC Runtime on the OS Server.
2. Close WinCC Explorer.
3. Launch an administrative Command Prompt and run CCCleaner.exe:
cmd "C:\Program Files (x86)\Siemens\WinCCin\CCCleaner.exe"
4. In Windows Explorer, navigate to the OS project directory:
<Project_Path>\<OS_Name>\
5. Locate the file <Project_Name>.dcf and delete it (WinCC automatically regenerates this file when the project is reopened).
6. Open the project in WinCC Explorer.
7. On the Engineering Station, execute a full OS compile (Entire OS) and perform an OS download.
8. Activate Runtime; all analog and binary archive tags will log continuously.

Preventive Best Practices for OS Delta Downloads in Redundant Systems

To avoid recurring tag logging freezes during routine engineering updates:

Avoid Frequent Micro-Downloads: Consolidate multiple small CFC/OS modifications into planned, batched downloads rather than executing rapid successive delta downloads.
Close Heavy Trend Views on Clients: Prior to initiating an OS delta download, ensure that engineering workstations and operator clients are not running extensive historical trend queries spanning months of data.
Verify Redundancy Synchronization Health: Always confirm that WinCC Redundancy reports Synchronized before triggering a delta download.
Install Latest WinCC Updates: Siemens regularly releases hotfixes addressing Tag Logging dynamic schema updates (e.g., PCS 7 V8.1 SP1 Upd updates). Ensure all servers are updated.

Archive Failure Symptoms and Resolution Reference Matrix

The following table outlines the diagnostic symptoms, causes, and corrective actions for archive tag stalls:

Symptom / ObservationQuality CodeRoot CauseCorrective ActionTrend line turns flat; live value updates16#40 (Uncertain)Tag Logging thread failed to re-attach tagRestart WinCC Runtime on affected serverAll new archive tags missing in trend16#00 (Bad)Tag not marked for archiving during compileVerify 'Archive' attribute in CFC / Process Object ViewTag stops archiving on Server B only16#4CRedundant archive sync interruptedCheck CCRedSync.log; wait for redundancy syncPersistent flatline across reboots16#40Corrupted <Project>.dcf connection cacheDelete <Project>.dcf and recompile Entire OSShadowed block icons and frozen tagsVisual artifactIncomplete OS delta picture transferPerform full picture transfer in OS download

Executing proper file maintenance preserves historical trend continuity without requiring unscheduled plant downtime.

Verification

To verify that the flatlined archive tags have resumed normal operation:
1. Open the WinCC process picture containing the affected motor or analog control faceplate.
2. Open the historical trend view for the affected variable (e.g., UserAna1 or PV_Out).
3. Verify that the trend line is actively updating with real-time dynamic variations rather than displaying a flat horizontal line.
4. Confirm that the quality status symbol on the trend control indicates 'Good' (16#80) without uncertain or bad status flags.
5. In WinCC Explorer -> Tag Logging, verify that the archive tag properties reflect the correct acquisition cycle and archiving parameters.

Limitations and Operational Precautions

Deleting <ProjectName>.dcf is completely safe as long as WinCC is fully closed; never delete or modify SQL .mdf or .ldf database files.
While a server is restarting to recover tag logging, ensure the redundant partner is healthy to maintain uninterrupted plant operations.
Do not perform 'Download Entire OS' while the process is running unless the server pair is switched over sequentially.
Always maintain identical software update revisions across both servers in a redundant pair.

Engineer FAQ

Why does the online trend show live values while the archive trend flatlines?

Online trends read live instantaneous values directly from AS communication drivers via RAM memory channels, whereas archive trends read from the Microsoft SQL Server Tag Logging database engine.

Does restarting one server in a redundant pair cause data loss in historical archives?

No. While one server restarts, the partner server continues logging all tags locally. Upon reconnection, WinCC Redundancy automatically backfills the missing time window via redundancy synchronization.

What does the quality code 16#40 mean in WinCC Tag Logging?

16#40 represents 'Uncertain - Initial value / Stale data'. In Tag Logging, it indicates that the archiving subsystem is not receiving fresh time-stamped samples from the communication driver.

Technical References

Related Tags

Tag Logging
Download Changes
Flatline Archive
Uncertain Status
WinCC Redundancy

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How to Resolve WinCC Archive Tags Flatlining with Uncertain Status After Download of Changes