Resolving Strikethrough Timestamps on Outgoing Alarms in SIMATIC PCS 7 WinCC

In SIMATIC PCS 7 WinCC operator stations, alarm timestamps that render with a horizontal strikethrough upon transitioning to an outgoing state indicate that the Alarm Logging engine has flagged the message timestamp as invalid, unverified, or temporally inconsistent. This defect typically occurs when controller blocks are deleted or recompiled in CFC while WinCC Runtime is active, when the block's enable input (EN) is dynamically switched off, or when controller and OS time-of-day clocks drift out of synchronization. Resolving strikethrough timestamps requires restarting WinCC Runtime to purge the in-memory alarm cache and re-establishing system clock synchronization.

Meaning of Strikethrough Timestamps in WinCC AlarmControl

In SIMATIC WinCC AlarmControl, graphic formatting conveys alarm validity and integrity states:
- Normal Font: The timestamp was generated by a synchronized automation controller (chronological message via ALARM_8P) or verified by local WinCC time-stamping, with proper sequential transitions.
- Strikethrough Font: The Alarm Logging engine has tagged the timestamp as Invalid or Inconsistent (internal message state flag MSG_STATE_INVALID). While the text description of the alarm remains legible, WinCC strikes out the date and time to alert operators that the event chronology cannot be legally guaranteed for sequence-of-events auditing.

Root Causes: Online Block Modifications and EN Toggling

Two prevalent engineering practices trigger strikethrough timestamps during live operations:

Online Deletion or Modification of Technological Blocks:
- When a CFC chart containing an active alarm block is deleted or when block instances are re-assigned while WinCC is in runtime, the WinCC alarm cache maintains an active transaction handle for the incoming event.
- When the outgoing event arrives from the recompiled block, internal message IDs (AR_ID / MsgNo) no longer match the active transaction table. WinCC accepts the state transition but invalidates the timestamp.
Dynamically Disabling Alarm Blocks via the EN (Enable) Input:
- Toggling the block's EN input from 1 to 0 halts internal block processing.
- If the technological fault clears while EN = 0, the block cannot emit the outgoing telegram. When EN is subsequently re-enabled, the block emits an asynchronous outgoing event whose internal timestamp context is detached, generating a strikethrough.

Time Synchronization Drift and Negative Duration Anomaly

A foundational cause of invalid timestamps is clock drift between the AS controller and OS server:
- Negative Alarm Duration: If an alarm transitions to Incoming at 12:00:05.100, but before the outgoing event occurs, the AS CPU clock synchronizes backward or drifts such that the Outgoing event is stamped at 12:00:04.900, WinCC detects a negative alarm duration.
- Protocol Invalidation: Because physical time cannot flow backward, the Alarm Logging engine flags the outgoing timestamp as corrupt and renders it with a strikethrough.
- Resolution: Enforce strict plant-wide time synchronization using a central NTP time server or SICLOCK, parameterizing all S7-400 CPUs as synchronization slaves over the plant bus.

Diagnostic Matrix for Alarm Timestamp Inconsistencies

The following table details diagnostic checks and corrective actions for strikethrough alarm timestamps:

Failure SymptomIdentified Root CauseCorrective Engineering ActionStrikethrough appears only on Outgoing eventS7 CPU clock drifted backward or was resetRe-establish NTP / SIMATIC time synchronization across plant busStrikethrough persists after acknowledgmentWinCC in-memory message buffer desynchronizedDeactivate and reactivate WinCC Runtime (double-cycle restart)Specific technological block shows invalid timeBlock EN input is being toggled dynamicallyKeep EN = 1 permanently; use MsgLock or MsgEn to suppress alarmsAll alarms show strikethrough timestampsOS Server time zone / DST configuration mismatchMatch Windows time zone, daylight savings, and UTC offset across all PCs

Note: In PCS 7, never use the EN pin to disable function blocks that contain ALARM_8P calls.

Verification

Verify recovery of clean, uncorrupted alarm timestamps:
1. Deactivate WinCC Runtime on the OS Server, wait 60 seconds for SQL background processes to detach, and reactivate Runtime.
2. In WinCC AlarmControl, confirm that previous strikethrough entries in the active alarm banner have cleared.
3. Test alarm transitions: Trigger a test alarm on a motor or valve block, verify the Incoming timestamp appears in standard crisp font.
4. Clear the alarm condition; verify that the Outgoing timestamp renders cleanly without strikethroughs.
5. In SIMATIC Manager, check PLC > Diagnostic Buffer to confirm zero time-synchronization jump warnings.

Limitations and Operational Precautions

Essential rules for maintaining alarm timestamp integrity:
- Never perform online CFC block deletions or re-addressing while active alarms are unacknowledged on the operator station.
- Always use the dedicated APL parameter MsgLock (Message Lock) to suppress alarm generation during plant maintenance, rather than disconnecting power or disabling block execution via EN.
- In redundant OS server configurations, ensure both servers synchronize their system time from the central domain time source to prevent archive synchronization collisions.

Engineer FAQ

Why did restarting WinCC runtime twice fix the issue?

A single restart occasionally reconnects to persistent SQL memory caches; performing a full cycle (Exit Runtime -> Wait -> Start Runtime) clears shared memory alarm queues completely.

Can a strikethrough alarm be acknowledged by the operator?

Yes. Operators can acknowledge strikethrough alarms, but the strikethrough remains visible in historical archive views to preserve audit integrity.

What is the proper way to suppress alarms during commissioning?

Connect a boolean control signal to the MsgLock input of the APL block; this suppresses alarm generation cleanly without interrupting internal block state sequencing.