Configuring Multi-Year Archive Retention for Simulation and Bypass Auditing in WinCC V7.4

In SIMATIC PCS 7 WinCC V7.4 environments, auditing which actuators and field instruments have been placed in simulation (SimOn) or interlock bypass over extended periods (such as 1 to 2 years) fails when Alarm Logging circular archives retain only 3 months of data. Overcoming this retention limit requires expanding archive size limits in Alarm Logging Archive Configuration, configuring automated segment backups to network storage, or deploying SIMATIC Process Historian for long-term historical compliance.

Role of Long-Term Audit Trails for Simulation and Interlock Bypasses

In regulated chemical, pharmaceutical, and offshore facilities, process safety standards (such as OSHA 1910.119, IEC 61511, and FDA 21 CFR Part 11) mandate rigorous accounting of safety overrides:
* The Audit Requirement: Plant safety auditors require reporting every instance where an actuator or transmitter was placed into Simulation mode (SimOn = 1) or had its interlock bypassed, including the exact timestamp, duration, and operator identity across the past 1 to 2 years.
* The Operational Problem: Engineers attempting to filter WinCC Alarm Logging for SimOn messages discover that records older than 3 to 6 months have completely vanished from the system.
* This is not a software malfunction; it is the deterministic result of WinCC's default circular database archive configuration.

Mechanics of WinCC Alarm Logging Circular Segmented Archives

WinCC stores historical alarm messages within Microsoft SQL Server using a segmented circular buffer architecture:
* Single Segment: A pair of SQL database files (.mdf data file and .ldf transaction log) covering a defined slice of time (e.g., 1 week or 1 month) or a maximum file size (e.g., 2 GB).
* Total Archive: Composed of multiple contiguous segments up to a configured Maximum Total Size (e.g., 10 GB) or Time Period of All Segments (e.g., 3 months).
* Circular Overwrite: As soon as either the total size limit or total time limit is reached, SQL Server automatically detaches and permanently overwrites the oldest segment to allocate space for incoming messages. If the total time period is configured for 3 months, messages from 4 months ago are purged automatically.

Step-by-Step Configuration to Extend Local Archive Retention to 1–2 Years

To expand the online retention period to 2 years directly on the OS Server:
1. Open WinCC Explorer on the OS Server.
2. Expand Alarm Logging, right-click Archive Configuration -> Messages, and select Properties.
3. Configure Single Segment Parameters:
* Set Time period covered by a single segment to 1 Month (or 1 Week).
* Set Max. size of a single segment to 2048 MB (2 GB).
4. Configure Total Archive Parameters:
* Under Time period covered by all segments, select 2 Years (or enter 730 days).
* Under Max. size of all segments, calculate adequate hard drive capacity:
$$ ext{Total Storage} = 24 ext{ segments} imes 2 ext{ GB} = 48 ext{ GB}$$
Ensure the target hard drive partition (e.g., D: drive) has at least 100 GB of free space.
5. Click OK. WinCC updates its internal retention parameters immediately without restarting runtime.

Automated Backup Strategies and SIMATIC Process Historian Integration

For facilities requiring multi-year compliance without burdening local OS server disks:
* WinCC Automated Backup:
* In the Archive Configuration -> Messages -> Properties dialog, check the box Activate Backup.
* Specify a destination path on a dedicated Network Attached Storage (NAS) or backup server (e.g., \BACKUP_SRV\WinCC_Archives\).
* When SQL Server finishes each monthly segment, it copies the .mdf/.ldf files to the backup share before overwriting local disk space.
* Historical backup segments can be temporarily linked back into WinCC runtime at any time using the Link Archive function.
* SIMATIC Process Historian (PH):
* In enterprise PCS 7 architectures, long-term archiving standardizes on Process Historian.
* OS servers retain only 1 to 3 months of local cache, while all alarm transactions stream in real time to the dedicated Process Historian server for 10+ year retention, auditable via Information Server reports.

Verification

In WinCC Alarm Logging, verify that the archive configuration properties reflect the new 2-year retention window.
In Windows File Explorer, open the project ArchiveManager/Message/ directory: verify that historical segment files accumulate with monthly timestamps.
In WinCC OS runtime, open the Long-Term Archive List in AlarmControl:
Apply a selection filter: Message text contains 'Simulation' or Tag = SimOn.
Specify a query start date 12 months in the past: confirm that historical simulation events populate with complete timestamps and operator names.

Limitations and Operational Precautions

Storing 2 years of high-frequency alarms locally requires substantial disk space; ensure the OS server drive is regularly monitored to prevent disk full lockups.
Running SQL queries across multi-year archives can take several seconds to minutes; advise operators to use tight date/time filters when auditing specific tags.
Local archive expansion does not require additional licenses; however, deploying SIMATIC Process Historian requires dedicated server hardware and PH archive licenses.

Engineer FAQ

Why did WinCC only show 3 months of historical simulation alarms?
Because the default Alarm Logging archive configuration was set to a 3-month total time limit or reached its maximum disk size limit.
Where in WinCC Explorer is alarm retention time adjusted?
Under Alarm Logging -> Archive Configuration -> Messages -> Properties.
What happens to old alarm segments when the archive limit is reached?
Without backup enabled, the oldest SQL database segment is permanently overwritten and destroyed.
How do I view archived alarm segments stored on a backup server?
Use the Link Archive function in WinCC Alarm Logging to mount historical .mdf files temporarily into runtime.
Does expanding the alarm archive retention require an OS re-compile?
No, archive configuration is an OS server setting adjusted directly in WinCC Explorer without compiling.
What S7 tag typically triggers an alarm when an actuator is simulated?
The channel driver parameter SimOn or technological block status SimAct.
Can Process Historian store alarms indefinitely?
Yes, Process Historian is designed for enterprise long-term storage across decades using scalable RAID storage.
What is the recommended single segment size for WinCC Alarm Logging?
Between 500 MB and 2048 MB (2 GB) covering a 1-month or 1-week time window.
What user authorization is required to modify archive configuration?
Windows Administrator rights and membership in the local SIMATIC HMI security group on the OS Server.
How can operators export simulation audit reports to Excel?
Click the Export button on the WinCC AlarmControl toolbar to save filtered records to a .csv file.

Technical References

SIMATIC HMI WinCC V7.4 / V7.5 Alarm Logging System Manual
SIMATIC PCS 7 Process Historian and Information Server Manual
Siemens Industry Online Support Entry: WinCC Archive Configuration and Retention (Entry ID 34473263 / 299910)
ISA-18.2 / OSHA 1910.119 Process Safety Management Guidelines