C135 PCS 7 (PCS7)
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Configuring Data Segregation and Archive Verification Between WinCC OS and Process Historian

Configuring Data Segregation and Archive Verification Between WinCC OS and Process Historian

In SIMATIC PCS 7 with Process Historian (PH), Alarm Logging Runtime and Tag Logging Runtime must remain permanently activated in the WinCC OS Server Startup list. The OS servers maintain short-term cyclic segment archives locally, while the background Process Historian Agent (PH-Ready) automatically intercepts and streams data to the central Historian server. All WinCC alarms are replicated to the Historian by default without special configuration, whereas process values require selecting 'Long-term archiving' in Tag Logging. Historical storage can be verified via the Process Historian Management Console dashboard and by querying historical trends beyond the OS retention window.

Table of Contents

Architecture of Tiered Archiving: WinCC OS vs Process Historian

In SIMATIC PCS 7, plant data management is partitioned into a two-tier archiving hierarchy:
* Tier 1: Short-Term Local Archiving (WinCC OS Servers):
Redundant WinCC OS servers record high-speed cyclic process values and alarm sequences into rolling Microsoft SQL Server database segments (TagLoggingFast, TagLoggingSlow, AlarmLogging). Local OS disk capacity is engineered for rapid operator retrieval over a rolling window (typically 1 to 7 days).
* Tier 2: Long-Term Enterprise Archiving (SIMATIC Process Historian):
The Process Historian (PH) (6ES7652-0XX08-1XB0) acts as the central, high-capacity historical repository for the entire plant. Running on dedicated redundant server hardware, PH stores decades of historical time-series data, batch records from SIMATIC BATCH, and alarm messages in a compressed Microsoft SQL database structure.
* The Bridge: Process Historian Ready Component (PH Agent):
Installed automatically on every OS server, the PH-Ready service acts as a background real-time data pump. It continuously monitors the local OS SQL archive segments, captures new data packets, compresses them, and securely transfers them across the terminal bus to the Process Historian database.

Why Alarm Logging and Tag Logging Runtime Must Remain Active on the OS

A frequent conceptual misunderstanding is assuming that because a Process Historian server is installed, the local WinCC OS servers should disable their internal archiving engines to save memory:

  • The Local Engine Requirement:
    The Process Historian does not poll automation stations or field instruments directly. It receives historical data exclusively from the WinCC OS runtime archiving engines.
  • Consequence of Deactivation:
    If an engineer unchecks Alarm Logging Runtime or Tag Logging Runtime in the WinCC Computer Properties startup list:
    1. The WinCC OS stops recording alarm sequences and cyclic analog tags into local SQL memory.
    2. The PH-Ready agent finds zero data to replicate.
    3. The Process Historian receives no updates, completely halting plant-wide historical archiving.
  • Operational Decoupling:
    Keeping local logging active ensures that even if the Process Historian server is shut down for maintenance or network cables are severed, the OS servers continue buffering alarms and trends locally. Once the Historian comes back online, the PH-Ready agent automatically backfills missing records without data loss.

Tag Logging Configuration: Short-Term vs Long-Term Archiving Flags

In the WinCC Tag Logging editor, each configured archive tag possesses an attribute that controls its lifecycle:

  • Standard Archive Tag:
    Recorded exclusively into the local OS rolling circular archive (TagLoggingFast or TagLoggingSlow). When the configured local disk quota is reached, older segments are permanently overwritten.
  • Long-Term Archiving Checkbox:
    Checking Long-term archiving on a tag flags that process variable for continuous extraction by the PH-Ready service. The tag is logged locally on the OS, and as each data block is written, the PH-Ready agent duplicates the records and transmits them to the Process Historian.
  • Cyclic Storage Tiers:
  • TagLoggingFast: Used for acquisition cycles <= 1 minute.
  • TagLoggingSlow: Used for acquisition cycles > 1 minute or event-driven archiving.

Automatic Alarm Replication to the Process Historian

Unlike analog tags in Tag Logging, WinCC Alarm Logging does not have a separate 'Long-Term Archiving' checkbox:

  • Universal Replication:
    In SIMATIC PCS 7, all messages processed by Alarm Logging (including process alarms, warnings, operator actions, and system faults) are automatically treated as long-term historical records.
  • Mechanism:
    The PH-Ready agent connects directly to the local WinCC Message Archive database (AlarmLogging). Whenever an alarm state transitions (COME, GO, ACK), the message frame is ingested by the PH agent and mirrored to the Process Historian database HistorianStorage.
  • Centralized Regulatory Audit:
    Because all alarms are archived globally, safety and compliance audits can query decades of operator actions and trip events directly from the Process Historian without relying on fragmented OS server disks.

Verifying Historian Data Ingestion and Archive Health

Engineers can prove that data is safely committed to the Process Historian using three independent verification techniques:

  1. Process Historian Management Console (PHMC):
    Open the PHMC dashboard on the Historian server:
    * Source Clients: Must show the number of active OS servers (e.g., 2 for a redundant OS pair).
    * Stored Values: Displays an incrementing counter of archived tag samples.
    * Stored Messages: Displays an incrementing counter of archived alarm frames.
  2. WinCC Trend and Alarm Controls Across Time Boundaries:
    * On an OS Client, configure a WinCC Online Trend Control.
    * Query a tag over a time range spanning 30 days ago (well past the 7-day OS local retention limit).
    * If the trend displays historical data seamlessly, WinCC is successfully routing the query through the OLE-DB SIMATIC Historian Provider to the Process Historian.
  3. Direct SQL Database Verification:
    On the Process Historian server, open SQL Server Management Studio (SSMS). Query the HistorianStorage database to verify records in dbo.TagHistory and dbo.MessageHistory.

Comparison Table: WinCC OS Local Archives vs Process Historian Storage

The following table details the operational differences between local WinCC OS archives and Process Historian:

Architectural FeatureWinCC OS Server Local ArchiveSIMATIC Process HistorianPrimary ScopeShort-term tactical operator monitoringLong-term enterprise reporting & complianceTypical Data Retention1 to 7 days (rolling circular buffer)Multi-year to multi-decade permanent storageStorage EngineLocal WinCC MS SQL Server Express / StandardEnterprise MS SQL Server with PH PartitioningTag ConfigurationTag Logging acquisition cycles"Long-term archiving" checkbox enabledAlarm ConfigurationAlarm Logging message classesAutomatic universal replication (all alarms)Data Recovery After OutageOverwritten when circular buffer fillsAuto-backfill via PH-Ready store-and-forwardLicensing PackageOS RT PO License (6ES7658-2CX58-0YB5)Process Historian Basic / Package License (6ES7652-0XX08-1XB0)Hardware TopologySingle or Redundant OS Server PairDedicated Simatic IPC / High-Capacity Server Pair

Step-by-Step Procedure to Verify and Audit Long-Term Archiving

Follow this verified engineering workflow to audit and validate Process Historian operation:

  1. Verify WinCC Startup Configuration:
    * Open WinCC Explorer on both Redundant OS Servers.
    * Right-click Computer > Properties > Startup.
    * Confirm that Alarm Logging Runtime and Tag Logging Runtime are checked.
  2. Audit Tag Logging Flags:
    * Open Tag Logging in WinCC Explorer.
    * Select the archive folder (e.g., ProcessValues).
    * In the tag table, verify that critical analog process tags have the Long-term archiving column checked.
  3. Check PH-Ready Service Status:
    * On the OS Server, open Windows Services (services.msc).
    * Confirm that the service SIMATIC Process Historian Ready is Running with Startup type Automatic.
  4. Inspect PH Management Console:
    * Log into the Process Historian server.
    * Launch Process Historian Management Console.
    * Under Status / Dashboard, verify that the state is Active and all OS Server clients show connected status with green indicators.
    * Confirm that Stored values and Stored messages increment continuously during plant operation.
  5. Execute a Cross-Retention Historical Query:
    * In WinCC Runtime on an OS Client, open a trend screen.
    * Set the time ruler to 14 days in the past (beyond the local OS buffer).
    * Confirm that historical curves render without gaps.

Verification

Verify overall system health and data integrity using the following checks:
1. In the Process Historian Management Console, ensure the status bar displays "Database state: Normal" with 0 pending migration errors.
2. Generate a test alarm in the AS (e.g., trip an analog transmitter high limit); confirm that the alarm appears in WinCC Alarm Logging and increments the "Stored messages" count in PH within seconds.
3. Verify that SQL Server database growth on the OS server stabilizes once the local circular archive reaches its maximum configured size (e.g., 10 GB), while the Process Historian database continues expanding normally.
4. Check <WinCC_Project>\Diagnostics\SIMATIC_Historian_Provider.log on the OS Server to verify that all historical queries execute cleanly.

Limitations and Operational Precautions

  • Never Disable Local Logging: Disabling Alarm Logging or Tag Logging on the OS server permanently severs the data pipeline to the Process Historian.
  • Network Bandwidth on Terminal Bus: Streaming hundreds of high-speed archive tags to the Process Historian consumes substantial network bandwidth. Ensure the terminal bus utilizes dedicated 1 Gbps industrial switches with quality-of-service (QoS) enabled.
  • Store-and-Forward Buffer Limits: If the Historian is offline, the OS server buffers data in local SQL segments. If the Historian remains offline longer than the OS circular buffer retention window, buffered data will be permanently overwritten and lost.
  • Commercial Accuracy: Ensure that the Process Historian Server package (6ES7652-0XX08-1XB0) and WinCC Archive licenses are correctly scaled to match the total number of long-term archive tags. Validate license tiers with an authorized Siemens distributor quotation.

Engineer FAQ

How does WinCC know whether to read trend data from the OS or the Process Historian?

WinCC uses an internal hybrid query engine (SIMATIC Historian Provider). When an operator requests a trend, WinCC first queries the local OS circular database for recent data; if the time range extends beyond the local buffer, it automatically routes the remaining query to the Process Historian via OLE-DB.

Can I configure Process Historian to archive alarms only from specific plant areas?

No. The PH-Ready agent replicates the entire WinCC Message Archive by default. Filtering is performed during visualization and reporting using WinCC Alarm Controls, Information Server, or SQL queries.

What happens to historical data if the local OS circular archive fills up while PH is offline?

If the Process Historian remains offline longer than the configured local OS buffer retention period (e.g., more than 7 days), the oldest local segments will be overwritten, resulting in permanent unrecoverable data loss for that time window.

Does Process Historian require a separate license for every WinCC client?

No. Process Historian licensing is based on the central Historian server capacity (archive tags and packages). Connected WinCC OS servers require the standard PCS 7 OS runtime licenses.

Technical References

Related Articles

Related Tags

  • Process Historian
  • WinCC Archiving
  • Tag Logging
  • Alarm Logging
  • PH-Ready
  • Long-Term Archiving
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