Comparing 'Archive' and 'Long-Term Archive' Attributes in PCS 7 CFC and Process Object View

In SIMATIC PCS 7 CFC and Process Object View, the 'Archive' attribute configures an analog or digital tag for standard short-term circular archiving in the OS Server's local WinCC Tag Logging database. The 'Long-term Archive' attribute configures the tag for OS Tag Logging and additionally flags it for continuous replication to a centralized Process Historian (PH) or Central Archive Server (CAS). In systems lacking a Process Historian, selecting 'Long-term Archive' causes no errors; the tag archives normally in local OS Tag Logging, ensuring standardized Control Module Types (CMTs) remain fully portable.

Archiving Attributes in PCS 7 CFC and Process Object View

In SIMATIC PCS 7, process data archiving is tightly integrated into the engineering workflow. Rather than manually creating archive tags inside the WinCC Tag Logging editor, automation engineers define archiving properties directly in the Continuous Function Chart (CFC) or the Process Object View.

When right-clicking a block output (such as MonAnL.PV_Out or PIDConL.MV) and opening Object Properties, the engineer can select an archiving option:
* No Archiving: Value is monitored in runtime but not stored in historical database tables.
* Archive: Configures standard circular archiving on the local OS Server.
* Long-Term Archive: Configures local archiving and marks the tag for replication to the plant-wide historian.

These properties can also be modified in bulk across thousands of block parameters using the Process Object View (Parameters tab).

Functional Comparison: 'Archive' vs 'Long-Term Archive'

The technical behavior and data lifecycle associated with each archiving attribute are detailed below:

Architectural Property'Archive' (Short-Term Archiving)'Long-Term Archive' (Historian Archiving)Target Storage NodeLocal OS Server SQL Database (WinCC Tag Logging)Process Historian (6ES7652-7AX58-0YB0) or legacy CASTypical Data RetentionCircular buffer: Days to weeks (e.g., 7 to 30 days)Multi-year retention: 1 year, 5 years, or permanentReplication MechanismLocal disk write via CCWriteArchiveServer.exeSpooled by PH Ready service and transferred via MSMQQuery ToolsWinCC Online Trend Control, local faceplate trendsSIMATIC Information Server web portal, Excel Add-inLicensing ImpactConsumes WinCC OS RT Archive Tags (512 included)Consumes Process Historian Archive Tag licenses

Table 1: Comparison of archiving attributes in SIMATIC PCS 7.

OS Compilation Workflow and Tag Logging Ingestion

During the Compile OS process, the PCS 7 AS/OS Engineering compiler scans all CFC charts for block parameters assigned archiving attributes:
1. Archive Generation: For every parameter marked Archive or Long-term Archive, the compiler creates a process tag in WinCC Tag Management and inserts an archive tag into the Process Value Archive (Tag Logging Fast or Tag Logging Slow based on acquisition cycle).
2. Historian Flagging: If the parameter is marked Long-term Archive, the compiler sets the internal database flag LongTerm = 1 in the WinCC Tag Logging archive catalog.
3. When the OS Server runs, the PH Ready service queries tags with LongTerm = 1 and registers them with Process Historian for continuous background replication.

System Behavior in Architectures Without Process Historian or CAS

A frequent practical concern in small or medium PCS 7 installations is whether marking parameters with Long-term Archive causes system faults or compiler warnings if the plant has only redundant OS Servers without Process Historian:
* Zero Fault Impact: The OS Compiler generates standard Tag Logging archive tags identically. WinCC Runtime records the data in local circular segments without error.
* Quiescent Service: On an OS Server without Process Historian configured, the PH Ready service simply remains idle or disabled. No alarms, compiler errors, or runtime degradation occur.
* Best Practice for Control Module Types (CMTs): Siemens and leading engineering standards recommend configuring Long-term Archive by default on all standardized technological templates (CMTs). This guarantees that the template library can be deployed seamlessly across small standalone plants and large enterprise multi-server sites without modifying CFC chart properties.

Verification

To confirm proper archiving configuration:

In SIMATIC Manager, select a plant hierarchy folder and open Process Object View > Parameters.
Filter the Archiving column: verify that intended parameters display Archive or Long-term Archive.
Execute Options > Compile OS (Changes Only).
Open WinCC Explorer on the ES or OS Server.
Open Tag Logging: verify that the tags appear in the Process Value Archive with the expected acquisition cycle (e.g., 1 s or 5 s).
Activate WinCC Runtime: open the trend window and confirm that historical process values are actively plotting.

Limitations and Operational Precautions

Archiving excessive numbers of high-frequency tags on an OS Server without a Process Historian can overburden local disk I/O and degrade WinCC runtime responsiveness.
Avoid marking noisy, non-critical status bits as Long-term Archive; reserve long-term storage for regulated process values, quality metrics, and batch parameters.
When Process Historian is deployed, ensure that Process Historian Archive Tag expansion licenses match the number of tags marked Long-term Archive.

Engineer FAQ

What replaced the Central Archive Server (CAS) in PCS 7?

Starting with SIMATIC PCS 7 v8.0, the legacy Central Archive Server (CAS) was completely replaced by SIMATIC Process Historian (PH), which utilizes modern Microsoft SQL Server enterprise database architecture.

Can I change a tag from Archive to Long-term Archive online?

Yes. In Process Object View, change the parameter archiving attribute and perform an OS Compile (Changes Only). The update applies without interrupting controller execution or stopping WinCC Runtime.

Does Tag Logging Slow use more CPU than Tag Logging Fast?

Tag Logging Fast stores high-frequency data (< 1 minute) directly in binary cache, while Tag Logging Slow stores lower-frequency data with additional compression, optimizing long-term disk consumption.