Evaluating Process Historian (PH) Archiving Capabilities for OS Reference Stations in SIMATIC PCS 7 Architectures

Evaluating Process Historian (PH) Archiving Capabilities for OS Reference Stations in SIMATIC PCS 7 Architectures

In SIMATIC PCS 7, an OS Reference (OS Ref) station cannot archive process tags or alarms directly into SIMATIC Process Historian (PH). In the Process Historian Management Console under 'Plant Structure', only the base OS Single Station (or primary OS Server) appears as an active data source, with client counts reflecting that the OS Ref stations are visual clients. Because an OS Reference station does not host an independent Tag Management or Alarm Logging database—it visualizes runtime data originating from the master OS Single Station—all historical archiving is executed exclusively by the base OS Single Station. Archiving the base station captures 100% of the plant's tags and alarms in Process Historian without requiring separate OS Ref archiving.

Table of Contents

• Process Historian Integration Principles and Database Binding
• Why OS Reference Stations Cannot Archive Directly to Process Historian
• Plant Structure Representation in Process Historian Management Console
• OS Station Type Archiving Capabilities and PH Support Table
• Verification
• Limitations and Operational Precautions
• Engineer FAQ
• Technical References
• Related Articles
• Related Tags

Process Historian Integration Principles and Database Binding

SIMATIC Process Historian (PH) serves as the centralized, long-term enterprise archive for SIMATIC PCS 7 plants:
- PH-Ready Ingestion Mechanism:
* Historical archiving relies on the Process Historian Ready (PH-Ready) service installed on participating WinCC operator stations.
* PH-Ready operates as a low-level database replication agent that binds directly to active Microsoft SQL Server database segments (ArchiveManager\TagLoggingFast, TagLoggingSlow, and AlarmLogging).
* When an OS station completes a database archive segment (e.g. 500 MB segment or 24-hour cycle), PH-Ready streams the binary chunk to the Process Historian over the Terminal Bus.
- The Requirement for an Autonomous Database:
* For PH-Ready to forward data, the host station must possess an active, compiling SQL Server database that registers unique station GUIDs and variable metadata tables (VariableID).

Why OS Reference Stations Cannot Archive Directly to Process Historian

In multi-monitor or satellite operator room designs, engineers often deploy OS Reference stations to minimize engineering:
1. The Nature of an OS Reference:
- An OS Reference station is an architectural clone of a base OS Single Station or OS Server.
- It possesses local graphic picture files (GraCS) and local computer communication properties, but it lacks an autonomous Tag Management or Alarm Logging database.
- When in runtime, an OS Reference station reads tags and historical trends directly across the network from the base OS station.
2. PH-Ready Behavior on OS Ref:
- Even if an engineer installs PH-Ready on an OS Reference PC, the service scans the local project directory and finds zero local Tag Logging or Alarm Logging archives.
- Consequently, PH-Ready reports no active database segments, and the station cannot register as an independent archiving entity in Process Historian.

Plant Structure Representation in Process Historian Management Console

When an engineer inspects the Process Historian Management Console under Plant Structure:
- The console displays:
text OS Single Station [Active / Connected] Number of Clients: 2 (or 1)
- Interpreting the Display:
* Process Historian recognizes the base OS Single Station as the sole data producer.
* The two OS Reference PCs are recognized strictly as client visualization nodes consuming data from that master server.
* Complete Archiving Integrity: Because all field instruments, controllers, alarms, and analog tags configured across the facility are monitored and logged by the base OS Single Station, Process Historian receives 100% of plant process history from the single station alone. Attempting to force the OS Reference stations to archive independently would simply result in redundant, duplicate database writes.

OS Station Type Archiving Capabilities and PH Support Table

The following table details archiving support across PCS 7 operator station types:

Verification

To confirm that all plant data from the OS Single Station and its Reference stations is safely archiving in Process Historian:
1. On the Process Historian PC, open Process Historian Management Console.
2. In the dashboard, verify that:
- Operating State is Active.
- Under Plant Structure, the OS Single Station shows status Connected.
- Incoming data counters display active throughput (e.g. Values Written/sec > 0).
3. On an OS Reference station, trigger a test alarm or observe an analog trend.
4. Launch SIMATIC Information Server from any client browser:
- Run an alarm query for the test event: confirm that the alarm is fully recorded with timestamp and tag name.
- Run a trend report for the analog variable: confirm that historical trend curves are continuously populated.

Limitations and Operational Precautions

When deploying OS Reference stations with Process Historian:
1. Single Point of Archiving Failure: Because the OS Single Station is the sole data source streaming to Process Historian, powering down or losing the OS Single Station halts data ingestion into PH. For critical continuous processes, deploy redundant OS Servers (WinCC Appl. and WinCC Appl. Stby) rather than a single station with OS References.
2. Terminal Bus Bandwidth: Ensure the network connection between the OS Single Station and Process Historian provides sufficient Gigabit bandwidth to handle both client visualization traffic and historical archive streaming simultaneously.
3. Never Convert to OS Server In-Place: If independent local archiving becomes necessary in the future, delete the OS Reference in HW Config and replace it with a standard WinCC Appl. followed by a complete OS recompilation.

Engineer FAQ

Are process values captured by OS Reference stations lost if they cannot archive directly?

No. OS Reference stations do not generate unique process values; they display values already processed and logged by the base OS Single Station. The base station archives all values into Process Historian completely.

Why does Process Historian Management Console show 'Number of Clients: 1' instead of 2?

This occurs if only one OS Reference station is currently connected and active in runtime, or if the second reference station has not yet loaded the runtime project across the network.

Can an OS Reference station use SIMATIC Information Server to view reports?

Yes. Any PC on the plant terminal bus (including OS Clients, OS References, and office workstations) can access the Information Server web portal via a standard web browser.

Does deploying OS Reference stations require additional Process Historian Archive PO licenses?

No. Process Historian licenses are based on the total number of archived process variables (Archive POs) streaming from data sources, not the number of client screens displaying the data.

Technical References

• SIMATIC Process Historian & Information Server Administration Manual
• SIMATIC PCS 7 Minimal Configurations Engineering Guide
• Siemens Industry Online Support Entry 168676 - Archiving OS Reference Stations in Process Historian

Related Articles

• Troubleshooting OS Download Discrepancies in SIMATIC PCS 7 - Why Tags Are Missing on Reference OS Stations
• Resolving Missing Tag Values in SIMATIC Information Server Reports with Process Historian V8.1
• Designing Long-Term Tag Archiving and Direct Process Access for Distributed OS Single Stations in SIMATIC PCS 7

Related Tags

• PCS7_Process_Historian
• OS_Reference
• OS_Single_Station
• PH_Ready
• Plant_Structure
• TagLogging
• Information_Server