Integrating OpenPCS 7 Server with Process Historian for External Data Access

In SIMATIC PCS 7 V8.1, the OpenPCS 7 configuration dialog 'Assign OS Server' displays only runtime OS Server pairs and Maintenance Stations, deliberately omitting the Process Historian (PH). This is by architectural design: OpenPCS 7 is an interface gateway that routes OPC DA/A&E queries to active OS Servers, while routing historical data queries (OPC HDA and OLE-DB) directly to the Process Historian database. To connect an external system (such as an OSIsoft PI Server) for secure read-only historical data access, point the OpenPCS 7 client to the PH SQL instance without requiring write permissions.

OpenPCS 7 Server Architecture and Data Routing Model

In enterprise automation architectures, Manufacturing Execution Systems (MES), Laboratory Information Management Systems (LIMS), and enterprise plant historians (such as OSIsoft PI, AspenTech IP.21, or Wonderware Historian) require access to PCS 7 production data.

To provide a secure, standard-compliant gateway that prevents external software from directly accessing sensitive DCS internal networks, Siemens developed SIMATIC OpenPCS 7:
* Installed on an independent PC station (e.g. in an Industrial Demilitarized Zone - IDMZ) or on an OS Client.
* Exposes standardized industrial interfaces:
- OPC DA (Data Access): Real-time process values.
- OPC HDA (Historical Data Access): Historical trend archives.
- OPC A&E (Alarms & Events): Process alarms, operator actions, and system diagnostics.
- OLE-DB / OpenPCS 7 SQL Interface: Relational tabular queries for batch logs and reporting.

Why Process Historian Is Omitted from the OS Server Assignment Dialog

Commissioning engineers configuring OpenPCS 7 in SIMATIC Manager frequently encounter confusion during station parameterization:
* Symptom: When opening the Assign OS Server... configuration dialog for the OpenPCS 7 PC station, the dialog lists the redundant OS Server pairs (OS_SRV01, OS_SRV02) and the Maintenance Station (MS_SRV), but Process Historian (PH) is completely absent from the list!
* The Reason:
1. The 'Assign OS Server' dialog is designed exclusively for Runtime Event and Real-Time Tag Routing: It tells OpenPCS 7 which active WinCC servers handle live OPC DA cyclic polling and OPC A&E message subscriptions.
2. The Process Historian is NOT a WinCC OS Server; it is an enterprise Microsoft SQL Server database.
3. OpenPCS 7 automatically resolves historical queries: when an external client requests historical data via OPC HDA or OLE-DB, OpenPCS 7 consults the central project topology, detects the Process Historian, and redirects the query directly to the PH database without requiring manual assignment in the OS Server dialog.

Configuring Read-Only OPC HDA and OLE-DB Access for External Systems

For plant cybersecurity (IEC 62443 compliance), enterprise integrations (like connecting corporate OSIsoft PI) mandate Strictly Read-Only Access:
* External systems must never have write access (Write / Poke) to DCS setpoints or valve positions.
* When connecting via OPC HDA (Historical Data Access) or OPC UA (Historical Access) through OpenPCS 7:
- OPC HDA protocol specification is intrinsically read-oriented for historical time-series queries.
- OpenPCS 7 enforces read-only permissions on historical database tables (HISTORIAN).
- By configuring the external connection user account in Windows as a member of SIMATIC HMI Viewer rather than SIMATIC HMI, write commands from external networks are blocked at the protocol gateway layer.

OpenPCS 7 Data Access Protocol Comparison Matrix

The following matrix compares data access channels provided by OpenPCS 7:

Protocol InterfaceTarget Data SourcePrimary ApplicationRead / Write CapabilityOPC DA ClassicLive OS ServersReal-time monitoring / SCADA bridgeRead / Write (Configurable)OPC HDA ClassicProcess Historian (PH)Historical trend extraction for PI/MESStrictly Read-OnlyOPC A&E ClassicLive OS ServersEnterprise Alarm Management / SoERead-Only (Alarms/Events)OPC UA (DA + HA)OS Servers & PHCross-platform secure enterprise linkRead / Write (Governed by policy)OLE-DB ProviderProcess Historian (PH)Relational reporting via SQL queriesStrictly Read-Only

Step-by-Step Procedure to Integrate OpenPCS 7 with Process Historian

Follow this procedure to configure OpenPCS 7 for historical data extraction:
1. Configure the OpenPCS 7 Station in SIMATIC Manager:
- In SIMATIC Manager Component View, insert a new PC Station named OpenPCS7_Station.
- In HW Config, insert the OpenPCS 7 Application into the virtual rack.
- Assign network adapters connected to both the Terminal Bus (DCS side) and Corporate DMZ (enterprise side).
2. Assign Runtime OS Servers:
- In SIMATIC Manager, right-click the OpenPCS 7 application and select Assign OS Server....
- Select your active runtime OS Server pairs (this provides the real-time tag namespace and alarm routing).
3. Configure Process Historian Connectivity in NetPro:
- In NetPro, verify that the Process Historian PC station and OpenPCS 7 station reside on the common Terminal Bus subnet.
- Save and Compile NetPro. Download the PC station configuration to the OpenPCS 7 machine.
4. Configure External Client Connection (e.g. OSIsoft PI):
- On the external PI Interface node, configure the PI-OPC-HDA Interface.
- Point the interface to the OpenPCS 7 node: OPCHDA.WinCC or OpenPCS7.OPCHDA.
- Configure authentication using a dedicated Windows service account.
5. Verify Firewall Exceptions:
- Ensure TCP port 135 (DCOM) or port 4840 (OPC UA) is open between the corporate DMZ and the OpenPCS 7 station.

Verification

Verify historical data extraction through OpenPCS 7:
1. On the OpenPCS 7 station, launch the Siemens OPC Scout diagnostic utility.
2. Expand OPC HDA -> OPCHDA.WinCC (or OpenPCS7.OPCHDA):
- Browse the tag hierarchy: Confirm process tags appear with their full plant hierarchy names.
- Select a tag and execute an asynchronous historical read across the last 7 days.
- Confirm that historical values, timestamps, and quality codes return successfully from the Process Historian.
3. In the external OSIsoft PI system: Confirm that PI tags populate with historical data matching the Process Historian archives.

Limitations and Operational Precautions

Never attempt to query high-frequency historical data across millions of raw tags simultaneously through OpenPCS 7; bulk queries should be staged in batches to avoid saturating PH SQL transaction memory.
Deploy OpenPCS 7 in an isolated DMZ between the control network and corporate network; never connect the DCS Terminal Bus directly to the corporate enterprise LAN.
Commercial licensing note: OpenPCS 7 requires dedicated software runtime licenses (e.g. 6ES7658-2G...); validate licensing requirements against an authorized Siemens distributor quotation.

Engineer FAQ

Why did the Process Historian not appear in the OpenPCS 7 OS assignment dialog?

Process Historian is an archive database repository, not a WinCC OS runtime server. OpenPCS 7 discovers the PH automatically via the project NetPro configuration for all historical OPC HDA queries.

Can external systems write setpoint changes through OpenPCS 7?

Yes, if using OPC DA and the connected user account has write privileges. However, for historical data over OPC HDA, the interface is strictly read-only by design.

Does OpenPCS 7 support OPC UA?

Yes. Modern OpenPCS 7 versions include a full OPC UA Server supporting Data Access (DA), Historical Access (HA), and Alarms & Conditions (AC) over encrypted TCP port 4840.