How to Configure a WinCC Reference OS Single Station Sharing the Same Plant Hierarchy in PCS 7

In SIMATIC PCS 7, configuring two independent OS Single Stations that access the same automation station (AS) and share the identical plant hierarchy without duplicating engineering effort is accomplished by deploying a 'WinCC Application Ref' (Reference OS). Because the PCS 7 plant hierarchy strictly prohibits assigning more than one standard OS to a single hierarchy folder, the engineer configures the primary station as a standard 'WinCC Application' (Base OS) and configures the secondary station as a 'WinCC Application Ref'. The Reference OS points to the Base OS in its object properties, inheriting all process graphics, compiled tags, and hierarchy layouts while operating independently on separate physical PC hardware.

Plant Hierarchy Allocation Constraints in SIMATIC PCS 7

In SIMATIC Manager, the Plant Hierarchy (PH) defines the physical and operational structure of the process plant:
* The Single-OS Assignment Rule:
* Every hierarchy folder (e.g., Area1, Boiler, TankFarm) can be assigned to one and only one Operator Station for compilation.
* Attempting to assign a second standard OS (WinCC Application) to the same hierarchy folder is blocked by SIMATIC Manager to prevent tag naming collisions and inconsistent archive generation.
* The Engineering Requirement:
* A plant requires two identical, independent OS Single Stations (e.g., one in the Central Control Room and one in the Field Operator Shelter) running standalone without server-client dependencies.
* The solution is deploying a Reference OS.

Architecture of the Base OS and Reference OS (WinCC Application Ref)

The Reference OS architecture allows multiple physical PC stations to share a single master engineering database:

The Base OS (WinCC Application):
Configured in the multi-project on PC_Station_1.
Assigned as the target OS for the plant hierarchy folders.
Fully compiled by the AS-OS compiler (Compile OS).
The Reference OS (WinCC Application Ref):
Configured on PC_Station_2.
Does NOT compile against the plant hierarchy.
Instead, it contains a pointer referencing the Base OS.
During download, SIMATIC Manager duplicates the compiled Base OS project files and automatically injects PC_Station_2's computer name into the duplicate database!

Step-by-Step Configuration of WinCC Application Ref in SIMATIC Manager

To configure the Reference OS in SIMATIC Manager:

Insert Second PC Station:
* In the multi-project, right-click: select Insert New Object > Preconfigured Station... or SIMATIC PC Station.
* Name the PC Station matching the second computer's Windows hostname (e.g., OS_SINGLE_2).
Configure HW Config for Reference Station:
* Open HW Config for OS_SINGLE_2.
* From the hardware catalog (SIMATIC PC Station > HMI), insert: WinCC Appl. (ref) into Slot 1.
* Insert network adapter (e.g., IE General or CP 1623) with its static IP address.
* Save and compile HW Config.
Link Reference OS to Base OS:
* In SIMATIC Manager Component View, locate the newly created OS object under OS_SINGLE_2.
* Right-click the OS object: select Object Properties.
* Open the OS Ref tab.
* Under Base OS, select the primary OS from the dropdown menu (e.g., OS_SINGLE_1).
* Under Target OS Path, browse across the network share to the destination folder on the second computer (e.g., \\OS_SINGLE_2\WinCC_Project\).

Target Path Synchronization and OS Download Rules

Deploying updates to Base and Reference OS stations:

Compilation:
The engineer executes Compile OS exclusively on the Base OS.
The Reference OS is updated automatically in memory during Base OS compilation.
Download Sequence:
1. Right-click the Base OS: execute PLC > Download.
2. Right-click the Reference OS: execute PLC > Download.
3. SIMATIC Manager transfers the synchronized files to OS_SINGLE_2, automatically updating local computer properties so runtime initializes cleanly without 'Configured server not available' warnings.

Comparison of Multi-Client vs Reference OS Single Station

The table below compares architectures for operating multiple operator stations from a common configuration.

Architectural FeatureOS Client / Server ArchitectureReference OS Single StationServer DependencyClients fail if OS Server halts100% Autonomous (Zero dependency)S7 Communication LinkHandled exclusively by ServerEach Single Station connects to ASLicensing RequiredOS Server + Client LicensesTwo full OS Single Station LicensesHistorical Data ArchivesCentralized on OS ServerSeparate local SQL databasesPlant Hierarchy CompileCompiled once to ServerCompiled to Base OS; copied to Ref

Verification

To confirm that both Base OS and Reference OS operate properly:
1. In SIMATIC Manager, perform a delta compile of the Base OS.
2. Download the Base OS to Computer 1, and download the Reference OS to Computer 2.
3. Activate WinCC Runtime on both computers simultaneously.
4. Verify that both screens render the identical plant overview graphics and process values.
5. Shut down Computer 1 (Base OS): confirm that Computer 2 (Reference OS) continues operating without interruption, maintaining active S7 communication and alarm monitoring with the controller.

Limitations and Operational Precautions

Operating two independent Single Stations connected to the same controller doubles communication connection resource consumption on the CPU/CP 443-1; verify controller S7 connection limits in HW Config.
Alarm acknowledgments and historical trend archives are stored locally in separate SQL databases on each station; acknowledging an alarm on Station 1 will not acknowledge it on Station 2.
Always ensure both computers maintain identical Windows user accounts, passwords, and SIMATIC user group memberships.
Always validate final software licensing, single-station runtime packages, and hardware specifications against the applicable Siemens catalog and authorized distributor quotation.

Engineer FAQ

Will the Reference OS go down if the Base OS crashes?

No. The Reference OS uses the Base OS only as an offline engineering template. Once downloaded, the Reference OS runs as a completely independent Single Station with its own direct connection to the controller.

Can a Reference OS connect directly to the PLC via CP 1623?

Yes. The Reference OS hardware configuration includes its own network adapter (CP 1623 or IE General) and establishes its own direct Named Connection to the S7-400 controller.

Can I compile the Reference OS directly in SIMATIC Manager?

No. Right-clicking a Reference OS does not offer the Compile option. You must compile the Base OS, which automatically updates the Reference OS template.