Configuring Plant Hierarchy AS-OS Assignments and Reference Stations for Dual OS Single Stations

In SIMATIC PCS 7 Multiprojects, the Plant Hierarchy (PH) 'AS-OS Assignment' establishes the target controller for CFC charts and target operator station for process pictures. In distributed multiprojects (separate AS, ES, and OS subprojects), AS assignment is performed in the AS subproject, while OS assignment is performed in the OS subproject. Because a Plant Hierarchy folder can only be assigned to a single primary OS target, configuring two independent OS Single Stations that display identical plant data requires assigning all PH folders to the primary OS Single Station (OS 1), and configuring the second station (OS 2) as an 'OS Reference Station' linked to OS 1. The Reference OS inherits pictures, tags, and archives without duplicate hierarchy maintenance.

Executive Summary

When structuring large-scale PCS 7 V9.0 SP2 multiprojects with redundant CPU 410-5H controllers, engineers frequently deploy two independent OS Single Stations to meet specific customer availability requirements without implementing full OS server redundancy. When configuring the Plant Hierarchy (PH) in Plant View, engineers discover that assigning both OS Single Stations to the same plant hierarchy folder is disallowed by SIMATIC Manager. Furthermore, subproject isolation prevents cross-assigning AS and OS targets in the same dialog. This guide clarifies the mechanics of Plant Hierarchy compilation scoping and details the configuration of OS Reference Stations for dual Single Station architectures.

Architecture and Fundamental Mechanics

The SIMATIC PCS 7 Plant Hierarchy (PH) is the central technological backbone governing both control code generation and human-machine visualization:
1. AS Assignment: Links a hierarchy folder to a specific Automation System (S7 Program). Any CFC or SFC chart inserted within that folder (or subfolders) compiles into that AS controller.
2. OS Assignment: Links a hierarchy folder to a specific WinCC OS Application. Any process graphic (.pdl) or block icon generated in that folder compiles into that OS database.

In a partitioned Multiproject containing separate subprojects (e.g., AS_Project, OS_Project, ES_Project):
- In AS_Project, the PH folder only recognizes controllers residing in that local subproject; the assigned OS field remains blank.
- In OS_Project, the PH folder recognizes local WinCC applications; the assigned AS field remains blank.
- During OS Compilation, the compiler scans the unified multiproject hierarchy, matches identical hierarchy paths, and maps AS chart tags to the assigned OS.

Dual Single Station Scoping Conflict:
PCS 7 enforces a strict 1-to-1 relationship: a single PH folder cannot possess dual primary OS assignments. If two identical OS Single Stations are needed:
- Creating a second independent OS project forces engineers to duplicate graphics or split the plant hierarchy.
- The official Siemens architectural solution is the OS Reference Station (Reference OS). An OS Reference Station points directly to a base OS Single Station. When the base OS compiles, the Reference OS automatically inherits all picture trees, tag connections, and faceplates, allowing independent downloads to the second physical IPC.

Step-by-Step Implementation Procedure

Configure AS Subproject Plant Hierarchy:
a. In SIMATIC Manager Plant View, expand the AS subproject.
b. Right-click the root Plant Hierarchy folder and select 'Object Properties'.
c. In the 'AS-OS Assignment' tab, select the CPU 410-5H S7 Program as the 'Assigned AS'. Leave the OS field unassigned.
d. Populate subfolders with CFC and SFC charts.
Configure Base OS Single Station in OS Subproject:
a. Open the OS subproject in SIMATIC Manager Component View.
b. Insert a SIMATIC PC Station named OS_SINGLE_01 and insert a WinCC Application and communications processor (CP 1623 or IE General) in HW Config.
c. Switch to Plant View in the OS subproject, open the root PH folder properties, and set 'Assigned OS' to OS_SINGLE_01.
Create the OS Reference Station for the Second IPC:
a. In the OS subproject Component View, right-click and select Insert New Object -> SIMATIC PC Station.
b. Rename the station to match the second physical computer (e.g., OS_SINGLE_02).
c. Open HW Config for OS_SINGLE_02.
d. From the catalog, expand SIMATIC PC Station -> HMI -> WinCC Appl. Ref. (WinCC Application Reference).
e. Insert 'WinCC Appl. Ref.' into the virtual rack and insert the network communications card.
f. In the properties of 'WinCC Appl. Ref.', link it to the base WinCC Application (OS_SINGLE_01).
g. Save and compile HW Config.
Configure S7 Connections in NetPro:
a. Open NetPro and configure S7 Named Connections from both OS_SINGLE_01 and OS_SINGLE_02 to the CPU 410-5H controllers.
b. Save and compile network routing.
Execute OS Compilation and Independent Downloads:
a. In SIMATIC Manager, right-click OS_SINGLE_01 and execute 'Compile'. The compiler processes the Plant Hierarchy and builds the runtime database.
b. Download OS_SINGLE_01 to the first physical IPC.
c. Right-click OS_SINGLE_02 (Reference OS) and select 'Download'. The engineering system transfers the synchronized project to the second physical IPC.

Verification

Launch WinCC Runtime on both physical OS Single Stations (OS_SINGLE_01 and OS_SINGLE_02).
Verify that both stations display identical process screens, plant hierarchy picture trees, and live tag values.
Issue a control command (e.g., start a motor from MotL faceplate) on OS_SINGLE_01: confirm the state change reflects immediately on OS_SINGLE_02.
In WinCC Channel Diagnosis on both stations, confirm independent active Named Connections to the CPU 410-5H.

Limitations and Operational Precautions

An OS Reference Station cannot possess independent process pictures or customized tags distinct from its base OS; any changes made to graphics must be made on the base OS and redeployed. Each OS Single Station (base and reference) requires its own autonomous 'SIMATIC PCS 7 OS Software Single Station' runtime license, plus AS/OS RT PO licenses. Sizing and procurement of single station runtime licenses should be verified through an authorized Siemens distributor or the Siemens Industry Mall.

Engineer FAQ

Why can't I assign two OS stations to the same hierarchy folder directly?

PCS 7 compiles process pictures and block icons into a single target WinCC project per hierarchy folder to maintain data integrity and prevent tag namespace collisions.

What is the difference between an OS Reference Station and an OS Client?

An OS Reference Station is an independent single station with direct AS connections and local archives that mirrors a base project. An OS Client has no direct AS connection and relies entirely on an OS Server.

Can an OS Reference Station operate if the base OS Single Station is powered off?

Yes. Once downloaded, the OS Reference Station is completely autonomous and communicates directly with the controller, operating independently of the base station.

Why is the Assigned OS field grayed out in the AS subproject Plant Hierarchy?

Because the WinCC OS project resides in a separate subproject; SIMATIC Manager links them during multiproject OS compilation based on matching folder paths.

How does historical archiving work on two OS Single Stations?

Each station maintains its own local SQL Server historical archive; because they are independent single stations (not a redundant pair), archive synchronization does not occur between them.