Configuring Multiproject Architecture for Dual AS, Dual ES, and Redundant OS Servers in SIMATIC PCS 7

In enterprise SIMATIC PCS 7 engineering, structuring complex plants into a distributed Multiproject architecture ensures optimal engineering performance, clear administrative boundaries, and conflict-free multi-user development. Standard Siemens practice dictates splitting the plant into modular single projects within the Multiproject: dedicated single projects for each Automation Station (e.g., AS01 for DCS control and AS02 for ESD/Safety), a single project for the redundant OS Server pair, a project for Engineering Stations (ES), and a project for Operator Clients (OS Clients). The global Plant Hierarchy is authored in a designated master project and synchronized across all projects using 'Options > Plant Hierarchy > Export / Update', while communication subnets (Plant Bus and Terminal Bus) are merged across project boundaries using NetPro plant-wide cross-project subnet merging.

Architectural Principles of PCS 7 Multiproject Engineering

A SIMATIC PCS 7 Multiproject acts as an overarching administrative umbrella that groups multiple independent S7 projects and a centralized master library. In medium to large process control deployments, hosting multiple AS controllers, redundant OS server pairs, multiple Engineering Stations (ES), and distributed OS clients within a single monolithic SIMATIC Manager project causes database contention, slow opening and archiving times, and lockouts during multi-user engineering.

By dividing the automation topology into discrete single projects under one Multiproject container, each engineering team or automation discipline operates independently without locking project databases. The global coherence is maintained through cross-project subnet links in NetPro and an identical Plant Hierarchy (PH). Cross-project references, such as AS-OS compilation and S7 cross-couplings between AS01 and AS02, resolve seamlessly across the multiproject structure.

Single Project Breakdown Strategy for Multi-Station Plants

When configuring an architecture consisting of two automation stations (e.g., DCS process control and ESD safety interlocks), two redundant OS servers, two engineering stations, and operator clients, the recommended folder and project distribution in SIMATIC Manager is as follows:

Master Library (Lib_Master): Contains the project-specific approved block versions (APL, F-Systems), CMT templates, models, and SFC types.
Automation Station Project DCS (Prj_AS01): Contains the S7-400 / CPU 410-5H hardware configuration, symbol table, CFC charts, and safety logic for process control.
Automation Station Project ESD (Prj_AS02): Contains the dedicated safety-instrumented controller hardware configuration, fail-safe CFC charts, and emergency shutdown interlocks.
Engineering Stations Project (Prj_ES): Hosts the PC station configurations for ES_A (Primary Engineering Station) and ES_B (Secondary/Standby ES Station).
Operator System Servers Project (Prj_OS_SRV): Houses the redundant WinCC PC Stations (e.g., SERV_A as Master and SERV_B as Standby Partner). Redundant server pairs must reside within the exact same project to allow WinCC Redundancy editor configuration.
Operator System Clients Project (Prj_OS_CLT): Houses the OS Client PC stations (e.g., OP_A and OP_B), configured with assigned server packages.

Cross-Project Plant Bus and Terminal Bus Merging in NetPro

For communication to traverse multiple single projects within the Multiproject, physical network cables must be logically mapped to plant-wide subnets. Without cross-project subnet merging, NetPro treats subnets in different projects as electrically isolated, preventing configured S7 connections and OS-to-AS compilation.

To merge subnets across the Multiproject:
1. Open SIMATIC Manager and highlight the top-level Multiproject node.
2. Select menu Options > Multiproject > Cross-Project Subnets (or open NetPro from any station).
3. Select the Industrial Ethernet subnet designated for the Plant Bus (connecting AS controllers, CP 1623 cards in OS Servers, and ES).
4. Click Merge, select the matching Plant Bus subnets from Prj_AS01, Prj_AS02, and Prj_OS_SRV, and assign them to a unified global subnet name (e.g., PlantBus_Ethernet).
5. Repeat the exact merging procedure for the Terminal Bus (connecting OS Servers, OS Clients, and ES stations).
6. In NetPro, configure the named S7 fault-tolerant connections from the redundant WinCC OS application to the S7-400H / CPU 410 controllers across the merged plant bus.

Plant Hierarchy Synchronization and AS-OS Assignment

A unified Plant Hierarchy (PH) is paramount for standard APL block icon generation, faceplate navigation, and Picture Tree management. When the plant hierarchy is configured in single projects, it must remain strictly synchronized:

Establish the master hierarchy folder levels (e.g., Plant > Unit > Function) within Prj_AS01.
In SIMATIC Manager, select menu Options > Plant Hierarchy > Export... to create an XML hierarchy definition, or use Options > Plant Hierarchy > Update in Multiproject to propagate folder structures to Prj_AS02 and Prj_OS_SRV.
In each AS project, assign hierarchy folders to the corresponding controller target system.
In the OS Server project, assign the root and graphic hierarchy folders to the target OS WinCC application. When 'Compile OS' is executed, the compiler traverses the merged subnets, reads block attributes across Prj_AS01 and Prj_AS02, and auto-generates pictures and tags into the centralized WinCC OS project.

Comparison of Single Multiproject vs Unified Monolithic Projects

The following table compares architectural and engineering characteristics between a modular Multiproject configuration and a monolithic single-project structure:

Architectural CriterionModular Multiproject StructureMonolithic Single ProjectEngineering Team ConcurrencyIndependent access per project; no database locksFrequent lockouts during simultaneous CFC editingNetwork Subnet ManagementRequires cross-project subnet merging in NetProSingle subnet automatically shared across stationsProject Archiving and BackupFast incremental archive of individual AS/OS projectsSlow full-project archive (often >10 GB)OS Server Pair RequirementRedundant servers must be in the same single projectNaturally located in the same single projectMaster Library EnforcementCentralized library distributed via MultiprojectLocal library inside project folderMultiuser Engineering SetupMinimal overhead; clean distributed multi-seat workflowHigh risk of Step 7 database corruption

Verification

Verify the multiproject configuration through the following procedural checkpoints:
1. Open NetPro at the Multiproject level; verify that the Plant Bus and Terminal Bus display continuous green lines spanning across all AS, ES, and OS stations with no orphan subnet stubs.
2. In NetPro, select the WinCC application on SERV_A and verify that S7 connections to AS01 and AS02 indicate 'Configured' and pass cross-project consistency checks without errors.
3. Execute 'Compile OS' on SERV_A with scope 'Entire OS' and memory reset; confirm that the compiler extracts tags and alarms from both Prj_AS01 and Prj_AS02 without connection warnings.
4. Verify that the WinCC Picture Tree Manager correctly displays the plant hierarchy tree populated from the synchronized multiproject hierarchy.

Limitations and Operational Precautions

When designing a modular PCS 7 Multiproject, redundant OS Servers (e.g., SERV_A and SERV_B) MUST be placed inside the same single project. WinCC Redundancy cannot establish a partner relationship across two separate S7 projects. Similarly, while OS Clients can reside in a separate project, their referenced OS Server packages must be generated in the server project and imported into the client project. Always ensure that time synchronization (CP 1623 or Simatic PDC) is configured globally across the merged plant bus before running multi-station AS-OS compilation.

Engineer FAQ

Can two Engineering Stations (ES_A and ES_B) configure the same AS controller at the same time?

No. While multiple engineers can work on different CFC charts within the same AS if Multiuser Engineering is licensed and configured, simultaneous conflicting changes to hardware configuration or chart compilations are locked out by Step 7 database semaphores. Best practice is to assign AS01 to ES_A and AS02 to ES_B, or use chart partition ownership.

Why does 'Compile OS' fail to detect blocks from AS02 after creating a new AS project?

This occurs if the Plant Bus subnet in AS02 was not merged with the Plant Bus in the OS Server project. Open NetPro, go to 'Options > Multiproject > Cross-Project Subnets', and verify that the Ethernet subnet of the CP 443-1 in AS02 is merged into the plant-wide bus.

Should OS Clients be placed in the same project as the OS Servers?

In smaller systems, clients and servers can share a single project. In larger systems, separating clients into a dedicated client project reduces project size, simplifies multi-seat graphics editing, and prevents client engineers from inadvertently altering server database settings.