C135 PCS 7 (PCS7)
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Best Practices for Connecting Multiple Automation Stations to an OS Server Using Multiprojects in PCS 7

Best Practices for Connecting Multiple Automation Stations to an OS Server Using Multiprojects in PCS 7

In SIMATIC PCS 7, connecting multiple Automation Stations (AS) to an Operator Station (OS) must always be structured within a unified Multiproject rather than an unmanaged single project. A Multiproject enables centralized management of Plant Hierarchy, Master Data Libraries, cross-project S7 connections, and OS Server data generation. Furthermore, direct chart-to-chart cross-AS interconnections in CFC are fully supported and automated within a Multiproject without requiring manual SFB/SFC programming, as SIMATIC Manager automatically creates the underlying cross-controller communication blocks (such as IK_SEND and IK_RCV) over the Plant Bus.

Table of Contents

Single Project Limitations vs Multiproject Architecture

When engineering medium-to-large SIMATIC PCS 7 installations comprising multiple controllers (e.g., 5 S7-400 or CPU 410-5H automation stations) communicating with a central OS Server pair, engineers sometimes make the mistake of creating a single monolithic Step 7 project or separate isolated projects.

Engineers often worry: 'If I split my controllers into a Multiproject with a Plant Hierarchy, will I lose the ability to connect CFC block outputs from AS01 directly to inputs on AS02?'

The Multiproject Advantage

Siemens PCS 7 mandates the Multiproject structure for multi-station architectures:
1. Performance and Sizing: Isolating each AS and OS into its own sub-project within a multiproject container prevents project database bloat, speeds up CFC compilation, and allows multi-user engineering where different engineers edit separate controllers simultaneously.
2. Master Data Library (MDL): Enforces uniform block types, versions, and system attributes across all controllers.
3. Plant View Integration: The Plant Hierarchy spans the entire multiproject. Hierarchy folders map to specific controllers and OS servers, enabling the OS Compiler to aggregate all AS tags into a single unified WinCC runtime database.

Cross-AS Communication Mechanisms in SIMATIC CFC

In SIMATIC CFC, engineers can interconnect a block output in one controller directly to a block input in another controller (e.g., AS01/Area1/ChartA/Block1.Out connected to AS02/Area2/ChartB/Block2.In).

This is known as a Cross-AS Interconnection:
* Automated Infrastructure: You do not need to manually program communication system function blocks (SFB12 BSEND / SFB13 BRCV) in CFC.
* System-Generated Drivers: When the cross-AS interconnection is made and the charts are compiled, SIMATIC Manager automatically creates dedicated communication blocks (IK_SEND, IK_RCV or IK_CP_OUT, IK_CP_IN) in system charts.
* NetPro Coordination: SIMATIC Manager automatically configures the underlying S7 connections in NetPro across the shared Plant Bus.
* Data Integrity: Cross-AS communication includes data cycle stamping, communication failure monitoring, and fallback safe-state handling.

Step-by-Step Multiproject Assembly and Cross-AS Engineering Procedure

To properly structure multiple controllers and an OS Server within a Multiproject:

Step 1: Create the Master Multiproject

  1. In SIMATIC Manager, select File -> New....
  2. Select the Multiproject tab, name the project (e.g., Plant_Master_MP), and click OK.
  3. Select File -> 'Save As' / Insert into Multiproject... to attach your existing AS projects and OS project into the multiproject container.
  4. Create a Master Data Library inside the multiproject to synchronize block types.

Step 2: Configure Plant Bus Subnets in NetPro

  1. In SIMATIC Manager, open NetPro.
  2. Merge the Industrial Ethernet subnets: ensure that the Plant Bus (e.g., Plant_Bus_Ethernet) is configured as a single shared subnet across all AS projects and the OS Server.
  3. Select Network -> Save and Compile -> Check and compile all.

Step 3: Establish Cross-AS Interconnections in CFC

  1. Open a CFC chart in AS01 and a CFC chart in AS02 simultaneously in CFC Editor.
  2. Click the output pin on the block in AS01, then click the input pin on the block in AS02.
  3. CFC renders a green cross-chart margin connector displaying the full path: AS01\ChartName\BlockName.PinName.
  4. The connection is established.

Step 4: Map Plant Hierarchy and Compile OS

  1. Switch to Plant View.
  2. Assign each plant folder to its respective AS and to the central OS Server (AS-OS Assignment).
  3. Right-click the OS Server and select Compile:
    * The compiler aggregates tags, alarms, and block icons from all 5 controllers into the single WinCC project.

Project Structure and Communication Method Comparison Matrix

The following table compares architectural approaches for multi-controller PCS 7 systems:

Architectural MetricSingle Monolithic ProjectIsolated Standalone ProjectsMultiproject ArchitectureSiemens Standard ComplianceDiscouraged for >2 ASNot supported for PCS 7Mandatory Standard PracticeMulti-User EngineeringSeverely limited (file locking)Manual file mergingFull simultaneous multi-user supportCross-AS CFC InterconnectionsSupportedNot supportedFully Automated via IK_SEND/RCVOS Compilation ScopeSingle AS focusManual tag exportUnified compile across all ASMaster Library SynchronizationNot applicableInconsistent block versionsCentralized Master Data LibraryNetPro Network RoutingLocal onlyDisconnected networksUnified cross-project routing

Adopting a Multiproject guarantees complete system scalability and automated network management.

Verification

To verify that multiple AS controllers communicate properly with the OS and with each other:
1. In NetPro, execute Network -> Check cross-project consistency; confirm zero errors.
2. Compile CFC on all AS controllers; verify that system communication charts (@Chart) are generated with valid S7 connections.
3. In CFC Editor on AS02, switch to Test Mode; confirm that live values transmitted from AS01 update dynamically.
4. Disconnect the network cable between AS01 and the switch; verify that the cross-AS input in AS02 detects communication timeout and asserts bad quality.
5. In WinCC Runtime, verify that process pictures display live data simultaneously from all 5 controllers.

Limitations and Operational Precautions

  • Cross-AS communication over Industrial Ethernet consumes CPU communication resources; avoid routing high-frequency fast-control loops across controllers (keep fast loops within a single AS).
  • For safety-instrumented systems (SIS), cross-AS communication between safety programs must utilize certified F_Send / F_Receive blocks with F-Connection safety CRC signatures.
  • Always execute 'Update Block Types' from the Master Data Library across all projects in the multiproject to prevent block version drift.
  • In redundant plant bus topologies, ensure all AS controllers and OS servers are connected to both redundant rings with proper subnet assignments.

Engineer FAQ

Does moving an existing project into a Multiproject break existing logic?

No. Moving projects into a Multiproject simply groups them under a common administrative umbrella. Existing CFC logic, HW Config, and connections remain completely intact.

How many AS controllers can be connected to a single PCS 7 OS Server?

A single PCS 7 OS Server (or redundant pair) can connect to up to 64 AS controllers, subject to overall Process Object (PO) and WinCC tag volume limits.

What block handles automated cross-AS communication in CFC?

Depending on library version, the CFC compiler automatically inserts IK_SEND and IK_RCV (or IK_CP_OUT / IK_CP_IN when communicating via CP 443-1) into system charts.

Technical References

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Related Tags

  • Multiproject
  • Cross_AS
  • Plant_Hierarchy
  • NetPro
  • OS_Server
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