Migrating a SIMATIC PCS 7 OS Single Station to a Redundant Client-Server Architecture

To migrate an existing PCS 7 OS Single Station to a redundant Client-Server architecture (redundant OS Server pair plus 3 OS Clients), change the primary server project from a Single-User Project to a Multi-User Project in WinCC Explorer, insert a 'WinCC Appl. (Stby.)' station in SIMATIC Manager for the redundant partner, and configure terminal bus networking. Generate the server data package on the server pair, create 3 PC Stations with 'WinCC Appl. Client' applications, import the server package, run the OS Project Editor across all nodes, and replace single station licenses with OS Server Redundancy and OS Client runtime licenses.

Executive Summary

Expanding an automation system from an initial single-station operator environment (OS Single Station) to a high-availability distributed supervisory architecture is a common plant expansion milestone in SIMATIC PCS 7 (V8.0 through V9.1). Migrating requires restructuring project database types, configuring redundant server pairs in STEP 7 HW Config, generating cross-network server packages, and establishing Terminal Bus connectivity for operator clients. This article outlines the step-by-step engineering migration methodology, hardware and network prerequisites, and licensing transitions required to deploy a redundant OS server pair with multiple OS clients.

Architecture and Fundamental Mechanics

Architectural Mechanics of Single Station to Distributed Redundant Client-Server Migration:

Structural Differences Between OS Architectures:
OS Single Station: Integrates controller communication (Plant Bus via CP 1623/BCE), project database, alarm logging, and operator visualization on a single computer using a WinCC 'Single-User Project' structure.
Redundant OS Server Pair: A master and standby server pair running a WinCC 'Multi-User Project'. Both servers communicate independently with the AS controllers over the Plant Bus, execute continuous runtime database synchronization over a dedicated redundant network cable, and serve process data to network clients.
OS Client: Workstations connected exclusively to the Terminal Bus running a 'WinCC Client Project'. Clients hold no local process database; they dynamically display process pictures and receive alarms via loaded Server Packages (.pck).
Network Architecture Separation:
Single stations often mix plant and terminal communications on a single adapter. A distributed client-server architecture strictly requires network physical or VLAN segregation:
1. Plant Bus (Industrial Ethernet): Connects OS Servers to AS controllers (CP 1623 / CP 1628 or standard BCE).
2. Terminal Bus (Industrial Ethernet): Connects OS Servers, OS Clients, Engineering Stations, and Process Historians.
3. Redundancy Serial/LAN Link: Direct cross-cable between OS Server 1 and OS Server 2 for cyclic heartbeat and archive synchronization.
Server Data Generation (.pck):
The OS Server compiles tag cross-references, alarm definitions, and picture tree hierarchies into a compressed package file. Loading this package onto OS Clients binds client picture windows to the redundant server pair without requiring per-client AS connections.

Step-by-Step Implementation Procedure

Step-by-Step Migration Procedure from OS Single Station to Redundant Client-Server:

Backup and Archive Master Single Station Project:
- Close all editors; execute File -> Archive... in SIMATIC Manager to secure a baseline project backup.
Restructure Primary OS Server in SIMATIC Manager:
- In Component View, rename the existing PC Station to represent the primary server (e.g. OS_SRV1).
- Open HW Config for OS_SRV1; ensure network adapters are assigned to both the Plant Bus and Terminal Bus.
- Open the WinCC project; in WinCC Explorer, right-click the project root -> select Properties -> change project type from Single-User Project to Multi-User Project.
Insert and Configure Redundant Standby Server:
- In SIMATIC Manager Component View, right-click the Project -> Insert New Object -> Pre-configured Station (or SIMATIC PC Station).
- Name it OS_SRV2.
- In HW Config, insert identical network adapters and a WinCC Appl. (Stby.) application.
- In Component View, open the properties of the master OS project -> select the Target OS and Standby OS Computer tab.
- Specify the standby OS computer name and target path on OS_SRV2.
Configure WinCC Redundancy and Generate Server Data:
- Open WinCC Explorer on the master server -> double-click Redundancy.
- Check Activate Redundancy; configure the redundant partner computer name and connection interface.
- Right-click Server Data -> Generate to create the unified server package.
Configure OS Client PC Stations:
- In Component View, insert 3 new SIMATIC PC Stations (e.g. OS_CL1, OS_CL2, OS_CL3).
- In HW Config, insert an IE General network adapter (Terminal Bus) and a WinCC Appl. Client.
- Open each OS Client project in SIMATIC Manager; right-click Server Data -> Load... and import the server package.
- Right-click Server Data -> Standard Server...; assign the server pair for Alarms and Split Screen Manager (SSM).
Run OS Project Editor Across All Stations:
- Run OS Project Editor on the master server (Server layout).
- Run OS Project Editor on each client (Client layout matching physical monitors).
Compile and Download:
- Download the server project to OS_SRV1 and duplicate/download to OS_SRV2.
- Download client projects to OS_CL1, OS_CL2, and OS_CL3.
- Activate runtime on the master server, standby server, and clients sequentially.

Verification

Verification Procedure:
1. Server Redundancy Test: In WinCC Runtime on the primary server, verify internal tag @RedundancyState equals 1 (Master). Verify internal tag @RedundancyState equals 2 (Standby) on the partner server.
2. Client Communication Audit: On each OS Client, open the 'States of Connected Servers' window (@ServerState.pdl). Confirm both server nodes report online with green indicators.
3. Redundant Failover Validation: Disconnect the network cable of the Master OS Server. Confirm that the Standby server immediately assumes the Master role, clients switch servers bumplessly without alarm loss, and all process faceplates remain responsive.

Limitations and Operational Precautions

Operational Precautions and Licensing Migration Rules:
- Licensing Transition: Single Station runtime licenses cannot be used directly on distributed servers. Procure SIMATIC PCS 7 OS Software Server Redundancy (or OS Software Server + redundancy license) and additive OS RT PO licenses for each server node, plus OS Software Client runtime licenses for each physical client workstation.
- User Management Synchronization: WinCC User Administrator accounts must be configured with identical credentials across both servers, or SIMATIC Logon must be deployed for centralized Windows domain authentication.
- Commercial and Procurement Boundaries: Validate all migration MLFBs, upgrade paths, and server redundancy order numbers against the official Siemens ST PCS 7 catalog and an authorized distributor quotation.

Engineer FAQ

Can an OS Single Station project be converted directly to a Multi-User Project?

Yes. In WinCC Explorer, right-click the project root, open Properties, and change the project type from Single-User Project to Multi-User Project.

What WinCC application type is inserted for the redundant server partner?

In STEP 7 HW Config, insert the application type WinCC Appl. (Stby.) for the redundant partner station.

Do OS Clients connect directly to the Plant Bus?

No. Standard OS Clients connect exclusively to the Terminal Bus; they receive all process data via server data packages exported by the OS Servers.

What happens to existing graphics and faceplates during migration?

All existing process pictures, scripts, and alarms are preserved in the Multi-User Project; running OS Project Editor updates system navigation pictures.

How do OS Clients know which server is active in a redundant pair?

The loaded Server Data package contains the network identities of both servers; the client's internal redundancy manager automatically routes requests to the active master server.