Configuring Multi-Client OS Stations with Cross-Multiproject Access to Multiple Redundant OS Servers

In SIMATIC PCS 7 (V8.0, V8.1, V8.2, and V9.0), configuring a single OS Multi-Client station to monitor and control equipment distributed across three separate Multiprojects hosted on three distinct redundant OS Server pairs is fully supported and managed seamlessly through Server Data packages. To achieve unified 'single-pane-of-glass' plant overview screens without switching projects, engineers must generate and export the server data packages from all three redundant OS Server pairs, import them into the Multi-Client's WinCC project, and construct local graphic displays on the client. Each redundant server pair is treated by the client as a single logical server entity; tag connections are referenced using the logical server prefix (e.g., OS1_Server::FIC_101.PV_Out), guaranteeing bumpless data continuity and transparent failover if any master server fails.

Architecture of Multi-Client Stations Across Multiple Multiprojects

Large manufacturing sites often partition their facility into independent operational zones (e.g., Area 1 - Raw Materials, Area 2 - Processing, Area 3 - Utilities), each managed by its own independent PCS 7 Multiproject with dedicated redundant OS Servers. However, central control room operations require a master supervisory station capable of visualizing the entire factory on unified overview displays.

SIMATIC PCS 7 facilitates this via the Multi-Client architecture. An OS Multi-Client does not possess its own process image or direct connection to AS controllers. Instead, it acts as an aggregator, opening simultaneous client-server channels across the Terminal Bus to up to 18 distinct OS Server pairs, displaying process tags, faceplates, and alarms in a unified workspace.

Redundant Server Pair Abstraction in Server Data Packages

A foundational design principle in WinCC multi-client engineering is that a redundant server pair is handled as a single logical server:

Single Common Package: When you generate Server Data on redundant OS Servers (SERV_A and SERV_B), the system generates ONE unified server package file (<ProjectName>.pck).
Internal Partner Identification: The package contains the network identities of both the Master and Standby servers, the symbolic server prefix, and the database schema.
Transparent Switchover: The Multi-Client connects to the currently active Master server. If the Master server fails or undergoes maintenance, the client automatically switches its communication channel to the Standby partner without interrupting graphic displays or operator controls.

Step-by-Step Procedure to Configure Cross-Multiproject Multi-Clients

To establish the cross-multiproject multi-client station:

Generate Server Packages in Each Multiproject:
- Open Multiproject 1. In SIMATIC Manager, select the OS Server pair, right-click, and select Server Data > Generate.
- Repeat this exact generation step in Multiproject 2 and Multiproject 3.
Transfer Packages to the Multi-Client:
- If the Multi-Client resides in a dedicated Client Multiproject, copy the generated .pck files from each server project.
- In WinCC Explorer on the Multi-Client, right-click Server Data, select Load..., and load the packages from Server Pair 1, Server Pair 2, and Server Pair 3.
Configure Default Server for Alarms: Under Server Data, select Configure...; designate which server pair acts as the default source for message acknowledgment.

Designing Unified Overview Graphics with Multi-Server Tags

Once the server packages are loaded on the client, engineers can construct comprehensive overview screens combining equipment from all three multiprojects:

Create Local Pictures: In WinCC Graphics Designer on the Multi-Client, create new local screens (e.g., Plant_Master_Overview.pdl). Local screens created on the client are preserved independently of server compiles.
Tag Addressing Syntax: When linking an I/O field, bar graph, or block icon to a process variable, use the symbolic server prefix:
- <ServerPrefix>::<TagName> (e.g., AREA1_SRV::FIC_101.PV_Out#Value and AREA2_SRV::TIC_204.PV_Out#Value).
Standard Faceplate Calling: APL block icons placed on the local client screen automatically retain their server associations. Clicking an icon resolves the server prefix dynamically and opens the corresponding faceplate from the appropriate server pair.

Comparison of Multi-Client Architectures (Single vs Multi-Server)

The following table compares the operational characteristics of single-server clients versus multi-server aggregator clients:

| Architectural Dimension | Dedicated Single-Server OS Client | Multi-Server Cross-Multiproject Client |
|---|---|---|---|
| Loaded Server Packages | 1 Redundant Server Pair Package | Multiple Packages (Up to 18 Server Pairs) |
| Project Visualization Scope | Restricted to one plant area | Unified overview of the entire enterprise |
| Picture Storage Location | Stored on the OS Server | Local screens stored directly on the OS Client |
| Redundancy Failover Behavior | Transparent automatic switchover | Transparent automatic switchover per server pair |
| OS Compile Handling | Fully automated via AS-OS compile | Client screens manually designed / preserved |
| Network Bandwidth Demand | Low (Queries one server pair) | Moderate (Distributes queries across multiple pairs) |

Verification

Verify Multi-Client operation across multiple redundant server pairs:
1. Activate WinCC Runtime on the Multi-Client station.
2. Open the custom Plant_Master_Overview.pdl screen; verify that process values from Area 1, Area 2, and Area 3 update simultaneously.
3. Click a motor block icon originating from Server Pair 1 and a valve block icon from Server Pair 2; verify that both faceplates open responsive to operator commands.
4. Physically power down the active Master server of Server Pair 1; observe that the Multi-Client continues displaying Area 1 values seamlessly via the Standby partner with zero interruption to Area 2 or Area 3 data.

Limitations and Operational Precautions

When designing local graphic screens on an OS Multi-Client, ensure that all participating OS Servers and Clients utilize synchronized system time via NTP or a central master clock. Time discrepancies across server packages cause alarm banner sequencing errors and broken historical trend curves. Ensure that identical user accounts and passwords exist across all domains or configure centralized authentication using SIMATIC Logon to prevent permission rejections when operating equipment across different server pairs.

Engineer FAQ

Do I need to configure redundancy twice on the multi-client?

No. Redundancy is configured exclusively on the server pairs. The generated server package encapsulates the redundancy pairing; the multi-client handles the redundant servers as a single logical entity.

Will compiling an OS Server overwrite my custom screens on the multi-client?

No, provided those screens were created locally inside the OS Client project directory. OS compilation on the servers only updates server-side pictures and packages.

What is the maximum number of OS Servers a multi-client can access?

In standard SIMATIC PCS 7 architectures, an OS Multi-Client can access up to 18 separate OS Server pairs (or single servers) simultaneously over the Terminal Bus.