Adding Redundant OS Servers to an Operating PCS 7 Plant Without Interrupting Controller Execution

Adding a new pair of redundant Operator Stations (such as a PCS 7 V8.2 redundant OS Server pair) to an operating PCS 7 V8.0 facility with CPU 410-5H controllers without interrupting production is fully supported and does not require stopping the controllers. CPU 410-5H supports dynamic S7 Named Connection creation in RUN. On the Engineering Station, configure the new PC Stations and compile their OS projects. In NetPro, establish the S7 Named Connections from the new OS Servers to the CPU 410-5H controllers, compile NetPro, and execute 'PLC > Download to Current Project > Connections and Routing' to download the connections to the running controllers in RUN mode. Finally, download the OS projects over the Terminal Bus and activate runtime on the new servers without any disruption to the existing OS servers or process control.

Executive Summary

Plant expansions, central control room modernizations, and phased DCS migrations often require introducing new redundant OS Server clusters into an active, continuously operating production facility. When the existing automation infrastructure is controlled by Siemens CPU 410-5H or S7-400H systems, engineers are often hesitant to download network configurations, fearing a catastrophic CPU stop. Under PCS 7 architecture, communication routing tables and S7 Named Connections can be dynamically expanded in RUN mode. By configuring the new PC Stations, compiling NetPro connection tables, and downloading solely 'Connections and Routing' to the AS, new supervisory servers are commissioned seamlessly without touching active controller logic.

Architecture and Fundamental Mechanics

The communication architecture of SIMATIC PCS 7 decouples controller logic execution from supervisory communication routing:

S7 Named Connections and NetPro:
* Communication between WinCC OS Servers and AS controllers utilizes S7 Named Connections managed by SIMATIC NET.
* In the AS controller, S7 connections are handled by the CPU's internal communication stack and CP 443-1 / onboard PROFINET interfaces.
* The connection descriptors reside in System Data Blocks (SDBs), specifically SDB 7xx (connection tables) and SDB 1000+ (routing tables).
Online Connection Downloading in RUN:
* In S7-400 (firmware V3.1+) and specifically CPU 410-5H, the operating system allows downloading modified connection and routing tables without stopping the CPU.
* By using the dedicated command PLC > Download to Current Project > Connections and Routing in NetPro, STEP 7 updates the active connection tables in the CPU's work memory on the fly. Active process control tasks (OB1, OB3x, OB8x) continue uninterrupted.
Cross-Version Coexistence (V8.0 AS and V8.2 OS):
* S7 communication protocols are backward compatible. A newly commissioned PCS 7 V8.2 OS Server can communicate with a PCS 7 V8.0 AS controller over S7 Named Connections seamlessly.
* The existing V8.0 OS Servers continue operating undisturbed on their existing connection channels, while the new V8.2 OS Servers establish their own concurrent S7 connections to the controllers.
AS Connection Capacity:
* CPU 410-5H supports up to 120 simultaneous S7 connections. Adding two redundant OS servers consumes 2 to 4 S7 connections, well within the controller's capacity.

Step-by-Step Implementation Procedure

Follow these procedures to add redundant OS servers to an operating plant without interrupting production:

Configure the New PC Stations in SIMATIC Manager:
* Open the multiproject on the Engineering Station.
* In SIMATIC Manager, insert a new SIMATIC PC Station for the primary server (e.g., OS_SRV_New_A) and another for the standby server (OS_SRV_New_B).
* In HW Config for each station, insert a WinCC Application (for Server A) and WinCC Application (stby) (for Server B).
* Insert the appropriate network interface cards (e.g., CP 1623 or IE General for Plant Bus, and standard NICs for Terminal Bus).
Configure S7 Named Connections in NetPro:
* Open NetPro.
* Select the WinCC Application of the new primary server.
* In the connection table, insert a new connection: select the CPU 410-5H controller, set Type to S7 connection (or Fault-tolerant S7 connection if using redundant plant bus).
* Repeat the connection configuration for the standby server (WinCC Application (stby)).
* Save and compile NetPro (Network > Save and Compile > Check cross-rack connections).
Download Connections to the CPU 410-5H in RUN Mode:
* In NetPro, select the CPU 410-5H controller.
* Select menu PLC > Download to Current Project > Selected Stations or PLC > Download to Current Project > Connections and Routing.
* A confirmation dialog appears asking to download connection data without stopping the CPU.
* Confirm the download; observe that the progress bar finishes and the CPU remains continuously in RUN.
Configure OS Redundancy and Compile the OS:
* In SIMATIC Manager, right-click the new OS project and configure Redundancy properties in WinCC Explorer (assign the standby partner server and redundant network adapter).
* Right-click the OS and select Compile.
* Select the target controllers, check 'Tags and messages', and perform a full OS compilation.
Download the OS Project to Target Machines:
* Ensure both physical new server PCs are connected to the Terminal Bus and Plant Bus.
* In SIMATIC Manager, right-click the OS project and select PLC > Download.
* Download the complete OS project to Server A and Server B over the Terminal Bus.
Activate Runtime and Verify:
* On Server A, open WinCC Explorer and click Activate.
* Once Server A is fully in runtime, activate Server B.
* Verify redundant synchronization in WinCC Redundancy Control.

Verification

Inspect the CPU 410-5H diagnostic buffer (PLC > Module Information > Diagnostic Buffer); confirm that no CPU STOP or error events occurred during the NetPro download. Open WinCC Channel Diagnosis on the new OS Servers; confirm that the S7 Named Connection to each CPU 410-5H displays a green checkmark and status Ready. Verify that process values and alarms update dynamically on the new server faceplates.

Limitations and Operational Precautions

Do NOT select PLC > Download to Current Project > Complete Station in NetPro, as downloading the entire hardware configuration may require a CPU STOP if non-CiR hardware changes are present. Always select specifically Connections and Routing. Verify that the CPU 410-5H connection resource limit (120 connections) is not exceeded.