Resolving CEMAT 'Too Many PLC-Connections for a Single Station' on Redundant OS Servers After Project Reload

When a redundant OS Server pair running the CEMAT library throws the error 'Too many PLC-Connections for a single station' on only one server after a project reload or restore, the root cause is project type desynchronization or an asymmetric license key. The CEMAT Single Station license limits controller connections to 6; a redundant server pair controlling 9 PLCs requires the CEMAT RSRTU unlimited server license on both servers. This error occurs if the reloaded server project was inadvertently opened as a 'Single-User Project' instead of 'Multi-User Project', if local computer name properties were reset, or if the CEMAT RSRTU license key was not transferred to the reloaded server's Automation License Manager (ALM).

CEMAT Multi-Server Licensing vs Single Station Enforcement

In mineral processing, cement manufacturing, and bulk materials plants running the SIMATIC PCS 7 CEMAT library, controllers communicate with central OS Servers handling hundreds of heavy technological blocks (C_GROUP, C_DRV_1D, C_VALVE). CEMAT enforces a strict licensing gatekeeper based on system topology:

CEMAT Single Station License: Restricted to standalone single-seat operator stations, capping the allowable Automation Stations (AS) at 6.
CEMAT Server Runtime License (CEMAT RSRTU): Designed for multi-server, redundant DCS architectures, permitting an unlimited number of AS connections across server pairs.

When a facility operates 9 controllers and reloads one OS Server, encountering 'Too many PLC-Connections for a single station' on that reloaded server proves that the CEMAT runtime supervisor is mistakenly evaluating the reloaded machine as a standalone single station rather than an integral member of a redundant multi-user server pair.

Root Causes of Server-Specific Single Station Errors

Because Server 1 continues to run cleanly while Server 2 fails, the issue is not a multiproject engineering defect, but an asymmetry between the two physical servers:

Corrupted or Converted Project Type: When the project was reloaded or restored onto Server 2, WinCC may have initialized the project as a Single-User Project instead of a Multi-User Project. Standalone project types immediately trigger single-station CEMAT validation.
Computer Name Mismatch: If the computer name in WinCC Explorer does not match the actual Windows hostname of Server 2 (for example, if the project still bears the name of the ES or Server 1), WinCC operates in an abnormal local loopback state, disabling redundancy services.
Missing License Key in ALM: When Server 2 was reloaded, the local hard drive may have been wiped or re-imaged, leaving Automation License Manager without the required CEMAT RSRTU license key. Lacking the server license, CEMAT falls back to single-station trial mode.
Manual File Copying instead of Duplication: Copying WinCC projects between redundant servers via Windows File Explorer leaves internal SQL server registration tables corrupted. Redundant servers must always be synchronized using the official WinCC Project Duplicator.

Auditing Project Type, Computer Name, and Redundancy Properties

Perform an immediate diagnostic audit on the affected Server 2:

Open WinCC Explorer on Server 2.
Right-click the project root and select Properties. Confirm that the Project Type displays Multi-User Project.
In the left navigation pane, select Computer. Verify that the listed computer name matches the exact Windows hostname of Server 2. Double-click the computer entry to confirm that the computer type is set to Server.
Open the Redundancy editor in WinCC Explorer. Verify that:
- The box Activate Redundancy is checked.
- The partner server name is set to Server 1.
- The redundant connection link (serial cable or dedicated network adapter) is properly mapped.

Automation License Manager (ALM) Symmetry Audit on Server 2

Open Automation License Manager (ALM) on both Server 1 and Server 2 and compare the installed license inventory:

Server 1 must possess:
PCS 7 OS Software Server
SIMATIC PCS 7 OS Software Server Redundancy (or redundancy license token)
CEMAT RSRTU V7.x or CEMAT Server (Unlimited)
Server 2 must possess an identical set of license keys installed on drive C:.
If Server 2 is missing CEMAT RSRTU, CEMAT detects 9 active AS connections against an absent server license, clamps to the default 6-connection threshold, and displays the error.

Step-by-Step Restoration Workflow Using WinCC Project Duplicator

To restore absolute symmetry between the redundant servers:

Deactivate Runtime on Server 2: Exit WinCC Runtime and close WinCC Explorer on Server 2.
Restore Licenses via ALM: Ensure the CEMAT RSRTU license is transferred to Server 2 via ALM network transfer or Siemens USB stick.
Delete Corrupt Target Project: On Server 2, delete or archive the existing project folder to ensure a clean target environment.
Launch Project Duplicator on Server 1:
- On Server 1 (or Master ES), open Start -> Siemens Automation -> SIMATIC -> WinCC -> Project Duplicator.
- Select the healthy master project as the source.
- Browse across the network to Server 2's shared project directory (\\SERV2\WinCC_Project\).
- Click Duplicate.
Verify Local Configuration: Open the duplicated project on Server 2, confirm the computer name matches Server 2, and activate Runtime.

Comparative Architecture Matrix: CEMAT Server Setup vs Single Station

The following table compares configuration requirements between CEMAT architectures:

| Engineering Dimension | CEMAT Single Station | CEMAT Redundant Server Pair (SERV 1 & SERV 2) |
|---|---|---|---|
| Maximum AS Connections | 6 AS Controllers | Unlimited (9+ AS supported) |
| WinCC Project Type | Single-User Project | Multi-User Project |
| Required CEMAT License | CEMAT Single Station | CEMAT RSRTU (Installed on BOTH servers) |
| Redundancy Service | Disabled (CCRedundantServer absent) | Active (CCRedundantServer continuously syncing) |
| Server Package Generation | None (Local tags only) | Generated and exported to OS Clients |
| Failure Symptom on 9 AS | Popup: 'Too many PLC-Connections' | Normal operation with complete faceplate access |

Verification

Verify full recovery on the reloaded server through the following steps:

Activate WinCC Runtime on Server 2.
Verify in the Windows Task Manager that CCRedundantServer.exe and C_SERVER.exe are active and consuming normal CPU resources.
Open the CEMAT overview screen and confirm that all 9 AS connections show healthy communication status (green quality codes).
Open a CEMAT Group Faceplate (C_GROUP) for an equipment area residing on AS 8 or AS 9. Verify that the faceplate opens immediately without license overrun popups.
Perform a simulated failover by pulling the plant bus connection on Server 1; confirm that Server 2 assumes the active server role seamlessly.

Limitations and Operational Precautions

Adhere to the following operational precautions:

Never Download While Partner Error Persists: Do not download changes to Server 1 while Server 2 is in an error state; resolve Server 2 first to maintain plant-wide supervisory redundancy.
Asymmetric Server Packages: Differences in server packages between servers can confuse OS Clients during failover, leading to stale tag displays.
ALM Transfer Media: Always use Automation License Manager for license movement; copying raw license files (*.sik, *.ekb) via Windows Explorer corrupts the license vault.

[!NOTE]
Commercial Accuracy Disclaimer: Software order numbers (MLFBs), package structures, and hardware capacity prerequisites vary across PCS 7 versions > and hardware platforms. System integrators must confirm exact software entitlements and licensing requirements against the official Siemens > Catalog CA 01 and obtain an authorized Siemens distributor quotation prior to purchasing.

Engineer FAQ

Does CEMAT RSRTU need to be purchased twice for a redundant server pair?

Yes. A redundant OS server pair requires the base CEMAT server runtime license and redundancy options installed on both Server 1 and Server 2 to ensure equal capacity upon failover.

Can package data differences between servers trigger the single station error?

Package differences alone do not cause the error, but an incorrect project type or missing server prefix generated during package creation causes CEMAT to evaluate the server as a standalone station.