Resolving CEMAT Error on OS Clients: 'Too Many PLC-Connections for a Single Station'

The error 'Too many PLC-Connections for a single station' appearing on an OS Client when opening CEMAT group faceplates occurs when the client's local WinCC project was inadvertently configured with Single-Station runtime properties, or when local S7 connections exist in the client's Tag Management instead of referencing the OS Server. The CEMAT Single Station license permits a maximum of 6 PLC connections. In a distributed multi-client architecture (e.g., 14 AS, 2 OS Servers, 8 Clients), clients must possess zero direct PLC connections. To resolve this, convert the client project type to 'Client Project' in WinCC Explorer, remove all local S7 connection drivers, update the server package, and verify the CEMAT RSRTU server license.

CEMAT Licensing Architecture: Single Station vs Distributed Server-Client

In industrial plants running the CEMAT Minerals & Mining library (V7.x, V8.x), runtime licensing is partitioned strictly by system topology:

CEMAT Single Station License: Sized for standalone autonomous stations, restricted to a maximum of 6 AS connections (orderable via Siemens CEMAT software packages). If the project communicates with more than 6 controllers, CEMAT halts group faceplate operations and displays license overrun dialogs.
CEMAT Server Runtime License (CEMAT RSRTU): Sized for multi-server distributed DCS systems. The base server license or upgrade package permits unlimited AS connections across redundant server pairs.
CEMAT Client Licensing: OS Clients in a distributed architecture do not connect directly to PLCs; they access process data via OS Server packages and do not require AS connection licenses.

Why Single-Station License Warnings Appear on OS Clients

In a system with 14 AS, 2 OS Servers, and 8 OS Clients, encountering 'Too many PLC-Connections for a single station' on only two specific clients indicates a configuration defect on those two machines:

Erronous Project Type: When the client project was created or duplicated, it was configured as a 'Single-User Project' or 'Multi-User Project' instead of a Client Project.
Local S7 Drivers: During migration or testing, an engineer imported S7 communication channels directly into the client's local Tag Management. The CEMAT license supervisor on the client detected 10+ active S7 connection references locally, triggered single-station validation, and asserted the 6-connection limit error.

Auditing Client Project Properties and Tag Management Connections

To diagnose the two failing clients:

Open WinCC Explorer on the failing OS Client.
Right-click the project root in the tree and select Properties. Inspect the Project Type field. If it reads 'Single-User Project' or 'Multi-User Project', it is misconfigured.
Expand Tag Management. Under SIMATIC S7 PROTOCOL SUITE, check whether Industrial Ethernet or Named Connections are configured. On an OS Client, the communication channel list should be empty (all tags are referenced via Server Data).

Step-by-Step Procedure to Reconfigure Affected OS Clients

Follow this sequence to restore the client to standard multi-client operation:

Deactivate Runtime: Exit WinCC Runtime on the client.
Delete Local Communication Channels: In WinCC Explorer, expand Tag Management. Delete any locally configured S7 connections (Named Connections, Industrial Ethernet, TCP/IP).
Change Project Type: Right-click the project name in WinCC Explorer, select Properties, and change the project type to Client Project.
Re-link Server Data: Expand Server Data. Delete the existing package, right-click, select Load Package, and select the .pck file generated by the OS Server.
Restart Station: Restart the client PC. Activate WinCC Runtime and verify faceplate opening.

CEMAT License Package and Station Architecture Comparison

The following table compares CEMAT license structures and connection thresholds:

CEMAT License PackageTarget Station TypeMax AS ConnectionsRequired ALM License KeyBehavior on Limit ExceededCEMAT Single StationStandalone PC6 AS ConnectionsCEMAT Single Station V7.xPop-up: 'Too many PLC-Connections'CEMAT Server (Base)OS Server (Single/Redundant)6 AS ConnectionsCEMAT Server V7.x (6 AS)Blocks group start on AS 7+CEMAT Server (Unlimited)OS Server (Distributed)Unlimited ASCEMAT RSRTU V7.x (Unlimited)Full plant access without warningsCEMAT OS ClientOS Multi-Client0 Local (Queries Server)CEMAT Client V7.xMust use Server Packages only

Verification

Verify client resolution through the following steps:

On the previously affected client, open WinCC Runtime.
Click the CEMAT Group Icon (C_GROUP) for an area controlled by AS 10 or AS 12.
Confirm that the group faceplate opens instantly without displaying 'Too many PLC-Connections for a single station'.
Verify that group start, stop, and interlock bypass commands function correctly from the client.

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.

Limitations and Operational Precautions

Consider these operational rules when configuring CEMAT clients:

Never Configure Local AS Connections on Clients: OS Clients must always query data via OS Server packages; configuring direct AS connections bypasses server redundancy and violates client licensing.
ALM License Location: Server runtime licenses (CEMAT RSRTU) must reside on the OS Server machines, not on clients.
Version Consistency: Ensure CEMAT software versions (e.g., V7.1 SP1) match identically across Engineering Station, OS Servers, and all OS Clients.

Engineer FAQ

What license is required for more than 6 AS in CEMAT?

You need the CEMAT RSRTU upgrade license on the OS Servers, which expands AS connection capacity to unlimited.

Can an OS Client communicate directly with a PLC if the server fails?

No. Standard OS Clients rely entirely on OS Servers. If autonomous survival is required, the station must be engineered as an OS Single Station with dedicated licenses.