C135 PCS 7 (PCS7)
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How to Troubleshoot WinCC Redundant Server Disconnects, Grey Process Values, and Workgroup Communication Failures in PCS 7

How to Troubleshoot WinCC Redundant Server Disconnects, Grey Process Values, and Workgroup Communication Failures in PCS 7

WinCC redundant server pairs show disconnected runtime elements, loss of network connection alarms, or greyed-out faceplates when communication settings fall out of synchronization. To resolve this, first verify that both OS servers and the Engineering Station reside in an identical Windows Workgroup or Active Directory domain with matching local administrator credentials. Next, open WinCC Explorer Tag Management on the faulty server and verify the communication driver is set to Named Connections rather than Simulation mode. Finally, open SIMATIC Shell, verify the terminal bus network adapter is selected, check that redundancy settings match across both partner stations, and perform a full OS project download to restore cross-server runtime data synchronization.

Table of Contents

Root Causes of Redundant Server Synchronization and Communication Loss

In a SIMATIC PCS 7 distributed architecture, an Operator Station (OS) redundant server pair operates in an active-hot-standby configuration. Both OS servers communicate independently with the automation stations (AS) via the Industrial Ethernet plant bus using Named Connections. Simultaneously, the servers exchange internal archive data, alarm states, and heartbeat signals across the terminal bus and an optional serial or Ethernet redundancy link.

When one server (such as Server 01) fails to update graphic pictures, turns process value fields grey, or generates redundancy alarms like Redundancy Control: Loss of connection via network cable, the issue rarely stems from physical cable breakage alone. Common underlying causes include:
1. Accidental Driver Simulation Mode: In WinCC Tag Management, the driver connection (Named Connections) may have been toggled to simulation or offline mode during local testing, preventing the runtime graphic manager from acquiring live AS tags.
2. Workgroup Credential Disconnects: In peer-to-peer Windows Workgroups without a central domain controller, mismatched passwords, missing local user accounts, or absent SIMATIC HMI group memberships prevent remote procedure call (RPC) and DCOM handshakes between OS clients, the partner OS server, and the Engineering Station (ES).
3. Improper Server Data (.pck) Generation: Deleting, re-importing, or corrupting OS server packages on redundant partners disrupts OS Client target assignments and internal server cross-referencing.
4. SIMATIC Shell Network Binding Errors: If the primary terminal bus network adapter is deselected or bound to the wrong virtual interface in SIMATIC Shell, heartbeat packets are dropped, prompting WinCC Redundancy Control to declare communication failure.

WinCC Tag Management Driver and Named Connection Validation

A frequent source of greyed-out graphics after downloading is an incorrect communication channel configuration inside WinCC Explorer. When an OS project is compiled from SIMATIC Manager, the system creates S7 Named Connections under the SIMATIC S7 PROTOCOL SUITE.

If Server 01 was edited locally or opened without compiling OS changes, the communication connection may default to an inactive or simulated state:
* Check Driver Mode: Open WinCC Explorer on Server 01, expand Tag Management > SIMATIC S7 Protocol Suite > Named Connections. Right-click the connection name linked to your AS CPU and select Properties. Ensure the connection status is set to active and bound to the correct S7 application name configured in NetPro.
* Driver Status via Channel Diagnosis: Launch WinCC Channel Diagnosis (available in Windows Start Menu under Siemens Automation or WinCC Tools). Review the Status tab for Named Connections. A healthy connection reports State: OK with a green indicator. If it reports State: Error or State: Inactive, the station cannot communicate with the AS over CP 1613, CP 1623, or standard network cards via Softnet-IE.
* Tag Export/Import Discrepancies: If a tag exists on Server 02 but is missing on Server 01, do not manually manipulate server packages (.pck) while redundancy is online. An OS Compilation (Compile OS > Entire OS with memory reset or changes only) must be executed from the ES to ensure both server databases contain identical tag GUIDs.

Windows Workgroup Security and Terminal Bus Configuration

Distributed WinCC architectures depend heavily on Microsoft Distributed Component Object Model (DCOM) and Windows RPC. In a workgroup setup, every node evaluates security locally. If Server 01, Server 02, the ES, and OS Clients do not share identical user credentials, cross-station access is denied.

Ensure the following Windows environment requirements are met across all stations:
* Identical User Accounts: Configure an administrative engineer account with the exact same username and password on the ES, Server 01, Server 02, and all OS Clients.
* Group Membership: The common user must be explicitly assigned to Administrators (or Power Users on legacy Windows installations) and the local group SIMATIC HMI.
* Identical Workgroup Name: Open Windows System Properties on each machine and confirm that the Workgroup name (e.g., PLANT_WORKGROUP) is identical.
* Network Profile: Ensure the terminal bus adapter is set to Private Network (or Domain Network). Windows Public Network firewall rules automatically block necessary WinCC RPC and SQL Server ports (such as TCP 1433, 1434, 135, and 445).

Step-by-Step Server Redundancy Recommissioning Procedure

To recover an out-of-sync redundant server pair and restore reliable client switching, execute the following procedure:

  1. Deactivate Runtime on the Faulty Server: On Server 01, exit WinCC Runtime cleanly using the WinCC Explorer deactivation button or system menu.
  2. Verify Network Adapter Binding in SIMATIC Shell:
    * Open Windows Explorer on Server 01 and locate SIMATIC Shell in the tree.
    * Right-click SIMATIC Shell and select Settings....
    * Confirm the selected network adapter corresponds to the physical Terminal Bus network card.
    * Enable Multicast settings if routing across managed layer-3 switches.
    * Verify all partner stations appear with status Available or Good.
  3. Inspect Redundancy Settings:
    * Open WinCC Explorer on the Master server (Server 02) and open the Redundancy editor.
    * Confirm Server 02 is defined as the partner of Server 01 and that the connection type matches your physical wiring (e.g., Network Cable Terminal Bus, with optional serial COM port).
    * Ensure Activate Redundancy is checked and synchronization options (Message synchronization after return of partner, Archive synchronization after return of partner) are enabled.
  4. Compile and Download OS from the ES:
    * On the Engineering Station, open SIMATIC Manager.
    * Right-click the OS Server object and select Compile.
    * Once compiled, right-click the OS Server object and select PLC > Download.
    * Download the complete OS project to Server 01 first while Server 02 continues serving live clients.
  5. Start WinCC Runtime on Server 01:
    * Launch WinCC Runtime on Server 01.
    * Observe the WinCC Redundancy Control messages in the alarm list. Server 01 will establish connection, request archive synchronization from Server 02, and resume hot-standby readiness.

Comparison of Redundancy Diagnostics and Status Indicators

The table below outlines common diagnostic symptoms observed on redundant PCS 7 WinCC servers and their corresponding recovery measures.

Diagnostic SymptomDiagnostic Tool / MessageRoot CauseCorrective ActionGreyed-out faceplates and missing process valuesWinCC Channel Diagnosis: State: ErrorTag Management driver set to simulation or wrong Named ConnectionOpen Tag Management, verify S7 connection parameters, and recompile OS from ES.Redundancy loss via network cableAlarm: Loss of connection via network cableTerminal bus adapter mismatch or disconnected redundancy linkCheck physical terminal bus link; configure correct NIC binding in SIMATIC Shell.Server package import failureError dialog: Package could not be importedAttempting to import package while redundancy is activeGenerate server data on ES, compile OS, and download via SIMATIC Manager rather than manual import.Client faceplates freeze when partner server stopsWinCC Redundancy Status: Standby not synchronizedIncomplete online synchronization or DCOM permission blockageAlign Windows Workgroup credentials, add user to SIMATIC HMI, and allow full archive sync.System tags show redundant partner offlineSystem tag @RedundancyState = 0SIMATIC Shell cannot resolve remote partner hostnameAdd partner IP and NetBIOS hostname entries to C:\Windows\System32\drivers\etc\hosts.

Verification

To confirm that the redundant OS server pair is fully functional and healthy:
1. Open the WinCC alarm journal on both Server 01 and Server 02. Verify that Redundancy Control: Partner server returned and Redundancy Control: Archive synchronization completed messages appear.
2. Read internal system tags in WinCC Tag Management: @RedundancyState must indicate active redundancy (value 1 or 2), and @RedundantServerState must report 1 (Master) on one server and 2 (Standby) on the other.
3. Verify on both OS Clients that process graphics display dynamic live values without grey hashing or invalid status bars.
4. Perform a controlled failover test: Deactivate WinCC Runtime on the Master server. Confirm that the Standby server assumes the master role seamlessly within 1 to 3 seconds, without client alarm bursts or loss of control.

Limitations and Operational Precautions

  • Never delete or manually manipulate WinCC server packages (.pck files) directly in project directories while WinCC Runtime is active on either partner.
  • Never run one server in Workgroup mode while the partner server or ES is joined to a Windows Active Directory domain; authentication mismatches will break database synchronization.
  • Avoid downloading an OS project to both servers simultaneously. Always download to the standby server first, verify operational integrity, fail over the clients, and then download to the partner station.
  • Ensure SQL Server instances on both OS servers match the exact version, service pack, and cumulative update required by the installed PCS 7 release.

Engineer FAQ

Why did deleting the server package on Server 01 cause 'Package could not be imported'?

In PCS 7 redundant server environments, server data (.pck) is created and assigned by the Engineering Station during OS compilation. Manually deleting and attempting to re-import server data while WinCC is partially loaded breaks internal database pointers and triggers security lockouts. Server packages must always be generated from SIMATIC Manager on the ES and deployed via standard project download.

Can WinCC redundancy operate without a dedicated serial cable or separate network link?

Yes, WinCC Redundancy supports synchronization and heartbeat monitoring over the standard Terminal Bus network adapter via TCP/IP. However, using a dedicated second network interface or serial connection provides fault tolerance against terminal bus traffic storms, preventing false failover events if terminal bus communication suffers transient latency.

What does the '@RedundancyServerState' tag indicate?

The internal system tag @RedredundancyServerState indicates the operational state of the local server: 0 = Undefined/Fault, 1 = Master, and 2 = Standby. Both servers must never report 1 simultaneously, as this indicates a split-brain condition caused by loss of redundancy communication.

Technical References

Related Articles

Related Tags

  • WinCC Redundancy
  • SIMATIC Shell
  • Named Connections
  • Terminal Bus
  • PCS 7 OS Server
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