Diagnosing OS Client Connection Failures and MaintenanceState Synchronization in PCS 7 Maintenance Station

In SIMATIC PCS 7 Maintenance Station (MS Basic and MS Standard), PC station diagnostic icons and faceplates reflect connection states via the internal structured variable MaintenanceState and cyclic WinCC redundancy tags. If an OS Client disconnects from a server but its maintenance icon remains green, the WinCC diagnostic evaluation script or cyclic polling trigger has failed to refresh. To correct this, verify the OS-Project Editor diagnostic structure, ensure @MaintenanceState cyclic update cycles are configured, and validate WinCC Redundancy tag synchronization.

PCS 7 Maintenance Station PC Diagnostics Architecture

SIMATIC PCS 7 Maintenance Station (MS) provides plant asset management by monitoring automation hardware, field devices, network components, and PC stations (OS Servers, OS Clients, ES, Batch, and Route Control stations). In MS Basic (integrated within standard PCS 7 OS runtime) and MS Standard (running on a dedicated Maintenance Server), PC objects are visualized using standardized block icons and faceplates (@pg_@pc_station.pdl).

The diagnostics engine on each PC station runs the SIMATIC WinCC System Diagnostics service and the OS-Project Editor diagnostic structure. Communication between OS Clients and OS Servers is monitored through internal WinCC system tags generated by the WinCC Redundancy option:
* @ConnectedServer: String tag identifying the server currently supplying process data.
* @RedundantServerState: Integer tag indicating server operating state (Master, Standby, Fault).
* @MaintenanceState: Double-word bitmask representing asset health.
* @EventState: Double-word bitmask representing alarm and acknowledgment status.

When an OS Client loses network communication with its primary server, it switches to the redundant partner. However, if the client PC's local maintenance display does not reflect the partial failure until a reboot occurs, the background cyclic script responsible for parsing @ConnectedServer and updating @MaintenanceState is either blocked or configured for event-driven execution on tags that failed to fire an edge transition.

MaintenanceState and EventState Variable Bit Structure

The structured variable MaintenanceState (DWORD) encodes the operational and diagnostic health of monitored automation assets according to NAMUR NE 107 recommendations. The following bit layout defines how WinCC faceplates and block icons interpret status:

Bit PositionSemantic DesignationIcon Display StateDescription and System TriggerBit 0Good / OperationalSolid Green CheckmarkComponent healthy, communication active, no maintenance requiredBit 16Maintenance Required (Low)Blue WrenchPreventive maintenance threshold reached; cyclic wear counter warningBit 17Maintenance Demanded (Medium)Yellow WrenchMaintenance required immediately; degraded performance or partner failureBit 18Maintenance Alarm (High)Red WrenchAsset failed; complete loss of redundancy or loss of communicationBit 24Configuration / Parameter WarningYellow Warning TriangleDiagnostic structure inconsistent with hardware configurationBit 30Diagnostic Evaluation InactiveGrey Question MarkComponent polling timed out or diagnostic block uninitializedBit 31Connection Fault / Link DownRed X over Grey BoxStation unreachable via Industrial Ethernet or Terminal Bus

For PC objects, Bit 17 is activated when a redundant partner server is lost, while Bit 31 is activated when all redundant connections to an asset group fail.

Diagnosing OS Client Disconnection and Stale Icon Indicators

To troubleshoot why an OS Client icon fails to display a connection drop dynamically:

Check Local Script Queue:
* Open the WinCC Explorer on the affected OS Client.
* Check Global Script > GSC Diagnostics. If global action queues are backed up with high execution times (>5000 ms), cyclic evaluation scripts will fail to update @MaintenanceState tags.
Inspect WinCC Redundancy Status Tags:
* Open the WinCC Variable Table or use APDiag.exe (located in C:\Program Files (x86)\Siemens\WinCC\bin).
* Read the tag @<ServerPrefix>_RedundantServerState and @<ServerPrefix>_ConnectionState.
* Verify whether the connection state changed from 1 (Connected) to 0 (Disconnected) when the network cable was pulled.
Verify OS-Project Editor Diagnostic Deployment:
* On the Engineering Station, open OS-Project Editor on the OS Client project.
* Under the Basic Data tab, ensure that @MaintenanceState and standard PC faceplates are selected for update.
* Verify that the option Create/update diagnostic screens is enabled and executed during OS compilation.

Configuring Cyclic Diagnostic Polling and WinCC Redundancy

To ensure continuous cyclic evaluation without requiring PC reboots:
1. Configure Cyclic Tag Triggers: In Graphics Designer, open the PC object block icon (@PC_STATION). Verify that the dynamic fill color and status icon properties are bound to @MaintenanceState using an explicit cyclic trigger (e.g., Upon change with a 2-second fallback cycle, rather than static property binding).
2. Synchronize System Diagnostic Configuration: In the Maintenance Station user diagnostic structure (SIMATIC Manager > Plant View > Maintenance Station > Update Diagnostic Structure), regenerate the diagnostics hierarchy.
3. Validate Terminal Bus Network Binding: Ensure the OS Client network adapter priority in Windows Network Connections sets the Terminal Bus adapter first. If DNS or NetBIOS resolution across redundant servers is misconfigured, TCP/IP keepalive timeouts can take up to 20 minutes to register a dropped connection, giving the impression of an unrefreshed icon.

Verification

Validate the correction by performing the following functional test:
1. Disconnect the primary OS Server's terminal bus network cable.
2. Observe the OS Client's overview area and Maintenance Station overview screen within 5 to 10 seconds.
3. The client block icon must transition from solid green to yellow wrench (Bit 17: Maintenance Demanded) or display a partial redundancy disconnection indicator.
4. Open the PC object faceplate and confirm that Server A indicates Disconnected while Server B indicates Active Standby without rebooting the client.

Limitations and Operational Precautions

Modifying standard @pg_@pc_station.pdl faceplates directly can lead to overwrites during the next OS-Project Editor execution. Always apply customizations through user-defined diagnostic blocks or project-specific faceplate templates.
Never shorten cyclic script execution times on large OS Client architectures below 1 second; doing so can saturate the WinCC scripting engine and degrade alarm response times across the terminal bus.
MS Basic provides limited asset monitoring compared to MS Standard; detailed SNMP hardware parameterization of third-party network switches requires MS Standard.

Engineer FAQ

What is the difference between MS Basic and MS Standard in PCS 7?

MS Basic is included with the standard PCS 7 OS runtime license and monitors core automation components (CPUs, CP cards, ET 200 stations, and PC nodes). MS Standard requires dedicated server hardware and runtime licenses, offering full asset management, calibration logging, cyclic wear monitoring, and extended SNMP device integration.

Why did restarting the client PC fix the maintenance icon display?

Restarting the PC forced WinCC Runtime to re-initialize its tag database and re-evaluate internal system variables from scratch. During runtime, if an event trigger failed to catch the server state change, the tag retained its last known state (Green) indefinitely.

Can I customize the bit assignment of MaintenanceState for custom PC objects?

Yes, but you must align custom bit assignments with NAMUR NE 107 guidelines (Bits 16-19 for maintenance states) to ensure full compatibility with standard PCS 7 overview screens and alarm horns.