C135 PCS 7 (PCS7)
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Preventing Screen Switching and Pop-up Closure on WinCC Web Clients During Redundancy Failover

Preventing Screen Switching and Pop-up Closure on WinCC Web Clients During Redundancy Failover

In SIMATIC PCS 7 V9.0, when an OS master-standby server failover causes WinCC Web Clients to unexpectedly close all open faceplate pop-ups and force the display back to the default Start screen, the fault is caused by custom scripting inside @screen.pdl or an un-synchronized server data package on the dedicated Web Server. In standard PCS 7 V9.0 / V9.1 architecture, Web Clients maintain active picture window handles during redundancy switchovers without reverting to the start screen. To resolve this: 1) Inspect @screen.pdl on the Web Server and remove custom C/VBS scripts that call OpenPicture() or re-initialize picture window visibility on @RedundancyState changes; 2) Delete the project .dcf file on the Web Server; and 3) Regenerate server data (*.pck) on the OS Servers and re-import onto the Web Server.

Table of Contents

Executive Summary

WinCC Web Navigator enables remote operations, supervisor auditing, and process monitoring over corporate networks using thin Web Clients connected to a dedicated WinCC Web Server (configured as an OS Client). In high-availability architectures with redundant OS Servers, an automated master-standby failover must be transparent to operators. A frustrating operational disturbance occurs when a server switch causes all Web Client terminals to abruptly close open faceplates, wipe diagnostic views, and reset the monitor to the top-level plant Start screen. Standard clients remain unaffected. This technical reference diagnoses the script triggers, evaluates the role of @screen.pdl, and provides the exact remediation steps to achieve bumpless Web Client failovers.

Architecture and Fundamental Mechanics

Web Navigator Redundancy and Screen Window Architecture

+-----------------------+                         +-----------------------+
| OS Server 1 (Master)  |<=== WinCC Redundancy ===| OS Server 2 (Standby) |
| [SERVER FAILS / REBOOT|                         | [BECOMES NEW MASTER]  |
+-----------|-----------+                         +-----------|-----------+
            |                                                 |
            +-----------------------+-------------------------+
                                    |
                                    v Seamless Redundant Tag Switching
+-------------------------------------------------------------------------+
|               WinCC Web Server (OS Client with Web Navigator)           |
|                                                                         |
|   - Switches internal data channel to OS Server 2                       |
|   - Triggers internal system tag: @RedundancyState                      |
+-----------------------------------|-------------------------------------+
                                    |
         +--------------------------+--------------------------+
         | STANDARD PCS 7 BEHAVIOR                             | BUGGY CUSTOM SCRIPT BEHAVIOR
         v                                                     v
+------------------------------------+           +------------------------+
| Standard @screen.pdl:              |           | Custom @screen.pdl:    |
| - Picture window handles preserved |           | - Script detects       |
| - Active screens remain displayed  |           |   @RedundancyState     |
| - Faceplates update dynamically!   |           | - Calls: OpenPicture() |
| - ZERO DISTURBANCE TO OPERATORS!   |           | - All Pop-ups CLOSED!  |
|                                    |           | - REVERTS TO START!    |
+------------------------------------+           +------------------------+

Root Cause Breakdown

  1. Custom @screen.pdl Scripting: In standard PCS 7, screen navigation is managed by the Picture Tree Manager and @screen.pdl. If custom engineering added a dynamic C-action or VBScript to @screen.pdl monitoring user login changes or @RedundancyState and commanding OpenPicture(StartScreen), the script executes during server failover, clearing all open picture windows.
  2. The autoload.pas Misconception: In WinCC Basic Runtime, autoload.pas handles screen switching on user logon. However, Global Script Pascal actions do not run directly on Web Clients; Web Clients execute Web-published C-actions and VBScript within WinCCViewerRT.
  3. Outdated Server Data and Corrupted .dcf: If the Web Server holds an obsolete server package (*.pck) or a corrupted .dcf configuration file, the Web Server briefly loses connection to the project context during failover, prompting the web engine to reload the default start picture.

Step-by-Step Implementation Procedure

Step 1: Inspect Custom Scripting in @screen.pdl

  1. On the Engineering Station, open the Web Server OS project in WinCC Explorer.
  2. Open Graphics Designer and open @screen.pdl.
  3. Inspect the event scripts on the background picture: Events > Picture Tree / Miscellaneous > Open Picture / Display Changed.
  4. Search for scripts monitoring the tags @RedundancyState, @CurrentServer, or @LocalMachineName.
  5. Look for function calls executing OpenPicture() or setting Visible := FALSE on picture windows (PW1, PW2, etc.).
  6. Remove or comment out any logic that forces a return to the start screen upon server failover events.

Step 2: Compare with Standard PCS 7 @screen.pdl

  1. If @screen.pdl was heavily customized and the source of the bug cannot be isolated:
  2. Navigate to the base template folder: C:\Program Files (x86)\Siemens\WinCC\Options\PDL\Base_Screen.
  3. Compare the project's @screen.pdl with the original template using WinCC Cross-Reference or a text diff tool.
  4. Restore the standard Siemens @screen.pdl if custom alterations violate standard navigation rules.

Step 3: Regenerate Server Data and Delete Web Server .dcf

  1. In SIMATIC Manager, select the master OS Server project.
  2. In WinCC Explorer, right-click Server Data and select Generate....
  3. Open the Web Server OS project.
  4. In WinCC Explorer, right-click Server Data > Update... to re-import current server packages.
  5. Deactivate WinCC Runtime on the Web Server and close WinCC Explorer.
  6. In Windows Explorer, navigate to the Web Server project folder and delete [ProjectName].dcf.
  7. Reopen WinCC Explorer on the Web Server to regenerate a clean configuration cache.

Step 4: Re-Publish Web Project via Web Configurator

  1. In WinCC Explorer on the Web Server, open Web Navigator > Web Configurator.
  2. Verify the Web site configuration and confirm the default start screen is assigned correctly.
  3. Open Web Navigator > Web Publisher.
  4. Select Publish All Pictures and Scripts to ensure modified PDLs are converted to web-compatible format.
  5. Restart the Web Server runtime and reconnect Web Clients.

Verification

  1. Web Client Active Monitoring: Connect a Web Client via WinCCViewerRT. Navigate to an area graphic and open three motor/valve faceplates in picture windows.
  2. Controlled Server Switchover Test: On the active Master OS Server, deactivate WinCC Runtime (simulating failover to the standby server).
  3. Failover Resilience Audit: Observe the Web Client. Verify that all open faceplate pop-ups remain open, live values continue updating from the new master, and the display does not revert to the start screen.

Limitations and Operational Precautions

  1. Unsupported Script Functions: Web Navigator clients do not support all WinCC C-script API functions (e.g., direct Windows API window hooks); ensure all scripts in web faceplates conform to the 'WinCC Web Navigator - Supported Functions' specification.
  2. Session Timeout Limits: If the Web Client loses network connectivity to the Web Server for longer than the configured Web Client session timeout (typically 20 minutes), the session is terminated and re-logging in will legitimately open the start screen.

Engineer FAQ

Why do Web Clients switch to the start screen during OS failover?

A custom script in @screen.pdl or an outdated server data package causes the Web Server to re-initialize screens when @RedundancyState changes.

Do standard PCS 7 Web Clients close pop-ups on failover?

No. Standard PCS 7 V9.0 and V9.1 Web Clients maintain open picture windows and faceplates seamlessly during server switchovers.

What is @screen.pdl?

It is the foundational WinCC screen template that hosts the Picture Tree navigation bar, overview area, working area, and faceplate windows.

What does deleting the .dcf file on the Web Server do?

It clears cached component and connection records, forcing WinCC to rebuild clean server data references.

Do Global Script actions run on Web Clients?

Global C-scripts and VBS actions published for web execution run in the web engine, but Pascal scripts (autoload.pas) do not.

What tool publishes pictures for Web Navigator?

The WinCC Web Publishing Wizard (Web Publisher) inside WinCC Explorer.

What tag indicates redundant server failover?

The internal system tag @RedundancyState changes value when mastership shifts between servers.

Can Web Clients run in standalone mode without a browser?

Yes, using the Siemens dedicated client application WinCCViewerRT.exe.

Does Web Navigator require extra software licenses?

Yes, Web Navigator requires client access licenses (CAL) based on concurrent active client connections.

Where are Web Navigator diagnostic logs stored?

On the Web Client under C:\Users\[User]\AppData\Local\Siemens\WinCC\WebNavigator\.

Technical References

Related Articles

Related Tags

  • Web Navigator
  • WebClient
  • @screen.pdl
  • WinCC Redundancy
  • Screen Switching
  • OS Failover
  • WinCC V7.5
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