Restricting WinCC Report Printing to Active Master OS Server Using @RM_MASTER Internal Tag

In a redundant SIMATIC PCS 7 OS Server pair, time-triggered print jobs configured identically across both servers will execute simultaneously on both nodes, resulting in duplicate printouts. To ensure that scheduled reports execute strictly on the active Master server, the print job script must evaluate the internal system tag @RM_MASTER. In WinCC Global Script (C or VBS), querying @RM_MASTER verifies server status: when @RM_MASTER == 1, the local server is operating in the active Master state and initiates RPTJobPrint(); when @RM_MASTER == 0, the server is in Standby and suppresses execution.

The Duplicate Print Challenge in Redundant OS Architectures

Redundant WinCC OS server pairs are engineered with identical project configurations, databases, and runtime scripts to ensure seamless hot-standby failover. When an automated report (such as a shift production log, daily alarm summary, or process value journal) is scheduled using the WinCC Print Job Editor or Global Script cyclic timers, both Server A and Server B execute the schedule simultaneously. If both servers output to the same physical network printer or shared network archive folder, plant operators receive duplicate physical paper copies or duplicate file entries with identical data.

To resolve this issue without creating asymmetrical project configurations (which would break OS Project Duplicator synchronization), engineers must implement conditional script logic that evaluates runtime redundancy status before invoking the WinCC reporting engine.

WinCC Redundancy Internal Tags and Master/Standby States

When the WinCC Redundancy option package is enabled, WinCC automatically instantiates specialized internal tags prefixed with @RM_ within the internal tag management hierarchy.

Internal Tag NameData TypeValue / StateDescription@RM_MASTERBinary (BOOL)1 = Active Master, 0 = StandbyIndicates whether the local server holds active master authority@RM_SERVER_NAMEText (16-bit)Local Computer NetBIOS NameReturns the computer name of the local server execution environment@RM_MASTER_NAMEText (16-bit)Active Master NetBIOS NameIdentifies the computer currently acting as the active master server@RedundancyServerState32-Bit Unsigned0 = Fault, 1 = Master, 2 = StandbyEncodes comprehensive server redundancy state machine status

By querying @RM_MASTER synchronously before invoking the print command, the standby server peacefully bypasses the report generation routine while the master server processes the print pipeline.

Implementation via Global Script (C and VBS Examples)

To implement master-only report printing, create a Global Script action triggered cyclically or via a scheduled time event.

ANSI-C Script Implementation:

#include "apdefap.h"
int gscAction(void)
{
    #define MasterTag "@RM_MASTER"
    BOOL isMaster = FALSE;

    // Synchronously read the master redundancy tag
    isMaster = GetTagBitWait(MasterTag);

    if (isMaster)
    {
        // Execute print job only on active master
        if (!RPTJobPrint("Shift_Report_Job"))
        {
            printf("WinCC Report Print Failed: Shift_Report_Job\r\n");
            RptShowError(NULL, NULL);
        }
        else
        {
            printf("WinCC Report Successfully Dispatched by Master Server\r\n");
        }
    }
    return 0;
}

VBScript Implementation:

Sub PrintMasterReport()
    Dim objTag, isMaster
    Set objTag = HMIRuntime.Tags("@RM_MASTER")
    isMaster = objTag.Read

    If isMaster = True Then
        ' Trigger report print job via WinCC Report Engine
        HMIRuntime.Execute "RPTJobPrint.exe Shift_Report_Job"
    End If
End Sub

Configure the Global Action trigger for the desired schedule (e.g., daily at 06:00:00). Because both servers share identical code, project synchronization remains 100% compliant.

Verification

Perform the following verification steps on the redundant server cluster:

Tag Value Inspection: Open WinCC Tag Simulator or WinCC Explorer status bar on Server A and Server B. Confirm that @RM_MASTER equals 1 on Server A and 0 on Server B.
Scheduled Execution Test: Temporarily set the script trigger to fire every 2 minutes. Verify that a single printout is generated by the master server and no output is produced by the standby server.
Failover Execution Test: Simulate an OS server failover by stopping runtime on Server A. Verify that Server B's @RM_MASTER tag switches to 1. Confirm that subsequent scheduled print cycles execute successfully from Server B.

Limitations and Operational Precautions

When configuring master-dependent print scripts, adhere to these operational precautions:

Network Printer Accessibility: Ensure that both physical server nodes have identical printer drivers installed, identical Windows default printer names configured, and equivalent network routing permissions to the target printer.
Failover Mid-Print Considerations: If a failover occurs during the precise moment a multi-page print job is rendering, the newly designated master might re-evaluate the trigger and re-dispatch the job. Use timestamp verification tags if strict once-only daily enforcement is mandatory.
GSC Runtime Activation: In the Computer Properties -> Startup tab, verify that Global Script Runtime is checked on both redundant servers, otherwise the background C/VBS action will not execute.

Engineer FAQ

Why should I use GetTagBitWait instead of GetTagBit for @RM_MASTER?

GetTagBitWait() performs a synchronous read directly from the data manager cache rather than relying on an asynchronous callback. This ensures that the conditional branch evaluates the true instantaneous state of the redundancy manager.

Does the WinCC Print Job Editor have a built-in checkbox for Master-only execution?

Standard WinCC Report Layout print jobs triggered via the native Report Designer scheduler do not include an automatic redundancy filter. Wrapping the print call in a Global Script action conditioned on @RM_MASTER is the standard solution.

What happens if both servers report @RM_MASTER == 0 during startup?

During initial synchronization or network split-brain recovery, @RM_MASTER may temporarily read 0 on both servers. The print script simply skips execution until the Redundancy Manager resolves mastership, preventing duplicate outputs.