Activating Acoustic Alarm Horn Sounds on Newly Commissioned OS Clients in SIMATIC PCS 7

When acoustic alarm horn sounds fail to trigger on a newly commissioned OS Client after hardware replacement (while visual alarms display normally), the failure occurs because the WinCC Horn Configuration was not executed on the client station, sound files (.wav) are missing from the local client directory, or the Windows default audio playback device is unassigned or muted. In WinCC Explorer on the Engineering Station, open the client OS project, launch the Horn editor, verify message assignment rules and sound file paths under the 'Signal Assignment' tab, download the project to the client, and ensure the Windows audio service is active.

WinCC Horn Architecture in Client-Server Systems

In industrial control rooms, acoustic alarm horns provide immediate auditory notification when high-priority process alarms (such as emergency trips, high-high pressure, or safety interlocks) occur. In SIMATIC PCS 7, acoustic signaling is managed by the WinCC Horn (Basic Process Control) option.

In a client-server architecture, each OS Client manages its own local sound hardware (sound card, internal speakers, or USB audio beacons). While the OS Server evaluates and archives alarm messages in SQL Server, the OS Client evaluates its own Horn configuration based on the messages arriving across its terminal bus connection.

Root Causes: Missing Configuration, Unassigned Devices, and Sound Files

When an OS Client is replaced with new PC hardware and the project downloaded, the loss of sound is almost always caused by:

Unassigned Windows Audio Device: Modern IPCs have multiple audio endpoints (Realtek onboard, DisplayPort audio through monitors, USB audio). If Windows defaults to a monitor without speakers, sound plays silently into a dead port.
Horn Option Not Configured on Client Project: In SIMATIC Manager, the Horn configuration is station-specific. If the client project in the Multiproject was newly created without running the Horn Editor, no acoustic triggers exist.
Missing .wav Sound Files on Local Disk: The Horn editor references audio files (e.g., Horn_Alarm.wav, Horn_Warning.wav). If these files reside only on the ES and were not copied to the client's local directory, the audio player fails silently.
Windows Audio Service Stopped: The Audiosrv service in Windows may be disabled on industrial server OS installations.

Configuring Message and Signal Assignments in the Horn Editor

The WinCC Horn Editor contains three configuration tabs:

Message Assignment: Defines which WinCC Message Classes (e.g., 'Alarm', 'Warning', 'Process Message') and Message Priorities (e.g., Priority 1 to 16) trigger which logical sound generator tags (@Horn_Sound1, @Horn_Sound2).
Signal Assignment: Maps each logical sound tag to a physical output: either a multimedia sound file (.wav) played through the sound card, or a hardware digital output via a signal module card.
Acknowledgment: Configures the acknowledgment behavior (e.g., clicking the 'Silence Horn' button @Horn_Reset in the bottom navigation bar silences the acoustic siren while leaving the visual alarm flashing).

Step-by-Step Procedure to Restore Client Acoustic Horns

Follow this sequence to restore acoustic horn operation on the replacement OS Client:

Verify Windows Audio Hardware: On the OS Client, open Windows Sound Settings. Verify that the correct speaker/line-out device is set as the Default Playback Device. Click Test; confirm test chimes are audible through the speakers.
Open Horn Editor in WinCC Explorer: On the ES (or directly on the client in standalone mode), open WinCC Explorer. Double-click Horn.
Configure Message Assignment: In the Message Assignment tab, ensure that Message Class Alarm is mapped to Signal Tag 1.
Configure Sound Files in Signal Assignment: In the Signal Assignment tab, set Signal Tag 1 to Sound. Click browse and select a valid sound file (e.g., C:\Siemens\WinCC\bin\Horn_Alarm.wav or <Project_Dir>\GraCS\alarm.wav).
Deploy Sound Files to Client: Ensure the selected .wav files physically exist in the identical path on the client PC.
Download OS Project: In SIMATIC Manager, execute a project download to the OS Client. Activate runtime.

Horn Trigger Parameter and Audio Configuration Matrix

The following table compares Horn configuration parameters across typical industrial setups:

Message ClassPriority FilterLogical Signal TagSignal Device TypeAudio File / Output DestinationAlarm (High Priority)Priority >= 12Signal Tag 1Multimedia SoundC:\Windows\Media\Ring05.wav (High Siren)Warning (Low Priority)Priority 1..11Signal Tag 2Multimedia SoundC:\Windows\Media\Ding.wav (Intermittent Beep)Control System FaultAll PrioritiesSignal Tag 3Multimedia SoundC:\Windows\Media\Chord.wav (Chime)Plant Trip (Hardware)Priority 16Hardware OutputSignal Module CardDigital Output relay to external plant horn

Verification

Verify acoustic alarm operation through the following test sequence:

On the OS Client, simulate a high-priority process alarm (e.g., trip an analog high-high limit).
Confirm that the alarm banner appears in @ALARMVIEW.PDL and that the siren sound loops continuously through the speakers.
Click the Silence Horn button (horn symbol with cross) in the bottom navigation bar (@BOTTOM.PDL).
Verify that the acoustic sound ceases immediately while the alarm banner continues to flash red until acknowledged.
Verify that acknowledging the alarm resets all visual and acoustic states cleanly.

Limitations and Operational Precautions

Consider these operational rules when configuring acoustic alarms:

Never Disable Horn Acknowledgment: The operator must always have a fast, single-click method to silence screaming horns in @BOTTOM.PDL so critical cognitive focus can shift to diagnosing root causes during emergency trips.
Continuous Looping Sound: In the Signal Assignment tab, ensure 'Continuous Loop' is checked for alarms so the horn does not sound only once and fall silent while an active trip persists.
Remote Desktop (RDP) Sound Traps: If testing the client via Windows Remote Desktop, audio may redirect to the remote laptop instead of playing through the physical control room speakers.

Engineer FAQ

What sound file format does the WinCC Horn support?

The WinCC Horn supports standard uncompressed Microsoft WAV audio files (.wav).

Can the Horn trigger external electrical sirens?

Yes, using an industrial signal module PCI card or mapping the @Horn_... tag to a PLC digital output driving a 24 VDC / 230 VAC siren.

Why does the horn play through my laptop instead of the control room speakers?

If you are connected to the OS Client via Windows Remote Desktop (RDP), Windows redirects audio playback to the remote client machine unless disabled in RDP options.