Configuring WinCC Horn for Alarm Priority Triggering in PCS 7

Overview

The WinCC Horn function is an audible alarm acknowledgement tool that plays a configured .wav file whenever a defined tag, message, or alarm priority is asserted. In a PCS 7 V9.0 SP3 environment running on top of WinCC 7.4 SP1, the horn is normally driven by the central Alarm Logging (ALG) subsystem and triggers on the standard alarm classes used by ALARM_8P, ALARM_8, NOTIFY_8P, and the operator-process-level block set (APL).

The default PCS 7 horn configuration is intentionally global: every WinCC client that is logged into the same server project receives the same sound event. Operators therefore commonly ask three follow-up questions that this reference addresses directly:

1. Which tags or messages actually drive the horn output?
2. How do you change the alarm priority that triggers the horn, or add new source tags?
3. How do you limit the audible output to a single OS client (for example, the operator station in the control room) without affecting engineering or remote stations?

Prerequisites

Before changing horn settings, capture a full OS project backup (SIMATIC Manager → OS → Archive OS Project) so that you can roll back if an alarm route breaks.

How the WinCC Horn Is Wired Internally

The horn pipeline is event-driven and travels through three layers:

1. AS layer: An ALARM_8P block raises a message with a defined priority (0 = highest, 15 = lowest in PCS 7 convention) and class (e.g., Alarm, high).
2. ALG layer: WinCC Alarm Logging receives the message via the S7 protocol. Each message row carries the priority, the trigger tag (default _PRIORITY_ or per-message binary tag), and the class.
3. Horn layer: The Horn attribute of Alarm Logging holds up to 16 source tags (one per priority). When any source tag goes to a non-zero value, the corresponding WAV is played on every WinCC client that has the Horn function enabled in its project.

In PCS 7, the source tags are auto-bound to the priorities of the standard message classes. This is why a fresh OS project sounds the horn automatically the first time you raise an alarm: all priorities are mapped by default.

Step-by-Step: Defining Which Tags Trigger the Horn

Step 1 - Open Alarm Logging

1. Start WinCC Explorer on the OS server.
2. In the left navigation tree, right-click Alarm Logging → Open.
3. The ALG editor opens with the message configuration loaded.

Step 2 - Open the Horn Configuration Dialog

1. In ALG, choose Tools → Horn from the menu bar.
2. The Horn dialog opens. It contains a grid of 16 rows, one per priority (0..15), and per row an assignment of:
   • Trigger tag (Boolean or integer)
   • Sound file (.wav path)
   • Loop count
   • Activation flag (enable/disable)

Step 3 - Map a Custom Trigger Tag

The trigger tag is any WinCC internal or external tag whose value change should sound the horn. Use the dialog's tag picker to bind your tag to a priority:

Tag name    : MyPlant_Alarm_Critical
Data type   : Binary Tag
Priority    : 0    (highest in PCS 7)
Sound file  : \Siemens\WinCC\Media\Horn\critical.wav
Loop count  : 3
Enabled     : [x]
Acknowledge : Operator must acknowledge in ALG message window

Step 4 - Choose Sound File and Loop Count

Step 5 - Restrict Triggering to Selected Alarm Priorities

To prevent unwanted horn activation, disable entire rows in the Horn dialog by clearing the Enabled checkbox. The corresponding priority still produces visible ALG messages and the message line still flashes, but no sound plays:

1. In the Horn dialog, clear the checkbox for priorities 8 through 15.
2. Click Apply → OK.
3. Compile the OS server and download the project to all clients.

This is the simplest mechanism for the engineer's original question: "How do I change the priority of alarms that are supposed to sound the horn?" The answer is that the Horn configuration table is the priority-to-sound mapping - you do not need to touch any block in the AS, only this table.

Step-by-Step: Adding Custom Source Tags as Triggers

Beyond alarm priorities, WinCC supports a second route: any tag in the project can be declared a Horn source. This is useful when an event is not an alarm (for example, a recipe validation failure, an operator-station heartbeat loss, or a SmartAlarm from PCS 7 Maintenance) but should still produce an audible notification.

1. Create a binary or integer tag in the WinCC tag manager, for example CustomHorn_RecipeError.
2. From your AS code, set this tag to 1 for as long as the event is active; reset it to 0 when the operator clears it.
3. Open Tools → Horn in ALG.
4. In the trigger-tag column of an unused priority row, browse to the tag and assign a short WAV file.
5. Click Apply. The change is live after the next OS compile and download.

Source tags are an extension, not a replacement. They run in parallel to the alarm-priority-driven horn. The two are OR-combined: a sound plays if either path raises it.

Step-by-Step: Limiting Horn Playback to a Single Client

The standard horn is global. To restrict it to one client (for example, only the control-room OS, not the engineering station or remote maintenance client), use one of three approaches. The first is preferred because it stays inside the project standard tooling.

Approach A - Server-Side Horn, Client-Side Project Filter (Recommended)

1. Disable the Horn on every client except the target client by unchecking Horn in the WinCC project properties on those clients.
2. WinCC Explorer → right-click the project → Properties → Options tab.
3. Clear the Activate Horn option on the engineering station and any non-target client.
4. Save, compile, and download the project to each client independently.

This approach satisfies the user's question "is there a way to only have one client sounding the alarm?" without any scripting.

Approach B - Single Horn Tag With Per-Client VBScript Filter

When you cannot split the project configuration (for example, all clients load the same ES configuration), filter the audible output in the Graphics Designer with VBScript.

1. Define a single WinCC internal binary tag Horn_Trigger that any alarm source sets to 1.
2. On each client's start screen, add a VBScript action that runs once on Open Picture and again whenever Horn_Trigger changes value.
3. The script checks the local machine name and only plays the WAV on the matching client.

' Client-specific horn trigger script
' Place on start picture: Actions tab -> On Open
Const ALLOWED_CLIENT = "OS_CLIENT_01"

Dim sHostName
sHostName = HMIRuntime.Tags("@localMachineName").Read

If sHostName <> ALLOWED_CLIENT Then
    ' Do nothing on non-target clients
    Exit Sub
End If

Dim oTrigger
Set oTrigger = HMIRuntime.Tags("Horn_Trigger")

If oTrigger.Read = 1 Then
    HMIRuntime.Sound.Play "\\Siemens\WinCC\Media\Horn\alarm.wav", False
End If

Wire the script to the tag change event from Tag Logging → right-click Horn_Trigger → Event → VBScript → On Change. This delivers sub-second response on the target client and silent behaviour on all others.

Approach C - WinCC Scheduler Horn Suppression

If horn suppression must follow a shift calendar (for example, off during night-shift with no operators), use the WinCC Scheduler to write 0 to a global Horn_Enable tag and check that tag in your script before playing.

Verification

1. Force an alarm from the AS (use SIMATIC Manager → AS → Online → Monitor/Modify on the ALARM_8P instance to set Ack to 0).
2. Confirm the visible ALG message line shows the priority you configured.
3. Listen for the WAV assigned to that priority on the target client only.
4. On a non-target client, verify silence but identical visible alarm indication.
5. Verify acknowledgement by clicking the alarm in the message window; the horn must stop within one loop.
6. Capture screenshots and tag-trace dumps (WinCC Channel Diagnosis) for the commissioning log.

Use the Alarm Logging runtime check Tools → Horn → Test to fire the WAV without a real alarm, useful during acceptance testing.

Troubleshooting Matrix

Performance and Licensing Notes

• Each WinCC client uses a Windows sound device handle for horn playback. Limit concurrent loop counts to 3 to avoid audio-driver contention on Windows Server 2016 / 2019.
• For multi-monitor stations, the WAV plays through the default Windows audio endpoint. Map the operator's preferred output via the Windows Sound control panel.
• PCS 7 V9.0 SP3 ships an updated ALG with deduplicated message rows; this prevents the same priority from firing the horn twice within 250 ms.
• If the project uses redundancy (OS Server A / B), configure the Horn identically on both servers to keep operator experience consistent during failover.

Reference Parameters and Interfaces

For full reference on the Horn function as documented in WinCC Help, see the WinCC 7.4 SP1 Information System under Working with WinCC → Alarm Logging → Configuring the Horn. A practical guide also ships with PCS 7 V9.0 SP3 as PDF "PCS 7 - Configuring the Horn" on the Siemens Industry Online Support portal; search entry ID 109792585 for the canonical Siemens-hosted reference.

Best-Practice Checklist

• Document the priority-to-WAV mapping in the OS Functional Specification.
• Keep one and only one trigger tag per priority row.
• Use the same WAV file set across OS Servers for failover consistency.
• Test horn playback after every OS compile; a stale client can break Horn silently.
• Validate the client-filter script with a hostname swap before handover.
• Store WAV files in the project folder (not a personal drive) so the package is portable.

FAQ