Implementing Automatic Voice Announcements on Siemens PCS7s

1. Overview

Automatic voice announcement on a Siemens PCS 7 process control system is required when an operator must be alerted to the start of operation of any unit (reactor, compressor, line, packaging machine) without watching the HMI. The audible cue must be triggered reliably from the Automation Station (AS), transmitted to the Operator Station (OS), and played through either a public address (PA) system, an intercom, or a PSTN telephone line to a predefined list of recipients.

The general announcement architecture described in US Patent 5,541,981 (Automated Announcement System) separates three functional blocks: a trigger source, a playback engine, and a distribution medium. The same architecture applies to PCS 7 V9.0/V9.1 when the AS is the trigger source, WinCC Runtime is the playback engine, and the medium is a PA amplifier, an analog telephone line, or a SIP gateway. Template-based expansion for multi-language announcements is documented in the IEEE paper Automated Public Address System Using Template-based Synthesis (IEEE, 2025); the same template principle is used here for storing up to N canned messages in a PCS 7 project.

2. Three Implementation Options

Most PCS 7 plants use Option A for in-plant announcement and add Option C for off-hours escalation. Option B is chosen when the announcement must survive a complete WinCC Runtime crash.

3. Prerequisites

1. PCS 7 Engineering Station (ES) with SIMATIC Manager / TIA Portal, configured for the target project (V9.0 SP2 or later recommended; V9.1 supports Windows Server 2019/2022 OS images).
2. Operator Station (OS) with WinCC Runtime, full installation of WinCC RT Advanced on Windows 10 IoT Enterprise LTSC 2019/2021 (or Server equivalent). Verify WinCC > "Computer" > "Properties" > "Startup" lists the desired runtime components.
3. Audio hardware: industrial-grade PC with on-board HDA codec, or add-on USB audio such as the ESI Maya 22 USB or Behringer UCA222 for line-level output to a PA amplifier (70 V or low-Z).
4. Modem hardware (Option C only): Hayes-compatible external modem on RS-232 or USB. Industrial-grade devices such as the MultiTech MT9234ZBA or US Robotics USR5637 are documented for 24/7 operation. Verify the device exposes a standard COM port or TAPI service provider.
5. Plant PA amplifier (Option A) with line-level input and 25 V / 70 V / 100 V constant-voltage output; sized per the loudspeaker line load.
6. Sample WAV files at 16-bit, 22.05 kHz or 44.1 kHz, mono, PCM, μ-law not required (linear PCM keeps the playback engine simple). File size for a 10-second message ≈ 220 KB at 22.05 kHz mono.

4. Option A — WinCC Audio Playback Architecture

The trigger originates from a Boolean tag in the AS (for example, Unit1_Start_Acknowledge). WinCC logs this as a message, which fires a global action script. The script invokes the Windows multimedia API to play the WAV file on the default audio device.

4.1 Tag Configuration on the AS

Create a single-cycle rising-edge tag in CFC/SCL on the AS:

// SCL on S7-410 AS (PCS 7 V9.0)
FUNCTION_BLOCK FB_UnitStartAnnounce
VAR
    bStartEdge : BOOL;  // one-shot
END_VAR
BEGIN
    IF i_bUnitStartCmd AND NOT bStartEdge THEN
        bStartEdge := TRUE;
        i_bAnnounceRequest := TRUE;   // drives WinCC tag "Unit1_StartAnnounce"
    ELSIF NOT i_bUnitStartCmd THEN
        bStartEdge := FALSE;
        i_bAnnounceRequest := FALSE;
    END_IF;
END_FUNCTION_BLOCK

Compile and download to the AS. The tag Unit1_StartAnnounce becomes visible in the OS tag database after the OS compile.

4.2 WinCC Alarm Wiring

Open WinCC Explorer > "Alarm Logging" > "Messages". Add a single-bit message on tag Unit1_StartAnnounce with class "System, Information", event "Incoming". On the "Actions" tab attach a global C or VBScript action that fires only on the "Message Came In" event.

4.3 Global VBScript Action (recommended)

' Global action: plays an audio file when tag rises
' Trigger: Tag "Unit1_StartAnnounce" (Boolean)
' File path: C:\PCS7\Announce\Unit1_Start.wav

Dim oShell, sCmd
Set oShell = CreateObject("WScript.Shell")
sCmd = """C:\PCS7\Announce\Unit1_Start.wav"""

' Use Windows Media Player COM in background mode
Dim oPlayer
Set oPlayer = CreateObject("WMPlayer.OCX")
oPlayer.URL = sCmd
oPlayer.Controls.Play

' Clean up after playback to release the audio device
Dim iDelay
For iDelay = 0 To 30     ' ~30 seconds max wait
    If oPlayer.playState = 1 Then Exit For   ' 1 = Stopped
    HMIRuntime.Trace "Playback in progress..." & vbCrLf
Next iDelay
Set oPlayer = Nothing

Place this script under "Global Script" > "Actions" and set its trigger to the message event "Unit1_StartAnnounce -> Incoming".

4.4 Alternative: C Script via mciSendString

// WinCC Global C Action
#include "apdefap.h"
void OnMessage(PMSG_MESSAGE msg)
{
    if (msg->dwEvent == MSG_EVENT_COMING)
    {
        // Open and play in background
        mciSendString("open \"C:\\PCS7\\Announce\\Unit1_Start.wav\" type waveaudio alias MSG1",
                      NULL, 0, NULL);
        mciSendString("play MSG1", NULL, 0, NULL);
    }
}

The C variant is preferred when sub-100 ms latency between tag rise and audible output matters; it bypasses Media Player initialization overhead.

5. Option B — PLC-Triggered Annunciator

For loops where the announcement must continue even when the WinCC OS is offline, install a dedicated voice module that listens directly on PROFINET or on a hard-wired digital output from the AS. Industrial voice modules include:

Wiring from the AS410 is straightforward: one Boolean tag is mapped to a digital output module (e.g., SIMATIC ET 200SP DQ 8x24VDC/0.5A) and the voice module's discrete input is wired to the same output. On activation, the module plays the corresponding message regardless of OS state.

6. Option C — PSTN Auto-Dialer Integration

To play a pre-recorded message over the public switched telephone network (PSTN), the OS PC dials a destination number, waits for answer, and plays the WAV file into the line. Two implementation paths exist:

6.1 External Modem with AT Commands (legacy path)

Recommended for brownfield plants with existing analog trunk lines. The modem presents a Hayes-compatible command interface.

sox Unit1_Start.wav -r 8000 -e mu-law -b 8 -c 1 Unit1_Start_modem.wav

6.2 TAPI (Microsoft Telephony API) Integration

Newer deployments use Windows TAPI 3.x instead of raw AT commands. TAPI abstracts the underlying hardware (modem, SIP gateway, or TDM card) and exposes a COM-based line device object. WinCC scripts can call TAPI directly through tapi3.dll and mscorlib.

Reference: Microsoft Telephony API documentation, Microsoft Learn — Telephony API (TAPI).

' WinCC VBScript via TAPI 3.x (Windows 10 / Server 2019)
Dim oTapi, oAddr, oCall
Set oTapi   = CreateObject("TAPI.AddressFamily.1")
Set oAddr   = oTapi.get_AddressesByName("Line1").Item(0)
Set oCall   = oAddr.CreateCall("+15551234567", 1, 1)   ' TAPICALLMEDIA_AUDIO

oCall.Connect False
Do While oCall.State < 3   ' CS_CONNECTED = 3
    HMIRuntime.Trace "Dialing..." & vbCrLf
Loop

' Stream WAV to line device via SAPI 5 / DirectShow
' (Implementation detail: use DirectShow FilterGraph with
'  Tee -> Sound Card Capture Filter -> TAPILineDevice)
HMIRuntime.Trace "Connected, playing message..." & vbCrLf
WScript.Sleep 10000   ' message length in ms
oCall.Disconnect

7. WAV File Preparation and Sizing

Each pre-recorded announcement must be stored in a deterministic path on every OS image. Recommended layout:

C:\PCS7\Announce\
   Unit1_Start.wav
   Unit1_Stop.wav
   Unit2_Start.wav
   Alarm_Critical.wav
   Alarm_Warning.wav
   language\
      de\
      es\
      zh\
      ...

Size the storage per the formula:

bytes = duration_seconds * sample_rate_Hz * (bits_per_sample / 8) * channels

For example, a 30-second mono message at 44.1 kHz, 16-bit:

bytes = 30 * 44100 * (16/8) * 1 = 2,646,000 bytes ≈ 2.6 MB

For 50 messages at 30 s each, plan ≥ 130 MB of free space on the OS drive. Keep an offline mirror for disaster recovery.

8. Plant Audio Output Sizing (Option A)

When the line-out of the OS PC feeds a PA amplifier, the amplifier must drive the total loudspeaker line load. The constant-voltage PA formula is:

P_amplifier_W = sum_over_taps( V_tap^2 / Z_speaker ) * 1.25   (25% headroom)

For a 70 V line with twenty 1 W taps:

P = 20 * 1 = 20 W → amplifier minimum = 25 W → choose 30 W or 40 W unit

9. PCS 7 AS–OS Engineering Steps

1. In SIMATIC Manager, open the project and place the Boolean tag Unit<n>_StartAnnounce in the AS program as an output of the unit control block. Use CFC for ladder-equivalent visual editing or SCL for text-based logic.
2. Compile the AS (right-click > "Compile and Download Objects") and verify the tag appears in the S7 connection list.
3. In the OS project, run the OS compile (WinCC Explorer > OS Project Editor > Compile OS). The tag becomes visible in the WinCC tag management under the area folder of the AS.
4. Create an internal WinCC tag Unit1_StartAnnounce_Pulse that is a 2-second one-shot derived from the AS tag using a "Linear Conversion" or a small C action. This debounces chatter on noisy input signals.
5. Create the alarm message and attach the global action as described in §4.
6. On the OS, place the WAV files in C:\PCS7\Announce and grant the WinCC Runtime user account read access.
7. Activate the OS Runtime and trigger the start of the unit. Listen for the announcement at the PA speaker.

10. Verification and Acceptance Test

11. Troubleshooting Matrix

12. Field-Proven Notes