Displaying Faceplate-Locked Alarms in the SIMATIC PCS 7 Measuring Point Browser

In SIMATIC PCS 7 WinCC, displaying alarms that were suppressed via the faceplate 'Lock Messages' button within the Measuring Point Browser (@PCS7_MeasuringPointBrowser.pdl) requires understanding the distinction between controller-level suppression (MsgLock) and operator-level alarm locking. When an operator locks messages from an APL faceplate toolbar, the lock action is executed exclusively inside the WinCC Alarm Logging server runtime lock list without modifying AS status words or MsgLock inputs in CFC. To display these faceplate-locked measuring points, open the Measuring Point Browser, enable the 'Locked Messages' (Meldung gesperrt) filter criterion, and ensure that WinCC user authorization levels permit viewing suppressed alarm states.

PCS 7 Alarm Suppression Architecture: AS-Level vs. OS-Level Locking

In modern process plants, alarm flood prevention during startup, maintenance, or abnormal conditions is a core tenet of ISA-18.2 and EEMUA 191 alarm management standards. SIMATIC PCS 7 provides two fundamentally distinct architectural mechanisms to suppress alarms:

Controller-Level Message Suppression (MsgLock): Implemented within the automation controller (AS) on technological blocks (such as MotL, PIDConL, or MonAnL). When block input MsgLock = 1 is asserted in CFC, the block suppresses calls to system alarm blocks (Alarm_8P / Notify_8P). The AS halts message dispatch completely; no alarm is transmitted to WinCC, and status bits (Status1, MsgState) reflect controller-level suppression.
Operator-Level Message Locking (Faceplate Lock Button): Executed by an authorized plant operator clicking the Lock Messages icon on the APL faceplate title bar. This action does not write to the AS controller. Instead, the faceplate script interacts directly with the WinCC Alarm Logging Server Runtime Lock List (LockList). The AS continues to evaluate alarms, but the WinCC alarm server suppresses audible sirens, inhibits visual banner flashes, and diverts the alarm from active process lists into the locked message archive.

Why Faceplate Message Locking Does Not Modify CFC Status Words

Engineers frequently inspect CFC instance parameters online and wonder why locking messages on the HMI does not change MsgLock or alter the Status1 double-word in the PLC:

Segregation of Safety and Control Layers: Writing lock commands from dozens of client stations directly to PLC instance DBs would consume unnecessary AS communication resources and create safety hazards if network latency delayed unlock commands during critical events.
Alarm Logging Server Authority: WinCC Alarm Logging maintains an internal database of locked message IDs. When the AS transmits an alarm telegram for a locked point, the WinCC alarm daemon matches the message number against its local lock list, marks the message as suppressed, and routes it to the Locked List (Gesperrt-Liste).
Measuring Point Browser Integration: Because the faceplate lock state resides on the OS server, query tools like the Measuring Point Browser (@PCS7_MeasuringPointBrowser.pdl) must query the WinCC Alarm Logging lock table rather than querying controller memory.

Alarm Locking States and Measuring Point Browser Filter Matrix

The following table compares alarm suppression mechanisms and their visibility within the Measuring Point Browser:

Suppression ModeInitiated FromStored InReflected in CFC?Measuring Point Browser FilterFaceplate Message LockOperator Faceplate ToolbarWinCC Alarm Server Lock ListNo (MsgLock remains 0)Filter: Locked MessagesAS Message Lock (MsgLock)CFC Interlock / LogicController Instance DBYes (MsgLock = 1)Filter: Suppressed by LogicManual Interlock BypassFaceplate Interlock ViewAS Interlock Block (Intlk08)Yes (BypassAct = 1)Filter: Active BypassesChannel SimulationDriver Block (Pcs7AnIn)AS Driver Instance DBYes (SimAct = 1)Filter: Simulation ActiveMeasuring Point Out of ServiceFaceplate Maintenance ViewAS Operating Mode (OosAct)Yes (OosAct = 1)Filter: Out of Service

Step-by-Step Procedure to Filter and View Locked Alarms

To display all faceplate-locked measuring points in the PCS 7 Measuring Point Browser:

Lock a Measuring Point from an APL Faceplate:
- In WinCC Runtime, open the faceplate for any technological point (e.g., FIC101 PIDConL).
- Ensure the logged-in user possesses Authorization Level 6 (Process Controlling) or Level 10 (Maintenance).
- In the faceplate title bar, click the Lock Messages button (symbolized by a bell with a slash).
- Confirm the operation; notice that the lock icon appears on the faceplate header and on the block icon in the process graphic.
Open the Measuring Point Browser:
- In the WinCC overview area (button bar), click the Measuring Point Browser icon (or access via System -> Measuring Point Browser).
- The window @PCS7_MeasuringPointBrowser.pdl opens displaying plant hierarchy areas.
Configure the Filter for Locked Messages:
- In the Measuring Point Browser toolbar, click the Filter / Selection Criteria icon.
- In the filter dialogue, locate the Message State section.
- Check the box Locked Messages (and uncheck normal process states if isolating locked points only).
- Select the target plant area (or choose root node for the entire plant).
- Click Apply.
Analyze and Unlock from the Browser:
- The table populates with all measuring points whose messages are currently locked on the OS server.
- Double-clicking any line in the browser directly navigates to the associated process graphic and highlights the block icon.
- Open the faceplate from the highlighted icon to unlock messages when maintenance is complete.

Verification

Verify locked alarm reporting:
1. Open the WinCC Alarm List and switch to the Locked Messages List (Gesperrt-Liste); confirm that the locked measuring point appears with its tag name and description.
2. Open the Measuring Point Browser; confirm that the locked point is listed under the 'Locked Messages' category.
3. In CFC, verify that MsgLock remains 0, confirming that AS logic was not altered.
4. Click Unlock Messages on the faceplate; confirm that the point immediately vanishes from both the Locked Messages List and the Measuring Point Browser.

Limitations and Operational Precautions

Redundant Server Synchronization: The WinCC Alarm Logging lock list is synchronized across redundant OS servers. If network disconnection occurs between servers, locked states may take several seconds to reconcile upon reconnection.
Emergency Alarms Consideration: Locking messages suppresses operator warnings. Ensure administrative operating procedures mandate periodic review of the Measuring Point Browser during shift handovers.
Authorization Prerequisite: The Lock Messages button is disabled if the logged-in user lacks Authorization Level 6 or higher.

Engineer FAQ

Why can't I see faceplate message locking in CFC online?

Faceplate message locking operates entirely within the WinCC Alarm Logging server runtime and does not alter controller variables in CFC.

What is the difference between locking an alarm and suppressing it with MsgLock?

MsgLock prevents the PLC from generating the alarm telegram. Faceplate locking lets the PLC generate the telegram, but WinCC suppresses visual and acoustic annunciations.

Can the Measuring Point Browser show bypassed interlocks and locked messages simultaneously?

Yes. The filter dialog allows selecting multiple criteria, including locked messages, bypassed interlocks, simulation states, and out-of-service modes.