Configuring Group Alarm Locking and Area Message Suppression in SIMATIC PCS 7 APL

In SIMATIC PCS 7 Advanced Process Library (APL), disabling or locking alarms across a specific group of technological blocks (such as multiple MonAnL analog monitoring blocks in a gas monitoring system) is implemented using the standardized message lock (MsgLock) or alarm suppression (MsgSup) inputs in CFC, rather than placing blocks into 'Out of service' mode. While 'Out of service' (OosOp) disables all technological processing, setting MsgLock = 1 leaves signal processing, scaling, and interlocking 100% active while suppressing all alarm message generation to the WinCC alarm screen. Group locking can be triggered from an area button on SCADA via a shared CFC control signal.

APL Alarm Management Architecture - Out of Service vs Message Locking

In SIMATIC PCS 7 APL, managing nuisance alarms and maintenance states distinguishes strictly between equipment operation and message generation:
* Out of Service (OosOp / OosLi): Completely shuts down the technological block. The block freezes outputs, clears status words, and sets quality codes to 'Bad'. Using Out of Service merely to silence alarms is dangerous because it disables interlocks and process monitoring.
* Message Lock (MsgLock): Disables all alarm messages from the block (high/low limits, gradient faults). The block continues calculating process values, evaluating interlocks, and animating faceplates; only alarm logging to the SCADA screen is suppressed.
* Message Suppression (MsgSup): Suppresses specific alarm classes dynamically based on operational state (e.g. suppressing low-pressure alarms while a compressor is stopped).

Configuring MsgLock and MsgSup for Area Group Control

To implement an operator button that silences alarms across an entire technological area:
1. Shared Interconnection in CFC: Group technological blocks (e.g. 4x MonAnL gas monitors) within the same plant hierarchy folder.
2. Control Signal Generation: Create a binary control signal from a digital operator block (OpDi01) or custom pushbutton in WinCC.
3. Interconnection: Connect the output of the control signal to the MsgLock input of all target MonAnL blocks.
4. Visual Indication: When MsgLock := TRUE, APL block icons automatically display a standardized blue lock badge, informing operators that alarms are actively suppressed.

Step-by-Step CFC Logic and WinCC Button Integration

Follow this procedure to configure group alarm locking:

[Phase 1: Instantiate Group Control Block in CFC]
   │  • In CFC, open the chart for the monitoring area
   │  • Insert an APL digital operator block: "OpDi01" (FB1866)
   │  • Configure block instance: "Area_Alarm_Lock"
   │  • Ensure "OCM possible" is enabled to allow operator control from WinCC
   │
[Phase 2: Interconnect to MonAnL Blocks]
   │  • Connect output "Area_Alarm_Lock.Out" to the "MsgLock" input of:
   │      - MonAnL_1.MsgLock
   │      - MonAnL_2.MsgLock
   │      - MonAnL_3.MsgLock
   │      - MonAnL_4.MsgLock
   │
[Phase 3: Compile and Test in WinCC Runtime]
   │  • Compile AS (Changes Only) and Compile OS (Changes Only)
   │  • In WinCC Graphics Designer, place a button linked to Area_Alarm_Lock.SetOp
   │  • In Runtime: Clicking the button asserts MsgLock = 1 across all 4 blocks;
   │    existing alarms are acknowledged/hidden, and no new alarms appear in the banner!

Alarm Suppression Modes and Operational Behavior Matrix

Compare alarm suppression and maintenance states in PCS 7 APL:

Mode / FeatureCFC ParameterProcess Monitoring ActiveSafety Interlocks ActiveWinCC Alarm OutputIcon BadgeNormal OperationMsgLock=0, OosOp=0YesYesActiveNoneMessage LockMsgLock = 1YesYesSuppressedBlue LockMessage SuppressionMsgSup = 1YesYesFiltered by classWhite BellOut of ServiceOosOp = 1No (Halted)No (Disabled)DisabledWrench

Verification

To confirm that group alarm locking functions accurately:
1. In WinCC Runtime, open the process graphic containing the 4 MonAnL blocks.
2. Click the 'Area Alarm Lock' button to assert MsgLock = 1.
3. Confirm that all 4 block icons display the blue lock badge.
4. Force a high gas concentration on one of the sensors exceeding the high-high trip limit.
5. Verify on the faceplate that the live process value shows the high level in red, but no alarm message enters the top alarm banner or WinCC Alarm Logging.

Limitations and Operational Precautions

Never use MsgLock to suppress safety-critical emergency shutdown alarms without strictly adhering to plant Management of Change (MOC) and bypass authorization procedures. Suppressing alarms can blind operators to hazardous gas leaks or thermal runaways. Always configure an automated alarm bypass timer or audible reminder in SCADA to prevent suppressed alarms from being forgotten.

Engineer FAQ

Why should I use MsgLock instead of Out of Service (Oos)?

Out of Service shuts down the block completely, disabling process calculations and interlocks. MsgLock silences alarms while keeping process monitoring fully active.

Does MsgLock clear existing alarms that are already active?

Yes. When MsgLock is set to 1, active unacknowledged alarms from that block are automatically cleared and removed from the active alarm list.

Can I lock alarms individually from the faceplate?

Yes. Standard APL faceplates include an alarm tab where authorized operators can toggle message locking individually for that specific instrument.

What block input suppresses alarms automatically when equipment is stopped?

Use input MsgSup (Message Suppression). For example, connect a motor's Run feedback inverted to MsgSup to suppress low-flow alarms while the pump is off.