How to Suppress Nuisance Hardware Fault Alarms in WinCC Without Masking Critical Diagnostics

To suppress repetitive "Module error entering state" alarms in SIMATIC PCS 7 (such as V8.2 SP1 with WinCC V7.4 SP1) during prolonged field maintenance without blinding operators to other hardware faults, configure channel-level message suppression on the technological driver block or apply WinCC Alarm Shelving. Disabling messages inside the WinCC Alarm Logging editor is permanently overwritten during the next OS Compile. Blanket disabling of parameter EN_MSG on central diagnostic blocks (OB_DIAG1, RACK, SUBNET) creates severe blind spots, silencing alarms across the entire backplane rack. The approved, safe engineering approach utilizes the channel driver's built-in message suppression input (MS_Sup) or temporary ISA-18.2 alarm shelving in the WinCC AlarmControl runtime interface.

Origin of 'Module Error Entering State' Alarms in the PCS 7 Architecture

System hardware diagnostic alarms in PCS 7 operate through an automated, multi-tiered hierarchy:
1. Hardware Interrupt Detection: An I/O module detects an electrical fault (wire break, open circuit, short to ground, or sensor supply fault) and triggers diagnostic interrupt organization block OB82.
2. The Driver Generator @ Charts: During project compilation, the driver generator instantiates specialized diagnostic blocks:
- OB_DIAG1 (FB118): Evaluates CPU and central rack operating states.
- RACK (FB107) / SUBNET (FB106): Monitors physical backplane racks and fieldbus segments.
- MOD_D1 / MOD_D2 (FB148/FB149): Evaluates health of individual analog and digital signal modules.
3. Dispatch via ALARM_8P: When the diagnostic block detects a channel fault, it invokes system function block ALARM_8P to transmit the alarm Module error entering state directly to WinCC Alarm Logging.

The Catastrophic Risk of Global EN_MSG Deactivation on RACK/SUBNET

When operators complain about nuisance alarms every two minutes due to an unresolved field sensor wire break, maintenance engineers often attempt quick fixes:
* The WinCC Alarm Logging Mistake: Manually deactivating the message in WinCC Explorer fails because the next OS Compile restores the default system configuration from SIMATIC Manager.
* The EN_MSG = 0 Blind Spot Hazard: If an engineer opens the @ charts and sets EN_MSG = 0 on OB_DIAG1, RACK, or SUBNET, the block completely stops sending ALARM_8P telegrams.
* The Danger: Silencing RACK or SUBNET suppresses ALL hardware alarms for that entire station. If a power supply fails, an optical link snaps, or an entire ET 200M rack catches fire, zero alarms will appear on operator screens, leading to catastrophic unmonitored plant trips.

Method 1: Channel-Specific Suppression via Driver Parameter MS_Sup

The safest, targeted engineering method suppresses alarms specifically at the individual faulty instrument channel without compromising rack diagnostics:

Step 1: Locate the Channel Driver in CFC

Open the CFC chart hosting the technological device associated with the damaged field wiring.
Locate the connected channel driver block (Pcs7DiIn for digital sensors, Pcs7AnIn for analog transmitters).

Step 2: Configure Message Suppression Parameter MS_Sup

In the parameter list, locate input MS_Sup (Message Suppression).
Set MS_Sup = 1 (or connect an operational maintenance bypass flag).
In the channel driver properties, you can also set SimOn = 1 and input a safe static process value to allow downstream interlocks to operate normally while wiring repairs proceed.

Step 3: Perform CFC Change Download

Save the CFC chart.
Execute PLC -> Download -> Changes Only to the AS CPU in RUN mode.
Result: MS_Sup suppresses the process alarm and prevents the channel driver from bubbling diagnostic discrepancy messages up to WinCC, while leaving central rack diagnostic blocks fully armed.

Method 2: Operational Alarm Shelving in WinCC AlarmControl (ISA-18.2)

For operations under active production where engineering downloads to the AS are prohibited, use standardized WinCC Alarm Shelving:

Step 1: Identify the Repeating Alarm in WinCC Runtime

In WinCC AlarmControl, locate the recurring "Module error entering state" alarm line.
Note the channel address or device identifier in the message text.

Step 2: Execute Alarm Shelving

Right-click the alarm line to open the context menu.
Select Shelve Alarm.
Choose an authorized shelving duration (e.g., 4 hours, 8 hours, 1 shift).
Enter an operational justification: Wire break on PT-104 pending instrumentation turnaround.
Click Shelve.
Result: The alarm disappears immediately from the active incoming alarm list (Neuliste) and moves to the Shelved Alarms tab.

Step 3: Automated Expiration Monitoring

Under ANSI/ISA-18.2 / IEC 62682, shelving is temporary. If the wire break is repaired, the alarm clears automatically in the background. If the fault persists when the timer expires, the alarm returns to the active list to prompt the incoming shift crew.

Verification

To verify that nuisance alarms are suppressed safely:
- Check WinCC incoming alarm banner: confirm that the repetitive "Module error entering state" alarm no longer appears every couple minutes.
- Check the WinCC Shelved Alarms list: verify that the shelved item displays the active countdown timer and technician note.
- Verify central diagnostic health: unplug an unrelated test I/O module on the same rack to confirm that genuine hardware faults continue to trigger system alarms instantly.
- Open SIMATIC Manager -> PLC -> Diagnostic Buffer: confirm that the underlying hardware events remain logged for maintenance traceability.

Limitations and Operational Precautions

Shelving Privileges: Alarm Shelving requires appropriate WinCC authorization (typically Authorization Level 5 or 6). Do not grant blanket shelving rights to unauthorized operators without audit logging.
Driver Generator Re-runs: If you must modify parameters inside the auto-generated @ charts, remember that compiling with Generate module drivers checked will revert manual edits unless the technological driver parameters in user charts are locked.
Physical Repair Priority: Software suppression is a temporary maintenance bridge; repairing field wire breaks, loose terminal blocks, and degraded cable shielding remains the primary objective.

Engineer FAQ

Why does the alarm recur every couple of minutes instead of staying steady?

Field wire breaks or loose terminal connections vibrate, intermittently making and breaking contact. Each transition triggers an incoming event (COME) followed shortly by an outgoing recovery (GO), generating a continuous stream of nuisance alarms.

Does setting MS_Sup = 1 on Pcs7AnIn stop the CPU from reading raw I/O?

No. MS_Sup only suppresses the dispatch of ALARM_8P messages to WinCC. The channel driver continues reading peripheral I/O words and evaluating signal status (ST).

Where can I view all currently shelved alarms in WinCC?

Open the standard WinCC AlarmControl screen and select the Shelved Alarms (or Hidden Alarms) tab on the alarm toolbar.

What is the difference between Alarm Shelving and Alarm Locking?

Alarm Shelving is a temporary, time-limited operator action that automatically un-shelves upon timer expiration. Alarm Locking is an indefinite administrative action that prevents alarm generation until manually unlocked by an engineer.

Technical References

Siemens Industry Online Support: SIMATIC PCS 7 Fault-Tolerant Process Control Systems (A5E00278788).
SIOS Entry 109742323: PCS 7 Compendium Part A - System Diagnostics and Driver Engineering.
ANSI/ISA-18.2-2016: Management of Alarm Systems for the Process Industries.
SIOS Entry 109809264: SIMATIC Process Control System PCS 7 Advanced Process Library Manual.

Related Tags

Diagnostics
Alarm Logging
ISA-18.2
Alarm Shelving
Channel Drivers
WinCC
Industrial Automation

How to Suppress Nuisance Hardware Fault Alarms in WinCC Without Masking Critical Diagnostics