C135 PCS 7 (PCS7)
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How to Suppress and Manage Module Error Entering State Alarms in PCS 7

How to Suppress and Manage Module Error Entering State Alarms in PCS 7

To temporarily suppress or manage recurring "Module error entering state" diagnostic alarms in SIMATIC PCS 7 while field wiring or hardware maintenance is pending, use WinCC Alarm Shelving (hiding) or configure message suppression on the specific diagnostic block. The "Module error entering state" message is an automated system diagnostic alarm generated by driver blocks (MOD_D1, MOD_D2, MOD_SWT, OB_DIAG1) inside the automatically generated @ charts whenever hardware channel diagnostics detect wire breaks, short circuits, or module loss. Disabling the alarm inside WinCC Alarm Logging is ineffective because subsequent OS compilations overwrite manual modifications. The supported methods are shelving the alarm at the WinCC operator interface or setting parameter EN_MSG = 0 on the individual channel/module diagnostic block.

Table of Contents

Architecture of PCS 7 System Diagnostic Alarms and Driver Blocks

In SIMATIC PCS 7, diagnostic alarms originate from low-level controller firmware diagnostics and the PCS 7 diagnostic block library:
1. Hardware Fault Detection: An I/O module (e.g., SM 321, ET 200SP, or ET 200M) detects a physical line disruption (wire break, power loss, sensor failure) and triggers diagnostic interrupt organization block OB82.
2. Module Driver Processing: The driver generator automatically creates @ charts (e.g., @(1), @(2)) containing diagnostic blocks:
- OB_DIAG1 (FB118): Monitors controller CPU operating states.
- RACK (FB107) / SUBNET (FB106): Monitors physical backplane racks and fieldbus segments.
- MOD_D1 / MOD_D2 (FB148/FB149): Monitors physical digital/analog signal modules.
3. Alarm Generation via ALARM_8P: When a fault occurs, the diagnostic block invokes system function block ALARM_8P to transmit the message Module error entering state directly to WinCC Alarm Logging with microsecond-accurate controller timestamps.

Why WinCC Alarm Logging Modifications Fail on OS Compile

Maintenance engineers often attempt to open WinCC Explorer, locate the message in the Alarm Logging editor, and uncheck "Message active":
* The Overwrite Mechanism: In PCS 7, the central engineering database in SIMATIC Manager is the single point of truth. Whenever an engineer executes Compile OS, the compilation wizard extracts message definitions directly from the CFC charts and system driver libraries.
* Consequence: Any manual deletions, text changes, or deactivations made directly inside WinCC Alarm Logging are wiped out and replaced by the original system definitions during the very next OS Compile.
* Proper Engineering Path: Message suppression must be executed either through runtime operational tools (Alarm Shelving) or directly on the CFC block interfaces.

Method 1: WinCC Alarm Shelving and Operator Locking (Recommended)

In PCS 7 V8.1 and higher (WinCC V7.3 and later), Siemens incorporates the international alarm management standard ANSI/ISA-18.2 / IEC 62682, providing native Alarm Shelving:

Operational Workflow:

  1. In WinCC OS Runtime, locate the recurring "Module error entering state" message in the incoming alarm list.
  2. Right-click the alarm line to open the context menu.
  3. Select Shelve Alarm (or Hide Alarm).
  4. In the dialog box, select a pre-configured shelving duration (e.g., 2 hours, 8 hours, 1 shift) and enter an operational justification (e.g., "Field sensor wiring repair in progress").
  5. Click OK.
  6. Result: The alarm is immediately removed from the active operator alarm screen and transferred to the Shelved Alarms list. If the fault persists after the timer expires, the alarm returns automatically to alert the crew.

Method 2: Diagnostic Block Alarm Suppression via EN_MSG

If the plant operates an older version of PCS 7 without shelving, or if an I/O channel will remain disconnected indefinitely during commissioning, disable message generation at the block level:

Engineering Procedure:

  1. In SIMATIC Manager, locate the @ chart corresponding to the affected hardware rack or module.
  2. Open the chart and find the specific diagnostic block monitoring the failing module (e.g., MOD_D1 or OB_DIAG1).
  3. Locate the input parameter EN_MSG (Enable Message):
    - By default, EN_MSG = 1 (message generation active).
  4. Change the value of EN_MSG to 0.
  5. Save the chart and perform a CFC Change Download to the AS CPU in RUN mode.
  6. Result: The diagnostic block continues evaluating hardware states internally, but ALARM_8P stops dispatching the "Module error entering state" alarm to WinCC.

Verification

To verify that the nuisance alarm has been properly suppressed without blinding other system faults:
- Check WinCC AlarmControl: confirm that the repetitive "Module error entering state" alarm no longer floods the incoming process alarm banner every few minutes.
- Check the WinCC Shelved Alarms list (if using Method 1): verify that the shelved entry displays the correct expiration countdown timer and operator note.
- Verify peripheral hardware visibility: ensure that genuine alarms from other I/O modules on the same fieldbus rack continue to trigger and display normally.
- Check CPU diagnostic buffer: open SIMATIC Manager -> PLC -> Diagnostic Buffer to confirm that the underlying hardware events remain logged for maintenance traceability.

Limitations and Operational Precautions

  • Extreme Risk of Setting EN_MSG = 0 on Central Blocks: Never set EN_MSG = 0 on high-level diagnostic blocks such as RACK (FB107) or SUBNET (FB106). Doing so suppresses all alarms for the entire fieldbus segment, preventing operators from seeing severe bus disruptions or rack power failures.
  • Driver Generator Overwrites: If you execute Compile -> Charts as Program with the checkbox Generate module drivers selected, the compiler may reset modified parameters on auto-generated blocks. To make modifications permanent, configure suppression at the technological channel driver block (Pcs7DiIn / Pcs7AnIn) using parameter MS_Sup (Message Suppression).
  • Temporary Shelving Policy: Establish strict plant operational policies requiring maintenance technicians to close out shelved alarms once physical wiring repairs are completed.

Engineer FAQ

Why does the alarm keep re-triggering every couple of minutes?

This occurs when an intermittent physical fault (such as a loose terminal screw, vibrating wire break, or unstable sensor supply voltage) causes the I/O channel to cycle repeatedly between fault detection (incoming) and recovery (outgoing).

Can I suppress alarms directly on the channel driver block?

Yes. On APL channel drivers (Pcs7DiIn, Pcs7AnIn), setting parameter MS_Sup = 1 or connecting an operational interlock suppresses message generation from that specific process instrument while leaving system hardware diagnostics active.

What is the difference between Locking and Shelving an alarm?

Shelving is a temporary, time-limited operator action defined by ISA-18.2 that automatically un-shelves when the timer expires. Locking an alarm requires engineering privileges and suppresses the message indefinitely until manually unlocked.

Will setting EN_MSG = 0 prevent the CPU from going to STOP during severe faults?

No. Controller stop behavior is determined by the presence of organization blocks (OB82, OB86, OB85) and hardware configuration fault masks, not by the HMI alarm reporting parameter EN_MSG.

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 PCS 7 Advanced Process Library Manual.

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Related Tags

  • Diagnostics
  • Alarm Logging
  • PCS 7
  • WinCC
  • ISA-18.2
  • Driver Generator
  • Industrial Automation
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