C135 PCS 7 (PCS7)
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Resolving Locked Alarms on Analog Blocks (MonAnL and PIDConL) in PCS 7 OS Runtime

Resolving Locked Alarms on Analog Blocks (MonAnL and PIDConL) in PCS 7 OS Runtime

In SIMATIC PCS 7 OS Runtime, when analog block faceplates (such as MonAnL or PIDConL) display messages permanently locked with a golden lock icon and clicking the unlock button fails, the condition is caused by one of three root causes: 1) The CFC input MsgLock is interconnected to an active logic signal (1 = Locked), which overrides operator faceplate commands; 2) The input signal status is Bad (16#00 or 16#28, marked by a red maintenance wrench), causing Feature Bit 24 to suppress and lock alarm processing; or 3) The underlying Alarm_8P system block encountered a data-type or pointer error in its associated values, causing the alarm channel to report an error state. To resolve this: set MsgLock to 0, ensure input signal status is Good (16#80), and verify Alarm_8P associated value interconnections.

Table of Contents

Executive Summary

During plant commissioning or simulated testing in S7-PLCSIM and WinCC Runtime, automation engineers frequently observe that analog monitoring blocks (MonAnL) and closed-loop controllers (PIDConL) display persistent golden padlock symbols across their faceplate alarm banners. Operators attempting to click the faceplate unlock button find that the lock remains stubbornly engaged. In the PCS 7 Advanced Process Library (APL), message locking is governed by a strict hierarchy combining operator authorizations, interconnected CFC chart pins, signal quality codes, and SFB35 Alarm_8P associated value formatting. This guide provides an in-depth diagnosis of each locking mechanism and the step-by-step troubleshooting workflow to restore active alarm annunciation.

Architecture and Fundamental Mechanics

APL Message Locking Hierarchy and Diagnostic Indicators

+-------------------------------------------------------------------------+
|                        APL Faceplate Alarm Evaluation                   |
+-------------------------------------------------------------------------+
                                    |
   +--------------------------------+--------------------------------+   |
   | CAUSE 1: CFC MsgLock Pin       | CAUSE 2: Signal Status Bad     |   |
   | - MsgLock.Value = 1            | - PV_In.ST = 16#00 or 16#28    |   |
   | - CFC interconnection OVERRIDES| - Red wrench icon displayed    |   |
   |   HMI operator unlock button!  | - Feature Bit 24 suppresses msg|   |
   +--------------------------------+--------------------------------+   |
                                    |
                                    v
   +-----------------------------------------------------------------+   |
   | CAUSE 3: SFB35 Alarm_8P Associated Value Corruption             |   |
   | - Associated Value (ExtVa104..08) assigned invalid type/pointer |   |
   | - Error code returned by Alarm_8P subsystem                     |   |
   | - WinCC marks message channel locked/invalid                    |   |
   +-----------------------------------------------------------------+   |
                                    |
                                    v
+-------------------------------------------------------------------------+
|                         WinCC Runtime Display                           |
|   - Golden Padlock Icon Displayed on Faceplate                          |
|   - Clicking 'Unlock' produces NO EFFECT                                |
+-------------------------------------------------------------------------+

Detailed Mechanism Breakdown

  1. CFC Interconnection Priority: If the CFC parameter MsgLock is interconnected to any chart signal (e.g., motor stopped status or safety lockout), the block ignores all faceplate operator lock/unlock requests. The operator button is only operational when MsgLock is unconnected and manipulated via internal operator tags (MsgLockOp).
  2. APL Signal Status (ST): In APL, every process variable is a structure containing .Value and .ST (Signal Status byte). If testing in PLCSIM and values are forced without updating the status byte, .ST defaults to 16#00 (Bad non-specific). APL blocks evaluate bad quality and suppress alarm messages to prevent nuisance trips, displaying a red wrench maintenance icon.
  3. Alarm_8P Associated Value Corruption: APL analog blocks pass auxiliary process values (associated values 1 through 10) to WinCC Alarm Logging to display live parameters within the message line. If user modifications corrupt these interconnections, Alarm_8P rejects the message telegram, leaving the message status permanently uninitialized in WinCC.

Step-by-Step Implementation Procedure

Step 1: Check CFC Parameter MsgLock Interconnection

  1. In SIMATIC Manager, open the CFC chart containing the affected MonAnL or PIDConL block.
  2. Locate the input pin MsgLock.
  3. Check if MsgLock is connected to another block:
    - If connected: The interconnected signal dictates the lock state. If the source signal is 1, the block will remain locked regardless of faceplate actions.
    - If the lock is unintentional, disconnect the signal or invert the logic.
  4. Check if the block has an internal parameter MsgLock = 1 set as a static constant. Change the default value to 0.

Step 2: Verify Input Signal Status (ST)

  1. In the same CFC chart, go online (Test > Open Test Mode).
  2. Inspect the primary process input pin: PV_In.
  3. Expand the structure to view PV_In.ST:
    - If ST = 16#80: Signal quality is Good. Alarms are evaluated normally.
    - If ST = 16#00 or 16#28: Signal quality is Bad. APL suppresses threshold evaluation.
  4. If simulating in S7-PLCSIM or using a raw input without an analog channel driver, insert block StruAnIn to construct a proper APL structure with ST := 16#80.

Step 3: Inspect Feature Bit 24 and Alarm Suppression Settings

  1. In the Object Properties of MonAnL / PIDConL, check the Feature word.
  2. Inspect Feature Bit 24 (Enable local operator permission for message lock):
    - Ensure the logged-in WinCC user has the required authorization level (typically Authorization Level 5 or 6).
  3. Inspect Feature Bit 23 (Limits evaluation inactive if MsgLock is active).

Step 4: Verify Alarm_8P Associated Values and Recompile

  1. If MsgLock is 0 and ST is 16#80, but the lock icon persists:
  2. Check if custom associated values (ExtVa104 through ExtVa108) were interconnected to incompatible data types (e.g., non-standard strings or uninitialized ANY pointers).
  3. Disconnect custom associated value pins.
  4. Perform a Chart > Compile > Changes Only in CFC.
  5. In SIMATIC Manager, execute Compile OS (Scope: Changes only).
  6. Deactivate and reactivate WinCC Runtime (or refresh faceplates).

Verification

  1. Padlock Disappearance: Open the faceplate in WinCC Runtime. Confirm that the golden lock icon is gone and alarm state fields display normal monitoring status.
  2. Manual Lock/Unlock Test: Click the golden lock button on the faceplate. Confirm that clicking Lock places a white cross or lock symbol on the messages, and clicking Unlock cleanly clears it.
  3. Threshold Alarm Test: Force the input variable above the High-High limit setpoint. Confirm that the alarm triggers immediately in the WinCC Alarm List with sound and flashing indicators.

Limitations and Operational Precautions

  1. User Administrator Rights: Even if MsgLock is 0, if the active logged-in user lacks WinCC Authorization Level 6 (Higher process controlling), the faceplate unlock button will be grayed out or inactive.
  2. Group Message Locking: If the parent Plant Hierarchy folder or technological unit has higher-level message suppression applied, individual subordinate blocks inherit the suppressed state.

Engineer FAQ

Why does clicking the unlock button on the faceplate do nothing?

Because the MsgLock pin in the CFC chart is interconnected to logic that is actively holding the lock signal at 1.

What does the red wrench icon on the faceplate mean?

It indicates that the interconnected input signal has Bad Signal Status (e.g., ST = 16#00), indicating sensor failure or uninitialized simulation.

What signal status byte represents Good quality in APL?

Status byte 16#80 (Valid / Good non-specific).

Can I unlock messages if MsgLock is interconnected?

No. Interconnected pins take absolute priority over HMI operator commands in APL architecture.

What is Alarm_8P?

SFB35 Alarm_8P is the standard Siemens system function block used by PCS 7 blocks to generate timestamped messages with associated values.

Why did this happen in S7-PLCSIM?

When forcing analog values directly into peripheral addresses, the APL channel driver may report Bad quality unless properly parameterized or forced.

What block creates APL structures with Good signal status?

Use StruAnIn or Pcs7AnIn with simulated mode enabled (SimOn = 1, SimPV_In, SimLiOp).

Which user authorization is required to unlock messages?

Typically Authorization Level 6 ('Higher process controlling') in WinCC User Administrator.

Does unlocking messages require compiling the OS?

No. If MsgLock is controlled via CFC, changes can be downloaded online via changes only in RUN.

What is the difference between message lock and alarm hiding?

Message lock stops the block from evaluating alarms; alarm hiding allows alarms to evaluate but filters them from the active operator banner.

Technical References

Related Articles

Related Tags

  • MsgLock
  • Alarm_8P
  • MonAnL
  • PIDConL
  • Signal Status
  • APL
  • Faceplate Unlock
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