Resolving AddFEM Uncertain Channel Quality Status (16#40000203) in Redundant AS Configurations

AddFEM front-end modules report uncertain channel status (Mode 16#40000203 for 4-20mA or 16#40000108 for +/-10V) when the AS-AddFEM redundancy diagnostic drivers in the @-charts fail to establish synchronous communication. In SIMATIC PCS 7 V8.2, this issue occurs when the AddFEM Library V8.2 is deployed alongside an outdated Master Data Library containing older versions of diagnostic block FB118 (OB_DIAG1). To resolve the uncertain quality status, update the Master Data Library with FB118 from PCS 7 Basic Library V8.2 Upd2 or higher, execute block type cleanup, and recompile CFC charts with 'Generate module drivers' enabled.

Root Cause Analysis - AddFEM Redundancy Diagnostic Interlock

The AddFEM (Additional Frontend Module) platform interfaces high-speed analog and digital signals directly to SIMATIC S7-400 and CPU 410-5H controllers via PROFIBUS DP. In high-availability redundant architectures (such as redundant AS 410-5H pairs communicating with single or redundant AddFEM racks), the system relies on automated diagnostic drivers placed in internal system charts (@1, @2, etc.) to monitor redundant link health.

When signal drivers query an AddFEM channel, the MODE parameter reflects signal quality according to PA Profile specifications. A leading byte of 16#40 represents 'Uncertain' quality (16#40000203 indicates uncertain 4-20 mA current input, whereas 16#80000203 represents healthy valid data). In non-redundant AS configurations, the driver readily evaluates link integrity. However, in redundant AS configurations, diagnostic block FB118 (OB_DIAG1) coordinates failover and primary state synchronization. If the engineering project uses AddFEM Library V8.2 but retains legacy FB118 blocks from prior Basic Library releases (prior to V8.2 Upd2), OB_DIAG1 fails to negotiate redundant status, forcing the channel driver into the uncertain quality state.

Module Status Codes and Diagnostic Telegram Parameters

The table below details the quality status codes, block dependencies, and diagnostic parameters associated with AddFEM redundancy integration:

Status Code / ParameterQuality StateSubsystem DescriptionRequired Action / Dependency16#80000203Good (Valid)Standard 4-20 mA current input signal operating normally.Normal operating condition; no action required.16#40000203Uncertain4-20 mA current input signal flagged as uncertain quality.Check AS redundancy state and update OB_DIAG1 (FB118).16#40000108Uncertain+/-10 V voltage input signal flagged as uncertain quality.Update Basic Library driver blocks in Master Data Library.FB118 (OB_DIAG1)Core Diagnostic BlockManages AS operating state and organization block diagnostic events.Must be at PCS 7 Basic Library V8.2 Upd2 or higher.FB130 (ADDF_MOD)AddFEM Module DriverMonitors AddFEM hardware rack status and channel validities.Delivered via AddFEM Library V8.2 (109744892).ACC_MODEAccess Mode SwitchToggles driver operating mode between direct I/O and process image.Parameter reset (0 -> 1 -> 0) used to reinitialize buffers.

Step-by-Step Master Library and Driver Remediation Procedure

Audit Master Data Library Version: Open SIMATIC Manager and expand the project's Master Data Library. Navigate to the Blocks container and inspect the version attributes of FB118 (OB_DIAG1).
Import Updated Basic Library Blocks: Open the installed PCS 7 Basic Library V8.2 (updated with Update 2 or Update 3). Copy FB118 (OB_DIAG1) and associated diagnostic blocks (FB108, FB115) into the project's Master Data Library, confirming file replacement.
Synchronize AS Offline Block Folders: In SIMATIC Manager, select Options -> Block Types.... Select the updated diagnostic blocks and click Clean Up to ensure obsolete interfaces are removed, followed by copying the updated blocks into each target AS program folder.
Recompile CFC with Driver Generation: Open any CFC chart in the target AS program. Select Chart -> Compile -> Changes Only. Ensure the checkbox Generate module drivers is explicitly checked. This regenerates the @ diagnostic charts using the updated FB118 algorithm.
Execute AS Delta Download: Download the compiled changes to the target CPU 410-5H pair. Verify that signal MODE values instantly transition from 16#40000203 to 16#80000203 without interrupting active process control.

Verification

Verify resolution through the following systematic checks:
1. In CFC test mode, inspect the MODE output on the AddFEM driver block (e.g., CH_AI or ADDF_AI): confirm that the value is 16#80000203 (good quality) instead of 16#40000203.
2. Verify that downstream APL channel drivers (e.g., Pcs7AnIn) report Bad = FALSE and Quality Code = 16#80 (Good).
3. Initiate a redundant CPU switchover (test master/standby failover): confirm that channel quality remains steady at 16#80000203 and does not degrade to uncertain status during or after the transition.

Limitations and Operational Precautions

Do not attempt to clear uncertain quality by manually overwriting the MODE parameter on CFC channel blocks. Any subsequent CFC compilation with driver generation will overwrite manual interconnections and restore the fault. Furthermore, do not initiate a Cold Restart on SIMATIC PCS 7 controllers; Cold Restarts are not released for PCS 7 systems and can cause severe operational disturbances. Always perform Warm Restarts (Restart) when controller reinitialization is required.