Visualizing Signal Quality and Bad Value Status on APL MonAnL Block Icons

To display the bad signal quality of a field transmitter on an APL MonAnL block icon in SIMATIC PCS 7, interconnect the Bad output of the channel driver block Pcs7AnIn to the CSF (Control System Fault) input of MonAnL in the CFC chart. Alternatively, when using structured variable interconnections, connect Pcs7AnIn.PV_Out directly to MonAnL.PV. The APL block icon automatically evaluates the Signal Status byte (ST = 16#00 or 16#28) and renders the standardized yellow warning triangle or maintenance wrench badge without requiring custom scripting.

Executive Summary

In industrial process automation, prompt visual identification of failed instrumentation is critical for plant safety and alarm management. In SIMATIC PCS 7 Advanced Process Library (APL), engineers often search for an explicit 'Bad' output pin on monitoring blocks like MonAnL to drive visual indications on WinCC graphic screens. However, APL avoids discrete alarm tags by utilizing structured variables containing IEEE 754 floating-point values paired with NAMUR NE107 signal status bytes. This article details how bad transmitter quality is propagated through channel drivers into technological blocks and explains the standard mechanisms to trigger automatic maintenance badges on SCADA block icons.

APL Signal Status Architecture and Quality Evaluation

Every analog process value in PCS 7 APL is packaged as a structured data type (STRUCT) consisting of Value (REAL) and ST (BYTE). The Signal Status byte adheres to the international PA profile standard:

16#80: Good (Value valid, normal operation).
16#60: Simulated (Value generated via software simulation).
16#28 / 16#00: Bad (Process value invalid due to channel failure, wire break, or hardware fault).

When Pcs7AnIn detects a channel fault, it updates PV_Out.ST = 16#00 and asserts Bad = 1. If MonAnL receives this structured signal at its PV input, its internal logic evaluates the status byte, inhibits normal limit alarm generation, and sets internal maintenance status bits.

CFC Interconnection Methods: CSF vs Structured Signal Status

Engineers can choose between two standard methods to convey transmitter failure to MonAnL:

Structured Direct Interconnection (Recommended): Connect Pcs7AnIn.PV_Out to MonAnL.PV. MonAnL extracts the signal status automatically, suppresses nuisance process alarms, and triggers the APL quality code badge.
Control System Fault (CSF) Interconnection: Connect Pcs7AnIn.Bad to MonAnL.CSF. The CSF input is specifically intended for external hardware and process faults. Activating CSF generates an explicit 'Control System Fault' process alarm in WinCC Alarm Logging and displays the flashing yellow fault indicator on the block icon.

WinCC Block Icon Representation of Bad Quality

The standard APL block icon for MonAnL (@MonAnL/1, @MonAnL/2, etc.) incorporates built-in visual layers managed by the APL_BLOCK_ICON dynamic scripts. When CSF = 1 or ST < 16#80, WinCC displays:
* Maintenance Badge: A yellow wrench or hand symbol in the upper right quadrant of the icon.
* Quality Code Indicator: A warning triangle indicating degraded process measurement.
* Alarm Line Generation: A high-priority operational alarm logged in the sequence of events archive.

Diagnostic and Signal Flow Comparison

The following table compares the behavior of direct structured interconnections versus CSF interconnections:

Diagnostic MechanismCFC Source ConnectionMonAnL Target PinWinCC Alarm BehaviorIcon Visual IndicationStructured Status (ST)Pcs7AnIn.PV_OutMonAnL.PVSuppresses high/low process alarms; logs quality warningDisplays yellow maintenance symbol without generating false tripControl System Fault (CSF)Pcs7AnIn.BadMonAnL.CSFGenerates high-priority 'Control System Fault' alarmTriggers flashing yellow/red fault indicatorMaintenance State (MS)Module Driver DiagnosticMonAnL.MS_ExtTransmits diagnostic repeat requestShows NAMUR NE107 maintenance required symbolSimulation ActivePcs7AnIn.SimOnInternal Block PinLogs simulation operational messageDisplays blue hand / simulation icon

Step-by-Step Implementation Procedure

Step 1: Establish Signal Connection in CFC

Open the CFC chart containing the analog measurement in SIMATIC Manager.
Verify that Pcs7AnIn (FB1869) and MonAnL (FB1845) are instantiated in the chart.
Interconnect Pcs7AnIn.PV_Out directly to MonAnL.PV (ensuring structured connection).
If an audible control system alarm is required upon sensor failure, interconnect Pcs7AnIn.Bad to MonAnL.CSF.

Step 2: Compile and Download

Execute an AS compilation with 'Generate module drivers' enabled.
Download changes to the Automation Station.
Perform an OS compile to ensure tag structures and alarm archives reflect the CSF interconnection.

Verification

To verify quality signal visualization:

In S7-PLCSIM or online in CFC, open Pcs7AnIn and toggle SimOn = 1, then set SimPV_In = 16#7FFF or set Bad = 1.
Verify online that MonAnL.PV.ST drops to 16#00 or MonAnL.CSF switches to TRUE.
In WinCC Runtime, inspect the @MonAnL block icon. Confirm that the yellow wrench icon appears automatically.
Open the WinCC Alarm List and confirm the entry: @1%s@ Control System Fault appears with the correct tag timestamp.

Limitations and Operational Precautions

Alarm Flooding Risk: Connecting Bad directly to CSF on hundreds of transmitters will generate massive alarm bursts during plant power outages or remote I/O link drops; use structured ST evaluation where alarm suppression is preferred.
Legacy Library Incompatibility: Legacy standard library blocks (MEAS_MON, FB65) do not evaluate structured APL signal status bytes and require explicit discrete wiring.

Engineer FAQ

Why does MonAnL not have a Bad output pin like Pcs7AnIn?

MonAnL is a technological monitoring block rather than an I/O driver; it outputs structured variables (PV_Out.Value and PV_Out.ST) that propagate quality status downstream to interlocks and controllers.

Can the wrench symbol be suppressed on the block icon during maintenance?

Yes, by putting the channel driver into Maintenance or Out-of-Service mode (OOS), the block icon displays the Out-of-Service badge, preventing nuisance operator calls.

Does bad quality automatically trigger an interlock trip in APL?

By default, APL interlock blocks (Intlk02, Intlk04, Intlk08) evaluate signal status; if an input has bad quality, the interlock can be parameterized via feature bits to trip or bypass.

Technical References

Related Tags

https://industrialautomation.net/search?query=simatic-pcs7
https://industrialautomation.net/search?query=signal-quality
https://industrialautomation.net/search?query=advanced-process-library
https://industrialautomation.net/search?query=wincc-scada

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Visualizing Signal Quality and Bad Value Status on APL MonAnL Block Icons