Troubleshooting Missing Interlock Text Displays on WinCC APL Faceplates in PCS 7

In SIMATIC PCS 7 Advanced Process Library (APL), an issue where interlock input descriptions appear correctly in the detailed view but remain blank on the standard overview faceplate occurs because the block I/O parameter Identifier (OS additional text) was omitted on the interlock block input pins (In01 to In08). Resolving this display failure requires populating the Identifier attribute in CFC or the Process Object View, executing an OS compilation with memory reset, and verifying faceplate text structures in WinCC Graphic Designer.

Architecture of APL Interlock Blocks: Overview vs. Detail Views

In SIMATIC PCS 7, process safety and equipment protection logic are implemented using standard APL interlock blocks: Intlk02 (2 inputs), Intlk04 (4 inputs), and Intlk08 (8 inputs).

When an operator clicks an interlock icon or opens an APL motor/valve faceplate (MotL, VlvL), the system presents two distinct visual levels:
* The Standard Overview Faceplate (@PG_Intlk...): Displays active interlock conditions, input bypassed states, and short signal labels indicating which protective condition is tripped (e.g., LSH-101 Tank High, PSLL-201 Oil Pressure Low).
* The Detailed View Faceplate: Shows the full boolean evaluation tree, inverted logic conditions, and the static state descriptions (Text0 for logic 0, Text1 for logic 1).

The Parameter Distinction: Text0/Text1 vs. Input Pin Identifier

A common engineering misunderstanding arises when configuring text properties on interlock blocks:
1. The Defect: An engineer configures the signal properties of the interlock input pins (In01 to In08), setting Text0 (e.g., TRIPPED) and Text1 (e.g., HEALTHY).
2. The Symptom: Upon running WinCC Runtime, the text appears in the detailed view home page, but the main standard faceplate display shows blank labels next to the input indicator LEDs.
3. The Root Cause: In the APL faceplate architecture, the text rendered on the standard overview faceplate is read from the parameter attribute Identifier (also designated as OS additional text) assigned to the specific input pin (In01..In08), not from Text0 or Text1.

Step-by-Step Procedure: Restoring Interlock Texts on WinCC Faceplates

Open CFC Editor:
* Open the CFC chart containing the target interlock block (e.g., Intlk04 or Intlk08).
Edit Input Pin Properties:
* Double-click the input pin In01 (or right-click the block and select Object Properties -> I/Os).
* Locate the column titled Identifier (or OS additional text).
* Enter the concise protective condition label (e.g., Emergency Stop PB101 or Lube Oil Pressure Low).
* Repeat this configuration for pins In02 through In08.
Save and Compile CFC:
* Close block properties and save the CFC chart.
* Execute Chart -> Compile -> Changes Only.
Compile the Operator Station (OS):
* In SIMATIC Manager, right-click the OS project and select Compile.
* Choose Scope: Entire OS (or Changes) and select With memory reset to ensure updated block I/O text attributes transfer into the WinCC text library.
Download to OS Server:
* Download the updated project to the WinCC OS Server and restart runtime or refresh the faceplate.

Bulk Text Management in Process Object View

For large projects with hundreds of interlock blocks:
* Open SIMATIC Manager and switch to Process Object View (Ctrl+Alt+P).
* Select the Signals or Parameters tab.
* Filter by block type Intlk02, Intlk04, and Intlk08.
* Locate the column OS additional text: bulk-edit or paste descriptive text directly into the grid without opening individual CFC charts.

Verification

In WinCC OS Runtime, click the motor or valve faceplate associated with the interlock block.
Click the interlock button to open the @PG_Intlk04 standard faceplate window.
Verify that every configured input line displays its distinct text label clearly next to the status LED.
Click the Detailed View button: confirm that detailed boolean logic and Text0/Text1 state descriptions also display properly.

Limitations and Operational Precautions

Text Length Limits: The standard overview faceplate accommodates short text strings (typically up to 16–24 characters depending on screen font resolution); excessively long strings will be truncated.
Multilingual Translation: If the plant operates in multiple runtime languages, ensure OS additional text is populated for each installed language using the Text Distributor utility.
Chart Consistency: Always execute an OS compilation after changing block pin identifiers; WinCC faceplates do not dynamically read offline CFC attributes without compilation.

Engineer FAQ

Which attribute controls the text on standard APL interlock faceplates?
The Identifier attribute (OS additional text) on input pins In01 through In08 controls the displayed label.
Why does Text0 show in detailed view but not on the main faceplate?
Text0 and Text1 describe discrete state values in detail views; the main faceplate specifically queries the Identifier attribute.
Which APL blocks provide interlock logic in PCS 7?
Intlk02 (2 inputs), Intlk04 (4 inputs), and Intlk08 (8 inputs) provide standard protective logic.
Can interlock identifiers be edited in bulk?
Yes, Process Object View (POV) allows mass editing and CSV import of OS additional text across all interlock blocks.
Does updating interlock text require a CPU STOP?
No, text attribute modifications can be compiled and downloaded to the AS in RUN mode.
Can interlocks be bypassed by operators from the faceplate?
Yes, if operator authorization levels and bypass parameters (BypProt) are enabled on the block.
What happens if OS compile is performed without memory reset?
Changes may not propagate if WinCC text library caches retain older tag descriptor definitions.
Are interlock texts stored in the WinCC Text Library?
Yes, OS compilation transfers block attribute strings into the central WinCC Text Library.
Can an interlock block cascade into another interlock block?
Yes, output Out of one Intlk08 block can connect to an input pin of another interlock block to handle >8 signals.
Where should APL library licenses be verified?
APL components are included with standard PCS 7 engineering and runtime licenses in ALM.

Technical References

Siemens Manual: SIMATIC Process Control System PCS 7 Advanced Process Library (A5E43360408-AA).
Siemens Industry Online Support Entry ID 109801081: Interlock Block Configuration in PCS 7 APL.
WinCC V7.4 / V7.5 Graphics Designer and Faceplate Architecture Guide.

Related Tags

PCS 7, APL, Interlock, Intlk04, Intlk08, Faceplates, WinCC, Identifier, OS Additional Text

Troubleshooting Missing Interlock Text Displays on WinCC APL Faceplates in PCS 7