Configuring Interlock Input Identifiers and Extended Descriptions in PCS 7 APL Faceplates

In SIMATIC PCS 7 Advanced Process Library (APL), the Identifier field displayed on interlock faceplates (Intlk02, Intlk04, Intlk08, Intlk16) is governed by the S7_shortcut system attribute on inputs In01 to In16 and is strictly limited by the system schema to 16 characters. To display extended text (up to 40 or 80 characters) such as 'MV Incoming2 Undervoltage', configure the OS additional text / Message text or connected block comment, and utilize the APL tooltip feature or custom faceplate description mapping.

Architecture of Interlock Text Representation in PCS 7 APL

In SIMATIC PCS 7 plants, interlock logic blocks—such as Intlk02 (FB1824), Intlk04 (FB1825), Intlk08 (FB1826), and Intlk16 (FB1827) from the Advanced Process Library (APL)—aggregate permissives, protections, and safety interlocks for technological equipment (valves, motors, drives).

When an operator opens an interlock faceplate (@pg_Intlk08.pdl), each interlock input channel displays:
1. Input Signal State: A green checkmark (healthy) or red cross / bypass lock (tripped / interlocked).
2. Identifier (Short Text): A concise label identifying the interlock cause (e.g., EMERG_STOP, HIGH_PRESS).
3. State Text (Text0 / Text1): The dynamic descriptive condition (e.g., Active / Inactive or Low Level / Normal).

Automation engineers often attempt to write long descriptive strings (e.g., Damper XB02B Is Closed OR 30S AFTER RUNNING, 45 characters) directly into the Identifier field. However, the system truncates the text or rejects the input. This is an architectural limitation: the Identifier field is bounded by the system attribute S7_shortcut to a maximum string length of 16 characters, sized specifically to maintain consistent visual alignment across standardized APL faceplates.

Interlock Parameter and Text Attribute Matrix

Understand how text properties are structured across APL interlock block parameters:

Parameter / AttributeSystem Attribute HandleMaximum LengthTarget Display LocationPurpose and RecommendationInput In01..In16 IdentifierS7_shortcut16 charactersInterlock faceplate main columnConcise functional mnemonic (e.g., OIL_PRESS_LO)Signal Text 0 (Text0)S7_string_016 charactersDynamic state display when In = 0State description (e.g., Tripped, Closed, Low)Signal Text 1 (Text1)S7_string_116 charactersDynamic state display when In = 1Normal state description (e.g., Healthy, Open, OK)Interconnected Block CommentS7_comment80 charactersFaceplate Tooltip / Extended InfoFull technological description of the interlock conditionAlarm Message Additional TextOS Additional Text128 charactersWinCC Alarm Logging listLegal and audited sequence of events text

Engineering notice: Adhere to consistent plant tagging standards when formulating 16-character mnemonics.

Configuring the 16-Character S7_shortcut Identifier and Text0/Text1

To configure the standard identifier and state texts within the 16-character boundary:

Open Interlock Block Properties in CFC:
* Open the CFC chart containing the Intlk08 instance.
* Right-click the block and select Object Properties.
* Switch to the Inputs/Outputs tab.
Assign Identifier and State Texts:
* Scroll to the input row (e.g., In01).
* In the Identifier column, enter a clear 16-character mnemonic (e.g., MV_IN2_UNDRVOLT).
* In the Text 0 column, enter Voltage Low.
* In the Text 1 column, enter Voltage Normal.
* Repeat for all configured interlock inputs (In02 to In08).
Compile OS:
* Run Compile OS (Scope: Changes only).
* The OS Compiler transfers the text strings to the WinCC Text Library, associating them with the interlock faceplate tags.

Implementing Extended Text Descriptions via APL Tooltips and OS Messages

When operational guidelines require full sentence descriptions (> 16 characters):

Leverage APL Interlock Tooltip Functionality:
* In CFC, open the properties of the upstream block providing the interlock signal (e.g., MonDi01 or OpDi01).
* In the block's Comment field, enter the full technological description:
Damper XB02B Is Closed OR 30S AFTER RUNNING (up to 80 characters).
* In the interlock faceplate in WinCC Runtime, hovering the mouse cursor over the In01 row automatically renders the full 80-character comment in a floating tooltip.
Utilize OS Alarm Message Text:
* In CFC, right-click the technological block (e.g., MotL), select Special Object Properties > Messages.
* Under the message event corresponding to the interlock trip, enter the extended 128-character text in the Event Text or Info Text field.
* This guarantees that when the interlock trips, the exact operational message appears in the WinCC Alarm List.

Verification

Verify interlock visualization in WinCC Runtime:
1. Open the process screen and click the block icon to open the technological faceplate (e.g., @pg_MotL.pdl).
2. Navigate to the Interlocks tab or click the Interlock button to open @pg_Intlk08.pdl.
3. Confirm that row 1 displays the 16-character identifier MV_IN2_UNDRVOLT alongside dynamic status Voltage Normal.
4. Hover the mouse over the row: Confirm that the extended tooltip pops up displaying the full 80-character explanation.
5. Force an interlock trip: Confirm that the indicator turns red and state text dynamically flips to Voltage Low.

Limitations and Operational Precautions

Never modify the internal C-scripts of @pg_Intlk08.pdl to forcibly expand the text column width unless creating a project-specific template; standard faceplates will be overwritten during subsequent OS-Project Editor runs.
Text entries in CFC must not contain quotation marks ("), backslashes (\), or non-ASCII special characters, as these can disrupt the WinCC Text Library parser.
For multi-language plants, always translate identifiers and state texts in the WinCC Text Library for all installed runtime languages.

Engineer FAQ

Can the 16-character limit of S7_shortcut be expanded in SCL?

No. The attribute 'S7_shortcut' is hardcoded within the STEP 7 compiler architecture to 16 bytes. Declaring a longer string in source code results in compilation truncation.

Why does the interlock faceplate show '???' instead of my text?

Displaying '???' indicates that the OS was not compiled after modifying the block properties, or the Text ID in the WinCC Text Library is empty for the currently active runtime language.