Resolving 'UNIT_BLOCK Missing in Folder' Errors in Multi-AS SIMATIC BATCH Configurations

In SIMATIC BATCH multiprojects spanning multiple AS controllers, the compilation error 'UNIT_BLOCK block missing in folder' occurs when an Equipment Unit folder in the Plant Hierarchy is configured as a 'shortcut folder' (Verknüpfungsordner) rather than an independent technological folder. When the Plant Hierarchy is initially created on AS 1 and exported across the multiproject using 'Plant Hierarchy > Update in Multiproject', subordinate folders on AS 2 are created as shortcuts referencing AS 1. If an engineer places the unit control block (UNIT_PLC / FB 266 or UNIT_APL) in AS 2 within a shortcut folder, SIMATIC BATCH searches the origin station (AS 1) and aborts compilation. To resolve this, right-click the Unit folder in AS 2, select 'Plant Hierarchy > Remove shortcut', verify the AS-OS Assignment points directly to AS 2, ensure UNIT_PLC resides in the local chart, and recompile SIMATIC BATCH.

Executive Summary

Large-scale batch chemical and pharmaceutical processes engineered with SIMATIC BATCH frequently divide production across multiple automation controllers (e.g., AS 1 controlling raw material dosing and AS 2 controlling reactor vessels). When establishing the multiproject structure, engineers typically synchronize the Plant Hierarchy from the master engineering project to satellite AS projects. However, this synchronization often introduces 'shortcut folders' across project boundaries. When the SIMATIC BATCH compiler evaluates the batch model, it encounters broken object references, flagging 'UNIT_BLOCK block missing in folder' even though UNIT_PLC is clearly visible on the CFC chart. Removing the shortcut attribute and re-establishing direct AS ownership restores clean batch model compilation.

Architecture and Fundamental Mechanics

The technological object hierarchy in SIMATIC BATCH integrates Plant Hierarchy folders with runtime controller blocks:

The ISA-88 Unit Concept in SIMATIC BATCH:
* In ISA-88 modeling, a Unit (e.g., Reactor 1, Mixing Tank B) is an independent equipment entity capable of executing one or more batch operations.
* In the PCS 7 Plant Hierarchy, a Unit is represented by a dedicated hierarchy folder marked with the technological attribute Unit.
* Inside the Unit's CFC chart, an automated interface block must be instantiated: UNIT_PLC (FB 266 in classic Batch) or UNIT_APL (FB 1102 in APL Batch). This block coordinates recipe phase arbitration, batch ID distribution, and unit allocation.
The Shortcut Folder Trap in Multiprojects:
* When Plant Hierarchy > Update in Multiproject is executed from the primary project (AS 1), the hierarchy tree is cloned into secondary projects (AS 2, OS projects).
* By default, to maintain global naming consistency, folders in secondary projects are created as Shortcut Folders (indicated by a small arrow overlay glyph on the folder icon).
* A shortcut folder does not own its technological contents; it acts as an alias pointing back to the master folder in AS 1.
Why the Batch Compiler Fails:
* The SIMATIC BATCH compiler (bfcomp.exe) traverses the plant hierarchy to resolve unit block instances.
* When it inspects Unit 2 in AS 2, it detects the shortcut pointer. Following the pointer, it searches for UNIT_PLC inside AS 1's chart folder.
* Because UNIT_PLC was placed in AS 2 (where the physical reactor I/O resides), the compiler finds no unit block in AS 1 and aborts with the fatal error: 'UNIT_BLOCK block missing in folder'.

Step-by-Step Implementation Procedure

Follow these procedures to eliminate shortcut folder conflicts and resolve the UNIT_BLOCK missing error:

Identify the Shortcut Folder in SIMATIC Manager:
* In SIMATIC Manager, switch to Plant View (View > Plant View).
* Expand the hierarchy tree under the secondary controller (AS 2).
* Inspect the Unit folder icon. Notice whether the folder displays a small link/arrow glyph, signifying a shortcut folder.
Remove the Shortcut Attribute:
* Right-click the affected Unit folder in AS 2.
* Navigate to Plant Hierarchy > Remove shortcut.
* A confirmation dialog appears warning that the folder will become an independent technological object.
* Confirm the removal; the arrow glyph disappears from the folder icon.
Verify AS-OS Assignment:
* Right-click the now-independent Unit folder and select Object Properties.
* Navigate to the AS-OS Assignment tab.
* Verify that Assigned AS is explicitly set to the secondary controller (e.g., AS2 / S7 Program).
* Ensure Assigned OS points to the active batch OS Server.
Verify UNIT_PLC Block Instantiation in AS 2:
* Open the primary control chart inside the Unit folder in AS 2.
* Ensure an instance of UNIT_PLC (FB 266) or UNIT_APL (FB 1102) is present.
* Ensure the unit name configured on the block matches the Plant Hierarchy folder name exactly.
* Compile the S7 Program in AS 2 (Scope: Entire program).
Compile and Propagate SIMATIC BATCH Data:
* In SIMATIC Manager, select Options > SIMATIC BATCH.
* Execute Compile.
* In the Batch compilation log, verify that both AS 1 and AS 2 units are scanned successfully.
* Confirm that the compilation finishes with 0 Errors, 0 Warnings.
Download Batch Data to Batch Server:
* In SIMATIC Manager, select Options > SIMATIC BATCH > Download.
* Launch Batch Control Center (BatchCC); update the batch plant model and verify that all units across both controllers appear online and available for recipe execution.

Verification

In SIMATIC Manager, run the SIMATIC BATCH compile wizard. Inspect the compilation log; verify that the Unit folder in AS 2 is validated without 'UNIT_BLOCK missing' errors. Open BatchCC; navigate to the Plant Model view. Confirm that the Unit from AS 2 is listed with all its associated Equipment Phases (EPH) and recipe operations, and that state transitions (Idle, Allocated, Running) respond to batch commands.

Limitations and Operational Precautions

Ensure that every Unit in the plant hierarchy contains exactly one UNIT_PLC or UNIT_APL block. Placing multiple unit blocks within the same hierarchy folder or leaving a unit folder without any unit block will cause batch compilation failure. Never delete a shortcut folder without verifying whether cross-project connections depend on its hierarchy path.

Engineer FAQ

Can a single SIMATIC BATCH recipe span across multiple AS controllers?

Yes. SIMATIC BATCH is specifically architected to coordinate recipes across multiple AS controllers. Recipes can allocate Unit 1 on AS 1 and Unit 2 on AS 2 within the same master recipe.

What is the difference between UNIT_PLC and UNIT_APL?

UNIT_PLC (FB 266) is used with classic PCS 7 standard libraries and SFC Types; UNIT_APL (FB 1102) is the modernized block designed specifically for Advanced Process Library (APL) batch systems.

Why did moving UNIT_PLC to AS 1 temporarily clear the error?

Because the folder was a shortcut pointing to AS 1, placing the block in AS 1 satisfied the shortcut reference, but incorrectly tied the unit's runtime execution to the wrong controller.

How do I prevent shortcut folders when updating the Plant Hierarchy?

When synchronizing the Plant Hierarchy across multiprojects, only export folders that are common to all projects, and manage unit-level folders locally within their respective AS projects.