Configuring Dynamic Unit Allocation and Availability Conditions in SIMATIC BATCH Recipes

In SIMATIC BATCH, preventing operators from selecting empty, uncleaned, or unavailable tanks during manual unit allocation in a Recipe Unit Procedure (RUP) is achieved by configuring dynamic 'Allocation Conditions' within the BATCH Recipe or Equipment Properties. Instead of relying solely on unconstrained 'Operator selection', engineers map technological status variables from the automation station's UNIT_PLC block (such as Level > Low_Limit and Status == CLEAN_READY) into the BATCH Unit Allocation Condition. When the recipe executes, SIMATIC BATCH dynamically filters the selection dialog, enabling only available, non-empty vessels.

Unit Allocation Strategies in SIMATIC BATCH (ANSI/ISA-88)

In SIMATIC BATCH, batch recipes adhere to the ANSI/ISA-88 standard, dividing batch execution into Hierarchical Recipe Procedures, Recipe Unit Procedures (RUP), and Recipe Operations (ROP).

When a batch recipe requires a vessel (e.g., a mixing tank chosen from Tank 01 and Tank 02):
* The RUP defines an Equipment Selection rule.
* Standard allocation strategies include:
1. Preferred Unit: Selects a default vessel if free.
2. Longest Out of Use: Selects the vessel idle for the longest duration to balance mechanical wear.
3. Operator Selection: Prompts the operator in the Batch Control Center (BCC) to choose a vessel at runtime.

The Hazard of Unconstrained Operator Selection

When a recipe uses Operator selection without defined availability constraints:
* The operator prompt displays all physical tanks mapped to that unit class in the plant model.
* If Tank 01 is currently empty, undergoing CIP (Clean-in-Place), or has an active agitator fault, the system still permits the operator to click and select it.
* Starting a mixing recipe on an empty vessel causes pump cavitation, agitator mechanical damage, or contaminated cross-batches.

Configuring Dynamic Allocation Conditions in Recipe Editor

To restrict operator selection strictly to available vessels:

[SIMATIC BATCH Recipe Editor -> Open Master Recipe]
   │
   ├─► Select the Recipe Unit Procedure (RUP)
   ├─► Open: Object Properties -> Tab: "Allocations"
   │
   ├─► Equipment Selection Strategy: Select "Operator selection"
   │
   ├─► In the "Condition" Section:
   │     • Click: "Edit Condition..."
   │     • Construct Boolean Expression using Equipment Attributes:
   │         (Unit.Level >= Min_Level) AND (Unit.CleanStatus == TRUE)
   │
   └─► Save, Validate, and Release Recipe for Production

When the batch engine reaches the RUP allocation step, it evaluates the condition online against live AS variables. Tanks failing the condition are greyed out or excluded from the operator selection window.

Mapping AS Unit Status Variables (UNIT_PLC / IEPH)

The following table details the technological parameters evaluated between the AS controller and SIMATIC BATCH:

Controller Block ParameterBlock TypeBATCH Equipment AttributeAllocation Condition EvaluationL_Lvl (REAL)UNIT_PLC / Analog TransmitUnit.LevelMust be greater than minimum recipe volume (> 15.0%).Ready_Clean (BOOL)UNIT_PLC (FB809)Unit.CleanStatusMust be TRUE indicating CIP sequence finished.QOCCUPIED (BOOL)UNIT_PLC (FB809)Unit.OccupiedEvaluated automatically; must be FALSE (not in another batch).Fault_Act (BOOL)UNIT_PLCUnit.HealthyMust be FALSE (no active motor/valve trips).

Verification

To confirm that dynamic unit allocation conditions are enforced:
1. In the Batch Control Center (BCC), create and start a test batch using the modified recipe.
2. In the AS simulation (or test plant), ensure Tank 01 is empty (Level = 0.0) and Tank 02 has sufficient volume (Level = 50.0).
3. When the batch execution halts at the RUP allocation prompt, open the operator selection dialog.
4. Verify that Tank 01 is displayed as Disabled / Unavailable with the tooltip indicating condition failure (Level below threshold).
5. Verify that Tank 02 is enabled, selectable, and accepts allocation without error.

Limitations and Operational Precautions

Ensure that process sensor signals evaluated in BATCH allocation conditions (such as tank level and temperature) have valid signal status (ST = 16#80). If an analog transmitter wire break occurs, the signal status goes bad (16#00), causing the condition evaluation to fail safely and lock the tank out of selection. Always include a manual supervisor override procedure for emergency batch recovery.

Engineer FAQ

Where are BATCH equipment attributes defined?

Equipment attributes and unit properties are configured in SIMATIC Manager under the Plant Hierarchy in the Equipment Properties dialog, and synchronized via 'Compile and Download Objects -> SIMATIC BATCH'.

Can an operator override an allocation condition?

Only if the operator possesses the administrative authorization level 'Bypass Allocation Conditions' in SIMATIC BATCH User Management.

What happens if no tanks meet the allocation condition?

The batch enters a 'Waiting for Unit' state. It remains paused at the RUP header until a vessel becomes available or an engineer resolves the condition.

Does changing an allocation condition require re-validating the recipe?

Yes. In regulated industries (FDA 21 CFR Part 11), modifying allocation conditions modifies the master recipe, requiring formal electronic signature release and version bumping.