Reset unit binding in recipe after unit procedure is completed

ISA-88 / Batch
1

Background
When starting a recipe in the BOI, a unit can be bound to a Unit Procedure (UP) in three different ways:

  1. FIXED
    The recipe author assigns a specific unit directly to the Unit Procedure in Recipe Studio.
    The UP will always run on that unit.
  2. DEFER
    The recipe uses a unit alias configured with Defer.
    When the recipe runs, the operator is prompted to choose which unit should be bound to the UP.
  3. FROM POLICY
    The recipe uses a unit alias and relies on a Unit Selection Policy.
    The system automatically selects the unit based on the conditions defined in the policy.
    Problem
    Once a unit is bound to a Unit Procedure—regardless of whether it was FIXED, DEFER, or FROM POLICY—the binding remains locked for the entire recipe execution.
    Expected Behavior (What you want)
    The operator starts the recipe and enters a recipe parameter (a named set listing all possible units in the unit class).
    The Unit Selection Policy checks whether the selected recipe parameter matches a unit.
    The UP runs on the correct unit.
    After the UP completes, the recipe loops back to the beginning.
    The operator enters a different recipe parameter.
    You expect the UP to bind to a new unit based on the updated parameter.
    Actual Behavior
    Even though the recipe parameter changes, the UP keeps the original unit binding.
    The Unit Selection Policy is not re-evaluated, and the UP does not switch to the new unit.
    Question??
    Has anyone found a way to force the Unit Procedure to rebind to a different unit when the recipe loops and the recipe parameter changes?
2

Make sure the “Retain unit after completion” option is not checked on the final Unit Procedure before the sequence loops back. That way, the unit is released and must be reacquired on the next pass.

I’m not entirely sure how your policy would handle this, but it would likely need to evaluate which loop iteration you’re on and which recipe parameters should apply.

I’ve never tested this specific scenario, but my understanding is that the Batch Executive won’t reassign an alias if it already has one. That means you’d probably need to structure the procedure with multiple Unit Procedures—each with its own alias—rather than looping through the same UP and alias repeatedly.