ISA-88 recipe management: keep process intent separate from equipment logic

Recipe management is the discipline of expressing what should be made separately from the controller logic that knows how equipment can make it. ISA-88 provides a vocabulary and model for that separation: physical models describe equipment, procedural models describe steps, and recipes describe product intent and parameters.

Separate the models

The physical model may describe an enterprise, site, area, process cell, unit, and equipment module. The procedural model describes procedures, unit procedures, operations, and phases. A phase such as “charge material” can be implemented by a unit’s equipment logic while a recipe supplies the material, quantity, temperature, and time for a product.

This separation lets one controller execute several products without turning the PLC into a maze of product-specific branches. It also gives operations and quality teams a place to review parameter changes without rewriting every interlock.

Version the recipe, not just the file

A recipe needs an identifier, revision, status, effective date, author, approval, limits, units, and the equipment or product context it is valid for. Keep the executed revision with the batch record. A value outside its allowed range should fail before a phase starts, not become a surprising process change halfway through.

Define how pauses, holds, aborts, restarts, and manual interventions affect the record. Operators need a clear route for recovery; engineers need evidence of what was actually executed. A recipe system that only stores a CSV export is not a controlled production history.

Keep equipment capability separate from product limits. A unit phase can expose the ranges and states it supports, while the recipe selects a permitted value for a particular product. That separation makes a capability change visible: if a new agitator cannot meet the required mixing profile, the recipe should fail validation before the batch is released to it.

Treat recipe changes as operational changes with a review path. Compare revisions, show the affected parameter and reason, and make the effective revision unambiguous at the point of execution. A controlled recipe does not remove operator judgment; it makes the judgment and any approved exception auditable.

Integrate carefully

MES may own order and genealogy context while the batch engine owns execution. The DCS or PLC owns interlocks, phase logic, and safe equipment behavior. Agree on command, status, acknowledgement, and exception semantics across the boundary. The SCADA, MES, and historian guide is a useful companion for placing those responsibilities.

For a broader view of plant data and control, Understanding the Shop Floor is a practical ebook companion.