ISA-88 (IEC 61512) batch control: physical model, procedures, recipes and phase states

What ISA-88 is

ANSI/ISA-88 (often called S88) is the ISA series of standards for batch control. It describes equipment and procedures; it is not a software standard and applies equally to a process run by hand. ISA approved the first part in 1995 and updated it in 2010. The IEC published that first part as IEC 61512-1 in 1997; a second edition of IEC 61512-1 was published on 19 February 2026 and replaces the 1997 edition.

The ISA-88 series currently lists four parts and several technical reports:

The models in this article follow the editions described by the sources used here (IEC 1997, ISA 2010). According to its abstract, IEC 61512-1:2026 removes the lower levels of the physical (role-based equipment) model to avoid redundancy, defines generic and recipe-aware equipment modules, and presents the procedural states as an example, with an expanded state reference model in an annex.

Batch, continuous and discrete processes

A guide from the integrator Hallam-ICS separates three kinds of production:

• Discrete: individual items move from station to station and keep their identity, such as light bulbs or staplers.
• Continuous: material flows through the equipment without interruption, and the output depends on how long the plant runs, as in oil refining.
• Batch: a finite quantity of product is made through an ordered set of activities over a set time; the result is called a batch. Specialty chemicals, pharmaceuticals and food are typical.

A tank that is filled with water, heated, dosed, mixed and emptied is the classic example; Rockwell's PhaseManager manual uses it to explain phases. ISA's technical report TR88.95.01 (Table 1) notes that ISA-88 is written mainly for batch manufacturing but is often applied elsewhere.

The physical model: from enterprise to control module

The physical model has seven levels: enterprise, site, area, process cell, unit, equipment module and control module. The upper three describe the company and its plants; the lower four describe equipment:

Levels may be left out, but not the unit. The Hallam-ICS guide notes that storage tanks are usually not units and suggests a test: does the recipe need this equipment to run? A CIP skid can be treated as a unit so that recipe rules apply to cleaning too.

The procedural control model: procedure, unit procedure, operation, phase

Recipe procedures have four levels, each an ordered set of the level below. After the FactoryTalk Batch Recipe Editor help and the Hallam-ICS guide:

• Procedure: the strategy for making a batch in a process cell, for example "Make product A". A procedure can span several units, which allows unit-to-unit transfers.
• Unit procedure: a set of related operations carried out in one unit.
• Operation: an ordered set of phases executed on a single unit (Hallam-ICS).
• Phase: the smallest procedural element and the level that links the recipe to the equipment, for example heat, mix, transfer or charge (Hallam-ICS).

The Hallam-ICS guide notes that S88 encourages operation boundaries at points where the process can safely be suspended, and that continuous functions such as agitation or temperature control are often better run as their own operation in parallel than inside every operation.

The phase is where the two models meet. In FactoryTalk Batch, tags link each recipe phase to an equipment phase in the controller. The recipe phase sends commands; the equipment phase changes state, reports back and works through equipment and control modules, so the recipe never addresses an individual valve. Quantities and setpoints are recipe parameters, downloaded to the equipment phase at run time.

Four recipe types, and keeping recipes out of equipment code

ISA-88 defines four recipe types (descriptions after the Hallam-ICS guide):

Part 3 covers general and site recipes. The Hallam-ICS guide treats the master recipe as required in any S88-based solution, as the template for control recipes. On the plant floor engineers build master recipes, for example in the FactoryTalk Batch Recipe Editor, whose help defines a batch as a control recipe being executed.

The idea behind it is separation. When recipe steps and equipment control are mixed in one PLC program, a new ingredient can take many man-hours of program changes and put other recipes at risk. With ISA-88 the recipe says what, how much and in which order; the equipment phase knows how to do it on this equipment. Rockwell's PhaseManager manual makes the same point, and the abstract of IEC 61512-1:2026 states the aim: recipes can change without changing equipment procedures.

The phase state model

Every equipment phase follows a state model. Rockwell's PhaseManager manual calls its model similar to S88 and PackML and splits the states into two kinds:

The commands are Start (Idle to Running), Hold (to Holding, then Held), Restart (Held to Restarting, then back to Running), Stop (to Stopping, then Stopped), Abort (to Aborting, then Aborted) and Reset (from Complete, Stopped or Aborted back to Idle). Per the Hallam-ICS guide, Stop is a controlled stop to a safe, recoverable state; Abort is immediate, and operators usually restore the equipment by hand afterwards. Sources differ on the details: the Hallam-ICS guide includes Resetting in its state model, while a FactoryTalk Batch help page describes Resetting as a PhaseManager addition for projects not based on S88 and lists Starting among the S88 active states, which the PhaseManager manual does not.

Where batch sits next to ISA-95

OPC Foundation's summary of ISA-95 places batch control systems that execute recipes at level 3 (manufacturing operations management), with SCADA and historians, and PLC and DCS real-time control at level 2. In a typical FactoryTalk Batch and PhaseManager system, the batch server sits at level 3 and the equipment phases run in the controllers at level 2; read this way, the split between recipe and equipment control falls on the boundary between the two levels.

ISA's technical report TR88.95.01 on using the two together explains the focus: ISA-95 covers information exchange between business systems and manufacturing control; ISA-88 works lower down, directing the people and equipment that transform materials. It warns that the two sometimes use different terms for one concept, or one term for different concepts, so align terminology early. For how these levels map to security zones, see the IEC 62443 article; for MES above batch, see MES on Ignition with Sepasoft.

Applying it on a project

• Draw the physical model before writing code: process cells, units, equipment and control modules from the P&ID, and which vessels are really units.
• Size each phase to one independent activity. Rockwell's manual gives adding water to a tank or mixing ingredients as good phases; opening one valve is too small, running a whole line too large.
• Fill a state worksheet for each phase. The PhaseManager manual asks one question per state, such as how the equipment pauses without making scrap (Holding). Implement only the states the equipment needs.
• Use the controller's phase tools. In Studio 5000 Logix Designer an equipment phase works much like a program, with one routine per acting state, in ladder, SFC, structured text or function block. Commands come from FactoryTalk Batch or the PCMD instruction, which can in turn be triggered by a start button on the machine or HMI.
• Keep recipe values as phase parameters, not constants in the ladder.

Common mistakes: recipe logic written into PLC code, so every new product is a PLC change and a new round of testing; units not clearly defined, so storage tanks become units or two unit procedures compete for one vessel (a unit runs one unit procedure at a time, so making and CIP cannot share it); and recipes commanding control modules directly instead of equipment modules.

TDL's batch control service covers FactoryTalk Batch and PlantPAx phase logic. At P&G Vietnam's Dong An plant, the scope since 2014 has included a FactoryTalk Batch upgrade with mixing-tank and material-tank units, recipes, reports and PLC phase control, and a new batch server and client for another mixing line with barcode material integration.