Batch Control with ISA-88 Standards

The ISA-88 standard (also known as IEC 61512) is the globally accepted framework for batch process control. It provides a consistent terminology, a physical equipment model, a procedural control model, and a recipe management structure that enables flexible, repeatable, and auditable batch manufacturing. Originally published in 1995 and updated through 2010, ISA-88 remains the standard governing everything from pharmaceutical tablet production to specialty chemical synthesis and food & beverage batching.

This article covers the full ISA-88 model — physical hierarchy, procedural hierarchy, recipe categories, state management, and integration with MES/ERP — with practical examples relevant to Turkish process industry professionals working in pharmaceuticals, chemicals, and food manufacturing.

The ISA-88 Physical Model

ISA-88 defines a hierarchical physical model that maps the plant equipment from the enterprise level down to individual control elements. Every batch process can be decomposed into these levels:

Enterprise                      (Corporate / Site)
    │
    └── Site                    (Factory / Plant)
            │
            └── Area            (Production Unit, e.g., "Reactor Hall 1")
                    │
                    └── Process Cell         (Group of equipment for one batch train)
                            │
                            ├── Unit         (Single major equipment item, e.g., "Reactor A")
                            │       │
                            │       ├── Equipment Module    (e.g., "Reactor A Jacket")
                            │       └── Control Module      (e.g., "Jacket Inlet Valve")
                            │
                            ├── Unit         (e.g., "Reactor B")
                            ├── Unit         (e.g., "Crystalliser C")
                            └── ...

Key principle: A Unit is the central concept in ISA-88. It is a piece of equipment that can carry out one or more major processing activities independently of other units. Units have a "unit recipe" associated with them and maintain their own state machine.

The ISA-88 Procedural Model

While the physical model describes what exists, the procedural model describes what happens. It is also hierarchical:

Procedure                (Overall process, e.g., "Batch Polymerisation")
    │
    ├── Unit Procedure   (Operations within a single unit, e.g., "Reactor A: Heat & Hold")
    │       │
    │       ├── Operation        (e.g., "Heat to 150°C")
    │       │       │
    │       │       ├── Phase    (e.g., "Ramp Heating")
    │       │       │       │
    │       │       │       └── Step    (e.g., "Check valve position, ramp SP")
    │       │       │
    │       │       └── Phase    (e.g., "Hold Temperature")
    │       │
    │       └── Operation        (e.g., "Cool to 80°C")
    │
    └── Unit Procedure   (e.g., "Crystalliser C: Cool & Seed")
            ...

Recipe Management

ISA-88 defines four recipe categories that reflect the recipe lifecycle from product development through production:

1. General Recipe

Purpose: Technology transfer and product development. The general recipe is equipment-independent — it describes the chemistry and process steps without reference to specific plant equipment.

• Created by: R&D / Process Development.
• Stored in: Corporate recipe database.
• Contains: Raw materials, target process conditions, quality specifications, order of operations.
• Does NOT contain: Equipment-specific parameters, production scheduling, or site-specific constraints.

2. Site Recipe

Purpose: Adapt the general recipe to a specific production site. Equipment references are added, and site-specific constraints (e.g., available utilities, local raw material sources) are incorporated.

• Created by: Site Process Engineering.
• Stored in: Site-level recipe management system.
• Adds: Equipment requirements, site-specific materials, local regulatory constraints (e.g., ÇEVRE İzni for Turkish facilities).

3. Master Recipe

Purpose: A fully equipment-specific recipe that serves as the template for all production batches of a given product.

• Created by: Control / Automation Engineering.
• Stored in: DCS/PLC recipe database (or MES recipe manager).
• Adds: Equipment allocation rules, process parameters (PV/SP limits), phase logic, procedural sequences, cleanup instructions.
• The master recipe is the source code for batch execution in the automation system.

4. Control Recipe

Purpose: A single-use instance of the master recipe for one specific batch. The control recipe is created when a batch is scheduled and destroyed when the batch is complete.

• Created by: MES or batch management system (or operator, for manual scheduling).
• Contains: Master recipe parameters + batch-specific data (batch ID, lot numbers, operator ID, actual start time, actual parameters).
• The control recipe is the executable object — the automation system reads the control recipe and executes it.

Recipe Structure Diagram

                    GENERAL RECIPE
                    (Equipment-Independent)
                          │
                    [Site Adaptation]
                          │
                          v
                    SITE RECIPE
                    (Site-Specific, Equipment-Flexible)
                          │
                    [Equipment Allocation]
                          │
                          v
                    MASTER RECIPE
                    (Equipment-Specific Template)
                          │
                    [Batch Scheduling]
                          │
                          v
                    CONTROL RECIPE
                    (Single Batch Instance)
                          │
                          v
                    ┌───────────────────┐
                    │   BATCH EXECUTION │
                    │   (DCS / PLC /    │
                    │    Batch Server)  │
                    └───────────────────┘

State Management

Every batch and every unit in ISA-88 follows a standard state machine. The states are defined in the standard and implemented by all compliant batch control systems:

                    ┌──────────┐
                    │  IDLE    │
                    └────┬─────┘
                         │
                    ┌────v─────┐
              ┌────>│ RUNNING  │────┐
              │     └────┬─────┘    │
              │          │          │
         ┌────┴───┐  ┌──v────┐  ┌──v──────┐
         │ HELD   │  │ PAUSED│  │ COMPLETE │
         └────┬───┘  └──┬────┘  └────┬─────┘
              │         │            │
              └─────────┘            │
                                     │
                               ┌─────v──────┐
                        ┌──────│  STOPPED   │──────┐
                        │      └─────┬──────┐      │
                   ┌────v───┐   ┌────v────┐  ┌────v────┐
                   │ABORTED │   │RESETTING│  │ RESTART │
                   └────┬───┘   └────┬────┘  └────┬────┘
                        │            │            │
                        └──────┬─────┘            │
                               │                  │
                          ┌────v────┐             │
                          │  IDLE   │<────────────┘
                          └─────────┘

Equipment Control vs. Procedural Control

A critical distinction in ISA-88 is between two parallel control layers:

• Equipment Control — The continuous, always-active control that keeps the equipment safe. This includes interlocks, permissives, alarm handling, and regulatory control (PID loops). Equipment control runs regardless of whether a batch is active.
• Procedural Control — The batch-specific, sequence-oriented control that executes the recipe. Procedural control phases are allocated to units, run to completion (or exception), and release the unit for the next operation.

Example: In a reactor unit, the jacket temperature PID loop and the overpressure interlock are equipment control — they run continuously. The "Heat to 150°C" phase is procedural control — it sets the PID setpoint, monitors the ramp rate, and transitions to the Hold phase when the target is reached.

ISA-106 for Continuous Processes

While ISA-88 was designed for batch processes, the standard's principles have been extended to continuous processes via ISA-106 (Procedure Automation for Continuous Process Operations). The key differences:

Integration with MES and ERP

ISA-88 is the bridge between the automation layer (PLC/DCS) and the business systems (MES/ERP). The standard integration model follows the ISA-95 functional hierarchy:

ERP (SAP, Oracle)          │
    │                       │ Business Planning
    ▼                       │ & Logistics
MES (Batch Management)     │ (ISA-95 Level 4 → Level 3)
    │                       │
    ├── Recipe Management   │
    ├── Batch Scheduling    │
    ├── Material Tracking   │
    └── Production Records  │
    │                       │
    ▼                       │
Batch Server / DCS           │
    │                       │ Automation
    ├── Control Recipe      │ (ISA-95 Level 2)
    ├── Unit Supervision    │
    ├── Phase Execution     │
    └── Data Collection     │
    │                       │
    ▼                       │
Field Devices (PLC, I/O)   │ (ISA-95 Level 1)

Integration points:

• MES → Batch Server: Sends the control recipe (product ID, batch size, parameters), receives batch status and production data.
• Batch Server → DCS/PLC: Executes phases via OPC UA, reads process values, writes setpoints.
• DCS/PLC → Batch Server: Reports equipment mode, alarm status, phase execution progress.
• Batch Server → MES: Returns actual materials consumed, actual parameters, batch deviation report, electronic batch record (EBR).

Example: Interface Table Between MES and Batch Server

Implementing ISA-88: Practical Guidance

1. Start with the physical model. Document every piece of equipment in the process cell. Assign each to a Unit, Equipment Module, or Control Module. This is the foundation of everything else.
2. Design phases, not monolithic programs. Write small, reusable phase logic modules. A "Charge" phase should work identically whether it is called from the "React" operation or the "Clean" operation.
3. Separate equipment control from procedural control. Your PLC code should have two distinct sections: continuous logic (alarms, interlocks, PID) running in a fast task, and sequential-logic phases running in a slower batch task.
4. Use the standard state machine. Do not invent your own. Every DCS and batch management system understands the ISA-88 states. Custom state machines break MES integration and confuse operators.
5. Build the recipe hierarchy. You may start with only master recipes, but plan for the general → site → master → control structure from day one. It is much harder to retrofit later.
6. Validate with a mock batch. Before running a real product, execute the control recipe with water (for chemical processes) or placebo (for pharmaceutical processes). Verify every phase transition, every state, every alarm.

Key takeaway: ISA-88 is not just a standard — it is a design methodology. When applied properly, it delivers batch processes that are flexible (change product without rewriting code), repeatable (every batch follows the same procedure), auditable (every deviation is recorded), and scalable (add new equipment or products without redesigning the control system). For Turkish process industry manufacturers facing regulatory pressure (TİTCK for pharmaceuticals, ISO 22000 for food) and competitive pressure for shorter batch cycle times, ISA-88 compliance is not optional — it is a competitive necessity.

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References & Further Reading

1. ISA-88 / IEC 61512 — Batch Control Standards — International standard defining the physical model, procedural model, recipe management, and state machine for batch process control across all process industries.
2. ISA-88.00.04 — Batch Production Records — ISA standard extension covering electronic batch records, data collection requirements, and audit trail specifications for compliant batch manufacturing.
3. ISA-95 / IEC 62264 — Enterprise-Control System Integration for Batch — International standard providing the integration framework between ISA-88 batch systems and MES/ERP enterprise layers for production scheduling and tracking.
4. IEC 61512-3 — Batch Control — Recipes and Recipe Management — IEC standard specifying the recipe data model, recipe categories (general, site, master, control), and recipe execution procedures for batch automation systems.
5. ISA-106 — Procedure Automation for Continuous Process Operations — ISA standard extending ISA-88 procedural control concepts to continuous processes, covering start-up, shutdown, and grade change automation.