Structuring ISA-88 Batch Hierarchy and SFC Type Classes in SIMATIC PCS 7 (EPH vs EM)

In SIMATIC PCS 7 and SIMATIC BATCH, the plant hierarchy follows ISA-88 physical and procedural models: a Unit folder contains Equipment Modules (EM) and Equipment Phases (EPH). An Equipment Module represents an engineering grouping of physical equipment (such as an agitator, dosing header, or heat exchanger), whereas an Equipment Phase represents a procedural function block (an SFC Type instance) that carries out a technological operation (e.g. Heating, Agitating, Dosing). In PCS 7 V9.0 and higher, Siemens introduced advanced SFC Type classes: 'EPH Interface' (a generic phase defining setpoints and strategies without sequencers) and 'EPH Derived' (concrete instances containing equipment sequencers), allowing a single standardized recipe phase in SIMATIC BATCH to control different physical equipment across units.

Executive Summary

Designing a batch automation project in SIMATIC PCS 7 requires organizing the Plant Hierarchy in SIMATIC Manager to conform with ANSI/ISA-88.01 (IEC 61512) standards. Automation engineers frequently encounter confusion regarding the distinct roles of Equipment Modules (EM) versus Equipment Phases (EPH), especially when structuring SFC Types for SIMATIC BATCH. Questions arise regarding whether a cleaning or washing routine constitutes an Equipment Module or an Equipment Phase, and how to leverage the modern SFC Type classes introduced in PCS 7 V9.x: 'EPH Interface' and 'EPH Derived'. This article clarifies the ISA-88 hierarchical terminology, demonstrates proper Plant Hierarchy folder structuring, and explains how to implement generic recipe phases across multi-unit plant environments.

Architecture and Fundamental Mechanics

ISA-88 Physical/Procedural Models, SFC Type Architecture, and PCS 7 V9.x Enhancements:

ISA-88 Structural Hierarchy in SIMATIC PCS 7:
Enterprise / Site / Area: Top-level administrative and geographical divisions.
Process Cell: A collection of units that can produce a complete batch of material.
Unit: A major processing container (e.g. Reactor, Fermenter, Crystallizer) capable of performing one or more major processing activities. In PCS 7 Plant View, a folder is marked as a Unit by checking the 'Unit' attribute.
Equipment Module (EM): A functional grouping of equipment (actuators, sensors, control loops) that can carry out a finite number of specific tasks (e.g. Temperature Control System, Dosing Manifold).
Equipment Phase (EPH): The smallest procedural element in the controller that can execute a process task. An SFC Type assigned the class EPH represents this phase.
Clarifying the Washing/Cleaning Example:
An SFC Type that executes a washing cycle on a vessel is an Equipment Phase (EPH), not an Equipment Module.
The physical spray balls, drainage valve, and rinse pump belong to an Equipment Module (or the Unit itself), while the sequence that opens valves, circulates water, and drains the tank is the procedural Equipment Phase.
SFC Type Classes in PCS 7 V9.0 and Higher (EPH Interface vs EPH Derived):
Prior to PCS 7 V9.0, each SFC Type required full procedural sequencer definitions. If Unit 1 had heating via steam valves and Unit 2 had heating via electrical elements, two distinct SFC Types were needed, complicating recipe management in SIMATIC BATCH.
EPH Interface (EPHT Interface): A generic, non-executable SFC Type containing only parameters, setpoints, and control strategies. It possesses NO sequencers. In SIMATIC BATCH, this interface represents the universal recipe phase (e.g. Heat_Phase).
EPH Derived: A concrete SFC Type derived from the EPH Interface. It inherits all setpoints and characteristics from the interface but contains the specific sequential logic and I/O connections tailored to the local physical equipment.
This abstraction decouples SIMATIC BATCH recipes from physical AS implementation details, allowing identical recipes to run transparently on divergent process hardware.

Step-by-Step Implementation Procedure

Configure the Plant Hierarchy in SIMATIC Manager:
* Switch to Plant View (View -> Plant View).
* Right-click the project root and select Insert New Object -> Hierarchy Folder.
* Create folders matching ISA-88 levels: Area -> ProcessCell -> Unit_1.
* Right-click the Unit_1 folder, select Properties, navigate to the Unit tab, and check Unit of plant hierarchy.
Define Equipment Module Folders (Optional / Technological Structuring):
* Beneath Unit_1, insert subfolders for functional groupings if needed (e.g., EM_Agitator, EM_Heating).
* Assign the folder type as 'Equipment Module' in folder properties.
Create and Classify SFC Types in the Master Data Library:
* Open the Master Data Library; navigate to the SFC Types folder.
* Create a new SFC Type (e.g., Wash_Phase).
* In SFC Type Object Properties -> Options, select the SFC Type class:
- Set Class to EPH (Equipment Phase).
- If using PCS 7 V9.x generic interfaces:
- Create an SFC Type named Interface_Heating with class set to EPH Interface.
- Define required parameters (e.g., Target_Temp, Heating_Rate, ControlStrategy).
- Create derived types (Heating_Steam, Heating_Electric) with class set to EPH Derived, linking them to Interface_Heating.
Instantiate the SFC Type in the Plant Hierarchy:
* Drag the SFC Type instance into the CFC chart located under Unit_1 (or Unit_1/EM_Cleaning).
* Interconnect equipment interlocks, actuators, and sensor signals.
Compile and Update SIMATIC BATCH:
* In SIMATIC Manager, select Options -> SIMATIC BATCH.
* Execute Compile and Download Objects -> Batch Objects.
* Open BatchCC; verify that the Equipment Phases appear properly under their respective Units in the BATCH plant hierarchy.

Verification

In SIMATIC Manager Plant View, verify the hierarchy icons: the Unit folder displays the unit symbol, and the CFC containing the SFC Type is nested beneath it.
Open SIMATIC BATCH Recipe Editor.
Create a master recipe for the unit; verify that the phase (Wash_Phase or Interface_Heating) is available in the library palette and can be inserted into the recipe operation.
Allocate the unit to a test batch in BatchCC; verify that when the phase starts, the controller SFC Type instance transitions into the Running state.

Limitations and Operational Precautions

Having no Equipment Module folders under a Unit is permissible in PCS 7; Equipment Phases can reside directly under the Unit folder. However, an Equipment Phase cannot exist without a parent Unit in SIMATIC BATCH because batches allocate resources at the Unit level. EPH Interface and EPH Derived features require PCS 7 V9.0 or higher and are not supported in PCS 7 V8.x or older classic BATCH releases.

Engineer FAQ

Is an SFC that washes a tank an Equipment Module or an Equipment Phase?

It is an Equipment Phase (EPH). The sequence of operations is the phase, while the physical equipment is an Equipment Module or Unit.

Can I place an SFC Type directly under a Unit without an Equipment Module folder?

Yes. ISA-88 allows phases to be subordinate directly to a Unit if separate equipment modules are not required.

What is an EPH Interface in PCS 7 V9.x?

It is a template SFC Type that defines inputs, setpoints, and control strategies without any internal sequencers, used as a generic recipe phase in SIMATIC BATCH.