Physical Model

The physical model within ISA-95 describes the hierarchy of physical production elements in an organisation.
The model provides structure for the way in which operational technology (OT) and information systems (IT) meet.

Structure of the model

The ISA-95 hierarchy consists of several levels that together represent the physical reality of a factory or installation:

• Enterprise – The complete organisation or corporate group.
• Site – A physical location or factory.
• Area – A functional zone within the site (for example mixing, assembly or packaging).
• Process Cell – A part of an Area where a specific process takes place.
• Unit – A component within a Process Cell that performs one processing step.
• Equipment Module – A group of devices that together perform a function within a Unit.
• Control Module – The layer of sensors, actuators and controllers that physically drive the process.

Purpose of the physical model

The physical model forms the backbone for data structuring and system integration.
By linking each physical component to a hierarchical level, OT systems (such as PLCs and SCADA) can communicate more effectively with IT systems (such as MES and ERP).

Benefits

• Clarity – A clear structure for all production components.
• Integration – Direct linkage between physical assets and information systems.
• Security – Segmentation makes OT networks safer and easier to oversee.
• Efficiency – Simplifies management, maintenance and data analysis.

Example structure

A packaging factory could, for example, be modelled as follows:

• Enterprise: Packaging Group BV
• Site: Eindhoven Plant
• Area: Packaging Line A
  • Process Cell: Cartoning
    • Unit: Folding and gluing unit
      • Equipment Module: Glue applicator #1
        • Control Module: PLC with temperature sensor

Conclusion

The physical model of ISA-95 provides a standardised way to describe the production environment.
It bridges IT and OT and makes visible how processes, machines and systems are interconnected — an indispensable foundation for successful IT/OT convergence.