IEC 62541-16:2025

Overview

IEC 62541-16:2025 - OPC Unified Architecture, Part 16: State Machines defines an Information Model for representing state machines in OPC UA. Published as Edition 1.0 (2025), this part moves the state-machine material formerly in IEC 62541‑5 Annex B into a dedicated standard. It specifies the modelling building blocks and how state machines are represented in an OPC UA AddressSpace to enable consistent, interoperable state modelling across devices and systems.

Key topics and technical coverage

• Information Model for state machines: formalizes the infrastructure to model states, transitions and sub‑machines in OPC UA.
• Types and modelling elements: defines ObjectTypes, VariableTypes and ReferenceTypes used to build state machines, including:
  • StateMachineType, StateVariableType, TransitionVariableType
  • FiniteStateMachineType, FiniteStateVariableType, FiniteTransitionVariableType
  • StateType, InitialStateType, TransitionType, FromState / ToState references
• AddressSpace representation: prescribes how state machines are instantiated and organized in the OPC UA AddressSpace (inheritance, containment, examples).
• Events and auditing: includes event types such as TransitionEventType and AuditUpdateStateEventType for runtime notifications and traceability.
• Choice states and guards: extensions to support conditional transitions (ChoiceStateType, GuardVariableType, ExpressionGuardVariableType, ElseGuardVariableType).
• Subtyping rules and status codes: special restrictions on subtyping StateMachine types and a set of specific StatusCodes for state-machine operations.
• Normative cross‑references: relies on other OPC UA parts (IEC 62541‑1, ‑3, ‑4, ‑5) for AddressSpace, services and core concepts.

Practical applications and users

This standard is practical for implementers seeking consistent state modelling in industrial automation and related domains:

• Device vendors and embedded developers - represent device operational states, modes and lifecycle transitions in a standardized way.
• System integrators and SCADA/IIoT architects - map machine states into supervisory systems and digital twins for visibility and control.
• Software developers - implement OPC UA servers/clients that expose or consume state machine models and transition events.
• Test labs and certification bodies - validate interoperability of state‑model implementations and conformance to OPC UA AddressSpace rules.
• Standards committees and solution architects - align higher‑level information models (assets, workflows) with a common state modelling approach.

Related standards

• IEC 62541-1: OPC Unified Architecture - Overview and Concepts
• IEC 62541-3: Address Space Model
• IEC 62541-4: Services
• IEC 62541-5: Information Model (previous location of State Machines material)

Keywords: IEC 62541-16:2025, OPC Unified Architecture, OPC UA state machines, Information Model, AddressSpace, StateMachineType, FiniteStateMachine, ChoiceState, TransitionEvent.