IEC 62541-16-2025 PDF

Full title and description

IEC 62541-16:2025 — OPC unified architecture - Part 16: State Machines. Defines an OPC UA Information Model that specifies the infrastructure to model state machines (states, transitions, substates, events and related types) for consistent representation of state-based behaviour in OPC UA AddressSpaces.

Abstract

This part of IEC 62541 establishes ObjectTypes, VariableTypes, ReferenceTypes, Events and modelling rules to represent finite and hierarchical state machines in OPC UA. It formalises StateMachineType, StateType, TransitionType, TransitionEventType and related constructs, and moves the state-machine material previously found in IEC 62541‑5 (Annex B) into a dedicated part to improve clarity and interoperability.

General information

• Status: Published / Current.
• Publication date: 5 December 2025.
• Publisher: International Electrotechnical Commission (IEC).
• ICS / categories: 25.040 – Industrial automation systems.
• Edition / version: Edition 1.0 (2025).
• Number of pages: 35 (English edition).

Scope

This part of IEC 62541 defines an OPC UA Information Model that describes the basic infrastructure to model state machines in an AddressSpace, including representation of current states, transitions, sub‑machines, choice/guard constructs, event generation for transitions and audit/update events, and subtyping restrictions and status codes specific to state‑machine operations. It replaces the previous Annex B material in IEC 62541‑5.

Key topics and requirements

• Information Model for state machines: StateMachineType, StateVariableType, TransitionVariableType and related types.
• Finite and hierarchical state machines: modelling of substates and initial states, containment and inheritance examples.
• Events and auditing: TransitionEventType and AuditUpdateStateEventType for runtime notifications and traceability.
• Choice states and guards: support for conditional transitions (ChoiceStateType, GuardVariableType, ExpressionGuardVariableType, ElseGuardVariableType).
• Subtyping rules and specific StatusCodes: constraints on subtyping StateMachine types and defined status codes for state-machine operations.
• Normative cross-references: normative links to IEC 62541‑1, ‑3, ‑4 and ‑5 for core OPC UA concepts, AddressSpace and services.

Typical use and users

Intended for OPC UA implementers — device vendors, industrial control and embedded developers, system integrators and software vendors — who need a standard, interoperable way to represent device and system states, mode transitions, lifecycle behaviour and state-related events in OPC UA AddressSpaces. It is also used by test labs and certification bodies to validate state‑machine modelling conformance.

Related standards

Part of the IEC 62541 (OPC UA) series. Normative references include IEC 62541‑1 (Overview and Concepts), IEC 62541‑3 (Address Space Model), IEC 62541‑4 (Services) and IEC 62541‑5 (Information Model), which together provide the underlying definitions, services and AddressSpace semantics required by Part 16. National/adopted variants and EN/BS/IS adoptions (e.g., EN IEC / BS EN / I.S. editions) may be available.

Keywords

OPC UA, IEC 62541, state machines, StateMachineType, TransitionEventType, AddressSpace, finite state machine, choice state, guard, industrial automation.

FAQ

Q: What is this standard?

A: IEC 62541-16:2025 is Part 16 of the OPC Unified Architecture (IEC 62541) series that defines an Information Model for representing state machines in OPC UA.

Q: What does it cover?

A: It covers the modelling elements (types, references, variables), instantiation rules, event and auditing types, guard/choice constructs, subtyping restrictions and status codes needed to model finite and hierarchical state machines in an OPC UA AddressSpace.

Q: Who typically uses it?

A: Device and embedded vendors, control-system and application developers, system integrators, test laboratories and certification bodies — anyone implementing or validating OPC UA models that include state‑based behaviour.

Q: Is it current or superseded?

A: It is the current published edition (Edition 1.0, 2025) and is published by IEC; stability information on the IEC webstore indicates the document’s stability period. For the authoritative status and any amendments check the IEC webstore or national adoption notices.

Q: Is it part of a series?

A: Yes — it is part of the IEC 62541 OPC UA series and cross‑references core parts such as IEC 62541‑1, ‑3, ‑4 and ‑5. The state‑machine material was previously included as Annex B of IEC 62541‑5 and has now been relocated to this dedicated part.

Q: What are the key keywords?

A: OPC UA, state machine, StateMachineType, TransitionEvent, AddressSpace, guards, choice state, finite state machine, IEC 62541.