Glossary · Fault behavior and system states
State model
Also known as: state machine
German: Zustandsautomat
In systems engineering, a state model is a model of the defined states of a system and the permitted transitions between them, including the conditions that trigger each transition.
- Systems engineering
- Functional safety
In one sentence
A state model defines a system's states and the permitted transitions between them; control software, safety analysis and manuals share it.
Example
The state model of a packaging machine defines Stopped, Starting, Running, Held, Stopping and Aborted, and allows Running to be reached only from Starting.
How it applies
- Integrated systems: A shared state model is how integrated machines agree on what “ready,” “running” or “fault” mean. Map the states of each subsystem explicitly; mismatched models lead to semantic drift and interaction faults.
- Functional safety: Identify which states are safe, which transitions are forbidden and how the system reaches a safe state from every other state. Unspecified states and transitions are a common source of hazards after faults.
- Verification: Test every permitted state transition and try the forbidden ones, including transitions under fault conditions.
- Technical documentation: The states and modes described in the manual must match the implemented model. A state diagram is often the clearest way to present them.
State model vs. operating mode
An operating mode such as automatic, setup or maintenance defines which functions and safeguards are active. A state model describes the states within and between these modes and how the system moves between them.