Glossary · Fault behavior and system states
State transition
Also known as: transition
In systems engineering, a state transition is a change from one defined system state to another under specified conditions, such as an event, a command or an elapsed time.
- Systems engineering
- Functional safety
In one sentence
A state transition is a specified change between system states; its trigger, guard conditions and timing decide whether it is safe to take.
Example
A press may change from setup to automatic operation only after the guard is closed, the mode selector has been switched and the operator gives a start command.
How it applies
- Integrated systems: Specify each transition in the state model with its trigger, guard conditions, actions and maximum duration. Communicate transitions to connected systems, for example through event-driven communication, so that their view of the state stays aligned.
- Functional safety: Transitions that start motion or change the active safeguards need particular care. Switching the operating mode must not by itself start hazardous motion, and no transition may cause unexpected startup.
- Verification: Test transitions, not only states. The path from a fault state back to running is where many incidents happen.
- Technical documentation: Instructions should describe what the user must do to trigger a transition and what the machine does during it.