Glossary · Fault behavior and system states
Reaction chain
German: Reaktionskette
In functional safety, a reaction chain is the linked sequence from detection through decision and control action to the achieved system state, for example sensor, logic, actuator and the machine reaching a safe state.
- Functional safety
- Integrated systems
- German source term
In one sentence
The reaction chain links detection, decision, control action and achieved state; its weakest and slowest links decide whether a safety function works.
Example
A laser scanner detects a person in the path of an AGV, the safety controller decides to brake, the drives execute SS1 and the vehicle comes to a standstill before reaching the person.
How it applies
- Functional safety: A safety function is only as good as its whole chain. Analyze every link (sensor, communication, logic, actuator, mechanics) for reliability and time; the achieved state must be reached before the hazard can occur, which is why stopping time is part of the chain.
- Integrated systems: In integrated lines, the chain often crosses system boundaries, for example when a safety signal is passed from one machine to another. Each handover adds latency and possible failure modes and needs a clear owner.
- Evidence: Document the chain element by element, with the values used in the calculation, so that it can be re-verified after changes.
- Terminology: The German Reaktionskette is an established term in German safety engineering, while the English phrase is less fixed; define it at first use in English documentation.
Reaction chain vs. fault reaction
A fault reaction is the response to a detected fault. The reaction chain describes the full path from detection to the achieved state, both for demands on a safety function and for detected faults.