Glossary · Fault behavior and system states
Fault reaction
In functional safety, a fault reaction is the defined system response to a detected fault, for example switching to a safe state, entering a degraded mode or raising an alarm.
- Functional safety
- Integrated systems
In one sentence
A fault reaction is what a system does once a fault is detected; it must be specified, fast enough and verified as part of the reaction chain.
Example
When a safety PLC detects a discrepancy between the two channels of a door switch, it removes torque from the robot drives via STO and requires a manual reset.
How it applies
- Functional safety: Detection alone does not reduce risk. Diagnostics and their diagnostic coverage only help if a fault reaction follows that brings the machine into a safe state in time. The time from detection to the achieved state is part of the reaction chain.
- Integrated systems: Specify reactions per fault class: which faults stop the machine, which allow degraded mode and which only raise a warning. Coordinate reactions across subsystems so that one system's reaction does not create a hazard in another.
- Verification: Verify each fault reaction, including its timing, by test or fault injection.
- Technical documentation: Fault messages and troubleshooting sections should state which reaction the machine has taken and how operation is restored.