Glossary · Functional safety
Redundancy
Also known as: redundant design, multi-channel architecture
German: Redundanz
In functional safety, redundancy is the use of multiple independent channels or elements so that a single failure does not cause loss of the required function. It is effective only if the channels are sufficiently independent and faults are detected.
- Functional safety
- Systems engineering
In one sentence
Redundancy uses multiple independent channels so that one failure does not remove a required safety function.
Example
Two contactors in series switch off the motor of a conveyor; if one contact welds, the other still interrupts the power, and feedback monitoring reveals the welded contact.
How it applies
- Functional safety: Redundancy is the basis of Categories 3 and 4 in ISO 13849-1 and of hardware fault tolerance in IEC 61508 and IEC 62061.
- Integrated systems: Redundancy without detection only postpones failure. The first fault must be found by diagnostics or a test before a second fault occurs.
- Evidence: Independence has to be shown, not assumed. The common-cause failure assessment is the evidence that the channels do not fail together.
- Technical documentation: Wiring diagrams, spare part rules and maintenance steps must keep the channels separate. A shortcut during repair can reduce a two-channel design to one channel.
Redundancy vs. diversity
Redundancy provides more than one channel. Diversity makes those channels different, which also covers shared design flaws.