Glossary · Functional safety
Diversity (functional safety)
Also known as: diverse redundancy, diversification
In functional safety, diversity is the use of dissimilar technologies or implementations to reduce susceptibility to common-cause failure. Diverse channels are less likely to fail together from one shared cause.
- Functional safety
- Systems engineering
In one sentence
Diversity uses dissimilar technologies or implementations in safety channels so that one shared cause is less likely to disable them all.
Example
A guard on a CNC machine is monitored by one mechanical position switch and one non-contact coded sensor from a different manufacturer, so a single design flaw or environmental effect is unlikely to defeat both.
How it applies
- Functional safety: Diversity is one of the measures credited against common-cause failure in ISO 13849-1. It can apply to technology, manufacturer, software, measurement principle or design team.
- Software: Two identical programs running on two processors fail together from the same bug. Diverse software or diverse monitoring logic reduces that systematic risk, at a cost in development effort.
- Technical documentation: Record which diversity is claimed and why. Spare parts lists and maintenance instructions must prevent replacing a diverse component with an identical one.
- Evidence: Diversity supports, but does not replace, a documented CCF assessment.
Diversity vs. redundancy
Redundancy means more than one channel. Diversity means those channels differ. Redundancy protects against random single failures; diversity additionally protects against shared systematic causes.