Glossary · Functional safety
Category B (ISO 13849-1)
Also known as: Cat. B, basic category
German: Kategorie B
In ISO 13849-1, Category B is the basic single-channel architecture: the safety-related parts are designed to withstand expected influences using basic safety principles, and a single fault can lead to the loss of the safety function.
- Functional safety
- Systems engineering
In one sentence
Category B is the basic ISO 13849-1 architecture with basic safety principles; a single fault can lead to loss of the safety function.
Example
A simple stop circuit using standard components rated for their operating conditions, without redundancy or monitoring, corresponds to Category B.
How it applies
- Architecture: Category B is single-channel, without fault detection. Its components must be selected and applied according to basic safety principles, for example correct ratings, protection against environmental influences and proper grounding.
- Achievable level: Category B can reach at most PL b, with low to medium MTTFd.
- Foundation: All other categories build on the requirements of Category B. The basic safety principles are listed in ISO 13849-2.
- Documentation: Even for Category B, state which basic safety principles were applied and which operating conditions were assumed. The documentation team should carry those conditions, such as supply voltage and ambient temperature, into the technical data of the manual.
Category B vs. Category 1
Both lack redundancy and diagnostics. Category 1 (ISO 13849-1) additionally requires well-tried components and principles and high MTTFd, which allows up to PL c.