Glossary · Functional safety
Category 1 (ISO 13849-1)
Also known as: Cat. 1
German: Kategorie 1
In ISO 13849-1, Category 1 is a single-channel architecture that meets the requirements of Category B and additionally uses well-tried components and well-tried safety principles. A single fault can still lead to the loss of the safety function, but its occurrence is less likely than in Category B.
- Functional safety
- Systems engineering
In one sentence
Category 1 in ISO 13849-1 is a single-channel architecture with well-tried components; a single fault can still cause loss of the safety function.
Example
A guard interlock with one positive-opening safety switch that directly de-energizes a contactor is a typical Category 1 design for a low-risk hazard.
How it applies
- Architecture: Category 1 has no fault detection and no redundancy. Its reliability comes from the components themselves, so the MTTFd of each channel must be high.
- Achievable level: Category 1 can reach at most PL c. Higher required levels need a different category.
- Components: Well-tried components are those widely used with good results in similar applications or made to relevant principles. Complex electronics such as standard PLCs are generally not regarded as well-tried in this sense.
- Documentation: State the category, MTTFd and resulting PL for each safety function in the safety calculation and technical file. The documentation team should describe any maintenance or replacement intervals the design relies on.
Category 1 vs. Category B
Both are single-channel without fault detection. Category B (ISO 13849-1) requires only basic safety principles and allows low to medium MTTFd. Category 1 adds well-tried components and principles and requires high MTTFd.