Glossary · Functional safety
Category (ISO 13849-1)
Also known as: designated architecture, control category
In functional safety of machinery, a Category is the architecture classification of safety-related parts of control systems under ISO 13849-1. The Categories B, 1, 2, 3 and 4 describe the behavior of the system in the event of faults, based on structure, fault detection and component reliability.
- Functional safety
- Systems engineering
In one sentence
ISO 13849-1 Categories B, 1, 2, 3 and 4 classify the fault behavior of a safety control architecture and feed into the Performance Level.
Example
A guard interlock on a packaging machine uses two position switches on two channels with cross-monitoring in a safety relay, a typical Category 3 structure in which a single fault does not lead to loss of the safety function.
How it applies
- Functional safety: Categories B and 1 are single-channel without fault detection; Category 1 relies on well-tried components. Category 2 adds periodic testing. Categories 3 and 4 are redundant; Category 4 also requires faults to be detected in time and accumulated faults to be considered.
- Performance Level: The Category alone does not determine the Performance Level. It is combined with MTTFd, diagnostic coverage and measures against common-cause failure.
- Technical documentation: State the Category for each safety function and show the architecture in block diagrams in the technical file. The information for use should explain the tests the user must perform, for example for Category 2.
- Evidence: Validation under ISO 13849-2 checks that the implemented structure matches the claimed Category, including fault analysis.
Category vs. Performance Level
The Category describes the structure and fault behavior. The Performance Level describes the achieved ability to perform the safety function, of which the Category is one input.