Glossary · Functional safety
Category 2 (ISO 13849-1)
Also known as: Cat. 2
German: Kategorie 2
In ISO 13849-1, Category 2 is a single-channel architecture with test equipment: it meets Category B, uses well-tried safety principles, and the safety function is checked at suitable intervals by the machine control system. A fault occurring between checks can lead to the loss of the safety function.
- Functional safety
- Systems engineering
In one sentence
Category 2 in ISO 13849-1 is a tested single-channel architecture; a periodic check detects faults, but a fault between checks can cause loss.
Example
A light curtain system is tested automatically at every machine cycle start; if the test fails, the output signal equipment prevents the next hazardous movement.
How it applies
- Architecture: Category 2 consists of an input, logic and output channel plus test equipment and a test output. The test must initiate a suitable reaction when it detects a fault, such as bringing the machine to a safe state or warning of the hazard.
- Requirements: Average diagnostic coverage must be at least low, and measures against common-cause failure are required. The test rate must be sufficiently high compared with the demand rate; the standard specifies the conditions.
- Achievable level: Category 2 can reach at most PL d.
- Documentation: Document what the test checks, when it runs and how the machine reacts to a failed test. Operating instructions should explain the resulting fault messages and the permitted recovery steps.
Category 2 vs. Category 3
Category 2 detects faults only through periodic testing of one channel. Category 3 (ISO 13849-1) uses two channels, so a single fault does not lead to loss of the safety function.