ISO 13849
Safety of Machinery - Safety-Related Parts of Control Systems
ISO 13849 defines Performance Levels (PL a through PL e) for safety functions, based on probability of dangerous failure per hour. Engineers calculate PL using the SISTEMA software tool, considering Mean Time to Dangerous Failure (MTTFd), Diagnostic Coverage (DC), and Common Cause Failures (CCF). Higher PLs require redundant architectures and extensive diagnostics. Category 3 and Category 4 systems employ dual-channel monitoring with automatic fault detection. Validation includes Failure Modes and Effects Analysis (FMEA) and proof testing at defined intervals.
Compliance Requirements
- Calculate required Performance Level via risk graph
- Select safety components with certified MTTFd values
- Implement diagnostic coverage per category
- Document architecture (Category 1–4)
- Define proof test intervals
Engineering Implications
Safety PLCs must execute certified safety logic blocks. Redundant sensors prevent single-point failures. Cross-monitoring detects discrepancies between safety channels.
Validation Process
FMEA validates fault detection capability. Functional testing confirms safe state transitions under simulated fault conditions. Third-party certification bodies review safety manuals.
Required Documentation
- • Safety requirements specification
- • SISTEMA calculation report
- • FMEA for safety-related components
- • Validation test protocol
- • Proof test procedures