Domain 1: Functional safety fundamentals and standards context
Domain 1 tests how functional safety standards fit together: IEC 61508 as the generic E/E/PE baseline, IEC 61784-3 for functional safety fieldbuses, and the machinery pair IEC 62061 / ISO 13849. Expect questions on SIL versus PL, the safety lifecycle, and how a black-channel profile like FSoE inherits its safety case from these standards rather than replacing them.
Core rules
- IEC 61508 defines SIL 1–4 from PFH/PFDavg and architectural constraints (HFT, SFF, systematic capability). The safety lifecycle, functional safety management, and verification/validation evidence are mandatory.
- IEC 61784-3 specifies functional safety fieldbus profiles; FSoE is the EtherCAT profile (CPF 12) in IEC 61784-3-12. It assumes a black channel and adds safety measures.
- IEC 62061 uses SIL CL 1–3 for machinery; ISO 13849-1 uses PL a–e with categories, MTTFd, DCavg and CCF. PL and SIL map approximately through PFHd ranges, but they are not interchangeable labels.
- Risk assessment inputs include hazard identification, severity, frequency/duration, probability of avoidance, and the possibility of limiting harm.
Worked example
A guard interlock needs PL d. ISO 13849-1 PL d corresponds to PFHd 10^-7 to 10^-6 per hour. If the safety function uses a light curtain, FSoE remote I/O, and a contactor, sum each subsystem's PFHd. If the FSoE path is claimed at 1×10^-9/h and the other parts total 4×10^-7/h, the result is about 4.01×10^-7/h, inside PL d and SIL 2 range. The claim still needs systematic capability and proof-test evidence.
Traps
Do not treat PL d as automatically SIL 2 without checking PFHd, architecture, and systematic measures. Do not apply IEC 61784-3 without IEC 61508 lifecycle evidence. Do not omit the black-channel residual error from the calculation.