20 Functional Safety Select the category EN ISO 13849 outlines 5 different categories (B, 1, 2, 3, 4) describing the respective architectures of the safety control system and with that the durability and the performance in the case of an error. • Category B: Single-channel, non-redundant safety system. One single fault leads to the loss of the safety function. • Category 1: Like Category B, but with a higher resistance to failure through use of well-tried components. • Category 2: Safety control system with additional test channels and cyclical tests for safety functions with suitable test rates. For PLr=d the output (OTE) shall initiate a safe state. • Category 3: Dual-channel, redundant safety system. One single error does not lead to the loss of the safety function, but accumulated undetected faults may. • Category 4: Dual-channel, redundant safety system. One single error or the accumulation of faults does not lead to the loss of the safety function. Cat. B+1 I L O Cat. 2 I L O TE OTE l1 L1 O1 l2 L2 O2 l1 L1 O1 l2 L2 O2 Cat. 3 Cat. 4 I = Input (for instance door switch) L = Logic (for instance safety relays) O= Output (for instance electropneumatic valves) Determination of the Performance Levels PL Simplified determination of the Performance Levels by means of the bar charts depending on: • the selected control architecture (category) • the MTTFD-value • the diagnostic coverage • and the CCF review a b c d e MTTFD low 3 years <= MTTFD <10 years Cat B Cat 1 DC < 60% no DC < 60% no CCF is not relevant Cat 2 Cat 3 60% <= DC < 90% 90% <= DC < 99% 60% <= DC < 90% 90% <= DC < 99% low resources low resources CCF >= 65% Cat 4 99% <= DC high MTTFD medium 10 years <= MTTFD <30 years MTTFD high 30 years <= MTTFD <= 100 years