What are the common voting architectures for SIS and when are they used?

Common voting architectures: 1oo1 (one-out-of-one) - single channel, simplest, limited SIL capability; 1oo2 (one-out-of-two) - either channel trips system, high safety but more spurious trips; 2oo2 (two-out-of-two) - both channels must agree to trip, fewer spurious trips but lower safety; 2oo3 (two-out-of-three) - majority voting, balances safety and availability, can tolerate one failure; 2oo4 - higher redundancy for critical applications. Selection based on required SIL, acceptable spurious trip rate, and maintenance philosophy. Architectures can be mixed (2oo3 sensors with 1oo2 valves). Higher redundancy enables longer proof test intervals.