How do you perform detailed PFDavg calculations for a complex SIF with multiple voting architectures?

Complex SIF PFDavg calculation: model each subsystem separately (sensor, logic solver, final element) using appropriate formulas - 1oo2: PFD = (lambda_DU * Ti)^2 * beta/3 + lambda_DU * Ti * (1-beta); 2oo3: PFD = (lambda_DU * Ti)^2 * (1-beta) + lambda_DU * Ti * beta. Apply common cause beta factor (typically 2-10% based on IEC 61511 Annex F scoring), include diagnostic coverage contribution (lambda_DD detected and repaired in MTTR), consider proof test coverage (<100% means residual undetected failures), and add systematic capability constraints. Total SIF PFDavg = sum of subsystem PFDavgs (series reliability). Verify against SIL target including margin. Use Markov models for complex dependencies or imperfect proof tests.