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• T₁ = Proof test interval (h)
• MTBF = Mean time between failures (hour)
• MTTR = Mean time to restoration (hour)
• MRT = Mean repair time (hour)
• DC = Diagnostic coverage
• β = The fraction of undetected failures that have a common cause
• β_D = Of those failures that are detected by the diagnostic tests, the fraction that have a common cause
• β_DU = Dangerous Failure rate (per hour) of a channel in a subsystem
• PFD_G = Average probability of failure on demand for the group of voted Channels
• PFD_S = Average probability of failure on demand for the sensor subsystem
• PFD_L = Average probability of failure on demand for the logic subsystem
• PFD_FE = Average probability of failure on demand for the final element subsystem
• PFD_SYS = Average probability of failure on demand of a safety function for the E/E/PE safety-related system
• PFH_G = Probability of failure per hour for the group of voted channels
• PFH_S = Probability of failure per hour for the sensor subsystem
• PFH_L = Probability of failure per hour for the logic subsystem
• PFH_FE = Probability of failure per hour for the final element subsystem
• PFH_SYS = Probability of failure per hour of a safety function for the E/E/PE safety-related system
• λ = Total Failure rate (per hour) of a channel in a subsystem
• λ_D = Dangerous failure rate (per hour) of a channel in a subsystem, equal to 0,5 λ
• λ_DD = Detected dangerous failure rate (per hour) of a channel in a subsystem
• λ_DU = Undetected dangerous failure rate (per hour) of a channel in a subsystem
• λ_SD = Detected safe failure rate (per hour) of a channel in a subsystem
• t_CE = Channel equivalent mean down time (hour)
• t_GE = Voted group equivalent mean down time (hour)
• t_CE’ = Channel equivalent mean down time (hour)
• t_GE’ = Voted group equivalent mean down time (hour)
• T₂ = Interval between demands (h)
• K = Fraction of the success of the auto test circuit in the 1oo2D system
• PTC = Proof Test Coverage
• 1 = High demand or continuous mode only
• 2 = Low demand mode only

SIL-käyttö eri turvallisuusmäärittelyissä

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