Safety integrity level logic solver

Safety instrumented system (SIS) Any combination of separate and independent devices (sensors, logic solvers, final elements, and support systems) designed and managed to achieve a specified safety integrity level. An SIS may implement one or more safety instrumented functions. 

The RPS is a sort of SIS (Safety Instrumented System) (Torrres et al., 2009). A SIS is defined as an instrumented system used to implement one or more safety instrumented control functions. A SIS is composed of any combination ofsensors, logic solver and final elements" (lEC 61511, 2003). The standard lEC 61508 requires every safety function to achieve a determined Safety Integrity Level (SIL). For low demand operating systems the SIL levels are defined in terms of average probability of failure on demand (PFDavg, see Table 2). 

Implementation of one or more Safety Instrumented Functions. A SIS is composed of any combination of sensor(s), logic solver(s), and final elements). A SIS usually has a number of safety functions with different safety integrity levels (SIL) so it is best to avoid describing it by a single SIL. See also Layers of Protection Analysis (LOPA) Safety Integrity Level (SIL). 

The term prior use is used in ANSI/ISA-84.00.01-2004-1. This term is applied when the owner/operator is justifying the implementation of a device in an SIF application based on prior use of the device in a similar operating profile. The standard provides specific requirements for assessing prior use for devices based on the device type, safety integrity level, and, in the case of PE logic solvers, the safe failure... 

Logic Solver Type Variations With Safety Integrity Level... 

ISA Standard, Safety Instrumented Functions (SIF)— Safety Integrity Level (SIL) Evaluation Techniques Part 5 Determining the PFD of SIS Logic Solvers via Markov Analysis, TR84.00.02-2002, Part 5, 2002. ISA-The Instrumentation, Systems, and Automation Society. Research Triangle Park, NC. 

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