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1、Functional safety Engineering - Intro to SIS,Intro to Safety Instrumented System,Safety Instrumented System Definition Safety Instrumented System Purpose Safety Instrumented Function SIS Equipment Terms and Abreviations,Safety Instrumented System Definition,Safety Instrumented System = SIS IEC 61511
2、 defines the Safety Instrumented System as: “Instrumented system used to implement one or more safety instrumented functions. A SIS is composed of any combination of sensor(s), logic solver(s) and final elements(s)IEC 61508 does not use the term Safety Instrumented System (SIS) and instead use the t
3、erm Safety Related System (SRS) to mean the same thing. This may change in next release of 61508,SIS Definition from IEC 61511,Safety Instrumented Systems Reduce risk by decrease the likelihood of a potential hazard Decrease risk by reducing the magnitude of the consequenceA SIS may be responsible f
4、or Shutdown function Permissive function And consequence reduction (mitigation) functionsAll these functions Reduce RISK,SIS Definition,A more functional definition of SIS such as: “A SIS is defined as a system composed of sensors, logic solvers and final elements designed for the purpose of 1. Auto
5、matically taking an industrial process to a safe state when specified conditions are violated 2. Permit a process to move forward in a safe manner when specified condition allow (permissive functions) 3. Taking action to mitigate the consequences of an industrial hazard,SIS = ”Automatic Risk Reducti
6、on Systems,SIS Purpose,The purpose of a SIS is to reduce the risk that a process may become Hazardious to a tolerable level, The amount of risk reduction that an SIS can provide is represented by its safety integrtity level (SIL), which is defined as a range of probability of failure on demand.Safe
7、state; state of the process when safety is achievedA SIS sences hazardious conditions and then take action to move the process to a safe state, preventing an unwatned accident from occuring,SIS Safety instrumented system,Logic Solver,Safety Instrumented System with multiple SIFs,SIF 1,SIF 2,SIF 3,SI
8、F 4,Safety function and safety integrity from IEC 61511,Safety function Function to be implemented by an E/E/PE safety-related system, other technology safety related system or external risk reduction facilities, which is intended to achieve or maintain a safe state for the EUC, in respect of a spec
9、ific hazardous event (see 3.4.1)Safety integrity Average probability of a safety instrumented system satisfactorily performing the required safety instrumented functions under all the stated conditions within a stated period of timeSafety integrity level (SIL) Discrete level (one out of four) for sp
10、ecifying the safety integrity requirements of the safety instrumented functions to be allocated to the safety instrumented systems. Safety integrity level 4 has the highest level of safety integrity; safety integrity level 1 has the lowest,Safety function & safety integrity,Safety function,“what has
11、 to be done”,Safety integrity of safety function,the “safety performance” of the safety function”; the likelihood of the safety function being achieved,Safety function & safety integrity,Safety function: In order to prevent the rupture of pressure vessel “X”, valve “Y” should open in 2 seconds when
12、the pressure in the vessel rises to 2.6 bar. Safety integrity: The safety integrity of the safety function shall be SIL 2,Safety Integrity Level,Functional safety requirements spec,Functional safety requirements specification,Safety integrity requirements specification,Safety functions requirements
13、specification,Determined from the risk assessment,Determined from the hazard analysis,BPCS vs. SIS,Both composed of sensors, controllers and final element Control loop maintain a process variable within prescribed limits SIS monitors a process variable and take action when required Differences in dy
14、namics BPCS - Signals moves often, failure can be detected by plant personnel SIS Signals may be motionless for years (normally static), failures difficult to detect,SIS Engineering Requirement,Design to fail-safe Design diagnostics to automatically detect fail-danger Design manual test procedures t
15、o detect fail-danger Design to meet international and local standardsAlso Satisfy the functional requirement Satisfy performance requirement,SIS - SIF,1 SIS can have 1 or more SIF(s) Multiple SIFs can include common equipment If an equipment is in more than 1 SIF it need to be designed for the highe
16、st SIL requirement.,SIF Safety Instrumented Function,Logic Solver,Safety instrumented function (SIF) (From IEC 61511 1) Safety function with a specified safety integrity level which is necessary to achieve functional safety and which can be either a safety instrumented protection function or a safet
17、y instrumented control functionRelated to a specific hazardous event,SIF Safety Instrumented Function,SIF is an action a SIS takes to bring the process or the equipment under control to a safe state.This function is a single set of actions that protects against a single specific hazard.A SIS is a co
18、llection of sensors, logic solvers and actuators that execute one or more safety instrumented functions (SIFs) that are implemented for a common purpose.SIF often refers to the equipment that carries out the single set of actions in response to the single hazard, as well to the particular set of actions itself,
