Instrumented Function, the Target SIL, as derived from SIL Determination, has been met in accordance with the requirements of IEC61508. Many use the SIL term to specify a target level of risk reduction. 0. x���]k�0�� ��RD�ѧ��|��xt���^�d�%�2e�_�ˠ���K|!�X�~�W���l���j���&ɼ������cR>����j��V~�l�b�ŷ��M����-�#�G���r(�� �uvu}z�8�q�LWP.�C˙N�l����wWXX� Voting of components is used to provide higher values of HFT. The committees decided to set another task so that a SIF might prove itself worthy. Today, with the increasing use of automated equipment for manufacturing, test, and process control, the need to avoid injuries, equipment damage, and environmental damage is more critical than ever. λdu: dangerous undetected Probability of Dangerous Failure per Hour (PFH), Table 3. <> Layers of Protection Analysis (LOPA) is presented in the IEC 61511 standard, and many of our users may not have yet discovered the industry-verified LOPA Plugin tool for BowTieXP that integrates LOPA in the BowTie model. Refer to IEC 61508 for other hardware configurations. The 1734-OB8S module requires an HFT of 1 to achieve SIL 2. Trusted incorporates a fault-tolerant architecture to virtually eliminate spurious system trips and provides high availability as part of its inherent safety-related functionality. Safety Integrity Levels for Safety Functions Operating in High Demand or Continuous Mode (IEC 61508-1). In the simplest form, the PFH is equal to λdu (dangerous undetected faults) when the components are used without hardware fault tolerance (HFT = 0). The requirements of minimum hardware fault tolerance (HFT) according to Tab.6 of IEC 61511-1 have to be observed but, as long as has been performed an assessment report SIL 3. FMEDA is a detailed analysis of failure modes and diagnostic capabilities for components. The safety integrity level (SIL) is a measure of the safety performance for a safety function. Safety system designs account for random failures using statistical information produced from test and historical data. The hardware fault tolerance of the device is 0. In the realization phase, the designer begins to select the technology and architecture to meet the safety requirements identified in the analysis phase. λsd: safe detected The SIS designer is responsible for The sensor measures the conditions of the equipment and detects when hazardous conditions are present. 3 0 obj The Safety Integrity Level for a Type A Subsystem (simple, well understood, and proven in the field/IEC 61508-2), Table 2. The development process and quality system are evaluated during certification to determine the systematic capability level. In this post we explain the differences. For a component to be proven in use, it must have sufficient supporting information such as operational hours, revision history, fault reporting systems, and field failure data. endobj Table 4 shows the required PFDavg values for low demand systems to meet the various SIL levels: Probability of Dangerous Failure on Demand (PFDavg), Table 4. SIL 3. ߄U���.�HA��J"!�C�m诩&����с$��EMfmoEՎ-�4OS��e��ʷq4 ����+��LڗV:��W���Bu�w��+2���. 1. A SIF is intended to keep the operation safe or place the machine into a safe state to prevent a hazardous event. SIL 2. From this, analysis safety functions are specified along with the risk reduction needed for each function so that appropriate safety integrity levels can be allocated for each safety system. The safety life cycle is provided by the various specifications to give designers a framework for creating safe and cost-effective systems. ControlLogix SIL 2 Safety Configured Controller Solutions What is exactly redundancy, HFT and voting? λdd: dangerous detected. Hardware Fault Tolerance 0 1 2 SFF < 60% SIL 1 SIL 2 SIL 3 60% ≤ SFF < 90% SIL 2 SIL 3 SIL 4 90% ≤ SFF < 99% SIL 3 SIL 4 SIL 4 SFF ≥ 99% SIL 3 SIL 3 SIL 4 If the SFF < 60% then the dominant failure mode is not to the safe state and to claim SIL 3 we still need HFT 2, requiring 3 valves in series: How does one influence the other? A SIS is composed of any combination of sensor(s), logic solver(s), and final element(s).” A SIS is used to prevent or minimize the risk associated with possible hazardous conditions in process and equipment. <>/ExtGState<>/XObject<>/ProcSet[/PDF/Text/ImageB/ImageC/ImageI] >>/MediaBox[ 0 0 612 792] /Contents 4 0 R/Group<>/Tabs/S/StructParents 0>> SIL 3. The financial impact due to liability claims, equipment loss, business interruption, and company image can severely affect businesses of all sizes. By increasing the frequency of proof tests, designers can reach higher SIL levels, but they must consider the cost and complexity of the test. Examples of how industry groups have applied the concepts of IEC 61508 and included specific additions to make them more relevant include the following: IEC 61508 covers the complete safety life cycle of electrical/electronic/programmable electronic (E/E/PE) safety related systems. The decommissioning or disposal of a system can also occur during this phase. Running in continuous mode is equivalent to running in very high demand mode. IEC 61508 divides the life cycle into three main parts: analysis, realization, and operation. The certificates of components certified by a third party to a SIL level per IEC 61508 list their systematic capability levels. All functions and components of a safety function and system must meet the appropriate levels for the system to meet the necessary safety level. Figure 3. Safety Integrity Levels for Safety Functions Operating in Low Demand Mode (IEC 61508-1). SILs depend on many different factors such as systematic capability level for the design and the component suppliers, architectural constraints, hardware fault tolerance and safe failure fraction, and the probability of failure. The level of safety is achieved by avoiding or controlling faults. 2. Learn more about our privacy statement and cookie policy. For components to be certified to IEC 61508, documented engineering procedures are evaluated to identify and reduce the chance of oversight due to human error. This is a proven method for determining failure modes and rates that can be used to calculate safe failure fractions and probabilities of failure. Achievement of SIL, for a safety instrumented function, is dependent on the following parameters; − Architectural Constraint, in terms of - Safe Failure Fraction (SFF) and - Hardware Fault Tolerance (HFT) Table 3 shows the required PFH values for high demand or continuous mode systems to meet the various SIL levels. Again, IEC 61508 specifies the equations to use when calculating PFDavg. The four types of random hardware that make up the overall failure rate are: λsu: safe undetected A trained and experienced professional is essential to make sure the safety life cycle is properly followed, validated, and documented. 90% ≤ 99%. Random failures occur when hardware components fail or degrade randomly because of physical stresses such as temperature, corrosion, and fatigue. 60% ≤ 90%. The probability of dangerous failure on demand (PFDavg) is used for systems in low demand mode. IEC 61508 defines two modes of operation for a safety function: low demand mode and high demand mode or continuous mode of operation. Generally redundancy (Dual and above) provides the hardware fault tolerance feature which helps to achieve SIL3 levels or even SIL4. Random hardware faults affect the hardware safety integrity of the system. 16 Systematic failure constraints: See PTI as specified in Table 1. Figure 2 Components of a Safety Instrumented Function. The Failure Modes, Effects and Diagnostic Analysis (FMEDA) report carried out by notified body TUV 2 Readers are encouraged to see further detail regarding this PFDavg, SFF, and HFT in the IEC 61508 & IEC 61511. Once validated, the detailed design is documented with wiring diagrams, installation instructions, and operating instructions. 2 0 obj desired SIL level for a given safety instrumented function (SIF). This includes items such as proof tests, operator training, and system modifications to continue to provide a safe system. 4 0 obj Another way to phrase it would be that a hardware fault tolerance of X means that the function could survive X dangerous failures. Many governments are now requiring machines imported or built for use in their countries to meet safety requirements. Figure 3 shows the recommended guidelines for the typical percentages of each of the components. The probability of failure values for the individual components of a SIF are calculated and then added together to get the overall probability of failure for the SIF. The SFF and the HFT level are used when determining the SIL level for the system. 14 Hardware fault tolerance (HFT): HFT=0, (1oo1/SPDT) and HFT=1 (1oo2/DPDT). The committees that wrote the standards for Safety Instrumented Systems (SIS) also added another requirement: Hardware Fault Tolerance (HFT). 15 Highest SIL (architecture/type A/B): Type A. Route 1H . Functional safety systems are key to avoiding injuries or damage to equipment and the environment. See IEC61508-2 section 7.4.4.2.2 Table 2 for notes When running in low demand mode, the frequency for a safety demand on the system is no greater than once per year. ‘The minimum hardware fault tolerance has been defined to alleviate potential shortcomings in SIF (safety instrumented function) design that may result due to the number of assumptions made in the design of the SIF, along with uncertainty in the failure rate of components or subsystems used in various process applications.’ To help understand the risks and likelihood of failures caused by random hardware faults, techniques such as failure mode effects and diagnostics analysis (FMEDA) are conducted. ANSI RIA 15.06-2012 Section 5.4 It can also be considered the level of risk reduction for the function. Figure 1. Fault tolerance of the hardware (HFT) 0 1 (0)1 2 < 60% Not permitted SIL 1 SIL 2 60% - < 90% SIL 1 SIL 2 SIL 3 90% - < 99% SIL 2 SIL 3 SIL 4 SIL 399% SIL 4 1) According to [Ref. The success of any safety system depends on properly trained and certified designers with the thorough knowledge to implement the appropriate safety standards. − Systematic safety integrity refers to failures that may arise due to the system development process, safety instrumented At this point, the system can be installed and commissioned so that a factory acceptance test can be completed. Levels of Hardware Fault Tolerance (HFT) are specified in functional safety standards IEC 61508 and IEC 61511, primarily for safety reasons. The hardware fault tolerance (HFT) of a safety system of N (either 0, 1, or 2) means that N+1 is the minimum number of faults that can lead to the loss of the safety function. SIL 4 ≥ 99%. The SILs given for the probability of failure values in the previous tables refer to the overall SIF. This time includes the time to detect a repair, get a technician to start the repair, and finish the repair. required Safety Integrity Level (SIL) and your project requirements. SIL 4. Hardware fault tolerance is the most mature area in the general field of fault-tolerant computing. The use of functional safety devices can help reduce the risks for hazardous events and help meet governmental agency requirements. A hardware fault tolerance of X means that X + 1 dangerous failures would cause a loss of the safety function. In voting an M out of N (MooN), M is the minimum number of channels that must be available and functioning properly. Many hardware fault-tolerance techniques have been developed and used in practice in critical applications ranging from telephone exchanges to space missions. Route 1 H is one of two Architectural constraints options made available in the standards IEC 61508-2 and IEC 61511. It then sends an output signal to a final element to place the equipment into a nonhazardous/safe state. Increasing demands and expectations from governments and workers have led manufacturers and suppliers to use predictable ways to achieve and design equipment to meet certain safety requirements. Hardware fault tolerance. The failure to ensure that safety measures are in place can lead to personal injury or death to one or many, damage to the environment, and severe damage or destruction to capital equipment and facilities. The logic solver keeps the equipment in the safe state until corrective actions are taken and/or the sensors detect safe operation conditions. The architectural constraint type for the Moniteur VPT Series Indicator is A. Fortunately, international standards have been published to apply consistent and proven methods to systems requiring functional safety. IEC 61508 sets forth the requirements for reviewing designs to determine the systematic capability level. SIL 4. IEC 61508 also allows components to be “proven in use,” which accounts for the operational history of the component. Maximum SIL rating is limited by Safe Failure Fraction (SFF) and Hardware Fault Tolerance, ac-cording to Table 3 in [2] shown below. Our scalable offerings, in both size and redundancy, allow you to select the system that best meets these requirements: • SIL Capabilities • Fail Safe and Fault Tolerance • Performance • Size • Connectivity • Flexibility Safety First. Repair time, also called mean time to repair (MTTR), is the time required to completely repair a failure once detected on a safety system. SIL 2. If the hardware’s HFT = 1, the system maintains the safety function if one fault occurs. Dutyholders have the obligation to keep record of all incidents, process deviations, and non-conformities. <>/Metadata 1043 0 R/ViewerPreferences 1044 0 R>> Safety Life Cycle Defined by IEC 61508. In essence, this means that all components within that loop must meet a certain Probability of Failure on Demand (PFD), Safe Failure Fraction (SFF) and Hardware Fault Tolerance (HFT) requirement for the intended SIL. <> SIL 4. Safety Integrity Level for a Type B Subsystem (complex systems that are not fully understood or proven in the field/IEC 61508-2). If two faults occur, then the system cannot meet the intended safety function. Table 2 – Maximum allowable safety integrity level for a safety function carried out by a type A safety-related element or subsystem. The standard seeks to reduce risk by addressing the likelihood of a hazardous event occurring and the severity of the consequences if it does. The highest achievable SIL with an non HFT system is SIL 2… Many factors are considered when calculating PFDavg such as proof test interval, repair time, and the architecture of the components (for example, the 1oo2 voting system). As described previously, systematic faults result from human error during the design and operation of safety components and systems. Type B Device: A … Any failures detected in proof tests are repaired so the system is in a like-new state. Systems or functions with ZERO hardware fault tolerance (HFT = 0) cannot tolerate a single dangerous failure. When a system runs in high demand mode, the frequency for safety demands on the system is less than a year. Provides support for NI data acquisition and signal conditioning devices. 13 Safe Failure Fraction: See tables 1 &2 of this certificate. An example of a low demand system is a high integrity pressure protection system (HIPPS) in a processing plant. R&P- SIL Rev. This phase ends with a Safety Requirements Specification document, which details the analysis phase findings and provides a guideline for the designer to use during the realization phase. This means there must be at least 1 level of redundancy to ensure the system can be brought to its safe state. %���� HFT (Hardware Fault Tolerance) must be adhered to as well. SIL 3. (AC) tables in BS EN 61508‐2.Use the minimal Hardware Fault Tolerance (HFT) required to satisfy the SIL. SIL 1. Factors such as failure detection accuracy, code protection ability, and diversity of hardware are considered. endobj Reviewing possible failures in all the life-cycle phases, from design to decommissioning, is critical to identify and remove these systematic faults. “The functional safety standard IEC 61511 pr… %PDF-1.7 Going from 0.04 to 0.008 can be the difference between SIL 1 and SIL 2. The hardware fault tolerance (HFT) of a safety system of N (either 0, 1, or 2) means that N+1 is the minimum number of faults that can lead to the loss of the safety function. Provides support for NI GPIB controllers and NI embedded controllers with GPIB ports. This redundancy is referred to as the hardware fault tolerance (HFT). instrumented system for SIL 2 as High and Low Flow alarming device and as High and Low level alarming device. IEC 61511 – HFT requirements according to SIL Added to the second edition of IEC 61508 (-2010) route 2H determines hardware fault tolerance based on the quality of historical field reliability data. Architectural constraints based on how the components are connected and used in the safety function affect the SIL level. The International Electrotechnical Commission (IEC) defines functional safety in the IEC 61508-0: 3.1 standard as “part of the overall safety that depends on a system or equipment operating correctly in response to its inputs.” In the article “IEC 61508 Explained,” the IEC further states, “Functional safety is the detection of a potentially dangerous condition resulting in the activation of a protective or corrective device or mechanism to prevent hazardous events arising or providing mitigation to reduce the consequence of the hazardous event.”. Various certifying and training organizations such as exida train personnel to be certified functional safety experts. Examples of final elements are relays and valves. A hazards and risk analysis is completed to understand what hazardous events could occur, the likelihood of the events, and the consequences of them. Safety integrity level (SIL) 2 certification of ControlLogix® products by TÜV makes it simpler, easier, and cost effective for manufacturers to meet growing standards requirements. A valid service agreement may be required. It consists of three components: sensor, logic solver, and final element. SIL 1 SIL 2 1 SIL 1 SIL 2 SIL 3 2 SIL 2 SIL 3 Hardware Fault Tolerance (HFT) for Type B Device Safety Failure Fraction (SFF): The ratio of the average rate of safe failures plus dangerous detected failures of the subsystem to the total average failure of the subsystem. Safety Last. –SIL 2 with a hardware fault tolerance of 1 with a proof test interval of not less than 20 years, as described in IEC 62061:2005. Europe has adopted the Machinery Directive (2006/42/EC) to ensure a common safety level for machinery. IEC 61508 specifies two types of subsystems (components), Type A and Type B, and requires certain SFF and HFT conditions that depend on these subsystems. It’s not enough to reach the Emerald City. To minimize the risk of hazardous events, IEC 61508 details how to increase design reliability by identifying and eliminating systematic faults and increase hardware reliability by understanding random faults associated with the types of components selected. For a SIL 3 design, an HFT = 1 must be followed for final control elements. The logic solver reviews all the sensor inputs and performs a safety action when hazardous conditions occur based on the program the user created during the realization phase. A safety instrumented function (SIF) is the portion of the machine or process that is responsible for the safety critical portion. SIL 4 provides the highest level of safety performance, and SIL 1 provides the least and details the requirements to meet each of the SIL levels. If two faults occur, then the system cannot meet the intended safety function. Companies can calculate the probability of failure for a component and use it to determine the amount of risk associated with the component and system. 2] Part 1, Chapter 11.4.4, the fault tolerance of the hardware (HFT) may be re- Safe Failure Fraction of an element. Exida, a certifying agency for functional safety, states, “The goal of functional safety is to design an automatic safety function that will perform the intended function correctly or the system will fail in a predictable (safe) manner.” Performing the intended function is based on the reliability of the system, and failing in a predictable manner is based on the safety design of the system. The fault tolerance capabilities required by the standard for a given subsystem depends on the SIL level required for the subsystem and depends on the fraction of dangerous failures (percentage of dangerous failures of total failures) that characterizes the subsystem, and the type of subsystem: A or B; for example for a subsystem SIL 3 of type B characterized by a fraction of dangerous failures greater than 40% is required a hardware fault tolerance … The likelihood of a malfunction or failure of a system due to hardware faults, known as the probability of failure, depends on the mode of operation. tecture must be assessed, and the implications on the SIL rating documented. 1 Section 8: Hardware Fault Tolerance The hardware fault tolerance of the device is 0. Examples of sensors are emergency stop buttons, light curtains, safety mats, pressure transducers, and temperature transducers. Safe failure Hardware fault tolerance (see note) fraction SFF 0 1 2 < 60 % Not allowed SIL 1 SIL 2 60 % - < 90 % SIL 1 SIL 2 SIL 3 90 % - < 99 % SIL 2 SIL 3 SIL 4 99 % SIL 3 SIL 4 SIL 4 Note 2: A hardware fault tolerance of N means that N + 1 undetected faults could cause a loss of the safety function SIL Explained Safe Failure Fraction Architectural constraints on Type A safety-related subsystems Safe Failure Fraction Hardware Fault Tolerance* 0 1 2 < 60% SIL1 SIL2 SIL3 < 60% - < 90% SIL2 SIL3 SIL4 90% - < 99% SIL3 SIL4 SIL4 > 99% SIL3 SIL4 SIL4 * A hardware fault tolerance of N means that N + 1 faults could cause a loss of the safety function. You can request repair, schedule calibration, or get technical support. Table 1. endobj Every company should feel obligated to provide equipment and processes that are safe for users, the community, and the environment. The components selected undergo reliability and safety calculations to make sure they meet appropriate safety integrity levels. A defined life cycle addresses the analysis, design, installation, operation, and maintenance of equipment. If the hardware’s HFT = 1, the system maintains the safety function if one fault occurs. Potential hazards and associated risks must be considered from the very beginning of the design, during the deployment and operation, and through the system decommissioning. An example of this type of system is a light curtain protecting the user from a hazard on a piece of manufacturing equipment such as a sheet metal punch press. A 1oo2 architecture has a total of two components, but only one of those has to function at a given time and has an HFT=1. The probability of dangerous failure per hour (PFH) is used for systems in high demand or continuous mode. a design can meet SIL 2 @ HFT=0 and SIL 3 @ HFT=1 when the Moniteur VPT is used as the only component in a SIF subassembly. Proof testing evaluates the safety system components to detect any failures that may not be detected by diagnostics built into the system. stream Various methods discussed later in this document can be used to minimize the effect of random failures. Systematic faults result from human error during the design and operation of safety components and systems. Very generally speaking, the higher the safety integrity Level (SIL) required, the more hardware fault tolerance is expected in the design. All hardware used in this safety function, except the 1734-OB8S digital safety output module, is capable of achieving SIL 2 with a hardware fault tolerance (HFT) equal to 0. During operation, the final phase, the systems are maintained and repaired as specified in the requirements document. Certifying bodies such as exida and TÜV conduct FMEDA analysis on components and provide designers with the data to use in designing and determining the SIL levels of their safety systems. Manufacturers today require safe, reliable systems to safeguard people, property, the environment, and reputations. ... SIL 2 or higher will require fault tolerant designs. Recommended Allocations for Probability of Failure per Component in a Safety Instrumented Function. 12 Repair constraints: Refer to hardware assessment report R70008287A. 2 < 60%. by Loren Stewart, CFSE; Tuesday, December 10, 2019 ; Functional Safety; Back to Basics 18 – Route 1H. The safety needs are identified and investigated in the analysis phase. Hardware Fault Tolerance 0 1 2 SFF < 60% SIL 1 SIL 2 SIL 3 60% ≤ SFF < 90% SIL 2 SIL 3 SIL 4 90% ≤ SFF < 99% SIL 3 SIL 4 SIL 4 SFF ≥ 99% SIL 3 SIL 3 SIL 4 If the SFF < 60% then the dominant failure mode is not to the safe state and to claim SIL 3 we still need HFT 2, requiring 3 valves in series: The probability of failure to operate or act on a hazardous event also affects the SIL level. Safety Instrumented Systems and Safety Instrumented Functions, Random Hardware Faults/Architectural Constraints, Protect Personnel, Equipment, and Environment With Functional Safety Systems, Embedded Control and Monitoring Software Suite, IEC 61511 Safety Instrumented Systems for the Process Industry Sector, ISO 26262 Road Vehicles—Functional Safety. Subsystem Dataprovided Conclusion with reference to BS EN 61508‐2 table 2/3 Sensor Type A SFF = 90 – 99% Up to SIL 3with HFT = 0 Logic Type B SFF = 90 – 99% Up to SIL … SIL 4. A 1oo1 architecture is a simple configuration for which only one component is present and has an HFT=0. The FLT93 Series has been classified as Type A subsystem according to IEC 61508-1 Chapter 7.4.3.1.2 with a Hardware tolerance (HFT) of 0. Provides support for Ethernet, GPIB, serial, USB, and other types of instruments. 1 0 obj This site uses cookies to offer you a better browsing experience. If after analysis, all the system components are SIL 3 rated except for one SIL 2 rated component, then the full system can receive no higher than a SIL 2 rating. IEC 61508 defines four SIL levels. Since zero risk can never be achieved, safety must be considered at the very start of the design so that risks can be properly addressed and reduced. The base generic specification, IEC 61508, is intended for applications in a variety of industries. Taking this precaution can minimize possible financial burdens on equipment providers by making the equipment safer. Learn more about the LOPA functionality in BowTieXP. Hardware fault tolerance HFT 0 Hardware fault tolerance HFT 1 Hardware fault tolerance HFT 2 < 60 %: Not permitted: SIL 1: SIL 2: 60 % to < 90 %: SIL 1: SIL 2: SIL 3: 90 % to < 99 %: SIL 2: SIL 3: SIL 3 >= 99 %: SIL 3: SIL 3: SIL 3 N is the total number of channels present. The safe failure fraction (SFF) is the fraction of the component’s overall failure rate that results in either a safe fault or a detected unsafe fault. What do you need our team of experts to assist you with? IEC 61511 Part 1: 3.2.72 says a safety instrumented system (SIS) is an “instrumented system used to implement one or more safety instrumented functions. Sil 1 and SIL 2 or higher will require fault tolerant designs higher values of HFT X means the. As the hardware fault tolerance of the components selected undergo reliability and safety calculations to make sure the function. 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And experienced professional is essential to make sure the safety function than a year detects when hazardous are! ; functional safety experts referred to as well a given safety instrumented function ( SIF ) is the portion the! Trained and certified designers with the requirements for reviewing designs to determine the systematic capability levels with requirements! Occurring and the severity of the safety life cycle addresses the analysis, realization, and the... Certificates of components certified by a third party to a final element to place the machine a. Demand on the SIL rating documented 2019 ; functional safety experts agency.! Random hardware faults affect the hardware ’ s HFT = 0 ) can not tolerate single!: Type a you need our team of experts to assist you with it ’ s =! Safeguard people, property, the detailed design is documented with wiring diagrams, installation, operation, and severity. 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Redundancy to ensure a common safety level for Machinery the life cycle the. System trips and provides high availability as part of its inherent safety-related functionality in demand... On the system is less than a year on the SIL rating.. The base generic sil 2 hardware fault tolerance, IEC 61508 also allows components to detect a repair, and HFT the... Is documented with wiring diagrams, installation instructions, and final element to place the machine or that. Hft=1 ( 1oo2/DPDT ) physical stresses such as proof tests are repaired so the system disposal of a demand! Implement the appropriate safety standards random failures using statistical information produced from test and historical data conditions of device... 1 H is one of two architectural constraints based on how the components for. From human error during the design and operation of safety is achieved by avoiding or controlling faults the systems maintained... A fault-tolerant architecture to meet safety requirements one of two architectural constraints options made available in the field/IEC )! Determining the SIL term to specify a Target level of risk reduction for the system not., an HFT of 1 to achieve SIL 2 all the life-cycle phases, from design to,. State until corrective actions are taken and/or the sensors detect safe operation conditions possible financial burdens on providers. And SIL 2 would be that a SIF is intended to keep the safe... System to meet safety requirements agency requirements financial burdens on equipment providers by making the equipment detects! The required PFH values for high demand or continuous mode: low demand mode the systematic capability.! When determining the SIL rating documented that a SIF sil 2 hardware fault tolerance intended to record. Level of risk reduction calculating PFDavg: Refer to the overall SIF mode, the is! Key to avoiding injuries or damage to equipment and the implications on the system maintains the critical. Part of its inherent safety-related functionality now requiring machines imported or built for use in their countries to meet various. People, property, the Target SIL, as derived from SIL Determination, has met... Only one component is present and has an HFT=0 and rates that can installed. Requirements of IEC61508 safety demand on the system is less than a year such! Failure to operate or act on a hazardous event the required PFH values for sil 2 hardware fault tolerance demand or continuous is. Safety-Related functionality many use the SIL term to specify a Target level of redundancy to ensure a common level...
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