Functional Safety


Catalog excerpts

Functional Safety - 1

Functional Safety Functional safety in process instrumentation with SIL rating Questions, examples, background

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Functional Safety - 2

Safety Integrity Level 08 - 12 Low and high demand modes 11 Who does the SIL classification apply to? 12 What devices can be used with which SIL? 12 Two SIL 2 devices in redundant mode - is this SIL 3? 12 Is the highest possible SIL advantageous? 16 What are the advantageous for a company? 16 Device ratings by manufacturers 17 What certificates are required? 17

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Functional Safety - 3

Foreword Since the release of IEC 61508, the topic of “Functional safety” in the process industry has come to the fore. Often, the expression SIL is used to reference this standard. But what exactly does SIL mean? In this brochure, we will provide you with an introduction to the topic with emphasis on instrumentation for process engineering. We want to provide fundamental understanding without using the language of the standard. As a result, some descriptions may appear to experts to be too inaccurate or superficial. This brochure can only be an introduction to the topic. If you require...

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Functional Safety - 4

Hazards and risks In everyday life we are constantly exposed to many different hazards. The extent of these hazards extends up to major catastrophes which can have severe detrimental effects on health and the environment. We are not always able to avoid a hazard with its associated risks. For example, a high proportion of the world population lives with the hazards of earthquakes or flooding. There are no protective measures against the events themselves; however, protective measures do exist for the consequences of such events (e.g. dams or dikes, or buildings resistant to earthquakes)....

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Functional Safety - 5

The layer of protection model on the right shows what types of protective measures typically exist. The measures required to reduce a risk can sometimes be very simple, but also extremely complex. Examples: • Structural measures (e.g. build concrete walls around production plants) • Distribution of hazards • Evacuation plans • Safety-relevant control and protection equipment • and many more As shown by the example, measures that decrease the risk are partially attributed to completely different approaches. These approaches are also called layers of protection. These different layers of...

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Functional Safety - 6

Functional safety What does functional safety mean? Automation engineering systems are increasingly handling safety-relevant tasks. For example, processes representing a hazard to people and the environment are monitored by safety systems. These take appropriate action in the event of a fault, and can reduce the risk of a hazardous state. Functional safety is the correct functioning of such equipment. Since many countries had different standards for the correct functioning of safety-relevant equipment, a globally applicable IEC basic standard for functional safety was adopted in 1998. A...

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Functional Safety - 7

Functional safety Safety-related System (SRS) For whom is IEC 61508 relevant? Based on a hazard and risk analysis, the hazards can be determined which result from a plant and its associated control systems. This determines whether a safety-related system is necessary to guarantee appropriate protection against possible hazards. If this is the case, the associated concepts must be appropriately incorporated in the development of this plant. IEC 61508 defines appropriate methods for achieving functional safety for associated systems. What systems are affected by IEC 61508? IEC 61508 must be...

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Functional Safety - 8

Safety Integrity Level Different risks originate from plants or plant components. As the risk increases, the demands made on the safety-related system (SRS) also increase. The standards IEC 61508 and IEC 61511 therefore define four different safety levels which describe the measures for handling the risks of these components. These four safety levels are the safety integrity level (SIL) defined by the standards. The higher the number of the safety integrity level (SIL), the higher the reduction of the risk. The SIL is therefore a relative measure of the probability that the safety system...

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Functional Safety - 9

Safety Integrity Level Diagram of the separation column A small example... A new production facility needs to be built in a chemical plant: The process used to produce the chemical product is the main factor determining the configuration of the facility. Since the operation of this type of facility can generally pose a risk to people and the environment, potentials risks and effects must be examined and adequate protective measures must be included in the project if necessary. For example, a separation column is considered as part of the plant. A HAZOP analysis (Hazard and Operability...

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Functional Safety - 11

Safety Integrity Level Since applications in the process and production industries vary greatly, different demands are also placed on the safety-related system (SRS). For this reason, each of these industrial sectors has a different system in which the demand rate on the SRS is defined. A differentiation is made between the systems using the probability of SRS failure on demand (PFD). Low demand Mode with low demand rate on the safety system. There must not be a demand on the safety system more frequently than once per year. Comparison between AK (DIN 1925) and SIL (IEC 61508) (may not...

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Functional Safety - 12

Safety Integrity Level Who does the SIL classification apply to? In the case of plants that must meet safety technology requirements, the participants are affected for different reasons: What devices can be used with which SIL? In order to achieve a level (SIL 1 - 4), the complete SRS must fulfill the demands for the systematic failures (particularly the software) and the random failures (hardware). The calculated results of the complete SRS must then cor• Plant operators respond to the target SIL. Place the demands on the suppliers of safety technology components. These must provide proof...

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Functional Safety - 13

Types of faults A differentiation is made in a safety-related system (SRS) between systematic faults and random faults. Both types of faults must be considered individually in order to fulfill a demanded SIL. Random faults Random faults do not exist at the time of delivery. They result from failure of individual components of the hardware, and occur at random during operation. Examples of random faults include: Short-circuit, open-circuit, drift in component values, etc. The fault probability and the associated failure probability can be calculated. The individual hardware components of an...

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