IEC 61508 is the technical reference for the design and maintanance of safety systems that use electrical, electronic and programmable electronic technologies (E/E/PE). IEC 61508 points to suppliers of industrial components and states a set of requirements aiming at determining the SIL level of an electrical – or electronic – system. Even though the IEC 61508 doesn’t mention any certification, the SIL certification has become more and more sought after by automation companies for various reasons.
SIL (Safety Integrity Level) is often part of contractual specifications in the field mechanical, electrical and electronic supply. Contractual specifications usually indicate the desiderable SIL level (SIL 1, SIL 2, SIL 3 or SIL 4) required to compete in a supply contract. SIL levels also guarantee conformity with IEC 61508 requirements. Despite the fact that it is not mandatory, with few exceptions, many users of electric and electronic systems increasingly require certified components in terms of safety.
The certification is mandatory in the automotive industry, while it can be rather obtained voluntarily for other industries such as processing and industrial machinery. A SIL certification can be used to substantially differentiate product characteristics from competitors’. Let us now better understand why.
Indeed, SIL certification is closely linked to product design. The safety design of an industrial component involves all the technical aspects of the product being certified. It also has significant effect on Product Lifecycle Management and involves the drafting of specific documents once the product is on the market.
The preparation of the document portion represents a big effort for manufacturers (it may also be considered onerous), but in spite of that, certified products turn out to be more and more valuable in the eyes of clients. Obtaining a SIL certification encourages product restyling and helps improve its usability. In summary, a certification represents a boost to product differentiation. Any product intervention represents an asset for manufacturers and give a second life to components by making them distinguishable from similar products that are not SIL-certified. For this reason, the certification process usually involves the Research and Development department as well as Marketing and Sales staff.
Since the IEC 61508 standard has been adopted all over the world, a SIL certification can be used at the international level and proves the superiority of a component compared to competitors’. A SIL certificate is also a guarantee of the greater system reliability.
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How to obtain SIL certification
Before initiating the formal certification process, it is necessary for the manufacturer to plan a series of preliminary activities related to an evaluation of the achievable SIL level.
We support companies on the road to SIL certification by performing the following activities:
- Reliability Analysis and calculation of SIL level for the safety functions in accordance to IEC 61508 requirements. This is a preliminary phase that consists in verifying the physical elements of a component in order to determine the fault tolerance and understand which gaps should be filled in order not to compromize the achievable SIL level.
- Definition of the Safety Life Cycle which consists in identifying the actions to be taken at each stage of a product Safety Life Cycle – and related maintenance actions -, in compliance with IEC 61508 requirements.
- Product design (or re-design) support, aimed at reaching the desired SIL level.
- Carrying out tests on the prototype or on the specific product depending on whether a type or a individual certification is required. We will discuss the distinction between the two types of certifications in the next paragraph.
After passing all the tests, the certification is issued directly; otherwise we will release the dossier related to non-conformities to be addressed in order to get the SIL certificate.
What products can be SIL certified
SIL certification is aimed at all products intended to be integrated into one or more safety functions, such as, for example, sensors, mechanical valves, complex measurement systems, logic firmware solvers or embedded software. There are two types of certification achievable at all SIL levels – from 1 to 4 – and covered by IEC 61508:
- SIL type certificate, which certifies the reliability of a type of product. Certification Bodies approve the degree of reliability of a component by analyzing a prototype. After the certification is issued, manufacturers can produce in series. A SIL type certificate is valid for three years. A product family can be certified through a type certificate as well.
- SIL individual certificate, which covers only the object expressly indicated in the certificate. It is generally applicable either to customized products or to project-based products. Tests are performed on directly the product subject to certification. This is a unique certificate that only covers a specific item exclusively and cannot be transferred to other products.
It is possible to certify either a product before launching it on the market or a product that is already on the market. In any case, but in particular for products that are already commercialized, the certificate is not retroactive: it covers items manufactured after it is issued (in the case of a type certificate) or the remaining lifetime of the product (in the case of individual certificate).
Some of our projects in the field of IEC 61508 implementation and SIL certification
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