IEC 61508 and the Safety Integrity Level: Relevance for software and component manufacturers

zenon for railwayIn the previous blog posts we already described the IEC 61508 safety standard and the so called “Safety Integrity Level”:

The Safety Integrity Level (SIL) is a system to evaluate the reliability and safety of electric, electronic and programmable electronic systems (E/E/PE systems). It is based on the IEC 61508 standard. COPA-DATA is SIL 2 certified which means the HMI/SCADA software zenon can be used for process visualization and control in safety-critical applications.

But why should software development be certified in accordance with SIL?

Relevance for software and component manufacturers

The set of standards describes the lifecycle of the complete safety-orientated system. This starts with the planning and ends with the decommissioning of E/E/PE systems with safety-related functions.

IEC 61508 is subdivided into seven parts, whereby only parts one to four are normative; parts five to seven are for information only. Of the seven parts, Parts 1 and 3 are of particular interest to the software industry.

Part 1: General requirements

IEC 61508 defines part 1 as a “general basic standard”. This can be used if there is no application-specific standard derived from it. It primarily defines a superordinate safety lifecycle in order to be able to handle all necessary activities and tasks systematically. In all phases of this lifecycle, measures for the management, verification and evaluation of the functional safety are carried out and – most of all – documented. This also applies for the creation and maintenance of software. The requirements for this are primarily defined in Part 3.

Part 3: Requirements for software

This part describes techniques and procedures for how software should be developed and documented. A detailed safety lifecycle is also defined for software for the overall system. The individual safety requirements for the software must be derived from the requirements of an E/E/PE system and the safety requirements defined there. In addition, Part 3 describes development techniques for each SIL and provides notes on how to select the appropriate procedure for designing and developing the software.

Software planning and development in accordance with IEC 61508-3 forces the manufacturer to precisely define its processes and procedures. Working stages must be documented and checked with precision. The work in each working stage must be checked by a second person.

zenon_IEC-61508_SIL2We have been practicing all these measures for many years with the development of our zenon Product Family and thus benefit from a correspondingly large knowledge base. Because we already meet the requirements of the IEC 61508-3 standard in many areas, it was a no-brainer that we should subject ourselves to SIL certification.

In our next blog post we will go more in details of the SIL certification for COPA-DATA.

 

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