9 - Introduction to standards for programmable systems

Abstract

This chapter focuses on several safety design standards for programmable systems. IEC 61508 is titled “Functional Safety of Electrical/Electronic/Programmable Electronic Systems.” It is intended to be a widely applicable generic standard, which suggests that it can be applied to many types of safety systems in many types of industries. The term “generic” implies that a more specific version of its rules can be used to suit a particular type of industry. The safety integrity level (SIL) rating of a safety function is a measure of the degree of confidence in its overall ability to provide the safety function for nearly all of the time and under nearly all circumstances. The new IEC 60261 has provided an approximate alignment of SIL ratings with the safety categories as defined by EN 954. This can be seen most easily in the fact that SIL-3 safety systems require a fault tolerance level of at least 1 with a high level of self-testing. The role of this standard appears likely to be found in support of individual applications by makers of manufacturing automation plants and the end users of any complex machinery where electronic or programmable safety controls are being deployed.