High reliability computing for control and safety

Safety Programmable Logic Controllers (PLCs) are special purpose computers that are used to provide critical control and safety applications for automation users. There are serious questions though about the use of programmable systems for critical control and safety automation. How can the use of these machines be justified? This paper covers the essential attributes of safety PLCs including high strength design, excellent self-diagnostics, redundancy, and high common cause strength. When these attributes are combined with third party functional safety certification, a reliable and safe machine is the result.