![]() Thus the ‘preferred list’ is all but non-existent when it comes to selecting components and subsystems that will produce a safety instrumented system (SIS) that conforms with International Electrotechnical Commission’s (IEC) 61511-1 Functional safety – Safety instrumented systems for the process industry sector standard. However, when asked to produce supporting documentation, most simply can not. When contributors to the list are asked about a specific component or subsystem they will expound, often in great detail, how a particular device achieved its preferred list status. Within the minds of those who helped develop these lists, each device is on the list because it has proven its capability, reliability and suitability in prior use. Because of unique process conditions, these preferred lists often include ‘no substitute’ notations for specific plant areas. ![]() ![]() Such lists are usually the result of long-time relationships between the engineering and maintenance departments and the various devices themselves. It is fairly common for companies to have developed a ‘preferred list’ of transmitters, valves, actuators and other process control components and subsystems.
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