Prior to 1968, most safety-instrumented systems, also known as emergency shutdown systems, were implemented using relays. The advent of the programmable logic controller (PLC) changed all that. Hard-wired solid-state systemsdesigned to replace relays without using softwarewere also popular for several decades. Software-based systems pose the majority of safety-instrumented systems installed today.
General purpose PLCs have a variety of weaknesses in safety applications that have been recognized for many years, primarily the lack of thorough diagnostics.1 Users, vendors and integrators have understood these weaknesses and some have engineered customized solutions to overcome man
Log in to view this article.
Not Yet A Subscriber? Here are Your Options.
1) Start a FREE TRIAL SUBSCRIPTION and gain access to all articles in the current issue of Hydrocarbon Processing magazine.
2) SUBSCRIBE to Hydrocarbon Processing magazine in print or digital format and gain ACCESS to the current issue as well as to 3 articles from the HP archives per month. $409 for an annual subscription*.
3) Start a FULL ACCESS PLAN SUBSCRIPTION and regain ACCESS to this article, the current issue, all past issues in the HP Archive, the HP Process Handbooks, HP Market Data, and more. $1,995 for an annual subscription. For information about group rates or multi-year terms, contact email Peter Ramsay or call +44 20 3409 2240*.
*Access will be granted the next business day.