Changes in technology have led to a variety of recent developments in process safety, with many suppliers releasing new systems that significantly depart from those traditionally available. So, choosing a safety instrumented system (SIS) may seem even more complicated now. However, paying attention to a few do's and don'ts can make picking the right system for your process easier.
Do take advantage of scalable systems. The first popular safety programmable logic controllers (PLCs) introduced in the mid-1980s were triplicated. These systems, of course, cost more than non-redundant general-purpose PLCs. Because multiple distributed systems scattered around a facility often were considered too expensive, many plants opted for a single large centralized system — one 1,000-input/output (I/O) system cost less than ten 100-I/O systems.