A Guide to Cost-Effective SIS

Not every safety function needs a full-blown safety PLC. Learn how engineers are closing the SIS “safety gap” with certified multi-loop logic solvers that reduce cost, simplify deployment, and maintain IEC 61511 compliance.
March 10, 2026

As Safety Instrumented Functions become more common, engineers are often faced with an uncomfortable choice: use multiple basic alarm trips that require excessive relay wiring or deploy a fully certified safety PLC that may be far more than the application requires. This challenge is especially common in smaller SIS applications with only a few safety loops.

This white paper explores the “Safety Gap” that exists between alarm trips and large safety PLC architectures. It examines how a hybrid approach, using certified multi-loop logic solvers, can meet IEC 61511 requirements while reducing engineering effort, hardware costs, and long-term maintenance burden. The paper focuses on practical considerations engineers face with their safety instrumented systems, including configuration effort, change management, and lifecycle costs, and offers a more balanced path to functional safety without overengineering.