Where others fear to tread [programmable automation controllers (PACs) and programmable logic controllers (PLCs)

Abstract

Until relatively recently, PLCs dominated the automation space, but, as plants cut costs and reduce system upgrade funding, engineers must continue to improve the plant while keeping overall costs low. Many plants are successfully implementing a strategy to locally optimise their processes by intelligently applying new technology to increase efficiency at bottlenecks. Local optimisation of processes requires higher speed signal acquisition and more sophisticated analysis operations, such as machine vision, Fourier transforms, order analysis and model-free adaptive control. The traditional PLC architecture, with I/O scanning and ladder logic, works well for sequential, discrete logic control, but extending this architecture to build in the more advanced functions required for local optimisation is often not practical. PACs combine the floating point processors, wide range of networking options and sophisticated programming tools more usually found on the PC with the industrial I/O and ruggedness usually associated with PLCs. The use of programmable automation controllers (PACs) in process control and automation is growing rapidly. In many applications, however PACs are not replacing PLCs; rather engineers use them to expand process monitoring and control into areas where PLCs fear to thread.