Programmable logic controllers

A source of mistrust and concern when it first appeared in an industrial world where electronics were rare, the PLC has become a commonplace product, not the subject of spectacular technical and commercial announcements. Today, some people see it as a mere particle of the PC world, or at best as a transparent component for the user. In fact, paradoxically, given its wide distribution, it has been forgotten, and is ultimately unknown.

However, it has its own specific qualities that place it in a special category of control devices, alongside PCs, microcontrollers, digital control systems (DCSs) and programmable automation controllers (PACs): robustness under industrial conditions, real-time positioning, variety of configurations, sizes and presentations, ease of programming by non-specialists, easy integration into business assemblies in many applications. Its memory and processing capacity limitations can be overcome by judicious association with other digital systems, via industrial local networks.

The development of numerous business functions, in the form of software and/or hardware modules, and the concomitant development of new means of communication and appropriate software tools to facilitate networking, leading to a reduction in wiring and the possibility of higher-level programming, make it a good fit for flexible automated production, taking into account today's requirements in terms of operating safety.