PLC HISTORY

PLC's have been around since the late '60's. The PLC systems evolved over the years with industry and technology.

The PLC was arguably the technology that kicked-off the 3rd industrial revolution. This achievement alone is worthy of recognition. However, the PLC isn’t just recent history as it remains a widely used technology that is continually improving manufacturing automation. The PLC’s reliable and flexible make-up allows it to be used in almost any application and in almost any environment.

Since PLCs are designed to be modular they can be used in almost every aspect of process control. PLCs are sometimes confused with Distributed Control Systems (DCS) controllers because both are a type of controller. A key difference between the two is linked to their application. While a DCS supervises the control of an entire plant, a PLC’s responsibility is typically limited to the regulation of an individual process. In many cases, the PLC is used in conjunction with a DCS or SCADA system.

In the 1970's the majority of control systems were all hard wired relay based. With changing requirements from industry the need for flexibility became more and more important. Hence "Programmable Controllers". These removed the need to rewire to enable process changes. The new system drastically increased the functionality of the controls while reducing the cabinet space that housed the logic. It was much quicker and less disruptive to effect changes via software.
There were two major types of systems. The American style and the European style.

The American way was led by Modicon (Richard (Dick) Morley), Allen-Bradley (Dr. Odo Struger) and GE. These largely derived from the motor industry requirements and were aimed at the factory floor, rugged, reliable and maintainable by electricians. Programming was developed to replicate standard electrical schematic diagrams as much as possible and referred to as "Ladder Logic".
The European style was led primarily by Siemens from 1973 with the Simatic S3. These were designed for a manufacturing environment, well enclosed, mounted in card racks with tricky and fragile connections, and maintainable by engineers. Programming was developed at the most machine efficient level and approximated low-level assembley language.

Modicon: The first PLC. Evolution
Allen Bradley: AB Story
GE, later.
Texas Instrument, later.
Square D, later.
Struthers-Dunn, later.
Siemens, later.
Japanese brands, Omron, Mitsubishi, etc.