The field of industrial automation has greatly evolved over the last few decades. From the initial use of programmable controllers in the automotive industry to the current application of Industrial IoT and Industry 4.0 , the field has come a long way. In the early days, the control logic was all hardwired and any changes in the logic meant rewiring of the whole relay based system, often stopping the production lines while the changes were being made and tested.
The advent of Programmable controllers enabled faster changes to the control system logic and also eliminating the need for the rewiring of relay systems. Though the industry was slow & skeptical to adapt to the programmable controllers in early days and often there used to be backup relay panels along with the PC based systems, just in case the new technology failed and somehow the plant then could still be made to run without stoppages. Often the backup panels stayed unutilized as the confidence grew over the use of the PC based systems.
The range of products in the factory automation soon grew with PLCs hitting the market for small to very large application needs. The micro/mini controllers could cater to small applications involving few I/O points and the large applications had higher end controllers offering more memory and faster processing speeds. Use of multiple controllers often became a norm in large industries, with individual plant sections being controlled by single controller along with its associated distributed I/O systems.
The need of the individual plant sections to exchange data among themselves led to the development of communication protocols that enabled the controllers to exchange data among themselves using some form of addressing and messaging system. Soon the entire graphical representation of the plant section became available on computer screens running the Supervisory Control & Data Acquisition (Scada) applications. The entire plant could now be monitored from central control rooms thereby providing the production team greater visibility into the production process and monitor the interdependencies between the different process parameters. The combination of controllers and visualization systems (HMIs) also became available as Distributed Control Systems (DCS) that offered programming and visualization on the same application environment.