A brief history of PLC

January 15, 2022

Do you know what a PLC is? Ever heard about Modicon PLCs? This article will give you a brief overview of the history of PLC.

Over the past decades, new technological advancements have continued to emerge to improve manufacturing processes and bring automation to factories. Over time, computers began to play a vital role in the industry. Innovations emerged that we're able to revolutionize manufacturing. One of these is the programmable logic controller, an industrial computer capable of controlling manufacturing processes, from assembly lines to fault diagnosis. Let's dive into the history of the PLC and see how it changed the way we do things.

The programmable logic controller (PLC)

First of all, it is important to understand what an industrial PLC is. A PLC is a computer that we use to monitor inputs. However, in the beginning, PLCs weren't that complex.

PLCs solve particular problems that manufacturers face. They make their lives a little bit easier.

Before the programmable controller

The first PLC was developed for the automotive industry, which pioneered this technology. The development of PLCs began in the late sixties, around 1968. It was developed at a request from the American automaker General Motors. The goal was to replace relay control systems and hard-wired timers, which were becoming too difficult to manage, with programmable controllers that offered much more flexibility. Since then, PLCs have been used widely as highly reliable automation controllers due to their adaptability to more harsh environments.

Before the advent of programmable logic controllers, factories used cam timers, relays, closed-loop controllers, and sequencers as control logic for manufacturing. If this system worked, it was extremely rigid and difficult to change. These systems were hardwired, which made it very difficult to make any changes to the manufacturing process. If a problem arose on an assembly line, for example, or if changes needed to be made, it would involve rewiring and updating the documentation. Worst of all, it was enough to put a wire in the wrong place for the system to fail, resulting in often costly production delays. Staff had to waste hours comparing existing wiring to schematics in an attempt to find the fault, which was counterproductive.

Further development

The first programmable logic controller was built in 1969 and was named 084 (Bedford Associates' 84th draft). Following the success of the first model, Bedford Associates created a new company called Modicon (modular digital controller) which focused entirely on the design, development, and production of controllers.

Richard E. Morley (better known as Dick Morley) worked on PLC development with Modicon and is considered the father of programmable logic controllers. And that's how the production of the Modicon 084 began. The programming technique used in Modicon 084 set it apart from other products on the market. Other controllers used the Boolean equations to calibrate and program the equipment.

Without going into overly technical considerations, Boolean mathematics uses 1s and 0s, or in other words, true and false statements. Computers, in general, use this logic, but it was not very suitable for manufacturing processes. Boolean equations were too difficult to use for factory engineers who were accustomed to hard-wired relay logic.

It is where Morley's ingenious idea revolutionized the whole process. He came up with a concept to implement hard-wired logic into his system, which is like using the language of relays that engineers understand in Boolean logic. It changed everything. Via this technique, it was possible to represent the Boolean logic as a graph with the hard-wired logic. With the success of the Modicon brand, it was sold in 1977 to Gould Electronics and then finally to its current owner, Schneider Electric.

Modicon also created a communication protocol called Modbus, used with programmable logic controllers to connect to many devices.