Programmable Logic Controllers (PLC) has revolutionized the control of industrial processes. They can be found basically everywhere: on assembly lines, in robotic devices, and also in vending machines serving coffee.
It’s really hard to believe that they did not appeared until 1968.
Before PLC for steering the machines we used relays. Many relays. Basically whole industrial cabinets. And miles of wires. It took up a lot of space, and the error diagnosis and implementation even a small change was a nightmare.
First controllers had roughly 4k memory and they were programmed using the devices the size of the suitcase. This software was the foundation of success, because the ladder structure of the program corresponded to the wiring diagram of the relays. This solution makes easier and faster transition for engineers to new technology. During programming, all they have to do is select the type of command and the address of the line, and then press the button to set the logical path. Unfortunately, there were 24 VDC and 120 VAC signals on the back of the PLC card cabinets, which could be very easily confused when solving problems which could erased the whole industrially programmed system. As always beginnings could be really tough.
The sale of the first driver, Modicon 084, went very reluctantly. Only another model, Modicon 184, has been a great success, because it was designed with the need of the market. And it was this model, not Modicon 084 or the invention of a programmable controller, that shaped the modern market for PLC controllers.
Currently PLC is a very universal microprocessor device used to control various processes. They are reliable devices resistant to difficult industrial conditions. They are universal, scalable, compact and modular - witch makes it very easy to repartee driver and quickly extend it’s functionality.
There are models available on the market from the simplest programmable relays, through compact modular and distributed object solutions, to advanced systems with the capabilities of industrial computers. And the process of programming them and diagnosing errors is nothing like the 1960s.
