The History of PLC Programming

7th May 2013 | Posted by Charlotte Miskell

Allen Bradley PLC’s are a fantastic way for you to monitor and control a production machine. When the PLC (Programmable Logic Controller) is properly installed its reliability and ease of maintenance is a fantastic advantage for its users. However, before the introduction of PLC programming the best way to control a production machine was through the use of relays.

The relay is made up of two main parts, a coil and switch contacts. The coil essentially acts like a push-button and applying power to the coil operates the switch contacts, when the power is removed, the switch contacts fall back to the off position. This means that applying and removing power acts as an on/off action. This process means that controlling a machine containing many motors, solenoids and valves would require many relays.

On top of this, to switch the coils on the relays, even more relays (control relays) are required. All of these relays need to be hard wired together and in the right order for the machine to operate as desired. This means that any problems, such as coil failures, are very difficult to diagnose and to replace, which means that too much expense can be incurred maintaining the system.

Eventually, an incredibly bright man named Richard E. Morley proposed the idea of something he called a Modular Digital Controller (MODICON) to a major American car manufacturer. And so, in 1968, the first PLC was born. The original reason for designing the PLC was to reduce the costs involved in replacing the complicated relay based machine control systems. This was due to the fact that as production changed, the relay panels also had to be changed and this often had to happen wire by wire. It wasn’t until several years later that the first commercial PLC was released but they didn’t take long to increase in popularity.

The great benefit of programmable automation control was that once the programming had been written, the system would work without human interaction. This is why in the modern day, PLC’s form the central hub of many manufacturing processes and are used almost everywhere in industry from simple operations to the tracking and control of highly sophisticated, fully automated warehouse systems.

The microprocessor will monitor the state of the inputs and use the data to perform the logic of the user program and will then update the state of the outputs accordingly. The versatility of the PLC is one of its great strengths, with some containing as little as 6 inputs and outputs whilst others can contain forty thousand or more.

If you are interested in gaining more information on our PLC programming services or would like to consult on the installation of AC Drives, please feel free to contact us today.

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